No abstract

With the increasing use of computer-controlled data acquisition systems which record data in digital form, there has developed a need for techniques which perform a general smoothing process on digitized experimental data. This processing enables the experimentalist to eliminate or greatly reduce the amount of high-frequency noise in order to obtain as accurate and clean representation of the true phenomenon as is consistent with his measurement accuracies. This filtering or smoothing process should be as simple and efficient (least amount of arithmetic per data sample) as is consistent with the experimental situation. The basic concepts of low-pass filters are discussed and four different low-pass filter design procedures are described, each with its own particular smoothing properties. These design procedures give directly the coefficients of a symmetrical weighting sequence having the desired passband width and the desired high-frequency noise rejection. The uses of the filters are illustrated with examples and the fortran code for implementing each of the design procedures is given in an Appendix.

An in situ birefringence measurement in conjunction with an atomic force microscope study shows that the geometric asymmetry of the side-writing process is a major cause of the induced birefringence in grating-based fiber devices. Measured refractive-index profiles of UV-exposed fibers clearly show the asymmetry in the induced index change. We demonstrate the use of a dual-exposure technique for producing low-birefringence devices.

We describe the design, construction, and application of what are believed to be the smallest fiber-optic probes used to date during imaging or diagnosis involving low-coherence interferometry (LCI). The probes use novel fiber-optic gradient-index (GRIN) lenses fabricated by a recently developed modified chemical-vapor-deposition (MCVD) process that avoids on-axis aberrations commonly marring MCVD-fabricated GRIN substrate. Fusing GRIN fiber lenses onto single-mode fiber yields automatically aligned all-fiber probes that insert into tissue through hypodermic needles as small as 31-gauge (inner diameter, 127 mum). We demonstrate the use of such probes with LCI by measuring microscopic brain motions in vivo.

The reaction of methane with copper oxide was investigated in a fluidized solid bed.The data indicate that copper oxide readily oxidizes methane to carbon monoxide and hydrogen with high selectivity at a temperature level of about 1700°F. The data were correlated on the assumption that the limiting factor is the reaction of carbon dioxide and water vapor with methane.