Encryption methods using formal power series rings

Recently there has been a great deal of work on noncommutative algebraic cryptography. This involves the use of noncommutative algebraic objects as the platforms for encryption systems. Most of this work, such as the Anshel-Anshel-Goldfeld scheme, the Ko-Lee scheme and the Baumslag-Fine-Xu Modular group scheme use nonabelian groups as the basic algebraic object. Some of these encryption methods have been successful and some have been broken. It has been suggested that at this point further pure group theoretic research, with an eye towards cryptographic applications, is necessary.In the present study we attempt to extend the class of noncommutative algebraic objects to be used in cryptography. In particular we explore several different methods to use a formal power series ring R && x1; :::; xn && in noncommuting variables x1; :::; xn as a base to develop cryptosystems. Although R can be any ring we have in mind formal power series rings over the rationals Q. We use in particular a result of Magnus that a finitely generated free group F has a faithful representation in a quotient of the formal power series ring in noncommuting variables.

Co-movements between US and UK stock prices: the roles of macroeconomic information and time-series varying conditional correlations

This paper provides evidence on the sources of co-movement in monthly US and UK stock price movements by investigating the role of macroeconomic and financial variables in a bivariate system with time-varying conditional correlations. Crosscountry communality in response is uncovered, with changes in the US Federal Funds rate, UK bond yields and oil prices having similar negative effects in both markets. Other variables also play a role, especially for the UK market. These effects do not, however, explain the marked increase in cross-market correlations observed from around 2000, which we attribute to time variation in the correlations of shocks to these markets. A regime-switching smooth transition model captures this time variation well and shows the correlations increase dramatically around 1999-2000. JEL classifications: C32, C51, G15 Keywords: international stock returns, DCC-GARCH model, smooth transition conditional correlation GARCH model, model evaluation.

Symmetry for a Dirichlet-Neumann problem arising in water waves

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Series enlazadas de algunos agregados económicos nacionales y regionales, 1955-2007 Versión 2.1

I construct "homogeneous" series of GVA at current and constant prices, employment and population for the Spain and its regions covering the period 1955-2007. The series are obtained by linking the Regional Accounts of the National Statistical Institute with the series constructed by Julio Alcaide and his team for the BBVA Foundation. The "switching point" at which this last source stops being used as a reference to construct the linked series is determined using a procedure that allows me to estimate which of the two competing series would produce an estimator with the lowest MSE when it is used as dependent variable in a regression on an arbitrary independent variable. To the extent that it is possible, the difference between the two series found at the point of linkage is distributed between the initial levels of the older series and its subsequent growth using external estimates of the relevant variables at the beginning of the sample period.

The non-linear Dirichlet problem in Hadamard manifolds

We prove existence theorems for the Dirichlet problem for hypersurfaces of constant special Lagrangian curvature in Hadamard manifolds. The first results are obtained using the continuity method and approximation and then refined using two iterations of the Perron method. The a-priori estimates used in the continuity method are valid in any ambient manifold.

Locally univalent functions, VMOA, and the Dirichlet space

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Inversion of analytic characteristic functions and infinite convolutions of exponential and Laplace densities

This paper shows that certain quotients of entire functions are characteristic functions. Under some conditions, we provide expressions for the densities of such characteristic functions which turn out to be generalized Dirichlet series which in turn can be expressed as an infinite linear combination of exponential or Laplace densities. We apply these results to several examples.

A mixed splicing procedure for economic time series

This note develops a flexible methodology for splicing economic time series that avoids the extreme assumptions implicit in the procedures most commonly used in the literature. It allows the user to split the required correction to the older of the series being linked between its levels and growth rates on the basis what he knows or conjectures about the persistence of the factors that account for the discrepancy between the two series that emerges at their linking point. The time profile of the correction is derived from the assumption that the error in the older series reflects the inadequate coverage of emerging sectors or activities that grow faster than the aggregate.

Series enlazadas de empleo asalariado y rentas del trabajo regionales (RegDat versión 2.2)

I construct "homogeneous" series of salaried employment, employee compensation and total labor income for Spain and its regions covering the period 1955-2008. I also estimate labor's share in regional and national GVA and construct an indicator of the average cost of labor including both employees and non-salaried workers.

Series anuales de algunos agregados económicos y demográficos regionales, 1955-2009 (RegDat versión 2.3)

En una serie de trabajos anteriores he construido series largas de diversos agregados económicos regionales enlazando las distintas bases de la Contabilidad Regional de España entre sí y con las series históricas elaboradas por la Fundación BBVA. Puesto que esta última fuente sólo ofrece datos para años impares, las series enlazadas heredan esta característica desde 1955 hasta 1989. En la presente nota se construyen series anuales completas de las variables de interés utilizando un sencillo procedimiento de interpolación que incorpora la información anual disponible a nivel nacional para estas variables.

Wiener type theorems for Jacobi series with nonnegative coefficients

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CO2 emissions and economic activity: heterogeneity across countries and non stationary series

This paper explores the homogeneity of the functional form, the parameters, and the turning point, when appropriate, of the relationship between CO2 emissions and economic activity for 31 countries (28 OECD, Brazil, China, and India) during the period 1950 to 2006 using cointegration analysis. With a sample highly overlapped over time between countries, the result reveals that the homogeneity across countries is rejected, both in functional form and in the parameters of long term relationship. This confirms the relevance of considering the heterogeneity in exploring the relationship between air pollution and economic activity to avoid spurious parameter estimates and infer a wrong behavior of the functional form, which could lead to induce that the relationship is reversed when in fact it is direct.

Series largas de algunos agregados demográficos regionales, 1950-2009

El presente trabajo resume los resultados de la primera fase de un proyecto cuyo objetivo es el de ofrecer series homogéneas de los principales agregados económicos y demográficos de las regiones españolas para el período desde 1950 hasta nuestros días. En él se recopilan, extienden o construyen series de movimientos naturales de población, población de derecho y residente habitual, saldos migratorios netos y estructura por edades de la población.

Eisenstein series for principal congruence subgroups of GL(2,Fq[T])

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Aproximación a la traducción de la terminología médica de series dobladas al español: el caso de "Urgencias"

A les darreres dècades, l'anglès mèdic col·loquial s'ha barrejat amb el llenguatge no especialitzat a dramatitzacions audiovisuals. Aquest argot pertany actualment a un sistema conceptual lligat a una cultura i constitueix l'oralitat prefabricada destinada a caracteritzar els personatges de ficció. Aquesta investigació verifica tant les tècniques de traducció emprades per traslladar la terminologia mèdica de la sèrie ER (Urgències) en el doblatge de l'anglès a l'espanyol, com el nivell d'adequació de la versió en la llengua meta. Acadèmicament, aquest treball està motivat per la manca d'estudis empírics de la traducció per el doblatge de la terminologia mèdica de les series televisives