Signatures of superconducting gap inhomogeneities in optical properties

Scanning tunneling spectroscopy applied to the high-$T_{c}$ cuprates has revealed significant spatial inhomogeneity on the nanoscale. Regions on the order of a coherence length in size show variations of the magnitude of the superconducting gap of order $\pm20$ or more. An important unresolved question is whether or not these variations are also present in the bulk, and how they influence superconducting properties. As many theories and data analyses for high-$T_{c}$ superconductivity assume spatial homogeneity of the gap magnitude, this is a pressing question. We consider the far-infrared optical conductivity and evaluate, within an effective medium approximation, what signatures of spatial variations in gap magnitude are present in various optical quantities. In addition to the case of d-wave superconductivity, relevant to the high-$T_c$ cuprates, we have also considered s-wave gap symmetry in order to provide expected signatures of inhomogeneities for superconductors in general. While signatures of gap inhomogeneities can be strongly manifested in s-wave superconductors, we find that the far-infrared optical conductivity in d-wave is robust against such inhomogeneity.Comment: 8 pages, 7 figure

Community detection in networks with positive and negative links

Detecting communities in complex networks accurately is a prime challenge, preceding further analyses of network characteristics and dynamics. Until now, community detection took into account only positively valued links, while many actual networks also feature negative links. We extend an existing Potts model to incorporate negative links as well, resulting in a method similar to the clustering of signed graphs, as dealt with in social balance theory, but more general. To illustrate our method, we applied it to a network of international alliances and disputes. Using data from 1993--2001, it turns out that the world can be divided into six power blocs similar to Huntington's civilizations, with some notable exceptions.Comment: 7 pages, 2 figures. Revised versio

Plasmon tunability in metallodielectric metamaterials

The dielectric properties of metamaterials consisting of periodically arranged metallic nanoparticles of spherical shape are calculated by rigorously solving Maxwell's equations. Effective dielectric functions are obtained by comparing the reflectivity of planar surfaces limiting these materials with Fresnel's formulas for equivalent homogeneous media, showing mixing and splitting of individual-particle modes due to inter-particle interaction. Detailed results for simple cubic and fcc crystals of aluminum spheres in vacuum, silver spheres in vacuum, and silver spheres in a silicon matrix are presented. The filling fraction of the metal f is shown to determine the position of the plasmon modes of these metamaterials. Significant deviations are observed with respect to Maxwell-Garnett effective medium theory for large f, and multiple plasmons are predicted to exist in contrast to Maxwell-Garnett theory.Comment: 6 pages, 4 figure

Vanishing Loss Effect on the Effective ac Conductivity behavior for 2D Composite Metal-Dielectric Films At The Percolation Threshold

We study the imaginary part of the effective $ac$ conductivity as well as its distribution probability for vanishing losses in 2D composites. This investigation showed that the effective medium theory provides only informations about the average conductivity, while its fluctuations which correspond to the field energy in this limit are neglected by this theory.Comment: 6 pages, 2 figures, submitted to Phys.Rev.

Biocomplexity: A pluralist research strategy is necessary for a mechanistic explanation of the "live" state

The biological sciences study (bio) complex living systems. Research directed at the mechanistic explanation of the "live" state truly requires a pluralist research program, i.e. BioComplexity research. The program should apply multiple intra-level and inter-level theories and methodologies. We substantiate this thesis with analysis of BioComplexity: metabolic and modular control analysis of metabolic pathways, emergence of osculations, and the analysis of the functioning of glycolysis

Localization and Absorption of Light in 2D Composite Metal-Dielectric Films at the Percolation Threshold

We study in this paper the localization of light and the dielectric properties of thin metal-dielectric composites at the percolation threshold and around a resonant frequency where the conductivities of the two components are of the same order. In particular, the effect of the loss in metallic components are examined. To this end, such systems are modelized as random $L-C$ networks, and the local field distribution as well as the effective conductivity are determined by using two different methods for comparison: an exact resolution of Kirchoff equations, and a real space renormalization group method. The latter method is found to give the general behavior of the effective conductivity but fails to determine the local field distribution. It is also found that the localization still persists for vanishing losses. This result seems to be in agreement with the anomalous absorption observed experimentally for such systems.Comment: 14 page latex, 3 ps figures. submitte

Modularity in signaling systems

Modularity is a property by which the behavior of a system does not change upon interconnection. It is crucial for understanding the behavior of a complex system from the behavior of the composing subsystems. Whether modularity holds in biology is an intriguing and largely debated question. In this paper, we discuss this question taking a control system theory view and focusing on signaling systems. In particular, we argue that, despite signaling systems being constituted of structural modules, such as covalent modification cycles, modularity does not hold in general. As in any engineering system, impedance-like effects, called retroactivity, appear at interconnections and alter the behavior of connected modules. We further argue that while signaling systems have evolved sophisticated ways to counter-act retroactivity and enforce modularity, retroactivity may also be exploited to finely control the information processing of signaling pathways. Testable predictions and experimental evidence are discussed with their implications

Models for Enhanced Absorption in Inhomogeneous Superconductors

We discuss the low-frequency absorption arising from quenched inhomogeneity in the superfluid density rho_s of a model superconductor. Such inhomogeneities may arise in a high-T_c superconductor from a wide variety of sources, including quenched random disorder and static charge density waves such as stripes. Using standard classical methods for treating randomly inhomogeneous media, we show that both mechanisms produce additional absorption at finite frequencies. For a two-fluid model with weak mean-square fluctuations <(d rho_s)^2 > in rho_s and a frequency-independent quasiparticle conductivity, the extra absorption has oscillator strength proportional to the quantity <(d rho_s)^2>/rho_s, as observed in some experiments. Similar behavior is found in a two-fluid model with anticorrelated fluctuations in the superfluid and normal fluid densities. The extra absorption typically occurs as a Lorentzian centered at zero frequency. We present simple model calculations for this extra absorption under conditions of both weak and strong fluctuations. The relation between our results and other model calculations is briefly discussed

Association Between the 1291-C/G Polymorphism in the Adrenergic alpha-2a Receptor and the Metabolic Syndrome

The prevalence of the metabolic syndrome is increased in patients with schizophrenia compared with the general population. The strong interindividual differences in susceptibility to developing the metabolic syndrome suggests that the genetic makeup is a modulating factor. Part of the genetic puzzle can possibly be explained by variations in the gene coding for the adrenergic alpha-2a receptor (ADRA2A) because this receptor plays an important role in lipolysis. Three studies have found an association between the alpha-2a 1291-C/G polymorphism and antipsychotic induced weight gain, with conflicting results between whites and Asians. No studies have been published investigating the association between the 1291-C/G polymorphism and the metabolic syndrome. The primary objective of this cross-sectional study was to investigate the association between the ADRA2A 1291-C/G polymorphism and the metabolic syndrome in 470 patients using antipsychotic drugs. There was no significant association between carriership of the variant 1291-G allele and prevalence of the metabolic syndrome (odds ratio, 0.73; 95% confidence interval, 0.49Y1.15). Exploratory analysis showed an association between carriership of the variant 1291-G allele and a reduced prevalence of the metabolic syndrome in patients not currently using antipsychotics (odds ratio, 0.05; 95% confidence interval, 0.003Y0.97; P = 0.048). In conclusion, this study shows that the ADRA2A 1291-C/G polymorphism does not seem to be a strong predictor for long-term occurrence of the metabolic syndrome in antipsychotic using patients. Studies investigating this association using a prospective, or retrospective, design, as well as studies investigating this association in a nonpsychiatric population, are warranted