7,103 research outputs found
Extraction of nuclear matter properties from nuclear masses by a model of equation of state
The extraction of nuclear matter properties from measured nuclear masses is
investigated in the energy density functional formalism of nuclei. It is shown
that the volume energy and the nuclear incompressibility depend
essentially on , whereas the symmetry energy
and the density symmetry coefficient as well as symmetry incompressibility
depend essentially on , where
, and are the
neutron and proton chemical potentials respectively, the nuclear energy,
and the Coulomb energy. The obtained symmetry energy is ,
while other coefficients are uncertain within ranges depending on the model of
nuclear equation of state.Comment: 12 pages and 7 figure
Effective nucleon-nucleon interactions and nuclear matter equation of state
Nuclear matter equations of state based on Skyrme, Myers-Swiatecki and
Tondeur interactions are written as polynomials of the cubic root of density,
with coefficients that are functions of the relative neutron excess .
In the extrapolation toward states far away from the standard one, it is shown
that the asymmetry dependence of the critical point ()
depends on the model used. However, when the equations of state are fitted to
the same standard state, the value of is almost the same in Skyrme
and in Myers-Swiatecki interactions, while is much lower in Tondeur
interaction. Furthermore, does not depend sensitively on the choice
of the parameter in Skyrme interaction.Comment: 15 pages, 9 figure
Nuclear matter properties and relativistic mean-field theory
Nuclear matter properties are calculated in the relativistic mean field
theory by using a number of different parameter sets. The result shows that the
volume energy and the symmetry energy are around the acceptable
values 16MeV and 30MeV respectively; the incompressibility is
unacceptably high in the linear model, but assumes reasonable value if
nonlinear terms are included; the density symmetry is around for
most parameter sets, and the symmetry incompressibility has positive sign
which is opposite to expectations based on the nonrelativistic model. In almost
all parameter sets there exists a critical point , where
the minimum and the maximum of the equation of state are coincident and the
incompressibility equals zero, falling into ranges
0.014fmfm and ; for a few
parameter sets there is no critical point and the pure neutron matter is
predicted to be bound. The maximum mass of neutron stars is predicted
in the range 2.45MM, the corresponding
neutron star radius is in the range 12.2kmkm.Comment: 10 pages, 5 figure
An Analytic Equation of State for Ising-like Models
Using an Environmentally Friendly Renormalization we derive, from an
underlying field theory representation, a formal expression for the equation of
state, , that exhibits all desired asymptotic and analyticity
properties in the three limits , and . The only
necessary inputs are the Wilson functions , and
, associated with a renormalization of the transverse vertex
functions. These Wilson functions exhibit a crossover between the Wilson-Fisher
fixed point and the fixed point that controls the coexistence curve.
Restricting to the case N=1, we derive a one-loop equation of state for naturally parameterized by a ratio of non-linear scaling fields. For
we show that a non-parameterized analytic form can be deduced. Various
asymptotic amplitudes are calculated directly from the equation of state in all
three asymptotic limits of interest and comparison made with known results. By
positing a scaling form for the equation of state inspired by the one-loop
result, but adjusted to fit the known values of the critical exponents, we
obtain better agreement with known asymptotic amplitudes.Comment: 10 pages, 2 figure
ALTERATIONS IN GROUND REACTION FORCES DURING TETHERED WALKING
