Supernova remnants, planetary nebulae and the distance to NGC 4214     

Michael A. Dopita  Daniela Calzetti  Jesús Maíz Apellániz  William P. Blair  Knox S. Long  Max Mutchler  Bradley C. Whitmore  Howard E. Bond  John MacKenty  Bruce Balick  Marcella Carollo  Michael Disney  Jay A. Frogel  Robert O’Connell  Donald Hall  Jon A. Holtzman  Randy A. Kimble  Patrick McCarthy  Francesco Paresce  Abhijit Saha  Alistair R. Walker  Joe Silk  Marco Sirianni  John Trauger  Rogier Windhorst  Erick Young 《Astrophysics and Space Science》2010,330(1):123-131

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.  相似文献   

Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism   总被引：5，自引：3，他引：2  

Galina P. Bulanova  Michael J. Walter  Chris B. Smith  Simon C. Kohn  Lora S. Armstrong  Jon Blundy  Luiz Gobbo 《Contributions to Mineralogy and Petrology》2010,160(4):489-510

We report on a suite of diamonds from the Cretaceous Collier 4 kimberlite pipe, Juina, Brazil, that are predominantly nitrogen-free type II crystals showing complex internal growth structures. Syngenetic mineral inclusions comprise calcium- and titanium-rich phases with perovskite stoichiometry, Ca-rich majoritic-garnet, clinopyroxene, olivine, TAPP phase, minerals with stoichiometries of CAS and K-hollandite phases, SiO₂, FeO, native iron, low-Ni sulfides, and Ca–Mg-carbonate. We divide the diamonds into three groups on the basis of the carbon isotope compositions (δ¹³C) of diamond core zones. Group 1 diamonds have heavy, mantle-like δ¹³C (−5 to −10‰) with mineral inclusions indicating a transition zone origin from mafic protoliths. Group 2 diamonds have intermediate δ¹³C (−12 to −15‰), with inclusion compositions indicating crystallization from near-primary and differentiated carbonated melts derived from oceanic crust in the deep upper mantle or transition zone. A ²⁰⁶Pb/²³⁸U age of 101 ± 7 Ma on a CaTiSi-perovskite inclusion (Group 2) is close to the kimberlite emplacement time (93.1 ± 1.5 Ma). Group 3 diamonds have extremely light δ¹³C (−25‰), and host inclusions have compositions akin to high-pressure–temperature phases expected to be stable in pelagic sediments subducted to transition zone depths. Collectively, the Collier 4 diamonds and their inclusions indicate multi-stage, polybaric growth histories in dynamically changing chemical environments. The young inclusion age, the ubiquitous chemical and isotopic characteristics indicative of subducted materials, and the regional tectonic history, suggest a model in which generation of sublithospheric diamonds and their inclusions, and the proto-kimberlite magmas, are related genetically, temporally and geographically to the interaction of subducted lithosphere and a Cretaceous plume.  相似文献   

The effects of spatial targeting of fishing effort on the distribution of the Norway lobster,Nephrops norvegicus,on the Farn Deeps grounds,northeast England     

Michael C. Bell  Jon M. Elson  Julian T Addison 《新西兰海洋与淡水研究杂志》2013,47(5):1023-1037

Nephrops norvegicus is an essentially sedentary species of lobster that forms the basis of valuable fisheries in the northwest Atlantic and western Mediterranean. Fishers exploiting a sedentary stock are likely to visit the most profitable (highest catch rate) areas first. Such spatial targeting of fishing effort is likely to have important consequences for stock monitoring and assessment. We used underwater television surveys of Nephrops burrow densities on the Farn Deeps grounds, northeast England, to describe changes in abundance and distribution between the beginning and end of a winter fishing season. Above a threshold of c. 0.6 burrows m^–2, overwinter depletion increased with burrow density, consistent with fishing effort being targeted at the highest densities. A simple simulation model showed that this pattern of mortality is an expected consequence of spatially targeted fishing behaviour. The model also predicted that there is decreased spatial variability in density after fishing. An overall decrease in variability was not evident from the survey data, but geostatistical analysis indicated that there was “flattening” of the density profile along a north‐south axis, consistent with the dominant direction of commercial trawling. We concluded that Nephrops fishers are able to find and exploit the highest densities of their target species. A potential consequence is that catch per unit effort (CPUE) data used to monitor trends in this stock potentially could mask declines in stock abundance. CPUE might be more effective if analysed at finer spatial scales, but this is not currently possible. In the absence of these fine scale commercial data, fishery‐independent surveys (e.g., underwater television) are an important source of information on trends in stock abundance.  相似文献   

