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211.
Marina Brozovi? Lance A.M. Benner Michael C. Nolan Christopher Magri Jon D. Giorgini Petr Pravec Julia Fang Michael W. Busch Daniel E. Reichart Joshua B. Haislip Joseph Jao Kenneth J. Lawrence 《Icarus》2011,216(1):241-256
We report radar, photometric, and spectroscopic observations of near-Earth Asteroid (136617) 1994 CC. The radar measurements were obtained at Goldstone (8560 MHz, 3.5 cm) and Arecibo (2380 MHz, 12.6 cm) on 9 days following the asteroid’s approach within 0.0168 AU on June 10, 2009. 1994 CC was also observed with the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) on May 21 and June 1-3. Visible-wavelength spectroscopy was obtained with the 5-m Hale telescope at Palomar on August 25. Delay-Doppler radar images reveal that 1994 CC is a triple system; along with (153591) 2001 SN263, this is only the second confirmed triple in the near-Earth population. Photometry obtained with PROMPT yields a rotation period for the primary P = 2.38860 ± 0.00009 h and a lightcurve amplitude of ∼0.1 mag suggesting a shape with low elongation. Hale telescope spectroscopy indicates that 1994 CC is an Sq-class object. Delay-Doppler radar images and shape modeling reveal that the primary has an effective diameter of 0.62 ± 0.06 km, low pole-on elongation, few obvious surface features, and a prominent equatorial ridge and sloped hemispheres that closely resemble those seen on the primary of binary near-Earth Asteroid (66391) 1999 KW4. Detailed orbit fitting reported separately by Fang et al. (Fang, J., Margot, J.-L., Brozovic, M., Nolan, M.C., Benner, L.A.M., Taylor, P.A. [2011]. Astron. J. 141, 154-168) gives a mass of the primary of 2.6 × 1011 kg that, coupled with the effective diameter, yields a bulk density of 2.1 ± 0.6 g cm−3. The images constrain the diameters of the inner and outer satellites to be 113 ± 30 m and 80 ± 30 m, respectively. The inner satellite has a semimajor axis of ∼1.7 km (∼5.5 primary radii), an orbital period of ∼30 h, and its Doppler dispersion suggests relatively slow rotation, 26 ± 12 h, consistent with spin-orbit lock. The outer satellite has an orbital period of ∼9 days and a rotation period of 14 ± 7 h, establishing that the rotation is not spin-orbit locked. Among all binary and triple systems observed by radar, at least 25% (7/28) have a satellite that rotates more rapidly than its orbital period. This suggests that asynchronous configurations with Protation < Porbital are relatively common among multiple systems in the near-Earth population. 1994 CC’s outer satellite has an observed maximum separation from the primary of ∼5.7 km (∼18.4 primary radii) that is the largest separation relative to primary radius seen to date among all 36 known binary and triple NEA systems. 1994 CC, (153591) 2001 SN263, and 1998 ST27 are the only triple and binary systems known with satellite separations >10 primary radii, suggesting either a detection bias, or that such widely-separated satellites are relatively uncommon in NEA multiple systems. 相似文献
212.
在调查、分析洋沙泡周边地质、水文地质和氟土壤特征的基础上,结合洋沙泡水库模拟实验结果对吉林西部洋沙泡水库高氟水的形成进行了深入研究。结果表明,吉林西部高氟环境的形成是地表环境长期演化的结果:大兴安岭岩浆岩和松嫩低平原松散沉积物提供了含氟丰富的物质基础,河流及地下水径流提供了氟迁移的动力条件,典型的低平原是高氟形成的地理条件,干旱半干旱的气候条件成为高氟环境的促进条件。洋沙泡的氟主要来源为二龙涛河径流携带,多年平均携带量占年内氟总来源的99%以上;周边径流占0.014%~0.28%;降水携带量占0.012%;蒸发浓缩作用对洋沙泡水库的氟质量浓度也有一定影响。此外,内源底泥的释放也是洋沙泡水库水体氟质量浓度增高的原因之一,并且在引嫩入白工程实施后,依然使洋沙泡水库水体中氟质量浓度增加。在每年引水的情况下,需要5年时间水库水体氟的质量浓度才会降至1.0mg/L以下。风动力和人为活动也对洋沙泡水库的氟质量浓度变化产生影响。 相似文献
213.
Lorella Francalanci Riccardo Avanzinelli Isabella Nardini Massimo Tiepolo Jon P. Davidson Riccardo Vannucci 《Contributions to Mineralogy and Petrology》2012,163(1):109-131
In situ Sr-isotope data by microdrilling, coupled with major and trace element analyses, have been performed on plagioclase
and clinopyroxene from seven samples collected during the 2002–2003 eruptive crisis at Stromboli volcano (Aeolian Islands,
Italy). On 28 December 2002, the persistent moderate explosive activity was broken by an effusive event lasting about 7 months.
