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Recent documents in Physics Faculty Research & Creative Worksen-usSat, 15 Feb 2020 07:44:10 PST3600The Role of Multiple Ionization of H₂O in Heavy Ion Collisions
https://scholarsmine.mst.edu/phys_facwork/2056
https://scholarsmine.mst.edu/phys_facwork/2056Thu, 16 Jan 2020 14:11:26 PST
Collisional ionization processes involving H_{2}O molecules and C^{6+}, O^{8+}, Si^{13+} ions are studied by means of the classical trajectory Monte Carlo method using molecular orbital calculations to define the ionization stages of the water molecule. Net total and single-differential cross sections in energy and angle are obtained by using a newly developed model that goes beyond the commonly applied one-active electron approximation. This model allows us to access the fraction of electron emission arising from single and multiple electron ionization. Calculated cross sections are contrasted and benchmarked against available experimental data at impact energies in the MeV/u range. The present results highlight the important role of multiple ionization in the emission of electrons where we find the majority of electrons emitted with energies greater than ∼50 eV arise from multiple ionization collisions.
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N. Bachi et al.Lorentz Breaking and SU(2)<sub>L</sub> x U(1)<sub>Y</sub> Gauge Invariance for Neutrinos
https://scholarsmine.mst.edu/phys_facwork/2055
https://scholarsmine.mst.edu/phys_facwork/2055Thu, 16 Jan 2020 14:11:23 PST
Conceivable Lorentz-violating effects in the neutrino sector remain a research area of great general interest, as they touch upon the very foundations on which the Standard Model and our general understanding of fundamental interactions are laid. Here, we investigate the relation of Lorentz violation in the neutrino sector in light of the fact that neutrinos and the corresponding left-handed charged leptons form SU(2)_{L} doublets under the electroweak gauge group. Lorentz-violating effects thus cannot be fully separated from questions related to gauge invariance. The model dependence of the effective interaction Lagrangians used in various recent investigations is explored with a special emphasis on neutrino splitting, otherwise known as the neutrino-pair Cerenkov radiation and vacuum-pair emission (electron-positron-pair Cerenkov radiation). We highlight two scenarios in which Lorentz-violating effects do not necessarily also break electroweak gauge invariance. The first of these involves a restricted set of gauge transformations, a subgroup of SU(2)_{L} x U(1)_{Y}, while in the second where differential Lorentz violation is exclusively introduced by the mixing of the neutrino flavor and mass eigenstates. Our study culminates in a model which fully preserves SU(2)_{L} x U(1)_{Y} gauge invariance, involves flavor-dependent Lorentz-breaking parameters, and still allows for Cerenkov-type decays to proceed.
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Ulrich D. Jentschura et al.Equivalence Principle for Antiparticles and its Limitations
https://scholarsmine.mst.edu/phys_facwork/2054
https://scholarsmine.mst.edu/phys_facwork/2054Thu, 16 Jan 2020 14:11:20 PST
We investigate the particle-antiparticle symmetry of the gravitationally coupled Dirac equation, both on the basis of the gravitational central-field problem and in general curved space-time backgrounds. First, we investigate the central-field problem with the help of a Foldy-Wouthuysen transformation. This disentangles the particle from the antiparticle solutions, and leads to a "matching relation" of the inertial and the gravitational mass, which is valid for both particles as well as antiparticles. Second, we supplement this derivation by a general investigation of the behavior of the gravitationally coupled Dirac equation under the discrete symmetry of charge conjugation, which is tantamount to a particle → antiparticle transformation. Limitations of the Einstein equivalence principle due to quantum fluctuations are discussed. In quantum mechanics, the question of where and when in the Universe an experiment is being performed can only be answered up to the limitations implied by Heisenberg's Uncertainty Principle, questioning an assumption made in the original formulation of the Einstein equivalence principle. Furthermore, at some level of accuracy, it becomes impossible to separate nongravitational from gravitational experiments, leading to further limitations.
