Some mathematical models of the pulsating fountain problem

We consider the motion of the center of gravity of a variable-mass reservoir under the action of gravitation and the pressure of a water jet discharged from a vertical spout. It is assumed that the entire discharged amount of water enters the reservoir. A basic mathematical model is provided by the Cauchy problem for a Volterra integrodifferential equation. Numerical results are reported for particular parameter values.Kiev University. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 74, pp. 60–63, 1992;     

Some studies on mathematical models for general elastic multi-structures

The aim of this paper is to study the static problem about a general elastic multi-structure composed of an arbitrary number of elastic bodies, plates and rods. The mathematical model is derived by the variational principle and the principle of virtual work in a vector way. The unique solvability of the resulting problem is proved by the Lax-Milgram lemma after the presentation of a generalized Korn's inequality on general elastic multi-structures. The equilibrium equations are obtained rigorously by only assuming some reasonable regularity of the solution. An important identity is also given which is essential in the finite element analysis for the problem.     

Reflected acting in mathematical learning processes

Acting and thinking are strongly interconnected activities. This paper proposes an approach to mathematical concepts from the angle of hands-on acting. In the process of learning, special emphasis is put on the reflection of the own actions, enabling learners to act consciously. An illustration is presented in the area number representation and extensions of number fields. Using didactical materials, processes of mathematical acting are stimulated and reflected. Mathematical concepts are jointly developed with the learners, trying to address shortcomings from own experiences. This is accompanied by reflection processes that make conscious to learners the rationale of mathematical approaches and the creation of mathematical concepts. Teaching mathematics following this approach does intent to contribute to the development of decision-making and responsibility capabilities of learners.     

Some mathematical problems in seriation

Some mathematical aspects of seriation are studied in this paper. Certain conditions on an abundance or an incidence matrix have been given in the past which imply that there exists a permutation of its rows so that the resulting matrix is a Q matrix (in which case the original matrix is said to be a pre-Q). These types of results have applications to chronologically ordering archaeological provenances under certain circumstances. Unfortunately these conditions are deficient both theoretically and practically, in that for much archaeological data the conditions are not necessarily true yet the corresponding provenances do have chronological orderings. Here we are able to generalize these results in two ways. First we are able to establish necessary and sufficient conditions on the rows of a matrix for it to be pre-Q. These conditions are local in that they concern only certain triples and quadruples of the rows. Secondly, we are able to interpret seriation in terms of a ternary relation R on a set A and prove the results in this general context. In this form the theorem says that if only certain of the triples and quadruples are R-strings, then the whole set A is an R-string, and so has a linear order consistent with the ternary relation R. This would appear to generalize a theorem of P. C. Fishburn. Both aspects of the generalization mean that the results stated herein have a wider applicability than those given heretofore. Possibly more importantly than this is that they lead to numerical invariants, called the fixing number and the related linear rigidity, of such an R-string on A. The archaeological interpretation of these is given in the paper and data supplied which illustrates this point. Finally various other conditions on products and representations of relations are stated which imply that A is an R-string. One of these generalizes and completes a theorem of D. G. Kendall.     

Some applications of mathematical programming to problems in mathematical physics

Siberian Mathematical Journal -     

Applications of mathematical programming models

A sizeable proportion of manufacturing expenses can be attributed to facility layout and material handling. Facility layout decisions involve designing the arrangement of elements in manufacturing systems. Among the most critical material handling decisions in this area are the arrangement and design of material flow patterns. This survey article reviews loop based facility planning and material handling decisions for trip based material handling equipment with an emphasis on unit load automated guided vehicles. The article examines issues related with facility design, material handling design, and fleet sizing and operating.     

