Orientational field-dependence of low-lying excitations in mixed state of unconventional su

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Förster resonance energy transferFrom Wikipedia, the free encyclopediaJump to: navigation, searchJablonski diagram of FRET with typical timescales indicatedFörster resonance energy transfer (FRET), fluorescence resonance energy transfer (FRET), resonance energy transfer (RET) orelectronic energy transfer (EET) is a mechanism describing energy transfer between two light-sensitive molecules (chromophores).[1] A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative dipole–dipole coupling.[2] The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, making FRET extremely sensitive to small changes in distance.[3]Measurements of FRET efficiency can be used to determine if two fluorophores are within a certain distance of each other.[4] Such measurements are used as a research tool in fields including biology and chemistry.FRET is analogous to near-field communication, in that the radius of interaction is much smaller than the wavelength of light emitted. In the near-field region, the excited chromophore emits a virtual photon that is instantly absorbed by a receiving chromophore. These virtual photons are undetectable, since their existence violates the conservation of energy and momentum, and hence FRET is known as a radiationless mechanism. Quantum electrodynamical calculations have been used to determine that radiationless (FRET) and radiative energy transfer are the short- and long-range asymptotes of a single unified mechanism.[5][6]Contents[hide]∙ 1 Terminology∙ 2 Theoretical basis∙ 3 Experimental co nfirmation of the Förster resonance energy transfer theory∙ 4 Methods to measure FRET efficiencyo 4.1 Sensitized emissiono 4.2 Photobleaching FRETo 4.3 Lifetime measurements∙ 5 Fluorophores used for FRETo 5.1 CFP-YFP pairso 5.2 BRETo 5.3 Homo-FRET∙ 6 Applicationso 6.1 Biology∙7 Other methods∙8 See also∙9 References∙10 External linksTerminology[edit]Förster resonance energy transfer is named after the German scientist Theodor Förster.[7] When both chromophores are fluorescent, the term "fluorescence resonance energy transfer" is often used instead, although the energy is not actually transferred by fluorescence.[8][9]In order to avoid an erroneous interpretation of the phenomenon that is always a nonradiative transfer of energy (even when occurring between two fluorescent chromophores), the name "Förster resonance energy transfer" is preferred to "fluorescence resonance energy transfer;" however, the latter enjoys common usage in scientific literature.[10] It should also be noted that FRET is not restricted to fluorescence. It can occur in connection with phosphorescence as well.[8]Theoretical basis[edit]The FRET efficiency () is the quantum yield of the energy transfer transition, i.e. the fraction of energy transfer event occurring per donor excitation event:[11]where is the rate of energy transfer, the radiative decayrate, and the 's are the rate constants of any other de-excitation pathways.[12]The FRET efficiency depends on many physical parameters that can be grouped as follows:∙The distance between the donor and the acceptor (typically in the range of 1-10 nm)∙The spectral overlap of the donor emission spectrum and the acceptor absorption spectrum.∙The relative orientation of the donor emission dipole moment and the acceptor absorption dipole moment.depends on the donor-to-acceptor separation distance with an inverse 6th power law due to the dipole-dipole coupling mechanism:with being the Förster distance of this pair of donor andacceptor, i.e. the distance at which the energy transfer efficiency is 50%.[12]The Förster distance depends on the overlap integral of the donor emission spectrum with the acceptor absorption spectrum and their mutual molecular orientation as expressed by the following equation.[13][14]where is the fluorescence quantum yield of the donor in the absence of the acceptor, κ2 is the dipole orientation factor, is the refractive index of the medium, is Avogadro's number, and is the spectral overlap integral calculated aswhere is the normalized donor emission spectrum, and is the acceptor molar extinction coefficient.[15] The orientation factor κ is given by,Where denotes the normalized transition dipole moment of therespective fluorophore and denotes the normalized inter-fluorophore displacement. κ2 =2/3 is often assumed. This value is obtained when both dyes are freely rotating and can be considered to beisotropically oriented during the excited state lifetime. If either dye is fixed or not free to rotate, then κ2 =2/3 will not be a valid assumption. In most cases, however, even modest reorientation of the dyes results in enough orientational averaging that κ2 = 2/3 doesnot result in a large error in the estimated energy transfer distance due to the sixth power dependence of R0 on κ2. Even when κ2 is quite different from 2/3 the error can be associated with a shift in R0 and thus determinations of changes in relative distance for a particular system are still valid. Fluorescent proteins do not reorient on a timescale that is faster than their fluorescence lifetime. In this case 0 ≤ κ2≤ 4.[15]The FRET efficiency relates to the quantum yield and the fluorescence lifetime of the donor molecule as follows:[16]where and are the donor fluorescence lifetimes in the presenceand absence of an acceptor, respectively, or aswhere and are the donor fluorescence intensities with and without an acceptor, respectively.Experimental confirmation of the Förster resonance energy transfer theory[edit]The inverse sixth-power distance dependence of Förster resonance energy transfer was experimentally confirmed by Wilchek, Edelhoch and Brand[17][18] using tryptophyl peptides. Stryer, Haugland and Yguerabide[19] also experimentally demonstrated the theoretical dependence ofFörster resonance ene rgy transfer on the overlap integral by using a fused indolosteroid as a donor and a ketone as an acceptor. However, a lot of contradictions of special experiments with the theory was oserved. The reason is that the theory has approximate character and gives overstimated distances of 50-100 Angstrems (Vekshin N.L. Energy Transfer in Macromolecules, SPIE, 1997; Vekshin N.L. Photonics of Biopolymers, Springer, 2002).Methods to measure FRET efficiency[edit]In fluorescence microscopy, fluorescence confocal laser scanning microscopy, as well as in molecular biology, FRET is a useful tool to quantify molecular dynamics in biophysics and biochemistry, such as protein-protein interactions, protein–DNA interactions, and protein conformational changes. For monitoring the complex formation between two molecules, one of them is labeled with a donor and the other with an acceptor. The FRET efficiency is measured and used to identify interactions between the labeled complexes. There are several ways of measuring the FRET efficiency by monitoring changes in the fluorescence emitted by the donor or the acceptor.[20]Sensitized emission[edit]One method of measuring FRET efficiency is to measure the variationin acceptor emission intensity.[14] When the donor and acceptor are in proximity (1–10 nm) due to the interaction of the two molecules, the acceptor emission will increase because of the intermolecularFRET from the donor to the acceptor. For monitoring protein conformational changes, the target protein is labeled with a donor and an acceptor at two loci. When a twist or bend of the protein brings the change in the distance or relative orientation of the donor and acceptor, FRET change is observed. If a molecular interaction or a protein conformational change is dependent on ligand binding, this FRET technique is applicable to fluorescent indicators for the ligand detection.Photobleaching FRET[edit]FRET efficiencies can also be inferred from the photobleaching rates of the donor in the presence and absence of an acceptor.[14] This method can be performed on most fluorescence microscopes; one simply shines the excitation light (of a frequency that will excite the donor but not the acceptor significantly) on specimens with and without the acceptor fluorophore and monitors the donor fluorescence (typically separated from acceptor fluorescence using a bandpass filter) over time. The timescale is that of photobleaching, which is seconds to minutes, with fluorescence in each curve being given bywhere is the photobleaching decay time constant and depends on whether the acceptor is present or not. Since photobleaching consists in the permanent inactivation of excited fluorophores, resonance energy transfer from an excited donor to an acceptor fluorophore prevents the photobleaching of that donor fluorophore, and thus high FRET efficiency leads to a longer photobleaching decay time constant:where and are the photobleaching decay time constants of thedonor in the presence and in the absence of the acceptor, respectively. (Notice that the fraction is the reciprocal of that used for lifetime measurements).This technique was introduced by Jovin in 1989.[21] Its use of anentire curve of points to extract the time constants can give it accuracy advantages over the other methods. Also, the fact that time measurements are over seconds rather than nanoseconds makes it easierthan fluorescence lifetime measurements, and because photobleaching decay rates do not generally depend on donor concentration (unless acceptor saturation is an issue), the careful control of concentrations needed for intensity measurements is not needed. It is, however, important to keep the illumination the same for the with- and without-acceptor measurements, as photobleaching increases markedly with more intense incident light.Lifetime measurements[edit]FRET efficiency can also be determined from the change in the fluorescence lifetime of the donor.[14] The lifetime of the donor will decrease in the presence of the acceptor. Lifetime measurements of FRET are used in Fluorescence-lifetime imaging microscopy.Fluorophores used for FRET[edit]If the linker is intact, excitation at the absorbance wavelength of CFP (414nm) causes emission by YFP (525nm) due to FRET. If the linker is cleaved by a protease, FRET is abolished and emission is at the CFP wavelength (475nm).CFP-YFP pairs[edit]One common pair fluorophores for biological use is a cyan fluorescent protein (CFP) – yellow fluorescent protein (YFP) pair.[22] Both are color variants of green fluorescent protein (GFP). Labeling with organic fluorescent dyes requires purification, chemical modification, and intracellular injection of a host protein. GFP variants can be attached to a host protein by genetic engineering which can be more convenient. Additionally, a fusion of CFP and YFP linked by a protease cleavage sequence can be used as a cleavage assay.[23]BRET[edit]A limitation of FRET is the requirement for external illumination to initiate the fluorescence transfer, which can lead to background noise in the results from direct excitation of the acceptor or to photobleaching. To avoid this drawback, Bioluminescence Resonance Energy Transfer (or BRET) has been developed.