bluuebunny/crossref_metadata_2025 huggingface dataset:
THE ATOMIC MOVING PROCESSES OF CLUSTER Ir18 DIFFUSION ON Ir(111)
Authors: ZHUANG GUOCE , WANG WEI
Published: July 2002

The motion of peripheral atoms of an Ir 18 cluster, which results in migration of the cluster on Ir (111), is studied by kinetic Monte Carlo simulations. Detailed moving processes of individual peripheral atoms of the cluster are proposed. Statistical average of staying times show that these atoms basically locate only at several energetical equilibrium positions, which makes the motion of atoms effectively in a form of jumping of dimer from one equilibrium position to another. The jumping of the dimers, which results in migration of the cluster, are further simulated by introducing effective energy barriers between these equilibrium positions. A temperature dependence of the diffusivity D for the migration of the cluster is in good agreement with the experimental results, which proves the suitable values of the effective energy barriers for the motion of the dimers.
Pairing, Crossover and Inhomogeneous Superconductivity in the Attractive Hubbard Model
Authors: Kocharian A. N. , Yang C. , Chiang Y. L.
Published: July 2002

One- and two-dimensional attractive Hubbard models in the presence of magnetic field h are studied in a wide range of on-site interaction strength U, temperature T and electron concentration n by means of the generalized self-consistent field (GSCF) approach with renormalized chemical potential. Pairing, the smooth crossover from the BCS regime into the Bose condensation state and the inhomogeneous superconductivity with the non-uniform order parameter are investigated. The excitation spectrum, the momentum distribution function and thermodynamic properties, including the concentration of double occupied sites, the kinetic energy, and the chemical potential, are calculated. The numerical calculations are found in a good agreement with the Bethe-ansatz results and quantum Monte-Carlo calculations in a wide range of system parameters U, n and h. The GSCF theory correctly displays the separation of the energy gap from the order parameter (crossover) as n or |U| decrease. The concentration of double occupied sites and the bound electron pairs n pair are calculated and we found a simple relationship between the order parameter and n pair , valid for the arbitrary U and all n in any dimension. The developed GSCF approach in magnetic field suggests a smooth transition into the inhomogeneous superconducting state.
COMPARISON OF DENSITY FUNCTIONAL APPROXIMATIONS IN THE JELLIUM MODEL FOR METAL CLUSTERS
Authors: FIOLHAIS CARLOS , ALMEIDA L. M.
Published: July 2002

We calculated the exchange, correlation and total energies of clusters of alkali metals with N=1-150 atoms in the spherical jellium model. The calculations were made using the Kohn-Sham method with exchange and correlation energies evaluated in the meta-generalized gradient approximation (MGGA), proposed by J. P. Perdew, S. Kurth, A. Zupan and P. Blaha, in the generalized gradient approximation (GGA) of J. P. Perdew, K. Burke and M. Ernzerhof, and in the Local Density Approximation (LDA).

We evaluated the relative deviations of MGGA and GGA energies with respect to LDA. Exchange energies of MGGA and GGA are more negative than the LDA exchange energy and become closer to this as the cluster size increases. On the other hand, the GGA and MGGA correlation energies, which are almost identical, are less negative than LDA. The deviations of GGA and MGGA exchange-correlation energies with respect to LDA are smaller than those of the exchange and correlation energies separately.

For clusters with 18 and 20 atoms we have compared our jellium results with Variational and Diffusion Monte-Carlo results. Errors of LDA for exchange and correlation tend to cancel so that the total exchange-correlation energy is close to the Monte-Carlo results. Similar cancellations occur with GGA and MGGA. We also examined the validity of the liquid drop model.
STRUCTURES AND OPTICAL PROPERTIES OF HYDRAZONES DERIVED FROM BIOLOGICAL POLYENES
Authors: NAKASHIMA TAKAYASU , YAMADA TAKASHI , HASHIMOTO HIDEKI , KOBAYASHI TAKAYOSHI
Published: July 2002

A set of hydrazone molecules was derived from a series of biological polyenes that have different polyene chain-lengths with common substituent group of 2,4-dinitrophenylhydrazine. Their structures were determined by high-resolution NMR spectroscopy as well as X-ray crystallography, and their optical properties were investigated by room and low temperature optical absorption spectroscopy. Among the derivatives so far synthesized, the one that has the shortest polyene chain (C13-DNPH) afforded single crystals without inversion symmetry, hence applicable for the second-order nonlinear optical devices. Molecular structures in the crystals were closely inspected in order to explain the cause to violate the inversion symmetry. Hydrazones derived in this study gave rise to two transition moments along the molecular axis. Comparison of the optical absorption spectra among the derivatives showed a unique phenomenon that could be attributed to the crossover of the excited state potential energy surfaces along the elongation of the polyene chain-lengths.
SPIN ALIGNMENT BETWEEN THE TRIPLET EXCITED STATE OF PHENYLANTHRACENE AND THE DANGLING VERDAZYL RADICAL AS STUDIED BY TIME-RESOLVED ELECTRON SPIN RESONANCE
Authors: TEKI YOSHIO , NAKATSUJI MASAAKI , MIURA YOZO
Published: July 2002

