A revised worm‐like chain model for elasticity of polypeptide chains

The elasticity of polypeptide chains is usually characterized by the worm‐like chain model that was proposed first to describe the elasticity of double‐stranded DNA. However, the molecular dynamics simulation data on the elasticity of the polypeptide chains are deviated significantly away from the theoretical data obtained based on the worm‐like chain model. Here, we provide a revised worm‐like chain model by considering entropic, enthalpic, and hydrophobic effects and the effect of the compressing force applied to the polypeptide chains. The theoretical data obtained based on the revised model are in good agreement with the molecular dynamics simulation data. Additionally, we reveal that, besides the positive‐force regime in the elasticity of polypeptide chains, the negative‐force regime also plays important roles in the biological functions of proteins. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 297–307     

Degradation performance of polyglutamic acid and its application of calcium supplement

Degradable biopolymers with functional groups play a crucial role in the biomedical field. In this case, the influences of temperature and pH values on the degradation performance of poly (γ‐glutamic acid) (γ‐PGA) were fully explored by gel permeation chromatography. Further, γ‐PGA‐Ca was prepared by using calcium chloride to react with the low molecular weight γ‐PGA and characterized by Fourier transform infrared, differential scanning calorimetry test, gel permeation chromatography, atomic absorption spectrophotometric, Ca²⁺ release in vivo, and cytotoxicity experiments. Furthermore, Caco‐2 cell model was constructed to study the mechanism of γ‐PGA‐Ca intestinal absorption. Results indicated that low pH value and high temperature are the suitable conditions for the degradation of γ‐PGA. It also suggested that γ‐PGA‐Ca can be used as calcium supplements due to its high rate of absorption.     

HPLC–MS/MS analysis of peramivir in rat plasma: Elimination of matrix effect using the phospholipid‐removal solid‐phase extraction method

A simple HPLC–MS/MS method has been developed for the determination of peramivir in rat plasma in the present study. The analytes were separated on a C₁₈ column (50 × 2.1 mm, 1.7 μm) and a triple‐quadrupole mass spectrometer equipped with an electrospray ionization source was applied for the detection. A phospholipid‐free cartridge solid‐phase extraction was used to pretreat the plasma and eliminate the endogenous phospholipid. The in‐source collision‐induced dissociation approach showed that this pretreatment could result in negligible ion suppression from the extracted sample and could produce cleaner samples when compared with the protein precipitation. The method was linear over the concentration range of 0.12–1200.0 ng/mL for peramivir. The method was validated and successfully applied to a pharmacokinetic study after peramivir was orally and intravenously administered to Sprague–Dawley rats.     

一种新的磁共振图像处理流水线的设计与实现

磁共振图像的重建、后处理及可视化是磁共振成像（MRI）系统的重要组成部分.本文开发了一个新的用于磁共振图像重建、后处理及可视化的开源框架YAP（Yet Another Pipeline）,利用此框架可以方便地构建图像处理流水线.与现有的一些其他开源框架相比,本文开发的框架具有如下特点：（1）采用基于接口的设计,可使用基于接口的插件对流水线的功能进行扩展;（2）允许用户使用编写脚本的方式构建图像处理流水线,编辑与修改流水线都很方便;（3）支持带有分支结构的流水线,便于流水线的构建与调试.目前,该框架已经在商用系统中获得了应用.     

Dynamic properties of the Monte Carlo method in statistical mechanics

By means of the Monte Carlo sampling technique the equilibrium thermodynamics of fluids and magnets can be calculated numerically. We show that the questions of convergence and accuracy of this method can be understood in terms of the dynamics of the appropriate stochastic model. Also, we discuss to what extent various choices of transition probabilities lead to different dynamic properties of the system. As examples of applications, we consider Ising and Heisenberg spin systems. The numerical results about the dynamic correlation functions are compared to simple approximations taken from the theory of the kinetic Ising model.     

Exact coexistence surfaces containing double critical points for a three-component solution on the Bethe,honeycomb, and square lattices

A model is considered in which the bonds of a lattice are covered by rodlike molecules. Neighboring molecular ends interact with orientation-dependent interactions. The model exhibits closed -loop phase diagrams and double critical points. Exact coexistence surfaces are calculated for the model on the Bethe, honeycomb, and square lattices. The nature of the doubling of the critical exponent near a double critical point is calculated. The behavior of the critical line in the neighborhood of a double critical point is calculated exactly.     

HIRFL注入器PIG离子源的研制

本文介绍了兰州重离子加速器(HIRFL)的注入器(SFC)所用PIG离子源的研制和改进工作,使用新研制的PIG源,已在注人器SFC上获得了5μA的O_(16)~(5+)及10μA的C_(16)~(4+)的离子束。     

Uniqueness of the standard model neutral current predictions

In view of an excellent agreement between the recently determinedv _μ-hadron couplings and predictions of the standard model, the basic question discussed is how far its neutral current predictions can be mimiced in going either from the isodoublet to an isotriplet (or an even higher isospin) left-handed representation or from SU _L (2) × U(1) toG × U(1), whereG is a simple group of rank two. This question is addressed with reference to a sufficiently broad class of schemes. Their most distinctive properties are: in the higher isospin scheme, neutrino couplings are precisely in the form obtainable with standard l.h. representation; the higher g.g. scheme isL+R type in which, to each light fermion of evenRU parity, a superheavy fermion of the same charge and oddRU parity is associated, parity conservation forbidding their mixing. Reasons for excluding theL-type andG ₂ higher g.g. schemes are given. Their neutral current predictions are compared with those of the standard model. A higher isospin representation can mimic the predictions of the standard model in inclusive and semi-inclusivev _μ-hadron reactions but is conclusively discriminated from the isodoublet representation by elasticv _μ ⁽⁻ p scattering. TheG × U(1) scheme can mimic standard model neutrino sector but is conclusively discriminated from minimal scheme by parity violating effects.     

Nonlinear stability of incoherence and collective synchronization in a population of coupled oscillators

A mean-field model of nonlinearly coupled oscillators with randomly distributed frequencies and subject to independent external white noises is analyzed in the thermodynamic limit. When the frequency distribution isbimodal, new results include subcritical spontaneous stationary synchronization of the oscillators, supercritical time-periodic synchronization, bistability, and hysteretic phenomena. Bifurcating synchronized states are asymptotically constructed near bifurcation values of the coupling strength, and theirnonlinear stability properties ascertained.     

一种考虑速度随机慢化概率动态演化的交通流元胞自动机模型

在NS模型的基础上,利用司机的记忆效应和当前交通环境动态地调整随机慢化概率,从而得到一个改进的交通流元胞自动机模型.数值实验表明,该模型可以很好地刻画司机记忆效应对交通流的影响,记忆效应的引入可以提高平均速度和流量. 关键词： 交通流 元胞自动机模型 记忆效应 随机慢化概率