Unexpected Kirkendall effect in twinned icosahedral nanocrystals driven by strain gradient

Nanoscale Kirkendall effect has been widely used for rationally fabricating high-quality hollow nanocrystals, but often requires the intrinsic diffusion coefficient of out-diffusion materials higher than that of in-diffusion components. Here we demonstrate an unexpected Kirkendall effect that occurs in diffusing intrinsically faster Cu atoms into Pd icosahedra, leading to the formation of PdCu alloyed hollow nanocrystals. The control experiment with Pd octahedra replacing icosahedra indicates the critical role of twin boundaries in facilitating such unexpected Kirkendall effect. In addition, geometric phase analysis and density functional theory calculation show that out-diffusion of Pd atoms in the icosahedra is faster than in-diffusion of Cu atoms, particularly through the twin boundaries, upon the strain gradient with an inward distribution from tensile to compressive strains. The unexpected Kirkendall effect is also found in the interdiffusion of Ag and Pd atoms in Pd icosahedra. Our finds break the limitation of the intrinsic diffusion coefficient for the synthesis of hollow nanocrystals through Kirkendall effect and are expected to enormously enrich the family of hollow nanocrystals which have shown great potential in broad areas, such as fine chemical production, energy storage and conversion, and environmental protection. This work also provides a deep understanding in the diffusion behavior of atoms upon the strain gradient.

     

Solar control: A general evaluation method for facades with venetian blinds or other solar control systems

A general method for realistic performance evaluation of solar control properties of facades for facades with sun-shading or other solar control systems has been developed. It is particularly designed to be used for venetian blinds. It can be used used ‘stand-alone’ or within building simulation programs. The new method has proven to be of great practical value to planning teams of huge office buildings in Germany, Austria and Switzerland. The method is presented in detail in this paper. It can be used either ’stand-alone’ (without building simulation) for comparisons of different facade variants or within building simulation programs. Some parts of the proposed methodology could be used in standards (e.g. EN13363) or to improve the accuracy of building simulation programs which are currently on the market. Practical experience with the new methodology led to insights which are the basis for the design of two new products. These new products are compared with state of the art products in [T.E. Kuhn, Solar control: comparsion of two new systems with the state of the art on the basis of a new general evaluation method for facades with venetian blinds or other solar control systems, Energy and Buildings, in press] on the basis of the new methodology.     

子午线轮胎鼓包问题的研究

概述子午线轮胎鼓包形成机理、影响因素以及试验研究情况。子午线轮胎鼓包影响因素包括轮胎选型、胎体帘布层层数、胎圈护胶、充气压力和断面高度等,研究鼓包的试验包括深坑撞击试验、路牙石撞击试验和摆锤冲击试验等。目前业内对子午线轮胎鼓包研究还处于起步阶段,但通过合理选择胎侧高度、增设胎圈护胶、采用双层胎体帘布层等措施,可以有效提高轮胎抗鼓包能力。     

Numerical study of cold start performance of proton exchange membrane fuel cell with coolant circulation

It has been well recognized that cold start is one of the key issues of proton exchange membrane fuel cell (PEMFC) used as the engine of vehicles. Coolant circulation is usually launched synchronously with the fuel cell during cold start to avoid sudden large temperature variation, which greatly increases the cell thermal mass, lowers the heating rate, and worsens the cell performance. Considering the flow and heat transfer of coolant circulation, a three-dimensional, transient, multi-disciplinary model for cold start is built up. The numerical results agree reasonably well with experimental data, indicating that the model can be used for the investigation of PEMFC cold start processes. The analysis of circulation parameter effects shows that increasing the coolant flow rate or coolant tank capacity has little influence on the cell voltage, but will increase the non-uniformity of temperature distribution along flow direction. At lower start-up temperature, this non-uniformity is more obvious. With higher coolant flow rate, although the distribution of current density becomes more evenly, the ice formation amount increases and its distribution and location are greatly affected.     

汽车顶蓬搬运折断风险计算及应用

针对聚氨酯汽车顶蓬在生产搬运过程中容易折断的问题,在分析顶蓬搬运折断失效模式的基础上,对顶蓬及其搬运过程进行了假设和简化,把搬运中的顶蓬简化为简支梁,然后使用与FEA相同的基本数学模型,设计了一种计算顶蓬侧边折断风险的方法,并用MathCAD编制程序实现项蓬受力的计算和折断风险的评估.使用编制的程序对某E级车双天窗顶蓬进行了分析,结果表明此计算方法使用简便,计算结果准确、可靠.最后对顶蓬折断问题的改进提出了可行的建议.     