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Ulrich D. JentschuraEffect of Grain Boundary Angle on the Thermal Conductivity of Nanostructured Bicrystal ZnO based on the Molecular Dynamics Simulation Method
https://scholarsmine.mst.edu/phys_facwork/2053
https://scholarsmine.mst.edu/phys_facwork/2053Thu, 16 Jan 2020 14:11:17 PST
ZnO is a widely used semiconductor material due to its excellent physical and mechanical properties. The thermal transport behavior across a single grain boundary (GB) of bicrystal ZnO with varying tilt angles from 5.45° to 67.38° was investigated using a nonequilibrium molecular dynamics simulation. The GB energy and Kapitza resistance as a function of tilt angle were determined and parameters of the extended Read-Shockley model were calculated. The Kapitza resistance varied monotonically with a GB angle < 36° and was nearly constant when the angle was > 36°. Furthermore, effective thermal conductivity and Kapitza resistance were found to depend strongly on the sample length and temperature. Finally, we compared the phonon density of states of the two types of GBs and found a mismatch in the low frequency that might explain the effect of the GBs structures on heat conduction.
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Yingguang Liu et al.Jet Geometry and Rate Estimate of Coincident Gamma-Ray Burst and Gravitational-Wave Observations
https://scholarsmine.mst.edu/phys_facwork/2052
https://scholarsmine.mst.edu/phys_facwork/2052Thu, 16 Jan 2020 14:11:14 PST
Short gamma-ray burst (SGRB) progenitors have long been thought to be coalescing binary systems of two neutron stars (NSNS) or a neutron star and a black hole. The 2017 August 17th detection of the GW170817 gravitational-wave (GW) signal by Advanced LIGO and Advanced Virgo in coincidence with the electromagnetic observation of the SGRB GRB 170817A confirmed this scenario and provided new physical information on the nature of these astronomical events. We use SGRB observations by the Neil Gehrels Swift Observatory Burst Alert Telescope and GW170817/GRB 170817A observational data to estimate the detection rate of coincident GW and electromagnetic observations by a GW detector network and constrain the physical parameters of the SGRB jet structure. We estimate the rate of GW detections coincident with SGRB electromagnetic detections by the Fermi Gamma-ray Burst Monitor to be between ~0.1 and ~0.6 yr^{-1} in the third LIGO-Virgo observing run and between ~0.3 and ~1.8 yr^{-1} for the LIGO-Virgo-KAGRA network at design sensitivity. Assuming a structured model with a uniform ultrarelativistic jet surrounded by a region with power-law decay emission, we find the jet half-opening angle and the power-law decay exponent to be θ_{c} ~ 7°-22° and s ~ 5-30 at a 1σ confidence level, respectively.
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Kentaro Mogushi et al.Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo
https://scholarsmine.mst.edu/phys_facwork/2051
https://scholarsmine.mst.edu/phys_facwork/2051Thu, 16 Jan 2020 14:11:10 PST
We present results on the mass, spin, and redshift distributions with phenomenological population models using the 10 binary black hole (BBH) mergers detected in the first and second observing runs completed by Advanced LIGO and Advanced Virgo. We constrain properties of the BBH mass spectrum using models with a range of parameterizations of the BBH mass and spin distributions. We find that the mass distribution of the more massive BH in such binaries is well approximated by models with no more than 1% of BHs more massive than 45 M_{⊙} and a power-law index of α = 1.3^{+1.4}-_{1.7} (90% credibility). We also show that BBHs are unlikely to be composed of BHs with large spins aligned to the orbital angular momentum. Modeling the evolution of the BBH merger rate with redshift, we show that it is flat or increasing with redshift with 93% probability. Marginalizing over uncertainties in the BBH population, we find robust estimates of the BBH merger rate density of R= 53.2^{+55.8}_{-28.2} Gpc^{-3} yr^{-1}(90% credibility). As the BBH catalog grows in future observing runs, we expect that uncertainties in the population model parameters will shrink, potentially providing insights into the formation of BHs via supernovae, binary interactions of massive stars, stellar cluster dynamics, and the formation history of BHs across cosmic time.
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B. P. Abbott et al.The Role of Multiple Electron Processes for Fast Ion H₂O Collisions
https://scholarsmine.mst.edu/phys_facwork/2050
https://scholarsmine.mst.edu/phys_facwork/2050Thu, 16 Jan 2020 14:11:07 PST
In this work, collision processes between C^{6+}, O^{8+} and Si^{13+} ions and H_{2}O molecules that lead to target ionization are studied by means of the classical trajectory Monte Carlo method. We employ an 8-electron model in which the H_{2}O electron densities and energies dynamically adapt during ionization processes to those corresponding to the H_{2}O^{q+} ions by assuming vertical transitions between the different molecular ionic states. Net total ionization cross sections and single differential cross sections in energy and angle are shown for 4 MeV/u projectiles and compared to available experimental data and theoretical predictions from distorted wave models.
