52 research outputs found
Bubble collisions and measures of the multiverse
To compute the spectrum of bubble collisions seen by an observer in an
eternally-inflating multiverse, one must choose a measure over the diverging
spacetime volume, including choosing an "initial" hypersurface below which
there are no bubble nucleations. Previous calculations focused on the case
where the initial hypersurface is pushed arbitrarily deep into the past.
Interestingly, the observed spectrum depends on the orientation of the initial
hypersurface, however one's ability observe the effect rapidly decreases with
the ratio of inflationary Hubble rates inside and outside one's bubble. We
investigate whether this conclusion might be avoided under more general
circumstances, in particular placing the observer's bubble near the initial
hypersurface. We find that it is not. As a point of reference, a substantial
appendix reviews relevant aspects of the measure problem of eternal inflation.Comment: 24 pages, two figures, plus 16-page appendix with one figure; v2:
minor improvements and clarifications, conclusions unchanged (version to
appear in JCAP
The Fate of Nearly Supersymmetric Vacua
Supersymmetric vacua are stable. It is interesting to ask: how long-lived are
vacua which are nearly supersymmetric? This question is relevant if our
universe is approximately supersymmetric. It is also of importance for a number
of issues of the physics of the landscape and eternal inflation. In this note,
we distinguish a variety of cases. In all of them the decay is slow. For a flat
space theory decaying to a deep AdS vacuum, the leading behavior of the decay
amplitude, if a thin wall approximation is valid, is (where the phase of is defined in the
text) for , and zero otherwise. Metastable supersymmetry
breaking generally yields parametrically more rapid decays. For nearly
supersymmetric decays, we will see that it is necessary to compute subleading
terms in the exponential to extraordinarily high accuracy before one can
meaningfully discuss the prefactor.Comment: 19 page
Drogodependencias: XX Curso de Actualización para Postgraduados en Farmacia
El consumo de drogas es un fenómeno multicausal en el que incide una serie de factores del ámbito personal, familiar, social, y cultural.
En los últimos años, asistimos a cambios tanto en la oferta de drogas como en los patrones de consumo. Así, mientras en los años 80 y primeros 90 la droga emblemática era la heroína, hoy en día su consumo se ha estabilizado, e incluso ha disminuido. Las nuevas formas de estar en sociedad afectan a grupos de jóvenes aceptablemente integrados en su medio familiar y social. A día de hoy, debe considerarse el consumo de otras drogas, fundamentalmente las llamadas drogas de síntesis, y la adopción de nuevos patrones en el consumo de algunas ya establecidas, como es el alcohol.
En este marco se está haciendo frente al fenómeno del consumo de drogas desde diferentes perspectivas que se extienden desde la investigación científica hasta la prevención, la reducción de daños y
la asistencia al drogodependiente.
Entre las estrategias del nuevo Plan Nacional Sobre Drogas (PND) destaca la de normalizar las redes asistenciales a drogodependientes,
integrándolas de forma coordinada en los sistemas públicos de salud y sistemas sociales. Se pretende que los diferentes
recursos que formen parte del denominado sistema de asistencia e integración social de drogodependientes se caractericen por su profesionalización, interdisciplinariedad y fácil accesibilidad.
En este sentido, hay que destacar la participación activa de algunos profesionales farmacéuticos en distintos programas de actuación, prevención y reducción de daños producidos por drogas. Por otra parte, se están realizando esfuerzos importantes en la investigación básica y clínica dirigidos a desentrañar los mecanismos que operan en la adicción a drogas.
Los capítulos que componen este texto son el resultado del trabajo coordinado entre investigadores, docentes, farmacéuticos comunitarios, psicólogos, psiquiatras y otros profesionales implicados en la problemática de las drogodependencias. Su lectura permitirá conocer la actual situación respecto al consumo de drogas, los mecanismos
neurobiológicos implicados en la drogadicción, la farmacología y la toxicología de las diferentes drogas, los riesgos asociados a su consumo, y los recursos disponibles que atienden a la población drogodependiente.
