193,303 research outputs found
Characterization of an alternatively spliced G(M2) activator protein, G(M2A) protein - An activator protein which stimulates the enzymatic hydrolysis of N-acetylneuraminic acid, but not N-acetylgalactosamine, from G(M2)
No full textG(M2) activator protein is a protein cofactor which stimulates the enzymatic hydrolysis of both GalNAc and NeuAc from G(M2). We have previously isolated two cDNA clones, G(M2) activator cDNA and G(M2A) cDNA, for human G(M2) activator protein (Nagarajan, S., Chen, H.-C., Li, S.-C., Li, Y.-T., and Lockyer, J. M. (1992) Biochem. J. 282, 807-813). G(M2A) mRNA is an RNA alternative splicing product that contains exons 1, 2, 3, and intron 3 of the genomic DNA sequence of G(M2) activator protein (Klima, H., Tanaka, A., Schnabel, D., Nakano, T., Schroder, M., Suzuki, K., and Sandhoff, K. (1991) FEES Left. 289, 260-264). G(M2A) cDNA encodes a protein (G(M2A) protein) containing 1-109 of the 160 amino acids of human G(M2) activator protein, plus a tripeptide (VST) encoded by intron 3 at the COOH terminus. Thus, G(M2A) protein can be regarded as a form (truncated version) of G(M2) activator protein. We have expressed G(M2A) cDNA in Escherichia coli using pT7-7 as the vector. The recombinant G(M2A) protein was purified to an electrophoretically homogeneous form and was found to stimulate the hydrolysis of NeuAc from G(M2) by clostridial sialidase, but not the hydrolysis of GalNAc from G(M2) by beta-hexosaminidase A. Like G(M2) activator protein, G(M2A) protein also specifically recognized the terminal G(M2) epitope in GalNAc-GD1a and stimulated the hydrolysis of only the external NeuAc from this ganglioside by clostridial sialidase. These results enabled us to discern the enzymatic hydrolyses of GalNAc and NeuAc from the G(M2) epitope and established that the NeuAc recognition domain of G(M2) activator protein is located within amino acids 1-109. The presence of G(M2A) mRNA in human tissues and the selective stimulation of NeuAc hydrolysis by G(M2A) protein indicate that this activator protein may be involved in the catabolism of G(M2) through the asialo-G(M2) pathway
Corrigendum to “Reliability assessment of generic geared wind turbines by GTST-MLD model and Monte Carlo simulation” (Renewable Energy (2015) 83 (222–233), (S0960148115003158), (10.1016/j.renene.2015.04.035))
No full textThe authors regret that the Order of Authors in this article published in November 2015 is incorrect. Thus, the objective of this Corrigendum is to re-establish the originally agreed Order of Authors, as described below. Order of Authors from published Article: Yan-Fu Li, PhD; Sebastien Valla; Enrico Zio, PhD. Corrected Order of Authors to implement with this Corrigendum: Sebastien Valla, Yan-Fu Li, PhD; Enrico Zio, PhD. The Corresponding author to contact for these changes are the Primary Author, Sebastien Valla (email below). The authors would like to apologise for any inconvenience caused
SPECIFIC RECOGNITION OF N-ACETYLNEURAMINIC ACID IN THE G(M2) EPITOPE BY HUMAN G(M2) ACTIVATOR PROTEIN
No full textG(M2) Activator is a low molecular weight protein cofactor that stimulates the enzymatic conversion of G(M2) into G(M3) by human beta-hexosaminidase A and also the conversion of G(M2) into G(A2) by clostridial sialidase (Wu, Y.-Y., Lockyer, J. M., Sugiyama, E., Pavlova, N. V., Li, Y.-T., and Li, S.- C. (1994) J. Biol. Chem. 269, 16276-16283). Among the five known activator proteins for the enzymatic hydrolysis of glycosphingolipids, only G(M2) activator is effective in stimulating the hydrolysis of G(M2). However, the mechanism of action of G(M2) activator is still not well understood, Using a unique disialosylganglioside, GalNAc-G(D1a), as the substrate, we were able to show that in the presence of G(M2) activator, GalNAc-G(D1a) was specifically converted into GalNAc-G(M1a) by clostridial sialidase, while in the presence of saposin B, a nonspecific activator protein, GalNAc-G(D1a) was converted into both GalNAc-G(M1a) and GalNAc-G(M1b). individual products generated from GalNAc-G(D1a) by clostridial sialidase were identified by thin layer chromatography, negative secondary ion mass spectrometry, and immunostaining with a monoclonal IgM that recognizes the G(M2) epitope. Our results clearly show that G(M2) activator recognizes the G(M2) epitope in GalNAc-G(D1a). Thus, G(M2) activator may interact with the trisaccharide structure of the G(M2) epitope and render the GalNAc and NeuAc residues accessible to beta-hexosaminidase A and sialidase, respectively
Accelerating S↔Li2S Reactions in Li–S Batteries through Activation of S/Li2S with a Bifunctional Semiquinone Catalyst
