Use of silica gel or polyurethane immobilized bacteria for self-healing concrete
Jianyun Wang a ,b ,Kim Van Tittelboom a ,Nele De Belie a ,?,Willy Verstraete b
a Magnel Laboratory for Concrete Research,Faculty of Engineering and Architecture,Ghent University,Technologiepark Zwijnarde 904,B-9052Ghent,Belgium b
Laboratory of Microbial Ecology and Technology (LabMET),Faculty of Bioscience Engineering,Ghent University,Coupure Links 653,B-9000Ghent,Belgium
a r t i c l e i n f o Article history:
Received 23December 2010
Received in revised form 14May 2011Accepted 17June 2011
Available online 14July 2011Keywords:
Bacillus sphaericus Immobilization Silica gel
Polyurethane CaCO 3
Strength regain
Coef?cient of water permeability
a b s t r a c t
Cracks in concrete are the main reason for a decreased service life of concrete structures.It is therefore more advisable and economical to restrict the development of early age small cracks the moment they appear,than to repair them after they have developed to large cracks.A promising way is to pre-add heal-ing agents to the concrete to heal early age cracks when they appear,i.e.the so-called self-healing approach.In addition to the more commonly studied polymeric healing materials,bacterial CaCO 3pre-cipitation also has the potential to be used for self-healing.It is more compatible with the concrete matrix and it is environment friendly.However,bacterial activity decreases a lot in the high pH (>12)environ-ment inside concrete.In this research,the possibility to use silica gel or polyurethane as the carrier for protecting the bacteria was investigated.Experimental results show that silica gel immobilized bacteria exhibited a higher activity than polyurethane immobilized bacteria,and hence,more CaCO 3precipitated in silica gel (25%by mass)than in polyurethane (11%by mass)based on thermogravimetric analysis.However,cracked mortar specimens healed by polyurethane immobilized bacteria had a higher strength regain (60%)and lower water permeability coef?cient (10à10–10à11m/s),compared with specimens healed by silica gel immobilized bacteria which showed a strength regain of only 5%and a water perme-ability coef?cient of 10à7–10à9m/s.The results indicated that polyurethane has more potential to be used as a bacterial carrier for self-healing of concrete cracks.
ó2011Elsevier Ltd.All rights reserved.
1.Introduction
Concrete is the one of the most popular construction materials.However,it is quite vulnerable to cracking because of its inherent heterogeneity and the non-ideal service environments.Since cracks provide an easy path for water and other aggressive substances like
Cl àand SO 2à
4to penetrate inside the concrete matrix,they should be repaired in time to prolong the service life of concrete structures.Generally,the normal repair methods follow the procedure of monitoring,detecting and repairing.The repair work will be per-formed after the cracks are discovered.Repair agents are applied from the outside and penetrate into the cracks.This technology is quite suitable for repairing large cracks.For small and deep cracks,it will be dif?cult for healing agents to reach the inner part.There-fore,an alternative repair method by means of a self-healing process is being strived for.Healing agents are incorporated into the concrete matrix during casting.When cracks appear,healing agents will be released from within the concrete and ?ow into cracks to seal the cracks from the inside to the outside.A self-healing method is especially useful to repair deep-micro cracks and it can restrain early-age cracks to develop to large cracks.
Self-healing properties in concrete may be obtained by different methodologies,such as secondary hydration of unhydrated cement,addition of ?bers,and encapsulation of polymers [1–5].Another alternative self-healing material is bacterially produced calcium carbonate [6–9].Compared with the healing agents like expanded additives and polymers,the proposed bio-mineral (CaCO 3)is more compatible with the concrete matrix and more environmentally friendly.Most bacteria are able to induce carbon-ate precipitation under suitable conditions [10–13].In general,there are three mechanisms associated with bio-carbonate precip-itation.One is the dissimilatory sulfate reduction carried out by sulfate reducing bacteria under anoxic conditions.The second is the degradation of organic acids.Another pathway is related to the nitrogen cycle,in particular the degradation of urea by ureolyt-ic bacteria [14].Among the three pathways to precipitate CaCO 3,decomposition of urea by ureolytic bacteria is easier to operate and control [15,16].
In our previous research,Bacillus sphaericus was found to be able to precipitate calcium carbonate (CaCO 3)on its cell constituents and in its micro-environment by decomposition of urea (CO(NH 2)2)into
ammonium (NH t4)and carbonate (CO 2à
3).The latter subsequently promotes the microbial deposition of CaCO 3in a calcium rich
0950-0618/$-see front matter ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.conbuildmat.2011.06.054
?Corresponding author.Tel.:+3292645522;fax:+3292645845.
E-mail addresses:jianyun.wang@ugent.be (J.Wang),kim.vantittelboom@u gent.be (K.Van Tittelboom),nele.debelie@ugent.be (N.De Belie),willy.verstrae te@ugent.be (W.Verstraete).
environment.Through this process,the bacterial cell is coated with a layer of CaCO3.The aim of this study is to use this bio-CaCO3to heal concrete cracks autonomously.The problem is that bacterial cells cannot be added to cement specimens directly.On one hand,bacte-rial activity decreases a lot in the high pH(>12)environment as pres-ent in concrete.On the other hand,bacterial cells might be destroyed during the process of hydration.Jonkers et al.indicated that bacteria did not survive due to the decreasing of pore diameters during the hydration of the cement materials[17].Therefore,a suitable carrier is necessary to immobilize bacteria and to protect them from the harsh environment in concrete.In this work,silica gel and polyure-thane were used as the carrier for the bacteria.
The term silica sol is derived from silicic acid sol.Silica sols are colloidal dispersions of silicic acid in water.Silica gel is a popular car-rier for microorganisms,like bacterial cells,yeast and algae,because it has good properties of mechanical,thermal and photochemical stability,biological inertness(not a food source for bacteria),and suitable matrix porosity for the transmission of molecules and ions [18,19].In our previous work,silica gel immobilized bacteria were used to manually heal cracks in concrete.The mixture made of silica sol and bacterial suspension(containing bacterial cells and NaCl) was injected into simulated cracks by a syringe.When gel formation (caused by high concentrations of Na+and Clà)began,the injection was repeated several times until the crack was completely?lled. After silica sol became a gel,the specimens were immersed into the medium consisting of urea and Ca2+and then precipitation of CaCO3occurred.Water permeability of the specimens decreased about3orders of magnitude after this treatment[20].In contrast to the previous work,in the current study the immobilized bacteria together with nutrients and other agents,encapsulated in glass tubes,were incorporated into the specimens during casting.When cracking occurs,the glass tubes will break and healing agents will ?ow out into the cracks.Silica gel forms in situ when silica sol meets with Ca2+from the concrete matrix and from the healing agent pre-incorporated inside the specimens.At the same time,bacterial cells are immobilized into the silica gel.When bacteria meet with urea and Ca2+,CaCO3precipitates.
Polyurethane(PU)is widely used as a waterproof material.PU with immobilized bacteria has already been used to repair concrete cracks[21].In2001Bang et al.?rst used PU foam to immobilize bacteria for manual repairing of concrete cracks.The PU foam,con-taining bacterial cells,was cut into equal-sized pieces.Afterwards, PU foam strips were placed into simulated cracks of mortar speci-mens.The specimens were then incubated in a urea-CaCl2medium at room temperature.As a result of CaCO3precipitation,the7d compressive strength of the cracked specimens remediated by PU immobilized bacteria was increased by12%compared with the ones only remediated with PU.Different from the method de-scribed above,in which PU foam with immobilized bacteria was applied externally(pre-formed and placed into the cracks manu-ally),in this work bacteria and PU prepolymer were applied inter-nally(to heal cracks from the inside).PU foam should form in the crack automatically when cracking occurs and bacteria are incor-porated inside the foam at the same time.The aim of this work was to investigate the potential use of silica gel or polyurethane immobilized bacteria to bring about self-healing concrete.
2.Materials and methods
2.1.Bacterial strain
The bacterial strain used in the experiments was B.sphaericus LMG22,557 (Belgian coordinated collection of microorganisms,Ghent).This strain has a high urease activity(40mM urea hydrolyzed.ODà1hà1),long survival time[22]and can produce CaCO3in a simple and controllable way[23].
The medium used to grow B.sphaericus consisted of yeast extract and urea.The yeast extract medium was?rst autoclaved for20min at120°C and the urea solu-tion was added which was sterilized by means of?ltration through a sterile 0.22l m Milipore?lter(Millipore,USA).The?nal concentrations of yeast extract and urea were20g/L.Cultures were incubated at28°C on a shaker at100rpm for24h.Bacterial cells were harvested by centrifuging(7000r/min,7min,Eppen-dorf MiniSpin,Hamburg,Germany)the24h-old grown culture and the cells were resuspended in saline solution(NaCl,8.5g/L).The concentration of bacterial cells was109cells/mL.
2.2.Survival test of the bacteria
In this experiment it was tested how long the bacteria can remain viable and sustain high urease activity.Batches of2mL bacterial solution(109cells/mL,same as in the Section2.1)were added into a sterile vial(12.5mm(diameter)?46mm (height),VWR).The vials were then closed tightly and put in the incubator at 28°C.At certain time intervals,three vials were taken out from the incubator.Bac-teria of each vial were inoculated into100mL sterile deposition medium(yeast ex-tract20g/L,urea20g/L and Ca(NO3)2.4H2O79g/L).The media were then put on the shaker(28°C,100rpm)for three days.The amount of urea decomposed by bacteria after three days was calculated based on the total ammonium nitrogen(TAN)mea-sured in the deposition medium.Since one mole of urea(CO(NH2)2)produces2mol of NHt
4
,the amount of NHt
4
can thus indicate the amount of urea decomposed,and hence the amount of CaCO3precipitation.TAN concentrations were measured calo-rimetrically by the method of Nessler[24].
