Potential of Core-Collapse Supernova Neutrino Detection at JUNO

JUNO is an underground neutrino observatory under construction in Jiangmen, China. It uses 20kton liquid scintillator as target, which enables it to detect supernova burst neutrinos of a large statistics for the next galactic core-collapse supernova (CCSN) and also pre-supernova neutrinos from the nearby CCSN progenitors. All flavors of supernova burst neutrinos can be detected by JUNO via several interaction channels, including inverse beta decay, elastic scattering on electron and proton, interactions on C12 nuclei, etc. This retains the possibility for JUNO to reconstruct the energy spectra of supernova burst neutrinos of all flavors. The real time monitoring systems based on FPGA and DAQ are under development in JUNO, which allow prompt alert and trigger-less data acquisition of CCSN events. The alert performances of both monitoring systems have been thoroughly studied using simulations. Moreover, once a CCSN is tagged, the system can give fast characterizations, such as directionality and light curve

Detection of the Diffuse Supernova Neutrino Background with JUNO

As an underground multi-purpose neutrino detector with 20 kton liquid scintillator, Jiangmen Underground Neutrino Observatory (JUNO) is competitive with and complementary to the water-Cherenkov detectors on the search for the diffuse supernova neutrino background (DSNB). Typical supernova models predict 2-4 events per year within the optimal observation window in the JUNO detector. The dominant background is from the neutral-current (NC) interaction of atmospheric neutrinos with 12C nuclei, which surpasses the DSNB by more than one order of magnitude. We evaluated the systematic uncertainty of NC background from the spread of a variety of data-driven models and further developed a method to determine NC background within 15\% with {\it{in}} {\it{situ}} measurements after ten years of running. Besides, the NC-like backgrounds can be effectively suppressed by the intrinsic pulse-shape discrimination (PSD) capabilities of liquid scintillators. In this talk, I will present in detail the improvements on NC background uncertainty evaluation, PSD discriminator development, and finally, the potential of DSNB sensitivity in JUNO

Real-time Monitoring for the Next Core-Collapse Supernova in JUNO

Core-collapse supernova (CCSN) is one of the most energetic astrophysical events in the Universe. The early and prompt detection of neutrinos before (pre-SN) and during the SN burst is a unique opportunity to realize the multi-messenger observation of the CCSN events. In this work, we describe the monitoring concept and present the sensitivity of the system to the pre-SN and SN neutrinos at the Jiangmen Underground Neutrino Observatory (JUNO), which is a 20 kton liquid scintillator detector under construction in South China. The real-time monitoring system is designed with both the prompt monitors on the electronic board and online monitors at the data acquisition stage, in order to ensure both the alert speed and alert coverage of progenitor stars. By assuming a false alert rate of 1 per year, this monitoring system can be sensitive to the pre-SN neutrinos up to the distance of about 1.6 (0.9) kpc and SN neutrinos up to about 370 (360) kpc for a progenitor mass of 30$M_{\odot}$ for the case of normal (inverted) mass ordering. The pointing ability of the CCSN is evaluated by using the accumulated event anisotropy of the inverse beta decay interactions from pre-SN or SN neutrinos, which, along with the early alert, can play important roles for the followup multi-messenger observations of the next Galactic or nearby extragalactic CCSN.Comment: 24 pages, 9 figure

Investigation of a High-Performance Nanofiber Cathode with Ultralow Platinum Loading for Proton Exchange Membrane Fuel Cells

Nanofiber electrodes fabricated by using the electrospinning technique in the cathode of proton exchange membrane fuel cells gave a peak power density of 0.692Wcm(-2) with an ultralow Pt loading of 0.087mgcm(-2). As the cathode, the electrospun (E_spun) electrodes exposed a high Pt surface to oxygen, with a highly uniform distribution of Pt catalyst and Nafion ionomer, which improved the utilization of Pt. The ionic resistance of the E_spun electrode was decreased owing to the nanofiber structure. The high porosity of the E_spun electrode enhanced the Knudsen diffusion in small pores, which mitigated the oxygen-transfer resistance. The addition of 5wt% polytetrafluoroethylene (PTFE) to the E_spun electrode optimized water management, especially at high current densities. The accelerated stability test showed that the long-term durability of the E_spun electrode is much better than the conventional decal electrode due to the interaction of the carbon support and hydrophilic poly(acrylic acid)

High-Performance Low-Platinum Electrode for Proton Exchange Membrane Fuel Cells: Pulse Electrodeposition of Pt on Pd/C Nanofiber Mat

