580 research outputs found
Rate-Adaptive Free-Space Optical Links Over Atmospheric Turbulence and Misalignment Fading Channels
Clipping the Wings of Industry: Uncertainty in Interpretation and Enforcement of the Migratory Bird Treaty Act
Apparent horizons in D-dimensional Robinson-Trautman spacetime
We derive the higher dimensional generalization of Penrose-Tod equation
describing apparent horizons in Robinson-Trautman spacetimes. New results
concerning the existence and uniqueness of its solutions in four dimensions are
proven. Namely, previous results of Tod are generalized to nonvanishing
cosmological constant.Comment: 4 pages, 1 figure, to appear in ERE 2008 conference proceedings, to
be published by AI
From speech to song: an interdisciplinary investigation of rhythm in English and Spanish
The general theoretical frame of this dissertation has to do with the study, from an
interdisciplinary and interlinguistic point of view, of the typological dichotomy
between stress-timed and syllable-timed languages, inasmuch as this distinction is
valid at all. As a preliminary step, I carry out a comparative examination of the basic
prosodic characteristics of English and Spanish, in order to then analyse the standard
versification systems of these two languages. In the central part of my dissertation, I
explore the most important text-setting Optimality Theory constraints as applied to a
corpus of English and Spanish folk and art songs.My main objective in carrying out these three-level analyses is to check
whether the actual setting of verse to music responds to some kind of underlying
rhythmic constraints common to language prosody, verse prosody and music, and
whether those constraints are ranked differently from language to language.The conclusions have to do with a correspondence between the timing
typologies of language and the rhythmic typologies of music. I find clear
inconsistencies or mismatches between speech prosody, on the one hand, and verse
and music rhythm, on the other. These inconsistencies work differently in a syllabletimed language like Spanish than in a stress-timed language like English. While in
the first type of languages I find a natural counterpoint or dialogue between speech
prosody and musical rhythm, in the second type this counterpoint tends to be
considered arhythmic. In other words, I establish a difference in kind in relation to
the dialogue between prosody and music for each of the two types of languages. In
English, the level of agreement between the two stress-patterns is really high, while
in Spanish the counterpoint between the two patterns is used as an expressive device
The wave equation on axisymmetric stationary black hole backgrounds
Understanding the behaviour of linear waves on black hole backgrounds is a
central problem in general relativity, intimately connected with the nonlinear
stability of the black hole spacetimes themselves as solutions to the Einstein
equations--a major open question in the subject. Nonetheless, it is only very
recently that even the most basic boundedness and quantitative decay properties
of linear waves have been proven in a suitably general class of black hole
exterior spacetimes. This talk will review our current mathematical
understanding of waves on black hole backgrounds, beginning with the classical
boundedness theorem of Kay and Wald on exactly Schwarzschild exteriors and
ending with very recent boundedness and decay theorems (proven in collaboration
with Igor Rodnianski) on a wider class of spacetimes. This class of spacetimes
includes in particular slowly rotating Kerr spacetimes, but in the case of the
boundedness theorem is in fact much larger, encompassing general axisymmetric
stationary spacetimes whose geometry is sufficiently close to Schwarzschild and
whose Killing fields span the null generator of the horizon.Comment: 20 pages, 6 pages, to appear in the proceedings of the Spanish
Relativity Meeting, Salamanca 200
How do compounds released by the green tide alga Ulvaria obscura affect development on invertebrate larvae?
Green tides are vast accumulations of green macroalgae that, in the last decade, have become a common nuisance worldwide. Due to compounds the algae release, the blooms may negatively affect other organisms. Ulvaria obscura, a dominant contributor to green tides along the Pacific coast of the United States, produces, among other compounds, dopamine, a catecholamine and neurotransmitter known to affect settlement and metamorphosis of marine invertebrates. We tested the effects of U. obscura exudates and commercially purchased dopamine on fertilization, early development, and larval survival and morphology of the sand dollar Dendraster excentricus and Pacific oyster Crassostrea gigas. The exudate and dopamine treatments did not strongly affect fertilization success of D. excentricus or C. gigas, but they did affect early development and larval morphology of D. excentricus and C. gigas. We found significant differences in archenteron length of D. excentricus gastrulae and shell morphology of C. gigas veligers exposed to the exudates or dopamine. Morphology of D. excentricus plutei also varied significantly among the exudate treatments with larval arm lengths being affected. Our data indicate that compounds released by U. obscura can impact development and, presumably, survival of embryos and larvae, but that the effects differ between species. The impacts could affect development rates, larval dispersal, recruitment and population dynamics of invertebrate species
Accelerated expansion through interaction
Interactions between dark matter and dark energy with a given equation of
state are known to modify the cosmic dynamics. On the other hand, the strength
of these interactions is subject to strong observational constraints. Here we
discuss a model in which the transition from decelerated to accelerated
expansion of the Universe arises as a pure interaction phenomenon. Various
cosmological scenarios that describe a present stage of accelerated expansion,
like the LCDM model or a (generalized) Chaplygin gas, follow as special cases
for different interaction rates. This unifying view on the homogeneous and
isotropic background level is accompanied by a non-adiabatic perturbation
dynamics which can be seen as a consequence of a fluctuating interaction rate.Comment: 4 pages, to appear in the Proceedings of the Spanish Relativity
Meeting ERE2008 in Salamanca, September 200
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