The Production of Methanol by Flowering Plants and the Global Cycle of Methanol   总被引：10，自引：0，他引：10  

I. E. Galbally  W. Kirstine 《Journal of Atmospheric Chemistry》2002,43(3):195-229

Methanol has been recognised as an important constituent of the background atmosphere, but little is known about its overall cycle in the biosphere/atmosphere system. A model is proposed for the production and emission to the atmosphere of methanol by flowering plants based on plant structure and metabolic properties, particularly the demethylation of pectin in the primary cell walls. This model provides a framework to extend seven sets of measurements of methanol emission rates to the global terrestrial biosphere. A global rate of release of methanol from plants to the atmosphere of 100 Tg y^–1 is calculated. A separate model of the global cycle of methanol is constructed involving emissions from plant growth and decay, atmospheric and oceanic chemical production, biomass burning and industrial production. Removal processes occur through hydroxyl radical attack in the atmosphere, in clouds and oceans, and wet and dry deposition. The model successfully reproduces the methanol concentrations in the continental boundary-layer and the free atmosphere, including the inter-hemispheric gradient in the free atmosphere. The model demonstrates a new concept in global biogeochemistry, the coupling of plant cell growth with the global atmospheric concentration of methanol. The model indicates that the ocean provides a storage reservoir capable of holding at least 66 times more methanol than the atmosphere. The ocean surface layer reservoir essentially buffers the atmospheric concentration of methanol, providing a physically based smoothing mechanism with a time constant of the order of one year.  相似文献   

Elemental particle size distributions. Measured and estimated dry deposition in Sfax region (Tunisia)     

M. Masmoudi  I. Belghith  M. Chaabane 《Atmospheric Research》2002,63(3-4)

Mass size distribution of the crustal elements (Al, Ca, Fe, Mg, Si, Ti), anthropogenic elements (Zn, Mn, Cr, Cu, K, P, Pb) and sea elements (Na, Cl) were obtained from measurements carried out with an inertial cascade impactor in Sfax. A fitting procedure by data inversion was applied to those data. This procedure yields accurate size distributions of aerosols in the diameter range 0.1–25 μm in two different sites. In a coastal industrial site, the mass distribution of the aerosol showed a bimodal structure; and in urban area, the lower particle mode cannot be observed. The elemental dry deposition flux was calculated as a function of particle size. The element flux size distribution increased rapidly with particle size. The modelling results indicate that the majority of the crustal and anthropogenic elements flux (>90%) was due to particles larger than 3 μm in diameter.  相似文献   

Variability of the photospheric radiation of active K-M dwarfs and their X-ray luminosities     

N. I. Bondar’ 《Astronomy Reports》2002,46(6):489-496

Variability of the photospheric radiation of 40 (dKe-dMe) dwarfs in the solar neighborhood due to variations in the spottedness of their surfaces is analyzed based on the behavior of their mean annual brightnesses over long time intervals. The amplitudes and characteristic time scales of the variations of the mean annual brightness are taken to be indicators of photospheric activity and were used to infer the levels of photospheric activity in the stars studied. The influence of axial rotation on the development of cyclic activity in young red dwarfs and F-M main-sequence stars is analyzed. The durations and amplitudes of the photospheric variability of rapidly rotating (dK0e-dK5e) stars testifies to a higher level of photospheric activity among red dwarfs and solar-type stars. The X-ray luminosities of these stars grow with the amplitude of the variations of the mean annual brightness. However, this is not typical of rapidly rotating M dwarfs, for which the X-ray emission varies by more than two orders of magnitude, although their degrees of spottedness are all virtually the same. A linear relationship between the X-ray and bolometric luminosities is observed for young (dKe-dMe) stars, with their ratios log(L _x/L _bol) being about ?3. These properties can be used to determine whether a red dwarf is a young star or is already on the main sequence.  相似文献   

Spatial structure of the old open cluster NGC 2420     

Z. I. Peikov  R. M. Rusev  T. Ruseva 《Astronomy Reports》2002,46(4):267-274

The spatial structure of the intermediate and outer regions of the old open cluster NGC 2420 is analyzed using data from the catalog of Paparó. The differential and integrated distributions of the projected [ΔF(r) and F(r)] and spatial [Δf(r) and f(r)] stellar densities are obtained for various subsystems of cluster stars using Kholopov’s star-count method. Analysis of these curves shows that: (1) the cluster has at least three distinct spatial zones with different stellar-density gradients, (2) the each cluster subsystem has a layered structure, and (3) the spatial structure of the cluster changes systematically in the transition to subsystems containing fainter main-sequence stars. Empirical relations describing the structure of the cluster are also derived. Similar structural features can also be found in other globular and open clusters.  相似文献   

Prediction of Ground Vibrations due to Construction Blasts in Different Types of Rock   总被引：1，自引：1，他引：1  

G. R. Tripathy  I. D. Gupta 《Rock Mechanics and Rock Engineering》2002,35(3):195-204

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A non-linear stress-stiffness model for geomaterials at small to intermediate strains     

S. Shibuya 《Geotechnical and Geological Engineering》2002,20(4):333-369

A double exponential fitting model (DEFM) capable of expressing the non-linear stress-stiffness relationship of geomaterials has been proposed by Shibuya et al. (1997). The model comprises two material constants; the elastic stiffness at very small strains and the strength, together with other free parameters to determine the complete stress-stiffness relationship. In this paper, the capability of the original function used for DEFM in simulating the tangent stiffness-stress relationship of geomaterials is first discussed. Second, the methods for determining the free model parameters, as well as its conversion to obtain a stress-strain relationship are proposed. The applicability of DEFM to predicting non-linear stress-stiffness relationship is examined in detail in a total of forty-nine fitting cases of compression test data on sedimentary rock, artificial soft rock and soft clay. It is found that the DEFM is effective in expressing the non-linear stress-stiffness relationship of various kinds of geomaterials at small to intermediate strains, say less than 0.5%. The superiority of this model compared to other fitting models currently in use is also demonstrated in some of the fitting cases.  相似文献   

Specific Compositional Features of Sediments from the Haakon Mosby Mud Volcano,Southwestern Barents Sea     

Krupskaya  V. V.  Andreeva  I. A.  Sergeeva  E. I.  Cherkashev  G. A. 《Lithology and Mineral Resources》2002,37(2):130-137

The submarine Haakon Mosby mud volcano was studied in detail during several cruises, resulting in the collection of an abundant and diverse lithological material. Comprehensive field and laboratory studies made it possible to identify different types of sediments with specific granulometric and pelite fraction (<0.005 mm) compositions, as well as the regularity of their spatial distribution relative to various morphostructural zones of the mud volcano.  相似文献   

Nature, age, and tectonic setting of granitoid-hosted, orogenic gold deposits of the Jiaodong Peninsula, eastern North China craton, China   总被引：28，自引：0，他引：28  

Yumin Qiu  David I. Groves  Neal J. McNaughton  Liang-gen Wang  Taihe Zhou 《Mineralium Deposita》2002,37(3-4):283-305

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Marymia: an Archean, amphibolite facies-hosted, orogenic lode-gold deposit overprinted by Palaeoproterozoic orogenesis and base metal mineralisation, Western Australia     

Noreen M. Vielreicher  John R. Ridley  David I. Groves 《Mineralium Deposita》2002,37(8):737-764

