Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces

Electron-hole excitations in the surface bands of GaAs(110) are analyzed using constrained density-functional theory calculations. The results show that Frenkel-type autolocalized excitons are formed. The excitons induce a local surface unrelaxation which results in a strong exciton-exciton attraction and makes complexes of two or three electron-hole pairs more favorable than separate excitons. In such microscopic exciton "droplets" the electron density is mainly concentrated in the dangling orbital of a surface Ga atom whereas the holes are distributed over the bonds of this atom to its As neighbors thus weakening the bonding to the substrate. This finding suggests the microscopic mechanism of a laser-induced emission of neutral Ga atoms from GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from: [email protected]

Charm Correlation as a Diagnostic Probe of Quark Matter

The use of correlation between two open-charm mesons is suggested to give information about the nature of the medium created in heavy-ion collisions. Insensitivity to the charm production rate is achieved by measuring normalized cumulant. The acollinearity of the D momenta in the transverse plane is a measure of the medium effect. Its dependence on nuclear size or E_T provides a signature for the formation of quark matter.Comment: 12 pages, no figure

Influence of adsorption and anaerobic granular sludge characteristics on long chain fatty acids inhibition process

The impact of LCFA adsorption on the methanogenic activity was evaluated in batch assays for two anaerobic granular sludges in the presence and absence of bentonite as synthetic adsorbent. A clear inhibitory effect at an oleate (C18:1) concentration of 0.5 g(C18:1) L(-1) was observed for both sludges. Palmitate (C16:0) was confirmed to be the main intermediate of C18:1 degradation in not adapted sludge and its accumulation was further evidenced by fluorescence staining and microscopy techniques. LCFA inhibition could be decreased by the addition of bentonite, reducing the lag-phase and accelerating the kinetics of LCFA degradation, concluding in the importance of the adsorptive nature of the LCFA inhibitory process. Granule morphology and molecular profiling of predominant microorganisms revealed that biomass adaptation to LCFA could modify the intermediates accumulation profiles and process rates.This work was funded by the Spanish Ministry of Science and Innovation (projects ENE 2007-65850 and CTM 2010-18212), and was partially supported by a grand from the Department of Universities, Research and Media Society of Catalonia Government (BE-DGR 2008 BE1 00261). We would like to thank Lucia Neves, Ana Nicolau, Madalena Vieira, and Ana Julia Cavaleiro, from University of Minho, for their assistance in microscopic observations and analytical methods. We also thank Miriam Guivernau (IRTA) for assistance in the PCR-DGGE profiling and ribotype sequencing. We are also grateful to David Bedoya (MWH) and Francesc Prenafeta (IRTA) for the revision and critical reading of the manuscript

The Thermal Structure of Gas in Pre-Stellar Cores: A Case Study of Barnard 68

We present a direct comparison of a chemical/physical model to multitransitional observations of C18O and 13CO towards the Barnard 68 pre-stellar core. These observations provide a sensitive test for models of low UV field photodissociation regions and offer the best constraint on the gas temperature of a pre-stellar core. We find that the gas temperature of this object is surprisingly low (~7-8 K), and significantly below the dust temperature, in the outer layers (Av < 5 mag) that are traced by C18O and 13CO emission. As shown previously, the inner layers (Av > 5 mag) exhibit significant freeze-out of CO onto grain surfaces. Because the dust and gas are not fully coupled, depletion of key coolants in the densest layers raises the core (gas) temperature, but only by ~1 K. The gas temperature in layers not traced by C18O and 13CO emission can be probed by NH3 emission, with a previously estimated temperature of ~10-11 K. To reach these temperatures in the inner core requires an order of magnitude reduction in the gas to dust coupling rate. This potentially argues for a lack of small grains in the densest gas, presumably due to grain coagulation.Comment: 33 pages, 11 figures, accepted by Astrophysical Journa

Dynamics of Weyl Scale Invariant non-BPS p=3 Branes

In this paper a Weyl scale invariant $p=3$ brane scenario is introduced, with the brane embedded in a higher dimensional bulk space with $N=1, 5D$ Super--Weyl symmetry. Its action, which describes its long wave oscillation modes into the ambient superspace and breaks the target symmetry down to the lower dimensional Weyl W(1,3) symmetry, is constructed by the approach of coset method.Comment: 12 pages, modified versio

ALMA polarimetric studies of rotating jet/disk systems

We have recently obtained polarimetric data at mm wavelengths with ALMA for the young systems DG Tau and CW Tau, for which the rotation properties of jet and disk have been investigated in previous high angular resolution studies. The motivation was to test the models of magneto-centrifugal launch of jets via the determination of the magnetic configuration at the disk surface. The analysis of these data, however, reveals that self-scattering of dust thermal radiation dominates the polarization pattern. It is shown that even if no information on the magnetic field can be derived in this case, the polarization data are a powerful tool for the diagnostics of the properties and the evolution of dust in protoplanetary disks.Comment: 9 pages, 3 figures, to appear in "Jet Simulations, Experiments and Theory. Ten years after JETSET, what is next ?", C. Sauty ed., Springer Natur

