118 research outputs found
Measurements of one-point statistics in 21 cm intensity maps via foreground avoidance strategy
Measurements of the one-point probability distribution function and
higher-order moments (variance, skewness, and kurtosis) of the high-redshift 21
cm fluctuations are among the most direct statistical probes of the
non-Gaussian nature of structure formation and evolution during reionization.
However, contamination from astrophysical foregrounds and instrument
systematics pose significant challenges in measuring these statistics in real
observations. In this work, we use forward modelling to investigate the
feasibility of measuring 21 cm one-point statistics through a foreground
avoidance strategy. Leveraging the well-known characteristic of foreground
contamination in which it occupies a wedge-shape region in k-space, we apply a
foreground wedge-cut filter that removes the contaminated modes from a mock
data set based on the Hydrogen Epoch of Reionization Array (HERA) instrument,
and measure the one-point statistics from the image-space representation of the
remaining non-contaminated modes. We experiment with wedge-cutting over
different frequency bandwidths and varying degrees of removal that correspond
to different assumptions on the extent of the foreground sources on the sky and
leakage from the Fourier Transform window function. We find that the centre of
the band is the least biased from wedge-cutting while the edges of the band are
unusable due to being highly down-weighted by the window function. Based on
this finding, we introduce a rolling filter method that allows reconstruction
of an optimal wedge-cut 21~cm intensity map over the full bandwidth using
outputs from wedge-cutting over multiple sub-bands. We perform Monte Carlo
simulations to show that HERA should be able to measure the rise in skewness
and kurtosis near the end of reionization with the rolling wedge-cut method if
foreground leakage from the Fourier transform window function can be
controlled.Comment: 12 pages, 8 figures, submitted to MNRA
Evaporation residue cross-section measurements for O 16 + Tl 203,205
Evaporation residue cross sections for the 16O+203,205Tl reactions were measured at laboratory beam energies in the range of 82–113 MeV using a gas-filled separator. Transmission efficiency of the separator was estimated using a calibration reaction 16O+197Au and by simulating the evaporation residues angular distributions. Statistical model calculations were performed for both the measured systems. These calculations overestimate the experimental evaporation residue cross sections. This could be attributed to the presence of noncompound nuclear fission. An estimation of noncompound nuclear fission contribution was carried out. Comparison with neighboring systems shows that a slight change in the entrance channel or the compound nucleus properties makes a large difference in evaporation residue cross sections
First results of evaporation residue cross-section measurements of S+Pb system
The dynamics of heavy ion-induced reactions play a critical role in forming
super heavy elements (SHE), and one clear signature of the SHE formation is the
evaporation residue (ER). In our pursuit of SHE, we present the heaviest
element populated in India for ER cross-section measurements. These are the
first-ever measurements of the Evaporation Residue (ER) cross-sections for the
nuclear reactions between S and Pb. These measurements were
conducted above the Coulomb barrier at four distinct beam energies in the
laboratory frame, ranging from 176 to 191 MeV at the pelletron Linac facility
at the Inter-University Accelerator Centre (IUAC), New Delhi. The Hybrid Recoil
Mass Analyzer (HYRA) in a gas-filled mode was employed for these experiments.
The obtained range of ER cross-sections enriches our knowledge and helps
advance the field of heavy ion-induced reactions, especially in the context of
super heavy element formation.Comment: 12 pages, 10 figures. arXiv admin note: text overlap with
arXiv:2311.0904
Measurements of evaporation residue cross-sections and evaporation residue-gated -ray fold distributions for S+Sm system
Evaporation Residue (ER) cross-sections and ER-gated -ray fold
distributions are measured for the S + Sm nuclear reaction above
the Coulomb barrier at six different beam energies from 148 to 191 MeV.
-ray multiplicities and spin distributions are extracted from the
ER-gated fold distributions. The ER cross-sections measured in the present work
are found to be much higher than what was reported in a previous work using a
very different target-projectile (Ti + Ba) combination, leading
to the same compound nucleus Pt, with much less mass asymmetry in the
entrance channel than the present reaction. This clearly demonstrates the
effect of the entrance channel on ER production cross-section. The ER
cross-sections measured in the present work are compared with the results of
both the statistical model calculations and the dynamical model calculations.
Statistical model calculations have been performed to generate a range of
parameter space for both the barrier height and Kramers' viscosity parameter
over which the ER cross-section data can be reproduced. The calculations
performed using the dinuclear system (DNS) model reproduce the data considering
both complete and incomplete fusion processes. DNS calculations indicate the
need for the inclusion of incomplete fusion channel at higher energies to
reproduce the ER cross-sections.Comment: 13 pages, 18 figure
The innovation of the symbiosome has enhanced the evolutionary stability of nitrogen fixation in legumes
Nitrogen-fixing symbiosis is globally important in ecosystem functioning and agriculture, yet the evolutionary history of nodulation remains the focus of considerable debate. Recent evidence suggesting a single origin of nodulation followed by massive parallel evolutionary losses raises questions about why a few lineages in the N2-fixing clade retained nodulation and diversified as stable nodulators, while most did not. Within legumes, nodulation is restricted to the two most diverse subfamilies, Papilionoideae and Caesalpinioideae, which show stable retention of nodulation across their core clades.
We characterize two nodule anatomy types across 128 species in 56 of the 152 genera of the legume subfamily Caesalpinioideae: fixation thread nodules (FTs), where nitrogen-fixing bacteroids are retained within the apoplast in modified infection threads, and symbiosomes, where rhizobia are symplastically internalized in the host cell cytoplasm within membrane-bound symbiosomes (SYMs).
Using a robust phylogenomic tree based on 997 genes from 147 Caesalpinioideae genera, we show that losses of nodulation are more prevalent in lineages with FTs than those with SYMs.
We propose that evolution of the symbiosome allows for a more intimate and enduring symbiosis through tighter compartmentalization of their rhizobial microsymbionts, resulting in greater evolutionary stability of nodulation across this species-rich pantropical legume clade
A Roadmap for Astrophysics and Cosmology with High-Redshift 21 cm Intensity Mapping
In this white paper, we lay out a US roadmap for high-redshift 21 cm
cosmology (30 < z < 6) in the 2020s. Beginning with the currently-funded HERA
and MWA Phase II projects and advancing through the decade with a coordinated
program of small-scale instrumentation, software, and analysis projects
targeting technology development, this roadmap incorporates our current best
understanding of the systematics confronting 21 cm cosmology into a plan for
overcoming them, enabling next-generation, mid-scale 21 cm arrays to be
proposed late in the decade. Submitted for consideration by the Astro2020
Decadal Survey Program Panel for Radio, Millimeter, and Submillimeter
Observations from the Ground as a Medium-Sized Project.Comment: 10 pages (plus a cover page and references), 6 figures. Submitted as
a APC White Paper for Astro202
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