Imaging the Sun at 21 cm: Budgetting the S-component     

I. E. Burke  K. F. Tapping 《Solar physics》1995,157(1-2):295-314

On fourteen days in July and August 1992 and June 1993, we used the 7-element synthesis radio telescope at the Dominion Radio Astrophysical Observatory to make full-disc, arc-min resolution images of the Sun at 21 cm, with the objective of budgetting the contributions to the slowly-varying component of solar radio emission. This instrument has the advantage that the mapping field at this wavelength is about 2.5° wide. However, it has also the severe disadvantage that with only 12 hours to record each image, the brightness distribution is severely undersampled. This difficulty, along with solar rotation and declination motion during each observation, required development of special image correction procedures.The two observing sessions spanned about 25% of the activity range over a solar cycle. Over this range, comparable contributions to the slowly-varying component came from active region sources and a weak emission, widely-distributed over the solar disk. Both these contributions are correlated with the total photospheric magnetic flux and with the 10.7 cm flux.  相似文献   

Concerning KAr dating of a basalt flow from the Tahoe-Tioga interglaciation,Sawmill Canyon,southeastern Sierra Nevada,California     

G.Brent Dalrymple  R.M. Burke  Peter W. Birkeland 《Quaternary Research》1982,17(1):120-122

New KAr ages for a basalt flow interbedded with Tahoe and Tioga tills in Sawmill Canyon, southeastern Sierra Nevada, slightly refine previously published ages for the flow and provide an estimate of 53,000 ± 44,000 yr for the Tahoe-Tioga interglaciation.  相似文献   

Light hydrocarbons in Red Sea brines and sediments     

Roger A. Burke  James M. Brooks  William M. Sackett 《Geochimica et cosmochimica acta》1981,45(5):627-634

Light hydrocarbon (C₁-C₃) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 85‰}$, $\text{CH}{}_4\text{=}\text{~ 71}\text{1}$) are apparently of biogenic origin as evidenced by $\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3$) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 73‰}$, CH₄ = ~ 155 μl/l) gas seems to be of biogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~1100}$], whereas the lower brine (T = ~ 61°C, $\text{Cl}{}^{\mathrm{?}}\text{= ~ 155‰}$, CH₄ = ~ 120μl/l) gas is apparently of thermogenic origin [$\text{C}{}_1\text{(C}{}_2\text{+ C}{}_3\text{) = ~ 50}$]. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin.  相似文献   

Extensional tectonics and mid-Paleozoic massive sulfide occurrences in Europe     

F. J. Sawkins  Kevin Burke 《International Journal of Earth Sciences》1980,69(2):349-360

The age and lithologic settings of mid-Paleozoic massive sulfide deposits in Central Europe and southwest Iberia are suggestive of extensional tectonic environments. This inference is supported by the facies configurations of contemporaneous clastic sediments, the presence of deepwater lithologies and pelagic faunas, and marked mafic-felsic bimodalism in associated volcanic rocks.The massive sulfide deposits of the Moravia-Silesia area, Rammelsberg, Meggen, and other deposits appear to have formed in the same tectonic environment: one dominated by crustal extension. The important massive sulfide deposits of the southwest Iberian province formed somewhat later, but appear to be related to a phase of crustal extension initiated in late Devonian time.These two sets of rifting (sensu latu) events correlate in time with Caledonide collision in the north and subsequent Acadian collision further south. The postulated extensional events thus may relate directly to these collisions.All the areas under consideration were subsequently affected by Hercynian compressional events. The high potash granites associated with Hercynian collisions are largely the products of crustal melting and consequently have associated with them ore deposits characterized by lithophile elements such as tin, tungsten and uranium. A significant fraction of the Paleozoic metallogeny of Europe can thus be understood in terms of extensional tectonic events followed by compressional events less than 100 m.y. later.

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Zusammenfassung Das Alter und die lithologische Zusammensetzung von massiven Sulfiderzlagerstätten des Devons in Mittel-Europa und Südwest-Iberien deuten auf eine Ausweitungstektonik. Diese Hypothese wird bekräftigt durch die Fazieskonfiguration gleichalter klastischer Sedimente, das Auftreten von Tiefseeablagerungen und pelagischen Faunen, und die ausgesprochen mafisch-felsische Bimodalität von assoziierten Vulkaniten.Die massiven Sulfidlagerstätten von Mähren und Schlesien, Rammelsberg, Meggen und andere Vorkommen scheinen sich unter den gleichen tektonischen Bedingungen gebildet zu haben, nämlich unter Dehnungseffekten der Kruste. Die wichtigsten massiven Sulfidlagerstätten der südwestlichen Iberischen Provinz entstanden etwas später, sie scheinen einer Dehnungsphase beginnend im höheren Devon zugeordnet zu sein.Diese zwei Phasen eines Riftings (sensu lato) stimmen zeitlich mit der kaledonischen Kollision im Norden und der darauffolgenden akadischen Kollision weiter südlich überein. Die angenommenen Dehnungsvorgänge können daher direkt mit diesen Kollisionen in Verbindung gebracht werden.Alle besprochenen Gebiete sind in der Folge von herzynischen Einengungs-Erscheinungen betroffen worden. Die hochgradig kali-haltigen Granite, die den herzynischen Kollisionen zugeordnet sind, sind größtenteils die Ergebnisse von krustalen Schmelzvorgängen und haben deshalb assoziierte Erzlagerstätten, die durch lithophile Elemente wie Zinn, Wolfram und Uran gekennzeichnet sind. Ein beträchtlicher Teil der paläozoischen Metallogenese Europas kann daher aus der Sicht distraktiver tektonischer Erscheinungen gesehen werden, deren Einengungs-Vorgänge weniger als 100 Millionen Jahre später folgten.

