位置度误差的测量

位置度是用以控制被测要素的位置要求，是零件上被测的点、线、面的实际位置偏离理想位置的程度。在实际测量中，位置度误差的测量是一项较为复杂的工作。它不能通过直接测量得到，而是要按基准合理地定位被测零件，并且根据孔组对基准的定位尺寸，测量值需要经过正确的计算，最后才能得出真正的位置度误差。位置度多用以控制孔的轴线的位置变动，因此，文章以图文并茂的形式，以线位置度为主体，给出了不同条件下其位置度误差的测量与计算方法。     

无线光通信类脉冲位置调制技术研究进展

调制解调是提高无线光通信传输效率的关键技术,不同的调制方式其性能也有所不同.类脉冲位置调制是指脉冲位置调制(PPM)、差分脉冲位置调制(DPPM)及其组合以及由此演变而成的各种脉冲位置调制方式.本文总结了国内外类脉冲位置调制的研究进展,同时介绍了西安理工大学在类脉冲位置调制方面所做的工作,主要对开关键控、脉冲位置调制、...     

与“圆周均布孔的位置度检测的数据处理方法”一文的商榷

读贵刊１９９７年第９期“圆周均布孔的位置度检测的数据处理方法”一文,笔者对该文有关按角向位置误差最小条件确定圆周均布孔位置度误差评定基准的方法提出不同的看法。根据ＧＢ１９５８—８０《形状和位置公差检测规定》,在形位误差的检测和评定中,必要时,应采用位置误差最小区域法来确定基准要素。在圆周均布孔的位置度评定中,其角向基准必须通过位置误差最小区域法来确定,通过基准坐标系的旋转使各孔的实际位置度误差的最大者为最小。笔者认为,该文以被测孔的实际角向位置误差的最大者为最小的原则来确定圆周均布孔位置度评定的…     

平稳序列极值的位置之渐近性质

本文研究平稳序列的极值顺序统计量位置的渐近分布,得到局部最大值和极值顺序统计量的位置依分布的收敛性,以及首次高水平上超位置与局部最大值位置的联合渐近性质.     

立式金属罐容量检定相关问题思考

一、基圆位置和光学垂准线法垂直测定位置的确定 JJG168—2005《立式金属罐容量》检定规程中的“观察第一圈板外高或内高的3／4上下100mm处……”笔者理解其正确表述应是：第一圈板外高或内高的3，4上下100mm区间内的任一位置．在其位置上不允许有障碍物存在．并且包括以上各个圈板无论是围尺法的围尺位置．还是光学垂准线法各个测站的同一圈板的同一位置（1，4或3，4位置）．都应满足同样相对高度的水平位置并不允许有障碍物存在．这就有必要在检定过程中保证该位置的正确选取．     

圆柱轴上与轴线垂直相交的孔的位置度误差检测

本文通过圆柱轴上与轴线垂直相交的孔的位置度误差检测分析，指出位置度误差很难直接测得，一般要根据其公差带合理分解成几项位置误差分别检测，再通过合成才能得到位置度误差值。并说明了分解及合成方法，以及对加工有位置度要求的零件的实用意义。     

多指灵巧手双闭环模糊控制

设计一种双位置闭环模糊控制器,用于多指灵巧手的位置控制。利用电机码盘反馈构成内位置环控制,采用一般的PID控制律;通过关节位置反馈形成外位置环控制,采用模糊控制算法。这种两层位置反馈控制可弥补只有码盘反馈的半闭环控制结构的不足,使具有强非线性的钢缆传动系统包含在闭环内,从而提高系统的稳定性和鲁棒性。实验证明跟踪精度明显提高。     

内隐学习与外显学习的系列位置效应比较

目的采用自由回忆的方法对内隐学习与外显学习在单字词记忆中的系列位置效应比较来判断不同识记方式对系列位置效应的影响。方法自行设计实验研究测试卷,对某大学30名大学生进行内隐学习与外显学习两种实验情境下的测试。结果 (1)内隐学习和外显学习两种实验情境下的正确呈现次数有着显著的差异,并且这种差异表现符合系列位置效应的规律。(2)不同位置正确呈现次数有着显著的差异,存在较为明显的系列位置效应;在前、中、后各位置内隐学习和外显学习正确呈现次数均有着显著性的差异。(3)内隐学习在尾组各位置之间有显著性差异,表现出系列位置效应;而外显学习在中间组②各位置之间有显著性差异,表现出系列位置效应。结论内隐学习和外显学习两种实验情境下均存在系列位置效应的规律。内隐学习一系列记忆材料中在回忆靠后的材料更容出现系列位置效应,而外显学习一系列记忆材料中在回忆中间的材料更容出现系列位置效应。     

