bluuebunny/crossref_metadata_2025 huggingface dataset:
On Hausdorff and packing dimension of product spaces
Authors: Howroyd J. D.
Published: November 2008

We show that for arbitrary metric spaces X and Y the following dimension inequalities hold:

where ‘dim’ denotes Hausdorff dimension and ‘Dim’ denotes packing dimension. The main idea of the proof is to use modified constructions of the Hausdorff and packing measure to deduce appropriate inequalities for the measure of X × Y.
Beurling's projection theorem via one-dimensional Brownian motion
Authors: Werner Wendelin
Published: November 2008

We prove some elementary intuitive estimates on moving boundaries hitting times by one-dimensional Brownian motion (in ℝ and on the circle). These results give an alternative approach to Beurling's radial projection theorem on harmonic measure in a disc.
On a class of aperiodic sum-free sets
Authors: Calkin Neil J. , Erdós Paul
Published: November 2008

We show that certain natural aperiodic sum-free sets are incomplete, that is that there are infinitely many n not in S which are not a sum of two elements of S.
Hyperkähler metrics associated to compact Lie groups
Authors: Dancer Andrew , Swann Andrew
Published: November 2008

It is well known that the cotangent bundle of any manifold has a canonical symplectic structure. If we specialize to the case when the manifold is a compact Lie group G, then this structure is preserved by the actions of G on T*G induced by left and right translation on G. We refer to these as the left and right actions of G on T*G.
Configurations of 2-spheres in the K3 surface and other 4-manifolds
Authors: Ruberman Daniel
Published: November 2008

A current theme in the theory of 4-manifolds is the study of which properties of complex surface are determined the underlying smooth 4-manifold. For instance, the genus of a complex curve in a complex surface is determined by its homology class, via the adjunction formula. Recent work in gauge theory [10–12] has shown that, to a great degree, a similar principal holds for an arbitrary (i.e. not necessarily complex) smooth representative of a 2-dimensional homology class. Another question, still unsolved even in the context of algebraic geometry, is to find the number of disjoint rational curves on a complex surface. The classical case, namely that of hypersurfaces in CP3, has only been settled for degrees d ≤ 6. The papers [1, 2, 4, 8, 14, 15] contain bounds on the number of such curves and constructions of surfaces with many ( — 2)-curves; the last two together establish that 65 is the correct bound in degree 6.
Derivations mapping into the socle
Authors: Brešar Matej , Šemrl Peter
Published: November 2008

Over the last few years a number of results giving conditions on a derivation of a Banach algebra implying that its range is contained in the radical have been obtained (see survey articles of Mathieu[7] and Murphy [8]). If an algebra is semi-simple, these conditions, of course, imply that a derivation is zero. In this paper we consider inner derivations that are non-zero in general, but their ranges are rather special and ‘small’ in some sense.
Representations of the spaces Cm(Ω) ∩ Hk, p (Ω)
Authors: Albanese A. A. , Metafune G. , Moscatelli V. B.
Published: November 2008

The present work has its motivation in the papers [2] and [6] on distinguished Fréchet function spaces. Recall that a Fréchet space E is distinguished if it is the projective limit of a sequence of Banach spaces En such that the strong dual E′β is the inductive limit of the sequence of the duals E′n. Clearly, the property of being distinguished is inherited by complemented subspaces and in [6] Taskinen proved that the Fréchet function space C(R) ∩ L1(R) (intersection topology) is not distinguished, by showing that it contains a complemented subspace of Moscatelli type (see Section 1) that is not distinguished. Because of the criterion in [1], it is easy to decide when a Frechet space of Moscatelli type is distinguished. Using this, in [2], Bonet and Taskinen obtained that the spaces open in RN) are distinguished, by proving that they are isomorphic to complemented subspaces of distinguished Fréchet spaces of Moscatelli type.
Geometric properties of Köthe–Bochner spaces
Authors: Cerdà Joan , Hudzik Henryk , Mastyło Mieczysław
Published: November 2008

Convexity, monotonicity and smoothness properties of Köthe spaces of vector-valued functions are described.
The local model of an isotropic map-germ arising from one-dimensional symplectic reduction
Authors: Ishikawa Goo
Published: November 2008

In this paper, we classify generic isotropic map-germs arising from the symplectic reduction process relative to a hypersurface (i.e. one-dimensional reduction), up to symplectic equivalence in the C category. These models are open Whitney umbrellas of arbitrary dimension and their suspensions. These singularities appear in the generalized Cauchy problem for HamiltonJacobi equations.
On the structure of generalized Albanese varieties
Authors: nsiper Hurit
Published: November 2008

Given a smooth projective surface X over an algebraically closed field k and a modulus (an effective divisor) m on X, one defines the idle class group Cm(X) of X with modulus m (see 1, chapter III, section 4). The corresponding generalized Albanese variety Gum and the generalized Albanese map um:X|m|Gum have the following universal mapping property (2): if :XG is a rational map into a commutative algebraic group which induces a homomorphism Cm(X)G(k) (1, chapter III, proposition 1), then factors uniquely through um.
The characterization of orders for regular functions
Authors: Linden C. N.
Published: November 2008

