bluuebunny/crossref_metadata_2025 huggingface dataset:
HIERARCHICAL TRAPPING ON A ONE-DIMENSIONAL LATTICE
Authors: GIACOMETTI ACHILLE
Published: November 2004

The effect of the nonconservation of the total probability in the presence of a hierarchy of transition rates is studied by renormalization group techniques and confirmed by numerical simulations on a one-dimensional lattice. The model can be considered as the static (or ideal chain) counterpart of the Hubermann-Kerszberg model. It is found that critical exponents are always nonuniversal in the presence of a hierarchy and jump discontinuously to universal values in the limit of no hierarchy. Qualitative agreement with recent simulations is found.
CRITICAL POINT OF THE KAGOME POTTS MODEL: A HISTOGRAM MONTE CARLO RENORMALIZATION GROUP DETERMINATION
Authors: HU CHIN-KUN , CHEN JAU-ANN , WU F. Y.
Published: November 2004

The histogram Monte Carlo renormalization group method proposed by Hu is used to determine the critical point of the q-state Potts model on the Kagome lattice. Our results are compared with the predictions of conjectures by Wu and Tsallis.
A CLOSED-FORM SOLUTION OF THE EVOLUTION OPERATOR IN TWO-LEVEL SYSTEMS
Authors: ZHAO XIAN-GENG
Published: November 2004

It is demonstrated by using the technique of Lie algebra SU(2) that the problem of two-level systems described by arbitrary time-dependent Hamiltonians can be solved exactly. A closed-form solution of the evolution operator is presented, from which the results for any special case can be deduced.
OXYGEN ADSORPTION ON ${\rm Co}(10\bar 10)$, A STRUCTURAL HCP-ANALOGUE TO FCC(110)
Authors: KOCH R. , BURG B. , RIEDER K. H. , SCHWARZ E.
Published: November 2004

[Formula: see text] is a hcp metal surface with a rectangular geometry analogous to fcc(110), consisting of close-packed rows separated by the c-axis distance. Oxygen adsorption on [Formula: see text] leads to three ordered superstructures: (i) a c (2 × 4) O phase at an oxygen coverage θ = 0.5, with oxygen forming alternating zigzag and zagzig chains in the troughs of the [Formula: see text] lattice, (ii) a p (2 × 1) O — the more stable phase at θ = 0.5 — which represents a novel type of surface reconstruction characterized by a double-layer missing-row configuration of the Co lattice, and (iii) a p (2 × 1) 2O — the stable phase at θ = 1.0 — which analogous to the c (2 × 4) O phase contains oxygen zigzag chains in the [Formula: see text] troughs. Recent scanning tunneling microscopy and low energy electron diffraction results are reviewed, which revealed the substantial differences between [Formula: see text] and the fcc(110) metal surfaces with their pronounced tendency to missing-row type reconstructions.
SIMPLE TOY MODEL OF SUPERCONDUCTIVITY
Authors: MATTIS DANIEL , BENDERSKI ALEXANDER
Published: November 2004

We examine a simple "toy" model of high-temperature superconductivity, having T c = ∞. It has the attributes of a two-fluid theory, with some novel twists. For example, although the quasiparticles have a continuous spectrum the optical absorption exhibits a gap g at low temperatures. The normal spectrum and most other normal-state properties are recovered for kT ≫ g, although some superconductivity persists out to arbitrarily high T.
QUANTUM FIELD APPROACH TO THE THEORY OF DEVELOPED TURBULENCE OF CONDUCTING FERROFLUIDS
Authors: HNATICH M. , HORVÁTH D. , KOPANSK P.
Published: November 2004

Universality of a principle of the renormalization group (RNG) enables to apply it to a wide spectrum of physical problems, including stochastic problems in the mechanics of continuum. In this paper we study using RNG method statistic properties of a randomly stirred ferrohydrodynamic systems with weak magnetization m. It is shown that also in these systems, similarly to magnetohydrodynamic systems, a steady state asymptotic regime exists in which the spectrum of the pulsation energy has Kolmogorov character k−5/3. In such a regime Lorentz force has no influence on the behavior of a turbulent system on large scales with the result that the magnetic field together with the field of magnetization behave as a passive admixture in the velocity field. It was also shown that strong nonlinear interactions of the velocity field with magnetization generate in the equation for dynamics of the field of magnetization term wν∇2m, which opens a new channel for energy dissipation. Dimensionless "magnetization" Prandtl number w−1 represents the relative intensity of the energy dissipation as compared with other channels and it attains a universal value in the turbulent regime.
AN EMPIRICAL FORMULA FOR Q STATE POTTS MODEL IN D DIMENSIONS
Authors: PAN C. Y.
Published: November 2004

Based upon the known results of the critical properties of the q state Potts ferromagnets obtained by different methods, we proposed an empirical formula of the model. It gives the critical points and the critical exponents for general Potts spin value q in any d dimensions which are in good agreement with all the available results. It improves the results given by Migdal–Kadanoff renormalization group method. It gives more accurate results than Hajdukovic conjecture to the problem of interest. This empirical formula may serve as the primary reference to the problem of interest.
LANDAU LEVEL MIXING AND SOLENOIDAL TERMS IN LOWEST LANDAU LEVEL CURRENTS
Authors: RAJARAMAN R. , SONDHI S. L.
Published: November 2004

