September 1998 arXiv papers — page 3

Krzysztof Sacha, Jakub Zakrzewski

The dynamics of Rydberg states of atomic hydrogen illuminated by resonant elliptically polarized microwaves is investigated both semiclassically and quantum mechanically in a simplified two-dimensional model of an atom. Semiclassical predictions for quasienergies of the system are found to be in a very good agreement with exact quantum data enabling a classi

Christopher J. Conselice, John S. Gallagher

We present the results of a study on galaxy interactions, tides, and other processes which produce luminous fine-scale substructures in the galaxy clusters: Coma, Perseus, Abell 2199, AWM 3 and AWM 5. All unusual structures in these clusters can be categorized in seven morphologies: interacting galaxies, multiple galaxies (non-interacting), distorted galaxie

M. L. McCollough, C. R. Robinson, S. N. Zhang, B. A. Harmon

In the period between May 1997 and August 1997 a series of pointed RXTE observations were made of Cyg X-3. During this period Cyg X-3 made a transition from a quiescent radio state to a flare state (including a major flare) and then returned to a quiescent radio state. Analyses of the observations are made in the context of concurrent observations in the har

Edward L. Fitzpatrick

This paper addresses the issue of how best to correct astronomical data for the wavelength-dependent effects of Galactic interstellar extinction. The main general features of extinction from the IR through the UV are reviewed, along with the nature of observed spatial variations. The enormous range of extinction properties found in the Galaxy, particularly i

Fred Hamann

Intrinsic emission and absorption lines of QSOs provide several independent probes of the metal abundances in QSO environments. They indicate that the metallicities are typically solar or higher out to redshifts z > 4. These results support models of galaxy evolution where galactic nuclei, or dense condensations that later become galactic nuclei, form stars

J. E. Horvath, H. Vucetich

We address the production of strangelets inside neutron stars by means of high-energy neutrino interactions (sparking). Requiring that neutron stars remain as such along their lifetimes, we obtain a bound on the probability of a strangelet in the final state and compare it with existing laboratory limits. It turns out that this mechanism is not likely to dri

H. Böhringer, L. Guzzo, C. A. Collins, D. M. Neumann

Based on the ROSAT All-Sky Survey we have conducted a large redshift survey as an ESO key programme to identify and secure redshifts for the X-ray brightest clusters found in the southern hemisphere. We present first results for a highly controlled sample for a flux limit of 3 10-12 erg/s/cm+2 comprising 475 clusters (87% with redshifts). The logN-logS funct

R. Hank Donnelly, M. Markevitch, W. Forman, C. Jones

We study the temperature structure of the central part (r<18&#39; ~0.7 h50**-1 Mpc) of the Coma cluster of galaxies using ASCA data. Two different analysis methods produce results in good agreement with each other and reveal the presence of interesting structures in the gas temperature distribution. Globally, the average temperature in the center of the clus

Tomas Dahlen, Claes Fransson

We use different assumptions for the combination of dust extinction and star formation up to redshifts z >= 5, as well as detailed modeling of supernova properties, to estimate the number of supernovae that should be observable with various instruments, in particular the NGST. In the model we use realistic light curves and spectral shapes that evolve with ti

Jeremy Goodman, Wyn Evans

Scale-free disks have no preferred length or time scale. The question has been raised whether such disks have a continuum of unstable linear modes or perhaps no unstable modes at all. We resolve this paradox by analysing the particular case of a gaseous, isentropic disk with a completely flat rotation curve (the Mestel disk) exactly. The heart of the matter

I. V. Moskalenko, W. Collmar

Assuming that the enhanced MeV emission from the MeV blazar PKS 0208-512 observed by COMPTEL on occasions is due to annihilation in a pair plasma, we estimate parameters of the annihilation region: its size, the number density of particles, and the variability timescale. The values we find are in accord with our present-day knowledge of emission mechanisms o

Gary A. Mamon

The DENIS survey is currently imaging the entire southern sky in the I, J, and K wavebands. The current star/galaxy separation algorithm is presented and the galaxy counts are nearly perfectly Euclidean. 95% complete and reliable galaxy samples with better than 0.2 magnitude photometry should include 50,000 (K < 12.0), 500,000 (J < 14.8), and 900,000 (I < 16

