bluuebunny/crossref_metadata_2025 huggingface dataset:
CHEMICAL EQUILIBRIUM MODEL FOR HIGH-TC AND HEAVY FERMION SUPERCONDUCTORS: THE DENSITY OF STATES
Authors: KALLIO A. , HISSA J. , HÄYRYNEN T. , BRÄYSY V. , SÄKKINEN T.
Published: July 2002

The chemical equilibrium model is based on the idea of correlated electron pairs, which in singlet state can exist as quasimolecules in the superfluid and normal states of a superconductor. These preformed pairs are bosons which can undergo a Bose-Einstein condensation in analogy with the superfluidity of 4 He+ 3 He -mixture. The bosons (B++) and the fermions (h+) are in chemical equilibrium with respect to the reaction B++⇌ 2 h+, at any temperature. The mean densities of bosons and fermions (quasiholes) nB(T) and nh(T) are determined from the thermodynamics of the equilibrium reaction in terms of a single function f(T). By thermodynamics the function f(T) is connected to equilibrium constant φ (T) by 1-f(T)= [1+φ(T)]-1/2. Using a simple power law, known to be valid near T=0, for the chemical constant φ(T)=α/t2γ, t=T/T*, the mean density of quasiholes is given in closed form. This enables one to calculate the corresponding density of states (DOS) D(E)=NS/N(0), by solving an integral equation. The NIS-tunneling conductivity near T=0, given by D(E) compares well with the most recent experiments: D(E)~ Eγ, for small E and a finite maximum of right size, corresponding to "finite quasiparticle lifetime". The corresponding SIS-tunneling conductivity is obtained from a simple convolution and is also in agreement with recent break junction experiments of Hancotte et al. The position of the maximum can be used to obtain the scaling temperature T*, which comes close to the one measured by Hall coefficient in the normal state. A simple explanation for the spingap effect in NMR is given.
DEFORMED FERMI SURFACE THEORY OF MAGNETO–ACOUSTIC RESPONSE IN MODULATED QUANTUM HALL SYSTEMS NEAR ν=1/2
Authors: ZIMBOVSKAYA NATALIYA A. , BIRMAN JOSEPH L.
Published: July 2002

We develop a magneto-transport theory for the nonlocal response of a two-dimensional electron gas (2DEG) in the Fractional Quantum Hall Regime near ν=1/2 in the presence of a periodic density modulation. We introduce a new generic model of a deformed Composite Fermion–Fermi Surface (CF–FS). Our model permits us to explain recent surface acoustic wave observations of anisotropic anomalies1 in sound velocity and attenuation, such as appearance of peaks and anisotropy, which originate from contributions to the conductivity tensor due to regions of the CF–FS which are flattened by the applied modulation. The calculated magnetic field and wave vector dependence of the CF conductivity, velocity shift and attenuation agree with experiments.
Fabrication and Properties of Epitaxial Buffer Layers on Nonmagnetic Textured Ni Based Alloy Substrates
Authors: Celentano G. , Boffa V. , Ciontea L. , Fabbri F. , Galluzzi V. , Mancini A. , Petrisor T. , Ceresara S. , Scardi P.
Published: July 2002

Biaxially aligned YBCO thick films on oxide buffered metallic substrates is a promising route toward the fabrication of superconducting tapes operating at liquid nitrogen temperature. The role of buffer layer is to reduce the lattice mismatch between the substrate and the YBCO film, to adapt the thermal expansion coefficient, to hamper the diffusion of Ni in YBCO film and to prevent the oxidation of the metallic substrate surface. This paper presents a study regarding CeO 2 buffer layer deposition on a new nonmagnetic (001)[100] textured Ni-V alloy substrates. The deposition of CeO 2 was performed by both pulsed laser ablation and e-beam evaporation techniques. The θ-2θ X-ray diffraction pattern mainly exhibits the (00l) peaks of CeO 2, indicating that the films are epitaxially grown with the c axis perpendicular to the substrate. Rocking curved through the CeO 2 (002) peak have a FWHM of about 6°. The SEM studies have shown that the surface is smooth, continuos and free of cracks. Texture analysis reveals a good in-plane orientation for the ablated CeO 2 film, whereas the electron beam evaporated CeO 2 shows two textures in the growth plane. Further efforts are focused on the deposition of YBCO thick film on the as buffered nonmagnetic metallic substrate.
Harmonic Analysis of the AC Magnetic Response on Directionally Solidified YBaCuO Samples
Authors: Polichetti M. , Pace S. , Vecchione A.
Published: July 2002

The transport properties and the dynamics of the flux lines have been investigated on YBaCuO melt textured by measuring the AC susceptibility harmonics as function of the temperature, at different frequencies and amplitudes of the AC magnetic field. The interpretation of the behavior of the experimental curves has been done by their comparison with the results obtained by critical state pictures and by simulations of the diffusion processes of the magnetic field which determine the AC response in presence of different regimes of flux dynamics. The temperature dependencies of the third harmonics of the AC susceptibility at different frequencies have been used in particular to determine what is the flux dynamic regime governing the magnetic response of melt textured samples in the different experimental conditions. A good qualitative agreement has been found between the experimental curves and the ones simulated by assuming that dissipation processes are a sequence of independent flux creep and flux flow events within a collective pinning framework.
Transient Response of an Immiscible Polymer Blend ER Fluid to a Step Electric Field
Authors: Tajiri Kozo , Orihara Hiroshi , Ishibashi Yoshihiro , Doi Masao , Inoue Akio
Published: July 2002

