Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 10(17)-10(18) electronvolts are essential to understanding whether ...they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers--cascades of secondary particles in the atmosphere-and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 10(17)-10(17.5) electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 10(17.5) electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 10(17)-10(17.5) electronvolt range.
The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These ...processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here, we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ~3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free-free) absorption or synchrotron self-absorption models are able to describe the low-frequency spectral shape of the hotspots; however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic.
The aim of the LOFAR epoch of reionization (EoR) project is to detect the spectral fluctuations of the redshifted HI 21 cm signal. This signal is weaker by several orders of magnitude than the ...astrophysical foreground signals and hence, in order to achieve this, very long integrations, accurate calibration for stations and ionosphere and reliable foreground removal are essential. One of the prospective observing windows for the LOFAR BoR project will be centered at the north celestial pole (NCP). We present results from observations of the NCP window using the LOFAR highband antenna (HBA) array in the frequency range 115 MHz to 163 MHz. The limitations present in our current results are mainly due to sidelobe noise from the large number of distant sources, as well as errors related to station beam variations and rapid ionospheric phase fluctuations acting on bright sources. We are confident that we can improve our results with refined processing.
Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across ...the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.
OBJECTIVE:To analyze the labor curves of nulliparous and multiparous women between 23.0 and 34.0 weeks of gestation who underwent induction of labor and achieved vaginal delivery.
METHODS:This is a ...retrospective cohort study of all live singletons delivered vaginally after medically indicated induction of labor between 23.0 and 34.0 weeks of gestation from 2011 through 2014 at our institution. We excluded those with one or no cervical examinations available during labor. Prior cesarean delivery, 5-minute Apgar score less than 5, and arterial cord pH less than 7.0 were exclusions. The course of cervical dilation was modeled using repeated measures analysis, and smoothed curves for nulliparous and parous women were generated separately. Estimates of the median (5th–95th percentile) traverse times between two dilations were computed using interval censored regression. Traverse times (ie, the elapsed time between two given dilation measures) were compared between nulliparous and parous women.
RESULTS:Sixty-seven nulliparous and 69 multiparous women were included. Each group exhibited similar rates of change from 1 to 3 cm of dilation (median 3.6 hours nulliparous and 3.4 hours multiparous, P=.90). Nulliparous women progressed from 3 to 6 cm more slowly than multiparous women (median 10 hours vs 4.4 hours, P<.001). After 6 cm, both groups rapidly progressed to 10 cm (median 0.3 hours vs 0.3 hours, P=.64). Although the 95th percentile traverse time from 6 to 10 cm was about 2 hours in each group, progression from 1 to 6 cm at the 95th percentile was much longer (64.0 vs 42.2 hours).
CONCLUSION:Early preterm labor induction takes less time in multiparous women owing to more rapid progression from 3 to 6 cm. At the 95th percentile, both nulliparous and multiparous women delivered vaginally, even with latent labor lasting well longer than 24 hours.
We present the results of a four-month campaign searching for low-frequency radio transients near the North Celestial Pole with the Low-Frequency Array (LOFAR), as part of the Multifrequency Snapshot ...Sky Survey (MSSS). The data were recorded between 2011 December and 2012 April and comprised 2149 11-min snapshots, each covering 175 deg2. We have found one convincing candidate astrophysical transient, with a duration of a few minutes and a flux density at 60 MHz of 15–25 Jy. The transient does not repeat and has no obvious optical or high-energy counterpart, as a result of which its nature is unclear. The detection of this event implies a transient rate at 60 MHz of
$3.9^{+14.7}_{-3.7}\times 10^{-4}$
d−1 deg−2, and a transient surface density of 1.5 × 10−5 deg−2, at a 7.9-Jy limiting flux density and ∼10-min time-scale. The campaign data were also searched for transients at a range of other time-scales, from 0.5 to 297 min, which allowed us to place a range of limits on transient rates at 60 MHz as a function of observation duration.
Background Smoking during pregnancy is associated with adverse maternal and neonatal outcomes such as preterm delivery, intrauterine growth restriction, stillbirth, and low birth weight. Because ...smoking causes oxidative stress, some have suggested using antioxidants to counteract the effects of oxidative stress. Smokers have lower serum levels of omega-3 fatty acids, an important antioxidant, and thus, investigating whether omega-3 supplementation in smokers reduces adverse maternal and neonatal outcomes represents an important area of research. Objective To investigate whether the antioxidant effect of omega-3 fatty acid supplementation on the incidence of adverse pregnancy outcomes differs between smokers and nonsmokers. Study Design Secondary analysis of a multicenter randomized controlled trial of omega-3 supplementation for preterm delivery prevention in women with a singleton pregnancy and a history of a previous singleton spontaneous preterm delivery. Subjects were randomized to begin omega-3 or placebo before 22 weeks, which was continued until delivery. All women received 17 alpha-hydroxyprogesterone caproate intramuscularly weekly beginning between 16 and 20 weeks of gestation and continued until 36 weeks of gestation or delivery, whichever occurred first. The primary outcome was spontaneous preterm delivery. Secondary outcomes were indicated preterm delivery, any preterm delivery (spontaneous and indicated), pregnancy-associated hypertension (gestational hypertension and preeclampsia), a neonatal composite (retinopathy of prematurity, intraventricular hemorrhage grade III or IV, patent ductus arteriosus, necrotizing enterocolitis, sepsis, respiratory morbidity, or perinatal death), low birth weight (<2500 g), small for gestational age (less than the 10th percentile), and neonatal intensive care unit or intermediate nursery admission. The study population was stratified into smokers and nonsmokers, and the incidence of each outcome was compared by omega-3 supplementation versus placebo in each subgroup. Zelen tests were performed to test for homogeneity of effect in smokers and nonsmokers. Results Of 851 subjects included in the analysis, 136 (16%) smoked. Baseline characteristics between omega-3 and placebo groups did not differ in smokers or nonsmokers. Omega-3 supplementation was associated with a lower risk of spontaneous preterm delivery in smokers (relative risk, 0.56, 95% confidence interval, 0.36–0.87) but not in nonsmokers (relative risk 1.04, 95% confidence interval 0.84–1.29); P value for interaction = 0.013. Low birth weight was also less frequent in smokers receiving omega-3 supplementation (relative risk 0.57, 95% confidence interval 0.36–0.90) compared with nonsmokers (relative risk 0.93, 95% confidence interval 0.71–1.24); P value for interaction = 0.047. The effect on other secondary outcomes did not differ significantly between smokers and nonsmokers. Conclusion Omega-3 supplementation in smokers may have a protective effect against recurrent spontaneous preterm delivery and low birth weight.