[24] This technique uses a bioluminescent luciferase (typically the luciferase from Renilla reniformis) rather than CFP to produce an initial photon emission compatible with YFP.Homo-FRET[edit]In general, "FRET" refers to situations where the donor and acceptor proteins (or "fluorophores") are of two different types. In many biological situations, however, researchers might need to examine the interactions between two, or more, proteins of the same type—or indeed the same protein with itself, for example if the protein folds or forms part of a polymer chain of proteins[25] or for other questions of quantification in biological cells.[26]Obviously, spectral differences will not be the tool used to detect and measure FRET, as both the acceptor and donor protein emit light with the same wavelengths. Yet researchers can detect differences in the polarisation between the light which excites the fluorophores andthe light which is emitted, in a technique called FRET anisotropy imaging; the level of quantified anisotropy (difference in polarisation between the excitation and emission beams) then becomes an indicative guide to how many FRET events have happened.[27]Applications[edit]Biology[edit]FRET has been used to measure distance and detect molecular interactions in a number of systems and has applications in biology and chemistry.[28] FRET can be used to measure distances between domains in a single protein and therefore to provide information about protein conformation.[29] FRET can also detect interaction between proteins.[30] Applied in vivo, FRET has been used to detect the location and interactions of genes and cellular structures including intergrins and membrane proteins.[31] FRET can be used to obtain information about metabolic or signaling pathways.[32] FRET is also used to study lipid rafts in cell membranes.[33]FRET and BRET are also the common tools in the study of biochemical reaction kinetics and molecular motors.The applications of Fluorescence Resonance Energy Transfer (FRET) have expanded tremendously in the last 25 years, and the technique has become a staple technique in many biological and biophysical fields. FRET can be used as spectroscopic ruler in various areas such as structural elucidation of biological molecules and their interactions in vitro assays, in vivo monitoring in cellular research, nucleic acid analysis, signal transduction, light harvesting and metallic nanomaterial etc. Based on the mechanism of FRET a variety of novel chemical sensors and biosensors have been developed.[34]Other methods[edit]A different, but related, mechanism is Dexter Electron Transfer.An alternative method to detecting protein–protein proximity is the bimolecular fluorescence complementation (BiFC) where two halves of a YFP are fused to a protein. When these two halves meet they form a fluorophore after about 60 s – 1 hr.[35]See also[edit]∙Förster coupling∙Surface energy transfer∙Dexter electron transfer∙Time-resolved fluorescence energy transferReferences[edit]1.Jump up ^ Cheng, Ping-Chin (2006). "The Contrast Formation in OpticalMicroscopy". In Pawley, James B. Handbook Of Biological Confocal Microscopy(3rd ed.). New York, NY: Springer. pp. 162–206. doi:10.1007/978-0-387-45524-2_8. ISBN 978-0-387-25921-5.2.Jump up ^ Helms, Volkhard (2008). "Fluorescence Resonance Energy Transfer".Principles of Computational Cell Biology. Weinheim: Wiley-VCH. p. 202.ISBN 978-3-527-31555-0.3.Jump up ^ Harris, Daniel C. (2010). "Applications of Spectrophotometry".Quantitative Chemical Analysis (8th ed.). New York: W. H. Freeman and Co.pp. 419–44. ISBN 978-1-4292-1815-3.4.Jump up ^ Zheng, Jie (2006). "Spectroscopy-Based Quantitative FluorescenceResonance Energy Transfer Analysis". In Stockand, James D.; Shapiro, MarkS. Ion Channels: Methods and Protocols. Methods in Molecular Biology,Volume 337. Totowa, NJ: Humana Press. pp. 65–77. doi:10.1385/1-59745-095-2:65. ISBN 978-1-59745-095-9.5.Jump up ^ Andrews, David L. (1989). "A unified theory of radiative andradiationless molecular energy transfer". Chemical Physics135 (2): 195–201. Bibcode:1989CP....135..195A. doi:10.1016/0301-0104(89)87019-3.6.Jump up ^ Andrews, David L; Bradshaw, David S (2004). "Virtual photons,dipole fields and energy transfer: A quantum electrodynamical approach".European Journal of Physics25 (6): 845. doi:10.1088/0143-0807/25/6/017.7.Jump up ^Förster, Theodor (1948). "Zwischenmolekulare Energiewanderung undFluoreszenz" [Intermolecular energy migration and fluorescence]. Annalender Physik (in German) 437: 55–75. Bibcode:1948AnP...437...55F.doi:10.1002/andp.19484370105.8.^ Jump up to: a b Valeur, Bernard; Berberan-Santos, Mario (2012). "ExcitationEnergy Transfer". Molecular Fluorescence: Principles and Applications, 2nded. Weinheim: Wiley-VCH. pp. 213–261. doi:10.1002/9783527650002.ch8.ISBN 9783527328376.9.Jump up ^ FRET microscopy tutorial from Olympus10.Jump up ^Glossary of Terms Used in Photochemistry (3rd ed.). IUPAC. 2007.p. 340.11.Jump up ^ Moens, Pierre. "Fluorescence Resonance Energy Transferspectroscopy". Retrieved July 14, 2012.12.^ Jump up to: a b Schaufele, Fred; Demarco, Ignacio; Day, Richard N. (2005)."FRET Imaging in the Wide-Field Microscope". In Periasamy, Ammasi; Day, Richard. Molecular Imaging: FRET Microscopy and Spectroscopy. Oxford:Oxford University Press. pp. 72–94. doi:10.1016/B978-019517720-6.50013-4.ISBN 978-0-19-517720-6.13.Jump up ^Förster, Th. (1965). "Delocalized Excitation and ExcitationTransfer". In Sinanoglu, Oktay. Modern Quantum Chemistry. IstanbulLectures. Part III: Action of Light and Organic Crystals3. New York and London: Academic Press. pp. 93–137. Retrieved 2011-06-22.14.^ Jump up to: a b c d Clegg, Robert (2009). "Förster resonance energytransfer—FRET: what is it, why do it, and how it's done". In Gadella,Theodorus W. J. FRET and FLIM Techniques. Laboratory Techniques inBiochemistry and Molecular Biology, Volume 33. Elsevier. pp. 1–57.doi:10.1016/S0075-7535(08)00001-6. ISBN 978-0-08-054958-3.15.^ Jump up to: a b Demchenko, Alexander P. (2008). "Fluorescence DetectionTechniques". Introduction to Fluorescence Sensing. Dordrecht: Springer.pp. 65–118. doi:10.1007/978-1-4020-9003-5_3. ISBN 978-1-4020-9002-8. 16.Jump up ^ Majoul, Irina; Jia, Yiwei; Duden, Rainer (2006). "PracticalFluorescence Resonance Energy Transfer or Molecular Nanobioscopy of Living Cells". In Pawley, James B. Handbook Of Biological Confocal Microscopy (3rd ed.). New York, NY: Springer. pp. 788–808. doi:10.1007/978-0-387-45524-2_45. ISBN 978-0-387-25921-5.17.Jump up ^ Template:ISRAEL JOURNAL OF CHEMISTRY. Vol. 1. No. Sa. 196318.Jump up ^ {Edelhoch, H., Brand, L., Wilchek, M. (1967). "Fluorescencestudies with tryptophyl peptides". Biochemistry 6 (2): 547–559.doi:10.1021/bi00854a024. PMID 6047638}19.Jump up ^ Lakowicz, Joseph R., ed. (1991). Principles. New York: PlenumPress. p. 172. ISBN 978-0-306-43875-2.20.Jump up ^ "Fluorescence Resonance Energy Transfer Protocol". WellcomeTrust. Retrieved 24 June 2012.[dead link]21.Jump up ^Szöllősi, János; Alexander, Denis R. (2007). "The Application ofFluorescence Resonance Energy Transfer to the Investigation ofPhosphatases". In Klumpp, Susanne; Krieglstein, Josef. ProteinPhosphatases. Methods in Enzymology, Volume 366. Amsterdam: Elsevier.pp. 203–24. doi:10.1016/S0076-6879(03)66017-9. ISBN 978-0-12-182269-9. 22.Jump up ^ Periasamy, Ammasi (July 2001). "Fluorescence resonance energytransfer microscopy: a mini review". Journal of Biomedical Optics6 (3): 287–291. Bibcode:2001JBO.....6..287P. doi:10.1117/1.1383063.PMID 11516318.23.Jump up ^ Nguyen, AW; Daugherty, PS (March 2005). "Evolutionaryoptimization of fluorescent proteins for intracellular FRET.". Naturebiotechnology23 (3): 355–60. doi:10.1038/nbt1066. PMID 15696158.24.Jump up ^ Bevan, Nicola; Rees, Stephen (2006). "Pharmaceutical Applicationsof GFP and RCFP". In Chalfie, Martin; Kain, Steven R. Green FluorescentProtein: Properties, Applications and Protocols. Methods of Biochemical Analysis, Volume 47 (2nd ed.). Hoboken, NJ: John Wiley & Sons. pp. 361–90. doi:10.1002/0471739499.ch16. ISBN 978-0-471-73682-0.25.Jump up ^ Gautier, I.; Tramier, M.; Durieux, C.; Coppey, J.; Pansu, R.B.;Nicolas, J.-C.; Kemnitz, K.; Coppey-Moisan, M. (2001). "Homo-FRETMicroscopy in Living Cells to Measure Monomer-Dimer Transition of GFP-Tagged Proteins". Biophysical Journal80 (6): 3000–8.Bibcode:2001BpJ....80.3000G. doi:10.1016/S0006-3495(01)76265-0.PMC 1301483. PMID 11371472.26.Jump up ^ Bader, Arjen N.; Hofman, Erik G.; Voortman, Jarno; Van Bergen EnHenegouwen, Paul M.P.; Gerritsen, Hans C. (2009). "Homo-FRET ImagingEnables Quantification of Protein Cluster Sizes with SubcellularResolution". Biophysical Journal97 (9): 2613–22.Bibcode:2009BpJ....97.2613B. doi:10.1016/j.bpj.2009.07.059. PMC 2770629.PMID 19883605.27.Jump up ^ Gradinaru, Claudiu C.; Marushchak, Denys O.; Samim, Masood;Krull, Ulrich J. (2010). "Fluorescence anisotropy: From single molecules to live cells". The Analyst135 (3): 452–9. Bibcode:2010Ana...135..452G.doi:10.1039/b920242k. PMID 20174695.28.Jump up ^ Lakowicz, Joseph R. (1999). Principles of fluorescencespectroscopy (2nd ed.). New York, NY: Kluwer Acad./Plenum Publ. pp. 374–443. ISBN 978-0-306-46093-7.29.Jump up ^ Truong, Kevin; Ikura, Mitsuhiko (2001). "The use of FRET imagingmicroscopy to detect protein–protein interactions and proteinconformational changes in vivo". Current Opinion in Structural Biology11(5): 573–8. doi:10.1016/S0959-440X(00)00249-9. PMID 11785758.30.Jump up ^ Pollok, B; Heim, R (1999). "Using GFP in FRET-basedapplications". Trends in Cell Biology9 (2): 57–60. doi:10.1016/S0962-8924(98)01434-2. PMID 10087619.31.Jump up ^ Sekar, R. B.; Periasamy, A (2003). "Fluorescence resonance energytransfer (FRET) microscopy imaging of live cell protein localizations". The Journal of Cell Biology160 (5): 629–33. doi:10.1083/jcb.200210140.PMC 2173363. PMID 12615908.32.Jump up ^ Ni, Qiang; Zhang, Jin (2010). "Dynamic Visualization of CellularSignaling". In Endo, Isao; Nagamune, Teruyuki. Nano/Micro Biotechnology.Advances in Biochemical Engineering/Biotechnology, Volume 119. Springer.pp. 79–97. Bibcode:2010nmb..book...79N. doi:10.1007/10_2008_48.ISBN 978-3-642-14946-7. PMID 19499207.33.Jump up ^ Silvius, John R.; Nabi, Ivan Robert (2006). "Fluorescence-quenching and resonance energy transfer studies of lipid microdomains in model and biological membranes (Review)". Molecular Membrane Biology23(1): 5–16. doi:10.1080/09687860500473002. PMID 16611577.34.Jump up ^ S. A., Hussain et al. (2015). "Fluorescence Resonance EnergyTransfer (FRET) sensor" (PDF). J. Spectrosc. Dyn.5 (7): 1–16.35.Jump up ^ Hu, Chang-Deng; Chinenov, Yurii; Kerppola, Tom K. (2002)."Visualization of Interactions among bZIP and Rel Family Proteins in Living Cells Using Bimolecular Fluorescence Complementation". Molecular Cell9(4): 789–98. doi:10.1016/S1097-2765(02)00496-3. PMID 11983170。

