bluuebunny/crossref_metadata_2025 huggingface dataset:
OCKHAM'S RAZOR MODELING OF THE MATRISOME CHANNELS OF THE BASAL GANGLIA THALAMOCORTICAL LOOPS
Authors: LŐRINCZ ANDRÁS , HÉVÍZI GYÖRGY , SZEPESVÁRI CSABA
Published: July 2002

A functional model of the basal ganglia-thalamocortical (BTC) loops is described. In our modeling effort, we try to minimize the complexity of our starting hypotheses. For that reason, we call this type of modeling Ockham's razor modeling. We have the additional constraint that the starting assumptions should not contradict experimental findings about the brain. First assumption: The brain lacks direct representation of paths but represents directions (called speed fields in control theory). Then control should be concerned with speed-field tracking (SFT). Second assumption: Control signals are delivered upon differencing in competing parallel channels of the BTC loops. This is modeled by extending SFT with differencing that gives rise to the robust Static and Dynamic State (SDS) feedback-controlling scheme. Third assumption: Control signals are expressed in terms of a gelatinous medium surrounding the limbs. This is modeled by expressing parameters of motion in parameters of the external space. We show that corollaries of the model fit properties of the BTC loops. The SDS provides proper identification of motion related neuronal groups of the putamen. Local minima arise during the controlling process that works in external space. The model explains the presence of parallel channels as the means to avoiding such local minima. Stability conditions of the SDS predict that the initial phase of learning is mostly concerned with selection of sign for the inverse dynamics. The model provides a scalable controller. State description in external space instead of configurational space reduces the dimensionality problem. Falsifying experiment is suggested. Computer experiments demonstrate the feasibility of the approach. We argue that the resulting scheme has a straightforward connectionist representation exhibiting population coding and Hebbian learning properties.
FINE STRUCTURES OF SOME LOW-LYING EXCITED STATES FOR Be-LIKE SYSTEM
Authors: HAN LIHONG , GOU BINGCONG , HU HAIYUN , WANG FEI
Published: July 2002

The fine structure energies and fine structure splittings of some low-lying excited states of the beryllium isoelectronic sequence (Z = 4–20) are calculated with multi-configuration-interaction method and restricted variation method. The relativistic corrections and mass polarization are included. The results are in good agreement with other theoretical and experimental data.
DERIVING PROCESS NETWORKS FROM NESTED LOOP ALGORITHMS
Authors: RIJPKEMA EDWIN , DEPRETTERE ED F. , KIENHUIS BART
Published: July 2002

High level modeling and (quantitative) performance analysis of signal processing systems requires high level models for the applications (algorithms) and the implementations (architectures), a mapping of the former into the latter, and a simulator for fast execution of the whole. Signal processing algorithms are very often nested-loop algorithms with a high degree of inherent parallelism. This paper presents – for such applications – a suitable application model and a method to convert a given imperative executable specification to a specification in terms of this application model. The methods and tools are illustrated by means of an example.
$\mathcal{HDC}$: A HIGHER-ORDER LANGUAGE FOR DIVIDE-AND-CONQUER
Authors: HERRMANN CHRISTOPH A. , LENGAUER CHRISTIAN
Published: July 2002

We propose the higher-order functional style for the parallel programming of algorithms. The functional language [Formula: see text], a subset of the language Haskell, facilitates the clean integration of skeletons into a functional program. Skeletons are predefined programming schemata with an efficient parallel implementation. We report on our compiler, which translates [Formula: see text] programs into C+MPI, especially on the design decisions we made. Two small examples, the n queens problem and Karatsuba's polynomial multiplication, are presented to demonstrate the programming comfort and the speedup one can obtain.
RENORMALIZATION GROUP FOR SPIN GLASSES
Authors: ROSATI F.
Published: July 2002

A renormalization group transformation suitable for spin glasses, and more generally for disordered systems, is presented. The approach is non-standard for two reasons. 1. The coarse graining transformation is performed on the distribution of site overlaps, which clearly is not a Boltzmann-Gibbs distribution. 2. The additional interactions are realized introducing a gauge-field disorder distribution, while the Hamiltonian is kept fixed. Universality classes are thus naturally defined on a large set of models, going from ℤ2 and Gaussian spin glasses to Ising and fully frustrated models, and others. The role of frustration and of the deconfinement transition can also be analysed in terms of fixed points. The proposed analysis is tested numerically on the ℤ2 Edwards-Anderson model in d=4. Good estimates of the critical index ν and of Tc are obtained, and an RG flow diagram is sketched for the first time.
DIRECT CP ASYMMETRY IN INCLUSIVE RARE B-DECAYS IN 2HDM
Authors: ASATRYAN H. H. , ASATRIAN H. M. , YEGHIYAN G. K. , SAVVIDY G. K.
Published: July 2002

