20,906 research outputs found
Knizhnik-Zamolodchikov-Bernard equations connected with the eight-vertex model
Using quasiclassical limit of Baxter's 8 - vertex R - matrix, an elliptic
generalization of the Knizhnik-Zamolodchikov equation is constructed. Via
Off-Shell Bethe ansatz an integrable representation for this equation is
obtained. It is shown that there exists a gauge transformation connecting this
equation with Knizhnik-Zamolodchikov-Bernard equation for SU(2)-WZNW model on
torus.Comment: 20 pages latex, macro: tcilate
Density-functionals not based on the electron gas: Local-density approximation for a Luttinger liquid
By shifting the reference system for the local-density approximation (LDA)
from the electron gas to other model systems one obtains a new class of density
functionals, which by design account for the correlations present in the chosen
reference system. This strategy is illustrated by constructing an explicit LDA
for the one-dimensional Hubbard model. While the traditional {\it ab initio}
LDA is based on a Fermi liquid (the electron gas), this one is based on a
Luttinger liquid. First applications to inhomogeneous Hubbard models, including
one containing a localized impurity, are reported.Comment: 4 pages, 4 figures (final version, contains additional applications
and discussion; accepted by Phys. Rev. Lett.
Irreversible magnetization under rotating fields and lock-in effect on ErBa_2Cu_3O_7 single crystal with columnar defects
We have measured the irreversible magnetization M_i of an ErBa_2Cu_3O_7
single crystal with columnar defects (CD), using a technique based on sample
rotation under a fixed magnetic field H. This method is valid for samples whose
magnetization vector remains perpendicular to the sample surface over a wide
angle range - which is the case for platelets and thin films - and presents
several advantages over measurements of M_L(H) loops at fixed angles. The
resulting M_i(\Theta) curves for several temperatures show a peak in the CD
direction at high fields. At lower fields, a very well defined plateau
indicative of the vortex lock-in to the CD develops. The H dependence of the
lock-in angle \phi_L follows the H^{-1} theoretical prediction, while the
temperature dependence is in agreement with entropic smearing effects
corresponding to short range vortex-defects interactions.Comment: 7 pages, 6 figures, to be published in Phys. Rev.
Recommended from our members
An analysis of media reporting on the closure of freestanding midwifery units in England
PROBLEM: Despite clinical guidelines and policy promoting choice of place of birth, 14 Freestanding Midwifery Units were closed between 2008 and 2015, closures justified by low use and financial constraints.
BACKGROUND: The Birthplace in England Programme found that freestanding midwifery units provided the most cost-effective birthplace for women at low risk of complications. Women planning birth in a freestanding unit were less likely to experience interventions than those planning obstetric unit birth, with no difference in outcomes for babies.
METHODS: This paper uses an interpretative technique developed for policy analysis to explore the representation of these closures in 191 news articles, to explore the public climate in which they occurred.
FINDINGS AND DISCUSSION: The articles focussed on underuse by women and financial constraints on services. Despite the inclusion of service user voices, the power of framing was held by service managers and commissioners. The analysis exposed how neoliberalist and austerity policies has privileged representation of individual consumer choice and market-driven provision as drivers of changes in health services. This normative framing makes the reasons given for closure as hard to refute and cultural norms persist that birth is safest in an obstetric setting, despite evidence to the contrary.
CONCLUSION: The rise of neoliberalism and austerity in contemporary Britain has influenced the reform of maternity services, in particular the closure of midwifery units. Justifications given for closure silence other narratives, predominantly from service users, that attempt to present women's choice in terms of rights and a social model of care
Chemical Potential and the Nature of the Dark Energy: The case of phantom
The influence of a possible non zero chemical potential on the nature
of dark energy is investigated by assuming that the dark energy is a
relativistic perfect simple fluid obeying the equation of state (EoS),
(). The entropy condition, ,
implies that the possible values of are heavily dependent on the
magnitude, as well as on the sign of the chemical potential. For , the
-parameter must be greater than -1 (vacuum is forbidden) while for not only the vacuum but even a phantomlike behavior () is
allowed. In any case, the ratio between the chemical potential and temperature
remains constant, that is, . Assuming that the dark energy
constituents have either a bosonic or fermionic nature, the general form of the
spectrum is also proposed. For bosons is always negative and the extended
Wien's law allows only a dark component with which includes
vacuum and the phantomlike cases. The same happens in the fermionic branch for
are permmited only if . The thermodynamics and statistical arguments constrain the
EoS parameter to be , a result surprisingly close to the maximal
value required to accelerate a FRW type universe dominated by matter and dark
energy ().Comment: 7 pages, 5 figure
Plant population and spatial arrangement studies in the intercropping of maize and beans in Northeast Brazil.
In Northeast Brazil the peasant farmer use to raise their cropa in mixture, and the intercropping of maise and beans is very frequent.Paper for International Intercropping Workshop at ICRISAT, Hydederabad, India, from jannuary 10 at 13, 1979
Desenvolvimento do Webservice EGENT - Estudo Gráfico da Evolução dos N-Grams no Tempo.
Este trabalho apresenta um conjunto de ferramentas computacionais para o mapeamento da cobertura temporal de n-grams e termos de um domínio específico do conhecimento agrícola. A partir de um corpus textual formado por textos enriquecidos com metadados anotados automaticamente sobre a cultura de cana-de-açúcar tais ferramentas criam e apresentam a evolução do uso dos termos ao longo tempo. Além dos metadados, e usando o programa REMBRANDT também foram mapeadas a Entidades Mencionadas com classe de Tempo constantes nos conteúdos de texto para futuras análises semânticas a partir destas marcações. Os resultados são bastante satisfatórios e podem ser analisados sob o aspecto estratégico, cuja análise pode ser feita do ponto de vista do alcance dos objetivos propostos e seus trabalhos futuros, e outro mais prático cuja análise foca o ambiente operacional das ferramentas produzidas.CIIC 2012. No 12616
Otimização e validação de método para determinação de ácidos orgânicos em vinhos por cromatografia líquida de alta eficiência.
Reagentes e soluções analíticas; Instrumentação e condição cromatográfica; Estabilidade dos padrões analíticos e da fase móvel; Validação do método; Preparação das amostras de vinho
Critical wave-packet dynamics in the power-law bond disordered Anderson Model
We investigate the wave-packet dynamics of the power-law bond disordered
one-dimensional Anderson model with hopping amplitudes decreasing as
. We consider the critical case ().
Using an exact diagonalization scheme on finite chains, we compute the
participation moments of all stationary energy eigenstates as well as the
spreading of an initially localized wave-packet. The eigenstates
multifractality is characterized by the set of fractal dimensions of the
participation moments. The wave-packet shows a diffusive-like spread developing
a power-law tail and achieves a stationary non-uniform profile after reflecting
at the chain boundaries. As a consequence, the time-dependent participation
moments exhibit two distinct scaling regimes. We formulate a finite-size
scaling hypothesis for the participation moments relating their scaling
exponents to the ones governing the return probability and wave-function
power-law decays
On Matrix Superpotential and Three-Component Normal Modes
We consider the supersymmetric quantum mechanics (SUSY QM) with three-
component normal modes for the Bogomol'nyi-Prasad-Sommerfield (BPS) states. An
explicit form of the SUSY QM matrix superpotential is presented and the
corresponding three-component bosonic zero-mode eigenfunction is investigated.Comment: 17 pages, no figure. Paper accepted for publication in Journal of
Physics A: Mathematical and Theoretica
- …