No abstract

A system for increasing culture water hardness at a soft‐water production facility for striped bass (Morone saxatilis) is described. This system increases the hardness of culture water from an ambient 35 mg/L to 200 mg/L CaCO3 equivalence. It has been used successfully for 4 years and has been reliable and inexpensive to construct and maintain.

Female striped bass Morone saxatilis with eggs in early stages of development were successfully spawned after being given a priming injection of luteinizing hormone releasing hormone analog followed by a resolving injection of human chorionic gonadotropin (HCG). Over 2 years, 18 of 19 injected fish spawned, producing over 3.5 million viable fry. Egg fertilization rates for all fish that spawned averaged 41%. This procedure, which differs from the traditional spawning method of HCG injection, can increase production by increasing the duration of the production season. In addition, broodfish that once would have been released at capture because they contained early egg developmental stages can now be spawned and used in production. *

The wave equation was integrated numerically by the finite-element method, using a number of different combinations of the acoustic impedance and the scaling parame. ters. For comparison, the acoustic field of the same propeller in free space was also computed.The calculations show that at flow speeds much less than that of sound, the wall must be lined with acoustical absorbers to make the free-field and ducted-propeller models agree in acoustic-pressure levels and directionality. The best agreement Would occur where the ratio of wall radius to propeller radius is large and the measurements are made away from the walls.At a flow speed half that of sound, the acoustic-pressure magnitude and directivity along the duct wall near the propeller are similar for a hard wall and for a variety of soft walls. However, the hard-wall results may be fortuitous, and additional studies are needed. Upstream or downstream from the propdie, r, soft wall liners having suitable admittances can suppress the usual duct acoustic m•c]es. In this case, the duct and free-field acoustic characteristics can agree over greater sideline distances. At high flow speeds, different upstream and downstream wall admittances are necessary for the equal suppression of duct modes on both sides of the propeller. Further information may be found in NASA TM-87333 [N86-29630/ NSP ], "Modeling the Effects of Wind Tunnel Absorption on th• Acoustic Radiation Chfiracteristics of Propellers." Copies may be purrchased (prepayment required) from the National Technica.[. Tel.: (703) 487-4650. Rush Orders may be placed for an extra fee by cal!ing (800) 336-4700. Advanced-degree dissertations in acousticsEdito?s note: Abstracts of Doctoral and Master's degree theses in acoustics will be welcomed at all times. Please note, however, that they must be double-spaced, formatted as shown below (don't make us retype them, please!) with PACS numbers, and not over 200 words in length.

Low-cost electret microphones are ubiquitous in telecommunications equipment. They are capable of providing nearly ideal response, while often employed as point receivers. However, uniform response is not always optimal, especially for digital applications or microphone arrays, nor is it easily achievable given mechanical packaging constraints. It is therefore essential for a given design to incorporate frequency-dependent effects of the microphone housing. Frequency shaping is typically done electrically, but acoustical filters can be realized by appropriate selection of series or parallel cavities at the microphone. Damping must be accounted for by estimating thermal-viscous effects of the cavity openings, or by introducing flow-resistive materials for which acoustical parameters are known or can be measured. The frequency effects of microphone housing geometries can be modeled using any one of several techniques, the choice dictated by the desired accuracy, complexity of the physical realization, and available resources. In this paper, two prediction methods will be discussed. First, classical lumped- and distributed-element models will be described along with analyses obtained using MATLAB. Second, some preliminary results of numerical models using boundary or finite element methods will be presented.