Cycle 23 Variation in Solar Flare Productivity

The NOAA listings of solar flares in cycles 21-24, including the GOES soft X-ray magnitudes, enable a simple determination of the number of flares each flaring active region produces over its lifetime. We have studied this measure of flare productivity over the interval 1975-2012. The annual averages of flare productivity remained approximately constant during cycles 21 and 22, at about two reported M or X flares per region, but then increased significantly in the declining phase of cycle 23 (the years 2004-2005). We have confirmed this by using the independent RHESSI flare catalog to check the NOAA events listings where possible. We note that this measure of solar activity does not correlate with the solar cycle. The anomalous peak in flare productivity immediately preceded the long solar minimum between cycles 23 and 24

The Hard X-rays and Gamma-rays from Solar Flares

Radiation of energies from 10 KeV to greater than 10 MeV has been observed during solar flares, and is interpreted to be due to bremsstrahlung by relativistic electrons. A complete treatment of this problem requires solution of the kinetic equation for relativistic electrons and inclusion of synchrotron energy losses. Using the electron distributions obtained from numerical solutions of this equation the bremsstrahlung spectra in the impulsive x ray and gamma-ray regimes are calculated, and the variation of these spectral indices and directivities with energy and observation angle are described. The dependences of these characteristics of the radiation of changes in the solar atmospheric model, including the convergence of the magnetic field, the injected electron spectral index, and most importantly, in the anisotropy of the injected electrons and of the convergence of the magnetic field are also described. The model results are compared with stereoscopic observations of individual flares and the constraints that this data sets on the models are discussed

Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic particles

Approximate analytic expressions are presented for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution. From these, an expression for the degree of polarization is derived. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles

Emission, absorption and polarization of gyrosynchrotron radiation of mildly relativistic paricles

Approximate analytic expressions for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution are given. From these, an expression for the degree of polarization is derived. To accomplish this, previously developed methods of integration are used. The analytic results are compared with numerical results for both thermal and non-thermal (power law) distributions of particles

The behavior of beams of relativistic non-thermal electrons under the influence of collisions and synchrotron losses

For many astrophysical situations, such as in solar flares or cosmic gamma-ray bursts, continuum gamma rays with energies up to hundreds of MeV were observed, and can be interpreted to be due to bremsstrahlung radiation by relativistic electrons. The region of acceleration for these particles is not necessarily the same as the region in which the radiation is produced, and the effects of the transport of the electrons must be included in the general problem. Hence it is necessary to solve the kinetic equation for relativistic electrons, including all the interactions and loss mechanisms relevant at such energies. The resulting kinetic equation for non-thermal electrons, including the effects of Coulomb collisions and losses due to synchrotron emission, was solved analytically in some simple limiting cases, and numerically for the general cases including constant and varying background plasma density and magnetic field. New approximate analytic solutions are presented for collision dominated cases, for small pitch angles and all energies, synchrotron dominated cases, both steady-state and time dependent, for all pitch angles and energies, and for cases when both synchrotron and collisional energy losses are important, but for relativistic electrons. These analytic solutions are compared to the full numerical results in the proper limits. These results will be useful for calculation of spectra and angular distribution of the radiation (x rays, gamma-rays, and microwaves) emitted via synchrotron or bremsstrahlung processes by the electrons. These properties and their relevance to observations will be observed in subsequent papers

Plasma heating in the very early and decay phases of solar flares

In this paper we analyze the energy budgets of two single-loop solar flares under the assumption that non-thermal electrons are the only source of plasma heating during all phases of both events. The flares were observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Geostationary Operational Environmental Satellite (GOES) on September 20, 2002 and March 17, 2002, respectively. For both investigated flares we derived the energy fluxes contained in non-thermal electron beams from the RHESSI observational data constrained by observed GOES light-curves. We showed that energy delivered by non-thermal electrons was fully sufficient to fulfil the energy budgets of the plasma during the pre-heating and impulsive phases of both flares as well as during the decay phase of one of them. We concluded that in the case of the investigated flares there was no need to use any additional ad-hoc heating mechanisms other than heating by non-thermal electrons.Comment: 22 pages, 10 figures, The Astrophysical Journal (accepted, March 2011

Investigation into the Predictive Capability of Macro-Economic Features in Modelling Credit Risk for Small Medium Enterprises

This research project investigates the predictive capability of macro-economic features in modelling credit risk for small medium enterprises (SME/SMEs). There have been indications that there is strong correlation between economic growth and the size of the SME sector in an economy. However, since the financial crisis and consequent policies and regulations, SMEs have been hampered in attempts to access credit. It has also been noted that while there is a substantial amount of credit risk literature, there is little research on how macro-economic factors affect credit risk. Being able to improve credit scoring by even a small amount can have a very positive effect on a financial institution\u27s profits, reputation and ability to support the economy. Typically, in the credit scoring process two methods of scoring are carried out, application scoring model and behavioural scoring model. These models for predicting customers who are likely to default usually rely upon financial, demographic and transactional data as the predictive inputs. This research investigates the use of a much coarser source of data at a macro-economic level by a low level and high level regions in Ireland. Features such as level of employment/unemployment, education attainment, consumer spending trends and default levels by different banking products will be evaluated as part of the research project. In the course of this research, techniques and methods are established for evaluating the usefulness of macro-economic features. These are subsequently introduced into the predictive models to be evaluated. It was found that while employing coarse classification and subsequently choosing the macro-economic features with the highest information value in the predictive model, the accuracy across all performance measures improved significantly. This has proven that macro-economic features have the potential to be used in modelling credit risk for SMEs in the future

Looptop Hard X-Ray Emission in Solar Flares: Images and Statistics

The discovery of hard X-ray sources near the top of a flaring loop by the HXT instrument on board the YOHKOH satellite represents a significant progress towards the understanding of the basic processes driving solar flares. In this paper we extend the previous study of limb flares by Masuda (1994) by including all YOHKOH observations up through August 1998. We report that from October 1991 to August 1998, YOHKOH observed 20 X-ray bright limb flares (where we use the same selection criteria as Masuda), of which we have sufficient data to analyze 18 events, including 8 previously unanalyzed flares. Of these 18 events, 15 show detectable impulsive looptop emission. Considering that the finite dynamic range (about a decade) of the detection introduces a strong bias against observing comparatively weak looptop sources, we conclude that looptop emission is a common feature of all flares. We summarize the observations of the footpoint to looptop flux ratio and the spectral indices. We present light curves and images of all the important newly analyzed limb flares. Whenever possible we present results for individual pulses in multipeak flares and for different loops for multiloop flares. We then discuss the statistics of the fluxes and spectral indices of the looptop and footpoint sources taking into account observational selection biases. The importance of these observations (and those expected from the scheduled HESSI satellite with its superior angular spectral and temporal resolution) in constraining acceleration models and parameters is discussed briefly.Comment: 27 pages (13 embedded figures). Accepted for publication in Ap

Lipid-membrane interactions of the bovine eye lens

The lens is a transparent, biconvex structure within the eye that has a very high refractive index. It focuses light onto the retina and enables vision. It is able to elastically deform to adjust the focal length of the eye for observing objects at varying distances, a process known as accommodation. With age or damage, the lens becomes stiffer and more likely to develop opaque regions called cataracts. Levels of oxidised lipids such as 7-ketocholesterol increase with age and raised levels of these oxysterols are observed in cataractous lenses. The goal of this project is to investigate the effect of raised levels of 7-ketocholesterol on the biophysical properties of lens membranes, which could in turn affect the structure of lens fibre cells and thereby impact on their individual function and the lens structure as a whole. Nanomechanical measurements of the lens elasticity with Atomic Force Microscopy (AFM) show that the Young’s Modulus of model and extracted bovine lens lipid membranes are lower when incubated with biologically-relevant levels of 7-ketocholesterol, signalling decreased membrane stiffness. In addition to this, the force required to extract individual thiol-tagged cholesterols from the model membranes was observed to decrease with the presence of 7-ketocholesterol, indicating this is consistent with Fluorescence Recovery After Photobleaching observations of model membranes which support a more fluid membrane with 7-ketocholesterol present as the diffusion coefficient (recovery rate of the membrane) is higher. Taken together, these findings show how the biophysical properties of the lipid membranes are altered by the presence of 7-ketocholesterol and provide insight for further investigations to examine how the eye lens is affected with age or oxidative damage. A novel model membrane for the lipids of the bovine eye lens was also created and tested, which could be used in further experiments