7,738 research outputs found
Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2
We report measurements of the temperature dependent anisotropies
( and ) of both the London penetration depth
and the upper critical field of MgB. Data for
was obtained from measurements of
and on a single crystal sample using a tunnel diode
oscillator technique. was
deduced from field dependent specific heat measurements on the same sample.
and have opposite temperature dependencies, but
close to tend to a common value (). These results are in good agreement with theories
accounting for the two gap nature of MgBComment: 4 pages with figures (New version
An apparent statistical relationship between polar heat budget and zonal circulation
Apparent statistical correlation between Arctic heat budget and zonal circulatio
The spectral content of SDO/AIA 1600 and 1700 \AA\ filters from flare and plage observations
The strong enhancement of the ultraviolet emission during solar flares is
usually taken as an indication of plasma heating in the lower solar atmosphere
caused by the deposition of the energy released during these events. Images
taken with broadband ultraviolet filters by the {\em Transition Region and
Coronal Explorer} (TRACE) and {\em Atmospheric Imaging Assembly} (AIA 1600 and
1700~\AA) have revealed the morphology and evolution of flare ribbons in great
detail. However, the spectral content of these images is still largely unknown.
Without the knowledge of the spectral contribution to these UV filters, the use
of these rich imaging datasets is severely limited. Aiming to solve this issue,
we estimate the spectral contributions of the AIA UV flare and plage images
using high-resolution spectra in the range 1300 to 1900~\AA\ from the Skylab
NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~\AA\
is { dominated by} the \ion{C}{4} 1550~\AA\ doublet (26\%), \ion{Si}{1}
continua (20\%), with smaller contributions from many other chromospheric lines
such as \ion{C}{1} 1561 and 1656~\AA\ multiplets, \ion{He}{2} 1640~\AA,
\ion{Si}{2} 1526 and 1533~\AA. For the AIA 1700~\AA\ band, \ion{C}{1} 1656~\AA\
multiplet is the main contributor (38\%), followed by \ion{He}{2} 1640 (17\%),
and accompanied by a multitude of other, { weaker} chromospheric lines, with
minimal contribution from the continuum. Our results can be generalized to
state that the AIA UV flare excess emission is of chromospheric origin, while
plage emission is dominated by photospheric continuum emission in both
channels.Comment: Accepted for publication in ApJ Skylab NRL SO82B data used in this
work available at http://dx.doi.org/10.5525/gla.researchdata.68
RC J1148+0455 identification: gravitational lens or group of galaxies ?
The structure of the radio source RC B1146+052 of the ``Cold'' catalogue is
investigated by data of the MIT-GB-VLA survey at 4850 MHz. This source belongs
to the steep spectrum radio sources subsample of the RC catalogue. Its spectral
index is = -1.04. The optical image of this source obtained with 6m
telescope is analysed. The radio source center is situated in a group of 8
galaxies of about 24 in the R-filter. The possible explanations of the
complex structure of radio components are considered.Comment: 6 pages, 5 figures, uses psfig.sty. This was the poster as presented
on Gamow Memorial Internat. Conference GMIC'99 "Early Universe: Cosmological
Problems and Instrumental Technologies" in St.Petersburg, 23-27 Aug., 1999.
Submitted to Proceedings to be published in A&A Transaction
Detection of brain functional-connectivity difference in post-stroke patients using group-level covariance modeling
Functional brain connectivity, as revealed through distant correlations in
the signals measured by functional Magnetic Resonance Imaging (fMRI), is a
promising source of biomarkers of brain pathologies. However, establishing and
using diagnostic markers requires probabilistic inter-subject comparisons.