No full textThe reaction rate bottleneck during interconversion between insulating S8 (S) and Li2S fundamentally leads to incomplete conversion and restricted lifespan of Li−S battery, especially under high S loading and lean electrolyte conditions. Herein, we demonstrate a new catalytic chemistry: soluble semiquinone, 2-tertbutyl-semianthraquinone lithium (Li+TBAQ⋅−), as both e-/Li+ donor and acceptor for simultaneous S reduction and Li2S oxidation. The efficient activation of S and Li2S by Li+TBAQ⋅− in the initial discharging/charging state maximizes the amount of soluble lithium polysulfide, thereby substantially improve the rate of solid–liquid-solid reaction by promoting long-range electron transfer. With in situ Raman spectra and theoretical calculations, we reveal that the activation of S/Li2S is the rate-limiting step for effective S utilization under high S loading and low E/S ratio. Beyond that, the S activation ratio is firstly proposed as an accurate indicator to quantitatively evaluate the reaction rate. As a result, the Li−S batteries with Li+TBAQ⋅− deliver superior cycling performance and over 5 times higher S utilization ratio at high S loading of 7.0 mg cm−2 and a current rate of 1 C compared to those without Li+TBAQ⋅−. We hope this study contributes to the fundamental understanding of S redox chemical and inspires the design of efficient catalysis for advanced Li−S batteries.No Full Tex
Multifunctional Cellulose Nanocrystals as a High-Efficient Polysulfide Stopper for Practical Li–S Batteries
No full textBecause of the severe shuttle effect of polysulfides, achieving durable Li-S batteries is still a great challenge, especially under practical operation conditions including the high sulfur content, high loading, and high operation temperature. Herein, for the first time, low-cost, eco-friendly, and hydrophilic cellulose nanocrystals (CNCs) are proposed as a multifunctional polysulfide stopper for Li-S batteries with high performance. CNCs display an intrinsically high aspect ratio and a large surface area and contain a large amount of hydroxyl groups offering a facile platform for chemical interactions. Density functional theory calculations suggest that the electron-rich functional groups on CNCs deliver robust binding energies with polysulfides. In this work, CNCs not only firmly confine sulfur and polysulfides in the cathode as a robust binder, but also further hinder polysulfide shuttling to the Li anode as a polysulfide stopper on a separator. Consequently, the as-prepared Li-S batteries demonstrate outstanding cycling performance even under the conditions of high sulfur content of 90 wt % (63 wt % in the cathode), high loading of 8.5 mg cm-2, and high temperature of 60 °C. These results sufficiently demonstrate that CNCs have significant application potential in Li-S battery technologies.No Full Tex
Electrical conductivity and Li-6,Li-7 NMR studies of Li1+yCoO2
No full textThe battery cathode material LiCoO2 was synthesized with a deliberate excess of Li, according to Li1+yCoO2, where y = 0.08 and 0.35 (nominally). The effect of divalent doping with Mg2+ was also explored for some samples, with y values of 0.0 (stoichiometric) and 0.08. Electrical conductivity measurements of the stoichiometric material, without Mg, as functions of oxygen partial pressure and temperature exhibit p-type semiconducting behaviour and suggest that the defects primarily responsible for the generation of holes are cobalt ion vacancies. Excess Li increases the electrical conductivity, while the incorporation of Mg leads to a more dramatic enhancement in conductivity, the latter interpreted as a transition to metallic behaviour. NMR spectroscopic measurements of both Li-6,Li-7 isotopes suggest that only a small fraction (< 20%) of the excess Li in the y = 0.35 material enters the structure ionically while reducing the formal Co valence. Most of the excess consists of Li2CO3 and possibly other impurity phases, the former also having been identified by X-ray diffraction. Another small portion of the excess Li (about 10%) appears to enter interstitial sites in close proximity to paramagnetic Co2+ ions
Decomposition of the mean friction drag in zero-pressure-gradient turbulent boundary layers
