199 research outputs found
Interband electron Raman scattering in a quantum wire in a transverse magnetic field
Electron Raman scattering (ERS) is investigated in a parabolic semiconductor
quantum wire in a transverse magnetic field neglecting by phonon-assisted
transitions. The ERS cross-section is calculated as a function of a frequency
shift and magnetic field. The process involves an interband electronic
transition and an intraband transition between quantized subbands. We analyze
the differential cross-section for different scattering configurations. We
study selection rules for the processes. Some singularities in the Raman
spectra are found and interpreted. The scattering spectrum shows
density-of-states peaks and interband matrix elements maximums and a strong
resonance when scattered frequency equals to the "hybrid" frequency or
confinement frequency depending on the light polarization. Numerical results
are presented for a GaAs/AlGaAs quantum wire.Comment: 8 pages, 5 figure
The GRANDMA network in preparation for the fourth gravitational-wave observing run
GRANDMA is a world-wide collaboration with the primary scientific goal ofstudying gravitational-wave sources, discovering their electromagneticcounterparts and characterizing their emission. GRANDMA involves astronomers,astrophysicists, gravitational-wave physicists, and theorists. GRANDMA is now atruly global network of telescopes, with (so far) 30 telescopes in bothhemispheres. It incorporates a citizen science programme (Kilonova-Catcher)which constitutes an opportunity to spread the interest in time-domainastronomy. The telescope network is an heterogeneous set of already-existingobserving facilities that operate coordinated as a single observatory. Withinthe network there are wide-field imagers that can observe large areas of thesky to search for optical counterparts, narrow-field instruments that dotargeted searches within a predefined list of host-galaxy candidates, andlarger telescopes that are devoted to characterization and follow-up of theidentified counterparts. Here we present an overview of GRANDMA after the thirdobserving run of the LIGO/VIRGO gravitational-wave observatories in and its ongoing preparation for the forthcoming fourth observational campaign(O4). Additionally, we review the potential of GRANDMA for the discovery andfollow-up of other types of astronomical transients.<br
K+ channel openers restore verapamil-inhibited lung fluid resolution and transepithelial ion transport
<p>Abstract</p> <p>Background</p> <p>Lung epithelial Na<sup>+ </sup>channels (ENaC) are regulated by cell Ca<sup>2+ </sup>signal, which may contribute to calcium antagonist-induced noncardiogenic lung edema. Although K<sup>+ </sup>channel modulators regulate ENaC activity in normal lungs, the therapeutical relevance and the underlying mechanisms have not been completely explored. We hypothesized that K<sup>+ </sup>channel openers may restore calcium channel blocker-inhibited alveolar fluid clearance (AFC) by up-regulating both apical and basolateral ion transport.</p> <p>Methods</p> <p>Verapamil-induced depression of heterologously expressed human αβγ ENaC in <it>Xenopus </it>oocytes, apical and basolateral ion transport in monolayers of human lung epithelial cells (H441), and <it>in vivo </it>alveolar fluid clearance were measured, respectively, using the two-electrode voltage clamp, Ussing chamber, and BSA protein assays. Ca<sup>2+ </sup>signal in H441 cells was analyzed using Fluo 4AM.</p> <p>Results</p> <p>The rate of <it>in vivo </it>AFC was reduced significantly (40.6 ± 6.3% of control, <it>P </it>< 0.05, n = 12) in mice intratracheally administrated verapamil. K<sub>Ca3.1 </sub>(1-EBIO) and K<sub>ATP </sub>(minoxidil) channel openers significantly recovered AFC. In addition to short-circuit current (Isc) in intact H441 monolayers, both apical and basolateral Isc levels were reduced by verapamil in permeabilized monolayers. Moreover, verapamil significantly altered Ca<sup>2+ </sup>signal evoked by ionomycin in H441 cells. Depletion of cytosolic Ca<sup>2+ </sup>in αβγ ENaC-expressing oocytes completely abolished verapamil-induced inhibition. Intriguingly, K<sub>V </sub>(pyrithione-Na), K <sub>Ca3.1 </sub>(1-EBIO), and K<sub>ATP </sub>(minoxidil) channel openers almost completely restored the verapamil-induced decrease in Isc levels by diversely up-regulating apical and basolateral Na<sup>+ </sup>and K<sup>+ </sup>transport pathways.</p> <p>Conclusions</p> <p>Our observations demonstrate that K<sup>+ </sup>channel openers are capable of rescuing reduced vectorial Na<sup>+ </sup>transport across lung epithelial cells with impaired Ca<sup>2+ </sup>signal.</p
Multi-band analyses of the bright GRB~230812B and the associated SN2023pel
GRB~230812B is a bright and relatively nearby () long gamma-ray
burst that has generated significant interest in the community and therefore
has been subsequently observed over the entire electromagnetic spectrum. We
report over 80 observations in X-ray, ultraviolet, optical, infrared, and
sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for
Multi-messenger Addicts) network of observatories and from observational
partners. Adding complementary data from the literature, we then derive
essential physical parameters associated with the ejecta and external
properties (i.e. the geometry and environment) and compare with other analyses
of this event (e.g. Srinivasaragavan et al. 2023). We spectroscopically confirm
the presence of an associated supernova, SN2023pel, and we derive a
photospheric expansion velocity of v 17 km . We
analyze the photometric data first using empirical fits of the flux and then
with full Bayesian Inference. We again strongly establish the presence of a
supernova in the data, with an absolute peak r-band magnitude . We find a flux-stretching factor or relative brightness and a time-stretching factor ,
both compared to SN1998bw. Therefore, GRB 230812B appears to have a clear long
GRB-supernova association, as expected in the standard collapsar model.
However, as sometimes found in the afterglow modelling of such long GRBs, our
best fit model favours a very low density environment (). We also find small values for
the jet's core angle and
viewing angle. GRB 230812B/SN2023pel is one of the best characterized
afterglows with a distinctive supernova bump
GRANDMA and HXMT Observations of GRB 221009A -- the Standard-Luminosity Afterglow of a Hyper-Luminous Gamma-Ray Burst
GRB 221009A is the brightest Gamma-Ray Burst (GRB) detected in more than 50
years of study. In this paper, we present observations in the X-ray and optical
domains after the GRB obtained by the GRANDMA Collaboration (which includes
observations from more than 30 professional and amateur telescopes) and the
Insight-HXMT Collaboration. We study the optical afterglow with empirical
fitting from GRANDMA+HXMT data, augmented with data from the literature up to
60 days. We then model numerically, using a Bayesian approach, the GRANDMA and
HXMT-LE afterglow observations, that we augment with Swift-XRT and additional
optical/NIR observations reported in the literature. We find that the GRB
afterglow, extinguished by a large dust column, is most likely behind a
combination of a large Milky-Way dust column combined with moderate
low-metallicity dust in the host galaxy. Using the GRANDMA+HXMT-LE+XRT dataset,
we find that the simplest model, where the observed afterglow is produced by
synchrotron radiation at the forward external shock during the deceleration of
a top-hat relativistic jet by a uniform medium, fits the multi-wavelength
observations only moderately well, with a tension between the observed temporal
and spectral evolution. This tension is confirmed when using the extended
dataset. We find that the consideration of a jet structure (Gaussian or
power-law), the inclusion of synchrotron self-Compton emission, or the presence
of an underlying supernova do not improve the predictions, showing that the
modelling of GRB22109A will require going beyond the most standard GRB
afterglow model. Placed in the global context of GRB optical afterglows, we
find the afterglow of GRB 221009A is luminous but not extraordinarily so,
highlighting that some aspects of this GRB do not deviate from the global known
sample despite its extreme energetics and the peculiar afterglow evolution.Comment: Accepted to ApJL for the special issue, 37 pages, 23 pages main text,
6 tables, 13 figure
The Disk Wind in the Young Binaries and the Origin of the Cyclic Activity of Young Stars
We present results of numerical modeling of the cyclic brightness modulation
in the young binary systems with the eccentric orbits and low-mass secondary
components. Brightness variations of the primary is due to the periodical
extinction variations on the line-of-sight caused by the disk wind of the
secondary and a common envelope it produces. A matter distribution in the
envelope has been calculated in the ballistic approach. Calculations showed
that for the young binaries with the elliptic orbits parameters of the
photometric minima (their depth, duration and the shape of light curves) depend
not only on the disk wind parameters and an inclination of the binary orbit to
the line-of-sight but also on the longitude of the periastron. A modulation of
the scattered radiation of the common envelope with a phase of the orbital
period has been investigated in the single scattering approach. It is shown
that an amplitude of the modulation is maximal when the system is seen edge-on
and has also a non-zero value in the binaries observed pole-on. Possible
applications of the theory to the young stellar objects are discussed. In
particular, an attention is payed to a resemblance of the light curves in some
models with light curves of the objects suspected as candidates to FUORs.Comment: 18 pages, 9 figures, accepted by Astronomy Letter
Ready for O4 II: GRANDMA Observations of Swift GRBs during eight-weeks of Spring 2022
We present a campaign designed to train the GRANDMA network and its
infrastructure to follow up on transient alerts and detect their early
afterglows. In preparation for O4 II campaign, we focused on GRB alerts as they
are expected to be an electromagnetic counterpart of gravitational-wave events.
Our goal was to improve our response to the alerts and start prompt
observations as soon as possible to better prepare the GRANDMA network for the
fourth observational run of LIGO-Virgo-Kagra (which started at the end of May
2023), and future missions such as SM. To receive, manage and send out
observational plans to our partner telescopes we set up dedicated
infrastructure and a rota of follow-up adcates were organized to guarantee
round-the-clock assistance to our telescope teams. To ensure a great number of
observations, we focused on Swift GRBs whose localization errors were generally
smaller than the GRANDMA telescopes' field of view. This allowed us to bypass
the transient identification process and focus on the reaction time and
efficiency of the network. During 'Ready for O4 II', 11 Swift/INTEGRAL GRB
triggers were selected, nine fields had been observed, and three afterglows
were detected (GRB 220403B, GRB 220427A, GRB 220514A), with 17 GRANDMA
telescopes and 17 amateur astronomers from the citizen science project
Kilonova-Catcher. Here we highlight the GRB 220427A analysis where our
long-term follow-up of the host galaxy allowed us to obtain a photometric
redshift of , its lightcurve elution, fit the decay slope of the
afterglows, and study the properties of the host galaxy
Heterosynaptic plasticity in the neocortex
Ongoing learning continuously shapes the distribution of neurons’ synaptic weights in a system with plastic synapses. Plasticity may change the weights of synapses that were active during the induction—homosynaptic changes, but also may change synapses not active during the induction—heterosynaptic changes. Here we will argue, that heterosynaptic and homosynaptic plasticity are complementary processes, and that heterosynaptic plasticity might accompany homosynaptic plasticity induced by typical pairing protocols. Synapses are not uniform in their susceptibility for plastic changes, but have predispositions to undergo potentiation or depression, or not to change. Predisposition is one of the factors determining the direction and magnitude of homo- and heterosynaptic changes. Heterosynaptic changes which take place according to predispositions for plasticity may provide a useful mechanism(s) for homeostasis of neurons’ synaptic weights and extending the lifetime of memory traces during ongoing learning in neuronal networks
Preliminary Evidence for Cell Membrane Amelioration in Children with Cystic Fibrosis by 5-MTHF and Vitamin B12 Supplementation: A Single Arm Trial
Cystic fibrosis (CF) is one of the most common fatal autosomal recessive disorders in the Caucasian population caused by mutations of gene for the cystic fibrosis transmembrane conductance regulator (CFTR). New experimental therapeutic strategies for CF propose a diet supplementation to affect the plasma membrane fluidity and to modulate amplified inflammatory response. The objective of this study was to evaluate the efficacy of 5-methyltetrahydrofolate (5-MTHF) and vitamin B12 supplementation for ameliorating cell plasma membrane features in pediatric patients with cystic fibrosis.A single arm trial was conducted from April 2004 to March 2006 in an Italian CF care centre. 31 children with CF aged from 3 to 8 years old were enrolled. Exclusion criteria were diabetes, chronic infections of the airways and regular antibiotics intake. Children with CF were supplemented for 24 weeks with 5-methyltetrahydrofolate (5-MTHF, 7.5 mg /day) and vitamin B12 (0.5 mg/day). Red blood cells (RBCs) were used to investigate plasma membrane, since RBCs share lipid, protein composition and organization with other cell types. We evaluated RBCs membrane lipid composition, membrane protein oxidative damage, cation content, cation transport pathways, plasma and RBCs folate levels and plasma homocysteine levels at baseline and after 24 weeks of 5-MTHF and vitamin B12 supplementation. In CF children, 5-MTHF and vitamin B12 supplementation (i) increased plasma and RBC folate levels; (ii) decreased plasma homocysteine levels; (iii) modified RBC membrane phospholipid fatty acid composition; (iv) increased RBC K(+) content; (v) reduced RBC membrane oxidative damage and HSP70 membrane association.5-MTHF and vitamin B12 supplementation might ameliorate RBC membrane features of children with CF.ClinicalTrials.gov NCT00730509
PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System
kappa Pegasi is a well-known, nearby triple star system. It consists of a
``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which
is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds).
Using high-precision differential astrometry and radial velocity observations,
the masses for all three components are determined and the relative
inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/-
3.0 degrees, just over the threshold for the three body Kozai resonance. The
system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with
trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4
can be found at http://stuff.mit.edu/~matthew1/kapPegTables
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