Variables Contributing to the Coordination of Rapid Eye/Head Gaze Shifts

In this article results of several published studies are synthesized in order to address the neural system for the determination of eye and head movement amplitudes of horizontal eye/head gaze shifts with arbitrary initial head and eye positions. Target position, initial head position, and initial eye position span the space of physical parameters for a planned eye/head gaze saccade. The principal result is that a functional mechanism for determining the amplitudes of the component eye and head movements must use the entire space of variables. Moreover, it is shown that amplitudes cannot be determined additively by summing contributions from single variables. Many earlier models calculate amplitudes as a function of one or two variables and/or restrict consideration to best-fit linear formulae. Our analysis systematically eliminates such models as candidates for a system that can generate appropriate movements for all possible initial conditions. The results of this study are stated in terms of properties of the response system. Certain axiom sets for the intrinsic organization of the response system obey these properties. We briefly provide one example of such an axiomatic model. The results presented in this article help to characterize the actual neural system for the control of rapid eye/head gaze shifts by showing that, in order to account for behavioral data, certain physical quantities must be represented in and used by the neural system. Our theoretical analysis generates predictions and identifies gaps in the data. We suggest needed experiments.     

Threshold conditions for infection persistence in complex host-vectors interactions

As classically defined by Macdonald in the early 1950s, for the case of diseases with one vector and one host, the Basic Reproduction Number, R0, is defined as the number of secondary infections caused by a single infective of the same type (vector or host) during its infectiousness period in an entirely susceptible population. In the case of a disease which has one vector and one host, it is easy to show that R0 coincides with the threshold for the establishment of an endemic state: if R0 > 1 (< 1), the disease can invade (cannot invade) the host population. In this paper we examine various epidemic situations in which there are more than one vector and/or host. We show that in those more complex systems it is not possible to deduce a single R0 but rather a threshold for infection persistence which is a composite of several quantities closely related to the classical expression of R0. Another definition of R0 given by Diekmann, Heesterbeek and Metz, and denoted in this paper R0NGO is discussed and applied as an alternative to calculate the thresholds for infection establishment.     

水分为限制因子的草地优化收获理论的研究

本文针对我国北方干旱、半干旱地区草地植物生长的主要限制因子,即水分问题,提出草地植物生物量和土壤水分的常微分方程模型。模拟的目标是一个生长期中植被生物量和土壤水分的变化。在此基础上,推导出了以维持系统平衡为前提,使总收获量达到可能的最大值的最优收获理论方程。最后求取模型在特定的情形下的解并讨论其表征和特点。具体模型求解的结果表明： (1)给定退化草地,围栏保护完全不加利用不一定是最佳恢复途径; (2)存在着最优的收获力投入,使草地植物的收获量达到极大值。     

Concept of the "physiological age" of animals and its application to ixodid ticks

The definition "physiological age" of animals has been revised. A new definition has been formulated on the basis of V. N. Beklemishev's (1962) and Ju. S. Balashov's (1962) theses as follows: physiological age of animals (= biological) is an extent of general irreversible morphophysiological change of organism during its whole life and determined by the accumulation of irreversible changes as a result of its normal vital activity. This definition is equivalent to that of "biological ages" of man. The contents of this definition is enlarged and the possibility of its use for different animals including their males is unified. On the basis of the general concept this definition is specified in regard to ixodid ticks: physiological age of hungry ixodid tick is an extent of general irreversible morpholophysiological change of its organism during the whole life and determined by the state of reserve nutrient and excretory substances. According to the amount of reserve and excretory substances in the organism of ixodid tick we distinguish 4 main physiological ages: new-born, young, mature and old which reflect general biological regularity of age development of animals.     

Comparison of definitions of the lag phase and the exponential phase in bacterial growth.

Different definitions for the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters microm, lambda and alpha. Therefore, it appeared to be unnecessary to use complicated mathematical equations; simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.     