G. I. Ogilvie

A new description of the dynamics of warped accretion discs is presented. A theory of fully nonlinear, slowly varying bending waves is developed, involving a proper treatment of viscous fluid dynamics but neglecting self-gravitation. The special case of resonant wave propagation found in inviscid Keplerian discs is not considered. The resulting description g

E. Athanassoula

I review the Marseille GRAPE systems and the N-body simulations done with them. I first describe briefly the available hardware and software, their possibilities and their limitations. I then describe work done on interacting galaxies and groups of galaxies. This includes simulations of the formation of ring galaxies, simulations of bar destruction by massiv

S. Andreon

Contradictory results on the evolution of lenticular galaxies (S0s) at intermediate redshift have been recently published. A careful analysis of the used methodology shows that in order to gain insights on the evolution of the morphological types it is necessary: (1) to use quantitative morphological types, (2) to propagate morphological errors in the quanti

Changbom Park, Sungho Lee

We have found that the two-point correlation function of the APM clusters of galaxies has an amplitude much higher than that claimed by the APM group. As the richness limit increases from R = 53 to 80, the correlation length increases from 17.5 to 28.9 h^{-1}Mpc. This indicates that the richness dependence of the APM cluster correlation function is also much

C. S. Kochanek, E. E. Falco, C. D. Impey, J. Lehar

We have obtained and modeled new NICMOS images of the lens system MG1131+0456, which show that its lens galaxy is an H=18.6 mag, transparent, early-type galaxy at a redshift of about z_l = 0.85; it has a major axis effective radius R_e=0.68+/-0.05 arcsec, projected axis ratio b/a=0.77+/-0.02, and major axis PA=60+/-2 degrees. The lens is the brightest member

Andrey Kravtsov, Anatoly Klypin, Pedro Colin, Alexei Khokhlov

We study the evolution of the halo-halo correlation function and bias in a LCDM model using very high-resolution N-body simulations. The high force and mass resolution allows dark matter (DM) halos to survive in the tidal fields in high-density regions and thus prevents the ambiguities related with the ``overmerging problem.&#39;&#39; Numbers of galaxy-size

Wayne Hu, Daniel J. Eisenstein

We study the general structure of models for structure formation, with applications to the reverse engineering of the model from observations. Through a careful accounting of the degrees of freedom in covariant gravitational instability theory, we show that the evolution of structure is completely specified by the stress history of the dark sector. The study

Fritjof Flechsig

Thermal perturbation theory based on the resummation scheme by Braaten and Pisarski suffers from unscreened collinear singularities whenever outer momenta become light-like. A recently proposed improvement of the hard thermal loops by an additional resummation of an asymptotic mass promises to solve this problem. Here we present a detailed investigation of t

M. B. Halpern, C. Schwartz

Extending early work, we formulate the large N matrix mechanics of general bosonic, fermionic and supersymmetric matrix models, including Matrix theory: The Hamiltonian framework of large N matrix mechanics provides a natural setting in which to study the algebras of the large N limit, including (reduced) Lie algebras, (reduced) supersymmetry algebras and fr

G. L. Thomas, V. E. Herscovitz, C. L. Schat, N. N. Scoccola

We develop the formalism to study the hyperon-nucleon interaction potential within the bound state approach to the SU(3) Skyrme model. The general framework is illustrated by applying it to the diagonal $ΛN$ potential. The central, spin-spin and tensor components of this interaction are obtained and compared with those derived using alternative schemes.

Harvey S. Reall

The cosmological solutions of Horava-Witten theory discovered by Lukas, Ovrut and Waldram are generalized to allow non vanishing spatial curvature. The solution with closed spatial sections has initial and final curvature singularities. We find two solutions with open spatial sections, both of which evolve from an initial curvature singularity to the supersy

E. M. Aitala

We present a study of correlations between D and $\bar{D}$ mesons produced in 500 GeV/$c$ $π^-$-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed $791 \pm 44$ charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for differe

E. M. Rains

The best bound known on 2-locally distillable entanglement is that of Vedral and Plenio, involving a certain measure of entanglement based on relative entropy. It turns out that a related argument can be used to give an even stronger bound; we give this bound, and examine some of its properties. In particular, and in contrast to the earlier bounds, the new b

