Investigating the differential emission measure and energetics of microflares with combined SDO/AIA and RHESSI observations

An important question in solar physics is whether solar microflares, the smallest currently observable flare events in X-rays, possess the same energetic properties as large flares. Recent surveys have suggested that microflares may be less efficient particle accelerators than large flares, and hence contribute less nonthermal energy, which may have implications for coronal heating mechanisms. We therefore explore the energetic properties of microflares by combining Extreme Ultraviolet (EUV) and X-ray measurements. We present forward-fitting differential emission measure (DEM) analysis of 10 microflares. The fitting is constrained by combining, for the first time, high temperature RHESSI observations and flux data from SDO/AIA. Two fitting models are tested for the DEM; a Gaussian distribution and a uniform DEM profile. A Gaussian fit proved unable to explain the observations for any of the studied microflares. However, 8 of 10 events studied were reasonably fit by a uniform DEM profile. Hence microflare plasma can be considered to be significantly multi-thermal, and may not be significantly peaked or contain resolvable fine structure, within the uncertainties of the observational instruments. The thermal and non-thermal energy is estimated for each microflare, comparing the energy budget with an isothermal plasma assumption. From the multithermal fits the minimum non-thermal energy content was found to average approximately 30% of the estimated thermal energy. By comparison, under an isothermal model the non-thermal and thermal energy estimates were generally comparable. Hence, multi-thermal plasma is an important consideration for solar microflares that substantially alters their thermal and non-thermal energy content.Comment: 13 pages, 10 Figures, 2 tables. Accepted for publication in the Astrophysical Journa

A Wang-Landau method for calculating Renyi entropies in finite-temperature quantum Monte Carlo simulations

We implement a Wang-Landau sampling technique in quantum Monte Carlo (QMC) for the purpose of calculating the Renyi entanglement entropies and associated mutual information. The algorithm converges an estimate for an analogue to the density of states for Stochastic Series Expansion QMC allowing a direct calculation of Renyi entropies without explicit thermodynamic integration. We benchmark results for the mutual information on two-dimensional (2D) isotropic and anisotropic Heisenberg models, 2D transverse field Ising model, and 3D Heisenberg model, confirming a critical scaling of the mutual information in cases with a finite-temperature transition. We discuss the benefits and limitations of broad sampling techniques compared to standard importance sampling methods.Comment: 9 pages, 7 figure

Quasi-periodic pulsations in solar and stellar flares: re-evaluating their nature in the context of power-law flare Fourier spectra

The nature of quasi-periodic pulsations in solar and stellar flares remains debated. Recent work has shown that power-law-like Fourier power spectra, also referred to as 'red' noise processes, are an intrinsic property of solar and stellar flare signals, a property that many previous studies of this phenomenon have not accounted for. Hence a re-evaluation of the existing interpretations and assumptions regarding QPP is needed. Here we adopt a Bayesian method for investigating this phenomenon, fully considering the Fourier power law properties of flare signals. Using data from the PROBA2/LYRA, Fermi/GBM, Nobeyama Radioheliograph and Yohkoh/HXT instruments, we study a selection of flares from the literature identified as QPP events. Additionally we examine optical data from a recent stellar flare that appears to exhibit oscillatory properties. We find that, for all but one event tested, an explicit oscillation is not required in order to explain the observations. Instead, the flare signals are adequately described as a manifestation of a power law in the Fourier power spectrum, rather than a direct signature of oscillating components or structures. However, for the flare of 1998 May 8, strong evidence for the existence of an explicit oscillation with P ~ 14-16 s is found in the 17 GHz radio data and the 13-23 keV Yohkoh HXT data. We conclude that, most likely, many previously analysed events in the literature may be similarly described in terms of power laws in the flare Fourier power spectrum, without the need to invoke a narrowband, oscillatory component. As a result the prevalence of oscillatory signatures in solar and stellar flares may be less than previously believed. The physical mechanism behind the appearance of the observed power laws is discussed.Comment: 11 pages, 7 figures, 1 table. Accepted for publication in The Astrophysical Journa

Electroshock protection circuit

Circuit was developed to prevent accidental shock through electrodes used to test subjects as part of Skylab program. This circuit is placed between electrical apparatus and electrode that is attached to patient's body. Thus, patient is effectively protected from dangerous electrical shock that might be caused by failure in electrical apparatus

Commitment to change in the work of Michel Butor

Michel Butor is one of the most prolific writers of post-war French literature. The size of his production is equalled only by its diversity. Originally a novelist, Butor has developed into an author of "open works", opera, poetry, dream texts and children's books. This study is a search for unity in the midst of this diversity. Taking as our starting point Butor's adoption of Rimbaud' s famous assertion ·'Il faut changer la vie", we elaborate a perspective of commitment to change in both writing and reality which we apply to the four most developed areas of Butor's production: the novels, the experimental texts, the Illustrations series and the Mati~re de Reves series. Devoting one section of the thesis to each of these four areas, we examine the parallel between the formal evolution of Butor's production, the change that can be seen in his writing, and the thematic evolution, the change that he would like to see in reality. In the novel section we discuss Butor's treat ment of the myth of imperial dominance as the expression of modern western man's existential outlook and its implications for the reader of novels together with Butor's own, different existential outlook and his consequent abandonment of the novel genre. In the second section we examine Butor's conception of the relationship between man and place together with his exp(,ri mental attempts to solve the problems raised by the novel form, the solution finally appearing in the thought 1?ehind the "open work". The Illustrations section contains a study of Butor's collaboration with the art world, his development of the corporate text and the elaboration of the concept of collage reality, a concept designed to replace the imperial organisation criticised in the novels. Finally in the Mati~re de Rives section we analyse Butor's method of using his own literary career as an example of the re-integration, re-organisation and attitude required for the construction and maintenance of the new, collage reality