The direct CP asymmetry in the inclusive B → Xdγ and B → Xde+e-decays is investigated in the two-Higgs doublet extension of the Standard Model (2HDM). The investigation is performed in the lowest nonvanishing order of the perturbation theory using the existing restrictions on the 2HDM parameters space. It is shown that the direct CP asymmetry in the B → Xdγ decay can deviate significantly from the Standard Model predictions. In the presence of only one source of CP violation (the CKM matrix weak phase) aCP(B → Xdγ) can have the sign opposite to that in the SM. The new source of CP violation can make |aCP(B → Xdγ)| arbitrary small (unlike the SM case) and hence unmeasurable. Quantitatively, the obtained results suffer from the uncertainty of the choice of renormalization scale. As for the B → Xde+e-rate asymmetry, its renormalization scale dependence in the lowest nonvanishing order does not allow to conclude if this quantity is efficient for testing new physics beyond the Standard Model.
ELIMINATION OF THE FIELD DEGREES OF FREEDOM IN RELATIVISTIC SYSTEM OF POINTLIKE CHARGES
Authors: NAZARENKO A.
Published: July 2002

The Hamiltonian formulation of relativistic system of charged particles plus electromagnetic field in the Dirac instant and front forms of dynamics is considered. The canonical realization of the Poincaré algebra in the terms of gauge-invariant variables is found. The procedure of elimination of the field degrees of freedom within the framework of the Dirac constraint theory is elaborated up to the first order in the coupling constant. The Poincaré generators in the terms of particle variables are obtained. The relations between the instant form generators and front form ones are examined. The instant form Hamiltonian in the weak-relativistic approximation results in the Darwin Hamiltonian.
QUINTESSENCE MODEL AND COSMIC MICROWAVE BACKGROUND
Authors: FRAMPTON PAUL H.
Published: July 2002

A particular kind of quintessence is considered with equation of motion pQ/ρQ = -1, corresponding to a cosmological term with the time-dependece Λ(t) = Λ(t0) (R(t0)/R(t))P and we examine how values of Ωm and ΩΛ depend on P.
PROGRESS WITH THE JLC/NLC X-BAND LINEAR COLLIDER DESIGN
Authors: Raubenheimer T. O.
Published: July 2002

An electron/positron linear collider with a center-of-mass energy between 0.5 and 1 TeV would be an important complement to the physics program of the LHC in the next decade. The Next Linear Collider (NLC) is being designed by a US collaboration (FNAL, LBNL, LLNL, and SLAC) which is working closely with the Japanese collaboration that is designing the Japanese Linear Collider (JLC). This paper will discuss the technical difficulties encountered as well as the changes that have been made to the NLC design over the last year. These changes include improvements to the X-band rf system as well as modifications to the beam delivery system. The net effect has been to reduce the length of the collider from about 32 km to 25 km and to reduce the number of klystrons and modulators by a factor of two. Together these lead to significant cost savings.
EXACT PARTITION FUNCTION FOR THE POTTS MODEL WITH NEXT-NEAREST NEIGHBOR COUPLINGS ON ARBITRARY-LENGTH LADDERS
Authors: CHANG SHU-CHIUAN , SHROCK ROBERT
Published: July 2002

We present exact calculations of partition function Z of the q-state Potts model with next-nearest-neighbor spin–spin couplings, both for the ferromagnetic and antiferromagnetic case, for arbitrary temperature, on n-vertex ladders with free, cyclic, and Möbius longitudinal boundary conditions. The free energy is calculated exactly for the infinite-length limit of these strip graphs and the thermodynamics is discussed. Considering the full generalization to arbitrary complex q and temperature, we determine the singular locus ℬ in the corresponding [Formula: see text] space, arising as the accumulation set of partition function zeros as n → ∞.
FORMATION OF SILICON NANOCRYSTALS AND INTERFACE ISLANDS IN SYNCHROTRON-RADIATION-IRRADIATED SiO2 FILMS ON Si(100)
Authors: AKAZAWA H.
Published: July 2002

Nucleation of nanocrystalline Si (nc-Si) in SiO 2 films irradiated with vacuum ultraviolet and soft x-ray radiation has been investigated by using in-situ spectroscopic ellipsometry, cross-sectional transmission electron microscopy, reflectivity measurement, and reflection high-energy electron diffraction. The formation of nc-Si proceeds in the repetition of two steps: (i) conversion of SiO 2 to SiO x through the creation of Frenkel pairs and the subsequent desorption of O 2, and (ii) separation of SiO x into Si and SiO 2 domains. The average diameter of nc-Si increases from 2 to 10 nm as the irradiation temperature increases from 470°C to 610°C. Above 700°C, oxide domains are gone and solid-phase recrystallization produces Si islands terminated by the Si(100) substrate interface. At temperatures higher than 800°C, these islands collapse and an atomically flat Si(100) interface appears.
Photoinduced infrared absorption spectra of CuCl quantum dots in NaCl
Authors: Yamanaka K. , Edamatsu K. , Itoh T.
Published: July 2002

We have studied infrared transient absorption spectra of CuCl QDs grown inside a NaCl matrix under tunable UV laser excitation on resonance with the confined excitons. In addition to the transient excited-state absorption, there appears induced IR absorption with lifetime much longer than that of the confined exciton. The peak energy remains at ~0.3 eV regardless of the QD size. The optical density is proportional to the square root of the UV laser power. The decay of the induced absorption is logarithmic on time and is accelerated by the irradiation of light below the band gap. We assign this absorption to be originated from the electron-bound defect center called I e center generated in the NaCl side of the interface and discuss it phenomenon in relation with photo-irradiation effects, such as photofatigue, blinking of the luminescence and hole burning.
GRAIN GROWTH DEPENDENCE OF MICROSTRUCTURE IN La0.67Ba0.33MnO3+δ OXIDES
Authors: LI S. , ZHANG Y. B. , LIANG M. H. , SUN C. Q. , WIDJAJA S. , HING P.
Published: July 2002

