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preprint astro-ph/9512122;ApJ,in press Creation of 7Li and Destruction of 3He,9Be,10B,and 11B in Low Mass Red Giants,Due to Deep Circulation I.-Juliana Sackmann W.K.Kellogg Radiation Laboratory 106-38,California Institute of Technology,Pasadena,CA 91125and Arnold I.Boothroyd 1Dept.of Mathematics &Statistics,Monash University,Clayton,VIC 3168,Australia ABSTRACT It has been demonstrated that 7Li can be created in low mass red giant stars via the Cameron-Fowler mechanism,due to extra deep mixing and the associated “cool bottom processing ”.Under certain conditions,this 7Li creation can take the place of the 7Li destruction normally expected.Note that such extra mixing on the red giant branch (RGB)has previously been invoked to explain the observed 13C enhancement.This new 7Li production can account for the recent discovery of surprisingly high lithium abundances in some low mass red giants (a few of which are super-rich lithium stars,with abundances higher than that in the interstellar medium).The amount of 7Li produced can exceed log ε(7Li)～4,but depends critically on the details of the extra mixing mechanism (mixing speeds,geometry,episodicity).If the deep circulation is a relatively long-lived,continuous process,lithium-rich RGB stars should be completely devoid of beryllium and boron.
Cool bottom processing leads to 3He destruction in low mass stars;in contrast to the 7Li creation,the extent of 3He depletion is largely independent of the details of the extra mixing mechanism.The overall contribution from solar-metallicity stars (from 1to 40M ⊙)is expected to be a net destruction of 3He,with an overall 3He survival fraction g 3≈0.9±0.2(weighted average over all stellar masses);this is in contrast to the conclusion from standard dredge-up theory,which would predict that stars are net producers of 3He (with g dr 3～2.4±0.5).Population II stars experience even more severe 3He depletion,with 0.3～ 0.7.Destruction of 3 He in low mass stars is consistent with the requirements of galactic chemical evolution models;it would also result in some relaxation of the upper bound on the primordial (D+3He)/H abundance,thus relaxing the lower bound on the cosmic baryon density?b from Big Bang nucleosynthesis calculations. For reference,we also present the e?ects of standard?rst and second dredge-up on the helium,lithium,beryllium,and boron isotopes. Subject headings:Galaxy:abundances—nuclear reactions,nucleosynthesis, abundances—stars:abundances—stars:AGB and Post-AGB—stars:giants 1.Introduction For some time,it has been known that stars super-rich in lithium exist,with abundances much higher than they could have been endowed with at birth,i.e,larger than the present interstellar medium value.A much clearer understanding of these super-rich lithium stars was provided by the recent Magellanic Cloud observations of Smith&Lambert(1989,1990),who obtained for the ?rst time a luminosity range for lithium-rich asymptotic giant branch(AGB)stars.They found that the most luminous AGB stars were lithium-rich,in excellent agreement with the predictions of theoretical models of hot bottom burning(Sackmann,Smith,&Despain1974;Scalo,Despain,& Ulrich1975;Sackmann&Boothroyd1992,1995,1998).Hot bottom burning is predicted to occur occur only in the most massive AGB stars(between～4and～7M⊙),which are also the most luminous ones(Iben1975;Bl¨o cker&Sch¨o nberner1991;Lattanzio1992;Sackmann&Boothroyd 1992,1995,1998;Boothroyd&Sackmann1992;Boothroyd,Sackmann,&Ahern1993).However, some lithium-rich stars do not?t into the above scenario. During most of the evolution of a star,lithium is destroyed,as it burns at relatively low temperatures.During the pre-main sequence phase,there can be signi?cant lithium destruction for stars of masses～<1M⊙(see,e.g.,D’Antona&Mazzitelli1984;Pro?tt&Michaud1989; VandenBerg&Poll1989;Michaud&Charbonneau1991).During the main sequence phase, considerable lithium destruction is observed in low mass stars(～<1.2M⊙),e.g.,by two orders of magnitude for the Sun;this is generally explained by rotation-induced slow mixing,with some di?usion(see,e.g.,Schatzman1977;Baglin,Morel,&Schatzman1985;Vauclair1988;Pinsonneault et al.1989;Michaud&Charbonneau1991;Pro?tt&Michaud1991;Charbonnel,Vauclair,& Zahn1992;Chaboyer,Demarque,&Pinsonneault1995),though part of this e?ect might possibly be due to early main sequence mass loss(Boothroyd,Sackmann,&Fowler1991;Swenson& Faulkner1992;Whitmire et al.1995;Guzik&Cox1995).As stars approach the base of the red giant branch(RGB),the surface lithium abundance declines further by two orders of magnitude, as the deepening convective envelope reaches into lithium-depleted interior layers.Thus RGB stars,and AGB stars of～<4M⊙,are expected to have surface lithium abundances from two to four orders of magnitude below the present interstellar medium value of logε(7Li)～3.3(where logε(7Li)≡log[n(7Li)/n(H)]+12). In general,this is observed to be the case;Population I red giants usually have lithium abundances lying in the range?1～ Another problem concerns3He.It is well known that deuterium(D)and3He are created in the Big Bang.Stars burn their initial D to3He while still on the pre-main sequence.Low mass stars create3He pockets in their interior during main sequence burning,as?rst pointed out by Iben (1967),which will subsequently be dredged up to the surface on the RGB,and injected into the interstellar medium via stellar mass loss on the RGB and AGB.Recent measurements of3He mass fractions of～0.001in the low-mass planetary nebulae NGC3242and IC289con?rm that this does indeed occur in at least some stars(Galli et al.1997).The sum of D+3He in the interstellar medium was predicted to increase with time,due to this stellar processing.The observed solar ratio (D+3He)/H≈4×10?5has thus been used as an upper bound on the primordial ratio,in order constrain Big Bang nucleosynthesis models(see,e.g.,Steigman1985);it provides the strongest lower limit on the baryon to photon number ratioη≥3×10?10,and thus to the baryon density of the universe?b≥0.01h?2(where h is the Hubble constant in units of100km s?1Mpc?1). Rood,Bania,&Wilson(1984)pointed out that the apparent observed trend with galactocentric radius of the3He abundances in H II regions was the opposite of what one would expect if the galactic3He abundance was increasing with time due to stellar processing.More recent data(Rood et al.1997;Bania et al.1997)show no signi?cant trend of the3He abundance in H II regions as a function of either galactocentric radius or metallicity,with an average abundance of3He/H=1.5+1.0 ×10?5.Some extragalactic measurements of deuterium have recently appeared; ?0.5 a high ratio D/H≈2×10?4recently observed in a high-redshift(z=3.32)absorption system in the quasar Q0014+813(Songaila et al.1994;Carswell et al.1994;Rugers&Hogan1996a)has sparked new interest in deuterium and3He,since this observation implied a much larger primordial (D+3He)/H value than had been inferred from the galactic observations.More recently,Rugers ×10?4in another absorber of Q0014+813(at redshift &Hogan(1996b)measured D/H=1.9+1.6 ?0.9 z=2.798).If the observed absorption lines do indeed correspond to deuterium and not some coincidental interloper cloud happening to lie at the corresponding velocity,then this leads to correspondingly lower values ofη～<1.7×10?10and?b～<0.006h?2,close to the baryon density ?b≈0.003observed in stars and gas,eliminating the need for the existence of large amounts of baryonic dark matter.These observations also imply a decline by a factor of order6from the primordial(D+3He)/H value to the presolar value.Galactic chemical evolution models can obtain such a decline only if low mass stars destroy3He,instead of creating it;even a low primordial D/H value tends to result in excessive amounts of3He at the present epoch if stars create3He(see,e.g., Yang et al.1984;Walker et al.1991;Steigman&Tosi1992;Vangioni-Flam,Olive,&Prantzos1994; Galli et al.1994,1995)—note that a low value of D/H=(2.3±0.3[stat]±0.3[syst])×10?5has been measured in an absorber at redshift z=3.572of the quasar1937?1009(Tytler&Fan1994; Tytler,Fan,&Burles1996),and that deuterium abundances in quasar absorbers are still being debated(see,e.g.,Tytler,Burles,&Kirkman1996;Rugers&Hogan1997;Webb et al.1997).Galli et al.