Functional diversity of nematode communities in the southwestern North Sea     

Schratzberger M  Warr K  Rogers SI 《Marine environmental research》2007,63(4):368-389

A range of biological traits of nematode species were combined to identify patterns in the functional composition of their assemblages collected at 19 soft-bottom stations in the southwestern North Sea with the primary aim to determine which environmental variables control communities. We used 19 categories of five biological traits thought or known to represent an important ecological function. These were related to buccal morphology, tail shape, body size, body shape and life history strategy. Data on trait membership was provided by biological information on species and genera. A total of 79 different trait combinations were recorded. Results from correlation analyses revealed several significant relationships between traits. Some trait combinations were shared by different species and genera, and the ratio of realised versus total number of possible trait combinations of < 1 suggested that some trait combinations were not represented by the nematode fauna from this region. The functional composition of nematodes was strongly linked to median particle diameter and silt content of the sediment and water depth. The approach adopted and our attempts at defining and analysing functional attributes of nematode communities raised a number of conceptual and methodological issues which are discussed.  相似文献   

The effects of frequency-dependent quasar variability on the celestial reference frame     

Stanislav S. Shabala  Jonathan G. Rogers  Jamie N. McCallum  Oleg A. Titov  Jay Blanchard  James E. J. Lovell  Christopher S. Watson 《Journal of Geodesy》2014,88(6):575-586

We examine the relationship between source position stability and astrophysical properties of radio-loud quasars making up the International Celestial Reference Frame (ICRF2). Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic very long baseline interferometry (VLBI) observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us about potential changes in source structure before they appear in VLBI images. We test how source position stability depends on three astrophysical parameters: (1) flux density variability at X band; (2) time lag between flares in S and X bands; (3) spectral index root-mean-square (rms), defined as the variability in the ratio between S and X band flux densities. We find that the time lag between S and X band light curves provides a good indicator of position stability: sources with time lags $<$ 0.06 years are significantly more stable ( $>$ 20 % improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low $(<$ 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position–frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames.  相似文献   

Stable (H,O, C) and noble-gas (He and Ar) isotopic compositions from calcite and fluorite in the Speewah Dome,Kimberley Region,Western Australia: implications for the conditions of crystallization and evidence for the influence of crustal-mantle fluid mixing     

Gy Czuppon  R. R. Ramsay  I. Özgenc  A. Demény  L. G. Gwalani  K. Rogers  A. Eves  L. Papp  L. Palcsu  M. Berkesi  P. J. Downes 《Mineralogy and Petrology》2014,108(6):759-775

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Graded-Density Reservoirs for Accessing High Stress Low Temperature Material States   总被引：1，自引：0，他引：1  

Raymond F. Smith  K. Thomas Lorenz  Darwin Ho  Bruce A. Remington  Alex Hamza  John Rogers  Stephen Pollaine  Seokwoo Jeon  Yun-Suk Nam  J. Kilkenny 《Astrophysics and Space Science》2007,307(1-3):269-272

In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap. Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile and extending these techniques to high peak pressures.  相似文献   

New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle     

Douglas S. Hall  Gregory W. Henry  Dietmar Böhme  Peter A. Brooks  Sandy Chang  Ales Dolzan  George L. Fortier  Robert E. Fried  Russell M. Genet  Bruce S. Grim  James Hannon  Darrel B. Hoff  Kevin Krisciunas  Howard J. Landis  Howard P. Louth  Larry P. Lovell  Paul Nielsen  Bobby E. Powell  Harry D. Powell  Don Pray  Thomas R. Renner  Charles W. Rogers  Stephen Shervais  Douglas M. Slauson  Samuel Slote  Harold J. Stelzer  Arthur J. Stokes  Jack C. Troeger  Louis C. Turner  Norman F. Wasson  Kenneth W. Zeigler 《Journal of Astrophysics and Astronomy》1991,12(4):281-287