The photo-excited quartet (S=3/2) high spin state of a radical-excited triplet pair of a novel compound, phenylanthracene-verdazyl radical, was detected by time-resolved electron spin resonance (TRESR) technique. The TRESR spectrum was well analyzed by the ordinary spin Hamiltonian with the Zeeman and fine-structure terms. The g value, fine-structure splitting, and relative population of the Ms sublevels have been determined to be g=2.0043, D=0.0230 cm -1, E=0.0 cm -1 and P1/2′=P-12′=0.5 and P3/2′=P-3/2′=0.0, respectively, by the spectral simulation. The direct observation of the excited quartet state shows tha the photo-induced intramolecular spin alignment is realized between the excited triplet state (S=1) of the phenylanthracene moiety and the doublet spin (S=1/2) of the dangling verdazyl radical.
TRANSPORT AND TRIPLET SUPERCONDUCTING CONDENSATE IN MESOSCOPIC FERROMAGNET-SUPERCONDUCTOR STRUCTURES
Authors: BERGERET F. S. , PAVLOVSKII V. V. , VOLKOV A. F. , EFETOV K. B.
Published: July 2002

We calculate the conductance of a superconductor/ferromagnet (S/F) mesoscopic structure in the dirty limit. First we assume that the ferromagnet exhibits a homogeneous magnetization and consider the case that the penetration of the condensate into the F wire is negligible and the case in which the proximity effect is taken into account. It is shown that if the exchange field is large enough, the conductance below the critical temperature T c , is always smaller than the conductance in the normal state. At last, we calculate the conductance for a F/S structure with a local inhomogeneity of the magnetization in the ferromagnet. We demonstrate that a triplet component of the condensate is induced in the F wire. This leads to a increase of the conductance below T c .
STRUCTURAL PHASE STABILITY OF Ti3Al UNDER HIGH PRESSURE
Authors: RAJAGOPALAN M. , SAHU P. CH. , SHEKAR N. V. CHANDRA , YOUSUF MOHAMMAD , RAJAN K. GOVINDA
Published: July 2002

Recently, the structural stability of the high temperature structural intermetallic Ti 3 Al has been investigated experimentally and a transition from the DO 19 to the DO 24 structure has been reported. We have performed band structure calculations as a function of reduced volume by tight binding linear muffin-tin orbital (TBLMTO) method to look into these transitions to understand their mechanisms in terms of its electronic structure. The mechanism of the DO 19 to the DO 24 structure is understood to be due to shifting of the Fermi energy into a valley in the density of states curve, thereby driving the system to a more stable structure.
Characteristics of Hg-Based Superconductors Prepared at 0.2 GPa by Hip
Authors: Celotti G. , Tampieri A. , Rinaldi D.
Published: July 2002

The preparation of Hg(Pb)BCCO (1201) and (1223) phases was performed by hot-isostatic-pressing (HIP) using simple oxides as precursors canned in silver tube. In the case of Hg 0.8 Pb 0.2 Ba 2 CuO 4+δ the preparation, carried out at 800 °C and 0.2 GPa for 5 hrs, yielded a single phase bulk sample. On the other hand the preparation of Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+δ at 820 °C and 0.2 Gpa for 5 hrs allowed the attainment of a high volume fraction of 1223 phase. Magnetic susceptibility of 1201 phase showed a granular transition around 90 K; in the case of 1223 the value was ≈128 K followed by a broadened intergranular transition.

These results show the feasibility of 1201 phase synthesis with high purity and of 1223 phase in large amount (>80%).

The possibility to obtain the samples directly in form of dense bulks (with density ≥ 85%) stresses the importance of this technique in relation to the intrinsic low thermal stability of the superconducting phases.
GALVANOMAGNETIC EFFECTS IN Gd and Zn-SUBSTITUTED Bi2Sr2Ca1-xGdx (Cu1-yZny)2O8+δ
Authors: ILONCA G. , POP A. V. , TARTA G. , JURCUT T. , DELTOUR R.
Published: July 2002

We had performed a study on magnetoresistivity Hall, Nernst and Seebeck effects in the mixed and normal state for "Bi2212" bulk with Gd (0≤x≤0.50) and Zn (0≤y≤0.03) prepared by the conventional solid state reaction method in magnetic fields between 0 and 5 T and in the temperature range 5–300 K. The critical temperatures, the Hall concentration, the Nernst and Seebeck coefficients depend strongly on the Zn and Gd contents in the samples. Also, we have found an anomalous suppression of superconductivity at x=0.30–0.35 and y=0.025–0.030, when the hole concentration per Cu is p~1/8 and the transport properties exhibit less metallic behavior than usual. There is a possibility that a kind of order of holes and/or spins is stabilized owing to pinning by Zn, as in the La-based cuprate.
SUPERCONDUCTIVITY IN CUPRATES, THE VAN HOVE SCENARIO
Authors: Bok J. , Bouvier J.
Published: July 2002

The existence of van Hove singularities close to the Fermi level in all high T c cuprates has been experimentally established. We develop a theory using these singularities which enables us to compute the main physical properties: T c gap and gap anisotropy, specific heat and magnetic susceptibility. All these results agree well with the experimental data in the optimal and overdoped regime. In the underdoped regime, we use the theory of electron-electron interaction in disordered conductors to explain the pseudo-gap behaviour.
SUPERCONDUCTIVITY WITHOUT COOPER'S PAIRING
Authors: FAN J. D. , MALOZOVSKY Y. M.
Published: July 2002

