176 research outputs found
Quantum spin systems at positive temperature
We develop a novel approach to phase transitions in quantum spin models based
on a relation to their classical counterparts. Explicitly, we show that
whenever chessboard estimates can be used to prove a phase transition in the
classical model, the corresponding quantum model will have a similar phase
transition, provided the inverse temperature and the magnitude of the
quantum spins \CalS satisfy \beta\ll\sqrt\CalS. From the quantum system we
require that it is reflection positive and that it has a meaningful classical
limit; the core technical estimate may be described as an extension of the
Berezin-Lieb inequalities down to the level of matrix elements. The general
theory is applied to prove phase transitions in various quantum spin systems
with \CalS\gg1. The most notable examples are the quantum orbital-compass
model on and the quantum 120-degree model on which are shown to
exhibit symmetry breaking at low-temperatures despite the infinite degeneracy
of their (classical) ground state.Comment: 47 pages, version to appear in CMP (style files included
Orientation of Galaxies in the Local Supercluster: A Review
The progress of the studies on the orientation of galaxies in the Local
Supercluster (LSC) is reviewed and a summary of recent results is given.
Following a brief introduction of the LSC, we describe the results of early
studies based on two-dimensional analysis, which were mostly not conclusive. We
describe next the three-dimensional analysis, which is used widely today.
Difficulties and systematic effects are explained and the importance of
selection effects is described. Then, results based on the new method and
modern databases are given, which are summarized as follows. When the LSC is
seen as a whole, galaxy planes tend to align perpendicular to the LSC plane
with lenticulars showing the most pronounced tendency. Projections onto the LSC
plane of the spin vectors of Virgo cluster member galaxies, and to some extent,
those of the total LSC galaxies, tend to point to the Virgo cluster center.
This tendency is more pronounced for lenticulars than for spirals. It is
suggested that 'field' galaxies, i.e., those which do not belong to groups with
more than three members, may be better objects than other galaxies to probe the
information at the early epoch of the LSC formation through the analysis of
galaxy orientations. Field lenticulars show a pronounced anisotropic
distribution of spin vectors in the sense that they lay their spin vectors
parallel to the LSC plane while field spirals show an isotropic spin-vector
distribution.Comment: 21 pages, 10 figures; Accepted for publication in Astrophysics and
Space Scienc
Adição de probiótico ao leite integral ou sucedâneo e desempenho de bezerros da raça holandesa
Gendering the careers of young professionals: some early findings from a longitudinal study. in Organizing/theorizing: developments in organization theory and practice
Wonders whether companies actually have employees best interests at heart across physical, mental and spiritual spheres. Posits that most organizations ignore their workforce – not even, in many cases, describing workers as assets! Describes many studies to back up this claim in theis work based on the 2002 Employment Research Unit Annual Conference, in Cardiff, Wales
Influences de la sylviculture sur le risque de dégâts biotiques et abiotiques dans les peuplements forestiers
- …