We calculate the lowest Landau level (LLL) current by working in the full Hilbert space of a two-dimensional electron system in a magnetic field and keeping all the nonvanishing terms in the high field limit. The answer i) is not represented by a simple LLL operator and ii) differs from the current operator, recently derived by Martinez and Stone in a field theoretic LLL formalism, by solenoidal terms. Though that is consistent with the inevitable ambiguities of their Noether construction, we argue that the correct answer cannot arise naturally in the LLL formalism.
A THEORETICAL AND EXPERIMENTAL STUDY OF ELECTRONIC CONFINEMENT, COUPLING, AND TRANSLAYER INTERACTION IN NOBLE-METAL QUANTUM-WELL STRUCTURES
Authors: MCMAHON W. E. , MILLER T. , CHIANG T.-C.
Published: November 2004

Noble-metal multilayer systems have been grown and examined with angle-resolved photoemission. Surface states, and single and double quantum wells have been studied experimentally; the results can be explained with a simple theoretical model based upon Bloch electrons. In this paper, we will present our model and then give a description of some experimental studies which utilize the model. In particular, we will consider double-quantum-well systems which can be used to examine basic aspects of electronic confinement, layer–layer coupling, and translayer interaction through a barrier.
GROWTH KINETICS IN THE Φ6N-COMPONENT MODEL: CONSERVED ORDER PARAMETER
Authors: CORBERI F. , MARCONI U. MARINI BETTOLO
Published: November 2004

We extend the discussion of the growth kinetics of the large N time-dependent Ginzburg–Landau model with an order parameter described by a Φ6 free energy functional to the conserved case. Quenches from a high temperature initial state to a zero-temperature state are studied for different selections of parameters entering the effective potential. In all cases we obtain the asymptotic form of the structure factor. As expected in analogy with the well-studied Φ4 model, we find multiscaling behavior whenever stable equilibrium is reached in the ordering region. On the other hand the present model also displays a novel feature, namely, the occurrence of metastable relaxation.
SIMULATION PROCEDURES IN CONDENSED MATTER PHYSICS: AN ALGORITHM ALTERNATIVE TO THE STANDARD RANDOM NUMBER GENERATORS
Authors: CORDELLI ALESSANDRO
Published: November 2004

Numerical simulation techniques play a very important role in solid state physics, in particular, as far as the determination of electronic and vibrational structure of non-periodic systems is concerned. The basis of these techniques is the construction of a random Hamiltonian and a random state of interest; to do that, standard congruential algorithms for the generation of pseudorandom numbers are commonly used. The aim of this paper is to propose a novel, alternative way for the generation of random operators and vectors. This technique, based on the concept of minimum correlation sequence, gives results equivalent to or better than the standard approach.
TIN ADDITION TO THE (Bi, Pb) 2223 SYSTEM
Authors: CHANDRA G. RAVI , KRISHNA B. GOPALA , SURYANARAYANA S. V. , MURTHY T. S. N.
Published: November 2004

The effect of the addition of Sn on the superconducting properties of the Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O y system as functions of Sn concentration and heat treatment has been studied by dc electrical resistance, ac magnetic susceptibility, and X-ray diffraction. Tin addition suppresses the volume fraction of the high T c phase. Samples with Sn > 0.1 show metallic behavior up to LNT. The formation of the Ca 2 PbO 4 phase is promoted by Sn. This depletes the amount of Pb and Ca necessary for the formation of the 2223 phase, thus reducing the volume fraction of the 2223 phase. It is possible that at least a small fraction of tin substitutes some of the cationic sites of the starting composition. The results of the different measurements are presented.
QUANTUM LIMIT OF CHAOTIC SYSTEMS AS QUANTUM DIFFUSION
Authors: SEROTA R.A.
Published: November 2004

We describe classical chaotic motion in terms of diffusion in configurational space. This approach is illustrated for chaotic billiards and an oscillator with anharmonic coupling. It is argued that in the quantum limit, physical phenomena ordinarily associated with disordered metals, such as localization and mesoscopic phenomena, carry over to chaotic systems in general which are in the universality class of the nonlinear σ model.
BIOPHOTON EMISSION: EXPERIMENTAL BACKGROUND AND THEORETICAL APPROACHES
Authors: POPP FRITZ-ALBERT , GU QIAO , LI KE-HSUEH
Published: November 2004

Biophoton emission is a general phenomenon of living systems. It concerns a weak photon radiation from a few to some hundred photons per second, per square centimeter surface area, at least within the spectral region from 200 to 800 nm. The results indicate that biophoton emission can be assigned to a coherent field within living organisms, its functions being intra and intercellular regulation and communication. This review deals with some central results and their interpretation.
A NEW SADDLE POINT STATE OF THE t-J MODEL
Authors: WENG Z.Y. , SHENG D.N. , TING C.S.
Published: November 2004

A new saddle point state is proposed for the lightly doped t-J model in both one-dimensional (1D) and two-dimensional (2D) cases. It is shown that in 2D a long range antiferromagnetic (AF) order is recovered in the zero-doping limit, while in the same limit the well-known power law spin-spin correlation can also be obtained in 1D. At finite doping, interesting properties for both dimensions are exhibited in this new saddle point state, known as the flux binding state.
THE PAULI PRINCIPLE AND QUANTUM TRANSPORT
Authors: GURVITZ S.A. , LIPKIN H.J. , PRAGER Ya. S.
Published: November 2004

A new method using Fock space wave functions is proposed for studying resonant tunneling in semiconductor quantum wells. The use of binary occupation numbers as dynamical variables, rather than properties of individual electrons, manifestly takes account of electron statistics, which enables investigation of the influence of the Pauli principle on resonant tunneling in the presence of inelastic scattering. Applied to the evaluation of the resonant current in semiconductor heterostructures, our approach predicts considerable deviations from the one-electron and rate equations pictures.
ELECTRICAL CONDUCTION PHENOMENA IN POLYIMIDE FILMS
Authors: CHOHAN M.H. , MAHMOOD H. , SHAH FARHANA
Published: November 2004