Grain growth dependence of microstructure in La 2/3 Ba 1/3 MnO 3+δ oxides has been studied in detail. The result shows that the crystals grew along three vertical axes with a concentric terrace pattern in the sample sintered at 1673K while the oxides sintered at 1573K grew with a lateral growth manner. However, the concentric terrace growth pattern resulted in twin microstructure in the cooling processing and the lateral growth manner produced non-twin microstrcuture in the oxides at ambient, respectively. It was found that the oxide with twin microstructure has a much higher saturation magnetization than the non-twin oxide. This may be due to the easier alignment of the domains in the twin-grained oxide through the rearrangement of dislocations in twin-boundaries.
THE CONDITIONAL TUNNELING TIME FOR REFLECTION USING THE WKB WAVE-FUNCTION
Authors: RAMAKRISHNA S. ANANTHA , JAYANNAVAR A. M.
Published: July 2002

We derive an expression for the conditional time for the reflection of a wave from an arbitrary potential barrier using the WKB wavefunction in the barrier region. Our result indicates that the conditional times for transmission and reflection are equal for a symmetric barrier within the validity of the WKB approach.
PHOTOEMISSION STUDY OF THE INTRA-UNIT-CELL COUPLING IN A TRILAYER CUPRATE
Authors: FENG D. L. , EISAKI H. , SHEN K. M. , DAMASCELLI A. , KIM C. , LU D. H. , SHEN Z.-X. , SHIMIZU K. , SHIMOYAMA J.-I. , KISHIO K. , MOTOYAMA N. , KANEKO N. , GREVEN M. , GU G. D.
Published: July 2002

The electronic structures of the nearly optimally doped single-layer, bilayer and trilayer Bi-based cuprates are investigated by angle-resolved photoemission spectroscopy. A lineshape analysis of data taken for different photon energies indicates that the interlayer coupling within the trilayer is not stronger than its counterpart in the bilayer system. This suggests that the higher T c of the trilayer cuprate superconductors is not due to an enhancement of the coupling strength between the neighboring CuO2 planes within each unit cell.
INTEGRABLE XYZ HAMILTONIAN WITH NEXT-NEAREST-NEIGHBOR INTERACTION
Authors: LAI YUN-ZHONG , HU ZHAN-NING , LIANG J. Q. , PU FU-CHO
Published: July 2002

In this paper, we construct a Hamiltonian of the impurity model with next-nearest-neighbor interaction within the framework of the open boundary Heisenberg XYZ spin chain. This impurity model is an exactly solved one and it degenerates to the integrable XXZ impurity model under the triangular limit. It is the first approach to add the impurities and next-nearest-neighbor interaction to the integrable completely anisotropic Heisenberg spin chain. We find also that the impurity parameters in the bulk are real when the cross parameter is imaginary for the Hermitian Hamiltonian, or vice versa, when the next-nearest-neighbor interaction is introduced. The eigenvalue of the Hamiltonian and the Bethe ansatz equations for the trigonometric limit case are derived also.
CORRELATION BETWEEN THE POTENTIAL CONTRIBUTION AND MAGNETIC TRANSPORT PROPERTIES FOR MAGNETIC MULTILAYERS
Authors: ZHANG LING-YUN , SUN HONG , LI BO-ZANG , PU FU-CHO
Published: July 2002

We discuss the exchange potential and impurity scattering potential effect on the magnetic transport properties of magnetic multilayers. In the case of Hartree–Fork approximation, the model Hamiltonian with respect to the magnetization and potential contribution is presented. The expression of giant magnetoresistance is obtained by considering both interface and bulk magnetization contribution. The results show that the giant magnetoresistance in magnetic multilayer is different for different layer thickness. Meanwhile, we also clarify the interface and bulk contribution of the giant magnetoresistance in magnetic multilayer for different exchange potential and impurity scattering potential.
BOSE CONDENSATION AND ELECTRON PAIRING IN ONE-DIMENSIONAL HUBBARD MODEL
Authors: Kocharian A. N. , Yang C. , Chiang Y. L.
Published: July 2002

The ground-state properties in one-dimensional Hubbard model with on-site attraction and repulsion of electrons in the presence of magnetic field h are calculated by means of the exact Bethe-ansatz formalism and the generalized self-consistent field (GSCF) approach for general electron concentrations n and arbitrary interaction strength. The ground-state properties, including the energy, the average spin (magnetization) and the kinetic energy are compared over a wide range of parameter space. The GSCF theory is in qualitative and in some cases in good quantitative agreement with the exact results. The GSCF theory at U≤0 (or U≥0) differentiates the spin (or charge) energy gap from the BCS (or antiferromagnetic) order parameter and suggests a smooth crossover from the phase with the itinerant BCS-like behavior to the Bose condensation regime of the local pairs.
HIGH RESOLUTION IBA ANALYSIS OF SPIN DEPENDENT TUNNEL JUNCTIONS
Authors: BARRADAS N. P. , DA SILVA M. F. , SOARES J. C. , KREISSIG U. , ARNOLDBIK W. M. , CARDOSO S. , FREITAS P. P.
Published: July 2002

Spin dependent tunnel junctions are of technological interest for applications in magnetic non-volatile random access memories due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical structures are Si/Al 2 O 3600Å/ Ta 70Å/ NiFe 70Å/ CoFe 30Å/ AlxNyOz t/CoFe 40Å/ MnIr 200Å/ Ta 30Å, with t = 6-30 Å, annealed to temperatures up to 400°C. The properties of these junctions are strongly influenced by the layer thicknesses and composition, and change on annealing. Standard technology for integrated circuits requires annealing at 400-450°C, and an understanding of the changing magnetic properties of the tunnel junction requires detailed knowledge of the behavior of the different interfaces. We performed Rutherford backscattering (RBS) experiments at a grazing angle of incidence to achieve high depth resolution for the transition metals signal. The composition of the AIxNyOz layers was determined with Heavy Ion Elastic Recoil Dtection Analysis. We also performed heavy ion RBS experiments for improved mass resolution. The thickness and composition of the individual layers is determined, and a high sensitivity to diffusion and layer intermixing is achieved.
Energetic Deposition and Surface Characterization of Thin Carbon Films on Nickel
Authors: Adhi K. P. , Sharma A. K. , Wagal S. S. , Joag D. S. , Kulkarni S. K.
Published: July 2002

Thin films deposited by rapidly quenching the energetic carbon species impinging onto polycrystalline nickel substrates were studied by X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and field ion microscopy (FIM). XPS and EELS of the deposited films, when compared with those recorded for graphite and synthetic diamond, indicated the growth of diamond like carbon films and amorphic diamond (a-D) phase. Surface atomic arrangement in the film is observed by FIM which magnifies the surface ~105 to 106 times. Facetting, lack of graphitic ordering, stability of the image inspite of raising or lowering the voltage about the field evaporation voltage indicate that the field ion micrograph is that of a-D.
Collective Spontaneous Emission in a q-Deformed Dicke Model
Authors: Mancini Stefano , Man'ko Vladimir I. , Tombesi Paolo
Published: July 2002

The q-deformation of a single quantized radiation mode interacting with a collection of two level atoms is introduced, analyzing its effects on the cooperative behavior of the system.
HYSTERESIS STUDIES IN MAPS
Authors: RAI RENUKA , SINGH HARJINDER
Published: July 2002

We define magnetization for a 1D bistable map driven by periodic and random forces. Numerical simulations are carried out to investigate the effect of drive amplitude and frequency and noise strength on the area of the hysteresis loop. We observe that for a given amplitude, the profile of the frequency plotted against the corresponding optimal noise for maximum synchronization, D max , can be modeled as an Arrhenius like behaviour.
MAGNETIC POLARONS MEDIATED PERCOLATIVE PHASE TRANSITION IN MANGANITES
Authors: LYUKSYUTOV I. F. , POKROVSKY V. L.
Published: July 2002

We discuss possible models for describing the metal-insulator phase transition coupled with paramagnetic-ferromagnetic phase transition in manganites. We argue that current models have apparent drawbacks. As a way to explain experiments we introduce the magnetic (large) polaron model. In this model, the conductivity appears as a result of percolative overlapping of magnetic polarons which coexist with small (Jahn-Teller) polarons. We compare this model with the experimental data.
EFFECTIVE COMPUTER VISION INSTRUCTION THROUGH EXPERIMENTAL LEARNING EXPERIENCES
Authors: GREWE LYNNE
Published: July 2002

The inclusion of video and image-based communications over the Internet and the explosion of multimedia in the last two decades have lead to a demand for education in computer imaging and vision at the undergraduate level. A curriculum developed for such an audience that features experimental-based learning experiences as a vehicle for student education and exploration in the field of computer imaging/vision is discussed. As computer imaging/vision has many unsolved problems and challenges, it is crucial that we impart to students not only knowledge but, the investigative skills necessary for tackling these problems. This paper presents the results of student work on a number of such experiences involving both software development and vision hardware system configuration. The paper culminates with the results of a student-composed survey discussing one of these experimental learning experiences, which illustrates the usefulness of this form of learning.
CHAOTIFICATION VIA ARBITRARILY SMALL FEEDBACK CONTROLS: THEORY, METHOD, AND APPLICATIONS
Authors: WANG XIAO FAN , CHEN GUANRONG
Published: July 2002

In this paper, the problem of making a stable nonlinear autonomous system chaotic or enhancing the existing chaos of an originally chaotic system by using a small-amplitude feedback controller is studied. The designed controller is a linear feedback controller composed with a nonlinear modulo or sawtooth function, which can lead to uniformly bounded state vectors of the controlled system with positive Lyapunov exponents, thereby yielding chaotic dynamics. We mathematically prove that the controlled system is indeed chaotic in the sense of Li and Yorke. A few potential applications of the new chaotification algorithm are briefly discussed.
TRACKING SUSTAINED CHAOS
Authors: SCHWARTZ IRA B. , TRIANDAF IOANA
Published: July 2002

Tracking unstable periodic states first introduced in [Schwartz & Triandaf, 1992] is the process of continuing unstable solutions as a systems parameter is varied in experiments. The tracked dynamical objects have been periodic saddles of well-defined finite periods. However, other saddles, such as chaotic saddles, have not been successfully "tracked," or continued. In this paper, we introduce a new yet simple method which can be used to track chaotic saddles in dynamical systems, which allows an experimentalist to sustain chaotic transients far away from crisis parameter values. The method is illustrated on a periodically driven CO 2 laser.
CONTROL OF NONLINEAR DYNAMICS: WHERE DO MODELS FIT IN?
Authors: AGUIRRE LUIS A. , TÔRRES LEONARDO A. B.
Published: July 2002

