Pacific herring, Clupea pallasi, studies and fishery management in Tomales Bay 1992-93, with notes on Humboldt Bay and Crescent City area landings

The 1992-93 spawning biomass estimate for Pacific herring, Clupea pallasi, in Tomales Bay increased for the fourth year in a row to 4,078 tons. This is the highest estimate since the 1986-87 season. The December spawning biomass total of 1,346 tons was the second highest December escapement total since surveys began in 1972-73. A total of 3.58 million m2 of eelgrass, Zostera marina, was measured in Tomales Bay this season. Eelgrass density increased in the majority of beds. The commercial catch of 222 tons was taken entirely from Tomales Bay since outer Bodega Bay was closed to herring fishing during the season. Gill net mesh size was increased to 2.125 inches from 2.0 inches this season. Herring aged 4,5, and 6 comprised 92% by number of the season's herring catch. Mean weight of herring for each age decreased while mean length for all ages combined increased slightly. Tomales Bay herring samples indicated that older year-classes, missing in commercial catch samples, were present prior to the January start of the commercial fishery. The abundance of 4-yr-old herring was low in samples from variable-mesh and commercial gill nets, indicating less than average recruitment of the 1989 year-class. In Humboldt Bay the 1992-93 season commercial herring catch totalled 28.6 tons, less than half of the 60-ton quota. Crescent City area herring fishermen nearly caught their 30-ton quota with a total of 28.5 tons landed. No spawning biomass estimate is available for the 1992-93 season for either area. (29pp.

Pacific herring, Clupea pallasi, studies and fishery management in Tomales Bay, 1993-94, with notes on Humbolt and Crescent City area landings

The 1993-94 spawning biomass estimate for Pacific herring, Clupea pallasi, in Tomales Bay declined 40% from last season to 2,449 tons. Although this estimate is below the 20-year average of 4,700 tons, the spawning biomass estimate this year is close to the post 1982 El Nino 11-year average of 2,054 tons. The overall trend of increasing biomass since the 1989-90 season still continues. There were eight distinct spawns this season, the most in five years, with the largest spawn occurring in late January. A total of 3.5 million m2 of eelgrass, Zostera marina, was measured in Tomales Bay this season. Eelgrass density increased in the majority of the beds. The commercial gillnet fleet in Tomales Bay caught a total of 219 tons of herring this season yielding an exploitation rate of 8.9%. Herring aged four, five, and six comprised 90% by number of this season's commercial gill net catch. Mean weight of herring ages three, six, and seven decreased slightly over last season while increases were seen for ages four, five, and eight. Mean length of commercial caught herring increased slightly over 1992-93. Department variable-mesh gill nets caught a total of 455 herring of which 232 were aged. The dominant age class was four-yr-olds comprising 27% of the sample by number, followed by six-yr-olds representing the highly successful 1988 year class. In Humboldt Bay, the 1993-94 commercial catch of 62.8 tons was about 5% over the 1993-94 season quota of 60 tons and was well above Humboldt Bay's 21-year average catch of 40.4 tons. Crescent City area herring fishermen caught 32.5 tons, approximately 2% over the season quota for the Crescent City area. The 1993-94 season commercial catch is well above the 20-year average of 23.7 tons for this area. (31pp.

Circumferential pressure probe

A probe for measuring circumferential pressure inside a body cavity is disclosed. In the preferred embodiment, a urodynamic pressure measurement probe for evaluating human urinary sphincter function is disclosed. Along the length of the probe are disposed a multiplicity of deformable wall sensors which typically comprise support tube sections with flexible side wall areas. These are arranged along the length of the probe in two areas, one just proximal to the tip for the sensing of fluid pressure inside the bladder, and five in the sensing section which is positioned within the urethra at the point at which the urinary sphincter constricts to control the flow of urine. The remainder of the length of the probe comprises multiple rigid support tube sections interspersed with flexible support tube sections in the form of bellows to provide flexibility

Failure analysis of a Stirling engine heat pipe

Failure analysis was conducted on a heat pipe from a Stirling Engine test rig which was designed to operate at 1073 K. Premature failure had occurred due to localized overheating at the leading edge of the evaporator fin. It was found that a crack had allowed air to enter the fin and react with the sodium coolant. The origin of the crack was found to be located at the inner surface of the Inconel 600 fin where severe intergranular corrosion had taken place

External stress-corrosion cracking of a 1.22-m-diameter type 316 stainless steel air valve

An investigation was conducted to determine the cause of the failure of a massive AISI Type 316 stainless steel valve which controlled combustion air to a jet engine test facility. Several through-the-wall cracks were present near welded joints in the valve skirt. The valve had been in outdoor service for 18 years. Samples were taken in the cracked regions for metallographic and chemical analyses. Insulating material and sources of water mist in the vicinity of the failed valve were analyzed for chlorides. A scanning electron microscope was used to determine whether foreign elements were present in a crack. On the basis of the information generated, the failure was characterized as external stress-corrosion cracking. The cracking resulted from a combination of residual tensile stress from welding and the presence of aqueous chlorides. Recommended countermeasures are included

Crossflow vorticity sensor

A crossflow vorticity sensor for the detection of crossflow vorticity characteristics is described. The sensor is comprised of crossflow sensors which are noninvasively adhered to a swept wing laminar surface either singularly, in multi-element strips, in polar patterns, or in orthogonal patterns. These crossflow sensors are comprised of hot-film sensor elements which operate as a constant temperature anemometer circuit to detect heat transfer rate changes. Accordingly, crossflow vorticity characteristics are determined via cross-correlation. In addition, the crossflow sensors have a thickness which does not exceed a maximum value h in order to avoid contamination of downstream crossflow sensors

Nondestructive testing techniques used in analysis of honeycomb structure bond strength

DOT /Driver-Displacement Oriented Transducer/, applicable to both lap shear type application and honeycomb sandwich structures, measures the displacement of the honeycomb composite face sheet. It incorporates an electromagnetic driver and a displacement measuring system into a single unit to provide noncontact bond strength measurements

Visual suppression of the vestibulo-ocular reflex during space flight

Visual suppression of the vestibulo-ocular reflex was studied in 16 subjects on 4 Space Shuttle missions. Eye movements were recorded by electro-oculography while subjects fixated a head mounted target during active sinusoidal head oscillation at 0.3 Hz. Adequacy of suppression was evaluated by the number of nystagmus beats, the mean amplitude of each beat, and the cumulative amplitude of nystagmus during two head oscillation cycles. Vestibulo-ocular reflex suppression was unaffected by space flight. Subjects with space motion sickness during flight had significantly more nystagmus beats than unaffected individuals. These susceptible subjects also tended to have more nystagmus beats before flight

Eye and head motion during head turns in spaceflight

Eye-head motion was studied pre-, in- and postflight during single voluntary head turns. A transient increase in vestibulo-ocular reflex (VOR) gain occurred early in the flight, but later trended toward normal. This increased gain was produced by a relative increase in eye counterrotation velocity. Asymmetries in gain with right and left turns also occurred, caused by asymmetries in eye counterrotation velocities. These findings were remarkably similar to those from Soviet primate studies using gaze fixation targets, except the human study trended more rapidly toward normal. These findings differ substantially from those measuring VOR gain by head oscillation, in which no significant changes were found inflight. No visual disturbances were noted in either test condition or in normal activities. These head turn studies are the only ones to date documenting any functional change in VOR in weightlessness

Fatigue failure of regenerator screens in a high frequency Stirling engine

Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenerator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain a 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens