The stochastic theory of compartments—A mammillary system

A stochastic mammalillary model with arbitrary holding times for each of the compartments is analyzed here both with and without input. Several results found earlier by other authors for a special case of this model are generalized and some new results are also added. In particular the distribution of the system content is determined at a finite time and also in the steady state. Computable bounds for the probability of exceeding a given threshold in the peripheral compartments are given. The time until the system becomes empty is also discussed.     

Positional behaviour of olive baboons (Papio anubis) and its relationship to maintenance and social activities

A troop of olive baboons (Papio anubis) was studied over a four week period. Total observation time was 140 hours, 118 hours of which were spent gathering quantitative data on positional behaviour and the maintenance and social behaviour with which it is associated. The contribution of each activity on a time basis to the positional repertoire is described and some data is presented on the development of positional activities in infants. The contribution of positional activities to various maintenance and social activities is also described quantitatively. The complex of positional, maintenance, social and environmental factors involved especially in feeding, foraging, play, and grooming are described and discussed. The similarities between the adaptive response shown during the study period and that of other ground living cercopithecines is also discussed.     

A short history of nuclear activation analysis

The major developments in the field of nuclear activation analysis, from 1936 to 1989, are discussed. The developments are grouped into five consecutive time periods. The impact of various scientists on the development of the field in the first 35 years is also discussed.     

Fixation of Strategies for an Evolutionary Game in Finite Populations

A stochastic evolutionary dynamics of two strategies given by 2x 2 matrix games is studied in finite populations. We focus on stochastic properties of fixation: how a strategy represented by a single individual wins over the entire population. The process is discussed in the framework of a random walk with site dependent hopping rates. The time of fixation is found to be identical for both strategies in any particular game. The asymptotic behavior of the fixation time and fixation probabilities in the large population size limit is also discussed. We show that fixation is fast when there is at least one pure evolutionary stable strategy (ESS) in the infinite population size limit, while fixation is slow when the ESS is the coexistence of the two strategies.     

Persistence times of populations with large random fluctuations

The growth of populations which undergo large random fluctuations can be modelled with stochastic differential equations involving Poisson processes. The problem of determining the persistence time is that of finding the time of first passage to some small critical population size. We consider in detail a simple model of logistic growth with additive Poisson disasters of fixed magnitude. The expectation and variability of the persistence time are obtained as solutions of singular differential-difference equations. The dependence of the persistence time of a colonizing species on the parameters of the model is discussed. The model may also be viewed as random harvesting with fixed quotas and a comparison is made between the mean extinction time and those for deterministic models.     

Analytical theory of the control equations for protein synthesis in the Goodwin model

The analytical expressions, and their convergent series expansions, for the time period and various time averages of the dynamical quantities are derived for the Goodwin model. The radius of convergence of the series expansions is also calculated. The changes necessary to fully take into account the restrictions on dynamical variable, following from the positivity of physical quantities of the model, for the statistical mechanical treatment of the system are also discussed.     

The acetone-butanol fermentation in pilot plant and pre-industrial scale

A summary of literature data concerning pilot or preindustrial scale trials of the acetone-butanol fermentation throughout its history is given. The recent pilot plant trials in Austria are also described for the first time. Some aspects of the current development of the acetone-butanol fermentation in general, especially from a technical point of view are also discussed.     

The Theory of Multistage Carcinogenesis

Cancerous cells in many tissues develop by stages. A normal cell must undergo several mutations to become a neoplastic cell. This paper presents a time-dependent stochastic model to describe the k-stage carcinogenic process. The distribution of the time required for a given number of mutations and the probability of developing neoplastic cells in a given time interval are derived. The problem of estimation for a special case is also discussed.     

An Estimate of the Variance of Estimators for Lead Time and Screening Benefit Time in Randomized Cancer Screening Trials

Variance estimators are derived for estimators of the average lead time and average benefit time due to screening in a randomized screening trial via influence functions. The influence functions demonstrate that these estimators are asymptotically equivalent to the mean difference, between the study and control case groups, in the appropriate survival times. For estimating benefit time, the survival time is measured since start of study; for estimating lead time, the survival time is measured since time of diagnosis. Asymptotic variances of these estimators can be calculated in a straightforward manner from the influence functions, and these variances can be estimated from actual trial data. The performance of the variance estimators is assessed via a simulated screening trial. The situation involving censored data is also discussed.     

激光时间分辨荧光谱仪＊以及荧光各向异性测量

就时间相关单光子计数荧光谱仪的工作原理、实验装置的建立等问题进行了探讨。利用国产的红离子锁模激光同步泵浦腔倒空输出染料激光器等器件与进口的时幅转换器、定时恒分器建成了激光时间分辨荧光谱仪,时间分辨率为８０ｐｓ。本文还建立了荧光各向异性的测量方法,利用该方法对Ｒ－ＰＥ的旋转弛豫时间进行了测量,并与英国Ｅｄｉｎｂｕｒｇｈ公司生产的２９９Ｔ型荧光谱仪的测量结果进行了比较,结果证明仪器及方法都是可靠的。     

Effects of pH probe lag on bioreactor mixing time estimation

Mixing time is one of the most important characteristics of bioreactors used to validate computational fluid dynamics (CFD) models in bioprocess. The pH tracer based method is commonly used to estimate mixing time by monitoring the pH change after perturbation to the system. However, pH probe lag is known to introduce errors in the test results. To determine the impact of probe lag on the measurement, pH probe response times were investigated. A second order mathematical model was established to describe the probe response profile and calculate the probe transfer function which was used to correct the empirical results. The corrected mixing time was used to validate the CFD models and also showed that the impact of pH probe response time on mixing time measurement is significant even in larger (pilot and manufacturing) scales. In addition, comparison with a conductance based tracer method is also discussed in this paper.     

