Physics
https://repository.iitgn.ac.in/handle/123456789/607
2021-01-23T05:23:27ZAn early warning system for electromagnetic follow-up of gravitational-wave events
https://repository.iitgn.ac.in/handle/123456789/6224
An early warning system for electromagnetic follow-up of gravitational-wave events
Reza, Amit et al.
Binary neutron stars (BNSs) will spend sime10�15 minutes in the band of Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors at design sensitivity. Matched-filtering of gravitational-wave (GW) data could in principle accumulate enough signal-to-noise ratio (S/N) to identify a forthcoming event tens of seconds before the companions collide and merge. Here we report on the design and testing of an early-warning GW detection pipeline. Early-warning alerts can be produced for sources that are at low enough redshift so that a large enough S/N accumulates ~10�60 s before merger. We find that about 7% (49%) of the total detectable BNS mergers will be detected 60 s (10 s) before the merger. About 2% of the total detectable BNS mergers will be detected before merger and localized to within 100 deg2 (90% credible interval). Coordinated observing by several wide-field telescopes could capture the event seconds before or after the merger. LIGO�Virgo detectors at design sensitivity could facilitate observing at least one event at the onset of merger.
2020-12-01T00:00:00ZRandom projections in gravitational wave searches from compact binaries II: efficient reconstruction of detection statistic within LLOID framework
https://repository.iitgn.ac.in/handle/123456789/6231
Random projections in gravitational wave searches from compact binaries II: efficient reconstruction of detection statistic within LLOID framework
Reza, Amit; Dasgupta, Anirban; Sengupta, Anand S.
Low-latency gravitational wave search pipelines such as LLOID take advantage of low-rank factorization of the template matrix via singular value decomposition (SVD). With unprecedented improvements in detector bandwidth and sensitivity in advanced-LIGO and Virgo detectors, one expects several orders of magnitude increase in the size of template banks. This poses a formidable computational challenge in factorizing extremely large matrices. Previously, [in Kulkarni et al. [6]], we introduced the idea of random projection (RP)-based matrix factorization as a computationally viable alternative to SVD, for such large template banks. In this follow-up paper, we demonstrate the application of a block-wise randomized matrix factorization (RMF) scheme using which one can compute the desired low-rank factorization corresponding to a fixed average SNR loss (h{\delta}\r{ho}/\r{ho}i). Unlike the SVD approach, this new scheme affords a much more efficient way of matrix factorization especially in the context of LLOID search pipelines. It is a well-known fact that for very large template banks, the total computational cost is dominated by the cost of reconstruction of the detection statistic and that the cost of filtering the data is insignificant in comparison. We are unaware of any previous work in literature that has tried to squarely address this issue of optimizing the reconstruction cost. We provide a possible solution to reduce the reconstruction cost using the matching pursuit(MP) algorithm. We show that it is possible to approximately reconstruct the time-series of the detection statistic at a fraction of the total cost using our MP algorithm. The combination of RMF along with MP can handle large template banks more efficiently in comparison to the direct application of SVD. Results from several numerical simulations have been presented to demonstrate their efficacy.
2021-01-01T00:00:00ZNatural solvent facilitated high-shear exfoliated graphene nanoplatelets enabled economically-efficient and stable DSSC
https://repository.iitgn.ac.in/handle/123456789/6221
Natural solvent facilitated high-shear exfoliated graphene nanoplatelets enabled economically-efficient and stable DSSC
Nemala, Siva Sankar; Ravulapalli, Sujitha; Kartikay, Purnendu; Banavath, Ramu; Mallick, Sudhanshu; Bhargava, Parag; Bhushan, Mayank; Mohapatra, Debananda
This work presents an efficient and stable platinum-free shear-exfoliated graphene nanoplatelets (SE-GNP) based counter electrode (CE) for dye-sensitized solar cells (DSSCs). The SE-GNP is prepared by the simple, low cost and eco-friendly high-shear liquid-phase exfoliation technique in bulk using natural graphite flakes as a starting material in an aqueous medium. Detailed electrochemical studies demonstrate that SE-GNP-based CE offers a superior electrocatalytic activity for the redox reaction of I?/I3? redox couple with an improved charge transfer kinetics and the exchange current density at the electrode/electrolyte interface, compared to the standard Pt CE. The SE-GNP-based counter electrode shows exceptionally high stability (>3000 h) and efficiency (? = 7.6%) under constant illumination at a negligible drop in DSSCs' performance.
2021-03-01T00:00:00ZBlack hole and singularity theorems
https://repository.iitgn.ac.in/handle/123456789/6212
Black hole and singularity theorems
Sarkar, Sudipta
Prof. Roger Penrose was awarded one-half of the Nobel prize in physics 2020 "for the discovery that black hole formation is a robust prediction of the general theory of relativity." Penrose�s landmark work on singularity theorems and black holes are the foundation of our understanding of these exotic objects. In this article, I describe the historical background of the singularity theorems and their impact on contemporary gravitational physics research.
2020-12-01T00:00:00Z