Convergence of a cell-centered finite volume discretization for linear elasticity

We show convergence of a cell-centered finite volume discretization for linear elasticity. The discretization, termed the MPSA method, was recently proposed in the context of geological applications, where cell-centered variables are often preferred. Our analysis utilizes a hybrid variational formulation, which has previously been used to analyze finite volume discretizations for the scalar diffusion equation. The current analysis deviates significantly from previous in three respects. First, additional stabilization leads to a more complex saddle-point problem. Secondly, a discrete Korn's inequality has to be established for the global discretization. Finally, robustness with respect to the Poisson ratio is analyzed. The stability and convergence results presented herein provide the first rigorous justification of the applicability of cell-centered finite volume methods to problems in linear elasticity

Stable cell-centered finite volume discretization for Biot equations

In this paper we discuss a new discretization for the Biot equations. The discretization treats the coupled system of deformation and flow directly, as opposed to combining discretizations for the two separate sub-problems. The coupled discretization has the following key properties, the combination of which is novel: 1) The variables for the pressure and displacement are co-located, and are as sparse as possible (e.g. one displacement vector and one scalar pressure per cell center). 2) With locally computable restrictions on grid types, the discretization is stable with respect to the limits of incompressible fluid and small time-steps. 3) No artificial stabilization term has been introduced. Furthermore, due to the finite volume structure embedded in the discretization, explicit local expressions for both momentum-balancing forces as well as mass-conservative fluid fluxes are available. We prove stability of the proposed method with respect to all relevant limits. Together with consistency, this proves convergence of the method. Finally, we give numerical examples verifying both the analysis and convergence of the method

Analysis of Human Spleen Contamination

Besides carbon, oxygen and nitrogen, numerous other elements and their compounds are significant in the body of humans and other animals. Accumulation of some elements and their compounds is recognized by clinical and biochemical evaluation. The physical-chemical properties and topical characteristics of elements in tissues may play a crucial role in evaluation their effect on human body. The ^57^Fe Mössbauer measurement was used for evaluation of iron–oxide biomagnetic nanoparticles composition and properties. Absorption spectra of the powdered spleen recorded at 77K and 300K were measured and subsequently analyzed. From fitted data it is possible to obtain material composition as well as discuss the mean particle size (received from decrease hyperfine field in comparison with bulk value)

A spatial version of the It\^{o}-Stratonovich correction

We consider a class of stochastic PDEs of Burgers type in spatial dimension 1, driven by space-time white noise. Even though it is well known that these equations are well posed, it turns out that if one performs a spatial discretization of the nonlinearity in the "wrong" way, then the sequence of approximate equations does converge to a limit, but this limit exhibits an additional correction term. This correction term is proportional to the local quadratic cross-variation (in space) of the gradient of the conserved quantity with the solution itself. This can be understood as a consequence of the fact that for any fixed time, the law of the solution is locally equivalent to Wiener measure, where space plays the role of time. In this sense, the correction term is similar to the usual It\^{o}-Stratonovich correction term that arises when one considers different temporal discretizations of stochastic ODEs.Comment: Published in at http://dx.doi.org/10.1214/11-AOP662 the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

Integral equation for spin dependent unintegrated parton distributions incorporating double ln^2(1/x) effects at low x

In this paper we derive an integral equation for the evolution of unintegrated (longitudinally) polarized quark and gluon parton distributions. The conventional CCFM framework is extended at small x in order to incorporate the QCD expectations concerning the double ln^2(1/x) resummation at low x for the integrated distributions. Complete Altarelli-Parisi splitting functions are included, that makes the formalism compatible with the LO Altarelli-Parisi evolution at large and moderately small values of x. The obtained modified polarized CCFM equation is shown to be partially diagonalized by the Fourier-Bessel transform. Results of the numerical solution for this modified CCFM equation for the non-singlet quark distributions are presented.Comment: 24 pages, 3 figures, LaTeX, some discussion added, none of the results changed, version to appear in Phys. Rev.

On approximate pseudo-maximum likelihood estimation for LARCH-processes

Linear ARCH (LARCH) processes were introduced by Robinson [J. Econometrics 47 (1991) 67--84] to model long-range dependence in volatility and leverage. Basic theoretical properties of LARCH processes have been investigated in the recent literature. However, there is a lack of estimation methods and corresponding asymptotic theory. In this paper, we consider estimation of the dependence parameters for LARCH processes with non-summable hyperbolically decaying coefficients. Asymptotic limit theorems are derived. A central limit theorem with $\sqrt{n}$-rate of convergence holds for an approximate conditional pseudo-maximum likelihood estimator. To obtain a computable version that includes observed values only, a further approximation is required. The computable estimator is again asymptotically normal, however with a rate of convergence that is slower than $\sqrt{n}.$Comment: Published in at http://dx.doi.org/10.3150/09-BEJ189 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm