A comparison of theoretical Sv emission line strengths with extreme ultraviolet observations of a sunspot     

F. P. Keenan  J. G. Doyle 《Solar physics》1990,128(2):345-351

Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR ₁ =I(854.8 Å)/I(786.9 Å),R ₂ =I(852.2 Å)/I(786.9 Å),R ₃ =I(849.2 Å)/I(786.9 Å), andR ₄ =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR ₁, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed.  相似文献   

Regional variation in springtime ichthyoplankton assemblages in the northeast Pacific Ocean     

Miriam J. Doyle  Kathryn L. Mier  Morgan S. Busby  Richard D. Brodeur   《Progress in Oceanography》2002,53(2-4)

The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log₁₀ (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast.  相似文献   

Patterns and controls of surface sediment distribution: west-central Florida inner shelf   总被引：2，自引：0，他引：2  

Gregg R. Brooks  Larry J. Doyle  Richard A. Davis  Nancy T. DeWitt  Beau C. Suthard   《Marine Geology》2003,200(1-4):307-324

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems.  相似文献   

Theoretical emission line strengths for Ov compared to EUV solar observations     

F. P. Keenan  G. A. Warren  J. G. Doyle  K. A. Berrington  A. E. Kingston 《Solar physics》1994,150(1-2):61-70

RecentR-matrix calculations of electron impact excitation rates in Ov are used to derive the emission line intensity ratios (in energy units) $$\begin{gathered} R_1 = I(2s2p^{ 3} P - 2p^{2 3} P)/I(2s^{2 1} S_0 - 2s2p^{ 1} P_1 ) = I(761.1\mathop A\limits^ \circ )/I(629.7\mathop A\limits^ \circ ), \hfill \\ R_2 = I(2s^{2 1} S_0 - 2s2p^{ 3} P_1 )/I(2s^{2 1} S_0 - 2s2p^{ 1} P_1 ) = I(1218.4\mathop A\limits^ \circ )/I(629.7\mathop A\limits^ \circ ), \hfill \\ \end{gathered} $$ and $$R_3 = I(2s2p^{ 1} P_1 - 2p^{2 1} S_0 )/I(2s^{2 1} S_0 - 2s2p^{ 1} P_1 ) = I(774.5\mathop A\limits^ \circ )/I(629.7\mathop A\limits^ \circ )$$ as a function of electron temperature (T _e) and density (N _e). These results are presented as plots ofR ₁ vsR ₂, andR ₁ vsR ₃, which should allowboth N _e andT _e to be deduced for the Ov line emitting region of a plasma. Electron densities derived from the (R ₁,R ₂) and (R ₁,R ₃) diagrams in conjunction with observational data for several solar features obtained with the Harvard S-055 spectrometer on boardSkylab are found to be compatible, and in good agreement with values ofN _e estimated from line ratios in species formed at similar electron temperatures to Ov. In addition, values ofT _e determined from (R ₁,R ₂) and (R ₁,R ₃) are generally close to that expected theoretically. These results provide experimental support for the accuracy of the diagnostic calculations presented in this paper, and hence the atomic data used in their derivation.  相似文献   

A heuristic model for potential geomorphic influences on trophic interactions in streams     

Martin W. Doyle   《Geomorphology》2006,77(3-4):235

Whereas certain linkages between stream channel morphology and stream ecology are fairly well-understood, how geomorphology influences trophic interactions remains largely unknown. As a first step, a simple, heuristic model is developed that couples reach-scale geomorphic morphology with trophic dynamics between vegetation, detritus, herbivores, and predators. Predation is assumed to increase with depth beyond a threshold depth, and herbivory is assumed to decrease with velocity beyond a threshold velocity. Results show that the modeled food chain is sensitive to channel geometry, particularly around the threshold conditions for predators and herbivores. Importantly, geomorphic influences are not isolated to a particular trophic level, but rather are transferred through the food chain via top-down and bottom-up effects. The modeled system is particularly sensitive to changes in the end-members of the food chain: vegetation and predators. Results illustrate that geomorphic disturbances, known to affect a single trophic level (e.g., fish), likely impact multiple trophic levels in the stream ecosystem via trophic interactions. Such impacts at the multiple trophic level are poorly understood. While limited by the lack of empirical long-term data for testing and calibration, this simple model provides a structure for generating hypotheses, collecting targeted data, and assessing the potential impacts of stream disturbance or restoration on entire stream ecosystems. Further, the model illustrates the potential for future coupled stream models to explore spatial and temporal linkages.  相似文献   

