271,725 research outputs found
Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an
excellent opportunity to perform simultaneous observations of violently
variable objects over a broad wavelength range. The UV and X-ray bright BL Lac
object PKS 2155-304 has been repeatedly observed with XMM-Ndewton about twice
per year. In this paper, we present a detailed analysis of the simultaneous
multiwavelength variability of the source from optical to X-rays, based on the
currently available XMM-Ndewton observations. These observations probed the
intra-day multiwavelength variability at optical-UV and X-ray wavelengths of
the source. The UV variability amplitude is substantially smaller than the
X-ray one, and the hardness ratios of the UV to X-rays correlates with the
X-ray fluxes: the brighter the source, the flatter the UV-X-ray spectra. On
2000 May 30-31 the UV and X-ray light curves were weakly correlated, while the
UV variations followed the X-ray ones with no detectable lags on 2000 November
19-21. On 2001 November 30 the source exhibited a major X-ray flare that was
not detected in the optical. The intra-day UV and X-ray variability presented
here is not similar to the inter-day UV and X-ray variability obtained from the
previous coordinated extensive multiwavelength campaigns on the source,
indicating that different ``modes'' of variability might be operating in PKS
2155-304 on different timescales or from epoch to epoch.Comment: Accepted by Ap
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In-situ Neutron Diffraction Studies of Various Metals on Engin-X at ISIS
Thermal measurement and modeling of multi-die packages
Thermal measurement and modeling of multi-die packages became a hot topic
recently in different fields like RAM chip packaging or LEDs / LED assemblies,
resulting in vertical (stacked) and lateral arrangement. In our present study
we show results for a mixed arrangement: an opto-coupler device has been
investigated with 4 chips in lateral as well as vertical arrangement. In this
paper we give an overview of measurement and modeling techniques and results
for stacked and MCM structures, describe our present measurement results
together with our structure function based methodology of validating the
detailed model of the package being studied. Also, we show how to derive
junction-to-pin thermal resistances with a technique using structure functions.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Nanofabricated media with negative permeability at visible frequencies
We report a nanofabricated medium made of electromagnetically coupled pairs
of gold dots with geometry carefully designed at a 10-nm level. The medium
exhibits strong magnetic response at visible-light frequencies, including bands
with negative \mu. The magnetism arises due to the excitation of quadrupole
plasmon resonances. Our approach shows for the first time the feasibility of
magnetism at optical frequencies and paves a way towards magnetic and
left-handed components for visible optics.Comment: 16 pages, 4 figures. submitted to Nature on 1 April 200
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