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.  相似文献   

Controlling the collimation and rotation of hydromagnetic disc winds     

Ralph E. Pudritz  Conrad S. Rogers  Rachid Ouyed 《Monthly notices of the Royal Astronomical Society》2006,365(4):1131-1148

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Sputtering and high altitude meteors     

K. A. Hill  L. A. Rogers  R. L. Hawkes 《Earth, Moon, and Planets》2004,95(1-4):403-412

Conventional ablation theory assumes that a meteoroid undergoes intensive heating during atmospheric flight and surface atoms are liberated through thermal processes. Our research has indicated that physical sputtering could play a significant role in meteoroid mass loss. Using a 4th order Runge-Kutta numerical integration technique, we tabulated the mass loss due to the two ablation mechanisms and computed the fraction of total mass lost due to sputtering. We modeled cometary structure meteoroids with masses ranging from 10⁻¹³ to 10⁻³ kg and velocities ranging from 11.2 to 71 km s⁻¹. Our results indicate that a significant fraction of the mass loss for small, fast meteors is due to sputtering, particularly in the early portion of the light curve. In the past 6 years evidence has emerged for meteor luminosity at heights greater than can be explained by conventional ablation theory. We have applied our sputtering model and find excellent agreement with these observations, and therefore suggest that sputtered material accounts for the new type of radiation found at great heights.  相似文献   

Collective effects in diffuse matter-antimatter plasma: II     

S. Rogers  W. B. Thompson 《Astrophysics and Space Science》1982,82(2):415-421

It is shown that even very slightly ionized clouds of matter and anti-matter can interpenetrate only a little on collision. Initial interpenetration produces fast electrons and positrons from annihilation. These, in turn, produce strong magneto-hydrodynamic shocks which give the small ionized component enough energy to ionize the neutral fraction and produce a Leidenfrost layer in about ten years after which interpenetration stops.  相似文献   

Proterozoic East Gondwana： supercontinent assembly and breakup     

JohnJ.W.Rogers 《《幕》》2004,27(2):149-149

The editors of this volume assembled a remarkable group of contributors to discuss both the geology of East Gondwana and also many related issues. The 19 papers in this book provide a wealth of information on East Gondwana, the assembly of Gondwana as a supercontinent, the configuration of Rodinia,and general problems of the origin of continental crust and movement of continental plates. They also illustrate some of the controversies, with most papers having at least some points of difference in both fact and interpretation from other oaoers in the book.  相似文献   

Mass loss due to sputtering and thermal processes in meteoroid ablation     

L.A. Rogers 《Planetary and Space Science》2005,53(13):1341-1354

Conventional meteoroid theory assumes that the dominant mode of ablation (which we will refer to as thermal ablation) is by evaporation following intense heating during atmospheric flight. Light production results from excitation of ablated meteoroid atoms following collisions with atmospheric constituents. In this paper, we consider the question of whether sputtering may provide an alternative disintegration process of some importance. For meteoroids in the mass range from 10^-3 to and covering a meteor velocity range from 11 to , we numerically modeled both thermal ablation and sputtering ablation during atmospheric flight. We considered three meteoroid models believed to be representative of asteroidal ( mass density), cometary () and porous cometary () meteoroid structures. Atmospheric profiles which considered the molecular compositions at different heights were use in the sputtering calculations. We find that while in many cases (particularly at low velocities and for relatively large meteoroid masses) sputtering contributes only a small amount of mass loss during atmospheric flight, in some cases sputtering is very important. For example, a porous meteoroid at will lose nearly 51% of its mass by sputtering, while a asteroidal meteoroid at will lose nearly 83% of its mass by sputtering. We argue that sputtering may explain the light production observed at very great heights in some Leonid meteors. We discuss methods to observationally test the predictions of these computations. A search for early gradual tails on meteor light curves prior to the commencement of intense thermal ablation possibly represents the most promising approach. The impact of this work will be most dramatic for very small meteoroids such as those observed with large aperture radars. The heights of ablation and decelerations observed using these systems may provide evidence for the importance of sputtering.  相似文献