1,866 research outputs found
Statistics of conductance and shot-noise power for chaotic cavities
We report on an analytical study of the statistics of conductance, , and
shot-noise power, , for a chaotic cavity with arbitrary numbers of
channels in two leads and symmetry parameter . With the theory
of Selberg's integral the first four cumulants of and first two cumulants
of are calculated explicitly. We give analytical expressions for the
conductance and shot-noise distributions and determine their exact asymptotics
near the edges up to linear order in distances from the edges. For a
power law for the conductance distribution is exact. All results are also
consistent with numerical simulations.Comment: 7 pages, 3 figures. Proc. of the 3rd Workshop on Quantum Chaos and
Localisation Phenomena, Warsaw, Poland, May 25-27, 200
Tensile strained membranes for cavity optomechanics
We investigate the optomechanical properties of tensile-strained ternary
InGaP nanomembranes grown on GaAs. This material system combines the benefits
of highly strained membranes based on stoichiometric silicon nitride, with the
unique properties of thin-film semiconductor single crystals, as previously
demonstrated with suspended GaAs. Here we employ lattice mismatch in epitaxial
growth to impart an intrinsic tensile strain to a monocrystalline thin film
(approximately 30 nm thick). These structures exhibit mechanical quality
factors of 2*10^6 or beyond at room temperature and 17 K for eigenfrequencies
up to 1 MHz, yielding Q*f products of 2*10^12 Hz for a tensile stress of ~170
MPa. Incorporating such membranes in a high finesse Fabry-Perot cavity, we
extract an upper limit to the total optical loss (including both absorption and
scatter) of 40 ppm at 1064 nm and room temperature. Further reductions of the
In content of this alloy will enable tensile stress levels of 1 GPa, with the
potential for a significant increase in the Q*f product, assuming no
deterioration in the mechanical loss at this composition and strain level. This
materials system is a promising candidate for the integration of strained
semiconductor membrane structures with low-loss semiconductor mirrors and for
realizing stacks of membranes for enhanced optomechanical coupling.Comment: 10 pages, 3 figure
Charged Particle with Magnetic Moment in the Aharonov-Bohm Potential
We considered a charged quantum mechanical particle with spin
and gyromagnetic ratio in the field af a magnetic string. Whereas the
interaction of the charge with the string is the well kown Aharonov-Bohm effect
and the contribution of magnetic moment associated with the spin in the case
is known to yield an additional scattering and zero modes (one for each
flux quantum), an anomaly of the magnetic moment (i.e. ) leads to bound
states. We considered two methods for treating the case . \\ The first is
the method of self adjoint extension of the corresponding Hamilton operator. It
yields one bound state as well as additional scattering. In the second we
consider three exactly solvable models for finite flux tubes and take the limit
of shrinking its radius to zero. For finite radius, there are bound
states ( is the number of flux quanta in the tube).\\ For the bound
state energies tend to infinity so that this limit is not physical unless along with . Thereby only for fluxes less than unity the results of
the method of self adjoint extension are reproduced whereas for larger fluxes
bound states exist and we conclude that this method is not applicable.\\ We
discuss the physically interesting case of small but finite radius whereby the
natural scale is given by the anomaly of the magnetic moment of the electron
.Comment: 16 pages, Latex, NTZ-93-0
Stability of the nonlinear dynamics of an optically injected VCSEL
Automated protocols have been developed to characterize time series data in terms of stability. These techniques are applied to the output power time series of an optically injected vertical cavity surface emitting laser (VCSEL) subject to varying injection strength and optical frequency detuning between master and slave lasers. Dynamic maps, generated from high resolution, computer controlled experiments, identify regions of dynamic instability in the parameter space. © 2012 Optical Society of America
MoDSS - a compact Mobile Decay Spectroscopy Set-up for the investigation of heavy and superheavy nuclei after separation
International audienc
VHE Gamma Rays from PKS 2155-304
The close X-ray selected BL Lac PKS 2155-304 has been observed using the
University of Durham Mark 6 very high energy (VHE) gamma ray telescope during
1996 September/October/November and 1997 October/November. VHE gamma rays with
energy > 300 GeV were detected from this object with a time-averaged integral
flux of (4.2 +/- 0.7 (stat) +/- 2.0 (sys)) x 10^(-11) per cm2 per s. There is
evidence for VHE gamma ray emission during our observations in 1996 September
and 1997 October/November, with the strongest emission being detected in 1997
November, when the object was producing the largest flux ever recorded in
high-energy X-rays and was detected in > 100 MeV gamma-rays. The VHE and X-ray
fluxes show evidence of a correlation.Comment: 14 pages, 6 figures, accepted for publication in Ap.
