分子绝对进化速率与物种分歧时间之间的定量关系

通过对美国国家生物技术信息中心数据库Gen Bank提供的一些蛋白质和核苷酸序列进行比对和分析,发现生物分子绝对进化速率k与进化时间或物种分歧时间t之间存在下列定量关系:lnk=-Ea/Rt+lnK0,式中Ea为位点突变活化能,k0为分子极限绝对进化速率,R为常数,并对其生物学意义进行了初步的探讨;数据分析还揭示出物种的分子极限绝对进化速率与进化时间或物种分歧时间之间也服从相似的定量公式,也就是说生物分子进化过程可能同时受到序列位点突变和控制物种分子极限绝对进化速率进化的两个"分子钟"作用,即存在"双重分子钟"现象。     

蛋白质功能基团的改变与其生物活力之间的定量关系

蛋白质(包括酶)分子结构与功能的关系一直是分子生物学的核心问题之一.用各种方法改变蛋白质分子中侧链基团的性质观察对其生物活力的影响是研究这一问题的主要方法.蛋白质化学修饰的研究,迄今已有约60年的历史.自20年代末到60年代初的30余年内,这一研究一直停留在定性描述阶段,大量的实验结果不能进行定量的数据处理.因为在蛋白质分子中某类侧链基团在功能上虽有必需与非必需之分,但是在与某试剂起反应上往往是相同的,即它们都能与某一试剂起反应.所以,虽然从实验上可以测得随侧链基团的被修饰导致其生物活力下降的关系,但是在所测得的被修饰的基团中,既有必需的,也有非必需的.由于长期以来人们没有找到生物活力与必需基团之间的定量关系,也就无     

定量结构-生物降解性能关系模型在21世纪农药发展中的应用

简要概述农药的概念、环保型农药的主要特点、农药的主要生产和设计途径以及农药在粮食增产的同时给环境带来的负面影响。定量结构一生物降解性能关系（QSBR）能够定量预测有机物的生物降解性能,可作为一种预测有机物降解过程和性能的模型。本文提出将其应用于环保型农药的设计和筛选中,从而减少由于农药生物降解给环境带来的影响。     

金线蛙入蛰时几顶生理常数间的关系研究

本文统计学分析处理,表明金钱蛙入蛰时的体长与体重,胴体重和体重与肝重,脂肪体重,生殖腺重之间均存在非常显著的线性相关关系。     

生物肽降压作用机制及定量构效关系的研究

高血压是心脑血管疾病的首要危险因素,严重威胁着人类的生命健康。生物肽能有效预防和治疗高血压,并且具有安全可靠、作用多靶点等特点。大量的研究表明生物肽存在多种降压作用机制,深入研究降压机制可为中药治疗高血压提供新思路。本文综述了近年来生物肽潜在的降压机制,并探索其定量构效关系,旨在为中药药效组分的研究以及相关药物设计和筛选提供理论指导。     

金线蛙入蛰时几项生理常数间的关系研究

本文经统计学分析处理,表明金钱蛙（Ｒａｎａｐｌａｎｃｙｉ）入蛰时的体长与体重、胴体重和体重与肝重、脂肪体重、生殖腺重之间均存在非常显著的线性相关关系。     

系统比较氨基酸描述子在多肽定量构效关系中的应用

氨基酸描述子是采用多元统计方法从大量氨基酸性质参数中提取得到的少数关键信息成分,目前已被广泛应用于多肽生物活性预测及蛋白质功能判别等领域。鉴于近年来氨基酸描述子种类的极速扩增,收集了目前国内外发表的27种氨基酸描述子,并将其用于8组经典多肽集的结构表征及定量构效关系研究。通过系统比较这些描述子对同一肽集与不同肽集的统计建模结果,我们认为物理化学描述子的建模效果优于拓扑描述子,拓扑描述子的建模效果优于三维结构描述子,且已有诸多氨基酸描述子已经达到性能限度,如未考虑肽链内部各氨基酸残基的交互影响,肽配基与相应靶标蛋白的相互结合,因此不再建议按照传统思路进一步提出新型描述子种类。     