The relationship between the electrorheological effect and the structure in an immiscible polymer blend was investigated in detail by observing the transient responses to a step field. It was clarified that the increase of the shear stress consists of two processes, the first and the second modes. The former may be ascribed to the elongation of droplets, and the origin of the latter is the formation of cylinders consisting of viscous polymer.
New Actuator Utilizing Phase Change of Functional Fluids
Authors: Tanaka Chigusa , Mai Jianqiang , Nakagawa Masamichi , Oshima Shuzo , Yamane Ryuichiro , Park Myeng-Kwan
Published: July 2002

This paper proposes a new actuator utilizing the phase change of the ER fluid. The dielectric coolant was used for the solvent and silica gel particles for the dispersion particle. The dynamic characteristics of the actuator was determined for the several patterns of the working conditions.
FORM FACTORS IN THE FINITE VOLUME
Authors: KOREPIN V. E. , SLAVNOV N. A.
Published: July 2002

We study exactly solvable models of quantum statistical mechanics. Our main example is the Quantum nonlinear Schrödinger equation. This model can be solved by algebraic Bethe Ansatz. We are interested in the expression for a form factor of the local field in the finite volume [Formula: see text]. We found a determinant representation for this form factor. We think that this is the universal feature: finite volume form factor of any exactly solvable model can be represented a determinant.
MODEL CALCULATION OF ELECTRON–PHONON COUPLINGS IN A DIMER WITH A NON-DEGENERATE ORBITAL
Authors: ACQUARONE M. , NOCE C.
Published: July 2002

We evaluate all the electron–phonon couplings derived from the one-body and two-body electronic interactions, in both the adiabatic and extreme non-diabatic limit, for a dimer with a non-degenerate orbital built from atomic wave functions of Gaussian shape. We find largely different values of the coupling parameters in the two limits, as well as different expressions of the corresponding terms in the Hamiltonian. Depending on the distance between the dimer ions, some of the two-body couplings are comparable, or even larger than the one-body ones.
Screening of the Electron-Phonon Coupling in Nb-doped SrTiO3
Authors: Jarlborg T.
Published: July 2002

The electronic part of the electron-phonon coupling, λ, in pure and Nb-doped SrTiO 3 has been calculated using the LMTO method. Supercells and the virtual crystal approximation has been used to treat the cases with dilute Nb-doping. It is found that the long-range part of the coupling is only weakly screened for low doping, when the material is close to be insulating. This makes the low-q part of λ large and can explain the appearance of superconductivity for low Nb concentration.
ESR STUDIES ON GMR RELATED MATERIALS III: ESR OF Mn IN La0.9Ca0.1MnO3
Authors: SUGAWARA K. , ARAI N. , KOUZUKI A. , HIROSE H.
Published: July 2002

ESR measurements have been done on La 0.9 Ca 0.1 MnO 3 from 4 K up to about 760 K. Two kinds of spectra (the high- and low-field signals) are observed below about 220 K, and clear signals above ≃233 K . The ESR linewidth, ΔH PP , of the high-field signal with g≃2 is nearly proportional to temperature times magnetic moment. The ESR intensity becomes maximum at around 233 K. Above 300 K, ΔH PP is nearly proportional to exp (-600/T), and the intensity follows Curie's law above 600 K, but gradually deviates upward from it with decreasing temperature below about 600 K, presumably due to the "spin-cluster" formation.
ROLE OF QUANTUM ENTANGLEMENT DUE TO A MAGNETIC IMPURITY ON CURRENT MAGNIFICATION EFFECT IN MESOSCOPIC OPEN RINGS
Authors: BENJAMIN COLIN , JOSHI SANDEEP K. , SAHOO DEBENDRANATH , JAYANNAVAR A. M.
Published: July 2002

We study the current magnification effect in presence of exchange scattering of electron from a magnetic impurity placed in one arm of an open mesoscopic ring. The exchange interaction causes entanglement of electron spin and impurity spin. Earlier studies have shown that such an entanglement causes reduction or loss of interference in the Aharonov–Bohm oscillations leading to decoherence. We find however, that this entanglement, in contradiction to the naive expectation of a reduction in current magnification leads to enhancement as well as suppression of the effect. We also observe additional novel features like new resonances and current reversals.
SUPERCONDUCTIVITY AND CuK-XANES OF (Hg, Re)Sr2CuO4+δ
Authors: BALAMURUGAN S. , GOPALAKRISHNAN I. K. , PRAKASH OM , PADALIA B. D. , YAKHMI J. V. , SELVAM P.
Published: July 2002

The 1201-type nominal ( Hg 0.9 Re 0.1) Sr 2 CuO 4+δ samples, synthesized at ~920°C in partial vacuum, show, from temperature dependent dc-magnetization, [Formula: see text]. The CuK-edge features obtained from X-ray absorption measurements on the sample show predominantly Cu 2+ state and a weak but distinct Cu 1+ signature due to superconducting 1201 phase (after taking due account of impurity Sr 2 CuO 3, and SrCuO 2 phases). The presence of Cu 1+ signature in SC samples is consistent with our earlier observations of Cu 1+ in Ba-free superconducting (Hg,Cr)-1201 and (Hg,Mo)-1201 materials.
SPACE PHOTOVOLTAICS – History, PROGRESS AND PROMISE
Authors: FLOOD DENNIS J.
Published: July 2002

The first space solar array was carried aloft on Vanguard I on March 17, 1958. Vanguard I was the second satellite successfully launched by the U.S. space program following the launch of Sputnik I by the (then) USSR on October 4, 1957. The array on Vanguard I consisted of six photovoltaic panels mounted on the outer surface of the satellite. The array produced about one watt of power for over six years. The cells on that first array were single crystal silicon, each 2 cm ×0.5 cm in size, and about 10% efficient at 28C. Solar arrays are now the primary source of power for all earth-orbiting satellites. Space solar arrays and power systems have grown in size and complexity since 1958. This paper will provide an overview of a typical satellite power system along with the current status of solar cell technology development in the U.S.
MODELING THE CVD GROWTH OF III-V- COMPOUNDS
Authors: MIMILA-ARROYO J. , REYES J. DIAZ
Published: July 2002

