17,512 research outputs found
Double axis X-Ray rocking curves simulation
No full textDouble axis X-ray diffraction has been in use since 1920. Recently the layer structures of optoelectronic devices have been characterised to control the optical properties, for the purpose of optical communication. By the advent of modern fast computers it is now possible to simulate experimental data. Here various techniques used for calculating double axis x-ray rocking curves are described. Mismatch, tilt, and composition of layers, can be quickly deduced by simulation. This approach has been widely used in the electronics industry. Recently it has been observed that a peak shift in the active layer of a double heterostructure could lead to a miscalculation of mismatch. An investigation in this direction was made to check this effect in the active layer of a double heterostructure laser. By comparing experimental and simulated data it has been observed that a shift occurs in the active layer peak and it appears that the calculated thickness is 0.018 µ m instead of 0.016 µ m of active layer of the laser. It is suggested that this peak shift could be studied in graded and multiple layer structures. The interactive part of SARCA programme which is a modification of CURVES programme needed changes to accept data for reflection (h,k,l) and accept data of material for entry of mixed mode of letters, to avoid unnecessary consumption of time. For this purpose two programmes in Pascal have been written. There is also much possibility of modelling double axis x-ray diffraction rocking curve profile
[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
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
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
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View synthesis for depth from motion 3D x-ray imaging.
No full textThe depth from motion or kinetic depth X-ray imaging (KDEX) technique is designed to enhance the luggage screening at airport checkpoints. The technique requires multiple views of the luggage to be obtained from an arrangement of linear X-ray detector arrays. This research investigated a solution to the unique problems defined when considering the possibility of replacing some of the X-ray sensor views with synthetic images. If sufficiently high quality synthetic images can be generated then intermediary X-ray sensors can be removed to minimise the hardware requirements and improve the commercial viability of the KDEX technique. Existing image synthesis algorithms are developed for visible light images. Due to fundamental differences between visible light and X-ray images, those algorithms are not directly applicable to the X-ray scenario. The conditions imposed by the X-ray images have instigated the original research and novel algorithm development and experimentation that form the body of this work. A voting based dual criteria multiple X-ray images synthesis algorithm (V-DMX) is proposed to exploit the potential of two matching criteria and information contained in a sequence of images. The V-DMX algorithm is divided into four stages
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
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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 polarization in relativistic jets
No full textWe investigate the polarization properties of Comptonized X-rays from relativistic jets in active galactic nuclei (AGN) using Monte Carlo simulations. We consider three scenarios commonly proposed for the observed X-ray emission in AGN: Compton scattering of blackbody photons emitted from an accretion disc; scattering of cosmic microwave background (CMB) photons and self-Comptonization of intrinsically polarized synchrotron photons emitted by jet electrons. Our simulations show that for Comptonization of disc and CMB photons, the degree of polarization of the scattered photons increases with the viewing inclination angle with respect to the jet axis. In both cases, the maximum linear polarization is ≈20 per cent. In the case of synchrotron self-Comptonization (SSC), we find that the resulting X-ray polarization depends strongly on the seed synchrotron photon injection site, with typical fractional polarizations P≈ 10–20 per cent when synchrotron emission is localized near the jet base, while P≈ 20–70 per cent for the case of uniform emission throughout the jet. These results indicate that X-ray polarimetry may be capable of providing unique clues to identify the location of particle acceleration sites in relativistic jets. In particular, if synchrotron photons are emitted quasi-uniformly throughout a jet, then the observed degree of X-ray polarization may be sufficiently different for each of the competing X-ray emission mechanisms (synchrotron, SSC or external Comptonization) to determine which is the dominant process. However, X-ray polarimetry alone is unlikely to be able to distinguish between disc and CMB Comptonization
A search for TeV gamma ray emission from X-ray binary stars
No full textThis work is concerned with the detection of pulsed TeV gamma ray emission from a number of X-ray binary systems by the use of the atmospheric Cerenkov technique. Chapters 1 and 2 give an overview of the development of gamma ray astronomy, with emphasis placed on progress made in the detection of TeV gamma rays by their Cerenkov radiation in the atmosphere. Chapters 3 and 4 describe the University of Durham atmospheric Cerenkov telescopes, which were used to make the observations reported in this work, and the standard data processing and analysis procedures adopted. The main part of the thesis deals with the application of these techniques to observations of five X-ray binaries. After a review of the properties of such objects in Chapter 5, Chapters 6 and 7 deal specifically with the results for two of the systems considered to be among the most likely candidates to give a detectable TeV photon flux; Centaurus X-3 and Vela X-1. A study of all data recorded on Cen X-3 over the course of six years suggests the presence of a weak gamma ray flux pulsed at the X-ray period. Previous reports of stronger emission near the ascending node of the orbit are confirmed here. For Vela X-1, the analysis of a dataset recorded during a single dark moon interval reveals evidence for two short outbursts of pulsed TeV gamma ray emission. Chapter 8 reports the series of observations made of SMC X-1, 4U1626-67 and X0G21-72, and upper limits are placed on the TeV gamma ray emission from each. Finally, the results reported here are compared with the predictions of a number of theoretical models, some of which are found to give good agreement with the limits and detections derived in this work. A discussion of the status of this field and future observational prospects is also given
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