Carrier extraction circuit

Feedback loop extracts demodulated reference signals from IF input and feeds signal back to demodulator. Since reference signal is extracted directly from carrier, no separate reference need be transmitted. Circuit obtains coherent carrier from balanced or unbalanced four-phase signal of varying characteristics

Error correcting method and apparatus Patent

Description of error correcting methods for use with digital data computers and apparatus for encoding and decoding digital dat

Advanced ceramic material for high temperature turbine tip seals

Forty-one material systems were evaluated for potential use in turbine blade tip seal applications at 1370 C. Both ceramic blade tip inserts and abradable ceramic tip shoes were tested. Hot gas erosion, impact resistance, thermal stability, and dynamic rub performance were the criteria used in rating the various materials. Silicon carbide and silicon nitride were used, both as blade tips and abradables. The blade tip inserts were fabricated by hot pressing while low density and honeycomb abradables were sintered or reaction bonded

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

Electron impact promoted fragmentation of alkyl-N-(1-Phenylethyl)-carbamates of primary, secondary and tertiary alcohols

Mass spectra of alkyl carbamates derived from primary, secondary, and teriary alcohols by use of deuterium labeling and high resolution mass spectroscop

A Brücke-Bartley effect for contrast

Accurate derivation of the psychophysical (a.k.a. transducer) function from just-noticeable differences requires accurate knowledge of the relationship between the mean and variance of apparent intensities. Alternatively, a psychophysical function can be derived from estimates of the average between easily discriminable intensities. Such estimates are unlikely to be biased by the aforementioned variance, but they are notoriously variable and may stem from decisional processes that are more cognitive than sensory. To circumvent minimise cognitive pollution, we used amplitude-modulated contrast. As the spatial or temporal (carrier) frequency increased, estimates of average intensity became less variable across observers, converging on values that were closer to mean power (i.e. contrast 2) than mean contrast. Simply put, apparent contrast increases when physical contrast flickers. This result is analogous to Brücke's finding that brightness increases when luminance flickers. It implies an expansive transduction of contrast in the same way that Brücke's finding implies an expansive transduction of luminance

The improvement of contrast sensitivity with practice is not compatible with a sensory threshold account

In forced-choice detection, incorrect responses are routinely ascribed to internal noise, because experienced psychophysical observers do not act as if they have a sensory threshold, below which all perceived intensities would be identical. To determine whether inexperienced observers have sensory thresholds, we examined psychometric functions (percent correct vs log contrast) for detection and detection in full-field, dynamic visual noise. Over 5 days, neither type of psychometric function changed shape, but both shifted leftwards, indicating increased sensitivity. These results are not consistent with a lowered sensory threshold, which would decrease psychometric slope. They are consistent with a combination of reduced internal additive noise and improved filtering of external noise

Fitting the Means to the Ends: One School’s Experience with Quantitative and Qualitative Methods in Curriculum Evaluation During Curriculum Change

Curriculum evaluation plays an important role in substantive curriculum change. The experience of the University of Texas Medical Branch (UTMB) with evaluation processes developed for the new Integrated Medical Curriculum (IMC) illustrates how evaluation methods may be chosen to match the goals of the curriculum evaluation process. Quantitative data such as ratings of courses or scores on external exams are useful for comparing courses or assessing whether standards have been met. Qualitative data such as students’ comments about aspects of courses are useful for eliciting explanations of observed phenomena and describing relationships between curriculum features and outcomes. The curriculum evaluation process designed for the IMC used both types of evaluation methods in a complementary fashion. Quantitative and qualitative methods have been used for formative evaluation of the new IMC courses. They are now being incorporated into processes to judge the IMC against its goals and objectives

Visible and near-ultraviolet spectroscopy at Thule AFB (76.5 N) from January 28 - February 15, 1988

Near-ultraviolet and visible spectrographs identical to those employed at McMurdo Station, Antarctica (77.8 S) during the austral spring seasons of 1986 and 1987 were used to study the stratosphere above Thule, Greenland (76.5 N) during early spring, 1988. Observations were carried out both at night using the direct moon as a light source, and during the day by collecting the scattered light from the zenith sky when solar zenith angles were less than about 94.5 degrees. Excellent meteorological conditions prevailed in the troposphere and stratosphere at Thule. Surface weather was extremely clear over most of the period, facilitating measurements of the direct light from the moon. The lower stratospheric arctic polar vortex was located very near Thule throughout the observing period, and temperature at the 30 mbar level were typically below -80 C above Thule, according to the National Meteorological Center daily analyses. Thus conditions were favorable for polar stratospheric cloud formation above Thule. Total column ozone abundances were about 350 to 400 Dobson units, and did not suggest a clear temporal trend over the observing period. Stratospheric nitrogen dioxide measurements were complicated by the presence of a large component of tropospheric pollution on many occasions. Stratospheric nitrogen dioxide could be identified on most days using the absorption in the scattered light from the zenith sky, which greatly enhances the stratospheric airmass while suppressing the tropospheric contribution. These measurements suggest that the total vertical column abundance of nitrogen dioxide present over Thule in February was extremely low, sometimes as low as 3 x 10 to the 14th per sq cm. The abundance of nitrogen dioxide increased systemically from about 3 x 10 to the 14th in late January to 1.0 x 10 to the 15th per sq cm in mid-February, perhaps because of photolysis of N2O5 in the upper part of the stratosphere, near 25 to 35 km