Two-phase pulsatile flows through porous conical tubes of small diameters. Modelisation of the blood microcirculation

A theoretical study concerning two-component fluid pulsating flow through porous conical ducts is presented. The model corresponds to blood flows through small diameter porous conical vessels. This approach is based on a finite difference method. The physical hypothesis used were based on findings from simultaneous visualization methods. The influence of geometrical, hydrodynamical and structural parameters is systematically examined and related to velocity profiles, hydrostatic pressure.     

A Universal Rank-Size Law

A mere hyperbolic law, like the Zipf’s law power function, is often inadequate to describe rank-size relationships. An alternative theoretical distribution is proposed based on theoretical physics arguments starting from the Yule-Simon distribution. A modeling is proposed leading to a universal form. A theoretical suggestion for the “best (or optimal) distribution”, is provided through an entropy argument. The ranking of areas through the number of cities in various countries and some sport competition ranking serves for the present illustrations.     

A diffusion limited reaction theory for a solid-phase immunoassay

Theoretical calculations are presented, describing the kinetics of a solid-phase immunoassay where reactants are allowed to diffuse through a gel wedge in the bottom of a circular basin. The analysis is based on the assumption of a diffusion rate limited reaction at the underlaying surface. The influence of initial concentration, incubation time, temperature and the effect of stirring are predicted by the theoretical model. Experimental data are found to follow the theoretical model with parameters consistent with previous values.     

大学附属医院临床科主任工作业绩考核评价体系研究

为了改善医院绩效,以目标管理法为理论基础,采用关键绩效指标法建立大学附属医院临床科主任工作业绩考核指标评价体系,并应用层次分析法进行权重分析,得出各层级指标的权重值,各指标的重要程度符合科主任的实际工作要求。以此对临床科主任的工作进行科学、有效的考核,提升临床科室绩效管理水平。     

Study of the conditions for reproducing the processes of antibiotic biosynthesis. Determining the limiting stage of the process of mass transfer of oxygen

A theoretical method for estimating limiting stage of oxygen mass transfer is proposed. The method is based on calculation and comparison of particular resistance of separate stages of mass transfer: mass transfer through the gas-liquid boundary, oxygen transport in the liquid phase, mass transfer through the liquid-cell boundary and oxygen consumption by microbial cells. With the proposed method, particular resistance was calculated and conditions for oxygen mass transfer were analyzed in the biosynthesis of sisomicin as an example. As a result the conditions for reproducibility of the process in apparatus of various size were determined.     

Buoyancy of some Palaeozoic ammonoids and their hydrostatic properties based on empirical 3D‐models

The interpretation of the function of the ammonoid phragmocone as a buoyancy device is now widely accepted among ammonoid researchers. During the 20^th century, several theoretical models were proposed for the role of the chambered shell (phragmocone); accordingly, the phragmocone had hydrostatic properties, which enabled it to attain neutral buoyancy, presuming it was partially filled with gas. With new three‐dimensional reconstructions of ammonoid shells, we are now able to test these hypothetical models using empirical volume data of actual ammonoid shells. We investigated three Palaeozoic ammonoids (Devonian and Carboniferous), namely Fidelites clariondi, Diallagites lenticulifer and Goniatites multiliratus, to reconstruct their hydrostatic properties, their syn vivo shell orientation and their buoyancy. According to our models, measurements and calculations, these specimens had aperture orientations of 19°, 64° and 125° during their lives. Although none of our results coincide with the aperture orientation of the living Nautilus, they do verify the predictions for shell orientations based on published theoretical models. Our calculations also show that the shorter the body chamber, the poorer was the hydrodynamic stability of the animal. This finding corroborates the results of theoretical models from the 1990s. With these results, which are based on actual specimens, we favour the rejection of hypotheses suggesting a purely benthonic mode of life of ammonoids. Additionally, it is now possible to assess hydrodynamic properties of the shells through ontogeny and phylogeny, leading to insights to validate theoretical modes of life and habitat through the animal's life.     

What does "local" firewood buy you? Managing the risk of invasive species introduction

Firewood can serve as a vector in the transport of non-native species, including wood-boring insects that feed within the wood and thus can be transported accidentally. Governments have enacted limitations on the movement of firewood in an effort to limit the anthropogenic movement of non-native species through, for example, recreational camping. Although the movement of invasive species through firewood is a documented invasion pathway, it is not trivial for governments to determine a "safe" allowable distance for moving firewood. We were motivated by this challenge and developed a theoretical simulation to determine the campgrounds that could be potentially exposed to infested firewood based upon the hypothetical distribution of an invasive species and the allowable distance for moving firewood. We extend this concept to the known distributions of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) and Asian longhorned beetle, Anoplophora glabripennis (Motschulsky) Coleoptera: Cerambycidae). We illustrate, based upon theoretical and empirical observations, that as the distribution of an invasive species increases, more rigid constraints on the movement of firewood would be required relative to those species that are distributed over a smaller scale. Also, on the level of management within a state, smaller states have far less margin for error than larger ones, as even extremely rigid restrictions on the movement of firewood could have little management effect unless the infested area is spatially limited. These results collectively suggest the potential for a dynamic management strategy that adjusts allowable distances for firewood movement based upon the distribution of the non-native species.     

