Effects of Thermostable Phytaseon the Growth Performance and Nutrient Digestibility of Broilers

合集下载

波色气体

The ﬁnite temperature trapped dipolar Bose gasR.N.Bisset,D.Baillie,and P.B.BlakieJack Dodd Centre for Quantum Technology,Department of Physics,University of Otago,Dunedin,New Zealand.We develop a ﬁnite temperature Hartree theory for the trapped dipolar Bose gas.We use this theory to study thermal effects on the mechanical stability of the system and density oscillating condensate states.We present results for the stability phase diagram as a function of temperature and aspect ratio.In oblate traps above the critical temperature for condensation we ﬁnd that the Hartree theory predicts signiﬁcant stability enhancement over the semiclassical result.Below the critical temperature we ﬁnd that thermal effects are well described by accounting for the thermal depletion of the condensate.Our results also show that density oscillating condensate states occur over a range of interaction strengths that broadens with increasing temperature.PACS numbers:03.75.Hh,64.60.MyI.INTRODUCTIONA signiﬁcant new area of interest in ultra-cold atomic gases is the study of systems in which the particles interact via a dipole-dipole interaction (DDI)[1].This interest is be-ing driven by a broad range of proposed applications from condensed matter physics to quantum information,e.g.see [2].Experimental progress in the quantum degenerate regime has been driven by seminal work with 52Cr [3],which was Bose condensed in 2005,and more recently the realization of Bose-Einstein condensates of 164Dy [4]and 168Er [5].Po-lar molecules,which have DDIs several orders of magnitude larger than those of the atomic gases,have already been pro-duced in their ground rovibrational state [6,7],and steady progress is being made towards cooling these into the degen-erate regime.We also note the recent achievement of a degen-erate Fermi gas of 161Dy [8].The DDI is long-ranged and anisotropic with both attractive and repulsive components.Therefore,an important consider-ation is under what conditions the system is mechanically sta-ble from collapse to a high density state.Theoretical studies on zero temperature dipolar condensates reveal a rich stabil-ity diagram where,due to the DDI anisotropy,the stability is strongly dependent on the geometry of the trapping potential and the properties of the short ranged (contact)interactions [9–12].Another interesting theoretical observation is that for appropriate parameters (near instability)the condensate mode exhibits spatial oscillations and has a density maximum away from the minimum of the trapping potential [11–14].How-ever,evidence for this density oscillating state has yet to be observed in experiment.In this work we study the properties of a trapped dipolar Bose gas at ﬁnite temperature –a regime largely unexplored in theory and experiments.In previous work [15]we stud-ied the stability of a normal Bose gas (i.e.above T c )using a self-consistent semiclassical approximation.In this work we extend this study to below T c and to include quantum pressure (i.e.beyond-semiclassical effects)by numerically solving for the condensate and its ing this theory we study the crossover from the high temperature (above T c )to zero temperature (pure condensate)stability.Our results reveal that beyond semiclassical effects play a signiﬁcant role above T c in oblate geometry traps and enhance the stability region,andthat the double instability phase diagram in this trap geome-try (predicted in [15])remains prominent.We also study the behavior of the emergent biconcave condensate (density oscil-lating ground state)in the ﬁnite temperature regime,and ﬁnd that thermal effects enhance the density oscillation and en-large the parameter regime over which this type of state exists.We demonstrate that the below T c temperature dependence of the stability boundary is well-characterized by a simple model that accounts for the thermal depletion of the condensate.II.FORMALISM AND NUMERICAL IMPLEMENTATIONA.FormalismHere we consider a set of particles of mass M conﬁned in a cylindrically symmetric harmonic potentialU tr (x )=12M [ω2ρ(x 2+y 2)+ω2z z 2],(1)of aspect ratio λ=ωz /ωρ,with z and ρrepresenting the axial and radial directions,respectively.We take the particles to have dipole moments polarized along the z axis by an external ﬁeld,such that the DDI potential between particles isU dd (r )=C dd 4π1−3cos 2θ|r |,(2)where C dd =µ0µ2(=d 2/ 0)is the magnetic (electric)dipole-dipole interaction strength and θis the angle between the z di-rection and the relative separation of the dipoles (r =x −x ).It is easy to extend our calculations to include local (con-tact)interactions,however here we focus on the case of pure dipole-dipole interactions,as has been realized in experiments by use of a Feshbach resonance (e.g.see [16]).The Hartree formalism we employ (see Appendix A for a discussion of the relation to Hartree-Fock theory and relevant terms neglected)involves solving for the system modes using the non-local equationj u j (x )= − 22M∇2+V eﬀ(x )u j (x ),(3)a r X i v :1207.1929v 1 [c o n d -m a t .q u a n t -g a s ] 9 J u l 20122whereV eﬀ(x )=U tr (x )+d x U dd (x −x )n (x ),(4)n (x )=jN j |u j (x )|2,(5)are the effective potential and total density,respectively,with N j =[e β( j −µ)−1]−1the equilibrium (Bose-Einstein)oc-cupation of the mode,β=1/k B T the inverse temperature,and µthe chemical potential.Equations (3)-(5)are solved self-consistently while the chemical potential is adjusted to ensure that the desired total number N = d 3x n (x )is ob-tained.Below the critical temperature T c a condensate forms in the lowest mode u 0(x )with N 0∼N ,but the theory,as written in Eqs.(3)-(5),requires no additional adjustment to account for the condensate (due to our neglect of exchange)and smoothly transitions across T c .We emphasize that our motivation for using this theory is that it includes the domi-nant direct interactions and the full discrete character of the low energy modes,yet is more computationally efﬁcient than Bogoliubov-based approaches.This enables us to study chal-lenging problems that have not been explored,in particular ﬁ-nite temperature mechanical stability,in which obtaining con-vergent self-consistent solutions is demanding and time con-suming.Our numerical approach builds on various develop-ments (particularly those described in [17])and includes a number of features to aid calculations in the ﬁnite tempera-ture regime where interaction effects dominate (see Appendix B for details).The neglect of dipole exchange is consistent with other work on ﬁnite temperature bosons [18]and zero temperature studies of fermion stability [19].We would like to note that there is some justiﬁcation for this approximation.Studies on a normal trapped dipolar Fermi gas suggest that exchange inter-actions will quantitatively,but not qualitatively,affect stabil-ity [19,20].Indeed,the thermodynamic study of that system presented in [21]found that exchange interactions are typi-cally less important than direct interactions except for traps that are close to being isotropic.Similarly,Ticknor studied the quasi-two-dimensional Bose gas using the Hartree-Fock-Bogoliubov-Popov (HFBP)meanﬁeld theory [22]and found that exchange terms were generally less important than direct terms.III.RESULTSA.Comparison to previous calculationsTo benchmark our Hartree calculations we perform a quan-titative comparison to the HFBP calculations that Ronen et al.[18]performed for the three-dimensional trapped Bose gas at ﬁnite temperature.In Secs.III A 1and III A 2we make this comparison for two different sets of results from [18].We note that those HFBP calculations excluded thermal exchange interactions,although they did include condensate exchange interactions (exchange interaction of condensateatoms on the thermal excitations)[23].We extended ourHartree algorithm to include condensate exchange but found it made negligible difference to the predictions and do not in-clude results with this term here.1.Condensate FractionThe results of the ﬁrst comparison we perform are presented in Fig.1(a).There we compare the condensate fraction,as a function of temperature,for a system with λ=7.We ob-serve that the Hartree and HFBP theories predict an appre-ciably lower condensate fraction than the ideal case,and are in very good agreement with each other over the full tem-perature range considered.The low energy excitations of a Bose-Einstein condensate are quasi-particles,which are ac-curately described by Bogoliubov theory (such as the HFBP theory),however the thermodynamic properties of the system are dominated by the single particle modes (e.g.see [24]).A comparison of the Bogoliubov and Hartree-Fock spectra of a T =0dipolar Bose-Einstein condensate (BEC)was made in [17].That comparison revealed that the spectra were al-most identical,except for low energy modes with low values of angular momentum,where small differences in the modeFIG.1.(a)Condensate fraction and (b)density oscillation contrast (see text)for a dipolar BEC in a λ=7pancake trap.Hartree re-sults (pluses),HFBP results (solid lines),ideal gas result (dashed line).HFBP data corresponds to results shown in Figs.5and 6of Ref.