In contrast to the wealth of asymmetric transformations for generating central chirality from alkyl radicals, the enantiocontrol over the allenyl radicals for forging axial chirality represents an ...uncharted domain. The challenge arises from the unique elongated linear configuration of the allenyl radicals that necessitates the stereo‐differentiation of remote motifs away from the radical reaction site. We herein describe a copper‐catalyzed asymmetric radical 1,4‐carboalkynylation of 1,3‐enynes via the coupling of allenyl radicals with terminal alkynes, providing diverse synthetically challenging tetrasubstituted chiral allenes. A chiral N,N,P‐ligand is crucial for both the reaction initiation and the enantiocontrol over the highly reactive allenyl radicals. The reaction features a broad substrate scope, covering a variety of (hetero)aryl and alkyl alkynes and 1,3‐enynes as well as radical precursors with excellent functional group tolerance.
A copper‐catalyzed asymmetric radical 1,4‐carboalkynylation of 1,3‐enynes is realized, providing diverse tetrasubstituted chiral allenes. The utilization of the copper/chiral N,N,P‐ligand is crucial for the enantiocontrol over the allenyl radicals, which is difficult due to their elongated linear configuration that necessitates the stereo‐differentiation of remote motifs away from the reaction site.
The author thanks Dr. R. Sinha very much for providing detailed design equations for the proposed dual-band impedance transformer in <xref ref-type="bibr" rid="ref1">1 . Note that the analytical ...solutions for Z 1 are very necessary, which are developed in <xref ref-type="bibr" rid="ref1">1 , in closed form. In fact, the generalized and closed-form solutions for this kind of impedance transformers have been published in <xref ref-type="bibr" rid="ref2">2 . It is very interesting that all results in <xref ref-type="bibr" rid="ref2">2 can be degenerated to the simple solutions in both <xref ref-type="bibr" rid="ref1">1 and the presented results in the comments by Dr. R. Sinha, when X In = 0 is considered in <xref ref-type="bibr" rid="ref2">2 .
Tin diselenide (SnSe2) nanosheets as novel 2D layered materials have excellent optical properties with many promising application prospects, such as photoelectric detectors, nonlinear optics, ...infrared photoelectric devices, and ultrafast photonics. Among them, ultrafast photonics has attracted much attention due to its enormous advantages; for instance, extremely fast pulse, strong peak power, and narrow bandwidth. In this work, SnSe2 nanosheets are fabricated by using solvothermal treatment, and the characteristics of SnSe2 are systemically investigated. In addition, the solution of SnSe2 nanosheets is successfully prepared as a fiber‐based saturable absorber by utilizing the evanescent field effect, which can bear a high pump power. 31st‐order subpicosecond harmonic mode locking is generated in an Er‐doped fiber laser, corresponding to the maximum repetition rate of 257.3 MHz and pulse duration of 887 fs. The results show that SnSe2 can be used as an excellent nonlinear photonic device in many fields, such as frequency comb, lasers, photodetectors, etc.
Tin diselenide (SnSe2) nanosheets as novel 2D layered materials have excellent optical properties. SnSe2 nanosheets fabricated by using solvothermal treatment are successfully prepared as fiber‐based saturable absorbers by utilizing the evanescent field effect, which can bear a high pump power. 31st‐order subpicosecond harmonic mode‐locking is generated, corresponding to 257.3 MHz repetition rate.
Covalent organic frameworks (COF) possess a robust and porous crystalline structure, making them an appealing candidate for energy storage. Herein, we report an exfoliated polyimide COF composite ...(P‐COF@SWCNT) prepared by an in situ condensation of anhydride and amine on the single‐walled carbon nanotubes as advanced anode for potassium‐ion batteries (PIBs). Numerous active sites exposed on the exfoliated frameworks and the various open pathways promote the highly efficient ion diffusion in the P‐COF@SWCNT while preventing irreversible dissolution in the electrolyte. During the charging/discharging process, K+ is engaged in the carbonyls of imide group and naphthalene rings through the enolization and π‐K+ effect, which is demonstrated by the DFT calculation and XPS, ex‐situ FTIR, Raman. As a result, the prepared P‐COF@SWCNT anode enables an incredibly high reversible specific capacity of 438 mA h g−1 at 0.05 A g−1 and extended stability. The structural advantage of P‐COF@SWCNT enables more insights into the design and versatility of COF as an electrode.
