bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compactifications of locally compact groups and quotients
Authors: Lau A. T. , Milnes P. , Pym J. S. 
Published: November 2008

AbstractLetNbe a compact normal subgroup of a locally compact groupG. One of our goals here is to determine when and how a given compactificationYofG/Ncan be realized as a quotient of the analogous compactification (ψ,X) ofGbyNψ= ψ(N) ⊂X; this is achieved in a number of cases for which we can establish that μNψ⊂Nψμ for all μ ∈XA question arises naturally, ‘Can the latter containment be proper?’ With an example, we give a positive answer to this question.The groupGis an extension ofNbyGNand can be identified algebraically withNx GNwhen this product is given the Schreier multiplication, and for our further results we assume that we can also identify G topologically withN x GN. WhenGNis discrete andXis the compactification ofGcoming from the left uniformly continuous functions, we are able to show thatXis an extension ofNby(GN)(X≅N x (G/N))even when G is not a semidirect product. Examples are given to illustrate the theory, and also to show its limitations.
On contractions with spectrum contained in the Cantor set
Authors: Esterle J. , Zarrabi M. , Rajoelina M. 
Published: November 2008

AbstractFor ξ ε (0, ½) let Eξ be the perfect symmetric set of constant ratio ξ and setIt was shown by the first author that if T is a contraction on the Hilbert space H with spectrum contained in Eξ, and if log ∥T−n∥ = O(nα) as n → ∞ for some α < b(ξ), then T is unitary. In the other direction, we show here that there exists a (non-unitary) contraction T on H such that SpT = Eξ, log ∥T-n∥ = O(nb(ξ)) as n → ∞, and lim supn → ∞ ∥T−n∥ = ∞.
Differential spaces of finite type
Authors: Gonzalez Juan A. Navarro 
Published: November 2008

AbstractThis paper shows that the localization theory for algebras of smooth functions and Fréchet modules provides a basis for a theory of differential spaces of finite type, as well as the usual localization theory for commutative rings and modules grounds the theory of schemes. Moreover, most of the elementary results and proofs in the theory of schemes remain valid for differential spaces.
The Askey–Wilson polynomials and q-Sturm–Liouville problems
Authors: Brown B. Malcolm , Evans W. Desmond , Ismail Mourad E. H. 
Published: November 2008

AbstractWe find the adjoint of the Askey–Wilson divided difference operator with respect to the inner product on L2(–1, 1, (1– x2)½dx) defined as a Cauchy principal value and show that the Askey-Wilson polynomials are solutions of a q-Sturm–Liouville problem. From these facts we deduce various properties of the polynomials in a simple and straightforward way. We also provide an operator theoretic description of the Askey-Wilson operator.
Marked homeomorphisms and the realization problem
Authors: Greenberg Peter 
Published: November 2008

The role played by the classical braid groups in the interplay between geometry, algebra and topology (see [Ca]) derives, in part, from their definition as the fundamental groups of configuration spaces of points in the plane. Seeking to generalize these groups and to understand them better, one is led to ask: are there other discrete groups whose topological invariants arise from configuration spaces?The groups of marked homeomorphisms (1·1) provide a positive response which is in some sense banal; the realization problem (1·5) is to find non-banal examples.
Entanglement complexity of graphs in Z3
Authors: Soteros C. E. , Sumners D. W. , Whittington S. G. 
Published: November 2008

