2,721 research outputs found
Self-consistent multi-mode lasing theory for complex or random lasing media
A semiclassical theory of single and multi-mode lasing is derived for open
complex or random media using a self-consistent linear response formulation.
Unlike standard approaches which use closed cavity solutions to describe the
lasing modes, we introduce an appropriate discrete basis of functions which
describe also the intensity and angular emission pattern outside the cavity.
This constant flux (CF) basis is dictated by the Green function which arises
when formulating the steady state Maxwell-Bloch equations as a self-consistent
linear response problem. This basis is similar to the quasi-bound state basis
which is familiar in resonator theory and it obeys biorthogonality relations
with a set of dual functions. Within a single-pole approximation for the Green
function the lasing modes are proportional to these CF states and their
intensities and lasing frequencies are determined by a set of non-linear
equations. When a near threshold approximation is made to these equations a
generalized version of the Haken-Sauermann equations for multi-mode lasing is
obtained, appropriate for open cavities. Illustrative results from these
equations are given for single and few mode lasing states, for the case of
dielectric cavity lasers. The standard near threshold approximation is found to
be unreliable. Applications to wave-chaotic cavities and random lasers are
discussed.Comment: 18 pages, 9 figure
Weak-Localization and Integrability in Ballistic Cavities
We demonstrate the existence of an interference contribution to the average
magnetoconductance, G(B), of ballistic cavities and use it to test the
semiclassical theory of quantum billiards. G(B) is qualitatively different for
chaotic and regular cavities, an effect explained semiclassically by the
differing classical distribution of areas. The magnitude of G(B) is poorly
explained by the semiclassical theory of coherent backscattering (elastic
enhancement factor)-- correlations beyond time-reversed pairs of trajectories
must be included-- but is in agreement with random matrix theory.Comment: 12 pages + 3 figures, revtex, hub-92-w
Quantum Mechanics Another Way
Deformation quantization (sometimes called phase-space quantization) is a
formulation of quantum mechanics that is not usually taught to undergraduates.
It is formally quite similar to classical mechanics: ordinary functions on
phase space take the place of operators, but the functions are multiplied in an
exotic way, using the star product. Here we attempt a brief, pedagogical
discussion of deformation quantization, that is suitable for inclusion in an
undergraduate course.Comment: 14 pages, 3 figures, to be published in Eur. J. Phy
Transcatheter arterial chemoembolization of liver tumors: Effects of embolization protocol on injectable volume of chemotherapy and subsequent arterial patency
Quantum chaos in a deformable billiard: Applications to quantum dots
We perform a detailed numerical study of energy-level and wavefunction
statistics of a deformable quantum billiard focusing on properties relevant to
semiconductor quantum dots. We consider the family of Robnik billiards
generated by simple conformal maps of the unit disk; the shape of this family
of billiards may be varied continuously at fixed area by tuning the parameters
of the map. The classical dynamics of these billiards is well-understood and
this allows us to study the quantum properties of subfamilies which span the
transition from integrability to chaos as well as families at approximately
constant degree of chaoticity (Kolmogorov entropy). In the regime of hard chaos
we find that the statistical properties of interest are well-described by
random-matrix theory and completely insensitive to the particular shape of the
dot. However in the nearly-integrable regime non-universal behavior is found.
Specifically, the level-width distribution is well-described by the predicted
distribution both in the presence and absence of magnetic flux when
the system is fully chaotic; however it departs substantially from this
behavior in the mixed regime. The chaotic behavior corroborates the previously
predicted behavior of the peak-height distribution for deformed quantum dots.
We also investigate the energy-level correlation functions which are found to
agree well with the behavior calculated for quasi-zero-dimensional disordered
systems.Comment: 25 pages (revtex 3.0). 16 figures are available by mail or fax upon
request at [email protected]
Semiclassical theory of magnetotransport through a chaotic quantum well
We develop a quantitative semiclassical formula for the resonant tunneling
current through a quantum well in a tilted magnetic field. It is shown that the
current depends only on periodic orbits within the quantum well. The theory
explains the puzzling evolution of the tunneling spectra near a tilt angle of
as arising from an exchange bifurcation of the relevant periodic
orbits.Comment: 4 pages, RevTeX, epsf, 2 PostScript Figures (1 with color
Toda Lattice Hierarchy and Generalized String Equations
String equations of the -th generalized Kontsevich model and the
compactified string theory are re-examined in the language of the Toda
lattice hierarchy. As opposed to a hypothesis postulated in the literature, the
generalized Kontsevich model at does not coincide with the
string theory at self-dual radius. A broader family of solutions of the Toda
lattice hierarchy including these models are constructed, and shown to satisfy
generalized string equations. The status of a variety of string
models is discussed in this new framework.Comment: 35pages, LaTeX Errors are corrected in Eqs. (2.21), (2.36), (2.33),
(3.3), (5.10), (6.1), sentences after (3.19) and theorem 5. A few references
are update
Origin of strong scarring of wavefunctions in quantum wells in a tilted magnetic field
The anomalously strong scarring of wavefunctions found in numerical studies
of quantum wells in a tilted magnetic field is shown to be due to special
properties of the classical dynamics of this system. A certain subset of
periodic orbits are identified which are nearly stable over a very large
interval of variation of the classical dynamics; only this subset are found to
exhibit strong scarring. Semiclassical arguments shed further light on why
these orbits dominate the experimentally observed tunneling spectra.Comment: RevTeX, 5 page
Open-label add-on treatment trial of minocycline in fragile X syndrome
<p>Abstract</p> <p>Background</p> <p>Fragile X syndrome (FXS) is a disorder characterized by a variety of disabilities, including cognitive deficits, attention-deficit/hyperactivity disorder, autism, and other socio-emotional problems. It is hypothesized that the absence of the fragile X mental retardation protein (FMRP) leads to higher levels of matrix metallo-proteinase-9 activity (MMP-9) in the brain. Minocycline inhibits MMP-9 activity, and alleviates behavioural and synapse abnormalities in <it>fmr1 </it>knockout mice, an established model for FXS. This open-label add-on pilot trial was conducted to evaluate safety and efficacy of minocycline in treating behavioural abnormalities that occur in humans with FXS.</p> <p>Methods</p> <p>Twenty individuals with FXS, ages 13-32, were randomly assigned to receive 100 mg or 200 mg of minocycline daily. Behavioural evaluations were made prior to treatment (baseline) and again 8 weeks after daily minocycline treatment. The primary outcome measure was the Aberrant Behaviour Checklist-Community Edition (ABC-C) Irritability Subscale, and the secondary outcome measures were the other ABC-C subscales, clinical global improvement scale (CGI), and the visual analog scale for behaviour (VAS). Side effects were assessed using an adverse events checklist, a complete blood count (CBC), hepatic and renal function tests, and antinuclear antibody screen (ANA), done at baseline and at 8 weeks.</p> <p>Results</p> <p>The ABC-C Irritability Subscale scores showed significant improvement (p < 0.001), as did the VAS (p = 0.003) and the CGI (p < 0.001). The only significant treatment-related side effects were minor diarrhea (n = 3) and seroconversion to a positive ANA (n = 2).</p> <p>Conclusions</p> <p>Results from this study demonstrate that minocycline provides significant functional benefits to FXS patients and that it is well-tolerated. These findings are consistent with the <it>fmr1 </it>knockout mouse model results, suggesting that minocycline modifies underlying neural defects that account for behavioural abnormalities. A placebo-controlled trial of minocycline in FXS is warranted.</p> <p>Trial registration</p> <p>ClinicalTrials.gov Open-Label Trial NCT00858689.</p
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