A more violent explosion (paroxysm) occurred on 5 April 2003. Two magma types were erupted, namely a volatile-poor and highly
porphyritic magma (HP-magma) poured out as scoria or lava and a volatile-rich, phenocryst-poor magma (LP-magma) found as pumice.
LP-magma differs from the HP-magma also for its slightly less-evolved chemistry, the groundmass composition and the lower
Sr-isotope ratios. Micro-Sr-isotope data show the presence of zoned minerals in strong isotope disequilibrium, as previously
found in products erupted in 1984, 1985 and 1996 AD, with 87Sr/86Sr values generally decreasing from cores to rims of minerals. Only some outer rims testify for equilibrium with the host
groundmass. The internal mineral zones with high Sr-isotope ratios (0.70665–0.70618) are interpreted as ‘antecrysts’, crystallised
during the previous activity and recycled in the present-day system since the opening shoshonitic activity of the Recent Period,
which occurred at about 2.5 ka ago. This result has implications for the dynamics of the present-day plumbing system of Stromboli
at intermediate pressure (about 2–3 km depth) and allows us to propose a model whereby an HP-magma reservoir is directly interconnected
at the bottom with a cumulate crystal much reservoir. Efficient mixing between residing HP- and input LP-magmas can occur
in this reservoir, due to more similar rheological characteristics of the two magmas than in the conduit, where crystallisation
is enhanced by degassing. Antecrysts (and possibly melts) re-enter in the HP-magma reservoir both from the bottom, recycled
by ascending LP-magmas crossing the crystal mush, and from the top, recycled by descending degassed and dense HP-magma, residual
of the periodic Strombolian explosions at the surface. The isotope variation measured in the groundmasses allows calculating
the proportion of the LP-magma entering the shallow HP-magma reservoir at ~20%. From this proportion, we estimate that the
total volume of LP-magma input during 2002–2003 closely matches the magma volume erupted in the effusive event, suggesting
a steady-state system at broadly constant volume. The comparison with estimates of the LP-magma volume ejected by the paroxysm
indicates that the LP-magma amount directly reaching the surface during the 5 April paroxysm is minimal with respect to that
entering the system. 相似文献
214.
A unified model for gold mineralisation in accretionary orogens and implications for regional-scale exploration targeting methods 总被引:1,自引:0,他引:1
Jon?M.?A.?HronskyEmail author David?I.?Groves Robert?R.?Loucks Graham?C.?Begg 《Mineralium Deposita》2012,47(4):339-358
Accretionary orogens are the sites of long-lived convergent margin tectonics, both compressional and extensional. They are
also the hosts to the majority of the world’s important gold deposits. A very diverse range of deposit types occurs within
accretionary orogens, commonly in close proximity in space and time to each other. These include porphyry and associated high-sulphidation
Au–Cu–Ag deposits, classic low-sulphidation Au–Ag deposits, low-sulphidation Au deposits centred on alkalic intrusive complexes,
Carlin-type Au deposits, Au-rich volcanic-hosted massive sulphide deposits, orogenic Au deposits, intrusion-related Au deposits
and iron oxide Cu–Au deposits. Empirical patterns of spatial distribution of these deposits suggest there must be fundamental
generic controls on gold metallogeny. Various lines of evidence lead to the proposal that the underlying key generic factor
controlling accretionary orogen gold metallogeny is regional-scale, long-term, pre- and syn-subduction heterogeneous fertilisation
of the lithospheric mantle that becomes a source of mineralisation-associated arc magma or hydrothermal fluid components.
This process provides a gold-enriched reservoir that can be accessed later in a diverse range of tectonomagmatic settings.
Based on this concept, a unified model is proposed in which the formation of a major gold deposit of any type requires the
conjunction in time and space of three essential factors: a fertile upper-mantle source region, a favourable transient remobilisation
event, and favourable lithospheric-scale plumbing structure. This framework provides the basis for a practical regional-scale
targeting methodology that is applicable to data-poor regions. 相似文献
215.
Schroeder T Devlin MJ Brando VE Dekker AG Brodie JE Clementson LA McKinna L 《Marine pollution bulletin》2012,65(4-9):210-223
Riverine freshwater plumes are the major transport mechanism for nutrients, sediments and pollutants into the Great Barrier Reef (GBR) lagoon and connect the land with the receiving coastal and marine waters. Knowledge of the variability of the freshwater extent into the GBR lagoon is relevant for marine park management to develop strategies for improving ecosystem health and risk assessments. In this study, freshwater extent has been estimated for the entire GBR lagoon area from daily satellite observations of the Moderate Resolution Imaging Spectroradiometer (MODIS) between 2002 and 2010. To enable a reliable mapping of freshwater plumes we applied a physics-based coastal ocean colour algorithm, that simultaneously retrieves chlorophyll-a, non-algal particulate matter and coloured dissolved organic matter (CDOM), from which we used CDOM as a surrogate for salinity (S) for mapping the freshwater extent. 相似文献
216.
