中立型时滞LOTKA—VOLTERRA系统解的稳定性和振动性

一、引言考虑中立型时滞Lotka-Volterra系统 (t)=N(t)[a_i-sum from j=1 to n b_(ij) N_i(t—τ_(ij))-sum from j=1 to n c_(ij) (t-σ_(ij))],i=1,2,…,n,(E)其中τ_(ij),σ_(ij)∈(0,∞),a,b_(ij),c_(ij)∈R,i,j=1,2,…,n,对正常数平衡点N~*的稳定性和振动性。由于系统(E)是描述种群所组成的生态群落中种群之间互相作用的生态     

三种群合作系统的全局渐近性态

考虑三种群合作系统:dχi/dt=χi(b-∑j3=1αijχj),χi(0)>0,b>0,αij<0,i≠j,i,j=1,2,3,完整地分析了其全局渐近性态:证明了该系统不存在闭轨,给出了正平衡点存在且全局渐近稳定的充要条件,证明了若系统不存在正平衡点,则所有解均趋于无穷.     

顶青霉D15木聚糖酶提纯及性质研究

经硫酸铵分级沉淀,BiO-gelP60凝胶过滤,和DEAE离子交换层析,从顶青霉D_15的麦麸培养物中提纯,得到4个具有凝胶电泳纯的木聚糖酶组分D_(x1)、D_(x2)、2_(x3)、D_(x4)、SDS—凝胶电泳法测得各个组分的分子量是:D_(x1),76000;D_(x2),4300;D_(x3),32500;D_(x4),29500。圆盘等电聚焦电泳法测得4个组分的等电点分别为4.50、5.70、5.30和5.20。热处理60分钟,D_(x1)、D_(x2),D_(x3)、D_(x4)的半失活温度分别为51.7℃、50.8℃、54.6℃和55.6℃。D_(x1)、D_(x4)在pH3.6—6.6稳定,D_(x2)和D_(x3)则在pH2.4—6.0稳定。各组分的A_(280)(1cm(?)mg/m1)分别是:D_(x1),0.97;D_(x2),1.46;D_(x3),0.98和D_(x4),1.07。     

干旱胁迫下氮素对胡杨幼苗生长及光合的影响

胡杨(Populus euphratica)是塔里木河流域荒漠河岸林重要的抗逆种质资源,胡杨幼苗的存活及生长受水分和氮素的限制。为了研究干旱胁迫下氮素供应对胡杨幼苗早期形态建成的影响,本试验以1年生胡杨实生幼苗为研究对象,采用温室盆栽试验,设置4个水分处理(D_1、D_2、D_3、D_4,土壤含水量为20%~25%、40%~45%、60%~65%、80%~85%)和3种施氮水平(N_0、N_1、N_2:0、3、6 g·pot-1),测定胡杨幼苗的生长指标、叶绿素荧光和光合参数。结果表明:轻度干旱胁迫(D_3)下,施氮量为N_1时,胡杨幼苗的表观生长和光合能力显著提高;幼苗根冠比在D_1时最低,施氮使其显著增大;干旱胁迫(D_1、D_2、D_3)下,N对幼苗生长的促进作用大于N_2;严重干旱胁迫(D_1)时,施氮显著提高幼苗荧光参数和光合速率,增强其光合能力;因此,胡杨幼苗在土壤相对含水量60%~65%(D3)、氮素量为3g·pot~(-1)(N_1)时,其生长表现为最佳状态;干旱胁迫下,氮素能显著增强幼苗地下部分生长和光合能力,表明氮素对干旱胁迫具有补偿效应,可促进幼苗的早期形态建成,有效帮助幼苗渡过生长脆弱期。     

在大鼠胚泡着床过程中孕酮及其受体含量的变化

本文测定了早期妊娠大鼠(D_1—D_7)血清和子宫组织中孕酮和孕酮受体含量;对着床点和未着床子宫组织中的孕酮和受体含量作了比较;分析了血清和子宫组织中孕酮与雌二醇-17β含量的比值。初步结果表明:(1)血清孕酮含量在 D_4明显升高,达到44.13±5.69ng/ml,但子宫组织中的孕酮含量一般随妊娠时间逐渐升高;(2)胞质受体在 D_1最高(45304±1008分子/细胞),在 D_6最低(1121±149分子/细胞),而核受体含量在 D_6比 D_5和 D_7显著升高;(3)孕酮与雌二醇-17β的比值无论在血清和子宫组织中都是在 D_5和 D_7为最高;(4)在 D_6着床点子宫组织孕酮含量明显高于非着床部位,在 D_7两者无异;(5)在 D_6着床点中核受体含量要比未着床点部位高4倍;在 D_7着床点中胞质受体含量明显高于 D_6,也明显高于 D_7中非着床部位子宫胞质受体量。上述资料表明,(1)在 D_5(大鼠胚泡着床时间)子宫贮留更多的孕酮,这可能有利于子宫处于一种“静态”环境,以利于胚泡着床;(2)在 D_6着床点孕酮核受体含量增加,这可能是由于着床的胚泡局部分泌一种或一些因子,发动或加强激素受体复合体由细胞质向细胞核的转入,(3)在 D_7子宫组织中,孕酮水平明显上升,这说明胚泡至少在 D_7已能合成孕酮。     

