737 research outputs found
Design of enantioselective catalysts in MOF architectures : a combined computational and experimental approach
Synthesis, characterization, adsorption and catalytic properties of an amino functionalized Metal-Organic Framework : NH2-MIL-47
Non equilibrium thermodynamics and cosmological pancakes formation
We investigate the influence of non equilibrium thermodynamics on
cosmological structure formation. In this paper, we consider the collapse of
planar perturbations usually called "Zel'dovich pancakes". We have developed
for that purpose a new two fluids (gas and dark matter) hydrodynamical code,
with three different thermodynamical species: electrons, ions and neutral
particles (T_e\ne T_i \ne T_n). We describe in details the complex structure of
accretion shock waves. We include several relevant processes for a low density,
high temperature, collisional plasma such as non-equilibrium chemical
reactions, cooling, shock heating, thermal energy equipartition between
electrons, ions and neutral particles and electronic conduction. We find two
different regions in the pancake structure: a thermal precursor ahead of the
compression front and an equipartition wave after the compression front where
electrons and ions temperatures differ significantly. This complex structure
may have two interesting consequences: pre-heating of unshocked regions in the
vicinity of massive X-ray clusters and ions and electrons temperatures
differences in the outer regions of X-rays clusters.Comment: 30 pages, including 8 figures, accepted for publication in The
Astrophysical Journa
The Nucleon-Nucleon Interaction in a Chiral Constituent Quark Model
We study the short-range nucleon-nucleon interaction in a chiral constituent
quark model by diagonalizing a Hamiltonian comprising a linear confinement and
a Goldstone boson exchange interaction between quarks. The six-quark harmonic
oscillator basis contains up to two excitation quanta. We show that the highly
dominant configuration is due to its specific
flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a
strong effective repulsion at zero separation between nucleons in both
and channels. The symmetry structure of the highly dominant
configuration implies the existence of a node in the S-wave relative motion
wave function at short distances. The amplitude of the oscillation of the wave
function at short range will be however strongly suppressed. We discuss the
mechanism leading to the effective short-range repulsion within the chiral
constituent quark model as compared to that related with the one-gluon exchange
interaction.Comment: 31 pages, LaTe
Transformation of the Poynting flux into the kinetic energy in relativistic jets
The acceleration of relativistic jets from the Poynting to the matter
dominated stage is considered. The are generally two collimation regimes, which
we call equilibrium and non-equilibrium, correspondingly. In the first regime,
the jet is efficiently accelerated till the equipartition between the kinetic
and electro-magnetic energy. We show that after the equilibrium jet ceases to
be Poynting dominated, the ratio of the electro-magnetic to the kinetic energy
decreases only logarithmically so that such jets become truly matter dominated
only at extremely large distances. Non-equilibrium jets remain generally
Poynting dominated till the logarithmically large distances. In the only case
when a non-equilibrium jet is accelerated till the equipartition level, we
found that the flow is not continued to the infinity but is focused towards the
axis at a finite distance from the origin.Comment: Submitted to MNRAS Minor changes in the Conclusion
Aging processes in reversible reaction-diffusion systems
Reversible reaction-diffusion systems display anomalous dynamics
characterized by a power-law relaxation toward stationarity. In this paper we
study in the aging regime the nonequilibrium dynamical properties of some model
systems with reversible reactions. Starting from the exact Langevin equations
describing these models, we derive expressions for two-time correlation and
autoresponse functions and obtain a simple aging behavior for these quantities.
The autoresponse function is thereby found to depend on the specific nature of
the chosen perturbation of the system.Comment: 12 pages, accepted for publication in Phys. Rev.
Symmetry and magnetically driven ferroelectricity in rare-earth manganites RMnO3 (R=Gd, Tb, Dy)
This work investigates the magnetically driven ferroelectricity in
orthorhombic manganites RMnO3 (R=Gd, Dy or Tb) from the point of view of the
symmetry. The method adopted generalizes the one used to characterize the polar
properties of displacive modulated structures to the case of an irreducible
magnetic order parameter. The symmetry conditions for magnetically induced
ferroelectricity are established and the Landau-Devonshire free energy
functionals derived from general symmetry considerations. The ferroelectric
polarisation observed in DyMnO3 and TbMnO3 at zero magnetic field is explained
in terms of the symmetry of a reducible magnetic order parameter. The
polarisation rotation induced in these compounds by external magnetic fields
and the stabilization of a ferroelectric phase in GdMnO3 are accounted for by a
mechanism in which magnetization and polarization are secondary order
parameters that are not directly coupled but compete with each other through
their coupling to competing primary modulated order parameters.Comment: Article submitted to Physical Review B, 39 page
Weak-Field Gravity of Revolving Circular Cosmic Strings
A weak-field solution of Einstein's equations is constructed. It is generated
by a circular cosmic string revolving in its plane about the centre of the
circle. (The revolution is introduced to prevent the string from collapsing.)
This solution exhibits a conical singularity, and the corresponding deficit
angle is the same as for a straight string of the same linear energy density,
irrespective of the angular velocity of the string.Comment: 13 pages, LaTe
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