bluuebunny/crossref_metadata_2025 huggingface dataset:
SIZES OF ORDERED DECISION TREES
Authors: ZANTEMA HANS , BODLAENDER HANS L.
Published: July 2002

Decision tables provide a natural framework for knowledge acquisition and representation in the area of knowledge based information systems. Decision trees provide a standard method for inductive inference in the area of machine learning. In this paper we show how decision tables can be considered as ordered decision trees: decision trees satisfying an ordering restriction on the nodes. Every decision tree can be represented by an equivalent ordered decision tree, but we show that doing so may exponentially blow up sizes, even if the choice of the order is left free.

Our main result states that finding an ordered decision tree of minimal size that represents the same function as a given ordered decision tree is an NP-hard problem; in earlier work we obtained a similar result for unordered decision trees.
RENORMALIZATION GROUP, HIDDEN SYMMETRIES AND APPROXIMATE WARD IDENTITIES IN THE XYZ MODEL
Authors: BENFATTO G. , MASTROPIETRO V.
Published: July 2002

Using renormalization group methods, we study the Heisenberg–Ising XYZ chain in an external magnetic field directed as the z axis, in the case of small coupling J3 in the z direction. In particular, we focus our attention on the asymptotic behaviour of the spin correlation function in the direction of the magnetic field and the singularities of its Fourier transform.

An expansion for the ground state energy and the effective potential is derived, which is convergent if the running coupling constants are small enough. Moreover, by using hidden symmetries of the model, we show that this condition is indeed verified, if J3 is small enough, and we derive an expansion for the spin correlation function. We also prove, by means of an approximate Ward identity, that a critical index, related with the asymptotic behaviour of the correlation function, is exactly vanishing, together with other properties, so obtaining a rather detailed description of the XYZ correlation function.
THE HALDANE GAP IN ANTIFERROMAGNETIC HEISENBERG CHAINS
Authors: AFFLECK IAN
Published: July 2002

Integer-spin Heisenberg antiferromagnetic chains are expected to have a singlet groundstate and a gap to the first excited state, as first argued by Haldane. We review rigorous results on this conjecture and discuss experimental realizations. Theoretical and experimental aspects of three recent developments in this field are then reviewed: chainend excitations and the non-local order parameter, a field theory mapping and behavior near zero wave-vector, high-field behavior and one-dimensional Bose condensation.
CONVERGENCE OF EXPONENTIAL PRODUCT FORMULAS FOR UNBOUNDED OPERATORS
Authors: SUZUKI MASUO
Published: July 2002

Some theorems on product formulas are presented for unbounded operators. These give the strong convergence of unitary product formulas and exponential contraction operators under some restricted conditions. Uniform convergence is also studied. Some new types of fourth-order exponential product formulas are also presented. These yield a simple review on the convergence of nonuniform exponential product formulas.
KAWACHI'S INVARIANT FOR NORMAL SURFACE SINGULARITIES
Authors: MAŞEK VLADIMIR
Published: July 2002

We study a useful numerical invariant of normal surface singularities, introduced recently by T. Kawachi. Using this invariant, we give a quick proof of the (well-known) fact that all log-canonical surface singularities are either elliptic Gorenstein or rational (without assuming a priori that they are ℚ-Gorenstein).

In Sec. 2 we prove effective results (stated in terms of Kawachi's invariant) regarding global generation of adjoint linear systems on normal surfaces with boundary. Such results can be used in proving effective estimates for global generation on singular threefolds. The theorem of Ein–Lazarsfeld and Kawamata, which says that the minimal center of log-canonical singularities is always normal, explains why the results proved here are relevant in that situation.
SYMBOLIC COMPUTATION FOR THE FISHER-TYPE EQUATION WITH VARIABLE COEFFICIENTS
Authors: GAO YI-TIAN , TIAN BO
Published: July 2002

For the variable-coefficient Fisher-type equation, which models such spatial spread as of an advantageous gene in a population or of early farming, we, in this paper, make use of computerized symbolic computation and report a new auto-Bäcklund transformation and a couple of new families of soliton-like solutions. Sample solitary waves are presented as the special cases.
STRUCTURAL AND ELECTRONIC PROPERTIES OF CARBON NANOBALLS: C20, C60, AND C20@C60
Authors: ERKOÇ ŞAKIR , TÜRKER LEMI
Published: July 2002

The structural stability of carbon nanoballs (fullerenes) C 20, C 60, and onion type C 20@ C 60 has been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that C 20 is relatively resistive to heat treatment, however, the onion type structure is relatively less strong against heat treatment. The electronic structure of the systems considered has been also studied by performing density functional theory type calculations.
A VARYING-e BRANE WORLD COSMOLOGY
Authors: YOUM DONAM
Published: July 2002

We study a varying electric charge brane world cosmology in the RS2 model obtained from a varying-speed-of-light brane world cosmology by redefining the system of units. We elaborate conditions under which the flatness problem and the cosmological constant problem can be resolved by such cosmological model.
THE CONDITION 0 < Z < 1 AND AN INTRINSIC MASS SCALE IN QUANTUM FIELD THEORY
Authors: JOGLEKAR SATISH D.
Published: July 2002

