University of St Andrews

About: University of St Andrews is a education organization based out in St Andrews, Fife, United Kingdom. It is known for research contribution in the topics: Population & Laser. The organization has 16260 authors who have published 43364 publications receiving 1636072 citations. The organization is also known as: St Andrews University & University of St. Andrews.

Predicting age of ovarian failure after radiation to a field that includes the ovaries

Abstract: Purpose: To predict the age at which ovarian failure is likely to develop after radiation to a field that includes the ovary in women treated for cancer. Methods and Materials: Modern computed tomography radiotherapy planning allows determination of the effective dose of radiation received by the ovaries. Together with our recent assessment of the radiosensitivity of the human oocyte, the effective surviving fraction of primordial oocytes can be determined and the age of ovarian failure, with 95% confidence limits, predicted for any given dose of radiotherapy. Results: The effective sterilizing dose (ESD: dose of fractionated radiotherapy [Gy] at which premature ovarian failure occurs immediately after treatment in 97.5% of patients) decreases with increasing age at treatment. ESD at birth is 20.3 Gy; at 10 years 18.4 Gy, at 20 years 16.5 Gy, and at 30 years 14.3 Gy. We have calculated 95% confidence limits for age at premature ovarian failure for estimated radiation doses to the ovary from 1 Gy to the ESD from birth to 50 years. Conclusions: We report the first model to reliably predict the age of ovarian failure after treatment with a known dose of radiotherapy. Clinical application of this model will enable physicians to counsel women on their reproductive potential following successful treatment.

The Damping of Coronal Loop Oscillations

Abstract: Motivated by recent Transition Region and Coronal Explorer (TRACE) observations of damped oscilla- tions in coronal loops, we consider analytically the motion of an inhomogeneous coronal magnetic tube of radius a in a zero-� plasma. An initially perturbed tube may vibrate in its kink mode of oscillation, but those vibrations are damped. The damping is due to resonant absorption, acting in the inhomogeneous regions of the tube, which leads to a transfer of energy from the kink mode to Alfven (azimuthal) oscillations within the inhomogeneous layer. We determine explicitly the decrement � (decay time � � 1 ) for a coronal flux tube whose plasma density varies only in a thin layer of thickness  on the tube boundary. The effect of viscosity is also considered. We show that, in general, the problem involves two distinct timescales, � � 1 and ! � 1 k R 1=3 , where R is the Reynolds number and !k is the frequency of the kink mode. Under coronal conditions (when � � 1 5 ! � 1 k R 1=3 ), the characteristic damping time of global oscillations is � � 1 . During this time, most of the energy in the initial perturbation is transferred into a resonant absorption layer of thickness of order  2 =a, with motions in this layer having an amplitude of order a= times the initial amplitude. We apply our results to the observations, suggesting that loop oscillations decay principally because of inhomogeneities in the loop. Our theory suggests that only those loops with density inhomogeneities on a small scale (confined to within a thin layer of order a�=! k in thickness) are able to support coherent oscillations for any length of time and so be observable. Loops with a more gradual density variation, on the scale of the tube radius a, do not exhibit pronounced oscillations. Subject headings: MHD — plasmas — Sun: corona — waves