Measurement of Pion Enhancement at Low Transverse Momentum and of the Delta-Resonance Abund

The Chroma 11022 and 11025 LCR Meters are passive component testers that can give you the most cost effective alternative equivalent to the high priced meters. They are designed for the demanding applications in production test, incoming inspection, component design and evaluation. Programmable test signal level settings are from10mV to 1V in a step of 10mV, and the VM/IM signal level monitor functions allow you to evaluate your devices at the level you specify. Ten test frequencies of 50Hz, 60Hz, 100Hz, 120Hz, 1kHz, 10kHz, 20kHz, 40kHz, 50kHz, and 100kHz, can be used to evaluate passive compo-nents and transformers/ LF coils.The low cost LCR meters on the market have shortcomings when used for low impedance components evaluation such as large capacitance of electrolytic capacitors and low inductance of coils. As the 11022/11025 equipped with high resolution (0.01m ) in low impedance and high accuracy (0.3%) till 100m range, it can be used to evaluate low impedance components to meet the measurement requirements.The 11025 LCR Meter can also measure DC resis-tance, turn ratio and mutual inductance of trans-former. It is suitable for pulse transformer or LF coil evaluation. Chroma A110207 Transformer Test Fixture used with the 11025, can measureboth the primary and the secondary parameters automatically by changing the internal relays of 11025. So there is no need to change the connec-tions required for measuring transformer param-eters. Adjustable internal DC bias current source can be up to 200mA(constant 25 ) which is a standard function, as the right tool for inductance inspection of telecom transformers and small power chokes under DC bias current.The 11022/11025 LCR Meter provides a powerful combination of features designed to maximize the productivity in all testing environments. The measurement speed in the SHORT integration time mode is 21mS( 100Hz). Handler interface and pin-out are compatible with 4263B. GPIB Interface and IEEE 488 commands are compatible with 4263B.In addition, the 11022/11025 have built in a comparator, 8 bin sorting, trigger delay functions and handler interface trigger function, which make them easy for system integration, and improve the measurement throughput as well as reliability.LCR METERMODEL 11022/11025198111022 : LCR Meter 11025 : LCR MeterA110104 : SMD Test Cable #17A110211 : Component Test FixtureA110212 : Component Remote Test Fixture A110232 : 4 BNC Test Cable with Clip#18A110234 : High Frequency Test Cable A110236 : Rack Mountain KitA110239 : 4 Terminals SMD Electrical Capacitor Test Box (Patent)A110242 : Battery ESR Test KitA110244 : High Capacitance Capacitor Test Fixture A110245 : Ring Core Test Fixture A133004 : SMD Test Box1. LCD Display2. LINE Switch3. Measurement Terminals4. Function Keys5. Power Code Receptacle6. LINE Fuse Holder7. LINE Voltage Selector8. GPIB Interface9. Handler Interface10. External DC Bias Terminal 11. Ground Terminal 12. Fan13. Ground Terminal14. DC Bias Trimmer Terminal711121623413*Note 1: 23 ± 5˚C after OPEN and SHORT correction. Slow measurement speed. Refer to Operation Manual for detail measurement accuracy descriptions.*Note 2: Measurement time includes sampling,calculation and judge of primary and secondary test parameter measurement.PANEL DESCRIPTIONORDERING INFORMATIONDistributed by:Worldwide Distribution and Service Network11022/11025-201108-500JAPANCHROMA JAPAN CORP .472 Nippa-cho, Kouhoku-ku, Yokohama-shi, Kanagawa,223-0057 Japanhttp://www.chroma.co.jp E-mail:******************U.S.A.CHROMA SYSTEMS SOLUTIONS, INC.25612 Commercentre Drive, Lake Forest, CA 92630-8830 Tel: +1-949-600-6400Fax: +1-949-600-6401Toll Free: +1-866-600-6050 E-mail:*******************Developed and Manufactured by :CHROMA ATE INC.HEADQUARTERSNo. 66, Hwa-Ya 1st Rd., Hwa-Ya Technology Park, Kuei-Shan Hsiang,33383 Taoyuan County, Taiwan Tel: +886-3-327-9999Fax: +886-3-327-8898 E-mail:******************EUROPECHROMA ATE EUROPE B.V .Morsestraat 32, 6716 AH Ede,The Netherlands Tel: +31-318-648282Fax: +31-318-648288 E-mail:******************CHINACHROMA ELECTRONICS (SHENZHEN) CO., LTD.8F, No.4, Nanyou Tian An Industrial Estate, Shenzhen, China PC: 518052Tel: +86-755-2664-4598Fax: +86-755-2641-9620。

污染源源强核算技术指南附着率英文回答：Introduction:The calculation of emission source strength is an essential step in assessing and managing air pollution. It provides valuable information for designing effectivecontrol strategies and evaluating their effectiveness. This guide aims to provide a comprehensive overview of the techniques used in the calculation of emission source strength, with a focus on the concept of particulate matter (PM) deposition velocity.1. Definition of Particulate Matter Deposition Velocity:Particulate matter deposition velocity refers to therate at which airborne particles settle onto a surface. Itis a critical parameter for estimating the mass flux of PM emitted from a source to the surrounding environment. Thedeposition velocity depends on various factors, including particle size, shape, density, and the characteristics of the surface onto which the particles are deposited.2. Importance of Estimating Deposition Velocity:Accurate estimation of deposition velocity is crucial for understanding the fate and transport of PM emitted from pollution sources. It helps in determining the distance over which the PM will travel and the areas that will be affected by its deposition. Additionally, deposition velocity estimation assists in evaluating the efficiency of control measures and predicting the potential health risks associated with PM exposure.3. Measurement Techniques:Several methods can be used to measure deposition velocity, including field measurements, laboratory experiments, and modeling approaches. Field measurements involve the use of samplers to collect particles at various distances from the pollution source. The collected samplesare then analyzed to determine the deposition velocity. Laboratory experiments simulate the conditions of the source and receptor environment in controlled settings. Modeling approaches utilize mathematical models to estimate deposition velocity based on particle properties and environmental factors.4. Factors Affecting Deposition Velocity:Deposition velocity is influenced by several factors, including particle size, shape, and density. Smaller particles tend to have higher deposition velocities due to their lower settling velocities. The shape of particles also affects their aerodynamic properties, which in turn influence their settling rates. Additionally, the density of particles and the characteristics of the surface onto which they are deposited play a significant role in determining the deposition velocity.5. Applications of Deposition Velocity:The estimation of deposition velocity has variousapplications in air pollution management. It helps in identifying the major contributors to PM pollution and prioritizing control measures accordingly. Furthermore, deposition velocity estimation is essential for evaluating the efficiency of emission control technologies and designing effective mitigation strategies. It also assistsin assessing the potential health risks associated with PM exposure in different regions.中文回答：介绍：污染源源强核算是评估和管理空气污染的重要步骤，为设计有效的控制策略和评估其有效性提供了宝贵的信息。