In terms of the geometric phase — Berry's phase, the authors have shown that the factor 2e appearing in the magnetic flux quantization in a bored cylindrical superconductor is a natural consequence of both London equation and gauge invariance. The same conclusion is also true for the Josephson effect. Thus, the factor 2e has nothing to do with electron (Cooper's) pairing. Moreover, the BCS Hamiltonian can be easily derived from the general formalism of the Hamiltonian of fermions in second quantization without invoking the concept of Cooper's pairing. It has been shown that in terms of a reinterpretation of the interaction potential in the BCS Hamiltonian, results from the BCS theory remain valid for conventional superconductors.
A Possible Mechanism of Superconductivity Based on Wigner Crystal and BEC
Authors: Dai JiXin , Tao Wen , Hor Peiherng , XianXi Dai
Published: July 2002

A new possible mechanism is suggested based on the Wigner crystal and Bose–Einstein condensation. Our previous studies on the singular states that Loudon's singular ground state is rejected by the orthogonality criteria. It is shown that 2D Wigner crystal can exist and to be a possible mechanism for HTS.
SUPERCONDUCTIVITY OF PrBa2Cu3O7 AND OF Pr2-zCezSr2Cu2NbO10
Authors: Blackstead Howard A. , Dow John D.
Published: July 2002

The data for superconducting PrBa 2 Cu 3 O 7 and Pr 2-z Ce z Sr 2 Cu 2 NbO 10 indicate that the superconductivity of these compounds is normally unaffected by rare-earth-site Pr but is quenched by a Pr Ba or Pr Sr defect on the other side of an adjacent cuprate-plane. Hence the primary superconducting condensate must reside not in the cuprate planes, but in the charge-reservoir regions containing hypocharged oxygen, namely in the BaO layers or the CuO chain layers of PrBa 2 Cu 3 O 7, and in the SrO layers of Pr 2-z Ce z Sr 2 Cu 2 NbO 10.
MICROSTRUCTURAL CHARACTERIZATION OF SPIN-VALVE MULTILAYERS BY X-RAY ANOMALOUS DIFFRACTION TECHNIQUE
Authors: LIU C. X. , XU M. , LUO G. M. , YANG T. , CHAI C. C. , MAI Z. H. , LAI W. Y. , JIANG H. Y. , WU Z. H. , DING Y. F. , WANG J.
Published: July 2002

It is impossible to directly analyze the microstructure of spin-valve multilayers based on Ni, Fe, Cu and Mn by a conventional X-ray diffraction technique because the lattice parameter and atomic scattering factors of them are very close. To solve this problem, we use an X-ray anomalous diffraction technique to characterize the microstructures of the [ Ni 80 Fe 20/ Fe 50 Mn 50]15 and [ Ni 80 Fe 20/ Cu ]15 superlattice systems. The results show that more diffraction peaks and higher intensity in the reflectivity profile are observed when the incident energy is close to the absorption edge of the lighter element (Mn) in [ Ni 80 Fe 20/ Fe 50 Mn 50]15 multilayer systems and to the absorption edge of the heavier element (Cu) in the [ Ni 80 Fe 20/ Cu ]15 multilayer systems. The interface and periodic structure of [ Ni 80 Fe 20/ Fe 50 Mn 50]15 are more perfect than that of the [ Ni 80 Fe 20/ Cu ]15 superlattices. The above results are discussed in this paper.
GENERALIZED WIGNER LATTICES AS A RIEMANN SOLID: FRACTALS IN THE HURWITZ ZETA FUNCTION
Authors: IGUCHI KAZUMOTO
Published: July 2002

We study the ground state configuration and the excitation energy gaps in the strong coupling limit of the extended Hubbard model with a long-range interaction in one dimension. As proved by Hubbard and Pokrovsky and Uimin, the ground state configuration is quasiperiodic and as proved by Bak and Bruinsma, the excitation energy has a finite gap which forms a devil's stair as a function of the density of particles in the system. We show that the quasiperiodicity and the fractal nature of the excitation energy come from the nature of the long-range interaction that is related to the fractal nature of the Hurwitz Zeta function and the Riemann Zeta function.
REENTRANT CHARGE ORDERING BEHAVIOUR IN THE EXTENDED HUBBARD MODEL
Authors: HOANG ANH TUAN
Published: July 2002

We study the charge ordering behavior in a three-dimensional extended Hubbard model using the Coherent potential approximation (CPA). It is shown that the charge ordering transition occurs due to the competition between kinetic and Coulomb energy. At various band fillings a simple reentrant behavior of the charge ordering transition is found.
EFFECT OF Nb2O5 ON THE ELASTIC BEHAVIOR OF PZT FERROELECTRIC MATERIALS
Authors: PURUSHOTHAM Y. , THAKUR O. P. , PRAKASH CHANDRA , REDDY P. VENUGOPAL
Published: July 2002

A series of ferroelectric ceramics with the compositional formula PbZr0.52Ti0.48O3 + x wt% of Nb2O5 were prepared by the solid state reaction method. Samples were characterized by studying their X-ray diffraction and dielectric measurements. The longitudinal and shear wave velocities and corresponding elastic moduli were determined at room temperature by using the pulse transmission technique. The values of Young's modulus (E), and the rigidity (n) and bulk (k) moduli were corrected to theoretical density and were found to increase with increasing dopant concentration. The variation of elastic moduli and other elastic parameters such as Debye temperature (θ D ) with composition are explained qualitatively.
TB-LMTO-AUGMENTED SPACE RECURSION FOR RANDOM BINARY ALLOYS: A TRACTABLE REPRESENTATION
Authors: GHOSH SUBHRADIP , DAS NITYANANDA , MOOKERJEE ABHIJIT
Published: July 2002

We had earlier presented a computationally feasible and fast technique for obtaining the electronic structure of random alloys which allowed us to incorporate short-ranged order and effects like clustering and local lattice distortions due to size mismatch effects. The technique combined the augmented space recursion with the tight-binding LMTO. We have recast the formalism in a way that allows us to sample many more configurations states and bring the basic equations in a one-to-one correspondence with the screed KKR formalism.
A CONTRAST-BASED APPROACH TO THE IDENTIFICATION OF TEXTURE FAULTS
Authors: DE NATALE FRANCESCO G. B. , GRANELLI FABRIZIO , VERNAZZA GIANNI
Published: July 2002

Texture analysis based on the extraction of contrast features is very effective in terms of both computational complexity and discrimination capability. In this framework, max–min approaches have been proposed in the past as a simple and powerful tool to characterize a statistical texture. In the present work, a method is proposed that allows exploiting the potential of max–min approaches to efficiently solve the problem of detecting local alterations in a uniform statistical texture. Experimental results show a high defect discrimination capability, and a good attitude to real-time applications, which make it particularly attractive for the development of industrial visual inspection systems.
A CAUTIONARY TALE OF COUPLING CELLS WITH INTERNAL SYMMETRIES
Authors: WOOD DAVID
Published: July 2002

We consider the implications of "all to all" coupling of n identical, Z2 symmetric cells. In particular we demonstrate that how this coupling is achieved with respect to these internal symmetries is important, even in this very simple scenario. The coupling we consider leads to a full symmetry of Sn, Z2×Sn or Z2≀Sn, where the latter is the "wreath product" symmetry. By considering the generic solutions of each case on their respective irreducible representations, we compare and contrast the three cases, and show how very different solutions could arise in essentially similar systems.
CONNECTIONS BETWEEN SADDLES FOR THE FITZHUGH–NAGUMO SYSTEM
Authors: ROCŞOREANU CARMEN , GIURGIŢEANU NICOLAIE , GEORGESCU ADELINA
Published: July 2002

By studying the two-dimensional FitzHugh–Nagumo (F–N) dynamical system, points of Bogdanov–Takens bifurcation were detected (Sec. 1). Two of the curves of homoclinic bifurcation emerging from these points intersect each other at a point of double breaking saddle connection bifurcation (Sec. 2). Numerical investigations of the bifurcation curves emerging from this point, in the parameter plane, allowed us to find other types of codimension-one and -two bifurcations concerning the connections between saddles and saddle-nodes, referred to as saddle-node–saddle connection bifurcation and saddle-node–saddle with separatrix connection bifurcation, respectively. The local bifurcation diagrams corresponding to these bifurcations are presented in Sec. 3. An analogy between the bifurcation corresponding to the point of double homoclinic bifurcation and the point of double breaking saddle connection bifurcation is also presented in Sec. 3.
DYNAMICAL BEHAVIOR OF THE LINEARIZED VERSION OF THE FITZHUGH–NAGUMO NEURAL MODEL
Authors: DI GARBO ANGELO , BARBI MICHELE , CHILLEMI SANTI
Published: July 2002

For a linearized version of the FitzHugh–Nagumo model, firing and resetting conditions are defined by analogy with the Integrate and Fire model. The dynamical behavior of the model, subject to periodic synaptic inputs, is investigated both theoretically and numerically, with particular emphasis on the synchronization properties. The study is then extended to a network of two synaptically coupled units.
AN OPEN-PLUS-CLOSED-LOOP APPROACH TO SYNCHRONIZATION OF CHAOTIC AND HYPERCHAOTIC MAPS
Authors: CHEN LI-QUN , LIU YAN-ZHU
Published: July 2002

In this paper, the open-plus-closed-loop control strategy is adapted to synchronize discrete chaos. Two synchronization problems of chaos are studied: one is to drive a chaotic map with the aim of obtaining desirable chaotic dynamics; the other is to identify chaotic behaviors of a nonlinear map for different initial conditions. It is shown that in the latter case the needed control signal can be arbitrarily small. Two numerical examples, namely, the Gaussian map and a hyperchaotic map, are investigated in detail for demonstration of the effectiveness of the approach. The results show that synchronization of discrete chaos can be realized if the control is activated in the basin of entrainment.
MIDDLEWARE FOR BUILDING ADAPTIVE MIGRATORY CONTINUOUS MEDIA APPLICATIONS
Authors: NAKAJIMA TATSUO , AIZU HIROYUKI
Published: July 2002

In this paper, we propose a middleware system for building adaptive migratory continuous media applications. In future computing environments, a variety of objects at home and in offices will embed computers, and various applications will be moved among these computers according to the user's locations. For example, a computer that executes an application may be changed to another computer according to the location of the application's user for monitoring his behavior. However, since the computers may have dramatically different hardware and software configurations, the application cannot be moved without taking into account the configurations of the computers that the application is migrated. Therefore, migratory applications should be aware of environments where they are executed.

