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Search Results: 1 - 10 of 710372 matches for " J. T. Mendon?a "
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Nonlinear laser driven donut wakefields for positron and electron acceleration
J. Vieira,J. T. Mendona
Physics , 2014, DOI: 10.1103/PhysRevLett.112.215001
Abstract: We show analytically and through three-dimensional particle-in-cell simulations that non-linear wakefields driven by Laguerre-Gaussian laser pulses can lead to hollow electron self-injection and positron acceleration. We find that higher order lasers can drive donut shaped blowout wakefields with strong positron accelerating gradients comparable to those of a spherical bubble. Corresponding positron focusing forces can be more than an order of magnitude stronger than electron focusing forces in a spherical bubble. Required laser intensities and energies to reach the non-linear donut shaped blowout are within state-of-the-art experimental conditions.
Twisted Phonons in Bose-Einstein condensates
J. T. Mendona,A. Gammal
Physics , 2013, DOI: 10.1088/0953-4075/47/6/065301
Abstract: We consider elementary excitations in a Bose Einstein condensate, carrying a finite amount of angular momentum. We show that these elementary excitations are modified Bogoliubov oscillations, or phonons with an helical wave structure. These twisted phonon modes can contribute to the total vorticity in a quantum fluid, thus complementing the contribution of the traditional quantum vortices. Linear and nonlinear versions of twisted phonon modes will be discussed. New envelope soliton solutions are shown to exist in a condensate.
Brazilian Journal of Aquatic Science and Technology , 2000,
Abstract: The fishery of Cananéia (S o Paulo, Brazil) is dominated by catches of the sea bob shrimp Xiphopenaeus kroyeri. The work was developed in the southern coast of S o Paulo State, between 1998 and 1999 and included collecting production, capture effort and economic value data of the Xiphopenaeus kroyeri. Mean landings of shrimp in the municipal district of Cananéia have been approximately 728 tons/year. The trade categories are divided into gross shrimp (without selection on board), chosen shrimp (with selection), clean shrimp (with selection and posterior processing) and small shrimp (after selection of larger ones). Largest landings occurred in the first semester and the second semester was characterized by the largest production of chosen shrimp. The results suggest presented that the fishery is declining, and do not agree with the current period of closure. The analysis of the by-catch composition of artesanal fishery is necessary, in order to improve the fishing administration and the rational use of the resource. A pesca de Cananéia tem o camar o-sete-barbas como principal produto desembarcado. O trabalho foi desenvolvido no litoral sul do Estado de S o Paulo, no período de 1998 e 1999, coletando dados de produ o, esfor o e valor econ mico do camar o-sete-barbas. A produ o média desembarcada de camar o-sete-barbas no município de Cananéia, nos anos estudados foi de 728 toneladas anuais. As categorias de comércio est o divididas entre camar o-sete-barbas bruto (sem sele o a bordo), camar o-sete-barbas escolhido (com sele o), camar o-setebarbas descabe ado (com sele o e posterior processamento) e camar o-sete-barbas miúdo (com sele o, sendo retirado os maiores). Os maiores desembarques ocorreram no primeiro semestre e o segundo semestre se caracterizou pela maior produ o de camar o escolhido. Os resultados mostraram que as capturas de camar o-sete-barbas est o em declínio, sugerindo pouca eficiência da portaria que estabelece o defeso da espécie para a conserva o do recurso. A análise da composi o da rejei o junto à pesca artesanal é necessária, com o intuito de melhorar a administra o pesqueira e o aproveitamento racional das capturas.
Neutrino orbital angular momentum in a plasma vortex
J. T. Mendona,B. Thidé
Physics , 2008, DOI: 10.1209/0295-5075/84/41001
Abstract: It is shown that an electron-neutrino beam, propagating in a background plasma, can be decomposed into orbital momentum (OAM) states, similar to the OAM photon states. Coupling between different OAM neutrino states, in the presence of a plasma vortex, is considered. We show that plasma vorticity can be transfered to the neutrino beam, which is relevant to the understanding of the neutrino sources in astrophysics. Observation of neutrino OAM states could eventually become possible.