read of unwrotten field valuestate in -回复什么是未书写的区域价值状态？未书写的区域价值状态（unwrotten field value state）是指一个人或一个团体在特定的地理区域内所感受到的、不一定是书面记录的，但对于他们生活和身份认同有重要意义的价值状态。

这些价值状态可能是与历史、文化、自然环境及社会关系等相关的。

在这篇文章中，我将探讨未书写的区域价值状态的特点、作用以及如何保护和传承。

首先，未书写的区域价值状态具有以下一些特点。

首先，它们通常是由于个人和团体在特定地理区域内的生活经历和环境所形成的。

这些经历和环境可能包括了多种因素，例如历史事件、民族文化、传统习俗以及地理特征等。

其次，这些价值状态并不一定被书写下来，而是通过口头传统、艺术形式和日常行为等方式传承和表达。

未书写的区域价值状态在人们生活中扮演着重要的角色。

它们不仅是对特定地理区域的认同和归属感的体现，还包含了人们对于历史文化传统的尊重和继承。

这些价值状态也可以促进社会凝聚力和社区认同感的形成，鼓励人们保护和维护地理区域的特色和文化传统。

为了保护和传承未书写的区域价值状态，我们需要采取一系列的措施。

首先，政府和社会组织可以通过设立专门的保护机构和政策来加强对区域文化遗产的保护。

这些机构可以进行相关的研究工作，整理和记录未书写的价值状态，并将其纳入到相关的保护规划中。

其次，教育是传承未书写的区域价值状态的重要途径之一。

通过开展相关的课程和活动，将这些价值状态传授给下一代，使他们能够理解和尊重地理区域的特点和文化传统。

此外，鼓励人们主动参与社区服务和文化活动也是非常重要的，这有助于增强社区凝聚力和保护未书写的价值状态。

当然，保护和传承未书写的区域价值状态并不是一件容易的事情。

在现代社会中，由于城市化和全球化的影响，一些地理区域的价值状态可能会受到冲击和改变。

因此，我们需要积极推动可持续发展的理念，寻找合理的平衡点，保护和传承未书写的价值状态与社会发展之间的关系。

Problems for the 28th IYPT 20151. PackingThe fraction of space occupied by granular particles depends on their shape. Pour non-spherical particles such as rice, matches, or M&M’s candies into a box. How do characteristics like coordination number, orientational order, or the random close packing fraction depend on the relevant parameters?1.堆积(Packing)被颗粒状物体(particles)占据的小部分空间取决于它们的形状。

将例如米、火柴或M&M糖果的非球状物体倾倒进一个盒子里，相关参量如何影响配位数(coordination number)、秩序性排列(orientational order)和随机紧密堆积分数(random close packing fraction)这样的特征？2. Plume of SmokeIf a burning candle is covered by a transparent glass, the flame extinguishes and a steady upward stream of smoke is produced. Investigate the plume of smoke at various magnifications.2.羽状的烟/烟羽(Plume of smoke)如果一支燃烧着的蜡烛被一块透明玻璃板覆盖，火焰会熄灭，并且产生一缕稳定的向上流动的轻烟。

