Interactions between brown-dwarf binaries and Sun-like stars     

M. Kaplan  D. Stamatellos  A. P. Whitworth 《Astrophysics and Space Science》2012,341(2):395-403

Several mechanisms have been proposed for the formation of brown dwarfs, but there is as yet no consensus as to which—if any—are operative in nature. Any theory of brown dwarf formation must explain the observed statistics of brown dwarfs. These statistics are limited by selection effects, but they are becoming increasingly discriminating. In particular, it appears (a) that brown dwarfs that are secondaries to Sun-like stars tend to be on wide orbits, a≳100 AU (the Brown Dwarf Desert), and (b) that these brown dwarfs have a significantly higher chance of being in a close (a≲10 AU) binary system with another brown dwarf than do brown dwarfs in the field. This then raises the issue of whether these brown dwarfs have formed in situ, i.e. by fragmentation of a circumstellar disc; or have formed elsewhere and subsequently been captured. We present numerical simulations of the purely gravitational interaction between a close brown-dwarf binary and a Sun-like star. These simulations demonstrate that such interactions have a negligible chance (<0.001) of leading to the close brown-dwarf binary being captured by the Sun-like star. Making the interactions dissipative by invoking the hydrodynamic effects of attendant discs might alter this conclusion. However, in order to explain the above statistics, this dissipation would have to favour the capture of brown-dwarf binaries over single brown-dwarfs, and we present arguments why this is unlikely. The simplest inference is that most brown-dwarf binaries—and therefore possibly also most single brown dwarfs—form by fragmentation of circumstellar discs around Sun-like protostars, with some of them subsequently being ejected into the field.  相似文献   

Transboundary aspect of assessing the impact of NPPs under construction on aquatic ecosystems: Case study of the Baltiiskaya NPP     

E. M. Kaplan  A. A. Shvarts  E. V. Luneva  M. E. Makushenko  V. G. Rumynin 《Water Resources》2016,43(7):911-922

The environmental feasibility assessment of the construction and operation of nuclear power stations in near-border areas must take into account the requirements of the international and European environmental legislation. For the study on environment feasibility assessment of the Baltic NPP to meet the international standards, the following steps were taken: the content and the application practice of UNECE Convention on Environmental Impact Assessment in a Transboundary Context (Espoo) to NPP substantiation were analyzed and compared with the Russian procedure of environmental impact assessment (EIA); water quality standards for water bodies used for fishery and the approaches to assessing the damage to aquatic bioresources in Russia, Lithuania (EU), and Belarus were compared. A transboundary network for monitoring aquatic ecosystems was developed in the zone of potential influence of the Baltic NPP, and a permanent mathematical model was developed and used to forecast the effect of the anticipated water discharge from the station on the hydrodynamic, chemical, and temperature regime of the Neman R., whose results were used to forecast the impact of water intake and discharge facilities of the Baltic NPP on the food base and migration character of ichthyofauna.  相似文献   

Evidence of biogeomorphic patterning in a low‐relief karst landscape          下载免费PDF全文

Adam C. Watts  Danielle L. Watts  Matthew J. Cohen  James B. Heffernan  Daniel L. McLaughlin  Jonathan B. Martin  David A. Kaplan  Todd Z. Osborne  Leda N. Kobziar 《地球表面变化过程与地形》2014,39(15):2027-2037

Patterned landscapes are often evidence of biotic control on geomorphic processes, emerging in response to coupled ecosystem processes acting at different spatial scales. Self‐reinforcing processes at local scales expand patches, while self‐inhibiting processes, operating at a distance, impose limits to expansion. In Big Cypress National Preserve (BICY) in southwest Florida, isolated forested wetland depressions (cypress domes) appear to be evenly distributed within a mosaic of short‐hydroperiod marshes and pine uplands. To test the hypothesis that the apparent patterning is regular, we characterized frequency distributions and spatial patterns of vegetation communities, surface and bedrock elevation, and soil properties (thickness and phosphorus content). Nearest neighbor distances indicate strongly significant wetland spatial overdispersion, and bedrock elevations exhibited periodic spatial autocorrelation; both observations are consistent with regular patterning. Bedrock elevations and soil P were clearly bimodal, suggesting strong positive feedbacks on wetland patch development. Soil‐surface elevations exhibited weaker bimodality, indicating smoothing of surface morphology by some combination of sediment transport, mineral reprecipitation, and organic matter production. Significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion. These findings support the inference of regular patterning, and are consistent with the presence of local positive feedbacks among hydroperiod, vegetation productivity and bedrock dissolution. These processes are ultimately constrained by distal negative feedbacks, potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A survey of ultraviolet-bright sources behind the halo of M31     