A study of the electrical conduction mechanism in polyimide (Kapton) films has been made. The measurements were carried out on films of 12.5 and 25 µm thick in the voltage range of 100 to 3000 V and in the temperature range of 300 to 373 K. The conduction mechanism in the low field region is a hopping type process while the high field phenomenon is a Poole-Frenkel behavior. The activation energy is about 1.1 eV at 100 V and 0.8 eV at 3000 V.
SPONTANEOUS CURRENTS IN MESOSCOPIC AND MACROSCOPIC SYSTEMS
Authors: CHOI M.Y.
Published: November 2004

The possibility of current-carrying ground states due to the Aharonov-Casher and the Aharonov-Bohm effect in mesoscopic and macroscopic systems is discussed in detail. In mesoscopic metal rings, the interplay between the two effects is not separable, and the spontaneous spin currents via the Aharonov-Casher effect are dominated by the charge currents due to the Aharonov-Bohm effect. In an annulus-shaped Josephson junction array, on the other hand, only the Aharonov-Casher effect comes in; the corresponding vortex current generates a spontaneous voltage across the annulus, which appears to be observable.
RELATION BETWEEN YANG-BAXTER AND PAIR PROPAGATION EQUATIONS IN 16-VERTEX MODELS
Authors: AHN CHANGRIM , HORIBE MINORU , SHIGEMOTO KAZUYASU
Published: November 2004

We study the relation between two integrability conditions, namely, the Yang-Baxter and the pair propagation equations, in 2D lattice models. While the two are equivalent in the 8-vertex models, discrepancies appear in the 16-vertex models. As explicit examples, we find the exactly solvable 16-vertex models which do not satisfy the Yang-Baxter equations.
A CLASS OF QUANTUM STATES WITH CLASSICAL-LIKE EVOLUTION
Authors: DE MARTINO SALVATORE , DE SIENA SILVIO , ILLUMINATI FABRIZIO
Published: November 2004

In the framework of the stochastic formulation of quantum mechanics we derive non-stationary states for a class of time-dependent potentials. The wave packets follow a classical motion with constant dispersion. The new states define a possible extension of the harmonic oscillator coherent states. As an explicit application, we study a sestic oscillator potential.
CHAIN OXYGEN DYNAMICS IN YBa2Cu3O7−δ UNDER APPLIED ELECTRIC FIELDS AND RELATED PHENOMENA
Authors: CHANDRASEKHAR N. , VALLS ORIOL T. , GOLDMAN A.M.
Published: November 2004

Three-terminal field effect devices are widespread in modern electronics due to their versatility. The possibility of tuning superconductivity, using electric fields to modulate carrier transport is of great interest. With the high temperature cuprate superconductors, which have fairly low carrier concentrations in comparison to metals, this would permit the study of properties in a systematic manner instead of relying on the stochastic nature of oxygen doping. Demonstrations of the phenomenon in YBa 2 Cu 3 O 7−δ have been analysed in terms of the conventional metal field effect. In this work, we show that contrary to earlier belief, the field effect in YBa 2 Cu 3 O 7−δ arises due to changes in the structure. The mechanism is one of ordering induced doping, and is not novel to this oxide, with Fe3O4 exhibiting a similar phenomenon, termed the Verwey transition. Our explanations and results are found to be consistent with experiments, both in terms of the magnitudes of the effects observed as well as their time scales. Also, explicit predictions of this model have recently been confirmed experimentally. Since the effect is omnipresent during the measurement of any physical property in this material, we present a qualitative discussion of its connotations for transport, tunneling, and magnetization. The phenomenon is of importance in a wide variety of device applications.
A GENERALIZED MODEL FOR CARBON MONOXIDE GAS-DYNAMIC LASER
Authors: GRADO CAFFARO M.A. , GRADO CAFFARO M.
Published: November 2004

A generalization of the McKenzie model of the carbon monoxide gas-dynamic laser is proposed. To this end, the involved molecules are regarded as anharmonic oscillators. Furthermore, population distribution is discussed in the light of our model.
APPROXIMATION OF SCALAR WAVES IN THE SPACE-FREQUENCY DOMAIN
Authors: DOUGLAS JIM , SHEEN DONGWOO , SANTOS JUAN E.
Published: November 2004

A numerical method for approximating a pseudodifferential system describing attenuated, scalar waves is introduced and analyzed. Analytic properties of the solutions of the pseudodifferential systems are determined and used to show convergence of the numerical method. Experiments using the method are reported.
CLASSICAL CHANGE OF SIGNATURE: THE GENERAL CASE?
Authors: ELLIS GEORGE F.R. , PIOTRKOWSKA KAMILLA
Published: November 2004

The possibility of classical change of signature is considered in the context of Friedmann-Robertson-Walker (FRW) space-times. A version of the Darmois junction conditions leads to exact classical analogues of the Hartle-Hawking no-boundary conditions in quantum cosmology. The general case of such classical changes of signature is briefly considered.
CHAOS IN SIMPLE COSMOLOGICAL MODELS
Authors: CALZETTA ESTEBAN
Published: November 2004

We study the occurrence of chaotic behavior in a simple cosmological model, consisting of a spatially closed Friedmann-Robertson-Walker universe filled with a conformally coupled but massive real scalar field, Chaos sets in when the field amplitude is large enough, in the guise of strong variability in the phase of the field oscillations. These nonlinear phase changes may cause significative information loss within cosmological time scales.
PHASE DIAGRAMS OF MULTIDIMENSIONAL COSMOLOGICAL MODELS
Authors: FABRIS Júlio C. , KERNER Richard , TOSSA Joël
Published: November 2004

