242 research outputs found
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
Friends of the Sherlock Holmes Collections Newsletter, 2014, Vol 18, No. 3
No full textQuarterly newsletter of the Friends of the Sherlock Holmes Collections at the University of Minnesota Libraries. This issue includes articles on Cheryll Fong's experience as interim curator during the curator's sabbatical; a Sherlockian parody published a hundred years ago in the Minneapolis Sunday
Tribune about the University of Minnesota; Sherlockian Martin J. Swanson; research experiences in using the Collections by Ray Betzner and Steve Mason; acquisition of the Berg Collection; and notice of the Friends annual meeting featuring author and critic Michael Dirda.Fong, Cheryll L; McKuras, Julie; Sveum, Richard J; Mason, Steve; Press, Charles; Betzner, Ray. (2014). Friends of the Sherlock Holmes Collections Newsletter, 2014, Vol 18, No. 3. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/212249
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Enhanced colour encoding of materials discrimination information for multiple view dual-energy x-ray imaging
No full textThis thesis reports an investigation into dual-energy X-ray discrimination techniques. These techniques are designed to provide colour-coded materials discrimination information in a sequence of perspective images exhibiting sequential parallax. The methods developed are combined with a novel 3D imaging technique employing depth from motion or kinetic depth effect (KDE). This technique when applied to X-ray images is termed KDEX imaging and was developed previously by the university team for luggage screening applications at security checkpoints. A primary motivation for this research is that the dual-energy X-ray techniques, which are routinely incorporated into ‘standard’ 2D luggage scanners, provide relatively crude materials discrimination information. In this work it was critical that robust materials discrimination and colour encoding process was implemented as the sequential parallax exhibited by the KDEX imagery may introduce colour changes, due to the different X-ray beam paths associated with each perspective image. Any introduction of ‘colour noise’ into the resultant image sequences could affect the perception of depth and hinder the ongoing assessment of the potential utility of the dual-energy KDEX technique. Two dual-energy discrimination methods have been developed, termed K-II and W-E respectively. Employing the total amount of attenuation measured at each energy level and the weight fraction of layered structures, a combination of the K-II and the W-E techniques enables the computation and extraction of a target objects’ effective atomic number (Zeff) and its surface density (ρS) in the presence of masking layers
X-ray spectroscopy of the IP PQ Gem
No full textUsing RXTE and ASCA data, we investigate the roles played by occultation and absorption in the X-ray spin pulse profile of the intermediate polar PQ Gem. From the X-ray light curves and phase-resolved spectroscopy, we find that the intensity variations are the result of a combination of varying degrees of absorption and the accretion regions rotating behind the visible face of the white dwarf. These occultation and absorption effects are consistent with those expected from the accretion structures calculated from optical polarization data. We can reproduce the changes in absorber covering fraction either from geometrical effects, or by considering that the material in the leading edge of the accretion curtain is more finely fragmented than in other parts of the curtain. We determine a white dwarf mass of ∼ 1.2 using the RXTE data
Structure of Rubidium and Strontium Nuclides of Mass 90 and 91
No full textTitle: Structure of Rubidium and Strontium Nuclides of Mass 90 and 91, Author: James F.A. Mason, Location: ThodeThe level structures of 90,91Rb and 90,91Sr, as populated in beta decay, have been investigated using Ge(Li) and NaI(Tl) gamma ray and plastic beta ray spectrometers, and standard spectroscopic techniques. Beta-gamma and gamma-gamma coincidence experiments have been used to establish twelve levels in 90Rb, four levels in 91Rb and to determine the ground state Q-values for the decay of
both 90Kr and 91Kr. Thirty-one levels have been proposed in 90Sr and eighteen in 91Sr on the basis of gamma-gamma coincidence experiments only. The lifetime of the first excited state in 91Sr has also been measured.ThesisDoctor of Philosophy (PhD
High time resolution optical/X-ray cross-correlations for X-ray binaries : anticorrelations and rapid variability
No full textUsing simultaneous observations in X-rays and optical, we have performed a homogeneous analysis of the cross-correlation behaviours of four X-ray binaries: SWIFT J1753.5-0127, GX339-4, Sco X-1 and CygX-2. With high-time-resolution observations using ULTRACAM and RXTE, we concentrate on the short time-scale, delta t < 20 s, variability in these sources. Here we present our data base of observations, with three simultaneous energy bands in both the optical and the X-ray, and multiple epochs of observation for each source, all with similar to second or better time resolution. For the first time, we include a dynamical cross-correlation analysis, i.e. an investigation of how the cross-correlation function changes within an observation. We describe a number of trends which emerge. We include the full data set of results, and pick a few striking relationships from among them for further discussion.
