359 research outputs found
The q-harmonic oscillators, q-coherent states and the q-symplecton
The recently introduced notion of a quantum group is discussed conceptually and then related to deformed harmonic oscillators ('q-harmonic oscillators'). Two developments in applying q-harmonic oscillators are reviewed: q-coherent states and the q-symplecton
Nonlinear self-flipping of polarization states in asymmetric waveguides
Waveguides of subwavelength dimensions with asymmetric geometries, such as
rib waveguides, can display nonlinear polarization effects in which the
nonlinear phase difference dominates the linear contribution, provided the
birefringence is sufficiently small. We demonstrate that self-flipping
polarization states can appear in such rib waveguides at low (mW) power levels.
We describe an optical power limiting device with optimized rib waveguide
parameters that can operate at low powers with switching properties
Spin dynamics of low-dimensional excitons due to acoustic phonons
We investigate the spin dynamics of excitons interacting with acoustic
phonons in quantum wells, quantum wires and quantum disks by employing a
multiband model based on the Luttinger Hamiltonian. We also use the
Bir-Pikus Hamiltonian to model the coupling of excitons to both longitudinal
acoustic phonons and transverse acoustic phonons, thereby providing us with a
realistic framework in which to determine details of the spin dynamics of
excitons. We use a fractional dimensional formulation to model the excitonic
wavefunctions and we demonstrate explicitly the decrease of spin relaxation
time with dimensionality. Our numerical results are consistent with
experimental results of spin relaxation times for various configurations of the
GaAs/AlGaAs material system. We find that longitudinal and
transverse acoustic phonons are equally significant in processes of exciton
spin relaxations involving acoustic phonons.Comment: 24 pages, 3 figure
Primitiver neuroektodermaler Tumor im Hoden: Molekulare Analyse und Diskussion der Entstehung
Zusammenfassung: Wir beschreiben einen testikulären primitiven neuroektodermalen Tumor (PNET) mit intratubulärer Keimzellneoplasie des angrenzenden Hodenparenchyms bei einem 25-jährigen Patienten. Testikuläre PNET sind selten. Ihre Entstehung wird auf eine maligne somatische Transformation in einem testikulären Keimzelltumor zurückgeführt. Morphologisch und molekularpathologisch ähneln diese Tumoren kindlichen zentralen PNET, die keine Rearrangierung des EWS-Gens auf Chromosom22 aufweisen. Auch im hier beschriebenen Fall konnte keine Translokation nachgewiesen werde
Fast transport of Bose-Einstein condensates
We propose an inverse method to accelerate without final excitation the
adiabatic transport of a Bose Einstein condensate. The method, applicable to
arbitrary potential traps, is based on a partial extension of the
Lewis-Riesenfeld invariants, and provides transport protocols that satisfy
exactly the no-excitation conditions without constraints or approximations.
This inverse method is complemented by optimizing the trap trajectory with
respect to different physical criteria and by studying the effect of noise
On the Hydrogen Atom via Wigner-Heisenberg Algebra
We extend the usual Kustaanheimo-Stiefel mapping to study and
discuss a constrained super-Wigner oscillator in four dimensions. We show that
the physical hydrogen atom is the system that emerges in the bosonic sector of
the mapped super 3D system.Comment: 14 pages, no figure. This work was initiated in collaboration with
Jambunatha Jayaraman (In memory), whose advises and encouragement were
fundamental. http://www.cbpf.b
Bogomol'nyi Equations of Maxwell-Chern-Simons vortices from a generalized Abelian Higgs Model
We consider a generalization of the abelian Higgs model with a Chern-Simons
term by modifying two terms of the usual Lagrangian. We multiply a dielectric
function with the Maxwell kinetic energy term and incorporate nonminimal
interaction by considering generalized covariant derivative. We show that for a
particular choice of the dielectric function this model admits both topological
as well as nontopological charged vortices satisfying Bogomol'nyi bound for
which the magnetic flux, charge and angular momentum are not quantized. However
the energy for the topolgical vortices is quantized and in each sector these
topological vortex solutions are infinitely degenerate. In the nonrelativistic
limit, this model admits static self-dual soliton solutions with nonzero finite
energy configuration. For the whole class of dielectric function for which the
nontopological vortices exists in the relativistic theory, the charge density
satisfies the same Liouville equation in the nonrelativistic limit.Comment: 30 pages(4 figures not included), RevTeX, IP/BBSR/93-6
Generalized Zeta Functions and One-loop Corrections to Quantum Kink Masses
A method for describing the quantum kink states in the semi-classical limit
of several (1+1)-dimensional field theoretical models is developed. We use the
generalized zeta function regularization method to compute the one-loop quantum
correction to the masses of the kink in the sine-Gordon and cubic sinh-Gordon
models and another two systems with polynomial
self-interactions.Comment: 29 pages, 4 figures; version to appear in Nucl. Phys.
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