2.3.Activity of bacteria after being immobilized into silica gel and polyurethane
2.3.1.Immobilization of bacteria
Immobilization of bacteria into silica gel:Levasilò200/30%sol,with a speci?c sur-face area of200m2/g and a solid content of30%was used to embed bacterial cells. Two concentrations of saline solutions were used.The saline solution with8.5g/L NaCl was used to re-suspend centrifuged bacteria.Another saline solution with 60g/L NaCl(represented as HS)was used to make silica sol become silica gel.Silica sol,bacterial suspension(BS,109cells/mL)and HS were mixed together with the volume ratio5:1:4.About2h later,the silica sol became gel and bacterial cells were thus incorporated inside the gel.
Immobilization of bacteria into polyurethane:A two-component polyurethane (MEYCO MP3551K,BASF),represented as PU,was also used to encapsulate bacte-rial cells.The volume ratio of component A of PU(polyurethane prepolymer,PU A), component B of PU(accelerator,PU B)and bacterial suspension(BS,109cells/mL) was5:0.5:1.About15min after mixing of the three components,PU foam formed and the bacterial cells were embedded inside the foam.
At the same time,silica sol and PU were also combined with dead bacteria(dead bacteria were obtained by autoclaving living cells at120°C for20min)and pre-pared without bacteria as a control.
2.3.2.Bacterial activity after immobilization
The bacterial activity was evaluated by bacterial ureolytic activity(ability to decompose urea)and carbonatogenesis activity(ability to precipitate CaCO3).The bacterial ureolytic activity was expressed as the amount of the urea decomposed by bacteria in the urea solution(20g/L),which was determined by measuring the conductivity of the urea solution.One mole of urea(CO(NH2)2)produces2mol of
NHt
4
and1mol of CO2à
3
.Therefore,the more urea is decomposed,the higher the conductivity of the urea solution will be.The relationship between urea decom-posed and conductivity is shown in the following equation[14]:
Urea decomposedemMT?conductivityems cmà1T?9:6e1TThe bacterial carbonatogenesis activity was determined by the decomposition of urea in the deposition medium(DM)consisting of20g/L urea and79g/L Ca(NO3)2.4H2O.The amount of CaCO3precipitated by bacteria can be indicated by the quantity of urea decomposed in the deposition medium.The more urea decom-posed,the more CaCO3formed.Since the deposition medium consisted of urea and
Ca(NO3)2,the increase of CO2à
3
because of urea decomposition and the decrease of
Ca2+and CO2à
3
because of the formation of CaCO3would make it dif?cult to relate conductivity with the amount of urea decomposed.Therefore,the decomposed urea was calculated also by measuring the TAN values in the deposition medium.
Living bacteria and dead bacteria,after being immobilized into silica gel and PU, were immersed into50mL urea solution and50mL deposition medium,separately. Besides,as the?rst control,the same amount of free bacterial cells(un-immobi-lized)was also added to the same urea solution and deposition medium.As the sec-ond control,silica gel and PU without bacteria were also immersed into the same media.The experiments were done in triplicate.The conductivity of the urea solu-tion was measured every24h for4days.The TAN value was measured after the dif-ferent series of silica gel and PU were immersed into the deposition medium for 3days.
One week later,the original urea solutions,which were used to immerse SG and PU immobilized bacteria,were poured out and50mL new urea solutions(also 20g/L)were added to the same SG and PU immobilized bacteria.The conductivity values of the new solutions were measured to investigate whether the immobilized bacteria still had urease activity after being in silica gel and PU for one week.
J.Wang et al./Construction and Building Materials26(2012)532–540533
2.3.3.Thermogravimetric analysis(TGA)of CaCO3precipitation
TGA was used to detect the formation of CaCO3inside the silica gel and PU foam. After being immersed into the deposition medium for three days,the different ser-ies of silica gel and PU foam mentioned in Section2.3.2were dried in the oven at 50°C for24h.Samples of silica gel were ground into powders and samples of PU foam were cut into small pieces to?t for the pan(used for loading samples)of the TGA instrument(SDT2960Simultaneous DSC–TGA).The temperature increased from room temperature to1000°C at a speed of10°C/min in argon atmosphere. The weight loss of the samples during the process of heating was recorded and shown in a weight-temperature graph.
2.3.4.Scanning electron microscope(SEM)analysis
The morphology of the calcium carbonate precipitated by immobilized bacteria was studied in a FEI QUANTA200F SEM at accelerating voltage of20kV.Secondary electron imaging(SEI)was used for electron micrography.Samples were com-pletely dried in the oven at50°C for2days and were gold coated by a Baltec SCD030Sputter Coater before examination.
2.4.Self-healing by means of immobilized bacteria
2.4.1.Glass tubes with healing agents
To incorporate immobilized bacteria into mortar specimens,glass tubes with a length of40mm and an inner diameter of3mm were used to carry the healing agents(shown in Fig.1).First,glass tubes were glued together and one of their ends was sealed by an adhesive(Schnellklebstoff X60,HBM).Then the healing agents were injected into each tube from the other end,which was sealed afterwards.
For self-healing by using silica-gel immobilized bacteria,two glass tubes were glued together.One tube was?lled with bacterial suspension(BS,same as in Sec-tion2.3.1)and silica-sol.The other tube was?lled with the same deposition med-ium(DM)as described in Section2.3.2.For self-healing by use of PU immobilized bacteria,three glass tubes were glued together.One compartment of the tubes was?lled with PU A.The second one was?lled with PU B together with deposition medium.The third one was?lled with BS.Since dead bacteria were obtained by autoclaving living cells at120°C for20min,BSA is used to represent dead bacteria in the following?gures and graphs.
2.4.2.Mortar specimens
The self-healing ef?ciency of bacteria incorporated mortar specimens was eval-uated by measuring the strength regain and the decrease of water permeability. Therefore,two kinds of mortar specimens,prisms(40mm?40mm?160mm) for investigating the strength regain and cylinders(U=80mm,H=22mm)for measuring water permeability,were made with a water to cement ratio of0.5 and a sand to cement ratio of3by using ordinary Portland cement CEM I52.5N. First,a10mm mortar layer was brought into the molds.After this layer was com-pacted by means of vibration,two reinforcement bars with a diameter of2mm and a length of14cm(for prisms)or two steel?bers with a diameter of1mm for cyl-inders were positioned on top of it(Fig.2).Meanwhile,two or three sets of glass tubes were also put on top of the layer.For the specimens with silica gel immobi-lized bacteria,three sets of glass tubes were embedded(Fig.2a)while for the spec-imens with PU immobilized bacteria,two sets of tubes were incorporated(Fig.2b) to make sure that the total volume of the healing agents was the same.Afterwards, the molds were completely?lled with mortar and vibrated.After casting,all molds were put in an air-conditioned room(curing room)with a temperature of20°C and a relative humidity of more than90%for24h.After demolding,the specimens were placed in the same room for two weeks.
For the prisms,?ve different series were made:four series containing glass tubes with healing agents SG–BS,SG–BSA,PU–BS and PU–BSA;one reference series without glass tubes or healing agents.Each series had three replicates.For the cyl-inders,also?ve different series were made:four series containing glass tubes with healing agents SG,SG–BS,PU and PU–BS;one reference series without glass tubes or healing agents.Each series consisted of six replicates.
Additionally,extra sets of glass tubes,which were the same as the ones used in mortar specimens,were also stored for two weeks under identical conditions in the curing room.Three sets of glass tubes were kept for each series of specimens.After two weeks,they were broken manually and the healing agents?owed into a beaker. In the beaker,silica gel or PU foam formed with or without bacteria,urea and Ca2+ incorporated inside.The beakers were put into a tightly closed jar with a high rel-ative humidity(more than90%)inside.One week later,samples from different beakers were taken out for TGA analysis to detect the formation of CaCO3.
2.4.
3.Crack formation
Two weeks later,the prisms were taken out from the curing room and realistic cracks were created in the prisms by means of a crack width controlled three-point bending test,as shown in Fig.3a.A metal plate was glued at the bottom of the prisms(in the middle part).Crack width was measured by a linear variable differ-ential transformer(LVDT),which was also attached at the bottom of the specimens [25].The crack width was increased with a speed of0.0005mm/s until a crack width of0.5mm was obtained,followed by unloading.After unloading,the remain-ing crack width was about0.35mm.
The cylinders were also taken out of the curing room after two weeks and were subjected to a splitting test to make cracks,as shown in Fig.4.The same kind of me-tal plates and plastic blocks were glued at both sides of the cylinder.The crack width was controlled by the average value of the crack opening measured by two LVDTs attached at both sides of the cylinders.At?rst,the average crack width was also developing with a velocity of0.0005mm/s until a crack width of 0.5mm was obtained.However,it was found that some of the cylinders(with steel ?bers)were easily broken when the crack width reached0.5mm.Therefore,the load was stopped when the crack width reached0.4mm.After de-loading,the remaining crack width was about0.25mm.
2.5.Evaluation of self-healing
2.5.1.Strength regain
After performing the bending test,all prisms were placed again into the air-conditioned room.One week later,strength regain was measured by reloading the prisms.The self-healing ef?ciency was evaluated by comparing the peak load obtained during the?rst loading cycle and the reloading cycle(L2/L1,in Fig.3b).
2.5.2.Water permeability test
The healing ef?ciency was also investigated by measuring the water permeabil-ity after crack healing.The method used is modi?ed from the low pressure water permeability test used by Wang et al.[26].After the splitting test,three specimens in each series were used for the water permeability test since some specimens had broken completely during the splitting test.
