罐装橙汁超高温瞬时灭菌的数值模拟研究

由于对橙汁的灭菌工艺没有进行精确的研究,在橙汁的实际生产中经常是使用过度灭菌来保证果汁灭菌的彻底。过度灭菌不但引起橙汁生产的能耗增加而且会导致橙汁的营养成分的损失。本文分析了果汁中常见的细菌,得出了灭菌结束时所需的最低温度;在此基础上利用数值模拟的方法对橙汁的超高温瞬时灭菌进行了计算。同时使用实验对CFD计算的结果进行了验证,误差在9.5%以内,表明CFD对橙汁的超高温灭菌的模拟是可行的。模拟得出了不同温度时的灭菌的最理想时间条件分别为:135℃(408 K),13 s;140℃(413K),12 s;145℃(418 K),12 s;150℃(423K),11 s。     

In vivo pharmacokinetics of and tissue distribution study of physalin B after intravenous administration in rats by liquid chromatography with tandem mass spectrometry

A rapid and sensitive liquid chromatography tandem mass spectrometry quantitative analysis method was established for the pharmacokinetics and tissue distribution study of physalin B in rat. Physalin B and physalin H (internal standard, IS) were separated on an Agilent Eclips XDB C₈ column. MS detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction monitoring mode with a positive eletrospray ionization source. The assay was validated in the concentration ranges of 22.6–22600 ng/mL for heart and lung and 4.52–4520 ng/mL for other tissues. The intra‐ and inter‐day precisions (RSD) were ≤9.23 and ≤12.51%, respectively, with accuracy (%) in the range of 88.07–113.2%. A pharmacokinetic study showed that physalin B has a long dwell time with a half‐life of 321.2 ± 29.5 min and clearance of 175.4 ± 25.7 mL/min/kg after intravenous administration. Additionally, physalin B showed a wide tissue distribution with a special higher penetration in lung. The data presented in this study could provide useful information for the further study of physalin B. Copyright © 2016 John Wiley & Sons, Ltd.     

Residual level of dimethachlon in rice‐paddy field system and cooked rice determined by gas chromatography with electron capture detector

In this study, a modified quick, easy, cheap, effective, rugged and safe method coupled with gas chromatography with electron capture detection was established to determine dimethachlon residues in paddy soil, rice husk, rice straw, brown rice and cooked rice. The limits of quantification of dimethachlon were 0.01 mg/kg for paddy soil, brown rice and cooked rice and 0.02 mg/kg for rice straw and rice husk. The mean recoveries were in the range 78.59–104.7% with relative standard deviation values of <10% for dimethachlon in the five matrices. For field experiments, the final residues of dimethachlon in paddy soil were < 0.05 mg/kg and were < 1.21 mg/kg in rice straw from six sites. The final residues of dimethachlon in the brown rice at 21, 28 and 35 days after spraying from six sites were 0.08–7.58 mg/kg, and 0.16–30.1 mg/kg in rice husk. Our six test sites covered the main rice–producing areas of China. The routine rice cooking process of a Chinese family could apparently increase the removal of dimethachlon in rice compared with brown rice, and the reduction ratios were > 96%.     

On the usage of NURBS as interface representation in free‐surface flows

When simulating free‐surface flows using the finite element method, there are many cases where the governing equations require information which must be derived from the available discretized geometry. Examples are curvature or normal vectors. The accurate computation of this information directly from the finite element mesh often requires a high degree of refinement—which is not necessarily required to obtain an accurate flow solution. As a remedy and an option to be able to use coarser meshes, the representation of the free surface using non‐uniform rational B‐splines (NURBS) curves or surfaces is investigated in this work. The advantages of a NURBS parameterization in comparison with the standard approach are discussed. In addition, it is explored how the pressure jump resulting from surface tension effects can be handled using doubled interface nodes. Numerical examples include the computation of surface tension in a two‐phase flow as well as the computation of normal vectors as a basis for mesh deformation methods. For these examples, the improvement of the numerical solution compared with the standard approaches on identical meshes is shown. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of aspect ratio and anisotropy distribution in ordered CoNi nanowire arrays

The size effects on magnetic properties of nanowires arrays were studied varying the nanowires diameter and maintaining the same periodicity among them, for two different nominal compositions of Co and Ni in the alloy form. The competition among magnetocrystalline and shape anisotropies changes drastically from smallest to biggest diameters altering the easy axis direction. In the case of 75% of Co in alloy, experimental values of the effective anisotropy constant (K_eff) vary from positive to negative depending on the diameter, which means a reversal of the easy axis direction. For 50% of Co the shape anisotropy dominates over the magnetocrystalline for all studied diameters.     

Localization of diffusion sources in complex networks with sparse observations

Locating sources in a large network is of paramount importance to reduce the spreading of disruptive behavior. Based on the backward diffusion-based method and integer programming, we propose an efficient approach to locate sources in complex networks with limited observers. The results on model networks and empirical networks demonstrate that, for a certain fraction of observers, the accuracy of our method for source localization will improve as the increase of network size. Besides, compared with the previous method (the maximum–minimum method), the performance of our method is much better with a small fraction of observers, especially in heterogeneous networks. Furthermore, our method is more robust against noise environments and strategies of choosing observers.     

Distributing points uniformly on the unit sphere under a mirror reflection symmetry constraint

Uniformly distributed point sets on the unit sphere with and without symmetry constraints have been found useful in many scientific and engineering applications. Here, a novel variant of the Thomson problem is proposed and formulated as an unconstrained optimization problem. While the goal of the Thomson problem is to find the minimum energy configuration of N electrons constrained on the surface of the unit sphere, this novel variant imposes a new symmetry constraint – mirror reflection symmetry with the x–y plane as the plane of symmetry. Qualitative features of the two-dimensional projection of the optimal configurations are briefly mentioned and compared to the ground-state configurations of the two dimensional system of charged particles laterally confined by a parabolic potential well.     

A mathematical model for the admission process in intensive care units

A mathematical model is given for the admission process in Intensive Care Units (ICUs). It is shown that the model exhibits bistability for certain values of its parameters. In particular, it is observed that in a two-dimensional parameter space, two saddle-node bifurcation curves terminate at a single point of the cusp bifurcation, creating an enclosed region in which the model has one unstable and two stable states. It is shown that in the presence of bistability, variations in the value of parameters may lead to undesired outcomes in the admission process as the value of state variables abruptly changes. Using numerical simulations, it is also discussed how such outcomes can be avoided by appropriately adjusting the parameter values.     

Objective Bayesian analysis of the Frechet stress–strength model

Several reference priors and a general form of matching priors are derived for a stress–strength system, and it is concluded that none of the reference priors is a matching prior. The study shows that the matching prior performs better than Jeffreys prior and reference priors in meeting the target coverage probabilities.     

固体的冲击拉伸碎裂

固体材料在冲击拉伸载荷作用下常常会断裂成多个碎片(碎片化)，固体材料碎片化的物理机制是多点损伤同时在固体中成核和发展，导致固体多处破坏。自 Mott 对固体的动态碎裂问题进行了开创性研究后，几十年来，对固体动态碎裂机制的研究一直是应用物理学、力学、航天和兵器工程等领域共同关心的重要课题。本文介绍了在冲击拉伸载荷作用下固体的动态碎裂研究的发展历史，给出相关的理论分析、实验研究和数值模拟的研究进展，特别针对现有的各种关于碎片尺度、碎片分布、以及碎片化物理机制的理论模型进行了较详尽的阐述和讨论，最后指出现有实验和理论研究中仍然存在的关键科学问题及进一步的研究展望。