K. S. Virbhadra

It is shown that for a general nonstatic spherically symmetric metric of the Kerr-Schild class several energy-momentum complexes give the same energy distribution as in the Penrose prescription, obtained by Tod. This result is useful for investigating the Seifert conjecture for naked singularities. The naked singularity forming in the Vaidya null dust collap

Jesper Christiansen

We consider QCD_3 with an odd number of flavors in the mesoscopic scaling region where the field theory finite-volume partition function is equivalent to a random matrix theory partition function. We argue that the theory is parity invariant at the classical level if an odd number of masses are zero. By introducing so-called pseudo-orthogonal polynomials we

Laura Covi, David H. Lyth

If the inflaton sector is described by softly broken supersymmetry, and the inflaton has unsuppressed couplings, the inflaton mass will run strongly with scale. Four types of model are possible. The prediction for the spectral index involves two parameters, while the COBE normalization involves a third, all of them calculable functions of the relevant masses

E. Epelbaoum, W. Glöckle, A. Krüger, Ulf-G. Meißner

We apply the method of unitary transformations to a model two-nucleon potential and construct from it an effective potential in a subspace of momenta below a given cut-off $Λ$. The S-matrices in the full space and in the subspace are shown to be identical. We solve numerically the Schrödinger equation in the small momentum space and recover exactly the bound

Marc Mars, Walter Simon

We show that the Riemannian Schwarzschild and the ``Taub-bolt&#39;&#39; instanton solutions are the only spaces (M,g) such that 1) M is a 4-dimensional, simply connected manifold with a Riemannian, Ricci-flat C^2-metric g which admits (at least) a 1-parameter group of isometries H without isolated fixed points on M. 2) The quotient (M L)/H (where L is the se

H. J. W. Müller-Kirsten, Nobuyoshi Ohta, Jian-Ge Zhou

The greybody factors in BTZ black holes are evaluated from 2D CFT in the spirit of AdS$_3$/CFT correspondence. The initial state of black holes in the usual calculation of greybody factors by effective CFT is described as Poincaré vacuum state in 2D CFT. The normalization factor which cannot be fixed in the effective CFT without appealing to string theory is

Mark Wardle

MHD in protostellar discs is modified by the Hall current when the ambipolar diffusion approximation breaks down. Here I examine the Balbus-Hawley (magnetorotational) instability of a weak, vertical magnetic field within a weakly-ionized disc. Vertical stratification is neglected, and a linear analysis is undertaken for the case that the wave vector of the p

Gen Kuroki, Takashi Takebe

We construct an integral representation of solutions of the Knizhnik-Zamolodchikov-Bernard equations, using the Wakimoto modules.

D. A. Lidar, D. Bacon, K. B. Whaley

An operator sum representation is derived for a decoherence-free subspace (DFS) and used to (i) show that DFSs are the class of quantum error correcting codes (QECCs) with fixed, unitary recovery operators, and (ii) find explicit representations for the Kraus operators of collective decoherence. We demonstrate how this can be used to construct a concatenated

J. Finkelstein

We consider the definition that might be given to the time at which a particle arrives at a given place, both in standard quantum theory and also in Bohmian mechanics. We discuss an ambiguity that arises in the standard theory in three, but not in one, spatial dimension.

Esteban Calzetta, Bei-lok Hu

We derive an influence action for the heat diffusion equation and from its spectral dependence show that long wavelength hydrodynamic modes are most readily decohered. The result is independent of the details of the microscopic dynamics, and follows from general principles alone.

Petre Diţă

We develop here a simple quantisation formalism that make use of Lie algebra properties of the Poisson bracket. When the brackets $\{H,ϕ_i\}$ and $\{ϕ_i,ϕ_j\}$, where $H$ is the Hamiltonian and $ϕ_i$ are primary and secondary constraints, can be expressed as functions of $H$ and $ϕ_i$ themselves, the Poisson bracket defines a Poisson-Lie structure. When this

Mikhail Khovanov, Greg Kuperberg

We compare two natural bases for the invariant space of a tensor product of irreducible representations of A_2, or sl(3). One basis is the web basis, defined from a skein theory called the combinatorial A_2 spider. The other basis is the dual canonical basis, the dual of the basis defined by Lusztig and Kashiwara. For sl(2) or A_1, the web bases have been di