During the splitting test,it was noticed that some?uid(silica sol or polyure-thane)came out of the tubes and migrated into the cracks.So the cracked cylinders were put in the curing room again to wait till the sol became gel and the polyure-thane foam formed.Since the healing agents were gradually?owing out because of the capillary force,it took more time in real specimens for the sol to become gel (about3–4h)and for polyurethane foam forming(about24h)than in beakers. Then,the cylinders were immersed into water for3days.After that,specimens were taken out from water and the surfaces were dried under room temperature. The surface dry cylinders were then mounted inside the PVC ring.Subsequently, they were vacuum saturated as described in NBN B24-213[27].The vacuum satu-ration allows to establish a steady state?ow condition in a specimen during the water permeability test.The specimens were?rst vacuumed in a vacuum chamber for2–3h and then de-mineralized water was added into the chamber while keep-ing the vacuum condition.When the cylinders were completely immersed into water,the vacuum was stopped.The cylinders were kept immersed in water for an-other24h.Then the cylinders were taken out from the chamber and put into the setup of the water permeability test.The PVC ring which was used to mount cylin-ders was accurately?t with the rubber seals of the setup for measuring the water permeability to avoid leakage(Fig.5).
The whole setup was kept watertight to make sure that the specimens were in a water saturated situation before every measurement.No water evaporation oc-curred from the specimens during the whole test period.The time for the decrease of the water level from h0till h f in the glass tube was measured at regular time intervals during30days of testing.This water?ow rate was related with the water permeability of the cracked specimens.Based on Darcy’s law,the coef?cient of water permeability of the specimen can be calculated by the following equation:
k?
aT
At
ln
h0
h f
e2T
534J.Wang et al./Construction and Building Materials26(2012)532–540
the coef?cient of water permeability(m/s);a is the cross-section (m2);A is the cross-section area of the cylinder(m2);T
(m);t is the time of water falling from h0to h f(s);h
water levels(cm).
and discussion
In the following curves and graphs,the average values are shown together with the standard deviation which is represented by means of error bars.
3.1.Survival of the free bacteria
It can be seen from Fig.6that bacterial ureolytic activity did not decrease at all after24weeks.The amount of urea decomposed by bacteria was almost the same from the beginning(Time0)till the end(24weeks).There was a slight increase in the amount of urea decomposed compared the values at the4th week and the6th week. This was due to the adjustment of the pH to7.The pH of the original media was about6.5.This indicates that a neutral pH is more pro?t-able for bacterial activity.Because of this long term viability,the bac-teria have great potential to be used in self-healing concrete.
3.2.Activity of bacteria immobilized in silica gel and polyurethane
From Fig.7a,it can be seen that the presence of dead bacteria did not result in an increase of the conductivity of the urea
(a) Silica sol as carrier(b) PU as carrier
Fig.2.Cylinders with the glass tubes which were?lled with healing agents.
(b)
Fig.3.Setup of the bending test and the obtained loading curves.
https://www.doczj.com/doc/fe15842918.html,yout of the splitting test.
Fig.5.Setup of the water permeability test.
J.Wang et al./Construction and Building Materials26(2012)532–540535
solutions.For the urea solutions to which SG or SG+BSA was
added,the increase of conductivity in the?rst24h was due to the release of ions(Na+or Clà),which were used to transform silica sol into a gel.Since the quantity of the released ions was limited, the conductivity after24h reached a stable state.The conductivity in the urea solution with the addition of free bacterial cells increased rapidly within24h and then decreased slightly until it became stable afterwards.The reason for the decrease is the volatilization of NH3produced from NHt
4
.After the equilibrium be-
tween NH3and NHt
4
was reached(after2days),the conductivity stabilized.The conductivity of the urea solution with silica gel immobilized bacteria increased at a slower rate compared with the one with free cells.Three days later,the conductivity reached a stable value.The slower decomposition rate of silica gel immobi-lized bacteria was due to the decrease of bacterial activity after being immobilized into silica gel.Therefore,it took more time to decompose the same amount of urea by immobilized bacteria than by non-immobilized bacteria.The slower increasing rate of con-ductivity of the urea solution with immobilized bacteria might also be attributed to the retarding effect of gel on the diffusion of urea. Therefore,bacterial cells inside silica gel gradually came in contact
with urea and then decomposed it.The produced NHt
4and CO2à
3
diffused through silica gel into the solution and caused the increase of the conductivity.The whole process took more time compared with when the reaction happened directly in the urea solution.It was also noticed that the?nal conductivity of the urea solution with SG+BS was even slightly higher than the one with free cells. The reason could be that some ammonia was trapped inside the gel and couldn’t escape anymore.
The situation with PU immobilized bacteria was to some extent similar,as shown in Fig.7b.The urea solutions,with only PU foam or PU foam together with dead bacteria,showed a limited increase in conductivity which indicated that no urea was decomposed.The urea solutions with PU immobilized living bacteria displayed an obvious increase of the conductivity as time went on,but at a slower speed compared with the ones with non-immobilized bacteria.This was also due to the in?uence of the carrier(polyurethane foam). The?nal value was about one-third of the peak value of the free cells. This indicated that bacteria still had activity to decompose urea after immobilization into PU foam.Yet the overall activity decreased con-siderably,which means that less CaCO3might be produced than ini-tially expected.
In Fig.7a and b,the data for free BS were the same.The amount of free BS was the same as that in SG and PU.So the activity of un-immobilized bacteria,SG immobilized bacteria and PU immobi-lized bacteria can be compared(Fig.7c).Based on the conductivity measurements,the amount of urea decomposed by bacteria(non-immobilized or immobilized)can be calculated.As shown in Fig.7c,free cells decomposed about70%of the urea and immobi-lized bacteria decomposed50%(silica gel immobilized bacteria) or30%(polyurethane immobilized bacteria).After being immobi-lized in the carriers,bacterial ureolytic activity can still be kept (from30%to70%).Bacteria immobilized into silica gel had higher ureolytic activity than those immobilized into polyurethane.
It can be seen from Fig.7d that the immobilized bacteria both in SG and PU can still decompose urea after one week.The amount of urea decomposed was almost the same as that in the?rst week which means the ureolytic activity of immobilized bacteria did not decrease.Although the bacteria did not decompose all the urea in the solution in the?rst week before the conductivity reached a stable value,they started to decompose urea again after removing the old urea solution and adding the new urea solution.That is be-cause the bio-decomposition of urea was governed by bacterial urease activity.Urea is the inducer or the substrate of this enzyme reaction.At?rst,the amount of urea was large enough to trigger the urease activity,so initially the speed of urea decomposition was fast.During the process of reaction,the amount of urea grad-ually decreased followed by a slowing of the reaction speed,and the amount of ammonium gradually increased.The ongoing reac-tion was also affected by the accumulation of ammonium and ammonia in the solution,which could inhibit bacterial activity [28].Indeed,when the quantity of urea decreased to a limited value and the ammonium and ammonia accumulated to a certain degree,the reaction was inhibited completely,resulting in some residual urea.However,when the urea solution was refreshed, the conductivity of the solution increased again.Hence,after removing the inhibitory end-products(ammonium and ammonia), and adding new urea,the bacterial urease activity can completely recover.
3.3.CaCO3precipitation in silica gel and PU foam
No urea was decomposed in the deposition medium with only silica gel,or only PU foam,or silica gel with dead bacteria or PU foam with dead bacteria.Dead bacteria did not decompose urea, which corresponded with the result stated in Section3.1.There was about14g/L(70%)and6g/L(30%)urea decomposed in the deposition medium by SG and PU immobilized bacteria,respec-tively,which indicated that about23g/L and10g/L CaCO3was formed.
CaCO3normally decomposes into CaO and CO2in the tempera-ture range of650–800°C[29].Therefore,due to the release of CO2, there should be a weight loss during that temperature range if CaCO3exists in the samples.As shown in Fig.8a and b,there was an obvious weight decrease at the temperature range from 650°C to800°C(gray lines).This decrease was due to the decom-position of CaCO3into CO2and CaO,which corroborated the exis-tence of CaCO3precipitated by SG and PU immobilized bacteria. Based on the graphs,it can be seen that CaCO3amounted to about 25%and11%(by mass)of the silica gel and polyurethane samples, respectively.There was more CaCO3precipitation in the silica gel than in the PU foam.The results correspond with the fact
that 536J.Wang et al./Construction and Building Materials26(2012)532–540
bacteria had a lower ureolytic activity after being immobilized in PU foam than in silica gel.
It can be seen from the described results that the bacteria,after being immobilized into silica gel or polyurethane,still have ureolyt-ic activity and carbonatogenesis activity,and can precipitate CaCO 3.However,for a real self-healing process,it is not practical to supply urea and Ca 2+by immersing concrete structures into the deposition medium or by spraying the deposition medium afterwards.Each necessary component should be incorporated inside concrete at one time.To mimic a real self-healing process,specimens were incorporated with healing agents ?lled in glass tubes during casting (see Section 2.4.2).During the ?rst loading cycle to make cracks,the glass tubes were broken and healing agents ?ew out into cracks and mixed together.It is assumed that bacteria could produce CaCO 3in this self-healing process.Therefore,some silica gel and polyure-thane samples were taken for TGA analysis to detect the formation of CaCO 3after breaking the glass tubes manually.The TGA results (see Fig.9)proved the existence of CaCO 3precipitation.In Fig.9,comparing (a and b)with (c),and (d and e)with (f),it can be seen that there is an obvious weight decrease in the temperature range from 650°C to 750°C,similar with Fig.8.This was due to the decomposition of CaCO 3.No DTG peak in this temperature range was observed in the series without living bacteria.The weight per-centage of CaCO 3precipitation in silica gel and polyurethane was about 12%and 10%by mass,respectively.The amount of precipita-tion decreased when the bacteria were subjected to a mimic self-healing process.This was due to the limited supply of the deposi-tion medium.Bacterial activity and the amount of deposition medium containing urea and Ca 2+are the two most important fac-tors for CaCO 3precipitation by immobilized bacteria.When more deposition medium was supplied,like in Section 2.3.2(by immers-ing into 50mL DM),more precipitation occurred.In the mimic self-healing process,the deposition medium was ?lled in glass tubes.The amount was limited by the volume and the number of the glass tubes used.The total volume was less than 50mL.Therefore,the quantity of CaCO 3precipitation in a mimic self-healing process was less than that was obtained from the immersion method.
Fig.10shows the scanning electron micrograph of CaCO 3pre-cipitation (indicated by the black arrow)in silica gel and PU foam.It can be seen that the CaCO 3particles from silica gel immobilized bacteria had a regular cubic shape,and the size was about 100l m.CaCO 3in PU foam showed an irregular block shape with a similar particle size (also about 100l m).It can be seen from Fig.10a and c that CaCO 3particles were distributed more homogenously in silica gel than in PU foam.The reason is that polyurethane pre-polymer is more viscous than silica sol (a state before gel).So it is easier for bacteria to distribute homogeneously in silica sol than in polyurethane before silica sol became gel or polyurethane foam formed.
3.4.Self-healing ef?ciency in cracked mortar specimens
3.4.1.Strength regain
The amount of strength regain of cracked specimens of different series is shown in Fig.11b.There was no strength regain in the specimens which had no healing agents incorporated (reference).One example of the loading curves of a reference specimen can be seen in Fig.11a.The strength regain in the series of SG +BSA were due to silica gel itself since dead bacteria cannot precipitate CaCO 3.Higher strength regain was obtained in the series of SG +BS because of the bacterial CaCO 3precipitation inside silica gel.Yet,the levels of strength regain of both series were quite limited,i.e.less than 5%.Specimens with PU immobilized bacteria had more strength regain,about 50%to 80%.No obvious difference of strength regain was observed in the specimens between the use of living bacteria and dead bacteria.It can be concluded that the strength regain was mainly due to polyurethane since the amount of CaCO 3precipitated inside PU foam was quite limited.Although
246810121416Free cells
SG+BS
PU+BS
u r e a s o l u t i o n (g /L )
(a)
(b)
(d)
Ureolytic activity of un-immobilized and immobilized (silica gel or polyure-bacteria,as indicated by the increase of the conductivity:(a)the conductivity urea solutions with different kinds of SG additions (added with immobilized bacteria (free cells),as a comparison with immobilized bacteria,with silica gel,added with silica gel immobilized dead bacteria,silica gel immobilized living bacteria),(b)The conductivity of the urea solutions different kinds of PU foam additions (added with un-immobilized bacteria cells),as a comparison with immobilized bacteria,same as the one in (a),with PU foam,added with PU immobilized dead bacteria,added immobilized living bacteria),(c)amount of urea decomposed (calculated from conductivity values in (a)and (b))by un-immobilized bacteria,SG immobilized bacteria and PU immobilized bacteria after three days,and (d)The conductivity urea solutions with the original SG and PU immobilized bacteria (The old solutions J.Wang et al./Construction and Building Materials 26(2012)532–540537
bacteria can precipitate more CaCO3in silica gel than in PU foam, silica gel itself has limited strength to contribute to the strength regain of the specimens.PU foam is an organic polymer.It has a higher strength and there will be a stronger bond between polymer and crack wall.Hence higher strength regain can be obtained when using PU.
3.4.2.Water permeability
During the30days of testing,the water permeability coef?cient k of the specimens gradually reached a stable value.The?nal k values of each series are shown in Fig.12.The k values of the reference spec-imens(without healing agents incorporated)ranged from4?10à6 to7?10à6m/s.The situation of the specimens with only silica gel was similar to the reference specimens and the?nal k value was about10à6m/s which indicated that silica gel in the crack had lim-ited capacity to decrease the water permeability.One specimen of this series had higher water permeability than the untreated ones. The reason was because this specimen had a larger crack width (the initial crack width was0.5mm and decreased to0.35after de-loading;the other specimens had an initial crack width of 0.4mm).This demonstrates that crack width has a profound in?u-ence on water permeability.The water permeability of the specimens with silica gel immobilized living bacteria(SG+BS)decreased about two orders of magnitude compared with the refer-ence ones.The?nal k values of this series varied from10à9to 10à7m/s.Adding living bacteria to silica gel decreased the water permeability because of the?lling effect of CaCO3produced by bac-teria.The specimens with polyurethane(with or without bacteria) showed lower water permeability compared to the ones with silica gel.For the series of PU,the?nal k value was about6?10à11to 7?10à11m/s.Due to the un-complete?lling of the crack by poly-urethane foam in one replicate,this specimen had an extremely high water permeability(with a k value about10à6m/s)compared with the other two replicates.For the series of PU+BS,the?nal k value was around3?10à11to6?10à11m/s,slightly lower than that of PU without living bacteria,because some pores of polyurethane foam were?lled by bacterial CaCO3precipitation,and hence helped to decrease the water permeability.
Bacterial CaCO3had a positive effect on decreasing the water permeability.This positive effect depended on the amount of CaCO3precipitation.When using silica gel as the carrier,the bacte-ria had a higher ureolytic activity and carbonatogenisis activity, and thus can produce more CaCO3precipitation inside silica gel. Therefore,there was an obvious difference in water permeability coef?cient of the specimens between the series of SG and SG+BS. Polyurethane is normally used as a waterproo?ng material.So the
(a) SG(b) SG+BSA(c) SG+BS
(d) PU(e) PU+BSA(f) PU+BS
9.TGA graphs(the gray and black lines were the weight(percentage)changes and the derivation of the weight(percentage)changes as a function of temperature, respectively)of the silica gel and polyurethane samples taken from the reaction products from the healing agents(?lled in the glass tubes)after breaking the glass tubes (series of(a–f)were shown in Fig.1).
538J.Wang et al./Construction and Building Materials26(2012)532–540
water permeability of the specimens can be decreased a lot when only using polyurethane.Since bacteria had a lower carbonatogen-esis activity after being immobilized in PU foam,less CaCO3precip-itation occurred inside PU foam than in silica gel.Therefore,the positive effect of the bacterial CaCO3in the polyurethane series was not as obvious as in the silica gel series.
After this proof of concept step in real mortar specimens,it
seen that the self-healing system in the study has a potential used in practical application.Self-healing has most bene?t structures where good durability and long service life are impor-tant,or for structures that are dif?cult to reach for inspection maintenance.More efforts will be done on getting more CaCO precipitation and searching for a more suitable capsule for The extra costs resulting from incorporating the self-healing healing system in concrete is dif?cult to estimate accurately for the moment since it is still in the state of‘proof of concept’. Based on the case of our current research,the cost for a concrete (80€/m3)with self-healing property would be increased by 7–28%(using PU+BS)and5–21%(using SG+BS),depending on the amount of healing agents added.However,the cost for the later maintenance and repair work would be greatly decreased.
(a) CaCO3 in silica gel (100x)(b) CaCO3 in silica gel (1000x)
(c) CaCO3 in PU foam (100x)(d)CaCO3 in PU foam (1000x)
Fig.10.Scanning electron micrographs of CaCO3precipitation in the silica gel and PU foam.
400600800
Crack width (μm)
Fig.12.Water permeability of the cracked cylinders after being repaired by
different incorporated healing agents.
J.Wang et al./Construction and Building Materials26(2012)532–540539
Therefore,applying the self-healing system in concrete structures is a potential solution for the sustainable development of con-crete structures.
4.Conclusions
Bacteria can still conserve ureolytic activity and carbonatogenesis activity after being immobilized into silica gel and polyurethane foam.TGA results proved the formation of the bacterial CaCO3 precipitation in a mimic self-healing process which indicated the great potential use of immobilized bacteria in self-healing concrete cracks.More self-healing ef?ciency(higher strength regain and more pronounced decrease of water permeability)was obtained from the specimens with incorporated polyurethane immobilized bacteria. Therefore it is promising to use polyurethane immobilized bacteria to self-heal early concrete micro cracks.Further research is needed to increase the amount of bio-CaCO3to obtain more self-healing ef?ciency.
Acknowledgements
The authors appreciate the?nancial support from the Research Foundation Flanders(FWO-Vlaanderen)for this study(Project No.
G.0157.08).The authors express their thanks to the Department of Inorganic Chemistry and the Department of Physics for providing TGA and SEM analysis.
