Comparison of short-range-order in liquid- and rotator-phase states of a simple molecular liquid: A reverse Monte Carlo and molecular dynamics analysis of neutron diffraction data

6 págs.; 6 figs.; 1 tab. ; PACS number s : 61.25.Em, 61.20. p, 61.43. j, 61.12. qThe short-range order (SRO) correlations in liquid- and rotator-phase states of carbon tetrachloride are revisited here. The correlation of some angular magnitudes is used to evaluate the positional and orientational correlations in the liquid as well as in the rotator phase. The results show significant similitudes in the relative position of the molecules surrounding a central one but striking differences in their relative orientations, which could explain the changes in SRO between the two phases and the puzzling behavior of the local density in the liquid and rotator phases. © 2007 The American Physical Society.We would also like to acknowledge “Generalitat de Catalunya” Project No. 2005SGR- 00535 and MEC Project No. FIS2005-00975 for partial support of this work.Peer Reviewe

Elaboration of Essential Oil From the Oregano for Medicinal Use Sheet

The extraction and industrialization of the oregano oil in Ecuador can represent an important source of work, from the harvest to the transformation of the raw material into finished product. The oregano is a plant known from many years back and has always been used for medicinal purposes and is currently being used in many fields such as perfumery, gastronomy, toiletries; But its main use is in medicine. The work proposes a methodology that allows extracting the essential oil of the plant for different medical uses such as: anti - inflammatory, analgesic, antioxidant and antibiotic, being of social benefit representing an economic impact in its industrializatio

Arsenite sorption and co-precipitation with calcite

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on the atomic displacement of As atoms along [0001] direction extend those published by Cheng et al., (1999) on calcite surface. This study provides a molecular-level explanation for why As(III) is trapped by calcite in industrial treatments.Comment: 9 page

Neutron scattering at high temperature and levitation techniques

Studies of the liquid state present an obvious fundamental interest and are also important for technological applications since the molten state is an essential stage in various industrial processes (e.g. glass making, single crystal growing, iron and steel making). Most of the physical properties of a high-temperature liquid are related to its atomic structure. Thus it is important to develop devices to probe the local environment of the atoms in the sample. At very high temperature, it is difficult to use conventional furnaces, which present several problems. In particular, physical contact with the container can contaminate the sample and/or modify its structural properties. Such problems encouraged the development of containerless techniques, which are powerful tools to study high-temperature melts. By eliminating completely any contact between sample and container, it is possible to study the sample with a very high degree of control and to access very high temperatures. An additional advantage of levitation methods is that it is possible to supercool hot liquids down to several hundred of degrees below their equilibrium freezing point, since heterogeneous nucleation processes are suppressed

Substitution site and effects on magnetism in Sr-for-Ca substituted CaBaCo4O7

Cationic substitutions in the novel magnetoelectric compound CaBaCo4O7 lead to profound changes in its magnetic and electric behaviors. In this work, we present a structural study of the isovalent substitution Sr-for-Ca in CaBaCo4O7. X-ray diffraction, as well as neutron powder diffraction experiments, are reported for a series of samples Ca1- xSrxBaCo4O7 with 0 = x = 0.10. Special emphasis is given to the identification of the substitution site, as Sr has also been reported to substitute for Ba in this crystal structure. The solubility limit for Sr at the Ca site is shown to be at x ¿ 0.08. The variation of lattice constants with Sr-doping firmly supports the Sr-for-Ca substitution. Rietveld refinements of the Sr-substituted samples are presented, and used as starting point to analyse the local structure around Sr by means of X-ray absorption spectroscopy at the Sr K-edge. Both the near-edge absorption and the extended absorption fine-structure confirm the substitution of Sr for Ca, giving definite support to the proposed nominal formula. In addition, macroscopic magnetization measurements are presented which reveal the striking effects of Sr-substitution over the magnetic landscape of this puzzling compound

Religious transformations in the Middle Ages: towards a new archaeological agenda

The study of religious change in Europe between the collapse of the Roman Empire and the Reformation forms one of the cornerstones of medieval archaeology but has been riven by period, denominational and geographical divisions. This paper lays the groundwork for a fundamental rethink of archaeological approaches to medieval religions, by adopting a holistic framework that places Christian, pagan, Islamic and Jewish case studies of religious transformation in a long-term, comparative perspective. Focused around the analytical themes of ‘hybridity and resilience’ and ‘tempo and trajectories’, our approach shifts attention away from the singularities of national narratives of religious conversion towards a deeper understanding of how religious beliefs, practices and identity were renegotiated by medieval people in their daily lives

Exciting spiral arms in protoplanetary discs from flybys

Spiral arms are observed in numerous protoplanetary discs. These spiral arms can be excited by companions, either on bound or unbound orbits. We simulate a scenario where an unbound perturber, i.e. a flyby, excites spiral arms during a periastron passage. We run three-dimensional hydrodynamical simulations of a parabolic flyby encountering a gaseous protoplanetary disc. The perturber mass ranges from $10\, \rm M_J$ to $1\, \rm M_{\odot}$. The perturber excites a two-armed spiral structure, with a more prominent spiral feature for higher mass perturbers. The two arms evolve over time, eventually winding up, consistent with previous works. We focus on analysing the pattern speed and pitch angle of these spirals during the whole process. The initial pattern speed of the two arms are close to the angular velocity of the perturber at periastron, and then it decreases over time. The pitch angle also decreases over time as the spiral winds up. The spirals disappear after several local orbital times. An inclined prograde orbit flyby induces similar disc substructures as a coplanar flyby. A solar-mass flyby event causes increased eccentricity growth in the protoplanetary disc, leading to an eccentric disc structure which dampens over time. The spirals' morphology and the disc eccentricity can be used to search for potential unbound stars or planets around discs where a flyby is suspected. Future disc observations at high resolution and dedicated surveys will help to constrain the frequency of such stellar encounters in nearby star-forming regions.Comment: 17 pages, 18 figures, accepted to MNRA

Azokh caves excavations 2002-2006: Middle-Upper palaeolithic transition in Nagorno-Karabagh

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu