301 research outputs found
The effects of grain shape and frustration in a granular column near jamming
We investigate the full phase diagram of a column of grains near jamming, as
a function of varying levels of frustration. Frustration is modelled by the
effect of two opposing fields on a grain, due respectively to grains above and
below it. The resulting four dynamical regimes (ballistic, logarithmic,
activated and glassy) are characterised by means of the jamming time of
zero-temperature dynamics, and of the statistics of attractors reached by the
latter. Shape effects are most pronounced in the cases of strong and weak
frustration, and essentially disappear around a mean-field point.Comment: 17 pages, 19 figure
Generation of Primordial Cosmological Perturbations from Statistical Mechanical Models
The initial conditions describing seed fluctuations for the formation of
structure in standard cosmological models, i.e.the Harrison-Zeldovich
distribution, have very characteristic ``super-homogeneous'' properties: they
are statistically translation invariant, isotropic, and the variance of the
mass fluctuations in a region of volume V grows slower than V. We discuss the
geometrical construction of distributions of points in with similar
properties encountered in tiling and in statistical physics, e.g. the Gibbs
distribution of a one-component system of charged particles in a uniform
background (OCP). Modifications of the OCP can produce equilibrium correlations
of the kind assumed in the cosmological context. We then describe how such
systems can be used for the generation of initial conditions in gravitational
-body simulations.Comment: 7 pages, 3 figures, final version with minor modifications, to appear
in PR
The Glass-like Universe: Real-space correlation properties of standard cosmological models
After reviewing the basic relevant properties of stationary stochastic
processes (SSP), defining basic terms and quantities, we discuss the properties
of the so-called Harrison-Zeldovich like spectra. These correlations, usually
characterized exclusively in k-space (i.e. in terms of power spectra P(k)), are
a fundamental feature of all current standard cosmological models. Examining
them in real space we note their characteristics to be a {\it negative} power
law tail \xi(r) \sim - r^{-4} and a {\it sub-poissonian} normalised variance in
spheres \sigma^2(R) \sim R^{-4} \ln R. We note in particular that this latter
behaviour is at the limit of the most rapid decay (\sim R^{-4}) of this
quantity possible for any stochastic distribution (continuous or discrete).
This very particular characteristic is usually obscured in cosmology by the use
of Gaussian spheres. In a simple classification of all SSP into three
categories, we highlight with the name ``super-homogeneous'' the properties of
the class to which models like this, with P(0)=0, belong. In statistical
physics language they are well described as glass-like. They do not have either
``scale-invariant'' features, in the sense of critical phenomena, nor fractal
properties. We illustrate their properties with some simple examples, in
particular that of a ``shuffled'' lattice.Comment: 20 pages, 3 postscript figures, corrected some typos and minor
changes to match the accepted version in Physical Review
Fontes de lipÃdio e monensina sódica na fermentação, cinética e degradabilidade ruminal de bovinos
Reorientation-effect measurement of the first 2+ state in 12C : Confirmation of oblate deformation
A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ−ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the 〈21 +‖E2ˆ‖21 +〉 diagonal matrix element in 12C from particle−γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (21 +) states in 12C have been calculated using chiral NN N4LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 21 + state at 4.439 MeV. The polarizability of the 21 + state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12C. Spectroscopic quadrupole moments of QS(21 +)=+0.053(44) eb and QS(21 +)=+0.08(3) eb are determined, respectively, yielding a weighted average of QS(21 +)=+0.071(25) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 21 + state of 12C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei
Mating disruption with low density diffusers for the management of oriental fruit moths (Lepidoptera: Tortricidae) in apple orchards under subtropical climate in southern Brazil
Rendimentos dos cortes e não-componentes das carcaças de cordeiros terminados com dietas contendo diferentes fontes de óleo vegetal
TIC 278956474: Two Close Binaries in One Young Quadruple System Identified by TESS
We have identified a quadruple system with two close eclipsing binaries in Transiting Exoplanet Survey Satellite (TESS) data. The object is unresolved in Gaia and appears as a single source at parallax 1.08 ± 0.01 mas. Both binaries have observable primary and secondary eclipses and were monitored throughout TESS Cycle 1 (sectors 1-13), falling within the TESS Continuous Viewing Zone. In one eclipsing binary (P = 5.488 days), the smaller star is completely occluded by the larger star during the secondary eclipse; in the other (P = 5.674 days) both eclipses are grazing. Using these data, spectroscopy, speckle photometry, spectral energy distribution analysis, and evolutionary stellar tracks, we have constrained the masses and radii of the four stars in the two eclipsing binaries. The Li i equivalent width indicates an age of 10-50 Myr and, with an outer period of 858+7-5 days, our analysis indicates this is one of the most compact young 2 + 2 quadruple systems known
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