616 research outputs found
Horizontal Stratification during Deep Convection in the Labrador Sea
No full textDeep convection—the process by which surface waters are mixed down to 1000 m or deeper—forms the primary downwelling of the meridional overturning circulation in the Northern Hemisphere. High-resolution hydrographic measurements from Seagliders indicate that during deep convection—though water is well mixed vertically—there is substantial horizontal variation in density over short distances (tens of kilometers). This horizontal density variability present in winter (January–February) contains sufficient buoyancy to restratify the convecting region to observed levels 2.5 months later, as estimated from Argo floating platforms. These results highlight the importance of small-scale heterogeneities in the ocean that are typically poorly represented in climate models, potentially contributing to the difficulty climate models have in representing deep convection
Determining vertical water velocities from Seaglider
No full textVertical velocities in the world's oceans are typically small, less than 1 cm/s, posing a significant challenge to observation techniques. Seaglider, an autonomous profiling instrument, can be used to estimate vertical water velocity in the ocean to about half a centimeter per second. Using a Seaglider flight model and pressure observations, vertical water velocities are estimated along glider trajectories in the Labrador Sea before, during and after deep convection. Results indicate that vertical velocities in the stratified ocean agree with theoretical WKB-scaling of w, and in the turbulent mixed layer, scale with buoyancy and wind forcing. We estimate that accuracy is within 0.6 cm/s. Due to uncertainties in the flight model, velocities are poor near the surface and deep apogees, and during extended roll maneuvers. Some of this may be improved by using a dynamic flight model permitting acceleration, and by better constraining flight parameters through pilot choices during the mission
Crafts in the Southern Mountains
No full textThis article appeared in the 1931, November/December issue of "Handicrafter" magazine. It traces author "P.B."'s travels to various craft centers in the southern Appalachian mountains. Mentioned in the article are Allanstand Cottage Industries, The Spinning Wheel, Clementine Douglas, Winogene Redding, Evelyn Bishop, Mrs. Stone, Blue Ridge Weavers, Penland's Weaving Institute, Penland Weavers and Potters, Crossnore School, Mrs. H. N. Johnson, Pi Beta Phi Fraternity School, and Berea College's Fireside Industries. The author only gives a brief impression of his or her visit to each place. It is likely that author P.B. is Paul Bernat, editor of "Handicrafter" magazine
Experimental and computational study of the influence of pre-damage patterns in unreinforced masonry crack propagation due to induced, repeated earthquakes
No full textInduced seismicity in the north of the Netherlands has recently exposed unprepared, unreinforced masonry structures to considerable earthquake risk. While the ultimate-limit state capacity of the structures is vital to assess the individual’s risk, their behavior during more frequent, lighter earthquakes, leading to ‘lighter damage’, has shown to be strongly linked to economic losses and societal unrest. When observing the light damage caused by minor earthquakes, the existing state of the structure appears to be highly relevant for the final damage intensity and configuration: earthquakes that may have otherwise caused no apparent damage, may intensify existing damage. In particular, incipient damage due to settlements is common in the baked-clay and calcium-silicate brick masonry structures of the region.This paper details the study of full-scale laboratory walls, pre-damaged following typical (crack) patterns caused by settlements and tested with quasi-static lateral loads. The aggravation of the damage during a relevant number of load cycles is monitored using full-field digital image correlation. The damage is quantified objectively using a purposely-developed damage parameter.The tests are used (together with previous studies) to further calibrate computational finite element models, which coupled with detailed soil-structure interaction boundary conditions, are then employed to assess a larger number of structural geometries and pre-damaged configurations exposed to (repeated) induced earthquake acceleration histories.Both experimental and computational approaches show that settlement pre-damage in masonry structures increases the likelihood and the amount of further damage. This is more easily observed when some initial, yet limited damage exists and the masonry wall is exposed to moderate earthquake vibrations in the order of 30 millimeters per second.Accepted Author ManuscriptApplied Mechanic
A Critical Look At Mias
No full textIn this report the author brings a figure of the costs that go with the implementation of a landing aid, being a successor to the currently used system ILS. These cost figures should give the reader an insight in the possible costs necessary for the implementation of MIAS. Also a little discussion concerning the market value and the inherent political issues going with it are interwoven in part one of this thesis. Part two deals with the question of how other systems proved their required integrity norms. Especially a closer look at the way ILS System 4000 proved its maturity is given. Two possible methods to decide the service level of the equipment will be described and a list of works where several test specifications are described. Also, a new conception will be introduced, the “AI product”. Part three gives an answer to the following question: there is in the Kalman filter of MIAS the postulation of Gaussian shaped white noise, with a certain variance and on the other hand we want to fetch the stringent ICAO requirements (especially those for the system integrity). Do these two matters go hand in hand or do they conflict each other? Is there a way to fulfil the norms and in the meanwhile make use of the mathematical simplicity of Gaussian shaped white noise? As a reaction on these issues some approaches to adaptive Kalman filtering are described and a new manner of tuning a Kalman filter is set up, based on a system identification algorithm called MOESP.Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
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