Plasma bubbles near the dawn terminator in the topside ionosphere     

William I. Burke 《Planetary and Space Science》1979,27(9):1187-1193

The physical properties of plasma bubbles in the topside ionosphere near the dawn terminator are investigated. It is assumed that the bubbles result from either a Rayleigh-Taylor or an $\text{E}\text{×}\text{B}$ instability on the bottom side of the F-layer. While the E-region is in darkness, the top and bottomsides of the ionosphere are electrically decoupled and the motion of bubbles can be described by non-linear, two-dimensional theory. After sunrise, electric fields within the bubbles discharge through the conducting lower ionosphere. The upward drift of the bubbles is effectively halted. To achieve a dayside state of diffusive equilibrium the bubbles slowly begin to collapse from the bottom.  相似文献   

Improving sub-salt imaging using 3D basin model derived velocities     

R. Stephan Petmecky  Martin L. Albertin  Nick Burke 《Marine and Petroleum Geology》2009

The quality of depth imaging is directly related to the accuracy of the underlying velocity model. In most sub-salt settings, lack of angular illumination severely degrades the resolution and accuracy of velocity information derived from the seismic data itself. A standard approach for building a starting velocity model uses more reliable velocity information outboard of salt which is subsequently extrapolated to populate the sub-salt regions. The shortcoming of this method lies in the assumption that the effective stress observed outboard of salt can be extrapolated beneath salt solely as a function of depth below mudline.  相似文献   

Orogenic andesites and plate tectonics: James B. Gill. Minerals and Rocks,xiv + 390 pp., 109 figs., DM. 98.00, Vol. 16, Springer-Verlag,Berlin, 1981, v U.S. $44.60 (approx.)     

Kevin Burke 《Precambrian Research》1983,19(3):317-318

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Nutrient and carbon removal ratios and fluxes in the Ross Sea, Antarctica     

Colm Sweeney  Walker O. Smith  Burke Hales  Robert R. Bidigare  Craig A. Carlson  L. A. Codispoti  Louis I. Gordon  Dennis A. Hansell  Frank J. Millero  Mi-OK Park  Taro Takahashi 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)

Net community production (NCP) and nutrient deficits (Def(X)) were calculated using decreases in dissolved CO₂ and nutrient concentrations due to biological removal in the upper 200 m of the water column during four cruises in the Ross Sea, Antarctica along 76°30′S in 1996 and 1997. A comparison to excess dissolved and particulate organic carbon showed close agreement between surplus total organic carbon (TOC) and NCP during bloom initiation and productivity maximum; however, when TOC values had returned to low wintertime values NCP was still significantly above zero. This seasonal NCP, 3.9±1 mol C m⁻², must be equivalent to the particle export to depths greater than 200 m over the whole productive season. We estimate that the annual export was 55±22% of the seasonal maximum in NCP. The fraction of the seasonal maximum NCP that is exported through 200 m is significantly higher than that measured by moored sediment traps at a depth of 206 m. The removal of carbon, nitrate and phosphate (based on nutrient disappearance since early spring) and their ratios showed significant differences between regions dominated by diatoms and regions dominated by the haptophyte Phaeocystis antarctica. While the ΔC/ΔN removal ratio was similar (7.8±0.2 for diatoms and 7.2±0.1 for P. antarctica), the ΔN/ΔP and ΔC/ΔP removal ratios for diatoms (10.1±0.3 and 80.5±2.3) were significantly smaller than those of P. antarctica (18.6±0.4 and 134.0±4.7). The similarity in ΔC/ΔN removal ratios of the two assemblages suggests that preferential uptake of phosphate by diatoms caused the dramatic differences in ΔC/ΔP and ΔN/ΔP removal ratios. In contrast to low ΔC/ΔP and ΔN/ΔP removal ratio in diatom-dominated areas early in the growing season, deficit N/P and C/P ratios in late autumn indicate that the elemental stochiometry of exported organic matter did not deviate significantly from traditional Redfield ratios. Changes in biologically utilized nutrient and carbon ratios over the course of the growing season indicated either a substantial remineralization of phosphate or a decrease in phosphate removal relative to carbon and total inorganic nitrogen over the bloom period. The species dependence in C/P ratios, and the relative constancy in the C/N ratios, makes N a better proxy of biological utilization of CO₂.  相似文献   

Silicon-on-Insulator-Based Single-Chip Image Sensors: Low-Voltage Scientific Imaging     

Vyshnavi Suntharalingam  Barry E. Burke  Michael J. Cooper 《Experimental Astronomy》2002,14(2):91-98

A low-voltage (≤3.3 V) imaging technology has been developed to enable scientific-grade imagers with low-power complex functions on chip. A 128 × 128 CCD imager with on-chip clocking and charge-domain analog-to-digital conversion, as well as an exploratory active pixel sensor have been demonstrated. A 640 × 960 CCD imager with optimized 12 bit charge-domain conversion and an improved active pixel sensor are presently in fabrication. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Evolution of Brightest Cluster Galaxies     

Ch. Collins  S. Brough  D. Burke  R. Mann  P. Lynam 《Astrophysics and Space Science》2003,285(1):51-60

