Identification and Reduction of Scattered Light Noise in LIGO

We ushered into a new era of gravitational wave astronomy in 2015 when Advanced LIGO gravitational wave detectors in Livingston, Louisiana and Hanford, Washington observed a gravitational wave signal from the merger of binary black holes. The first detected GW150914 was a part of first Observing run (O1) and since then there have been a total of 3 Observing runs. Advanced Virgo detector in Cascina, Italy joined the efforts in the third Observing run (O3) which spanned from April 1, 2019, to March 27, 2020. It was split into O3a and O3b with a month long break between them, during October 2019, for commissioning upgrades. The first half of the run, O3a, from April 1, 2019, to October 1, 2019, resulted in detection of 39 gravitational-wave events with false alaram rate (FAR) $The gravitational wave data quality is hurt by environmental or instrumental noise artifacts in the data. These short duration noise transients can mask or mimic a gravitational wave. Identification of transient noise coupling, which may lead to a reduced rate of noise is thus of primary concern. This dissertation focuses on my work during O3 on identifying and reducing noise transients associated with scattered light in the detector. Light scattering adversely affects the LIGO data quality and is linked to multiple retractions of gravitational wave signals. The noise impacts the detector sensitivity in the$10 - 150$ Hz frequency band critical to the discovery of collision of compact objects, especially heavier black holes. Scattered light noise rate is correlated with an increase in ground motion near the detectors. During O3, two different populations of transients due to light scattering: \textit{Slow Scattering} and \textit{Fast Scattering} were observed. In this dissertation, I document my research that led to the identification of Slow Scattering noise couplings in the detector. This was followed by instrument hardware changes resulting in noise mitigation. This dissertation also discusses transient noise data quality studies I performed during and after O3. These studies shed light on environmental or instrumental correlation with the transient noise in the detector. Improved noise characterization is a significant step that can lead to the recognition of noise couplings in the detector and consequent reduction, which is one of the main objectives of detector characterization. Finally, I examine the importance of Machine Learning (ML) in gravitational-wave data analysis and discuss my work on training an ML algorithm to identify Fast Scattering noise in the data. I also discuss how this identification led to an improved understanding of the Fast Scattering noise and its dependence on ground motion in two different frequency bands

Noise in the LIGO Livingston Gravitational Wave Observatory due to Trains

Environmental seismic disturbances limit the sensitivity of LIGO gravitational wave detectors. Trains near the LIGO Livingston detector produce low frequency (0.5-10 Hz) ground noise that couples into the gravitational wave sensitive frequency band (10-100 Hz) through light reflected in mirrors and other surfaces. We investigate the effect of trains during the Advanced LIGO third observing run, and propose a method to search for narrow band seismic frequencies responsible for contributing to increases in scattered light. Through the use of the linear regression tool Lasso (least absolute shrinkage and selection operator) and glitch correlations, we identify the most common seismic frequencies that correlate with increases in detector noise as 0.6-0.8 Hz, 1.7-1.9 Hz, 1.8-2.0 Hz, and 2.3-2.5 Hz in the LIGO Livingston corner station.Comment: 18 pages (including bibliography), 17 figures, 2 tables, and 1 appendix. Submitted to Classical and Quantum Gravit

Modeling and Reduction of High Frequency Scatter Noise at LIGO Livingston

The sensitivity of aLIGO detectors is adversely affected by the presence of noise caused by light scattering. Low frequency seismic disturbances can create higher frequency scattering noise adversely impacting the frequency band in which we detect gravitational waves. In this paper, we analyze instances of a type of scattered light noise we call "Fast Scatter" that is produced by motion at frequencies greater than 1 Hz, to locate surfaces in the detector that may be responsible for the noise. We model the phase noise to better understand the relationship between increases in seismic noise near the site and the resulting Fast Scatter observed. We find that mechanical damping of the Arm Cavity Baffles (ACBs) led to a significant reduction of this noise in recent data. For a similar degree of seismic motion in the 1-3 Hz range, the rate of noise transients is reduced by a factor of ~ 50.Comment: 23 pages, 19 figure

Telling Fragments: Politics of the Short Story in Late-Colonial India

Arguing with dominant understandings of the novel as a form best suited to respond to the urgencies of anticolonial nationalism and the challenges of secular democracy, this thesis stakes a claim for the short story as a form that played a vital role in instilling a radical consciousness in the period leading up to the Independence and Partition of India in August 1947. It also argues that within the frames of reference for the short story, and especially the bhasas (Indian-vernacular) short story, the ‘nation’ must not be treated as the epochal ideology or the only conceived category for literary and cultural radicalism. In order to understand the politics of the short story in late-colonial India, there needs to be a deeper engagement with the historical, material, and print-cultural contexts in which these texts appeared, as well as with the institutional sites and circuits through which they are received in the comparative academy. Starting with the publication of the 1932 pamphlet Angaarey (Embers) and going through to Manto’s Siya Hashiye (Black Marginalia) in 1948, this thesis is a comparative study of short stories written in three prominent languages in North India—English, Hindi, and Urdu—in the 1930s and 1940s. Some of the writers considered in the thesis are Mulk Raj Anand, Ahmed Ali, Rashed Jahan, Sajjad Zaheer, and Sa’adat Hasan Manto. This thesis also places European short story theory in dialogue with the bhasas with the help of Premchand’s collection of essays, Kahanikala (The Art of the Short Story, 1922). The thesis demonstrates that by examining the ‘politics’ of the short story form, we can complicate settled critical narratives about nation and nationalism, and further reconstellate the ideals of body, sexuality, self-identity, freedom, and resistance forged under colonial rule and communal violence in late-colonial India. I propose here an approach to reading the ‘postcolonial text’ that goes beyond reading texts as mere testaments to their politics. I study the way these texts are radically invested in their aesthetics, their ethics, and the materiality of their production, thus disrupting many privileged assumptions within postcolonial studies about aesthetic form and ethical thinking

