A first detection of terrestrial gravity noise in gravitational-wave detectors is a formidable challenge. With the help of environmental sensors, it can in principle be achieved before the noise ...becomes dominant by estimating correlations between environmental sensors and the detector. The main complication is to disentangle different coupling mechanisms between the environment and the detector. In this paper, we analyze the relations between physical couplings and correlations that involve ground motion and LIGO strain data h(t) recorded during its second science run in 2016 and 2017. We find that all noise correlated with ground motion was more than an order of magnitude lower than dominant low-frequency instrument noise, and the dominant coupling over part of the spectrum between ground and h(t) was residual coupling through the seismic-isolation system. We also present the most accurate gravitational coupling model so far based on a detailed analysis of data from a seismic array. Despite our best efforts, we were not able to unambiguously identify gravitational coupling in the data, but our improved models confirm previous predictions that gravitational coupling might already dominate linear ground-to-h(t) coupling over parts of the low-frequency, gravitational-wave observation band.
The Laser Interferometer Gravitational Wave Observatory (LIGO) has been directly detecting gravitational waves from compact binary mergers since 2015. We report on the first use of squeezed vacuum ...states in the direct measurement of gravitational waves with the Advanced LIGO H1 and L1 detectors. This achievement is the culmination of decades of research to implement squeezed states in gravitational-wave detectors. During the ongoing O3 observation run, squeezed states are improving the sensitivity of the LIGO interferometers to signals above 50 Hz by up to 3 dB, thereby increasing the expected detection rate by 40% (H1) and 50% (L1).
We report on the spectral analysis of individual terrestrial gamma‐ray flashes (TGFs) observed with the Fermi Gamma‐ray Burst Monitor (GBM). The large GBM TGF sample provides 46 events suitable for ...individual spectral analysis: sufficiently bright, localized by ground‐based radio, and with the gamma rays reaching a detector unobstructed. These TGFs exhibit diverse spectral characteristics that are hidden when using summed analysis methods. We account for the low counts in individual TGFs by using Poisson likelihood, and we also consider instrumental effects. The data are fit with models obtained from Monte Carlo simulations of the large‐scale Relativistic Runaway Electron Avalanche (RREA) model, including propagation through the atmosphere. Source altitudes ranging from 11.6 to 20.2 km are simulated. Two beaming geometries were considered: In one, the photons retain the intrinsic distribution from scattering (narrow), and in the other, the photons are smeared into a wider beam (wide). Several TGFs are well fit only by narrow‐beam models, while others favor wide‐beam models. Large‐scale RREA models can accommodate both narrow and wide beams, with narrow beams suggest large‐scale RREA in organized electric fields while wide beams may imply converging or diverging electric fields. Wide beams are also consistent with acceleration in the electric fields of lightning leaders, but the TGFs that favor narrow‐beam models appear inconsistent with some lightning leader models.
Key Points
Spectral analysis of individual TGFs is done
Individual TGFs exhibit spectral diversity
Constraints on TGF source properties are obtained
We have done a thorough simulation analysis on the variability of the photon spectra produced with (due to Relativistic Runaway Electron Avalanche—RREA) and without (Modification of Spectra) the ...avalanche multiplication process. Despite some measurements obviously showing a variability of the spectra, numerous theoretical studies consider RREA spectrum independent on the electric field. However, analytical calculations by Cramer et al. (2014) have shown that RREA spectrum under low electric fields is not constant and stops being exponential. Using the Relativistic Electron Avalanche Model code, we model various layouts of the electric field configuration and study the predicted photon spectra. The primary focus of the present paper is to study the photon energy spectra, as gamma rays are more often observed by ground‐based detectors. The simulation analysis of photon spectra potentially can help to deduce electric fields in thunderclouds.
Key Points
Photon spectra show a variability near the runaway threshold value of the electric field
We estimate the spectral hardness ratio and intensity dependence on the electric field in thunderclouds
The variability of the photon spectra means that spectral measurements contain important information on atmospheric electric fields
The Gamma‐ray Burst Monitor (GBM) onboard the Fermi spacecraft has observed many tens of sufficiently bright events, which are suitable for individual analysis. In our previous study, we fit ...individual, bright terrestrial gamma‐ray flashes (TGFs) with Relativistic Runaway Electron Avalanche (RREA) models for the first time. For relativistic‐feedback‐based models, the TGF‐producing electrons, which are seeded internally by a positive feedback effect, are usually accelerated in a large‐scale field with fully developed RREAs. Alternatively, lightning leader models may apply to either a large‐scale thunderstorm fields with fully developed RREAs or to inhomogeneous fields in front of lightning leaders where RREAs only develop partially. The predictions of the latter, inhomogeneous models for the TGF‐beaming geometry show some differences from estimations of the relativistic feedback models in homogeneous fields. In this work, we analyze a large sample of 66 bright Fermi GBM TGFs in the framework of lightning leader models, making comparisons with previous results from the homogeneous‐field RREA models. In most cases, the spectral analysis does not strongly favor one mechanism over the other, with 59% of the TGF events being best fit with the fully developed RREA mechanism, which corresponds to high‐potential leader models. The majority of the GBM‐measured TGFs can be best fit if the source altitude is below 15 km and 70% of events best fit by leader models cannot be satisfactorily modeled unless a tilted photon beam is used. For several spectrally soft TGFs, the tilted beam low‐potential leader model can best fit the data.
Key Points
Fermi GBM individual TGF spectra are analyzed using lightning leader models of various leader potentials, beaming tilts, and source altitudes
Lightning leader models with potentials of 200 MV and tilted beams often best fit the data
A few, exceptionally soft TGFs can be well explained using 60‐MV lightning leaders with tilted beams
Controversy exists as to whether the threshold for blood pressure-lowering treatment should differ between people with and without type 2 diabetes. We aimed to investigate the effects of blood ...pressure-lowering treatment on the risk of major cardiovascular events by type 2 diabetes status, as well as by baseline levels of systolic blood pressure.
We conducted a one-stage individual participant-level data meta-analysis of major randomised controlled trials using the Blood Pressure Lowering Treatment Trialists' Collaboration dataset. Trials with information on type 2 diabetes status at baseline were eligible if they compared blood pressure-lowering medications versus placebo or other classes of blood pressure-lowering medications, or an intensive versus a standard blood pressure-lowering strategy, and reported at least 1000 persons-years of follow-up in each group. Trials exclusively on participants with heart failure or with short-term therapies and acute myocardial infarction or other acute settings were excluded. We expressed treatment effect per 5 mm Hg reduction in systolic blood pressure on the risk of developing a major cardiovascular event as the primary outcome, defined as the first occurrence of fatal or non-fatal stroke or cerebrovascular disease, fatal or non-fatal ischaemic heart disease, or heart failure causing death or requiring hospitalisation. Cox proportional hazard models, stratified by trial, were used to estimate hazard ratios (HRs) separately by type 2 diabetes status at baseline, with further stratification by baseline categories of systolic blood pressure (in 10 mm Hg increments from <120 mm Hg to ≥170 mm Hg). To estimate absolute risk reductions, we used a Poisson regression model over the follow-up duration. The effect of each of the five major blood pressure-lowering drug classes, including angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, β blockers, calcium channel blockers, and thiazide diuretics, was estimated using a network meta-analysis framework. This study is registered with PROSPERO, CRD42018099283.
We included data from 51 randomised clinical trials published between 1981 and 2014 involving 358 533 participants (58% men), among whom 103 325 (29%) had known type 2 diabetes at baseline. The baseline mean systolic/diastolic blood pressure of those with and without type 2 diabetes was 149/84 mm Hg (SD 19/11) and 153/88 mm Hg (SD 21/12), respectively. Over 4·2 years median follow-up (IQR 3·0–5·0), a 5 mm Hg reduction in systolic blood pressure decreased the risk of major cardiovascular events in both groups, but with a weaker relative treatment effect in participants with type 2 diabetes (HR 0·94 95% CI 0·91–0·98) compared with those without type 2 diabetes (0·89 0·87–0·92; pinteraction=0·0013). However, absolute risk reductions did not differ substantially between people with and without type 2 diabetes because of the higher absolute cardiovascular risk among participants with type 2 diabetes. We found no reliable evidence for heterogeneity of treatment effects by baseline systolic blood pressure in either group. In keeping with the primary findings, analysis using stratified network meta-analysis showed no evidence that relative treatment effects differed substantially between participants with type 2 diabetes and those without for any of the drug classes investigated.
Although the relative beneficial effects of blood pressure reduction on major cardiovascular events were weaker in participants with type 2 diabetes than in those without, absolute effects were similar. The difference in relative risk reduction was not related to the baseline blood pressure or allocation to different drug classes. Therefore, the adoption of differential blood pressure thresholds, intensities of blood pressure lowering, or drug classes used in people with and without type 2 diabetes is not warranted.
British Heart Foundation, UK National Institute for Health Research, and Oxford Martin School.
High-quality optical resonant cavities require low optical loss, typically on the scale of parts per million. However, unintended micron-scale contaminants on the resonator mirrors that absorb the ...light circulating in the cavity can deform the surface thermoelastically and thus increase losses by scattering light out of the resonant mode. The point absorber effect is a limiting factor in some high-power cavity experiments, for example, the Advanced LIGO gravitational-wave detector. In this Letter, we present a general approach to the point absorber effect from first principles and simulate its contribution to the increased scattering. The achievable circulating power in current and future gravitational-wave detectors is calculated statistically given different point absorber configurations. Our formulation is further confirmed experimentally in comparison with the scattered power in the arm cavity of Advanced LIGO measured by in situ photodiodes. The understanding presented here provides an important tool in the global effort to design future gravitational-wave detectors that support high optical power and thus reduce quantum noise.
