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991.
We study global existence and long time behaviour for the inhomogeneous nonlinear BGK model for the Boltzmann equation with
an external confining potential. For an initial datum f
0≥0 with bounded mass, entropy and total energy we prove existence and strong convergence in L
1 to a Maxwellian equilibrium state, by compactness arguments and multipliers techniques. Of particular interest is the case
with an isotropic harmonic potential, in which Boltzmann himself found infinitely many time-periodic Maxwellian steady states.
This behaviour is shared with the Boltzmann equation and other kinetic models. For all these systems we study the multistability
of the time-periodic Maxwellians and provide necessary conditions on f
0 to identify the equilibrium state, both in L
1 and in Lyapunov sense. Under further assumptions on f, these conditions become also sufficient for the identification of the equilibrium in L
1. 相似文献
992.
Ramaprasad Maiti Dipankar Chakravorty 《Journal of magnetism and magnetic materials》2009,321(19):3274-3277
Single phase nanocrystalline YFeO3 has been synthesized by a simple solution method. The average particle diameter is 42.2 nm. The particles exhibit ferromagnetic behaviour in the temperature range 10-300 K with a coercivity of 23 kOe. The magnetization versus temperature over the temperature range 2-300 K obeys Bloch equation with a Bloch constant value 9.98×10−6 K−3/2. Ferromagnetic hysteresis loops have been observed up to a temperature of 300 K. At 10 K a field-cooled sample shows an exchange bias field. 相似文献
993.
A competition model of three species in exchange-driven aggregation growth is proposed. In the model, three distinct aggregates grow by exchange of monomers and in parallel, birth of species A is catalyzed by species B and death of species A is catalyzed by species C. The rates for both catalysis processes are proportional to kj^v and ky respectively, where ν(ω) is a parameter reflecting the dependence of the catalysis reaction rate of birth (death) on the catalyst aggregate's size. The kinetic evolution behaviors of the three species are investigated by the rate equation approach based on the mean-field theory: The form of the aggregate size distribution of A-species αk(t) is found to be dependent crucially on the two catalysis rate kernel parameters. The results show that (i) in case of ν ≤O, the form of ak (t) mainly depends on the competition between self-exchange of species A and species-C-catalyzed death of species A; (ii) in case of ν 〉 0, the form of αk(t) mainly depends on the competition between species-B-catalyzed birth of species A and species-C-catalyzed death of species A. 相似文献
994.
995.
Yen‐Cheng Chen Shu‐Chuan Chuang Lo‐Yao Yeh Jiun‐Long Huang 《Wireless Communications and Mobile Computing》2011,11(10):1366-1375
The use of anonymous channel tickets was proposed for authentication in wireless environments to provide user anonymity and to probably reduce the overhead of re‐authentications. Recently, Yang et al. proposed a secure and efficient authentication protocol for anonymous channel in wireless systems without employing asymmetric cryptosystems. In this paper, we will show that Yang et al.'s scheme is vulnerable to guessing attacks performed by malicious visited networks, which can easily obtain the secret keys of the users. We propose a new practical authentication scheme not only reserving the merits of Yang et al.'s scheme, but also extending some additional merits including: no verification table in the home network, free of time synchronization between mobile stations and visited networks, and without obsolete anonymous tickets left in visited networks. The proposed scheme is developed based on a secure one‐way hash function and simple operations, a feature which is extremely fit for mobile devices. We provide the soundness of the authentication protocol by using VO logic. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
996.
