bluuebunny/crossref_metadata_2025 huggingface dataset:
NONADIABATIC THEORY OF THE SUPERCONDUCTING STATE
Authors: BOTTI MICHELA , CAPPELLUTI EMMANUELE , GRIMALDI CLAUDIO , PIETRONERO LUCIANO
Published: May 2003

Fermi energies in fullerence compounds and cuprates are extremely small as consequence of the small number of charge carriers and are comparable to the phonon frequency scale. In this situation the conventional Migdal-Eliashberg theory does not hold anymore and nonadiabatic effects need to be taken into account. In previous studies, a generalization of Eliashberg theory in the nonadiabatic regime has been proposed to calculate normal state properties and the onset temperature T c of the superconductive phase. Here we extend the nonadiabatic theory below T c where the opening of the superconducting order parameter affects the nonadiabatic correction. The superconducting gap Δ is calculated in a self-consistent way. We find that large values of the ratio 2Δ/T c are obtained in the nonadiabatic theory by smaller electron-phonon coupling λ than in Migdal-Eliashberg theory. This agrees with the picture that strong-coupling phenomenology can be achieved in nonadiabatic theory by "reasonable" values of λ. We apply our analysis to the case of the fullerene compounds.
s- AND d-WAVE SYMMETRIES IN NONADIABATIC THEORY OF SUPERCONDUCTIVITY
Authors: PACI PAOLA , GRIMALDI CLAUDIO , PIETRONERO LUCIANO , CAPPELLUTI EMMANUELE
Published: May 2003

High-T c superconductors have Fermi energies EF much smaller than conventional metals comparable to phonon frequencies. In such a situation nonadiabatic effects are important. A generalization of Eliashberg theory in the nonadiabatic regime has previously been shown to reproduce some anomalous features of the high-T c superconductors as for instance the enhancement of T c or the isotopic effects on T c and m*. In this contribution we address the issue of the symmetry of the gap in the context of nonadiabatic superconductivity. We show that vertex corrections have a momentum structure which favours d-wave superconductivity when forward scattering is predominant. An additional increase of T c is also found.
FLUCTUATION CONTRIBUTION TO THE SPECIFIC HEAT IN NON-FERMI MODELS FOR SUPERCONDUCTIVITY
Authors: Tifrea I. , Grosu I. , Crisan M.
Published: May 2003

We investigate the fluctuation contribution to the specific heat of a two-dimensional superconductor with a non-Fermi normal state described by a Anderson Green's function [Formula: see text]. The specific heat corrections contain a term proportional to [Formula: see text] and another logarithmic one. We define a coherence length as function of the non-Fermi paramter α, which shows that a crossover study between BCS and Bose-Einstein condensation is possible by varying the non-Fermi parameter α.
OPTICAL CONDUCTIVITY OF THE HOLSTEIN MODEL AT LOW DENSITY
Authors: FRATINI S. , DE PASQUALE F. , CIUCHI S.
Published: May 2003

We apply the dynamical mean field theory to calculate the low-density limit of the small polaron optical conductivity in the Holstein model. Classical schemes of approximation are recovered in weak coupling and in the adiabatic and anti-adiabatic strong coupling limits. Such schemes are not suitable for the intermediate coupling regime, where our theory gives an anomalous behaviour of the spectral weight at low energy as the temperature decreases.
FLUXON DYNAMICS AND RESONANCES IN STACKED ARRAYS OF JOSEPHSON JUNCTIONS
Authors: CAPUTO P. , CARAPELLA G. , COSTABILE G. , FILATRELLA G. , LATEMPA R. , MARTUCCIELLO N. , PAGANO S.
Published: May 2003

We consider a structure consisting of two parallel arrays of long Josephson junctions sharing a common electrode that allows inductive coupling between the arrays. Cavity modes excitations exhibiting 2D synchronization as well as solitonic excitations are inferred from the mathematical model of the system. The stable coherent solitonic solutions of the coupled sine-Gordon equations describing the system is found to consist of a fluxon-antifluxon string travelling in the structure.
NON-EQUILIBRIUM IN JOSEPHSON JUNCTIONS: POSSIBLE TRANSISTOR-LIKE APPLICATIONS
Authors: PEPE G. P. , PARLATO L. , AMMENDOLA G. , ESPOSITO E. , GRIECO G. , PELUSO G. , BARONE A. , BOOTH N.
Published: May 2003

Interest in superconducting transistors is due to some potential benefits of these devices, such as the possibility to have large current gain and bandwidth at low temperatures. In this work we present experimental results concerning with a new superconducting 3-terminal device showing true transistor-like properties at T=4.2K. It is a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb with an Al quasiparticle trap which can be either in the superconducting or in the normal metal state. Current amplification factors of up to 2.0 are observed at a temperature of 4.2 K when the Al is superconducting. When the Al is in the normal state, large current gains of more than 50 are observed. The operation is highly directional, i.e. practically no effect is observed when the roles of the injector and detector junctions are reversed. The results are explained according to the recently proposed QUAsiparticle TRApping TRANnsistor model.
JOSEPHSON JUNCTION NETWORK AS A TOOL TO SIMULATE INTERGRAIN SUPERCONDUCTING CHANNELS IN YBCO FILMS
Authors: ROTOLI G. , DE LEO C. , GHIGO G. , GOZZELINO L. , CAMERLINGO C.
Published: May 2003

Recent considerations on the physics of YBa 2 Cu 3 O 7-δ films made possible explaining their transport properties as flow of supercurrents through links between the granular structure of the film. The present work deals with the analysis of the Josephson junction network as a discrete set of parallel junctions (1D array) in quasi-static conditions and is aimed to compare the results of the simulations with the experimental findings, in particular with the plateau-like features in the critical current dependence on the magnetic field. Different regimes and vortex phases have been individuated and discussed.
TRANSPORT PROPERTIES OF JOSEPHSON JUNCTIONS AND SQUIDS EMPLOYING DIFFERENT TYPES OF YBCO GRAIN BOUNDARIES OBTAINED THROUGH THE BIEPITAXIAL TECHNIQUE
Authors: CARILLO F. , LOMBARDI F. , MILETTO GRANOZIO F. , PUNZO V. , RICCI F. , SCOTTI DI UCCIO U. , TAFURI F. , TESTA G. , SARNELLI E.
Published: May 2003

Concepts and experimental procedures to obtain different types of YBa 2 Cu 3 O 7 grain boundaries Josephson junction through the biepitaxial technique have been developed. Various seed layers (MgO, CeO 2 and SrTiO 3) and substrates (MgO, SrTiO 3) have been used providing, for the biepitaxial technique, additional flexibility in circuit design. A detailed investigation on transport properties evidenced good performances for both junctions and superconducting quantum interference devices. Experimental evidence is given of a conventional magnetic field behavior in 45° tilt Artificial Grain Boundary (AGB) for which no π-loops are predicted along the interface.
TEMPERATURE DEPENDENCE OF GAP RELATED STRUCTURES IN YBa2Cu3O7-δ BREAK JUNCTIONS
Authors: GIUBILEO F. , BOBBA F. , CUCOLO A. M. , AKIMENKO A. I.
Published: May 2003

We have applied the break junction technique to highly epitaxial c-axis oriented YBaCuO thin films with T c (ρ=0)=91 K deposited on (001) SrTiO 3 or LaAlO 3 substrates by a high oxygen pressure d.c. sputtering technique. The film thickness was about 1500 Å and a photolithographic process was used to reduce to 100 μm the junction width across the fracture. By this procedure, tunable resistance break junctions with tunneling current favored along the ab-planes have been realized. The junctions were formed at low temperatures with freshly fractured surfaces and an inert tunnel barrier was created by helium gas or liquid. A good stability was obtained with the normal-state resistance R N changing about 15% in the temperature range between 4.2 K and 100 K. We have measured the temperature dependence of the conductance maxima that are related to superconducting energy gap at the Fermi level.
HIGH POWER HANDLING SUPERCONDUCTING PLANAR FILTERS FOR TELECOMMUNICATION APPLICATIONS
Authors: CASSINESE A. , ANDREONE A. , ORGIANI P. , PALOMBA F. , PICA G. , VAGLIO R. , PANARIELLO G. , SCHETTINO F. , CIRILLO M. , RUSSO R.
Published: May 2003

Passive microwave filters based on HTS films are very promising for telecommunication applications. We report on the design, obtained using a commercial 2.5D software, and the realization of filters, fabricated with double sided YBCO films grown on LaAlO 3 substrates, for both receiving and transmission systems. For the receiving side, planar multi-pole interdigital L-band filters with 75 MHz transmission bandwidths have been fabricated on 2" substrates. Up to 80 K this kind of filter, based on a Tchebischev response, shows an insertion loss lower than 0.5 dB with a ripple of 0.3 dB for a maximum input power of 2 Watts. For the transmitting side, dual-mode filters represent one of the main interesting configuration to exploit since they can combine a high power handling capability with miniaturization requirements. A novel kind of dual-mode C-band filter based on cross slotted square resonators is presented. The novelty of the proposed structure is to use a pair of unequal crossed slots that are formed on a square patch resonator such that its structure size can be significantly reduced. A prototypal device operating at 3.7 GHz is fabricated with different type of couplings on 10 × 10 mm 2 LaAlO 3 substrate to showcase our proposal. The behavior of the filter as a function of the input power has been tested up to 2 Watts limited by the amplified power supply.
PHASE LOCKING AND AC AMPLIFICATION OF SMALL JOSEPHSON JUNCTIONS
Authors: CAPUTO P. , CARAPELLA G. , COSTABILE G. , FILATRELLA G. , LATEMPA R. , MARTUCCIELLO N. , PAGANO S.
Published: May 2003

We have addressed the problem of the phase-locking mechanism of a single Josephson junction irradiated with microwaves, and have numerically and theoretically explored the possibility to achieve ac gain in this system. By investigating the capability of Josephson junctions to enhance the signal received form an external rf source we obtain useful information of the possibility of mutual phase-locking of large arrays of junctions.
LTC JOSEPHSON DEVICE TECHNOLOGY FOR LOW NOISE APPLICATIONS
Authors: GRANATA C. , MONACO A. , RUSSO M.
Published: May 2003

Improved procedures to fabricate LTc superconducting devices based on high quality all refractive Nb/Nb junctions have been developed. Such reliable procedures have allowed the fabrication of Nb/AlOx/Nb structures and non-conventional light-sensitive junctions involving semiconducting tunneling barriers. Junctions and SQUID devices have been used in basic Physic investigations and in biomagnetic instrumentations.
SUPERCONDUCTING-RESISTIVE-TRANSITION DEVICE FOR THE PRECISION MEASUREMENT OF LOW AC VOLTAGE
Authors: MONTICONE E. , POGLIANO U. , LACQUANITI V. , MAGGI S. , STENI R. , POLCARI A.
Published: May 2003

Single and multijunctions thermal converters are devices widely utilized for AC measurements at room temperature. However, low sensitivity and high noise of these devices limits their applications at voltage level above 10 mV. A cryogenic thermal transfer sensor has been developed to realise AC measurements at 1 mV voltage level. This device consists of a superconducting-resistive-transition Nb thin film, which detects the AC power, dissipated on a Cr film resistor. To improve the sensitivity, the sensor has been fabricated on a 500 nm thick square silicon nitride membrane with size ranging from 1 × 1 mm 2 to 3.5 × 3.5 mm 2. The device has been tested at liquid helium and a thermal conductance lower than 10-6 W/K has been measured. From these data we expect an increasing of responsivity higher than three order of magnitude and a noise limited by intrinsic thermal noise.
A NEW METALLIC NON MAGNETIC SUBSTRATE FOR COATED TAPE SUPERCONDUCTORS
Authors: GIUNCHI G. , CERESARA S. , CORTI R. , PETRISOR T. , MANCINI A. , CELENTANO G.
Published: May 2003

