357 research outputs found
Modeling the adsorption of benzeneacetic acid on CaO2 nanoparticles using artificial neural network
The present work reported a method for removal of benzeneacetic acid from water solution using CaO2 nanoparticle as adsorbent and modeling the adsorption process using artificial neural network (ANN). CaO2 nanoparticles were synthesized by a chemical precipitation technique. The characterization and confirmation of nanoparticles have been done by using different techniques such as X-ray powder diffraction (XRD), high resolution field emission scanning electron microscope (HR-FESEM),transmittance electron microscopy (TEM) and high-resolution TEM (HRTEM) analysis. ANN model was developed by using elite-ANN software. The network was trained using experimental data at optimum temperature and time with different CaO2 nanoparticle dosage (0.002-0.05 g) and initial benzeneacetic acid concentration (0.03-0.099 mol/L). Root mean square error (RMS) of 3.432, average percentage error (APE) of 5.813 and coefficient of determination (R2 ) of 0.989 were found for prediction and modeling of benzeneacetic acid removal. The trained artificial neural network is employed to predict the output of the given set of input parameters. The single-stage batch adsorber design of the adsorption of benzeneacetic acid onto CaO2 nanoparticles has been studied with well fitted Langmuir isotherm equation which is homogeneous and has monolayer sorption capacity
The Moment of Inertia of the Binary Pulsar J0737-3039A: Constraining the Nuclear Equation of State
We construct numerical models of the newly discovered binary pulsar
J0737-3039A, both with a fully relativistic, uniformly rotating, equilibrium
code that handles arbitrary spins and in the relativistic, slow-rotation
approximation. We compare results for a representative sample of viable nuclear
equations of state (EOS) that span three, qualitatively different, classes of
models for the description of nuclear matter. A future dynamical measurement of
the neutron star's moment of inertia from pulsar timing data will impose
significant constraints on the nuclear EOS. Even a moderately accurate
measurement (<~ 10 %) may be able to rule out some of these competing classes.
Using the measured mass, spin and moment of inertia to identify the optimal
model computed from different EOSs, one can determine the pulsar's radius.Comment: 4 pages, ApJL in pres
Cold Bose gases with large scattering lengths
We calculate the energy and condensate fraction for a dense system of bosons
interacting through an attractive short range interaction with positive s-wave
scattering length . At high densities, , the energy per particle,
chemical potential, and square of the sound speed are independent of the
scattering length and proportional to , as in Fermi systems.Comment: 4 pages, 3 figure
Spin-Isospin Structure and Pion Condensation in Nucleon Matter
We report variational calculations of symmetric nuclear matter and pure
neutron matter, using the new Argonne v18 two-nucleon and Urbana IX
three-nucleon interactions. At the equilibrium density of 0.16 fm^-3 the
two-nucleon densities in symmetric nuclear matter are found to exhibit a
short-range spin-isospin structure similar to that found in light nuclei. We
also find that both symmetric nuclear matter and pure neutron matter undergo
transitions to phases with pion condensation at densities of 0.32 fm^-3 and 0.2
fm^-3, respectively. Neither transtion occurs with the Urbana v14 two-nucleon
interaction, while only the transition in neutron matter occurs with the
Argonne v14 two-nucleon interaction. The three-nucleon interaction is required
for the transition to occur in symmetric nuclear matter, whereas the the
transition in pure neutron matter occurs even in its absence. The behavior of
the isovector spin-longitudinal response and the pion excess in the vicinity of
the transition, and the model dependence of the transition are discussed.Comment: 44 pages RevTeX, 15 postscript figures. Minor modifications to
original postin
Head-on collisions of binary white dwarf--neutron stars: Simulations in full general relativity
We simulate head-on collisions from rest at large separation of binary white
dwarf -- neutron stars (WDNSs) in full general relativity. Our study serves as
a prelude to our analysis of the circular binary WDNS problem. We focus on
compact binaries whose total mass exceeds the maximum mass that a cold
degenerate star can support, and our goal is to determine the fate of such
systems. A fully general relativistic hydrodynamic computation of a realistic
WDNS head-on collision is prohibitive due to the large range of dynamical time
scales and length scales involved. For this reason, we construct an equation of
state (EOS) which captures the main physical features of NSs while, at the same
time, scales down the size of WDs. We call these scaled-down WD models
"pseudo-WDs (pWDs)". Using pWDs, we can study these systems via a sequence of
simulations where the size of the pWD gradually increases toward the realistic
case. We perform two sets of simulations; One set studies the effects of the NS
mass on the final outcome, when the pWD is kept fixed. The other set studies
the effect of the pWD compaction on the final outcome, when the pWD mass and
the NS are kept fixed. All simulations show that 14%-18% of the initial total
rest mass escapes to infinity. All remnant masses still exceed the maximum rest
mass that our cold EOS can support (1.92 solar masses), but no case leads to
prompt collapse to a black hole. This outcome arises because the final
configurations are hot. All cases settle into spherical, quasiequilibrium
configurations consisting of a cold NS core surrounded by a hot mantle,
resembling Thorne-Zytkow objects. Extrapolating our results to realistic WD
compactions, we predict that the likely outcome of a head-on collision of a
realistic, massive WDNS system will be the formation of a quasiequilibrium
Thorne-Zytkow-like object.Comment: 24 pages, 14 figures, matches PRD published version, tests of HRSC
schemes with piecewise polytropes adde
Many-body effects in 16O(e,e'p)
Effects of nucleon-nucleon correlations on exclusive reactions on
closed-shell nuclei leading to single-hole states are studied using
( MeV, ) as an example. The quasi-hole wave
function, calculated from the overlap of translationally invariant many-body
variational wave functions containing realistic spatial, spin and isospin
correlations, seems to describe the initial state of the struck proton
accurately inside the nucleus, however it is too large at the surface. The
effect of short-range correlations on the final state is found to be largely
cancelled by the increase in the transparency for the struck proton. It is
estimated that the values of the spectroscopic factors obtained with the DWIA
may increase by a few percent due to correlation effects in the final state.Comment: 21 Pages, PHY-7849-TH-9
Superfluid Fermi Gases with Large Scattering Length
We report quantum Monte Carlo calculations of superfluid Fermi gases with
short-range two-body attractive interactions with infinite scattering length.