In this work, we suggest a viewpoint that leads to an intrinsic mass scale in quantum field theories. This viewpoint is fairly independent of dynamical details of a QFT and does not rely on any particular framework to go beyond the Standard Model. We use the setting of the nonlocal quantum field theories (NLQFT) with a finite scale parameter Λ, which are unitary for finite Λ. We propose that the condition 0 < Z < 1 (wherever proven) can be rigorously implemented/imposed in such theories and that it implies the existence of a mass scale Λ that can be determined from this condition. We derive the nonlocal analog of the above relation (which is a finite relation in NLQFT) and demonstrate that it can be arrived at only from general principles. We further propose that the nonlocal formulation should be looked as an effective field theory that incorporates the effect of dynamics beyond an energy scale and which breaks at the intrinsic scale Λ so obtained. Beyond this scale it should be replaced by another (perhaps, a more fundamental) theory. We provide a heuristic justification for this viewpoint.
Yukawa Textures in Horava-Witten M-Theory
Authors: Arnowitt R. , Dutta B.
Published: July 2002

We examine the structure of the Yukawa couplings in the 11 dimensional Horava-Witten M-theory based on non-standard embeddings. We find that the CKM and quark mass hierarchies can be explained in M Theory without introducing undue fine tuning. A phenomenological example is presented satisfying all CKM and quark mass data requiring the 5-branes cluster near the second orbifold plane, and that the instanton charges of the physical orbifold plane vanish. the latter condition is explicitly realized on a Calabi-Yau manifold with del Pezzo base dP7.
THE EFFECT OF RELIC PARTICLE ANNIHILATIONS ON THE COSMIC MICROWAVE BACKGROUND
Authors: SCHERRER ROBERT J.
Published: July 2002

A relic particle X which annihilates with its antiparticle [Formula: see text] into electromagnetically-interacting particles, e.g. [Formula: see text], γγ, etc., will lead to a distortion in the spectrum of the cosmic microwave background (CMB). The magnitude of this effect is calculated and compared with known limits on the deviations of the CMB from a Planck spectrum. Limits which can be placed on such a particle are found to be competitive with similar limits from Big Bang nucleosynthesis.
DUFFIN–KEMMER–PETIAU THEORY IN THE CAUSAL APPROACH
Authors: LUNARDI J. T. , PIMENTEL B. M. , VALVERDE J. S. , MANZONI L. A.
Published: July 2002

In this paper we consider the scalar sector of Duffin–Kemmer–Petiau theory in the framework of Epstein–Glaser causal method. We calculate the lowest order distributions for Compton scattering, vacuum polarization, self-energy and vertex corrections. By requiring gauge invariance of the theory we recover, in a natural way, the scalar propagator of the usual effective theory.
KONDO EFFECT AND SPIN-CHARGE SEPARATION IN QUANTUM DOTS
Authors: GLAZMAN L. I. , HEKKING F. W. J. , LARKIN A. I.
Published: July 2002

The Kondo effect in a quantum dot is discussed. In the standard Coulomb blockade setting, tunneling between the dot and the leads is weak, the number of electrons in the dot is well-defined and discrete; the Kondo effect may be considered in the framework of the conventional one-level Anderson impurity model. It turns out however, that the Kondo temperature TK in the case of weak tunneling is extremely low. In the opposite case of almost reflectionless single-mode junctions connecting the dot to the leads, the average charge of the dot is not discrete. Surprisingly, its spin may remain quantized: s=1/2 or s=0, depending (periodically) on the gate voltage. Such a "spin-charge separation" occurs because, unlike an Anderson impurity, a quantum dot carries a broad-band, dense spectrum of discrete levels. In the doublet state, the Kondo effect develops with a significantly enhanced TK. Like in the weak-tunneling regime, the enhanced TK exhibits strong mesoscopic fluctuations. The statistics of the fluctuations is universal, and related to the Porter-Thomas statistics of the wave function fluctuations.
EVOLUTION OF FERMIONIC SYSTEMS AS AN EXPECTATION OVER POISSON PROCESSES
Authors: BECCARIA M. , PRESILLA C. , DE ANGELIS G. F. , JONA-LASINIO G.
Published: July 2002

We derive an exact probabilistic representation for the evolution of a Hubbard model with site- and spin-dependent hopping coefficients and site-dependent interactions in terms of an associated stochastic dynamics of a collection of Poisson processes.
MONTE CARLO SIMULATION STUDY OF THE GROWTH OF A POLYCRYSTALLINE MATERIAL IN THE SUBMONOLAYER REGIME
Authors: MEYER MARCOS , ALBANO EZEQUIEL
Published: July 2002

A model for the polycrystalline growth of materials on an amorphous substrate, in the submonolayer regime, is introduced and studied by means of Monte Carlo simulations. Starting from an initial density of nucleation centers (ρ0), all crystals grow up incorporating particles at perimeter sites. Due to the formation of intercrystalline gaps, the saturation coverage decreases monotonically when ρ0 is increased. The time evolution of growing sites and the crystal size distribution are analyzed and discussed in detail. Scaling approaches for those quantities are derived and tested with the Monte Carlo data.
GAUGE SIMPLIFICATION OF HAMILTONIAN WITH OFF-DIAGONAL ± 1
Authors: SCHWALM MIZUHO , SCHWALM WILLIAM
Published: July 2002

Tight-binding Hamiltonians with off-diagonal disorder are studied extensively in connection with localization phenomena. For instance, applying a random magnetic field to a square lattice amounts to assigning phases to the off-diagonal entries of H. A gauge transformation simplifies the resulting H to an equivalent Hamiltonian with apparently less disorder. This paper concerns the special case when non-zero entries of a Hamiltonian H are ± 1 between nearest-neighbor sites. Some thought shows that a one-dimensional chain Hamiltonian with this type of randomness can be transformed to that of an ordered chain by flipping the signs of selected basis functions, i.e. by a unitary transformation. Hence such a chain is not disordered at all. On the other hand, whether or not a similar H for a square lattice implies actual disorder is a topological question. The question can be put this way: Can one find a set of simple closed curves such that reversing the signs of basis functions inside the curves will change all non-zero H entries to +1? More generally one can ask about the extent of residual disorder and its effect on electronic properties of the model. We take up these questions on a periodic square lattice.
ON THE NUMBER OF METASTABLE STATES IN A STRIPE GLASS
Authors: SCHMALIAN JÖRG , WESTFAHL HARRY , WOLYNES PETER G.
Published: July 2002

