15,087 research outputs found
High-speed X-ray Images Of Triggered Lightning Dart Leaders
No full textWe present the first high-time resolution two-dimensional images of X-ray emissions from lightning. The images were recorded at a rate of 10 million per second using a new pinhole-type camera, located 44 m from rocket-and-wire- triggered lightning. We report observations of two dart leaders, one in each of two lightning flashes triggered during the summer of 2010 in north-central Florida. In both events, as the dart leader approached the ground, the X-ray source was also seen to descend along the previous lightning channel. For the second event, the X-ray source exhibited a downward speed of 4.5 × 10 7 m/s, in agreement with independent dE/dt time-of-arrival (TOA) measurements of the speed of the dart leader front, demonstrating that the dart leader front was the source of the X-ray emission. The camera also recorded bursts of MeV gamma rays originating from the dart leader and/or the ground attachment process of the leader. Overall, these results provide new insight into the production of energetic radiation and the propagation and attachment of lightning, all of which remain poorly understood
poly-DART : a discrete algebraic reconstruction technique for polychromatic X-ray CT
No full textAbstract: The discrete algebraic reconstruction technique (DART) is a tomographic method to reconstruct images from X-ray projections in which prior knowledge on the number of object materials is exploited. In monochromatic X-ray CT (e.g., synchrotron), DART has been shown to lead to high-quality reconstructions, even with a low number of projections or a limited scanning view. However, most X-ray sources are polychromatic, leading to beam hardening effects, which significantly degrade the performance of DART. In this work, we propose a new discrete tomography algorithm, poly-DART, that exploits sparsity in the attenuation values using DART and simultaneously accounts for the polychromatic nature of the X-ray source. The results show that poly-DART leads to a vastly improved segmentation on polychromatic data obtained from Monte Carlo simulations as well as on experimental data, compared to DART
[Letter from Alex Bradford to Lieutenant and Mrs. Ray Starner - November 4, 1940]
No full textLetter from Alex Bradford to Lieutenant and Mrs. Ray Starner describing the the current state of affairs that the author was experiencing, including: the London blitz, the moral of the troops on the ground, and the collective company of men opposing the Nazi regime
Opportunities and Limitations of the Euniv Concept
No full textThere is a relatively significant recent growth of discourses regarding the practice of ‘enterprising’ and ‘entrepreneurial’ universities (eg. Gibb and Haskins, 2013, Vostal and Robertson, 2012, Gibb, 2012, Philpott et al, 2011, Kasim, 2011, Weingart and Maasen, 2007, Kirby, 2007). Universities are exhorted to become entrepreneurial and enterprising, both in terms of business-like processes (creating adaptable, flexible and market-responsive structures) and in terms of business-like goals (diversifying revenue streams beyond traditional reliance of government and classical-student tuition revenue streams) (Dart, 2004). Despite widespread discussion, nearly ubiquitous rhetoric and fairly widespread experimentation-at-the-margins, there is as yet very little of empirical or analytical substance to ground serious discussions of significant institutional change in the post-secondary education sector. Perhaps because of their important role in many nations as fundamental social institutions, the pressures to marketize and/or commercialize universities - the pressures to become dramatically enterprising – have only occurred more recently in the university sector than in the broader civil society, nonprofit and charitable sectors. Here, the movement for ‘enterprising nonprofits’ and ‘social entrepreneurs’ (Hansmann, 1980, Young, 1980) began much earlier and became mainstream discourse almost twenty years ago (Emerson and Twersky, 1996, Leadbeater, 1997, Dees, Emerson and Economy, 2002). Here the experience with the evolution of both the idea and the practice of an ‘enterprising’ field has been much more widespread and much more developed. This paper proposes to examine both the hopes and rhetorics of the ‘enterprising nonprofit’ field, as well as the ensuing empirical experience of nonprofits as they reposition themselves along various locations of the ‘social enterprise continuum’ in order to develop some postulates for those planning and/or implementing ‘enterprising university’ reform to consider. Based on the experience of the social enterprise and ‘enterprising nonprofits’ fields, this paper will discuss several fundamental themes from which may be germinal to discussions of a similar kind of discursive and practice field in the postsecondary education sector. Themes developed in the paper will include … 1. the oft-documented role of ‘enterprising’ discourse in the creation and maintenance of organizational legitimacy and organizational identity (Grant and Dart, 2014, Dart, 2004b), 2. the frequently overestimated capacity for commercial or ‘alternative’ revenue generation that is found in ‘enterprising’ organizations which attempt to redeploy into new markets (eg Dart et al, 2010), 3. the underappreciated role of unlabeled ‘enterprising’ activities which have long taken place in the sector, prior to any policy directives to be more entrepreneurial (Dees, Emerson and Economy, 2002), 4. the manners in which ‘enterprising’ can overshadow opportunities for both innovation and revenue generation more central to and accessible to the more ‘traditional’ elements of the operation (Oster, 2004, Bryson, 2008)
DART-RAY: a 3D ray-tracing radiative transfer code for calculating the propagation of light in dusty galaxies
