18,130 research outputs found
Time synchronization via the transit satellite at Mizusawa
Time signals emitted from Transit satellites and received by the NAVICODE type receiver at Mizusawa, Japan are presented. The International Latitude Observatory of Mizusawa and the U. S. Naval Observatory were compared using the time signals. Propagation delays, a receiver delay, effects of relative motion of satellites, and effects of the ionosphere are discussed
Modelling of EIS spectrum drift from instrumental temperatures
An empirical model has been developed to reproduce the drift of the spectrum
recorded by EIS on board Hinode using instrumental temperatures and relative
motion of the spacecraft. The EIS spectrum shows an artificial drift in
wavelength dimension in sync with the revolution of the spacecraft, which is
caused by temperature variations inside the spectrometer. The drift amounts to
70 km s in Doppler velocity and introduces difficulties in velocity
measurements. An artificial neural network is incorporated to establish a
relationship between the instrumental temperatures and the spectral drift. This
empirical model reproduces observed spectrum shift with an rms error of 4.4 km
s. This procedure is robust and applicable to any spectrum obtained with
EIS, regardless of of the observing field. In addition, spectral curvatures and
spatial offset in the North - South direction are determined to compensate for
instrumental effects.Comment: 16 pages, 12 Figures, accepted for publication in Solar Physics.
Added description of neural networ
Ensemble learning of linear perceptron; Online learning theory
Within the framework of on-line learning, we study the generalization error
of an ensemble learning machine learning from a linear teacher perceptron. The
generalization error achieved by an ensemble of linear perceptrons having
homogeneous or inhomogeneous initial weight vectors is precisely calculated at
the thermodynamic limit of a large number of input elements and shows rich
behavior. Our main findings are as follows. For learning with homogeneous
initial weight vectors, the generalization error using an infinite number of
linear student perceptrons is equal to only half that of a single linear
perceptron, and converges with that of the infinite case with O(1/K) for a
finite number of K linear perceptrons. For learning with inhomogeneous initial
weight vectors, it is advantageous to use an approach of weighted averaging
over the output of the linear perceptrons, and we show the conditions under
which the optimal weights are constant during the learning process. The optimal
weights depend on only correlation of the initial weight vectors.Comment: 14 pages, 3 figures, submitted to Physical Review
Free Field Approach to the Dilute A_L Models
We construct a free field realization of vertex operators of the dilute A_L
models along with the Felder complex. For L=3, we also study an E_8 structure
in terms of the deformed Virasoro currents.Comment: (AMS-)LaTeX(2e), 43page
Long duration thermal hard X-ray sources observed in two eruptive flares
We present observations of two eruptive flares on 17 of December 2006 (C1.9) and 19 of May 2007 (B9.7) which had good coverage with both Hinode and RHESSI. In these flares we see a long lived, gradual thermal hard X-ray source of low emission measure and, relative to the loops observed with GOES and XRT, high temperature. The lack of a non-thermal hard X-ray component and impulsive behaviour is inconsistent with electron beam driven chromospheric evaporation
Dual-camera system for high-speed imaging in particle image velocimetry
Particle image velocimetry is an important technique in experimental fluid
mechanics, for which it has been essential to use a specialized high-speed
camera. However, the high speed is at the expense of other performances of the
camera, i.e., sensitivity and image resolution. Here, we demonstrate that the
high-speed imaging is also possible with a pair of still cameras.Comment: 4 pages, accepted by Journal of Visualization (see
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Scaling and data collapse for the mean exit time of asset prices
We study theoretical and empirical aspects of the mean exit time of financial
time series. The theoretical modeling is done within the framework of
continuous time random walk. We empirically verify that the mean exit time
follows a quadratic scaling law and it has associated a pre-factor which is
specific to the analyzed stock. We perform a series of statistical tests to
determine which kind of correlation are responsible for this specificity. The
main contribution is associated with the autocorrelation property of stock
returns. We introduce and solve analytically both a two-state and a three-state
Markov chain models. The analytical results obtained with the two-state Markov
chain model allows us to obtain a data collapse of the 20 measured MET profiles
in a single master curve.Comment: REVTeX 4, 11 pages, 8 figures, 1 table, submitted for publicatio
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