Evidence for a supercooled plastic-crystal phase in solid ethanol

4 págs.; 2 figs.The existence of an orientationally disordered cubic phase of solid ethanol is revealed by x-ray diffraction and Raman spectroscopic measurements. Such a phase, whose existence was postulated some time ago on the basis of specific-heat measurements, is produced by quenching below some 95 K a plastic crystal formed upon melting and subsequent annealing of the topologically disordered (glassy) solid. The relevance of the present findings for current discussions on glassy dynamics is analyzed in some detail. ©1996 American Physical SocietyThis work was supported in part by DGICYT Grant No. PB92-0114-C04.Peer Reviewe

Microscopic dynamics of glycerol in its crystalline and glassy states

9 págs.; 6 figs.; 1 tab.The dynamics of crystalline glycerol are studied by means of Raman spectroscopy and lattice dynamics calculations employing a semiflexible model to represent the low-lying molecular vibrations. The latter is validated against structural, thermodynamic, and spectroscopic data. The results serve to set an absolute frequency scale for glassy glycerol, which is also studied by Raman and incoherent inelastic-neutron scattering. Some implications of the present findings regarding ensuing discussions on glassy dynamics are finally commented on. ©1996 American Physical SocietyThis work has been supported in part by DGICYT Grant No. PB92- 0114-C04.Peer Reviewe

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

Low-frequency excitations in glassy selenium: A comparison of neutron-scattering and molecular-dynamics results

12 págs.; 9 figs.; 1 tab.The microscopic low-frequency dynamics of glassy selenium is investigated by means of the concurrent use of neutron inelastic scattering and computer simulations. A separation of the dynamic response in terms of intra- and interchain processes is achieved from the analysis of the simulation results. The S(Q,E) dynamic structure factors are analyzed in terms of the frequency moments or from a model scattering law, and the wave-vector dependence of the relevant quantities is established. Finally, the anomalous behavior of the heat capacity at moderately low temperatures is shown to be originated by mostly interchain interactions. © 1993 The American Physical Society.This work has been supported in part by DGICYT Grant No. PB89-0037-C03.Peer Reviewe

Rotational dynamics in the plastic-crystal phase of ethanol: Relevance for understanding the dynamics during the structural glass transition

12 págs.; 14 figs.; 1 tab.; 1 apéndiceThe reorientational dynamics within the rotationally disordered cubic plastic phase of solid ethanol is investigated by means of the concurrent use of computer molecular dynamics and quasielastic neutron scattering. Motions involving widely different time scales are shown to take place above the calorimetric >glass transition> which is centered at Tg≈97 K. These correspond to well-defined reorientations belonging to the cubic point group. The dynamics of this solid exhibits features remarkably close to those of the supercooled liquid that can exist at the same temperature. Such similitude of dynamic behavior serves to provide some clues for the understanding of the nature of molecular motions at temperatures close to the canonical liquid→glass transition. ©2000 The American Physical Society.This work was supported in part by Grant No. DGICYTPB95- 0072-C03 (Spain). Work at ANL was supported by the U.S. Department of Energy, BES–Materials Sciences, under Contract No. W-31-109-ENG-38.Peer Reviewe

OntoTrader

Modern Web-based Information Systems (WIS) are becoming increasingly necessary to provide support for users who are in different places with different types of information, by facilitating their access to the information, decision making, workgroups, and so forth. Design of these systems requires the use of standardized methods and techniques that enable a common vocabulary to be defined to represent the underlying knowledge. Thus, mediation elements such as traders enrich the interoperability of web components in open distributed systems. These traders must operate with other third-party traders and/or agents in the system, which must also use a common vocabulary for communication between them. This paper presents the OntoTrader architecture, an Ontological Web Trading agent based on the OMG ODP trading standard. It also presents the ontology needed by some system agents to communicate with the trading agent and the behavioral framework for the SOLERES OntoTrader agent, an Environmental Management Information System (EMIS). This framework implements a “Query-Searching/Recovering-Response” information retrieval model using a trading service, SPARQL notation, and the JADE platform. The paper also presents reflection, delegation and, federation mediation models and describes formalization, an experimental testing environment in three scenarios, and a tool which allows our proposal to be evaluated and validated

