528 research outputs found
Photoelectron Spectra Of Amorphous Sixhy Alloy Films: The Effect Of Microstructure On The Si-2p Level Shift
Depending on the deposition conditions, amorphous SixH y alloy films prepared by planar rf reactive magnetron sputtering exhibit one of three types of microstructure: (i) type A with no discernible microstructural features down to the 20-Ă
level and with a smooth uniform density; (ii) type B consisting of high-density regions of 50-200-Ă
lateral dimensions separated by a low-density network; and (iii) a two-level (type C) microstructure consisting of 300-500-Ă
dimensions columns separated by a pronounced low-density network. The columns, in turn, are composed of 50-200-Ă
dimension high-density regions interspersed with low-density network. The Si-2p level in these alloy films, determined by x-ray photoelectron spectroscopy, is observed to be strongly influenced by the microstructure of the film. A shift in the Si-2p level, systematically varying with the hydrogen concentration, is observed in alloy films with type B and type C microstructures. No shift is observed, irrespective of the hydrogen concentration, in alloy films with type A microstructure. The photoelectron spectra are examined in the light of the vibrational spectra of the films as measured by Fourier transform infrared techniques. The dependence of the Si-2p level shift on the microstructure and the variation with hydrogen concentration are explained qualitatively in terms of the differences in the silicon-hydrogen bonding in amorphous SixHy films with dissimilar microstructures.6072530253
Os sistemas agroflorestais como alternativa de sustentabilidade em ecossistemas de vĂĄrzea no Amazonas.
Os sistemas agroflorestais (SAFs) representam uma alternativa agroecolĂłgica de produção, sob regime sustentĂĄvel, para os agricultores familiares na vĂĄrzea dos Rios SolimĂ”es/Amazonas, principalmente no que se refere ao manejo florestal, Ă diversidade de produtos e Ă geração de renda. Diante disso, o objetivo deste trabalho foi compreender as diferentes formas de apropriação e de manejo dos recursos naturais atravĂ©s dos SAFs, nos subsistemas roça, sĂtio e lagos, como componente para a sustentabilidade dos agricultores familiares da localidade Costa da Terra Nova, municĂpio do Careiro da VĂĄrzea, Amazonas. O mĂ©todo empregado foi o Estudo de Caso com aplicação de questionĂĄrios, entrevistas e observação participante. A produção familiar na Costa da Terra Nova Ă© representada pelos SAFs, constituĂdo pelos os subsistemas: roça quintal e lago, que proporcionam produtos tanto para subsistĂȘncia quanto para comercialização local, e estabelecendo a agricultura como fundamental atividade na localidade. O principal produto para comercialização Ă© obtido das hortaliças cultivadas na Ă©poca da vazante no subsistema roça nas comunidades SĂŁo Francisco e Nossa Senhora da Conceição; e do extrativismo pesqueiro no subsistema lago, na Ă©poca da cheia, principalmente na comunidade SĂŁo JosĂ©. A criação de animal se dĂĄ no subsistema sĂtio e Ă© apenas para subsistĂȘncia, sendo as aves e os suĂnos os principais animais domĂ©sticos criados nas trĂȘs comunidades. Portanto os SAFs tradicionais, constituĂdos pelos subsistemas, roça, sitio e lago, sĂŁo responsĂĄveis pela sustentabilidade socioeconĂŽmica da localidade pesquisada, servindo, como alternativa agrĂcola melhor adaptada Ă s condiçÔes locais das ĂĄreas de vĂĄrzea na AmazĂŽnia
Microstate Dependence of Scattering from the D1-D5 System
We investigate the question of distinguishing between different microstates
of the D1-D5 system (with charges Q_1 and Q_5), by scattering with an
incoherent beam, composed of a supergravity probe, with central energy E_0 and
width (\Delta E). The scattering is studied in the dual CFT description in the
orbifold limit for finite R, where R is the radius of the circle on which the
D1 branes are wrapped. When R(\Delta E) >> 1, the absorption cross-section is
found to be independent of the microstate and identical to the leading
semiclassical answer computed from the naive geometry. For smaller (\Delta E),
the answer depends on the particular microstate, which we examine for both
typical and atypical microstates. We derive an upper bound for the leading
correction to the cross-section when 1/R >> \Delta E >> (the average energy gap
1/{R [sqrt(Q_1Q_5)]}. For a typical state the bound is proportional to the area
of the stretched horizon, [\sqrt(Q_1 Q_5)], up to [log (Q_1Q_5)] terms.
Furthermore, when E_0 << (\Delta E), the proportionality constant is a pure
number independent of all energy scales. Numerical calculations using
Lorentzian profiles show that the actual value of the correction is in fact
proportional to [sqrt(Q_1Q_5)] without the logarithmic factor. We offer some
speculations about how this result can be consistent with a resolution of the
naive geometry by higher derivative corrections to supergravity.Comment: 42 pages, 5 figure
Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV
Mid-rapidity transverse mass spectra and multiplicity densities of charged
and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC.
The spectra are exponential in transverse mass, with an inverse slope of about
280 MeV in central collisions. The multiplicity densities for these particles
scale with the negative hadron pseudo-rapidity density. The charged kaon to
pion ratios are and
for the most central collisions. The ratio is lower than the same
ratio observed at the SPS while the is higher than the SPS result.
Both ratios are enhanced by about 50% relative to p+p and +p
collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl
Scattering theory and ground-state energy of Dirac fermions in graphene with two Coulomb impurities
We study the physics of Dirac fermions in a gapped graphene monolayer containing two Coulomb impurities. For the case of equal impurity charges, we discuss the ground-state energy using the linear combination of atomic orbitals (LCAO) approach. For opposite charges of the Coulomb centers, an electric dipole potential results at large distances. We provide a nonperturbative analysis of the corresponding low-energy scattering problem
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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