Several control design techniques applied to nonlinear dynamics and chaos assume that a model of the uncontrolled dynamics is available. The extent to which the controller performance is influenced by the model largely depends on many factors such as control effort and the control objective. It is suggested that model quality and control gains, which are strongly related to the control effort, define an uncertainty region in state space around the goal dynamics. For the unrealistic, but frequently assumed case in which model accuracy and admissible control effort are unlimited and there is no noise, the uncertainty region reduces to zero. But what happens when the model is realistically inaccurate, the maximum control effort is limited and the system state is observed with some noise? The objective of this paper is to discuss some issues related to model-based control techniques for nonlinear dynamical systems and to try to shed some light on questions like: How does model accuracy influence control performance? How can model inaccuracies be compensated for in the design? Which limits exist for such compensation? Extensive simulations are carried out and the results suggest that the requirements on nonlinear models might be different if the final objective is the reconstruction of nonlinear dynamics or controller design, and that even linear models can be used in some control design problems.
BIFURCATION ANALYSIS OF A PWL CHAOTIC CIRCUIT BASED ON HYSTERESIS THROUGH A ONE-DIMENSIONAL MAP
Authors: BIZZARRI FEDERICO , STORACE MARCO , GARDINI LAURA , LUPINI RENZO
Published: July 2002

Bifurcations in the dynamics of a chaotic circuit based on hysteresis are evaluated. Owing to the piecewise-linear nature of the nonlinear elements of the circuit, such bifurcations are discussed by resorting to a suitable one-dimensional map. As the ordinary differential equations governing the circuit are piecewise linear, the analytical expressions of their solutions can be derived in each linear region. Consequently, the proposed results have been obtained not by resorting to numerical integration, but by properly connecting pieces of planar flows. The bifurcation analysis is carried out by varying one of the three dimensionless parameters that the system of normalized circuit equations depends on. Local and global bifurcations, regular and chaotic asymptotic behaviors are pointed out by analyzing both the one-dimensional map and the three-dimensional flow induced by the circuit dynamics.
FINITE PRESENTABILITY OF SEMIGROUP CONSTRUCTIONS
Authors: ARAÚJO ISABEL M.
Published: July 2002

We survey some recent results concerning finite presentability of several semigroup constructions. Namely we study direct products, wreath products, Rees matrix semigroups, Bruck–Reilly extensions, general products and strong semilattices of semigroups.
HOMOTHETIC WYMAN SPACETIMES
Authors: CLAYTON M. A.
Published: July 2002

The time-dependent, spherically symmetric, Wyman sector of the Unified Field Theories is shown to be equivalent to a self-gravitating scalar field with a positive-definite, repulsive interaction potential. A homothetic symmetry is imposed on the fundamental tensor, and the resulting autonomous system is numerically integrated. Near the critical point (between the collapsing and noncollapsing spacetimes) the system displays an approximately periodic alternation between collapsing and dispersive epochs.
ON LÉVY STABLE AND SEMISTABLE DISTRIBUTIONS
Authors: HUILLET THIERRY , PORZIO ANNA , ALAYA MOHAMED BEN
Published: July 2002

This work emphasizes the special role played by semistable and log-semistable distributions as relevant statistical models of various observable and "internal" variables in physics. Besides of their representation, some of their remarkable properties (chiefly semi-self-similarity) are displayed in some detail. One of their characteristic features is a log-periodic variation of the scale parameter which appears in the standard Lévy α-stable distributions whose Fourier representations are re-derived in a self-contained way.
STRUCTURE AND THERMAL STABILITY OF THE SULFIDE OVERLAYERS ON CH3CSNH2-PASSIVATED GaAs(100) SURFACES
Authors: XU F. Q. , LU E. D. , PAN H. B. , XIE C. K. , XU P. S. , ZHANG X. Y.
Published: July 2002

Chemically sulfur passivation of GaAs(100) by thioacetamide ( CH 3 CSNH 2) has been studied using synchrotron radiation photoemission spectroscopy (SRPES), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The measurement of SRPES and AES showed that the top layer of native oxides over GaAs(100) was removed and the sulfides of Ga and As were formed after the passivation process. The thermal stability and surface structure have also been studied by annealing the passivated samples at different temperatures. We found that the surface sulfides could be removed gradually; as a result, a clean, ordered and thus Fermi level unpinning surface was finally achieved. The surface restructures with GaAs(100)–S(2×1) and 4×1 LEED patterns were observed on annealing above 260°C and at 550°C respectively.
OSCILLATIONS IN CATALYTIC REACTIONS: CARBON MODEL WITH ADSORBATE–ADSORBATE LATERAL INTERACTIONS
Authors: ZHDANOV V. P.
Published: July 2002

We present Monte Carlo simulations of kinetic oscillations in CO oxidation on Pt in the framework of the model including carbon deposition on and removal from the catalyst surface. Some of the elementary reaction steps (such as carbon removal and diffusion) are considered to be dependent on adsorbate–adsorbate lateral interactions. The results obtained indicate that the lateral interactions may play a key role in kinetic oscillations. In particular, the interactions may result in the appearance of oscillations and also in their suppression. The former takes place if the interactions form a feedback between the high and low reactive states of the bistable catalytic cycle. The latter may be connected, for example, with the formation of carbon islands on the surface.
DEFORMATION TWINNING IN Bi-Sb CRYSTALS UNDER DYNAMIC INDENTATION
Authors: SHAH R. C.
Published: July 2002