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Résumé L'âge et la composition lithologique des gisements de sulferes massifs du Paléozoïque moyen de l'Europe Centrale et du sud-ouest de la Péninsule ibérique suggèrent un environement tectonique de distension. Cette hypothèse est appuyée par la configuration des facies des sédiments clastiques contemporains, la présence de lithologies d'eau profonde et de faunes pélagiques et par l'existence d'un net bimodalisme mafique-felsique dans les roches volcaniques associées.Les importants gisements de sulfere de Moravie et de Silésie, du Rammelsberg, de Meggen et autressemblent s'être formés sous un régime tectonique semblable, principalement sous l'effet de distensions de la croûte. Les gisements du sud-ouest de la Péninsule ibérique se sont formés un jeu plus tard, mais semblent être liés à une phase de distension crustale ayant débutéau Dévonien supérieur.Ces deux séries de ruptures (sensu latu) sont corrélés dans le temps avec la collision calédonienne au nord et la collision acadienne subséquente plus au sud.Les évènements de distension invoqués peuvent done être directement liés à ces collisions.Toutes les régions considérées ici furent affectées plus tard par la compression hercynienne. Les granites à haute teneur en potasse, liés aux collisions hercyniennes sont, en grande partie, des produits de la fusion crustale. Ils sont par conséquent associés à des gisements de minerais d'étain, de tungstène et d'uranium. Une partie importante de la métallogénie paléozoïque de l'Europe peut être ainsi comprise en termes d'événements tectoniques de distensions suivis moins de 100 millions d'années plus tard, par une compression.

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Reevaluation of multiparameter relative dating techniques and their application to the glacial sequence along the eastern escarpment of the Sierra Nevada,California   总被引：1，自引：0，他引：1  

R.M. Burke  Peter W. Birkeland 《Quaternary Research》1979,11(1):21-51

Four valleys, recently studied by other workers, were examined along the eastern Sierra Nevada to refine relative-dating techniques. A variety of weathering parameters and soil properties fail to delineate more than two major post-Sherwin Pleistocene glaciations. We correlate these two glaciations with the Tahoe and Tioga Glaciations. Type Mono Basin Till, usually considered to be pre-Tahoe, exhibits the following weathering similarities with Tahoe Till, if both are under sagebrush: (1) grusification of subsurface granitic boulders; (2) degree of pitting, mineral relief, and rind development on surface granitic boulders; and (3) very slight clay increase in the B horizon. Type Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my (Bailey et al. 1976), which bracket type Casa Diablo, may provide age control on the Tahoe glaciation. In addition, we are unable to demonstrate that the Tenaya is a separate glaciation. In three of the four valleys studied our weathering data for Tenaya Till are equivalent with those for Tioga Till, but with those for Tahoe Till in the fourth valley. We were not satisfied with our ability to differentiate the Casa Diablo, Mono Basin, and Tenaya as separate glaciations even though data were collected in the type areas for two of these deposits. Reasons for suggesting a change back to a two-fold Tahoe-Tioga glacial sequence, rather than the present five-fold sequence, are that we have measured a greater number of parameters than has been done previously, soils were submitted to detailed laboratory analyses, and surface weathering features were studied under consistent present vegetation cover to avoid possible problems induced by ancient forest fires. Nevertheless our relative-dating scheme does not rule out the possibility of a more detailed glacial sequence.  相似文献   

Nucleus content of air in occupied rooms     

T. Burke  O. Carm  P. J. Nolan 《Pure and Applied Geophysics》1955,31(1):191-196

Summary 1)Indoor concentration is less than outdoor concentration when precautions are taken to prevent indoor contamination of the air; 2) Nuclei are not produced by breathing. The nucleus content of exhaled air is less than that of the inhaled air; the loss appears to be mainly a diffusion loss; 3) Occupancy does not produce any detectable change in nucleus content; 4) A hypothesis is advanced to explain how occupancy might cause a slight decrease in small ion content without causing any increase in nucleus content.