Kennedy K Devlin M Bentley C Lee-Chue K Paxman C Carter S Lewis SE Brodie J Guy E Vardy S Martin KC Jones A Packett R Mueller JF 《Marine pollution bulletin》2012,64(7):1495-1507
The 2010-2011 wet season was one of extreme weather for the State of Queensland, Australia. Major rivers adjacent to the Great Barrier Reef (GBR) were discharging at rates 1.5 to >3 times higher than their long term median. Exposure to photosystem II herbicides has been routinely monitored over a period of up to 5 years at 12 inshore GBR sites. The influence of this wet season on exposure to photosystem II herbicides was examined in the context of this long-term monitoring record and during flood plume events in specific regions. Median exposures expressed as diuron equivalent concentration were an average factor of 2.3 times higher but mostly not significantly different (p<0.05) to the median for the long-term monitoring record. The herbicides metolachlor and tebuthiuron were frequently detected in flood plume waters at concentrations that reached or exceeded relevant water quality guidelines (by up to 4.5 times). 相似文献
217.
The paraglacial reworking of glacial sediments by rivers and mass wasting is an important conditioning factor for modern sediment yields in mountainous catchments in formerly glaciated regions. Catchment scale and patterns of sediment storage are important influences in the rate of postglacial adjustment. We develop a quantitative framework to estimate the volume, sediment type, and fractional size distribution of legacy glacial materials in a large (1230 km2) watershed in the North Cascade Mountains in south‐western British Columbia, Canada. Chilliwack Valley is exceptional because of the well‐dated bounds of deglaciation. Interpolation of paleo‐surfaces from partially eroded deposits in the valley allows us to estimate the total evacuated sediment volume. We present a chronology of sediment evacuation from the valley and deposition in the outlet fan, based on infrared stimulated luminescence (IRSL) and 14 C dating of river terraces and fan strata, respectively. The effects of paraglacial sedimentation in Chilliwack Valley were intensified through a major fall in valley base‐level following ice retreat. The steepened mainstem valley gradient led to deep incision of valley fills and fan deposits in the lower valley network. The results of this integrated study provide a postglacial chronology and detailed sediment budget, accounting for long‐term sorting of the original sediments, lag deposit formation in the mainstem, deposition in the outlet fan, and approximate downstream losses of suspended sediment and wash load. The mass balance indicates that a bulk volume of approximately 3.2 km3 of glacial material has been evacuated from the valley. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
218.
Imag(in)ing 'homeless places': using auto-photography to (re)examine the geographies of homelessness 总被引:1,自引:0,他引:1
Despite its growing popularity as a method across the social sciences, the methodological literature on auto-photography is remarkably sparse. In an effort to begin redressing this gap, this paper provides an account of the ways in which auto-photography was used to complement other research methods in a (re)examination of the geographies of homelessness. It describes how auto-photography illuminated 'hidden' spaces that do not typically feature in public (or academic) imaginations of homelessness, and provided more nuanced understandings of the use, meanings and dynamics associated with other, apparently already 'known' spaces. It concludes that whilst auto-photography presents a number of logistical and ethical challenges – particularly when used with such a vulnerable group – it is nevertheless a powerful heuristic tool. 相似文献
219.
Jim Braun Jon Dumm Francesco De Palma Chad Finley Albrecht Karle Teresa Montaruli 《Astroparticle Physics》2008,29(4):299-305
Neutrino telescopes are moving steadily toward the goal of detecting astrophysical neutrinos from the most powerful galactic and extragalactic sources. Here we describe analysis methods to search for high energy point-like neutrino sources using detectors deep in the ice or sea. We simulate an ideal cubic kilometer detector based on real world performance of existing detectors such as AMANDA, IceCube, and ANTARES. An unbinned likelihood ratio method is applied, making use of the point spread function and energy distribution of simulated neutrino signal events to separate them from the background of atmospheric neutrinos produced by cosmic ray showers. The unbinned point source analyses are shown to perform better than binned searches and, depending on the source spectral index, the use of energy information is shown to improve discovery potential by almost a factor of two. 相似文献
220.
Jon S. Harding 《新西兰海洋与淡水研究杂志》2013,47(5)
Metal contamination in aquatic environments: science and lateral management. By Samuel N. Luoma and Philip S. Rainbow. Published in 2008 by Cambridge University Press, Cambridge, United Kingdom (www.cambridge.org). 573 p, hardcover. ISBN 978–0‐521–86057–4. Price au$200.00. 相似文献