Experimental study of bent multimode optical waveguides

Bend losses of bent multimode waveguides have been experimentally studied. The results experimentally verify a simple analytical expression based on ray optics that can be used to determine bend losses in bent multimode waveguides. We have also shown that bend-induced losses in such multimode optical waveguides are wavelength independent.     

In vitro analysis of oocyte cumulus complex pickup rate in the hamster Mesocricetus auratus

In mammals, the oocyte and its surrounding cumulus cells constitute on oocyte cumulus complex (OCC). During ovulation, OCCs are extruded into the peritoneal or bursal cavity, depending on the species, and are then rapidly picked up by the fimbria on the outer surface of the oviductal infundibulum and transported to the ampulla, where fertilization occurs. We developed a method to measure OCC pickup rates quantitatively in vitro, and we used this method to evaluate the effects of viscosity and temperature on pickup rates. Hamster infundibula are placed in a holding pipette in a chamber modified to study OCC pickup. Ciliary beat frequencies (CBF) can be measured in the same preparation. Pickup rates vary depending on the pathway on which the OCC travels over the surface of the infundibulum; however, rates for a given pathway are very consistent. The average pickup rate at room temperature calculated from three different pathways/infundibulum was 55.2 +/- 10.6 microns/sec. Both rates between infundibula from the same female and rates among infundibula from different females were in most cases similar. Preparations preincubated in vitro for 2.75 hr produced rates similar to nonpreincubated samples, while longer preincubation resulted in decreased rates. Inclusion of Ficoll in culture medium to increase viscosity caused a concentration-dependent decrease in both OCC pickup rate and in CBF. However, a significant decrease in OCC pickup rate was only observed at viscosities higher than those found in bursal fluid. When trials were run at physiological temperature (36.4 degrees C) rather ambient temperature, rates increased to 136.7 +/- 29.9 (SD) microns/sec. Linear regression analysis demonstrated a strong positive correlation (r = 0.94) between OCC pickup rate and temperature. The OCC pickup rate assay can be used experimentally, and should be valuable in evaluating factors that affect rate and in studies dealing with the mechanism of OCC pickup.     

Multi-input square iterative learning control with input ratelimits and bounds

We present a simple modification of the iterative learning control algorithm of Arimoto et al. (1984) for the case where the inputs are bounded and time-rate-limited. The Jacobian error condition for monotonicity of input-error, rather than output-error, norms, is specified, the latter being insufficient to assure convergence, as proved herein. To the best of our knowledge, these facts have not been previously pointed out in the iterative learning control literature. We present a new proof that the modified controller produces monotonically decreasing input error norms, with a norm that covers the entire time interval of a learning trial.     

Experimental determination of the equation of state of solid hydrogen and deuterium at high pressures

Isochores of solid hydrogen and deuterium have been measured for melting line pressures up to 2000 bar. These are corrected to correspond to para-H₂ and ortho-D₂. The 4.2 K isotherm of H₂ has been determined and compared to the extrapolated low-pressure isochore of Anderson and Swenson (AS). Deviations have led us to reanalyze the AS data. The 4.2 K isotherm and the isochores are used, with the aid of a Mie-Grüneisen analysis, to determine P-V-T data for these solids up to 25 kbar. An analysis is presented which enables a determination of P-V-T-C ₁ for all values of C ₁, the ortho-para concentration. Results, including the Debye temperature, Grüneisen constant, and bulk modulus, are presented both in tabulated and graphical form. We also present what we feel to be the best of the 4.2 K, zero-pressure molar volumes of disordered H₂ and D₂ as a function of C ₁. Our measurements show no indication of the premelting phase transition reported in recent Russian literature and a possible explanation is presented.Supported in part by the Stichting FOM.     

Improved frame synchronization performance for CCITT algorithmsusing bit erasures

For the CCITT recommendations on frame synchronization (as enhanced in Jones and Al-Subbagh, 1985), the performance in the presence of jamming, interference or other disturbance is improved by using bit erasure information. The acquisition time and misalignment detection times are reduced and the false exit time is increased, with only a minor reduction in the already large false entry time     

Psychiatric disorders in homeless persons--Anglo-American studies of epidemiology and management]

Bleeding from gastro-oesophageal varices is a serious medical emergency associated with high morbidity and mortality. Recent advances in treatment include the use of safer vasoactive agents, endoscopic injection of cyanoacrylate, endoscopic variceal ligation and radiological porto-systemic shunt. This article will discuss these new therapies and suggest an integrated approach to the management of variceal haemorrhage.     

MANUS--a wheelchair-mounted rehabilitation robot.

Rehabilitation robots are assistive devices designed for use by people with severe disability in order to gain independence in tasks of daily living. MANUS is a wheelchair-mounted general-purpose manipulator now in use with over 100 people in their homes in the Netherlands, in France and in other countries. MANUS has six main degrees of freedom, excluding the gripper. To keep the arm slim, the motors are placed in the main base. The resulting low mass of the arm ensures a reduced impulse in case of collision. A complex system of toothed belts, hollow shafts and geared wheels drives the end-effector. MANUS is equipped with a two-fingered gripper. The fingers have passive canting mechanisms which ensure a three-point grasping action for most objects. A modular control system is used for steering the manipulator to its desired position. For this, a simple but effective user interface has been developed which is configurable by the end-user as well as by the therapist.