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Zusammenfassung 1)Die Konzentration der Kondensatjionskerne innerhalb eines Hauses ist geriuger als jene im Freien, wenn Vorsichtsmassnahmen gegen Verunreinigung der Luft innerhalb des Hauses getroffen werden; (2) Kerne werden nicht durch Atmen erzeugt. Der Kerngehalt der ausgeatmeten Luft ist geringer als jener der eingeatmeten Luft; der Verlust scheint hauptsächlich durch Diffusion zu erfolgen;3) Bewohnen der Räume scheint keine nachweisbare Aeuderung im Kerngehalte zu erzeugen; 4) Es wird eine Hypothese aufgestellt, wie das Bewohnen der Räume eine kleine Abnahme des Gehaltes an kleinen Ionen erzeugen kann, ohne eine Vermehrung des Kerngehaltes zu verursachen.

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Fluid inclusions in Scourian granulites from the Lewisian complex of NW Scotland: evidence for CO₂-rich fluid in Late Archaean high-grade metamorphism     

T. Andersen  M.J. Whitehouse  E.A.J. Burke 《Lithos》1997,40(2-4):93-104

In this paper the first fluid-inclusion data are presented from Late Archaean Scourian granulites of the Lewisian complex of mainland northwest Scotland. Pure CO₂ or CO₂-dominated fluid inclusions are moderately abundant in pristine granulites. These inclusions show homogenization temperatures ranging from − 54 to + 10 °C with a very prominent histogram peak at − 16 to − 32 °C. Isochores corresponding to this main histogram peak agree with P-T estimates for granulite-facies recrystallization during the Badcallian (750–800 °C, 7–8 kbar) as well as with Inverian P-T conditions (550–600 °C, 5 kbar). The maximum densities encountered could correspond to fluids trapped during an early, higher P-T phase of the Badcallian metamorphism (900–1000 °C, 11–12 kbar). Homogenization temperatures substantially higher than the main histogram peak may represent Laxfordian reworking (≤ 500 °C, < 4 kbar). In the pristine granulites, aqueous fluid inclusions are of very subordinate importance and occur only along late secondary healed fractures. In rocks which have been retrograded to amphibolite facies from Inverian and/or Laxfordian shear zones, CO₂ inclusions are conspicuously absent; only secondary aqueous inclusions are present, presumably related to post-granulite hydration processes. These data illustrate the importance of CO₂-rich fluids for the petrogenesis of Late Archaean granulites, and demonstrate that early fluid inclusions may survive subsequent metamorphic processes as long as no new fluid is introduced into the system.  相似文献   

An X-ray absorption study of the fate of technetium in reduced and reoxidised sediments and mineral phases     

K. Morris  F.R. Livens  J.M. Charnock  I.T. Burke  J.M. McBeth  J.D.C. Begg  C. Boothman  J.R. Lloyd 《Applied Geochemistry》2008

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The Orthogonal Transfer CCD     

John Tonry  Barry E. Burke 《Experimental Astronomy》1998,8(1):77-87

The Orthogonal Transfer CCD (OTCCD) is a device to carry out image motion compensation within a CCD. This paper presents three main points about the OTCCD: 1) Science grade OTCCD devices have been produced and work better than expected. 2) The big concern we had about the OTCCD was that pocket pumping would make it useless, but this appears to be a fairly minor problem. 3) Finally, the atmosphere is more benign than we might have feared, and significant gains in sharpening the point spread function (PSF) can be had simply with image motion compensation.  相似文献   

How special are Etendeka mesas? Flora and elevation gradients in an arid landscape in north-west Namibia     

Antje Burke   《Journal of Arid Environments》2003,55(4):747-764

Seven mesas (i.e. flat-topped, isolated mountains) and the Grootberg mountain in arid north-west Namibia were investigated with regard to floristic relationships in relation to environmental gradients. Relationships between mesas and their surrounding, species richness and number of mesa specialists were used as measures to explore the influence of elevation on these floristic parameters. Also soil properties were investigated along these elevation gradients. The overall questions were designed to investigate the importance, i.e. ‘special status’, of these mesas in terms of contributing to species diversity and to elucidating ecological processes in this arid landscape.With regard to special floristic status, the tops of mesas supported different plant communities than their surrounding plains, while slopes indicated various levels of intermingling with plain vegetation. Differences between mesas and plains became more pronounced with increasing elevation. There were, however, no clear vegetation belts related to elevation. Plant species richness and number of mesa specialists showed a trend of increasing numbers with elevation, but these trends were statistically poorly supported, largely due to high variability between samples.Do soil gradients and elevation, as two important environmental variables, affect this ‘special’ status? Pronounced soil gradients were evident for many soil properties. These in combination with altitudinal effects of increased moisture and lower temperatures were believed to directly influence plant species composition and richness. The soil gradients may also indicate nutrient flow from the mesas to the surrounding lowlands, a process of ecological importance, particularly should degradation due to over grazing become a problem in the lowland areas.  相似文献