New mathematical definition and calculation of axial rotation of anatomical joints

In the field of joint kinematics, clinical terms such as internal-external, or medical-lateral, rotations are commonly used to express the rotation of a body segment about its own long axis. However, these terms are not defined in a strict mathematical sense. In this paper, a new mathematical definition of axial rotation is proposed and methods to calculate it from the measured Euler angles are given. The definition and methods to calculate it from the measured Euler angles are given. The definition is based on the integration of the component of the angular velocity vector projected onto the long axis of the body segment. First, the absolute axial rotation of a body segment with respect to the stationary coordinate system is defined. This definition is then generalized to give the relative axial rotation of one body segment with respect to the other body segment where the two segments are moving in the three-dimensional space. The well-known Codman's paradox is cited as an example to make clear the difference between the definition so far proposed by other researchers and the new one.     

Comparison of definitions of the lag phase and the exponential phase in bacterial growth

M.H. ZWIETERING, F.M. ROMBOUTS AND K. VAN 'T RIET. 1992. Different definitions of the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models, and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters μ _m , and a. Therefore, it appeared to be unnecessary to use complicated mathematical equations: simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.     

Yeast ferrochelatase: expression in a baculovirus system and purification of the expression protein.

The terminal step of the heme biosynthetic pathway is catalyzed by the enzyme ferrochelatase (EC 4.99.1.1). In eukaryotes this enzyme is bound to the inner mitochondrial membrane with its active site facing the matrix side of the membrane. Previously this laboratory has characterized this enzyme via kinetic and protein chemical modification techniques, and with the recent cloning of the enzyme from yeast, mouse, and human sources it now becomes possible to approach structure-function questions by using site-directed mutagenesis. Of primary significance to this is the development of an efficient expression vector. This is of particular significance for ferrochelatase, as it is a low-abundance protein whose DNA coding sequence has a very low codon bias. In the current work we describe the production of yeast ferrochelatase in a baculovirus system. This system is shown to be an excellent one in which to produce large quantities of active ferrochelatase. The expressed enzyme is membrane associated and is not released into the growth medium either during or after virus development and cell lysis. The expressed protein can be purified in a procedure that requires only 1 day and makes use of a Pharmacia Hi Trap blue affinity column. The measured Km's for the substrates mesoporphyrin and iron are the same as those reported previously for the yeast enzyme. To our knowledge this is the first example of a mitochondrial membrane protein that has been expressed in a baculovirus system.     

Pandemic swine influenza virus (H1N1): A threatening evolution

“Survival of the fittest” is an old axiom laid down by the great evolutionist Charles Darwin and microorganisms seem to have exploited this statement to a great extent. The ability of viruses to adapt themselves to the changing environment has made it possible to inhabit itself in this vast world for the past millions of years. Experts are well versed with the fact that influenza viruses have the capability to trade genetic components from one to the other within animal and human population. In mid April 2009, the Centers for Disease Control and Prevention and the World Health Organization had recognized a dramatic increase in number of influenza cases. These current 2009 infections were found to be caused by a new strain of influenza type A H1N1 virus which is a re-assortment of several strains of influenza viruses commonly infecting human, avian, and swine population. This evolution is quite dependent on swine population which acts as a main reservoir for the reassortment event in virus. With the current rate of progress and the efforts of heath authorities worldwide, we have still not lost the race against fighting this virus. This article gives an insight to the probable source of origin and the evolutionary progress it has gone through that makes it a potential threat in the future, the current scenario and the possible measures that may be explored to further strengthen the war against pandemic.     

On the use of cartographic projections in visualizing phylo-genetic tree space

Phylogenetic analysis is becoming an increasingly important tool for biological research. Applications include epidemiological studies, drug development, and evolutionary analysis. Phylogenetic search is a known NP-Hard problem. The size of the data sets which can be analyzed is limited by the exponential growth in the number of trees that must be considered as the problem size increases. A better understanding of the problem space could lead to better methods, which in turn could lead to the feasible analysis of more data sets. We present a definition of phylogenetic tree space and a visualization of this space that shows significant exploitable structure. This structure can be used to develop search methods capable of handling much larger data sets.     

The definitions of information and meaning two possible boundaries between physics and biology.

