Ultralow-concentration Sm codoping in CsI:Tl scintillator: A case of little things can make a big difference

CsI:Tl scintillators were hindered from computer tomography and high-speed imaging applications by a serious afterglow problem. In this study, the effects of ultralow-concentration Sm codoping on the scintillation characteristics of CsI:Tl were investigated. Pulsed X-ray excited afterglow after 50 ms in 0.005 mol% Sm-codoped CsI:Tl was lowered by over one order of magnitude in comparison with Sm-free one. The beneficial effects of ultralow-concentration Sm codoping also appeared to be maintaining the light yield and energy resolution. The light yield and energy resolution after 0.005 mol% Sm codoping were 71,700 ± 6000 photons/MeV and 6.9% at 662 keV, respectively.     

Hollow silica nanoparticles: A tiny pore with big dreams

Hollow nanoparticles exhibit unique functions such as thermal insulation, low dielectricity, and abnormal light scattering, especially when the inner size reaches less than twice the mean free path of air molecules (mean free path of air is 68 nm). It is easy to imagine that a nano-sized pore improves the thermal insulation performance due to less air convection flow inside. However, not only the hollow interior but also the shell microstructure (size, thickness, and density) strongly affect the functionalities. For example, a lower apparent shell density induces a higher thermal insulation probably due to phonon scattering on the siloxane bond cleavages. The best performance for the thermal conductivity of the hollow particle/polymer composite was 0.019 W/m·K, which is superior to air. The structure design of the hollow nanoparticle is quite important to produce this effect. In this review, based on important parameters, how to design the structure and wide applications of hollow nanoparticles are reviewed and a bright outlook for the future is expected.     

Teaching engineering design: Can reading a textbook make a difference?

Teaching design is an integral part of most engineering curricula. Often, students are introduced to the engineering design process through a chapter in a textbook. Does this passive approach to teaching an active process aid the students' learning? An experiment was conducted to assess what students learn about the design process when they read a text. Here, 10 students enrolled in a freshman course were asked to read aloud from a freshmen engineering textbook. Half of the subjects read the text prior to solving three open-ended engineering design problems and the other half solved the same problems before they read the text. Both the subjects' process in solving the problems, as well as the quality of their solutions (the product), are assessed. Results show that subjects that read the text before they solved the three problems spent significantly more time solving the problems and were more sophisticated in their problem solving strategies. These subjects also scored better when judged on the quality of their approach to the problem (including the number of design criteria considered, communications, assumptions, and technical accuracy). However, these subjects did not score better on a quality measure of the final solution.     

大截面差空心件内高压成形研究

截面周长差较大的空心零件的内高压成形需要解决膨胀区的轴向补料问题和预成形问题,才能获得壁厚分布较为均匀的合格零件.以某轿车转向节臂零件的成形过程为例,对上述问题进行了试验研究.首先设计、试制了瓶形预制件,在预成形中利用"有益起皱"实现了大量的补料,获得了壁厚分布符合要求的预制件;然后在终成形前使零件截面具有合理的形状,再进行终成形,既保证了圆角部位的外形尺寸,又提高了壁厚均匀性.采用本文介绍的方法实现了截面周长差达70%的瓶形预制件的制备,从而获得了壁厚、外形尺寸均满足设计要求的转向节臂零件.     

How models can make a difference for a sustainable future of the building industry

Models play a vital role in science and technology and in the evolution of modern societies. They are used for describing processes and mechanisms, experimental observations, analyses and predictions. In spite of the fact that models are a reduction of reality, the achievements of modern societies are impressive and would have been inconceivable without the role of models. These achievements can be qualified with one term: growth. The impressive growth in past decades, however, now appears to be unsustainable. In this contribution the above-mentioned dilemma is dealt with. First the evolution and use of models is discussed from a more general sustainability perspective. In the second part of the paper the application of models for sustainable solutions in the field of cementitious materials is emphasized.     

Using big data to make better decisions in the digital economy

The question this special issue would like to address is how to harvest big data to help decision-makers to deliver better fact-based decisions aimed at improving performance or to create better strategy? This special issue focuses on the big data applications in supporting operations decisions, including advanced research on decision models and tools for the digital economy. Responds to this special issue was great and we have included many high-quality papers. We are pleased to present 13 of the best papers. The techniques presented include data mining, simulation and expert system with applications span across online reviews, food retail chain to e-health.     

Silicon Nanocrystals: Size Matters

This paper reviews new approaches to size‐controlled silicon‐nanocrystal synthesis. These approaches allow narrowing of the size distribution of the nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO₂ or phase separation of sub‐stoichiometric SiO_x layers. This size control is realized by different approaches to introducing a superlattice‐like structure into the synthesis process, by velocity selection of silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 10¹² cm^–2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO₂ layers with superlattices of fully passivated silicon nanocrystals within a SiO₂ matrix. The demands on silicon nanocrystals for various applications such as non‐volatile memories or light‐emitting devices are discussed for different size‐controlled nanocrystal synthesis approaches.     

大温差小流量的空调水系统方案

在楼宇空调水系统设计中,冷水机组的冷水供、回水温差通常为5℃.近年来冷水机组的效率提高很快,同时大温差小流量的空调水系统方案受到了更多关注.本文分析说明大温差小流量的空调水系统方案经过优化可以减少空调系统的总能耗和配套设备的初投资,探讨在该方案中末端设备的选择问题,并结合工程实例说明该方案的应用效果.