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N. Bachi et al.The Conundrum of Relaxation Volumes in First-Principles Calculations of Charged Defects in UO₂
https://scholarsmine.mst.edu/phys_facwork/2049
https://scholarsmine.mst.edu/phys_facwork/2049Thu, 16 Jan 2020 14:11:04 PST
The defect relaxation volumes obtained from density-functional theory (DFT) calculations of charged vacancies and interstitials are much larger than their neutral counterparts, seemingly unphysically large. We focus on UO2 as our primary material of interest, but also consider Si and GaAs to reveal the generality of our results. In this work, we investigate the possible reasons for this and revisit the methods that address the calculation of charged defects in periodic DFT. We probe the dependence of the proposed energy corrections to charged defect formation energies on relaxation volumes and find that corrections such as potential alignment remain ambiguous with regards to its contribution to the charged defect relaxation volume. We also investigate the volume for the net neutral defect reactions comprising individual charged defects, and find that the aggregate formation volumes have reasonable magnitudes. This work highlights the issue that, as is well-known for defect formation energies, the defect formation volumes depend on the choice of reservoir. We show that considering the change in volume of the electron reservoir in the formation reaction of the charged defects, analogous to how volumes of atoms are accounted for in defect formation volumes, can renormalize the formation volumes of charged defects such that they are comparable to neutral defects. This approach enables the description of the elastic properties of isolated charged defects within an overall neutral material.
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Anuj Goyal et al.Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1
https://scholarsmine.mst.edu/phys_facwork/2048
https://scholarsmine.mst.edu/phys_facwork/2048Thu, 16 Jan 2020 14:11:01 PST
The detection of gravitational waves by Advanced LIGO and Advanced Virgo provides an opportunity to test general relativity in a regime that is inaccessible to traditional astronomical observations and laboratory tests. We present four tests of the consistency of the data with binary black hole gravitational waveforms predicted by general relativity. One test subtracts the best-fit waveform from the data and checks the consistency of the residual with detector noise. The second test checks the consistency of the low- and high-frequency parts of the observed signals. The third test checks that phenomenological deviations introduced in the waveform model (including in the post-Newtonian coefficients) are consistent with 0. The fourth test constrains modifications to the propagation of gravitational waves due to a modified dispersion relation, including that from a massive graviton. We present results both for individual events and also results obtained by combining together particularly strong events from the first and second observing runs of Advanced LIGO and Advanced Virgo, as collected in the catalog GWTC-1. We do not find any inconsistency of the data with the predictions of general relativity and improve our previously presented combined constraints by factors of 1.1 to 2.5. In particular, we bound the mass of the graviton to be m_{g} ≤ 4.7 x 10^{-23} eV/c^{2} (90% credible level), an improvement of a factor of 1.6 over our previously presented results. Additionally, we check that the four gravitational-wave events published for the first time in GWTC-1 do not lead to stronger constraints on alternative polarizations than those published previously.
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B. P. Abbott et al.Search for the Isotropic Stochastic Background using Data from Advanced LIGO's Second Observing Run
https://scholarsmine.mst.edu/phys_facwork/2047
https://scholarsmine.mst.edu/phys_facwork/2047Thu, 16 Jan 2020 14:10:58 PST
The stochastic gravitational-wave background is a superposition of sources that are either too weak or too numerous to detect individually. In this study, we present the results from a cross-correlation analysis on data from Advanced LIGO's second observing run (O2), which we combine with the results of the first observing run (O1). We do not find evidence for a stochastic background, so we place upper limits on the normalized energy density in gravitational waves at the 95% credible level of Ω_{GW} < 6.0 x 10^{-8} for a frequency-independent (flat) background and Ω_{GW} < 4.8 x 10^{-8} at 25 Hz for a background of compact binary coalescences. The upper limit improves over the O1 result by a factor of 2.8. Additionally, we place upper limits on the energy density in an isotropic background of scalar- and vector-polarized gravitational waves, and we discuss the implication of these results for models of compact binaries and cosmic string backgrounds. Finally, we present a conservative estimate of the correlated broadband noise due to the magnetic Schumann resonances in O2, based on magnetometer measurements at both the LIGO Hanford and LIGO Livingston observatories. We find that correlated noise is well below the O2 sensitivity.
