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101.
Marek Gierliski Juri Poutanen † 《Monthly notices of the Royal Astronomical Society》2005,359(4):1261-1276
We have undertaken an extensive study of X-ray data from the accreting millisecond pulsar XTE J1751 − 305 observed by RXTE and XMM–Newton during its 2002 outburst. In all aspects this source is similar to the prototypical millisecond pulsar SAX J1808.4 − 3658, except for the higher peak luminosity of 13 per cent of Eddington, and the optical depth of the hard X-ray source, which is larger by a factor ∼2. Its broad-band X-ray spectrum can be modelled by three components. We interpret the two soft components as thermal emission from a colder ( kT ∼ 0.6 keV) accretion disc and a hotter (∼1 keV) spot on the neutron star surface. We interpret the hard component as thermal Comptonization in plasma of temperature ∼40 keV and optical depth ∼1.5 in a slab geometry. The plasma is heated by the accretion shock as the material collimated by the magnetic field impacts on to the surface. The seed photons for Comptonization are provided by the hotspot, not by the disc. The Compton reflection is weak and the disc is probably truncated into an optically thin flow above the magnetospheric radius. Rotation of the emission region with the star creates an almost sinusoidal pulse profile with an rms amplitude of 3.3 per cent. The energy-dependent soft phase lags can be modelled by two pulsating components shifted in phase, which is naturally explained by a different character of emission of the optically thick spot and optically thin shock combined with the action of the Doppler boosting. The observed variability amplitude constrains the hotspot to lie within 3°–4° of the rotational pole. We estimate the inner radius of the optically thick accreting disc to be about 40 km. In that case, the absence of emission from the antipodal spot, which can be blocked by the accretion disc, gives the inclination of the system as ≳70°. 相似文献
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This report is a comment on two papers by Matese and Whitman (1989, 1992). We discuss here the applicability of uniform probability densities for the orbital parameters of the Oort cloud comets. 相似文献
107.
Anna J. Pieńkowski Roy D. Coulthard Mark F. A. Furze 《Boreas: An International Journal of Quaternary Research》2023,52(2):145-167
Appropriate marine–terrestrial reservoir offset (ΔR) values are essential for accurate calibration of marine radiocarbon dates. However, ΔR values are only valid for the specific calibration curve that their calculation is based on. Here, we present revised ΔR values for the Marine20 calibration curve from Arctic North America, based on previously published 14C dates on pre-bomb live-collected marine molluscs (n = 124) and cetaceans (beluga whales; tooth dentine; n = 12), and bowhead whale–driftwood age comparisons from the same glacio-isostatically uplifted shorelines (n = 18). Molluscan-based ΔR are: Chukchi/Beaufort sea coasts, 265±116 14C years; NW Canadian Arctic Archipelago, 188±91 14C years; NE Baffin Island, 81±18 14C years; SE Baffin Island, 14±58 14C years; Hudson Strait, −73±64 14C years; Ungava Bay, 0±86 14C years; Foxe Basin, 175±89 14C years; Hudson Bay, −21±72 14C years; James Bay, 209±114 14C years; West Greenland, −93±111 14C years. Species-specific marine mammal ΔR terms are 107±59 14C years for beluga and 24±58 14C years for bowheads. Our revised ΔR values are applicable for as long as the same broad oceanographic conditions (circulation, ventilation) have persisted, i.e. through the Holocene. While molluscan values are applicable to other marine carbonate (e.g. foraminifera), cetacean ΔR are valid only for the species they were calculated for and should not be applied to other marine mammals. Importantly, the ΔR terms calculated here are only valid for Marine20 and should not be used with earlier or later calibration curves. 相似文献
108.
Salvatore Erminio Modoni Giuseppe Spagnoli Giovanni Arciero Michela Mascolo Maria Cristina Ochmański Maciej 《Acta Geotechnica》2022,17(11):5073-5087
Acta Geotechnica - Plasticity of clays makes Deep Soil Mixing (DSM) problematic due to the tendency of the material to congest the rotating blades, reduce mixing efficiency and remain... 相似文献
109.
The Kamieniec Metamorphic Belt comprises a volcano-sedimentary succession exposed within a collision zone between the Saxothuringian and Brunovistulian crustal domains of the European Variscides. The studied rocks recorded two metamorphic episodes. The first episode, M1, occurred at conditions of c. 485 ± 25 °C and 18 ± 1.8 kbar related to burial within a subduction zone. The subsequent episode, M2, was linked to the final phases of exhumation to mid-crustal level, associated with pressure and temperature (P–T) conditions ranging from c. 520 ± 26 °C and 6 ± 0.6 kbar through 555 ± 28 °C and 7 kbar ± 0.7 to ~590 ± 30 °C and 3–4 ± 0.4 kbar. The documented deformation record is ascribed to three events, D1 to D3, interpreted as related to the burial and subsequent exhumation of the Kamieniec Metamorphic Belt. The D1 event must have witnessed the subduction of the Kamieniec Metamorphic Belt rock succession whereas the D2 event was associated with the exhumation and folding of the Kamieniec Metamorphic Belt in an E-W-directed shortening regime. A subsequent folding related to the D2 event was initiated at HP conditions, however, the planar fabric produced during a late stage of the D2 event, defined by a low-pressure mineral assemblage M2, indicates that the D2 final stage was synchronous with the onset of the M2 episode. Consequently, the entire D2 event seems to have been associated with the exhumation of the Kamieniec Metamorphic Belt to mid crustal level. The third deformation event D3, synchronous with the M2 episode, marked the last stage of the exhumation, and was linked to emplacement of granitoid veins and lenses. The latter resulted in heating and rheological weakening of the entire rock succession and in the formation of non-coaxial shear zones. 相似文献
110.
Periglacial and Fluvial Factors Controlling the Sedimentation of Pleistocene Breccia in NW Poland 下载免费PDF全文
Piotr Weckwerth Małgorzata Pisarska‐Jamroży 《Geografiska Annaler: Series A, Physical Geography》2015,97(2):415-430
Breccias were investigated on the terrace of the Toruń‐Eberswalde ice‐marginal valley at Rozwarzyn (NW Poland). Breccia layers include soft‐sediment clasts with diameters between 2 and 256 mm and soft‐sediment megaclasts with diameters from 256 mm to 7 m. The shape of the soft‐sediment clasts and megaclasts (derived from frozen sediments) in the breccia is diverse: from angular and irregular in the case of debris‐flow breccias to slightly rounded and tabular in fluvial breccias. These two types of breccias were developed during the Late Weichselian when the periglacial climate favored extensive lateral erosion by currents of frozen braided channels in the ice‐marginal valley. The dual presence of breccias of fluvial and debris‐flow origin in channel deposits is unique for Quaternary sediments. Zones of breccias existed in the channels where scours and obstacle marks related to megaclasts developed. The study of breccias shed new light on the fluvial processes in ice‐marginal valleys during the Pleistocene and can be considered as diagnostic for fluvio‐periglacial conditions. 相似文献