Segmented block copolymers based on dimerized fatty acids and poly(butylene terephthalate)

Segmented block copolymers based on dimerized fatty acids and poly(butylene terephthalate) (PBT) have been synthesized in the melt. Branched C36, C44 and C70 dimerized fatty acids with a low degree of unsaturation were used. The fraction of PBT was varied from 50 to 100wt%. The resulting polymers were analysed with d.s.c. and d.m.a. The glass transition temperature (Tg) increased with increasing weight fraction of PBT. Tg decreased with increasing molecular mass of the dimerized fatty acid. The melting temperature increased with increasing weight fraction of PBT and increasing molecular mass of the dimerized fatty acid. The range of service temperatures of the thermoplastic elastomers can therefore be enlarged by using dimerized fatty acid with a high molecular mass. With increasing molecular mass of the dimerized fatty acid the storage modulus and the melting and crystallization enthalpy did not change significantly. The storage modulus can be described as a function of the volume fraction of crystalline PBT, but is not a function of the type of dimerized fatty acid

Silica stable isotopes and silicification in a carnivorous sponge Asbestopluma sp.

The stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotope composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the vital effects on silica, silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that are related to unusual spicule silicification. The largest variation in both isotope systems was associated with the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotope signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotope signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements

Quantum cavitation in liquid helium

Using a functional-integral approach, we have determined the temperature below which cavitation in liquid helium is driven by thermally assisted quantum tunneling. For both helium isotopes, we have obtained the crossover temperature in the whole range of allowed negative p essures. Our results are compatible with recent experimental results on 4He.Comment: Typeset using Revtex, 10 pages and 2 figures, Phys. Rev B (1996

Intertidal endangered species from “The Strait Natural Park”

En el marco de dos campos de trabajo (2006 y 2007) financiados por el Patronato Municipal de Juventud del Ayuntamiento de Tarifa y el Instituto Andaluz de la Juventud respectivamente, se estudiaron cinco especies intermareales amenazadas del Parque Natural del Estrecho: Patella ferruginea Gmelin, 1791, Cymbula nigra (Da Costa, 1771), Dendropoma petraeum (Monterosato, 1884) Charonia lampas lampas (Linnaeus, 1758) y Astroides calycularis (Pallas, 1776). Se seleccionaron 8 estaciones, y en cada estación se realizaron 4 transectos de 100 m de longitud paralelos a la costa. Se registraron un total de 211 ejemplares de C. nigra (5,3±1,6 cm) y 100 ejemplares de P. ferruginea (4,1±1,3 cm). Destacó la presencia de un ejemplar de P. ferruginea en Punta Camarinal, representando la cita más occidental para la especie encontrada hasta el momento. C. nigra y P. ferruginea mostraron mayores densidades en la zona oriental del Parque mientras que D. petraeum fue más abundante en la.In the framework of the labour camps (2006 and 2007) supported by the “Patronato Municipal de Juventud del Ayuntamiento de Tarifa” and the “Instituto Andaluz de la Juventud” respectively, five intertidal endangered species from “The Straits Natural Park” were studied: Patella ferruginea Gmelin, 1791, Cymbula nigra (Da Costa, 1771), Dendropoma petraeum (Monterosato, 1884) Charonia lampas (Linnaeus, 1758), Astroides calycularis (Pallas, 1776). Eight stations were selected, and 4 transects of 100 m were disposed parallel to the coastline. A total of 211 specimens of C. nigra (5,3±1,6 cm) and 100 specimens of P. ferruginea (4,1±1,3 cm) were registered. A specimen of P. ferruginea was collected from Punta Camarinal, representing the most occidental record of the species so far. C. nigra and P. ferruginea showed the highest densities in the oriental zone of the Natural Park, whereas D. petraeum was more abundant in the occidental sites. When a qualitative evaluation of the stations was conducted based on the relative abundance of species, Guadalmesí (with 17 points of 20) showed the highest interest, with high abundances of the 5 species. Tarifa Island (with 13 points) was also remarkable. Regarding with the limpet populations of P. ferruginea and C. nigra, San García was especially interesting, showing high densities of both species. The qualitative assessment of “The Strait Natural Park” conducted in the present study should be considered by the authorities to properly address future management and conservation estrategie

