October 1998 arXiv papers — page 3

Dante Minniti, Albert Zijlstra, M. Victoria Alonso

We have obtained V and I-band photometry for about 17500 stars in the field of the dwarf irregular galaxy NGC3109, located in the outskirts of the Local Group. The photometry allows us to study the stellar populations present inside and outside the disk of this galaxy. From the VI color-magnitude diagram we infer metallicities and ages for the stellar popula

J. A. Peacock

This paper reviews selected aspects of the growth of cosmological structure, covering the following general areas: (1) expected characteristics of linear density perturbations according to various candidate theories for the origin of structure; (2) low-order theory for statistical measures of fluctuations; (3) formation of nonlinear structures and nonlinear

B. Revenu, F. Couchot, J. Delabrouille, J. Kaplan

We show how to take advantage of a circle scanning strategy, such as that planned for the Planck mission, to get rid of low frequency noises for polarised data.

A. Lancon

Asymptotic giant branch stars are essential contributors to the near and mid-IR emission of intermediate age (0.1-1Gyr old) stellar populations. Detecting this light sets constraints on the star formation history in galaxies and, conversely, the search for AGB signatures in well studied populations will help us reduce some of the still large uncertainties in

Jacques Moret-Bailly

It is known since 1968 that the interaction of a pulse of light with matter redshifts the spectrum; the theory is clarified, to obtain the conditions for which, with incoherent light, one gets a redshift similar to a Doppler shift rather than Raman lines. The explanation of the appearance of the same absorption line with various z becomes trivial, requiring.

B. M. Gaensler, K. T. S. Brazier, R. N. Manchester, S. Johnston

G320.4-01.2 is a complex radio and X-ray source, coinciding on the sky with the young energetic pulsar B1509-58. A young pulsar embedded in a SNR would seem to accord with expectations, but previous observations suggest that all may not be what it seems. Controversy persists over whether the pulsar and the SNR are associated, and as to what causes the remnan

Yuri Levin

Recently Andersson et. al., and Bildsten have independently suggested that an r-mode instability might be responsible for stalling the neutron-star spin-up in strongly accreting, Low Mass X-ray Binaries (LMXBs). We show that if this does occur, then there are two possibilities for the resulting neutron-star evolution: If the r-mode damping is a decreasing fu

Stephanie Cote, Tom Broadhurst, Jon Loveday, Shannon Kolind

We present preliminary results of a neutral hydrogen (HI) redshift survey to find low surface brightness (LSB) galaxies in the very nearby universe. Our sample consists of all galaxies in the APM catalog (Maddox et al 1990) with a mean surface brightness of mu > 24 mag/arcsec^2, down to a magnitude limit of b_j < 17. With the Parkes 64m Radiotelescope 35 obj

J. Bland-Hawthorn, P. R. Maloney

The Magellanic Stream and several high velocity clouds have now been detected in optical line emission. The observed emission measures and kinematics are most plausibly explained by photoionization due to hot, young stars in the Galactic disk. The highly favorable orientation of the Stream allows an unambiguous determination of the fraction of ionizing photo

I. I. Ivans, C. Sneden, R. P. Kraft

We present a chemical composition analysis of a sample of 20 giant branch stars in the &#34;CN-bimodal&#34; globular cluster M4 observed using high resolution echelle spectrographs at Lick & McDonald Observatories. M4, a mildly metal-poor ([Fe/H] ~ -1.1) globular cluster, is the nearest, brightest, and one of the most accessible targets to study the CN-bimod

J. Garcia-Ojalvo, J. Casademont, C. R. Mirasso, M. C. Torrent

The dynamics of a semiconductor-laser array whose individual elements are coupled in a global way through an external mirror is numerically analysed. A coherent in-phase solution is seen to be preferred by the system at intermediate values of the feedback coupling strength. At low values of this parameter, a strong amplification of the spontaneous emission n

Nick Evans, Stephen Hsu, Myckola Schwetz

Quark matter at sufficiently high density exhibits color superconductivity, due to attractive gluonic interactions. At lower densities of order $Λ_{QCD}^3$, it has been proposed that instanton generated vertices may play an important role in the Cooper pair formation. We study the renormalization group flow to the Fermi surface of the full set of couplings g