花背蟾蜍冬眠期几项生理常数间的关系

本文揭示了花背蟾蜍ＢｕｆｏｒａｄｄｅｉＳｔｒａｕｃｈ冬眠前、后雌性和雄性之体长、胴体重、肝重、脂肪体重以及生殖腺重与体重之间,均呈显著的正相关,回归系数ｔ检验表明,雌雄间差异显著,且冬眠期间雌性主要消耗物来自躯体和脂肪体,雄性来自躯体、肝脏和脂肪体。     

头孢菌素类抗生素的定量构效关系研究

目的:建立一种预测精度较高的定量构效关系(QSAR)模型,为设计和合成活性更高的头孢菌素类抗生素提供理论依据。方法:发展了一种基于支持向量回归(SVR)和k-最近邻(KNN)的非线性组合预测方法(SVR-KNN),系统研究了48种抗流感嗜血杆菌头孢菌素衍生物的QSAR。结果:留一法预测结果表明,非线性筛选描述符和子模型能明显提高预测精度,汰选子模型后的组合预测精度优于单一子模型,SVR-KNN的MSE、MAPE分别为0.019、1.81%;独立样本预测结果显示,SVR-KNN在所有参比模型中具有最优的预测精度及稳定性,其MSE、MAPE分别为0.010、1.33%。结论:SVR-KNN模型具有较强的预测能力和优异的泛化推广能力,在抗生素及其他药物的QSAR研究中有广泛应用前景。     

稻麦叶片氮含量与冠层反射光谱的定量关系

作物氮素含量是评价作物长势、估测产量与品质的重要参考指标,叶片氮素含量的无损快速监测对于指导作物氮素营养的精确管理及生产力的预测预报具有重要意义.以5个小麦品种和3个水稻品种在不同施氮水平下的3a田间试验为基础,综合研究了稻麦叶片氮含量与冠层反射光谱的定量关系.结果显示：（1）不同试验中拔节后稻麦叶片氮含量均随施氮水平呈上升趋势;（2）稻麦冠层光谱反射率在不同施氮水平下存在明显差异,在可见光区（460～710 nm）的反射率一般随施氮水平的增加逐渐降低,而在近红外波段（760～1100 nm）却随施氮水平的增加逐渐升高;（3）就单波段光谱而言,610、660 nm和680 nm处的冠层反射率均与稻麦叶片氮含量具有较好的相关性;（4）在光谱指数中,归一化差值植被指数NDVI（1220,610）与水稻和小麦叶片氮含量均具有较好的相关性,且相关性好于单波段反射率;（5）对于小麦和水稻,可以利用共同的波段和光谱指数来监测其叶片氮含量,采用统一的回归方程来描述其叶片氮含量随单波段反射率和冠层反射光谱参数的变化模式,但若采用单独的回归系数则可以提高稻麦叶片氮含量估测的准确性.     

A quantitative structure-activity relationship study on matrix metalloproteinase inhibitors: Piperidine sulfonamide aryl hydroxamic acid analogs

A quantitative structure-activity relationship (QSAR) study has been made on a series of piperidine sulfonamide aryl hydroxamic acid analogs acting as matrix metalloproteinase (MMP) inhibitors. The inhibitory potencies of the compounds against two MMPs, MMP-2 and MMP-13, are found to be significantly correlated with the hydrophobic properties of the molecules, suggesting that in both enzymes the hydrophobic interaction is playing a dominant role.     

Whole genome approaches to quantitative genetics

Apart from parent-offspring pairs and clones, relative pairs vary in the proportion of the genome that they share identical by descent. In the past, quantitative geneticists have used the expected value of sharing genes by descent to estimate genetic parameters and predict breeding values. With the possibility to genotype individuals for many markers across the genome it is now possible to empirically estimate the actual relationship between relatives. We review some of the theory underlying the variation in genetic identity, show applications to estimating genetic variance for height in humans and discuss other applications.     