(1994,1995)suggested that a low-energy resonance in the3He+3He reaction could increase this rate su?ciently for low mass stars to become net destroyers of3He.Hogan(1995)suggested a less speculative mechanism,namely,the extra deep mixing below the conventional convective envelope on the RGB,which is generally invoked to explain the anomalously low12C/13C ratios observed in low mass stars(below the12C/13C values resulting from?rst dredge-up). Over the last two decades,the need for some such deep mixing process on the RGB has been pointed out by many investigators,in order to understand the puzzle of the low12C/13C ratios observed in low mass Population I RGB stars,and the12C depletion and the[O/Fe]–[Na/Fe] anticorrelation discovered in low mass Population II RGB stars(see,e.g.,Dearborn,Eggleton,& Schramm1976;Genova&Schatzman1979;Sweigart&Mengel1979;Gilroy1989;Gilroy&Brown 1991;Dearborn1992;Smith&Tout1992;Charbonnel1994,1995a,b;Boothroyd,Sackmann,& Wasserburg1995,hereafter BSW95;Wasserburg,Boothroyd,&Sackmann1995,hereafter WBS95; Denissenkov&Weiss1996;Charbonnel,Brown,&Wallerstein1998).Recently,BSW95and WBS95 suggested that such deep circulation might also occur in AGB stars of low mass,in order to account for the anomalously low18O abundances observed in these stars. In this paper,we present consistent computations of the e?ects of standard?rst and second dredge-up(in RGB and AGB stars,respectively)on7Li and3He.In addition,we have included 9Be,10B,and11B in our calculations,since they are also destroyed at relatively low temperatures in stars,and therefore can provide additional signatures of stellar mixing.For completeness,we include the results for4He.We also present calculations of the e?ects on these isotopes of“cool bottom processing”(CBP).In this process,deep extra mixing transports envelope material into the outer wing of the hydrogen-burning shell,where it undergoes partial nuclear processing,and then transports the material back out to the envelope.We have modelled CBP by a deep circulation process,determining some of the free parameters of our model by requiring that our computations yield results that agree with the observed RGB12C/13C ratios.The CNO isotopes for these models are discussed in detail in Boothroyd&Sackmann(1998). 2.Methods We considered stars of29di?erent masses from0.85to9.0M⊙,evolving them self-consistently from the pre-main sequence through?rst dredge-up up to either the helium core?ash(which terminates the RGB for low mass stars),or through second dredge-up to the?rst helium shell?ash (for intermediate mass stars and some low mass stars),or to core carbon ignition during second dredge-up(for higher masses).For evolutionary program details,see Boothroyd&Sackmann (1988),Sackmann,Boothroyd,&Fowler(1990),and Sackmann,Boothroyd,&Kraemer(1993). For solar metallicity,we used a helium mass fraction Y=0.28,with solar CNO abundances. For lower metallicities,we reduced Y(taking?Y/?Z≈2),and increased the oxygen content, approximating the observed trend by[O/Fe]∝?0.5[Fe/H]for[Fe/H]≥?1,and constant [O/Fe]=+0.5for[Fe/H] A fuller discussion of the CNO elements is given in Boothroyd&Sackmann(1998).In addition to solar metallicity(Z=0.02),we considered metallicities appropriate to the Magellanic Clouds (Z=0.012and0.007,with[Fe/H]≈?0.35and?0.7,respectively),an intermediate value of Z=0.003([Fe/H]≈?1.2),a Population II metallicity of Z=0.001([Fe/H]≈?1.7),and an extreme Population II metallicity of Z=0.0001([Fe/H]≈?2.7).Since stars convert deuterium to3He on the pre-main sequence,our program lumps deuterium in with3He;our initial3He abundance is actually the sum of deuterium and3He.Since the variation of(D+3He)as a function of time(or metallicity)is not well known,we generally chose an initial ratio3He/4He=4×10?4 by number(solar abundances),but also considered extreme values of this ratio,namely,4×10?3 and4×10?5.For solar metallicity we used a7Li abundance logε(7Li)=3.0,close to that of the present interstellar medium(logε(7Li)ISM≈3.3);for Population II metallicities,we reduced the initial7Li abundance to logε(7Li)=2.6,a factor of5below the present cosmic abundance.Note that stellar models which include microscopic di?usion of7Li suggest that this is a reasonable initial value to match the observations of Spite plateau lithium abundances in Population II stars(Vauclair&Charbonnel1995),as do models which include rotational e?ects(Pinsonneault, Deliyannis,&Demarque1992;Deliyannis,Boesgaard,&King1995;Vauclair&Charbonnel 1995);it is hard to avoid some main sequence7Li depletion in these stars.Beryllium and boron isotopes were considered only for the cases Z=0.02and Z=0.001;we used solar abundances (Be/H=1.3×10?11,B/H=4×10?10,and11B/10B=4.0,by number:Grevesse[1984]),scaled linearly with metallicity.Note that initial abundances of the light elements are generally not critical, as the depletion factors that we report in this paper are insensitive to the absolute starting value. Mass loss on the RGB and AGB was included via a Reimers’(1975)wind,with mass loss parameterη≈0.6,as discussed in Boothroyd&Sackmann(1998)(see also Sackmann et al.1993); values up toη=1.4for Population I cases with masses>2.5M⊙were tested,but the amount of mass lost was still insigni?cant at the points where?rst and second dredge-up take place.We used the OPAL1995interior opacities(Iglesias&Rogers1996),and Alexander molecular opacities (Alexander&Ferguson1994)at low temperatures;these latter require a value ofα=1.67(whereαis the ratio of the convective mixing length to the pressure scale height)in order to obtain a correct model of the Sun(Sackmann et al.1990,1993).Tests were made using older opacity https://www.doczj.com/doc/ea5878893.html,e of the interior opacities from the Los Alamos Opacity Library(LAOL:from Keady[1985])yielded only slightly di?erent amounts of dredge-up(Boothroyd&Sackmann1998),while use of molecular opacities from Sharp(1992)required a value ofα=2.1but had no e?ect on dredge-up.(Note that the value ofαhas almost no e?ect on the depth of dredge-up,as has already been noted by Charbonnel[1994]).Nuclear reaction rates from Caughlan&Fowler(1988)were used,except for the17O-destruction reactions17O(p,α)14N and17O(p,γ)18F(e+ν)18O,where the rates of Blackmon (1996)(from measurements of Blackmon et al.[1995])or of Landr′e et al.(1990)were used. For cool bottom processing(CBP),parametric computations were performed,with envelope structures obtained from full evolution models of a1M⊙star in the appropriate stages of evolution. Two types of models were considered.In the?rst type,as described in WBS95,the star’s structure was taken to be unchanging in time(“single episode”);it was taken at the point on the RGB where CBP is expected to begin(when the hydrogen shell erases the composition discontinuity left behind by?rst dredge-up).The CBP was then computed over time period less than or comparable to the RGB lifetime.In the second type of model,the change in envelope structure as the star climbs the RGB was taken into account by interpolating between full evolution models at15points on the RGB (“evolving RGB”).The CBP was assumed to start when the hydrogen shell erases the composition discontinuity from?rst dredge-up,and continue until the tip of the RGB was reached.For these “evolving RGB”cases,metallicities Z=0.02,0.007,0.001,and0.0001were considered(taking structures from the relevant full evolution models),and higher masses were simulated by adding envelope mass,and starting at the appropriate(higher-luminosity)RGB position(this should be a good approximation,since the structure near the burning shell on the RGB is almost independent of the envelope mass).Isotopic abundances were taken from full evolutionary models,except for 7Li,where an additional main sequence depletion by a factor of50was assumed for the1M⊙case(note that the observed main sequence7Li depletion in low mass stars cannot be predicted by standard stellar models). In our two-stream“conveyor-belt”circulation model for CBP,matter from the bottom of envelope convection streamed downward,reaching a maximum temperature T P,then returned upward and was mixed with the convective envelope(i.e.,a composition advection equation with nuclear burning,and no mixing between downward and upward streams).Envelope and stream compositions were followed through time.We assumed that the temperature di?erence ?log T=log T P?log T H between the bottom of mixing and the bottom of the hydrogen-burning shell was constant,and treated it as a free parameter;values selected for discussion were those satisfying the observational data,as discussed in WBS95and Boothroyd&Sackmann(1998).For a thin H-burning shell,assuming constant?log T is roughly equivalent to assuming extra mixing always reaches down to the same value of the molecular weight gradient?