The paper focuses on middleware for building adaptive migratory continuous media applications that are one of the most important classes of migratory applications. Our middleware consists of three components. The first component is an environment server that monitors computing environments that applications run, and it notifies the changes of the environments to the applications. The second component is a continuous media toolkit that enables us to build adaptive migratory continuous media applications easily. The toolkit enables us to build continuous media applications in a highly configurable way. This makes applications to be adapted to every computing environment by changing their configurations. The third component is a migration manager that makes applications migratory. We also show an example of a migratory application, and describe some experiences with building the application.
ON THE ROOT OF LANGUAGES
Authors: MASSAZZA P.
Published: July 2002

In this work we study the problem of determining an unambiguous p-root of a language, i.e. a solution of the equation Xp=L when L is a language and the product is unambiguous. We show that every language admits at most one unambiguous root and that the problem of the existence of the unambiguous root is undecidable for the class of context free languages. We also prove that it is decidable whether a regular language admits a regular unambiguous root and that if a language is in P and admits the unambiguous root, then the root is in P.
HEURISTICS FOR A DEFAULT LOGIC REASONING SYSTEM
Authors: NICOLAS PASCAL , SAUBION FRÉDÉRIC , STÉPHAN IGOR
Published: July 2002

In Artificial Intelligence, Default Logic is recognized as a powerful framework for knowledge representation when one has to deal with incomplete information. Its expressive power is suitable for non monotonic reasoning, but the counterpart is its very high level of theoretical complexity. Today, some operational systems are able to deal with real world applications. However, finding a default logic extension in a practical way is not yet possible in whole generality. This paper which is an extended version of18 shows how heuristics such as Genetic Algorithms and Local Search techniques can be used and combined to build an automated default reasoning system. We give a general description of the required basic components and we exhibit experimental results.
AN ASSUMPTIVE LOGIC PROGRAMMING METHODOLOGY FOR PARSING
Authors: VOLL KIMBERLY D. , YEH TOM P. , DAHL VERONICA
Published: July 2002

We show how two novel tools in logic programming for AI (namely, continuation-based linear and timeless assumptions, and Datalog grammars) can assist us in producing terse treatments of difficult language processing phenomena. As a proof of concept, we present a concise parser for Datalog grammars (logic grammars where strings are represented with numbered word boundaries rather than as lists of words) that uses assumptions and a combination of left-corner parsing and charting. We then study two test cases of this parser's application: complete constituent coordination, and error diagnosis and correction.
VACUUMLESS COSMIC STRINGS IN BRANS–DICKE THEORY
Authors: SEN A. A.
Published: July 2002

The gravitational fields of vacuumless global and gauge strings have been studied in Brans–Dicke theory under the weak field assumption of the field equations. It has been shown that both global and gauge string can have repulsive as well as attractive gravitational effect in Brans–Dicke theory which is not so in General Relativity.
ROTATING STRING COSMOLOGIES WITH SCALAR FIELD AND HEAT FLUX
Authors: BAYSAL HÜSNÜ , YILMAZ İHSAN , TARHAN İSMAIL
Published: July 2002

We obtain some cosmological model that are exact solutions of Einstein field equations. The metric utilized is the nonstatic Gödel-type cosmological model and the curvature source is a string cloud with scalar field and heat flow. The solutions have nonzero expansion, shear, and rotating. The properties of the solutions are studied and the temperature distribution is also given explicitly.
COSMIC RELIC TORSION FROM INFLATIONARY COSMOLOGY
Authors: GARCIA DE ANDRADE L. C.
Published: July 2002

An inflationary de Sitter solution of Teleparallel Equivalent of General Relativity (TERG) is obtained. In this model Cartan torsion is shown to be a cosmological relic in the sense that it decays from earlier epochs of the Universe until extremely small values at the present epoch. This would be the reason why it is very difficult to measure cosmological torsion at the present epoch and only extremely small relic torsion would be left. Torsion plays a role similar to the inflaton field in its interaction with the scalar field. The torsion mass is determined from the teleparallel action in terms of the Planck mass. The value of the torsion mass is of the order of Planck mass. An upper limit for torsion of 10-18s-1 is obtained for the de Sitter phase. By considering the Friedmann phase it is possible to show that torsion induces an oscillation on the Universe.
INFORMATION ON THE SIZE AND OTHER QUANTITIES OF Λ-ORBITALS IN HYPERNUCLEI FROM EXPERIMENTAL Λ-ENERGIES
Authors: GRYPEOS M. E. , KOUTROULOS C. G. , PETRIDOU TH. A.
Published: July 2002

An approach is proposed on the basis of which the experimentally known two lower energy eigenvalues of a Λ-particle, assumed to be bound in a hypernucleus by a central potential (from a fairly wide class of them), are able to provide in certain cases rather direct information on estimates of other useful quantities, such as the r.m.s. radii of the Λ orbitals, kinetic energies, etc.
NON-DETERMINISM AND UNCERTAINTY IN THE SITUATION CALCULUS
Authors: PINTO JAVIER , SERNADAS AMÍLCAR , SERNADAS CRISTINA , MATEUS PAULO
Published: July 2002

The purpose of this article is to extend the situation calculus, a logical framework for the specification of theories of action and change, with actions that have a non-deterministic or uncertain nature. Our approach is based upon the idea that actions may have a deterministic component, and a probabilistic component. For example, the act of flipping a coin has a deterministic component (the actual coin toss) and an uncertain component (the outcome). We extend the language of the situation calculus in order to make explicit this distinction between these two action components. Furthermore, we provide means to reason about the outcomes of processes specified only in terms of deterministic action components (which we call behaviors). In particular, we show how one can compute the probability that some fluent will hold after specific behavior is realized. An important feature of our approach is that the syntactic and semantic structure of actions and situations is independent of the decomposition of actions into deterministic and uncertain components. Thus, we inherit solutions to the frame problem ramification problem, etc.
APPROXIMATE EXPRESSIONS FOR AVAILABILITY OF REPAIRABLE SERIES–PARALLEL STRUCTURES
Authors: DINESH KUMAR U. , BIROLINI A.
Published: July 2002

