bluuebunny/crossref_metadata_2025 huggingface dataset:
DIFFUSION MONTE CARLO STUDY OF GROUND STATE PROPERTIES OF QUANTUM DOTS
Authors: PEDERIVA FRANCESCO
Published: July 2002

We present the results of Diffusion Monte Carlo (DMC) calculations based on accurate multiconfiguration wave functions for N electrons (N≤13) confined to a parabolic quantum dot. The density and correlation energies have been computed and compared with the predictions of local spin density approximation theory (LSDA). We also computed the addition energy a function of the number of electrons in the dot, and compared them with the results of LSDA and Hartree Fock calculations. DMC results show a behavior qualitatively closer to the result of recent capacitance experiments.
3He DIMERS IN TWO-DIMENSIONAL 3He-4He MIXTURE FILMS
Authors: SAARELA M. , PAASO J. , KROTSCHECK E. , SCHÖRKHUBER K.
Published: July 2002

We have studied the ground state properties of two-dimensional 3 He -4 He mixtures at zero temperature. 3 He atoms with opposite spins form loosely bound dimers in free space and in low concentration mixtures with 4 He . The binding energy of the dimer ranges from milli-Kelvins near the saturation density to micro-Kelvins at the solidification density. The radius of such a weakly bound dimer is tens of Ångstöms. We also calculate the phase diagram of the mixture. The maximum solubility of 3 He ≈7% is determined by comparing chemical potentials in the pure and mixed fluids. The upper stability limit of the super-saturated mixture is obtained from the second derivative of the enthalpy. It becomes negative at the concentration 10-15% depending of the pressure, indicating a softening of the concentration-fluctuation mode. We also find an indication of the phase transition from the dimerized to atomic mixture.
FERROMAGNETIC RESONANCE IN TERFENOL-D AT 17 GHz
Authors: DEWAR G. , PAGEL S. , SOURIVONG P.
Published: July 2002

Ferromagnetic resonance measurements have been performed on several samples of Terfenol-D ( Dy0.73Tb0.27Fe1.95 ) at 16.95 GHz and over the temperature range 293 to 305 K. We find that the first magnetocrystalline anisotropy constant, obtained from one sample under nearly zero stress, is K1 = (-1.4±1.0)× l06 erg/cm 3 at 294 K. Our measurement is distinct from quasistatic torque measurements in that the lattice does not deform during the measurement and, hence, the anisotropy contribution due to magnetoelastic strain does not enter. The bare anisotropy constant, unmodified by static elastic strain, is [Formula: see text] and [Formula: see text]. The samples exhibited hysteresis; the position of FMR shifted by 4.0 kOe between measurements made with the magnetic field increasing and those made with the field decreasing.
EXCITONS IN QUASI-ONE-DIMENSIONAL CRYSTALLINE PERYLENE DERIVATIVES: BAND STRUCTURE AND RELAXATION DYNAMICS
Authors: HOFFMANN M. , HASCHE T. , SCHMIDT K. , CANZLER T. W. , AGRANOVICH V. M. , LEO K.
Published: July 2002

The exciton structure of crystalline MePTCDI (N-N'-dimethylperylene-3,4,9,10-dicarboximide) is modeled by a one-dimensional Hamiltonian, which includes the interactions between Frenkel excitons with several vibronic levels and charge-transfer excitons. Using appropriate fitting parameters, which are verified by quantum chemical calculations, this model can explain the main features of the low temperature absorption spectrum. Polarized absorption spectra show different polarization ratios for the various peaks. This polarization behavior is explained by the varying contribution of the charge-transfer transition dipole, which has a direction different from the Frenkel transition dipole. Our model for the exciton band structure is supported by transient emission measurements.
Growth of epitaxial ZnO thin film by oxidation of epitaxial ZnS thin films on Si(111)
Authors: Miyake A. , Kominami H. , Aoki T. , Tatsuoka H. , Kuwabara H. , Nkanishi Y. , Hatanaka Y.
Published: July 2002

The growth of epitaxial ZnO thin film on Si substrate by the oxidation of epitaxial ZnS film is a novel method and we are reporting this first time. The merits of the use of Si substrate are to make driving voltage in LED lower and less expensive than sapphire substrate. In this study, the epitaxial ZnO thin film could be successfully grown on the Si substrate. The epitaxial films showed a strong near ultraviolet emission peaked at around 3.32 eV at room temperature under 325 nm excitation.
X-RAY ANALYSIS AND MICROHARDNESS CHARACTERIZATION OF TiN/Ti MULTILAYERS
Authors: LI WENMING , GONG HAO , CAI JIANLING , WANG YUMING
Published: July 2002

TiN/Ti multilayers have been grown by using Hollow Cathode Discharge (HCD) ion plating and studied by x-ray diffraction analysis. Low-angle diffraction profile indicated the quasi-periodic structure. The parameters of the multilayer microstructure were obtained through x-ray double-line analysis on the high-angle profile. The results of the subgrain size D eff showed that the multilayer structure lead to grain refining. The microhardness of TiN was calculated following the idea of evaluating thin film microhardness by crystal plastic deformation. It was revealed that the multilayer microhardness could be improved by grain refining. Comparing the experimental values to the calculated data, the interface was found to be an important factor for the microhardness of TiN/Ti multiplayer film.
GROWTH OF COLLOIDAL CRYSTALS UNDER MICROGRAVITY
Authors: ISHIKAWA M. , MORIMOTO H. , OKUBO T. , MAEKAWA T.
Published: July 2002

The growth dynamics of colloidal crystallization was evaluated under sedimentation free conditions using sounding rocket and Brownian Dynamics (BD) simulation. The Bragg's reflections of colloidal crystals were measured during microgravity flight and average sizes of crystallites were obtained by the Sherrer's method. Results showed a power-law relationship between size and time, L ∝ tα where L is the size of crystallites and t is time. The obtained α s were 0.33 ± 0.03 in microgravity and 0.25 ± 0.02 in normal gravity, respectively. Browninan Dynamics (BD) simulation showed the time evolution of ordered domains that consisted of connected structures of crystalline clusters. The power law relationship n ∝ t0.5 in post-nucleation period was confirmed between the number of particles (n) in clusters and time. The calculated power was related to α using the fractal dimension of crystalline clusters and α = 0.31 was obtained. The value was matched well with that of the microgravity experiment.
DYNAMICAL CONDUCTIVITY OF LOW-DIMENSIONAL SYSTEMS
Authors: SHARMA A. C. , BAJPAI A.
Published: July 2002

A calculation of dynamical conductivity is performed for low-dimensional systems, by taking into account the screening of field. Our calculation is valid for all value of wave vector and frequency. The Drude conductivity of three, two and one-dimensional free electron gas, layered electron gas and quantum wire system can be deduced from our calculation. However, our calculation suggests that the use of Drude formulae of conductivity to explain experimental result on microwave and infra-red conductivity, in long wave length limit, can be highly erroneous in case of low-dimensional system that offer larger value of relaxation time. It is found that; (i) screening of a dynamical field becomes less significant on reduction in dimensionality and (ii) unlike the case of three dimensional electron gas, transverse electric field cannot excite collective excitation modes (penetration depth cannot be defined) in a two-dimensional electron gas and quantum wire system. In comparison with prior reported calculation ours is more rigorous calculation as it includes the possibility of propagation of collective excitation modes in all direction. The plasmons in a low-dimensional system cannot be excited for negligibly small value of momentum transfer.
PREPARATION OF ULTRA THIN CARBON OVERCOAT FOR MAGNETIC RECORDING MEDIUM BY HOT FILAMENT PLASMA CVD
Authors: FUJIMAKI S. , OHNO T. , KOKAKU Y. , HONDA Y.
Published: July 2002

The deposition process of carbon coating by plasma CVD was studied for the development of a high-density magnetic disk with an ultra thin overcoat of about 4nm thickness. A hot filament discharge system was installed to disk production equipment for the simultaneous deposition of a carbon thin coating on both sides of the disk. The hot filament high-density plasma, in a low-pressure atmosphere of 0.5Pa, was found to be more advantageous, compared with other CVD sources, such as radio frequency plasma, in deposition of the hard carbon thin coating on a negatively biased substrate with ion incidence to the sample. Ion impinging on the substrate was evaluated by calculating its contribution ratio, roughly, from growth rate and bias current density, then examined in relation to the hardness of the carbon thin coatings. In conclusion, hot filament plasma, as a stable CVD source, enables the deposition of the hard carbon overcoat at over 10GPa at the rate of about 1 nm/s, by generating high-density plasma in a low-pressure atmosphere.
PAIRING AND SPONTANEOUS POLARIZATION IN DENSE HYDROGEN
Authors: ASHCROFT N. W.
Published: July 2002

The many-body problem associated with dense hydrogen can represented by the standard interacting electron gas problem (complete with compensating charge continuum) augmented by the proton equivalent and a coupling between the two. This viewpoint is useful as a starting point in the pursuit of ground-state instabilities (particularly the onset of a charge density wave) as a function of the continuum charge density, and even more generally in the identification of forms for the fields required to establish a thermodynamic treatment via coherent state functional integral representations of the partition function for dense hydrogen.
Spin and Charge Correlations in the Extended Hubbard-Holstein Model
Authors: Acquarone M. , Cuoco M. , Noce C.
Published: July 2002

From the complete extended Hubbard-Holstein Hamiltonian we obtain a polaronic effective Hamiltonian by successive application of generalized displacement and squeezing transformations, with wavevector dependent characteristic parameters which make possible a phonon-induced long range interaction between charges, whose sign can change with the distance. As an application we consider the four-site chain, in which the bare electronic interactions are evaluated by model Wannier functions of gaussian shape. The ground states for different ranges of interactions are obtained by exact diagonalization of the effective Hamiltonian, followed by simultaneous and independent optimization of the displacement and squeezing parameters. We consider the behaviour of the static spin and charge correlation functions for the half-filled case, upon varying the shape of the Wannier functions for given electron-phonon coupling. Special attention is devoted to the influence of the phonon coupling on the presence of competing or coexisting charge- and spin-ordered states.
Semiconductor-Like Behavior in Superconducting Nb/Al Films
Authors: Greco M. , Menichetti E. , Rinaudo G. , Maggi S. , Lacquaniti V.
Published: July 2002

We report here the experimental evidence of semiconductor-superconductor transitions in relatively thick Nb/Al structures. The temperature dependence of resistivity ρ(T) shows a sharp superconducting transition followed by either a normal metallic behavior in low-resistivity samples, or a semiconducting behavior when the sample resistivity at 10 K is above 100 μΩ cm. We discuss here the fabrication conditions and the electron localization regime associated with the measured ρ(T) dependence.
Field-Induced Columnar and Bent-Wall-Like Patterns in a Ferrofluid Emulsion
Authors: Flores G. A. , Liu J. , Mohebi M. , Jamasbi N.
Published: July 2002

Using optical microscopy, we studied magnetic-field-induced structures in a confined ferrofluid emulsion. Disks, "worms" and branch-like patterns are observed in 2-D, reflecting columnar, bent-wall-like and labyrinthine structures in 3-D. These structures are controlled by varying either the thickness of the cell used to confine the sample, the particle concentration, or the rate of the magnetic field application. The induced structures are characterized by both the ratio of "worms" vs. total aggregates and the average complexity of the aggregates. "Phase" diagrams are obtained between these tuning parameters to characterize columnar to bent-wall structural transitions.
PHYSICAL FOUNDATION OF PROTEIN ARCHITECTURE
Authors: SAITÔ NOBUHIKO , KOBAYASHI YUKIO
Published: July 2002