Background When delivery is indicated prior to 34 weeks, many providers perform a cesarean delivery rather than induce labor based on perceptions of a high failure rate. Given the morbidity of ...cesarean delivery, an accurate estimate of the success rate and factors associated with success in preterm induction of labor is important in management decisions. Objective We sought to develop a prediction model for successful induction of labor in preterm patients using factors known at the time the decision is made to deliver. Study Design A retrospective cohort study of all live singletons undergoing an indicated induction of labor between 23 and 34 0/7 weeks from 2011 through 2015. Pregnancies with major fetal anomalies or no intrapartum fetal monitoring were excluded. Successful induction of labor was defined as vaginal delivery. The cohort was randomly split into a training cohort to develop a prediction model for vaginal delivery and a validation cohort to test the model. Factors significantly associated with vaginal delivery were identified using univariate analyses, and candidate factors were used in the multivariate logistic regression model. Only factors known at the start of the induction of labor were used in the model. Receiver-operating characteristic curves were created to estimate the predictive value of the model. Sensitivity and specificity of the model were assessed. Results Of 331 patients who underwent induction of labor, 208 (62.8%) delivered vaginally and 123 (37.1%) by cesarean delivery. Of the factors significantly associated with cesarean delivery, the final model included gestational age, simplified Bishop score, suspected intrauterine growth retardation, chronic hypertension, and body mass index. In the training cohort, the model correctly classified 72.3% of subjects with a sensitivity (cesarean delivery predicted/cesarean delivery performed) of 56.7% and a specificity (vaginal delivery predicted/vaginal delivery performed) of 84.1%. When applied to the validation cohort, 73.9% of subjects were correctly classified, with a sensitivity of 44.6% and specificity of 89.0%. Receiver-operating characteristic curves had an area under the curve of 0.75 for the training cohort and 0.77 for the validation cohort. Conclusion More than 60% of women undergoing induction of labor at <34 0/7 weeks deliver vaginally. For women undergoing induction of labor at <34 0/7 weeks, this prediction model rarely classifies individuals who can have a vaginal delivery as needing a cesarean delivery. This model may provide an accurate assessment tool to evaluate which patients will likely deliver vaginally to avoid the morbidity of cesarean delivery while conversely identifying subjects at high risk of cesarean delivery <34 0/7 weeks.
We outline the LOFAR Long-Baseline Calibrator Survey (LBCS), whose aim is to identify sources suitable for calibrating the highest-resolution observations made with the International LOFAR Telescope, ...which include baselines >1000 km. Suitable sources must contain significant correlated flux density (≳ 50 − 100 mJy) at frequencies around 110−190 MHz on scales of a few hundred milliarcseconds. At least for the 200−300-km international baselines, we find around 1 suitable calibrator source per square degree over a large part of the northern sky, in agreement with previous work. This should allow a randomly selected target to be successfully phase calibrated on the international baselines in over 50% of cases. Products of the survey include calibrator source lists and fringe-rate and delay maps of wide areas – typically a few degrees – around each source. The density of sources with significant correlated flux declines noticeably with baseline length over the range 200−600 km, with good calibrators on the longest baselines appearing only at the rate of 0.5 per sq. deg. Coherence times decrease from 1−3 min on 200-km baselines to about 1 min on 600-km baselines, suggesting that ionospheric phase variations contain components with scales of a few hundred kilometres. The longest median coherence time, at just over 3 min, is seen on the DE609 baseline, which at 227 km is close to being the shortest. We see median coherence times of between 80 and 110 s on the four longest baselines (580−600 km), and about 2 min for the other baselines. The success of phase transfer from calibrator to target is shown to be influenced by distance, in a manner that suggests a coherence patch at 150-MHz of the order of 1 deg. Although source structures cannot be measured in these observations, we deduce that phase transfer is affected if the calibrator source structure is not known. We give suggestions for calibration strategies and choice of calibrator sources, and describe the access to the online catalogue and data products.
The Sun’s activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high ...to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).
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