256 research outputs found
Molecular computing: From conformational pattern recognition to complex processing networks
First-principles extrapolation method for accurate CO adsorption energies on metal surfaces
We show that a simple first-principles correction based on the difference
between the singlet-triplet CO excitation energy values obtained by DFT and
high-level quantum chemistry methods yields accurate CO adsorption properties
on a variety of metal surfaces.
We demonstrate a linear relationship between the CO adsorption energy and the
CO singlet-triplet splitting, similar to the linear dependence of CO adsorption
energy on the energy of the CO 2* orbital found recently {[Kresse {\em et
al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations
underestimate the CO singlet-triplet excitation energy ,
whereas coupled-cluster and CI calculations reproduce the experimental . The dependence of on is used
to extrapolate for the top, bridge and hollow sites for the
(100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to
the coupled-cluster and CI value. The correction
reproduces experimental adsorption site preference for all cases and obtains
in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure
Interrelações entre minerais no solo, plantas forrageiras e tecido animal no norte de Mato Grosso 4. Zinco, magnésio, sódio e potássio
An experiment was conducted with samples from six farms in northearn Mato Grosso, Brazil, to study the interrelationships among levels of minerals in soil, forage, and animal tissues during the wet and dry seasons of the year. Soil extractable Zn levels were low in three out of six farms. Forage Zn levels were defficient in five farms. Levels of Zn in the liver were defficient in all six farms, being much lower (68 ppm) during the wet season than during the dry season (113 ppm). Magnesium levels in soil were low in one farm and adequated in five. Forage and animal tissue Mg levels were adequated in all six farms. Soil extractable sodium was normal and the salinity in all six farms was considered negligible. Forage sodium was highly defficient, being able to meet only between 14 to 30% of the animal requirements. Soil potassium levels were low in two out of six farms, but forage levels were adequate in all six farms to meet the requirement of grazing beef cattle.Levantamento das deficiências minerais de seis fazendas localizadas ao norte do Estado de Mato Grosso, tendo sido amostrados os solos, plantas forrageiras e tecido animal, nas estações seca e chuvosa. Foram constatadas deficiências de Zn no solo em três das seis fazendas estudadas. Cinco das seis fazendas apresentaram deficiência de zinco nas forrageiras. Os nÃveis de Zn no fÃgado dos animais foram deficientes em todas as seis fazendas, mas sendo muito mais deficientes ainda no perÃodo chuvoso (68 ppm) do que no perÃodo seco, (113 ppm). Os nÃveis de Mg nos solos foram mais baixos em apenas uma fazenda. Nas forrageiras e no tecido dos animais amostrados, os nÃveis de Mg foram normais. Os nÃveis de Na nos solos foram considerados normais, e a salinidade nas regiões estudadas foi considerada insignificante. Em todas as fazendas, as forrageiras mostraram-se altamente deficientes em Na, satisfazendo apenas entre 14 a 30% das exigências nutricionais dos bovinos. Os nÃveis de K nos solos mostraram-se deficientes em duas das seis fazendas estudadas. As forrageiras apresentaram nÃveis médios adequados à s exigências nutricionais dos bovinos em todas as fazendas
Block bond-order potential as a convergent moments-based method
The theory of a novel bond-order potential, which is based on the block
Lanczos algorithm, is presented within an orthogonal tight-binding
representation. The block scheme handles automatically the very different
character of sigma and pi bonds by introducing block elements, which produces
rapid convergence of the energies and forces within insulators, semiconductors,
metals, and molecules. The method gives the first convergent results for
vacancies in semiconductors using a moments-based method with a low number of
moments. Our use of the Lanczos basis simplifies the calculations of the band
energy and forces, which allows the application of the method to the molecular
dynamics simulations of large systems. As an illustration of this convergent
O(N) method we apply the block bond-order potential to the large scale
simulation of the deformation of a carbon nanotube.Comment: revtex, 43 pages, 11 figures, submitted to Phys. Rev.
Impurity (Fe, Cl, and P)-induced grain boundary and secondary phases in commercially pure titanium (CP-Ti)
A detailed transmission electron microscopy (TEM) study has been made of the microstructures of two as-sintered CP-Ti materials. We show that iron content at the impurity level of 1280 ppm, less than the limit (2000 ppm) for CP-Ti ASTM Grade 1, is sufficient to lead to the formation of a grain boundary (GB) β-Ti phase in the as-sintered microstructure due to segregation. The Fe-stabilized GB β-Ti phase contains ∼7 at. pct Fe and ∼1.5 at. pct Cl. In addition, nano-precipitates of ω-Ti exist in the Fe-stabilized GB β-Ti phase. A phosphorus (P)-enriched Ti-P-based phase was also identified, which has a tetragonal crystal structure with lattice parameters of (a = b = 8.0 ± 0.2 Å and c = 2.7 ± 0.2 Å) and is new to the existing database for Ti-P-enriched phases. As-sintered CP-Ti materials are thus not necessarily a single α-Ti phase material. These impurity-induced phases may exert potential impacts on the properties of sintered CP-Ti
Photoneutron Flux Measurement via Neutron Activation Analysis in a Radiotherapy Bunker with an 18 MV Linear Accelerator
Shadowing in Inelastic Scattering of Muons on Carbon, Calcium and Lead at Low XBj
Nuclear shadowing is observed in the per-nucleon cross-sections of positive
muons on carbon, calcium and lead as compared to deuterium. The data were taken
by Fermilab experiment E665 using inelastically scattered muons of mean
incident momentum 470 GeV/c. Cross-section ratios are presented in the
kinematic region 0.0001 < XBj <0.56 and 0.1 < Q**2 < 80 GeVc. The data are
consistent with no significant nu or Q**2 dependence at fixed XBj. As XBj
decreases, the size of the shadowing effect, as well as its A dependence, are
found to approach the corresponding measurements in photoproduction.Comment: 22 pages, incl. 6 figures, to be published in Z. Phys.
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
Investigating Gamma-Ray Lines from Dark Matter with Future Observatories
We study the prospects for studying line features in gamma-ray spectra with
upcoming gamma-ray experiments, such as HESS-II, the Cherenkov Telescope Array
(CTA), and the GAMMA-400 satellite. As an example we use the narrow feature at
130 GeV seen in public data from the Fermi-LAT satellite. We found that all
three experiments should be able to confidently confirm or rule out the
presence of this 130 GeV feature. If it is real, it should be confirmed with a
confidence level higher than 5 sigma. Assuming it to be a spectral signature of
dark matter origin, GAMMA-400, thanks to a projected energy resolution of about
1.5% at 100 GeV, should also be able to resolve both the \gamma\gamma-line and
a corresponding Z\gamma- or H\gamma-feature, if the corresponding branching
ratio is comparable to that into two photons. It will also allow to distinguish
between a gamma-ray line and the similar feature resulting from internal
bremsstrahlung photons.Comment: 12 pages, 6 figures, 1 tabl
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