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B. P. Abbott et al.Search for Intermediate Mass Black Hole Binaries in the First and Second Observing Runs of the Advanced LIGO and Virgo Network
https://scholarsmine.mst.edu/phys_facwork/2046
https://scholarsmine.mst.edu/phys_facwork/2046Thu, 16 Jan 2020 14:10:55 PST
Gravitational-wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar-mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational-wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event is detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses M = m_{1} + m_{2} ∈ [120,800] M_{⊙} and mass ratios q = m_{2}/m_{1} ∈ [0.1,1.0]. For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of 0.20 Gpc^{-3} yr^{-1} (in comoving units at the 90% confidence level) for equal-mass binaries with individual masses m^{1,2} = 100 M_{⊙} and dimensionless spins X^{1,2} = 0.8 aligned with the orbital angular momentum of the binary. This improves by a factor of ~5 that reported after Advanced LIGO's first observing run.
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B. P. Abbott et al.Search for Gravitational Waves from Scorpius X-1 in the Second Advanced LIGO Observing Run with an Improved Hidden Markov Model
https://scholarsmine.mst.edu/phys_facwork/2045
https://scholarsmine.mst.edu/phys_facwork/2045Thu, 16 Jan 2020 14:10:52 PST
We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h_{0}^{95%} = 3.47 x 10^{-25} when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering.
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B. P. Abbott et al.Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during their First and Second Observing Runs
https://scholarsmine.mst.edu/phys_facwork/2044
https://scholarsmine.mst.edu/phys_facwork/2044Thu, 16 Jan 2020 14:10:49 PST
When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳ 100 Gpc^{-3} yr^{-1} for e > 0.1, assuming a black hole mass spectrum with a power-law index ≲2.
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B. P. Abbott et al.Neutrino Splitting for Lorentz-Violating Neutrinos: Detailed Analysis
https://scholarsmine.mst.edu/phys_facwork/2043
https://scholarsmine.mst.edu/phys_facwork/2043Thu, 16 Jan 2020 14:10:46 PST
Lorentz-violating neutrino parameters have been severely constrained on the basis of astrophysical considerations. In the high-energy limit, one generally assumes a superluminal dispersion relation of an incoming neutrino of the form E≈ |p ⃗|v , where E is the energy, p ⃗ is the momentum and v ₌ √(1+ δ) > 1. Lepton-pair creation due to a Cerenkov-radiation-like process (ν → ν + е^{-}+e^{+}) becomes possible above a certain energy threshold, and bounds on the Lorentz-violating parameter δ can be derived. Here, we investigate a related process, ν_{i}→ ν_{i}+ ν_{f}+ ν ‾_{f}, where ν_{i} is an incoming neutrino mass eigenstate, while ν_{f} is the final neutrino mass eigenstate, with a superluminal velocity that is slightly slower than that of the initial state. This process is kinematically allowed if the Lorentz-violating parameters at high energy differ for the different neutrino mass eigenstates. Neutrino splitting is not subject to any significant energy threshold condition and could yield quite a substantial contribution to decay and energy loss processes at high energy, even if the differential Lorentz violation among neutrino flavors is severely constrained by other experiments. We also discuss the SU(2)L-gauge invariance of the superluminal models and briefly discuss the use of a generalized vierbein formalism in the formulation of the Lorentz-violating Dirac equation.
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G. Somogyi et al.Local Orbital Degeneracy Lifting as a Precursor to an Orbital-Selective Peierls Transition
https://scholarsmine.mst.edu/phys_facwork/2042
https://scholarsmine.mst.edu/phys_facwork/2042Thu, 16 Jan 2020 14:10:43 PST
Fundamental electronic principles underlying all transition metal compounds are the symmetry and filling of the d-electron orbitals and the influence of this filling on structural configurations and responses. Here we use a sensitive local structural technique, x-ray atomic pair distribution function analysis, to reveal the presence of fluctuating local-structural distortions at high temperature in one such compound, CuIr_{2}S_{4}. We show that this hitherto overlooked fluctuating symmetry-lowering is electronic in origin and will modify the energy-level spectrum and electronic and magnetic properties. The explanation is a local, fluctuating, orbital-degeneracy-lifted state. The natural extension of our result would be that this phenomenon is likely to be widespread amongst diverse classes of partially filled nominally degenerate d-electron systems, with potentially broad implications for our understanding of their properties.
