Time-of-Flight Optical Ranging System Based on Time-Correlated Single-Photon Counting

The design and implementation of a prototype time-of-flight optical ranging system based on the time-correlated single-photon-counting technique are described. The sensor is characterized in terms of its longitudinal and transverse spatial resolution, single-point measurement time, and long-term stability. The system has been operated at stand-off distances of 0.5-5 m, has a depth repeatability of <30 mum, and has a lateral spatial resolution of <500 mum.     

Multilayer dielectric structure for enhancement of evanescent waves

We describe a type of multilayer dielectric coating designed to enhance the intensity of evanescent waves. The coating consists of a stack of alternating high- and low-index quarter-wave layers followed by a final low-index layer whose thickness is chosen to optimize the evanescent-wave intensity. Indirect measurements of the film properties are in good agreement with theory.     

Reversible suppression of the so-called fishtail effect in ultra pure single crystals of YBa2Cu3O7−δ achieved by proper oxygenation

We report on the absence of the so-called fishtail or peak effect in the magnetisation curves of properly oxygenated high purity (5N) single crystals of YBa₂Cu₃O_7–. As we recently reported [1] high pressure oxygenation procedures are suitable to produce a monotonous dependence of the critical current density with the magnetic field. In this article we report furthermore how to reversibly produce or remove this effect on the same crystal by proper oxygenation methods. Along with the high purity of the samples, — due to crystal growth in non reactive BaZrO₃ crucibles —, this proves that at least in pure samples the fishtail effect is due to different oxygenation states and/or oxygen distributions. In less pure samples, however, other sources for this anomaly like metallic impurities can act as an additional source for the fishtail anomaly.     

Components for the implementation of free-space optical crossbars

We describe an optical system developed to form the basis of a 64 × 64 free-space optical matrix-matrix crossbar switch. The design and performance of each of the main optical components is discussed: lenses, diffractive optical elements, and polarizing beamsplitters, together with the optomechanical hardware design. For these components, throughput levels of -6.9 dB have been achieved, which is compatible with full system operation at 10(-12) bit error rates at ≥270 Mbits s(-1).     

Scanning tunneling spectroscopy studies on YBa2Cu3O7−δ

Scanning Tunneling Spectroscopy (STS) measurements have been carried out on the high T_c superconductor (HTS) YBa₂Cu₃O_7– (YBCO). Using very high quality single crystals as well as hard tips, we obtained differential conductance spectra which showed various conductance features in agreement with other spectroscopic techniques. The reproducibility of our spectra allowed us to map for the first time the vortex lattice on a HTS using a STS technique¹. The vortices are arranged in a short range order oblique lattice, while the cores of the flux lines show an anisotropic shape. These observations can be related to the in-plane anisotropy of YBCO.     

The lactulose breath hydrogen test and small intestinal bacterial overgrowth

OBJECTIVES: To i) document the sensitivity and specificity of a combined scintigraphic/lactulose breath hydrogen test for small intestinal bacterial overgrowth and ii) investigate the validity of currently accepted definitions of an abnormal lactulose breath hydrogen test based on "double peaks" in breath hydrogen concentrations. METHODS: Twenty-eight subjects were investigated with culture of proximal small intestinal aspirate and a 10-g lactulose breath hydrogen test combined with scintigraphy. Gastroduodenal pH, the presence or absence of gastric bacterial overgrowth, and the in vitro capability of overgrowth flora to ferment lactulose were determined. RESULTS: Sensitivity (16.7%) and specificity (70.0%) of the lactulose breath hydrogen test alone for small intestinal bacterial overgrowth were poor. Combination with scintigraphy resulted in 100% specificity, because double peaks in serial breath hydrogen concentrations may occur as a result of lactulose fermentation by cecal bacteria. Sensitivity increased to 38.9% with scintigraphy, because a single rise in breath hydrogen concentrations, commencing before the test meal reaches the cecum, may occur in this disorder. Sensitivity remained suboptimal irrespective of the definition of small intestinal bacterial overgrowth used, the nature of the overgrowth flora, favorable luminal pH, the presence of concurrent gastric bacterial overgrowth, or the in vitro ability of the overgrowth flora to ferment lactulose. CONCLUSIONS: Definitions of an abnormal lactulose breath hydrogen test based on the occurrence of double peaks in breath hydrogen concentrations are inappropriate. Not even the addition of scintigraphy renders this test a clinically useful alternative to culture of aspirate for diagnosing small intestinal bacterial overgrowth.     

