7,886 research outputs found
A model of the magnetospheric temperature distribution
Turbulent heat transfer and heat conductivity effects on magnetospheric temperature distributio
Superconducting Puddles and "Colossal'' Effects in Underdoped Cuprates
Phenomenological models for the antiferromagnetic (AF) vs. d-wave
superconductivity competition in cuprates are studied using conventional Monte
Carlo techniques. The analysis suggests that cuprates may show a variety of
different behaviors in the very underdoped regime: local coexistence or
first-order transitions among the competing orders, stripes, or glassy states
with nanoscale superconducting (SC) puddles. The transition from AF to SC does
not seem universal. In particular, the glassy state leads to the possibility of
"colossal'' effects in some cuprates, analog of those in manganites. Under
suitable conditions, non-superconducting Cu-oxides could rapidly become
superconducting by the influence of weak perturbations that align the randomly
oriented phases of the SC puddles in the mixed state. Consequences of these
ideas for thin-film and photoemission experiments are discussed.Comment: RevTeX 4, revised expanded version, 8 pages, 8 figure
Phase Fluctuations in Strongly Coupled -Wave Superconductors
We present a numerically exact solution for the BCS Hamiltonian at any
temperature, including the degrees of freedom associated with classical phase,
as well as amplitude, fluctuations via a Monte Carlo (MC) integration. This
allows for an investigation over the whole range of couplings: from weak
attraction, as in the well-known BCS limit, to the mainly unexplored
strong-coupling regime of pronounced phase fluctuations. In the latter, for the
first time two characteristic temperatures and , associated with
short- and long-range ordering, respectively, can easily be identified in a
mean-field-motivated Hamiltonian. at the same time corresponds to the
opening of a gap in the excitation spectrum. Besides introducing a novel
procedure to study strongly coupled d-wave superconductors, our results
indicate that classical phase fluctuations are not sufficient to explain the
pseudo-gap features of high-temperature superconductors (HTS).Comment: 5 pages, 3 figure
Colossal Effects in Transition Metal Oxides Caused by Intrinsic Inhomogeneities
The influence of quenched disorder on the competition between ordered states
separated by a first-order transition is investigated. A phase diagram with
features resembling quantum-critical behavior is observed, even using classical
models. The low-temperature paramagnetic regime consists of coexisting ordered
clusters, with randomly oriented order parameters. Extended to manganites, this
state is argued to have a colossal magnetoresistance effect. A scale T* for
cluster formation is discussed. This is the analog of the Griffiths
temperature, but for the case of two competing orders, producing a strong
susceptibility to external fields. Cuprates may have similar features,
compatible with the large proximity effect of the very underdoped regime.Comment: 4 pages, 4 figure
Amorphous thin film growth: theory compared with experiment
Experimental results on amorphous ZrAlCu thin film growth and the dynamics of
the surface morphology as predicted from a minimal nonlinear stochastic
deposition equation are analysed and compared. Key points of this study are (i)
an estimation procedure for coefficients entering into the growth equation and
(ii) a detailed analysis and interpretation of the time evolution of the
correlation length and the surface roughness. The results corroborate the
usefulness of the deposition equation as a tool for studying amorphous growth
processes.Comment: 7 pages including 5 figure
Untangling the Conceptual Isssues Raised in Reydon and Scholz’s Critique of Organizational Ecology and Darwinian Populations
Reydon and Scholz raise doubts about the Darwinian status of organizational ecology by arguing that Darwinian principles are not applicable to organizational populations. Although their critique of organizational ecology’s typological essentialism is correct, they go on to reject the Darwinian status of organizational populations. This paper claims that the distinction between replicators and interactors, raised in modern philosophy of biology but not discussed by Reydon and Scholz, points the way forward for organizational ecologists. It is possible to conceptualise evolving Darwinian populations providing the inheritance mechanism is appropriately specified. By this approach, adaptation and selection are no longer dichotomised, and the evolutionary significance of knowledge transmission is highlightedPeer reviewe
Unusual Non-Fermi Liquid Behavior of CeLaNiGe Analyzed in a Single Impurity Anderson Model with Crystal Field Effects
CeNiGe exhibits unusual non-Fermi liquid behavior with the largest
ever recorded value of the electronic specific heat
JKmol without showing any evidence of magnetic order. Specific
heat measurements show that the logarithmic increase of the Sommerfeld
coefficient flattens off below 200 mK. In marked contrast, the local
susceptibility levels off well above 200 mK and already becomes
constant below 1 K. Furthermore, the entropy reaches 2ln2 below 20 K
corresponding to a four level system. An analysis of and was
performed in terms of an single impurity Anderson model with
additional crystal electric field (CEF) splitting. Numerical renormalization
group calculations point to a possible consistent description of the different
low temperature scales in and stemming from the
interplay of Kondo effect and crystal field splitting.Comment: 2 pages, 2 figure
The Bak-Sneppen Model on Scale-Free Networks
We investigate by numerical simulations and analytical calculations the
Bak-Sneppen model for biological evolution in scale-free networks. By using
large scale numerical simulations, we study the avalanche size distribution and
the activity time behavior at nodes with different connectivities. We argue the
absence of a critical barrier and its associated critical behavior for infinite
size systems. These findings are supported by a single site mean-field analytic
treatment of the model.Comment: 5 pages and 3 eps figures. Final version appeared in Europhys. Let
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