bluuebunny/crossref_metadata_2025 huggingface dataset:
Genome-Wide Transcriptional Profiling Analysis of Adaptation ofBacillus subtilisto High Salinity
Authors: Steil Leif , Hoffmann Tamara , Budde Ina , Völker Uwe , Bremer Erhard
Published: October 2003

The gram-positive soil bacteriumBacillus subtilisoften faces increases in the salinity in its natural habitats. A transcriptional profiling approach was utilized to investigate both the initial reaction to a sudden increase in salinity elicited by the addition of 0.4 M NaCl and the cellular adaptation reactions to prolonged growth at high salinity (1.2 M NaCl). Following salt shock, asigBmutant displayed immediate and transient induction and repression of 75 and 51 genes, respectively. Continuous propagation of this strain in the presence of 1.2 M NaCl triggered the induction of 123 genes and led to the repression of 101 genes. In summary, our studies revealed (i) an immediate and transient induction of the SigW regulon following salt shock, (ii) a role of the DegS/DegU two-component system in sensing high salinity, (iii) a high-salinity-mediated iron limitation, and (iv) a repression of chemotaxis and motility genes by high salinity, causing severe impairment of the swarming capability ofB. subtiliscells. Initial adaptation to salt shock and continuous growth at high salinity share only a limited set of induced and repressed genes. This finding strongly suggests that these two phases of adaptation require distinctively different physiological adaptation reactions by theB. subtiliscell. The large portion of genes with unassigned functions among the high-salinity-induced or -repressed genes demonstrates that major aspects of the cellular adaptation ofB. subtilisto high salinity are unexplored so far.
Genome-Scale Analysis of the Uses of the
Escherichia coli
Genome: Model-Driven Analysis of Heterogeneous Data Sets
Authors: Allen Timothy E. , Herrgård Markus J. , Liu Mingzhu , Qiu Yu , Glasner Jeremy D. , Blattner Frederick R. , Palsson Bernhard Ø.
Published: October 2003

The recent availability of heterogeneous high-throughput data types has increased the need for scalable in silico methods with which to integrate data related to the processes of regulation, protein synthesis, and metabolism. A sequence-based framework for modeling transcription and translation in prokaryotes has been established and has been extended to study the expression state of the entire
Escherichia coli
genome. The resulting in silico analysis of the expression state highlighted three facets of gene expression in
E. coli
: (i) the metabolic resources required for genome expression and protein synthesis were found to be relatively invariant under the conditions tested; (ii) effective promoter strengths were estimated at the genome scale by using global mRNA abundance and half-life data, revealing genes subject to regulation under the experimental conditions tested; and (iii) large-scale genome location-dependent expression patterns with approximately 600-kb periodicity were detected in the
E. coli
genome based on the 49 expression data sets analyzed. These results support the notion that a structured model-driven analysis of expression data yields additional information that can be subjected to commonly used statistical analyses. The integration of heterogeneous genome-scale data (i.e., sequence, expression data, and mRNA half-life data) is readily achieved in the context of an in silico model.
Why Is Carbonic Anhydrase Essential to
Escherichia coli
?
Authors: Merlin Christophe , Masters Millicent , McAteer Sean , Coulson Andrew
Published: October 2003

The
can
(previously
yadF
) gene of
Escherichia coli
encodes a β-class carbonic anhydrase (CA), an enzyme which interconverts CO
2
and bicarbonate.Various essential metabolic processes require either CO
2
or bicarbonate and, although carbon dioxide and bicarbonate spontaneously equilibrate in solution, the low concentration of CO
2
in air and its rapid diffusion from the cell mean that insufficient bicarbonate is spontaneously made in vivo to meet metabolic and biosynthetic needs. We calculate that demand for bicarbonate is 10
3
- to 10
4
-fold greater than would be provided by uncatalyzed intracellular hydration and that enzymatic conversion of CO
2
to bicarbonate is therefore necessary for growth. We find that
can
expression is ordinarily required for growth in air. It is dispensable if the atmospheric partial pressure of CO
2
is high or during anaerobic growth in a closed vessel at low pH, where copious CO
2
is generated endogenously. CynT, the single
E. coli
Can paralog, can, when induced with azide, replace Can; also, the γ-CA from
Methanosarcina thermophila
can at least partially replace it. Expression studies showed that
can
transcription does not appear to respond to carbon dioxide concentration or to be autoregulated. However,
can
expression is influenced by growth rate and the growth cycle; it is expressed best in slow-growing cultures and at higher culture densities. Expression can vary over a 10-fold range during the growth cycle and is also elevated during starvation or heat stress.
Isolation and Characterization of Mutants of the
Bacillus subtilis
Oligopeptide Permease with Altered Specificity of Oligopeptide Transport
Authors: Solomon Jonathan , Su Laura , Shyn Stanley , Grossman Alan D.
Published: October 2003