In this study, we analyze 44 terrestrial gamma‐ray flashes (TGFs) detected by the Fermi Gamma‐ray Burst Monitor (GBM) occurring in 2014–2016 in conjunction with data from the U.S. National Lightning ...Detection Network (NLDN). We examine the characteristics of magnetic field waveforms measured by NLDN sensors for 61 pulses that occurred within 5 ms of the start‐time of the TGF photon flux. For 21 (out of 44) TGFs, the associated NLDN pulse occurred almost simultaneously with (that is, within 200 μs of) the TGF. One TGF had two NLDN pulses within 200 μs. The median absolute time interval between the beginning of these near‐simultaneous pulses and the TGF flux start‐time is 50 μs. We speculate that these RF pulses are signatures of either TGF‐associated relativistic electron avalanches or currents traveling in conducting paths “preconditioned” by TGF‐associated electron beams. Compared to pulses that were not simultaneous with TGFs (but within 5 ms of one), simultaneous pulses had higher median absolute peak current (26 kA versus 11 kA), longer median threshold‐to‐peak rise time (14 μs versus 2.8 μs), and longer median peak‐to‐zero time (15 μs versus 5.5 μs). A majority (77%) of our simultaneous RF pulses had NLDN‐estimated peak currents less than 50 kA indicating that TGF emissions can be associated with moderate‐peak‐amplitude processes. The lightning flash associated with one of the TGFs in our data set was observed by a Lightning Mapping Array, which reported a relatively high‐power source at an altitude of 25 km occurring 101 μs after the GBM‐reported TGF discovery‐bin start‐time.
Key Points
TGF‐associated RF pulses have a wide range of NLDN‐estimated peak currents, which are proportional to their magnetic field peak amplitudes
Median rise time and peak‐to‐zero time for TGF‐simultaneous RF pulses were significantly longer than those for nonsimultaneous pulses
A TGF that was associated with relatively high‐power VHF radiation is described in detail
Simplified equations describing the transport and energy spectrum of runaway electrons are derived from the basic kinematics of the continuity equations. These equations are useful in modeling the ...energy distribution of energetic electrons in strong electric fields, such as those found inside thunderstorms. Dwyer and Babich (2011) investigated the generation of low‐energy electrons in relativistic runaway electron avalanches. The paper also developed simple analytical expressions to describe the detailed physics of Monte Carlo simulations of relativistic runaway electrons in air. In the current work, the energy spectra of the runaway electron population are studied in detail. Dependence of electron avalanche development on properties such as the avalanche length, radiation length, and the effective Møller scattering efficiency factor are discussed in detail. To describe the shapes of the electron energy spectra for a wide range of electric field strengths, the diffusion term responsible for random deviation of electron energy ionization loss from the mean value is added to the kinetic equation. We find that the diffusion in energy space helps maintain an exponential energy spectrum for electric fields that approach the runaway electron threshold field.
Key Points
New theoretical investigation into runaway electron physicsEquations can be used to model electron energy spectraEnergy space diffusion maintains an exponential energy spectrum near threshold
This paper explores the impact of the geomagnetic field on the relativistic runaway electron avalanche length,
λe−. Coleman and Dwyer (2006) developed an analytical fit to Monte Carlo simulations ...using the Runaway Electron Avalanche Model. In this work, we repeat this process but with the addition of the geomagnetic field in the range of 100,900/n μT, where n is the ratio of the density of air at altitude to the sea level density. As the ambient electric field approaches the runaway threshold field (Eth≈284 kV/m sea level equivalent), it is shown that the magnetic field has an impact on the orientation of the resulting electron beam. The runaway electrons initially follow the vertically oriented electric field but then are deflected in the v × B direction, and as such, the electrons experience more dynamic friction due to the increase in path length. This will be shown to result in a difference in the avalanche length from the case where B = 0. It will also be shown that the average energy of the runaway electrons will decrease while the required electric field to produce runaway electrons increases. This study is also important in understanding the physics of terrestrial gamma ray flashes (TGFs). Not only will this work impact relativistic feedback rates determined from simulations, it may also be useful in studying spectroscopy of TGFs observed from balloon and aircraft measurements. These models may also be used in determining beaming properties of TGFs originating in the tropical regions seen from orbiting spacecraft.
Key Points
An empirical relation for the runaway electron avalanche length is found when a magnetic field is introduced
The runaway electron threshold electric field is modified by the magnetic field and on average increases the break‐even value by 42%
Electron beams may experience tilts up to 18 degrees, which could possibly be detectable by future spacecraft measurements
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