41 research outputs found
The cosomological evolution of the environments of powerful radio galaxies
We present the results from the analysis of 26 extragalactic radio sources of
type FRII which were observed with the VLA at 5 GHz and around the 1.4 GHz
band. The sources were selected to have redshifts in the range ,
radio powers between and angular size . We found
that the depolarisation and the rms variations in the rotation measure
increased with redshift. The flux values obtained from the observations were
used to derive by means of analytical modelling the jet--power, density of the
central environment, age of the source and its lobe pressure and the results
were then compared with the observations. We find no significant correlations
with the density parameter suggesting that the depolarisation and the rms
variations in the rotation measure are indicative of the environment becoming
more disordered rather than denser. The age and size of a source are correlated
and both were found to be independent of redshift and radio--power. Jet--power
strongly correlated with the radio--power. The lobe pressure was found to be
anti--correlated with size which could explain why there are no sources beyond
a few Mpc in size. We found no significant correlation between size and density
which demonstrates that the sample is a fair representation of the population.Comment: 2 pages, Cozumel AGN 2003 conference proceeding
The depolarisation properties of powerful extragalactic radio sources as a function of cosmic epoch
We use the observed polarisation properties of a sample of 26 powerful radio
galaxies and radio-loud quasars to constrain the conditions in the Faraday
screens local to the sources. We adopt the cosmological redshift, low-frequency
radio luminosity and physical size of the large-scale radio structures as our
`fundamental' parameters. We find no correlation of the radio spectral index
with any of the fundamental parameters. The observed rotation measure is also
independent of these parameters. The difference between the rotation measures
of the two lobes of an individual source as well as the dispersion of the
rotation measure show significant correlations with the source redshift, but
not with the radio luminosity or source size. Thus the small-scale structure
observed in the rotation measure is caused by a Faraday screen local to the
sources. The observed asymmetries between the lobes of our sources show no
significant trends with each other or other source properties. Finally, we show
that the commonly used model for the depolarisation of synchrotron radio
emission by foreground Faraday screens is inconsistent with our observations.
We apply alternative models to our data and show that they require a strong
increase of the dispersion of the rotation measure inside the Faraday screens
with cosmological redshift. Correcting our observations with these models for
redshift effects, we find a strong correlation of the depolarisation measure
with redshift and a significantly weaker correlation with radio luminosity. All
our results are consistent with a decrease in the order of the magnetic field
structure of the Faraday screen local to the sources for increasing
cosmological redshift. (abridged)Comment: 14 pages, 16 eps figures, accepted by MNRA
Process Compensated Resonance Testing Modeling for Damage Evolution and Uncertainty Quantification
Process Compensated Resonance Testing (PCRT) is a nondestructive evaluation method that measures and analyzes the resonance frequencies of a component for material state characterization, defect detection and process monitoring. PCRT inspections of gas turbine engine components have demonstrated the sensitivity of resonance frequencies to manufacturing defects and in-service thermal and mechanical damage. Prior work on PCRT modeling has developed forward modeling and model inversion techniques that simulate the effects of geometry variation, material property variation, and damage on Mar-M-247 nickel-based superalloy samples. Finite element method (FEM) forward model simulations predicted the effects of variation in geometry, material properties and damage on resonance frequencies. Model inversion used measured resonance frequencies to characterize the material state of components. Parallel work developed a process for uncertainty quantification (UQ) in PCRT models and measurements. The UQ process evaluated the propagation of uncertainty from various sources, identified the most significant uncertainty sources, and enabled uncertainty mitigation to improve model and measurement accuracy. Current efforts have expanded on those developments in several areas. One-factor-at-a-time (OFAT) forward model simulations were conducted on cylindrical dog bone coupons made from Mar-M-247. The simulations predicted the resonance frequency response to variation in geometry, elastic properties, crystallographic orientation, creep strain and cracking. The OFAT studies were followed by forward model Monte Carlo simulations that predicted the effects of multiple, concurrent sources of variation and damage on resonance frequencies, allowing characterization of virtual populations and quantification of uncertainty propagation. The Monte Carlo simulation design points were used to demonstrate the generation of a virtual database of components for training PCRT inspection applications, or “sorting modules.” Virtual database training sets can potentially overcome the limitations imposed by the availability of components and material states for training sets based on physical examples. Forward modeling tools and techniques were applied to titanium to simulate the effects of material variation, damage, and crystallographic texture. Forward modeling was also applied to more complex geometries, including a notional turbine blade, to demonstrate the application of modeling tools to shapes representative of gas turbine engine components. Model inversion tools and techniques have also advanced under the current effort. Prior inversion methods relied on iterative fitting to polynomial expressions for simple geometries and bulk material properties. Current efforts have demonstrated FEM-based model inversion which allows characterization of complex shapes and material states. FEM-based design spaces were generated, model inversion was carried out for surrogate modeled resonance spectra, and inversion performance was evaluated. Analysis of PCRT modeling results led to the development of automated resonance mode matching tools based on the calculation of modal assurance criteria (MAC) values, mode shape displacement metrics and Hungarian Algorithm sorting methods
Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions
tThe influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNSN08031 stainless steel in a contaminated phosphoric acid solution were evaluated. Stabilisation of thepassive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemicalimpedance spectroscopy (EIS) measurements, Mott Schottky analysis and X-ray photoelectron spec-troscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The filmformed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed thepresence of fluoride ions.Authors express their gratitude to the Ministry of Education of Spain (MHE2011-00202) for its financial support during the stay at University of Manchester, to MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10) and to the Generalitat Valenciana (GV/2011/093) for the financial support. The authors would also like to acknowledge the support of the School of Materials at the University of Manchester for providing analytical and technical support for the study.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Akid, R.; Walton, J. (2013). Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions. Electrochimica Acta. 111:552-561. https://doi.org/10.1016/j.electacta.2013.08.040S55256111
The Financial Services Sector: Past Changes and Future Prospects
The financial service industry has been undergoing significant change in recent years. This paper analyzes some key developments affecting the industry and examines some important issues facing the industry and its regulators. Changes discussed include the way services are provided, the instruments used to provide servces, and the nature of the financial service providers. Factors driving these changes include technological developments, the changing role of competition, and demographically led changes in household portfolios.CANADA ; REGULATION ; FINANCIAL INSTITUTIONS
Bayesian inference of elastic properties with resonant ultrasound spectroscopy.
Bayesian modeling and Hamiltonian Monte Carlo (HMC) are utilized to formulate a robust algorithm capable of simultaneously estimating anisotropic elastic properties and crystallographic orientation of a specimen from a list of measured resonance frequencies collected via Resonance Ultrasound Spectroscopy (RUS). Unlike typical optimization procedures which yield point estimates of the unknown parameters, computing a Bayesian posterior yields probability distributions for the unknown parameters, and HMC is an efficient way to compute this posterior. The algorithms described are demonstrated on RUS data collected from two parallelepiped specimens of structural metal alloys. First, the elastic constants for a specimen of fine-grain polycrystalline Ti-6Al-4 V with random crystallographic texture and isotropic elastic symmetry are estimated. Second, the elastic constants and crystallographic orientation for a single crystal Ni-based superalloy CMSX-4 specimen are accurately determined, using only measurements of the specimen geometry, mass, and resonance frequencies. The unique contributions of this paper are as follows: the application of HMC for sampling the Bayesian posterior of a probabilistic RUS model, and the procedure for simultaneous estimation of elastic constants and lattice-specimen misorientation. Compared to previous approaches these algorithms demonstrate superior convergence behavior, particularly when the initial parameterization is unknown, and enable substantially simplified experimental procedures