1,102 research outputs found
Local Molecular Dynamics with Coulombic Interaction
We propose a local, O(N) molecular dynamics algorithm for the simulation of
charged systems. The long ranged Coulomb potential is generated by a
propagating electric field that obeys modified Maxwell equations. On coupling
the electrodynamic equations to an external thermostat we show that the
algorithm produces an effective Coulomb potential between particles. On
annealing the electrodynamic degrees of freedom the field configuration
converges to a solution of the Poisson equation much like the electronic
degrees of freedom approach the ground state in ab-initio molecular dynamics.Comment: 4 pages with 3 figure
Numerical Simulations of Shock Wave-Driven Jets
We present the results of numerical simulations of shock wave-driven jets in
the solar atmosphere. The dependence of observable quantities like maximum
velocity and deceleration on parameters such as the period and amplitude of
initial disturbances and the inclination of the magnetic field is investigated.
Our simulations show excellent agreement with observations, and shed new light
on the correlation between velocity and deceleration and on the regional
differences found in observations.Comment: 7 pages, 11 figures, submitted to Ap
Local Simulation Algorithms for Coulomb Interaction
Long ranged electrostatic interactions are time consuming to calculate in
molecular dynamics and Monte-Carlo simulations. We introduce an algorithmic
framework for simulating charged particles which modifies the dynamics so as to
allow equilibration using a local Hamiltonian. The method introduces an
auxiliary field with constrained dynamics so that the equilibrium distribution
is determined by the Coulomb interaction. We demonstrate the efficiency of the
method by simulating a simple, charged lattice gas.Comment: Last figure changed to improve demonstration of numerical efficienc
On realizations of nonlinear Lie algebras by differential operators
We study realizations of polynomial deformations of the sl(2,R)- Lie algebra
in terms of differential operators strongly related to bosonic operators. We
also distinguish their finite- and infinite-dimensional representations. The
linear, quadratic and cubic cases are explicitly visited but the method works
for arbitrary degrees in the polynomial functions. Multi-boson Hamiltonians are
studied in the context of these ``nonlinear'' Lie algebras and some examples
dealing with quantum optics are pointed out.Comment: 21 pages, Latex; New examples added in Sect.
Gravity effects on a gliding arc in four noble gases: from normal to hypergravity
A gliding arc in four noble gases (He, Ne, Ar, Kr) has been studied under previously unexplored conditions of varying artifiial gravity, from normal 1 g gravity up to 18 g hypergravity. Signifiant differences, mainly the visual thickness of the plasma channel, its maximum elongation and general sensitivity to hypergravity conditions, were observed between the discharges in individual gases, resulting from their different atomic weights and related quantities, such as heat conductivity or ionisation potential. Generally, an increase of the artifiial gravity level leads to a faster plasma channel movement thanks to stronger buoyant force and a decrease of maximum height reached by the channel due to more intense losses of heat and reactive species. In relation to this, an increase in current and a decrease in absorbed power was observed
Statistics of Q-Oscillators, Quons and Relation to Fractional Satistics
The statistics of -oscillators, quons and to some extent, of anyons are
studied and the basic differences among these objects are pointed out. In
particular, the statistical distributions for different bosonic and fermionic
-oscillators are found for their corresponding Fock space representations in
the case when the hamiltonian is identified with the number operator. In this
case and for nonrelativistic particles, the single-particle temperature Green
function is defined with -deformed periodicity conditions. The equations of
state for nonrelativistic and ultrarelativistic bosonic -gases in an
arbitrary space dimension are found near Bose statistics, as well as the one
for an anyonic gas near Bose and Fermi statistics. The first corrections to the
second virial coefficients are also evaluated. The phenomenon of Bose-Einstein
condensation in the -deformed gases is also discussed.Comment: 21 pages, Latex, HU-TFT-93-2
q-Functional Wick's theorems for particles with exotic statistics
In the paper we begin a description of functional methods of quantum field
theory for systems of interacting q-particles. These particles obey exotic
statistics and are the q-generalization of the colored particles which appear
in many problems of condensed matter physics, magnetism and quantum optics.
Motivated by the general ideas of standard field theory we prove the
q-functional analogues of Hori's formulation of Wick's theorems for the
different ordered q-particle creation and annihilation operators. The formulae
have the same formal expressions as fermionic and bosonic ones but differ by a
nature of fields. This allows us to derive the perturbation series for the
theory and develop analogues of standard quantum field theory constructions in
q-functional form.Comment: 15 pages, LaTeX, submitted to J.Phys.
On some nonlinear extensions of the angular momentum algebra
Deformations of the Lie algebras so(4), so(3,1), and e(3) that leave their
so(3) subalgebra undeformed and preserve their coset structure are considered.
It is shown that such deformed algebras are associative for any choice of the
deformation parameters. Their Casimir operators are obtained and some of their
unitary irreducible representations are constructed. For vanishing deformation,
the latter go over into those of the corresponding Lie algebras that contain
each of the so(3) unitary irreducible representations at most once. It is also
proved that similar deformations of the Lie algebras su(3), sl(3,R), and of the
semidirect sum of an abelian algebra t(5) and so(3) do not lead to associative
algebras.Comment: 22 pages, plain TeX + preprint.sty, no figures, to appear in J.Phys.
Off-limb (spicule) DEM distribution from SoHO/SUMER observations
In the present work we derive a Differential Emission Measure (DEM) dis-
tribution from a region dominated by spicules. We use spectral data from the
Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER
wavelength range taken off-limb in the Northern polar coronal hole to construct
this DEM distribution using the CHIANTI atomic database. This distribution is
then used to study the thermal properties of the emission contributing to the
171 {\AA} channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar
Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in
the AIA 171 {\AA} channel is dominated by emission from the Fe ix 171.07 {\AA}
line and has sparingly little contribution from other lines. The product of the
Fe ix 171.07 {\AA} line contribution function with the off-limb DEM was found
to have a maximum at logTmax (K) = 5.8 indicating that during spicule
observations the emission in this line comes from plasma at transition region
temperatures rather than coronal. For comparison, the same product with a quiet
Sun and prominence DEM were found to have a maximum at logT max (K) = 5.9 and
logTmax (K) = 5.7, respectively. We point out that the interpretation of data
obtained from the AIA 171 {\AA} filter should be done with foreknowledge of the
thermal nature of the observed phenomenon. For example, with an off-limb DEM we
find that only 3.6% of the plasma is above a million degrees, whereas using a
quiet Sun DEM, this contribution rises to 15%.Comment: 12 pages, 6 figures accepted by Solar Physic
The quantum superalgebra : deformed para-Bose operators and root of unity representations
We recall the relation between the Lie superalgebra and para-Bose
operators. The quantum superalgebra , defined as usual in terms
of its Chevalley generators, is shown to be isomorphic to an associative
algebra generated by so-called pre-oscillator operators satisfying a number of
relations. From these relations, and the analogue with the non-deformed case,
one can interpret these pre-oscillator operators as deformed para-Bose
operators. Some consequences for (Cartan-Weyl basis,
Poincar\'e-Birkhoff-Witt basis) and its Hopf subalgebra are
pointed out. Finally, using a realization in terms of ``-commuting''
-bosons, we construct an irreducible finite-dimensional unitary Fock
representation of and its decomposition in terms of
representations when is a root of unity.Comment: 15 pages, LaTeX (latex twice), no figure
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