The standard approach to the definition of the physical quantities has not produced satisfactory results with the concepts of information and meaning. In the case of information we have at least two unrelated definitions, while in the case of meaning we have no definition at all. Here it is shown that both information and meaning can be defined by operative procedures, but it is also pointed out that we need to recognize them as a new type of natural entities. They are not quantities (neither fundamental nor derived) because they cannot be measured, and they are not qualities because are not subjective features. Here it is proposed to call them nominable entities, i.e., entities which can be specified only by naming their components in their natural order. If the genetic code is not a linguistic metaphor but a reality, we must conclude that information and meaning are real natural entities, and now we must also conclude that they are not equivalent to the quantities and qualities of our present theoretical framework. This gives us two options. One is to extend the definition of physics and say that the list of its fundamental entities must include information and meaning. The other is to say that physics is the science of quantities only, and in this case information and meaning become the exclusive province of biology. The boundary between physics and biology, in short, is a matter of convention, but the existence of information and meaning is not. We can decide to study them in the framework of an extended physics or in a purely biological framework, but we cannot avoid studying them for what they are, i.e., as fundamental components of the fabric of Nature.     

On control and optimal control in biodynamic systems

In any control system for which the number of independent controls is smaller than the number of degrees of freedom to be controlled, our choice of control in any state is restricted to a submanifold of smaller dimension than the tangent space. This simple fact has a number of important consequences for questions of biological import; we consider its implications for adaptation, for senescent phenomena and for the determination of tertiary structures of polypeptides through control of certain average properties. We also formulate the Pontryagin Maximum Principle of Optimal control theory in such a way as to inquire whether specific biodynamic systems can be regarded as optimal with respect to rate of accumulation of particular quantities of the system. We find that if this is possible, the quantity in question must play the role of a clock.     

Unconventional modes for STEM imaging of biological structures

In this paper recent developments are discussed in instrumentation and methodology associated with scanning transmission electron microscopes (STEM), which are of great potential interest for solving structural and chemical problems in biological specimens. After describing the main features of the instrument, an attempt is made to define which type of signal acquisition and processing is best suited to obtain a given type of information. Starting with a definition of cross sections of interest, a discussion follows of methods using angular selection, energy selection of the transmitted beam, and several ways of signal mixing. More specific attention is devoted to two main modes of processing signals: ratio contrast, which emphasizes slight changes in scattering factors, rather independent of thickness variations; and elemental mapping, which provides semi-quantitative information on the distribution of low Z elements of great significance in biological specimens. Data relevant to typical biological objects are presented and discussed; they allow for the definition of the capabilities and limitations of these methods. These unconventional imaging modes define a new attitude for improving the efficiency of this modern generation of electron microscopes.     

A joint model of the contractile system of striated muscle (preliminary calculations)

Values of the variables of a model of the muscle contractile apparatus were calculated on the basis of a previously described theoretical system JMCSM (i.e. the Joint Model of the Contractile System of Muscle) and after introducing some necessary simplifying presuppositions. The calculations made it possible to compare the model with the original biological system and provided data needed for the subsequent stage of simulation experiments. The properties of the model are apparently not inconsistent with the properties of the original biological system. The basic equation of the theoretical model could be expressed in the form analogous to Hill's equation; the procedure by which the equations were derived and the interpretation of their parameters are mutually independent. The model also suggests a different interpretation of the dependence of the heat of shortening on other quantities of the system. It is necessary to consider these calculations and their results as preliminary with regard to the simplifying presuppositions and to the possible inaccuracies of the estimations of input data.     

Extending the viability theory framework of resilience to uncertain dynamics,and application to lake eutrophication

Resilience, the capacity for a system to recover from a perturbation so as to keep its properties and functions, is of growing concern to a wide range of environmental systems. The challenge is often to render this concept operational without betraying it, nor diluting its content. The focus here is on building on the viability theory framework of resilience to extend it to discrete-time stochastic dynamical systems. The viability framework describes properties of the system as a subset of its state space. This property is resilient to a perturbation if it can be recovered and kept by the system after a perturbation: its trajectory can come back and stay in the subset. This is shown to reflect a general definition of resilience. With stochastic dynamics, the stochastic viability kernel describes the robust states, in which the system has a high probability of staying in the subset for a long time. Then, probability of resilience is defined as the maximal probability that the system reaches a robust state within a time horizon. Management strategies that maximize the probability of resilience can be found through dynamic programming. It is then possible to compute a range of statistics on the time for restoring the property. The approach is illustrated on the example of lake eutrophication and shown to foster the use of different indicators that are adapted to distinct situations. Its relevance for the management of ecological systems is also discussed.     