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E. S. Bozin et al.Lattice Thermal Conductivity of Quartz at High Pressure and Temperature from the Boltzmann Transport Equation
https://scholarsmine.mst.edu/phys_facwork/2041
https://scholarsmine.mst.edu/phys_facwork/2041Thu, 16 Jan 2020 14:10:40 PST
The thermal conductivities along the basal and hexagonal directions of α-quartz silica, the low-temperature form of crystalline SiO_{2}, are predicted from the solution of the Boltzmann transport equation combined with the van Beest, Kramer, and van Santen potential for the temperature up to 900 K and the pressure as high as 4 GPa. The thermal conductivities at atmospheric pressure, which show a negative and nonlinear dependence on temperature, are in reasonable agreement with the experimental data. The influence of pressure on thermal conductivity is positive and linear. The pressure (P) and temperature (T) dependences of the thermal conductivity (λ) in basal and hexagonal directions are fitted to a function of the form λ = (b + cP) T^{a}. The thermal conductivity, influenced by temperature and pressure, is analyzed based on phonon properties, including spectral thermal conductivity, dispersion relation, phonon density of states, phonon lifetime, and phonon probability density distribution function.
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Xue Xiong et al.GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs
https://scholarsmine.mst.edu/phys_facwork/2040
https://scholarsmine.mst.edu/phys_facwork/2040Thu, 16 Jan 2020 14:10:36 PST
We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 Ma™ during the first and second observing runs of the advanced gravitational-wave detector network. During the first observing run (O1), from September 12, 2015 to January 19, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30, 2016 to August 25, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818, and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties.
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B. P. Abbott et al.Erratum: Searches for Gravitational Waves from Known Pulsars at Two Harmonics in 2015-2017 LIGO Data (Astrophysical Journal (2019) 879 (10) DOI: 10.3847/1538-4357/Ab20cb)
https://scholarsmine.mst.edu/phys_facwork/2039
https://scholarsmine.mst.edu/phys_facwork/2039Thu, 16 Jan 2020 14:10:33 PST
Due to an error at the publisher, in the published article the number of pulsars presented in the paper is incorrect in multiple places throughout the text. Specifically, "222" pulsars should be "221." Additionally, the number of pulsars for which we have EM observations that fully overlap with O1 and O2 changes from "168" to "167." Elsewhere, in the machine-readable table of Table 1 and in Table 2, the row corresponding to pulsar J0952-0607 should be excised as well. Finally, in the caption for Table 2 the number of pulsars changes from "188" to "187." IOP Publishing sincerely regrets this error.
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B. P. Abbott et al.Directional Limits on Persistent Gravitational Waves using Data from Advanced LIGO's First Two Observing Runs
https://scholarsmine.mst.edu/phys_facwork/2038
https://scholarsmine.mst.edu/phys_facwork/2038Thu, 16 Jan 2020 14:10:30 PST
We perform an unmodeled search for persistent, directional gravitational wave (GW) sources using data from the first and second observing runs of Advanced LIGO. We do not find evidence for any GW signals. We place limits on the broadband GW flux emitted at 25 Hz from point sources with a power law spectrum at F_{α,Θ} < (0.05-25) x 10^{−8} erg cm^{−2} s^{−1} Hz^{−1} and the (normalized) energy density spectrum in GWs at 25 Hz from extended sources at Ω_{α}(Θ) < (0.19-2.89) x 10^{−8} sr^{−1} where α is the spectral index of the energy density spectrum. These represent improvements of 2.5-3x over previous limits. We also consider point sources emitting GWs at a single frequency, targeting the directions of Sco X-1, SN 1987A, and the Galactic center. The best upper limits on the strain amplitude of a potential source in these three directions range from h_{0} < (3.6-4.7) x 10^{−25}, 1.5x better than previous limits set with the same analysis method.We also report on a marginally significant outlier at 36.06 Hz. This outlier is not consistent with a persistent gravitational-wave source as its significance diminishes when combining all of the available data.
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B. P. Abbott et al.Angular Memory Effect of Transmission Eigenchannels
https://scholarsmine.mst.edu/phys_facwork/2037
https://scholarsmine.mst.edu/phys_facwork/2037Thu, 16 Jan 2020 14:10:27 PST
The optical memory effect has emerged as a powerful tool for imaging through multiple-scattering media; however, the finite angular range of the memory effect limits the field of view. Here, we demonstrate experimentally that selective coupling of incident light into a high-transmission channel increases the angular memory-effect range. This enhancement is attributed to the robustness of the high-transmission channels against perturbations such as sample tilt or wave front tilt. Our work shows that the high-transmission channels provide an enhanced field of view for memory-effect-based imaging through diffusive media.
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Hasan Yllmaz et al.