Model-independent extraction of two-photon effects in elastic electron–proton scattering

We address the discrepancy between the Rosenbluth and polarization transfer data for the electromagnetic form factors of the nucleon. Assuming that the effect of two-photon corrections on the polarization transfer data is negligible, we obtain a model-independent estimate of the two-photon correction Δ2γ${\Delta }^{2\gamma }$. We analyze the polarization transfer data and the cross section data separately using dispersion relations. A central value as well as an error estimate for Δ2γ${\Delta }^{2\gamma }$ is then obtained from a comparison of the two analyses. The resulting values for Δ2γ${\Delta }^{2\gamma }$ are in good agreement with direct calculations available in the literature.     

Maxwell equations in complex form of Majorana–Oppenheimer,solutions with cylindric symmetry in Riemann <Emphasis Type=Italic>S</Emphasis><Subscript>3</Subscript> and Lobachevsky <Emphasis Type=Italic>H</Emphasis><Subscript>3</Subscript> spaces

Complex formalism of Riemann–Silberstein–Majorana–Oppenheimer in Maxwell electrodynamics is extended to the case of arbitrary pseudo-Riemannian space-time in accordance with the tetrad recipe of Tetrode–Weyl–Fock–Ivanenko. In this approach, the Maxwell equations are solved exactly on the background of static cosmological Einstein model, parameterized by special cylindrical coordinates and realized as a Riemann space of constant positive curvature. A discrete frequency spectrum for electromagnetic modes depending on the curvature radius of space and three parameters is found, and corresponding basis electromagnetic solutions have been constructed explicitly. In the case of elliptical model a part of the constructed solutions should be rejected by continuity considerations. Similar treatment is given for the Maxwell equations in hyperbolic Lobachevsky model, the complete basis of electromagnetic solutions in corresponding cylindrical coordinates has been constructed as well, no quantization of frequencies of electromagnetic modes arises.     

Maximally Disjoint Solutions of the Set Covering Problem

This paper is concerned with finding two solutions of a set covering problem that have a minimum number of variables in common. We show that this problem is NP-complete, even in the case where we are only interested in completely disjoint solutions. We describe three heuristic methods based on the standard greedy algorithm for set covering problems. Two of these algorithms find the solutions sequentially, while the third finds them simultaneously. A local search method for reducing the overlap of the two given solutions is then described. This method involves the solution of a reduced set covering problem. Finally, extensive computational tests are given demonstrating the nature of these algorithms. These tests are carried out both on randomly generated problems and on problems found in the literature.     

Reverse-engineering country risk ratings: a combinatorial non-recursive model

The central objective of this paper is to develop a transparent, consistent, self-contained, and stable country risk rating model, closely approximating the country risk ratings provided by Standard and Poor’s (S&P). The model should be non-recursive, i.e., it should not rely on the previous years’ S&P ratings. The set of variables selected here includes not only economic-financial but also political variables. We propose a new model based on the novel combinatorial-logical technique of Logical Analysis of Data (which derives a new rating system only from the qualitative information representing pairwise comparisons of country riskiness). We also develop a method allowing to derive a rating system that has any desired level of granularity. The accuracy of the proposed model’s predictions, measured by its correlation coefficients with the S&P ratings, and confirmed by k-folding cross-validation, exceeds 95%. The stability of the constructed non-recursive model is shown in three ways: by the correlation of the predictions with those of other agencies (Moody’s and The Institutional Investor), by predicting 1999 ratings using the non-recursive model derived from the 1998 dataset applied to the 1999 data, and by successfully predicting the ratings of several previously non-rated countries. This study provides new insights on the importance of variables by supporting the necessity of including in the analysis, in addition to economic variables, also political variables (in particular “political stability”), and by identifying “financial depth and efficiency” as a new critical factor in assessing country risk.     

DC Power Supply Protection Against Load Short Circuits

Journal of Communications Technology and Electronics - The protection of DC power circuits against short circuits in the load is considered and a possibility of preventing emergencies is...     

Steiner degree distance indices: Chemical applicability and bounds

The k-center Steiner degree distance ( SDD _k(G) ) has recently been introduced as a natural extension of the degree distance DD(G). In this paper, the prediction potential of SDD _k(G) is discussed. Then, the relation between this and some other well-known distance-based indices of trees is derived to explain its prediction potential. Finally, the lower and upper bounds of SDD _k(G) in terms of some other graph invariants are presented.     

Adaptive delivery of video data over wireless and mobile environments

We present an architecture for the adaptable delivery of video data under variable connection characteristics and into devices of variable capabilities. The main application of the proposed architecture is video delivery in wireless and mobile environments. The architecture is based on the Universal Multimedia Access concept and the MPEG‐7 standard. Based on the network and the mobile device, as well as constraints imposed by user preferences and the multimedia content, video is delivered through a careful application of a combination of off‐line and on‐line reductions to the video stream. We present our architecture and describe an implementation of a system based on the architecture. We present basic performance evaluation results to quantify the merit of our approach. Copyright © 2002 John Wiley & Sons, Ltd.