6,761 research outputs found
Recent advances and open challenges in percolation
Percolation is the paradigm for random connectivity and has been one of the
most applied statistical models. With simple geometrical rules a transition is
obtained which is related to magnetic models. This transition is, in all
dimensions, one of the most robust continuous transitions known. We present a
very brief overview of more than 60 years of work in this area and discuss
several open questions for a variety of models, including classical, explosive,
invasion, bootstrap, and correlated percolation
Neutron Charge Radius: Relativistic Effects and the Foldy Term
The neutron charge radius is studied within a light-front model with
different spin coupling schemes and wave functions. The cancellation of the
contributions from the Foldy term and Dirac form factor to the neutron charge
form factor is verified for large nucleon sizes and it is independent of the
detailed form of quark spin coupling and wave function. For the physical
nucleon our results for the contribution of the Dirac form factor to the
neutron radius are insensitive to the form of the wave function while they
strongly depend on the quark spin coupling scheme.Comment: 12 pages, 5 figures, Latex, Int. J. Mod. Phys.
Genetic variation and correlation of agronomic traits in meadow bromegrass (Bromus riparius Rehm) clones.
Meadow bromegrass (Bromus riparius Rehm.) is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it a major grass species for pasturing beef animals in this region. As relatively little breeding work kas been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate total genetic variability, broad-sense heritability, phenotypic and genetic correlations. Forty-four meadow bromegrass clones were evaluated for agronomic characters. Genetic variation for dry matter yield, seed yield, fertility index, harvest index, plant height, plant spread, crude protein, neutral de ter gent fiber and acid de ter gent fiber, was significant. Broad-sense heritability estimates exceeded 50% for all characters. Heritability estimates were at least 3.5 times greater than their standard errors. Phenotypic and genetic correlation between all possible characters were measured There was general agreement in both sign and magnitude between genetic and phenotypic correlations. Correlations between the different characters demonstrated that it is possible to simultaneously improve seed and forage yield. Based on the results, it appears that the development of higher yielding cultivars with higher crude protein, and lower acid and neutral detergent fibers concentration should be possible
Screening effects in flow through rough channels
A surprising similarity is found between the distribution of hydrodynamic
stress on the wall of an irregular channel and the distribution of flux from a
purely Laplacian field on the same geometry. This finding is a direct outcome
from numerical simulations of the Navier-Stokes equations for flow at low
Reynolds numbers in two-dimensional channels with rough walls presenting either
deterministic or random self-similar geometries. For high Reynolds numbers,
when inertial effects become relevant, the distribution of wall stresses on
deterministic and random fractal rough channels becomes substantially dependent
on the microscopic details of the walls geometry. In addition, we find that,
while the permeability of the random channel follows the usual decrease with
Reynolds, our results indicate an unexpected permeability increase for the
deterministic case, i.e., ``the rougher the better''. We show that this complex
behavior is closely related with the presence and relative intensity of
recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure
Classical and Quantum Elliptical Billiards: Mixed Phase Space and Short Correlations in Singlets and Doublets
Billiards are flat cavities where a particle is free to move between elastic
collisions with the boundary. In chaos theory these systems are simple
prototypes, their conservative dynamics of a billiard may vary from regular to
chaotic, depending only on the border. The results reported here seek to shed
light on the quantization of classically chaotic systems. We present numerical
results on classical and quantum properties in two bi-parametric families of
Billiards, Elliptical Stadium Billiard (ESB) and Elliptical- Billiards
(E-B). Both are elliptical perturbations of chaotic billiards with
originally circular sectors on their borders. Our numerical calculations show
evidence that the elliptical families can present a mixed classical phase
space, identified by a parameter , which we use to guide our
analysis of quantum spectra. We explored the short correlations through nearest
neighbor spacing distribution , which showed that in the mixed region of
the classical phase space, is well described by the Berry-Robnik-Brody
(BRB) distributions for the ESB. In agreement with the expected from the
so-called ergodic parameter , the ratio between
the Heisenberg time and the classical diffusive-like transport time signals the
possibility of quantum dynamical localization when . For the
E-B family, the eigenstates can be split into singlets and doublets. BRB
describes for singlets as the previous family in the mixed region.
However, the for doublets are described by new distributions recently
introduced in the literature but only tested in a few cases for . We observed that as decreases, the 's tend to move
away simultaneously from the GOE (singlets) and GUE (doublets) distributions.Comment: 9 pages, 8 figure
Desempenho produtivo de ovinos em pastagem cultivada.
bitstream/CPAMN/20263/1/CircularTec42.pd
Gramíneas forrageiras para uso de caprinos e ovinos em pastejo.
bitstream/CPAMN-2009-09/16598/1/CT134.pd
Retorno da atividade reprodutiva pós-parto em ovelhas deslanadas.
bitstream/item/80690/1/comunicado-221.pd
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