The energy of such gases is estimated to be times that of the
noninteracting gas, and their pairing gap is approximately twice the energy per
particle.Comment: 4 pages, 4 figure
Quadratic momentum dependence in the nucleon-nucleon interaction
We investigate different choices for the quadratic momentum dependence
required in nucleon-nucleon potentials to fit phase shifts in high
partial-waves. In the Argonne v18 potential L**2 and (L.S)**2 operators are
used to represent this dependence. The v18 potential is simple to use in
many-body calculations since it has no quadratic momentum-dependent terms in
S-waves. However, p**2 rather than L**2 dependence occurs naturally in
meson-exchange models of nuclear forces. We construct an alternate version of
the Argonne potential, designated Argonne v18pq, in which the L**2 and (L.S)**2
operators are replaced by p**2 and Qij operators, respectively. The quadratic
momentum-dependent terms are smaller in the v18pq than in the v18 interaction.
Results for the ground state binding energies of 3H, 3He, and 4He, obtained
with the variational Monte Carlo method, are presented for both the models with
and without three-nucleon interactions. We find that the nuclear wave functions
obtained with the v18pq are slightly larger than those with v18 at
interparticle distances < 1 fm. The two models provide essentially the same
binding in the light nuclei, although the v18pq gains less attraction when a
fixed three-nucleon potential is added.Comment: v.2 important corrections in tables and minor revisions in text;
reference for web-posted subroutine adde
Curvature effects on the surface thickness and tension at the free interface of He systems
The thickness and the surface energy at the free interface of
superfluid He are studied. Results of calculations carried out by using
density functionals for cylindrical and spherical systems are presented in a
unified way, including a comparison with the behavior of planar slabs. It is
found that for large species is independent of the geometry. The obtained
values of are compared with prior theoretical results and experimental
data. Experimental data favor results evaluated by adopting finite range
approaches. The behavior of and exhibit overshoots
similar to that found previously for the central density, the trend of these
observables towards their asymptotic values is examined.Comment: 35 pages, TeX, 5 figures, definitive versio
Merger of binary neutron stars with realistic equations of state in full general relativity
We present numerical results of three-dimensional simulations for the merger
of binary neutron stars (BNSs) in full general relativity. Hybrid equations of
state (EOSs) are adopted to mimic realistic nuclear EOSs. In this approach, we
divide the EOSs into two parts, i.e., the thermal part and the cold part. For
the cold part, we assign a fitting formula for realistic EOSs of cold nuclear
matter slightly modifying the formula developed by Haensel and Potekhin. We
adopt the SLy and FPS EOSs for which the maximum allowed ADM mass of cold and
spherical neutron stars (NSs) is ~ 2.04Mo and 1.80Mo, respectively. Simulations
are performed for BNSs of the total ADM mass in the range between 2.4Mo and
2.8Mo with the rest-mass ratio Q_M to be in the range 0.9 < Q_M < 1. It is
found that if the total ADM mass of the system is larger than a threshold
M_{thr}, a black hole (BH) is promptly formed in the merger irrespective of the
mass ratios. In the other case, the outcome is a hypermassive NS of a large
ellipticity, which results from the large adiabatic index of the realistic EOSs
adopted. The value of M_{thr} depends on the EOS: ~ 2.7Mo and ~ 2.5Mo for the
SLy and FPS EOSs, respectively. Gravitational waves are computed in terms of a
gauge-invariant wave extraction technique. In the formation of the hypermassive
NS, quasiperiodic gravitational waves of a large amplitude and of frequency
between 3 and 4 kHz are emitted. The estimated emission time scale is < 100 ms,
after which the hypermassive NS collapses to a BH. Because of the long emission
time, the effective amplitude may be large enough to be detected by advanced
laser interferometric gravitational wave detectors if the distance to the
source is smaller than ~ 100 Mpc.Comment: Typos corrected, 2 references and comments on them added, 26 pages,
54 Postscript figures, Phys.Rev.D in pres
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