On the Compatibility of a Flux Transport Dynamo with a Fast Tachocline Scenario     

Bidya Binay Karak  Kristof Petrovay 《Solar physics》2013,282(2):321-334

The compatibility of the fast-tachocline scenario with a flux-transport dynamo model is explored. We employ a flux-transport dynamo model coupled with simple feedback formulae relating the thickness of the tachocline to the amplitude of the magnetic field or to the Maxwell stress. The dynamo model is found to be robust against the nonlinearity introduced by this simplified fast-tachocline mechanism. Solar-like butterfly diagrams are found to persist and, even without any parameter fitting, the overall thickness of the tachocline is well within the range admitted by helioseismic constraints. In the most realistic case of a time- and latitude-dependent tachocline thickness linked to the value of the Maxwell stress, both the thickness and its latitudinal dependence are in excellent agreement with seismic results. In nonparametric models, cycle-related temporal variations in tachocline thickness are somewhat larger than admitted by helioseismic constraints; we find, however, that introducing a further parameter into our feedback formula readily allows further fine tuning of the thickness variations.  相似文献   

Inuit spring hunting techniques and local knowledge of the ringed seal in Arctic Bay (Ikpiarjuk), Nunavut     

Chris M. Furgal  Stuart Innes  Kit M. Kovacs 《Polar research》2002,21(1):1-16

Inuit hunting techniques used to catch ringed seals ( Phoca hispida ) were observed April-June 1993 on the land-fast ice of Admiralty Inlet, Nunavut, and adjoining fjords and bays. In addition, a survey of hunting techniques and knowledge of ringed seal biology and behaviour was conducted in the community of Arctic Bay (Ikpiarjuk), Nunavut, January-February 1994. A total of 246 seal structures were found in 31 days of hunting and 34 successful kills were observed. An experienced Inuk hunter found subnivean structures by sight, by walking on drifts and by probing snowdrifts with a harpoon ( unaaq ). Most structures were found using subtle visual cues. Breaking through the roof of a lair was the most common hunting technique observed in this study. Pups captured in this manner were subsequently used to lure the mother back into the breathing hole where she was harpooned. Ringed seals were also hunted by a number of other methods that have been described previously in the literature. Respondents in the hunter survey indicated that the ringed seal was the most important animal used by Arctic Bay Inuit. They also reported a variety of biological findings about ringed seals including: size differences among seals in different regions of the pack ice; that adult male ringed seals ( tiggak ) emitted a strong, mustelid-like odour from December until late May or early June. Hunters also reported that males were occasionally caught when coming to retrieve pups. All respondents reported seeing increasing frequencies of liver abnormalities in their ringed seal catches.  相似文献   

Effect of Nitrate Addition on Biorestoration of Fuel-Contaminated Aquifer: Field Demonstration   总被引：2，自引：0，他引：2  

S. R. Hutchins  W. C. Downs  J. T. Wilson  G. B. Smith  D. A. Kovacs  D. D. Fine  R. H. Douglass  D. J. Hendrix 《Ground water》1991,29(4):571-581

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The Canada Basin: Aeromagnetic constraints on structure and evolution     

P.R. Vogt  P.T. Taylor  L.C. Kovacs  G.L. Johnson 《Tectonophysics》1982,89(1-3)

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Results from an aeromagnetic investigation of the nares strait region     

Louis C. Kovacs  S.P. Srivastava  H. Ruth Jackson 《Journal of Geodynamics》1986,6(1-4)

An analysis of published and recently collected aeromagnetics in the Naires Strait region shows that short wavelength, moderate amplitude magnitic anomalies are coincident with previously mapped Precambrian Shield rocks under southeast Ellesmere Island. Similar magnetic anomalies are also observed in northwestern Greenland across Nares Strait. On Greenland the characteristic magnetic anomalies persist about 105 km beyond and northeast of the exposed Precambrian outcrops. This suggests that the Greenland Pre-Cambrian Shield structures previously shown as only occuring as far north as Inglefield Land actually extend at least 100 km further north. Correlation of the magnetic anomalies with mapped geological units suggest a 105+−10 km left lateral displacement in the boundary between the Lower Paleozoic and Precambrain terrains across Nares Strait. This, we interpret, is due to the relative motion between Greenland and Ellesmere Island during the evolution of the Labrador Sea and Baffin Bay in the Early to Mid Tertiary.  相似文献   