Development of a tundra-specific snow water equivalent retrieval algorithm for satellite passive microwave data

Airborne and satellite brightness temperature (T_B) measurements were combined with intensive field observations of sub-Arctic tundra snow cover to develop the framework for a new tundra-specific passive microwave snow water equivalent (SWE) retrieval algorithm. The dense snowpack and high sub-grid lake fraction across the tundra mean that conventional brightness temperature difference approaches (such as the commonly used 37 GHz-19 GHz) are not appropriate across the sub-Arctic. Airborne radiometer measurements (with footprint dimensions of approximately 70 × 120 m) acquired across sub-Arctic Canada during three field campaigns during the 2008 winter season were utilized to illustrate a slope reversal in the 37 GHz T_B versus SWE relationship. Scattering by the tundra snowpack drives a negative relationship until a threshold SWE value is reached near 130 mm at which point emission from the snowpack creates a positive but noisier relationship between 37 GHz T_B and SWE.The change from snowpack scattering to emission was also evident in the temporal evolution of 37 GHz T_B observed from satellite measurements. AMSR-E brightness temperatures (2002/03-2006/07) consistently exhibited decreases through the winter before reaching a minimum in February or March, followed by an increase for weeks or months before melt. The cumulative absolute change (Σ|Δ37V|) in vertically polarized 37 GHz T_B was computed at both monthly and pentad intervals from a January 1 start date and compared to ground measured SWE from intensive and regional snow survey campaigns, and climate station observations. A greater (lower) cumulative change in |Δ37V| was significantly related to greater (lower) ground measured SWE (r² = 0.77 with monthly averages; r² = 0.67 with pentad averages). Σ|Δ37V| was only weakly correlated with lake fraction: monthly r² values calculated for January through April 2003-2007 were largely less than 0.2. These results indicate that this is a computationally straightforward and viable algorithmic framework for producing tundra-specific SWE datasets from the complete satellite passive microwave record (1979 to present).     

Automatic metro map layout using multicriteria optimization

This paper describes an automatic mechanism for drawing metro maps. We apply multicriteria optimization to find effective placement of stations with a good line layout and to label the map unambiguously. A number of metrics are defined, which are used in a weighted sum to find a fitness value for a layout of the map. A hill climbing optimizer is used to reduce the fitness value, and find improved map layouts. To avoid local minima, we apply clustering techniques to the map-the hill climber moves both stations and clusters when finding improved layouts. We show the method applied to a number of metro maps, and describe an empirical study that provides some quantitative evidence that automatically-drawn metro maps can help users to find routes more efficiently than either published maps or undistorted maps. Moreover, we have found that, in these cases, study subjects indicate a preference for automatically-drawn maps over the alternatives.     

Podcasting in education: Are students as ready and eager as we think they are?

Instructors in higher education are disseminating instructional content via podcasting, as many rally behind the technology’s potential benefits. Others have expressed concern about the risks of deleterious effects that might accompany the adoption of podcasting, such as lower class attendance. Yet, relatively few studies have investigated students’ perceptions of podcasting for educational purposes, especially in relation to different podcasting forms: repetitive and supplemental. The present study explored students’ readiness and attitudes towards these two forms of podcasting to provide fundamental information for future researchers and educators. The results indicated that students may not be as ready or eager to use podcasting for repetitive or supplemental educational purposes as much as we think they are, but they could be persuaded.