290 research outputs found
A Distant Fast Radio Burst Associated with Its Host Galaxy by the Very Large Array
We present the discovery and subarcsecond localization of a new fast radio burst (FRB) by the Karl G. Jansky Very Large Array (VLA) and realfast search system. The FRB was discovered on 2019 June 14 with a dispersion measure of 959 pc cm⁻³. This is the highest DM of any localized FRB and its measured burst fluence of 0.6 Jy ms is less than nearly all other FRBs. The source is not detected to repeat in 15 hr of VLA observing and 153 hr of CHIME/FRB observing. We describe a suite of statistical and data quality tests we used to verify the significance of the event and its localization precision. Follow-up optical/infrared photometry with Keck and Gemini associate the FRB with a pair of galaxies with r ∼ 23 mag. The false-alarm rate for radio transients of this significance that are associated with a host galaxy is roughly 3×10⁻⁴ hr⁻¹. The two putative host galaxies have similar photometric redshifts of z_(phot) ∼ 0.6, but different colors and stellar masses. Comparing the host distance to that implied by the dispersion measure suggests a modest (~ 50 pc/cm⁻³) electron column density associated with the FRB environment or host galaxy/galaxies
A Search for Fast Radio Bursts with the GBNCC Pulsar Survey
We report on a search for Fast Radio Bursts (FRBs) with the Green Bank
Northern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointings amounting to
a total on-sky time of 61 days were searched to a DM of 3000 pc cm while
the rest (23 days; 29% of the total time) were searched to a DM of 500 pc
cm. No FRBs were detected in the pointings observed through May 2016. We
estimate a 95% confidence upper limit on the FRB rate of FRBs
sky day above a peak flux density of 0.63 Jy at 350 MHz for an
intrinsic pulse width of 5 ms. We place constraints on the spectral index
by running simulations for different astrophysical scenarios and
cumulative flux density distributions. The non-detection with GBNCC is
consistent with the 1.4-GHz rate reported for the Parkes surveys for in the absence of scattering and free-free absorption and in the presence of scattering, for a Euclidean flux distribution. The
constraints imply that FRBs exhibit either a flat spectrum or a spectral
turnover at frequencies above 400 MHz. These constraints also allow estimation
of the number of bursts that can be detected with current and upcoming surveys.
We predict that CHIME may detect anywhere from several to 50 FRBs a day
(depending on model assumptions), making it well suited for interesting
constraints on spectral index, the log -log slope and pulse profile
evolution across its bandwidth (400-800 MHz).Comment: 18 pages, 10 figures, Accepted for publication in Ap
Disposable Platform Provides Visual and Color-Based Point-of-Care Anemia Self-Testing
Anemia, or low blood hemoglobin (Hgb) levels, afflicts 2 billion people worldwide. Currently, Hgb levels are typically measured from blood samples using hematology analyzers, which are housed in hospitals, clinics, or commercial laboratories and require skilled technicians to operate. A reliable, inexpensive point-of-care (POC) Hgb test would enable cost-effective anemia screening and chronically anemic patients to self-monitor their disease. We present a rapid, standalone, and disposable POC anemia test that, via a single drop of blood, outputs color-based visual results that correlate with Hgb levels.
METHODS. We tested blood from 238 pediatric and adult patients with anemia of varying degrees and etiologies and compared hematology analyzer Hgb levels with POC Hgb levels, which were estimated via visual interpretation using a color scale and an optional smartphone app for automated analysis.
RESULTS. POC Hgb levels correlated with hematology analyzer Hgb levels (r = 0.864 and r = 0.856 for visual interpretation and smartphone app, respectively), and both POC test methods yielded comparable sensitivity and specificity for detecting any anemia (n = 178) (/dl) (sensitivity: 90.2% and 91.1%, specificity: 83.7% and 79.2%, respectively) and severe anemia (n = 10) (/dl) (sensitivity: 90.0% and 100%, specificity: 94.6% and 93.9%, respectively).
CONCLUSIONS. These results demonstrate the feasibility of this POC color-based diagnostic test for self-screening/self-monitoring of anemia.
TRIAL REGISTRATION. Not applicable.
FUNDING. This work was funded by the FDA-funded Atlantic Pediatric Device Consortium, the Georgia Research Alliance, Children\u27s Healthcare of Atlanta, the Georgia Center of Innovation for Manufacturing, and the InVenture Prize and Ideas to Serve competitions at the Georgia Institute of Technology
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The effect of asymmetries on stock index return value-at-risk estimates
It is widely accepted that equity return volatility increases more following negative shocks rather than positive shocks. However, much of value-at-risk (VaR) analysis relies on the assumption that returns are normally distributed (a symmetric distribution). This article considers the effect of asymmetries on the evaluation and accuracy of VaR by comparing estimates based on various models
Simultaneous X-Ray and Radio Observations of the Repeating Fast Radio Burst FRB ∼ 180916.J0158+65
LOFAR Detection of 110-188 MHz Emission and Frequency-Dependent Activity from FRB 20180916B
FRB 20180916B is a well-studied repeating fast radio burst source. Its
proximity (~150 Mpc), along with detailed studies of the bursts, have revealed
many clues about its nature -- including a 16.3-day periodicity in its
activity. Here we report on the detection of 18 bursts using LOFAR at 110-188
MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are
seen down to the lowest-observed frequency of 110 MHz, suggesting that their
spectra extend even lower. These observations provide an order-of-magnitude
stronger constraint on the optical depth due to free-free absorption in the
source's local environment. The absence of circular polarization and nearly
flat polarization angle curves are consistent with burst properties seen at
300-1700 MHz. Compared with higher frequencies, the larger burst widths
(~40-160 ms at 150 MHz) and lower linear polarization fractions are likely due
to scattering. We find ~2-3 rad/m^2 variations in the Faraday rotation measure
that may be correlated with the activity cycle of the source. We compare the
LOFAR burst arrival times to those of 38 previously published and 22 newly
detected bursts from the uGMRT (200-450 MHz) and CHIME/FRB (400-800 MHz).
Simultaneous observations show 5 CHIME/FRB bursts when no emission is detected
by LOFAR. We find that the burst activity is systematically delayed towards
lower frequencies by ~3 days from 600 MHz to 150 MHz. We discuss these results
in the context of a model in which FRB 20180916B is an interacting binary
system featuring a neutron star and high-mass stellar companion.Comment: Accepted for publication by ApJ
Menopausal Status Modifies Breast Cancer Risk Associated with the Myeloperoxidase (MPO) G463A Polymorphism in Caucasian Women: A Meta-Analysis
BACKGROUND: Breast cancer susceptibility may be modulated partly through polymorphisms in oxidative enzymes, one of which is myeloperoxidase (MPO). Association of the low transcription activity variant allele A in the G463A polymorphism has been investigated for its association with breast cancer risk, considering the modifying effects of menopausal status and antioxidant intake levels of cases and controls. METHODOLOGY/PRINCIPAL FINDINGS: To obtain a more precise estimate of association using the odds ratio (OR), we performed a meta-analysis of 2,975 cases and 3,427 controls from three published articles of Caucasian populations living in the United States. Heterogeneity among studies was tested and sensitivity analysis was applied. The lower transcriptional activity AA genotype of MPO in the pre-menopausal population showed significantly reduced risk (OR 0.56-0.57, p = 0.03) in contrast to their post-menopausal counterparts which showed non-significant increased risk (OR 1.14; p = 0.34-0.36). High intake of antioxidants (OR 0.67-0.86, p = 0.04-0.05) and carotenoids (OR 0.68-0.86, p = 0.03-0.05) conferred significant protection in the women. Stratified by menopausal status, this effect was observed in pre-menopausal women especially those whose antioxidant intake was high (OR 0.42-0.69, p = 0.04). In post-menopausal women, effect of low intake elicited susceptibility (OR 1.19-1.67, p = 0.07-0.17) to breast cancer. CONCLUSIONS/SIGNIFICANCE: Based on a homogeneous Caucasian population, the MPO G463A polymorphism places post-menopausal women at risk for breast cancer, where this effect is modified by diet
Detection of Repeating FRB 180916.J0158+65 Down to Frequencies of 300 MHz
We report on the detection of seven bursts from the periodically active,
repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400-MHz
frequency range with the Green Bank Telescope (GBT). Emission in multiple
bursts is visible down to the bottom of the GBT band, suggesting that the
cutoff frequency (if it exists) for FRB emission is lower than 300 MHz.
Observations were conducted during predicted periods of activity of the source,
and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB
backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
telescope. We find that one of the GBT-detected bursts has potentially
associated emission in the CHIME band (400-800 MHz) but we detect no bursts in
the LOFAR band (110-190 MHz), placing a limit of on the
spectral index of broadband emission from the source. We also find that
emission from the source is severely band-limited with burst bandwidths as low
as 40 MHz. In addition, we place the strictest constraint on observable
scattering of the source, 1.7 ms, at 350 MHz, suggesting that the
circumburst environment does not have strong scattering properties.
Additionally, knowing that the circumburst environment is optically thin to
free-free absorption at 300 MHz, we find evidence against the association of a
hyper-compact HII region or a young supernova remnant (age 50 yr) with the
source.Comment: Accepted for publication in ApJ
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