Bacterial oligopeptide permeases are members of the large family of ATP binding cassette transporters and typically import peptides of 3 to 5 amino acids, apparently independently of sequence. Oligopeptide permeases are needed for bacteria to utilize peptides as nutrient sources and are sometimes involved in signal transduction pathways. The
Bacillus subtilis
oligopeptide permease stimulates competence development and the initiation of sporulation, at least in part, by importing specific signaling peptides. We isolated rare, partly functional mutations in
B. subtilis opp
. The mutants were resistant to a toxic tripeptide but still retained the ability to sporulate and/or become competent. The mutations, mostly in the oligopeptide binding protein located on the cell surface, affected residues whose alteration appears to change the specificity of oligopeptide transport.
The Gene
yjcG
, Cotranscribed with the Gene
acs
, Encodes an Acetate Permease in
Escherichia coli
Authors: Gimenez Rosa , Nuñez María Felisa , Badia Josefa , Aguilar Juan , Baldoma Laura
Published: October 2003

We isolated an
Escherichia coli
mutant strain that suppresses the glycolate-negative phenotype of a strain deficient in both GlcA and LldP transporters of this compound. This suppressing phenotype was assigned to
yjcG
, a gene whose function was previously unknown, which was found to encode a membrane protein able to transport glycolate. On the basis of sequence similarity, the
yjcG
gene product was classified as a member of the sodium:solute symporter family. Northern experiments revealed that
yjcG
is cotranscribed with its neighbor,
acs
, encoding acetyl coenzyme A synthetase, which is involved in the scavenging acetate. The fortuitous presence of an IS
2
element in
acs
, which impaired
yjcG
expression by polarity in our parental strain, allowed us to conclude that the alternative glycolate carrier became active after precise excision of IS
2
in the suppressed strain. The finding that
yjcG
encodes a putative membrane carrier for glycolate and the cotranscription of
yjcG
with
acs
suggested that the primary function of the
yjcG
gene product (proposed gene name,
actP
) could be acetate transport and allowed us to define an operon involved in acetate metabolism. The time course of [1,2-
14
C]acetate uptake and the results of a concentration kinetics analysis performed with cells expressing ActP or cells deficient in ActP supported the the hypothesis that this carrier is an acetate transporter and suggested that there may be another transport system for this monocarboxylate.
Nucleotide Sequence of the Integration Site of the Temperate Bacteriophage 6220, Which Carries the Shiga Toxin Gene
stx
1ox3
Authors: Koch Claudia , Hertwig Stefan , Appel Bernd
Published: October 2003

The integration site,
attR
, of the Shiga toxin-encoding phage 6220 (
stx
1ox3
) has been determined. The phage integrates into the chromosome of its
Escherichia coli
host strain, CB6220, within a gene that is homologous to gene Z2577 and encodes an oxidoreductase. This new integration site was found in different Stx1ox3-producing enterohemorrhagic
E. coli
strains, which were analyzed by PCR.
The adsorption of cyclohexanone on aluminum oxide  hydroxide powders in relation to its electrocatalytic hydrogenation
Authors: Laplante François , Bouchard Nicolas-Alexandre , Dubé Patrick , Ménard Hugues , Brossard Louis
Published: October 2003

Henry's law constants were determined for cyclohexanone adsorption onto aluminium oxide  hydroxide powders by dynamic isotherm measurements using the HPLC method. The key parameters that control cyclohexanone adsorption were established. Further, it is suggested that the amount of cyclohexanone adsorbed onto aluminium oxide  hydroxide compounds (AOHC) is of paramount importance for its electrocatalytic hydrogenation in the presence of composite nickelAOCH powders.Key words: adsorption isotherm, electrocatalytic hydrogenation (ECH), cyclohexanone, aluminum oxide  hydroxide powders.
The photochemistry of indenyl alcohols and esters: Substituent effects on the competition between ion- and radical-derived products
Authors: Pincock J A , Young I S
Published: October 2003

The photochemistry of the indenyl acetates 1 and pivalates 2, substituted with X = H, 5-CH3O, and 6-CH3O, have been examined in both methanol and cyclohexane. The precursor alcohols 3 were also found to be photoreactive. Although only radical-derived products were obtained in cyclohexane, both ion- and radical-derived products were formed in methanol. The absence of significant fluorescence emission from any of the substrates 1, 2, and 3 indicates that the excited singlet states are highly reactive. A mechanism is proposed for the ion-derived products that proceeds through direct heterolytic cleavage to give an indenyl cation  carboxylate anion pair. The indenyl cations generated are anti-aromatic in the ground state and their efficient generation by this photochemical solvolysis is in sharp contrast to the very low reactivity of related ground-state substrates. For the pivalate esters 2, an excited-state migratory decarboxylation is proposed for the formation of tert-butyl derived products.Key words: ester photochemistry, indenyl cations, indenyl radicals.
A theoretical analysis of the conformational behaviour of substituted methylenecyclohexanes
Authors: Mawhinney Robert C , Muchall Heidi M , Lessard Jean
Published: October 2003

The use of the PBE0 hybrid density functional theory method in conjunction with the COSMO solvation model allowed us to reproduce, both qualitatively and quantitatively, the experimentally observed conformational compositions of 2-substituted and 2,7-disubstituted methylenecyclohexanes. An analysis revealed several different interactions that influence the overall equilibrium. It was found that the endo (general) anomeric effect plays a significant role in the equilibrium and that the "unsaturation effect" possibly comprises two effects.Key words: conformational analysis, methylenecyclohexanes, anomeric effect, unsaturation effect.
Constructivizing Membership Proofs in Complexity Classes
Authors: Arvind V.
Published: October 2003

