91 research outputs found
Effects of Nitrogen and Planting Seed Size on Cotton Growth, Development, and Yield
A standardized experiment was conducted during 2009 and 2010 at 20 location-years across U.S. cotton (Gossypium hirsutum L.)-producing states to compare the N use requirement of contemporary cotton cultivars based on their planting seed size. Treatments consisted of three cotton varieties with planting seed of different numbers of seed per kg and N rates of 0, 45, 90, and 134 kg ha⁻¹. Soil at each trial location was sampled and tested for nitrate presence. High levels of soil nitrate (>91 N-NO₃⁻kg ha⁻¹) were found in Arizona and western Texas, and soil nitrate in the range of 45 to 73 kg N-NO₃⁻ ha⁻¹ was found at locations in the central United States. Cotton lint yield responded to applied N at 11 of 20 locations. Considering only sites that responded to applied N, highest lint yields were achieved with 112 to 224 kg ha⁻¹of applied plus pre-plant residual soil NO₃—translating to an optimal N requirement of 23 kg ha⁻¹ per 218 kg bale of lint produced. Among the varieties tested those with medium-sized seed produced higher yields in response to N than did larger and smaller seeded varieties. Varieties with larger seed had longer and stronger fibers, higher fiber length uniformity than small seeded varieties and decreased micronaire. Seed protein and oil increased and decreased slightly in response to increasing amounts of soil nitrate plus applied N, respectively
The Thousand-Pulsar-Array program on MeerKAT -- IX. The time-averaged properties of the observed pulsar population
We present the largest single survey to date of average profiles of radio
pulsars, observed and processed using the same telescope and data reduction
software. Specifically, we present measurements for 1170 pulsars, observed by
the Thousand Pulsar Array (TPA) programme at the 64-dish SARAO MeerKAT radio
telescope, in a frequency band from 856 to 1712 MHz. We provide rotation
measures (RM), dispersion measures, flux densities and polarization properties.
The catalogue includes 254 new RMs that substantially increase the total number
of known pulsar RMs. Our integration times typically span over 1000 individual
rotations per source. We show that the radio (pseudo)luminosity has a strong,
shallow dependence on the spin-down energy, proportional to
, that contradicts some previous proposals of population
synthesis studies. In addition, we find a significant correlation between the
steepness of the observed flux density spectra and , and correlations
of the fractional linear polarization with , the spectral index, and
the pulse width, which we discuss in the context of what is known about pulsar
radio emission and how pulsars evolve with time. On the whole, we do not see
significant correlations with the estimated surface magnetic field strength,
and the correlations with are much stronger than those with the
characteristic age. This finding lends support to the suggestion that magnetic
dipole braking may not be the dominant factor for the evolution of pulsar
rotation over the lifetimes of pulsars. A public data release of the
high-fidelity time-averaged pulse profiles in full polarization accompanies our
catalogue.Comment: Accepted for publication in MNRAS. 21 pages, 25 figures, 6 Table
Evaluation of the current knowledge limitations in breast cancer research: a gap analysis
BACKGROUND
A gap analysis was conducted to determine which areas of breast cancer research, if targeted by researchers and funding bodies, could produce the greatest impact on patients.
METHODS
Fifty-six Breast Cancer Campaign grant holders and prominent UK breast cancer researchers participated in a gap analysis of current breast cancer research. Before, during and following the meeting, groups in seven key research areas participated in cycles of presentation, literature review and discussion. Summary papers were prepared by each group and collated into this position paper highlighting the research gaps, with recommendations for action.
RESULTS
Gaps were identified in all seven themes. General barriers to progress were lack of financial and practical resources, and poor collaboration between disciplines. Critical gaps in each theme included: (1) genetics (knowledge of genetic changes, their effects and interactions); (2) initiation of breast cancer (how developmental signalling pathways cause ductal elongation and branching at the cellular level and influence stem cell dynamics, and how their disruption initiates tumour formation); (3) progression of breast cancer (deciphering the intracellular and extracellular regulators of early progression, tumour growth, angiogenesis and metastasis); (4) therapies and targets (understanding who develops advanced disease); (5) disease markers (incorporating intelligent trial design into all studies to ensure new treatments are tested in patient groups stratified using biomarkers); (6) prevention (strategies to prevent oestrogen-receptor negative tumours and the long-term effects of chemoprevention for oestrogen-receptor positive tumours); (7) psychosocial aspects of cancer (the use of appropriate psychosocial interventions, and the personal impact of all stages of the disease among patients from a range of ethnic and demographic backgrounds).
