In situ Raman spectroscopy and cyclic voltammetry were used to investigate the mechanism of sulfur reduction in lithium–sulfur battery slurry cathodes with 1 M lithium bis(trifluoromethane ...sulfonyl)imide (LiTFSI) and tetraethylene glycol dimethyl ether (TEGDME)/1,3-dioxolane (DIOX) (1/1, v/v). Raman spectroscopy shows that long-chain polysulfides (S8 2–) were formed via S8 ring opening in the first reduction process at ∼2.4 V vs Li/Li+ and short-chain polysulfides such as S4 2–, S4 –, S3 •–, and S2O4 2– were observed with continued discharge at ∼2.3 V vs Li/Li+ in the second reduction process. Elemental sulfur can be reformed in the end of the charge process. Rate constants obtained for the appearance and disappearance polysulfide species shows that short-chain polysulfides are directly formed from S8 decomposition. The rate constants for S8 reappearance and polysulfide disappearance on charge were likewise similar. The formation of polysulfide mixtures at partial discharge was found to be quite stable. The CS2 additive was found to inhibit the sulfur reduction mechanism allowing the formation of long-chain polysulfides during discharge only and stabilizing the S8 2– product.
Understanding the role of the oxidation state of the Cu surface and surface-adsorbed intermediate species in electrochemical CO2 reduction is crucial for the development of selective CO2-to-fuel ...electrocatalysts. In this study, the electrochemical CO2 reduction mechanism over the Cu catalysts with various oxidation states was studied by using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), in situ soft X-ray absorption spectroscopy (Cu L-edge), and online gas chromatography measurements. The atop-adsorbed CO (COatop) intermediate is obtained on the electrodeposited Cu surface which primarily has the oxidation state of Cu(I). COatop is further reduced, followed by the formation of C1 product such as CH4. The residual bridge-adsorbed CO (CObridge) is formed on the as-prepared Cu surface with Cu(0) which inhibits hydrocarbon formation. In contrast, the CV-treated Cu electrode prepared by oxidizing the as-prepared Cu surface contains different amounts of Cu(I) and Cu(0) states. The major theme of this work is that in situ SEIRAS results show the coexistence of COatop and CObridge as the reaction intermediates during CO2 reduction and that the selectivity of CO2-to-ethylene conversion is further enhanced in the CV-treated Cu electrode. The Cu catalysts modulated by the electrochemical method exhibit different oxidation states and reaction intermediates as well as electrocatalytic properties.
Lithium metal anodes form a dendritic structure after cycling which causes an internal short circuit in flammable electrolytes and results in battery fires. Today's separators are insufficient for ...suppressing the formation of lithium dendrites. Herein, we report on the use of mesoporous silica thin films (MSTFs) with perpendicular nanochannels (pore size ∼5 nm) stacking on an anodic aluminum oxide (AAO) membrane as the MSTF⊥AAO separator for advancing Li metal batteries. The nanoporous MSTF⊥AAO separator with novel inorganic structures shows ultra-long term stability of Li plating/stripping in Li–Li cells at an ultra-high current density and capacity (10 mA cm
−2
and 5 mA h cm
−2
). A significant improvement over the state-of-the-art separator is evaluated based on three performance indicators,
e.g.
cycle life, current density and capacity. In Li–Cu cells, the MSTF⊥AAO separator shows a coulombic efficiency of >99.9% at a current density of 10 mA cm
−2
for more than 250 h of cycling. The separator gives improved rate capability in Li–LiFePO
4
(LFP) batteries. The excellent performance of the MSTF⊥AAO separator is due to good wetting of electrolytes, straight nanopores with negative charges, uniform Li deposition and blocking the finest dendrite.
