663 research outputs found
Strategic Long-Term Financial Risks: Single Risk Factors
The question of the measurement of strategic long-term financial risks is of considerable importance. Existing modelling instruments allow for a good measurement of market risks of trading books over relatively small time intervals. However, these approaches may have severe deficiencies if they are routinely applied to longer time periods. In this paper we give an overview on methodologies that can be used to model the evolution of risk factors over a one-year horizon. Different models are tested on financial time series data by performing backtesting on their expected shortfall prediction
The LAB@FUTURE Project - Moving Towards the Future of E-Learning
This paper presents Lab@Future, an advanced e-learning platform that uses novel Information and Communication Technologies to support and expand laboratory teaching practices. For this purpose, Lab@Future uses real and computer-generated objects that are interfaced using mechatronic systems, augmented reality, mobile technologies and 3D multi user environments. The main aim is to develop and demonstrate technological support for practical experiments in the following focused subjects namely: Fluid Dynamics - Science subject in Germany, Geometry - Mathematics subject in Austria, History and Environmental Awareness ĂąâŹâ Arts and Humanities subjects in Greece and Slovenia. In order to pedagogically enhance the design and functional aspects of this e-learning technology, we are investigating the dialogical operationalisation of learning theories so as to leverage our understanding of teaching and learning practices in the targeted context of deployment
The Contribution of Microbunching Instability to Solar Flare Emission in the GHz to THz Range of Frequencies
Recent solar flare observations in the sub-terahertz range have provided evidence of a new spectral component with fluxes increasing for larger frequencies, separated from the well-known microwave emission that maximizes in the gigahertz range. Suggested interpretations explain the terahertz spectral component but do not account for the simultaneous microwave component. We present a mechanism for producing the observed double spectra. Based on coherent enhancement of synchrotron emission at long wavelengths in laboratory accelerators, we consider how similar processes may occur within a solar flare. The instability known as microbunching arises from perturbations that produce electron beam density modulations, giving rise to broadband coherent synchrotron emission at wavelengths comparable to the characteristic size of the microbunch structure. The spectral intensity of this coherent synchrotron radiation (CSR) can far exceed that of the incoherent synchrotron radiation (ISR), which peaks at a higher frequency, thus producing a double-peaked spectrum. Successful CSR simulations are shown to fit actual burst spectral observations, using typical flaring physical parameters and power-law energy distributions for the accelerated electrons. The simulations consider an energy threshold below which microbunching is not possible because of Coulomb repulsion. Only a small fraction of the radiating charges accelerated to energies above the threshold is required to produce the microwave component observed for several events. The ISR/CSR mechanism can occur together with other emission processes producing the microwave component. It may bring an important contribution to microwaves, at least for certain events where physical conditions for the occurrence of the ISR/CSR microbunching mechanism are possible
Rapid pulsations in sub-THz solar bursts
A new solar burst emission spectral component has been found showing sub-THz
fluxes increasing with frequency, spectrally separated from the well known
microwave component. Rapid pulsations are found present in all events observed
at the two frequencies of the solar submillimeter-wave telescope (SST): 212 and
405 GHz. They were studied in greater detail for three solar bursts exhibiting
the new THz spectral component. The pulse amplitudes are of about 5-8% of the
mean flux throughout the bursts durations, being comparable for both
frequencies. Pulsations range from one pulse every few seconds to 8-10 per
second. The pulse repetition rates (R) are linearly proportional to the mean
burst fluxes (S), following the simple relationship S = k R, suggesting that
the pulsations might be the response to discrete flare particle accelerator
injections quantized in energy. Although this result is consistent with
qualitative trends previously found in the GHz range, the pulse amplitude
relative to the mean fluxes at the sub-THz frequencies appear to be nearly ten
times smaller than expected from the extrapolation of the trends found in the
GHz range. However there are difficulties to reconcile the nearly simultaneous
GHz and THz burst emission spectrally separated components, exhibiting rapid
pulsations with considerably larger relative intensities in the GHz range.Comment: 9 pages and 11 figures, submitted to Astrophys. J; Revised version
accepted by ApJ on 4 March 200
Lâexpression de la destinĂ©e dans lâartÂ
DĂšs 1959, avant son ouvrage fondamental de 1967, LâExpĂ©rience Ă©motionnelle de lâespace, Pierre Kaufmann (1916-1995) dĂ©finit trĂšs clairement un projet dont lâactualitĂ© est toujours aussi brĂ»lante : en quoi les diffĂ©rents arts nous renvoient-ils une image, chaque fois diffĂ©rente, de notre destinĂ©e ?Even before his essential 1967 volume on âThe emotional experience of spaceâ, Kaufmann had already clearly delineated a project that remains a burning question today: how do various arts reflect an ever different image of our destiny?Im Jahre 1959, Pierre Kauffmann (1916-1995), vor der Publikation seines Grundwerkes : LâExpĂ©rience Ă©motionnelle de lâespace, (1967), antwortet schon klar auf die folgende und sehr aktuelle Frage : wie die verschiedene KĂŒnste ein immer neues Bild unseres Schicksals uns wiedergeben könnenÂ
Episodic Reinforcement Learning in Finite MDPs: Minimax Lower Bounds Revisited
In this paper, we propose new problem-independent lower bounds on the sample
complexity and regret in episodic MDPs, with a particular focus on the
non-stationary case in which the transition kernel is allowed to change in each
stage of the episode. Our main contribution is a novel lower bound of
on the sample complexity of an
-PAC algorithm for best policy identification in a
non-stationary MDP. This lower bound relies on a construction of "hard MDPs"
which is different from the ones previously used in the literature. Using this
same class of MDPs, we also provide a rigorous proof of the
regret bound for non-stationary MDPs. Finally, we
discuss connections to PAC-MDP lower bounds
Fast Mid-IR Flashes Detected During Small Solar X-Ray Bursts
Solar observations in the mid-infrared 8-14 \mu\m band continuum were carried
out with cadence of 5 frames per second, in December 2007. Rapid small heated
sources, with typical duration of the order of seconds, were found on the
bright plage-like areas around sunspots, in association with relatively weak
GOES soft X-ray bursts. This work presents the analysis of fast mid-infrared
flashes detected during a GOES B2.0-class event on 10 December 2007, beginning
at about 10:40 UT. Rapid brightness temperature enhancements of 0.5 to 2.0 K
were detected at the Earth by a microbolometer array, using a telescope with
10.5 cm diameter aperture producing a diffraction limited field-of-view of 25
arcsec. Minimum detectable temperature change was of 0.1 K. The corresponding
fluxes are 30-130 solar flux units. At the solar surface the estimated rapid
brightenings were of 50-150 KComment: 12 pages including 6 figures. Accepted by Solar Physics, April 201
Fixed-confidence guarantees for Bayesian best-arm identification
We investigate and provide new insights on the sampling rule called Top-Two Thompson Sampling (TTTS). In particular, we justify its use for fixed-confidence best-arm identification. We further propose a variant of TTTS called Top-Two Transportation Cost (T3C), which disposes of the computational burden of TTTS. As our main contribution, we provide the first sample complexity analysis of TTTS and T3C when coupled with a very natural Bayesian stopping rule, for bandits with Gaussian rewards, solving one of the open questions raised by Russo (2016). We also provide new posterior convergence results for TTTS under two models that are commonly used in practice: bandits with Gaussian and Bernoulli rewards and conjugate priors
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