Book Review of Accretion Power in Astrophysics (3rd Edition) by Juhan Frank,Andrew King,Derek Raine Cambridge University Press, 2002, XIV+384 pp., £27.95, hardback (ISBN 0 521 62053 8), paperback (ISBN 0 521 62957 8).     

Jim Stone 《地球物理与天体物理流体动力学》2013,107(6):507-508

The velocity, pressure, perturbation magnetic field, helicity and electromotive force driven by an isolated buoyant parcel in an unbounded, rapidly rotating, electrically conducting fluid in the limit of small Elsasser number and very small Ekman number are calculated, visualized and analyzed. On the scale of the parcel, the solution is identical to that obtained in the limit of small Ekman number and zero Elsasser number. On the scale of the Taylor-column, it is elongated in the direction of the applied magnetic field and compressed in the direction perpendicular to it. The α-effect calculated by averaging the electromotive force on planes normal to rotation is strongly anisotropic: near the parcel and in the inner part of the Taylor-column it is strongest when the applied magnetic field is perpendicular to rotation and gravity; in the outer part of the Taylor-column it is strongest when the applied magnetic field is in the same plane as rotation and gravity.  相似文献   

Interrelations between socio-economic development and environmental quality: a simulation integrating system dynamics models with GIS     

Yu Jie  Bian Fuling  Peterson Jim  Li Pingxiang 《地球空间信息科学学报》2013,16(3):176-182

System dynamics (SD) theory has long been deployed in modeling complex non-linear interrelationships but, so far it has not been common to do the kind of modeling in support of bringing environmental sustainability policies to practice. This is largely because the challenge of including spatial data has not yet been well met. Potential for adoption of SD and GIS methods in combination is exemplified with the results of a decision-support exercise designed for simulation and prediction of the dynamic inter-relationships between socio-economic development and environmental quality for the “Wen, Pi, Du” county in Sichuan province, southwestern China.  相似文献   

Sub-daily alias and draconitic errors in the IGS orbits   总被引：6，自引：2，他引：4  

J. Griffiths  Jim R. Ray 《GPS Solutions》2013,17(3):413-422

Harmonic signals with a fundamental period near the GPS draconitic year (351.2 days) and overtones up to at least the sixth multiple have been observed in the power spectra of nearly all products of the International GNSS Service (IGS), including station position time series, apparent geocenter motions, orbit jumps between successive days, and midnight discontinuities in earth orientation parameter (EOP) rates. Two main mechanisms have been suggested for the harmonics: mismodeling of orbit dynamics and aliasing of near-sidereal local station multipath effects. Others have studied the propagation of local multipath errors into draconitic position variations, but orbit-related processes have been less examined. We elaborate our earlier analysis of GPS day-boundary orbit discontinuities where we observed some draconitic features as well as prominent spectral bands near 29-, 14-, 9-, and 7-day periods. Finer structures within the sub-seasonal bands fall close to the expected alias frequencies for 24-h sampling of sub-daily EOP tide lines but do not coincide precisely. While once-per-revolution empirical orbit parameters should strongly absorb any sub-daily EOP tide errors due to near-resonance of their respective periods, the observed differences require explanation. This has been done by simulating EOP tidal errors and checking their impact on a long series of estimated daily GPS orbits and EOPs. Indeed, simulated tidal aliases are found to be very similar to the observed IGS orbital features in the sub-seasonal bands. Moreover and unexpectedly, some low draconitic harmonics were also produced, potentially a source for the widespread errors in most IGS products. The results from this study are further evidence for the need of an improved sub-daily EOP tide model.  相似文献   

Rapid magmatic processes accompany arc–continent collision: the Western Bismarck arc, Papua New Guinea     

Heather Cunningham  Jim Gill  Simon Turner  John Caulfield  Louise Edwards  Simon Day 《Contributions to Mineralogy and Petrology》2012,164(5):789-804

New U–Th–Ra, major and trace element, and Sr–Nd–Pb isotope data are presented for young lavas from the New Britain and Western Bismarck arcs in Papua New Guinea. New Britain is an oceanic arc, whereas the latter is the site of an arc–continent collision. Building on a recent study of the Manus Basin, contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc–continent collision and possible slab detachment. All three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle. However, the Western Bismarck arc lavas diverge from the Pb isotope mixing array formed by the New Britain and the Manus Basin lavas toward elevated ²⁰⁸Pb/²⁰⁴Pb. We interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision. ²³⁸U and ²²⁶Ra excesses are preserved in all of the lavas and are greatest in the Western Bismarck arc. High-Mg andesites with high Sr/Y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge. Data for two historical rhyolites are also presented. Although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions, both formed from mafic parents within millennia.  相似文献   

Effects of an Omnivorous Katydid,Salinity, and Nutrients on a Planthopper-<Emphasis Type="Italic">Spartina</Emphasis> Food Web     

Juan M. Jiménez  Kazimierz Więski  Laurie B. Marczak  Chuan-Kai Ho  Steven C. Pennings 《Estuaries and Coasts》2012,35(2):475-485

Top–down and bottom–up effects interact to structure communities, especially in salt marshes, which contain strong gradients in bottom–up drivers such as salinity and nutrients. How omnivorous consumers respond to variation in prey availability and plant quality is poorly understood. We used a mesocosm experiment to examine how salinity, nutrients, an omnivore (the katydid Orchelimum fidicinium) and an herbivore (the planthopper Prokelisia spp.) interacted to structure a simplified salt marsh food web based on the marsh grass Spartina alterniflora. Bottom–up effects were strong, with both salinity and nutrients decreasing leaf C/N and increasing Prokelisia abundance. Top–down effects on plants were also strong, with both the herbivore and the omnivore affecting S. alterniflora traits and growth, especially when nutrients or salt were added. In contrast, top–down control by Orchelimum of Prokelisia was independent of bottom–up conditions. Orchelimum grew best on a diet containing both Spartina and Prokelisia, and in contrast to a sympatric omnivorous crab, did not shift to an animal-based diet when prey were present, suggesting that it is constrained to consume a mixed diet. These results suggest that the trophic effects of omnivores depend on omnivore behavior, dietary constraints, and ability to suppress lower trophic levels, and that omnivorous katydids may play a previously unrecognized role in salt marsh food webs.  相似文献   

Quality assessment of GPS reprocessed terrestrial reference frame   总被引：5，自引：1，他引：4  

Xavier Collilieux  Laurent Métivier  Zuheir Altamimi  Tonie van Dam  Jim Ray 《GPS Solutions》2011,15(3):219-231

The International GNSS Service (IGS) contributes to the construction of the International Terrestrial Reference Frame (ITRF) by submitting time series of station positions and Earth Rotation Parameters (ERP). For the first time, its submission to the ITRF2008 construction is based on a combination of entirely reprocessed GPS solutions delivered by 11 Analysis Centers (ACs). We analyze the IGS submission and four of the individual AC contributions in terms of the GNSS frame origin and scale, station position repeatability and time series seasonal variations. We show here that the GPS Terrestrial Reference Frame (TRF) origin is consistent with Satellite laser Ranging (SLR) at the centimeter level with a drift lower than 1 mm/year. Although the scale drift compared to Very Long baseline Interferometry (VLBI) and SLR mean scale is smaller than 0.4 mm/year, we think that it would be premature to use that information in the ITRF scale definition due to its strong dependence on the GPS satellite and ground antenna phase center variations. The new position time series also show a better repeatability compared to past IGS combined products and their annual variations are shown to be more consistent with loading models. The comparison of GPS station positions and velocities to those of VLBI via local ties in co-located sites demonstrates that the IGS reprocessed solution submitted to the ITRF2008 is more reliable and precise than any of the past submissions. However, we show that some of the remaining inconsistencies between GPS and VLBI positioning may be caused by uncalibrated GNSS radomes.  相似文献   