The folding mechanism of a nascent protein synthesized according to the information contained in DNA is presented with the aid of the island model developed by Saitô and his collaborators. The purpose of this review article is twofold: to give a summary of their researches on protein folding and to provide an ab initio method of prediction of protein structure from physics principles. The method based on the island model has been developed to have rich contents through various attempts of refolding proteins of known three-dimensional structures. A statistical mechanical theory of the formation of secondary structures is discussed first and then the mechanism of their packing into the tertiary structure is elucidated by applying the island model to typical proteins such as myoglobin, lysozyme, flavodoxin, bovine pancreatic trypsin inhibitor, etc. Topics related to protein structures are also described such as modules, molecular chaperones, membrane proteins and empirical methods of structure prediction based on protein data. Appendices are prepared for the supplements of the text.
LIQUID–VAPOUR EQUILIBRIUM WITH DOUBLE YUKAWA POTENTIAL
Authors: ALI ISSAM , OSMAN S. M. , AL-BUSAIDI M. , SINGH R. N.
Published: July 2002

A statistical mechanical based theory is developed for incorporating the long range correlations in the frame work of the first order perturbation theory to study the liquid–vapour equilibrium. The transition temperature and the liquid–vapour coexistence curves are found to depend considerably on the long range correlations and on the realistic radial distribution function. The calculated liquid–vapour equilibrium curves are in good agreement with the computer simulation results.
BEC-DRIVEN SUPERCONDUCTIVITY IN THE CUPRATES
Authors: CASAS M. , PUENTE A. , RIGO A. , DAVIDSON M. J. , QUICK R. M. , FORTES M. , SOLIS M. A. , DE LLANO M. , NAVARRO O. , VALLADARES A. A. , ROJO O.
Published: July 2002

We apply to cuprates a three-fluid ideal boson-fermion statistical model of superconductivity in two dimensions (2D) derived from three extrema of the system Helmholtz free energy (subject to constant total fermion-number) for the BCS model interaction between fermions. The same interactions absent in BCS theory are neglected here. As the ensuing bosonic Cooper pairs move not in vacuum but in a Fermi sea we employ the correct linear — as opposed to the commonly-assumed quadratic — dispersion relation in the center-of-mass momentum (CMM). More importantly, pair breakup beyond a certain (very small) CMM is accounted for. Bose–Einstein condensation (BEC) critical temperatures of about 800 K result for moderate coupling with cuprate parameters.
MUON SPIN ROTATION IN SR2YRU1-UCUUO6
Authors: HARSHMAN D. R. , BLACKSTEAD H. A. , KOSSLER W. J. , GREER A. J. , STRONACH C. E. , KOSTER E. , HITTI B. , WU M. K. , CHEN D. Y. , CHIEN F. Z. , DOW JOHN D.
Published: July 2002

The magnetic and superconducting behaviors of sintered Sr 2 YRu 1-u Cu u O 6 (for u=0.05, 0.10, 0.15) were probed using transverse- and zero-field muon spin rotation (μ+ SR). In general, positive muons are attracted to oxygen ions in the high-T c oxides, and so, Sr 2 YRu 1-u Cu u O 6 should (and does) present two types of μ+ sites, those associated with the oxygen in the YRuO 4 layers and those associated with the SrO-layer oxygen. The tranverse- and zero-field data for all three stoichiometries u exhibit a sudden onset of magnetic structure at TN~30 K, with a static local field of ~3 kG. This transition is marked by a dramatic increase in the relaxation rate as the temperature decreases below TN, corresponding to an increased static disordering of the magnetic moments. Above TN no static fields are observed. Instead the data exhibit a slow dynamic depolarization, presumably due to the rapid fluctuation of paramagnetic moments. Both transverse- and zero-field data also indicate a smaller second component (~10%) which we associate with the SrO layer, exhibiting superconducting behavior in transverse field with an observed T c ≈TN~30 K.
su(2) AND su(1,1) DISPLACED NUMBER STATES AND THEIR NONCLASSICAL PROPERTIES
Authors: FU HONGCHEN , WANG XIAOGUANG , LI CHONG , WANG JIANGONG
Published: July 2002

We study su(2) and su(1,1) displaced number states. These states are eigenstates of density-dependent interaction systems of quantized radiation field with classical current. These states are intermediate states interpolating between number and displaced number states. Their photon number distribution, statistical and squeezing properties are studied in detail. It shows that these states exhibit strong nonclassical properties.
OPTICAL AND ELECTRICAL PROPERTIES OF THALLIUM SULPHIDE AND TlxMySz (M=Cu,Bi,Sb) thin films
Authors: ESTRELLA VERÓNICA , MEJÍA ROGELIO , NAIR M.T.S. , NAIR P.K.
Published: July 2002

Tl2S thin films (0.05μm-1μm) were deposited from chemical bath containing thallium nitrate and thiourea. These films possess an indirect optical band gap of about 1 eV. Multi-layer films: Tl2S-CuS , Tl2S-Bi2S3 and Tl2S-Sb2S3 films were prepared, which when annealed at 300°C led to the formation of CuTlS2 (tetragonal, E g.dir = 1.25 eV), Bi2Tl4S5 (orthorhombic, E g.dir = 2.05 eV), TlSbS2 (triclinic, E g.dir = 1.92 eV), as confirmed by XRD. Optical band gap of 1.4 eV - 2 eV suggests possible application as absorber materials in solar cell.
Synthesis and Characterization of La2CaCu3O7 Compound
Authors: Jeyabalan K. , Kaliyaperumal L. K. , Sekar A. , Arumugam S. , Srinivas J.
Published: July 2002