Behrouz Shahgholi Ghahfarokhi Naser Movahhedinia 《Wireless Communications and Mobile Computing》2011,11(6):723-741
Growing demands for pervasive and ubiquitous services over wireless mobile networks and evolution of such networks towards heterogeneous solutions have emphasized the necessity of more intelligent handoff decisions. The existing handoff management methods in the literature are mostly using signal strength measurements and other link quality evaluations not addressing the knowledge about context of mobile devices, users and networks. Recently, context‐aware handoff management has been considered as a novel candidate for fourth generation (4G) wireless technology. In this paper, user perceived quality of service has been considered in addition to traditional contexts such as user preferences, application requirements, network parameters and link quality for decision making. User perceived quality (UPQ) has been employed as a trigger source, in addition to link layer triggers which are emerged using media independent handover (MIH) event service. This paper presents a policy based mechanism for handoff decision making where fuzzy petri nets (FPNs) have been utilized as its evaluation algorithm. A case study has been provided by simulations to show the usability and user level satisfaction. Simulation results show superior performance in terms of UPQ, jitter and packet delivery measures. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
997.
Michel Guerro 《Tetrahedron》2009,65(31):6123-8746
A series of tetrathiafulvalene (TTF) derivatives functionalized by one or two β-diketonatoboron difluoride groups were synthesized through the addition of borontrifluoride to TTF substituted by one or two acetylacetone functions. The influence of the β-diketonatoboron difluoride moiety on the redox properties of the TTF has been investigated by cyclic voltammetry. 相似文献
998.
R. Schlegel M. Thunga G. Heinrich Jimmy W. Mays H. Iatrou 《European Polymer Journal》2009,45(10):2902-9383
The stress-strain behaviour of multigraft copolymers consisting of a polyisoprene (PI) backbone and grafted polystyrene (PS) arms have been characterized by applying models of rubber elasticity such as Mooney-Rivlin, slip-tube and the extended non-affine tube model. Additionally, the range of low deformation has been investigated by relaxation tests for determining the stress relaxation. Multigraft copolymers show high strain at break and low residual strain caused by the large number of physical cross links resulting from several grafted PS side chains. From the model fits the material parameters and of the slip-tube model, representing the influence of chemical cross links and entanglements effects, respectively, and the ne/Te-value (ne - number of statistical segments between two successive entanglements, Te - Langley trapping factor) of the extended non-affine tube model, are used to describe the tensile behaviour of these thermoplastic elastomers. The PS content was considered as filler phase taking into account the effect of hydrodynamic amplification. The influence of functionality and the number of branch points per molecule on the strain at break and the tensile strength is explained by the model parameters describing the stress-strain curve at low to medium (?400%, slip-tube, Mooney-Rivlin) and low to high (?900%, extended non-affine tube) elongations. It was observed that for the material with a spherical morphology is increasing with the number of branch points β (each branch point consists of a PI backbone segment, depending on the functionality one, two or four grafted PS arms). For cylindrical and lamellar morphologies the was decreasing with increasing β, which could be reconfirmed by applying the extended non-affine tube model where the ne/Te-parameter is increasing with β. 相似文献
999.
We study asymptotics as t → ∞ of solutions to a linear, parabolic system of equations with time‐dependent coefficients in Ω × (0, ∞), where Ω is a bounded domain. On ? Ω × (0, ∞) we prescribe the homogeneous Dirichlet boundary condition. For large values of t, the coefficients in the elliptic part are close to time‐independent coefficients in an integral sense which is described by a certain function κ (t). This includes in particular situations when the coefficients may take different values on different parts of Ω and the boundaries between them can move with t but stabilize as t → ∞. The main result is an asymptotic representation of solutions for large t. As a corollary, it is proved that if κ ∈ L1(0, ∞), then the solution behaves asymptotically as the solution to a parabolic system with time‐independent coefficients (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
Technora fibres are high performance aramid fibres which have been used in ropes and protective clothing for many years. They are also now being proposed as geotextiles for soil reinforcement. However, there is a lack of experience on the long-term behaviour of Technora fibres in an alkaline environment (lime-treated ground…). Consequently, aging studies have been performed under different conditions (deionised water, pH9 and pH11). Hydrolytic degradation has been evaluated by FTIR, viscometry, TGA, density measurements, SEM, and by tensile measurements. Some chain degradation and finish rearrangements have been highlighted, but Technora fibres retain their mechanical properties for all the conditions considered here. 相似文献