Refrigerants for vapour compression refrigeration systems

With the mandate of Montreal Protocol banning ozone depleting substances, and Kyoto Protocol later on curtailing the use of substances which contribute to global warming, conventional refrigerants are to be replaced by environment-friendly working fluids. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are being substituted by hydrofluorocarbons (HFCs), hydrofluorooelifins (HFOs), and a variety of mixtures. In view of the global warming potential of these newly synthesized refrigerants, the recent trend is to go back to the originally used natural fluids such as ammonia, carbon dioxide, hydrocarbons, water vapour, etc. In this article, various issues related to this changeover of refrigerants being used in vapour compression refrigeration systems are discussed.     

Theoretical Study on CO_2 Transcritical Cycle Combined Ejector Cycle Refrigeration System

Mechanicalvapourcompressioncyclesaremainlyemployedinmostrefrigerationsystems .Chlorofluoro carbons(CFCs)orhydrochlorofluorocarbons(HCFCs)aregenerallyusedasrefrigerantsinthesesystemsdrivenbyelectricityfromburningfossilfuels ,whichresultsino zonedepletionduetotheleakageandpoorrecoveryofthoseman maderefrigerants,andglobalwarmingowingtoCO2 emissionfrom powerstationsandthereasonisthatCFCsorHCFCsarepowerfulgreenhousegases.Inaddition,otherenvironmentalissuesarealsocausedbytheNOx,SO2 andpartic…     

Metal hydride work pair development and its application on automobile air conditioning systems

INTRODUCTION Metal hydrides are special alloys which absorb and desorb hydrogen reversibly. At room temperature, metal hydrides could absorb as much hydrogen as liquid hydrogen of the same volume under much lower pressure and much higher temperature (Güther and Otto, 1999). Massive reaction heat is generated accompanying this reaction, which could be used for waste heat recovery, solar energy utilization and re-frigeration with no side effect to environment (Izhvanov et al., 1996). Con…     

Eco-friendly alternative refrigeration systems

We saw in Part 1¹ of this article the need, suitability and the technological developments of two eco-friendly alternative, i.e. magnetic and thermoelectric, refrigeration systems. In the present article, we briefly introduce the principle of thermoacoustic refrigeration technique along with the latest developments in this technology. S S Verma is a senior lecturer in the Department of Physics, Sant Longowal Institute of Engineering and Technology, Longowal, Punjab.     

Distributed retrieval practice promotes superior recall of anatomy information

Effortful retrieval produces greater long‐term recall of information when compared to studying (i.e., reading), as do learning sessions that are distributed (i.e., spaced apart) when compared to those that are massed together. Although the retrieval and distributed practice effects are well‐established in the cognitive science literature, no studies have examined their additive effect with regard to learning anatomy information. The aim of this study was to determine how the benefits of retrieval practice vary with massed versus distributed learning. Participants used the following strategies to learn sets of skeletal muscle anatomy: (1) studying on three different days over a seven day period (SSSS_7,2,0), (2) studying and retrieving on three different days over a seven day period (SRSR_7,2,0), (3) studying on two different days over a two day period (SSSSSS_2,0), (4) studying and retrieving on two separate days over a two day period (SRSRSR_2,0), and (5) studying and retrieving on one day (SRx6₀). All strategies consisted of 12 learning phases and lasted exactly 24 minutes. Muscle information retention was assessed via free recall and using repeated measures ANOVAs. A week after learning, the recall scores were 24.72 ± 3.12, 33.88 ± 3.48, 15.51 ± 2.48, 20.72 ± 2.94, and 12.86 ± 2.05 for the SSSS_7,2,0, SRSR_7,2,0, SSSSSS_2,0, STSTST_2,0, and SRx6₀ strategies, respectively. In conclusion, the distributed strategies produced significantly better recall than the massed strategies, the retrieval‐based strategies produced significantly better recall than the studying strategies, and the combination of distributed and retrieval practice generated the greatest recall of anatomy information. Anat Sci Educ 10: 339–347. © 2016 American Association of Anatomists.     

磁热效应与磁致冷材料

阐述了磁热效应的基本概念及磁致冷的原理,介绍了磁工质的选择依据,概述了磁致冷材料,特别是室温磁致冷材料的研究进展．     

Meeting Needs of Young Children at Risk for or Having a Disability

Poverty-related factors place children at higher risk for disabilities and also serve as barriers to families accessing services for their children and themselves. Early childhood practitioners can play a critical role in supporting families by providing services to overcome these obstacles and by working in partnership with specialized early intervention programs to assure the families and children receive those services. Families (N = 3,001) enrolled in the Early Head Start (EHS) Research and Evaluation Project were randomly assigned to the program group (who received EHS services) or the control group in a rigorous, experimental design study in order to evaluate program impacts. All participating families were living in poverty, included a pregnant woman or a child below age 1, and were eligible for EHS. The majority of children enrolled in the EHS Research and Evaluation Project was identified as having at least one of a great variety of disability indicators (e.g., family received Part C services, child has been diagnosed as having asthma). There was a very small number of families, however, actually enrolled in Part C services. Enrollment in EHS was associated with children being less likely to have cognitive or language delays and their families being more likely to receive early intervention (Part C) services and have Individualized Family Service Plans (IFSPs) when they needed them.     