Synthesis and characterization of the compound La 2 CaCu 3 O 7 has been reported here. The X-ray powder diffraction analysis reveals that the compound crystallizes in an orthorhombic crystal system with unit cell dimensions of a=5.496(6) Å, b=5.685(5) Å and c=24.356(11) Å.
Thermal Vorticity Dynamics in Turbulent Shear Flow
Authors: Dekker H.
Published: July 2002

In a novel systematic analysis of the 3D Navier-Stokes-Boussinesq equations, hydrodynamic turbulence is considered as the dynamics of a self-driven self-consistent stochastic field.
HIGH PRESSURE SYNTHESIS AND STRUCTURAL STUDIES ON (Ca0.3Sr0.7)0.9Cu1-xZnxO2 (0≤ x ≤0.3)
Authors: VENKATESWARAN C. , ANBUKUMARAN K. , JAYA N. VICTOR , NATARAJAN S.
Published: July 2002

High pressure synthesis and structural studies on the reported high pressure phase compound ( Ca 0.3 Sr 0.7)0.9 CuO 2 have been carried out using zinc. Substitution of zinc seriously affects the superconducting transition temperature T c , which gets lowered to around 60 K for the x=0.1 compound. Further increase in zinc concentration destroys superconductivity. All the compounds could be well indexed to the tetragonal system with little variation in lattice parameters showing structural phase stability.
EPR AND MAGNETIC SUSCEPTIBILITY STUDIES OF B2O3–SrO–Fe2O3 GLASSES
Authors: ARDELEAN I. , SALVAN G. , PETEANU M. , SIMON V. , HIMCINSCHI C. , CIORCAS F.
Published: July 2002

Structural and magnetic properties of B 2 O 3– SrO – Fe 2 O 3 glasses were explored by a controlled doping of 2B 2 O 3· SrO vitreous matrix with iron oxide. The information concerning the structural units involving iron ions, their valence states and the types of interactions between them, was obtained using electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements.
SELFTRAPPING DYNAMICS IN TWO-DIMENSIONAL NONLINEAR LATTICES
Authors: MOLINA M. I.
Published: July 2002

We compute numerically the selftrapping dynamics for an electron or excitation initially located on a single site of a two-dimensional nonlinear lattice of arbitrary nonlinear exponent. The time evolution is given by the Discrete Nonlinear Schrödinger (DNLS) equation and we focus on the long-time average probability at the initial site and the mean square displacement in terms of both the exponent and strength of the nonlinearity. For the square and triangular nonlinear lattices, we find selftrapping for nonlinearity parameters greater than an exponent-dependent critical value, whose magnitude increases (decreases) with the nonlinear exponent when this is larger (smaller) than one, approximately.
FITTING TRAPPING REGIONS FOR CHUA'S ATTRACTOR — A NOVEL METHOD BASED ON ISOCHRONIC LINES
Authors: BOUGHABA SORAYA , LOZI RENE
Published: July 2002

We present in this paper a novel method for fitting trapping regions for a Spiral Chua's attractor. For the values: σ0= -0.465716…, γ0= 0.0932544…, k = 0.3279262…, σ1= 0.4152731…, γ1= -0.3446764… of the parameters, the iterates of the attractor belong to two trapping regions P1and P3we construct with this method based uniquely on the isochronic lines. Both P1and P3are bounded accurately with more than 450 segments of isochronic lines. We show graphically that the inclusions π (P1) ⊂ P3, π (P3) ⊂ P1hold. The traps for the half-Poincaré map π0have to be constructed.
CONCEPTUAL MODEL OF RUNOFF FROM A FORESTED CATCHMENT
Authors: ROMANO M. C. , THIEL M. , SCHWARZ U. , KURTHS J. , LANGE H. , HAUHS M.
Published: July 2002

We investigate the relationship between precipitation and runoff data from a small forested catchment in the Harz mountains (Germany). For this purpose, we develop a conceptual model including memory effects to predict the runoff signal using the precipitation data as input. An enhanced variant of the model also includes air temperature as input variable. We show in terms of correlation functions that this model describes the main dynamical properties of the runoff, especially the delay between rain event and runoff response as the annual persistence in the runoff data.
TIME DELAYED REPETITIVE LEARNING CONTROL FOR CHAOTIC SYSTEMS
Authors: SONG YANXING , YU XINGHUO , CHEN GUANRONG , XU JIAN-XIN , TIAN YU-PING
Published: July 2002

In this paper, a time-delayed chaos control method based on repetitive learning is proposed. A general repetitive learning control structure based on the invariant manifold of the chaotic system is given. The integration of the repetitive learning control principle and the time-delayed chaos control technique enables adaptive learning of appropriate control actions from learning cycles. In contrast to the conventional repetitive learning control, no exact knowledge (analytic representation) of the target unstable periodic orbits is needed, except for the time delay constant, which can be identified via either experiments or adaptive learning. The controller effectively stabilizes the states of the continuous-time chaos on desired unstable periodic orbits. Simulations on the Duffing and Lorenz chaotic systems are provided to verify the design and analysis.
THE "NOT QUITE" INVERTED PENDULUM
Authors: BISHOP S. R. , SUDOR D. J.
Published: July 2002

The planar pendulum has been used as an example of a simple oscillator for over 300 years with notable historical contributions by Galileo and Huygens. Initially interest was focused on small displacements from the stable hanging position specifically to determine the period of oscillation. More recently attention has switched to larger amplitude and chaotic motions as a consequence of periodic forcing to the pivot point. To explain experimentally observed behavior, we investigate here the existence of stable inverted solutions of a pendulum sinusoidally driven, in the first instance by a purely vertical force and then by an almost vertical force by giving a small tilt to the system. An effective potential function is considered to provide analytical justification of the numerical simulations.
LIMITED AREA WEATHER PREDICTION MODELS VIEWED AS DYNAMICAL SYSTEMS
Authors: CHOMÉ F. , NICOLIS C.
Published: July 2002