9Organic CompoundsWhile there has always been some interest in the nature of the organic com-pounds in seawater,identification of actual compounds has progressed slowly because of the low concentrations present.With a total organic carbon concen-tration of0.5–1.5mg/l of carbon,the total concentration of any single organic compound is likely to be less than10–7M.Therefore,in the past,identification of individual compounds has been limited to those few for which specific, sensitive chemical methods existed.These methods were usually spectropho-tometric,and were often developments of methods originally used in clinical chemistry.The advent of the newer physical methods of separation and identification, together with the impetus given to thefield by the imposition of anti-pollution legislation,has resulted in aflood of new and often unproven methods.While most of these methods were specifically designed to measure materials added to the environment by man’s activities,in many cases they have added greatly to our knowledge of the naturally occurring compounds as well.Until the advent of modern instrumental methods of analysis,the best we could hope to do was to measure the amounts of certain broad classes of compounds present,as,for example,the total protein or total carbohydrate.Using the newer methods,such as gas chromatography,liquid–liquid chro-matography,fluorometry,and mass spectrometry,it is possible to measure many compounds at the parts-per-billion level,and a few selected compounds with special characteristics at the parts-per-trillion level.Even with these sen-sitivities,however,a considerable concentration must usually be undertaken to permit the chemical or physical fractionation necessary to render thefinal analyses interpretable.A major effort has therefore been expended on the study of methods of separation and concentration,and this is discussed further in Chap.8.A problem which has been less well recognised is that of contamination in sampling and sample handling.The oceanographic vessel itself is a major source of contamination;from the moment that the ship stops on station, a surfacefilm of oil,flakes of metal and rust spreads out in all directions. The means of sampling also often acts as a source of contamination.Once the sample is on board,along with the normal problems of contamination through sample handling and through high blank values from the reagents used,we3669Organic Compounds must also attempt to cope with chemical and biological changes occurring during storage,since many of the modern instruments are not easily taken to sea.In environmental chemistry,the work of Analyst does not begin with the delivery of the sample to the laboratory;every aspect of sampling,storage, and pretreatment must be considered part of the analyst’s domain.This is discussed further in Chap.1.HydrocarbonsProbably the most studied group of organic compounds in seawater is the hydrocarbons,not because of the importance of the naturally occurring ma-terials,but because of the continuing threat of large-scale pollution.However, the methods devised for the measurement of anthropogenic hydrocarbons will also measure the natural materials.A major problem,not altogether solved,is that of distinguishing between the two sources.There have been many reviews of analytical methods for hydrocarbons, particularly those given in[1–11].Burgess[538]has reviewed the charactisation and identification of organic toxicants in marine waters9.1Aliphatic Hydrocarbons9.1.1SpectrofluorometryFam et al.[11]determined hydrocarbons in run-off water from catchments in San Francisco Bay using liquid chromatography and high-resolution gas chromatography.Wade and Quinn[12]measured the hydrocarbon content of sea surface and subsurface samples.Hydrocarbons were extracted from the samples and analysed by thin-layer and gas–liquid chromatography.The hydrocarbon con-tent of the surface micro layer samples ranged from14to599µg/l with an average of155µg/l,and the concentration in the subsurface samples ranged from13to239µg/l and averaged73µg/l.Several isolated hydrocarbon frac-tions were analysed by infrared spectrometry and each fraction was found to contain a minimum of95%hydrocarbon material,including both alkenes and aromatics.9.1.2Dynamic Headspace AnalysisMay et al.[13]have described a gas chromatographic method for analysing hydrocarbons in marine sediments and seawater which is sensitive at the9.1Aliphatic Hydrocarbons367 sub microgram per kilogram level.Dynamic headspace sampling for volatile hydrocarbon components,followed by coupled-column chromatography for analysing the nonvolatile components,requires minimal sample handling,thus reducing the risk of sample component loss and/or sample contamination. The volatile components are concentrated on a Tenax gas chromatographic precolumn and determined by gas chromatography or gas chromatography–mass spectrometry.Other workers have discussed the application of dynamic headspace analysis to the determination of aliphatic hydrocarbons in seawater[14–18].A second system,the removal of volatiles by vacuum,can be set up in two ways;either as aflow-through or as a batch process.As aflow-through process, the sample is drawn continuously through the system,and the gases taken off by the vacuum pass through a sampling loop.Periodically,the material in the loop is injected into the gas chromatograph.In this manner it is possible to derive almost continuous profiles of volatile hydrocarbon concentrations[19].In the batch mode,a larger sample can be treated over a longer period, and the volatiles collected by cold-trapping or adsorption.These techniques are not as fast asflow-through sampling,nor do they permit semi-continuous profiling,but they result in greater concentrations of the hydrocarbons,and thus in greater sensitivity[20].The third technique,stripping-out,is by far the most common.In this tech-nique,an inert gas is bubbled through the sample to remove the volatile ma-terials.When the concentration of hydrocarbons is great enough,as,perhaps, after a petroleum spill,the emergent gas stream can be sampled directly[21]. This is seldom the case in true oceanic samples,however,and some form of concentration is needed.It is possible to collect the volatiles in a cold trap[22].A more favoured technique is the collection of the gases by adsorption on some support such as one of the Chromosorbs,or Tenax GC[13,22,23].The volatiles are then desorbed by heating and injected into a gas chromatograph.Of the three general methods,the last seems to be the most practical.Theo-retically,with high enough concentrations of hydrocarbons,thefirst method, the headspace analysis,should be both the most accurate and the easiest to cal-ibrate.Operationally,it leaves much to be desired both because of the problems of sensitivity and those of the accommodation of the larger molecules in water. The second method,vacuum degassing,requires much more equipment than the third method and requires that large amounts of water vapor be removed before the sample is injected into the gas chromatograph.The last method is so much less complicated that even with its calibration problems it has been adopted almost universally.While the gases used in stripping are usually air,nitrogen,or helium, electrolytically evolved hydrogen has been used as a collector for hydrocar-bons[24].In this technique the gas is not passed through a column of adsor-bent,but instead collects in the headspace of the container.Since the volume3689Organic Compounds of seawater and of hydrogen is known,the hydrocarbon concentration in the headspace can be used to calculate the partition coefficients and the concen-trations of hydrocarbon in the seawater.This method is capable of determining 1µg/l of volatile hydrocarbons in seawater.9.1.3Raman SpectroscopyAhmadyian and Brown[25]have used laser Raman spectroscopy to identify petroleums.9.1.4Flow CalorimetryZsolnay and Kiel[26]have usedflow calorimetry to determine total hydro-carbons in seawater.In this method the seawater(1litre)was extracted with trichlorotrifluoroethane(10ml)and the extract was concentrated,first in a vac-uum desiccator,then with a stream of nitrogen to10µl.A50µl portion of this solution was injected into a stainless steel column(5cm×1.8mm)packed with silica gel(0.063–0.2mm)deactivated with10%of water.Elution was ef-fected,under pressure of helium,with trichlorotrifluoroethane at5.2ml per hour and the eluate passed through the calorimeter.In this the solutionflowed over a reference thermistor and thence over a detector thermistor.The latter was embedded in porous glass beads on which the solutes were adsorbed with evolution of heat.The difference in temperature between the two thermistors was recorded.The area of the desorption peak was proportional to the amount of solute present.9.2Aromatic Hydrocarbons9.2.1SpectrofluorometryBooksh et al.[27]employed an excitation/emission matrix imaging spectroflu-orometer for quantitation of twofluorescent compounds,naphthalene and styrene,contained in ocean water exposed to gasoline.Multidimensional par-allel factor(PARAFAC)analysis models were used to resolve the naphthalene and styrenefluorescence spectra from a complex background signal and over-lapping spectral interferents not included in the calibration set.Linearity was demonstrated over2orders of magnitude for determination of naphthalene with a detection limit of8parts per billion.Similarly,nearly2orders of mag-nitude of linearity were demonstrated in the determination of styrene with an9.3Polyaromatic Hydrocarbons369 11ppb limit of detection.Furthermore,the synthesis of the EEM spectroflu-orometer and the PARAFAC analysis for unbiased prediction of naphthalene and styrene concentration in mixture samples containing uncalibrated spectral interferents was demonstrated.9.2.2High-Performance Liquid Chromatography(HPLC)By its very nature,the gas chromatograph is only useful with those compounds which can be made volatile in some pounds that are nonvolatile at the temperatures that can be achieved in the gas chromatograph injection port, or those that degrade and polymerise,will be left as a residue in the injection port or at the top of the column.For these compounds,high-performance liquid chromatography is the natural technique.The weak point of this technique has been the sensitivity of the detectors;the common commercially available detectors measure refractive index,and light absorption andfluorescence in the ultraviolet and visible.Of these,only thefluorescence detector can approach the sensitivity of the gas chromatograph detectors,and it is useful only for those few compounds that are naturallyfluorescent.There have also been attempts to link the liquid chromatograph toflame ionisation detectors and atomic absorption spectrometers.HPLC has been used,with an ultraviolet absorption detector set for254nm, for the determination of aromatic hydrocarbons and with aflow calorimeter for the detection of all hydrocarbons.Increased sensitivity and decreased inter-ference can be achieved with the ultraviolet absorption detector by measuring absorption at two wavelengths and using the ratios of the absorption at those wavelengths[28].9.3Polyaromatic HydrocarbonsHiltabrand[29]has investigated thefluorometric determination of polyaro-matic aromatic hydrocarbons in seawater.Payne[30]carried out afield investigation of benzopyrene hydrolysate induction as monitor for marine petroleum pollution.Isaaq et al.[31]isolated stable mutagenic ultraviolet photodecomposition products of benzo(a)pyrene by thin-layer chromatography.Fuoco et al.[539]has reported the analysis of priority pollutants in seawater using online supercriticalfluid chromatography,cryotrap gas chromatogra-phy–mass ing this system polynuclear aromatic hydrocarbons and polychlorobiphenyls were measured in seawater with recoveries better than75%.Law et al.[540]have recently reviewed methods for the analysis of polyaro-matic hydrocarbons in marine water.3709Organic Compounds 9.4Oil SpillsIn the early days of pollution research,many methods were investigated in the hope offinding a single technique which would infallibly link the deed and the doer,the oil spill and the leaking container.The research was aided by a number of cases in which the provenance was obvious;the Torrey Canyon and the Arrow incidents are two examples.Thus it was possible to study the changes brought about by weathering and to discover how these changes would hamper identification of the source of the spill.The difficulty of attempting such identification using only a single technique was clearly shown by the number of proposals to add radioactive or chemical labels to petroleum products as they were loaded into the tankers.Of the methods developed for the identification of hydrocarbon mixtures, only coupled gas chromatography–mass spectrometry holds any real promise of certain identification and this only at a prohibitive cost in time spent charac-terising minor peaks.It would be far more efficient to develop rapid screening procedures which would eliminate all but a few possibilities,and then use gas chromatography–mass spectrometry to isolate and identify a few key peaks to confirm the characterisation.This is precisely the scheme adopted indepen-dently by a number of laboratories.9.4.1SpectrofluorometryThis method was originally used to detect oil in surveys of oil in seawater (Zitko and Carson[32];Michalik and Gordon[33];Levy[34,35];Levy[36]).Van Duuren[37]examined the use of emission and excitation spectra in the identification of aromatic hyorocarbons.Contour diagrams offluorescence activity at various excitation and emission wavelengths have been used as a means of identifying petroleum residues.However,the main use offluorescence has been in the semi-quantitative determination of aromatic hydrocarbons by extraction into an organic solvent, followed by excitation at a standard wavelength and comparison with the emission from a chosen standard.These techniques have been studied by many workers[38–42].The difficulties in the use offluorescence for quantitative measurement of hydrocarbons are much like those for the ultraviolet absorption methods.Each compound has its own excitation and emission maxima,with thefluorescence quantum yields varying sometimes by an order of magnitude.Thus the amount of hydrocarbon reported by an analysis will depend upon the emission and ex-citation wavelengths chosen,and upon the compound selected as the standard.Petroleum products contain manyfluorescing compounds,e.g.,aromatic hydrocarbons,polycyclic aromatic hydrocarbons,and various heterocyclic9.4Oil Spills371 compounds.The use offluorescence technique and instrumentation has led to the use of this technique for the identification of crude and residual oil pollutants in a marine environment[43,44]and of motor oils and related petroleum products[45–48].Maher[49]usedfluorescence spectroscopy for monitoring petroleum hy-drocarbon contamination in estuarine and ocean waters.An ingenious variation on the standardfluorescence methods was proposed by Red’kin et al.[50].Water samples were extracted with non-polar solvents, transferred into hexane and the hexane solution frozen at77K.At that temper-ature the normally diffuse luminescence emission bands are present as sharp emission lines,making identification offluorescing compounds considerably simpler.In the case of a complex mixture,some separation by column or thin layer chromatography might be necessary.Second-order and fourth-order derivative synchronous spectrometry has been used tofingerprint crude oil and fuel oil spills in seawater[51].9.4.2Infrared SpectroscopyKawahara[52–54]has described an infrared spectroscopic method applicable to essentially nonvolatile petroleum products.Heavy residual fuel oils and asphalts are not amenable to gas chromatogra-phy and give similar infrared spectra.However,a differentiation can be made by comparing certain absorption intensities[52].Samples were extracted with chloroform,filtered,dried,and the solvent evaporated off at100◦C for a few minutes using an infrared lamp.A rock salt smear was prepared from the residue in a little chloroform,and thefinal traces of solvent removed using the infrared lamp.The method,which in effect compares the paraffinic and aromatic nature of the sample,involves calculation of the following absorption intensity ratios:•(13.88µm polymethylene chain)/(7.27µm methyl groups)•(3.28µm aromatic C–H)/(3.42µm aliphatic C–H)•(12.34µm aromatic rings)/(7.27µm methyl groups)•(6.25µm aromatic C–C)/(7.27µm methyl groups)•(12.34µm aromatic rings)/(13.88µm polymethylene chain)•(6.25µm aromatic C–C)/(13.88µm polymethylene chain)Peaks observed at5.90µm and8.70µm were thought to reflect oxidative effects on the asphaltic material,while asphaltic sulfoxide and sulfone were tentatively inferred from bands at9.76,8.66,and7.72µm.The12.34/13.88,12.34/7.27, and6.25/13.88µm ratios tended to show the greatest difference between dif-ferent samples.When the ratio12.34/7.27µm versus12.34/13.88µm were plot-ted graphically,the intermediate fuel oils behaved similarly[53].Weathering caused fuel oils to fall below the curve although with asphalts the effect was3729Organic Compoundssignificantly less.Since no prior purification was employed the method relies on an uncontaminated,unweathered sample of oil being available.Mattson and Mark[55,56]reported some criticism of Kawahara’s technique. They claim that evaporation of the solvent chloroform by infrared heating re-moves volatiles and causes large changes in the ratios.An oil sample was shown to suffer such alteration by the infrared during repeated analysis.The absorp-tion of all bands decreased nonuniformly between20and100%over a period of30min.They propose the application of internal reflection spectrometry as a rapid,direct qualitative technique requiring no sample pretreatment.In contrast to infrared spectrometry there is no decrease in relative sen-sitivity in the lower energy region of the spectrum,and since no solvent is required,no part of the spectrum contains solvent absorptions.Oil samples contaminated with sand,sediment,and other solid substances have been anal-ysed directly,after being placed between0.5mm23-reflection crystals.Crude oils,which were relatively uncontaminated and needed less sensitivity,were smeared on a2mm5-reflection crystal.The technique has been used to differ-entiate between crude oils from natural marine seepage,and accidental leaks from a drilling platform.The technique overcomes some of the faults of in-frared spectroscopy,but is still affected by weathering and contamination of samples by other organic matter.The absorption bands shown in Table9.1are important in petroleum product identification.Kawahara and Ballinger[53,57]has used their method to characterise a number of known and unknown petroleum samples.All of these studies used the normal transmission method to obtain infrared spectra;however, the feasibility of using internal reflection to obtain infrared spectra has been demonstrated by several groups(Mattson and Mark[55],Mark et al.[58], Table9.1.Absorption bands important in petroleum products identificationBand(µm)Compound3.23–2.78Water3.28Aromatic CH3.29–CH33.42>CH23.51>CH25.88>C=O6.25Aromatic C–C6.90>CH27.27–CH39.71>S=O,PO411.63Aromatic CH13.60Aromatic CH13.98Long chain–CH2–Source:Author’s ownfiles9.4Oil Spills373 Baier[59]).The advantage of the latter method is that chemical extraction of petroleum from such as sand and water is unnecessary.Pierre[60]has reported a study of the characterisation of the surface of oil slicks by infrared reflective spectroscopy.A double-beam spectrophotometer was modified for studying the reflectance spectra(at angles of incidence45◦, 60◦,70◦)of oil layers(20–30µm thick)on the surface of water using pure water as reference.Various other workers have discussed the application of this technique to oil spill analysis[61–63].9.4.3Gas ChromatographyVarious workers have discussed this technique[43,64–72].Ramsdale and Wilkinson[66]have identified petroleum sources of beach pollution by gas chromatography.Samples containing up to90%of sand or up to80%of emulsified water were identified,without pretreatment by gas chromatography,on one of a pair of matched stainless steel columns (750×3.2mm id)fitted with precolumns(100mm)to retain material of high molecular weight,the second column being used as a blank.The column packing is5%of silicone E301on Celite(52–60mesh),the temperature is programmed at5◦C per minute from50◦C to300◦C,nitrogen was used as carrier gas,and twinflame ionisation detectors were used.Adlard et al.[74]improved the method of Ramsdale and Wilkinson[66] by using an S-selectiveflame photometric detector in parallel with theflame ionisation detector.Obtaining two independent chromatograms in this way greatly assists identification of a sample.Evaporative weathering of the oil samples has less effect on the information attainable byflame photometric detection than on that attainable byflame ionisation detection.A stainless steel column(1m×3mm id)packed with3%of OV-1on A WDMCS Chro-mosorb G(85–100mesh)was used,temperature programmed from60◦C to 295◦C per minute with helium(35ml/min)as carrier gas,but the utility of the two-detector system is enhanced if it is used in conjunction with a stainless steel capillary column(20×0.25mm)coated with OV-101and temperature programmed from60◦C to300◦C at5◦per minute,because of the greater detail shown by the chromatograms.Brunnock et al.[67]have also determined beach pollutants.They showed that weathered crude oil,crude oil sludge,and fuel oil can be differentiated by the n-paraffin profile as shown by gas chromatography,wax content,wax melting point,and asphaltene content.The effects of weathering at sea on crude oil were studied;parameters unaffected by evaporation and exposure are the contents of vanadium,nickel,and n-paraffins.The scheme developed for the identification of certain weathered crude oils includes the determination of these constituents,together with the sulfur content of the sample.3749Organic Compounds Adlard and Matthews[75]applied theflame photometric sulfur detector to pollution identification.A sample of the oil pollutant was submitted to gas chromatography on a stainless steel column(1m×3mm)packed with3%of OV-1on A WDMCS Chromosorb G(85–100mesh).Helium was used as carrier gas(35ml/min)and the column temperature was programmed from60◦C to295◦C at5◦per minute.The column effluent was split between aflame ionisation and aflame photometric detector.Adlard and Matthews[75]claim that the origin of oil pollutants can be deduced from the two chromatograms. The method can also be used to measure the degree of weathering of oil samples.Boylan and Tripp[76]determined hydrocarbons in seawater extracts of crude oil and crude oil fractions.Samples of polluted seawater and the aqueous phases of simulated samples(prepared by agitation of oil–kerosene mixtures and unpolluted seawater to various degrees)were extracted with pentane. Each extract was subjected to gas chromatography on a column(8ft×0.06in) packed with0.2%of Apiezon L on glass beads(80–100mesh)and temper-atures programmed from60◦C to220◦C at4◦C per minute.The compo-nents were identified by means of ultraviolet and mass spectra.Polar aro-matic compounds in the samples were extracted with methanol-dichlorome-thane(1:3).Investigations on pelagic tar in the North West Atlantic have been car-ried out using gas chromatography[77].This report collects together the results of various preliminary investigations.It is in the Sargasso Sea where the highest concentrations(2–40mg/m2)occur,and on beaches of isolated islands,such as Bermuda.These workers discuss the occurrence,structure, possible sources,and possible fate of tar lumps found on the surface of the ocean.Zafiron and Oliver[78]have developed a method for characterising envi-ronmental hydrocarbons using gas chromatography.Solutions of samples con-taining oil were separated on an open-tubular column(50ft×0.02in)coated with OV-101and temperature programmed from75◦C to275◦C at6◦C per minute;helium(50ml/min)was used as carrier gas and detection was byflame ionisation.To prevent contamination of the columns from sample residues the sample was injected into a glass-lined injector assembly,operated at175◦C, from which gases passed into a splitter before entering the column.Analysis of an oil on three columns gave signal intensity ratios similar enough for direct comparison or for comparison with a standard.The method was adequate for correlating artificially weathered oils with sources and for differentiating most of30oils found in a sea port.Garra and Muth[80]and Wasik and Brown[81]characterised crude,semi-refined,and refined oils by gas chromatography.Separation followed by dual-response detection(flame ionisation for hydrocarbons andflame photometric detection for S-containing compounds)was used as a basis for identifying oil samples.By examination of chromatograms,it was shown that refinery9.4Oil Spills375 oils can be artificially weathered so that the source of the oils can be deter-mined.Hertz et al.[79]have discussed the methodology for the quantitative and qualitative assessment of oil spills.They describe an integrated chromato-graphic technique for studies of oil spills.Dynamic headspace sampling, gas chromatography,and coupled-column liquid chromatography are used to quantify petroleum-containing samples,and the individual components in these samples are identified by gas chromatography and mass spectrometry.Rasmussen[82]describes a gas chromatographic analysis and a method for data interpretation that he has successfully used to identify crude oil and bunker fuel spills.Samples were analysed using a Dexsil-300support coated open tube(SCOT)column and aflame ionisation detector.The high-resolution chromatogram was mathematically treated to give“GC patterns”that were a characteristic of the oil and were relatively unaffected by moderate weath-ering.He compiled the“GC patterns”of20crude oils.Rasmussen[82]uses metal and sulfur determinations and infrared spectroscopy to complement the capillary gas chromatographic technique.The gas chromatograms of most oil samples examined had similar basic features.All were dominated by the n-paraffins,with as many as13resolved but unidentified smaller peaks appearing between the n-paraffin peaks of adjacent carbon numbers.Each oil had the same basic peaks,but their relative size within bands of one carbon number varied significantly with crude source.9.4.4Gas Chromatography–Mass Spectrometry(GC–MS)In some cases it is necessary unambiguously to identify selected components separated during gas chromatographic examination of oil spill material.Such methods are needed from the standpoint of the enforcement of pollution control laws.The coupling of a mass spectrometer to the separated components emerging from a gas chromatographic separation column enables such positive identifications to be made.Smith[83]classified large sets of hydrocarbon oil infrared spectral data by computer into“correlation sets”for individual classes of compounds.The correlation sets were then used to determine the class to which an unknown compound belongs from its mass spectral parameters.A correlation set is constructed by use of an ion-source summation,in which a low resolution mass spectrum is expressed as a set of numbers representing the contribution to the total ionisation of each of14ion series.The technique is particularly valuable in the examination of results from coupled gas chromatography–mass spectrometry of complex organic mixtures.Walker et al.[84]examined several methods and solvents for use in the extraction of petroleum hydrocarbons from estuarine water and sediments, during an in situ study of petroleum degradation in sea water.The use of。

