bluuebunny/crossref_metadata_2025 huggingface dataset:
THE BARRIER-LOCK CLOCK: A SCALABLE SYNCHRONIZATION-ORIENTED LOGICAL CLOCK
Authors: ARANTES LUCIANA , POITRENAUD DENIS , SENS PIERRE , FOLLIOT BERTIL
Published: July 2002

In this article, we introduce a new logical clock, the barrier-lock clock, whose conception is based on the lazy release consistency memory model (LRC) supported by several distributed shared memory (DSM) systems. Since in the LRC, the propagation of shared memory updates performed by the processes of a parallel application is induced by lock and barrier operations, our logical clock has been modeled on those operations. Each barrier-lock times-tamp encodes the synchronization operation with which it is associated. Its size is not dependent on the number of processes of the system, as the traditional logical vector clocks, but it is proportional to the number of locks. The barrier-lock time characterizes the causality of shared memory updates performed by processes of a parallel application running on a LRC-based DSM system. A formal proof and experimental tests have confirmed such property.
PERFORMANCE ANALYSIS OF MULTI-STAGE INTERCONNECTION NETWORKS WITH DETERMINISTIC SERVICE TIMES
Authors: REIJNS G. L. , VAN GEMUND A. J. C. , GAUTAMA H.
Published: July 2002

In this paper we present a performance model for a constant service time, globally synchronized multistage interconnection network that is an improvement on earlier work in this field. The events at the network input are assumed to have a geometric distribution in time. As the events are combined within the network, it can happen that two events arrive simultaneously at one of the network server elements, called a double arrival rate stream (DAR) server. Analytical methods are described to derive the response time and inter-departure time distribution of the double arrival rate constant service time server, which has a queuing property (DAR/D/1). Due to the queuing effect of the servers in the first stage of the network, their outputs show a "distorted" geometric distribution, which is known to introduce analytical difficulties in the performance evaluation of the subsequent stages. A method is presented to derive the response time of servers in the second stage, when the network has a uniform workload distribution. It is shown that the knowledge of the response times of the first and second stage of the network is sufficient to predict the total response time of a large network with an accuracy better than 3%, even under a heavy workload.
PT-SYMMETRIC NONPOLYNOMIAL OSCILLATORS AND HYPERBOLIC POTENTIAL WITH TWO KNOWN REAL EIGENVALUES IN A SUSY FRAMEWORK
Authors: BAGCHI B. , QUESNE C.
Published: July 2002

Extending the supersymmetric method proposed by Tkachuk to the complex domain, we obtain general expressions for superpotentials allowing generation of quasi-exactly solvable PT-symmetric potentials with two known real eigenvalues (the ground state and first-excited state energies). We construct examples, namely those of complexified nonpolynomial oscillators and of a complexified hyperbolic potential, to demonstrate how our scheme works in practice. For the former we provide a connection with the sl(2) method, illustrating the comparative advantages of the supersymmetric one.
STRING WEBS AND THE DECAY OF SUPERSYMMETRIC PARTICLES
Authors: ARGYRES PHILIP C. , NARAYAN K.
Published: July 2002

The spectrum of stable electrically and magnetically charged supersymmetric particles can change discontinously due to the decay of these particles as the vacuum on the Coulomb branch is varied. We show that this decay process is well described by semiclassical field configurations even when it occurs at strong coupling. the resulting picture of the stable supersymmetric spectrum is a generalization of the "string web" picture of these states found in string constructions.
DERIVATIVE CORRECTIONS TO DIRAC–BORN–INFELD AND CHERN–SIMON ACTIONS FROM NONCOMMUTATIVITY
Authors: PAL SHESANSU SEKHAR
Published: July 2002

We show that the higher-order derivative α′ corrections to the Dirac–Born–Infeld (DBI) and Chern–Simon actions is derived from noncommutativity in the Seiberg–Witten limit, and is shown to agree with Wyllard's (hep-th/0008125) result, as conjectured by Das et al., (hep-th/0106024). In calculating the corrections, we have expressed [Formula: see text] in terms of F, Â in terms of A up to order [Formula: see text], and made use of it.
VACUUM POLARIZATION IN THE GLOBAL MONOPOLE SPACETIME AT FINITE TEMPERATURE
Authors: BEZERRA DE MELLO E. R. , CARVALHO F. C.
Published: July 2002

In this paper we calculate the thermal Green functions associated with massless scalar and spin-1/2 fields in the pointlike global monopole spacetime. The thermal average values of their respective energy-momentum tensors are formally presented and explicit calculations are performed for specific values of the parameter α which codify the presence of the monopole. Moreover their high-temperature limit behaviors are explicitly exhibited by numerical analysis.
PHOTON PROPAGATION IN A MAGNETIZED MEDIUM
Authors: KONAR SUSHAN
Published: July 2002

Using the real time formalism of the finite temperature field theory we calculate the 1-loop polarization tensor in the presence of a background magnetic field in a medium. The expression is obtained to linear order in the background field strength. We discuss the Faraday rotation as well as the photon absorption probabilities in this context.
BIEXCITON SQUEEZING DUE TO OPTICAL EXCITON-BIEXCITON CONVERSION
Authors: TINH VO , NHA DO HUU , AN NGUYEN BA
Published: July 2002

