661 research outputs found
Asymptotics of self-similar solutions to coagulation equations with product kernel
We consider mass-conserving self-similar solutions for Smoluchowski's
coagulation equation with kernel with
. It is known that such self-similar solutions
satisfy that is bounded above and below as . In
this paper we describe in detail via formal asymptotics the qualitative
behavior of a suitably rescaled function in the limit . It turns out that as . As becomes larger
develops peaks of height that are separated by large regions
where is small. Finally, converges to zero exponentially fast as . Our analysis is based on different approximations of a nonlocal
operator, that reduces the original equation in certain regimes to a system of
ODE
Parallel Excluded Volume Tempering for Polymer Melts
We have developed a technique to accelerate the acquisition of effectively
uncorrelated configurations for off-lattice models of dense polymer melts which
makes use of both parallel tempering and large scale Monte Carlo moves. The
method is based upon simulating a set of systems in parallel, each of which has
a slightly different repulsive core potential, such that a thermodynamic path
from full excluded volume to an ideal gas of random walks is generated. While
each system is run with standard stochastic dynamics, resulting in an NVT
ensemble, we implement the parallel tempering through stochastic swaps between
the configurations of adjacent potentials, and the large scale Monte Carlo
moves through attempted pivot and translation moves which reach a realistic
acceptance probability as the limit of the ideal gas of random walks is
approached. Compared to pure stochastic dynamics, this results in an increased
efficiency even for a system of chains as short as monomers, however
at this chain length the large scale Monte Carlo moves were ineffective. For
even longer chains the speedup becomes substantial, as observed from
preliminary data for
Axisymmetric pulse recycling and motion in bulk semiconductors
The Kroemer model for the Gunn effect in a circular geometry (Corbino disks)
has been numerically solved. The results have been interpreted by means of
asymptotic calculations. Above a certain onset dc voltage bias, axisymmetric
pulses of the electric field are periodically shed by an inner circular
cathode. These pulses decay as they move towards the outer anode, which they
may not reach. As a pulse advances, the external current increases continuously
until a new pulse is generated. Then the current abruptly decreases, in
agreement with existing experimental results. Depending on the bias, more
complex patterns with multiple pulse shedding are possible.Comment: 8 pages, 15 figure
Partial domain wall partition functions
We consider six-vertex model configurations on an n-by-N lattice, n =< N,
that satisfy a variation on domain wall boundary conditions that we define and
call "partial domain wall boundary conditions". We obtain two expressions for
the corresponding "partial domain wall partition function", as an
(N-by-N)-determinant and as an (n-by-n)-determinant. The latter was first
obtained by I Kostov. We show that the two determinants are equal, as expected
from the fact that they are partition functions of the same object, that each
is a discrete KP tau-function, and, recalling that these determinants represent
tree-level structure constants in N=4 SYM, we show that introducing 1-loop
corrections, as proposed by N Gromov and P Vieira, preserves the determinant
structure.Comment: 30 pages, LaTeX. This version, which appeared in JHEP, has an
abbreviated abstract and some minor stylistic change
A gene-tree test of the traditional taxonomy of American deer: the importance of voucher specimens, geographic data, and dense sampling
The taxonomy of American deer has been established almost entirely on the basis of morphological data and without the use of explicit phylogenetic methods; hence, phylogenetic analyses including data for all of the currently recognized species, even if based on a single gene, might improve current understanding of their taxonomy. We tested the monophyly of the morphology-defined genera and species of New World deer (Odocoileini) with phylogenetic analyses of mitochondrial DNA sequences. This is the first such test conducted using extensive geographic and taxonomic sampling. Our results do not support the monophyly of Mazama, Odocoileus, Pudu, M. americana, M. nemorivaga, Od. hemionus, and Od. virginianus. Mazama contains species that belong to other genera. We found a novel sister-taxon relationship between “Mazama” pandora and a clade formed by Od. hemionus columbianus and Od. h. sitkensis, and transfer pandora to Odocoileus. The clade formed by Od. h. columbianus and Od. h. sitkensis may represent a valid species, whereas the remaining subspecies of Od. hemionus appear closer to Od. virginianus. Pudu (Pudu) puda was not found sister to Pudu (Pudella) mephistophiles. If confirmed, this result will prompt the recognition of the monotypic Pudella as a distinct genus. We provide evidence for the existence of an undescribed species now confused with Mazama americana, and identify other instances of cryptic, taxonomically unrecognized species-level diversity among populations here regarded as Mazama temama, “Mazama” nemorivaga, and Hippocamelus antisensis. Noteworthy records that substantially extend the known distributions of M. temama and “M.” gouazoubira are provided, and we unveil a surprising ambiguity regarding the distribution of “M.” nemorivaga, as it is described in the literature. The study of deer of the tribe Odocoileini has been hampered by the paucity of information regarding voucher specimens and the provenance of sequences deposited in GenBank. We pinpoint priorities for future systematic research on the tribe Odocoileini.Eliécer E. Gutiérrez, Kristofer M. Helgen, Molly M. McDonough, Franziska Bauer, Melissa T.R. Hawkins, Luis A. Escobedo-Morales, Bruce D. Patterson, Jesus E. Maldonad
Temperature and density extrapolations in canonical ensemble Monte Carlo simulations
We show how to use the multiple histogram method to combine canonical
ensemble Monte Carlo simulations made at different temperatures and densities.
The method can be applied to study systems of particles with arbitrary
interaction potential and to compute the thermodynamic properties over a range
of temperatures and densities. The calculation of the Helmholtz free energy
relative to some thermodynamic reference state enables us to study phase
coexistence properties. We test the method on the Lennard-Jones fluids for
which many results are available.Comment: 5 pages, 3 figure
Free boundary problems describing two-dimensional pulse recycling and motion in semiconductors
An asymptotic analysis of the Gunn effect in two-dimensional samples of bulk
n-GaAs with circular contacts is presented. A moving pulse far from contacts is
approximated by a moving free boundary separating regions where the electric
potential solves a Laplace equation with subsidiary boundary conditions. The
dynamical condition for the motion of the free boundary is a Hamilton-Jacobi
equation. We obtain the exact solution of the free boundary problem (FBP) in
simple one-dimensional and axisymmetric geometries. The solution of the FBP is
obtained numerically in the general case and compared with the numerical
solution of the full system of equations. The agreement is excellent so that
the FBP can be adopted as the basis for an asymptotic study of the
multi-dimensional Gunn effect.Comment: 19 pages, 9 figures, Revtex. To appear in Phys. Rev.
Dependência da cobertura de céu nas frações solares Global, Difusa e Direta do espectro infravermelho em Botucatu/SP/Brasil