Li‐rich layered oxide cathodes with conventional transition metal cation and unique oxygen anion redox reactions deliver high capacities in Li‐ion batteries. However, the oxygen redox process causes ...the oxygen release, voltage fading/hysteresis, and sluggish electrochemical kinetics, which undermine the performance of these materials. By combining operando quick‐scanning X‐ray absorption spectroscopy with online gas chromatography, the effect of the local electronic structure is elucidated on the reaction mechanism and electrochemical kinetics of Li‐rich cathodes. The local electronic structure of Li‐rich cathodes varies with the excess Li (i.e., Li2MnO3 phase) and Ni contents. Compared to the Li‐rich cathodes with higher amounts of Li2MnO3 phase (high excess lithium content (HLC) cathode), those with lower Li2MnO3 contents (low excess lithium content (LLC) cathode) exhibit reversible anion redox reactions and suppressed voltage hysteresis. The cation oxidation process of LLC cathode is kinetically slower than that of HLC cathode and the cation oxidation potential is shifted, likely due to the local coordination associated with different Li/O ratios. The obtained insights into the effect of local electronic structure on the reaction mechanism and kinetics provide a better understanding and control of Li‐rich cathodes.
This research reveals the reaction mechanism and electrochemical kinetics of Li‐rich cathodes using in operando quick‐scanning X‐ray absorption spectroscopy. With the control of Li2MnO3 domain, cation migration and voltage decay were suppressed. The electrochemical stability and kinetics of tradition metal (TM) redox can be tuned by modifying the local coordination structure of Li‐rich cathode.
Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability ...and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES–PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m–2 h–1 bar–1 and a 99.4% Na2SO4 rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.
Accurate location information is essential for mobile systems such as wireless sensor networks. A location-aware sensor network generally includes two types of nodes: Sensors whose locations to be ...determined and anchors whose locations are known a priori. For range-based cooperative positioning, sensors' locations are deduced from anchor-to-sensor and sensor-to-sensor range measurements. Positioning accuracy depends on the network parameters such as network connectivity and size. This paper provides a generalized theory that quantitatively characterizes such a relation between network parameters and positioning accuracy. We use the average degree as a connectivity metric and use geometric dilution of precision (DOP) to quantify positioning accuracy. Under the assumption that nodes are randomly deployed, we prove a novel lower bound on expectation of average geometric DOP (LB-E-AGDOP) and derives a closed-form formula that relates LB-E-AGDOP to only three parameters: Average anchor degree, average sensor degree, and number of sensor nodes. The formula shows that positioning accuracy is approximately inversely proportional to the average degree, and a higher ratio of average anchor degree to average sensor degree yields better positioning accuracy. Furthermore, the paper shows a strong connection between LB-E-AGDOP and the best achievable accuracy. Finally, we demonstrate the theory via numerical simulations with three different random graph models.
In this study, samples of activated mesoporous carbon are fabricated with pore structures with cylinder and gyroid nanostructures through the templating effect of amphiphilic poly(ethylene ...oxide‐block‐caprolactone) (PEO‐PCL) and by using specific resol/PEO‐PCL weight ratios (e.g., 60:40 for cylinders; 55:45 for gyroids). After carbonization and KOH activation, the activated mesoporous carbons were tested as electrode materials for electric double‐layer capacitor (EDLC) supercapacitors. The electrochemical properties were examined by using three‐electrode (6 m KOH(aq) as electrolyte) and CR2032 coin‐cell (1 m tetraethylammonium tetrafluoroborate (TEABF4)/CN as the electrolyte) systems. The gyroid carbon samples provided specific capacitances higher than those of the cylinder carbon samples in both aqueous and organic systems: 155 F g−1 compared with 135 F g−1 in 6 m KOH(aq), and 105.6 compared with 96 F g−1 in 1 m TEABF4/MeCN, after 100 charge/discharge cycles. It is suspected that the bi‐continuous mesochannels of the gyroid‐type activated mesoporous carbons provided a relatively higher effective adsorption surface area; in other words, the greater surface area for energy storage originated from a moderate pore size and an interconnected pore structure.
Activated mesoporous carbons are fabricated with pore structures with cylinder and gyroid nanostructures through the templating effect of amphiphilic poly(ethylene oxide‐block‐caprolactone) (PEO‐PCL) and by using specific resol/PEO‐PCL weight ratios (e.g., 60:40 for cylinders; 55:45 for gyroids). After carbonization and KOH activation, the activated mesoporous carbons were tested as electrode materials for electric double‐layer capacitor (EDLC) supercapacitors.
