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Abstract-A fiber-optic interferometric sensor has been developed which consists of a seismic mass of 520 gm supported by two rubber mandrels, each wound with a single layer of single-mode optical fiber 6.5 m long. One end of each fiber is cleaved to enhance reflection. The other ends are interconnected via a fiber-to-fiber 3-dB coupler, forming a Michelson interferometer. When the case of the sensor is displaced, the fiber around one mandrel extends in length while the other contracts. The resulting "push-pull" mechanical operation of the sensor allows both legs of the interferometer to be active, providing good common mode rejection of spurious effects, as a reference leg is not required. This, together with the fact that the light traverses each leg of a Michelson interferometer twice due to reflection, provides the sensor with four times the sensitivity of a conventionally constructed interferometric sensor. sensitivities of 8500 rad of optical phase shift per micrometer of case displacement have been measured above the massspring resonance, where the sensor operates as a seismometer. Below resonance the sensor operates as an accelerometer with a measured sensitivity of 10 500 rad/g, the highest reported to date. Including both thermodynamic and demodulator noise sources ( = 10 p r a d / J H z ) , below resonance the sensor has a detection threshold of l ng/JHz, a 20-dB improvement over the best existing conventional low noise vibration sensors.M

Chronic leg ulcers have many different causes and therefore need an accurate diagnosis in order to give the most effective treatment. A specialized clinic was set up in Fremantle Hospital in July 1988 with the aims of performing a thorough clinical and laboratory assessment to establish the cause of ulceration in every patient, and treating patients according to the cause of ulceration. Patients with arterial, neoplastic or dermatological conditions were treated as appropriate for their diagnosis and patients with other chronic ulcers were managed as outpatients where possible. Patients were seen between July 1988 and July 1989. Only 43% had purely venous ulcers, 32.6% had a venous component plus some other abnormality, and 5.2% were purely arterial. Using an outpatient treatment regimen, 67% of all ulcerated limbs and 73.7% of limbs with purely venous ulcers were healed within 6 months. Only 11 patients with venous ulceration (15 limbs) failed on this therapy and required admission during the observation period. The initial ulcer size was shown to influence the time to total healing of the limb. The healing rates achieved compare favourably with studies from other specialized centres and suggest that the majority of patients with chronic leg ulcers can be treated successfully using ambulatory outpatient dressing techniques.

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The Biot structural factor δ of a porous solid [M. A. Biot, J. Acoust. Soc. Am. 28, 168 (1956)] can be extracted from measurements of sound speed and attenuation when the solid is saturated with superfluid helium [S. Baker et al., J. Acoust. Soc. Am. Suppl. 1 74, S59 (1983)]. The results of such measurements made in sintered bronze spheres (nom. diam. 75, 110, and 500 μ) yield values of δ from 3.3 to 4.5. [We take δ to be defined by κ = δ(αωk/vP)1/2, where κ is the argument of Biot's high-frequency correction function F(κ), α is the tortuosity, ω is the angular frequency, k is the permeability, v is the kinematic viscosity, and P is the porosity.] If δvisc is the normal fluid viscous penetration depth and a is a characteristic pore size, then the range of(δvisc/a) covered by these measurements is approximately 10−2 to 1. The values of δ reported here are about 112 to 2 times larger than has been estimated for typical marine sediments [R. Stoll, in Physics of Sound in Marine Sediments (Plenum, New York, 1974)]. [Work supported by ONR.]

Considerations for a new high-accuracy transfer-coupler reciprocity system for absolute electro-acoustic calibration J F Zalesak IntroductionPrimary calibrations of hydrophones at frequencies less than about 1 kHz are typically performed in a coupler reciprocity chamber ('coupler'). The closed and controlled environment in the coupler allows for the performance of primary calibrations over the temperature and hydrostatic pressure range found in the ocean. The coupler reciprocity chamber is designed together with a primary reference standard hydrophone and two other reciprocal transducers because the volume and stiffness of the closed coupler system must be known precisely.The Underwater Sound Reference Division (USRD), a laboratory within the US Navy's (USN) research and development enterprise, provides metrology services related to underwater sound in the United States, including device calibration and leasing of underwater transducers, hydrophones, and projectors. Primary standards are maintained in-house. A coupler reciprocity system provides the primary standard calibration for frequencies less than 2 kHz [1]. The primary reference standard hydrophone is the USRD type H48 [2].To completely reproduce the acoustic waveform measured with a hydrophone, magnitude and phase information are required. Coupler reciprocity calibrations are historically performed measuring only magnitude [1, 3], and [4]. Phase response is more difficult to measure accurately and can be assumed constant when hydrophones are operating well below their resonance frequencies and, for hydrophones with preamplifiers, above their low-frequency cutoff. The type H48 reference is used well below it first resonance, but the low end of the frequency range can be affected by the low-frequency cutoff, problematic when secondary references are needed to measure frequencies below 5 Hz. Extending the coupler reciprocity calibration measurement to include phase is important to provide traceability for secondary references and to reduce AbstractA primary calibration method is demonstrated to obtain the magnitude and phase of the complex sensitivity for a hydrophone at frequencies between 1 Hz and 2 kHz. The measurement is performed in a coupler reciprocity chamber ('coupler'); a closed test chamber where time harmonic oscillations in pressure can be achieved and the reciprocity conditions required for a primary calibration can be realized. Relevant theory is reviewed and the reciprocity parameter updated for the complex measurement. Systematic errors and corrections for magnitude are reviewed and more added for phase. The combined expanded uncertainties of the magnitude and phase of the complex sensitivity at 1 Hz were 0.1 dB re 1 V µPa −1 and ±1• , respectively. Complex sensitivity, sensitivity magnitude, and phase measurements are presented on an example primary reference hydrophone.

Self-determination is now widely recognized in the literature as a best-practice procedure in the education of students with disabilities, particularly regarding facilitating students' transition from high school to adult life. But what do teachers know about how to facilitate student self-determination? In this study, special educators and university professors were surveyed to determine what teachers know about self-determination, what the primary source of their information about self-determination is, what strategies related to facilitating student self-determination teachers have heard of and/or used to facilitate student self-determination, and how important the core competencies of self-determination are in teachers' own lives. In addition, university professors were asked what methods and strategies they teach in their courses that are related to facilitating student self-determination. Implications for teacher education, research, and dissemination are discussed in this article.