In this contribution we review the properties of Brightest Cluster Galaxies (BCGs) and discuss the impact that X-ray cluster selection is having on their use as cosmological probes. BCGs form a unique galaxy population. They are located near the gravitational centre of galaxy clusters and are the most massive galaxies in the universe, being some 10 times more luminous than L* systems. Historically, BCGs have been credited with small intrinsic dispersion in their absolute magnitudes (Δ≃0.2–0.3 mag) and used as standard candles to constrain the cosmological parameters. Although indirect signs of mass accretion out to z≃1 have been observed, uncovering their full evolutionary picture has remained an elusive goal. Studies of BCGs based on serendipitiously discovered X-ray cluster samples, particularly from ROSAT, provide large numbers of unbiased clusters at z≤1. Furthermore X-ray emission guarantees the presence of a large gravitationally bound potential well and the X-ray information can be used to locate the centroids of clusters, aiding the identification of the BCG. We show that this has important consequences for studies of distance determination and large-scale streaming flows based on the optical properties of BCGs. Recent results based on X-ray selected clusters show large differences in near-IR BCG properties with their cluster environment; such that those in clusters with L _x≥1.9×10⁴⁴erg s^-1 are brighter and more uniform than those in their low-L _x counterparts. The BCGs in highL _x systems show no evidence of having undergone mass growth, whereas those in low L _x systems show a widerrange of evolution, with evidence that some have grown by a factor of 4 ormore since z≃1. These results are a direct indication of howa single homogeneous population of galaxies evolves and are a challenge to simple semi-analytical hierarchical models. If future observations at high redshift are to seriously challenge theory then better predictions of the evolutionary process are required. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

New Minerals Approved in 2003 and Nomenclature Modifications Approved in 2003 by the Commission on New Minerals and Mineral Names, International Mineralogical Association     

E. A. J. Burke  G. Ferraris 《Mineralogy and Petrology》2004,82(1-2):161-177

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Geological interpretation of current subsidence and uplift in the London area,UK, as shown by high precision satellite-based surveying     

Don Aldiss  Helen Burke  Barrie Chacksfield  Richard Bingley  Norman Teferle  Simon Williams  David Blackman  Richard Burren  Nigel Press 《Proceedings of the Geologists' Association. Geologists' Association》2014

Long term planning for flood risk management in coastal areas requires timely and reliable information on changes in land and sea levels. A high resolution map of current changes in land levels in the London and Thames estuary area has been generated by satellite-based persistent scatterer interferometry (PSI), aligned to absolute gravity (AG) and global positioning system (GPS) measurements. This map has been qualitatively validated by geological interpretation, which demonstrates a variety of controlling influences on the rates of land level change, ranging from near-surface to deep-seated mechanisms and from less than a decade to more than 100,000 years’ duration.  相似文献   

The effects of surface weathering on the geochemical analysis of archaeological lithic samples using non‐destructive polarized energy dispersive XRF     

Gilles Gauthier  Adrian L. Burke 《Geoarchaeology》2011,26(2):269-291

The purpose of this paper is to show the effects of lithic artifact surface weathering on whole rock non‐destructive polarized energy dispersive X‐ray fluorescence (P‐ED‐XRF) major and trace element determinations. Chemical results for a weathered and subsequently mechanically ground subset of New Hampshire Ossipee archaeological flakes, cataloged as hornfels, show that both groups of elements are variably affected by weathering. A graphic approach is developed and proposed to highlight the role and importance of immobile elements. A case is made and an analytical method is proposed for the routine use of P‐ED‐XRF spectrometers to determine the chemical makeup of lithic artifacts and therefore provide a data set compatible with existing geochemical databases and literature. The use of specific variation diagrams is adopted to portray the weathering trend. Internationally approved geochemical rock type diagrams are used to correct the rock type previously assigned to Ossipee artifacts and in turn narrow down potential quarry sources. © 2011 Wiley Periodicals, Inc.  相似文献   

Solar wind contribution to surficial lunar water: Laboratory investigations     

D.J. Burke 《Icarus》2011,211(2):1082-1088

Remote infrared spectroscopic measurements have recently re-opened the possibility that water is present on the surface of the Moon. Analyses of infrared absorption spectra obtained by three independent space instruments have identified water and hydroxyl (-OH) absorption bands at ∼3 μm within the lunar surface. These reports are surprising since there are many mechanisms that can remove water but no clear mechanism for replenishment. One hypothesis, based on the spatial distribution of the -OH signal, is that water is formed by the interaction of the solar wind with silicates and other oxides in the lunar basalt. To test this hypothesis, we have performed a series of laboratory simulations that examine the effect of proton irradiation on two minerals: anorthite and ilmenite. Bi-directional infrared reflection absorption spectra do not show any discernable enhancement of infrared absorption in the 3 μm spectral region following 1 or 100 keV proton irradiation at fluences between 10¹⁶ and 10¹⁸ ions cm⁻². In fact, the post-irradiation spectra are characterized by a decrease in the residual O-H band within both minerals. Similarly, secondary ion mass spectrometry shows a decrease rather than an increase of the water group ions following proton bombardment of ilmenite. The absence of significant formation of either -OH or H₂O is ascribed to the preferential depletion of oxygen by sputtering during proton irradiation, which is confirmed by post-irradiation surface analysis using X-ray photoelectron spectroscopy measurements. Our results provide no evidence to support the formation of H₂O in the lunar regolith via implantation of solar wind protons as a mechanism responsible for the significant O-H absorption in recent spacecraft data. We determine an upper limit for the production of surficial -OH on the lunar surface by solar wind irradiation to be 0.5% (absorption depth).  相似文献