1,180 research outputs found
Functional characterization of generalized Langevin equations
We present an exact functional formalism to deal with linear Langevin
equations with arbitrary memory kernels and driven by any noise structure
characterized through its characteristic functional. No others hypothesis are
assumed over the noise, neither the fluctuation dissipation theorem. We found
that the characteristic functional of the linear process can be expressed in
terms of noise's functional and the Green function of the deterministic
(memory-like) dissipative dynamics. This object allow us to get a procedure to
calculate all the Kolmogorov hierarchy of the non-Markov process. As examples
we have characterized through the 1-time probability a noise-induced interplay
between the dissipative dynamics and the structure of different noises.
Conditions that lead to non-Gaussian statistics and distributions with long
tails are analyzed. The introduction of arbitrary fluctuations in fractional
Langevin equations have also been pointed out
Non-equilibrium transition from dissipative quantum walk to classical random walk
We have investigated the time-evolution of a free particle in interaction
with a phonon thermal bath, using the tight-binding approach. A dissipative
quantum walk can be defined and many important non-equilibrium decoherence
properties can be investigated analytically. The non-equilibrium statistics of
a pure initial state have been studied. Our theoretical results indicate that
the evolving wave-packet shows the suppression of Anderson's boundaries
(ballistic peaks) by the presence of dissipation. Many important relaxation
properties can be studied quantitatively, such as von Neumann's entropy and
quantum purity. In addition, we have studied Wigner's function. The
time-dependent behavior of the quantum entanglement between a free particle -in
the lattice- and the phonon bath has been characterized analytically. This
result strongly suggests the non-trivial time-dependence of the off-diagonal
elements of the reduced density matrix of the system. We have established a
connection between the quantum decoherence and the dissipative parameter
arising from interaction with the phonon bath. The time-dependent behavior of
quantum correlations has also been pointed out, showing continuous transition
from quantum random walk to classical random walk, when dissipation increases.Comment: Submitted for publication. 17 pages, 6 figure
Toward NS5 Branes on the Resolved Cone over Y^{p,q}
Motivated by recent developments in the understanding of the connection
between five branes on resolved geometries and the corresponding
generalizations of complex deformations in the context of the warped resolved
deformed conifold, we consider the construction of five branes solutions on the
resolved cone over Y^{p,q} spaces. We establish the existence of supersymmetric
five branes solutions wrapped on two-cycles of the resolved cone over Y^{p,q}
in the probe limit. We then use calibration techniques to begin the
construction of fully back-reacted five branes; we present an Ansatz and the
corresponding equations of motion. Our results establish a detailed framework
to study back-reacted five branes wrapped on the resolved cone over Y^{p,q} and
as a first step we find explicit solutions and construct an asymptotic
expansion with the expected properties.Comment: 23+17pp, no figures; v2: references added, various clarification
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Drag Force in a Charged N=4 SYM Plasma
Following recent developments, we employ the AdS/CFT correspondence to
determine the drag force exerted on an external quark that moves through an N=4
super-Yang-Mills plasma with a non-zero R-charge density (or, equivalently, a
non-zero chemical potential). We find that the drag force is larger than in the
case where the plasma is neutral, but the dependence on the charge is
non-monotonic.Comment: 16 pages, 1 eps figure; v2: references added, typos fixed; v3: more
general ansatz, new nontrivial solution obtained, nonmonotonicity of the drag
force made explicit in new figure, version to appear in JHE
Early development of vocal interaction rules in a duetting songbird
This work was supported by the Maytag Endowment from the University of Miami, a Research Grant from the Animal Behavior Society, a Research Grant from the Organization for Tropical Studies and a Doctoral Dissertation Improvement Grant by the National Science Foundation awarded to K.D.R.-C., and funds from Pacific University and the M.J. Murdock Charitable Trust to C.N.T.Exchange of vocal signals is an important aspect of animal communication. Although birdsong is the premier model for understanding vocal development, the development of vocal interaction rules in birds and possible parallels to humans have been little studied. Many tropical songbirds engage in complex vocal interactions in the form of duets between mated pairs. In some species, duets show precise temporal coordination and follow rules (duet codes) governing which song type one bird uses to reply to each of the song types of its mate. We determined whether these duetting rules are acquired during early development in canebrake wrens. Results show that juveniles acquire a duet code by singing with a mated pair of adults and that juveniles gradually increase their fidelity to the code over time. Additionally, we found that juveniles exhibit poorer temporal coordination than adults and improve their coordination as time progresses. Human turn-taking, an analogous rule to temporal coordination, is learned during early development. We report that the ontogeny of vocal interaction rules in songbirds is analogous to that of human conversation rules.Publisher PDFPeer reviewe
Mammalia, Chiroptera, Phyllostomidae, <i>Platyrrhinus lineatus</i>: Range expansion to the state of Rio Grande do Sul, Brazil
The Period-Luminosity Relation of RR Lyrae Stars in the SDSS Photometric System
We provide the first detailed study of the RR Lyrae period-luminosity (PL)
relation in the ugriz bandpasses of the Sloan Digital Sky Survey (SDSS) filter
system. We argue that tight, simple PL relations are not present in the SDSS
filters, except for the redder bandpasses i and (especially) z. However, for
all bandpasses, we show that, by incorporating terms involving a (fairly
reddening-independent) "pseudo-color" C_0 = (u-g)_0 - (g-r)_0, tight
(non-linear) relations do obtain. We provide theoretically calibrated such
relations in the present paper, which should be useful to derive precise
absolute magnitudes (hence distances) and intrinsic colors (hence reddening
values) to even {\em individual} field RR Lyrae stars. For applications to
cases where photometry in all five passbands may not be available, we also
provide simple (though less precise) average PL relations for the i and z
bandpasses, which read as follows:
M_z = 0.839 - 1.295 log P + 0.211 log Z,
M_i = 0.908 - 1.035 log P + 0.220 log Z.
Similarly, simple period-color relations for (r-i)_0, (g-r)_0, and (u-z)_0
are also provided.Comment: 7 pages, 9 figures. ApJS, in pres
A duetting perspective on avian song learning
This work was supported with funds from Pacific University and the M.J. Murdock Charitable Trust (to C.N.T.) and a Doctoral Dissertation Improvement Grant (DDIG) provided by the National Science Foundation (NSF), a Student Research Grant provided by the Animal Behavior Society, a Research Grant provided by the Organization for Tropical Studies (OTS), and funds from the University of Miami (to K.D.R.C.).Avian song learning has a rich history of study and has become the preeminent system for understanding the ontogeny of vocal communication in animals. Song learning in birds has many parallels with human language learning, ranging from the neural mechanisms involved to the importance of social factors in shaping signal acquisition. While much has been learned about the process of song learning, virtually all of the research done to date has focused on temperate species, where often only one sex (the male) sings. Duetting species, in which both males and females learn to sing and learn to combine their songs into temporally coordinated joint displays, could provide many insights into the processes by which vocal learning takes place. Here we highlight three key features of song learning—neuroendocrine control mechanisms, timing and life history stages of song acquisition, and the role of social factors in song selection and use—that have been elucidated from species where only males sing, and compare these with duetting species. We summarize what is known about song learning in duetting species and then provide several suggestions for fruitful directions for future research. We suggest that focusing research efforts on duetting species could significantly advance our understanding of vocal learning in birds and further cement the importance of avian species as models for understanding human conversations and the processes of vocal learning more broadly.PostprintPeer reviewe
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