772 research outputs found
Black Holes with Varying Flux: A Numerical Approach
We present a numerical study of type IIB supergravity solutions with varying
Ramond-Ramond flux. We construct solutions that have a regular horizon and
contain nontrivial five- and three-form fluxes. These solutions are
holographically dual to the deconfined phase of confining field theories at
finite temperature. As a calibration of the numerical method we first
numerically reproduce various analytically known solutions including singular
and regular nonextremal D3 branes, the Klebanov-Tseytlin solution and its
singular nonextremal generalization. The horizon of the solutions we construct
is of the precise form of nonextremal D3 branes. In the asymptotic region far
away from the horizon we observe a logarithmic behavior similar to that of the
Klebanov-Tseytlin solution.Comment: 40 pages, 15 figure
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Past and present potential distribution of the Iberian Abies species: A phytogeographic approach using pollen data and species distribution models
This is the accepted version of the following article: Alba-Sánchez, F., López-Sáez, J. A., Pando, B. B.-d., Linares, J. C., Nieto-Lugilde, D. and López-Merino, L. (2010), Past and present potential distribution of the Iberian Abies species: a phytogeographic approach using fossil pollen data and species distribution models. Diversity and Distributions, 16: 214–228, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4642.2010.00636.x/abstract.Aim - Quaternary palaeopalynological records collected throughout the Iberian Peninsula and species distribution models (SDMs) were integrated to gain a better understanding of the historical biogeography of the Iberian Abies species (i.e. Abies pinsapo and Abies alba). We hypothesize that SDMs and Abies palaeorecords are closely correlated, assuming a certain stasis in climatic and topographic ecological niche dimensions. In addition, the modelling results were used to assign the fossil records to A. alba or A. pinsapo, to identify environmental variables affecting their distribution, and to evaluate the ecological segregation between the two taxa.
Location - The Iberian Peninsula.
Methods - For the estimation of past Abies distributions, a hindcasting process was used. Abies pinsapo and A. alba were modelled individually, first calibrating the model for their current distributions in relation to the present climate, and then projecting it into the past—the last glacial maximum (LGM) and the Middle Holocene periods—in relation to palaeoclimate simulations. The resulting models were compared with Iberian-wide fossil pollen records to detect areas of overlap.
Results - The overlap observed between past Abies refugia—inferred from fossil pollen records—and the SDMs helped to construct the Quaternary distribution of the Iberian Abies species. SDMs yielded two well-differentiated potential distributions: A. pinsapo throughout the Baetic mountain Range and A. alba along the Pyrenees and Cantabrian Range. These results propose that the two taxa remained isolated throughout the Quaternary, indicating a significant geographical and ecological segregation. In addition, no significant differences were detected comparing the three projections (present-day, Mid-Holocene and LGM), suggesting a relative climate stasis in the refuge areas during the Quaternary.
Main conclusions - Our results confirm that SDM projections can provide a useful complement to palaeoecological studies, offering a less subjective and spatially explicit hypothesis concerning past geographic patterns of Iberian Abies species. The integration of ecological-niche characteristics from known occurrences of Abies species in conjunction with palaeoecological studies could constitute a suitable tool to define appropriate areas in which to focus proactive conservation strategies.The Andalusian Innovation,
Science, and Industry Regional Ministry and the National Plan of the Spanish Government
Scientific Bounty Among Meteorites Recovered from the Dominion Range, Transantarctic Mountains
The US Antarctic Meteorite Pro-gram has visited the Dominion Range in the Transantarctic Mountains during several different sea-sons, including 1985, 2003, 2008, 2010, 2014 and 2018. Total recovered meteorites from this region is close to 3000. The 1985 (11 samples), 2003 (141 samples), 2008 (521 samples), 2010 (901 samples), 2014 (562 samples) seasons have been fully classified, and 2018 (865 samples) are in the process of being classified and characterized. Given that close to 2200 samples have been classified so far, with more expected in 2020, now is a good time to summarize the state of the collection. Here we describe the significant samples documented from this area, as well as a large meteorite shower that dominates the statistics of the region
Turbulence and Chaos in Anti-de-Sitter Gravity
Due to the AdS/CFT correspondence the question of instability of
Anti-de-Sitter spacetimes sits in the intersection of mathematical and
numerical relativity, string theory, field theory and condensed matter physics.
