儿童的惯性－惯量特征及其生长

本文应用排水法得到儿童肢体沿长轴的体积分布函数。根据关于人类肢体体积－质量的假定,肢体的质心、转动惯量及旋转半径等动力学常数可由前述的体积分布函数中求出。本文结果显示,部分力学参数与儿童的生长有着密切的联系,并受到性别的影响。因此,这些参数可以用来作为儿童的生长指标。以往数据的离散性表明,无论从系统上或技术上,这一领域都有许多工作要做。     

界面发酵红曲霉的图像解析*

利用计算机视觉技术研究了红曲霉界面发酵过程中菌体形态变化与菌体生长的关系。在界面培养中通过检测前期菌落面积,后期隆起部分的表征体积——基于颜色变化的生长点分布,可以有效表示菌体生长状况。基于此建立了含有相应形态参数的动力学模型,该模型与常规动力学模型具有相似的表达形式。     

反卷积在生物组织光传输特性研究中的应用

生物组织中的光传输特性可以以点扩散函数表征,即在线状光束入射条件下,生物组织中某一深度层面上的光强度场分布。为获得点扩散函数的具体形式,已发展了多种理论分析方法,其中以Monte Carlo模拟方法最具代表性。但现有理论计算方法都要以生物组织的光学参数已知为前提,而光学参数的准确度直接影响着计算的精度。从线性平移不变系统理论出发,生物组织内一定深度层面上的光强分布被看成是光源强度分布与点扩散函数的卷积,从而提出通过测量在轴对称的准直扩展光源照射条件下,组织中特定层面上的光强度分布,利用反卷积重建生物组织的点扩散函数的方法,并将这种方法应用于典型生物组织透射面上点扩散函数的重建,得到了相应的点扩散函数。实验结果与Monte Carlo模拟的结果吻合较好,表明该方法从实验上获得生物组织点扩散函数的正确性和有效性。     

樟子松沙地人工林直径分布模拟

利用反 Weibull函数模拟了章古台沙地樟子松人工林的直径分布规律 .结果表明 ,反 Weibull分布函数模拟樟子松人工林的直径分布效果好 ,具有精度高、适应性强等特点 .分别建立了反 Weibull分布函数 3个参数与林分年龄及密度之间的关系方程以及直径分布与 3个参数的回归方程 ,这些方程可用来预估林分产量、出材量以及评价经营效果     

一类含间隙分布时滞的种群增长模型的稳定性

本文首先利用间隙分布时滞函数来建立更为符合实际的种群增长模型,然后运用两种不同的方法,对其平衡位置的局部稳定性进行了全面的讨论,得出了局部渐近稳定的充分必要条件,在参数平面上划分出了稳定和不稳地的区域。     

小兴安岭低山区红松生长的气候响应机制

基于小兴安岭红松的树轮资料,确定了Tree-Ring生态机理模型模拟红松树木生长的参数.应用Tree-Ring模型对小兴安岭红松的生长过程进行了模拟,结果显示Tree-Ring模型在该地具有较好的适用性.参数敏感性分析表明红松树木生长比较敏感的参数是光合最低温度、光合最适温度下限、最适土壤体积含水率上限和最大土壤体积含水率.模拟发现,红松树轮宽度变化主要受到生长季上一年10月份气温和当年4月份气温变化控制.形成层开始生长平均是在4月下旬,这时水分充足,而温度在光合最低温度和最适温度下限之间,温度愈高,光合速率愈大,储存的养料愈多,因此表现为与树轮宽度的正相关关系.形成层生长结束的时间平均在10月上旬,用于形成层细胞生长的光合产物的消耗减少,而光合速率随着温度的升高而增大,因此,10月份的气温越高为下一年储存的养料越多,翌年易形成宽轮.     

基于全局灵敏度分析的浒苔生长影响参数研究

近年来,以浒苔为主的绿潮灾害频发。构建了浒苔生长模型,以定量分析浒苔生长过程,探索浒苔爆发机理。参数不确定性是模型不确定性的主要来源,以参数灵敏度分析为基础的参数优化有利于提高模型精度,采用Morris方法对模型涉及的主要参数进行了全局灵敏度分析,以研究浒苔生长的主要影响参数。不同于其他有关大型绿藻的模型模拟,模型同时考虑了幼体浒苔和成熟浒苔的生物量变化,并修正了营养盐限制函数以及温度计算函数。全局性的参数灵敏度分析结果表明,最适温度(T_(opt))、光合作用最适光强(Is)、最大发芽率(G_(max))、浒苔生长所需的氮含量的半饱和系数(kqn)、最大氮摄取率(V_(maxn))这5个参数在浒苔生长模型中具有较大灵敏性。其中,T_(opt)影响最大,Is和V_(maxn)其次,说明浒苔生长主要受温度光照和氮含量限制。相较于局部灵敏度分析仅关注单个参数变化、依赖于初值选取等缺陷,全局灵敏度分析同时从各个参数的取值范围上分析参数对模型结果的影响,能揭示参数之间相互作用的影响。此外,灵敏度较大的参数往往和其他参数之间存在较大相关性。     

