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131.
Darren S. Baskill Peter J. Wheatley Julian P. Osborne 《Monthly notices of the Royal Astronomical Society》2005,357(2):626-644
We present the complete set of 34 ASCA observations of non-magnetic cataclysmic variables. Timing analysis reveals large X-ray flux variations in dwarf novae in outburst (Z Cam, SS Cyg and SU UMa) and orbital modulation in high inclination systems (including OY Car, HT Cas, U Gem, T Leo). We also found episodes of unusually low accretion rate during quiescence (VW Hyi and SS Cyg). Spectral analysis reveals broad temperature distributions in individual systems, with emission weighted to lower temperatures in dwarf novae in outburst. Absorption in excess of interstellar values is required in dwarf novae in outburst, but not in quiescence. We also find evidence for subsolar abundances and X-ray reflection in the brightest systems.
LS Peg, V426 Oph and EI UMa have X-ray spectra that are distinct from the rest of the sample and all three exhibit candidate X-ray periodicities. We argue that they should be reclassified as intermediate polars.
In the case of V345 Pav we found that the X-ray source had been previously misidentified. 相似文献
LS Peg, V426 Oph and EI UMa have X-ray spectra that are distinct from the rest of the sample and all three exhibit candidate X-ray periodicities. We argue that they should be reclassified as intermediate polars.
In the case of V345 Pav we found that the X-ray source had been previously misidentified. 相似文献
132.
Abrupt climate warming during glacial–interglacial transitions promotes regional thermokarst activity in areas of ice-rich permafrost. The ensuing thaw-related processes of melt-out, soft-sediment deformation and resedimentation may produce widespread thermokarst sediments and sedimentary structures. Examples of the most distinctive thermokarst sediments and sedimentary structures from the Tuktoyaktuk Coastlands, western Arctic Canada, comprise: (1) soft-sediment deformation structures (thermokarst involutions) in a palaeoactive layer; (2) ice-wedge casts and composite-wedge casts; (3) peaty to sandy diamicton deposited mainly by debris flows in retrogressive thaw slumps; and (4) a basal unit of diamicton and/or impure sand in some thermokarst-basin sequences, deposited by progradation of resedimented materials in thermokarst lakes. Many of the thermokarst sediments and sedimentary structures in the Tuktoyaktuk Coastlands formed as a result of rapid climate warming during the last glacial–interglacial transition, although some continue to form at present due to local (non-climatic) factors.Identification of thermokarst sediments and sedimentary structures in the geological record requires evidence for the thaw of excess ice. Direct evidence for the former occurrence of excess ice includes: (1) ice-wedge casts; (2) composite-wedge casts; (3) lenticular platy microstructures in frost-susceptible sediment; (4) certain near-surface brecciation of frost-susceptible bedrock; and (5) ramparted depressions attributed to the decay of frost mounds. Indirect evidence for former excess ice results where thaw consolidation initiates soft-sediment deformation or gelifluction. 相似文献
133.
Victor L. Vinograd Julian D. Gale Björn Winkler 《Physics and Chemistry of Minerals》2007,34(10):713-725
Static lattice energy calculations (SLEC), based on empirical interatomic potentials, have been performed for a set of 800
different structures in a 2 × 2 × 4 supercell of C2/c diopside with compositions between diopside and jadeite, and with different states of order of the exchangeable Na/Ca and
Mg/Al cations. Excess static energies of these structures have been cluster expanded in a basis set of 37 pair-interaction
parameters. These parameters have been used to constrain Monte Carlo simulations of temperature-dependent properties in the
range of 273–2,023 K and to calculate a temperature–composition phase diagram. The simulations predict the order–disorder
transition in omphacite at 1,150 ± 20°C in good agreement with the experimental data of Carpenter (Mineral Petrol 78:433–440,
1981). The stronger ordering of Mg/Al within the M1 site than of Ca/Na in the M2 site is attributed to the shorter M1–M1 nearest-neighbor
distance, and, consequently, the stronger ordering force. The comparison of the simulated relationship between the order parameters
corresponding to M1 and M2 sites with the X-ray refinement data on natural omphacites (Boffa Ballaran et al. in Am Mineral
83:419–433, 1998) suggests that the cation ordering becomes kinetically ineffective at about 600°C. 相似文献
134.
Julian Daniels Noah Brosch Elchanan Almoznino Ohad Shemmer Stuart Bowyer Michael Lampton 《Monthly notices of the Royal Astronomical Society》2001,324(3):580-598
Analysis of ultraviolet (UV) observations with the FAUST shuttle-borne telescope toward the Antennae and NGC 6752 celestial regions resulted in the detection of 46 and 221 candidate sources respectively, for a signal-to-noise ratio of 8. We discuss the source detection process and the identification of UV sources with optical counterparts. Using correlations with existing catalogues, we present reliable identifications for approximately 60 per cent of the sources. We find that most identified objects are B, A and F stars. The remaining identified objects are galaxies, a white dwarf in a binary system, and two K-type stars. Nearly all of the remaining unidentified objects have assigned optical counterparts but, lacking additional information, we give these only as best estimates. With help from new diagnostic diagrams, we suggest that these unclassified objects are main-sequence (or giant) stars within the local spiral arm or halo; or other hot evolved objects within the local spiral arm. We discuss the nature of the objects found and compare our results with those predicted from spectral and Galactic models. 相似文献
135.
136.
Julian I. Palmore 《Celestial Mechanics and Dynamical Astronomy》1981,25(1):79-80
We elaborate a variational method used recently in the proof of Saari's conjecture.Research supported in part by NSF grant MCS 78-00395. 相似文献
137.