[18].Other parameters:{ωρ,ωz }=2π×{100,700}s −1,N =16.3×10352Cr atoms with contact interactions tuned tozero.T 0c =3 N/ζ(3) ω/k B is the ideal condensation tempera-ture,where ω=3 ω2ρωz and ζ(α)is the Riemann zeta function with ζ(3)≈1.202.2.Density Oscillating Ground StatesAn interesting feature of dipolar condensates is the occur-rence of ground states with density oscillation features,where the condensate density has a local minimum at trap center.For3 a cylindrically symmetric trap these states are biconcave(redblood cell shaped–surfaces of constant density are shown inFig.6)ﬁrst predicted for T=0condensates in Ref.[11].In the purely dipolar case such biconcave states occur undercertain conditions of trap and dipole parameters,but notablyonly forλ 6and for dipole strengths close to instability.In[18]the HFBP technique was used to assess the effect oftemperature on the density oscillating states.This was char-acterized by the contrast,a measure of the magnitude of thedensity oscillation,deﬁned asc=1−n(0)n max,(6)where n(0)is the density at trap center and n max is the maxi-mum density of the system.In Fig.1(b)we compare our Hartree and HFBP theories for the contrast.This comparison reveals some small residual dif-ferences between the theories,however the results are in rea-sonable agreement and both predict that the contrast goes to zero(i.e.the condensate returns to having maximum density at trap center)at T≈0.65T0c.B.Mechanical stabilityOurﬁrst application of the Hartree theory is to study the ﬁnite temperature mechanical stability of a trapped dipolar Bose gas.To do this we construct a phase diagram for the range of dipole strengths for which the gas is stable for a num-ber of different trap geometries.Such stability properties,and the dependence on interactions and trap geometry,have been measured accurately in the dipolar system in the zero temper-ature limit(e.g.see[16]).We note theoretical studies[25–27] showing the important role of temperature on the observed stability of7Li condensates[28],which have an attractive con-tact interaction.1.Locating the stability boundaryWe consider a trapped sample ofﬁxed mean number N and wish to determine the values of the dipole interaction param-eter for which the system is mechanically stable as a function of temperature.In doing so we construct a phase diagram in{C dd,T}-space that indicates the stable region.In prac-tice we locate the stability boundary(i.e.a curve)that sep-arates the stable and unstable regions.Our procedure to ob-tain this boundary involves a computationally intensive search through parameter space toﬁnd the self-consistent solutions on the verge of instability.Determining the stability boundary forﬁxed mean number N complicates this process:since we work in the grand-canonical ensemble where the proper vari-ables are{µ,C dd,T},an additional iterative search over the parameterµis required toﬁx N to the desired target number. In Fig.2we provide some examples to illustrate how we identify the value of the DDI at the stability boundary for a gas with(target number)N=2×105atoms at a particularFIG.2.Locating instability(upper subplots):(a)The total num-ber of atoms of the self-consistent Hartree solution versus chem-ical potential forλ=1/8,k B T=40 ωand C dd=7×10−4 ωa3ho(dashed,case A),1.5×10−4 ωa3ho(solid,case B), with a ho=Each line terminates at the point of in-stability and occurs at the respective critical number N crit.(b) Same results as in(a)but plotted against 0−µ.The dotted line represents the target number,in this case N=2×105.Den-sity Proﬁles(lower subplots):Solid(dashed)line represents the ra-dial(axial)density n,higher curves are near the stability bound-ary.λ=1,N=2×105.(c)T/T0c=0.82(N0/N≈0.43) and C dd/4πC0={3.65×10−4(gray),1.83×10−4(black)}.(d)T/T0c=1.27and C dd/4πC0={2.91(gray),1.22(black)}. We have introduced the interaction strength unit C0= ωa3ho/6√N which is convenient for cases where N isﬁxed,and allows our sub-sequent results to be directly compared to those in[15].temperature.To do this we show the dependence of total atom number onµfor two different values of the DDI[Fig.2(a)]. For both curves the total number increases as we move along these curves until some maximum value N crit is reached at which the system becomes unstable.The non-monotonic be-havior of these curves arises because the ground state energy 0changes as the number of atoms increases,and hence the role of DDIs increases.For this reason we also show the same two cases,but as a function of 0−µ,in Fig.2(b).The sharp cusps in Figs.2(a)and(b)correspond to the point where the system condenses[i.e.where 0−µ≈0].The dependence of 0on N0is strongly dependent on the trap ge-ometry,and for the cases we consider here withλ=1/8, 0 decreases with increasing N0.This is because the head-to-tail character,in the cigar geometry,emphasizes the attractive part of the DDI so that as the condensate number increases, 0 (≈µ)decreases.a stringent numerical task and requires careful convergence tests.For condensates with contact interactions this type of numerical instability analysis was applied in Refs.[25–27](also see Ref.[15]).In Fig.2(a)the instability point occurs at the end of the upper horizontal plateau in the N versus µcurves (compare to Fig.1of [25]).We show examples of the spatial density proﬁles for a spherical trap in Figs.2(c)and (d).The system considered in Fig.2(c)is condensed,while that considered in Fig.2(d)is above the critical temperature.For both cases a result is shown that is well inside the stable region (black curves)and near the stability boundary (gray curves).Despite a large difference in the density scales of the two regimes they both exhibit a similar sharpening of the density proﬁle near instability.An additional consideration emerges for stability calcula-tions below T c in regimes where the condensate is in a density oscillating state.Here the ﬁrst mode to go soft (and then de-velop imaginary parts)as the stability boundary is reached is a m =0quasi-particle mode [29],where m is the angular mo-mentum projection quantum number (so called angular roton mode [11]).This instability is not revealed in the Hartree exci-tations,and as we solve for the condensate in the m =0space (see Appendix B),the condensate does not exhibit numerical instability.Thus in cases where the condensate exhibits a den-sity oscillating state we perform a Bogoliubov analysis of the condensate mode (within the effective potential of the self-consistent Hartree solution)to determine if any m =0modes have become unstable [30].2.Stability above T cIn Fig.3we show our results for the stability of the normal phase.In previous work we examined this regime using a semiclassical Hartree approach in which the density isn (x )=λ−3dB ζ3/2 e β[µ−V eff (x )],(7)where V eﬀ(x )is the effective potential calculated using n (x )[see Eq.(4)],ζα(z )= ∞j =1z j /j αis the Bose function,andλdB =h/√2πMk B T .The semiclassical results are shown as solid lines in Fig.3.FIG.3.(Color online)Stability regions in DDI-temperature space.Shaded regions indicate stability for each geometry,from top to bot-tom λ={8,4,2,1,1/2,1/8},the geometric mean trap frequency is ﬁxed and N =2×105.Actual data points represented by symbols while the shading of the stable regions interpolates to guide the eye,the semiclassical model is given by the solid curves.Error bars rep-resent the 1σspread in the convergence test (see Appendix B 3for more details).We observe that as a general trend the stability region grows with increasing λ.The strong geometry dependence of these results arises from the anisotropy of the dipole interaction:In oblate geometries (λ>1)the dipoles are predominantly side-by-side and interact repulsively (stabilizing),whereas in pro-late geometries (λ<1)the attractive (destabilizing)head-to-tail interaction of the dipoles dominates (a similar geometry dependence is observed for the stability of T =0dipolar con-densates [11,12]).A primary concern is the nature of beyond semiclassi-cal effects,i.e.what differences emerge from our diagonal-ized Hartree theory over the semiclassical formulation.Most prominently in the results of Fig.3we observe that while the Hartree and semiclassical stability boundaries are in good agreement for prolate geometries,in oblate traps the Hartree results are signiﬁcantly more stable.This difference between the boundaries predicted by the two theories increases with increasing λ.This observation is surprising because our cal-culation is for a rather large number of atoms (N =2×105),where the semiclassical approximation would normally be ex-pected to furnish an accurate description of the above T c be-havior.We attribute this failure of the semiclassical theory to its inappropriate treatment of the interactions between the low energy modes [31].The nature of the DDI,when tightly con-ﬁned along the polarization direction,has been extensively studied in application to pure BECs [14,32],where it has been shown that it confers additional stability on the system,as veriﬁed in recent experiments [33].This arises from a con-ﬁnement induced momentum dependence of the interaction:the interaction is repulsive (stabilizing)for low momentum interactions,but decays to being attractive with a character-istic wavevector k ∼1/a z set by the z conﬁnement length5a z=zNotably these features of the conﬁned inter-action mediate BEC instability through the softening of radi-ally excited modes with a wavelength∼a z[32,34–37].It is not clear that these conﬁnement effects will be applica-ble at a modestly oblate trap withλ=8,however numerical studies have revealed that quasi-particle modes with a wave-length∼a z soften in a BEC withλ=7[11].Within the limited range of results we have forλ>1we see evidence consistent with conﬁnement induced effects playing an impor-tant role in the above T c Hartree calculations.Notably,that the relative difference between the stability boundaries of the Hartree and semiclassical calculations scale with1/a2z.Also, when the system is unstable,during the self-consistency it-erations(prior to collapse)strong radial densityﬂuctuations develop in the systemA key prediction from our semiclassical study[15]is a dou-ble instability feature in oblate trapping geometries arising from the interplay of thermal gas saturation and the anisotropy of the DDI.Our Hartree calculations in this oblate regime, despite shifting the stability boundary from the semiclassical prediction by a considerable amount,reveal that the double instability feature is robust to beyond-semiclassical effects.A prominent feature of the semiclassical calculation is that the stability curves for the purely dipolar gas terminate at the critical point with C dd=0(i.e.predicting that without con-tact interactions only an ideal gas is stable below T c).This oc-curs because the local compressibility at trap center diverges at the critical point and the gas is unstable to any attractive in-teraction(see[15]).In the beyond-semiclassical calculations the trap provides aﬁnite momentum cutoff that prevents the divergence of compressibility,and thus the system has aﬁ-nite residual stability at and below T c(which we consider in Sec.III B3).3.Stability below T cIn Fig.4we consider the stability below T c where the semi-classical model does not apply.These results are identical to those shown in Fig.3,but the below T c details are revealed us-ing a logarithmic vertical pared to the above T c gas the condensate is rather fragile,with the critical DDI strength deﬁning the stability boundary decreasing by∼3to4orders of magnitude.In the zero temperature limit our results agree with previ-ous calculations based on solving the Gross-Pitaevskii equa-tion[11].This agreement is expected as the two theories are identical when the excited modes have vanishing population. For a pure condensate,the critical DDI strength depends on the condensate number and trap geometry according to[11]C dd=F(λ)N0,(T=0)(8)with F(λ)a rather interesting function of trap geometry alone, as characterized in Fig.1of[11][41].More generally,beyond the case of pure DDIs,F also depends on the contact interac-tion strength,e.g.see[12,37].FIG.5.(Color online)Stability boundary scaling.The stability boundary results(symbols)have been taken from Fig.4forλ= {8,1,1/8}(top to bottom).Dashed line prediction is based on a non-interacting N0scaling(see text)and the solid line uses the N0calcu-lated from the Hartree solutions.As temperature increases,but focusing on T<T0c,we ob-serve in Fig.4that the stability boundary increases signiﬁ-cantly.This occurs because as the temperature increases the condensate is thermally depleted.Indeed,by simply account-ing for the thermal depletion we can immediately extend result(8)to predict the critical value of the DDI atﬁnite temperatureC dd(T):C dd(T)=F(λ)N0(T)=C dd(0)NN0(T),(9)where the last expression is obtained using N0(T=0)=N. Equation(9)predicts that the stability atﬁnite temperaturewas in Ref.[18][which we reproduce in Fig.1(b)].That study considered a single line (at ﬁxed C dd and N and varying T )through the phase diagram,and showed that biconcavity per-sisted at small ﬁnite temperatures (T 0.25T 0c ),but then was rapidly washed out as temperature increased further.Using our Hartree theory we provide a broad characteriza-tion of the thermal effects on biconcavity.We focus on the case λ=8,which supports a biconcave condensate at T =0.In Fig.6(a)we present contours of biconcave contrast [as de-ﬁned in Eq.(6)]over the entire range of parameters where this state is stable.These results show that biconcavity is not destroyed as temperature increases.Instead the parameter re-gion over which biconcavity occurs grows,with large bicon-cave contrasts emerging at higher temperature.The general trends seen can be understood by considering the thermal de-pletion of the condensate,using similar arguments to those made to obtain Eq.(9):as the temperature increases the value of C dd required for the condensate to exhibit a biconcave den-sity proﬁle should increase in a manner that is approximately inversely proportional to the condensate occupation.Thus,the washing out observed in [18][our Fig.1(b)]arises because they considered C dd ﬁxed.Thermal depletion of the conden-sate is not sufﬁcient to explain all aspects observed in our re-sults,e.g.the deepening of the biconcave contrast that devel-ops at higher temperatures in Fig.6(a).This arises from ad-ditional effects of the thermal interaction with the condensate,e.g.small changes in the aspect ratio of the effective poten-tial that the condensate experiences can signiﬁcantly changeeral trends seen can be understood by considering the ther-mal depletion of the condensate,using similar arguments to those made to obtain Eq.(9):as the temperature increases a the value of C dd required for the condensate to exhibit a bi-concave density proﬁle should increase in a manner that is approximately inversely proportional to the condensate occu-pation.Thus,the washing out observed in [18][our Fig.1(b)]arises because they considered C dd ﬁxed.Thermal depletion of the condensate is not sufﬁcient to explain all aspects ob-served,e.g.the deepening of the biconcave contrast.This arises from additional effects of the thermal interaction with the condensate,e.g.small changes in the aspect ratio of the ef-fective potential from the condensate can signiﬁcantly change the contrast (c.f.Fig.1of Ref.[11]).In Fig.6(lower)we show two examples of the biconcave density proﬁles at different temperatures.Case B displays the very pronounced biconcavity for a system at T ≈0.9T 0c ,where the condensate fraction is N 0/N ≈0.07.IV .CONCLUSIONSIn this paper we have developed a Hartree theory for a trapped dipolar Bose gas that can be applied to make predic-tions above and below the critical temperature T c for conden-sation.We have used this theory to quantify the role of ther-mal ﬂuctuations on the mechanical stability of the cloud,and present results for the stability phase diagram as a function of 6810ρ/a h o(b)FIG.6.(Color online)Biconcave characteristics for λ=8and N =2×105at ﬁnite temperature.(a)Stability diagram for λ=8from Fig.3with biconcave contrast contours {0,0.05,0.1,0.15,0.2,0.25}(bottom to top)added.The solid curves are interpolations be-tween the calculated contours points.The white dotted line marks where we terminate the contours due to the condensate fraction be-coming negligibly small.Triangles indicate the stability boundary from Fig.5.Inset:Magniﬁcation of the high temperature region.(b)Radial densities for phase space points marked by A and B of the upper ﬁgure.A:T/T 0c=0.0910,C dd /4πC 0=0.00268and N 0/N =1.00(thermal depletion <1%).B:T/T 0c =0.910,C dd/4πC 0=0.0291and N 0/N =0.0716.Solid (dashed)lines represent the total (condensate)density.Insets:corresponding sur-face contour at 67%of the peak density.temperature and aspect ratio.Our results show that the ther-mal depletion of the condensate can lead to an enhancement of the parameter regime over which biconcave density oscil-lations are found.Furthermore,a large thermal cloud may actually enhance the biconcave contrast making direct imag-ing of an in situ blood cell more feasible,see Fig.6(lower).Above T c we ﬁnd that the results of our theory predict signif-icant corrections to the stability boundary over the equivalent Hartree semiclassical theory.Most notably,the semiclassical theory underestimates the size of the stability region for oblate FIG.6.(Color online)Biconcave characteristics for λ=8and N =2×105at ﬁnite temperature.(a)Stability diagram with bi-concave contrast contours {0,0.05,0.1,0.15,0.2,0.25}(bottom to top)added.The solid curves are interpolations between the cal-culated contour points.The white dotted line marks where we ter-minate the contours due to the condensate fraction becoming negli-gibly small.Triangles indicate the stability boundary from Fig.4.Inset:Magniﬁcation of the high temperature region.(b)Radial densities for phase space points marked by A and B in (a).A:T/T 0c =0.0910,C dd /4πC 0=0.00268and N 0/N =1.00(ther-mal depletion <1%).B:T/T 0c =0.910,C dd /4πC 0=0.0291and N 0/N =0.0716.Solid (dashed)lines represent the total (conden-sate)density.Insets:corresponding surface contours at 67%of the peak density.the contrast (c.f.the strong dependence of biconcavity on trap aspect ratio near λ=8in Fig.1of Ref.[11]).In Fig.6(b)we show two examples of the biconcave density proﬁles at different temperatures.Case B displays the verypronounced biconcavity for a system at T ≈0.9T 0c ,wherethe condensate fraction is N 0/N ≈0.07.IV .CONCLUSIONSIn this paper we have developed a Hartree theory for a trapped dipolar Bose gas that can be applied to make predic-。

