The D-CIXS X-ray mapping spectrometer on SMART-1     

M Grande  R BrowningN Waltham  D ParkerS.K Dunkin  B KentB Kellett  C.H PerryB Swinyard  A PerryJ Feraday  C HoweG McBride  K PhillipsJ Huovelin  P MuhliP.J Hakala  O VilhuJ Laukkanen  N ThomasD Hughes  H AlleyneM Grady  R LundinS Barabash  D BakerP.E Clark  C.D MurrayJ Guest  I CasanovaL.C d'Uston  S MauriceB Foing  D.J Heather  V FernandesK Muinonen  S.S RussellA Christou  C OwenP Charles  H KoskinenM Kato  K SipilaS Nenonen  M HolmstromN Bhandari  R ElphicD Lawrence 《Planetary and Space Science》2003,51(6):427-433

The D-CIXS Compact X-ray Spectrometer will provide high quality spectroscopic mapping of the Moon, the primary science target of the ESA SMART-1 mission. D-CIXS consists of a high throughput spectrometer, which will perform spatially localised X-ray fluorescence spectroscopy. It will also carry a solar monitor, to provide the direct calibration needed to produce a global map of absolute lunar elemental abundances, the first time this has been done. Thus it will achieve ground breaking science within a resource envelope far smaller than previously thought possible for this type of instrument, by exploiting two new technologies, swept charge devices and micro-structure collimators. The new technology does not require cold running, with its associated overheads to the spacecraft. At the same time it will demonstrate a radically novel approach to building a type of instrument essential for the BepiColombo mission and potential future planetary science targets.  相似文献   

Tensile stresses around boreholes due to transient fluid flow     

Derek Y. C. Chan  Barry D. Hughes  Lincoln Paterson 《国际地质力学数值与分析法杂志》1993,17(9):659-667

We present solutions for the effective stress induced by gas flow through a porous solid into a borehole resulting from sudden pressure reduction. Tensile effective stress that exceeds the strength of the solid will lead to borehole failure. This has applications to the intentional creation of cavities, relevant to the efficient recovery of coalbed methane, and the avoidance of borehole stability problems in conventional gas production.  相似文献   

Sublethal abnormalities in embryos of winter flounder,Pseudopleuronectes americanus,from Long Island Sound     

D. M. Perry  J. B. Hughes  A. T. Hebert 《Estuaries and Coasts》1991,14(3):306-317

Sublethal abnormalities were examined in developing embryos of the winter flounder,Pseudopleuronectes americanus, as part of a study of its early reproductive success in Long Island Sound and two sites in Boston Harbor. These sites represented varying levels of anthropogenic contamination that were possibly affecting reproduction, as ascertained by chromosomal abnormalities and lowered developmental rates in the embryos. Effort was focused on examination of blastula and tail-bund embryos from field-captured females spawned at the laboratory. Abnormalities observed included evidence of cytotoxicity and chromosome damage. Embryos of fish from New Haven were usually the most aberrant, while embryos from other sites, notably Hempstead, Shoreham, and both Boston Harbor stations, showed subtle indications of abnormality.  相似文献   

Relict olivine grains, chondrule recycling, and implications for the chemical, thermal, and mechanical processing of nebular materials     

Alex Ruzicka  Christine Floss 《Geochimica et cosmochimica acta》2008,72(22):5530-5557

Chondrules and isolated forsterites in five low-subtype ordinary chondrites [NWA 3127 (LL3.1), Sahara 97210 (LL3.2), Wells (LL3.3), Chainpur (LL3.4), and Sahara 98175 (LL3.5)] were studied using petrographic, EMPA, and SIMS techniques to better constrain the origin of chondrules and the olivine grains within them. Our results imply that igneous crystallization, vapor fractionation, redox effects, and open-system behavior were important processes. All olivine grains, including normal, relict, and isolated forsterite grains, show evidence for igneous fractionation under disequilibrium conditions, with olivine crystallizing during rapid cooling (closer to 2000 °C/h than to 100 °C/h). Vapor fractionation is manifested by anti-correlated abundances between refractory elements (Al, Sc, Y, Ti, Ca, V) and volatile elements (Cr, Mn, P, Rb, Fe) in olivine. Redox effects are evidenced in various ways, and imply that Fe, Co, Ni, and P were partitioned more into metal, and V was partitioned more into olivine, under reducing conditions in the most FeO-poor melts. There is no obvious evidence for systematic variations in olivine composition according to meteorite subtype, but shock melting in Sahara 97210 resulted in the injection of glass-derived melt into olivine, resulting in artificially high abundances of Ba, Sr, Na, Ti, and some other incompatible elements in olivine. Terrestrial weathering in a hot desert environment may have mobilized Ba and Sr in some glasses.Our data suggest that chondrules in ordinary chondrites experienced repeated thermal, chemical, and mechanical processing during a “recycling” process over an extended time period, which involved multiple episodes of melting under fluctuating redox and heating conditions, and multiple episodes of chondrule break-up in some cases. Forsterite grains, including normal grains in forsterite-bearing type I chondrules, the cores of isolated forsterites, and relict forsterite in type II chondrules, all crystallized from similar, refractory melts under reducing conditions; relict Mg-olivine and isolated forsterite grains were thus derived from type I chondrules. Olivine in type II chondrules, including normal grains and ferroan overgrowths on relict Mg-olivine, crystallized from more volatile-rich, oxidized, and relatively unfractionated melts. Relict dusty olivine grains in type I chondrules were derived from type II chondrules during incomplete melting episodes involving reduction and some vaporization, with clear (non-dusty) grains in dusty olivine-bearing chondrules crystallizing from the reduced and partly vaporized melts. Melt compositions parental to normal olivine grains in type I and II chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions, implying that chondrules often experienced open-system exchange with more volatile-rich surroundings after some olivine had crystallized, possibly while the chondrules were still partly molten. Type II chondrules could have been derived from type I chondrules by the addition of relatively volatile-rich material, followed by re-melting and little evaporation under oxidizing conditions. In contrast, type I chondrules could have been derived from type II chondrules by re-melting involving more-or-less evaporation under reducing conditions. Chemical, oxygen isotope, and petrographic data are best accommodated by a model in which there were several (>2-3, sometimes ?4-5) melting episodes for most chondrules in ordinary chondrites.  相似文献   

