125 research outputs found
LEED studies of lead on copper (100)
Lead layers on copper (100) at coverages from 0.5 to 0.6 were investigated by quantitative LEED and AES measurements and dynamical LEED calculations. Comparisons of intensity measurements with dynamical calculations for the (Wurzel2 x Wurzel2)R45° structure show that the Pb atoms are adsorbed in hollow sites. The Cu---Pb distance is close to the sum of both metallic radii. The dense lead monolayer at a coverage of 0.6 exhibits a c(5 Wurzel2 x Wurzel2)R45° superstructure with cmm symmetry of the diffraction pattern. Calculations for five models were performed under variation of several geometric parameters. Most analogies were found for regular arrangements of distorted (Wurzel2 x Wurzel2)R45° domains, separated by antiphase boundaries. This result is in consistency with observations of poorly ordered (Wurzel2 x Wurzel2)R45° antiphase domains at intermediate coverages
Scaling of Island Growth in Pb Overlayers on Cu(001)
The growth and ordering of a Pb layer deposited on Cu(001) at 150 K has been
studied using atom beam scattering. At low coverage, ordered Pb islands with a
large square unit cell and nearly hexagonal internal structure are formed. This
is a high order commensurate phase with 30 atoms in the unit cell. From the
measurement of the island diffraction peak profiles we find a power law for the
mean island - size versus coverage with an exponent . A
scaling behavior of growth is confirmed and a simple model describing island
growth is presented. Due to the high degeneracy of the monolayer phase,
different islands do not diffract coherently. Therefore, when islands merge
they still diffract as separate islands and coalescence effects are thus
negligible. From the result for we conclude that the island density is
approximately a constant in the coverage range where the
ordered islands are observed. We thus conclude that most islands nucleate at
and then grow in an approximately self similar fashion as
increases.Comment: 23 pages, 10 Figures (available upon request). SU-PHYS-93-443-375
Inter- and intragrain currents in bulk melt-grown YBaCuO rings
A simple contactless method suitable to discern between the intergrain
(circular) current, which flows in the thin superconducting ring, and the
intragrain current, which does not cross the weakest link, has been proposed.
At first, we show that the intergrain current may directly be estimated from
the magnetic flux density measured by the Hall sensor positioned
in the special points above/below the ring center. The experimental
and the numerical techniques to determine the value are discussed. Being
very promising for characterization of a current flowing across the joints in
welded YBaCuO rings (its dependencies on the temperature and the external
magnetic field as well as the time dissipation), the approach has been applied
to study corresponding properties of the intra- and intergrain currents flowing
across the -twisted grain boundaries which are frequent in bulk
melt-textured YBaCuO samples. We present experimental data related to the flux
penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin
state and during the field reversal. The shielding properties and their
dependence on external magnetic fields are also studied. Besides, we consider
the flux creep effects and their influence on the current re-distribution
during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version,
corrections to perturbing effects near the weak links are introduced, one
more figure is added. lin
SLAC's polarized electron source laser system for the E-158 parity violation experiment
SLAC E158 is an experiment to make the first measurement of parity violation in Moller scattering. The left-right cross-section asymmetry in the elastic scattering of a 45-GeV polarized electron beam off unpolarized electrons in a liquid hydrogen target will be measured to an accuracy of better than 10-8, with the expected Standard Model asymmetry being approximately 10-7. An intense circularly polarized laser beam for the polarized electron source is required with the ability to quickly switch between left and right polarization states with minimal left-right asymmetries in the parameters of the electron beam. This laser beam is produced by a unique SLAC-designed, flash-lamp pumped, Ti:Sapphire laser. We present this laser system design and initial results from recent commissioning runs
SLAC's polarized electron source laser system for the E-158 parity violation experiment
SLAC E158 is an experiment to make the first measurement of parity violation in Moller scattering. The left-right cross-section asymmetry in the elastic scattering of a 45-GeV polarized electron beam off unpolarized electrons in a liquid hydrogen target will be measured to an accuracy of better than 10-8, with the expected Standard Model asymmetry being approximately 10-7. An intense circularly polarized laser beam for the polarized electron source is required with the ability to quickly switch between left and right polarization states with minimal left-right asymmetries in the parameters of the electron beam. This laser beam is produced by a unique SLAC-designed, flash-lamp pumped, Ti:Sapphire laser. We present this laser system design and initial results from recent commissioning runs
Density and community structure of soil- and bark-dwelling microarthropods along an altitudinal gradient in a tropical montane rainforest
Microarthropod communities in the soil and on the bark of trees were investigated along an elevation gradient (1,850, 2,000, 2,150, 2,300 m) in a tropical montane rain forest in southern Ecuador. We hypothesised that the density of microarthropods declines with depth in soil and increases with increasing altitude mainly due to the availability of resources, i.e. organic matter. In addition, we expected bark and soil communities to differ strongly, since the bark of trees is more exposed to harsher factors. In contrast to our hypothesis, the density of major microarthropod groups (Collembola, Oribatida, Gamasina, Uropodina) was generally low and decreased with altitude. However, as we predicted the density of each of the groups decreased with soil depth. Density of microarthropods on tree bark was lower than in soil. Overall, 43 species of oribatid mites were found, with the most abundant higher taxa being Poronota, pycnonotic Apheredermata, Mixonomata and Eupheredermata. The oribatid mite community on bark did not differ significantly from that in soil. The number of oribatid mite species declined with altitude (24, 23, 17 and 13 species at 1,850, 2,000, 2,150 and 2,300 m, respectively). Rarefaction curves indicate that overall about 50 oribatid mite species are to be expected along the studied altitudinal gradient. Results of this study indicate (1) that microarthropods may be limited by the quality of resources at high altitudes and by the amount of resources at deeper soil layers, and (2) that the bark of trees and the soil are habitats of similar quality for oribatid mites
Pelvic trauma : WSES classification and guidelines
Complex pelvic injuries are among the most dangerous and deadly trauma related lesions. Different classification systems exist, some are based on the mechanism of injury, some on anatomic patterns and some are focusing on the resulting instability requiring operative fixation. The optimal treatment strategy, however, should keep into consideration the hemodynamic status, the anatomic impairment of pelvic ring function and the associated injuries. The management of pelvic trauma patients aims definitively to restore the homeostasis and the normal physiopathology associated to the mechanical stability of the pelvic ring. Thus the management of pelvic trauma must be multidisciplinary and should be ultimately based on the physiology of the patient and the anatomy of the injury. This paper presents the World Society of Emergency Surgery (WSES) classification of pelvic trauma and the management Guidelines.Peer reviewe
Desempenho e rendimento de carcaça de frangos de corte alimentados com mistura de aditivos fitogênicos na dieta
Educação holística para o empreendedorismo: uma estratégia de desenvolvimento integral, de cidadania e cooperação
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