bluuebunny/crossref_metadata_2025 huggingface dataset:
FOR ELECTRON GAS: AN EXCITONIC PHASE
Authors: CHAKRABARTI J.
Published: November 2004

A new state is possible for an electron gas due to magnetic interactions. We argue that such a phase sets in for a value of Fermi velocity close to unity. It is an excitonic phase, fairly uniform in space, different from the particle–hole condensates conceived earlier in condensed matter physics.
UPPER BOUND ON THE GROUND-STATE ENERGY FOR THE FRÖHLICH POLARON IN A MAGNETIC FIELD
Authors: SOLDATOV A. V.
Published: November 2004

The ground-state energy of the Fröhlich polaron model in a magnetic field is investigated by means of the Wick symbols formalism. The upper bound on the ground-state energy is derived which is valid for all values of magnetic field and coupling strength.
EXPRESSION OF THE PARTITION FUNCTION AND RENORMALIZATION EQUATION OF SPIN-1/2 TOMONAGA–LUTTINGER CHAINS
Authors: LI Y. M. , YU Y. , D'AMBRUMENIL N. , YU L. , SU Z. B.
Published: November 2004

We derive an exact expression for the partition function of two spin-1/2 Tomonaga–Luttinger chains, and obtain the renormalization group equation for the normal state. Anderson's confinement is then discussed. We find that spin–charge separation is irrelevant to the confinement.
CRITICAL OSMOTIC PRESSURE OF COLLOIDS
Authors: HU JIAN-GUO , OU-YANG ZHONG-CAN
Published: November 2004

The osmotic pressure for electrocratic colloids is considered. Assuming monodispersed colloidal particles arranged in face-centered cube (fcc) or body-centered cube (bcc) structures, we calculate the critical osmotic pressures of colloids in the framework of DLVO theory. The quantitative dependences of critical osmotic pressures upon physical parameters (such as particle radius and concentration of ions in medium, etc.) are obtained. These theoretical results may provide better knowledge about van der Waals forces and double layer structures of these suspensions when they are compared with experimental results.
FRÖHLICH'S ONE-DIMENSIONAL SUPERCONDUCTOR WITH PARA-FERMI STATISTICS
Authors: SAFONOV V. L. , ROZHKOV A. V.
Published: November 2004

The hypothesis that conduction electrons in a one-dimensional crystal obey para-Fermi statistics is discussed. Thermal properties of Fröhlich's model in the mean-field approximation are calculated within the framework of this hypothesis. It is shown that the temperature of the phase transition to a charge density wave state is greater in a system with parastatistics.
CONDITIONALLY AVERAGED DYNAMICS OF TURBULENCE
Authors: NOVIKOV EVGENY A. , DOMMERMUTH DOUGLAS G.
Published: November 2004

The conditionally averaged Navier-Stokes equations with fixed vorticity in a point are considered. It is found in particular that the conditionally averaged rates of vortex stretching and dissipation increase exponentially with the vorticity magnitude. The local imbalance of these effects leads to the formation and destruction of twisted vortex strings.
THERMAL SOFTENING OF THE INTERPLANE JOSEPHSON COUPLING IN HIGHLY ANISOTROPIC HIGH Tc SUPERCONDUCTORS
Authors: KOPELEVICH Y. , ESQUINAZI P. , ZIESE M.
Published: November 2004

Different experimental techniques reveal a nearly magnetic-field-independent depinning of the flux line lattice (FLL) between 20 and 30 K in highly anisotropic high temperature superconductors like Bi 2:2:1:2 and similar compounds. This anomalous behavior of the FLL has been partially unnoticed in the literature and is the subject of this experimental review. We compare data from literature obtained with different experimental techniques and discuss a possible common origin based on a “softening” of the interplane Josephson coupling.
AN INVESTIGATION OF THE MAGNETIC DILUTION EFFECT IN CaO-CuO AND SrO-CuO SYSTEMS
Authors: IKRAM MOHD. , PUNNOOSE ALEX , MAURYA B.P. , SINGH R.J.
Published: November 2004

A systematic study of the effect of magnetic dilution of CuO by diamagnetic CaO and SrO using electron paramagnetic resonance and X-ray diffraction studies was carried out. Three different combinations of CuO with CaO/SrO were prepared and calcined at different temperatures from room temperature (RT) to 800ºC. In both the CaO-CuO and SrO-CuO systems, the first appearance of the signal occurred at much lower calcination temperatures compared to that of CuO. On increasing the concentration of the diamagnetic additives, the emergence of the signals became earlier. XRD study showed that below 800ºC, no chemical reaction takes place, indicating that the EPR spectral variations are governed only by the dilution effect of the diamagnetic CaO/SrO molecules. The magnetically coupled Cu-O-Cu chains in CuO are interspersed with the diamagnetic molecules and thus effectively enhance the reduction of the spin correlation length. The spectrum that emerged as a result of this consists of a broad low field signal and a sharp signal at g≃2. The broad signal is attributed to the remnants of short range order and the sharp g≃2 signal to the Cu 2+ monomers formed. At higher temperatures, the high field shift and weakening of the low field signal indicate the destruction of magnetic coupling in CuO.
LOGARITHMIC BISOLITONS IN THE HIGH Tc SUPERCONDUCTING MATERIALS
Authors: RAJILIĆ Z. , MIRJANIĆ D.
Published: November 2004