AbstractIn this paper we are concerned with questions about the knottedness of a closed curve of given length embedded in Z3. What is the probability that such a randomly chosen embedding is knotted? What is the probability that the embedding contains a particular knot? What is the expected complexity of the knot? To what extent can these questions also be answered for a graph of a given homeomorphism type?We use a pattern theorem due to Kesten 12 to prove that almost all embeddings in Z3 of a sufficiently long closed curve contain any given knot. We introduce the idea of a good measure of knot complexity. This is a function F which maps the set of equivalence classes of embeddings into 0, ). The F measure of the unknot is zero, and, generally speaking, the more complex the prime knot decomposition of a given knot type, the greater its F measure. We prove that the average value of F diverges to infinity as the length (n) of the embedding goes to infinity, at least linearly in n. One example of a good measure of knot complexity is crossing number.Finally we consider similar questions for embeddings of graphs. We show that for a fixed homeomorphism type, as the number of edges n goes to infinity, almost all embeddings are knotted if the homeomorphism type does not contain a cut edge. We prove a weaker result in the case that the homeomorphism type contains at least one cut edge and at least one cycle.
Oblique reflexion of electromagnetic waves from isotropic media with limiting Epstein-type stratifications
Authors: Westcott B. S. 
Published: November 2008

AbstractAnalytical reflexion coefficients are obtained for horizontally and vertically polarized electromagnetic waves respectively, obliquely incident from below two recently devised models of horizontally stratified isotropic media. It is shown that both models are totally reflecting and the phases of the reflexion coefficients may be expressed in terms of arg Γ(z).
On an eigenfunction expansion associated with a condition of radiation. II
Authors: Naylor D. , Choo F. C. , Barclay D. W. 
Published: November 2008

In this paper the authors consider a problem, frequently encountered in diffraction theory, of expanding a given function f(r) in terms of a set of orthogonal functions which is not complete. The expansion in question can be written aswhere r < a and
Encapsulating non-determinacy in an abstract data type with determinate semantics
Authors: Burton F. Warren 
Published: November 2008

AbstractA parallel program may be indeterminate so that it can adapt its behavior to the number of processors available.Indeterminate programs are hard to write, understand, modify or verify. They are impossible to debug, since they may not behave the same from one run to the next.We propose a new construct, a polymorphic abstract data type called an improving value, with operations that have indeterminate behavior but simple determinate semantics. These operations allow the type of indeterminate behavior required by many parallel algorithms.We define improving values in the context of a functional programming language, but the technique can be used in procedural programs as well.
Tail recursion without space leaks
Authors: Jones Richard 
Published: November 2008

AbstractThe G-machine (Johnsson, 1987; Peyton Jones, 1987) is a compiled graph reduction machine for lazy functional languages. The G-machine compiler contains many optimizations to improve performance. One set of such optimizations is designed to improve the performance of tail recursive functions. Unfortunately, the abstract machine is subject to a space leak—objects are unnecessarily preserved by the garbage collector. This paper analyses why a particular form of space leak occurs in the G-machine, and presents some ideas for fixing this problem. This phenomena in other abstract machines is also examined briefly.
Computing with lattices: An application of type classes
Authors: Jones Mark P. 
Published: November 2008

AbstractThis paper presents a simple framework for performing calculations with the elements of (finite) lattices. A particular feature of this work is the use of type classes to enable the use of overloaded function symbols within a strongly typed language. Previous applications of type classes have been in areas that are of most interest to language implementors. This paper suggests that type classes might also be useful as a general tool in the development of clear and modular programs.
Partially strict non-recursive data types
Authors: Nöcker Eric , Smetsers Sjaak 
Published: November 2008

AbstractValues belonging to lazy data types have the advantage that sub-components can be accessed without evaluating the values as a whole: unneeded components remain unevaluated. A disadvantage is that often a large amount of space and time is required to handle lazy data types properly. Many special constructor cells are needed to ‘glue’ the individual parts of a composite object together and to store it in the heap. We present a way of representing data in functional languages which makes these special constructor cells superfluous. In some cases, no heap at all is needed to store this data. To make this possible, we introduce a new kind of data type: (partially) strict non-recursive data types. The main advantage of these types is that an efficient call-by-value mechanism can be used to pass arguments. A restrictive subclass of (partially) strict non-recursive data types, partially strict tuples, is treated more comprehensively. We also give examples of important classes of applications. In particular, we show how partially strict tuples can be used to define very efficient input and output primitives. Measurements of applications written in Concurrent Clean which exploit partially strict tuples have shown that speedups of 2 to 3 times are reasonable. Moreover, much less heap space is required when partially strict tuples are used.
Program transformation with metasystem transitions
Authors: Turchin Valentin F. 
Published: November 2008