We theoretically investigate the evolution of biexcitons from a coherent into a squeezed state in a fully quantum system described by a trilinear Hamiltonian allowing the transition "photons + excitons ⇌ biexcitons". Curious dependences of the direction and degree of biexciton squeezing on the initial states of photons and excitons are obtained. The theoretical results are well reproduced by numerical calculations.
COMMON MAGNETIC ORIGIN OF THE RESONANCE PEAK AND INCOMMENSURATION IN HIGH-Tc SUPERCONDUCTORS
Authors: BATISTA C. D. , ORTIZ G. , BALATSKY A. V.
Published: July 2002

We present a unified theory for the resonance peak and low-energy incommensurate response observed in high-Tc cuprate superconductors. The origin of both features is purely magnetic and they represent universal features signaling the existence of an incommensurate spin state both below and above the superconducting transition temperature. We argue that the resonance peak is the reflection of commensurate antiferromagnetism. Our theoretical scenario gives an account of the main universal features observed in various families of superconductors and predicts those that have not been observed yet experimentally.
A PERTURBATIVE APPROACH TO NONLINEARITIES IN THE INFORMATION CARRIED BY A TWO LAYER NEURAL NETWORK
Authors: KORUTCHEVA E. , DEL PRETE V. , NADAL J.-P.
Published: July 2002

We evaluate the mutual information between the input and the output of a two layer network in the case of a noisy and nonlinear analogue channel. In the case where the nonlinearity is small with respect to the variability in the noise, we derive an exact expression for the contribution to the mutual information given by the nonlinear term in first order of perturbation theory. Finally we show how the calculation can be simplified by means of a diagrammatic expansion. Our results suggest that the use of perturbation theories applied to neural systems might give an insight on the contribution of nonlinearities to the information transmission and in general to the neuronal dynamics.
BOUND STATES IN DIMERIZED AND FRUSTRATED HEISENBERG CHAINS
Authors: BOUZERAR G. , SIL S.
Published: July 2002

Using the Bond-Operator Technique (BOT), we have studied the low energy excitation spectrum of a frustrated dimerized antiferromagnetic Heisenberg chain. In particular, we have compared our analytical results with previous Exact Diagonalization (ED) data. Qualitatively, the BOT results are in good agreement with the ED data. And even a very good quantitative agreement is obtained in some parameter region. It is clearly shown that there is only one elementary excitation branch (lowest triplet branch) and that the two other well defined excitations which appear below the continuum, one singlet and one triplet, are bound states of two elementary triplets.
Optical responses of one-dimensional exciton system in correlated random potentials
Authors: Noba Kenichi , Kayanuma Yosuke , Nojima Kouichiro
Published: July 2002

Urbach tails at absorption edge and photon echo signals are theoretically investigated for one-dimensional exciton systems which have correlated random potentials. As two limits, these correlated random potentials include inhomogeneous distribution of energy levels and random distribution of site-energies for excitons. It is shown that spectral profile of the optical responses reflects the continuous change of the correlated potentials between the two limits.
HEISENBERG INTEGER SPIN CHAINS IN A UNIFORM MAGNETIC FIELD
Authors: CAMPOS VENUTI L. , ERCOLESSI E. , MORANDI G. , PIERI P. , RONCAGLIA M.
Published: July 2002

We investigate both numerically and analytically the behavior of a spin-1 antiferromagnetic isotropic Heisenberg chain in an external uniform magnetic field. Extensive DMRG studies of chains up to N = 80 sites extend previous analyses and obtain the zero-temperature correlation functions. We argue that, despite the presence of a magnetic field, the model is still well described by an O(3) nonlinear σ-model. A saddle-point analysis, that also includes Gaussian fluctuations, is developed for the latter both at zero and finite temperatures. Its predictions are compared with those of the numerical analysis and with the existing experimental literature.
SIGNATURE OF LOCAL STRUCTURE ANOMALY AT Tc IN THE Nb3Ge SUPERCONDUCTOR
Authors: FILLIPPI M. , SAINI N. L. , OYANAGI H. , BIANCONI A.
Published: July 2002

We report local structure of Nb3Ge intermetallic superconductor by Ge K-edge extended X-ray absorption fine structure (EXAFS) measurements performed in the temperature range of 6–300 K, with an emphasis to determine the local and instantaneous atomic displacements across the superconducting transition temperature T c . We find that the temperature dependent correlated Debye–Waller factor of the Ge-Nb bonds shows a drop at the T c while cooling the sample, similar to the one observed in the high-T c cuprate superconductors. The results provide a clear indication of an intimacy between the local atomic displacements and the short coherence superconductivity, and suggests that local electron-lattice interaction should be considered to explain the high-T c superconductivity in these materials.
SURFACE STATES, INTERPRETATION OF ARPES DATA, AND POSSIBLE CONSEQUENCES FOR THE SUPERCONDUCTIVITY IN MgB2
Authors: SERVEDIO V. D. P. , DRECHSLER S.-L. , MISHONOV T.
Published: July 2002

We report layer-Korringa–Kohn–Rostocker calculations for bulk and surface states (SFS) as well as the corresponding photoemission intensities of MgB2 . Our theoretical results reproduce very well the recent angle resolved photoemission data by Uchiyama et al. At least two SFS are assigned. Consequences of SFS on the anisotropy of the upper critical fields and other properties in the superconducting state of grains in micro-powder samples are discussed.
MANY-BODY ASPECTS OF QUANTUM CHAOS
Authors: ZELEVINSKY VLADIMIR
Published: July 2002