Bi–Sb single crystals (with Sb concentration varied up to 30 at. %) have been subjected to impact loading in the form of dynamic indentation on their (111) cleavage planes. The resulting mechanical twins are the theme of this report. The tensile and compressive stresses developed by the spherical indenter employed have been differentiated with respect to their role in producing the twins. While the twins produced in the crystals with Sb ≤15 at. % are interpreted as being due to tensile stresses, those in the crystals with Sb>15 at. % are found to be due to compressive stresses.
AN INFRARED-SPECTROSCOPIC STUDY OF METHYL IODIDE AND METHYLENE IODIDE ON Ag(111)
Authors: WU G. , STACCHIOLA D. , COLLINS M. , TYSOE W. T.
Published: July 2002

The adsorption of methylene iodide and methyl iodide is studied on Ag(111) using reflection-absorption infrared spectroscopy. Molecular methylene iodide adsorbs in a random orientation at 80 K and converts into a species with the H–C–H plane adsorbed perpendicular to the surface on heating to 155 K, and also dissociates into iodomethyl species. These undergo further decomposition eventually to form ethylene, although no methylene species are detected on the surface. Methyl iodide forms both multilayers and a metastable state on Ag(111) at 180 K, where the C–I axis of the metastable state is oriented nearly parallel to the surface. Infrared data suggest that the metastable state both desorbs almost simultaneously with the multilayer and converts to adsorbed methyl iodide with the C–I axis oriented nearly perpendicular to the surface. The latter species decomposes into adsorbed methyl fragments and adsorbed iodine where the frequency of the methyl bending mode for CH3(ads) and for CH3I(ads) are identical at 1230 cm -1.
OPTICAL TRANSITIONS IN A PARABOLIC GaAs/Ga1-xAlxAs SUPERLATTICES
Authors: ERKOÇ ŞAKIR , KÖKTEN HATICE
Published: July 2002

We have performed self-consistent field (SCF) calculations of the electronic structure of GaAs/Ga 1-x Al x As superlattices with parabolic potential profile within the effective mass theory. We have calculated the optical transition matrix elements involving transitions from the hole states to the electron states, and we have also computed the oscillator strength matrix elements for the transitions among the electron states.
MONTE CARLO SIMULATION OF THE ADSORBATE- ASSISTED ADSORPTION IN THE CASE OF CO/ZnO
Authors: BURGHAUS U.
Published: July 2002

Recently, a detailed study of the adsorption dynamics of CO on metal oxides, i.e. for the polar ZnO surfaces, has been published [Becker et al., JCP113, 6334 (2000)]. For both polar surfaces, an increase in the adsorption probabilities with increasing surface coverage (adsorbate-assisted adsorption) has been observed. A Monte Carlo (MC) version of the so-called modified Kisliuk model is presented, which accounts for the main features observed experimentally. The model, which includes two fit parameters, is based on the differences in the mass differences in the mass mismatch of the gas phase species and the surfaces. Therefore, in particular, the polar surfaces of ZnO, which differ by the mass of the atoms in the first surface layer, are perfectly suited for discussing the proposed MC algorithm.
A CASE OF A NEW SYNDROME OR A VARIANT OF THE RARE POPLITEAL PTERYGIUM SYNDROME
Authors: Öğün Tunç Cevat , Tosun Zekeriya , Arazi Mehmet , Kapicioğlu M. I. Safa
Published: July 2002

The popliteal pterygium syndrome is very rare, and is characterized by a congenital popliteal web accompanying the genitourinary, craniofacial, and musculoskeletal anomalies. We described a case of presumably popliteal pterygium syndrome with severe right popliteal web, right renal agenesis, left bifurcated ninth rib, urethral orifice in the vagina, right presacral discoloration resembling A-V malformation, imperforate anus, skin dimple in the left gluteal region, right calcaneovalgus foot with supernumerary digits and aberrant profunda femoris artery. This is the first report of this combination in the pertinent literature.
THE STOCHASTIC BURGERS EQUATION: FINITE MOMENTS AND SMOOTHNESS OF THE DENSITY
Authors: LEÓN JORGE A. , NUALART D. , PETTERSSON ROGER
Published: July 2002

We apply a stochastic version of the Hopf–Cole transformation to the solution of the stochastic Burgers equation with Dirichlet boundary conditions driven by a space–time Gaussian white noise. As a consequence, we deduce that the solution of the Burgers equation has moments of all orders.

Using the techniques of the Malliavin calculus we show that if the dispersion is state-independent, then the solution of the stochastic Burgers equation has a smooth density at any point (t, x), with t>0 and x ∈(0,1).
ENVIRONMENTAL ASSESSMENT IN SRI LANKA: ITS STATUS AND THE POTENTIAL FOR THE INTRODUCTION OF STRATEGIC ENVIRONMENTAL ASSESSMENT
Authors: MACKEE JAMIE , OBBARD JEFFREY , BRIFFETT CLIVE
Published: July 2002

Sri Lanka is an island republic situated off the southern tip of the Indian subcontinent. It has a long and continuous recorded history dating back approximately 2,500 years, and claims to have one of the oldest nature reserves in the world.

However, Environmental Assessment (EA) in the country has a much shorter history. This can be traced back to the early eighties and the dramatic change in economic policies when initial legislation was enacted. The final three amendments to this legislation making EAs mandatory came into force in 1993, although there were some EIAs predating this legislation that were voluntary and prepared for large infrastructure projects. Since then, a number of EAs and Initial Environmental Examinations (IEEs) have been prepared for a wide variety of projects with varying degrees of success. Despite this, the natural environment is still undergoing rapid deterioration, while proper implementation of good EIA practice is still needed.

The research presented in this paper, which is part of a larger study on implementation of EA and Strategic Environmental Assessment (SEA) in Asia, discusses the current status of environmental assessment in Sri Lanka based on information collected from field visits and interviews, as well as published and unpublished data. EA practices are discussed in the context of investigating the potential for introducing the process of SEA in Sri Lanka.

Two case studies demonstrate the consideration of environmental issues in the development of strategic sectoral policies programmes and plans. These case studies highlight the potential benefits of an effective SEA strategy in Sri Lanka, as well as identifying some of the weaknesses in the current EA system within the country.

Findings from the study suggest that rapid industrialisation combined with poor monitoring, a dearth of technically skilled personnel, the lack of baseline information and the continuing protracted civil war are key factors restricting the successful implementation of the EA process. It is from this perspective that the paper looks at the possible role that SEA may play in overcoming the failings of EA.
ENVIRONMENTAL ANALYSIS OF THE LOWER CAMAQUÃ RIVER WATERSHED (BRAZIL) — A STUDY OF PLANNING AND ENVIRONMENTAL EDUCATION
Authors: KALIKOSKI DANIELA COSWIG , ASMUS MILTON L. , LAVKULICH LES
Published: July 2002

The Lower Camaquã River Watershed is settled within two major geologic systems: the Pre-Cambrian basement and the Southern Brazilian Coastal Plain. Geological, environmental and socio-economic characteristics of this section of the watershed provide a heterogeneous landscape mosaic of interconnected natural and anthropic elements. In this work, the Sapato Creek watershed is used as a case study for an environmental analysis of the Lower Camaquã system. Landscape elements were identified, described and modelled as a way to understand their structure and dynamics. Satellite images (1:100,000) and field checking were utilised in the characterisation of the landscape elements and identification of land use categories. The results supported the characterisation of the structural and functional organisation of the watershed, potential impacts and the suitability of land use for the system. A conceptual methodological strategy is presented as an effective tool for transferring the recommendations produced in this work to decision-makers directly involved with environmental management in the region. The strategy relies on the interaction between scientists, decision-makers and watershed stakeholders to foster the identification of possible educational actions that could lead to a rational use of land and natural resources in the watershed.
FUZZY POWER COMMAND ENHANCEMENT IN MOBILE COMMUNICATIONS SYSTEMS
Authors: GAO X. Z. , OVASKA S. J.
Published: July 2002

In this paper, we propose a fuzzy logic-based power command enhancement scheme for the mobile station in the cellular communications systems. By defining necessary linguistic terms of the power commands and corresponding fuzzy inference rules, an Embedded Fuzzy Unit (EFU) is constructed. The role of our EFU is to produce appropriate digital power commands instead of the one-bit discrete commands directly obtained from the base station. Simulations show that the EFU-based mobile station can generate considerably smoother received power at the base station. The transient overshoot and steady channel tracking error are small. Moreover, our method has the advantage of simplicity in both structure and algorithm, and is thus easy for hardware implementation.
Optimal sample cost residues for differential database batch query problems
Authors: Willard Dan E.
Published: July 2002

In many computing applications, there are several equivalent algorithms capable of performing a particular task, and no one is the most efficient under all statistical distributions of the data. In such contexts, a good heuristic is to take a sample of the database and use it to guess which procedure is likely to be the most efficient. This paper defines the very general notion of a differentiable query problem and shows that the ideal sample size for guessing the optimal choice of algorithm is
O
(
N
2/3
) for all differential problems involving approximately
N
executing steps.
Simplification rules and complete axiomatization for relational update transactions
Authors: Karabeg Dino , Vianu Victor
Published: July 2002

Relational update transactions consisting of line programs of inserts, deletes, and modifications are studied with respect to equivalence and simplification. A sound and complete set of axioms for proving transaction equivalence is exhibited. The axioms yield a set of simplification rules that can be used to optimize efficiently a large class of transactions of practical interest. The simplification rules are particularly well suited to a dynamic environment where transactions are presented in an on-line fashion, and where the time available for optimization may consist of arbitrarily short and sparse intervals.
Principles of delay-sensitive multimedia data storage retrieval
Authors: Gemmell Jim , Christodoulakis Stavros
Published: July 2002

This paper establishes some fundamental principles for the retrieval and storage of delay-sensitive multimedia data. Delay-sensitive data include digital audio, animations, and video. Retrieval of these data types from secondary storage has to satisfy certain time constraints in order to be acceptable to the user. The presentation is based on digital audio in order to provide intuition to the reader, although the results are applicable to all delay-sensitive data. A theoretical framework is developed for the real-time requirements of digital audio playback. We show how to describe these requirements in terms of the consumption rate of the audio data and the nature of the data-retrieval rate from secondary storage. Making use of this framework, bounds are derived for buffer space requirements for certain common retrieval scenarios. Storage placement strategies for multichannel synchronized data are then categorized and examined. The results presented in this paper are basic to any playback of delay-sensitive data and should assist the multimedia system designer in estimating hardware requirements and in evaluating possible design choices.
Semantics for null extended nested relations
Authors: Levene Mark , Loizou George
Published: July 2002

The nested relational model extends the flat relational model by relaxing the first normal form assumption in order to allow the modeling of complex objects. Much of the previous work on the nested relational model has concentrated on defining the data structures and query language for the model. The work done on integrity constraints in nested relations has mainly focused on characterizing subclasses of nested relations and defining normal forms for nested relations with certain desirable properties.