For a given function f, regular in the unit disk D(0, 1), logarithmic means of order p may be defined in terms of integrals by the formulae

for 0 < p < , and by

when 0 < r < 1. Associated p-orders are subsequently defined by

for 0 < p .
Ends of graphs. II
Authors: Möllert Rögnvaldur G.
Published: November 2008

This paper deals with locally finite connected graphs with infinitely many ends. The structure of such graphs with a transitive group of automorphisms that fixes an end is investigated.
Some remarks on the restriction of the Fourier transform to surfaces
Authors: Drury S. W. , Guo K.
Published: November 2008

For a class of kernels, we prove the Lp estimate for the exotic Riesz potential, with which a restriction theorem of the Fourier transform to surfaces of half the ambient dimension is proved. A simpler proof of Barcelo's result is given. We also find that it is possible to combine the Hausdorff–Young theorem with the Fefferman–Zygmund method to prove some optimal results on the restriction theorem.
L2 estimates for convolution operators with oscillating kernels
Authors: Pan Yibiao
Published: November 2008

Consider the operator

where , and K is smooth away from the origin and homogeneous of degree —μ, for some μ ≥ 0. The following theorem was proved in [4].
Infinite loop spaces with trivial Dyer-Lashof operations
Authors: Slack Michael
Published: November 2008

Letpbe any prime. It is well known that the modp Dyer-Lashof algebra acts trivially on the modphomology of an Eilenberg-MacLane space. The main result of this paper is a converse of this fact. Specifically, it is shown that any connected infinite loop space with trivial action of the modpDyer-Lashof algebra is (localized atp) homotopy equivalent to a product of Eilenberg-MacLane spaces. It is then shown that this equivalence does not necessarily respect the infinite loop structures involved.
Diophantine approximation and Hausdorff dimension in Fuchsian groups
Authors: Velani S. L.
Published: November 2008

The Poincaré disc model

of two-dimensional hyperbolic space supports a metric ρ derived from the differential

Geodesics for the metric ρ are arcs of circles orthogonal to the unit circle S, and straight lines through the origin.
Poincaré and Friedrichs inequalities in abstract Sobolev spaces
Authors: Edmunds D. E. , Opic B. , Pick L.
Published: November 2008

Given any domain Ω in ℝNwe consider spacesX = X(Ω),Y = Y(Ω) which are Banach function spaces in the sense of Luxemburg [12]. From these we form what we call the abstract Sobolev spaceW(X, Y), which is denned to be the linear space of allƒ ∈ Xsuch that fori= 1, …,N, the distributional derivative ∂ƒ/∂xibelongs toY; equipped with the norm

W(X, Y)is a Banach space. The closure of(Ω) inW(X, Y)is denoted byW0(X, Y). Letwto bea weight function on Ω, that is, a measurable function which is positive and finite almost everywhere on Ω. We say that [w, X, Y] supports the (weighted) Poincaré inequality if there is a positive constantKsuch that for allu ∈ W(X, Y),

analogously, [X, Y] is said to support the Friedrichs inequality if there is a positive constant K such that for allu ∈ W0(X, Y),
The Brauer group of cubic surfaces
Authors: Swinnerton-Dyer Sir Peter
Published: November 2008

1. Let V be a non-singular rational surface defined over an algebraic number field k. There is a standard conjecture that the only obstructions to the Hasse principle and to weak approximation on V are the Brauer–Manin obstructions. A prerequisite for calculating these is a knowledge of the Brauer group of V; indeed there is one such obstruction, which may however be trivial, corresponding to each element of Br V/Br k. Because k is an algebraic number field, the natural injection

is an isomorphism; so the first step in calculating the Brauer–Manin obstruction is to calculate the finite group H1 (k), Pic .
The Hopf invariant and homotopy groups of spheres
Authors: Hilton P. J.
Published: November 2008

In (5), Whitehead introduced a generalization of the Hopfinvariant in the form of a homomorphism H: πr(Sn) → πr(S2n−1), valid† if r < 3n − 3. In (2), the author extended Whitehead's definition to cover the cases r ≤ 4n − 4; r = 5, n = 2; r = 13, n = 4. He also defined, without restriction, a homomorphism

which was related to H, whenever H was defined, by the equation H* = FH, F being the Freudenthal suspension
Large-sample theory of sequential estimation
Authors: Anscombe F. J.
Published: November 2008

In a previous large-sample treatment of sequential estimation (1), it was shown that in certain circumstances, when there was only one unknown parameter in the distribution of the observations, an estimation formula valid for fixed sample sizes remained valid when the sample size was determined by a sequential stopping rule. The proof was heuristic, in that it depended on an application of the central limit theorem of which the justification was not obvious. Another proof has recently been given by Cox (2) (in the course of deriving a correction term to my result). Dr Cox pointed out to me that this work suggested that fixed-sample-size formulae might be valid generally for sequential sampling, provided the sample size was large. In establishing a proposition to that effect, I have now been able to by-pass some of the complexity of my previous approach by concentrating attention on a condition of ‘uniform continuity in probability’ to be satisfied by the statistic used. Theorem 1 is the basic result, which is applied in Theorem 2 to determine a sequential stopping rule giving required accuracy of estimation of an unknown parameter. Theorems 3–6 indicate some situations in which the uniform continuity condition postulated in Theorems 1 and 2 is satisfied. A few examples are discussed.
The three-dimensional inverse scattering problem for the Helmholtz equation
Authors: Sleeman B. D.
Published: November 2008

In this paper we are concerned with solutions of the three-dimensional Helmholtz equation which are of class C2 (i.e. regular) in the exterior of a bounded domain D. In cylindrical polar coordinates (r, z, φ) such solutions satisfy the equation

in which we have dimensionalized the radial coordinate r so that the wave number is normalized to unity. If we further assume that u satisfies the Sommerfeld radiation condition

then u may be regarded as being generated by volume sources, surface sources, or point singularities, all of which are contained in D.
Note on a Theorem of Myrberg
Authors: Gillis J.
Published: November 2008

1. Prof. Fekete, in a letter to the author, wrote: “…Satz von Myrberg über den Zusammenhang zwischen dem transfiniten Durchmesser und dem logarithmischen Mass zugehörig zum Exponenten 1 + ε, ε > 0 (vgl. Satz 10 in seiner Acta Arbeit).…Ich würde einen elementaren Beweis für den letzteren Satz sehr begrüssen.” The object of this note is to supply such a proof but, since the concepts involved may not all be matters of common knowledge, I shall begin by outlining the necessary definitions, the relevant known results, the nature of the theorem and its relation to what is known.
A study of sparse matrix representations for solving linear systems in a functional language
Authors: Wainwright Roger L. , Sexton Marian E.
Published: November 2008

This paper compares three different sparse matrix representations in Miranda for solving linear systems of equations: quadtrees, binary trees and run-length encoding. It compares the three data structures in each of two common linear system solvers, Conjugate Gradient and SOR. The test problems used in the paper arise from a simple reservoir model.
Implementing lazy functional languages on stock hardware: the Spineless Tagless G-machine
Authors: Jones Simon L. Peyton
Published: November 2008

The Spineless Tagless G-machine is an abstract machine designed to support non-strict higher-order functional languages. This presentation of the machine falls into three parts. Firstly, we give a general discussion of the design issues involved in implementing non-strict functional languages. Next, we present the STG language, an austere but recognizably-functional language, which as well as a denotational meaning has a well-defined operational semantics. The STG language is the ‘abstract machine code’ for the Spineless Tagless G-machine. Lastly, we discuss the mapping of the STG language onto stock hardware. The success of an abstract machine model depends largely on how efficient this mapping can be made, though this topic is often relegated to a short section. Instead, we give a detailed discussion of the design issues and the choices we have made. Our principal target is the C language, treating the C compiler as a portable assembler.
Quantifier elimination and parametric polymorphism in programming languages
Authors: Mairson Harry G.
Published: November 2008

We present a simple and easy-to-understand explanation of ML type inference and parametric polymorphism within the framework of type monomorphism, as in the first order typed lambda calculus. We prove the equivalence of this system with the standard interpretation using type polymorphism, and extend the equivalence to include polymorphic fixpoints. The monomorphic interpretation gives a purely combinatorial understanding of the type inference problem, and is a classic instance of quantifier elimination, as well as an example of Gentzen-style cut elimination in the framework of the Curry-Howard propositions-as-types analogy.
Polymorphic type, region and effect inference
Authors: Talpin Jean-Pierre , Jouvelot Pierre
Published: November 2008

We present a new static system which reconstructs the types, regions and effects of expressions in an implicitly typed functional language that supports imperative operations on reference values. Just as types structurally abstract collections of concrete values, regions represent sets of possibly aliased reference values and effects represent approximations of the imperative behaviour on regions.

We introduce a static semantics for inferring types, regions and effects, and prove that it is consistent with respect to the dynamic semantics of the language. We present a reconstruction algorithm that computes the types and effects of expressions, and assigns regions to reference values. We prove the correctness of the reconstruction algorithm with respect to the static semantics. Finally, we discuss potential applications of our system to automatic stack allocation and parallel code generation.
Special Issue on ML
Authors: Appel Andrew W , Harper Robert
Published: November 2008

The MetaLanguage of the Edinburgh LCF theorem proving system has become a programming language in its own right, popular among a reasonably wide segment of the research community. ML has also become a lingua franca among applied type theorists, as they investigate type systems for the 90's as extensions of the remarkably influential Hindley-Milner type system.
Theoretical Pearl Yet yet a counterexample for λ+SP
Authors: Curien Pierre-Louis , Hardin Thérèse
Published: November 2008

In 1979, Klop (1980), answering a question raised by Mann in 1972, showed that the extension of λ-calculus with subjective pairing is not confluent. We refer to Klop (1980) and Barendregt (1981, revised 1984) for a perspective. The term presented by Klop to provide a counterexample is fairly simple, but the proof of non-confluence, although intuitively quite simple, involves some technical properties. Among others, a suitable standardization result on derivations in the extended system is needed in the proof. Klop's proof was revisited by Bunder (1985), who seemingly used less technical apparatus than Klop, starting with the same term as Klop. Although Bunder's proof does not explicitly use a standardization result, his proof proceeds internally with some rearrangements of derivations, so that it is fair to say that some standardization technique is present in Bunder (1985).
Algorithmic debugging for lazy functional languages
Authors: Nilsson Henrik , Fritzson Peter
Published: November 2008

Lazy functional languages have non-strict semantics and are purely declarative, i.e. they support the notion of referential transparency and are devoid of side-effects. Traditional debugging techniques are, however, not suited for lazy functional languages, since computations generally do not take place in the order one might expect. Sincealgorithmic debuggingallows the user to concentrate on the declarative aspects of program semantics, and will semi-automatically find functions containing bugs, we propose to use this technique for debugging lazy functional programs. Because of the non-strict semantics of lazy functional languages, arguments to functions are in general partially evaluated expressions. The user is, however, usually more concerned with the values that these expressions represent. We address this problem by providing the user with astrictifiedview of the execution trace whenever possible. In this paper, we present an algorithmic debugger for a lazy functional language based on strictification and some experience in using it. A number of problems with the current implementation of the debugger (e.g. too large trace size and too many questions asked) are also discussed and some techniques for overcoming these problems, at least partially, are suggested. The key techniques areimmediate strictificationandpiecemeal tracing.
Simple and efficient purely functional queues and deques
Authors: Okasaki Chris
Published: November 2008

We present purely functional implementations of queues and double-ended queues (deques) requiring only O(1) time per operation in the worst case. Our algorithms are considerably simpler than previous designs with the same bounds. The inspiration for our approach is the incremental behaviour of certain functions on lazy lists.
Type classes with existential types
Authors: Läufer Konstantin
Published: November 2008

We argue that the novel combination of type classes and existential types in a single language yields significant expressive power. We explore this combination in the context of higher-order functional languages with static typing, parametric polymorphism, algebraic data types and Hindley–Milner type inference. Adding existential types to an existing functional language that already features type classes requires only a minor syntactic extension. We first demonstrate how to provide existential quantification over type classes by extending the syntax of algebraic data type definitions, and give examples of possible uses. We then develop a type system and a type inference algorithm for the resulting language. Finally, we present a formal semantics by translation to an implicitly-typed second-order λ-calculus and show that the type system is semantically sound. Our extension has been implemented in the Chalmers Haskell B. system, and all examples from this paper have been developed using this system.
Functional Pearls
Authors: Gibbons Jeremy
Published: November 2008

The Third Homomorphism Theorem is a folk theorem of the constructive algorithmics community. It states that a function on lists that can be computed both from left to right and from right to left is necessarily a list homomorphism – it can be computed according to any parenthesization of the list. We formalize and prove the theorem, and use it to improve an O(n2) sorting algorithm to O(n log n).
Linear stability analysis in the numerical solution of initial value problems
Authors: van Dorsselaer J.L.M. , Kraaijevanger J.F.B.M. , Spijker M.N.
Published: November 2008

This article addresses the general problem of establishing upper bounds for the norms of the nth powers of square matrices. The focus is on upper bounds that grow only moderately (or stay constant) where n, or the order of the matrices, increases. The so-called resolvant condition, occuring in the famous Kreiss matrix theorem, is a classical tool for deriving such bounds.

Recently the classical upper bounds known to be valid under Kreiss's resolvant condition have been improved. Moreover, generalizations of this resolvant condition have been considered so as to widen the range of applications. The main purpose of this article is to review and extend some of these new developments.

The upper bounds for the powers of matrices discussed in this article are intimately connected with the stability analysis of numerical processes for solving initial(-boundary) value problems in ordinary and partial linear differential equations. The article highlights this connection.

The article concludes with numerical illustrations in the solution of a simple initial-boundary value problem for a partial differential equation.
Numerical geometry of surfaces
Authors: Sabin Malcolm
Published: November 2008

The mathematical techniques used within Computer Aided Design software for the representation and calculation of surfaces of objects are described. First the main techniques for dealing with surfaces as computational objects are described, and then the methods for enquiring of such surfaces the properties required for their assessment and manufacture.
Orthogonal polynomials: applications and computation
Authors: Gautschi Walter
Published: November 2008

We give examples of problem areas in interpolation, approximation, and quadrature, that call for orthogonal polynomials not of the classical kind. We then discuss numerical methods of computing the respective Gauss-type quadrature rules and orthogonal polynomials. The basic task is to compute the coefficients in the three-term recurrence relation for the orthogonal polynomials. This can be done by methods relying either on moment information or on discretization procedures. The effect on the recurrence coefficients of multiplying the weight function by a rational function is also discussed. Similar methods are applicable to computing Sobolev orthogonal polynomials, although their recurrence relations are more complicated. The paper concludes with a brief account of available software.
On the computation of crystalline microstructure
Authors: Luskin Mitchell
Published: November 2008

Microstructure is a feature of crystals with multiple symmetry-related energy-minimizing states. Continuum models have been developed explaining microstructure as the mixture of these symmetry-related states on a fine scale to minimize energy. This article is a review of numerical methods and the numerical analysis for the computation of crystalline microstructure.
Lanczos-type solvers for nonsymmetric linear systems of equations
Authors: Gutknecht Martin H.
Published: November 2008

Among the iterative methods for solving large linear systems with a sparse (or, possibly, structured) nonsymmetric matrix, those that are based on the Lanczos process feature short recurrences for the generation of the Krylov space. This means low cost and low memory requirement. This review article introduces the reader not only to the basic forms of the Lanczos process and some of the related theory, but also describes in detail a number of solvers that are based on it, including those that are considered to be the most efficient ones. Possible breakdowns of the algorithms and ways to cure them by look-ahead are also discussed.
Nonlinear approximation
Authors: DeVore Ronald A.
Published: November 2008

This is a survey of nonlinear approximation, especially that part of the subject which is important in numerical computation. Nonlinear approximation means that the approximants do not come from linear spaces but rather from nonlinear manifolds. The central question to be studied is what, if any, are the advantages of nonlinear approximation over the simpler, more established, linear methods. This question is answered by studying the rate of approximation which is the decrease in error versus the number of parameters in the approximant. The number of parameters usually correlates well with computational effort. It is shown that in many settings the rate of nonlinear approximation can be characterized by certain smoothness conditions which are significantly weaker than required in the linear theory. Emphasis in the survey will be placed on approximation by piecewise polynomials and wavelets as well as their numerical implementation. Results on highly nonlinear methods such as optimal basis selection and greedy algorithms (adaptive pursuit) are also given. Applications to image processing, statistical estimation, regularity for PDEs, and adaptive algorithms are discussed.
Computation of pseudospectra
Authors: Trefethen Lloyd N.
Published: November 2008

There is more to the computation of pseudospectra than the obvious algorithm of computing singular value decompositions on a grid and sending the results to a contour plotter. Other methods may be hundreds of times faster. The state of the art is reviewed, with emphasis on methods for dense matrices, and a Matlab code is given.
Mandibular Reconstruction Using Computer-Generated Three-Dimensional Solid Models
Authors: Ueda Koichi , Tajima Sadao , Tanaka Yoshio , Imai Keisuke , Maejima Seiji , Yabu Konosuke , Song Kichol
Published: November 2008

In mandibular reconstruction, it is necessary to know the exact, three-dimensional extent of the mandible and its defect; the bone graft must be the exact size and dimension of the defect, to assure a precise three-dimensional configuration of the mandible. Previously, the bone graft had to be reshaped during the operation by trial and error, often a time-consuming procedure. The operative procedure has been simulated in advance using three-dimensional, solid models, which has shortened the operating time required.
Sehstörungen als Leitsymptome der okulären Migräne
Authors: Pittke E. C.
Published: November 2008

Monokulare Sehstörungen auf der Basis vaskulärer Beeinträchtigungen der peripheren Sehbahn können von Migräne verursacht werden. Eine seltene Variante der komplizierten Migräne stellt die retinale oder okuläre Migräne dar. Zwei Patientinnen mit okulärer Migräne werden vorgestellt und pathophysiologische Beziehungen zu oralen Kontrazeptiva und Schwangerschaft diskutiert.
Solitäre metachrone ipsilaterale Nebennierenmetastase eines Nierenzellkarzinoms 14 Jahre nach Nephrektomie
Authors: Schröder A. , Lampel A. , Golz R. , Thüroff J. W.
Published: November 2008

Bei radikaler Tumornephrektomie mit Entfernung der Nebenniere finden sich nur in 1,9-5,8% Nebennierenmetastasen, so daß die Notwendigkeit einer routinemäßigen Nebennierenentfernung in Frage gestellt wird. Das metachrone Auftreten isolierter Metastasen der kontralateralen Nebenniere ist allerdings so selten, daß sich hieraus auch kein Argument zum Belassen der ipsilateralen Nebenniere ableiten läßt. Wir berichten über den außergewöhnlichen Fall einer isolierten ipsilateralen Nebennierenmetastase, die 14 Jahre nach Tumornephrektomie chirurgisch entfernt wurde.
Microfluidic electromanipulation with capacitive detection for the mechanical analysis of cells
Authors: Ferrier G. A. , Hladio A. N. , Thomson D. J. , Bridges G. E. , Hedayatipoor M. , Olson S. , Freeman M. R.
Published: November 2008

The mechanical behavior of cells offers insight into many aspects of their properties. We propose an approach to the mechanical analysis of cells that uses a combination of electromanipulation for stimulus and capacitance for sensing. To demonstrate this approach, polystyrene spheres and yeast cells flowing in a 25μm×100μm microfluidic channel were detected by a perpendicular pair of gold thin film electrodes in the channel, spaced 25μm apart. The presence of cells was detected by capacitance changes between the gold electrodes. The capacitance sensor was a resonant coaxial radio frequency cavity (2.3GHz) coupled to the electrodes. The presence of yeast cells (Saccharomyces cerevisiae) and polystyrene spheres resulted in capacitance changes of approximately 10 and 100 attoFarad (aF), respectively, with an achieved capacitance resolution of less than 2aF in a 30Hz bandwidth. The resolution is better than previously reported in the literature, and the capacitance changes are in agreement with values estimated by finite element simulations. Yeast cells were trapped using dielectrophoretic forces by applying a 3V signal at 1MHz between the electrodes. After trapping, the cells were displaced using amplitude and frequency modulated voltages to produce modulated dielectrophoretic forces. Repetitive displacement and relaxation of these cells was observed using both capacitance and video microscopy.
Development and application of a hybrid method involving interpolation and ab initio calculations for the determination of transition states
Authors: Goodrow Anthony , Bell Alexis T. , Head-Gordon Martin
Published: November 2008

Transition state search algorithms, such as the nudged elastic band can fail, if a good initial guess of the transition state structure cannot be provided. The growing string method (GSM) [J. Chem. Phys. 120, 7877 (2004)] eliminates the need for an initial guess of the transition state. While this method only requires knowledge of the reactant and product geometries, it is computationally intensive. To alleviate the bottlenecks in the GSM, several modifications were implemented: Cartesian coordinates were replaced by internal coordinates, the steepest descent method for minimization of orthogonal forces to locate the reaction path was replaced by the conjugate gradient method, and an interpolation scheme was used to estimate the energy and gradient, thereby reducing the calls to the quantum mechanical (QM) code. These modifications were tested to measure the reduction in computational time for four cases of increasing complexity: the Müller–Brown potential energy surface, alanine dipeptide isomerization, H abstraction in methanol oxidation, and C–H bond activation in oxidative carbonylation of toluene to p-toluic acid. These examples show that the modified GSM can achieve two- to threefold speedups (measured in terms of the reduction in actual QM gradients computed) over the original version of the method without compromising accuracy of the geometry and energy of the final transition state. Additional savings in computational effort can be achieved by carrying out the initial search for the minimum energy pathway (MEP) using a lower level of theory (e.g., HF/STO-3G) and then refining the MEP using density functional theory at the B3LYP level with larger basis sets (e.g., 6-31G∗, LANL2DZ). Thus, a general strategy for determining transition state structures is to initiate the modified GSM using a low level of theory with minimal basis sets and then refining the calculation at a higher level of theory with larger basis sets.
High resolution infrared spectroscopy of the asymmetric C–H stretch of 1,2,4,5-tetracyanobenzene (TCNB) and (TCNB)2 in superfluid helium nanodroplets
Authors: Gutberlet Anna , Birer Özgür , Poerschke Torsten , Havenith Martina
Published: November 2008

We report the observation of the C–H stretch vibration of 1,2,4,5-tetracyanobenzene (TCNB) and (TCNB)2 embedded in superfluid helium droplets. The asymmetric C–H stretch of TCNB was observed at 3053.488(3) cm−1. The corresponding band of the (TCNB)2 is slightly blueshifted and was observed at 3054.651(2) cm−1. The intensity of the IR band is increased compared to the monomer absorption. Based on a comparison of our experimental results with predicted IR bands, we conclude that (TCNB)2 is formed in a C2h structure in the droplet.
Analytic energy gradients in closed-shell coupled-cluster theory with spin-orbit coupling
Authors: Wang Fan , Gauss Jürgen
Published: November 2008

Gradients in closed-shell coupled-cluster (CC) theory with spin-orbit coupling included in the post Hartree-Fock treatment have been implemented at the CC singles and doubles (CCSD) level and at the CCSD level augmented by a perturbative treatment of triple excitations [CCSD(T)]. The additional computational effort required in analytic energy-gradient calculations is roughly the same as that for ground-state energy calculations in the case of CCSD, and it is about twice in the case of CCSD(T) calculations. The structures, harmonic frequencies, and dipole moments of some heavy-element compounds have been calculated using the present analytic energy-gradient techniques including spin-orbit coupling. The results show that spin-orbit coupling can have a significant influence on both the equilibrium structure and the harmonic vibrational frequencies and that its inclusion is essential to obtain reliable and accurate estimates for geometrical parameters of heavy-element compounds.
Native defects and oxygen and hydrogen-related defect complexes in CdTe: Density functional calculations
Authors: Du Mao-Hua , Takenaka Hiroyuki , Singh David J.
Published: November 2008

We study structural and electronic properties of various intrinsic and extrinsic defects in CdTe based on first-principles calculations. The focus is given to the role of these defects in the carrier compensation in semi-insulating CdTe, which is essential for the CdTe-based radiation detectors. The semi-insulating behavior of CdTe has been attributed to the Fermi level pinning near middle of the band gap by deep donors. These deep donors compensate shallow acceptors and are generally assumed to be Te antisites. However, we find that intrinsic defects, including the Te antisite, may not have a significant effect on the carrier compensation due either to lack of deep levels near midgap or to low defect concentration. We demonstrate instead that an extrinsic defect, OTe–H complex, may play an important role in the carrier compensation in CdTe. Other hydrogen-related defects are also discussed.
Simulations of electron transport and ignition for direct-drive fast-ignition targets
Authors: Solodov A. A. , Anderson K. S. , Betti R. , Gotcheva V. , Myatt J. , Delettrez J. A. , Skupsky S. , Theobald W. , Stoeckl C.
Published: November 2008

