In designing distributed database systems, concurrency control and recovery mechanisms must be selected from a field of candidates. The crucial criterion for choosing a combination of particular algorithms is their in...
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In designing distributed database systems, concurrency control and recovery mechanisms must be selected from a field of candidates. The crucial criterion for choosing a combination of particular algorithms is their individual and integrated performance. Instead of applying analytical and/or conventional simulation techniques, we suggest that distributed discrete event simulation be applied. The technology developed is based on subjecting to distributed simulation the distributed transaction management of the real system. It captures, in a distributed environment, the processing, storage and communication resources of the whole distributed database system. After introducing a methodological motivation, this technology is presented in the form of: a reference performance model of distributed database systems, corresponding distributed simulation model, and a distributed simulation algorithm based on Chandy-Misra-Bryant approach.
If A is an n x n sign pattern matrix, then Q(A) denotes the set of all real n x n matrices B such that the signs of the entries in B match the corresponding entries in A. In this paper, we consider various requires/al...
If A is an n x n sign pattern matrix, then Q(A) denotes the set of all real n x n matrices B such that the signs of the entries in B match the corresponding entries in A. In this paper, we consider various requires/allows questions connected with sign pattern matrices and generalized inverses. In particular, we investigate the class G of all square patterns A for which there exist B, C is-an-element-of Q(A) where BCB = B. For nonnegative patterns, we characterize G and show that G coincides with the class of all square patterns A for which there exists B is-an-element-of Q(A) where B3 = B. Nonnegative square patterns that allow an idempotent and those that allow a (1,3)-inverse are each characterized. Some interesting open questions are also indicated.
For the Tricomi equation with Dirichlet boundary conditions, we study the relationship between singularites at the boundary and singularities in the interior of a bounded planar region with smooth non-characteristic b...
For the Tricomi equation with Dirichlet boundary conditions, we study the relationship between singularites at the boundary and singularities in the interior of a bounded planar region with smooth non-characteristic boundary. Necessary and sufficient conditions for interior smoothness are stated in terms of microlocal regularity at the boundary and are proven via known microlocal propagation of singularities results along the generalized bicharacteristic flow. In particular, a trapped gliding ray phenomenon at parabolic boundary points is demonstrated under a sharp geometric hypothesis, which provides a microlocal explanation for the possibility of having only isolated singularities at the boundary, which is a question left open in the work of Morawetz. (C) 1996 Academic Press, Inc.
A method for studying natural oscillations of fluids and plasmas in the neighborhood of two-dimensional elliptical hows is presented. The method uses scaling combined with the Fourier transformation to reduce the spec...
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A method for studying natural oscillations of fluids and plasmas in the neighborhood of two-dimensional elliptical hows is presented. The method uses scaling combined with the Fourier transformation to reduce the spectral stability problem for such flows to a spectral problem for an: ordinary differential operator. This reduction is used to obtain a complete description of the spectrum for fluid hows and a qualitative description of the spectrum (including bounds for the complex part of the spectrum) for plasma flows. It is shown that a steady planar fluid flow with elliptical streamlines is spectrally unstable. It is also shown that all planar magnetized plasma flows with elliptical streamlines are spectrally unstable, except for the case when the magnitudes of the fluid velocity and the Alfven velocity are exactly equal to each other. (C) 1995 American Institute of Physics.
In this paper, the fourth order parabolic partial differential equation, that governs the behavior of a vibrating beam, is solved by using the Adomian Decomposition Method. The solution is derived in the form of a pow...
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In this paper, the fourth order parabolic partial differential equation, that governs the behavior of a vibrating beam, is solved by using the Adomian Decomposition Method. The solution is derived in the form of a power series with easily computable components. The nonhomogeneous problem is quickly solved by observing the self-canceling ''noise'' terms whose sum vanishes in the limit. Comparing this methodology with some known techniques shows that the present approach is highly accurate.
Aphasia is a language disorder caused by brain damage. Naming errors which are common in aphasia are applied to reveal the type and the effects of a disorder. Naming in this research field refers to psycholinguistic t...