Soft X-ray spectroscopic studies of the reaction of fractured pyrite surfaces with Cr(VI)-containing aqueous solutions     

Colin S. Doyle  Tom Kendelewicz  Gordon E. Brown Jr 《Geochimica et cosmochimica acta》2004,68(21):4287-4299

We have used synchrotron-based soft X-ray core-level photoemission and adsorption spectroscopies to study the reaction of aqueous sodium chromate solutions with freshly fractured pyrite surfaces. Pyrite surfaces were reacted with 50 μM sodium chromate solution at pH 7 for reaction times between 1 min and 37 hr. Additional experiments were performed at pH 2 and pH 4 with 50 μM sodium chromate solutions and at pH 7 with 5 mM solutions. At chromate concentrations of 50 μM, all chromium present on the pyrite surface was in the form of Cr(III), while at 5 mM, both Cr(III) and Cr(VI) were present at the pyrite surface. Minor quantities of oxidized sulfur species (sulfate, sulfite, and zero-valent sulfur) were identified as reaction products on the pyrite surface. The amount of oxidized sulfur species observed on the surface was greater when pyrite was reacted with 5 mM Cr(VI) solutions because the rate of chromium deposition exceeded the rate of dissolution of pyrite oxidation products, effectively trapping Cr(VI) and oxidized sulfur species in an overlayer of iron(III)-containing Cr(III)-hydroxide. This work shows that pyrite, an extremely cheap and readily available waste material, may be suitable for the removal of hexavalent chromium from acidic to circumneutral waste streams. The reduced chromium ultimately forms a coating on the pyrite surface, which passivates the pyrite surface towards further oxidation.  相似文献   

Mineral inclusions and geochemical characteristics of microdiamonds from the DO27, A154, A21, A418, DO18, DD17 and Ranch Lake kimberlites at Lac de Gras, Slave Craton, Canada   总被引：1，自引：0，他引：1  

Rondi M. Davies  William L. Griffin  Suzanne Y. O''Reilly  Buddy J. Doyle 《Lithos》2004,77(1-4):39-55

A mineral inclusion, carbon isotope, nitrogen content, nitrogen aggregation state and morphological study of 576 microdiamonds from the DO27, A154, A21, A418, DO18, DD17 and Ranch Lake kimberlites at Lac de Gras, Slave Craton, was conducted. Mineral inclusion data show the diamonds are largely eclogitic (64%), followed by peridotitic (25%) and ultradeep (11%). The paragenetic abundances are similar to macrodiamonds from the DO27 kimberlite (Davies, R.M., Griffin, W.L., O'Reilly, S.Y., 1999. Diamonds from the deep: pipe DO27, Slave craton, Canada. In: Gurney, J.J., Gurney, J.L., Pascoe, M.D., Richardson, S.H. (Eds.), The J. B. Dawson Vol., Proc. 7th Internat. Kimberlite Conf., Red Roof Designs, Cape Town, pp. 148–155) but differ to diamonds from nearby kimberlites at Ekati (e.g., Lithos (2004); Tappert, R., Stachel, T., Harris, J.W., Brey, G.P., 2004. Mineral Inclusions in Diamonds from the Panda Kimberlite, S. P., Canada. 8th International Kimberlite Conference, extended abstracts) and Snap Lake to the south (Dokl. Earth Sci. 380 (7) (2001) 806), that are dominated by peridotitic stones.

Eclogitic diamonds with variable inclusion compositions and temperatures of formation (1040–1300 °C) crystallised at variable lithospheric depths sometimes in changing chemical environments. A large range to very ¹³C-depleted C-isotope compositions (δ¹³C=−35.8‰ to −2.2‰) and an NMORB bulk composition, calculated from trace elements in garnet and clinopyroxene inclusions, are consistent with an origin from subducted oceanic crust and sediments. Carbon isotopes in the peridotitic diamonds have mantle compositions (δ¹³C mode −4.0‰). Mineral inclusion compositions are largely harzburgitic. Variable temperatures of formation (garnet T_Ni=800–1300 °C) suggest the peridotitic diamonds originate from the shallow ultra-depleted and deeper less depleted layers of the central Slave lithosphere. Carbon isotopes (δ¹³C av.=−5.1‰) and mineral inclusions in the ultradeep diamonds suggest they formed in peridotitic mantle (670 km). The diamonds may have been entrained in a plume and subcreted to the base of the central Slave lithosphere.

