Here, novel ferroelectric ceramics of (0.95 − x)BiScO3‐xPbTiO3‐0.05Pb(Sn1/3Nb2/3)O3 (BS‐xPT‐PSN) of complex perovskite structure are reported with compositions near the morphotropic phase boundary ...(MPB), and which exhibit a piezoelectric coefficient d33 = 555 pC N−1, a large‐signal coefficient d33∗ ≈ 1200 pm V−1 at room temperature, and a high Curie temperature TC of 408 °C. More interestingly, this ternary system exhibits a giant and stable piezoelectric response at 200 °C with a large‐signal d33∗ ≈ 2500 pm V−1, matching that of the costly relaxor‐based piezoelectric single crystals at room temperature. The mechanisms of such giant piezoelectricity and its characteristic temperature dependence are attributed to the spontaneous polarization rotation and extension under an electric field and the MPB‐related phase transition. The findings reveal that the BS‐xPT‐PSN ceramics constitute a new family of high‐performance piezoelectric materials suitable for electromechanical transducers that can be operated at high temperatures (at 200 °C, or higher).
Ferroelectric ceramics of (0.95 − x)BiScO3‐xPbTiO3‐0.05Pb(Sn1/3Nb2/3)O3 exhibit a giant and stable piezoelectric response at 200 °C with a large‐signal d33∗ ≈ 2500 pm V−1, which is comparable to piezoelectric single crystals. Relevant physical mechanisms underlying the temperature‐enhanced spontaneous polarization rotation and extension under an electric field is demonstrated by Landau–Ginsburg–Devonshire phenomenological model.
The rapid development in wearable electronics has spurred a great deal of interest in flexible energy storage devices, particularly fiber‐shaped energy storage devices (FSESDs), such as fiber‐shaped ...supercapacitors (FSSCs) and fiber‐shaped batteries (FSBs). Depending on their electrode configurations, FSESDs can contain five differently structured electrodes, including parallel fiber electrodes (PFEs), twisted fiber electrodes (TFDs), wrapped fiber electrodes (WFEs), coaxial fiber devices (CFEs), and rolled electrodes (REs). Various rational methods have been devised to incorporate these fiber‐shaped electrodes into multifunctional FSESDs, including fiber‐shaped supercapacitors, lithium‐ion batteries, lithium–sulfur batteries, lithium–air batteries, zinc–air batteries, and aluminum–air batteries. Although significant progress has been made in FSESDs, it remains a major challenge to make high‐performance fiber‐shaped devices at low cost. A focused and critical review of the recent advancements in fiber‐shaped supercapacitors and lithium‐ion batteries is provided here. The pros and cons for each of the aforementioned electrode configurations and FSESDs are discussed, along with current challenges and future opportunities for FSESDs.
The recent development of fiber‐shaped energy systems is reviewed, highlighting the structural design of fiber‐based electronic devices in combination with their applications in energy storage, energy harvesting, and other related fields. Current challenges and future outlooks regarding this emerging area are discussed.
By virtue of a fundamentally new reaction model of azomethine ylide serving as a two‐atom synthon, we present the first example of stereodivergent preparation of γ‐butyrolactones via synergistic ...Cu/Ir‐catalyzed asymmetric cascade allylation/lactonization, and all four stereoisomers of γ‐butyrolactones bearing two vicinal stereocenters are accessible with excellent diastereoselective and enantioselective control. The chiral IrIII‐π‐allyl intermediate was separated and characterized to understand the origin of the regio‐ and stereoselectivity of the initial C−C bond formation process. Control experiments shed some light on the catalyst/substrate and catalyst/catalyst interactions in this dual catalytic system to rationalize the related kinetic/dynamic kinetic resolution process with different catalyst combinations. The enantioenriched γ‐butyrolactone products were converted into an array of structurally complex chiral molecules and organocatalysts that were otherwise inaccessible.
An unprecedented asymmetric cascade allylation/lactonization between racemic aldimine esters and racemic vinylethylene carbonate catalyzed by synergistic Cu/Ir catalysis is presented. The metalated azomethine ylide acts as a two‐atom unit and opens up access to a broad range of γ‐butyrolactones bearing two vicinal stereogenic centers in a stereodivergent manner.
We examine the liquidity of 456 different cryptocurrencies, and show that return predictability diminishes in cryptocurrencies with high market liquidity. We show that whilst Bitcoin returns are ...showing signs of efficiency, numerous cryptocurrencies still exhibit signs of autocorrelation and non-independence. Our findings also show a strong relationship between the Hurst exponent and liquidity on a cross-sectional basis. Therefore, we conclude that liquidity plays a significant role in market efficiency and return predictability of new cryptocurrencies.
•We examine 456 cryptocurrencies.•Return predictability diminishes as liquidity increases in cryptocurrencies.•Volatility decreases as liquidity increases in cryptocurrencies.•There are no signs of an illiquidity premium.
Spirocyclic pyrrolidines are structural motifs frequently found in a wide variety of natural products, pharmaceuticals and biologically significant compounds. In the past few years, catalytic ...asymmetric 1,3-dipolar cycloaddition reactions of azomethine ylides have shown to be one of the most straightforward methods for the stereoselective preparation of diverse biologically important spiropyrrolidine heterocycles in high yields with excellent enantioselectivities under mild reaction conditions. In this review, we will discuss the recent major developments in the catalytic enantioselective synthesis of chiral spiropyrrolidine derivatives since 2009.
In this review, recent progress on the catalytic enantioselective synthesis of chiral spiropyrrolidine derivatives
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1,3-dipolar cycloaddition of azomethine ylides has been discussed.
Depth Estimation with Occlusion Modeling Using Light-Field Cameras Ting-Chun Wang; Efros, Alexei A.; Ramamoorthi, Ravi
IEEE transactions on pattern analysis and machine intelligence,
2016-Nov.-1, 2016-11-00, 2016-11-1, 20161101, Letnik:
38, Številka:
11
Journal Article
Recenzirano
Light-field cameras have become widely available in both consumer and industrial applications. However, most previous approaches do not model occlusions explicitly, and therefore fail to capture ...sharp object boundaries. A common assumption is that for a Lambertian scene, a pixel will exhibit photo-consistency, which means all viewpoints converge to a single point when focused to its depth. However, in the presence of occlusions this assumption fails to hold, making most current approaches unreliable precisely where accurate depth information is most important - at depth discontinuities. In this paper, an occlusion-aware depth estimation algorithm is developed; the method also enables identification of occlusion edges, which may be useful in other applications. It can be shown that although photo-consistency is not preserved for pixels at occlusions, it still holds in approximately half the viewpoints. Moreover, the line separating the two view regions (occluded object versus occluder) has the same orientation as that of the occlusion edge in the spatial domain. By ensuring photo-consistency in only the occluded view region, depth estimation can be improved. Occlusion predictions can also be computed and used for regularization. Experimental results show that our method outperforms current state-of-the-art light-field depth estimation algorithms, especially near occlusion boundaries.
Conspectus Optically active nitrogen-containing compounds have attracted substantial attention due to their ubiquity in the cores of natural products and bioactive molecules. Among the various ...synthetic approaches to nitrogenous frameworks, catalytic asymmetric 1,3-dipolar cycloadditions are one of the most attractive methods because of their powerful ability to rapidly construct various chiral N-heterocycles. In particular, N-metallated azomethine ylides, common and readily available 1,3-dipoles, have been extensively applied in dipolar cycloaddition reactions. Despite the fact that asymmetric transformations of azomethine ylides have been investigated for decades, most of the efforts have been directed toward the preparation of pyrrolidines using glycinate-derived α-unsubstituted aldimine esters as the precursors of the azomethine ylides. While α-substituted azomethine ylides derived from amino esters other than glycinate have seldom been harnessed, the construction of non-five-membered chiral N-heterocycles via 1,3-dipolar cycloadditions remains underexplored. In addition, the asymmetric α-functionalization of aldimine esters to prepare acyclic nitrogenous compounds such as α-amino acids, in which an in situ-generated N-metallated azomethine ylide serves as the nucleophile, has not been sufficiently described. In this Account, we mainly discuss the achievements we have made in the past decade toward broadening the applications of N-metallated azomethine ylides for the preparation of nitrogen-containing compounds. We began our investigation with the design and synthesis of a new type of chiral ligand, TF-BiphamPhos, which not only coordinates with Lewis acids to activate dipolar species but also serves as an H-bond donor to increase the reactivity of dipolarophiles with significantly enhanced stereochemical control. Using the Cu(I) or Ag(I)/TF-BiphamPhos complex as the catalyst, we achieved highly stereoselective (3+2) cycloadditions of glycinate and non-glycinate-derived azomethine ylides with diverse dipolarophiles, producing a variety of enantioenriched pyrrolidines with multiple stereocenters in a single step. To further expand the synthetic utility of N-metallated azomethine ylides, we successfully developed higher order cycloadditions with fulvenes, tropone, 2-acyl cycloheptatrienes, and pyrazolidinium ylides serving as the reaction partner, and this reaction provides straightforward access to enantioenriched fused piperidines, bridged azabicyclic frameworks, and triazines via (3+6)- and (3+3)-type cycloadditions. Using N-metallated azomethine ylides as the nucleophile, we realized Cu(I)-catalyzed asymmetric 1,4-Michael additions with α,β-unsaturated bisphosphates/Morita–Baylis–Hillman products, furnishing an array of structurally diverse unnatural α-amino acids. Based on the strategy of synergistic activation, we achieved highly efficient dual Cu/Pd and Cu/Ir catalysis for the α-functionalization of aldimine esters via the asymmetric allylic/allenylic alkylation of N-metallated azomethine ylides. Notably, Cu/Ir catalysis allowed the stereodivergent synthesis of α,α-disubstituted α-amino acids via a branched allylic alkylation reaction, in which the two distinct chiral metal catalysts independently have full stereochemical control over the corresponding nucleophile and electrophile. Furthermore, an expedient and stereodivergent preparation of biologically important tetrahydro-γ-carbolines was realized through a Cu/Ir-catalyzed cascade allylation/iso-Pictet–Spengler cyclization. In addition, when the steric congestion in the allylation intermediates was increased, the combined Cu/Ir catalysts provided an asymmetric cascade allylation/2-aza-Cope rearrangement, producing various optically active homoallylic amines with impressive results.
This study is the first to demonstrate that ferroelectric R3c LiNbO3‐type ZnSnO3 nanowires (NWs), through the piezocatalysis and piezophototronic process, demonstrate a highly efficient hydrogen ...evolution reaction (HER). The polarization and electric field curves indicate that ZnSnO3 NWs exhibit typical ferroelectric hysteresis loops. Time‐resolved photoluminescence spectra reveal that the relaxation time increases with the increasing concentration of oxygen vacancies. Moderated 3H‐ZnSnO3 NWs (thermally annealed for 3 h in a hydrogen environment) have the longest extended carrier lifetime of approximately 8.3 ns. The piezoelectricity‐induced HER, via the piezocatalysis process (without light irradiation), reaches an optimal H2‐production rate of approximately 3453.1 µmol g−1 h−1. Through the synergistic piezophototronic process, the HER reaches approximately 6000 µmol g−1 in 7 h. Crucially, the mechanical force–induced spontaneous polarization functions as a carrier separator, driving the electron and hole in opposite directions in ferroelectric ZnSnO3 NWs; this separation reduces the recombination rate, enhancing the redox process. This theoretical analysis indicates that the photocatalytic and piezocatalytic effects can synergistically enhance piezophototronic performance through capitalizing on well‐modulated oxygen vacancies in ferroelectric semiconductors. This study demonstrates the essential role of this synergy in purifying water pollutants and converting water into hydrogen gas through the piezophototronic process.
The well‐controlled oxygen vacancies of ferroelectric R3c ZnSnO3 nanowires show that a highly efficient hydrogen evolution reaction (HER) reaches approximately 6000 mol g−1 in 7 h through the synergistic piezophototronic process. This is the first study to investigate how the oxygen vacancy concentration can be tuned in ferroelectric crystals to enhance the performance of piezodegradation and HER through the piezophotoelectric effect.
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.
Organocatalysis has proven to be one of the most rapidly developing and competitive research areas in asymmetric catalysis since 2000, and has become a third branch besides biocatalysis and ...transition metal catalysis. In this feature article, recent progress from our research group on asymmetric organocatalysis, focusing on fine-tunable amine-thiourea catalysis, is described. Design of novel bifunctional amine-thiourea organocatalysts based upon the synergistic activation strategy
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multiple hydrogen bonds and their applications in asymmetric C-C, C-N, and C-S bond-forming reactions under mild conditions are discussed in detail. The most attractive feature of the newly designed fine-tunable amine-thiourea catalysts is the incorporation of multiple hydrogen bonding donors and stereogenic centers.
Recent progress in asymmetric organocatalysis, focusing on fine-tunable amine-thiourea catalysis, is described. Design of novel bifunctional amine-thiourea organocatalysts bearing multiple hydrogen-bonding donors and their applications in asymmetric C-C, C-N, and C-S bond-forming reactions under mild conditions are discussed.
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