混凝土钢筋位置测定仪的量值溯源

为了解决交通运输行业内混凝土钢筋位置测定仪的量值溯源问题,分析了混凝土钢筋位置测定仪的使用和计量现状,确定了计量参数,研制了标准器组和标准装置,并开展重复性实验验证。通过建立的"混凝土钢筋位置测定仪—混凝土钢筋位置测定仪标准器组—混凝土钢筋位置测定仪计量标准装置—国家长度基准"溯源链,能够满足混凝土钢筋位置测定仪检定/校准的需要。     

变焦距物镜光学像面稳定性问题

本文主要讨论变焦距光学系统的凸轮误差、各移动组焦距误差和安装位置误差对变焦距物镜光学像面位置稳定性的影响,以及如何调整移动组的起始位置使三个焦面位置一致。     

Influence of surface roughness on the bonding quality in twin-roll cast clad strip

Manufacturing of aluminum-steel clad strips by means of twin-roll casting is of great interest due to a shorter production chain in comparison with convenient technologies. Experiments on twin-roll casting of clad strips of pure aluminum and an austenitic stainless steel of 2.5?mm total thickness with the inline abrasive cleaning of a steel substrate’s surface performed. The corresponding device for the inline surface preparation is designed. The influence of surface roughness of the substrate’s surface on the bonding strength between strip layers is analyzed. The mechanism of intermetallic bonding on the roughened surfaces is discussed. It is shown that surface roughness of steel substrate up to 4.2?µm provides bonding strength above 100?MPa.     

Central Venous Catheter Associated Infections Pathophysiology,Incidence, Clinical Diagnosis,and Prevention – A Review

The incidence of catheter related bloodstream infections poses a substantial burden on patient’s life’s and well‐being. Estimated 2 – 6 % of patients suffer from catheter associated bloodstream infections (BSI). Reports on mortality of these patients are up to 30 % in addition to a substantial prolongation of hospital days. The estimated cost of therapy of a BSI is approximately 10 000 € per patient. There is a definitive need for antimicrobially active medical devices for prophylaxis. Endowment of catheters with antibiotics and desinfectants have substantial limitations regarding spectrum of activity, duration of activity and clinical efficacy. The oligodynamic activity of silver has the greatest potential for prevention of catheter related infections. Various technologies in particular surface coating of these medical devices have been advocated previously with limited success. A new technology with impregnation of the entire catheter matrix with billions of nanoparticles of silver⁰ which results in a surface of 2000 cm²/g polyurethane (PU) has been developed. Central venous catheters manufactured according to the technology of the first and second generation have been investigated with good results of antimicrobial activity and biocompatibility. Favorable results in experimental investigations and good clinical results in controlled prospective, randomized, investigator blinded studies of the first generation silver catheter have been obtained. In 660 patients in an overall reduction of BSI of 66 % was observed. Favorable results in a postmarketing surveillance with 3000 patients were seen. The premarketing surveillance of the second generation silver‐catheter indicated an even greater reduction of catheter related BSI. In 204 patients with a mean duration of catheter placement of 9.2 days only one catheter related BSI was diagnosed. The rate of catheter colonization was <10 %. The catheter was well tolerated. A further improvement with increased antimicrobial activity was achieved by activation of silver nanoparticles in the third generation catheter: The superior results of in vitro tests and excellent biocompatibility lets us expect an additional improvement of preventive measures. The duration of antimicrobial activity has been investigated and lasts at least 370 days. The concept of impregnation of a polymer matrix and silicone can be extended to various other clinical applications e.g. Sheldon, Hickman and urologic catheters. Substantial savings in the cost of patient care through prevention of complications can be expected which is of particular importance with the disease oriented (DRG) remuneration system.     

Energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption refrigeration systems

In this paper, the energy and exergy analysis of single effect and series flow double effect water–lithium bromide absorption systems is presented. A computational model has been developed for the parametric investigation of these systems. Newly developed computationally efficient property equations of water–lithium bromide solution have been used in the computer code. The analysis involves the determination of effects of generator, absorber and evaporator temperatures on the energetic and exergetic performance of these systems. The effects of pressure drop between evaporator and absorber, and effectiveness of heat exchangers are also investigated. The performance parameters computed are coefficient of performance, exergy destruction, efficiency defects and exergetic efficiency. The results indicate that coefficient of performance of the single effect system lies in range of 0.6–0.75 and the corresponding value of coefficient of performance for the series flow double effect system lies in the range of 1–1.28. The effect of parameters such as temperature difference between heat source and generator and evaporator and cold room have also been investigated. Irreversibility is highest in the absorber in both systems when compared to other system components.     

Thermal conductivity of composites

A general expression for the effective thermal conductivity of inhomogeneous media in terms of the Fourier components of the spatial variation of the conductivity is applied to composites consisting of inclusions in a continuous matrix. It is reformulated in terms of the mean square fluctuations of the conductivity. Specific cases treated are spherical inclusions and long cylinders, both random and with preferred directions. The results hold provided the difference in thermal conductivities is small or provided the concentration of inclusions is not too large. The theory fails if the thermal conductivity of the matrix is much smaller than that of the inclusions. The same considerations also apply to electrical conductivity.     

Einfluss der Werkstoffzähigkeit auf das Festigkeitsverhalten unter mehrachsiger Beanspruchung am Beispiel von Schweißverbindungen aus Stahl und Aluminium

Influence of Ductility on the Multiaxial Fatigue Behaviour by the Example of Welded Joints of Steel and Aluminium The multiaxial fatigue behaviour of materials with different ductility under constant and changing principal stress directions is also applicable to welded joints of different materials. For this, welded flange tube connections of the fine grained steel StE 460 and the artificially aged aluminium alloy AlSi1MgMn T6 were investigated under constant amplitude combined bending and torsion. Out‐of‐phase loading, i. e. changing principal stress directions, of the steel joints led to a decrease of fatigue life, which is observed at ductile material states. However, for the aluminium joints out‐of‐phase loading resulted same behaviour as in‐phase loading, which indicates a semi‐ductile material behaviour. The results for the welded steel joints were evaluated on basis of local stresses by the integral hypothesis of the Effective Equivalent Stress EES (WVS). This hypothesis for ductile material states takes into account the life decreasing influence of out‐of‐phase loading by considering the interaction of the shear stresses on different planes. The fatigue behaviour of the aluminium welds is described by the critical plane based combination of shear and normal stresses (KoNoS), which is valid for semi‐ductile material states.     

Surface State Control by Ultrasonic Plastic Deformation at the Final Machining Stage

Basic results of research into the process of the surface geometry formation during ultrasonic plastic deformation of metallic materials are presented. The results of mathematical modeling of the microgeometry and surface undulation formation in the machining of materials of different hardness are also presented. Experimental validation of the adequacy of the proposed models is provided.     

Multiple-jet electrospinning methods for nanofiber processing: A review

Electrospinning is a versatile method of producing continuous nanofibers through the application of an electric field. The simplest and earliest form of electrospinning involves the use of a single-needle spinneret to draw the solution out and form fibers. The process, however, is very time consuming, limiting the potential wide-scale application of electrospun nanofibers. Many multiple-jet electrospinning methods have been proposed to overcome the problem of low productivity, but the generation of multiple jets brought about other problems such as jet repulsion, lower process controllability, and deterioration of fiber quality. Thus, continuous development is necessary for the optimization of the process. The aim of this review is to provide an overview of the recent electrospinning technologies reported in the literature, particularly on various multiple-jet electrospinning methods from both nozzles and free surfaces. The general principle underlying the electrospinning process, as well as important parameters involved are also presented in this paper.     

Certified reference materials of trace elements in water

Measurement of trace elements is playing a vital role in industries and various sectors of science and technology including semiconductors, food, health and environmental sectors. In most of the cases a small error in measurement can vitiate all the measures taken for quality control and management. Many decisions regarding the suitability of material/products are based on the analysis. To reduce or eliminate the rejection rate of the products, accurate and reliable measurements are needed which can be achieved by the use of certified reference materials (CRMs). Their use in calibration of analytical equipments and validation of test methods ensures high quality in measurements and it provides traceability to the measurement data with national/international measurement systems (SI unit) also. In the present scenario of globalization of economy, use of certified reference materials (CRMs) in measurements is essential for global acceptance of products and test reports. Their use fulfil a mandatory requirement of international quality systems (ISO 9000, ISO/IEC standard 17025) including our national accreditation body, National Accreditation Board for Testing and Calibration Laboratories (NABL), World Trade Organization (WTO) etc. International manufacturers of CRMs are meeting most of the requirement of CRMs of the country. To meet the demand of CRMs indigenously, the National Physical Laboratory, India initiated a national programme on preparation and dissemination of certified reference materials.