Walleye pollock respond to trawling vessels     

De Robertis  Alex; Wilson  Christopher D. 《ICES Journal of Marine Science》2006,63(3):514-522

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Laboratory wave reflection analysis using co-located gages     

Steven A. Hughes 《Coastal Engineering》1993,20(3-4)

Most coastal and ocean engineering laboratories employ techniques that use two or three spatially separated wave gages to estimate reflection of irregular waves in two-dimensional wave flumes. This paper presents a frequency domain method for separating incident and reflected wave spectra from co-located gages (gages located on the same vertical line). The technique is based on linear wave theory, and it can be applied to time series of sea surface elevation and horizontal water velocity collected in a vertical array, or it can be used with horizontal and vertical water velocity time series collected at the same point in the water column. Application of the method is limited to those frequencies showing good coherence between time series signals. Outside the range of good coherence, gross inaccuracies occur.The utility of the co-located gage method is illustrated using water velocity data collected in a wave flume with a laser Doppler velocimeter, and the method is validated for the case of complete reflection by a vertical wall. Side-by-side comparison to the spatially-separated wave gage method of Goda and Suzuki (1976) exhibited close agreement for a variety of irregular wave trains being weakly reflected by a mild sloping beach. The co-located gage method is useful in situations where there are spatial variations in the wavelength, such as on a mildly sloping bottom, or in the region close to highly reflective structures where errors arising from spatial variations in characteristic wave parameters would corrupt estimates made using the spatially-separated wave gage method.  相似文献   

Effects of beta-naphthoflavone on hepatic biotransformation and glutathione biosynthesis in largemouth bass (Micropterus salmoides)     

Hughes EM  Gallagher EP 《Marine environmental research》2004,58(2-5):675-679

We are investigating the effects of in vivo exposure of prototypical enzyme inducing agents on hepatic biotransformation enzyme expression in largemouth bass (Micropterus salmoides), a predatory game fish found throughout the United States and Canada. The current study targeted those genes involved in biotransformation and oxidative stress that may be regulated by Ah-receptor-dependent pathways. Exposure of bass to beta-naphthoflavone (beta-NF, 66 mg/kg, i.p.) elicited a 7-9-fold increase in hepatic microsomal cytochrome P4501A-dependent ethoxyresorufin O-deethylase (EROD) activities, but did not affect cytosolic GST catalytic activities toward 1-chloro-2,4-dinitrobenzene (CDNB) or 5-androstene-3,17-dione (ADI). Glutathione S-transferase A (GST-A) mRNA expression exhibited a transient, but non-significant increase following exposure to beta-NF, and generally tracked the minimal changes observed in GST-CDNB activities. Expression of the mRNA encoding glutamate-cysteine ligase catalytic subunit (GCLC), the rate-limiting enzyme in glutathione (GSH) biosynthesis, was increased 1.7-fold by beta-NF. Changes in GCLC mRNA expression were paralleled by increases in intracellular GSH. In summary, largemouth bass hepatic CYP1A-dependent and GSH biosynthetic pathways, and to a lesser extent GST, are responsive to exposure to beta-NF.  相似文献   

Dynamics of the long-period tides     

Carl Wunsch  Dale B. Haidvogel  Mohamed Iskandarani  R. Hughes 《Progress in Oceanography》1997,40(1-4)

