Impact of a snow avalanche against an obstacle. Formation of shock waves

The paper is devoted to the effect of compressibility of the avalanche snow impacting an obstacle. Compression shocks generated by obstacle cause high pressure peaks at first instants of impact. That is why the account of compressibility is essential for the understanding of measurements and the design of structures. The main problem in calculation compression shocks in avalanches is to formulate an equation of state for moving snow in impact. Two different types of equations of state are proposed depending on the type of the avalanche (low-density and high-density flows). The approach is not totally new. It was earlier proposed mainly in Russian literature. Here a brief review of the previous work is given with discussion of some gaps in it. The theory is reformulated and further developed to account thermodynamical equations. The simplest case of a normal compression shock in an avalanche flow is studied. Examples of estimations of pressure and density behind a shock are given. It is important to emphasize that the Mach number plays an important role in the theory of compressible flows so it should be taken into account (together with the Froude number) in calculation and modelling an avalanche impact pressure.     

大学生树立科学世界观的障碍及其克服措施

调查分析了目前我国大学生的知识状况、情感状况、信仰状况和行为状况。认为 ,我国大学生在树立科学世界观过程中存在知识、情感、信仰、行为等四个方面的障碍。要帮助大学生克服这些障碍 ,必须高度重视和切实搞好“两课”教学 ,加强马克思主义理论灌输 ,强化爱国主义情感教育和共产主义理想信念教育 ,积极引导学生参加社会实践 ,扩大学生的知识面 ,同时需要教育者树立和坚定共产主义信念 ,实行学校、家庭、社会的“综合治理”。     

论网络环境下采访信息交流的障碍及其克服

阐述网络环境下的采访信息交流特点和作用，并对其障碍的产生和现象进行分析、描述，最后提出如何克服这些障碍。     

谈中国白酒出口的障碍

白酒是我国的传统产品,但是长期以来出口量极少。探其原因,主要在于两大方面。我国酒类生产销售的大环境存在着无序、贸易壁垒等五个整体性障碍;白酒业自身也存在着原料与工艺的复杂、产品不合外国消费者饮用习尚等障碍问题。只有真正深入了解这些问题才能设计有效的排障措施,促进白酒长期畅销国外,真正使国酒飘香全球。     

Experimental and numerical study of heat and moisture transfers by natural convection in a cavity filled with solid obstacles

Heat, moisture transfers and airflow by natural convection in a rectangular cavity containing on line cylinders were studied. The work zone was arranged in such a way that 2D transfer and flow were established. At steady state, temperature, velocity and humidity fields on the symmetry plane were measured in un-humidified and humidified cavity. These results were then used to compare with CFD simulation. The thermal stratification and circular air flow in the cavity was observed. Humidification at the bottom face of cavity contributes to increase air velocity. The influence of radiation near the cold and warm walls is significant.     

Renewable energies in the EU-Accession States

The aim of this article is to discuss obstacles and success conditions for renewable energy sources in the EU-Accession States and to compare them with the framework in the EU-15. Besides the ten states which will join the EU in 2004, Bulgaria and Romania which will probably join in 2007 as well as Turkey are analysed. Most of these countries have had a century-long tradition in the utilisation of RES, primarily in biomass and hydropower. However, the communist regimes were convinced of the superiority of large-scale systems and converted the energy sectors into centralised units. Due to this dominating belief system more decentralised applications such as installations using renewable energies had to close.     

The sunshine revolution

People working to increase the use of renewables — the solar people - will play an increasingly important role as the oil reserves dwindle and the nuclear reactors grow old and fail. The demand on us to “deliver” will increase. We may find a lot of new allies. That may give us power. But are we willing to use our power to secure The Sunshine Revolution?     

Performance evaluation of empirical models for vented lean hydrogen explosions

This paper aims to provide a comprehensive review of available empirical models for overpressures predictions of vented lean hydrogen explosions. Empirical models and standards are described briefly, with discussion on salient features of each model. Model predictions are then compared with the available experimental results on vented hydrogen explosions. First comparison is made for standards tests, with empty container and quiescent starting conditions. Comparisons are then made for realistic cases with obstacles and initial turbulent mixture. Recently, a large number of experiments are carried out with standard 20-foot container for the HySEA project. Results from these tests are also used for model comparison. Comments on accuracy of model predictions, their applicability and limitations are discussed.A new model for vented hydrogen explosion is proposed. This model is based on external cloud formation, and explosion. Available experimental measurements of flame speed and vortex ring formation are used in formulation of this model. All assumptions and modelling procedure are explained in detail. The main advantage of this model is that it does not have any tuning parameter and the same set of equations is used for all conditions. Predictions using this model show a reasonably good match with experimental results.     

基于行星轮系的移动机器人及其特性分析

提出了一种新的移动机器人——基于行星轮系的移动机器人,并主要研究了其越障性能、跨沟性能和静态稳定性,证明这种机器人具有很好的环境适应能力,越障能力强。