2,368 research outputs found
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.
Classical Rotons in Cold Atomic Traps
We predict the emergence of a roton minimum in the dispersion relation of
elementary excitations in cold atomic gases in the presence of diffusive light.
In large magneto-topical traps, multiple-scattering of light is responsible for
the collective behavior of the system, which is associated to an effective
Coulomb-like interaction between the atoms. In optically thick clouds, the
re-scattered light undergoes diffusive propagation, which is responsible for a
stochastic short-range force acting on the atoms. We show that the dynamical
competition between these two forces results on a new polariton mode, which
exhibits a roton minimum. Making use of Feynman's formula for the static
structure factor, we show that the roton minimum is related to the appearance
of long-range order in the system.Comment: 5 pages, 3 figure
Asymmetric Ramsey properties of random graphs involving cliques and cycles
We prove that for every ℓ, r ≥ 3, there exists c > 0 such that for (image found), with high probability there is a 2-edge-colouring of the random graph Gn,p with no monochromatic copy of Kr of the first colour and no monochromatic copy of Cℓ of the second colour. This is a progress on a conjecture of Kohayakawa and Kreuter
Photon Orbital Angular Momentum and Mass in a Plasma Vortex
We analyse the Anderson-Higgs mechanism of photon mass acquisition in a
plasma and study the contribution to the mass from the orbital angular momentum
acquired by a beam of photons when it crosses a spatially structured charge
distribution. To this end we apply Proca-Maxwell equations in a static plasma
with a particular spatial distribution of free charges, notably a plasma
vortex, that is able to impose orbital angular momentum (OAM) onto light. In
addition to the mass acquisition of the conventional Anderson-Higgs mechanism,
we find that the photon acquires an additional mass from the OAM and that this
mass reduces the Proca photon mass.Comment: Four pages, no figures. Error corrections, improved notation, refined
derivation
Composição botânica da dieta consumida por bovinos em pastagens de quicuio-da-amazônia (Brachiaria humidicola) através da analise microhistologica de fezes em área de pequeno produtor da Zona Bragantina.
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
Correlação entre distância genética e heterose para comprimento de panÃcula por cruzamento dialélico entre acessos de arroz (Oryza sativa L.) de base genética ampla.
O objetivo desse trabalho foi correlacionar os dados de distância genética de Rogers modificada por Wright e a heterose observada no caractere comprimento de panÃcula, um dos componentes de produtividade do arroz, dos 120 hÃbridos obtidos nesses cruzamentos
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