20,670 research outputs found
Connection between the two branches of the quantum two-stream instability across the k space
The stability of two quantum counter-streaming electron beams is investigated
within the quantum plasma fluid equations for arbitrarily oriented wave
vectors. The analysis reveals that the two quantum two-stream unstable branches
are indeed connected by a continuum of unstable modes with oblique wave
vectors. Using the longitudinal approximation, the stability domain for any k
is analytically explained, together with the growth rate
Low Momentum Classical Mechanics with Effective Quantum Potentials
A recently introduced effective quantum potential theory is studied in a low
momentum region of phase space. This low momentum approximation is used to show
that the new effective quantum potential induces a space-dependent mass and a
smoothed potential both of them constructed from the classical potential. The
exact solution of the approximated theory in one spatial dimension is found.
The concept of effective transmission and reflection coefficients for effective
quantum potentials is proposed and discussed in comparison with an analogous
quantum statistical mixture problem. The results are applied to the case of a
square barrier.Comment: 4 figure
Relativistic Klein-Gordon-Maxwell multistream model for quantum plasmas
A multistream model for spinless electrons in a relativistic quantum plasma
is introduced by means of a suitable fluid-like version of the
Klein-Gordon-Maxwell system. The one and two-stream cases are treated in
detail. A new linear instability condition for two-stream quantum plasmas is
obtained, generalizing the previously known non-relativistic results. In both
the one and two-stream cases, steady-state solutions reduce the model to a set
of coupled nonlinear ordinary differential equations, which can be numerically
solved, yielding a manifold of nonlinear periodic and soliton structures. The
validity conditions for the applicability of the model are addressed
Some neutron and gamma radiation characteristics of plutonium cermet fuel for isotopic power sources
Gamma and neutron measurements on various types of plutonium sources are presented in order to show the effects of O-17, O-18 F-19, Pu-236, age of the fuel, and size of the source on the gamma and neutron spectra. Analysis of the radiation measurements shows that fluorine is the main contributor to the neutron yields from present plutonium-molybdenum cermet fuel, while both fluorine and Pu-236 daughters contribute significantly to the gamma ray intensities
Optimal control of electromagnetic field using metallic nanoclusters
The dielectric properties of metallic nanoclusters in the presence of an
applied electromagnetic field are investigated using non-local linear response
theory. In the quantum limit we find a non-trivial dependence of the induced
field and charge distribution on the spatial separation between the clusters
and on the frequency of the driving field. Using a genetic algorithm, these
quantum functionalities are exploited to custom-design sub-wavelength lenses
with a frequency controlled switching capability.Comment: accepted for publication in New Journal of Physic
The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?
We discuss the interpretation of the dust SED from the mid-infrared to the
millimeter range of NGC 1569. The model developed by D\'esert et al. (1990)
including three dust components (Polyaromatic Hydrocarbons, Very Small Grains
and big grains) can explain the data using a realistic interstellar radiation
field and adopting an enhanced abundance of VSGs. A simple three-temperature
model is also able to reproduce the data but requires a very low dust
temperature which is considered to be unlikely in this low-metallicity
starburst galaxy. The high abundance of Very Small Grains might be due to large
grain destruction in supernova shocks. This possibility is supported by ISO
data showing that the emission at 14.3 m, tracing VSGs, is enhanced with
respect to the emission at 6.7 m and 850 m in regions of high star
formation.Comment: 4 pages, conference proceedings paper, "The Spectral Energy
Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg,
4-8 Oct. 2004, eds. C.C. Popescu & R.J. Tuffs, AIP Conf. Ser., in pres
Jacobi Structures in
The most general Jacobi brackets in are constructed after
solving the equations imposed by the Jacobi identity. Two classes of Jacobi
brackets were identified, according to the rank of the Jacobi structures. The
associated Hamiltonian vector fields are also constructed
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