130 research outputs found
Hydrodynamic Models for Heavy-Ion Collisions, and beyond
A generic property of a first-order phase transition in equilibrium, and in
the limit of large entropy per unit of conserved charge, is the smallness of
the isentropic speed of sound in the ``mixed phase''. A specific prediction is
that this should lead to a non-isotropic momentum distribution of nucleons in
the reaction plane (for energies around 40 AGeV in our model calculation). On
the other hand, we show that from present effective theories for low-energy QCD
one does not expect the thermal transition rate between various states of the
effective potential to be much larger than the expansion rate, questioning the
applicability of the idealized Maxwell/Gibbs construction. Experimental data
could soon provide essential information on the dynamics of the phase
transition.Comment: 10 Pages, 4 Figures. Presented at 241st WE-Heraeus Seminar: Symposium
on Fundamental Issues in Elementary Matter: In Honor and Memory of Michael
Danos, Bad Honnef, Germany, 25-29 Sep 200
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Using reanalysis data to quantify extreme wind power generation statistics: a 33 year case study in Great Britain
With a rapidly increasing fraction of electricity generation being sourced from wind, extreme wind power generation events such as prolonged periods of low (or high) generation and ramps in generation, are a growing concern for the efficient and secure operation of national power systems. As extreme events occur infrequently, long and reliable meteorological records are required to accurately estimate their characteristics.
Recent publications have begun to investigate the use of global meteorological âreanalysisâ data sets for power system applications, many of which focus on long-term average statistics such as monthly-mean generation. Here we demonstrate that reanalysis data can also be used to estimate the frequency of relatively short-lived extreme events (including ramping on sub-daily time scales). Verification against 328 surface observation stations across the United Kingdom suggests that near-surface wind variability over spatiotemporal scales greater than around 300 km and 6 h can be faithfully reproduced using reanalysis, with no need for costly dynamical downscaling.
A case study is presented in which a state-of-the-art, 33 year reanalysis data set (MERRA, from NASA-GMAO), is used to construct an hourly time series of nationally-aggregated wind power generation in Great Britain (GB), assuming a fixed, modern distribution of wind farms. The resultant generation estimates are highly correlated with recorded data from National Grid in the recent period, both for instantaneous hourly values and for variability over time intervals greater than around 6 h. This 33 year time series is then used to quantify the frequency with which different extreme GB-wide wind power generation events occur, as well as their seasonal and inter-annual variability. Several novel insights into the nature of extreme wind power generation events are described, including (i) that the number of prolonged low or high generation events is well approximated by a Poission-like random process, and (ii) whilst in general there is large seasonal variability, the magnitude of the most extreme ramps is similar in both summer and winter.
An up-to-date version of the GB case study data as well as the underlying model are freely available for download from our website: http://www.met.reading.ac.uk/~energymet/data/Cannon2014/
Topological String Defect Formation During the Chiral Phase Transition
We extend and generalize the seminal work of Brandenberger, Huang and Zhang
on the formation of strings during chiral phase transitions(berger) and discuss
the formation of abelian and non-abelian topological strings during such
transitions in the early Universe and in the high energy heavy-ion collisions.
Chiral symmetry as well as deconfinement are restored in the core of these
defects. Formation of a dense network of string defects is likely to play an
important role in the dynamics following the chiral phase transition. We
speculate that such a network can give rise to non-azimuthal distribution of
transverse energy in heavy-ion collisions.Comment: 10 pages, 4 figures, minor correction
11 beta-hydroxysteroid dehydrogenase type 1 regulates glucocorticoid-induced insulin resistance in skeletal muscle
OBJECTIVE: Glucocorticoid excess is characterized by increased adiposity, skeletal myopathy, and insulin resistance, but the precise molecular mechanisms are unknown. Within skeletal muscle, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts cortisone (11-dehydrocorticosterone in rodents) to active cortisol (corticosterone in rodents). We aimed to determine the mechanisms underpinning glucocorticoid-induced insulin resistance in skeletal muscle and indentify how 11beta-HSD1 inhibitors improve insulin sensitivity. \ud
RESEARCH DESIGN AND METHODS: Rodent and human cell cultures, whole-tissue explants, and animal models were used to determine the impact of glucocorticoids and selective 11beta-HSD1 inhibition upon insulin signaling and action. \ud
RESULTS: Dexamethasone decreased insulin-stimulated glucose uptake, decreased IRS1 mRNA and protein expression, and increased inactivating pSer insulin receptor substrate (IRS)-1. 11beta-HSD1 activity and expression were observed in human and rodent myotubes and muscle explants. Activity was predominantly oxo-reductase, generating active glucocorticoid. A1 (selective 11beta-HSD1 inhibitor) abolished enzyme activity and blocked the increase in pSer IRS1 and reduction in total IRS1 protein after treatment with 11DHC but not corticosterone. In C57Bl6/J mice, the selective 11beta-HSD1 inhibitor, A2, decreased fasting blood glucose levels and improved insulin sensitivity. In KK mice treated with A2, skeletal muscle pSer IRS1 decreased and pThr Akt/PKB increased. In addition, A2 decreased both lipogenic and lipolytic gene expression.\ud
CONCLUSIONS: Prereceptor facilitation of glucocorticoid action via 11beta-HSD1 increases pSer IRS1 and may be crucial in mediating insulin resistance in skeletal muscle. Selective 11beta-HSD1 inhibition decreases pSer IRS1, increases pThr Akt/PKB, and decreases lipogenic and lipolytic gene expression that may represent an important mechanism underpinning their insulin-sensitizing action
Deconfinement in Matrix Models about the Gross--Witten Point
We study the deconfining phase transition in SU(N) gauge theories at nonzero
temperature using a matrix model of Polyakov loops. The most general effective
action, including all terms up to two spatial derivatives, is presented. At
large N, the action is dominated by the loop potential: following Aharony et
al., we show how the Gross--Witten model represents an ultra-critical point in
this potential. Although masses vanish at the Gross--Witten point, the
transition is of first order, as the fundamental loop jumps only halfway to its
perturbative value. Comparing numerical analysis of the N=3 matrix model to
lattice simulations, for three colors the deconfining transition appears to be
near the Gross--Witten point. To see if this persists for N >= 4, we suggest
measuring within a window ~1/N^2 of the transition temperature.Comment: 22 pages, 7 figures; revtex4. A new Fig. 2 illustrates a strongly
first order transition away from the GW point; discussion added to clarify
relation to hep-th/0310285. Conclusions include a discussion of recent
lattice data for N>3, hep-lat/0411039 and hep-lat/050200
The K/pi ratio from condensed Polyakov loops
We perform a field-theoretical computation of hadron production in large
systems at the QCD confinement phase transition associated with restoration of
the Z(3) global symmetry. This occurs from the decay of a condensate for the
Polyakov loop. From the effective potential for the Polyakov loop, its mass
just below the confinement temperature T_c is in between the vacuum masses of
the pion and that of the kaon. Therefore, due to phase-space restrictions the
number of produced kaons is roughly an order of magnitude smaller than that of
produced pions, in agreement with recent results from collisions of gold ions
at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate
is characterized by a (spatial) correlation scale of 1/m_\ell ~ 1/2 fm. For
systems of deconfined matter of about that size, the free energy may not be
dominated by a condensate for the Polyakov loop, and so the process of
hadronization may be qualitatively different as compared to large systems. In
that vein, experimental data on hadron abundance ratios, for example K/pi, in
high-multiplicity pp events at high energies should be very interesting.Comment: 7 pages, 4 figures; discussion of the two-point function of Polyakov
Loops in small versus large systems adde
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