Chemical vapor deposition is widely used for growing semiconductors. In it the best growing conditions are obtained on an empirical way. Its theoretical models are sophisticated and not accurate enough to correctly explain the experimental results. In this work, we present a general model to explain the epitaxial growth kinetics of III-V semiconductor materials by chemical vapor deposition. The model is based on a reversible chemical reaction between the transporting gas and the III element at the source and the same reaction, at the substrate surface. However, the model considers that the III element might have a different chemical activity at each one of those surfaces. The model explains experimental results reported in the literature on III-V materials, by several laboratories, over decades.
OPTICAL AND MORPHOLOGICAL CHARACTERIZATION OF (ZnO)x(CdO)1-x THIN FILMS
Authors: VAILLANT L. , VIGIL O. , CONTRERAS-PUENTE G. , MEJÍA-GARCÍA C.
Published: July 2002

The optical and morphological properties of (ZnO)x(CdO)1-x semiconductor thin films with x composition in the range 0 □ x □ 0.5 are studied by the photoluminescence optical technique (PL), and the Scanning Electron Microscopy (SEM). The evolution of the band associated with oxygen content in the films is observed and described as a function of the film composition and the thermal annealing. The surface morphology is presented, where two different binary semiconducting species can be discerned in proportions dependent on the films composition.
COHERENT TWO-PHOTON PULSE PROPAGATION THROUGH A COHERENTLY PREPARED MEDIUM
Authors: JOSHI AMITABH
Published: July 2002

Propagation of pulses through a medium comprising of coherently prepared two-level atoms undergoing two-photon transition has been studied using Maxwell–Bloch equations. The solution of the electromagnetic field envelopes has been obtained under various conditions and the effect of initial atomic coherence is clearly brought out in these solutions.
TRANSPORT PHENOMENA IN THE MIXED STATE AND FLUCTUATION REGIME IN (Bi1.6Pb0.4)Sr2Ca1-xHox(Cu1-yZny)2O8+d
Authors: ILONCA G. , POP A. V. , STIUFIUC R. , STIUFIUC G. , LUNG C. , PATAPIS S.
Published: July 2002

Measurements of the magnetoresistivity, Seebeck, Nernst and Hall coefficients in Bi:2212 superconductors doped with Ho and Zn are reported. The critical temperature and the transport coefficients depend strongly on the Ho and Zn contents. The tails of the transport coefficients versus temperature curves are caused by fluctuation effects, which increase with increasing magnetic field. An anomalous suppression of superconductivity at x = 0.25–0.35 and y = 0.025–0.032 was also found when the hole concentration per Cu is P H = 1/8 and the transport properties exhibit metallic behavior. It was found that dB c2 /dT = -2.4 ± 0.2 T/K , corresponding to a Ginzburg–Landau coherence length ξ = 15 Å. The Hall resistivity ρxy scaling with the longitudinal resistivity ρxx as [Formula: see text] with α ≈ 1.8 is in agreement with the theory of Vinokur et al. The experimental data in the mixed state are in agreement with the prediction of the time-dependent Ginzburg–Landau theory.
ELECTRON–ELECTRON INTERACTIONS IN THE 2D FERROMAGNETIC ELECTRON FLUID
Authors: SICA G. , POLINI M. , TOSI M. P.
Published: July 2002

Motivated by current interest in spin-polarized states of the electron fluid at strong coupling, we evaluate the effective screened potential V↑↑(r) between two electrons in the 2D ferromagnetic jellium model. Exchange and correlation are treated in local approximation, following the approach given by C. A. Kukkonen and A. W. Overhauser (Phys. Rev.B20, 550 (1979)) for the paramagnetic fluid in 3D. The main features of V↑↑(r) in the fluid near freezing are discussed with reference to Wigner crystallization and to paired interstitial defects in the 2D Wigner crystal.
DEVELOPMENT AND CHARACTERISATION OF Ba2RENbO6 (RE = Yb, Er AND Ho) AND POTENTIAL USE AS SUBSTRATE FOR SUPERCONDUCTING YBCO FILMS
Authors: NAIR S. U. K. , WARRIAR P. R. S. , KOSHY J.
Published: July 2002

A group of complex perovskite oxides Ba2RENbO6 (RE = Yb, Er and Ho) have been synthesised and developed for their use as substrate for YBa2Cu3O7-δ superconductors. These materials have a complex cubic perovskite ( A2BB′O6 ) structure with lattice constants, a=8.3–8.5 Å. Ba2RENbO6 did not show any phase transition in the temperature range 30–1100°C. The dielectric constant and loss factor of Ba2RENbO6 are in the range suitable for their use as substrate for microwave applications. YBa2Cu3O7-δ superconductors did not show any detectable chemical reaction with Ba2RENbO6 even under extreme processing conditions. Dip-coated YBa2Cu3O7-δ thick films on polycrystalline Ba2RENbO6 substrate gave a T c (0) of 92 K and a current density of ~ 1.2 × 104 A cm-2.
POSITRON ANNIHILATION IN OXYGEN-DEFICIENT YBa2Cu3O7-δ CUPRATE AT 77 K AND 300 K
Authors: ZHANG JINCANG , CHEN ZHENPING , LI PINGLIN , CAO SHIXUN
Published: July 2002

