关于真空泵基础压力与罗茨真空泵特征性能指标的探讨

本文阐述了真空泵的极限压力与基础压力两者的概念和关系,对国际标准ISO21360-1:2012中有关基础压力的条款做了详细的解读。对影响中真空罗茨泵抽气性能的特性指标进行了分析,给出了用罗茨泵零流量压缩比K0和最大允许压差作为罗茨真空泵的抽气性能指标的合理性,建议选择罗茨泵零流量压缩比K0作为罗茨泵抽气能力的主要考核指标之一,将最大允许压差作为罗茨泵的辅助考核指标。     

罗茨真空泵特性指标及测试方法研究

本文分析阐明了罗茨泵的特征性能为漏率、零流量压缩比、最大容许压差和噪声。提出了新概念—基础压力的定义:即泵按规定条件工作,在不引入气体的情况下,标准测试罩内趋向稳定的压力。并建议以漏率取代极限压力作为罗茨泵的性能考核指标,使罗茨泵性能的测量方法更接近、更符合实际运行状态。根据实验数据,提出了对零流量压缩比测量装置中的前级管路规定的改进,对最大容许压差测量方法提出了修改以及对噪声的测量方法提出一些新的见解。     

罗茨泵主要性能指标与转子型线加工误差

介绍了罗茨泵主要性能指标－零流量压缩比和最大允许压差与罗茨泵转子型线加工误差的关系，分析了机械仿形刨削加工中各种主要误差的形成原因和解决方法，提出了建议。     

ZJ5000大型罗茨真空泵的研制

主要介绍大型罗茨真空泵高零流量压缩比转子型线的设计方法及其提高泵最大允许压差的几个要点。     

罗茨真空泵性能考核指标——抽速和零流量压缩比的探讨

罗茨泵以抽速作为主性能考核指标不够确定，它不能真实反映罗茨泵的质量水平，建议以零流量压缩比作为考核罗茨泵抽气能力的性能指标。     

罗茨真空泵运行可靠性指标考核探讨

目前罗茨真空泵验收规范中采用零流量压缩比和最大允许压差来考核罗茨真空泵的性能。本文作者根据实际应用及可操作性,建议采用零流量压缩比和罗茨真空泵的排气口气体温度考核罗茨真空泵的性能。由于零流量压缩比的测量与现在的测量方法没有多大区别,因此本文没有详细讨论。     

罗茨真空泵试验方法的研究

罗茨泵的抽气速率和极限压力是泵的主要性能,但它在很大程度上要依赖于前级泵的型式和性能,因此它并不是罗茨泵本身特有的性能。能代表罗茨泵特征性能,而又与前级泵无关的是零流量压缩比、最大允许压差与溢流阀压差、漏率和噪声,它们与罗茨泵的真空状态、抽气性能和运行质量有着极其密切的关系。文中对特征性能的试验方法和装置进行了分析和研究,提出了有异于国内外现行标准的,更精粹、独特的见解。     

基于TRIZ理论的一种提升罗茨真空泵基础压力的设计方法

以TRIZ理论为研究工具,采用因果分析方法得到了影响罗茨真空泵基础压力的根本原因和薄弱点,通过技术矛盾和技术系统进化法则解决方案模型的启示,进一步改进了罗茨真空泵的密封结构和转子型线,然后基于改进方案,对ZJP70型罗茨真空泵进行了优化。测试结果表明：在同等条件下,优化后的新型罗茨真空泵基础压力提升明显,同时最大零流量压缩比、整机漏率和噪声等核心指标也得到了显著改善。     

罗茨真空泵性能试验方法探讨

本文把试验研究提高到一个前所未有的高度来认识,罗茨泵的特性和质量是设计和制造出来的,试验是产品特性的前导和鉴证。分析探讨了试验研究与设计、工艺之间的关系,以及它们对罗茨泵的特性,如漏率、零流量压缩比、最大容许压差、噪声和振动以及运转的安全性、可靠性所带来的影响,对多发性和容易出现的问题提出了解决和改进的措施。分析研究了试验条件、试验装置和试验方法对保证和鉴证罗茨真空泵特性的重要性,指出试验研究为产品的发展提供了设计依据和研究方向。尝试了设计、标准和试验研究三结合,取得了丰硕的成果。     

圆弧-摆线-渐开线型罗茨泵转子型线参数选择范围

罗茨泵转子型线是罗茨泵的关键。零流量压缩比高的罗茨真空泵、湿式罗茨泵真空泵和罗茨鼓风机均要求泵工作时转子与壳体之间及两转子之间气体泄漏较小，这样可改善泵的低压下性能，即提高泵的抽气效率。转子型线为“圆弧－摆线－渐开线”就可以满足这一要求。文中给出了泵的参数选择图，从图中可以看出泵的参数选择范围，文中说明了该图边界的性状．由该图可查出泵的容积利用系数λ同转子顶圆半径Ｒｍ与节圆半径Ｒ之比 Ｒｍ／Ｒ以及同渐开线压力角α的关系。 λ＝ｆ（Ｒｍ／Ｒ，ａ）。图中用计算机绘出了几个比较特征参数下转子型线及其啮合情况，借此可根据实际需要来选择系的转子型线参数。此种转子型线工艺性良好。可仿型法加工（只需两个工位）。还可以用范成法加工其渐开线部分，余下部分用成型铣刀加工。若以范成法加工型线渐开线部分时，设计转子型线时可选取渐开线基圆半径ｒ为整数．以便于其工艺装备的设计。     

基于分析软件“CiteSpace”的声景研究英文文献知识图谱分析

国外关于声景的探索经历了数十年的发展,对其进行系统梳理与总结对于中国声景研究具有重要的借鉴价值。文章以"Web of Science"核心数据库中近20年的相关英文文献作为研究对象,依托科学计量分析软件CiteSpace的知识图谱绘制功能,展现国外声景研究的学科及期刊分布特征、理论基础与研究热点。研究发现,国外声景研究呈现出明显的多学科特征。在研究热点上,从接续Schafer的理念、关注人类对声景的感知,到兼顾生物圈中非人类生物对声景的响应,再到以"格局-过程"为指导关注区域层面的声景生态特征与演变机制,是国外声景研究的主要发展脉络。声景研究框架的拓展使国外声景研究得以越来越全面和科学地解释和理解声景现象,并为声景实践的开展奠定了良好的基础。不足之处在于研究内容有待深化、研究学科有待融合、声景标准化建设有待加强、声景普及有待提高,而这也是国内声景研究实现跨越发展需要积极补足的方面。     

Detailed thermodynamic characterization of hermetic reciprocating compressors

The aim of this paper is the detailed analysis of different well-known thermodynamic efficiencies usually used to characterize hermetic compressors. Attention is focussed on the volumetric efficiency, the isentropic efficiency, and the combined mechanical–electrical efficiency. A procedure is presented to detach these efficiencies into their main components (physical sub-processes) to get deeper insight on the overall behavior.The volumetric efficiency is split into partial efficiencies related to pressure drop and heat transfer effects, supercharging effects, superdischarging effects, leakages, etc. The isentropic efficiency is detached using two different points of view: the work associated to the individual sub-processes (compression, discharge, expansion, suction), and the work associated to the underpressures, overpressures, and between the inlet and outlet mean compressor pressures. Finally, the combined mechanical–electrical efficiency is related to the heat transfer losses/gains, and to the exergy transfers and exergy destroyed.Even though some of the concepts introduced in the paper can be applied to different kinds of compressors, the discussion is specially focussed on hermetic reciprocating compressors. An advanced simulation model developed by the authors has been used to generate data to illustrate the possibilities of the detailed thermodynamic characterization proposed. The criteria developed are useful tools for comparison purposes, to characterize compressors, and to assist designers during the optimization process.     

Investigating driving behaviour of older drivers with mild cognitive impairment using a portable driving simulator

While there is a large body of research indicating that individuals with moderate to severe dementia are unfit to drive, relatively little is known about the driving performance of older drivers with mild cognitive impairment (MCI). The aim of the current study was to examine the driving performance of older drivers with MCI on approach to intersections, and to investigate how their healthy counterparts perform on the same driving tasks using a portable driving simulator. Fourteen drivers with MCI and 14 age-matched healthy older drivers (aged 65–87 years) completed a 10-min simulator drive in an urban environment. The simulator drive consisted of stop-sign controlled and signal-controlled intersections. Drivers were required to stop at the stop-sign controlled intersections and to decide whether or not to proceed through a critical light change at the signal-controlled intersections. The specific performance measures included; approach speed, number of brake applications on approach to the intersection (either excessive or minimal), failure to comply with stop signs, and slower braking response times on approach to a critical light change. MCI patients in our sample performed more poorly than controls across a number of variables. However, because the trends failed to reach statistical significance it will be important to replicate the study using a larger sample to qualify whether the results can be generalised to the broader population.     

Analytical evaluation of aircraft operational risks from runway rutting

Runway surface distortions such as rutting allow water to accumulate on the runway surface which may cause aircraft operational risks related to hydroplaning and loss of friction. This may increase the runway excursion risk during wet weather conditions. Several standards relating to airfield pavement maintenance have documented that rutting can cause safety hazards to aircrafts due to hydroplaning risk. This paper proposes an analytical approach to evaluate the hydroplaning potential for aircrafts due to the flooded ruts of a runway pavement and evaluate the operational risk. A finite element model is developed to simulate aircraft tyre hydroplaning under given set of operating conditions. By performing this evaluation for different rut depths, an assessment of the relative severity levels of different rut depths with respect to hydroplaning can be made. A numerical example is presented to illustrate the application of the procedure to evaluate operational risks to aircraft from runway rutting.     

