The deflection of jets by clouds     

Steve Higgins  Tim O'Brien  James Dunlop 《Astrophysics and Space Science》1995,233(1-2):311-315

The role of collisions between extragalactic jets and dense clouds in determining the appearance of high-redshift radio galaxies is discussed and investigated through numerical hydrodynamic simulations in three dimensions. The code has the facility to track jet material separately from ambient material. This allows us to use simplifying assumptions to calculate synthetic radio images. The results indicate that the most powerful radio sources are likely to be observed during or shortly after an interaction, and that such interactions can explain both the radio structures and the spatial association between optical and radio light found in powerful radio galaxies. In some cases such a scenario may provide an alternative explanation of jet properties to mechanisms based on variations in the source or fluid-dynamical instabilities.This author is supported by a PPARC research studentship  相似文献   

X-ray reflection in the nearby Seyfert 2 galaxy NGC 1068     

Ken Pounds  Simon Vaughan 《Monthly notices of the Royal Astronomical Society》2006,368(2):707-714

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Validating lidar depolarization calibration using solar radiation scattered by ice clouds     

Zhaoyan Liu McGill  M. Yongxiang Hu Hostetler  C. Vaughan  M. Winker  D. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(3):157-161

This letter proposes the use of solar background radiation scattered by ice clouds for validating space lidar depolarization calibration. The method takes advantage of the fact that the background light scattered by optically thick ice clouds is almost entirely unpolarized. The theory is examined with background light measurements acquired by the Cloud Physics Lidar.  相似文献   

A fundamental dispute: A discussion of “On some fundamentals of igneous petrology” by Bruce D. Marsh,Contributions to Mineralogy and Petrology (2013) 166: 665–690     

Rais Latypov  Tony Morse  Brian Robins  Richard Wilson  Grant Cawthorn  Christian Tegner  Marian Holness  Charles Lesher  Steve Barnes  Brian O’Driscoll  Ilya Veksler  Michael Higgins  Allan Wilson  Olivier Namur  Sofya Chistyakova  Richard Naslund  Peter Thy 《Contributions to Mineralogy and Petrology》2015,169(2):1-10

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Radar and photometric observations and shape modeling of contact binary near-Earth Asteroid (8567) 1996 HW1     

Christopher Magri  Ellen S. Howell  Patrick A. Taylor  Michael Mueller  Lance A.M. Benner  Steven J. Ostro  Michael D. Hicks  James M. Somers  Vladimir V. Kouprianov  Igor E. Molotov  Jean-Luc Margot  Vojislava Protitch-Benishek  David Higgins  Donald P. Pray 《Icarus》2011,214(1):210-227

We observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008-2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8 × 1.6 × 1.5 km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243 ± 0.00004 h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.  相似文献   

Binary asteroid population. 2. Anisotropic distribution of orbit poles of small,inner main-belt binaries     

P. Pravec  P. Scheirich  D. Vokrouhlický  A.W. Harris  P. Kušnirák  K. Hornoch  D.P. Pray  D. Higgins  A. Galád  J. Világi  Š. Gajdoš  L. Kornoš  J. Oey  M. Husárik  W.R. Cooney  J. Gross  D. Terrell  R. Durkee  F. Marchis 《Icarus》2012,218(1):125-143

Our photometric observations of 18 main-belt binary systems in more than one apparition revealed a strikingly high number of 15 having positively re-observed mutual events in the return apparitions. Our simulations of the survey showed that it cannot be due to an observational selection effect and that the data strongly suggest that poles of mutual orbits between components of binary asteroids in the primary size range 3–8 km are not distributed randomly: The null hypothesis of an isotropic distribution of the orbit poles is rejected at a confidence level greater than 99.99%. Binary orbit poles concentrate at high ecliptic latitudes, within 30° of the poles of the ecliptic. We propose that the binary orbit poles oriented preferentially up/down-right are due to either of the two processes: (i) the YORP tilt of spin axes of their parent bodies toward the asymptotic states near obliquities 0° and 180° (pre-formation mechanism) or (ii) the YORP tilt of spin axes of the primary components of already formed binary systems toward the asymptotic states near obliquities 0° and 180° (post-formation mechanism). The alternative process of elimination of binaries with poles closer to the ecliptic by dynamical instability, such as the Kozai effect due to gravitational perturbations from the Sun, does not explain the observed orbit pole concentration. This is because for close binary asteroid systems, the gravitational effects of primary’s irregular shape dominate the solar-tide effect.  相似文献   

A less‐is‐more approach to geovisualization – enhancing knowledge construction across multidisciplinary teams     

Catherine Emma Jones  Mordechai Haklay  Sam Griffiths  Laura Vaughan 《International journal of geographical information science》2013,27(8):1077-1093

The ‘less‐is‐more’ concept in interface design for computer applications has recently gained ground. In this article, the concept is adopted for a user‐centered design of geovisualization application. The premise is that using simple and clear design can lead to successful applications with improved ease of use. Over the last three decades, the development of GIS and geovisualization has seen a marked increase in the levels of interaction between the user, the system and the information. However, these enthusiastic advances in technology have not resulted in a significant increase in the number of users.

This article suggests that types of user interaction should not simply emphasize traditional GIS functions such as zooming and panning but move towards interaction based on facilitating the knowledge construction process. Considerations are made for the complexity of the system, the task at hand and the skills and limitations of the users. These elements are particularly important when maps act as the mediators in collaboration with users across disciplinary backgrounds. In such cases, the emphasis on simplicity and usability becomes as important as functionality. In these situations a geovisualization application designed for specific uses can maximize effective development of geographic knowledge.

In this article, a minimalistic design approach to geovisualization is adopted by creating a geographic profiling tool which shifts the emphasis from technological advances or interaction with the map to the interaction elements key to building the spatial knowledge of GIS experts and non‐experts alike. To evaluate this notion of ‘less‐is‐more geovisualization’ the profiling tool is evaluated according to usability matrices: efficiency, effectiveness and learnability. How well the Suburban Profiler contributes to these elements is assessed by conducting a video analysis of the types and forms of user interaction available. The video analysis demonstrates the usefulness and usability of the Suburban Profiler, providing proof of concept for ‘less‐is‐more geovisualization’.  相似文献   

Uptake of nitrate and ammonium,and distribution of related variables,in the upwelled plume of western Cook Strait/Taranaki Bight,New Zealand     

Anthony B. Viner  Vaughan H. Wilkinson 《新西兰海洋与淡水研究杂志》2013,47(4):565-576

To distinguish the manner of spread of upwelling effects in the Cook Strait/Taranaki Bight (New Zealand) region, nitrogen uptake and the distribution of nutrients and chlorophyll a are described. NO3 concentrations were closely linked to upwelled water, but this was distributed irregularly and not necessarily with the upwelling focus. NH4, SRP, and chlorophyll a showed varying degrees of association with recycling processes, but linear correlations were not present. NO3 uptake was strongly inhibited by ambient NH4, but not completely. There was no evidence of either N or P limitation of total planktonic biomass, and there was indirect evidence from C/N uptake and cellular ratios that a high growth rate prevailed. N uptake increased with irradiance (= decreasing depth) similar to photosynthesis, but without high light inhibition, and could be related to light by a simple equation. The irregularity of distribution of features suggests that future modelling of the phytoplankton biomass in the region could benefit from analysis of event occurrence rather than of evenly progressive changes.  相似文献   

The Effect of Scale on the Applicability of Taylor’s Frozen Turbulence Hypothesis in the Atmospheric Boundary Layer     

Chad W. Higgins  Martin Froidevaux  Valentin Simeonov  Nikki Vercauteren  Caitlin Barry  Marc B. Parlange 《Boundary-Layer Meteorology》2012,143(2):379-391

Taylor’s frozen turbulence hypothesis is the central assumption invoked in most experiments designed to investigate turbulence physics with time resolving sensors. It is also frequently used in theoretical discussions when linking Lagrangian to Eulerian flow formalisms. In this work we seek to quantify the effectiveness of Taylor’s hypothesis on the field scale using water vapour as a passive tracer. A horizontally orientated Raman lidar is used to capture the humidity field in space and time above an agricultural region in Switzerland. High resolution wind speed and direction measurements are conducted simultaneously allowing for a direct test of Taylor’s hypothesis at the field scale. Through a wavelet decomposition of the lidar humidity measurements we show that the scale of turbulent motions has a strong influence on the applicability of Taylor’s hypothesis. This dependency on scale is explained through the use of dimensional analysis. We identify a ‘persistency scale’ that can be used to quantify the effectiveness of Taylor’s hypothesis, and present the accuracy of the hypothesis as a function of this non-dimensional length scale. These results are further investigated and verified through the use of large-eddy simulations.  相似文献   

Geochemistry and mineralogy of metalliferous minewastes: An issue in honor of John Jambor     

David J. Vaughan 《Applied Geochemistry》2009

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