Jürgen G. Körner, Dan Pirjol

We consider spin-momentum correlations between the spin of the bottom baryon $Λ_{\mathrm{b}}$ and the momenta of its decay products in its inclusive semileptonic decay. We define several polar and azimuthal spin-momentum correlation measures in different event coordinate systems. The values of the spin-momentum correlation measures are calculated up to ${\ca

C. -W. H. Lee, S. G. Rajeev

We formulate Yang-Mills theory in terms of the large-N limit, viewed as a classical limit, of gauge-invariant dynamical variables, which are closely related to Wilson loops, via deformation quantization. We obtain a Poisson algebra of these dynamical variables corresponding to normal-ordered quantum (at a finite value of $\hbar$) operators. Comparing with a

L. V. Fil&#39;kov, V. L. Kashevarov

The Compton scattering on a charged pion and the process γγ\to π^0π^0 are studied using the dispersion relations. Unknown parameters of the S-wave ππinteraction, represented as a board Breit-Wignar resonance, and a sum and a difference of the π^0 meson polarizabilities are found from a fit to the experimental data for the process γ+γ\to π^0+π^0. This fit giv

B. Ludoph, M. H. Devoret, D. Esteve, C. Urbina

The conductance of atomic size contacts has a small, random, voltage dependent component analogous to conductance fluctuations observed in diffusive wires (UCF). A new effect is observed in gold contacts, consisting of a marked suppression of these fluctuations when the conductance of the contact is close to integer multiples of the conductance quantum. Usin

Y. F. Huang, Z. G. Dai, T. Lu

Soft gamma-ray repeaters are at determined distances and their positions are known accurately. If observed, afterglows from their soft gamma-ray bursts will provide important clues to the study of the so called &#34;classical gamma-ray bursts&#34;. On applying the popular fireball/blastwave model of classical gamma-ray bursts to soft gamma-ray repeaters, it

Artan Borici

We compute Neuberger&#39;s overlap operator by the Lanczos algorithm applied to the Wilson-Dirac operator. Locality of the operator for quenched QCD data and its eigenvalue spectrum in an instanton background are studied.

Stefano Capitani, Martin Lüscher, Rainer Sommer, Hartmut Wittig

The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal factor times another factor, which depends on the details of the lattice theory but is easy to compute, since

Boris Shoikhet

It is shown, that each Lifting cocycle $\Psi_{2n+1},\Psi_{2n+3},\Psi_{2n+5},...$ ([Sh1], [Sh2]) on the Lie algebra $\Dif_n$ of polynomial differential operators on an $n$-dimensional complex vector space is the sum of two cocycles, its even and odd part. We study in more details the first case $n=1$. It is shown, that any nontrivial linear combination of two

Marc-Thierry Jaekel, Serge Reynaud

We present a new quantum algebraic description of an electron localized in space-time. Positions in space and time, mass and Clifford generators are defined as quantum operators. Commutation relations and relativistic shifts under frame transformations are determined within a unique algebraic framework. Redshifts, i.e. shifts under transformations to uniform

V. Lafage, T. Ishikawa, T. Kaneko, T. Kon

A possibility to measure the spin and spin-spin correlations of a chargino pair is investigated in the process electron positron -> chargino_1 anti-chargino_1 -> (neutralino_1 quark anti-quark) (neutralino_1 quark anti-quark) at future linear-collider energies. The total and the differential cross sections are calculated by the GRACE system which allows for

T. DeGrand, A. Hasenfratz, T. G. Kovacs

We study exceptional modes of both the Wilson and the clover action in order to understand why quenched clover spectroscopy suffers so severely from exceptional configurations. We show that, in contrast to the case of the Wilson action, a large clover coefficient can make the exceptional modes extremely localized and thus very sensitive to short distance flu

J. A. de Azcarraga, J. M. Izquierdo, J. C. Perez Bueno, P. K. Townsend

The OSp(2|2)-invariant planar dynamics of a D=4 superparticle near the horizon of a large mass extreme black hole is described by an N=2 superconformal mechanics, with the SO(2) charge being the superparticle&#39;s angular momentum. The {\it non-manifest} superconformal invariance of the superpotential term is shown to lead to a shift in the SO(2) charge by

