Efficient Collision Detection for Moving Ellipsoids Using Separating Planes

We present a simple, accurate and efficient algorithm for collision detection among moving ellipsoids. Its efficiency is attributed to two results: (i) a simple algebraic test for the separation of two ellipsoids, and (ii) an efficient method for constructing a separating plane between two disjoint ellipsoids. Inter-frame coherence is exploited by using the separating plane to reduce collision detection to simpler subproblems of testing for collision between the plane and each of the ellipsoids. Compared with previous algorithms (such as the GJK method) which employ polygonal approximation of ellipsoids, our algorithm demonstrates comparable computing speed and much higher accuracy.     

美国陆军航天发展及启示

从20世纪40年代起,美国陆军航天经历了曲折的历程,取得了很大的发展。为推动新世纪美国陆军转型,陆军航天被赋予新的任务。阐述了美国陆军航天发展的历程,分析了美国陆军航天在转型时期的任务、面临的挑战和采取的措施,并提出几点启示。     

Electrochemical behaviors of uranium and plutonium at simultaneous recoveries into liquid cadmium cathodes

Experiments were conducted on simultaneous recovery of uranium and plutonium electrochemically into laboratory scale liquid cadmium cathodes (LCCs) at different U/Pu ratios in the salt phase, and the influence of the salt composition on the recovered amounts of uranium and plutonium, the morphologies of uranium and plutonium in the LCC, and the behavior of americium, which is present as a decay product of plutonium-241, were examined. As a result, it was shown that there is a threshold in the U/Pu ratio in the salt phase between 1/4.3 and 1/1.73 for the successful simultaneous recovery of uranium and plutonium up to 10 wt% in the LCC at high current efficiencies. In the LCC, uranium and plutonium existed in the forms of intermetallic compounds, (U, Pu)Cd₆ and (U, Pu)Cd₁₁, and also pure uranium metal. It was also revealed that americium associates with plutonium according to the separation factor during the LCC operation.     

Change of fuel-to-cladding gap width with the burn-up in FBR MOX fuel irradiated to high burn-up

In order to study the dependence of the gap width change on the burn-up, the fuel-to-cladding gap widths were investigated by ceramography in a large number of FBR MOX fuel pins irradiated to high burn-up. The dependence of gap widths on the burn-up was closely connected with the formations of JOG (joint oxyde-gaine) and rim structure. The gap widths decreased gradually due to the fuel swelling until ∼30 GWd/t, but beyond this burn-up the dependence showed two different tendencies. With the increase of burn-up, the gap widths decreased due to the increase of fuel swelling in the low fuel temperature region where the rim structure was observed, but they increased in the high fuel temperature region where the JOG rich in Cs and Mo formed in the gap.     

Effect of burn-up on the thermal conductivity of uranium dioxide up to 100.000 MWd t

The thermal diffusivity and specific heat of reactor-irradiated UO₂ fuel have been measured. Starting from end-of-life conditions at various burn-ups, measurements under thermal annealing cycles were performed in order to investigate the recovery of the thermal conductivity as a function of temperature. The separate effects of soluble fission products, of fission gas frozen in dynamical solution and of radiation damage were determined. In this context, particular emphasis was given to the behaviour of samples displaying the high burn-up rim structure. Recovery stages could be thoroughly investigated in samples that were irradiated at low burn-ups and/or at high irradiation temperatures. Other samples, in particular those exhibiting the characteristic rim structure, disintegrated at temperatures slightly higher than the irradiation temperature. Finally, from a database of several thousand measurements, an accurate formula for the in-pile thermal conductivity of UO₂ up to 100 GWd t⁻¹ was developed, taking into account all the relevant effects and structural changes induced by reactor burn-up.     

Investigation of physico-mechanical properties of ceramic oxide kernels for nuclear applications

In the present work, two different classes of oxide kernels were investigated: unirradiated thoria, urania and (Th,U)O₂ fuel kernels and low-density Al₂O₃ kernels for the incorporation of minor actinides. The physical mechanism of oxide kernel failure under uniaxial compression was investigated. A new method for determining the physico-mechanical properties of kernels has been developed and the parameters P_S and δ, characterising the level of stress required for destruction of the material structure and the brittleness of the investigated materials, respectively, were evaluated and discussed. It was shown that the value of P_S is analogous to traditional characteristics of material such as microhardness Hv. The `quantisation' effect was revealed in the kernel crushing strength and deformation distributions. The physico-mechanical properties of ceramic kernels (average particle size, microstructure, phase state, density, P_S and δ) were investigated and comparative analysis of different kernel types was performed. Additionally, the impact of annealing time on the properties of low-density Al₂O₃ kernels was examined.     

Characterization and densification studies on ThO2-UO2 pellets derived from ThO2 and U3O8 powders

ThO₂ containing around 2-3% ²³³UO₂ is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO₂ and U₃O₈ powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar-8%H₂, CO₂ and air. Air was found to be the best medium for sintering among them. For Ar and Ar-8%H₂ atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO₂-2%U₃O₈ granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U₃O₈ in enhancing the sintering of ThO₂ has been established.     

电沉积法制备~(235)U靶

电沉积法制备用于反应堆生产裂变99Mo的235U靶,是在一个密闭的圆筒形不锈钢结构的容器内进行的。不锈钢靶容器的内表面薄薄地镀一层铀,镀层应牢固而均匀。文中介绍了两种电沉积方法:一种是铀以氧化物的形式从含有铀盐的UO2(NO3)2(NH4)2CO4·H2O水溶液中沉积出来;另一种方法是从熔盐体系中直接电沉积金属铀,其电沉积效率和电沉积量都要高于水溶液体系电沉积铀。     

Frequency effect and influence of testing technique on the fatigue behaviour of quenched and tempered steel and aluminium alloy

Influences of testing technique and frequency on the fatigue behaviour of 50CrMo4 and EN AW-5083 were investigated. To clarify the effect of test frequency on the fatigue behaviour, tests with 20 kHz and f < 400 Hz were performed. The frequency effect can be caused by temperature, environment and strain rate. For the aluminium alloy, the influence of environment is responsible for the dependence of fatigue lifetime on the frequency. The fatigue lifetime of the steel showed in both environments similar frequency dependency, i.e. the strain rate is assumed to be responsible for the differences in fatigue lifetime.     

几种碳酸钙对给水用硬PVC管材性能的影响

研究几种PVC常用的碳酸钙物理形貌及其对给水用硬PVC管材性能的影响。研究证明重钙在PVC颗粒上的吸附能力较轻钙差,轻钙颗粒越细,越易被PVC颗粒吸附,干混料的流动性越好;几种碳酸钙中,使用纳米钙的给水用硬PVC管材的冲击强度最高,重钙的最低;加不同碳酸钙的给水用硬PVC管材的密度和维卡软化温度相近。