A. A. Barybin

A unified electrodynamic approach to the guided wave excitation by external sources in the waveguiding structures with bianisotropic media is developed. Effect of electric, magnetic, and magneto- electric losses in such media manifests itself in the special form of eigenmode orthogonality referred to as the quasi-orthogonality relation. It reflects the exist

V. Yu. Denisov

We discuss a model for the description of subbarrier fusion of heavy ions which takes into account the coupling to the low-energy surface vibrational states and to the few-nucleon transfer with arbitrary reaction Q-value. The fusion reactions ^{28,30}Si+^{58,62,64}Ni, ^{40}Ca+^{90,96}Zr, ^{28}S+^{94,100}Mo, ^{16,18,20,22,24}O+^{58}Ni and ^{28}Si+^{124,126,12

P. Duclos, P. Stovicek, O. Vana

A resolvent formula, originally presented by Karner in his habilitation, is discussed. First the formula is considered abstractly and then it is demonstrated on an explicit example -- the so called simplified Fermi accelerator.

T. D. Palev, N. I. Stoilova

Two classes of irreducible highest weight modules of the general linear Lie superalgebra $gl(1/\infty)$ are constructed. Within each module a basis is introduced and the transformation relations of the basis under the action of the algebra generators are written down.

Dmitry E. Tamarkin

We prove that the chain operad of small squares is formal. This fact clarifies situation with the proof of M. Kontsevich formality theorem in the paper of the author math.QA/9803025, revised Sept 24. The formality of the operad follows quite easily from the existence of an associator.

Tim Cochran, Amir Gerges, Kent Orr

When can one 3-manifold be transformed to another by a finite sequence of Dehn surgeries which are restricted to preserve the first homology of the manifolds ? What is the resulting equivalence relation on 3-manifolds ? What if the surgery circle is further restricted to lie more deeply in the lower central series of the fundamental group ? We answer these q

C. J. Neugebauer

For w in A_p(RH_r), we determine the precise range of indices so that w in RH_r(A_p), the precise range of q smaller than p for which w in A_q, and the precise range of s bigger than 1 for which w^s in A_p.

Pavel Etingof, Olivier Schiffmann

The purpose of this note is to define and construct highest weight modules for Felder&#39;s elliptic quantum groups. This is done by using exchange matrices for intertwining operators between (not necessarily finite-dimensional) modules over quantum affine algebras.

B. L. Cerchiai, R. Hinterding, J. Madore, J. Wess

We show how one can construct a differential calculus over an algebra where position variables x and momentum variables p have be defined. As the simplest example we consider the one-dimensional q-deformed Heisenberg algebra. This algebra has a subalgebra generated by x and its inverse which we call the coordinate algebra. A physical field is considered to b

E B Davies

We review the literature concerning the Hardy inequality for regions in Euclidean space and in manifolds, concentrating on the best constants. We also give applications of these inequalities to boundary decay and spectral approximation.

Yao-Zhong Zhang, Mark D. Gould

We introduce the quasi-Hopf superalgebras which are $Z_2$ graded versions of Drinfeld&#39;s quasi-Hopf algebras. We describe the realization of elliptic quantum supergroups as quasi-triangular quasi-Hopf superalgebras obtained from twisting the normal quantum supergroups by twistors which satisfy the graded shifted cocycle condition, thus generalizing the qu

Hessam Hamidi-Tehrani

We classify groups generated by powers of 2 Dehn twists which are 1) free or 2) have no ``unexpected&#39;&#39; reducible elements. We give some sufficient conditions in the case of groups generated by powers of more than two twists.

Hessam Hamidi-Tehrani

We prove that the word problem in the mapping class group of the once-punctured surface of genus g has complexity O(|w|^2 g for |w| > log(g) where |w| is the length of the word in a (standard) set of generators. The corresponding bound in the case of the closed surface is O(|w|^2 g^2). We also carry out the same methods for the braid groups, and show that th

P. Maraner

The effective classical/quantum dynamics of a particle constrained on a closed line embedded in a higher dimensional configuration space is analyzed. By considering explicit examples it is shown how different reduction mechanisms produce unequivalent dynamical behaviors. The relation with a formal treatment of the constraint is discussed. While classically i

Alan Kostelecky

The sensitivity of experiments with neutral mesons to possible indirect CPT violation is examined. It is shown that experiments conventionally regarded as equivalent can have CPT reaches differing by orders of magnitude within the framework of a minimal CPT- and Lorentz-violating extension of the standard model.

