A Barometer Element for Radio-Sondes

The barometer unit described herein has proven to be extremely reliable when used on balloon flights to high altitudes. It consists of an aneroid element which moves an arm, making a series of contacts with no mechanical amplification involved. Working on the digital principle it gives its information when certain definite pressures have been reached

Vibrating Vane, Absolute Gas Pressure Gauge

An oscillating rectangular vane suspended by a fine quartz fiber is used to determine the absolute pressure of the gas in which it is located. Aside from being an absolute instrument, the advantages of such a device are (1) simplicity, (2) the fact that it does not change the pressure when an observation is made as do many other types of gauges, and (3) the absence of a heated filament which may decompose the gas under study

Millikan-Teacher and Friend

As a result of support by Addison-Wesley Publishing Company, the American Association of Physics Teachers has established an annual lectureship, named in honor of Robert A. Millikan. It is anticipated that this will bring to each summer meeting of the Association a physicist who will speak on a topic of current interest and that the summer meeting will thus have a feature comparable with the Richtmyer Lecture at the annual meeting. The committee responsible for the first Millikan Lecture chose H. V. Neher, long time associate of Millikan. This highly suitable choice was as appropriate as was Neher's choice of a topic- Millikan himself. The editors of the American Journal of Physics are grateful for permission to publish this pleasantly informal biographical lecture, spiced as it is with personal reminiscences

Metal System for Chemical Reactions and for Studying Properties of Gases and Liquids

An all-metal system, made of copper, is herein described. It is suitable for working with those chemicals which do not attack copper. In particular it has been found very useful in the purification of BF3 and B(CH3)3. Some important features of such a system are (1) a complete absence of contaminants; (2) reactions may be carried out up to 500°C; (3) pressures up to several hundred pounds per square inch may be used; (4) flow of gases from very low to very high pressures may be easily controlled; (5) the system is very rugged. This latter point is particularly desirable where noxious or inflammable gases (such as B(CH3)3) are used. A method is also described whereby gases from sealed-off containers under either high or low pressures may be easily retrieved without introducing impurities. Other important advantages of such a system are mentioned in the text

Modification to the Automatic Ionization Chamber

The automatic ionization chamber has been described previously [1,2]. It has proven quite reliable in service and has many desirable features, especially for balloon-borne equipment. A disadvantage has been that the time of discharge was dependent upon the potential applied to the quartz fiber. Thus, during the comparison of the instrument to be used with the standards, careful measurement of the potential used on the standards was required. Furthermore, care was required to make sure that the battery used during the flight remained constant in potential. It has now been found that the time between rechargings can be made nearly independent of the potential of the fiber by inserting a metal conductor inside and insulating it from the outer conductor surrounding the quartz fiber, and making the potential of this inner conductor the same as that of the fiber

Ionization experiment

Mariner space probe ionization chamber and Geiger counter experiments on galactic radiation entering solar syste

Techniques Useful in Evacuating and Pressurizing Metal Chambers

The aforementioned problems arose in connection with the automatic ionization chamber described previously (1). It was fund that the functioning of these instruments was more consistent if the ion chamber was baked at 350°C for several hours and then filled with pure argon. This procedure resulted in the elimination of organic impurities from the inner surfaces. The impurities, settling on the gold-coated quartz fiber and the collector, apparently altered the contact, resulting in some uncertainty in the recharging. The baking procedure has completely curved this difficulty

Extensions and block decompositions for finite-dimensional representations of equivariant map algebras

Suppose a finite group acts on a scheme $X$ and a finite-dimensional Lie algebra $\mathfrak{g}$. The associated equivariant map algebra is the Lie algebra of equivariant regular maps from $X$ to $\mathfrak{g}$. The irreducible finite-dimensional representations of these algebras were classified in previous work with P. Senesi, where it was shown that they are all tensor products of evaluation representations and one-dimensional representations. In the current paper, we describe the extensions between irreducible finite-dimensional representations of an equivariant map algebra in the case that $X$ is an affine scheme of finite type and $\mathfrak{g}$ is reductive. This allows us to also describe explicitly the blocks of the category of finite-dimensional representations in terms of spectral characters, whose definition we extend to this general setting. Applying our results to the case of generalized current algebras (the case where the group acting is trivial), we recover known results but with very different proofs. For (twisted) loop algebras, we recover known results on block decompositions (again with very different proofs) and new explicit formulas for extensions. Finally, specializing our results to the case of (twisted) multiloop algebras and generalized Onsager algebras yields previously unknown results on both extensions and block decompositions.Comment: 41 pages; v2: minor corrections, formatting changed to match published versio

An Automatic Ionization Chamber

The ionization chamber described herein has the following characteristics: 1. It recharges itself after having collected a definite charge. 2. It generates a pulse at the instant of recharging that is easily amplified electronically. 3. The constant of the ionization chamber is independent of the constants of vacuum tubes but does depend on the constancy of a quartz fiber, the pressure of the gas, and the potential of the charging battery. It has been successfully used to measure cosmic-ray ionization at balloon altitudes both in the United States and in northern Greenland

Ozone Depletion from Nearby Supernovae

Estimates made in the 1970's indicated that a supernova occurring within tens of parsecs of Earth could have significant effects on the ozone layer. Since that time, improved tools for detailed modeling of atmospheric chemistry have been developed to calculate ozone depletion, and advances have been made in theoretical modeling of supernovae and of the resultant gamma-ray spectra. In addition, one now has better knowledge of the occurrence rate of supernovae in the galaxy, and of the spatial distribution of progenitors to core-collapse supernovae. We report here the results of two-dimensional atmospheric model calculations that take as input the spectral energy distribution of a supernova, adopting various distances from Earth and various latitude impact angles. In separate simulations we calculate the ozone depletion due to both gamma-rays and cosmic rays. We find that for the combined ozone depletion roughly to double the ``biologically active'' UV flux received at the surface of the Earth, the supernova must occur at <8 pc. Based on the latest data, the time-averaged galactic rate of core-collapse supernovae occurring within 8 pc is ~1.5/Gyr. In comparing our calculated ozone depletions with those of previous studies, we find them to be significantly less severe than found by Ruderman (1974), and consistent with Whitten et al. (1976). In summary, given the amplitude of the effect, the rate of nearby supernovae, and the ~Gyr time scale for multicellular organisms on Earth, this particular pathway for mass extinctions may be less important than previously thought.Comment: 24 pages, 4 Postscript figures, to appear in The Astrophysical Journal, 2003 March 10, vol. 58