Different strategies for building high-resolution models providing a more detailed description of a limited area of interest as for example, in regional weather forecasts are developed. They are subsequently compared, on the basis of the dynamical behavior generated by the corresponding models. The statistical properties of the relevant fields are analyzed, and predictability experiments are performed on statistical ensembles of close lying trajectories whose mean distance represents the uncertainty in the initial state of the system. The results show that a global, variable-mesh model performs much better than a limited area fine mesh one embedded into a coarser global model.
TORSION-FREE QUOTIENTS OF BRAID GROUPS
Authors: HUMPHRIES STEPHEN P.
Published: July 2002

In this paper we show that the braid groups Bn, n≤6, have proper torsion-free non-abelian quotients. We also show that for n≤6 the homotopy braid groups are torsion-free.
A NORMAL FORM FOR MULTISTEP COMPANION MATRICES
Authors: EDER ALEXANDER , KIRLINGER GABRIELA
Published: July 2002

Linear multistep methods, in particular Backward Differentiation Formulas (BDF), are widely used for the numerical integration of differential equations and in particular for stiff systems. Although the classical convergence theory for linear multistep methods is quite well-developed, there is no comprehensive stiff convergence theory. Special classes of stiff problems have been covered so far, see e.g. Hairer, Wanner11 for the analysis of stiff linear systems or Lubich13 for the analysis of problems in standard singular perturbation form. We present a theoretical approach for the analysis of stiff linear systems which will be extended to nonlinear problems in forthcoming papers.
THE FROZEN FLOW AND THE EQUILIBRIUM LIMITS IN A POLYATOMIC GAS WITH RELAXATION EFFECTS
Authors: GASSER INGENUIN , SZMOLYAN PETER
Published: July 2002

A traveling waves analysis for a polyatomic gas with n internal energy storage modes is performed. In both the frozen flow and the equilibrium limit the existence and qualitative behavior of traveling waves are investigated. Methods from geometric singular perturbation theory are used to study these limits.
FICTITIOUS DOMAINS METHODS WITH DISTRIBUTED LAGRANGE MULTIPLIERS PART I: APPLICATION TO THE SOLUTION OF ELLIPTIC STATE PROBLEMS
Authors: HASLINGER JAROSLAV , MAITRE JEAN-FRANCOIS , TOMAS LAURENT
Published: July 2002

Fictitious domain approaches are an attractive way to overcome the usual drawbacks of the so-called boundary variation technique for solving optimal shape problems. In the first part of this paper, we introduce fictitious domain methods with distributed Lagrange multipliers for elliptic state problems. Continuous formulations as well as their finite element discretizations are discussed. The second part of the paper will be devoted to the application of these methods to shape optimization.
CONVERGENCE RATES TO SUPERPOSITION OF TWO TRAVELLING WAVES OF THE SOLUTIONS TO A RELAXATION HYPERBOLIC SYSTEM WITH BOUNDARY EFFECTS
Authors: HSIAO LING , LI HAILIANG , MEI MING
Published: July 2002

This paper is to study the asymptotic behavior of solutions for an initial–boundary value problem to Jin–Xin's 2×2 relaxation hyperbolic system. When the initial data are small perturbation of the superposition of two travelling waves at t=0, subsequent to the previous work,6 we further show the convergence rates of the IBVP solutions to the superposition of two waves. Precisely, when the initial perturbations decay in the exponential or algebraic forms, we prove that the corresponding solutions tend to the superposition of two waves time-asymptotically in the exponential or algebraic forms, respectively. The method adopted is the weighted energy method. The use of a shift function for the forward travelling wave and the special choice of shift functions for backward travelling plays a key role to overcome the difficulties caused by the boundary and degeneration.
EXISTENCE RESULT FOR A NONLINEAR MODEL RELATED TO IRREVERSIBLE PHASE CHANGES
Authors: LUTEROTTI FABIO , SCHIMPERNA GIULIO , STEFANELLI ULISSE
Published: July 2002

This paper deals with an initial and boundary value problem for a nonlinear evolution system which may be used to describe irreversible phase transition phenomena. The existence of a global solution is established via a regularization — a priori estimate — passage to the limit procedure. Moreover, uniqueness is also discussed under additional regularity assumptions on data.
EXISTENCE AND UNIQUENESS OF STEADY, FULLY DEVELOPED FLOWS OF SECOND ORDER FLUIDS IN CURVED PIPES
Authors: COSCIA V. , ROBERTSON A. M.
Published: July 2002

Steady, fully developed flows of second order fluids in curved pipes of circular cross-section have previously been studied using regular perturbation methods.2,3,12,20 These perturbation solutions are applicable for pipes with small curvature ratio: The cross sectional radius of the pipe divided by the radius of curvature of the pipe centerline. It was shown by Jitchote and Robertson12 that perturbation equations could be ill-posed when the second normal stress coefficient is nonzero. Motivated by the singular nature of the perturbation equations, here, we study the full governing equations without introducing assumptions inherent in perturbation methods. In particular, we examine the existence and uniqueness of solutions to the full governing equations for second order fluids. We show rigorously that a solution to the full problem exists and is locally unique for small non-dimensional pressure drop, in agreement with earlier results obtained using a formal expansion in the curvature ratio.12 The results obtained here are valid for arbitrarily shaped cross-section (sufficiently smooth) and for all curvature ratios. An operator splitting method has been employed which may be useful for numerical studies of steady and unsteady flows of second order fluids in curved pipes.
A KINETIC MULTISCALE MODEL
Authors: BABOVSKY HANS
Published: July 2002