No full textWe present DART-Ray, a new ray-tracing 3D dust radiative transfer (RT) code designed specifically to calculate radiation field energy density (RFED) distributions within dusty galaxy models with arbitrary geometries. In this paper, we introduce the basic algorithm implemented in . DART-Ray which is based on a pre-calculation of a lower limit for the RFED distribution. This pre-calculation allows us to estimate the extent of regions around the radiation sources within which these sources contribute significantly to the RFED. In this way, ray-tracing calculations can be restricted to take place only within these regions, thus substantially reducing the computational time compared to a complete ray-tracing RT calculation. Anisotropic scattering is included in the code and handled in a similar fashion. Furthermore, the code utilizes a Cartesian adaptive spatial grid and an iterative method has been implemented to optimize the angular densities of the rays originated from each emitting cell. In order to verify the accuracy of the RT calculations performed by DART-Ray, we present results of comparisons with solutions obtained using the dusty 1D RT code for a dust shell illuminated by a central point source and existing 2D RT calculations of disc galaxies with diffusely distributed stellar emission and dust opacity. Finally, we show the application of the code on a spiral galaxy model with logarithmic spiral arms in order to measure the effect of the spiral pattern on the attenuation and RFED. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
The student's guide to completing an author study
No full textThe 'Student's guide to completing an author study' emerged during the early development of the school library resource center program at Glen Stewart Elementary School in Stratford Canada on Prince Edward Island. This research process centered on an author study, with direct teaching and clear assignment. The resulting model has been adapted to various grade levels and subject areas in different schools.Source type: Electronic(1)http://proquest.umi.com/pqdweb?did=49237063&Fmt=7&clientId=65345&RQT=309&VName=PQ
Active X-ray optics for the next generation of X-ray space telescopes
No full textDescribed within is the design, manufacture, metrology and X-ray testing of an active X-ray
prototype intended for the next generation of X-ray telescopes. One of the challenges faced by
the X-ray telescope community is how to combine high resolution and high sensitivity into one
system, as weight limitations place constraints on the optics that can be launched. Therefore the
mandate of the active X-ray prototype is to provide high sensitivity through the ability of the optics
to be nested and to deliver high angular resolution through the active control of the optic’s form.
Piezoelectric unimorph actuators provide the active component: it is intended that they will correct
for figure errors within the optic and therefore increase the angular resolution capability.
The prototype’s design is based upon an ellipsoidal segment which provides point-to-point
focussing of an X-ray source. The prototype itself is composed of an electroformed nickel optic
where the non-reflective surface is populated with 30 piezoelectric actuators and it is the production
of the prototype that is the core of the presented research. Metrology of the actuators’ influence
functions is presented and highlight the prototype’s ability to deform its optic surface by microns.
In addition, the measured influence functions are compared against finite element models and a
distinct similarity between the functions is observed.
The prototype was tested at an X-ray beamline facility in November 2008 and the results
showed the prototype’s ability to correct the optic to achieve an improved angular resolution: from
0.786 arc-minutes to 0.686 arc-minutes in terms of full width half maximum. Finally, difficulties
in the manufacture of the prototype and X-ray testing shall be presented alongside future work in
conclusion to this thesis
Chromosome composition of an F2 Triticum aestivum×T. turgidum spp. durum cross analysed by DArT markers and MCFISH
No full textThis study has employed multicolour fluorescence in situ hybridisation (MCFISH) and Diversity Arrays Technology (DArT) markers to determine the segregation of parental A, B and D genome material into the progeny of a cross between a hexaploid bread wheat (Triticum aestivum L. var. 2-49) and a tetraploid durum wheat [T. turgidum L. spp. durum (Desf.) var. Bellaroi]. In the F2 progeny from a 2-49/Bellaroi cross, 82 out of 83 F2 plants investigated with DArT analysis carried some D genome material, principally as entire chromosomes, while 40 plants included at least one complete copy of all seven D genome chromosomes. Twelve plants containing partial D chromosomes were identified. MCFISH analysis of 26 additional F2 plants of the same cross showed that all 26 plants contained varying amounts of D genome material of which three carried single A-D translocations. In addition two telocentric D genome chromosomes were detected. The D genome content of each line and the breakpoint positions of the three A-D translocations were confirmed with DArT marker analysis. Overall results indicate a random recombination of A and B genome loci from the hexaploid female parent and the tetraploid male parent in this F2 population and a significant retention of the maternal D genome material. This study illustrates that the combined application of the MCFISH and DArT techniques provides a powerful approach for the analysis of crosses between cereal genotypes of different ploidy.</jats:p
Author, Geraldine Brooks at the National Library of Australia for the 2009 Ray Mathew Lecture, Canberra, 23 October 2009 [picture] /
No full textTitle from acquisitions documentation.; Part of the collection: Portraits of author, Geraldine Brooks during her visit to the National Library of Australia for the 2009 Ray Mathew Lecture, Canberra, 23 October 2009.; Acquired in digital format; access copy available online.; Mode of access: Internet via World Wide Web.; Photographed by a staff member of the National Library of Australia
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
- …