Seismic Properties of Anita Bay Dunite: an Exploratory Study of the Influence of Water     

Aizawa  Yoshitaka; Barnhoorn  Auke; Faul  Ulrich H.; Fitz Gerald  John D.; Jackson  Ian; Kovacs  IstvAn 《Journal of Petrology》2008,49(4):841-855

As a pilot study of the role of water in the attenuation ofseismic waves in the Earth's upper mantle, we have performeda series of seismic-frequency torsional forced-oscillation experimentson a natural (Anita Bay) dunite containing accessory hydrousphases, at high temperatures to 1300°C and confining pressure(P_c) of 200 MPa, within a gas-medium high-pressure apparatus.Both oven-dried and pre-fired specimens wrapped in Ni–Fefoil within the (poorly) vented assembly were recovered essentiallydry after 50–100 h of annealing at 1300°C followedby slow staged cooling. The results for those specimens indicatebroadly similar absorption-band viscoelastic behaviour, butwith systematic differences in the frequency dependence of strain-energydissipation Q^–1, attributed to differences in the smallvolume fraction of silicate melt and its spatial distribution.In contrast, it has been demonstrated that a new assembly involvinga welded Pt capsule retains aqueous fluid during prolonged exposureto high temperatures—allowing the first high-temperaturetorsional forced-oscillation measurements under high aqueousfluid pore pressure P_f. At temperatures >1000°C, a markedreduction in shear modulus, without concomitant increase inQ^–1, is attributed to the widespread wetting of grainboundaries resulting from grain-scale hydrofracturing and themaintenance of conditions of low differential pressure P_d =P_c – P_f . Staged cooling from 1000°C is accompaniedby decreasing P_f and progressive restoration of significantlypositive differential pressure resulting in a microstructuralregime in which the fluid on grain boundaries is increasinglyrestricted to arrays of pores. The more pronounced viscoelasticbehaviour observed within this regime for the Pt-encapsulatedspecimen compared with the essentially dry specimens may reflectboth water-enhanced solid-state relaxation and the direct influenceof the fluid phase. The scenario of overpressurized fluids andhydrofracturing in the Pt-encapsulated dunite specimen may havesome relevance to the high Q^–1 and low-velocity zonesobserved in subduction-zone environments. The outcomes of thisexploratory study indicate that the presence of water can havea significant effect on the seismic wave attenuation in theupper mantle and provide the foundation for more detailed studieson the role of water. KEY WORDS: seismic wave attenuation; water; dunite; hydrous mineral; shear modulus; viscoelasticity; olivine; grain-scale hydrofracturing  相似文献   

Mapping the 3D dark matter with weak lensing in COMBO-17     

A. N. Taylor  D. J. Bacon  M. E. Gray  C. Wolf  K. Meisenheimer  S. Dye  A. Borch  M. Kleinheinrich  Z. Kovacs  L. Wisotzki 《Monthly notices of the Royal Astronomical Society》2004,353(4):1176-1196

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Gamma ray spectrum of the crab nebula in the multi TeV region     

THEMISTOCLE collaboration  P. Baillon  L. Behr  S. Danagoulian  B. Dudelzak  P. Espigat  P. Eschstruth  B. Fabre  G. Fontaine  R. George  C. Ghesqui  re  F. Kovacs  C. Meynadier  Y. Pons  R. Riskalla  M. Rivoal  P. Roy  P. Schune  T. Socroun  A. M. Touchard  J. Vrana 《Astroparticle Physics》1993,1(4):341-355