We work out the phase diagram for a multidimensional cosmological model based on the Seven Dimensional Supergravity. From this phase diagram, we can study a possible scenario for a post- inflationary phase. We study also the evolution of scalar perturbations in this primordial scenario.
PULSARS AS PARTICLE ACCELERATORS — THE ROLE OF THOMSOM SCATTERING
Authors: THIELHEIM K.O.
Published: November 2004

Particle dynamics in extremely strong electromagnetic wave fields as expected for pulsars and cosmic jets is described by a momentum transfer equation. This equation of motion incorporates the Lorentz force as well as the radiation force. While the latter is deduced entirely from multi-photon Thomson scattering the resulting equation of motion can be shown to be closely related to the Lorentz-Dirac-Landau equation.
EXTENDED SUPERSYMMETRY AND CALABI HYPERKAHLER METRICS
Authors: VALENT GALLIANO
Published: November 2004

Alvarez-Gaumé and Freedman had conjectured that the non-linear σ-model with [Formula: see text] global supersymmetry constructed by Curtright and Freedman was nothing but Calabi’s hyperkähler metric. We prove this conjecture by giving the change of coordinates which relates the two metrics.
QUANTUM AND THERMAL EFFECTS IN THE MATTER-GRAVITY SYSTEM
Authors: VENTURI G.
Published: November 2004

The matter-gravity system is examined in a path integral approach for the case of conformal matter coupled to a Friedmann-Robertson-Walker space time. In particular the case of gravitational potentials of interest in cosmology for which the universe tunnels from a small radius is examined. It is observed that in the presence of such gravitational horizons the universe evolves in a complex time and it is shown how a classical time and temperature emerge. Correspondingly one will have compensating quantum and thermal fluctuations for the matter and gravity system and it is noted that the unstable mode of gravity corresponding to the universe tunnelling into existence will be compensated by analogous modes for matter corresponding to its creation.
MEAN FIELD APPROACH TO THE GIANT WORMHOLE PROBLEM
Authors: GAMBA A. , KOLOKOLOV I. , MARTELLINI M.
Published: November 2004

We introduce a gaussian probability density for the space-time distribution of worm-holes, thus taking effectively into account wormhole interaction. Using a mean-field approximation for the free energy, we show that giant wormholes are probabilistically suppressed in a homogenous isotropic “large” universe.
ON QUANTUM PROPERTIES OF THE LARGE-SCALE INHOMOGENEITIES OF METRIC IN THE VICINITY OF COSMOLOGICAL SINGULARITY
Authors: KIRILLOV A.A.
Published: November 2004

The question on the influence of quantum effects on the properties of large-scale inhomogeneities of metric is analyzed. A model with short-distance fluctuations omitted is considered. An assumption of absence of short-scale perturbations allows one to solve the Wheeler-DeWitt equation exactly, for the case of asymptotical closeness to a singularity. Probability interpretation of the wave function is discussed. In the framework of the model it is possible to define the stationary states. It is found that the metric inhomogeneities are spatially delta-correlated in a stationary state. In contrast to the classical theory, the properties of inhomogeneities are essentially dependent upon the choice of initial conditions.
STELLAR WIND MODEL IN RELATIVISTIC HYDRODYNAMICS
Authors: SHIKIN I.S.
Published: November 2004

A study is made of the dynamics of spherically symmetric outflow of test matter in a gravitational field of a central attracting body of mass M (a star) in the framework of relativistic hydrodynamics. A solution for stellar wind with transition across a critical point is discussed.
NON-ABELIAN TOPOLOGICAL SOLUTIONS IN STRINGY GRAVITY
Authors: GAL’TSOV D.V. , DONETS E.E.
Published: November 2004

Non-Abelian solutions of the low-energy heterotic string effective action are discussed. Three types of solutions are shown to exist: regular uncharged shaleron-like solutions, uncharged non-Abelian black holes and charged black holes with non-Abelian hair. In the extremal limit charged non-Abelian black holes generate regular throat structure in the string frame similar to that of the Gibbons-Maeda-Horowitz-Strominger solution.
MAPPING DARK MATTER IN HOT STELLAR SYSTEMS
Authors: MERRITT DAVID
Published: November 2004

Recent work on the dynamics of elliptical galaxies suggests that it is possible to determine the radial distribution of mass in hot stellar systems using only line-of-sight velocities of a sample of stars, without any a priori assumptions about either the relative distribution of dark and luminous components, or the stellar velocity distribution. The technique differs from the point-by-point estimation of the gravitational acceleration in disk galaxies in that it requires the construction of a complete dynamical model describing the observed population. An algorithm is described which should yield strong, model-independent constraints on the central density of dark matter in dwarf spheroidal galaxies once the number of observed radial velocities reaches a few hundred.
DOUBLE GIANT RESONANCES
Authors: MORDECHAI SHAUL , MOORE C. FRED
Published: November 2004

A long-standing issue in nuclear structure is whether double giant resonances do exist. Exotic excitations like the double giant-dipole were predicted for many years but not observed experimentally until recently. Several experiments have been carried out at Los Alamos National Laboratory and other laboratories to search for these new collective modes of the nucleus. The results discover the existence of two previously unobserved types of double giant resonances. This work presents a review of the pion double charge exchange data and the analysis which support the existence of two such exotic vibrational nuclear modes: the giant dipole resonance built on the isobaric analog state and the double isovector giant-dipole resonance. Excitation of multiphonon states also becomes a very likely process in relativistic heavy-ion reactions where a direct identification of the double giant-dipole resonance has been reported recently.
SUPER-ASYMMETRIC COLD FISSION AND EXOTIC CLUSTER-DECAY
Authors: KUMAR SATISH , GUPTA RAJ K. , SCHEID WERNER
Published: November 2004

