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  • 1
    In: Classical and Quantum Gravity, IOP Publishing, Vol. 37, No. 21 ( 2020-11-05), p. 215015-
    Abstract: The Advanced LIGO gravitational-wave detectors are limited by optical quantum noise in most of their detection band. To overcome this limit, squeezed vacuum states have been injected into the Advanced LIGO detectors during the third observing run (O3), leading to an increase of their detection rate by about 40% to 50%. Here we present a key element of LIGO’s squeezed vacuum source: the seismic isolation platform that houses core components placed in ultra-high vacuum. This paper describes the architecture of the isolation platform as well as the active control system, tuned to minimize backscattered light that otherwise deteriorates the sensitivity of the detectors. This architecture permits fewer optical Faraday isolators in the optical path of the squeezing system, minimizing optical losses to maximize the quantum noise improvement. The system reliably operated throughout LIGO’s O3 with no evidence of noise from backscattered light. The innovative architecture of this platform makes it ideal for straightforward reshaping and adaptation to other gravitational-wave detector subsystems and low-noise optical instrumentation.
    Type of Medium: Online Resource
    ISSN: 0264-9381 , 1361-6382
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 1473117-4
    SSG: 16,12
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  • 2
    In: Physiological Measurement, IOP Publishing, Vol. 43, No. 8 ( 2022-08-31), p. 085007-
    Abstract: The photoplethysmogram (PPG) signal is widely used in pulse oximeters and smartwatches. A fundamental step in analysing the PPG is the detection of heartbeats. Several PPG beat detection algorithms have been proposed, although it is not clear which performs best. Objective: This study aimed to: (i) develop a framework with which to design and test PPG beat detectors; (ii) assess the performance of PPG beat detectors in different use cases; and (iii) investigate how their performance is affected by patient demographics and physiology. Approach: Fifteen beat detectors were assessed against electrocardiogram-derived heartbeats using data from eight datasets. Performance was assessed using the F 1 score, which combines sensitivity and positive predictive value. Main results: Eight beat detectors performed well in the absence of movement with F 1 scores of ≥90% on hospital data and wearable data collected at rest. Their performance was poorer during exercise with F 1 scores of 55%–91%; poorer in neonates than adults with F 1 scores of 84%–96% in neonates compared to 98%–99% in adults; and poorer in atrial fibrillation (AF) with F 1 scores of 92%–97% in AF compared to 99%–100% in normal sinus rhythm. Significance: Two PPG beat detectors denoted ‘MSPTD’ and ‘qppg’ performed best, with complementary performance characteristics. This evidence can be used to inform the choice of PPG beat detector algorithm. The algorithms, datasets, and assessment framework are freely available.
    Type of Medium: Online Resource
    ISSN: 0967-3334 , 1361-6579
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 2002076-4
    SSG: 11
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