Consistent modified gravity: dark energy, acceleration and the absence of cosmic doomsday

We discuss the modified gravity which includes negative and positive powers of the curvature and which provides the gravitational dark energy. It is shown that in GR plus the term containing negative power of the curvature the cosmic speed-up may be achieved, while the effective phantom phase (with $w$ less than -1) follows when such term contains the fractional positive power of the curvature. The minimal coupling with matter makes the situation more interesting: even 1/R theory coupled with the usual ideal fliud may describe the (effective phantom) dark energy. The account of $R^2$ term (consistent modified gravity) may help to escape of cosmic doomsday.Comment: LaTeX file, 9 pages, based on the talk given by S.D. Odintsov (Int. Conference Mathematical Methods in Physics, Rio de Janeiro, Augest, 2004), to appear in CQG, Letter

Dietas compostas por palma forrageira "in natura", resíduo de vitivinícola e diferentes níveis de uréia para caprinos.

O objetivo desse trabalho foi determinar o consumo de matéria seca (CMS), de matéria orgânica (CMO), de proteína bruta (CPB), de fibnra em detergente neutro (CFDN), de carboidratos totais (CCHOT), de carboidratos não fibrosos (CCNF) e de nutrientes digestíveis totais (CNDT) para avaliar os efeitos da adição de diferentes níveis de uréia em dietas compostas por palma forrageira "in natura" (40%) e resíduo desidratado de vitivinícolas (60%). Foram utilizados quatro níveis de uréia, 0%, 0,5%, 1% e 1,5%. Usaram-se 24 caprinos sem padrão racial definido, castrados e distribuídos em delineamento experimental de seis blocos casualizados, o peso vivo (PV) foi o fator de controle. Houve efeito linear crescente (P0,05) no consumo de NDT e CHOT em kg/dia e CCNF em kg/dia e %PV. O consumo de extrato etéreo não foi significativo (P>0,05), apresentando médis de 0,03 kg/dia, 0,17 % PV e 3,54 g/PV0,75, apesar do aumento no consumo da matéria seca. Os níveis crescentes de uréia nas dietas incrementaram as ingestões de nutrientes, porém não foram suficientes para promover aumento no ganho de peso, principalmente, devido ao baixo aporte energético

Exactly Solvable Hydrogen-like Potentials and Factorization Method

A set of factorization energies is introduced, giving rise to a generalization of the Schr\"{o}dinger (or Infeld and Hull) factorization for the radial hydrogen-like Hamiltonian. An algebraic intertwining technique involving such factorization energies leads to derive $n$-parametric families of potentials in general almost-isospectral to the hydrogen-like radial Hamiltonians. The construction of SUSY partner Hamiltonians with ground state energies greater than the corresponding ground state energy of the initial Hamiltonian is also explicitly performed.Comment: LaTex file, 21 pages, 2 PostScript figures and some references added. To be published in J. Phys. A: Math. Gen. (1998

Estoques e fluxos de N em sistema agroflorestal, região de Cerrado (Brasil).

Sistemas Agroflorestais surgem como opção na busca por sistemas produtivos conservacionistas, por sua diversificação e promoção de serviços ambientais. O objetivo deste estudo foi avaliar estoques e fluxos de N no sistema solo-planta-serapilheira de um SAF, em região de Cerrado do Brasil Central. O teor médio de N no solo foi 0,18%, decrescendo com a profundidade (0-20cm). O estoque médio de N no solo foi 3,08 Mg.ha-1 (0-20cm). N-NH4+ predominou em relação à N-NO3 ao longo do experimento. Maiores emissões de N2O ocorreram na transição chuva-seca de 2014, com fluxo médio de 45,9 &#956;g m-2 h-1 N2-N2O enquanto na estação seca do mesmo ano foi 16,6 ug m-2 h-1 N2-N2O. A razão C:N da serapilheira apresentou valor médio de 20,4 ± 1,4 e concentração de N de 1,7% ± 0,2, enquanto a perda da massa foliar média no experimento de decomposição por litterbags, aos 120 dias, foi apenas 19,6%. A concentração média de N foliar para as espécies arbóreas avaliadas, foi de 2,3%, enquanto para a serapilheira o valor médio de N foi 1,5%. Assim, espécies frutíferas apresentaram taxa de retranslocação média de N de 36,6% e madeireiras 32,7%. Após ajustar a taxa de retranslocação foliar média de N, encontrou-se a taxa de 49,3%. A disponibilidade de N no solo indicou que a qualidade do material foliar das espécies plantadas, favoreceu a disponibilidade de N no sistema solo-planta-serapilheira. As taxas de retranslocação foliar de N idicaram a importância da ciclagem interna para a manutenção do N no sistema