Solar noise storms coordinated observations: May 16–24, 1981     

C. Mercier  Ø. Elgarøy  A. Tlamicha  P. Zlobec 《Solar physics》1984,92(1-2):375-381

We present the main results obtained from the coordinated observations of solar radio noise storms organized by C.E.S.R.A. in May 1981. They concern the structure and polarization of radio sources, and the relation with the photospheric magnetic field. A model of coronal magnetic field, accounting for the observations, is briefly discussed.  相似文献   

Structure and oscillations in quiescent filaments from observations in He i λ10830 å     

Yi Zhang  Oddbjørn Engvold  Stephen L. Keil 《Solar physics》1991,132(1):63-80

Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures.  相似文献   

Distribution of lunar impacts by objects in parabolic low inclination orbits     

Nils Aall Barricelli  Ragnar Thorbjørnsen 《Earth, Moon, and Planets》1978,18(4):479-490

This paper presents a computer investigation extending to the case of parabolic orbits, an earlier investigation conducted by Barricelli and Metcalfe (1969) on lunar impacts by external low eccentricity satellites as a means to interpret the asymmetric distribution of lunar maria. Parabolic orbits can be approximated by two kinds of objects:

1. High eccentricity external satellites may, near periapsis, approach the Moon with orbital velocity and other characteristics closely resembling those of a parabolic orbit.
2. Asteroids and meteoroids approaching the Earth-Moon system with a low velocity may have moved in a nearly parabolic orbit when they reached the lunar distance from the Earth at the time when the impacts which carved the lunar maria took place.

The investigation gives, therefore, not only additional information relevant to the interpretation of the distribution of lunar maria by the satellite impacts hypothesis (in this case high eccentricity ones), but also information about the alternative hypothesis (Wood, 1973) that asteroid impacts rather than satellite impacts were involved.  相似文献   

The fine structure of prominences     

Oddbjørn Engvold 《Solar physics》1976,49(2):283-295

The fine structure of nonspot prominences are studied from H filtergrams. The size of the smallest prominence structures increases with height above the chromosphere. Some prominences contain structures close to 1/2 arc second, which is the spatial resolution in the present data. The effective thickness of many nonspot prominences ranges between 4 × 10⁷ cm and 1.5 × 10⁸ cm. An apparent downward directed motion is observed in the majority of the prominences. No preferred direction of the motion is seen in regions composed of comparatively large diffuse structures. Some bright threads are visible for 1 hr and longer. Bright knots have an average observed lifetime of about 8 min. The process of condensation and subsequent destruction of prominence fine structure appears to take place on a very short time scale compared to the life time of the regions where prominences may exist. The observed H brightness of the prominences in the present data may be accounted for as scattered chromospheric radiation.  相似文献   

Water equivalent method for city phytostructure of Indonesia     

G. Samudro B. Eng.  M. Eng.  S. Mangkoedihardjo B. Eng.  M.Sc.  E.S.  Ph.D. 《International Journal of Environmental Science and Technology》2006,3(3):261-267

This paper proposed a simple method and rapid to carry out for organizing city phytostructure. Carbon dioxide sequestration was addressed and referred to population number instead of city area. The unit storage of carbon dioxide, which was nothing less than greenspace area, was determined using equivalent method of determining unit storage of water. For various population number (P) of city area in Indonesia, the greenspace unit (GU) was 29P^?0.3 ? 3.2, and the greenspace area (GA) was 29P⁰⁷–3.2P. Greenspace distribution was preferably on wetlands, river lines, top ground level, and north south direction.  相似文献   

T-distributed Random Fields: A Parametric Model for Heavy-tailedWell-log Data1     

Jo Røislien  Henning Omre 《Mathematical Geosciences》2006,38(7):821-849

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Single frequency processing of Ørsted GPS radio occultation measurements     

Georg Bergeton Larsen  Stig Syndergaard  Per Høeg  Martin Bjært Sørensen 《GPS Solutions》2005,9(2):144-155

