734 research outputs found
Classifying the unknown: discovering novel gravitational-wave detector glitches using similarity learning
The observation of gravitational waves from compact binary coalescences by
LIGO and Virgo has begun a new era in astronomy. A critical challenge in making
detections is determining whether loud transient features in the data are
caused by gravitational waves or by instrumental or environmental sources. The
citizen-science project \emph{Gravity Spy} has been demonstrated as an
efficient infrastructure for classifying known types of noise transients
(glitches) through a combination of data analysis performed by both citizen
volunteers and machine learning. We present the next iteration of this project,
using similarity indices to empower citizen scientists to create large data
sets of unknown transients, which can then be used to facilitate supervised
machine-learning characterization. This new evolution aims to alleviate a
persistent challenge that plagues both citizen-science and instrumental
detector work: the ability to build large samples of relatively rare events.
Using two families of transient noise that appeared unexpectedly during LIGO's
second observing run (O2), we demonstrate the impact that the similarity
indices could have had on finding these new glitch types in the Gravity Spy
program
One Channel to Rule Them All? Constraining the Origins of Binary Black Holes using Multiple Formation Pathways
The second LIGO-Virgo catalog of gravitational wave transients has more than
quadrupled the observational sample of binary black holes. We analyze this
catalog using a suite of five state-of-the-art binary black hole population
models covering a range of isolated and dynamical formation channels and infer
branching fractions between channels as well as constraints on uncertain
physical processes that impact the observational properties of mergers. Given
our set of formation models, we find significant differences between the
branching fractions of the underlying and detectable populations, and that the
diversity of detections suggests that multiple formation channels are at play.
A mixture of channels is strongly preferred over any single channel dominating
the detected population: an individual channel does not contribute to more than
of the observational sample of binary black holes. We calculate
the preference between the natal spin assumptions and common envelope
efficiencies in our models, favoring natal spins of isolated black holes of
, and marginally preferring common envelope efficiencies of
while strongly disfavoring highly inefficient common envelopes.
We show that it is essential to consider multiple channels when interpreting
gravitational wave catalogs, as inference on branching fractions and physical
prescriptions becomes biased when contributing formation scenarios are not
considered or incorrect physical prescriptions are assumed. Although our
quantitative results can be affected by uncertain assumptions in model
predictions, our methodology is capable of including models with updated
theoretical considerations and additional formation channels.Comment: 27 pages (14 pages main text + 13 pages appendices/references), 8
figures, 1 table, published in Ap
Elastic Spin Relaxation Processes in Semiconductor Quantum Dots
Electron spin decoherence caused by elastic spin-phonon processes is
investigated comprehensively in a zero-dimensional environment. Specifically, a
theoretical treatment is developed for the processes associated with the
fluctuations in the phonon potential as well as in the electron procession
frequency through the spin-orbit and hyperfine interactions in the
semiconductor quantum dots. The analysis identifies the conditions (magnetic
field, temperature, etc.) in which the elastic spin-phonon processes can
dominate over the inelastic counterparts with the electron spin-flip
transitions. Particularly, the calculation results illustrate the potential
significance of an elastic decoherence mechanism originating from the
intervalley transitions in semiconductor quantum dots with multiple equivalent
energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity
and phonon decay in spin relaxation is also examined along with that of the
local effective field fluctuations caused by the stochastic electronic
transitions between the orbital states. Numerical estimations are provided for
typical GaAs and Si-based quantum dots.Comment: 57 pages, 14 figure
Black Hole Mergers from Hierarchical Triples in Dense Star Clusters
Hierarchical triples are expected to be produced by the frequent binary-mediated interactions in the cores of globular clusters. In some of these triples, the tertiary companion can drive the inner binary to merger following large eccentricity oscillations, as a result of the eccentric KozaiâLidov mechanism. In this paper, we study the dynamics and merger rates of black hole (BH) hierarchical triples, formed via binaryâbinary encounters in the CMC Cluster Catalog, a suite of cluster simulations with present-day properties representative of the Milky Way's globular clusters. We compare the properties of the mergers from triples to the other merger channels in dense star clusters, and show that triple systems do not produce significant differences in terms of mass and effective spin distribution. However, they represent an important pathway for forming eccentric mergers, which could be detected by LIGOâVirgo/Kamioka Gravitational-Wave Detector (LVK), and future missions such as LISA and the DECi-hertz Interferometer Gravitational wave Observatory. We derive a conservative lower limit for the merger rate from this channel of 0.35 Gpcâ»Âł yrâ»Âč in the local universe and up to ~9% of these events may have a detectable eccentricity at LVK design sensitivity. Additionally, we find that triple systems could play an important role in retaining second-generation BHs, which can later merge again in the core of the host cluster
Stress Priming in Reading and the Selective Modulation of Lexical and Sub-Lexical Pathways
Four experiments employed a priming methodology to investigate different mechanisms of stress assignment and how they are modulated by lexical and sub-lexical mechanisms in reading aloud in Italian. Lexical stress is unpredictable in Italian, and requires lexical look-up. The most frequent stress pattern (Dominant) is on the penultimate syllable [laVOro (work)], while stress on the antepenultimate syllable [MAcchina (car)] is relatively less frequent (non-Dominant). Word and pseudoword naming responses primed by words with non-dominant stress â which require whole-word knowledge to be read correctly â were compared to those primed by nonwords. Percentage of errors to words and percentage of dominant stress responses to nonwords were measured. In Experiments 1 and 2 stress errors increased for non-dominant stress words primed by nonwords, as compared to when they were primed by words. The results could be attributed to greater activation of sub-lexical codes, and an associated tendency to assign the dominant stress pattern by default in the nonword prime condition. Alternatively, they may have been the consequence of prosodic priming, inducing more errors on trials in which the stress pattern of primes and targets was not congruent. The two interpretations were investigated in Experiments 3 and 4. The results overall suggested a limited role of the default metrical pattern in word pronunciation, and showed clear effect of prosodic priming, but only when the sub-lexical mechanism prevailed
Kondo Effect in a Metal with Correlated Conduction Electrons: Diagrammatic Approach
We study the low-temperature behavior of a magnetic impurity which is weakly
coupled to correlated conduction electrons. To account for conduction electron
interactions a diagrammatic approach in the frame of the 1/N expansion is
developed. The method allows us to study various consequences of the conduction
electron correlations for the ground state and the low-energy excitations. We
analyse the characteristic energy scale in the limit of weak conduction
electron interactions. Results are reported for static properties (impurity
valence, charge susceptibility, magnetic susceptibility, and specific heat) in
the low-temperature limit.Comment: 16 pages, 9 figure
A time-varying inertia pendulum: Analytical modelling and experimental identification
In this paper two of the main sources of non-stationary dynamics, namely the time-variability and the presence of nonlinearity, are analysed through the analytical and experimental study of a time-varying inertia pendulum. The pendulum undergoes large swinging amplitudes, so that its equation of motion is definitely nonlinear, and hence becomes a nonlinear time-varying system. The analysis is carried out through two subspace-based techniques for the identification of both the linear time-varying system and the nonlinear system. The flexural and the nonlinear swinging motions of the pendulum are uncoupled and are considered separately: for each of them an analytical model is built for comparisons and the identification procedures are developed. The results demonstrate that a good agreement between the predicted and the identified frequencies can be achieved, for both the considered motions. In particular, the estimates of the swinging frequency are very accurate for the entire domain of possible configurations, in terms of swinging amplitude and mass positio
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