We find, that the surprising form of X-ray/optical cross-correlation functions, a positive correlation signal preceded by an anticorrelation signal, is seen in all the sources at least some of the time. Such behaviour suggests a mechanism other than reprocessing as being the dominant driver of the short-term variability in the optical emission. This behaviour appears more pronounced when the X-ray spectrum is hard. Furthermore, we find that the cross-correlation relationships themselves are not stable in time, but vary significantly in strength and form. This all hints at dynamic interactions between the emitting components which could be modelled through non-linear or differential relationships
Detection of the irradiated donor in the LMXBs 4U 1636-536 (=V801 Ara) and 4U 1735-444 (=V926 Sco)
No full textPhase-resolved VLT spectroscopy of the bursting low-mass X-ray binaries 4U 1636-536/V801 Ara and 4U 1735-444/V926 Sco is presented. Doppler images of the N iiiλ4640 Bowen transition reveal compact spots which we attribute to fluorescent emission from the donor star and enable us to define a new set of spectroscopic ephemerides. We measure Kem= 277 ± 22 and 226 ± 22 km s−1 from the N iii spots in V801 Ara and V926 Sco, respectively, which represent strict lower limits to the radial velocity semi-amplitude of the donor stars. Our new ephemerides provide confirmation that light-curve maxima in V801 Ara and likely V926 Sco occur at superior conjunction of the donor star and hence photometric modulation is caused by the visibility of the X-ray heated donor. The velocities of He iiλ4686 and the broad Bowen blend are strongly modulated with the orbital period, with phasing supporting emission dominated by the disc bulge. In addition, a reanalysis of burst oscillations in V801 Ara, using our spectroscopic T0, leads to K1= 90–113 km s−1. We also estimate the K-corrections for all possible disc flaring angles and present the first dynamical constraints on the masses of these X-ray bursters. These are K2= 360 ± 74 km s−1, f(M) = 0.76 ± 0.47 M⊙ and q= 0.21–0.34 for V801 Ara and K2= 298 ± 83 km s−1, f(M) = 0.53 ± 0.44 M⊙ and q= 0.05–0.41 for V926 Sco. Disc flaring angles α≥ 12° and q≃ 0.26–0.34 are favoured for V801 Ara whereas the lack of K1 constraint for V926 Sco prevents tight constraints on this system. Although both binaries seem to have intermediate inclinations, the larger equivalent width of the narrow N iii line in V801 Ara at phase 0.5 relative to phase 0 suggests that it has the higher inclination of the two
The Foliose and Fruticose Lichen Flora of the Ohio River Valley Between Gallipolis, Ohio, and Parkersburg, West Virginia
No full textAuthor Institution: Environmental Engineering Division, American Electric Power Service CorporationLichens were surveyed in a relatively uncollected region composed of parts of Gallia, Meigs, Athens, and Washington Counties, Ohio, and parts of Mason, Jackson, and Wood Counties, West Virginia. A total of 87 species of foliose and fruticose lichens were recorded. New state records for West Virginia are Cetraria fendleri, Parmelia crozalsiana, P. flaventior, Parmeliopsis aleurites, Physcia adscendens, P. endococcinea, and P. lacinulata. Pseudevernia consocians was the only new species found in Ohio
Echoes from the companion star in Sco X-1
No full textWe present simultaneous X-ray (RXTE) and optical (ULTRACAM) narrow-band ( Bowen blend/He II and nearby continuum) observations of Sco X-1 at 2-10 Hz time resolution. We find that the Bowen/He II emission lags the X-ray light curves with a light traveltime of similar to 11-16 s which is consistent with reprocessing in the companion star. The echo from the donor is detected at orbital phase similar to 0.5 when Sco X-1 is at the top of the flaring branch (FB). Evidence of echoes is also seen at the bottom of the FB but with time-lags of 5-10 s which are consistent with reprocessing in an accretion disc with a radial temperature profile. We discuss the implication of our results for the orbital parameters of Sco X-1
Regulating privatized infrastructures and airport services
No full textFor a World Bank Institute course on transport privatization, the authors cover basic issues associated with the regulation of privatized airport infrastructure and services: 1) Economic characteristics of airport. Three types of activities are carried out in airports: essential operational services (aeronautical and non-aeronautical), handling services (aeronautical and non-aeronautical), and commercial activities. Demand for basic airport services is directly influenced by trip purpose. The two types of airline customers (business and leisure travelers) need different levels of flexibility and tend to travel at different times. Analyzing airport capacity (practical and saturation) under peak demand is essential to airport success. Among other important issues: runway cost, level and volume of service, pollution, congestion, and air traffic control. 2) Recent trends in the airport industry. The movement toward privatization may involve public ownership and private operation, including joint ventures; partial or majority divestiture; management contracts; and BOT (build-operate-transfer) schemes and variants, including BOOT (build-own-operate-transfer) schemes and LDO (lease-develop-operate) schemes. Or it may involve private ownership and operation. 3) Price regulation. Topics covered include traditional pricing policies'price regulation through an RPI-X formula; charges for congestion, noise, and other externalities; investment plans; and design of the regulatory system. 4) Regulation of quality in the industry. Topics covered: regulation of services to passengers (as measured by targets for check-in queues, immigration queues, baggage reclaim queues, concourse crowding, shopping, parking, and so on); fault repair times; average levels of passenger boarding and disembarkation and baggage delivery; safety; and investment obligation. 5) Performance indicators in the industry. Topics covered: strategic indicators and other financial indicators (including revenues), as well as indicators of cost, productivity, and quality of service.Transport and Trade Logistics,Public Sector Economics&Finance,Banks&Banking Reform,Environmental Economics&Policies,Decentralization,Roads&Highways,Airports and Air Services,Public Sector Economics&Finance,Banks&Banking Reform,Transport and Trade Logistics
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