Numerical Implementation of a Critical State Model for Soft Rocks

This paper details the basic tasks for the numerical implementation of a simple elasto-plastic critical state model for bonded materials (i.e. soft rocks-hard soils) into the finite element program SNAC developed at the University of Newcastle in Australia. The first task described focusses on the derivation of the incremental constitutive relationships used to represent the mechanical response of a bonded/cemented material under saturated conditions. The second task presents how these stress-strain relations can be numerically integrated using an explicit substepping scheme with automatic error control. The third task concentrates on the verification of the substepping algorithm proposed. The model used to represent the saturated mechanical response of a bonded material combines the modified Cam clay with the constitutive relationships for cemented materials proposed in Gens & Nova (1993), but incorporates some flexibility on the degradation law adopted. The role of suction and other relevant aspects of unsaturated behaviour are also discussed at the end of the paper

Tagging single muons and other long-flying relativistic charged particles by ultra-fast timing in air Cherenkov telescopes

Atmospheric air Cherenkov telescopes are successfully used for ground-based, very high-energy (VHE) gamma ray astronomy. Triggers from the so-called single muon and other long-flying relativistic charged particle events are an unwanted background for the Cherenkov telescope. Because of low rate at TeV energies the muon background is unimportant. It is much more intense for telescopes with high photon sensitivity and low energy threshold. Below a few hundred GeV energy, the so-called muon background becomes so intense, that it can deteriorate the sensitivity of telescopes (the so-called muon-wall problem). From general considerations it can be anticipated that the signature of these particles should be a light pulse with a narrow time structure. In fact, simulations show that the pulses from muons have a very narrow time profile that is well below the time resolutions of nearly all currently operating telescopes. In this report we elaborate on the time profile of Cherenkov light from the so-called single muons and show that a telescope with ultra-fast time response can open a new dimension allowing one to tag and to reject those events.Comment: Accepted by Astroparticle Physic

Range of orbital angular momenta available for complete fusion between heavy ions

The same compound nucleus, 158Er, has been formed through three different entrance channels, with projectiles 16O, 40Ar and 84Kr. Excitation functions for reactions (HI, 5n) and (HI, 6n) are well fitted by statistical model calculations, provided that a certain window in orbital angular momentum should be taken in order to produce complete fusion in the case of Ar ions and Kr ions. Curiously enough, low l-waves should be avoided. It implies that, during the interaction leading to complete fusion, the energy dissipation by tangential friction should be rather large

La colección herpetológica de Bolivia depositada en la Estación Biológica de Doñana

The collection consists of 822 specimens, of which 529 are amphibians, all of them anurans (5 families, 17 genera and 51 species) and 293 specimens are reptiles (10 families, 28 genera and 49 species). The collection has around 25% of the amphibians species known to occur in Bolivia and about 19% of the reptile species. They come from 55 localities of the Bolivian Departments of Beni, Chuquisaca, Cochabamba, La Paz, Potosí and Santa Cruz and represent the following bioregions: Puna, Chaco, Chiquitanian Forest, Wet Savannas, Ceja de Montaña, Yungas, Interandean Dry Valleys and Humid Lowland Forest. The specimens of Scinax chiquitanus and Phrynopus kempffi are paratypes. The record of Pleurodema borelli is the first for the Santa Cruz Department and second for Bolivia. Liolaemus dorbignyi also constitutes the second report for the country and Tropidurus melanopleurus is cited for the first time for the Beni Department.La colección se compone de 822 ejemplares, 529 anfibios y 293 reptiles. Los anfibios son todos anuros, pertenecientes a 51 especies de 17 géneros y cinco familias. Los reptiles estan representados por 49 especies, incluidas en 28 géneros de 10 familias. Los ejemplares provienen de 55 localidades repartidas en los Departamentos bolivianos de Beni, Chuquisaca, Cochabamba, La Paz, Potosí y Santa Cruz, y representan las siguientes bioregiones: Puna, Chaco, Bosque Chiquitano, Sabanas Húmedas, Ceja de Montaña, Yungas, Valles Secos Interandinos y Bosque Húmedo de Llanura. Los ejemplares de Scinax chiquitanus y Phrynopus kempffi son paratipos. Pleurodema borelli es citada por primera vez para el Departamento de Santa Cruz y por segunda vez para Bolivia; también el registro de Liolaemus dorbignyi constituye el segundo para el país y el de Tropidurus melanopleurus el primero para el Departamento Beni

Determination of the aqueous pKa of very insoluble drugs by capillary electrophoresis: Internal standards for methanol-water extrapolation

A fast determination of acidity constants (pKa) of very insoluble drugs has become a necessity in drug discovery process because it often produces molecules that are highly lipophilic and sparingly soluble in water. In this work the high throughput internal standard capillary electrophoresis (IS-CE) method has been adapted to the determination of pKa of water insoluble compounds by measurement in methanol/aqueous buffer mixtures. For this purpose, the reference pKa values for a set of 46 acid-base compounds of varied structure (internal standards) have been established in methanol-water mixtures at several solvent composition levels (with a maximum of 40% methanol). The IS-CE method has been successfully applied to seven test drugs of different chemical nature with intrinsic solubilities lower than 10-6 M. pKa values have been determined at different methanol/aqueous buffer compositions and afterwards Yasuda-Shedlovsky extrapolation method has been applied to obtain the aqueous pKa. The obtained results have successfully been compared to literature ones obtained by other methods. It is concluded that the IS-CE method allows the determination of aqueous pKa values using low proportions of methanol, becoming then more accurate in the extrapolation procedure than other reference methods

Geosynchronous inclined orbits for high-latitude communications

We present and discuss a solution to the growing demand for satellite telecommunication coverage in the high-latitude geographical regions (beyond 55◦N), where the signal from geostationary satellites is limited or unavailable. We focus on the dynamical issues associated to the design, the coverage, the maintenance and the disposal of a set of orbits selected for the purpose. Specifically, we identify a group of highly inclined, moderately eccentric geosynchronous orbits derived from the Tundra orbit (geosynchronous, eccentric and critically inclined). Continuous coverage can be guaranteed by a constellation of three satellites in equally spaced planes and suitably phased. By means of a highprecision model of the terrestrial gravity field and the relevant environmental perturbations, we study the evolution of these orbits. The effects of the different perturbations on the ground track (which is more important for coverage than the orbital elements themselves) are isolated and analyzed. The physical model and the numerical setup are optimized with respect to computing time and accuracy. We show that, in order to maintain the ground track unchanged, the key parameters are the orbital period and the argument of perigee. Furthermore, corrections to the right ascension of the ascending node are needed in order to preserve the relative orientation of the orbital planes. A station-keeping strategy that minimizes propellant consumption is then devised, and comparisons are made between the cost of a solution based on impulsive maneuvers and one with continuous thrust. Finally, the issue of end-of-life disposal is discussed