Optimal design of sintered Ce_9Nd_(21)Fe_(bal)B_1 magnets with a low-melting-point (Ce,Nd)-rich phase

A systemic investigation was done on the chemistry and crystal structure of boundary phases in sintered Ce9Nd21FebalB1 （wt%） magnets. Ce2Fe14B is believed to be more soluble in the rare-earth （RE）-rich liquid phase during the sintering process. Thus, the grain size and oxygen content were controlled via low-temperature sintering, resulting in high coercivity and maximum energy products. In addition, Ce formed massive agglomerations at the triple-point junctions, as confirmed by elemental mapping results. Transmission electron micros- copy （TEM） images indicated the presence of （Ce,Nd）Ox phases at grain boundaries. By controlling the composition and optimizing the preparation process, we successfully obtained Ce9Nd21FebalBx sintered magnets; the prepared magnets exhibited a residual induction, coerciv- ity, and energy product of 1.353 T, 759 kA/m, and 342 kJ/m3, respectively.

A MICROMECHANICS ANALYSIS FOR THE MICROSTRUCTURE DESIGN OF A TWO-PHASE PSEUDOELASTIC COMPOSITE

A micromechanics analysis on the possibility of designing a two-phase pseudoelastic composite is made for the case where ductile transformable shape mem- ory alloy plastic particles are imbedded coherently in an elastic matrix. It is demon- strated that a pseudoelastic stress-strain loop in a macroscopic loading-unloading cy- cle can be obtained by microscopically stress induced forward and reverse martensitic transformations in the SMA particles. The relation between the macroscopic stress- strain response and the material parameters of the constituents of this composite is quantified through the micromechanics calculations, which reveals that the best duc- tility and thus the greatest energy absorption capacity of this novel microstructure can be obtained by the optimum material design.

DESIGN OF TWO-PHASE SINUSOIDAL POWER CLOCK AND CLOCKED TRANSMISSION GATE ADIABATIC LOGIC CIRCUIT

First the research is conducted on the design of the two-phase sinusoidal power clock gen- erator in this paper. Then the design of the new adiabatic logic circuit adopting the two-phase sinusoidal power clocks—Clocked Transmission Gate Adiabatic Logic (CTGAL) circuit is presented. This circuit makes use of the clocked transmission gates to sample the input signals, then the output loads are charged and discharged in a fully adiabatic manner by using bootstrapped N-Channel Metal Oxide Semiconductor (NMOS) and Complementary Metal Oxide Semiconductor (CMOS) latch structure. Finally, with the parameters of Taiwan Semiconductor Manufacturing Company (TSMC) 0.25μm CMOS device, the transient energy consumption of CTGAL, Bootstrap Charge-Recovery Logic (BCRL) and Pass-transistor Adiabatic Logic (PAL) including their clock generators is simulated. The simula-tion result indicates that CTGAL circuit has the characteristic of remarkably low energy consumption.

Risk Assessment at the Design Phase of Construction Projects in Ghana

The study was carried out exclusively in Ghana to explore the approaches employed by consultants in risk assessment at the design phase of projects in Ghana. One hundred and fourteen (114) consultants were selected out of a population of one hundred and eighty six (186) from three main professional associations in Ghana made up of the Ghana Institute of Architects, Ghana Institution of Engineers and the Ghana Institution of Surveyors (Quantity Surveying Division) practicing in Ghana for the study. Both primary and secondary data were collected. A descriptive survey was also used to observe and describe the presence, frequency or absence of characteristics of a phenomenon as it naturally occurred, in order to gain additional information. A questionnaire was also designed to collect data from the architects, engineers and quantity surveyors. The data was analyzed using Statistical Package for the Social Scientists (SPSS) 17.0. Descriptive and inferential statistics, such as frequency tables, percentages and cross tabulations were used in the data analysis and summaries. Simple tests of associations were undertaken by using Chi square and Cramer’s V statistics to compare relationships between variables. Again, relative importance index was also used to analyze some of the data by computing to deduce their rankings. The relative importance index was used to analyze some of the data by computing to deduce their rankings. The research revealed that majority of consultants had an average knowledge of risk management. Based on the findings it was recommended that consultants undergo advanced training in risk assessment. It was therefore suggested that consultancy firms should develop a set of laid down procedures for consultants to use in risk assessment in order that the use of intuition employed by majority is lessened. The challenges observed in risk assessment and the remedial steps suggested curtailing the detrimental effects of risks would be of wide importance to many developing economies.

