Effects of vertical boundaries on infinite Prandtl number thermal convection   总被引：1，自引：0，他引：1  

Jun Korenaga  Thomas H. Jordan 《Geophysical Journal International》2001,147(3):639-659

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Occurrence and morphology of pyrite in Bulgarian coals   总被引：2，自引：0，他引：2  

Jordan Kortenski  Irena Kostova 《International Journal of Coal Geology》1996,29(4):273-290

Coals with different degrees of coalification (ranging from lignite to anthracite) from seven Bulgarian coal basins have been investigated. The forms of pyrite and their distribution have been established. The types found are: massive pyrite, represented by the homogeneous, cluster-like and microconcretionary varieties; framboidal pyrite, appearing in inorganic and bacterial forms; euhedral pyrite, which is either isolated or clustered; anhedral pyrite, in its infilling and replacement varieties; and infiltrational pyrite, as a replacement or infilling mineral.Most of the forms of the euhedral, framboidal and massive pyrite developed during peat deposition. The anhedral replacement pyrite formed in the peat bed during early diagenesis. Infiltrational pyrite filled fractures and cleats formed during the diagenesis, catagenesis and metagenesis.Both similarities and differences with respect to the distribution of the pyrite types have been determined between coals of different ranks from Bulgarian coal basins. These differences are due to: the presence of Fe and S in the rocks adjacent to ancient peat bogs; the activities of ground and surface waters which brought Fe and S into the peat bogs; the geochemical character (pH and Eh) of the peat bogs and the sulphur bacteria development; and the tectonic situation during diagenesis, catagenesis and metagenesis.  相似文献   

Further aspects of weak shock theory applied to the solar chromosphere     

Stuart D. Jordan 《Solar physics》1973,30(2):327-334

The low chromosphere now seems definitely to require mechanical heating, and dissipation of initially acoustic waves by shocking is one of the most promising possibilities. Results of recent calculations indicate that the weak shock theory may be applicable here, but discrepancies exist among various applications of this theory, and the explanations offered to date are not completely satisfactory. It is shown here that the different approximations used by different authors to evaluate the mechanical flux integral play an important role in producing these discrepancies, in addition to the already well known effects of the density scale heights and the wave periods. Arguments are presented favoring Ulmschneider's method for evaluation of this flux integral.  相似文献   

The relative intensities of CI lines in the solar EUV spectrum     

Carole Jordan 《Solar physics》1967,2(4):441-450

The relative intensity of two Ci lines at 1993.6 Å and 1657.4 Å, observed in the limb spectrum of the sun, is a factor 2.6 × 10³ larger than that expected if both lines were optically thin. It is shown that the observed intensity ratio may be explained in terms of the transfer of photons from 1657.4 Å to 1993.6 Å due to a large optical depth in the line at 1657.4 Å. The observed upper limit on the relative intensity of two further lines at 1992.0 Å and 1657.0 Å has been used to show that the line at 1993.6 Å is optically thin. Hence it is shown that (1657.4 Å) = 1300, and (1993.6 Å) = 0.44. These values provide an independent evaluation of optical depths against which chromospheric models may be checked. Assuming a mean temperature of T _e = 8000 °K, and a mean scale height of 350 km, the optical depths lead to a mean hydrogen-particle density of N (H) = 1.4 × 10¹² cm^–3.  相似文献   

Properties and depositional environment of the Neogene Elhovo Lignite, Bulgaria     

Alexander Zdravkov  Irena Kostova  Jordan Kortenski 《International Journal of Coal Geology》2007,71(4):488

Several Mio-Pliocene aged lignite seams occur as part of a non-marine transgressive sequence in the Elhovo graben in south-eastern Bulgaria. The present study is focused on 45 samples collected from three boreholes in the eastern part of the basin. Petrographic data along with ash and sulphur contents were used in order to determine the lateral and vertical variations of the coal facies and depositional environment of the Elhovo lignite.The lignite seams accumulated in a rheotrophic, low-lying mire with high pH value and are characterized by high ash yields and sulphur contents. Despite of the neutral to weakly alkaline environment the bacterial activity was limited and the tissue preservation and gelification were mainly controlled by the redox conditions.Vegetation rich in decay resistant conifers dominated in the Elhovo basin together with mesophytic angiosperm species. The absence of algal remains and sapropelic coal indicated that open water areas were not present during peat accumulation. The latter processed in an environment, characterized by low subsidence rate, in which prior to the burial the woods were subjected to severe mechanical destruction. According to our interpretation, the enhanced impregnation of the tissues bacteria and fungi played only a secondary role in the process of humification. The lignite from borehole 122 and partly from BH 145 deposited in an environment characterized by relatively low (ground)water table, whereas to the south an area dominated by a flooded forest swamp (BH 104) formed. This is suggested by the better tissue preservation and gelification of the organic matter in BH 104. The vertical variation of the maceral composition in the studied lignite is interpreted as a consequence of vegetational changes, rather than to changes in the depositional environment. The low contents of inertinite macerals indicate that despite of the low water level the environment was relatively wet and the thermal and oxidative destruction of the tissues was limited.Peat accumulation was terminated by a major flooding event and a short term establishment of a lake. In contrast to the West Maritsa basin, no seam formed in the Elhovo basin during the filling stage of the lake.  相似文献   