The high Tc superconductors, realised in form of coated tapes, rely on the quality of the substrate on which they are growing. Furthermore the aim to produce a long superconducting tape, carrying the high engineering current densities typical of the power applications, push the search of a very robust and thin metallic tape as substrate. Looking for a trade off between the mechanical strength at high temperature and the chemical and structural compatibility of the substrate with the growing oxide superconductors, a new metallic alloy is proposed and a systems combining the metallic tape plus one micron thick textured oxide buffer layer is presented. The system fulfils also the demanding characteristics of a low manufacturing cost, being based on production technologies easily scalable at high volumes, like the melt flow casting of the metallic tape and the Electron Beam (EB) evaporation of the oxide film.

The main physical characteristic of the new substrate, with the deposited buffer layer, are presented.
MICROSTRUCTURAL CHARACTERISATION OF NON-MAGNETIC Ni-BASED BIAXIALLY TEXTURED SUBSTRATES FOR HTS COATED CONDUCTOR APPLICATIONS
Authors: VILLA E. , TUISSI A. , TOMOV R. , EVETTS J. E.
Published: May 2003

For the production of HTS coated conductor devices, NiV and NiCr (Ni-based alloys) are the most important, non-magnetic, high strength and biaxially textured substrates developed from pure Ni. The Ni 88 V 12 and Ni 85 Cr 15 (at. %) alloys have been melted in Plasma Arc Furnace and textured tapes have been prepared, after heavy cold rolling, by recrystallization heat treatment under high vacuum. The suitable working conditions have been found to obtain not only the {100} <001> cube texture but also the correct grain shape and size for the following deposition process. Out of plane orientation of these substrates has been investigated by θ-2θ X-ray diffraction measurements and in plane orientation study has been completed by pole figures. The microstructure has been observed by optical microscopy: it has been carried out on samples obtained after an annealing treatment (Grain Size Adjustment) and on recrystallized samples in different conditions. As preliminary mechanical investigation the microhardness values have been detected for each step of the working procedure.

The accuracy of the cubic texture and the grain structure are affected by the processing condition, in particular the temperature of the GSA seems a very important parameter which influences the final characteristics of the tapes.
DESIGN, CONSTRUCTION AND CHARACTERIZATION OF TRANSPORT CURRENT PROPERTIES OF AN HTS COIL
Authors: BIGONI L. , BARBERIS F. , BERTI R. , CEREDA E. , MARTINI L. , OTTOBONI V. , LA CASCIA P.
Published: May 2003

The objective of this work was the design, the realization and the characterization of a superconducting coil, capable of generating a peak magnetic field of 100 mT. The measured degradation due to magnetic field and mechanical strain of the electrical properties of Bi-2223/Ag tapes has been taken into account in optimizing the design. The resulting configuration consisted in a 10 double-pancakes coil realised with about 300 m of Bi-2223/Ag tape. The real degradation of each double pancake has been investigated by measuring the DC characteristic and the AC losses. The stacking configuration was finally defined by the measured differences among the critical current of each double pancake. To minimise the effect of the perpendicular magnetic field degradation on the electrical properties of the whole coil, the pancakes with higher I c were mounted at the top and at the bottom. The DC electrical properties as well as the AC losses of the elementary components and of the whole coil have been measured and the results are presented and discussed in this paper.
TESTS AND SIMULATION OF THERMAL-HYDRAULIC TRANSIENTS IN THE US PROTOTYPE JOINT SAMPLE
Authors: SAVOLDI L. , ZANINO R. , MICHAEL P.
Published: May 2003

A limited set of data measured on the US Prototype (USP) joint sample is used to assess the capability of the Mithrandir code to simulate heat-slug transients among the complex assembly of joint components. The Multi-conductor Mithrandir (M&M) code is then applied to simulate heat exchange in a joint of the Central Solenoid Model Coil (CSMC) inner module.
SIGN OF THE VIRIAL COEFFICIENTS AND GAS–LIQUID PHASE TRANSITION
Authors: BISWAS A. C.
Published: May 2003

We have shown that, for a stable interaction with an attractive part, if the virial coefficients are all negative at low temperature, there exists a unique density ρ0 beyond which the canonical partition functions become unstable. The physical implication of this is discussed with reference to gas–liquid phase transition.
MINIMUM UNCERTAINTY STATES FOR ANGULAR-MOMENTUM–PHASE UNCERTAINTY RELATION IN RADIUS–PHASE DESCRIPTION OF AN ELECTRON IN UNIFORM MAGNETIC FIELD
Authors: FAN HONG-YI
Published: May 2003

Based on the |λ> representation and the radius–phase description of an electron's orbit track in a uniform magnetic field, we introduce the phase operator and derive the minimum uncertainty states for the angular-momentum–phase uncertainty relation. The derivation makes full use of the newly constructed |l, r> representation which is the common eigenvector of the angular momentum Lz and the radius operator (K- - iΠ+)(K+ + iΠ-).
DEVIATION OF COHERENT STATE CAUSED BY DISSIPATION
Authors: JIN Y. H. , KOU S. P. , LIANG J. Q. , LI B. Z.
Published: May 2003

The time evolution of a coherent state was studied in the dissipative system, a harmonic oscillator coupling with a bath of harmonic oscillators with Ohmic spectral density. We define a deviation of uncertainty relation versus the squeezed coherent state as [Formula: see text]. It is found that for the case of η ≪ ω0, namely, the weak dissipation, Δ oscillates with a small amplitude. The system is in a squeezed coherent state essentially and the dissipation only leads to a small deviation. For both strong (η ≫ ω0) and critical (η ~ ω0) dissipations, Δ is divergent with respect to t and the coherence of state is destroyed.
ENHANCED ADHESION OF DIAMOND-LIKE CARBON COATINGS ON 316 STAINLESS STEEL
Authors: CHEN M. , GAO J.
Published: May 2003

Diamond-like carbon (DLC) has been a candidate prosthetic coating due to its excellent physical and chemical properties, and biocompatibility. However, the adhesion to a number of prosthetic materials is still an issue. Different techniques have been used to improve the adhesion of DLC on various substrates. In this paper, we report the fabrication of an adherent DLC coating on commercial 316 stainless steel by using pulsed laser deposition and a composition-graded intermediate layer. Intermediate layers with graded composition from stainless steel to DLC were obtained by designing an inlaid target. Raman spectrum analysis indicated that the grown DLC films are rich in sp3 bonds. The adhesion of the coatings as well as other properties of the intermediate layers are also discussed.
THERMAL STABILITY AND SPECIFIC MATERIAL PROPERTIES OF NANOSYSTEMS
Authors: RIETH M. , SCHOMMERS W. , BASKOUTAS S.
Published: May 2003

Various material properties, which are well defined and clearly fixed for macroscopic systems, get a modified significance in nanophysics and nanotechnology, respectively. We show, as an example, that the temperature behavior of nanosystems is considerably changed when we go from macroscopic systems to those of nanometer size. It is pointed out that the standard model of solid-state physics (ordered structure, harmonic approximation) is in general not sufficient for the description of nanosystems.
RED EMISSION FROM GaN NANOCRYSTALLINE SOLIDS
Authors: CAO Y. G. , CHEN X. L. , LAN Y. C. , LI J. Y. , ZHANG Y. , XU Y. P. , XU T. , LIANG J. K.
Published: May 2003

The photoluminescence of the transparent G a N nanocrystallite solids is studied. Three new intensive isolated narrow red emission bands and one broad blue band are observed. A mechanism to explain the origin of these bands is proposed. The three red bands may originate from the transitions of deep donor levels to shallow acceptors, while the blue band may be from the transitions of shallow donors to deep levels with ground and excited states.
CHARACTERISTICS OF LOCALIZED ACOUSTIC MODES IN A N -LAYER-BASED SUPERLATTICE WITH DEFECT LAYERS
Authors: CHEN KE-QIU , WANG XUE-HUA , GU BEN-YUAN
Published: May 2003

We present general expressions to calculate localized acoustic modes in a N -layer-based superlattice with defect layers by using a transfer-matrix method. Numerically, we investigate the properties of the localized modes in an AlAs–AlxGa1-xAs–GaAs superlattice with a defect layer AlyGa1-yAs. The influences of material and structural parameters on the localized modes are revealed with analyses. A comparison between the higher and lower branches of the localized modes is made. We show that the minigap and optimum localization are determined by the material and structural parameters of constituent layers in a unit cell as well as periodicity, while localized modes are dependent on both constituent and defect layers. Moreover, we find that the localized modes vary periodically with the width of the defect layer, and the number of branches of localized modes increases with the index of minigaps.
CORRELATION OF THE STATE OF INTERACTED ELECTRONS WITH CRYSTAL STRUCTURE AND CHEMICAL COMPOSITION
Authors: TOVSTYUK K. D. , TOVSTYUK N. K.
Published: May 2003

Correlation between the structure and chemical composition of materials has been considered. The full Green's function by theory group technique has been constructed. From the analytical expression for Green's function, structural conditions of the stationary state, mechanisms of relaxation and Hund's rule are determined.
INTERACTION OF MESOSCOPIC JOSEPHSON JUNCTION WITH A SUCCESSIVE SQUEEZED COHERENT FIELD
Authors: POPESCU V. A.
Published: May 2003

Signal-to-quantum noise ratio for quantum current in mesoscopic Josephson junction of a circular superconducting ring can be improved if the electromagnetic field is in a successive squeezed coherent state. The mesoscopic Josephson junctions can feel the difference between the successive squeezed coherent states and other types of squeezed coherent states because their current–voltage Shapiro steps are different. We compare our method with another procedure for superposition of two squeezed coherent states (a squeezed even coherent state) and consider the effect of different large inductances on the supercurrent.
HIGHER-ORDER SUCCESSIVE SQUEEZED NUMBER AND COHERENT STATES
Authors: POPESCU V. A.
Published: May 2003

The statistical properties of the higher-order squeezed thermal states [V. A. Popescu, Mod. Phys. Lett. B14, 203 (2000)] and of the higher-order squeezed number and coherent states (this paper) can be improved by successive application of the squeeze operator. We compare our method with the usual procedure for higher-order squeezing and with another way for superposition of two squeezed coherent states.
MAGNETIC SUSCEPTIBILITY OF THE NONRELATIVISTIC BOSON GAS
Authors: HOMORODEAN LAUREAN
Published: May 2003

The magnetic susceptibilities of the degenerate (below the Bose–Einstein condensation temperature) and nondegenerate ideal gases of nonrelativistic charged spinless bosons are presented. In both cases, the boson gas is diamagnetic. The magnetic susceptibility of the degenerate boson gas below the Bose–Einstein condensation temperature increases in modulus as the temperature increases. As expected, the magnetic susceptibility of the nondegenerate boson gas decreases in modulus with increasing temperature according to the Curie law in low magnetic fields.
TRANSPORT PHENOMENA IN La2-xBaxCuOy EPITAXIAL THIN FILMS
Authors: ILONCA G. , POP A. V. , JURCUT T. , LUNG C. , STIUFIUC G. , STIUFIUC R. , FURDUI O. , MOCOCEANU E. , DELTOUR R.
Published: May 2003

