The equilibrium shapes of non-uniform vortices in the ocean

The problem of the equilibrium shapes of rotating vortices in a stratified ocean, which is in a statically stable state, is considered within the framework of the model of an ideal incompressible fluid. An equilibrium shape is a surface on which the pressures in the vortex and in the ocean are equal, in which case, on this surface the normal components of the velocities of the media are equal to zero, but a discontinuity of the tangential components is allowed. The case of stratification of the media along the local vertical is considered. The external medium (the ocean) may consist of several layers, differing sharply in density.     

On flat equilibrium shapes of inhomogeneous anisotropic elastic plates and rods

An asymptotic analysis of deformations of anisotropic inhomogeneous thin elastic plates and rods is performed. In the linear formulation, the flat equilibrium shapes of the limiting surface and the limiting line of such thin bodies are shown to be unstable.     

Precise integration method for natural frequencies and mode shapes of ocean risers with elastic boundary conditions

The effects of the elastic constraints simulating damaged and undamaged boundaries on the natural frequencies and mode shapes of ocean risers with a variable axial tension are investigated using the precise integration method (PIM). The classical high-order variable-coefficient partial-differential governing equation of the free vibration of ocean risers is reduced to a set of first-order ordinary differential equations and efficiently solved by the PIM. The main advantages of the PIM are that the numerical results can be calculated with high accuracy even when total element number n, number of iterations N and Taylor expansion terms r are small. Moreover, the computing time is quite short. Various boundary conditions are modeled as linear elastic constraints using a pair of translational and torsional springs, and four types of boundary damage coefficients are proposed to investigate the effects of a damaged boundary on the natural frequencies. The results for specific boundary conditions show agreement with those reported in the literature, and the calculation errors are very small in comparison with the analytical solution. Overall, the methodology of PIM is applicable for the investigation of the natural frequencies and mode shapes of ocean risers with a variable axial tension and cross-section and various boundary conditions.     

Exact transient analysis of a planar random motion with three directions

Consider a planar random motion with constant velocity and three directions forming the angles ~ /6, 5 ~ /6 and 3 ~ /2 with the x -axis, such that the random times between consecutive changes of direction perform an alternating renewal process. We obtain the probability law of the bidimensional stochastic process which describes location and direction of the motion. In the Markovian case when the random times between consecutive changes of direction are exponentially distributed, the transition densities of the motion are explicitly given. These are expressed in term of a suitable modified two-index Bessel function.     

Minimising movements for the motion of discrete screw dislocations along glide directions

In Alicandro et al. (J Mech Phys Solids 92:87–104, 2016) a simple discrete scheme for the motion of screw dislocations toward low energy configurations has been proposed. There, a formal limit of such a scheme, as the lattice spacing and the time step tend to zero, has been described. The limiting dynamics agrees with the maximal dissipation criterion introduced in Cermelli and Gurtin (Arch Ration Mech Anal 148, 1999) and predicts motion along the glide directions of the crystal. In this paper, we provide rigorous proofs of the results in [3], and in particular of the passage from the discrete to the continuous dynamics. The proofs are based on \(\Gamma \)-convergence techniques.     

Numerical modeling of the equilibrium shapes of a ferrofluid drop in an external magnetic field

A numerical solution strategy for calculating equilibrium free surfaces of a magnetic fluid under the action of a magnetic field is proposed and applied to determine shapes of a linear magnetisable ferrofluid drop in a uniform magnetic field. Hysteresis phenomena for the drop deformation and the drop shapes with ends, close to conical, were observed numerically. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the rate of convergence to equilibrium for reflected Brownian motion

This paper discusses the rate of convergence to equilibrium for one-dimensional reflected Brownian motion with negative drift and lower reflecting boundary at 0. In contrast to prior work on this problem, we focus on studying the rate of convergence for the entire distribution through the total variation norm, rather than just moments of the distribution. In addition, we obtain computable bounds on the total variation distance to equilibrium that can be used to assess the quality of the steady state for queues as an approximation to finite horizon expectations.     

Software for the analysis of extreme events: The current state and future directions

The last few years have seen a significant increase in publicly available software specifically targeted to the analysis of extreme values. This reflects the increase in the use of extreme value methodology by the general statistical community. The software that is available for the analysis of extremes has evolved in essentially independent units, with most forming extensions of larger software environments. An inevitable consequence is that these units are spread about the statistical landscape. Scientists seeking to apply extreme value methods must spend considerable time and effort in determining whether the currently available software can be usefully applied to a given problem. We attempt to simplify this process by reviewing the current state, and suggest future approaches for software development. These suggestions aim to provide a basis for an initiative leading to the successful creation and distribution of a flexible and extensible set of tools for extreme value practitioners and researchers alike. In particular, we propose a collaborative framework for which cooperation between developers is of fundamental importance. AMS 2000 Subject Classification Primary—62P99     

Stability and controllability of the motion of dynamical systems far off from equilibrium positions

We prove theorems that establish the connection between the stability and the controllability of the motion far off from the equilibrium positions and the existence of homogeneous -attractors, -repellers, and -shunts in the extended state space of dynamical systems.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 8, pp. 1145–1149, August, 1992.     

Growth rates for the linearized motion of fluid interfaces away from equilibrium

We consider the motion of a two-dimensional interface separating an inviscid, incompressible, irrotational fluid, influenced by gravity, from a region of zero density. We show that under certain conditions the equations of motion, linearized about a presumed time-dependent solution, are wellposed; that is, linear disturbances have a bounded rate of growth. If surface tension is neglected, the linear equations are well-posed provided the underlying exact motion satisfies a condition on the acceleration of the interface relative to gravity, similar to the criterion formulated by G. I. Taylor. If surface tension is included, the linear equations are well-posed without qualifications, whether the fluid is above or below the interface. An interesting qualitative structure is found for the linear equations. A Lagrangian approach is used, like that of numerical work such as [3], except that the interface is assumed horizontal at infinity. Certain integral equations which occur, involving double layer potentials, are shown to be solvable in the present case. © 1993 John Wiley & Sons, Inc.     

On the convergence to equilibrium of Brownian motion on compact simple Lie groups

Let M =G/H be an irreducible homogeneous compact manifold of dimension n equipped with its canonical Riemannian metric. Let γ be the lowest nonzero eigenvalue of the Laplace operator. Let μ be the normalized Haar measure and μ _t be the heat diffusion measure, i.e., the law of Brownian motion started at a fixed origin in M. We show that the total variation distance between μ_t and μ is not small for t ≪λ ⁻¹ logn.This is sharp, up to a factor of two, in the case of compact irreducible simply connected symmetric spaces.     

Numerical study of the influence of diffusion of magnetic particles on equilibrium shapes of a free magnetic fluid surface

A mathematical model and a computational method for studying the influence of the particle diffusion on equilibrium shapes of a magnetic liquid is developed. It is then applied on the ferrohydrostatic problem of doubly connected equilibrium shapes of a magnetic fluid located on a horizontal plate around a vertical cylindrical conductor with a direct current. Numerical simulations show the limits of the uniform concentration approximation.     

The regularity of munn rings and semigroup rings

In this paper, the author studies the regularity of Munn rings and completely 0-simple semigroup rings. When either (i)R is a ring with identity andI and are infinite, or (ii)R is a strong IBN and fully Dedekind-finite ring with identity and eitherI or is finite, in Section 2, the regularity of the Munn ringM(R; I, ; P) is characterized; in Section 3, for a completely 0-simple semigroupS =M°(G; I, ; P), the regularity ofRS is characterized. Meantime, the author shows that for a locally finite monoidS and a ringR with identity,RS is a strong IBN ring if and only ifR is so;RS is fully Dedekind-finite if and only ifR is so.     

M-McCoy环和M-Armendariz环的多项式扩张

研究非交换环上的相对于幺半群的McCoy环和Armendariz环的多项式扩张.对于包含无限循环子幺半群的交换可消幺半群M,证明了若R是M-McCoy（或M-Armendariz）环,则R上的洛朗多项式环R[x,x-1]是M-McCoy（或M-Armendariz）环.