A Quantitative Method to Optimise Magnetic Field Line Fitting of Observed Coronal Loops     

Carcedo  L.  Brown  D.S.  Hood  A.W.  Neukirch  T.  Wiegelmann  T. 《Solar physics》2003,218(1-2):29-40

Many authors use magnetic-field models to extrapolate the field in the solar corona from magnetic data in the photosphere. The accuracy of such extrapolations is usually judged qualitatively by eye, where a less judgemental quantitative approach would be more desirable. In this paper, a robust method for obtaining the best fit between a theoretical magnetic field and intensity observations of coronal loops on the solar disk will be presented. The method will be applied to Yohkoh data using a linear force-free field as an illustration. Any other theoretical model for the magnetic field can be used, provided there is enough freedom in the model to optimize the fit.  相似文献   

A lower limit to the field strength in magnetic reconnection sites in solar flares inferred from hard X-ray bursts     

Jon M. Loran  John C. Brown 《Astrophysics and Space Science》1985,117(1):173-177

It is shown how the hard X-ray burst count rate and itse-folding ime can be used to estimate the minimum magnetic fieldB _min required in a flare magnetic reconnection site for the burst to be interpreted in terms of a thick target model. Application of the method to data from the Solar Maximum Mission (HXRBS) indicates absolute minimum fields well in excess of 100 G, and impossibly high values for some reconnection geometries.  相似文献   

Weak lensing with COMBO-17: estimation and removal of intrinsic alignments     

Catherine Heymans  Michael Brown  Alan Heavens  Klaus Meisenheimer  y Taylor  Christian Wolf 《Monthly notices of the Royal Astronomical Society》2004,347(3):895-908

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Observations with the Visual and Infrared Mapping Spectrometer (VIMS) during Cassini's flyby of Jupiter     

R.H. Brown  K.H. Baines  J.-P. Bibring  F. Capaccioni  R.N. Clark  D.P. Cruikshank  V. Formisano  Y. Langevin  T.B. McCord  V. Mennella  P.D. Nicholson  C. Sotin  M.A. Chamberlain  G. Hansen  M. Showalter 《Icarus》2003,164(2):461-470

The Cassini Visual and Infrared Mapping Spectrometer (VIMS) is an imaging spectrometer covering the wavelength range 0.3-5.2 μm in 352 spectral channels, with a nominal instantaneous field of view of 0.5 mrad. The Cassini flyby of Jupiter represented a unique opportunity to accomplish two important goals: scientific observations of the jovian system and functional tests of the VIMS instrument under conditions similar to those expected to obtain during Cassini's 4-year tour of the saturnian system. Results acquired over a complete range of visual to near-infrared wavelengths from 0.3 to 5.2 μm are presented. First detections include methane fluorescence on Jupiter, a surprisingly high opposition surge on Europa, the first visual-near-IR spectra of Himalia and Jupiter's optically-thin ring system, and the first near-infrared observations of the rings over an extensive range of phase angles (0-120°). Similarities in the center-to-limb profiles of H⁺₃ and CH₄ emissions indicate that the H⁺₃ ionospheric density is solar-controlled outside of the auroral regions. The existence of jovian NH₃ absorption at 0.93 μm is confirmed. Himalia has a slightly reddish spectrum, an apparent absorption near 3 μm, and a geometric albedo of 0.06±0.01 at 2.2 μm (assuming an 85-km radius). If the 3-μm feature in Himalia's spectrum is eventually confirmed, it would be suggestive of the presence of water in some form, either free, bound, or incorporated in layer-lattice silicates. Finally, a mean ring-particle radius of 10 μm is found to be consistent with Mie-scattering models fit to VIMS near-infrared observations acquired over 0-120° phase angle.  相似文献   

Modelling enhanced density shells in the circumstellar envelope of IRC +10216     

J. M. Brown  T. J. Millar † 《Monthly notices of the Royal Astronomical Society》2003,339(4):1041-1047

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From the Workshop Organizers     

Allan Treiman 《Meteoritics & planetary science》2003,38(12):1711-1712

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Metals in tissues and skeleton of Fungia fungites from Phuket, Thailand     

L.S. Howard  B.E. Brown   《Marine pollution bulletin》1986,17(12):569-570

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Atomistic simulation of the mechanisms of noble gas incorporation in minerals     

