4,695 research outputs found
Topological Quintessence
A global monopole (or other topological defect) formed during a recent phase
transition with core size comparable to the present Hubble scale, could induce
the observed accelerating expansion of the universe. In such a model,
topological considerations trap the scalar field close to a local maximum of
its potential in a cosmologically large region of space. We perform detailed
numerical simulations of such an inhomogeneous dark energy system (topological
quintessence) minimally coupled to gravity, in a flat background of initially
homogeneous matter. We find that when the energy density of the field in the
monopole core starts dominating the background density, the spacetime in the
core starts to accelerate its expansion in accordance to a \Lambda CDM model
with an effective inhomogeneous spherical dark energy density parameter
\Omega_\Lambda(r). The matter density profile is found to respond to the global
monopole profile via an anti-correlation (matter underdensity in the monopole
core). Away from the monopole core, the spacetime is effectively
Einstein-deSitter (\Omega_\Lambda(r_{out}) -> 0) while at the center
\Omega_\Lambda(r ~ 0) is maximum. We fit the numerically obtained expansion
rate at the monopole core to the Union2 data and show that the quality of fit
is almost identical to that of \Lambda CDM. Finally, we discuss potential
observational signatures of this class of inhomogeneous dark energy models.Comment: Accepted in Phys. Rev. D (to appear). Added observational bounds on
parameters. 10 pages (two column revtex), 6 figures. The Mathematica files
used to produce the figures of this study may be downloaded from
http://leandros.physics.uoi.gr/topquin
Detailed theoretical predictions of the outskirts of dark matter halos
In the present work we describe the formalism necessary to derive the
properties of dark matter halos beyond two virial radius using the spherical
collapse model (without shell crossing), and provide the framework for the
theoretical prediction presented in Prada et al. (2005). We show in detail how
to obtain within this model the probability distribution for the
spherically-averaged enclosed density at any radii P(delta,r). Using this
probability distribution, we compute the most probable and mean density
profiles, which turns out to differ considerably from each other. We also show
how to obtain the typical profile, as well as the probability distribution and
mean profile for the spherically averaged radial velocity. Two probability
distributions are obtained: a first one is derived using a simple assumption,
that is, if Q is the virial radius in Lagrangian coordinates, then the enclosed
linear contrast delta_l(q,Q) must satisfy the condition that delta_l(q=Q) =
delta_vir, where delta_vir is the linear density contrast within the virial
radius Rvir at the moment of virialization. Then we introduce an additional
constraint to obtain a more accurate P(delta,r) which reproduces to a higher
degree of precision the distribution of the spherically averaged enclosed
density found in the simulations. This new constraint is delta_l(q,Q) <
delta_vir for all q > Q, which means that there are no radii larger than Rvir
where the density contrast is larger than that used to define the virial
radius. Finally, we compare in detail our theoretical predictions for the
probability distributions with the results found in the simulations.Comment: 12 pages, 8 figures, 1 table, replaced to match the published versio
Micropulse Transscleral Cyclophotocoagulation: A Hypothesis for the Ideal Parameters
MicroPulse transscleral cyclophotocoagulation (IRIDEX Corp., Mountain View, CA) is a novel technique that uses repetitive micropulses of active diode laser (On cycles) interspersed with resting intervals (Off cycles). It has been proposed that the OFF cycles allow thermal dissipation and, therefore, reduce collateral damage. The literature suggests that Micropulse has a better safety profile compared to traditional continuous-wave cyclophotocoagulation. However, because it is a relatively new technique, there are no clear guidelines stating the ideal laser parameters that would allow the best balance between high and sustained effectiveness with minimal side effects. This research reviewed the literature to approximate ideal parameters for single-session treatment. To simplify the comparison between studies, this study used Joules (J) as a way to standardize the energy levels employed. The reviewed