This study explores how parametric uncertainties in the production affect failure tensile loads of reinforced thermoplastic pipes (RTPs) under combined loading conditions. The stress distributions in ...RTPs are examined with three-dimensional (3D) elasticity theory, and the analytical micromechanics of composites are evaluated. To evaluate the failure mechanisms for RTPs, 3D Hashin—Yeh failure criteria are combined with the damage evolution model to establish a progressive failure model. The theoretical model has been validated through numerical simulations and axial tensile tests data. To analyze how randomness of relevant parameters affects the first-ply failure (FPF) tensile load and final failure (FF) tensile load in RTPs, many samples are produced with the Monte—Carlo approach. The stochastic analysis results are statistically evaluated through the Weibull probability density distribution function. For the randomness of production parameters, the failure tensile load of RTPs fluctuates near the mean value. As the ply number at the reinforced layer increases, the dispersion of failure tensile load increases, with a high probability that the FPF tensile load of RTPs is lower than the mean value.
Platinum-based catalysts represent a state of the art in the electrocatalysis of oxygen reduction reaction (ORR) from the point of view of their activity and durability in harnessing the chemical ...energy via direct electrochemical conversion. However, because platinum is both expensive and scarce, its widespread implementation in such clean energy applications is limited. Recent breakthroughs in the synthesis of high-performance nonprecious metal catalysts (NPMCs) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this Account, we discuss how we can obtain highly promising M–N–C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800–1000 °C. The activity and durability of resulting catalysts depend greatly on the selection of precursors and synthesis chemistry. In addition, they correlate quite well with the catalyst nanostructure. While chemists have presented no conclusive description of the active catalytic site for this class of NPMCs, they have developed a designed approach to making active and durable materials, focusing on the catalyst nanostructure. The approach consists of nitrogen doping, in situ carbon graphitization, and the usage of graphitic structures (possibly graphene and graphene oxides) as carbon precursors. Various forms of nitrogen, particularly pyridinic and quaternary, can act as n-type carbon dopants in the M–N–C catalysts, assisting in the formation of disordered carbon nanostructures and donating electrons to the carbon. The CNx structures are likely a crucial part of the ORR active site(s). Noteworthy, the ORR activity is not necessarily governed by the amount of nitrogen, but by how the nitrogen is incorporated into the nanostructures. Apart from the possibility of a direct participation in the active site, the transition metal often plays an important role in the in situ formation of various carbon nanostructures by catalyzing the decomposition of the nitrogen/carbon precursor. We can control the formation of different nanostructures during the synthesis of M–N–C catalysts. For example, in situ formed nitrogen-doped graphene-sheets can only be derived from polyaniline (PANI), probably due to structural similarities between the aromatic structures of PANI and graphene. Highly-graphitized carbon nanostructures may serve as a matrix for the formation of ORR-active groups with improved catalytic activity and durability, containing nitrogen and most probably also metal atoms. In the future, we will likely focus NPMC synthesis approaches on precise control of interactions between precursors of the metal and carbon/nitrogen during the heat treatment. The main purposes will be to maximize the number of active sites, optimize nitrogen doping levels, and generate morphologies capable of hosting active and stable ORR sites.
Perovskite quantum dots are emerging as attractive materials for photonic and optoelectronic applications. Patterning is an important step to incorporate them into display, anti‐counterfeiting, and ...optical chip applications. In this work, an in situ inkjet printing strategy is demonstrated for fabricating perovskite quantum dots patterns by printing perovskite precursor solutions onto a polymeric layer. Importantly, this strategy can achieve bright photoluminescence with a quantum yield up to 80% and shows broad applicability to a variety of perovskites and polymers. Moreover, the as‐fabricated perovskite quantum dots patterns are composed of a microdisks array on the surface of polymeric layer. The size of these microdisks can be varied by adjusting the printing temperature. To demonstrate the potential use in display and advanced anti‐counterfeiting applications, color pixel patterns and 2D code pattern are fabricated by varying the precursor solutions. The combination of superior photoluminescence properties, simple process, and low cost makes the in situ inkjet printing strategy very promising for patterning perovskite quantum dots toward photonic integrations.
An in situ inkjet printing strategy is developed for fabricating perovskite quantum dot patterns by printing perovskite precursor solutions onto a polymeric layer. The strategy is versatile, simple, and low cost to achieve color pixel patterns and/or 2D codes with strong photoluminescence, which are promising for anti‐counterfeiting and display applications.
The urgent need to address the high-cost issue of proton-exchange membrane fuel cell (PEMFC) technologies, particularly for transportation applications, drives the development of simultaneously ...highly active and durable platinum group metal-free (PGM-free) catalysts and electrodes. The past decade has witnessed remarkable progress in exploring PGM-free cathode catalysts for the oxygen reduction reaction (ORR) to overcome sluggish kinetics and catalyst instability in acids. Among others, scientists have identified the newly emerging atomically dispersed transition metal (M: Fe, Co, or/and Mn) and nitrogen co-doped carbon (M-N-C) catalysts as the most promising alternative to PGM catalysts. Here, we provide a comprehensive review of significant breakthroughs, remaining challenges, and perspectives regarding the M-N-C catalysts in terms of catalyst activity, stability, and membrane electrode assembly (MEA) performance. A variety of novel synthetic strategies demonstrated effectiveness in improving intrinsic activity, increasing active site density, and attaining optimal porous structures of catalysts. Rationally designing and engineering the coordination environment of single metal MN
x
sites and their local structures are crucial for enhancing intrinsic activity. Increasing the site density relies on the innovative strategies of restricting the migration and agglomeration of single metal sites into metallic clusters. Relevant understandings provide the correlations among the nature of active sites, nanostructures, and catalytic activity of M-N-C catalysts at the atomic scale through a combination of experimentation and theory. Current knowledge of the transferring catalytic properties of M-N-C catalysts to MEA performance is limited. Rationally designing morphologic features of M-N-C catalysts play a vital role in boosting electrode performance through exposing more accessible active sites, realizing uniform ionomer distribution, and facilitating mass/proton transports. We outline future research directions concerning the comprehensive evaluation of M-N-C catalysts in MEAs. The most considerable challenge of current M-N-C catalysts is the unsatisfied stability and rapid performance degradation in MEAs. Therefore, we further discuss practical methods and strategies to mitigate catalyst and electrode degradation, which is fundamentally essential to make M-N-C catalysts viable in PEMFC technologies.
The review provides a comprehensive understanding of the atomically dispersed metal-nitrogen-carbon cathode catalysts for proton-exchange membrane fuel cell applications.
Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless ...systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.
Perovskite quantum dots have been proven promising for photonic and optoelectronic applications, particularly, as bright and narrow band emitters for display technology. Despite the advantageous ...properties, the stability issues have to be resolved to unleash the full industrial potential of perovskite quantum dots in display technology.
Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low ...photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2–8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn4+ as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.
The gastrointestinal tract is known as the largest endocrine organ that encounters and integrates various immune stimulations and neuronal responses due to constant environmental challenges. ...Enterochromaffin (EC) cells, which function as chemosensors on the gut epithelium, are known to translate environmental cues into serotonin (5-HT) production, contributing to intestinal physiology. However, how immune signals participate in gut sensation and neuroendocrine response remains unclear. Interleukin-33 (IL-33) acts as an alarmin cytokine by alerting the system of potential environmental stresses. We here demonstrate that IL-33 induced instantaneous peristaltic movement and facilitated Trichuris muris expulsion. We found that IL-33 could be sensed by EC cells, inducing release of 5-HT. IL-33-mediated 5-HT release activated enteric neurons, subsequently promoting gut motility. Mechanistically, IL-33 triggered calcium influx via a non-canonical signaling pathway specifically in EC cells to induce 5-HT secretion. Our data establish an immune-neuroendocrine axis in calibrating rapid 5-HT release for intestinal homeostasis.
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•IL-33-ST2 signaling regulates gut motility and intestinal host defense•Enterochromaffin (EC) cell-derived ST2 responds to IL-33 for 5-HT release•TRPA1 is required for IL-33-mediated 5-HT release•IL-33 induces PLC-γ1 activation for 5-HT release in both mouse and human EC cells
Enterochromaffin (EC) cells are known to act as chemosensors on the gut epithelium, translating environmental cues into serotonin (5-HT) production. Chen et al. demonstrate that an alarmin cytokine IL-33 could be sensed by EC cells, inducing release of 5-HT, regulating intestinal homeostasis and host defense.
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•A general theoretical frame for nuclear quadrupole relaxation in liquids.•Fundamentals of quadrupole-central-transition NMR spectroscopy in solution.•Recent 17O ...quadrupole-central-transition NMR studies of biological macromolecules.•Review of solid-state 17O NMR studies of organic/biological molecules since 2008.
This review describes the latest developments in the field of 17O NMR spectroscopy of organic and biological molecules both in aqueous solution and in the solid state. In the first part of the review, a general theoretical description of the nuclear quadrupole relaxation process in isotropic liquids is presented at a mathematical level suitable for non-specialists. In addition to the first-order quadrupole interaction, the theory also includes additional relaxation mechanisms such as the second-order quadrupole interaction and its cross correlation with shielding anisotropy. This complete theoretical treatment allows one to assess the transverse relaxation rate (thus the line width) of NMR signals from half-integer quadrupolar nuclei in solution over the entire range of motion. On the basis of this theoretical framework, we discuss general features of quadrupole-central-transition (QCT) NMR, which is a particularly powerful method of studying biomolecules in the slow motion regime. Then we review recent advances in 17O QCT NMR studies of biological macromolecules in aqueous solution. The second part of the review is concerned with solid-state 17O NMR studies of organic and biological molecules. As a sequel to the previous review on the same subject G. Wu, Prog. Nucl. Magn. Reson. Spectrosc. 52 (2008) 118–169, the current review provides a complete coverage of the literature published since 2008 in this area.
In recent years, significant progress has been achieved in the development of platinum group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts for proton exchange membrane (PEM) fuel ...cells. At the same time the limited durability of these catalysts remains a great challenge that needs to be addressed. This mini‐review summarizes the recent progress in understanding the main causes of instability of PGM‐free ORR catalysts in acidic environments, focusing on transition metal/nitrogen codoped systems (M‐N‐C catalysts, M: Fe, Co, Mn), particularly MNx moiety active sites. Of several possible degradation mechanisms, demetalation and carbon oxidation are found to be the most likely reasons for M‐N‐C catalysts/cathodes degradation.
The current understanding of the degradation mechanisms of platinum‐group‐metal (PGM)‐free oxygen reduction reaction catalysts in proton exchange membrane fuel cells is reviewed with a focus on transition metal/nitrogen codoped carbon catalysts (M–N–C; M: Fe, Co, Mn). Among others, demetalation and carbon oxidation are believed to be the main pathways for M–N–C catalysts/cathodes degradation.
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