GPS Signal Authentication From Cooperative Peers Liang Heng; Work, Daniel B.; Gao, Grace Xingxin
IEEE transactions on intelligent transportation systems,
08/2015, Letnik:
16, Številka:
4
Journal Article
Recenzirano
Secure reliable position information is indispensable for many transportation systems and services, such as traffic monitoring, fleet management, electronic toll collection, route guidance, vehicle ...telematics, and emergency response. Unfortunately, civil Global Positioning System (GPS) signals are vulnerable to spoofing attacks. This paper introduces a signal authentication architecture based on a network of cooperative GPS receivers. A receiver in the network correlates its received military P(Y) signal with those received by other receivers (hereinafter referred to as cross-check receivers) to detect spoofing attacks. This paper describes three candidate structures to implement this architecture and evaluates spoofing detection performance through theoretical analyses and field experiments. We show that the spoofing detection performance improves exponentially with increasing number of cross-check receivers. Even if the cross-check receivers are low cost, unreliable, and in challenging environment, cooperative authentication can match, if not outperform, a single high-quality reliable reference receiver in terms of spoofing detection performance.
Background: We estimated the incidence and mortality of nasopharyngeal carcinoma (NPC) in China in 2010 according to the data of 145 domestic population-based cancer registries in 2014, and no such ...reports since then.Hence, to further and better understand its epidemiology in China and to provide more precise scientific information for its control and prevention in China, we analyzed the NPC incidence and mortality of 255 domestic populationbased cancer registries, and estimated the national rates in 2013 again.Methods: NPC incidence and mortality data of 255 domestic cancer registries in 2013, accepted by the 2016 National Cancer Registry Annual Report, were collected and collated, and the indices of NPC such as the numbers of new cases and deaths, crude rates, age-standardized rates, and truncated rates of incidence and mortality were calculated and analyzed. The incidence and mortality in China and its constituent areas were estimated according to the national population in 2013.Results: An estimated 42,100 new cases and 21,320 deaths were attributed to NPC in China in 2013, accounting for 1.14% of all new cancer cases and 0.96% of all cancer-related deaths that year in China. Crude incidence and mortality of NPC were 3.09/100,000 and 1.57/100,000, respectively. World age-standardized incidence and mortality were 2.17/100,000 and 1.08/100,000, respectively. The incidence and mortality of males were obviously higher than those of females and slightly higher in urban areas than in rural areas. Among seven Chinese administrative regions, NPC incidence and mortality were obviously higher in South China than in other regions and lowest in North China. Top 3 incidence and mortality provinces and registering areas all located in South China. The age-specific incidence and mortality rose quickly from age 25–29 and 35 to 39 years, respectively, peaked at different ages and varied by location.Conclusions: These results demonstrated that NPC incidence and mortality in China in 2013 were also at high levels worldwide, which suggested that its control and prevention should be enhanced.
Wolf-Rayet (WR) galaxies are a rare galaxy type that hosts living high-mass stars during the WR phase (i.e., WR stars) and can thus provide constraints on the stellar initial mass function, massive ...star formation, stellar evolution models, etc. Spatially resolved spectroscopy should in principle identify WR galaxies more efficiently than single-fiber surveys of galactic centers, as WR stars should be more preferentially found in disks. Using integral field unit data from the ongoing SDSS-IV MaNGA survey, we have performed a thorough search for WR galaxies. We first identify H ii regions in each datacube and carry out full spectral fitting to the stacked spectra. We then visually inspect the residual spectrum of each H ii region and identify significant WR "blue bumps" at 4600-4750 . The WR catalog includes 267 WR regions of ∼500 pc (radius) sizes, distributed in 90 galaxies from MaNGA Product Launch-7. We find that WR regions are exclusively found in galaxies with the bluest colors and highest star formation rates. Most WR galaxies have late-type morphologies and show relatively large asymmetry in their images, implying WR regions exist more in interacting galaxies. We estimate the stellar mass function of WR galaxies and the mass-dependent detection rate (typically ∼2%). This rate is about 40 times higher than that in catalogs from SDSS single-fiber surveys and half that of the CALIFA-based catalog. The difference in detection rates can be explained mainly by three factors: spatial coverage, spectral signal-to-noise ratio, and redshift ranges of parent samples. We tabulate WR galaxy properties for future studies.
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