研究在各种放大倍数下的羽状的烟。

8. Surfaces and Interfaces8.1 IntroductionThere exist differences in the important parameters describing interfaces and surfaces:Surfaces Interfacesroughness composition conformation chain ends width (roughness) profile conformation fluctuationssnapshot of a coarse-grained moleculardynamics simulation of a block co-polymer double bilayer in waterGoundla Srinivas, IBM Almaden Research Centerthermodynamic: To allow contact between two different phases, an interface with a free energy between them is needed. Across this interface the intensive properties of the systems are changing from one phase to the other.Free energy of the interface ΔG = ΔW = 2σAA change of the interface requires a free energy ΔG, meaning a work ΔW, proportional to the area A and interfacial tension σ, is needed.work of cohesion W c = 2σwork of adhesion W c= σ1+σ2-σ12The process is assumed to be fully reversible.8.2 Polymer Surfaceair / vacuumpolymer surfacepolymer volume (bulk)Simple microscopic view: attractive forces between the atoms (spring-bead model) with force equilibrium in the volume, but missing partners at the surface→ attraction oriented towards the bulk→ surface tension / surface energy→ change of the structure at surfacea) Chain conformation in the vicinity of the surfaceComputer simulation: Structural properties of a dense polymer melt confined between two hard walls are investigated over a wide range of temperatures by dynamic Monte Carlo simulation using the bondfluctuation lattice model.The effect is present in a region close to the polymer surface. Deviation of the chain conformation is found in a region with an extension of ≈2R g .Baschnagel, Binder, Macromolecules 28, 6808 (1995)As the wall is further approached, the ability of the chains to reorient is progressively hindered, leading to an increase of R g|| and to a decrease of R g ⊥. Therefore the main effect of the wall is to reduce the orientational entropy of the polymers and to align them preferentially parallel to it.Experiments (GISANS): The samples consist of blend films of protonated and deuterated polystyrene (PS) spin coated onto glass substrates. A variation of the thickness of the blend films in a range of about 41 down to 0.66 times the radius of gyration R g of the chains in the bulk enables the determination of film thickness and confinement effects with the advanced scattering technique grazing incidence small angle neutron scattering (GISANS).The effect of the breaking of the translation symmetry by the presence of a surface is found in a more extended region of ≈8R g .Kraus et al., Europhys. Lett. 49, 210 (2000)The polymer molecule is altered in its conformation from an isotropic Gaussian chain (sphere) into an ellipsoidal shapechain segments are oriented in parallel to surfaceb) Chain end distribution Theory:Density of chain ends at the surface (de Gennes, 1992):φφρee N 2=with N length of chainφe number of ends at surfaceφ number of monomers per volume→ chain ends from a region 2R g are enriched in a layer of thickness d (typically 1-2 nm):N dae 2=ρ with segmental length aenrichment of chain ends at the surface due to entropic effects Experiments (NR): Mono-terminated polystyrenes (PS) are synthesized anionically to include a short perdeuteriostyrene sequence adjacent to the end groups for the purpose of selective contrast labeling of the end groups for neutron reflectivity (NR).The location of deuterium serves as a marker to indicate the location of the adjacent end group. Damped oscillatory end group concentration depth profiles at both the air and substrate interfaces are found. The periods of these oscillations correspond approximately to the polymer chain dimensions.contrast density depth profileKoberstein et al; Macromolecules 27,5341 (1994)c) Segment distribution in the vicinity of surfaceComputer simulation: Strong orientation of segments due to the breaking of the translational symmetry of the system by the presence of a surface. The effect is present in region close to surface only, with extension of ≈2R g.Experiments (Force balance): Strong modulation in the density in the vicinity of the surface (effect much more pronounced in case of a solid wall).transition region with significantly decreased densityd) Influence on the kineticsComputer simulation:At the polymer surface a very mobileand quasi-liquid layer is existing wellbelow a melting temperature T m. In thislayer the chain mobility is increased.at surface mobility in movement in parallel to the surface is increased in a thinlayer of thickness d (typically 2 nm)This behavior is similar to many crystal samples. The origin is the reduced number of entanglements at the surface.Experiments (FCS): Comparison of polymer diffusion, polyethyleneglycol (PEG), when adsorbed to a solid surface and in free solution(a) Flexible polymer chains that adsorb are nearly flat at dilute surface coverage (i.e., de Gennes pancake). The sticking energy for each segment is small, so no single segment is bound tightly, but the molecular sticking energy is large. (b) Diffusion coefficients (D) in dilute solution (blue circles) and at dilute coverage on a solid surface (red squares) plotted against the degree of polymerization (N) at 22°C.on surface: changed power law due to excluded volume statisticsDepending on the interaction between polymer and wall the mobility can by unchanged to bulk (neutral wall) or slowed down (attractive wall).How do polymer surfaces look in experiments?Examples:polystyrene machined titanium dual-acid-etched (DAE)titaniumSEMAFMNakamura et al, JDR 84, 515 (2005)Typically polymer surfaces are significantly smoother as compared to metal and metal oxide surfaces (independent of the surface treatment).PMDEGA after swelling in water vapor after 6 days storage in airZhong, PMB et al, Colloid. Polym. Sci. 289, 569 (2011)Homopolymer surfaces are only smooth with low surface roughness and good homogeneity if the homopolymer film is stable. If it is unstable the surface can roughen.If the polymer crystallizes a completely different polymer surface is observed. Due to the crystals present at the polymer surface, the surface roughness is significantly increased.8.3 Interface between polymerscase I: identical polymers A/A or compatible polymers A/B• interdiffusion of segments • adhesion • model of segment movementexample: PS/PS, PMMA/PMMA, PMMA/PVCcase II: incompatible polymers A/B• width of the interface in equilibrium • polymer-polymer interaction parameter (Flory-Huggins parameter) χexample: PS/PBrS, PS/PMMA, PS/PpMS, PS/PnBMAMathematical description of the interface:Rough interface j with mean z-coordinate set to zero and fluctuations in height z j (x)The rough interface can be replaced by an ensemble of smooth interfaces weighted by a probability density P j (φ)with a mean value ∫=dz z zP j j )(μand root-mean-square (rms) roughness ()∫−=dz z P z j j j )(22μσDifferent probability density function are possible and result in different interfaces: Normalized error-function (solid line) and hyperbolic-tangent (dashed line) have very similar refractive index profiles n j (z).Error function profile⎟⎟⎠⎞⎜⎜⎝⎛−−−+=++j j j j j j j z z erf n n n n z n σ222)(11 results from Gaussian probability density (μi =0) ⎟⎟⎠⎞⎜⎜⎝⎛−=222exp 21)(j jj z z P σσπand hyperbolic-tangent profile ⎟⎟⎠⎞⎜⎜⎝⎛−−−+=++j j j j j j j z z n n n n z n σπ32tanh 22)(11results from probability density (μi =0) ⎟⎟⎠⎞⎜⎜⎝⎛=−j jj z z P σπσπ32cosh 34)(2Both examples are based on symmetric probability functions, however, for real samples this symmetry is not ensured and thus asymmetric profiles can occur (e.g. polymer brush with exponential decay).a) Interface width of polymer interfacesComputer simulation (Monte-Carlo simulation by Binder, 1994):A symmetric binary mixture (polymer1, polymer2) below its critical temperature T c of unmixing is considered in a thin-film geometry confined between two parallel walls, where it is assumed that one wall prefers polymer1 and the other wall prefers polymer2. Then an interface between the coexisting unmixed phases is stabilized.with interface width χ6a L = yields rms-roughness πσ2L rms =only valid for smooth interfaces (σrmssmall) with qR g >1 and N →∞with segment length a scattering vector ()dq πλπ2sin 4=Θ=Not taking into account: - concentration dependence of χDifferent approximations in the framework of Mean Field theories:• Binder: expansion of free energy for φ=0.5 and N 1=N 2=N (with qR g >1 and χN>>1)()NaL 26−=χ• Brosetta: Integration of the quadratic gradient term in the vicinity of φ=0.5⎟⎠⎞⎜⎝⎛⎥⎦⎤⎢⎣⎡+−=21112ln 26N N aL χ• Stamm: minimization of the free energy using a "trial"-function⎟⎟⎠⎞⎜⎜⎝⎛⎥⎦⎤⎢⎣⎡+−=2121166N N aL πχ ⇒ It is possible to determine the polymer-polymer interaction parameter χ froma measurement of the interface width L, in case the degree of polymerization Nand the segment length a are known!