A. M. Gago, V. Pleitez, R. Zukanovich Funchal

We discuss the use of the CP asymmetry parameter (Acp) as a possible observable of CP violation in the leptonic sector. In order to do this, we study for a wide range of values of L/E the behavior of this asymmetry for the corresponding maximal value of the CP violation factor allowed by all present experimental limits on neutrino oscillations in vacuum and

Jerzy Stelmach

We discuss the horizon problem in a universe dominated by fluid with negative pressure. We show that for generally accepted value of nonrelativistic matter energy density parameter $\Omega_{m0}<1$, the horizon problem can be solved only if the fluid influencing negative pressure (the so-called ``X'' component) violates the point-wise strong energy condition

Takashi Nakamura, Takeshi Chiba

Even if the luminosity distance as a function of redshift is obtained accurately using, for example, Type Ia supernovae, the equation of state of the Universe cannot be determined uniquely but depends on one free parameter $Ω_{k0} ={k}/(a_0^2H_0^2)$, where $a_0$ and $H_0$ are the present scale factor and the Hubble parameter, respectively. This degeneracy mi

S. M. Klishevich

We study the interaction of gauge fields of arbitrary integer spins with the constant electromagnetic field. We reduce the problem of obtaining the gauge-invariant Lagrangian of integer spin fields in the external field to purely algebraic problem of finding a set of operators with certain features using the representation of the high-spin fields in the form

Charles R. Lawrence, Douglas Scott, Martin White

The COBE satellite, and the DMR experiment in particular, was extraordinarily successful. However, the DMR results were announced about 7 years ago, during which time a great deal more has been learned about anisotropies in the Cosmic Microwave Background (CMB). The CMB experiments currently being designed and built, including long-duration balloons, interfe

K. Behrndt, M. Cvetic, W. A. Sabra

We derive and analyse the full set of equations of motion for non-extreme static black holes (including examples with the spatial curvatures k=-1 and k=0) in D=5 N=2 gauged supergravity by employing the techniques of &#34;very special geometry&#34;. These solutions turn out to differ from those in the ungauged supergravity only in the non-extremality functio

M. Gunaydin, D. Minic, M. Zagermann

We continue our study of the unitary supermultiplets of the N=8, d=5 anti-de Sitter (AdS_5) superalgebra SU(2,2|4), which is also the N=4 extended conformal superalgebra in d=4. We show explicitly how to go from the compact SU(2)XSU(2)XU(1) basis to the non-compact SL(2,C)XD basis of the positive energy unitary representations of the conformal group SU(2,2)

A. I. Bobenko, Yu. B. Suris

We develop the theory of discrete time Lagrangian mechanics on Lie groups, originated in the work of Veselov and Moser, and the theory of Lagrangian reduction in the discrete time setting. The results thus obtained are applied to the investigation of an integrable time discretization of a famous integrable system of classical mechanics, -- the Lagrange top.

D. Jaksch, H. -J. Briegel, J. I. Cirac, C. W. Gardiner

We show that by using cold controlled collisions between two atoms one can achieve conditional dynamics in moving trap potentials. We discuss implementing two qubit quantum--gates and efficient creation of highly entangled states of many atoms in optical lattices.

V. V. Dodonov, O. V. Man&#39;ko, V. I. Man&#39;ko, A. Wuensche

We introduce the concept of the ``polarized&#39;&#39; distance, which distinguishes the orthogonal states with different energies. We also give new inequalities for the known Hilbert-Schmidt distance between neighbouring states and express this distance in terms of the quasiprobability distributions and the normally ordered moments. Besides, we discuss the d

Luis J. Boya, Mark Byrd, Mark Mims, E. C. G. Sudarshan

An explicit parameterization is given for the density matrices for $n$-state systems. The geometry of the space of pure and mixed states and the entropy of the $n$-state system is discussed. Geometric phases can arise in only specific subspaces of the space of all density matrices. The possibility of obtaining nontrivial abelian and nonabelian geometric phas

GianCarlo Ghirardi, Angelo Bassi

We analyze a recent paper in which an alleged devastating criticism to the so called GRW proposal to account for the objectification of the properties of macroscopic systems has been presented and we show that the author has not taken into account the precise implications of the GRW theory. This fact makes his conclusions basically wrong. We also perform a s

Masahito Hayashi

Concerning state estimation, we will compare two cases. In one case we cannot use the quantum correlations between samples. In the other case, we can use them. In addition, under the later case, we will propose a method which simultaneously measures the complex amplitude and the expected photon number for the displaced thermal states.