We estimate the number of metastable states of a self generated stripe glass, relevant for the formation of glassy doped Mott insulators. Using replica bound states, we demonstrate that the configurational entropy is the difference between the entropy of the stripe liquid and of an amorphous stripe solid with phonon-type excitations. Using simple scaling laws we then determine the relationship between the modulation length and the configurational entropy.
MÖSSBAUER QUADRUPOLE SPLITTING of Fe2+ in NH4CoCl3 UNDER ORBIT–LATTICE INTERACTION
Authors: SINHA T. P.
Published: July 2002

The effect of orbit–lattice interaction (vibronic coupling) has been considered to explain the observed temperature dependence of Mössbauer quadrupole splitting of Fe2+ ions in NH4CoCl3 over 27 to 250 K. The orbit–lattice interaction accounts for the thermal modulation of the electronic charge distribution of Fe2+ due to vibration of the surrounding ligands. The various lattice dynamical parameters are estimated and then quadrupole splitting is explicitly calculated as a function of temperature. One obtains a reasonably good agreement with the experimental data which shows that the vibronic coupling is quite realistic and important.
DISORDER-INDUCED RELAXATION OF FRENKEL EXCITONS IN MOLECULAR AGGREGATES
Authors: BEDNARZ M. , LEMAISTRE J. P.
Published: July 2002

A model, based on the intraband scattering of excitons in one-dimensional J-aggregates is proposed to describe the lengthening of the experimentally observed radiative lifetime with temperature. According to this mechanism, the exciton-phonon scattering transfers the oscillator strength fromt he lowest k≅0 optically allowed state to the other states within the excitonic band. A Pauli master equation, in which the hopping rates are calculated, is used to describe the thermalization of the excitonic band. Assuming a fast relaxation mechanism, the temperature dependence of the exciton radiative lifetime is simulated for various chain lengths.
ORDER FORMATION AND ELEMENTARY EXCITATIONS IN TYPE-II QUANTUM-WELL EXCITON SYSTEM
Authors: Iida T. , Tsubota M.
Published: July 2002

The ordered state and the elementary excitations are theoretically studied in an interacting dilute quasi-two-dimensional Bose gas of excitons in a type-II quantum well. This system is advantageous for studying the macroscopic quantum phenomena because those excitons have a long lifetime of the order of 10-6 s, and their transport mechanism can be directly studied in experiments by observing electric current since the excitons consist of spatially separated electron-hole pairs. Using the obtained dispersion relations for excitations, we examine the Landau criterion for exciton superflow and the temperature dependence of the off-diagonal long-range order which characterizes the quasi-Bose-Einstein condensation in two-dimensional systems.
COMPARISON OF THERMAL CONDUCTIVITIES ON ABRADED AND UNTREATED CVD-DIAMOND OBTAINED BY SCANNING THERMAL MICROSCOPY
Authors: ALTES A. , HEIDERHOFF R. , BALK L. J. , JENTSCH H. G. , ROSIWAL S. M.
Published: July 2002

Diamond materials have become progressively significant in the fabrication of heat sinks for power devices and lasers. To investigate the influence of polishing on CVD-Diamond, the surfaces of <100> and <110> coatings were analyzed, after a first abrasive treatment on a 30μm diamond grit by scanning thermal microscopy based on a resistive platinum-probe. This technique describes in first order approximation the heat transfer of a metal-diamond interface. Through this method it was possible to diagnose a relevant reduction in thermal conductivity by a harsh sample preparation depending on the crystal orientation. The thermal conductivity of as deposited <100> diamond was measured at 1290 W/mK and was reduced to 250 W/mK. The thermal conductivity of as deposited <110> diamond was determined at 1780 W/mK whereas the same diamond surface, but abraded, shows a thermal conductivity of just 460 W/mK. Additionally the received images which represents the thermal conductivity qualitatively bring forward micro structures like e.g. grain boundaries.
THEORY OF QUANTUM LIQUIDS: WHERE WE ARE AND WHERE WE ARE GOING
Authors: KROTSCHECK E.
Published: July 2002

The present status of the microscopic understanding of quantum liquids is reviewed. We take a conservative approach and focus thoroughly on two examples: the neutral quantum liquids 4 He and 3 He . The first part of this contribution reviews the present state of the microscopic theory of these systems. Results of both simulation methods and semi-analytic theories are discussed and compared. Quantum liquids in non-uniform geometries lead, due to symmetry breaking, to a number of new and interesting effects and also to new experimental possibilities and theoretical challenges. Finally, we highlight a number of yet open problems where present microscopic approaches have so far been unsuccessful.
STATIC AND DYNAMICAL PROPERTIES OF A SINGLE IMPURITY IN A STRONGLY CORRELATED HOST
Authors: NANDGAONKAR AJAY , DURGANANDINI P. , ARJUNWADKAR MIHIR , KANHERE D. G.
Published: July 2002

We study, using numerical exact diagonalisation, some static and dynamical properties of a single impurity substituted into a one-dimensional repulsive Hubbard chain. A systematic scan of the parameter-space reveals a rich magnetic phase diagram. Interactions on the lattice stabilize the local moment phase of the impurity. A scalar impurity is seen to induce local moments on the neighbouring sites near Half Filling. Static spin and charge correlation functions reflect a non-Fermi liquid character of the ground state in the presence of a scalar impurity.
MAPPING OF A BOSE SYSTEM ONTO ONE WITH A CUTOFF: SCALING FUNCTION FOR PRESSURE AND DENSITY
Authors: MUTHU S. K. , BHALLA G. L. , BHARDWAJ ATUL , SINGH K. K.
Published: July 2002

