On the ionisation of hydrogen in optical flares     

John C. Brown 《Solar physics》1973,29(2):421-427

Non-steady state and non-LTE effects on the ionisation equilibrium of hydrogen in optical flares are considered in terms of a two-level hydrogen atom. It is shown that, just as in the quiet low chromosphere, the ionisation equation is controlled by spontaneous recombination to the second level and by photoionisation from this level by photospheric radiation, and is independent of the nature of the flare energy input mechanism.Adjustment of the ionisation then occurs on the recombination time scale which is short compared to the flare heating time scale. Consequently the ionisation is given by a simple LTE-modification of Saha's equation at the instantaneous electron temperature obtained from the energy equation. These conclusions are contrasted with those of previous authors who, by using one-level atoms only, have omitted the optically thin Balmer continuum which dominates the optically thick Lyman transitions.  相似文献   

Temporal fine structure of X-rays from trapped electrons in solar flares     

John C. Brown 《Solar physics》1973,32(1):227-229

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The possible protogalactic role of eddies in a turbulent early universe     

Wilbur K. Brown 《Astrophysics and Space Science》1985,115(2):257-265

It is shown that eddies, present in a turbulent early universe, can form excellent galaxies upon collapse of the eddies and a small amount of viscous evolution. The resulting model galaxies display realistically flat rotation curves as well as exponential-like luminosity profiles. The dark mass is allowed to be non-baryonic in this model.Work performed under the auspices of the U.S. Department of Energy.  相似文献   

Distribution of bottom stress and tidal energy dissipation in a well-mixed estuary     

M.Robinson Swift  Wendell S. Brown 《Estuarine, Coastal and Shelf Science》1983,17(3):297-317

Estimates of area-averaged tidal bottom stress are made for four channel segments of the Great Bay Estuary, N.H. Current and sealevel measurements are used to estimate acceleration and pressure gradient terms in the equation of motion, while the equation of motion itself is used to infer the remaining stress term. Dynamic terms, bottom stress values, friction coefficients and energy dissipation rates are estimated for each site. The analysis shows that while throughout the estuary the principal force balance is between the frictional stress and the pressure gradient forcing, RMS values of total bottom stress range from 2·67 to 10·38 Nm^?2 and friction coefficients vary from 0·015 to 0·054. Both stress and energy dissipation are largest in the seaward portion of the estuary with an order of magnitude decrease in dissipation at the most inland site.These distributions of stress and energy dissipation are consistent with cotidal charts of the principal semi-diurnal tidal constituent (M₂) which indicate that the estuary is composed of a highly dissipative more progressive tidal wave regime seaward and a less dissipative standing wave regime landward.  相似文献   

HIGH TEMPERATURE WETAMORPHIS AND ZRUSTAL ANATEXIS     

Ashworth  Brown 《地学学报》1991,3(2):218-219

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G-MODE CLASSIFICATION OF SPECTROSCOPIC DATA     

F. Tosi  A. Coradini  A. I. Gavrishin  A. Adriani  F. Capaccioni  P. Cerroni  G. Filacchione  R. H. Brown 《Earth, Moon, and Planets》2005,96(3-4):165-197

We present the results of the application of the G-mode method to the spectral classification of the icy satellites of the giant planets. G-mode is a multivariate statistical technique for the classification of samples depending on many variables. Here this method is tested on the infrared spectra acquired by the Cassini/VIMS instrument onboard the Cassini spacecraft. This work demonstrates the suitability of automatic spectral classification methods for the study of fair resolution spectra, such as those from VIMS. Our data set is composed by two different kinds of data: observations of point targets (Galilean satellites data) and observations with medium spatial resolution (Phoebe data). In both situations, the G-mode classification performed well. In the first case, of a large number of subpixel observations of the Galilean satellites, through the G-mode it was possible to find statistically meaningful spectral groups of observations. In the case of Phoebe, of some spatially resolved observations, the G-mode classification of␣the infrared spectra of the surface led to several types, dominated by the different illumination geometry of the pixels, because, due to the irregular shape of the satellite, a proper illumination correction was not trivial to apply. Nevertheless, the decrease of the confidence level of the test as well as the re-application of the G-mode on the main type found, led to further types, whose statistical distance can be related to different chemical abundances. We plan to use the G-mode also on the data coming from ongoing and future observations of the icy Saturnian satellites.In the helioseismology literature, G-modes are gravity wave modes of the frequencies of oscillations of the Sun. Here we are dealing with a clustering method, which is essentially different.*E-mail: federico.tosi@rm.iasf.cnr.it  相似文献   

Nitrogen on Triton     

Dale P. Cruikshank  Robert Hamilton Brown  Roger N. Clark 《Icarus》1984,58(2):293-305

The near-infrared spectrum of Triton is characterized by strong absorption bands of methane, probably in the solid state. An additional absorption band at 2.16 μm is tentatively identified as the density-induced (2-0) band of molecular nitrogen in the liquid state. The fundamental overtones of this band system cannot presently be observed because of limitations of the terrestrial atmosphere or spectral signal precision. Using the absorption coefficient for this band derived from laboratory observations and from the literature, it is calculated that Triton must have a layer of nitrogen at least tens of centimeters deep over much of its surface; this quantity is plausible in terms of the cosmic abundance of nitrogen and by comparison with Titan where a massive atmosphere of nitrogen exists. The Triton spectrum has been modeled with liquid nitrogen and solid methane, and it is found that the shape of the continuum in two spectral regions can be properly accounted for by adding a spectral component corresponding to fine-grained water frost. It is speculated that yet another component, a dark, solid, photochemical derivative of methane, may occur as a trace contaminant of the surface materials. If much of the surface of Triton is liquid, the radiometric observations of the satellite must be reinterpreted to derive the radius and surface albedo. If there is liquid nitrogen exposed on the surface, the atmosphere of Triton is probably dominated by nitrogen rather than methane because of the much higher vapor pressure of the former. At the calculated subsolar temperature of Triton, the vapor pressure of nitrogen implies a surface atmospheric pressure in the range 0.13 to 0.30 atm.  相似文献   

Rockall and the limits of national jurisdiction of the UK: Part 1     

E.D. Brown 《Marine Policy》1978,2(3):181-211

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The rotation period of Neptune's upper atmosphere     

R.Hamilton Brown  Dale P. Cruikshank  Alan T. Tokunaga 《Icarus》1981,47(2):159-165

Significant variations in the near-infrared brightness of Neptune during July and August 1980 were observed. These observations show a well-defined, large-amplitude variation in Neptune's J-K color, with a period of 17.73 ± 0.1 hr and are interpreted as diurnal variations resulting from the 17.73-hr rotation period of the upper atmosphere of Neptune in the presence of inhomogeneous weather. These results qualitatively corroborate those of D. P. Cruikshank (1978, Astrophys. J.220, L57-L59) in an earlier study using similar techniques. In addition, variations were observed in the 5-μm spectral region which are in phase with the variations seen at shorter wavelengths. A new 5-μm measurement of Uranus is also reported.  相似文献   

The gamma ray lens – an ESA technology reference study     

Craig Brown  Nicola Rando  Alexander Short  Aleksander Lyngvi  Tone Peacock 《Experimental Astronomy》2005,20(1-3):279-288

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