bluuebunny/crossref_metadata_2025 huggingface dataset:
VARIATIONS ON A THEME OF ROMANOFF
Authors: MURTY M. RAM , ROSEN MICHAEL , SILVERMAN JOSEPH H.
Published: October 2004

Fix an integer a≥2. For each m≥1, let fa(m) be the smallest power f so that af≡1 (mod m). We give explicit upper bounds for the series Σm1/mfa(m)ε and Σplog(p)/pfa(p)ε, generalizing and strengthening results of Romanoff, Landau, Erdös and Turan. We also prove analogous results over number fields and for abelian varieties.
DOUBLE GROUP CONSTRUCTION FOR COMPACT WORONOWICZ ALGEBRAS
Authors: NAKAGAMI YOSHIOMI
Published: October 2004

A double group construction for compact Woronowicz algebras gives us a noncompact unimodular Woronowicz algebra. We can apply this result to the compact Woronowicz algebra [Formula: see text] for the quantum group SUq(n), n≥2. When n=2, it is the noncompact Woronowicz algebra [Formula: see text] corresponding to the quantum Lorentz group SLq(2, C) due to Podleś and Woronowicz.
MODULI SPACES OF PARABOLIC HIGGS BUNDLES AND PARABOLIC K(D) PAIRS OVER SMOOTH CURVES: I
Authors: BODEN HANS U. , YOKOGAWA KÔJI
Published: October 2004

This paper concerns the moduli spaces of rank-two parabolic Higgs bundles and parabolic K(D) pairs over a smooth curve. Precisely which parabolic bundles occur in stable K(D) pairs and stable Higgs bundles is determined. Using Morse theory, the moduli space of parabolic Higgs bundles is shown to be a non-compact, connected, simply connected manifold, and a computation of its Poincaré polynomial is given.
ON BOUNDARY RIGIDITY AND REGULARITY OF HOLOMORPHIC MAPPINGS
Authors: COUPET BERNARD , PINCHUK SERGEY , SUKHOV ALEXANDRE
Published: October 2004

We prove that a continuous CR mapping between two pseudoconvex hypersurfaces of finite type in [Formula: see text] is smooth if at least one of the hypersurfaces is strictly pseudoconex.
ANALYTICAL APPROXIMATE SOLUTIONS OF NONLINEAR OSCILLATORS BY THE MODIFIED DECOMPOSITION METHOD
Authors: MOMANI SHAHER
Published: October 2004

Analytical approximate solutions for the nonlinear oscillators of the form [Formula: see text] are derived using the modified decomposition method. The analytical solutions of our model equations are calculated in the form of convergent series with easily computable components. Then the Laplace transformation and Padè approximant are effectively used to improve the convergence rate and accuracy of the computed series. The validity of the solutions is verified through some numerical examples. The results compare well with those obtained by the Runge–Kutta fourth-order method. The proposed scheme avoids the complexity provided by perturbation techniques.
Astragalus mongholicus and Polygonum multiflorum's Protective Function Against Cyclophosphamide Inhibitory Effect on Thymus
Authors: Wei Xiyun , Zhang Jinkun , Li Jun , Chen Subiao
Published: October 2004

The protective effects of two Chinese herbs, Astragalus mongholicus, Polygonum multiflorum and Astragalus mongholicus-Polygonum multiflorum in combination against thymus injury induced by cyclophosphamide were evaluated by transmission electron microscopy, image analysis, DNA gel electrophoresis as well as flow cytometry. Results showed that mice pretreated with cyclophosphamide had degenerated thymus with less normal thymocytes; when those mice were treated with the herbs, thymus morphology improved. The apoptosis analysis showed the thymus treated with the herbs had fewer apoptotic thymocytes than the thymus pretreated with cyclophosphamide only. In conclusion, Astragalus mongholicus and Polygonum multiflorum have protective effects on the thymus against cyclophosphamide-induced injury. Their protective effects partly attribute to reduced apoptosis. Astragalus mongholicus-Polygonum multiflorum in combination has better effects than either of the two herbs.
SPACETIME SYMMETRIES IN NONCOMMUTATIVE GAUGE THEORY: A HAMILTONIAN ANALYSIS
Authors: GHOSH SUBIR
Published: October 2004

We study spacetime symmetries in noncommutative (NC) gauge theory in the (constrained) Hamiltonian framework. The specific example of NC CP(1) model, posited in Ref. 9, has been considered. Subtle features of Lorentz invariance violation in NC field theory were pointed out in Ref. 13. Out of the two — observer and particle — distinct types of Lorentz transformations, symmetry under the former, (due to the translation invariance), is reflected in the conservation of energy and momentum in NC theory. The constant tensor θμν (the noncommutativity parameter) destroys invariance under the latter.

In this paper we have constructed the Hamiltonian and momentum operators which are the generators of time and space translations respectively. This is related to the observer Lorentz invariance. We have also shown that the Schwinger condition and subsequently the Poincaré algebra is not obeyed and that one cannot derive a Lorentz covariant dynamical field equation. These features signal a loss of the Particle Lorentz symmetry. The basic observations in the present work will be relevant in the Hamiltonian study of a generic noncommutative field theory.
THE COLOR TRIPLET $qq\bar{q}$ CLUSTER AND PENTAQUARK MODELS
Authors: HOGAASEN H. , SORBA P.
Published: October 2004

We study the properties of the color triplet [Formula: see text] quark cluster when flavor symmetry is broken. The relevance of such a cluster for some models of pentaquarks is then examined in the light of recent experimental signals.
ANALYTICAL BOUNCE SOLUTION IN A DISSIPATIVE QUANTUM TUNNELING
Authors: PARK D. K.
Published: October 2004

