Ultraviolet hydrogen-discharge lamp

Device provides stable flux output for calibration of ultraviolet spectrum

A near-earth optical communications terminal with a corevolving planetary sun shield

The umbra of a planet may serve as a sun shield for a space based optical communications terminal or for a space based astronomical observatory. An orbit that keeps the terminal or observatory within the umbra is desirable. There is a corevolution point behind every planet. A small body stabilized at the planet corevolution point will revolve about the sun at the same angular velocity as the planet, always keeping the planet between itself and the sun. This corevolution point is within the umbra of Mars but beyond the end of the umbra for Mercury, Venus, and earth. The Mars corevolution point is an ideal location for an astronomical observatory. There Mars obstruct less than 0.00024 percent of the sky at any time, and it shades the observatory completely from the sun. At the earth corevolution point, between 51 and 84 percent of the solar disk area is blocked, as is up to 92 percent of the sunlight. This provides a reduction from 3 dB to 11 dB in sunlight that could interfere with optical communications if scattered directly into the detectors. The variations is caused by revolution of the earth about the earth-moon barycenter

Fraunhofer filters to reduce solar background for optical communications

A wavelength that lies within a spectral interval of reduced solar emission (a Fraunhofer line) can carry optical communications with reduced interference from direct or reflected background sunlight. Suitable Fraunhofer lines are located within the tuning range of good candidate lasers. The laser should be tunable dynamically to track Doppler shifts in the sunlight incident on any solar system body that may appear in the background as viewed by the receiver. A Fraunhofer filter used with a direct-detection receiver should be tuned to match the Doppler shifts of the source and background. The required tuning calculated here for various situations is also required if, instead, one uses a heterodyne receiver with limited post-detection bandwidth

On the Distribution of Values and Zeros of Polynomial Systems over Arbitrary Sets

Let G_1,..., G_n \in \Fp[X_1,...,X_m] be $n$ polynomials in $m$ variables over the finite field \Fp of $p$ elements. A result of {\'E}. Fouvry and N. M. Katz shows that under some natural condition, for any fixed $\varepsilon$ and sufficiently large prime $p$ the vectors of fractional parts (\{\frac{G_1(\vec{x})}{p}},...,\{\frac{G_n(\vec{x})}{p}}), \qquad \vec{x} \in \Gamma, are uniformly distributed in the unit cube $[0,1]^n$ for any cube $\Gamma \in [0, p-1]^m$ with the side length $h \ge p^{1/2} (\log p)^{1 + \varepsilon}$. Here we use this result to show the above vectors remain uniformly distributed, when $\vec{x}$ runs through a rather general set. We also obtain new results about the distribution of solutions to system of polynomial congruences

On the isomorphism question for complete Pick multiplier algebras

Every multiplier algebra of an irreducible complete Pick kernel arises as the restriction algebra \mv = \{f\big|_V : f \in \cM_d\}, where $d$ is some integer or $\infty$, \cM_d is the multiplier algebra of the Drury-Arveson space $H^2_d$, and $V$ is a subvariety of the unit ball. For finite $d$ it is known that, under mild assumptions, every isomorphism between two such algebras \mv and \mw is induced by a biholomorphism between $W$ and $V$. In this paper we consider the converse, and obtain positive results in two directions. The first deals with the case where $V$ is the proper image of a finite Riemann surface. The second deals with the case where $V$ is a disjoint union of varieties.Comment: 17 pages. Final version, to appear in Integral Equations and Operator Theor

Shutters and slats for the integral sunshade of an optical reception antenna

Optical reception antennas used at a small Sun-Earth-probe angle (small solar elongation E) require sunshading to prevent intolerable scattering of light from the surface of the primary mirror. An integral sunshade consisting of hexagonal tubes aligned with the segmentation of a large mirror was proposed for use down to E = 12 degrees. For smaller angles, asterisk-shaped vanes inserted into the length of the hexagonal tubes would allow operation down to about 6 degrees with a fixed obscuration of 3.6 percent. Two alternative methods are investigated to extend the usefulness of the integral sunshade to smaller angles by adding either variable-area shutters to block the tube corners that admit off-axis sunlight or by inserting slats (partial vanes) down the full length of some tubes. Slats are effective for most operations down to 6 degrees, and obscure only 1.2 percent. For E between 10.75 and 12 degrees, shutters cause even less obscuration