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Establishment of correlated states in a quantum dot interacting with an acoustic-phonon reservoir

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PHYSICAL REVIEW A90,023815(2014)Establishment of correlated states in a quantum dot interacting with an acoustic-phonon reservoir Hui Huang,1Gao-xiang Li,1,*Wen-ju Gu,1and Zbigniew Ficek21Department of Physics,Huazhong Normal University,Wuhan430079,People’s Republic of China2The National Center for Mathematics and Physics,KACST,P.O.Box6086,Riyadh11442,Saudi Arabia(Received29March2014;published11August2014)We investigate the effects of a low-frequency(acoustic)phonon bath on the dynamics of a quantum dotmodeled as a cascade three-level system.We show that the phonon bath appears to the upper transition of thecascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators.The action ofthe annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usualharmonic oscillator that it serves as a linear amplifier to the system,and thereby gives rise to unusual featuresin the dynamics of the quantum dot.Wefind that the phonon bath,although being in a thermal state,affects thequantum dot as a correlated-type reservoir which results in the decay of the system to a correlated two-photonstate with the population distribution no longer obeying a Boltzmann distribution.It is particularly interestingthat even for a zero-temperature phonon reservoir,the steady state is a correlated state which,under appropriateconditions on the Rabi frequencies and the damping rates,can reduce to a strongly correlated pure state.It isshown that the two-photon correlations result in a significant squeezing and strong two-photon correlations inthe radiationfield emitted by the quantum dot.The presence of the correlations in the system is manifest in thepresence of quantum beats in the time evolution of the populations and the radiation intensity.The effect of theordinary spontaneous emission on the features induced by the phonon bath is also discussed.DOI:10.1103/PhysRevA.90.023815PACS number(s):42.50.Ct,42.50.Lc,78.67.HcI.INTRODUCTIONThe interaction of a quantum dot(QD)with a phonon reservoir has been studied extensively and a number of interesting effects has been predicted.Most of these studies have considered the QD consisting of a single electron-hole pair,a two-state system,and many features characteristic of a two-state system,such as the Mollow triplet,the Autler-Townes doublet,and vacuum Rabi splitting,have been predicted and experimentally observed[1–6].Recently,interest has arisen in the problem of sensitivity of a QD to the nature of a phonon bath to which it is coupled. The phonon bath serves as a low-frequency reservoir and,as a result,the radiative properties of the QD change.Various problems related to the temperature of the phonon bath have been studied,including phonon-mediated excitation transfer [7,8],damping of Rabi oscillations[9–14],modifications of thefluorescence spectrum[15–17],and the creation of a steady-state population inversion between the bare states of a two-level QD system[18–20].The population inversion gives the possibility to achieve lasing in the two-level system [21,22].In the case of a QD,the most important damping mechanism is a decay associated with the coupling of the QD to afinite-temperature phonon bath.In general,an excited QD is expected to decay to a mixed state characteristic of conventional thermodynamic equilibrium with the population distribution that obeys a Boltzmann distribution.The decay process can be modified and the nature of the equilibrium state could be different if the QD decays in a correlated reservoir, such as a squeezed vacuum[23–30].The energy structure of a QD does not have to be confined to two levels only,that is,to a single exciton state.It can be *gaox@ extended to include a biexciton state,which could be realized in a semiconductor QD consisting of two electron-hole pairs driven by appropriate laser pulses with the help of phonons [31–33].In this paper,we examine the effect of a phonon thermal bath on the dynamics of a single QD modeled as a three-level system of the cascade configuration.In addition to the phonon bath,the QD is driven by a single laserfield which couples to both transitions of the cascade system. Using the master-equation approach,we calculate the steady-state populations of the energy levels,transient behaviors of the populations,and the radiation intensity,including nonclassical features such as squeezing and antibunching.We show that the phonon bath couples to the upper transition of the cascade system as a broadband reservoir of inverted harmonic oscillators,which serves as a linear amplifier to the system[34].This causes the phonon bath to behave as a correlated rather than conventional thermal reservoir, which may lead to many interesting features such as one-and two-photon population inversions,squeezing,super-bunching, and antibunching.Even though the interaction of the QD with the phonon reservoir is a dissipative process,we demonstrate that the reservoir can turn the system to decay to a strongly correlated state.Depending on the temperature of the reservoir, the correlated steady state of the QD can be a pure state which reflects these correlations.The paper is organized as follows.In Sec.II,the effective Hamiltonian of the quantum dot interacting with a phonon bath is derived.We then apply the Hamiltonian to derive the master equation for the reduced density operator describing the properties of the quantum dot interacting with the phonon bath.We also include a possible coupling of the quantum dot to the ordinary vacuum modes that leads to the radiative sponta-neous emission.The steady-state population distributions are presented in Sec.IV,along with a discussion of one-and two-photon inversions.Squeezing and the second-order coherenceHUI HUANG,GAO-XIANG LI,WEN-JU GU,AND ZBIGNIEW FICEK PHYSICAL REVIEW A90,023815(2014)function are calculated in Sec.V.A detailed discussion of the transient behavior of the system is presented in Sec.VI.We find that the temporal behavior of the population distribution and the radiation intensity may differ dramatically for different initial conditions.The effect of the ordinary spontaneous emission on the features induced by the phonon bath is discussed in Sec.VII.Finally,in Sec.VIII,we summarize our results.II.EFFECTIVE HAMILTONIAN OF THE SYSTEMWe consider a quantum dot modeled as a nondegeneratethree-level cascade system with the ground level|1 ,theintermediate level|2 ,and the upper level|3 of energies E3>E2>E1.The levels are separated by energies E2−E1= (ω2−ω1)= ω21and E3−E2= (ω3−ω2)= ω32.In practical terms,the level|1 corresponds to the electronicground state of the QD,the level|2 to the single-excitonstate,and|3 to the biexciton state.The system is