城市街道峡谷单侧自然通风研究进展

自然通风广泛存在于城市之中，了解城市自然通风建筑室内环境质量现状及存在的问题，是改善城市建筑室内环境质量的基础. 通过文献整理，首先研究城市街道峡谷中单侧自然通风的驱动因素，其次从建筑几何特征、通风能力、污染率、颗粒物浓度以及街谷设施等方面综述单侧自然通风的相关研究，最后提出建议. 研究表明，合理的展弦比、更好的城市布局以及精心的街谷设施设计能够最大限度地利用单侧自然通风，提升城市街道峡谷的室内环境品质.     

Enhanced methanol oxidation on PtNi nanoparticles supported on silane-modified reduced graphene oxide

Developing low cost, highly efficient, and long-term stability electrocatalysts are critical for direct oxidation methanol fuel cell. Despite huge efforts, designing low-cost electrocatalysts with high activity and long-term durability remains a significant technical challenge. Here, we prepared a new kind of platinum-nickel catalyst supported on silane-modified graphene oxide (NH₂-rGO) by a two-step method at room temperature. Powder X-ray diffraction, UV–vis spectroscopy, Raman, FTIR spectroscopy and X-ray photoelectron spectroscopy results confirm that GO was successfully modified with 3-aminopropyltriethoxysilane (APTES), which helps to uniformly disperse PtNi nanoparticles. Cyclic voltammetry, chronoamperometry, CO-stripping and rotating disk electrode (RDE) results imply that PtNi/NH₂-rGO catalyst has significantly higher catalytic activity, enhance the CO toxicity resistance, higher stability and much faster kinetics of methanol oxidation than commercial Pt/C under alkaline conditions.     

Synchronized motion and compliant control for dual control moment gyroscopes by realizing the impedance transformation matrix

In this paper, dual control moment gyroscopic actuators (CMG) were formed in a scissored-pair configuration to maximize the induced torque in the desired direction. A robust synchronizing motion control method was proposed to regulate the directional gyroscopic torque. In order for the two CMGs to form a scissored-pair structure having opposite angular momentum vectors, the synchronization of two CMGs was done without losing the control capability due to axial drift. A transformation matrix was designed for the robust synchronization control performance by realizing the empirically discovered impedance models of CMGs. Three different control modes were realized by selecting the components of the impedance transformation matrix (ITM): a robustly independent control mode, a synchronized motion control mode, and a mixed motion control mode. Each CMG played the role of either a master or a slave and copied the motion from another to follow it under the synchronization mode. The experimental results show that two CMGs can generate a robust and directional torque under the mixed control mode of both robust and synchronization control.     

Improved electrochemical performance of silicon-carbon anodes by different conductive agents

Journal of Materials Science: Materials in Electronics - Silica/silicon/polyacrylonitrile (SiO2/Si/PAN) composites were prepared as active anode for lithium-ion batteries (LIBs) using a rational...     

Enhanced oxygen evolution reaction kinetics through biochar-based nickel-iron phosphides nanocages in water electrolysis for hydrogen production

Highly-efficient and stable non-noble metal electrocatalysts for overcoming the sluggish kinetics of oxygen evolution reaction (OER) is urgent for water electrolysis. Biomass-derived biochar has been considered as promising carbon material because of its advantages such as low-cost, renewable, simple preparation, rich structure, and easy to obtain heteroatom by in-situ doping. Herein, Ni₂P–Fe₂P bimetallic phosphide spherical nanocages encapsulated in N/P-doped pine needles biochar is prepared via a simple two-step pyrolysis method. Benefiting from the maximum synergistic effects of bimetallic phosphide and biochar, high conductivity of biochar encapsulation, highly exposed active sites of Ni₂P–Fe₂P spherical nanocages, rapid mass transfer in porous channels with large specific surface area, and the promotion in adsorption of reaction intermediates by high-level heteroatom doping, the (Ni_0.75Fe_0.25)₂P@NP/C demonstrates excellent OER activity with an overpotential of 250 mV and a Tafel slope of 48 mV/dec at 10 mA/cm² in 1 M KOH. Also it exhibits a long-term durability in 10 h electrolysis and its activity even improves during the electrocatalytic process. The present work provides a favorable strategy for the inexpensive synthesis of biochar-based transition metal electrocatalysts toward OER, and improves the water electrolysis for hydrogen production.     

