以x(m/n)为功能性反应函数的食饵-捕食系统的定性分析

研究了功能性反应函数ψ(x)为x(m/n)(0＜m/n＜1)的食饵-捕食系统dx/dt=ax-bψ(x)y-cx2,dy/dt=-dy+eψ(x)y-fy2.证明了此系统当1/2≤m/n＜1时至多存在唯一正平衡点;当0＜m/n＜1/2时必有出现三个正平衡点的可能.并讨论了此系统的拓扑结构,给出了数值例子.     

一类含单奇点的极限环的三次系统

证明具体三次系统x=y-εy~3,y=x(1-x~2)+(α-x~2)y,当α≥1或0<α≤1/3时,在区域|y|<1/ε~(1/2)内无含单奇点的极限环,这里ε>0.     

捕食者厌食的Predator-prey系统极限环存在性与唯一性

一、引言捕食系统的捕食者具有Ⅱ类功能反应时,功能函数为Φ(x)=αx/1+ωx,其中α,ω均为正常数,当x→+∞时,Φ(x)→α/ω>0,呈捕食饱和状态。而有些捕食生物种群,由于食饵过多而逐渐形成不爱捕食的习惯,这时用功能函数Φ(x)=αx/1+ωx+βx~2描述捕食状态,其中β>0,当x→+∞时,Φ(x)→0。系统为     

种群生态系统的持续生存

一、引言许多描述种群生态的数学模型都可以由一常微分方程组 x＇=f(x) (x＇=dx/dt) (1.1)来描述。这里, x=(x_1,x_2,…,x_1)~T∈R_+~n,t∈R_+,R_+~n={x|x≥0,i=1,2,…,n},R_+={t|t≥0},f(x)=〔f_1(x),f_2(x),…,f_2(x)〕~T,x_i表示种群的数量或密度。记intR_+~n为R_+~n的内部,bdR_+~n为RR_+~n的边界。对于一个生态系统,我们通常最关心的是生态平衡问题,这就需要研究系统(1.1)的动力学行为。对于系统(1.1)而言,若存在正平衡位置,且它相对于intR_+~n是全局渐近稳定     

x~2-统计量及其在生物科学中的应用

1引言设(x,,工:xk)产一几f(,:;万l(0),…,万k(0)),二:(口)介0,I簇:(无,(8)=1.0=(0,02,…oq)“日,日为Rq中的开集,简记二(0)二二1(艺《k, 厅左乙=I定义向量(仆之一n汀2 v厅2 / \找7Tk九k一”7Tk了7Tk)(I)I一一儿 / V 一一 V必=(、7T:) nk乙其「},,(nl,n:x:,‘二,xk) (2)=n.根据独立同分布情形i=]的中心极限定理 nx一们厅, 了万丁 、/7T2, nk)二 LV*Nk(0,必必了)(二。L*…表示某随机向量是依分布收敛于某分布的随机向量).1991年2月8仁j收到修改不I期x“一统计量及其在生物科学中的应用子j L引理1“’.二次型V产CV*xZ(:)的充要条件为(…     

苏云金杆菌对中华稻蝗的毒力和致染色体畸变研究

本研究采用注射法测定了苏云金杆菌 (Bacillusthuringiensis,B .t)对中华稻蝗 5龄蝻和初羽化成虫的毒力。结果显示 ,B .t对中华稻蝗蝻和成虫均有一定的杀伤力。在 4 8h ,B .t对蝻和成虫的毒力回归线分别为 y =1 15 2 61x (相关系数r =0 993 8)和 y =2 0 6 2 11x (r =0 992 1) ,LD50 分别为 0 18IU/头和 0 2 0IU/头 ,蝗蝻较成虫对药剂稍敏感 ;成虫在 2 4h的LD50 ( 0 2 7IU/头 )比 4 8h的LD50 ( 0 2 0IU/头 )大 ,在较短的作用时间达到同样的杀伤效果需要较高的作用效价。此外 ,还观察分析了B .t悬浮液对 5龄蝗蝻精巢细胞染色体的致畸效应。结果发现 ,B .t可诱发蝗蝻一定比例的染色体畸变 ,其畸变类型主要是染色单体断裂和染色体断裂。统计分析认为 ,它是一种较强的致蝗虫染色体畸变剂。     