AbstractA new program transformation method is presented. It is a further refinement of supercompilation where the supercompiler is not applied directly to the function to be transformed, but to a metafunction, namely an interpreter which computes this function using its definition and an abstract (i.e. including variables) input. It is shown that with this method such tranformations become possible which the direct application of the supercompiler cannot perform. Examples include the merging of iterative loops, function inversion, and transformation of deterministic into non-deterministic algorithms, and vice-versa.
Efficient analyses for realistic off-line partial evaluation
Authors: Bondorf Anders , Jørgensen Jesper 
Published: November 2008

AbstractBased on Henglein's efficient binding-time analysis for the lambda calculus (with constants and ‘fix’) (Henglein, 1991), we develop three efficient analyses for use in the preprocessing phase of Similix, a self-applicable partial evaluator for a higher-order subset of Scheme. The analyses developed in this paper are almost-linear in the size of the analysed program. (1) A flow analysis determines possible value flow between lambda-abstractions and function applications and between constructor applications and selector/predicate applications. The flow analysis is not particularly biased towards partial evaluation; the analysis corresponds to the closure analysis of Bondorf (1991b). (2) A (monovariant) binding-time analysis distinguishes static from dynamic values; the analysis treats both higher-order functions and partially static data structures. (3) A new is-used analysis, not present in Bondorf (1991b), finds a non-minimal binding-time annotation which is ‘safe’ in a certain way: a first-order value may only become static if its result is ‘needed’ during specialization; this ‘poor man's generalization’ (Holst, 1988) increases termination of specialization. The three analyses are performed sequentially in the above mentioned order since each depends on results from the previous analyses. The input to all three analyses are constraint sets generated from the program being analysed. The constraints are solved efficiently by a normalizing union/find-based algorithm in almost-linear time. Whenever possible, the constraint sets are partitioned into subsets which are solved in a specific order; this simplifies constraint normalization. The framework elegantly allows expressing both forwards and backwards components of analyses. In particular, the new is-used analysis is of backwards nature. The three constraint normalization algorithms are proved correct (soundness, completeness, termination, existence of a best solution). The analyses have been implemented and integrated in the Similix system. The new analyses are indeed much more efficient than those of Bondorf (1991b); the almost-linear complexity of the new analyses is confirmed by the implementation.
Specifying the correctness of binding-time analysis
Authors: Wand Mitchell 
Published: November 2008

AbstractMogensen has exhibited a very compact partial evaluator for the pure lambda calculus, using binding-time analysis followed by specialization. We give a correctness criterion for this partial evaluator and prove its correctness relative to this specification. We show that the conventional properties of partial evaluators, such as the Futamura projections, are consequences of this specification. By considering both a flow analysis and the transformation it justifies together, this proof suggests a framework for incorporating flow analyses into verified compilers.
A-translation and looping combinators in pure type systems
Authors: Coquand Thierry , Herbelin Hugo 
Published: November 2008

AbstractWe present here a generalization of A-translation to a class of pure type systems. We apply this translation to give a direct proof of the existence of a looping combinator in a large class of inconsistent type systems, a class which includes type systems with a type of all types. This is the first non-automated solution to this problem.
Lilac: a functional programming language based on linear logic
Authors: Mackie Ian 
Published: November 2008

AbstractWe take Abramsky's term assignment for Intuitionistic Linear Logic (the linear term calculus) as the basis of a functional programming language. This is a language where the programmer must embed explicitly the resource and control information of an algorithm. We give a type reconstruction algorithm for our language in the style of Milner's W algorithm, together with a description of the implementation and examples of use.
Lexical profiling: theory and practice
Authors: Clack Chris , Clayman Stuart , Parrott David 
Published: November 2008

