Quantifying metastatic inefficiency:rare genotypes versus rare dynamics

abstract: We introduce and solve a ‘null model’ of stochastic metastatic colonization. The model is described by a single parameter θ: the ratio of the rate of cell division to the rate of cell death for a disseminated tumour cell in a given secondary tissue environment. We are primarily interested in the case in which colonizing cells are poorly adapted for proliferation in the local tissue environment, so that cell death is more likely than cell division, i.e. θ 1), i.e. the statistics show a duality mapping (1 − θ) → (θ − 1). We conclude our analysis with a study of heterogeneity in the fitness of colonising cells, and describe a phase diagram delineating parameter regions in which metastatic colonization is dominated either by low or high fitness cells, showing that both are plausible given our current knowledge of physiological conditions in human cancer

Evaluation of Target Date Funds

Target date funds are an emerging class of investment products, designed for retirement savings. The project considered methodologies for ranking such funds

La transición política: una revisión crítica

La situación económica, social y política del país, con la que se inicia el sexenio de Miguel de la Madrid, ha generado un proceso de transformaciones, tanto en el comportamiento y estructura del gobierno como en las relaciones de éste con los diversos sectores de la sociedad. El denominador común de dichos cambios es el abandono paulatino de los rasgos característicos del Estado populista y de los compromisos sociales derivados de la Revolución Mexicana. Mientras en el plano económico, el llamado proyecto de transformaciones estructurales es aplicado, en el nivel de la política, la pretendida modernización no ha significado aún un cambio sustantivo en las reglas del juego político

The Stationary Phase Method for a Wave Packet in a Semiconductor Layered System. The applicability of the method

Using the formal analysis made by Bohm in his book, {\em "Quantum theory"}, Dover Publications Inc. New York (1979), to calculate approximately the phase time for a transmitted and the reflected wave packets through a potential barrier, we calculate the phase time for a semiconductor system formed by different mesoscopic layers. The transmitted and the reflected wave packets are analyzed and the applicability of this procedure, based on the stationary phase of a wave packet, is considered in different conditions. For the applicability of the stationary phase method an expression is obtained in the case of the transmitted wave depending only on the derivatives of the phase, up to third order. This condition indicates whether the parameters of the system allow to define the wave packet by its leading term. The case of a multiple barrier systems is shown as an illustration of the results. This formalism includes the use of the Transfer Matrix to describe the central stratum, whether it is formed by one layer (the single barrier case), or two barriers and an inner well (the DBRT system), but one can assume that this stratum can be comprise of any number or any kind of semiconductor layers.Comment: 15 pages, 4 figures although figure 4 has 5 graph

1968 y la teoría política de Norberto Bobbio

En este artículo, el autor explora la evolución del pensamiento y la reflexión política de Norberto Bobbio poniendo énfasis en los nexos entre filosofía y ciencia política que llevaron a este pensador a construir su conocida teoría de la democracia. Asimismo, el artículo aborda el análisis de Bobbio respecto a los cambios en el pensamiento comunista -referencia fundamental en su pensamiento político- al tiempo que matiza las características particulares del 68 italiano, sus determinantes e interconexiones con la política y la vida civil, destacando el papel de este filósofo de la política como promotor de la crítica política y de la duda sistemática y la manera como las puso en práctica en aquel 1968 italiano. Finalmente, el autor rescata algunos de los elementos centrales de la teoría política de Bobbio, como la distinción teórica entre derechas e izquierdas, la crisis del comunismo histórico, las relaciones del individuo con el poder político y la problematización de la democracia.In this article, the author explores the evolution of Norberto Bobbio's thinking and political considerations emphasizing the existing ties between philosophy and political science that led this thinker to build his well-known theory of democracy. Also, the article undertakes Bobbio's analysis regarding the changes in communist thinking -a fundamental reference in his political thought- and at the same time he looks into the distinctive characteristics of the Italian '68, its determinants and interconnections with politics and civilian life, highlighting the role of this politics philosopher as a promoter of political critique and systematic doubt and the way he put them in practice during that Italian 1968. Finally, the author rescues some of the central elements of Bobbio's political theory such as the theoretical distinction between right and left, the crisis of historical communism, the relations between the individual and political power and the problematization of democracy

Tolerancia: Voltaire entre nosotros

Este ensayo constituye un ejercicio de interpretación acerca de las influencias intelectuales y políticas que confluyen en la concepción volteriana sobre la tolerancia. La tesis fundamental que aquí se examina es que para Voltaire la tolerancia no es una relación de aceptación condescendiente del "error", sino que su idea de tolerancia tiende a identificarse principalmente con la libertad de conciencia, elemento constitutivo de las libertades democráticas. Considerado un autor fundamental en el progreso de la idea de tolerancia, Voltaire continúa siendo un punto de referencia en el análisis de los problemas de la convivencia social y política en el contexto del pluralismo y la diversidad que caracteriza a las sociedades de fin de siglo.This essay represents a true excercise in interpretation with regard to the intellectual and |X)litical influences that come together in Voltaire's notion of tolerance. The main theses here examined is that for Voltaire tolerance is not a relation based on a condescending acceptance of "error". On the contrary, his notion of tolerance is related, mainly, to freedom of conscience, a basic trait of democratic liberties. As a fundamental writer in the development of the notion of tolerance, Voltaire continues to be considered as a necessary reference in the analysis of the problem of social and political coexistence in the context of pluralism and diversity within societal frameworks at the end of our century