Building Information Modeling for Environmental Impact Assessment in Early Design Phases: A Literature Review

The building sector is the largest consumer of energy in industrial countries. Saving energy in new buildings or building renovations can thus lead to significant global environmental impacts. In this endeavor, building information modeling (BIM) and building energy modeling (BEM) are two important tools to make the transition to net-zero energy buildings (NZEB). So far, little attention has been devoted, in the literature, to discuss the connection between BIM, BEM, and Life-cycle assessment (LCA), which is the main topic of this article. A literature review of 157 journal articles and conference proceedings published between 1990 and 2020 is presented. This review outlines knowledge gaps concerning BIM, BEM, and environmental impact assessment. It suggests that defining the process with the right technology (at the right time) would result in a more integrated design process (IDP) and bridge current gaps. The most efficient way to improve process and technology is related to the competences of the architects, engineers and constructors (AEC). The review also indicates that the IDP in the early design phases (EDP) is in need of improvement for architects and engineers, where a better connection between design phases, specific levels of development (LOD) and BIM tools is needed. Competences, process and technology are the three main themes addressed in the review. Their relation to design phases and LOD is discussed. The aim is to propose possible solutions to the current hinders in BIM-to-BEM (BIM2BEM) and BIM-for-LCA (BIM4LCA) integration.

Assessment of a Proposed Software Design for the Solution of Multi-Phase Mechanics Problems on Networked Laptops

This paper presents the design of a computational software system that enables solutions of multi-phase and multi-scale problems in mechanics. It demonstrated how mechanicians can design “process-driven” software systems directly, and that such efforts are more suitable in solving multi-phase or multi-scale problems, rather than utilizing the “data-driven” approaches of legacy network systems. Specifically, this paper demonstrates how this approach can be used to solve problems in flexible dynamics. Then it suggests a view of mechanics algorithms as ‘state equilibrium’ enforcers residing as servers, rather than as computer programs that solve field equations. It puts forth the need for identical input/output files to ensure widespread deployment on laptops. Then it presents an assessment of the laptop platform. A software system such as the one presented here can also be used to supply virtual environments, animations and entertainment/education software with physics.

Design of a Hardware-Implemented Phase Calculating System for Feedback Control in the LHCD Experiments on EAST

A fully hardware-implemented phase calculating system for the feedback control in the lower-hybrid current drive （LHCD） experiments is presented in this paper. By taking advantages of field programmable gate array （FPGA） chips with embedded digital signal processing （DSP） cores and the Matlab-aided design method, the phase calculating algorithm with a square root operation and parallel process are efficiently implemented in a single FPGA chip to complete the calculation of phase differences fast and accurately in the lower-hybrid wave （LHW） system on EAST.

IRS辅助的车联网相移设计和信道对齐策略

针对车联网中车辆的动态移动以及信号的随机散射所导致的信道快速变化问题,研究了智能反射面(intelligent reflecting surface,IRS)辅助的车联网通信并提出了联合相移设计和信道对齐策略,以削减车联网中多普勒频移的影响并提升通信性能。提出的策略由两个阶段构成。在第一阶段设计IRS的相移以改善级联信道的衰落状态,在策略的第二阶段进行修正函数的设计,实现了直接信道和级联信道的信道对齐,从而减少直接信道快衰落状态对通信性能的影响。通过联合相移设计和信道对齐策略中设计的反射相移以及修正函数,实现了通信性能的提升。仿真结果表明,所提策略相比于相移优化策略可以提升8.8%的频谱效率。

一种应用于两相交错Boost的耦合电感的优化设计

两相交错Boost变换器具有纹波电流小的优势,但其采用的交错并联技术增加了电感数量,进而增加了装置的体积和重量,不利于其功率密度的提升。耦合电感通过将多个磁性元件集成到一个磁芯实现磁路的部分共享,从而减小了磁元件的数量和重量。因此,设计了一种反向耦合电感,并将其应用于两相交错Boost变换器,实现了装置功率密度的提升。首先,对反向耦合电感的工作原理和损耗来源进行分析;然后,在此基础上设计了一种改进的“EE”型磁芯,一方面有效提高了磁芯利用率,另一方面降低了电感的体积与重量;最后,通过有限元仿真对所提优化设计方案进行验证,同时搭建了功率等级为2 kW的两相交错Boost变换器实验平台。仿真和实验结果均验证了所提优化设计方案的有效性。

