3,320 research outputs found
Exploring the Venus global super-rotation using a comprehensive General Circulation Model
The atmospheric circulation in Venus is well known to exhibit strong
super-rotation. However, the atmospheric mechanisms responsible for the
formation of this super-rotation are still not fully understood. In this work,
we developed a new Venus general circulation model to study the most likely
mechanisms driving the atmosphere to the current observed circulation. Our
model includes a new radiative transfer, convection and suitably adapted
boundary layer schemes and a dynamical core that takes into account the
dependence of the heat capacity at constant pressure with temperature.
The new Venus model is able to simulate a super-rotation phenomenon in the
cloud region quantitatively similar to the one observed. The mechanisms
maintaining the strong winds in the cloud region were found in the model
results to be a combination of zonal mean circulation, thermal tides and
transient waves. In this process, the semi-diurnal tide excited in the upper
clouds has a key contribution in transporting axial angular momentum mainly
from the upper atmosphere towards the cloud region. The magnitude of the
super-rotation in the cloud region is sensitive to various radiative parameters
such as the amount of solar radiative energy absorbed by the surface, which
controls the static stability near the surface. In this work, we also discuss
the main difficulties in representing the flow below the cloud base in Venus
atmospheric models.
Our new radiative scheme is more suitable for 3D Venus climate models than
those used in previous work due to its easy adaptability to different
atmospheric conditions. This flexibility of the model was crucial to explore
the uncertainties in the lower atmospheric conditions and may also be used in
the future to explore, for example, dynamical-radiative-microphysical
feedbacks.Comment: Accepted for publication in Planet. Space Sc
Effective action for a quantum scalar field in warped spaces
We investigate the one-loop corrections at zero, as well as finite
temperature, of a scalar field taking place in a braneworld motived warped
background. After to reach a well defined problem, we calculate the effective
action with the corresponding quantum corrections to each case.Comment: 10 pages, to appear in The European Physical Journal
Modulational instability of spatially broadband nonlinear optical pulses in four-state atomic systems
The modulational instability of broadband optical pulses in a four-state
atomic system is investigated. In particular, starting from a recently derived
generalized nonlinear Schr\"odinger equation, a wave-kinetic equation is
derived. A comparison between coherent and random phase wave states is made. It
is found that the spatial spectral broadening can contribute to the nonlinear
stability of ultra-short optical pulses. In practical terms, this could be
achieved by using random phase plate techniques.Comment: 9 pages, 3 figures, to appear in Phys. Rev.
Dual descriptions of spin two massive particles in via master actions
In the first part of this work we show the decoupling (up to contact terms)
of redundant degrees of freedom which appear in the covariant description of
spin two massive particles in . We make use of a master action which
interpolates, without solving any constraints, between a first, second and
third order (in derivatives) self-dual model. An explicit dual map between
those models is derived. In our approach the absence of ghosts in the third
order self-dual model, which corresponds to a quadratic truncation of
topologically massive gravity, is due to the triviality (no particle content)
of the Einstein-Hilbert action in . In the second part of the work, also
in , we prove the quantum equivalence of the gauge invariant sector of a
couple of self-dual models of opposite helicities (+2 and -2) and masses
and to a generalized self-dual model which contains a quadratic
Einstein-Hilbert action, a Chern-Simons term of first order and a Fierz-Pauli
mass term. The use of a first order Chern-Simons term instead of a third order
one avoids conflicts with the sign of the Einstein-Hilbert action.Comment: title and abstract slightly modified, 3 references added, comments on
interactions include
Entanglement versus Quantum Discord in Two Coupled Double Quantum Dots
We study the dynamics of quantum correlations of two coupled double quantum
dots containing two excess electrons. The dissipation is included through the
contact with an oscillator bath. We solve the Redfield master equation in order
to determine the dynamics of the quantum discord and the entanglement of
formation. Based on our results, we find that the quantum discord is more
resistant to dissipation than the entanglement of formation for such a system.
We observe that this characteristic is related to whether the oscillator bath
is common to both qubits or not and to the form of the interaction Hamiltonian.
Moreover, our results show that the quantum discord might be finite even for
higher temperatures in the asymptotic limit.Comment: 14 pages, 8 figures (new version is the final version to appear in
NJP
THOR 2.0: Major Improvements to the Open-Source General Circulation Model
THOR is the first open-source general circulation model (GCM) developed from
scratch to study the atmospheres and climates of exoplanets, free from Earth-
or Solar System-centric tunings. It solves the general non-hydrostatic Euler
equations (instead of the primitive equations) on a sphere using the
icosahedral grid. In the current study, we report major upgrades to THOR,
building upon the work of Mendon\c{c}a et al. (2016). First, while the
Horizontally Explicit Vertically Implicit (HEVI) integration scheme is the same
as that described in Mendon\c{c}a et al. (2016), we provide a clearer
description of the scheme and improved its implementation in the code. The
differences in implementation between the hydrostatic shallow (HSS),
quasi-hydrostatic deep (QHD) and non-hydrostatic deep (NHD) treatments are
fully detailed. Second, standard physics modules are added: two-stream,
double-gray radiative transfer and dry convective adjustment. Third, THOR is
tested on additional benchmarks: tidally-locked Earth, deep hot Jupiter,
acoustic wave, and gravity wave. Fourth, we report that differences between the
hydrostatic and non-hydrostatic simulations are negligible in the Earth case,
but pronounced in the hot Jupiter case. Finally, the effects of the so-called
"sponge layer", a form of drag implemented in most GCMs to provide numerical
stability, are examined. Overall, these upgrades have improved the flexibility,
user-friendliness, and stability of THOR.Comment: 57 pages, 31 figures, revised, accepted for publication in ApJ
Static potential in scalar QED with non-minimal coupling
Here we compute the static potential in scalar at leading order in
. We show that the addition of a non-minimal coupling of Pauli-type
(\eps j^{\mu}\partial^{\nu}A^{\alpha}), although it breaks parity, it does
not change the analytic structure of the photon propagator and consequently the
static potential remains logarithmic (confining) at large distances. The
non-minimal coupling modifies the potential, however, at small charge
separations giving rise to a repulsive force of short range between opposite
sign charges, which is relevant for the existence of bound states. This effect
is in agreement with a previous calculation based on Mller
scattering, but differently from such calculation we show here that the
repulsion appears independently of the presence of a tree level Chern-Simons
term which rather affects the large distance behavior of the potential turning
it into constant.Comment: 13 pages, 3 figure
A phonon laser in ultra-cold matter
We show the possible excitation of a phonon laser instability in an
ultra-cold atomic gas confined in a magneto-optical trap. Such an effect
results from a negative Landau damping of the collective density perturbations
in the gas, leading to the coherent emission of phonons. This laser instability
can be driven by a blue-detuned laser superimposed to the usual red-detuning
laser beams which usually provide the cooling mechanism. Threshold conditions,
instability growth rates and saturation levels are derived. This work
generalizes, on theoretical grounds, the recent results obtained with single
ion phonon laser, to an ultra-cold atomic gas, where real phonons can be
excited. Future phonon lasers could thus adequately be called phasers.Comment: 4 pages, submitted to PR
Detecção de ovino sororreagente para Maedi-Visna no estado de Sergipe.
Resumo - O vírus da Maedi-Visna pertence à família Retroviridae, gênero Lentivírus e afeta ovinos criados especialmente de forma intensiva. Apesar de variável patogenicidade, é responsável por manifestação clínica crônica e debilitante. Amplamente distribuído pelo mundo, é relacionado a subestimado impacto econômico na ovinocultura, porém com dados imprecisos no Brasil. O presente trabalho objetivou a obtenção da prevalência da Maedi-Visna no município de Lagarto/Sergipe. Foram analisadas 151 amostras séricas de ovinos Santa Inês, oriundas de nove propriedades rurais, identificadas quanto ao sexo e idade dos animais. Utilizou-se o teste de Imunodifusão em Gel de Ágar através da técnica de microaglutinação. A prevalência obtida foi de 0,66%, o que representa o primeiro relato da Maedi-Visna em Sergipe e que pode estar correlacionado ao íntimo contato entre ovinos e caprinos ou a submissão dos animais às exposições agropecuárias, inclusive extra-estaduais, onde há a aproximação de animais infectados e sadios promovida de forma inconsciente pelos produtores, ou ainda à transmissão a partir de animais exóticos inseridos em rebanho para melhoramento genético. Devido ao sistema de criação ao qual os animais são mantidos, confinamento de reprodutores e regime semi-intensivo aos demais, a doença pode não ter conseguido condições propicias para disseminar-se. O resultado indica riscos à ovinocultura desenvolvida no estado e as relações comerciais com os demais, e sugere a necessidade de estudos mais amplos para melhor caracterizar o perfil do estado em relação à ocorrência de Lentiviroses de Pequenos Ruminantes e implantação de medidas de controle e prevenção da disseminação desta enfermidade. Detection of sheep sororeaction for maedi-visna in State of Sergipe. Abstract - The virus of Maedi Visna belongs to Retroviridae family, gender Lentivirus affects raise of sheep especially at intensive way. Despite variable pathogenicity, is responsible for chronic and debilitating clinical. Widely distributed throughout the world, is linked underestimated the economic impact in raise of sheep, but with inaccurate data in Brazil. This study aimed to obtain the prevalence of Maedi Visna in the municipality of Lagarto / Sergipe. It were analyzed 151 samples of serum taken from sheep of Santa Ines breed, from nine farms, identified as to sex and age of animals. It was used in the test of Imunodifusion in Agar Gel whith microaglutination technique. The prevalence obtained was 0.66%, which represents the first report of Maedi Visna in Sergipe and can be correlated to the close contact between sheep and goats or the submission of animals for agricultural exhibitions where there is the nearest of infected and healthy animals unconscious promoted by producers or the transmission from exotic animals entered in farms for breeding herd. Because the system of creation which animals are kept, confinement of males and semi-intensive system to the others, the disease may not have achieved favorable conditions to spread itself. The results indicates the risk in raised of sheep developed in the state and trade relations with the others, and suggests the need for more extensive studies to better characterize the profile of the state in relation to the occurrence of Lentiviroses of Small Ruminants and implementation of measures for control and prevention spread of this disease
Manuel Castells and Informationalism
Understanding how the social appropriation of information and communication technologies came to define the contemporary period is critical for researchers and practitioners of innovation, business and management. This paper explores how the work of Manuel Castells as a social theorist provides the intellectual tools and the encompassing lenses to enable the study and navigate the process of structural transformation in which our lives have been engulfed from the 1970s onwards. Castells’ procedure of considering technology, social usages and structural history leads him to a key conceptual result: the introduction of the “Network Society” concept. His ideas have most notably been applied to the field of communications studies, which he analyses through the prism of power. However, these insights are not containable in one single discipline as the implications of informationalism stretch in a variety of directions, making other dimensions of society amenable to the network perspective. Organisational studies are one topic in which this line of enquiry may fruitfully be pursued.info:eu-repo/semantics/acceptedVersio
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