The one-dimensional bigausson model at zero temperature is generalized. The results of this generalization are the logarithmic soliton and logarithmic bisoliton which are, for special choice of parameters, equal to the gausson and bigausson respectively. The logarithmic bisoliton model of high temperature superconductivity explains (i) the different critical temperatures for the same crystal lattice and the same density of the charge carriers, (ii) the localization and its effect on superconductivity, (iii) the different coherence lengths for the same crystal lattice, the same density of the charge carriers, and the same T c , (iv) the complexity of the normal state, and (v) the nonstability of the anomalous high Tc superconductivity (T>150 K ).
FINE STRUCTURE IN CORE LEVEL PHOTOEMISSION INTENSITIES — A STUDY OF THE Si(111)−(7×7) SURFACE
Authors: CARLISLE J.A. , SIEGER M.T. , MILLER T. , CHIANG T.-C.
Published: November 2004

Photoemission intensities from core levels derived from surface and bulk atoms of a solid exhibit oscillations as a function of the excitation photon energy. These oscillations cannot be described by the classical layer attenuation model, which has been the basis for intensity analysis and quantitative structural modeling in a number of studies. The physics responsible for these oscillations is the extended photoemission fine structure (EPFS) above the core level absorption edge, which contains structural information in regard to surface bond lengths. The present paper examines in detail this phenomenon for the Si 2p core level of the Si (111)−(7×7) surface. The EPFS is found to modulate the surface-to-bulk Si 2p core level intensity ratios up to ~50%; thus, structural models based on a surface-to-bulk intensity ratio analysis using the classical layer attenuation model at a few photon energies may suffer large errors. This EPFS may be responsible for the ongoing debate in the literature over the assignment of the surface core levels to structural features on both the (111) and (100) surfaces of Si and Ge. This dilemma is resolved for the (7×7) surface. Using the usual three-component fit of the Si 2p core level (a bulk component and two surface components, S1 and S2), the EPFS signals from the individual components are separately analyzed. The results show the S2 component to be derived from adatom emission. The S1 component is unresolved, and represents emission from several different types of atoms in the top double layer of the (7×7) reconstruction.
A BGK MODEL FOR CHEMICAL PROCESSES: THE REACTION-DIFFUSION APPROXIMATION
Authors: SPIGLER RENATO , ZANETTE DAMIÁN H.
Published: November 2004

A BGK-type kinetic model is derived for describing the interaction of chemical substances. The ensuing equation is then solved asymptotically on certain space-time scales on which an appreciable interplay between kinetic and chemical effects, or the prevailing of one on the other, can be observed. The description of the interaction at the macroscopic level consists of a hierarchy of reaction-diffusion equations satisfied by the densities. Comparison is made with similar results previously obtained from certain phenomenological models, and illustrative examples are given.
SOLVABILITY OF A PROBLEM OF VISCOUS FLUID MOTION WITH FREE SURFACE
Authors: MOGILEVSKIY I. SH.
Published: November 2004

The problem of the stationary motion of a liquid which filled partially a certain container is considered. The motion is due to the rotation of a rod inserted in the center of a container. The solvability of this problem is proved in a weighted Hölder spaces for arbitrary wetting angle. The proof is based on the results of Solonnikov .
APPROXIMATION AND PARAMETER ESTIMATION PROBLEMS FOR ALGAL AGGREGATION MODELS
Authors: ACKLEH AZMY S. , FITZPATRICK BEN G. , HALLAM THOMAS G.
Published: November 2004

Aggregation processes are intrinsic to many biological phenomena including sedimentation and coagulation of algae during bloom periods. A fundamental but unresolved problem associated with aggregate processes is the determination of the “stickiness function,” a measure of the ability of particles to adhere to other particles. This leads to an inverse problem associated with a class of nonlinear integro-differential equations. The purpose of this article is to develop convergence theory for this algal coagulation model utilizing a spline-based collocation scheme within the context of the parameter identification problem.
INTERFACIAL KINETICS EFFECT IN PLANAR SOLIDIFICATION PROBLEMS WITHOUT INITIAL UNDERCOOLING
Authors: CHARACH CH. , ZALTZMAN B. , GÖTZ I.G.
Published: November 2004

This paper addresses the continuum models of solidification of a monocomponent substance, that generalize the classical Stefan problem by incorporating effects of interfacial kinetics. We consider the key planar solidification problem of this sort. The model implies a rigid solid and an incompressible liquid of equal densities and accounts for a linear attachment kinetics at the interface. The correctness of this formulation is proved and the asymptotic solutions at the onset of freezing and at sufficiently long times are developed. An analytical solution, valid uniformly in time, is developed and validated against the finite difference solution.
NEW RESULTS ON THE ASYMPTOTIC BEHAVIOR OF DIRICHLET PROBLEMS IN PERFORATED DOMAINSDIRICHLET PROBLEMS IN PERFORATED DOMAINS
Authors: MASO GIANNI DAL , GARRONI ADRIANA
Published: November 2004

Let A be a linear elliptic operator of the second order with bounded measurable coefficients on a bounded open set Ω of Rn and let (Ωh) be an arbitrary sequence of open subsets of Ω. We prove the following compactness result: there exist a subsequence, still denoted by (Ωh), and a positive Borel measure μ on Ω, not charging polar sets, such that, for every f∈H−1(Ω) the solutions [Formula: see text] of the equations Auh=f in Ωh, extended to 0 on Ω\Ωh, converge weakly in [Formula: see text] to the unique solution [Formula: see text] of the problem [Formula: see text] When A is symmetric, this compactness result is already known and was obtained by Γ-convergence techniques.

