April 1996 arXiv papers — page 13

D. Fisher

Clustering is often used for discovering structure in data. Clustering systems differ in the objective function used to evaluate clustering quality and the control strategy used to search the space of clusterings. Ideally, the search strategy should consistently construct clusterings of high quality, but be computationally inexpensive as well. In general, we

E. Marchiori

Termination of logic programs with negated body atoms (here called general logic programs) is an important topic. One reason is that many computational mechanisms used to process negated atoms, like Clark's negation as failure and Chan's constructive negation, are based on termination conditions. This paper introduces a methodology for proving termin

T. Walsh

Inductive theorem provers often diverge. This paper describes a simple critic, a computer program which monitors the construction of inductive proofs attempting to identify diverging proof attempts. Divergence is recognized by means of a ``difference matching'' procedure. The critic then proposes lemmas and generalizations which ``ripple'' th

M. B. Walker, J. Luettmer-Strathmann

This article describes the Josephson tunneling from time-reversal symmetry-breaking states and compares it with that from time-reversal invariant states for both twinned and untwinned crystals and for both $c$-axis and basal-plane currents, in a model for orthorhombic YBCO. A macroscopic invariance group describing the superconducting state of a twinned crys

D. J. Scalapino, S. A. Trugman

The high $T_c$ cuprate superconductors doped near half-filling have short range antiferromagnetic correlations. Here we describe an intuitive local picture of why, if pairing occurs in the presence of short-range antiferromagnetic correlations, the orbital state will have $d_{x^2-y^2}$ symmetry.

Frank Wilczek

I discuss in an elementary and self-contained way the nature of the current-carrying state in Hall superfluids. The explicit connection of fractional charge and rationality of the filling fraction $ν$ with quantization of angular momentum, and the discussion of the preferred velocity profile for bulk current flows may be new; the latter might provide an inte

J. K. Freericks, G. D. Mahan

A strong-coupling expansion is applied to the anharmonic Holstein model and to the Holstein-Hubbard model through fourth order in the hopping matrix element. Mean-field theory is then employed to determine transition temperatures of the effective (pseudospin) Hamiltonian. We find that anharmonic effects are not easily mimicked by an on-site Coulomb repulsion

P. Schmitteckert, U. Eckern

Using the density matrix renormalization group algorithm, we study the model of spinless fermions with nearest-neighbor interaction on a ring in the presence of disorder. We determine the spatial decay of the density induced by a defect (Friedel oscillations), and the phase sensitivity of the ground state energy $\DE= (-)^{N} (E(ϕ=0) - E(ϕ=π))$, where $ϕ= 2π

M. W. Wu, H. L. Cui, N. J. M. Horing

Momentum transfer due to electron-electron interaction (Coulomb drag) between two quantum wells, separated by a distance $d$, in the presence of a perpendicular magnetic field, is studied at low temperatures. We find besides the well known Shubnikov-de Haas oscillations, which also appear in the drag effect, the momentum transfer is markedly enhanced by the

W. T. Gozdz, R. Holyst

We present the novel method for generation of periodic surfaces based on the simple Landau-Ginzburg model of microemulsion. We test the method on four minimal surfaces (P,D,G, and I-WP), find two new surfaces of cubic symmetry, show how to obtain periodic surfaces of high genus and n-tuply-continuous phases. We point that the Landau model used here should be

A. D. Zaikin, F. K. Wilhelm, A. A. Golubov

We develop a detailed analysis of electron transport in normal diffusive con- ductors in the presence of proximity induced superconductivity. A rich structure of temperature and energy dependencies for the system condcutcance, density of states and related quantities was found and explained. If the nor- mal conductor forms a loop its conductance changes h/2e

P. M. A. Cook, R. Raimondi, C. J. Lambert

We examine the effect of d-wave symmetry on zero bias anomalies in normal-superconducting tunnel junctions and phase-periodic conductances in Andreev interferometers. In the presence of d-wave pairing, zero-bias anomalies are suppressed compared with the s-wave case. For Andreev interferometers with aligned islands, the phase-periodic conductance is insensis

David Branch, Adam Fisher, E. Baron, Peter Nugent

An interesting way to calibrate the absolute magnitudes of remote Type Ia supernovae (SNe Ia) that are well out in the Hubble flow, and thus determine the value of the Hubble constant, H_0, has been introduced by van den Bergh. His approach relies on calculations of the peak absolute magnitudes and broad--band colors for SN Ia explosion models. It does not r

Eli Waxman, Karl B. Fisher, Tsvi Piran

We analyze the anisotropy signature expected if the high energy (above $10^{19}$eV) cosmic ray (CR) sources are extra-Galactic and trace the distribution of luminous matter on large scales. We investigate the dependence of the anisotropy on both the relative bias between the CR sources and the galaxy distribution and on the (unknown) intrinsic CR source dens

R. Srianand

Detection of a large void ($\sim $7 Mpc) is reported between the redshifts 2.16286 and 2.20748 in the Ly~$α$ forest of TOL 1038-2712. This void is centered near a foreground QSO TOL 1037-2704 which is at a distance $\sim$4.4 Mpc away from the void. The estimated probability for the void to occure by chance in front of the foreground QSO is few times $10^{-3}

Shude Mao, Bohdan Paczyński

We present a simple toy model of the distribution of objects responsible for gravitational microlensing. We use Monte Carlo simulations to demonstrate how difficult it is to determine the parameters of the lens mass distribution on the basis of the observed distribution of event time scales. A robust determination requires $ \sim 100 $ events, or more, even

R. Kaufmann, Yu. Manin, D. Zagier

Moduli spaces of compact stable $n$-pointed curves carry a hierarchy of cohomology classes of top dimension which generalize the Weil-Petersson volume forms and constitute a version of Mumford classes. We give various new formulas for the integrals of these forms and their generating functions. We also discuss their relation to the Kuenneth formula in quantu