Mapping of a Bose system of interacting particles onto an effective Bose system having an upper cutoff momentum is derived by integrating out momenta between infinity and p0 where p0 is small compared to the inverse de Broglie wavelength λ-1 of the particles. The mapping, within the ∊-expansion scheme, is a general result independent of any argument specific to the critical region. The cross-over behaviour of pressure and density is worked out in the normal phase as well as in the condensed phase. The results are manifestly independent of the cutoff p0 as expected on physical grounds.
Experimental and Theoretical Study of the Field Induced Phase Separation in Electro- and Magnetorheological Suspensions
Authors: Cutillas S. , Bossis G. , Lemaire E. , Meunier A. , Cebers A.
Published: July 2002

We present here the study of field induced phase separation in E.R. and M.R. fluids. Two thermodynamic models — one for the formation of chais of particles and the other for phase separation are presented and compared with experimental results obtained with two kinds of suspensions. One was made of silica particles in silicone oil and the other was made of magnetic polystyrene particles in water. In the presence of a flow the phase separation occurs with the dense phase forming a regular pattern of stripes. The dependence of the period of these stripes on the intensity of the magnetic field is well reproduced by the same kind of thermodynamic model if we add the effect of normal stresses induced by the shear flow.
Electrorheology of Suspension of Sulfonated Styrene-Co-Divinylbenzene Particles — Approach Based on the Dielectric Properties of the Suspension —
Authors: Ikazaki F. , Kawai A. , Kawakami T. , Konishi M. , Asako Y.
Published: July 2002

Effects of particle concentration, water content and temperature on the electrorheology of suspensions of highly sulfonated styrene-co-divinylbenzene (SSD) particles in a silicone oil were investigated. The induced shear stress was measured with a modified rotary rheometer. The electrorheology of the suspension was largely affected by the particle concentration, the water content and the measurement temperature. The induced shear stress for the particle concentration of 40 wt% was about twice as large as that of 20 wt%. The induced shear stress for the water content of 4 wt% was about twice as large as that of 2 wt%. The induced shear stress for the temperature of 80°C was about 15 times as large as that of 20°C.

Dielectric properties were measured to elucidate the mechanism of electrorheology. In order for an ER fluid to have large ER effect, relaxation frequency of the ER fluid should be between 100 and 105 Hz and the difference of the dielectric constant below and above the relaxation frequency (Δ∊′) must be large, which we refer to as the dielectric property mechanism. The relation between measured ER effect and dielectric property mechanism was discussed.
Design and Performance of an Electro-Rheological Grease (ERG) Shock Absorber
Authors: Marksmeier Thomas M. , Gordaninejad Faramarz , Wang Eric L. , Stipanovic Arthur
Published: July 2002

The use of an electro-rheological fluid (ERF) in some applications may require a high damping capacity. This paper presents the design and evaluation of a prototype damper using an electro-rheological grease (ERG) with high zero electric field viscosity. In designing the ERG damper several issues such as: a) maintaining a constant internal damper volume, b) minimizing the fluid shear in flow paths (other than in the electrode gap region) which reduces adverse effects on damper performance and, c) allowing the adjustment of the electrode gaps, are considered. Comparisons are made between the performance of the ERG and an existing ERF. The ERG demonstrates higher damping capacities at low frequencies than those of the ERF.
NON-DEMOLITIVE PHOTON NUMBER MEASUREMENT VIA χ(2) NONLINEARITY
Authors: CASTELLETTO STEFANIA , DEGIOVANNI IVO PIETRO , RASTELLO MARIA LUISA
Published: July 2002

The aim of this paper is to present a possible experiment for measuring photon number by a non-demolitive scheme. We show that, in principle, it is possible to deduce the number of photons of an intense pump coherent field by measuring the phase-shift on two frequency conjugated beams due to the interaction with the pump in a nonlinear crystal, which exhibits χ(2) nonlinearity. We perform a theoretical evaluation of the relative uncertainty associated to the photon number measurement, obtaining high accuracy results when high pump power levels, low coupling between pump and crystal and squeezing generators are used. The accuracy obtained are compared with results obtainable with a beam splitter setup.
PSEUDOGAP AND SUPERCONDUCTIVITY UNDER HIGH MAGNETIC FIELD IN UNDERDOPED HIGH-Tc CUPRATE
Authors: ZHENG G.-Q. , KITAOKA Y. , ASAYAMA K. , KODAMA Y. , CLARK W. G. , KUHNS P. , MOULTON W. G.
Published: July 2002

The responses to the magnetic field (H) of the superconductivity and the pseudogap in the underdoped high- T c cuprate YBa 2 Cu 4 O 8(Tc=74 K) are reported up to 23.2 T based on NMR measurements. Even though H=23.2 T reduces Tc by 19 K, no effect is seen on the normal-state pseudogap, which continues in the temperature region where the superconductivity is destroyed by the field. This suggests that the pseudogap is a consequence of strong electron correlation effects. For temperatures T≤15 K, the H- and T-variation of the 63 Cu nuclear spin-lattice relaxation rate (1/T1) is 1/T1∝TH and also the Knight shift increases with increasing H. We interpret our results as evidence for H-induced quasiparticle states that extend from the d-wave vortex centers with an ungapped spectrum.
CHAOS IN DILUTED NETWORKS WITH CONTINUOUS NEURONS
Authors: CAROPPO D. , MANNARELLI M. , NARDULLI G. , STRAMAGLIA S.
Published: July 2002