WATER ANALYSIS INSTRUMENTS UV-Vis spectrophotometerChlorophyll is the green pigment in plants that allows them to create energy fromlight to photosynthesize. By measuring chlorophyll, you are indirectly measuring the amount of photosynthesizing plants (such as algae or phytoplankton) found in a sample. Chlorophyll a pigment is universal to all plant types, while other chlorophylls (such as b, c1, c2, d, f ) may be specific to certain plants, algae, or cyanobacteria and may be used to identify major algal groups present.1Why measure chlorophyll a ?The flow of nutrients, such as phosphorous and nitrogen, into inland and coastal waters contributes to enhanced algae growth. Figure 1, on the next page, shows how chlorophyll a can correlate to dissolved inorganic nitrogen (DIN).2 Changes to nutrient loadings can also change the phytoplankton species composition and diversity.High levels of algae often indicate poor water quality and low levels often suggest good conditions. Elevated phytoplankton levels can lead to reduced water clarity, affecting sea grass growth and related fisheries. In extreme cases, eutrophication can lead to hypoxia (oxygen-depleted “dead zones” that kill fish, shellfish, and crustaceans) and harmful and/or toxic algal blooms. From a water quality perspective, chlorophyll a is the best available, most direct measure of the amount and quality of phytoplankton and the potential to lead to reduced water clarity and low dissolved oxygen impairments.3 Chlorophyll a is often reported in mass per unit volume, e.g. µg/L, mg/L. The chlorophyll a threshold for impacts on fish is generally considered to be 100 µg/L.2 The cleanest waters will have chlorophyll a levels of less than 5 µg/L.5 The specific, applicable water quality standard will depend on the uses and goals for that water body.S mart NotesWhat is chlorophyll a?Who measures chlorophyll a?Drinking water treatment plants with surface water impoundments will measure chlorophyll a to manage the source water. This may include predicting and controlling algae blooms or determining where to draw water to avoid algae intake, which can clog filtration systems, increase organic load, cause a public health nuisance, and necessitate extra treatment. In the United States, other agencies analyzing chlorophyll a include: US Army Corps of Engineers; US Environmental Protection Agency (US EPA); state environmental agencies and laboratories; Chesapeake Bay Program; US Geological Survey (USGS); National Oceanic and Atmospheric Administration (NOAA); Audubon of Florida; academic institutions, and others.How is chlorophyll a measured?Chlorophyll a is measured by filtering a known amount of sample water through a filter, usually a glass fiber filter. The filter is ground up in an acetone solution, which is then processed and analyzed. There are three standard techniques for determining chlorophyll a concentrations: spectrophotometry, fluorometry, and high-performance liquid chromatography (HPLC). Spectrophotometry is the most commonly used laboratory method. The sample processing time is typically 1–5 minutes, the estimated detection limit (DL) is 0.08 mg/L6 (using a 1 cm cell;use larger for lower DL), and the instrumentation cost is low. The HPLC method is able to differentiate between chlorophyll types and accessory pigments, but is a slower and more demanding technique, e.g., 20–25 minutes of sample processing time. The cost of an HPLC instrument may be 10 times the cost of a spectrophotometer, and there are considerable ongoing consumables costs. Fluorescence is an indirect method for measuring chlorophyll a, and is well suited for remote monitoring.To measure chlorophyll a by the spectrophotometric technique, a spectrophotometer with a narrow band width (pass) is used to take measurements at multiple wavelengths. For example, the trichromatic method uses measurements at 750 nm (turbidity correction), 664 nm (chlorophyll a), 647 nm (chlorophyll b correction), and 630 nm (chlorophyll c1, c2 correction). See absorption spectra for chlorophyll a and b in the image to the right,, Figure 2.An alternate method uses measurements at 750, 664, and/ or 665 nm before and after acidification, which corrects for pheophytin a and turbidity interferences. The wavelengths and equations used will depend on the method chosen. Examples of accepted chlorophyll a testing methods include US EPA 446.0, Standard Methods 10200 H, ASTM D3731, DIN 38412-16, ISO 10260, and others. Equipment for testing chlorophyll a by spectrophotometerThe Thermo Scientific™ Orion™ AquaMate™ UV-Vis Spectrophotometer is a good choice for this testingand meets the requirements for accepted chlorophyll a testing methods, such as listed above. The instrumenthas the necessary narrow band pass, covers the required wavelengths, accommodates sample cells from 1 to 10 cm, and is designed to offer the accuracy, dependability andease of use your lab requires.Figure 1. Chlorophyll a corresponds to DIN.Figure 2. Absorption spectra for chloropylla and b.References1. Method 10200 H. Chlorophyll, Standard Methods for the Examination of Water andWastewater, .2. Chlorophyll a concentrations, Ozcoasts, Marine & Coastal Environment Group,Geoscience Australia, .au/indicators/chlorophyll_a.jsp.3. Ambient Water Quality Criteria, USEPA April 2003, /content/publications/cbp_13142.pdf.4. Nielson, J. and P. Jernakoff, P. 1996. A review of the interaction of sediment and waterquality with benthic communities. Port Phillip Bay Environmental Study. TechnicalReport No. 25, 1-130.5. Method 446.0 In Vitro Determination of Chlorophylls a, b, c1 + c2 and Pheopigmentsin Marine and Freshwater Algae by Visible Spectrophotometry. National ExposureResearch Laboratory, US EPA, Cincinnati, OH. https:///si/si_public_file_download.cfm?p_download_id=525241&Lab=NERL.6. Absorption spectra for chlorophyll a and b, https:///biol13100/index.php/File:Chlorophyll.JPGF ind out more at /aquamateThis product is intended for General Laboratory Use. It is the customer’s responsibility to ensure that the performance of the product is suitable for customer’s specific use or application. © 2016, 2020 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific and its subsidiaries unless otherwise specified. SN-CHLOROPHYLL-E 1020。

