4,202 research outputs found
Fatores de risco envolvidos na dermatite necrótica dos frangos de corte.
Projeto/Plano de Ação: 16.00.30.004
Granular cooling of hard needles
We have developed a kinetic theory of hard needles undergoing binary
collisions with loss of energy due to normal and tangential restitution. In
addition, we have simulated many particle systems of granular hard needles. The
theory, based on the assumption of a homogeneous cooling state, predicts that
granular cooling of the needles proceeds in two stages: An exponential decay of
the initial configuration to a state where translational and rotational
energies take on a time independent ratio (not necessarily unity), followed by
an algebraic decay of the total kinetic energy . The simulations
support the theory very well for low and moderate densities. For higher
densities, we have observed the onset of the formation of clusters and shear
bands.Comment: 7 pages, 8 figures; major changes, extended versio
Pattern Formation in the Inhomogeneous Cooling State of Granular Fluids
We present results from comprehensive event-driven (ED) simulations of
nonlinear pattern formation in freely-evolving granular gases. In particular,
we focus on the the morphologies of density and velocity fields in the
inhomogeneous cooling state (ICS). We emphasize the strong analogy between the
ICS morphologies and pattern formation in phase ordering systems with a
globally conserved order parameter.Comment: 11 pages, 4 figures. to appear in Europhys. Let
Oscillatory instability in a driven granular gas
We discovered an oscillatory instability in a system of inelastically
colliding hard spheres, driven by two opposite "thermal" walls at zero gravity.
The instability, predicted by a linear stability analysis of the equations of
granular hydrodynamics, occurs when the inelasticity of particle collisions
exceeds a critical value. Molecular dynamic simulations support the theory and
show a stripe-shaped cluster moving back and forth in the middle of the box
away from the driving walls. The oscillations are irregular but have a single
dominating frequency that is close to the frequency at the instability onset,
predicted from hydrodynamics.Comment: 7 pages, 4 figures, to appear in Europhysics Letter
Effects of Velocity Correlation on Early Stage of Free Cooling Process of Inelastic Hard Sphere System
The free cooling process in the inelastic hard sphere system is studied by
analysing the data from large scale molecular dynamics simulations on a three
dimensional system. The initial energy decay, the velocity distribution
function, and the velocity correlation functions are calculated to be compared
with theoretical predictions. The energy decay rate in the homogeneous cooling
state is slightly but distinctively smaller than that expected from the
independent collision assumption. The form of the one particle velocity
distribution is found not to be stationary. These contradict to the predictions
of the kinetic theory based on the Enskog-Boltzmann equation and suggest that
the velocity correlation is already important in the early stage of homogeneous
cooling state. The energy decay rate is analysed in terms of the velocity
correlation.Comment: 9 pages (figures included). To be published in J. Phys. Soc. Jpn.
Vol. 73 No. 1 (2004) Added two references and removed one. Changed the name
of T_{L}. Added unit constants in Sec. 5 and
Resistência antimicrobiana y patogenicidad de muestras de los Escherichia coli aisladas de lesiones de celulites em polos.
Projeto/Plano de Ação: 11.11.11.111
Loss of genetic variation in a strongly isolated Azorean population of the edible calm, <i>Tapes decussatus</i>
We used allozyme electrophoresis to compare the genetic variation of an introduced and strongly isolated population of the edible clam Tapes decussatus in the Azores (Lagoa de Santo Cristo, Sao Jorge) with populations from the main range of the species (Ria and Thau). Observed and expected heterozygosity values, number of polymorphic loci, and mean number of alleles per locus in the main-range populations fall within the limits reported for T. decussatus and other Venerid clams. In contrast to previous studies on Venerid clams, we observed no heterozygote deficiencies. In the introduced Lagoa population, we observed a strong reduction of allelic diversity and expected heterozygosities and an effective population size of only 5.30. The Lagoa population is only slightly differentiated from populations from the species' main range and may thus be of low "biological value." Exploitation of T. decussatus could therefore be allowed to continue but must follow strict collection guidelines, especially given that only 15% of the area is suitable for exploitation. Otherwise, a unique component of the Azorean fauna that also serves as a fishery resource may be lost
The Environmental History of Cetaceans in Portugal: Ten Centuries of Whale and Dolphin Records
The history between cetaceans and humans is documented throughout time not only in reports, descriptions, and tales but also in legal documents, laws and regulations, and tithes. This wealth of information comes from the easy spotting and identification of individuals due to their large size, surface breathing, and conspicuous above water behaviour. This work is based on historical sources and accounts accounting for cetacean presence for the period between the 12th and 17th centuries, as well as scientific articles, newspapers, illustrations, maps, non-published scientific reports, and other grey literature from the 18th century onwards. Information on whale use in Portugal's mainland has been found since as early as the 12th century and has continued to be created throughout time. No certainty can be given for medieval and earlier events, but both scavenging of stranded whales or use of captured ones may have happened. There is an increasing number of accounts of sighted, stranded, used, or captured cetaceans throughout centuries which is clearly associated with a growing effort towards the study of these animals. Scientific Latin species denominations only started to be registered from the 18th century onwards, as a consequence of the evolution of natural sciences in Portugal and increasing interest from zoologists. After the 19th century, a larger number of observations were recorded, and from the 20th century to the present day, regular scientific records have been collected. Research on the environmental history of cetaceans in Portugal shows a several-centuries-old exploitation of whales and dolphins, as resources mainly for human consumption, followed in later centuries by descriptions of natural history documenting strandings and at sea encounters. Most cetaceans species currently thought to be present in Portuguese mainland waters were at some point historically recorded
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