17,003 research outputs found
Effective model of the electronic Griffiths phase
We present simple analytical arguments explaining the universal emergence of
electronic Griffiths phases as precursors of disorder-driven metal-insulator
transitions in correlated electronic systems. A simple effective model is
constructed and solved within Dynamical Mean Field Theory. It is shown to
capture all the qualitative and even quantitative aspects of such Griffiths
phases.Comment: 9 pages, 7 figures, one reference corrected; minor corrections
include
Collapse of Primordial Clouds
We present here studies of collapse of purely baryonic Population III objects
with masses ranging from to . A spherical Lagrangian
hydrodynamic code has been written to study the formation and evolution of the
primordial clouds, from the beginning of the recombination era () until the redshift when the collapse occurs. All the relevant processes
are included in the calculations, as well as, the expansion of the Universe. As
initial condition we take different values for the Hubble constant and for the
baryonic density parameter (considering however a purely baryonic Universe), as
well as different density perturbation spectra, in order to see their influence
on the behavior of the Population III objects evolution. We find, for example,
that the first mass that collapses is for ,
and with the mass scale . For
we obtain for the first
mass that collapses. The cooling-heating and photon drag processes have a key
role in the collapse of the clouds and in their thermal history. Our results
show, for example, that when we disregard the Compton cooling-heating, the
collapse of the objects with masses occurs earlier. On
the other hand, disregarding the photon drag process, the collapse occurs at a
higher redshift.Comment: 10 pages, MN plain TeX macros v1.6 file, 9 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Thinking after Drinking: Impaired Hippocampal-Dependent Cognition in Human Alcoholics and Animal Models of Alcohol Dependence
Alcohol use disorder currently affects approximately 18 million Americans, with at least half of these individuals having significant cognitive impairments subsequent to their chronic alcohol use. This is most widely apparent as frontal cortex dependent cognitive dysfunction, where executive function and decision making are severely compromised, as well as hippocampus dependent cognitive dysfunction, where contextual and temporal reasoning are negatively impacted. This review discusses the relevant clinical literature to support the theory that cognitive recovery in tasks dependent on the prefrontal cortex and hippocampus is temporally different across extended periods of abstinence from alcohol. Additional studies from preclinical models are discussed to support clinical findings. Finally, the unique cellular composition of the hippocampus and cognitive impairment dependent on the hippocampus is highlighted in the context of alcohol dependence
Collapse of Primordial Clouds II. The Role of Dark Matter
In this article we extend the study performed in our previous article on the
collapse of primordial objects. We here analyze the behavior of the physical
parameters for clouds ranging from to . We
studied the dynamical evolution of these clouds in two ways: purely baryonic
clouds and clouds with non-baryonic dark matter included. We start the
calculations at the beginning of the recombination era, following the evolution
of the structure until the collapse (that we defined as the time when the
density contrast of the baryonic matter is greater than ). We analyze the
behavior of the several physical parameters of the clouds (as, e.g., the
density contrast and the velocities of the baryonic matter and the dark matter)
as a function of time and radial position in the cloud. In this study all
physical processes that are relevant to the dynamical evolution of the
primordial clouds, as for example photon-drag (due to the cosmic background
radiation), hydrogen molecular production, besides the expansion of the
Universe, are included in the calculations. In particular we find that the
clouds, with dark matter, collapse at higher redshift when we compare the
results with the purely baryonic models. As a general result we find that the
distribution of the non-baryonic dark matter is more concentrated than the
baryonic one. It is important to stress that we do not take into account the
putative virialization of the non-baryonic dark matter, we just follow the time
and spatial evolution of the cloud solving its hydrodynamical equations. We
studied also the role of the cooling-heating processes in the purely baryonic
clouds.Comment: 8 pages, MN plain TeX macros v1.6 file, 13 PS figures. Also available
at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES").
MNRAS in pres
Comparative case study investigating sociotechnical processes of change in the context of a national electronic health record implementation
Transport properties in antiferromagnetic quantum Griffiths phases
We study the electrical resistivity in the quantum Griffiths phase associated
with the antiferromagnetic quantum phase transition in a metal. The resistivity
is calculated by means of the semi-classical Boltzmann equation. We show that
the scattering of electrons by locally ordered rare regions leads to a singular
temperature dependence. The rare-region contribution to the resistivity varies
as with temperature where the is the usual Griffiths
exponent which takes the value zero at the critical point and increases with
distance from criticality. We find similar singular contributions to other
transport properties such as thermal resistivity, thermopower and the Peltier
coefficient. We also compare our results with existing experimental data and
suggest new experiments.Comment: 4 pages, 1 figur
Sustentabilidade agrícola na Amazônia: 23 anos de monitoramento da agricultura em Machadinho d' Oeste - RO.
O projeto de assentamento de Machadinho d'Oeste, RO, na fronteira agrícola da Amazônia Ocidental, criado há 23 anos atrás como um projeto de colonização agrícola, vem sendo acompanhado por uma equipe de pesquisadores da Embrapa Monitoramento por Satélite. Os pesquisadores acompanhado um grupo de 438 famílias de produtores rurais oriundos, principalmente, das Regiões Sul e Sudeste do país, que ocuparam lotes e praticaram atividades de produção familiar. O monitoramento é realizado por intermédio de métodos baseados na utilização de imagens de satélite, sistemas de informações geográficas (SIG) e tratamentos numéricos. A extensa base de dados tem sido utilizada para análise da evolução e diferenciação da pequena agricultura familiar em termos da produção agrícola e da manutenção de sua sustentabilidade agrícola. Procurando saber as principais razões que diferenciam evolutivamente os lotes amostrados, foram analisados os dados dos questionários respondidos por produtores entrevistados em 1986, 1989, 1996, 1999, 2002 e 2005. A evolução nos 20 anos mostra as dificuldades enfrentadas pelos pequenos agricultores familiares que praticam as atividades agrícolas e pecuárias em seus lotes, sendo que em 2005, mais da metade dos agricultores avaliados adquiriram mais de um lote que foram comprados pela melhoria da renda. O aumento da utilização da área que se destacou em 2005, em relação aos anos anteriores, foi a pastagem que encontra-se distribuída em cerca de um quarto das propriedades, gerando, através da atividade de pecuária pela criação de bovinos, grande renda para os agricultores, tanto ao longo do ano com a produção de leite, como de forma mais esporádica com a venda de bezerros, novilhos e vacas. Quanto aos cultivos houve uma diferenciação nos sistemas de produção vegetal, com a redução do cultivo de cereais e o aumento de cultivo do café. Os sistemas agropecuários vêm se caracterizando ao longo dos anos pelo emprego crescente de tecnologia e aumento de produção
- …