Modelling radiation emission in the transition from the classical to the quantum regime

An emissivity formula is derived using the generalised Fermi-Weizacker-Williams method of virtual photons which accounts for the recoil the charged particle experiences as it emits radiation. It is found that through this derivation the formula obtained by Sokolov et al using QED perturbation theory is recovered. The corrected emissivity formula is applied to nonlinear Thomson scattering scenarios in the transition from the classical to the quantum regime, for small values of the nonlinear quantum parameter \chi. Good agreement is found between this method and a QED probabilistic approach for scenarios where both are valid. In addition, signatures of the quantum corrections are identified and explored.Comment: 11 pages, 4 figures, submitted for publicatio

Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region

We present an analysis of the visible through near infrared spectrum of Eta Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES at the ESO VLT". This is a part of larger effort to present a complete Eta Carinae spectrum, and extends the previously presented analyses with the HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorption lines from the circumstellar shells are present. This paper provides a description of the spectrum between 3060 and 10,430 A, including line identifications of the ejecta absorption spectrum, the emission spectrum from the Weigelt condensations and the P-Cygni stellar wind features. The high spectral resolving power of VLT/UVES enables equivalent width measurements of atomic and molecular absorption lines for elements with no transitions at the shorter wavelengths. However, the ground based seeing and contributions of nebular scattered radiation prevent direct comparison of measured equivalent widths in the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a small overlap in wavelength coverage which allows us to compare and adjust for the difference in scattered radiation entering the instruments' apertures. This paper provides a complete online VLT/UVES spectrum with line identifications and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160 A.Comment: 13 pages, 11 figures + atlas. The paper accepted for the ApJS and is accompanied with an atlas in the online edition pape

Dinâmica espaço-temporal do parque caffeiro da Região de Três Pontas - MG.

A região de Três Pontas é uma das regiões cafeeiras mais importantes do Brasil e do mundo. O município é considerado o maior produtor mundial de café. Por esse motivo, conhecer a extensão e a localização desse parque cafeeiro torna-se de extrema importância. O objetivo desse trabalho foi analisar esse parque cafeeiro no tempo e no espaço, por meio de geotecnologias. No trabalho foram utilizadas imagens TM/Landsat de quatro diferentes datas, contemplando um período de sete anos de estudo. Foram confeccionados os mapas de uso da terra para os anos de 2000, 2003, 2005 e 2007. Por meio de ferramentas de análise espacial do sistema de informação geográfica SPRING, conclui-se que, durante esse período, o parque cresceu 7,45%. As áreas de café em produção aumentaram 11,24%, o que provavelmente elevou a produtividade da região. Não foram encontrados padrões de mudança no crescimento do parque

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

Beam loading in the nonlinear regime of plasma-based acceleration

A theory that describes how to load negative charge into a nonlinear, three-dimensional plasma wakefield is presented. In this regime, a laser or an electron beam blows out the plasma electrons and creates a nearly spherical ion channel, which is modified by the presence of the beam load. Analytical solutions for the fields and the shape of the ion channel are derived. It is shown that very high beam-loading efficiency can be achieved, while the energy spread of the bunch is conserved. The theoretical results are verified with the Particle-In-Cell code OSIRIS.Comment: 5 pages, 2 figures, to appear in Physical Review Letter

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

Dinâmica da ocupação de áreas cafeeiras de Minas Gerais utilizando geotecnologias.

O objetivo deste trabalho foi fazer uma avaliação espaço temporal das regiões cafeeiras de Machado e Patrocínio no estado de Minas Gerais, utilizando técnicas de geoprocessamento e dados de sensores remotos. Mapas de uso da terra dos anos 2000 e 2003 dessas duas áreas foram gerados com auxílio do software SPRING. Por intermédio do cruzamento dos dados percebeu-se que as culturas cafeeiras nesses dois ambientes tiveram comportamentos diferentes. Em Machado, o parque cafeeiro teve um pequeno decréscimo de cerca de 2% entre os anos avaliados, porém, percebe-se uma renovação do parque, já que existem cerca de 7% de áreas novas sendo plantadas e 9% de áreas sendo podadas ou retiradas da produção. Já em Patrocínio, a área total de café plantada não foi alterada, mas a área de café em produção aumentou significativamente, tendo provavelmente provocado um aumento também significativo na produção da região

Oxidation reactions of derivatives of cis-octalins promoted by thallium trinitrate (TTN)

The reaction of ten cis-octalins and cis-octalones with thallium trinitrate (TTN) leads to different products, depending mainly on the substitution pattern of the substrate. Functionalized cis-hydrindanes were obtained from the reaction of 1,2,3,4,4a,5,8,8a-octahydro-4a-methylnaphthalene and of 1,2,3,4,4a,5,8,8a-octahydro-4a,7-dimethylnaphthalene with TTN in acetonitrile, whereas a cyclic ether was formed treating 1,2,3,4,4a,5,8,8a-octahydro-6,8a-dimethylnaphthalen-1-ol with TTN in trimethylorthoformate (TMOF).FAPESPCNPqCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

One-to-one full scale simulations of laser wakefield acceleration using QuickPIC

We use the quasi-static particle-in-cell code QuickPIC to perform full-scale, one-to-one LWFA numerical experiments, with parameters that closely follow current experimental conditions. The propagation of state-of-the-art laser pulses in both preformed and uniform plasma channels is examined. We show that the presence of the channel is important whenever the laser self-modulations do not dominate the propagation. We examine the acceleration of an externally injected electron beam in the wake generated by 10 J laser pulses, showing that by using ten-centimeter-scale plasma channels it is possible to accelerate electrons to more than 4 GeV. A comparison between QuickPIC and 2D OSIRIS is provided. Good qualitative agreement between the two codes is found, but the 2D full PIC simulations fail to predict the correct laser and wakefield amplitudes.Comment: 5 pages, 5 figures, accepted for publication IEEE TPS, Special Issue - Laser & Plasma Accelerators - 8/200

Movimentação de inseticidas de tratamento de sementes no solo sob efeito da irrigação.

Este trabalho foi desenvolvido no Centro Nacional de Pesquisa de Milho e Sorgo (CNPMS), EMBRAPA, Sete Lagoas, MG, e teve como objetivo avaliar o movimento de inseticidas de tratamento de sementes de milho no perfil do solo em areas irrigadas. Foram utilizadas tres laminas de irrigacao: deficiente (50% da adequada), adequada e excessiva (100% superior a adequada), e dois inseticidas de tratamento de semente de milho: Semevin 350 RA (Thiodicarb) e Furadan 350 TS (Carbofuran), nas doses recomendadas pelos fabricantes. O monitoramento da lixiviacao desses inseticidas no solo foi feito em camadas de 5 cm e em quatro intervalos de 10 dias, a partir semeadura. A analise de residuo das amostras de solo foi feita utilizando-se cromatografia liquida de alta performance (HPLC). Nas condicoes em que foi realizado o experimento obtiveram-se as seguintes conclusoes: o Thiodicarb apresentou-se o mais instavel (com relacao a sua atividade) no solo com baixo risco de contaminacao do lencol freatico; o Carbofuran apresentou-se com um potencial maior de lixiviacao no perfil do solo devido, possivelmente, a sua resistencia a degradacao e, com baixo risco de contaminacao do lencol freatico para as condicoes apresentadas. Para todos os tratamentos, houve maior retencao do principio ativo dos inseticidas nas camadas mais superficiais (0 a 15 cm) do solo