基于延边三角形接法的24脉波移相变压器设计与电磁特性分析

针对核心设备24脉波移相变压器,从移相原理出发进行设计,并建立场路耦合模型对电磁设计和绕组短路力进行核算,其中关键设计参数移相角与理论值最大偏差仅为0.53%。在此基础上加工实验样机进行实验,移相角度偏差最大仅为0.2°。综合仿真与实验结果,24脉波移相变压器设计有效,且场路耦合模型适用于多脉波移相变压器的电磁仿真。

WC-Ni基硬质合金的基础研究进展

WC-Ni基硬质合金可应用在磁性材料成形模具和核主泵机械密封关键部件等极端工况领域。由于材料体系的本征特性,WC-Ni基硬质合金的高性能化和质量稳定性控制一直面临挑战。两相区碳窗口、固液转变温度、液相烧结过程中的润湿行为,以及合金组元在黏结相中的固溶特性,是硬质复合材料成分及其制备工艺设计的关键参数。本文以制备工艺体系最完善的WC-Co基硬质合金为参比对象,从上述4个方面对WC-Ni基硬质合金的本征特性及其研究进展进行综述,旨在强化对WC-Ni基硬质合金本征特性的理解,为高性能WC-Ni基硬质合金新材料高效开发提供参考。

Evaluation of Thermal Effect of PCM Wallboards by Coupling Simplified Phase Change Model with Design Tool

A simplified PCM wallboard model is coupled to an existing design-oriented model of multi-zone buildings. Using a reference model and a basic simulation configuration, the accuracy of the resulting PCM wallboard-building thermal design tool is evaluated. A new performance indicator, called PCM utilization factor, is then proposed in order to estimate the thermal efficiency of using PCM wallboards in buildings. Using this PCM Utilization factor and a degrees-hours indicator, the ability of the PCM wallboard-building thermal design tool to evaluate the effect of PCM wallboards on heating loads and summer thermal comfort in the early design phase of a project is examined in two real case studies: a family house project and an existing office building. The user-friendliness of this design tool, and the short calculation times it leads to when performing a year-long simulation using a standard office computer, make it a well-adapted tool for sensibility studies or multi-criterion optimization for buildings that contain PCM wallboards.

三相CLLC谐振变换器磁集成平面变压器设计与优化

三相CLLC谐振变换器凭借其高效率、大容量、低器件应力等优势而受到广泛关注。然而,多相结构的磁性元件数量多、体积大,是制约功率变换器尺寸的主要因素。随着宽禁带(WBG)半导体器件的出现,功率变换器的开关频率显著提高,这也为印制电路板(PCB)绕组的使用提供了有利条件。与传统绕线式绕组相比,PCB绕组的扁平特性更适用于平面磁性元件。此外,由于高频带来的低电感需求也使得基于PCB绕组的平面磁性元件更有利于实现集成。该文提出一种新型的基于PCB绕组的电感和变压器的集成结构,详细分析磁心结构的磁路模型,并给出集成磁件的优化设计方法,最后通过搭建一台基于SiC器件的800 V/10 kW的实验样机进行验证。实验结果表明,该集成方案可有效减小变换器的体积和损耗,具有高功率密度和高效率。

RIS辅助通感一体化:波束成形和反射相移的联合设计

ISAC允许通信和雷达共享频谱资源,被视为解决未来无线网络频谱拥塞的一项有前途的技术。当信道退化严重时,仅依靠基站侧天线获得的性能增益十分有限,RIS因其能够创建有利的传播环境已成为一项革命性技术,借助RIS可为ISAC系统创建额外的链路以提高系统性能。基于此,提出RIS辅助ISAC,通过联合设计基站的有源波束成形和RIS的反射相移,以最大化加权和速率与探测功率,并提出了基于加权均方最小误差和分数规划的交替算法来解决这一问题。仿真结果证明在ISAC中部署RIS并合理优化其相移可以有效提升通信和感知的性能。

