Super-accelerating bouncing cosmology in asymptotically free non-local gravity

Application of the effective action approach to amplitudes with loop integration is studied for collisions on two and three centers with possible gluon emission. A rule is formulated for the integration around pole singularities in the induced vertices which brings the results in agreement with the QCD. It is demonstrated that the amplitudes can be restored from the purely transverse picture by introducing the standard Feynman propagators for intermediate gluons and quarks.     

Medlar (<Emphasis Type="Italic">Achras Sapota</Emphasis> L.) as Oral Contrast Agent for MRI of the Gastrointestinal Tract

Magnetic resonance imaging (MRI) of the gastrointestinal (GI) tract is still limited due to the lack of widely available oral contrast agents (OCA). The availability of OCA for MRI of the GI tract is a necessity; different fruits might be implemented as OCA in order to solve this need throughout the year. The objective of this study is to present an alternative fruit as a clinical OCA for MRI of the GI tract, Achras sapota L. (common medlar). Both physical and chemical characterization of the medlar was performed. It was also tested in situ and in vivo as an OCA for MRI of the GI tract. Results showed that this fruit had a diamagnetic behavior, although it has enough iron, manganese and copper to contrast the GI tract in T ₁- and T ₂-weighted images. Thus we conclude that the medlar fruit has shown a potential as an OCA in GI evaluation by MRI, so it can be considered as an alternative in complementation of natural OCA.     

k-Cosymplectic Classical Field Theories: Tulczyjew and Skinner–Rusk Formulations

The k-cosymplectic Lagrangian and Hamiltonian formalisms of first-order classical field theories are reviewed and completed. In particular, they are stated for singular and almost-regular systems. Subsequently, several alternative formulations for k-cosymplectic first-order field theories are developed: First, generalizing the construction of Tulczyjew for mechanics, we give a new interpretation of the classical field equations. Second, the Lagrangian and Hamiltonian formalisms are unified by giving an extension of the Skinner–Rusk formulation on classical mechanics.     

Preparation of well-dispersed magnetorheological fluids and effect of dispersion on their magnetorheological properties

In this work, we describe methods for the preparation of suspensions of micron-sized iron particles grafted with different surfactants. The aim is to obtain well-dispersed magnetorheological (MR) fluids. The effectiveness of the surfactants as dispersants was analyzed quantitatively by means of rheological measurements. With this objective, the viscosity of the suspensions was measured, and the results were compared with the prediction of the Batchelor’s formula (Batchelor, J Fluid Mech 83:97–117, 1977). The effect of dispersion on the MR properties of the suspensions was also studied. It was found that the quality of the dispersion of a suspension does not have an important effect on the magnitude of the field-induced yield stress but does on the change of viscosity induced by the field. It was also found that the transition from the solid-like state to the liquid-like one happens very smoothly for well-dispersed suspensions, contrarily to the abrupt transition for poorly dispersed suspensions.     

Theoretical studies of d(A:T)-based parallel-stranded DNA duplexes.

Poly d(A:T) parallel-stranded DNA duplexes based on the Hoogsteen and reverse Watson-Crick hydrogen bond pairing are studied by means of extensive molecular dynamics (MD) simulations and molecular mechanics coupled to Poisson-Boltzmann (MM-PB/SA) calculations. The structural, flexibility, and reactivity characteristics of Hoogsteen and reverse Watson-Crick parallel duplexes are described from the analysis of the trajectories. Theoretical calculations show that the two parallel duplexes are less stable than the antiparallel Watson-Crick duplex. The difference in stability between antiparallel and parallel duplexes increases steadily as the length of the duplex increases. The reverse Watson-Crick arrangement is slightly more stable than the Hoogsteen duplex, the difference being also increased linearly with the length of the duplex. A subtle balance of intramolecular and solvation terms is responsible for the preference of a given helical structure.     

Methane Conversion Over Sr2+/La2O3 Catalyst Modified with Nickel and Copper

Methane transformation over Ni and Cu modified Sr²⁺/La₂O₃ catalysts has been studied. These species favor formation of reducible mixed oxides and change the surface reactivity of the Sr²⁺/La₂O₃ system, modifying the reaction mechanism, since Sr²⁺/La₂O₃ favors methane oxidative coupling but with copper methane combustion is favored and nickel favors partial oxidation.     

Study of the Polymerization Kinetic of Lactic Acid

Summary: Biodegradable polymers production is growing, mainly poly (lactic) acid, due to the fact that it is environmentally friendly and might be used in different fields i.e. medicine, agriculture, textiles, etc. Hence the importance of studying the polymerization process and its kinetic parameters. The polymerization process is performed by polycondensation of lactic acid using different kinds and amounts of tin based catalysts. This process is monitored during 12 hours and samples are taking for analyses every hour. Each sample is measured by gel permeation chromatography (GPC) to determine its molecular weight and by Fourier transformed infrared (FTIR) to study the evolution of alkyl absorption bands and the disappearing of hydroxyl ones. Modulated differential scanning calorimetric analysis (MDSC) is used to study the thermal behavior of every sample during each period, such as Tg displacement and changes in crystallization and melting. These data are used for the construction of the kinetic curve.     

Reliability of MEP and MEP-derived properties computed from DFT methods for molecules containing P, S and CL

We present a systematic study on the reliability of different theoretical methods to represent the molecular electrostatic potential (MEP), and MEP-derived properties of prototypical compounds containing phosphorus, sulfur and chlorine. Calculations at the Hartree-Fock and M?ller-Plesset up to fourth-order level of theory, as well as local, non-local and hybrid density functional computations were performed for a representative set of neutral molecules. The study was carried out using different basis sets ranging from the medium-sized 6-31G(d ) to the large 6-31G(2d,2p) basis set, but in some test calculations more extended basis sets were also considered. The analysis of the results was performed discussing separately the effect of the basis set and of the level of theory used to determine the molecular wavefunction on the reliability of the MEP and MEP-derived properties. Received: 4 March 1997 / Accepted: 27 June 1997     

Structure and Bonding in CE5− (E=Al–Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon

The structure, bonding, and stability of clusters with the empirical formula CE₅^? (E=Al–Tl) have been analyzed by means of high‐level computations. The results indicate that, whereas aluminum and gallium clusters have C_2v structures with a planar tetracoordinate carbon (ptC), their heavier homologues prefer three‐dimensional C_4v forms with a pentacoordinate carbon center over the ptC one. The reason for such a preference is a delicate balance between the interaction energy of the fifth E atom with CE₄ and the distortion energy. Moreover, bonding analysis shows that the ptC systems can be better described as CE₄^?, with 17‐valence electrons interacting with E. The ptC core in these systems exhibits double aromatic (both σ and π) behavior, but the σ contribution is dominating.     

Time response of a coupled atoms-cavity system

We study the time response of a quantum optical system to a step excitation. The system is composed of a collection of N two-level atoms coupled to a single mode of the electromagnetic field of an optical cavity. The size of the step excitation is not limited to the low-intensity regime. Before the system reaches steady state there is an oscillatory exchange of energy between the atoms and the cavity. We compare the experimental results quantitatively with theoretical calculations and with previous transmission spectroscopy measurements.