Numerical methods for stiff systems of two-point boundary value problems

Numerical procedures are developed for constructing asymptotic solutions of certain nonlinear singularly perturbed vector two-point boundary value problems having boundary layers at one or both endpoints. The asymptotic approximations are generated numerically and can either be used as is or to furnish a general purpose two-point boundary value code with an initial approximation and the nonuniform computational mesh needed for such problems. The procedures are applied to a model problem that has multiple solutions and to problems describing the deformation of thin nonlinear elastic beam that is resting on an elastic foundation

Experimental investigation of a mach 5 isentropic spike inlet at and below design speed

Zero angle of attack performance of isentropic spike inlet designed for maximum external compression at hypersonic spee

A very high frequency radio interferometer for investigating ionospheric disturbances using geostationary satellites. Determination of changes in exospheric electron content by a comparison of group delay and Faraday rotation

The theory and development of a VHF correlation radio interferometer for investigating ionospheric disturbances are discussed. The system was developed to receive signals from the geostationary Applications Technology Satellites. Amplitude and phase variations of the signal passing through the ionosphere can be detected by this instrument. The system consists of two superheterodyne receivers separated by a distance known as the baseline of the system. Since the system is a phase sensitive instrument, the local oscillators of the two receivers must be phase coherent. This is accomplished by using phase-locked loops for generating the local oscillators. The two signals from the separate receivers are cross-correlated by multiplying the two signals together and then time averaging the result. The sensitivity of the instrument is increased by off-setting one of the local oscillators by a small amount

Homelessness in Oxford : risks and opportunities across housing and homeless transitions

This report presents initial findings from CSI’s Homelessness in Oxford project. The project was designed by Dr. Garratt and Dr. Flaherty to be the first systematic attempt to track and understand people’s transitions into and out of different experiences of homelessness in Oxford. The project also explored the roles played by statutory and non-statutory homelessness prevention and relief services in Oxford

An explanation of the Newman-Janis Algorithm

After the original discovery of the Kerr metric, Newman and Janis showed that this solution could be ``derived'' by making an elementary complex transformation to the Schwarzschild solution. The same method was then used to obtain a new stationary axisymmetric solution to Einstein's field equations now known as the Kerr-newman metric, representing a rotating massive charged black hole. However no clear reason has ever been given as to why the Newman-Janis algorithm works, many physicist considering it to be an ad hoc procedure or ``fluke'' and not worthy of further investigation. Contrary to this belief this paper shows why the Newman-Janis algorithm is successful in obtaining the Kerr-Newman metric by removing some of the ambiguities present in the original derivation. Finally we show that the only perfect fluid generated by the Newman-Janis algorithm is the (vacuum) Kerr metric and that the only Petrov typed D solution to the Einstein-Maxwell equations is the Kerr-Newman metric.Comment: 14 pages, no figures, submitted to Class. Quantum Gra

‘There’s nothing I can do to stop it’ : homelessness among autistic people in a British city

Autistic people appear to have a higher risk of becoming and remaining homeless than people without autism. This article is based on a wider research study exploring diverse homelessness experiences in Oxford, UK. Using life mapping, a visual research method, we gained verbal and visual accounts of participants’ housing and homeless histories. These accounts support past evidence of higher than expected levels of autism among homeless people, while highlighting for the first time specific, additional risks of homelessness among autistic people. This group also appeared to have fewer means to reduce the risk of homelessness, and faced multiple challenges to resolving their homelessness. Our findings extend existing understandings of autism and homelessness, and of the disabling practices that autistic people may face within the diversity of homeless experiences, while adding valuable biographic detail to the factors leading to homelessness and attempts to exit homelessness. We also discuss potential policy interventions

Characterization Of Individual Submicron Perfluorocarbon Gas Bubbles By Ultrasonic Backscatter

Measurements were undertaken to determine the unknown microbubble-size distribution of a dodecafluoropentane (DDFP) emulsion consisting of in surfactant-stabilized water. The acoustic backscatter of 2-microsecond-duration tonebursts of 30-MHz focused ultrasound was measured from the emulsion as it moved in a coaxial flow. Calibration for the system was accomplished using 3-μm-radius polystyrene spheres, using a linear scattering model and literature values for polystyrene. Applying viscous linear scattering theory to the backscatter data from individual DDFP bubbles allowed inversion of the radius–backscatter relation. A mean microbubble radius of 130 nm was inferred for the DDFP population. © 2005 Acoustical Society of America