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

Flare gamma ray continuum emission from neutral pion decay

We investigate, in detail, the production of solar flare gamma ray emission above 100 MeV via the interaction of high energy protons with the ambient solar atmosphere. We restrict our considerations to the broadband gamma ray spectrum resulting from the decay of neutral pions produced in p-H reactions. Thick-target calculations are performed to determine the photon fluences. However, proton transport is not considered. Inferences about the form of the proton spectrum at 10-100 MeV have already been drawn from de-excitation gamma ray lines. Our aim is to constrain the proton spectrum at higher energies. Thus, the injected proton spectrum is assumed to have the form of a Bessel Function, characteristics of stochastic energy at higher energies. The detailed shape of the gamma ray spectra around 100 MeV is found to have a strong dependence on the spectral index of the power law and on the turnover energy (from Bessel function to power law). As would be expected, the harder the photon spectrum the wider the 100 MeV feature. The photon spectra are to be compared with observations and used to place limits upon the number of particles accelerated and to constrain acceleration models

Adherence to the MoodGYM program: Outcomes and predictors for an adolescent school-based population

Background Program adherence has been associated with improved intervention outcomes for mental and physical conditions. The aim of the current study is to investigate adolescent adherence to an Internet-based depression prevention program in schools to identify the effect of adherence on outcomes and to ascertain the predictors of program adherence. Methods Data for the current study (N=1477) was drawn from the YouthMood Project, which was conducted to test the effectiveness of the MoodGYM program in reducing and preventing symptoms of anxiety and depression in an adolescent school-based population. The current study compares intervention effects across three sub-groups: high adherers, low adherers and the wait-list control condition. Results When compared to the control condition, participants in the high adherence intervention group reported stronger intervention effects at post-intervention and 6-month follow-up than participants in the low adherence group for anxiety (d=0.34–0.39 vs. 0.11–0.22), and male (d=0.43–0.59 vs. 0.26–0.35) and female depression (d=0.13–0.20 vs. 0.02–0.04). No significant intervention effects were identified between the high and low adherence groups. Being in Year 9, living in a rural location and having higher pre-intervention levels of depressive symptoms or self-esteem were predictive of greater adherence to the MoodGYM program. Limitations The program trialled is Internet-based and therefore the predictors of adherence identified may not generalise to face-to-face interventions. Conclusions The current study provides preliminary support for the positive relationship between program adherence and outcomes in a school environment. The identification of significant predictors of adherence will assist in identifying the type of user who will engage most with an online depression prevention program.ALC is supported by National Health and Medical Research Council (NHMRC)Fellowship 1013199, HC is supported by NHMRC Fellowship 525411, and KMG is supported by NHMRC Fellowship 42541

Temporal evolution of an energetic electron population in an inhomogeneous medium: Application to solar hard X-ray bursts

Energetic electrons accelerated during solar flares can be studied through the hard X-ray emission they produce when interacting with the solar ambient atmosphere. In the case of the non thermal hard X-ray emission, the instanteous X-ray flux emitted at one point of the atmosphere is related to the instantaneous fast electron spectrum at that point. A hard X-ray source model then requires the understanding of the evolution in space and time of the fast particle distribution. The physical processes involved here are energy losses due to Coulomb collisions and pitch angle scattering due to both collisions and magnetic field gradients

Numerical simulations of chromospheric hard X-ray source sizes in solar flares

X-ray observations are a powerful diagnostic tool for transport, acceleration, and heating of electrons in solar flares. Height and size measurements of X-ray footpoints sources can be used to determine the chromospheric density and constrain the parameters of magnetic field convergence and electron pitch-angle evolution. We investigate the influence of the chromospheric density, magnetic mirroring and collisional pitch-angle scattering on the size of X-ray sources. The time-independent Fokker-Planck equation for electron transport is solved numerically and analytically to find the electron distribution as a function of height above the photosphere. From this distribution, the expected X-ray flux as a function of height, its peak height and full width at half maximum are calculated and compared with RHESSI observations. A purely instrumental explanation for the observed source size was ruled out by using simulated RHESSI images. We find that magnetic mirroring and collisional pitch-angle scattering tend to change the electron flux such that electrons are stopped higher in the atmosphere compared with the simple case with collisional energy loss only. However, the resulting X-ray flux is dominated by the density structure in the chromosphere and only marginal increases in source width are found. Very high loop densities (>10^{11} cm^{-3}) could explain the observed sizes at higher energies, but are unrealistic and would result in no footpoint emission below about 40 keV, contrary to observations. We conclude that within a monolithic density model the vertical sizes are given mostly by the density scale-height and are predicted smaller than the RHESSI results show.Comment: 19 pages, 9 figures, accepted for publication in Ap