No full textThe ability to understand and predict mean friction drag generation in wall-bounded turbulence is highly desirable in many engineering applications. In this paper, we decompose the mean friction drag in incompressible (250 ≤ Reτ ≤ 1270) and compressible (M = 2.0 and 250 ≤ Reτ ≤ 1110) zero-pressure-gradient turbulent boundary layers (TBLs) into three physics-informed contributions, by using the identity of Renard and Deck ["A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer," J. Fluid Mech. 790, 339-367 (2016)] and its compressible-flow extension [Li et al., "Decomposition of the mean skin-friction drag in compressible turbulent channel flows," J. Fluid Mech. 875, 101-123 (2019)], respectively. The Reynolds number effects and scaling of each contributing term are investigated. Proportionality of the viscous and logarithmic increase with Reτ of the turbulent one when scaled by Cf3/2 are found, with different scaling coefficients in incompressible and compressible TBLs, owing to variation in the thermodynamic properties in the compressible cases. On use of compressibility transformations to account for variation in the thermodynamic properties in the wall-normal direction, the terms contributing to friction in compressible TBLs are found to reduce to those in the incompressible limit, with good accuracy. At M = 2.0, deviations from universality are mainly confined to the near-wall region, say y+ < 30, and account for approximately 16% of the generated friction
Modeling of Electrochemical Performance and its Relation to Mechanical Responses of Li Metal Batteries
No full textThe development and commercialization of Li metal batteries are hindered by safety challenges. Accordingly, significant efforts have been made to improve the stability of Li anodes. However, only a few studies have focused on the impact of mechanical deformation caused by Li deposition at the cell level. The strain changes are considerably large and should be further investigated for their mechanical impact. Therefore, in this study, we focused on the development of a physics-based model for Li metal batteries. To the best of our knowledge, this is the first attempt to develop a model that can describe the electrochemical and mechanical responses of a full Li metal cell with different material properties, external pressures, and boundary conditions. The Young's modulus and higher expansion ratio of the negative electrode increase overall stress generation. However, overall cell pressure decreases with an increasing expansion ratio of the positive electrode. This is because the positive electrode contracts in response to the significant expansion of the lithium metal. The current model provides insights into the mechanisms by which these factors affect the electrochemical and mechanical behaviors of Li metal cells. This model provides guidance for battery design and management of Li metal cells.
Effects of vinyl ethylene carbonate additive on elevated-temperature performance of cathode material in lithium ion batteries
No full textThe addition of 2% vinyl ethylene carbonate (VEC) into LiPF6/EC + DMC electrolyte can significantly improve the cyclic performance of a LiNio.8Co0.2O2/Li cell at elevated temperatures such as 50 °C. In situ electrochemical mass spectrometry (EMS) was used to investigate the gas evolution spectroscopy in the cell during a charge/discharge process with and without VEC additive. Fourier transform infrared (FTIR), ultraviolet-visible (UV-vis), and liquid nuclear magnetic resonance (NMR) spectroscopies were also carried out to investigate the reactions between various electrolyte components and VEC without the electrochemical reaction. We propose the possible polymerized products based on the spectroscopy and the acting mechanism of the VEC additives. © 2008 American Chemical Society
Recognizing the Mechanism of Sulfurized Polyacrylonitrile Cathode Materials for Li-S Batteries and beyond in Al-S Batteries
No full textSulfurized polyacrylonitrile (SPAN) is the most promising cathode for next-generation lithium-sulfur (Li-S) batteries due to the much improved stability. However, the molecular structure and reaction mechanism have not yet been fully understood. Herein, we present a new take on the structure and mechanism to interpret the electrochemical behaviors. We find that the thiyl radical is generated after the cleavage of the S-S bond in molecules in the first cycle, and then a conjugative structure can be formed due to electron delocalization of the thiyl radical on the pyridine backbone. The conjugative structure can react with lithium ions through a lithium coupled electron transfer process and form an ion-coordination bond reversibly. This could be the real reason for the superior lithium storage capability, in which the lithium polysulfide may not be formed. This study refreshes current knowledge of SPAN in Li-S batteries. In addition, the structural analysis is applicable to analyze the current organic cathodes in rechargeable batteries and also allows further applications in Al-S batteries to achieve high performance
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