High Power CW Wattmeter Calibration at NIST

The National Institute of Standards and Technology has established a measurement capability to support high power systems and devices. The automated wattmeter calibration system operates at power levels of 1 to 1000 W for frequencies from 1 to 30 MHz and 1 to 500 W from 30 to 400 MHz. A cascaded coupler technique is used to extend power measurements to high levels which are traccable to a 10 mW standard thermistor mount. This technique uses an arrangement of nominal 10, 20, 30, 40, and 50 dB couplers with sidearm power meters. The initial step transfers the calibration of the 10 mW standard to the 10 dB coupler/power meter. The standard is then replaced with a wattmeter to be calibrated. RF power is increased 10 dB and the calibration is transferred to the adjacent 20 dB eoupler/power meter. This sequence is repeated with the remaining coupler/power meters until the wattmeter is calibrated at the desired power levels and frequencies. Power ratios calculated from simultaneous power measurements made at each transfer are used to calculate the incident power at the wattmeter. Due to nonideal components, corrections are made for nonlinearities, mismatch, and other errors. Two types of wattmeters have been evaluated at selected frequencies and power levels. Total uncertainties are based on the random and systematic components.     

Biocompatibility Pathways in Tissue-Engineering Templates

Tissue engineering, which involves the creation of new tissue by the deliberate and controlled stimulation of selected target cells through a systematic combination of molecular and mechanical signals, usually involves the assistance of biomaterials-based structures to deliver these signals and to give shape to the resulting tissue mass. The specifications for these structures, which used to be described as scaffolds but are now more correctly termed templates, have rarely been defined, mainly because this is difficult to do. Primarily, however, these specifications must relate to the need to develop the right microenvironment for the cells to create new tissue and to the need for the interactions between the cells and the template material to be consistent with the demands of the new viable tissues. These features are encompassed by the phenomena that are collectively called biocompatibility. However, the theories and putative mechanisms of conventional biocompatibility (mostly conceived through experiences with implantable medical devices) are inadequate to describe phenomena in tissue-engineering processes. The present author has recently redefined biocompatibility in terms of specific materials- and biology-based pathways; this opinion paper places tissue-engineering biocompatibility mechanisms in the context of these pathways.     

感官代偿设计在产品中的应用

通过对人的感知系统进行分析,将感官代偿这一生理现象应用到设计中,不仅能够方便产品的使用,也能够锻炼感官障碍者的感官代偿功能,从而验证感官代偿设计是一种行之有效的设计方法,让其人本关怀的特征发挥的淋漓尽致。     

United states regulations for siting LNG terminals: problems and potential

The regulations being applied to liquefied natural gas (LNG) import terminal siting in the United States are reviewed. There are no requirements for exclusion zones to protect the public from LNG spills onto water. Serious problems with current practices used to determine exclusion zones on the land-based part of the facility are identified. Many of the questions that are considered relate to the use of computational fluid dynamic (CFD) models, which appear to offer the best potential for realistic modeling to determine vapor cloud exclusion zones that result from LNG spills into impounded areas with or without dispersion in the presence of other obstacles to the wind flow. Failure to use CFD models, which are already approved by the regulation, and continued use of practices which have been demonstrated to be in error, raises important questions of credibility as well as denies the applicant full use of scientific tools that are available to optimize the design of such facilities so as to best provide for safety of the public.     

Some guidelines for promoting high temperature deformation of metallic alloys

Capacity to reach large deformation at high temperature is an important issue in many forming processes of metallic alloys. It is well known that a low value of the stress exponent (or a concomitant high value of the strain rate sensitivity parameter) is a key point for controlling resistance to necking. A first way for decreasing the stress exponent is to get superplastic properties but it frequently requires dealing with fine microstructures which can be difficult to produce and to preserve. Moreover, in the case of single phase alloys, like aluminum or magnesium alloys, superplastic deformation generally induces damage which can result in premature fracture or damaged components after forming. The aim of this paper is to give some guidelines for promoting high temperature deformation of metallic alloys, with a particular attention given to superplastic forming. The possibility to reduce the temperature of superplastic forming (SPF) for titanium alloys, the capacity to get a better understanding of the specificities of damage process in the case of superplastic deformation and the ability to get large strains to fracture avoiding the production of fine grains before strain are more specifically discussed.     

Control of mechanical deformation of a laminate by electrical load to piezoelectric actuator considering the effects of damping and transverse shear

In this paper, we treat the control of dynamic deformation of a laminate by applying electrical load to piezoelectric actuators. Dynamic behavior of the laminate is analyzed considering the effect of damping due to interlaminar shear and the effect of transverse shear. The analytical model is a rectangular laminate composed of fiber-reinforced laminae and piezoelectric layers. The model is assumed to be a symmetric cross-ply laminate with all edges simply supported and to be subjected to unavoidable mechanical load and to electrical loads to piezoelectric actuators. Behavior of the laminate is analyzed based on the first-order shear deformation theory. The effect of damping due to interlaminar shear is incorporated into our analysis by introducing the interlaminar shear stresses which satisfy the Newton’s law of viscosity. The following quantities are obtained: (1) natural frequencies of the laminate, (2) weight functions for the deflection and rotations and (3) transient deflection due to loads varying arbitrarily with time. Moreover, the methods to control the deflection due to mechanical load by applying electrical voltage to the piezoelectric actuator are shown.