Streptococcus oligofermentans inhibits Streptococcus mutans through conversion of lactic acid into inhibitory H2O2: a possible counteroffensive strategy for interspecies competition

The oral microbial flora contains over 500 different microbial species that often interact as a means to compete for limited space and nutritional resources. Streptococcus mutans, a major caries-causing pathogen, is a species which tends to interact competitively with other species in the oral cavity, largely due to its ability to generate copious quantities of the toxic metabolite, lactic acid. However, during a recent clinical study, we discovered a novel oral streptococcal species, Streptococcus oligofermentans, whose abundance appeared to be inversely correlated with that of S. mutans within dental plaque samples and thus suggested a possible antagonistic relationship with S. mutans. In this study, we used a defined in vitro interspecies interaction assay to confirm that S. oligofermentans was indeed able to inhibit the growth of S. mutans. Interestingly, this inhibitory effect was relatively specific to S. mutans and was actually enhanced by the presence of lactic acid. Biochemical analyses revealed that S. oligofermentans inhibited the growth of S. mutans via the production of hydrogen peroxide with lactic acid as the substrate. Further genetic and molecular analysis led to the discovery of the lactate oxidase (lox) gene of S. oligofermentans as responsible for this biological activity. Consequently, the lox mutant of S. oligofermentans also showed dramatically reduced inhibitory effects against S. mutans and also exhibited greatly impaired growth in the presence of the lactate produced by S. mutans. These data indicate that S. oligofermentans possesses the capacity to convert its competitor's main 'weapon' (lactic acid) into an inhibitory chemical (H(2)O(2)) in order to gain a competitive growth advantage. This fascinating ability may be an example of a counteroffensive strategy used during chemical warfare within the oral microbial community.     

Chitosan’s biological activity upon skin-related microorganisms and its potential textile applications

Over the years the body of work relating chitosan and its possible skin-related applications has grown, showing that chitosan is active both as a free compound and as a functional finishing of textiles. As a free molecule chitosan proved itself to be an attractive option as it is biocompatible and has a demonstrated biological activity (e.g. growth inhibition or adhesion inhibition) upon multiple skin pathogens, even upon multidrug resistant species. Furthermore, chitosan has wound healing accelerating properties, which make it a prime candidate for possible control of skin related infections. Almost inconspicuously, textiles have been one the main lines of defense of the skin against foreign threats, acting as a physical barrier to microbial colonization and infection. With the advent of textile functionalization specially designed textiles with enhanced protective characteristics, such as antimicrobial capacity, have come to the forefront. Chitosan functionalized textiles have been shown to be effective inhibitors of microbial growth with even invasive multidrug resistant species, as MRSA, being inhibited. Therefore, chitosan and chitosan functionalized textiles present themselves as both an interesting alternative to traditional antibiotics and as a possible means to enhance current treatment strategies.     

昆虫群落中天敌间的致死干扰竞争作用

致死干扰竞争作用(lethal interference competition)是近些年来才被人们认识到的更为复杂的种间竞争关系, 是昆虫天敌间竞争的一种极端形式, 广泛存在于寄生性天敌昆虫之间。本文从其定义、 作用机制、 方式及其与害虫生物防治的相互关系几个方面介绍了天敌群落中的这一典型的种间相互关系。根据作用机制的不同, 可将致死干扰竞争作用分为外竞争和内竞争; 其通常的作用方式包括多寄生(超寄生)、 复寄生、 杀卵作用、 寄主取食、 物理攻击和生理抑制等。深入全面地研究这一种间关系对于有效生防作用物的筛选和引入, 以及整个生防系统群落的稳定性具有重要意义。