Andrew Fittingoff  J. Xavier Prochaska  Jasonjot S. Kalirai  Jay Strader †  Puragra Guhathakurta  Kyle F. Kaplan 《Monthly notices of the Royal Astronomical Society》2009,399(2):728-736

We have performed a wide-area ultraviolet (UV) imaging survey using the GALaxy Evolution eXplorer to search for bright, point-like UV sources behind M31's extended halo. Our survey consisted of 46 pointings covering an effective area of ≈50 deg², in both the far-UV and near-UV channels. We combined these data with optical R -band observations acquired with the WIYN Mosaic-1 imager on the Kitt Peak National Observatory 0.9-m WIYN telescope. An analysis of the brightness and colours of sources matched between our photometric catalogues yielded ≈100 UV-bright quasar candidates. We have obtained discovery spectra for 76 of these targets with the Kast spectrometer on the Lick 3-m telescope and confirmed 30 active galactic nuclei and quasars, 29 galaxies at   z > 0.02  including several early-type systems, 16 Galactic stars (hot main-sequence stars) and one featureless source previously identified as a BL Lac object. Future UV spectroscopy of the brightest targets with the Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a systematic search for diffuse gas in the extended halo of M31.  相似文献   

Structure of the Siberian platform and its western margin in the Riphean-Early Paleozoic     

T. N. Kheraskova  S. A. Kaplan  V. I. Galuev 《Geotectonics》2009,43(2):115-132

The results of geological interpretation of large fragments of seismic transects SB-1 (Batolit), SB-2, and SB-3 (Altai-Severnaya Zemlya), which cross the western and southern margins of the Siberian Platform and its fold framework, specify substantially the structure and geological history of the sedimentary cover. The most important data have been obtained for the structure of the Baikit Anteclise, the Angara-Lena Terrace, and the Kas Block of the West Siberian Plate. The geological interpretation of the recorded wavefield specifies substantially the genetic features of these structural elements and their mutual relationships, allowing a reliable reconstruction of the western, and partially the southwestern, margins of the Siberian Platform in the Riphean-Early Paleozoic before and after the Baikalian Orogeny.  相似文献   

Design considerations for the USNO astrometric optical interferometer     

J. A. Hughes  G. H. Kaplan  M. Shao 《Astrophysics and Space Science》1991,177(1-2):151-159

The USNO will undertake the construction and operation of a phase coherent, astrometric, optical interferometer which will be dedicated to the determination of stellar positions and motions. Building upon the experience gained from the MARK III Interferometer at Mount Wilson, the USNO instrument is currently in the very early stages of conceptualization and initial design. An abbreviated account of the experience gained with the MARK III is given. Examples of the issues and possibilities to be addressed in designing the new USNO instrument are outlined. Some background discussion involving interferometric techniques is included.  相似文献   

Meso-beta scale numerical simulations of terrain drag-induced along-stream circulations Part I: Midtropospheric frontogenesis     