The properties of macroscopic chaos displayed by diluted neural networks with continuous neurons and nonmonotonic transfer function is analyzed, with both fixed and dynamic synapses. The responce to external noisy stimuli is also considered: a proper amount of external perturbation removes the chaotic behaviour.
WETTING–DEWETTING TRANSITION AND CONFORMAL TO NON-CONFORMAL INTERFACIAL ROUGHNESS TRANSITION IN ULTRA-THIN LIQUID CRYSTAL FILMS ON SOLID SUBSTRATES
Authors: SURESH K. A. , SHI YUSHAN , BHATTACHARYYA A. , KUMAR SATYENDRA
Published: July 2002

High-resolution X-ray reflectivity has been employed to study the structure, wetting properties, and interfacial roughness of ultra-thin liquid crystal films. The films were prepared at the air–water interface and transferred on to glass substrates by a modified horizontal deposition technique. A 3-layer film was found to partially-wet the substrate in the nematic and isotropic phases and dewet upon cooling to the crystalline phase. The surface roughnesses at the air-film and the film-glass interfaces exhibited a gradual reversible but hysteretic conformal (strongly correlated) to non-conformal transition between the isotropic and smectic-A phases.
ULTRASONIC ATTENUATION IN d-WAVE SUPERCONDUCTORS
Authors: GUPTA TRIBIKRAM , GAITONDE D. M.
Published: July 2002

We consider a BCS-like model of interacting electrons on a square lattice. Within mean field theory, our model has an instability towards the formation of a d-wave superconducting state. We calculate the longitudinal ultrasonic attenuation rate in the superconducting phase in the clean limit for parameters appropriate to the cuprates. We find that the temperature dependence of the attenuation rate is similar to that observed in conventional superconductors for phonon wavevectors along the direction of the anti-nodes of the gap. However, the attenuation rate for phonon wavevectors along the nodal direction is found to be strikingly different in its temperature and doping dependence. The attenuation rate α S (T) increases in magnitude and shows a sign change in its curvature (when plotted as a function of temperature) with increasing value of dopant concentration.
LOW TEMPERATURE CHARACTERISTIC OF GaAlAs TEMPERATURE SENSOR DIODE
Authors: OTA SNEHADRI BIHARI , BASCUÑÁN JUAN , OTA SMITA
Published: July 2002

We have measured the forward characteristics of a GaAlAs temperature sensor diode (Lake Shore) in the temperature range 10–70 K and for fixed current values between 10 nA to 500 μA. On the basis of certain extrapolations, we suggest that these diodes can be used for temperature measurement at at ultra low temperatures.
PREPARATION AND CHARACTERIZATION OF Cu/ZnO NANOCOMPOSITES
Authors: VÁZQUEZ-CUCHILLO O. , PAL U. , VÁZQUEZ-LOPEZ C.
Published: July 2002

The Cu/ZnO composite films of different Cu contents were prepared on quartz substrates by r.f. co-sputtering technique. The as-grown films were annealed at different temperatures in argon atmosphere to study the effect of annealing on the growth of particles. TEM images revaled the formation of nanometric particles in the matrix. For the films prepared with lower Cu contents, the size of the particles did not increase significantly on annealing them up to 400°C. Whereas, for the films grown with higher Cu contents, the cluster size increased with the increase of amlealing temperature. Optical absorption spectra of the films revealed a peak at about 560 nm correspond to the plasmon resonance absorption in small Cu particles. XRD and TED patterns revealed that the copper in the composites remain in partially oxidized state.
INFLUENCE OF OXYGEN IMPURITIES ON ION BEAM INDUCED INTERDIFFUSION IN THIN Au-Al MULTILAYERS DEPOSITED ON DIFFERENT SUBSTRATES
Authors: MARKWITZ ANDREAS , DEMORTIER GUY
Published: July 2002

Au-Al interdiffusion processes in thin layers deposited on various substrates were investigated with RBS during high current ion irradiation. The atomic movements were identified simultaneously (in-situ RBS) with a depth resolution of a few nanometers. It was observed that heating of the specimens due to ion irradiation was the most evident mechanism inducing atom transport. After only 8 min of irradiation with 300 nA 2.0 MeV 4 He + ions (beam spot diameter 0.5 mm), two Au-Al layers (total thickness 600 nm) deposited on glassy carbon or gold were found to be fully interdiffused. In contrast to that, no significant interdiffusion was measured for the same systems deposited on wafer silicon and polished aluminium substrates. To understand this behaviour, depth distributions of oxygen impurities were measured using enhanced elastic backscattering spectroscopy (σ ≈ 102 σ R with 7.6 MeV 4 He ions.
EPR INVESTIGATION OF La0.7Ca0.3MnO3: EVIDENCE OF SPIN-GLASS FORMATION
Authors: RAO G. NARSINGA , BABU Y. , SASTRY M. D. , BABU D. SURESH , CHEN J. W.
Published: July 2002

EPR investigations on La 0.7 Ca 0.3 MnO 3 were carried out in the temperature range from 14 K to 300 K. The important observations are: (i) a coincidence of resistivity maxima with the disappearance of paramagnetic EPR line I, which suggests that there exists a strong electron–phonon interaction, (ii) the appearance of an "out of phase" line near the Curie temperature T c due to the formation of spin clusters consisting of Mn3+ and Mn4+ ions, and (iii) the appearance of an intense EPR line III and the splitting of FC and ZFC magnetization curves below 160 K, ascribed to local magnetic frustrations. The above EPR observations provide experimental evidence for the co existence of spin fluctuations and magnetic disorders in this sample, which leads to the formation of spin-glass features below T c .
INDUCED EMISSION OF COLD ATOMS PASSING THROUGH A MICROMASER CAVITY: SPATIAL DEPENDENCE
Authors: ABDEL-ATY MAHMOUD , OBADA ABDEL-SHAFY F.
Published: July 2002

The emission probability of a cold atom in a microcavity when its center-of-mass motion is described quantum mechanically is presented, but is distinguished from other treatments by the inclusion of the spatial variation along the cavity axis. In particular, the mesa mode cavity profile is considered. The quantum theory of the one-photon mazer is constructed in the framework of the dressed-state coordinate formalism. Simple expressions for the atomic populations, the cavity photon statistics, and the reflection and transmission probabilities are given for any initial state of the atom-field system. The general conclusions reached are illustrated by numerical results.
Dynamical Behavior of a Thermostated Quartic Oscillator
Authors: Andrecut M.
Published: July 2002

We present a numerical study of a quartic oscillator coupled to a Nosé-Hoover thermostat. The time-centered algorithm was used for integrating the equations of motion. The numerical simulations have shown that in this system, the ergodic behavior can be achieved only by extending the Nosé-Hoover dynamics to the Bulgac–Kusnetov dynamics.
DYNAMICS OF LOCAL SURFACE FLUCTUATIONS IN GROWTH MODELS WITH POWER-LAW NOISE
Authors: LÓPEZ JUAN M.
Published: July 2002

We study one-dimensional surface growth models with power-law noise. We focus on the time behavior of the models to show that the surfaces behave anomalously in the sense that the local surface fluctuations scale with time as tβ* for t > lz, where the time exponent β* is in excellent agreement with a recent theory for anomalous roughening. According to the anomalous roughening picture, we also find that the local fluctuations of the height in the stationary regime scale with a local roughness exponent w(l) ~ lα loc that is different from the global exponent α, which is obtained from the scaling of the saturated width as W(L)~ Lα. Our results suggest that, despite initial hopes, these types of model are not a plausible explanation for the values of the exponents observed in experiments of two-phase flow in disordered media.
EQUIVALENCE OF THE TWO METHODS IN CALCULATING THE EQUILIBRIUM SHAPES OF CYLINDRICAL VESICLES
Authors: ZHANG SHAOGUANG , OUYANG ZHONGCAN , LIU JIXING
Published: July 2002

So far, two methods are often used in solving the equilibrium shapes of vesicles. One method is by starting with the general shape equation and restricting it to the shapes with particular symmetry. The other method is by assuming the symmetry and topology of the vesicle first and treating it with the calculus of variation to get a set of ordinary differential equations. The relationship between these two methods in the case of cylindrical vesicles, and a comparison of the results are given.
MAGNETIC IMPURITY IN A SYSTEM OF INTERACTING ELECTRONS
Authors: DUC HUYNH THANH , THANG NGUYEN TOAN
Published: July 2002

The Kondo effect of the Anderson impurity in a correlated conduction electron system is studied with the slave boson mean-field theory. The interacting conduction electrons are described by a Hubbard model with an interaction of strength U. It is shown that the Kondo temperature T K decreases with an increase of U. In the intermediate regime at half-filling, the exponential scale of the Kondo temperature T K is already lost at the saddle-point level of slave boson formulation.
REAL CONTINUATION FROM THE COMPLEX QUADRATIC FAMILY: FIXED-POINT BIFURCATION SETS
Authors: PECKHAM BRUCE B. , MONTALDI JAMES
Published: July 2002

This paper is primarily a numerical study of the fixed-point bifurcation loci — saddle-node, period-doubling and Hopf bifurcations — present in the family: [Formula: see text] where z is a complex dynamic (phase) variable, [Formula: see text] its complex conjugate, and C and A are complex parameters. We treat the parameter C as a primary parameter and A as a secondary parameter, asking how the bifurcation loci projected to the C plane change as the auxiliary parameter A is varied. For A=0, the resulting two-real-parameter family is a familiar one-complex-parameter quadratic family, and the local fixed-point bifurcation locus is the main cardioid of the Mandlebrot set. For A ≠ 0, the resulting two-real-parameter families are not complex analytic, but are still analytic (quadratic) when viewed as a map of ℛ2. Saddle-node and period-doubling loci evolve from points on the main cardioid for A=0 into closed curves for A ≠ 0. As A is varied further from 0 in the complex plane, the three sets interact in a variety of interesting ways.

More generally, we discuss bifurcations of families of maps with some parameters designated as primary and the rest as auxiliary. The auxiliary parameter space is then divided into equivalence classes with respect to a specified set of bifurcation loci. This equivalence is defined by the existence of a diffeomorphism of corresponding primary parameter spaces which preserves the specified set of specified bifurcation loci. In our study there is a huge amount of complexity added by specifying the three fixed-point bifurcation loci together, rather than one at a time.