The analytical bounce solution is derived in terms of the polygamma function in the Caldeira–Leggett's dissipative quantum tunneling model. The classical action for the bounce solution lies between the upper and lower bounds in the full range of α, where α is a dissipation coefficient. The bounce peak point increases from 1 to 4/3 with the increase of α. In spite of various nice features, we have shown that the solution we have derived is not exact one by making use of the zero-mode argument in the linearized fluctuation equation. However, our solution can be a starting point for approximate computation of the prefactor in this model.
STRUCTURAL CHANGES CAUSED BY ERROR AND ATTACK TOLERANCE IN US AIRPORT NETWORK
Authors: CHI L. P. , CAI X.
Published: October 2004

Through the study of US airport network, we find that the network displays a high degree of error tolerance and an extreme vulnerability to attacks. The topological properties, including average degree, clustering coefficient, diameter and efficiency, are slightly affected when a few least connected airports are removed. Such properties change drastically with the removal of a few most connected ones. The degree distribution and the weight distribution under errors behave similarly to those of the original network. Under attacks, the degree distribution changes from a two-segment power-law to a monotonic one. While the under-attacked weight distribution still displays a power-law tail, with the exponent changing from 1.50 to 1.24.
AMINO ACID COMPOSITION-DEPENDENT ELASTICITY OF SPIDER SILK
Authors: ZHANG YONG , DAI LURU , OU-YANG ZHONG-CAN
Published: October 2004

Spider silk exhibits excellent mechanical features in both toughness and extensibility. In recent years considerable investigations have focused on it. The understanding of spider silk protein is important for the development bionic silk. In this paper, we study by Monte Carlo simulation the force-of-extension property of spider silk proteins as a function of the residue composition for major and minor ampullate glands of typical Araneid orb weaver as well as that for one artificial spider silk. The results are also compared with those from a designed protein whose amino acid composition is uniform. The results clearly show that the major and minor ampullate gland proteins are much tougher than the designed protein, whereas the artificial protein, as a model of a nature spider silk, does have good mechanical properties. Our simulation reveals that mechanical property of a spider silk protein is dependent on its amino acid composition and that an excellent result of natural evolution is manifest in the composition of the spider silk protein.
SIMULATED ANNEALING SCHEMES IN TRANSIENTLY CHAOTIC NEURAL NETWORK MODEL
Authors: FENG Y. C. , CAI X.
Published: October 2004

A transiently chaotic neural network (TCNN) is an approximation method for combinatorial optimization problems. The evolution function of self-back connect weight, called annealing function, influences the accurate and search speed of TCNN model. This paper analyzes two common annealing schemes. Furthermore we proposed a new subsection exponential annealing function. Finally, we compared these annealing schemes in TSP problem.
A CHARACTERISTIC OF THE TRANSITION TO CHAOS VIA TYPE V INTERMITTENCY
Authors: WANG YINGMEI , WANG WEN-XIU , WANG XUMING , HE DA-REN
Published: October 2004

In the transition to chaos via type V intermittency, when a periodic motion loses stability, there may be no intermediate higher-period orbits displayed before chaos or a sequential such orbits that form a staircase. The staircase may take a form of a conventional devil's staircase, a multiple devil's staircase or a seemingly irregular form. This article briefly presents typical examples for these situations.
TRAFFIC FLOW INFLUENCED BY TRAFFIC LIGHT AND TURNING PROBABILITY FOR A CROSSROAD
Authors: TAN HUILI , ZHANG CHAOYING , KONG LINGJIANG , LIU MUREN
Published: October 2004

A cellular automaton model with open boundary condition for a crossroad system controlled by a traffic light is presented. The traffic flow and speed of the first part of the road are quite different from those of the second part behind the crossing. The impact of turning probabilities and the cycle times of traffic light on the flow are investigated.
HYPERCHAOTIC SYNCHRONIZATION IN DETERMINISTIC SMALL-WORLD DYNAMICAL NETWORKS
Authors: JIANG PIN-QUN , WANG BING-HONG , BU SHOU-LIANG , XIA QING-HUA , LUO XIAO-SHU
Published: October 2004

In this paper, hyperchaotic synchronization in a network of continuous-time dynamical systems with small-world connections is investigated. The small-world network is obtained by selecting a part of nodes to be hubs and then using a globally coupled network to interconnect these hubs in an originally nearest-neighbor coupled network. We show that, the deterministic small-world dynamical network will also synchronize when the maximal Lyapunov exponent of the self-feedback system of single node is equated to, even great than zero. This explains why many real-world complex networks exhibit strong tendency toward synchronization even with a relatively weak coupling. Our study may shed some new light on synchronization phenomena in real complex networks.
ENERGY SPECTRAL STATISTICS IN THE QUANTUM SYSTEM WITH TWO PARTICLES
Authors: YANG SHIPING , YUAN GUOYONG , LI ZHE , CHANG HONG , LIU DE
Published: October 2004

In this paper, the quantum system with two particles is analyzed and the energy level spacing statistics distribution and Δ3-statistic are given. The results show that hard quantum chaos appear in the system with a certain potential. Tunnelling effect develops quantum chaos.
DENSITY-OF-STATES MONTE CARLO METHOD FOR SIMULATION OF TWO-DIMENSIONAL RANDOM BOND POTTS MODEL
Authors: YU YOU , YING HE-PING , CHEN QING-HU , PAN ZHENG-QUAN
Published: October 2004