We derive a system of kinetic equations which realize the Broadwell model on a variety of scales. For a 16-velocity model we verify constraints giving rise to "realistic" Euler equations. Applications to rarefied flow dynamics are developed.
ASYMPTOTIC BEHAVIOR OF THE INDUCTANCE COEFFICIENT FOR THIN CONDUCTORS
Authors: AMIRAT YOUCEF , TOUZANI RACHID
Published: July 2002

We study the asymptotic behavior of the inductance coefficient for a thin toroidal inductor whose thickness depends on a small parameter ε > 0. We give an explicit form of the singular part of the corresponding potential uε which allows to construct the limit potential u (as ε → 0) and an approximation of the inductance coefficient Lε. We establish some estimates of the deviation uε - u and of the error of approximation of the inductance. We show that Lε behaves asymptotically as ln ε, when ε → 0.
SOME RESULTS ON A NEW MODEL OF PHASE RELAXATION
Authors: RECUPERO VINCENZO
Published: July 2002

This paper deals with the analysis of the relaxed Stefan problem with the relaxation dynamics for the phase variable χ [Formula: see text] where θ stands for the temperature. We prove the well-posedness of the problem by means of a fixed point-technique for multivalued maps and show that its solution converges to the solution of the Stefan problem as the relaxation parameter ε tends to zero.
ON THE MEASURE-THEORETIC FOUNDATIONS OF THE SECOND LAW OF THERMODYNAMICS
Authors: MARZOCCHI ALFREDO , MUSESTI ALESSANDRO
Published: July 2002

Balance laws of the type of entropy are treated in the framework of geometric measure theory, and a weak version, although conceptually simple, of the Second Law of Thermodynamics is introduced, allowing extensions to measure-valued entropy productions and to sets of finite perimeter as subbodies.
INVARIANT DIFFERENCE SCHEMES FOR PARABOLIC EQUATIONS WITH TRANSFORMATIONS OF INDEPENDENT VARIABLES
Authors: SAMARSKII A. A. , MAZHUKIN V. I. , MATUS P. P. , RYCHAGOV V. G. , SMUROV I.
Published: July 2002

In this paper, invariant difference schemes for nonstationary equations under independent variables transformation constructed and investigated. Under invariance of difference scheme we mean its ability to preserve basic properties (stability, approximation, convergency, etc.) in various coordinate systems. Difference schemes of the second-order approximation that satisfy the invariance property are constructed for equations of parabolic type. Stability and convergency investigation of correspondent difference problems are carried out; a priori estimates in various grid norms are obtained.
FINITE ELEMENT APPROXIMATION OF A MODEL FOR PHASE SEPARATION OF A MULTI-COMPONENT ALLOY WITH NONSMOOTH FREE ENERGY AND A CONCENTRATION DEPENDENT MOBILITY MATRIX
Authors: BARRETT JOHN W. , BLOWEY JAMES F.
Published: July 2002

We consider a model for phase separation of a multi-component alloy with nonsmooth free energy and a concentration dependent mobility matrix. In particular we prove that there exists a unique solution for sufficiently smooth initial data. Further, we prove an error bound for a fully practical piecewise linear finite element approximation in one and two space dimensions. Finally numerical experiments with three components in one space dimension are presented.
MATHEMATICAL ANALYSIS OF ELASTIC SURFACE WAVES IN TOPOGRAPHIC WAVEGUIDES
Authors: DHIA A. S. BONNET-BEN , DUTERTE J. , JOLY P.
Published: July 2002

We present here a theoretical study of the guided waves in an isotropic homogeneous elastic half-space whose free surface has been deformed. The deformation is supposed to be invariant in the propagation direction and localized in the transverse ones. We show that finding guided waves amounts to solving a family of 2-D eigenvalue problems set in the cross-section of the propagation medium. Then using the min-max principle for non-compact self-adjoint operators, we prove the existence of guided waves for some particular geometries of the free surface. These waves have a smaller speed than that of the Rayleigh wave in the perfect half-space and a finite transverse energy. Moreover, we prove that the existence results are valid for arbitrary high frequencies in the presence of singularities of the free boundary. Finally, we prove that no guided mode can exist at low frequency, except maybe the fundamental one.
OPTIMAL INTERFACE ERROR ESTIMATES FOR A DISCRETE DOUBLE OBSTACLE APPROXIMATION TO THE PRESCRIBED CURVATURE PROBLEM
Authors: CECON BARBARA , PAOLINI MAURIZIO , ROMEO MARIANGELA
Published: July 2002

In this paper we consider the so-called prescribed curvature problem approximated by a singularly perturbed double obstacle variational inequality. We extend Ref. 10 with the introduction of the same nonregular potential used for the evolution problem in Ref. 9 and prove an optimal [Formula: see text] error estimate for nondegenerate minimizers (where ε represents the perturbation parameter). Following Ref. 10 the result relies on the construction of precise barriers suggested by formal asymptotics combined with the use of the maximum principle. Key ingredients are the construction of a sub(super)solution containing appropriate shape corrections and the use of a modified distance function based on the principal eigenfunction of the second variation of the prescribed curvature functional. This analysis is next extended to a piecewise linear finite element discretization of the elliptic PDE of bistable type to prove the same error estimate for discrete minima using the Rannacher–Scott L∞-estimates and under appropriate restrictions on the mesh size ([Formula: see text] with σ>5/2).
NONLINEAR SYSTEMS DESCRIBING PHASE TRANSITION MODELS COMPATIBLE WITH THERMODYNAMICS
Authors: COLLI PIERLUIGI , GENTILI GIORGIO , GIORGI CLAUDIO
Published: July 2002

