Structural and dynamic properties of SPC/E water

I have investigated the structural and dynamic properties of water by performing a series of molecular dynamic simulations in the range of temperatures from 213 K to 360 K, using the Simple Point Charge-Extended (SPC/E) model. I performed isobaric-isothermal simulations (1 bar) of 1185 water molecules using the GROMACS package. I quantified the structural properties using the oxygen-oxygen radial distribution functions, order parameters, and the hydrogen bond distribution functions, whereas, to analyze the dynamic properties I studied the behavior of the history-dependent bond correlation functions and the non-Gaussian parameter alpha_2(t) of the mean square displacement of water molecules. When the temperature decreases, the translational (tau) and orientational (Q) order parameters are linearly correlated, and both increase indicating an increasing structural order in the systems. The probability of occurrence of four hydrogen bonds and Q both have a reciprocal dependence with T, though the analysis of the hydrogen bond distributions permits to describe the changes in the dynamics and structure of water more reliably. Thus, an increase on the caging effect and the occurrence of long-time hydrogen bonds occur below 293 K, in the range of temperatures in which predominates a four hydrogen bond structure in the system.Comment: 7 pages, 6 figure

Preliminary study of advanced turboprop and turboshaft engines for light aircraft

The effects of engine configuration, advanced component technology, compressor pressure ratio and turbine rotor-inlet temperature on such figures of merit as vehicle gross weight, mission fuel, aircraft acquisition cost, operating, cost and life cycle cost are determined for three fixed- and two rotary-wing aircraft. Compared with a current production turboprop, an advanced technology (1988) engine results in a 23 percent decrease in specific fuel consumption. Depending on the figure of merit and the mission, turbine engine cost reductions required to achieve aircraft cost parity with a current spark ignition reciprocating (SIR) engine vary from 0 to 60 percent and from 6 to 74 percent with a hypothetical advanced SIR engine. Compared with a hypothetical turboshaft using currently available technology (1978), an advanced technology (1988) engine installed in a light twin-engine helicopter results in a 16 percent reduction in mission fuel and about 11 percent in most of the other figures of merit

Description of nuclear octupole and quadrupole deformation close to the axial symmetry: Octupole vibrations in the X(5) nuclei 150Nd and 152Sm

The model, introduced in a previous paper, for the description of the octupole and quadrupole degrees of freedom in conditions close to the axial symmetry, is used to describe the negative-parity band based on the first octupole vibrational state in nuclei close to the critical point of the U(5) to SU(3) phase transition. The situation of 150Nd and 152Sm is discussed in detail. The positive parity levels of these nuclei, and also the in-band E2 transitions, are reasonably accounted for by the X(5) model. With simple assumptions on the nature of the octupole vibrations, it is possible to describe, with comparable accuracy, also the negative parity sector, without changing the description of the positive-parity part.Comment: 8 pages, 5 figure

The nucleus as a fluid of skyrmions: Energy levels and nucleon properties in the medium

A model of a fluid of skyrmions coupled to a scalar and to the \o meson mean fields is developed. The central and spin-orbit potentials of a skyrmion generated by the fields predict correct energy levels in selected closed shell nuclei. The effect of the meson fields on the properties of skyrmions in nuclei is investigated.Comment: Latex format, 6 figures, Journal of Physics G, to be publishe

Consequences of wall stiffness for a beta-soft potential

Modifications of the infinite square well E(5) and X(5) descriptions of transitional nuclear structure are considered. The eigenproblem for a potential with linear sloped walls is solved. The consequences of the introduction of sloped walls and of a quadratic transition operator are investigated.Comment: RevTeX 4, 8 pages, as published in Phys. Rev.

Simplified approach to the application of the geometric collective model

The predictions of the geometric collective model (GCM) for different sets of Hamiltonian parameter values are related by analytic scaling relations. For the quartic truncated form of the GCM -- which describes harmonic oscillator, rotor, deformed gamma-soft, and intermediate transitional structures -- these relations are applied to reduce the effective number of model parameters from four to two. Analytic estimates of the dependence of the model predictions upon these parameters are derived. Numerical predictions over the entire parameter space are compactly summarized in two-dimensional contour plots. The results considerably simplify the application of the GCM, allowing the parameters relevant to a given nucleus to be deduced essentially by inspection. A precomputed mesh of calculations covering this parameter space and an associated computer code for extracting observable values are made available through the Electronic Physics Auxiliary Publication Service. For illustration, the nucleus 102Pd is considered.Comment: RevTeX 4, 15 pages, to be published in Phys. Rev.