Softening of the phase transition and critical phenomena for the 2D random-bond Potts ferromagnet is investigated by using the density-of-states Monte Carlo method to calculate the thermodynamic properties with a variety of the quenched bond-randomness characterized by a disorder amplitude r=Ks/Kw. The numerical results show that the crossover from the 1st- to 2nd-order transition was induced at finite lattices for the self-dual bimodal distribution.
CAUSALITY VERSUS WARD IDENTITY IN DISORDERED ELECTRON SYSTEMS
Authors: JANIŠ V. , KOLORENČ J.
Published: October 2004

We address the problem of fulfilling consistency conditions in solutions for disordered noninteracting electrons. We prove that if we assume the existence of the diffusion pole in an electron–hole symmetric theory we cannot achieve a solution with a causal self-energy that would fully fit the Ward identity. Since the self-energy must be causal, we conclude that the Ward identity is partly violated in the diffusive transport regime of disordered electrons. We explain this violation in physical terms and discuss its consequences.
SYNTHESIS AND CHARACTERISATION OF Ba5Cu3Oy
Authors: KALIYAPERUMAL L.K. , JEYABALAN K.
Published: October 2004

Synthesis and characterisation of Ba 5 Cu 3 O y compound is reported here. Powder XRD analysis shows that the system belongs to orthorhombic structure and the lattice parameters are a=8.664(8) Å, b=8.931(2) Å, c=9.072(9) Å.
SUPERFLUID BEHAVIOUR OF A QUANTUM q-GAS
Authors: R-MONTEIRO M. , RODRIGUES L.M.C.S.
Published: October 2004

We explore some consequences of the inequivalent representations of a q-oscillator algebra on a highly deformed quantum q-gas. By a simple choice of the continuum limit of the background ν0, the constant volume specific heat per mass C shows a λ-point transition and has a T3 dependence for low temperatures. Choosing a particular value of the deformation parameter q, we are able to reproduce the experimental value of the He II specific heat for T<0.5° K .
BACKSCATTERING AND THE DECAY OF TRANSMITTANCE IN A COHERENTLY ABSORBING OR AMPLIFYING ORDERED CHAIN
Authors: SEN ASOK K.
Published: October 2004

We study electronic properties of a one-dimensional, semi-infinite ordered chain in the presence of either absorption or amplification at each site (the site potentials having imaginary positive or negative parts) within a single-band, tight binding Hamiltonian. The spectrum in either case for an isolated (closed) quantum system becomes broader compared to the regular Bloch case. For an infinitely long ordered chain (open quantum system), the reflectance saturates to a value greater (lesser) than unity in the amplifying (absorbing) case and the transmittance decays to zero in either case. Thus, in contrast to a recent work of Pradhan and Kumar [Phys. Rev.B50, 9644 (1994)], it is not necessary to have any “synergy between wave confinement” due to any disorder or interaction induced confining mechanism on the transmitted wave and “coherent amplification by the active medium” to achieve an amplification in the reflectance.
NONCOLLINEAR MAGNETISM: EFFECTS OF SYMMETRY AND RELATIVITY
Authors: SANDRATSKII L.M. , KÜBLER J.
Published: October 2004

We give a brief review of the theory of noncollinear order in itinerant electron systems. The theory is an example of the use of the local density-functional approximation for first-principles calculations. We emphasize the role of symmetry arguments since they facilitate the calculations and make the physics of the problem transparent. We choose as examples spiral structures like those found experimentally in fcc Fe, the canted states of U 3 P 4 and weak ferromagnetism in α- Fe 2 O 3 and show that these different phenomena are explained by the theory.
EMPIRICAL ESTIMATES OF PHYSICAL PARAMETERS FROM ELECTRICAL RESISTIVITY MEASUREMENTS ON FERRITES
Authors: ISLAM MISBAH UL , BILAL M. SHAKEEL , ABBAS T. , RANA M.U. , RAZA S. MOHSIN
Published: October 2004

Measurements on the electrical resistivity of Mn 1−x Zn x Fe 2 O 4 ferrites with 0<x< 0.15 in the temperature range 300 K <T<450 K , have been carried out. Analysis of the normalised electrical resistivity of these ferrites shows deviations from linearity both at low and high temperatures. There exists a deviation in the electrical resistivity at 300 K at high zinc concentration which may be due to hopping of electrons between Fe +2 and Fe +3 ions at octahedral sites.
REMARK ON THE EXISTENCE OF LONG-RANGE ORDER IN QUASI-TWO-DIMENSIONAL HUBBARD MODEL
Authors: BELKASRI A. , RICHARD J.L.
Published: October 2004

Recently in many works on the mechanism of high temperature superconductivity (see for example Refs. 1–6), quasi-averages like  were considered even in the case of a dimension less or equal two. But it is well known from the old work of Hohenberg7 that these quasi-averages are zero at T≠0 in case of 1 and 2 dimensions. In this communication we generalize the Hohenberg’s result to any kind of Hubbard type model on lattice and prove that in the case of quasi-two-dimension, the theorem of Hohenberg is not in contradiction with having ≠0 (at T≠0). In practice this makes sense to compare the data for a thin film (which can be considered as quasi-2D system) to the theoretical analysis based on quasi-two-dimensional models, but not for strictly two-dimensional case.
A THEORETICAL INTERPRETATION FOR THE EXCITATION ENERGY TRANSFER BETWEEN IDENTICAL MOLECULES IN LIQUID AND SOLID SOLUTION OF HIGH CONCENTRATION
Authors: PHILIPPETIS A.L.
Published: October 2004

In this work we refer to some experimental results related. as we believe, with excitation energy transfer between molecules of the same kind in liquid and solid solutions of high concentration. We try to explain these results by a theoretical interpretation based on the assumption that the “migration of energy” depends on the distance between the molecules, the orientation of these molecules and on a coupling constant related with the type of these molecules.
HIGH PRESSURE ELECTRICAL RESISTIVITY STUDY ON ORTHORHOMBIC SnTe1−xSx
Authors: ARIPONNAMMAL S. , NATARAJAN S.
Published: October 2004

