Mathematics

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An Historical and Critical Development of the Theory of Legendre Polynomials Before 1900
(1938) Laden, Hyman N.; Lancaster, O.E.; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Sonic Limit Singularities in the Hodograph Method
(1958) Schot, Steven H.; Ludford, Geoffrey S.S.; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
In the hodograph transformation, introduced to linerize the equations governing the two-dimensional inviscid potential flow of a compressible fluid, there may appear so-called limit-points and limit-lines at which the Jacobian J = ∂(x,y)/ ∂(q,θ) of the transformation vanishes. This thesis investigate these singularities when they occur at points or segments of arc of the sonic line (Mach number unity). Assuming the streamfunction to be regular in the hodograph variables, it is show that sonic limit points cannot be isolated but must lie on a supersonic limit line or form a sonic limit line [cf. H. Geiringer, Math. Zeitschr., 63, (1956), 514-524]. Using this dichotomy a classification of sonic limit points is set up and certain geometrical properties of the mapping in the neighborhood of the singularity are discussed. In particular the general sonic limit line is shown to be an equipotential and an isovel; an envelope of both families of characteristics; and the locus of cusps of the streamlines and the isoclines. Flows containing sonic limit lines may be constructed by forming suitable linear combinations of the Chaplygin product solutions for any value of the separation constant n ≥ 0. For n less than a certain value n0 and greater than zero (n = 0 corresponds to the well-known radial flow), these flows represent a compressible analogue of the incompressible corner flows and may be envisaged as taking place on a quadruply-sheeted surface. The sheets are joined at a super-sonic limit line and at the sonic limit line which has the shape of a hypocycloid (n >1), cycloid (n = 1), or epicycloid (n <1). To exemplify the general behavior, the flows are constructed explicitly for n = 1/2, 1, and 2. The shape of the sonic limit line is also discussed when solutions corresponding to different n are superposed, and it is shown how then the supersonic limit line can be eliminated so that an isolated sonic limit line is obtained. A flow containing such an isolated sonic limit line is presented. An appendix derives the asymptotic solution for large values of n which corresponds to the sonic limit solution. The above results have been published in part in Math. Zeitschr., 67, (1957), 229-237. Other portions of this thesis will appear in two papers in Archive Rational Mech. and Anal., 2, (1958).
A COMBINATORIAL REPRESENTATION FOR ORIENTED POLYHEDRAL SURFACES
(1960) Edmonds, John Robert Jr; Reinhart, Bruce; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Completions
(1964) Nielsen, Robert Maurice; Brace, John W.; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This paper presents a new approach to the theory of completions. The treatment is based on the concept of convergence on filters and related topologies. For a given uniform Hausdorff space Xu and a collection S of Cauchy filters in Xu, the basic result is the construction of a uniform Hausdorff space. Xu having the properties that Xu is isomorphic to a dense subspace of Xu and every filter in S converges to a point in S. As a special case, the completion of Xu of Xu is obtained. The construction is so given as to prove the existence of the space Xu. The technique involves embedding the object X to be "completed" in a space of functions F which has as its domain a space of continuous functions C(X) defined on X. The procedure is analogous to the process of taking the bidual E" of a locally convex topological vector space. Indeed, E" is obtained as a special case. In the absence of sufficient structure on X, the Xu is obtained as the closure of X in F. In a locally convex space or an abelian topological group having enough character to separate points, Xu is obtained as a bidual or a second character group of the object X.
The Axiom of Choice for Collections of Finite Sets
(1969) Gauntt, Robert James; Karp, Carol R.; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Some implications among finite versions of the Axiom of Choice are considered. In the first of two chapters some theorems are proven concerning the dependence or independence of these implications on the theory ZFU, the modification of ZF which permits the existence of atoms. The second chapter outlines proofs of corresponding theorems with "ZFU" replaced by "ZF" . The independence proofs involve Mostowski type permutation models in the first chapter and Cohen forcing in the second chapter. The finite axioms considered are C^n , "Every collection of n-element sets has a choice function"; W^n, "Every well-orderable collection of n-element sets has a choice function"; D^n, "Every denumerable collection of n-element sets has a choice function"; and A^n (x), "Every collection Y of n-element sets, with Y ≈ X, has a choice function". The conjunction C^nl &...& C^nk is denoted by CZ where Z = {nl ,...,nk}. Corresponding conjunctions of other finite axioms are denoted similarly by Wz, Dz and Az (X). Theorem: The following are provable in ZFU: W^k1n1+...+krnr ➔ W^n1 v...v W^nr, D^k1n1+...+krnr ➔ D^n1 v...v D^nr, and C^k1n1+...+krnr ➔ C^n1 v W^n2 v...v W^nr
Submaximal Function Algebras
(1971) Van Meter, Garrett Oliver II; Gulick, Denny; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
Let X be a compact Hausdorff space. A function algebra on X is a complex Banach subalgebra of C(X) which separates the points of X and contains the constants. Moreover, a function algebra on X is maximal if it is contained properly in no proper subalgebra of C(X). We mention that maximal function algebras are large enough to have a goodly amount of structure. In order that we be able to state the ideas and results simply let us assume that for each algebra A the underlying space X is so adjusted that A contains no non-trivial ideals of C(X). Generally if A is a maximal function algebra on X, then the topological dimension of X is at most one. The idea of this thesis is to extend the notion of maximal function algebra so that on the one hand features of maximal algebras would be retained, while on the other hand the topological dimension of the underlying space could be forced to be arbitrarily large. Thus our introduction of the notion of submaximal function algebra. We prove that all maximal algebras are submaximal. A submaximal, non-maximal algebra is A(Tn), the completion of the polynomials in n-complex variables on the unit n-torus in Cn. However, if A is submaximal on X, then each proper function algebra between A and C(X) is contained in a proper maximal function algebra on X. Moreover, we show by example that the converse to this last statement is false. If A is a submaximal function algebra on X, then every point in X has a compact neighborhood in X such that the algebra of restrictions of functions in A is dense in the continuous functions on the neighborhood. This is the (natural) analogue of the "pervasive" property of maximal function algebras. It turns out that maximal function algebras are antisymmetric, which means that they contain no non-constant real-valued functions. This is not true in general for submaximal function algebras. However, if we render the antisymmetric property in the following way, then it holds true for submaximal algebras: if the real-valued continuous functions f1,...,fn on X along with A together generate a dense subalgebra of C(X), then the continuous real-valued functions h1,...,hn on X and A together generate a dense subalgebra of C(X), provided only that each hj is sufficiently close to fj. In addition, we show that if A is submaximal on X, then there are always exist finitely many real-valued continuous functions on X which together with A generate a dense subalgebra of C(X). Finally we discuss tensor products of submaximal algebras. In particular, we prove that under certain restrictions, the tensor product of two submaximal algebras is submaximal.
Elementary Hadamard Difference Sets
(1974) Dillon, John F.; Owings, James C. Jr.; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
This paper is primarily a study of difference sets in elementary abelian 2-groups. It is, however, somewhat wider in scope and includes an exposition of the fundamental notions relating to the more general topics of difference sets and the Fourier analysis of Boolean functions.
Regular homomorphisms of minimal sets
(1974) Shoenfeld, Peter; Auslander, Joseph
The classification of minimal sets is a central theme in abstract topological dynamics. Recently this work has been strengthened and extended by consideration of homomorphisms. Background material is presented in Chapter I. Given a flow on a compact Hausdorff space, the action extends naturally to the space of closed subsets, taken with the Hausdorff topology. These hyperspaces are discussed and used to give a new characterization of almost periodic homomorphisms. Regular minimal sets may be described as minimal subsets of enveloping semigroups. Regular homomorphisms are defined in Chapter II by extending this notion to homomorphisms with minimal range. Several characterizations are obtained. In Chapter III, some additional results on homomorphisms are obtained by relativizing enveloping semigroup notions. In Veech's paper on point distal flows, hyperspaces are used to associate an almost one-to-one homomorphism with a given homomorphism of metric minimal sets. In Chapter IV, a non-metric generalization of this construction is studied in detail using the new notion of a highly proximal homomorphism. An abstract characterization is obtained, involving only the abstract properties of homomorphisms. A strengthened version of the Veech Structure Theorem for point distal flows is proved. In Chapter V, the work in the earlier chapters is applied to the study of homomorphisms for which the almost periodic elements of the associated hyperspace are all finite. In the metric case, this is equivalent to having at least one fiber finite. Strong results are obtained by first assuming regularity, and then assuming that the relative proximal relation is closed as well.
Scheme-independent stability criteria for difference approximations of hyperbolic initial-boundary value problems.
(American Mathematical Society, 1978-10) Goldberg, Moshe; Tadmor, Eitan
Scheme-independent stability criteria for difference approximations of hyperbolic initial-boundary value problems. II
(American Mathematical Society, 1981-04) Goldberg, Moshe; Tadmor, Eitan
The unconditional instability of inflow-dependent boundary conditions in difference approximations to hyperbolic systems
(American Mathematical Society, 1983-10) Tadmor, Eitan
The large-time behavior of the scalar, genuinely nonlinear Lax-Friedrichs scheme
(American Mathematical Society, 1984-10) Tadmor, Eitan
Numerical viscosity and the entropy condition for conservative difference schemes
(American Mathamatical Society, 1984-10) Tadmor, Eitan
Convenient stability criteria for difference approximations of hyperbolic initial-boundary value problems
(American Mathematical Society, 1985-04) Goldberg, Moshe; Tadmor, Eitan
THE WELL-POSEDNESS OF THE KURAMOTO-SIVASHINSKY EQUATION
(copyright: Society for Industrial and Applied Mathematics, 1986-07) Tadmor, Eitan
The Kuramoto-Sivashinsky equation arises in a variety of applications, among which are modeling reaction-diffusion systems, flame-propagation and viscous flow problems. It is considered here, as a prototype to the larger class of generalized Burgers equations: those consist of quadratic nonlinearity and arbitrary linear parabolic part. We show that such equations are well-posed, thus admitting a unique smooth solution, continuously dependent on its initial data. As an attractive alternative to standard energy methods, existence and stability are derived in this case, by "patching" in the large short time solutions without "loss of derivatives".
Stability analysis of spectral methods for hyperbolic initial-boundary value systems
(Copyright: Society for Industrial and Applied Mathematics, 1987-04) Gottlieb, David; Lustman, Liviu; Tadmor, Eitan
Convenient stability criteria for difference approximations of hyperbolic initial-boundary value problems. II
(American Mathematical Society, 1987-04) Goldberg, Moshe; Tadmor, Eitan
Convergence of spectral methods for hyperbolic initial-boundary value systems
(Copyright: Society for Industrial and Applied Mathematics, 1987-06) Gottlieb, David; Lustman, Liviu; Tadmor, Eitan
Convergence of spectral methods for hyperbolic initial-boundary value systems
(Copyright: Society for Industrial and Applied Mathematics, 1987-06) Gottlieb, David; Lustman, Liviu; Tadmor, Eitan
The numerical viscosity of entropy stable schemes for systems of conservation laws. I.
(American Mathematical Society, 1987-07) Tadmor, Eitan

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