• Frisch: modification of the profile on different length scales: deviation from the simple tanh-shapeb) entanglement density at the interface between two immiscible polymers The variation of entanglement density with interface width at an interface between two polymers is calculated using the relationships between chain packing and entanglement. The chain packing is obtained by the use of self-consistent mean-field techniques to calculate the average chain conformations within the interface region.calculated number of segmentsbetween entanglements as a functionof χassuming a bulk value of N e,typical for polystyrene, of 130Oslanec and Brown, Macromolecules 36, 5839 (2003)b) time dependent evolution of the interface widthHowever, all these models describe a time average and the final equilibrium interface. With experimental techniques it is possible to prepare interface between polymers far from equilibrium and to follow changes with time resolution.covering a large range of time and length scales the crossover between 4different regimes is observedt < τe: Rouse regimeτe < t < τf: Reptation regimeτf < t < τd: Blob movementτd < t: Fick diffusioncharacteristic power laws: tαRouse regime: α = 0.5Reptation regime: α = 0.25Fick Diffusion: α= 1.08.4 Rouse Model(P.E.Rouse 1953, extension B. Zimm 1956)The Rouse model describes the conformational dynamics of ideal chains. The main assumptions are: 1. no excluded volume interaction2. no hydrodynamic interactionTherefore one expects this model to work at Θ-condition or polymer melt condition.Polymers are interconnected objects with a large conformational entropy. As a consequence, the universal entropy-driven Rouse dynamics prevails at intermediate scales, where local potentials have ceased to be important and entanglements are not yet active. Key signature of the Rouse motion is the sublinear evolution of the segmental mean-square displacement2)(t2/1tr≈neutron spin echo (NSE) results on the single-chain dynamic structure factor: dynamics of poly(vinyl ethylene) on length scales covering Rouse dynamicsMean-square displacementof the protons, the solid linerepresents Rouse dynamicsRicher et al., Europhys. Lett., 66, 239(2004)Both molecular-dynamics (MD) simulations and MCT calculations on coarse-grained polymer models (bead and spring models)Bead-spring modelIn this model of a polymer molecule it consists of beads and springs forming a chain. The beads are hydrodynamics resistance sites that are dragged on by the suspending fluid. They also experience random Brownian forces caused by the thermal fluctuations in the fluid which are significant on the molecular scale. The spring is an entropic force pulling the adjacent beads together. In fact, the spring represents many monomer units that can coil and uncoil in response to the forces. This model is a reasonable representation of the polymer chain dynamics that actual polymer molecules undergo.8.5 Reptation Model(de Gennes, Doi, Edwards, 1971 + 1978)Reptation is the snake-like thermal motion of very long linear, entangled macromolecules in polymer melts or concentrated polymer solutions. It comprises:• entanglements with other chains hinder diffusion• each polymer chain is envisioned as occupying a tube of length L • movement of polymer chain is only possible within this fictive tube• special type of movement: diffusion only via movement of chain ends,keeping chain conformation unchangedtube diameter ddifferent types of movement:t < τe : no hindering in movement by tube (Rouse type movement)t = τe : density fluctuations within the chain are extended up to the length scale of the tube diameterτe < t < τf : polymer chain moves along the tubeτf < t < τd : chain starts to escape the tubet = τd : chain left the original tubet > τd : completely free movement of the chain with no remembering of the tubeExample:PE M w = 190k d = 49Å or PE M w = 17k d = 54ÅPS d ≈ 50ÅN R e , density ρ und temperature TInfluence on the interface profile:shown for different relative diffusion times t/t f 0.1 s mall →0.9 largeThe jump in the concentration profile is caused by the movement of the chain ends across the interface in the framework of the Reptation model.Attention: the profile needs to be convoluted with the tube diameter d8.6 Fick diffusionTranslation of the complete polymer chain is described as diffusion of the centerof masswith diffusion coefficient D Attention: different diffusion coefficients are existing D S self-diffusion coefficient (A moves in a matrix of A) D I inter-diffusions coefficient (A und B move with respect to each other) D T tracer-diffusion coefficient (marker T moves in matrix A)a) self-diffusion:Movement of chains in the identical environment → very difficult to detect experimentally, because no contrast between chain and environmentPossibility of marking individual chains (by deuteration or with fluorescent end-groups), but strictly this is a tracer experiment already Example: PS volume D S ≈4*10-14 cm 2/s thin film (300Å) D S ≈1.5*10-15 cm 2/s surface D S ≈9.3*10-16 cm 2/s⇒ slowing down of the diffusion due to the spatial confinementb) inter-diffusion:An interface between two polymers, which was prepared out of equilibrium (e.g. with the floating technique) is annealed above the glass transition temperature of both polymers→ broadening of the interface following the above arguments → late stages are caused by diffusion (t > τd )Experiment: X-ray- or neutron reflectivity measurementshydrogenated and deuterated polystyrene has been measured at 115 °C in-situ and in real time using NRdiffusion coefficientD = (1.7±0.2) × 10-17 cm 2/sBucknall et al., Macromolecules 32, 5453 (1999)• "fast-mode" theory B T B A A T A B I D N D N D ,,φφ+= • "slow-mode" theoryB T B A A T A B I D N D N D ,,111φφ+=Examples:Low molecular weight liquids D ≈10-6 cm 2/s polymers D ≈10-12-10-17 cm 2/s depending on temperaturec) tracer-diffusionusing small markers, e.g gold atoms in a well defined layered approachAnnealing the sample above the glass transition temperature of the polymer and probing the distances which the gold atoms had moved after defined times tReiter et al. Macromolecules 24, 1179 (1991)Dependence on molecular weight:Stamm et al., Macromolecules, 26, 2134 (1993)tracer-diffusions constant2−∝W T M D8.7 additional contributions to the interface widthIn addition to the width of the interface between two polymers which results from interdiffusion, contribution from other sources have to be taken into account. They arise from preparation: thickness variation of the filmwrinkles, dust particles, holes, impuritiesintrinsic: capillary wavesA capillary wave is a wave traveling along the phase boundary of a fluid, whose dynamics are dominated by the effects of surface tension. These waves are of thermal origin .Assuming a semi-infinite liquid with surface tension γLV a complex movement of the atoms makes a surface wavehaving a dispersion relation()g q q q LV rr r +=ργω32with ρ liquid density g Earth's accelerationSo thermal fluctuations cause a deviation from the ideal flat surface with an excess free energy density()()()()()Ζ⎥⎦⎤⎢⎣⎡ΖΔ+⎟⎠⎞⎜⎝⎛−Ζ∇+=Ζ∫∫22111d l P h A h fA L LV L exr r r γ ()()()()()Ζ⎥⎦⎤⎢⎣⎡Ζ+Ζ∇≈Ζ∫∫221d h P h A h f A L L LV L ex r r r γ yielding the height-height-autocorrelation function and power spectral density()Ζ=Ζr r c LV B q K Tk C 02)(πγ and 22214)(c LV LV B q q T k q L γγπ+=rwith K 0 modified Bessel function of zero ordercapillary waves can only be excited in an interval between λmin and λc for T>>0KA gravitation cut-off of the larges possible wavelength being excited isc c q πλ2=with LVc g q γρ=2 with the capillary length gLVργξ=being the lateral correlation length characteristic for the liquid (on the order of mm)and a short-range cut-off on the scale of the molecule diameter a is needed to avoid divergence of C(Ζ)a q 22maxmin ==πλ with a q π=maxExample: ethanol-vapor interface, σ=6.9 Åx-ray reflectivity and longitudinal diffuse scattering x-ray transverse diffuse scatteringSanyal et al.; Phys. Rev. Lett. 66, 628 (1991)Attention: in case of interfaces instead of surfaces the surface tension γLV is replaced by the interface tension γLL which is orders of magnitude smaller than the surface tension→ contribution of capillary waves to rms-roughness of interface increasedExample: Direct visual observation of thermal capillary waves at the free liquid-gas interface in a phase-separated colloid-polymer mixture imaged with laser scanning confocal microscopy (LSCM) at four different state points approaching the critical point(2004) each image is 17.5 μm by 85 μmAarts et al. Science 304,847Simple liquid → polymer:For highly viscous liquids and polymer melts the capillary waves are overdamped, their amplitude reduced.While, in general, both damped and propagating modes exist, for highly viscous polymers all modes are overdamped, which can be characterized solely by relaxation times τ.physical meaning of the over-damped relaxation timeconstantSinha, University of CaliforniaRoughness measurements are time averaged and cannot reveal the dynamic behavior of the waves.→ Need to probe the dynamics!Experiments: XPCSExample: capillary wave dynamics on glycerol surfaces investigated with XPCS performed at grazing anglesnormalized time correlation function22)()()()(ttt I t I t I g ττ+=described by exponential behavior1exp )(002+⎟⎟⎠⎞⎜⎜⎝⎛−=τττg g→ relaxation times τSeydel et al., Phys. Rev. B 63, 073409 (2001)The capillary wave is identified by its wave vector q and complex frequencyΓ+=i f p ωwhere the real part reflects the propagation frequency and the imaginary part the damping.At the transition from propagating to overdamped behavior f becomes purely imaginary; i.e., ωp =0.The transition from propagating (inelastic) to overdamped (quasielastic) behavior takes place at critical wave vector254ηργLV c q =with surface tension γLV , the dynamic viscosity η, and the density ρ of the polymerExample: Mixture of water and glycerol with 65% weight concentration of glycerolMadsen et al., Phys. Rev. Lett. 92, 096104 (2004)propagation frequency ωp (circles) and the dampingconstant Γ (squares) for the water -glycerol mixture at (a)30 °C and (b) 12 °C.8.8 Thin Film Preparation Techniques a) Solution-castingpreparation of thick polymer films (thickness from 100 nm to several μm)• polymer solution deposited on top of a horizontally oriented substrate• cover full substrate to have chance for uniform film if liquid is not spreading • solvent evaporates under controlled condition (T, p, atmosphere) → a solid film remains on the substrate→ allows for slow drying: films close to equilibrium can be preparedOn the scale of the capillary length the film at the substrate edges differs from the average film.Problems occur in case of pinning effects. If the contact line gets pinned during drying, no homogenous film is formed.Example: ternary blend PS, P αMS and PI cast from toluenePanagiotou, PhD Thesis TU Munich (2004)For complex fluids (highly viscous polymer solutions), the morphology is not determined by the evaporation process, the "coffee stain" effect but essentially by the capillary instabilities.Using the appropriate couple of polymer/solvent, a outward, inward or a lack of Marangoni flow in the droplets, leading to the formation of a rim, a drop or a uniform film, respectively, occurs.b) Spin-coatingpreparation of thin polymer films with thicknesses from 1 to 1000 nm• prepare polymer solution with desired concentration c • cover substrate entirely with polymer solution• select acceleration profile and spinning parameters (time, rotational speed) • start spin-coater after defined wait time → a solid film remains on the substrate→ due to non-equilibrium the film can have enrichment or lateral structuresDepending on rotational speed ω, concentration c, molecular weight Mw and apersonal parameter (wait time, person, machine)Attention: change in slope at entanglement concentration of solutionRuderer, PMB, Chem.Phys.Chem. 10, 664 (2009)Spin-coating is a complicated non-equilibrium processTheoretical description in the framework of a 3-step model (Lawrence, 1988) 1. step – start phasedeposition of solution with C 0 → strong height variationsacceleration of the substrate → most of the solution is flung-off the substrate → film thickness ≈100 μmEnd: Homogeneous film with thickness h 0 with concentration C 0 2. step – mass reduction by conventionevaporation can be neglected in comparison with the flow of solution towards to substrate edges → change of film thickness by convection2/102020341)(−⎟⎟⎠⎞⎜⎜⎝⎛+=t h h t h ηρω 3. step – evaporation of solvent through film surfaceevaporation rate of solvent larger than change in thickness by convection at a film thickness h w → mass reduction only by solvent evaporation, no polymer can leave the substrate anymore → dry, solid film remains()0,1s w f h h φ−=With the initial amount of solvent φs,0Polymer surface depends on the used solvent and on the spin-coating parameters:I: problems with solvents which have very high evaporation rate: → formation of skin on solution surface→ elastic film surface has a changed flow field of the confined polymer solution → hydrodynamic instabilities→ resulting lateral structures which have a star-shape with the center in the center of rotationII: problems with solvents which are hygroscopic and attract water from the surrounding, but are non miscible with water:→ demixing of both components (solvent and water) gives rise to lateral structuresMüller-Buschbaum et al.; Macromolecules 31, 3686 (1998)c) Floating-techniquepreparation of single and multiple polymer films (on non-wetable substrates)Schindler, Diploma Thesis TU Munich (2010)• scratch film with scalpel at 2 mm from substrate edge • put substrate into float box (tilt angle optimal at 10-15°) • add 2-3 drops of deionized water per second • remove substrate after film had decoupled• put second substrate with larger tilt angle into the water • fix polymer film on upper edge of this second substrate • remove water with 2-3 drops/sec • dry films (e.g. 4 h at 50°C)→ typically the needed time is 3-6 hours depending on the M w and film thickness→ not possible for all film thickness (thinner films are more difficult, integer number of R g can work), not possible for heat treated filmsProblems occur in case of wrinkle formation, incorporation of dust particles or trapping of water.Example: freely floating polymer film, tens of nanometers in thickness, wrinkles under the capillary force exerted by a drop of water placed on its surfaceThe wrinkling pattern is characterized by the number and length of the wrinkles.The PS film thickness h was varied from 31 to 233 nm. As the film is made thicker, the number of wrinkles N decreases (there are 111, 68, 49, and 31 wrinkles in these images).Huang et al.; Science 317, 650 (2007)d) Adsorption from solutiondeposition of single molecules, thin layers or thick films from solution with a controlled concentrationSketch:Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if liquid) at constant temperature.Isotherms are described bydifferent models:Langmuir isotherm (red) andBET isotherm (green)Computer simulation:Adsorption and self-assembly of linear polymers on smooth surfaces are studied using coarse-grained, bead-spring molecular models and Langevin dynamics computer simulations. The aim is to gain insight on atomic-force microscopy images of polymer films on mica surfaces, adsorbed from dilute solution following a good-solvent to bad-solvent quenching procedure.Chremos et al., Soft Matter5, 637 (2009)Molecular Weight Competition: Upon initial mixing of a formulation, all chains attempt to adsorb on a surface. For adsorbing homopolymers, thermodynamics dictates a preference for adsorption of long chains, and so short chains, originally adsorbed, are displaced form the surface at longer times.Santore+ Fu, Macromolecules 30, 8516 (1997)Fu + Santore, Macromolecules 31, 7014 (1998) Large scale industrial applications involving substantial quantities of complex fluids such as paints, inks, and coatings employ water soluble polymers with a broad distribution of molecular weights: The likelihood that some fraction of the added chains impart the desired interfacial properties means that changes in molecular weight distribution from batch to batch can dramatically impact the properties of a formulation.Experiments: Adsorption of polymers is very common in case of polyeletrolytes and used to build up multi-layers.Layer-by-Layer (LBL) assembly: fabrication of multilayers by consecutive adsorption of polyanions and polycationsDecher et al.; Science 277, 1232 (1997)Fine-tuning the film thickness by ionic strength (addition of salt yields thicker layers; polyanion from salt, polycation from pure water)Decher + Schmitt, Progr. Colloid Polym. Sci. 89, 160 (1992) A small list of polyions already used for multilayer fabrication:e) Spray coatingdeposition of thick films from solution with a controlled concentration, depending on deposition conditions (wet droplets = spraying, dry polymer = airbrush)control parameters: number of depositions, deposition time, solvent, polymer concentration, distance nozzle-surface。

