21 research outputs found
Kappa-deformed Statistics and the Formation of a Quark-Gluon Plasma
The effect of the non-extensive form of statistical mechanics proposed by
Tsallis on the formation of a quark-gluon plasma (QGP) has been recently
investigated in ref. \cite{1}. The results show that for small deviations
() from Boltzmann-Gibbs (BG) statistics in the QGP phase, the
critical temperature for the formation of a QGP does not change substantially
for a large variation of the chemical potential. In the present effort we use
the extensive -deformed statistical mechanics constructed by Kaniadakis
to represent the constituents of the QGP and compare the results with ref. [1].Comment: 2 Figure
Nonextensive statistical effects on the relativistic nuclear equation of state
Following the basic prescriptions of the Tsallis' nonextensive
thermodynamics, we study the relativistic nonextensive thermodynamics and the
equation of state for a perfect gas at the equilibrium. The obtained results
are used to study the relativistic nuclear equation of state in the hadronic
and in the quark-gluon plasma phase. We show that small deviations from the
standard extensive statistics imply remarkable effects into the shape of the
equation of state.Comment: Contribution to International Workshop on: Trends and Perspectives in
Extensive and Non-Extensive Statistical Mechanics (in Honour to the q-60th
Birthday of Constantino Tsallis) November 19-21, 2003, Angra dos Reis,
Brazil. 8 pages including 2 figure
Resonant Raman study of local vibrational modes in AlGaAsN layers
We report on resonant inelastic light scattering in dilute AlGaAsN films. Intense narrow peaks associated to N-related local vibration modes (LVM) have been observed around 325, 385, 400, 450, 500 and 540 cmâ1. Their frequencies are compared to density functional theory supercell calculations of AlnGa4ânN complexes (n=1â4). We find clear indications of the formation of Al4N complexes. The values of the extended phonon frequencies reveal changes in the N distribution depending on the growth conditions. The LVM spectra are resonant in the energy range from 1.75 to 1.79 eV, which corresponds to an N-related electronic transition. Our results confirm the preferential bonding of N to Al in AlGaAsN
Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies
We investigate the relativistic equation of state of hadronic matter and
quark-gluon plasma at finite temperature and baryon density in the framework of
the non-extensive statistical mechanics, characterized by power-law quantum
distributions. We impose the Gibbs conditions on the global conservation of
baryon number, electric charge and strangeness number. For the hadronic phase,
we study an extended relativistic mean-field theoretical model with the
inclusion of strange particles (hyperons and mesons). For the quark sector, we
employ an extended MIT-Bag model. In this context we focus on the relevance of
non-extensive effects in the presence of strange matter.Comment: 12 pages, 5 figure
Large amplitude fluxional behaviour of elemental calcium under high pressure
Experimental evidences are presented showing unusually large and highly anisotropic vibrations in the âsimple cubicâ (SC) unit cell adopted by calcium over a broad pressure ranging from 30â90 GPa and at temperature as low as 40â
K. X-ray diffraction patterns show a preferential broadening of the (110) Bragg reflection indicating that the atomic displacements are not isotropic but restricted to the [110] plane. The unusual observation can be rationalized invoking a simple chemical perspective. As the result of pressure-induced s â d transition, Ca atoms situated in the octahedral environment of the simple cubic structure are subjected to Jahn-Teller distortions. First-principles molecular dynamics calculations confirm this suggestion and show that the distortion is of dynamical nature as the cubic unit cell undergoes large amplitude tetragonal fluctuations. The present results show that, even under extreme compression, the atomic configuration is highly fluxional as it constantly changes
Simple Metals at High Pressure
In this lecture we review high-pressure phase transition sequences exhibited
by simple elements, looking at the examples of the main group I, II, IV, V, and
VI elements. General trends are established by analyzing the changes in
coordination number on compression. Experimentally found phase transitions and
crystal structures are discussed with a brief description of the present
theoretical picture.Comment: 22 pages, 4 figures, lecture notes for the lecture given at the Erice
course on High-Pressure Crystallography in June 2009, Sicily, Ital
Pressure-induced amorphous-to-amorphous configuration change in Ca-Al metallic glasses
Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40â
GPa. Changes in compressibility at about 18â
GPa, 15.5â
GPa and 7.5â
GPa during compression are detected in Ca80Al20, Ca72.7Al27.3, and Ca66.4Al33.6 MGs, respectively, whereas no clear change has been detected in the Ca50Al50 MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs