15,193 research outputs found
Estrutura Genética do Marsupial Marmosops Incanus em Paisagens de Mata Atlântica no Espírito Santo
A estrutura, a configuração e a quantidade de hábitat disponível no ambiente ajudam a determinar a viabilidade genética de uma população ou espécie. Em genética da paisagem, conceitos de ecologia da paisagem e genética de populações são utilizados em conjunto para avaliar a conectividade estrutural do ambiente de modo a permitir o entendimento da conectividade funcional de populações na paisagem. Marmosops incanus é um marsupial didelfídeo dependente de floresta com ampla distribuição no bioma Mata Atlântica que é encontrada em maior abundância em ambiente de floresta contínua em algumas regiões, mas em ambientes mais fragmentados em outras regiões, como no Espírito Santo. Nesse trabalho, comparamos a estrutura genética de M. incanus em paisagens de Mata Atlântica do Espírito Santo através de técnicas de isolamento por resistência com o objetivo de se identificar a conectividade genética e possíveis rotas de fluxo gênico entre as populações. Utilizamos oito loci de marcadores microssatélite para avaliar a estrutura, divergência e diversidade genética em 13 localidades. Também testamos a hipótese de que a quantidade de floresta nas diferentes paisagens é determinante para a diversidade e distinção genética da espécie. Marmosops incanus está estruturada em seis agrupamentos genéticos distintos: quatro ao norte do rio Doce que apresentaram maior isolamento genético, e dois ao sul, incluindo o maior agrupamento (denominado Centro-Sul), formado por seis localidades com grande fluxo gênico e valores altos de riqueza alélica. Os resultados obtidos apontam para respostas genéticas diferenciadas da espécie à fragmentação ao norte e ao sul do Rio Doce. No geral, populações de M. incanus em ambientes de floresta contínua ao norte estão mais isoladas geneticamente do que populações em hábitats mais fragmentadas no sul estado. Os mapas das possíveis rotas de fluxo gênico indicam que isso se deve principalmente à configuração dos fragmentos remanescentes. Deve-se exercer cautela ao extrapolar resultados de genética da paisagem encontrados em uma região para outra e que a configuração do hábitat na paisagem é mais determinante para a saúde genética de espécies florestais do que a quantidade de hábitat.
Palavras-chave: conectividade, Didelphidae, isolamento por resistência, genética da paisagem, microssatélites
Conditions for the onset of the current filamentation instability in the laboratory
Current Filamentation Instability (CFI) is capable of generating strong
magnetic fields relevant to explain radiation processes in astrophysical
objects and lead to the onset of particle acceleration in collisionless shocks.
Probing such extreme scenarios in the laboratory is still an open challenge. In
this work, we investigate the possibility of using neutral
beams to explore the CFI with realistic parameters, by performing 2D
particle-in-cell simulations. We show that CFI can occur unless the rate at
which the beam expands due to finite beam emittance is larger than the CFI
growth rate and as long as the role of competing electrostatic two-stream
instability (TSI) is negligible. We also show that the longitudinal energy
spread, typical of plasma based accelerated electron-positron fireball beams,
plays a minor role in the growth of CFI in these scenarios
Structured Deformations of Continua: Theory and Applications
The scope of this contribution is to present an overview of the theory of
structured deformations of continua, together with some applications.
Structured deformations aim at being a unified theory in which elastic and
plastic behaviours, as well as fractures and defects can be described in a
single setting. Since its introduction in the scientific community of rational
mechanicists (Del Piero-Owen, ARMA 1993), the theory has been put in the
framework of variational calculus (Choksi-Fonseca, ARMA 1997), thus allowing
for solution of problems via energy minimization. Some background, three
problems and a discussion on future directions are presented.Comment: 11 pages, 1 figure, 1 diagram. Submitted to the Proceedings volume of
the conference CoMFoS1
All-optical trapping and acceleration of heavy particles
A scheme for fast, compact, and controllable acceleration of heavy particles
in vacuum is proposed, in which two counterpropagating lasers with variable
frequencies drive a beat-wave structure with variable phase velocity, thus
allowing for trapping and acceleration of heavy particles, such as ions or
muons. Fine control over the energy distribution and the total charge of the
beam is obtained via tuning of the frequency variation. The acceleration scheme
is described with a one-dimensional theory, providing the general conditions
for trapping and scaling laws for the relevant features of the particle beam.
Two-dimensional, electromagnetic particle-in-cell simulations confirm the
validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic
Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions
The strong influence of the electron dynamics provides the possibility of
controlling the expansion of laser-produced plasmas by appropriately shaping
the laser pulse. A simple irradiation scheme is proposed to tailor the
explosion of large deuterium clusters, inducing the formation of shock
structures, capable of driving nuclear fusion reactions. Such a scenario has
been thoroughly investigated, resorting to two- and three-dimensional
particle-in-cell simulations. Furthermore, the intricate dynamics of ions and
electrons during the collisionless expansion of spherical nanoplasmas has been
analyzed in detail using a self-consistent ergodic-kinetic model. This study
clarifies the transition from hydrodynamic-like to Coulomb-explosion regimes
Determination of the level of defective beans in coffee samples by using array of nanostructured sensors.
Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering
Twisted Laguerre-Gaussian lasers, with orbital angular momentum and
characterised by doughnut shaped intensity profiles, provide a transformative
set of tools and research directions in a growing range of fields and
applications, from super-resolution microcopy and ultra-fast optical
communications to quantum computing and astrophysics. The impact of twisted
light is widening as recent numerical calculations provided solutions to
long-standing challenges in plasma-based acceleration by allowing for high
gradient positron acceleration. The production of ultrahigh intensity twisted
laser pulses could then also have a broad influence on relativistic
laser-matter interactions. Here we show theoretically and with ab-initio
three-dimensional particle-in-cell simulations, that stimulated Raman
backscattering can generate and amplify twisted lasers to Petawatt intensities
in plasmas. This work may open new research directions in non-linear optics and
high energy density science, compact plasma based accelerators and light
sources.Comment: 18 pages, 4 figures, 1 tabl
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