Bell Labs

About: Bell Labs is a based out in . It is known for research contribution in the topics: Laser & Optical fiber. The organization has 36499 authors who have published 59862 publications receiving 3190823 citations. The organization is also known as: Bell Laboratories & AT&T Bell Laboratories.

Theory of Surface States

Abstract: The properties of metal-to-semiconductor junctions and of free semiconductor surfaces are usually explained on the basis of surface states. The theory of the metal contacts is discussed critically, because strictly speaking localized surface states cannot exist in such junctions. However, it is shown that virtual or resonance surface states can exist which behave for practical purposes in the same way. They are really the tails of the metal wave functions rather than separate states. In the past, the length of this tail has often been ignored. Some estimates of its length are made and its consequences pointed out. A semiquantitative discussion is given of various recent data, including the effect of an oxide layer on barrier height, the variation of barrier height with the metal, the work function of a free surface at high doping, and the effect of a cesium layer on the work function.

Thermally activated dissipation in Bi2.2Sr2Ca0.8Cu2O8+δ

Abstract: A new dissipation behavior is reported in superconducting Bi2.2Sr2Ca0.8Cu2Oa+δfor all temperatures belowTc and all magnetic fields exceeding Hc1. The current-independent electrical resistivity is thermally activated and can be described by an Arrhenius law with a single prefactor and a magnetic-field-and orientation-dependent activation energyU 0 (H,o).This behavior is markedly different from past observations and will be discussed in terms of flux creep and flux flow. This thermally activated behavior implies a finite resistance at all temperatures and all fields exceeding H c1 determined by the activation energy as the only parameter.

Some General Properties of Nonlinear Elements-Part I. General Energy Relations

Abstract: Two independent equations relating the average powers at the different frequencies in nonlinear inductors and capacitors are derived. These equations are a consequence only of the assumption of a single-valued characteristic for the nonlinear element. They are independent of the particular shape of this characteristic, of the power levels at the various frequencies, and of the external circuit in which the nonlinear reactor is connected. These general energy relations give information regarding the gain and stability of nonlinear reactor modulators and demodulators, and consequently of magnetic and dielectric amplifiers, without requirng detailed information about these devices. The utility of these equations is illustrated by discussing the gain and stability of the simplest types of nonlinear reactor modulators and demodulators and harmonic generators. This analysis for nonlinear inductors and capacitors is extended to include the effects of hysteresis in the nonlinear characteristic in the special case where the operating hysteresis loop is no more than double-valued. A similar analysis applied to nonlinear resistors yields two equations relating the reactive powers at the different frequencies, rather than the real powers as above. The interpretation of reactive power under these conditions is not clear.

First-Order Phase Transitions in Superconductors and Smectic- A Liquid Crystals

Abstract: The superconducting phase transition is predicted to be weakly first order, because of effects of the intrinsic fluctuating magnetic field, according to a Wilson-Fisher $\ensuremath{\epsilon}$-expansion analysis, as well as a generalized mean-field calculation appropriate to a type-I superconductor. Similar results hold for the phase transition from a smectic-$A$ to a nematic liquid crystal.

Complexity measures of supervised classification problems

Abstract: We studied a number of measures that characterize the difficulty of a classification problem, focusing on the geometrical complexity of the class boundary. We compared a set of real-world problems to random labelings of points and found that real problems contain structures in this measurement space that are significantly different from the random sets. Distributions of problems in this space show that there exist at least two independent factors affecting a problem's difficulty. We suggest using this space to describe a classifier's domain of competence. This can guide static and dynamic selection of classifiers for specific problems as well as subproblems formed by confinement, projection, and transformations of the feature vectors.