2,224 research outputs found
Density-dependent interactions and structure of charged colloidal dispersions in the weak screening regime
We determine the structure of charge-stabilized colloidal suspensions at low
ionic strength over an extended range of particle volume fractions using a
combination of light and small angle neutron scattering experiments. The
variation of the structure factor with concentration is analyzed within a
one-component model of a colloidal suspension. We show that the observed
structural behavior corresponds to a non-monotonic density dependence of the
colloid effective charge and the mean interparticle interaction energy. Our
findings are corroborated by similar observations from primitive model computer
simulations of salt-free colloidal suspensions.Comment: Revised version, accepted to Phys. Rev. Let
Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis
The problem of detecting specific features of microscopic dynamics in the
macroscopic behavior of a many-degrees-of-freedom system is investigated by
analyzing the position and momentum time series of a heavy impurity embedded in
a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results
obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204
(2004)] suggest that the impurity does not contribute significantly to the
dynamics of the chain and can be considered as a probe for the dynamics of the
system to which the impurity is coupled. The () entropy, which measures
the amount of information generated by unit time at different scales of
time and of the observable, is numerically computed by methods of nonlinear
time-series analysis using the position and momentum signals of the heavy
impurity for various values of the energy density (energy per degree
of freedom) of the system and some values of the impurity mass . Results
obtained from these two time series are compared and discussed.Comment: 7 pages, 5 figures, RevTeX4 PRE format; to be published in Phys. Rev.
Railway deformation detected by DInSAR over active sinkholes in the Ebro Valley evaporite karst, Spain
Subsidence was measured for the first time on railway tracks in the central sector of Ebro Valley (NE Spain) using Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques. This area is affected by evaporite karst and the analysed railway corridors traverse active sinkholes that produce deformations in these infrastructures. One of the railway tracks affected by slight settlements is the Madrid-Barcelona high-speed line, a form of transport infrastructure highly vulnerable to ground deformation processes. Our analysis based on DInSAR measurements and geomorphological surveys indicates that this line shows dissolution-induced subsidence and compaction of anthropogenic deposits (infills and embankments). Significant sinkhole-related subsidence was also measured by DInSAR techniques on the Castejón-Zaragoza conventional railway line. This study demonstrates that DInSAR velocity maps, coupled with detailed geomorphological surveys, may help in the identification of the railway track sections that are affected by active subsidence
The Agua Prieta Powerhouse Slope Instability
The slope instability that endangered seriously the powerhouse of the Aqua Prieta Hydroelectric Project and involved about one million cubic meters of soils and breccias is described. The evolution of the geotechnical instrumentation measurements done from October 1987 to date, the geomechanic analysis performed and the stabilization works are discussed
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Assessment of Haitian mango value chain: a participatory assessment of mango chain actors in southern Haiti, July 12–August 30, 2010
Spatial partial coherence in Young's interferograms
Young's interferograms with high visibility reveals a high degree of spatial coherence of first order. But, spatially partial coherence of second order can be observed when it interferes itself through a compensated Michelson's interferometer attached at the exit of the Young's slit pair. We show that the patterns at the exit of the Michelson's interferometer are Young's interferograms with modulation fringes, which allow an estimation of the degree of the high order spatial coherence
Integrating socio-ecological information to address human–top predator conflicts: the case of an endangered eagle in the eastern Andes of Colombia
Fragmentation of the world's most intact forest landscapes will likely increase the severity of Human Wildlife Conflict (HWC). The way these threats affect top predators involves a series of complex social and ecological relationships, which are not completely understood, and thus require socio-ecological studies. The aim of this study is to examine the socio-ecological factors that affect the tolerance of local people towards the endangered Black-and-chestnut Eagle (Spizaetus isidori) in rural villages of the eastern Andes of Colombia. We conducted 172 interviews in 20 rural villages and estimated the proportion of forest cover (i.e. amount of remaining native forest), human density, the yearly losses of domestic fowl by the Black-and-chestnut Eagle, and socio-demographic parameters (i.e. economic activity, domestic fowl ownership, age, education, gender). The likelihood of villagers being tolerant towards the Black-and-chestnut Eagle decreased when the forest cover, human density and yearly losses of domestic fowl were higher. The integration of socio-ecological information allowed us to identify key areas with increasing HWC. Our findings were in consonance with the most recent evidence indicating that declines of top predator populations, as well as other vertebrate biodiversity, can be severely affected by the exacerbation of HWC on the border of intact native habitat and deforested areas.Fil: Zuluaga Castañeda, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina. Fundación Proyecto Águila Crestada-Colombia; Colombia. Peregrine Fund; Estados UnidosFil: Vargas, F. Hernán. Peregrine Fund; Estados UnidosFil: Grande, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentin
Arrested dynamics of the dipolar hard-sphere model
We report the combined results of molecular dynamics simulations and
theoretical calculations concerning various dynamical arrest transitions in a
model system representing a dipolar fluid, namely, N (softcore) rigid spheres
interacting through a truncated dipole-dipole potential. By exploring different
regimes of concentration and temperature, we find three distinct scenarios for
the slowing down of the dynamics of the translational and orientational degrees
of freedom: At low ({} = 0.2) and intermediate ( = 0.4) volume
fractions, both dynamics are strongly coupled and become simultaneously
arrested upon cooling. At high concentrations ({} 0.6), the
translational dynamics shows the features of an ordinary glass transition,
either by compressing or cooling down the system, but with the orientations
remaining ergodic, thus indicating the existence of partially arrested states.
In this density regime, but at lower temperatures, the relaxation of the
orientational dynamics also freezes. The physical scenario provided by the
simulations is discussed and compared against results obtained with the
self-consistent generalized Langevin equation theory, and both provide a
consistent description of the dynamical arrest transitions in the system. Our
results are summarized in an arrested states diagram which qualitatively
organizes the simulation data and provides a generic picture of the glass
transitions of a dipolar fluid
Infinite-contrast periodic composites with strongly nonlinear behavior: Effective-medium theory versus full-field simulations
This paper presents a combined numerical-theoretical study of the macroscopic
behavior and local field distributions in a special class of two-dimensional
periodic composites with viscoplastic phases. The emphasis is on strongly
nonlinear materials containing pores or rigid inclusions. Full-field numerical
simulations are carried out using a Fast-Fourier Transform algorithm [H.
Moulinec, P. Suquet, C. R. Acad. Sci. Paris II 318, 1417 (1994)]
Moulinec, P. Suquet, C. R. Acad. Sci. Paris II 318, 1417 (1994), while the
theoretical results are obtained by means of the `second-order' nonlinear
homogenization method [P. Ponte Castaneda, J. Mech. Phys. Solids 50, 737
(2002)]. The effect of nonlinearity and inclusion concentration is investigated
in the context of power-law (with strain-rate sensitivity m) behavior for the
matrix phase under in-plane shear loadings. Overall, the `second-order'
estimates are found to be in good agreement with the numerical simulations,
with the best agreement for the rigidly reinforced materials. For the porous
systems, as the nonlinearity increases (m decreases), the strain field is found
to localize along shear bands passing through the voids (the strain
fluctuations becoming unbounded) and the effective stress exhibits a singular
behavior in the dilute limit. More specifically, for small porosities and fixed
nonlinearity m>0, the effective stress decreases linearly with increasing
porosity. However, for ideally plastic behavior (m = 0), the dependence on
porosity becomes non-analytic. On the other hand, for rigidly-reinforced
composites, the strain field adopts a tile pattern with bounded strain
fluctuations, and no singular behavior is observed (to leading order) in the
dilute limit.Comment: 28 pages, 28 B&W figures, 2 tables of color maps, to be published in
International Journal of Solids and Structures (in press
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