Parametric scaling of mathematical models

Parametric scaling, the process of extrapolation of a modelling result to new parametric conditions, is often required in model optimization, and can be important if the effects of parametric uncertainty on model predictions are to be quantified. Knowledge of the functional relationship between the model solution (y) and the system parameters (α) may also provide insight into the physical system underlying the model. This paper examines strategies for parametric scaling, assuming that only the nominal model solution y(α) and the associated parametric sensitivity coefficients (?y/?α, ?²y/?α², etc.) are known. The truncated Taylor series is shown to be a poor choice for parametric scaling, when y has known bounds. Alternate formulae are proposed which ‘build-in’ the constraints on y, thus expanding the parametric region in which the extrapolation may be valid. In the case where y has a temporal as well as a parametric dependence, the extrapolation may be further improved by removing from the Taylor series coefficients the ‘secular’ components, which refer to changes in the time scale of y(t), not to changes in y as a function of α.     

Characterizing optimality in mathematical programming models

This paper is a survey of basic results that characterize optimality in single- and multi-objective mathematical programming models. Many people believe, or want to believe, that the underlying behavioural structure of management, economic, and many other systems, generates basically continuous processes. This belief motivates our definition and study of optimality, termed structural optimality. Roughly speaking, we say that a feasible point of a mathematical programming model is structurally optimal if every improvement of the optimal value function, with respect to parameters, results in discontinuity of the corresponding feasible set of decision variables. This definition appears to be more suitable for many applications and it is also more general than the usual one: every optimum is a structural optimum but not necessarily vice versa. By characterizing structural optima, we obtain some new, and recover the familiar, optimality conditions in nonlinear programming.The paper is self-contained. Our approach is geometric and inductive: we develop intiution by studying finite-dimensional models before moving on to abstract situations.Research partly supported by the National Research Council of Canada.     

Some remarks on the behaviour of the solution in dynamic processes for rate-type models

This work examines a dynamic problem in the study of semilinear rate-type models for which the plastic rate of deformation depends also on a parameter . The continuous dependence of the solution with respect to is obtained and the problem of finite time stability is also discussed. In the case when is interpreted as the absolute temperature, the dynamic problem is studied in the context of a Cattaneo-type heat law and also using the classical Fourier law. In the case when is interpreted as an internal state variable an existence and uniqueness result is obtained using a fixed point method and the finite time stability is also investigated.     

Some mathematical aspects of reinsurance

In two earlier papers, Waters (1979) and Andreadakis and Waters (1980), the effect on an insurer as a result of varying his retention limits has been studied. This present paper represents an extension of this earlier work. In particular we investigate whether it is possible to prove some of the results of the earlier papers without making restrictive assumptions about the distribution of annual claims or about the way in which the reinsurance premium is calculated. It will be shown that this is possible in the case of proportional but not possible in the case of non-proportional reinsurance.     

Some research directions in mathematical economics

A brief survey of the publications in mathematical economics, dealing with utility theory, probabilistic microeconomic models, and equilibrium under price rigidities, is given.Translated from Igoti Nauki i Tekhniki, Seriya Sovremennye Problemy Matematiki, Vol. 19, pp. 3–22, 1982.     

Some mathematical problems in computer vision

Several interesting mathematical problems arising in computer vision are discussed. Computer vision deals with image understanding at various levels. At the low level, it addresses issues like segmentation, edge detection, planar shape recognition and analysis. Classical results on differential invariants associated to planar curves are relevant to planar object recognition under partial occlusion, and recent results concerning the evolution of closed planar shapes under curvature controlled diffusion have found applications in shape decomposition and analysis. At higher levels, computer vision problems deal with attempts to invert imaging projections and shading processes toward depth recovery, spatial shape recognition and motion analysis. In this context, the recovery of depth from shaded images of objects with smooth, diffuse surfaces require the solution of nonlinear partial differential equations. Here results on differential equations, as well as interesting results from low-dimensional topology and differential geometry are the necessary tools of the trade. We are still far from being able to equip our computers with brains capable to analyze and understand the images that can easily be acquired with camera-eyes; however the research effort in this area often calls for both classical and recent mathematical results.This work was supported in part by NSF grant DMS-8811084, Air Force Office of Scientific Research Grant AFOSR-90-0024, and the Army Research Office DAAL03-91-G-0019, and by the Technion Fund for Promotion of Research.     

