Quantum Effects in Matter-Wave Diffraction

Advances in micro-technology of the last years have made it possible to carry optics textbooks experiments over to atomic and molecular beams, such as diffraction by a double slit or transmission grating. The usual wave-optical approach gives a good qualitative description of these experiments. However, small deviations therefrom and sophisticated quantum mechanics yield new surprising insights on the size of particles and on their interaction with surfaces.Comment: 6 pages, 3 Postscript figures. To appear in the Proceedings of Quantum Theory and Symmetry, Cracow, July 2001, edited by E. Kapuscik and A. Horzela, World Scientifi

Compression of ultrashort UV pulses in a self-defocusing gas

Compression of UV femtosecond laser pulses focused into a gas cell filled with xenon is reported numerically. With a large negative Kerr index and normal dispersion, xenon promotes temporal modulational instability (MI) which can be monitored to shorten ~ 100 fs pulses to robust, singly-peaked waveforms exhibiting a fourfold compression factor. Combining standard MI theory with a variational approach allows us to predict the beam parameters suitable for efficient compression. At powers < 30 MW, nonlinear dispersion is shown to shift the pulse temporal profile to the rear zone.Comment: 4 pages, 4 figure

Measurements of wall-shear stress fields on the piston crown in an IC engine flow using fluorescent labelled micro-pillar imaging

The measurement of wall shear-stress along the crown of a moving piston is accomplished with an array of hair-like, flexible micro-pillar sensors (MPS) in an internal combustion (IC) engine during intake flow conditions. The MPS are wall-clamped flexible micro-cylinders of 20micron diameter made of polydimethylsiloxane (PDMS) positioned on the surface of a transparent planar piston crown and protruding into the boundary layer flow above the piston at a height of 390micron. Their tips are labelled with fluorophores and are illuminated with a scanning laser-sheet system that follows the piston motion in synchronous manner. The flow-induced deflection is recorded through the transparent piston crown from below with a compact shaft-mounted high-speed camera recording the fluorescent re-emitted light from the pillar tips and using the fact of optical wave-guide features of the transparent micro-pillars. The experiments were performed in a transparent 4-valve engine setup (1.6 liter Prince 2, N13B16) during the intake phase. In order to improve the temporal resolution, the running speed of the engine was scaled down using water as working liquid. A static and dynamic sensor-calibration enabled the precise measurements of the wall-shear stress distribution with the sensor array. Due to spatial resolution limits of current available compact high-speed camera the recorded region along the piston was limited to 4x2 mm2 with 8x4 pillars in full view. The recordings at 300fps show the WSS fluctuations induced by the valve-jet / piston-wall interaction in the beginning of the intake with strong wall-normal motion forming critical points in the WSS field such as saddles, nodes and foci. Over the intake cycle > CA 80° these fluctuations die out and flow is transformed into wall-parallel coherent motion prescribed by the formation of the tumble

Investigating the Controls on Surface Snow δ18O Values in the Coastal Northeast Pacific: Implications for Paleoclimate Interpretations

Stable water isotope ratios (18O and D) in snow pit (Juneau Icefield) and fresh snow (Eclipse Icefield) samples are included in a compilation of all available snow isotope data from coastal Alaska, and used to evaluate observed isotope shifts in regional paleoclimate records. I compiled existing isotope data in coastal Alaska (primarily the Saint Elias Range) in order to better understand the elevation dependence of stable atmospheric water isotope ratios in the region. The values that make up the compilation are reflective of multiple fractionation regimes associated with synoptic scale cyclonic events, described using the Cyclone-Water Isotope Model (Holdsworth and Krouse 2002). Using this Cyclone-Water Isotope Model as a link between high frequency spatial and temporal variability, fresh snow data characterizing five different events within a 17 day time span from the Eclipse Icefield were analyzed for δ18O values. Average isotope values among these five events vary by as much as 8‰. Meteorological conditions over the domain are investigated with NCEP Climate Forecast System Reanalysis (CFSR), and show that events with more depleted δ18O are associated with systems that have higher pressure and a zonal (northern) moisture source, whereas events with less depleted δ18O are related to events with lower pressure and a more significant component of southern moisture. These observations of event-based meteorological controls on δ18O variability shed light on paleoclimate interpretations of shifts in the isotopic record seen in the Mount Logan ice core and Jellybean Lake sediment core at around A.D. 800 and A.D. 1840. The findings in the paper support Fields et al. (2010) in the interpretation that the shift to lower δ18O values seen in the isotopic record is caused by a transition to a more zonal (northern) moisture source paradigm

Bipolar Nickel-hydrogen Batteries for Aerospace Applications

A bipolar nickel-hydrogen battery which effectively addresses all key requirements for a spacecraft power system, including long-term reliability and low mass, is discussed. The design of this battery is discussed in the context of system requirements and nickel-hydrogen battery technology in general. To achieve the ultimate goal of an aerospace application of a bipolar Ni-H2 battery several objectives must be met in the design and development of the system. These objectives include: maximization of reliability and life; high specific energy and energy density; reasonable cost of manufacture, test, and integration; and ease in scaling for growth in power requirements. These basic objectives translate into a number of specific design requirements, which are discussed