Markoff-Rosenberger triples in geometric progression

Solutions of the Markoff-Rosenberger equation ax^2+by^2+cz^2 = dxyz such that their coordinates belong to the ring of integers of a number field and form a geometric progression are studied.Comment: To appear in Acta Mathematica Hungaric

Flujos de capital privado y calificaciones soberanas a mercados emergentes

La desaceleración coyuntural de la economía mundial iniciada en la segunda mitad del año 2000 –impulsada por los aumentos de las tasas de interés internacionales y de los precios del petróleo- se profundizó en el transcurso del presente año, debido, a la pérdida de dinamismo de la economía de los Estados Unidos. Así, los pronósticos apuntaban hacia una desaceleración de la economía global más pronunciada que la anticipada inicialmente. Los atentados terroristas del 11 de septiembre confirmaron esta percepción y propiciaron una mayor aversión al riesgo en los mercados financieros internacionales; aspecto que redundará, inevitablemente, en un menor acceso de las economías emergentes a los mercados voluntarios de capital. Al respecto, las proyecciones del flujo neto de capital privado hacia los países en desarrollo para 2001 y 2002 se ubican muy por debajo de los volúmenes observados durante la mayor parte de la década de los noventa

Very long-range attractive and repulsive forces in Model Colloidal Dispersions

Experiments with polymer latex solutions show the coexistence of order-disorder structures of macroions. Because of the large macroions' sizes, this order-disorder phase coexistence imply the existence of very long-range attractive and repulsive forces, which can not be explained in terms of conventional direct interaction potentials, which are short-range. Here we apply an integral equations theory to a simple model for colloidal dispersions, at finite concentrations, calculate the particles distribution functions and the involved effective forces. We find very long-range attractive and repulsive forces among the like-charged macroions. The distribution functions are in qualitative agreement with experimental results. The origin of these forces are discussed in terms of an energy-entropy balance.Comment: 16 pages, seven figures. ECIS-201

Markoff-Rosenberger triples in arithmetic progression

We study the solutions of the Rosenberg--Markoff equation ax^2+by^2+cz^2 = dxyz (a generalization of the well--known Markoff equation). We specifically focus on looking for solutions in arithmetic progression that lie in the ring of integers of a number field. With the help of previous work by Alvanos and Poulakis, we give a complete decision algorithm, which allows us to prove finiteness results concerning these particular solutions. Finally, some extensive computations are presented regarding two particular cases: the generalized Markoff equation x^2+y^2+z^2 = dxyz over quadratic fields and the classic Markoff equation x^2+y^2+z^2 = 3xyz over an arbitrary number field.Comment: To appear in Journal of Symbolic Computatio

Determinants of Higher Mortality at Six Months in Patients with Hip Fracture: A Retrospective Study

Hip fracture is a pathology with high mortality, but the lack of a universal adaptation of the factors associated with death makes it difficult to predict risk and implement prevention in this group. This study aimed to identify the factors that determine a higher mortality at six months following hip fracture