The thermal nature of soft X-ray flares     

I. J. D. Craig 《Solar physics》1973,31(1):197-205

Soft X-ray flare data in the wavelength range 2.6–10 Å are used to examine the time variation of emission measure and electron temperature. The thermal plasma parameters were derived according to a two-temperature model proposed by Herring and Craig (1973). Estimates of electron density and source volume are made by assuming conductive and radiative cooling mechanisms. It is suggested that the present observations imply a multi-thermal interpretation of the soft X-ray flare.  相似文献   

Rotating disk electrode oxygen sensor and corrosion rate probe     

Prentice  J. Craig  H.  Jr. 《Oceanic Engineering, IEEE Journal of》1979,4(4):137-141

A rotating disk electrode (RDE) is applied as a dissolved oxygen sensor and corrosion rate probe. As an oxygen sensor, the RDE is capable ofpm0.004-ml/l resolution andpm0.17-ml/l accuracy. As a corrosion rate probe, the RDE behaves more closely to theory than stationary electrodes. These applications make use of the RDE's unique hydrodynamic properties.  相似文献   

Thermonuclear detonations in collapsing white dwarf stars     

J. Craig Wheeler  Carl J. Hansen 《Astrophysics and Space Science》1971,11(3):373-397

Collapsing white dwarf stars (or degenerate cores) may occur in binary systems, in the formation of Type I supernovae or in the formation of pulsars. These collapsing configurations may explode their nuclear fuel (¹²C or¹⁶O) by the detonation wave mechanism. A combination of analytical and numerical models is used to investigate the formation of detonation waves. The tentative conclusion is that a detonation wave will form which will lead to the ignition of esentially all the fuel in such a collapsing star. This potentially explosive configuration will be strongly affected, however, by rapid beta processes which occur in the detonated matter and which should cause a fraction of the stellar mass to collapse toward a neutron star state. The nature and effect of such beta processes, which have not yet been incorporated in the dynamical calculations, are discussed.An appendix gives approximate expressions for the pressureP(,T) and the internal energy densityU(,T) for a degenerate relativistic electron gas and an analysis of the errors expected in making such approximations to the standard parametric form of the equation of state. These expressions are useful in analyzing shock waves in a degenerate electron gas.Supported in part by the National Science Foundation [GP-15911, GP-9114, GP-19887] and the Office of Naval Research [Nonr-220 (47)] at the California Institute of Technology, and National Science Foundation Grant GP-12455 at the University of Colorado.  相似文献   

Modelling of diffusion boundary-layers in subtidal macroalgal canopies: The response to waves and currents     

Craig L. Stevens  Catriona L. Hurd  Pål E. Isachsen 《Aquatic Sciences - Research Across Boundaries》2003,65(1):81-91

  相似文献   

Groundwater flow and solute transport at the Mourquong saline-water disposal basin, Murray Basin, southeastern Australia   总被引：5，自引：0，他引：5  

Craig T. Simmons  Kumar A. Narayan  Juliette A. Woods  Andrew L. Herczeg 《Hydrogeology Journal》2002,10(2):278-295

Saline groundwater and drainage effluent from irrigation are commonly stored in some 200 natural and artificial saline-water disposal basins throughout the Murray-Darling Basin of Australia. Their impact on underlying aquifers and the River Murray, one of Australia's major water supplies, is of serious concern. In one such scheme, saline groundwater is pumped into Lake Mourquong, a natural groundwater discharge complex. The disposal basin is hydrodynamically restricted by low-permeability lacustrine clays, but there are vulnerable areas in the southeast where the clay is apparently missing. The extent of vertical and lateral leakage of basin brines and the processes controlling their migration are examined using (1) analyses of chloride and stable isotopes of water (²H/¹H and ¹⁸O/¹⁶O) to infer mixing between regional groundwater and lake water, and (2) the variable-density groundwater flow and solute-transport code SUTRA. Hydrochemical results indicate that evaporated disposal water has moved at least 100 m in an easterly direction and that there is negligible movement of brines in a southerly direction towards the River Murray. The model is used to consider various management scenarios. Salt-load movement to the River Murray was highest in a "worst-case" scenario with irrigation employed between the basin and the River Murray. Present-day operating conditions lead to little, if any, direct movement of brine from the basin into the river. Electronic Publication  相似文献   

