A comparison of three maximum likelihood models for stage-frequency data

A comparison has been made between the estimates obtained from maximum likelihood estimation of gamma, inverse normal, and normal distribution models for stage-frequency data. Results have been compared for six of sets of test data, and from many sets of simulated data. It is concluded that (1) some estimates may differ substantially between the models, (2) estimates from the correct model have little bias, and estimated standard errors are generally close to theoretical values, (3) there are problems in determining degrees of freedom for chi-squared goodness of fit tests, so that it is best to compare test statistics with simulated distributions, and (4) goodness of fit tests may not discriminate well between the three models.     

动物内温性进化研究进展

对动物内温性进化的研究进行了较为系统的论述,包括内温性动物概念的由来、特点和起源的选择因子。内温性起源的选择因子包括8个模型：热生态位扩展模型、恒温与代谢效率模型、降低个体大小模型、姿势改变模型、增加脑大小模型、有氧呼吸能力模型、双亲行为模型和同化能力模型。其中后3个模型较为重要。有氧呼吸能力模型认为,选择提高支持物理运动的最大呼吸能力,而增加的静止代谢作为其相关反应而得以进化。该假说得到种内研究数据的支持,而种问的数据并小完全支持。双亲行为模型是指在鸟兽类中,内温性是对双亲行为选择的结果,因为内温性为双亲控制抚育温度提供了保证。同化能力模型认为,在鸟类和兽类中内温性进化由以下两个因素所推动：①子代出生后双亲行为加强;②为支持每日总体能量高速消耗所需,动物内脏器官能力增强而导致的较高维持消耗。     

Computer simulations of in vitro morphogenesis

One of the most important challenges of contemporary biology is understanding how cells assemble into tissues. The complexity of morphogenesis calls for computational tools able to identify the dominant mechanisms involved in shaping tissues. This narrative review presents individual-based computational models that proved useful in simulating phenomena of interest in tissue engineering (TE), a research field that aims to create tissue replacements in the laboratory. First, we briefly describe morphogenetic mechanisms. Then, we present several computational models of cellular and subcellular resolution, along with applications that illustrate their potential to address problems of TE. Finally, we analyze experiments that may be used to validate computational models of tissue constructs made of cohesive cells. Our analysis shows that the models available in the literature are not exploited to their full potential. We argue that, upon validation, a computational model can be used to optimize cell culture conditions and to design new experiments.     

模型实验教学在组织学与胚胎学实验教学中的尝试

组织学与胚胎学是重要的医学基础课,属于形态学科。目前,组织学与胚胎学实验教学多采用数码互动实验教学,切片观察为主要手段,而切片观察主要是观察组织的平面结构,欠缺立体结构的观察。模型实验教学是以组织学与胚胎学的形态为中心组织学生制作立体模型,启发学生思维,充分发挥想象力,培养学生的动手能力和实践能力。     

结核病动物模型研究进展

结核病是由结核分枝杆菌感染引起的传染病,是危害人类健康的主要传染病之一。动物模型已经成为研究人类传染病的标准化工具。虽然对于结核分枝杆菌而言并没有真正意义的动物资源,但由于不同种类的动物,对分枝杆菌的敏感性不一样,因此可以成为结核病研究的有利工具。结核病最常用的实验动物模型包括小鼠、兔和豚鼠。每种动物有其自身特点,但并不能完全模拟人类疾病。通过建立结核病的动物模型,可以大大增加我们对疾病的病因、毒力和发病机制的理解。除了这三种模型外,非人灵长类也常被用于结核病的研究。本文总结了这几种结核病模型的研究状况。     

Equivalence relationships between stage-structured population models

Matrix population models are widely applied in conservation ecology to help predict future population trends and guide conservation effort. Researchers must decide upon an appropriate level of model complexity, yet there is little theoretical work to guide such decisions. In this paper we present an analysis of a stage-structured model, and prove that the model's structure can be simplified and parameterised in such a way that the long-term growth rate, the stable-stage distribution and the generation time are all invariant to the simplification. We further show that for certain structures of model the simplified models require less effort in data collection. We also discuss features of the models which are not invariant to the simplification and the implications of our results for the selection of an appropriate model. We illustrate the ideas using a population model for short-tailed shearwaters (Puffinus tenuirostris). In this example, model simplification can increase parameter elasticity, indicating that an intermediate level of complexity is likely to be preferred.     

