18,751 research outputs found
Four-dimensional gravity on supersymmetric dilatonic domain walls
We investigate the localization of four-dimensional metastable gravity in
supersymmetric dilatonic domain walls through massive modes by considering
several scenarios in the model. We compute corrections to the Newtonian
potential for small and long distances compared with a crossover scale given in
terms of the dilatonic coupling. 4D gravity behavior is developed on the brane
for distance very much below the crossover scale, while for distance much
larger, the 5D gravity is recovered. Whereas in the former regime gravity is
always attractive, in the latter regime due to non-normalizable unstable
massive graviton modes present on the spectrum, in some special cases, gravity
appears to be repulsive and signalizes a gravitational confining phase which is
able to produce an inflationary phase of the Universe.Comment: 11 pages, 4 figures, Latex. Version to appear in PL
Three-body Faddeev-Alt-Grassberger-Sandhas approach to direct nuclear reactions
Momentum space three-body Faddeev-like equations are used to calculate
elastic, transfer and charge exchange reactions resulting from the scattering
of deuterons on 12C and 16O or protons on 13C and 17O; 12C and 16O are treated
as inert cores. All possible reactions are calculated in the framework of the
same model space. Comparison with previous calculations based on approximate
methods used in nuclear reaction theory is discussed.Comment: 10 pages, 13 figures, to be published in Phys. Rev.
A global simulation for laser driven MeV electrons in -diameter fast ignition targets
The results from 2.5-dimensional Particle-in-Cell simulations for the
interaction of a picosecond-long ignition laser pulse with a plasma pellet of
50- diameter and 40 critical density are presented. The high density
pellet is surrounded by an underdense corona and is isolated by a vacuum region
from the simulation box boundary. The laser pulse is shown to filament and
create density channels on the laser-plasma interface. The density channels
increase the laser absorption efficiency and help generate an energetic
electron distribution with a large angular spread. The combined distribution of
the forward-going energetic electrons and the induced return electrons is
marginally unstable to the current filament instability. The ions play an
important role in neutralizing the space charges induced by the the temperature
disparity between different electron groups. No global coalescing of the
current filaments resulted from the instability is observed, consistent with
the observed large angular spread of the energetic electrons.Comment: 9 pages, 6 figures, to appear in Physics of Plasmas (May 2006
Benchmark calculation of p-3H and n-3He scattering
p-3H and n-3He scattering in the energy range above the n-3He but below the
d-d thresholds is studied by solving the 4-nucleon problem with a realistic
nucleon-nucleon interaction. Three different methods -- Alt, Grassberger and
Sandhas, Hyperspherical Harmonics, and Faddeev-Yakubovsky -- have been employed
and their results for both elastic and charge-exchange processes are compared.
We observe a good agreement between the three different methods, thus the
obtained results may serve as a benchmark. A comparison with the available
experimental data is also reported and discussed.Comment: 13 pages, 6 figures. arXiv admin note: text overlap with
arXiv:1109.362
A new software application for footwear industry
Today, the footwear industry is facing many
challenges. First, consumers demand for new products with better comfort and design; second, competition is becoming stronger in current global market. Due to these factors,
flexibility and rapidity in developing new products are key factors for the medium and long-term survival and success of the footwear industry. This paper proposes a new software application based in simple image processing techniques for
optimization of two important steps of the processes involved in footwear manufacturing: the shoe sole halogenation and lead roughing process. The application presented in this paper has a friendly interface where the sole contour points for shoe sole halogenation and lead roughing are automatically determined. The operator can easily change and set new points to improve
details within the interest region where tools will be applied, when the halogenation or the roughing process is executed.
Another feature of this application is the automatic transformation of the 2D coordinates of the dominant points to
3D real world coordinates. This feature simplifies further ongoing work – automatic code generation for different industrial robots to execute the halogenation and roughing
processes
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Three-dimensional quantification of the morphology and intragranular void ratio of a shelly carbonate sand
Shelly carbonate sands represent an extreme soil type in terms of their mechanical behavior which derives from the bioclastic nature of the constituent grains. In their uncemented form, these deposits exhibit very high compressibility, which has posed a number of geotechnical engineering problems; in most cases related to the reduction in the bearing capacities of both shallow and deep foundations. Remarkable features of these carbonate sands include the complex shape and the structural weakness of the grains and the high inter and intra granular porosity. Previous studies, have quoted the interlocking of the angular shelly particles to be at the origin of their high friction angles and high initial void ratio, however, up until now, no scientific micro-scale examination has been carried out. This paper presents a non-invasive image based investigation into the grain morphology of a carbonate sand from the Persian Gulf. This sand has a median grain size of 570μm and a high CaCO3 content in the form of aragonite and calcite. Three-dimensional images from x-ray computed tomography (3DXRCT) with a size of 6μm were used. The presence of various skeletal bodies such as shells of small organisms with distinct densities and composition poses real challenges for an accurate segmentation. Image processing algorithms were developed in order to identify the individual sand grains and quantify their properties. Earlier work on silica sands has highlighted the importance of 3D non-invasive techniques in providing an accurate distribution of the grain sizes when compared to more traditional techniques such as sieving analysis and 2D microscopy. The methodology here proposed allows an accurate quantification of grain shape and size and the assessment of grain damage following mechanical deformation. This study, contributes towards improving our understanding of the engineering properties of carbonate sands and thus, predicting their response under loading
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