The long-period tides are a tool for understanding oceanic motions at low frequencies and large scales. Here we review observations and theory of the fortnightly, monthly and pole tide constitutents. Observations have been plagued by low signal-to-noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes. A new spectral element model is used to compute the oceanic response to tidal forcing at 2-week and monthly periods. The general response is that of a heavily damped (Q ≈ 5) system with both the energy input from the moon and the dissipation strongly localized in space. The high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions. Over much of the ocean, the response has both the character of a large-scale and a superposed Rossby wave-like character, thus vindicating two apparently conflicting earlier interpretations. To the extent that free waves are excited they are consistent with their being dominated by Rossby and topographic Rossby wave components, although gravity modes are also necessarily excited to some degree. In general, a modal representation is not very helpful. The most active regions are the Southern Ocean and the western and northern North Atlantic. These results are stable to changes in geometry, topography, and tide period. On a global average basis, the dynamical response of Mm is closer to equilibrium than is Mf.  相似文献   

Tidally incised valleys on tropical carbonate shelves: An example from the northern Great Barrier Reef, Australia     

Peter T. Harris  Andrew Heap  Vicki Passlow  Michael Hughes  James Daniell  Mark Hemer  Ole Anderson 《Marine Geology》2005,220(1-4):181-204

The formation of incised valleys on continental shelves is generally attributed to fluvial erosion under low sea level conditions. However, there are exceptions. A multibeam sonar survey at the northern end of Australia's Great Barrier Reef, adjacent to the southern edge of the Gulf of Papua, mapped a shelf valley system up to 220 m deep that extends for more than 90 km across the continental shelf. This is the deepest shelf valley yet found in the Great Barrier Reef and is well below the maximum depth of fluvial incision that could have occurred under a − 120 m, eustatic sea level low-stand, as what occurred on this margin during the last ice age. These valleys appear to have formed by a combination of reef growth and tidal current scour, probably in relation to a sea level at around 30–50 m below its present position.

Tidally incised depressions in the valley floor exhibit closed bathymetric contours at both ends. Valley floor sediments are mainly calcareous muddy, gravelly sand on the middle shelf, giving way to well-sorted, gravely sand containing a large relict fraction on the outer shelf. The valley extends between broad platform reefs and framework coral growth, which accumulated through the late Quaternary, coincides with tidal current scour to produce steep-sided (locally vertical) valley walls. The deepest segments of the valley were probably the sites of lakes during the last ice age, when Torres Strait formed an emergent land-bridge between Australia and Papua New Guinea. Numerical modeling predicts that the strongest tidal currents occur over the deepest, outer-shelf segment of the valley when sea level is about 40–50 m below its present position. These results are consistent with a Pleistocene age and relict origin of the valley.

Based on these observations, we propose a new conceptual model for the formation of tidally incised shelf valleys. Tidal erosion on meso- to macro-tidal, rimmed carbonate shelves is enhanced during sea level rise and fall when a tidal, hydraulic pressure gradient is established between the shelf-lagoon and the adjacent ocean basin. Tidal flows attain a maximum, and channel incision is greatest, when a large hydraulic pressure gradient coincides with small channel cross sections. Our tidal-incision model may explain the observation of other workers, that sediment is exported from the Great Barrier Reef shelf to the adjacent ocean basins during intermediate (rather than last glacial maximum) low-stand, sea level positions. The model may apply to other rimmed shelves, both modern and ancient.  相似文献   

Optical water type discrimination and tuning remote sensing band-ratio algorithms: Application to retrieval of chlorophyll and K_d(490) in the Irish and Celtic Seas     

David McKee  Alex Cunningham  Agnes Dudek 《Estuarine, Coastal and Shelf Science》2007,73(3-4):827-834

This paper assesses the feasibility of applying remote sensing algorithms based on blue/green reflectance ratios to Case 2 waters. Two algorithms from the SeaDAS (NASA) image processing package, OC4v4 for surface chlorophyll concentration, Chl, and K(490) for the attenuation coefficient for downward irradiance at 490 nm, K_d(490), were investigated using an extensive set of observations from the Irish and Celtic Seas. In situ data from a profiling radiometer were used as inputs for the algorithms to avoid uncertainties in atmospheric correction procedures, and direct measurements of Chl and K_d490 and were used for validation purposes. The standard versions of the algorithms performed poorly: OC4v4 generally overestimated Chl (with a very low coefficient of determination), and K(490) progressively underestimated K_d490 for values greater than 0.3 m⁻¹. A two-step procedure for level 2 product generation was therefore devised in which the numerical coefficients of OC4v4 and K(490) were tuned for the two optical water types known to occur most frequently in this region (McKee, D., Cunningham, A., 2006. Identification and characterisation of two optical water types in the Irish Sea from in situ inherent optical properties and seawater constituents. Estuarine, Coastal and Shelf Science 68, 305–316) by statistical regression on a data set of 102 stations from the Irish and Celtic Seas. The water types were distinguished by the magnitude of their normalised water leaving radiance signals at 665 nm, nL_w(665), and appropriate versions of the tuned algorithms applied to each water type. When this procedure was tested on an independent data set of 19 stations from the Bristol Channel, Chl values were recovered with an RMS error of 0.36 mg m⁻³ and K_d(490) values with an RMS error of 0.095 m⁻¹. The identification of water types from water-leaving radiance signals, and the application of band-ratio algorithms tuned for specific water types, may therefore provide a simple means of improving the quality of remote sensing products in optically complex shelf seas.  相似文献