Our new proof, based on the method of oscillating test functions, extends the result to the non-symmetric case. The new technique, which is completely independent of Γ-convergence, relies on the study of the behavior of the solutions [Formula: see text] of the equations [Formula: see text] where A* is the adjoint operator.

We prove also that the limit measure μ does not change if A is replaced by A*. Moreover, we prove that µ depends only on the symmetric part of the operator A, if the coefficients of the skew-symmetric part are continuous, while an explicit example shows that μ may depend also on the skew-symmetric part of A, when the coefficients are discontinuous.
QUALITATIVE MATHEMATICAL MODEL OF CARDIAC FIBER ELECTRODYNAMICS
Authors: PETROV VALKO G.
Published: November 2004

This paper introduces an approach for modeling the calcium electrodynamics in cardiac fiber taking into account the electrostatic capacitance, non-reactive (ohmic) resistance, negative reactive resistance and small inductivity of the reticulum membrane. Proposing the simplest analytic form of competition between Ca2+ ions and ATP molecules at the calcium pump, the nonlinear differential equation of Van der Pol type for the calcium concentration in the myoplasma is derived. Using the capacitance formula the same equation is transformed for describing the action potential behavior in muscle contraction process. The phase and bifurcation analyses of this model are presented. Physiologic interpretation of the qualitative results, oriented to further development of the problem is made.
AXIOMATIC DERIVATION OF IMAGE PROCESSING MODELS
Authors: LIONS PIERRE-LOUIS
Published: November 2004

We briefly review the derivation due to Alvarez, Guichard, Morel and the author of mathematical models in Image Processing. We deduce from classical axions in Computer Vision some nonlinear partial differential equations of evolution type that correspond to general multi-scale analysis (scale-space). We also obtain specific nonlinear models that satisfy additional invariances which are relevant for the analysis of images.
RECENT DEVELOPMENTS IN THE NUMERICAL SIMULATION OF SHALLOW WATER EQUATIONS II: TEMPORAL DISCRETIZATION
Authors: AGOSHKOV V. , OVCHINNIKOV E. , QUARTERONI A. , SALERI F.
Published: November 2004

This paper deals with time-advancing schemes for shallow water equations. We review some of the existing numerical approaches, propose new schemes and investigate their stability. We present numerical results obtained using the time-advancing schemes proposed, with finite element and finite difference approximation in space variables.
SPECTRAL STUDY OF A COUPLED COMPACT-NONCOMPACT PROBLEM IN A NON-SELF-ADJOINT CASE
Authors: BENKADDOUR A. , SANCHEZ-HUBERT J. , RIDHA A.
Published: November 2004

We consider a coupled problem of acoustic vibration of air in a porous medium Ω p that is in contact, by a plane interface Γ (x1=0), with free air in some region Ω f . The porous medium is made of infinitely narrow thin channels parallel to the x1-axis.

In Refs. 1–3 and 5, problems of this type were considered with homogeneous Neumann boundary conditions on the exterior boundary of the whole domain Ω, Ω= Ω f ∪Γ∪Ω p . In this paper, we study the problem in the mentioned configuration but with the impedance condition ∂u/∂n=u/Z (where Z is a given complex number) on a part of the boundary of the porous medium Ω p defined by x1=–ℓ(x2, x3), where ℓ is a smooth positive function.

Let us denote by A the operator associated with the coupled eigenvalue problem –Au=ω2u, and by Ap(x2, x3) the corresponding problem in a channel x2= const , x3= const . As in Ref. 1, two cases appear according to the values of ω2. In the first case ω2 is not an eigenvalue of Ap(x2, x3), and then we show that ω2 is either a point of the resolvent set or an isolated eigenvalue with finite multiplicity of A. In the second case ω2 is an eigenvalue of Ap(a2, a3) for some value (a2, a3) of (x2, x3), and then ω2 is a point of the essential spectrum of A. The novelty of this paper is the study of the spectrum of the operator A which is non self-adjoint and has a noncompact resolvent. We find a complex essential spectrum of A and we study its topological structure.
HYPERBOLICITY OF GRAD’S EXTENSION OF HYDRODYNAMIC MODELS FOR IONOSPHERIC PLASMA PART II: THE TWO SPECIES CASE
Authors: CORDIER STEPHANE
Published: November 2004

We investigate the hyperbolicity of the five-, eight-, 10-, 13- and 16-moment Grad systems for two species of particles under the quasineutrality hypothesis. The analysis is based on an asymptotic expansion with respect to the mass ratio. We show that the hyperbolicity of the systems which involve the heat flux as an independent variable requires a limitation on this heat flux.
ON THE ABSORPTION PROBLEM FOR RANDOM DISPERSIONS
Authors: MARKOV KONSTANTIN Z. , KOLEV MIKHAIL K.
Published: November 2004