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Aphasia is a language disorder caused by brain damage. Naming errors which are common in aphasia are applied to reveal the type and the effects of a disorder. Naming in this research field refers to psycholinguistic tests where a subject is asked to say the name of an object presented as a picture to him or her. We have earlier presented a simulation model on the basis of neural networks [1,2]. The model is further developed here, and its properties and behaviour are described in the present paper. The simulation model includes a bounded set of Finnish words in their base lingual form. The principle of activation spreading Is used to process naming errors with the method to simulate actual aphasic errors. All computation in the model is executed with words as text or with textual components of words, although the system processes naming errors, i.e. human speech.
Let Ax = b be a system of linear equations where A is symmetric and positive definite. Suppose that the associated block Jacobi matrix B is consistently ordered, weekly cyclic of index 2, and convergent [i.e., mu(1) :...
Let Ax = b be a system of linear equations where A is symmetric and positive definite. Suppose that the associated block Jacobi matrix B is consistently ordered, weekly cyclic of index 2, and convergent [i.e., mu(1) := rho(B) < 1]. Consider using the overrelaxation methods (SOR, AOR, MSOR, SSOR, or USSOR), x(n+1) = T(omega)x(n) + c(omega) for n greater than or equal to 0, to solve the system. We derive a uniform error bound for the overrelaxation methods, \\x - x(n)\\(2) less than or equal to 1/[1 + s(mu(1)(2)) + t(mu(1)(2))](2) x [(t(0) + \t(1)\mu(1)(2))(2)\\delta(n)\\(2) - 2t(0) [delta(n), delta(n+1)] + \t(1)\mu(1)(2)\\delta(n)\\ \\delta(n + 1)\\ + \\delta(n + 1)\\(2)], where \\.\\ = \\.\\(2), delta(n) = x(n) - x(n - 1), and s(mu(2)) and t(mu(2)) := t(0) + t(1) mu(2) are two coefficients of the corresponding functional equation connecting the eigenvalues lambda of T-omega to the eigenvalues mu of B, As special cases of the uniform error bound, we will give two error bounds for the SSOR and USSOR methods. (C) Elsevier science Inc., 1997.
The stability of an explicit discretization of Fisher's equation from reaction-diffusion is studied from the point of view of long time calculations with a fixed time step. The method is found to be stable under t...
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The stability of an explicit discretization of Fisher's equation from reaction-diffusion is studied from the point of view of long time calculations with a fixed time step. The method is found to be stable under the same conditions as those required by the linearized scheme in the neighbourhood of the constant, stable, fixed point of the underlying partial differential equation. When these conditions are violated, it is shown that a variety of different period-doubling bifurcations can occur which extend, through the addition of a (discrete) diffusion term, known results from ordinary differential equations and maps on the line.
Consider the retarded Lienard equation x '' + f(x)x' + g(x(t - h)) = 0, where f,g: R --> R are continuous and h greater than or equal to 0. Using Liapunov's direct method, we give necessary and suff...
Consider the retarded Lienard equation x '' + f(x)x' + g(x(t - h)) = 0, where f,g: R --> R are continuous and h greater than or equal to 0. Using Liapunov's direct method, we give necessary and sufficient conditions to ensure boundedness and oscillation of all solutions and their derivatives. (C) 1996 Academic Press, Inc.
The amplitude ratio and latency between peaks of the auditory brainstem response are widely used as medical parameters of response in the clinical assessment. Several methodological factors affect the medical paramete...
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The amplitude ratio and latency between peaks of the auditory brainstem response are widely used as medical parameters of response in the clinical assessment. Several methodological factors affect the medical parameters. The sampling frequency, the resolution of the averager and filtering of the signal are important factors. Typically the signal is highly oversampled inthe recording phase. The resolution of the averager should be as good as possible to ensure adequacy of the amplitude parameter. The latency parameter is more tolerant to the reduction of the sampling frequency, and the signal can be decimated down to 10 kHz to reduce computational complexity.
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