44,237 research outputs found
Reflection matrices for the vertex model
The graded reflection equation is investigated for the
vertex model. We have found four classes of diagonal
solutions and twelve classes of non-diagonal ones. The number of free
parameters for some solutions depends on the number of bosonic and fermionic
degrees of freedom considered.Comment: 30 page
Field-induced phase transitions of repulsive spin-1 bosons in optical lattices
We study the phase diagram of repulsively interacting spin-1 bosons in
optical lattices at unit filling, showing that an externally induced quadratic
Zeeman effect may lead to a rich physics characterized by various phases and
phase transitions. We find that the main properties of the system may be
described by an effective field model, which provides the precise location of
the phase boundaries for any dimension, being in excellent agreement with our
numerical calculations for one-dimensional systems. Our work provides a
quantitative guide for the experimental analysis of various types of
field-induced quantum phase transitions in spin-1 lattice bosons. These
transitions, which are precluded in spin-1/2 systems, may be realized using an
externally modified quadratic Zeeman coupling, similar to recent experiments
with spinor condensates in the continuum.Comment: 4 pages, 2 figure
Radial distribution function of penetrable sphere fluids to second order in density
The simplest bounded potential is that of penetrable spheres, which takes a
positive finite value if the two spheres are overlapped, being 0
otherwise. In this paper we derive the cavity function to second order in
density and the fourth virial coefficient as functions of (where is the Boltzmann constant and is the
temperature) for penetrable sphere fluids. The expressions are exact, except
for the function represented by an elementary diagram inside the core, which is
approximated by a polynomial form in excellent agreement with accurate results
obtained by Monte Carlo integration. Comparison with the hypernetted-chain
(HNC) and Percus-Yevick (PY) theories shows that the latter is better than the
former for only. However, even at zero temperature (hard sphere
limit), the PY solution is not accurate inside the overlapping region, where no
practical cancelation of the neglected diagrams takes place. The exact fourth
virial coefficient is positive for , reaches a minimum
negative value at , and then goes to zero from below as
for high temperatures. These features are captured qualitatively,
but not quantitatively, by the HNC and PY predictions. In addition, in both
theories the compressibility route is the best one for , while
the virial route is preferable if .Comment: 10 pages, 2 figures; v2: minor changes; to be published in PR
Area Quantization in Quasi-Extreme Black Holes
We consider quasi-extreme Kerr and quasi-extreme Schwarzschild-de Sitter
black holes. From the known analytical expressions obtained for their
quasi-normal modes frequencies, we suggest an area quantization prescription
for those objects.Comment: Final version to appear in Mod. Phys. Lett.
Collective action and property rights in fisheries management
"Fisheries are complex and interdependent ecological and social systems that require integrated management approaches. The actions of one person or group of users affect the availability of the resource for others. Managing such common pool resources requires conscious efforts by a broad range of stakeholders to organize and craft rules enabling equitable and sustainable use of the resources for everyone's benefit. Collective action is often a prerequisite for the development of community-based institutions and the devolution of authority... in the 1990s the WorldFish Center conducted an issuebased, multisectoral, and multidisciplinary analysis (including ecological, economic, social, political, and administrative perspectives) that led to the production of a coastal environmental profile, a technical report detailing the status of fisheries, and an integrated fisheries management plan.... San Miguel's experience highlights (1) the critical role of an appropriate human perception of the situation; (2) the importance of collective action and stakeholder participation at key stages of research, planning, and implementation; (3) the usefulness of structured decision methods for research, planning, and associated debates; and (4) the efficacy of research combined with planning efforts to ensure its utilization and relevance on the one hand and to provide a scientific basis for management planning on the other." - from Text.Public goods ,Poverty alleviation ,Collective action ,
Static, spherically symmetric solutions with a scalar field in Rastall gravity
Rastall's theory belongs to the class of non-conservative theories of
gravity. In vacuum, the only non-trivial static, spherically symmetric solution
is the Schwarzschild one, except in a very special case. When a canonical
scalar field is coupled to the gravity sector in this theory, new exact
solutions appear for some values of the Rastall parameter . Some of these
solutions describe the same space-time geometry as the recently found solutions
in the -essence theory with a power function for the kinetic term of the
scalar field. There is a large class of solutions (in particular, those
describing wormholes and regular black holes) whose geometry coincides with
that of solutions of GR coupled to scalar fields with nontrivial
self-interaction potentials; the form of these potentials, however, depends on
the Rastall parameter . We also note that all solutions of GR with a zero
trace of the energy-momentum tensor, including black-hole and wormhole ones,
may be re-interpreted as solutions of Rastall's theory.Comment: Latex file, 18 pages. To fit published versio
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