445 research outputs found
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
Long-term Variation of the Corona in Quiet Regions
Using Hinode EUV Imaging Spectrometer (EIS) spectra recorded daily at Sun
center from the end of 2006 to early 2011, we studied the long-term evolution
of the quiet corona. The light curves of the higher temperature emission lines
exhibit larger variations in sync with the solar activity cycle while the
cooler lines show reduced modulation. Our study shows that the high temperature
component of the corona changes in quiet regions, even though the coronal
electron density remains almost constant there. The results suggest that heat
input to the quiet corona varies with the solar activity cycle.Comment: 9 pages, 5 figures, Accepted for publication in Solar Physic
Adaptive sidelobe control for clutter rejection of atmospheric radars
International audienceClutter rejection is among the most important issues in radar signal processing, for which the adaptive antenna technique can be a powerful means. Compared to other applications of the adaptive antenna, however, atmospheric radars require strict conditions, which have prevented application of this technique; the main antenna beam pattern should not be altered since the target region is defined by its shape. In particular, the loss of the antenna gain should be kept to no more than about 0.5dB, in order to maintain the high sensitivity of the system. Also, clutter from surrounding mountains is often stronger than the desired weak scattering from atmospheric turbulence. We introduce a new algorithm which satisfies the above conditions, and confirms its capability by applying it to actual data taken by the MU radar. This paper presents the first report that demonstrates the effectiveness of the adaptive antenna technique in atmospheric radar applications. Despite the fact that no information is given on the spectral features of the desired and undesired signals, only the clutter echoes from surrounding mountains were effectively cancelled without affecting the desired echoes from atmospheric turbulence
An Interference Cancellation Scheme for TFI-OFDM in Time-Variant Large Delay Spread Channel
In the mobile radio environment, signals are usually impaired by fading and multipath delay phenomenon. In such channels, severe fading of the signal amplitude and inter-symbol-interference (ISI) due to the frequency selectivity of the channel cause an unacceptable degradation of error performance. Orthogonal frequency division multiplexing (OFDM) is an efficient scheme to mitigate the effect of multipath channel. Since it eliminates ISI by inserting guard interval (GI) longer than the delay spread of the channel. In general, the GI is usually designed to be longer than the delay spread of the channel, and is decided after channel measurements in the desired implementation scenario. However, the maximum delay spread is longer than GI, the system performance is significantly degraded. The conventional time-frequency interferometry (TFI) for OFDM does not consider timevariant channel with large delay spread. In this paper, we focus on the large delay spread channel and propose the ISI and inter-carrier-interference (ICI) compensation method for TFI-OFDM
Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 90(9):093125 (2007) and may be found at https://doi.org/10.1063/1.2710778 .ArticleAPPLIED PHYSICS LETTERS. 90(9):093125 (2007)journal articl
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