measurement of noise power spectrum in photon counting PMT's and the effect of the observed (1/f) noise on astronomical photometry

In astronomical photometry, the sensitivity of observations is limited by the dark counts of the photomultiplier tube. In the present work, the effect of dark count noise in photon counting systems is investigated by theory and experimental measurements. Dark counts are considered to be originating from two sources, namely: dc fluctuations and random pulses.Experimental measurements were carried out to determine noise effects in different operating regions of noise dominance. The results provide strong evidence that: in normal operating mode, where the effect of random pulses is dominant, dark counts do not follow Poisson statistics. The observed noise shows strong (1/f) power spectrum, where the observed noise power is found to increase with time of observation.The results are important in photon counting systems operating under dark count limited mode. The conclusions drawn can be useful in obtaining more accurate error estimates and in assessing astronomical photometric observations and data reduction techniques.     

The search for exsolved ferromagnesian olivines: A meteoritic survey

Abstract— Olivine grains from selected meteorites (the Springwater pallasite, the Lowicz mesosiderite, the ALH 84025 brachinite, the Krymka LL3 chondrite, and the Calcalong Creek lunar meteorite) and terrestrial rocks (San Carlos forsterite and Rockport fayalite) were studied by optical microscopy and high-precision electron microprobe analysis. Detailed microprobe traverses revealed regular igneous zoning in the Krymka and Calcalong Creek olivines. Traverses across the San Carlos forsterite grain are flat and display no chemical variations larger than the 2σ range of counting error (±0.2 mol% Fa). Traverses across olivine grains in the ALH 84025, Lowicz, and Springwater meteorites show regular patterns of periodic or wavy chemical variations well exceeding the 2σ uncertainty range. However, no lamellar structure was seen in backscattered electron images. It is suggested that the periodic chemical variations may be due to spinodal decomposition of primary, more or less homogeneous grains. I conclude that the absence of earlier reports of such variations simply means that olivine grains in equilibrated meteorites have not been examined closely enough to detect them.     

Long-Term Changes of Polar Activity of the Sun

We discuss long-time changes of polar activity of the Sun using the new observational data sets in the optical range during 1872–2001. A study of the secular and cycle variations of the magnetic activity at the high-latitude regions is the main goal that includes polar magnetic field reversals during 1872–2001 and secular changes of the duration of polar activity cycles. The secular increase of the area of polar zones during the minimum activity in the last 120 years and as consequence a decrease of coronal temperature of the Sun in the high-latitude zones during the last 50 years. Correlation between the polar cycles of Caii-K bright points with the Wolf sunspot numbers cycles, W(t), and the 22-year polar magnetic cycles of Caii-K bright points at the high latitudes during 1905–1995 is discussed.     

On the stability of particular solutions of the singly averaged Hill problem

We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem.     

Geochemistry of metabauxites in the Bergsträsser Odenwald (Mid German Crystalline Rise) and palaeoenvironmental implications

Summary Pre- to early Variscan metamorphosed volcano-sedimentary series of the western (Bergstr?sser) Odenwald have been intruded by Variscan calc-alkaline magmatites with plate margin affinities. Within the NE-SW trending metabasic and metapelitic series, intercalations of anomalously aluminous- and iron-rich compositions representing former bauxites are distinguishable. Geochemical data indicate that the Al-, Fe-rich rocks are the metamorphic equivalents of a former bauxitic-ferralitic weathering profile, now comprising spinel fels (top) with relics of pisolitic structures, corundum-chlorite fels, corundum-cordierite-plagioclase gneiss, sillimanite-cordierite-plagioclase gneiss, cordierite-plagioclase gneiss and kinzigite (base) displaying a decrease of weathering in the order as listed. The evolution of such terrestrial sediments is related to specific climatic, environmental, and physico-chemical conditions similar to those of the present-day tropical to subtropical humid regions with high seasonal rains and intensive drainage. Comparison with palaeomagnetic and palaeoclimatic data indicate that the Odenwald metabauxites originally formed during the Lower to Mid-Devonian. Our results imply that, during this geological time span, parts of the precursors of the Mid-German Crystalline Rise not only transversed low latitudes but also were exposed to terrestrial weathering.

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Zusammenfassung Die Geochemie der Metabauxite im Bergstr?sser Odenwald (Mitteldeutsche Kristallinschwelle) und ihre Bedeutung für das Pal?omilieu Im westlichen (Bergstr?sser) Odenwald intrudierten variszische Plattenrand-Kalkalkali-Magmatite in pr?- bis früh-variszische, ehemalige vulkano-sediment?re Serien. Innerhalb der heute NE-SW streichenden Metabasit- und Metapelitzüge treten lokal Al-Fe-reiche Einschaltungen auf, die strukturell und geochemisch als metamorphe ?quivalente eines ehemaligen bauxitisch-ferralitischen Verwitterungsprofils klassifiziert werden k?nnen. Sie umfassen Spinellfelse mit erhaltenen, ehemaligen zonierten Pisolithen, Korund-Chloritfelse, Korund-Cordierit-Plagioklasgneise, Sillimanit-Cordierit-Plagioklasgneise, Cordierit-Plagioklasgneise und Kinzigite. Bauxite k?nnen als terrestrische Bildungen nur unter speziellen klimatischen und physiko-chemischen Bedingungen entstehen. Pal?omagnetische und pal?oklimatische Daten legen die Bildung der ehemaligen Bauxite im unteren bis mittleren Devon nahe. Daraus folgt, da? w?hrend dieser geologischen Zeitspanne die Vorl?ufer der mitteldeutschen Kristallinschwelle bei der Norddrift nicht nur ?quatorn?he passierten, sondern auch partiell ungest?rte, terrestrische, tropisch-subtropische Verwitterungsprozesse abliefen.

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Received June 10, 1999; revised version accepted October 30, 2000     

Self-similar solutions for the blast wave problem in radiative gasdynamics,I

Similarity solutions, describing the flow of a perfect gas behind spherical shock waves, are investigated including the radiation heat flux. The shock is assumed to be propagating in a medium at rest. Shock radius varies exponentially with time and density is inversely proportional to fifth power of the shock radius immediately ahead of the shock front.     

Oceanic Engineering: The making of an IEEE Society

In connection with the celebration of the centennial of the Institute of Electrical and Electronics Engineers (UEEE) in 1984, the history of electrical engineering in relation to the world's oceans is traced, with emphasis on the 20-year period from the 1960's to the present. Note is taken of the breadth of the cross-disciplinary interests involved, as exemplified by the active participation of a score of IEEE Societies and Professional Groups, how they organized to cooperate, the periodic meetings and annual conferences they sponsored, the publications they undertook, the tokens of recognition they adopted, and how they adapted to changes in emphasis to reflect shifts in the areas of technology served. Finally, an assessment is made of the future of the recently organized IEEE Oceanic Engineering Society.     

Thermal stability of a layer with permeable boundaries and variable gravitational field

The aim of this paper is to investigate the thermal stability of a fluid layer with permeable boundaries and a variable gravitational field. It is observed that the principle of exchange of stabilities is valid when the layer is heated form below and the complex growth rate of an arbitrary oscillatory mode exists outside of a circle whose radius depends upon the permeability parameter, Prandtl number and wavelength of the mode. In the case of a layer heated from below, gravity increasing upward has a destabilizing effect whereas the permeability parameter has a stabilizing effect.