This paper is devoted to the steady-state problem of absorption of a diffusing species (say, irradiation defects) in a random dispersion of spheres. The defects are created at a constant rate throughout the medium and are absorbed afterward, with different sink strengths, by the matrix and by the inclusions. One is to find the random diffusing species field and, in particular, the effective sink strength of the dispersion, having assumed the statistics of the spheres known. The problem is modeled by a Helmhotz equation with a random coefficient (the randomly fluctuating sink strength of the dispersion). The statistical solution of the latter is explicitly constructed, in a simple form, by means of the so-called factorial functional series, recently introduced by one of the authors. In particular, analytical formulas, correct to the order “square of sphere fraction,” are obtained for the effective sink strength of the dispersion and for the two-point correlation function of the diffusing species field. An effective numerical procedure, allowing to specify these quantities, is described and numerical results are finally presented and discussed.
IDENTIFYING MEMORY KERNELS IN LINEAR THERMOVISCOELASTICITY OF BOLTZMANN TYPE
Authors: CAVATERRA CECILIA , GRASSELLI MAURIZIO
Published: November 2004

The evolution of the displacement u and the temperature ϑ in a three-dimensional, linear, thermoviscoelastic material of Boltzmann type is governed by a system of two coupled Volterra integrodifferential equations. The damping mechanism is characterized by some time-dependent memory kernels which are a priori unknown. These kernels are identified via measurements of boundary tractions and localized temperatures, provided that the pair (u, ϑ) solves a suitable initial and boundary value problem for the evolution system.
SUPERSYMMETRIC STRING WAVES
Authors: BERGSHOEFF ERIC
Published: November 2004

We present plane-wave-type solutions to the superstring effective action which have unbroken space-time supersymmetries. They describe dilaton, axion and gauge fields in a generalization of the Brinkmann metric. A crucial property of the solutions is a conspiracy between the metric and the axion field. Furthermore, due to a relation between the geometry and the gauge fields, the α′ string corrections to the effective on-shell action and to the solutions themselves vanish. We call these solutions supersymmetric string waves.
STATICITY, CIRCULARITY, AND THE FIRST LAW OF BLACK HOLE PHYSICS
Authors: HEUSLER MARKUS , STRAUMANN NORBERT
Published: November 2004

We give a brief summary of some of our ongoing work on stationary black holes for non-linear matter models, such as gauge field theories (including Higgs fields) or general sigma models. Our main result is a generalization of the Bardeen-Carter-Hawking formula for the variation of the mass of stationary black holes, which involves only global quantities and boundary integrals. Results and open questions related to the staticity problem for non-rotating black holes, and to the circularity and Frobenius conditions for rotating ones, are briefly discussed.
ANOMALOUS SUPERGRAVITY INFLATION
Authors: CARDOSO GABRIEL LOPES , OVRUT BURT
Published: November 2004

We review the fundamental structure of ℛ2 inflation and discuss its fundamental problems. It is then showed that these problems are all simply and naturally resolved within the context of N=1 supergravity.
AUTOMATIC SYMMETRY INVESTIGATION OF SPACE-TIME METRICS
Authors: WOLF THOMAS , GREBOT GUY
Published: November 2004

Computer algebra programs, [Formula: see text] and [Formula: see text] for automatically formulating and solving Killing equations and calculating the corresponding Lie algebra are described and examples are given.
MAXIMAL ACCELERATION TUNNELING FROM “NOTHING”
Authors: CAIANIELLO E.R. , FEOLI A. , SCARPETTA G. , CAPOZZIELLO S. , DE RITIS R.
Published: November 2004

We find the Wheeler-DeWitt equation for a Friedman-Robertson-Walker metric modified according to a model with maximal acceleration and discuss the new conditions in which the wave function of the universe tunnels from the Euclidean regime to the Lorentzian one. We argue that the acceleration induces a nonminimal coupling of the scalar field with the gravitational degrees of freedom and provides a new dynamical possibility of tunneling through the quantum boundary when [Formula: see text].
ON THE ESTIMATES TO MEASURE HAWKING EFFECT AND UNRUH EFFECT IN THE LABORATORY
Authors: ROSU H.C.
Published: November 2004

A comparison between the proposals made to measure Hawking-like effects and the Unruh effect in the laboratory is given at the level of their estimates. No satisfactory scheme exists as yet for their detection.
ON THE WHEELER-DEWITT EQUATION FOR BLACK HOLES
Authors: POLLOCK M.D.
Published: November 2004

Integration over the angular coordinates of the evaporating, four-dimensional Schwarzschild black hole leads to a two-dimensional action, for which the Wheeler-DeWitt equation has been found by Tomimatsu, on the apparent horizon, where the Vaidya metric is valid, using the Hamiltonian formalism of Hajicek. For the Einstein theory of gravity coupled to a massless scalar field ζ, the wave function Ψ obeys the Schrödinger equation [Formula: see text], where M is the mass of the hole. The solution is [Formula: see text], where k2 is the separation constant, and for k2>0 the hole evaporates at the rate Ṁ=−k2/4M2, in agreement with the result of Hawking. Here, this analysis is generalized to the two-dimensional theory [Formula: see text], which subsumes the spherical black holes formulated in D≥4 dimensions, when A = ½ (D - 2) (D - 3)ϕ2 (D - 4)/(D - 2), B=2(D−3)/(D−2), C=1, and also the twodimensional black hole identified by Witten and by Gautam et al., when A=4/α′, B=2, C=1/8π, c=+8/α′ being (minus) the central charge. In all cases an analogous Schrödinger equation is obtained. The evaporation rate is [Formula: see text] when D≥4 and [Formula: see text] when D=2. Since Ψ evolves without violation of unitarity, there is no loss of information during the evaporation process, in accord with the principle of black-hole complementarity introduced by Susskind et al. Finally, comparison with the four-dimensional, cosmological Schrödinger equation, obtained by reduction of the ten-dimensional heterotic superstring theory including terms [Formula: see text], shows in both cases that there is a positive semi-definite potential which evolves to zero, this corresponding to the ground state, which is Minkowski space.
NÖTHER’S SYMMETRIES IN QUANTUM COSMOLOGY
Authors: CAPOZZIELLO SALVATORE , DE RITIS RUGGIERO , SCUDELLARO PAOLO
Published: November 2004

