578 research outputs found
Quasiequational Theories of Flat Algebras
We prove that finite flat digraph algebras and, more generally, finite compatible flat algebras satisfying a certain condition are finitely q-based (possess a finite basis for their quasiequations). We also exhibit an example of a twelve-element compatible flat algebra that is not finitely q-based
The endomorphism semiring of a semilattice
We prove that the endomorphism semiring of a nontrivial semilattice is always subdirectly irreducible and describe its monolith. The endomorphism semiring is congruence simple if and only if the semilattice has both a least and a largest element
Polar communications: Status and recommendations. Report of the Science Working Group
The capabilities of the existing communication links within the polar regions, as well as between the polar regions and the continental United States, are summarized. These capabilities are placed in the context of the principal scientific disciplines that are active in polar research, and in the context of how scientists both utilize and are limited by present technologies. Based on an assessment of the scientific objectives potentially achievable with improved communication capabilities, a list of requirements on and recommendations for communication capabilities necessary to support polar science over the next ten years is given
Nucleation in dilute 3He-4He liquid mixtures at low temperatures
We present a study of phase separation from supersaturated 3He-4He liquid
mixtures at low temperatures addressing both the degree of critical
supersaturation Dx and the thermal-to-quantum crossover temperature T* for the
nucleation process. Two different nucleation seeds are investigated, namely 3He
droplets and 4He vortex lines with cores filled with 3He. We have found that
the experimental T* is reproduced when we consider that nucleation proceeds
from 3He droplets, whereas Dx is reproduced when we consider 4He vortex lines
filled with 3He. However, neither nucleation configuration is able to
simultaneously reproduce the current experimental information on Dx and T*.Comment: To appear in J. of Low Temp. Physic
The variety generated by order algebras
Every ordered set can be considered as an algebra in a natural way. We investigate the variety generated by order algebras. We prove, among other things, that this variety is not finitely based and, although locally finite, it is not contained in any finitely generated variety; we describe the bottom of the lattice of its subvarieties
Quantum cavitation in liquid helium
Using a functional-integral approach, we have determined the temperature
below which cavitation in liquid helium is driven by thermally assisted quantum
tunneling. For both helium isotopes, we have obtained the crossover temperature
in the whole range of allowed negative p essures. Our results are compatible
with recent experimental results on 4He.Comment: Typeset using Revtex, 10 pages and 2 figures, Phys. Rev B (1996
Dipolar condensates confined in a toroidal trap: ground state and vortices
We study a Bose-Einstein condensate of 52Cr atoms confined in a toroidal trap
with a variable strength of s-wave contact interactions. We analyze the effects
of the anisotropic nature of the dipolar interaction by considering the
magnetization axis to be perpendicular to the trap symmetry axis. In the
absence of a central repulsive barrier, when the trap is purely harmonic, the
effect of reducing the scattering length is a tuning of the geometry of the
system: from a pancake-shaped condensate when it is large, to a cigar-shaped
condensate for small scattering lengths. For a condensate in a toroidal trap,
the interaction in combination with the central repulsive Gaussian barrier
produces an azimuthal dependence of the particle density for a fixed radial
distance. We find that along the magnetization direction the density decreases
as the scattering length is reduced but presents two symmetric density peaks in
the perpendicular axis. For even lower values of the scattering length we
observe that the system undergoes a dipolar-induced symmetry breaking
phenomenon. The whole density becomes concentrated in one of the peaks,
resembling an origin-displaced cigar-shaped condensate. In this context we also
analyze stationary vortex states and their associated velocity field, finding
that this latter also shows a strong azimuthal dependence for small scattering
lengths. The expectation value of the angular momentum along the z direction
provides a qualitative measure of the difference between the velocity in the
different density peaks.Comment: 9 pages, 12 figure
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