630 research outputs found
Flow of magnetic repelling grains in a two-dimensional silo
During a typical silo discharge, the material flow rate is determined by the
contact forces between the grains. Here, we report an original study concerning
the discharge of a two-dimensional silo filled with repelling magnetic grains.
This non-contact interaction leads to a different dynamics from the one
observed with conventional granular materials. We found that, although the flow
rate dependence on the aperture size follows roughly the power-law with an
exponent found in non-repulsive systems, the density and velocity
profiles during the discharge are totally different. New phenomena must be
taken into account. Despite the absence of contacts, clogging and intermittence
were also observed for apertures smaller than a critical size determined by the
effective radius of the repulsive grains.Comment: 6 pages, 8 figure
Segregation induced by inelasticity in a vibrofluidized granular mixture
We investigate the segregation of a dense binary mixture of granular
particles that only differ in their restitution coefficient. The mixture is
vertically vibrated in the presence of gravity. We find a partial segregation
of the species, where most dissipative particles submerge in the less
dissipative ones. The segregation occurs even if one type of the particles is
elastic. In order to have a complete description of the system, we study the
structure of the fluid at microscopic scale (few particle diameters). The
density and temperature pair distribution functions show strong enhancements
respect the equilibrium ones at the same density. In particular, there is an
increase in the probability that the more inelastic particles group together in
pairs (microsegregation). Microscopically the segregation is buoyancy driven,
by the appearance of a dense and cold region around the more inelastic
particles.Comment: 7 pages, 9 figures, accepted in Phys. Rev
Individual stochasticity in the life history strategies of animals and plants
The life histories of organisms are expressed as rates of development, reproduction, andsurvival. However, individuals may experience differential outcomes for the same set ofrates. Such individual stochasticity generates variance around familiar mean measures oflife history traits, such as life expectancy and the reproductive number R0. By writing lifecycles as Markov chains, we calculate variance and other indices of variability for longevity,lifetime reproductive output (LRO), age at offspring production, and age at maturity for 83animal and 332 plant populations from the COMADRE and COMPADRE matrix databases. Wefind that the magnitude within and variability between populations in variance indices inLRO, especially, are surprisingly high. We furthermore use principal components analysis toassess how the inclusion of variance indices of different demographic outcomes affects lifehistory constraints. We find that these indices, to a similar or greater degree than the mean,explain the variation in life history strategies among plants and animals
Stereodynamical studies of velocity aligned photofragments
The state resolved stereodynamics of bimolecular reactions can be probed using velocity aligned photofragments as reagents, and polarised, Doppler resolved laser detection techniques for the products. The new strategy and its application to the reaction O(1D) + N2O→ NO + NO are outlined
Interpretation of the microwave non-thermal radiation of the Moon during impact events
The results of recent observations of the non-thermal electromagnetic (EM) emission at wavelengths of 2.5cm, 13cm, and 21cm are summarized. After strong impacts of meteorites or spacecrafts (Lunar Prospector) with the Moon's surface, the radio emissions in various frequency ranges were recorded. The most distinctive phenomenon is the appearance of quasi-periodic oscillations with amplitudes of 3–10K during several hours. The mechanism concerning the EM emission from a propagating crack within a piezoactive dielectric medium is considered. The impact may cause the global acoustic oscillations of the Moon. These oscillations lead to the crackening of the Moon's surface. The propagation of a crack within a piezoactive medium is accompanied by the excitation of an alternative current source. It is revealed that the source of the EM emission is the effective transient magnetization that appears in the case of a moving crack in piezoelectrics. The moving crack creates additional non-stationary local mechanical stresses around the apex of the crack, which generate the non-stationary electromagnetic field. For the cracks with a length of 0.1–1µm, the maximum of the EM emission may be in the 1–10GHz range
Analysis of the ULF electromagnetic emission related to seismic activity, Teoloyucan geomagnetic station, 1998-2001
Results of ULF geomagnetic measurements at station Teoloyucan (Central Mexico, 99.11'35.735''W, 19.44'45.100''N, 2280m height) in relation to seismic activity in the period 1998-2001 and their analysis are presented. Variations of spectral densities for horizontal and vertical components, polarization densities and spectrograms of magnetic field, their derivatives are analyzed as a part of traditional analysis in this study. Values of spectral density were calculated for 6 fixed frequencies <i>f</i>=1, 3, 10, 30, 100 and 300mHz. Fractal characteristics of spectra were analyzed in the conception of SOC (Self-Organized Criticality). 2 nighttime intervals, 0-3 and 3-6h by local time have been used to decrease the noise interference in row data. In order to exclude the intervals with a high geomagnetic activity from analysis we referred to <i>Ap</i> indices, calculated for corresponding time intervals. The contribution of seismic events to geomagnetic emission was estimated by seismic index <i>k<sub>s</sub></i>=10<sup>0.75<i>Ms</i></sup>/10<i>D</i>, where <i>Ms</i> is the amplitude of the earthquake and <i>D</i> is the distance from its epicenter to the station
Investigation of ULF magnetic anomaly during Izu earthquake swarm and Miyakejima volcano eruption at summer 2000, Japan
International audienceResults of the ULF electromagnetic emission during the Izu, 2000 earthquake (EQ) swarm and Miyake volcano eruptions during the summer period of 2000 are presented and analyzed. The analysis of the obtained data has been performed in 3 main directions: traditional statistical analysis, i.e. analysis of time dynamics of spectral density, polarization ratios and their derivatives, Principal Component Analysis, and Fractal Analysis. The statistical characteristics were studied at different frequency sub-bands in a frequency range 10-3-0.3 Hz. These methods of data processing are described and the obtained results are illustrated and discussed. Some peculiarities of the obtained results such as the rise of the second principal component and the rise of the fractal index can be interpreted as possible short-time precursors
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