Scattering of a Long Cosmic String by a Rotating Black Hole

The scattering of a straight, infinitely long string by a rotating black hole is considered. We assume that a string is moving with velocity v and that initially the string is parallel to the axis of rotation of the black hole. We demonstrate that as a result of scattering, the string is displaced in the direction perpendicular to the velocity by an amount kappa(v,b), where b is the impact parameter. The late-time solution is represented by a kink and anti-kink, propagating in opposite directions at the speed of light, and leaving behind them the string in a new ``phase''. We present the results of the numerical study of the string scattering and their comparison with the weak-field approximation, valid where the impact parameter is large, b/M >> 1, and also with the scattering by a non-rotating black hole which was studied in earlier works.Comment: 27 pages, 14 figures, to be published in Classical and Quantum Gravit

Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

This research focuses on the inversion of geomagnetic variation field measurements to obtain the source currents in the ionosphere and magnetosphere, and to determine the geoelectric fields at the Earth’s surface. During geomagnetic storms, the geoelectric fields create geomagnetically induced currents (GIC) in power networks. These GIC may disturb the operation of power systems, cause damage to power transformers, and even result in power blackouts. In this model, line currents running east–west along given latitudes are postulated to exist at a certain height above the Earth’s surface. This physical arrangement results in the fields on the ground being composed of a zero magnetic east component and a nonzero electric east component. The line current parameters are estimated by inverting Fourier integrals (over wavenumber) of elementary geomagnetic fields using the Levenberg–Marquardt technique. The output parameters of the model are the ionospheric current strength and the geoelectric east component at the Earth’s surface. A conductivity profile of the Earth is adapted from a shallow layered-Earth model for one observatory, together with a deep-layer model derived from satellite observations. This profile is used to obtain the ground surface impedance and therefore the reflection coefficient in the integrals. The inputs for the model are a spectrum of the geomagnetic data for 31 May 2013. The output parameters of the model are spectrums of the ionospheric current strength and of the surface geoelectric field. The inverse Fourier transforms of these spectra provide the time variations on the same day. The geoelectric field data can be used as a proxy for GIC in the prediction of GIC for power utilities. The current strength data can assist in the interpretation of upstream solar wind behaviour

Instability of a membrane intersecting a black hole

The stability of a Nambu-Goto membrane at the equatorial plane of the Reissner-Nordstr{\o}m-de Sitter spacetime is studied. The covariant perturbation formalism is applied to study the behavior of the perturbation of the membrane. The perturbation equation is solved numerically. It is shown that a membrane intersecting a charged black hole, including extremely charged one, is unstable and that the positive cosmological constant strengthens the instability.Comment: 12 pages, 3 figures, to be published in Physical Review

Rigidly Rotating Strings in Stationary Spacetimes

In this paper we study the motion of a rigidly rotating Nambu-Goto test string in a stationary axisymmetric background spacetime. As special examples we consider the rigid rotation of strings in flat spacetime, where explicit analytic solutions can be obtained, and in the Kerr spacetime where we find an interesting new family of test string solutions. We present a detailed classification of these solutions in the Kerr background.Comment: 19 pages, Latex, 9 figures, revised for publication in Classical and Quantum Gravit

Thick domain walls around a black hole

We discuss the gravitationally interacting system of a thick domain wall and a black hole. We numerically solve the scalar field equation in the Schwarzschild spacetime and obtain a sequence of static axi-symmetric solutions representing thick domain walls. We find that, for the walls near the horizon, the Nambu--Goto approximation is no longer valid.Comment: 18 pages, 11 figures, one reference adde

Sacroiliac tuberculosis masquerading as mechanical lower back pain in a collegiate basketball athlete: a case presentation

Background: Sacroiliac tuberculosis is a rare condition for which early diagnosis and effective management frequently proves challenging. This report describes a case that was initially overlooked due to its presentation and unreported constitutional symptoms.Aim: To alert clinicians about skeletal tuberculosis, an often neglected diagnostic differential, which requires a high index of clinical suspicion, especially for patients from endemic areas.Findings: This patient’s presentation (sports injury) and unreported constitutional symptoms resulted in a delay in the diagnosis and initial institution of treatment.Implications: This report illustrates the importance of specifically asking about constitutional symptoms, even in sports injury settings and being mindful of infectious diseases or other chronic medical conditions, which may masquerade as common sports injuries.Keywords: skeletal tuberculosis, sacroiliitis, hip pai

Increase in childhood asthma admissions in an urbanising population

Objective. In South Africa, rapid urbanisation has increased the risk of childhood asthma. This report reviews the pattern of asthma admissions to the Paediatric Department of Ga-Rankuwa Hospital, South Africa, from 1986 to 1996. Design. Inpatient admission data were reviewed for 1986- 1996. A detailed analysis of the records of asthma patients admitted between 1992 and 1996 was done. Outpatient data were reviewed from 1992.Setting. Ga-Rankuwa Hospital, situated on the border of the Gauteng and orth West provinces of South Africa and serving a large black population in various stages of urbanisation.Main outcome measures. Trends in admission numbers and demographic characteristics.Results. Asthma admissions were 2.5 times higher in 1996 than 1986. The greatest increase in admissions was in the 1 - 47-month age group. The male to female ratio was 1.5:1. More patients came from urban than from rural areas. Admissions peaked during the summer. Re-admissions occurred most frequently within 3 months of the first admission.Conclusion. Paediatric asthma admissions have shown an increase in the past decade. This may be associated with changes in the environment of the community. There is a need for preventive programmes for asthma at community and national level

Reissner-Nordstrom Black Holes and Thick Domain Walls

We solve numerically equations of motion for real self-interacting scalar fields in the background of Reissner-Nordstrom black hole and obtained a sequence of static axisymmetric solutions representing thick domain walls charged black hole systems. In the case of extremal Reissner-Nordstrom black hole solution we find that there is a parameter depending on the black hole mass and the width of the domain wall which constitutes the upper limit for the expulsion to occur.Comment: 18 pages, 10 figures, accepted for Phys. Rev.