Strong exciton binding in quantum structures through remote dielectric confinement

We propose a new type of hybrid systems formed by conventional semiconductor nanostructures with the addition of remote insulating layers, where the electron-hole interaction is enhanced by combining quantum and dielectric confinement over different length scales. Due to the polarization charges induced by the dielectric mismatch at the semiconductor/insulator interfaces, we show that the exciton binding energy can be more than doubled. For conventional III-V quantum wires such remote dielectric confinement allows exciton binding at room temperature.Comment: 4 pages, 3 PostScript figures embedded, best printed in color. Uses RevTex, multicol, and psfig styles. To appear in Phys. Rev. Let

Source extraction and photometry for the far-infrared and sub-millimeter continuum in the presence of complex backgrounds

(Abridged) We present a new method for detecting and measuring compact sources in conditions of intense, and highly variable, fore/background. While all most commonly used packages carry out the source detection over the signal image, our proposed method builds from the measured image a "curvature" image by double-differentiation in four different directions. In this way point-like as well as resolved, yet relatively compact, objects are easily revealed while the slower varying fore/background is greatly diminished. Candidate sources are then identified by looking for pixels where the curvature exceeds, in absolute terms, a given threshold; the methodology easily allows us to pinpoint breakpoints in the source brightness profile and then derive reliable guesses for the sources extent. Identified peaks are fit with 2D elliptical Gaussians plus an underlying planar inclined plateau, with mild constraints on size and orientation. Mutually contaminating sources are fit with multiple Gaussians simultaneously using flexible constraints. We ran our method on simulated large-scale fields with 1000 sources of different peak flux overlaid on a realistic realization of diffuse background. We find detection rates in excess of 90% for sources with peak fluxes above the 3-sigma signal noise limit; for about 80% of the sources the recovered peak fluxes are within 30% of their input values.Comment: Accepted on A&

Corruption and Positive Selection in Privatization

We consider the supply of a public good based on a publicly-owned facility. The Government has a choice between provision in-house and privatizing the facility and then outsourcing the production. In particular, we focus on corruption in the decision to privatize and on its effect on social welfare when there is asymmetric information on the public and private manager's efficiency. Our analysis shows that a corrupt Government, that chooses to privatize only in exchange for a bribe, makes a positive selection on the private firm's efficiency and, thus, may raise expected social welfare above what an honest Government could get.Corruption, Privatization, Private vs. public provision.

The luminosity function of cluster galaxies. II. Data reduction procedures applied to the cluster Abell 496

We initiated a large project aimed to estimate the Luminosity Function of galaxies in clusters and to evaluate its relation to cluster morphology. With this paper we deem necessary to outline the general procedures of the data reduction and details of the data analysis. The cluster sample includes the brightest southern ROSAT all-sky survey clusters with z < 0.1. These have been observed in three colours g, r, i, and mapped up to a few core radii using a mosaic of CCD frames. E/S0 galaxies in the cluster core are singled out both by morphology (for the brightest galaxies), and by colour. The details of the data reduction procedure are illustrated via the analysis of the cluster Abell 496, which has been used as a pilot cluster for the whole program. The related photometric catalogue consists of 2355 objects. The limiting magnitudes (the reference Surface Brightness is given in parenthesis) in the various colours are respectively g(25.5) = 24.14, r(25.5) = 24.46, i(25.0) = 23.75$. These correspond to the limiting absolute magnitudes -12.28, -11.96 and -12.67 (H_0=50 km/sec/Mpc).Comment: 17 pages, 19 ps figures, aa.cl

G-quartet biomolecular nanowires

We present a first-principle investigation of quadruple helix nanowires, consisting of stacked planar hydrogen-bonded guanine tetramers. Our results show that long wires form and are stable in potassium-rich conditions. We present their electronic bandstructure and discuss the interpretation in terms of effective wide-bandgap semiconductors. The microscopic structural and electronic properties of the guanine quadruple helices make them suitable candidates for molecular nanoelectronics.Comment: 7 pages, 3 figures, to be published in Applied Physics Letters (2002

Measures of Prices and Price Competitiveness in International Trade in Manufactured Goods

The purpose of this paper is to present, and to explain the construction of, a set of price indexes relating to international trade in manufactured goods. These include: 1. Indexes of export prices for the U.S., Germany, and Japan, based on their weights, and indexes of competitors' prices for each of those countries based on the sane set of weights; 2. Indexes of domestic prices for the U. S., Germany, and Japan based on export weights; 3. Indexes for developed country exports of manufactures based on weights of developed country exports of manufactures to developing countries and of total developed country exports of manufactures, and indexes for exports of the U.S., Germany, and Japan on the sane sets of weights. The indexes for developed country exports make use of a method for estimating missing prices that takes account not only of contemporaneous price changes in the same country within the sane community groups, but also of price changes for the particular commodity in other countries. Comparisons are made between movements of domestic and export prices and between price indexes based on weights of early and late base years. In addition, an attempt is made to correct the price indexes for changes in the quality of some manufactured goods not usually taken account of in measures of export or import prices.

High-finesse optical quantum gates for electron spins in artificial molecules

A doped semiconductor double-quantum-dot molecule is proposed as a qubit realization. The quantum information is encoded in the electron spin, thus benefiting from the long relevant decoherence times; the enhanced flexibility of the molecular structure allows to map the spin degrees of freedom onto the orbital ones and vice versa, and opens the possibility for high-finesse (conditional and unconditional) quantum gates by means of stimulated Raman adiabatic passage.Comment: To appear in Phys. Rev. Let