2,161 research outputs found
The harmonic hyperspherical basis for identical particles without permutational symmetry
The hyperspherical harmonic basis is used to describe bound states in an
--body system. The approach presented here is based on the representation of
the potential energy in terms of hyperspherical harmonic functions. Using this
representation, the matrix elements between the basis elements are simple, and
the potential energy is presented in a compact form, well suited for numerical
implementation. The basis is neither symmetrized nor antisymmetrized, as
required in the case of identical particles; however, after the diagonalization
of the Hamiltonian matrix, the eigenvectors reflect the symmetries present in
it, and the identification of the physical states is possible, as it will be
shown in specific cases. We have in mind applications to atomic, molecular, and
nuclear few-body systems in which symmetry breaking terms are present in the
Hamiltonian; their inclusion is straightforward in the present method. As an
example we solve the case of three and four particles interacting through a
short-range central interaction and Coulomb potential
Variational Estimates using a Discrete Variable Representation
The advantage of using a Discrete Variable Representation (DVR) is that the
Hamiltonian of two interacting particles can be constructed in a very simple
form. However the DVR Hamiltonian is approximate and, as a consequence, the
results cannot be considered as variational ones. We will show that the
variational character of the results can be restored by performing a reduced
number of integrals.
In practice, for a variational description of the lowest n bound states only
n(n+1)/2 integrals are necessary whereas D(D+1)/2 integrals are enough for the
scattering states (D is the dimension of the S matrix). Applications of the
method to the study of dimers of He, Ne and Ar, for both bound and scattering
states, are presented.Comment: 30 pages, 7 figures. Minor changes (title modified, typos corrected,
1 reference added). To be published in PR
General integral relations for the description of scattering states using the hyperspherical adiabatic basis
In this work we investigate 1+2 reactions within the framework of the
hyperspherical adiabatic expansion method. To this aim two integral relations,
derived from the Kohn variational principle, are used. A detailed derivation of
these relations is shown. The expressions derived are general, not restricted
to relative partial waves, and with applicability in multichannel
reactions. The convergence of the -matrix in terms of the adiabatic
potentials is investigated. Together with a simple model case used as a test
for the method, we show results for the collision of a He atom on a \dimer
dimer (only the elastic channel open), and for collisions involving a Li
and two He atoms (two channels open).Comment: Accepted for publication in Physical Review
Variational description of continuum states in terms of integral relations
Two integral relations derived from the Kohn Variational Principle (KVP) are
used for describing scattering states. In usual applications the KVP requires
the explicit form of the asymptotic behavior of the scattering wave function.
This is not the case when the integral relations are applied since, due to
their short range nature, the only condition for the scattering wave function
is that it be the solution of in the internal region.
Several examples are analyzed for the computation of phase-shifts from bound
state type wave functions or, in the case of the scattering of charged
particles, it is possible to obtain phase-shifts using free asymptotic
conditions. As a final example we discuss the use of the integral relations in
the case of the Hyperspherical Adiabatic method.Comment: 34 pages, 7 figures, accepted in Phys. Rev.
Electrostatic fluidized bed deposition of a high performance polymeric powder on metallic substrates
The electrostatic fluidized bed deposition of a single-layer PPA 571 coating onto low carbon steel rods is reported. A full factorial experimental design was developed in order to study the influence of several operative variables on the effectiveness of the coating process and on the coating thickness and uniformity. The operative variables included exposure time, air flow, the applied voltage, attitude, and the radial and vertical location of the work-piece in the fluid bed. After the experimentation, several process maps were developed as a support to identify the best way to lead the coating process. Finally, by using a statistical approach, the reliability and repeatability of the coating process was also established. Experimental trends were consistent with theoretical expectation. A significant growth in achievable coating thickness was obtained by increasing voltage and air flow. Furthermore, at higher values of exposure time and applied voltage, relevant back ionization phenomena occurred, which simultaneously caused a top limit in coating thickness and a worsening of surface finishing. Process characteristics, leading mechanisms, and some practical aspects are also discussed in detail. (c) 2005 Elsevier B.V. All rights reserved
On the use of CrN/Cr and CrN interlayers in hot filament chemical vapour deposition (HF-CVD) of diamond films onto WC-Co substrates
CrN/Cr-based films were deposited using PVD-arc technique onto Co-cemented tungsten carbide (WC-Co) substrates and, then, seeded with diamond powder suspension or mechanically treated by Fluidized Bed Peening (FBP) of brittle diamond powders. Multilayered coatings were obtained from the superimposition of 4 mu m-thick diamond coatings, deposited on the PVD interlayer using hot filament chemical vapour deposition (HFCVD). The effectiveness of fluidized bed peened CrN/Cr interlayers on the adhesion enhancement of diamond on WC-Co substrates was studied and compared to diamond coated WC-Co substrates with unpeened CrN/Cr or CrN interlayers, or pre-treated with two-step chemical etching (Murakatni's reagent and Caro's acid, MC-treatment). In particular, growth, morphology, wear endurance and adhesion of the CVD deposited diamond films onto peened CrN/Cr interlayer were looked into. Diamond coatings on peened CrN/Cr interlayers exhibited a rougher surface morphology than as-prepared CrN/Cr films as a result of the surface roughening of the ductile Cr layer produced by the repeated impacts on it of the diamond powders during FBP. FBP was found to be a necessary step in improving the scarce adhesion of CVD diamond onto CrN/Cr-interlayer. However, the use of FB peened CrN/Cr interlayer did not represent the best way to pre-treat WC-Co substrates, as the unpeened single-layer CrN, or the use of MC pretreatment, was found to ensure better adhesion and wear endurance. (C) 2008 Published by Elsevier B.V
Yang-Mills fields on CR manifolds
We study pseudo Yang-Mills fields on a compact strictly pseudoconvex CR
manifold.Comment: 52 page
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