driven by asingle-mode laserfield of frequencyωL,which is resonant witha two-photon transition from|3 to|1 ,(E3−E1=2 ωL), as shown in Fig.1.Because of the unequal spacing of the energy levels,the laser is not resonant with the one-photon transitions.In addition,the system interacts with modes of a low-frequency(acoustic)phonon reservoir,which we assume are in a thermal state with the average occupation phonon number of a mode p,¯n p=[exp( ωp/k B T)−1]−1,where k B is the Boltzmann constant and T is the temperature of the reservoir.The density of the phonon modes is considered to be large only in the frequency range close to the detuning =ω21−ωL of the laser frequency from the transition frequency ω21.The total Hamiltonian for this system may be written in theform( ≡1)H=H0+H1+H2,(1)where H0is the free Hamiltonian of the QD and the phonon reservoir,H0= A22+pωp b†p b p,(2)FIG.1.Energy-level scheme of the three-level quantum dot under a laser excitation of frequencyωL.The laser is on two-photon resonance with the|3 ↔|1 transition frequency,detuned from the transition frequencyω21by .H1is the interaction Hamiltonian between the QD and the laserfield mode,H1=χ1(A21+A12)+χ3(A32+A23),(3) and H2is the interaction Hamiltonian between the QD and the phonon reservoir,H2=p(g3p A33−g1p A11)(b†p+b p).(4)Here,A ij=|i j|are the usual atomic operators representing populations(i=j)of the energy levels of the QD and coherences(i=j)between them,b†p and b p are,respectively, the creation and annihilation operators of mode p of the phonon reservoir, =ω21−ωL is the one-photon detuning of the laser frequencyωL from the transition frequencyω21, andχ1andχ3are the Rabi frequencies associated with the laser field driving|1 ↔|2 and|2 ↔|3 transitions,respectively. The parameters g1p and g3p are the coupling strengths of the mode p of the phonon reservoir to the one-photon transitions |2 ↔|1 and|3 ↔|2 ,respectively.We make the unitary transformation of the Hamiltonian˜H=e iS H e−iS,(5) withS=p−iωp(g3p A33−g1p A11)(b†p−b p),(6) andfind˜H=˜H0+˜H F+˜V,(7) in which˜H0= A22+i=1,3i(A2i+A i2),(8)˜HF=pωp b†p b p,and˜V=pg1p 1ωp(b†p−b p)(A21−A12)+pg3p 3ωp(b†p−b p)(A32−A23),(9) where i= B i χi,withB i =exp−12p(g ip/ωp)2(2¯n p+1)(10)as an effective Rabi frequency of the laserfield.In the derivation of Eq.(9),we have performed a Born approximation which corresponds to afirst-order term in a systematic expansion of Eq.(5)in g ip,which means that we assumed that the interaction between the QD and the phonon reser-voir is not very strong so that the one-phonon transitions play a dominant role as compared with the multiphonon transitions.The interaction Hamiltonian˜V contains the rotating and counter-rotating terms.We may transform the HamiltonianESTABLISHMENT OF CORRELATED STATES IN A ...PHYSICAL REVIEW A 90,023815(2014)(7)to the interaction picture with the unitary transformationU (t )=exp[−i (˜H0+˜H F )t ],and find ˜V (t )= pb †p e i (ωp − )t g 3p 3ωp A 32−g 1p 1ωp A 12+b †p e i (ωp + )tg 1p 1ωp A 21−g 3p 3ωpA 23 +H .c .(11)In what follows,we consider the situation where ωp ≈ and the coupling strengths g i i /ωp are much smaller than ωp ,(g i i /ωp ) ωp .This prompts us to make the rotating-wave approximation in which we ignore rapidly oscillating terms at frequency 2ωp ,and obtain˜V (t )≈pb †p e i (ωp − )t (˜g3p A 32−˜g 1p A 12)+H .c .,(12)where ˜gip =g ip i / is an effective coupling strength of the phonon reservoir to the i th transition of the QD.Thus,we have arrived at the effective Hamiltonian with parameters that can be controlled through the laser frequency and amplitude and where the characteristic frequency scales are no longer those of optical frequencies but those associated with detunings and Rabi frequencies.The properties of the entire system of the QD interacting with a phonon bath are described by the density operator ρT .The reduced density operator ρdescribing the properties of the QD is obtained by taking the trace of ρT over the space of the phonon modes,ρ=Tr p ρT .Assuming that the phonon modes provide a broadband reservoir,we may perform the Markov approximation,as is usually done when dealing with spontaneous emission processes.Actually the non-Markovian effects are likely to affect the QD dynamics only at short times;the difference between non-Markovian and Markovian dynamics diminishes or vanishes at longer time scales [35].It is reported that for a QD transition driven by a detuned continuous-wave laser by mediation of acoustic phonons,the Markov approximation is found to be an excellent approximation to describe the effect of the interaction between the QD and the phonon reservoir on the properties of the QD [5,6,18,36].In addition,taking into account radiation damping through the ordinary spontaneous emission,we derive the master equation for the reduced density operator ρas∂∂tρ=−i [˜H 0,ρ]+L p ρ+L s 2ρ+L s 3ρ,(13)in which L p ρ=j =1,3(¯n+1)γj {[A j 2ρ,A 2j ]+[A j 2,ρA 2j ]}+j =1,3¯nγj {[A 2j ρ,A j 2]+[A 2j ,ρA j 2]}−(¯n+1)γ13{[A 32ρ,A 21]+[A 32,ρA 21]+H .c .}−¯nγ13{[A 21ρ,A 32]+[A 21,ρA 32]+H .c .}(14)describes phonon-bath-induced decay of the QD.The coeffi-cients γ1and γ3are the phonon-bath-induced damping ratesof the levels |2 and |3 ,respectively,and γ13=√γ1γ3is thecross-damping rate resulting from the phonon-bath-induceddissipative coupling between the transitions.The remaining two terms L s 2ρand L s 3ρare of the formL s 2ρ= 2{[A 12ρ,A 21]+[A 12,ρA 21]},(15)L s 3ρ= 3{[A 23ρ,A 32]+[A 23,ρA 32]},and represent deexcitation of the levels |2 and |3 by radiative spontaneous emission with damping rates 2and 3,respectively.There are several interesting remarks that should be made about the expression for the Liouvillean L p ρ,given by Eq.(14).First of all,we may identify the first two terms with incoherent damping and incoherent pumping of the two transitions.However,a close look reveals that the phonon reservoir couples to the |1 ↔|2 and |2 ↔|3 transitions in decidedly different ways.It is easy to see that the first term corresponds to the damping of the |1 ↔|2 transition but it appears as an incoherent pumping of the |3 ↔|2 transition.Similarly,the second term corresponds to an incoherent pumping of the |1 ↔|2 transition but it appears as an incoherent damping of the |3 ↔|2 transition.In other words,the phonon bath couples to the lower transition |1 ↔|2 as an ordinary harmonic-oscillator thermal bath with dampingrate (¯n+1)γ1and with incoherent pumping rate ¯nγ1,whereas it couples to the upper transition |2 ↔|3 as an invertedharmonic-oscillator thermal bath with damping rate ¯nγ3and with incoherent pumping rate (¯n+1)γ3.Figure 2helps to explain the situation.It illustrates the action of the phonon bath on the transitions between the energy levels of the system.What is more surprising than the coupling to the upper transition as the inverted harmonic oscillator is the presence in Eq.