We also provide a preliminary classification of the types of codimension-one bifurcations one should expect in general studies of families of two-parameter families of maps of the plane. Comments on numerical continuation techniques are provided as well.
ON THE CONTROL OF CHAOTIC DYNAMICAL SYSTEMS USING NONLINEAR APPROXIMATIONS
Authors: HILL D. L.
Published: July 2002

The technique of using nonlinear approximations to increase the effectiveness of the OGY method of controlling chaotic dynamical systems is investigated and a way of further increasing the effectiveness of this general approach is presented.
OSCILLATIONAL RESPONSES AND BASIN STRUCTURE ON ONE-WELL QUINTIC POTENTIAL
Authors: HASEGAWA YOSHITAKA
Published: July 2002

The cubic escape equation system and the swing equation system have been widely researched because of their applicability to various physical systems and technological areas. They have confinement well structure and then have some bound solutions, which can be chaotic under periodic excitation, and a solution divergent to infinity. The inherent potential nature of these systems is described as the action variable versus the angular frequency characteristic of closed orbits of their originating Hamiltonian systems, which is important to explain the occurrence of subharmonic and harmonic resonances under the injection of external periodic driven force. This characteristic of the above systems is qualitatively same and their steady oscillational response and the basin structure, where often some attractors coexist, have some common features. The quintic potential system can also have one confinement well and the divergent solution so that it seems to exhibit similar responses under periodic excitation. However the action variable versus the angular frequency characteristic is remarkably different, which has one maximum point, while the first two systems have monotonically decreasing ones. This produces more complicated pattern of existence region of periodic points, and more various oscillational responses are observed. In this paper the author will report about the steady state oscillations and their basin structure in the quintic potential system driven by external periodic force with numerical simulations and geometrical methods of dynamical systems.
WAVELET ANALYSIS OF TIME-SERIES: COHERENT STRUCTURES, CHAOS AND NOISE
Authors: STASZEWSKI W. J. , WORDEN K.
Published: July 2002

The continuous and orthogonal wavelet transforms are used to analyze time-series data. The analysis involves signal decomposition into scale components using both Grossman–Morlet and Daubechies type wavelets. A number of simulated and experimental data vectors exhibiting different types of coherent structures, chaos and noise is analyzed. The study shows that wavelet analysis provides a unifying framework for the description of many phenomena in time-series.
COMPOSITION METHODS FOR THE SIMULATION OF ARRAYS OF CHUA'S CIRCUITS
Authors: MOREAU YVES , VANDEWALLE JOOS
Published: July 2002

Composition methods are methods for the integration of ordinary differential equations arising from differential geometry, or more precisely, Lie algebra theory. We apply them here to the simulation of arrays of Chua's circuits. In these methods, we split the vector field of the array of Chua's circuits into its linear part and its nonlinear part. We then solve the elementary differential equation for each part separately — which is easy since the equations for the nonlinear part are all decoupled — and recombine these contributions into a sequence of compositions. This splitting gives rise to simple integration rules for arrays of Chua's circuits, which we compare to more classical approaches: fixed time-step explicit Euler and adaptive fourth-order Runge–Kutta.
INTERNAL TIME PECULIARITIES AS A CAUSE OF BIFURCATIONS ARISING IN CLASSICAL TRAJECTORY PROBLEM AND QUANTUM CHAOS CREATION IN THREE-BODY SYSTEM
Authors: BOGDANOV A. V. , GEVORKYAN A. S. , GRIGORYAN A. G. , MATVEEV S. A.
Published: July 2002

A new formulation of the theory of quantum mechanical multichannel scattering for three body collinear systems is proposed. It is shown that for this simple case, the principle of quantum determinism in the general case breaks down, and we have a micro-irreversible quantum mechanics. The first principle calculations of the quantum chaos (wave chaos) were pursued on the example of an elementary chemical reaction Li+(FH)→(LiFH)*→(LiF)+ H.
ON HYPERDECIDABLE PSEUDOVARIETIES OF SIMPLE SEMIGROUPS
Authors: ALMEIDA JORGE
Published: July 2002

Recent results related to hyperdecidability and their applications to decidability of semidirect products are reviewed. Hyperdecidability is studied for pseudovarieties of completely simple semigroups as a means of illustrating the kind of techniques that may be used in this area.
BOUNDARY OF CAT(-1) COXETER GROUPS
Authors: BENAKLI N.
Published: July 2002

In this paper, we study the topological properties of the hyperbolic boundaries of CAT(-1) Coxeter groups of virtual cohomological dimension 2. We will show how these properties are related to combinatorial properties of the associated Coxeter graph. More precisely, we investigate the connectedness, the local connectedness and the existence problem of local cut points.

In the appendix, in a joint work with Z. Sela, we will construct the JSJ decomposition of the Coxeter groups for which the corresponding Coxeter graphs are complete bipartite graphs.
ANALYSIS OF A HETEROGENEOUS DOMAIN DECOMPOSITION FOR COMPRESSIBLE VISCOUS FLOW
Authors: COCLICI CRISTIAN A. , WENDLAND WOLFGANG L.
Published: July 2002

We analyze a nonoverlapping domain decomposition method for the treatment of two-dimensional compressible viscous flows around airfoils. Since at some distance to the given profile the inertial forces are strongly dominant, there the viscosity effects are neglected and the flow is assumed to be inviscid. Accordingly, we consider a decomposition of the original flow field into a bounded computational domain (near field) and a complementary outer region (far field). The compressible Navier–Stokes equations are used close to the profile and are coupled with the linearized Euler equations in the far field by appropriate transmission conditions, according to the physical properties and the mathematical type of the corresponding partial differential equations. We present some results of flow around the NACA0012 airfoil and develop an a posteriori analysis of the approximate solution, showing that conservation of mass, momentum and energy are asymptotically attained with the linear model in the far field.
INCOMPLETE INPUT INFERENCE ON FUZZY PRODUCTION SYSTEMS SUPPORTED BY PETRI NETS
Authors: WANG SHYUE-LIANG , HONG TZUNG-PEI
Published: July 2002

This paper proposes a new reasoning technique on fuzzy production systems while given input knowledge is incomplete. Based on the fuzzy Petri net formalism, the proposed algorithm can infer all possible conclusions and their corresponding missing inputs. The most possible conclusion can also be determined based on the criteria of the minimum number of missing inputs as well as the degree of truth of the conclusion. In addition, finiteness and computational complexity of the algorithm is investigated. As real decisions are typically made under incomplete input knowledge, this reasoning technique provides more realistic applications for fuzzy production systems.
HIGH-LEVEL FUZZY PETRI NETS AS A BASIS FOR MANAGING SYMBOLIC AND NUMERICAL INFORMATION
Authors: LIU KEVIN F.R. , LEE JONATHAN , CHIANG WEILING
Published: July 2002

