We have analyzed theoretically and experimentally the linewidth of the first harmonic of the photocurrent (radio-frequency (RF) linewidth) in monolithic passively mode-locked semiconductor lasers. ...Due to the absence of restoring force, the timing jitter is directly related to the RF linewidth, avoiding possible underestimations made with conventional methods of phase noise measurement. The RF linewidth is also analytically related to the pulse characteristics using Haus's model. The timing stability performance of a promising two-section quantum-dot laser is presented using RF linewidth measurements. Experimental evolution of the RF linewidth with power and pulsewidth is finally compared to the analytical expression.
The “en caul” technique, i.e. delivery with intact membranes, may reduce the risk of obstetric trauma in vaginal breech delivery of extreme preterm infants. We aimed at comparing perinatal mortality ...and morbidity among extremely preterm breech vaginal deliveries between infants delivered “en caul” and those with “ruptured membranes”.
We performed a fourteen-year retrospective study in a tertiary university center. All vaginal deliveries of singleton breech live infants with an antenatal decision of active resuscitation between 24 weeks and 27+6 weeks were included. Perinatal outcomes were compared between the “en caul” group, with intact membranes at the onset of pushing efforts and the “ruptured membranes” group, with ruptured membranes at the onset of pushing efforts. The primary outcome was perinatal mortality defined by intrapartum or neonatal death. The secondary outcomes were fetal extraction difficulties, arterial pH and 5 min Apgar score.
We included 52 infants in the “en caul” group and 71 in the “ruptured membranes” group. The perinatal mortality rate did not differ between the two groups (19.2% in the “en caul” group versus 28.2% in the “ruptured membranes” group, p = 0.25). The mean arterial pH at birth was higher in the « en caul » group (7.32 ± 0.1 vs 7.24 ± 0.1, p = 0.001). There were no differences between the groups for fetal extraction difficulties, especially fetal head entrapment (9.6% versus 9.9%).
Even though the “en caul” technique does not seem to decrease the perinatal mortality rate, it remains a simple technique, which could improve neonatal morbidity.
An analytical theory is presented for the study of injection locking in multisection semiconductor lasers. The Helmoltz equation for the electric field is solved using the Green's function method and ...the injected fields are included via the boundary conditions. Two cases are distinguished, injection through the front facet of the laser and injection through the rear facet. In both cases, an equation of evolution for the envelope of the electric field is established, taking into account the longitudinal distribution of the carrier and photon densities and the nonlinear gain. The expressions of the intensity, phase and carrier density noise spectra are derived using a matrix formulation. Comparison to classical equations used for Fabry-Perot lasers is discussed. The locking properties of a distributed feedback laser with an antireflection coated front facet are studied in detail. Results demonstrate the strong sensitivity of the locking properties on the phase grating and rear facet reflectivity.
We report on gravitational wave discoveries from compact binary coalescences detected by Advanced LIGO and Advanced Virgo in the first half of the third observing run (O3a) between 1 April 2019 15:00 ...UTC and 1 October 2019 15:00 UTC. By imposing a false-alarm-rate threshold of two per year in each of the four search pipelines that constitute our search, we present 39 candidate gravitational wave events. At this threshold, we expect a contamination fraction of less than 10%. Of these, 26 candidate events were reported previously in near real-time through GCN Notices and Circulars; 13 are reported here for the first time. The catalog contains events whose sources are black hole binary mergers up to a redshift of ~ 0.8, as well as events whose components could not be unambiguously identified as black holes or neutron stars. For the latter group, we are unable to determine the nature based on estimates of the component masses and spins from gravitational wave data alone. The range of candidate event masses which are unambiguously identified as binary black holes (both objects ≥ 3 M⨀) is increased compared to GWTC-1, with total masses from ∼ 14M⨀ for GW190924 021846 to ∼ 150M⨀ for GW190521. For the first time, this catalog includes binary systems with significantly asymmetric mass ratios, which had not been observed in data taken before April 2019. We also find that 11 of the 39 events detected since April 2019 have positive effective inspiral spins under our default prior (at 90% credibility), while none exhibit negative effective inspiral spin. Given the increased sensitivity of Advanced LIGO and Advanced Virgo, the detection of 39 candidate events in ∼26 weeks of data (∼1.5 per week) is consistent with GWTC-1.
The first direct gravitational‐wave detection was made by the Advanced Laser Interferometer Gravitational Wave Observatory on September 14, 2015. The GW150914 signal was strong enough to be apparent, ...without using any waveform model, in the filtered detector strain data. Here, features of the signal visible in the data are analyzed using concepts from Newtonian physics and general relativity, accessible to anyone with a general physics background. The simple analysis presented here is consistent with the fully general‐relativistic analyses published elsewhere, in showing that the signal was produced by the inspiral and subsequent merger of two black holes. The black holes were each of approximately 35M⊙, still orbited each other as close as ∼350 km apart and subsequently merged to form a single black hole. Similar reasoning, directly from the data, is used to roughly estimate how far these black holes were from the Earth, and the energy that they radiated in gravitational waves.
Advanced LIGO made the first gravitational‐wave detection on September 14, 2015. The GW150914 signal was strong enough to be apparent in the cleaned detector strain data. Those features of the signal visible in these data are analyzed, using only such concepts from Newton and general relativity as are accessible to anyone with a general physics background. This simple analysis presented here is consistent with the full published analyses, in showing that the signal was produced by the inspiral and merger of two black holes, and in estimating the distance from the Earth and the energy radiated in gravitational waves.
ABSTRACT This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current ...EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.
PDF