Microplastics as contaminants in the marine environment: a review   总被引：15，自引：0，他引：15  

Cole M  Lindeque P  Halsband C  Galloway TS 《Marine pollution bulletin》2011,62(12):2588-2597

Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.  相似文献   

Quantitative multi-risk analysis for natural hazards: a framework for multi-risk modelling   总被引：2，自引：1，他引：1  

Jochen Schmidt  Iain Matcham  Stefan Reese  Andrew King  Rob Bell  Roddy Henderson  Graeme Smart  Jim Cousins  Warwick Smith  Dave Heron 《Natural Hazards》2011,58(3):1169-1192

This paper introduces a generic framework for multi-risk modelling developed in the project ‘Regional RiskScape’ by the Research Organizations GNS Science and the National Institute of Water and Atmospheric Research Ltd. (NIWA) in New Zealand. Our goal was to develop a generic technology for modelling risks from different natural hazards and for various elements at risk. The technical framework is not dependent on the specific nature of the individual hazard nor the vulnerability and the type of the individual assets. Based on this generic framework, a software prototype has been developed, which is capable of ‘plugging in’ various natural hazards and assets without reconfiguring or adapting the generic software framework. To achieve that, we developed a set of standards for treating the fundamental components of a risk model: hazards, assets (elements at risk) and vulnerability models (or fragility functions). Thus, the developed prototype system is able to accommodate any hazard, asset or fragility model, which is provided to the system according to that standard. The software prototype was tested by modelling earthquake, volcanic ashfall, flood, wind, and tsunami risks for several urban centres and small communities in New Zealand.  相似文献   

Distribution, characterization, and geochemical controls of elements of concern in uranium mine tailings, Key Lake, Saskatchewan, Canada     

Sean A. Shaw  M. Jim Hendry  Joseph Essilfie-Dughan  Tom Kotzer  Dirk Wallschläger 《Applied Geochemistry》2011,26(12):2044-2056

The distribution of As, Mo, Ni and Se in the aqueous and solid phases of U mine tailings in the Deilmann Tailings Management Facility (DTMF), located at the Key Lake mine in northern Saskatchewan, Canada, was defined using as-discharged tailings samples collected monthly starting in 1996 and core samples collected from the DTMF from 3 locations on 3 occasions between 2004 and 2009. These data indicated that the DTMF can be divided into two geochemical zones; tailings generated from the Deilmann ore body between 1996 and 2000 and tailings from the McArthur River ore body, mined after July 2000. The Deilmann tailings solids are generally characterized by greater elemental concentrations than those in the McArthur River tailings, particularly for As, Co and Ni. These elevated concentrations are attributed to the abundance of Ni–Co–As–S minerals in this ore. The mean aqueous concentrations of As, Mo, Ni, and Se are 3.7, 23.2, 0.14, and 0.02 mg L⁻¹, respectively, in the Deilmann porewaters and 0.20, 4.16, 0.06, and 0.03 mg L⁻¹, respectively, in the McArthur River porewaters. Similarly, the mean As, Mo, Ni, and Se solid phase concentrations are 5.89 × 10³, 69.9, 3.20 × 10³, and 17.4 μg g⁻¹, respectively, for the Deilmann tailings and 440, 13.6, 551, and 3.03 μg g⁻¹ in the McArthur River tailings. Statistically, pH remained unchanged from the time of discharge while Eh values have remained oxic with no significant change between the two tailings types over 15 a of residence time. Results from sequential extractions, thermodynamic modeling, and results of complimentary research indicated that ferrihydrite solubility is the dominant control on aqueous As concentrations and also plays a role in controlling dissolved Mo, Ni and Se.  相似文献   

Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis     

Thomas B. Hofstetter  Jakov Bolotin  Marita Skarpeli-Liati  Reto Wijker  Zohre Kurt  Shirley F. Nishino  Jim C. Spain 《Applied Geochemistry》2011

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