顶青霉D_(15)木聚糖酶性质研究

本文对项青霉D_(1(?))的四个木聚糖酶组分的特性进行了研究。木聚糖酶组分D_(x1)、D_(x4)的最佳反应pH为4.8,最适温度分别为40℃和50℃,D_(x2)和D_(x3)的最适pH和温度都分别为pH4.2和50℃。Ag~(++)、Hg~(++),Cu~(++)对四个组分的活性均有强烈的抑制作用,SDS也能产生明显的抑制效果。Mn~(++)对D_(x1)具有促进作用。D_(x1)、D_(x4)在以燕麦木聚糖为底物时活性最高,其Km值分别为11.7(mg/ml)和8.3(mg/ml),D_(x2)和D_(x3)则分别在水解红麻杆木聚糖和落叶松木聚糖时活性最强,Km值分别为8.4(mg/ml)和6.3(mg/ml)。水解燕麦木聚糖,D_(x1)的产物主要为木糖,同时带有少量的低聚木糖。D_(x2)、D_(x3)和D_(x4)的产物则包括木糖和较多的低聚木糖。D_(x4)与D_(x2)及D_(x3)之间在水解燕麦木聚糖时存在协同作用关系。     

陕西红富士苹果矿质营养DRIS标准研究

通过对60个红富士苹果园叶片中N、P、K、Ca、Mg、Fe等6种元素含量的测定和统计分析表明,苹果产量和品质是叶片N、P、K、Ca、Mg、Fe等元素含量综合作用的结果;通过主因素分析,各因素对产量的影响顺序为产量(Y1)x3(K)>x2(P)>x1(N)>x4(Mg)>x5(Ca)>x6(Fe);对可溶性固形物浓度(Y2)的影响顺序为x4(Mg)>x3(K)>x6(Fe)>x1(N)>x5(Ca)>x2(P);对硬度(Y3)的影响顺序为x1(N)>x6(Fe)>x3(K)>x4(Mg)>x2(P)>x5(Ca);对>80%果面红色果占有率(Y4)的影响顺序为x3(K)>x2(P)>x1(N)>x4(Mg)>x5(Ca)>x6(Fe);对低产组(产量<22 500 kg/hm2)大量元素需肥强度影响最大的为K,占该组的53.4%,对中量元素需肥强度影响最大的为Ca和Mg,均占该组的40%;对高产组(产量≥22 500 kg/hm2)DRIS重要参数的表达式为N/K、P/N、K/P,Ca/Mg、Fe/Ca、Fe/Mg,N/K、Ca/K、Ca/N,K/P、Fe/P、Fe/K,Ca/K、Mg/K、Ca/Mg,根据试验结果制定出红富士苹果园N、P、K、Ca、Mg、Fe的DRIS适宜指数范围分别为-8.355～23.011、-13.784～22.078、-12.772～9.544、-2.114～11.532、-2.503～8.902、-4.617～5.291;各园的需肥顺序用图示法和指数法判断,其结果一致.     

一类被开发的捕食系统的定性分析

讨论了一类食饵种群被开发的两种群捕食系统: dx/dt=x(a0+a1x-a2x2-a3y3)-h0, dy/dt=y(x-1)其中a0>0,a2>0,a3>0,h0>0,a1不定号.文中主要讨论了系统平衡点的行为以及系统的稳定性.用Pioncare切性曲线法及Dulac函数法讨论闭轨不存在的充分条件;用Hopf分支方法及张芷芬唯一性定理证明了极限环的存在性与唯一性.同时对相应结论的生态学意义给予了说明.     

