Performance of a single-stage Linde-Hampson refrigerator operating with binary refrigerants at the temperature level of-60 ℃＊

The optimization of the performance of a single-stage Linde-Hampson refrigerator （LHR） operating with six different binary refrigerants （R23/R134a, R23/R227ea, R23/R236ea, R170/R290, R170/R600a and R170/R600） with ozone depletion potentials （ODPs） of zero was conducted using a new approach at the temperature level of-60℃. Among these binary refrig- erants, the 0.55 and the 0.6 mole fractions of R23 for R23/R236ea are the most prospective nonflammable ones for the medium and low suction pressure compressors, respectively. For these two kinds of compressors, the 0.6 and the 0.65 mole fractions of R170 for R 170/R600, respectively, are the most prospective binary refrigerants with low global warming potentials （GWPs）. The results of optimization of pressure levels indicate that the optimum low pressure value for coefficients of performance （COP） is achieved when the minimum temperature differences occur at both the hot and the cold ends of the recuperator at a specified composition and pressure ratio. Two useful new parameters, the entropy production per unit heat recuperated and the ratio of heat recuperating capacity to the power consumption of the compression, were introduced to analyze the exergy loss ratio in the recuperator. The new approach employed in this paper also suggests a promising application even to the optimization of the performance with multi-component refrigerants.     

Influence of baffle position on liquid sloshing during braking and turning of a tank truck

The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.     

A long-term in situ calibration system for chemistry analysis of seawater

An in situ calibration system is a versatile exploration instrument for electrochemical sensors investigating the biochemical properties of the marine environment. The purpose of this paper is to describe the design of an auto-calibrating system for electrochemical （pH） sensors, which permits two-point in situ calibration, suitable for long-term measurement in deep sea aqueous environments. Holding multiple sensors, the instrument is designed to perform long-term measurements and in situ calibrations at abyssal depth （up to 4000 m）. The instrument is composed of a compact fluid control system which is pressure-equilibrated and designed for deep-sea operation. In situ calibration capability plays a key role in the quality and reproducibility of the data. This paper focuses on methods for extending the lifetime of the instrument, considering the fluidics design, mechanical design, and low-power consumption of the electronics controller. The instrument can last 46 d under normal operating conditions, fulfilling the need for long-term operation. Data concerning pH measured during the KNOX18RR cruise （Mid-Atlantic Ridge, July-August, 2008） illustrate the desirable properties of the instrument. Combined with different electrodes （pH, H2, H2S, etc.）, it should be of great utility for the study of deep ocean environments, including water column and diffuse-flow hydrothermal fluids.     

利用网络进行协作学习的研究

建构主义理论强调以学习者为中心,学生是学习过程的主体,是知识意义的主动建构者。网络环境下的协作学习恰好体现了建构主义理论的观点。利用网络进行学习,满足了广大学习者的要求,促进了教学,但也给教师和学习者提出更高的要求。     

废报纸制取吸水树脂研究

以废报纸为原料,经脱墨、碱煮、酸煮可得纤维素,以N,N-亚甲基双丙烯酰胺为交联剂,过二硫酸钾为引发剂,与丙烯酸接枝共聚制备了吸水树脂。讨论了原料单体配比、交联剂用量等因素对吸水树脂性能的影响,考查了制得的吸水树脂对蒸馏水、自来水和一定浓度NaCl溶液的吸收性能。在最佳条件下制得的吸水树脂对蒸馏水的吸水倍率为340 g/g,对自来水的吸水倍率为280 g/g,对0.05 mol/L NaCl溶液的吸水倍率达50 g/g。     

交易成本的处理:补偿与降低

交易完成前除生产成本之外的所有成本都可界定为交易成本,即成本模型中总成本等于生产成本与交易成本之和.对交易成本处理主要有补偿与降低两种方式.在不同的市场结构和不同的市场定价法下,交易成本通过价格机制补偿的程度不一,在成本加成定价无法实现的情况下,交易成本的处理就从补偿转向了降低.通过制度规范、重复博弈和适度规模是厂商降低交易成本的一般措施.     

儿童人际冲突与自我调解冲突能力之我见

通过观察儿童日常行为,了解其在人际冲突情境下的行为表现,进而研究人际冲突与攻击行为的关系。本次研究主要包括三个方面：1．儿童人际冲突的主要特点;2．儿童自我调解冲突能力的发展特点;3．如何发展儿童调解冲突的能力？研究发现儿童之间发生的人际冲突频繁,但冲突时间较短,而且很少引起暴力攻击行为,随着年龄的增长,儿童自我调节冲突的能力也在不断的增强,发生在同辈之间的人际冲突是儿童发展调节冲突能力的最佳环境,教师在冲突应提供必要支持,促进儿童人际交往能力的发展。     

Chinese perceptions of the interface between school and museum education

The current political and social backdrop in China that is characterized by rapid educational reforms to the K-12 education system, rapid growth in the number of science museum institutions, and Central Government policy which encourages collaboration between museums and school has the potential to be fertile ground for meaningful engagement between museums and schools. Notwithstanding, the Chinese K-12 education system generally does not utilize museum resources to support the curriculum, as is common in Western countries. This hermeneutic phenomenographic study elucidates the current Chinese views and perceptions among three stakeholders—school teachers, museum staffs and science educators—around this collaborative concept. The outcomes demonstrate that strongly entrenched cultural views and long-standing practices among stakeholder groups are obstacles to meaningful collaboration despite Central Government policy which encourages such engagement. The cultural values and perceptual views of stakeholder groups were discerned with the purpose of promoting mutual understandings and ultimately enabling meaningful collaboration in support of K-12 education in China.     

嵌入式Linux系统开发模式

嵌入式Linux是指固化在存储器或单片机中、执行独立功能的专用Linux操作系统．嵌入式Linux以源码开放,容易移植,成为嵌入式领域最有发展前景的嵌入式操作系统．本文首先简单介绍嵌入式Linux的定义、系统软件和硬件操作平台,重点论述了嵌入式Linux系统开发模式,并提出一种基于arm芯片和uClinux操作系统的新型开发模式．     

大学"去行政化"难在哪里?

老百姓都知道,温家宝总理有很深厚的教育情结,情结背后有深思熟虑的教育理念.他担任总理,领导国务院的工作,对行政体制改革当有很全面的思考.他如此明确地提出教育体制中行政化倾向的问题,是十分值得我们每一个教育工作者深思的.