1,437 research outputs found
Swapping trajectories: a new wall-induced cross-streamline particle migration mechanism in a dilute suspension of spheres
Binary encounters between spherical particles in shear flow are studied for a
system bounded by a single planar wall or two parallel planar walls under
creeping flow conditions. We show that wall proximity gives rise to a new class
of binary trajectories resulting in cross-streamline migration of the
particles. The spheres on these new trajectories do not pass each other (as
they would in free space) but instead they swap their cross-streamline
positions. To determine the significance of the wall-induced particle
migration, we have evaluated the hydrodynamic self-diffusion coefficient
associated with a sequence of uncorrelated particle displacements due to binary
particle encounters. The results of our calculations quantitatively agree with
the experimental value obtained by \cite{Zarraga-Leighton:2002} for the
self-diffusivity in a dilute suspension of spheres undergoing shear flow in a
Couette device. We thus show that the wall-induced cross-streamline particle
migration is the source of the anomalously large self-diffusivity revealed by
their experiments.Comment: submited to JF
HESS J1632-478: an energetic relic
HESS J1632-478 is an extended and still unidentified TeV source in the
galactic plane. In order to identify the source of the very high energy
emission and to constrain its spectral energy distribution, we used a deep
observation of the field obtained with XMM-Newton together with data from
Molonglo, Spitzer and Fermi to detect counterparts at other wavelengths. The
flux density emitted by HESS J1632-478 peaks at very high energies and is more
than 20 times weaker at all other wavelengths probed. The source spectrum
features two large prominent bumps with the synchrotron emission peaking in the
ultraviolet and the external inverse Compton emission peaking in the TeV. HESS
J1632-478 is an energetic pulsar wind nebula with an age of the order of 10^4
years. Its bolometric (mostly GeV-TeV) luminosity reaches 10% of the current
pulsar spin down power. The synchrotron nebula has a size of 1 pc and contains
an unresolved point-like X-ray source, probably the pulsar with its wind
termination shock.Comment: A&A accepted, 9 pages, 5 figures, 4 table
Financial Crisis, Health Outcomes and Aging: Mexico in the 1980s and 1990s
We study the impact of economic crisis on health in Mexico. There have been four wide-scale economic crises in Mexico in the past two decades, the most recent in 1995-96. We find that mortality rates for the very young and the elderly increase or decline less rapidly in crisis years as compared with non-crisis years. In late 1995-96 crisis, mortality rates were about 5 to 7 percent higher in the crisis years compared to the years just prior to the crisis. This translates into a 0.4 percent increase in mortality for the elderly and a 0.06 percent increase in mortality for the very young. We find tentative evidence that economic crises affect mortality by reducing incomes and possibly by placing a greater burden on the medical sector, but not by forcing less healthy members of the population to work or by forcing primary caregivers to go to work.
Probing Clumpy Stellar Winds in SFXTs
Quantitative constraints on the wind clumping of massive stars can be
obtained from the study of the hard X-ray variability of SFXTs. In these
systems, a large fraction of the hard X-ray emission is emitted in the form of
flares with typical duration of 3 ksec, frequency of 7 days and luminosity of
ergs/s. Such flares are most probably emitted by the interaction of a
compact object orbiting at R with wind clumps ( g).
The density ratio between the clumps and the inter-clump medium is .
The parameters of the clumps and of the inter-clump medium are in good
agreement with macro-clumping scenario and line-driven instability simulations.Comment: 3 pages, A Population Explosion: The Nature and Evolution of X-ray
Binaries in Diverse Environment
Influence of Rhizobium and Mycorrhizae in the Production of Seedlings of Caesalpinia Spinosa L. Taya in San Pablo, Peru
This research study evaluated the symbiotic influence of Mycorrhizae in the production of propagating material of Caesalpinia Spinosa L. Taya, as well as the characterization of strains of mycorrhitic fungi in field, nursery, and laboratory work. No nodules were found as a product of nitrifying bacteria in the roots of plants Caesalpinea spinosa L., and ectomycorrhitic fungi were identified in the rhizosphere, such as Basidiomicetes and species of Rhizoctonia sp and Fusarium sp. From the evaluations, T4 exceeded all treatments, such as in height, neck diameter, number of leaves, root length, and the wet and dry weight of Taya seedling. In conclusion, we say that the Caesalpinia Spinosa L. Taya, despite of belonging to the legume family, does not present nodulation; but the presence of ectomycorrhitic fungi such as the basidiomicetes in the rhizosphere and high content of organic matter, positively influences the increase in the volume of seedling in the nursery, also reflected in the absorption of protein and phosphorus.
Keywords: mycorrhizal association, seedlings, rhizobium.
Resumen
En el presente trabajo de investigación se evaluó la influencia simbiótica de micorrizas en la producción de plantones de Caesalpinea spinosa L. Taya, así como la caracterización de cepas de hongos micorríticos, realizándose el trabajo en campo, vivero, y laboratorio. No se encontró nódulos como producto de bacterias nitrificantes en las raíces de las plantas de Caesalpinea spinosa L., y se identificó hongos ectomicorríticos en la rizósfera, tales como Basidiomicetes y especies de Rhizoctonia sp y Fusarium sp. De las evaluaciones el T4, supera a todos los tratamientos como en altura, diámetro de cuello, número de hojas, longitud de raíz, peso húmedo y peso seco de plántula.Concluyendo finalmente, diremos que la Caesalpinea spinosa L. taya, a pesar de pertenecer a la familia de las Leguminosas no presenta nodulación; pero la presencia de los hongos ectomicorríticos como los basidiomicetes en la rizósfera y el alto contenido de materia orgánica, influye positivamente en el incremento del volumen de la plántula en vivero, reflejado también en la absorción de proteínas y fosforo.
Palabras clave: asociación micorrítica, plantones, rizobium
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