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951.
Solomon Fekade Mulugeta Bekele 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):369-374
We analyze the relaxation behavior of a bistable system when the background temperature profile is inhomogeneous due to the
presence of a localized hot region (blowtorch) on one side of the potential barrier. Since the diffusion equation for inhomogeneous
medium is model-dependent, we consider two physical models to study the kinetics of such system. Using a conventional stochastic
method, we obtain the escape and equilibration rates of the system for the two physical models. For both models, we find that
the hot region enhances the escape rate from the well where it is placed while it retards the escape rate from the other well. However, the value of the escape rate from the well where the hot region is placed differs
for the two models while that of the escape rate from the other well is identical for both. This work, for the first time,
gives a detailed report of the similarities and differences of the escape rates and, hence, exposes the common and distinct
features of the two known physical models in determining the way the bistable system relaxes.
Received 25 September 2001 相似文献
952.
惯性约束中子测温的误差研究 总被引:1,自引:0,他引:1
综合分析了ICF(惯性约束)中子测温系统的误差与其参数的关系,这些参数包括靶核温度,探测的中子数、靶到探测器的距离、探测器的响应函数以及闪烁体厚度等,考虑到中子与探测器的相互作用,探测器的响应与靶的烧蚀过程,在此基础上提出了新的统计误差计算方法,该方法对于改善中子测温的相对误差并应用于闪烁体的设计具有重要意义。 相似文献
953.
A method for the deposition of BN onto graphite and other substrates is described. Boron trichloride (BCl3) and ammonia (NH3) diluted with Ar were used as reacting gases. The deposition process was carried out at 1300 K as well as lower temperatures in an open system at pressures of 1 atm. The consequences of the introduction of hydrogen to the system were considered. It was demonstrated that the replacement of argon with hydrogen increases the efficiency of the process as well as the theoretical rate of BN deposition. However, the acceleration of the deposition seems to be unprofitable, because the resulting supersaturation leads to the formation of an amorphous phase. The modification of the experimental conditions were proposed.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
954.
T. Charitat B. Fourcade 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):333-336
An o-ring takes spontaneously the shape of a chair when strong enough torsion is applied in its tangent plane. This state
is metastable, since work has to be done on the o-ring to return to the circular shape. We show that this metastable state
exists in a Hamiltonian where curvature and torsion are coupled via an intrinsic curvature term. If the o-ring is constrained to be planar (2d case), this metastable state displays a kink-anti-kink
pair. This state is metastable if the ratio is less than , where C and A are the torsion and the bending elastic constants [#!landau!#]. In three dimensions, our variational approach shows that
. This model can be generalized to the case where the bend is induced by a concentration field which follows the variations
of the curvature.
Received: 27 August 1997 / Revised: 23 October 1997 / Accepted: 12 November 1997 相似文献
955.
Polyethyleneimine (PEIM) samples crosslinked by a commercial epoxy resin (Epon 828) were prepared, and their adsorption capacity for acidic gases was studied. The swelling and deswelling characteristics of the crosslinked samples were also examined as part of this program. Reactivation of these adsorbents could be carried out by heat, or by a combination of heat and treatment in dilute alkalies. 相似文献
956.
本文采用高压X光衍射方法在金刚石对顶压砧中在位地(in situ)研究了Fe68Co24Ni8(wt%)合金在室温下的压致bcc→hcp结构相变和直到40.5 GPa的等温压缩行为。实验结果表明该合金在常压下为bcc结构,晶格常数a0=(0.287 0±0.000 1) nm,体积V0=(7.119±0.007) cm3/mol,密度ρ0=(7.981±0.008) g/cm3;在20.9 GPa附近出现bcc→hcp结构相变,两相共存压力区约10 GPa,在此区域内有晶面间距d(002)hcp=d(110)bcc,且原子平面(002)hcp//(110)bcc,hcp相比bcc相体积减小(0.33±0.02) cm3/mol;高压相hcp结构的晶格参数比值c/a=1.608±0.004;相变后原子配位数的增加使得hcp相(002)平面内及(002)平面间的最近邻原子间距比bcc相最近邻原子间距分别增大约1.6%和0.5%;用Murnaghan状态方程对实验数据进行最小二乘法拟合,得到bcc相B0=(130±13) GPa,B0'=12.6±0.5;hcp相V0=(6.62±0.04) cm3/mol,B0=(243±21) GPa,B0'=6.8±0.3;对于该合金的bcc→fcp相变时的结构转变机制做了详细的讨论。 相似文献
957.
A multidimensional version of the first Darboux problem is considered for a model second-order degenerating hyperbolic equation. Using the technique of functional spaces with a negative norm, the correct formulation of this problem in the Sobolev weighted space is proved. 相似文献
958.
Summary We discuss a null experiment to search for the fifth force at ranges around 10 km. It is proposed to use a three-axis gravity
gradiometer to measure the trace of the Earth gravity tensor from a freely falling elevator dropped by a balloon. The main
error sources are considered to some extent.
Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990. 相似文献
959.
侯旻 《新疆大学学报(理工版)》1991,(1)
本文比较了循环图类{c_p(n_1,…,n_p)}和{c-p(n_1…,n_p,p/α)}的直径下界。对于p和α满足一定条件的循环图类{c_p(n_1,n_2,p/α)},本文给出了达到或几乎达到此图类直径下界的一类几乎最优循环图{c_p(m,m+1,p/α)}。 相似文献
960.
Philip T. Keenan 《Numerical Algorithms》1994,7(2):269-293
We describe a new family of discrete spaces suitable for use with mixed methods on certain quadrilateral and hexahedral meshes. The new spaces are natural in the sense of differential geometry, so all the usual mixed method theory, including the hybrid formulation, carries over to these new elements with proofs unchanged. Because transforming general quadrilaterals into squares introduces nonlinearity and because mixed methods involve the divergence operator, the new spaces are more complicated than either the corresponding Raviart-Thomas spaces for rectangles or corresponding finite element spaces for quadrilaterals. The new spaces are also limited to meshes obtained from a rectangular mesh through the application of a single global bilinear transformation. Despite this limitation, the new elements may be useful in certain topologically regular problems, where initially rectangular grids are deformed to match features of the physical region. They also illustrate the difficulties introduced into the theory of mixed methods by nonlinear transformations. 相似文献