Seminars this week
John Armstrong (University of Glasgow)
ESPOS: Learning to Invert Solar Flares with RADYN PhysicsThursday, 20 February at 10:00
During a solar flare, it is believed that reconnection takes place in the corona followed by fast energy transport to the chromosphere. The resulting intense heating strongly disturbs the chromospheric structure and induces complex radiation hydrodynamic effects. Interpreting the physics of the flaring solar atmosphere is one of the most challenging tasks in solar physics. We present a novel deep learning approach, an invertible neural network, to understanding the chromospheric physics of a flaring solar atmosphere via the inversion of observed solar line profiles in Hα and Ca II λ8542. The network is trained using flare simulations from the 1D radiation hydrodynamic code RADYN as the expected atmosphere and line profile. This model is then applied to whole images from an observation of an M1.1 solar flare taken with the Swedish 1 m Solar Telescope/CRisp Imaging SpectroPolarimeter instrument. The inverted atmospheres obtained from observations provide physical information on the electron number density, temperature and bulk velocity flow of the plasma throughout the solar atmosphere ranging in height from 0 to 10 Mm. Our method can invert a 1k x 1k field-of-view in approximately 30 minutes and we show results from the whole image inversions and error calculations on the inversions. Furthermore, we delve into the mammoth task of analysing the wealth of data we have accumulated through these inversions.
Niall Taggart (Queen's University Belfast)
Comparing functor calculiThursday, 20 February at 16:00
Functor calculus is a categorification of Taylor's Theorem from differential calculus. Given a functor, one can assign a sequence of polynomial approximations, which assemble into a Taylor tower, similar to the Taylor series from differential calculus. In this talk, I will introduce several variants of functor calculus together with their associated model categories, and demonstrate how one may compare these calculi both on a point-set and model categorical level.
Cosmology, Relativity and Gravitation
Rodrigo Panosso Macedo (Queen Mary University of London)
Revisiting black-hole perturbation theory: the hyperboloidal slice approachThursday, 27 February at 15:00
After reviewing the well-stablished notion of black-hole perturbation theory and the concept of quasinormal modes, we present a spectral representation of solutions to relativistic wave equations based on a geometrical approach in which the constant-time surfaces extend until future null infinity. Here, we restrict ourselves to an asymptotically flat, spherical symmetric spacetime (with focus on the Reisnner-Nordstrom solution), though the geometrical framework extends also to the Kerr spacetime. With the help of a Laplace transformation on the wave equation in question, we provide a geometrical interpretation to known algorithms (i.e. Leaver’s approach) apart from deriving an algorithm for obtaining all ingredients of the desired spectral decomposition, including quasi-normal modes, quasi-normal mode amplitudes as well as the jump of the Laplace-transform along the branch cut.
Ai Guan (Lancaster)
Thursday, 27 February at 16:00
Plasma Dynamics Group
Sandra Milena Conde Cuellar (University of São Paulo, Brazil)
Oscillation of coronal loops associated with flaring eventsThursday, 27 February at 16:00
Room F28 (Hicks Building)
Loops are fascinating structures that bring us a lot of information about the exchange of energy in the solar atmosphere. Oscillations and waves represent one of the most fascinating events in the loops, which also plays a key role in the study of coronal seismology. It is not clear how the disturbances are excited, however, there are several candidates, e.g., flares, emerging flux, and eruptions. In this talk, I present a summary of oscillations observed in different active regions in the presence of flares and other events. This analysis has been done with data provided by IRIS, SDO and GOES-15 spacecraft. We have found excitation sources of some disturbances in lower heights of the solar atmosphere. This matches with oscillations found in the top and the footpoints of the coronal loops. We used this information together with semi-empirical models to study the distribution of physical variables in the loops.
Mark Dunning, Tim Freeman, Sorkatis Kariotis (Sheffield)
Statistical and Data Analysis Challenges in BioinformaticsThursday, 27 February at 16:30
Bioinformatics is a multi-disciplinary subject that combines aspects of biology, computer science and statistics. Modern experimental techniques are able to generate vast amounts of data that can profile an individual's genome and offer insights into the development of disease and potential novel therapeutics. In this talk, I will describe the challenges faced by Bioinformaticians trying to deal with such data on a daily basis and the opportunities for collaboration with other disciplines to develop new analytical methods.
Effect of a spatially arbitrary flow on MHD waves in solar waveguides (Samuel Skirvin)\n URL: /maths/sem_week.html?id=3444\n
Axel Polaczek and Samuel Skirvin (Sheffield)
Aspects of public key cryptography (Axel Polaczek)
Friday, 28 February at 16:00
Effect of a spatially arbitrary flow on MHD waves in solar waveguides (Samuel Skirvin)
Aspects of public key cryptography
How can you exchange secrets with your friends when the available means of communication is being constantly monitored by your adversary? This is the scenario dealt with in public key cryptography. One widespread solution to this problem is based on the concept of trapdoor functions, i.e. functions that are easy to evaluate but difficult to invert unless you have some additional information. An example for this is the RSA cryptosystem which is based on the problem of integer factorization. This talk aims at providing an overview of the ideas underlying cryptography in general and RSA in particular.
Effect of a spatially arbitrary flow on MHD waves in solar waveguides
Magnetohydrodynamic (MHD) waves are thought to play a crucial role in the energy budget of the solar atmosphere. It is well thought that these waves contribute to the heating of the solar chromosphere and corona. As a result, understanding the physics and behaviour of these waves within the context of a realistic solar atmospheric environment is of great importance. We derive a new governing equation describing the generalised case for a spatially arbitrary flow in a 2-dimensional magnetic slab. We therefore also introduce the idea for a new method of retrieving the dispersion diagram describing the types of waves which can exist in the system.