An avalanche photodiode photon counting camera for high-resolution astronomy     

Oliver Ryan  Mike Redfern  Andrew Shearer 《Experimental Astronomy》2006,21(1):23-30

A system is described which makes best use of the high quantum efficiency and high count rate capability of avalanche photodiodes for high time resolution observations of optical pulsars. The use of three APDs allows simultaneous photometry of the target and a reference star, and the monitoring of the sky background. By minimising the optical components in the light path the optical efficiency of the system is maximised. The TRIFFID (Shearer, A., Stappers, B., O'Connor, P., Golden, A., Strom, R., Redfern, M., Ryan, O.: Science 301, 493–495 (2003)) and OPTIMA (Straubmeier, C., Kanbach, G., Schrey, F.: Exp. Astron. 11, 157–170 (2001)) have shown that fibre-fed APD arrays can produce excellent results. This, new, system was used on the 6m BTA in November 2003 – results on the Crab pulsar are presented.  相似文献   

A new method for computing synthetic seismograms   总被引：10，自引：0，他引：10  

C. H. Chapman 《Geophysical Journal International》1978,54(3):481-518

Summary. The computation of theoretical seismograms for models in which the elastic parameters and density vary only with depth (in a plane, cylindrical or spherical geometry) reduces to the solution of an ordinary differential equation plus the evaluation of inverse transformations. In principle, the problem is straightforward. In practice, many techniques and approximations can be used at each stage and many combinations and variants are possible. In this paper, we discuss a new method of evaluating the inverse transforms. Any method can be used to solve the differential equation and we only discuss a few analytic approximations to illustrate the new method. The inverse transformations are a frequency and wavenumber integral. Essentially four techniques can be used to evaluate these depending on the order of integration and whether the wavenumber integral is distorted from the real axis. Three of these have been widely used, but the technique of evaluating the frequency integral first and keeping the wavenumber real is new. In this paper, we discuss some of the advantages of this combination.  相似文献   

Shock wave dissipation in magnetically active regions     

C. J. Durrant  Andrew G. Michalitsanos 《Solar physics》1971,18(1):60-62

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Lateral inhomogeneities in the Venus atmosphere: Analysis of thermal infrared maps     

Andrew P. Ingersoll  Glenn S. Orton 《Icarus》1974,21(2):121-128

The thermal infrared maps of Venus published by Murray, Wildey, and Westphal (1963) and Westphal, Wildey, and Murray (1965) have been analyzed systematically in order to separate the observed intensity into a limb-darkening component and a solar-associated component representing fixed patterns of intensity corotating with the earth and sun, respectively. Interesting new results are obtained for the solar-associated component. Regions near the subsolar point and the poles are not covered in the original maps or in the analysis.The solar-associated pattern of intensity is very nearly symmetric about the equator. In both northern and southern hemispheres, an intensity minimum seems to occur near the morning terminator at middle to high latitudes, slightly beyond the limit of the maps. An intensity maximum occurs on the equator slightly to the east of the antisolar point. Three broad ridges of relatively high intensity radiate away from this point, one pointing to the west along the equator, the others pointing to the northeast and southeast, respectively. The eastward tilt of the latter two ridges may indicate that horizontal exchange is important in maintaining the equatorial maximum of zonal momentum which is associated with the 4-day circulation of the Venus atmosphere.  相似文献   

On the origin of variations in the composition of granitic rocks of Chile and Bolivia     

Andrew B. Vistelius  Carlos Ruiz Fuller 《Mathematical Geology》1969,1(1):113-114

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The effects of partial redistribution on facular K line profiles     

J. N. Heasley  F. Kneer  G. A. Chapman 《Solar physics》1977,52(2):309-313

We present theoretical Ca ii K-line profiles and filtergram contrasts for several recent models of solar faculae. The line profiles vary greatly between models and between complete and partial frequency redistribution non-LTE calculations for any given model. The filtergram contrasts are relatively insensitive to the line formation theory which greatly simplifies the calculation for comparison with observations. All of the models considered exhibit K-line contrasts smaller than the mean value observed by Mehltretter.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.  相似文献   

A Model Midnight Meridian Magnetospheric Field     

P. C. Kendall  D. W. Windle  S. I. Akasofu  S. Chapman 《Geophysical Journal International》1969,17(2):185-194

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An unsteady wind-driven ocean circulation model     

John A. Johnson  Andrew J. Willmott 《Dynamics of Atmospheres and Oceans》1981,6(1):1-27

This model of a continuously stratified ocean, consisting of surface Ekman and thermal layers and a deep abyssal region, is driven by an unsteady surface wind stress. The model yields a nonlinear planetary wave equation for the surface temperature which is solved by the method of characteristics. Horizontal distributions of the surface temperature, the heat content and the potential energy are computed. For a model zonal wind stress relevant to the North Atlantic, a parameter sensitivity study is made.Long time scale observations of the heat content in the North Atlantic north of 45°N show that periods of heating and cooling of a few decades duration frequently occur. Using a zonal wind stress consisting of the superposition of a mean and two time harmonic components, secular variations in the surface temperature field manifest themselves as a beat period, provided the time harmonic frequencies are close together. Finally, to investigate the effects on the circulation produced by the changing intensity of the westerly winds, numerical results are presented for the case when the wind stress distribution oscillates in the north-south direction with time. Results from the study show that the heating and cooling periods of a few decades duration in the North Atlantic can be reproduced.  相似文献   

POTENTIOSTATIC STUDY OF IRON METEORITE CORROSION     

Stanford L. Tackett  Andrew J. Goudy 《Meteoritics & planetary science》1972,7(4):487-508

A potentiostat was used to study the electrolytic corrosion of iron meteorites in a neutral solution. Low current densities were chosen so that the observed potentials would more closely approximate the theoretical Nernst values. Iron, nickel, and cobalt ions, the products of corrosion, were soluble in the electrolyte solution, and were determined after each electrolysis by atomic absorption spectrophotometry. Kamacite and taenite dissolved as individual phases, with kamacite dissolving preferentially. Cobalt dissolved along with iron and nickel from each phase. There is a direct relationship between nickel content and the potential at which a meteorite first starts to dissolve; the higher the nickel content, the more resistant the meteorite is to corrosion. None of the six meteorites observed started to dissolve at a lower potential than pure iron, nor at a higher potential than pure nickel  相似文献   

Seismograms from Epstein Transition Zones     

M. Hron  C. H. Chapman 《Geophysical Journal International》1974,37(2):305-322

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