Principled comparison of functional-connectivity structures is still a
challenging issue. We give a new matrix-variate probabilistic model suitable
for inter-subject comparison of functional connectivity matrices on the
manifold of Symmetric Positive Definite (SPD) matrices. We show that this model
leads to a new algorithm for principled comparison of connectivity coefficients
between pairs of regions. We apply this model to comparing separately
post-stroke patients to a group of healthy controls. We find
neurologically-relevant connection differences and show that our model is more
sensitive that the standard procedure. To the best of our knowledge, these
results are the first report of functional connectivity differences between a
single-patient and a group and thus establish an important step toward using
functional connectivity as a diagnostic tool
de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2
We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al
doped crystals of MgB. We have measured crystals with % Al which
have a of 33.6 K, (% lower than pure MgB). dHvA frequencies
for the tube orbits in the doped samples are lower than in pure
MgB, implying a reduction in the number of holes in this sheet of
Fermi surface. The mass of the quasiparticles on the larger orbit is
lighter than the pure case indicating a reduction in electron-phonon coupling
constant . These observations are compared with band structure
calculations, and found to be in excellent agreement.Comment: 4 pages with figure
A simplified protocol for detecting two systemic bait markers (Rhodamine B and iophenoxic acid) in small mammals
We developed a method of quantifying levels of fluorescence in the whiskers of wild stoats (Mustela erminea) using fluorescence microscopy and Axiovision 3.0.6.1 software. The method allows for discrimination between natural fluorescence present in or on a whisker, and the fluorescence resulting from the ingestion of the systemic marker Rhodamine B (RB), although some visual judgement is still required. We also developed a new high performance liquid chromatography (HPLC) protocol for detecting the systemic marker iophenoxic acid (IPA) in the blood of laboratory rats (Rattus norvegicus) and wild stoats. With this method, the blood of an animal that has consumed IPA can be tested for the presence of the foreign IPA compound itself. This is a more reliable test than the previous method, which measured the raised level of natural blood protein-bound iodine correlated with IPA absorption. The quantity of blood required from animal subjects is very small (10 μl), so the testing is less intrusive and the method can be extended to smaller species. The extraction technique uses methanol, rather than acids and heavy metal salts, thereby simplifying the procedure. Recovery of IPA is quantitative, giving a highly reliable reading. In experiments on captive rats the IPA method proved successful. Of 12 positively marked carcasses, two that had not been frozen for the 24 h before blood samples were taken showed relatively lower IPA levels. The same IPA detection method, as well as the whisker analysis for RB, was applied successfully to a population of wild stoats to which both Rhodamine B and IPA were made available at bait stations. The presence of both bait markers was detectable in rats for at least 21 days and in stoats for at least 27 days
Overall evaluation of Skylab imagery for mapping of Latin America
The author has identified the following significant results. Skylab imagery is both desired and needed by the Latin American catographic agencies. The imagery is cost beneficial for the production of new mapping and maintenance of existing maps at national topographic series scales. If this information was available on a near time routine coverage basis, it would provide an excellent additional data base to the Latin American cartographic community, specifically Argentina, Bolivia, Chile, Colombia, Dominican Republic, Guatemala, Paraguay, and Venezuela
Observations of the post shock break-out emission of SN 2011dh with XMM-Newton
After the occurrence of the type cIIb SN 2011dh in the nearby spiral galaxy M
51 numerous observations were performed with different telescopes in various
bands ranging from radio to gamma-rays. We analysed the XMM-Newton and Swift
observations taken 3 to 30 days after the SN explosion to study the X-ray
spectrum of SN 2011dh. We extracted spectra from the XMM-Newton observations,
which took place ~7 and 11 days after the SN. In addition, we created
integrated Swift/XRT spectra of 3 to 10 days and 11 to 30 days. The spectra are
well fitted with a power-law spectrum absorbed with Galactic foreground
absorption. In addition, we find a harder spectral component in the first
XMM-Newton spectrum taken at t ~ 7 d. This component is also detected in the
first Swift spectrum of t = 3 - 10 d. While the persistent power-law component
can be explained as inverse Compton emission from radio synchrotron emitting
electrons, the harder component is most likely bremsstrahlung emission from the
shocked stellar wind. Therefore, the harder X-ray emission that fades away
after t ~ 10 d can be interpreted as emission from the shocked circumstellar
wind of SN 2011dh.Comment: Accepted for publication as a Research Note in Astronomy and
Astrophysic
Determining the global minimum of Higgs potentials via Groebner bases - applied to the NMSSM
Determining the global minimum of Higgs potentials with several Higgs fields
like the next-to-minimal supersymmetric extension of the Standard Model (NMSSM)
is a non-trivial task already at the tree level. The global minimum of a Higgs
potential can be found from the set of all its stationary points defined by a
multivariate polynomial system of equations. We introduce here the algebraic
Groebner basis approach to solve this system of equations. We apply the method
to the NMSSM with CP conserving as well as CP violating parameters. The results
reveal an interesting stationary-point structure of the potential. Requiring
the global minimum to give the electroweak symmetry breaking observed in Nature
excludes large parts of the parameter space.Comment: 10 pages, 2 figure
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