3D NIR spectroscopy at subarcsecond resolution     

Ruben J. Diaz  Horacio Dottori  Evencio Mediavilla  Maria Aguero  Damian Mast 《New Astronomy Reviews》2006,49(10-12):547

We present a scientific case approached through high quality 3D NIR spectroscopy performed with CIRPASS, attached to the Gemini South telescope. A binary mass concentration at the nucleus of the galaxy M 83 was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al. [BAAA 45 (2002) 98. Astroph#0505264] determined the possible position of the hidden secondary mass concentration with 2D H-alpha kinematics. The preliminary results of the NIR study presented here are based in almost 1500 spectra centered in the wavelength 1.3 μm, with a spectral resolving power of 3200. They allow us to unveil, with 0.36″ (6.4 pc) sampling and subarcsecond resolution, the velocity field in a region of 13″ × 9″ around the optical nucleus. We confirm that the optical nucleus is not located at the most important center of symmetry of the ionized gas velocity field. The largest black hole that could fit to the circular motion in this kinematic center should have a mass not larger than 3 × 10⁶(sin i)⁻¹ M solar masses.  相似文献   

Late Pleistocene fans and terraces in the Majes valley, southern Peru, and their relation to climatic variations     

Damian Steffen  Fritz Schlunegger  Frank Preusser 《International Journal of Earth Sciences》2010,99(8):1975-1989

This study investigates the connection between sediment aggradation, erosion and climate in a desert environment of the Majes valley, southern Peru. Luminescence dating of terraces and fans shows that sediment aggradation correlates with wet time intervals on the Altiplano, suggesting a climatic influence on the aggradation–degradation cycles. Major periods of aggradation occurred between ~110–100, ~60–50 and 12–8 ka. More precipitation in the Majes catchment resulted in increased erosion and transportation of sediment from the hillslopes into the trunk river. As a result, the sediment loads exceeded the transport capacity of the Majes River and aggradation started in the lower reaches where the river gradient is less. Depletion of the hillslope sediment reservoirs caused a relative increase in the capacity of the trunk river to entrain and transport sediment, resulting in erosion of the previously deposited sediment. Consequently, although climate change may initiate a phase of sediment accumulation, degradation can be triggered by an autocyclic negative feedback and does not have to be driven by climatic change.  相似文献   

'On the rocks': New Zealand's coastal bach landscape and the case of Rangitoto Island     

Robin Kearns  Damian Collins 《New Zealand geographer》2006,62(3):227-235

Abstract:  A distinctive feature of many of New Zealand's coastal landscapes has been the rudimentarily constructed holiday home known as a 'bach'. In recent years, however, rapidly escalating beachfront property prices, and the associated development of elite residential landscapes, have threatened the status of the bach. This commentary examines the diminishing number of 'classic' kiwi baches, and specifically considers the case of Rangitoto, a volcanic island close to central Auckland. Here, the location of baches on publicly owned land has been controversial and the small number that remains symbolize curiosities from another time and place.  相似文献   

Gold scavenged by bismuth melts: An example from Alpine shear-remobilizates in the Highiş Massif, Romania     

C. L. Ciobanu  N. J. Cook  F. Damian  G. Damian 《Mineralogy and Petrology》2006,87(3-4):351-384

Summary Gold mineralization occurs in the Şoimuş Ilii vein, the main Cu prospect in the Highiş Massif, Western Apuseni Mts., Romania. The Highiş Massif is part of the Highiş Biharia Shear Zone, a 320–300 Ma Variscan greenschist belt, with a 114–100 Ma Alpine overprint. In Highiş, phyllonites enclose an igneous core consisting of an Early Permian basic complex intruded by Middle Permian granitoids. The vein is hosted within basalt hornfels at its contact with the 264 Ma Jernova granite. Gold is not only present as native gold, but also as jonassonite (ideally AuBi₅S₄). The latter occurs as inclusions 1–30 μm in size in chalcopyrite; microanalysis gives the empirical formulae Au_1.02(Pb_0.47Bi_4.51)_4.98S_4. The two Au minerals are spatially associated with Bi–(Pb) sulfosalts (oversubstituted bismuthinite, cosalite) and sulfotellurides/selenides (ingodite, ikunolite and laitakarite) in blebs/patches, mainly hosted in chalcopyrite. This Au–Bi–Te association overprints an earlier, chalcopyrite-quartz assemblage, occurring as trails along discrete zones of brecciation that crosscut former mineral boundaries. Curvilinear and cuspate boundary textures within the blebs/patches suggest deposition in a molten form. Mineral associations in combination with phase relations indicate that the Au–Bi–Te association formed as a result of melting of pre-existing native Bi (and possibly sulfosalts) at 400 °C under sulfidation conditions. These melts incorporated Au, Pb, Te and S as they moved in the vein during shearing and were locked within dilational sites. Native Bi occurs as coarse aggregates along vein margins, but in the Au–Bi–Te association, it is present only as small droplets in shear gashes, never together with other Bi- and Au-minerals. The Bi-derived melts are part of an internal remobilizate which also includes chlorite and adularia. Minerals in the system Au–Bi–Te were deposited from a neutral low reducing fluid during Alpine shearing in the Early Cretaceous. The fluid also assisted solid-state mobilisation of chalcopyrite and cobaltite. This study illustrates the significant potential of Bi, a low melting-point chalcophile element (LMCE), to act as Au scavenger at temperatures as low as 400 °C.  相似文献   