Comment on Cowling's "Spatial methods for line transect surveys"

We consider the problem of estimating the parameters of a two-dimensional Neyman-Scott process, from data collected through a line transect survey. Cowling (1998, Biometrics 54, 828-839) suggested an estimation method based on a one-dimensional K-function along the transect line. However, her expression for the theoretical K-function is wrong. In this article, we correct her K-function.     

Influenza outbreaks

Influenza is a virus that causes considerable morbidity and mortality in human populations every year. This fact, coupled with its perceived pandemic potential, means that influenza features prominently in both scientific literature and the media. In this review we focus on the biological assumptions behind theoretical attempts to understand the seasonal and evolutionary dynamics of influenza through mathematical modelling and suggest that the largely unchallenged dogma upon which most efforts are currently based is sorely lacking.     

Dynamics of human milk extraction: A comparative study of breast feeding and breast pumping

We describe a mathematical model of the flow and deformation in a human teat. Our aim is to compare the theoretical milk yield during infant breast feeding with that obtained through the use of a breast pump. Infants use a peristaltic motion of the tongue, along with some suction, to extract milk, whereas breast pumps use a cyclic pattern of suction only. Our model is based on quasi-linear poroelasticity whereby the teat is modelled as a cylindrical porous elastic material saturated with fluid. We impose a cyclic axial suction pressure difference across the teat and impose a radial compressive force moving along the teat which mimics infant suckling. This is compared to the case of cyclic and steady pumping only which models the action of breast pumps. The results illustrate that there is an optimal time to apply the compressive force during the suction cycle that will increase the flow rate in our theoretical teat. The model and results may be of use in the future design of effective breast pumps.     

Quasi-boundary based on exchange symmetry theory for multilevel simulations

In this contribution we propose a novel method (QUEST) which enables the simulation of diffusive systems through quantum mechanical/molecular mechanical (QM/MM) molecular dynamics. The method is an evolution of boundary based on exchange symmetry theory (BEST), an approach based on imposing a bias potential to hinder exchanges between QM and MM particles. This new method corrects for the main shortcoming of BEST, namely that only static properties could be studied, as the dynamics was disrupted. With Quasi-BEST (QUEST) the dynamics is still preserved, albeit at some additional cost in the computation of energy and forces as they are needed for the exchanged configurations between QM and MM particles. Here we describe the theoretical basis of QUEST, and we present the results on a small toy system.     

Ordered dusty structures in nuclear-track neon and argon plasmas

Ordered dusty structures formed of spherical monodisperse and polydisperse grains are obtained for the first time in a nuclear-track plasma produced by α-particles and fission fragments of ²⁵²Cf nuclei passing through neon or argon. A theoretical model of such a plasma is proposed. Monte Carlo computer simulations based on this model are carried out to explain the formation of such structures.     

Recovery in complex ecosystems

Current ecosystem theory has a deceptively simple representation of recovery. In actual practice,recovery is affected by the frequency and extent of disturbances and by the spatial heterogeneity of the ecological system. Environmental changes may pass through thresholds causing recovery to a different plant and animal community. The sheer complexity of the system combined with unanticipated synergistic effects can make recovery trajectories difficult or impossible to predict. New theoretical constructs,based on stochastic nonlinear theory, will be needed to guide research and applications. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modeling DNA shuffling.

In vitro evolution is a new, important laboratory method to evolve molecules with desired properties. It has been used in a variety of biological studies and drug development. In this paper, we study one important mutagenesis method used in in vitro evolution experiments called DNA shuffling. We construct a mathematical model for DNA shuffling and study the properties of molecules after DNA shuffling experiments based on this model. The model for DNA shuffling consists of two parts. First we apply the Lander-Waterman model for physical mapping by fingerprinting random clones to model the distribution of regions that can be reassembled through DNA shuffling. Then we present a model for recombination between different DNA species with different mutations. We compare our theoretical results with experimental data. Finally we propose novel applications of the theoretical results to the optimal design of DNA shuffling experiments and to physical mapping using DNA shuffling.     