A Robust Surface Matching Technique for Integrated Monitoring of Coastal Geohazards     

Pauline Miller  Jon Mills  Stuart Edwards  Paul Bryan  Stuart Marsh  Peter Hobbs 《Marine Geodesy》2013,36(1-2):109-123

At the dynamic coastal fringe, numerous processes interact with local morphology. In soft-cliff environments, this can often lead to the occurrence of coastal geohazards. These can pose a major threat to property and cultural heritage, and an effective monitoring strategy is therefore essential. While contemporary monitoring techniques have been applied, these are often unsuitable in isolation. This paper presents an integrated approach, with the development of weighted surface matching software enabling reliable dataset fusion and multi-temporal change detection, even where significant surface differences exist. Evaluation of this approach is presented and discussed.  相似文献   

Radar observations and the shape of near-Earth asteroid 2008 EV5     

Michael W. Busch  Steven J. Ostro  Lance A.M. Benner  Jon D. Giorgini  Daniel J. Scheeres  Michael C. Nolan  Patrick A. Taylor  Walter Brisken 《Icarus》2011,212(2):649-660

We observed the near-Earth ASTEROID 2008 EV5 with the Arecibo and Goldstone planetary radars and the Very Long Baseline Array during December 2008. EV5 rotates retrograde and its overall shape is a 400 ± 50 m oblate spheroid. The most prominent surface feature is a ridge parallel to the asteroid’s equator that is broken by a concavity about 150 m in diameter. Otherwise the asteroid’s surface is notably smooth on decameter scales. EV5’s radar and optical albedos are consistent with either rocky or stony-iron composition. The equatorial ridge is similar to structure seen on the rubble-pile near-Earth asteroid (66391) 1999 KW4 and is consistent with YORP spin-up reconfiguring the asteroid in the past. We interpret the concavity as an impact crater. Shaking during the impact and later regolith redistribution may have erased smaller features, explaining the general lack of decameter-scale surface structure.  相似文献   

Climate change,migration and adaptation in Funafuti,Tuvalu   总被引：1，自引：0，他引：1  

Colette Mortreux  Jon Barnett 《Global Environmental Change》2009,19(1):105-112

This paper shows the extent to which people in Funafuti – the main island of Tuvalu – are intending to migrate in response to climate change. It presents evidence collected from Funafuti to challenge the widely held assumption that climate change is, will, or should result in large-scale migration from Tuvalu. It shows that for most people climate change is not a reason for concern, let alone a reason to migrate, and that would-be migrants do not cite climate change as a reason to leave. People in Funafuti wish to remain living in Funafuti for reasons of lifestyle, culture and identity. Concerns about the impacts of climate change are not currently a significant driver of migration from Funafuti, and do not appear to be a significant influence on those who intend to migrate in the future.  相似文献   

The prize of peace (is eternal vigilance): a cautionary editorial essay on climate geopolitics   总被引：1，自引：1，他引：0  

Jon Barnett 《Climatic change》2009,96(1-2):1-6

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Trace element partitioning between orthopyroxene and anhydrous silicate melt on the lherzolite solidus from 1.1 to 3.2 GPa and 1,230 to 1,535°C in the model system Na<Subscript>2</Subscript>O–CaO–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>     

Dirk Frei  Axel Liebscher  Gerhard Franz  Bernd Wunder  Stephan Klemme  Jon Blundy 《Contributions to Mineralogy and Petrology》2009,157(4):473-490