Electrical resistivity measurements under pressure and lattice parameter study on SnTe 1–xSx(0.5≤x≤1) are reported here. The structure of these samples is confirmed by the theoretical calculation of X ray intensities using Lazy-Pulverix programme. The electrical resistivity decreases with the increase of pressure and also with the decrease of sulphur concentration. High pressure electrical resistivity study has produced more evidence that the compounds are layered material.
CALCULATION OF MADELUNG CONSTANT OF VARIOUS IONIC STRUCTURES BASED ON THE SEMISIMPLE LIE ALGEBRAS
Authors: JAFARIZADEH M.A. , NAZERI F. , KESHISHI A.
Published: October 2004

Periodic structures are constructed by using semisimple Lie algebras. Then these structures are generalized to ionic structures. Finally Madelung constant of these structures are calculated by solving Poisson equation in the fundamental domain of corresponding Lie algebras with Dirichlet boundary conditions. The obtained results are consistent with data of the ionic crystals with the same coordination numbers as our structures.
ON THE DETERMINATION OF CRITICAL POINT IN HIGHER-ORDER VARIATIONAL CUMULANT EXPANSION
Authors: OU X.F. , OU J.T. , LIN D.L.
Published: October 2004

To the lowest order approximation, the method of variational cumulant expansion has been successful in the determination of the critical point of a spin system on the Ising model. In the second order calculation, unphysical phase transition arises. In this letter, we first analyze the origin of unphysical phase transitions in high-order variational cumulant expansion calculations. We then explain the basis on which a conjecture is proposed that to any order m of the variational cumulant expansion, the critical point is given by the bifurcation point of the free energy. The theory is finally verified numerically for the two-dimensional case.
A CONSTRAINT ON THE ANOMALOUS GREEN’S FUNCTION
Authors: KIM YONG-JIHN
Published: October 2004

It is shown that the physical constraint of the Anomalous Green’s function gives a natural pairing condition. The resulting self-consistency equation is directly related to the BCS gap equation. Both inhomogeneous and homogeneous systems are considered to illustrate the importance of the constraint. Especially we find weak localization correction to the phonon-mediated interaction.
COMPTON PROFILE ANISOTROPIES IN SODIUM MICROCLUSTERS
Authors: ANNAPOORNI P.C. SUDHA , NEELAKANDAN K.
Published: October 2004

Anisotropies in the Compton profile of microclusters of sodium as a function of the cluster size as well as the direction of the scattering vector is presented. The anisotropy is the result of the shape deformations of the cluster which can be described in terms of a modified harmonic oscillator potential as suggested by Clemenger.1
COMPETING DYNAMICAL BEHAVIOR OF THE ISING MODEL IN ONE DIMENSION
Authors: GRANDI B.C.S. , FIGUEIREDO W.
Published: October 2004

We have studied the behavior of the one-dimensional ferromagnetic Ising model in contact with a heat bath and subject to an external source of energy. The contact with the heat bath is simulated by a process of Glauber type, while the continuous flux of energy into the system by a process of Kawasaki type. We show, within the dynamical pair approximation that the phase diagram exhibits a line of continuous nonequilibrium transitions between the paramagnetic and antiferromagnetic phases. However, detailed Monte Carlo simulations on the same model show clearly that the only stationary state is the paramagnetic one, whatever is the value of the competition parameter between the Glauber and Kawasaki dynamics.
NEW NON-MARKOVIAN TREATMENT OF THE SPONTANEOUS DECAY OF AN UNSTABLE ATOMIC STATE IN RELATIVISTIC QED
Authors: SEKE J.
Published: October 2004

It is shown that the application of a self-consistent projection-operator method, developed recently by the author, makes a complete treatment of the spontaneously decaying atomic state in relativistic QED possible. In a new physical real-transition interaction picture (in which the unobservable interaction of the free electron with the vacuum radiation field is eliminated) explicit finite analytic results for the non-Markovian time evolution and the radiative line shape in the case of relativistic Lyman-α spontaneous emission are obtained.
DIMENSIONAL CROSSOVER IN Bi1.8Pb0.4Sr2Ca2Cu3Oy TEXTURED THICK FILM
Authors: WANG Z.H.
Published: October 2004

The temperature dependence of resistance of C -axis oriented Bi (2223) thick film from 300 K to 100 K at 0 T (zero magnetic field) were measured. By choosing T c in different ways, such as R/Rn=0.9, 0.5, 0.1, 0.01 and 0.001, they are shown that the different results could be obtained. The data were described in terms of the classic theory of thermodynamic fluctuations. Two crossover from 2D to 3D and 1D to 2D was observed very close to the critical temperature T c when T c only was defined as zero-resistance temperature. The zero-temperature coherence length was estimated.
SIGNAL-TO-NOISE RATIO IN STOCHASTIC RESONANCE
Authors: CHATTAH A.K. , BRIOZZO C.B. , OSENDA O. , CÁCERES M.O.
Published: October 2004

We solve the Fokker-Planck equation for an overdamped Brownian particle in a periodically forced bistable potential by means of a path integral method, obtaining the propagators in the steepest-descent (small-noise) approximation. We compute the long-times asymptotic probability distribution, the asymptotic correlation functions, and the time-averaged spectral density, which allows us the immediate calculation of the signal to noise ratio, a directly measurable quantity useful to characterize the phenomenon of stochastic resonance. Our numerical algorithm is fast and runs on a desktop computer, and the results agree with experiments and with former theoretical calculations of the amplification factor; in addition it allows us to calculate the experimentally more accessible signal to noise ratio.
EFFECT OF THERMAL NOISE ON THE CURRENT-VOLTAGE CHARACTERISTICS OF JOSEPHSON JUNCTIONS
Authors: CHATTAH A.K. , BRIOZZO C.B. , OSENDA O. , CÁCERES M.O.
Published: October 2004

