Search for gravitational waves associated with gamma-ray bursts detected by Fermi and Swift during the LIGO–Virgo run O3b

We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC–2020 March 27 17:00 UTC). We conduct two independent searches: a generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate

Influence of coastal structures on the beaches of southern Karnataka, India

Eight beaches of Dakshina Kannada and Udupi districts were regularly surveyed and monitored between 1985 and 1999 to understand morphological changes. During SW monsoon the wide summer beaches of this coast experience erosion. Eroded beaches start growing during post-monsoon period and are fully developed by April/May. These erosional and accretional trends are cyclic and annual in nature. Minimum sediment is stored on the beaches during July/August and maximum during April/May. Sediment budget estimates reveal a net gain and hence, there is an accretional trend along this coast. Wherever erosion becomes severe, construction of seawalls is taken up as a preventive measure. In fact, these structures enhance erosion or shift erosional sites towards adjacent areas or they undergo destruction. Occupation of protected beaches is an added problem. Material from cliff erosion of northern coast and that contributed by rivers of these districts are the major sources of littoral drift and beach sediments. Net littoral drift is towards south and any construction as barrier to this results in erosion on downdrift side. Three case studies conducted at Old Mangalore Port, New Mangalore Port and Kapu-Mulur areas exemplify this trend. Significant morphological changes have taken place at Old Mangalore Port area after the recent construction of breakwaters. The shoreline has prograded by about 225 m on updrift side and retreated by 165 m on downdrift side between December 1993 and July 1995