The investigation of approximate expressions for availability of complex repairable structures is an important problem facing researchers in the field of reliability engineering. This is due to the fact that the availability evaluation of complex structures becomes time consuming even under the assumption that the failure and repair rates are constant and only the steady-state availability and mean time to failure (MTTF) are needed. The main reason for complexity is due to the large number of states required to describe the system. In such cases, approximate expressions can be useful. In this paper, approximate expressions for steady-state availability and MTTF of large series–parallel structures are derived under three different assumptions on maintenance strategy, namely, independent elements, macro-structures and independent macro-structures. An example is presented to illustrate the application of the method under the three assumptions. Numerical evaluation of the example problem shows a good convergence of the results.
GROWTH MODE OF ULTRATHIN Co FILMS ON Fe(001) PREPARED BY LOW ENERGY ION-ASSISTED DEPOSITION
Authors: LUCHES P. , DI BONA A. , BORGHI A. , GIOVANARDI C. , VALERI S.
Published: July 2002

Co films were epitaxially grown on Fe(001) by simultaneous thermal evaporation of Co atoms and ion bombardment with low-energy (300–1000 eV) Ar ions in a wide range of ion-to-atom flux ratio (0.02–0.5). The 0–50 ML coverage range was investigated. Transition from island growth to a continuous layer growth occurs on passing from purely thermal to ion-assisted deposition procedure. Structural characterization was performed by Primary-beam Diffraction Modulated Electron Emission (PDMEE). For purely thermal deposition, transition from the bcc phase to the equilibrium, hcp phase has been observed at a critical coverage of about 15 ML, both structures showing a significant strain (7% contraction and 5% expansion with respect to the ideal bcc and hcp phase, respectively). Ion assistance has proved to be effective in lowering both the strains in the Co film and the critical thickness of the bcc phase.
PATHOGENESIS OF THE GRADUALLY ELONGATED NERVE
Authors: Ikeda Kazuo , Okada Kazuko , Tomita Katsuro , Tanaka Shigenori
Published: July 2002

The rabbits' sciatic nerves were lengthened by 30 mm in increments of 2.0 mm/day (2-mm group) and 4.0 mm/day (4-mm group). In the 2-mm group, the phosphorylated neurofilament (p-NF) immunoreactivity of axons was similar to that of the control group. However, in the 4-mm group, number of p-NF positive axons decreased. The number of p-NF positive cells at the seventh lumbar dorsal root ganglion cells of the 4-mm group was significantly larger than that of the control group. Abnormal p-NF immunoreactivity in the 4-mm group suggested an impairment of the axonal flow. Leakage of Evans blue-albumin into the endoneurial space, which meant destruction of the blood-nerve barrier function, was clearly evident in the 4-mm group, but minor in the 2-mm group. A speed of 2.0 mm/day, therefore, appears to be critical for safe nerve elongation in this model.
CONGENITAL TRUE COMPLETE SYMPHALANGISM OF ALL PROXIMAL INTERPHALANGEAL JOINTS OF HANDS WITH CARPAL ANOMALIES: A CASE REPORT
Authors: Tuncay Ibrahim , Akpinar Fuat , Tosun Nihat
Published: July 2002

Symphalangism is a rare condition which manifests in either PIP or DIP joint congenital fusion. Symphalangism may be with some other skeletal deformities. In our case, all PIP joints of both hands were fused with bilateral hypoplasia of carpal bones and Minaar type III lunatotriquetral coalition congenitally. No motion was detected in PIP joints with absence of cutaneous creases over all PIP joints. Radiologically, carpal hypoplasia and lunatotriquetral coalition were seen in all fingers with the absence of PIP joints. The patient's skeletal survey revealed no other pathology. He had no complaints related to his hands. So, regular follow-up was recommended. This pathology was presented as rarely observed although clinical problem is usually not so much.
THE CORE AND CONSISTENCY PROPERTIES: A GENERAL CHARACTERISATION
Authors: FUNAKI YUKIHIKO , YAMATO TAKEHIKO
Published: July 2002

In this paper, we unify various axiomatisations of the core of TU games by means of consistency with respect to different definitions of reduced games. First, we introduce a general definition of reduced games including the reduced games due to Davis and Maschler (1965), Moulin (1985), and Funaki (1995) as special cases. Then, we provide a general theorem from which the characterisations due to Peleg (1986), Tadenuma (1992), and Funaki (1995) can be obtained. Our general theorem clarifies how the three characterisations of the core differ and are related.
Random environmental processes for complex computer systems: a theoretical approach
Authors: Assimakopoulos Nikitas A.
Published: July 2002

In this paper, we consider various computer inventory, computer queueing and reliability computer models where complexity due to interacting components of subsystems is apparent. In particular, our analysis focuses on a multi-item inventory computer model with stochastically dependent demands, a queueing computer network where there are dependent arrival and service processes, or a reliability computer model with stochastically dependent component lifetimes. We discuss cases where this dependence is induced only by a random environmental process which the system operates in. This process represents the sources of variation that affect all deterministic and stochastic parameters of the model. Thus, not only are the parameters of the model now stochastic processes, but they are all dependent due to the common environment they are all subject to. Our objective is to provide a convincing argument that, under fairly reasonable conditions, the analytical techniques used in these models as well as their solutions are not much more complicated than those where there is no environmental variation.
TECHNOLOGY, INNOVATION AND COMPETITIVE ADVANTAGE: MAKING A BUSINESS PROCESS PERSPECTIVE PART OF INVESTMENT APPRAISAL
Authors: LLOYD ASHLEY D.
Published: July 2002

Investments in technology are an important focus for innovation but, like other forms of change, they also carry risk. The risk associated with a poor decision in part depends on the number of processes impacted by the technology, ranging from low with a small and reversible production line enhancement, to high with the irreversible implementation of an enterprise-wide information system. In terms of competitiveness, just as a local innovation can remove efficiency-sapping bottlenecks from a wide range of related business processes, so can the same business processes amplify any negative effects.