A computational problem is said to have the Ptime self-witnessing property if we can design a Turing machine code M such that if the problem is polynomial-time computable, then M actually encodes a polynomial-time algorithm for it. This notion captures constructivizing proofs of membership in P. In this paper we define and study analogous notions of self-witnessing corresponding to other complexity classes like DLOG, PSPACE, and NC. In particular, we show that logspace self-reducible sets are DLOG self-witnessing and wdq-self-reducible sets are PSPACE self-witnessing. As a consequence of this we derive that for any complexity class [Formula: see text], if [Formula: see text] then [Formula: see text] is constructively equal to DLOG. Likewise, we show that is PSPACE = EXP then PSPACE is constructively equal to EXP. We also show connections between the self-witnessing property and self-helping and program checking
Implementation of Information Technologies in the Teaching of "Science for the 21st Century"
Authors: Catterall S. , Goldberg M. , Lipson E. , Middleton A. , Vidali G.
Published: October 2003

We illustrate the use of World Wide Web technologies for the teaching of general science topics to undergraduate non-science majors. The newly developed course, Science for the 21st Century, consists of modules each presenting scientific topics of current interest and broad appeal. Network- and computer-based tools are used by instructors to: 1) present multimedia material in lectures; 2) produce and store Web-based modules; 3) communicate notices about the course. Students use computers to: 1) access and review lecture material; 2) explore information sources (located on our server or elsewhere) for term projects and homework assignments; 3) obtain information about the course and communicate with instructors. We describe our experiences with this course and formulate some general conclusions which might be of interest to others wishing to use network-based resources for teaching.
Networked Physics Curriculum: From Static Web to Dynamic Java
Authors: Bothun G. D. , Kevan S. D. , Micklavzina S. , Mason D.
Published: October 2003

We describe our efforts at the University of Oregon to use Web-based Instructional Technology (IT) supplemented with interactive Java virtual experiments to change the standard pedagogy associated with large, introductory undergraduate classes in physics and astronomy. We begin by examining some of the problems associated with the standard pedagogy in these classes and how these problems motivated our development of networked courseware. Although we identify and describe five empirical positive outcomes associated with IT, we conclude that the use of HTML-based course material and assignments does not substantially alter the standard pedagogy as this medium alone is not conducive to interactive exercises. To build interactivity into our courseware, we have undertaken a vigorous effort of creating Java-based experiments which are grounded in physical reality and duplicate the kinds of experiments that are done in the physical lab. In so doing, we build experimentation into a curriculum for large lecture-based classes in which the standard pedagogy and resource constraints normally preclude lab sections. The main goal is to create a networked environment where the student can easily retrieve the notes and the demonstrations that were done in class as well as to engage in experiments that are designed to illustrate basic principles. In so doing, we hope to move to a more learner-centered environment which is driven by student inquiry. Five specific Java experiments are described here and each is accompanied by a snapshot of the experimental apparatus and controls. An appendix contains the relevant URLs of the experiments, courseware, and animation described herein.
Web Activities in an Introductory Class
Authors: Zollman Dean , Zollman Kevin
Published: October 2003

The students in an introductory physics class for non-science majors are not likely to have sophisticated computer skills. However, many of them have become Web surfers and can be enticed to use the Web as part of their study of physics. Our initial efforts have focused on using the Web to improve courses for elementary and secondary education majors. Materials available to the students include both academic and administrative activities. Students may have access to items such as the course syllabus and up-to-date information on their grades. On the academic side, practice tests, textbook pages, and some interactive programs are available. In developing these materials we have incorporated a variety of techniques including HTML files, C programs, the Macromedia Director Shockwave plug-in, and the Adobe Acrobat plug-in. In all of the efforts we have attempted to minimize the amount of time spent on software development.
Numerical Diagonalization of Fermion Mass Matrices
Authors: Aguilar-Saavedra J. A.
Published: October 2003

The diagonalization of general mass matrices is a more delicate problem when eigenvalue degeneracies exist. In this case, often overlooked in the literature, some difficulties arise related to the freedom in the choice of basis in degenerate subspaces. Here two simple algorithms are developed to deal with quark and neutrino mass matrices with arbitrary degeneracies.
Development of Parallel Codes for the Study of Nonlinear Beam Dynamics
Authors: Giovannozzi M. , Mcintosh E.
Published: October 2003

We consider the nonlinear transverse motion in a circular particle accelerator. A key parameter for accelerator performance is the so-called dynamic aperture. This quantity is defined as the volume in phase space of the stable initial conditions. The accurate numerical computation of such a volume is very CPU-time consuming.