Realistic many-body quantum systems with strong interaction reveal generic chaotic properties in level statistics and structure of eigenfunctions. In complex atoms and nuclei onset of chaos is driven by the residual interaction. We discuss specific features of many-body chaos in mesoscopic systems (complexity and thermalization; coexistence of chaos and collective motion; spreading widths of simple modes; geometric chaoticity).
TOWARDS BOSE–EINSTEIN CONDENSATION OF ELECTRON PAIRS: ROLE OF SCHWINGER BOSONS
Authors: SU GANG , SUZUKI MASUO
Published: July 2002

It can be shown that the bosonic degree of freedom of the tightly bound on-site electron pairs could be separated as Schwinger bosons. This is implemented by projecting the whole Hilbert space into the Hilbert subspace spanned by states of two kinds of Schwinger bosons (to be called binon and vacanon) subject to a constraint that these two kinds of bosonic quasiparticles cannot occupy the same site. We argue that a binon is actually a kind of quantum fluctuations of electron pairs, and a vacanon corresponds to a vacant state. These two bosonic quasiparticles may be responsible for the Bose–Einstein condensation (BEC) of the system associated with electron pairs. These concepts are also applied to the attractive Hubbard model with strong coupling, showing that it is quite useful. The relevance of the present arguments to the existing theories associated with the BEC of electron pairs is briefly commented.
Sr Substitution for Ba in Y(Ba1-xSrx)2Cu3O7-d at Varying d
Authors: Licci F. , Gauzzi A. , Marezio M. , Radaelli G. P. , Masini R. , Chaillout-Bougerol C.
Published: July 2002

In order to understand the difference between the effects induced by chemical substitutions and those induced by applying mechanical pressure, we synthesised and characterised samples of Y ( Ba 1-x Sr x)2 Cu 3 O 7-d. The structural refinements based on powder neutron diffraction data were carried out as a function of x and, for x = 0.5, as a function of d. The electric and magnetic properties have also been measured and correlated with the structural parameters and oxygen content. It seems that the Ba cations play an important role in the high T c of YBCO. Its substitution with a smaller cation corresponds to the application of a chemical pressure, but the release of the associated strain seems to play a negative role on T c .
Fluorine Substitution in High Temperature Superconductors
Authors: Bellingeri E. , Grasso G. , Gladyshevskii R. , Giannini E. , Marti F. , Dhallé M. , Flükiger R.
Published: July 2002

Fluorine substitution in the Bi(2223), Bi(2212) and Tl(1223) superconducting phases was studied. We obtained superconducting structures, never observed before, of the Bi-based superconductors by a low temperature (200-400 °C) fluorination process. Fluorine substitutes completely the oxygen sites in the Bi layers and additional F atoms are inserted in the structure. As a consequence, changes in the arrangements of cation and anions were induced, especially in the Bi and partially in the Sr layer. F-doped Tl(1223) has been prepared in the same way as Bi(2223) and Bi(2212) (low temperature fluorination), but also starting from precursor containing fluorides of different elements. No significant differences in the crystal structure have been observed between the Tl-based samples with F inclusions and without. The critical temperature (116 K) remains unchanged but a significant increase of the irreversibility field at low temperature was found.
In-Plane Properties of (103)/(013) Oriented YBCO Films
Authors: Camerlingo C. , Nappi C. , Russo M. , Jung G.
Published: July 2002

The anisotropic in-plane electrical and superconducting behavior of (103)/(013) oriented YBCO films has been investigated. The 150 nm thick samples were fabricated on (110) SrTiO3 substrates by dc sputtering from an inverted cylindrical magnetron, using a self-template growth process. The (103)/(013) lattice orientation was confirmed by the X-ray diffractometry measurements and by polarised-light Raman spectroscopy. The film was patterned in 20 μm width lines, in-oriented along different directions, in order to estimated the dependence of properties on the crystal orientation. Concerning the normal state electrical resistance, measured by a four contacts method at 100 K, a value ρab = 0.64 m Ω cm and ρc = 3.50 m Ω cm is found for the bias current directed respectively along and across the copper planes. The current voltage (I-V) characteristics were measured at different temperatures. As expected the critical current density Jo is larger for the lines aligned with the copper planes, and decreases with decreasing of the angle between current bias direction and the normal to the copper planes. The influence on vortex pinning of lattice twins occurring at the (103) and (013) grain boundaries is considered by analyzing the Jo vs T dependence and the I-V characteristics compared with c-axis YBCO film standard features.
The Place of Dielectric Spectroscopy in Probing Electrorheology
Authors: Kyvelidis S. , Maistros G. M. , Rattray P. , Block H. , Akhavan J. , Tsangaris G.
Published: July 2002

The measurement of the dielectric spectra of PAnQR based ER fluids under shear and electric fields is discussed and results presented. Data in which either but not both shear or electric fields are present are submitted to analysis in terms of known theories. For flow alone, that analysis provides information on the attenuation of polarization by the uniform shear fields whilst the polarization of quiescent fluids by electric fields may lead to estimates of particles packing within the columns. Permittivity data when both fields are acting is presented, but in the absence of suitable theory, not modelled quantitatively. Empirical correlations are discussed and the conclusion drawn that fibrillation is readily suppressed by even moderate shear rates, although long range dipolar forces still persist to high shear rates.

