348 research outputs found
Replenishment of selenium deficient rats with selenium results in redistribution of the selenocysteine tRNA population in a tissue specific manner
AbstractWe reported previously that the selenium status of rats influences both the steady-state levels and distributions of two selenocysteine tRNA isoacceptors and that these isoacceptors differ by a single methyl group attached to the ribosyl moiety at position 34. In this study, we demonstrate that repletion of selenium-deficient rats results in a gradual, tissue-dependent shift in the distribution of these isoacceptors. Rats fed a selenium-deficient diet possess a greater abundance of the species unmethylated on the ribosyl moiety at position 34 compared to the form methylated at this position. A redistribution of the Sec–tRNA isoacceptors occurred in tissues of selenium-supplemented rats whereby the unmethylated form gradually shifted toward the methylated form. This was true in each of four tissues examined, muscle, kidney, liver and heart, although the rate of redistribution was tissue-specific. Muscle manifested a predominance of two minor serine isoacceptors under conditions of extreme selenium-deficiency which also appeared to respond to selenium. Ribosomal binding studies revealed that one of the two additional isoacceptors decodes the serine codeword, AGU, and the second decodes the serine codeword, UCU. Interestingly, muscle and heart were the slower tissues to return to a `selenium adequate' tRNA distribution pattern
Managing Wicked Herbicide-Resistance: Lessons from the Field
Herbicide resistance is ‘wicked’ in nature; therefore, results of the many educational efforts to encourage diversification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides; there is no need for more regulation; there is a need for more education, especially for others who were not present; diversity is hard; the agricultural economy makes it difficult to make changes; and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance
Managing Wicked Herbicide-Resistance: Lessons from the Field
Herbicide resistance is ‘wicked’ in nature; therefore, results of the many educational efforts to encourage diversification of weed control practices in the United States have been mixed. It is clear that we do not sufficiently understand the totality of the grassroots obstacles, concerns, challenges, and specific solutions needed for varied crop production systems. Weed management issues and solutions vary with such variables as management styles, regions, cropping systems, and available or affordable technologies. Therefore, to help the weed science community better understand the needs and ideas of those directly dealing with herbicide resistance, seven half-day regional listening sessions were held across the United States between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide resistance management. The major goals of the sessions were to gain an understanding of stakeholders and their goals and concerns related to herbicide resistance management, to become familiar with regional differences, and to identify decision maker needs to address herbicide resistance. The messages shared by listening-session participants could be summarized by six themes: we need new herbicides; there is no need for more regulation; there is a need for more education, especially for others who were not present; diversity is hard; the agricultural economy makes it difficult to make changes; and we are aware of herbicide resistance but are managing it. The authors concluded that more work is needed to bring a community-wide, interdisciplinary approach to understanding the complexity of managing weeds within the context of the whole farm operation and for communicating the need to address herbicide resistance
Managing Herbicide Resistance: Listening to the Perspectives of Practitioners. Procedures for Conducting Listening Sessions and an Evaluation of the Process
Seven half-day regional listening sessions were held between December 2016 and April 2017 with groups of diverse stakeholders on the issues and potential solutions for herbicide-resistance management. The objective of the listening sessions was to connect with stakeholders and hear their challenges and recommendations for addressing herbicide resistance. The coordinating team hired Strategic Conservation Solutions, LLC, to facilitate all the sessions. They and the coordinating team used in-person meetings, teleconferences, and email to communicate and coordinate the activities leading up to each regional listening session. The agenda was the same across all sessions and included small-group discussions followed by reporting to the full group for discussion. The planning process was the same across all the sessions, although the selection of venue, time of day, and stakeholder participants differed to accommodate the differences among regions. The listening-session format required a great deal of work and flexibility on the part of the coordinating team and regional coordinators. Overall, the participant evaluations from the sessions were positive, with participants expressing appreciation that they were asked for their thoughts on the subject of herbicide resistance. This paper details the methods and processes used to conduct these regional listening sessions and provides an assessment of the strengths and limitations of those processes
What does an interferometer really measure? Including instrument and data characteristics in the reconstruction of the 21cm power spectrum
Combining the visibilities measured by an interferometer to form a
cosmological power spectrum is a complicated process in which the window
functions play a crucial role. In a delay-based analysis, the mapping between
instrumental space, made of per-baseline delay spectra, and cosmological space
is not a one-to-one relation. Instead, neighbouring modes contribute to the
power measured at one point, with their respective contributions encoded in the
window functions. To better understand the power spectrum measured by an
interferometer, we assess the impact of instrument characteristics and analysis
choices on the estimator by deriving its exact window functions, outside of the
delay approximation. Focusing on HERA as a case study, we find that
observations made with long baselines tend to correspond to enhanced low-k
tails of the window functions, which facilitate foreground leakage outside the
wedge, whilst the choice of bandwidth and frequency taper can help narrow them
down. With the help of simple test cases and more realistic visibility
simulations, we show that, apart from tracing mode mixing, the window functions
can accurately reconstruct the power spectrum estimator of simulated
visibilities. We note that the window functions depend strongly on the
chromaticity of the beam, and less on its spatial structure - a Gaussian
approximation, ignoring side lobes, is sufficient. Finally, we investigate the
potential of asymmetric window functions, down-weighting the contribution of
low-k power to avoid foreground leakage. The window functions presented in this
work correspond to the latest HERA upper limits for the full Phase I data. They
allow an accurate reconstruction of the power spectrum measured by the
instrument and can be used in future analyses to confront theoretical models
and data directly in cylindrical space.Comment: 18 pages, 18 figures, submitted to MNRAS. Comments welcome
Characterization Of Inpaint Residuals In Interferometric Measurements of the Epoch Of Reionization
Radio Frequency Interference (RFI) is one of the systematic challenges
preventing 21cm interferometric instruments from detecting the Epoch of
Reionization. To mitigate the effects of RFI on data analysis pipelines,
numerous inpaint techniques have been developed to restore RFI corrupted data.
We examine the qualitative and quantitative errors introduced into the
visibilities and power spectrum due to inpainting. We perform our analysis on
simulated data as well as real data from the Hydrogen Epoch of Reionization
Array (HERA) Phase 1 upper limits. We also introduce a convolutional neural
network that capable of inpainting RFI corrupted data in interferometric
instruments. We train our network on simulated data and show that our network
is capable at inpainting real data without requiring to be retrained. We find
that techniques that incorporate high wavenumbers in delay space in their
modeling are best suited for inpainting over narrowband RFI. We also show that
with our fiducial parameters Discrete Prolate Spheroidal Sequences (DPSS) and
CLEAN provide the best performance for intermittent ``narrowband'' RFI while
Gaussian Progress Regression (GPR) and Least Squares Spectral Analysis (LSSA)
provide the best performance for larger RFI gaps. However we caution that these
qualitative conclusions are sensitive to the chosen hyperparameters of each
inpainting technique. We find these results to be consistent in both simulated
and real visibilities. We show that all inpainting techniques reliably
reproduce foreground dominated modes in the power spectrum. Since the
inpainting techniques should not be capable of reproducing noise realizations,
we find that the largest errors occur in the noise dominated delay modes. We
show that in the future, as the noise level of the data comes down, CLEAN and
DPSS are most capable of reproducing the fine frequency structure in the
visibilities of HERA data.Comment: 26 pages, 18 figure
Direct Optimal Mapping Image Power Spectrum and its Window Functions
The key to detecting neutral hydrogen during the epoch of reionization (EoR)
is to separate the cosmological signal from the dominating foreground
radiation. We developed direct optimal mapping (Xu et al. 2022) to map
interferometric visibilities; it contains only linear operations, with full
knowledge of point spread functions from visibilities to images. Here we
present an FFT-based image power spectrum and its window functions based on
direct optimal mapping. We use noiseless simulation, based on the Hydrogen
Epoch of Reionization Array (HERA) Phase I configuration, to study the image
power spectrum properties. The window functions show power leakage
from the foreground-dominated region into the EoR window; the 2D and 1D power
spectra also verify the separation between the foregrounds and the EoR.
Furthermore, we simulated visibilities from a -complete array and
calculated its image power spectrum. The result shows that the foreground--EoR
leakage is further suppressed below , dominated by the tapering
function sidelobes; the 2D power spectrum does not show signs of the horizon
wedge. The -complete result provides a reference case for future 21cm
cosmology array designs.Comment: Submitted to Ap
Direct Optimal Mapping for 21cm Cosmology: A Demonstration with the Hydrogen Epoch of Reionization Array
Motivated by the desire for wide-field images with well-defined statistical
properties for 21cm cosmology, we implement an optimal mapping pipeline that
computes a maximum likelihood estimator for the sky using the interferometric
measurement equation. We demonstrate this direct optimal mapping with data from
the Hydrogen Epoch of Reionization (HERA) Phase I observations. After
validating the pipeline with simulated data, we develop a maximum likelihood
figure-of-merit for comparing four sky models at 166MHz with a bandwidth of
100kHz. The HERA data agree with the GLEAM catalogs to <10%. After subtracting
the GLEAM point sources, the HERA data discriminate between the different
continuum sky models, providing most support for the model of Byrne et al.
2021. We report the computation cost for mapping the HERA Phase I data and
project the computation for the HERA 320-antenna data; both are feasible with a
modern server. The algorithm is broadly applicable to other interferometers and
is valid for wide-field and non-coplanar arrays.Comment: 16 pages, 10 figures, 2 tables, published on Ap
- …