É descrito no trabalho a obtenção das frações solares KGIV = (HdGIV/HGd), KdIV = (HddIV/Hdd) e KDIV = (HdDIV/HDd) nas condições de cobertura de céu total e para quatro tipos discretos de coberturas de céu. A base de dados das radiações dos dois espectros foi medida no período de 2003 a 2006 em Botucatu/SP/Brasil. Os valores obtidos para cobertura de céu total foram: KdGIV = 46,1%, KddIV = 38,2% e KdDIV = 51,1%. Nas coberturas discretas o valor da fração KGIV = 43,3%foi menor na cobertura nebulosa, e KGIV = 46,9% foi maior na cobertura céu aberto. Ao contrario,a fração KdIV = 41,0% foi maior na cobertura nebulosa, e KdIV = 25,0%foi menor na céu aberto. O valor da fração KDIV não variou em função da cobertura de céu: KDIV = 51,0%foi igual nas coberturas nebulosa e aberta.The study describes linear equations for four sky covers, which express the dependence of cloud, water vapour and aerosol variations in the atmosphere on the values of the ratios HGNIR/HG, HdNIR/HdeandHDNIR/HD. The value of the fraction HGNIR/HG = 43,3% is lower in the cloudy cover, while HGNIR/HdG = 46,9% is higher in the clear sky condition. On the contrary, the fraction HdNIR/Hd = 41,0% is higher in the cloudy cover, while HdNIR/Hd = 25,0% is lower in the clear sky condition. No variation was found in the value of the fraction HDNIR/HD as a function of the sky cover. The ratio HDNIR/HD = 51,0% is the same in the cloudy cover and clear sky condition.Tema 11: Radiación solar y clima.Facultad de Arquitectura y Urbanism
Dependência da cobertura de céu nas frações solares Global, Difusa e Direta do espectro infravermelho em Botucatu/SP/Brasil
É descrito no trabalho a obtenção das frações solares KGIV = (HdGIV/HGd), KdIV = (HddIV/Hdd) e KDIV = (HdDIV/HDd) nas condições de cobertura de céu total e para quatro tipos discretos de coberturas de céu. A base de dados das radiações dos dois espectros foi medida no período de 2003 a 2006 em Botucatu/SP/Brasil. Os valores obtidos para cobertura de céu total foram: KdGIV = 46,1%, KddIV = 38,2% e KdDIV = 51,1%. Nas coberturas discretas o valor da fração KGIV = 43,3%foi menor na cobertura nebulosa, e KGIV = 46,9% foi maior na cobertura céu aberto. Ao contrario,a fração KdIV = 41,0% foi maior na cobertura nebulosa, e KdIV = 25,0%foi menor na céu aberto. O valor da fração KDIV não variou em função da cobertura de céu: KDIV = 51,0%foi igual nas coberturas nebulosa e aberta.The study describes linear equations for four sky covers, which express the dependence of cloud, water vapour and aerosol variations in the atmosphere on the values of the ratios HGNIR/HG, HdNIR/HdeandHDNIR/HD. The value of the fraction HGNIR/HG = 43,3% is lower in the cloudy cover, while HGNIR/HdG = 46,9% is higher in the clear sky condition. On the contrary, the fraction HdNIR/Hd = 41,0% is higher in the cloudy cover, while HdNIR/Hd = 25,0% is lower in the clear sky condition. No variation was found in the value of the fraction HDNIR/HD as a function of the sky cover. The ratio HDNIR/HD = 51,0% is the same in the cloudy cover and clear sky condition.Tema 11: Radiación solar y clima.Facultad de Arquitectura y Urbanism
Dependência da cobertura de céu nas frações solares Global, Difusa e Direta do espectro infravermelho em Botucatu/SP/Brasil
É descrito no trabalho a obtenção das frações solares KGIV = (HdGIV/HGd), KdIV = (HddIV/Hdd) e KDIV = (HdDIV/HDd) nas condições de cobertura de céu total e para quatro tipos discretos de coberturas de céu. A base de dados das radiações dos dois espectros foi medida no período de 2003 a 2006 em Botucatu/SP/Brasil. Os valores obtidos para cobertura de céu total foram: KdGIV = 46,1%, KddIV = 38,2% e KdDIV = 51,1%. Nas coberturas discretas o valor da fração KGIV = 43,3%foi menor na cobertura nebulosa, e KGIV = 46,9% foi maior na cobertura céu aberto. Ao contrario,a fração KdIV = 41,0% foi maior na cobertura nebulosa, e KdIV = 25,0%foi menor na céu aberto. O valor da fração KDIV não variou em função da cobertura de céu: KDIV = 51,0%foi igual nas coberturas nebulosa e aberta.The study describes linear equations for four sky covers, which express the dependence of cloud, water vapour and aerosol variations in the atmosphere on the values of the ratios HGNIR/HG, HdNIR/HdeandHDNIR/HD. The value of the fraction HGNIR/HG = 43,3% is lower in the cloudy cover, while HGNIR/HdG = 46,9% is higher in the clear sky condition. On the contrary, the fraction HdNIR/Hd = 41,0% is higher in the cloudy cover, while HdNIR/Hd = 25,0% is lower in the clear sky condition. No variation was found in the value of the fraction HDNIR/HD as a function of the sky cover. The ratio HDNIR/HD = 51,0% is the same in the cloudy cover and clear sky condition.Tema 11: Radiación solar y clima.Facultad de Arquitectura y Urbanism
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