This study examined t h e e f f e c t s of tethering conditions on ground forces while walking a t 2.5 mph. Six males w e r e unweighted 0%, 25%, 50% and 75% of t h e i r BWT while supported i n a Kinney upper body vest by an active traction prototype (Conva-Lift). They walked 10 min. a t each randomly selected unweighting condition in a 12 f t . dia. c i r c l e . Ten right and l e f t s t r i d e impacts w e r e collected a t 1000 Hz with an Ariel APAS system using a K i s t l e r force plate during each condition a t 2.5 mph (27%). Walking velocity was verified by an infra-red timing system. 5 right and l e f t s t r i d e s in which the velocity was closest t o 2.5 mph w e r e selected for analysis. The s t r i d e was delineated into the phases of heelstrike (HS), midfoot support (MFS), and toe-off (TO). The v e r t i c a l forces (F,) a t the 3 phases, the fore-aft forces (Fy) a t HS and TO and the contact time w e r e calculated. A 4x2x5 ANOVA (WtxFtxLeg) with repeated measures on a l l factors was used t o analyze (F,) forces a t HS, MFS, and TO, fore-aft forces (Fy) a t HS, TO, and contact t i m e . The v e r t i c a l forces (Fz) a t HS w e r e 902.0+112.9 Nt(76% BWT), and 389.3276.8 Nt(45% BWT) for the unweighting conditions. The i n i t i a l impact forces w e r e consistent with normal overland walking and the F, forces w e r e significantly reduced when the subject was unweighted a t 50% and 75% of t h e i r BWT. The forea f t forces representing the decelerative forces w e r e 16%, 16%, lo%, and 4% BWT for the weight conditions. Significant differences w e r e found t o exist between the i n i t i a l contact force a t 0% ( f u l l BWT) and 75% unweighting. The MFS v e r t i c a l forces (F,) w e r e 682.7±73.4, 595.7±73.3, 395.9±49.8, and 234.3±28.7 N t for the loading conditions. The midfoot forces represented about a 30% reduction or absorption of the i n i t i a l impact forces, while the 75% condition exhibited only a 18% reduction in the impact force which would suggest that weight bearing mechanism of the arch of the foot functioned differently when unloaded. The F, forces a t TO significantly differed from 869.1±118.5, 76.56±105.4, 537.9±91.8, and 281.4±78.2 f o r t h e conditions. The percentage of reduction of F, forces a t HS and TO for the unweighting conditions, and the v e r t i c a l forces a t TO w e r e decreased more for a similar degree of unweighting. This finding would suggest that t h i s active traction prototype might be beneficial in t h e r e h a b i l i t a t i o n of posterior compartment injuries. When examining the reduction i n the fore-aft accelerative forces a t TO, the % BWT w e r e similar t o the F, forces a t HS for similar unloading conditions. The s t r i d e contact times significantly differed between ,705±03 sec for t h e r i g h t s t r i d e s and ,68±.04 sec for the l e f t s t r i d e s and no differences existed for the weighting condition. Significant time differences w e r e attributable t o the outside leg having t o travel a greater distance in the same t i m e a s t h e inner leg, while walking in a c i r c l e . The Conva-Lift's travel direction is reversible t o prevent any imbalances due t o circular walking. The significant differences in the ground reaction forces in the v e r t i c a l and fore-aft direction as the subjects w e r e unweighted would indicate that the Conva-Lift is a viable means of reducing ground reaction forces while ambulating
Wetting phenomenon in the liquid-vapor phase coexistence of a partially miscible Lennard-Jones binary mixture
We have carried out extensive equilibrium molecular dynamics (MD) simulations
to study the structure and the interfacial properties in the liquid-vapor (LV)
phase coexistence of partially miscible binary Lennard-Jones (LJ) mixtures. By
analyzing the structural properties as a function of the miscibility parameter,
, we found that at relatively low temperatures the system separates
forming a liquid A-liquid B interface in coexistence with the vapor phase. At
higher temperatures and, , we found a temperature range,
, where the liquid phases
are wet by the vapor phase. Here, represents the wetting
transition temperature (WTT) and is the consolute
temperature of the mixture. However, for , no wetting
phenomenon occurs. For the particular value, , we analyzed
quantitatively the versus , and versus
phase diagrams and found, , and
. We also studied quantitatively, as a function of
temperature, the surface tension and the adsorption of molecules at the
liquid-liquid interface. It was found that the adsorption shows a jump from a
finite negative value up to minus infinity, when the vapor wets the liquid
phases, suggesting that the wetting transition (WT) is of first order. The
calculated phase diagram together with the wetting phenomenon strongly suggest
the existence of a tricritical point. These results agree well with some
experiments carried out in fluid binary mixtures.Comment: Enlarged version that include results of more extensive simulations.
A total of 24 LaTeX pages that include 12 encapsulated poscript figures. To
appear in PRE, Vol. 70, issue Sept. 1st (2004
- âŠ