Backward bifurcation of an epidemic model with treatment

An epidemic model with a limited resource for treatment is proposed to understand the effect of the capacity for treatment. It is assumed that treatment rate is proportional to the number of infectives below the capacity and is a constant when the number of infectives is greater than the capacity. It is found that a backward bifurcation occurs if the capacity is small. It is also found that there exist bistable endemic equilibria if the capacity is low.     

Influx of γ-Aminobutyric Acid and α-Aminoisobutyric Acid into Mouse Cerebrum Slices Incubated in a Pyruvate Medium with or without Added Glucose or Glucose Analogues Compared with Influx from a Glucose Medium

Concentrative influx of γ-aminobutyric acid (GABA) and α-aminoisobutyric acid (AIB) into incubated mouse cerebrum slices is decreased when pyruvate is substituted for glucose. Influx of GABA from pyruvate medium is not increased by presence of glucose, 2-deoxy-d -glucose (2-DOG), or 3-O-methyl-d -glucose (3-O-MeG). Influx of AIB is restored to the rate from glucose medium if 2-DOG is present initially, but is not restored if 2-DOG is added with AIB. Influx is not restored if 3-O-MeG is present initially, but is restored if 3-O-MeG is added with AIB. Influx is restored if glucose is present initially or is added with AIB.     

Time-Dependent Effects of Inosine on Competence Development in Haemophilus influenzae

The effect of inosine on the development of competence is dependent upon the time at which it is added to the competence medium. Competence is inhibited if inosine is added within 15 min after the development begins, but is stimulated if the addition is made at later times. Protein synthesis is stimulated by the addition of inosine, but the effect is quantitatively similar regardless of the time at which inosine is added.     

268例难治性下呼吸道感染的细菌学分析

通过本组２６８ 例难治性呼吸道感染病人标本培养结果分析,阳性２４６ 例占９１．８ ％ ,有１５４ 例检出厌氧菌,占５７ ％ ,１０４ 例检出需氧菌,占３９ ％ ,混合感染１３３ 例,占５０ ％ 。试验结果证实,厌氧菌感染在难治性下呼吸道感染病例中占了很大比例,这一结果为难治性下呼吸道感染的治疗提供了有价值的参考数据。     

Autogenous control of Escherichia coli threonyl-tRNA synthetase expression in vivo

The regulation of the expression of thrS, the structural gene for threonyl-tRNA synthetase, was studied using several thrS-lac fusions cloned in lambda and integrated as single copies at att lambda. It is first shown that the level of beta-galactosidase synthesized from a thrS-lac protein fusion is increased when the chromosomal copy of thrS is mutated. It is also shown that the level of beta-galactosidase synthesized from the same protein fusion is decreased if wild-type threonyl-tRNA synthetase is overproduced from a thrS-carrying plasmid. These results strongly indicate that threonyl-tRNA synthetase controls the expression of its own gene. Consistent with this hypothesis it is shown that some thrS mutants overproduce a modified form of threonyl-tRNA synthetase. When the thrS-lac protein fusion is replaced by several types of thrS-lac operon fusions no effect of the chromosomal thrS allele on beta-galactosidase synthesis is observed. It is also shown that beta-galactosidase synthesis from a promoter-proximal thrS-lac operon fusion is not repressed by threonyl-tRNA synthetase overproduction. The fact that regulation is seen with a thrS-lac protein fusion and not with operon fusions indicates that thrS expression is autoregulated at the translational level. This is confirmed by hybridization experiments which show that under conditions where beta-galactosidase synthesis from a thrS-lac protein fusion is derepressed three- to fivefold, lac messenger RNA is only slightly increased.     

两型豆花粉和叶表皮的扫描电镜观察

两型豆花粉和叶表皮在扫描电镜下的形态特征：花粉近球形至矩球形,三孔沟,外壁表面较粗糙,侧壁具疣状突起至块状突起,极面具粗网状纹饰,但两型豆祖山居群属于萌发沟不明显型,两型豆燕塞湖居群属于萌发沟明显型。叶表皮细胞不规则,排列紧密,叶脉表皮细胞长圆柱形,长轴与叶脉平行,角质膜薄,表皮毛均为单细胞非腺毛,气孔器仅分布在下表皮,属于平列型,偶见不规则型。表皮毛和气孔器在叶片上分布不均匀,两型豆祖山居群叶表皮毛和气孔器的平均密度大于两型豆燕塞湖居群叶表皮毛和气孔器的平均密度,自然生长的两型豆叶表皮毛和气孔器的平均密度大于遮光条件下的两型豆。     

Discrete three-stage population model: persistence and global stability results

A general three-stage discrete-time population model is studied. The inherent net reproductive number for this model is derived. Global stability of the origin is established provided that the inherent net reproductive number is less than one. If it is larger than one the existence of a unique positive fixed point is proved and the persistence of the system is established. Finally, for certain parameter ranges global stability of the positive fixed point is proved.     

沙冬青淀粉粒及其与叶绿体发育的关系

沙冬青叶绿体中的淀粉粒一般为１－３个,主要有４种类型。第１种外周部分电子密度较高,中央部分较低,但每个部分的电子密度十分均匀。它们近似椭圆形,附近的类囊体形态正常,结构清晰。第２种电子密度由外向内逐渐变低,多为椭圆形,附近的类囊体较清晰。第３种外周部分的电子密度很高,中央部分不均匀,形状多种多样,附近的类囊体有的不清晰。第４种电子密度很低,十分均匀,形状不规则,附近的类囊体已经解体或正在解体。分析表明,淀粉的形态变化明显与叶绿体发育有关。     

药敏药片对临床235株细菌实验观察报告

药敏药片经临床对金黄色葡萄球菌、大肠埃希氏菌、铜绿假单胞菌等２３５株考核．表明药片工艺研究先进,药片与培养基结合牢固,无断裂、崩解,不渗出颗粒,抑菌圈呈同心园扩散．边缘清楚。药物含量均匀,释放度好。药片抑菌差仅１～３ｍｍ;而纸片抑菌差为２～１２ｍｍ。药片变黑系数ＣＶ为２．７１～４．２１;而纸片ＣＶ为３．８２～１４．３６。表明纸片片间差大,药片精密度明显好于纸片。     

Colcemid-resistant mutants of fission yeast have an altered cell cycle

Cell-cycle progression is altered in some colcemid-resistant mutants of fission yeast. The duration of particular stages of the cell cycle is different but total doubling time is unchanged from that of wild type. Cell-plate formation is prolonged relative to wild type but concomitant DNA synthesis is not affected. Separation of daughter cells is inhibited in some strains, giving rise to unusual cell morphologies. Control of cell division is altered in two ways: Critical size for division is increased. The probability of division a function of size is decreased.     

Failure to Maintain Glycolysis in Anoxic Nerve Terminals

Synaptosomal glycolysis is stimulated eight- to 10-fold when the respiratory chain is inhibited by cyanide or by anoxia. However, the stimulation is transient and after 15 min declines toward the preanoxic rate. The decline is not seen when Ca2+ is absent or when the respiratory chain is inhibited by rotenone. The decline in glycolysis is reversible, is not due to substrate exhaustion, and is the cause, rather than the effect, of lowered synaptosomal ATP/ADP ratios. The failure to maintain glycolysis when the terminal oxidase of the respiratory chain is inhibited may have relevance to the sensitivity of the brain to anoxic damage.     

Discrete three-stage population model: persistence and global stability results

A general three-stage discrete-time population model is studied. The inherent net reproductive number for this model is derived. Global stability of the origin is established provided that the inherent net reproductive number is less than one. If it is larger than one the existence of a unique positive fixed point is proved and the persistence of the system is established. Finally, for certain parameter ranges global stability of the positive fixed point is proved.     

矮沙冬青雌配子体及胚胎发育研究

矮沙冬青子房单心皮1室,边缘胎座,弯生胚珠,胚珠具双珠被、厚珠心。大孢子孢原细胞发生于珠心表皮下,大孢子母细胞减数分裂形成直线排列的四分体,合点端大孢子具功能,并按蓼型胚囊发育,雌配子体成熟于4月中旬。双受精后,胚乳发育为核型。在矮沙冬青大孢子发生、雌配子体和胚胎发育过程中未发现异常现象,因此认为矮沙冬青濒危不存在雌性生殖结构与发育过程异常的内在因素。     

清栓酶治疗脑血栓冠心病微循环变化初步观察

本文报导40例脑心血管疾病在清栓酶治疗前后进行甲皱微循环对比观察,其中脑血栓组20例,冠心病组20例,两组均在清栓酶治疗2～3疗程后复查,分别对其甲皱微循环微血管袢的形态及功能,血液流态和微血管周围变化等三方面进行治疗前后对比观察,结果发现,治疗前甲皱微循环改变是明显的,临床症状较重,治疗后甲皱微循环障碍均得到了明显改善,临床症状也随着减轻或消失。治疗前后比较,其差异有显著的意义 P<0.05,P<0.01.从临床对比观察所见,脑心血管疾病的微循环改变与病情有关,其改变与病情轻重相吻合,与疾病转归相一致,提示微血管病变是动脉硬化临床可识别的象征.微循环障碍与疾病的发生发展有着内在联系,是脑心血管疾病的病因和发病的中间环节.治疗后微循环障碍的明显改善,提示清栓酶有着较好的改善微循环的功能.     

Effect of binding on melting transitions in polymer–diluent systems

An expression is derived for the melting point of a polymer when in equilibrium with a solution in which binding of low molecular weight compounds to the polymer takes place. Allowance is made for the possibility that the crystalline polymer itself is a complex. The argument is a purely thermodynamic one and is based on a consideration of the change in free energy as a result of a change in binding. Allowance is made also for non-specific polymer–solvent interactions, in which the mixture of low molecular weight solvents is treated as a single solvent. Special attention is paid to “inverted” melting transitions, i.e., cases in which the melting point increases with increasing dilution of the polymer. It is shown that as a rule this is accompanied by a corresponding, inverted effect of the solvent composition on the melting point. It is further shown that-in the absence of binding, “normal” behavior at the critical point (i.e., phase separation is induced by lowering the temperature) is always accompanied by “normal” melting behavior (i.e., a decrease in melting point when the polymer is diluted). Also, “inverted” melting always implies that phase separation at the critical point is induced by heating, but the reverse is not necessarily true.     

Homology and function in the wings of Heteroptera

Abstract. The homology of veins and other wing characters in Heteroptera is reviewed in the light of palaeontology and new functional studies. A cladogram is given for the higher taxa of Hemiptera. It is probable that the vannus is an autapomorphy of Auchenorrhyncha+Heteropteroidea; that the leading edge vein of heteropteran fore- and hindwings is C+Sc; that Rs cannot be distinguished from R; that the hamus is part of M; that the glochis is a secondary structure. The difficulty of defining a vein is stressed. The functional significance of the hemielytron, cuneal fracture and longitudinal flexion lines is discussed. A preliminary ground-plan for Heteroptera wings is presented.     

Selection intensity against deleterious mutations in RNA secondary structures and rate of compensatory nucleotide substitutions

A two-locus model of reversible mutations with compensatory fitness interactions is presented; single mutations are assumed to be deleterious but neutral in appropriate combinations. The expectation of the time of compensatory nucleotide substitutions is calculated analytically for the case of tight linkage between sites. It is shown that selection increases the substitution time dramatically when selection intensity Ns > 1, where N is the diploid population size and s the selection coefficient. Computer simulations demonstrate that recombination increases the substitution time, but the effect of recombination is small when selection is weak. The amount of linkage disequilibrium generated in the process of compensatory substitution is also investigated. It is shown that significant linkage disequilibrium is expected to be rare in natural populations. The model is applied to the mRNA secondary structure of the bicoid 3' untranslated region of Drosophila. It is concluded that average selection intensity Ns against single deleterious mutations is not likely to be much larger than 1.     

The consequences of dominance and gene flow for local adaptation and differentiation at two linked loci

For a subdivided population the consequences of dominance and gene flow for the maintenance of multilocus polymorphism, local adaptation, and differentiation are investigated. The dispersing population inhabits two demes in which selection acts in opposite direction. Fitness is determined additively by two linked diallelic loci with arbitrary intermediate dominance (no over- or underdominance). For weak as well as strong migration, the equilibrium structure is derived. As a special case, a continuous-time continent–island model (CI model) is analyzed, with one-way migration from the continent to the island. For this CI model, the equilibrium and stability configuration is obtained explicitly for weak migration, for strong migration, for independent loci, and for complete linkage. For independent loci, the possible bifurcation patterns are derived as functions of the migration rate. These patterns depend strongly on the degree of dominance. The effects of dominance, linkage, and migration on the amount of linkage disequilibrium (LD) and the degree of local adaptation are explored. Explicit formulas are obtained for $D$   $(=x_1{x}_4-x_2{x}_3)$ and $r^2$ (the squared correlation in allelic state). They demonstrate that dominant island alleles increase $D$ and decrease $r^2$. Local adaptation is elevated by dominance of the locally adaptive alleles. The effective migration rate at a linked neutral locus is calculated. If advantageous alleles are dominant, it is decreased only slightly below the actual migration rate. For a quantitative trait that is determined by two additive loci, the influence of dominance on measures of differentiation is studied. Explicit expressions for $Q_{ST}$ and two types of $F_{ST}$ at equilibrium are deduced and their relation is discussed.     

杉木人工林水量平衡和蒸散的研究

 本文根据我们严密设计的小集水区径流场连续6年的水文测定数据,进行了杉木人工林水量平衡和蒸散的研究。结果表明：集水区年平均降雨量1065.5mm, 在林冠作用面降雨量的分配中,林冠截留雨量264.6mm,截留率24.8%;穿透过林冠层的雨量799.82mm,树干径流量1.08mm,分别占降雨量的75.1%和0.1%。林内降水到达林地时,在枯枝落叶层这个作用面上净降水进行再分配,其中,地表径流量9.27mm,地下径流量203.00mm,总径流系数0.199。土壤蓄水量月变化较大,但年变化很小,占降雨量的1.2%。系统水量最大的输出是蒸散,每年以气态形式返回大气的水量866.03mm,占降雨量81.3%。在蒸散的水量中,林冠截留雨量的直接物理蒸发量为264.6mm,占总蒸散量的31.6%。     

The consumer's risk in clinical trials

In any formal statistical test of the null hypothesis (the statement that a population parameter is equal to a specific value), there are two possible types of error. Type 1 or alpha error has occurred if the investigator rejects the null hypothesis when it is true. For example, an experimental treatment is declared an advance over standard treatment when it is not. Type 2 or beta error has occurred if the null hypothesis is not rejected when it is false. In this case, the investigator concludes that the experimental treatment is no different than the standard when it actually is. The two types of error can be conceptualized, respectively, as the consumer's risk and the producer's risk. In many reports of clinical trial methodology, it is the producer's risk that is emphasized. It is understandable why producer's risk would be of concern to authors of clinical studies. There are, however, numerous potential sources of consumer's risk. It is the latter type of risk that is the primary subject of this report.