70,224 research outputs found
Physical constraints on interacting dark energy models
Physical limits on the equation-of-state (EoS) parameter of a dark energy
component non-minimally coupled with the dark matter field are examined in
light of the second law of thermodynamics and the positiveness of entropy. Such
constraints are combined with observational data sets of type Ia supernovae,
baryon acoustic oscillations and the angular acoustic scale of the cosmic
microwave background to impose restrictions on the behaviour of the dark
matter/dark energy interaction. Considering two EoS parameterisations of the
type , we derive a general expression for the evolution
of the dark energy density and show that the combination of thermodynamic
limits and observational data provide tight bounds on the parameter
space.Comment: 7 pages, 4 figures. Accepted for publication in European Physical
Journal
Vortex state microwave resistivity in Tl-2212 thin films
We present measurements of the field induced changes in the 47 GHz complex
resistivity, , in TlBaCaCuO
(TBCCO) thin films with 105 K, prepared on CeO buffered
sapphire substrates. At low fields (10 mT) a very small irreversible
feature is present, suggesting a little role of intergranular phenomena. Above
that level exhibits a superlinear dependence with the
field, as opposed to the expected (at high frequencies) quasilinear behaviour.
We observe a crossover between predominantly imaginary to predominantly real
(dissipative) response with increasing temperature and/or field. In addition,
we find the clear scaling property , where the scaling field maps closely the melting
field measured in single crystals. We discuss our microwave results in terms of
loss of flux lines rigidity.Comment: 8 pages, 3 figures, proceedings of 9th HTSHFF, accepted for
publication on J. Supercon
Metallic Continuum Quantum Ferromagnets at Finite Temperature
We study via renormalization group (RG) and large N methods the problem of
continuum SU(N) quantum Heisenberg ferromagnets (QHF) coupled to gapless
electrons. We establish the phase diagram of the dissipative problem and
investigate the changes in the Curie temperature, magnetization, and magnetic
correlation length due to dissipation and both thermal and quantum
fluctuations. We show that the interplay between the topological term (Berry's
phase) and dissipation leads to non-trivial effects for the finite temperature
critical behavior.Comment: Corrected typos, new discussion of T=0 results, to appear in
Europhys. Let
"The Keynesian Roots of Stock-flow Consistent Macroeconomic Models: Peering Over the Edge of the Short Period"
This paper argues that institutionally rich stock-flow consistent models—that is, models in which economic agents are identified with the main social categories/institutional sectors of actual capitalist economies, the short period behavior of these agents is thoroughly described, and the "period by period" balance sheet dynamics implied by the latter is consistently modeled—are (1) perfectly compatible with John Maynard Keynes's theoretical views, (2) the ideal tool for rigorous post-Keynesian analyses of the medium run, and (3) therefore crucial to the consolidation of the broad post-Keynesian research program.
"Revisiting (and Connecting) Marglin-Bhaduri and Minsky--An SFC Look at Financialization and Profit-led Growth"
Many heterodox strands of thought share both a concern with the study of different phases or growth regimes in the history of capitalism and the use of formal short-run models as an analytical tool. This text suggests that (1) this strategy is potentially misleading; (2) that the stock-flow consistent (SFC) approach, while providing a general framework that may facilitate the dialogue among those currents, is particularly well suited to all those who think that macroeconomic models may illuminate historical quests; and (3) that the main intuitions may be conveyed through the "benchmark" Post Keynesian SFC model presented by Dos Santos and Zezza (2008), dispensing with the complex computer simulations that are normally employed by SFC authors.
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