林分耗水的尺度扩展研究进展

蒸散耗水是森林生态系统水分循环过程的主要构成,是现代生态水文研究的重点和难点。直接测定和尺度上推提供了两种获取蒸散量的技术手段。受限于复杂的冠层结构、非均质的下垫面和迥异的环境条件,直接测定难以准确获取林分水平的耗水信息,因此有必要讨论单木与冠层结构、环境因子之间的耦合关系,利用时空尺度扩展得到合理的耗水量。本文综述了理论基础相对牢固的3种尺度扩展技术:基于生物计量参数、遥感影像和水文模型的尺度扩展,剖析各模型的控制因子,探讨模型的适用性和优缺点,对尺度扩展技术的发展做了展望。     

Capturing microscopic features of bone remodeling into a macroscopic model based on biological rationales of bone adaptation

To understand Wolff’s law, bone adaptation by remodeling at the cellular and tissue levels has been discussed extensively through experimental and simulation studies. For the clinical application of a bone remodeling simulation, it is significant to establish a macroscopic model that incorporates clarified microscopic mechanisms. In this study, we proposed novel macroscopic models based on the microscopic mechanism of osteocytic mechanosensing, in which the flow of fluid in the lacuno-canalicular porosity generated by fluid pressure gradients plays an important role, and theoretically evaluated the proposed models, taking biological rationales of bone adaptation into account. The proposed models were categorized into two groups according to whether the remodeling equilibrium state was defined globally or locally, i.e., the global or local uniformity models. Each remodeling stimulus in the proposed models was quantitatively evaluated through image-based finite element analyses of a swine cancellous bone, according to two introduced criteria associated with the trabecular volume and orientation at remodeling equilibrium based on biological rationales. The evaluation suggested that nonuniformity of the mean stress gradient in the local uniformity model, one of the proposed stimuli, has high validity. Furthermore, the adaptive potential of each stimulus was discussed based on spatial distribution of a remodeling stimulus on the trabecular surface. The theoretical consideration of a remodeling stimulus based on biological rationales of bone adaptation would contribute to the establishment of a clinically applicable and reliable simulation model of bone remodeling.     

单分子免疫检测技术研究进展*

早诊断、早发现、早治疗是提升肿瘤患者生存率的主要手段。临床常用的免疫学检测方法如酶联免疫吸附法、化学发光法等,其检测灵敏度多限制在10^-14~10^-12 mol/L,无法满足早期诊断的需求。单分子免疫检测法,可将待检测分子限制在极小空间范围内(nL以下),对检测信号进行绝对计数,从而实现痕量(可达10^-18 mol/L)标志物的检测。这一超高灵敏度技术实现的关键在于将检测范围限制在极小体积内。经过数十年发展,不论是物理隔离还是利用纳米孔,抑或通过改进显微镜性能,均可在极小体积内(10^-21 L)对信号进行检测。目前基于微阵列的SimoA检测系统已成为单分子免疫检测的金标准,Quanterix公司基于此开发的HD-1分析仪已进入市场应用。基于微液滴的单分子免疫检测技术主要限于实验室,但具有床旁检测的优势。重点介绍了基于物理隔离形式如微阵列和微液滴的单分子免疫检测进展,为进一步开发超高灵敏度检测方法并促进未来临床应用提供理论基础。     

A theoretical and numerical approach to optimal positioning of the patellar surface replacement in a total knee endoprosthesis

The clinical results of total knee joint arthroplasty with patellar replacement have shown that postoperative problems arise, especially under unfavourable biomechanical conditions. The findings concerning retropatellar contact forces have been obtained by means of different methods, partly through experimental investigations and partly through theoretical considerations. But so far patellar replacement criteria and the resulting changes of the retropatellar contact force were not taken into consideration in other studies. Our mathematical model is based on a mechanical one and the parameter study considers the influence of the height of the patellar surface replacement upon different biomechanical parameters at varying positions. The results suggest that the patellar replacement should therefore be kept as low as possible, thus reducing the retropatellar contact force to a minimum, especially in the extremely stressed flexion areas of up to about 90 degrees.     

The membrane potential and its representation by a constant electric field in computer simulations

A theoretical framework is elaborated to account for the effect of a transmembrane potential in computer simulations. It is shown that a simulation with a constant external electric field applied in the direction normal to the membrane is equivalent to the influence of surrounding infinite baths maintained to a voltage difference via ion-exchanging electrodes connected to an electromotive force. It is also shown that the linearly-weighted displacement charge within the simulation system tracks the net flow of charge through the external circuit comprising the electromotive force and the electrodes. Using a statistical mechanical reduction of the degrees of freedom of the external system, three distinct theoretical routes are formulated and examined for the purpose of characterizing the free energy of a protein embedded in a membrane that is submitted to a voltage difference. The W-route is constructed from the variations in the voltage-dependent potential of mean force along a reaction path connecting two conformations of the protein. The Q-route is based on the average displacement charge as a function of the conformation of the protein. Finally, the G-route considers the relative charging free energy of specific residues, with and without applied membrane potentials. The theoretical formulation is illustrated with a simple model of an ion crossing a vacuum slab surrounded by two aqueous bulk phases and with a fragment of the voltage-sensor of the KvAP potassium channel.     

Genetic diversity among the Newars of Nepal

Genetic diversity among the Newars of Nepal has been studied using Wright's FST and the ratio of observed variance to theoretical variance following Lewontin and Krakauer's 1973 method, based on six genetic characteristics. The gene differentiation among the Newars is only 1.7%. These observations are further corroborated by the results obtained through genetic distance analysis. The average heterozygosity per locus is high (ranging from 35 to 42%) for all the groups. About 95% of total gene diversity exists within the Newar groups, the intergroup components being only about 5%.