The authors acknowledge the support of the Consejo Superior de Investigaciónand the Facultad de Ciencias Físicas of the Universidad Nacional Mayor de SanMarcos, and of our Consejo Nacional de Ciencia y Tecnología, CONCYTEC, Perú. We are grateful to the personnel of our Mössbauer and Soils Laboratories for helpwith the equipment.

Proechimys pattoni da Silva, 1998 is one of the 3 small-bodied species of Proechimys and its geographic range is only known in western Brazil and eastern and southern Peru. However, based on morphological and molecular analyses, we report P. pattoni from the lowland forest of Bolivia (Pando: Rio Madre de Dios, near San Rosa). This is the first report of P. pattoni in Bolivia and extends its distributional range 315 km to the southeast in the Amazon biogeographic region of Bolivia, representing the southeastern most record. Furthermore, we document the karyotype (2n = 40 / FN = 56) and morphological variation in diagnostic characters. © Sánchez-Vendizú et al.

En el presente trabajo se reporta un estudio preliminar sobre la composición mineralógica y la identificación de las fases portadoras de hierro presentes en los peloides de una laguna ubicada en la provincia de Cañete, Lima-Perú. Las técnicas experimentales empleadas en el desarrollo del presente trabajo fueron la difracción de rayos X, espectroscopia Mössbauer por transmisión y fluorescencia de rayos X. Así mismo, se realizaron análisis físico-químicos midiendo el grado de acidez de las muestras. Los resultados obtenidos muestran que en los peloides analizados las fases portadoras del hierro están asociadas a la pirita y al sulfato ferroso. También se detectó la presencia de arcilla tipo bentonita.

In this work a strategy for the estimation of absorption and scattering coefficients in one-dimensional participating media is presented. Media are considered with the absorption coefficient in the range [0.1 to 1.0] and the scattering coefficient between [0.1-1.0]. The direct problem was solved with the discrete ordinates and finite difference methods. In order to solve the inverse problem the following strategy consists of (a) find the absorption coefficient considering the scattering coefficient with an approximate value. 0.01, (b) find the scattering coefficient value using the absorption coefficient estimated in (a). The error function is defined as the difference between the measured value by the detector and the calculated by the direct problem. The algorithm used for the solution is to minimize the Bregman distance subject to the error function. Bregman distance was constructed w...