化工进展Chemical Industry and Engineering Progress2024 年第 43 卷第 2 期低强度超声波对高负荷厌氧氨氧化EGSB 反应器运行性能的影响杨杰源1，朱易春1，赖雅芬1，张超1，田帅2，谢颖1（1 江西理工大学赣州市流域污染模拟与控制重点实验室，江西 赣州 341000；2 江西理工大学资源与环境工程学院，江西 赣州 341000）摘要：研究了低强度超声波对厌氧氨氧化EGSB 反应器处理无机高氨氮废水的影响，考察了超声波处理对反应器脱氮性能、厌氧氨氧化颗粒污泥特征、胞外聚合物以及微生物菌群的变化情况。

结果表明，低强度超声波可提高厌氧氨氧化反应器脱氮效能，在进水氮负荷为6.03kg N/(m³·d)时，总氮去除率提高了11.40%，抵抗氮负荷冲击能力也得到了增强。

周期性超声波辐照后，颗粒污泥粒径维持在1.0~1.5mm ，有利于改善传质效率，提升厌氧氨氧化颗粒污泥活性和减少颗粒漂浮。

污泥EPS 总量有显著增加，其中紧密结合型胞外聚合物（TB-EPS ）增加较为明显，有助于维持颗粒污泥的结构稳定性。

污泥表面官能团种类不变，但羟基、羧基、氨基等基团有所增多。

颗粒污泥的比厌氧氨氧化活性提高了33.2%，通过简化的Gompertz 方程模型发现超声组的厌氧氨氧化菌生长速率（0.0127d -1）高于对照组（0.0107d -1）。

高通量测序显示，超声波促进了厌氧氨氧化菌及其共生菌，其中Candidatus Brocadia 提升了22.03%。

同时严重抑制了部分反硝化细菌，使厌氧氨氧化菌的底物和生存空间更加充足。

关键词：低强度超声波；厌氧氨氧化；颗粒污泥；微生物群落；氮负荷中图分类号：X703.1 文献标志码：A 文章编号：1000-6613（2024）02-1098-11Effect of low intensity ultrasound on operation performance of high loadAnammox-EGSB reactorYANG Jieyuan 1，ZHU Yichun 1，LAI Yafen 1，ZHANG Chao 1，TIAN Shuai 2，XIE Ying 1(1 Ganzhou Key Laboratory of Basin Pollution Simulation and Control, Jiangxi University of Science and Technology,Ganzhou 341000, Jiangxi, China; 2 School of Resources and Environmental Engineering, Jiangxi University of Science andTechnology, Ganzhou 341000, Jiangxi, China)Abstract: The effect of low intensity ultrasound on the treatment of high-ammonia-nitrogen wastewater by Anammox-EGSB reactor was studied. The effects of ultrasound treatment on the nitrogen removal performance of the reactor, characteristics of Anammox granular sludge, extracellular polymer and microbial flora were investigated. The results showed that low intensity ultrasound could improve the nitrogen removal efficiency of Anammox reactor, and the nitrogen load of influent was 6.03kg N/(m³·d), the total nitrogen removal rate of ultrasonic group was increased by 11.40%, and the impact resistance of nitrogen load was also enhanced. After periodic ultrasonic irradiation, the particle size of granular sludge研究开发DOI ：10.16085/j.issn.1000-6613.2023-0315收稿日期：2023-03-02；修改稿日期：2023-04-02。

