2,276 research outputs found
Photonic heterostructures with Levy-type disorder: statistics of coherent transmission
We study the electromagnetic transmission through one-dimensional (1D)
photonic heterostructures whose random layer thicknesses follow a long-tailed
distribution --L\'evy-type distribution. Based on recent predictions made for
1D coherent transport with L\'evy-type disorder, we show numerically that for a
system of length (i) the average for
for , being the
exponent of the power-law decay of the layer-thickness probability
distribution; and (ii) the transmission distribution is independent of
the angle of incidence and frequency of the electromagnetic wave, but it is
fully determined by the values of and .Comment: 4 pages, 4 figure
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
Non-equilibrium phase transition in a sheared granular mixture
The dynamics of an impurity (or tracer particle) immersed in a dilute
granular gas under uniform shear flow is investigated. A non-equilibrium phase
transition is identified from an exact solution of the inelastic Boltzmann
equation for a granular binary mixture in the tracer limit, where the impurity
carries either a vanishing (disordered phase) or a finite (ordered phase)
fraction of the total kinetic energy of the system. In the disordered phase,
the granular temperature ratio (impurity "temperature" over that of the host
fluid) is finite, while it diverges in the ordered phase. To correctly capture
this extreme violation of energy equipartition, we show that the picture of an
impurity enslaved to the host fluid is insufficient
Discrete breathers in dissipative lattices
We study the properties of discrete breathers, also known as intrinsic
localized modes, in the one-dimensional Frenkel-Kontorova lattice of
oscillators subject to damping and external force. The system is studied in the
whole range of values of the coupling parameter, from C=0 (uncoupled limit) up
to values close to the continuum limit (forced and damped sine-Gordon model).
As this parameter is varied, the existence of different bifurcations is
investigated numerically. Using Floquet spectral analysis, we give a complete
characterization of the most relevant bifurcations, and we find (spatial)
symmetry-breaking bifurcations which are linked to breather mobility, just as
it was found in Hamiltonian systems by other authors. In this way moving
breathers are shown to exist even at remarkably high levels of discreteness. We
study mobile breathers and characterize them in terms of the phonon radiation
they emit, which explains successfully the way in which they interact. For
instance, it is possible to form ``bound states'' of moving breathers, through
the interaction of their phonon tails. Over all, both stationary and moving
breathers are found to be generic localized states over large values of ,
and they are shown to be robust against low temperature fluctuations.Comment: To be published in Physical Review
Breather trapping and breather transmission in a DNA model with an interface
We study the dynamics of moving discrete breathers in an interfaced piecewise
DNA molecule.
This is a DNA chain in which all the base pairs are identical and there
exists an interface such that the base pairs dipole moments at each side are
oriented in opposite directions.
The Hamiltonian of the Peyrard--Bishop model is augmented with a term that
includes the dipole--dipole coupling between base pairs. Numerical simulations
show the existence of two dynamical regimes. If the translational kinetic
energy of a moving breather launched towards the interface is below a critical
value, it is trapped in a region around the interface collecting vibrational
energy. For an energy larger than the critical value, the breather is
transmitted and continues travelling along the double strand with lower
velocity. Reflection phenomena never occur.
The same study has been carried out when a single dipole is oriented in
opposite direction to the other ones.
When moving breathers collide with the single inverted dipole, the same
effects appear. These results emphasize the importance of this simple type of
local inhomogeneity as it creates a mechanism for the trapping of energy.
Finally, the simulations show that, under favorable conditions, several
launched moving breathers can be trapped successively at the interface region
producing an accumulation of vibrational energy. Moreover, an additional
colliding moving breather can produce a saturation of energy and a moving
breather with all the accumulated energy is transmitted to the chain.Comment: 15 pages, 11 figure
Two New Species of \u3ci\u3eHermeuptychia\u3c/i\u3e from North America and Three Neotype Designations (Nymphalidae: Satyrinae)
Abstract
Two new species of Hermeuptychia Forster, 1964 are described. Hermeuptychia sinuosa Grishin, sp. n. (type locality Guatemala: El Progreso, MorazĂĄn) is an isolated member of the genus that does not readily fit into known species groups, as suggested by its distinct male and female genitalia and COI DNA barcode sequences. It is distinguished from its congeners by prominently wavy submarginal lines, rounder wings and distinctive genitalia, and can typically be identified by a white dot, instead of an eyespot, near the ventral hindwing apex. Hermeuptychia occidentalis Grishin, sp. n. (type locality Mexico: Guerrero, Acapulco) belongs to the Hermeuptychia sosybius group as indicated by the presence of androconia on the dorsal surface of the wings, genitalia and COI DNA barcodes, and in addition to DNA characters, differs from its relatives in the shape of the uncus and female genitalia. Neotypes of Oreas strigata canthe HĂŒbner, [1811] (type locality Suriname: Gelderland, Suriname River), Megisto acmenis HĂŒbner, 1823 (type locality Argentina: Buenos Aires), and Satyrus cantheus Godart, [1824] (type locality USA: Florida, Pinellas County, St. Petersburg) and lectotype of Euptychia celmis var. bonaĂ«rensis [sic] Burmeister, 1878 (type locality Argentina: Buenos Aires) are designated. These designations establish Hermeuptychia canthe as a valid species widely distributed in South America from Colombia to Bolivia and southeast Brazil, Euptychia celmis var. bonaĂ«rensis [sic] Burmeister, 1878 as a junior objective synonym of Yphthimoides acmenis, and S. cantheus as a junior subjective synonym of Hermeuptychia sosybius (Fabricius, 1793). Papilio camerta Cramer, 1780 is treated as nomen dubium requiring further studies to determine an identity that is consistent with the original description, as it may be conspecific with Paryphthimoides poltys (Prittwitz, 1865) instead of being a Hermeuptychia species as currently assumed.
Resumen
Se describe dos nuevas especies de Hermeuptychia Forster, 1964. Hermeuptychia sinuosa Grishin, sp. n. (localidad tipo Guatemala: El Progreso, MorazĂĄn), es un componente aislado del gĂ©nero que no encaja fĂĄcilmente en los grupos de especies conocidas, como lo indica su distintiva genitalia masculina y femenina y las secuencias de ADN del cĂłdigo de barras COI. Se distingue de sus congĂ©neres por tener lĂneas submarginales prominentemente onduladas, alas mĂĄs redondas y genitales diferentes, y se puede identificar tĂpicamente por un punto blanco, en lugar de una mancha ocular, cerca del ĂĄpice ventral del ala anterior. Hermeuptychia occidentalis Grishin, sp. n. (localidad tipo MĂ©xico: Guerrero, Acapulco) pertenece al grupo de Hermeuptychia sosybius como lo indica la presencia de androconia en las alas anteriores, la estructura genital y secuencias de ADN de la regiĂłn del cĂłdigo de barras COI, y ademĂĄs de caracteres del ADN, se diferencia de sus parientes en la forma del uncus y la genitalia femenina. Se designa neotipos para Oreas strigata canthe HĂŒbner, [1811] (localidad tipo Surinam: Gelderland, RĂo Surinam), Megisto acmenis HĂŒbner, 1823 (localidad tipo Argentina: Buenos Aires), y Satyrus cantheus Godart, [1824] (localidad tipo Estados Unidos: Florida, Pinellas County, St. Petersburg), y el lectotipo de Euptychia celmis var. bonaĂ«rensis [sic] Burmeister, 1878 (localidad tipo Argentina: Buenos Aires). Estas designaciones establecen a Hermeuptychia canthe como una especie vĂĄlida ampliamente distribuida en AmĂ©rica del Sur desde Colombia hasta Bolivia y el sureste de Brasil, a Euptychia celmis var. bonaĂ«rensis [sic] Burmeister, 1878 como sinĂłnimo objetivo mĂĄs reciente de Yphthimoides acmenis, y a S. cantheus como sinĂłnimo subjetivo mĂĄs reciente de Hermeuptychia sosybius (Fabricius, 1793). Papilio camerta Cramer, 1780 es tratado como un nomen dubium requiriendo mĂĄs estudios para determinar una identidad que sea consistente con la descripciĂłn original, ya que puede ser coespecĂfica con Paryphthimoides poltys (Prittwitz, 1865) en lugar de ser una especie de Hermeuptychia como se asume actualmente.
COI = c oxidase subunit
Building the genomic nation: âHomo Brasilisâ and the âGenoma Mexicanoâ in comparative cultural perspective
This is the final version of the article. Available from SAGE Publications via the DOI in this record.This article explores the relationship between genetic research, nationalism and the construction of collective social identities in Latin America. It makes a comparative analysis of two research projects â the âGenoma Mexicanoâ and the âHomo Brasilisâ â both of which sought to establish national and genetic profiles. Both have reproduced and strengthened the idea of their respective nations of focus, incorporating biological elements into debates on social identities. Also, both have placed the unifying figure of the mestizo/mestiço at the heart of national identity constructions, and in so doing have displaced alternative identity categories, such as those based on race. However, having been developed in different national contexts, these projects have had distinct scientific and social trajectories: in Mexico, the genomic mestizo is mobilized mainly in relation to health, while in Brazil the key arena is that of race. We show the importance of the nation as a frame for mobilizing genetic data in public policy debates, and demonstrate how race comes in and out of focus in different Latin American national contexts of genomic research, while never completely disappearing.This article arises out of two projects: âRace, genomics and mestizaje (mixture) in Latin America:
a comparative approachâ funded by the ESRC (grant RES-062-23-1914) and âPublic engagement
with genomic research and race in Latin Americaâ funded by The Leverhulme Trust (grant
RPG-044)
Stability of non-time-reversible phonobreathers
Non-time reversible phonobreathers are non-linear waves that can transport
energy in coupled oscillator chains by means of a phase-torsion mechanism. In
this paper, the stability properties of these structures have been considered.
It has been performed an analytical study for low-coupling solutions based upon
the so called {\em multibreather stability theorem} previously developed by
some of the authors [Physica D {\bf 180} 235]. A numerical analysis confirms
the analytical predictions and gives a detailed picture of the existence and
stability properties for arbitrary frequency and coupling.Comment: J. Phys. A.:Math. and Theor. In Press (2010
Tracer diffusion in granular shear flows
Tracer diffusion in a granular gas in simple shear flow is analyzed. The
analysis is made from a perturbation solution of the Boltzmann kinetic equation
through first order in the gradient of the mole fraction of tracer particles.
The reference state (zeroth-order approximation) corresponds to a Sonine
solution of the Boltzmann equation, which holds for arbitrary values of the
restitution coefficients. Due to the anisotropy induced in the system by the
shear flow, the mass flux defines a diffusion tensor instead of a
scalar diffusion coefficient. The elements of this tensor are given in terms of
the restitution coefficients and mass and size ratios. The dependence of the
diffusion tensor on the parameters of the problem is illustrated in the
three-dimensional case. The results show that the influence of dissipation on
the elements is in general quite important, even for moderate values
of the restitution coefficients. In the case of self-diffusion (mechanically
equivalent particles), the trends observed in recent molecular dynamics
simulations are similar to those obtained here from the Boltzmann kinetic
theory.Comment: 5 figure
The influence of the C+N+O abundances on the determination of the relative ages of Globular Clusters: the case of NGC 1851 and NGC 6121 (M4)
The color magnitude diagram (CMD) of NGC 1851 presents two subgiant branches
(SGB), probably due the presence of two populations differing in total CNO
content. We test the idea that a difference in total CNO may simulate an age
difference when comparing the CMD of clusters to derive relative ages. We
compare NGC 1851 with NGC 6121 (M4), a cluster of very similar [Fe/H]. We find
that, with a suitable shift of the CMDs that brings the two red horizontal
branches at the same magnitude level, the unevolved main sequence and red giant
branch match, but the SGB of NGC 6121 and its red giant branch "bump" are
fainter than in NGC 1851. In particular, the SGB of NGC 6121 is even slightly
fainter than the the faint SGB in NGC 1851. Both these features can be
explained if the total CNO in NGC 6121 is larger than that in NGC 1851, even if
the two clusters are coeval. We conclude by warning that different initial
C+N+O abundances between two clusters, otherwise similar in metallicity and
age, may lead to differences in the turnoff morphology that can be easily
attributed to an age difference.Comment: accepted for publication in MNRA
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