Cold fission of radioactive nuclei is studied in the super-asymmetric mass region of exotic cluster radioactivity, using the quantum-mechanical fragmentation theory (QMFT) based saddle-point fission (SPF) model for calculating the decay half-life times. The calculations show that cold fission also prefers light fragments like 24–26Ne, 28,30Mg, 32,34,36Si, 37P 38S, 46Ar and 48,50Ca, some of which are observed in exotic cluster radioactivity. The predictions of the SPF model calculations are compared with the available exotic cluster-decay experimental data and the calculations based on the preformed-cluster model (PCM). The SPF model calculations show large disagreements with both the PCM and cluster-decay experimental data. For clusters of mass A2<46, the predicted half-lives for the SPF model are much smaller than for the PCM, which apparently means predicting the cold fission as a more probable process than the cluster-decay. The cold fission predicts some new decay modes which are far more probable (smaller log10 T1/2-values) as cold fission fragments than as cluster-decay products. For heavier clusters (A2≥46), the two models (SPF and PCM) make nearly identical predictions, which means predicting an overlap of two processes (cold fission and cluster-decay) for A2>46. Also, cold fission is found to be more probable than hot fission and a new fission mode (known as bimodel fission) is identified in the neighbourhood of the doubly magic [Formula: see text] fragment. Our calculations are made for 234U, 238Pu, 241Am and 252Cf.
A NEW APPROACH TO THE STUDY OF NUCLEAR MATTER
Authors: TRIPATHY D.N. , MISHRA L.K.
Published: November 2004

By invoking the existence of the zero-sound mode we have succeeded in generalizing the Bohm-Pines method, for the collective description of the interparticle interactions in a dense electron gas, to calculate the binding energy per nucleon in the ground state of a nuclear matter. The present calculation gives rise to a saturation Fermi wave vector kFO=1.74 fm−1, which is larger than the mostly accepted value of 1.43 fm−1. Our calculated result for the velocity of the zero-sound mode is found to be well-agreeable with those of other theories. It is further seen that there is an instability in the nuclear matter, with respect to long wavelength density fluctuations, in the low density region n≤0.78n0, n0 being the saturation nuclear density. From the present theory, we obtain a compression modulus K=116.7 MeV at the saturation density, which is smaller than the well-known result (210±30) MeV. However, by adjusting the value of the effective mass, M*, of the nucleon, we are able to reproduce the correct result for the compression modulus. Such a value of M* is found to be greater than the bare nucleon mass M. From the present theory, we obtain the energy of the monopole resonance Eph=32.38 MeV, which agrees reasonably well with the experimental data for heavy nuclei. By lowering the value of the saturation Fermi wave vector, we observe a decrease in the value of the compression modulus, which is just the opposite to the results of other theoretical calculations.
STUDY OF BACKWARD SHOWER PARTICLE PRODUCTION FROM THE INTERACTIONS OF 22Ne AND 28Si WITH EMULSION NUCLEI AT DUBNA ENERGY
Authors: EL-NADI M. , ABDELSALAM A. , MOUSSA N. ALI
Published: November 2004

The backward multiplicity and angular distributions of the shower particles produced in the interactions of 22Ne and 28Si nuclei at 3.6 GeV in emulsions are presented, analysed and compared with the data from the interactions of 12C nuclei at the same incident energy. The results yield quite interesting information regarding the mechanism of production of backward shower particles. The pseudorapidity distributions of the produced shower particles in the backward hemisphere are independent of the projectile mass. The multiplicity distributions of the shower particles emitted in the backward direction, using the KNO representation, are described by an exponential form.
A NEW MICROSCOPIC VIEW OF NUCLEAR DEFORMATION
Authors: LI Z.-P. , GUIDRY M.W. , WU C.-L. , FENG D.H.
Published: November 2004

The microscopic origin of deformation for heavy nuclei is discussed. Evidence is presented that the systematic features of nuclear deformation are determined primarily by filling of the normal-parity shell model orbitals of the valence shells, and that the abnormal-parity orbitals play crucial but subsidiary roles. This is in accord with the point of view underlying the Fermion Dynamical Symmetry Model. In addition, we demonstrate that the deformation systematics of the FDSM are consistent with those of the Nilsson model, despite their very different starting points, and that the assumptions of the FDSM are consistent with the assertion that the n-p quadrupole-quadrupole residual interaction is the essential reason for deformation. Finally, application of the same principles to superdeformation suggests that abnormal parity orbitals have a much more direct influence on superdeformation than on normal deformation.
EXTENSION OF THE SPIN-DEPENDENT GENERALIZED COLLECTIVE MODEL TO EVEN-ODD NUCLEI WITH SPIN 1/2 AND 5/2
Authors: HEUMANN DIRK , GREINER MARTIN , SCHEID WERNER , BRAUNSS GÜNTHER
Published: November 2004

The Spin-dependent Generalized Collective Model, derived from a linearized collective Schrödinger equation in quadrupole coordinates, describes nuclei with spin 3/2 in the ground state. In this paper, we extend this model to arbitrary half-integer spins and apply it to even-odd nuclei with spins 1/2 and 5/2.
Mapping of genetic determinants of the sympathoneural response to stress
Authors: Klimeš I. , Weston K. , Gašperíková D. , Kovács P. , Kvetňanský R. , Ježová D. , Dixon R. , Thompson J. R. , Šeböková E. , Samani N. J.
Published: November 2004