环状三维捕食—被捕食Volterra系统的全局渐近稳定性

引言 n维捕食-被捕食Volterra系统是指如下系统 x_i=x_i(e_i+sum from i=1 ton a_(ij)x_i), (*) x_i(0)≥0,i=1,2,…,n 其中,常假设 a_(ij)为常数,a_(ij)≤0及a_(ij)a_(ij)<0(i-j)     

趣蝶莲的离体快速繁殖

1　植物名称　趣蝶莲 (Kalanchoesynsepala)。2　材料类别　不定芽、茎尖、带节茎段。3　培养条件　丛生芽诱导培养基 :( 1 )MS + 6 BA2 .0mg·L- 1 (单位下同 ) +NAA 0 .2 ,( 2 )MS +6 BA 1 .0 +NAA 0 .1 ;增殖培养基 :( 3)MS + 6 BA0 .5 +NAA 0 .0 5 ,( 4 )MS + 6 BA 0 .2 +NAA 0 .0 5 ,( 5 )MS + 6 BA 0 .1 +NAA 0 .0 5 ;生根培养基 :( 6)MS ,( 7)MS +IBA 1 .0 +NAA 0 .2 ,( 8)MS +NAA 0 .5。以上培养基均含 30 g·L- 1 蔗糖、0 .7%琼脂 ,pH 5 .5～5 .8。培养温度 ( 2 8± 2 )℃ ,光照度1 5 0 0～ 2 0 0 0lx ,光照…     

吊篮矮牵牛的组织培养和快速繁殖

1　植物名称　吊篮矮牵牛 (Petuniaspreding)。2　材料类别　茎尖、带腋芽的茎段、叶片。3　培养条件　芽诱导培养基 :( 1 )MS + 6 BA 2 .0mg·L- 1 (单位下同 ) +NAA 0 .5 ,( 2 )MS + 6 BA 1 .0 ,( 3)MS + 6 BA 0 .5 ,( 4 )MS + 6 BA 1 .5 +NAA0 .2 ;增殖培养基 :( 5 )MS + 6 BA 0 .5 ;生根培养基 :( 6) 1 /2MS +NAA 0 .0 5。以上培养基均附加蔗糖3%、卡拉胶 0 .62 % ,pH 5 .8。培养温度 ( 2 5±1 )℃。光照 1 0h·d- 1 ,光照度 2 0 0 0lx。4　生长与分化情况　取盆栽于温室中的植株枝条约 1 0cm ,在室内用自来水冲洗干净 ,…     

血型遗传规律的马氏链特性

1、两个命题命题1.设有限状态马氐链的转移概率阵为(p_(ij))n×n,通过有限次交换不同的行和对应的列后变为(p_(i′j))n×n,若p′_(ii+1)>0,i=1,2,……,n-1;p_(n1)>0,则该马氏链为不可约的。证同时交换不同的行和列,只不过是将状态的记号作对应的改变,     

黎豆的组织培养和快速繁殖

1　植物名称　黎豆 (Ｓｔｉｚｏｌｏｂｉｕｍｃｏｃｈｉｎｃｈｉｎｅｎｓｉｓ) ,别名猫豆、狗爪豆。2　材料类别　无菌种子苗。3　培养条件　基本培养基为ＭＳ。种子萌发及壮苗培养基 :(1 )ＭＳ Ｖｃ 0 .5ｍｇ·Ｌ-1(单位下同 ) 0 .1 %活性炭 ;诱导丛芽培养基 :(2 )ＭＳ 6 ＢＡｌ.0 ＮＡＡ 0 .1 Ｖｃ 0 .5 ;诱导愈伤组织培养基 :(3 )ＭＳ 6 ＢＡ 0 .5 ＮＡＡ 0 .0 5 ,(4)ＭＳ 2 ,4 Ｄ 0 .5 ,(5 )ＭＳ 2 ,4 Ｄ 1 .0 ,(6 )ＭＳ 2 ,4 Ｄ 2 .0 ;分化培养基 :(7)ＭＳ 6 Ａ3 .0 Ｖｃ 0 .5 ＮＡＡ 0 .0 5 ;芽体生长及诱导生根培养基…     

Dynamical models of pollutant transport in the atmosphere

Summary In dealing with pollutant transport and diffusion, we need to develop numerical models to reduce the complexity of the phenomena. This paper briefly presents the main characteristics of the different approaches used, attempting to define their field of applicability.     

