103 research outputs found
Quasiregular mappings and Royden algebras.
No full textLet be as domain in euclidean n-space and A() the Royden algebra of . Then A() is the Banach algebra of all functions \rm u \in C(\Omega) \cap L\sp\infty (\Omega) \cap L\sbsp{n}{1}(\Omega) with addition and multiplication defined pointwise and norm \rm \Vert u \Vert \sb\Omega = \Vert u \Vert \sb\infty + \Vert \nabla u \Vert \sb{L\sp n}\sb{(\Omega)}. It is known that domains and \Omega\sp\prime are quasiconformally equivalent if and only if there exists an algebra isomorphism T:A( \Omega \sp\prime)\to\rm A(\Omega). In this thesis, we characterize quasiregular mappings f:\Omega\to\Omega\sp\prime with finite multiplicity as exactly those mappings induced by algebra isomorphisms T:A(\Omega\sp\prime)\to\rm A where A is a subalgebra of A() which satisfies certain conditions concerning the separation of sets in by functions in A. We characterize closed quasiregular mappings in a similar fashion and show that the multiplicity of a quasiregular mapping induced by T:A(\Omega \sp\prime )\to \rm A \subset A(\Omega) is bounded above by T\Vert \sp{\rm n \sp2}. We also investigate the maximal ideal space * of A(), which is a compact, Hausdorff, topological space. We let denote the Royden boundary of which is the set *. If two domains are quasiconformally equivalent, then their Royden boundaries must be homeomorphic. Using the theory of nets, we are able to characterize elements of as certain types of nets for which no subnet is a sequence. We define fibers over points in and show that even in the special case that is the unit ball and all fibers over are homeomorphic, is not the natural topological product of with any particular fiber. Finally, we discuss two ways in which A() reflects the geometry of . First, we define a condition on sequences of level sets linked in which guarantees that is not quasiconformally equivalent to the unit ball. Second, we use Sario's and Nakai's definition of the harmonic boundary of to give a simple condition on the Royden algebra which is equivalent to the existence of a Green's function on .PhDMathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105449/1/9124109.pdfDescription of 9124109.pdf : Restricted to UM users only
Proof of principle X-ray reflection mass measurement of the black hole in H1743-322
No full text\ua9 2024 The Author(s). The black hole X-ray binary H1743-322 lies in a region of the Galaxy with high extinction, and therefore it has not been possible to make a dynamical mass measurement. In this paper, we make use of a recent model which uses the X-ray reflection spectrum to constrain the ratio of the black hole mass to the source distance. By folding in a reported distance measurement, we are able to estimate the mass of the black hole to be 12 \ub1 2 M☉ (1σ credible interval). We are then able to revise a previous disc continuum fitting estimate of black hole spin a∗ (previously relying on a population mass distribution) using our new mass constraint, finding a∗ = 0.47 \ub1 0.10. This work is a proof of principle demonstration of the method, showing it can be used to find the mass of black holes in X-ray binaries
A Ghost Story: Remnant Structures in Corroded Ancient Iron Objects
No full textABSTRACTThe applicability of a broad spectrum of laboratory analytical methods to the study of remnant structures still observable in the corrosion products of ancient iron objects is discussed. These methods range from examination by light optical microscopy and SEM to direct microanalysis using x-ray mapping in EPMA. Samples ranging from low carbon iron to steels to cast iron have been examined and it has been found possible to observe remnant structures and infer fabrication information from the large majority of objects studied. The author thanks the Nathan Rubin-Ida Ladd Foundation for its support.</jats:p
Forensic Signatures of Nuclear Materials Processing
No full textPoster presented at the 2018 Defence and Security Doctoral Symposium.The field of nuclear forensics has been noted of relevance in the effort to tackle illicit trafficking of nuclear material. Forensic signatures can be considered a ‘fingerprint’ of the material, obtained by analytical methods such as X-Ray diffraction spectroscopy (XRD) and scanning electron microscopy (SEM). The forensic signatures obtained from characterising nuclear material may help to determine the origin and processing conditions of the sample. The aim of this project is to investigate how the physical and chemical characteristics of UO3 powder produced from aqueous reprocessing are affected by the processing route, conditions and impurities present. This will be used to