In this paper we define the semantics of nested relations, which may contain null values, in terms of integrity constraints, called
null extended data dependencies
, which extend functional dependencies and join dependencies encountered in flat relational database theory. We formalize incomplete information in nested relations by allowing only one unmarked
generic null value
, whose semantics we do not further specify. The motivation for the choice of a generic null is our desire to investigate only fundamental semantics which are common to all unmarked null types. This lead us to define a preorder on nested relations, which allows us to measure the relative information content of nested relations. We also define a procedure, called the
extended chase procedure
, for testing satisfaction of null extended data dependencies and for making inferences by using these null extended data dependencies. The extended chase procedure is shown to generalize the classical chase procedure, which is of major importance in flat relational database theory. As a consequence of our approach we are able to capture the novel notion of losslessness in nested relations, called herein
null extended lossless decomposition
. Finally, we show that the semantics of nested relations are a natural extension of the semantics of flat relations.
Fast text searching for regular expressions or automaton searching on tries
Authors: Baeza-Yates Ricardo A. , Gonnet Gaston H.
Published: July 2002

We present algorithms for efficient searching of regular expressions on preprocessed text, using a Patricia tree as a logical model for the index. We obtain searching algorithms that run in logarithmic expected time in the size of the text for a wide subclass of regular expressions, and in sublinear expected time for any regular expression. This is the first such algorithm to be found with this complexity.
SPRINT2D
Authors: Berzins M. , Fairlie R. , Pennington S. V. , Ware J. M. , Scales L. E.
Published: July 2002

SPRINT2D is a set of software tools for solving both steady an unsteady partial differential equations in two-space variables. The software consists of a set of coupled modules for mesh generation, spatial discretization, time integration, nonlinear equations, linear algebra, spatial adaptivity, and visualization. The software uses unstructured triangular meshes and adaptive local error control in both space and time. The class of problems solved includes systems of parabolic, elliptic, and hyperbolic equations; for the latter by use of Riemann-solver-based methods. This article describes the software and shows how the adaptive techniques may be used to increase the reliability of the solution for a Burgers' equations problem, an electrostatics problem from elastohydrodynamic lubrication, and a challenging gas jet problem.
Hierarchical schemata for relational databases
Authors: Lien Y. Edmund
Published: July 2002

Most database design methods for the relational model produce a flat database, that is, a family of relations with no explicit interrelational connections. The user of a flat database is likely to be unaware of certain interrelational semantics. In contrast, the entity-relationship model provides schema graphs as a description of the database, as well as for navigating the database. Nevertheless, the user of an entity-relationship database may still commit semantic errors, such as performing a lossy join. This paper proposes a nonflat, or hierarchical, view of relational databases. Relations are grouped together to form
relation hierarchies
in which lossless joins are explicitly shown whereas lossy joins are excluded. Relation hierarchies resemble the schema graphs in the entity-relationship model.

An approach to the design of relation hierarchies is outlined in the context of data dependencies and relational decomposition. The approach consists of two steps; each is described as an algorithm. Algorithm DEC decomposes a given universal relation according to a given set of data dependencies and produces a set of nondecomposable relation schemes. This algorithm differs from its predecessors in that it produces no redundant relation schemes. Algorithm RH further structures the relation schemes produced by Algorithm DEC into a hierarchical schema. These algorithms can be useful software tools for database designers.
High-level programming features for improving the efficiency of a relational database system
Authors: Van de Riet Reind P. , Kersten Martin L. , de Jonge Wiebren , Wasserman Anthony I.
Published: July 2002

This paper discusses some high-level language programming constructs that can be used to manipulate the relations of a relational database system efficiently. Three different constructs are described: (1) tuple identifiers that directly reference tuples of a relation; (2) cursors that may iterate over the tuples of a relation; and (3) markings, a form of temporary relation consisting of a set of tuple identifiers. In each case, attention is given to syntactic, semantic, and implementation considerations.

The use of these features is first presented within the context of the programming language PLAIN, and it is then shown how these features could be used more generally to provide database manipulation capabilities in a high-level programming language. Consideration is also given to issues of programming methodology, with an important goal being the achievement of a balance between the enforcement of good programming practices and the ability to write efficient programs.
Deadlock freedom using edge locks
Authors: Korth Henry F.
Published: July 2002

We define a series of locking protocols for database systems that all have three main features: freedom from deadlock, multiple granularity, and support for general collections of locking primitives. A rooted directed acyclic graph is used to represent multiple granularities, as in System R. Deadlock freedom is guaranteed by extending the System R protocol to require locks on edges of the graph in addition to the locks required on nodes.