冬小麦根系各种参数垂直分布实验研究

本文根据田间实测资料研究了冬小麦根系各种参数(长度、重量、活性表面和根径)的垂直分布。结果表明,在所观测地区的土壤条件下,冬小麦根系的长度、重量、表面积和体积随深度呈指数分布,而累积根系的长度、重量和表面积随深度呈双曲线型分布。根据作者的观测资料和国内外其它观测资料分析研究表明,对于不同土壤,根区各层土壤中累计根重及根长的百分比随相对深度的变化都符合下列双曲线函数形式:这一研究结果可为根系生态研究和作物对水分吸收的模拟工作提供参考。     

对生玉米冠层光强分布的模拟研究

本文通过数学模拟的方法从理论上建立了对生玉米群体中的光强分布模型.此模型中作者引入了叶数密度函数的概念体现对生玉米和互生玉米在株高、节数和每节叶数等株型参数上的区别,从而大大简化了相关的计算,提高了模型的实际应用效果.     

生物组织光散射等效颗粒模型及Mie相函数计算

为研究生物组织的散射特性,将其从散射效果上等效为离散的球形散射体的集合,结合经典的Mie散射理论对生物组织散射相函数进行数值计算。计算结果表明:Mie散射相函数能够描述生物组织后向(大角度)散射光强振荡特性与等效粒径的对应关系,可为基于后向散射光的无创伤或微创伤诊疗提供理论依据;Mie散射相函数能够解释生物组织散射光空间分布与波长的相关性,为医学诊疗上入射光波长选择提供参考;合理选择集群散射体粒度分布参数,可实现对复杂生物组织散射相函数的精确描述。     

Parametric analysis of volume distributions of Schizosaccharomyces pombe and other cells

Time-lapse photomicrographic data have been obtained on mating strains of the yeast Schizosaccharomyces pombe to evaluate the effect of the variability of the patterns of cell cycle behavior on population structure. These have been used to design a computer model which accepts volume distribution data from exponential cultures of a cell and yields estimates of the mean and standard deviation of daughter cell volume and telophase cell volume, as well as a stop-grow point, and the degree of cell volume doubling. Given a cell population's volume distribution and a volume distribution from a subpopulation, the program will estimate the mean age and display how the age is distributed in the subpopulation. Several cell types have been examined.     

Analysis of protein and cell volume distribution in glucose-limited continuous cultures of budding yeast

Method of flow cytometric analysis have recently been developed that make it possible to obtain segregated data on a single cell basis. In particular, it has been previously demonstrated that protein distributions obtained by flow cytometry give information about the law of growth of the cell population and the law of growth of the single cell; thus these distribution show how the microbial population is actually growing at the moment of the analysis and may yield more accurate and predictive information. We have extended the analysis of protein distribution and cell volume distribution to continuous cultures of Saccharomyces cerevisiae growing in a glucose-limited chemostat. We have found that: (1) to each dilution rate corresponds a given protein and volume distribution that does not change with time in steady state cultures; (2) there is a good proportionality between the average cell volume and the average protein content; (3) the protein distribution obtained can be easily analyzed with the model of growth of yeast previously developed in our laboratory; (4) the analysis of perturbed states shows that both protein distribution and volume distribution change very quickly; thus they are very sensitive parameters and can be used for monitoring and controlling industrial fermentation.     

Amine promiscuity and toxicology analysis

Drug discovery programs often face challenges to obtain sufficient duration of action of the drug (i.e. seek longer half-lives). If the pharmacodynamic response is driven by free plasma concentration of the drug then extending the plasma drug concentration is a valid approach. Half-life is dependent on the volume of distribution, which in turn can be dependent upon the ionization state of the molecule. Basic compounds tend to have a higher volume of distribution leading to longer half-lives. However, it has been shown that bases may also have higher promiscuity. In this work, we describe an analysis of in vitro pharmacological profiling and toxicology data investigating the role of primary, secondary, and tertiary amines in imparting promiscuity and thus off-target toxicity. Primary amines are found to be less promiscuous in in vitro assays and have improved profiles in in vivo toxicology studies compared to secondary and tertiary amines.     

Body water content and distribution in nonpregnant adult female baboons

Water contents of the various body water compartments were estimated in 16 nonpregnant adult female baboons and compared to human data. Total body water, extracellular water, and plasma volumes were determined by dilution studies. Intracellular water, interstitial water, blood volume, and red cell volume were calculated. The data were compatible with the finding that baboon females probably have less body fat than their human counterparts. Our data establish a basis for longitudinal studies of the changes in body water content and distribution during normal and pathological pregnancies.     