The wall shear rate distribution for flow in random sphere packings

The wall shear rate distribution P(gamma) is investigated for pressure-driven Stokes flow through random arrangements of spheres at packing fractions 0.1 <= phi <= 0.64. For dense packings, P(gamma) is monotonic and approximately exponential. As phi --> 0.1, P(gamma) picks up additional structure which corresponds to the flow around isolated spheres, for which an exact result can be obtained. A simple expression for the mean wall shear rate is presented, based on a force-balance argument.Comment: 4 pages, 3 figures, 1 table, RevTeX 4; significantly revised with significantly extended scop

Exact diagonalization of the Bohr Hamiltonian for rotational nuclei: Dynamical gamma softness and triaxiality

Detailed quantitative predictions are obtained for phonon and multiphonon excitations in well-deformed rotor nuclei within the geometric framework, by exact numerical diagonalization of the Bohr Hamiltonian in an SO(5) basis. Dynamical gamma deformation is found to significantly influence the predictions through its coupling to the rotational motion. Basic signatures for the onset of rigid triaxial deformation are also obtained.Comment: 17 pages, 10 figures; to be published Phys. Rev.

The tensor part of the Skyrme energy density functional. I. Spherical nuclei

We perform a systematic study of the impact of the J^2 tensor term in the Skyrme energy functional on properties of spherical nuclei. In the Skyrme energy functional, the tensor terms originate both from zero-range central and tensor forces. We build a set of 36 parameterizations, which covers a wide range of the parameter space of the isoscalar and isovector tensor term coupling constants, with a fit protocol very similar to that of the successful SLy parameterizations. We analyze the impact of the tensor terms on a large variety of observables in spherical mean-field calculations, such as the spin-orbit splittings and single-particle spectra of doubly-magic nuclei, the evolution of spin-orbit splittings along chains of semi-magic nuclei, mass residuals of spherical nuclei, and known anomalies of charge radii. Our main conclusion is that the currently used central and spin-orbit parts of the Skyrme energy density functional are not flexible enough to allow for the presence of large tensor terms.Comment: 38 pages, 36 figures; Minor correction

Magnetic Resonance Imaging Pilot Study of Intravenous Glyburide in Traumatic Brain Injury.

Pre-clinical studies of traumatic brain injury (TBI) show that glyburide reduces edema and hemorrhagic progression of contusions. We conducted a small Phase II, three-institution, randomized placebo-controlled trial of subjects with TBI to assess the safety and efficacy of intravenous (IV) glyburide. Twenty-eight subjects were randomized and underwent a 72-h infusion of IV glyburide or placebo, beginning within 10 h of trauma. Of the 28 subjects, 25 had Glasgow Coma Scale (GCS) scores of 6-10, and 14 had contusions. There were no differences in adverse events (AEs) or severe adverse events (ASEs) between groups. The magnetic resonance imaging (MRI) percent change at 72-168 h from screening/baseline was compared between the glyburide and placebo groups. Analysis of contusions (7 per group) showed that lesion volumes (hemorrhage plus edema) increased 1036% with placebo versus 136% with glyburide (p = 0.15), and that hemorrhage volumes increased 11.6% with placebo but decreased 29.6% with glyburide (p = 0.62). Three diffusion MRI measures of edema were quantified: mean diffusivity (MD), free water (FW), and tissue MD (MDt), corresponding to overall, extracellular, and intracellular water, respectively. The percent change with time for each measure was compared in lesions (n = 14) versus uninjured white matter (n = 24) in subjects receiving placebo (n = 20) or glyburide (n = 18). For placebo, the percent change in lesions for all three measures was significantly different compared with uninjured white matter (analysis of variance [ANOVA], p &lt; 0.02), consistent with worsening of edema in untreated contusions. In contrast, for glyburide, the percent change in lesions for all three measures was not significantly different compared with uninjured white matter. Further study of IV glyburide in contusion TBI is warranted