A note on population densities of mollusca in the river Great Ouse at Ely,Cambridgeshire

Population density and dispersion of ten species of freshwater molluscs have been estimated by random quadrat sampling. An apparent association between four of the species is described.     

A study of dielectric dispersions of bacteriorhodopsin

Dielectric measurements in the MHz region of bacteriorhodopsin (bR) in aqueous solution have shown the existence of ₁-dispersion with five distinct parts. This dispersion and the -dispersion at low frequencies conform approximately to the Debye relaxation equations. The derived apparent relaxation times showed dependence on various physical parameters. The relaxation effect at low frequencies is attributed to the reorientation of bR chromophore within the purple membrane (PM) fragments. The mechanism which gives rise to the ₁-dispersion may well be due to the Maxwell-Wagner effect, although the first two parts of the dispersion could also be attributed to counterion relaxation or to bR reorientation.     

Structural analysis of a ternary complex of allantoate amidohydrolase from Escherichia coli reveals its mechanics

Purine metabolism plays a major role in regulating the availability of purine nucleotides destined for nucleic acid synthesis. Allantoate amidohydrolase catalyzes the conversion of allantoate to (S)-ureidoglycolate, one of the crucial alternate steps in purine metabolism. The crystal structure of a ternary complex of allantoate amidohydrolase with its substrate allantoate and an allosteric effector, a sulfate ion, from Escherichia coli was determined to understand better the catalytic mechanism and substrate specificity. The 2.25 A resolution X-ray structure reveals an alpha/beta scaffold akin to zinc exopeptidases of the peptidase M20 family and lacks the (beta/alpha)(8)-barrel fold characteristic of the amidohydrolases. Arrangement of the substrate and the two co-catalytic zinc ions at the active site governs catalytic specificity for hydrolysis of N-carbamyl versus the peptide bond in exopeptidases. In its crystalline form, allantoate amidohydrolase adopts a relatively open conformation. However, structural analysis reveals the possibility of a significant movement of domains via rotation about two hinge regions upon allosteric effector and substrate binding resulting in a closed catalytically competent conformation by bringing the substrate allantoate closer to co-catalytic zinc ions. Two cis-prolyl peptide bonds found on either side of the dimerization domain in close proximity to the substrate and ligand-binding sites may be involved in protein folding and in preserving the integrity of the catalytic site.     

Why two species of parasitoids showed promise in the laboratory but failed to control the soybean aphid under field conditions

Following the rapid spread of soybean aphid, Aphis glycines in North America in the early 2000’s, biological control was identified as a cost-effective approach for management of this invasive pest. Two parasitoid species, Binodoxys communis and Aphidius colemani, were considered as potential candidates for classical and inundative biological control, respectively. The objectives of the present study were to determine the overwintering capacity of B. communis under climatic conditions prevailing in northeastern North America, and to measure parasitism and dispersal capacity of A. colemani when released in soybean fields. Field and laboratory assessments showed that the Chinese strain of B. communis, Harbin 2002, has a very poor capacity to enter into diapause (<0.8%), and thus to establish in North America. We suggest that this strain has gradually lost its ability to enter diapause during the extended periods of quarantine and laboratory confinement, during which it was continuously exposed to non-diapause rearing conditions. A. colemani did not show strong potential to control A. glycines. Following the release of approximately 8400 females in experimental plots, only 113 mummies were recovered within a radius of 60 m from the release point. Although both parasitoids were promising in controlled environments, the B. communis Harbin 2002 strain and the A. colemani commercial strain did not show strong potential to control A. glycines populations in soybean fields.     

