4,900 research outputs found
Various correspondence from members of 89'ers, 1957
No full textVarious correspondence from members of 89'ers International Highway Association, Inc. including Ray Stewart, Bentley Mitchell, and Martin Cantwell
New insights on accretion in supergiant fast X-ray transients from XMM-Newton and INTEGRAL observations of IGR J17544-2619
No full textXMM–Newton observations of the supergiant fast X-ray transient IGR J17544?2619 are reported and placed in the context of an analysis of archival INTEGRAL/IBIS data that provide a refined estimate of the orbital period at 4.9272?±?0.0004?d. A complete outburst history across the INTEGRAL mission is reported. Although the new XMM–Newton observations (each lasting ?15 ks) targeted the peak flux in the phase-folded hard X-ray light curve of IGR J17544?2619, no bright outbursts were observed, the source spending the majority of the exposure at intermediate luminosities of the order of several 1033?erg?s?1 (0.5–10 keV) and displaying only low level flickering activity. For the final portion of the exposure, the luminosity of IGR J17544?2619 dropped to ?4?×?1032?erg?s?1 (0.5–10 keV), comparable with the lowest luminosities ever detected from this source, despite the observations being taken near to periastron. We consider the possible orbital geometry of IGR J17544?2619 and the implications for the nature of the mass transfer and accretion mechanisms for both IGR J17544?2619 and the supergiant fast X-ray transients (SFXTs) population. We conclude that accretion under the ‘quasi-spherical accretion’ model provides a good description of the behaviour of IGR J17544?2619 and suggests an additional mechanism for generating outbursts based upon the mass accumulation rate in the hot shell (atmosphere) that forms around the neutron star under the quasi-spherical formulation. Hence, we hope to aid in explaining the varied outburst behaviours observed across the SFXT population with a consistent underlying physical model
X-Ray Scattering Studies of Charge and Orbital Ordering in Transition Metal Oxides
Full text linkThis thesis focusses on the phenomena of charge ordering and orbital ordering in transition metal oxides, using the technique of resonant x-ray diffraction (RXD). The technique is suited to such studies, as it provides an elemental and band specific probe of long range electronic correlations. Here, we present hard and soft x-ray diffraction results on iron and manganese compounds, and demonstrate the utility of resonant x-ray diffraction in revealing their electronic properties.
By performing comprehensive hard x-ray RXD studies on the complex charge ordered structures of magnetite and iron oxyborate, we demonstrate that both systems possess non-integer charge order by using the FDMNES simulation code. We find certain reflections have anisotropic polarisation dependencies, due entirely to the crystal structure, with no need to invoke orbital order to explain the observations. In both materials we demonstrate that the anomalous scattering components can result in a surprising conversion from linearly to non-linearly polarised light, through two subtly different interference processes. This is the first report of such mechanisms.
By performing soft x-ray scattering on Pr(SrCa)MnO, we have provided the first direct observation of the orbital rotation within this compound. We have found that there is no apparent change in the orbital occupation during the stripe rotation, but an increase in the charge disproportionation upon cooling. We have used soft x-ray RXD on lutetium ferrate to discover an anisotropic contribution to the scattering at the charge order wavevector. This is not apparent when probing the crystal structure directly using hard x-rays. We attribute such a signal to charge-orbital order within the system, in contrast to previous claims that the system is an orbital glass
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
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
A study of X-ray binaries in the local universe
No full textIn this thesis I present the research carried out on X-ray binaries in the Local Universe. These X-ray binaries are found in a wide variety of environments and display an array of interesting characteristics. I present strong evidence for the discovery of a new black hole X-ray binary in a globular cluster of a nearby elliptical galaxy. At the time of discovery it was only the second such system known. I also present the first X-ray spectroscopic analysis of a source found in the central region of the nearby starburst galaxy, M82. This source is most likely a high mass X-ray binary system and displays peculiar X-ray characteristics relative to its behaviour at other wavelengths. I study the temporal and spectroscopic behaviour of the first black hole binary found in a globular cluster. The spectra of this source show evidence for a strong, soft X-ray emission line. I also study the global properties of X-ray binaries. I analyse the X-ray binary population of NGC4472, a nearby elliptical galaxy. I compare these sources to those of other galaxies and also analyse the characteristics of subpopulations of X-ray binaries within the galax
Comparison of Straight and Curved-Ray Surface Wave Tomography at Near-Surface Scale: a 3D Numerical Example
No full textSurface Wave Tomography (SWT) is used to build shear-wave velocity models. In some studies, it is assumed that surface waves propagation follows a straight line between the source and the receiver. This assumption might be violated in near-surface studies because of high level of complexity and lateral heterogeneity. In curved-ray SWT, the actual ray paths between every receiver couple are computed. Curved-ray SWT can increase the accuracy of the model and will increase the computational effort. It is important to investigate the gained model improvement together with the associated additional computational cost from curved-ray over straight-ray SWT for near-surface applications. We apply straight- and curved-ray SWT on a generated 3D synthetic dataset and compare the results in terms of accuracy and computational costs.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Geophysics and Petrophysic
Recommended from our members
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
Changes in the Algal Flora of East Harbor, Ottawa County, Ohio, Since 1900
Full text linkAuthor Institution: Department of Botany and Center for Lake Erie Area Research, The Ohio State UniversityFREDERICK, v. RAY. Changes in the Algal Flora of East Harbor, Ottawa County, Ohio since 1900. Ohio J. Sci. 75(5): 229, 1975
- …