(14)of two terms involving cross coupling between the transitions |1 ↔|2 and |2 ↔|3 .This is a form of interference,although it involves transitions of ordinary and inverted harmonic oscillators.In particular,the third term in Eq.(14)reflects the fact that,as the QD decays from the level |2 to the level |1 ,it drives absorption to level |3 .Similarly,the fourth term reflects the fact that,as theQDFIG.2.Three-level cascade system interacting with a phonon bath and driven by a coherent laser field.The phonon bath couples to the transition |1 ↔|2 as an ordinary harmonic-oscillator thermal bath,whereas it couples to the |2 ↔|3 transition as an inverted harmonic-oscillator thermal bath.In addition,levels |1 and |2 are coupled by the driving laser field with the Rabi frequency 1and levels |2 and |3 with the Rabi frequency 3.Level |3 decays to level |2 with rate 3,and level |2 decays to level |1 with rate 2.HUI HUANG,GAO-XIANG LI,WEN-JU GU,AND ZBIGNIEW FICEK PHYSICAL REVIEW A90,023815(2014) is incoherently pumped from the level|1 to level|2 ,it drivesemission from level|3 to level|2 .In physical terms,the thirdterm in Eq.(14)represents the process of a deexcitation of thelevel|2 simultaneously to the levels|1 and|3 ,whereas thefourth term represents the process of an excitation of the level|2 simultaneously from the levels|1 and|3 .We shall seethat the effect of the simultaneous deexcitation of level|2 tolevels|1 and|3 may result in a strong coherence betweenthese levels.Thus,we may conclude that the phonon bath,althoughbeing in a thermal state,affects the QD as a correlated-typereservoir.One could argue that the action of the phonon bath onthe system is similar in form to the ones of a squeezed reservoircoupled to a cascade three-level system.However,the analogyis not complete.For example,the cross coupling betweenthe transitions preserves even in the case of zero-temperaturephonon bath,where¯n=0.This is in striking contrast to thesqueezed reservoir that requires¯n=0for the cross couplingto be present.Although the analogy is not complete,we shallshow that various results predicted for the cascade systeminteracting with a phonon bath are analogous to that obtainedin the cascade system interacting with a squeezed reservoir[26,27].III.COHERENT SUPERPOSITION STATESThe presence of the cross-coupling(interference)termsin Eq.(14)indicates that the phonon bath induces a directcoupling between the states|1 and|3 ,which may resultin a coherence between these states.When the coherence ispresent,the states become a linear superposition of the barestates.Therefore,it is convenient to introduce symmetric andantisymmetric superpositions|u =α|3 +β|1 ,(16)|w =β|3 −α|1 ,whereα=γ1γ1+γ3,β=γ3γ1+γ3.(17)Physically,the states|u and|w are the effective states between which the quantum dot evolves when interacting with the phonon bath.It is then easily verified that in terms of the superposition states(16),the master equation(13)assumes the simplified form with˜H0= A22+ w(A2w+A w2)+ u(A2u+A u2),(18) wherew=β 3−α 1, u=α 3+β 1,(19) with the dissipative phonon-reservoir part L pρreduced to L pρ=(¯n+1)γ(2A w2ρA2w−A22ρ−ρA22)+¯nγ(2A2wρA w2−A wwρ−ρA ww),(20) in whichγ=γ1+γ3.The Liouvillians L s2ρand L s3ρ,representing dissipation due to the radiative spontaneous emission,written in thebasisFIG.3.The three-level quantum-dot system in the superposition state basis{|2 ,|w ,|u }.In the superposition state basis,the system is equivalent to a -type system in which the phonon bath couples exclusively to the|2 ↔|w transition as an ordinary harmonic-oscillator thermal bath.The transition|2 ↔|u is not affected by the phonon bath.The transition|2 ↔|u is driven by the laser with an effective Rabi frequency u,whereas the transition|2 ↔|w is driven with an effective Rabi frequency w.of the superposition states|w and|u ,take the formL s2ρ=α2 2([A w2ρ,A2w]+[A w2,ρA2w])+β2 2([A u2ρ,A2u]+[A u2,ρA2u])−αβ 2([A w2ρ,A2u]+[A w2,ρA2u]+H.c.),(21) andL s3ρ=β2 3([A2wρ,A w2]+[A2w,ρA w2])+α2 3([A2uρ,A u2]+[A2u,ρA u2])+αβ 3([A2wρ,A u2]+[A2w,ρA u2]+H.c.).(22) It is seen from Eq.(20)that the phonon reservoir couplesonly to the|2 ↔|w transition.The superposition state|uis completely decoupled from the phonon bath.There is,however,a strong coherent coupling between|u and|2 withan effective Rabi frequency u,as shown in Fig.3.The laserfield couples the states|w and|2 with an effective Rabifrequency w.Figure3clearly illustrates that the three-level QD systeminteracting with the phonon bath effectively behaves as a -type system.It is particularly well seen in the properties of theradiative damping.The Liouvillian L s2ρhas the same formas the Liouvillian for a three-level type system with cross-coupled transitions.It is easy to see that thefirst term in Eq.(21)describes spontaneous decay from the level|2 to level|w withthe rateα2 2.The second term describes spontaneous decayfrom the level|2 to level|u with the rateβ2 2.Clearly,theLiouvillian(21)describes dissipation of the three-level -typesystem with the upper level|2 and two ground levels|w and |u .The third term in Eq.(21)describes the dissipative cross coupling between these transitions with an amplitudeαβ 2.What is more interesting is that the spontaneous emission fromthe level|3 has the same effect as an incoherent pumping of thesystem.It is seen from Eq.(22)that spontaneous emission from the level|3 excites transitions from the ground levels |w and|u to the upper level|2 with ratesβ2 3andα2 3, respectively.Thus,it represents a process of an incoherent pumping of the system.We may conclude that the role of the radiative spontaneous emission in the ladder system interacting with a phonon bath is analogous to that of theESTABLISHMENT OF CORRELATED STATES IN A ...PHYSICAL REVIEW A 90,023815(2014)dissipation and an incoherent driving of the -type system with cross-coupled transitions.There are two interesting limits for the effective Rabi frequency w : w =0and w = u .The limit w =0corresponds to 1/ 3=β/α,whereas the case w = u corresponds to 1/ 3=(β−α)/(α+β).A.The case w =0When 1/ 3=β/α≡√γ3/γ1,we see from Eq.(19)that the effective Rabi frequency w is equal to zero.Under such condition,the laser field couples exclusively to the |2 ↔|u transition.The absence of the driving field on the |w ↔|2 transition causes the system to behave as a three-level V -type rather than -type system.To demonstrate this analogy,we diagonalizethe Hamiltonian ˜H0= A 22+ u (A 2u +A u 2)and find that the eigenstates of the Hamiltonian,the so-called semiclassical dressed states,are|m =sin θ|2 +cos θ|u ,(23)|n =cos θ|2 −sin θ|u ,wherecos 2θ=12− 2,(24)and =2+4 2u .In the space spanned by the dressed states |w ,|m ,and |n ,the master equation (13)takes the form∂∂t ρ=−i [˜H 0,ρ]+ k =m,nγk ([A wk ρ,A kw ]+[A wk ,ρA kw ])+¯n¯n +1 k =m,n γk ([A kw ρ,A wk ]+[A kw ,ρA wk ])−√γm γn ([A wm ρ,A nw ]+[A wm ,ρA nw ]+H .c .),(25)where the Hamiltonian ˜H0can be written in the form ˜H 0=12( + )A mm +12( − )A nn ,(26)withγm =2(¯n+1)γsin 2θ,γn =2(¯n+1)γcos 2θ.