Walter J. Wild

Synthesis of high rejection filters with the Fourier transform method

Although in theory the Fourier transform method is valid only for small rejections, in practice it can be modified for the synthesis of high rejection filters with minimum transmittances as low as 10(-4). Two new spectral functions are proposed for use in the Fourier transforms. An empirical procedure which is much faster than refinement is described for optimization of the spectral performance. The method and optimization are illustrated numerically for several different spectral shapes.

Fresnel reflection and transmission at a planar boundary from media of equal refractive indices

Some interesting properties of the Fresnel equations governing the reflection of plane electromagnetic waves at an interface between differing media are presented. The phenomenon of reflection that is independent of angle of incidence is shown to be theoretically possible if the media possess different magnetic permeabilities.

Dilute uniformly redundant sequences for use in coded-aperture imaging

A class of binary sequences with ideal autocorrelation properties is given for several lengths. These sequences possess the property that their periodic autocorrelation sidelobes are a constant unity; they represent a class of codes that are both uniformly redundant and nonredundant. Application to coded-aperture imaging is discussed.

Thin-film multilayer design optimization using a Monte Carlo approach.

An iterative Monte Carlo thickness-varying strategy is presented and used to optimize normal-incidence thin-film multilayer designs and demonstrated for a variety of circumstances. The technique does not get trapped in local minima and, in principle, can home in on the best global design.

Development of Small in-Vivo Imaging Probes for Tumor Detection

We have developed coded-aperature ¿-ray imaging devices which are small enough to be incorporated in medical probes that are inserted into the upper or lower gastrointestinal tract to image concentrations of tumor-seeking radiotracers. We have designed two different types of imaging probes, rotating and nonrotating, and have constructed and tested prototypes of each.

The CA II resonance lines in M dwarf stars without H-alpha emission

Spectra of the Ca II H and K lines in a sample of 31 M dwarf stars without H-alpha emission are used to calculate chromospheric K line radiative losses, F(k), and to study the joint response of Ca II K and H-alpha to chromospheric heating in dwarf M stars. It is suggested that the poor correlation found in the equivalent width - log F(K) diagram may be due either to radial segregation of the H-alpha and K line forming regions or to lateral inhomogeneities in the chromospheres. The results confirm the existence of dM stars with weak H-alpha absorption and K line emission only slightly weaker than that of the dMe stars, and show that dM stars with weak H-alpha but kinematics and metallicities representative of the young disk population belong to a class characterized by a comparatively high degree of chromospheric activity. 32 refs.

Black hole in a gravitational field

An exact solution of the vacuum Einstein field equations representing a Schwarzschild black hole in an external gravitational field is derived using a formalism developed by Ernst.

Rapid in vivo localization of a lost brachytherapy seed.

We adapted a small sodium iodide scintillation detector for rapid, in vivo localization of a lost brachytherapy seed. Using the detector, we were able to locate and remove an Ir-192 seed that was not visible to the unaided eye.

Thermal runaway in germanium laser windows.

A 1-D model of thermal runaway in germanium induced by IR laser radiation is presented. The model examines the influence of the temperature dependent thermal conductivity.