The Physics of Liquid Para-Hydrogen

Macroscopic systems of hydrogen molecules exhibit a rich thermodynamic phase behavior. Due to the simplicity of the molecular constituents a detailed exploration of the thermal properties of these boson systems at low temperatures is of fundamental interest. Here,we report theoretical and experimental results on various spatial correlation functions and corresponding distributions in momentum space of liquid para-hydrogen close to the triple point. They characterize the structure of the correlated liquid and provide information on quantum effects present in this Bose fluid. Numerical calculations employ Correlated Density-Matrix(CDM)theory and Path-Integral Monte-Carlo(PIMC)simulations. A comparison of these theoretical results demonstrates the accuracy of CDM theory. This algorithm therefore permits a fast and efficient quantitative analysis of the normal phase of liquid para-hydrogen.We compare and discuss the theoretical results with available experimental data.Comment: 14 pages, 7 figure

Consideraciones didácticas sobre la enseñanza de lenguas extranjeras asistida por ordenador.

El desarrollo de las nuevas tecnologías en las últimas décadas nos ha impulsado a reflexionar sobre las posibilidades que la tecnología multimedia puede aportar a la enseñanza de la lengua extranjera, con sus ventajas y limitaciones. Partiendo de la evolución de los distintos enfoques en este campo, examinamos algunos programas actuales en CD-ROM y evaluamos sus diferentes actividades y contenidos. También consideramos de qué manera Internet está cambiando la concepción de la enseñanza y el papel del profesor y del alumno

Implanted muon spin spectroscopy on 2-O-adamantane: a model system that mimics the liquid

The transition taking place between two metastable phases in 2-O-adamantane, namely the [Formula: see text] cubic, rotator phase and the lower temperature P21/c, Z  =  4 substitutionally disordered crystal is studied by means of muon spin rotation and relaxation techniques. Measurements carried out under zero, weak transverse and longitudinal fields reveal a temperature dependence of the relaxation parameters strikingly similar to those exhibited by structural glass[Formula: see text]liquid transitions (Bermejo et al 2004 Phys. Rev. B 70 214202; Cabrillo et al 2003 Phys. Rev. B 67 184201). The observed behaviour manifests itself as a square root singularity in the relaxation rates pointing towards some critical temperature which for amorphous systems is located some tens of degrees above that shown as the characteristic transition temperature if studied by thermodynamic means. The implications of such findings in the context of current theoretical approaches concerning the canonical liquid-glass transition are discussed.Postprint (author's final draft

Anomalous temperature dependence of the first diffraction peak in vitreous boron trioxide

11 págs.; 9 figs.The temperature dependence of the parameters characterizing the first peak in the S(Q) and S(Q,E=0) diffraction patterns of vitreous boron trioxide is considered in some detail. The analysis of the experimental spectra is aided by results derived from molecular-dynamics simulations, which enable us to isolate the most relevant features driving the variation with temperature of both structure factors. The relevance of the present results regarding some recent phenomenological approaches developed towards the understanding of the dynamics of glasses at intermediate temperatures is finally discussed. ©1996 American Physical SocietyWork was performed in part under D.G.I.C.Y.T (Spain) Grant No. PB92-0114-C03-01. Financial support from the Large Scale Facilities Programme of the European Union for the measurements carried at Risoe National Laboratory (Denmark) is acknowledged. J.D. wishes to thank CONICET (Argentina) and CSIC (Spain) for financial support.Peer Reviewe

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

Thermal study of a transport container

A thermal study of a container for international transport has been carried out in order to determine the temperature distributions. Several experimental conditions such as cooling modes, the onset of defrosting, the existence of cargo inside the container and two varying set points have been evaluated. It was observed that the difference between the temperature inside the container and the set point raised up to 30% of ambient temperature. Moreover, it was observed that the modulated cooling allowed to obtain a more homogeneous refrigeration. However, temperature differences up to 8 °C were observed under on–off control cooling

Thermal transport in glassy selenium: The role of low-frequency librations

7 págs.; 3 figs.The experimental curves giving the temperature dependence of the thermal conductivity of glassy selenium are considered in detail. The observed behavior can be taken into account quantitatively if the densities of states for short-wavelength phonons as well as for low-energy librations arising from computer simulations are used for the calculations. In particular, it is shown that the lowest frequency excitations of a chain of selenium atoms can give due account of the plateau observed at temperatures about 2-10 K. The implications of the present findings for the current debate regarding the mechanisms for thermal transport in glasses are finally discussed. © 1994 The American Physical Society.This work has been supported by DGICYT Grant No. PB92-0114-C03Peer Reviewe

Caracterización mecánica de pistas deportivas fabricadas con materiales procedentes de neumáticos fuera de uso (NFU)

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.The European Framework Directive 2008/98/EC on waste established as priority reuse and recycling before other recovery alternatives. In this normative reference, one the main waste flows identified are the end-of-life tyres, as a material whose mechanical properties could provide advantage in the construction of new structures. This paper presents the mechanical characterization of a layer made with shredded tires out of use, inside a section of a sportive track which included a sand layer. The use of the shredded tires out of use provides special features related with elasticity and damping to the sportive surface. In order to do that, a new test based on UNE-14809 was designed. A number of tests were performed using different configuration of sand and shredded tires. From the results obtained, a numerical model was implemented in FEA software

Rotura no traumática de componente cerámica-cerámica en PTC: presentación de un caso y revisión de la literatura.

Las fracturas de los componentes cerámicos empleados en artroplastia total de cadera (ATC) son infrecuentes. El objetivo de nuestro trabajo es presentar un caso de rotura precoz no traumática de componente ce - rámica-cerámica en ATC y revisar la literatura en relación con esta complicación. Se trata de un paciente de 58 años diagnosticado de necrosis avascular de cabeza femoral, fue intervenido mediante ATC, implantándosele un par cerámica-cerámica. A los 4 meses de la intervención, sin antecedente traumático previo, se observó fractura de la cúpula de cerámica de la prótesis. El paciente precisó de recambio protésico, utilizándose el par cerámica-polietileno. La fractura de los componentes del par cerámica- cerámica es poco frecuente. El fallo puede ser debido a un defecto de fabricación o en la colocación del implante. Los pacientes deben ser informados sobre la posibilidad de sufrir esta complicación antes de la implantación de una PTC con par cerámica-cerámica.Fractures of ceramic components used in total hip replacement (THR) are uncommon. To report a case of early non-traumatic rupture ceramic-ceramic component in THR and review the literature regarding this complication. A 58 years diagnosed with avascular necrosis of the femoral head, was operated by THR, a ceramic-on -ceramic. At 4 months after surgery, without previous trauma, fracture was observed ceramic dome of the prosthesis. The patient required replacement, using the ceramic-on-polyethylene. The fracture of ceramic components is rare. The failure may be due to a manufacturing defect or implant placement. Patients should be informed about the possi - bility of having this complication before implantation of a THR ceramic-on-ceramic