Early hydration and setting of Portland cement monitored by IR,SEM and Vicat techniquesRikard Ylmén,Ulf Jäglid,Britt-Marie Steenari,Itai Panas ⁎Department of Chemistry and Biotechnology,Environmental Inorganic Chemistry,Chalmers University of Technology,S-41296Gothenburg,Swedena b s t r a c ta r t i c l e i n f o Article history:Received 26November 2007Accepted 30January 2009Keywords:HydrationCalcium-silicate-hydrate (C-S-H)Spectroscopy Cement paste Portland cementDiffuse Re flectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement.To obtain a suf ficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process.Rapid re-crystallization of sulphates is observed during the first 15s,and appears to be complete after ~30min.After ~60min,spectroscopic signatures of polymerizing silica start to emerge.A hump at 970–1100cm −1in conjunction with increasing intensity in the water bending mode region at 1500–1700cm −1is indicative of the formation of Calcium Silicate Hydrate,C-S-H.Simultaneously with the development of the C-S-H signatures,a dip feature develops at 800–970cm −1,re flecting the dissolution of Alite,C 3S.Setting times,180(initial)and 240(final)minutes,are determined by the Vicat bining DR-FTIR,SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H.©2009Elsevier Ltd.All rights reserved.1.IntroductionToday,Portland cement is a widely used binder in concrete construction.C 3S (alite)and C 2S (belite)is essential to the build-up of strength in Portland cement.These two calcium-silicate phases are formed above 800°C,where C 3S is preferentially formed upon elevating the temperature and increasing amount of added burned lime,CaO.C 3S is responsible for short term strength development (days to months)while C 2S displays the better long term strength development performances (~years).The quest for increasingly shorter setting time and early strength has seen the C 3S/C 2S ratio increase in commercial Portland cement.In recent years,the increased attention on environmental aspects of material conversion has in fluenced research towards possible modi fications of Portland cement to better meet the increasing demands for sustainability in the construction sector.This is done by using additives and changing the composition of the cement.Many different experimental techniques have been employed to investigate the effects on material conversion as Portland cement is dissolved and transformed into calcium-silicate-hydrate,C-S-H.For determination of setting times,Vicat measurements are often employed.At later stages in the hydration process,an ultrasonic cement analyser may be used to determine changes in the elastic modulus of the mortar [1,2].Calorimetry is employed to monitor the heat released upon hydration [3–7],whereas X-ray diffraction [8–13],nuclear magnetic resonance [14–16]and Fourier transform infrared spectroscopy,FTIR,are used toobtain chemical information.Morphological information may be obtained by means of scanning electron microscopy and transmission electron microscopy [11,12,15,17].Spectroscopic methods are commonly used to study the chemistry of cement hydration.In the present work the hydration of Portland cement has been monitored mainly by means of infrared spectroscopy.In infrared spectroscopy one utilizes that molecules or groups of atoms on large molecules absorbs different wavelengths of infrared light depend-ing on which atoms that constitute the molecule or group,its geometry and its immediate surroundings.It can therefore be used to study both crystalline and amorphous samples.The sample is irradiated with infrared light with a span of different wavelengths.The sample will absorb some of the light at wavelengths that are characteristic to its chemical composition.To see at which wavelengths the sample has absorbed light the intensity at each wavelength is measured with and without sample.IR radiation only penetrates about 1wavelength into the sample (~10µm for 1000cm −1),making it ideal in the study of surface processes.In previous studies where FTIR was used to study the hydration of cement and its components,the sample was prepared by mixing the cement with KBr and pressing the mixture into pellets [18–21].The usefulness of Diffuse Re flectance Fourier Transform Infrared Spectro-scopy,DR-FTIR,as a tool for studying the hydration of cement has also been demonstrated in previous work [22,23].A comparison between DR-FTIR and the KBr pellet technique has been done by Delgado et al.[24],who showed that the methods produce similar spectra.The advantage of the KBr technique is that it provides better de fined bands than DR-FTIR,but the sample preparation is more labour intensive.The results of the present study suggest that the DR-FTIR technique employed is indeedCement and Concrete Research 39(2009)433–439⁎Corresponding author.Tel.:+46317722860;fax:+46317722853.E-mail address:itai@chalmers.se (I.Panas).0008-8846/$–see front matter ©2009Elsevier Ltd.All rights reserved.doi:10.1016/j.cemconres.2009.01.017Contents lists available at ScienceDirectCement and Concrete Researchj ou r n a l h o m e pa g e :ht t p ://e e s.e l s e v i e r.c o m /C E MC ON /d e f a ul t.a s ppreferred in that external physico-chemical interference is minimized,i.e.the hydration products are studied in the proper cement matrix with a minimum of sample tampering,and avoiding contact with foreign chemicals.Differential IR light absorption of samples which have been allowed to hydrate for different times is reported here.Water displays strong absorption in the mid-IR range,which makes it virtually impossible to perform in situ studies of cement hydration.A second draw back of in situ DR-FTIR for the study of cement hydration is that the surface of the cement paste,while hydrating,may become too flat for the diffuse re flectance technique to be ef ficiently used.These considerations validate selection of an ex situ DR-FTIR approach.To study very early hydration using an ex situ technique,it is imperative that the hydration is stopped instantaneously at a predetermined time.To satisfy this requirement,a freeze-dry technique is adopted in this research.The freezing of the sample with liquid nitrogen ensures that all chemical processes are very much retarded,while the subsequent water evaporation step at low temperature minimizes any thermally induced chemical transforma-tions other than water removal while drying.Indeed,earlier microscopy work [25–27]has shown that freezing is a relatively mild method to stop hydration.The drying will of course affect the structures of some phases.Bound water,like in ettringite,could be partially removed,and morphological properties may change upon removal of water.The purpose of the present study is to demonstrate the ef ficiency of the freeze-dry procedure in conjunction with DR-FTIR spectroscopy for studying the complex hydration chemistry of Portland cement.An attempt to correlate relevant spectroscopic signatures to the devel-opment of strength in the system is also made.Strength development is monitored here by means of Vicat measurements.2.ExperimentalThe Portland cement used was a Portland limestone cement,“byggcement Std PK Skövde CEM II/A-LL 42,5R ”,from Cementa AB.An automatic/manual mortar mixer 39-0031from ELE International was used.The cement was mixed with distilled deionized water that was poured into the mixing bowl before adding the cement.The ratio of water to as received dry cement was 0.4by weight in both DR-FTIR and Vicat measurements.The cement was carefully added and the paste was mixed at 140rpm on the mixing blade and 62rpm on the mixing head.The hydration time was measured from the instant when the cement was added to the water.2.1.DR-FTIRThe spectrometer used was a Nicolet Magna-IR 560with an insert cell for diffuse re flectance spectroscopy.The measurement range liesbetween 400and 4000cm −1.The diffuse re flectance technique is utilized,in which the incident beam is allowed to be re flected off the ground sample towards an overhead mirror upon which the diffusely scattered rays are collected and measured in the detector.A more detailed description is given by Fuller and Grif fiths [28].The sample is scanned 64times with a resolution of 2.0cm −1and the presented data is an average value.Each sample was prepared and analyzed 3times and the final spectrum was an average of these 3measurements to minimize differences due to sample preparation.The batch size was 200g of as received dry cement.As the cement hydration was studied from 15s the cement paste was only mixed for 15s.However,the chemical development of the cement paste was found to be insensitive of mixing time as long as the cement was completely wetted [29].Samples were prepared in plastic dishes of 35mm in diameter.The thickness of the paste in the dishes was ~2–3mm.Lids were placed over the dishes while they hydrated to prevent water from evaporating.The samples were hydrated between 15s and 360min in normal laboratory environment,then frozen by immersion in liquid nitrogen and subsequently placed in the freeze drier overnight.Measurements were made the following day.Before measurement the sample was ground and placed in the sample holder of the DR-FTIR spectrometer.To obtain good reproducibility,great care was taken when grinding the samples and placing them in the sample cup to make the samples as similar as possible.2.2.VicatThe batch size was 300g of as received dry cement and the cement paste was mixed for 2⁎90s with a stop in between for 15s to scrape the paste from the inside walls.The Vicat apparatus used was a Vicatronic automatic recording apparatus E040and measurements were performed in a 40mm mould with a calibrated weight of 300g and a cylindrical needle with flat tip area of 1mm 2.2.3.Scanning electron microscopyThe microscope used was a FEI Quanta 200FEG ESEM operated in secondary electron detection mode with high-vacuum and an acceleration voltage of 2kV.Some of the freeze-dried samples were pulverized.Since the freeze-dried samples were barely holding together this was easily done with a metal spoon.Some of the powder was placed on carbon tape attached to the sampleholder.Fig.1.Vicat measurement showing the depth of penetration of the Vicat needle into the cement as function of time.The height of the mould was 40mm.Table 1Possible assignment to some of the peaks observed in Figs.2–5.Wave number [cm −1]Possible assignment Reference656–658υ4of SiO 4[21,40]714υ4of CO 3[22,32,35,37]847–848Al –O,Al –OH [21,35]877–878υ2of CO 3[21,22,35,37]1011–1080Polymerized silica [19]~1100–1200υ3of SO 4[19,22,31,32]1200–1202Syngenite,thenardite [32–34]1400–1500CO 3[19,21,22,35,37]1620–1624υ2of water in sulphates [22,31,33]1640–1650υ2H 2O[21,35,36]1682–1684υ2of water in sulphates [22,31,33]1795–1796CaCO 3Own measurement,[22]2513–2514CaCO 3Own measurement,[22]2875–2879CaCO 3Own measurement,[22]2983–2984CaCO 3Own measurement,[22]3319–3327Syngenite,thenardite [32–34]3398–3408υ3of H 2O,capillary water [36]3457υ1+υ3of H 2O[21,36]3554υ3of H 2O in gypsum [22,31]3611Bassanite [22]3641–3644Ca(OH)2Own measurement,[20,23,24,37]434R.Ylmén et al./Cement and Concrete Research 39(2009)433–439Several regions were examined to make sure that the observed structures were representative of the sample.3.ResultsThe present study attempts to correlate setting with the evolution of spectral features in DR-FTIR spectra during early hydration of cement.The Vicat setting time measurement for the used Portland cement is displayed in Fig.1.Initial andfinal set are seen to occur at 180min and240min respectively.In Section3.1,the overall time evolution of DR-FTIR absorption intensities is presented.Possible assignments of the different bands are shown in Table1,and interpreted in Sections3.1.2–3.1.4.3.1.Time resolved spectra of hydrating cementThe hydration process was monitored for thefirst six hours by applying the freeze dry method,grinding of sample and subsequently acquiring the DR-FTIR spectra.The recorded absolute spectra of dry and hydrated cement are displayed in Fig.2.It shows the spectra of theas received dry cement together with the cement just after it has been mixed(15s),after180min and360min of hydration.Weak signatures of hydration can be seen in the900–1200cm−1region.To enhance these effects,various difference spectra were constructed.In Fig.3,the difference spectra employ as received dry cement as reference.Now, the spectroscopic features can be seen significantly clearer and we observe the development and saturation band at1100–1200cm−1 already after15s.This is complemented by a more slowly growing feature at900–1100cm−1.Because the bands that developed after 15s cannot be associated with the actual hardening of cement paste, the15s spectrum was taken as reference in Figs.4and5.Fig.3 supports the overall procedure in that a smooth background is observed in the relevant spectral regions.Having found this,Fig.5 focuses on the500–2000cm−1interval and the spectra for twelve different hydration times are displayed.3.1.1.Sulphate bandsThe sulphates originally present in Portland cement are gypsum (CaSO4·2H2O),hemihydrate(bassanite,CaSO4·0.5H2O)and anhy-drite(CaSO4).The latter ones are formed when the gypsum is ground with the cement clinker.The heat makes some of the crystal water in the gypsum to dissociate.When water is added to the cement the sulphates react with the aluminate and ferrite phases of the cement to produce AFt phase.This phase in turn reacts further with the aluminate and ferrite phases to form the AFm phase[30].Characteristic sulphate absorption bands are generally found in the range1100–1200cm−1due to theυ3vibration of the SO42−-group in sulphates[19,22,31,32].It is very difficult to interpret this area by studying FTIR-spectra only,since the many forms of sulphates give rise to several peaks here and cause lots of overlaps,but also because the υ3vibration of the SiO42−-group can absorb in this region,especially when it has polymerized[21].Therefore no in-depth analysis of it will be done in this work.In the DR-FTIR spectrum of as received dry cement(Fig.2,bottom spectrum),a broad feature is seen in1100–1200cm−1region reflecting mainly amorphous sulphates.Immedi-ately after mixing with water,some sharp absorption bands develop at 1100cm−1,1200cm−1and3320cm−1,indicative of very rapid dissolution of sulphates followed by crystallization(Fig.2,15s spectrum).This can also be inferred by considering the15s difference spectrum in Fig.3.This spectrum corresponds to the difference between that acquired after15s of hydration,and the spectrum of dry cement.Spectral signatures of sulphate chemistry after15s of hydration,corresponding to re-crystallization are obtained.Appar-ently,crystalline sulphate phases form very early in the hydration process,after which they become inactive spectator phases.The extent to which this holds true can be assessed by replacing the as received dry cement reference spectrum for that of15s hydrated cement(Figs.4and5).From Fig.5we observe significant changes in the sulphate absorption bands up to30min of hydration.Apparently, intermediate phases are formed consistent with theabsorptionFig.2.Absorbance of as received dry cement and cement that has been allowed tohydrate for15s,180min and360min after the cement was added to the water.Thespectra are shown offset forclarity.Fig.3.Difference spectra where the absorbance spectrum of as received dry cement hasbeen subtracted from the absorbance spectra of cement hydrated for15s,180min and360min.The spectra are shown offset forclarity.Fig.4.Difference spectra in the range400–4000cm−1where the absorbance spectrumof the freshly mixed cement(15s)has been subtracted from the absorbance spectra ofcement hydrated for30s,5min,120min and360min.The spectra are shown offset forclarity.435R.Ylmén et al./Cement and Concrete Research39(2009)433–439spectra of syngenite (K 2Ca(SO 4)2·H 2O)and thenardite (Na 2SO 4)or closely related compounds [32–34].At any rate,after 60min,little changes can be seen in the sulphate absorption region of the spectra.3.1.2.Water associated bandsIn the spectrum for as received dry cement there is a peak at 1623cm −1and a smaller one at 1684cm −1.These are caused by the bending vibration υ2of water in sulphates,mainly gypsum [22,31,33].The peak at 3554cm −1is caused by the υ3vibration of water in gypsum [22,31]and the peak at 3611cm −1could be caused by bassanite (CaSO 4·0.5H 2O).As hydration progresses there is a broad feature forming with its centre at ~1650cm −1,caused by the bending vibration υ2of irregularly bound water [21,35,36].The consumption of gypsum can be seen as dips in this feature at 1623cm −1and 1680cm −1(Figs.4and 5).A small increase in gypsum during the first 10min is implied,and may be due to the transformations of anhydrite and bassanite.The “background ”level for wave numbers N 1600cm −1is steadily increasing with increasing hydration times.Since there seems to be no corresponding decrease in any other area,this is probably caused by the incorporation of water.The absorption intensities due to the υ2vibration mode of water at ~1650cm −1and the υ1+υ3modes at ~3450cm −1and results from Mollah et al.and Yu et al.support this observation [21,36].3.1.3.Silica associated bandsAfter about 2h of hydration new spectral intensity shifts are observed from ~900cm −1towards ~1000–1100cm −1(see Figs.3–5),neither associated with sulphates nor water,suggestive of rearrange-ments in the silica subsystem.These dip-hump features are taken to re flect dissolution of alite and simultaneously the polymerization ofsilica [21,23,37,38]to form calcium silicate hydrate C-S-H (vide infra ).In order to focus on the silica chemistry,the 15s reference spectrum is replaced by that acquired after 30min (see Fig.6),i.e.after the sulphate chemistry has stopped.Monotonous growth of the C-S-H associated absorption intensities (970–1100cm −1)is observed.The dip in the absorption spectrum at 800–970cm −1,which deepens with time,is due to the dissolution of the C 3S clinker phase [39].The intensities in the dip (800–970cm −1)and hump (970–1100cm −1)regions in Fig.6were integrated in an attempt to correlate the clinker dissolution with the silica polymerization.A horizontal line at the intensity at 970cm −1was used as baseline.The result is plotted in Fig.7.3.1.4.Hydroxides and carbonatesThe peak at 3643cm −1(see Table 1and Figs.2and 3)corresponds to Ca(OH)2,which is formed as silicate phases in the cement dissolve.The peaks at 1796cm −1,2513cm −1,2875cm −1,2983cm −1and the shoulder at 1350–1550cm −1are due to that portion of calcium carbonate,which is added to the cement by the manufacturer after clinker calcination.The amount of calcium carbonate is seen to decrease as the hydration progresses,i.e.negative absorption bands in the difference spectra of Figs.3and 4.This may partly be due to the reaction of calcite with the aluminate to form less crystalline phases such as carboxyaluminates [40,41]or the carbonate ion can substitute for sulphate ions in Aft and AFm phases [13,30].The peak growing at ~1070cm −1could be the υ1vibration of CO 3-group in the formed carbonates [33,35],but this observation would contradict theoverallFig.6.Difference spectra in the range 500–2000cm −1where the absorbance spectrum of cement hydrated for 30min has been subtracted from the absorbance spectra of cement with hydration times from 60–360min.The spectra are shown offset forclarity.Fig.7.Integrated value of the absorbance in the intervals 800–970cm −1(upper dots)and 970–1100cm −1(lower dots)in Fig.6as function of hydration time of the cement.The lines are drawn on free hand to guide the eye and does not represent a mathematicalmodel.Fig.5.Difference spectra in the range 500–2000cm −1where the absorbance spectrum of the freshly mixed cement (15s)has been subtracted from the absorbance spectra of cement with hydration times from 30s to 360min.The spectra are shown offset for clarity.436R.Ylmén et al./Cement and Concrete Research 39(2009)433–439Fig.8.SEM pictures of cement at different stages of hydration.a)Surface of unhydrated particle.b)Surface of particle hydrated for 15s.c)Surface of particle hydrated for 120min.d)Surface of particle hydrated for 240min.e)Surface of particle hydrated for 480min.f)Surface of particle hydrated for 480min at larger magni fication.437R.Ylmén et al./Cement and Concrete Research 39(2009)433–439reduction of carbonate absorption intensities with time.A more plausible candidate for this absorption band is the stretching vibration of Si–O,which is also found in jennite(Ca8(Si6O18H2)(OH)8Ca·6H2O) [37,38].3.2.SEMSEM pictures of cement grains at different stages of hydration are displayed in Fig.8.The surfaces of the unhydrated particles are bare, with debris lying on top(Fig.8a).After15s and120min of hydration (Fig.8b,c)the surfaces of the cement particles are still found to be bare,but lumps and platelets have formed in addition to the debris present already on the unhydrated particles.Fig.8d shows cement after240min of hydration.Now a carpet is covering the cement particles.The carpet has grown even more after480min of hydration and is seen to consist of needle-like protruding structures(Fig.8e,f).4.DiscussionA longstanding issue concerns the roles of various phases during early hardening of Portland cement.In particular the roles of sulphates,added to the Portland cement as anhydrous(CaSO4), hemihydrate(CaSO4·0.5H2O),and gypsum(CaSO4·2H2O)have been much discussed in this context.Indeed,the general consensus is that the dissolution and re-crystallization of the various sulphate contain-ing phases is completed well before the setting occurs[42,43].Yet,due to the complexity and instability of the early cement chemistry,the sulphates,besides their well known function as water absorbents, have been empirically found to affect the morphology of the hydrating paste both by providing a background ionic strength and by forming intermediate phases,which suppress“flash setting”.In the present study,results show that the sulphate related DR-FTIR absorption bands display large changes in the1100–1200cm−1interval but that this occurs mainly during thefirst10min of hydration,during which the development of sharp bands imply the formation of crystalline phases.The appearing platelets and hexagonal crystals seen with SEM are possibly associated with these phases.After30min,the inter-conversion of sulphate phases has apparently stopped.The sulphates formed are most probably ettringite or monosulphate,as earlier studies on cement hydration have shown that these sulphates are formed during thefirst minutes of hydration[11,43,44].In this study of the evolution of the C-S-H absorption bands,the30min spectrum was chosen as reference.The degree to which the sulphate chemistry is completed at this time can be appreciated by studying1100–1200cm−1region in Fig.6,keeping in mind that C-S-H also displays absorption bands in this interval.By DR-FTIR spectroscopy,detectable amounts of polymerized silica are formed after approximately1h of hydration,as seen in Fig.6in the 900–1100cm−1interval.It is gratifying to note how well the integrated intensities at800–970cm−1as function of time(Fig.7) correlate with the quantitative X-ray diffraction study on C3S hydration by Taylor et al.[45],who interpreted their results to imply C-S-H formation.The fact that the growth of the hump feature at970–1100cm−1follows the C3S dissolution process implies that the signature of polymeric silica indeed corresponds to C-S-H formation.It can be noted how the formation of polymerized silica(970–1100cm−1) is correlated in time with an increased incorporation of water in the structure as seen in the absorption interval at1500–1700cm−1.This supports further that calcium silica hydrate C-S-H is a major product formed upon early Portland cement hydration,as C-S-H consists of polymerized silica and calcium ions with water incorporated.It becomes interesting to attempt to correlate the materials conversion observed with DR-FTIR with morphological changes as seen with SEM.The acceleration phase of C-S-H formation starts somewhere between120and180min(Figs.6and7).Simulta-neously a growth of a needle-like phase is developed on the cement particles(Fig.8).This phase has been attributed to C-S-H in previous studies of alite,C3S,where no other phase than C-S-H and portlandite(Ca(OH)2)is formed[25,46].It is seen in Fig.1that the setting starts after180min,and that it is completed after240min. Since the conversion of the sulphates occurs during thefirst30min, the possibility that the needle-like phase is due to sulphates is ruled out.However,the acceleration phase of C-S-H formation(vide supra) occurs on the same time scale as the formation of the needle-like phase seen by SEM as well as that of the setting process.An identification of C-S-H as the phase responsible for the setting of the Portland cement is thus arrived at.Support is produced to the claim that C-S-H is responsible for the initial development of strength in Portland cement pastes.Also,it is suggested that C-S-H is formed continuously during hydration and in particular so prior to the setting.This implies that the actual setting is due to coalescence of clinker grains and that it is associated with the formation of sufficient amounts of C-S-H,to increase friction and bridge the inter-grain distances.The presentfindings are consistent with those of Chen and Odler [43],who reach the conclusion that setting in ordinary Portland cement is mainly due to the formation of C-S-H as long as the ratio between sulphates and C3A+C4AF is balanced,else“false setting”results due to the formation of ettringite or monosulphate.5.ConclusionsCement is a complex material,and its hydration possibly provides additional complexity.Indeed,as yet no single method exists which completely determines all chemical reactions taking place in a cement structure from the mixing and onward.Therefore several comple-mentary techniques must be used.In the present study,signatures of early setting of an untampered limestone Portland cement were extracted by correlating DR-FTIR,SEM, and Vicat measurements.The objective of this paper was to demonstrate how diffuse reflectance Fourier transform infrared spectroscopy in combination with freeze-drying may add a piece of the puzzle regarding material conversion during the very early stages of cement hydration, down to fractions of a minute.Whereas setting of each unique cement must be addressed separately,a method to monitor the material conversions during early hydration has been presented.Summarizing:•the time evolution of the sulphate chemistry displays very rapid crystallization followed by a slow recrystallization phase,which is completed within approximately30min;•the appearance of a broad absorption hump at970–1100cm−1after 60min of hydration is due to polymeric silica.It is correlated with the development of water bending vibration bands(1500–1700cm−1). This implies the formation of calcium silicate hydrate,C-S-H;•time dependent changes in morphology due to the hydration process,as monitored with SEM,were found to correlate with the DR-FTIR signatures of C-S-H formation,•the growth of a dip feature in the spectra at800–970cm−1,identified as the dissolution of C3S Alite,correlates with the formation of C-S-H.Vicat setting begins after180min and is completed after240min. This occurs well after the sulphate reactions have stopped.However, the C-S-H formation in the acceleration phase of C3S dissolution, displays the same time dependence as that of the setting process.The observations support the understanding of setting in terms of coalescing C-S-H coated Portland cement particles.AcknowledgementsThe support from the Knowledge foundation(KK stiftelsen),the Swedish Research Council,and Eka Chemicals Inc.,Bohus is gratefully acknowledged,as well as valuable discussions with Inger Jansson.438R.Ylmén et al./Cement and Concrete Research39(2009)433–439。

NotesA. Performance and quality attributes and conditions not expressly stated in this specification document are intended to be excluded and do not form a part of this specification document.B. Electrical specifications and performance data contained in this specification document are based on Mini-Circuit’s applicable established test performance criteria and measurement instructions.C. The parts covered by this specification document are subject to Mini-Circuits standard limited warranty and terms and conditions (collectively, “Standard Terms”); Purchasers of this part are entitled to the rights and benefits contained therein. For a full statement of the Standard Terms and the exclusive rights and remedies thereunder, please visit Mini-Circuits’ website at /MCLStore/terms.jsp Mini-Circuits® P .O.Box350166,Brooklyn,NY11235-0003(718)******************************75Ω 30 to 1200 MHzDirectional CouplerSurface MountCASE STYLE: QQQ569PRICE: $15.95 ea. QTY (1-9)Demo Board MCL P/N: TB-34Suggested PCB Layout (PL-043)Outline Dimensions ( )inchmmMaximum RatingsPin ConnectionsINPUT 6OUTPUT 1COUPLED 4GROUND 2,5ISOLA TE (DO NOT USE)3Outline DrawingDirectional Coupler Electrical SpecificationsA B C D E F G .390.31.225.060--.100.0459.917.87 5.72 1.52-- 2.541.14H J K L M wt .420.120.060.100--grams 10.673.051.522.54--0.50Typical Performance DataLRDC-10-2W-75J+LRDC-10-2W-75JOperating T emperature -40°C to 85°C Storage Temperature-55°C to 100°CFeatures• low mainline loss, 1.1 dB typ.• high directivity, 22 dB typ. • aqueous washable• J-leads for strain relief and excellent solderabilityApplications• VHF/UHF • cellular• communications • cable tvLRDC-10-2W-75J MAINLINE LOSS1.01.21.41.61.82.002404807209601200FREQUENCY (MHz)M A I N L I N E L O S S (d B )at RF level of -10 dBmLRDC-10-2W-75JCOUPLING & DIRECTIVITY102030405002404807209601200FREQUENCY (MHz)C O U P L I N G &D I RE C T I V I T Y (d B )LRDC-10-2W-75J RETURN LOSS2404807209601200FREQUENCY (MHz)R E T U R N L O S S (d B )Frequency (MHz)Mainline Loss(dB)In-OutCoupling (dB)In-Cpl Directivity (dB)InReturn Loss(dB)OutCplREV . A M119986LRDC-10-2W-75J WZ/TD/CP/AM 120914Suggested Layout,Tolerance to be within ±.002Permanent damage may occur if any of these limits are exceeded.23.68 1.21 10.10 26.05 21.46 17.01 17.25 31.16 1.18 10.06 27.31 23.65 17.77 17.99 61.06 1.10 10.05 30.20 31.44 19.11 19.37 158.23 1.04 10.06 30.12 28.87 19.46 19.51 315.21 1.10 10.15 25.69 20.41 17.63 17.24 520.77 1.20 10.22 23.25 16.78 15.56 15.15 674.01 1.32 10.29 23.99 15.97 14.88 14.50 879.57 1.39 10.25 30.70 17.10 15.37 14.92 1088.87 1.50 10.27 22.42 21.86 17.37 17.06 1201.00 1.6510.2817.0527.27 18.70 19.19FREQ.(MHz)COUPLING(dB)MAINLINE LOSS 1(dB)DIRECTIVITY(dB)VSWR (:1)POWER INPUT, WNom. Flatness LMU L M U LMUf L -f U T yp.Max.Typ.Max.T yp.Max.T yp.Min.T yp.Min.Typ.Min.Typ.Max.Max.30-120010.0±0.5±0.81.01.51.11.61.32.02117221718151.31.01.0L = low range [f L to 10 f L ] M = mid range [10 f L to f U /2] U = upper range [f U /2 to f U ]1. Mainline loss includes theoretical power loss at coupled port.。

DCWTechnology Study技术研究17数字通信世界2024.02科氏质量流量计是一种利用科里奥利效应原理直接测量管道流体质量流量的仪器，由传感器与变送器两部分组成。

其中，传感器通过法兰连接到管道，用于检测流体介质信号；变送器主要用于驱动传感器振动，对传感器输出的信号进行转换和处理，并将检测出的质量流量信号传到上位机控制系统中。

目前，科氏质量流量计被广泛应用于石油化工生产装置中，可以满足对流体质量流量的测量要求。

随着社会发展和人们对流量测量精度需求的提高，对科氏质量流量计数字信号处理方法也提出了更高的要求。

对于科氏质量流量计，相位差与质量流量存在比例关系。

通过测量相位差的大小，可以计算出流体的质量流量。

当前科氏质量流量计的信号处理方法主要针对相位差的估计方法，常用频谱分析法[1]、相关法[2]和时域法[3]对相位差进行分析。

采用合适的方法可以减小对质量流量的测量误差。

本文将对DFT 估计法、相关法和希尔伯特变换法的原理及发展过程进行介绍。

1 DFT相位差估计法DFT 相位差估计法是一种传统且高效的数字信号处理方法，能满足对相位差计算的基本要求。

该方法首先对两路信号进行离散傅里叶变换，得到在频域上的幅度和相位信息，然后利用频谱特性计算相位差。

DFT 算法能较好地消除谐波、噪音等对系统性能的干扰，能在较低的信噪比情况下对系统进行频率、相位的检测。

DFT 相位差估计法在对非整周期信号进行计算时会产生频谱泄漏现象，导致相位差估计结果的准确性受到影响。

另外，如果信号存在噪声或者频率偏移较大，会在频域上出现额外的能量分布，使信号频率和相位计算结果包含较大误差。

鉴于DFT 在计算非整周期信号时会产生频谱泄露现象，并在相位计算中引起严重误差的问题，美国和国内的一些研究人员建议使用频率扫描[4]的方法来实现DFT 的整周期截断。

但由于该算法对硬件资源的要求科氏质量流量计信号处理方法探究徐 媛，代显智(西华师范大学电子信息工程学院，四川 南充 637009）摘要：科氏质量流量计因能实现高精度的直接质量流量测量，成为目前国内外发展最为迅速的流量计之一。

Home Search Collections Journals About Contact us My IOPscienceGallium nitride devices for power electronic applicationsThis content has been downloaded from IOPscience. Please scroll down to see the full text.2013 Semicond. Sci. Technol. 28 074011(/0268-1242/28/7/074011)View the table of contents for this issue, or go to the journal homepage for moreDownload details:IP Address: 121.33.190.167This content was downloaded on 26/09/2013 at 01:23Please note that terms and conditions apply.IOP P UBLISHING S EMICONDUCTOR S CIENCE AND T ECHNOLOGY Semicond.Sci.Technol.28(2013)074011(8pp)doi:10.1088/0268-1242/28/7/074011INVITED REVIEWGallium nitride devices for power electronic applicationsB Jayant BaligaElectrical and Computer Engineering Department,North Carolina State University,Raleigh,NC27695,USAE-mail:bjbaliga@Received27July2012,infinal form30August2012Published21June2013Online at /SST/28/074011AbstractRecent success with the fabrication of high-performance GaN-on-Si high-voltage HFETs hasmade this technology a contender for power electronic applications.This paper discusses theproperties of GaN that make it an attractive alternative to established silicon and emerging SiCpower devices.Progress in development of vertical power devices from bulk GaN is reviewedfollowed by analysis of the prospects for GaN-on-Si HFET structures.Challenges andinnovative solutions to creating enhancement-mode power switches are reviewed.(Somefigures may appear in colour only in the online journal)IntroductionSilicon power devices have dominated the power electronics application space during the second half of the20th century. Beginning with bipolar power transistors and thyristors in the 1950s,the industry migrated to MOS-gated devices in the 1980s.The silicon power MOSFET became well established as the device of choice for applications operating at power supply voltages below200V.This includes the lucrative automotive market and the computing sector.The high specific on-resistance of silicon power MOSFETs with larger breakdown voltages spurred the creation of MOS-bipolar functional integration resulting in the emergence of the insulated gate bipolar iransistor(IGBT)in the1980s[1].The low on-state voltage drop of high-voltage IGBTs,together with ease of control and superb ruggedness,greatly reduced the cost and size of power electronic circuits making it the predominant technology in consumer,industrial,transportation,lighting and renewable energy applications.Any new technology must offer substantial improvements to the on-state voltage drop and switching losses,while retaining all the other attributes of ease of control and ruggedness,in order to displace this widely accepted technology.A detailed description and analysis of silicon unipolar and bipolar power devices is available in a recent textbook[2].During the1990s,many innovative ideas have been proposed and demonstrated for silicon power devices that have now become available as products.These ideas have been described and analyzed in supplementary books published during the last several years[3–5].Any new proposed technology must surpass the performance of not only the traditional silicon power devices but be able to compete with these enhanced-performance silicon devices as well.Thefirst analysis relating the performance of power devices to the basic material properties of semiconductors was developed at GE in1980and published in1982[6].The analysis produced a simple equation,now commonly referred to as Baliga’sfigure of merit(BFOM),to evaluate the potential improvements in the drift region resistance of unipolar power devices by substituting silicon with other semiconductor materials.This analysis indicated a13.7-times improvement by replacing silicon with gallium arsenide.Based upon this projection,GaAs power devices with high performance were developed at GE in the1980s[7,8].Subsequently,GaAs Schottky power rectifiers with breakdown voltage of200V became commercially available from several companies by leveraging this work.These devices represent thefirst-power semiconductor products based upon replacing silicon with wide bandgap semiconductor material.The predicted BFOM for silicon carbide of more than 1000provided strong motivation for development of unipolar devices from the available6H-SiC polytype material in the 1990s.Thefirst high-voltage(400V)SiC Schottky rectifier with low(∼1V)on-state voltage drop and excellent reverse recovery characteristics was reported by NCSU in1992[9]. This work demonstrated the promise of SiC-based power devices for mainstream power electronic applications whichchanged the industry perspective that was focused until that time on specialty high-temperature niche markets for power devices made from this material.Significant effort in the 1990s to grow high-quality4H-SiC polytype material with large wafer diameter and the development of processes for making ohmic contacts,Schottky contacts and improved MOS interfaces has resulted in the introduction of SiC Schottky rectifier and power MOSFET products by many companies including CREE Inc,Rohm,Infineon and GeneSiC.These devices represent a new benchmark that must be surpassed by any emerging technology such as GaN-based power devices.A comprehensive review of the design and operating characteristics of SiC power devices was published in 2006[10].Interest in gallium nitride grew in the1990s due its potential for applications in the lighting and cellular amplifier markets[11,12].Commercial products based upon this material have become highly successful in these markets. Recently,significant interest has emerged in utilizing this material for making power devices that could surpass the performance of silicon high-voltage devices and be more cost effective than silicon carbide power devices.This review provides a description of GaN power device options. Recent measurements of the impact ionization coefficients are included here because of their important role in defining the critical electricfield for breakdown,which is essential to the design of any GaN high-voltage structures.Impact ionization coefficientsThe maximum voltage that a semiconductor device can sustain is limited by the on-set of avalanche breakdown created by the impact ionization process[2].The impact ionization phenomenon is characterized by the impact ionization coefficients for electrons and holes which are defined as the number of electron-hole pairs created by the mobile particle traversing1cm through the depletion region along the direction of the electricfield.The measurement of these coefficients is complicated by the presence of defects in the semiconductor material,nonuniform electricfields within the structure,and the onset of premature breakdown at the edges of the chips.The impact ionization coefficients for electrons and holes in gallium nitride have been successfully measured after a3year effort at NCSU by using a pulsed electron beam technique[13].A pulsed electron beam technique was used for this work to localize the measurements to avoid defects detected in the material using electron beam induced current (EBIC)scans.Schottky barrier diodes were fabricated on N-type GaN epitaxial layers with low doping concentration grown on highly doped N+GaN substrates.The problem of high electricfields at the edges of the diodes was solved by using argon ion implantation which raised the breakdown voltage from300V to1650V[14].Pulsing the electron beam during the impact ionization measurements greatly improved the signal to noise ratio by using a lock-in amplifier.Extensive numerical simulations of the experimental procedure for extraction of the impact ionization coefficients from the multiplication factor obtained as a function ofthe Figure1.Measured impact ionization coefficients for electrons and holes in gallium nitride.reverse bias on the Schottky diodes were performed.It was found that the impact ionization coefficient for electrons could be obtained by using low electron beam energy to produce excitation close to the Schottky contact.In contrast,it was found that the impact ionization coefficient for holes could be obtained by using high electron beam energy to produce excitation through most of the depletion region[15].The experimental results are shown infigure1as the data points with appropriate standard deviation due to performing multiple measurements at a site and across multiple diodes.The straight lines provide afit to Chynoweth’s equation[16]:α=a e(−b/E).(1) From the measured data for electrons in GaN,a n has a value of1.5×105(+or−0.2×105)cm−1and b n has a value of1.41×107(+or−0.03×107)V cm−1at room temperature.From the measured data for holes in GaN,a p has a value of6.4×105(+or−0.1×105)cm−1and b p has a value of1.46×107(+or−0.01×107)V cm−1at room temperature.The temperature dependence of these parameters for GaN has also been measured by using a heating stage installed inside the scanning electron microscope used for the pulsed electron beam experiments[13]:a n=2.82×106−6.34×103T(2)a p=2.98×106−7.02×103T.(3) The coefficientsb n and b p were found to be independent of temperature within experimental tolerances.These data are valuable for use in numerical simulation software used for the analysis of any GaN devices such as lateral microwave transistors,and vertical or lateral power devices.Vertical power devicesMost silicon power devices are manufactured with a vertical device structure because this allows placement of the highFigure2.One-dimensional electricfield distribution within vertical power devices.current carrying terminals on opposite surfaces of the silicon chip.This design allows maintaining a uniform current density within the chip and avoids the need to pattern veryfine metal lines during device processing.The typical structures for the vertical Schottky power rectifier and the vertical planar power MOSFET are shown infigure2together with the electric field distribution obtained using one-dimensional analysis of Poisson’s equation for the drift region.In these devices,the maximum electricfield(E M)occurs at the blocking interface (metal–semiconductor contact in the Schottky rectifier or the P–N junction in the power MOSFET)with a linear reduction in magnitude to zero at a width W D for the depletion region. The devices undergo avalanche breakdown when the ionization integral across the depletion region becomes equal to unity[2]. Simple equations for the breakdown condition can be derived if a power law approximation is used for the impact ionization coefficients.For a given doping concentration(N D)in the drift region,the analysis then predicts that avalanche breakdown occurs when the maximum electricfield becomes equal to a critical electricfield for breakdown(E C)with a corresponding maximum depletion width W PP.The ideal specific on-resistance is defined as the resistance of this drift region for unit cross sectional area.It is given byR ON,SP=4BV2εSμn E3C(4)where BV is the breakdown voltage,εS is the dielectric constant andμn is the mobility.The denominator of this expression is commonly referred to as Baliga’sfigure of merit(BFOM).In order to obtain the BFOM for GaN,it is necessary to obtain the critical electricfield for breakdown which is a function of the doping concentration of the drift region.The critical electricfield for breakdown in silicon is commonly obtained by using a Fulops power lawfit to the impact ionization data[17].In a similar manner,the Ozbek–Baliga power lawfit for GaN has been proposed[13]:α=1.5×10−42E7.(5)parison of GaN maximum depletion width with Si andSiC.parison of GaN critical electricfield with Si and SiC. Solving the ionization integral with this power law provides the following relationships for the drift region for an ideal GaN vertical power device:W PP=1.57×1011N(−7/8)D(6)E C=3.19×104N(1/8)D(7)BV PP=2.51×1015N(−3/4)D.(8) The values for the maximum depletion layer width,the critical electricfield for breakdown and the breakdown voltage predicted by these equations are plotted infigures3–5, respectively.In order to verify the accuracy of the analytical model,data were obtained by performing numerical simulations with the impact ionization coefficients given by equation(1)[13].The data obtained from the numerical simulations for the above parameters are shown by the dots in thefigures.It can be concluded that the proposed analytical model in equation(5)provides an accurate match to the results of numerical ing the analytical model,it is found that the critical electricfield for GaN is1.23-timesFigure parison of GaN breakdown voltage with Si andSiC.Figure parison of GaN ideal specific on-resistance with Si and SiC.larger than that for 4H–SiC and 7.97-times larger than that for silicon.Using the above equations,the ideal specific on-resistance for the drift region of a vertical GaN power device is given byR ON ,SP (GaN )=3.12×10−12BV 2.5(9)if a mobility of 1000cm 2(V s)−1is used independent of the doping concentration.Values for the specific on-resistance for GaN obtained by using this equation are compared with those for silicon and 4H-SiC devices in figure 6.It can be concluded that the ideal specific on-resistance for GaN vertical power devices is 1.78-times smaller than that for 4H-SiC and 2130-times smaller than that for silicon at all breakdown voltages.Vertical GaN power devices can be fabricated either from bulk GaN substrates or by the homo-epitaxial growth of lightly doped thin GaN layers on thick more heavily doped GaN substrates.The development of Schottky rectifiers from GaN grown on a variety of substrates has been reviewed by Zhang et al [18].The emphasis of this work was on achieving high breakdown voltages with relatively poor on-state characteristics.Edge terminations for the devices playan important role in determining the breakdown voltages [19].Recently,nearly ideal breakdown voltage has been achieved by using an argon implanted edge termination [14,20].With this approach,the breakdown voltage of GaN Schottky rectifiers was improved from 300V to 1600V for a 4μm thick epitaxial layer with doping concentration of 1×1014cm −3grown on a N +GaN substrate.The critical electric field for breakdown extracted from these punch-through diode structures was 3.75×106V cm −1.It is worth pointing out that this is much larger than the critical electric field of 1.8×106V cm −1at a doping concentration of 1×1014cm −3(see figure 4)obtained for GaN using the impact ionization coefficients.This difference is due to the very small depletion width of 4μm where impact ionization occurs for the punch-through structure when compared with a depletion width of 900μm for the nonpunch through structure represented in figure 4.Using eqution (9),the projected ideal specific on-resistance for GaN power MOSFETs at a breakdown voltage of 600V is found to be 0.0275m cm 2.Although the projected drift region resistance is extremely small,it is unfortunately overwhelmed by the specific on-resistance of available GaN substrates (in the range of 2m cm 2).From this observation,it can be concluded that vertical GaN power devices will not be competitive with SiC devices until the GaN substrate technology is substantially improved.Despite this limitation,vertical FET structures have been reported on GaN substrates using a ‘current aperture vertical electron transistor (CA VET)structure’[21,22].Although the basic functionality of the FET structure has been demonstrated,these devices had low blocking voltages (∼65V)with relatively high specific on-resistance (2.6m cm 2).Vertical GaN FETs are being considered for automotive applications but their voltage ratings are well below system requirements [23].Consequently,most of the focus of the development effort in academia and the industry has been directed toward lateral GaN devices based upon GaN layers grown on silicon substrates as discussed in the next section.Lateral HEMT figure-of-meritThe ability to grow high-quality gallium nitride layers on silicon substrates has been a major technological breakthrough.Due to the low cost of large diameter silicon wafers,this has created the opportunity to develop high-performance GaN power devices circumventing the road-block of the high cost and small size of GaN substrates.In addition,a powerful approach to achieving low on-resistance has evolved based upon using the high electron mobility transistor (HEMT)structure.The HEMT structure was first developed for microwave applications using GaN layers grown on high-resistivity SiC and sapphire substrates [24].In the HEMT structure shown in figure 7,an AlGaN layer is grown on top of the GaN layer to create a large polarization effect which produces a two-dimensional electron gas at the AlGaN /GaN interface.A typical sheet carrier density of 1×1013cm −2with an electron mobility of 2000cm 2(V s)−1has been reported in the 2D-gas [25].Figure7.GaN HEMT structure with ideal electricfield distribution.A simple analysis of the ultimate performance for the lateral HEMT structure can be performed by assuming an idealized uniform electricfield distribution along the x-axis between the edge of the gate and the drain.The structure undergoes breakdown when the maximum electricfield becomes equal to the critical electricfield(E C,L)for breakdown in a structure with uniform electricfield along the drift region. This critical electricfield is different from the previously derived critical electricfield for devices with triangular shaped electricfield distribution as discussed later in this section.The length of the drift region is given byL D(HEMT)=BVE C,L.