The dc conductance of these fluids have also been measured. This together with permittivity data under ER fluid working conditions has importance in establishing the electrical parameters for any ER fluid.
Electrorheological Fluids in Squeeze under AC and DC Excitation
Authors: Sproston J. L. , Wahed A. K. El , Stanway R.
Published: July 2002

This paper is concerned with an experimental investigation of the performance of an ER fluid in oscillatory squeeze-flow and a comparison of the results with those predicted by a quasi-steady theoretical model in which the rheological behaviour of the fluid is assumed to follow a bi-viscous shears stress/shear rate characteristic. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. Of particular interest is the temporal variation in the force transmitted through the fluid in response to changes in the oscillation frequency and amplitude and the level of applied AC and DC voltages. The magnitude of the transmitted forces in the AC case is seen to be not only a function of the applied voltage but also of the shape of the input waveform and the electrical excitation frequency. In all cases these forces are found to be smaller than those seen in the corresponding DC case.
Characterization of the Mechanical Properties of Electrorheological Fluids Made of Starch and Silicone Fluid
Authors: Vieira Sheila Lopes , de Arruda Antonio Celso Fonseca
Published: July 2002

In the majority of published articles on the topic, ER fluids have been studied as if they were viscous liquids. In this work, electrorheological fluids were characterized as solids and their mechanical properties were determined. The results infer that ER materials are controllably resistant to compression, tensile and shear stress, in this order of magnitude. More precisely, fluids made of starch have elasticity modulus similar to that of rubber, they have tensile strength 103 to 5×104 times lower than that of low density polyethylene (LDPE), static yield stress 4×104 to 8×105 times lower than that of acrylonitrile-butadiene-styrene terpolymer (ABS) and fatigue life similar to some polymers like polyethylene(PE) and polypropylene (PP).
DENSITY MATRIX AND PARTITION FUNCTION FOR A GENERALIZED NONDEGENERATE PARAMETRIC AMPLIFIER GAINED VIA A TYPE OF TWO-MODE SPECIAL SQUEEZED COHERENT STATE REPRESENTATION
Authors: FAN HONGYI , FAN YUE , SUN MINGZHAI
Published: July 2002

By introducing a type of two-mode special squeezed coherent state, we directly derive the density matrix and partition function for a generalized nondegenerate parametric amplifier. The derivation is neat because the states make up a new, complete representation.
TRANSPORT PHENOMENA IN THE MIXED STATE OF (Bi1.6Pb0.4) Sr2Ca2 (Cu1-xGax)3Oy BULK MATERIALS
Authors: ILONCA G. , POP A. V. , STIUFIUC G. , STIUFIUC R. , LUNG C.
Published: July 2002

We have performed a study of magnetoresistivity, Seebeck, Nernst and Hall effects in the mixed state and in the fluctuation regime above T c 0 for Bi:2223 bulk doped with Ga (0 ≤ x ≤ 0.05), prepared by the conventional solid state reaction method, in magnetic fields between 0 and 5 T and in the temperature range 5–120 K. It was found that critical temperatures, the Hall concentration, and the Nernst and Seebeck coefficients depend strongly on the Ga contents in the samples. The Hall resistivity ρxy showed a sign anomaly in the mixed state and scaled with longitudinal resistivity ρxx with a power coefficient β ≅ 2. The experimental data are in agreement with the predictions of the time-dependent Ginzburg–Landau theory.
TEMPERATURE DEPENDENCE OF CRITICAL CURRENT AND RESISTANCE FLUCTUATIONS IN BULK POLYCRYSTALLINE YBCO SUPERCONDUCTORS
Authors: POPESCU V. , STEPANESCU A.
Published: July 2002

The critical current and resistance fluctuations, in the presence of a magnetic field in polycrystalline YBCO samples, decrease with the temperature at high temperatures and are strongly correlated at lower temperatures but strongly anticorrelated at higher temperatures.
EXCHANGE BIAS IN FERROMAGNETIC/ANTIFERROMAGNETIC BILAYERS
Authors: HU JING-GUO , JIN GUO-JUN , MA YU-QIANG
Published: July 2002

We present a theoretical investigation on the thickness dependence of exchange bias in ferromagnetic (FM)/antiferromagnetic (AFM) bilayer systems, in which the exchange coupling at the interface between the FM layer and the AFM layer includes both bilinear (direct exchange) and biquadratic (spin-flop) terms. Based on the above model, the basic formula is derived for the first time. From the formula, a lot of interesting facts can be extracted, and a number of recent experimental results can be illustrated. We find that the exchange bias linearly depends on the reciprocal of FM layer thickness. However, another factor is the switching thickness of the AFM layer to display exchange bias, which approaches saturation with a relatively thick AFM layer. In general, the biquadratic term reduces exchange bias. When the biquadratic coupling is properly selected, the discrepancies in the previous theories and experiments can be efficiently eliminated.
STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF La2CuO4+δ OXIDIZED BY KMnO4 UNDER HYDROTHERMAL CONDITIONS
Authors: TU Q. Y. , MA B. K. , CHEN X. L. , LAN Y. C. , XU Y. X. , LIANG J. K. , ZHAO Z. X. , LI J. Q.
Published: July 2002