Tunable microwave signal generator with an optically-injected 1310nm QD-DFB laser
Tunable microwave signal generation with frequencies ranging from below 1 GHz to values over 40 GHz is demonstrated experimentally with a 1310nm Quantum Dot (QD) Distributed-Feedback (DFB) laser. Microwave signal generation is achieved using the period 1 dynamics induced in the QD DFB under optical injection. Continuous tuning in the positive detuning frequency range of the quantum dot's unique stability map is demonstrated. The simplicity of the experimental configuration offers promise for novel uses of these nanostructure lasers in Radio-over-Fiber (RoF) applications and future mobile networks. © 2013 Optical Society of America
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Observations of Past Lunar Landing Sites by the D-CIXS X-Ray Spectrometer on SMART-1
D-CIXS initial observations show a first unambiguous remote sensing of calcium in the lunar regolith. Data obtained are broadly consistent with current understanding of mare and highland composition. Ground truth is provided by the returned Apollo and Luna sample sets
A Novel Clustering Algorithm Based on Quantum Games
Enormous successes have been made by quantum algorithms during the last
decade. In this paper, we combine the quantum game with the problem of data
clustering, and then develop a quantum-game-based clustering algorithm, in
which data points in a dataset are considered as players who can make decisions
and implement quantum strategies in quantum games. After each round of a
quantum game, each player's expected payoff is calculated. Later, he uses a
link-removing-and-rewiring (LRR) function to change his neighbors and adjust
the strength of links connecting to them in order to maximize his payoff.
Further, algorithms are discussed and analyzed in two cases of strategies, two
payoff matrixes and two LRR functions. Consequently, the simulation results
have demonstrated that data points in datasets are clustered reasonably and
efficiently, and the clustering algorithms have fast rates of convergence.
Moreover, the comparison with other algorithms also provides an indication of
the effectiveness of the proposed approach.Comment: 19 pages, 5 figures, 5 table
High-sensitivity troponin I concentrations are a marker of an advanced hypertrophic response and adverse outcomes in patients with aortic stenosis
Aims:
High-sensitivity cardiac troponin I (cTnI) assays hold promise in detecting the transition from hypertrophy to heart failure in aortic stenosis. We sought to investigate the mechanism for troponin release in patients with aortic stenosis and whether plasma cTnI concentrations are associated with long-term outcome.
Methods and results:
Plasma cTnI concentrations were measured in two patient cohorts using a high-sensitivity assay. First, in the Mechanism Cohort, 122 patients with aortic stenosis (median age 71, 67% male, aortic valve area 1.0 ± 0.4 cm2) underwent cardiovascular magnetic resonance and echocardiography to assess left ventricular (LV) myocardial mass, function, and fibrosis. The indexed LV mass and measures of replacement fibrosis (late gadolinium enhancement) were associated with cTnI concentrations independent of age, sex, coronary artery disease, aortic stenosis severity, and diastolic function. In the separate Outcome Cohort, 131 patients originally recruited into the Scottish Aortic Stenosis and Lipid Lowering Trial, Impact of REgression (SALTIRE) study, had long-term follow-up for the occurrence of aortic valve replacement (AVR) and cardiovascular deaths. Over a median follow-up of 10.6 years (1178 patient-years), 24 patients died from a cardiovascular cause and 60 patients had an AVR. Plasma cTnI concentrations were associated with AVR or cardiovascular death HR 1.77 (95% CI, 1.22 to 2.55) independent of age, sex, systolic ejection fraction, and aortic stenosis severity.
Conclusions:
In patients with aortic stenosis, plasma cTnI concentration is associated with advanced hypertrophy and replacement myocardial fibrosis as well as AVR or cardiovascular death
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