The Effect of pH on the Solubility of Salts

The Effect of pH on the Solubility ofSaltsHave you ever wondered why sugar easily dissolves in water, while salt seems to require more effort? Or why some substances dissolve better in acidic solutions, while others dissolve better in alkaline solutions? The answer lies in the effect of pH on the solubility of salts. In this article, we will explore the science behind this phenomenon and its practical applications.Understanding the BasicsBefore delving into the specifics, it is important to understand the concept of solubility. Solubility refers to the ability of a substance (known as the solute) to dissolve in another substance (known as the solvent) to form a homogeneous mixture. The degree of solubility is affected by various factors, such as temperature, pressure, and the chemical nature of the solute and solvent.Salt is a common example of a solute that can be dissolved in water, which is a common polar solvent. Salts are composed of positively charged ions (known as cations) and negatively charged ions (known as anions), which are held together by electrostatic forces. When salt is added to water, the polar nature of water molecules attracts the ions, causing the salt crystals to dissociate into their constituent ions.The degree of dissociation can be quantified using the concept of molarity, which refers to the number of moles of solute per liter of solution. The molarity of a solution depends on the quantity of solute added, as well as its solubility in the solvent. Salts that are highly soluble in water, such as sodium chloride (NaCl), have a high molarity at saturation (i.e., the point at which no more solute can be dissolved in the solution).The Effect of pHThe pH of a solution is a measure of its acidity or alkalinity, based on the concentration of hydrogen ions (H+) in the solution. Acids have a high concentration ofH+ ions, while bases (alkaline solutions) have a low concentration of H+ ions. The pH scale ranges from 0 (very acidic) to 14 (very alkaline), with 7 being neutral (pure water has a pH of 7).The effect of pH on the solubility of salts depends on the nature of the salt. Some salts are more soluble in acidic solutions, while others are more soluble in alkaline solutions. This is due to the fact that the pH affects the degree of ionization of the salt.For example, consider the salt calcium carbonate (CaCO3), which is found in limestone and coral reefs. In its pure form, it is insoluble in water. However, in acidic solutions, it can be dissolved by the reaction:CaCO3 + 2H+ → Ca2+ + CO2 + H2OThe acidity of the solution causes the H+ ions to react with the carbonate ion (CO32-) in the salt, forming carbonic acid (H2CO3) and releasing carbon dioxide (CO2) gas. This reaction effectively increases the concentration of Ca2+ ions in the solution, making it more soluble.On the other hand, some salts are more soluble in alkaline solutions. For example, iron(III) hydroxide (Fe(OH)3) is insoluble in neutral or acidic solutions, but can be dissolved in alkaline solutions, according to the reaction:Fe(OH)3 + OH- → [Fe(OH)4]-The alkalinity of the solution causes the hydroxide ions (OH-) to react with theiron(III) ions in the salt, forming the complex ion [Fe(OH)4]-, which is soluble in water.Applications in Science and IndustryThe effect of pH on the solubility of salts has important implications in various fields of science and industry. For example, in agriculture, the pH of the soil affects the availability of nutrients to plants, as certain nutrients may be more soluble in acidic or alkaline soils. The pH of water sources also affects the solubility of pollutants, such as heavy metals, which can be harmful to aquatic organisms.In the pharmaceutical industry, the solubility of drugs can be enhanced by adjusting the pH of the solution in which they are administered. This can improve their bioavailability (i.e., the percentage of the drug that is absorbed into the bloodstream), making them more effective.In conclusion, the effect of pH on the solubility of salts is a fascinating topic that highlights the dynamic nature of chemical reactions. By understanding the principles behind this phenomenon, we can make use of it to solve practical problems and improve our daily lives.。

遵义2024年10版小学Y卷英语第二单元全练全测(含答案)

遵义2024年10版小学英语第二单元全练全测(含答案)考试时间：80分钟（总分:120）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题共100分)1. 填空题：A frog has long _______ for jumping.2. 选择题：What do you call the place where we buy groceries?A. RestaurantB. Grocery storeC. SchoolD. Library3. 填空题：The salmon swims upstream to lay its ______ (卵).4. 填空题：My toy ________ is very colorful.5. 听力题：Photosynthesis uses sunlight to convert carbon dioxide and water into _____.6. 听力题：The teacher is _____ the students to listen. (asking)7. 填空题：The _____ (植物象征) can represent cultural meanings.8. 听力题：The chemical formula for capsaicin is ______.9. 听力题：In a chemical reaction, products are formed from ________.10. 填空题：In the fall, the leaves turn ________ (红色) and ________ (黄色). It looks very ________ (美丽).11. 选择题：What is the main ingredient in bread?A. RiceB. FlourC. SugarD. Yeast答案:B12. 听力题：The chemical formula for zinc oxide is _____.13. 听力题：The Earth’s axial tilt causes the ______ of the seasons.14. 选择题：What is 30 divided by 6?A. 4B. 5C. 6D. 715. 听力题：The sun is shining ___. (brightly)16. 选择题：Which of these is a type of pasta?A. RiceB. TortelliniC. BreadD. Cake17. 听力题：She is _______ (climbing) the stairs.18. 听力题：A __________ is a measure of how tightly packed particles are in a substance.19. 选择题：What do we use to read?A. BookB. SpoonC. PlateD. Cup答案:A20. 填空题：The __________ (历史的多重解读) enriches narratives.21. 选择题：What do you call a story that is made up?A. FactB. FictionC. BiographyD. History答案: B22. 填空题：The parrot has a curved _________ (喙).23. 听力题：A chemical equation can be used to predict the products of a ______.24. 填空题：The __________ (历史的影响) shapes our world.25. 填空题：The tortoise is very _______ (慢).26. 听力题：The girl sings very ________.27. 听力题：We planted flowers in the ___. (garden)28. 选择题：What do you call a person who studies human behavior?A. PsychologistB. SociologistC. AnthropologistD. Historian29. 听力题：A shadow is formed when light is ______.30. 选择题：What is the name of the story about a girl who befriends seven dwarfs?A. CinderellaB. Snow WhiteC. RapunzelD. Aladdin答案: B31. 听力题：A mineral's hardness is measured on the ______ scale.32. 听力题：A _______ is formed when two or more atoms bond together.33. 听力题：My uncle is a great ____ (listener).34. 选择题：What do you call a young turaco?A. ChickB. KitC. PupD. Calf35. 填空题：The tortoise is slow but very _______ (坚韧).36. 听力题：The color of a substance is a physical ______.37. 选择题：What is the main ingredient in mashed potatoes?a. Riceb. Potatoesc. Cornd. Carrots答案:B38. 填空题：The __________ (历史的教学) guides our learning.39. 填空题：My best friend's little sister is very _______ (形容词). 她总是 _______ (动词).40. 填空题：My favorite thing to do on a rainy day is _______ (阅读).41. 填空题：My grandfather was a ____.The chemical symbol for iron is __________.43. 选择题：What is the capital of Slovakia?A. PragueB. BratislavaC. BudapestD. Ljubljana答案:B. Bratislava44. 填空题：My ________ (玩具名称) helps me with my math skills.45. 听力题：The ____ has bright eyes and can see well at night.46. 选择题：What do we call a group of lions?A. PackB. PrideC. FlockD. School47. 填空题：I love my __________ (玩具名) because it is __________ (形容词).48. 选择题：Which animal is known for its ability to change color?A. ChameleonB. ElephantC. DogD. Cat答案:A49. 填空题：This boy, ______ (这个男孩), loves to draw cartoons.50. 选择题：What is the name of the ocean that is the largest?A. AtlanticB. IndianC. ArcticD. PacificThe main component of the human body is __________.52. 填空题：The first people to fly were the _______ brothers. (莱特)53. 听力题：A mixture can be separated through physical _______.54. 选择题：What is 15 divided by 5?A. 2B. 3C. 4D. 5答案: B55. 选择题：What is the name of the famous detective created by Arthur Conan Doyle?A. Hercule PoirotB. Sherlock HolmesC. Miss MarpleD. Sam Spade答案:B56. 听力题：The chemical symbol for hafnium is __________.57. 选择题：What do you call a baby dog?A. KittenB. PuppyC. CubD. Calf答案:B58. 听力题：A __________ is formed by the action of glaciers.59. 听力题：The chemical formula for ammonia is ________.60. 选择题：What is the freezing point of water?A. 0°CB. 50°CC. 100°CD. 25°C答案:A61. 填空题：The __________ (历史的多样性) enriches dialogue.62. 填空题：My sister loves to _______ (动词) in the park. 我们常常一起 _______ (动词).63. 听力题：A chemical reaction that produces heat is called a ______ reaction.64. 听力题：The chemical symbol for neon is ______.65. 选择题：Which one is not a fruit?A. AppleB. CarrotC. BananaD. Orange答案: B66. 选择题：What do you call a group of birds?A. FlockB. SwarmC. SchoolD. Pack答案:A67. 听力题：A polymer is a large molecule made up of many ______.68. 听力题：I can ___ (jump) really high.69. 听力题：The ____ hops around and loves to explore.70. 填空题：My friend is very __________ (好奇的) about the world.71. island) is surrounded by water on all sides. 填空题：The ____A _____ (小狗) loves to go for walks with its owner.73. 选择题：What do we call the process of converting solid into liquid?A. FreezingB. MeltingC. EvaporatingD. Condensing答案:B74. 填空题：My favorite dish is ______ (汤).75. 选择题：What is the name of the famous American rock band known for hits like "Hotel California"?A. The EaglesB. Fleetwood MacC. Led ZeppelinD. The Rolling Stones答案: A. The Eagles76. 听力题：The ____ is known for its beautiful singing voice.77. 填空题：My sister has a fluffy _______ (我妹妹有一只毛茸茸的_______).78. 填空题：She is _______ (喜欢) to draw.79. 填空题：The chicken lays ______ (蛋) every day.80. 填空题：A hamster gathers food in its ______ (窝).81. 选择题：What do we call the outer layer of the Earth?A. CoreB. MantleC. CrustD. BedrockThe arrangement of atoms in a molecule is known as its _____ structure.83. 听力题：The chemical formula for zinc oxide is __________.84. 填空题：I love animals, especially ______ (狗) and ______ (猫). They are great companions and bring ______ (快乐) to our lives.85. 填空题：The __________ (历史的影响) shapes perceptions.86. 听力题：The _______ can be found in many colors.87. 填空题：When I grow up, I want to work in the ________ (名词) industry.88. 填空题：My grandpa shares his wisdom about ____.89. 填空题：My dad is a __________ (市场分析师).90. 选择题：What do we use to write on paper?A. BrushB. PenC. KnifeD. Ruler91. 填空题：The rabbit hops on the _______ (兔子在_______上跳).92. 选择题：What do you call a person who studies the stars?A. AstronomerB. AstrologerC. ScientistD. All of the above答案:A93. 填空题：The ________ is a good friend.94. 选择题：Which word means "not heavy"?A. LightB. HeavyC. BurdensomeD. Weighty95. 选择题：What is the opposite of big?A. SmallB. LargeC. HugeD. Tall96. 选择题：What do we call the process of a caterpillar becoming a butterfly?a. Metamorphosisb. Evolutionc. Growthd. Development答案:a97. 填空题：I carry a water bottle on hot ______ (日子).98. 填空题：The kitten chases a ______.99. 听力题：The capital of Malta is __________.100. 听力题：The chemical formula for ammonium nitrate is __________.。

