An experimental measurement of galactic cosmic radiation dose in conventional aircraft between San Francisco and London compared to theoretical values for conventional and supersonic aircraft

These direct measurements are in fair agreement with computations made using a program which considers both basic cosmic ray atmospheric physics and the focusing effect of the earth's magnetic field. These measurements also agree with those made at supersonic jet aircraft altitudes in Rb-57 aircraft. It is concluded that experiments and theory show that the doses received at conventional jet aircraft altitudes are slightly higher than those encountered in supersonic flights at much higher altitudes

Rotating gravity currents: small-scale and large-scale laboratory experiments and a geostrophic model

Laboratory experiments simulating gravity-driven coastal surface currents produced by estuarine fresh-water discharges into the ocean are discussed. The currents are generated inside a rotating tank filled with salt water by the continuous release of buoyant fresh water from a small source at the fluid surface. The height, the width and the length of the currents are studied as a function of the background rotation rate, the volumetric discharge rate and the density difference at the source. Two complementary experimental data sets are discussed and compared with each other. One set of experiments was carried out in a tank of diameter 1 m on a small-scale rotating turntable. The second set of experiments was conducted at the large-scale Coriolis Facility (LEGI, Grenoble) which has a tank of diameter 13 m. A simple geostrophic model predicting the current height, width and propagation velocity is developed. The experiments and the model are compared with each other in terms of a set of non-dimensional parameters identified in the theoretical analysis of the problem. These parameters enable the corresponding data of the large-scale and the small-scale experiments to be collapsed onto a single line. Good agreement between the model and the experiments is found

Some Heuristic Semiclassical Derivations of the Planck Length, the Hawking Effect and the Unruh Effect

The formulae for Planck length, Hawking temperature and Unruh-Davies temperature are derived by using only laws of classical physics together with the Heisenberg principle. Besides, it is shown how the Hawking relation can be deduced from the Unruh relation by means of the principle of equivalence; the deep link between Hawking effect and Unruh effect is in this way clarified.Comment: LaTex file, 6 pages, no figure

Derivation of the Blackbody Radiation Spectrum from a Natural Maximum-Entropy Principle Involving Casimir Energies and Zero-Point Radiation

By numerical calculation, the Planck spectrum with zero-point radiation is shown to satisfy a natural maximum-entropy principle whereas alternative choices of spectra do not. Specifically, if we consider a set of conducting-walled boxes, each with a partition placed at a different location in the box, so that across the collection of boxes the partitions are uniformly spaced across the volume, then the Planck spectrum correspond to that spectrum of random radiation (having constant energy kT per normal mode at low frequencies and zero-point energy (1/2)hw per normal mode at high frequencies) which gives maximum uniformity across the collection of boxes for the radiation energy per box. The analysis involves Casimir energies and zero-point radiation which do not usually appear in thermodynamic analyses. For simplicity, the analysis is presented for waves in one space dimension.Comment: 11 page

PROMISSORY ESTOPPEL: PRINCIPLE FROM PRECEDENTS: I

The doctrine of promissory estoppel is an outstanding modem example of the way in which the Anglo-American legal system develops significant rules and principles out of the day-to-day decisions of our courts. Progress in the law comes about through the formulation and acceptance of generalizations. However, merely stating the results of a number of different instances does not result in clarification and simplification. That comes only when the precedents are studied with a view to discovering the \u27\u27binding thread of principle that runs through them all. Such a principle, if discovered in the course of the appraisal of a series of cases, will make for a more ready understanding of the cases which have already been decided. Even more important, however, is the future use which can be made of the principle thus discovered. It may thereafter be employed in variant and diverse fact situations to produce workable, logical and rational solutions to problems which had previously been solved only by resort to fiction or by the use of historical anomalies and conceptual distortions. As Cohen has so aptly remarked, A legal system that works with general principles has powerful instruments .... [A] generalized jurisprudence enlarges the law\u27s control over the diversity of legal situations. It is like fishing with large nets instead of with single lines

The transition to conduction in diffusion-controlled gas breakdown

Measurements have been made of ultra-high-frequency (l80Mc/s) breakdown fields in hydrogen, nitrogen and neon, in a Rogowski-profiled spark gap, under conditions of pressure in which both the electron ambit and the mean-free-path were less than the gap width (0.494cm). The measurements were made with sustained fields and also with pulsed fields in overvolted conditions to obtain data on the variation of breakdown delays with overvoltage. The delays were measured by photographing an oscilloscope trace which displayed the gap voltage, and a range of 400 to 0.2 microseconds was observed with over voltages up to 100%. Breakdown was initiated during a pulse by irradiating the gas in the mid-gap region with a short (about 0.1 microsecond) burst of ultraviolet photons, A theory is proposed which determines the shape of the oscillograms, and hence gives breakdown delays. Good agreement was obtained between theoretical and experimental delays for hydrogen and nitrogen, but predicted delays were too short by factors up to ten for neon. A qualitative explanation is given for the anomalous results for neon. Maintaining voltages have been measured in hydrogen and nitrogen, as a function of the gas pressure, but were too low to measure in neon. In all three gases it is shown that the maintaining fields are consistent with losses by ambi-polar diffusion, although electrons which approach within one ambit of an electrode are driven into that electrode by the action of the field. Immediately after breakdown in overvolted conditions the voltage approached zero and then recovered to approach the maintaining voltage asymptotically. The recovery time- constants were of the order which might be expected if an initial excess electron population were being diminished by ambi-polar diffusion

Demand for Multimedia in the Classroom: Do Students and Faculty Really Want it All?

Teaching/Communication/Extension/Profession,