VSX J074727.6 + 065050: A dwarf nova with a non-radially pulsating white dwarf primary     

Patrick A. Woudt  Brian Warner 《Astrophysics and Space Science》2011,333(1):119-123

High speed photometric observations of the dwarf nova VSX J074727.6 + 065050 made in December 2009 during quiescence show an orbital modulation at P _orb =85.6 min. They also show that the star is a member of the relatively rare CV/ZZ group, i.e. the accreting white dwarf primary has non-radial pulsations. The two regions of oscillating power are at 684 s and 238 s. There is some evidence for hidden ∼1 μHz fine structure splitting, which has been seen in three other CV/ZZ stars.  相似文献   

The effects of sulfur intercalation on the optical properties of artificial ‘hackmanite’, Na8[Al6Si6O24]Cl1.8S0.1; ‘sulfosodalite’, Na8[Al6Si6O24]S; and natural tugtupite, Na8[Be2Al2Si8O24](Cl,S)2?δ     

T. E. Warner  J. Hutzen Andersen 《Physics and Chemistry of Minerals》2012,39(2):163-168

The minerals ??hackmanite?? and tugtupite exhibit tenebrescence (reversible photochromism) and photoluminescence. These features are generally attributed to the presence of sulfide species within their structures. But how these optical properties might be affected by intercalating additional amounts of sulfur into their structures was until now unknown. Artificial ??hackmanite??, Na₈[Al₆Si₆O₂₄]Cl_1.8S_0.1, and ??sulfosodalite??, Na₈[Al₆Si₆O₂₄]S, were heated with sulfur in evacuated quartz-glass ampoules over the temperature range 450?C1,050°C. This work has shown that sulfur intercalation into Na₈[Al₆Si₆O₂₄]Cl_1.8S_0.1 destroys the tenebrescence and induces a permanently pale blue and, at higher temperature, a pale green coloration. The effect on Na₈[Al₆Si₆O₂₄]S induced similar colorations but of a deeper hue. Annealing tugtupite, Na₈[Be₂Al₂Si₈O₂₄](Cl,S)_2??? under a sulfur atmosphere over the range 600?C700°C, destroyed the tenebrescence and resulted in a colorless tugtupite; but did not effect the photoluminescence. This suggests that the chemical species responsible for the tenebrescence in tugtupite is unlikely to be the same as that for the luminescence.  相似文献   

Probabilistic tsunami hazard assessment for Messina Strait Area (Sicily, Italy)     

Grezio Anita  Laura Sandri  Warner Marzocchi  Andrea Argnani  Paolo Gasparini  Jacopo Selva 《Natural Hazards》2012,64(1):329-358

The general modular Bayesian procedure is applied to provide a probabilistic tsunami hazard assessment (PTHA) for the Messina Strait Area (MSA), Italy. This is the first study in an Italian area where the potential tsunamigenic events caused by both submarine seismic sources (SSSs) and submarine mass failures (SMFs) are examined in a probabilistic assessment. The SSSs are localized on active faults in MSA as indicated by the instrumental data of the catalogue of the Italian seismicity; the SMFs are spatially identified using their propensity to failure in the Ionian and Tyrrhenian Seas on the basis of mean slope and mean depth, and using marine geology background knowledge. In both cases the associated probability of occurrence is provided. The run-ups were calculated at key sites that are main cities and/or important sites along the Eastern Sicily and the Southern Calabria coasts where tsunami events were recorded in the past. The posterior probability distribution combines the prior probability and the likelihood calculated in the MSA. The prior probability is based on the physical model of the tsunami process, and the likelihood is based on the historical data collected by the historical catalogues, background knowledge, and marine geological information. The posterior SSSs and SMFs tsunami probabilities are comparable and are combined to produce a final probability for a full PTHA in MSA.  相似文献   

News & Views          下载免费PDF全文

Vicki Kretsinger Grabert  Dawn Samara Kaback  Jeanne Briskin  Susan L. Brantley  Thomas H. Darrah  Robert B. Jackson  Avner Vengosh  Nathaniel R. Warner  Robert J. Poreda 《Ground water》2015,53(1):19-28

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Storm-driven sediment transport in Massachusetts Bay     

John C. Warner  Bradford Butman  P. Soupy Dalyander 《Continental Shelf Research》2008

Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50 km wide and 100 km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast (‘Northeasters’) generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave–current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin.  相似文献   

Circulation and Mixing of Water Masses of Tatar Strait and the Northwestern Boundary Region of the Japan Sea   总被引：2，自引：0，他引：2  

Stephen C. Riser  Mark J. Warner  Gennady I. Yurasov 《Journal of Oceanography》1999,55(2):133-156

The deep waters of the northern portions of the Japan Sea are examined. It is found that the flow regime south of the southern Tatar Strait region is generally cyclonic in the upper ocean, with only weak flows present below depths of a few hundred meters. The Japan Sea appears to be remarkably well-mixed below depths of a few hundred meters, both horizontally and vertically. Based on chlorofluorocarbon measurements, it is concluded that the deep waters of the Japan Sea have been only weakly ventilated in recent decades. Results from a simple box model suggest two possible scenarios for the ventilation of the Japan Sea since the 1930s. In the first scenario, deep ventilation of the Japan Sea was relatively weak, but constant, from the 1930s to the present, with a deep-water residence time of approximately 500 years. In the second scenario, ventilation was relatively vigorous through the mid-1960s, with a deep-water residence time of approximately 100 years; after the mid-1960s, the ventilation of the deep waters stopped. The model results are consistent with the idea that presently the ventilation of the deep water of the Japan Sea is weak or nonexistent. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York          下载免费PDF全文

Rebecca L. Kreuzer  Thomas H. Darrah  Benjamin S. Grove  Myles T. Moore  Nathaniel R. Warner  William K. Eymold  Colin J. Whyte  Gautam Mitra  Robert B. Jackson  Avner Vengosh  Robert J. Poreda 《Ground water》2018,56(2):225-244

Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south‐central New York. All samples were collected ?1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [⁴He], thermogenic [CH₄], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon‐rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.  相似文献   

Holocene fossil Habrotrocha angusticollis (Bdelloidea: Rotifera) in North America     

B. G. Warner  R. Chengalath 《Journal of Paleolimnology》1988,1(2):141-147

Holocene fossil shells of the rotifer, Habrotrocha angusticollus (Bdelloidea: Rotifera) is reported from two peatlands in northern Ontario, Canada. H. angusticollis is a common component of the microfauna in Sphagnum peatlands and other wet mossy habitats. Our knowledge of the distribution and ecology of H. angusticollis is limited and this paper is the first detailed report of the shells as fossils in North America. Fossil shells of H. angusticollis may prove to be a valuable paleoecological indicator in peat deposits once Quaternary paleoecologists learn to recognize them and neoecologists extend their surveys to peatlands.  相似文献   

Numerical simulations of pinhole and single-mode fibre spatial filters for optical interferometers     

J.W. Keen  D_f. Buscher  P.J. Warner 《Monthly notices of the Royal Astronomical Society》2001,326(4):1381-1386

We use a numerical simulation to investigate the effectiveness of pinhole spatial filters for optical/IR interferometers and to compare them with single-mode optical fibre spatial filters and interferometers without spatial filters. We show that fringe visibility measurements in interferometers containing spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters. This reduces visibility calibration uncertainties, and hence can reduce the need for frequent observations of separate astronomical sources for calibration of visibility measurements. We also show that spatial filters can increase the signal-to-noise ratios (SNRs) of visibility measurements and that pinhole filters give SNRs within 17 per cent of the values obtained with single-mode fibres for aperture diameters up to 3 r ₀. Given the simplicity of the use of pinhole filters we suggest that it represents a competitive, if not optimal, technique for spatial filtering in many current and next generation interferometers.  相似文献   

Torques and instabilities in intermediate polars     

Brian Warner 《Astrophysics and Space Science》1996,241(2):263-294

The observed spin periods of the primaries in intermediate polars require the presence of torques additional to the standard expectation of material and magnetic torques from an accretion disc. In an extension of earlier work by Wickramasinghe, Wu and Ferrario, from rates of mass transfer deduced from optical and X-ray fluxes, and assuming surface magnetic fields similar to those observed in the most rapidly rotating low mass main sequence stars, it is shown that the magnetohydrodynamic torque between the partially shielded primary and the secondary is sufficient to account for the observed spin periods. It is further found that there is a range of magnetic moments and mass transfer rates in which synchronized rotation of the primary can occur even though it possesses an accretion disc. This may account for the structures deduced for V795 Her and V2051 Oph.An analysis of the observed outbursts (or lack of) in the intermediate polars shown that wheres many systems are explainable in terms of the standard theory of -discs, in some systems the magnetic structure is supressing expected outbursts and instabilities that are as yet not understood appear in their place.  相似文献