M. R. Kibler

The algebra su(2) is derived from two commuting quon algebras for which the parameter q is a root of unity. This leads to a polar decomposition of the shift operators of the group SU(2). The Wigner-Racah algebra of SU(2) is developed in a new basis arising from the simultanenous diagonalization of two commuting operators, viz., the Casimir of SU(2) and a uni

Vyjayanthi Chari, Nanhua Xi

We construct a monomial basis of the positive part of the quantized enveloping algebra associated to a finite-dimensional simple Lie algebra. As an application we give a simple proof of the existence and uniqueness of the canonical basis of the positive part.

Andrew Kresch

We construct an algebraic homology functor for Artin stacks of finite type over a field, and we develop intersection-theoretic properties.

Soren Eilers, Ruy Exel

The soft tori constitute a continuous deformation, in a very precise sense, from the commutative C*-algebra C(T^2) to the highly non-commutative C*-algebra C*(F_2). Since both of these C*-algebras are known to have a separating family of finite dimensional representations, it is natural to ask whether that is also the case for the soft tori. We show that thi

Alexander R. Pruss

A method for proving symmetrization inequalities for some elliptic p.d.e.&#39;s on manifolds equipped with appropriate isoperimetric inequalities is outlined. The method is based on a modification of an approach of Baernstein. The question of what is the most general result that can be proved in this way is still open, and the author can be consulted if the

Alexander R. Pruss

Let X_1,X_2,... be a sequence of independent and identically distributed random variables, and put S_n=X_1+...+X_n. Under some conditions on the positive sequence tau_n and the positive increasing sequence a_n, we give necessary and sufficient conditions for the convergence of sum_{n=1}^infty tau_n P(|S_n|>t a_n) for all t>0, generalizing Baum and Katz&#39;s

C. Quesne

$GL_h(n) \times GL_h(m)$-covariant $h$-bosonic algebras are built by contracting the $GL_q(n) \times GL_q(m)$-covariant $q$-bosonic algebras considered by the present author some years ago. Their defining relations are written in terms of the corresponding $R_h$-matrices. Whenever $n=2$, and $m=1$ or 2, it is proved by using U_h(sl(2)) Clebsch-Gordan coeffic

Ferruccio Orecchia

We extend results of our previous papers, on ordinary multiple points of curves, and on the computation of their conductor, to ordinary multiple subvarieties of codimension one.

Sergei Ivashkovich, Alessandro Silva

We prove in this note a result on extension of meromorphic mappings, which can be considered as a direct generalisation of the Hartogs extension theorem for holomorphic functions. Namely: THEOREM. Every meromorphic mapping $f:H_n^q(r)\to Y$, where $Y$ is a $q$ - -complete complex space, extends to a meromorphic mapping from $Δ^{n+q}$ to $Y$. Here $H_n^q(r):=

S. A. Merkulov

Contrary to the classical methods of quantum mechanics, the deformation quantization can be carried out on phase spaces which are not even topological manifolds. In particular, the Moyal star product gives rise to a canonical functor $F$ from the category of affine analytic spaces to the category of associative (in general, non-commutative) $\C$-algebras. Cu

Udo Hertrich-Jeromin, Emilio Musso, Lorenzo Nicolodi

Various transformations of isothermic surfaces are discussed and their interrelations are analyzed. Applications to cmc-1 surfaces in hyperbolic space and their minimal cousins in Euclidean space are presented: the Umehara-Yamada perturbation, the classical and Bryant&#39;s Weierstrass type representations, and the duality for cmc-1 surfaces are interpreted

Antoine Balan

The derivation is studied in relation with the space of Schwartz of functions. This paper has been withdrawn by the author.