Alasdair MacIntyre: introducción narrativa a su obra

A raíz de la publicación del último libro del filósofo británico Alasdair MacIntyre, Ethics in the Conflicts of Modernity: An Essay on Desire, Practical Reasoning, and Narrative, este trabajo propone una manera de comprender su producción bibliográfica en el contexto de la narrativa de su trayectoria vital e intelectual. Se elabora una periodización del itinerario de MacIntyre, basada en las referencias que el propio autor ha hecho sobre su vida académica y en las propuestas de varios estudiosos de su pensamiento. Se concluye que el examen narrativo de la obra de Alasdair MacIntyre revela que su proyecto filosófico está marcado básicamente por Aristóteles y Tomás de Aquino, cuyo pensamiento ayudó a nuestro autor a articular una propuesta sólida sobre las principales cuestiones de filosofía moral y la filosofía de la religión, y a elaborar un nuevo marco de interpretación y conocimiento sapiencial de la realidad, también en su aspecto científico. Este trabajo se concibe como introductorio porque se centra solamente en los libros de MacIntyre, pero se espera que sirva como base sólida para realizar un estudio crítico minucioso — sobre todo, desde una perspectiva cronológica— de la práctica totalidad de su obra, que incluye también capítulos de libros, artículos académicos, entrevistas, entre otros.In the wake of the publication of the last book of the British philosopher Alasdair MacIntyre, Ethics in the Conflicts of Modernity: An Essay on Desire, Practical Reasoning, and Narrative, this work proposes a way to understand his bibliographical production in the context of the narrative of his life and his intellectual career. It is elaborated a periodization of the itinerary of MacIntyre, based on the references that the author himself has made of his academic life and in the proposals of several scholars of his thought. It is concluded that the narrative examination of MacIntyre’s work reveals that his philosophical project is basically marked by Aristotle and Aquinas, whose thought helped our author to articulate a solid proposal on the main issues of moral philosophy and philosophy of religion, and to elaborate a new framework of interpretation and sapiential knowledge of reality, including its scientific dimension. This work is conceived as introductory because it focuses only on MacIntyre’s books, but it’s expected to serve as a solid basis for a thorough critical study —especially from a chronological perspective— of his entire work, which includes chapters of books, papers, interviews, among others

ESTRO/ACROP IORT recommendations for intraoperative radiation therapy in primary locally advanced rectal cancer

Summary: Carcinoma of the rectum is a heterogeneous disease. The clinical spectrum identifies a subset of patients with locally advanced tumours that are close to or involve adjoining structures, such as the sacrum, pelvic sidewalls, prostate or bladder. Within this group of patients categorized as ‘‘locally advanced”, there is also variability in the extent of disease with no uniform definition of resectability. A practice-oriented definition of a locally advanced tumour is a tumour that cannot be resected without leaving microscopic or gross residual disease at the resection site. Since these patients do poorly with surgery alone, irradiation and chemotherapy have been added to improve the outcome. Intraoperative irradiation (IORT) is a component of local treatment intensification with favourable results in this subgroup of patients. International guidelines (National Comprehensive Cancer Network (NCCN) guidelines) currently recommend the use of IORT for rectal cancer resectable with very close or positive margins, especially for T4 and recurrent cancers. We report the ESTRO-ACROP (European Society for Radiotherapy and Oncology - Advisory Committee on Radiation Oncology Practice) recommendations for performing IORT in primary locally advanced rectal cancer

Green functions for generalized point interactions in 1D: A scattering approach

Recently, general point interactions in one dimension has been used to model a large number of different phenomena in quantum mechanics. Such potentials, however, requires some sort of regularization to lead to meaningful results. The usual ways to do so rely on technicalities which may hide important physical aspects of the problem. In this work we present a new method to calculate the exact Green functions for general point interactions in 1D. Our approach differs from previous ones because it is based only on physical quantities, namely, the scattering coefficients, $R$ and $T$, to construct $G$. Renormalization or particular mathematical prescriptions are not invoked. The simple formulation of the method makes it easy to extend to more general contexts, such as for lattices of $N$ general point interactions; on a line; on a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR

Thermal desorption of CH4 retained in CO2 ice

CO2 ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density, refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that CO2 traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH4 in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of several retaining mechanisms related to the structure of CO2 ice.Comment: 8 pages, accepted for publication in Astrophysics & Space Scienc

Quantum magnetism in two dimensions: From semi-classical N\'eel order to magnetic disorder

This is a review of ground-state features of the s=1/2 Heisenberg antiferromagnet on two-dimensional lattices. A central issue is the interplay of lattice topology (e.g. coordination number, non-equivalent nearest-neighbor bonds, geometric frustration) and quantum fluctuations and their impact on possible long-range order. This article presents a unified summary of all 11 two-dimensional uniform Archimedean lattices which include e.g. the square, triangular and kagome lattice. We find that the ground state of the spin-1/2 Heisenberg antiferromagnet is likely to be semi-classically ordered in most cases. However, the interplay of geometric frustration and quantum fluctuations gives rise to a quantum paramagnetic ground state without semi-classical long-range order on two lattices which are precisely those among the 11 uniform Archimedean lattices with a highly degenerate ground state in the classical limit. The first one is the famous kagome lattice where many low-lying singlet excitations are known to arise in the spin gap. The second lattice is called star lattice and has a clear gap to all excitations. Modification of certain bonds leads to quantum phase transitions which are also discussed briefly. Furthermore, we discuss the magnetization process of the Heisenberg antiferromagnet on the 11 Archimedean lattices, focusing on anomalies like plateaus and a magnetization jump just below the saturation field. As an illustration we discuss the two-dimensional Shastry-Sutherland model which is used to describe SrCu2(BO3)2.Comment: This is now the complete 72-page preprint version of the 2004 review article. This version corrects two further typographic errors (three total with respect to the published version), see page 2 for detail