A novel electrode (E-P electrode) with a nanofiber structure and Pd/C@dendritic Pt catalysts is prepared by using electrospinning and pulse electrodeposition (PED) techniques. The maximum power density of the E-P electrode is 1.43-fold larger than that of the conventional electrode at the same cathode Pt loadings of 0.1 mg cm(-1). Owing to the in situ deposition of dendritic Pt on the surface of Pd in the Pd/C nanofiber mat, almost all Pt catalysts are accessible for oxygen. The electronic tuning between Pd and Pt enhances the oxygen reduction reaction activity of Pt catalysts. The large Pt surface area of the E-P electrode mitigates the oxygen-transport resistance in comparison with that of the conventional electrode. After the accelerated degradation test for 10000 cyclic voltammetry cycles, the maximum power density of the E-P electrode only decreases by 12%. The long-term stability of the E-P electrode is ascribed to the Pd/C@dendritic Pt catalysts and nanofiber structure

A high-performance PEM fuel cell with ultralow platinum electrode via electrospinning and underpotential deposition

A novel PEMFC electrode (E-U electrode) with ultralow platinum is prepared by electrospinning and underpotential deposition techniques. The platinum skin (Ptskin) is in situ deposited on the surface of Pd nanoparticle in the electrospun Pd/ C catalyst layer. The energy-dispersive X-ray spectroscopy (EDS) mapping of the cross-section of a single fiber confirms that the distribution of Pd/C@ Pt-skin catalysts and Nafion1 ionomer matches well in the E-U electrode. The high porosity and large electrochemical surface area (ECSA) of the E-U electrode mitigates the oxygen transfer resistance. The peak power density of the E-U electrode arrives at 0.62 W cm(-2) with a Pt loading of 19 mg cm(-2), which is higher than that of the conventional electrode (0.55 W cm(-2)) with a Pt loading of 100 mg cm(-2). The degradation rate of peak power density of the E-U electrode is only 4.8% after accelerated stability test (AST) for 30000 cyclic voltammetry (CV) cycles, demonstrating a better durability than that of the conventional electrode. The enhanced durability of the E-U electrode is attributed to nanofiber structure and interaction between Pd and Pt in the Pd/C@ Pt-skin catalyst. (C) 2017 Published by Elsevier Ltd

Integrated Metagenomic and Metabolomic Analysis on Two Competing Mussels, <i>Mytella strigata</i> and <i>Perna viridis</i>, in China

Biological invasion is a primary direct driver of biodiversity loss. Recently, owing to exploitation competition with an invasive mussel, Mytella strigata (Hanley, 1843), there has been a drastic decrease in the population of native Perna viridis (Linnaeus, 1758) in several western Pacific regions. In the present study, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between the two competing mussels, M. strigata and P. viridis, to elucidate the differences in intestinal microbiota and metabolic points. We observed that Proteobacteria, Firmicutes, and Bacteroidota were the three predominant bacterial phyla in the two species. The relative abundance of Bacteroidota related to carbohydrate-degrading ability was significantly higher in M. strigata than in P. viridis. Compared to P. viridis, different metabolites including maltose and trehalose were enriched in M. strigata. Lastly, higher carbohydrases activities of alpha-amylase, cellulase, and xylanase were observed in M. strigata than in P. viridis. These differences might play an important role in the adaptation process of M. strigata to the new environment. This study provides important basic knowledge for investigating the competition between M. strigata and P. viridis in terms of food resources utilization

Determination of ultra-low level Am-241 in soil and sediment using chemical separation and triple quadrupole inductively coupled plasma mass spectrometry measurement with He-NH3 as collision-reaction gas

Inductively coupled plasma mass spectrometry (ICP-MS) has been becoming a competitive technique for the measurement of trace americium isotopes, but the isobaric and polyatomic ions interference (Pu-241, (PbCl)-Pb-206-Cl-35, (PbCl)-Pb-204-Cl-37, etc.) will deteriorate the analysis accuracy for soil and sediment samples with high concentration of interfering elements (e.g., Pb). This study developed a novel analysis method to determine Am-241 using ICP-MS with tandem quadrupoles and collision/reaction cell. The interference of isobaric and polyatomic ions was effectively removed by the mass filter of quadrupole and reactions with NH3, with the contribution efficiency of interfering elements at m/z 241 or 243 lower than 1 x 10(-8), and the measurement sensitivity in this mode relatively (1170 Mcps/(mg/L)) higher than in other modes. The detection limit of 0.091 fg/g for Am-241 was achieved, 3 times better than other types of ICP-MS (Q-ICP-MS, SF-ICP-MS, etc.). The collision focusing by He and the chemical reaction with NH3 played an important role in the improvement of Am sensitivity and elimination of polyatomic ions. This study suggested that the presence of Cl- could significantly increase the polyatomic ions interference ((PbCl)-Pb-206-Cl-35, (PbCl)-Pb-204-Cl-37, (PbCl)-Pb-208-Cl-35, (PbCl)-Pb-206-Cl-37, etc.) because of the high Pb concentration in the soil or sediment samples, and thus should be completely removed. The developed method had been validated with two certified reference materials of soil (IAEA-375 and IAEA-Soil-6) and successfully applied to measure Am-241 concentrations in seven soil samples collected in different regions of China and one sediment sample collected in Denmark