M. L. Kaplan  V. M. Karyampudi 《Meteorology and Atmospheric Physics》1992,49(1-4):133-156

Summary The problem of along-stream ageostrophic frontogenesis is studied by employing a numerical model at meso-alpha and meso-beta scales in simulations of the downstream circulations over the Front Range of the Rocky Mountains. Three-dimensional real data simulations at these two scales of motion are used to diagnose the transition from semigeostrophic cross-stream frontogenesis accompanying a propagating baroclinic upper-level jet streak to midtropospheric along-stream ageostrophic frontogenesis. This along-stream ageostrophic frontogenesis results from the perturbation of the jet streak by the Rocky Mountain range. The case study represents an example of internal wave dynamics which are forced by the drag of the Rocky Mountains on a strong jet streak in the presence of a low-level inversion.The simulation results indicate that, unlike semi-geostrophic frontogenesis, a front (which is alligned perpendicular to the axis of the jet stream) may form when significant adiabatic heating occurs within a stratified shear flow over horizontal length scales shorter than the Rossby radius of deformation. The mechanism responsible for the frontogenesis is the growth of the divergent along-stream wind velocity component which becomes coupled to the front's along-stream pressure gradient force. This nonlinear interaction produces hydrostatic mesoscale frontogenesis as follows: 1) vertical wind shear in the along-stream plane strengthens resulting in the increasingly nonuniform vertical variation of horizontal temperature advection as the ageostrophic wind component grows in magnitude downstream of the meso-scale terrain-induced adiabatic heating, 2) increasing along-stream differential vertical motions (i.e., along-stream thermally indirect circulation with warm air sinking to the west and cold air rising to the east) tilt the vertical gradient of isentropes into the horizontal as the vertical temperature gradient increases due to the previous process in proximity to horizontal gradients in the along-stream component of the ageostrophic wind, 3) as tilting motions act to increase the along-stream horizontal temperature gradient, the along-stream confluence acts to nonuniformly increase the along-stream frontal temperature gradient which increases the along-stream pressure gradient force resulting in further accelerations, ageostrophy, and frontal steepening as part of a scale contraction process.The evolution of the aforementioned processes results in the three-dimensional hydrostatic frontogenesis accompanying the overturning of isentropic surfaces. These adjustments act to turn air parcels to the right of the southwesterly geostrophic wind vector at successively lower atmospheric levels as the scale contraction continues. This simulated along-stream front is verified from diagnostic analysis of the profiler-derived temperature and wind fields.With 17 Figures  相似文献   

The stereoisomeric composition of phytanyl chains in lipids of Dead Sea sediments     

R. Anderson  M. Kates  M.J. Baedecker  I.R. Kaplan  R.G. Ackman 《Geochimica et cosmochimica acta》1977,41(9):1381-1390

Lipid extracts from five recent Dead Sea sediments were analyzed for isoprenoid compounds and the following were isolated: free and phospholipid-bound di-O-phytanylglycerol, free phytanol and free and esterifled phytanic acid. The phytanyl groups of the diether and the free phytanol were oxidized to the corresponding phytanic acid; the stereoisomeric composition of the derived phytanic acids as well as of the ester-bound phytanic acid was determined by open-tubular gas-liquid chromatography of the corresponding methyl esters on butanediolsuccinate polyester. Only the 3R,7R,11R-isomer of phytanic acid was detected in each of the phytanate samples, indicating that these phytanyl chains in the Dead Sea sediments are most likely derived from extremely halophilic bacteria rather than from phytol of chlorophyll origin. These findings also provide further evidence that the mixtures of RRR and SRR-phytanic acids previously isolated from organic-rich shales were most likely derived from the phytyl chain in chlorophyll.  相似文献   

Hydrocarbons in age-dated sediment cores from two basins in the Southern California Bight     

M.I Venkatesan  S Brenner  E Ruth  J Bonilla  I.R Kaplan 《Geochimica et cosmochimica acta》1980,44(6):789-802

The distributions of hydrocarbons in sediment cores dated by ²¹⁰Pb (1845–1977) from San Pedro and San Nicolas Basins in the Southern California Bight have been determined by gas Chromatographic and combined gas chromatographic-mass spectrometric analysis. The chromatograms of the hydrocarbons contain peaks of resolved alkanes and cycloalkanes, as well as an unresolved complex mixture which decrease in content with increasing depth in both of the cores. The concentrations of o,p' andp,p'-DDE are highest in the top 50 mm of the San Pedro core section. The 45–50 mm segment of this core was deposited in the 1945–1950 period when DDT (the precursor of DDE compounds) came into common use. The relatively high content of hydrocarbons and DDE in this core is attributable to the proximity of the site to the San Pedro Harbor which receives petroleum residues from shipping, sewage outfalls and industrial effluents. The presence of only traces of DDE throughout the San Nicolas core, and the low hydrocarbon content are explainable by the greater distance of this basin from anthropogenic inputs and probably a greater rate of degradation of deposited organic matter during bioturbation. δ¹³C, δ¹⁵N and electron-spin resonance analyses of kerogens and humic substances in these cores, indicate that most of this organic matter in these sediments is of a marine origin.  相似文献   

Thermal alteration experiments on organic matter in recent marine sediment—I. Pigments     

Raphael Ikan  Zeev Aizenshtat  Mary Jo Baedecker  Isaac R Kaplan 《Geochimica et cosmochimica acta》1975,39(2):173-185

Sediment from Tanner Basin, located at the outer continental shelf off southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65°, 100°, 150°C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of α-ionene and 2,6-dimethylnaphthalene, thermal-degradation products of β-carotene. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms and geochemical significance of these transformations are presented.  相似文献