μ. For CBP in the“single episode”circulation models,?log T≈0.17yielded a reasonable match to the observed12C/13C ratio on the RGB(～13±3for a1.2M⊙star,or～11for a1.0M⊙star: see Gilroy[1989]),after a processing time t mix:RGB≈1.25×107yr(see Fig.7).During this time, the star’s luminosity increases by only60%(Sackmann et al.1993),so the assumption of static envelope structure is not unreasonable(the luminosity increase is by a factor of100at the tip of the RGB,after a timeτRGB～7×107yr).For CBP in the“evolving RGB”circulation models,?log T=0.262±0.010matched the above observed carbon isotope ratios on the RGB(Fig.9a; see also Boothroyd&Sackmann1998). The other key free parameter was the stream mass?ow rate˙M p.This must be slower than that of convection in RGB or AGB envelopes(˙M p?˙M conv～1M⊙/yr),while the streams must move faster than the speed with which the H-shell burns its way outward(˙M p～>˙M c).We explored a wide range of˙M p values.For equal downward and upward velocities,the fractional areas at the base of the convective envelope occupied by downward and upward streams are equal.The downward stream then spends a time?t d=0.5?M r/˙M p in a layer?M r,the upward stream spending the same time?t u there on its way out.When downward and upward velocities(and respective fractional areas f d and f u)are not equal,these times become?t d=f d?M r/˙M p and ?t u=f u?M r/˙M p.The total time spent in any mass layer is independent of f d and f u,for f d+f u=1;thus the total amount of nuclear burning is generally independent of f u/f d.The7Li production via the Cameron-Fowler mechanism(Cameron1955;Cameron&Fowler1971)is an exception;it does depend on f u,which a?ects the speed with which7Be is transported upwards, and thus the amount which survives to reach cool layers before decaying into7Li.Let f≡f u/f d; besides f=1(i.e.,f d=f u=0.5),we considered f=9and99. 3.Results We present?rst and second dredge-up results from standard stellar models,and cool bottom processing(CBP)results from our“single episode”and“evolving RGB”circulation models of extra mixing.Note that some results for4He,3He,and the CNO isotopes are tabulated in Boothroyd& Sackmann(1998);more detailed tables are available from the authors1. 3.1.Standard First and Second Dredge-up Figure1a presents the mass layer M r/M down to which the convective envelope reaches,at its deepest penetration during standard?rst and second dredge-up(for stars of>7M⊙,the depth of second dredge-up is shown at the moment when the program failed during core carbon ignition). Note that we de?ne“second dredge-up”in low mass stars as the stage of deepest convective penetration on the early AGB,even if this is shallower than?rst dredge-up.Figure1b displays the corresponding temperatures T ce at the base of the convective envelope.For Z=0.02stars of mass Fig.1.—(a)Maximum depth in mass of the convective envelope(M dr r),relative to the initial stellar mass M,of?rst and second dredge-up(solid and dashed curves,respectively)as a function of stellar mass M.The metallicities are indicated on the curves for?rst dredge-up;the second dredge-up curves are in the same order.For Z=0.02,0.007,and0.0001,the dotted continuations of the dashed curves show the depth reached by second dredge-up at the point where the program failed during core carbon ignition.(b)The maximum temperature T ce at the bottom of the convective envelope during?rst and second dredge-up(solid and dashed curves,respectively)for the same metallicities as(a);for Z=0.02,the value of T ce is also shown at the time of core carbon ignition, for stars of mass>7M⊙(dotted continuation of dashed curve). ≤1M⊙,there is some burning of7Li during?rst dredge-up,when T ce reaches nearly4×106K. Higher temperatures are attained during second dredge-up in intermediate mass stars,but no7Li burning takes place in any but the highest mass stars(～6?7M⊙),as the timescales are too short. Figure2illustrates where in a star’s envelope7Li,9Be,10B,and11B are destroyed,and where in the interior the pocket of3He has been created,prior to?rst dredge-up.One sees that7Li is burned up?rst,followed by9Be;further in,11B and10B burn at similar depths(11B slightly before10B).The pocket of3He peaks considerably deeper in the interior.First dredge-up will dilute the pockets of7Li,9Be,11B,and10B,and will enrich the surface with3He from the pocket Fig.2.—The abundance pro?les of the light elements as a function of the mass coordinate M r/M at the end of the main sequence for Z=0.02stars(a)of1M⊙,and(b)of6M⊙.The depth of standard?rst dredge-up on the RGB is shown by the arrows. below.Table1illustrates the depths of these pockets in stars of di?erent masses and metallicities, prior both to?rst dredge-up on the RGB and to second dredge-up on the AGB. Figure3displays the envelope4He enrichment produced by?rst and second dredge-up.There is little metallicity dependence;?rst dredge-up in low mass stars increases the helium mass fraction by?Y～0.02,while second dredge-up in～7M⊙stars yields?Y～0.1.One can compute the contribution of these stars to the4He enrichment of the interstellar medium(similar estimates for CNO isotopes are discussed in more detail in Boothroyd&Sackmann[1998]).Using the initial–?nal mass relationship(Weidemann&Koester1983;Weidemann1984),one can estimate the envelope mass ejected for a given initial stellar mass.Multiplying mass ejected by the mass fraction of 4He from Figure3,and weighting the results by an initial mass functionφ(M)∝M?2.3(Salpeter 1955),one can estimate the contribution to the interstellar https://www.doczj.com/doc/ea5878893.html,paring with similar4He computations for supernovae(Weaver&Woosley1993),one?nds that low and intermediate mass stars(1?12M⊙)inject nearly as much4He into the interstellar medium as do supernovae. Figure4is a key diagram.It illustrates the conventional viewpoint that low mass stars (M～<4M⊙)should be a considerable source of3He in the universe,according to the predictions of standard dredge-up theory.Note that the?rst and second dredge-up results of Figure4are in good agreement(～10%)with the low mass star results of Charbonnel(1995a,b),the low and intermediate mass star results of Dearborn,Steigman,&Tosi(1996),and the intermediate mass star results of Weiss,Wagenhuber,&Denissenkov(1996)(though the latter?nd～30%less3He dredge-up than the other authors,for stellar masses below1.5M⊙).Figure4also illustrates the3He depletion that is expected due to extra mixing in low mass stars,as computed via our “evolving RGB”CBP models(diamonds on long-dashed curves).For low enough stellar masses, overall depletion of3He is obtained,relative to its initial abundance.On average,one?nds that stars are net destroyers of3He in the universe,particularly low-metallicity stars;this is discussed below in§3.2.