A. Ster, T. Csorgo, B. Lorstad

Analytic and numerical approximations to a hydrodynamical model describing longitudinally expanding, cylindrically symmetric, finite systems are fitted to preliminary NA44 data measured in 200 AGeV central $S + Pb$ reactions. The model describes the measured spectra and HBT radii of pions, kaons and protons, simultaneously. The source is characterized by a c

H. -Th. Elze, T. Kodama, Y. Hama, M. Makler

We derive the special and general relativistic hydrodynamic equations of motion for ideal fluids from a variational principle. Our approach allows to find approximate solutions, whenever physically motivated trial functions can be used. Illustrating this, a Rayleigh-Plesset type equation for the relativistic motion of a spherical (QGP) droplet is obtained. A

Petre Diţă

We test the positivity property of the chiral perturbation theory (ChPT) pion-pion scattering amplitudes within the Mandelstam triangle. In the one-loop approximation, ${\cal O}(p^4)$, the positivity constrains only the coefficients $b_3$ and $b_4$, namely one obtains that $b_4$ and the linear combination $b_3+3 b_4$ are positive quantities. The two-loops ap

M. A. Braun, P. Gauron, B. Nicolescu

The odderon intercept is calculated directly, from its expression via an average energy of the odderon Hamiltonian, using both trial wave functions in the variational approach and the wave function recently constructed by R.A.Janik and J.Wosiek. The results confirm their reported value for the energy. The odderon intercept is calculated directly, from its ex

Katri Huitu, Cai-Dian Lü, Paul Singer, Da-Xin Zhang

For any new physics possibly emerging in the future B experiments, the problem is how to extract the signals from the SM background. We consider the decay $b\to s s\bar d$ which is very small in the SM. In the MSSM this decay is possibly accessible in the future experiments. In the supersymmetric models with R-parity violating couplings, this channel is not

P. Rehberg, L. Bot, J. Aichelin

Using a chirally symmetric Lagrangian, which contains quarks as elementary degrees of freedom and mesons as bound states, we investigate the expansion and hadronization of a fireball, which initially contains only quarks and produces mesons by collisions. For this model, we study the time scales of expansion and thermal and chemical equilibration. We find th

N. K. Watson

Recent measurements of the properties of W+W- events produced in e+e- collisions at Ecm=183 GeV at LEP are reviewed. The data are used to investigate the predicted effects of final state interactions, specifically &#34;colour reconnection&#34;.

Neven Bilic, Raoul D. Viollier

The Thomas-Fermi model at finite temperature is extended to describe a system of self-gravitating weakly interacting massive fermions in a general-relativistic framework. By cooling a nondegenerate gas of weakly interacting massive fermions below some critical temperature, a condensed phase emerges, consisting of quasidegenerate fermion stars. For fermion ma

Sergey Troshin, Nikolai Tyurin

We consider low-x behavior of the spin structure functions g_1(x) and h_1(x) in the unitarized chiral quark model that combines the ideas on constituent quark structure of hadrons with a geometrical scattering picture and unitarity. A nondiffractive singular low-x dependence of g^p_1(x) and g_1^n(x) is obtained and a diffractive type smooth behavior of h_1(x

Alan Kostelecky

Apparent violations of CPT and Lorentz symmetry might arise in nature as a result of spontaneous symmetry breaking in a theory beyond the standard model. This talk summarizes a few relevant theoretical and experimental issues, with some emphasis on implications for CPT tests with neutral-B mesons.