表征心室复极不一致有效参数的仿真研究

建立了从心内膜到心外膜的一维心肌几何模型,采用心肌双域模型建立心电电位的仿真模型,通过改变缺血程度构造不同的心室复极不一致状态,利用有限差分法求解控制方程,模拟了心电兴奋在心室复极不一致状态下形成的心电电位,并从中提取QT离散度和兴奋恢复间期(activation-recovery interval,ARI)离散度。分析结果显示：缺血区与正常区电位的QT间期没有明显差异,QT离散度接近于零,不能有效地表征心室肌复极不一致;缺血区ARI明显区别于正常区,ARI离散度与缺血程度有很好的对应关系,可以用来表征心室复极不一致。     

Problems,successes and challenges for the application of dispersion-corrected density-functional theory combined with dispersion-based implicit solvent models to large-scale hydrophobic self-assembly and polymorphism

The recent advent of dispersion-corrected density-functional theory (DFT) methods allows for quantitative modelling of molecular self-assembly processes, and we consider what is required to develop applications to the formation of large self-assembled monolayers (SAMs) on hydrophobic surfaces from organic solution. Focus is on application of the D3 dispersion correction of Grimme combined with the solvent dispersion model of Floris, Tomasi and Pascual–Ahuir to simulate observed scanning-tunnelling microscopy (STM) images of various polymorphs of tetraalkylporphyrin SAMs on highly oriented pyrolytic graphite surfaces. The most significant problem is identified as the need to treat SAM structures that are incommensurate with those of the substrate, providing a challenge to the use of traditional periodic-imaging boundary techniques. Using nearby commensurate lattices introduces non-systematic errors into calculated lattice constants and free energies of SAM formation that are larger than experimental uncertainties and polymorph differences. Developing non-periodic methods for polymorph interface simulation also remains a challenge. Despite these problems, existing methods can be used to interpret STM images and SAM atomic structures, distinguishing between multiple feasible polymorph types. They also provide critical insight into the factors controlling polymorphism. All this stems from a delicate balance that the intermolecular D3 and solvent Floris, Tomasi and Pascual–Ahuir corrections provide. Combined optimised treatments should yield fully quantitative approaches in the future.     

Particle dispersion for further Cryptosporidium and Giardia detection by flow cytometry

AIMS: The aim of this study was to overcome the analytical problems encountered during the detection of protozoans by flow cytometry resulting from particle compaction. METHODS AND RESULTS: Malvern Mastersizer (Malvern Instruments, Malvern, UK) was used to characterize the particle distribution of four different water samples and/or particle concentrates incubated with (i) low ionic strength solution or sequestring agent, (ii) anionic or non-ionic surfactants (iii) industry detergent formulations and (iv) physical treatment. The recovery of oocysts and cysts in seeded and treated particle concentrates was estimated by cytometry and microscopy. The decrease in ionic strength of the aqueous solution was most efficient in particle dispersion for different types of water. Moreover, samples treated with deionized water or tetrasodium pyrophosphate showed the highest recovery with more than 80% of the oocysts and cysts recovered. CONCLUSIONS: Chemical treatments that act by altering the ionic strength of the medium are the most efficient for all water types tested here but the overall detergency performance cannot be predicted for all water types. SIGNIFICANCE AND IMPACT OF THE STUDY: Flow cytometric detection has been replaced largely by immunomagnetic separation but the data recorded still have relevance in this technique as well as in molecular techniques requiring DNA or RNA extraction.     

A simple parameter of dispersion index that serves as an adjunct to karyotype asymmetry

In order to refine the measure of karyotype asymmetry a new chromosomal parameter of dispersion index is proposed that has the potential to decipher even the minor karyotypic variations, thus permitting further evolutionary gradations to the karyotype asymmetry classes of Stebbins. The higher the dispersion index, the more specialized would be the karyotype. The dispersion index takes into account the variance lor gradual change in chromosome size within a complementvis-a-vis variance for the position of centromere in a karyotypic totality. The dispersion index is calculated as the proportionate measure of centromeric gradient to the coefficient of variation for chromosome length; wherin centromeric gradient = length of median short arm — length of median chromosome. Thus, the three most important karyotypic criteriaviz., differences in: absolute chromosome size, position of centromere and relative chromosome size, are all covered in the proposed parameter. The effectiveness of dispersion index has been tested on a plant taxa,Papaver L., where karyomorphological details, nuclear DNA content, and morphotaxonomic parameters have been amply elucidated from an evolutionary stand point. It is hoped that dispersion index would find immense utility in delimiting species interrelationships particularly in the closely related taxa, when applied in conjunction with other systematic parameters.     

Microfluidics and the quantification of biomolecular interactions

Microfluidic systems under laminar flow conditions provide in-solution information about species size and binding affinities at very modest sample costs. Flow-induced dispersion analysis directly measures the spread of the analyte profile using Taylor dispersion analysis, whereas microfluidic diffusional sizing quantifies the transfer of analyte from one phase to another. Species of sizes between 0.5 and 1000 nm can be analyzed, and different populations resolved. Both techniques also allow analysis in complex media and medium throughput analysis. These properties make them valuable complements to existing approaches to measure biomolecular interactions.