(Note that Fig.4does not show the e?ect of hot bottom burning in intermediate mass AGB stars,which would destroy almost all the3He in Population I stars of4?7M⊙,and in Population II stars of3.5?6M⊙[Boothroyd&Sackmann1992;Sackmann&Boothroyd1998].) Figure5summarizes the reduction of the surface7Li abundance due to pre-main sequence burning and?rst and second dredge-up.Pre-main sequence burning(dot-dashed curve in Fig.5) is important only for masses～<1.2M⊙at near-solar metallicity;there is no signi?cant pre-main Table1:Size of the Pockets of7Li,9Be,10B,and11B Prior to First and Second Dredge-up a 3He p d Z&M...........................(M?M r)/M........................... stage(M⊙)dr b7Li9Be10B11B3He3He p c 0.02, 1.00.7560.0370.0600.1940.1520.8260.39149. RGB 2.50.8580.01480.03120.11720.08720.7770.369 5.8 6.00.7690.01320.02750.10550.07700.6040.327 1.37 0.001, 1.00.6890.0240.0550.1760.1390.7240.33654. RGB 2.50.7460.01040.02400.09320.06960.7510.2838.0 6.00.00080.00800.02050.07880.05750.5100.260 1.69 0.02, 2.50.7880.6690.7170.7600.7530.7830.778 1.10 AGB 6.00.8450.5590.6470.7080.6910.7540.741 1.01 0.001, 2.50.7290.2550.3240.5080.4640.6590.627 1.08 AGB 6.00.8370.00790.02040.07870.05740.5120.260 1.68 a Bottom of pocket is de?ned as point where abundance drops by a factor of2. b Fraction of the star’s mass contained in the convective envelope at the time of deepest dredge-up. c Depth of the3He peak. d Peak3H e abundance,relative to its surface abundance.Note that the peak subsequently grows somewhat higher than the values quoted here,before it is actually dredged up. Fig. 3.—Envelope4He mass fraction Y due to standard?rst and second dredge-up(solid and dashed curves,respectively),or at core carbon ignition during second dredge-up(dotted continuation of dashed curves),as a function of initial stellar mass M for various input metallicities Z.The initial stellar abundance is given by the dot-dashed lines. sequence7Li burning in Population II stars of≥0.85M⊙.Possible e?ects of main-sequence7Li depletion on the?rst dredge-up depletion factors of Figure5are discussed below. The7Li depletion due to?rst and second dredge-up is usually due entirely to dilution(by a factor of～60)of the surface lithium pocket,and this dilution is relatively insensitive to the stellar mass and metallicity(varying by less than a factor of3).In addition to dilution,however,there are some cases where7Li also burns during dredge-up,at the bottom of the(standard)deep convective envelope.This occurs during?rst dredge-up only for Population I stars of masses≤1M⊙,and during second dredge-up only for Population I stars of～7M⊙and Population II stars of～6M⊙. Extra mixing on the main sequence can destroy lithium there;one may question whether this would a?ect the?rst dredge-up dilution factors.Low mass stars are observed to experience considerable7Li depletion on the main sequence(see,e.g.,Hobbs&Pilachowski1988,and references Fig. 4.—Envelope3He abundance due to standard?rst and second dredge-up(solid and dashed curves,respectively),or at core carbon ignition(dotted continuation of dashed curves);dot-dashed lines show initial stellar3He abundances.Heavy(central)curves are for our standard initial ratio 3He/4He=4×10?4by number;light curves are for extreme cases4×10?3and4×10?5.Diamonds connected by long-dashed curves show the e?ect of cool bottom processing(CBP)on the RGB, from our“evolving RGB”CBP models. therein).This will a?ect the RGB abundances,but not the dilution factor(since the size of the lithium pocket on the main sequence cannot be reduced signi?cantly—it does not extend much below the main sequence convective envelope,at least for stars～<1M⊙).Stars of mass～>1.4M⊙do not exhibit reduced surface lithium abundances while on the main sequence(see,e.g.,Boesgaard &Tripicco1987;Balachandran1991).However,there may be some evidence that extra mixing can cause additional lithium depletion in the interior,reducing the size of the lithium pocket(and thus increasing the?rst dredge-up dilution factor).For the Hyades,there is no such evidence:the lithium abundances on the RGB are completely explainable by?rst dredge-up dilution alone,as pointed out by Duncan et al.(1998).Possible evidence for additional lithium depletion comes from Gilroy’s(1989)observations of7Li in open cluster giants of intermediate mass;non-LTE corrections to the observed lithium abundances(Carlsson et al.1994)may reduce the e?ect,but probably will not eliminate it. Fig.5.—Envelope7Li abundance changes due to standard?rst and second dredge-up(solid and dashed curves,respectively),or at core carbon ignition(dotted continuation of dashed curves), relative to the values at the end of the main sequence(depletion during the main sequence is not shown).Dot-dashed curves show the pre-main sequence7Li burning,relative to the initial (interstellar medium)value.Separated symbols show the e?ect of AGB hot bottom burning for Z=0.02and0.001:the minimum AGB7Li abundance at the start of hot bottom burning(open circles),peak AGB7Li abundance(solid circles),and?nal equilibrium hot bottom burning7Li abundances(solid diamonds—note that this equilibrium may not be reached by Population I stars and lower mass Population II stars).Arrows indicate directions of possible shifts in values, as expected from variations in AGB mass loss rates,or from continuation of an incomplete model run(see Sackmann&Boothroyd1995,1998). Figure5also summarizes the7Li creation in AGB stars of～4?7M⊙due to hot bottom burning(Sackmann&Boothroyd1992,1995,1998).First,7Li is burned,being depleted by several orders of magnitude.As hot bottom burning becomes stronger,the Cameron-Fowler mechanism (Cameron1955;Cameron&Fowler1971)yields a large increase in the envelope7Li abundance. Independent of past7Li history,such super-rich lithium stars attain peak7Li abundances10?20 times the present interstellar7Li abundance,and may contribute signi?cant amounts of7Li to the interstellar medium(Sackmann&Boothroyd1995,1998).The envelope7Li is produced from3He; as3He is burned,the7Li abundance declines again.If hot bottom burning continues long enough, Fig.6.—Envelope9Be,10B,and11B depletions due to standard?rst and second dredge-up,as a function of initial stellar mass M,for solar(Z=0.02)and Population II(Z=0.001)metallicities. 3He destruction reaches equilibrium with its creation via the p-p chain,and the7Li abundance reaches a?nal value4?5orders of magnitude below the interstellar abundance(see5and6M⊙Z=0.001cases in Fig.5);stellar runs for Population I stars were terminated before this stage was reached,since they approach this?nal equilibrium much more slowly than Population II stars(and may in fact never reach it at all,depending on the point of onset of the AGB“superwind”). Figure6shows the e?ect of?rst and second dredge-up on the surface abundances of9Be,10B, and11B,for both solar and Population II compositions.For?rst dredge-up,the abundance changes are entirely due to dilution;since the extent of the pockets being diluted is greater than for7Li, the dilution is less.For solar metallicity,this dilution is a factor of～30for9Be,and a factor of～10for10B and11B;this dilution is fairly independent of stellar mass except for M<2M⊙(as was the case for7Li).The e?ect of second dredge-up is minor compared to that of?rst dredge-up; there is burning of9Be during second dredge-up by as much as several orders of magnitude in stars of～7M⊙,but relatively little burning of11B,and no signi?cant burning of10B. There is very little data published on beryllium and boron observations in evolved stars of low or intermediate mass.Boesgaard,Heacox,&Conti(1977)searched for beryllium in four giants in the Hyades cluster,and were only able to obtain upper limits,namely,Be/H≤3.1×10?13. For eight Hyades dwarfs,they measured Be/H≈1.0×10?11(Boesgaard et al.1977;Boesgaard& Budge1989).This implies that the giants had a beryllium dilution factor of≥32.From Gilroy (1989),the turn-o?mass of the Hyades is about2.2M⊙;for this mass,our work shows that standard ?rst dredge-up would give a dilution factor of about28,which is consistent.Note that possible non-LTE e?ects were not considered in the above observations. Note that boron abundances on the RGB should be at least a factor of～30higher than beryllium abundances there,due to its higher initial abundance.If there were no reduction of the main sequence pockets from extra mixing,there would be an additional factor of3from the fact that the boron pocket is three times as big(in mass extent)as the beryllium pocket(see Table1or Fig.2,or the?rst dredge-up dilution factors from Fig.6).On the other hand,it is more di?cult to observe boron:the2498?A line can only be observed from space,and in addition red giant stars have very little?ux in the UV(compare to beryllium,where the3130?A line can be observed using ground-based telescopes,and there is somewhat more?ux).Recently,Duncan et al.(1994, 1998)made the?rst observations of boron abundances in two red giants in the Hyades.They?nd [B/H]=?1.1±0.2in the giants,as opposed to[B/H]=?0.1±0.2on the main sequence,yielding a boron depletion of order10,consistent with?rst dredge-up predictions.They point out that corrections for non-LTE e?ects for boron in giants are yet to be calculated. 3.2.Deep Circulation on the RGB and AGB Observations indicate that surface13C abundances continue to change on the RGB after the end of conventional?rst dredge-up(Gilroy&Brown1991;Charbonnel1994;Charbonnel et al. 1998),suggestive of nuclear processing resulting from extra mixing below the base of the convective envelope,i.e.,cool bottom processing(CBP).Slow deep circulation tends to be opposed by a gradient in the mean molecular weightμ.A largeμ-discontinuity is left behind by?rst dredge-up. For Population I stars,the post-dredge-up decrease in12C/13C is observed to commence on the RGB only after the point where the hydrogen shell has subsequently burned its way out to(and destroyed)this“μ-barrier”(see,e.g.,Charbonnel1994;Charbonnel et al.1998).As discussed in Boothroyd&Sackmann(1998),the12C/13C observations suggest that CBP begins when the “μ-barrier”is erased,and then“tails o?”in a manner intermediate between the behavior assumed in our“single episode”and“evolving RGB”CBP models.Unfortunately,the data are su?ciently sparse that this scenario is not completely certain—for example,an earlier starting point for CBP cannot be completely ruled out,though it seems unlikely.Note that the depth of extra mixing in our CBP models was normalized to reproduce the observed ratio12C/13C～13in the galactic open cluster M67,which has a turn-o?mass of～1.2M⊙(see§2). The relatively sparse observations of?eld Population II stars are consistent with the scenario in which CBP does not begin until theμ-barrier is erased(Sneden,Pilachowski,&VandenBerg 1986;Pilachowski et al.1993,1997),and are also consistent with our“evolving RGB”CBP models. However,as discussed in Boothroyd&Sackmann(1998),Population II stars in globular clusters exhibit signs of continuous CBP throughout most or all of the RGB evolution,starting well before the hydrogen shell has erased theμ-barrier(possibly even before deepest?rst dredge-up),and exhibit more processing at a given metallicity than?eld Population II stars(see,e.g.,Carbon et al.1982;Trefzger et al.1983;Langer et al.1986;Suntze?&Smith1991;Boothroyd&Sackmann 1998).Since our models made the assumption that no CBP took place until theμ-barrier was erased,they may be expected to underestimate the amount of processing in globular cluster stars. The“evolving RGB”models make the reasonable assumption that the extra mixing process continues throughout the subsequent RGB evolution;note that if this is the case,then extra mixing and CBP might occur on the AGB as well.The stellar structure on the AGB of a low mass star is similar to the structure near the tip of the RGB,and thus lithium abundances on the AGB might be produced at a level similar to those predicted at the tip of the RGB by the“evolving RGB”model.On the other hand,the“single episode”models assume that extra mixing terminates before the star’s luminosity increases much(e.g.,due to spin-down resulting from the RGB mass loss). This is also a possible scenario,but little or no CBP would be expected on the AGB in this case (the driving mechanism being exhausted on the RGB).The post-RGB lithium abundance in this case would be expected to be nearly constant,at whatever value was left behind when CBP turned o?on the RGB(probably a low lithium abundance,as the mixing would presumably slow down before stopping,and low˙M p values yield low lithium abundances—see Figs.8and9c). For stellar masses above～2.3M⊙,the RGB ends before the hydrogen shell reaches the μ-barrier,and thus no CBP is expected on the RGB;even if some CBP did take place,these stars spend little time on the RGB,and processing should be negligible.On the early AGB,CBP cannot be extensive,as the hydrogen shell largely stops burning;CBP might take place later on the thermally pulsing AGB,when the hydrogen shell burns strongly(albeit interrupted intermittently by the helium shell?ashes).For a fuller discussion,see Boothroyd&Sackmann(1998). In the present work,extra mixing in both Population I and Population II stars are modelled via a conveyor-belt model of deep circulation similar to that of WBS95,as discussed in§2.Charbonnel (1995a,b)and Denissenkov&Weiss(1996)have modelled such mixing in Population II stars using a di?usion algorithm.As discussed in WBS95,these two approaches should yield similar results for the CNO isotopes,since the nuclear processing of CNO isotopes should be insensitive to the speed or geometry of mixing.However,as discussed below,the lighter elements are more dependent on the mixing speed,especially7Li.They are discussed in detail in the following sections. 3.2.1.7Li Figure7shows the abundances of the light elements(and12C/13C)as a function of time on the RGB,for one of our“single episode”CBP models(note that12C/13C reaches the observed value after1.25×107yr,but most of the activity in the light elements takes place much earlier; computations were terminated after5×107yr).It is a key diagram,demonstrating that under Fig.7.—The e?ect of CBP in our“single episode”models,as a function of time on the RGB. These are for a solar metallicity1M⊙star with an envelope mass M env=0.7M⊙and a mixing rate of deep circulation˙M p=10?3M⊙/yr;circulation was assumed to reach to?log T=0.17from the base of the hydrogen-burning shell,such that the envelope12C/13C ratio reaches the observed value of～11after a time t mix:RGB～1.25×107yr(vertical line),although the computations were continued for5×107yr.The quantities plotted are the log of the12C/13C number ratio,the log of the3He mass fraction,and logεvalues for the other light elements.Hatched regions of7Li curves emphasize cases where abundances are higher than the upper bound of typical RGB?eld stars. certain conditions a major amount of7Li can be created on the RGB due to CBP in a1M⊙star of solar metallicity.Figure8a shows the7Li abundances similarly,for various mixing speeds˙M p.One sees that7Li is enhanced for models with rapid enough circulation(namely,˙M p～>10?4M⊙/yr); lower mixing speeds yield lithium destruction. Figure9shows the abundances of the light elements(and12C/13C)as a function of luminosity on the RGB,for our“evolving RGB”CBP models with various mixing speeds˙M p.Note that in these models the total mass drops from0.984to0.710M⊙(due to mass loss on the RGB),the Fig.8.—(a)Dependence of the7Li creation and depletion on the mixing speed˙M p and on our geometry factor f≡f u/f d in our“single episode”CBP models on the RGB.Curves are labelled by log˙M p,and by f for cases with f=1;hatched regions of curves emphasize high lithium abundance cases(as in Fig.7).Note that models with˙M p<10?7M⊙/yr do not produce enough13C to match the observations by the time t mix:RGB is reached(indicated by vertical line).(b)Dependence of 9Be destruction,similarly.Note that boron isotope destruction curves would have the same form, except for having higher initial abundance. core mass grows from0.243to0.462M⊙,and the convective envelope mass M env thus drops from 0.718to0.246M⊙(for lower metallicities or higher stellar masses,these changes are smaller).In these models,the value reached by12C/13C at the tip of the RGB agrees with the observed values (i.e.,the circulation was assumed to operate throughout the RGB);it is essentially independent of the mixing speed or geometry(see Fig.9a).As in the“single episode”cases,the7Li abundance is rapidly enhanced for˙M p～>10?4M⊙/yr;but even at lower mixing speeds(˙M p～>10?6M⊙/yr), signi?cant7Li enhancements occur as the star climbs the RGB. The present work shows for the?rst time that low mass RGB stars can also become super-rich Fig.9.—The e?ect of CBP(for various mixing speeds˙M p)in our“evolving RGB”solar metallicity 1M⊙CBP models as a function of luminosity on the RGB;curves are labelled by log˙M p.Initial and?rst dredge-up abundances are shown schematically in the left portion of each panel(open circles).(a)The12C/13C number ratio;the initial ratio(o?scale)was90.(b)The log of the3He mass fraction.(c)The logε(7Li)values.The?lling between cases with geometry factors f=1 (solid curves)and f=9(dotted curves)having the same˙M p indicates the e?ect of varying the circulation geometry(see text).Hatched regions of curves and heavy?lled regions emphasize high lithium abundance cases,as in Fig.7.(d)Values of logε(9Be)(solid curves),logε(10B)(dotted curves),and logε(11B)(dashed curves);low-˙M p cases are omitted for clarity.Curves for Be and B having the same˙M p value are connected by?lled regions. lithium stars.This allows one to understand the“K Giant Lithium Problem”(de la Reza&da Silva 1995),of anomalously high lithium abundances discovered in otherwise normal low-mass K giants of relatively low luminosity(Wallerstein&Sneden1982;Hanni1984;Brown et al.1989;Gratton &D’Antona1989;Pilachowski et al.1990;Pallavicini et al.1990;Fekel&Marschall1991;Fekel& Balachandran1993;da Silva et al.1995a,b;de la Reza&da Silva1995;de la Reza et al.1996,1997; Fekel et al.1996).The presence and amount of lithium creation are critically dependent on the assumed speed˙M p of extra mixing,as well as on the geometry of mixing(as measured by our factor f≡f u/f d,the fractional area of upward streams relative to downward streams in our conveyor-belt circulation model).Deeper extra mixing yields higher lithium enhancements for a given(rapid) mixing rate(as may be seen by comparing peak7Li values from Fig.8with the values attained in Fig.9c near log L=1.5).However,it is noteworthy that the amount of7Li created does not depend on the previous lithium abundance,i.e.,on the lithium history of the star.A qualitative understanding of this mechanism for RGB lithium enrichment is relatively straightforward. In order to produce the observed additional13C,the extra mixing must reach temperatures high enough that3He is also burned(as shown in Figs.7and9),resulting in7Be creation via 3He(α,γ)7Be.If the extra mixing is slow,this7Be is destroyed while still at high temperatures via7Be(p,γ)8B(e+ν)8Be→2αor7Be(e?,ν)7Li,and any7Li produced from7Be electron capture is immediately burned up via7Li(p,α)4He.However,for su?ciently high mixing speeds,7Be can be transported out to cooler regions before the electron capture takes place,where the resulting 7Li can survive and enrich the stellar envelope.In other words,under special conditions the Cameron-Fowler mechanism can work in low-mass,low-luminosity RGB stars.The resulting envelope7Li abundance is determined by the balance between7Be being transported out(to form7Li),and7Li being transported back inwards(and being destroyed).The envelope7Li abundance reaches equilibrium relative to the abundance of3He on a timescale t proc～M env/˙M p, the time required for circulation to process the entire envelope;t proc is the timescale on which the 7Li abundance reaches its peak values in Figures7,8a,and9c. The e?ect on the envelope7Li abundance of changing the mixing speed˙M p or the relative areas of upward and downward streams f≡f u/f d can be readily understood.For mixing speeds ˙M >10?7M⊙/yr,only a small fraction of the3He in a circulating blob of matter is destroyed p during a single circulation pass,and the total3He burning rate per unit time is then independent of˙M p(see Fig.9b):the amount burned per circulation pass is then inversely proportional to˙M p, and the number of circulation passes per unit time is proportional to˙M p.The amount of7Be produced per unit time is thus independent of˙M p,but the amount that survives to reach cool temperatures is not.If one increases˙M p,at?rst the amount of surviving7Be increases,as does the resulting7Li production.However,as˙M p increases still more,there comes a point where essentially all the7Be survives;the7Li production rate cannot increase further.The7Li destruction rate, however,still increases with increasing˙M p(since all7Li transported down is burned),and the resulting envelope7Li abundance decreases with increasing˙M p.The value of˙M m p which yields the maximum7Li production depends on the temperature at the base of the circulation(as may be seen from Fig.9c,where this temperature grows as the star ascends the RGB).If the circulation speed is less than˙M m p,then changing the stream geometry will a?ect the7Li abundance.Increasing f u/f d yields a wider and slower upward stream;less of the7Be produced at the base of the circulation survives out to cool regions,yielding a lower7Li abundance(see Fig.9c). Figures7and9show that the peak7Li abundance can be attained prior to any signi?cant13C enrichment,but that the7Li abundance can remain high or even grow during the13C enrichment process.These preliminary models would thus predict that low mass super-rich lithium stars could occur with12C/13C ratios throughout the range from～30to～4.This is in reasonable agreement 脐带间充质干细胞的研究进展 间充质干细胞（mesenchymal stem cells,MSC S ）是来源于发育早期中胚层 的一类多能干细胞[1-5]，MSC S 由于它的自我更新和多项分化潜能，而具有巨大的 治疗价值 ,日益受到关注。MSC S 有以下特点：(1)多向分化潜能，在适当的诱导条件下可分化为肌细胞[2]、成骨细胞[3、4]、脂肪细胞、神经细胞[9]、肝细胞[6]、心肌细胞[10]和表皮细胞[11, 12]；(2)通过分泌可溶性因子和转分化促进创面愈合；(3) 免疫调控功能，骨髓源（bone marrow ）MSC S 表达MHC-I类分子，不表达MHC-II 类分子，不表达CD80、CD86、CD40等协同刺激分子，体外抑制混合淋巴细胞反应，体内诱导免疫耐受[11, 15]，在预防和治疗移植物抗宿主病、诱导器官移植免疫耐受等领域有较好的应用前景；(4)连续传代培养和冷冻保存后仍具有多向分化潜能，可作为理想的种子细胞用于组织工程和细胞替代治疗。1974年Friedenstein [16] 首先证明了骨髓中存在MSC S ，以后的研究证明MSC S 不仅存在于骨髓中，也存在 于其他一些组织与器官的间质中：如外周血[17]，脐血[5]，松质骨[1, 18]，脂肪组织[1]，滑膜[18]和脐带。在所有这些来源中，脐血(umbilical cord blood)和脐带(umbilical cord)是MSC S 最理想的来源，因为它们可以通过非侵入性手段容易获 得，并且病毒污染的风险低，还可冷冻保存后行自体移植。然而，脐血MSC的培养成功率不高[19, 23-24]，Shetty 的研究认为只有6%，而脐带MSC的培养成功率可 达100%[25]。另外从脐血中分离MSC S ，就浪费了其中的造血干/祖细胞(hematopoietic stem cells/hematopoietic progenitor cells,HSCs/HPCs) [26, 27]，因此，脐带MSC S (umbilical cord mesenchymal stem cells, UC-MSC S )就成 为重要来源。 一．概述 人脐带约40 g, 它的长度约60–65 cm, 足月脐带的平均直径约1.5 cm[28, 29]。脐带被覆着鳞状上皮，叫脐带上皮，是单层或复层结构，这层上皮由羊膜延续过来[30, 31]。脐带的内部是两根动脉和一根静脉，血管之间是粘液样的结缔组织，叫做沃顿胶质，充当血管外膜的功能。脐带中无毛细血管和淋巴系统。沃顿胶质的网状系统是糖蛋白微纤维和胶原纤维。沃顿胶质中最多的葡萄糖胺聚糖是透明质酸，它是包绕在成纤维样细胞和胶原纤维周围的并维持脐带形状的水合凝胶，使脐带免受挤压。沃顿胶质的基质细胞是成纤维样细胞[32]，这种中间丝蛋白表达于间充质来源的细胞如成纤维细胞的，而不表达于平滑肌细胞。共表达波形蛋白和索蛋白提示这些细胞本质上肌纤维母细胞。 脐带基质细胞也是一种具有多能干细胞特点的细胞，具有多项分化潜能，其 形态和生物学特点与骨髓源性MSC S 相似[5, 20, 21, 38, 46]，但脐带MSC S 更原始，是介 于成体干细胞和胚胎干细胞之间的一种干细胞，表达Oct-4, Sox-2和Nanog等多 1) With the rapid improvement in.../growing awareness of..., more and more.../sth.... 1 随着…的飞速发展/越来越多的关注，越来越… (e.g. With the considerable improvement in building industry, more and more structures are being erected to set the people's minds at ease.) 例：随着建筑业的大力推进，人们对建立越来越多的房屋建筑感到宽心。 2) Recently, sth./the problem of...has been brought to popular attention/ has become the focus of public concern. 2 近来，某事/某问题引起了人们的普遍关注/成了公众关注的焦点。 (e.g. Recently, the problem of unemployment has been brought to such popular attention that governments at all levels place it on the agenda as the first matter.) 例：近来失业问题引起了人们的普遍关注，各级政府已把它列为首要议程。 3) One of the universal issues we are faced with/that cause increasing concern is that... 3 我们面临的一个普遍问题是… /一个越来越引人关注的普遍问题 是… (e.g. One of the universal issues that draw (cause) growing concern is whether it is wise of man to have invented the automobile.) 例：一个越来越引人关注的普遍问题是，发明汽车是否为人 4) In the past few years, there has been a boom/sharp growth/decline in.. . 4 在过去的几年里，…经历了突飞猛进/迅猛增长/下降。 (e.g. In the past ten years, there has been a sharp decline in the number of species.) 例：在过去的几年里，物种数量骤然下降。 5) Nowadays, more/most important/dangerous for our society is... 5 如今对我们社会更（最）为重要的（危险的）事情是… (e.g. Nowadays, most dangerous for our society is the tendency to take advantage of each other in political circles.) 例：对我们社会最为危险的事情是政界倾向于互相利用。 6) According to the information given in the table/graph, we can find that... 6 根据图表资料，我们可以发现… 7) As can be seen from the table/graph/figure, there is a marked increase /decline/favorable (an unfavorable) change in... 7 根据图表（数字）显示，…明显增长（下降）/发生了有利（不利）变化。 8) As we can see from the table/graph/figure above, drastic/considerable/ great changes have taken place in...over the period of time from...(年份)to...( 年份) 8 据上面图表（数字）所示，从某年到某年某方面发生了剧烈的（相当大的；巨大的）变化。 脐带血造血干细胞库管理办法（试行） 第一章总则 第一条为合理利用我国脐带血造血干细胞资源，促进脐带血造血干细胞移植高新技术的发展，确保脐带血 造血干细胞应用的安全性和有效性，特制定本管理办法。 第二条脐带血造血干细胞库是指以人体造血干细胞移植为目的，具有采集、处理、保存和提供造血干细胞 的能力，并具有相当研究实力的特殊血站。 任何单位和个人不得以营利为目的进行脐带血采供活动。 第三条本办法所指脐带血为与孕妇和新生儿血容量和血循环无关的，由新生儿脐带扎断后的远端所采集的 胎盘血。 第四条对脐带血造血干细胞库实行全国统一规划，统一布局，统一标准，统一规范和统一管理制度。 第二章设置审批 第五条国务院卫生行政部门根据我国人口分布、卫生资源、临床造血干细胞移植需要等实际情况，制订我 国脐带血造血干细胞库设置的总体布局和发展规划。 第六条脐带血造血干细胞库的设置必须经国务院卫生行政部门批准。 第七条国务院卫生行政部门成立由有关方面专家组成的脐带血造血干细胞库专家委员会（以下简称专家委 员会），负责对脐带血造血干细胞库设置的申请、验收和考评提出论证意见。专家委员会负责制订脐带血 造血干细胞库建设、操作、运行等技术标准。 第八条脐带血造血干细胞库设置的申请者除符合国家规划和布局要求，具备设置一般血站基本条件之外， 还需具备下列条件： （一）具有基本的血液学研究基础和造血干细胞研究能力； （二）具有符合储存不低于1 万份脐带血的高清洁度的空间和冷冻设备的设计规划； （三）具有血细胞生物学、HLA 配型、相关病原体检测、遗传学和冷冻生物学、专供脐带血处理等符合GMP、 GLP 标准的实验室、资料保存室； （四）具有流式细胞仪、程控冷冻仪、PCR 仪和细胞冷冻及相关检测及计算机网络管理等仪器设备； （五）具有独立开展实验血液学、免疫学、造血细胞培养、检测、HLA 配型、病原体检测、冷冻生物学、 管理、质量控制和监测、仪器操作、资料保管和共享等方面的技术、管理和服务人员； （六）具有安全可靠的脐带血来源保证； （七）具备多渠道筹集建设资金运转经费的能力。 第九条设置脐带血造血干细胞库应向所在地省级卫生行政部门提交设置可行性研究报告，内容包括： 北语14秋《高级英语I》导学资料一 Unit1, Unit2& Unit3 一、本阶段学习内容概述 各位同学，大家好，本课程第一阶段学习的主要内容为Unit1：Party Politics, Unit2：The New Singles, Unit3：教材课文：Doctor’s Dilemma: Treat or Let Die? 网络课件课文：Computer Violence中包括课前练习（Warm-up）、单词和词组（New words and phrases）、课文（Text）、课后练习（Exercises）及补充阅读（Supplementary readings）中的指定内容。 课前练习：大家应先了解课前练习的要求，根据已有的知识思考其中问题，或者利用网络与同学开展一些讨论，争取在阅读课文前了解文章主要论述的问题，有利于更好的了解作者的思想观点和思维过程，从而了解文章所反映的思想文化，这样既能提高阅读理解能力又能获取知识和信息。 单词和词组:名词、动词和形容词是词汇练习和记忆中的重要部分。Unit 1、2、3中所列出的新单词绝大部分都是这三类，因此，大家一定要掌握好新单词。要开发利用多种方法记单词，如联想法、音节法、构词法等。单词和词组基本上给出了英语直接释义，可以培养大家英语思维的习惯。如果在阅读释义后还有疑问，一定要查阅英语词典，寻找一些相关的解释来加深对单词的理解和记忆。许多词的释义中给出了若干同义词或近义词，能帮助大家迅速扩大词汇量，同时，课后练习的词汇（Vocabulary Study）部分又给出了一些相关的练习，大家可以在学习完单词和词组后，乘热打铁，立即做词汇练习的第一小题（选择填空）和第二小题（找出意义相近的替代词）这样可以及时巩固所学单词，大概了解这些词的用法，为正确阅读课文打下基础，也能使得练习题做起来不是那么难。 （特别说明：高级英语阶段的学习，提高词汇量和词汇运用能力是一个很大，并且很重要，同时又是比较难的问题，这是我们必须面对的问题，所以，请大家务必花时间多熟悉单词。所谓的磨刀不误砍材功，先熟悉单词和短语，才能流畅的阅读文章。更关键的是，单词和短语在考试中所占比例不少！） 课文：每单元有一篇课文（Unit1：Party Politics, Unit2：The New Singles, Unit3：教材课文：Doctor’s Dilemma: Treat or Let Die? 网络课件课文：Computer Violence）。在掌握单词和词组之后，阅读课后注释，学习课文的背景资料、作者介绍和相关内容，如人物、事件、地点等的解释，这能帮助大家准确快速的理解文章的内容。在课件资源的帮助下，认真学习课文，包括课文中常用词语和句型的用法。文章比较长，大家一定要有耐心和毅力，坚持就是胜利。在学习完整篇文章后，及时完成课文理解（Comprehension Check）的练习。其中第一小题是根据课文内容选择最佳答案，第二小题是将部分文中的句子用英语注释。只要认真学习了课件资料，相信能很快准确地完成。同时也考察大家对课文理解的程度，督促大家很好的阅读课文。 课后练习：共有四个大题。 1.课文理解（Comprehension Check）：有两个题型。在借助课件学习完课文之后，大家可以先自己做这一部分的练习，然后再看课件，对正答案的同时，再重温课文的大意。 2.词汇（Vocabulary Study）：有两个题型。在学完课文和单词后，大家可以自己先做这一部分的词汇练习，不会做得可以看课件，并牢固掌握，对于补充的单词也要掌握。这样有利于快速扩充词汇量。 3.翻译（Translation）：有的单元是汉译英，有的单元是英译汉。都是一段与课文内容相近的短文。先认真思考，仔细看文章，如果有一定的难度，可以参考课件的解说，然后再组织语言完成翻译练习。 高级英语写作1-10课翻译 The Delicate Art of the Forest 库珀的创造天分并不怎么样；但是他似乎热衷于此并沾沾自喜。确实，他做了一些令人感到愉快的事情。在小小的道具箱内，他为笔下的森林猎人和土人准备了七八种诡计或圈套，这些人以此诱骗对方。利用这些幼稚的技巧达到了预期的效果，没有什么更让他高兴得了。其中一个就是他最喜欢的，就是让一个穿着鹿皮靴的人踩着穿着鹿皮靴敌人的脚印，借以隐藏了自己行踪。这么做使库珀磨烂不知多少桶鹿皮靴。他常用的另一个道具是断树枝。他认为断树枝效果最好，因此不遗余力地使用。在他的小说中，如果哪章中没有人踩到断树枝惊着两百码外的印第安人和白人，那么这一节则非常平静/那就谢天谢地了。每次库珀笔下的人物陷入危险，每分钟绝对安静的价格是4美元/一分静一分金，这个人肯定会踩到断树枝。尽管附近有上百种东西可以踩，但这都不足以使库珀称心。他会让这个人找一根干树枝；如果找不到，就去借一根。事实上，《皮袜子故事系列丛书》应该叫做《断树枝故事集》。 很遗憾，我没有足够的篇幅，写上几十个例子，看看奈迪·班波和其他库伯专家们是怎样运用他的森林中的高招。大概我们可以试着斗胆举它两三个例子。库伯曾经航过海—当过海军军官。但是他却一本正经/煞有介事地告诉我们，一条被风刮向海岸遇险的船，被船长驶向一个有离岸暗流的地点而得救。因为暗流顶着风，把船冲了回来。看看这森林术，这行船术，或者叫别的什么术，很高明吧？库珀在炮兵部队里待过几年，他应该注意到炮弹落到地上时，要么爆炸，要么弹起来，跳起百英尺，再弹再跳，直到跳不动了滚几下。现在某个地方他让几个女性—他总是这么称呼女的—在一个迷雾重重的夜晚，迷失在平原附近一片树林边上—目的是让班波有机会向读者展示他在森林中的本事。这些迷路的人正在寻找一个城堡。他们听到一声炮响，接着一发炮弹就滚进树林，停在他们脚下。对女性，这毫无价值。但对可敬的班波就完全不同了。我想，如果班波要是不马上冲出来，跟着弹痕，穿过浓雾，跨过平原，找到要塞，我就再也不知道什么是“和平”了。是不是非常聪明？如果库伯不是对自然规律一无所知，他就是故意隐瞒事实。比方说，他的精明的印地安专家之一，名叫芝稼哥（我想，该读作芝加哥）的，跟踪一个人，在穿过树林的时候，脚印就找不到了。很明显，脚印是再也没法找到了。无论你还是我，都猜不出，怎么会 卫生部办公厅关于印发《脐带血造血干细胞治疗技术管理规 范(试行)》的通知 【法规类别】采供血机构和血液管理 【发文字号】卫办医政发[2009]189号 【失效依据】国家卫生计生委办公厅关于印发造血干细胞移植技术管理规范(2017年版)等15个“限制临床应用”医疗技术管理规范和质量控制指标的通知 【发布部门】卫生部(已撤销) 【发布日期】2009.11.13 【实施日期】2009.11.13 【时效性】失效 【效力级别】部门规范性文件 卫生部办公厅关于印发《脐带血造血干细胞治疗技术管理规范（试行）》的通知 （卫办医政发〔2009〕189号） 各省、自治区、直辖市卫生厅局，新疆生产建设兵团卫生局： 为贯彻落实《医疗技术临床应用管理办法》，做好脐带血造血干细胞治疗技术审核和临床应用管理，保障医疗质量和医疗安全，我部组织制定了《脐带血造血干细胞治疗技术管理规范（试行）》。现印发给你们，请遵照执行。 二〇〇九年十一月十三日 脐带血造血干细胞 治疗技术管理规范（试行） 为规范脐带血造血干细胞治疗技术的临床应用，保证医疗质量和医疗安全，制定本规范。本规范为技术审核机构对医疗机构申请临床应用脐带血造血干细胞治疗技术进行技术审核的依据，是医疗机构及其医师开展脐带血造血干细胞治疗技术的最低要求。 本治疗技术管理规范适用于脐带血造血干细胞移植技术。 一、医疗机构基本要求 （一）开展脐带血造血干细胞治疗技术的医疗机构应当与其功能、任务相适应，有合法脐带血造血干细胞来源。 （二）三级综合医院、血液病医院或儿童医院，具有卫生行政部门核准登记的血液内科或儿科专业诊疗科目。 1.三级综合医院血液内科开展成人脐带血造血干细胞治疗技术的，还应当具备以下条件： （1）近3年内独立开展脐带血造血干细胞和（或）同种异基因造血干细胞移植15例以上。 （2）有4张床位以上的百级层流病房，配备病人呼叫系统、心电监护仪、电动吸引器、供氧设施。 （3）开展儿童脐带血造血干细胞治疗技术的，还应至少有1名具有副主任医师以上专业技术职务任职资格的儿科医师。 2.三级综合医院儿科开展儿童脐带血造血干细胞治疗技术的，还应当具备以下条件： 英语专业(高级翻译)简介 ·日期：2007-06-07 ·点击次数： 1446 培养目标：本专业培养具有扎实的英语语言基础，较强的语言交际能力和跨文化交际能力，掌握多方面的翻译知识和技巧，能熟练地运用英、汉语在外事、外交、经贸、文化、科技等部门从事口译、笔译的专门人才。 知识能力 要求：1．语音、语调准确，清楚自然。 2．词法、句法、章法(包括遣词造句与谋篇布局)规范、表达得体。 3．认知词汇10000~12000，且能正确而熟练地使用其中的5000~6000个单词及其最常用的搭配。 4．听、说、读、写、译技能熟练，具有较强的英语综合运用能力。毕业时达到英语专业八级水平。 听的能力：听懂真实交际场合中各种英语会话；听懂英 语国家广播电台以及电视台(如VOA, BBC, CNN)有关政治、经济、文化、教育、科技 等方面的新闻、现场报道、专题报道、综合 评述以及与此类题材相关的演讲和演讲后 的问答；听懂电视时事报道和电视短剧中的 对话。语速为每分钟150~180个单词，理解 准确率不低于60%。 说的能力：能就国内外重大问题与外宾进行流利而得体 的交流；能系统、深入、连贯地发表自己的 见解。 读的能力：能读懂一般英美报刊杂志上的社论和书评、 英语国家出版的有一定难度的历史传记和 文学作品；能分析上述题材文章的思想观 点、语篇结构、语言特点和修辞手法。能在 5分钟内速读1600词左右的文章，掌握文章 的主旨和大意，理解事实和细节。 写的能力：能写各类体裁的文章，做到内容充实，语言 通顺，用词恰当，表达得体。写作速度为30 分钟300~400个单词。能撰写长度为 5000~6000个单词的毕业论文，要求思路清 晰、内容充实、语言通顺。 译的能力：1)笔译：能运用翻译的理论和技巧，将英美报 刊上的文章、文学、科技、文化、经贸方面 的原文译成汉语，或将我国报刊、杂志上的 文章、一般文学作品、科技、文化、经贸方 面的原文译成英语，速度为每小时250~300 个单词。译文要求忠实原意，语言流畅。 2)口译：掌握连续或同步口译所需的技巧及基 本要求，能担任外经外贸、外事、外交、国 际文化、科技交流活动的口译和国际会议的 同声传译任务。 5．具有宽广的英语专业知识和相关学科知识。英语专业知识包括文学、语言学和对象国社会与文化的知识。相关学科的知识涉及教育学、教育心理学、语言习得理论、英语教学法、英语测试理论与实践、课程设置等领域。6．具有获取知识的能力、运用知识的能力、分析问题的能力、独立提出见解的能力和创新的能力。 7．熟悉中、英两种文字计算机基本技术并能实际应用。 主干课程：基础英语、高级英语、散文选读、英语泛读、英语口语、基础英语写作、高级英语写作、英汉/汉英口译、英汉笔译、英语视听说、英语报刊选读、英美文学，同声传译、连续传译、经贸法律翻译等。 修业年4年 卫生部关于印发《脐带血造血干细胞库设置管理规范(试行)》的通知 发文机关：卫生部(已撤销) 发布日期： 2001.01.09 生效日期： 2001.02.01 时效性：现行有效 文号：卫医发(2001)10号 各省、自治区、直辖市卫生厅局： 为贯彻实施《脐带血造血干细胞库管理办法（试行）》，保证脐带血临床使用的安全、有效，我部制定了《脐带血造血干细胞库设计管理规范（试行）》。现印发给你们，请遵照执行。 附件：《脐带血造血干细胞库设置管理规范（试行）》 二○○一年一月九日 附件： 脐带血造血干细胞库设置管理规范（试行） 脐带血造血干细胞库的设置管理必须符合本规范的规定。 一、机构设置 （一）脐带血造血干细胞库（以下简称脐带血库）实行主任负责制。 （二）部门设置 脐带血库设置业务科室至少应涵盖以下功能：脐带血采运、处理、细胞培养、组织配型、微生物、深低温冻存及融化、脐带血档案资料及独立的质量管理部分。 二、人员要求 （一）脐带血库主任应具有医学高级职称。脐带血库可设副主任，应具有临床医学或生物学中、高级职称。 （二）各部门负责人员要求 1．负责脐带血采运的人员应具有医学中专以上学历，2年以上医护工作经验，经专业培训并考核合格者。 2．负责细胞培养、组织配型、微生物、深低温冻存及融化、质量保证的人员应具有医学或相关学科本科以上学历，4年以上专业工作经历，并具有丰富的相关专业技术经验和较高的业务指导水平。 3．负责档案资料的人员应具相关专业中专以上学历，具有计算机基础知识和一定的医学知识，熟悉脐带血库的生产全过程。 4．负责其它业务工作的人员应具有相关专业大学以上学历，熟悉相关业务，具有2年以上相关专业工作经验。 （三）各部门工作人员任职条件 1．脐带血采集人员为经过严格专业培训的护士或助产士职称以上卫生专业技术人员并经考核合格者。 2．脐带血处理技术人员为医学、生物学专业大专以上学历，经培训并考核合格者。 3．脐带血冻存技术人员为大专以上学历、经培训并考核合格者。 4．脐带血库实验室技术人员为相关专业大专以上学历，经培训并考核合格者。 三、建筑和设施 （一）脐带血库建筑选址应保证周围无污染源。 （二）脐带血库建筑设施应符合国家有关规定，总体结构与装修要符合抗震、消防、安全、合理、坚固的要求。 （三）脐带血库要布局合理，建筑面积应达到至少能够储存一万份脐带血的空间；并具有脐带血处理洁净室、深低温冻存室、组织配型室、细菌检测室、病毒检测室、造血干/祖细胞检测室、流式细胞仪室、档案资料室、收/发血室、消毒室等专业房。 （四）业务工作区域应与行政区域分开。 脐带血间充质干细胞的分离培养和鉴定 【摘要】目的分离培养脐带血间充质干细胞并检测其生物学特性。方法在无菌条件下用密度梯度离心的方法获得脐血单个核细胞，接种含10%胎牛血清的DMEM培养基中。单个核细胞行贴壁培养后，进行细胞形态学观察，绘制细胞生长曲线，分析细胞周期，检测细胞表面抗原。结果采用Percoll(1.073 g/mL)分离的脐血间充质干细胞大小较为均匀，梭形或星形的成纤维细胞样细胞。细胞生长曲线测定表明接后第5天细胞进入指数增生期，至第9天后数量减少;流式细胞检测表明50%～70%细胞为CD29和CD45阳性。结论体外分离培养脐血间充质干细胞生长稳定，可作为组织工程的种子细胞。 