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

Development of a Fast, Sensitive and Robust LC-MS/MS Method for the Analysis of Natamycin in Wine

Natamycin is a naturally occurring antifungal agent used to inhibit the growth of moulds and yeasts.Characteristics such as low effective concentrations, broad applicability and neutral flavour impact make thiscompound an ideal preservative. Although widely used in the global food industry, natamycin is forbidden inwine in the European Union (EU). It is a permitted wine additive in South Africa, although export wines mustcomply with EU standards. Germany in particular implemented strict measures to prevent wines containingnatamycin from entering their market. Sensitive analytical methodologies with the capacity to regulate thissegment of the wine export industry are therefore required. Here we report on the development of a simple,robust and fast liquid chromatography-electrospray ionisation tandem mass spectrometric (LC-ESI-MS/MS)method for the determination of natamycin in wine. Sample cleanup involves dilution followed by direct elutionof natamycin from aminopropyl SPE cartridges. Recoveries are better than 80% relative standard deviation(RSD < 10%), while the limit of detection (LOD) of the method is 0.0003 mg/L, which renders it compliantwith EU standards. The method also yields qualitative information for positive compound identification. Thedegradation of natamycin in wine was also studied and kinetic parameters are reported in this matrix for thefirst time. The activation energy for the decomposition reaction is ~80 kJ/mol and the half-life under normalwine storage conditions is in the order of 20 days. As in the wine matrix, natamycin in aqueous calibrationstandards are labile, necessitating regular preparation and cold storage of standard solutions to ensure accuratequantitation

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

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

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

Compounded laxative formulations for substituting phenolphthalein with sennosides A & B in solid dosage forms

Purpose: Following the discovery of the carcinogenicity of phenolphthalein and the subsequent ban of this compound in several countries this study was undertaken to develop compounded formulations of laxative products containing the stimulant laxatives sennosides A and B. Methods: DSC and HPLC analysis was used to determine the compatibility of sennosides with commonly used excipients before compounding capsules, tablets and effervescent tablets containing sennosides A & B. The physical and chemical stability and release properties of these dosage forms were determined for 12 weeks at increased temperature and relative humidity. Results: Sennosides A & B were compatible with a wide variety of powdered excipients. However, these were incompatible with propyl paraben, sodium carbonate, stearic acid, citric acid, PEG, and sugar derivatives such as lactose, glucose and sorbitol when granulated with water. Not withstanding these interactions, it was possible to compound simple capsule, tablet and even an effervescent tablet formulations containing sennosides A & B that complied with pharmacopeial specifications. However, all these formulations were sensitive to moisture because when stored at increased temperature and relative humidity, disintegration times increased and dissolution rates decreased. Conclusion: Based on compatibility and stability studies simple, stable and elegant solid dosage forms containing sennosides A & B were compounded that can be used to replace phenolphthalein in a variety of solid dosage forms. Keywords: Compounding; Sennosides A & B; Phenolphthalein replacement; Drug-Excipient Compatibility > Tropical Journal of Pharmaceutical Research Vol. 3 (1) 2004: pp. 265-27

Quantitative Survey of 3-alkyl-2-methoxypyrazines and First Confirmation of 3-ethyl-2-methoxypyrazine in South African Sauvignon blanc Wines

3-Alkyl-2-methoxypyrazines are important aroma components in Sauvignon blanc wine, contributing tothe typical vegetative character associated with the cultivar. The analysis of methoxypyrazines is highlychallenging and, as a result, limited quantitative data are available for South African Sauvignon blancwines. In this study, liquid chromatography-tandem mass spectrometry was applied for the sensitivequantification of the three principal methoxypyrazines in 881 South African Sauvignon blanc wines. Thetotal wine methoxypyrazine concentration exceeded the combined recognition threshold for the vegetativearoma in more than 60% of the samples, demonstrating the involvement of these compounds in the typicalaroma of the cultivar. The analytical method was adapted to allow the accurate quantitation and spectralconfirmation of 3-ethyl-2-methoxypyrazine in Sauvignon blanc wines for the first time. Concentrationsranged between 1.1 and 4.9 ng/L. Statistically significant relationships between wine methoxypyrazineconcentrations and parameters related to the maturity of the grapes and to the climate, as well asgeographical origin and vintage, were found

Scattering of Straight Cosmic Strings by Black Holes: Weak Field Approximation

The scattering of a straight, infinitely long string moving with velocity $v$ by a black hole is considered. We analyze the weak-field case, where the impact parameter ($b_{imp}$) is large, and obtain exact solutions to the equations of motion. As a result of scattering, the string is displaced in the direction perpendicular to the velocity by an amount $\Delta b\sim -2\pi GMv\gamma/c^3 -\pi (GM)^2/ (4c^3 v b_{imp})$, where $\gamma=(1-(v/c)^2)^{-1/2}$. The second term dominates at low velocities $v/c<(GM/b_{imp})^{1/2}$ . 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''. The solutions are applied to the problem of string capture, and are compared to numerical results.Comment: 19 pages, 5 figure

Thick Domain Walls and Charged Dilaton Black Holes

We study a black hole domain wall system in dilaton gravity which is the low-energy limit of the superstring theory. We solve numerically equations of motion for real self-interacting scalar field and justify the existence of static axisymmetric field configuration representing the thick domain wall in the background of a charged dilaton black hole. It was also confirmed that the extreme dilaton black hole always expelled the domain wall.Comment: 10 pages, 8 figures; to be published in Phys. Rev. D1