11,122 research outputs found
Interaction patterns of brain activity across space, time and frequency. Part I: methods
We consider exploratory methods for the discovery of cortical functional
connectivity. Typically, data for the i-th subject (i=1...NS) is represented as
an NVxNT matrix Xi, corresponding to brain activity sampled at NT moments in
time from NV cortical voxels. A widely used method of analysis first
concatenates all subjects along the temporal dimension, and then performs an
independent component analysis (ICA) for estimating the common cortical
patterns of functional connectivity. There exist many other interesting
variations of this technique, as reviewed in [Calhoun et al. 2009 Neuroimage
45: S163-172]. We present methods for the more general problem of discovering
functional connectivity occurring at all possible time lags. For this purpose,
brain activity is viewed as a function of space and time, which allows the use
of the relatively new techniques of functional data analysis [Ramsay &
Silverman 2005: Functional data analysis. New York: Springer]. In essence, our
method first vectorizes the data from each subject, which constitutes the
natural discrete representation of a function of several variables, followed by
concatenation of all subjects. The singular value decomposition (SVD), as well
as the ICA of this new matrix of dimension [rows=(NT*NV); columns=NS] will
reveal spatio-temporal patterns of connectivity. As a further example, in the
case of EEG neuroimaging, Xi of size NVxNW may represent spectral density for
electric neuronal activity at NW discrete frequencies from NV cortical voxels,
from the i-th EEG epoch. In this case our functional data analysis approach
would reveal coupling of brain regions at possibly different frequencies.Comment: Technical report 2011-March-15, The KEY Institute for Brain-Mind
Research Zurich, KMU Osak
Superconductivity in WO2.6F0.4 synthesized by reaction of WO3 with Teflon
WO3-xFx (x < 0.45) perovskite-like oxyfluorides were prepared by a chemically
reducing fluorination route using the polymer polytetrafluoroethylene (Teflon).
The symmetry of the crystal structures of WO3-xFx changes from monoclinic to
tetragonal to cubic as the fluorine content increases. Fluorine doping changes
insulating WO3 to a metallic conductor, and superconductivity (Tc = 0.4 K) was
discovered in the samples with fluorine contents of 0.41 < x < 0.45. This easy
fluorination method may be applicable to other systems and presents an
opportunity for finding new oxyfluoride superconductors.Comment: 9 pages, 3 figures, 2 tables. To be published in Phys Rev
Stochastic resonance with weak monochromatic driving: gains above unity induced by high-frequency signals
We study the effects of a high-frequency (HF) signal on the response of a
noisy bistable system to a low-frequency subthreshold sinusoidal signal. We
show that, by conveniently choosing the ratio of the amplitude of the HF signal
to its frequency, stochastic resonance gains greater than unity can be measured
at the low-frequency value. Thus, the addition of the HF signal can entail an
improvement in the detection of weak monochromatic signals. The results are
explained in terms of an effective model and illustrated by means of numerical
simulations.Comment: 5 pages, 2 figure
Research on WASH sector, environment and water resources in the Central Rift Valley of Ethiopia
Peer ReviewedPostprint (published version
Learning English with travel blogs: A genre-based process-writing teaching proposal
Current communication is increasingly computer-mediated, dynamic, dialogic, and global, so students should master new information, communication technologies, and digital genres, as well as acknowledge the global role of the English language. Thus, this paper aims to offer a teaching proposal, to be ideally implemented in the secondary education English as a foreign language classroom, on how to develop students’ communicative and digital competences based on a digital genre like the travel blog. First, a corpus of travel blogs was compiled, and the blogs’ communicative purposes and prominent linguistic and discursive features were identified. Next, different lesson plans were designed on the principles of communicative language teaching and task-based learning, together with the corpus-based results. Overall, students are expected to follow a process-writing approach that enables them to interact digitally in travel blogs.
La comunicación actual es cada vez más informática, dinámica, dialógica e internacional, por lo que los estudiantes deberían dominar nuevas tecnologías de información y comunicación y géneros digitales, así como reconocer el papel global del inglés. Este artículo pretende ofrecer una propuesta didáctica, idealmente para la clase de inglés como lengua extranjera en educación secundaria, sobre cómo desarrollar la competencia comunicativa y digital de los estudiantes basándose en un género digital como el blog de viajes. Para ello, se ha compilado un corpus de blogs de viajes, se han identificado sus propósitos comunicativos y sus características lingüísticas y discursivas más relevantes, y después se ha planificado una secuencia didáctica tomando los principios del enfoque comunicativo y el aprendizaje por tareas y los resultados obtenidos del análisis del corpus. Se espera que los estudiantes sigan un enfoque de la escritura como proceso que les permita interactuar digitalmente en los blogs de viajes
Stars and brown dwarfs in the sigma Orionis cluster. III. OSIRIS/GTC low-resolution spectroscopy of variable sources
Context. Although many studies have been performed so far, there are still
dozens of low-mass stars and brown dwarfs in the young sigma Orionis open
cluster without detailed spectroscopic characterisation. Aims. We look for
unknown strong accretors and disc hosts that were undetected in previous
surveys. Methods. We collected low-resolution spectroscopy (R ~ 700) of ten
low-mass stars and brown dwarfs in sigma Orionis with OSIRIS at the Gran
Telescopio Canarias under very poor weather conditions. These objects display
variability in the optical, infrared, Halpha, and/or X-rays on time scales of
hours to years. We complemented our spectra with optical and near-/mid-infrared
photometry. Results. For seven targets, we detected lithium in absorption,
identified Halpha, the calcium doublet, and forbidden lines in emission, and/or
determined spectral types for the first time. We characterise in detail a
faint, T Tauri-like brown dwarf with an 18 h-period variability in the optical
and a large Halpha equivalent width of -125+/-15 AA, as well as two M1-type,
X-ray-flaring, low-mass stars, one with a warm disc and forbidden emission
lines, the other with a previously unknown cold disc with a large inner hole.
Conclusions. New unrevealed strong accretors and disc hosts, even below the
substellar limit, await discovery among the list of known sigma Orionis stars
and brown dwarfs that are variable in the optical and have no detailed
spectroscopic characterisation yet.Comment: A&A, in press (accepted for publication in section 14. Catalogs and
data of Astronomy and Astrophysics
Empirical Exchange Rate Models of the Nineties: Are Any Fit to Survive?
Previous assessments of nominal exchange rate determination have focused upon a narrow set of models typically of the 1970's vintage. The canonical papers in this literature are by Meese and Rogoff (1983, 1988), who examined monetary and portfolio balance models. Succeeding works by Mark (1995) and Chinn and Meese (1995) focused on similar models. In this paper we re-assess exchange rate prediction using a wider set of models that have been proposed in the last decade: interest rate parity, productivity based models, and behavioral equilibrium exchange rate' models. The performance of these models is compared against a benchmark model the Dornbusch-Frankel sticky price monetary model. The models are estimated in error correction and first-difference specifications. Rather than estimating the cointegrating vector over the entire sample and treating it as part of the ex ante information set as is commonly done in the literature, we recursively update the cointegrating vector, thereby generating true ex ante forecasts. We examine model performance at various forecast horizons (1 quarter, 4 quarters, 20 quarters) using differing metrics (mean squared error, direction of change), as well as the consistency' test of Cheung and Chinn (1998). No model consistently outperforms a random walk, by a mean squared error measure; however, along a direction-of-change dimension, certain structural models do outperform a random walk with statistical significance. Moreover, one finds that these forecasts are cointegrated with the actual values of exchange rates, although in a large number of cases, the elasticity of the forecasts with respect to the actual values is different from unity. Overall, model/specification/currency combinations that work well in one period will not necessarily work well in another period.
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