3,953 research outputs found
Low Cost Solar Array Project: Composition Measurements by Analytical Photon Catalysis
The applicability of the photon catalysis technique for effecting composition analysis of silicon samples was assessed. Third quarter activities were devoted to the study of impurities in silicon matrices. The evaporation process was shown to be congruent; thus, the spectral analysis of the vapor yields the composition of the bulk sample. Qualitative analysis of metal impurities in silicon was demonstrated e part per million level. Only one atomic spectral interference was noted; however, it is imperative to maintain a leak tight system due to chemical and spectral interferences caused by the presence of even minute amounts of oxygen in the active nitrogen afterglow
Performance of two transferred modules in the Lagunera Region: Water relations
Water policy / Performance / Privatization / Irrigation systems / Operations / Maintenance / Irrigation efficiency / Water users' associations / Water rights / Water allocation / Water supply / Water distribution
Lifetime Measurement of the 8s Level in Francium
We measure the lifetime of the 8s level on a magneto-optically trapped sample
of ^{210}Fr atoms with time-correlated single-photon counting. The 7P_{1/2}
state serves as the resonant intermediate level for two-photon excitation of
the 8s level completed with a 1300 nm laser. Analysis of the fluorescence decay
through the the 7P_{3/2} level gives 53.30 +- 0.44 ns for the 8s level
lifetime.Comment: 4 pages, 4 figure
Plasmin Deficiency in Alzheimer's Disease Brains: Causal or Casual?
Substantial recent evidence suggests that defects in amyloid peptide degradation can be at the base of cases of sporadic Alzheimer's disease (AD). Among the discovered brain enzymes with the capacity to degrade amyloid peptide, the serine protease plasmin acquires special physiological relevance because of its low levels in areas of AD human brains with a high susceptibility to amyloid plaque accumulation. In this article we comment on a series of observations supporting the fact that plasmin paucity in the brain is not simply a secondary event in the disease but rather a primary defect in certain cases of sporadic AD. We also refer to recent data pointing to alterations in raft membrane domains and diminished membrane cholesterol as the underlying cause. Finally, we discuss the possibility that plasmin deficiency in the brain could lead to AD symptomatology because of amyloid aggregation and the triggering of cell death signaling cascades
Testing the diffusion hypothesis as a mechanism of self-healing in Disperse orange 11 doped in PMMA
In this work, we show that reversible photodegradation of Disperse Orange 11
doped in PMMA is not due to dye diffusion - a common phenomenon observed in
many dye-doped polymers. The change in linear absorbance due to
photodegradation of the material shows an isobestic point, which is consistent
with the formation of a quasi-stable damaged species. Spatially-resolved
amplified spontaneous emission and fluorescence, both related to the population
density, are measured by scanning the pump beam over a burn mark. A numerical
model of the time evolution of the population density due to diffusion is
inconsistent with the experimental data suggesting that diffusion is not
responsible.Comment: 5 pages, 6 figure
Investimentos estrangeiros em países em via de industrialização
Trata-se da economia nacional, portanto de modelos que analisam as diferentes variáveis que formam o produto nacional em suas inter-relações e na geração do próprio produto. Em tal contexto, examino algumas variáveis que influem na distribuição do produto e que, consequentemente, podem ser responsáveis por um processo de concentração da renda
Statistics of Core Lifetimes in Numerical Simulations of Turbulent, Magnetically Supercritical Molecular Clouds
We present measurements of the mean dense core lifetimes in numerical
simulations of magnetically supercritical, turbulent, isothermal molecular
clouds, in order to compare with observational determinations. "Prestellar"
lifetimes (given as a function of the mean density within the cores, which in
turn is determined by the density threshold n_thr used to define them) are
consistent with observationally reported values, ranging from a few to several
free-fall times. We also present estimates of the fraction of cores in the
"prestellar", "stellar'', and "failed" (those cores that redisperse back into
the environment) stages as a function of n_thr. The number ratios are measured
indirectly in the simulations due to their resolution limitations. Our approach
contains one free parameter, the lifetime of a protostellar object t_yso (Class
0 + Class I stages), which is outside the realm of the simulations. Assuming a
value t_yso = 0.46 Myr, we obtain number ratios of starless to stellar cores
ranging from 4-5 at n_thr = 1.5 x 10^4 cm^-3 to 1 at n_thr = 1.2 x 10^5 cm^-3,
again in good agreement with observational determinations. We also find that
the mass in the failed cores is comparable to that in stellar cores at n_thr =
1.5 x 10^4 cm^-3, but becomes negligible at n_thr = 1.2 x 10^5 cm^-3, in
agreement with recent observational suggestions that at the latter densities
the cores are in general gravitationally dominated. We conclude by noting that
the timescale for core contraction and collapse is virtually the same in the
subcritical, ambipolar diffusion-mediated model of star formation, in the model
of star formation in turbulent supercritical clouds, and in a model
intermediate between the previous two, for currently accepted values of the
clouds' magnetic criticality.Comment: 25 pages, 8 figures, ApJ accepted. Fig.1 animation is at
http://www.astrosmo.unam.mx/~e.vazquez/turbulence/movies/Galvan_etal07/Galvan_etal07.htm
Electronic structure calculations for PrFe4P12 filled skutterudite using Extended Huckel tight-binding method
To get insight into the electronic properties of PrFe4P12 skutterudite, band
electronic structure calculations, Total and Projected Density of States,
Crystal Orbital Overlap Population and Mulliken Population Analysis were
performed. The energy bands yield a semi metallic behavior with a direct gap
(at gamma) of 0.02 eV. Total and Projected Density of States provided
information of the contribution from each orbital of each atom to the total
Density of States. Moreover, the bonding strength between some atoms within the
unit cell was obtained. Mulliken Population analysis suggests ionic behavior
for this compound
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