13,993 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
Optical and X-ray studies of Be/X-ray binaries in the Small Magellanic Cloud
No full textHigh-mass X-ray binaries (HMXBs) have proved to be some of the most interesting X-ray sources in the sky. The growing opulation of Small Magellanic Cloud (SMC) Be/X-ray binaries is monitored weekly with two 15ks RXTE observations. My thesis focuses on presenting the analysis of the X-ray data and the optical follow-up that enhances it. I present detailed studies of the H emission features in several prominent Be/X-ray binaries in the SMC and examine their outbursting nature by combining the OGLE optical light curves with the RXTE light curves. This has culminated in an orbital solution for SXP18.3 as well as measured orbital periods for SXP2.37, SXP172 and SXP202B. Through detections of quasi-periodic variations in the optical light curves, the details of interactions taking place between the Be star’s circumstellar disk and the neutron star are being revealed. These data are providing the building blocks that may help explain the physical processes that produce the circumstellar disk. In addition, the optical counterpart to SXP15.3 is discussed in the light of recent XMM-Newton results, raising doubt over the true optical counterpart
Fast Reliable Ray-tracing of Procedurally Defined Implicit Surfaces Using Revised Affine Arithmetic
No full textFast and reliable rendering of implicit surfaces is an important area in the field of implicit modelling. Direct rendering, namely ray-tracing, is shown to be a suitable technique for obtaining good-quality visualisations of implicit surfaces. We present a technique for reliable ray-tracing of arbitrary procedurally defined implicit surfaces by using a modification of Affine Arithmetic called Revised Affine Arithmetic. A wide range of procedurally defined implicit objects can be rendered using this technique including polynomial surfaces, constructive solids, pseudo-random objects, procedurally defined microstructures, and others. We compare our technique with other reliable techniques based on Interval and Affine Arithmetic to show that our technique provides the fastest, while still reliable, ray-surface intersections and ray-tracing. We also suggest possible modifications for the GPU implementation of this technique for real-time rendering of relatively simple implicit models and for near real-time for complex implicit models
Corolla size and temporal displacement of flowering times among sympatric diploid and tetraploid highbush blueberry (Vaccinium corymbosum)
No full textPolyploidy (whole-genome duplication) is common in vascular plants, but the modes of establishment and persistence, as well as the ecological consequences, of polyploidy remain vague. Highbush blueberry (Vaccinium corymbosum L.) is an ecologically and economically important understory shrub with an unclear species definition, coexisting in sympatric populations of diploid and tetraploid cytotypes. This study analyzes differences in bloom time between sympatric diploid and tetraploid V. corymbosum in natural populations, testing the potential for these cytotypes to interbreed and contributing to the formation and continuity of ploidy-level diversification within this species. Ploidal level was confirmed through DNA flow cytometry of sympatric plants from two populations in New Jersey, USA. Flower bloom date and corolla size were recorded over a three-year period. Diploid corollas were 32% smaller than tetraploid corollas, making them easily identifiable in the field. Ploidy accounted for 55-69% of the variation in bloom date, with diploids flowering about one week before tetraploids, and the remaining variation distributed among plants, among branches, and within branches. Notwithstanding these differences, there was modest overlap in flowering time between cytotypes, suggesting that cross-pollination is possible. This contributes evidence to the most current species definition of V. corymbosum as a single (mixed ploidy) species.Poster's Graduate Student Thesis Publication.Peer reviewed
Tales of the Hoy [electronic resource] : interspersed with song, ode, and dialogue. By Peter Pindar, Esq.