The THEMISTOCLE array of 18 Cherenkov detectors which has a 3 TeV gamma energy threshold, has detected a signal from the Crab nebula at a 5.8 standard deviation level. Information on the energy spectrum is obtained in the range 3–15 TeV. The integrated flux can be fitted with the form, Φ (> E) = (3.7 ± 0.5) × 10^-12 (E/5)-^{−1.5 ± 0.20} cm⁻² s⁻¹ (E in TeV) compatible with the extrapolation of results at lower energies. The Crab signal is used to measure the angular resolution of the multi-telescope technique. The value obtained is 2.3 mr (0.15°) in agreement with the results of simulations, and confirms the interest of this new method for multi-TeV gamma-ray detection.  相似文献   

Neogene-Quaternary Volcanic forms in the Carpathian-Pannonian Region: a review   总被引：1，自引：0，他引：1  

Jaroslav Lexa  Ioan Seghedi  Karoly Németh  Alexandru Szakács  Vlastimil Koneĉny  Zoltan Pécskay  Alexandrina Fülöp  Marinel Kovacs 《Central European Journal of Geosciences》2010,2(3):207-270

Neogene to Quaternary volcanic/magmatic activity in the Carpathian-Pannonian Region (CPR) occurred between 21 and 0.1 Ma with a distinct migration in time from west to east. It shows a diverse compositional variation in response to a complex interplay of subduction with rollback, back-arc extension, collision, slab break-off, delamination, strike-slip tectonics and microplate rotations, as well as in response to further evolution of magmas in the crustal environment by processes of differentiation, crustal contamination, anatexis and magma mixing. Since most of the primary volcanic forms have been affected by erosion, especially in areas of post-volcanic uplift, based on the level of erosion we distinguish: (1) areas eroded to the basement level, where paleovolcanic reconstruction is not possible; (2) deeply eroded volcanic forms with secondary morphology and possible paleovolcanic reconstruction; (3) eroded volcanic forms with remnants of original morphology preserved; and (4) the least eroded volcanic forms with original morphology quite well preserved. The large variety of volcanic forms present in the area can be grouped in a) monogenetic volcanoes and b) polygenetic volcanoes and their subsurface/intrusive counterparts that belong to various rock series found in the CPR such as calc-alkaline magmatic rock-types (felsic, intermediate and mafic varieties) and alkalic types including K-alkalic, shoshonitic, ultrapotassic and Na-alkalic. The following volcanic/subvolcanic forms have been identified: (i) domes, shield volcanoes, effusive cones, pyroclastic cones, stratovolcanoes and calderas with associated intrusive bodies for intermediate and basic calclkaline volcanism; (ii) domes, calderas and ignimbrite/ash-flow fields for felsic calc-alkaline volcanism and (iii) dome flows, shield volcanoes, maars, tuffcone/tuff-rings, scoria-cones with or without related lava flow/field and their erosional or subsurface forms (necks/ plugs, dykes, shallow intrusions, diatreme, lava lake) for various types of K- and Na-alkalic and ultra-potassic magmatism. Finally, we provide a summary of the eruptive history and distribution of volcanic forms in the CPR using several sub-region schemes.  相似文献   

Reconstructing ancient topography through erosion modelling   总被引：1，自引：1，他引：1  

Iris Peeters  Tom Rommens  Gert Verstraeten  Gerard Govers  Anton Van Rompaey  Jean Poesen  Kristof Van Oost 《Geomorphology》2006,78(3-4):250-264

One of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales. Over the last decades several landscape evolution models have been developed in order to study this question. However, evaluation of such models has often been very limited due to the lack of necessary field data. In this study we present a topography based hillslope erosion and deposition model that is based on the WATEM/SEDEM model structure and works on a millennial time scale. Soil erosion, transport and deposition are calculated using slope and unit contributing area. The topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates, thereby simulating topographic development backwards in time. A first attempt has been made to spatially evaluate the model, using detailed estimates for historical soil erosion and sediment deposition volumes, obtained from an augering campaign in a small catchment in the Belgian Loess Belt. The results show that the model can simulate realistic soil redistribution patterns. However, further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results. Common problems and issues related to this type of backward modelling are also discussed.  相似文献