37,707 research outputs found
A solar spectroscopic absolute abundance of argon from RESIK
Observations of He-like and H-like Ar (Ar XVII and Ar XVIII) lines at 3.949
Angstroms and 3.733 Angstroms respectively with the RESIK X-ray spectrometer on
the CORONAS-F spacecraft, together with temperatures and emission measures from
the two channels of GOES, have been analyzed to obtain the abundance of Ar in
flare plasmas in the solar corona. The line fluxes per unit emission measure
show a temperature dependence like that predicted from theory, and lead to
spectroscopically determined values for the absolute Ar abundance, A(Ar) = 6.44
pm 0.07 (Ar XVII) and 6.49 pm 0.16 (Ar XVIII) which are in agreement to within
uncertainties. The weighted mean is 6.45 pm 0.06, which is between two recent
compilations of the solar Ar abundance and suggest that the photospheric and
coronal abundances of Ar are very similar.Comment: 4 figure
The Extended Methanol Maser Emission in W51
The European VLBI Network (EVN) has been used to make phase referenced,
wide-field (several arcminute) spectral line observations of the 6.7-GHz
methanol maser emission towards W51. In the W51main region, the bulk of the
methanol is offset from an UCHII region. This probably indicates the methanol
emission arises at the interface of the expanding UCHII region and not from an
edge-on circumstellar disc, as previously suggested. Near the W51 IRS2 region,
the methanol emission is associated with a very compact, extremely embedded
source supporting the hypothesis that methanol masers trace the earliest stages
of massive star formation. As well as these two previously well studied sites
of star formation, many previously unknown regions star formation are detected,
demonstrating that methanol masers are powerful means of detection young
massive stars.Comment: 5 pages, 3 figure
The endocenter and its applications to quasigroup representation theory
summary:A construction is given, in a variety of groups, of a ``functorial center'' called the endocenter. The endocenter facilitates the identification of universal multiplication groups of groups in the variety, addressing the problem of determining when combinatorial multiplication groups are universal
Highly Ionized Potassium Lines in Solar X-ray Spectra and the Abundance of Potassium
The abundance of potassium is derived from X-ray lines observed during flares
by the RESIK instrument on the solar mission CORONAS-F between 3.53 A and 3.57
A. The lines include those emitted by He-like K and Li-like K dielectronic
satellites, which have been synthesized using the CHIANTI atomic code and newly
calculated atomic data. There is good agreement of observed and synthesized
spectra, and the theoretical behavior of the spectra with varying temperature
estimated from the ratio of the two GOES channels is correctly predicted. The
observed fluxes of the He-like K resonance line per unit emission measure gives
log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9.
This is higher than photospheric abundance estimates by a factor 5.5, a
slightly greater enhancement than for other elements with first ionization
potential (FIP) less than about 10 eV. There is, then, the possibility that
enrichment of low-FIP elements in coronal plasmas depends weakly on the value
of the FIP which for K is extremely low (4.34 eV). Our work also suggests that
fractionation of elements to form the FIP effect occurs in the low chromosphere
rather than higher up, as in some models.Comment: 14 pages, 3 figure
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
Greenstone belts: Their components and structure
Greenstone sucessions are defined as the nongranitoid component of granitoid-greenstone terrain and are linear to irregular in shape and where linear are termed belts. The chemical composition of greenstones is described. Also discussed are the continental environments of greenstone successions. The effects of contact with granitoids, geophysical properties, recumbent folds and late formation structures upon greenstones are examined. Large stratigraphy thicknesses are explained
Search for Rapid Changes in the Visible-Light Corona during the 21 June 2001 Total Solar Eclipse
Some 8000 images obtained with the SECIS fast-frame CCD camera instrument
located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been
analyzed to search for short-period oscillations in intensity that could be a
signature of solar coronal heating mechanisms by MHD wave dissipation. Images
were taken in white- light and Fe XIV green-line (5303 A) channels over 205
seconds (frame rate 39 s-1), approximately the length of eclipse totality at
this location, with a pixel size of four arcseconds square. The data are of
considerably better quality than were obtained during the 11 August 1999 total
eclipse, observed by us (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in
that the images are much better exposed and enhancements in the drive system of
the heliostat used gave a much improved image stability. Classical Fourier and
wavelet techniques have been used to analyze the emission at 29518 locations,
of which 10714 had emission at reasonably high levels, searching for periodic
fluctuations with periods in the range 0.1-17 seconds (frequencies 0.06-10 Hz).
While a number of possible periodicities were apparent in the wavelet analysis,
none of the spatially and time-limited periodicities in the local brightness
curves was found to be physically important. This implies that the pervasive
Alfven wave-like phenomena (Tomczyk et al.: Science 317, 1192, 2007) using
polarimetric observations with the CoMP instrument do not give rise to
significant oscillatory intensity fluctuations.Comment: Accepted by Solar Physics; 16 figure
Chiral effective theory predictions for deuteron form factor ratios at low Q^2
We use chiral effective theory to predict the deuteron form factor ratio
G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are
calculated to next-to-next-to-leading order. At this order the chiral expansion
for the NN isoscalar charge operator (including consistently calculated 1/M
corrections) is a parameter-free prediction of the effective theory. Use of
this operator in conjunction with NLO and NNLO chiral effective theory wave
functions produces results that are consistent with extant experimental data
for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment
G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance
contributions to this quantity. The variation is of the same size as the
discrepancy between the theoretical result and the experimental value. This
motivates the renormalization of G_Q via a two-nucleon operator that couples to
quadrupole photons. After that renormalization we obtain a robust prediction
for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise,
model-independent predictions for the values of this ratio that will be
measured at the lower end of the kinematic range explored at BLAST. We also
present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure
The 1983 tail-era series. Volume 1: ISEE 3 plasma
Observations from the ISEE 3 electron analyzer are presented in plots. Electrons were measured in 15 continuous energy levels between 8.5 and 1140 eV during individual 3-sec spacecraft spins. Times associated with each data point are the beginning time of the 3 sec data collection interval. Moments calculated from the measured distribution function are shown as density, temperature, velocity, and velocity azimuthal angle. Spacecraft ephemeris is shown at the bottom in GSE and GSM coordinates in units of Earth radii, with vertical ticks on the time axis corresponding to the printed positions
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