Activation of the sympathoadrenal system (SAS, comprising the sympathetic nervous system and the adrenal medulla) in response to stressful stimuli is an important defense mechanism as well as a contributor to several cardiovascular diseases. There is variability in the SAS response to stress, although the extent to which this is genetically regulated is unclear. Some rodent models, including the hereditary hypertriglyceridemic (hHTg) rat, are hyperresponsive to stress. We investigated whether quantitative trait loci (QTLs) that affect sympathoadrenal response to stress could be identified. Second filial generation rats ( n = 189) derived from a cross of the hHTg rat and the Brown Norway rat had plasma norepinephrine (NE) and epinephrine (Epi) levels, indices of activation of the sympathoneural and adrenal medulla components, respectively, measured in the resting state and in response to an immobilization stress. Responses were assessed early (20 min) and late (120 min) after the application of the stress. A genome scan was conducted using 153 microsatellite markers. Two QTLs (maximum peak LOD scores of 4.17 and 3.52, respectively) influencing both the early and late plasma NE response to stress were found on chromosome 10. Together, the QTLs accounted for ∼20% of the total variation in both the early and late NE responses in the F2rats. Interestingly, the QTLs had no effect on plasma Epi response to stress. These findings provide evidence for a genetic determination of the response of a specific component of the SAS response to stress. Genetically determined variation in sympathetic nervous system response to stress may contribute to cardiovascular diseases.
The Biochemical and Genetic Odyssey to the Function of a Nicastrin-Like Protein
Authors: Haffner Christof , Haass Christian
Published: November 2004

γ-Secretase is a high-molecular-weight protein complex required for the proteolytic processing of various transmembrane proteins including the Alzheimer’s disease-associated amyloid precursor protein and the signaling receptor Notch. One of the γ-secretase complex components is the type I transmembrane protein nicastrin. Here we review the odyssey to a cyclopic fish, which at the end allowed the functional analysis of nicalin, a novel member of the nicastrin protein family. This 60-kDa protein is part of a previously unknown membrane protein complex unrelated to γ-secretase and binds to Nomo (Nodal modulator, previously known as pM5), a novel 130-kDa transmembrane protein. Both proteins are highly conserved in metazoans and show almost identical tissue distribution in humans. Functional studies in zebrafish embryos and cultured human cells revealed that nicalin and Nomo collaborate to antagonize the Nodal/TGFβ signaling pathway. Thus, nicastrin and nicalin are both associated with protein complexes involved in cell fate decisions during early embryonic development.
A Model System to Study Intracellular Trafficking and Processing of the Alzheimer’s Amyloid Precursor Protein
Authors: da Cruz e Silva Odete A.B. , Vieira Sandra Isabel , Rebelo Sandra , da Cruz e Silva Edgar F.
Published: November 2004

The occurrence of consensus phosphorylation sites in the intracellular domain of the Alzheimer’s amyloid precursor protein (APP), coupled with observations of their in vivo phosphorylation, prompted several workers to investigate the effects that phosphorylation of such sites could have on APP metabolism and subsequent Aβ production. However, hitherto all attempts to dissect the role played by such phosphorylation events failed to reveal substantial effects. Having decided to revisit this problem, our new approach was based on the following vectors: (1) site-directed mutagenesis of the target amino acids to mimic a specific phosphorylation state, (2) expression of wild-type and mutant APP-GFP (green fluorescent protein) fusion proteins for ease of visualization, (3) controlled low level expression to avoid ‘flooding’ cellular pathways, and (4) the use of cycloheximide to inhibit de novo protein synthesis. Using this method we were able to detect specific differences in APP processing that were correlated with the mimicked phosphorylation state of several phosphorylation sites. New combined methodologies, like the one described here, allow for the detailed analysis of key control points in the cellular metabolism of specific proteins that are central to neurodegenerative diseases and may be under the control of specific posttranslational modifications, such as reversible phosphorylation.
Computer Aided Diagnosis in Ultrasound
Authors: Walshaw Colin , Blindell Peter F
Published: November 2004

Image processing software is being used increasingly to assist in the interpretation of medical images, and this will accelerate with the roll-out of Picture Archiving and Communication Systems (PACS). The issue of patient confidentiality must be addressed. Research on computer-aided diagnosis techniques has been on going in many areas of radiology though little has been published in the area of fetal ultrasound. We have found that standard approaches show promising results when applied to fetal age estimation.
Interleukin-7 deficiency in rheumatoid arthritis: consequences for therapy-induced lymphopenia
Authors: Ponchel Frederique , Verburg Robert J , Bingham Sarah J , Brown Andrew K , Moore John , Protheroe Andrew , Short Kath , Lawson Catherine A , Morgan Ann W , Quinn Mark , Buch Maya , Field Sarah L , Maltby Sarah L , Masurel Aurelie , Douglas Susan H , Straszynski Liz , Fearon Ursula , Veale Douglas J , Patel Poulam , McGonagle Dennis , Snowden John , Markham Alexander F , Ma David , van Laar Jacob M , Papadaki Helen A , Emery Paul , Isaacs John D
Published: November 2004