具状态依赖时滞单种群模型周期正解的存在性

用重合度论的连续性定理,本文获得如下具状态依赖时滞的单种群增长模型周期正解的存在性x(t)=x(t)[a(t)+b(t)xp(t-τ(t,x(t)))-c(t)xq(t-τ(t,x(t)))]这里a,b,c∈C((0,∞),R)是周期为ω(ω>0)的连续函数,且a>0,c>0.m,p,q为正整数且q>p.     

井冈山山顶矮林乔木层优势种的生态位研究

对34个井冈山山顶矮林样地乔木层14个优势种的频度、重要值、Levins生态位宽度( Bi )和Morisita生态位重叠指数( Oik )进行了分析。结果表明：在井冈山山顶矮林乔木层的14个优势种中,鹿角杜鹃( Rhododendron latoucheae Franch.)、交让木( Daphniphyllum macropodum Miq.)、云锦杜鹃( Rhododendron fortunei Lindl.)、猴头杜鹃(Rhododendron simiarum Hance)和柃木(Eurya japonica Thunb.)的频度、重要值和Bi值均较高,其频度分别为0.59、0.53、0.38、0.38和0.35,重要值平均值分别为12.46%、24.63%、31.97%、38.03%和11.48%,Bi值分别为1.278、1.190、1.047、1.046和1.046;而甜槠也Castanopsis eyrei (Champ. ex Benth.) Tutch.页和野山楂(Crataegus cuneata Sieb. et Zucc.)的频度、重要值和Bi值基本上均较低,频度均为0.21,重要值分别为11.02%和5.95%,Bi值分别为0.781和0.654。14个优势种间的生态位重叠程度总体偏低,89.01%种对间的Oik值低于0.4。研究结果显示：井冈山山顶矮林乔木层优势种的生态位宽度与其重要值、频度、生物学特性和种间关系有关,且各优势种对共同资源的竞争较弱;总体来看,井冈山山顶矮林处于相对稳定阶段。     

阿维菌素起始酰基转移酶的底物特异性

[背景]阿维菌素起始酰基转移酶(AveAT0)能够以2-甲基丁酰-辅酶A (coenzyme A,CoA)和异丁酰-CoA作为起始单元分别合成"a"系列或"b"系列的阿维菌素。[目的]探究AveAT0对两种底物的偏好性并进行改造。[方法]通过与识别不同底物的起始酰基转移酶(loading acyltransferases,AT0s)进行序列比对,找到AveAT0底物结合重要的氨基酸,利用活性位点定点突变的方法得到对底物偏好性改变的特定突变体。以2-甲基丁酰-CoA、异丁酰-CoA的类似物2-甲基丁酰-N-乙酰半胱氨(N-acetylcysteamine,SNAC)和异丁酰-SNAC为底物,用Ellman测试法检测释放SNAC的游离巯基(sulfhydryl,SH),测定AveAT0及其突变体的动力学常数,以此表征AveAT0及其突变体的底物偏好性。[结果]AveAT0对2-甲基丁酰SNAC的Km值为0.4 mmol/L,kcat值为14.1 min^-1,kcat/Km为32.1 L/(mmol·min);对异丁酰-SNAC的Km值为0.8 mmol/L,kcat值为6.4 min^-1,kcat/Km为7.5 L/(mmol·min)。选定的突变位点为V224M、Q149L、L121M。按顺序累积突变后发现三突变株AveAT0 V224M/Q149L/L121M对两个底物的偏好性区别最大,对2-甲基丁酰SNAC的Km值为0.8 mmol/L,kcat值为5.4 min^-1,kcat/Km为6.9 L/(mmol·min);对异丁酰-SNAC的kcat/Km为0.1 L/(mmol·min)。[结论]研究发现了AveAT0识别底物过程中的关键氨基酸,为改造阿维菌素聚酮合酶酰基转移酶提供了依据。     

Range of the influence of the carbohydrate moiety on the conformation of the poly(amino acid) backbone in glycosylated mucins

