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  1. The topic of friction reduction has been studied through the decades for numerous engineering applications that involve internal and external flows. Inspired by the natural surface structure of different plants and animals, engineered microtexturing of surfaces is one of the effective ways of reducing the drag. By introducing different texture geometries, the flow behavior close to the solid boundary can be altered and thus manipulated towards achieving a reduced net drag force on the surface. Despite considerable research on the subject, most works have concentrated on optimization of the surface texturing for maximizing the friction reduction and minimizing the pumping power requirements, and less attention has been paid to characterization of the flow and boundary layer in the vicinity of the wall, especially in laminar regime. In this work we investigate the role that microtexturing has on friction reduction under low to moderate Reynolds numbers (Re). We perform a parametric study on the shape and dimensions of the surface textures and investigate the boundary layer and streamline behavior as well as the local shear stress and pressure distribution along the solid-fluid interface under different flow conditions. The outcomes of this work will provide a guideline for optimal design of artificial textures with major implications for many engineering applications such as microfluidic systems used in thermal management and biochemical diagnostics. 
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  3. Abstract

    We search for gravitational-wave (GW) transients associated with fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project, during the first part of the third observing run of Advanced LIGO and Advanced Virgo (2019 April 1 15:00 UTC–2019 October 1 15:00 UTC). Triggers from 22 FRBs were analyzed with a search that targets both binary neutron star (BNS) and neutron star–black hole (NSBH) mergers. A targeted search for generic GW transients was conducted on 40 FRBs. We find no significant evidence for a GW association in either search. Given the large uncertainties in the distances of our FRB sample, we are unable to exclude the possibility of a GW association. Assessing the volumetric event rates of both FRB and binary mergers, an association is limited to 15% of the FRB population for BNS mergers or 1% for NSBH mergers. We report 90% confidence lower bounds on the distance to each FRB for a range of GW progenitor models and set upper limits on the energy emitted through GWs for a range of emission scenarios. We find values of order 1051–1057erg for models with central GW frequencies in the range 70–3560 Hz. At the sensitivity of this search, we find these limits to be above the predicted GW emissions for the models considered. We also find no significant coincident detection of GWs with the repeater, FRB 20200120E, which is the closest known extragalactic FRB.

     
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    Free, publicly-accessible full text available September 28, 2024
  4. Abstract The global network of gravitational-wave observatories now includes five detectors, namely LIGO Hanford, LIGO Livingston, Virgo, KAGRA, and GEO 600. These detectors collected data during their third observing run, O3, composed of three phases: O3a starting in 2019 April and lasting six months, O3b starting in 2019 November and lasting five months, and O3GK starting in 2020 April and lasting two weeks. In this paper we describe these data and various other science products that can be freely accessed through the Gravitational Wave Open Science Center at https://gwosc.org . The main data set, consisting of the gravitational-wave strain time series that contains the astrophysical signals, is released together with supporting data useful for their analysis and documentation, tutorials, as well as analysis software packages. 
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    Free, publicly-accessible full text available July 28, 2024