能量天平永磁体系统的温度场分析

提出基于COMSOL有限元仿真的方法对永磁体系统的温度场进行分析。通过分析,得到永磁体在不同工作模式下的温度上升曲线。仿真结果表明永磁体磁盘在两种工作模式下存在10^-4 K量级的温度差异,由于钐钴永磁体磁盘存在-3×10^-4 K^-1的温度系数,温度对磁链差的测量影响在10^-8量级。为改善能量天平永磁体系统中悬挂线圈的发热问题,提出调整悬挂线圈电流,增大辐射面辐射系数,改变天平支撑结构3种方案,以改善温度波动引入的普朗克常数测量不确定度。     

浅析砝码的磁性

电子天平是采用高精度传感器借助电磁力补偿达到平衡，并通过功能强大的微处理器和高性能MD转换器．实现快速、准确地测量。由于它在衡量过程中采用的是电磁平衡的原理，即在天平失衡的情况下。通过内部线圈中电流大小的改变使天平重新达到平衡，因此在天平的周围会产生一个较强的电磁场。而砝码多采用不锈钢制造．如果电子天平的电磁屏蔽不好，砝码的剩磁过大，     

用居里磁秤法测定铝合金的磁化率

本文论述了用Curie磁秤法测定铝合金磁化率的实际工作经验。同时也介绍了Curie磁秤法的原理和计算磁化率的方法。实践表明,在测定铝合金磁化率时,测试设备的选择、标样材料的确定、以及试样重量和安放位置等因素,对测试结果均有明显的影响。在使用磁天平的情况下,试样自重和磁场作用力均会使天平的横梁倾斜,致使试样在磁场中的位置发生移动,并对测试结果产生一定的影响,移动幅度愈大,影响也愈大。标样的场化率值愈接近被测试样的磁化率值,测得的结果愈准确。为了减少天平横梁倾斜所产生的不良影响,试样重量小数点后第三位数(对于精度为0.0001克的天平)或第四位数(对于精度为0.00001克的天平)应当限制在0—3之间。在此情况下,天平横梁倾斜程度减小,试样下移距离不超过0.8mm,从而保证了必要的测试精度。试样在磁场中的位置以处于最大磁场梯度处为宜。此外,悬挂试样的吊杆和夹具材料具有的磁性、空气中的水份、磁极头在工作时的发热情况、震动和流动空气,以及粘附于试样表面的其它物质等因素,对测磁结果也有较大的影响。因而,必须适当地选择和控制。     

能量天平悬挂线圈姿态调整方法研究北大核心CSCD

能量天平悬挂线圈初始位姿不理想会引入准直误差,线圈中心水平位置的精密控制可以借助两轴高精度位移平台实现;但调整线圈姿态的3路连杆调整机构之间存在的相互耦合,使得对姿态的精确调整难以实现。基于能量天平悬挂系统初始位姿与寄生位移之间的数学模型,确定线圈绝对水平位置。在线圈绝对水平位置附近进行姿态控制实验,利用递推最小二乘法得到悬挂线圈姿态控制系统的离散状态空间模型。在此基础上,建立基于状态空间的模型预测控制策略,将悬挂线圈姿态调整逼近至绝对水平,其3路连杆控制准确度优于0.25μm,姿态控制准确度优于1μrad。     

TG328A型机械天平常见故障及调修

正0引言TG328A型机械加码天平准确度高,性能可靠,广泛应用于分析、化学等精密测量实验室。TG328A型机械天平组成部件较多,主要由框罩、机械挂砝码装置、横梁、立柱、制动系统、悬挂系统、光学读数系统、底座等组成。由于其结构精巧,微小的变化都会影响其使用,因此对使用者的要求较高。在日常实验中TG328A型机械天平往往会突发各种     

影响磁天平测量结果的因素

介绍了磁天平装置测量弱磁材料磁化率的工作原理和装置组成,对影响测量结果的各种因素进行仔细的分析和研究,主要是由于测量时因质量称重、磁场稳定性、样品形状、磁干扰等多种因素给磁化率测量结果带来影响。通过实验验证,提出解决测量误差的方法,以提高磁天平测量不确定度水平。     

肿瘤磁致热疗的研究进展及其原理分析

介绍了肿瘤热疗的研究现状以及热疗的方法——微波、射频、超声波、电磁场加热、红外线等。重点论述了用磁性液体进行热疗的原理，并根据Rosensweig理论对其电磁场产热率等进行了理论计算及分析，最后对肿瘤磁致热疗的应用前景进行了展望。     

磁场环境下导电圆形薄板的磁弹性强迫振动

研究了电磁场环境下机械载荷作用圆形导电薄板的磁弹性强迫振动问题。首先给出了圆形薄板的磁弹性轴对称振动方程,并依据麦克斯韦方程,得到了相应的电磁场方程和电磁力表达式,在此基础上,对横向恒定磁场中周边固支和周边简支边界约束圆板的振动问题进行了分析。基于位移函数的设定,应用伽辽金法,推得了导电圆板的磁弹性强迫振动微分方程。通过数值计算,得到了两种边界约束条件下圆板磁弹性振动的幅频和相频曲线图,并对结果进行了分析,讨论了磁感应强度和板厚等参数对系统振动特性的影响。     

铝熔体中磁性杂质颗粒的电磁分离

分析了磁性杂质颗粒在电磁场中的受力情况,采用磁平衡法测量了铝熔体中两种典型富铁相杂质颗粒的磁化率,指出铝熔体中的富铁相杂质是顺磁性物质,在电磁场中受到电磁力和磁场力的驱动作用,确定其在分离器上的聚集方式．静态电磁分离试验结果表明,当磁场强度大于145mT时,电磁力起主要作用;当磁场强度小于120mT时,磁场力起主要作用．     

风雨耦合环境结构荷载与响应的理论及试验研究

采用理论分析及试验研究方法对风雨共同作用下的结构荷载与响应进行了较为系统的研究。首先在确定风雨联合作用概率模型的基础上通过对降雨作用特性的分析，比较了雨滴冲击作用模型和空气密度等效变化模型的对于建筑结构等效静力作用性能；其次，基于高精度风雨耦合荷载环境模拟试验设备，进行了风雨定常气动力荷载模型高频天平测力试验研究，研究了简单几何形体的风雨定常荷载变化规律；然后，采用二维悬挂系统测振试验方法，研究了风雨非定常气动力荷载模型及其结构振动响应特点；最后，对缆索承重桥梁拉索风雨激振现象进行耦合荷载环境参数精细化控制试验研究，揭示了拉索空间姿态、拉索动力特性、来流风速和不同雨强组合等条件对拉索风雨振的影响规律。     

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 ...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

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