All-fiber source of 20-fs pulses at 1550 nm using two-stage linear-nonlinear compression of parabolic similaritons

Parabolic pulses from a similariton amplifier at 1550nm are compressed using a two-stage fiber compressor employing linear compression in photonic bandgap fiber and soliton effect compression in highly nonlinear fiber. Precise optimization of the compressor design using frequency resolved optical gating allows the generation of minimally chirped pulses as short as 20fs. This duration corresponds to only four optical cycles of the underlying electric field at this wavelength.     

Cylindrical and spherical shells with cracks

The symmetric problem for the cylindrical and spherical shells containing a meridional crack is considered. The problem is solved for a uniform membrane load and a uniform bending moment applied to the surface of the crack. The extensional and bending components of the stress intensity factor ratio are obtained as functions of shell parameter and are tabulated. The results are also plotted in order to compare them with the existing asymptotic solutions.

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Zusammenfassung Das symmetrische Problem für zylindrische and sphärische Schalen, die einen meridionalen Riß haben, wurde behandeft. Das Problem wurde für eine einheitliche Membranlast and ein einheitliches Biegungsmoment auf der Oberfläche des Risses angewandt, gelöst.Die ausdehnenden und biegenden Komponente des Druckstärkefaktorenradius wurden als Funktionen des Schalenparameters erhalten and tabuliert. Die Ergebnisse wurden auch aufgezeichnet, um sie mit den bestehenden asymmetrischen Lösungen zu vergleichen.

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Résumé On considère le problème symétrique d'enveloppes cylindriques et sphériques comportant une fissure qui se développe suivant un méridien. La solution est apportée dans le cas d'une contrainte de membrane uniforme et d'un moment de flexion uniformément appliqué aux lèvres de la fissure.Ces composantes de traction et de flexion qui agissent sur le facteur d'intensité des contraintes sont determinées en fonction des paramètres de l'enveloppe, et présentées sous forme de tableaux. Les résultats ont 6t6 également portés en diagrammes, de manière à les comparer aux solutions asymptotiques existantes.

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This work was supported by the National Aeronautics and Space Administration under the Grant NGR 39-007-011.     

Electronic surface barrier properties of boron-doped diamond oxidized by plasma treatment

The electronic surface barrier characteristics of single-crystal and nanocrystalline boron-doped diamond in electrolytes are evaluated. Two cases are compared: Oxidation by RF oxygen plasma treatment and oxidation by anodic polarization in alkaline electrolyte. It is shown that the plasma treatment reduces the surface barrier to about 1.0 eV compared to 1.7 eV when subjected to anodic oxidation. For single-crystalline diamond, the oxygen evolution reaction in 0.1 M H₂SO₄ electrolyte is almost insensitive to the oxidation method while the plasma-treated nanocrystalline diamond electrode shows an enhanced activity of grain boundary defects at anodic potentials. X-ray photoemission spectroscopy measurements reveal that the plasma oxidation induces a higher content of carbonyl surface groups than anodic oxidation as well as a small amount of non-sp³ contents.     

Power rail logic: a low power logic style for digital GaAs circuits

This paper describes a new logic style called Power Rail Logic (PRL), which is compatible with direct-coupled FET logic (DCFL) circuits. Multiplexors, latches, flip-flops, and exclusive-OR gates can be built using this logic style. Compared to DCFL, PRL uses fewer transistors, has larger noise margins, and up to 40% lower power-delay products. A test chip containing 32-b barrel shifters designed in DCFL and in PRL was successfully fabricated and tested. Test results are given for both circuits     

AND parallelism and nondeterminism in logic programs

This paper defines an abstract interpreter for logic programs based on a system of asynchronous, independent processors which communicate only by passing messages. Each logic program is automatically partitioned and its pieces distributed to available processors. This approach permits two distinct forms of parallelism. OR parallelism arises from evaluating nondeterministic choices simultaneously. AND parallelism arises when a computation involves independent, but necessary, subcomputations. Algorithms like quicksort, which follow a divide and conquer approach, usually exhibit this form of parallelism. These two forms of parallelism are conjointly achieved by the parallel interpreter.     

Suspended core tellurite glass optical fibers for infrared supercontinuum generation

We report the fabrication and characterization of tellurite TeO₂-ZnO-Na₂O (TZN) microstructured suspended core optical fibers (MOFs). These fibers are designed for infrared supercontinuum generation with zero dispersion wavelength (ZDW) at 1.45 μm. The measured losses at this wavelength are approximately 6 dB/m for a MOF with a 2.2 μm diameter core. The effective area of a particular fiber is 3.5 μm² and the nonlinear coefficient is calculated to be 437 W⁻¹km⁻¹. By pumping a 20 cm long fiber at 1.56 μm with a sub-nJ femtosecond laser source, we generate a supercontinuum (SC) spanning over 800 nm in the 1-2 μm wavelength range.     

Fiber-based device for the detection of low-intensity fluctuations of ultrashort pulses

We describe a fiber-based device that can significantly enhance the low-intensity fluctuations of an ultrashort pulse train to detect them more easily than with usual direct detection systems. Taking advantage of the Raman intrapulse effect that progressively shifts the central frequency of a femtosecond pulse propagating in an anomalous dispersion fiber, a subsequent spectral filtering can efficiently increase the level of fluctuations by more than 1 order of magnitude. We show that attention has to be paid to maintain the shape of the statistical distribution unaffected by the nonlinear process.     

Minimum Generalization Via Reflection: A Fast Linear Threshold Learner

The number of adjustments required to learn the average LTU function of d features, each of which can take on n equally spaced values, grows as approximately n^2d when the standard perceptron training algorithm is used on the complete input space of n points and perfect classification is required. We demonstrate a simple modification that reduces the observed growth rate in the number of adjustments to approximately d2(log (d) + log(n)) with most, but not all input presentation orders. A similar speed-up is also produced by applying the simple but computationally expensive heuristic ";don't overgeneralize" to the standard training algorithm. This performance is very close to the theoretical optimum for learning LTU functions by any method, and is evidence that perceptron-like learning algorithms can learn arbitrary LTU functions in polynomial, rather than exponential time under normal training conditions. Similar modifications can be applied to the Winnow algorithm, achieving similar performance improvements and demonstrating the generality of the approach.