带有分段常数变量的单种群模型的稳定性和分支行为（英文）

本文研究了带有分段常数变量的单种群连续模型的稳定性和分支行为.首先,通过计算将连续模型转化为对应的差分模型,使用线性稳定性理论在三种情况下研究了差分模型在正平衡态处局部渐近稳定的充分条件.其次,将参数r作为分支参数,利用分支理论研究了差分模型在正平衡态处产生翻转分支的条件.最后,数值模拟验证了理论分析的正确性.     

一类Leslie-Gower捕食食饵模型的分歧

本文研究了一类具有扩散的Leslie-Gower模型.利用谱分析和稳定性理论得到了两个正常数平衡态的局部稳定性;利用最大值原理、Harnack不等式和能量积分的方法得到了正稳态解的上下界估计和非常数正解的存在性;利用单特征值分歧理论研究了系统发自两个正常数平衡态的解分支,得到了非常数正解的存在性;利用Hopf分歧理论,得到了在平衡解处Hopf分歧的存在性.     

一类带有恐惧效应的捕食-食饵模型的定性分析

反应扩散系统解的性质蕴含了丰富的信息,对于刻画种群生态现象有着重要的意义．本文研究了一类带有恐惧效应的捕食-食饵模型平衡态正解问题．首先,利用最值原理,得到平衡态正解的先验估计,为后续问题的研究奠定了基础;其次,给出了正常数平衡解的唯一存在的充分条件,并借助线性稳定性理论,得到了正常数平衡解的稳定性;最后,根据度理论,得到非常数正解的存在性．     

一类具时滞和收获的捕食模型的稳定性与Hopf分支

本文研究一类具有常数收获率和时滞的捕食模型,其中时滞描述了捕食种群的妊娠期。通过分析特征方程,得到了正平衡点局部稳定的条件。当时滞τ增加时,正平衡点失去稳定性,当τ跨过临界值时系统将出现Hopf分支。应用中心流形定理和规范型理论,得到了确定Hopf分支方向和分支周期解的稳定性的计算公式。最后对所得理论结果进行了数值模拟。     

HIV相关癌症的动力学模型研究(英文)

本文通过建立两个动力学模型,研究了HIV感染者中癌症的高发现象。我们分别研究了其平衡态的存在性及稳定性。对正平衡态还发现了Hopf分支的存在,并发现随着分支参数的变化,系统出现了周期解与混沌交替出现的现象。     

基于Logistic模型的型号研制异地协同模式

引用生态种群中的Logistic理论分析航空型号研制异地协同模式及稳定条件。设计航空型号研制异地协同的结构,建立型号研制“O A”、“A A”2种异地协同logistic模型,计算2种模式的稳定条件并分析策略含义,通过数值仿真模拟协同模型的动态演化过程。结果表明,型号研制异地协同的稳定性与研制单位的协同地位、内禀增长率、初值大小及最大产出量等密切相关。对参与型号研制的协同单位需采用不同的策略以保证协同模式的稳定。     

N维Lengyel-Epstein模型常数平衡解的分歧

本文借助于Leray-Schauder度理论和分歧理论,研究了n维Lengyel-Epstein模型平衡态系统发自常数平衡态解的局部分歧和整体分歧,得到了非常数平衡态解存在的充分条件.     

具有脉冲效应的Holling—Tanner捕食-被捕食系统的正周期解

为了描述突然性因素对捕食一被捕食系统的影响,本文建立了具有固定时刻脉冲影响的Holling-Tanner捕食-被捕食系统模型,研究了系统的正周期解的存在性.利用基于叠合度理论的连续定理,证明了模型的正T-周期解的存在性,给出了系统存在正周期解的条件,该条件由两个种群的内禀增长率、脉冲周期及一个脉冲周期内的脉冲影响总量给出,这说明脉冲影响可能导致种群系统的平衡状态发生改变.     

两个艾滋病相关的癌症动力学模型研究

考虑到癌症在HIV感染者中的高发特点,本文建立两个艾滋病与癌症相结合的HIV-1动力学模型:一个ODE模型;一个DDE模型.该类系统有四个平衡态.我们讨论了在不同的免疫状况下这些平衡态的存在性、稳定性以及其生物学意义.在DDE模型中,我们讨论了正平衡态Hopf分支的存在条件.文中结果与一些医学临床结果及试验室观察相吻合.     

带有种群密度制约接触率的SIR流行病模型的全局分析

本文研究了两类具有种群密度制约接触率的SIR流行病模型,其生态学结构分别为常数输／Logistic出生。可以证明两模型均存在在强阈值现象,阈值参数即模型的基本再生数,它决定了疾病的绝灭和流行也决定了模型的全局性态。为了证明地方病平衡点的全局稳定性,对具有常数输入的SIR模型,引入了一个变量代换将三维模型转化为具有极限方程的二维渐近自治系统;对具有Logistic出生的SIR模型,构造了Lyapunov函数。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.