484 research outputs found
Habenular expression of rare missense variants of the β4 nicotinic receptor subunit alters nicotine consumption
The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the {alpha}5, {alpha}3, and {beta}4 nicotinic acetylcholine receptor (nAChR) subunits, has been linked to nicotine dependence. The habenulo-interpeduncular (Hb-IPN) tract is particularly enriched in {alpha}3{beta}4 nAChRs. We recently showed that modulation of these receptors in the medial habenula (MHb) in mice altered nicotine consumption. Given that {beta}4 is rate-limiting for receptor activity and that single nucleotide polymorphisms (SNPs) in CHRNB4 have been linked to altered risk of nicotine dependence in humans, we were interested in determining the contribution of allelic variants of {beta}4 to nicotine receptor activity in the MHb. We screened for missense SNPs that had allele frequencies >0.0005 and introduced the corresponding substitutions in Chrnb4. Fourteen variants were analyzed by co-expression with {alpha}3. We found that {beta}4A90I and {beta}4T374I variants, previously shown to associate with reduced risk of smoking, and an additional variant {beta}4D447Y, significantly increased nicotine-evoked current amplitudes, while {beta}4R348C, the mutation most frequently encountered in sporadic amyotrophic lateral sclerosis (sALS), showed reduced nicotine currents. We employed lentiviruses to express {beta}4 or {beta}4 variants in the MHb. Immunoprecipitation studies confirmed that {beta}4 lentiviral-mediated expression leads to specific upregulation of {alpha}3{beta}4 but not {beta}2 nAChRs in the Mhb. Mice injected with the {beta}4-containing virus showed pronounced aversion to nicotine as previously observed in transgenic Tabac mice overexpressing Chrnb4 at endogenous sites including the MHb. Habenular expression of the {beta}4 gain-of-function allele T374I also resulted in strong aversion, while transduction with the {beta}4 loss-of function allele R348C failed to induce nicotine aversion. Altogether, these data confirm the critical role of habenular {beta}4 in nicotine consumption, and identify specific SNPs in CHRNB4 that modify nicotine-elicited currents and alter nicotine consumption in mice
Gauge-invariant tree-level photoproduction amplitudes with form factors
We show how the gauge-invariance formulation given by Haberzettl is
implemented in practice for photoproduction amplitudes at the tree level with
form factors describing composite nucleons. We demonstrate that, in contrast to
Ohta's gauge-invariance prescription, this formalism allows electric current
contributions to be multiplied by a form factor, i.e., it does not require that
they be treated like bare currents. While different in detail, this
nevertheless lends support to previous ad hoc approaches which multiply the
Born amplitudes by an overall form factor. Numerical results for kaon
photoproduction off the nucleon are given. They show that the gauge procedure
by Haberzettl leads to much improved values as compared to Ohta's
prescription.Comment: 5 pages, RevTeX, two eps figure
The Multi-slit Approach to Coronal Spectroscopy with the Multi-slit Solar Explorer (MUSE)
The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed at understanding the physical mechanisms driving the heating of the solar corona and the eruptions that are at the foundation of space weather. MUSE contains two instruments, a multi-slit EUV spectrograph and a context imager. It will simultaneously obtain EUV spectra (along 37 slits) and context images with the highest resolution in space (0.33-0.4 arcsec) and time (1-4 s) ever achieved for the transition region and corona. The MUSE science investigation will exploit major advances in numerical modeling, and observe at the spatial and temporal scales on which competing models make testable and distinguishable predictions, thereby leading to a breakthrough in our understanding of coronal heating and the drivers of space weather. By obtaining spectra in 4 bright EUV lines (Fe IX 171A, Fe XV 284A, Fe XIX-XXI 108A) covering a wide range of transition region and coronal temperatures along 37 slits simultaneously, MUSE will be able to "freeze" the evolution of the dynamic coronal plasma. We describe MUSE's multi-slit approach and show that the optimization of the design minimizes the impact of spectral lines from neighboring slits, generally allowing line parameters to be accurately determined. We also describe a Spectral Disambiguation Code to resolve multi-slit ambiguity in locations where secondary lines are bright. We use simulations of the corona and eruptions to perform validation tests and show that the multi-slit disambiguation approach allows accurate determination of MUSE observables in locations where significant multi-slit contamination occurs
Detection of supersonic downflows and associated heating events in the transition region above sunspots
IRIS data allow us to study the solar transition region (TR) with an
unprecedented spatial resolution of 0.33 arcsec. On 2013 August 30, we observed
bursts of high Doppler shifts suggesting strong supersonic downflows of up to
200 km/s and weaker, slightly slower upflows in the spectral lines Mg II h and
k, C II 1336 \AA, Si IV 1394 \AA, and 1403 \AA, that are correlated with
brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout
the 2 hr observation, with average burst durations of about 20 s. The locations
of these short-lived events appear to be the umbral and penumbral footpoints of
EUV loops. Fast apparent downflows are observed along these loops in the SJIs
and in AIA, suggesting that the loops are thermally unstable. We interpret the
observations as cool material falling from coronal heights, and especially
coronal rain produced along the thermally unstable loops, which leads to an
increase of intensity at the loop footpoints, probably indicating an increase
of density and temperature in the TR. The rain speeds are on the higher end of
previously reported speeds for this phenomenon, and possibly higher than the
free-fall velocity along the loops. On other observing days, similar bright
dots are sometimes aligned into ribbons, resembling small flare ribbons. These
observations provide a first insight into small-scale heating events in
sunspots in the TR.Comment: accepted by ApJ
Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful
tool for observing the Sun at high spatial, temporal, and spectral resolution.
These capabilities can address a broad range of fundamental scientific
questions in solar physics. The radiation observed by ALMA originates mostly
from the chromosphere - a complex and dynamic region between the photosphere
and corona, which plays a crucial role in the transport of energy and matter
and, ultimately, the heating of the outer layers of the solar atmosphere. Based
on first solar test observations, strategies for regular solar campaigns are
currently being developed. State-of-the-art numerical simulations of the solar
atmosphere and modeling of instrumental effects can help constrain and optimize
future observing modes for ALMA. Here we present a short technical description
of ALMA and an overview of past efforts and future possibilities for solar
observations at submillimeter and millimeter wavelengths. In addition, selected
numerical simulations and observations at other wavelengths demonstrate ALMA's
scientific potential for studying the Sun for a large range of science cases.Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th,
2015); accepted versio
Potential of the three-Terminal heterojunction bipolar transistor solar cell for space applications
Multi-Terminal multi-junction solar cells (MJSC) offer higher efficiency potential than series connected (two-Terminal) ones. In addition, for terrestrial applications, the efficiency of multi-Terminal solar cells is less sensitive to solar spectral variations than the two-Terminal series-connected one. In space, generally, cells are always illuminated with AM0 spectrum and no impact is expected from spectral variations. Still, in space, the multi-Terminal approach offers some advantages in comparison with the series-connected architecture approach derived from a higher end of life (EOL) efficiency. In this work we review the potential of multi-Terminal solar cells for achieving extended EOL efficiencies with emphasis in the potential of the three-Terminal heterojunction bipolar transistor solar cell, a novel multi-Terminal MJSC architecture with a simplified structure not requiring, for example, tunnel junctions
The Kaon-Photoproduction Of Nucleons In The Quark Model
In this paper, we develop a general framework to study the
meson-photoproductions of nucleons in the chiral quark model. The S and U
channel resonance contributions are expressed in terms of the
Chew-Goldberger-Low-Nambu (CGLN) amplitudes. The kaon-photoproduction
processes, , , and , are calculated. The initial results show that the quark
model provides a much improved description of the reaction mechanism for the
kaon-photoproductions of the nucleon with less parameters than the traditional
phenomenological approaches.Comment: 25 pages, 9 postscript figures can be obtained from the author
Iberian cured-ham consumption improves endothelial function in healthy subjects
Objectives: Previous studies have shown that dietary components such as oleic acid or polyphenols exert beneficial effects on endothelium. We aimed to assess the impact of regular consumption of Iberian cured-ham (ICH) on endothelial function. Design: An open-label, randomized controlled parallel study. Setting: Volunteers recruited through advertisements at a hospital in Madrid, Spain. Participants: 102 Caucasian adults (76.8% females) aged 25-55 years, and free from cardiometabolic disease. Intervention: Participants were randomized to an ICH-enriched ad libitum diet or an ad libitum diet without ICH for 6 weeks. Subjects in ICH group were randomly provided with either acorn- or mixed-fed ICH, and followed up for an additional 6-week period under their usual diet. Measurements: Clinical parameters, biomarkers of endothelial function and oxidative stress, microvascular vasodilatory response to hyperemia and arterial stiffness were measured before and after the intervention. Results: After 6 weeks, a larger decrease in PAI-1 was observed in subjects consuming ICH compared to the Control group (-6.2±17.7 vs. 0.3±1.4 ng/ml; p=0.020). Similarly, microvascular vasodilatory response to hyperemia showed a significant increase (112.4±391.7 vs. -56.0±327.9%; p=0.007). However, neither oxidative stress, hemodynamic nor clinical parameters differed significantly over the study. Additionally, after stopping ICH consumption, improvements in PAI-1 remained for 6 additional weeks with respect to baseline (p=0.006). Conclusion: The present study demonstrates, for the first time, that regular consumption of ICH improves endothelial function in healthy adults. Strategies aimed to preserve or improve the endothelial function may have implications in vascular aging beyond the prevention of the atherothrombotic disease
Towards ensemble asteroseismology of the young open clusters Chi Persei and NGC 6910
As a result of the variability survey in Chi Persei and NGC6910, the number
of Beta Cep stars that are members of these two open clusters is increased to
twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational
properties, in particular the frequency spectra, of Beta Cep stars in both
clusters and explain the differences in terms of the global parameters of the
clusters. We also indicate that the more complicated pattern of the variability
among B type stars in Chi Persei is very likely caused by higher rotational
velocities of stars in this cluster. We conclude that the sample of pulsating
stars in the two open clusters constitutes a very good starting point for the
ensemble asteroseismology of Beta Cep-type stars and maybe also for other
B-type pulsators.Comment: 4 pages, Astronomische Nachrichten, HELAS IV Conference, Arecife,
Lanzarote, Feb 2010, submitte
Estimation of solar prominence magnetic fields based on the reconstructed 3D trajectories of prominence knots
We present an estimation of the lower limits of local magnetic fields in
quiescent, activated, and active (surges) promineces, based on reconstructed
3-dimensional (3D) trajectories of individual prominence knots. The 3D
trajectories, velocities, tangential and centripetal accelerations of the knots
were reconstructed using observational data collected with a single
ground-based telescope equipped with a Multi-channel Subtractive Double Pass
imaging spectrograph. Lower limits of magnetic fields channeling observed
plasma flows were estimated under assumption of the equipartition principle.
Assuming approximate electron densities of the plasma n_e = 5*10^{11} cm^{-3}
in surges and n_e = 5*10^{10} cm^{-3} in quiescent/activated prominences, we
found that the magnetic fields channeling two observed surges range from 16 to
40 Gauss, while in quiescent and activated prominences they were less than 10
Gauss. Our results are consistent with previous detections of weak local
magnetic fields in the solar prominences.Comment: 14 pages, 12 figures, 1 tabl
- …