Passive Mode-Locking of Monolithic InGaAs/AlGaAs Double Quantum Well Lasers at 42GHz Repetition Rate

Pulse trains with a 42GHz repetition rate were generated by monolithic InGaAs/AlGaAs double quantum well lasers at a wavelength of 985 [angstroms]. The cavity was electrically divided into three regions, one providing gain and the other two providing saturable absorption. The optical modulation has a depth greater than 98% and full-width at half-maximum under 6ps, and bias conditions for sustained mode-locking are determined

Evaluation of roughness lengths at the NSSL- WKY meteorological tower

Wind and temperature sensors installed on NSSL-WKY /Oklahoma City/ meteorological tower to evaluate roughness length

Fine structure of distributions and central limit theorem in diffusive billiards

We investigate deterministic diffusion in periodic billiard models, in terms of the convergence of rescaled distributions to the limiting normal distribution required by the central limit theorem; this is stronger than the usual requirement that the mean square displacement grow asymptotically linearly in time. The main model studied is a chaotic Lorentz gas where the central limit theorem has been rigorously proved. We study one-dimensional position and displacement densities describing the time evolution of statistical ensembles in a channel geometry, using a more refined method than histograms. We find a pronounced oscillatory fine structure, and show that this has its origin in the geometry of the billiard domain. This fine structure prevents the rescaled densities from converging pointwise to gaussian densities; however, demodulating them by the fine structure gives new densities which seem to converge uniformly. We give an analytical estimate of the rate of convergence of the original distributions to the limiting normal distribution, based on the analysis of the fine structure, which agrees well with simulation results. We show that using a Maxwellian (gaussian) distribution of velocities in place of unit speed velocities does not affect the growth of the mean square displacement, but changes the limiting shape of the distributions to a non-gaussian one. Using the same methods, we give numerical evidence that a non-chaotic polygonal channel model also obeys the central limit theorem, but with a slower convergence rate.Comment: 16 pages, 19 figures. Accepted for publication in Physical Review E. Some higher quality figures at http://www.maths.warwick.ac.uk/~dsander

Ordered Measurements of Permutationally-Symmetric Qubit Strings

We show that any sequence of measurements on a permutationally-symmetric (pure or mixed) multi-qubit string leaves the unmeasured qubit substring also permutationally-symmetric. In addition, we show that the measurement probabilities for an arbitrary sequence of single-qubit measurements are independent of how many unmeasured qubits have been lost prior to the measurement. Our results are valuable for quantum information processing of indistinguishable particles by post-selection, e.g. in cases where the results of an experiment are discarded conditioned upon the occurrence of a given event such as particle loss. Furthermore, our results are important for the design of adaptive-measurement strategies, e.g. a series of measurements where for each measurement instance, the measurement basis is chosen depending on prior measurement results.Comment: 13 page

Chaos in cylindrical stadium billiards via a generic nonlinear mechanism

We describe conditions under which higher-dimensional billiard models in bounded, convex regions are fully chaotic, generalizing the Bunimovich stadium to dimensions above two. An example is a three-dimensional stadium bounded by a cylinder and several planes; the combination of these elements may give rise to defocusing, allowing large chaotic regions in phase space. By studying families of marginally-stable periodic orbits that populate the residual part of phase space, we identify conditions under which a nonlinear instability mechanism arises in their vicinity. For particular geometries, this mechanism rather induces stable nonlinear oscillations, including in the form of whispering-gallery modes.Comment: 4 pages, 4 figure

Silicon nitride-aluminum oxide solid solution (SiAION) formation and densification by pressure sintering

Stirred-ball-mill-blended Si3N4 and Al2O3 powders were pressure sintered in order to investigate the mechanism of solid solution formation and densification in the Si3N4-Al2O3 system. Powder blends with Si3N4:Al2O3 mole ratios of 4:1, 3:2, and 2:3 were pressure sintered at 27.6-MN/sq m pressure at temperatures to 17000 C (3090 F). The compaction behavior of the powder blends during pressure sintering was determined by observing the density of the powder compact as a function of temperature and time starting from room temperature. This information, combined with the results of X-ray diffraction and metallographic analyses regarding solutioning and phase transformation phenomena in the Si3N4-Al2O3 system, was used to describe the densification behavior

Condoms are more effective when applied by males: a study of young black males in the United States

PurposeTo determine, among a sample of young black male (YBM), whether female application of male condoms for penile–vaginal intercourse would be associated with higher or lower rates of breakage or slippage. A secondary aim was to investigate if higher rates of breakage or slippage were associated with increased odds of acquiring chlamydia and/or gonorrhea.MethodsA cross-sectional study of 412 YBM, aged 15 to 23 years, was conducted in three US cities located in the Southern United States.ResultsAmong YBM reporting frequent female application of condoms, 43.5% reported one or more instance of breakage or slippage, compared with those reporting less frequent female application (27.2%, P = .003). Among YBM reporting one or more event of breakage or slippage, 25.4% tested positive for chlamydia and/or gonorrhea. In contrast, among those not reporting breakage or slippage, 17.2% tested positive (P = .047).ConclusionsFindings suggest that educational and behavioral interventions should seek to improve young women's skills relative to condom application and use. Further studies could also investigate whether intervention efforts should encourage some YBM to be responsible for their own condom application

Furnace and high-velocity oxidation of aluminide-coated cobalt super-alloy WI-52

Furnace and high velocity oxidation of aluminide coated cobalt superalloy WI-5

Ground-based measurements of O3, NO2, OClO, and BrO during the 1987 Antarctic ozone depletion event

Near-ultraviolet absorption spectroscopy in the wavelength range from 330 to 370 nm was used to measure O3, NO2, OClO, and BrO at McMurdo Station (78S) during 1987. Visible absorption measurements of O3, NO2, and OClO were also obtained using the wavelength range from about 403 to 453 nm. These data are described and compared to observations obtained in 1986. It is shown that comparisons of observations in the two wavelength ranges provide a sensitive measure of the altitude where the bulk of atmospheric absorption takes place

Elastocapillary folding of three dimensional micro-structures using water pumped through the wafer via a silicon nitride tube

In this paper we present the first investigation of a batch method for folding of threedimensional micrometer-sized silicon nitride structures by capillary forces. Silicon nitride tubes have been designed and fabricated using DRIE at the center of the planar origami patterns of the structures. Water is brought to the structures by pumping the liquid through the wafer via those tubes. Isolated micro-structures were successfully folded using this method. The potential of this technique for batch self-assembly is discussed