13,283 research outputs found
Mapping the interface between the Local and Loop I bubbles using Stromgren photometry
The Sun is located inside an extremely low density region of quite irregular
shape called the Local Bubble. Close to the Local Bubble, there is an even
larger cavity known as Loop I. A ring-like feature observed in X-ray and HI has
been proposed as the contour of the bubbles interaction zone around 70 pc. Our
goal is to identify the interface between the Local and Loop I Bubbles and
discuss the ring's existence using Stromgren uvbyH\beta data. We have used the
uvbyH\beta data of the General Catalogue of Photometric Data, covering the
region defined by the Galactic coordinates: 250\degr <= l <= 50\degr and
-60\degr <= b <= 60\degr to obtain E(b-y) colour excess and distances. The
final sample is composed of 4346 stars located up to 500 pc from the Sun.
The expected transition to E(b-y) ~ 0.070 - 0.100 mag, corresponding to the
ring's column density, occurs on the western part of the ring at d = 110 +/- 20
pc, whereas on the eastern side it is not clearly seen before d = 280 +/- 50
pc. Near the Galactic plane the presence of the dark clouds is clearly
established by E(b-y) >= 0.100 mag on the western side at about 100 - 150 pc
and about 120 - 180 pc on the eastern side. In the southernmost part of the
ring the reddening remains very low, typically E(b-y) = 0.020 in all its
extension, except towards the Mensa constellation where a possible transition
is observed at d = 200 +/- 20 pc. In the northernmost part the colour excess
increases with distance in a gradual way, such that 0.020 <= E(b-y) <= 0.040
mag becomes predominant only after d=120 +/-15 pc.
If the ring really exists the colour excess distribution indicates that it is
very fragmented and distorted. However, the different characteristics of the
reddening inside and along the ring do not support the existence of a ring.Comment: 16 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Cluster growth in far-from-equilibrium particle models with diffusion, detachment, reattachment and deposition
Monolayer cluster growth in far-from-equilibrium systems is investigated by
applying simulation and analytic techniques to minimal hard core particle
(exclusion) models. The first model (I), for post-deposition coarsening
dynamics, contains mechanisms of diffusion, attachment, and slow activated
detachment (at rate epsilon<<1) of particles on a line. Simulation shows three
successive regimes of cluster growth: fast attachment of isolated particles;
detachment allowing further (epsilon t)^(1/3) coarsening of average cluster
size; and t^(-1/2) approach to a saturation size going like epsilon^(-1/2).
Model II generalizes the first one in having an additional mechanism of
particle deposition into cluster gaps, suppressed for the smallest gaps. This
model exhibits early rapid filling, leading to slowing deposition due to the
increasing scarcity of deposition sites, and then continued power law (epsilon
t)^(1/2) cluster size coarsening through the redistribution allowed by slow
detachment. The basic (epsilon t)^(1/3) domain growth laws and epsilon^(-1/2)
saturation in model I are explained by a simple scaling picture. A second,
fuller approach is presented which employs a mapping of cluster configurations
to a column picture and an approximate factorization of the cluster
configuration probability within the resulting master equation. This allows
quantitative results for the saturation of model I in excellent agreement with
the simulation results. For model II, it provides a one-variable scaling
function solution for the coarsening probability distribution, and in
particular quantitative agreement with the cluster length scaling and its
amplitude.Comment: Accepted in Phys. Rev. E; 9 pages with figure
Ising-type Magnetic Anisotropy in CePdAs
We investigated the anisotropic magnetic properties of CePdAs by
magnetic, thermal and electrical transport studies. X-ray diffraction confirmed
the tetragonal ThCrSi-type structure and the high-quality of the single
crystals. Magnetisation and magnetic susceptibility data taken along the
different crystallographic directions evidence a huge crystalline electric
field (CEF) induced Ising-type magneto-crystalline anisotropy with a large
-axis moment and a small in-plane moment at low temperature. A detailed CEF
analysis based on the magnetic susceptibility data indicates an almost pure
CEF ground-state doublet with the dominantly
and the doublets at 290 K and 330
K, respectively. At low temperature, we observe a uniaxial antiferromagnetic
(AFM) transition at K with the crystallographic -direction being
the magnetic easy-axis. The magnetic entropy gain up to reaches almost
indicating localised -electron magnetism without significant
Kondo-type interactions. Below , the application of a magnetic field along
the -axis induces a metamagnetic transition from the AFM to a
field-polarised phase at T, exhibiting a text-book example
of a spin-flip transition as anticipated for an Ising-type AFM.Comment: 9 Pages, 8 figure
Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry
A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in
asymmetric Laue (transmission) geometry with an arbitrary propagating strain
perpendicular to the crystal surface is presented. We present two case studies
for possible strain generation by short-pulse laser irradiation: (i) a
thermoelastic-like analytic model; (ii) a numerical model including effects of
electron-hole diffusion, Auger recombination, deformation potential and thermal
diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure
Adubação nitrogenada para o milho em sucessão a culturas de cobertura de solo no sistema plantio direto.