clinical publications allowed reduction of these parameters to a range between 112 and 150 J of total energy, which allows a moderate IOP lowering effect of around 30% with few/no complications. An additional narrowing of the parameters was achieved after analyzing recently published experimental data. These data suggest a different mechanism of action for the Micropulse, similar to that of the pilocarpine. This effect was maximum at 150 J. Since clinical studies show few or no complications, even at those energy levels, it could be hypothesized that the ideal parameters can be located at a point closer to 150 J. This data also leads to the concept of dosimetry; the capacity to dose mTSCPC treatment based on desired IOP lowering effect and risk exposure. Further prospective studies are needed to test the proposed evidence-based hypothesis
Muyurina y el presente profundo: poéticas andino-amazónicas
Este libro es una trenza entre investigación, creación y oralidad. Su
origen se remonta a la canción “Memorias muertas” del álbum “Remembranza
Huamanguina” que el Trío Ayacucho diera a conocer en 1974, y que fuera hallada
hace poco en una calle de Lima. La primera estrofa de la canción se convirtió
en motivo poético o sonido subyacente que prestó el nombre al performance
MUYUNA (A place to move), hecho por jóvenes estudiantes y artistas de Cornell
University en 1986. Este mismo motivo dio origen al poema “Muyurina” de Fredy
A. Roncalla, palabra que en este libro/kipu funciona como lugar de encuentro de
varias voces y direcciones
Uranio / Uranium
Difícil es imaginar un elemento que la gran mayoría
nunca ha visto o tocado. Sin embargo, dicho elemento
mineral de la Madre Naturaleza se encuentra conectado
a la energía que consume nuestra civilización, a sus
comodidades y a algunas de las historias más terribles y
dolorosas del siglo XX y XXI.
La poesía de Juan Sánchez hace el Uranio visible no
como un objeto de estudio científico, sino mostrándonos
cómo es su relación con el ser humano. El poema “Uranio”
de este libro es un entretejido de historias, sentires
y hechos sobre la minería extractiva en los sagrados
territorios de las comunidades nativo americanas del
suroeste de los Estados Unidos. En este libro también hemos querido hacer visible una
conexión transpacífica, pues la industria extractiva del
uranio está ligada al desarrollo de la energía nuclear y las
armas nucleares (que utilizan el uranio como una de sus
materias primas). [...
Micropulse Transscleral Cyclophotocoagulation: A Hypothesis for the Ideal Parameters
MicroPulse transscleral cyclophotocoagulation (IRIDEX Corp., Mountain View, CA) is a novel technique that uses repetitive micropulses of active diode laser (On cycles) interspersed with resting intervals (Off cycles). It has been proposed that the OFF cycles allow thermal dissipation and, therefore, reduce collateral damage. The literature suggests that Micropulse has a better safety profile compared to traditional continuous-wave cyclophotocoagulation. However, because it is a relatively new technique, there are no clear guidelines stating the ideal laser parameters that would allow the best balance between high and sustained effectiveness with minimal side effects. This research reviewed the literature to approximate ideal parameters for single-session treatment. To simplify the comparison between studies, this study used Joules (J) as a way to standardize the energy levels employed. The reviewed clinical publications allowed reduction of these parameters to a range between 112 and 150 J of total energy, which allows a moderate IOP lowering effect of around 30% with few/no complications. An additional narrowing of the parameters was achieved after analyzing recently published experimental data. These data suggest a different mechanism of action for the Micropulse, similar to that of the pilocarpine. This effect was maximum at 150 J. Since clinical studies show few or no complications, even at those energy levels, it could be hypothesized that the ideal parameters can be located at a point closer to 150 J. This data also leads to the concept of dosimetry; the capacity to dose mTSCPC treatment based on desired IOP lowering effect and risk exposure. Further prospective studies are needed to test the proposed evidence-based hypothesis
Source of Variant Creutzfeldt-Jakob Disease outside United Kingdom
Bovine imports during the 1980s and the first half of the 1990s from the UK contributed substantially to the global spread of this disease
- …