271 research outputs found
Nonlinear coupling between scissors modes of a Bose-Einstein condensate
We explore the nonlinear coupling of the three scissors modes of an
anisotropic Bose-Einstein condensate. We show that only when the frequency of
one of the scissors modes is twice the frequency of another scissors mode,
these two modes can be resonantly coupled and a down conversion can occur. We
perform the calculation variationally using a gaussian trial wave function.
This enables us to obtain simple analytical results that describe the
oscillation and resonance behaviour of the two coupled modes.Comment: 12 pages, 3 figures, submitted to Phys. Rev.
Kinetic Theory of Collective Modes in Atomic Clouds above the Bose-Einstein Transition Temperature
We calculate frequencies and damping rates of the lowest collective modes of
a dilute Bose gas confined in an anisotropic trapping potential above the
Bose-Einstein transition temperature. From the Boltzmann equation with a
simplified collision integral we derive a general dispersion relation that
interpolates between the collisionless and hydrodynamic regimes. In the case of
axially symmetric traps we obtain explicit expressions for the frequencies and
damping rates of the lowest modes in terms of a phenomenological collision
time. Our results are compared with microscopic calculations and experiments.Comment: Nordita preprint NORDITA-1999/46 C
Phase fluctuations in atomic Bose gases
We improve on the Popov theory for partially Bose-Einstein condensed atomic
gases by treating the phase fluctuations exactly. As a result, the theory
becomes valid in arbitrary dimensions and is able to describe the
low-temperature crossover between three, two and one-dimensional Bose gases,
which is currently being explored experimentally. We consider both homogeneous
and trapped Bose gases.Comment: 4 pages. Title changed Major changes involve extension of theory to
include trapped Bose gases. Deletion of reference to and comparison with
hydrogen experiment. Due to these changes, second author added. Modified
manuscript accepted for PR
Doxycycline inhibition of proteases and inflammation in abdominal aortic aneurysms
The aim of this thesis is to evaluate the effect of doxycycline on the proteolytic and inflammatory processes in abdominal aneurysms. This data is essential for the development of pharmaceutical strategies for the stabilization of an AAA. Such an approach could reduce the need for elective surgery and endovascular repair. It has repeatedly been shown that AAA progression and rupture is related to the failure of collagen in the aortic wall. Yet the exact mechanism underlying this failure remains unknown. Furthermore, the precise mechanism of activation of collagenases and their inflammatory mediators that are responsible for the collagen turnover of AAA are unknown. In this thesis we attempt to determine how collagen metabolism is balanced in aneurysmal diseases and contribute to the knowledge which collagenases and inflammatory mediators are involved in the destruction of the collagen network in AAA disease. Moreover, we evaluate some of the effects of doxycycline on the proteases and inflammatory mediators in AAA. Analyses showed that doxycycline inhibits specific MMPs and inflammatory pathways that are involved in the collagen balance and aneurysm growth. Together, these observations provide a rationale for a randomized clinical trial studying the effect of doxycycline on aneurysm growth.HartstichtingUBL - phd migration 201
Unidirectional soliton flows in PT-symmetric potentials
We study the soliton scattering by parity-time- (PT) symmetric potentials and demonstrate that, for a certain range of parameters, both single and multiple soliton scattering exhibit almost perfect unidirectional flow. We employ direct numerical simulati
Modulational instability of the Kuznetsov-Ma breather in optical fibers with constant and periodic dispersion
We perform modulational instability analysis of the Kuznetsov-Ma breather (KMB) propagating
in a medium with constant and periodic dispersions. In the constant dispersion case, we
show that the most unstable modulational instability eigenmode leads to bifurcation of the
KMB into a sequence of breathers. The time at which bifurcation starts and the bifurcation
rate are quantitatively accounted for. In the case of a KMB propagating in an optical fiber with
a constant dispersion perturbed by a sinusoidal time-dependent modulation our results suggest
that the KMB is most unstable just before and after the breather reaches its maximum
peak height. Parametric resonance occurs when the frequency of the dispersion modulation
is much larger than the natural frequency of the breather
Bright soliton trains of trapped Bose-Einstein condensates
We variationally determine the dynamics of bright soliton trains composed of
harmonically trapped Bose-Einstein condensates with attractive interatomic
interactions. In particular, we obtain the interaction potential between two
solitons. We also discuss the formation of soliton trains due to the quantum
mechanical phase fluctuations of a one-dimensional condensate.Comment: 4 pages, 2 figures, submitted to PR
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