In this essay we revisit that important question emphasizing the power of
spectral methods and highlighting the effectiveness of standard techniques for
studying nonlinear dynamical systems. In particular we display explicitly how
the problem can be modeled as a system on nonlinearly coupled harmonic
oscillators. We highlight some of the many open questions that stem from this
result and point out that a full understanding will necessarily required the
interdisciplinary cooperation of various communities.Comment: 6 pages, 12 figures. Essay awarded honorable mention in the Gravity
Research Foundation essay competition 201
Tensions and Luscher Terms for (2+1)-dimensional k-strings from Holographic Models
The leading term for the energy of a bound state of k-quarks and k-antiquarks
is proportional to its separation L. These k-string configurations have a
Luscher term associated with their quantum fluctuations which is typically a
1/L correction to the energy. We review the status of tensions and Luscher
terms in the context of lattice gauge theory, Hamiltonian methods, and
gauge/gravity correspondence. Furthermore we explore how different
representations of the k-string manifest themselves in the gauge/gravity
duality. We calculate the Luscher term for a strongly coupled SU(N) gauge
theory in (2+1) dimensions using the gauge/gravity correspondence. Namely, we
compute one-loop corrections to a probe D4-brane embedded in the Cvetic,
Gibbons, Lu, and Pope supergravity background. We investigate quantum
fluctuations of both the bosonic and the fermionic sectors.Comment: 39 pages, reference added, same version to be published in JHE
Black Holes in Cascading Theories: Confinement/Deconfinement Transition and other Thermal Properties
We present numerical evidence for a transition between the Klebanov-Strassler
background and a solution describing a black hole in the class of cascading
solutions in the chirally restored phase. We also present a number of
properties of this solution, including the running of the coupling constant,
the viscosity to entropy ratio and the drag force on a quark moving in this
background.Comment: 34 pages, 7 figures. Version to be published by JHE
Quasi-local evolution of cosmic gravitational clustering in the weakly non-linear regime
We investigate the weakly non-linear evolution of cosmic gravitational
clustering in phase space by looking at the Zel'dovich solution in the discrete
wavelet transform (DWT) representation. We show that if the initial
perturbations are Gaussian, the relation between the evolved DWT mode and the
initial perturbations in the weakly non-linear regime is quasi-local. That is,
the evolved density perturbations are mainly determined by the initial
perturbations localized in the same spatial range. Furthermore, we show that
the evolved mode is monotonically related to the initial perturbed mode. Thus
large (small) perturbed modes statistically correspond to the large (small)
initial perturbed modes. We test this prediction by using QSO Ly
absorption samples. The results show that the weakly non-linear features for
both the transmitted flux and identified forest lines are quasi-localized. The
locality and monotonic properties provide a solid basis for a DWT
scale-by-scale Gaussianization reconstruction algorithm proposed by Feng & Fang
(Feng & Fang, 2000) for data in the weakly non-linear regime. With the
Zel'dovich solution, we find also that the major non-Gaussianity caused by the
weakly non-linear evolution is local scale-scale correlations. Therefore, to
have a precise recovery of the initial Gaussian mass field, it is essential to
remove the scale-scale correlations.Comment: 22 pages, 13 figures. Accepted for publication in the Astrophysical
Journa
Effect of Silicon on Activity Coefficients of P, Bl, CD, SN, and AG in Liquid Fe-Si, and Implications for Differentiation and Core Formation
Cores of differentiated bodies (Earth, Mars, Mercury, Moon, Vesta) contain light elements such as S, C, Si, and O. We have previously measured small effects of Si on metal-silicate partitioning of Ni and Co [1,2], and larger effects for Mo, Ge, Sb, As [2]. The effect of Si on many siderophile elements could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of Bi, Cd, Sn, Ag, and P between metal and silicate melt. The results will be applied to Earth, Mars, Mercury, Moon, and Vesta, for which we have excellent constraints on the mantle Bi, Cd, Sn, Ag, and P concentrations from mantle and/or basalt samples
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