We previously demonstrated prolonged, profound CD4+ T-lymphopenia in rheumatoid arthritis (RA) patients following lymphocyte-depleting therapy. Poor reconstitution could result either from reduced de novo T-cell production through the thymus or from poor peripheral expansion of residual T-cells. Interleukin-7 (IL-7) is known to stimulate the thymus to produce new T-cells and to allow circulating mature T-cells to expand, thereby playing a critical role in T-cell homeostasis. In the present study we demonstrated reduced levels of circulating IL-7 in a cross-section of RA patients. IL-7 production by bone marrow stromal cell cultures was also compromised in RA. To investigate whether such an IL-7 deficiency could account for the prolonged lymphopenia observed in RA following therapeutic lymphodepletion, we compared RA patients and patients with solid cancers treated with high-dose chemotherapy and autologous progenitor cell rescue. Chemotherapy rendered all patients similarly lymphopenic, but this was sustained in RA patients at 12 months, as compared with the reconstitution that occurred in cancer patients by 3–4 months. Both cohorts produced naïve T-cells containing T-cell receptor excision circles. The main distinguishing feature between the groups was a failure to expand peripheral T-cells in RA, particularly memory cells during the first 3 months after treatment. Most importantly, there was no increase in serum IL-7 levels in RA, as compared with a fourfold rise in non-RA control individuals at the time of lymphopenia. Our data therefore suggest that RA patients are relatively IL-7 deficient and that this deficiency is likely to be an important contributing factor to poor early T-cell reconstitution in RA following therapeutic lymphodepletion. Furthermore, in RA patients with stable, well controlled disease, IL-7 levels were positively correlated with the T-cell receptor excision circle content of CD4+ T-cells, demonstrating a direct effect of IL-7 on thymic activity in this cohort.
Quantitative ultrasonic assessment for detecting microscopic cartilage damage in osteoarthritis
Authors: Hattori Koji , Ikeuchi Ken , Morita Yusuke , Takakura Yoshinori
Published: November 2004

Osteoarthritis (OA) is one of the most prevalent chronic conditions. The histological cartilage changes in OA include surface erosion and irregularities, deep fissures, and alterations in the staining of the matrix. The reversibility of these chondral alterations is still under debate. It is expected that clinical and basic science studies will provide the clinician with new scientific information about the natural history and optimal treatment of OA at an early stage. However, a reliable method for detecting microscopic changes in early OA has not yet been established. We have developed a novel system for evaluating articular cartilage, in which the acoustic properties of the articular cartilage are measured by introducing an ultrasonic probe into the knee joint under arthroscopy. The purpose of this study was to assess microscopic cartilage damage in OA by using this cartilage evaluation system on collagenase-treated articular cartilage in vivo and in vitro. Ultrasonic echoes from articular cartilage were converted into a wavelet map by wavelet transformation. On the wavelet map, the maximum magnitude and echo duration were selected as quantitative indices. Using these indices, the articular cartilage was examined to elucidate the relationships of the ultrasonic analysis with biochemical, biomechanical and histological analyses. In the in vitro study, the maximum magnitude decreased as the duration of collagenase digestion increased. Correlations were observed between the maximum magnitude and the proteoglycan content from biochemical findings, and the maximum magnitude and the aggregate modulus from biomechanical findings. From the histological findings, matrix staining of the surface layer to a depth of 500 μm was closely related to the maximum magnitude. In the in vivo study, the maximum magnitude decreased with increasing duration of the collagenase injection. There was a significant correlation between the maximum magnitude and the aggregate modulus. The evaluation system therefore successfully detected microscopic changes in degenerated cartilage with the use of collagen-induced OA.
Model-independent fluxome profiling from 2H and 13C experiments for metabolic variant discrimination
Authors: Zamboni Nicola , Sauer Uwe
Published: November 2004

We introduce a conceptually novel method for intracellular fluxome profiling from unsupervised statistical analysis of stable isotope labeling. Without a priori knowledge on the metabolic system, we identified characteristic flux fingerprints in 10 Bacillus subtilis mutants from 132 2H and 13C tracer experiments. Beyond variant discrimination, independent component analysis automatically mapped several fingerprints to their metabolic determinants. The approach is flexible and paves the way to large-scale fluxome profiling of any biological system and condition.
PKA phosphorylation of Src mediates Rap1 activation in NGF and cAMP signaling in PC12 cells
Authors: Obara Yutaro , Labudda Kirstin , Dillon Tara J. , Stork Philip J. S.
Published: November 2004

Recent studies suggest that the tyrosine kinase Src plays an important role in the hormonal regulation of extracellular signal-regulated kinases (ERKs) via cyclic AMP (cAMP). Src has also been proposed to mediate signals downstream of nerve growth factor (NGF). Here, we report that the cAMP-dependent protein kinase A (PKA) induced the phosphorylation of Src at residue serine17 (S17) in multiple cell types including PC12, Hek293, AtT-20 and CHO cells. In PC12 cells, Src phosphorylation on S17 participates in the activation of the small G protein Rap1 by both cAMP and NGF. In these cells, Rap1 is required for cAMP/PKA signaling to ERKs and also for the sustained activation of ERKs by NGF. The activation of Rap1 by both cAMP and NGF was blocked by PP2, an inhibitor of Src family kinases, and by a Src mutant incapable of being phosphorylated by PKA (SrcS17A), consistent with the requirement of PKA phosphorylation of Src at S17 in these actions. PP2 and SrcS17A also inhibited the Rap1-dependent activation of ERKs by both agents. These results strongly indicate that PKA phosphorylation of Src at S17 is essential for cAMP and NGF signaling in PC12 cells and identify PKA as an important downstream target of NGF. PKA phosphorylation of Src may therefore be required for Rap1 activation in PC12 cells.
LAP2α and BAF transiently localize to telomeres and specific regions on chromatin during nuclear assembly
Authors: Dechat Thomas , Gajewski Andreas , Korbei Barbara , Gerlich Daniel , Daigle Nathalie , Haraguchi Tokuko , Furukawa Kazuhiro , Ellenberg Jan , Foisner Roland
Published: November 2004

Lamina-associated polypeptide (LAP) 2α is a LEM (lamina-associated polypeptide emerin MAN1) family protein associated with nucleoplasmic A-type lamins and chromatin. Using live cell imaging and fluorescence microscopy we demonstrate that LAP2α was mostly cytoplasmic in metaphase and associated with telomeres in anaphase. Telomeric LAP2α clusters grew in size, formed `core' structures on chromatin adjacent to the spindle in telophase, and translocated to the nucleoplasm in G1 phase. A subfraction of lamin C and emerin followed LAP2α to the core region early on, whereas LAP2β, lamin B receptor and lamin B initially bound to more peripheral regions of chromatin, before they spread to core structures with different kinetics. Furthermore, the DNA-crosslinking protein barrier-to-autointegration factor (BAF) bound to LAP2α in vitro and in mitotic extracts, and subfractions of BAF relocalized to core structures with LAP2α. We propose that LAP2α and a subfraction of BAF form defined complexes in chromatin core regions and may be involved in chromatin reorganization during early stages of nuclear assembly.
Schizosaccharomyces pombeRgf3p is a specific Rho1 GEF that regulates cell wall β-glucan biosynthesis through the GTPase Rho1p
Authors: Tajadura Virginia , García Blanca , García Ignacio , García Patricia , Sánchez Yolanda
Published: November 2004

Rho1p regulates cell integrity by controlling the actin cytoskeleton and cell-wall synthesis. Here, we describe the cloning and characterization of rgf3+, a member of the Rho family of guanine nucleotide exchange factors (Rho GEFs). The rgf3+ gene was cloned by complementation of a mutant (ehs2-1) hypersensitive to drugs that interfere with cell-wall biosynthesis. The rgf3+ gene was found to be essential for cell viability and depletion of Rgf3p afforded phenotypes similar to those obtained following depletion of Rho1p. However, the cell death caused by Rgf3p depletion could be rescued by the presence of 1.2 M sorbitol, whereas depletion of Rho1 was lethal under the same conditions. We show that Rgf3p is a specific Rho1-GEF. The hypersensitivity to drugs affecting the cell wall of the ehs2-1 mutant was suppressed by overexpression of rho1+ but not by any of the other GTPases of the Rho family. Rgf3p interacted with the GDP-bound form of Rho1p and promoted the GDP-GTP exchange. In addition, we show that overexpression of Rgf3p produces multiseptated cells and increases β-1,3-glucan synthase activity and the amount of cell wall β-1,3-glucan. Rgf3p localized to the septum and the mRNA level was regulated in a cell-cycle-dependent manner peaking during septation. Our results suggest that Rgf3p acts as a positive activator of Rho1p, probably activating the Rho functions that coordinate cell-wall biosynthesis to maintain cell integrity during septation.
Microscopic Infrared Mapping of Chloromethylated Polystyrene Resin Beads
Authors: Mandair Gurjit S. , Yu Zhanru , Galaffu Nicola , Bradley Mark , Russell Andrea E.
Published: November 2004

In solid-phase combinatorial chemistry, analyses are performed using a wide range of analytical techniques ranging from gel-phase nuclear magnetic resonance (NMR) to colorimetric tests to elemental analysis. However, these techniques cannot be used to interrogate functional group distribution at the single-bead level. This paper explores the feasibility of using Fourier transform infrared (FT-IR) microscopy to examine site distribution on chloromethylated polystyrene resin beads and to quantify the loading after coupling with 4-cyanophenol, an IR tagging agent. FT-IR microscopy also provides a unique opportunity to better understand the reactivity of highly cross-linked polymer beads under a range of chemical conditions.
Cosine Histogram Analysis for Spectral Image Data Classification
Authors: Zhang Jing , O'Connor Anne , Turner John F.
Published: November 2004

Conventional multivariate strategies for making qualitative estimates of sample composition rely chiefly on identifying subtle differences in spectral shape. In some instances, such as in biological tissues, the spectra obtained from a single sample class may consist of many shapes. Likewise, two distinctly different sample classes, such as normal and abnormal tissue, may produce similar variations in spectral shape. In our work, we employ statistical analysis of the set of cosine correlation scores obtained from multispectral visible absorption images of stained cervical Papanicolaou samples. By analyzing the cosine correlation score frequency for spectra obtained from the cell nuclei, abnormal cells can be differentiated from the background of normal cells, which vary considerably in their optical properties and morphology. Our method, called cosine histogram analysis (CHA), returns the percent likelihood of abnormality for each pixel in the field of view and is presented here for the first time.
Theoretical Modeling of Optimal Focusing Conditions Using Laser-Induced Breakdown Spectroscopy in Liquid Jets
Authors: Yaroshchyk Pavel , Morrison Richard J. S. , Body Doug , Chadwick Bruce L.
Published: November 2004

Optimal conditions are determined for laser-induced breakdown spectroscopy in liquid jets by investigating laser de-focusing and laser energy variation in aqueous liquid jets containing dilute levels of calcium chloride. It has been found that the atomic emission shows a strong correlation with both laser pulse energy and focal position. The data cannot be rationalized on the basis of electron density or ionization temperature changes alone, but rather it requires the additional consideration of the volume of the liquid sample interacting with the laser and that portion of the volume which is above the threshold energy for plasma formation. A moving breakdown model has been applied to the plasma formation in the jet to calculate the amount of sample ablated with sufficient energy for plasma formation, which models well the observed results and allows prediction of optimal focusing conditions for a given laser energy.