共晶物相变蓄热材料制备及性能测试的实验设计

节能减排是当今社会的关注重点。利用共晶物相变蓄热材料在相变过程的蓄放热技术是实现太阳能、工厂余热等能源综合利用、提高能效、降低二氧化碳排放、保护环境的最有效手段之一。共晶物相变蓄热材料实验涉及原料配方及制备工艺、晶体结构及形成机理以及产品热物性能等专业内容,可设计为综合化学实验。该课题的实施培养大学生配方设计能力和大型仪器设备动手操作技能。

两相式混合步进电机速度和位移控制案例设计

步进电机在电脉冲信号的控制下能实现一定的角位移或线位移,掌握步进电机的控制技术非常重要。以两相混合式步进电机为控制对象,以单片机AT89C52和可编程计数器/定时器8253为主对电机进行速度和位移控制设计,对某一具体案例采用Proteus软件进行设计与仿真,包括控制电路和程序的设计。仿真和实验结果表明:该系统结构简单、容易实现、成本低,可用于其他步进电机的控制,并为教学或工程应用提供了参考。

机器学习指导相和硬度可控的AlCoCrCuFeNi系高熵合金设计

采用机器学习辅助高熵合金设计,致力于解决传统试错实验方法时间周期长、成本高的问题。以经典的AlCoCrCuFeNi系高熵合金为研究对象,采用机器学习方法,分别构建高熵合金的相结构预测模型和硬度预测模型。其中支持向量机模型(SVM)在两个任务中均有最好的训练表现,最佳的相分类准确率达0.944,硬度预测模型的均方根误差为56.065HV。进一步串联两种机器学习模型,基于样本数据集上下限的成分空间,对AlCoCrCuFeNi系高熵合金同时进行相和硬度的高效预测和筛选,实现新型合金成分的快速设计。实验验证5种新合金符合相预测结果,测试硬度与预测硬度值的RMSE为12.58HV,表明建立的机器学习模型实现对高熵合金相和硬度的高效预测。

基于条件加权似然方法的BOIN12设计的改进研究

目的基于条件加权似然方法对BOIN12设计进行改进,解决试验药物毒性和有效性出现延迟的情况下的最优剂量探索问题。方法利用条件加权似然方法给出延迟情况下的似然函数,对毒性率和条件有效率进行估计。通过模拟将改进后的BOIN12设计与其他Ⅰ-Ⅱ期设计方法进行比较,评估其性能。结果模拟研究表明,在多个不同场景下,改进后的设计仍然具有优良的统计性能,同时大大缩短了试验时长。结论改进后的设计可以解决Ⅰ-Ⅱ期试验中的毒性和有效性同时延迟问题。

一种幅相联合调制雷达波形设计与处理方法

随着脉内特征识别、信号分选等电子侦察技术的发展,雷达波形设计正面临严峻的挑战。幅度调制作为一种新型脉冲调制方式,能够增加信号时域的复杂性,提升波形的反识别能力。本文提出一种幅相联合编码雷达波形,通过幅度相位联合调制提升雷达波形的复杂度,具有良好的反侦察潜力;利用幅度上的稀疏采样特点,提出匹配滤波与压缩感知相结合的回波信号处理方法处理此信号,有效提升低信噪比条件下的检测概率。最后通过仿真实验证明了所提幅相联合调制雷达波形设计与处理方法的有效性。

新型钴基高温合金成分设计的研究进展

传统钴基高温合金的强化机制为固溶强化和碳化物强化,弱于有序γ′相沉淀强化的镍基高温合金的强化效果,日本学者发现了有序γ′相强化的Co-Al-W系新型钴基高温合金,其强化效果明显优于传统钴基高温合金。由于新型钴基高温合金具有较传统镍基高温合金更高的承温能力以及更加优异的高温抗蠕变性能和抗氧化性能,因此被认为是最具潜力的航空发动机热端材料之一,近年来得到迅速发展。基于国内外学者对新型钴基高温合金的研究成果,系统总结多种合金元素(如Ta,Ti,W和Nb等)对新型钴基高温合金组织和性能的影响。在组织方面,总结合金元素对合金相变温度、γ′相的体积分数及形态、γ′相的尺寸、γ/γ′两相晶格错配度和有害相的影响;在性能方面,总结合金元素对合金抗氧化性能、力学性能及抗蠕变性能的影响,以期为新型钴基高温合金的成分设计提供参考。最后对新型钴基高温合金成分的高效率设计进行展望。