S. M. Darbinyan, N. L. Ter-Isaakyan

The radiation emission spectra of polarized photons emitted from charged particles in single oriented crystals are obtained in Bayer-Katkov quasiclassical approach. The results of numerical calculations are presented in the region of small angles of incidence for which the coherent theory fails but magnetic bremsstrahlung region isn&#39;t yet achieved. The s

Y. Takeuchi, Y. Tazaki, S. Y. Tsai, T. Yamazaki

Neutrino oscillation is discussed with emphases placed more on its conceptual aspects. After reviewing the two conventional formulations, referred to here as the same-energy prescription and the same-momentum prescription, wave packet treatments are developed for each of these two prescriptions. Both wave packets localized in space and those in time are cons

A Kulyavtsev

A description is given of BTeV, a proposed program at the Fermilab collider sited at the C0 intersection region. The main goals are measurement of mixing, CP violation and rare decays in both the $b$ and charm systems. The detector is a two-arm-forward spectrometer capable of triggering on detached vertices and dileptons, and possessing excellent particle id

H. Nishiura, K. Matsuda, T. Fukuyama

We discuss the constraints of lepton mixing angles from lepton number violating processes such as neutrinoless double beta decay, (μ^-)-(e^+) conversion and K decay, $K^- \to π^+μ^-μ^-$ which are allowed only if neutrinos are Majorana particles. The rates of these processes are proportional to the averaged neutrino mass defined by $<m_ν >_{a b}\equiv |\sum_{

V. A. Kuzmin, I. I. Tkachev

Cosmic rays of the highest energy, above the Greisen-Zatsepin-Kuzmin cut-off of the spectrum, may originate in decays of superheavy long-living X-particles. These particles may be produced in the early Universe from vacuum fluctuations during or after inflation and may constitute a considerable fraction of Cold Dark Matter. We calculate numerically their abu

V. Elias, F. Chishtie, T. G. Steele

Padé-improvement of four-loop beta-functions in massive phi^4 scalar field theory is shown to predict the known five-loop contribution with astonishing (0.2%) accuracy, supporting the applicability of Pade-summations for approximating all-orders MS-bar QCD beta-functions, as suggested by Ellis, Karliner, and Samuel. Surprisingly, the most general set of [2|2

G. Burgio, F. Di Renzo, C. Parrinello, C. Pittori

We investigate the occurrence of power terms in the running QCD coupling by analysing non-perturbative measurements of alpha_s (p) at low momenta obtained from the lattice three-gluon vertex. Our exploratory study provides some evidence for power contributions to alpha_s (p) proportional to 1/p^2. Possible implications for physical observables are discussed.

S. Capitani, M. Göckeler, R. Horsley, H. Perlt

The evaluation of the higher twist contributions to Deep Inelastic Scattering amplitudes involves a non trivial choice of operator bases for the higher orders of the OPE expansion of the two hadronic currents. In this talk we discuss the perturbative renormalization of the four-fermion operators that appear in the above bases.

J. Acacio de Barros, N. Pinto-Neto, I. L. Shapiro

We take the first nontrivial coefficient of the Schwinger-DeWitt expansion as a leading correction to the action of the second-derivative metric-dilaton gravity. To fix the ambiguities related with an arbitrary choice of the gauge fixing condition and the parametrization for the quantum field, one has to use the classical equations of motion. As a result, th

V. V. Kassandrov, J. A. Rizcalla

The criterion of differentiability of functions of quaternion variable is used as the basis of some algebraic field theory. Its necessary consequences are free Maxwell and Yang-Mills equations. The differentiability equations may be integrated in twistor variables and are reduced to algebraic ones. In the article we present bisingular solution and its topolo

R. W. Kuhne

Recently, Anderson et al. presented possible evidence for an anomalous acceleration acting on spacecrafts. Furthermore, the motions of several planets and comets are known to experience unexplained disturbances. A transneptunian comet or asteroid belt might be the common origin of these anomalies.

Heinz Schmitz, Klaus W. Wagner

For some fixed alphabet A, a language L of A* is in the class L(1/2) of the Straubing-Therien hierarchy if and only if it can be expressed as a finite union of languages A*aA*bA*...A*cA*, where a,b,...,c are letters. The class L(1) is defined as the boolean closure of L(1/2). It is known that the classes L(1/2) and L(1) are decidable. We give a membership cr

Steffen Reith, Heribert Vollmer

We consider the problems of finding the lexicographically minimal (or maximal) satisfying assignment of propositional formulae for different restricted formula classes. It turns out that for each class from our framework, the above problem is either polynomial time solvable or complete for OptP. We also consider the problem of deciding if in the optimal assi

Heribert Vollmer

A notion of generalized quantifier in computational complexity theory is explored and used to give a unified treatment of leaf language definability, oracle separations, type 2 operators, and circuits with monoidal gates. Relations to Lindstroem quantifiers are pointed out.