The (001) oriented thin films of La 2-x Ba xCuO4+d on SrAlO4 substrates with barium composition x = 0 to 2 were grown by DC sputtering and characterized by X-ray diffraction and resistivity measurement. The films with oxygen composition d=0 showed superconductivity for x between 0.055 and 0.30. For x = 0.15, the superconducting transition was maximized to 4.3 K. When the films had d>0, Tc reached 47 K. These values are higher than those for bulk samples. The depression of Tc around x =0.125 is smaller than that for the bulk samples. The compressive strain expands the c-axis and suppresses formation of the low-temperature tetragonal phase. Both effects result in an increase in the bond length between Cu and the apical oxygen, which is responsible for the enhancement of Tc. The samples with lower residual resistivity show a higher Tc, so we suppose that the Tc enhancement is caused by reduced antiferromagnetic spin fluctuation in the CuO2 planes due to the change in the Cu–O apical bond length.
SELF-SIMILAR EXTRAPOLATION OF ASYMPTOTIC SERIES AND FORECASTING FOR TIME SERIES
Authors: YUKALOV V. I.
Published: May 2003

The method of extrapolating asymptotic series, based on the self-similar approximation theory, is developed. Several important questions are answered, which makes the foundation of the method unambiguous and its application straightforward. It is shown how the extrapolation of asymptotic series can be reformulated as forecasting for time series. The probability measure is introduced characterizing the ensemble of forecasted scenarios. The method of choosing the complete family of databases is put forward.
NORMAL STATE TRANSPORT PROPERTIES OF (Bi0.8Pb0.2-yVy)2Sr2Ca2Cu3O10+δ SUPERCONDUCTING PELLETS
Authors: DHAMI A. K. , BASAK S. , GHATAK S. K. , DEY T. K.
Published: May 2003

The electrical resistivity and thermoelectric power of (B i 0.8P b 0.2-yVy)2S r 2C a 2C u 3O10+δ pellets with 0≤y≤0.05 is reported between Tc0 and 300 K. Thermoelectric power values of all samples were found to be positive and increase almost linearly with decrease of temperature down to ~120 K, before falling to zero at Tc0. With increasing vanadium content in (Bi,Pb)-2223 compounds, the magnitude of both the electrical resistivity and thermoelectric power increases. General features, however, remain the same. The results have been discussed on the framework of a "three-state model". Our analysis shows an excellent agreement between the measured electrical resistivity and thermoelectric power data and those calculated using the three-state model.
ON THE SUSCEPTIBILITY IN La2-xSrxCuO4
Authors: FUJITA SHIGEJI , OBATA TSUNEHIRO , OKAMURA YOSHINOBU
Published: May 2003

The magnetic susceptibility χ in La 2-x Sr x CuO 4 shows unusual concentration x- and temperature T-behaviors. The χ at 400 K increases with x in the range 0.04<x<0.25 and decreases in the range 0.25<x<0.33. The maximum at x=0.25 is interpreted in terms of the curvature invension of the O-Fermi surface. At the inflection point the density of states is extremely high, which causes χ to have a temperature behavior: χ=A0+B0/T. The Cooper pair (pairon) has no net spin, and hence its spin contribution to χ is zero. But its motion with the linear dispersion relation: ∊=(2/π)vFp, where vF=Fermi speed, can generate a T-dependent contribution -B1/T. These two contributions generate a χ-maximum at Tm in the range 0.15<x<0.25.
THEORETICAL STUDY ON THE ELECTRICAL PROPERTIES OF Eu, Tm AND Sm CHALCOGENIDE COMPOUNDS
Authors: ARIPONNAMMAL S. , NATARAJAN S.
Published: May 2003

A theoretical study on Eu, Tm and Sm Chalcogenide compounds has been made for determining the electrical transport properties using only two parameters, namely lattice constant and activation energy. The calculated electrical properties such as electrical resistivity, carrier mobility, carrier concentration, carrier effective mass and dielectric constant of different pressures are compared with the available experimental results. They are found to be in good agreement with each other. Then, the limitation of this theoretical study is also discussed.
FINITE SIZE SCALING AND CRITICAL TRANSITION IN CONSTRAINED TRAVELING SALESMAN PROBLEM
Authors: ANDRECUT M. , ALI M. K.
Published: May 2003

We investigate the finite size scaling of the mean optimal tour length as a function of the density of defects in a new constrained variant of the traveling salesman problem (TSP). The computational experience has pointed out a critical transition (at ρc≈85%) in the functional dependence of the mean optimal tour length on the density of defects.
EFFECT OF AHARONOV–BOHM PHASE ON SPIN TUNNELING
Authors: PARK CHANG-SOO , PARK D. K.
Published: May 2003

The role of Aharonov–Bohm effect in quantum tunneling is examined when a potential is defined on the S1 and has N-fold symmetry. We show that the low-lying energy levels split from the N-fold degenerate ground state oscillate with the Aharonov–Bohm phase, from which general degeneracy conditions depending on the magnetic flux is obtained. We apply these results to the spin tunneling in a spin system with N-fold rotational symmetry around a hard axis.
SOME EXTENSIONS AND APPLICATIONS OF DISPERSION RELATIONS
Authors: PEREL'MAN M. E. , ENGLMAN R.
Published: May 2003

The rationale of dispersion relations (DR) is traced to von Neumann's "state properties" and is given a unifying formulation by the introduction of "equations of restriction". Some questions surrounding reciprocal relations in the time domain are discussed. Then, extensions of DR to multi-variable cases are formulated through extended "equations of restrictions", which may be exact or approximate. These equations are applied to nonlocal dielectrics (admitting of polariton modes), which are shown to obey (in general) light-cone causality, though cases might occur in which a modification of the postulated dielectric functions is needed.
HIGH-FREQUENCY SUPERCONDUCTING PROPERTIES OF THE NdBa2Cu3O6+x SYSTEM
Authors: CHAUDHARY KHALIQ A. , ZAKAULLAH MUHAMMAD
Published: May 2003

