40,942 research outputs found
Spin and pseudospin symmetries of the Dirac equation with confining central potentials
We derive the node structure of the radial functions which are solutions of
the Dirac equation with scalar and vector confining central potentials,
in the conditions of exact spin or pseudospin symmetry, i.e., when one has
, where is a constant. We show that the node structure for exact
spin symmetry is the same as the one for central potentials which go to zero at
infinity but for exact pseudospin symmetry the structure is reversed. We obtain
the important result that it is possible to have positive energy bound
solutions in exact pseudospin symmetry conditions for confining potentials of
any shape, including naturally those used in hadron physics, from nuclear to
quark models. Since this does not happen for potentials going to zero at large
distances, used in nuclear relativistic mean-field potentials or in the atomic
nucleus, this shows the decisive importance of the asymptotic behavior of the
scalar and vector central potentials on the onset of pseudospin symmetry and on
the node structure of the radial functions. Finally, we show that these results
are still valid for negative energy bound solutions for anti-fermions.Comment: 7 pages, uses revtex macro
New solutions of the D-dimensional Klein-Gordon equation via mapping onto the nonrelativistic one-dimensional Morse potential
New exact analytical bound-state solutions of the D-dimensional Klein-Gordon
equation for a large set of couplings and potential functions are obtained via
mapping onto the nonrelativistic bound-state solutions of the one-dimensional
generalized Morse potential. The eigenfunctions are expressed in terms of
generalized Laguerre polynomials, and the eigenenergies are expressed in terms
of solutions of irrational equations at the worst. Several analytical results
found in the literature, including the so-called Klein-Gordon oscillator, are
obtained as particular cases of this unified approac
Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)X
High-resolution thermal expansion measurements have been performed for
exploring the mysterious "structureless transition" in (TMTTF)X (X =
PF and AsF), where charge ordering at coincides with the
onset of ferroelectric order. Particularly distinct lattice effects are found
at in the uniaxial expansivity along the interstack
-direction. We propose a scheme involving a charge
modulation along the TMTTF stacks and its coupling to displacements of the
counteranions X. These anion shifts, which lift the inversion symmetry
enabling ferroelectric order to develop, determine the 3D charge pattern
without ambiguity. Evidence is found for another anomaly for both materials at
0.6 indicative of a phase transition
related to the charge ordering
Consistent Truncation to Three Dimensional (Super-)gravity
For a general three dimensional theory of (super-)gravity coupled to
arbitrary matter fields with arbitrary set of higher derivative terms in the
effective action, we give an algorithm for consistently truncating the theory
to a theory of pure (super-)gravity with the gravitational sector containing
only Einstein-Hilbert, cosmological constant and Chern-Simons terms. We also
outline the procedure for finding the parameters of the truncated theory. As an
example we consider dimensional reduction on S^2 of the 5-dimensional minimal
supergravity with curvature squared terms and obtain the truncated theory
without any curvature squared terms. This truncated theory reproduces correctly
the exact central charge of the boundary CFT.Comment: LaTeX file, 22 page
Localization to Enhance Security and Services in Wi-Fi Networks under Privacy Constraints
Developments of seamless mobile services are faced with two broad challenges, systems security and user privacy - access to wireless systems is highly insecure due to the lack of physical boundaries and, secondly, location based services (LBS) could be used to extract highly sensitive user information. In this paper, we describe our work on developing systems which exploit location information to enhance security and services under privacy constraints. We describe two complimentary methods which we have developed to track node location information within production University Campus Networks comprising of large numbers of users. The location data is used to enhance security and services. Specifically, we describe a method for creating geographic firewalls which allows us to restrict and enhance services to individual users within a specific containment area regardless of physical association. We also report our work on LBS development to provide visualization of spatio-temporal node distribution under privacy considerations
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