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教育资料 《短歌行》 《短歌行》赏析(林庚) 曹操这一首《短歌行》是建安时代杰出的名作，它代表着人生的两面，一方面是人生的忧患，一方面是人生的欢乐。而所谓两面也就是人生的全面。整个的人生中自然含有一个生活的态度，这就具体地表现在成为《楚辞》与《诗经》传统的产儿。它一方面不失为《楚辞》中永恒的追求，一方面不失为一个平实的生活表现，因而也就为建安诗坛铺平了道路。 这首诗从“对酒当歌，人生几何”到“但为君故，沉吟至今”，充分表现着《楚辞》里的哀怨。一方面是人生的无常，一方面是永恒的渴望。而“呦呦鹿鸣”以下四句却是尽情的欢乐。你不晓得何以由哀怨这一端忽然会走到欢乐那一端去，转折得天衣无缝，仿佛本来就该是这么一回事似的。这才是真正的人生的感受。这一段如是，下一段也如是。“明明如月，何时可掇?忧从中来，不可断绝。越陌度阡，枉用相存。契阔谈宴，心念旧恩。月明星稀，乌鹊南飞。绕树三匝，何枝可依。”缠绵的情调，把你又带回更深的哀怨中去。但“山不厌高，海不厌深”，终于走入“周公吐哺，天下归心”的结论。上下两段是一个章法，但是你并不觉得重复，你只觉得卷在悲哀与欢乐的旋涡中，不知道什么时候悲哀没有了，变成欢乐，也不知道什么时候欢乐没有了，又变成悲哀，这岂不是一个整个的人生吗?把整个的人生表现在一个刹那的感觉上，又都归于一个最实在的生活上。“我有嘉宾，鼓瑟吹笙”，不正是当时的情景吗?“周公吐哺，天下归心”，不正是当时的信心吗? “青青子衿”到“鼓瑟吹笙”两段连贯之妙，古今无二。《诗经》中现成的句法一变而有了《楚辞》的精神，全在“沉吟至今”的点窜，那是“青青子衿”的更深的解释，《诗经》与《楚辞》因此才有了更深的默契，从《楚辞》又回到《诗经》，这样与《鹿鸣》之诗乃打成一片，这是一个完满的行程，也便是人生旅程的意义。“月明星稀”何以会变成“山不厌高，海不厌深”?几乎更不可解。莫非由于“明月出天山”，“海上生明月”吗?古辞说：“枯桑知天风，海水知天寒”，枯桑何以知天风，因为它高；海水何以知天寒，因为它深。唐人诗“一叶落知天下秋”，我们对于宇宙万有正应该有一个“知”字。然则既然是山，岂可不高?既然是海，岂可不深呢?“并刀如水，吴盐胜雪”，既是刀，就应该雪亮；既是盐，就应该雪白，那么就不必问山与海了。 山海之情，成为漫漫旅程的归宿，这不但是乌鹊南飞，且成为人生的思慕。山既尽其高，海既尽其深。人在其中乃有一颗赤子的心。孟子主尽性，因此养成他浩然之气。天下所以归心，我们乃不觉得是一个夸张。 .
The way 的用法 Ⅰ常见用法： 1)the way+ that 2)the way + in which（最为正式的用法） 3)the way + 省略（最为自然的用法） 举例：I like the way in which he talks. I like the way that he talks. I like the way he talks. Ⅱ习惯用法： 在当代美国英语中，the way用作为副词的对格，“the way+ 从句”实际上相当于一个状语从句来修饰整个句子。 1)The way =as I am talking to you just the way I’d talk to my own child. He did not do it the way his friends did. Most fruits are naturally sweet and we can eat them just the way they are—all we have to do is to clean and peel them. 2）The way= according to the way/ judging from the way The way you answer the question, you are an excellent student. The way most people look at you, you’d think trash man is a monster. 3）The way =how/ how much No one can imagine the way he missed her. 4）The way =because
孩子。 Does your throat hurt you? Added the mother to the child. 女孩的表情没有任何变化，而她的目光却一直没有从我的脸上移开。 But the little girl’s expression didn’t change nor did she move her eyes from my face. 你看过她的嗓子了吗？ Have you looked? 我想看，孩子的母亲说，但看不见。 I tried to, said the mother but II couldn’t see. 这个月碰巧她上学的那个学校已经有好几例白喉病。虽然到目前为止没有人说出这件事，但很显然，我们心里都想到了。 As it happens we had been having a number of cases of diphtheria in the school to which this child went during that month and we were all, quite apparently, thinking of that, though no one had as yet spoken of the thing. 好了，我说，我们先看看嗓子吧。 Well, I said, suppose we take a look at the throat first. 我以医生特有的职业方式微笑着，叫着孩子的名字。我说，来吧，玛蒂尔达，张开嘴，让我看一下你的嗓子。 I smiled in my best professional manner and asking for the child’s first name I said, come on, Mathilda, open your mouth and let’s take a look at your throat.没有任何反应。 Nothing doing. 哦，来吧，我劝道，张大你的嘴，让我看看。看，我说着把两只手伸开，我的手里没有东西，张大嘴，让我看看。 Aw, come on, I coaxed, just open your mouth wide and let me take a look. Look, I said opening both hands wide, I haven’t anything in my hands. Just open up and let me see.
曹操《短歌行【对酒当歌】》原文、翻译、赏析译文 原文 面对美酒应该高歌，人生短促日月如梭。对酒当歌，人生几何？ 好比晨露转瞬即逝，失去的时日实在太多！譬如朝露，去日苦多。 席上歌声激昂慷慨，忧郁长久填满心窝。慨当以慷，忧思难忘。 靠什么来排解忧闷？唯有狂饮方可解脱。何以解忧？唯有杜康。 那穿着青领（周代学士的服装）的学子哟，你们令我朝夕思慕。青青子衿，悠悠我心。 正是因为你们的缘故，我一直低唱着《子衿》歌。但为君故，沉吟至今。 阳光下鹿群呦呦欢鸣，悠然自得啃食在绿坡。呦呦鹿鸣，食野之苹。 一旦四方贤才光临舍下，我将奏瑟吹笙宴请宾客。我有嘉宾，鼓瑟吹笙。 当空悬挂的皓月哟，你运转着，永不停止；明明如月，何时可掇？ 我久蓄于怀的忧愤哟，突然喷涌而出汇成长河。忧从中来，不可断绝。 远方宾客踏着田间小路，一个个屈驾前来探望我。越陌度阡，枉用相存。 彼此久别重逢谈心宴饮，争着将往日的情谊诉说。契阔谈讌，心念旧恩。 明月升起，星星闪烁，一群寻巢乌鹊向南飞去。月明星稀，乌鹊南飞。 绕树飞了三周却没敛绕树三匝，何枝
翅，哪里才有它们栖身之 所？ 可依？ 高山不辞土石才见巍 峨，大海不弃涓流才见壮阔。（比喻用人要“唯才是举”，多多益善。）山不厌高，水不厌深。 只有像周公那样礼待贤 才（周公见到贤才，吐出口 中正在咀嚼的食物，马上接 待。《史记》载周公自谓： “一沐三握发，一饭三吐哺， 犹恐失天下之贤。”），才 能使天下人心都归向我。 周公吐哺，天 赏析 曹操是汉末杰出的政治家、军事家和文学家，他雅好诗章，好作乐府歌辞，今存诗22首，全是乐府诗。曹操的乐府诗多描写他本人的政治主张和统一天下的雄心壮志。如他的《短歌行》，充分表达了诗人求贤若渴以及统一天下的壮志。 《短歌行》是政治性很强的诗作，主要是为曹操当时所实行的政治路线和政策策略服务的，但是作者将政治内容和意义完全熔铸在浓郁的抒情意境之中，全诗充分发挥了诗歌创作的特长，准确而巧妙地运用了比兴手法，寓理于情，以情感人。诗歌无论在思想内容还是在艺术上都取得了极高的成就，语言质朴，立意深远，气势充沛。这首带有建安时代"志深比长""梗概多气"的时代特色的《短歌行》，读后不觉思接千载，荡气回肠，受到强烈的感染。 对酒当歌，人生几何？ 譬如朝露，去日苦多。 慨当以慷，幽思难忘。 何以解忧，唯有杜康。 青青子衿，悠悠我心。 但为君故，沈吟至今。 呦呦鹿鸣，食野之苹。 我有嘉宾，鼓瑟吹笙。 明明如月，何时可掇？ 忧从中来，不可断绝。 越陌度阡，枉用相存。 契阔谈，心念旧恩。 月明星稀，乌鹊南飞， 绕树三匝，何枝可依？ 山不厌高，海不厌深， 周公吐哺，天下归心。 《短歌行》是汉乐府的旧题，属于《相和歌?平调曲》。这就是说它本来是一个乐曲的名称，这种乐曲怎么唱法，现在当然是不知道了。但乐府《相和歌?平调曲》中除了《短歌行》还有《长歌行》，唐代吴兢《乐府古题要解》引证古诗“长歌正激烈”，魏文帝曹丕《燕歌行》“短歌微吟不能长”和晋代傅玄《艳歌行》“咄来长歌续短歌”等句，认为“长歌”、“短
外国文学名著鉴赏期末论文院—系：数学学院 科目：外国文学名著鉴赏（期末论文）班级： 08级数学与应用数学A班 姓名：沈铁 学号： 200805050149 上课时段：周五晚十、十一节课
奋斗了，才有出路 ——读《鲁宾逊漂游记》有感小说《鲁宾逊漂游记》一直深受人们的喜爱。读完这篇小说，使我对人生应该有自己的一个奋斗历程而受益匪浅。当一个人已经处于绝境的时候，还能够满怀信心的去面对和挑战生活，实在是一种可贵的精神。他使我认识到，人无论何时何地，不管遇到多大的困难，都不能被困难所吓倒，我们要勇敢的面对困难，克服困难，始终保持一种积极向上、乐观的心态去面对。在当今社会只有努力去奋斗，才会有自己的出路！ 其实现在的很多人都是那些遇到困难就退缩，不敢勇敢的去面对它。不仅如此，现在很多人都是独生子女，很多家长视子女为掌上明珠，不要说是冒险了，就连小小的家务活也不让孩子做，天天总是说：“我的小宝贝啊，你读好书就行了，其它的爸爸妈妈做就可以了。”读书固然重要，但生活中的小事也不能忽略。想一想，在荒无人烟的孤岛上，如果你连家务活都不会做，你能在那里生存吗？读完这部著作后，我不禁反问自己：“如果我像书中的鲁宾逊那样在大海遭到风暴，我能向他那样与风暴搏斗，最后逃离荒岛得救吗？恐怕我早已经被大海所淹没；如果我漂流到孤岛，能活几天？我又能干些什么？我会劈柴吗？会打猎做饭吗？我连洗洗自己的衣服还笨手笨脚的。”我们应该学习鲁宾逊这种不怕困难的精神，无论何时何地都有坚持地活下去，哪怕只有一线希望也要坚持到底，决不能放弃！我们要像鲁宾