AbstractThis paper addresses the issue of analysing the run-time behaviour of lazy, higher-order functional programs. We examine the difference between the way that functional programmers and functional language implementors view program behaviour. Existing profiling techniques are discussed and a new technique is proposed which produces results that are straightforward for programmers to assimilate. The new technique, which we call lexical profiling, collects information about the run-time behaviour of functional programs, and reports the results with respect to the original source code rather than simply listing the actions performed at run-time. Lexical profiling complements implementation-specific profiling and is important because it provides a view of program activity which is largely independent of the underlying evaluation mechanism. Using the lexical profiler, programmers may easily relate results back to the source program. We give a full implementation of the lexical profiling technique for a sequential, interpretive graph reduction engine, and extensions for compiled and parallel graph reduction are discussed.
Weak polymorphism can be sound
Authors: Greiner John 
Published: November 2008

AbstractThe weak polymorphic type system of Standard ML of New Jersey (SML/NJ) (MacQueen, 1992) has only been presented as part of the implementation of the SML/NJ compiler, not as a formal type system. As a result, it is not well understood. And while numerous versions of the implementation have been shown unsound, the concept has not been proved sound or unsound. We present an explanation of weak polymorphism and show that a formalization of this is sound. We also relate this to the SML/NJ implementation of weak polymorphism through a series of type systems that incorporate elements of the SML/NJ type inference algorithm.
Canonical typing and ∏-conversion in the Barendregt Cube
Authors: Kamareddine Fairouz , Nederpelt Rob 
Published: November 2008

AbstractIn this article, we extend the Barendregt Cube with ∏-conversion (which is the analogue of β-conversion, on product type level) and study its properties. We use this extension to separate the problem of whether a term is typable from the problem of what is the type of a term.
Benchmarking implementations of functional languages with ‘Pseudoknot’, a float-intensive benchmark
Authors: Hartel Pieter H. , Feeley Marc , Alt Martin , Augustsson Lennart , Baumann Peter , Beemster Marcel , Chailloux Emmanuel , Flood Christine H. , Grieskamp Wolfgang , Van Groningen John H. G. , Hammond Kevin , Hausman Bogumil , Ivory Melody Y. , Jones Richard E. , Kamperman Jasper , Lee Peter , Leroy Xavier , Lins Rafael D. , Loosemore Sandra , Röjemo Niklas , Serrano Manuel , Talpin Jean-Pierre , Thackray Jon , Thomas Stephen , Walters Pum , Weis Pierre , Wentworth Peter 
Published: November 2008

AbstractOver 25 implementations of different functional languages are benchmarked using the same program, a floating-point intensive application taken from molecular biology. The principal aspects studied are compile time and execution time for the various implementations that were benchmarked. An important consideration is how the program can be modified and tuned to obtain maximal performance on each language implementation. With few exceptions, the compilers take a significant amount of time to compile this program, though most compilers were faster than the then current GNU C compiler (GCC version 2.5.8). Compilers that generate C or Lisp are often slower than those that generate native code directly: the cost of compiling the intermediate form is normally a large fraction of the total compilation time. There is no clear distinction between the runtime performance of eager and lazy implementations when appropriate annotations are used: lazy implementations have clearly come of age when it comes to implementing largely strict applications, such as the Pseudoknot program. The speed of C can be approached by some implementations, but to achieve this performance, special measures such as strictness annotations are required by non-strict implementations. The benchmark results have to be interpreted with care. Firstly, a benchmark based on a single program cannot cover a wide spectrum of ‘typical’ applications. Secondly, the compilers vary in the kind and level of optimisations offered, so the effort required to obtain an optimal version of the program is similarly varied.
Introduction to Adaptive Methods for Differential Equations
Authors: Eriksson Kenneth , Estep Don , Hansbo Peter , Johnson Claes 
Published: November 2008