Poorly aggregated nitrogen (IaA without platelets) in a large number of eclogitic (67%) and peridotitic (32%) diamonds, with similar nitrogen contents, indicates the diamonds were stored in the mantle at low temperatures (1060–<1100 °C) following crystallisation in the Archean. Type IaA diamonds have largely cubo-octahedral growth forms, and Type II and Type IaAB diamonds, with higher nitrogen aggregation states, mostly have octahedral morphologies. However, no correlation between these groups and their mineral inclusion compositions, C-isotopes, and N-contents rules out the possibility of unique source origins and suggests eclogitic and peridotitic diamonds experienced variable mantle thermal states. Variation in mineral inclusion chemistries in single diamonds, possible overgrowths of ¹³C-depleted eclogitic diamond on diamonds with peridotitic and ultradeep inclusions, and Type I ultradeep diamond with low N-aggregation is consistent with diamond growth over time in changing chemical environments.  相似文献   

Dynamics and role of the Durban cyclonic eddy in the KwaZulu-Natal Bight ecosystem     

LA Guastella  MJ Roberts 《African Journal of Marine Science》2016,38(1):S23-S42

The semi-permanent Durban Eddy is a mesoscale, lee-trapped, cold-core cyclonic circulation that occurs off the east coast of South Africa between Durban in the north and Sezela, some 70 km to the south. When present, strong north-eastward countercurrents reaching 100 cm s^–1 are found inshore. It is hypothesised that the cyclone is driven by the strong south-westward flowing Agulhas Current offshore of the regressing shelf edge near Durban. Analysis of ADCP data and satellite imagery shows the eddy to be present off Durban approximately 55% of the time, with an average lifespan of 8.6 days, and inter-eddy periods of 4 to 8 days. After spin-up the eddy breaks loose from its lee position and propagates downstream on the inshore boundary of the Agulhas Current. The eddy is highly variable in occurrence, strength and downstream propagation speeds. There is no detectable seasonal cycle in eddy occurrence, with the Natal Pulse causing more variability than any seasonal signal. A thermistor array deployed in the eddy centre, together with ship CTD data, indicates upward doming of the thermal structure in the eddy core associated with cooler water and nutrients being moved higher in the water column, stimulating primary production. Together with the use of satellite imagery, our findings indicate a second mechanism of upwelling, viz. divergent upwelling in the northern limb of the eddy. Satellite-tracked surface drifters released in the eddy demonstrated the potential for nutrient-rich eddy water to be transported northwards along the inshore regions of the KwaZulu-Natal (KZN) Bight, thus contributing to the functioning of the bight ecosystem, as well as southwards along the KZN and Transkei coasts – both by the eddy migrating downstream and by eddy water being recirculated into the inshore boundary of the Agulhas Current itself.  相似文献   

Inversion of arrival-times in a region of dilatancy anisotropy     

Mark Doyle  Stuart Crampin  Robert McGonigle  Russ Evans 《Pure and Applied Geophysics》1985,123(3):375-387

Shear-wave splitting has been identified in many three-component seismograms from two separate field experiments on a section of the North Anatolian Fault in North-West Turkey. These observations are consistent with shear-wave propagation through a zone of extensive-dilitancy anisotropy. A preliminary attempt has been made to confirm this interpretation by simultaneously inverting suites of arrival-times for hypocentral locations and for parameters describing an anisotropic halfspace. Although the inversion procedure is not globally convergent, it is possible to recognize the true solution by systematically varying the initial conditions. Applied to selected data sets, the inversion defines several anisotropic models that fit the data significantly better than a simple isotropic model, and display the anisotropy required by the shear-wave splitting. However, most of these anisotropic models are not superior when they are used to individually locate events in a much larger data set. However, for each experiment, there is a single model that produces clearly superior locations for the larger data sets than those of other anisotropic or simple isotropic models. Both models display similar velocity variations which are characteristic of propagation through distributions of biplanar cracks displaying orthorhombic symmetry. The principal axes of the two models are oriented in similar directions and are within 20° of the principal axis of regional stress derived from fault-plane solutions. The solutions indicate low velocities close to the tensional axis, as would be expected in extensive-dilatancy anisotropy.  相似文献   

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?     

Sonja Aulbach  William L. Griffin  Norman J. Pearson  Suzanne Y. O’Reilly  Buddy J. Doyle 《Contributions to Mineralogy and Petrology》2007,154(4):409-427

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr₂O₃ contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al₂O₃ content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites (<7.5 wt%) indicative of melt loss at pressures >3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO₂ contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).  相似文献