Curve fitting approach for measurement of cellular osmotic properties by the electrical sensing zone method. I. Osmotically inactive volume

We have investigated the confounding effects of dynamic range limitations on measurement of the osmotically inactive volume using electrical sensing zone instruments (e.g., Coulter counters), and propose an improved approach to parameter estimation. The conventional approach for analysis of cell size distributions measured by such particle sizing instruments requires data truncation: the mean cell volume is computed after exclusion of data below a specified lower bound (typically chosen to remove artifacts due to small-volume noise) and above an upper bound (typically governed by instrument limitations). The osmotically inactive volume is then estimated from a Boyle–van’t Hoff plot of the averaged volume data obtained after exposure to various solution osmolalities. We demonstrate that systematic exclusion of data in the conventional approach introduces bias that results in erroneously high estimates of the osmotically inactive volume fraction. To minimize this source of error, we have devised a new algorithm based on fitting a bimodal distribution model to the non-truncated volume data. In experiments with mouse insulinoma (MIN6) cells, the osmotically inactive volume fraction was estimated to be 0.15 ± 0.01 using the new method, which was significantly smaller than the estimate of 0.37 ± 0.02 obtained using the conventional method (p < 0.05). In silico experiments indicated that the parameter estimate obtained by the new method was accurate within 5%, whereas the error associated with the conventional approach was approximately 150%. Parametric analysis was used to elucidate the sensitivity of errors to variations in instrument dynamic range and cell volume distribution width.     

Estimation of flattening coefficient for absorption and circular dichroism using simulation

The absorbance and circular dichroism (CD) of suspensions is lower than if the same amount of chromophore were uniformly distributed throughout the medium. Several mathematical treatments of this absorption flattening phenomenon have been presented using various assumptions and approximations. This article demonstrates an alternative simulation approach that allows relaxation of assumptions. On current desktop computers, the algorithm runs quickly with enough particles and light paths considered to get answers that are usually accurate to better than 3%. Results from the simulation agree with the most popular analytical model for 0.01 volume fraction of particles, showing that the extent of flattening depends mainly on the absorbance through a particle diameter. Unlike previous models, the simulation can show that flattening is significantly lower when volume fraction increases to 0.1 but is higher when the particles have a size distribution. The simulation can predict the slope of the nearly linear relationship between flattening of CD and the absorbance of the suspension. This provides a method to correct experimental CD data where volume fraction and particle size are known.     

Changes in myocardial contractility and contractile proteins after four weeks of simulated [correction of simulate] weightlessness in rats

The interaction between the gravitational field, the position of the body, and the functional characteristics of the blood vessels determines the distribution of intravascular volume. In turn, this distribution determines cardiac pump function. One of the most profound circulatory changes that occurs in man during exposure to weightlessness is a cephalad redistribution of fluid caused by the lack of hydrostatic pressure in this microgravitative environment. The cephalad redistribution of fluid results in a loss of blood volume and then induces a decrease in preload. Recently, a decrease in sensitivity of arteriole to catecholamine has reported in rats of simulated weightlessness. This change in arteriole may reduce afterload. As a result, cardiovascular system may be shifted to a hypokinetic state during weightlessness condition for long-term. Echocardiographic data from astronauts during space flight showed an increase in heart rate, a 12 % decrease in stroke volume, and a 16 % decrease in left end diastolic volume. Electron-microscopic studies have shown changes in cardiac morphology in rats after exposure to microgravity for 7-12.5 days. After the COSMOS 2044 flight for 14 days, the light-microscopic studies have shown an atrophy of papillary muscles in rats left cardiac ventricle. It is not clear whether the function of atrophic myocardium is impaired. The data in three aspects as mentioned above suggest that weightlessness or simulated weightlessness may decrease the myocardial function. However, definite changes in cardiac performance have been hard to prove due to many limits. This studies were to answer two questions: Is the myocardial contractility depressed in rats subjected to simulated weightlessness for four weeks? What are the underlying mechanisms of the changing contractility?     

A calculator program for clinical application of the Bayesian method of predicting plasma drug levels

A pharmacokinetic program that allows individualization of drug dosage regimens through the Bayesian method is described. The program, which is designed for the Hewlett-Packard HP-41 CV calculator, is based upon the one-compartment open model with either instantaneous or zero-order absorption. Individualized estimation of the patient's kinetic parameters (clearance and volume of distribution) is performed by analyzing the plasma levels measured in the patient as well as considering the population data of the drug. After estimating the individual kinetic parameters by the Bayesian method, the program predicts the dosage regimen that will elicit the desired peak and trough plasma levels at steady state. For comparison purposes, the least-squares estimates for clearance and volume of distribution are calculated, and dosage prediction can also be made on the basis of the least-squares estimates. The least-squares estimates can be used to calculate population pharmacokinetic parameters according to the Standard Two-Stage method. Several examples of clinical use of the program are presented. The examples refer to patients with classic hemophilia who were treated with Factor VIII concentrates. In these patients, the Bayesian kinetic parameters of Factor VIII have been estimated through the calculator program. The Bayesian parameter estimates generated by the HP-41 have been compared with those determined by a Bayesian program (ADVISE) designed for microcomputers.