Finite difference modeling of contaminant transport using analytic element flow solutions     

James R. Craig  Alan J. Rabideau 《Advances in water resources》2006

The two-dimensional implementation of the analytic element method (AEM) is commonly used to simulate steady-state saturated groundwater flow phenomena at regional and local scales. However, unlike alternative groundwater flow simulation methods, AEM results are not ordinarily used as the basis for simulation of reactive solute transport. The use of AEM-simulated flow fields is impeded by the discrepancy between a continuous representation of flow and a typically discrete representation of transport, and requires translation of the flow solution to a discrete analog. This paper presents a variety of methods for analytically calculating conservative discrete water fluxes and integrated components of the dispersion tensor across cell interfaces. An Eulerian finite difference method based on these AEM-derived parameters is implemented for use in simulation of 2D (vertically averaged) solute transport. This implementation is first benchmarked against existing methods that use standard finite difference flow solutions, then used to investigate the effects of an inaccurate discrete water balance. It is shown that improper translation of AEM fluxes leads to significant water balance errors and inaccurate simulation of contaminant transport.  相似文献   

A Pb-Ra-Th-U study of Klyuchevskoy and Bezymianny volcanoes, Kamchatka     

Simon Turner  Kenneth W.W. Sims  Craig Cook 《Geochimica et cosmochimica acta》2007,71(19):4771-4785

Lavas from Klyuchevskoy and Bezymianny volcanoes, Kamchatka, appear to show a link between the extent of partial melting in their mantle source region and the subsequent degree of fractionation suffered by the magmas during passage through the crust. This fractionation may have occurred on timescales significantly less than 1000 years if observed ²²⁶Ra excesses largely reflect variable residual porosity in the source melting region. Unlike most arc lavas, those with the highest MgO contents and Ba/Th ratios have the lowest ²²⁶Ra excess. Forward models suggest that those portions of the source which had undergone the greatest addition of U by fluids from the subducting plate also underwent the greatest extents of partial melting at the highest residual porosity. At Kluchevskoy, a change from eruption of high-MgO to high-Al₂O₃ basaltic andesites around 1945 is reflected in an increase in size of ²²⁶Ra excess which seems to require a simultaneous decrease in residual porosity and suggests a rapid changes in the melting regime. The eruption of andesites at Bezyminanny, simultaneous with the eruption of basaltic andesites at Klyuchevskoy, further suggests that different degree melts produced at differing residual porosity can be formed and extracted from the melt region at the same time. Thus, the melting processes beneath Klyuchevskoy and Bezyminanny are demonstrably complex. They have clearly been influenced by both fluid addition from the subducting plate and extension and decompression beneath the Central Kamchatka Depression. Finally, the ²¹⁰Pb data are, with one or two exceptions, in equilibrium with ²²⁶Ra, suggesting that there was restricted relative magma-gas movement in this highly productive magmatic system.  相似文献   

Lu–Hf geochronology and trace element distribution in garnet: Implications for uplift and exhumation of ultra-high pressure granulites in the Sudetes, SW Poland     

Robert Anczkiewicz  Jacek Szczepa&#x;ski  Stanis&#x;aw Mazur  Craig Storey  Quentin Crowley  Igor M. Villa  Matthew F. Thirlwall  Teresa E. Jeffries 《Lithos》2007,95(3-4):363-380

Combining Lu–Hf garnet geochronology with in situ trace element analyses in garnet allowed us to gain new insight into the metamorphic evolution of UHP–UHT rocks in the Stary Gierałtów region, in the Polish Sudetes. Prograde garnet growth recorded by Rayleigh-type heavy REE (HREE) zoning in the felsic granulites indicates that the obtained 386.6 ± 4.9 Ma Lu–Hf age represents the time of garnet crystallization on a prograde UHP metamorphic path. The surrounding rocks were metamorphosed at the same time as indicated by 381.2 ± 6.7 Ma Sm–Nd garnet age obtained for the mid-crustal metapelites. The second metamorphic episode, which affected most of the lower crust in the Orlica–Śnieżnik Massif (OSM) occurred at ca. 340 Ma as determined by U–Pb zircon and Sm–Nd garnet dating of granulites in this and previous studies is interpreted as a high temperature event, which took place on a retrograde path.

