77 research outputs found

    Multi-messenger observations of a binary neutron star merger

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    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

    Finite element modeling of hard turning process via a micro-textured tool

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    Literature survey showed that the micro-textures on the tool rake face can help in reduction in friction at chip-tool interface and therefore, reduction in the cutting forces. Consequently, the current work is based on FE simulation of hard turning of bearing steel (AISI52100). Four types of micro-textures have been considered on the tool rake face: non-texture, perpendicular, parallel, and rectangle. Johnson-Cook (J-C) material constitutive law has been considered for the workpiece with temperature-dependent material properties. Experimental work has been performed at cutting conditions: type, parallel; edge distance, 0.195 mm; pitch size, 0.110 mm; and height of the texture, 0.049 mm to validate the current machining model. Parametric study of effect of tool feature parameters on the cutting forces has been performed. Based on the current model, it is observed that the perpendicular shape showed the minimum cutting force. The maximum reduction of 28 % was predicted in the effective coefficient of friction compared to the non-textured surface. Additionally, effect of size of the texture (edge distance, pitch size, texture height) and the friction factor at tool-chip interface on the process responses is predicted. The perpendicular texture at an edge distance of 100 ??m, pitch size of 100 ??m, and texture height of 50 ??m showed the most effective shape and size for the minimum cutting forces and effective friction. It is simulated that the chip flow angle can be governed by the shape/size of the texture on the tool rake face. It is expected that the current model can further be helpful in the characterization of other hard materials and complex texture shape/size.close1
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