This paper is devoted to analyzing solutions of a nonlinear evolution system describing the phase transition in a rigid heat conductor in the presence of phase relaxation. First, in a general framework, a rate type constitutive law for the phase variable is considered and matched with the Helmholtz free energy involving the state of the material. Thermodynamic compatibility of the resulting models is scrutinized. Moreover, a comparison with a different phase change modelling is performed. Under proper assumptions, a nonlinear system in the (absolute) temperature and phase variable is achieved. For it, existence and uniqueness of the solution is proved and positivity of temperature is recovered.
On Linked Spatial Representations
Authors: Alfonsín J. L. Ramírez
Published: July 2002

What is the smallest positive integer m=m(L) such that every linear spatial representation of the complete graph with n vertices, n≥m contain cycles isotopic to link L? In this paper, we show that [Formula: see text]. The proof uses the well-known cyclic polytope and its combinatorial description in terms of oriented matroids.
DELTA LINK HOMOTOPY FOR TWO COMPONENT LINKS, II
Authors: NAKANISHI YASUTAKA , OHYAMA YOSHIYUKI
Published: July 2002

In this note, we will study Δ link homotopy (or self Δ-equivalence), which is an equivalence relation of ordered and oriented link types. Previously, a necessary condition is given in the terms of Conway polynomials for two link types to be Δ link homotopic. A pair of numerical invariants δ1 and δ2 classifies all (ordered and oriented) prime 2-component link types with seven crossings or less up to Δ link homotopy. We will show here that for any pair of integers n1 and n2 there exists a 2-component link κ such that δ1(κ) = n1 and δ2(κ) = n2 provided that at least one of n1 and n2 is even.
GEOMETRIC CHARACTERIZATIONS OF THE KERR ISOLATED HORIZON
Authors: LEWANDOWSKI JERZY , PAWLOWSKI TOMASZ
Published: July 2002

We formulate conditions on the geometry of a nonexpanding horizon Δ which are sufficient for the spacetime metric to coincide on Δ with the Kerr metric. We introduce an invariant which can be used as a measure of how different the geometry of a given nonexpanding horizon is from the geometry of the Kerr horizon. Directly, our results concern the spacetime metric at Δ at the zeroth and the first orders. Combined with the results of Ashtekar, Beetle and Lewandowski, our conditions can be used to compare the spacetime geometry at the nonexpanding horizon with that of Kerr to every order. The results should be useful to numerical relativity in analyzing the sense in which the final black hole horizon produced by a collapse or a merger approaches the Kerr horizon.
BLACK HOLE ENTROPY IN THE MEMBRANE PARADIGM
Authors: SHIMOMURA TAKESHI , OKAMURA TAKASHI , MISHIMA TAKASHI
Published: July 2002

We study whether the black hole entropy can be understood in terms of thermodynamical properties of a fluid membrane in the Membrane Paradigm. In particular, by using local observable quantities of the membrane and thermodynamical relations, we calculate the entropy of the membrane in a phenomenological manner. It is shown that one can assign the entropy [Formula: see text] of black hole to that of the membrane such that the entropy, together with other physical quantities of the membrane, composes thermodynamics consistently. This result concerning entropy gives a new support for the Membrane Paradigm, and consequently, supports a kind of holographic viewpoint about black hole for external observers, i.e., black hole entropy for external observers can be regarded consistently as a measure of some degrees of freedom associated with the horizon boundary. In addition, our result also suggests that the generalized second law of thermodynamics hold in quite general process.
DISTRIBUTED PARALLEL PROCESSING TECHNIQUES FOR ADAPTIVE SONAR BEAMFORMING
Authors: GEORGE ALAN D. , GARCIA JESUS , KIM KEONWOOK , SINHA PRIYABRATA
Published: July 2002

Quiet submarine threats and high clutter in the littoral environment increase computation and communication demands on beamforming arrays, particularly for applications that require in-array autonomous operation. By coupling each transducer node in a distributed array with a microprocessor, and networking them together, embedded parallel processing for adaptive beamformers can glean advantages in execution speed, fault tolerance, scalability, power, and cost. In this paper, a novel set of techniques for the parallelization of adaptive beamforming algorithms is introduced for in-array sonar signal processing. A narrowband, unconstrained, Minimum Variance Distortionless Response (MVDR) beamformer is used as a baseline to investigate the efficiency and effectiveness of this method in an experimental fashion. Performance results are also included, among them execution times, parallel efficiencies, and memory requirements, using a distributed system testbed comprised of a cluster of workstations connected by a conventional network.
PARALLEL ALGORITHMS FOR ROBUST BROADBAND MVDR BEAMFORMING
Authors: SINHA PRIYABRATA , GEORGE ALAN D. , KIM KEONWOOK
Published: July 2002

Rapid advancements in adaptive sonar beamforming algorithms have greatly increased the computation and communication demands on beamforming arrays, particularly for applications that require in-array autonomous operation. By coupling each transducer node in a distributed array with a microprocessor, and networking them together, embedded parallel processing for adaptive beamformers can significantly reduce execution time, power consumption and cost, and increase scalability and dependability. In this paper, the basic narrowband Minimum Variance Distortionless Response (MVDR) beamformer is enhanced by incorporating broadband processing, a technique to enhance the robustness of the algorithm, and speedup of the matrix inversion task using sequential regression. Using this Robust Broadband MVDR (RB-MVDR) algorithm as a sequential baseline, two novel parallel algorithms are developed and analyzed. Performance results are included, among them execution time, scaled speedup, parallel efficiency, result latency and memory utilization. The testbed used is a distributed system comprised of a cluster of personal computers connected by a conventional network.
ELECTRON MOMENTUM SPECTROSCOPY OF SURFACES
Authors: TIXIER S. , ZHENG Y. , TIEDJE T. , COOPER G. , BRION C. E.
Published: July 2002