Quantifying BSE control by calculating the basic reproduction ratio R 0 for the infection among cattle

The safety of using meat and bone meal (MBM) in mammal feed was studied in view of BSE, by quantifying the risk of BSE transmission through different infection routes. This risk is embodied in the basic reproduction ratio R ₀ of the infection, i.e. the average number of new infections induced by one initial infection. Only when R ₀ is below 1, will the disease die out with certainty and the population will become free from BSE. Unfortunately this is a slow process due to the slow progression of the disease. We calculate R ₀ explicitly from basic ingredients taking several different transmission routes into account. Several of the basic ingredients are functions of age or of infection-age. We also calculate the exponential growth rate r in terms of the same basic ingredients. Next we quantify the ingredients from available data and compute the effects on R ₀ of various scenarios for controlling BSE, with examples for the UK and the Netherlands. This revised version was published online in November 2003. A correction was made to formula 10 of this paper, indicies were previously printed in an incorrect order and an extraneous element has been removed.     

基于GIS的农田土壤、作物特征空间变异性及其相互关系

The objective of this research was to investigate the variability and the quantitative relationships among soil nutrients and crop growth status and yield. All data were analyzed by both classical statistics and geostatistics based on GIS. Soil properties included soil pH, total N, organic matter, available P and available K, while crop growth status was indicated by SPAD, LAI and SPAD × LAI. All parameters except soll pH exhibited spatial correlation.Soil total N and organic matter, SPAD, LAI and SPAD × LAI were all correlated to rice yield. Kriged interpolation maps provided good indication of the spatial variability in crop yield and growth status. Spatial interpolation and correlation analysis proved that SPAD × LAI was more indicative of crop growth status than individual variables, and useful for implementing growth season and topdressing as needed.     

The relationship of intercompartmental excitation transfer rate constants to those of an underlying physical model

In studies on photosynthetic systems it is common practice to interpret the results of time-resolved fluorescence experiments on the basis of compartmental, or target, models. Each compartment represents a group of molecules with similar fluorescence characteristics. In cases of practical interest, the members of each compartment are spatially contiguous and make up part of an overall energy-transferring system. Since a rate constant describing the overall transfer between compartments is not that of any pair of molecules in the system, this question naturally rises: what do we learn about the microscopic structure from these data? In this note we introduce ‘compartment melting’, a smooth mathematical connection between the compartmental and microscopic levels. We then show, on the basis of model calculations on finite lattices in one, two, and three dimensions, that average microscopic rates at the interfaces between compartments may be estimated from observed intercompartmental rates. The estimate involves a modest number of structural assumptions about the system. As examples of the method, which is applicable mainly to systems containing homogeneous pigment pools, some recent chlorophyll-protein antenna studies are analyzed.     

Determination of the viscometric constants for chitosan

The viscometric constants a and K_m in the Mark-Houwink equation have been determined for chitosan in 0.1 m acetic acid 0.2 m sodium chloride solution, using the approach of Sharples and Major. The number-average molecular weights were determined by absorbance measurements on solutions of the phenylosazone derivatives. The values obtained a = 0.93, K_m = 1.81 × 10^?3 cm³ g¹ differ considerably from those reported previously by Lee but are in agreement with values found for other ionic polysaccharides having related β-(1 → 4)-linked structures.     

The estimated elastic constants for a single bone osteonal lamella

Micromechanical estimates of the elastic constants for a single bone osteonal lamella and its substructures are reported. These estimates of elastic constants are accomplished at three distinct and organized hierarchical levels, that of a mineralized collagen fibril, a collagen fiber, and a single lamella. The smallest collagen structure is the collagen fibril whose diameter is the order of 20 nm. The next structural level is the collagen fiber with a diameter of the order of 80 nm. A lamella is a laminate structure, composed of multiple collagen fibers with embedded minerals and consists of several laminates. The thickness of one laminate in the lamella is approximately 130 nm. All collagen fibers in a laminate in the lamella are oriented in one direction. However, the laminates rotate relative to the adjacent laminates. In this work, all collagen fibers in a lamella are assumed to be aligned in the longitudinal direction. This kind of bone with all collagen fibers aligned in one direction is called a parallel fibered bone. The effective elastic constants for a parallel fibered bone are estimated by assuming periodic substructures. These results provide a database for estimating the anisotropic poroelastic constants of an osteon and also provide a database for building mathematical or computational models in bone micromechanics, such as bone damage mechanics and bone poroelasticity.