We analyze the influence of thermal noise on the Shapiro steps appearing in the current-voltage characteristics of Josephson junctions. We solve the Fokker-Planck equation describing the system by a path integral method in the steepest-descent approximation, previously applied to the stochastic resonance problem. We obtain the Asymptotic Time-Periodic Distribution Pas(ϕ, t), where ϕ∈[0, 2π] and compute from it the voltage [Formula: see text], constructing the I-V characteristics. We find a defined “softening” of the Shapiro steps as temperature increases, for values of the system parameters in the experimentally accessible range.
IRREVERSIBLE TRANSITIONS IN A TWO SPECIES BRANCHING ANNIHILATING RANDOM WALKER PROCESS
Authors: HOYUELOS MIGUEL , ALBANO EZEQUIEL V. , MÁRTIN HÉCTOR O.
Published: October 2004

We introduce a branching annihilating random walker process with two species, particles A and B, which diffuse creating particles of opposite kind (A→A+B, B→B+A) and annihilating instantaneously (A+B→0) when they meet. The model is defined in a one dimensional discrete lattice. For particles A and B, the rate of jumping are pA and pB, and the rate of branching (1−pA) and (1−pB), respectively (0≤pA, pB≤1). In the [pA, pB]-plane it is found two different phases: the vacuum state and the active phase with finite density of particles. The system undergoes irreversible second order phase transitions between these states along a critical line. Monte Carlo results show that the transitions belong to the same universality class as directed percolation.
DENDRITIC PHASE BOUNDARY OF A SUPERCONDUCTOR
Authors: LINGAM LYDIA S. , SHRIVASTAVA KESHAV N.
Published: October 2004

Fluctuation in the distance between flux lines in a superconductor is calculated in a fractal dimension and from that using Lindemann criterion of melting, a field versus temperature phase boundary is deduced for the dendritic phase of a superconductor. This phase boundary is predicted to be B−4∝(1−T FM /T c ) where T FM is the flux-lattice melting temperature. When both the fractal as well as the spectral dimensionalities are considered the phase boundary is predicted to be determined by B8/5∝(1−T FM /T c ).
ENERGY BAND OVERLAPPING IN HIGH-Tc SUPERCONDUCTORS
Authors: MORENO M. , MÉNDEZ-MORENO R. M. , ORTIZ M. A. , OROZCO S.
Published: October 2004

Multi-band superconductors are analyzed and the relevance of overlapping energy bands to the high-T c of these materials is studied. Within the BCS framework, a two band model with generalized Fermi surface topologies is developed. Values of the overlapped occupancy parameters for typical cuprate superconductors are obtained as a function of the ratio R and the effective coupling constant, λ, in the weak-coupling limit. The overlap scale is of the order or lower than the cutoff (Debye) energy. The typical behavior of the isotope effect is obtained. As these superconductors have transition temperatures above the phonon barrier, the results of this approach are important to the generic understanding of the high-T c superconducting mechanism.
MÖSSBAUER SECOND-ORDER DOPPLER SHIFT AND THE RECOILLESS FRACTION OF 119Sn IN SUPERCONDUCTORS
Authors: LINGAM LYDIA S. , SHRIVASTAVA KESHAV N.
Published: October 2004

The second-order Doppler shift (SODS) of the Mössbauer spectra in a superconductor, δ SC , is calculated for the first time. The shift depends on the fourth power of the ratio of the gap energy of the superconductor to that of the matrix element of the electron–phonon interaction. At T=T c where the gap vanishes, the shift reduces to that in the normal state. The relative values of the SODS and the isomer shifts are found in several superconductors. The isomer shift for 119 Sn in EuBa 2 Cu 2.98 Sn 0.02 O 7−δ has been found. The recoilless fraction of the 119 Sn in EuBa 2 Cu 2.98 Sn 0.02 O 7−δ is compared with a previous theory. It is found that the ordinary BCS type gap agrees with the experimental measurements of the recoilless fraction only when the gap is modified to include a lattice distortion in the superconducting state.
BRANE UNIVERSES TESTED AGAINST ASTRONOMICAL DATA
Authors: DABROWSKI MARIUSZ P. , GODŁOWSKI WŁODZIMIERZ , SZYDŁOWSKI MAREK
Published: October 2004

We discuss observational constrains coming from supernovae imposed on the behaviour of the Randall–Sundrum models. We test the models using the Perlmutter SNIa data as well as the new Knop and Tonry/Barris samples. The data indicates that, under the assumption that we admit zero pressure dust matter on the brane, the cosmological constant is still needed to explain current observations. We estimate the model parameters using the best-fitting procedure and the likelihood method. The observations from supernovae give a large value of the density parameter for brane matter Ωλ,0≃0.01 as the best fit. For high redshifts z>1.2, the difference between the brane model and the ΛCDM (Perlmutter) model becomes detectable observationally. From the maximum likelihood method we obtained the favored value of Ωλ,0=0.004±0.016 for Ωk,0=0 and Ω m ,0=0.3. This gives the limit Ωλ,0<0.02 at 1σ level. While the model with brane effects is preferred by the supernovae type Ia data, the model without brane fluid is still statistically admissible. We also discuss how fit depends on restrictions of the sample, especially with respect to redshift criteria. We also pointed out the property of sensitive dependence of results with respect to the choice of ℳ parameter. For comparison the limit on brane effects which comes from CMB anisotropies and BBN is also obtained. The uncertainty in the location of the first peak gives a stronger limit Ωλ,0<1.0×10-12, whereas from BBN we obtain that Ωλ,0<1.0×10-27. However, both very strict limits are obtained with the assumption that brane effects do not change the physics in the pre-recombination era, while the SNIa limit is model independent.