B. Enriquez, G. Felder

We introduce twists by Cartan elements of conformal blocks on a curve X, corresponding to a Lie algebra g. We show that these twists define holomorphic functions, with theta-like behaviour, on a product of copies of its Jacobian J(X)^r. We then parametrise the conformal blocks by their twisted correlation functions of nilpotent currents, in the spirit of Fei

Lowell Abrams

We characterize noncommutative Frobenius algebras A in terms of the existence of a coproduct which is a map of left A^e-modules. We show that the category of right (left) comodules over A, relative to this coproduct, is isomorphic to the category of right (left) modules. This isomorphism enables a reformulation of the cotensor product of Eilenberg and Moore

Teodor Banica

We associate Popa systems (= standard invariants of subfactors) to the finite dimensional representations of compact quantum groups. We characterise the systems arising in this way: these are the ones which can be ``represented&#39;&#39; on finite dimensional Hilbert spaces. This is proved by an universal construction. We explicitely compute (in terms of som

A. K. Aringazin

We present BRST gauge fixing approach to quantum mechanics in phase space. The theory is obtained by $\hbar$-deformation of the cohomological classical mechanics described by d=1, N=2 model. We use the extended phase space supplied by the path integral formulation with $\hbar$-deformed symplectic structure.

R. Rosenfelder, C. Alexandrou, A. W. Schreiber

Following Feynman&#39;s treatment of the non-relativistic polaron problem, similar techniques are used to study relativistic field theories: after integrating out the bosonic degrees of freedom the resulting effective action is formulated in terms of particle trajectories (worldlines) instead of field operators. The Green functions of the theory are then app

R. R. Metsaev

Arbitrary spin free massless bosonic fields propagating in even $d$ - dimensional anti-de Sitter spacetime are investigated. Free wave equations of motion, subsidiary conditions and the corresponding gauge transformations for such fields are proposed. The lowest eigenvalues of the energy operator for the massless fields and the gauge parameter fields are der

Sergiu I. Vacaru

We propose an approach to the theory of higher order anisotropic field interactions and curved spaces (in brief, ha-field, ha-interactions and ha-spaces). The concept of ha-space generalises various types of Lagrange and Finsler spaces and higher dimension (Kaluza-Klein) spaces. This work consists from two parts. In the first we outline the theory of Yang-Mi

Boris Kayser

We discuss the three major hints of neutrino mass: the strong evidence of mass from the behavior of atmospheric neutrinos, the very promising further hint from the behavior of solar neutrinos, and the so-far unconfirmed hint from the LSND experiment. Then, we describe two illustrative neutrino-mass scenarios suggested by the observed hints. We identify the n

Andrzej Czarnecki, William J. Marciano

Standard Model contributions to the electron, muon, and tau lepton anomalous magnetic moments, a_l=(g_l-2)/2, are reviewed and updated. The fine structure constant is obtained from the electron g_e-2 and used to refine the QED contribution to the muon g_mu-2. Recent advances in electroweak and hadronic effects on g_mu-2 are summarized. Examples of ``New Phys

S. W. Mansour, T. K. Kuo

In this Brief Report, a non-standard solution to the solar neutrino problem is revisited. This solution assumes that neutrino flavors could have different couplings to gravity, hence, the equivalence principle is violated in this mechanism. The gravity induced mixing has the potential of accounting for the current solar neutrino data from several experiments

Thomas Schaefer, Frank Wilczek

We consider the most general four fermion operators in QCD for two and three massless flavors and study their renormalization in the vicinity of the Fermi surface. We show that, asymptotically, the largest coupling corresponds to scalar diquark condensation. Asymptotically the direct and iterated (molecular) instanton interactions become equal. We provide si

M. J. Menon

It is argued that Centauro events observed in cosmic ray experiments may be characteristic of only pp and not p(bar)p interactions.

A. Gehrmann-De Ridder

The production of final state photons in hadronic $Z$-boson decays can be used to study the quark-to-photon fragmentation function $D_{q\to γ}(z,μ_{F})$. Currently, two different observables are used at LEP to probe this function: the `photon&#39; +~1 jet rate and the inclusive photon energy distribution. We outline the results of a calculation of the `photo

Stephen Godfrey, Tao Han, Pat Kalyniak

In a strongly-interacting electroweak sector with an isosinglet vector state, such as the techni-omega, $ω_T$, the direct $ω_T Z γ$ coupling implies that an $ω_T$ can be produced by $Z γ$ fusion in $eγ$ collisions. This is a unique feature for high energy $e^+e^-$ or $e^-e^-$ colliders operating in an $eγ$ mode. We consider the processes $e^- γ\to e^- Zγ$ an