动脉粥样硬化动物模型制作方法的介绍

动脉粥样硬化动物模型在病因学、病理学及预防方面的研究中起着非常重要的作用。近年来,运用兔子、小鼠、大鼠、鹌鹑等成功地建立了大量高脂饲料、单纯药物、高脂饲料加药物、基因敲除鼠及基因工程模型等诱导的动物模型。本文介绍了这几种动物模型的制作方法,以期为动脉粥样硬化的深入研究提供参考。     

延河流域本氏针茅(Stipa bungeana)分布预测——广义相加模型及其应用

物种分布预测,对于物种的保护、利用和恢复具有重要意义.利用广义相加模型(GAM,Generalized Additive Model),对延河流域典型地带性物种本氏针茅(Stipa bungeana)的空间分布预测进行研究,以期为该流域本氏针茅草地的保护、恢复等提供依据.结果表明,本氏针茅分布的环境梯度较广,在坡度、坡向、温度与降雨的各个梯度上都有分布,除高平地和侵蚀剧烈的沟道外,各种地形部位上亦可以存在.建立的广义相加模型表明,本氏针茅的分布主要取决于年均蒸发量和温度季节变化两个因子,而非单纯的降雨、温度因素.从其分布概率看,本氏针茅在延河流域大部分地区都有可能分布,但其分布集中区主要在中北部,与实际观测相符.模型检验表明,建立的模型满足统计要求.     

实验小鼠在癌症研究中的应用及其进展

小鼠是生物医学研究中使用数量最多的哺乳类实验动物。人类利用小鼠模型进行癌症研究已有100多年的历史,小鼠大量的遗传变异可作为研究人类癌症的借鉴。特别是近年来,培育成功的转基因、基因敲除等遗传工程小鼠模型,使我们对人类癌症发生有了深刻的认识,为评估癌症的诊断方法,革新预防和治疗方案提供了一个很有价值的平台。本文着重介绍了癌症研究中常用的小鼠模型、GEM模型及取得的最新进展等,分析了小鼠肿瘤模型的局限性,并对其发展趋势进行展望。     

类别学习的双系统模型

概念和类别学习是认知心理学研究的核心问题之一,以往的理论主要基于类别学习的单系统理论假设,而近十多年来概念和类别的研究关注类别学习的双重系统问题。目前双系统模型不仅得到了行为学实验的支持,更重要的是得到了临床神经心理和认知神经研究的广泛支持,本文回顾了双系统模型的非行为学研究证据,并指出了今后概念和类别研究应该注意的问题。     

Spatial modelling of succession-disturbance dynamics in forest ecosystems: Concepts and examples

Over the last few decades it has become increasingly obvious that disturbance, whether natural or anthropogenic in origin, is ubiquitous in ecosystems. Disturbance-related processes are now considered to be important determinants of the composition, structure and function of ecological systems. However, because disturbance and succession processes occur across a wide range of spatio-temporal scales their empirical investigation is difficult. To counter these difficulties much use has been made of spatial modelling to explore the response of ecological systems to disturbance(s) occurring at spatial scales from the individual to the landscape and above, and temporal scales from minutes to centuries. Here we consider such models by contrasting two alternative motivations for their development and use: prediction and exploration, with a focus on forested ecosystems. We consider the two approaches to be complementary rather than competing. Predictive modelling aims to combine knowledge (understanding and data) with the goal of predicting system dynamics; conversely, exploratory models focus on developing understanding in systems where uncertainty is high. Examples of exploratory modelling include model-based explorations of generic issues of criticality in ecological systems, whereas predictive models tend to be more heavily data-driven (e.g. species distribution models). By considering predictive and exploratory modelling alongside each other, we aim to illustrate the range of methods used to model succession and disturbance dynamics and the challenges involved in the model-building and evaluation processes in this arena.     

