Abstract: A line circuit for serving a digital telephone set over a link of indeterminate length and attenuation characteristics includes a processor for issuing test messages over the link to the telephone set and which responds to the receipt of an acknowledgment message from the telephone set by inserting increasing amounts of finite attenuation into the link until the acknowledgment message fails to be received, at which point the value of inserted attenuation is a measure of the excess link margin.

Abstract: Polarization dependencies exhibited by components of optical apparatus, such as equalizers having chromatically variable transmissivity, are reduced by splitting the incoming light stream to be equalized into two orthogonally polarized streams which are applied to opposite ends of the apparatus through polarization maintaining fibers oriented such that the light polarization is the same for both directions of transmission through the apparatus and is aligned with one of the eigenpolarizations of the chip on which the apparatus is implemented. In an illustrative embodiment of an equalizer, the incoming light stream entering one port of a circulator and emerging from a second port is applied to the splitter on its way to the equalizer while the light streams emerging from the equalizer, after being spectrally recombined, re-enter the second port of the circulator and emerge from its third port to the output thereby eliminating any polarization dependencies of the equalizer.

Abstract: A arcuate resistive sensor element is imprinted upon a ceramic substrate forming a wall of a ceramic body in which an electrolyte, advantageously silver nitrate dissolved in a mixture of methanol, water and butanol, is sealed. To avoid the effects of electroplating, an AC exciting voltage is applied between the ends of the sensor element which is bridged by a discharge resistor whose resistance is much lower than the internal resistance of the sensor element so as to dissipate any polarization caused by asymmetry of the voltage supply. A signal output is taken from a midpoint of the sensor element which is always immersed in the electrolyte so that the effect of any leakage current is minimized. Linearity of output with change in the tilt angle achieved with an illustrative embodiment has been measured at better than 99.9% in tilt angle range of −50 to +50 degrees.

Abstract: Analog modems are enabled to better learn the slicing levels employed at the interface to a digital transmission network by reducing the effects of the various noise sources. Initially a training sequence is received to preliminarily adjust the analog modem's equalizer. Thereafter, a special training sequence, protected against intersymbol interference, is employed to collect samples of each slicing level, to ascertain the least mean squared value of each slicing level from the received samples and to obtain the channel's impulse response at each slicing level. Thereafter, the analog modem's equalizer may be fine tuned in accordance with the channel impulse response ascertained at each slicing level.

Abstract: Speech recognition in which the log probabilities of the null and alternative hypothesis are computed for an input speech sample by comparison with specific stored speech vocabularies/grammars and with general speech characteristics. The difference in probabilities is normalized by the magnitude of the null hypothesis to derive a likelihood factor which is compared with a rejection threshold that is utterance-length dependent. Advantageously, a high-order polynomial representation of the rejection threshold length dependency may be simplified by a series of piece-wise constants which are stored as rejection thresholds to be selected in accordance with the length of the input speech sample.

Abstract: A method is presented to enable the impulse response of a channel to be identified when the received signal contains a large amount of quantization noise. A probabilistic estimate of the distribution of the quantization noise is subtracted from the summation of the products of the received training signal samples and tap coefficients to provide a more accurate error signal for the adjustment of the tap coefficients.

Abstract: A torque-limiting fastener in which a threaded member having a drivable head portion is rotationally mounted within a capsule containing a calibrated spring loading element which is adapted to be compressed in one direction of rotation and released in the opposite direction of rotation, the capsule frictionally engaging the drivable head portion in the one direction of rotation until the compressed spring element exerts sufficient axial force to overcome the frictional engagement between the capsule and the drivable head.

Abstract: Quantitative measurement of corneal surface topography is obtained by processing a two-dimensional image of the surface which reflects a quasi-periodic illuminated pattern, such as series of concentric rings, from a Placido disk source. The local spatial phases exhibited by the image of the illuminated pattern when reflected from the corneal surface and when reflected from standard specular surfaces are obtained by processing the images which includes use of specially filtered Fourier and inverse transforms. The distances at which predetermined local spatial phases are observed in the image from the cornea are compared with the distances at which these same phases are observed in the images of the standard surfaces. The distances are also compared with certain corresponding distances on the Placido disk source and converted to reveal the dioptric powers of refraction of the corneal surface without the need for parametric interpolation.

