Low-loss singlemode waveguide and fibre bends

A new theoretical strategy for reducing bend loss is presented. It is based on the concept of introducing both depressed and increased index regions into the cladding of planar waveguides on the outside of the bent core. A similar strategy can be applied to optical fibres. In both cases, the bending loss is reduced beyond that achievable with the presence of depressed regions alone in the cladding     

In Vitro antimicrobial susceptibilities of Streptococcus pneumoniae isolated from two teaching hospitals in Taiwan, 1989-1995

The susceptibility of 46 pneumococcal isolates collected during October 1989 to May 1995 from National Taiwan University Hospital and Taipei Municipal Yang Ming Hospital was studied. Among these isolates, the resistant rate of penicillin G was 21.7%; the penicillin G-resistant strains were more frequently resistant than the penicillin-sensitive strains to other beta-lactam antimicrobial drugs. The minimum bactericidal concentrations (MBCs) of penicillin G for all isolates were equal to, or one dilution higher than, minimum inhibitory concentrations (MICs). Three strains were false positive for penicillin resistance among isolates of Streptococcus pneumoniae screened with oxacillin. On the other hand, resistance to penicillin G was often independent of resistance to erythromycin. Vancomycin was the most active agent tested.     

Generalized hull properties for location problems

This paper considers a general form of the single facility minisum location model, also known as the Fermat-Weber problem, in which the cost components are increasing differentiable functions of a norm. In particular, attention is restricted to a broad class of norms referred to as round norms, a formal definition of which is included. It is shown that all locally optimal locations of the new facility in the two-dimensional problem (N-dimensional for the Euclidean norm) must be within the convex hull of the destinations. The results are extended to a general form of the multifacility minisum location problem.     

Polarisation modulation in long couplers

A simple mathematical model of long tapered couplers shows that the modulation of the output power due to polarisation has a period which varies inversely with the square of wavelength. This prediction is in agreement with experimental measurements.     

Modal cutoffs in single- and few-mode fiber couplers

Optical coupling, or crosstalk, between two parallel, identical single- or few-mode fibers is describable as a superposition of the modes of the composite waveguide. Like the modes of a single-fiber waveguide, the modes of the two-fiber waveguide are cut off. Exact and simple accurate asymptotic formulae are derived giving the cutoff value as a function of separation. For single-mode couplers, perturbation theory gives the fundamental and second modesPsi+andPsi-as the sum and difference of the fundamental modesPsi_{1}andPsi_{2}of each fiber. In realityPsi+is the fundamental mode of the composite waveguide, whereasPsi-is the second mode and has a finite cutoff. This limits the smallestV-value for which low-loss coupling is possible. The limitation is least severe for step-profile fibers.     

SPOC-a stored program optical computer

The Digital Optical Computing (DOC) group at the University of Colorado at Boulder have built the world's first stored program optical computer (SPOC). Several features that distinguish this computer from traditional electronic computers are: the use of optical fibers and pulses of light instead of wires and electronic signals; the use of space and time to store information instead of flip-flops; synchronization based on the predictable propagation time of signals; and return to zero signal encoding. One goal was to show that optics could be used to build a general purpose stored program computer. Another goal was to demonstrate that predictable signal propagation time could replace flip flops for synchronization. The SPOC is a functionally complete computer. The constant speed of light was used to synchronize the signals in the SPOC. We adjusted the length of the input fibers to the logic gates so the signals would arrive at the same time. This synchronization technique is called time-of-flight design. The group developed a design tool, called XHatch, to help design time-of-flight circuits. We used XHatch to determine the lengths of the optical fibers for the SPOC based on its circuit design. The fibers act as registers by storing the signals in space and time until they are fed into a logic element     

Randomised trial of octreotide for long term management of cirrhosis after variceal haemorrhage

OBJECTIVE: To assess the efficacy of long term octreotide as adjuvant treatment to programmed endoscopic sclerotherapy after acute variceal haemorrhage in cirrhotic portal hypertension. DESIGN: Randomised clinical trial. SETTING: University hospital. SUBJECTS: 32 patients with cirrhotic portal hypertension. INTERVENTIONS: Programmed injection sclerotherapy with subcutaneous octreotide 50 micrograms twice daily for 6 months, or programmed injection sclerotherapy alone. MAIN OUTCOME MEASURES: Episodes of recurrent variceal bleeding and survival. RESULTS: Significantly fewer patients receiving combined octreotide and sclerotherapy had episodes of recurrent variceal bleeding compared with patients given sclerotherapy alone (1/16 v 7/16; P = 0.037, Fisher's exact test), and their survival was significantly improved (P < 0.02, log rank test); this improvement was maintained for 12 months after the end of the study. Combined treatment also resulted in a sustained decrease in portal pressure (median decrease -6.0 mm Hg, interquartile range -10 to -4.75 mm Hg, P = 0.0002) compared with sclerotherapy alone (median increase 1.5 mm Hg, interquartile range 0.25 to 3.25 mm Hg), as well as a significant improvement in liver function as assessed by plasma concentrations of bilirubin, albumin, and alanine aminotransferase and by hepatocyte metabolism of aminopyrine labelled with carbon-14. CONCLUSION: Long term octreotide may be a valuable adjuvant to endoscopic sclerotherapy for acute variceal haemorrhage in cirrhotic portal hypertension.