Breakup of 17^{17}F on 208^{208}Pb near the Coulomb barrier

Angular distributions of oxygen produced in the breakup of $^{17}$F incident on a $^{208}$Pb target have been measured around the grazing angle at beam energies of 98 and 120 MeV. The data are dominated by the proton stripping mechanism and are well reproduced by dynamical calculations. The measured breakup cross section is approximately a factor of 3 less than that of fusion at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure

Some Finite Size Effects in Simulations of Glass Dynamics

We present the results of a molecular dynamics computer simulation in which we investigate the dynamics of silica. By considering different system sizes, we show that in simulations of the dynamics of this strong glass former surprisingly large finite size effects are present. In particular we demonstrate that the relaxation times of the incoherent intermediate scattering function and the time dependence of the mean squared displacement are affected by such finite size effects. By compressing the system to high densities, we transform it to a fragile glass former and find that for that system these types of finite size effects are much weaker.Comment: 12 pages of RevTex, 4 postscript figures available from W. Ko

Microbiota cultivable fecal, crecimiento y parámetros clínicos de terneros suplementados con bacterias ácido lácticas y lactosa previo y durante una infección experimental con Salmonella Dublin DSPV 595T

The aim of this study was to evaluate the probiotic inoculum + lactose effect on weight, intestinal culturable microbiota, morbidity and mortality of young calves challenged with Salmonella Dublin DSPV 595T. Twenty eight calves were used, divided in control group (CG) and probiotic group (PG). The PG was provided with 100 g lactose.calf-1.d-1 and 1010 CFU.calf-1.d-1 of each strain of a probiotic inoculum composed of Lactobacillus casei DSPV 318T, Lactobacillus salivarius DSPV 315T and Pediococcus acidilactici DSPV 006T throughout the experiment. The pathogen was administered on day 11 of the experiment, at an oral dose of 109 CFU.calf-1. Lactobacillus and yeast populations were modified in PG because of inoculum + lactose administration. Severity of diarrhea was lower in PG. No differences were found on the rest of clinical sings, live weight and mortality between the two groups analyzed. In our study, the periodic administration of a probiotic inoculum of bovine origin and lactose, favoured the establishment of a more stable and balanced intestinal culturable microbiota, even during an infection with Salmonella. The generated model of acute infection gave opportunity to the probiotic to exert its beneficial effect on severity of diarrhea. However, for future studies use of lower doses of S. Dublin DSPV 595T are recommended, to generate less severe model for evaluate if the inoculum is able to exert a differential response in the clinical symptoms of young calves.El objetivo de este trabajo fue evaluar el efecto del inóculo probiótico + lactosa sobre el peso, la microbiota intestinal, la morbilidad y la mortalidad de terneros jóvenes desafiados con Salmonella Dublin DSPV 595T. Se utilizaron 24 terneros divididos en un grupo control (GC) y un grupo probiótico (GP). Al GP se le administró 100 g lactosa.ternero–1.d–1 y 1010 UFC.ternero-1.d–1 de cada cepa de un inóculo probiótico compuesto por Lactobacillus casei DSPV318T, Lactobacillus salivarius DSPV315T y Pediococcus acidilactici DSPV006T a lo largo de todo el experimento. El patógeno fue administrado el día 11 del experimento, en una dosis oral de 109 UFC.animal–1. Las poblaciones de Lactobacillus y levaduras fueron modificadas en el GP a causa de la administración del inóculo + lactosa. La severidad de la diarrea fue menor en el GP. No se encontraron diferencias en el resto de los signos clínicos, el peso vivo y la mortalidad entre los dos grupos analizados. En este estudio, la administración periódica de un inóculo probiótico de origen bovino y lactosa, favoreció el establecimiento de una microbiota intestinal más estable y balanceada, aun durante una infección con Salmonella. El modelo de infección aguda le dio la oportunidad al probiótico de ejercer su efecto benéfico sobre la severidad de la diarrea. Sin embargo, para futuros estudios se recomienda el uso de dosis menores de S. Dublin DSPV 595T, para generar un modelo menos severo para evaluar si el inóculo es capaz de ejercer una respuesta diferente en los signos clínicos de terneros jóvenes.Fil: Soto, Lorena Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Ciencias Veterinarias del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias. Departamento de Salud Pública Veterinaria; ArgentinaFil: Frizzo, Laureano Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Ciencias Veterinarias del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias. Departamento de Salud Pública Veterinaria; ArgentinaFil: Signorini Porchietto, Marcelo Lisandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Ciencias Veterinarias del Litoral; Argentina. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Zbrun, María Virginia. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias. Departamento de Salud Pública Veterinaria; ArgentinaFil: Lavari, Luisina. Universidad Católica de Córdoba. Facultad de Ciencias Agrarias; ArgentinaFil: Bertozzi, E.. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias. Departamento de Salud Pública Veterinaria; ArgentinaFil: Sequeira, G. J.. Universidad Católica de Córdoba. Facultad de Ciencias Agrarias; ArgentinaFil: Rosmini, M.R.. Universidad Católica de Córdoba. Facultad de Ciencias Agrarias; Argentin

