A note on the classical brachistochrone

Summary It is shown that the classical Bernoulli's brachistochrone problem and the brachistochrone problem in a central force field may be solved by the maximum principle of Pontryagin. According to the optimum control theory these problems are singular.

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Zusammenfassung In der Arbeit ist gezeigt, daß das klassische Bernoullische brachistochrone Problem und Brachistochronen im zentralen Schwerefeld durch das Pontryagin Maximum Prinzip gelöst werden können. Gemäss Theorie der optimalen Regelung sind diese Probleme singulär.

     

A note on the classical brachistochrone

It is shown that the classical Bernoulli's brachistochrone problem and the brachistochrone problem in a central force field may be solved by the maximum principle of Pontryagin. According to the optimum control theory these problems are singular.     

Neural net versus classical models for the detection and localization of leaks in pipelines

Four models of a pipeline are compared in the paper: a nonlinear distributed-parameter model, a linear distributed-parameter model, a simplified lumped-parameter model and an extended neural-net-based model. The transcendental transfer function of the linearized model is obtained by a Laplace transformation and corresponding initial and boundary conditions. The lumped-parameter model is obtained by a Taylor series extension of the transencdental transfer function. Based on the experience of linear models the structure of the neural net model, as an addendum to the nonlinear distributed-parameter model, is obtained. All four models are tested on a real pipeline data with an artificially generated leak.     

A note on discrete heat conduction

If the longitudinal line method is applied to the Cauchy problem u_t = u_xx, u(0, x) = u₀(x) with a bounded function u₀, one is led to a linear initial value problem v￠(t)=A v(t), v(0)=wv'(t)=A v(t),\, v(0)=w in l^￥ (\Bbb Z)l^\infty (\Bbb Z). Using Banach limit techniques we study the asymptotic behaviour of the solutions of these problems as t tends to infinity.     

A note on discrete Borg-type theorems

We consider the discrete versions of the well-known Borg’s theorem and use simple linear algebraic techniques to obtain new versions of the discrete Borg-type theorems. To be precise, we prove that the periodic potential of a discrete Schrödinger operator is almost a constant if and only if the possible spectral gaps of the operator are of small width. This result is further extended to more general settings and the connection to the well-known Ten Martini problem is also discussed.     

A note on the well-posed anisotropic discrete BVPs

Using the direct method of the calculus of variations, we investigate the existence, uniqueness and continuous dependence on parameters for solutions of second-order discrete anisotropic equations with Dirichlet boundary conditions.     

A note on the capacity of discrete noiseless channels

Zusammenfassung Diese Mitteilung gibt einen mathematischen Beweis einer Darstellung vonShannon, betreffend die Kanalkapazität einer Klasse von einfachen Kanälen ohne Gedächtnis.     

A note on Toeplitz operators on discrete groups

We study Toeplitz algebras associated to partially-ordered and quasi-partially ordered discrete groups.

     

A note on Opial and Wirtinger type discrete inequalities

The aim of the present note is to establish some new discrete inequalities of the Opial and Wirtinger type involving sequences of real numbers and their forward differences. The analysis used in the proofs is quite elementary and based on some simple observations and the applications of some fundamental inequalities.     

A note on assessing agreement for frailty models

Assessing agreement is often of interest in biomedical sciences to evaluate the similarity of measurements produced by different raters or methods on the same subjects. We investigate the agreement structure for a class of frailty models that are commonly used for analyzing correlated survival outcomes. Conditional on the shared frailty, bivariate survival times are assumed to be independent with Weibull baseline hazard distribution. We present the analytic expressions for the concordance correlation coefficient (CCC) for several commonly used frailty distributions. Furthermore, we develop a time-dependent CCC for measuring agreement between survival times among subjects who survive beyond a specified time point. We characterize the temporal pattern in the time-dependent CCC for various frailty distributions. Our results provide a better understanding of the agreement structure implied by different frailty models.     

A note on capacity models for network design

In network design problems,capacity constraints are modeled in three different ways depending on the application: directed, bidirected and undirected. In the literature, polyhedral investigations for strengthening mixed-integer formulations are done separately for each model. In this note, we examine the relationship between these models to provide a unifying approach and show that one can indeed translate valid inequalities from one to the others.