The influence of glycosylation on the conformational properties of porcine submaxillary gland mucin has been investigated using rotational isomeric state theory. The specific objective was to determine the conditions under which the polypeptide has the relatively large mean square unperturbed radius of gyration mean value of s2(0), demanded by the measurements of Shogren et al., while retaining the overall architecture of a random coil. The mean square dimensions were monitored as the dimensionless characteristic ratio defined as C = mean value of s2(0)/npl2p, and the overall architecture was monitored by another dimensionless ratio mean value of r2(0)/mean value of s2(0), where mean value of r2(0) denotes the mean square unperturbed end-to-end distance. The computed values of C cannot reproduce the measured values if the conformational influence of glycosylation is restricted to each Ser or Thr, or if this influence extends only as far as their nearest neighbors. Values of C compatible with experiment can be obtained if the influence extends to next nearest neighbors. The behavior of the computed values of mean value of r2(0)/mean value of s2(0) permits an assignment of 7 +/- 1 as the likely upper limit to the number of consecutive amino acid residues that experience alterations in phi and psi if the sequence contains a glycosylated Ser or Thr.     

杨梅黄素及蛇葡萄素对酪氨酸酶的抑制作用

杨梅黄素及蛇葡萄素对酪氨酸酶有显著的抑制作用;在２ｍｍｏｌ／Ｌ的Ｌ－多巴浓度下,５０％抑制的药物浓度分别为０．０８２ｍｍｏｌ／Ｌ及０．２０８ｍｍｏｌ／Ｌ,用Ｌ－多巴作底物,蛇葡萄素对酪氨酸酶是竞争性抑制,其Ｋ＿ｉ是０．０８５ｍｍｏｌ／Ｌ;而杨梅黄素对酪氨酸酶则是混合性抑制,其Ｋ＿ｉ与Ｋ′＿ｉ分别是０．０２６ｍｍｏｌ／Ｌ与０．０７２ｍｍｏｌ／Ｌ。     

The relative biological effectiveness in V79 Chinese hamster cells of the neutron capture reactions in boron and nitrogen

V79 Chinese hamster cells were irradiated in the presence of different amounts of boric acid with thermal neutrons at the Medical Research Reactor at Brookhaven National Laboratory. From the linear dose-survival curves observed, a D0 value of 66 rad for the 10B(n, alpha) 7Li neutron capture reaction was obtained. No dependence of this value on the concentration of boric acid was found. Comparing this value to the D0 value of 150 rad obtained with 250 kVp X rays between 10 and 0.01% survival, an extrapolated RBE value of 2.3 was calculated. By irradiation of the same line of cells with cold neutrons at the Institut Laue - Langevin , a D0 value for the 14N(n,p)14C reaction of 77 rad was obtained, with a corresponding RBE value of 1.9. Comparison is made with previously published RBE values for the 10B(n, alpha) 7Li reaction.     

The optimal value of BMI for the lowest risk of osteoporosis in postmenopausal women aged 40–88 years

The aim of this paper is to establish the optimal values of the body mass index (BMI) which would indicate the most favourable preservation of the bone mineral density in postmenopausal women. The material consists of the data of 369 healthy women aged between 40 and 88 years (mean age 67.84, SD = 6.70) inhabitants of Wroc?aw, which were followed up between 2001 and 2006. The absolute measure of bone mineral density (BMD) of the femoral neck was assessed using dual energy X-ray absorptiometry (DEXA), expressed in g/(100 mm²) and was transformed to T-score values. According to the value of BMI, the women were divided into eight groups, the reference group with value between 18.0 and 21.9 kg/m² and seven other groups beginning with the value 22.0 with a 2-point interval. Postmenopausal status was defined according to the occurrence of menstruation within the last 360 days. The women with osteopenia and osteoporosis were pooled together and comprised the risk group, whereas the other women comprised the normal group (T-score values above −1.0). The adjusted odds ratio showed the highest value for intervals between 24.0 and 25.9 units of BMI, and the lowest value for interval 26.0–27.9 units of BMI. The Youden index showed the lowest value in the 26.0–27.9 BMI kg/m² interval. For our sample the optimal value of BMI, with the lowest risk of osteopenia and/or osteoporosis was the value of 26.9 kg/m². A further increase of BMI does not result in a favourable effect on the bones, it rather intensifies negative phenomena in the body resulting in the onset of many diseases.     

光化学反射指数在比较葡萄叶片耐霜冻能力中的应用

以12个葡萄(Vitis vinifera)品种为试材,在秋季采集叶片,进行霜冻处理,测定了霜冻过程中叶片光化学反射指数(PRI)的变化。提取有效参数,采用隶属函数法比较了不同叶片的耐霜冻能力。结果表明,随着温度的降低,叶片光化学反射指数呈下降趋势。在–8–0°C范围内,PRI及其相对值Rt与温度都存在显著的线性关系;叶片PRI在0°C、–8°C时的相对值R0、R–8,以及–8–0°C范围中,Rt与温度的回归直线斜率SLP都具有品种特异性,可以反映不同品种的耐霜冻能力。隶属函数法结合聚类分析结果显示,在12个候选品种中,抗霜冻能力最好的是Cabernet Sauvignon,其R0、R–8和SLP分别为72.3%、50.19%和2.78。     

大鼠正中神经一级传入纤维在脊髓胶状质定位投射的定量分析——FRAP法

本文用抗氟化物酸性磷酸酶(FRAP)法和显微测量,对大鼠正中神经一级传入纤维在脊髓胶状质(SG)的定位投射进行了定量分析.大鼠正中神经向SG的纵向投射主要为C_5～T_1.C_5～T_1各节段SG水平向眉毛状反应带所测均值(mm)分别为0.888、0.935、0.957、0.905和 0.776,而正中神经向C_5～T_1各节段SG水平向投射所测均值(mm)分别在0～0.204、0～0.303、0～0.409、0～0.432和0～0.336的范围,这显示了正中神经投射区均位于SG的内侧带和部分中间带.     

Cell population kinetics in the rat jejunal crypt.

Cell kinetics in the jejunal crypt of the male Wistar rat were studied using autoradiographic techniques with tritiated thymidine and a stathmokinetic technique with vincristine. The migration rate measured by following the movement of the 50% peak on the labelling index distribution curve with time after injection of tritiated thymidine gave a value of 1-43 +/- 0-14 (SE) cell positions per hour, compared with a value from a cumulative birth rate of 1-78 cell positions per hour. Tht crypt column length was 32-9 +/- 0-2 cells and the column count was 22-3 +/- 0-2. This measurement gave a total crypt population of 734 cells, compared with an estimate of 650 +/- l from direct observation of squashed, microdissected crypts. In each crypt 22-5 +/- 0-5 mitoses were present, and the crypt cell production rate was 32 cells per crypt per hour; this latter value was confirmed using two independent techniques. The crypt growth fraction calculated from the durations of phases of the cell cycle and the labelling index was 0-62. A value of 0-61 was found from the labelling index distribution curve. As assessed from crypt squashes, there were 403 proliferating cells per crypt.     

Thermodynamics of the Ca2+ binding to bovine alpha-lactalbumin

Bovine alpha-lactalbumin contains one strong Ca2+-binding site. The free energy (delta G0), enthalpy (delta H0), and entropy (delta S0) of binding of Ca2+ to this site have been calculated from microcalorimetric experiments. The enthalpy of binding was dependent on the metal-free bovine alpha-lactalbumin concentration. At 0.8 mg ml-1, metal-free bovine alpha-lactalbumin delta H0 was -110 +/- 6 kJ mol-1. At this concentration the binding constant was estimated from a mathematical analysis of the titration curves to be greater than 10(7) M-1. This means that delta G0 is smaller than -40 kJ mol-1 and delta S0 is less negative than -235 J.K-1 mol-1. The binding of Ca2+ is therefore enthalpy-driven. From binding experiments as a function of temperature, a delta Cp value of -4.1 kJ.K-1 mol-1 was calculated. This value is dependent on the protein concentration. A tentative explanation for this large value is given.