A flexible framework for metacognitive modelling and development

Research in eLearning and technology enhanced learning (TEL) has predominantly focused on the creation of learning materials in appropriate forms, such as learning objects, the assessment methods that can usefully be applied online, and the delivery mechanisms for these materials, particularly in virtual learning environments (VLEs). In more recent times, research has begun to focus on pedagogical issues, and in particular whether there is some specific model that applies explicitly to online learning situations. Through a number of projects over the last ten years the authors have considered issues of learning style, learning strategy, pedagogy, immersive environments, student engagement and motivation, games-based learning, adaptation and personalisation. Emerging from this work, and from extensive consideration of the existing research in this area, this paper argues a need to move not only to a different pedagogic model, but also to change the existing structural approach to learning to support the rising demand for online distance learning provision worldwide. Fundamental to this argument is a need to support a heutagogic model of student learning, which requires that the students involved are sufficiently educationally mature to take control of their own learning experience. Whilst within traditional teaching models in higher education there is an explicit aspiration that students will emerge as educationally mature, metacognitive graduates, this is often seen as an outcome of the learning process itself, rather than as a skillset which can be taught and assessed. The paper describes an approach to metacognitive assessment that has already been used to determine the level and skills displayed by students in making selections of learning materials online. Based on this approach, a structural model for online learning support is proposed, using an assessment, feedback and training loop to ensure that students have the level of metacognitive skills necessary to take effective control of their own online learning experience

Metal-insulator transition in three dimensional Anderson model: universal scaling of higher Lyapunov exponents

Numerical studies of the Anderson transition are based on the finite-size scaling analysis of the smallest positive Lyapunov exponent. We prove numerically that the same scaling holds also for higher Lyapunov exponents. This scaling supports the hypothesis of the one-parameter scaling of the conductance distribution. From the collected numerical data for quasi one dimensional systems up to the system size 24 x 24 x infinity we found the critical disorder 16.50 < Wc < 16.53 and the critical exponent 1.50 < \nu < 1.54. Finite-size effects and the role of irrelevant scaling parameters are discussed.Comment: 4 pages, 2 figure

Critical regime of two dimensional Ando model: relation between critical conductance and fractal dimension of electronic eigenstates

The critical two-terminal conductance $g_c$ and the spatial fluctuations of critical eigenstates are investigated for a disordered two dimensional model of non-interacting electrons subject to spin-orbit scattering (Ando model). For square samples, we verify numerically the relation $\sigma_c=1/[2\pi(2-D(1))] e^2/h$ between critical conductivity $\sigma_c=g_c=(1.42\pm 0.005) e^2/h$ and the fractal information dimension of the electron wave function, $D(1)=1.889\pm 0.001$. Through a detailed numerical scaling analysis of the two-terminal conductance we also estimate the critical exponent $\nu=2.80\pm 0.04$ that governs the quantum phase transition.Comment: IOP Latex, 7 figure

Multifractal properties of critical eigenstates in two-dimensional systems with symplectic symmetry

The multifractal properties of electronic eigenstates at the metal-insulator transition of a two-dimensional disordered tight-binding model with spin-orbit interaction are investigated numerically. The correlation dimensions of the spectral measure $\widetilde{D}_{2}$ and of the fractal eigenstate $D_{2}$ are calculated and shown to be related by $D_{2}=2\widetilde{D}_{2}$. The exponent $\eta=0.35\pm 0.05$ describing the energy correlations of the critical eigenstates is found to satisfy the relation $\eta=2-D_{2}$.Comment: 6 pages RevTeX; 3 uuencoded, gzipped ps-figures to appear in J. Phys. Condensed Matte

Effectiveness of an inlet flow turbulence control device to simulate flight noise fan in an anechoic chamber

A hemispherical inlet flow control device was tested on a 50.8 cm. (20-inch) diameter fan stage in the NASA-Lewis anechoic chamber. The control device used honeycomb and wire mesh to reduce turbulence intensities entering the fan. Far field acoustic power level results show about a 5 db reduction in blade passing tone and about 10 dB reduction in multiple pure tone sound power at 90% design fan speed with the inlet device in place. Hot film cross probes were inserted in the inlet to obtain data for two components of the turbulence at 65 and 90% design fan speed. Without the flow control device, the axial intensities were below 1.0%, while the circumferential intensities were almost twice this value. The inflow control device significantly reduced the circumferential turbulence intensities and also reduced the axial length scale