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951.
A 2D spherulite grows in a linear-temperature field from a nucleus of polypropylene at (0,0). The growth lines and the growth fronts are computed by the calculus of variations. The agreement between theory and experiment is satisfactory 相似文献
952.
953.
W. -S. Dai M. Xie 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):125-128
The electromagnetic transition of two-level atomic systems in a waveguide is calculated. Compared with the result in free
space, the spontaneous emission rate decrease because the phase space is smaller, and meanwhile, some resonance appears in
some cases. Moreover, the influence of non-uniform electromagnetic field in a waveguide on absorption and stimulated emission
is considered. Applying the results to lasers, a method to enhance the laser power is proposed.
Received 29 May 2001 and Received in final form 25 October 2001 相似文献
954.
The notion of fire/light/heat/energy is recognized as an integrating element in the pathway of ordering matter and society,
and its historical aspects are thoroughly reviewed. Fire is argued to be a philosophical archetype and its role in the early
concept of four elements is discussed. The Indian, Arabic and Greek historical bases are mentioned. Alchemy is briefly reviewed
as a source of the wider adoption of fire. The era of renaissance and the new age are also included. The message of fire/heat
is nowadays focused on the progress of civilization, with the assumption of engines as information transducers based on the
conscious exploitation of fire. The role of chaos is emphasized. Overall, a condensed but consistent view is given of the
various concepts that emerged during the historical progress of the understanding of heat (noting 61 references).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
955.
Laboratory and Simulation Investigation of Enhanced Coalbed Methane Recovery by Gas Injection 总被引:2,自引:0,他引:2
Methane/carbon dioxide/nitrogen flow and adsorption behavior within coal is investigated simultaneously from a laboratory
and simulation perspective. The samples are from a coalbed in the Powder River Basin, WY. They are characterized by methane,
carbon dioxide, and nitrogen sorption isotherms, as well as porosity and permeability measurements. This coal adsorbs almost
three times as much carbon dioxide as methane and exhibits significant hysteresis among pure-component adsorption and desorption
isotherms that are characterized as Langmuir-like. Displacement experiments were conducted with pure nitrogen, pure carbon
dioxide, and various mixtures. Recovery factors are greater than 94% of the OGIP. Most interestingly, the coal exhibited ability
to separate nitrogen from carbon dioxide due to the preferential strong adsorption of carbon dioxide. Injection of a mixture
rich in carbon dioxide gives slower initial recovery, increases breakthrough time, and decreases the volume of gas needed
to sweep out the coalbed. Injection gas rich in nitrogen leads to relatively fast recovery of methane, earlier breakthrough,
and a significant fraction of nitrogen in the produced gas at short times. A one-dimensional, two-phase (gas and solid) model
was employed to rationalize and explain the experimental data and trends. Reproduction of binary behavior is characterized
as excellent, whereas the dynamics of ternary systems are predicted with less accuracy. For these coals, the most sensitive
simulation input were the multicomponent adsorption–desorption isotherms, including scanning loops. Additionally, the coal
exhibited a two-porosity matrix that was incorporated numerically. 相似文献
956.
A dynamic bulge testing technique is developed to perform biaxial tests on metals at high strain rates. The main component
of the dynamic testing device is a movable bulge cell which is directly mounted on the measuring end of the input bar of a
conventional split Hopkinson pressure bar system. The input bar is used to apply and measure the bulging pressure. The experimental
system is analyzed in detail and the measurement accuracy is discussed. It is found that bars made of low impedance materials
must be used to achieve a satisfactory pressure measurement accuracy. A series of dynamic experiments is performed on aluminum
6111-T4 sheets using viscoelastic nylon bars to demonstrate the capabilities of the proposed experimental technique. The parameters
of the rate-dependent Hollomon–Cowper–Symonds J2 plasticity model of the aluminum are determined using an inverse analysis
method in conjunction with finite element simulations. 相似文献
957.
通过对炮兵营系统作战机制的分析 ,将层次分析法和美国工业界系统效能咨询委员会 (WSEIAC)提出的系统效能分析模型结合 ,建立了一个炮兵营系统效能分析模型。利用该模型对炮兵营系统内各要素进行灵敏度分析 ,为炮兵营战术和射击指挥程式的优化 ,以及系统内各要素的编制数量和武器装备战术技术性能指标的确定提供理论依据。 相似文献
958.
J.-M. Courty A. Heidmann M. Pinard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):399-408
Thermal noise of a mirror can be reduced by cold damping. The displacement is measured with a high-finesse cavity and controlled
with the radiation pressure of a modulated light beam. We establish the general quantum limits of noise in cold damping mechanisms
and we show that the optomechanical system allows to reach these limits. Displacement noise can be arbitrarily reduced in
a narrow frequency band. In a wide-band analysis we show that thermal fluctuations are reduced as with classical damping whereas
quantum zero-point fluctuations are left unchanged. The only limit of cold damping is then due to zero-point energy of the
mirror.
Received 1st August 2001 and Received in final form 12 October 2001 相似文献
959.
田立英 《太原理工大学学报》2001,32(6):632-635
依据高层建筑的特点和消防自动化系统的主旨,对火灾自动报警系统、消防联动控制系统和消防控制方式等进行了研究。结果表明,智能防火系统是现代高层建筑消防安全的发展趋势,必须引起有关部门的高度重视。 相似文献
960.
简要回顾了钢管混凝土力学性能研究现状 ,探讨了组成钢管混凝土的钢管及其核心混凝土之间的相互作用问题 ,介绍了钢管混凝土在单层和多层工业厂房柱、设备构架柱、各种支架、栈桥柱、地铁站台柱、送变电杆塔、桁架压杆、桩、空间结构、高层和超高层建筑以及桥梁结构中的应用情况 .最后 ,对需要进一步开展的研究工作进行了探讨 相似文献