The YBa2Cu3O7-δ cuprate with oxygen-deficiency (δ=0.06~0.68) has been systematically studied by positron lifetime experiment at 77 K and 300 K. It is found that there exists an evident dependence of positron lifetime parameters on oxygen-deficiency δ and an abrupt change near the orthorhombic–tetragonal phase transition. The local electron density n e and vacancy concentration C v are evaluated as a function of oxygen deficiency δ. The effect of the mechanism of charge transfer on local electronic structure is given in detail. The results show the existence of a weak localization of electrons in the tetragonal phase. The positron annihilation mechanism and its relation to superconductivity are also discussed.
POLYHEDRAL NANO-CLUSTERS WITH THE POTENTIAL FOR SELF-REPLICATION
Authors: BURSILL LESLIE A. , BOURGEOIS LAURE N.
Published: July 2002

It is proposed that certain non-crystallographic polyhedral clusters, which are not able to grow, possess the potential to bifurcate, regroup and self-replicate. Conditions under which this self-replicating growth mechanism may become favoured energetically over normal crystal growth are stated. The basic idea is illustrated by some polyhedral structural models related to those designed for the solution of the structure of the clay mineral allophane, an alumino-silicate analog of the spheroidal fullerenes.
THERMAL FLUCTUATION INFLUENCE ON THE RESISTIVE NOISE IN High-Tc GRANULAR SUPERCONDUCTORS
Authors: POPESCU V. , CRISTEA M. , STEPANESCU A.
Published: July 2002

Using a recently developed percolative model, we have simulated the contribution of the thermal noise to the total electrical resistance fluctuation in YBCO granular superconductors under a dc magnetic field. The theoretical model is in good agreement with the experimental results.
SEL DEPOSITION OF CADMIUM CHALCOGENIDES AND OPTIMIZATION FOR PHOTOVOLTAIC USE
Authors: KHAN M. USMAN , NASEEM SHAHZAD , MUNAWWAR M. IQBAL , NAZAR E. M.
Published: July 2002

The stacked elemental layer (SEL) technique has been used to deposit thin films of CdTe, CdSe and CdSeTe. The deposited films are then annealed in air at various temperatures in the range 50–150°C for 60 minutes. The resultant films are then studied for their optoelectrical and structural properties in order to find the optimum conditions for their use in the field of photovoltaics. It is found that resulting films possess low values of resistivity and the optical band gap lies in the range suitable for photovoltaic use. Structural analysis indicates that films of CdSe and CdSeTe are a mixture of cubic and hexagonal phases whereas CdTe tends to crystallize in hexagonal structure.
TWO TYPES OF CORRELATED BINOMIAL-NEGATIVE BINOMIAL STATES AND THEIR NONCLASSICAL PROPERTIES
Authors: FAN HONG-YI , LIU NAI-LE , LI HENG
Published: July 2002

Based on the single-mode binomial states and the negative binomial states, we construct two types of two-mode correlated states of the quantized radiation field. Their nonclassical properties are investigated. It is also shown that these states can be viewed as correlated su(2) and su(1,1) coherent states.
UNDERSTANDING ARITHMETIC PROBLEMS IN TURKISH
Authors: SAY A. C. CEM
Published: July 2002

This paper describes ALİ, the first computer program which can solve primary school-level arithmetic problems stated in Turkish. This task involves several subtasks: morphological analysis of every word in the input, syntactic analysis of each sentence, semantic analysis of words, providing a description of the commonsense world that is large enough to enable the correct answering of the problems, and generating the answer in human-readable form.
FAILURE OF A MEAN-FIELD APPROACH FOR THE MILLER–HUSE PHASE TRANSITION
Authors: SASTRE FRANCISCO , PÉREZ GABRIEL
Published: July 2002

The diffusively coupled lattice of odd-symmetric chaotic maps introduced by Miller and Huse undergoes a continuous ordering phase transition, belonging to a universality class close but not identical to that of the two-dimensional Ising model. Here we consider a natural mean-field approach for this model, and find that it does not have a well-defined phase transition. We show how this is due to the coexistence of two attractors in its mean-field description, for the region of interest in the coupling. The behavior of the model in this limit then becomes dependent on initial conditions, as can be seen in direct simulations.
DEFECT DYNAMICS DURING A QUENCH IN A BÉNARD–MARANGONI CONVECTION SYSTEM
Authors: GONZÁLEZ-VIÑAS W. , CASADO S. , BURGUETE J. , MANCINI H. , BOCCALETTI S.
Published: July 2002

We report experimental evidence of defect formation and dynamics in a symmetry breaking transition for a conduction–convection Bénard–Marangoni system. As opposite to the behavior of perfect patterns, defects appear to interact in a spatial region, responsible for the formation of bounded states that survive much longer than the characteristic time scales. The analysis of the transient defect dynamics allows to define this defect interaction region in the space, giving rise to penta–hepta-like defects on top of the hexagonal pattern. Other defect configurations are shown to disappear rapidly either through dislocations moving toward the boundaries or through dislocation–dislocation annihilation. This evidence suggests that the scaling law of defects in the final structure versus quench time might be investigated by analyzing the probability of two or more dislocations to appear in the same interaction region.
DYNAMICS OF VORTICES IN TWO-DIMENSIONAL BOSE–EINSTEIN CONDENSATES
Authors: CHANG SHU-MING , LIN WEN-WEI , LIN TAI-CHIA
Published: July 2002

We derive the asymptotic motion equations of vortices for the time-dependent Gross–Pitaevskii equation with a harmonic trap potential. The asymptotic motion equations form a system of ordinary differential equations which can be regarded as a perturbation of the standard Kirchhoff problem. From the numerical simulation on the asymptotic motion equations, we observe that the bounded and collisionless trajectories of three vortices form chaotic, quasi 2- or quasi 3-periodic orbits. Furthermore, a new phenomenon of 1:1-topological synchronization is observed in the chaotic trajectories of two vortices.
Ω-GLOBALLY ATTRACTIVE EQUILIBRIUM POINTS OF THE CNN
Authors: MIN LEQUAN , CROUNSE KENNETH R. , CHUA LEON O.
Published: July 2002