We determined experimentally the Nernst distribution coefficient between orthopyroxene and anhydrous silicate melt for trace elements i in the system Na₂O–CaO–MgO–Al₂O₃–SiO₂ (NCMAS) along the dry model lherzolite solidus from 1.1 GPa/1,230°C up to 3.2 GPa/1,535°C in a piston cylinder apparatus. Major and trace element composition of melt and orthopyroxene were determined with a combination of electron microprobe and ion probe analyses. We provide partitioning data for trace elements Li, Be, B, K, Sc, Ti, V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Sm, Nd, Yb, Lu, Hf, Ta, Pb, U, and Th. The melts were chosen to be boninitic at 1.1 and 2.0 GPa, picritic at 2.3 GPa and komatiitic at 2.7 and 3.2 GPa. Orthopyroxene is Tschermakitic with 8 mol% Mg-Tschermaks MgAl[AlSiO₆] at 1.1 GPa while at higher pressure it has 18–20 mol%. The rare earth elements show a continuous, significant increase in compatibility with decreasing ionic radius from D _La^opx−melt ∼ 0.0008 to D _Lu^opx−melt ∼ 0.15. For the high-field-strength elements compatibility increases from D _Th^opx−melt ∼ 0.001 through D _Nb^opx−melt ∼ 0.0015, D _U^opx−melt ∼ 0.002, D _Ta^opx−melt ∼ 0.005, D _Zr^opx−melt ∼ 0.02 and D _Hf^opx−melt ∼ 0.04 to D _Ti^opx−melt ∼ 0.14. From mathematical and graphical fits we determined best-fit values for D ₀^M1, D ₀^M2, r ₀^M1, r ₀^M2, E ₀^M1, and E ₀^M2 for the two different M sites in orthopyroxene according to the lattice strain model and calculated the intracrystalline distribution between M1 and M2. Our data indicate extreme intracrystalline fractionation for most elements in orthopyroxene; for the divalent cations D _i ^M2−M1 varies by three orders of magnitude between D _Co^M2−M1 = 0.00098–0.00919 and D _Ba^M2−M1 = 2.3–28. Trivalent cations Al and Cr almost exclusively substitute on M1 while the other trivalent cations substitute on M2; D _La^M2−M1 reaches extreme values between 6.5 × 10⁷ and 1.4 × 10¹⁶. Tetravalent cations Ti, Hf, and Zr almost exclusively substitute on M1 while U and Th exclusively substitute on M2. Our new comprehensive data set can be used for polybaric-polythermal melting models along the Earth’s mantle solidus. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

‘I’ve paid to observe lions, not map roads!’ – An emotional journey with conservation volunteers in South Africa     

Jenny A. Cousins  James Evans  Jon P. Sadler 《Geoforum》2009,40(6):1069-1080

As fundamental as emotions may be in our experiences with wildlife, very little research addresses this topic. The following paper provides insight into the emotional responses of conservation volunteers participating on conservation holidays through four ethnographic case-studies. Six common emotional responses were identified: anguish, disappointment, frustration, exhilaration, awe and compassion. These emotional highs and lows shaped the volunteer experience, as the realities of wildlife conservation in South Africa upset the culturally constructed, emotionally appealing vision of African wilderness that the volunteers expected. While the positive emotions associated with idealised expectations of African wildlife provide an ideal basis upon which to commercialise nature conservation, they generate a series of tensions in practice. The paper makes an important empirical contribution to current debates surrounding the economic exploitation of affect, showing how emotions underpin the commercialisation of conservation, both through the configuration of the volunteers’ wildlife experiences and the scope of conservation that is practised.  相似文献   

Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target     

Marina Brozovic  Steven J. Ostro  Jon D. Giorgini  Randy Rose  Alice A. Hine  Daniel J. Scheeres 《Icarus》2009,201(1):153-166

Near-Earth Asteroid 4660 Nereus has been identified as a potential spacecraft target since its 1982 discovery because of the low delta-V required for a spacecraft rendezvous. However, surprisingly little is known about its physical characteristics. Here we report Arecibo (S-band, 2380-MHz, 13-cm) and Goldstone (X-band, 8560-MHz, 3.5-cm) radar observations of Nereus during its 2002 close approach. Analysis of an extensive dataset of delay-Doppler images and continuous wave (CW) spectra yields a model that resembles an ellipsoid with principal axis dimensions X=510±20 m, Y=330±20 m and . The pole direction is approximately located at ecliptic pole longitude and latitude of λ=+25°, β=+80° with the uncertainty radius of 10°. Our modeling yields a refined rotation period of 15.16±0.04 h. Nereus has a circular polarization (SC/OC) ratio of 0.74±0.08, which implies substantial near-surface centimeter-to-decimeter scale roughness. Dynamical analysis of our model suggests that YORP alteration of the rotation period may become evident within a few years. Nereus has two stable synchronous orbits where natural material may remain in orbit, while most asteroids observed to date do not have such stable synchronous orbits. We also find that spacecraft orbits about Nereus are feasible.  相似文献