In this paper we present some original parallel algorithms to speed up the evaluation of the dynamic aperture. A detailed analysis of different algorithms implemented is carried out. Furthermore, we studied the dependence of the CPU-time on the phase space parameters as well as the load balancing of the proposed techniques.
Bushfire Automata and Their Phase Transitions
Authors: Duarte J. A. M. S.
Published: October 2003

Cellular automata for heterogeneous bushfire propagation are introduced and their critical properties studied. The underlying models assume continuous fuel with variable moisture characterized by either a fixed value or a random choice of extinction determined by the moisture level. Elliptical (circular) propagation from a single ignition point is assumed. Classes of universality are very stably identified to be those of directed and undirected percolation, despite a significant range of variation of the many parameters involved.
A Model for First-Ranked Galaxies in Rich Clusters Using Extreme Value Theory
Authors: Bhavsar Suketu P.
Published: October 2003

First-ranked galaxies in rich clusters are among the brightest objects in the Universe. Their extremely uniform luminosities have been the cause of much debate. Are these objects a special class of galaxies or merely the tail end of a distribution? A model can be constructed for the distribution in luminosity of these galaxies using a classical result from extreme value theory by Fisher and Tippett in 1928. Their amazing result on the distribution of extremes and its application in resolving the debate on the nature of the brightest galaxies is discussed here.
Cluster–Cluster Correlations in the Two-Dimensional Stationary Ising-Model
Authors: Klassmann Alexander
Published: October 2003

In computer simulations of the two-dimensional stationary binary Ising model, we show that cluster–cluster correlations do not scale with respect to the cluster size.
Dirac Field, Gravity, Inertial Effects, and Computer Algebra
Authors: Vulcanov Dumitru N. , Cotăescu Ion I.
Published: October 2003

The article presents some new results obtained for the non-relativistic approximation of the Dirac equation in a non-inertial reference frame — rotated and accelerated — and in Schwarzschild gravitational field. These results are obtained with new routines of algebraic programming in REDUCE + EXCALC language for the Dirac equation in a non-inertial reference frame and after three successive Foldy–Wouthuysen transformations.
Universality of Derrida Coarsening in Ising Models
Authors: Stauffer Dietrich
Published: October 2003

After improving the Monte Carlo statistics, Derrida's exponent θ for the never damaged sites in Ising models at finite temperatures is shown to be compatible with θ(T=0) =0.22 in two dimensions. In three and more dimensions the number of these sites decays differently from zero temperature.
The Effect of Social Alliances on Wolf Population on Their Survival Under Hunting
Authors: Cebrat Stanisław , Kakol Jerzy
Published: October 2003

We have introduced the modified Verhulst factor to simulate the dynamics of wolves' population. The new factor enlarges the capacity of environment for organisms living in organized groups. Under this factor, social behavior allows the population to reach the larger size in the same ecological niche. The other effect of the introduced factor is that additional non-selective killing factors limit the population size not only directly but also by shrinking the effective ecological niche capacity.
Dynamic Load Balancing for Simulations of Biological Aging
Authors: Meisgen Frank
Published: October 2003

The efficient usage of parallel computers and workstation clusters for biologically motivated simulations depends first of all on a dynamic redistribution of the workload. For the development of a parallel algorithm for the Penna model of aging we have used a dynamic load balancing library, called PLB. It turns out that PLB manages a nearly balanced load situation during runtime taking only a low communication overhead. We compare different architectures like parallel computers and nondedicated heterogeneous networks, and give some results for large populations.
Monte Carlo Simulation of Relaxation in Polymer Solutions After a Temperature Jump
Authors: Fobbe Marcus
Published: October 2003

This article discusses the results of simulations of polymer solutions with the Larson model. The point of interest was the relaxation behavior after a temperature jump. It could be shown that the relaxation time is not independent from the polymer size.
Genetic Crossing vs Cloning by Computer Simulation
Authors: Dasgupta Subinay
Published: October 2003

We perform Monte Carlo simulation using Penna's bit string model, and compare the process of asexual reproduction by cloning with that by genetic crossover. We find them to be comparable as regards survival of a species, and also if a natural disaster is simulated.
An Efficient Monte Carlo Approach to Low-Lying Excitations of Quantum Spin Chains
Authors: Yamamoto Shoji
Published: October 2003

We give a full description of a recently developed efficient Monte Carlo Approach to low-lying excitations of one-dimensional quantum spin systems. The idea is in a word expressed as extracting the lower edge of the excitation spectrum from imaginary-time quantum Monte Carlo data at a sufficiently low temperature. First, the method is applied to the antiferromagnetic Heisenberg chains of S=1/2, 1, 3/2, and 2. In the cases of S=1/2 and S=1, comparing the present results with the previous findings, we discuss the reliability of the method. The spectra for S=3/2 and S=2 turn out to be massless and massive, respectively. In order to demonstrate that our method is very good at treating long chains, we calculate the S=2 chain with length up to 512 spins and give a precise estimate of the Haldane gap. Second, we show its fruitful use in studying quantum critical phenomena of bond-alternating spin chains. Using the conformal invariance of the system as well, we calculate the central charge of the critical S=1 chain, which results in the Gaussian universality class. Third, we study an alternating-spin system composed of two kinds of spins S=1 and 1/2, which shows the ferrimagnetic behavior. We find a quadratic dispersion relation in the small-momentum region. The numerical findings are qualitatively explained well in terms of the spin-wave theory. Finally, we argue a possibility of applying the method to the higher excitations, where we again deal with the S=1 Heisenberg antiferromagnet and inquire further into its unique low-energy structure. All the applications demonstrate the wide applicability of the method and its own advantages.
Nonlinear Hydrodynamics of Lattice-Gas Automata with Semi-Detailed Balance
Authors: Suárez Alberto , Boon Jean Pierre
Published: October 2003