develop a library of characteristic forensic signatures to aid in the discrimination of material from different sources.To date, work in this project has included the investigation of forensic signatures of studtite calcination products, whereby calcination products up to 1050 ˚C were characterised. Further investigations are being carried out into using X-Ray absorption spectroscopy (XAS) as a means of characterising amorphous UO3 phases produced by calcination. Additionally, an investigation into the effect of a fractional factorial matrix of processing variables on UO3signatusignatures (from studtite intermediate) is being conducted. Note from author: In this presentation, the thermal decomposition of synthetic studtite is examined for its potential nuclear forensic signatures. The morphologies of the finished particles are presented for discussion.</div
On measuring the Hubble constant with X-ray reverberation mapping of active galactic nuclei
No full text\ua9 2022 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. We show that X-ray reverberation mapping can be used to measure the distance to type 1 active galactic nuclei (AGNs). This is because X-ray photons originally emitted from the \u27corona\u27 close to the black hole irradiate the accretion disc and are reemitted with a characteristic \u27reflection\u27 spectrum that includes a prominent 6.4 keV iron emission line. The shape of the reflection spectrum depends on the irradiating flux, and the light-crossing delay between continuum photons observed directly from the corona and the reflected photons constrain the size of the disc. Siltaneously modelling the X-ray spectrum and the time delays between photons of different energies therefore constrains the intrinsic reflected luminosity, and the distance follows from the observed reflected flux. Alternatively, the distance can be measured from the X-ray spectrum alone if the black hole mass is known. We develop a new model of our reltrans X-ray reverberation mapping package, called rtdist, that has distance as a model parameter. We silate a synthetic observation that we fit with our new model, and find that this technique applied to a sample of 25 AGNs can be used to measure the Hubble constant with a 3σ statistical uncertainty of . Since the technique is completely independent of the traditional distance ladder and the cosmic microwave background radiation, it has the potential to address the current tension between them. We discuss sources of modelling uncertainty, and how they can be addressed in the near future
Dramatic Drop in the X-Ray Polarization of Swift J1727.8-1613 in the Soft Spectral State
No full text\ua9 2024. The Author(s). Published by the American Astronomical Society.Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8-1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2-8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system
Report of the Double-Molybdate Phase Cs<sub>2</sub>Ba(MoO<sub>4</sub>)<sub>2</sub> with a Palmierite Structure and Its Thermodynamic Characterization
No full textThe existence of a novel double-molybdate phase with a palmierite-type structure, Cs2Ba(MoO4)2, is revealed in this work, and its structural properties at room temperature have been characterized in detail using X-ray and neutron diffraction measurements. In addition, its thermal stability and thermal expansion are investigated in the temperature range 298-673 K using high-temperature X-ray diffraction, leading to the volumetric thermal expansion coefficient αV ≈ 43.0 × 10-6 K-1. The compound's standard enthalpy of formation at 298.15 K has been obtained using solution calorimetry, which yielded ΔfHm°(Cs2Ba(MoO4)2, cr, 298.15 K) = -3066.6 ± 3.1 kJ· mol-1, and its standard entropy at 298.15 K has been derived from low-temperature (2.1-294.3 K) thermal-relaxation calorimetry as Sm°(Cs2Ba(MoO4)2, cr, 298.15 K) = 381.2 ± 11.8 J K-1 mol-1.RST/Reactor Physics and Nuclear MaterialsRST/Neutron and Positron Methods in Material
Using X-ray photoelectron spectroscopy to understand the solid electrolyte interphase formation in sodium ion batteries