A series of samples of La2CuO4+δ chemically oxidized in KMnO 4 solution under hydro-thermal conditions have been prepared. A large orthorhombic distortion and the increased unit cell volume of the oxidized sample have been observed by means of X-ray powder diffraction, compared with that of the starting material. Selected-area electron diffraction investigations reveal that two kinds of incommensurate modulation structures exist in the oxidized samples. Magnetic susceptibility measurements indicate that the oxidized samples are multiphase with two superconducting phases, one is dominant with onset of superconducting transition temperature at 43 K or 40 K, and the other at 19 K. Up to now, a T c of 43 K is the highest value achieved in KMnO 4-treated samples. The excess oxygen content determined by iodometric titration increases with the oxidation temperature. Average grain sizes observed by scanning electron microscope have no obvious changes for the samples before and after oxidation.
Computational Study of a Primitive Life Model
Authors: Andrecut Mircea
Published: July 2002

We present a computational study of a primitive life model. The calculation involves a discrete treatment of a partial differential equation and some details of that problems are explained. We show that the investigated model is equivalent to a diffusively coupled logistic lattice. The bifurcation diagrams were calculated for different values of the control parameters. The obtained diagrams have shown that the time dependence of the population of the investigated model exhibits transitions between ordered and chaotic behavior. We have investigated also the patterns formation in this system.
STABILIZATION OF UNSTABLE PERIODIC ORBITS OF CHAOTIC DISCRETE-TIME SYSTEMS USING PREDICTION-BASED FEEDBACK CONTROL
Authors: HINO TORU , YAMAMOTO SHIGERU , USHIO TOSHIMITSU
Published: July 2002

In this paper, we consider feedback control that stabilizes unstable periodic orbits (UPOs) of chaotic discrete-time systems. First, we show that there exists a strong necessary condition for stabilization of the UPOs when we use delayed feedback control (DFC) that is known as one of the useful methods for controlling chaotic systems. The condition is similar to that in the fixed point stabilization problem, in which it is impossible to stabilize the target unstable fixed point if the Jacobian matrix of the linearized system around it has an odd number of real eigenvalues greater than unity.

In order to stabilize UPOs which cannot be stabilized by the standard DFC, we adopt prediction-based control. We show a necessary and sufficient condition for the stabilization of the UPOs with arbitrary period.
A VIRTUAL LEAF
Authors: WALCZAK P. G.
Published: July 2002

First, we study the growth rate of separation of pseudo-orbits of a finitely generated group acting on a compact space. Then, suspending a suitable group action and a suitable pseudo-orbit we get, after a minor modification, a foliation and a Riemannian manifold which is not quasi-isometric to any leaf of any compact foliated manifold but which is quasi-isometric to pseudoleaves of the constructed foliation intersecting its leaves at arbitrarily small angle. Such an object is called a virtual leaf here.
COMPONENT-BASED EMBEDDED SOFTWARE ENGINEERING: DEVELOPMENT FRAMEWORK, QUALITY ASSURANCE AND A GENERIC ASSESSMENT ENVIRONMENT
Authors: CAI XIA , LYU MICHAEL R. , WONG KAM-FAI
Published: July 2002

Embedded software is used to control the functions of mechanical and physical devices by dedicated digital signal processor and computers. Nowadays, heterogeneous and collaborative embedded software systems are widely adopted to engage the physical world. To make such software extremely reliable, very efficient and highly flexible, component-based embedded software development can be employed for the complex embedded systems, especially those based on object-oriented (OO) approaches. In this paper, we introduce a component-based embedded software framework and the features it inherits. We propose a quality assurance (QA) model for component-based embedded software development, which covers both the component QA and the system QA as well as their interactions. Furthermore, we propose a generic quality assessment environment for component-based embedded systems: ComPARE. ComPARE can be used to assess real-life off-the-shelf components and to evaluate and validate the models selected for their evaluation. The overall component-based embedded systems can then be composed and analyzed seamlessly.
LENGTH AND AREA FUNCTIONS ON GROUPS AND QUASI-ISOMETRIC HIGMAN EMBEDDINGS
Authors: OĹSHANSKII ALEXANDER YU. , SAPIR MARK V.
Published: July 2002

We survey recent results about asymptotic functions of groups, obtained by the authors in collaboration with J.-C. Birget, V. Guba and E. Rips. We also discuss methods used in the proofs of these results.
ON THE INTERSECTION OF FINITELY GENERATED SUBGROUPS IN FREE PRODUCTS OF GROUPS
Authors: IVANOV S. V.
Published: July 2002

A subgroup H of a free product [Formula: see text] of groups Gα, α∈ I, is called factor free if for every [Formula: see text] and β ∈ I one has S H S-1∩ Gβ = {1} (by Kurosh theorem on subgroups of free products, factor free subgroups are free). If K is a finitely generated free group, denote [Formula: see text], where r(K) is the rank of K. It is proven that if H, K are finitely generated factor free subgroups of a free product [Formula: see text] then [Formula: see text]. It is also shown that the inequality [Formula: see text] of Hanna Neumann conjecture on subgroups of free groups does not hold for factor free subgroups of free products.
HNN EXTENSION OF CYCLICALLY PRESENTED GROUPS
Authors: SZCZEPAŃSKI ANDRZEJ , VESNIN ANDREI
Published: July 2002