Morphology of functioning trabeculectomy blebs using anterior segment optical coherence tomography

Purpose: To image trabeculectomy blebs using anterior segment optical coherence tomography (AS-OCT), and to correlate the bleb morphologic features at one month postoperatively with bleb function at six months. Materials and Methods: This prospective, observational study included 56 eyes undergoing trabeculectomy with MMC, followed up for minimum of six months. Postoperatively, bleb imaging was done using AS-OCT at one and six month. Bleb morphology was assessed for bleb wall reflectivity, bleb pattern in multiform reflectivity, visibility of drainage route and presence of hyper-reflectivity area. Bleb function was considered successful if IOP was <18 mmHg without medication at six month. Bleb morphology one month postoperatively was correlated with bleb function at six months. Results: At six months successful bleb function was noted in 44 (81.5%) eyes. Morphology of bleb at one month showed uniform bleb wall reflectivity in 6 eyes (11%) and multiform wall reflectivity in 48 eyes (89%). In eyes with multiform wall reflectivity, microcysts with multiple layers was seen in 26 eyes (48%), microcysts with subconjunctival separation in 12 eyes (22%) and only microcyst in 10 eyes (19%). When bleb features at one month were correlated with the bleb function at six months, logistic regression analysis revealed that blebs with multiform reflectivity with multiple internal layers with microcysts were associated with higher chances of success (P < 0.001). Conclusion : AS-OCT demonstrated early bleb morphological features that may be used to predict the functioning of a bleb. Multiform bleb wall reflectivity with a pattern of multiple internal layers and microcysts was associated with increased chances of success of a bleb

QoQ: a Q-transform based test for Gravitational Wave transient events

The observation of transient gravitational waves is hindered by the presence of transient noise, colloquially referred to as glitches. These glitches can often be misidentified as gravitational waves by searches for unmodeled transients using the excess-power type of methods and sometimes even excite template waveforms for compact binary coalescences while using matched filter techniques. They thus create a significant background in the searches. This background is more critical in getting identified promptly and efficiently within the context of real-time searches for gravitational-wave transients. Such searches are the ones that have enabled multi-messenger astrophysics with the start of the Advanced LIGO and Advanced Virgo data taking in 2015 and they will continue to enable the field for further discoveries. With this work we propose and demonstrate the use of a signal-based test that quantifies the fidelity of the time-frequency decomposition of the putative signal based on first principles on how astrophysical transients are expected to be registered in the detectors and empirically measuring the instrumental noise. It is based on the Q-transform and a measure of the occupancy of the corresponding time-frequency pixels over select time-frequency volumes; we call it ``QoQ''. Our method shows a 40% reduction in the number of retraction of public alerts that were issued by the LIGO-Virgo-KAGRA collaborations during the third observing run with negligible loss in sensitivity. Receiver Operator Characteristic measurements suggest the method can be used in online and offline searches for transients, reducing their background significantly.Comment: 39 Figures, 5 Table

Utility of tissue Xpert-Mtb/Rif for the diagnosis of intestinal tuberculosis in patients with ileocolonic ulcers

Introduction: Data on the use of Xpert Mtb/Rif for the diagnosis of intestinal tuberculosis is sparse. We report on the utility of Xpert Mtb/Rif testing for diagnosis of intestinal tuberculosis (ITB) in patients with ileocecal ulcers Methodology: We performed a retrospective analysis of patients with ileocecal ulcers and suspected to have ITB and in whom testing of intestinal tissue for Xpert Mtb/Rif was performed. The patients were divided into two groups: those with a final diagnosis of intestinal tuberculosis and those with other diagnosis. These patients were compared for clinical features and presentation. The sensitivity, specificity, positive predictive value, and negative predictive value of Xpert Mtb/Rif for the diagnosis of ITB were calculated. Results: Of the 40 patients studied, 23 were women and the mean age was 32.92 ± 12.78 years. Abdominal pain was present in 33 (88.5%) patients and diarrhea in 12 (30%). A total of 25 patients had underlying ITB whereas 15 patients had other diagnoses (Crohn’s disease, amebiasis, nonspecific ileitis, etc.). The sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of GeneXpert-Mtb/Rif was 32% (CI: 14.95–53.50%), 100% (78.2–100), 46.88% (40.27–53.59%), 100 & 57.50 (40.89–72.89%) respectively. Conclusion: A positive GeneXpert-Mtb/Rif helps in the diagnosis of ITB, but the sensitivity is low

Discovering features in gravitational-wave data through detector characterization, citizen science and machine learning

The observation of gravitational waves is hindered by the presence of transient noise (glitches). We study data from the third observing run of the Advanced LIGO detectors, and identify new glitch classes: Fast Scattering/Crown and Low-frequency Blips. Using training sets assembled by monitoring of the state of the detector, and by citizen-science volunteers, we update the Gravity Spy machine-learning algorithm for glitch classification. We find that Fast Scattering/Crown, linked to ground motion at the detector sites, is especially prevalent, and identify two subclasses linked to different types of ground motion. Reclassification of data based on the updated model finds that 27% of all transient noise at LIGO Livingston belongs to the Fast Scattering class, while 8% belongs to the Low-frequency Blip class, making them the most frequent and fourth most frequent sources of transient noise at that site. Our results demonstrate both how glitch classification can reveal potential improvements to gravitational-wave detectors, and how, given an appropriate framework, citizen-science volunteers may make discoveries in large data sets