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排序方式: 共有65条查询结果,搜索用时 828 毫秒
11.
We show that the heat semigroup is well defined on the Banach space \({\mathcal{X}_{m,\gamma} = \{ \psi:\Omega_m \to \mathbb{R} ;\; |x|^{\gamma +2m}(\prod_{i=1}^m x_i)^{-1}\psi(x) \in L^\infty(\Omega_m)\},}\) \({0 < \gamma < N}\), where \({\Omega_m=\{(x_1,\, x_2,\, \ldots,\, x_N) \in \mathbb{R}^{N};\; x_i > 0,\, 1\leq i\leq m\},}\) \({1\leq m\leq N}\). We then investigate the large time behavior of solutions of the heat equation \({u_{t}-\Delta u=0}\) for t > 0 and \({x \in \Omega_m.}\) Using certain notions from dynamical systems, we show that the large time behavior is related to the spatial asymptotic behavior of its initial value. Since the space \({\mathcal{X}_{m, \gamma}}\) contains highly singular initial data, which can be extended to all of \({\mathbb{R}^{N}}\) by antisymmetry, we also obtain new results on the complexity in the asymptotic behavior of solutions for the heat equation on the whole space. 相似文献
12.
Stability analysis of internally damped rotating composite shafts using a finite element formulation
Safa Ben Arab José Dias Rodrigues Slim Bouaziz Mohamed Haddar 《Comptes Rendus Mecanique》2018,346(4):291-307
This paper deals with the stability analysis of internally damped rotating composite shafts. An Euler–Bernoulli shaft finite element formulation based on Equivalent Single Layer Theory (ESLT), including the hysteretic internal damping of composite material and transverse shear effects, is introduced and then used to evaluate the influence of various parameters: stacking sequences, fiber orientations and bearing properties on natural frequencies, critical speeds, and instability thresholds. The obtained results are compared with those available in the literature using different theories. The agreement in the obtained results show that the developed Euler–Bernoulli finite element based on ESLT including hysteretic internal damping and shear transverse effects can be effectively used for the stability analysis of internally damped rotating composite shafts. Furthermore, the results revealed that rotor stability is sensitive to the laminate parameters and to the properties of the bearings. 相似文献
13.
14.
The potential of a series of newly synthesized poly(N,N-dimethylacrylamide) (PDMA) grafted polyacrylamide (PAM) copolymers (P(AM-PDMA)) as a replaceable separation medium for protein analysis was studied. A comparative study with and without copolymers was performed; the separation efficiency, analysis reproducibility and protein recovery proved that the P(AM-PDMA) copolymers were efficient in suppressing the adsorption of basic proteins onto the silica capillary wall. Furthermore, the size-dependent retardation of native proteins in a representative P(AM-PDMA) copolymer was demonstrated by Ferguson analysis. The results showed that the P(AM-PDMA) copolymers combine the good coating property of PDMA and the sieving property of PAM and could be applied as a sieving matrix for the analysis of native proteins. 相似文献
15.
We consider the general nonlinear heat equation on where and g satisfies certain growth conditions. We prove the existence of global solutions for small initial data with respect to a
norm which is related to the structure of the equation. We also prove that some of those global solutions are asymptotic for
large time to self-similar solutions of the single power nonlinear heat equation, i.e. with
Received: 23 July 1999 / Accepted: 14 December 2000 / Published online: 23 July 2001 相似文献
16.
Ghislain Bare Aaron Diakiese Slim Zgoulli Ahmed Sabri Charles Gerday Philippe Thonart 《Applied biochemistry and biotechnology》1999,79(1-3):857-865
The thermoresistance of a cold-adapted subtilisin dried by spray-drying was studied. Proteolytic activity of this enzyme was
measured before and after spray-drying. Without chemical additives, spray-drying yields ranged from 2–13%. The use of arabic
gum and lactose in the composition of the enzyme solutions allowed the strengthening of the enzyme structures and increased
water mobility in the product. Increase of water mobility led to a shorter residence time of the product in the spray-drier
and a net yield increase was obtained (yield higher than 50%). The effect of two selective mutations on the thermoresistance
to spray-drying of the cold-adapted subtilisin was also investigated. Mutation T85D (introduction of an additional link with
an ion Ca2+ necessary for enzyme activity, by substitution of Asp for Thr 85) had no effect on the thermoresistance of the subtilisin
to spray-drying. Mutation H121W (introduction of an additional aromatic link by substitution of Trp for His 121) reduced the
drying yield from 66% (not modified subtilisin) to 52%. This higher thermosensitivity could be explained by an increase of
the hygroscopic character of the modified subtilisin (mutation H121W). 相似文献
17.
We define and study the Fock space associated with the spherical mean operator. Next, we establish some results for the Segal-Bergmann
transform for this space. Lastly, we prove some properties concerning Toeplitz operators on this space.
Received: May 11, 2007. Revised: May 20, 2008. Accepted: May 23, 2008. 相似文献
18.
Walid Fakhfakh Slim Kaddeche Ali Abdennadher Daniel Henry Hamda Ben Hadid 《Comptes Rendus Mecanique》2006,334(5):332-339
A numerical study is conducted in order to determine the influence of a vertical magnetic field, the Reynolds number and a temperature stratification on the instabilities occurring in the Hartmann flow heated from below. For and , the results show that the vertical magnetic field has a stabilizing effect on both transverse oscillatory travelling waves and longitudinal stationary rolls . The temperature stratification is responsible of a destabilization of the transverse modes and the appearance of longitudinal modes non-existent for the isothermal Hartmann flow. Moreover, the extent of the domains of Re where the transverse modes prevail is found to narrow when Ha increases and to widen when Ra increases for a given value of Ha. On the other hand, for the modes, the extent of the domains of Re where they prevail increases when Ha grows. To cite this article: W. Fakhfakh et al., C. R. Mecanique 334 (2006). 相似文献
19.
Mhand Hifi Slim Sadfi Abdelkader Sbihi 《Computational Optimization and Applications》2002,23(1):27-45
The Knapsack Sharing Problem (KSP) is an NP-Hard combinatorial optimization problem, admitted in numerous real world applications. In the KSP, we have a knapsack of capacity c and a set of n objects, namely N, where each object j, j = 1,...,n, is associated with a profit p
j and a weight w
j. The set of objects N is composed of m different classes of objects J
i, i = 1,...,m, and N =
m
i=1
J
i. The aim is to determine a subset of objects to be included in the knapsack that realizes a max-min value over all classes.In this article, we solve the KSP using an approximate solution method based upon tabu search. First, we describe a simple local search in which a depthparameter and a tabu list are used. Next, we enhance the algorithm by introducing some intensifying and diversifying strategies. The two versions of the algorithm yield satisfactory results within reasonable computational time. Extensive computational testing on problem instances taken from the literature shows the effectiveness of the proposed approach. 相似文献
20.