We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a scalar field. We show that when a Nöther symmetry exists, it is always possible to integrate the Wheeler-DeWitt equation and recover the semiclassical regime for the wave function of the universe. In this sense, we can interpret the Nöther symmetries as a selection rule in the philosophy of the so called Hartle criterion: when they exist, it is possible to select classical universes.
GRAVITY AND YANG-MILLS THEORY: TWO FACES OF THE SAME THEORY?
Authors: CHAKRABORTY SUBENOY , PELDÁN PETER
Published: November 2004

We introduce a gauge and diffeomorphism invariant theory on the Yang-Mills phase space. The theory is well defined for an arbitrary gauge group with an invariant bilinear form, it contains only first class constraints, and the spacetime metric has a simple form in terms of the phase space variables. With gauge group SO (3, C), the theory equals the Ashtekar formulation of gravity with a cosmological constant. For Lorentzian signature, the theory is complex, and we have not found any good reality conditions. In the Euclidean signature case, everything is real. In a weak field expansion around de Sitter spacetime, the theory is shown to give the conventional Yang-Mills theory to the lowest order in the fields. We show that the coupling to a Higgs scalar is straightforward, while the naive spinor coupling does not work. We have not found any way of including spinors that gives a closed constraint algebra. For gauge group U(2), we find a static and spherically symmetric solution.
QUARTETS OF SUPERDEFORMED BANDS AND SUPERSYMMETRY BREAKING
Authors: AMADO R.D. , BIJKER R. , CANNATA F. , DEDONDER J.P. , WALET N.R.
Published: November 2004

We examine the prediction of supersymmetric quantum mechanics that bands with identical gamma-ray energies occur in quartets. The experimental data suggest that this scenario is actually realized in nature. In the A=150 mass region, four known pairs of isospectral bands can be grouped in two quartets, while there are indications of such patterns around A=190. We introduce a small supersymmetry breaking, necessary to describe the details of the data. We derive relations among the transition rates that can be used to test our predictions.
ALPHA PARTICLE INDUCED REACTIONS ON VANADIUM
Authors: RAO A.V. MOHAN , CHINTALAPUDI S.N.
Published: November 2004

Alpha particle-induced reactions on the target element vanadium were investigated from threshold up to 55 MeV using the foil-stack activation technique and the Ge(Li) gamma ray spectroscopy method. Excitation functions for the formation of reaction residues 54Mn, 52Mn, 51Cr, 48V, 47Sc, 46Sc were investigated. The experimental cross-sections were compared with the predictions based on updated hybrid model (ALICE/90) using n0=4 (4p0h) and level density parameter a=A/9. A general agreement was found for all the reactions of (α, xn) type. However, the model failed badly in all cases of (α, zαxn) type of reactions.
PHENOMENOLOGICAL RELATIVISTIC STUDY OF THE ENERGY OF A Λ IN ITS GROUND AND EXCITED STATES IN HYPERNUCLEI
Authors: PAPADOPOULOS G.J. , KOUTROULOS C.G. , GRYPEOS M.E.
Published: November 2004

The binding energy BΛ of a Λ-particle in hypernuclei is studied by means of the Dirac equation with attractive and repulsive potentials of rectangular shapes and of the same radius. The energy eigenvalue equation in this case is obtained analytically for every bound state, as well as the large and small component of the wave function (for given BΛ). A first attempt is also made to investigate the possibility of deriving in particular cases approximate analytic expressions of BΛ for the excited states. Using various least squares fittings, numerical results for the binding energy of the Λ are given and comparisons and comments are also made.
A FUNCTIONAL INTEGRAL APPROACH TO THE THERMODYNAMICS OF THE σ-ω MODEL
Authors: RISCHKE D.-H. , GREINER W.
Published: November 2004

We study the σ-ω model for nuclear matter at finite temperature and density in the functional integral approach. Particular emphasis is put on the treatment of the degrees of freedom of the massive vector meson. Various ways to calculate the grand partition function for free massive vector particles are presented. Then we show how field theories of two mutually interacting fields can be alternatively formulated in terms of a theory containing one free field and a nonlocal self-interaction of the other field. For a perturbative expansion in powers of the coupling constant and in the mean-field approximation, this formulation gives the same results as the standard treatment, e.g., the loop-expansion scheme of the effective potential. However, in contrast to the latter, the mean-field approximation is now obtained in a very simple and physically obvious way which closely resembles the analogous derivation for statistical-mechanical systems. We apply our alternative formulation to the case of scalar and massive vector particles interacting with another field. Combining both cases and taking the nucleon field as the interaction partner, we finally arrive at the grand partition function for the σ-ω model in mean-field approximation.
AMPK activation is not critical in the regulation of muscle FA uptake and oxidation during low-intensity muscle contraction
Authors: Raney Marcella A. , Yee Alice J. , Todd Mark K. , Turcotte Lorraine P.
Published: November 2004