Z. Du  N.L. Allan  J.A. Purton 《Geochimica et cosmochimica acta》2008,72(2):554-573

Atomistic simulations have been carried out to investigate the mechanisms of noble gas incorporation in minerals using both the traditional two-region approach and the “supercell” method. The traditional two-region approach has been used to calculate defect energies for Ne, Ar, Kr and Xe incorporation in MgO, CaO, diopside and forsterite in the static limit and at one atmosphere pressure. The possibilities of noble gas incorporation via both substitution and interstitial mechanisms are studied. The favored mechanism varies from mineral to mineral and from noble gas to noble gas. In all minerals studied, the variation of the solution energies of noble gas substitution with atomic radius appears approximately parabolic, analogous to those for 1⁺, 2⁺, 3⁺ and 4⁺ trace element incorporation on crystal lattice sites. Noble gas solution energies thus also fall on a curve, similar to those previously observed for cations with different charges, but with much lower curvature.The “supercell” method has been used to investigate the pressure dependence of noble gas incorporation in the same systems. Results indicate a large variation of the solubility of the larger noble gases, Kr and Xe with pressure. In addition, explicit simulation of incorporation at the (0 0 1) surface of MgO shows that the solubility of the heavier noble gases may be considerably enhanced by the presence of interfaces.  相似文献   

Participation in payments for ecosystem services: Case studies from the Lacandon rainforest, Mexico   总被引：3，自引：0，他引：3  

Nicolas Kosoy  Esteve Corbera  Kate Brown 《Geoforum》2008,39(6):2073-2083

Understanding people’s willingness to participate in projects and programmes of payments for ecosystem services (PES) has not been a key analytical concern of the scholarly literature around this new field of environmental policy and practice. This paper analyses participation in four communities benefiting from payments for biodiversity and carbon fixation in Mexico, and contrasts the results for each case with neighbouring communities that do not receive payments. We take a holistic approach that accounts for procedural rules, actors’ interactions, institutions and values, and individuals’ characteristics. We show that the nature of PES rules and the effectiveness of communication with government officers and NGOs influence resource managers’ ability and willingness to participate. We highlight community size, resource managers’ ability to diversify livelihood activities and local perspectives on the conservation of common forests, particularly sacred values and intergenerational concerns on forest conservation, as critical participation drivers. This analysis provides insights on why and how these new institutions may be attractive for some resource managers and permits to draw some recommendations for the future design of PES projects and programmes.  相似文献   

Nanoscale study of As biomineralization in an acid mine drainage system     

K. Benzerara  G. Morin  J. Miot  C. Casiot  F. Farges  G.E. Brown Jr. 《Geochimica et cosmochimica acta》2008,72(16):3949-3963

Spatial and seasonal variations of the oxidation of Fe(II) and As(III) have been previously documented in the Carnoulès (Gard, France) Acid Mine Drainage (AMD) by bulk analyses. These variations may be correlated with the variations in the activity of indigenous As(III)- and Fe(II)-oxidizing bacteria living in the As-rich Carnoulès water. The activity of these bacteria indeed plays an important role in the nature and composition of the solid phases that sequester arsenic at this site. In order to better understand the interactions of microbes with Fe and As in the Carnoulès AMD, we combined Transmission Electron Microscopy (TEM) and Scanning Transmission X-ray Microscopy (STXM) to collect near-edge X-ray absorption fine structure (NEXAFS) spectra at high spatial and energy resolution and to perform high spatial resolution imaging at the 30-50 nm scale. Spectromicroscopy was performed at the C K-edge, Fe L_2,3-edge, and As L_2,3-edge, which allowed us to locate living and/or mineralized bacterial cells and to characterize Fe and As oxidation states in the vicinity of those cells. TEM was used to image the same areas, providing higher resolution images and complementary crystallographic and compositional information through electron diffraction and EDXS analysis. This approach provides unique information on heterogeneous geochemical processes that occur in a complex microbial community in an AMD environment at the micrometer and submicrometer-scale. Bacterial cells in the Carnoulès AMD were frequently associated with mineral precipitates, and a variety of biomineralization patterns were observed. While many mineral precipitates were not associated with bacterial cells, they were associated with pervasive organic carbon. Finally, abundant biomineralized organic vesicles were observed in the Carnoulès AMD. Such vesicles may have been overlooked in highly mineralized extreme environments in the past and may represent an important component in a common biomineralization process in such environments.  相似文献