We demonstrate that the fit to supernovae data can also be obtained if we admit the phantom matter p=-(4/3)ϱ on the brane, where this matter mimics the influence of the cosmological constant. We show that phantom matter enlarges the age of the universe on the brane which is demanded in cosmology. Finally, we propose to check for dark radiation and brane tension by the application of the angular diameter of galaxies minimum value test.
SYSTEMATIC STUDY OF SHELL EFFECT NEAR DRIP-LINES
Authors: ADHIKARI S. , SAMANTA C.
Published: October 2004

The variation of nuclear shell effects with nucleon numbers is evaluated using the modified Bethe–Weizsäcker mass formula (BWM) and the measured atomic masses. The shell effects at magic neutron numbers N=8, 20, 28, 50, 82 and 126 and magic proton numbers Z=8, 20, 28, 50 and 82 are found to vary rapidly approaching the drip-lines. The shell effect due to one magic number increases on approaching another magic number. Thus, shell effects are not always negligible near the drip-lines.
EFFECTIVE MESON MASS IN NUCLEAR MATTER BASED ON DISPERSION EQUATION INCLUDING ${\rm N} \bar{\rm N},\ \Delta \bar{\rm N},\ \bar\Delta {\rm N}$ EXCITATIONS
Authors: NAKANO MASAHIRO , LIU LIANG-GANG , MATSUURA HIROYUKI , NAGASAWA TAISUKE , MAKINO KEN-ICHI , NODA NOBUO , KOUNO HIROAKI , HASEGAWA AKIRA
Published: October 2004

Effective meson masses of σ, ω, ρ and π in nuclear matter are calculated from the meson self-energy of the particle–antiparticle excitations. Instead of the traditional renormalization, the dispersion relation method is used to calculate the real part from the finite imaginary part, since the tensor coupling of the pion and ρ meson is not renormalized in the usual sense. In this paper, we show the effects from antidelta-nucleon and delta-antinucleon excitations in π meson mass beside nucleon–antinucleon excitation. It is also shown that agreement is obtained on the ω meson mass predicted by the subtraction method and ρ meson mass by the QCD sum rule method. It is concluded that the dispersion equation method leads to the fact that all the meson mass decreases as the baryon density increases, and it supports the chiral symmetry restoration.
EVALUATION OF MASSIVELY PARALLEL COMPUTING FOR EXHAUSTIVE AND CLUSTERED MATCHED-FIELD PROCESSING
Authors: RACCA R.G. , MENG Z. , OZARD J.M. , WILMUT M.J.
Published: October 2004

Many computer algorithms contain an operation that accounts for a substantial portion of the total execution cost in a frequently executed loop. The use of a parallel computer to execute that operation may represent an alternative to a sheer increase in processor speed. The signal processing technique known as matched-field processing (MFP) involves performing identical and independent operations on a potentially huge set of vectors. To investigate a massively parallel approach to MFP and clustered nearest neighbors MFP, algorithms were implemented on a DECmpp 12000 massively parallel computer (from Digital Equipment and MasPar Corporation) with 8192 processors. The execution time for the MFP technique on the MasPar machine was compared with that of MFP on a serial VAX9000–210 equipped with a vector processor. The results showed that the MasPar achieved a speedup factor of at least 17 relative to the VAX9000. The speedup was 3.5 times higher than the ratio of the peak ratings of 600 MFLOPS for the MasPar versus 125 MFLOPS for the VAX9000 with vector processor. The execution speed on the parallel machine represented 64% of its peak rating. This is much better than what is commonly assumed for a parallel machine and was obtained with modest programming effort. An initial implementation of a massively parallel approach to clustered MFP on the MasPar showed a further order of magnitude increase in speed, for an overall speedup factor of 35.
ESTIMATING GEOACOUSTIC BOTTOM PROPERTIES FROM TOWED ARRAY DATA
Authors: JESUS S.M. , CAITI A.
Published: October 2004

Estimating the seabottom geophysical structure from the analysis of acoustic returns of an explosive source (air-gun, sparker,…) has been used for a longtime as a routine survey technique. Recent work showed the possibility of using well-suited numerical models to invert the acoustic field for estimating detailed geoacoustic sediment properties. Common implementations used long synthetic aperture arrays (up to 2 km and more) in order to resolve potential environmental ambiguities of the acoustic field. Others, used vertical arrays of sensors covering a significant part of the water column to identify the channel normal mode structure and thus gather information for the bottom physical relevant properties. This paper investigates, with simulated data, the concept of using a moderate aperture physical line array and a sound source simultaneously towed by a single ship for inverting the bottom geoacoustic structure from the acoustic returns received on the array. First, bottom parameter estimators are derived and their system sensitivity is investigated. In particular, it is shown that such a system may be used to sense compressional and shear velocities on the bottom first layers. Density and attenuations (both compressional and shear) have in general small influence on the acoustic field structure and are therefore difficult to estimate. Increasing the signal frequency bandwidth by incoherent module averaging has no significant influence on sensitivity. Mismatch cases, mainly those related to array/source relative position, showed that deviations of more than λ/3 in range and λ/5 in depth may give erroneous extremum location and therefore biased final estimates. Second, two bottom parameter estimators are compared and their performance tested on a typical shallow water environment. In order to solve the underlying multiparameter inverse problem, global search optimization is used. In particular, it is shown that the use of an adaptive genetic algorithm may, in conjunction with a well-suited maximum likelihood based parameter estimator, rapidly converge to the surface extremum. Inversion results are in agreement with the predictions obtained from the sensitivity study. The mean relative error at 10 dB signal-to-noise ratio is within 1% for the compressional velocity, while greater errors are reported for the shear velocity, Comparison with recent results obtained with a radial basis functions (RBF) inversion strategy showed similar performance. Finally, results obtained with a 156 m aperture towed array showed a good agreement between the inverted compressional velocities and the ground truth measurements.
A NUMERICAL STUDY OF NONLINEAR PROPAGATION OF DISTURBANCES IN TWO-DIMENSIONS
Authors: SHEU TONY W.H. , FANG C.C.
Published: October 2004