Knowing thus the Algorithm of this calculus, which I call Differential Calculus, all differential equations can be solved by a common method (Gottfried Wilhelm von Leibniz, 1646–1719).When, several years ago, I saw for the first time an instrument which, when carried, automatically records the number of steps taken by a pedestrian, it occurred to me at once that the entire arithmetic could be subjected to a similar kind of machinery so that not only addition and subtraction, but also multiplication and division, could be accomplished by a suitably arranged machine easily, promptly and with sure results…. For it is unworthy of excellent men to lose hours like slaves in the labour of calculations, which could safely be left to anyone else if the machine was used…. And now that we may give final praise to the machine, we may say that it will be desirable to all who are engaged in computations which, as is well known, are the managers of financial affairs, the administrators of others estates, merchants, surveyors, navigators, astronomers, and those connected with any of the crafts that use mathematics (Leibniz).
Numerical Solutions to Free Boundary Problems
Authors: Hou Thomas Y. 
Published: November 2008

Many physically interesting problems involve propagation of free surfaces. Vortex-sheet roll-up in hydrodynamic instability, wave interactions on the ocean's free surface, the solidification problem for crystal growth and Hele-Shaw cells for pattern formation are some of the significant examples. These problems present a great challenge to physicists and applied mathematicians because the underlying problem is very singular. The physical solution is sensitive to small perturbations. Naïve discretisations may lead to numerical instabilities. Other numerical difficulties include singularity formation and possible change of topology in the moving free surfaces, and the severe time-stepping stability constraint due to the stiffness of high-order regularisation effects, such as surface tension.This paper reviews some of the recent advances in developing stable and efficient numerical algorithms for solving free boundary-value problems arising from fluid dynamics and materials science. In particular, we will consider boundary integral methods and the level-set approach for water waves, general multi-fluid interfaces, Hele–Shaw cells, crystal growth and solidification. We will also consider the stabilising effect of surface tension and curvature regularisation. The issue of numerical stability and convergence will be discussed, and the related theoretical results for the continuum equations will be addressed. This paper is not intended to be a detailed survey and the discussion is limited by both the taste and expertise of the author.
HOWWAS RACE CONSTRUCTED IN THE NEW SOUTH?
Authors: Steedman Marek D. 
Published: November 2008

AbstractThis article focuses on the construction and reconfiguration of race in the U.S. South during the late nineteenth and early twentieth centuries. Much literature on race is designed to show that race is socially constructed, with the inference that race ismerelya social construction. Thus, talk about race, which is not demonstrably grounded in human biology, must be akin to talk about unicorns. But so what? Does race being a social construction make any difference to the historical accounts we give of how racial practices work? This article suggests that it can if we focus on the process of construction itself, in a particular time and place, and askhowrace was socially constructed. I trace how race was made, unmade, and remade in the years between 1865 and 1920. During the postemancipation era, Southern White elites constructed race as and through naturalized relations of dependence and independence. This construction was held in place and then undermined by the prevailing social order. I offer an account of the sharp increase in racist practices at the turn of the century, focused on the notion ofmobility. I show how, in the decades since the war, mobility undermined race as it had been socially constructed.
Quantitative Evaluation of the Effects of Gravity and Dependency on Microvascular Tissue Transfer to the Lower Limb, with Clinical Applications
Authors: Isenberg Jeffrey Scott , Siegal Ann , Sherman Randolph 
Published: November 2008

Accepted for publication June 15 1996The authors have attempted quantitatively to evaluate the effects of gravity and dependency on free-tissue transfers to the lower limb, particularly in the immediate postoperative period, using the diagnostic modalities of Doppler ultrasonography and interstitial compartment pressure measurements. Results of these quantitative evaluations promoted a change in postoperative management among patients undergoing lower-limb tissue transfer. The experience in two patient cohorts is presented.