管理学英语试题及答案一、选择题（每题2分，共20分）1. The term "management" refers to the process of:A. Making decisionsB. Organizing resourcesC. Directing and controlling activitiesD. All of the above答案：D2. Which of the following is NOT a function of management?A. PlanningB. StaffingC. MotivatingD. Selling答案：D3. The process of setting goals and deciding on actions to achieve these goals is known as:A. OrganizingB. LeadingC. PlanningD. Controlling答案：C4. Which of the following is an example of a managementprinciple?A. Division of laborB. CentralizationC. DelegationD. All of the above答案：D5. In the context of management, "controlling" refers to:A. The process of ensuring that things are done as plannedB. The process of making plansC. The process of organizing resourcesD. The process of motivating employees答案：A6. The concept of "span of control" is related to:A. The number of employees a manager can effectively superviseB. The range of activities a manager is responsible forC. The level of authority a manager hasD. The type of control systems a manager uses答案：A7. The management function that involves influencing people to work towards organizational goals is:A. OrganizingB. LeadingC. PlanningD. Controlling答案：B8. Which of the following is a characteristic of effective communication?A. ClarityB. AmbiguityC. DisorganizationD. Lack of feedback答案：A9. The "scientific management" theory was developed by:A. Henri FayolB. Max WeberC. Frederick TaylorD. Abraham Maslow答案：C10. In the context of management, "empowerment" means:A. Giving employees the authority to make decisionsB. Centralizing all decision-making powerC. Reducing the role of employees in decision-makingD. Ignoring employee input in decision-making答案：A二、填空题（每题1分，共10分）1. The four basic functions of management are planning, organizing, leading, and ________.答案：controlling2. The management principle that suggests that there is an optimal span of control for each manager is known as ________.答案：span of control3. The management approach that focuses on the social needsof employees is known as the ________ approach.答案：human relations4. The process of identifying, selecting, orienting, training, and compensating employees is known as ________.答案：staffing5. A management style that involves a high level of task orientation and a low level of relationship orientation is known as ________ leadership.答案：autocratic6. The concept of "management by objectives" was developed by ________.答案：Peter Drucker7. The "Maslow's hierarchy of needs" theory suggests that people are motivated by a series of needs, starting with physiological needs and ending with ________ needs.答案：self-actualization8. In a ________ structure, there is a clear chain of command and a narrow span of control.答案：hierarchical9. The process of comparing actual performance with planned performance is known as ________.答案：budgeting10. The management function that involves setting goals and determining the sequence of actions needed to achieve them is known as ________.答案：strategic planning三、简答题（每题5分，共30分）1. What are the three key characteristics of an effective organizational structure?答案：An effective organizational structure should havethe following characteristics: clarity of roles and responsibilities, a clear chain of command, and a balance between centralization and decentralization.2. Explain the difference between leadership and management.答案：Leadership is the process of influencing, motivating, and directing individuals towards the achievement of organizational goals. Management, on the other hand, is a broader concept that includes planning, organizing, leading, and controlling organizational resources to achieve goals.3. What are the main principles of scientific management according to Frederick Taylor?答案：The main principles of scientific management includethe scientific selection and training of workers, the scientific selection of tasks and tools, the scientific determination of work methods, and the scientific scheduling of work and rest periods.4. Describe the four stages of the control process.。