Stability analysis of the time delay in a host-parasitoid model

The effect of a time delay on the local stability of a host-parasitoid model is analyzed. The delay is between the time of parasitization of the host and the emergence of the parasitoid from the host. Both analytic methods and computer simulations are used in this study. By linearizing and transforming the original equations, sufficient conditions for the local stability are found. In the case of the parameters considered, the results illustrate the destabilizing effect of the time delay. As the lag increases the number of stable points decreases and the points become more scattered in the parameter space. Simulations of the original model are also produced. The region of stability indicated by the simulations is greater than that predicted by the use of the analytic technique. The analysis also reveals the impact of the population parameters upon the stability of the time delay model.The importance of understanding time lags is discussed with reference to population regulation.     

An Ecological Approach to Prospective and Retrospective Timing of Long Durations: A Study Involving Gamers

To date, most studies comparing prospective and retrospective timing have failed to use long durations and tasks with a certain degree of ecological validity. The present study assessed the effect of the timing paradigm on playing video games in a “naturalistic environment” (gaming centers). In addition, as it involved gamers, it provided an opportunity to examine the effect of gaming profile on time estimation. A total of 116 participants were asked to estimate prospectively or retrospectively a video game session lasting 12, 35 or 58 minutes. The results indicate that time is perceived as longer in the prospective paradigm than in the retrospective one, although the variability of estimates is the same. Moreover, the 12-minute session was perceived as longer, proportionally, than the 35- and 58-minute sessions. The study also revealed that the number of hours participants spent playing video games per week was a significant predictor of time estimates. To account for the main findings, the differences between prospective and retrospective timing are discussed in quantitative terms using a proposed theoretical framework, which states that both paradigms use the same cognitive processes, but in different proportions. Finally, the hypothesis that gamers play more because they underestimate time is also discussed.     

A mathematical model to study the effects of drugs administration on tumor growth dynamics

A mathematical model for describing the cancer growth dynamics in response to anticancer agents administration in xenograft models is discussed. The model consists of a system of ordinary differential equations involving five parameters (three for describing the untreated growth and two for describing the drug action). Tumor growth in untreated animals is modelled by an exponential growth followed by a linear growth. In treated animals, tumor growth rate is decreased by an additional factor proportional to both drug concentration and proliferating cells. The mathematical analysis conducted in this paper highlights several interesting properties of this tumor growth model. It suggests also effective strategies to design in vivo experiments in animals with potential saving of time and resources. For example, the drug concentration threshold for the tumor eradication, the delay between drug administration and tumor regression, and a time index that measures the efficacy of a treatment are derived and discussed. The model has already been employed in several drug discovery projects. Its application on a data set coming from one of these projects is discussed in this paper.     

Metabolism in bacteria at low temperature: A recent report

The adaptability of bacteria to extreme cold environments has been demonstrated from time to time by various investigators. Metabolic activity of bacteria at subzero temperatures is also evidenced. Recent studies indicate that bacteria continue both catabolic and anabolic activities at subzero temperatures. Implications of these findings are discussed.     

Uroleucon sonchi (Linnaeus) (Hemiptera: Aphididae) in Australia

Uroleucon sonchi, an aphid species of Palaearctic origin, is a recent adventive to Australia. It is now widespread in anthropic areas of all states and the Australian Capital Territory, principally on sowthistles ( Sonchus spp.) but also on lettuce. It is occasionally parasitised by Aphidius sonchi Marshall (Hymenoptera: Braconidae). Its possible economic importance in Australia is discussed. The species is also recorded for the first time from Norfolk and Philip Islands.     

A simple model for periodic cyclostat growth of algae

Summary This paper provides a simple model of nutrient limited periodic cyclostat growth for algae.The basic growth function is assumed to be a time dependent variation of the empirical growth equation developed by Droop (1968). The authors also present the relations for n species' cyclostat coexistence and a stability analysis for the model growth equation.The model, although limited in some respects, agrees very well with available experimental data on Euglena gracilis. The significance of the time dependent amplitude functions developed in this study is also discussed.The term used to describe this system is the cyclostat (see Chisholm et al., 1975).     

自尊研究综述

自尊是一个系统,它不仅涉及了个体的认知层面,还包括个体的情感层面,并且根据个体所处的特定的情景,其表现有时稳定,有时不稳定。自尊的情感模型主要探讨了自尊的组成成分与自尊的起源;自尊的认知模型把自尊看成个体对自己作为人的价值的有意识判断;以恐惧管理理论为代表的自尊的社会学模型又从新的角度解释了自尊的理论模型。罗森伯格的自尊量表开启了自尊测量的先河,我国学者在自尊的测量方面也取得了相应的进展。同时,从社会比较理论与评价性反馈两个角度阐述了自尊的作用。自尊的研究遍布群体从幼儿、青少年到大学生,都有丰富的实证研究。自尊结构的研究领域内出现了一些新进展,主要表现在内隐自尊、具体自尊及集体自尊研究的逐步兴起。     

Physiological time and time-invariance

An operational definition of physiological time is suggested that involves a non-linear transformation of a physical time-scale such that a certain temperature-dependent process becomes time-invariant. The definition expresses that physiological time has the dimension of time, and can be measured in units such as days or weeks. It is shown that the quantification of a physiological time-scale requires the specification of an arbitrary constant, which equals the rate of change of the process in physiological time. When the process-rate also depends on some internal variable, the interaction of this variable with temperature must be multiplicative, if a single physiological time-scale is to be used. The relationship with conventional uses of physiological time is discussed. The time-scale, as defined here, reduces to degree-day summation or development accumulation if certain multiplicative constants are deleted.