Routine antibiotics in hospital management of acute asthma.

The value of antibiotics was assessed in a randomised, double-blind study of amoxycillin and placebo in sixty adults admitted to hospital with acute exacerbations of asthma. 37 exacerbations were treated with amoxycillin and 34 were treated with placebo. Response to treatment was closely monitored but no significant difference in improvement was demonstrated between groups for length of hospital stay, time taken for 50% improvement in symptoms, patient's self assessment and respiratory function, and symptoms and respiratory function at time of discharge from hospital. Antibiotics should not be given routinely to patients admitted to hospital with acute exacerbations of asthma.

Simulation of mid-infrared clutter rejection. 1: One-dimensional LMS spatial filter and adaptive threshold algorithms.

Several 1-D signal processing techniques have been evaluated by simulation with a digital computer using high-spatial-resolution (0.15 mrad) noise data gathered from back-lit clouds and uniform sky with a scanning data collection system operating in the 4.0-4.8-microm spectral band. Two ordinary bandpass filters and a least-mean-square (LMS) spatial filter were evaluated in combination with a fixed or adaptive threshold algorithm. The combination of a 1-D LMS filter and a 1-D adaptive threshold sensor was shown to reject extreme cloud clutter effectively and to provide nearly equal signal detection in a clear and cluttered sky, at least in systems whose NEI (noise equivalent irradiance) exceeds 1.5 x 10(-13) W/cm(2) and whose spatial resolution is better than 0.15 x 0.36 mrad. A summary gives highlights of the work, key numerical results, and conclusions.

Least-mean-square spatial filter for IR sensors.

A new least-mean-square filter is defined for signal-detection problems. The technique is proposed for scanning IR surveillance systems operating in poorly characterized but primarily low-frequency clutter interference. Near-optimal detection of point-source targets is predicted both for continuous-time and sampled-data systems.

Optical access couplers and a comparison of multiterminal fiber communication systems.

Optical T and multiple T access couplers designed for tapped trunk line multiterminal communication systems that use bundles of multimode fibers as the transmission media have been investigated. The particular coupler designs tested used bent Pyrex rods for bifurcation and scrambling. Coupler throughput losses (not counting packing fraction losses) are 1.5-2.5 dB. The bent rod optical T and multiple T access couplers must be used with high N.A., low packing fraction loss fibers. To avoid the use of a repeater a multiple T or star configuration must be used in a system comprising ten or more terminals.

Optical modal evolution 3-dB coupler.

A planar optical 3-dB coupler is proposed that uses only a single region of mode conversion followed by a region of adiabatic modal evolution. These two regions are provided by an overlay with fast and slow tapers, which makes the device synchronous at a single point. Device length is noncritical. The device was fabricated with sputtered barium silicate and fused silica films and tested experimentally. Maximum power transfer of 40% was limited by a fabrication problem with the fast taper, but agreement with theory was obtained. An approximate coupled mode representation of the coupling between local normal modes is used to estimate power transfer at an abrupt transition and to provide design requirements for the fast and slow tapers. The theoretical concepts developed are applied to describe the operation of conventional directional 3-dB couplers and channel modal evolution 3-dB couplers which use branching waveguides.

Tapered velocity couplers for integrated optics: design.

The operation of tapered velocity couplers is analyzed from the point of view of mode conversion between local-normal modes. An approximate coupled mode representation of the local-normal modes is used with a step transition model to estimate analytically power transfer. This yields an upper limit for the maximum permissible variation in mode synchronism across the coupler to achieve satisfactory coupler operation. The analysis has also been used to demonstrate the importance of obtaining a large total change in mode synchronism to minimize coupler length.

Upconversion-a Systems View.

A review is given of the properties of birefringently phase-matched parametric upconversion using proustite as the nonlinear material. Photon conversion efficiency, field-of-view limitations, spectral acceptance bandwidths, and resolution are discussed in terms of the upconversion of radiation from the 10-mu region to wavelengths shorter than 1 mu. The competitive potential of upconversion detection systems is examined for a wide variety of sensor applications. This analysis shows that upconversion represents a special-purpose detection technology appropriate for low-duty-cycle, small field-of-view imaging systems that use laser illumination. Competitive development of upconversion to detect thermal imagery appears unlikely.