It is shown that if the defining word of a cyclically presented group is admissable then its natural HNN extension is the group of a high dimensional knot. As an example we define a family of cyclically presented groups which contains Sieradski groups, Fibonacci groups, and Gilbert-Howie groups. It is proven that HNN extensions of these groups are LOG groups and so, are fundamental groups of complements of codimension two closed orientable connected tamely embeded ℓ-dimensional manifolds (ℓ≥2).
EQUILIBRIUM CONFIGURATIONS FOR QUARK–DIQUARK STARS AND THE PROBLEM OF HER X-1 MASS
Authors: HORVATH J. E. , DE FREITAS PACHECO J. A.
Published: July 2002

We report new calculations of the physical properties of a quark–diquark plasma. A vacuum contribution is taken into account and is responsible for the appearance of a stable state at zero pressure and at a baryon density of about 2.2 times the nuclear matter density in this model. The resulting equation of state was used to integrate numerically the Tolman–Oppenheimer–Volkoff equations. The mass-radius relationship has been derived from a series of equilibrium configurations constituted by a mixture of quarks and diquarks. These stellar models, which are representative of a whole class, may be helpful to understand the possible compactness of the X-ray source Her X-1 and related objects.
WEAK AND ELECTROMAGNETIC INTERACTIONS OF HYPERONS: A CHIRAL APPROACH
Authors: HOLSTEIN BARRY R.
Published: July 2002

A range of issues in the field of weak and electromagnetic interactions of hyperons is presented from the perspective of (broken) chiral symmetry, together with an assessment of where important challenges remain.
EIKONAL MODEL ANALYSIS FOR 9Li+p AND 11Li+p ELASTIC SCATTERINGS AND HALO EFFECT
Authors: KIM YONG JOO , CHA MOON HOE
Published: July 2002

The elastic angular distributions for 9 Li+p and 11 Li+p at E lab /A = 60 and 62 MeV/nucleon, respectively, have been analyzed within the framework of the eikonal model. It is assumed that 11 Li has the halo structure of a 9 Li core plus two weakly bound neutrons and is treated such that the nuclear potential has a sum of the core and halo neutron contributions. We have found that the break-up effect of halo neutrons is essential to understand the elastic cross sections of 11 Li+p system at E lab /A = 62 MeV/nucleon. The near- and the far-side decompositions of elastic cross sections have also been performed by following the Fuller's formalism.
A POLICY OF FISHERIES MANAGEMENT BASED ON CONTINUOUS FISHING EFFORT
Authors: JERRY M. , RAISSI N.
Published: July 2002

This work is composed by two parts: the first part consists of the development and the analysis of a bioeconomical model of fisheries management, where the dynamic is controlled by the variation of the fishing effort; the second part of this work consists of the study of the asymptotical stability of the equilibrium point (stock/fishing effort) of the model; the optimal strategy is described briefly.
THE Au3Pd(001) SURFACE STUDIED BY ION SCATTERING AND LEED
Authors: SPELLER S. , ASCHOFF M. , KUNTZE J. , HEILAND W. , ATREI A. , BARDI U. , PLATZGUMMER E.
Published: July 2002

The (001) surface of a Au 3 Pd single crystal was studied with different surface analytical techniques. The main results reported about structure, composition and dynamics of the surface are based on ion scattering methods and LEED. We find segregation of Au to the surface forming a complete Au overlayer. The second layer has approximately the bulk Pd concentration. There is no evidence for chemical order in the near surface layers, i.e. Pd is randomly distributed in the lattice. The Au and Pd atoms in the first and the second layer respectively have approximately the same thermal vibrational amplitudes.
THE GROWTH AND ELECTRONIC STRUCTURES OF EPITAXIAL CrSi2 FILMS PREPARED ON Si(111) SUBSTRATE
Authors: KIM K. H. , KANG J.-S. , OLSON C. G.
Published: July 2002

Highly epitaxial CrSi 2 films were grown on Si(111) substrate by Cr deposition on Si(111)-(7×7) surface at 450°C followed by in situ annealing at 900–1100°C in ultrahigh vacuum. CrSi 2 (001) plane was grown parallel to the Si(111) plane with a CrSi 2 <210>// Si <110> matching face relationship. The valence band (VB photoemission for the 1200-Å-thick CrSi 2 was measured at room temperature and 20 K by using synchrotron radiation (hν=20–120 eV). Overall shapes of the two energy distribution curves (EDC's) were similar. Two peaks were observed in the EDC's corresponding to the bonding and the nonbonding Cr -d states in the CrSi 2. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap opening at low temperature.
THE ROLE OF THE SURFACE ELECTRONIC STRUCTURE IN THE OXIDATION OF IRON
Authors: ROOSENDAAL S. J. , VREDENBERG A. M. , HABRAKEN F. H. P. M.
Published: July 2002

