Development of a piezopolymer pressure sensor for a portable fetalheart rate monitor

A piezopolymer pressure sensor has been developed for service in a portable fetal heart rate monitor, which will permit an expectant mother to perform the fetal nonstress test, a standard predelivery test, in her home. Several sensors are mounted in an array on a belt worn by the mother. The sensor design conforms to the distinctive features of the fetal heart tone, namely, the acoustic signature, frequency spectrum, signal amplitude, and localization. The components of a sensor serve to fulfill five functions: signal detection, acceleration cancellation, acoustical isolation, electrical shielding, and electrical isolation of the mother. A theoretical analysis of the sensor response yields a numerical value for the sensor sensitivity, which is compared to experiment in an in vitro sensor calibration. Finally, an in vivo test on patients within the last six weeks of term reveals that nonstress test recordings from the acoustic monitor compare well with those obtained from conventional ultrasound     

PET: a proton/electron telescope for studies of magnetospheric,solar, and galactic particles

The proton/electron telescope (PET) on SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) is designed to provide measurements of energetic electrons and light nuclei from solar, Galactic, and magnetospheric sources. PET is an all solid-state system that will measure the differential energy spectra of electrons from ~1 to ~30 MeV and H and He nuclei from ~20 to ~300 MeV/nucleon, with isotope resolution of H and He extending from ~20 to ~80 MeV/nucleon. As SAMPEX scans all local times and geomagnetic cutoffs over the course of its near-polar orbit, PET will characterize precipitating relativistic electron events during periods of declining solar activity, and it will examine whether the production rate of odd nitrogen and hydrogen molecules in the middle atmosphere by precipitating electrons is sufficient to affect O₃ depletion. In addition, PET will complement studies of the elemental and isotopic composition of energetic heavy (Z>2) nuclei on SAMPEX by providing measurements of H, He, and electrons. Finally, PET has limited capability to identify energetic positrons from potential natural and man-made sources     

Recursive optimal pruning with applications to tree structuredvector quantizers

A pruning algorithm of P.A. Chou et al. (1989) for designing optimal tree structures identifies only those codebooks which lie on the convex hull of the original codebook's operational distortion rate function. The authors introduce a modified version of the original algorithm, which identifies a large number of codebooks having minimum average distortion, under the constraint that, in each step, only modes having no descendents are removed from the tree. All codebooks generated by the original algorithm are also generated by this algorithm. The new algorithm generates a much larger number of codebooks in the middle- and low-rate regions. The additional codebooks permit operation near the codebook's operational distortion rate function without time sharing by choosing from the increased number of available bit rates. Despite the statistical mismatch which occurs when coding data outside the training sequence, these pruned codebooks retain their performance advantage over full search vector quantizers (VQs) for a large range of rates.     

Information exchange and governance structures in US and JapaneseR&D consortia: institutional and organizational influences

We examine institutional and organizational influences upon information exchange and governance structures within R&D consortia in the United States and Japan. We hypothesized that national differences in institutional environments would lead to less active governance and information-exchange activities within Japanese R&D consortia relative to their US counterparts. At the consortium level, we expected that internal consortium diversity would increase information exchange and governance requirements, and that structures stabilizing relations between consortium members would reduce information exchange and governance requirements. We tested these hypotheses on 39 US and 54 Japanese multifirm R&D consortia, involving, respectively, 1801 US member organizations and 1647 Japanese member organizations. Controlling for organizational age, size, and strategic focus, we found that internal diversity and interorganizational relations are both associated with information-exchange and governance mechanisms. Our model has much greater explanatory power for the United States than for Japan     

Propagation characteristics of coherent array beams from carbondioxide waveguide lasers

The characteristics of coherent array beams generated by waveguide carbon dioxide laser structures have been investigated, with particular emphasis on their propagation and transformation properties. Methods of array beam generation are presented, and measurements of array beam quality are given through the use of the M² parameter. Efficient transformation of an array beam from the antisymmetric to symmetric pattern is achieved through the use of a binary phase plate, and spatial filtering is shown to improve the beam quality at the expense of only a moderate loss of total beam power. Coherence effects in the near-field propagation of array beams are also explored     

Comfort criteria for passively cooled buildings a pascool task

The application of passive cooling techniques to buildings in warm climates creates the need for appropriate comfort criteria. Conventional comfort criteria, usually based upon laboratory experiments, seem to be unnecessarily severe. The paper describes preliminary findings of the PASCOOL Thermal Comfort task which, responding to renewed interest in behavioural aspets of thermal comfort, sets out to establish appropriate limits by field studies and theoretical considerations.     

Summary of HgCdTe 2D array technology in the U.K.

HgCdTe 2D arrays are needed in both medium (MW) and long (LW) wavebands for imaging, search, and track and guidance applications. Often the detector is the performance-limiting component in the system, and it is necessary to use detectors with very low excess noise and few defective pixels. Normally the detector is cooled sufficiently to freeze-out thermally generated leakage currents, so the main interest is to understand the mechanisms that determine the general detector performance and the cause of defective pixels. This paper describes the detector technology and the ion beam junction-forming process. The fundamental performance limits of homojunction HgCdTe technology and the doping levels needed to produce a detector with impact-ionization limited performance are discussed. Extensive studies have been made on defective pixels in long wavelength arrays and some technologies for reducing them are described here. Defective pixels have been found to be associated with material dislocations crossing the p-n junction and a model has been proposed for the noise-generating mechanism.     

Electronically scanned cmt detector array for the 8?14 ?m band

A cadmium-mercury-telluride photovoltaic hybrid array of 1024 elements is described. The device operates in the 8?14 ?m band and is electronically scanned by means of MOS silicon switches. An example of a `staring? image obtained with the device is shown.     

CO/sub 2/ laser processing of alumina (Al/sub 2/O/sub 3/) printed circuit board substrates

We report the results of an investigation of the laser-material interaction processes involved in laser drilling of alumina, through the use of an enhanced peak power (2.5 kW) CO/sub 2/ laser and novel temporal pulse formats. Peak power was varied from 30 W to 2 kW for pulses of constant energy to observe the effect produced on scribe depth. High-speed videography of hole formation has been combined with microscopic analysis to investigate the key processes involved in laser processing of alumina. Plasma screening was observed for short, high peak power laser pulses, and optimal scribing was achieved in the weakly plasma absorbing regime. A new processing technique for scribing alumina has been developed, which exploits the fast response of the laser to produce novel temporal pulse shapes, which can be modified to generate cleaner holes. Scribe speeds of up to 280 mm/spl middot/s/sup -1/ were obtained for scribe holes >200 /spl mu/m deep and 150 /spl mu/m apart, with no material plugging the hole, in 0.635-mm-thick 96% alumina.