An index to assess agricultural drought in India     

A. Chowdhury  P. G. Gore 《Theoretical and Applied Climatology》1989,40(3):103-109

Summary Crop drought or moisture stress is a function of the difference between actual evapotranspiration and evapotranspiration requirements of the crop under given atmospheric conditions.In the present work the climatic water balance approach is utilized to develop a crop moisture index for the kharif crop season over India.The difference between actual and climatologically derived evapotranspiration have been accumulated for different consecutive weeks of the crop season and made comparable in time and space through suitable weights. The lowest weighted deficit values have then been used for successive weeks to evolve the Crop Moisture Index. This index enables detection of degree of moisture stress experienced by the crop and can be used in drought monitoring.

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Zusammenfassung Dürre oder Feuchtestreß ist eine Funktion der Differenz zwischen tatsächlicher Verdunstung und dem Verdunstungsbedarf für bestimmte Kulturpflanzen unter gegebenen atmosphärischen Bedingungen. In vorliegender Studie wird die klimatische Wasserbilanz verwendet, um einen Feuchtigkeitsindex für die Kharif-Anbauzeit in Indien zu erstellen.Die Differenz zwischen aktueller und klimatologisch errechneter Verdunstung wurde für einige aufeinanderfolgende Wochen der Erntezeit aufsummiert und durch geeignete Gewichtungen in Zeit und Raum vergleichbar gemacht. Die am wenigsten veränderten Defizitwerte wurden dann für aufeinanderfolgende Wochen zur Errechnung eines Feuchtigkeitsindex herangezogen. Dieser Index ermöglicht die Quantifizierung des für die Pflanzen relevanten Feuchtestresses und kann für die Aufzeichnung von Dürren verwendet werden.

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With 2 Figures  相似文献   

Tethyan, Mediterranean, and Pacific analogues for the Neoproterozoic–Paleozoic birth and development of peri-Gondwanan terranes and their transfer to Laurentia and Laurussia     

J.Duncan Keppie  R.Damian Nance  J.Brendan Murphy  J. Dostal 《Tectonophysics》2003,365(1-4):195

