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Fabrication and characterisation of Si micropillar PV structures
Arrays of vertical silicon micropillar radial junction solar cells have been fabricated by diffusion of direct application spin on dopant and from the vapour phase through proximity rapid thermal diffusion. The micropillars were fabricated by optical lithography and deep reactive ion etching. The micropillar arrays show superior antireflective properties over the measured spectrum and good correlation to finite difference time domain modelling of identical geometry arrays. Junctions formed by a conventional spin on doping process of phosphorus containing dopant solution produced Suns-Voc values in the region of 0·3 V. This value is likely due to difficulties encountered in achieving an even distribution of dopant over the entire surface of the arrays. An alternative method utilising spin on dopant but employing an intermediate vapour phase diffusion step produced promising results with Suns-Voc values reaching 0·5 V following a post-diffusion drive-in ste
Automatic eduction and statistical analysis of coherent structures in the wall region of a confine plane
This paper describes a vortex detection algorithm used to expose and statistically characterize the
coherent flow patterns observable in the velocity vector fields measured by Particle Image
Velocimetry (PIV) in the impingement region of air curtains. The philosophy and the architecture of
this algorithm are presented. Its strengths and weaknesses are discussed. The results of a
parametrical analysis performed to assess the variability of the response of our algorithm to the 3
user-specified parameters in our eduction scheme are reviewed. The technique is illustrated in the
case of a plane turbulent impinging twin-jet with an opening ratio of 10. The corresponding jet
Reynolds number, based on the initial mean flow velocity U0 and the jet width e, is 14000. The
results of a statistical analysis of the size, shape, spatial distribution and energetic content of the
coherent eddy structures detected in the impingement region of this test flow are provided.
Although many questions remain open, new insights into the way these structures might form,
organize and evolve are given. Relevant results provide an original picture of the plane turbulent
impinging jet
Nonlinear wavelength conversion in photonic crystal fibers with three zero dispersion points
In this theoretical study, we show that a simple endlessly single-mode
photonic crystal fiber can be designed to yield, not just two, but three
zero-dispersion wavelengths. The presence of a third dispersion zero creates a
rich phase-matching topology, enabling enhanced control over the spectral
locations of the four-wave-mixing and resonant-radiation bands emitted by
solitons and short pulses. The greatly enhanced flexibility in the positioning
of these bands has applications in wavelength conversion, supercontinuum
generation and pair-photon sources for quantum optics
Soliton blue-shift in tapered photonic crystal fiber
We show that solitons undergo a strong blue shift in fibers with a dispersion
landscape that varies along the direction of propagation. The experiments are
based on a small-core photonic crystal fiber, tapered to have a core diameter
that varies continuously along its length, resulting in a zero-dispersion
wavelength that moves from 731 nm to 640 nm over the transition. The central
wavelength of a soliton translates over 400 nm towards shorter wavelength. This
accompanied by strong emission of radiation into the UV and IR spectral region.
The experimental results are confirmed by numerical simulation.Comment: 10 pages, 4 figure
Different types of X-ray bursts from GRS 1915+105 and their origin
We report the X-ray observations of the Galactic X-ray transient source GRS
1915+105 with the PPCs of the Indian X-ray Astronomy Experiment(IXAE) onboard
the Indian satellite IRS-P3 during 1997 June - August, which have revealed the
presence of four types of intense X-ray bursts. All the observed bursts have a
slow exponential rise, a sharp linear decay, and they can broadly be put in two
classes: irregular and quasi-regular bursts in one class, and regular bursts in
another class. The regular bursts are found to have two distinct time scales
and they persist over extended durations. There is a strong correlation between
the preceding quiescent time and the burst duration for the quasi-regular and
irregular bursts. No such correlation is found for the regular bursts. The
ratio of average flux during the burst time to the average flux during the
quiescent phase is high and variable for the quasi- regular and irregular
bursts while it is low and constant for the regular bursts. We suggest that the
peculiar bursts that we have seen are charact- eristic of the change of state
of the source. The source can switch back and forth between the low-hard state
and the high-soft state near critical accretion rates in a very short time
scale. A test of the model is presented using the publicly available 13-60 keV
RXTE/PCA data for irregular and regular bursts concurrent with our
observations.Comment: 13 pages, 12 figures, Accepted in APJ, emulateapj style use
Evolving temporal association rules with genetic algorithms
A novel framework for mining temporal association rules by discovering itemsets with a genetic algorithm is introduced. Metaheuristics have been applied to association rule mining, we show the efficacy of extending this to another variant - temporal association rule mining. Our framework is an enhancement to existing temporal association rule mining methods as it employs a genetic algorithm to simultaneously search the rule space and temporal space. A methodology for validating the ability of the proposed framework isolates target temporal itemsets in synthetic datasets. The Iterative Rule Learning method successfully discovers these targets in datasets with varying levels of difficulty
Monte Carlo simulations of pulse propagation in massive multichannel optical fiber communication systems
We study the combined effect of delayed Raman response and bit pattern
randomness on pulse propagation in massive multichannel optical fiber
communication systems. The propagation is described by a perturbed stochastic
nonlinear Schr\"odinger equation, which takes into account changes in pulse
amplitude and frequency as well as emission of continuous radiation. We perform
extensive numerical simulations with the model, and analyze the dynamics of the
frequency moments, the bit-error-rate, and the mutual distribution of amplitude
and position. The results of our numerical simulations are in good agreement
with theoretical predictions based on the adiabatic perturbation approach.Comment: Submitted to Physical Review E. 8 pages, 5 figure
Numerical Verification of an Analytical Model for Phase Noise in MEMS Oscillators.
A new analytical formulation for phase noise in MEMS oscillators was recently presented encompassing the role of essential nonlinearities in the electrical and mechanical domains. In this paper, we validate the effectiveness of the proposed analytical formulation with respect to the unified theory developed by Demir et al. describing phase noise in oscillators. In particular, it is shown that, over a range of the second-order mechanical nonlinear stiffness of the MEMS resonator, both models exhibit an excellent match in the phase diffusion coefficient calculation for a square-wave MEMS oscillator.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/TUFFC.2016.257536
High-speed tunable photonic crystal fiber-based femtosecond soliton source without dispersion pre-compensation
We present a high-speed wavelength tunable photonic crystal fiber-based
source capable of generating tunable femtosecond solitons in the infrared
region. Through measurements and numerical simulation, we show that both the
pulsewidth and the spectral width of the output pulses remain nearly constant
over the entire tuning range from 860 to 1160 nm. This remarkable behavior is
observed even when pump pulses are heavily chirped (7400 fs^2), which allows to
avoid bulky compensation optics, or the use of another fiber, for dispersion
compensation usually required by the tuning device.Comment: 8 pages, 11 figure
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