CONCLUSION
Through recommendations to address these gaps with future research, the long-term benefits to patients will include: better estimation of risk in families with breast cancer and strategies to reduce risk; better prediction of drug response and patient prognosis; improved tailoring of treatments to patient subgroups and development of new therapeutic approaches; earlier initiation of treatment; more effective use of resources for screening populations; and an enhanced experience for people with or at risk of breast cancer and their families. The challenge to funding bodies and researchers in all disciplines is to focus on these gaps and to drive advances in knowledge into improvements in patient care
Practical approaches to analyzing PTA data: Cosmic strings with six pulsars
We search for a stochastic gravitational wave background (SGWB) generated by
a network of cosmic strings using six millisecond pulsars from Data Release 2
(DR2) of the European Pulsar Timing Array (EPTA). We perform a Bayesian
analysis considering two models for the network of cosmic string loops, and
compare it to a simple power-law model which is expected from the population of
supermassive black hole binaries. Our main strong assumption is that the
previously reported common red noise process is a SGWB. We find that the
one-parameter cosmic string model is slightly favored over a power-law model
thanks to its simplicity. If we assume a two-component stochastic signal in the
data (supermassive black hole binary population and the signal from cosmic
strings), we get a upper limit on the string tension of () for the two cosmic string models we consider. In extended
two-parameter string models, we were unable to constrain the number of kinks.
We test two approximate and fast Bayesian data analysis methods against the
most rigorous analysis and find consistent results. These two fast and
efficient methods are applicable to all SGWBs, independent of their source, and
will be crucial for analysis of extended data sets.Comment: 13 pages, 5 figure
The second data release from the European Pulsar Timing Array I. The dataset and timing analysis
Pulsar timing arrays offer a probe of the low-frequency gravitational wave
spectrum (1 - 100 nanohertz), which is intimately connected to a number of
markers that can uniquely trace the formation and evolution of the Universe. We
present the dataset and the results of the timing analysis from the second data
release of the European Pulsar Timing Array (EPTA). The dataset contains
high-precision pulsar timing data from 25 millisecond pulsars collected with
the five largest radio telescopes in Europe, as well as the Large European
Array for Pulsars. The dataset forms the foundation for the search for
gravitational waves by the EPTA, presented in associated papers. We describe
the dataset and present the results of the frequentist and Bayesian pulsar
timing analysis for individual millisecond pulsars that have been observed over
the last ~25 years. We discuss the improvements to the individual pulsar
parameter estimates, as well as new measurements of the physical properties of
these pulsars and their companions. This data release extends the dataset from
EPTA Data Release 1 up to the beginning of 2021, with individual pulsar
datasets with timespans ranging from 14 to 25 years. These lead to improved
constraints on annual parallaxes, secular variation of the orbital period, and
Shapiro delay for a number of sources. Based on these results, we derived
astrophysical parameters that include distances, transverse velocities, binary
pulsar masses, and annual orbital parallaxes.Comment: 29 pages, 9 figures, 13 tables, Astronomy & Astrophysics in pres
Practical approaches to analyzing PTA data: Cosmic strings with six pulsars
We search for a stochastic gravitational wave background (SGWB) generated by a network of cosmic strings using six millisecond pulsars from Data Release 2 (DR2) of the European Pulsar Timing Array (EPTA). We perform a Bayesian analysis considering two models for the network of cosmic string loops, and compare it to a simple power-law model which is expected from the population of supermassive black hole binaries. Our main strong assumption is that the previously reported common red noise process is a SGWB. We find that the one-parameter cosmic string model is slightly favored over a power-law model thanks to its simplicity. If we assume a two-component stochastic signal in the data (supermassive black hole binary population and the signal from cosmic strings), we get a 95% upper limit on the string tension of log10(Gμ)<-9.9 (-10.5) for the two cosmic string models we consider. In extended two-parameter string models, we were unable to constrain the number of kinks. We test two approximate and fast Bayesian data analysis methods against the most rigorous analysis and find consistent results. These two fast and efficient methods are applicable to all SGWBs, independent of their source, and will be crucial for analysis of extended datasets
Searching for continuous Gravitational Waves in the second data release of the International Pulsar Timing Array
The International Pulsar Timing Array 2nd data release is the combination of
datasets from worldwide collaborations. In this study, we search for continuous
waves: gravitational wave signals produced by individual supermassive black
hole binaries in the local universe. We consider binaries on circular orbits
and neglect the evolution of orbital frequency over the observational span. We
find no evidence for such signals and set sky averaged 95% upper limits on
their amplitude h 95 . The most sensitive frequency is 10nHz with h 95 = 9.1
10-15 . We achieved the best upper limit to date at low and high frequencies of