System design and analysis of the trans-critical carbon-dioxide automotive air-conditioning system

As an environmentally harmless and feasible alternate refrigerant, CO₂ has attracted worldwide attention, especially in the area of automobile air-conditioning (AAC). The thermal property of CO₂ and its trans-critical refrigeration cycle is very different from that of the traditional CFC or HCFC system. The detailed process of CO₂ system thermal cycle design and optimization is described in this paper. System prototype and performance test bench were developed to analyze the performance of the CO₂ AAC system.     

Thermodynamic Analysis and Comparison on Low Temperature CO_2-NH_3 Cascade Refrigeration Cycle

Intheapplicationsofindustrialandcommercialrefrig erationsystem ,iftherequiredrefrigerationtemperatureisverylow ,theconventionalvaporcompressionsystemisdiffi culttomeettherequirementbecausewhenthedifferencebe tweentheevaporatingtemperatureandthecondensingtemper atureissohighthatitishardtofindarefrigeranttomeettheneedsasthecondensingpressureisnottoohighandtheevap oratingpressureisnottoolow .Whentherefrigeratingtemper atureisverylow ,thecascaderefrigerationcycleissuitabletobeused .Itcannotonlysat…     

Development of Metal and Metal-Based Composites Anode Materials for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) are considered the next powerful potential generation energy storage system because of substantial potassium resource availability and similar characteristics with lithium. Unfortunately, the actual application of KIBs is inferior to that of lithium-ion batteries (LIBs), in which the finite energy density, ordinary circular life, and underdeveloped fabrication technique dominate the key constraints. Various works have recently been directed to growing novel anode electrodes with superior electrochemical capability. Noticeably, metals/metal oxides materials (e.g., Sb, Sn, Zn, SnO₂, and MoO₂) have been widely investigated as KIBs anodes because of high theoretical capacity, suggesting outstanding promise for high-energy KIBs. In this review, the latest research of metals/metal oxides electrodes for potassium storage is summarized. The major strategies to control the electrochemical property of metals/metal oxides electrodes are discussed. Finally, the future investigation foreground for these anode electrodes has been proposed.

     

半导体制冷系统设计与非稳态性能分析

为了研究半导体制冷系统的工作性能,建立了半导体制冷系统的应用系统,并对该应用系统进行数学建模,通过对半导体制冷系统的各个工作状态建模分析,研究了半导体制冷系统在非稳态下的工作性能,模拟和仿真结果和预期的实验分析数值基本一致。     

Rapid prototyping in automated instructional design

In this article the impact of the tools being developed as part of the Second Generation Instructional Design (ID₂) Research Program on the process of instructional design is described. ID₂ supports rapid prototyping as a design and development process. Rapid prototyping is described and contrasted with the instructional systems development (ISD) process. This article is based on research supported by Utah State University, Human Technology Inc., and the U.S. Office of Personnel Management.     

Coating behavior and surface hardening of Pd77Cu6Si17 thin film metallic glass on AZ31 magnesium alloy

Pd77Cu6Si17 （PCS） tbin film metallic glasses （TFMGs） with high glass forming ability and hardness were selected as a hard coating for improving the surface hardness ofAZ31 magnesium alloy. Both microindentation and nanoindentation tests were conducted on specimens with various PCS film thicknesses from 30 to 2000 nm. The apparent hardness and the relative indenta- tion depth （fl） were integrated using a quantitative model. The interaction parameters involved and relative hardness values were extracted from iterative calculations. According to the results, surface hardness can be enhanced greatly by PCS TFMGs in the shallow region, followed by gradual decrease with increasing fl ratio. In addition, specimens with thinner coatings （e.g., 200 nm） showed greater substrate-film interaction and those with thick coatings （e.g., 2000 nm） became prone to film cracking. The op- timum TFMG coating thickness in this study was estimated to be around 200 nm.     