The dynamic behavior of the standard Cellular Neural Network (CNN) was studied via explicit solutions of the CNN vector state equations for certain piecewise linear domains Ω. The concepts of Ω-globally attractive domain, Ω-globally attractive equilibrium point, and Ω-globally expelling domain for the CNN state equations are presented. The terminology "Ω-global" indicates that the property is global relative to a domain Ω. It is shown that every "saturated domain" D (i.e. for every vector X∈ D, each corresponding component of X has the same sign as all others and its absolute value is greater than or equal to 1), is either Ω-globally attractive or Ω-globally expelling. Attractive equilibrium points in another special domain were also studied. Sufficient conditions for convergence to such equilibria are given, along with concrete new computer simulation examples which demonstrate this theory. Finally, several definitions and simulation results are given to explicate the complex dynamical relationships which were observed between initial states in the linear domain Ω (0) (i.e. every vector X∈Ω(0) has the property that the absolute value of each component is less that 1) and Ω-globally attractive equilibrium points in the saturated domain.
A MODEL OF PACKET TRAFFIC USING A RANDOM WALL MODEL
Authors: MONDRAGÓN C. RAÚL J.
Published: July 2002

We consider the problem of modeling self-similar bursty packet traffic using chaotic maps. In particular, we introduce a family of maps to overcome the difficulties of describing the self-similar statistics of the packet traffic as a function of the maps' parameters. The packet traffic that can be modeled with these maps varies from Poisson to bursty traffic with different decay tails in the ON and OFF regions. In contrast with Fractional Brownian Models, these maps have a multifractal spectrum so they can generate packet traffic with the same mean, variance and self-similar parameter but different higher order statistics.
INEVITABLE GRAPHS AND PROFINITE TOPOLOGIES: SOME SOLUTIONS TO ALGORITHMIC PROBLEMS IN MONOID AND AUTOMATA THEORY, STEMMING FROM GROUP THEORY
Authors: STEINBERG BENJAMIN
Published: July 2002

This paper deals with several algorithmic problems in monoid and automata theory arising from group theory. For H a pseudovariety of groups, we give a characterization of the regular elements of the H-kernel of a finite monoid. In particular, we show that if the extension problem for partial one-to-one maps for H is decidable, then so is the set of regular elements of the H-kernel. The extension problem for partial one-to-one maps for H asks if there is an algorithm to determine, given a finite set X and a set S of partial one-to-one maps on X, whether there is a finite set Y containing X so that each of the maps of S can be extended to permutations of Y in such a manner that the group generated by these permutations is in H. This problem is decidable for the pseudovariety of p-groups and nilpotent groups. We explore some other examples here.

We also show that if the above problem is decidable, then so is the membership problem for JⓜH. Some applications to the membership problem for J*H are given.

Finally, we show that certain pseudovarieties of groups, including the pseudovarieties of p-groups for p prime, are hyperdecidable. The techniques used here lay the groundwork for several future results on problems of this nature.
THE TYPE SET OF A VARIETY IS NOT COMPUTABLE
Authors: McKENZIE RALPH , WOOD JAPHETH
Published: July 2002

Several problems involving the local structure of finite algebras are shown to be unsolvable by interpreting the halting problem of Turing machines. Specifically, these problems are to decide, given a finite algebra A, whether the type-set of the variety generated by A, which is a subset of {1,2,3,4,5}, omits 2, or 3, or 4, or 5, respectively.
ON p-SUMMETRIC HEEGAARD SPLITTINGS
Authors: MULAZZANI MICHELE
Published: July 2002

We show that every p-fold strictly-cyclic branched covering of a b-bridge link in S3 admits a p-symmetric Heegaard splitting – in the sense of Birman and Hilden – of genus g = (b - 1)(p - 1). This gives a complete converse of one of the results of the two authors. Moreover, we introduce the concept of weakly p-symmetric Heegaard splittings and prove similar results in this more general context.
A CHARACTERIZATION OF KNOTS IN A SPATIAL GRAPH
Authors: ONDA KAZUKO
Published: July 2002

For a finite graph G, let Γ(G) be the set of all cycles of G. Suppose that for each γ∈Γ(G), an embedding ϕγ:γ→S3 is given. A set {ϕγ|γ∈Γ(G)} of embeddings is said to be realizable if there is an embedding f:G→S3 such that the restriction map f|γ is ambient isotopic to ϕγ for any γ∈Γ(G). In this paper on seven specified graphs G, we give a necessary and sufficient condition for the set {ϕγ|γ∈Γ(G)} to be realizable by using the second coefficients of Conway polynomials of knots.
APPLICATIONS OF THE LANTERN IDENTITY
Authors: GAROUFALIDIS STAVROS
Published: July 2002

The purpose of this note is to unify the role of the lantern identity in the proof of several finiteness theorems. In particular, we show that for every nonnegative integer m, the vector space (over the rationals) of type m (resp. T-type m) invariants of integral homology 3-spheres are finite dimensional. These results have already been obtained by [Oh] and [GL2] respectively; our derivation however is simpler, conceptual and relates to several other applications of the lantern identity.
IMPOSSIBILITY OF OBTAINING SPLIT LINKS FROM SPLIT LINKS VIA TWISTINGS
Authors: OZAWA MAKOTO
Published: July 2002

We show that if a split link is obtained from a split link L in S3 by 1/n-Dehn surgery along a trivial knot C, then the link L∪C is splittable. That is to say, it is impossible to obtain a split link from a split link via a non-trivial twisting. As its corollary, we completely determine when a trivial link is obtained from a trivial link via a twisting.
TOWARDS AN UNDERSTANDING OF ULTRA-HIGH-ENERGY COSMIC RAYS
Authors: POLLOCK M. D.
Published: July 2002

Previously, we have argued that the cosmic magnetic field B c is attributable to the indeterminacy principle, applied to metric fluctuations [Formula: see text] at the time t e ≈4.4×1010h-4 s of equipartition of energy (the last time of dynamical coupling) between matter and radiation in the Universe, stemming from the intrinsic uncertainty in the initial conditions (the phase of the wave function) at the Planck time t P ≈ 5.4×10-44 s, which leads to a present-day magnetic field B c (t0)≈ 10-9 G coherent on the length scale ℓ(t0)≈ 50 Mpc. Here, we discuss this result à propos the ultra-high-energy cosmic rays of energy E ≳ 1020 eV, suggesting that they may be due to nearby radio galaxies within ~ 10 Mpc, the primary components being heavy nuclei of charge Z≳ 10 deflected through large angles.
SOME UNPOLARIZED GOWDY COSMOLOGIES AND NONCOLINEAR COLLIDING PLANE WAVE SPACETIMES
Authors: GRIFFITHS J. B. , ALEKSEEV G. A.
Published: July 2002

A method for obtaining a class of complex solutions of the Ernst equation is described which is based on a set of linear equations. This method is applied to generate families of unpolarized vacuum and electrovac G2 cosmologies and nondiagonal solutions describing colliding plane gravitational and gravito-electromagnetic waves.
BLACK HOLE ENERGETICS AND THE PRODUCTION OF GAMMA RAY BURSTS
Authors: GIBILISCO MARINA
Published: July 2002

In this paper I study the energetics of massive, charged black holes, pointing out the importance of the discharge process in increasing the energy loss of these objects. The decrement of the energy of a black hole is due to three contributions, namely the Hawking evaporation, the kinetic energy loss (for rotating black holes) and the pair production following the discharge process (for charged black holes). Here I evaluate the energy balance for Kerr, Kerr–Newman and Reissner–Nordström black holes, showing that, even if the discharge process is very fast, it can increase in a significant way the energy loss: that enables the emission of gamma ray bursts whose characteristics are similar to those of the experimentally observed bursts. Following this idea, one can explain in a quite satisfactory way both the peculiar bimodality observed in the gamma ray burst duration and their isotropic but inhomogeneous distribution.
A NONSINGULAR UNIVERSE IN STRING COSMOLOGY
Authors: AL-NOWAISER A. A. , ÖZER MURAT , TAHA M. O.
Published: July 2002

We consider the low-energy effective string action in four dimensions including the leading order-α′ terms. An exact homogeneous solution is obtained. It represents a nonsingular expanding cosmological model in which the tensor fields tend to vanish as t→∞. The scale factor a(t) of the very early universe in this model has the time dependence [Formula: see text]. The violation of the strong energy condition of classical General Relativity to avoid the initial singularity requires that the central charge deficit of the theory be larger than a certain value. The significance of this solution is discussed.
INFLATION FROM AN EFFECTIVE STANDARD MODEL OF PARTICLE PHYSICS FOR CURVED SPACETIME
Authors: MATOS TONATIUH , ARREAGA GUILLERMO , PICCINELLI GABRIELLA
Published: July 2002

Beginning from an effective theory in eight dimensions, in Ref. 1, Macias, Camacho and Matos proposed an effective model for the electroweak part of the Standard Model of particles in curved spacetime. Using this model, we investigate the cosmological consequences of the electroweak interaction in the early universe. We use the approximation that, near the Planck epoch, the Yang–Mills fields behave like a perfect fluid. Then we recover the field equations of inflationary cosmology, with the Higgs field directly related to the inflaton. We present some qualitative discussion about this and analyze the behavior of isospin space using some known exact solutions.
HAWKING RADIATION IN THE DILATON GRAVITY WITH A NONMINIMALLY COUPLED SCALAR FIELD
Authors: ALVES M.
Published: July 2002

We discuss the two-dimensional dilaton gravity with a scalar field as the source matter where the coupling with gravity is given, besides the minimal one, trough an external field. This coupling generalizes the conformal anomaly in the same way as those found in recent literature, but with a different motivation. The modification to the Hawking radiation is calculated explicitly and show an additional term that introduces a dependence on the (effective) mass of the black-hole.
INDUCED COLOR CURRENT BY GLUON IN BACKGROUND QCD
Authors: WANG Q. , KAO C.-W. , NAYAK G. C. , GREINER W.
Published: July 2002

By using the background field method of QCD in a path integral approach, we derive the equation of motion for the classical chromofield and that for the gluon in a system containing the gluon and the classical chromofield simultaneously. This inhomogeneous field equation contains an induced current term, which is the expectation value of a combination of composite operators including linear, square and cubic terms of the gluon field. We also derive identities for the current from gauge invariance and calculate the current at the leading order where the current induced by the gluon is opposite in sign to that induced by the quark. This is just the feature of the non-Abelian gauge field theory which has asymptotic freedom. Physically, the induced current can be treated as a "displacement" current in the polarized vacuum, and its effect is equivalent to redefining the field and the coupling constant.
VARIABILITY, INHOMOGENEITY AND HETEROGENEITY: TOWARDS A TERMINOLOGICAL CONSENSUS IN ECOLOGY
Authors: SEURONT LAURENT , LAGADEUC YVAN
Published: July 2002

Current widespread use of ecological terms such as variability, heterogeneity and homogeneity is misleading and prevents ecologists from reaching a terminological consensus on what is meant when discussing these concepts, in particular with regard to the descriptor 'heterogeneous.' We propose the use of 'inhomogeneity' to define patterns or processes exhibiting a scale-dependent structure, whether spatial or temporal. Thus, the concept of 'inhomogeneity' can be regarded as a structural ecological entity. A descriptor exhibiting different kinds of inhomogeneity, either spatially or temporally, will then be qualified as being heterogeneous. The terminological consensus introduced here in the particular frame of ecological sciences is finally discussed and generalized to the actual scientific thought process.
METASTABLE (23S) HELIUM ATOM SCATTERING FROM MOLECULAR ADSORBATES ON Pd AND Cu SURFACES
Authors: FOUQUET P. , WITTE G.
Published: July 2002

The de-excitation of metastable (23 S1) He* atoms upon scattering from clean, NO- and CO-covered Cu(100) and Pd(111) surfaces has been investigated, and the He* survival probability was measured as a function of the NO and CO coverage. The corresponding adlayer structures were characterized in situ by ground state He atom scattering (HAS). The present results support an earlier interpretation of metastable de-excitation spectroscopy (MDS) data indicating a suppression of the resonance ionization (RI) de-excitation channel in the case of CO adsorption due to a screening of the metal surface by the adsorbate layer. In contrast, for NO on Pd(111) no increase of the He* survival probability was observed.
STRUCTURAL EFFECTS INDUCED BY CO ADSORPTION ON Pt–BIMETALLIC SURFACES
Authors: LUCAS C. A. , MARKOVIC N. M. , ROSS P. N.
Published: July 2002

Synchrotron surface X-ray scattering (SXS) studies have been performed during the coadsorption of metal adatoms and carbon monoxide on single crystal Pt surfaces in an electrochemical environment. As the applied electrode potential is the driving force behind adsorption, the electrochemical system is in chemical equilibrium, which results in a range of structural phenomena, such as mixing, segregation, compression and displacement. The mechanisms behind these effects are studied by monitoring the diffraction signals from ordered adsorbed metal and CO adlayers that occur on the Pt(111) and Pt(100) surfaces.
PHOTOELECTRON DIFFRACTION STUDY OF THE (3×3)-Sn/Ge(111) STRUCTURE
Authors: FLOREANO L. , PETACCIA L. , BENES M. , CVETKO D. , GOLDONI A. , GOTTER R. , GRILL L. , MORGANTE A. , VERDINI A. , MODESTI S.
Published: July 2002

The photoemission spectra of the Sn 4d electrons from the (3×3)-Sn/Ge(111) surface present two components which are attributed to inequivalent Sn atoms in T4 bonding sites. This structure has been explored by photoelectron diffraction experiments performed at the ALOISA beamline of the Elettra storage ring in Trieste (Italy). The modulation of the intensities of the two Sn components, caused by the backscattering of the underneath Ge atoms, has been measured as a function of the emission angle at fixed kinetic energies and vice versa. The bond angle between Sn and its nearest neighbor atoms in the first Ge layer ( Sn–Ge 1) has been measured by taking polar scans along the main symmetry directions and it was found almost equivalent for the two components. The corresponding bond lengths are also quite similar, as obtained by studying the dependence on the photoelectron kinetic energy with the photon polarization and the collection direction parallel to the Sn–Ge 1 bond orientation (bond emission). A clear difference between the two bonding sites is observed when studying the energy dependence at normal emission, where the sensitivity to the Sn height above the Ge atom in the second layer is enhanced. The (3×3)-Sn/Ge(111) is thus characterized by a structure where the Sn atom and its three nearest neighbor Ge atoms form a rather rigid unit that presents a strong vertical distortion with respect to the underneath atom of the second Ge layer.
The Proposed Merger of GK Goh and Vickers Ballas
Authors: Chu Singfat , Lim Guan Hua
Published: July 2002

The opposition of some shareholders to the proposed merger of stockbrokers GK Goh and Vickers Ballas in Singapore highlights a number of interesting issues pertaining to the valuation of companies in mergers and acquisitions. In particular, what are rationalisations for market capitalisation versus book value? The case also discusses the appropriateness of schemes of arrangement as a means to effect a merger and the judiciousness of appointing independent financial advisors to advise minority shareholders.
"BEHAVIORAL ECONOMETRIC" INTERPRETATION OF DYNAMIC SUPPLY AND DEMAND FUNCTIONS IN A MARKET PRICING MODEL
Authors: WANG JOSEPH K.
Published: July 2002

I present a model of stock market price fluctuations incorporating effects of share supply as a history-dependent function of previous purchases and share demand as a function of price deviation from moving averages. I discuss interpretation of model parameters and of the form of dynamically evolving supply and demand functions. Parameters and dynamic supply and demand functions can be regarded as providing quantitative behavioral characterization of investors within markets. Price charts generated assuming different dynamic supply functions exhibit structure consistent with the hypothesis that dominant investor behavior is different on different time scales.
GREEN'S FUNCTIONS APPROACH TO MOS PHYSICS-BASED COMPACT NOISE MODELLING
Authors: BONANI F. , GUERRIERI S. DONATI , GHIONE G.
Published: July 2002

A Green's function approach, akin to the classical Impedance Field Method, is exploited to derive a compact noise model for long-gate MOSFETs. The model includes diffusion noise as microscopic noise source, accounting for high field mobility and diffusivity effects in the microscopic noise source and in the Green's function evaluation. The analytical model with nominal parameters compares very well with results obtained from an accurate 2D numerical drift-diffusion model, both for the noise density distributions and the device terminal noise spectra.
STATISTICAL FAILURE MODEL OF BONES
Authors: PITHIOUX M. , CHABRAND P. , MAZEROLLE F.
Published: July 2002

