1,721,008 research outputs found
2ND-ORDER ACCURATE DIFFERENCE-METHODS FOR A ONE-SEX MODEL OF POPULATION-DYNAMICS
No full textA first-order hyperbolic equation of age and time variables describes a one-sex model of population dynamics. The second-order finite difference method in the characteristic (age,time) direction is used to approximate simultaneously both the age distribution u(x, t) of the solution and the total population P(t). Algorithms and error analysis are given for the second-order convergence rate.open1119sciescopu
Analysis of handover characteristics in shadowed LEO satellite communication networks
No full textIn the near future, low earth orbit (LEO) satellite communication networks will partially substitute the fixed terrestrial multimedia networks especially in sparsely populated areas. Unlike fixed terrestrial networks, ongoing calls may be dropped if satellite channels are shadowed. Therefore, in most LEO satellite communication networks more than one satellite needs to be simultaneously visible in order to hand over a call to an unshadowed satellite when the communicating satellite is shadowed. In this paper, handover characteristics for fixed terminals (FTs) in LEO satellite communication networks are analysed. The probability distribution of multiple satellite visibility is analytically obtained and the shadowing process of satelites for FTs are modelled. Using the proposed analysis model, shadowing effects on the traffic performance are evaluated in terms of the number of intersatellite and interbeam handovers during a call. Copyright (C) 2001 John Wiley & Sons, Ltd
Parameter estimation by spectral approximation
No full textIn this paper, Chebyshev and Legendre approximations are proposed for estimating parameters in differential equations, which are easy to be performed. The convergence and the spectral accuracy are proved, even without some conditions as imposed in other papers. The numerical results show the advantages of this new approach. (C) 1999 Elsevier Science Inc. All rights reserved. AMS Classification: 34A55; 65L10; 65L99.X11sciescopu
Parameter estimation for an infiltration problem.
No full textThe Burgers equation is considered as a mathematical model for nonhysteretic infiltration in nonswelling soil under appropriate physical conditions. For this nonlinear partial differential equation, the modal approximation scheme for estimating parameters such as initial water distribution and precipitation-evaporation history is introduced. The function space parameter estimation convergence property of this scheme is proved. The idea is to change the nonlinear problem to a linear one by an appropriate change of variables. Also, numerical simulations are performed.X114sciescopu
A variational spectral method for the two-dimensional Stokes problem
No full textA spectral Galerkin scheme for solving the two-dimensional stationary Stokes problem is considered. In vorticity-stream function formulation, the Stokes problem is reduced to a biharmonic one. A new formulation for the decomposition of the biharmonic operator is introduced. Main difficulty in this decomposition is to find the trace of the vorticity. Using the adjoint of the composition of trace operator and Green's operator, a variational form is obtained for computing the boundary value of the vorticity. The discrete variational form preserves the properties such as coercivity and continuity of the continuous case which are important for our convergence analysis. Convergence of our scheme is proved, and numerical experiments are performed for the steady driven cavity problem.X112sciescopu
A spectral approximation scheme for the Stokes equations
No full textThe two-dimensional steady state Stokes equations are considered. By introducing the vorticity to the stream function form of the Stokes equations, we have a coupled system of two elliptic equations. An efficient approximation scheme for solving the equations is introduced. The method consists of finding the trace of the normal derivative of the vorticity by means of the trace and the inverse Green operators. This method is noniterative in the sense that the vorticity is obtained directly from the trace of its normal derivative. Convergence of our scheme is proved and numerical experiments are presented. (C) 2004 Elsevier Ltd. All rights reserved.X11sciescopu
Satellite selection scheme for reducing handover attempts in LEO satellite communication systems
No full textLow earth orbit (LEO) satellite communication systems perform frequent intersatellite handovers for both foxed and mobile users. This paper proposes a satellite selection scheme for new/handover call requests when two or more satellites can be seen simultaneously. Each satellite in this scheme has a non-uniform transmitter antenna gain according to its relative position inside the coverage area. The antenna gain is proportional to the residual distance in the satellite's direction of movement and it compensates for the difference in path losses between satellite links. The residual distance distribution of the selected satellite and the mean number of intersatellite handovers during a call connection are calculated and compared with the results based on conventional methods. The proposed scheme can reduce the intersatellite handover call attempt rate without increasing system load and terminal complexity. Furthermore, this scheme can be extended to reduce both intersatellite and interbeam handover call attempt rates in a multiple spot beam environment. Especially, the average number of intersatellite and interbeam handovers during a call can be significantly reduced by using a hybrid algorithm with the proposed non-uniform power transmission scheme. (C) 1998 John Wiley & Sons, Ltd
Construction of Equivalence Classes through Automatic Extraction and Identification of Foreign Word
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