To determine the role of AMP-activated protein kinase (AMPK) activation on the regulation of fatty acid (FA) uptake and oxidation, we perfused rat hindquarters with 6 mM glucose, 10 μU/ml insulin, 550 μM palmitate, and [14C]palmitate during rest (R) or electrical stimulation (ES), inducing low-intensity (0.1 Hz) muscle contraction either with or without 2 mM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR). AICAR treatment significantly increased glucose and FA uptake during R ( P < 0.05) but had no effect on either variable during ES ( P > 0.05). AICAR treatment significantly increased total FA oxidation ( P < 0.05) during both R (0.38 ± 0.11 vs. 0.89 ± 0.1 nmol·min−1·g−1) and ES (0.73 ± 0.11 vs. 2.01 ± 0.1 nmol·min−1·g−1), which was paralleled in both conditions by a significant increase and significant decrease in AMPK and acetyl-CoA carboxylase (ACC) activity, respectively ( P < 0.05). Low-intensity muscle contraction increased glucose uptake, FA uptake, and total FA oxidation ( P < 0.05) despite no change in AMPK (950.5 ± 35.9 vs. 1,067.7 ± 58.8 nmol·min−1·g−1) or ACC (51.2 ± 6.7 vs. 55.7 ± 2.0 nmol·min−1·g−1) activity from R to ES ( P > 0.05). When contraction and AICAR treatment were combined, the AICAR-induced increase in AMPK activity (34%) did not account for the synergistic increase in FA oxidation (175%) observed under similar conditions. These results suggest that while AMPK-dependent mechanisms may regulate FA uptake and FA oxidation at rest, AMPK-independent mechanisms predominate during low-intensity muscle contraction.
A self-calibrating telemetry system for measurement of ventricular pressure-volume relations in conscious, freely moving rats
Authors: Uemura Kazunori , Kawada Toru , Sugimachi Masaru , Zheng Can , Kashihara Koji , Sato Takayuki , Sunagawa Kenji
Published: November 2004

Using Bluetooth wireless technology, we developed an implantable telemetry system for measurement of the left ventricular pressure-volume relation in conscious, freely moving rats. The telemetry system consisted of a pressure-conductance catheter (1.8-Fr) connected to a small (14-g) fully implantable signal transmitter. To make the system fully telemetric, calibrations such as blood resistivity and parallel conductance were also conducted telemetrically. To estimate blood resistivity, we used four electrodes arranged 0.2 mm apart on the pressure-conductance catheter. To estimate parallel conductance, we used a dual-frequency method. We examined the accuracy of calibrations, stroke volume (SV) measurements, and the reproducibility of the telemetry. The blood resistivity estimated telemetrically agreed with that measured using an ex vivo cuvette method ( y = 1.09 x − 11.9, r2 = 0.88, n = 10). Parallel conductance estimated by the dual-frequency (2 and 20 kHz) method correlated well with that measured by a conventional saline injection method ( y = 1.59 x − 1.77, r2 = 0.87, n = 13). The telemetric SV closely correlated with the flowmetric SV during inferior vena cava occlusions ( y = 0.96 x + 7.5, r2 = 0.96, n = 4). In six conscious rats, differences between the repeated telemetries on different days (3 days apart on average) were reasonably small: 13% for end-diastolic volume, 20% for end-systolic volume, 28% for end-diastolic pressure, and 6% for end-systolic pressure. We conclude that the developed telemetry system enables us to estimate the pressure-volume relation with reasonable accuracy and reproducibility in conscious, untethered rats.
Bifurcation asymmetry of the porcine coronary vasculature and its implications on coronary flow heterogeneity
Authors: Kalsho Ghada , Kassab Ghassan S.
Published: November 2004

The branching pattern of the coronary arteries and veins is asymmetric, i.e., many small vessels branch off of a large trunk such that the two daughter vessels at a bifurcation are of unequal diameters and lengths. One important implication of the geometric vascular asymmetry is the dispersion of blood flow at a bifurcation, which leads to large spatial heterogeneity of myocardial blood flow. To document the asymmetric branching pattern of the coronary vessels, we computed an asymmetry ratio for the diameters and lengths of all vessels, defined as the ratio of the daughter diameters and lengths, respectively. Previous data from silicone elastomer cast of the entire coronary vasculature including arteries, arterioles, venules, and veins were analyzed. Data on smaller vessels were obtained from histological specimens by optical sectioning, whereas data on larger vessels were obtained from vascular casts. Asymmetry ratios for vascular areas, volumes, resistances, and flows of the various daughter vessels were computed from the asymmetry ratios of diameters and lengths for every order of mother vessel. The results show that the largest orders of arterial and venous vessels are most asymmetric and the degree of asymmetry decreases toward the smaller vessels. Furthermore, the diameter asymmetry at a bifurcation is significantly larger for the coronary veins (1.7–6.8 for sinus veins) than the corresponding arteries (1.5–5.8 for left anterior descending coronary artery) for orders 2–10, respectively. The reported diameter asymmetry at a bifurcation leads to significant heterogeneity of blood flow at a bifurcation. Hence, the present data quantify the dispersion of blood flow at a bifurcation and are essential for understanding flow heterogeneity in the coronary circulation.
Basolateral K+conductance in principal cells of rat CCD
Authors: Gray Daniel A. , Frindt Gustavo , Zhang Yu-Yang , Palmer Lawrence G.
Published: November 2004