大鼠免疫性血小板减少模型的研究

采用注射兔抗大鼠血小板血清（ＡＰＳ）方法,建立了大鼠免疫性血小板减少模型。大鼠腹腔注射１：４稀释的ＡＰＳ（０．７ｍｌ／２００ｇ体重）,连续３ｄ,可使血小板数量显著降低,其降低率为８１±９％（ｎ＝１２）,且其骨随巨核细胞增生活跃,但注射ＡＰＳ后对血中红细胞数和白细胞数无明显影响．在注射ＡＰＳ的同时,给予大鼠灌胃强的松（１ｍｇ／２００ｇ体重）,可抑制ＡＰＳ所致的血小板减少的下降程度,并促进停止注射ＡＰＳ后血小板数的恢复。以上结果表明,该模型符合免疫性血小板减少性紫癜的病理特征。     

A generic model of electron transport in mitochondria

In this paper, a simplified, generic model of mitochondrial metabolism is explored. In particular the following question is addressed: To what extent are phenomena observed in experiments and simulations of mitochondrial metabolism generic, in the sense that they must occur in all models with this basic structure? Of particular interest are the electron transport chain and oxidative phosphorylation, and how flux through the system and the redox states of intermediates respond to physiologically important stimuli. These stimuli include changes in substrate supply (NADH/FADH(2)), in oxygenation, and in membrane proton gradient/ATP demand. Analytical techniques are used to show that certain experimentally observed effects must occur in the generic model. These include the responses of both flux and redox states to changed substrate and oxygen concentrations. At the same time other effects, such as the responses of redox states to changes in proton gradient, are dependent on the details of the model, and are not common to every model with the same basic structure. The phenomenon of saturation in response to large inputs is also discussed.     

Formation of heterocyclic aromatic amines in model systems

Heterocyclic aromatic amines (HAs) are mutagenic and carcinogenic substances that are formed in significant amounts during heating of meat or fish at temperatures of at least 150 degrees C. To investigate the chemistry lying behind the formation of these harmful substances model systems were established. The first aim was to identify the naturally occurring precursors, namely creatinine, amino acids and carbohydrates. Later these model systems were used to develop strategies for a reduction of the content of the heterocyclic aromatic amines and for the evaluation of the reaction mechanisms that lead to the formation of these substances. All these aspects are discussed in this review.     

Optimality,stochasticity, and variability in motor behavior

Recent theories of motor control have proposed that the nervous system acts as a stochastically optimal controller, i.e. it plans and executes motor behaviors taking into account the nature and statistics of noise. Detrimental effects of noise are converted into a principled way of controlling movements. Attractive aspects of such theories are their ability to explain not only characteristic features of single motor acts, but also statistical properties of repeated actions. Here, we present a critical analysis of stochastic optimality in motor control which reveals several difficulties with this hypothesis. We show that stochastic control may not be necessary to explain the stochastic nature of motor behavior, and we propose an alternative framework, based on the action of a deterministic controller coupled with an optimal state estimator, which relieves drawbacks of stochastic optimality and appropriately explains movement variability. Action Editor: Frances K. Skinner     

Wistar大鼠胶原诱导的关节炎造模因素的分析

目的通过比较不同的造模方法,分析影响胶原诱导关节炎（collagen-induced arthritis,CIA）大鼠模型建立的因素。方法选用Wistar大鼠造模,通过改变性别、剂量、年龄、注射部位及免疫方式,来比较造模成功率。结果不同性别、剂量、年龄及免疫方式造模成功率不同。结论4～5周龄Wistar雌性大鼠,初次免疫注射乳剂4点共0.20 mL,加强免疫在14 d之后3点共0.15 mL的造模成功率最高。     

动物心肌挫伤模型的研究进展

心肌挫伤实验动物模型在研究人类心肌挫伤的发病机制及治疗等方面起着非常重要的作用,根据制备方法和研究目的的不同,可分为开放性及非开放性,每种实验模型都有各自的特点和应用条件。     

A test of a model for estimating production in the sea

Primary productivity was measured in the sea off the coasts of Florida and Georgia with the radiocarbon method at four stations during March, 1971. Integral photosynthesis per square meter surface was determined with a mathematical model from empirical data gathered from in situ and shipboard incubation experiments. The mathematical model provided shipboard incubators to be used to estimate primary production rates while overcoming the problem of relating light quality and quantity simulated by the incubators to that found in the euphotic zone. The use of shipboard incubation can allow for measurements to be made on a moving vessel, more stations visited per day and water samples incubated at a constant light intensity. Primary productivity at the four sampling stations ranged from 0.026 to 0.042 mg C/M² hr.     

医学遗传学实验教学中实施研究性教学的探索实践

我们根据我校实际情况在医学遗传学实验教学中实施开放式研究性教学手段,培养学生具有自主建构的学习能力,掌握现代医学遗传学的基本理论和遗传性疾病诊断的实验方法,培养学员的综合实践能力,启发创造性思维,促进实验教学的改革。