The Marymia gold deposit, comprising two orebodies, Keillor 1 and Keillor 2, is at the northern end of the Plutonic Well greenstone belt in the Marymia Inlier, in the southern Capricorn Orogen, just north of the Yilgarn craton. The Marymia Inlier is a discrete fault-bounded Archean gneiss-granitoid-greenstone domain surrounded by sedimentary basins that were formed and variably metamorphosed and deformed during several Palaeoproterozoic orogenic cycles. The greenstone sequence at Marymia is stratigraphically and geochemically similar to greenstone sequences in the Yilgarn craton, but was subjected to further deformation and metamorphism in the Palaeoproterozoic. Late Archean deformation (D1-D2) was ductile to brittle-ductile in style, whereas Palaeoproterozoic deformation was predominantly brittle. Equilibrium mineral assemblages indicate that peak amphibolite-facies metamorphism (540-575 °C, <3 kb) was overprinted by greenschist-facies metamorphism (300-360 °C). Petrographic textures indicate that prograde metamorphism was coeval with D1-D2, with peak metamorphism early to syn D2. Gold mineralisation at Marymia is hosted in metamorphosed tholeiitic basalts and banded iron formation. On a gross scale, the distribution of gold is controlled by D2 folds and shear zones. Lithological contacts with strong rheological or chemical contrasts provide local controls. Gold-related alteration comprises subtle millimetre- to centimetre-wide zones of silicification with variable amounts of quartz, hornblende, biotite, K-feldspar, plagioclase, calcite/siderite, scheelite, titanite, epidote, sulfide and telluride minerals. Quartz veins are generally narrow and discontinuous with low total volume of quartz. Gold is sited in the wall rock, at vein salvedges or within stringers of wall rock within veins. There are two distinct opaque-mineral assemblages: pyrite-pyrrhotite-chalcopyrite-galena and hessite-petzite-altaite-Bi-telluride-galena. Ore samples are variably enriched in Ag, Te, Pb, W, Cu, S and Fe reflecting heterogeneity of the ore mineralogy. Structural timing and temperature of formation of alteration and ore minerals support deposition of gold during late peak amphibolite-facies metamorphism from neutral to alkaline (pH=5-6), moderately oxidising (log P_O2,-21-22) and CO₂-bearing (X_CO2 Ƹ.2) fluids. The total sulfur content of the fluid is estimated at 1mDS. Lead isotope compositions support derivation of lead from within the local greenstone sequence. Gold lodes were deformed by faults and shear zones in the Palaeoproterozoic, with only limited remobilisation. Subeconomic, carbonate vein- and breccia-hosted base metal mineralisation is locally hosted within Palaeoproterozoic fault zones, which clearly cut gold lodes. Base-metal-related alteration is characterised by intense carbonatisation, chloritisation, and albitisation of the mafic host rocks. Mineral assemblages are consistent with formation at greenschist facies conditions. Lead isotope compositions support crystallisation at ca. 1.7 Ga from lead that is similar in composition to earlier gold-related galena.  相似文献   

Origin of prolonged X-ray flares on active late-type stars     

I. M. Livshits  M. A. Livshits 《Astronomy Reports》2002,46(4):327-338

Soft X-ray data for prolonged flares in subgiants in RS CVn binary systems and some other active late-type stars (AB Dor, Algol) are analyzed. During these nonstationary events, a large amount of hot plasma with temperatures exceeding 10⁸ K exists for many hours. Numerical simulations of gas-dynamical processes in the X-ray source—giant loops—can yield reliable estimates of the plasma parameters and flare-source size. This confirms that such phenomena exist while considerable energy is supplied to the top part of a giant loop or system of loops. Refined estimates of the flare energy (up to 10³⁷ erg) and scales contradict the widely accepted idea that prolonged X-ray flares are associated with the evolution of local magnetic fields. The energy of the current component of the large-scale magnetic field arising during the ejection of magnetic field by plasma jets or stellar wind is estimated. Two cases are considered: a global stellar field and fields connecting regions with oppositely directed unipolar magnetic fields. The inferred energy of the current component of the magnetic field associated with distortion of the initial MHD configuration is close to the total flare energy, suggesting that large-scale magnetic fields play an important role in prolonged flares. The flare process encompasses some portion of a streamer belt and may propagate along the entire magnetic equator of the star during the most powerful prolonged events.  相似文献