Agradecemos la participación de los profesionales que asisten desde diferentes ámbitos a las personas afectadas directa o indirectamente por los problemas derivados del consumo de drogas, que ha hecho posible integrar aspectos básicos y prácticos de un tema tan complejo como es el de las drogodependencias
Out of equilibrium: understanding cosmological evolution to lower-entropy states
Despite the importance of the Second Law of Thermodynamics, it is not
absolute. Statistical mechanics implies that, given sufficient time, systems
near equilibrium will spontaneously fluctuate into lower-entropy states,
locally reversing the thermodynamic arrow of time. We study the time
development of such fluctuations, especially the very large fluctuations
relevant to cosmology. Under fairly general assumptions, the most likely
history of a fluctuation out of equilibrium is simply the CPT conjugate of the
most likely way a system relaxes back to equilibrium. We use this idea to
elucidate the spacetime structure of various fluctuations in (stable and
metastable) de Sitter space and thermal anti-de Sitter space.Comment: 27 pages, 11 figure
Selenium tolerance, accumulation, localization and speciation in a Cardamine hyperaccumulator and a non-hyperaccumulator
Cardamine violifolia (family Brassicaceae) is the first discovered selenium hyperaccumulator from the genus Cardamine with unique properties in terms of selenium accumulation, i.e., high abundance of selenolanthionine. In our study, a fully comprehensive experiment was conducted with the comparison of a non-hyperaccumulator Cardamine species, Cardamine pratensis, covering growth characteristics, chlorophyll fluorescence, spatial selenium/sulfur distribution patterns through elemental analyses (synchrotron-based X-Ray Fluorescence and ICP-OES) and speciation data through selenium K-edge micro X-ray absorption near-edge structure analysis (μXANES) and strong cation exchange (SCX)-ICP-MS. The results revealed remarkable differences in contrast to other selenium hyperaccumulators as neither Cardamine species showed evidence of growth stimulation by selenium. Also, selenite uptake was not inhibited by phosphate for either of the Cardamine species. Sulfate inhibited selenate uptake, but the two Cardamine species did not show any difference in this respect. However, μXRF derived speciation maps and selenium/sulfur uptake characteristics provided results that are similar to other formerly reported hyperaccumulator and non-hyperaccumulator Brassicaceae species. μXANES showed organic selenium, "C-Se-C", in seedlings of both species and also in mature C. violifolia plants. In contrast, selenate-supplied mature C. pratensis contained approximately half "C-Se-C" and half selenate. SCX-ICP-MS data showed evidence of the lack of selenocystine in any of the Cardamine plant extracts. Thus, C. violifolia shows clear selenium-related physiological and biochemical differences compared to C. pratensis and other selenium hyperaccumulators
Agnesi Weighting for the Measure Problem of Cosmology
The measure problem of cosmology is how to assign normalized probabilities to
observations in a universe so large that it may have many observations
occurring at many different spacetime locations. I have previously shown how
the Boltzmann brain problem (that observations arising from thermal or quantum
fluctuations may dominate over ordinary observations if the universe expands
sufficiently and/or lasts long enough) may be ameliorated by volume averaging,
but that still leaves problems if the universe lasts too long. Here a solution
is proposed for that residual problem by a simple weighting factor 1/(1+t^2) to
make the time integral convergent. The resulting Agnesi measure appears to
avoid problems other measures may have with vacua of zero or negative
cosmological constant.Comment: 26 pages, LaTeX; discussion is added of how Agnesi weighting appears
better than other recent measure
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
An artificial fish swarm filter-based Method for constrained global optimization
Ana Maria A.C. Rocha, M. Fernanda P. Costa and Edite M.G.P. Fernandes, An Artificial Fish Swarm Filter-Based Method for Constrained Global Optimization, B. Murgante, O. Gervasi, S. Mirsa, N. Nedjah, A.M. Rocha, D. Taniar, B. Apduhan (Eds.), Lecture Notes in Computer Science, Part III, LNCS 7335, pp. 57–71, Springer, Heidelberg, 2012.An artificial fish swarm algorithm based on a filter methodology
for trial solutions acceptance is analyzed for general constrained
global optimization problems. The new method uses the filter set concept
to accept, at each iteration, a population of trial solutions whenever
they improve constraint violation or objective function, relative to the
current solutions. The preliminary numerical experiments with a wellknown
benchmark set of engineering design problems show the effectiveness
of the proposed method.Fundação para a Ciência e a Tecnologia (FCT
The Born Rule Dies
The Born rule may be stated mathematically as the rule that probabilities in
quantum theory are expectation values of a complete orthogonal set of
projection operators. This rule works for single laboratory settings in which
the observer can distinguish all the different possible outcomes corresponding
to the projection operators. However, theories of inflation suggest that the
universe may be so large that any laboratory, no matter how precisely it is
defined by its internal state, may exist in a large number of very distantly
separated copies throughout the vast universe. In this case, no observer within
the universe can distinguish all possible outcomes for all copies of the
laboratory. Then normalized probabilities for the local outcomes that can be
locally distinguished cannot be given by the expectation values of any
projection operators. Thus the Born rule dies and must be replaced by another
rule for observational probabilities in cosmology. The freedom of what this new
rule is to be is the measure problem in cosmology. A particular volume-averaged
form is proposed.Comment: LaTeX, 16 pages, typos in Eqs. (4.3) and (6.2) correcte
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
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