Modern Tethyan, Mediterranean, and Pacific analogues are considered for several Appalachian, Caledonian, and Variscan terranes (Carolina, West and East Avalonia, Oaxaquia, Chortis, Maya, Suwannee, and Cadomia) that originated along the northern margin of Neoproterozoic Gondwana. These terranes record a protracted geological history that includes: (1) 1 Ga (Carolina, Avalonia, Oaxaquia, Chortis, and Suwannee) or 2 Ga (Cadomia) basement; (2) 750–600 Ma arc magmatism that diachronously switched to rift magmatism between 590 and 540 Ma, accompanied by development of rift basins and core complexes, in the absence of collisional orogenesis; (3) latest Neoproterozoic–Cambrian separation of Avalonia and Carolina from Gondwana leading to faunal endemism and the development of bordering passive margins; (4) Ordovician transport of Avalonia and Carolina across Iapetus terminating in Late Ordovician–Early Silurian accretion to the eastern Laurentian margin followed by dispersion along this margin; (5) Siluro-Devonian transfer of Cadomia across the Rheic Ocean; and (6) Permo-Carboniferous transfer of Oaxaquia, Chortis, Maya, and Suwannee during the amalgamation of Pangea. Three potential models are provided by more recent tectonic analogues: (1) an “accordion” model based on the orthogonal opening and closing of Alpine Tethys and the Mediterranean; (2) a “bulldozer” model based on forward-modelling of Australia during which oceanic plateaus are dispersed along the Australian plate margin; and (3) a “Baja” model based on the Pacific margin of North America where the diachronous replacement of subduction by transform faulting as a result of ridge–trench collision has been followed by rifting and the transfer of Baja California to the Pacific Plate. Future transport and accretion along the western Laurentian margin may mimic that of Baja British Columbia. Present geological data for Avalonia and Carolina favour a transition from a “Baja” model to a “bulldozer” model. By analogy with the eastern Pacific, we name the oceanic plates off northern Gondwana: Merlin (≡Farallon), Morgana (≡Pacific), and Mordred (≡Kula). If Neoproterozoic subduction was towards Gondwana, application of this combined model requires a total rotation of East Avalonia and Carolina through 180° either during separation (using a western Transverse Ranges model), during accretion (using a Baja British Columbia “train wreck” model), or during dispersion (using an Australia “bulldozer” model). On the other hand, Siluro-Devonian orthogonal transfer (“accordion” model) from northern Africa to southern Laurussia followed by a Carboniferous “Baja” model appears to best fit the existing data for Cadomia. Finally, Oaxaquia, Chortis, Maya, and Suwannee appear to have been transported along the margin of Gondwana until it collided with southern Laurentia on whose margin they were stranded following the breakup of Pangea. Forward modeling of a closing Mediterranean followed by breakup on the African margin may provide a modern analogue. These actualistic models differ in their dictates on the initial distribution of the peri-Gondwanan terranes and can be tested by comparing features of the modern analogues with their ancient tectonic counterparts.  相似文献   

The oxidation states of copper and iron in mineral sulfides, and the oxides formed on initial exposure of chalcopyrite and bornite to air     

Siew Wei Goh  Robert N. Lamb  Damian Moran 《Geochimica et cosmochimica acta》2006,70(9):2210-2228

Metal L_2,3, sulfur K and oxygen K near-edge X-ray absorption fine structure (NEXAFS) spectra for chalcopyrite, bornite, chalcocite, covellite, pyrrhotite and pyrite have been determined from single-piece natural mineral specimens in order to assess claims that chalcopyrite should be regarded as Cu^IIFe^IIS₂ rather than Cu^IFe^IIIS₂, and that copper oxide species are the principal initial oxidation products on chalcopyrite and bornite exposed to air. Spectra were obtained using both fluorescence and electron yields to obtain information representative of the bulk as well as the surface. Where appropriate, NEXAFS spectra have been interpreted by comparison with the densities of unfilled states and simulated spectra derived from ab initio calculations using primarily the FEFF8 code and to a lesser extent WIEN2k. Metal 2p and S 2p photoelectron spectra excited by monochromatised Al K_α X-rays were determined for each of the surfaces characterised by NEXAFS spectroscopy. The X-ray excited Cu LMM Auger spectrum was also determined for each copper-containing sulfide. FEFF8 calculations were able to simulate the experimental NEXAFS spectra quite well in most cases. For covellite and chalcocite, it was found that FEFF8 did not provide a good simulation of the Cu L₃-edge spectra, but WIEN2k simulations were in close agreement with the experimental spectra. Largely on the basis of these simulations, it was concluded that there was no convincing evidence for chalcopyrite to be represented as Cu^IIFe^IIS₂, and no strong argument for some of the Cu in either bornite or covellite to be regarded as Cu(II). The ab initio calculations for chalcopyrite and bornite indicated that the density of Cu d-states immediately above the Fermi level was sufficient to account for the Cu L₃-edge absorption spectrum, however these incompletely filled Cu d-states should not be interpreted as indicating some Cu(II) in the sulfide structure. It was also concluded that the X-ray absorption spectra were quite consistent with the initial oxidation products on chalcopyrite and bornite surfaces being iron oxide species, and inconsistent with the concomitant formation of copper-oxygen species.  相似文献   

Saline degradation of Indian agricultural lands : A case study in Khambhat Taluka,Gujarat state (India), using satellite remote sensing     

Sandhya R. Gore  K.A. Bhagwat 《国际地球制图》2013,28(3):5-13

In certain agricultural fields of Khambhat Taluka in Gujarat State, the salinity has increased considerably rendering the land completely infertile. The occurrence of salinity in this area can be attributed partly to subsurface sea‐water ingress and partly to improper land and water management practices prior to implementation of irrigation. Landsat MSS or TM and IRS IA LISS II data was used to test the feasibility of delineating saline soils by both visual image interpretation and digital analysis. The study of saline soils using multi‐temporal Landsat images of the year 1977, 1983, and 1987, indicated an evident increase in saline areas in past few years. The Soil Brightness Index (SBI) generated from the IRS‐IA data by the application of MSS equivalent coefficients brought out different categories of soil degradation. The supervised classification scheme aided in generating various salinity levels. The analysis of the soil samples of the above area exhibited increasing values of Electrical Conductivity (ECe), and the soluble cations with increasing levels of salinity.  相似文献   

Observations and implications of damage from the magnitude Mw 6.3 Christchurch, New Zealand earthquake of 22 February 2011   总被引：1，自引：1，他引：0  

Sean Wilkinson  Damian Grant  Elizabeth Williams  Sara Paganoni  Stuart Fraser  David Boon  Anna Mason  Matthew Free 《Bulletin of Earthquake Engineering》2013,11(1):107-140

This paper describes the observations made by a reconnaissance team following the 22nd February 2011, M_w 6.3, Christchurch, New Zealand earthquake (GNS Science, 2011). The team comprised of members of the UK based Earthquake Engineering Field Investigation Team who spent 5 days collecting observations on damage resulting from the earthquake. Although the magnitude of this earthquake was not particularly high (M_w 6.3), the shallow focus and close proximity resulted in locally very high ground motions, widespread damage and 182 fatalities. The earthquake is also particularly notable for the widespread liquefaction it caused, landslides and rockfalls in the hills south of Christchurch, and the significant damage suffered by unreinforced masonry and historic structures. Over wide areas of central Christchurch, recorded accelerations were in excess of those required by the current New Zealand seismic loadings standard (NZS1170.5:2004: Standards New Zealand 2004) and therefore the earthquake presented a valuable opportunity to assess performance of modern buildings under code-level ground acceleration.  相似文献   

Potential geodynamic relationships between the development of peripheral orogens along the northern margin of Gondwana and the amalgamation of West Gondwana     

J. Brendan Murphy  Sergei Pisarevsky  R. Damian Nance 《Mineralogy and Petrology》2013,107(5):635-650

The Neoproterozoic-Early Cambrian evolution of peri-Gondwanan terranes (e.g. Avalonia, Carolinia, Cadomia) along the northern (Amazonia, West Africa) margin of Gondwana provides insights into the amalgamation of West Gondwana. The main phase of tectonothermal activity occurred between ca. 640–540 Ma and produced voluminous arc-related igneous and sedimentary successions related to subduction beneath the northern Gondwana margin. Subduction was not terminated by continental collision so that these terranes continued to face an open ocean into the Cambrian. Prior to the main phase of tectonothermal activity, Sm-Nd isotopic studies suggest that the basement of Avalonia, Carolinia and part of Cadomia was juvenile lithosphere generated between 0.8 and 1.1 Ga within the peri-Rodinian (Mirovoi) ocean. Vestiges of primitive 760–670 Ma arcs developed upon this lithosphere are preserved. Juvenile lithosphere generated between 0.8 and 1.1 Ga also underlies arcs formed in the Brazilide Ocean between the converging Congo/São Francisco and West Africa/Amazonia cratons (e.g. the Tocantins province of Brazil). Together, these juvenile arc assemblages with similar isotopic characteristics may reflect subduction in the Mirovoi and Brazilide oceans as a compensation for the ongoing breakup of Rodinia and the generation of the Paleopacific. Unlike the peri-Gondwanan terranes, however, arc magmatism in the Brazilide Ocean was terminated by continent-continent collisions and the resulting orogens became located within the interior of an amalgamated West Gondwana. Accretion of juvenile peri-Gondwanan terranes to the northern Gondwanan margin occurred in a piecemeal fashion between 650 and 600 Ma, after which subduction stepped outboard to produce the relatively mature and voluminous main arc phase along the periphery of West Gondwana. This accretionary event may be a far-field response to the breakup of Rodinia. The geodynamic relationship between the closure of the Brazilide Ocean, the collision between the Congo/São Francisco and Amazonia/West Africa cratons, and the tectonic evolution of the peri-Gondwanan terranes may be broadly analogous to the Mesozoic-Cenozoic closure of the Tethys Ocean, the collision between India and Asia beginning at ca. 50 Ma, and the tectonic evolution of the western Pacific Ocean.  相似文献