This paper reports on an ESRC Innovation Programme funded project that has made a detailed study of investments in both the manufacturing and service sectors. Detailed maps of the business processes related to an investment have been recorded both before and after implementation to allow identification of where process versus technology benefits actually arise. These observations are used to construct a framework for investment appraisal that links local enhancements to process performance improvements experienced by the customer. In addition to providing a benchmark for future competitive enhancements of the technology/process, the standardised maps may also help the transfer of technologies across, and between, organisations.
Computational strategies for object recognition
Authors: Suetens Paul , Fua Pascal , Hanson Andrew J.
Published: July 2002

This article reviews the available methods for automated identification of objects in digital images. The techniques are classified into groups according to the nature of the computational strategy used. Four classes are proposed: (1) the simplest strategies, which work on data appropriate for feature vector classification, (2) methods that match models to symbolic data structures for situations involving reliable data and complex models, (3) approaches that fit models to the photometry and are appropriate for noisy data and simple models, and (4) combinations of these strategies, which must be adopted in complex situations. Representative examples of various methods are summarized, and the classes of strategies with respect to their appropriateness for particular applications.
Delivery of time-critical messages using a multiple copy approach
Authors: Ramanathan Parameswaran , Shin Kang G.
Published: July 2002

Reliable and timely delivery of messages between processing nodes is essential in distributed real-time systems. Failure to deliver a message within its deadline usually forces the system to undertake a recovery action, which introduces some cost (or overhead) to the system. This recovery cost can be very high, especially when the recovery action fails due to lack of time or resources.

Proposed in this paper is a scheme to minimize the expected cost incurred as a result of messages failing to meet their deadlines. The scheme is intended for distributed real-time systems, especially with a point-to-point interconnection topology. The goal of minimizing the expected cost is achieved by sending multiple copies of a message through disjoint routes and thus increasing the probability of successful message delivery within the deadline. However, as the number of copies increases, the message traffic on the network increases, thereby increasing the delivery time for each of the copies. There is therefore a tradeoff between the number of copies of each message and the expected cost incurred as a result of messages missing their deadlines. The number of copies of each message to be sent is determined by optimizing this tradeoff. Simulation results for a hexagonal mesh and a hypercube topology indicate that the expected cost can be lowered substantially by the proposed scheme.
Analyzing algorithms by simulation
Authors: McGeoch Catherine
Published: July 2002

Although experimental studies have been widely applied to the investigation of algorithm performance, very little attention has been given to experimental method in this area. This is unfortunate, since much can be done to improve the quality of the data obtained; often, much improvement may be needed for the data to be useful. This paper gives a tutorial discussion of two aspects of good experimental technique: the use of
variance reduction techniques
and
simulation speedups
in algorithm studies.

In an illustrative study, application of variance reduction techniques produces a decrease in variance by a factor 1000 in one case, giving a dramatic improvement in the precision of experimental results. Furthermore, the complexity of the simulation program is improved from Θ
mn
/H

n

) to Θ(
m
+
n
log
n
) (where
m
is typically much larger than
n
), giving a much faster simulation program and therefore more data per unit of computation time. The general application of variance reduction techniques is also discussed for a variety of algorithm problem domains.
A logic for reasoning about security
Authors: Glasgow Janice , Macewen Glenn , Panangaden Prakash
Published: July 2002

A formal framework called
Security Logic
(
SL
) is developed for specifying and reasoning about security policies and for verifying that system designs adhere to such policies. Included in this modal logic framework are definitions of
knowledge, permission,
and
obligation
. Permission is used to specify secrecy policies and obligation to specify integrity policies. The combination of policies is addressed and examples based on policies from the current literature are given.
VAXcluster
Authors: Kronenberg Nancy P. , Levy Henry M. , Strecker William D.
Published: July 2002

A VAXcluster is a highly available and extensible configuration of VAX computers that operate as a single system. To achieve performance in a multicomputer environment, a new communications architecture, communications hardware, and distributed software were jointly designed. The software is a distributed version of the VAX/VMS operating system that uses a distributed lock manager to synchronize access to shared resources. The communications hardware includes a 70 megabit per second message-oriented interconnect and an interconnect port that performs communications tasks traditionally handled by software. Performance measurements show this structure to be highly efficient, for example, capable of sending and receiving 3000 messages per second on a VAX-11/780.
Transforming FORTRAN DO loops to improve performance on vector architectures
Authors: Cowell Wayne R. , Thompson Christopher P.
Published: July 2002

The performance of programs executing on vector computers is significantly improved when the number of accesses to memory can be reduced. Unrolling Fortran DO loops, followed by substitutions and eliminations in the unrolled code, can reduce the number of loads and stores. In this paper we characterize the unrolling transformation and associated transformations of Fortran DO loops and describe a set of software tools to carry out these transformations. The tools use the machinery available in Toolpack and have been integrated into that environment. We describe the results of applying these tools to a collection of linear algebra subroutines.
The asymptotic complexity of merging networks
Authors: Miltersen Peter Bro , Paterson Mike , Tarui Jun
Published: July 2002

Let
M(m,n)
be the minimum number of comparators needed in a comparator network that merges
m
elements x
1
≤ x
2
≤ … ≤ x
m
and
n
elements y
1
≤ y
2
≤ … ≤ y
m
, where n ≥ m. Batcher's odd-even merge yields the following upper bound:

M(m,n) ≤ ½(m + n)log
2
m + O(n);

in particular,

M(n,n) ≤ n log
2
n + o(n)

We prove the following lower bound that matches the upper bound above asymptotically as
n ≥ m →∞;

M(m,n) ≥ ½(m+n)log
2
m - O(m)

in particular,

M(n,n) ≥ n log
2
- O(n).

