6,188 research outputs found
Nonequilibrium Fluctuation Relation for Sheared Micellar Gel in a Jammed State
We show that the shear rate at a fixed shear stress in a micellar gel in a
jammed state exhibits large fluctuations, showing positive and negative values,
with the mean shear rate being positive. The resulting probability distribution
functions (PDF's) of the global power flux to the system vary from Gaussian to
non-Gaussian, depending on the driving stress and in all cases show similar
symmetry properties as predicted by Gallavotti-Cohen steady state fluctuation
relation. The fluctuation relation allows us to determine an effective
temperature related to the structural constraints of the jammed state. We have
measured the stress dependence of the effective temperature. Further,
experiments reveal that the effective temperature and the standard deviation of
the shear rate fluctuations increase with the decrease of the system size.Comment: 5 pages 3 figure
Universal canonical black hole entropy
Non-rotating black holes in three and four dimensions are shown to possess a
canonical entropy obeying the Bekenstein-Hawking area law together with a
leading correction (for large horizon areas) given by the logarithm of the area
with a {\it universal} finite negative coefficient, provided one assumes that
the quantum black hole mass spectrum has a power law relation with the quantum
area spectrum found in Non-perturbative Canonical Quantum General Relativity.
The thermal instability associated with asymptotically flat black holes appears
in the appropriate domain for the index characterising this power law relation,
where the canonical entropy (free energy) is seen to turn complex.Comment: Revtex, 5 pages, no figures. Typos corrected and a footnote and some
references adde
Magnetic behavior of single crystalline HoPdSi
The magnetic behavior of single-crystal HoPdSi, crystallizing in an
AlB-derived hexagonal structure, is investigated by magnetic susceptibility
() and electrical resistivity () measurements along two directions.
There is no dramatic anisotropy in the high temperature Curie-Weiss parameter
or in the and isothermal magnetization data, though there is a
noticeable anisotropy in the magnitude of between two perpendicular
orientations. The degree of anisotropy is overall less prominent than in the Gd
(which is an S-state ion!) and Tb analogues. A point of emphasis is that this
compound undergoes long range magnetic ordering below 8 K as in the case of
analogous Gd and Dy compounds. Considering this fact for these compounds with
well-localised f-orbital, the spin glass freezing noted for isomorphous U
compounds in the recent literature could be attributed to the role of the
f-ligand hybridization, rather than just Pd-Si disorder.Comment: Physical Review B, in pres
Non-collinear Magnetic Order in the Double Perovskites: Double Exchange on a Geometrically Frustrated Lattice
Double perovskites of the form A_2BB'O_6 usually involve a transition metal
ion, B, with a large magnetic moment, and a non magnetic ion B'. While many
double perovskites are ferromagnetic, studies on the underlying model reveal
the possibility of antiferromagnetic phases as well driven by electron
delocalisation. In this paper we present a comprehensive study of the magnetic
ground state and T_c scales of the minimal double perovskite model in three
dimensions using a combination of spin-fermion Monte Carlo and variational
calculations. In contrast to two dimensions, where the effective magnetic
lattice is bipartite, three dimensions involves a geometrically frustrated face
centered cubic (FCC) lattice. This promotes non-collinear spiral states and
`flux' like phases in addition to collinear anti-ferromagnetic order. We map
out the possible magnetic phases for varying electron density, `level
separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour)
hopping t'.Comment: 15 pages pdflatex + 19 figs, revision: removed redundant comment
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