Role of break-up processes in fusion enhancement of drip-line nuclei at energies below the Coulomb barrier

We carry out realistic coupled-channels calculations for $^{11}$Be + $^{208}$Pb reaction in order to discuss the effects of break-up of the projectile nucleus on sub-barrier fusion. We discretize in energy the particle continuum states, which are associated with the break-up process, and construct the coupling form factors to these states on a microscopic basis. The incoming boundary condition is employed in solving coupled-channels equations, which enables us to define the flux for complete fusion inside the Coulomb barrier. It is shown that complete fusion cross sections are significantly enhanced due to the couplings to the continuum states compared with the no coupling case at energies below the Coulomb barrier, while they are hindered at above barrier energies.Comment: RevTex, 3 pages, 5 figure

Simultaneous Optical Model Analyses of Elastic Scattering, Breakup, and Fusion Cross Section Data for the 6^{6}He + 209^{209}Bi System at Near-Coulomb-Barrier Energies

Based on an approach recently proposed by us, simultaneous $\chi^{2}$-analyses are performed for elastic scattering, direct reaction (DR) and fusion cross sections data for the $^{6}$He+$^{209}$Bi system at near-Coulomb-barrier energies to determine the parameters of the polarization potential consisting of DR and fusion parts. We show that the data are well reproduced by the resultant potential, which also satisfies the proper dispersion relation. A discussion is given of the nature of the threshold anomaly seen in the potential

Testing Mode-Coupling Theory for a Supercooled Binary Lennard-Jones Mixture II: Intermediate Scattering Function and Dynamic Susceptibility

We have performed a molecular dynamics computer simulation of a supercooled binary Lennard-Jones system in order to compare the dynamical behavior of this system with the predictions of the idealized version of mode-coupling theory (MCT). By scaling the time $t$ by the temperature dependent $\alpha$-relaxation time $\tau(T)$, we find that in the $\alpha$-relaxation regime $F(q,t)$ and $F_s(q,t)$, the coherent and incoherent intermediate scattering functions, for different temperatures each follows a $q$-dependent master curve as a function of scaled time. We show that during the early part of the $\alpha$-relaxation, which is equivalent to the late part of the $\beta$-relaxation, these master curves are well approximated by the master curve predicted by MCT for the $\beta$-relaxation. This part is also fitted well by a power-law, the so-called von Schweidler law. We show that the effective exponent $b'$ of this power-law depends on the wave vector $q$ if $q$ is varied over a large range. The early part of the $\beta$-relaxation regime does not show the critical decay predicted by MCT. The $q$-dependence of the nonergodicity parameter for $F_{s}(q,t)$ and $F(q,t)$ are in qualitative agreement with MCT. On the time scale of the late $\alpha$-relaxation the correlation functions show a Kohlrausch-Williams-Watt behavior (KWW). The KWW exponent $\beta$ is significantly different from the effective von Schweidler exponent $b'$. At low temperatures the $\alpha$-relaxation time $\tau(T)$ shows a power-law behavior with a critical temperature that is the same as the one found previously for the diffusion constant [Phys. Rev. Lett. {\bf 73}, 1376 (1994)]. The critical exponent of this power-law and the von Schweidler exponent $b'$ fulfill the connection proposed by MCT between these two quantities. We also show that theComment: 28 Pages of REVTEX, Figures available from W. Ko

Towards an effective potential for the monomer, dimer, hexamer, solid and liquid forms of hydrogen fluoride

We present an attempt to build up a new two-body effective potential for hydrogen fluoride, fitted to theoretical and experimental data relevant not only to the gas and liquid phases, but also to the crystal. The model is simple enough to be used in Molecular Dynamics and Monte Carlo simulations. The potential consists of: a) an intra-molecular contribution, allowing for variations of the molecular length, plus b) an inter-molecular part, with three charged sites on each monomer and a Buckingham "exp-6" interaction between fluorines. The model is able to reproduce a significant number of observables on the monomer, dimer, hexamer, solid and liquid forms of HF. The shortcomings of the model are pointed out and possible improvements are finally discussed.Comment: LaTeX, 24 pages, 2 figures. For related papers see also http://www.chim.unifi.it:8080/~valle

Nonlinear Hydrodynamics of a Hard Sphere Fluid Near the Glass Transition

We conduct a numerical study of the dynamic behavior of a dense hard sphere fluid by deriving and integrating a set of Langevin equations. The statics of the system is described by a free energy functional of the Ramakrishnan-Yussouff form. We find that the system exhibits glassy behavior as evidenced through stretched exponential decay and two-stage relaxation of the density correlation function. The characteristic times grow with increasing density according to the Vogel-Fulcher law. The wavenumber dependence of the kinetics is extensively explored. The connection of our results with experiment, mode coupling theory, and molecular dynamics results is discussed.Comment: 34 Pages, Plain TeX, 12 PostScript Figures (not included, available on request