Equations governing the evolution of the hydrodynamic variables in a lattice-gas automaton, arbitrarily far from equilibrium, are derived from the micro-dynamical description of the automaton, under the condition that the local collision rules satisfy semi-detailed balance. This condition guarantees that a factorized local equilibrium distribution (for each node) of the Fermi–Dirac form is invariant under the collision step but not under propagation. The main result is the set of fully nonlinear hydrodynamic equations for the automaton in the lattice-Boltzmann approximation; these equations have a validity domain extending beyond the region close to equilibrium. Linearization of the hydrodynamic equations derived here leads to Green–Kubo formulae for the transport coefficients.
Lattice-Boltzmann Simulations of Complex Fluids
Authors: Gonnella G. , Orlandini E. , Yeomans J. M.
Published: October 2003

We show that by including thermodynamic functions derived from a chosen free energy in a lattice-Boltzmann simulation of fluid flow it is possible to ensure that the fluid relaxes to a well-defined equlilibrium corresponding to the minimum of the input free energy. Two examples are given of phase separation in a binary fluid: bulk two-phase coexistence and a lamellar phase stabilised by a competition between negative surface tension and positive curvature energy. The lattice-Boltzmann framework simulates the Navier–Stokes equations of fluid flow and hence allows investigation of the effects of hydrodynamics on the kinetics of phase separation and on the rheology of the ordered structures.
Anomalies in Simulations of Nearest Neighbor Ballistic Deposition
Authors: D'souza Raissa M.
Published: October 2003

Ballistic Deposition (BD) is a prototypical model for interface growth and for dynamic scaling behavior in non-equilibrium systems. BD is typically investigated with computer simulations where randomness is replaced by the use of deterministic Pseudo Random Number Generators (PRNGs). In this study of BD, several results discrepant with the prevailing paradigm, were observed. First, the value of the roughness exponent, χ, obtained is below the value for a random walk (i.e., χ < 1/2). The value χ=1/2 is predicted by the KPZ equation, and many models of growth obtain this exponent. Second, height fluctuations of the growing interface appear not to satisfy simple scaling. Third, a decrease in the surface roughness is observed in a conjectured steady state regime. Computer implementations of BD may be responsible for the discrepancies. A coupling between the BD algorithm and a PRNG algorithm is identified, and statistically discrepant results are obtained for an implementation with a different PRNG.
Convergence to Uniformity in a Cellular Automaton via Local Coevolution
Authors: Sipper Moshe , Tomassini Marco
Published: October 2003

Cellular programming is a coevolutionary algorithm by which parallel cellular systems evolve to solve computational tasks. The evolving system is a massively parallel, locally interconnected grid of cells, where each cell operates according to a local interaction rule. If this rule is identical for all cells, the system is referred to as uniform, otherwise, it is non-uniform. This paper describes an experiment that addresses the following question: Employing a local coevolutionary process to solve a hard problem, known as density classification, can an optimal uniform solution be found? Since our approach involves the evolution of non-uniform CAs, where cellular rules are initially assigned at random, such convergence to uniformity cannot be a priori expected to easily emerge. The question is of both theoretical and practical interest. As for the latter, one major advantage of local evolutionary processes is their amenability to parallel implementation, using commercially available parallel machines or specialized hardware. Our experiment shows that when such local evolution is applied to the density problem, the optimal solution can be found.
Improving the Hopfield–Tank Approach for the Traveling Salesman Problem
Authors: Argollo de Menezes M. , Penna T. J. P.
Published: October 2003

In this work we revisit the Hopfield–Tank algorithm for the traveling salesman problem (J. J. Hopfield and D. W. Tank, Biol. Cybern. 52, 141 (1985)) and report encouraging results, with a different dynamics, that makes the algorithm more efficient, finding better solutions in much less computational time.
Lekner Summation of Long Range Interactions in Periodic Systems
Authors: Grønbech-Jensen Niels
Published: October 2003

We present a complete set of practical expressions for fast and accurate evaluation of Coulomb interactions, forces and energies, in any rectangular periodic medium. This analysis also includes explicit expressions for energy constants and self-energies of charged particles in periodic lattices. Energy constants and self-energies are further evaluated for logarithmic interactions in two-dimensional rectangular systems with periodic boundary conditions. The expressions are optimized for computational speed and tested by direct numerical implementation.
Structural Study of the Fe2O3–B2O3–BaO Glass System by FTIR Spectroscopy
Authors: Ardelean I. , Toderas Monica , Paşcuţa P.
Published: October 2003

Glasses belonging to the x Fe 2 O 3·(100-x)[3 B 2 O 3· BaO ] system, with 0≤x≤50 mol% were prepared and characterized by IR spectroscopy in order to obtain information about the influence of Fe 2 O 3 on the local structure in the 3 B 2 O 3· BaO glass matrix. The mode in which both Fe 2 O 3 and BaO influences the structure of glass former B 2 O 3 was analyzed.
Practical Realization of Multiple-Input Exclusive-OR Circuits for Low-Power Applications
Authors: Lin Kun-Jin , Wu Cheng-Wen
Published: October 2003