2025年研究生考试考研英语(一201)模拟试题及答案指导一、完型填空（10分）研究生考试考研英语(一201)一、完形填空（共20题，每小题1分，满分20分）Passage:In recent years, there has been a surge in interest in mindfulness. Mindfulness, simply put, is the practice of paying attention to the present moment without judgment. It involves observing your thoughts, feelings, and sensations (1)they arise, acknowledging them without getting caught up in them.This approach to awareness has its roots in ancient Eastern traditions, such as Buddhism, where it was (2) as a path to enlightenment. However, mindfulness has gained widespread (3) in the West (4) research has shown its numerous benefits for mental and physical health.Practicing mindfulness can help reduce stress, improve focus, (5)emotional regulation, and boost overall well-being. Studies have (6) a link between mindfulness and a decreased risk of chronic diseases, such as heart disease and depression. (7), mindfulness can enhance (8)skills, such as communication and empathy.Some people (9) mindfulness through formal meditation practices, while others (10) it into their daily lives by paying attention (11) while walking, eating, or (12) to music. Regardless of the approach, the key is (13) present and (14) judgment.Mindfulness is not a quick fix. It requires (15) and (16). However, with (17) practice, it can become a powerful tool for (18) stress, enhancing well-being, and living a more (19) life.(20) all, mindfulness teaches us to be present and appreciate the beauty of the now.Answer Key:1.as2.viewed3.acceptance4.because5.enhance6.established7.Furthermore8.interpersonal9.cultivate10.incorporate11.fully12.listening13.staying14.non-judgmentally15.patiencemitment17.consistent18.managing19.fulfilling20.Above二、传统阅读理解（本部分有4大题，每大题10分，共40分）第一题文章正文：Title: The Last of the TitansIn the heart of the Indian Ocean, lies a small, obscure island known as Kikonyogo. Unlike the grandeur of Maldives or the allure of Bali, Kikonyogo is a place many would scarcely bother to find on a map. Yet, it holds within its shrunken frame a peculiar secret: it is home to the largest living tree in the world.This colossal tree, estimated to be over 70 meters in circumference and with a girth thick enough to wrap around four average-sized cars, towers above the surrounding vegetation. Its branches stretch out like ancient fingers reaching for the sky, embracing the sunlight that filters through the dense canopy. Thetree, though largely surrounded by ruins of what once was a thriving civilization, stands tall, its roots deeply entrenched in the earth and its leaves whispering tales of centuries passed.The locals, a remnant of the once vibrant community that thrived around these ancient woods, have long held traditions of respecting and protecting this solitary tree. They believe it to be sacred, a guardi an of the island’s life force, a reminder of the these lands’ untouched beauty before human intervention. Despite the passage of time and the changes that have swept over Kikonyogo, the last of the titans, as it is affectionately called, remains steadfast, a testament to resilience and endurance.1.How old is the largest living tree in Kikonyogo?The largest living tree in Kikonyogo is estimated to be over 70 meters in circumference, indicating it is significantly older than any living tree on Earth.2.What does the tree look like?The tree looks like a colossal structure, with an estimated circumference of over 70 meters and a girth thick enough to wrap around four average-sized cars. Its branches stretch out like ancient fingers, and its leaves whisper tales of centuries passed.3.What role does the tree play in the local community’s traditions?The tree plays a role of being a guardian of the island’s life force and a reminder of the untouched beauty of the land before human intervention. It is considered sacred and is respected and protected by the local community.4.What is the significance of Kikonyogo’s colossal tree?The significance of Kikonyogo’s colossal tree is that it stands as a testament to resilience and endurance, surviving years and changes that have swept over Kikonyogo.5.According to the text, how does the tree fit into the natural landscape of Kikonyogo?The tree fits into the natural landscape of Kikonyogo as a solitary tree surrounded by ruins of what once was a thriving civilization. It stands tall, embracing the sunlight, and its presence is deeply intertwined with the island’s history and the local community’s traditions.第二题阅读下列短文，从每题所给的四个选项中，选出最佳答案。

一、名词解释（4分，16分）英文两个：1.policy science:multidisciplinary,problem-solving,explicitly normative.2.Policy analysis: the disciplined application of intellect to publicproblems.3.Policy cycle:”stage heuristic”,is a political process through which mostpublic policies pass over the course of their lifetime. Is often viewed as a “vonveyor belt”.4.Kuhn’s Scientific Revolution:As the natural sciences progressed,theyamassed(积累，收集) a body of ever-changing theory.Scientific advances were not based on the accumulation of knowledge and facts,but rather on a dominant paradigm used in any specific period to explain the phenomena under study.Rather than refuting previous theories,each paradigm would build upon the body of relevant knowledge and theories.Once a paradigm was accepted by consensus among current scholars,it would last as long as it remained useful.Ultimately it would be displaced by a more relevant and useful paradigm,this process of replacement was Kuhn’s Specific Revolution.5.Policy universe:Afundamental unit containing all possibleinternational state,social actors and institutions directly or indirectly affecting a specific policy area.6.Policy subsystem:A space where relevant actors discuss policy issuesand persuade and bargain in pursuit of their interests.7.Counteracting:growth in the size,scope and complexity ofgovernment functions over the years prevents generalist politicians from controlling.8.Prime mover(发起者，原动力) in the policy respone:problemstructuring is a central guidance system or steering mechanism that affects the success of all subsequent phases of policy analysis…policy analysts…fail more often because they solve the wrong problem than because they get the wrong solutions to the right problem.9.Problem:substantial discrepancy between what is and what shouldbe.10.P roblem Recognition:According to Kingdon 1995,problem recognitionis often stimulated by widely agreed-upon indicators and routine monitoring that turns up discrepancies or patterns that hint that something is amiss(出了差错的).11.P olicy images:a mixture of empirical information and emotiveappeals that explain the issue and justify the public policy respone. 12.A ttention Cycle:explain how policy problems evolve on the politicalagenda by Downs.Public attention rarely remains focused to any one issue.13.P unctuated Equilibrium（间断平衡）:convey a process thatsimultaneously combines ong stable periods of policy consensus followed by bursts of change around new issues and new policyimages.14.I ncrementalism（渐进主义）:seem to describe most budgetarydecision-making in Western democracies,less useful when encounter some considerable shock:a war,crisis.15.P olicy design:the process of organizing and delivering outcomesthrough the chosen policy instruments.16.P olicy tool or instrument:an identifiable method through whichcollective action is structured to address a public problem.17.P olicy implementation:implementation is the process of putting agovernment program into effect;it is the total process of translating a legal mandate(授权),whether an executive order an enacted statute(法规),into appropriate program directives and structures that provide services or create goods.18.P olicy evaluation:policy evaluation refers broadly to the stage of thepolicy process at which it is determined how a public policy has actually fared in action.It involves the means being employed and the objectives being served.中文两个：1．什么是政策过程？从政治系统论看，政策过程指政策主体、政策客体以及政策环境之间相互联系和相互作用，政策系统呈现的动态运行过程；从政策过程的是只看，政策过程实质上是一种政治过程。