2,385 research outputs found
Criticality for charged black branes
We show that the inclusion of higher curvature terms in the gravitational
action can lead to phase transitions and critical behaviour for charged black
branes. The higher curvature terms considered here belong to the recently
constructed generalized quasi-topological class [ArXiv: 1703.01631], which
possess a number of interesting properties, such as being ghost-free on
constant curvature backgrounds and non-trivial in four dimensions. We show that
critical behaviour is a generic feature of the black branes in all dimensions
, and contextualize the results with a review of the properties of
black branes in Lovelock and quasi-topological gravity, where critical
behaviour is not possible. These results may have interesting implications for
the CFTs dual to this class of theories.Comment: 31 pages, 6 figures. v2: minor typos corrected, references added;
updated to match published versio
The metabolism of the Antartic crytoendolithic microbiota
The carbon metabolism of the cryptoendolithic microbiota in sandstones from the Ross Desert region of Antarctica was studied in situ and in vitro. Organic and inorganic compounds were metabolized by the microbiota, with bicarbonate being metabolized maximally in the light. There was a linear response of photosynthesis to light up to 200 to 300 micromole photons/sq m/s. The community photosynthetic response to temperature was a minimum at -5 C, two optima at +5 and +15 C and a maximum at +35 C. Photosynthetic metabolism occurred maximally in the presence of liquid water, but could occur in an environment of water vapor. Biomass of the cryptoendolithic microbiota was measured as the amount of lipid phosphate present. The in situ biomass ranged from 1.92 to 3.26 g carbon/sq m of rock and 2 orders of magnitude less than epilithic lichen microbiota from Antarctica in a location 7 degrees more north in latitude. With these data, it was possible to calculate primary production and carbon turnover in this simple microbiota. Production values ranged from 0.108 to 4.41 mg carbon/sq m/yr, while carbon turnover values ranged from 576 to 23,520 years. These values are the lowest and longest yet recorded for any ecosystem on Earth. If life did evolve on Mars to the level of prokaryotes or primitive eukaryotes, the possibility that the organisms retreated, to the protection of the inside of the rock so that metabolism could continue during planetary cooling, cannot be overlooked
Water as a constraint to the use of coal for California
The contraints for using water to cool coal-fired power plants are discussed
Reentrant phase transitions and van der Waals behaviour for hairy black holes
We study the extended phase space thermodynamics for hairy AdS black hole
solutions to Einstein-Maxwell- theory conformally coupled to a scalar
field in five dimensions. We find these solutions to exhibit van der Waals
behaviour in both the charged/uncharged cases, and reentrant phase transitions
in the charged case. This is the first example of reentrant phase transitions
in a five dimensional gravitational system which does not include higher
curvature corrections.Comment: 11 pages, 5 figures, REVTeX 4-
Thermalon mediated phase transitions in Gauss-Bonnet gravity
Thermalons can mediate phase transitions between different vacua in higher
curvature gravity, potentially changing the asymptotic structure of the
spacetime. Treating the cosmological constant as a dynamical parameter, we
study these phase transitions in the context of extended thermodynamic phase
space. We find that in addition to the AdS to dS phase transitions previously
studied, thermal AdS space can undergo a phase transition to an asymptotically
flat black hole geometry. In the context of AdS to AdS transitions, we comment
on the similarities and differences between thermalon transitions and the
Hawking-Page transition.Comment: 20 pages, 11 figures; reference added, corrected to match published
versio
Hairy black holes in cubic quasi-topological gravity
We construct a class of five dimensional black hole solutions to cubic
quasi-topological gravity with conformal scalar hair and study their
thermodynamics. We find these black holes provide the second example of black
hole -lines: a line of second order (continuous) phase transitions,
akin to the fluid/superfluid transition of He. Examples of isolated
critical points are found for spherical black holes, marking the first in the
literature to date. We also find various novel and interesting phase
structures, including an isolated critical point occurring in conjunction with
a double reentrant phase transition. The AdS vacua of the theory are studied,
finding ghost-free configurations where the scalar field takes on a non-zero
constant value, in notable contrast to the five dimensional Lovelock case.Comment: 29 pages, 12 figure
Hot-wired media
Papua New Guinea's two daily newspapers are leading the way in the response of the South Pacific news media to the challenge of cyberspace. Both websites came of age during the Sandline mercenary crisis, underscoring the value of content on the Internet. 
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