CMOS Exclusive-OR (EXOR) gate implementation using conventional logic structures results in high hardware cost and long propagation delay, making it unattractive to logic designers. A number of more efficient two-input CMOS EXOR-gate structures with only six transistors have been proposed in the past. In many applications, such as parity generator, checker, and Exclusive-OR Sum-of-Product (ESOP) circuits, multiple-input EXOR circuits are required. Two kinds of multiple-input EXOR circuit structures are presented, which are smaller, faster, and more power-saving than those formed by simply connecting two-input EXOR gates in a conventional way. The proposed structures are shown to be suitable for ESOP circuits in which four transistors can be saved for each product term. The reduction in area and power makes them attractive for low-power required applications such as mobile computing and wireless communications.
Enhancements to the Adaptive Polyphase Structure
Authors: Nayeri Majid , Iyer Umashankar
Published: October 2003

The PPS algorithm1 offers an attactive solution to the identification of very long impulse responses by providing alias-free spectral estimates. Its speed of convergence however is limited by a need of excitation at points spaced uniformly over the entire frequency axis. This paper proposes to generalize PPS based on some a priori knowledge of the spectral distribution of the signal. Using rotations and dilations PPS can zoom in on the spectral range of interest and provide more accurate estimates at a fast rate. It is shown that low computational complexity and better performance under low SNRs make PPS a good alternative to the existing algorithms.
Analysis of Stability Control of a Power System with a Distributed Constant Circuit Model
Authors: Takigawa Kiyoshi , Hamada Atushi , Kawasaki Kensuke , Ariyoshi Hiromu
Published: October 2003

From the load cut off tests on generators, it is well known that the power disturbance is transmitted from the test point to the other points with constant delay time. The phenomena shows that the electric power system has a similar dynamic characteristic to the distributed constant circuits. In this paper, the electric power system is expressed with the distributed constant circuit, so that the main disturbance characteristics are obtained without difficulty. Moreover, the method of suppressing the plural disturbances is discussed by employing the active sink method.
An Implementation of a Matrix Cache to Speed up the Conventional Transient Simulation of Piecewise Linear Circuits
Authors: Leelarasmee Ekachai , Hwangkhunnatham Methee
Published: October 2003

A few techniques based on an efficient use of memory resources, called matrix caches, to speed up the transient analysis of piecewise linear circuits such as power electronic circuits are presented. These techniques use the fact that the matrix in the linear equation solving routines can only have a finite number of different values. Hence, by adding a cache memory management technique to store the LU factor of these matrices for future reuse, the linear equation solver can be performed much faster than that of a general purpose simulation program in which these LU factors have to be recomputed every time. Since most of the CPU analysis time is spent in solving linear equations, these techniques can actually speed up the transient analysis of piecewise linear circuits significantly. An experimental circuit simulator has been developed to implement the matrix cache and tested with a few piecewise linear power electronic circuits. The results indicate a speed increase of 2–10 times as compared with its non-matrix cache version.
Semi-State Models for VLSI Hair-Cell Circuits
Authors: Sellami Louiza , Wong Kuan , Newcomb Robert W.
Published: October 2003

Cochlea hair-cells act as neural interfaces of sound signals and, therefore, circuit representations are important to signal processing systems based upon characteristics of the ear. Here nonlinear semi-state equations for a bidirectional circuit representing a generic cochlea hair-cell are presented. The circuit can be specialized to inner or outer hair-cells depending upon the choice of circuit parameter values. Also developed are a canonical semi-state description for the hair-cell potassium and sodium channels, and circuits suitable for a transistorized hardware implementation. Circuit simulations are run with numerical data to correlate with the Howard–Hudspeth experiments.
Stochastic Convergence of Optimal Bounding Ellipsoid Algorithms
Authors: Nayeri Majid , Deller J. R. , Liu Ming-Shou
Published: October 2003

Given appropriate persistency of excitation, the ellipsoidal seta associated with optimal bounding ellipsoid (OBE) algorithms with an interpretable optimization (volume) criterion, converge to a point under the condition that the model disturbance process visit the error bounds infinitely often. The spectral properties of the disturbance are not primary in the convergence behavior of OBE algorithms, rendering these identifiers distinctly different from the structurally similar RLS. Rigorous proof of the sufficiency of the "infinite visitation" property is given for both independent and correlated noise. In the colored noise case, it is shown that a mixing condition on the observations will assure convergence if the OBE algorithm is slightly modified. Examples of simulations are used to illustrate the theoretical developments.
Fusing Cooperative Technical-Specification Knowledge Components
Authors: Grégoire É.
Published: October 2003

In this paper, the problem of fusing various logic-based technical specification knowledge components about a same physical device or process is investigated. It is shown that most standard logic approaches to beliefs and knowledge fusion are not relevant in this context since some rules should be merged even in the case of mutually consistent knowledge components. Accordingly, we discuss the various types of formulas that should be merged during a fusion process, in order to avoid necessary conditions for the absence of failure to become sufficient conditions. This transformation is then described formally. It can be performed as an efficient preprocessing step on the knowledge components to be fused. The properties of this transformation schema are then investigated from a semantical point of view. Finally, a series of subsumption tests are proposed, preventing conditions for the absence of failure from being overridden by subsumption.
Diagnosis of Component Failures in the Space Shuttlemain Engines Using Bayesian Belief Network: A Feasibility Study
Authors: Liu Edwina , Zhang Du
Published: October 2003