Using Strong Solar Coronal Emission Lines as Coronal Flux Proxies     

Falconer  David A.  Jordan  Stuart D.  Brosius  Jeffrey W.  Davila  Joseph M.  Thomas  Roger J.  Andreatta  Vicenzo  Hara  Hirohisa 《Solar physics》1998,180(1-2):179-191

We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv 284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the cooler Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 Ú line formation problem are also briefly considered.  相似文献   

Sensitivity of frequency-dependent traveltimes to laterally heterogeneous, anisotropic Earth structure     

Li Zhao  & Thomas H. Jordan 《Geophysical Journal International》1998,133(3):683-704

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Erratum to: Variability of gas composition and flux intensity in natural marine hydrocarbon seeps     

Jordan F. Clark  Libe Washburn  Katherine Schwager Emery 《Geo-Marine Letters》2010,30(3-4):389-389

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Last interglacial climates of south-eastern Australia: plant and beetle-based reconstructions from Yarra Creek,King Island,Tasmania     

Nick Porch  Gregory J. Jordan  David M. Price  Richard W. Barnes  Mike K. Macphail  Mike Pemberton 《Quaternary Science Reviews》2009,28(27-28):3197-3210

This paper explores the palaeoclimatic significance of a fossil plant and insect record from Yarra Creek, on King Island, between Tasmania and the Australian mainland. The record dates, based upon a thermoluminescence chronology and other evidence, to Marine Isotope Stage 5 (MIS 5); the exact timing is impossible to ascertain given the resolution of the thermoluminescence results and the presence of an unconformity in the dated section. The presence of a cool-temperate rainforest flora, outside its modern range, and other independent evidence, suggest the sequence may represent the last interglacial (MIS 5e) rather than a later MIS 5 substage. Using coexistence methods that compare modern climatic ranges of the taxa in the assemblage we reconstruct independent beetle and plant based annual and seasonal temperate and precipitation parameters. The results imply the assemblage was deposited under a wetter summer climate and suggest conditions of enhanced temperature seasonality. It is probable that enhanced temperature seasonality is a methodological artefact reflecting the rarity of extremely equable climates (like King Island) in modern climate space. This would indicate a limitation of most methods of palaeoclimatic reconstruction that rely on modern datasets – it is only possible to reconstruct past climates as being within the range of values in that currently exist in modern climate space.  相似文献   

O i line emission in cool stars: calculations using partial redistribution     

R. Koncewicz  C. Jordan 《Monthly notices of the Royal Astronomical Society》2007,374(1):220-231

Radiative transfer calculations have been performed for five cool stars: α Tau, β Gem, Procyon, ε Eri and the Sun, for the purpose of investigating the behaviour of the O  i emission over a wide range of stellar types, and its dependence on coherent photon scattering. These stars span a range of spectral types from F5 iv – v to K5 iii and surface gravities  1.25 < log  g * < 4.75  . Particular attention has been paid to the calculation of the flux in the resonance triplet around 1305 Å which is pumped by H Lyβ, including the effects of partial redistribution (PRD) and cross-redistribution of photons. These are the first calculations for the resonance triplet in giant stars using a full PRD treatment. Calculations of the predominantly collisionally excited intersystem doublet at 1355, 1358 Å are included, and it is found that the ratio of these fluxes shows the effects of opacity. The flux in the forbidden line at 1641 Å is calculated for the giant stars and the effects of coherent scattering on this line are investigated. The discrepancy between the calculated and observed fluxes in the O  i lines is used to infer the inadequacy of single-component chromospheric models.  相似文献