92 research outputs found
The Interaction of Obesity Related Genotypes, Phenotypes, and Economics: An Experimental Economics Approach with Mice
Food intake is greatly influenced by economic factors. Consequently, neuroeconomics has been identified as a new and important area for understanding the interaction between genotypes and phenotypes related to food intake. A foundational element of economics is choice between alternatives. Changing food choices are a central element in the explanation of the increasing obesity rates in human populations. The purpose of this research is to incorporate the key element of choice into the investigation of food intake and weight-related phenotypes for mice in an operant chamber setting. Using normal mice, and mice with a mutation in the Tubby gene (Tub-Mut) which results in adult onset obesity, this research will investigate different behavioral responses among genotypes, as well as unexplored phenotype outcomes when mice are confronted with a falling price of a high fat food relative to a low fat food. Results for both genotypes indicate that as the price of the high fat food falls, consumption of that food increases, but consumption of the low fat food does not decrease in a compensatory fashion. For both genotypes, weight and body fat percentage increases with decreasing high fat food price, but ghrelin and leptin levels do not significantly change. The Tub-Mut shows a significant increase in the area under the glucose tolerance curve, suggestive of a diabetic state. These results show that accounting for choice in neuroeconomic studies is important to understanding the complex regulation of body weight and diabetes.Food Consumption/Nutrition/Food Safety,
Non-detection of CHIME/FRB sources with the Arecibo Observatory
In this work, we present follow-up observations of two known repeating fast
radio bursts (FRBs) and seven non-repeating FRBs with complex morphology
discovered with CHIME/FRB. These observations were conducted with the Arecibo
Observatory 327 MHz receiver. We detected no additional bursts from these
sources, nor did CHIME/FRB detect any additional bursts from these sources
during our follow-up program. Based on these non-detections, we provide
constraints on the repetition rate, for all nine sources. We calculate
repetition rates using both a Poisson distribution of repetition and the
Weibull distribution of repetition presented by Oppermann et al. (2018). For
both distributions, we find repetition upper limits of the order for all sources. These rates are much lower
than those recently published for notable repeating FRBs like FRB 20121102A and
FRB 20201124A, suggesting the possibility of a low-repetition sub-population.Comment: 12 pages, 4 figures, 5 tables; submitted to Ap
Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder
We present results from a new incoherent-beam Fast Radio Burst (FRB) search
on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its
large instantaneous field of view (FoV) and relative thermal insensitivity
allow us to probe the ultra-bright tail of the FRB distribution, and to test a
recent claim that this distribution's slope, , is quite small. A 256-input incoherent beamformer was
deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were
described by a single power-law with , we would expect an FRB
detection every few days, making this the fastest survey on sky at present. We
collected 1268 hours of data, amounting to one of the largest exposures of any
FRB survey, with over 2.4\,\,10\,deg\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
\,sky\,day above \,220 Jy\,ms
for between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out with 95 confidence, after
marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we
show that for a cosmological population and a large dynamic range in flux
density, is brightness-dependent. Since FRBs now extend to large
enough distances that non-Euclidean effects are significant, there is still
expected to be a dearth of faint events and relative excess of bright events.
Nevertheless we have constrained the allowed number of ultra-intense FRBs.
While this does not have significant implications for deeper, large-FoV surveys
like full CHIME and APERTIF, it does have important consequences for other
wide-field, small dish experiments
The second set of pulsar discoveries by CHIME/FRB/Pulsar: 14 Rotating Radio Transients and 7 pulsars
The Canadian Hydrogen Mapping Experiment (CHIME) is a radio telescope located
in British Columbia, Canada. The large field of view (FOV) of 200 square
degrees has enabled the CHIME/FRB instrument to produce the largest FRB catalog
to date. The large FOV also allows CHIME/FRB to be an exceptional pulsar and
Rotating Radio Transient (RRAT) finding machine, despite saving only the
metadata information of incoming Galactic events. We have developed a pipeline
to search for pulsars/RRATs using DBSCAN, a clustering algorithm. Output
clusters are then inspected by a human for pulsar/RRAT candidates and follow-up
observations are scheduled with the more sensitive CHIME/Pulsar instrument. The
CHIME/Pulsar instrument is capable of a near-daily search mode observation
cadence. We have thus developed the CHIME/Pulsar Single Pulse Pipeline to
automate the processing of CHIME/Pulsar search mode data. We report the
discovery of 21 new Galactic sources, with 14 RRATs, 6 regular slow pulsars and
1 binary system. Owing to CHIME/Pulsar's daily observations we have obtained
timing solutions for 8 of the 14 RRATs along with all the regular pulsars. This
demonstrates CHIME/Pulsar's ability at finding timing solutions for transient
sources
An Injection System for the CHIME/FRB Experiment
Dedicated surveys searching for Fast Radio Bursts (FRBs) are subject to
selection effects which bias the observed population of events. Software
injection systems are one method of correcting for these biases by injecting a
mock population of synthetic FRBs directly into the realtime search pipeline.
The injected population may then be used to map intrinsic burst properties onto
an expected signal-to-noise ratio (SNR), so long as telescope characteristics
such as the beam model and calibration factors are properly accounted for. This
paper presents an injection system developed for the Canadian Hydrogen
Intensity Mapping Experiment Fast Radio Burst project (CHIME/FRB). The system
was tested to ensure high detection efficiency, and the pulse calibration
method was verified. Using an injection population of ~85,000 synthetic FRBs,
we found that the correlation between fluence and SNR for injected FRBs was
consistent with that of CHIME/FRB detections in the first CHIME/FRB catalog. We
also noted that the sensitivity of the telescope varied strongly as a function
of the broadened burst width, but not as a function of the dispersion measure.
We conclude that some of the machine-learning based Radio Frequency
Interference (RFI) mitigation methods used by CHIME/FRB can be re-trained using
injection data to increase sensitivity to wide events, and that planned
upgrades to the presented injection system will allow for determining a more
accurate CHIME/FRB selection function in the near future.Comment: 13 pages, 8 figures. Submitted to A
Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set
When galaxies merge, the supermassive black holes in their centers may form
binaries and, during the process of merger, emit low-frequency gravitational
radiation in the process. In this paper we consider the galaxy 3C66B, which was
used as the target of the first multi-messenger search for gravitational waves.
Due to the observed periodicities present in the photometric and astrometric
data of the source of the source, it has been theorized to contain a
supermassive black hole binary. Its apparent 1.05-year orbital period would
place the gravitational wave emission directly in the pulsar timing band. Since
the first pulsar timing array study of 3C66B, revised models of the source have
been published, and timing array sensitivities and techniques have improved
dramatically. With these advances, we further constrain the chirp mass of the
potential supermassive black hole binary in 3C66B to less than using data from the NANOGrav 11-year data set. This
upper limit provides a factor of 1.6 improvement over previous limits, and a
factor of 4.3 over the first search done. Nevertheless, the most recent orbital
model for the source is still consistent with our limit from pulsar timing
array data. In addition, we are able to quantify the improvement made by the
inclusion of source properties gleaned from electromagnetic data to `blind'
pulsar timing array searches. With these methods, it is apparent that it is not
necessary to obtain exact a priori knowledge of the period of a binary to gain
meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap
CHIME Discovery of a Binary Pulsar with a Massive Non-Degenerate Companion
Of the more than 3000 radio pulsars currently known, only ∼300 are in binary systems, and only five of these consist of young pulsars with massive nondegenerate companions. We present the discovery and initial timing, accomplished using the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope, of the sixth such binary pulsar, PSR J2108+4516, a 0.577 s radio pulsar in a 269 day orbit of eccentricity 0.09 with a companion of minimum mass 11 M⊙. Notably, the pulsar undergoes periods of substantial eclipse, disappearing from the CHIME 400–800 MHz observing band for a large fraction of its orbit, and displays significant dispersion measure and scattering variations throughout its orbit, pointing to the possibility of a circumstellar disk or very dense stellar wind associated with the companion star. Subarcsecond resolution imaging with the Karl G. Jansky Very Large Array unambiguously demonstrates that the companion is a bright, V ≃ 11 OBe star, EM* UHA 138, located at a distance of 3.26(14) kpc. Archival optical observations of EM* UHA 138 approximately suggest a companion mass ranging from 17.5 M⊙ < Mc < 23 M⊙, in turn constraining the orbital inclination angle to 50fdg3 ≲ i ≲ 58fdg3. With further multiwavelength follow-up, PSR J2108+4516 promises to serve as another rare laboratory for the exploration of companion winds, circumstellar disks, and short-term evolution through extended-body orbital dynamics
The NANOGrav 12.5-Year Data Set:Dispersion Measure Misestimations with Varying Bandwidths
Noise characterization for pulsar-timing applications accounts for interstellar dispersion by assuming a known frequency dependence of the delay it introduces in the times of arrival (TOAs). However, calculations of this delay suffer from misestimations due to other chromatic effects in the observations. The precision in modeling dispersion is dependent on the observed bandwidth. In this work, we calculate the offsets in infinite-frequency TOAs due to misestimations in the modeling of dispersion when using varying bandwidths at the Green Bank Telescope. We use a set of broadband observations of PSR J1643−1224, a pulsar with unusual chromatic timing behavior. We artificially restricted these observations to a narrowband frequency range, then used both the broad- and narrowband data sets to calculate residuals with a timing model that does not account for time variations in the dispersion. By fitting the resulting residuals to a dispersion model and comparing the fits, we quantify the error introduced in the timing parameters due to using a reduced frequency range. Moreover, by calculating the autocovariance function of the parameters, we obtained a characteristic timescale over which the dispersion misestimates are correlated. For PSR J1643−1224, which has one of the highest dispersion measures (DM) in the NANOGrav pulsar timing array, we find that the infinite-frequency TOAs suffer from a systematic offset of ∼22 μs due to incomplete frequency sampling, with correlations over about one month. For lower-DM pulsars, the offset is ∼7 μs. This error quantification can be used to provide more robust noise modeling in the NANOGrav data, thereby increasing the sensitivity and improving the parameter estimation in gravitational wave searches
- …