Whole cell K+current was measured by forming seals on the luminal membrane of principal cells in split-open rat cortical collecting ducts. The mean inward, Ba2+-sensitive conductance, with 40 mM extracellular K+, was 76 ± 12 and 141 ± 22 nS/cell for animals on control and high-K+diets, respectively. The apical contribution to this was estimated to be 3 and 16 nS/cell on control and high-K+diets, respectively. To isolate the basolateral component of whole cell current, we blocked ROMK channels with either tertiapin-Q or intracellular acidification to pH 6.6. The current was weakly inward rectifying when bath K+was ≥40 mM but became more strongly rectified when bath K+was lowered into the physiological range. Including 1 mM spermine in the pipette moderately increased rectification, but most of the outward current remained. The K+current did not require intracellular Ca2+and was not inhibited by 3 mM ATP in the pipette. The negative log of the acidic dissociation constant (p Ka) was ∼6.5. Block by extracellular Ba2+was voltage dependent with apparent Kiat −40 and −80 mV of ∼160 and ∼80 μM, respectively. The conductance was TEA insensitive. Substitution of Rb+or NH4+for K+led to permeability ratios of 0.65 ± 0.07 and 0.15 ± 0.02 and inward conductance ratios of 0.17 ± 0.03 and 0.57 ± 0.09, respectively. Analysis of Ba2+-induced noise, with 40 mM extracellular K+, yielded single-channel currents of 0.39 ± 0.04 and −0.28 ± 0.04 pA at voltages of 0 and −40 mV, respectively, and a single-channel conductance of 17 ± 1 pS.
Quantitative Analyses of Dynamic Strain Sensitivity in Human Skin Mechanoreceptors
Authors: Edin Benoni B.
Published: November 2004

Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64% · s−1, i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities >8% · s−1. Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains <0.5% and a typical SAII unit began to discharge at <1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The “typical” peak discharge rate at the highest strain velocity studied was 50–95 imp/s−1 depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions ( r2 > 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.
Integration of Synaptic Responses to Neighboring Whiskers in Rat Barrel Cortex In Vivo
Authors: Higley Michael J. , Contreras Diego
Published: November 2004

Characterizing input integration at the single-cell level is a critical step to understanding cortical function, particularly when sensory stimuli are represented over wide cortical areas and single cells exhibit large receptive fields. To study synaptic integration of sensory inputs, we made intracellular recordings from the barrel cortex of anesthetized rats in vivo. For each cell, we deflected the principal whisker (PW) either alone or preceded by the deflection of a single adjacent whisker (AW) at an interval of 20 or 3 ms. At the 20-ms interval in all cases, prior AW deflection significantly suppressed the PW-evoked spike output and caused the underlying synaptic response to reach a peak Vm less depolarized than that arising from PW deflection alone. The decrease in peak Vm was not attributed to hyperpolarizing inhibition but to a divisive reduction in PW-evoked PSP amplitude. The reduction in amplitude was not a result of shunting inhibition but was mostly a result of removal of the synaptic drive, or disfacilitation. When the AW–PW interval was shortened to 3 ms, spike suppression was observed in a subset of the cells studied. In most cases, a divisive reduction in synaptic response amplitude was offset by summation with the preceding AW-evoked depolarization. To determine whether suppression is a general feature of synaptic integration by barrel cortex neurons, we also characterized the interaction of responses evoked by local electrical stimulation. In contrast to the whisker data, we found that responses to paired stimulation at the same intervals produced more spikes and reached a peak Vm more depolarized than the individual responses alone, suggesting that whisker-evoked suppression is not a result of postsynaptic mechanisms. Instead, we propose that cross-whisker response suppression depends on sensory-specific mechanisms at cortical and subcortical levels.
Impact of Catheter Shaft Angulation on the Accuracy of Atherosclerotic Plaque Volume Measurement by Three-Dimensional Intravascular Ultrasound
Authors: Palmer N D , Lessells A , Fox K A , Northridge D B
Published: November 2004

Computerized three-dimensional reconstruction of intravascular ultrasound (IVUS) images is a relatively new imaging modality for the study of atheromatous coronary disease with particular use in serial study of atheroma regression. Distortion of the acquired IVUS images has an important influence on the quality and accuracy of volume measurements made from the 3-D reconstruction. We evaluated the impact of commonly encountered sources of image distortion, catheter shaft angulation and luminal transducer position, on the accuracy of plaque and vessel volume measurements. A segment of diseased post-mortem human coronary artery was studied in a specially designed water bath, which enabled IVUS examination. A number of angulations of the arterial segment and the IVUS catheter were made to reproduce the areas of tortuousity encountered in the in vivo setting. Nine conformations were made. Following acquisition of IVUS images the segment was fixed in formalin and sectioned. Vessel, lumen and plaque volumes were determined by histomorphometry. These were compared to volume measurements made from 3-D reconstruction of the IVUS images in each conformation. Minimal catheter angulation produced acceptable variability for vessel (–7.9%), lumen (–6.0%) and plaque volume (-8.5%). Proximal angulations significantly over-estimated vessel, lumen and plaque volumes. Variability was greatest when multiple, severe angulations were applied (–17.7 to –21.3%). Eccentric catheter tip positioning produced greater variability in vessel (mean 16.8 ± 2.6 v. 14.2 ± 3.1%, p < 0.01) and plaque volume (18.1 ± 2.8 v. 15.3 ± 3.5%, p < 0.01). Technical factors, such as catheter shaft angulation and transducer tip position, significantly influence the degree of image distortion and subsequent volume measurement by computerized three-dimensional reconstruction of IVUS images. Recognition of these factors is important particularly in longitudinal studies of atheroma regression.
Microbubble Ultrasound Contrast Agents in the Visualization of Peripheral Vasculature in 'Doppler Rescue': A Review
Authors: Satchithananda K , Sellars M E K , Ryan S M , Sidhu P S
Published: November 2004

Microbubble ultrasound contrast agents were developed for use in the macrovascular circulation as an adjunct to a colour Doppler ultrasound examination — 'Doppler-rescue'. Although technical developments and the unique behavior of microbubble contrast in the liver have eclipsed the original perceived use, there remains an important role for microbubble contrast in the peripheral vasculature. This review details the applications of microbubble contrast agents in 'Doppler-rescue', with illustrations of important disease processes suitable for examination with microbubble contrast in order to reduce further radiological investigations.
A rich chemokine environment strongly enhances leukocyte migration and activities
Authors: Paoletti Samantha , Petkovic Vibor , Sebastiani Silvia , Danelon M. Gabriela , Uguccioni Mariagrazia , Gerber Basil O.
Published: November 2004

The migration of leukocytes in immune surveillance and inflammation is largely determined by their response to chemokines. While the chemokine specificities and expression patterns of chemokine receptors are well defined, it is still a matter of debate how leukocytes integrate the messages provided by different chemokines that are concomitantly produced in physiologic or pathologic situations in vivo. We present evidence for a novel regulatory mechanism of leukocyte trafficking. Our data are consistent with a mode of action where CC-chemokine receptor 7 (CCR7) agonists and unrelated, nonagonist chemokines first form a heteromeric complex, in the presence of which the triggering of CCR7 can occur at a much lower agonist concentration. The increase is synergistic and can be evoked by many but not all chemokines. Chemokine-induced synergism might provide an amplification system in “chemokine-rich” tissues, rendering leukocytes more competent to respond to migratory cues.
Outcomes of the Bobath concept on upper limb recovery following stroke
Authors: Luke Carolyn , Dodd Karen J , Brock Kim
Published: November 2004

Objective: To determine the effectiveness of the Bobath concept at reducing upper limb impairments, activity limitations and participation restrictions after stroke.

Methods: Electronic databases were searched to identify relevant trials published between 1966 and 2003. Two reviewers independently assessed articles for the following inclusion criteria: population of adults with upper limb disability after stroke; stated use of the Bobath concept aimed at improving upper limb disability in isolation from other approaches; outcomes reflecting changes in upper limb impairment, activity limitation or participation restriction.

Results: Of the 688 articles initially identified, eight met the inclusion criteria. Five were randomized controlled trials, one used a single-group crossover design and two were single-case design studies. Five studies measured impairments including shoulder pain, tone, muscle strength and motor control. The Bobath concept was found to reduce shoulder pain better than cryotherapy, and to reduce tone compared to no intervention and compared to proprioceptive neuromuscular facilitation (PNF). However, no difference was detected for changes in tone between the Bobath concept and a functional approach. Differences did not reach significance for measures of muscle strength and motor control. Six studies measured activity limitations, none of these found the Bobath concept was superior to other therapy approaches. Two studies measured changes in participation restriction and both found equivocal results.

Conclusions: Comparisons of the Bobath concept with other approaches do not demonstrate superiority of one approach over the other at improving upper limb impairment, activity or participation. However, study limitations relating to methodological quality, the outcome measures used and contextual factors investigated limit the ability to draw conclusions. Future research should use sensitive upper limb measures, trained Bobath therapists and homogeneous samples to identify the influence of patient factors on the response to therapy approaches.
Reliability and validity of functional balance tests post stroke
Authors: Tyson Sarah F , DeSouza Lorraine H
Published: November 2004

Objective: To contribute to the reliability and validity of a series of functional balance tests for use post stroke.

Design: Within-session, test-retest and intertester reliability was tested using the kappa coefficient and intraclass correlations. The tests were performed three times and the first and third attempts compared to test the within-session reliability. The tests were repeated a few days later to assess test-retest reliability and were scored simultaneously by two physiotherapists to assess the intertester reliability. To test criterion-related validity the tests were compared with the sitting section of the Motor Assessment Scale, Berg Balance Scale and Rivermead Mobility Index using Spearman's rho.

Setting: Stroke physiotherapy services of six National Health Service hospitals.

Participants: People with a post stroke hemiplegia attending physiotherapy who had no other pathology affecting their balance took part. Thirty-five people participated in the reliability testing and 48 people took part in the validity testing.

Main outcome measures: The following functional balance tests were used: supported sitting balance, sitting arm raise, sitting forward reach, supported standing balance, standing arm raise, standing forward reach, static tandem standing, weight shift, timed 5-m walk with and without an aid, tap and step-up tests.

Results: The ordinal level tests (supported sitting and standing balance and static tandem standing tests) showed 100% agreement in all aspects of reliability. Intraclass correlations for the other tests ranged from 0.93 to 0.99. All the tests showed significant correlations with the appropriate comparator tests (r=0.32-0.74 p≤0.05), except the weight shift test and step-up tests which did not form significant relationship with Berg Balance Scale (r=0.26 and 0.19 respectively).

Conclusion: These functional balance tests are reliable and valid measures of balance disability post stroke.