管理激励在企业中的创新

为了探索符合时代发展要求的企业管理激励机制,首先从管理激励的必要性与重要性方面,探索了管理激励的一般理论;其次对上海易初通用公司实践的基础上,提出的具有操作性、创新性的企业管理激励机制新模式——M管理模式进行分析;第三,M管理模式的形成或思想来源,可以从当代经济理论与现代管理理论中找到其若干理论依据;最后,对上海汽车股份有限公司实施M管理模式的背景、具体做法、产生的效果及各界人士对M管理模式的评价进行了分析。实施M管理模式都取得了重大成果,表明M管理模式具有重要的推广价值。     

Pool boiling heat transfer on the microheater surface with and without nanoparticles by pulse heating

We study the pool boiling heat transfer on the microheater surface with and without nanoparticles by pulse heating. Nanofluids are the mixture of de-ionized water and Al₂O₃ particles with 0.1%, 0.2%, 0.5% and 1.0% weight concentrations. The microheater is a platinum surface by 50 × 20 μm. Three types of bubble dynamics were identified. The first type of bubble dynamics is for the boiling in pure water, referring to a sharp microheater temperature increase once a new pulse cycle begins, followed by a continuous temperature increase during the pulse duration stage. Large bubble is observed on the microheater surface and it does not disappear during the pulse off stage. The second type of bubble dynamics is for the nanofluids with 0.1% and 0.2% weight concentrations. The microheater surface temperature has a sharp increase at the start of a new pulse cycle, followed by a slight decrease during the pulse duration stage. Miniature bubble has oscillation movement along the microheater length direction, and it disappears during the pulse off stage. The third type of bubble dynamics occurs at the nanofluid weight concentration of 0.5% and 1.0%. The bubble behavior is similar to that in pure water, but the microheater temperatures are much lower than that in pure water. A structural disjoining pressure causes the smaller contact area between the dry vapor and the heater surface, decreasing the surface tension effect and resulting in the easy departure of miniature bubbles for the 0.1% and 0.2% nanofluid weight concentrations. For the 0.5% weight concentration of nanofluids, coalescence of nanoparticles to form larger particles is responsible for the large bubble formation on the heater surface. The microlayer evaporation heat transfer and the heat transfer mechanisms during the bubble departure process account for the higher heat transfer coefficients for the 0.1% and 0.2% nanofluid weight concentrations. The shortened dry area between the bubble and the heater surface, and the additional thin nanofluid liquid film evaporation heat transfer, account for the higher heat transfer coefficient for the 0.5% nanofluid weight concentration, compared with the pure water runs.     

基于离合器接合速度的重型越野车辆起步控制研究

建立起步过程动力学模型并提出了起步过程评价指标,选取转速、位移等为控制参量,设计了基于接合速度的干式离合器分段控制策略。设计了起步分段控制模型,利用试验数据库统计得出分段控制的主要参数阈值。对所设计的控制策略进行了实车平路起步试验。以当量冲击度、起步时间和滑转圈数为评价指标,分析了起步控制效果。结果表明,所设计的基于离合器接合速度的起步控制策略满足起步平稳性和快捷性的要求,为后续开展适应全工况的优化控制奠定了基础。     

油品差异对汽车发动机性能影响的试验研究

国内外汽车用油存在较大差异,为了让国产车更好地满足国外市场需求,以我国出口汽车使用的甲基叔丁基醚（MTBE）（体积分数为10%）混合汽油、乙醇体积分数为20%（E20）的含水乙醇汽油和我国92号汽油为对象,基于某排量为2.0 T的汽油发动机台架试验,进行了三种油品对发动机性能影响的分析及验证。通过试验结果对比发现,使用MTBE混合汽油和E20含水乙醇汽油的动力性均低于92号汽油。在经济性方面,E20含水乙醇汽油略低于92号汽油,而MTBE混合汽油能使燃料消耗下降7%左右。在排放性方面,使用E20含水乙醇汽油和MTBE混合汽油对CO、HC的排放都有显著的改善效果,而在低转速、低负荷时对NO_x的排放有一定改善,随着转速和负荷的上升,E20含水乙醇汽油对NO_x的排放改善不明显,使用MTBE混合汽油时NO_x的排放反而变差。     

Modeling of air compressor for proton exchange membrane fuel cell

空压机的性能对燃料电池的性能有很大影响,为准确建立空压机数学模型,使用等效电路结构方法,建立关于转速、流量、压力这三个变量的非线性函数。对空压机等效电路数学模型参数和空压机性能参数数据进行拟合,并根据拟合效果依次采用基于最大流量偏差和基于出口压力加权两种方法改进拟合方法,实现对静态模型较高精度的拟合。