Particle-in-cell plasma simulations of the modified two-stream instability     

K. Schlegel  H. Thiemann 《Annales Geophysicae》1994,12(10-11):1091-1100

We model the modified two-stream plasma instability occuring in the ionospheric E-region using a 2.5-dimensional particle-in-cell code. Compared to previous similar work we concentrate on simulated quantities that can easily be measured in the real ionosphere by coherent radars or rockets, such as the Doppler velocity, the backscattered power, backscattered spectra, aspect angle behaviour and electron temperature enhancement. Despite using a relatively small simulation model, we obtain remarkably good agreement between actual observed and simulated plasma parameters. The advantage of such a small system is that we were able to perform (other than in previous related work) many simulation runs with different sets of input parameters, thus studying the unstable plasma under various conditions.  相似文献   

Simulations of baryon oscillations     

Eric Huff  A.E. Schulz  Martin White  David J. Schlegel  Michael S. Warren   《Astroparticle Physics》2007,26(6):351-366

The coupling of photons and baryons by Thomson scattering in the early universe imprints features in both the cosmic microwave background (CMB) and matter power spectra. The former have been used to constrain a host of cosmological parameters, the latter have the potential to strongly constrain the expansion history of the universe and dark energy. Key to this program is the means to localize the primordial features in observations of galaxy spectra which necessarily involve galaxy bias, non-linear evolution and redshift space distortions. We present calculations, based on mock catalogs produced from high-resolution N-body simulations, which show the range of behaviors we might expect of galaxies in the real universe. We investigate physically motivated fitting forms which include the effects of non-linearity, galaxy bias and redshift space distortions and discuss methods for analysis of upcoming data. In agreement with earlier work, we find that a survey of several Gpc³ would constrain the sound horizon at z  1 to about 1%.  相似文献   

Streaming motions of galaxy clusters within 12 000 km s⁻¹– III. A standardized catalogue of Fundamental Plane data     

Michael J. Hudson  John R. Lucey  Russell J. Smith  David J. Schlegel  Roger L. Davies 《Monthly notices of the Royal Astronomical Society》2001,327(1):265-295

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Panchromatic properties of 99 000 galaxies detected by SDSS, and (some by) ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveys     

M. Obri&#;  &#;. Ivezi&#;  P. N. Best  R. H. Lupton  C. Tremonti  J. Brinchmann  M. A. Agüeros  G. R. Knapp  J. E. Gunn  C. M. Rockosi  D. Schlegel  D. Finkbeiner  M. Ga&#;e&#;a  V. Smol&#;i&#;  S. F. Anderson  W. Voges  M. Juri&#;  R. J. Siverd  W. Steinhardt  A. S. Jagoda  M. R. Blanton  D. P. Schneider 《Monthly notices of the Royal Astronomical Society》2006,370(4):1677-1698

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Business start-up promotional aid in Hungary     

Bernd Schlegel 《GeoJournal》1994,32(4):373-379

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Comparison of fluid geochemistry and microbiology of multiple organic-rich reservoirs in the Illinois Basin, USA: Evidence for controls on methanogenesis and microbial transport     

Melissa E. Schlegel  Jennifer C. McIntosh  Matthew F. Kirk  Anna M. Martini 《Geochimica et cosmochimica acta》2011,75(7):1903-40

Microbial methane in sedimentary basins comprises approximately 20% of global natural gas resources, yet little is known about the environmental requirements and metabolic rates of these subsurface microbial communities. The Illinois Basin, located in the midcontinent of the United States, is an ideal location to investigate hydrogeochemical factors controlling methanogenesis as microbial methane accumulations occur: (1) in three organic-rich reservoirs of different geologic ages and organic matter types - Upper Devonian New Albany Shale (up to 900 m depth), Pennsylvanian coals (up to 600 m depth), and Quaternary glacial sediments (shallow aquifers); (2) across steep salinity gradients; and (3) with variable concentrations of . For all three organic-rich reservoirs aqueous geochemical conditions are favorable for microbial methanogenesis, with near neutral pH, concentrations <2 mM, and Cl⁻ concentrations <3 M. Also, carbon isotopic fractionation of CH₄, CO₂, and DIC is consistent with microbial methanogenesis, and increased carbon isotopic fractionation with average reservoir depth corresponds to a decrease of groundwater flushing rates with average depth of reservoir. Plots of stable isotopes of water and Cl⁻ show mixing between a brine endmember and freshwater, suggesting that meteoric groundwater recharge has affected all microbial methanogenic systems. Additionally, similar methanogenic communities are present in all three reservoirs with comparable cell counts (8.69E3-2.58E6 cells/mL). TRFLP results show low numbers of archaea species with only two dominant groups of base pairs in coals, shale, and limestone aquifers. These results compare favorably with other methanogen-containing deep subsurface environments. Individual hydrogeochemical parameters that have a Spearman correlation coefficient greater than 0.3 to variations in methanogenic species include stable isotopes of water (δ¹⁸O and δD), type of substrate (i.e. coals versus shale), pH, and Cl⁻ concentration. The matching of variations between methanogenic TRFLP data and conservative tracers suggests that deep circulation of meteoric waters influenced archaeal communities in the Illinois Basin. In addition, coalification and burial estimates suggest that in the study area, coals and shale reservoirs were previously sterilized (>80 °C in nutrient poor environments), necessitating the re-introduction of microbes into the subsurface via groundwater transport.  相似文献   