bitstream/item/30285/1/boletim-36.pd
Proteolytic processing of human cytomegalovirus glycoprotein B (gpUL55) is mediatedby the human endoprotease furin
AbstractInhibition of endoproteolytic cleavage of glycoprotein B (gB; gpUL55) of human cytomegalovirus was achieved by treatmentof infected fibroblasts with decanoyl peptidyl chloromethyl ketone (decRVKR-CMK), which inhibits the action of cellular subtilisin-like endoproteases with the amino acid recognition motif R × K/R R. Uncleaved gB precusor molecules of 160 kDa that were accumulated were endoglycosidase H resistant, suggesting that correct cellular transport occurred in the presence of the drug. The inhibitor also prevented endoproteolytic gB processing in CV-1 cells infected with a recombinant vaccinia virus-gB construct (VVgB). Evidence for direct involvement of the ubiquitous subtilisin-like endoprotease furin in gB cleavage was obtained from the observation that coinfection of CV-1 cells with WgB and a recombinant vaccinia-human furin construct reestablished endoproteolytic activity which was normally absent late after infection with WgB alone
Picosecond laser-pump, x-ray probe spectroscopy of GaAs
A laser-pump, x-ray probe spectroscopic experiment is described, and the results are shown. The Ga KαKα x-ray fluorescence following x-ray absorption, at the Ga K absorption edge was measured, and its increase due to excitation with subpicosecond pulses of laser light at 4.6 eV photon energy was determined. The x-ray absorption, and thus the fluorescence, is increased for about 200 ps after the laser pulse because additional final states for the x-ray absorption are cleared in the valence band by the laser excitation. The technique could eventually lead to a femtosecond pump-probe spectroscopy with an absolute reference energy level and also to a femtosecond x-ray detector. This is of particular importance to future short-pulse x-ray sources, such as free-electron lasers. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69690/2/RSINAK-73-12-4150-1.pd
Densidade e tamanho de formigueiros de Acromyrmex crassispinus em plantios de Pinus taeda.
O objetivo deste trabalho foi avaliar a densidade e o tamanho dos formigueiros de Acromyrmex crassispinus, ao longo do ano, em plantios de Pinus taeda de diferentes idades. Os experimentos foram realizados, em Rio Negrinho e em Três Barras, SC, em talhões de P. taeda com diferentes idades (recém-plantado, três anos e seis anos de idade). Em cada tratamento, foram demarcadas três parcelas de 1 ha. Os formigueiros foram classificados em três classes de tamanho: classe I, até 30 cm de diâmetro; classe II, 31 a 60 cm; e classe III, mais que 61 cm. A densidade de formigueiros de A. crassispinus foi menor no início do desenvolvimento da floresta, praticamente duplicou nos plantios com três anos, e reduziu quando a floresta estava com seis anos. A maior densidade de formigueiros ocorreu no período de dezembro a abril. Os formigueiros aumentaram de tamanho com a idade do pínu
Racionalização da aplicação de fertilizante nitrogenado na produção de arroz irrigado.
bitstream/item/31420/1/comunicado-200.pd
Short small-polaron lifetime in the mixed-valence perovskite CsAuI from high-pressure pump-probe experiments
We study the ultrafast phonon response of mixed-valence perovskite
CsAuI using pump-probe spectroscopy under high-pressure in a
diamond anvil cell. We observed a remarkable softening and broadening of the Au
- I stretching phonon mode with both applied pressure and photoexcitation.
Using a double-pump scheme we measured a lifetime of the charge transfer
excitation into single valence Au of less than 4 ps, which is an
indication of the local character of the Au excitation. Furthermore, the
strong similarity between the pressure and fluence dependence of the phonon
softening shows that the inter-valence charge transfer plays an important role
in the structural transition.Comment: 4 pages, 4 figure
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