Zhijian Tao

We investigate the maximal approximate flavor symmetry in the framework of generic minimal supersymmetric standard model. We consider the low energy effective theory of the flavor physics with all the possible operators included. Spontaneous flavor symmetry breaking leads to the approximate flavor symmetry in Yukawa sector and the supersymmetry breaking sect

K. G. Klimenko

Phase structure of the four dimensional Nambu -- Jona-Lasinio model has been investigated in two cases: 1) in nonsimply connected space-time of the form $R^3\times S^1$ (space coordinate is compactified and the length of the circle $S^1$ is $L$) with nonzero chemical potential $μ$ and 2) in Minkowski space-time at nonzero values of $μ,H$, where $H$ is the ex

Hisao Nakkagawa, Hiroshi Yokota

In this paper a resummation method inspired by the renormalization-group improvement is applied to the one-loop effective potential (EP) in massive scalar $ϕ^4$ model at $T\neq0$. By investigating the phase structure of the model at $T \neq 0$ we get the following observations; i) Starting from the perturbative calculations with the theory renormalized at an

N. N. Achasov

It is presented a critical consideration of all unusual properties of the scalar $a_0(980)$ and $f_0(980)$-mesons in the four-quark, two-quark and molecular models. The arguments are adduced that the four-quark model is more preferable. It is discussed the complex of experiments that could finally resolve this issue.

Terrence Draper

The status of lattice calculations of some phenomenology of heavy quarks is presented. Emphasis is on progress made in calculating those quantities relevant to estimating parameters of the quark mixing matrix, namely leptonic decay constants, the bag parameter of neutral $B$ mixing, and semileptonic form factors. New results from studies of quarkonia are hig

R. Kirchner, S. Luckmann, I. Montvay, K. Spanderen

In a numerical Monte Carlo simulation of SU(2) Yang-Mills theory with dynamical gauginos we find evidence for two degenerate ground states at the supersymmetry point corresponding to zero gaugino mass. This is consistent with the expected pattern of spontaneous discrete chiral symmetry breaking $Z_4 \to Z_2$ caused by gaugino condensation.

ZEUS Collaboration

The cross section for the photoproduction of events containing three jets with a three-jet invariant mass of M_3J > 50 GeV has been measured with the ZEUS detector at HERA. The three-jet angular distributions are inconsistent with a uniform population of the available phase space but are well described by parton shower models and O(alpha alpha_s^2) pQCD calc

F. Richard

Table of contents 1. Introduction 2. Theory 3. Searches at LEP2 4. Results 5. Futur colliders 6. Final remarks

C. D. Batista, A. A. Aligia, J. Eroles

Starting from a multiband Hamiltonian containing the relevant Ni and O orbitals, we derive an effective Hamiltonian $H_{eff}$ for the low energy physics of doped Y$_{2}$BaNiO$_{5}.$ For hole doping, $H_{eff}$ describes O fermions interacting with S=1 Ni spins in a chain, and cannot be further reduced to a simple one-band model. Using numerical techniques, we

D. Bolle, G. Jongen, G. M. Shim

The parallel dynamics of extremely diluted symmetric Q-Ising neural networks is studied for arbitrary Q using a probabilistic approach. In spite of the extremely diluted architecture the feedback correlations arising from the symmetry prevent a closed-form solution in contrast with the extremely diluted asymmetric model. A recursive scheme is found determini

Chris G. van de Walle, Catherine Stampfl, Joerg Neugebauer

Doping problems in GaN and in AlGaN alloys are addressed on the basis of state-of-the-art first-principles calculations. For n-type doping we find that nitrogen vacancies are too high in energy to be incorporated during growth, but silicon and oxygen readily form donors. The properties of oxygen, including DX-center formation, support it as the main cause of

M. Sifkovits, H. Smolinski, S. Hellwig, W. Weber

Using spin density functional theory we have carried out a comparative study of chemical bonding and magnetism in Fe_4N, Fe_3N and Fe_2N. All of these compounds form close packed Fe lattices, while N occupies octahedral interstitial positions. High spin fcc Fe and hypothetical FeN with rock salt structure have been included in our study as reference systems.