We prepare a polyimide covalent organic framework composite anode by effective in‐situ condensation of anhydride and amine on the surface of single‐walled carbon nanotubes. The construction of the conductive network accelerates the transport of electron. Dual electroactive sites in the framework, carbonyls and aromatic naphthalene rings, could store more potassium ions by the enolization and π‐K+ effect.
Single-epoch virial black hole (BH) mass estimators utilizing broad emission lines have been routinely applied to high-redshift quasars to estimate their BH masses. Depending on the redshift, ...different line estimators (H alpha , H beta , Mg II lambda2798, C IV lambda1549) are often used with optical/near-infrared spectroscopy. Here, we use a homogeneous sample of 60 intermediate-redshift (z ~ 1.5-2.2) Sloan Digital Sky Survey quasars with optical and near-infrared spectra covering C IV through H alpha to investigate the consistency between different single-epoch virial BH mass estimators. We discuss controversial claims in the literature on the correlation between C iv and H beta FWHMs, and suggest that the reported correlation is either a result based on small samples or only valid for low-luminosity objects.
In this paper, I examine Aristotle’s cosmological proof of God’s existence, Avicenna’s metaphysical proof, and Thomas Aquinas’s five-way proof. By comparing these proofs, I argue that philosophers ...and theologians take different approaches to proving God’s existence not only because they follow different epistemological principles but, more fundamentally, because they construct different metaphysical frameworks in which God as the Supreme Being plays different roles and is thus clarified differently. The proof of God’s existence is also of theological significance. This paper makes an original contribution by showing that, despite Avicenna’s harsh criticism, Aquinas returns to Aristotelian cosmological proof. Moreover, Aquinas goes beyond Aristotle by identifying God not only as the First Mover but also as the Creator. The theme of God’s existence bridges philosophy and theology, and it also clearly reflects the interplay and mutual influence of Greek philosophy, Arabic Aristotelianism, and Latin Scholastics.
The rational combination of conductive nanocarbon with sulfur leads to the formation of composite cathodes that can take full advantage of each building block; this is an effective way to construct ...cathode materials for lithium–sulfur (Li–S) batteries with high energy density. Generally, the areal sulfur‐loading amount is less than 2.0 mg cm−2, resulting in a low areal capacity far below the acceptable value for practical applications. In this contribution, a hierarchical free‐standing carbon nanotube (CNT)‐S paper electrode with an ultrahigh sulfur‐loading of 6.3 mg cm−2 is fabricated using a facile bottom–up strategy. In the CNT–S paper electrode, short multi‐walled CNTs are employed as the short‐range electrical conductive framework for sulfur accommodation, while the super‐long CNTs serve as both the long‐range conductive network and the intercrossed mechanical scaffold. An initial discharge capacity of 6.2 mA·h cm−2 (995 mA·h g−1), a 60% utilization of sulfur, and a slow cyclic fading rate of 0.20%/cycle within the initial 150 cycles at a low current density of 0.05 C are achieved. The areal capacity can be further increased to 15.1 mA·h cm−2 by stacking three CNT–S paper electrodes—resulting in an areal sulfur‐loading of 17.3 mg cm−2—for the cathode of a Li–S cell. The as‐obtained free‐standing paper electrode are of low cost and provide high energy density, making them promising for flexible electronic devices based on Li–S batteries.
A hierarchical free‐standing paper electrode is fabricated using short multi‐walled carbon nanotubes (MWCNTs) and super‐long CNTs. The MWCNTs function as a short‐range electrical conductive framework for sulfur accommodation, while super‐long CNTs act as both a long‐range conductive network and mechanical scaffold.
Frictional Characteristics of Atomically Thin Sheets Lee, Changgu; Li, Qunyang; Kalb, William ...
Science (American Association for the Advancement of Science),
04/2010, Volume:
328, Issue:
5974
Journal Article
Peer reviewed
Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS₂), niobium diselenide, and hexagonal boron ...nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS₂ exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length-dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets' increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.
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