(10)In order to obtain the ideal specific on-resistance for a lateral HEMT structure,only the resistance of the drift region is taken into account while neglecting the space occupied by the source, gate and drain contacts.The on-resistance of the drift region is given byR ON(HEMT)=L DqμQ S Z(11)whereμis the free carrier mobility in the2D-gas,Q S is the sheet carrier density and Z is the width of the structure orthogonal to the cross-section.The specific on-resistance for the lateral HEMT structure is obtained by multiplying the on-resistance by the area(L D.Z):R ON,SP(HEMT)=L2DqμQ S.(12)Using equation(10)yieldsR ON,SP(HEMT)=BV2qμQ S E2C,L.(13)The denominator of this equation serves as afigure-of-merit for lateral HEMT structures:BFOM(HEMT)=qμQ S E2C,L.(14) The critical electricfield for breakdown for the lateral HEMT structure is a function of the breakdown voltage of the structure (as is also the case for the vertical power FET structures).The critical electricfield for breakdown for the lateral HEMT structure can be derived by performing the ionization integral with a uniform electricfield in the drift region with equation(5) for the impact ionization coefficient.Equating the ionization integral to unity yieldsE C,L=6.667×1041BV1/6.(15) The solution indicates that the critical electricfield for breakdown of a lateral HEMT structure will decrease with increasing breakdown voltage.This is due to the longer impact ionization path along the drift region with increasing breakdown bining equation(15)with equation(10),L D(HEMT)=1.07×10−7BV7/6.(16) Substituting this expression into equation(12),R ON,SP(HEMT)=7.154×104BV7/3S.(17) Using the typical sheet carrier density of1×1013cm−2with an electron mobility of2000cm2(V s)−1reported in the2D-gas for the AlGaN/GaN HEMT structures yieldsR ON,SP(HEMT)=3.577×10−12BV7/3.(18) It is worth pointing out that the power law relating the specific on-resistance to the breakdown voltage for a lateral HEMT structure is different from that given by equation(9)for a vertical power FET structure.The specific on-resistance for the lateral GaN HEMT structure is plotted infigure6.The line corresponding to the lateral GaN HEMT devices is not parallel to the lines for the other vertical device structures shown in thefigure.The above analysis indicates that the ideal specific on-resistance for lateral GaN HEMT devices is lower than that predicted for the vertical GaN FET devices,and consequently superior to4H-SiC and Si devices as well.The lateral GaN HEMT structures are expected to have an ideal specific on-resistance that is1.88,2.76and4.05-times smaller than for the vertical GaN FET devices at breakdown voltages of100,1000and 10000V,respectively.Lateral GaN HEMT devicesAlGaN/GaN HEMT structures fabricated on GaN layers grown on silicon substrates have attracted the most commercial interest for power electronic applications in recent years due to the prospects for creating a high-performance FET technology on a low-cost panies that are pursuing this approach include International Rectifier[26],MicroGaN[27], Transphorm[28]and EPC[29].Although the research effort on GaN HFETs spans a broad range of blocking voltages, 600V devices are considered an important target for solar inverters and motor drives for hybrid electric cars[30].Several reviews of the development activity for GaN HFETs have been recently published[31,32].Most of the early work has been focused on achieving high breakdown voltages and preventing the current collapse phenomenon.This was achieved by using gate and source connectedfield plates asFigure 8.Improved GaN HEMT structures.illustrated in the structure on the left-hand side of figure 8[33].Normally on or depletion-mode devices with blocking voltage of 1.3kV were successfully fabricated with a maximum current of 120amperes and a specific on-resistance of 5.2m cm 2.Although an excellent low specific on-resistance was achieved when compared with silicon devices,it is 2orders of magnitude above the ideal specific on-resistance predicted by the analysis in the previous section indicating room for further improvements.For example,the gate-to-drain length used for these devices was 15μm when compared with only 3.4μm for the ideal case indicating that there is opportunity to make the electric field more uniform along the drift region.Promising approaches that have been proposed and demonstrated to increase the breakdown voltage are a greater buffer layer thickness [34]and source vias to ground the silicon substrate [35].For power electronic applications,it is essential that transistors have a normally off or enhancement-mode characteristic to prevent shoot-through problems during circuit power up.Since the basic AlGaN /GaN HFET structure has a normally on or depletion mode characteristic,modifications have been proposed to move the threshold voltage from negative to positive values.One of the methods to achieve normally off behavior in the AlGaN /GaN HFETs is to make a ‘recessed-gate’structure as illustrated on the left-hand side of figure 8.The typical thickness for the AlGaN layer is 20nm.In order to obtain a zero threshold voltage,it is necessary to reduce the AlGaN layer under the gate to only 5nm [36].The recess process must not only accurately reduce the AlGaN layer thickness but must be uniform across the wafer.580V HFETs have been fabricated with AlGaN layer thickness of only 2nm [37]with zero threshold voltage and a specific on-resistance of 1.25m cm 2.A 600V HFET with a positive threshold voltage of 0.8V and specific on-resistance of 2.8m cm 2has also been reported by using a recessed-gate structure with NiOx gate material [38].These results are far superior to the specific on-resistance of 100m cm 2for the typical 600V silicon power MOSFET and 30m cm 2for the 600V silicon COOLMOS technology [4].However,the threshold voltages of these HFETs are too low for secure operation in power circuits.Another approach taken to achieve a normally off AlGaN /GaN HFET device is to use the recessed MOS gate structure illustrated on the right-hand side of figure 8.Furukawa Electric has reported 500V ,70-A devices with a positive threshold voltage of 2.8V in 2009[39]with specific on-resistance of 16m cm 2.These structures utilized a p-type magnesium-doped GaN layer.Subsequently,600V ,100-A normally off AlGaN /GaN HFET devices with a threshold voltage of 2.7V and specific on-resistance of 9.3m cm 2have been reported by this group in 2010[40].Although these results are very promising,the specific on-resistance for the AlGaN /GaN MOS-HFET structures remains substantially larger than that for normally on AlGaN /GaN HFET structures with the same blocking voltage.Hybrid GaN /Si devicesIn the 1990s,the development of power MOSFETs from silicon carbide was stymied by poor mobility for electrons in inversion layers and catastrophic failure of devices due to high electric fields generated in the gate oxide [10].Better progress was made on the development of high-voltage JFET structures with low specific on-resistance but these devices had normally on characteristics.The Baliga–Pair configuration [41],named after the inventor analogous to the Darlington–Pair [42],was proposed to address these problems.The concept was first reported in the literature in 1996[43].In the Baliga–Pair configuration,a high-voltage normally on SiC JFET or MESFET structure is paired with a low-voltage normally off Si power MOSFET to create a composite three-terminal device as shown in figure 9.In the Baliga–Pair configuration,the source of the high-voltage FET is connected to the drain of the Si power MOSFET and the gate of the high-voltage FET is connected to the source of the Si power MOSFET which serves as the ground or reference terminal.The device can be controlled by biasing the gate of the Si power MOSFET while the drain of the high-voltage FET is connected to the load and the output power source.If the SiC JFET /MESFET is designed with a pinch-off voltage of 20V ,a 30V Si power MOSFET with very low on-resistance can be used in this circuit while very high voltages can be controlled viaFigure9.The Baliga–Pair device configuration.the high-voltage JFET/MESFET.The circuit provides the benefits of high blocking voltage capability with very low specific on-resistance,excellent switching behavior and wide safe-operating-area characteristics[2,10].Although these references discuss the use of a normally on high-voltage SiC JFET,it is obvious that the idea would work well with a normally on high-voltage FET made from any other material.The Baliga–Pair concept has been experimentally validated by extensive work done by Siemens[44,45]using their planar-gate vertical SiC JFET technology.These authors refer to the Baliga–Pair configuration as a‘cascode circuit’. This is a misnomer because the term cascode has been previously used to describe an analog circuit where one bipolar transistor serves as the load for a second bipolar transistor to increase the output resistance[46].Neither bipolar transistor is normally on in these circuits.In contrast,a normally on high-voltage FET made from wide band gap material is controlled by a silicon power MOSFET in the Baliga–Pair circuit.As discussed previously,currently normally on high-voltage AlGaN/GaN FET structures have the best specific on-resistance.Consequently,the Baliga–Pair circuit with a normally on high-voltage AlGaN/GaN HFET and a low-voltage Si power MOSFET is considered the most commercially viable solution at this time[27–29].With this approach,very high efficiencies have been demonstrated for a dc to dc boost circuit operating at100kHz with220V at the input[47].ConclusionsThis paper provides a review of GaN-based devices for power electronic applications.Recent measurements of the impact ionization coefficients for holes and electrons in GaN confirm and quantify the larger critical electricfield for breakdown for this material when compared with Si and ing the impact ionization data,analytical models for the breakdown voltage and the ideal specific on-resistance for the drift region of vertical power devices have been derived.The ideal specific on-resistance for vertical GaN devices is found to be1.78-times smaller than that for4H-SiC and2130-times smaller than that for silicon at all breakdown voltages.The prospects for vertical GaN power devices fabricated from GaN substrates is hindered by the high-resistivity,small size and high cost of the substrates.The demonstration of high-quality GaN layers on silicon substrates has created the opportunity to create a high-performance power device technology that is potentially less expensive than silicon carbide devices.Normally on high-voltage AlGaN/GaN HFETs have been demonstrated with nearly2orders of magnitude smaller specific on-resistance when compared to silicon devices with the same blocking voltage capability.Although normally off high-voltage HFETs have also been demonstrated,their specific on-resistance is much larger than for the normally on structures.Consequently, most commercial manufacturers are using a normally on high-voltage AlGaN/GaN HFET with a low-voltage silicon power MOSFET in the Baliga–Pair configuration to produce a high-performance normally off high-voltage power switch for solar inverter and motor drive applications.One barrier to commercial viability of GaN-based HEMT power devices is their reliability.Degradation of the output characteristics and on-resistance of AlGaN/GaN HEMT structures has been reported due to hot electron induced charge trapping[48].The generation of traps has been ascribed to strain produced in the AlGaN layer due to the inverse piezoelectric effect[49]resulting from the high electricfield at the edge of the gate electrode.The electricfield at the gate edge can be reduced by usingfield plates as already described in the paper.An alternative approach that is being explored is the InAlN/GaN HEMT structure which has been projected to have two to three times superior quantum well polarization induced charge[50].The projections have been validated by several recent experimental results[51–53]for GaN grown on4H-SiC and sapphire.This work needs to be extended to silicon substrates to make the technology cost effective. References[1]Baliga B J1988Evolution of MOS-bipolar powersemiconductor technology Proc.IEEE74409–18[2]Baliga B J2008Fundamentals of Power SemiconductorDevices(New York:Springer-Science)[3]Baliga B J2009Advanced Power Rectifier Concepts(NewYork:Springer-Science)[4]Baliga B J2010Advanced Power MOSFET Concepts(NewYork:Springer-Science)[5]Baliga B J2011Advanced High Voltage Power DeviceConcepts(New York:Springer-Science)[6]Baliga B J1982Semiconductors for high voltage verticalchannelfield effect transistors J.Appl.Phys.531759–64 [7]Campbell P M et al1982150-V vertical channel GaAs FETIEEE Int.Electron Devices Meeting258–60Abstract10.4 [8]Baliga B J et al1985Gallium Arsenide Schottky powerrectifiers IEEE Trans.Electron Devices ED-321130–4 [9]Bhatnagar M et al1992Silicon carbide high-voltage(400V)Schottky barrier diodes IEEE Electron Device Lett.EDL-13501–3[10]Baliga B J2006Silicon Carbide Power Devices(Singapore:World Scientific Publishers)[11]Denbaars S P1997Gallium-nitride-based materials for blueand ultraviolet optoelectronic devices Proc.IEEE851740–9[12]Mishra U K,Parikh P and Wu Y F2002AlGaN/GaNHEMTs—an overview of device operation and applicationsProc.IEEE901022–31[13]Ozbek A M Measurement of impact ionization coefficients inGaN PhD Thesis North Carolina State University。