The Effect of Temperature on Protein Conformation

The Effect of Temperature on ProteinConformationProteins are essential components of living organisms and are responsible for carrying out various cellular functions. They are composed of long chains of amino acids that are folded into intricate 3-dimensional structures. The specific shape of a protein, or its conformation, plays a critical role in its function. Temperature is one of the key factors that can influence protein conformation. In this article, we will explore the effect of temperature on protein conformation and how it impacts their function.Temperature-induced protein denaturationProtein denaturation is a process in which the protein loses its native conformation and unfolds into a linear or random coil structure. This process can be triggered by several factors, including pH, salts, mechanical stress, and temperature. Among these, temperature is the most commonly studied factor that can induce protein denaturation.When proteins are exposed to high temperatures, the thermal energy causes the bonds that hold the protein structure together to break. Hydrogen bonds, which are weaker than covalent bonds, are the first to be broken. As the temperature continues to rise, the more significant covalent bonds that hold the protein together begin to break, further destabilizing the structure. Ultimately, the protein loses its native conformation, and its function is impaired.The effect of temperature on protein stabilityThe stability of a protein refers to its ability to maintain its native conformation in the face of various environmental conditions, including temperature. The stability of a protein is influenced by several factors, including the amino acid sequence, solvent conditions, and the presence of ligands or cofactors. Temperature can disrupt the stability of a protein by altering its structure and causing it to denature.Proteins have a range of thermal stability that depends on their amino acid sequence and their specific structure. Generally, proteins that are stable at higher temperatures have a higher content of hydrophobic amino acids, which can help to stabilize the structure through hydrophobic interactions. In contrast, proteins that are stable at lower temperatures tend to have more polar amino acids and a lower content of hydrophobic amino acids.The temperature at which a protein denatures is known as its melting temperature or Tm. The Tm of a protein is influenced by its intrinsic stability as well as the specific conditions under which it is studied. For example, the pH, salt concentration, and presence of other molecules can all affect the Tm of a protein.The effect of temperature on protein functionThe specific conformation of a protein plays a critical role in its function. Therefore, changes in protein conformation due to temperature can have a significant impact on their function. The effect of temperature on protein function can vary depending on the specific protein and the conditions under which it is studied.Some proteins are more sensitive to changes in temperature than others. For example, enzymes, which catalyze chemical reactions in the cell, have a specific optimal temperature range at which they function best. Outside of this range, the reaction rate can slow down or even stop altogether due to changes in protein conformation.Other proteins, such as transporters and receptors, are also sensitive to changes in temperature. Changes in protein conformation due to temperature can affect the ability of these proteins to bind to their ligands and carry out their function.ConclusionIn conclusion, temperature has a significant impact on protein conformation. High temperatures can cause proteins to denature, while changes in temperature can alter their stability and affect their function. Understanding the effect of temperature on protein conformation and function is essential for designing experiments and developing new drugs and therapies that target specific proteins.。

小学下册第十四次英语第6单元期末试卷

小学下册英语第6单元期末试卷考试时间：90分钟（总分:140）A卷一、综合题(共计100题共100分)1. 选择题：What is the smallest continent?A. AsiaB. AfricaC. AustraliaD. Europe答案:C2. 选择题：What is the term for a small rocky body that orbits the sun?A. CometB. AsteroidC. MeteorD. Planet3. 听力题：I want to ________ (create) something special.4. 选择题：What is the main purpose of a compass?A. To tell timeB. To find directionC. To measure distanceD. To calculate speed答案: B5. 填空题：The ______ (蚂蚁) works hard to gather food.6. 选择题：What is the name of the famous explorer who sailed the Pacific Ocean?A. Ferdinand MagellanB. Christopher ColumbusC. Vasco da GamaD. John Cabot答案: A7. 填空题：中国的________ (historical) 文化深深植根于传统和信仰中。

8. 选择题：What is the capital city of France?A. BerlinB. LondonC. ParisD. Madrid9. 选择题：What do we call a person who plays the piano?A. PianistB. MusicianC. ArtistD. All of the above10. 选择题：What is the name of the fairy tale character who has long hair?A. MulanB. RapunzelC. ArielD. Belle11. 填空题：The _______ (青蛙) likes to jump around.12. 选择题：What do you call a collection of books?A. LibraryB. ArchiveC. AnthologyD. Gallery答案:A13. 填空题：The _____ (小狗) is barking at the mailman.14. 听力题：The Ptolemaic model placed the Earth at the _______ of the universe.I enjoy making ______ (手工艺品) from recycled materials. It’s a fun way to be creative and eco-friendly.16. 填空题：The ancient Egyptians created vast ________ (陵墓) for their pharaohs.17. 填空题：I have a toy ______ (飞机) that can fly high in the sky. It is very ______ (酷).18. 选择题：What instrument has strings and is played with a bow?A. FluteB. PianoC. ViolinD. Drum答案: C19. 填空题：We have a ______ (特别的) day planned for school.20. 填空题：The __________ (历史的分析工具) aid in research.21. 填空题：My mom loves __________ (参加志愿活动).22. 听力题：A _______ is a reaction that releases heat.23. 选择题：What is 7 x 2?A. 12B. 14C. 16D. 18答案: B24. 听力题：The _____ (telescope) helps us see stars.25. 填空题：I enjoy watching the _______ (小动物) in the park.We are learning about _______ (动物) in school.27. 选择题：What is the name of the ocean between Africa and Australia?A. Atlantic OceanB. Indian OceanC. Arctic OceanD. Southern Ocean答案: B28. 选择题：What do you call a drink made from fermented grapes?A. BeerB. WhiskeyC. WineD. Cider答案:C29. 填空题：The ________ was a famous artist known for his paintings.30. 填空题：The __________ (历史的价值) is foundational.31. 填空题：The flamingo stands gracefully on one _________. (腿)32. 填空题：A ________ (植物景观规划) beautifies spaces.33. 填空题：The _______ (The 19th Amendment) granted women the right to vote in the US.34. 填空题：The discovery of ________ has had extensive implications for health.35. 听力题：I want to _____ (visit/see) my grandma.36. 听力题：When vinegar and baking soda mix, they produce ________.37. 填空题：The __________ (历史的讨论) can lead to greater understanding.What do you call the main character in a story?a. Antagonistb. Protagonistc. Narratord. Villain答案:B39. 填空题：My favorite subject to study is ______.40. 填空题：I want to learn how to ________ (骑车).41. 选择题：What instrument is known as the "king of instruments"?A. PianoB. OrganC. GuitarD. Violin42. 填空题：People often plant flowers for __________ (美观).43. 听力题：I like to ______ movies with my family. (watch)44. 选择题：What do we call a sweet food made from sugar and typically eaten after a meal?A. DessertB. SnackC. AppetizerD. Side dish答案：A45. 听力题：Planetary atmospheres can protect from harmful _______ radiation.46. 选择题：What do we call a story that is meant to teach a lesson?A. FableB. MythC. LegendD. Folktale答案: AThe chicken lays ______ (鸡蛋). They are a good source of ______ (蛋白质).48. 选择题：What do we call a collection of maps?A. AtlasB. DictionaryC. EncyclopediaD. Almanac答案:A49. 填空题：The __________ (历史的深度) enhances insight.50. 选择题：What do we call the person who designs buildings?A. EngineerB. ArchitectC. ContractorD. Carpenter答案: B51. 选择题：What is your name in English?A. NameB. TitleC. IdentityD. Label52. 听力题：The state of matter that fills its container is a _______.53. 选择题：Which planet is known as the Blue Planet?A. MarsB. EarthC. VenusD. Jupiter答案: B54. 听力题：The __________ can help reveal the effects of human activities on the environment.55. 听力题：The chemical formula for linoleic acid is ______.A __________ (溶胶) is a colloidal mixture with solid particles dispersed in a liquid.57. 听力题：The chemical formula for sodium acetate is _______.58. 选择题：What is the main ingredient in sushi?A. RiceB. NoodlesC. BreadD. Potatoes答案: A59. 填空题：My sister has a keen interest in __________ (天文学).60. 填空题：We saw a _______ (电影) last night.61. 选择题：What is the capital city of Nigeria?A. LagosB. AbujaC. Port HarcourtD. Kano62. 听力题：A _______ can symbolize friendship.63. 填空题：I can ______ (提升) my creativity through art.64. 选择题：What do bees make?A. MilkB. HoneyC. BreadD. Cheese答案:B65. 选择题：What do you call the act of putting something away in a safe place?A. StoringB. HidingC. KeepingD. Securing答案: A66. an Revolution led to the establishment of the ________ (苏维埃政权). 填空题：The Russ67. 填空题：I saw a _______ (小鹿) drinking water.68. 填空题：The capital of Greece is ________ (雅典).69. 填空题：The __________ (国际合作) is needed for global issues.70. 填空题：My dad enjoys helping me with ____.71. 填空题：The flamingo stands gracefully on _______ (一条腿).72. 听力题：Some birds build nests to protect their __________.73. 填空题：My brother is really _____ (幽默) and always makes me laugh.74. 选择题：How many continents are in the world?A. 5B. 6C. 7D. 875. 听力题：A __________ is a substance that cannot be broken down into simpler substances.76. 填空题：The __________ (历史的交织) creates understanding.77. 填空题：I love my _____ (毛绒玩具) that is soft.78. 听力题：The capital of Thailand is ________.79. 填空题：The __________ (历史的桥梁) connect past and present.80. 听力题：Soil is essential for ______ growth.81. 填空题：The _____ (紫罗兰) blooms in spring.82. 听力题：If you drop a feather and a rock, the rock will fall _______.83. 听力题：I want to be a ________.84. 填空题：I like to _______ new things every day.85. 选择题：How many legs does an octopus have?A. 6B. 8C. 10D. 12答案: B86. 填空题：A dolphin is a playful _______ that enjoys swimming in the sea.87. 听力题：The chemical formula for lithium hydroxide is _______.88. 填空题：I have a toy _______ that can change colors.89. 填空题：I am learning how to ________ (游泳) this summer.90. 听力题：The train is coming ___. (soon)91. 选择题：What do we call the holiday celebrated on January 1st?A. ChristmasB. New Year's DayC. Valentine's DayD. Thanksgiving92. 听力题：His favorite food is ________.93. 选择题：What do we call the force that pulls objects toward the Earth?A. MagnetismB. GravityC. FrictionD. Pressure答案:B94. 听力题：The ____ is often seen in gardens looking for food.95. 听力题：The soup is ___ (hot/cold) today.96. 填空题：__________ (植物) use water and sunlight for photosynthesis.97. 选择题：What is the main purpose of a compass?A. To measure weightB. To tell timeC. To find directionD. To measure temperature答案:C98. 填空题：A _____ (海豚) is very friendly.99. 填空题：The raccoon is known for its _______ (聪明) nature.100. 选择题：What is the capital of Estonia?a. Tallinnb. Tartuc. Narvad. Pärnu答案:a。

新发展大学英语阅读与写作3课文翻译What Is a Scientific Theory 什么是科学理论

What Is a Scientific Theory?In order to talk the mature of the universe and to discuss questions such as whether it has a beginning or an end, you have to be clear about what a scientific theory is. I shall take the simple-minded view that a a theory is just a model of the universe, of a restricted part of it, and a set of rules that relate quantities in the model to observations that we make, It exists only in our minds an does not have any other reality (whatever that night mean). A theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations. For exampl e, Aristotle’s theory that everything was made out of four elements, earth, air, fire, and water, was simple enough to qualify, but it did not make any definite predictions. On the other hand, Newton’s theory was proportional to a quantity called their mass and inversely proportional to the square of the distance between them. Yet it predicts the motions of the sun, the moon, and the planets to a high degree of accuracy.Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments, agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory. At least that is what is supposed to happen, but you can always question the competence of the person who carried out the observation.In practice, what often happens is that a new theory is devised that is really an extension of the previous theory. For example, very accurate observations of the planet Mercury revealed a small difference between its motion and the predictions of Newton’s theory of gravity. Einstein’s general theory of relativity predicted a slightly different motion from Newton’s theory. The fact that Einstein’s predictions matched what was seen, while Newton’s did not, was one of the crucial confirmations of the new theory. However, we still use Newton’s theory for all practical purposes because the difference between its predictions and those of general relativity is very small in the situations that we normally deal with. (Newton’s theory also has the great advantage that it is much simpler to work with than Einstein’s!)The eventual goal of science is to provide a single theory that describes the whole universe. However, the approach most scientists actually follow is to separate the problem into two parts. First, there are the laws that tell us how the universe changes with time. (If we know what the universe is like at any one time, these physical laws tell us how it will look at any later time.) Second, there is the question of the initial state of the universe. Some people feel that science should be concerned with only the first part; they regard the question of the initial situation as a matter for meta-physics of religion. They would say that God, being omnipotent, could have made it develop in a company way he wanted. That may be so, but in that case he also could have made it develop in a completely arbitrary way. Yet it appears that he chose to make it evolve in a very regular way according to certain laws. It therefore seems equally reasonable to suppose that there are also laws governing the initial state.It turns out to be very difficult to device a theory to describe the universe all in one go. Instead, we break the problem up into bits and invent a number of partial theories. Each of these partial theories describes and predicts a certain limited class of observations, neglecting the effects of other quantities, or representing them by simple sets of numbers. It may be that this approach is completely wrong. If everything in the universe depends on everything else in a fundamental way, it might be impossible to get close to a full solution by investigating parts of the past. The classic example again is the Newtonian theory of gravity, which tells us that the gravitational force between two bodies depends only on one number associated with each body, its mass, but is otherwise independent of what the bodies are made of. Thus one does not need to have a theory of the structure and constitution of the sun and the planets in order to calculate their orbits.Today scientists describe the universe in terms of two basic partial theories –the general theory of relativity and quantum mechanics. They are the great intellectual achievements of the first half of this century. The general theory of relativity describes the force of gravity and the large-scale structure of the universe, that is , the structure on scales from only a few miles to as large as a million million million (1 with zeros after it) miles, the size of the observable universe. Quantum mechanics, on the other hand, deals with phenomena ion extremely small scales, such as a millionth of a millionth of an inch. Unfortunately, however, these two theories are known to be inconsistent with each other – they cannot both be correct. One of the major endeavors in physics today, is the search for a new theory, and we may still be a long way from having one, but we do already know many of the properties that it must have.o什么是科学理论?为了谈宇宙的成熟和讨论这样的问题是否有一个开始或结束,你必须清楚科学理论是什么。

高一英语气候科学研究进展单选题40题

高一英语气候科学研究进展单选题40题1. The _______ of climate change on agriculture is a major concern.A. impactB. effectC. influenceD. result答案：A。

本题考查名词的辨析。

“impact”强调强烈的冲击和影响；“effect”侧重于效果、结果；“influence”侧重潜移默化的影响；“result”指最终的结果。

在描述气候变化对农业的影响时，“impact”更能突出其强烈和直接的作用。

2. Scientists are constantly _______ new methods to predict the weather.A. developingB. inventingC. creatingD. finding答案：A。

本题考查动词的辨析。

“develop”有开发、发展的意思，常用于新方法、新技术的开发；“invent”侧重于发明全新的事物；“create”强调创造出原本不存在的东西；“find”主要指找到已存在的事物。

科学家不断开发新的方法，用“develop”更恰当。

3. The recent _______ in temperature has caused many problems.A. riseB. increaseC. growthD. raise答案：B。

本题考查名词的辨析。

“rise”常指位置、高度的上升；“increase”可指数量、程度的增加；“growth”侧重于生长、发展；“raise”是动词，此处需要名词，所以排除。

温度的增加用“increase”更合适。

4. The _______ climate makes it difficult for plants to grow.A. dryB. wetC. hotD. cold答案：A。

本题考查形容词的辨析。

the effects of light on plant 雅思阅读

the effects of light on plant 雅思阅读
【最新版】
目录
1.光对植物生长的影响
2.光照强度对植物生长的影响
3.光照时间对植物生长的影响
4.光质对植物生长的影响
5.结论
正文
光是植物进行光合作用的重要因素，对植物的生长发育起着至关重要的作用。

本文将从光照强度、光照时间和光质三个方面探讨光对植物生长的影响。

首先，光照强度对植物生长具有重要影响。

适当的光照强度可以促进植物光合作用的进行，有利于植物的生长发育。

然而，过高或过低的光照强度都会对植物生长产生不利影响。

过高的光照强度会导致植物叶片灼伤，影响植物的生长；过低的光照强度则会导致植物光合作用不足，影响植物的生长速度。

其次，光照时间也是影响植物生长的重要因素。

植物需要充足的光照时间进行光合作用，从而积累足够的养分供生长发育所需。

不同的植物对光照时间的需求不同，有的植物需要长日照，有的需要短日照。

因此，合理控制光照时间对于植物生长具有重要意义。

再者，光质也对植物生长产生影响。

植物对不同波长的光有不同的反应，例如红光和蓝光对植物生长具有促进作用，而绿光对植物生长作用较小。

通过改变光质，可以调节植物的生长发育，提高植物的产量和品质。

综上所述，光对植物生长具有重要影响。

通过合理控制光照强度、光
照时间和光质，可以促进植物的生长发育，提高植物的产量和品质。

高二英语生物学原理与生态现象单选题50题

高二英语生物学原理与生态现象单选题50题1.The function of chlorophyll is to ___.A.absorb sunlightB.produce oxygenC.absorb carbon dioxideD.produce water答案：A。

解析：叶绿素的功能是吸收太阳光进行光合作用。

选项B，产生氧气是光合作用的结果之一但不是叶绿素的主要功能；选项C，吸收二氧化碳的主要结构不是叶绿素；选项D，产生水也是光合作用的结果之一但不是叶绿素的直接功能。

2.Which one is not a characteristic of living things?A.GrowthB.ReproductionC.MovementD.Response to stimuli答案：C。

解析：生物的特征包括生长、繁殖、对刺激作出反应等。

并不是所有生物都能运动，比如植物大多数不能自主运动，所以运动不是生物的普遍特征。

3.The basic unit of life is ___.A.cellB.tissueananism答案：A。

解析：细胞是生命的基本单位。

组织是由细胞组成的，器官是由不同组织构成的，生物体是由多个器官等组成的。

4.What is DNA short for?A.Deoxyribonucleic acidB.Ribonucleic acidC.Deoxyribose acidD.Ribose acid答案：A。

解析：DNA 是脱氧核糖核酸的英文缩写。

选项B 是核糖核酸；选项C 和D 不是正确的缩写。

5.Which process involves the conversion of light energy into chemical energy?A.RespirationB.PhotosynthesisC.DigestionD.Excretion答案：B。

解析：光合作用涉及将光能转化为化学能。

建筑环境学chapter4.1-2 thermal comfortable (9)

comprehensive tables of thermal conductivities
should be used to obtain specific values.
3.1.4
Emissivity and absorptivity 发射率吸收率
the ability of a material to absorb or give off radiant heat is a property of the surface of the material.
Benefits of good thermal insula Nhomakorabeaion ?
(1) to save energy needed to run the heating plant The internal surface temperature ??
A
well-insulated structure and a poorly-insulated structure, which one will stay cooler in summer?
近似的人工黑体。
黑体模型
Emissivity发射率 is the fraction of energy radiated by a body compared to that radiated by a black body at the same temperature Absorptivity 吸收率 is the fraction of ( ) by a body compared to that ( ) by a black body

Rough black surfaces absorb most heat and emit most heat. Conversely, shiny slivered surfaces absorb least heat and emit least heat.

1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。

International Journal of Poultry Science 12 (8): 441-444, 2013ISSN 1682-8356© Asian Network for Scientific Information, 2013Corresponding Author:Yanmin Zhou, College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, 210095,Peopl’s of Republic, China441Effects of Thermostable Phytase Supplementation on the GrowthPerformance and Nutrient Digestibility of BroilersY.P. Chen , W.G. Duan , L.L. Wang , S.L. Zhang and Y.M. Zhou 1 2 2 2 1College of Animal Science and Technology, Nanjing Agricultural University,1Nanjing, Jiangsu, People’s of Republic ChinaAnimal Metabolism Laboratory of KDN Biotech Group, Qingdao, Shandong, People’s of Republic China2Abstract: A study was conducted to investigate the effects of thermostable phytase supplementation on the growth performance and nutrient digestibility of broilers for 42 d. 1-day-old Arbor Acres chicks with similar initial body weight were randomly divided into 3 treatments consisting 6 pens of 20 chicks per pen. The control group was given maize-soybean meal basal diet and the other two groups were fed the basal diet including either 500 U ordinary phytase/kg diet or 500 U thermostable phytase/kg diet. The results indicated that broilers given diets supplemented with thermostable phytase have increased body weight, body weight gain and feed intake than these fed basal diet (p<0.05). However, the same effect was only noted for body weight in ordinary phytase-supplemented group (p<0.05). Birds fed diet supplemented with thermostable phytase had enhanced crude protein utilization when compared with these given basal diet (p<0.05) but the same effect was not observed for broilers fed ordinary phytase-supplemented diet. As expected, dietary phytase supplementation significantly enhanced nitrogen-corrected apparent metabolizable energy of broilers (p<0.05) and this effect was more pronounced in the thermostable phytase-supplemented group.The results suggested that phytase supplementation, especially thermostable phytase supplementation,can improve the growth performance and nutrient utilization of broilers.Key words: Thermostable phytase, growth performance, nutrient digestibility, broilersINTRODUCTIONPoultry diets are based primarily on cereals, legumes and oilseed crops and their by-products. However, the major form of phosphorus present in these feed ingredients is phytate which is poorly available to poultry since monogastric animals have inadequate endogenous mucosal phytase to effectively digest dietary phytate (Nelson, 1967). Besides, phytate can chelate minerals, react with dietary protein and other nutrients, thus reducing the availability of many nutrients (Selle and Ravindran, 2007). One way to overcome these problems is the introduction of microbial phytase as feed additive. Addition of microbial phytase has been shown to release phytate-bound P, reduce P load on the environment and improve energy, protein and amino acid utilization (Selle and Ravindran, 2007; Pirgozliev et al ., 2009). The efficacy of phytase preparation depends not only on type, inclusion rate and the level of activity present but also on the ability of enzyme to maintain its activity in different conditions, especially the conditions used for the pre-treatment of a diet as pelleting. The stability of added enzyme to pelleting process is a major concern of feed manufactures (Silversides and Bedford,1999). Ordinary phytase feed enzymes can not withstand high pelleting temperature up to 85°C and then the residual activity of exogenous phytase present in thefinished pellets might become low and can not play the expected role. However, phytase feed enzymes can be included in animal rations in stable form to avoid thermostability problems at high pelleting temperatures.Therefore, the present study was conducted to study the effect of thermostable phytase supplementation on the growth performance and nutrient digestibility of broilers in comparison with ordinary phytase.MATERIALS AND METHODSExperimental design, animals and diets: The animal care and use protocol were approved by Nanjing Agricultural University Institutional Animal Care and Use Committee. The study was conducted to study the effects of thermostable phytase supplementation on the growth performance and nutrient digestibility of broilers for 42 d. 360 1-day-old Arbor Acres chicks with similar initial body weight (47.02±0.04 g) were randomly divided into 3 treatments consisting 6 replicates of 20 chicks per replicate (1 replicate per cage). The control group (CO group) was given maize-soybean meal basal diet (Table 1), the other two groups were fed basal diets including either 500 U ordinary phytase/kg diet (OP group) or 500U thermostable phytase U/kg diet (TP group). The two phytase-supplemented diets were formulated by adding 100 g ordinary phytase/kg of diet (provided by WeifangTable 1:Ingredients and nutrient composition of basal diet (g/kg, as-fed basis unless otherwise stated)Ingredients1-21 d22-42 d Maize591643 Soybean meal306243 Corn gluten meal3845 Lard1725 Dicalcium phosphate1816 Limestone1312L-Lysine 1.5 1.6 DL-Methionine (99%) 1.5 1.0 Sodium chloride 4.2 3.3 Premix1010 aCalculated compositionME (MJ/kg)12.312.8 CP212193 bCalcium109.1 Available phosphorus 4.3 3.8 Lysine11.09.5 bMethionine 5.0 4.3 bMethionine + cystine8.27.3 Premix provided per kilogram of diet: transretinyl acetate, 24 mg; acholecalciferol, 6 mg; all-rac-"-tocopherol acetate, 20 mg; menadione, 1.3 mg; thiamin, 2.2 mg; riboflavin, 8 mg; nicotinamide, 40 mg; choline chloride, 400 mg; calcium pantothenate, 10 mg; pyridoxine. HCl, 4 mg; biotin, 0.04 mg; folic acid, 1 mg; vitamin B12 (cobalamin), 0.013 mg; Fe (from ferrous sulfate), 80 mg; Cu (from copper sulphate), 7.5 mg; Mn (from manganese sulphate), 110 mg; Zn (from zinc oxide), 65 mg;I (from calcium iodate), 1.1 mg; Se (from sodium selenite), 0.3 mg; bacitracin zinc, 30 mgValues calculated based on the Table of Feed Composition and bNutritive Values in ChinaTable 2:Effects of thermostable phytase supplementation on growth performance of broilersItem BW (g)BWG (g/d)FI (g/d)FGR CO268362.9109 1.74c b bOP270963.4113 1.78b b abTP283066.3118 1.77a a aSEM250.60.90.02 1SEM = Standard error of means (n = 8). BW: Body weight, BWG: 1Body weight gain, FI: Feed intake, FGR: Feed gain ratio.Means within a column with no common superscript differ a-csignificantly (p<0.05)Table 3:Effects of thermostable phytase supplementation on coefficient of total tract apparent retention and nitrogen-corrected apparent metabolizable energy (AMEn) ofbroilersItem DM CP EE AMEn, MJ/kg CO0.690.500.7211.4b cOP0.660.470.6911.9b bTP0.710.590.7412.5a aSEM0.010.010.020.06 1SEM = Standard error of means (n = 8). DM: Dry matter, CP: 1Crude protein, EE: Ether extract.Means within a column with no common superscript differ a-csignificantly (p<0.05)Bio-Tech Co., Ltd., Weifang, China, Trade name is KINGPHOS) and 100 g thermostable phytase/kg of diet ®(provided by the same company mentioned above,Trade name is KINGPHOS HS), respectively. The®declared activity was both 5000 U/g of product for the two phytase enzymes. One unit of enzyme is defined as the amount of enzyme that liberates 1 µmol inorganic orthophosphate per min from 5 mmol/L sodium phytate at pH 5.5 and a temperature of 37°C. Diets were given in the pellet form (Pelleting temperature 83°C). Feed and fresh water were available ad libitum at all time. Body weight and feed intake on a cage basis were recorded from d 1-42 for the calculation of the average daily gain, average daily feed intake and Feed/gain ratio. Feed was withdrawn for 12 h, with water being provided ad libitum, before the chicks were weighed at d 42. At the end of the experimental period, 36-poult sample (two chicks per replicate) was randomly selected and allocated into individual cages. The birds were fed their respective experimental diet for a 3 d period followed by a 72 h complete excreta collection. Excreta were collected twice per day from a plastic tray placed under the cages, stored at -20°C and finally pooled for each cage. The determination of coefficient of total tract apparent retention of nutrients and the nitrogen-corrected Apparent Metabolizable Energy (AMEn) were calculated according to Wen et al. (2012). Briefly, The excreta samples were then dried for 48 h in an oven at 65°C.The dried excreta were allowed to equilibrate to atmospheric conditions for 24 h before being weighed.Feed and excreta samples were then ground through a0.45-mm screen. The samples were analyzed (AOAC,1990) for dry matter (DM, 934.01), ether extract after HCl treatment (EE, 920.39), Gross energy was determined using an adiabatic calorimeter (SXHW-III, Tianyu, Hebi, China). The coefficient of total tract apparent retention (CTTAR) of nutrients and the nitrogen-corrected apparent metabolizable energy (AMEn) were calculated according to Adeola et al. (2008).Statistical analysis: All data were analyzed as a completely randomized design using one-way ANOVA (SPSS, 2008). The differences were considered to be significant at p<0.05.RESULTSGrowth performance: Broilers given diet supplemented with thermostable phytase had increased growth performance in terms of body weight, body weight gain and feed take, rather than feed conversion ratio, than these fed the basal diet (p<0.05). The same effect was only noted for body weight in ordinary phytase-supplemented group (p<0.05), though feed intake and body weight gain in this group were numerically higher when compared with control. Besides, it is worth noting that the effect of thermostable phytase in improving growth performance of broiler chickens is more efficient when compared to the ordinary one as evidenced by increased body weight and body weight gain (p<0.05).442443Nutrient digestibility: Birds fed diet supplemented with and protein, thereby allowing a greater utilization of thermostable phytase had enhanced crude protein nutrients from the diet. It is worth noting that the ability to utilization when compared with these given basal diet improve nutrient retention and energy is more (p<0.05), however, the same effect was not observed for pronounced with thermostable phytase-supplemented broilers fed ordinary phytase-supplemented diet.diet in present study, as evidenced by various As expected, dietary phytase supplementation parameters measured above. Most of the added feed significantly enhanced AMEn of broilers (p<0.05) and enzymes inactivation takes place during conditioning,this effect was more pronounced in the thermostable when the feed is heated with steam, especially the phytase-supplemented group. Dry matter and ether pelleting process (Eeckhout et al ., 1995). Thus, by extract retention were uninfluenced by phytase adding the thermostable enzymes to the formulation supplementation (p>0.05).partially overcomes this problems and the result DISCUSSIONIn our experiment, the effect in improving growth performance is more effective in thermostable phytase-supplemented group which may attribute to the thermostability of this kind of phytase since ordinary phytase can not withstand high pelleting temperature and therefore residual activity present in the finished pellets is relative lower. It is generally thought that responses to exogenous phytase supplementation in REFERENCESfeed intake and body weight gain are more consistent Adeola, O., D.J. Shafer and C.M. Nyachoti, 2008. Nutrientthan feed efficiency responses (Selle and Ravindran,and energy utilization in enzyme-supplemented 2007). The results in present study confirmed the starter and grower diets for White Pekin ducks.beneficial influence of dietary phytase on the growth Poult. Sci., 87: 255-263.performance of broilers in terms of body weight, weight Ahmad, T., S. Rasool, M. Sarwar, M. Haq and M. Hasangain and feed intake rather than feed conversion rate Zia-ul, 2000. Effect of microbial phytase produced which was in accordance with the previous repots by from a fungus Aspergillus niger on bioavailability of Ahmad et al . (2000) and Viveros et al . (2002). This effect phosphorus and calciumin broiler chickens. Anim.is probably as result of simultaneous increases in Feed Sci. Technol., 83: 103-114.weight gain and feed consumption or declining feed AOAC, 1990. Official Methods of Analysis, 15th Edn.,efficiency responses to phytase with time (Rosen, 2003).Association of Official Analytical Chemists,The ability of phytase to improve AMEn and protein Washington, DC.utilization has been well documented. Shirley and Camden, B.J., P.C.H. Morel, D.V. Thomas, V. RavindranEdwards (2003) demonstrated an improvement in AMEn and M.R. Bedford, 2001. Effectiveness of exogenous when feeding broilers a corn and soy-based diet microbial phytase in improving the bioavailabilities supplemented with phytase. Camden et al . (2001)of phosphorus and other nutrients in maize-soya-evaluated two phytase feed enzymes in broilers offered bean meal diets for broilers. Anim. Sci., 73: 289-maize-soy diets. Overall, phytase increased ileal 297.digestibility coefficients of fat by 3.5%, protein by 2.6%Eeckhout, M., M. DeSchrijver and E. Vanderbeke, 1995.and starch by 1.4% which was associated with phytase-induced increases in AME of 0.17 MJ. Alternatively,Tejedor et al . (2001) reported that phytase supplementation of maize-soy diets did not enhance N-corrected AME in broiler chicks and the similar result was also reported by Liebert et al . (2005) in layers. The discrepancy in the aforementioned reports may attribute to avian species, diet compositions, efficacy of phytase enzyme preparation mainly depending on type, inclusion rate, the level of activity present and the ability of enzyme to maintain its activity in vivo and in vitro . The results obtained form present study confirmed the beneficial influence on crude protein digestibility and energy utilization of broilers by phytase supplementation which may result from the ability of phytase to disrupt the various interactions between phytate, minerals, starchobtained in our study may because of the high residual activity of the thermostable phytase in the finished pellets after high temperature pelleting process.Conclusion: The effect of dietary thermostable phytase supplementation in enhancing the growth performance,crude protein utilization and AMEn of broilers is more efficient when compared with ordinary one.In: Proceedings of the 2nd European Symposium on Feed Enzymes, The influence of process parameters on the stability of feed enzymes during steam pelleting. Noordwijkerhout, The Netherlands,pp: 163-169.Liebert, F., J.K. Htoo and A. Sunder, 2005. Performanceand nutrient utilization of laying hens fed low-phosphorus corn-soybean and wheat-soybean diets supplemented with microbial phytase. Poult.Sci., 84: 1576-1583.Nelson, T.S., 1967. The utilization of phytate phosphorusby poultry-A review. Poult. Sci., 46: 862-871.Pirgozliev, V.R., T. Acamovic and M.R. Bedford, 2009.Previous exposure to dietary phytase reduces the endogenous energy losses from precision-fed chickens. Br. Poult. Sci., 50: 598-605.Rosen, G., 2003. Microbial phytase in broiler nutrition. In:Tejedor, A.A., L.F.T. Albino, H.S. Rostagno and F.M.Garnsworthy, P.C. and J. Wiseman (Eds.), Recent Vieites, 2001. Effect of phytase supplementation on Advances in Animal Nutrition. Nottingham University the performance and ileal digestibility of nutrients.Press, Nottingham, UK, pp: 105-117.Rev. Bras Zootec., 30: 802-808.Selle, P.H. and V. Ravindran, 2007. Microbial phytase in Viveros, A., A. Brenes, I. Arija and C. Centeno, 2002.poultry nutrition. Anim. Feed Sci. Technol., 135: 1-Effects of microbial phytase supplementation on41.mineral utilization and serum enzyme activities in Shirley, R.B. and H.M. Edwards, 2003. Graded levels of broiler chicks fed different levels of phosphorus.phytase past industry standards improves broiler Poult. Sci., 81: 1172-1183.performance. Poult. Sci., 82: 671-680.Wen, C., L.C. Wang, Y.M. Zhou, Z.Y. Jiang and T. Wang, Silversides, F.G. and M.R. Bedford, 1999. Effect of2012. Effect of enzyme preparation on egg pelleting temperature on the recovery and efficacy of production, nutrient retention, digestive enzymea xylanase enzyme in wheat-based diets. Poult. Sci.,activities and pancreatic enzyme messenger RNA78: 1184-1190.expression of late-phase laying hens. Anim. Feed SPSS, 2008. SPSS 16. 0 forWindows. SPSS Inc.,Sci. Technol., 172: 180-186.Chicago, IL, USA.444。