No full text2022 Summer.Includes bibliographical references.Sodium-ion batteries offer a more sustainable energy storage alternative to lithium while maintaining many of lithium's important characteristics. The solid electrolyte interphase (SEI) forms on the surface of the anode in both sodium and lithium-ion batteries. The SEI effects battery performance, particularly in sodium batteries, and understanding how it forms is critical for developing sodium ion batteries. Chapter I of this dissertation motivates sodium ion batteries, outlines the important differences between sodium and lithium, introduces the SEI, and establishes how the SEI is studied, ultimately placing this work in context with the field. As the SEI is derived from the electrolyte and is affected by electrolyte additives, the small molecule electrolyte additive fluoroethylene carbonate (FEC) is introduced as it is investigated throughout the dissertation. Chapter II explains how X-ray photoelectron spectroscopy can be used to study the SEI, providing examples of important protocols and pitfalls. Chapter III examines SEI formation by correlating electrochemistry from differential capacity with X-ray photoelectron spectroscopy (XPS). It is revealed that SEI species appear as a result of applied chemistry when the small molecule additive FEC is present. Without FEC, the SEI is present without significant electrochemistry in the differential capacity. Chapter IV builds off the results in Chapter III, identifying the conditions of spontaneous SEI formation due to sodium metal reactivity with the electrolyte. The spontaneous formation of the SEI is mitigated by FEC, the role of which is understood to be pre-passivation of sodium metal to prevent further electrolyte decomposition. Chapter V summarizes the work in this dissertation and outlines different directions the work can take moving forward
Discovery of X-Ray Polarization from the Black Hole Transient Swift J1727.8−1613
No full text\ua9 2023. The Author(s). Published by the American Astronomical Society.We report the first detection of the X-ray polarization of the bright transient Swift J1727.8−1613 with the Imaging X-ray Polarimetry Explorer. The observation was performed at the beginning of the 2023 discovery outburst, when the source resided in the bright hard state. We find a time- and energy-averaged polarization degree of 4.1% \ub1 0.2% and a polarization angle of 2.\ub02 \ub1 1.\ub03 (errors at 68% confidence level; this translates to ∼20σ significance of the polarization detection). This finding suggests that the hot corona emitting the bulk of the detected X-rays is elongated, rather than spherical. The X-ray polarization angle is consistent with that found in submillimeter wavelengths. Since the submillimeter polarization was found to be aligned with the jet direction in other X-ray binaries, this indicates that the corona is elongated orthogonal to the jet
Synthesis, Characterization, and Optimization of Superconductor-Dielectric Interfaces
No full textabstract: The chemical, structural, and electrical properties of niobium-silicon, niobium-germanium, and YBCO-dielectric interfaces are characterized. Reduction in the concentration of interfacial defects in these structures can improve the performance of (i) many devices including low-loss coplanar, microstrip, and stripline microwave resonators used in next-generation cryogenic communication, sensor, and quantum information technologies and (ii) layers used in device isolation, inter-wiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication.
Methods were developed to synthesize amorphous-Ge (a-Ge) and homoepitaxial-Si dielectric thin-films with loss tangents of 1–2×10 -6 and 0.6–2×10 -5 at near single-photon powers and sub-Kelvin temperatures (≈40 mK), making them potentially a better choice over undoped silicon and sapphire substrates used in quantum devices. The Nb/Ge interface has 20 nm of chemical intermixing, which is reduced by a factor of four using 10 nm Ta diffusion layers. Niobium coplanar resonators using this structure exhibit reduced microwave losses.
The nature and concentration of defects near Nb-Si interfaces prepared with commonly-used Si surface treatments were characterized. All samples have H, C, O, F, and Cl in the Si within 50 nm of the interface, and electrically active defects with activation energies of 0.147, 0.194, 0.247, 0.339, and 0.556 eV above the valence band maximum (E vbm ), with concentrations dominated by a hole trap at E vbm +0.556 eV (presumably Nb Si ). The optimum surface treatment is an HF etch followed by an in-situ 100 eV Ar ion mill. RCA etches, and higher energy ion milling processes increase the concentration of electrically active defects.
A thin SrTiO 3 buffer layer used in YBa 2 Cu 3 O 7-δ superconductor/high-performance Ba(Zn 1/3 Ta 2/3 )O 3 and Ba(Cd 1/3 Ta 2/3 )O 3 microwave dielectric trilayers improves the structural quality of the layers and results in 90 K superconductor critical temperatures. This advance enables the production of more compact high-temperature superconductor capacitors, inductors, and microwave microstrip and stripline devices.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 202
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