The high-frequency behavior of superconducting NdBa 2 Cu 3 O 6+x (NBCO) has been investigated by the standing-wave technique in the microwave region. The joule loss of the bulk NBCO sample, as determined from the voltage standing wave ratio (VSWR), falls markedly at Tc. In the low temperature region, i.e. for T<Tc it tends towards the formula, A=18.5 exp (-0.052 eV/kT).
TRIALS TO IMPROVE THE CONTINUUM WAVEFUNCTIONS OF AUGER ELECTRONS EMITTED FROM ALUMINIUM AND OXYGEN IONS USING A LEAST SQUARES VARIATIONAL TECHNIQUE
Authors: ABDEL-RAOUF M. A. , EL-BAKRY S. Y. , EL-BAKRY M. Y.
Published: May 2003

The least-squares variational method is employed in order to derive iterative improvements upon the wavefunctions of Auger electrons emitted by Aluminum and Oxygen ions. The Auger electrons are considered free electrons seen by the remaining target and not as in the conventional Hartree–Fock programmes through which the continuum wavefunction of the Auger electron was determined by assuming that it occurs in a relatively higher excited state of the related bound system and this proceeds towards the real physical picture. The core potential seen by the Auger electron is evaluated on the basis of the Hartree–Fock orbitals delivered by the conventional Hartree–Fock computer codes. The Auger transition rates are calculated for different configurations of Aluminum and Oxygen ions. Our results show the stability of our variational iteration technique for improving the continuum wavefunctions and consequently the Auger rates of Auger electrons emitted from atoms or ions.
ESR STUDIES OF GMR RELATED MATERIALS I: ESR of Mn IN LaMnO3 AND La0.99Ca0.01MnO3
Authors: ARAI N. , SUGAWARA K.
Published: May 2003

ESR measurements are carried out for La 1-x Ca x MnO 3 (x=0, 0.01) from 760 K down to 4 K. A clear signal was observed above 260 K, presumably arising from Mn 3+ and Mn 4+, but two kinds of signals, the low-field and high-field ESR with g≃2, were observed below it. The high- and low-field signals are tentatively assumed to originate from Mn 4+ and Mn 3+, respectively. The g-value, linewidth, and intensity of the high-field signal nearly follow ∝1/(T-106). The temperature dependence of g-shift of the low-field signal is similar to that of magnetic susceptibility of LaMnO 3. The ESR intensity anomalously increases at temperatures between about 150 K and 250 K, which is tentatively ascribed to the occurrence of "spin-clusters". Above ≃300 K, the ESR intensity nearly follows Curie's law, and the linewidth is proportional to exp (-500/T), an indication of some kind of energy-gap existence in the Mn spin system.
REDUCIBLE FRACTIONAL HARMONICS GENERATED BY THE NONAUTONOMOUS DUFFING–RAYLEIGH EQUATION: POCKETS OF REDUCIBLE HARMONICS AND ARNOLD'S TONGUES
Authors: QRIOUET M. TOUZANI , MIRA C.
Published: May 2003

This paper deals with bifurcation structures related to families of fractional harmonics (or ultra-subharmonics) solutions generated by the Duffing–Rayleigh equation with a nonsymmetrical periodic external force. It presents some results on fractional reducible harmonics and their bifurcations. In particular a new type of contact of fold curves with Neimark's bifurcation curves (improperly called "Hopf bifurcation"), due to such fractional harmonics, is described. This contact is different from the one related to an Arnold's tongue. The corresponding configuration is called pocket of a reducible harmnonics.
GEOMETRIC CONSIDERATIONS FOR THE PREVENTION OF CHAOS IN HEATED PLATE VIBRATIONS
Authors: FERMEN-COKER MÜGE , JOHNSON GLEN E.
Published: May 2003

In this paper, Lyapunov exponents are successfully calculated and employed to design a sinusoidally excited heated plate system representing hypersonic skin panels on transatmospheric vehicles, for the prevention of chaotic oscillations. The single mode equation of motion governing the vibrations of the heated plate system is of Duffing form. The coefficients of the equation are obtained as functions of the design variables. The boundaries of regular and chaotic regions of motion are defined in various two-dimensional parametric spaces defined by the values of the largest Lyapunov exponent at each point. The critical buckling temperatures that transform the potential form from single-well to double-well are discussed for various plate aspect ratios. It is shown that finding chaos-free aspect ratios is possible, and chaos can be eliminated or delayed at the design stage simply by choosing the appropriate size and aspect ratio for the panel. The influence of the thickness of panels on the chaotic response of the system is investigated. The results of this research have direct impact on shape optimization considerations for skin panels subject to high temperatures, and on the design of various other dynamical systems that are influenced by a combination of thermal loads and external excitation.
MODEL SELECTION, CONFIDENCE AND SCALING IN PREDICTING CHAOTIC TIME-SERIES
Authors: BOLLT ERIK M.
Published: May 2003

Assuming a good embedding and additive noise, the traditional approach to time-series embedding prediction has been to predict pointwise by (usually linear) regression of the k-nearest neighbors; no good mathematics has been previously developed to appropriately select the model (where to truncate Taylor's series) to balance the conflict between noise fluctuations of a small k, and large k data needs of fitting many parameters of a high ordered model. We present a systematic approach to: (1) select the statistically significant neighborhood for a fixed (usually linear) model, (2) give an unbiased estimate of predicted mean response together with a statement of quality of the prediction in terms of confidence bands.
TRANSIENT BEHAVIOR FOR ONE-DIMENSIONAL OGY CONTROL
Authors: HOLZHÜTER Th. , KLINKER Th.
Published: May 2003