The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation.  相似文献   

The fall and rise of metropolitan government in Copenhagen     

Hans Thor Andersen  Frank Hansen  John Jørgensen 《GeoJournal》2002,58(1):43-52

In this paper it is argued that the re-establishment of a metropolitan government in the Greater Copenhagen Area in 2000 (Greater Copenhagen Authority) is not to be seen as a return to the kind of regional, coordinative authority (Greater Copenhagen Council) that was abolished in the Thatcherite climate of the 1980s. Throughout the 1980s and 1990s new forms of urban governance, entrepreneurialism and a higher national priority to the capital region were introduced, which changed the conditions under which the new metropolitan government is operating. This `contextualization' of the analysis of the two generations of metropolitan government points to the fact that typologies of metropolitan government, such as the one put forward by Sharpe (1995), often lacks analytical cogency. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Electrons in feldspar II: a consideration of the influence of conduction band-tail states on luminescence processes     

N. R. J. Poolton  K. B. Ozanyan  J. Wallinga  A. S. Murray  L. Bøtter-Jensen 《Physics and Chemistry of Minerals》2002,29(3):217-225

 Most natural feldspars contain many charged impurities, and display a range of bond angles, distributed about the ideal. These effects can lead to complications in the structure of the conduction band, giving rise to a tail of energy states (below the high-mobility conduction band) through which electrons can travel, but with reduced mobility: transport through these states is expected to be thermally activated. The purpose of this article is twofold. Firstly, we consider what kind of lattice perturbations could give rise to both localized and extended conduction band-tail states. Secondly, we consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04–0.05-eV phonons play in both the luminescence excitation and emission processes of these materials. It also has relevance in the dating of feldspar sediments at elevated temperatures. Received: 11 May 2001 / Accepted: 6 September 2001  相似文献   

Comparison of isotope pairing and N2:Ar methods for measuring sediment denitrification—Assumption, modifications, and implications     

Bradley D. Eyre  Søren Rysgaard  Tage Dalsgaard  Peter Bondo Christensen 《Estuaries and Coasts》2002,25(6):1077-1087

Denitrification has been measured during the last few years using two different methods in particular: isotope pairing measured on a triple-collector isotopic ratio mass spectrometer and N₂:Ar ratios measured on a membrane inlet mass spectrometer (MIMS). This study compares these two techniques in short-term batch experiments. Rates obtained using the original N₂∶Ar method were up to 3 to 4 times higher than rates obtained using the isotope pairing technique due to O₂ reacting with the N₂ during MIMS analysis. Oxygen combines with N₂ within the mass spectrometer ion source forming NO⁺ which reduces the N₂ concentration. The decrease in N₂ is least at lower O₂ concentrations and since oxygen is typically consumed during incubations of sediment cores, the result is often a pseudo-increase in N₂ concentration being interpreted as denitrification activity. The magnitude of this ocygen effect may be instrument specific. The reaction of O₂ with N₂ and the subsequent decrease in N₂ was only partly correctly using an O₂ correction curve for the relationship between N₂ and O₂ concentrations. The O₂ corrected N₂∶Ar denitrification rates were lower, but still did not match the isotope pairing rates and the variability between replicates was much higher. Using a copper reduction column heated to 600°C to remove all of the O₂ from the sample before MIMS analysis resulted in comparable rates (slightly lower), and comparable variability between replicates, to the isotope pairing technique. The N₂:Ar technique determines the net N₂ production as the difference between N₂ production by denitrification and N₂ consumption by N-fixation, while N-fixation has little effect on the isotope pairing technique which determines a rate very close to the gross N₂ production. When the two different techniques were applied on the same sediment, the small difference in rates obtained by the two methods seemed to reflect N-fixation as also supported from measurements of ethylene production in acetylene enriched sediment cores. The N₂:Ar and isotope pairing techniques may be combined to provide simultaneous measurements of denitrification and N-fixation. Both techniques have several assumptions that must be met to achieve accurate rates; a number of tests are outlined that can be applied to demonstrate that these assumptions are being meet.  相似文献