(27)The second term in Eq.(25)describes decay processes from the states |m and |n to the state |w occurring with rates γm and γn ,respectively.The third term describes an incoherent pumping from state |w to states |m and |n ,whereas the last term describes cross correlations between the decay processeswith rate √γm γn .Figure 4shows the energy-level structure of the QD system interacting with the phonon bath and driven by a laser field with the effective Rabi frequency w =0.Clearly,the dynamics of the system is completely equivalent to that of an undriven three-level V -type system with nondegenerate transitions of the frequency difference ,the upper states decaying with unequal rates γm and γn ,and the transitions cross correlatedwith the rate √γm γn.FIG.4.Energy levels of the QD system in the dressed states basis {|w ,|m ,|n }.The system is equivalent to a nondegenerate V -type system with the upper dressed states |m and |n decaying to the lower state |w with rates γm and γn ,respectively.B.The case w = uWhen w and u are both different from zero,the lower states |w and |u are resonantly coupled to the upper state |2 by the laser field with the effective Rabi frequencies w and u ,respectively.It is well known that in this configuration,the system is optically pumped into coherent superpositions of the two lower states,i.e.,the so-called bright and dark states [37–41],|b =( w |w + u |u )/2w + 2u ,(28)|d =( u |w − w |u )/2w + 2u .In the case of w = u ,the states (28)simplify to|b =1√2[(α+β)|3 −(α−β)|1 ],(29)|d =1√[(α−β)|3 +(α+β)|1 ].Comparing Eq.(29)with Eq.(16),we see that the states |b ,|d and |u ,|w are similar coherent superpositions of the bare states |1 and |3 .However,their coherence properties are mutually exclusive in the sense that under a condition in which the states |u and |w are maximally coherent,the states |b and |d are reduced to bare states,and vice versa.In particular,when α=β,the states |u ,|w reduce to superposition states with maximal coherence between |1 and |3 ,whereas the states |b ,|d reduce to bare states |3 ,|1 with no coherence between them.Similarly,when α β,the superposition states |u and |w reduce to the bare states |3 and |1 ,respectively,whereas the states |b and |d reduce to superposition states with maximal coherence.Thus,in the case of w = u ,the effect of the driving laser field is to destroy the coherent superpositions between the states |1 and |3 induced by the phonon bath.IV .POPULATION DISTRIBUTIONAll of the effects of the phonon reservoir discussed in the previous section should be reflected in the distribution of the populations between the energy levels of the QD.The usual way to study the population distribution is to derive equations of motion for the density-matrix elements using the master equation of a given system.HUI HUANG,GAO-XIANG LI,WEN-JU GU,AND ZBIGNIEW FICEK PHYSICAL REVIEW A 90,023815(2014)Since we are interested in the population distribution and coherences between the superposition states,we determine the density-matrix elements in the basis {|2 ,|w ,|u }.Within this basis,the resulting density-matrix elements satisfy equations that show considerably less coupling.Including both phonon-bath and radiative dampings,it is straightforward to show that the density-matrix elements obey the following set of coupled differential equations:˙ρ22=−2[ 2+(¯n+1)γ]ρ22+2 β2 3+¯nγρww +2α2 3ρuu +2αβ 3(ρwu +ρuw )+i u (ρ2u −ρu 2)+i w (ρ2w −ρw 2),˙ρww=−2 β2 3+¯nγρww +2 α2 2+(¯n +1)γρ22−αβ 3(ρwu +ρuw )−i w (ρ2w −ρw 2),˙ρuu =−2α2 3ρuu +2β2 2ρ22−αβ 3(ρwu +ρuw )−i u (ρ2u −ρu 2),˙ρ2w =− 2+β2 3+(2¯n+1)γ+iρ2w −αβ 3ρ2u −i u ρuw +i w (ρ22−ρww ),˙ρ2u=− 2+α2 3+(¯n+1)γ+iρ2u −αβ 3ρ2w −i w ρwu +i u (ρ22−ρuu ),˙ρwu =−αβ 3−( 3+¯nγ)ρwu −αβ(2 2− 3)ρ22+i u ρw 2−i w ρ2u .(30)Equations (30)plus the equations for ρw 2,ρu 2,ρuw form a set ofnine coupled differential equations with constant coefficients.These equations are cumbersome because of a complicated coupling,which exists in general between all three pairs of the states,|w ↔|2 ,|2 ↔|u ,and |u ↔|w .The equations can be simplified substantially for particular choices of the parameters,such as 2, 3≈0.In physical terms,it would correspond to the situation where the radiation modes occupy only a small fraction of modes surrounding the QD.Suppose first that 2, 3≈0and that the system is affected solely by the phonon bath.It is seen from Eq.(30)that in this case,the population ρuu does not decay.In other words,the state |u appears as a decoherence-free state.The decay occurs only from the state |2 to the state |w .Thus,owing to the equivalence of the system with a nondegenerate three-level V -type system,we may conclude that in the space spanned by the states |2 ,|w ,and |u ,the state |2 coincides with a symmetric state which decays to the ground state |w ,whereas the state |u coincides with a nondecaying asymmetric state coherently coupled to the state |2 with the amplitude u .Further simplification can be made by choosing the Rabi frequencies such as w =0or w = u .In the first case of w =0,the set of the differential equations (30)splits into two independent sets,one involving four equations,˙ρ22=−2(¯n+1)γρ22+2¯nγρww +i u (ρ2u −ρu 2),˙ρww =−2¯nγρww +2(¯n +1)γρ22,(31)˙ρuu =−i u (ρ2u −ρu 2),˙ρ2u =−[(¯n+1)γ+i ]ρ2u +i u (ρ22−ρuu ),and the other involving two coupled equations,˙ρ2w =−[(2¯n+1)γ+i ]ρ2w −i u ρuw ,(32)˙ρwu =−¯nγρwu +i u ρw 2.Equations (31)and (32)can be solved strictly.The system ofequations (31)can be transformed using the Laplace transform method into a set of algebraic equations which can be solved,for example,by matrix inversion.We will consider the time evolution of the density-matrix elements in Sec.VI .Here,we focus on the steady-state solutions.The set (31)can have a nonzero steady-state solution,while the steady-state solution of Eq.(32)is zero.The steady state can be a pure state when the phonon bathis at zero temperature (¯n=0)and the Rabi frequency w is made zero by a suitable choice of the ratio 3/ 1=γ1/γ3.Inthe case when ¯n=0and w =0,we easily find that ρww =1.We should point out the fact that the decay of the system to the pure state does not depend on the particular values of the decay rates and is valid for γ1=γ3as well as for γ1=γ3.In the case of w =0,the steady-state solution of Eq.(30)is given byρww =¯n+13¯n+1,ρuu =ρ22=¯n3¯n+1,(33)from which we see that the populations are independent ofγ1and γ3.Moreover,the populations are independent of u .Note that there is no population inversion between |2 and |w .Thus,there is no population inversion in the basis of the superposition states.However,there is population inversion between the bare states.It is straightforward to show that the steady-state populations of the bare states areρ33=¯n+β23¯n+1,ρ22=¯n 3¯n +1,ρ11=¯n+α23¯n+1.