Abstract: A two-piece connector includes a collar having an aperture in its relatively thick end-wall which bears an internal annular groove. The skirt of the collar is adapted to be slipped over the end of a length of tubing and contains tines to graspingly engage the outer surface of the tubing. The barb portion of the connector is adapted to fit through the aperture in the end-wall to frictionally engage the lumen of the tubing. An interrupted flange at the upper portion of the barb is adapted to twistably engage the internal annular groove in the end-wall to securely lock the barb to the collar.

Abstract: Over heat protection for a portable space heater equipped with a reflector for directing the radiation from a heating element through a frontal emitting window of the heater enclosure is provided by a conventional thermostat which is thermally insulated from the thermal mass of the heater enclosure and which is mounted so as to sense the temperature of convective air drafted up from in front of the window. The thermostat is mounted above a slot cut in the upper front edge of the reflector out of the path of the radiation directed by the reflector.

Abstract: A hand-holdable, portable welding apparatus for smoothly joining the lumens of sections of thermoplastic tubing systems, including those that may be located in a cramped work site. The integrity of the lumens is maintained when the tubes are being welded by use of a selectively rigidizable, non-elastomeric mandrel of PTFE or PFA having a predetermined maximum size dimensioned to the ID of the lumens being joined. The welding unit employs a resiliently mounted coaxial heater block in conjunction with arcuate radiator inserts that are centered about the tubes to be welded regardless of the diameter of the tubes. Spring-loaded dogs grab the periphery of the tubes as they are inserted into the welding unit and prevent them from moving apart when heat is applied.

Abstract: A keratoscope image processing system having a compact keratoscope usable with a variety of light ring cones employs an improved cone and lightbox combination in which the light transmitting rings of the cone are more sharply defined by being positioned between incised opaque rings, and in which the lightbox has facets for mounting and heat-sinking a pair of laser diodes, a semi-toroidal cavity for mounting a ring-shaped fluorescent lamp for illuminating the cone and tunnels that direct the laser beams into the cone to intersect on the visual axis of the cone. The light box provides a surface for fixedly mounting a pair of mirrors that redirect the laser beams. The different cones are identified by patterns of light pervious spots illuminated from the lightbox and sensed by detectors mounted in the lightbox. Signals from the detectors modify the image processing in accordance with stored optical characteristics corresponding to the detected patterns.

Abstract: An improved conical keratometer wherein the parent image of the pattern to be reflected upon a target positioned adjacent to the illuminated bore is recorded on a film slide retained within the keratometer bore. Opposite edges of the slide are chamfered at equal but opposite angles so that, when the spindeled slide is released, the chamfered edges will meet along a line of contact rather than butting squarely together. The film slide is rolled so that the emulsion side is toward the periphery of the cone bore and the chamfering allows that side to lie smoothly against the cone bore without any gaps so that an undistorted image may reliably be reflected upon a standard target.

Abstract: Color-coded corneal topographic information contained in a polar plot of plurality of different traces taken over the corneal surface, such as that disclosed in the U.S. Pat. 4,863,260, is reprocessed to present the color topographic map in a "hills and valleys", Cartesian coordinate display; polar position being presented along the x-axis and elevation being presented along the y-axis. The different circular traces are separated one from the other in a perspective dispersion to emphasize the elevation data with the more apical traces being presented at one end and the more limbal trace being presented at the other end of the perspective dispersion.

Abstract: A method of operating a digital signal processor to detect DTMF tones in a digital voice telephone system in which the digitally encoded signals appearing on the telephone channel are decimated to compress the spectrum to be monitored for the appearance of call signalling tones. The signals received in a decimated block are "correlated" or convolved with one another on a forward and backward time-shifted basis and each forward and backward correlation product is summed to form the elements of a 5.times.5 modified covariance matrix. The modified covariance matrix exhibits the desirable property that its eigenvectors will be symmetric. Since all eigenvectors of the modified covariance matrix are orthogonal and the eigenvectors associated with the signal span the signal subspace, the signal subspace is orthogonal to the eigenvector associated with the noise. The dot product of the noise eigenvector with the signal subspace is set to zero.