T. G. Perring, G. Aeppli, T. Kimura, Y. Tokura

The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of metallic MnO2 sheets separated by insulating material. The compound exhibits markedly anisotropic magnetoresistance at temperatures well below the three-dimensional magnetic ordering temperature TC=90 K in addition to colossal magnetoresistance around TC. We present neutron diffraction da

E. T. Seppala, V. Petaja, M. J. Alava

Ground states and domain walls are investigated with exact combinatorial optimization in two-dimensional random field Ising magnets. The ground states break into domains above a length scale that depends exponentially on the random field strength squared. For weak disorder, this paramagnetic structure has remnant long-range order of the percolation type. The

M. A. Martin-Delgado, J. Dukelsky, G. Sierra

Using the Lanczos method we determine the phase diagram of the 2-leg AF-Heisenberg ladder with alternating dimerization. It consists of a resonating valence bond phase and a dimer phase separated by a critical line. Our results are in good agreement with previous conjectures obtained with the non linear sigma model.

Michel Droz, Max-Olivier Hongler

We exhibit a one to one correspondence between some universal probabilistic properties of the ordering coordinate of one-dimensional Ising-like models and a class of continuous time random walks. This correspondence provides an new qualitative picture of the properties of the ordering coordinate of the Ising model.

A. M. C. Valkering, P. K. H. Sommerfeld, R. A. M. van de Ven, R. W. van der Heijden

The magnetocapacitance of a two-dimensional electron system (2DES) is investigated experimentally, both under and away from Quantum Hall (QH) conditions, at frequencies between 1 kHz and 100 MHz. The nature of the capacitive signal in a bounded 2DES is determined by a resistive cut-off frequency 1/$τ\propto σ_{xx}$, the longitudinal magnetoconductivity. A ne

Jun-jie Shi, Barry C. Sanders, Shao-hua Pan

Based on the dielectric continuum model, we calculated the phonon assisted tunneling (PAT) current of general double barrier resonant tunneling structures (DBRTSs) including both symmetric and antisymmetric ones. The results indicate that the four higher frequency interface phonon modes (especially the one which peaks at either interface of the emitter barri

Jun-jie Shi, Barry C. Sanders, Shao-hua Pan

We present a self-consistent calculation, based on the global coherent tunnelling model, and show that structural asymmetry of double barrier resonant tunnelling structures significantly modifies the current-voltage characteristics compared to the symmetric structures. In particular, a suitably designed asymmetric structure can produce much larger peak curre

Girish S. Setlur, Yia-Chung Chang

In this article, we revisit the question of the validity of Hartree-Fock and random-phase approximations. We show that there is a connection between the two and while the RPA as it is known in much of the physics literature is of limited validity, there is a generalised sense in which the random phase approximation is of much wider applicability including to

Hiroshi Ezawa, Koichi Nakamura, Keiji Watanabe

After a discussion on the state of local equilibrium with temperature inhomogeneity, comparing mixture state reprsentation in statistical mechanics and pure state representation in thermo field dynamics, a simple model is solved to show that a reversible equation of motion with the initial condition having inhomogeneous temperature can lead to irreversible,

Lapo Casetti, Raoul Gatto, Marco Pettini

A Riemannian geometrization of dynamics is used to study chaoticity in the classical Hamiltonian dynamics of a U(1) lattice gauge theory. This approach allows one to obtain analytical estimates of the largest Lyapunov exponent in terms of time averages of geometric quantities. These estimates are compared with the results of numerical simulations, and turn o

Mark Wardle, Cindy Ng

We evaluate the conductivity tensor for molecular gas at densities ranging from 10^4 to 10^15 cm^-3 for a variety of grain models. The Hall contribution to the conductivity has generally been neglected in treatments of the dynamics of molecular gas. We find that it is not important if only 0.1 micron grains are considered, but for a Mathis-Rumpl-Nordsieck gr

Daniel A. Dale, Riccardo Giovanelli, Martha P. Haynes, Luis E. Campusano

We have obtained new Tully-Fisher (TF) peculiar velocity measurements for 52 Abell galaxy clusters distributed throughout the sky between ~ 50 and 200 Mpc/h.The measurements are based on I band photometry and optical rotation curves for a sample of 522 spiral galaxies, from which an accurate TF template relation has been constructed. Individual cluster TF re

Brian R. McNamara, Buell T. Jannuzi, Craig L. Sarazin, Richard Elston

We have obtained U-band polarimetry of the spatially extended, blue optical continuum associated with the FR I radio source PKS 2322-122. PKS 2322-122 is located in the Abell 2597 cluster central galaxy. We find a three sigma upper limit to the degree of polarization of the optical continuum of less than 6%. This limit is inconsistent with the blue continuum

