16,192 research outputs found
Diagnosing and mapping pulmonary emphysema on X-ray projection images
No full textTo assess whether grating-based X-ray dark-field imaging can increase the sensitivity of X-ray projection images in the diagnosis of pulmonary emphysema and allow for a more accurate assessment of emphysema distribution. Lungs from three mice with pulmonary emphysema and three healthy mice were imaged ex vivo using a laser-driven compact synchrotron X-ray source. Median signal intensities of transmission (T), dark-field (V) and a combined parameter (normalized scatter) were compared between emphysema and control group. To determine the diagnostic value of each parameter in differentiating between healthy and emphysematous lung tissue, a receiver-operating-characteristic (ROC) curve analysis was performed both on a per-pixel and a per-individual basis. Parametric maps of emphysema distribution were generated using transmission, dark-field and normalized scatter signal and correlated with histopathology. Transmission values relative to water were higher for emphysematous lungs than for control lungs (1.11 vs. 1.06, p<0.001). There was no difference in median dark-field signal intensities between both groups (0.66 vs. 0.66). Median normalized scatter was significantly lower in the emphysematous lungs compared to controls (4.9 vs. 10.8, p<0.001), and was the best parameter for differentiation of healthy vs. emphysematous lung tissue. In a per-pixel analysis, the area under the ROC curve (AUC) for the normalized scatter value was significantly higher than for transmission (0.86 vs. 0.78, p<0.001) and dark-field value (0.86 vs. 0.52, p<0.001) alone. Normalized scatter showed very high sensitivity for a wide range of specificity values (94% sensitivity at 75% specificity). Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology. In a murine model, the complementary information provided by X-ray transmission and dark-field images adds incremental diagnostic value in detecting pulmonary emphysema and visualizing its regional distribution as compared to conventional X-ray projections
[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
1D and 2D X-ray waveguides: Optics and applications
No full textX-ray waveguides [1-4] offer a novel approach for nanobeam production, which may become useful in
coherent beam imaging and phase contrast projection microscopy [5]. Internal field enhancement, coherency
properties, and coupling efficiency of these devices have been measured and compared to theoretic predictions. The
fundamentals of x-ray wave guide optics can be derived from a scalar wave equation. Up to now, x-ray waveguide
optics have exclusively been one-dimensional (1D), while many applications demand two-dimensionally (2D) confined
point beams. We have recently demonstrated the first proof of principle that x-ray waveguide effects can be generalized
to 2D devices using e-beam defined lithographic nanostructures [6], delivering of a coherent hard x-ray beam with
nanometer sized cross-section (69 nm 33 nm)
Lehman\u27s Cave, July 23-24, 1932. Ray Arnold, Leone Chambers, Chick Pfeiffer, and Elanor Wright
No full textBlack and white photograph of Ray Arnold, Leone Chambers, Chick Pfeiffer, and Elanor Wright during a Wasatch Mountain Club trip to Lehman Caves National Monument in Nevada, July 23-24, 1932
White beam x-ray waveguide optics
No full textWe report a white beam x-ray waveguide (WG) experiment. A resonant beam coupler x-ray waveguide (RBC) is used simultaneously as a broad bandpass (or multibandpass) monochromator and as a beam compressor. We show that, depending on the geometrical properties of the WG, the exiting beam consists of a defined number of wavelengths which can be shifted by changing the angle of incidence of the white x-ray synchrotron beam. The characteristic far-field pattern is recorded as a function of exit angle and energy. This x-ray optical setup may be used to enhance the intensity of coherent x-ray WG beams since the full energetic acceptance of the WG mode is transmitted. (C) 2004 American Institute of Physics
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
Simulations of X-ray bursts and superbursts
No full textObservations of neutron star in binary systems provide powerful constrains on the physics at the surface of neutron stars. During the accretion of matter from the companion star, periodic nuclear explosion are triggered in the outer layers of the neutron star, increasing the luminosity during a time range of a few minutes. Rarely, one can also detect day-long explosions in accreting binary systems. The nature of those two kind of bursts is still not well understood. In fact, simplified simulations of the outer layers of an accreting neutron star in a binary are not yet able to reproduce all observable features.
The work presented in this thesis is devoted to the one-dimensional simulations of X-ray bursts and superbursts. The numerical code used in this work has initially been programmed by J. Fisker in 2006. By updating and optimizing the code, we are able to simulate X-ray bursts as well as superbursts in a feasible time range. Using a large nulear network, we study the features of X-ray bursts and compare them with observations. To understand the link between various properties entering our simulations as parameters or boundary conditions, we present several models which reproduces hunderds of X-ray burst. In this current work, we focus mainly on changes in crustal heating, accretion rate and accretion composition. Analyzing the influence on the light curve as well as on the ashes of X-ray bursts, we are able to compare our results with observations. To shed some light on the self-consistent ignition of a superburst, we model a setup which may lead to the ignition of a superburst.
Our results suggest that additional helium, heavier isotopes and the lack of hydrogen in the accretion composition help to generate carbon-rich X-ray burst ashes. Strong heating below the superburst ignition layer prevents the destruction of carbon after an X-ray bursts and might be the key ingredience in the self-consistent ignition of a superburst within the time range of the observed recurrence tim
Two-dimensional x-ray waveguides and point sources
No full textWe show that resonant coupling of synchrotron beams into suitable nanostructures can be used for the generation of coherent x-ray point sources. A two-dimensionally con ning x-ray waveguide structure has been fabricated by e-beam lithography. By shining a parallel undulator beam onto the structure, a discrete set of resonant modes can be excited in the dielectric cavity, depending on the two orthogonal coupling angles between the beam and the waveguide interfaces. The resonant excitation of the modes is evidenced from the characteristic set of coupling angles as well as the observed far-field pattern. The x-ray nanostructure may be used as coherent x-ray point sources with a beam cross section in the nanometer range
Simulations of multi-contrast x-ray imaging using near-field speckles
No full textX-ray dark-field and phase-contrast imaging using near-field speckles is a novel technique that overcomes limitations inherent in conventional absorption x-ray imaging, i.e. poor contrast for features with similar density. Speckle-based imaging yields a wealth of information with a simple setup tolerant to polychromatic and divergent beams, and simple data acquisition and analysis procedures. Here, we present a simulation software used to model the image formation with the speckle-based technique, and we compare simulated results on a phantom sample with experimental synchrotron data. Thorough simulation of a speckle-based imaging experiment will help for better understanding and optimising the technique itself
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