Semiconductor quantum tubes: dielectric modulation and excitonic response

We study theoretically the optical properties of quantum tubes, one-dimensional semiconductor nanostructures where electrons and holes are confined to a cylindrical shell. In these structures, which bridge between 2D and 1D systems, the electron-hole interaction may be modulated by a dielectric substance outside the quantum tube and possibly inside its core. We use the exact Green's function for the appropriate dielectric configuration and exact diagonalization of the electron-hole interaction within an effective mass description to predict the evolution of the exciton binding energy and oscillator strength. Contrary to the homogeneous case, in dielectrically modulated tubes the exciton binding is a function of the tube diameter and can be tuned to a large extent by structure design and proper choice of the dielectric media.Comment: 9 pages, 6 figures, in print for Phys. Rev.

Rankin--Eisenstein classes and explicit reciprocity laws

We construct three-variable $p$-adic families of Galois cohomology classes attached to Rankin convolutions of modular forms, and prove an explicit reciprocity law relating these classes to critical values of L-functions. As a consequence, we prove finiteness results for the Selmer group of an elliptic curve twisted by a 2-dimensional odd irreducible Artin representation when the associated $L$-value does not vanish.Comment: Final version, to appear in Cambridge J Math; small correction to acknowlegement

On Cosmological Perturbations of Quasidilaton

A theory of the quasidilaton is an extension of massive gravity by a scalar field, nonlinearly realizing a certain new global symmetry of the Lagrangian. It has been shown that unlike pure massive gravity, this theory does admit homogeneous and isotropic spatially flat solutions. Among the latter, selfaccelerated solutions attract a special attention. Previous studies of perturbations, performed in the decoupling limit, revealed one healthy scalar mode, while the second relevant scalar was not captured in that limit. Here we study full cosmological perturbations above the simplest selfaccelerated background. We show that the fluctuations of a mixed state of the quasidilaton and the helicity-0 graviton necessarily have a negative kinetic term at short distances, making this background unphysical. In addition, these cosmologies exhibit an order one sensitivity to higher dimensional terms suppressed by an energy scale that is parametrically higher than the strong coupling scale of the quasidilaton effective theory: such terms include Galileons, Goldstone-like selfinteractions and derivatives of the quasidilaton coupled to curvature, none of which introduce extra Ostrogradsky states. As one consequence, cosmology at the Hubble distances for this particular class of solutions depends on an unknown extension of the quasidilaton below its strong coupling distance scale. We note that non-FRW solutions that are similar to those of pure massive gravity should not necessarily suffer from these pathologies.Comment: 15 page

Embedding Defeasible Logic into Logic Programming

Defeasible reasoning is a simple but efficient approach to nonmonotonic reasoning that has recently attracted considerable interest and that has found various applications. Defeasible logic and its variants are an important family of defeasible reasoning methods. So far no relationship has been established between defeasible logic and mainstream nonmonotonic reasoning approaches. In this paper we establish close links to known semantics of logic programs. In particular, we give a translation of a defeasible theory D into a meta-program P(D). We show that under a condition of decisiveness, the defeasible consequences of D correspond exactly to the sceptical conclusions of P(D) under the stable model semantics. Without decisiveness, the result holds only in one direction (all defeasible consequences of D are included in all stable models of P(D)). If we wish a complete embedding for the general case, we need to use the Kunen semantics of P(D), instead.Comment: To appear in Theory and Practice of Logic Programmin

Optimal encoding of interval timing in expert percussionists

We measured temporal reproduction in expert drummers, string-musicians and non-musical subjects. While duration reproduction of the controls showed a characteristic regression to the mean, drummers responded veridically. This behavior is well explained by a model that combines optimally the sensory estimate for duration (more precise in drummers) with a prior, given by the average of the past few trials. These results highlight the efficiency and adaptability of sensori-motor mechanisms estimating temporal duration

A flexible framework for defeasible logics

Logics for knowledge representation suffer from over-specialization: while each logic may provide an ideal representation formalism for some problems, it is less than optimal for others. A solution to this problem is to choose from several logics and, when necessary, combine the representations. In general, such an approach results in a very difficult problem of combination. However, if we can choose the logics from a uniform framework then the problem of combining them is greatly simplified. In this paper, we develop such a framework for defeasible logics. It supports all defeasible logics that satisfy a strong negation principle. We use logic meta-programs as the basis for the framework.Comment: Proceedings of 8th International Workshop on Non-Monotonic Reasoning, April 9-11, 2000, Breckenridge, Colorad

The influence of anesthesia and fluid-structure interaction on simulated shear stress patterns in the carotid bifurcation of mice

Background: Low and oscillatory wall shear stresses (WSS) near aortic bifurcations have been linked to the onset of atherosclerosis. In previous work, we calculated detailed WSS patterns in the carotid bifurcation of mice using a Fluid-structure interaction (FSI) approach. We subsequently fed the animals a high-fat diet and linked the results of the FSI simulations to those of atherosclerotic plaque location on a within-subject basis. However, these simulations were based on boundary conditions measured under anesthesia, while active mice might experience different hemodynamics. Moreover, the FSI technique for mouse-specific simulations is both time- and labor-intensive, and might be replaced by simpler and easier Computational Fluid Dynamics (CFD) simulations. The goal of the current work was (i) to compare WSS patterns based on anesthesia conditions to those representing active resting and exercising conditions; and (ii) to compare WSS patterns based on FSI simulations to those based on steady-state and transient CFD simulations. Methods: For each of the 3 computational techniques (steady state CFD, transient CFD, FSI) we performed 5 simulations: 1 for anesthesia, 2 for conscious resting conditions and 2 more for conscious active conditions. The inflow, pressure and heart rate were scaled according to representative in vivo measurements obtained from literature. Results: When normalized by the maximal shear stress value, shear stress patterns were similar for the 3 computational techniques. For all activity levels, steady state CFD led to an overestimation of WSS values, while FSI simulations yielded a clear increase in WSS reversal at the outer side of the sinus of the external carotid artery that was not visible in transient CFD-simulations. Furthermore, the FSI simulations in the highest locomotor activity state showed a flow recirculation zone in the external carotid artery that was not present under anesthesia. This recirculation went hand in hand with locally increased WSS reversal. Conclusions: Our data show that FSI simulations are not necessary to obtain normalized WSS patterns, but indispensable to assess the oscillatory behavior of the WSS in mice. Flow recirculation and WSS reversal at the external carotid artery may occur during high locomotor activity while they are not present under anesthesia. These phenomena might thus influence plaque formation to a larger extent than what was previously assumed. (C) 2016 Elsevier Ltd. All rights reserved

Mechanics of nonlinear biomembranes: application to ophthalmology

Changes in the mechanics of the lens capsule of the eye arising from alterations of its native configuration can lead to undesirable clinical results. One example is the surgical introduction of a hole into the lens capsule and subsequent removal of the cloudy lens during cataract surgery. The adverse effect is secondary cataract on the posterior lens capsule, brought about by a sudden proliferation of lens epithelial cells in the region. Understanding the biomechanics of the anterior lens capsule is necessary in order to model its behavior under various physiological conditions and predict its response to alterations and perturbations such as those during cataract surgery. Such knowledge will help in the improvement of techniques during cataract surgery, and in the design of artificial intraocular lens. In this study we present, for the first time, results that demonstrate that the anterior lens capsule exhibits non-homogeneity and regionally varying anisotropy. We also compute stresses in the lens capsule due to normal loading conditions and procedures such as a capsulorhexis