the PTA band thanks to improved effective cadence of observations. In our
analysis, we have taken into account the recently discovered common red noise
process, which has an impact at low frequencies. We also find that the peculiar
noise features present in some pulsars data must be taken into account to
reduce the false alarm. We show that using custom noise models is essential in
searching for continuous gravitational wave signals and setting the upper
limit
The second data release from the European Pulsar Timing Array IV. Search for continuous gravitational wave signals
We present the results of a search for continuous gravitational wave signals
(CGWs) in the second data release (DR2) of the European Pulsar Timing Array
(EPTA) collaboration. The most significant candidate event from this search has
a gravitational wave frequency of 4-5 nHz. Such a signal could be generated by
a supermassive black hole binary (SMBHB) in the local Universe. We present the
results of a follow-up analysis of this candidate using both Bayesian and
frequentist methods. The Bayesian analysis gives a Bayes factor of 4 in favor
of the presence of the CGW over a common uncorrelated noise process, while the
frequentist analysis estimates the p-value of the candidate to be 1%, also
assuming the presence of common uncorrelated red noise. However, comparing a
model that includes both a CGW and a gravitational wave background (GWB) to a
GWB only, the Bayes factor in favour of the CGW model is only 0.7. Therefore,
we cannot conclusively determine the origin of the observed feature, but we
cannot rule it out as a CGW source. We present results of simulations that
demonstrate that data containing a weak gravitational wave background can be
misinterpreted as data including a CGW and vice versa, providing two plausible
explanations of the EPTA DR2 data. Further investigations combining data from
all PTA collaborations will be needed to reveal the true origin of this
feature.Comment: 12 figures, 15 pages, to be submitte
The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). A robust GWB detection is conditioned upon resolving the Hellings-Downs angular pattern in the pairwise cross-correlation of the pulsar timing residuals. Additionally, the GWB is expected to yield the same (common) spectrum of temporal correlations across pulsars, which is used as a null hypothesis in the GWB search. Such a common-spectrum process has already been observed in pulsar timing data. We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of 4%. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of 60 and a false alarm probability of about 0.1% (≳3σ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The latest EPTA data from new generation observing systems show non-negligible evidence for the GWB. At the same time, the inferred spectrum is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of (2.5 ± 0.7) × 10−15 at a reference frequency of 1 yr−1. Further investigation of these issues is required for reliable astrophysical interpretations of this signal. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years
The second data release from the European Pulsar Timing Array: II. Customised pulsar noise models for spatially correlated gravitational waves
Aims. The nanohertz gravitational wave background (GWB) is expected to be an aggregate signal of an ensemble of gravitational waves emitted predominantly by a large population of coalescing supermassive black hole binaries in the centres of merging galaxies. Pulsar timing arrays (PTAs), which are ensembles of extremely stable pulsars at approximately kiloparsec distances precisely monitored for decades, are the most precise experiments capable of detecting this background. However, the subtle imprints that the GWB induces on pulsar timing data are obscured by many sources of noise that occur on various timescales. These must be carefully modelled and mitigated to increase the sensitivity to the background signal.Methods. In this paper, we present a novel technique to estimate the optimal number of frequency coefficients for modelling achromatic and chromatic noise, while selecting the preferred set of noise models to use for each pulsar. We also incorporated a new model to fit for scattering variations in the Bayesian pulsar timing package temponest. These customised noise models enable a more robust characterisation of single-pulsar noise. We developed a software package based on tempo2 to create realistic simulations of European Pulsar Timing Array (EPTA) datasets that allowed us to test the efficacy of our noise modelling algorithms.Results. Using these techniques, we present an in-depth analysis of the noise properties of 25 millisecond pulsars (MSPs) that form the second data release (DR2) of the EPTA and investigate the effect of incorporating low-frequency data from the Indian Pulsar Timing Array collaboration for a common sample of ten MSPs. We used two packages, enterprise and temponest, to estimate our noise models and compare them with those reported using EPTA DR1. We find that, while in some pulsars we can successfully disentangle chromatic from achromatic noise owing to the wider frequency coverage in DR2, in others the noise models evolve in a much more complicated way. We also find evidence of long-term scattering variations in PSR J1600-3053. Through our simulations, we identify intrinsic biases in our current noise analysis techniques and discuss their effect on GWB searches. The analysis and results discussed in this article directly help to improve the sensitivity to the GWB signal and they are already being used as part of global PTA efforts
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