逊那样有志气、有毅力、爱劳动，凭自己的双手创造财富，创造奇迹，取得最后的胜利。这样的例子在我们的生活中屡见不鲜。 《史记》的作者司马迁含冤入狱，可它依然在狱中完成《史记》一书，他之所以能完成此书，靠的也是他心中那顽强的毅力，永不放弃的不断努力的精神。著名作家爱迪生从小就生活在一个贫困的家庭中，可是他从小就表现出了科学方面的天赋。长大后爱迪生着力于电灯的发明与研究，他经过了九百多次的失败，可它依然没有放弃，不断努力，最后终于在第一千次实验中取得了成功。 鲁宾逊在岛上生活了二十八年，他面对了各种各样的困难和挫折，克服了许多常人无法想象的困难，自己动手，丰衣足食，以惊人的毅力，顽强的活了下来。他自从大船失事后，找了一些木材，在岛上盖了一间房屋，为防止野兽，还在房子周围打了木桩，来到荒岛，面对着的首要的就是吃的问题，船上的东西吃完以后，鲁宾逊开始打猎，有时可能会饿肚子，一是他决定播种，几年后他终于可以吃到自己的劳动成果，其实学习也是这样，也有这样一个循序渐进的过程，现在的社会，竞争无处不在，我们要懂得只有付出才会有收获，要勇于付出，在战胜困难的同时不断取得好成绩。要知道只有付出，才会有收获。鲁宾逊在失败后总结教训，终于成果；磨粮食没有石磨，他就用木头代替；没有筛子，就用围巾。鲁宾逊在荒岛上解决了自己的生存难题，面对人生挫折，鲁宾逊的所作所为充分显示了他坚毅的性格和顽强的精神。同样我们在学习上也可以做一些创新，养成一种创新精神，把鲁宾逊在荒岛，不畏艰险，不怕失败挫折，艰苦奋斗的精
The way的用法及其含义（二） 二、the way在句中的语法作用 the way在句中可以作主语、宾语或表语： 1.作主语 The way you are doing it is completely crazy.你这个干法简直发疯。 The way she puts on that accent really irritates me. 她故意操那种口音的样子实在令我恼火。The way she behaved towards him was utterly ruthless. 她对待他真是无情至极。 Words are important, but the way a person stands, folds his or her arms or moves his or her hands can also give us information about his or her feelings. 言语固然重要,但人的站姿,抱臂的方式和手势也回告诉我们他(她)的情感。 2.作宾语 I hate the way she stared at me.我讨厌她盯我看的样子。 We like the way that her hair hangs down.我们喜欢她的头发笔直地垂下来。 You could tell she was foreign by the way she was dressed. 从她的穿著就可以看出她是外国人。 She could not hide her amusement at the way he was dancing. 她见他跳舞的姿势，忍俊不禁。 3.作表语 This is the way the accident happened.这就是事故如何发生的。 Believe it or not, that's the way it is. 信不信由你, 反正事情就是这样。 That's the way I look at it, too. 我也是这么想。 That was the way minority nationalities were treated in old China. 那就是少数民族在旧中
曹操《短歌行》其二翻译及赏析 引导语：曹操(155—220)，字孟德，小名阿瞒，《短歌行 二首》 是曹操以乐府古题创作的两首诗， 第一首诗表达了作者求贤若渴的心 态，第二首诗主要是曹操向内外臣僚及天下表明心迹。 短歌行 其二 曹操 周西伯昌，怀此圣德。 三分天下，而有其二。 修奉贡献，臣节不隆。 崇侯谗之，是以拘系。 后见赦原，赐之斧钺，得使征伐。 为仲尼所称，达及德行， 犹奉事殷，论叙其美。 齐桓之功，为霸之首。 九合诸侯，一匡天下。 一匡天下，不以兵车。 正而不谲，其德传称。 孔子所叹，并称夷吾，民受其恩。 赐与庙胙，命无下拜。 小白不敢尔，天威在颜咫尺。 晋文亦霸，躬奉天王。 受赐圭瓒，钜鬯彤弓， 卢弓矢千，虎贲三百人。 威服诸侯，师之所尊。 八方闻之，名亚齐桓。 翻译 姬昌受封为西伯，具有神智和美德。殷朝土地为三份，他有其中两分。 整治贡品来进奉，不失臣子的职责。只因为崇侯进谗言，而受冤拘禁。 后因为送礼而赦免， 受赐斧钺征伐的权利。 他被孔丘称赞， 品德高尚地位显。 始终臣服殷朝帝王，美名后世流传遍。齐桓公拥周建立功业，存亡继绝为霸 首。
聚合诸侯捍卫中原，匡正天下功业千秋。号令诸侯以匡周室，主要靠的不是 武力。 行为磊落不欺诈，美德流传于身后。孔子赞美齐桓公，也称赞管仲。 百姓深受恩惠，天子赐肉与桓公，命其无拜来接受。桓公称小白不敢，天子 威严就在咫尺前。 晋文公继承来称霸，亲身尊奉周天王。周天子赏赐丰厚，仪式隆重。 接受玉器和美酒，弓矢武士三百名。晋文公声望镇诸侯，从其风者受尊重。 威名八方全传遍，名声仅次于齐桓公。佯称周王巡狩，招其天子到河阳，因 此大众议论纷纷。 赏析 《短歌行》 (“周西伯昌”)主要是曹操向内外臣僚及天下表明心 迹，当他翦灭群凶之际，功高震主之时，正所谓“君子终日乾乾，夕惕若 厉”者，但东吴孙权却瞅准时机竟上表大说天命而称臣，意在促曹操代汉 而使其失去“挟天子以令诸侯”之号召， 故曹操机敏地认识到“ 是儿欲据吾著炉上郁!”故曹操运筹谋略而赋此《短歌行 ·周西伯 昌》。 西伯姬昌在纣朝三分天下有其二的大好形势下， 犹能奉事殷纣， 故孔子盛称 “周之德， 其可谓至德也已矣。 ”但纣王亲信崇侯虎仍不免在纣王前 还要谗毁文王，并拘系于羑里。曹操举此史实，意在表明自己正在克心效法先圣 西伯姬昌，并肯定他的所作所为，谨慎惕惧，向来无愧于献帝之所赏。 并大谈西伯姬昌、齐桓公、晋文公皆曾受命“专使征伐”。而当 今天下时势与当年的西伯、齐桓、晋文之际颇相类似，天子如命他“专使 征伐”以讨不臣，乃英明之举。但他亦效西伯之德，重齐桓之功，戒晋文 之诈。然故作谦恭之辞耳，又谁知岂无更讨封赏之意乎 ?不然建安十八年(公元 213 年)五月献帝下诏曰《册魏公九锡文》，其文曰“朕闻先王并建明德， 胙之以土，分之以民，崇其宠章，备其礼物，所以藩卫王室、左右厥世也。其在 周成，管、蔡不静，惩难念功，乃使邵康公赐齐太公履，东至于海，西至于河， 南至于穆陵，北至于无棣，五侯九伯，实得征之。 世祚太师，以表东海。爰及襄王，亦有楚人不供王职，又命晋文登为侯伯， 锡以二辂、虎贲、斧钺、禾巨 鬯、弓矢，大启南阳，世作盟主。故周室之不坏， 系二国是赖。”又“今以冀州之河东、河内、魏郡、赵国、中山、常 山，巨鹿、安平、甘陵、平原凡十郡，封君为魏公。锡君玄土，苴以白茅，爰契 尔龟。”又“加君九锡，其敬听朕命。” 观汉献帝下诏《册魏公九锡文》全篇，尽叙其功，以为其功高于伊、周，而 其奖却低于齐、晋，故赐爵赐土，又加九锡，奖励空前。但曹操被奖愈高，心内 愈忧。故曹操在曾早在五十六岁写的《让县自明本志令》中谓“或者人见 孤强盛， 又性不信天命之事， 恐私心相评， 言有不逊之志， 妄相忖度， 每用耿耿。
（一）文学常识 一、古希腊罗马 1．（1）宙斯(罗马神话称为朱庇特)，希腊神话中最高的天神，掌管雷电云雨，是人和神的主宰。 （2）阿波罗，希腊神话中宙斯的儿子，主管光明、青春、音乐、诗歌等，常以手持弓箭的少年形象出现。 （3）雅典那，希腊神话中的智慧女神，雅典城邦的保护神。 （4）潘多拉，希腊神话中的第一个女人，貌美性诈。私自打开了宙斯送她的一只盒子，里面装的疾病、疯狂、罪恶、嫉妒等祸患，一齐飞出，只有希望留在盒底，人间因此充满灾难。“潘多拉的盒子”成为“祸灾的来源”的同义语。 （5）普罗米修斯，希腊神话中造福人间的神。盗取天火带到人间，并传授给人类多种手艺，触怒宙斯，被锁在高加索山崖，受神鹰啄食，是一个反抗强暴、不惜为人类牺牲一切的英雄。 （6）斯芬克司，希腊神话中的狮身女怪。常叫过路行人猜谜，猜不出即将行人杀害；后因谜底被俄底浦斯道破，即自杀。后常喻“谜”一样的人物。与埃及狮身人面像同名。 2．荷马，古希腊盲诗人。主要作品有《伊利亚特》和《奥德赛》，被称为荷马史诗。《伊利亚特》叙述十年特洛伊战争。《奥德赛》写特洛伊战争结束后，希腊英雄奥德赛历险回乡的故事。马克思称赞它“显示出永久的魅力”。 3．埃斯库罗斯，古希腊悲剧之父，代表作《被缚的普罗米修斯》。6．阿里斯托芬，古希腊“喜剧之父”代表作《阿卡奈人》。 4．索福克勒斯，古希腊重要悲剧作家，代表作《俄狄浦斯王》。5．欧里庇得斯，古希腊重要悲剧作家，代表作《美狄亚》。 二、中世纪文学 但丁，意大利人，伟大诗人，文艺复兴的先驱。恩格斯称他是“中世纪的最后一位诗人，同时又是新时代的最初一位诗人”。主要作品有叙事长诗《神曲》，由地狱、炼狱、天堂三部分组成。《神曲》以幻想形式，写但丁迷路，被人导引神游三界。在地狱中见到贪官污吏等受着惩罚，在净界中见到贪色贪财等较轻罪人，在天堂里见到殉道者等高贵的灵魂。 三、文艺复兴时期 1．薄迦丘意大利人短篇小说家，著有《十日谈》拉伯雷，法国人，著《巨人传》塞万提斯，西班牙人,著《堂?吉诃德》。 2．莎士比亚，16-17世纪文艺复兴时期英国伟大的剧作家和诗人，主要作品有四大悲剧——《哈姆雷特》、《奥赛罗》《麦克白》、《李尔王》，另有悲剧《罗密欧与朱丽叶》等，喜剧有《威尼斯商人》《第十二夜》《皆大欢喜》等，历史剧有《理查二世》、《亨利四世》等。马克思称之为“人类最伟大的戏剧天才”。 四、17世纪古典主义 9．笛福，17-18世纪英国著名小说家，被誉为“英国和欧洲小说之父”，主要作品《鲁滨逊漂流记》，是英国第一部现实主义长篇小说。10．弥尔顿，17世纪英国诗人，代表作：长诗《失乐园》，《失乐园》，表现了资产阶级清教徒的革命理想和英雄气概。 25．拉伯雷，16世纪法国作家，代表作：长篇小说《巨人传》。 26．莫里哀，法国17世纪古典主义文学最重要的作家，法国古典主义喜剧的创建者，主要作品为《伪君子》《悭吝人》（主人公叫阿巴公）等喜剧。 五、18世纪启蒙运动 1）歌德，德国文学最高成就的代表者。主要作品有书信体小说《少年维特之烦恼》，诗剧《浮士德》。 11．斯威夫特，18世纪英国作家，代表作：《格列佛游记》，以荒诞的情节讽刺了英国现实。 12．亨利·菲尔丁，18世纪英国作家，代表作：《汤姆·琼斯》。 六、19世纪浪漫主义 （1拜伦， 19世纪初期英国伟大的浪漫主义诗人，代表作为诗体小说《唐璜》通过青年贵族唐璜的种种经历，抨击欧洲反动的封建势力。《恰尔德。哈洛尔游记》 （2雨果，伟大作家，欧洲19世纪浪漫主义文学最卓越的代表。主要作品有长篇小说《巴黎圣母院》、《悲惨世界》、《笑面人》、《九三年》等。《悲惨世界》写的是失业短工冉阿让因偷吃一片面包被抓进监狱，后改名换姓，当上企业主和市长，但终不能摆脱迫害的故事。《巴黎圣母院》 弃儿伽西莫多，在一个偶然的场合被副主教克洛德.孚罗洛收养为义子，长大后有让他当上了巴黎圣母院的敲钟人。他虽然十分丑陋而且有多种残疾，心灵却异常高尚纯洁。 长年流浪街头的波希米亚姑娘拉.爱斯梅拉达，能歌善舞，天真貌美而心地淳厚。青年贫诗人尔比埃尔.甘果瓦偶然同她相遇，并在一个更偶然的场合成了她名义上的丈夫。很有名望的副教主本来一向专心于"圣职"，忽然有一天欣赏到波希米亚姑娘的歌舞，忧千方百计要把她据为己有，对她进行了种种威胁甚至陷害，同时还为此不惜玩弄卑鄙手段，去欺骗利用他的义子伽西莫多和学生甘果瓦。眼看无论如何也实现不了占有爱斯梅拉达的罪恶企图，最后竟亲手把那可爱的少女送上了绞刑架。 另一方面，伽西莫多私下也爱慕着波希米亚姑娘。她遭到陷害，被伽西莫多巧计救出，在圣母院一间密室里避难，敲钟人用十分纯朴和真诚的感情去安慰她，保护她。当她再次处于危急中时，敲钟人为了援助她，表现出非凡的英勇和机智。而当他无意中发现自己的"义父"和"恩人"远望着高挂在绞刑架上的波希米亚姑娘而发出恶魔般的狞笑时，伽西莫多立即对那个伪善者下了最后的判决，亲手把克洛德.孚罗洛从高耸入云的钟塔上推下，使他摔的粉身碎骨。 （3司汤达，批判现实主义作家。代表作《红与黑》，写的是不满封建制度的平民青年于连，千方百计向上爬，最终被送上断头台的故事。“红”是将军服色，指“入军界”的道路；“黑”是主教服色，指当神父、主教的道路。 14．雪莱，19世纪积极浪漫主义诗人，欧洲文学史上最早歌颂空想社会主义的诗人之一，主要作品为诗剧《解放了的普罗米修斯》，抒情诗《西风颂》等。 15．托马斯·哈代，19世纪英国作家，代表作：长篇小说《德伯家的苔丝》。 16．萨克雷，19世纪英国作家，代表作：《名利场》 17．盖斯凯尔夫人，19世纪英国作家，代表作：《玛丽·巴顿》。 18．夏洛蒂?勃朗特，19世纪英国女作家，代表作：长篇小说《简?爱》19艾米丽?勃朗特，19世纪英国女作家，夏洛蒂?勃朗特之妹，代表作：长篇小说《呼啸山庄》。 20．狄更斯，19世纪英国批判现实主义文学的重要代表，主要作品为长篇小说《大卫?科波菲尔》、《艰难时世》《双城记》《雾都孤儿》。21．柯南道尔，19世纪英国著名侦探小说家，代表作品侦探小说集《福尔摩斯探案》是世界上最著名的侦探小说。 七、19世纪现实主义 1、巴尔扎克，19世纪上半叶法国和欧洲批判现实主义文学的杰出代表。主要作品有《人间喜剧》，包括《高老头》、《欧也妮·葛朗台》、《贝姨》、《邦斯舅舅》等。《人间喜剧》是世界文学中规模最宏伟的创作之一，也是人类思维劳动最辉煌的成果之一。马克思称其“提供了一部法国社会特别是巴黎上流社会的卓越的现实主义历史”。
定冠词the的用法： 定冠词the与指示代词this ,that同源,有“那(这)个”的意思,但较弱,可以和一个名词连用,来表示某个或某些特定的人或东西. (1)特指双方都明白的人或物 Take the medicine.把药吃了. (2)上文提到过的人或事 He bought a house.他买了幢房子. I've been to the house.我去过那幢房子. (3)指世界上独一无二的事物 the sun ,the sky ,the moon, the earth (4)单数名词连用表示一类事物 the dollar 美元 the fox 狐狸 或与形容词或分词连用,表示一类人 the rich 富人 the living 生者 (5)用在序数词和形容词最高级,及形容词等前面 Where do you live?你住在哪? I live on the second floor.我住在二楼. That's the very thing I've been looking for.那正是我要找的东西. (6)与复数名词连用,指整个群体 They are the teachers of this school.(指全体教师) They are teachers of this school.(指部分教师) (7)表示所有,相当于物主代词,用在表示身体部位的名词前 She caught me by the arm.她抓住了我的手臂. (8)用在某些有普通名词构成的国家名称,机关团体,阶级等专有名词前 the People's Republic of China 中华人民共和国 the United States 美国 (9)用在表示乐器的名词前 She plays the piano.她会弹钢琴. (10)用在姓氏的复数名词之前,表示一家人 the Greens 格林一家人(或格林夫妇) (11)用在惯用语中 in the day, in the morning... the day before yesterday, the next morning... in the sky... in the dark... in the end... on the whole, by the way...
The use of force 大意: Mathilda had been ill for three days. Her mother had given her some medicine, but it didn’t do any good. So they had to ask the doctor to come. There had been a number of cases of diphtheria in Mathilda School and two of them had been dead. When the doctor arrived at Olson’s home, he wanted to examine Mathilda throat first. But no matter how he coaxed, She wouldn’t open her mouth. So the doctor had to get the tongue depressor into her mouth. But Mathilda reduced it to splinters. In orde r to protect Mathilda herself and other children, the doctor had to make sure whether she had diphtheria or not, so that he could treat her in time. Letting Mathilda‘s father hold her wrists he tried his best to open her mouth and found she really had diphtheria. This story made us can think such a question that something in life can’t only depend on self-willingness. Under some circumstances, certain force seems necessary. 对医生的评价:After the doctor arrived at the girl’s home, he wanted to see her throat. As there had been a number of cases of diphtheria in the school to which the girl went during that month, the doctor also thought that of the girl. So he smiled to the girl and asked her to open her mouth and let him have a look at her throat. No matter how the doctor coaxed, the girl shut her mouth firmly. Thinking that the girl might have diphtheria and possibly die of it, the doctor decided to use force to open her mouth. He had seen at least two children lying dead in bed of neglect in such cases. He felt that he must get a diagnosis now. So he grasped the girl’s head with his left hand and tried to get the wooden tongue depressor between her teeth. But when the doctor got the wooden spatula behind her last teeth. She gripped the blade between her molars and reduced it to splinters. In the final unreasoning assault the doctor outer powered the girl. He forced the heavy silver spoon back of her teeth and down her throat till she gagged. Her both tonsils were covered with membrane. From that the doctor had done, I thought he was a responsible person. In order to save the lives of the patients, especially those children who did not know how to co-operate with the doctor, he had to take some measure. Otherwise a good or suitable time of treatment would be missed. The doctor appears to be compassionate and keen to human behavior, characteristic of a good doctor, though he is also undeniably blunt and slightly prejudiced. 思想: Though there are reasons often justifiable, what compels the use of force against others isn't simply altruism alone. The overall theme of the story revolves around power and submission and the doctor's unnerved feeling following the forceful encounter. 作者如何写的: The story is narrated in first person by a doctor, who is answering a house visit to see a sick girl. Williams uses interior monologue as a "stream-of-consciousness" tool reflects the narrator's experience of dialogue and gives insight into the character and his appraisal of the situations he encounters. The story is written without the use of quotation marks, and the dialogue is not distinguished from the narrator's comments. The story is rendered from the subjective point of view of the doctor, and explores his subdued enjoyment of forcefully subduing the stubborn child in an attempt to acquire the throat sample.