The Sloan Digital Sky Survey monitor telescope pipeline     

D.L. Tucker  S. Kent  M.W. Richmond  J. Annis  J.A. Smith  S.S. Allam  C.T. Rodgers  J.L. Stute  J.K. Adelman‐McCarthy  J. Brinkmann  M. Doi  D. Finkbeiner  M. Fukugita  J. Goldston  B. Greenway  J.E. Gunn  J.S. Hendry  D.W. Hogg  S.‐I. Ichikawa   . Ivezi&#x;  G.R. Knapp  H. Lampeitl  B.C. Lee  H. Lin  T.A. McKay  A. Merrelli  J.A. Munn  E.H. Neilsen  H.J. Newberg  G.T. Richards  D.J. Schlegel  C. Stoughton  A. Uomoto  B. Yanny 《Astronomische Nachrichten》2006,327(9):821-843

The photometric calibration of the Sloan Digital Sky Survey (SDSS) is a multi‐step process which involves data from three different telescopes: the 1.0‐m telescope at the US Naval Observatory (USNO), Flagstaff Station, Arizona (which was used to establish the SDSS standard star network); the SDSS 0.5‐m Photometric Telescope (PT) at the Apache Point Observatory (APO), NewMexico (which calculates nightly extinctions and calibrates secondary patch transfer fields); and the SDSS 2.5‐m telescope at APO (which obtains the imaging data for the SDSS proper). In this paper, we describe the Monitor Telescope Pipeline, MTPIPE, the software pipeline used in processing the data from the single‐CCD telescopes used in the photometric calibration of the SDSS (i.e., the USNO 1.0‐m and the PT). We also describe transformation equations that convert photometry on the USNO‐1.0m u ′g ′r ′i ′z ′ system to photometry the SDSS 2.5m ugriz system and the results of various validation tests of the MTPIPE software. Further, we discuss the semi‐automated PT factory, which runs MTPIPE in the day‐to‐day standard SDSS operations at Fermilab. Finally, we discuss the use of MTPIPE in current SDSS‐related projects, including the Southern u ′g ′r ′i ′z ′ Standard Star project, the u ′g ′r ′i ′z ′ Open Star Clusters project, and the SDSS extension (SDSS‐II). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The generation of non aspect sensitive plasma density irregularities by field aligned drifts in the lower ionosphere     

T. R. Robinson  K. Schlegel 《Annales Geophysicae》2000,18(7):799-806

A theory of the generation of plasma density irregularities with virtually no aspect sensitivity, in the lower ionosphere at high latitudes, by electron drifts aligned with the geomagnetic field, is presented. The theory is developed through fluid equations in which the destabilising mechanism involves positive feedback from electron collisional heating. When field aligned electron drift speeds exceed a few km s^–1, this effect destabilises waves with wavelengths in excess of a few tens of metres in the lower E-region, where collisional effects are sufficiently large. Furthermore, the threshold conditions are almost independent of the wave propagation direction and the unstable waves propagate at speeds well below the ion acoustic speed. The role that this new instability may play in recent radar backscatter observations of short scale irregularities propagating in directions close to that of the geomagnetic field, in the lower E-region is also considered.  相似文献   

Sharks caught in the KwaZulu-Natal bather protection programme,South Africa. 14. The smooth hammerhead shark Sphyrna zygaena (Linnaeus)     

ML Dicken  H Winker  MJ Smale  G Cliff 《African Journal of Marine Science》2018,40(2):157-174

The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p < 0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats.  相似文献   

Structure and dynamics of demersal fish assemblages over three decades (1985–2012) of increasing fishing pressure in Guinea     

ML Camara  B Mérigot  F Leprieur  JA Tomasini  I Diallo  M Diallo 《African Journal of Marine Science》2016,38(2):189-206

In a context of growing fishing pressures and recommendations for an ecosystem approach to fisheries, there is a need to monitor changes in fish communities over time. In this study, we analysed data from scientific trawl surveys carried out on the continental shelf off Guinea between 1985 and 2012. We performed factorial analyses and calculated biodiversity indices to characterise the changes in the structure and composition of fish communities that occurred over the 28-year period in this area, particularly given intensive fishing activities. We show that, over the study period, fish communities on the Guinean shelf were structured primarily according to spatial factors, with temporal changes being less pronounced than expected. However, a temporal analysis of biodiversity indices and species dominance showed that the intensification of fishing had significant effects on the general ecological features of the fish assemblages under study. There was a decrease in fish density and in mean trophic level. In addition, there were changes in species dominance, whereby large, slow-growing species with high commercial value were gradually replaced by smaller, fast-growing species of lesser commercial interest. These results from field observations are in line with some conclusions from previous modelling studies in the same geographical area, and provide further support for the hypothesis of a progressive ‘ecosystem effect of fishing’ occurring in Guinean waters.  相似文献