Clemens Lautemann, Pierre McKenzie, Thomas Schwentick, Heribert Vollmer

Building upon the known generalized-quantifier-based first-order characterization of LOGCFL, we lay the groundwork for a deeper investigation. Specifically, we examine subclasses of LOGCFL arising from varying the arity and nesting of groupoidal quantifiers. Our work extends the elaborate theory relating monoidal quantifiers to NC1 and its subclasses. In the

L. Marquez, L. Padro, H. Rodriguez

We present a bootstrapping method to develop an annotated corpus, which is specially useful for languages with few available resources. The method is being applied to develop a corpus of Spanish of over 5Mw. The method consists on taking advantage of the collaboration of two different POS taggers. The cases in which both taggers agree present a higher accura

L. Padro, L. Marquez

This paper addresses the issue of {\sc pos} tagger evaluation. Such evaluation is usually performed by comparing the tagger output with a reference test corpus, which is assumed to be error-free. Currently used corpora contain noise which causes the obtained performance to be a distortion of the real value. We analyze to what extent this distortion may inval

Lex Weaver, Terry Bossomaier

Dots-and-Boxes is a child&#39;s game which remains analytically unsolved. We implement and evolve artificial neural networks to play this game, evaluating them against simple heuristic players. Our networks do not evaluate or predict the final outcome of the game, but rather recommend moves at each stage. Superior generalisation of play by co-evolved populat

F. Lema, A. A. Aligia

We extend to the spectral function an approach which allowed us to calculate the quasiparticle weight for destruction of a real electron Z_c sigma (k) (in contrast to that of creation of a spinless holon Z_h(k) in a generalized $t-J$ model, using the self-consistent Born approximation (SCBA). We compare our results with those obtained using the alternative a

E. Dagotto, S. Yunoki, A. Moreo

This paper is an informal review of the present status of the computational studies of models for manganites that recently reported the existence of phase separation at low temperatures (S. Yunoki et al., Phys. Rev. Lett. 80, 845 (1998) and cond-mat/9807149). Results for both the one-orbital and two-orbital models, the latter with Jahn-Teller phonons, are in

S. Tinte, M. G. Stachiotti, C. O. Rodriguez, D. L. Novikov

The Perdew-Burke-Ernzerhof generalized gradient approximation to the density functional theory is tested with respect to sensitivity to the choice of the value of the parameter $κ$, which is associated to the degree of localization of the exchange-correlation hole. A study of structural and dynamical properties of four selected ferroelectric perovskites is p

Sergey N. Rashkeev, Sukit Limpijumnong, Walter R. L. Lambrecht

A first-principles study of the birefringence and the frequency dependent second harmonic generation (SHG) coefficients of the ternary pnictide semiconductors with formula ABC$_2$ (A = Zn, Cd; B = Si, Ge; C = As, P) with the chalcopyrite structures was carried out. We show that a simple empirical observation that a smaller value of the gap is correlated with

Mehran Kardar

In many growth processes particles are highly mobile in an active layer at the surface, but are relatively immobile once incorporated in the bulk. We study models in which atoms are allowed to interact, equilibrate, and order on the surface, but are frozen in the bulk. Order parameter correlations in the resulting bulk material are highly anisotropic, reflec

Y. Martinez-Raton, J. A. Cuesta

A previously developed fundamental measure fucntional [J. Chem. Phys. vol.107, 6379 (1997)] is used to study the phase behavior of a system of parallel hard cubes. The single-component fluid exhibits a continuous transition to a solid with an anomalously large density of vacancies. The binary mixture has a demixing transition for edge-length ratios below 0.1

C. M. Newman, D. L. Stein

We consider nonequilibrium systems such as the Edwards-Anderson Ising spin glass at a temperature where, in equilibrium, there are presumed to be (two or many) broken symmetry pure states. Following a deep quench, we argue that as time goes to infinity, although the system is usually in some pure state locally, either it never settles permanently on a fixed

A. Cuccoli, V. Tognetti, R. Giachetti, R. Vaia

An appropriate extension of the effective potential theory is presented that permits the approximate calculation of the dynamical correlation functions for quantum systems. These are obtained by evaluating the generating functionals of the Mori products of quantities related to the relaxation functions in the (PQSCHA) pure self consistent harmonic approximat