Anharmonic dynamics in crystalline, glassy, and supercooled-liquid glycerol: A case study on the onset of relaxational behavior

10 págs.; 8 figs.The temperature dependence of the spectral distributions of the glass, crystalline, and supercooled-liquid phases of glycerol is investigated by means of neutron inelastic scattering. The importance of anharmonic effects is quantified by the temperature dependence of reduced spectral frequency moments. The onset of relaxational (i.e., stochastic, zero-frequency) motions in the supercooled liquid state is monitored by neutron quasielastic scattering. A substantial deviation of the observed linewidths from the hydrodynaimc prescription is observed and is interpreted at a microscopic level, by comparison with the crystalline phase. ©1998 American Physical SocietyWork supported in part by DGICYT ~Spain! Grant No. PB95-0075-c03-01. Dr. O. Randl of the Institute Laue Langevin is acknowledged for the help given during the measurements at the IN10 spectrometer. The work at ANL was supported by the U.S. Department of Energy, BESMaterials Sciences, under Contract No. W-31-109-ENG-38.Peer Reviewe

Kinetic study of the oxidation of phenolic derivatives of α,α,α-trifluorotoluene by singlet molecular oxygen [O₂(¹Δg)] and hydrogen phosphate radicals

The oxidation kinetics and mechanism of the phenolic derivatives of α,α,α-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(¹Δg), and hydrogen phosphate radicals were studied, employing time-resolved O2(¹Δg) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(¹Δg)-mediated mechanism. The phenols show overall quenching constants for O2(¹Δg) of the order of 106 M⁻¹ s⁻¹ in D2O, while the values for the phenoxide ions in water range from 1.2 × 10⁸ to 3.6 × 10⁸ M⁻¹ s⁻¹. The effects of the pH and polarity of the medium on the kinetics of the photo-oxidative process suggest a charge-transfer mechanism. 2-Trifluoromethyl-1,4-benzoquinone is suspected to be the main photo-oxidation product for the substrate 3-TFMP. The absolute rate constants for the reactions of HPO4•− with the substrates range from 4 × 10⁸ to 1 × 10⁹ M⁻¹ s⁻¹. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO₄•⁻, yielding 2,2’-bis(fluorohydroxymethyl)biphenyl-4,4’-diol as the end product. The observed results indicate that singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of α,α,α-trifluorotoluene, but the reactions also proceed through different reaction channels.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasLaboratorio de Estudio de Compuestos Orgánico

Influence of elevated-CRP level-related polymorphisms in non-rheumatic Caucasians on the risk of subclinical atherosclerosis and cardiovascular disease in rheumatoid arthritis

Association between elevated C-reactive protein (CRP) serum levels and subclinical atherosclerosis and cardiovascular (CV) events was described in rheumatoid arthritis (RA). CRP, HNF1A, LEPR, GCKR, NLRP3, IL1F10, PPP1R3B, ASCL1, HNF4A and SALL1 exert an influence on elevated CRP serum levels in non-rheumatic Caucasians. Consequently, we evaluated the potential role of these genes in the development of CV events and subclinical atherosclerosis in RA patients. Three tag CRP polymorphisms and HNF1A, LEPR, GCKR, NLRP3, IL1F10, PPP1R3B, ASCL1, HNF4A and SALL1 were genotyped in 2,313 Spanish patients by TaqMan. Subclinical atherosclerosis was determined in 1,298 of them by carotid ultrasonography (by assessment of carotid intima-media thickness-cIMT-and presence/absence of carotid plaques). CRP serum levels at diagnosis and at the time of carotid ultrasonography were measured in 1,662 and 1,193 patients, respectively, by immunoturbidimetry. Interestingly, a relationship between CRP and CRP serum levels at diagnosis and at the time of the carotid ultrasonography was disclosed. However, no statistically significant differences were found when CRP, HNF1A, LEPR, GCKR, NLRP3, IL1F10, PPP1R3B, ASCL1, HNF4A and SALL1 were evaluated according to the presence/absence of CV events, carotid plaques and cIMT after adjustment. Our results do not confirm an association between these genes and CV disease in RA