Although the Space Shuttle is a high reliability system, the health of the Space Shuttle must be accurately diagnosed in real-time. Two problems current plague the system, false alarms that may be costly, and missed alarms which may be not only expensive, but also dangerous to the crew. This paper describes the results of a feasibility study where a multivariate state estimation technique is coupled with a Bayesian Belief Network to provide both fault detection and fault diagnostic capabilities for the Space Shuttle Main Engines (SSME). Five component failure modes and several single sensor failures are simulated in our study and correctly diagnosed. The results indicate that this is a feasible fault detection and diagnosis technique and fault detection and diagnosis can be made earlier than standard redline methods allow.
Casson-Walker Invariant of Seifert Fibered Rational Homology Spheres as Quantum SO(3)-Invariant
Authors: Sato Chifumi
Published: October 2003

In this paper, we shall give a general formula for the quantum SO(3)-invariant of Seifert fibered rational homology spheres over a 2-sphere, based on the linear skein theory. We shall derive the Casson-Walker invariant from the quantum SO(3)-invariant. Also, we shall give a formula for the Ohtsuki second invariant.
Bifurcations of Links of Periodic Orbits in Non-Singular Systems with Two Rotational Symmetries on S3
Authors: Campos B. , Martínez Alfaro J. , Vindel P.
Published: October 2003

A topological characterization of all possible links composed of the periodic orbits of a Non Singular Morse-Smale flow on S3 has been made by M. Wada.

The presence of symmetry forces the appearance of given types of links. In this paper we introduce a geometrical tool to represent these type of links when a symmetry around two axes is considered on NMS systems: mosaics.

On the other hand, we use mosaics to study what kind of bifurcation can occur in this type of system maintaining the symmetry.
Integrality of the Averaged Jones Polynomial of Algebraically Split Links
Authors: Boden Hans U.
Published: October 2003

We study the integrality of the coefficients of the Jones polynomial of algebraically and geometrically split links and answer a question of Lin and Wang.
Nullification Writhe and Chirality of Alternating Links
Authors: Cerf Corinne
Published: October 2003

In this paper, we show how to split the writhe of reduced projections of oriented alternating links into two parts, called the nullification writhe wx, and the remaining writhe wy, such that the sum of these quantities equals the writhe w and each quantity remains an invariant of isotopy. The chirality of oriented alternating links can be detected by a non-zero wx or wy, which constitutes an improvement compared to the detection of chirality by a non-zero w. An interesting corollary is that all oriented alternating non-split links with an even number of components are chiral, a result that also follows from properties of the Conway polynomial.
4-Punctured Tori in the Exteriors of Knots
Authors: Eudave-Muñoz Mario
Published: October 2003

In this paper we construct an infinite family of hyperbolic knots, each having a Dehn surgery which produces a manifold containing an incompressible torus, which hits the core of the surgered solid torus in four points, but containing no incompressible torus hitting it in less than four points.
Embeddings of 4-Regular Graphs into 3-Space
Authors: Sawollek Jörg
Published: October 2003

Embeddings of 4-regular graphs into 3-space are examined by studying graph diagrams, i.e. projections of embedded graphs to an appropriate plane. New diagrams can be constructed from the old ones by replacing graph vertices with rational tangles, and these diagrams lead to topological invariants of embedded graphs. The new invariants are calculated for some examples, in particular for classes of alternating diagrams of the figure-eight graph. As an application, it is shown that these diagrams have minimal crossing number, which gives generalizations to some of the so-called Tait conjectures.
On the Reducibility and the η-Invariant of Periodic Automorphisms of Genus 2 Surface
Authors: Morifuji Takayuki
Published: October 2003

We give a characterization for the reducibility of elements of any finite subgroup of the mapping class group of genus 2 surface in terms of the η-invariant of finite order mapping tori.
Two-Pion Exchange Nuclear Potential — Chiral Cancellations
Authors: Ballot J.-L. , Robilotta M. R. , da Rocha C. A.
Published: October 2003

We show that chiral symmetry is responsible for large cancellations in the two-pion exchange nucleon-nucleon interaction, which are similar to those occurring in free pion-nucleon scattering.
Elastodynamic Features of Nuclear Matter from Macroscopic Model of Giant Magnetic Resonances
Authors: Bastrukov S. I. , Libert J. , Molodtsova I. V.
Published: October 2003

The collective model is presented providing a descriptive treatment of the magnetic resonant response of spherical nuclei. The model is based on macroscopic equations assuming elastodynamic behavior of the nuclear Fermi-continuum. Modelling a heavy nucleus by a spherical piece of an elastic continuous substance made up of a degenerate Fermi-system of nucleons, it is argued that nuclear resonant magnetization may be interpreted as the resultant of torsional wavelike vibrations excited inside a nuclear macroparticle. The emphasis is placed on the description of the giant magnetic dipole resonance. This resonance is associated with long wavelength vibrations of the magnetization current induced in the peripheral layer of finite depth, whereas the internal spherical region presumably unaffected by external perturbations is considered as an unperturbed core. The excited collective motion is found to behave like shear non-radial vibrations of a massive peripheral layer against a rotationally invariant core. The Extended Thomas-Fermi method is employed to generate a bulk density profile on the basis of Skyrme forces which is used as an input parameter in calculations of torsional inertia and stiffness of the collective Hamiltonian. Systematic calculations for the energy and total excitation probability of the giant M1 resonance are compared with data obtained both by nuclear resonance fluorescence measurements and by means of backward (e,e′) scattering.
The Reaction e-+p→ νe+n at Intermediate Energies
Authors: Mintz S. L. , Barnett M. A. , Gerstner G. M. , Pourkaviani M.
Published: October 2003

