27 research outputs found
Temperature dependence of volume and surface symmetry energy coefficients of nuclei
AbstractThe thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature ThomasâFermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified SeylerâBlanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild
Liquid-gas phase transition in finite nuclei
In a finite temperature Thomas-Fermi framework, we calculate density
distributions of hot nuclei enclosed in a freeze-out volume of few times the
normal nuclear volume and then construct the caloric curve, with and without
inclusion of radial collective flow. In both cases, the calculated specific
heats show a peaked structure signalling a liquid-gas phase transition.
Without flow, the caloric curve indicates a continuous phase transition whereas
with inclusion of flow, the transition is very sharp. In the latter case, the
nucleus undergoes a shape change to a bubble from a diffuse sphere at the
transition temperature.Comment: Proc. of 6th Int. Conf. on N-N Collisions (Gatlinburg); Nuclear
Physics A (in press
Nuclear expansion with excitation
The expansion of an isolated hot spherical nucleus with excitation energy and
its caloric curve are studied in a thermodynamic model with the SkM* force as
the nuclear effective two-body interaction. The calculated results are shown to
compare well with the recent experimental data from energetic nuclear
collisions. The fluctuations in temperature and density are also studied. They
are seen to build up very rapidly beyond an excitation energy of 9 MeV/u.
Volume-conserving quadrupole deformation in addition to expansion indicates,
however, nuclear disassembly above an excitation energy of 4 MeV/uComment: 17 pages, 5 figures, revtex4; calculations with deformation adde
Spin polarised nuclear matter and its application to neutron stars
An equation of state(EOS) of nuclear matter with explicit inclusion of a
spin-isospin dependent force is constructed from a finite range, momentum and
density dependent effective interaction. This EOS is found to be in good
agreement with those obtained from more sophisticated models for unpolarised
nuclear matter. Introducing spin degrees of freedom, it is found that at
density about 2.5 times the density of normal nuclear matter the neutron matter
undergoes a ferromagnetic transition. The maximum mass and the radius of the
neutron star agree favourably with the observations. Since finding quark matter
rather than spin polarised nuclear matter at the core of neutron stars is more
probable, the proposed EOS is also applied to the study of hybrid stars. It is
found using the bag model picture that one can in principle describe both the
mass and size as well as the surface magnetic field of hybrid stars
satisfactorily.Comment: 26 pages, 11 figures available on reques
Isospin influences on particle emission and critical phenomenon in nuclear dissociation
Features of particle emission and critical point behavior are investigated as
functions of the isospin of disassembling sources and temperature at a moderate
freeze-out density for medium-size Xe isotopes in the framework of isospin
dependent lattice gas model. Multiplicities of emitted light particles,
isotopic and isobaric ratios of light particles show the strong dependence on
the isospin of the dissociation source, but double ratios of light isotope
pairs and the critical temperature determined by the extreme values of some
critical observables are insensitive to the isospin of the systems. Values of
the power law parameter of cluster mass distribution, mean multiplicity of
intermediate mass fragments (), information entropy () and Campi's
second moment () also show a minor dependence on the isospin of Xe
isotopes at the critical point. In addition, the slopes of the average
multiplicites of the neutrons (), protons (), charged particles
(), and IMFs (), slopes of the largest fragment mass number
(), and the excitation energy per nucleon of the disassembling source
() to temperature are investigated as well as variances of the
distributions of , , , , and . It
is found that they can be taken as additional judgements to the critical
phenomena.Comment: 9 Pages, 8 figure
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Computer applications for engineering/structural analysis
Analysts and organizations have a tendency to lock themselves into specific codes with the obvious consequences of not addressing the real problem and thus reaching the wrong conclusion. This paper discusses the role of the analyst in selecting computer codes. The participation and support of a computation division in modifying the source program, configuration management, and pre- and post-processing of codes are among the subjects discussed. Specific examples illustrating the computer code selection process are described in the following problem areas: soil structure interaction, structural analysis of nuclear reactors, analysis of waste tanks where fluid structure interaction is important, analysis of equipment, structure-structure interaction, analysis of the operation of the superconductor supercollider which includes friction and transient temperature, and 3D analysis of the 10-meter telescope being built in Hawaii. Validation and verification of computer codes and their impact on the selection process are also discussed
Application of the Ising model to the study of cluster multiplicities in finite excited systems
The political debat around the Iraqi war was not engaged only at the level of international organisations, such as NATO or UNO, but also in cyberspace. This debate does not reproduce the one that involves the traditional media. The semiotic analysis of the virtual discourses shows that these are developed according to a specific rhetorics. As soon as the papers published some fragments from e-mails and web-postings, the difference became obvious. Moreover, the objection against the public character of the virtual discourse is meaningful, as it points to the fact that the cyber-people themselves doubt the legitimacy of their own discourses. The case-study shows how cyber-self-awareness that emerges from cyber-practices is coupled to a self-cyber-awareness
NON-EQUILIBRIUM NUCLEON EMISSION AROUND THE FERMI ENERGY REGION
Emission of fast energetic nucleons in intermediate energy nuclear collisions is investigated in the framework of two specific non-equilibrium models. In the lower energy region considered, the Fermi Jet mechanism dominates whereas results in the higher energy region are suggestive of emission from a hot dense source formed inside cold nuclear matter