【关键词】脐血;间充质干细胞;细胞周期;免疫细胞化学 Abstract: Objective Isolation and cultivation of mesenchymal stem cells (MSCs) in human umbilical cord in vitro, and determine their biological properties. Methods The mononuclear cells were isolated by density gradient centrifugation from human umbilical cord blood in sterile condition, and cultured in DMEM medium containing 10% fetal bovine serum. After the adherent mononuclear cells were obtained, the shape of cells were observed by microscope, then the cell growth curve, the cell cycle and the cell surface antigens were obtained by immunocytochemistry and flow cytometry methods. Results MSCs obtained by Percoll (1.073 g/mL) were similar in size, spindle-shaped or star-shaped fibroblasts-liked cells. Cell growth curve analysis indicated that MSCs were in the exponential stage after 5d and in the stationary stages after 9d. Flow cytometry analysis showed that the CD29 and CD44 positive cells were about 50%～70%. Conclusions The human umbilical cord derived mesenchymal stem cells were grown stably in vitro and can be used as the seed-cells in tissue engineering. Key words:human umbilical cord blood; mesenchymal stem cells; cell cycle; immunocytochemistry 间充质干细胞(mesenchymal stem cells，MSCs)在一定条件下具有多向分化的潜能，是组织工程研究中重要的种子细胞来源。寻找来源丰富并不受伦理学制约的间充质干细胞成为近年来的研究热点[1]。脐血(umbilical cord blood, UCB)在胚胎娩出后，与胎盘一起存在的医疗废物。与骨髓相比，UCB来源更丰富，取材方便，具有肿瘤和微生物污染机会少等优点。有人认为脐血中也存在间充质干细胞(Umbilical cord blood-derived mesenchymal stem cells，UCB-MSCs)。如果从脐血中培养出MSCs，与胚胎干细胞相比，应用和研究则不受伦理的制约，蕴藏着巨大的临床应用价值[2,3]。本研究将探讨人UCB-MSCs体外培养的方法、细胞的生长曲线、增殖周期和细胞表面标志等方面，分析UCB-MSCs 作为间充质干细胞来源的可行性。 北京理工大学翻硕(MTI)考研应用文写 作复习方法及指导 有无目标是成功者与平庸者的根本差别。凯程北京理工大学翻译硕士老师给大家详细讲解所遇到的问题。特别申明，以下信息绝对准确，凯程就是王牌的北京理工大学翻译硕士考研机构！ 一、北京理工大学翻译硕士考研复习指导 1．基础英语： 基础英语选择题考的特别细致，没有专门的教材，还是重在平时积累，凯程老师在讲课过程中特别重视对于考生基础知识的积累。凯程老师会对考生的阅读理解进行系统的训练。阅读理解也是偏政治，凯程老师会重点训练同学的答题速度，培养同学们阅读答题技巧，针对作文这方面，凯程老师也会对考生进行一系列的训练，让同学们勤加练习，多做模拟作文。 2．翻译英语： 翻译硕士基础这门课是需要下功夫的，英汉词条互译的部分完全需要你的积累，主要是词汇量和分析抓取能力。凯程老师会对学生的这两个方面进行很完善的训练。 凯程老师总结了以下提升翻译技巧的方法，供考研学子参考。 词组互译：大多考的都很常见，所以多看看中英文的报纸还是有好处的。 英汉：对文章的背景有一定的了解是最好的，如果没有，就需要体现出自身的翻译素养。翻译也要注意文风，语气之类的，要符合原文的风格。 凯程老师也很重视答题技巧，在此凯程名师友情提示大家，最好在开头就能让老师看到你的亮点，不管怎样至少留下个好印象。不管风格怎么变，翻译功底扎实，成绩都不会太差。所以还是提高自己翻译水平，才能以不变应万变。 3．百科： 先说说名词解释。这道题考得知识面很全，可能涉及到天文、地理、历史、法律、政治、中外文学、中外文化、音乐、翻译专有名词等，准备起来比较棘手，但是凯程老师会给学生准备好知识库，方便学生复习。百科的准备，一要广泛，二要抓重点，尤其要重视学校的参考书目，同时凯程也会提供凯程自己的教材及讲义来帮助大家。 接下来是应用文写作。其实这个根本不用担心，常出的无非是那几个：倡议书、广告、感谢信、求职信、计划书、说明书等，到12月份再看也不晚。但要注意一点，防止眼高手低，貌似很简单，真到写的时候却写不出来，所以还是需要练习的，凯程老师会在学生复习过程中对应用文的写作进行系统的训练。另外，考试的时候也要注意格式、合理性，如果再加上点文采，无异于锦上添花。 最后说说大作文。这个让很多同学担心，害怕到考场上无素材可写，或者语言生硬，拼凑一篇，毕竟大学四年，写作文的机会很少，早没有手感了。所以，凯程老师会针对这种情况，让考生从复习开始时，就进行写作训练，同时也会为考生准备好素材。 最后，注意考场上字体工整，不要乱涂乱画，最好打上横线，因为答题纸一般是白纸。 二、北京理工大学翻译硕士考研的复习方法解读 （一）、参考书的阅读方法 （1）目录法：先通读各本参考书的目录，对于知识体系有着初步了解，了解书的内在逻辑结构，然后再去深入研读书的内容。 （2）体系法：为自己所学的知识建立起框架，否则知识内容浩繁，容易遗忘，最好能 脐带血干细胞检测 对每份脐血干细胞进行下列检测： ①母体血样做梅毒、HIV和CMV等病原体检测，这一检测使脐血干细胞适合于其它家庭成员应用。如任何一种病原体测试阳性，需重复测定。 ②每份脐血干细胞样本同时检测确定没有微生物污染。 ③细胞活性检测、有核细胞数、CD34+细胞数、集落形成试验等。CD34是分子量115KD 的糖蛋白分子，使用特定单克隆抗体（抗-CD34）确定，脐血祖细胞的大部分，包括体外培养产生造血集落的细胞都包含在表达CD34抗原的细胞群中。 ④HLA组织配型、ABO血型。 一、采血方式及其优点 再生缘生物科技公司采用最严谨的封闭式血袋收集法，避免在收集脐带血液时可能遭受微生物污染的发生，且以最少之操作步骤，收集最大量之脐带血液方式，在产房内即可完成。 二、脐带血处理与保存 脐带血收集于血袋，经专人运送至再生缘生物科技公司之无菌细胞分离实验室后，由专业的技术人员于完全无菌的环境下，依标准操作程序将血液进行分离，收集具有细胞核的细胞，其中含有丰富的血液干细胞，经加入冷冻保护剂和适当品管检测后，并进行以最适合 血液干细胞的冷冻降温程序方式，进行细胞冷冻程序，达到避免细胞受到冷冻过程之伤害。完成后，冷冻细胞立刻保存于摄氏零下196度的液态氮槽中。所有操作程序记录和细胞保存相关数据，均由计算机条形码系统追踪确认，完全符合国际脐带血库之标准操作程序和品管要求。 母亲血液之检测 为确保所操作和保存的脐带血液细胞，符合国际血液操作规范，并提供客户最大的保障，对于产妇血液必须同时进行一些病毒传染病的检测，以确保没有下列病毒，如艾滋病毒(HIV)、C型肝炎病毒(HCV)、人类T细胞淋巴病毒(HTLV)和梅毒(syphilis)，同时对于B型肝炎病毒(HBV)和巨细胞病毒(CMV)加以侦测和纪录，作为将来可能应用脐带血细胞时之必要参考数据并符合卫生医疗之要求。 脐带血细胞之品管 对于所保存之脐带血细胞均进行多项操作流程监控和品管检测，如微生物污染检测、血液细胞浓度、细胞存活率、细胞活性测定等，每一步骤均有详细之纪录，在操作方法和使用仪器方面均定期进行验证和校验，以符合国际医疗标准。 三、实验室、贮存处所介绍 再生缘生物科技公司拥有符合美国联邦标准(FED-STD-209E)和中华民国优良药品制造标准（一区、二区、三区）的生物安全实验室和无菌操作设备，在专业的技术人员依标准操作程序下进行血液分离和保存步骤，保障客户珍贵样品和权益。 分离后之细胞将依浓度分装入4-6个冷冻管，计算机降温冷冻完成后，即由食品工业发展研究所国家细胞库专业液态氮库房人员，将冷冻细胞分别存放于二个不同的脐带血细胞专属液态氮槽中保存，在安全机制上更有保障。液态氮库房拥有五吨的液态氮供应系统，每一液氮槽均有自动充填装置和异常警报系统，和每日值勤人员监控，确保冷冻细胞处于最佳的冷冻状态。 四、安全管制措施 脐带血液经快递送达无菌细胞分离实验室后，每一步骤均有专业技术人员操作和监督，并将所有分析数值详细填于具有条形码管制之分析表格和计算机数据表中，利用条形码和读码系统确认样品之专一性，避免人为失误，且便于追溯和数据品管。 在冷冻细胞保存上 T h e D e l i c a t e A r t o f t h e F o r e s t 库珀的创造天分并不怎么样；但是他似乎热衷于此并沾沾自喜。确实，他做了一些令人感到愉快的事情。在小小的道具箱内，他为笔下的森林猎人和土人准备了七八种诡计或圈套，这些人以此诱骗对方。利用这些幼稚的技巧达到了预期的效果，没有什么更让他高兴得了。其中一个就是他最喜欢的，就是让一个穿着鹿皮靴的人踩着穿着鹿皮靴敌人的脚印，借以隐藏了自己行踪。这么做使库珀磨烂不知多少桶鹿皮靴。他常用的另一个道具是断树枝。他认为断树枝效果最好，因此不遗余力地使用。在他的小说中，如果哪章中没有人踩到断树枝惊着两百码外的印第安人和白人，那么这一节则非常平静/那就谢天谢地了。每次库珀笔下的人物陷入危险，每分钟绝对安静的价格是4美元/一分静一分金，这个人肯定会踩到断树枝。尽管附近有上百种东西可以踩，但这都不足以使库珀称心。他会让这个人找一根干树枝；如果找不到，就去借一根。事实上，《皮袜子故事系列丛书》应该叫做《断树枝故事集》。 很遗憾，我没有足够的篇幅，写上几十个例子，看看奈迪·班波和其他库伯专家们是怎样运用他的森林中的高招。大概我们可以试着斗胆举它两三个例子。库伯曾经航过海—当过海军军官。但是他却一本正经/煞有介事地告诉我们，一条被风刮向海岸遇险的船，被船长驶向一个有离岸暗流的地点而得救。因为暗流顶着风，把船冲了回来。看看这森林术，这行船术，或者叫别的什么术，很高明吧？库珀在炮兵部队里待过几年，他应该注意到炮弹落到地上时，要么爆炸，要么弹起来，跳起百英尺，再弹再跳，直到跳不动了滚几下。现在某个地方他让几个女性—他总是这么称呼女的—在一个迷雾重重的夜晚，迷失在平原附近一片树林边上—目的是让班波有机会向读者展示他在森林中的本事。这些迷路的人正在寻找一个城堡。他们听到一声炮响，接着一发炮弹就滚进树林，停在他们脚下。对女性，这毫无价值。但对可敬的班波就完全不同了。我想，如果班波要是不马上冲出来，跟着弹痕，穿过浓雾，跨过平原，找到要塞，我就再也不知道什么是“和平”了。是不是非常聪明？如果库伯不是对自然规律一无所知，他就是故意隐瞒事实。比方说，他的精明的印地安专家之一，名叫芝稼哥（我想，该读作芝加哥）的，跟踪一个人，在穿过树林的时候，脚印就找不到了。很明显，脚 In return作为（对某物）的付款或回报What do we give them in return. Conceive of 想像、认为 I laughed to myself at the men and the ladies. Who never conceived of us billion-dollar Babies（俚语：人）。 对于那些认为我们从不会成为腰缠万贯的巨富的先生和女士们，我们总是暗自嘲笑他们。 Scores of很多 Scores of young people. Strike sb. as … 给某人留下印象 These conclusion strike me as reasonable. 我认为他们的话是合情合理的 Drop out 脱离传统社会 Ever since自从 In hopes of 怀着…希望 Every since civilization began，certain individuals（人）have tried to run away from it in hopes of finding a simpler，more pastoral，and more peaceful life Support oneself自食其力 Run out of没有，用完，耗尽 Our planet is running out of noble savages and unsullied landscapes. 我们地球上高尚的野蛮人和未玷污的地方越来越少 the other way （round）相反 come off 成功 These are the ones whose revolutions did not come off. In need of 需要 It dawns on a familiar，workaday place，still in need of groceries and sewage disposal. 它洒在一个司空见惯，平凡庸碌的地方，一个仍然无法摆脱食品杂货，污水处理的地方。 In short supply供应不足，短缺 Break down瓦解，崩溃 Broke down our resolve. 丧失了我们的决心 Out of work失业 dawn on sb. 逐渐明白 It dawned on us rather suddenly that the number of passengers on the small spaceship we inhabit is doubling about every forty years. Come down （from…）（to…）从一处来到另一处 Eat sth. up 吃光 In profusion 大量地 She had magnificent blonde hair，in profusion. Take a shot猜测 As a point of departure 起点 As doctors often do I take a trial shot at it as a point of departure. 作为医生我经常根据猜测可能出现的总是进行提问 as yet到现在为止 As yet,no man has set foot on Mars. 到目前为止还没有人登上火星。 Get somewhere 有进展，取得一些成就 If only 只要 If only they wouldn‘t use the word “hurt” I might be able to get somewhere. Up to sb.取决于某人 《高级英语》课程教学大纲 一、课程说明 1．课程的性质与目的 《高级英语》是一门训练学生综合英语技能尤其是阅读理解、语法修辞与写作能力的课程。课程通过阅读和分析内容广泛的材料，包括涉及政治、经济、社会、语言、文学、教育、哲学等方面的名家作品，培养学生对名篇的分析和欣赏能力、逻辑思维与独立思考的能力，拓宽学生的人文学科知识和科技知识，增强学生对文化差异的敏感性，加深学生对社会和人生的理解，帮助学生继续打好语言基本功，牢固掌握英语专业知识，巩固和提高学生的英语语言技能以及综合运用英语进行交际的能力。 2．教学要求和任务 1）要求学生能读懂难度相当于美国Times 或New York Times的社论和政论文；能读懂难度相当于The Great Gatsby的文学原著，难度相当于The Rise and Fall of the Third Reich 的历史传记；语言能力较高的学生要求能读懂一般英美报刊杂志上的社论和书评、英语国家出版的有一定难度的历史传记和文学作品。要求在理解的基础上分析文章的思想观点、语篇结构、语言特点和修辞手法。 2）选材涉及政治、经济、社会、语言、文学、教育、哲学等方面的名家作品，体裁多样。学生阅读后能够进行说、写、译方面的表达：能够比较系统地口头描述所阅读材料的概要，能够比较流畅和准确地跟同学交流自己的思想和观点；能够写出故事梗概、读书报告等，还能够撰写课程论文以及正式的书信等，要求内容充实、语言正确，表达得体，具有一定的思想深度；能够运用翻译理论和技巧对所阅读的材料进行英汉互译，译文忠实原文，语言通顺。 3）学生能够熟练使用各种英英词典、大型百科全书，独立解决语言问题和部分知识方面的疑难问题，能够有效地通过计算机网络查阅资料，获取知识，独立从事某些简单课题研究。 4）学生能够加深对当代英语的不同侧面，西方社会和文化等的认识，能够在扩大知识面的同时习得语言，提高文化素养。 二、学生在选读本课程之前应具有的语言知识和能力 1) 具有比较扎实的语言基本知识，掌握一定的听、说、读、写、译技能以及各项技能的综合运用能力； 2）大量阅读英语简易读物，基本看懂英语原著，具有较好的语言理解能力、分析能力、综合能力与概括能力；具有一定的思维能力和语言学习过程中的发现问题和解决问题等创新能力； 3）具有课外自主收集相关阅读材料进行拓展性学习的能力； 4）具有英汉语言和英汉文化差异的敏感性，掌握一定的跨文化交际能力。 三、采用的教材和学生应读的参考书 目前使用的教材是李观仪主编的A New English Cours e Book 5 — 6 (revised edition) {《新编英语教程》5、6册。学生在修读本课程期间还须完成以下读物的学习： A、词汇类脐带干细胞综述
高级英语写作黄金句型和新词
脐带血造血干细胞库管理办法(试行)
高级英语一
高级英语写作1-10课翻译
卫生部办公厅关于印发《脐带血造血干细胞治疗技术管理规范(试行)
英语专业(高级翻译)简介
卫生部关于印发《脐带血造血干细胞库设置管理规范(试行)》的通知
脐带血间充质干细胞的分离培养和鉴定
北京理工大学翻硕(MTI)考研应用文写作复习方法及指导
脐带血干细胞检测
高级英语写作课翻译
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