Some mathematical models related to the Zhukovskii problem of the flow around a sheet pile

The seepage under a Zhukovskii sheet pile through a layer of soil underlain by a highly permeable pressurized horizon is considered. The left semi-infinite part of the roof of this horizon is simulated by an impermeable foundation. The flow when the velocity on the edges of the sheet pile is equal to infinity and, on the two water permeable parts of the boundary of the domain of motion, the flow rate takes extremal values, is investigated. The limiting cases, associated with the absence of both a backwater and an impermeable inclusion, are mentioned. The problem of seepage from a foundation pit formed by two Zhukovskii sheet piles is solved within the limits of a flow with a highly permeable pressurized stratum lying below. In the case when there is no infiltration onto the free surface, a solution of the well-known Vedernikov problem is obtained. A contact scheme, arising when there are no such indicated critical points, is considered; it is described outside the scope of the constraints imposed on the unknown conforming mapping parameters ensuring the realization of the basic mathematical model. Solutions are given for two schemes of motion in a semi-inverse formulation. The classical Zhukovskii problem is the limiting case of one of them. The special features of such models are mentioned. The Polubarinova-Kochina method is used to study all the above-mentioned flows. This method enables exact analytical representations of the elements of the motion to be obtained. The results of numerical calculations and an analysis of the effect of all the physical factors on the seepage characteristics are presented.     

New mathematical models of porous flow

A new, viable mathematical approach to the analysis of porous flow is developed. Liquids and solids are modelled as sets of particles which interact in accordance with both long range (gravity) and short range (molecular type) forces. The resulting nonlinear, n-body problem is resolved numerically on a digital computer. A variety of fundamental porous flow type problems, solved on the University of Texas at Arlington IBM 370-155, are described and analysed.     

Chattering in dynamic mathematical two-phase flow models

This paper presents a chattering problem which arises in a dynamic mathematical two-phase flow model. The real system under study is also introduced, the DISS test facility, a parabolic-trough solar thermal power plant. The heat transfer fluid in the DISS facility is the steam-water mixture. A dynamic model of this plant, using Modelica as the modeling language, was previously developed in order to study its behavior. Chattering arises in the pipe model reducing the computational performance and hence limiting the applicability of the model. The problem source is studied and analysed together with an approach to the problem which is based on the smooth interpolation of some thermodynamic properties.     

Role of time-delay in mathematical models of ecology

Conclusions It is of great interest to compare the theoretic results with other experimental results. In particular, it is of interest to discover populations in which two-frequency oscillations are possible. Elucidation of the role of resonance conditions is extremely interesting. We note that =0.83 in the example considered in Sec. 3, i.e., it is quite close to resonance value. This does not have too great an effect owing to the smallness of r₂. It is clear that resonance is only dangerous to predators. Thus, the prey should strive to make approach 1 or 2, and the predators must keep this from happening. It is entirely possible that for most real predator-prey populations is close to one of these values. If this is so, then when the environment changes the parameter may approximate 1 or 2, which results when the difference r₂h₂-/2 is quite small in large oscillations of the predator population, and this can easily lead to their extinction.Yaroslavl' State University. Institute of Mathematics and Cybernetics, Academy of Sciences of the Lithuanian SSR. Translated from Litovskii Matematicheskii Sbornik (Lietuvos Matematikos Rinkinys), Vol. 19, No. 1, pp. 115–128, January–March, 1979.     

On some mathematical models in nonlinear elasticity

Some nonlinear models of one-dimensional elastic systems are introduced and existence and uniqueness theorems for the solution of the Cauchy-Dirichlet problem are given. Bibliography: 4 titles. Published inZapiski Nauchnykh Seminarov POMI, Vol. 233, 1996, pp. 210–216.