81 research outputs found
Survey of X-rays from Massive Stars Observed at High Spectral Resolution with Chandra
Identifying trends between observational data and the range of physical
parameters of massive stars is a critical step to the still-elusive full
understanding of the source, structure, and evolution of X-ray emission from
the stellar winds, requiring a substantial sample size and systematic analysis
methods. The \emph{Chandra} data archive as of 2022 contains 37 high resolution
spectra of O, B, and WR stars, observed with the \emph{Chandra}/HETGS and of
sufficient quality to fit the continua and emission line profiles. Using a
systematic approach to the data analysis, we explore morphological trends in
the line profiles (i.e., O, Ne, Mg, Si) and find that the centroid offsets of
resolved lines versus wavelength can be separated in three empirically-defined
groups based on the amount of line broadening and centroid offset. Using
\ion{Fe}{17} (15.01 \AA, 17.05 \AA) and \ion{Ne}{10} (12.13 \AA) lines
which are prevalent among the sample stars, we find a well-correlated linear
trend of increasing Full Width Half Maximum (FWHM) with faster wind terminal
velocity. The H-like/He-like total line flux ratio for strong lines displays
different trends with spectral class depending on ion species. Some of the
sources in our sample have peculiar properties (e.g., magnetic and
Cas-analogue stars) and we find that these sources stand out as outliers from
more regular trends. Finally, our spectral analysis is presented summarily in
terms of X-ray spectral energy distributions in specific luminosity for each
source, plus tables of line identifications and fluxes.Comment: 78 pages, 46 figures, 41 tables, Accepted for publication in Ap
Effects of a Standardized Phenolic-Enriched Maple Syrup Extract on β-Amyloid Aggregation, Neuroinflammation in Microglial and Neuronal Cells, and β-Amyloid Induced Neurotoxicity in \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e
Published data supports the neuroprotective effects of several phenolic-containing natural products, including certain fruit, berries, spices, nuts, green tea, and olive oil. However, limited data are available for phenolic-containing plant-derived natural sweeteners including maple syrup. Herein, we investigated the neuroprotective effects of a chemically standardized phenolic-enriched maple syrup extract (MSX) using a combination of biophysical, in vitro, and in vivo studies. Based on biophysical data (Thioflavin T assay, transmission electron microscopy, circular dichroism, dynamic light scattering, and zeta potential), MSX reduced amyloid β1−42 peptide (Aβ1−42) fibrillation in a concentration-dependent manner (50–500 μg/mL) with similar effects as the neuroprotective polyphenol, resveratrol, at its highest test concentration (63.5 % at 500 μg/mL vs. 77.3 % at 50 μg/mL, respectively). MSX (100 μg/mL) decreased H2O2-induced oxidative stress (16.1 % decrease in ROS levels compared to control), and down-regulated the production of lipopolysaccharide (LPS)-stimulated inflammatory markers (22.1, 19.9, 74.8, and 87.6 % decrease in NOS, IL-6, PGE2, and TNFα levels, respectively, compared to control) in murine BV-2 microglial cells. Moreover, in a non-contact co-culture cell model, differentiated human SH-SY5Y neuronal cells were exposed to conditioned media from BV-2 cells treated with MSX (100 μg/mL) and LPS or LPS alone. MSX-BV-2 media increased SH-SY5Y cell viability by 13.8 % compared to media collected from LPS-BV-2 treated cells. Also, MSX (10 μg/mL) showed protective effects against Aβ1−42 induced neurotoxicity and paralysis in Caenorhabditis elegans in vivo. These data support the potential neuroprotective effects of MSX warranting further studies on this natural product
Accreting on the edge: a luminosity-dependent cyclotron line in the Be/X-ray Binary 2S 1553-542 accompanied by accretion regimes transition
Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which
the luminosity-dependent spectral and timing features of the neutron star's
emission can be analyzed in detail, thus shedding light on the accretion regime
at work. We took advantage of a monitoring campaign performed with NuSTAR,
Swift/XRT, AstroSat and NICER, to follow the Be/X-ray Binary 2S 1553-542 along
one of its rare outbursts and trace its spectral and timing evolution. We
report the discovery of a luminosity-dependent cyclotron line energy for the
first time in this source. The pulse profiles and pulsed fraction also show
variability along the outburst, consistently with the interpretation that the
source transitions from the sub-critical to the super-critical accretion
regime, separated by a critical luminosity of L
erg/s.Comment: Accepted on ApJ. 11 pages, 7 figures, 3 table
Prospects for Time-Domain and Multi-Messenger Science with AXIS
The Advanced X-ray Imaging Satellite (AXIS) promises revolutionary science in
the X-ray and multi-messenger time domain. AXIS will leverage excellent spatial
resolution (<1.5 arcsec), sensitivity (80x that of Swift), and a large
collecting area (5-10x that of Chandra) across a 24-arcmin diameter field of
view to discover and characterize a wide range of X-ray transients from
supernova-shock breakouts to tidal disruption events to highly variable
supermassive black holes. The observatory's ability to localize and monitor
faint X-ray sources opens up new opportunities to hunt for counterparts to
distant binary neutron star mergers, fast radio bursts, and exotic phenomena
like fast X-ray transients. AXIS will offer a response time of <2 hours to
community alerts, enabling studies of gravitational wave sources, high-energy
neutrino emitters, X-ray binaries, magnetars, and other targets of opportunity.
This white paper highlights some of the discovery science that will be driven
by AXIS in this burgeoning field of time domain and multi-messenger
astrophysics.Comment: This White Paper is part of a series commissioned for the AXIS Probe
Concept Mission; additional AXIS White Papers can be found at
http://axis.astro.umd.ed
Weed dynamics, wheat (Triticum aestivum) yield and irrigation water-use efficiency under conservation agriculture
A field experiment was conducted to evaluate the impacts of a 12-year old conservation agriculture (CA)- based pigeon pea-wheat system on weeds, wheat crop, and resource use during winter (rabi) 2021–22. Results indicated that surface retention of residue irrespective of ZT permanent bed and N dose led to significant reduction in weed interference at 60 DAS. CA-based systems reduced weed density and dry weight considerably than CT. CA- based systems led to significantly higher wheat grain yield (by 11.6–14.9%) and net B:C (by 24.0 –28.0%) than CT, and PFBR100N and PBBR100N were slightly superior to others. PBBR100N and PBBR75N had lower irrigation water use and significantly higher irrigation water productivity than CT. Contrast analysis showed that wheat yield and water productivity were comparable between 75% N and 100% N in CA, indicating a saving of 25% N under CA
Metastable states from multinucleon excitations in Tl 202 and Pb 203
The excited level structures of Tl202 and Pb203, above the 7+ and 29/2- isomers, respectively, have been studied. An isomer with Iπ=20+ and T1/2=215(10)μs has been established in Tl202, and the level scheme extended from I=10 to 20ℏ with the placement of fifteen new transitions. In Pb203, the Iπ=37/2+ state is established to be metastable, with T1/2=2.5(3)ns. Levels in both nuclei arise from intrinsic excitations, with likely particle-hole character for the higher-lying states in Pb203. The 20+ isomer in Tl202 is most likely associated with a πh11/2-1 - ν(i13/2-2,f5/2-1) configuration, while the 37/2+ state in Pb203 results from the excitation of five neutrons. Calculations, using both an empirical approach and the oxbash code, have been performed to aid in the description of the excited level structure
Opto-structural studies of well-dispersed silicon nano-crystals grown by atom beam sputtering
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