In the spirit of the method of characteristics, we present in this paper a generalized Taylor-Galerkin finite element model to simulate the nonlinear propagation of finite-amplitude disturbances. In a nonlinear Euler system, the multi-dimensional formulation is constructed through the conservation variables. Noticeable is that the scheme is found to exhibit high-phase-accuracy, together with minimal numerical damping. This scheme, therefore, is best-suited to simulation of disturbances in an acoustic field. To begin with, we validate the characteristic model by simulating two transport problems amenable to analytic solutions. Motivated by the apparent success, we apply the proposed third-order accurate upwind model to investigate a truly nonlinear acoustic field. The present analysis is intended to elucidate to what extent the nondissipative, nondispersive and isotropic characteristics pertaining to three wave modes of the acoustic system are still valid.
BROADBAND SOURCE LOCALIZATION IN THE GULF OF MEXICO
Authors: MICHALOPOULOU ZOI-HELENI , PORTER MICHAEL B. , IANNIELLO JOHN P.
Published: October 2004

The Gulf of Mexico experiment involved a broadband source (100–600 Hz) transmitting pseudorandom noise. The acoustic field was received by five hydrophones positioned vertically in the water column. By performing a correlation between the received time series and the transmitted signal, an approximation of the impulse response for the ocean channel is obtained. This impulse response is readily interpretable to yield information about the experiment, especially its geometry including receiver and bottom depths. With this refined environmental information, we then apply matched-field processing to obtain the source position.
SOURCE TRACKING IN THE HUDSON CANYON EXPERIMENT
Authors: MICHALOPOULOU ZOI-HELENI , PORTER MICHAEL B.
Published: October 2004

In the Hudson Canyon experiment, a broadband source, transmitting simultaneously in four frequencies, moved in range at a constant depth and bearing. Using broadband matched-field processing we demonstrate that the source can be localized and tracked. Incoherent broadband approaches for matched-field processing, based on the averaging of ambiguity surfaces obtained with the narrowband Bartlett and Minimum Variance processors, are compared to a new coherent variant. Localization is very successful when either the incoherent or coherent Bartlett estimator is used. The Minimum Variance processor performance in determining the source location is very poor in the incoherent case but improves significantly with the introduction of the coherent scheme.
MEK1 restores migration of polyamine-depleted cells by retention and activation of Rac1 in the cytoplasm
Authors: Vaidya Rajiv J. , Ray Ramesh M. , Johnson Leonard R.
Published: October 2004

We previously showed that polyamines are required for proliferation and migration both in vivo and in a cultured intestinal epithelial cell (IEC-6) model. Wounding of the IEC-6 monolayer induced transient ERK activation, which was further enhanced by EGF. EGF stimulated migration in control and polyamine-depleted cells, but the degree of stimulation was significantly less in polyamine-depleted cells. Inhibition of MEK1 inhibited basal as well as EGF-induced ERK activation and migration. Expression of constitutively active (CA)-MEK and dominant-negative (DN)-MEK had significant effects on F-actin structure. CA-MEK increased stress fiber and lamellipodia formation, while DN-MEK showed loss of stress fibers and abnormal actin cytoskeletal structure. Unlike EGF, CA-MEK significantly increased migration of both control and polyamine-depleted cells. The most important and significant finding in this study was that polyamine depletion caused localization of Rac1 and RhoA to the nuclear as well as perinuclear regions. Interestingly, CA-MEK completely reversed the subcellular distribution of Rac1 and RhoA proteins in polyamine-depleted cells. Polyamine depletion increased Rac1 in the nuclear fraction and decreased it in the cytoplasmic and membrane fractions of vector-transfected cells. CA-MEK prevented accumulation of Rac1 in the nucleus. Polyamine depletion significantly decreased Rac1 activity during 6-h migration in vector-transfected cells. Cells transfected with CA-MEK had almost identical levels of activated Rac1 in all three groups. These results suggest that polyamine depletion prevents activation of Rac1 and RhoA by sequestering them to the nucleus and that expression of constitutively active MEK reverses this effect, creating the cellular localization required for activation.
Decrease in Synaptic Transmission Can Reverse the Propagation Direction of Epileptiform Activity in Hippocampus In Vivo
Authors: Feng Zhouyan , Durand Dominique M.
Published: October 2004