The Fromhold–Cook coupled-currents theory of metal oxidation states that below ~ 150° C , a saturation thickness is reached, which is independent of temperature, as a result of the diminution of the electron tunnel current. However, Fe and Co show a strong temperature dependence of the oxide saturation thickness. In this study, we combine ellipsometry, X-ray Photoelectron Spectroscopy (XPS) and the high energy ion beam technique Elastic Recoil Detection (ERD) for the detailed determination of oxidation rate and oxide thickness, composition, and electronic structure on Fe(100) in O 2. At room temperature, first a 1 nm thin FeO film forms, followed by the growth of a 1 nm mixed Fe 2+/ Fe 3+ layer, which forms the effective barrier against further oxidation. By vacuum annealing at 200°C, the Fe 3+ is reduced to Fe 2+ and the oxidation kinetics through a single Fe 2+ containing layer can be studied, yielding results in excellent agreement with the FC theory. At T<150° C , the transport of metal ions to the surface is rate-limiting and the saturation thickness is independent of temperature (3.2 nm of FeO). At T ≥ 150° C , the thermionic emission of electrons determines the oxidation rate. Thus, a complete and consistent picture of the initial thin oxide layer growth on Fe single crystals is obtained.
FORMULATION AND APPLICATIONS OF HIERARCHY GAMES
Authors: MATSUMOTO MITSUTAKA
Published: July 2002

In this paper, I discuss the formulation and some applications of a framework called "hierarchy games". Hierarchy games are a game theoretical framework in which two or more games interact with one another. The interaction among games can be best described by the following two characteristics: (1) the outcome of a lower-level game could restrict the available actions of a player in higher-level. (2) the payoff of a higher-level player is shared by lower-level players. The above ideas were first proposed by Hausken in 1995. The paper attempts to develop further those ideas. First, some parts of the framework are defined more rigorously than Hausken's formulation. Secondly, some applications of the framework to the field of International Relations are discussed.
COMPRESSIVE FAILURE PREDICTION FROM NONLINEAR FINITE ELEMENT ANALYSIS OF A NOTCHED 0 DEGREE COMPOSITE SPECIMEN
Authors: VIOLETTE MELANIE G.
Published: July 2002

The strength of unidirectional composites is often lower in compression than in tension, making compressive strength an especially important design criterion. The compressive strength is sensitive to the presence of notches and stress gradients. Finite element analysis was used to determine the strain gradient at a shallow circular notch in one edge of a 0 degree carbon/epoxy composite specimen, and to predict failure due to a localized buckling instability. The specimen was first analyzed with a "global" model of the full specimen, and displacements along a curve near the notch were stored and used as boundary conditions for a more detailed "submodel" in the immediate vicinity of the notch. At the onset of instability, a displaced plot of the finite element model shows oscillations in the transverse direction along the arc of the notch, just off the centerline, which is essentially at the same location where failure initiated in the test specimens. Results are compared with experimental values for failure stress and notch strain concentration for a range of loading rates and test temperatures.
ABSOLUTE: AN INFORMATION VISUALIZATION SYSTEM FOR DECISION SUPPORT IN SOURCING
Authors: LEE JUHNYOUNG
Published: July 2002

ABSolute is a general-purpose, multi-dimensional decision support system which has a highly sophisticated visualization-based user interface for direct data manipulation. The interface and analysis facilities of this system enable the users to effectively view, explore, search, compare and classify data items to make discoveries, decisions or explanations about patterns, groups of items, or individual items with the highest level of confidence and knowledge. The usefulness of this system is demonstrated in solving a complex decision-making problem in a business environment: a bid evaluation and selection problem in corporate procurement using a RFQ (Request-For-Quotes) process.
RHEOLOGY OF DENSE GRANULAR FLOW
Authors: HALSEY THOMAS C. , ERTAŞ DENIZ , GREST GARY S. , SILBERT LEONARDO E. , LEVINE DOV
Published: July 2002

We have performed numerical studies of dense granular flows on an incline with a rough bottom in two and three dimensions. This flow geometry produces a constant density profile that satisfies scaling relations of the Bagnold, rather than the viscous, kind. No surface-only flows were observed. The bulk and the surface layer differ in their rheology, as evidenced by the change in principal stress directions near the surface; a Mohr–Coulomb type failure criterion is seen only near the surface. In the bulk, normal stress anomalies are observed both in two and in three dimensions. We do not observe isostaticity in static frictional piles obtained by arresting the flow.
Evolutionary study of interethnic cooperation
Authors: Kvasnicka Vladimir , Pospichal Jiri
Published: July 2002

The purpose of this communication is to present an evolutionary study of cooperation between two ethnic groups. The used model is stimulated by the recent seminal paper of J. D. Fearon and D. D. Laitin (Explaining Interethnic Cooperation, American Political Science Review, Vol. 90 (1996), pp. 715-735), where the iterated prisoner's dilemma was used to model intra- and interethnic interactions. We reformulated their approach in a form of evolutionary prisoner's dilemma method, where a population of strategies is evolved by applying simple reproduction process with a Darwin metaphor of natural selection (a probability of selection to the reproduction is proportional to a fitness). Our computer simulations show that an application of a principle of collective guilt does not lead to an emergence of an interethnic cooperation. When an administrator is introduced, then an emergence of interethnic cooperation may be observed. Furthermore, if the ethnic groups are of very different sizes, then the principle of collective guilt may be very devastating for smaller group so that intraethnic cooperation is destroyed. The second strategy of cooperation is called the personal responsibility, where agents that defected within interecthinic interactions are punished inside of their ethnic groups. It means, unlikely to the principle of collective guilt, that there exists only one type of punishment, loosely speaking, agents are punished "personally". All the substantial computational results were checked and interpreted analytically within the theory of evolutionary stable strategies. Moreover, this theoretical approach offers mechanisms of simple scenarios explaining why some particular strategies are stable or not.
PREDICTION OF DRUG DISSOLUTION PROFILES USING ARTIFICIAL NEURAL NETWORKS
Authors: QUEK SIOW SAN , LIM CHEE PENG , PEH KOK KHIANG
Published: July 2002