Kyu-Hyun Chae, David A. Turnshek

We investigate gravitational lens models for the quadruply-lensed Cloverleaf BAL QSO H1413+1143 based on the HST WFPC/WFPC2 astrometric and photometric data of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The accurate image positions and the dust-extinction-corrected relative amplifications, along with a possible detection of the l

D. Barret, J. E. Grindlay, I. M. Harrus, J. F. Olive

The bright persistent X-ray source and type I X-ray burster 1E1724-3045 located in the globular cluster Terzan 2 was observed by ASCA for about 10 ksec on September 24-25th, 1995 while it was in its hard state, with a luminosity of \~6x10^36 erg/s in the 0.5-10 keV band (d=7.7 kpc). The ASCA spectrum is hard, and reveals the presence of a soft component belo

M. M. Colavita

Visibility estimators and their performance are presented for use with the Palomar Testbed Interferometer (PTI). One operational mode of PTI is single-baseline visibility measurement using pathlength modulation with synchronous readout by a NICMOS-3 infrared array. Visibility is estimated from the fringe quadratures, either incoherently, or using source phas

Andrew C. Layden

I review statistical parallax absolute magnitude determinations which employ data from the HIPPARCOS satellite for RR Lyrae and Cepheid variables, and for several other stellar classes. Five groups have studied the RR Lyrae stars, and the results are reassuringly consistent: M_V(RR) = 0.77 +- 0.13 mag at [Fe/H] = -1.6 dex. Extensive Monte Carlo simulations s

G. Bono, M. Marconi

We present the comparison between theoretical and empirical PL relations in V and I bands for the Large Magellanic Cloud. We found that, within the current intrinsic dispersions, theoretical predictions are in remarkable agreement with observational data. We also discuss the PLC relations in (V,B-V) and (V,V-I) as well as the dependence of distance determina

John S. Mulchaey, Ann I. Zabludoff

Numerical simulations predict that some poor groups of galaxies have merged by the present epoch into giant ellipticals (cf. Barnes 1989). To identify the possible remnants of such mergers, we have compiled a sample of nearby, isolated ellipticals (Colbert, Mulchaey, & Zabludoff 1998). ASCA observations of the first galaxy studied, NGC 1132 reveal an X-ray h

G. Gonzalez-Casado, A. Raig, E. Salvador-Sole

We analyze the physical justification of the picture proposed by Salvador-Sole et al. in these proceedings for the time evolution of the universal density profile of dark-matter halos. According to this picture, halos have at formation a stable (i.e. independent of mass and time) dimensionless density profile, the characteristic length and density scales of

A. Jorissen

It is currently admitted that an AGB star in a binary system is likely to pollute its companion with carbon- and s-process-rich matter. After the AGB star has faded into an unconspicuous white dwarf, the polluted companion enters the zoo of stars with chemical peculiarities. In this paper, the progeny of AGB stars in binary systems are identified among exist

G. Catanzaro, F. Leone, F. A. Catalano

Chemically peculiar stars present spectral and photometric variability with a single period. In the oblique rotator model, the non homogeneous distribution of elements on the stellar surface is at the origin of the observed variations. As to helium weak stars, it has been suggested that photometric and helium line equivalent width variations are out of phase

T. Oka, T. Hasegawa, F. Sato, M. Tsuboi

The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. Clouds are identified in an automated manner throughout the main part of the survey data for all CO emission peaks exceeding 10 K ($T_R^*$). Correlations between the si

Crystal L. Martin

Both galaxies and the intergalactic medium evolve dramatically between $z \approx 2$ and the present. These changes are coupled via galactic winds, cloud accretion, and ionizing radiation. Measurements of these interactions are critical for building a physical understanding of galaxy assembly. This paper reviews the role of starburst galaxies in heating, enr

D. R. Marlow, I. W. A. Browne, N. Jackson, P. N. Wilkinson

NICMOS observations of the complex gravitational lens system B1933+503 reveal infrared counterparts to two of the inverted spectrum radio images. The infrared images have arc-like structures. The corresponding radio images are also detected in a VLBA map made at 1.7 GHz with a resolution of 6 mas. We fail to detect two of the four inverted radio spectrum com