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Search Results: 1 - 10 of 2660 matches for " Bethan Lang "
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Applications of, and Extensions to, Selected Exact Solutions in General Relativity
Bethan Cropp
Physics , 2011,
Abstract: In this thesis we consider several aspects of general relativity relating to exact solutions of the Einstein equations. In the first part gravitational plane waves in the Rosen form are investigated, and we develop a formalism for writing down any arbitrary polarisation in this form. In addition to this we have extended this algorithm to an arbitrary number of dimensions, and have written down an explicit solution for a circularly polarized Rosen wave. In the second part a particular, ultra-local limit along an arbitrary timelike geodesic in any spacetime is constructed, in close analogy with the well-known lightlike Penrose limit. This limit results in a Bianchi type I spacetime. The properties of these spacetimes are examined in the context of this limit, including the Einstein equations, stress-energy conservation and Raychaudhuri equation. Furthermore the conditions for the Bianchi type I spacetime to be diagonal are explicitly set forward, and the effect of the limit on the matter content of a spacetime are examined.
Faith and Music: A Personal Exploration of the Implication of Religious Faith in Music Therapy, within an Intercultural, Group Music-Making Context
Bethan Lee Shrubsole
Approaches : Music Therapy & Special Music Education , 2010,
Abstract: In July 2008 Music for Peaceful Minds (MPM), a peripatetic music therapy service in post-conflict northern Uganda, was established. To date, MPM serves four schools and two orphanages with a specially-trained peripatetic Ugandan music counsellor. Weekly music therapy groups are run, each consisting of six children, referred by orphanage or school staff. The mixed- and single sex- groups run for a term (10-12 weeks). They are split into age ranges of 4-11 and 12-18.This is a clinical discussion drawing on my personal experience as a music therapist in Uganda in 2008. It is not intended to be a theoretical or research paper and as such does not contain a thorough literature review. I will be considering various religious aspects of an English therapist working in northern Uganda, focusing on the music that was made in sessions. I will discuss the questions of how important it is for a therapist to have a shared culture, faith or musical background with her clients, and how a language barrier can affect the therapy.
General polarization modes for the Rosen gravitational wave
Bethan Cropp,Matt Visser
Physics , 2010, DOI: 10.1088/0264-9381/27/16/165022
Abstract: Strong-field gravitational plane waves are often represented in either the Rosen or Brinkmann forms. While these two metric ansatze are related by a coordinate transformation, so that they should describe essentially the same physics, they rather puzzlingly seem to treat polarization states quite differently. Both ansatze deal equally well with + and X linear polarizations, but there is a qualitative difference in they way they deal with circular, elliptic, and more general polarization states. In this article we will develop a general formalism for dealing with arbitrary polarization states in the Rosen form of the gravitational wave metric, representing an arbitrary polarization by a trajectory in a suitably defined two dimensional hyperbolic plane.
Any spacetime has a Bianchi type I spacetime as a limit
Bethan Cropp,Matt Visser
Physics , 2010, DOI: 10.1088/0264-9381/28/5/055007
Abstract: Pick an arbitrary timelike geodesic in an arbitrary spacetime. We demonstrate that there is a particular limiting process, an "ultra-local limit", in which the immediate neighborhood of the timelike geodesic can be "blown up" to yield a general (typically non-diagonal) Bianchi type I spacetime. This process shares some (but definitely not all) of the features of the Penrose limit, whereby the immediate neighborhood of an arbitrary null geodesic is "blown up" to yield a pp-wave as a limit.
Polarization modes for strong-field gravitational waves
Bethan Cropp,Matt Visser
Physics , 2010, DOI: 10.1088/1742-6596/314/1/012073
Abstract: Strong-field gravitational plane waves are often represented in either the Rosen or Brinkmann forms. These forms are related by a coordinate transformation, so they should describe essentially the same physics, but the two forms treat polarization states quite differently. Both deal well with linear polarizations, but there is a qualitative difference in the way they deal with circular, elliptic, and more general polarization states. In this article we will describe a general algorithm for constructing arbitrary polarization states in the Rosen form.
Acute Measles Encephalitis in Partially Vaccinated Adults
Annette Fox, Than Manh Hung, Heiman Wertheim, Le Nguyen Minh Hoa, Angela Vincent, Bethan Lang, Patrick Waters, Nguyen Hong Ha, Nguyen Vu Trung, Jeremy Farrar, Nguyen Van Kinh, Peter Horby
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071671
Abstract: Background The pathogenesis of acute measles encephalitis (AME) is poorly understood. Treatment with immune-modulators is based on theories that post-infectious autoimmune responses cause demyelination. The clinical course and immunological parameters of AME were examined during an outbreak in Vietnam. Methods and Findings Fifteen measles IgM-positive patients with confusion or Glasgow Coma Scale (GCS) score below 13, and thirteen with uncomplicated measles were enrolled from 2008–2010. Standardized clinical exams were performed and blood collected for lymphocyte and measles- and auto-antibody analysis. The median age of AME patients was 21 years, similar to controls. Eleven reported receiving measles vaccination when aged one year. Confusion developed a median of 4 days after rash. Six patients had GCS <8 and four required mechanical ventilation. CSF showed pleocytosis (64%) and proteinorrhachia (71%) but measles virus RNA was not detected. MRI revealed bilateral lesions in the cerebellum and brain stem in some patients. Most received dexamethasone +/? IVIG within 4 days of admission but symptoms persisted for ≥3 weeks in five. The concentration of voltage gated calcium channel-complex-reactive antibodies was 900 pM in one patient, and declined to 609 pM ~ 3 months later. Measles-reactive IgG antibody avidity was high in AME patients born after vaccine coverage exceeded 50% (~ 25 years earlier). AME patients had low CD4 (218/μl, p = 0.029) and CD8 (200/μl, p = 0.012) T-cell counts compared to controls. Conclusion Young adults presenting with AME in Vietnam reported a history of one prior measles immunization, and those aged <25 years had high measles-reactive IgG avidity indicative of prior vaccination. This suggests that one-dose measles immunization is not sufficient to prevent AME in young adults and reinforces the importance of maintaining high coverage with a two-dose measles immunization schedule. Treatment with corticosteroids and IVIG is common practice, and should be assessed in randomized clinical trials.
Tackling the Saturation of Oxygen: The Use of Phosphorus and Sulphur as Proxies Within the Neutral ISM of Star-Forming Galaxies
Bethan L. James,Alessandra Aloisi
Physics , 2015,
Abstract: The abundance of oxygen in galaxies is widely used in furthering our understanding of galaxy formation and evolution. Unfortunately, direct measurements of O/H in the neutral gas are extremely difficult to obtain due to the fact that the only OI line available within the HST UV wavelength range (1150-3200A) is often saturated. As such, proxies for oxygen are needed to indirectly derive an O/H via the assumption that solar ratios based on local Milky Way sight lines hold in different environments. In this paper, we assess the validity of using two such proxies, PII and SII, within more typical star-forming environments. Using HST-COS FUV spectra of a sample of nearby star-forming galaxies, we find that P and S follow a trend, log(PII/SII)=1.73+/-0.18, which is in excellent agreement with the solar ratio of log(P/S)_sol=-1.71+/-0.04 over a large range of galaxy properties, i.e., metallicities in the range 0.03-3.2 Z_sol and HI column densities of log[N(HI)/cm^-2]=18.44-21.28. We additionally show evidence from literature data that both elements are individually found to trace oxygen according to their respective solar ratios across a wide-range of environments, such as stars, ionized gas in nearby galaxies, and neutral gas in DLAs and along Milky Way sight lines. Our findings demonstrate that the solar ratios of log(P/O)_sol=-3.28+/-0.06 and log(S/O)_sol=-1.57+/-0.06 can both be used to derive reliable O/H abundances in the neutral gas of local and high-redshift star-forming galaxies.
Surface gravities for non-Killing horizons
Bethan Cropp,Stefano Liberati,Matt Visser
Physics , 2013, DOI: 10.1088/0264-9381/30/12/125001
Abstract: There are many logically and computationally distinct characterizations of the surface gravity of a horizon, just as there are many logically rather distinct notions of horizon. Fortunately, in standard general relativity, for stationary horizons, most of these characterizations are degenerate. However, in modified gravity, or in analogue spacetimes, horizons may be non-Killing or even non-null, and hence these degeneracies can be lifted. We present a brief overview of the key issues, specifically focusing on horizons in analogue spacetimes and universal horizons in modified gravity.
The Study of Multi-Expression Classification Algorithm Based on Adaboost and Mutual Independent Feature  [PDF]
Liying Lang, Zuntao Hu
Journal of Signal and Information Processing (JSIP) , 2011, DOI: 10.4236/jsip.2011.24038
Abstract: In the paper conventional Adaboost algorithm is improved and local features of face such as eyes and mouth are separated as mutual independent elements for facial feature extraction and classification. The multi-expression classification algorithm which is based on Adaboost and mutual independent feature is proposed. In order to effectively and quickly train threshold values of weak classifiers of features, Sample of training is carried out simple improvement. We obtain a good classification results through experiments.
The Initial Boundary Value Problem for Modified Zakharov System  [PDF]
Lang Li, Shaomei Fang
Advances in Pure Mathematics (APM) , 2015, DOI: 10.4236/apm.2015.55028
Abstract:

In this paper, we consider the initial boudary value problem for modified Zakharov system in 3 dimensions with small initial condition. By using the continuity lemma and the linear interpolation theory, together with the properties of Sobolev spaces and the Galerkin method, we obtain the existence and uniqueness of the global solution.

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