The control process for a chaotic system as proposed by Ott, Grebogi and Yorke (OGY) is investigated for systems with a one-dimensional Poincaré map. The calculation of the Poinaré map for the controlled system turns out to be an instructive method to analyze the mechanism of OGY control. We introduce the notion of a region of immediate capturing, characterizing the maximum control region that guarantees success of OGY control. Concerning the mean time to achieve control, we show that the simple probability argument in OGY's original paper has to be refined. The exponent of OGY's asymptotic power law is not affected by this detail, but the scale factor is incorrect. For the case of one-dimensional maps we derive a modified law for the dependence of the mean time to achieve control on the size of the control region. In contrast to OGY's prediction this formula is also valid for large control bounds and fits well with numerical calculations. The revised statistical argument is corroborated by investigating the time evolution of the density during control. This approach allows an alternative determination of the mean time to achieve control. The evolution of a stationary density shape is demonstrated, which notably differs from the invariant density even for moderate control bounds. This observation explains minor deviations from the modified law that can be found especially for large control bounds.
ESTIMATING CORRELATION EXPONENTS OF THE HEARTBEAT TIME SERIES
Authors: CAMMAROTA CAMILLO
Published: May 2003

The heartbeat time series commonly used in diagnostics is investigated. Since this series is not stationary, the difference series is considered and in the framework of stochastic processes its stationarity and mixing properties are tested. For this kind of data, affected by noise and low precision, a notion of correlation exponent, in some sense related to the correlation dimension, is proposed. The data analysis shows the existence of a profile of the correlation exponents, which evidentiates the amounts of randomness and of determinism in the heartbeat dynamics.
GENERATING DIFFERENT STATISTICAL DISTRIBUTIONS BY THE CHAOTIC SKEW TENT MAP
Authors: LAI DEJIAN , CHEN GUANRONG
Published: May 2003

This paper uses the skew tent map as a basic endomorphism to generate pseudo-random numbers of several familiar statistical distributions. For a special value of the parameter a in the skew tent map, we obtain the F-distribution and the Z-distribution in [Golubentsev & Anikin, 1998].
UNBOUNDED SETS OF ATTRACTION
Authors: BISCHI GIAN-ITALO , MIRA CHRISTIAN , GARDINI LAURA
Published: May 2003

In this paper we show that unbounded chaotic trajectories are easily observed in the iteration of maps which are not defined everywhere, due to the presence of a denominator which vanishes in a zero-measure set. Through simple examples, obtained by the iteration of one-dimensional and two-dimensional maps with denominator, the basic mechanisms which are at the basis of the existence of unbounded chaotic trajectories are explained. Moreover, new kinds of contact bifurcations, which mark the transition from bounded to unbounded sets of attraction, are studied both through the examples and by general theoretical methods. Some of the maps studied in this paper have been obtained by a method based on the Schröoder functional equation, which allows one to write closed analytical expressions of the unbounded chaotic trajectories, in terms of elementary functions.
APPROXIMATING THE DIAMETER, WIDTH, SMALLEST ENCLOSING CYLINDER, AND MINIMUM-WIDTH ANNULUS
Authors: CHAN TIMOTHY M.
Published: May 2003

We study (1+ε)-factor approximation algorithms for several well-known optimization problems on a given n-point set: (a) diameter, (b) width, (c) smallest enclosing cylinder, and (d) minimum-width annulus. Among our results are new simple algorithms for (a) and (c) with an improved dependence of the running time on ε, as well as the first linear-time approximation algorithm for (d) in any fixed dimension. All four problems can be solved within a time bound of the form O(n+ε-c) or O(n log (1/ε)+ε-c).
AN ALGORITHM FOR SEARCHING A POLYGONAL REGION WITH A FLASHLIGHT
Authors: LAVALLE STEVEN M. , SIMOV BORISLAV H. , SLUTZKI GIORA
Published: May 2003

We present an algorithm for a single pursuer with one flashlight searching for an unpredictable, moving target in a 2D environment. The algorithm decides whether a simple polygon with n edges and m concave regions can be cleared by the pursuer, and if so, constructs a search schedule of length O(m) in time O(m2+m log n+n). The key ideas in this algorithm include a representation called "visibility obstruction diagram" and its "skeleton": a combinatorial decomposition based on a number of critical visibility events. An implementation is presented along with a computed example.
A SIMPLE ALGORITHM FOR HOMEOMORPHIC SURFACE RECONSTRUCTION
Authors: AMENTA NINA , CHOI SUNGHEE , DEY TAMAL K. , LEEKHA NAVEEN
Published: May 2003

The problem of computing a piecewise linear approximation to a surface from a set of sample points is important in solid modeling, computer graphics and computer vision. A recent algorithm1 using the Voronoi diagram of the sample points gave a guarantee on the distance of the output surface from the original sampled surface assuming that the sample was sufficiently dense. We give a similar algorithm, simplifying the computation and the proof of the geometric guarantee. In addition, we guarantee that our output surface is homeomorphic to the original surface; to our knowledge this is the first such topological guarantee for this problem.
FAST SOFTWARE FOR BOX INTERSECTIONS
Authors: ZOMORODIAN AFRA , EDELSBRUNNER HERBERT
Published: May 2003

We present fast implementations of a hybrid algorithm for reporting box and cube intersections. Our algorithm initially takes a divide-and-conquer approach and switches to simpler algorithms for low numbers of boxes. We use our implementations as engines to solve problems about geometric primitives. We look at two such problems in the category of quality analysis of surface triangulations.
RECTANGLE AND BOX VISIBILITY GRAPHS IN 3D
Authors: FEKETE SÁNDOR R. , MEIJER HENK
Published: May 2003

We discuss rectangle and box visibility representations of graphs in 3-dimensional space. In these representations, vertices are represented by axis-aligned disjoint rectangles or boxes. Two vertices are adjacent if and only if their corresponding boxes see each other along a small axis-parallel cylinder. We concentrate on lower and upper bounds for the size of the largest complete graph that can be represented. In particular, we examine these bounds under certain restrictions: What can be said if we may only use boxes of a limited number of shapes?

Some of the results presented are as follows:

• There is a representation of K8 by unit boxes.

• There is no representation of K10 by unit boxes.

• There is a representation of K56, using 6 different box shapes.

• There is no representation of K184 by general boxes.

A special case arises for rectangle visibility graphs, where no two boxes can see each other in the x- or y-directions, which means that the boxes have to see each other in z-parallel direction. This special case has been considered before; we give further results, dealing with the aspects arising from limits on the number of shapes.
AN IMPROVED HYPERCUBE BOUND FOR MULTISEARCHING AND ITS APPLICATIONS
Authors: ATALLAH MIKHAIL J.
Published: May 2003

We give a result that implies an improvement by a factor of log log  n in the hypercube bounds for the geometric problems of batched planar point location, trapezoidal decomposition, and polygon triangulation. The improvements are achieved through a better solution to the multisearch problem on a hypercube, a parallel search problem where the elements in the data structure S to be searched are totally ordered, but where it is not possible to compare in constant time any two given queries q and q′. Whereas the previous best solution to this problem took O( log  n( log log  n)3) time on an n-processor hypercube, the solution given here takes O( log  n( log log  n)2) time on an n-processor hypercube. The hypercube model for which we claim our bounds is the standard one, SIMD, with O(1) memory registers per processor, and with one-port communication. Each register can store O( log  n) bits, so that a processor knows its ID.
OPTIMAL LINE BIPARTITIONS OF POINT SETS
Authors: DEVILLERS OLIVIER , KATZ MATTHEW J.
Published: May 2003

Let S be a set of n points in the plane. We study the following problem: Partition S by a line into two subsets Sa and Sb such that max{f(Sa), f(Sb)} is minimal, where f is any monotone function defined over 2S. We first present a solution to the case where the points in S are the vertices of a convex polygon and apply it to some common cases — f(S′) is the perimeter, area, or width of the convex hull of S′⊆S — to obtain linear solutions (or O(n log  n) solutions if the convex hull of S is not given) to the corresponding problems. This solution is based on an efficient procedure for finding a minimal entry in matrices of some special type, which we believe is of independent interest. For the general case we present a linear space solution which is in some sense output sensitive. It yields solutions to the perimeter and area cases that are never slower and often faster than the best previous solutions.
COMPUTING CONSTRAINED SHORTEST SEGMENTS: BUTTERFLY WINGSPANS IN LOGARITHMIC TIME
Authors: KIRKPATRICK DAVID , SNOEYINK JACK
Published: May 2003

We give a logarithmic-time algorithm to compute the shortest segment joining two convex n-gons A and B while avoiding another convex n-gon C. Our algorithm uses a tentative prune-and-search technique on standard representations of the polygons as arrays or balanced binary search trees.
EDGE GUARDS IN STRAIGHT WALKABLE POLYGONS
Authors: TAN XUEHOU
Published: May 2003

We study the art gallery problem restricted to edge guards and straight walkable polygons. An edge guard is the guard that patrols individual edges of the polygon. A simple polygon P is called straight walkable if there are two vertices s and t in P and we can move two points montonically on two polygonal chains of P from s to t, one clockwise and the other counterclockwise, such that two points are always mutually visible. For instance, monotone polygons and spiral polygons are straight walkable. We show that ⌊(n+2)/5⌋ edge guards are always sufficient to watch and n-vertex gallery of this type. Furthermore, we also show that if the given polygon is straight walkable and rectilinear, then ⌊(n+3)/6⌋ edge guards are sufficient. Both of our upper bounds match the known lower bounds.
COMPUTING A SHORTEST WEAKLY EXTERNALLY VISIBLE LINE SEGMENT FOR A SIMPLE POLYGON
Authors: BHATTACHARYA BINAY K. , MUKHOPADHYAY ASISH , TOUSSAINT GODFRIED T.
Published: May 2003

A simple polygon P is said to be weakly extrenally visible from a line segment L if it lies outside P and for every point p on the boundary of P there is a point q on L such that no point in the interior of [Formula: see text] lies inside P. In this paper, a linear time algorithm is proposed for computing a shortest line segment from which P is weakly externally visible. This is done by a suitable generalization of a linear time algorithm which solves the same problem for a convex polygon.
ON THE WIDTH AND ROUNDNESS OF A SET OF POINTS IN THE PLANE
Authors: SMID MICHIEL , JANARDHAN RAVI
Published: May 2003

Let S be a set of points in the plane. The width (resp. roundness) of S is defined as the minimum width of any slab (resp. annulus) that contains all points of S. We give a new characterization of the width of a point set. Also, we give a rigorous proof of the fact that either the roundness of S is equal to the width of S, or the center of the minimum-width annulus is a vertex of the closest-point Voronoi diagram of S, the furthest-point Voronoi diagram of S, or an intersection point of these two diagrams. This proof corrects the characterization of roundness used extensively in the literature.
COMPUTING A DOUBLE-RAY CENTER FOR A PLANAR POINT SET
Authors: GLOZMAN ALEX , KEDEM KLARA , SHPITALNIK GREGORY
Published: May 2003

A double-ray configuration is a configuration in the plane consisting of two rays emanating from one point. Given a set S of n points in the plane, we want to find a double-ray configuration that minimizes the Hausdorff distance from S to this configuaration. We call this problem the double-ray center problem. We present an efficient algorithm for computing the double-ray center for set S of n points in the plane which runs in time O(n3α(n) log 2n).