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An analysis is presented of the dynamics of small droplets near the mouth of a purged or unpurged pitot tube in two-phase flow. Under certain conditions, that part of the total pressure which is attributable to loss of droplet momentum is shown to be only weakly dependent upon droplet size and density, vapour viscosity, tube size and purging rate. A new method is formulated for calculating the velocity from measured static and total pressures in compressible flow, which does not include the assumption that the fluid behaves as a homogeneous equilibrium mixture. When compared with results based upon the mixture assumption, for condensing flows of steam at low pressures, the new method yields velocities which are greater by one or two per cent and which approach the dry vapour values as the wetness fraction tends to zero. The absolute accuracy of the method has yet to be determined through experiment.
The Global Positioning System (GPS) has been widely used in positioning and attitude (orientation) determination (PAD) for a variety of sensor platforms. It is well known that for such satellite-based PAD systems, the accuracy, availability and reliability of the positioning and attitude determination results is heavily dependent on the number and geometric distribution of satellites being tracked. However, in some situations, such as in urban canyons and in deep open-cut mines, the number and geometry of visible satellites may not be sufficient to reliably determine the position and attitude parameters of a platform. Therefore, in order to improve the performance of satellited-based PAD systems, the integration of GPS with other technologies has been extensively investigated. In this paper the authors present details of both theoretical and experimental investigations into the potential integration of GPS and pseudolite technologies for positioning and attitude determination applications. Initial experiments indicate that positioning and attitude determination of a platform using a combination of GPS and pseudolite signals is feasible. The accuracy and reliability of GPS-only position and attitude determination results can be improved.
The long-term biomonitoring for fish and shellfish in Boston Harbor and Massachusetts Bay provide data to assess potential environmental impacts from the diversion of effluent into Massachusetts Bay in September 2000. Condition of the indicator species (i.e., winter flounder, lobster, blue mussels) are characterized in terms of length, weight, biological condition, the presence of external or internal disease, and inorganic and organic contaminant tissue concentrations. The key findings of the fish and shellfish monitoring program are the documented improvements in tumor incidence and bioaccumulation of contaminants in fish and shellfish taken from the bays, and the limited response to the diverted effluent in the organisms collected in Massachusetts Bay to date.
Lung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression. The depth of estimated lung compression ranged from 58 m in the gray seal with lungs inflated to 50% total lung capacity (TLC) to 133 m in the harbor porpoise with lungs at 100% TLC. These observations provide evidence for the possible behavior of gas within the chest of a live, diving mammal. The estimated depths of full compression of the lungs exceeds previous indirect estimates of the depth at which gas exchange ceases, and concurs with pulmonary shunt measurements. If these results are representative for living animals, they might suggest a potential for decompression sickness in diving mammals.
Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life-history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of individual whales. Differences in measured blubber thicknesses and estimated blubber volumes between normal and entangled, emaciated whales indicate between 7.4 × 1010 J and 1.2 × 1011 J of energy are consumed during the course to death of a lethal entanglement. Increased thrust power requirements to overcome drag forces suggest that when entangled, whales require 3.95 × 109 to 4.08 × 1010 J more energy to swim. Individuals who died from their entanglements performed significantly more work (energy expenditure × time) than those that survived; entanglement duration is therefore critical in determining whales' survival. Significant sublethal energetic impacts also occur, especially in reproductive females. Drag from fishing gear contributes up to 8% of the 4-year female reproductive energy budget, delaying time of energetic equilibrium (to restore energy lost by a particular entanglement) for reproduction by months to years. In certain populations, chronic entanglement in fishing gear can be viewed as a costly unnatural life-history stage, rather than a rare or short-term incident.
Gas bubbles were found in 15 of 23 gillnet-drowned bycaught harp ( Pagophilus groenlandicus), harbor ( Phoca vitulina) and gray ( Halichoerus grypus) seals, common ( Delphinus delphis) and white-sided ( Lagenorhyncus acutus) dolphins, and harbor porpoises ( Phocaena phocaena) but in only 1 of 41 stranded marine mammals. Cases with minimal scavenging and bloating were chilled as practical and necropsied within 24 to 72 hours of collection. Bubbles were commonly visible grossly and histologically in bycaught cases. Affected tissues included lung, liver, heart, brain, skeletal muscle, gonad, lymph nodes, blood, intestine, pancreas, spleen, and eye. Computed tomography performed on 4 animals also identified gas bubbles in various tissues. Mean ± SD net lead line depths (m) were 92 ± 44 and ascent rates (ms -1 ) 0.3 ± 0.2 for affected animals and 76 ± 33 and 0.2 ± 0.1, respectively, for unaffected animals. The relatively good carcass condition of these cases, comparable to 2 stranded cases that showed no gas formation on computed tomography (even after 3 days of refrigeration in one case), along with the histologic absence of bacteria and autolytic changes, indicate that peri- or postmortem phase change of supersaturated blood and tissues is most likely. Studies have suggested that under some circumstances, diving mammals are routinely supersaturated and that these mammals presumably manage gas exchange and decompression anatomically and behaviorally. This study provides a unique illustration of such supersaturated tissues. We suggest that greater attention be paid to the radiology and pathology of bycatch mortality as a possible model to better understand gas bubble disease in marine mammals.