Electron momentum spectroscopy [binary (e,2e) spectroscopy] using transmission geometry is a unique experimental tool for imaging the electron momentum distribution in gas phase samples as well as in thin films. In a solid, the electron momentum distribution is related to the band structure. Development of the (e,2e) technique using a more versatile reflection geometry is attractive since a much wider range of surfaces could be studied. The design of a new reflection (e,2e) spectrometer is presented. It is based on a two-step scattering model in which an incident electron successively reflects and ejects a valence electron from the surface. The scattered and ejected electrons are detected in coincidence and their energies and momentum vectors are simultaneously determined using a high throughput 90° truncated spherical electrostatic analyzer and position-sensitive detectors.
ARTHROSCOPICALLY-ASSISTED REDUCTION OF INTRA-ARTICULAR FRACTURES AND SOFT TISSUE MANAGEMENT OF DISTAL RADIUS
Authors: Shih Jui-Tien , Lee Hung-Maan , Hou Yao-Tung , Tan Chuan-Ming
Published: July 2002

Arthroscopy was used to help to reduce intra-articular fractures of the distal radius and treat soft tissue injuries in 33 acute cases. The fractures were treated by reduction under arthroscopic control and percutaneous fixation either with or without external fixation. The triangular fibrocartilage complex (TFCC) was torn in 18 of 33 patients (54%). All tears were peripheral and were repaired with arthroscopic procedures. Scapholunate (SL) ligament injuries prevailed in six (18%) patients; most of them exhibited instability in the SL joint. They received SL ligament debrided and transfixed with K-wires. Four (12%) of the patients suffered lunotriquetral (LT) ligament injuries; three of them also received transfixation with K-wires. Six (18%) of the patients exhibited chondral fractures. All fractures healed without measurable incongruity of joint surface and at follow-up (24 to 36 months), 11 patients displayed excellent results and 22 patients displayed good results according to the Mayo modified wrist score.
Hand Abnormalities Associated with Non-Insulin-Dependent Diabetes Mellitus in Japan
Authors: Wada Takuro , Minagi Yasuhiko , Kirita Takashi , Ishii Seiichi
Published: July 2002

We carried out a survey of hand abnormalities in 65 Japanese adult diabetics (non-insulin-dependent diabetes mellitus) and compared the result with that of 65 non-diabetic adults as controls. A significantly higher incidence of Dupuytren's contracture, limited joint mobility, carpal tunnel syndrome, and flexor tenosynovitis was found in the diabetic group. In the diabetic group, Dupuytren's contracture was noted in 10 patients (15%), limited joint mobility in 34 patients (52%), carpal tunnel syndrome in 21 patients (32%), and flexor tenosynovitis in 10 patients (15%). Dupuytren's contracture in the diabetic patients involved the fourth and fifth rays. In diabetic carpal tunnel syndrome, as compared to the idiopathic form, men were more frequently affected than women. Carpal tunnel syndrome showed a positive correlation with duration of the diabetes and use of insulin during the last twelve months prior to the examination. All of 10 diabetic patients with flexor tenosynovitis also had limited joint mobility. Six of these 10 patients also had carpal tunnel syndrome.
SQUAMOUS CELL CARCINOMA OF THE NAILBED: A CASE REPORT AND REVIEW OF THE LITERATURE
Authors: Chee B P , Hasegawa K , Chia John C S , Chachlani N
Published: July 2002

Squamous cell carcinomas of the nailbed are rare occurrences. We report one such case in the digit of a middle aged man.
EXPLAINING THE FORWARD INTEREST RATE TERM STRUCTURE
Authors: MATACZ ANDREW , BOUCHAUD JEAN-PHILIPPE
Published: July 2002

We present compelling empirical evidence for a new interpretation of the Forward Rate Curve (FRC) term structure. We find that the average FRC follows a square-root law, with a prefactor related to the spot volatility, suggesting a Value-at-Risk like pricing. We find a striking correlation between the instantaneous FRC and the past spot trend over a certain time horizon. This confirms the idea of an anticipated trend mechanism proposed earlier and provides a natural explanation for the observed shape of the FRC volatility. We find that the one-factor Gaussian Heath–Jarrow–Morton model calibrated to the empirical volatility function fails to adequately describe these features.
ALL FOR ONE … ONE FOR ALL? A PRINCIPAL COMPONENT ANALYSIS OF LATIN AMERICAN BRADY BOND DEBT FROM 1994 TO 2000
Authors: SCHERER KEVIN PAUL , AVELLANEDA MARCO
Published: July 2002

We use Principal Component Analysis (PCA) to study the Brady Bond Debt of the four primary Latin American sovereign issuers: Argentina, Brazil, Mexico, and Venezuela. Our dataset covers a period of 5½ years starting in July 1994 and consists of daily sovereign ("stripped") yield levels for the par and discount debt securities of each country. We examine the behavior of the characteristic roots and eigenvectors of the empirical covariance matrices computed sequentially over different periods. We show that, by and large, there exist two statistically significant components, or factors, which explain up to 90% of the realized variance. The eigenvector with largest eigenvalue corresponds to the variance attributable to "regional" ("Latin") risk. The second component strongly suggests the existence of a volatility risk factor associated to Venezuelan debt in relation to the rest of the region. A time-dependent factor analyis reveals that the importance of the variance explained by the factor changes over time and that this variation can be interpreted to some extent in terms of market events. In particular, we investigate the relation between the evolution of the PCA factors with the market dislocations that ocurred during the observation period, including the so-called Tequila effect, Asian flu, Ruble devaluation, and Real devaluation.