Symmetries and conservation laws in classical and quantum mechanics 2. Quantum mechanics

In Part 1 of this two-part article we have spelt out, in some detail, the link between symmetries and conservation principles in the Lagrangian and Hamiltonian formulations of classical mechanics (CM). In this second part, we turn our attention to the corresponding question in quantum mechanics (QM). The generalization we embark upon will proceed in two directions: from the classical formulation to the quantum mechanical one, and from a single (infinitesimal) symmetry to a multi-dimensional Lie group of symmetries. Of course, we always have some definite physical system in mind. We also assume that the reader is familiar with the elements of quantum mechanics at the level of a standard first course on the subject. Operators will be denoted with an overhead caret, e.g., $ \hat A,\hat G,\hat U $ \hat A,\hat G,\hat U , etc., while $ [\hat A,\hat B] = \hat A\hat B - \hat B\hat A $ [\hat A,\hat B] = \hat A\hat B - \hat B\hat A is the commutator of $ \hat A $ \hat A and $ \hat B $ \hat B .     

TiO_2基自清洁粉末涂料的制备与性能研究

利用蒸发法制备了含有TiO_2的自清洁涂料,考察了相关条件对涂层材料自清洁效果的影响。结果显示:随着TiO_2含量的增加,涂层干燥时间逐渐提高,涂层的水接触角增大;TiO_2含量为15%时涂层的光催化性能最强;含TiO_2的涂层对灰尘、油污、咖啡都具有较好的自清洁效果,其机械性能满足涂料应用的一般性要求。     

Morningness and state academic self-concept in students: Do early birds experience themselves as more competent in daily school life?

The purpose of the present study was to investigate the role of circadian preference for students’ state academic self-concept (ASC). We focused on students’ tendency to be morning-oriented (i.e., morningness) and examined the association between morningness as a trait and mean levels of state (momentary) general-school ASC in everyday school life using intensive longitudinal data collected among N = 285 (N_obs = 6,140; M_lessons = 21.54) German ninth and tenth graders. Furthermore, we tested whether the strength of this relation between morningness and state general-school ASC was modulated by the time of day (i.e., synchrony effect). Results of multilevel analyses showed that morningness was positively related to students’ mean levels of state general-school ASC. However, our results refuted a synchrony effect on state ASC, as higher morningness related to equally high mean levels of state general-school ASC both early and late in the school day with respect to a typical school schedule with lessons occurring in the morning to early afternoon. The present findings contribute to our understanding of ASC and provide relevant information about how morningness should be positioned with regard to ASC in everyday school life.     

Green epoxidation of cyclooctene with molecular oxygen over an ecofriendly heterogeneous polyoxometalate-gold catalyst Au/BW<Subscript>11</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

An ecofriendly heterogeneous polyoxometalate (POM)-gold catalyst Au/BW₁₁/Al₂O₃ was synthesized and used for solvent-free epoxidation of cyclooctene under mild reaction conditions using molecular oxygen as an oxidant and t-butyl hydroperoxide (TBHP) as an initiator. The catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), induced coupled plasma optical emission spectrometry (ICP-OES), and Brunauer-Emmett-Teller (BET). The catalyst showed good conversion and high selectivity without use of solvents or environmentally harmful oxidants. Moreover, the catalyst is recyclable up to three cycles with no significant loss in selectivity towards epoxide.     

Affordances of Augmented Reality in Science Learning: Suggestions for Future Research

Augmented reality (AR) is currently considered as having potential for pedagogical applications. However, in science education, research regarding AR-aided learning is in its infancy. To understand how AR could help science learning, this review paper firstly has identified two major approaches of utilizing AR technology in science education, which are named as image-based AR and location-based AR. These approaches may result in different affordances for science learning. It is then found that students’ spatial ability, practical skills, and conceptual understanding are often afforded by image-based AR and location-based AR usually supports inquiry-based scientific activities. After examining what has been done in science learning with AR supports, several suggestions for future research are proposed. For example, more research is required to explore learning experience (e.g., motivation or cognitive load) and learner characteristics (e.g., spatial ability or perceived presence) involved in AR. Mixed methods of investigating learning process (e.g., a content analysis and a sequential analysis) and in-depth examination of user experience beyond usability (e.g., affective variables of esthetic pleasure or emotional fulfillment) should be considered. Combining image-based and location-based AR technology may bring new possibility for supporting science learning. Theories including mental models, spatial cognition, situated cognition, and social constructivist learning are suggested for the profitable uses of future AR research in science education.     

双元非共沸制冷剂在喷射制冷中应用的可能性(英文)

分析了双元非共沸制冷剂在喷射制冷中应用的可能性．使用相平衡关联式和ＰＲ状态方程完成了两种混合工质对（Ｒ３０／Ｒ１４２ｂ,Ｒ３０／Ｒ１２４）的热力循环性能计算,对计算结果进行了分析讨论．理论计算表明,实施双元工质在低温域的蒸发可提高制冷品质,而喷射器可压缩双相流介质的特点保证了这种循环的正常运行．