Field Emission Dark Current of Technical Metallic Electrodes

In the framework of the Low Emittance Gun (LEG) project, high gradient acceleration of a low emittance electron beam will be necessary. In order to achieve this acceleration a -500 kV, 250 ns FWHM, pulse will be applied in between two electrodes. Those electrodes should sustain the pulsed field without arcing, must not outgass and must not emit electrons. Ion back bombardment, and dark current will be damageable to the electron source as well as for the low emittance beam. Electrodes of commercially available OFE copper, aluminium, stainless steel, titanium and molybdenum were tested following different procedures including plasma glow discharge cleaning.Comment: 22 pages, 6 tables, 10 figures Vs 2 : graphics more readable, enhanced content Vs 3 : typo correcte

Comparison among native floating aquatic macrophytes for bioconcentration of heavy metals

This work was aimed to show the development of a comparative study of the capability of bioindicators to reveal the presence of heavy metals among species of floating aquatic macrophytes such as Spirodela sp (giant duckweed), Pistia stratiotes (water lettuce), Salvinia sp used as a parameter for bioconcentration factors plant / sediment. We performed a simple sampling at six sites in the region of Pelotas, southern Brazil, in which it was collected sediments and plants. The plants experienced the nitric perchloric acid digestion method, while the sediment suffered pseudo total acid digestion method. The determination of Cr, Cu, Pb and Zn in the extracts was conducted by atomic absorption spectrophotometry in flame. In general, the floating aquatic macrophytes studied showed better bioconcentration factor for metals from the sediment in the following order: Cu>Zn>Pb>Cr. For copper, the figures obtained with Pistia stratiots ranged from 5.7 to 82.8. The BCF for Zn ranged from 3.0 to 11.6 and Salvinia sp. For the Pb bioconcentration factor, it ranged from 5.4 to 0.6 in Spirodela sp. The in situ study showed that all species had high bioaccumulation potential, especially Pistia stratiotes that was employed to remove copper

γ∗p\gamma^*p cross section from the dipole model in momentum space

We reproduce the DIS measurements of the proton structure function at high energy from the dipole model in momentum space. To model the dipole-proton forward scattering amplitude, we use the knowledge of asymptotic solutions of the Balitsky-Kovchegov equation, describing high-energy QCD in the presence of saturation effects. We compare our results with the previous analysis in coordinate space and discuss possible extensions of our approach.Comment: 9 pages, 3 figure

Época de semeadura, fenologia e crescimento de plantas de fisális no Sul do Brasil.

Os objetivos do presente trabalho foram avaliar o comportamento fenológico e os componentes do crescimento de plantas de fisális (Physalis peruviana L.) em função de três épocas de semeadura, na região de Pelotas-RS. São determinados as datas de ocorrência, os dias após a emergência (DAE) e a soma térmica (GD) para os seguintes estádios: folhas verdadeiras, primeira ramificação, brotação floral, botões florais, flores abertas, formação de brotos basais, frutos caídos, início de queda das folhas e colheita. Quinzenalmente, a partir do transplante, foram realizadas avaliações de comprimento do ramo principal, número total de folhas do ramo principal, número de flores e frutos por planta. Nas condições edafoclimáticas de Pelotas, as plantas de fisális, oriundas da semeadura em novembro, necessitaram de menor número de DAE para completar os estádios fenológicos; contudo, esta tendência não se manteve para GD. A semeadura de fisális realizada no início do mês de setembro resultou em plantas com maior crescimento vegetativo e número de frutos, bem como com características de crescimento e de produção semelhantes às principais regiões de cultivo.DOI: 10.1590/0100-2945-292/1

Dilepton low pTp_T suppression as an evidence of the Color Glass Condensate

The dilepton production is investigated in proton-nucleus collisions in the forward region using the Color Glass Condensate approach. The transverse momentum distribution ($p_T$), more precisely the low $p_T$ region, where the saturation effects are expected to increase, is analyzed. The ratio between proton-nucleus and proton-proton differential cross section for RHIC and LHC energies is evaluated, showing the effects of saturation at small $p_T$, and presenting a Cronin type peak at moderate $p_T$. These features indicate the dilepton as a most suitable probe to study the properties of the saturated regime and the Cronin effect.Comment: 10 pages, 8 figures, replaced with the version to appear in Physical Review

Non-linear QCD dynamics in two-photon interactions at high energies

Perturbative QCD predicts that the growth of the gluon density at high energies should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky-Kovchegov (BK) equation. In this paper we study the $\gamma \gamma$ interactions at high energies and estimate the main observables which will be probed at future linear colliders using the color dipole picture. We discuss in detail the dipole - dipole cross section and propose a new relation between this quantity and the dipole scattering amplitude. The total $\gamma \gamma$, $\gamma^{*} \gamma^{*}$ cross-sections and the real photon structure function $F_2^{\gamma}(x,Q^2)$ are calculated using the recent solution of the BK equation with running coupling constant and the predictions are compared with those obtained using phenomenological models for the dipole-dipole cross section and scattering amplitude. We demonstrate that these models are able to describe the LEP data at high energies, but predict a very different behavior for the observables at higher energies. Therefore we conclude that the study of $\gamma \gamma$ interactions can be useful to constrain the QCD dynamics.Comment: 11 pages, 5 figures. Version to be published in European Physical Journal

Non-linear QCD dynamics and exclusive production in epep collisions

The exclusive processes in electron-proton ($ep$) interactions are an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of proton which is strongly subject to parton saturation effects. In this paper we compute the cross sections for the exclusive vector meson production as well as the deeply virtual Compton scattering (DVCS) relying on the color dipole approach and considering the numerical solution of the Balitsky-Kovchegov equation including running coupling corrections. We show that the small-$x$ evolution given by this evolution equation is able to describe the DESY-HERA data and is relevant for the physics of the exclusive observables in future electron-proton colliders and in photoproduction processes to be measured in coherent interactions at the LHC.Comment: 6 pages, 4 figure