The performance of high-gain, fast-ignition fusion targets is investigated using one-dimensional hydrodynamic simulations of implosion and two-dimensional (2D) hybrid fluid-particle simulations of hot-electron transport, ignition, and burn. The 2D/3D hybrid-particle-in-cell code LSP [D. R. Welch et al., Nucl. Instrum. Methods Phys. Res. A 464, 134 (2001)] and the 2D fluid code DRACO [P. B. Radha et al., Phys. Plasmas 12, 056307 (2005)] are integrated to simulate the hot-electron transport and heating for direct-drive fast-ignition targets. LSP simulates the transport of hot electrons from the place where they are generated to the dense fuel core where their energy is absorbed. DRACO includes the physics required to simulate compression, ignition, and burn of fast-ignition targets. The self-generated resistive magnetic field is found to collimate the hot-electron beam, increase the coupling efficiency of hot electrons with the target, and reduce the minimum energy required for ignition. Resistive filamentation of the hot-electron beam is also observed. The minimum energy required for ignition is found for hot electrons with realistic angular spread and Maxwellian energy-distribution function.
Consistent solution for space-charge-limited current in the relativistic regime for monoenergetic initial velocities
Authors: Feng Y. , Verboncoeur J. P.
Published: November 2008

The solution for space-charge-limited (SCL) currents in electron vacuum diodes with monoenergetic initial velocity is extended to the relativistic regime. Two types of solutions are found: Type I corresponds to zero steady state surface electric field (field emission with high enhancement factor), and Type II corresponds to a finite steady state surface electric field (other emission mechanisms). Our solution compares well to the classical space-charge-limited currents with initial energy and relativistic space-charge limited currents without initial energy in the appropriate limits. The scaling law between the true SCL and the applied voltage is discussed and the two solution types are verified by particle-in-cell simulation.
Exciton scattering approach for branched conjugated molecules and complexes. II. Extraction of the exciton scattering parameters from quantum-chemical calculations
Authors: Wu Chao , Malinin Sergey V. , Tretiak Sergei , Chernyak Vladimir Y.
Published: November 2008

We obtain the parameters of the exciton scattering (ES) model from the quantum-chemical calculations of the electronic excitations in simple phenylacetylene-based molecules. We determine the exciton dispersion and the frequency-dependent scattering matrices which describe scattering properties of the molecular ends as well as of meta- and orthoconjugated links. The extracted functions are smooth, which confirms the validity of the ES picture. We find a good agreement between the ES and quantum-chemical results for the excitation energies in simple test molecules.
Scaling behavior of internal stress in electrodeposited nickel thin films
Authors: Saitou M. , Oshiro S. , Sagawa Y.
Published: November 2008

We have investigated the effects of the current density, film thickness, temperature, and additive agent on the internal stress in electrodeposited nickel thin films using a bent strip measurement. The internal stress is found to obey a scaling law expressed in terms of the current density and film thickness. The additive agent is shown to behave as a noise leading to different exponents in the dynamic scaling theory. In addition, the Arrhenius temperature dependence of the internal stress indicates the presence of thermal activation related to grain growth.
Solid-phase epitaxial regrowth of amorphous silicon containing helium bubbles
Authors: Beaufort M. F. , Pizzagalli L. , Gandy A. S. , Oliviero E. , Eyidi D. , Donnelly S. E.
Published: November 2008

Transmission electron microscopy has been used to study processes occurring when a layer of amorphous silicon (a-Si) containing helium-filled cavities buried in crystalline silicon (c-Si) recrystallizes by solid phase epitaxial growth (SPEG). The buried layer was formed in (100) silicon by means of bombardment with 150 keV Li ions with the bubbles resulting from subsequent implantation of 80 keV He ions; the energies being chosen to ensure that the resulting bubble distribution was entirely contained within the amorphous layer. The presence of bubbles in a-Si undergoing SPEG at a (100) interface with c-Si has previously been observed to give rise to the formation of microtwin lamellas, assumed to nucleate at the bubble surfaces; however, the present work indicates clearly that, in fact during SPEG, many microtwins nucleate remote from the bubbles. There is also an apparent interaction between the amorphous-crystalline (a-c) interface and the bubbles, in which the bubbles seem to be swept by the moving interface. The paper will discuss possible mechanisms for both phenomena, in terms of interstitial defects for the nucleation of microtwins and in terms of enhanced bubble mobility in a-Si for the apparent interaction between the a-c interface and the bubbles.
On blow-up space jets for the Navier–Stokes equations in R3 with convergence to Euler equations
Authors: Galaktionov V. A.
Published: November 2008

Formation of blow-up singularities for the Navier–Stokes equations ut+(u⋅∇)u=−∇p+Δu and div u=0 in R3×(0,T) is studied. In cylindrical polar coordinates {r,φ,z} in R3, their restriction to the linear subspace W2=Span{1,z} is shown to be consistent. Using links with blow-up theory for nonlinear reaction-diffusion partial differential equations, the following questions are under scrutiny: (ii) introducing a self-similar blow-up “swirl mechanism” with the angular swirl divergences φ(t)=−σ ln(T−t) and φ̇(t)=(σ/(T−t))→∞ as t→T−, where σ∊R is a parameter; (ii) existence of a countable family of space jets via a nonlocal semilinear parabolic equation with effective regional/global blow-up of the z component of the velocity; (iii) as an intrinsic part of the construction, convergence of the above rescaled patterns as t→T− to smooth blow-up self-similar solutions of the corresponding three-dimensional Euler equations ut+(u⋅∇)u=−∇p and div u=0 in R3×(0,T), which (iv) are also shown to admit single point blow-up in the similarity variables.
Phonon modes in self-assembled GaN quantum dots
Authors: Yamanaka Takayuki , Alexson Dimitri , Stroscio Michael A. , Dutta Mitra , Petroff Pierre , Brown Jay , Speck James
Published: November 2008

Phonons in GaN quantum dots (QDs) fabricated by Stranski–Krastanov growth are analyzed using Raman scattering and continuum models of phonon confinement. The QD samples are evaluated by Raman spectroscopy with four different excitation energies. Each excitation energy has a different penetration depth, and this makes it possible to distinguish Raman signals associated with the QDs from any other signals. In addition, the phonon frequency shift in GaN QDs are analyzed using theoretical models of the confined geometry and the internal stress, the calculated results are compared to the measured results.
Analytical distributions for stochastic gene expression
Authors: Shahrezaei Vahid , Swain Peter S.
Published: November 2008

Gene expression is significantly stochastic making modeling of genetic networks challenging. We present an approximation that allows the calculation of not only the mean and variance, but also the distribution of protein numbers. We assume that proteins decay substantially more slowly than their mRNA and confirm that many genes satisfy this relation by using high-throughput data from budding yeast. For a two-stage model of gene expression, with transcription and translation as first-order reactions, we calculate the protein distribution for all times greater than several mRNA lifetimes and thus qualitatively predict the distribution of times for protein levels to first cross an arbitrary threshold. If in addition the fluctuates between inactive and active states, we can find the steady-state protein distribution, which can be bimodal if fluctuations of the promoter are slow. We show that our assumptions imply that protein synthesis occurs in geometrically distributed bursts and allows mRNA to be eliminated from a master equation description. In general, we find that protein distributions are asymmetric and may be poorly characterized by their mean and variance. Through maximum likelihood methods, our expressions should therefore allow more quantitative comparisons with experimental data. More generally, we introduce a technique to derive a simpler, effective dynamics for a stochastic system by eliminating a fast variable.
The crystal structure of mouse VDAC1 at 2.3 Å resolution reveals mechanistic insights into metabolite gating
Authors: Ujwal Rachna , Cascio Duilio , Colletier Jacques-Philippe , Faham Salem , Zhang Jun , Toro Ligia , Ping Peipei , Abramson Jeff
Published: November 2008

The voltage-dependent anion channel (VDAC) constitutes the major pathway for the entry and exit of metabolites across the outer membrane of the mitochondria and can serve as a scaffold for molecules that modulate the organelle. We report the crystal structure of a β-barrel eukaryotic membrane protein, the murine VDAC1 (mVDAC1) at 2.3 Å resolution, revealing a high-resolution image of its architecture formed by 19 β-strands. Unlike the recent NMR structure of human VDAC1, the position of the voltage-sensing N-terminal segment is clearly resolved. The α-helix of the N-terminal segment is oriented against the interior wall, causing a partial narrowing at the center of the pore. This segment is ideally positioned to regulate the conductance of ions and metabolites passing through the VDAC pore.
Psychometric Characteristics of the Teen Addiction Severity Index-Two (T-ASI-2)
Authors: Brodey Benjamin B. , McMullin Darcy , Kaminer Yifrah , Winters Ken C. , Mosshart Edward , Rosen Craig S. , Brodey Inger S.
Published: November 2008

The Teen Addiction Severity Index-Two (T-ASI-2) was developed as an extension of the T-ASI to assess the severity of substance abuse and related problems among adolescents (N = 371) 12-19 years of age. The T-ASI-2 consists of 18 domains that assess current use of alcohol, tobacco, marijuana, and other drugs, as well as mental health service utilization, treatment satisfaction, school difficulties, social functioning with family members and peers, substance use by family members and peers, depression, anxiety, attention deficit, hyperactivity, defiant and risky behaviors, and readiness for change. Results show that all domains have adequate to excellent internal consistency (.54 to.88, median.80). New domains assessing psychological factors strongly correlated with gold standard assessments in the respective areas. The T-ASI-2 was designed to be a user friendly, cost-effective, viable assessment of substance use behavior and related factors.
Stability of Comorbid Psychiatric Diagnosis among Youths in Treatment and Aftercare for Alcohol Use Disorders
Authors: Hawke Josephine M. , Kaminer Yifrah , Burke Rebecca , Burleson Joseph A.
Published: November 2008

Objectives

To examine the stability of comorbid psychiatric diagnoses among a sample of 50 adolescents in cognitive-behaviorally-based treatment for alcohol and other substance use disorders (AOSUD).

Methods

A standardized psychiatric interview was administered at baseline and 12 month later to obtain current comorbid psychiatric disorders. Chi square and Wilconxon sign tests coefficients were used to examine changes in threshold status by type of disorder. Pearson's coefficients were used to identify correlates with improvements in threshold status, include the need for alcohol treatment and alcohol consumption at follow-up.

Results

Diagnostic status changes considerably over time. Prevalence rates for comorbid disorders overall declined. Only declines in mood and externalizing disorders achieved statistical significance. Improvements were positively correlated with mental health service utilization and negatively correlated with the need for alcohol treatment and consumption at 12 months.

Conclusions

Further investigation on the stability and change in diagnostic status of AOSUD youths is warranted.