Most types of epileptiform activity with synaptic transmission have been shown to propagate from the CA3 to CA1 region in hippocampus. However, nonsynaptic epileptiform activity induced in vitro is known to propagate slowly from the caudal end of CA1 toward CA2/CA3. Understanding the propagation modes of epileptiform activity, and their causality is important to revealing the underlying mechanisms of epilepsy and developing new treatments. In this paper, the effect of the synaptic transmission suppression on the propagation of epilepsy in vivo was investigated by using multiple-channel recording probes in CA1. Nonsynaptic epileptiform activity was induced by calcium chelator EGTA with varied concentrations of potassium. For comparison, disinhibition synaptic epileptiform activity was induced by picrotoxin (PTX) with or without partial suppression of excitatory synaptic transmission. The propagation velocity was calculated by measuring the time delay between two electrodes separated by a known distance. The results show that in vivo nonsynaptic epileptiform activity propagates with a direction and velocity comparable to those observed in in vitro preparations. The direction of propagation for nonsynaptic activity is reversed from the PTX-induced synaptic activity. A reversal in propagation direction and change in velocity were also observed dynamically during the process of synaptic transmission suppression. Even a partial suppression of synaptic transmission was sufficient to significantly change the propagation direction and velocity of epileptiform activity. These results suggest the possibility that the measurement of propagation can provide important information about the synaptic mechanism underlying epileptic activity.
The distribution of Mahler′s measures of reciprocal polynomials
Authors: Sinclair Christopher D.
Published: October 2004

We study the distribution of Mahler′s measures of reciprocal polynomials with complex coefficients and bounded even degree. We discover that the distribution function associated to Mahler′s measure restricted to monic reciprocal polynomials is a reciprocal (or antireciprocal) Laurent polynomial on [1, ∞) and identically zero on [0, 1). Moreover, the coefficients of this Laurent polynomial are rational numbers times a power of π. We are led to this discovery by the computation of the Mellin transform of the distribution function. This Mellin transform is an even (or odd) rational function with poles at small integers and residues that are rational numbers times a power of π. We also use this Mellin transform to show that the volume of the set of reciprocal polynomials with complex coefficients, bounded degree, and Mahler′s measure less than or equal to one is a rational number times a power of π.
Extended Fibonacci numbers and polynomials with probability applications
Authors: Antzoulakos Demetrios L.
Published: October 2004

The extended Fibonacci sequence of numbers and polynomials
is introduced and studied. The generating function,
recurrence relations, an expansion in terms of multinomial
coefficients, and several properties of the extended Fibonacci
numbers and polynomials are obtained. Interesting relations
between them and probability problems which take into account
lengths of success and failure runs are also established.
Diagnosis of Sleep-Related Breathing Disorders by Visual Analysis of Transthoracic Impedance Signals in Pacemakers
Authors: Scharf Christoph , Cho Yong K. , Bloch Konrad E. , Brunckhorst Corinna , Duru Firat , Balaban Kryzstof , Foldvary Nancy , Liu Lynn , Burgess Richard C. , Candinas Reto , Wilkoff Bruce L.
Published: October 2004

Background—

Minute ventilation sensors of cardiac pacemakers measure ventilation by means of transthoracic impedance changes between the pacemaker case and the electrode tip. We investigated whether this technique might detect sleep-related breathing disorders.

Methods and Results—

In 22 patients, analog waveforms of the transthoracic impedance signal measured by the pacemaker minute ventilation sensor over the course of a night were visualized, scored for apnea/hypopnea events, and compared with simultaneous polysomnography. Analysis of transthoracic impedance signals correctly identified the presence or absence of moderate to severe sleep apnea (apnea/hypopnea index, AHI >20 h
−1
) in all patients (receiver operating characteristics, ROC=1.0). The ROC for AHI scores of ≥5 h
−1
and ≥10 h
−1
showed an area under the curve of 0.95,
P
<0.005, and 0.97,
P
<0.0001, respectively. Accuracy over time assessed by comparing events per 5-minute epochs was high (Cronbach α reliability coefficient, 0.85; intraclass correlation, 0.73). Event-by-event comparison within ±15 seconds revealed agreement in 81% (κ, 0.77;
P
<0.001).

Conclusions—

Detection of apnea/hypopnea events by pacemaker minute ventilation sensors is feasible and accurate compared with laboratory polysomnography. This technique might be useful to screen and monitor sleep-related breathing disorders in pacemaker patients.
Right Bundle-Branch Block Ventricular Tachycardias
Authors: Patel Vickas V. , Rho Robert W. , Gerstenfeld Edward P. , Hsia Henry H. , Callans David J. , Marchlinski Francis E.
Published: October 2004

Background—

Identifying the septal versus lateral site of origin of ventricular tachycardia (VT) with a right bundle-branch block (RBBB)–type pattern and an R-S ratio >1 in lead V
1
is difficult with the 12-lead ECG, especially in patients with prior apical infarction.

Methods and Results—

We prospectively evaluated 58 patients with VT. Sixteen patients had apical infarcts (group 1), 29 had nonapical infarcts (group 2), and 13 had no heart disease (group 3). QRS complex onset to activation at the right ventricular apex (stim-RVA) was measured during left ventricular (LV) apical septal and lateral pacing, and 47 RBBB-type VTs (QRS-RVA) were localized to the septal or lateral apex by using entrainment techniques. Pacing and VT site of origin were confirmed by electroanatomic mapping. The stim-RVA time was 59±16 ms for septal versus 187±24 ms for lateral sites in group 1,
P
<0.001; 70±14 ms for septal versus 169±19 ms for lateral sites in group 2,
P
<0.001; and 42±15 ms for septal versus 86±16 ms for lateral sites in group 3,
P
<0.005. The QRS-RVA time was 50±13 ms for apical septal VTs versus 178±21 ms for lateral VTs in group 1,
P
<0.001; 71±17 ms for apical septal versus 157±20 ms for lateral VTs in group 2,
P
<0.001; and 32±12 ms for septal versus 71±16 ms for lateral VTs in group 3,
P
<0.01.

Conclusions—

The QRS-RVA differs for the VT site of origin from the LV septal versus lateral apex. These data prove useful in rapidly regionalizing the VT site of origin with a V
1
R-S ratio >1, particularly in instances of an apical infarct, where surface ECG distinctions are less identifiable.