Antony?Z.?OwinohEmail author Julian?C.?R.?Hunt Andrew?Orr Peter?Clark Rupert?Klein H.?J.?S.?Fernando Frans?T.?M.?Nieuwstadt 《Boundary-Layer Meteorology》2005,116(2):331-361
We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u * when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t<inf>θ</inf> less than about h /(10u *). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to
the heat flux and mean shear. Analytical solutions for changes in temperature, mean wind and shear stress profile are obtained
for the surface layer, when there are small changes in h /|LMO| over the time scale tMO~|L MO|/(10u*) (where L MO and t MO are the length and time scales, respectively). They show that a maximum in the wind speed profile occurs at the top of the
thermal boundary layer for weak surface cooling, i.e. a wind jet, whereas there is a flattening of the profile and no marked
maximum for weak surface heating. The modelled profiles are approximately the same as those obtained from the U.K. Met Office
Unified Model when operating as a mesoscale model at 12-km horizontal resolution. The theoretical model is modified when strong
surface heating is suddenly applied, resulting in a large change in h /|L MO| (>>1), over the time scale t MO. The eddy structure is predicted to change significantly and the addition of convective turbulence increases the shear turbulence
at the ground. A low-level wind jet can form, with convective turbulence adding to the mean momentum of the flow. This was
verified by our laboratory experiment and direct numerical simulations. Additionally, it is shown that the effects of Coriolis
acceleration diminish (rather than as suggested in the literature, amplify) the formation of the wind jets in the situations
considered here. Hence, only when the surface heat flux changes over time scales greater than 1/f (where f is the Coriolis parameter) does the ABL adjust monotonically between its equilibrium states. These results are also applicable
to the ABL passing over spatially varying surface heat fluxes. 相似文献
138.
Julian Holloway 《Geoforum》2000,31(4)
This paper is concerned with the production and reproduction of different institutional geographies of the New Age movement. Instead of taking institutional geographies to be given and fixed co-ordinates in the social field, the paper seeks to understand how they are relational outcomes and effects that require constant upkeep. After characterising the New Age movement, in terms of its central cosmology and visions of transformation, the paper takes an actor-network theory (ANT) approach to the understanding of institutional geographies. Through analysing how New Age knowledges and practices travel through time and space, and utilising ANT’s concept of ‘centres of translation’, institutional geographies are taken to be active space-times that are both enrolled into New Age teachers and practitioners programs of action, and space-times that actively enrol teachers and practitioners. It is argued that the intertwining of different engineered actor-networks in and through these space-times maintains the New Age movement itself and thus examining institutional geographies can tell of the movement’s shape or topology. A controversy over the work of David Icke is explored to reveal how institutional geographies are sites for regulation of what counts as New Age knowledge. Finally, this paper seeks, partially at least, to assess in terms of the ANT approach taken, the visions of transformation propounded by the New Age movement. 相似文献
139.
Palaeoenvironmental records in Holocene Spanish tufas: a stable isotope approach in search of reliable climatic archives 总被引:3,自引:0,他引:3
Tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information. This study assesses the potential of stable isotopic archives from two closely juxtaposed Holocene tufa sites in SE Spain. The Ruidera site contains deep‐water lacustrine micrites and tufas, whereas the nearby Alcaraz site represents a shallow barrage tufa. Understanding site characteristics is critical to interpreting the stable isotopic variations. These Holocene lacustrine micrites have isotopic compositions consistent with modern European lake shore microbial carbonates, where the isotopic chemistry is strongly influenced by hydrological and residence time effects. All the lacustrine micrite δ13C values were influenced by microenvironmental microbial effects to some degree. Because of these effects, stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation, temperature or vegetation composition of an area. In contrast, Holocene tufas that formed in shallow, fast‐flowing riverine settings may contain valuable palaeoclimatic archives. The tufa deposits must be largely autochthonous, as at Alcaraz, where in situ reed stem encrustations are present. Records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the δ18O data. These interpretations can be verified by other independent climatic data where chronology is constrained. Variations in riverine tufa δ13C values probably record changes in local vegetation and/or soil respiration. Covariation between δ18O and δ13C values may be intrinsically linked to climatic factors such as aridity. Tentative palaeoclimatic interpretations for the middle Holocene at Alcaraz based on the isotope data suggest warming (or increasing influence of Mediterranean‐sourced precipitation) between approximately 5000–3000 radiocarbon years BP, accompanied by increased aridity. These interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the Holocene of SE Spain. This study supports the growing evidence that well‐chosen tufa sites could yield valuable palaeoclimatic information. 相似文献
140.
Sergey V. Marchenko Gregor Rauw Eleonora A. Antokhina Igor I. Antokhin Dominique Ballereau Jacques Chauville Michael F. Corcoran Rafael Costero Juan Echevarria Thomas Eversberg Ken G. Gayley Gloria Koenigsberger Anatoly S. Miroshnichenko Anthony F. J. Moffat Nidia I. Morrell Nancy D. Morrison Christopher L. Mulliss Julian M. Pittard Ian R. Stevens Jean-Marie Vreux Jean Zorec 《Monthly notices of the Royal Astronomical Society》2000,317(2):333-342
With the objective of investigating the windwind collision phenomenon and supporting contemporaneous X-ray observations, we have organized a large-scale, coordinated optical monitoring campaign of the massive, highly eccentric O9 III+B1 III binary Iota Orionis. Successfully separating the spectra of the components, we refine the orbital elements and confirm the rapid apsidal motion in the system. We also see strong interaction between the components during periastron passage and detect phase-locked variability in the spectrum of the secondary star. However, we find no unambiguous signs of the bow shock crashing on the surface of the secondary, despite the predictions of hydrodynamic simulations. Combining all available photometric data, we find rapid, phase-locked variations and model them numerically, thus restricting the orbital inclination to 50° i 70°. 相似文献