Effective interaction between helical bio-molecules

The effective interaction between two parallel strands of helical bio-molecules, such as deoxyribose nucleic acids (DNA), is calculated using computer simulations of the "primitive" model of electrolytes. In particular we study a simple model for B-DNA incorporating explicitly its charge pattern as a double-helix structure. The effective force and the effective torque exerted onto the molecules depend on the central distance and on the relative orientation. The contributions of nonlinear screening by monovalent counterions to these forces and torques are analyzed and calculated for different salt concentrations. As a result, we find that the sign of the force depends sensitively on the relative orientation. For intermolecular distances smaller than $6\AA$ it can be both attractive and repulsive. Furthermore we report a nonmonotonic behaviour of the effective force for increasing salt concentration. Both features cannot be described within linear screening theories. For large distances, on the other hand, the results agree with linear screening theories provided the charge of the bio-molecules is suitably renormalized.Comment: 18 pages, 18 figures included in text, 100 bibliog

Results of the Search for Strange Quark Matter and Q-balls with the SLIM Experiment

The SLIM experiment at the Chacaltaya high altitude laboratory was sensitive to nuclearites and Q-balls, which could be present in the cosmic radiation as possible Dark Matter components. It was sensitive also to strangelets, i.e. small lumps of Strange Quark Matter predicted at such altitudes by various phenomenological models. The analysis of 427 m^2 of Nuclear Track Detectors exposed for 4.22 years showed no candidate event. New upper limits on the flux of downgoing nuclearites and Q-balls at the 90% C.L. were established. The null result also restricts models for strangelets propagation through the Earth atmosphere.Comment: 14 pages, 11 EPS figure

Primeiro registro de Tomoplagia reimoseri Hendel e Xanthaciura mallochi Aczél (Diptera: Tephritidae) para o Estado de Santa Catarina, Brasil First records of Tomoplagia reimoseri Hendel e Xanthaciura mallochi Aczél (Diptera: Tephritidae) for Santa Catarina state, Brazil

O presente trabalho tem como objetivo levantar as espécies de tefritídeos endófagos associados a capítulos de asteráceas em Chapecó, Santa Catarina. Para tanto, foram efetuadas coletas quinzenais no município de Chapecó, Santa Catarina, durante o período de setembro de 2005 a setembro de 2006, concentradas na primavera e no verão. Os capítulos foram destacados diretamente das plantas, no campo, e acondicionados em sacos plásticos. Este trabalho constitui o primeiro registro de Tomoplagia reimoseri Hendel e Xanthaciura mallochi Aczél coletados em capítulos de Asteraceae no município de Chapecó, elevando para 72 espécies de tefritídeos registradas para o referido Estado.<br>The present research aimed to inventory the species of endophagous tephritids associated to Asteraceae capitula in Chapecó, Santa Catarina. Samples of capitula were collected every two weeks in Chapecó, from september 2005 to september 2006, concentrating efforts on spring and summer. The capitula were collected directly from the plants and conditioned in plastic bags. This research constitutes the first register of Tomoplagia reimoseri Hendel and Xanthaciura mallochi Aczél specimens collected from Asteraceae capitula in Chapecó, elevating to 72 the number of tephritid species registered to the State of Santa Catarina