Stimulated Raman and Brillouin backscattering of collimated beams carrying orbital angular momentum
J. T. Mendona,B. Thidé,H. Then
Physics , 2009, DOI: 10.1103/PhysRevLett.102.185005
Abstract: We study theoretically the exchange of angular momentum between electromagnetic and electrostatic waves in a plasma, due to the stimulated Raman and Brillouin backscattering processes. Angular momentum states for plasmon and phonon fields are introduced for the first time. We demonstrate that these states can be excited by nonlinear wave mixing, associated with the scattering processes. This could be relevant for plasma diagnostics, both in laboratory and in space. Nonlinearly coupled paraxial equations and instability growth rates are derived.
Polytropic equilibrium and normal modes in cold atomic traps
H. Ter?as,J. T. Mendona
Physics , 2013, DOI: 10.1103/PhysRevA.88.023412
Abstract: The compressibility limit of a cold gas confined in a magneto-optical trap due to multiple scattering of light is a long-standing problem. This scattering mechanism induces long-range interactions in the system, which is responsible for the occurrence of plasma-like phenomena. In the present paper, we investigate the importance of the long-range character of the mediated atom-atom interaction in the equilibrium and dynamical features of a magneto-optical trap. Making use of a hydrodynamical formulation, we derive a generalized Lane-Emden equation modeling the polytropic equilibirum of a magneto-optical trap, allowing us to describe the cross-over between the two limiting cases: temperature dominated and multiple-scattering dominated traps. The normal collective modes of the system are also computed.
Exciton-polariton wakefields in semiconductor microcavities
H. Ter?as. J. T. Mendona
Physics , 2014,
Abstract: We consider the excitation of polariton wakefields due to a propagating source in a semiconductor micro cavity. We show that two kinds of wakes are possible, depending on the constituents fraction (either exciton or photon) of the polariton wavefunction. The nature of the wakefields (pure excitonic or polaritonic) can be controled by changing the speed of propagation of the external pump. This process could be used as a diagnostic for the internal parameters of the microcavity.
Laser scattering by density fluctuations of ultra-cold atoms in a magneto-optical trap
J. T. Mendona,H. Ter?as
Physics , 2011, DOI: 10.1088/0953-4075/44/9/095301
Abstract: We study the spectrum of density fluctuations in the ultra-cold gas of neutral atoms, confined in a magneto-optical trap. We determine the corresponding amplitude and spectra of laser light scattered by this medium. We derive an expression for the dynamical structure function, by using a test particle method. We propose to use the collective laser scattering as a diagnostic method for the microscopic properties of the ultra-cold matter. This will also allow us to check on the atomic correlations which are mediated by the collective mean field inside the gas.
Satellite rings and normal modes in rotating clouds of ultra cold atoms
J. D. Rodrigues,J. T. Mendona,J. A. Rodrigues
Physics , 2014,
Abstract: The multiple scattering of light in a gas of ultra cold atoms is responsible for many exciting features observed in magneto-optical traps including the collective behavior forced by a Coulomb like potential. This field also induces plasma like phenomena in the cloud which allows the treatment of the system as a one component trapped plasma. With a fluid description and casting the thermodynamical behavior in the form of a polytropic equation of state we investigate the equilibrium profiles of rotating clouds and its dependence on the experiment characteristics. Numerical solutions predict the formation of stable orbital modes both in rotating and non rotating clouds. We also investigate the normal modes on such rotating systems.
Rossby waves in rapidly rotating Bose-Einstein condensates
H. Ter?as,J. P. A. Martins,J. T. Mendona
Physics , 2009, DOI: 10.1088/1367-2630/12/9/093001
Abstract: We predict and describe a new collective mode in rotating Bose-Einstein condensates, which is very similar to the Rossby waves in geophysics. In the regime of fast rotation, the Coriolis force dominates the dynamics and acts as a restoring force for acoustic-drift waves along the condensate. We derive a nonlinear equation that includes the effects of both the zero-point pressure and the anharmonicity of the trap. It is shown that such waves have negative phase speed, propagating in the opposite sense of the rotation. We discuss different equilibrium configurations and compare with those resulting from the Thomas-Fermi approximation.
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