No full textPeter Pindar = John Wolcot.Verse.On p. 64: "End of Part I.".Price from imprint: price three shillings. N. B. An clegant Engraving of the Author is prefixed to each Number, (entered at Stationers-Hall.At foot of titlepage: "N.B. An elegant engraving of the author is prefixed to each number"Electronic reproduction.English Short Title Catalog,Reproduction of original from British Library
3D ultrastructural organization of whole Chlamydomonas reinhardtii cells studied by nanoscale soft x-ray tomography
No full textThe complex architecture of their structural elements and compartments is a hallmark of eukaryotic cells. The creation of high resolution models of whole cells has been limited by the relatively low resolution of conventional light microscopes and the requirement for ultrathin sections in transmission electron microscopy. We used soft x-ray tomography to study the 3D ultrastructural organization of whole cells of the unicellular green alga Chlamydomonas reinhardtii at unprecedented spatial resolution. Intact frozen hydrated cells were imaged using the natural x-ray absorption contrast of the sample without any staining. We applied different fiducial-based and fiducial-less alignment procedures for the 3D reconstructions. The reconstructed 3D volumes of the cells show features down to 30 nm in size. The whole cell tomograms reveal ultrastructural details such as nuclear envelope membranes, thylakoids, basal apparatus, and flagellar microtubule doublets. In addition, the x-ray tomograms provide quantitative data from the cell architecture. Therefore, nanoscale soft x-ray tomography is a new valuable tool for numerous qualitative and quantitative applications in plant cell biology
X-ray waveguides with multiple guiding layers
No full textWe have generalized the principle of resonant x-ray beam coupling to waveguides containing multiple guiding layers and characterized their x-ray optical properties. In such a device, several coherent beams of a width on the order of 10-100 nm can be extracted at the end of the waveguide. By measuring the farfield pattern formed by the interference of the beams, we demonstrate the possibility of using these devices as new tools to tailor the field distribution in the near- and far-field region for specific applications: Besides coherent diffraction and imaging, interferometry with two or more nanometer sized beams can be envisioned
Synthesis and structures of mono and binuclear nickel(II) thiolate complexes of a dicompartmental pseudo-macrocycle with N(imine)2S2 and N(oxime)2S2 metal-binding sites
No full textThe reaction of [Ni(pftp)] [pftp = N,N-propane-1,3-diyl-(6-formyl-4-methyliminatothiophenolato)] with hydroxylamine hydrochloride in the presence potassium acetate in MeOH resulted in the formation of the complex [Ni(LH2)] [L = N,N-propane-1,3-diyl-(4-methyl-2-methyliminato-6-methyloxime-thiophenolato)] in good yield. A single crystal X-ray diffraction structural determination showed a mononuclear nickel(II) complex with the new acyclic ligand LH2 that had been functionalised with two oxime groups containing an empty N(oxime)2S2 pocket to which another metal ion could be added. A further reaction of [Ni(LH2)] with NiCl2·6H2O, triethylamine and ammonium hexafluorophosphate in MeOH gave a dark red product that yielded red crystals of [Ni2(LH)]PF6·DMF via slow recrystallisation from a DMF/PriOH solvent mixture. A single crystal X-ray diffraction study of these crystals confirmed the presence of a dinuclear nickel(II) complex linked by a dithiolato-bridge. Both nickel(II) ions exhibited square-planar geometry where the metal centres are coordinated in two distinct cis-S2N(imine)2 and cis-S2N(oxime)2 binding sites provided by the new dicompartmental oxime/thiolate-containing ligand L
Zechariah 9-14 as the substructure of 1 Peter’s eschatological program
No full textThe principal aim of this study is to discern what has shaped the author of 1 Peter to regard Christian suffering as a necessary (1.6) and to-be-expected (4.12) component of faithful allegiance to Jesus Christ. Most research regarding suffering in 1 Peter has limited the scope of inquiry to two particular aspects—its cause and nature, and the strategies that the author of 1 Peter employs in order to enable his addressees to respond in faithfulness. There remains, however, the need for a comprehensive explanation for the source that has generated 1 Peter’s theology of Christian suffering. If Jesus truly is the Christ, God’s chosen redemptive agent who has come to restore God’s people, then how can it be that Christian suffering is a necessary part of discipleship after his coming, death and resurrection? What led the author of 1 Peter to such a startling conclusion, which seems to runs against the grain of the eschatological hopes and expectations of Jewish restoration ideology?
This thesis analyzes the appropriation of shepherd and fiery trials imagery,
and argues that the author of 1 Peter is dependent upon Zechariah 9-14 for his
theology of Christian suffering. Said in another way, the eschatological program of
Zechariah 9-14, read through the lens of the Gospel, functions as the substructure
for 1 Peter’s eschatology and thus its theology of Christian suffering.
