116 research outputs found
Estudio de la fauna de aves de la cueva de Pico Ramos (Muskiz, Bizkaia).
Se estudian los restos de Aves de la cuenca de Pico Ramos. Destaca entre las especies halladas la presencia de Alca Gigante (Pinguinus impennis) a cuya extinción y hallazgos holocenos se dedica especial atención. Se ofrecen datos osteométricos y biogeográficos de las restantes especies
IBM: parameter symmetry, hidden symmetries and transformations of boson operators
A symmetry of the parameter space of interacting boson models IBM-1 and IBM-2
is studied. The symmetry is associated with linear canonical transformations of
boson operators, or, equivalently, with the existence of different realizations
of the symmetry algebras of the models. The relevance of the parameter symmetry
to physical observables is discussed.Comment: LATEX, 11 pages including 1 eps figure and 1 table prepared as an eps
figure; a talk given by A. M. Siirokov at XXII Symposium on Nuclear Physics,
Oaxtepec, Morelos, M\'exico, 5--8 January, 1999; to be published in Revista
Mex. Fi
Noether's Theorem and time-dependent quantum invariants
The time dependent-integrals of motion, linear in position and momentum
operators, of a quantum system are extracted from Noether's theorem
prescription by means of special time-dependent variations of coordinates. For
the stationary case of the generalized two-dimensional harmonic oscillator, the
time-independent integrals of motion are shown to correspond to special
Bragg-type symmetry properties. A detailed study for the non-stationary case of
this quantum system is presented. The linear integrals of motion are
constructed explicitly for the case of varying mass and coupling strength. They
are obtained also from Noether's theorem. The general treatment for a
multi-dimensional quadratic system is indicated, and it is shown that the
time-dependent variations that give rise to the linear invariants, as conserved
quantities, satisfy the corresponding classical homogeneous equations of motion
for the coordinates.Comment: Plain TeX, 23 pages, preprint of Instituto de Ciencias Nucleares,
UNAM Departamento de F\ii sica and Matem\'aticas Aplicadas, No. 01 (1994
Entanglement of a three-level atom interacting with two-modes field in a cavity
The dynamics of the interaction between an atom of three levels interacting
with a quantized field of two modes in a cavity is studied within the rotating
wave approximation, by taking into account experimental values of the
accessible hyperfine levels of alkaline atoms. An equal detuning is considered
to determine the matter-field entanglement, the statistical properties of the
photons, and the occupation probabilities of the atom. For a large detuning or
weak dipolar strength appear the Raman condition, that is, the suppression of
one of his atomic transitions. Analytic expression for the time evolution
operator allows to have also explicit closed expressions for the field and
matter observables.Comment: 37 pages, 9 figure
On the meaning and interpretation of Tomography in abstract Hilbert spaces
The mechanism of describing quantum states by standard probability
(tomographic one) instead of wave function or density matrix is elucidated.
Quantum tomography is formulated in an abstract Hilbert space framework, by
means of the identity decompositions in the Hilbert space of hermitian linear
operators, with trace formula as scalar product of operators. Decompositions of
identity are considered with respect to over-complete families of projectors
labeled by extra parameters and containing a measure, depending on these
parameters. It plays the role of a Gram-Schmidt orthonormalization kernel. When
the measure is equal to one, the decomposition of identity coincides with a
positive operator valued measure (POVM) decomposition. Examples of spin
tomography, photon number tomography and symplectic tomography are reconsidered
in this new framework.Comment: Submitted to Phys. Lett.
Partial Dynamical Symmetry in the Symplectic Shell Model
We present an example of a partial dynamical symmetry (PDS) in an interacting
fermion system and demonstrate the close relationship of the associated
Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding
new light on this important interaction. Specifically, in the framework of the
symplectic shell model of nuclei, we prove the existence of a family of
fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction
process for the PDS eigenstates with good symmetry and give analytic
expressions for the energies of these states and E2 transition strengths
between them. Characteristics of both pure and mixed-symmetry PDS eigenstates
are discussed and the resulting spectra and transition strengths are compared
to those of real nuclei. The PDS concept is shown to be relevant to the
description of prolate, oblate, as well as triaxially deformed nuclei.
Similarities and differences between the fermion case and the previously
established partial SU(3) symmetry in the Interacting Boson Model are
considered.Comment: 9 figure
Shell model description of normal parity bands in odd-mass heavy deformed nuclei
The low-energy spectra and B(E2) electromagnetic transition strengths of
159Eu, 159Tb and 159Dy are described using the pseudo SU(3) model. Normal
parity bands are built as linear combinations of SU(3) states, which are the
direct product of SU(3) proton and neutron states with pseudo spin zero (for
even number of nucleons) and pseudo spin 1/2 (for odd number of nucleons). Each
of the many-particle states have a well-defined particle number and total
angular momentum. The Hamiltonian includes spherical Nilsson single-particle
energies, the quadrupole-quadrupole and pairing interactions, as well as three
rotor terms which are diagonal in the SU(3) basis. The pseudo SU(3) model is
shown to be a powerful tool to describe odd-mass heavy deformed nuclei.Comment: 11 pages, 2 figures, Accepted to be published in Phys. Rev.
Study of the micromammals from the Upper Pleistocene of Ventalaperra (Karrantza, Bizkaia)
In this paper the micromammal assemblage found in the site of Ventalaperra (Karrantza, Bizkaia) is described.
The studied remains come from two different stratigraphic levels with archaeological remains. The lower
level has been placed in the Mousterian whereas the upper one is dated as Upper Palaeolithic. The
micromammals are represented in this site by one lagomorph, eight rodents, one chiropteran and two
insectivorous. The micromammal assemblage indicates a humid temperate climate with forest similar to
those occurring in the area at present da
Supersymmetry and superalgebra for the two-body system with a Dirac oscillator interaction
Some years ago, one of the authors~(MM) revived a concept to which he gave
the name of single-particle Dirac oscillator, while another~(CQ) showed that it
corresponds to a realization of supersymmetric quantum mechanics. The Dirac
oscillator in its one- and many-body versions has had a great number of
applications. Recently, it included the analytic expression for the eigenstates
and eigenvalues of a two-particle system with a new type of Dirac oscillator
interaction of frequency~. By considering the latter together with its
partner corresponding to the replacement of~ by~, we are able
to get a supersymmetric formulation of the problem and find the superalgebra
that explains its degeneracy.Comment: 21 pages, LaTeX, 1 figure (can be obtained from the authors), to
appear in J. Phys.
SU(3) realization of the rigid asymmetric rotor within the IBM
It is shown that the spectrum of the asymmetric rotor can be realized quantum
mechanically in terms of a system of interacting bosons. This is achieved in
the SU(3) limit of the interacting boson model by considering higher-order
interactions between the bosons. The spectrum corresponds to that of a rigid
asymmetric rotor in the limit of infinite boson number.Comment: 9 pages, 2 figures, LaTeX, epsfi
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