Clustering in iron-doped magnesium oxide

The distribution of iron in single crystals of magnesium oxide has been investigated using electron paramagnetic resonance (EPR), ferrimagnetic resonance (FMR) and reflection electron diffraction (RED). The total iron content of the samples was in the range 100 - 13000 ppm by weight, the crystals being examined in the as-received state, after solution treatment, and following various aging treatments. The solution treatment involved the samples being held at 1400ºC for 24 hours in an oxygen atmosphere, and then quenched to room temperature. The samples were aged in oxygen at temperatures in the range 600 - 800ºC for various lengths of time. The EPR investigations were carried out at 9 GHz, over the temperature range from 4 - 300 K. Comparison of the integrated intensity of the EPR spectral lines with those of a standard suggested that in both the as-received and solution treated crystals very little (in some cases <0.1%) of the iron contributes to the Fe(^3+) isolated ion cubic site spectrum. Analysis of the experimental linewidths and shapes lends support to this suggestion. The experimental linewidths are in all cases broader than is expected on the basis of dipolar broadening theory, and it is suggested that this broadening is partly due to interactions with the undetected fraction of the iron. An unusual broad (1,3 kG wide) line which shows a complex structure at liquid helium temperatures was detected in two of the samples following solution treatment. Its appearance was accompanied by a complete absence of fine structure lines from the spectra in which it appeared. It is probable that the disappearance of the fine structure and the appearance of this broad line are related, but the relationship is not at present clear. Following aging treatments ferrimagnetic resonance was detected at 9 GHz, in the temperature range 4 - 500 K. This resonance arises out of the precipitation of magnesioferrite from the host lattice. In most of the samples which showed evidence of precipitation two quite different FMR lines were found - an isotropic line which appeared after short aging times, and an anisotropic line which apparently replaces the isotropic one as aging progresses. Analysis of the measured anpsotropy field of the particles precipitated at 800ºC indicated that the rate of growth of the volume of the precipitates is linear with time, after about one hour's aging. The chemical formula for these particular precipitates was determined to be Mg(_x)Fe(_3-x)O(_4-(x-1)/2')) where x = 1.29, the fraction of Mg ions on tetrahedral sites being taken to be 0.30. Analysis of the magnetic characteristics of the precipitates generally gave agreement with what published data are available. In addition the measured anisotropy field H(^sp)(_ɑ) in all samples was found to obey the empirical relationship where D = -0.045 + .004 G(^0.5) K(^-1), T is the temperature and C is a sample dependent constant. The widths of the FMR lines obtained from the high concentration samples aged at 800ºC were independent of sample, and after aging for one hour decreased monotonically with continued aging. This change in width is possibly a consequence of 'voids' of host material in the initial precipitates filling with aging. These linewidths were also remarkable in that they showed a marked decrease with increased recording temperature. Since this behaviour is quite at variance with the behaviour of bulk magnesioferrite it is probably a consequence of the superparamagnetic nature of the particles. Reflection electron diffraction studies of the etched surfaces of the crystals showed only one pattern - the standard spinel pattern - when ferrimagnetic precipitates were present, regardless of the type of FMR spectral line produced by the precipitates. This spinel had a lattice parameter almost exactly twice that of the host. Two other RED patterns were recorded from some of the samples - one possibly due to the calcium-stabilised zirconia discussed by Venables, and the other tentatively assigned to an aluminium spinel

The differential contribution of tumour necrosis factor to thermal and mechanical hyperalgesia during chronic inflammation

Therapies directed against tumour necrosis factor (TNF) are effective for the treatment of rheumatoid arthritis and reduce pain scores in this condition. In this study, we sought to explore mechanisms by which TNF contributes to inflammatory pain in an experimental model of arthritis. The effects of an anti-TNF agent, etanercept, on behavioural pain responses arising from rat monoarthritis induced by complete Freund's adjuvant were assessed and compared with expression of TNF receptors (TNFRs) by dorsal root ganglion (DRG) cells at corresponding time points. Etanercept had no effect on evoked pain responses in normal animals but exerted a differential effect on the thermal and mechanical hyperalgesia associated with rat arthritis induced by complete Freund's adjuvant (CFA). Joint inflammation was associated with increased TNFR1 and TNFR2 expression on DRG cells, which was maintained throughout the time course of the model. TNFR1 expression was increased in neuronal cells of the DRG bilaterally after arthritis induction. In contrast, TNFR2 expression occurred exclusively on nonneuronal cells of the macrophage-monocyte lineage, with cell numbers increasing in a TNF-dependent fashion during CFA-induced arthritis. A strong correlation was observed between numbers of macrophages and the development of mechanical hyperalgesia in CFA-induced arthritis. These results highlight the potential for TNF to play a vital role in inflammatory hyperalgesia, both by a direct action on neurons via TNFR1 and by facilitating the accumulation of macrophages in the DRG via a TNFR2-mediated pathway