We obtain the differential cross section for the reaction, e-+p→ νe+n, a weak electron scattering process, for incident electron energies from 0.1 GeV to 6.0 GeV. The contributions from the form factors are obtained and the possibility of observing this reaction at accelerators such as CEBAF is discussed. The results for this process are compared to those for the reaction e-+3 He → νe+3 H
Covariant Equation of State for Two Colliding Nuclear Matters in the Relativistic Meson Field Theory
Authors: Rashdan M.
Published: October 2003

The relativistic mean field theory (linear and nonlinear) models are extended to the case of two colliding nuclear matters, relevant to heavy ion scattering and reactions. The effect of vacuum corrections is taken into account through the relativistic Hartree approximation. The Fermi sea is assumed to consist of two colliding Lorentz elongated spheres. A relativistic covariant Pauli correction is considered for the overlap case. This relativistic Pauli correction is found to be very important due to its dependence on the effective nucleon mass which strongly depends on the model equation of state. It is found that by increasing the velocity the energy per baryon increases and saturates at higher densities. The increase in the energy per baryon at low density (the region of no overlap) is much larger than that at high density (the region of large overlap), due to Pauli correction effects. The saturation density of the nonlinear model is shifted to larger values than that of the linear model. Vacuum corrections effects are found to reduce largely te overlap region.
Quark Propagator and Meson Correlators in the QCD Vacuum
Authors: Sheel Varun , Mishra Hiranmaya , Parikh Jitendra C.
Published: October 2003

Equal time, point to point correlation functions for spatially separated meson currents are calculated with respect to a variational construct for the ground state of QCD. Given such an ansatz we make no further approximations in the evaluation of the correlators. Our calculations for the vector, axial vector and scalar channels show qualitative agreement with the phenomenological predictions, whereas the pseudoscalar channel does not. However, the pseudoscalar correlator, when approximated by saturating with intermediate one-pion states agrees with results obtained from spectral density functions parameterised by pion decay constant and [Formula: see text] value obtained from chiral perturbation theory. We discuss this departure in the pseudoscalar channel, in the context of the quark propagation in the vacuum.
Another Look at "Soft" Lepton Pair Production in Nucleon-Nucleon Bremsstrahlung
Authors: Zhang Jianming , Tabti Rahma , Gale Charles , Haglin Kevin
Published: October 2003

We compare different formalisms for the calculation of lepton pair emission in hadron-hadron collisions and discuss the consequences of the approximations inherent to each of them. Using a Lorentz-covariant and gauge-invariant formalism proposed by Lichard, we calculate lepton pair emission via bremsstrahlung in proton-proton and neutron-proton reactions at energies between 1 and 5 GeV to leading order in the virtual photon four-momentum. These new results suggest that some previous bremsstrahlung calculations based on varieties of the soft-photon approximation might have somewhat overestimated the DLS low-mass dilepton cross sections. We find that the respective intensities of dilepton production through pp and np bremsstrahlung are energy-dependent and become comparable at E kin ≳ 2 GeV. We also calculate the polar angle anisotropy of the lepton spectrum.
Baryon Spin and Magnetic Moments in Relativistic Chiral Quark Models
Authors: Weber H. J. , Bodoor K.
Published: October 2003

The spin and flavor fractions of constituent quarks in the baryon octet are obtained from their lowest order chiral fluctuations involving Goldstone bosons. SU(3) breaking suggested by the mass difference between the strange and up, down quarks is included, as are relativistic effects by means of a light-cone quark model for the proton, and the gluon contribution from the axial anomaly in the singlet channel. Magnetic moments from the Karl-Sehgal formulas are analyzed in this framework as well.
An Efficient Technique to Ensure the Logical Consistency of Interacting Knowledge Bases
Authors: Mazure Bertrand , Saïs Lakhdar , Grégoire Éric
Published: October 2003

In this paper, we address a fundamental problem in the formalization and implementation of cooperative knowledge bases: the difficulty of preserving consistency while interacting or combining them. Indeed, knowledge bases that are individually consistent can exhibit global inconsistency. This stumbling-block problem is an even more serious drawback when knowledge and reasoning are expressed using logical terms. Indeed, on the one hand, two contradictory pieces of information lead to global inconsistency under complete standard rules of deduction: every assertion and its contrary can be deduced. On the other hand, checking the logical consistency of a propositional knowledge base is an NP-complete problem and is often out of reach for large real-life applications. In this paper, a new practical technique to locate inconsistent interacting pieces of information is presented in the context of cooperative logical knowledge bases. Based on a recently discovered heuristic about the work performed by local search techniques, it can be applied in the context of large interacting knowledge bases.