On a problem of Skiba from the Kourovka Notebook

In this paper, we give a positive answer to a recent open problem of Skiba in Kourovka Notebook without using the odd order theorem and other deep theorems. Some of the techniques are improved.     

Generalization of problem 9.25 from “the Kourovka notebook”

Translated from Matematicheskie Zametki, Vol. 47, No. 2, pp. 15–19, February, 1990.     

Local convexity of the growth function of finitely generated groups and question 5.2 in the Kourovka Notebook

Using the group <a,b|a³=b³=(ab)³=1>, we refute the conjecture dubbed in 1976 by V. Belyaev and N. Sesekin, which maintained that the growth function σ(n) of a finitely generated group satisfies the inequality σ(n)≤(σ(n−1)+σ(n+1))/2 for all sufficiently large n. Supported by the National Research Foundation of Switzerland, and by RFFR grant No. 96-01-00974. Translated fromAlgebra i Logika, Vol. 37, No. 6, pp. 621–626, November–December, 1998.     

On a Pair of Identities from Ramanujan's Lost Notebook

Using a pair of two variable series-product identities recorded by Ramanujan in the lost notebook as inspiration, we find some new identities of similar type. Each identity immediately implies an infinite family of Rogers-Ramanujan type identities, some of which are well-known identities from the literature. We also use these identities to derive some general identities for integer partitions.     

On a phase-change problem arising from inductive heating

In this paper we study a phase-change problem arising from induction heating. The mathematical model consists of time-harmonic Maxwell’s system in a quasi-stationary field coupled with nonlinear heat conduction. The enthalpy form is used to characterize the phase-change in the material. It is shown that the problem has a global solution. Moreover, it is shown that the solution is unique and regular in one-space dimension even with an unbounded resistivity. This work is supported in part by a NSF grant: DMS-0102261     

On a differential problem coming from cell biology

Summary An initial and boundary value problem for a system of first order linear partial differential equations is studied. This problem arises in cell biology, when the evolution of a homogeneous cell population is modelled. Some existence, uniqueness and regularity results are proven; an estimate for the growth of the cell population is also obtained.This work was in part supported by the Istituto di Analisi Numerica of the C.N.R. in Pavia (Italy), the G.N.A.F.A. of the C.N.R. (Italy) and the Ministero della Pubblica Istruzione (Italy).     

On a problem with deviation from a characteristic for the gellerstedt equation

We prove the unique regular solvability of a problem with deviation from a characteristic for the Gellerstedt equation.     

On the generalized Ritt problem as a computational problem

The Ritt problem asks if there is an algorithm that decides whether one prime differential ideal is contained in another one if both are given by their characteristic sets. We give several equivalent formulations of this problem. In particular, we show that it is equivalent to testing whether a differential polynomial is a zero divisor modulo a radical differential ideal. The technique used in the proof of this equivalence yields algorithms for computing a canonical decomposition of a radical differential ideal into prime components and a canonical generating set of a radical differential ideal. Both proposed representations of a radical differential ideal are independent of the given set of generators and can be made independent of the ranking.     

On a saddle point problem arising from magneto-elastic coupling

This paper deals with the analysis of a coupled problem arising from linear magneto-elastostatics. The model, which can be derived by an energy principle, gives valuable insight into the coupling mechanism and features a saddle point structure with the elastic displacement and magnetic scalar potential as independent variables. As main results, the existence and uniqueness of the solution are proven for the continuous and discrete cases and special properties of the corresponding bilinear forms are shown. In particular, the coupled magneto-elastic bilinear form satisfies an inf–sup condition for a certain class of magnetostrictive materials, that is essential for the stability of the problem.     

On a weakly formulated exterior problem from linear hydrodynamics

In this paper we investigate a certain exterior boundary value problem for the inhomogeneous Helmholtz equation. We give sufficient conditions for the unique solvability of a weak formulation of this problem and show an interior regularity result for all weak solutions. As a special case the incompresible, irrotational and stationary fluid flow around a totally immersed obstacle (submarine problem) is included.     

On a singular differential system arising from a min-max control problem

The feedback law for a control problem with a nondifferentiable cost functional is characterized by an initial-value problem for a differential system with singular right-hand side. This system is characteristic for a partial differential equation formally satisfied by the feedback law. A regularization of the differential system and the partial differential equation is given, and the feedback laws for the smoothed problems are shown to converge to the original feedback law.This work was supported by the Gruppo Nazionale per l'Analisi Funzionale e le sue Applicazioni of the Consiglio Nazionale delle Ricerche.     

On a Quasi-Ramsey problem

It is proved that if a graph G has atleast cn log n vertices, then either G or its complement G contains a subgraph H with atleast n vertices and minimum degree atleast | V(H)|/2. This result is not far from being best possible, as is shown by a rather unusual random construction. Some related questions are also discussed.     

On a differential-algebraic problem

The method of quasilinearization is a procedure for obtaining approximate solutions of differential equations. In this paper, this technique is applied to a differential-algebraic problem. Under some natural assumptions, monotone sequences converge quadratically to a unique solution of our problem.     

On a Smale problem

We derive conditions under which a linear coupling between two globally stable nonlinear nth-order systems results in a system of order 2n whose almost every solution asymptotically approaches an orbitally stable cycle. These results permit one to solve a problem posed by Smale and pertaining to the theory of chemical kinetics of biological cells.