The focus of this paper is on an attempt towards a unified formalism to manage both symbolic and numerical information based on high-level fuzzy Petri nets (HLFPN). Fuzzy functions, fuzzy reasoning, and fuzzy neural networks are integrated in HLFPN In HLFPN model, a fuzzy place carries information to describe the fuzzy variable and the fuzzy set of a fuzzy condition. An arc is labeled with a fuzzy weight to represent the strength of connection between places and transitions. A fuzzy set and a fuzzy truth-value are attached to an uncertain fuzzy token to model imprecision and uncertainty. We have identified six types of uncertain transition: calculation transitions to compute functions with uncertain fuzzy inputs; inference transitions to perform fuzzy reasoning; neuron transitions to execute computations in neural networks; duplication transitions to duplicate an uncertain fuzzy token to several tokens carrying the same fuzzy sets and fuzzy truth values; aggregation transitions to combine several uncertain fuzzy tokens with the same fuzzy variable; and aggregation-duplication transitions to amalgamate aggregation transitions and duplication transitions. To guide the computation inside the HLFPN, an algorithm is developed and an example is used to illustrate the proposed approach.
Braid lift representations of Artin's Braid Group
Authors: Häring-Oldenburg Reinhard
Published: July 2002

We recast the braid-lift representation of Contantinescu, Lüdde and Toppan in the language of B-type braid theory. Composing with finite dimensional representations of these braid groups we obtain various sequences of finite dimensional multi-parameter representations.
SATELLITE DOUBLE TORUS KNOTS
Authors: OZAWA MAKOTO
Published: July 2002

We characterize satellite double torus knots. Especially, if a satellite double torus knot is not a cable knot, then it has a torus knot companion. This answers Question 12 (a) raised by Hill and Murasugi in [4].
QUANDLE HOMOMORPHISMS OF KNOT QUANDLES TO ALEXANDER QUANDLES
Authors: INOUE AYUMU
Published: July 2002

A quandle is a set with a binary operation satisfying some properties. A quandle homomorphism is a map between quandles preserving the structure of their binary operations. A knot determines a quandle called a knot quandle. We show that the number of all quandle homomorphisms of a knot quandle of a knot to an Alexander quandle is completely determined by Alexander polynomials of the knot. Further we show that the set of all quandle homomorphisms of a knot quandle to an Alexander quandle has a module structure.
CROSSING AND BASE NUMBERS OF RIBBON 2-KNOTS
Authors: YASUDA TOMOYUKI
Published: July 2002

It has been a fundamental problem to study the crossing number and the bridge index for an 1-knot. By spinning an arbitrary 1-knot about R2 in R4, we have a ribbon 2-knot in R4; therefore, for a ribbon 2-knot, we can also naturally induce notions corresponding to the crossing number and the bridge index. In this note, we will define these notions, and for a property on these notions, we will study a great contrast between 1-knots and ribbon 2-knots and in addition we will enumerate all ribbon 2-knots with the crossing number under four.
BLACK HOLES OF A MINIMAL SIZE IN STRING GRAVITY
Authors: ALEXEYEV S. O. , SAZHIN M. V. , POMAZANOV M. V.
Published: July 2002

A lower limit for a neutral black hole size is obtained in the frames of the string gravity model with the second order curvature correction. It is shown that this effect remains when the third order curvature correction is also taken into account and argued that such restriction does exist in all perturbative orders of curvature expansions.
QUADRATIC REHEATING
Authors: CHIMENTO LUIS P. , JAKUBI ALEJANDRO S.
Published: July 2002

The reheating process for the inflationary scenario is investigated phenomenologically. The decay of the oscillating massive inflaton field into light bosons is modeled after an out of equilibrium mixture of interacting fluids within the framework of irreversible thermodynamics. Self-consistent, analytic results for the evolution of the main macroscopic magnitudes like temperature and particle number densities are obtained. The models for linear and quadratic decay rates are investigated in the quasiperfect regime. The linear model is shown to reheat very slowly while the quadratic one is shown to yield explosive particle and entropy production. The maximum reheating temperature is reached much faster and its magnitude is comparable with the inflaton mass.
INHOMOGENEOUS SCALAR FIELD SOLUTIONS AND INFLATION
Authors: PEREZ BERGLIAFFA S. E. , HIBBERD K. E.
Published: July 2002

We present new exact cosmological inhomogeneous solutions for gravity coupled to a scalar field in a general framework specified by the parameter λ. The equations of motion (and consequently the solutions) in this framework correspond to either low-energy string theory or Weyl integrable spacetime according to the sign of λ. We show that different inflationary behaviors are possible, as suggested by the study of the violation of the strong energy condition. Finally, by the analysis of certain curvature scalars we found that some of the solutions may be nonsingular.
THE EFFECT OF ANTISYMMETRIZATION IN DIQUARK MODELS OF BARYONS
Authors: MABUZA B. R. , ADAM R. M. , BAKKER B. L. G.
Published: July 2002

The effect of antisymmetrization in diquark models of baryons composed of light (u&d) quarks is investigated. The diquark in this study is considered alternately as a point-like and as a composite particle where antisymmetrization is taken into account by means of Generator Coordinate Model operator kernels. The effect on ground state masses and form factors is striking and we are able to conclude that there is a strong dynamical effect due to the presence of antisymmetrization in diquark models of baryons.