This paper investigates the efficacy and reliability of Artificial Neural Networks (ANNs) as an intelligent decision support tool for pharmaceutical product formulation. Two case studies have been employed to evaluate capabilities of the Multilayer Perceptron network in predicting drug dissolution/release profiles. Performances of the network were evaluated using similarity factor (f2) — an index recommended by the United States Food and Drug Administration for profile comparison in pharmaceutical research. In addition, the bootstrap method was applied to assess the network prediction reliability by estimating confidence intervals associated with the results. The Multilayer Perceptron network also demonstrated a superior performance in comparison with multiple regression models. The results reveal that the ANN system has potentials to be a decision support tool for profile prediction in pharmaceutical experimentation, and the bootstrap method could be used as a means to assess reliability of the network prediction.
Reducing the latency of a real-time garbage collector
Authors: Johnson Ralph E.
Published: July 2002

This paper shows how to make the latency of scanning a page in the Appel-Ellis-Li real-time garbage collector be proportional only to the number of object references on a page (the page size), instead of to the sum of the sizes of the objects referenced by the page. This makes the garbage collection algorithm much more suitable for real-time systems.
Time warp simulation using time scale decomposition
Authors: Ammar Hany H. , Deng Su
Published: July 2002

In this paper we consider time scale decomposition as well as spatial decomposition to induce massive parallelism and reduce overhead in distributed discrete-event simulations. We confine our study to the Time Warp strategy and to systems where the durations of activities differ by several orders of magnitude (i.e., systems with fast and slow activities). We show that, for such systems, a large overhead due to rollbacks is encountered when spatial decomposition is used. Moreover, performance degrades as the difference increases between the rates of fast and slow events.

Several initial experiments using queueing-network models were designed to evaluate the effectiveness of time scale decomposition in increasing the parallelism and reducing the overhead. These experiments were conducted on a distributed simulation testbed that was implemented on an 18-processor Multimax 320. The application of the above simulation techniques to stochastic Petri net models is illustrated using an example of performability analysis of a fault-tolerant distributed system.
Efficient decision procedures for graph properties on context-free graph languages
Authors: Lengauer Thomas , Wanke Egon
Published: July 2002

Efficient ways of analyzing families of graphs that are generated by a certain type of context-free graph grammars are considered. These graph grammars are called
cellular graph grammars
. They generate the same graph families as hyperedge replacement systems, but are defined in a way that supports complexity analysis. A characteristic called “finiteness” of graph properties are defined, and combinatorial algorithms are presented for deciding whether a graph language generated by a given cellular graph grammar contains a graph with a given finite graph property. Structural parameters are introduced that bound the complexity of the decision procedure and special cases for which the decision can be made in polynomial time are discussed. Extensions to graph grammars that are not context-free are also given. Our results provide explicit and efficient combinatorial algorithms where, so far, only the existence of algorithms has been shown, or the best known algorithms are highly inefficient.
Template-driven interfaces for numerical subroutines
Authors: Bentley Jon L. , Fernandez Mary F. , Kernighan Brian W. , Schryer Norman L.
Published: July 2002

This paper describes a set of interfaces for numerical subroutines. Typing a short (often one-line) description allows one to solve problems in application domains including least-squares data fitting, differential equations, minimization, root finding, and integration. Our approach of “template-driven programming” makes it easy to build such an interface: a simple one takes a few hours to construct, while a few days suffice to build the most complex program we describe.
Tight lower bounds for probabilistic solitude verification on anonymous rings
Authors: Abrahamson Karl , Adler Andrew , Highám Lisa , Kirkpatrick David
Published: July 2002

A model that captures communication on asynchronous unidirectional rings is formalized. Our model incorporates both probabilistic and nondeterministic features and is strictly more powerful than a purely probabilistic model. Using this model, a collection of tools are developed that facilitate studying lower bounds on the expected communication complexity of Monte Carlo algorithms for language recognition problems on anonymous asynchronous unidirectional rings. The tools are used to establish tight lower bounds on the expected bit complexity of the Solitude Verification problem that asymptotically match upper bounds for this problem. The bounds demonstrate that, for this problem, the expected bit complexity depends subtly on the processors' knowledge of the size of the ring and on whether or not processor-detectable termination is required.
On solving equations and disequations
Authors: Buntine Wray L. , Bürckert Hans-Jürgen
Published: July 2002

We are interested in the problem of solving a system

〈s
l
= t
l
: 1 ≤ i ≤ n, p
j
≠ q
j
: 1 ≤ j ≤ m 〉

of equations and disequations, also known as
disunification
. Solutions to disunification problems are substitutions for the variables of the problem that make the two terms of each equation equal, but leave those of the disequations different. We investigate this in both algebraic and logical contexts where equality is defined by an equational theory and more generally by a definitive clause equality theory E. We show how E-disunification can be reduced to E-unification, that is, solving equations only, and give a disunification algorithm for theories given a unification algorithm. In fact, this result shows that for theories in which the solutions of all unification problems can also be represented finitely. We sketch how disunification can be applied to handle negation in logic programming with equality in a similar style to Colmerauer's logic programming with rational trees, and to represent many solutions to AC-unification problems by a few solutions to ACI-disunification problems.