5,897 research outputs found
Comparative Analysis of Non-thermal Emissions and Study of Electron Transport in a Solar Flare
We study the non-thermal emissions in a solar flare occurring on 2003 May 29
by using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This
flare shows several typical behaviors of the HXR and microwave emissions: time
delay of microwave peaks relative to HXR peaks, loop-top microwave and
footpoint HXR sources, and a harder electron energy distribution inferred from
the microwave spectrum than from the HXR spectrum. In addition, we found that
the time profile of the spectral index of the higher-energy (\gsim 100 keV)
HXRs is similar to that of the microwaves, and is delayed from that of the
lower-energy (\lsim 100 keV) HXRs. We interpret these observations in terms
of an electron transport model called {\TPP}. We numerically solved the
spatially-homogeneous {\FP} equation to determine electron evolution in energy
and pitch-angle space. By comparing the behaviors of the HXR and microwave
emissions predicted by the model with the observations, we discuss the
pitch-angle distribution of the electrons injected into the flare site. We
found that the observed spectral variations can qualitatively be explained if
the injected electrons have a pitch-angle distribution concentrated
perpendicular to the magnetic field lines rather than isotropic distribution.Comment: 32 pages, 12 figures, accepted for publication in The Astronomical
Journa
Weiss oscillations in the electronic structure of modulated graphene
We present a theoretical study of the electronic structure of modulated
graphene in the presence of a perpendicular magnetic field. The density of
states and the bandwidth for the Dirac electrons in this system are determined.
The appearance of unusual Weiss oscillations in the bandwidth and density of
states is the main focus of this work.Comment: 8 pages, 2 figures, accepted in J. Phys.: Conden. mat
Predicting the outcome of Disability Living Allowance (DLA) adult claims
This working paper considers how well coded data from Disability Living Allowance (DLA) adult claim packs can predict the outcome of these claims. The probability of receiving a care or mobility award is estimated. A range of control variables are considered. First using items that reflect the entitlement criteria for care and mobility awards and then looking at whether additional evidence was required as part of the claim process. Predicted results from these estimates were then compared with real world decisions and those made by Decision Makers on the basis of the coded information from claim packs
Teaching percutaneous renal biopsy using unfixed human cadavers
Background:
Percutaneous renal biopsy (PRB) is an important diagnostic procedure. Despite advances in its safety profile there remains a small but significant risk of bleeding complications. Traditionally, operators train to perform PRB through tutor instruction and directly supervised PRB attempts on real patients. We describe an approach to teaching operators to perform PRB using cadaveric simulation.
Methods:
We devised a full day course hosted in the Clinical Anatomy Skills Centre, with places for nine candidates. Course faculty consisted of two Consultant Nephrologists, two Nephrology trainees experienced in PRB, and one Radiologist.
Classroom instruction included discussion of PRB indications, risk minimisation, and management of complications. Two faculty members acted as models for the demonstration of kidney localisation using real-time ultrasound scanning. PRB was demonstrated using a cadaveric model, and candidates then practised PRB using each cadaver model.
Results:
Written candidate feedback was universally positive. Faculty considered the cadaveric model a realistic representation of live patients, while the use of multiple cadavers introduced anatomical variation.
Conclusions:
Our model facilitates safe simulation of a high risk procedure. This might reduce serious harm associated with PRB and improve patient safety, benefiting trainee operators and patients alike
Tunneling edges at strong disorder
Scattering between edge states that bound one-dimensional domains of opposite
potential or flux is studied, in the presence of strong potential or flux
disorder. A mobility edge is found as a function of disorder and energy, and we
have characterized the extended phase. "paper_FINAL.tex" 439 lines, 20366
characters In the presence of flux and/or potential disorder, the localization
length scales exponentially with the width of the barrier. We discuss
implications for the random-flux problem.Comment: RevTeX, 4 page
Comment on the paper I. M. Suslov: Finite Size Scaling from the Self Consistent Theory of Localization
In the recent paper [I.M.Suslov, JETP {\bf 114} (2012) 107] a new scaling
theory of electron localization was proposed. We show that numerical data for
the quasi-one dimensional Anderson model do not support predictions of this
theory.Comment: Comment on the paper arXiv 1104.043
Fast electron slowing-down and diffusion in a high temperature coronal X-ray source
Finite thermal velocity modifications to electron slowing-down rates may be important for the deduction of solar flare total electron energy. Here we treat both slowing-down and velocity diffusion of electrons in the corona at flare temperatures, for the case of a simple, spatially homogeneous source. Including velocity diffusion yields a consistent treatment of both "accelerated" and "thermal" electrons. It also emphasises that one may not invoke finite thermal velocity target effects on electron lifetimes without simultaneously treating the contribution to the observed X-ray spectrum from thermal electrons. We present model calculations of the X-ray spectra resulting from injection of a power-law energy distribution of electrons into a source with finite temperature. Reducing the power-law distribution low-energy cutoff to lower and lower energies only increases the relative magnitude of the thermal component of the spectrum, because the lowest energy electrons simply join the background thermal distribution. Acceptable fits to RHESSI flare data are obtained using this model. These also demonstrate, however, that observed spectra may in consequence be acceptably consistent with rather a wide range of injected electron parameters
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