Michael J. Manfra, Justin C. Pniower, Bennett B. Goldberg, Aron Pinczuk

We present the first magneto-absorption studies of coupled electron double layers in the quantum Hall regime. Optical absorption spectra in the vicinity of total filling factor nu = 1 reveal intriguing behavior that have no analog in the single electron layer nu = 1 state and demonstrate the interplay between single-particle tunneling and inter-layer Coulomb

M. K. Aliev, G. R. Alimov, I. Kholbaev, T. M. Muminov

A light-beam-assisted temperature-control system operating within a temperature range from 77 to 180 K is developed for investigating the absorption of electromagnetic waves by high-temperature superconductors in the vicinity of superconducting transition with an ESR spectrometer. The advantage of this system is the feasibility of modulating the temperature

E. Cerboneschi, R. Mannella, E. Arimondo, L. Salasnich

We investigate the dynamics of a Bose condensate, interacting with either repulsive or attractive forces, confined in a fully anisotropic harmonic potential. The (3+1)-dimensional Gross-Pitaevskii equation is integrated numerically to derive the collective excitation frequencies, showing a good agreement with those calculated with a variational technique.

Michael Schreiber, Uwe Grimm, Rudolf A. Roemer, Jian-Xin Zhong

We study statistical properties of energy spectra of a tight-binding model on the two-dimensional quasiperiodic Ammann-Beenker tiling. Taking into account the symmetries of finite approximants, we find that the underlying universal level-spacing distribution is given by the Gaussian orthogonal random matrix ensemble, and thus differs from the critical level-

Rudolf A. Roemer, Mark Leadbeater, Michael Schreiber

Using a numerical decimation method, we compute the localisation length $λ_{2}$ for two onsite interacting particles (TIP) in a one-dimensional random potential. We show that an interaction $U>0$ does lead to $λ_2(U) > λ_2(0)$ for not too large $U$ and test the validity of various proposed fit functions for $λ_2(U)$. Finite-size scaling allows us to obtain i

P. V. Shevchenko, O. P. Sushkov

We consider the two-layer Heisenberg antiferromagnet near a zero temperature quantum phase transition from a disordered dimer phase to a collinear Neel state. At approaching the transition point the spin-wave gap vanishes as $Δ\propto (J_\perp-J_{\perp c})^ν$. To account for strong correlations between the S=1 elementary excitations we apply the Brueckner di

Ziqiang Wang, Vasiliki Plerou

This is a Reply to a Comment by Tanaka and Machida. We provide some details of the derivation of the effective field theory for integer quantum Hall transitions using the non-Abelian chiral anomaly.

Eugene Kogan, Mark Auslender

We study temperature induced metal-insulator transition in doped ferromagnetic semiconductors, described by s-d exchange model. The transition is a result of the mobility edge movement, the disorder being due to magnetic ions spin density fluctuations. The electrons are described in the tight binding approximation. Using ideas and methods of Anderson localiz

Julia K. Steinberger, Victoria M. Kaspi, Eric V. Gotthelf

We report on X-ray observations of the young, energetic radio pulsar PSR J1105-6107 obtained using the Rossi X-ray Timing Explorer. Our timing analysis of Proportional Counter Array data finds no evidence for X-ray pulsations from this source. We set a new upper limit on the pulsed X-ray flux from the pulsar of 18% in the 2-10 keV band, for a duty cycle of 0

E. M. Corsini, A. Pizzella, M. Sarzi, P. Cinzano

We present stellar and ionized-gas velocity curves and velocity dispersion profiles for the Sa galaxies NGC 2179 and NGC 2775. Using their luminosity profiles and modeling both their stellar and gaseous kinematics, we have derived the mass distribution of the dark and the luminous matter. This unambiguously shows that, inside one disk length-scale R_D, the s

Zoltan Haiman

We review observable signatures of the first generation of stars and low-luminosity quasars, including the metal enrichment, radiation background, and dust opacity/emission that they produce. We compute the formation history of collapsed baryonic halos based on an extension of the Press-Schechter formalism, incorporating the effects of pressure and H2-dissoc