题目：浅析从简爱到女性的尊严和爱 学院工商学院 专业新闻学3 学号 姓名闫万里 学科外国文学名着赏析 [摘要] 十九世纪中期，英国伟大的女性存在主义先驱，着名作家夏洛蒂勃朗特创作出了她的代表作--《简爱》，当时轰动了整个文坛,它是一部具有浓厚浪漫主义色彩的现实主义小说，被认为是作者"诗意的生平"的写照。它在问世后的一百多年里，它始终保持着历史不败的艺术感染力。直到现在它的影响还继续存在。在作品的序幕、发展、高潮和结尾中，女主人公的叛逆、自由、平等、自尊、纯洁的个性都是各个重点章节的主旨，而这些主旨则在女主人公的爱情观中被展露的淋漓尽致，它们如同乌云上方的星汉，灼灼闪耀着光芒，照亮着后来的女性者们追求爱情的道路。? [关键词] 自尊个性独特新女性主义自由独立平等 《简爱》是一部带有自转色彩的长篇小说，它阐释了这样一个主题：人的价值=尊严+爱。从小就成长在一个充满暴力的环境中的简爱，经历了同龄人没有的遭遇。她要面对的是舅妈的毫无人性的虐待，表兄的凶暴专横和表姐的傲慢冷漠，尽管她尽力想“竭力赢得别人的好感”，但是事实告诉她这都是白费力气的，因此她发出了“不公平啊！--不公平！”的近乎绝望的呼喊。不公平的生长环境，使得简爱从小就向往平等、自由和爱，这些愿望在她后来的成长过程中表现无疑，
譬如在她的爱情观中的种种体现。? 1.桑菲尔德府? 谭波儿小姐因为出嫁，离开了洛伍德学校，同时也离开了简爱，这使简爱感觉到了“一种稳定的感觉，一切使我觉得洛伍德学校有点像我家的联想，全都随着她消失了”，她意识到：真正的世界是广阔的，一个充满希望和忧虑、激动和兴奋的变化纷呈的天地，正等待着敢于闯入、甘冒风险寻求人生真谛的人们。意识形态的转变促使着简爱走向更广阔的社会，接受社会的挑战，尽管她才只有十八岁。于是，简爱来到了桑菲尔德府，当了一名在当时地位不高的家庭教师。?桑菲尔德府使简爱感受到“这儿有想象中的完美无缺的家庭安乐气氛”，事实证明了她的预感的正确性，。从和简爱相见、相识到相爱的过程当中，简爱的那种叛逆精神、自强自尊的品质深深地征服了罗切斯特，而罗切斯特的优雅风度和渊博知识同样也征服了简爱。最初开始，简爱一直以为罗切斯特会娶高贵漂亮的英格拉姆为妻，她在和罗切斯特谈到婚姻时，曾经义正言辞的对罗切斯特说：“你以为因为我穷，低微，不美，矮小，就没有灵魂了吗？你想错了！我跟你一样有灵魂—也同样有一颗心！我现在不是凭着肉体凡胎跟你说话，而是我的心灵在和你的心灵说话，就好像我们都已经离开人世，两人平等地站在上帝面前—因为我们本来就是平等的。”这充分表现出简爱的叛逆，她这种维护妇女独立人格、主张婚姻独立自主以及男女平等的主张可以看成是他对整个人类社会自由平等的向往追求，罗切斯特正是爱上了她这样的独特个性，同时他也同样重复道：我们本来就是平等的。罗切斯特自始自终爱的是简爱的心灵—有着意志的力量，美德和纯洁的心灵，正是基于如此，简爱才真正的爱着罗切斯特。因为爱情是来不得半点虚假的，一方为另一方付出了真情的爱，假如得到对方的是虚情假意，那么这份爱
“tｈｅwａｙ+从句”结构的意义及用法 首先让我们来看下面这个句子: Ｒead the foｌloｗｉnｇpassagｅａnd talkａbout ｉt wi ｔh your classmaｔes．Try tｏｔeｌl whaｔyｏu thiｎk ｏf Tom aｎd ｏｆｔhe ｗay the chiｌｄrenｔrｅated ｈim. 在这个句子中，ｔhe waｙ是先行词,后面是省略了关系副词that或in whｉch的定语从句。 下面我们将叙述“the ｗaｙ+从句”结构的用法。 1.tｈe wａy之后，引导定语从句的关系词是tｈat而不是hoｗ,因此，<<现代英语惯用法词典＞＞中所给出的下面两个句子是错误的：Ｔhｉs is ｔｈeｗayｈowｉtｈａppened. This is the way how he ａlwａｙs treats me. 2．在正式语体中,thaｔ可被in which所代替;在非正式语体中，ｔhat则往往省略。由此我们得到theｗay后接定语从句时的三种模式：1) tｈe ｗaｙ＋ｔhａt-从句２）the way +ｉn whiｃh－从句3) the ｗay +从句 例如：Ｔｈe way(in whiｃh ，thａt) ｔhｅｓｅｃomｒade ｓloｏｋａｔｐrobｌems is wrong．这些同志看问题的方法
不对。 Ｔｈｅｗａy(that ,ｉn ｗhiｃh)yoｕ’ｒe doinｇit is comple ｔeｌy crａzy.你这么个干法,简直发疯。 Wｅａdmiｒｅd him for thｅｗay ｉｎｗhｉch he fａｃeｓdiｆficultieｓ． Waｌlａｃe ａｎd Ｄarwiｎｇreed ｏn the way ｉｎwhi ｃh ｄｉfｆｅrｅnt forms ｏf life had ｂegｕn.华莱士和达尔文对不同类型的生物是如何起源的持相同的观点。 Thｉs is ｔｈe ｗaｙ（tｈａｔ) hｅdｉd it. I lｉkeｄｔhe waｙ(ｔhat) ｓｈeｏｒganized ｔhe ｍeetｉng． 3.theｗay(tｈat)有时可以与hｏw(作“如何”解）通用。例如： That’s tｈe ｗaｙ(tｈaｔ) shｅspoke. = Tｈat’s how shｅspoke.
短歌行赏析介绍 说道曹操， 大家一定就联想到三国那些烽火狼烟岁月吧。 但是曹操其实也是 一位文学 大家，今天就来分享《短歌行 》赏析。 《短歌行》短歌行》是汉乐府旧题，属于《相和歌辞·平调曲》。这就是说 它本来是一个乐曲名称。最初古辞已经失传。乐府里收集同名诗有 24 首，最早 是曹操这首。 这种乐曲怎么唱法， 现在当然是不知道。 但乐府 《相和歌·平调曲》 中除《短歌行》还有《长歌行》，唐代吴兢《乐府古题要解》引证古诗 “长歌正激烈”， 魏文帝曹丕 《燕歌行》 “短歌微吟不能长”和晋代傅玄 《艳 歌行》 “咄来长歌续短歌”等句， 认为“长歌”、 “短歌”是指“歌声有长短”。 我们现在也就只能根据这一点点材料来理解《短歌行》音乐特点。《短歌行》这 个乐曲，原来当然也有相应歌辞，就是“乐府古辞”，但这古辞已经失传。现在 所能见到最早《短歌行》就是曹操所作拟乐府《短歌行》。所谓“拟乐府”就是 运用乐府旧曲来补作新词，曹操传世《短歌行》共有两首，这里要介绍是其中第 一首。 这首《短歌行》主题非常明确，就是作者希望有大量人才来为自己所用。曹 操在其政治活动中，为扩大他在庶族地主中统治基础，打击反动世袭豪强势力， 曾大力强调“唯才是举”，为此而先后发布“求贤令”、“举士令”、“求逸才 令”等;而《短歌行》实际上就是一曲“求贤歌”、又正因为运用诗歌 形式，含有丰富抒情成分，所以就能起到独特感染作用，有力地宣传他所坚 持主张，配合他所颁发政令。 《短歌行》原来有“六解”(即六个乐段)，按照诗意分为四节来读。 “对酒当歌，人生几何?譬如朝露，去日苦多。慨当以慷，忧思难忘。何以 解忧，唯有杜康。” 在这八句中，作者强调他非常发愁，愁得不得。那么愁是什么呢?原来他是 苦于得不到众多“贤才”来同他合作， 一道抓紧时间建功立业。 试想连曹操这样 位高权重人居然在那里为“求贤”而发愁， 那该有多大宣传作用。 假如庶族地主 中真有“贤才”话， 看这些话就不能不大受感动和鼓舞。 他们正苦于找不到出路