(34)It is apparent from Eq.(34)that ρ33>ρ22always.Hence thereis always a population inversion between the levels |3 and |2 .The maximum inversion is reached at ¯n=0and decreases with an increasing ¯n.The steady state also possesses a large two-photon coherence,ρ13=−αβ3¯n+1.(35)Thus,the system decays to a strongly correlated state inwhich the population distribution no longer obeys a Boltzmanndistribution.Moreover,for ¯n=0,the correlated state is a pure state.It is particularly seen when one calculates the purity factor,Tr(ρ2)=3¯n2+2¯n +1(3¯n+1)2,(36)from which it is evident that Tr(ρ2)=1for ¯n=0.Furthermore,if β>α,then ρ33>ρ11for any ¯n,corre-sponding to a population inversion between levels |3 and |1 .Thus,in the case of γ3>γ1,we can have not only a one-photon inversion between levels |3 and |2 but also a two-photon inversion between levels |3 and |1 .The above considerations are illustrated in Fig.5,whichshows the populations of the bare states as a function of ¯n。

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老托福阅读真题及答案：passage11

老托福阅读真题及答案：passage11

老托福阅读真题及答案:passage11为了帮助大家备考托福阅读，提高成绩，下面小编给大家带来老托福阅读真题及答案:passage 11，希望大家喜欢！老托福阅读真题及答案:passage 11Plants are subject to attack and infection by a remarkable variety of symbiotic species and have evolved a diverse array of mechanisms designed to frustrate the potential colonists. These can be divided into preformed or passive defense mechanisms and inducible or active systems. Passive plant defense comprises physical and chemical barriers that prevent entry of pathogens, such as bacteria, or render tissues unpalatable or toxic to the invader. The external surfaces of plants, in addition to being covered by an epidermis and a waxy cuticle, often carry spiky hairs known as trichomes, which either prevent feeding by insects or may even puncture and kill insect larvae. Other trichomes are sticky and glandular and effectively trap and immobilize insects.If the physical barriers of the plant are breached, then preformed chemicals may inhibit or kill the intruder, and plant tissues contain a diverse array of toxic or potentially toxic substances, such as resins, tannins, glycosides, and alkaloids, many of which are highly effective deterrents to insects that feed on plants. The success of the Colorado beetle in infesting potatoes, for example, seems to be correlated with its high tolerance to alkaloids that normally repel potential pests. Other possible chemical defenses, while not directly toxic to the parasite, may inhibit some essential step in the establishment of a parasitic relationship. For example, glycoproteins in plant cell walls may inactivate enzymes that degrade cell walls. These enzymes are often produced by bacteria and fungi.Active plant defense mechanisms are comparable to the immune system of vertebrate animals, although the cellular and molecular bases are fundamentally different. Both, however, are triggered in reaction to intrusion, implying that the host has some means of recognizing the presence of a foreign organism. The most dramatic example of an inducible plant defense reaction is the hypersensitive response. In the hypersensitive response, cells undergo rapid necrosis — that is, they become diseased and die —after being penetrated by a parasite; the parasite itself subsequently ceases to grow and is therefore restricted to one or a few cells around the entry site. Several theories have been put forward to explain the basis of hypersensitive resistance.1. What does the passage mainly discuss?(A) The success of parasites in resisting plant defense mechanisms(B) Theories on active plant defense mechanisms(C) How plant defense mechanisms function(D) How the immune system of animals and the defense mechanisms of plants differ2. The phrase "subject to" in line 1 is closest in meaning to(A) susceptible to(B) classified by(C) attractive to(D) strengthened by3. The word "puncture" in line 8 is closest in meaning to(A) pierce(B) pinch(C) surround(D) cover .4. The word "which" in line 12 refers to(A) tissues(B) substances(C) barriers(D) insects5. Which of the following substances does the author mention as NOT necessarily being toxic to the Colorado beetle?(A) resins(B) tannins(C) glycosides(D) alkaloids6. Why does the author mention "glycoproteins" in line 17?(A) to compare plant defense mechanisms to the immune system of animals(B) to introduce the discussion of active defense mechanisms in plants(C) to illustrate how chemicals function in plant defense(D) to emphasize the importance of physical barriers in plant defense7. The word "dramatic" in line 23 could best be replaced by(A) striking(B) accurate(C) consistent(D) appealing8. Where in the passage does the author describe an active plant-defense reaction?(A) Lines 1-3(B) Lines 4-6(C) Lines 13-15(D) Lines 24-279. The passage most probably continues with a discussion of theories on(A) the basis of passive plant defense(B) how chemicals inhibit a parasitic relationship.(C) how plants produce toxic chemicals(D) the principles of the hypersensitive response.正确答案:CAABD CADD托福阅读易错词汇的整理1) quite 相当 quiet 安静地2) affect v 影响, 假装 effect n 结果, 影响3) adapt 适应 adopt 采用 adept 内行4) angel 天使 angle 角度5) dairy 牛奶厂 diary 日记6) contend 奋斗, 斗争content 内容, 满足的context 上下文contest 竞争, 比赛7) principal 校长, 主要的 principle 原则8) implicit 含蓄的 explicit 明白的9) dessert 甜食 desert 沙漠 v 放弃 dissert 写论文10) pat 轻拍 tap 轻打 slap 掌击 rap 敲，打11) decent 正经的 descent n 向下, 血统 descend v 向下12) sweet 甜的 sweat 汗水13) later 后来 latter 后者 latest 最近的 lately adv 最近14) costume 服装 custom 习惯15) extensive 广泛的 intensive 深刻的16) aural 耳的 oral 口头的17) abroad 国外 aboard 上(船，飞机)18) altar 祭坛 alter 改变19) assent 同意 ascent 上升 accent 口音20) champion 冠军 champagne 香槟酒 campaign 战役21) baron 男爵 barren 不毛之地的 barn 古仓22) beam 梁，光束 bean 豆 been have 过去式23) precede 领先 proceed 进行，继续24) pray 祈祷 prey 猎物25) chicken 鸡 kitchen 厨房26) monkey 猴子 donkey 驴27) chore 家务活 chord 和弦 cord 细绳28) cite 引用 site 场所 sight 视觉29) clash (金属)幢击声 crash 碰幢，坠落 crush 压坏30) compliment 赞美 complement 附加物31) confirm 确认 conform 使顺从32) contact 接触 contract 合同 contrast 对照33) council 议会 counsel 忠告 consul 领事34) crow 乌鸦 crown 王冠 clown 小丑 cow 牛35) dose 一剂药 doze 打盹36) drawn draw 过去分词 drown 溺水托福阅读学术词汇的解析什么是学术词汇在托福阅读的课堂上，经常有学生对繁杂的学术词汇头疼不已。

新标准大学英语2 unit1-unit9 单词短语汇总

新标准大学英语2 unit1-unit9 单词短语汇总

New Words 1. 2. 3. 4. 5. 6. overthrow rebel destruction assert era profound 1. 2. 3. 4.
Phrases
by definition take to be associated with make sense
Active reading 2: Resources
15. 撕碎文件
16. 制造假身份 17. 在谷歌上搜索 18. 个人信息 19. 注销电脑 20. 犯罪记录
16. to create a false identity
17. do a Google search 18. personal information
19. log off
20. criminal record
2.历史性和国际性
3.坏事传千里。
4.重大国际影响
5.全球却颇有反响
6.比…优势大多了
7.设定的方针 8.独特的视点
8. a unique viewpoint
More
Active reading 1: Resources
Useful expressions
9. 未必比…更客观可靠
9.