In clinical research, knowledge of the mechanical behavior of bones is helpful for diagnostics and therapeutic processes and the failure of compact bones is a necessary study in clinical analysis, accidentology, and traumatology. The purpose of this paper is to analyse the failure properties of compact bones using a statistical model to interpret stress and strain measurements obtained by INSTRON and X-ray scanner devices. Samples were prepared from a lamellar structure of compact bovine bones and the density of each sample is controlled and taken to be constant (1.9 g/cm3). The experimental results data thus depend only on defects in the samples. This model may help physicians and surgeons predict bone failure when inserting a prosthesis, for example.
THE GROWTH OF ALIGNED CARBON NANOTUBES ON FeNiCo CATALYST FILMS
Authors: HO G. W. , WEE A. T. S. , LIN J. , LIU R.
Published: July 2002

Aligned multi-wall nanotubes (MWNT) have been grown using hot filament plasma enhanced chemical vapor deposition (HF-PECVD) on a variety of substrates. The growth kinetics of carbon nanotubes is found to be governed by the morphology of the metal film, the precursor gas composition as well as the temperature of the hot filament. It is observed that nanosized grain particles formed on FeNiCo films are optimum for carbon nanotube growth, since it is known that the substrate morphology has a direct influence on the growth of carbon nanotubes. The aligned MWNT and graphite films are also studied using secondary ion mass spectroscopy (SIMS) and ultraviolet photoelectron spectroscopy (UPS). Our results suggest that bi-directional growth, namely the root and tip growth, takes place during the synthesis of the carbon nanotubes using HF-PECVD.
Real-time knowledge-based control systems
Authors: Schoppers Marcel
Published: July 2002

This special section is the outgrowth of a workshop on real-time knowledge-based control systems, held during the 1990 national conference of the American Association for Artificial Intelligence (AAAI). The workshop was motivated by the recognition that constructing robotic systems capable of autonomous, flexible,
intelligent
behavior is an inherently interdisciplinary task. In particular, professionals from the fields of artificial intelligence (AI), control theory, process control and real-time scheduling were invited. To facilitate communication among these fields, the workshop organizers decided to focus on software design principles for real-time systems, and so sought out those who had built working systems and could express their experiences in terms of techniques they had tested and/or refuted.
An efficient method for the numerical evaluation of partial derivatives of arbitrary order
Authors: Neidinger Richard D.
Published: July 2002

For any typical multivariable expression
f
, point
a
in the domain of
f
, and positive integer maxorder, this method produces the numerical values of all partial derivatives at
a
up through order maxorder. By the technique known as automatic differentiation, theoretically exact results are obtained using numerical (as opposed to symbolic) manipulation. The key ideas are a hyperpyramid data structure and a generalized Leibniz's rule. Any expression in
n
variables corresponds to a hyperpyramid array, in
n
-dimensional space, containing the numerical values of all unique partial derivatives (not wasting space on different permutations of derivatives). The arrays for simple expressions are combined by hyperpyramid operators to form the arrays for more complicated expressions. These operators are facilitated by a generalized Leibniz's rule which, given a product of multivariable functions, produces any partial derivative by forming the minimum number of products (between two lower partials) together with a product of binomial coefficients. The algorithms are described in abstract pseudo-code. A section on implementation shows how these ideas can be converted into practical and efficient programs in a typical computing environment. For any specific problem, only the expression itself would require recoding.
The generalized Schur decomposition of an arbitrary pencil A–λB—robust software with error bounds and applications. Part II
Authors: Demmel James , Kågström Bo
Published: July 2002

Robust software with error bounds for computing the generalized Schur decomposition of an arbitrary matrix pencil A – λB (regular or singular) is presented. The decomposition is a generalization of the Schur canonical form of A – λI to matrix pencils and reveals the Kronecker structure of a singular pencil. The second part of this two-part paper describes the computed generalized Schur decomposition in more detail and the software, and presents applications and an example of its use. Background theory and algorithms for the decomposition and its error bounds are presented in Part I of this paper.
Error detection methods
Authors: Gallian Joseph A.
Published: July 2002

The use of check digits with identification numbers for error detection is now standard practice. Notable exceptions such as social security numbers, telephone numbers and serial numbers on currency predate computers. Despite their ubiquity and utility, few people are knowledgeable about the myriad of check digit schemes in use by businesses. In this article we survey many of these schemes. Among them are three that have not been described in journal articles previously.
Algorithm 782
Authors: Bischof C. H. , Quintana-Ortí G.
Published: July 2002

This article describes a suite of codes as well as associated testing and timing drivers for computing rank-revealing QR (RRQR) factorizations of dense matrices. The main contribution is an efficient block algorithm for approximating an RRQR factorization, employing a windowed version of the commonly used Golub pivoting strategy and improved versions of the RRQR algorithms for triangular matrices orginally suggersted by Chandrasekaran and Ipsen and by Pan and Tang, respectively, We highlight usage and features of these codes.
Structured hypertext with domain semantics
Authors: Wang Weigang , Rada Roy
Published: July 2002

One important facet of current hypertext research involves using knowledge-based techniques to develop and maintain document structures. A semantic net is one such technique. However, most semantic-net-based hypertext systems leave the linking consistency of the net to individual users. Users without guidance may accidentally introduce structural and relational inconsistencies in the semantic nets. The relational inconsistency hinders the creation of domain information models. The structural inconsistency leads to unstable documents, especially when a document is composed by computation with traversal algorithms. This work tackles to above problems by integrating logical structure and domain semantics into a semantic net. A semantic-net-based structured-hypertext model has been formalized. The model preserves structural and relational consistency after changes to the semantic net. The hypertext system (RICH) based on this model has been implemented and tested. The RICH system can define and enforce a set of rules to maintain to integrity of the semantic net and provide particular support for creating multihierarchies with the reuse of existing contents and structures. Users have found such flexible but enforceable semantics to be helpful.