猪胴体冷却降温特性及耗能分析

猪肉是我国消耗量最大的肉类品，尤其是冷鲜猪肉更受人们青睐。猪胴体冷却保鲜加工工艺既要满足优质猪肉的成熟条件，又要保证猪肉的安全卫生。猪胴体冷却温度和降温速度对保证加工工艺合理性和降低耗能都至关重要。在实测数据基础上经过判断、分析提出，在常规0～4 ℃冷却前先在-10～-5 ℃低温快速冷却猪胴体1 h从而更好地保证猪胴体的冷却效果。实验发现：猪胴体开始冷却时，内部温度先有2～4 ℃的升温，然后才会降温，因此需对热负荷计算进行修正；根据两段冷却过程中猪胴体的冷却降温特点，提出了对应的冷量要求，为配备冷却装置提供了依据。     

丁二酸酐酯化改性糯米淀粉的研究

目的 为了提高糯米淀粉的粘度，以达到标签胶的要求。方法 对糯米淀粉进行丁二酸酐酯化改性，通过单因素试验及响应面优化确定出最佳酯化条件，测定其理化性质，并对其进行结构表征。结果 丁二酸酐酯化改性糯米淀粉的最优工艺条件：丁二酸酐添加量（丁二酸酐占淀粉干基的质量百分比）为10.3%，酯化温度为41.5℃，酯化时间为2.0 h,pH为9.0，在此条件下制得的糯米淀粉胶的粘度较高，可达到61.6 Pa·s，且溶解性与溶胀度均有不同程度的提高。电镜与热力学性质分析表明，酯化后淀粉颗粒结晶结构受到破坏，表面粗糙，出现凹陷与裂缝。结论 经过丁二酸酐酯化后，糯米淀粉胶的粘度得到提高。     

消色差超构表面复合透镜

超构表面因其体积轻薄易于集成化，有望在某些特定场合取代传统透镜实现多功能光学器件。超构表面的光束偏转角随波长的增加而增大，与传统折射透镜相比产生相反的色散，这种色散又被称为“异常色散”或“负色散”。理论上利用超构表面的负色散和传统折射光学器件的正色散相抵消，可以完全矫正光学系统的色差。由此出发，设计了一种基于光刻胶材料，由Pancharatnam-Berry（PB）相位型超构表面作为第一透镜，传统球面透镜作为第二透镜的消色差超构表面复合透镜，利用时域有限差分数值模拟软件FDTD Solutions探索了该透镜在780～980 nm波段的聚焦性能，证明了消色差光刻胶超构表面复合透镜优异的消色差效果。相对传统的消色差超构表面通过相位补偿来消色差的方法，这种消色差设计简单且高效，为特定波段内的消色差成像提供了一定的借鉴意义。     

Optical properties and radiation stability of SiO2/ZnO composite pigment prepared by co-sintering method

Thermal control coatings (TCCs) are an essential part of the thermal control systems in the spacecraft. Solar absorptance and emittance are the key performance parameters of TCCs. To develop an ultra-low solar absorption and stable inorganic TCCs for surface radiator, different TCCs were prepared by co-sintering ZnO and SiO₂ nanoparticles to form Zn₂SiO₄/SiO₂ pigment in this work, and the optical properties and radiation stability were systematically studied. It is found that the coating based on composite pigment has high reflectivity in the ultraviolet band and excellent optical performance possessing the low solar absorption of 0.06. In addition, the Zn₂SiO₄/SiO₂ coating demonstrates the highest proton and electron radiation stability because that SiO₂ between Zn₂SiO₄ particles acts as the relaxation center of the defects caused by radiation.     

Transition from random packing to stable state in a continuously avalanching granular flow

We investigate the transition evolution from the initial state with the random packing of the particles to the stable state in which successive avalanches exhibit consistent characteristics under the slumping regime. It is found that there exist three distinct stages in the transition evolution, considering the change of the volume fraction. The coordination number is almost unchanged during the transition evolution, which indicates the particle contact form is consistent in the three stages. The pause phenomena are discovered in some avalanches, and the probability of pause occurrence increases continuously in the three consecutive stages. We also explore the distribution of particles in the passive layer at the stable state. The particles in the middle region of the passive layer have the closest packing status, and the deeper the region is located, the later it reaches the stable state.