Multi-messenger observations of a binary neutron star merger

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

Multi-messenger Observations of a Binary Neutron Star Merger

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 {M}ȯ . 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 NGC 4993 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.</p

High-Quality 3-D Microct Imaging Of Source Rocks – Novel Methodology To Measure And Correct For X-Ray Scatter

Micro Computed Tomography (microCT) of cores yields valuable information about rock and fluid properties at pore-scale for conventional rock and at rock heterogeneity scale for unconventionals. High levels of uncorrected X-ray scatter in CT data leads to strong image artifacts and erroneous Hounsfield Unit (HU) values making reconstructed images unsuitable for accurate digital rock characterization (e.g., segmentation, material decomposition, and others). MicroCT scanners typically do not include scatter correction techniques. To fill this gap, we developed a new methodology to measure and remove the scatter component from raw projection microCT data collected during rock core scans, and to ultimately improving image quality of scanned cores. Widely used approaches for scatter estimation, based on Monte-Carlo simulation and simplified analytical models, are time-consuming and may lose accuracy when imaging complex unconventional shale cores. In this paper, we propose a more practical approach to perform scatter correction from direct scatter measurements, which is based on the Beam-Stop Array (BSA) method. The BSA method works as follows. The radiation scattered by the core sample is emitted in random directions. By placing an array of small, highly-absorbing beads between the source and the core, the primary X-ray signal through the beads is blocked, but the overall object scatter signal is not affected. The observed values in the beads’ shadows on the detector are assumed to be scatter signal. Performing interpolation of the scatter signal between the observed pixels on the detector gives an estimate of the scatter signal at every pixel on the detector. Subtracting scatter from projection data yields corrected data used for 3D CT core image reconstruction. To develop the core scatter correction methodology, we (1) performed modeling of primary and scatter signals to optimize the BSA design (beads layout, size, scan parameters); (2) developed and implemented an accurate scatter correction algorithm into our 3D microCT image reconstruction workflow, and (3) tested the proposed methodology using four shale core samples from the United States and the Middle East. To better assess the impact of scatter, all experiments with shale core plugs presented in this paper were conducted using a source energy of 160 kVp. Our results demonstrated that in many cases, especially with higher attenuating cores, scatter cannot be ignored due to its significant impact reducing accuracy of image reconstruction. We also showed that the developed methodology allows for accurate estimation and removal of scatter from the raw (projection) CT data, enabling reconstruction of high-quality core images required for performing digital rock analysis. The presented scatter correction methodology is general and can be utilized with any microCT scanner employed by the petroleum industry to improve image quality and derive accurate HU values. This is of significant importance for quantitative characterization of highly-heterogeneous rock with fine structural changes as is the case for shale. Ultimately, this methodology should expand the operational envelope and value of microCT imaging in the Exploration & Production (E&P) workflows

Controlled Design and Fabrication of SERS–SEF Multifunctional Nanoparticles for Nanoprobe Applications: Morphology-Dependent SERS Phenomena

Dual-mode surface-enhanced Raman scattering (SERS)–surface-enhanced fluorescence (SEF) composite nanoparticles have been developed for possible use as oil reservoir tracers. These composite nanoparticles are composed of metal Ag nanostructured cores, specific dye molecules, and a SiO₂ shell coating. Herein, we show that the embedded dye molecules are detectable by both Raman and fluorescence spectroscopies and yield dramatically enhanced detectability due to strong SERS–SEF phenomena with limits of detection (LOD) as low as 1 ppb by fluorescence spectroscopy and 10 ppb by Raman spectroscopy. To determine the optimal structures for signal enhancement for both SERS and SEF, we show how these phenomena are significantly affected by morphologies of the composite nanoparticles. The aggregation status of metal dots and the distance between the metal and dye probe molecules are the crucial factors for enhancement of SERS and SEF signals. Through well-controlled one-pot reactions in microemulsion media, composite nanoparticles with designed morphologies, Ag@SiO₂ core–shell structures, or Ag@SiO₂/Ag satellite structures have been synthesized, and various dyes have been encoded into these composite nanoparticles. We have demonstrated that the Ag@SiO₂/Ag satellite nanoparticles exhibit the highest dye molecule signal enhancement through both SERS and SEF phenomena. Imaging studies on the detection and mobility of these specifically designed nanoparticles in microchannels show their detection within micron-sized pores and at low concentrations. The multifunctional composite nanoparticles presented herein contain different dyes which exhibit different fluorescence emission wavelengths and fingerprinted Raman signals. Thus, these strategically designed nanoparticles provide a possible pathway for future use as barcoded smart reservoir tracers

Terahertz scattering and water absorption for porosimetry

© 2017 Optical Society of America. We use terahertz transmission through limestone sedimentary rock samples to assess the macro and micro porosity. We exploit the notable water absorption in the terahertz spectrum to interact with the pores that are two orders of magnitude smaller (<1μm) than the terahertz wavelength. Terahertz water sensitivity provides us with the dehydration profile of the rock samples. The results show that there is a linear correlation between such a profile and the ratio of micro to macro porosity of the rock. Furthermore, this study estimates the absolute value of total porosity based on optical diffusion theory. We compare our results with that of mercury injection capillary pressure as a benchmark to confirm our analytic framework. The porosimetry method presented here sets a foundation for a new generation of less invasive porosimetry methods with higher penetration depth based on lower frequency (f<10THz) scattering and absorption. The technique has applications in geological studies and in other industries without the need for hazardous mercury or ionizing radiation

High-Performance Carbon Nanotube Transparent Conductive Films by Scalable Dip Coating

Transparent conductive carbon nanotube (CNT) films were fabricated by dip-coating solutions of pristine CNTs dissolved in chlorosulfonic acid (CSA) and then removing the CSA. The film performance and morphology (including alignment) were controlled by the CNT length, solution concentration, coating speed, and level of doping. Using long CNTs (∼10 μm), uniform films were produced with excellent optoelectrical performance (∼100 Ω/sq sheet resistance at ∼90% transmittance in the visible), in the range of applied interest for touch screens and flexible electronics. This technique has potential for commercialization because it preserves the length and quality of the CNTs (leading to enhanced film performance) and operates at high CNT concentration and coating speed without using surfactants (decreasing production costs)