513 research outputs found
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
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
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding
rocket payload built to study the crucial interface between the solar
chromosphere and the corona by observing the strongest line in the solar
spectrum, the Ly-a line at 1216 {\AA}. In two flights, VAULT succeeded in
obtaining the first ever sub-arcsecond (0.5") images of this region with high
sensitivity and cadence. Detailed analyses of those observations have
contributed significantly to new ideas about the nature of the transition
region. Here, we present a broad overview of the Ly-a atmosphere as revealed by
the VAULT observations, and bring together past results and new analyses from
the second VAULT flight to create a synthesis of our current knowledge of the
high-resolution Ly-a Sun. We hope that this work will serve as a good reference
for the design of upcoming Ly-a telescopes and observing plans.Comment: 28 pages, 11 figure
Gaussian Tunneling Model of c-Axis Twist Josephson Junctions
We calculate the critical current density for c-axis Josephson
tunneling between identical high temperature superconductors twisted an angle
about the c-axis. We model the tunneling matrix element squared as a
Gaussian in the change of wavevector q parallel to the junction, . The
obtained for the s- and extended-s-wave order parameters (OP's) are consistent
with the BiSrCaCuO data of Li {\it et al.}, but only
for strongly incoherent tunneling, . A -wave OP
is always inconsistent with the data. In addition, we show that the apparent
conventional sum rule violation observed by Basov et al. might be
understandable in terms of incoherent c-axis tunneling, provided that the OP is
not -wave.Comment: 6 pages, 6 figure
Electron Dynamics in NdCeCuO: Evidence for the Pseudogap State and Unconventional c-axis Response
Infrared reflectance measurements were made with light polarized along the a-
and c-axis of both superconducting and antiferromagnetic phases of electron
doped NdCeCuO. The results are compared to
characteristic features of the electromagnetic response in hole doped cuprates.
Within the CuO planes the frequency dependent scattering rate,
1/, is depressed below 650 cm; this behavior is a
hallmark of the pseudogap state. While in several hole doped compounds the
energy scales associated with the pseudogap and superconducting states are
quite close, we are able to show that in NdCeCuO
the two scales differ by more than one order of magnitude. Another feature of
the in-plane charge response is a peak in the real part of the conductivity,
, at 50-110 cm which is in sharp contrast with the
Drude-like response where is centered at . This
latter effect is similar to what is found in disordered hole doped cuprates and
is discussed in the context of carrier localization. Examination of the c-axis
conductivity gives evidence for an anomalously broad frequency range from which
the interlayer superfluid is accumulated. Compelling evidence for the pseudogap
state as well as other characteristics of the charge dynamics in
NdCeCuO signal global similarities of the cuprate
phase diagram with respect to electron and hole doping.Comment: Submitted to PR
Feeding dihydroquercetin and vitamin E to broiler chickens reared at standard and high ambient temperatures
The use of natural antioxidants, in particular polyphenols such as dihydroquercetin (DHQ), in animal nutrition has recently increased in popularity. This may partly be due to the risk of increased incidences of heat stress associated with raising livestock in warmer ambient temperatures, facilitated by global warming, reducing antioxidant capacity. The current research demonstrates the effect of dietary DHQ, vitaminEand standard or high ambient temperatures on growth performance, energy and nutrient metabolism, gastrointestinal tract (GIT) development, jejunal villus morphometry and antioxidant status in broiler chickens. Each of the four experimental diets was fed to 16 pens of five birds, which were allocated to four rooms (four pens in each room). The temperature in two rooms was maintained at aconstant 35°C (high temperature; HT), and the temperature in the other two rooms was gradually reduced from 27°C at 7 dof age to 22°C at 20 dof age (standard temperature; ST). Rearing birds at HT reduced feed intake, weight gain, weight of small intestine, total GIT, liver, spleen, heart, villus height, villus surface area and lowered blood glutationperoxidase (GSH-Px). Dietary DHQ increased blood GSH-Px and total antioxidant status, increased heart weight and reduced caecal size. When fed separately, DHQ and vitamin E improved hepatic vitamin E concentration. Feeding vitamin Eincreased spleen and liver weights. When fed together, DHQ and vitamin Ereduced villus height, villus height to crypt depth ratio and villus surface area. Temperature and antioxidants did not affect energy and nutrient metabolism. There were no effects of dietary antioxidants on growth performance of broiler chickens and there were no mortalities. At present, it is unclear if feeding antioxidants (in particular DHQ) at different levels, using different dietary formulations, and rearing birds under arange of environmental conditions may be effective at enhancing production performance and bird health in hot ambient climates
Time-of-flight and activation experiments on 147Pm and 171Tm for astrophysics
The neutron capture cross section of several key unstable isotopes acting as branching points in the s-process are crucial for stellar nucleosynthesis studies, but they are very challenging to measure due to the difficult production of sufficient sample material, the high activity of the resulting samples, and the actual (n,γ) measurement, for which high neutron fluxes and effective background rejection capabilities are required. As part of a new program to measure some of these important branching points, radioactive targets of 147Pm and 171Tm have been produced by irradiation of stable isotopes at the ILL high flux reactor. Neutron capture on 146Nd and 170Er at the reactor was followed by beta decay and the resulting matrix was purified via radiochemical separation at PSI. The radioactive targets have been used for time-of-flight measurements at the CERN n-TOF facility using the 19 and 185 m beam lines during 2014 and 2015. The capture cascades were detected using a set of four C6D6 scintillators, allowing to observe the associated neutron capture resonances. The results presented in this work are the first ever determination of the resonance capture cross section of 147Pm and 171Tm. Activation experiments on the same 147Pm and 171Tm targets with a high-intensity 30 keV quasi-Maxwellian flux of neutrons will be performed using the SARAF accelerator and the Liquid-Lithium Target (LiLiT) in order to extract the corresponding Maxwellian Average Cross Section (MACS). The status of these experiments and preliminary results will be presented and discussed as well
Characterization of the n-TOF EAR-2 neutron beam
The experimental area 2 (EAR-2) at CERNs neutron time-of-flight facility (n-TOF), which is operational since 2014, is designed and built as a short-distance complement to the experimental area 1 (EAR-1). The Parallel Plate Avalanche Counter (PPAC) monitor experiment was performed to characterize the beam prole and the shape of the neutron 'ux at EAR-2. The prompt γ-flash which is used for calibrating the time-of-flight at EAR-1 is not seen by PPAC at EAR-2, shedding light on the physical origin of this γ-flash
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