Our proof technique extends to give similarily tight lower bounds for the size of monotone Boolean circuits for merging, and for the size of switching networks capable of realizing the set of permutations that arise from merging.
Optimal clock period FPGA technology mapping for sequential circuits
Authors: Pan Peichen , Liu C. L.
Published: July 2002

We study the technology mapping problem for sequential circuits for look-up table (LUT) based field programmable gate arrays (FPGAs). Existing approaches to the problem simply remove the flip-flops (FFs), then map the remaining combinational logic, and finally put the FFs back. These approaches ignore the sequential nature of a circuit and assume the positions of the FFs are fixed. However, FFs in a sequential circuit can be reposistioned by a functionality-preserving transformation called retiming. As a result, existing approaches can only consider a very small portion of the available solution space. We propose in this paper a novel approach to the technology mapping problem. In our approach, retiming is integrated into the technology mapping process so as to consider the full solution space. We then present a polynomial technology mapping algorithm that, for a given circuit, produces a mapping solution with the minimum clock period among all possible ways of retiming. The effectiveness of the algorithm is also demonstrated experimentally.
Algorithm 786: multiple-precision complex arithmetic and functions
Authors: Smith David M.
Published: July 2002

This article describes a collection of Fortran routines for multiple-precision complex arithmetic and elementary functions. The package provides good exception handling, flexible input and output, trace features, and results that are almost always correctly rounded. For best efficiency on different machines, the user can change the arithmetic type used to represent the multiple-precision numbers.
A Mechanical Analysis of the Cyclic Structure of Undirected Linear Graphs
Authors: Welch John T.
Published: July 2002

A method of finding every cycle of an undirected linear graph by computation, rather than search, is presented. The method consists of three algorithms. The first produces a fundamental set of cycles from which all others can be generated. The second groups these cycles according to the nonseparable subgraphs of the original graph, and produces an ordering among groups that satisfies a condition required for the third algorithm. The third algorithm generates all and only cycles of the graph, without duplicates.
File Organization: On the Selection of Random Access Index Points for Sequential Files
Authors: Ghosh S. P. , Senko M. E.
Published: July 2002

The construction of a hierarchy of indexes (the indexed sequential access method) is one means of providing rapid random access to sequential files. An examination is made of the consequences of partially or completely replacing one or more index levels by linear interpolation procedures. For all possible configurations of the several types of key distributions investigated, linear interpolation on the average provides significant performance improvements. Typically, the two accesses required to obtain track index and data are reduced to 1.1 to 1.7 accesses per record. Extremely unusual key distribution will, however, raise the number of accesses required above 2.
Generalized Feedback Shift Register Pseudorandom Number Algorithm
Authors: Lewis T. G. , Payne W. H.
Published: July 2002

The generalized feedback shift register pseudorandom number algorithm has several advantages over all other pseudorandom number generators. These advantages are: (1) it produces multidimensional pseudorandom numbers; (2) it has an arbitrarily long period independent of the word size of the computer on which it is implemented; (3) it is faster than other pseudorandom number generators; (4) the “same” floating-point pseudorandom number sequence is obtained on any machine, that is, the high order mantissa bits of each pseudorandom number agree on all machines— examples are given for IBM 360, Sperry-Rand-Univac 1108, Control Data 6000, and Hewlett-Packard 2100 series computers; (5) it can be coded in compiler languages (it is portable); (6) the algorithm is easily implemented in microcode and has been programmed for an Interdata computer.
Nonlinear programming on generalized networks
Authors: Ahlfeld David P. , Mulvey John M. , Dembo Ron S. , Zenios Stavros A.
Published: July 2002

We describe a specialization of the primal truncated Newton algorithm for solving nonlinear optimization problems on networks with gains. The algorithm and its implementation are able to capitalize on the special structure of the constraints. Extensive computational tests show that the algorithm is capable of solving very large problems. Testing of numerous tactical issues are described, including maximal basis, projected line search, and pivot strategies. Comparisons with NLPNET, a nonlinear network code, and MINOS, a general-purpose nonlinear programming code, are also included.
Scan line methods for displaying parametrically defined surfaces
Authors: Lane Jeffrey M. , Carpenter Loren C. , Whitted Turner , Blinn James F.
Published: July 2002

This paper presents three scan line methods for drawing pictures of parametrically defined surfaces. A scan line algorithm is characterized by the order in which it generates the picture elements of the image. These are generated left to right, top to bottom in much the same way as a picture is scanned out on a TV screen. Parametrically defined surfaces are those generated by a set of bivariate functions defining the
X
,
Y
, and
Z
position of points on the surface. The primary driving mechanism behind such an algorithm is the inversion of the functions used to define the surface. In this paper, three different methods for doing the numerical inversion are presented along with an overview of scan line methods.