10. 或多或少隐蔽地影响 10. 公众的权力
1. count on 2. look through
Active reading 1: Resources
1. 冒充飞行员
Useful expressions
1. impersonate a airplane pilot 3. fictional FBI agent 4. white collar crime 5. a career as a fraudster 6. run a consultancy 7. identity theft 8. leave… for pickup 9. anonymous victims 10.change one’s mindset
全新版大学英语(第二版)综合教程4_课后练习答案

全新版大学英语(第二版)综合教程4_课后练习答案

全新版大学英语综合教程4〔第二版〕习题答案Unit 1VocabularyI.1.1) alliance 2) at the cost of3) stroke 4) limp5) minus 6) regions7) declarations 8) siege9) raw 10) bide his time11) have taken their toll 12) in the case of2.1) is faced with 2) get bogged down3) is pressing on / pressed on 4) drag on5) get by 6) dine out7) have cut back 8) get through3.1) lead to the conquest of cancer in the near future2) has been brought to a halt by the delayed arrival of raw materials due to the dock workers’ strike3) will/should never get in the way of her career4) caught the foreign minister off guard5) of the electronic calculator has rendered the slide rule out of date/obsolete4.1) Being faced with … the occupation of …regions2) crucial to … efficient … to reckon with … weaken … be brought to a halt3) a heroic … the decisive … turned the tide … siege … by launchingII.More Synonyms in Context1) During the First World War, battles occurred here and there over vast areas. Some of the most dramatic fighting took place inthe gloomy trenches of France and Belgium.2) Elizabeth made careful preparations for the interview and her efforts / homework paid off.3) I spent hours trying to talk him into accepting the settlement, but he turned a deaf ear to all my words.4) Pneumonia had severely weakened her body, and I wondered how her fragile body could withstand the harsh weather.III. Usage1) fall ill2) lay dead at home for two weeks3) dropped dead from a heart attack4) fell asleep.5) marrying young6) to sit still for longer than a few minutesComprehensive ExercisesI. Cloze1. 1) invasion 2) stand in the way3) Conquest 4) catching... off his guard5) launching 6) declaration7) campaign 8) drag on9) reckon with 10) bringing...to a halt2. 1) allow2) reckoned3) highly 4) forecasts5) rapidly 6) instant7) delivery 8) advantage9) observing 10)powerfulII. Translation1. 1) Mr. Doherty and his family are currently engaged in getting the autumn harvest in on the farm.2) We must not underestimate the enemy. They are equipped with the most sophisticated weapons.3) Having been cut of a job/Not having had a job for 3months, Phil is getting increasingly desperate.4) Sam, as the project manager, is decisive, efficient, and accurate in his judgment.5) Since the chemical plant was identified as the source of solution, the village neighborhood committee decided to close it down at the cost of 100 jobs.2. The offensive had already lasted three days, but we had not gained much ground. The division commander instructed our battalion to get around to the rear of the enemy at night and launch a surprise attack. To do so, however, we had to cross a marshland and many of us were afraid we might get bogged down in the mud. Our battalion commander decided to take agamble. By a stroke of luck, thanks to the severely cold weather which made the marshland freeze over, we arrived at our destination before dawn and began attacking the enemy from the rear. This turned the tide of the battle. The enemy, caught off guard, soon surrendered.Unit 2VocabularyI.1. 1) expansion 2) automated 3) vapor 4) take control of5) hazards 6) satellite 7) vibrated 8) magnetic9) bunched 10) in the air 11) got/was stuckin 12) approximately2. 1) send out 2) stand up for 3) pass for 4) were closing inon5) starting up 6) went through 7) fill out 8) fall into3. 1) incorporates all the latest safety features2) two trees ten feet apart3) awarding lucrative contracts to his construction firm4) the prototype of a new model before they set up a factory to makethe cars5) are correlated in all racial groups4.1) the application… remote… has turned into a reality… are poisedto2) that vibrate… can detect… frequency3) lanes… are mounted in… alert a… hazardII. Word FormationClipped Words Blendskilo kilogram Medicare medical carememo memorandum email electronic mailgym gymnasium comsat communications satellitelib liberation newscast news broadcastdoc doctor skyjack sky hijackvet veterinarian Eurodollar European dollarprep preparatory brunch breakfast and lunchauto automobile telecast television broadcastflu influenza Oxbridge Oxford and CambridgeIII. Usage1. swimming pool2. drawing board3. enriched Middle English4. disturbing change5. fully developed prototype6. Canned foods7. working population 8. puzzling differencesComprehensive ExercisesI. Cloze1. 1) computerized 2) start up 3) be poised to 4) alert5)hazards6) monotonous 7) take control of 8) steer 9) lane 10) decrease11) calculate 12) eliminate 13) getting stuck in 14) mounted15) detect 16) vapor2.1) generates 2) related 3) revolutionized 4) enabled 5) opportunities 6) overall 7) manufacturing 8)dependent9) interact 10) fatalitiesII. Translation1. 1) There was an unusual quietness in the air, except for the sound of artillery in the distance.2) The expansion of urban areas in some African countries has been causing a significant fall in living standards and an increase in social problem.3) The research shows that atmospheric carbon dioxide levels are closely correlated with global temperatures.4) The frequency of the bus service has been improved from 15 to 12 minute recently.5) The diver stood on the edge of the diving board, poised to jump at the signal from the coach.2. Automobiles have, since their invention, revolutionized transportation, changing forever the way people live, travel, and do business. On the other hand, they have brought hazards, especially highway fatalities. However, today the application of computer technology and electronic sensors in designing and manufacturing cars makes it possible to eliminate most of traffic accidents. For example, electronic sensors mounted in your car can detect alcohol vapor in the air and refuse to start up the engine. They can also monitor road conditions by receiving radio signals sent out from orbiting satellites and greatly reduce your chances of getting stuck in traffic jams.Unit 3Language Sense Enhancement1. (1) checked with (2) interview (3) grill (4) clippings (5) be right for (6) follow up (7) indicating(8) hand-delivered (9) prepared (10) prospectiveVocabularyI.1.1) rude 2) physically 3) structure 4) made a difference5) blurted (out) 6) chuckling 7) measurable 8) prospective9) preparations 10) sparkled 11) took a crack at 12) partner2.1) go after 2) look back at/on 3) be put up 4) stood for5) build in 6) follow up 7) be hooked up to 8) closed up3.1) grilled her about where she had been all night2) beyond Cinderella's wildest dreams that she could one day dance in the King’s palace3) will be in readers’ hands soon4) do your homework before going on an interview5) was in the neighborhood of 150 dollars4. 1) applicants…veteran…th e prospective2) From his standpoint…has made every endeavor to go after3) as the saying goes…to have a crack at…barelyII. Words with Multiple Meanings1. behave2. keep (used to avoid repetition)3. clean4. get along5. perform/complete6. perform/complete7. study8. be enough9. be acceptableIII. Usage1. There is so much to say and it is hard to know where to begin. OK, I’ll talk about myself first.2. Thank you very much, John, for your beautiful Christmas card. By the way, I have something here for you.3. The new computer language can be quite easily understood by anyone who can read the daily newspaper. Now, why is this an advantage?4. I’m going to work out the outline and will let you know how it goes. By the way, I will see you in February, as I plan to attend your seminar in Shanghai.5. OK, you got the job. Now, how to maximize your profits with as little effort as possible?6. Chris is back from Australia. Incidentally, those pictures you sent me are wonderful.Comprehensive ExercisesI. Cloze1. 1) prospective 2) As I see it 3) done your homework4) beforehand5) endeavor 6) structure7) partners 8) Respond 9) take a crack10) from the standpoint (11) make a difference 12) follow up 2. 1) encouraging 2) inquiry 3) relevant 4) samples5) references 6) advice 7) preparing 8) seriously9) probably 10) exhibitII. Translation1. 1) Despite the inadequate length of the airstrip in this emergency landing, the veteran pilot managed to stop the plane after taxiing for only a short while.2) Grilled by the reporters, the movie star eventually blurted (out) that she had undergone two plastic surgeries.3) We have the technology and our partner has the capital. Working toget her, we’ll have the future in our hands.4) If I had known beforehand that you would bring so many friends home,I would have made better preparations. You see, I have barely enough food and drinks for a snack.5) People gave generously upon learning that new school rooms with stronger structures were to be built in the earthquake-stricken area.2. Well begun, half done, as the saying goes. It is extremely important for a job applicant to do his homework while seeking employment. From my standpoint, whether or not one has done his homework clearly makes a differences in his chance of success.I have a friend who is earning somewhere in the neighborhood of 100,000 dollars a year in a large computer software company. He told me that from his own experience the decision makers who interview prospective employees like people who are well prepared. Those who make no endeavor to learn as much about his prospective employer as possible don't have much of a chance of success.Unit 4VocabularyI.1. 1) advantageous2) let alone3) witnessing…vanishing 4) landmark5) entitled 6) displace7) Establishment 8) patriotic…strengthen9) contradictions 10) aspires11) divorced 12) pendulums2.1) come to 2) dozed off3) believed in 4) was set apart5) take in6) sucks in7) clean up 8) turn away3. 1) makes no/little difference whether we go there by train or by bus2)overtaken General Motors as the world’s biggest car maker3)at odds with his wife over money matters4)been at the forefront of nanotechnology research5)let alone cook a meal4. a) is increasingly…to accelerate…their investmentb) economy…make an earnest…domestic…strike a balance betweenc) a handful of…be endorsed by…on a large scaleComprehensive ExercisesI. Cloze1. 1) academics 2) networking3) a variety of 4) growth5) vanish 6) facilitate7) endorsing 8) outlook9) sweeping aside 10) patriotic11) erasing 12) strike a balance2.1. aided2.effects3.distances4. connected5. invested6. features7. prevailing 8. qualitatively9. volume 10. DistinguishingII. Translation1. 1) Due to his pessimistic outlook on the European economy, John has moved his assets from Europe to elsewhere.2) I like hiring young people. They are earnest learners and committed to work.3) Unlike her girl friends who center their lives on their children, Mary cares more about her personal growth.4) Why is it that a considerable number of colleagues are at odds with you?5) The Chinese government has introduced a variety of policies to strengthen cooperation with developing countries.2. Globalization has great implications for young Chinese. For example, young farmers are moving on a large scale to urban areas to look for jobs. And for those young people who aspire to study abroad or work in foreign-invested enterprises, English has become increasingly important. At the same time, a considerable number of overseas Chinese students have returned home in recent years, for they hold an optimistic outlook for the long-term growth of the Chinese economy. The Internet has strengthened the links between Chinese young people and those elsewhere. They follow the latest trend and copy foreign fashions. Some of them don’t seem to care for traditional Chinese virtues,let alone carry them forward, which has given rise to worries that the traditional Chinese culture might one day vanish.Unit 5VocabularyI.1. 1) In a way 2) in accordance with 3) vacancy 4) in good condition5) transparent 6) rub 7) spicy 8) hitherto 9) with (a) bad grace 10) instinct 11) pawned 12) current 2.1) turned up 2) will stick to 3) brought back 4)go about 5) driving at 6) put …away 7) turning …over 8) took …aback3. 1) has a very weak constitution --- she may not be able to survive the operation.2) was taken aback by the insurance company’s rejection of my compensation claim3) was something of a surprise when we ran into each other in a place like that.4) needs trimming/ to be trimmed ---it’s getting too long.5) are often deceptive4.1) Oddly en ough …went broke …wrinkled … he had gone all to pieces2) definite … is capable of …her vanity3) too mild … sipping … strokeII. Usage1. Except for2. except that3. except4. except when5. except to6. except what7. except where8. except thatComprehensive exercisesI. Cloze1.1) insane 2)current 3) candid 4) capable 5) was taken aback6) in good condition 7) constitution 8) go all to pieces 9)gone broke 10) vacancy 11) mild 12) deceptive2.1) suspected 2) pleading 3) confirmed 4) stunned 5) lucrative6) jewellery 7) wealthy 8) urge 9) spell 10) arrestedII.Translation1. 1) I have an instinct that Henry will seek to join the expedition, because he is something of an adventurer.2) He is capable of sticking to the task at hand, even if he is exposed to noises.3) The trademark was registered in accordance with the laws hitherto in force.4)Oddly enough, many people volunteered to help organize the meeting, but only a few turned up.5) The teacher’s affectionate words, along with his candid comments, changed the way Mike perceived the society and himself.2. For my own part, I find that appearances are all too often deceptive. For instance, you might be wrong if you judged by appearances only people like Edward Hyde Burton. In appearance, he seemed a man all of a piece. He was a tiny little fellow with white hair and mild blue eyes, gentle and candid. Nevertheless, he turned out to be very cruel. He insulted and fooled Lenny who was down and out and made him commit himself to an insane venture. What was still more surprising was that he was completely indifferent to Lenny’s death. Without doubt, Burton was a man with a heart of stone.Unit 6Vocabulary1. 1) appliances 2) comparative 3) multiply4) distribution5) prosperity 6) decorate7) famine8) large quantities of/ a large quantity of9) streamline10) fax11) pointed the way to 12) bewildered2. 1) eat into 2) cling to3) stand out/ stood out 4) wears away5) set about 6) switch off7) will be turned loose 8) poured in3. 1) is forecast to be below average next year, which at the moment is4 percent.2) to enter the building and find the baby girl proved futile as rescuers were driven out by the heat and flames.3) was urged to divert some of its attention from expanding production and get more involved with issues of market demand.4) can really eat heavily into your profits when you are selling suits at ￡900 and dresses at ￡2,000.5) has toiled endlessly over the exercise machine for the last twenty years in order to keep her body in shape.4. 1) reaction to… discontent… provoked2) C onvention… evading tax… the confines of3) a burden… are always on the go/ seem forever on the go… to copeII. Confusable Words1. 1) nervousness 2) tension 3) stress… stress 4) tension2. 1) honorary 2) Honorable 3) honorable4) honorary 5) honorable 6) HonoraryIII. Usage1) Dealing with the extinction crisis is no simple matter. Is it sensible, we may ask, to spend large sums of money to save some species – be it an elephant or an orchid – in a nation in which a large proportion of the population is living below the poverty line?2) This new technology could be used anywhere large numbers of people need to be quickly screened --- at airports, train stations, bus terminals or border crossings. However, experts suspect, there is also the risk that people will learn to fool the machine the same way they try to fool polygraph readings by controlling their breath or taking drugs to relax themselves.3) With a high percentage of marriages ending in divorce, often due to financial difficulties, you would say that money is a big factor in making a good marriage. But, believe it or not, it isn’t money that ensures youa happy marriage; it is your philosophy of life that does.4) Not all the risks on the Internet are sexual, you know. Sites promoting violence are just a click away, and may include instructions for making bombs and other destructive devices.Comprehensive Exercises1. 