2,259 research outputs found
Comment on "Breakdown of the Internet under Intentional Attack"
We obtain the exact position of the percolation threshold in intentionally
damaged scale-free networks.Comment: 1 page, to appear in Phys. Rev. Let
Kondo model for the "0.7 anomaly" in transport through a quantum point contact
Experiments on quantum point contacts have highlighted an anomalous
conductance plateau at , with features suggestive of the Kondo
effect. Here we present an Anderson model for transport through a point contact
which we analyze in the Kondo limit. Hybridization to the band increases
abruptly with energy but decreases with valence, so that the background
conductance and the Kondo temperature are dominated by different valence
transitions. This accounts for the high residual conductance above . A
spin-polarized current is predicted for Zeeman splitting .Comment: 4 page
Sandpile avalanche dynamics on scale-free networks
Avalanche dynamics is an indispensable feature of complex systems. Here we
study the self-organized critical dynamics of avalanches on scale-free networks
with degree exponent through the Bak-Tang-Wiesenfeld (BTW) sandpile
model. The threshold height of a node is set as with
, where is the degree of node . Using the branching
process approach, we obtain the avalanche size and the duration distribution of
sand toppling, which follow power-laws with exponents and ,
respectively. They are given as and
for , 3/2 and 2 for
, respectively. The power-law distributions are modified by a
logarithmic correction at .Comment: 8 pages, elsart styl
Stability of the Black Hole Horizon and the Landau Ghost
The stability of the black hole horizon is demanded by both cosmic censorship
and the generalized second law of thermodynamics. We test the consistency of
these principles by attempting to exceed the black hole extremality condition
in various process in which a U(1) charge is added to a nearly extreme
Reissner--Nordstr\"om black hole charged with a {\it different\/} type of U(1)
charge. For an infalling spherical charged shell the attempt is foiled by the
self--Coulomb repulsion of the shell. For an infalling classical charge it
fails because the required classical charge radius exceeds the size of the
black hole. For a quantum charge the horizon is saved because in order to avoid
the Landau ghost, the effective coupling constant cannot be large enough to
accomplish the removal.Comment: 12 pages, RevTe
Local moment formation in quantum point contacts
Spin-density-functional theory of quantum point contacts (QPCs) reveals the
formation of a local moment with a net of one electron spin in the vicinity of
the point contact - supporting the recent report of a Kondo effect in a QPC.
The hybridization of the local moment to the leads decreases as the QPC becomes
longer, while the onsite Coulomb-interaction energy remains almost constant.Comment: 10 pages, 3 figures, accepted for publication in Physical Review
Letter
Linear Response Calculations of Spin Fluctuations
A variational formulation of the time--dependent linear response based on the
Sternheimer method is developed in order to make practical ab initio
calculations of dynamical spin susceptibilities of solids. Using gradient
density functional and a muffin-tin-orbital representation, the efficiency of
the approach is demonstrated by applications to selected magnetic and strongly
paramagnetic metals. The results are found to be consistent with experiment and
are compared with previous theoretical calculations.Comment: 11 pages, RevTex; 3 Figures, postscript, high-resolution printing
(~1200dpi) is desire
Chern-Simons matrix model: coherent states and relation to Laughlin wavefunctions
Using a coherent state representation we derive many-body probability
distributions and wavefunctions for the Chern-Simons matrix model proposed by
Polychronakos and compare them to the Laughlin ones. We analyze two different
coherent state representations, corresponding to different choices for electron
coordinate bases. In both cases we find that the resulting probability
distributions do not quite agree with the Laughlin ones. There is agreement on
the long distance behavior, but the short distance behavior is different.Comment: 15 pages, LaTeX; one reference added, abstract and section 5
expanded, typos correcte
Ising Model on Networks with an Arbitrary Distribution of Connections
We find the exact critical temperature of the nearest-neighbor
ferromagnetic Ising model on an `equilibrium' random graph with an arbitrary
degree distribution . We observe an anomalous behavior of the
magnetization, magnetic susceptibility and specific heat, when is
fat-tailed, or, loosely speaking, when the fourth moment of the distribution
diverges in infinite networks. When the second moment becomes divergent,
approaches infinity, the phase transition is of infinite order, and size effect
is anomalously strong.Comment: 5 page
Survival of verapamil-poisoned rats treated with triiodothyronine.
Life-threatening toxicity due to calcium channel blocker ingestion is commonly encountered by emergency medicine physicians and toxicologists. Despite a vast array of research on its treatment, results have proven inconsistent. The goal of this study is to evaluate potential vasopressor effects of triiodothyronine (T3) in rats poisoned with verapamil. Following anesthesia and intubation, ten Sprague-Dawley rats were given intravenous verapamil infusion of 10 mg/kg/h. This dose was titrated until a mean arterial pressure (MAP) of 50-55 mmHg was achieved and maintained for a period of at least 5 min. The verapamil infusion was then maintained at that rate. Five rats were randomized to receive a T3 bolus of 0.4 mcg/kg preceding an infusion of 1.5 mcg/kg/day which was doubled every 2 min until any of the following endpoints: systolic blood pressure of 100 mmHg, an elapsed time of 60 min, or death. The other five received an equal volume of normal saline solution. The primary outcome measure was survival with secondary outcomes of MAP and heart rate. The T3 group did have a slightly longer, yet not statistically significant, average time to cessation of electrical activity-30.0 +/- 14.4 min versus 23.8 +/- 9.5 min in the placebo group. Average MAP decreased nearly identically in the two groups. Heart rates were not reliable indicators of toxicity in this rat model as there was little decrease until immediately prior to death in most animals. Despite significant variability in toxicity among individual animals, no statistically significant difference in survival time, heart rate, or MAP was found between groups treated with T3 and those receiving saline
Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains
We study the quasiparticle band structure of isolated, infinite HF and HCl
bent (zigzag) chains and examine the effect of the crystal field on the energy
levels of the constituent monomers. The chains are one of the simplest but
realistic models of the corresponding three-dimensional crystalline solids. To
describe the isolated monomers and the chains, we set out from the Hartree-Fock
approximation, harnessing the advanced Green's function methods "local
molecular orbital algebraic diagrammatic construction" (ADC) scheme and "local
crystal orbital ADC" (CO-ADC) in a strict second order approximation, ADC(2,2)
and CO-ADC(2,2), respectively, to account for electron correlations. The
configuration space of the periodic correlation calculations is found to
converge rapidly only requiring nearest-neighbor contributions to be regarded.
Although electron correlations cause a pronounced shift of the quasiparticle
band structure of the chains with respect to the Hartree-Fock result, the
bandwidth essentially remains unaltered in contrast to, e.g., covalently bound
compounds.Comment: 11 pages, 6 figures, 6 tables, RevTeX4, corrected typoe
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