Comparison of interface models to account for surface tension in SPH method

The Smoothed Particle Hydrodynamics method (SPH) is a meshfree Lagrangian simulation methodwidely applied for fluid simulations due to the advantages presented by this method for solvingproblems with free and deformable surfaces. In many scientific and engineering applications, surface tension forces play an important or evendominating role in the dynamics of the system. For instance, the breakage (instability) of a liquid jetor film is strongly affected by the strength of the surface tension at the liquid-air interface.Simulating deforming phase interfaces with strong topological changes is still today a challengingtask. As a promising numerical method, here we use SPH to predict the interface instability at awater-air interface.With SPH, the main challenge in modelling surface tension at a free-surface is the accuratedescription of the interface (normal direction and curvature). When only the liquid phase is modelled(to decrease the computational cost), the standard SPH approximations to calculate the normaldirection and curvature of the interface suffer from a lacking “full support”, i.e. the omitted andtherefore missing gas particles. Various models for such free surface surface tension corrections werepresented, see e.g. among others Sirotkin et al., Ordoubadi et al. or Ehigiamusoe et al. Many of thesemodels follow the classical Continuum Surface Force (CSF) approach (Morris, Adami et al.) andincorporate different corrections/treatments at the surface. The objective of our ongoing study is to investigate the influence of different interface descriptions.We compare different free surface particle detection schemes, normal vector calculations andcurvature estimations for the quality of the resulting surface-tension effect. In this work, we focus ontwo-dimensional problems and consider a static drop and oscillating drops as test cases

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bitstream/item/135173/1/Documento-383-Com-capa.pd

Semileptonic decays of baryons in a relativistic quark model

We calculate semileptonic decays of light and heavy baryons in a relativistically covariant constituent quark model. The model is based on the Bethe-Salpeter-equation in instantaneous approximation. It generates satisfactory mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of electronic and muonic semileptonic decays of baryons. We thus obtain form factor ratios and decay rates in good agreement with experiment.Comment: 8 pages, 10 figures, 2 tables, typos remove

A Study of Lyman-Alpha Quasar Absorbers in the Nearby Universe

Spectroscopy of ten quasars obtained with the Goddard High Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST) is presented. A clustering analysis reveals an excess of nearest neighbor line pairs on velocity scales of 250-750 km/s at a 95-98% confidence level. The hypothesis that the absorbers are randomly distributed in velocity space can be ruled out at the 99.8% confidence level. No two-point correlation power is detected (xi < 1 with 95% confidence). Lyman-alpha absorbers have correlation amplitudes on scales of 250-500 km/s at least 4-5 times smaller than the correlation amplitude of bright galaxies. A detailed comparison between absorbers in nearby galaxies is carried out on a limited subset of 11 Lyman- alpha absorbers where the galaxy sample in a large contiguous volume is complete to M_B = -16. Absorbers lie preferentially in regions of intermediate galaxy density but it is often not possible to uniquely assign a galaxy counterpart to an absorber. This sample provides no explicit support for the hypothesis that absorbers are preferentially associated with the halos of luminous galaxies. We have made a preliminary comparison of the absorption line properties and environments with the results of hydrodynamic simulations. The results suggest that the Lyman-alpha absorbers represent diffuse or shocked gas in the IGM that traces the cosmic web of large scale structure. (abridged)Comment: 36 pages of text, 15 figures, 4 tables, 36 file

Adubação com compostos orgânicos e cobertura verde do solo em pomar de tangerineiras sob cultivo orgânico.

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An Upper Limit on the Infrared Background Density from HEGRA data on Mkn501

The energy spectrum of Mkn501 in the TeV energy regime, as measured by the HEGRA (High Energy Gamma Ray Astronomy) Cerenkov telescopes during its low state in 1995/96 and during a fraction of the 1997 outburst in the TeV energy regime, is shown to place stringent upper limits on the still unknown infrared photon density in the energy region between 3 x 10**(-3) and 3 xt 10**(-1) eV. Assuming two different shapes for the unknown infrared photon spectrum in this energy range we calculate upper limits on the infrared photon density on the basis of the power-law fit obtained for the observed spectrum up to the maximum energy.Comment: 11 pages, 6 Postscript figures, Accepted for publication in Astroparticle Physic

Evaluating the Application of Microbial Induced Calcite Precipitation Technique to Stabilize Expansive Soils

Expansive soils, also known as swell-shrink soils have been a problem for civil infrastructures including roads and foundations from ancient times. The use of chemical additives such as cement and lime to stabilize expansive soils is a common practice among geotechnical engineers, especially for lightly loaded structures. However, several occurrences of subgrade failures have been observed after stabilizing with chemical additives. Hence, engineers are in search of sustainable stabilization alternatives. Microbial Induced Calcite Precipitation (MICP) is gaining attention as an environmentally friendly soil improvement technique. Several researchers have successfully tested its feasibility in mitigating liquefaction-induced problems in sandy soils. In this research, the authors are evaluating its effectiveness in stabilizing expansive soils. For this purpose two natural expansive soils with high and low plasticity properties were subjected to MICP treatments. The soil samples were first augmented with bacterium Sporosarcina Pasteurii and then treated with Calcium Chloride and Urea. Variables such as microbial concentrations and curing times were studied in this research. Geotechnical testing including Atterberg limits and unconfined compression strength were performed to evaluate the efficacy of MICP treatments. Preliminary results indicate that there is a reduction in plasticity and swelling characteristics of the soils and increase in the unconfined compression strength