In support of this hypothesis, this study highlights the fact that Zechariah 9-
14 was available and appropriated in early Christianity, in particular in the Passion
Narrative tradition; that the shepherd imagery of 1 Pet 2.25 is best understood
within the milieu of the Passion Narrative tradition, and that it alludes to the
eschatological program of Zechariah 9-14; that the fiery trials imagery found in 1
Peter 1.6-7 and 1 Pet 4.12 is distinct from that which we find in Greco-Roman and OT
wisdom sources, and that it shares exclusive parallels with some unique features of
the eschatological program of Zechariah 9-14; that Zechariah 9-14 offers a more
satisfying explanation for the modification of Isa 11.2 in 1 Pet 4.14, the transition
from 4.12-19 to 5.1-4, why Peter has oriented his letter with the term διασπορά,
and why he has described his addresses as οἶκος τοῦ θεοῦ; and finally that 1 Peter
contains an implicit foundational narrative that shares distinct parallels with the
eschatological program of Zechariah 9-14.
We can conclude that 1 Peter offers a unique vista into the way in which at
least one early Christian witness came to understand and to communicate the fact
that Christian suffering was a necessary feature of faithful allegiance to Jesus Christ
The development of X-ray excited optical luminescence (XEOL) spectroscopic techniques for mineralogical and petrological applications
No full textThis thesis investigates the use of X-ray Excited Optical Luminescence (XEOL) and Time
Resolved X-ray Excited Optical Luminescence (TR XEOL) within the Earth sciences. The
project contains two primary objectives, the first of which is the design and building of a high-resolution luminescence spectroscopy facility. This includes the installation and
commissioning of the facility on the I18 microfocus beamline at Diamond, the UK's
national synchrotron facility. In describing the system's design and commissioning, I
explore many implications of the technique.
The second objective is using this new facility to investigate a suite of minerals to develop new analytical techniques utilizing XEOL and TR XEOL spectroscopy for
applications within the Earth sciences. An aspect of this investigation is to explore the potential of Time Resolved Optically Derived X-ray Absorption Spectroscopy (TR OD XAS) of substitute trace elements in minerals. To date CW OD XAS has been shown to have very limited application within the Earth sciences. (Soderholm et al., 1998-120) The thesis explores differences between photoluminescence (PL) and XEOL responses in
mineral systems, and investigates how these differences can be exploited.
Luminescence, the phenomenon upon which the thesis is based, is a complex and poorly
utilised phenomena within Earth sciences, it is however, orders of magnitude more
sensitive, than many of the more accepted techniques used for the detection of trace
elements, on this basis alone I would suggest it deserves further consideration.
Luminescence techniques have developed much further in other disciplines; I therefore
have incorporated many descriptions, models, and interpretations from other disciplines in order to identify methodologies and techniques that have the potential to be utilized in the study and interpretation of luminescence within the Earth sciences.
The thesis demonstrates that luminescence in minerals with measured lifetimes, as fast
as ~ 20 ps exist. Previously the recorded luminescent lifetimes, for minerals, in the
literature are measured in ns. This finding leads to the novel concept that the
measurement of TR XEOL with ps resolution combined with the measurement of the
intensity of a luminescent signal as a function of excitation can provide significant new insights into the nature of the emission and the luminescent processes. I explore and demonstrate the potential of using dose dependence techniques of continuous wave and TR XEOL as a new analytical technique.
I also demonstrate the use of a technique used extensively within Biology has an
application with Earth sciences. The methodology incorporates the calculation of the natural lifetime of an emission through the relationship between the absorption and
emission coefficients. (Strickler and Berg, 1962). I discuss how knowledge of the natural
lifetime of an emission allows quantification of luminescence through measurement of a modified lifetime of emission. The quantification of a luminescent emission has significant potential within the geosciences one example being the identification of disputed emissions. I also consider the potential to use TR XEOL techniques in mapping
complex heterogeneous rocks and minerals
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