1) switch off 2) obliged 3) on the go 4) cope5) shortage 6) large quantity of 7) pouring in 8) by nature9) fraction 10) futile2. 1) advantage 2) wisely 3) faithfully4) waking 5) includes6) schedule7) sticking 8) priorities 9) set10) respectTranslation1. 1) They are exploring the new frontiers of medical science in an attempt to find remedies for incurable diseases/ cures for diseases that are beyond remedy so far.2) Her unique teaching methods apart, Ms Wilson, my math teacher, never tried to cram knowledge into my head.3) The regular weather forecast by the Central TV Station keeps us up with the changes of weather wherever we go on a trip.4) The appalling explosion started a big fire and caused the partial collapse of the building.5) In the modern world, there are more ways than ever to waste away time, and all kinds of distractions are eating into our precious time.2. Today we are under constant pressure to work longer hours, to produce more, and to possess more. Lots of people hold the wrong perception that happiness lies in working hard and earning well/ good money.Many women today feel the same stress to work and get ahead and, at the same time, to nurture their offspring and shoulder the burden of domestic responsibilities.Research shows that workaholism tends to distance us from our immediatefamilies. It forces us to toil longer and longer hours, leaving a minute fraction of our time to be physically and emotionally available to our loved ones. Intimacy among family members is doomed to die in the process.Unit 7Vocabulary:I.1. 1) divined 2) nerves 3) solidarity 4) sacred… mourn 5) coated6) perish 7) hijack 8) grief9) farewell 10) take revenge on 11) revolves 12) denounced 2. 1) drop… off2) applied for 3) went off 4) are gaining on5) bring down 6) blotted out 7) think back on 8) picking at3. 1) brought down the American housing market in 20082) what will happen after his son steps into his shoes?3) not in the mood to go out4) long before the market began to show signs of weakness5) mourn the loss of the tranquil life we had in the countryside 4. 1) in the aftermath of… to blot our… the tragic2) armed… at dust… accomplices… explosives3) in the space of… no illusionII. Collocation:1. a little of2. a few; most of / many of3. much4. few5. many6. many of7. much of8. little9. few of 10. Someage:1. As the boy grew older2. she sings as beautifully as a nightingale / sings like a nightingale3. they don’t see themselves as servants of the people4. As she had left her key in the office5. Just do as you are told6. Areas once regarded as rural7. as they do in China8. As he was brave and loyal as wellComprehensive Exercises:I. Cloze1. 1) mood 2) tragic 3) in the … aftermath of4) chaos 5) toppling 6) solidarity7) take revenge on8) thinking back on9) mourning 10) perished2. 1) crashed 2) horrible 3) harsh 4) protect 5) remove6) utterly 7) truly 8) justify 9) rewarded 10) devastatingII. Translation1. 1) Some high-ranking officers of the armed forces started a coup, toppling the government and throwing the country into chaos.2) The falling market shattered the illusion about getting rich quickly.3) Thinking back on the history of World War II, we can see that the formation of theAllies was the natural product of the development of political and military circumstances then.4) Paul felt stung when Jim called him a religious fanatic. But as he was in no mood for a quarrel/not in a quarreling mood, he simply pretended not to hear it.5) People say that time heals all wounds. But for those who have lost their loved ones in the event, will time fill up the void in their hearts?2. Today, long after the earthquake shook/hit my tometown, I can still recall, in crystal detail, what I saw as I ran out of my home with my parents. The building just across the street toppled right before our eyes, debris flew everywhere and a cloud of choking dust blotted out the sun. Horror-stricken people ran in all directions, crying and screaming. Now, many years after that tragic event, a new town has risen on the wreckage of the old one. In the town square, a memorial has been build to remember those killed in the disaster. It seems the wounds in people’s hearts have healed, but the memory will linger.Unit 8VocabularyI.1. 1) heap 2) was smeared 3) w armed 4) dissolve5) thrash 6) out of the w ay 7) hollows 8) tangled9) get his hands on 10) opaque11) at the edge of …illumined 12) hop2. 1) take…apart2) result from3) run out of 4) feed on5) come forward 6) woke up 7) focused on 8) set tled over3. 1) was dying to see the movie bases on it2) as a rule, the sheer distance mutes all sounds from the ground3) fuss too much over details4) slumped into anarmchair (feeling) completely exhausted5)was reputed to be the wittiest woman of her time4. 1) swarmed to…the spectacular…paddled2) in the heart of…out of the range of …trailing over … gliding in3) Day after day…strip…the heaving…slapII. Confusable Words1. 1) worth 2) worthy 3) wort hwhile4) worth…worth5) worthwhile 6) worthy2. 1) lone 2) alone 3) alon e4) lonely 5) lonely 6) alone…lonelyIII. Usage1. ice-cream2. teas3. wines 4 . cloth 5. soap6. beer7. fuels8. soils9. sugars10. grassComprehensive ExercisesI. Cloze1. 1) are dying to 2) in the heart of 3) tangled4) paddles5) loop 6) out of sight 7) in flocks 8) hopping9) gliding 10) opaque 11) th rashing 12) darting13) swarms 14) spectacular2.1) running 2) fancy 3) incorpo rate 4) exploring5) guide 6) adventure 7) r arely 8) diverse9) survive 10) luckyII. Translation1. 1) Janet was just the kind of girl Mike knew he could trust, so he bared his heart to her on their first date.2) At first the girls played on the fringe of the dark forest, now laughing, now screaming, but before long they were out of sight.3) The moment the football players disembarked from the plane, they sawa fleet of cars waiting for their arrival.4) Carson condemned his opponent for using misleading information to smear his character.5) Alex gave the policeman a wallet stuffed with banknotes. He said he had found it on the curb when he hopped off his school bus.2. Last Wednesday, my classmate Caroline and I visited Zhouzhuang, a well-known town looped all around by streams. When we arrived at the town, Caroline was so excited that she darted towards the first bridge she saw and began singing loudly there. Suddenly her voice hushed when she found that she had startled a flock of ducks not too far from us. Now as Caroline was dying for a boat ride, we decided to tour the town by boat. Now loud, now soft, Caroline talked to all the creatures in the stream and was fussing about everything while I looked at the boats gliding over the water in silence. Though we did not see anything spectacular, we enjoyed every minute in the town that lies out of the range of the heavy traffic and noise of the large city.Zhouzhuang is worth visiting and, time permitting, I’d like to go there again.。

高尿酸血症动物模型的建立及抗痛风中药的筛选解析

高尿酸血症动物模型的建立及抗痛风中药的筛选解析

山东大学博士学位论文高尿酸血症动物模型的建立及抗痛风中药的筛选姓名：刘文波申请学位级别：博士专业：内科学（风湿病学）指导教师：李兴福20080420山东大学博士学位论文符号说明英文缩写ＸＯＤＣＯＸ英文全称ｘａｎｔｈｉｎｅｏｘｉｄａｓｅｃｙｃｌｏｘｙｇｅｎａｓｅｉｎｔｅｒｌｅｕｋｉｎ．１中文全称黄嘌岭氧化酶环氧化酶白细胞介素１Ｂ肿瘤坏死因子Ｑ微晶型尿酸钠ＩＬ—ｌｐＴＮＦ．ａＢｔｕｍｏｒｎｅｃｒｏｓｉｓｆａｃｔｏｒ．ｎＭＳＵＵＡＯＡＮＳＡＩＤｓｍｏｎｏｓｏｄｉｕｍｕｒａｔｅｃｒｙｓｔａｌｕｒｉｃａｃｉｄｏｘｏｎｉｃａｃｉｄＮｏｎ．ｓｔｅｒｏｉｄａｌａｎｔｉ．．尿酸氧嗪酸非甾体抗炎药ｉｎｆｌａｍｍａｔｏｒｙｄｒｕｇＬＴＰＧＩｇＩｐｌｅｕｋｏｔｒｉｅｎｅｐｒｏｓｔａｇｌａｎｄｉｎｉｎｔｒａｇａｓｔｒｉｃａｄｍｉｎｉｓｔｒａｔｉｏｎｉｎｔｒａｐｅｒｉｔｏｎｅａＩｉｎｏｓｉｎｅ白细胞三烯前列腺素灌胃给药腹腔注射次黄嘌呤核苷酸５一磷酸核糖一１一焦磷酸花生四烯酸质量／电荷，质荷比表面增强激光解吸电离飞行时间质谱技术ｉｎｊｅｃｔｉｏｎＩＭＰＰＲＰＰｍｏｎｏｐｈｏｓｐｈａｔｅ５一Ｐｈｏｓｐｈｏｒｂｏｓｙｌ—ｌ－ｐｙｒｏｐｈｏｓ—ｐｈａｔｅＡＡａａｃｈｉｄｏｎｉｃａｃｉｄＭ／ＺＳＥＬＤＩ．ＴＯＦＭＳＭａｓｓ／ＣｈａｒｇｅＳｕｒｆａｃｅｅｎｈａｎｃｅｄｌａｓｅｒｄｅｓｏｒｐｔｉｏｎ／ｉｏｎｉｚａｔｉｏｎｔｉｍｅ－ｏｆ－ｆｌｉｇｈｔｍａｓｓｓｐｅｃｔｒｏｍｅｔｒｙｌｌ原创性声明本人郑重声明：所呈交的学位论文，是本人在导师的指导下，独立进行研究所取得的成果。

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论文作者签名：翻童遗Ｅｌ期：矽扎５．矽关于学位论文使用授权的声明本人完全了解山东大学有关保留、使用学位论文的规定，同意学校保留或向国家有关部门或机构送交论文的复印件和电子版，允许论文被查阅和借阅；本人授权山东大学可以将本学位论文的全部或部分内容编入有关数据库进行检索，可以采用影印、缩印或其他复制手段保存论文和汇编本学位论文。