Trace element distribution in garnets from the layered granulites showed significant differences in distribution of medium and HREE in garnets from mafic and felsic protoliths over the course of the metamorphic evolution. This had strong impact on the isotopic dating results and led to “decoupling” of the Sm–Nd and Lu–Hf clocks, which recorded timing of the two different metamorphic episodes separated by as much as 40 Ma. Moreover, the preservation of the HREE growth zonation profile in garnets from the felsic granulites whose minimum metamorphic temperature was established at 900 °C implies that the Lu–Hf system under relatively dry conditions does not undergo significant diffusional re-equilibration even at such extreme temperatures and therefore it sill provides the age of prograde garnet growth. Under hydrous conditions, at least some resetting will take place, as documented by the partially relaxed HREE zonation profile in the amphibolitised mafic granulite, which yielded a 10 Ma younger age. The HREE distribution study appeared to be a particularly valuable and essential tool, which allowed us to distinguish garnet growth from post-growth complexities and hence, provide improved age interpretation. Medium REE, on the other hand, did not show any obvious correlation with the isotopic signature of garnet.

Two distinct metamorphic episodes recorded in the Stary Gierałtów region show that buoyancy-driven uplift of UHP rocks can be arrested at the base of a continental crust if not supported by any additional force. In our case study, the UHP rocks would have never reached the surface if their uplift had not been resumed after a long pause under a different tectonic regime. The multistage, discontinuous uplift revealed by the UHP rocks of the OSM provides a new scenario for the exhumation of continental crust from mantle depths distinct from the fast-track exhumation histories recognized in UHP terranes elsewhere.  相似文献   

The influence of human activity in the Arctic on climate and climate impacts   总被引：1，自引：0，他引：1  

Henry P. Huntington  Michelle Boyle  Gwenn E. Flowers  John W. Weatherly  Lawrence C. Hamilton  Larry Hinzman  Craig Gerlach  Rommel Zulueta  Craig Nicolson  Jonathan Overpeck 《Climatic change》2007,82(1-2):77-92

Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the more complicated but more likely possibility that human activities themselves can interact with climate or environmental change in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend. Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence the trajectory of arctic system change.  相似文献   

Pyrite: physical and chemical textures   总被引：9，自引：0，他引：9  

J. R. Craig  F. M. Vokes  T. N. Solberg 《Mineralium Deposita》1998,34(1):82-101

Pyrite may crystallize initially in forms as diverse as framboids or cubes depending upon the temperatures and pressures. Fluid-rich diagenesis or low-grade metamorphism clearly results in thorough recrystallization and the common formation of cubes. Once these have formed, the pyrite becomes much more refractory and retains many characteristics even in deposits which have undergone penetrative deformation. This is in strong contrast to the behavior of most of the accompanying sulfides, which often undergo ductile deformation, solid state or chemical remobilization, and annealing. Pyrite deforms sparingly until there is brittle failure; however, there may be significant pyrite corrosion and regrowth during metamorphism as the result of sulfur exchange with other minerals, especially pyrrhotite. Pyrite fabrics may also be significantly modified by pressure solution or Coble creep. Optical microscopic examination and electron microprobe chemical mapping of pyrites from a variety of mineral deposits, including several high-grade metamorphic ones, reveals that the pyrites frequently contain both physical and chemical textures that may be interpreted in terms of the depositional and the post-depositional history of the deposits. Inclusions of sulfides or other minerals reveal information on the timing of the crystallization or recrystallization of the pyrite; chemical mapping of elements such as Ni, Co, and As reveals information on the relative time of transport of these elements in the ore fluids. Received: 19 March 1997 / Accepted: 14 May 1998  相似文献