4,336 research outputs found
Svestka's Research: Then and Now
Zdenek Svestka's research work influenced many fields of solar physics,
especially in the area of flare research. In this article I take five of the
areas that particularly interested him and assess them in a "then and now"
style. His insights in each case were quite sound, although of course in the
modern era we have learned things that he could not readily have envisioned.
His own views about his research life have been published recently in this
journal, to which he contributed so much, and his memoir contains much
additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour
of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a
contribution to a Topical Issue in Solar Physics, based on the presentations
at this meeting (Editors Lyndsay Fletcher and Petr Heinzel
Evaluation of contemporary guidelines for floor vibration serviceability assessment
This is the author accepted manuscript. The final version is available from the publisher, Society for Experimental Mechanics.IMAC-XXXV,: 35th International Modal Analysis Conference, 30 January - 2 February 2017, Garden Grove, California, USATechnological advances in the construction sector and innovative lightweight and large span structural layouts in modern building
floors increasingly mean that vibration serviceability is the governing design criterion. As this trend continues, excessive
vibrations induced by human activities are becoming a significant concern. Prediction of floor vibrations at the design stage is
often done using currently available design guidelines, such as AISC Design Guide 11, Concrete Society Technical Report 43
Appendix G, SCI P354, Concrete Centre CCIP-016 and HiVoSS.
In this paper, the aforementioned design guidelines are used to predict the vibration responses of a typical office floor, which are
then compared with the actual measured responses. It is clear that different guidelines provide different tolerance limits which
make the satisfactory/unsatisfactory decision imprecise. The results show that the case-study floor is unsatisfactory according
to CSTR43 App G and CCIP-016, whereas it satisfies the requirements of AISC-DG11, SCI P354 and HiVoSS. Nevertheless,
the experimental vibration response indicates that there is a perceptible level of vibrations but with no adverse comments. These
discrepancies highlight the need for a better prediction techniques and more reliable assessment criteria.The authors gratefully acknowledge the financial support of the Qatar National Research Fund (QNRF) through grant NPRP8-
836-2-353 entitled “A Unified Approach to Vibration Serviceability Assessment of Floors
Accounting for both electron--lattice and electron--electron coupling in conjugated polymers: minimum total energy calculations on the Hubbard--Peierls hamiltonian
Minimum total energy calculations, which account for both electron--lattice
and electron--electron interactions in conjugated polymers are performed for
chains with up to eight carbon atoms. These calculations are motivated in part
by recent experimental results on the spectroscopy of polyenes and conjugated
polymers and shed light on the longstanding question of the relative importance
of electron--lattice vs. electron--electron interactions in determining the
properties of these systems.Comment: 6 pages, Plain TeX, FRL-PSD-93GR
Imaging Spectroscopy of a White-Light Solar Flare
We report observations of a white-light solar flare (SOL2010-06-12T00:57,
M2.0) observed by the Helioseismic Magnetic Imager (HMI) on the Solar Dynamics
Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI). The HMI data give us the first space-based high-resolution imaging
spectroscopy of a white-light flare, including continuum, Doppler, and magnetic
signatures for the photospheric FeI line at 6173.34{\AA} and its neighboring
continuum. In the impulsive phase of the flare, a bright white-light kernel
appears in each of the two magnetic footpoints. When the flare occurred, the
spectral coverage of the HMI filtergrams (six equidistant samples spanning
\pm172m{\AA} around nominal line center) encompassed the line core and the blue
continuum sufficiently far from the core to eliminate significant Doppler
crosstalk in the latter, which is otherwise a possibility for the extreme
conditions in a white-light flare. RHESSI obtained complete hard X-ray and
\Upsilon-ray spectra (this was the first \Upsilon-ray flare of Cycle 24). The
FeI line appears to be shifted to the blue during the flare but does not go
into emission; the contrast is nearly constant across the line profile. We did
not detect a seismic wave from this event. The HMI data suggest stepwise
changes of the line-of-sight magnetic field in the white-light footpoints.Comment: 14 pages, 7 figures, Accepted by Solar Physic
Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers
We present full phase stabilization of an amplified Yb:fiber femtosecond
frequency comb using an intra-cavity electro-optic modulator and an
acousto-optic modulator. These transducers provide high servo bandwidths of 580
kHz and 250 kHz for frep and fceo, producing a robust and low phase noise fiber
frequency comb. The comb was self-referenced with an f - 2f interferometer and
phase locked to an ultra-stable optical reference used for the JILA Sr optical
clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors
(over 1 mHz - 1 MHz) respectively. Alternatively, the comb was locked to two
optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of
integrated phase errors respectively
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