Since the first demonstration, remarkable progress has been made in the theoretical analysis, structural design, numerical simulation, and potential applications of metamaterial absorbers (MAs). With ...the continuous advancement of novel materials and creative designs, the absorption of MAs is significantly improved over a wide frequency spectrum from microwaves to the optical regime. Further, the integration of active elements into the MA design allows the dynamical manipulation of electromagnetic waves, opening a new platform to push breakthroughs in metadevices. In the last several years, numerous efforts have been devoted to exploring innovative approaches for incorporating tunability to MAs, which is highly desirable because of the progressively increasing demand on designing versatile metadevices. Here, a comprehensive and systematical overview of active MAs with adaptive and on‐demand manner is presented, highlighting innovative materials and unique strategies to precisely control the electromagnetic response. In addition to the mainstream method by manipulating periodic patterns, two additional approaches, including tailoring dielectric spacer and transforming overall structure are called back. Following this, key parameters, such as operating frequency, relative tuning range, and switching speed are summarized and compared to guide for optimum design. Finally, potential opportunities in the development of active MAs are discussed.
Metamaterial absorbers (MAs), designed using artificial subwavelength structures, feature low profile and unique absorption. Employing active components into the element designs facilitate multifunction and miniaturization of MAs. A comprehensive and systematical review covering the work essentially conducted in the domain of cutting‐edge active MAs is presented, highlighting innovative materials and unique strategies to manipulate electromagnetic response at frequencies up to optical regions.
An unprecedented radical difluoromethylarylation reaction of alkynes has been developed by discovering a new difluoromethylation reagent, CF2HSO2NHNHBoc. This air-stable and solid reagent can be ...prepared in one step from commercially available reagents CF2HSO2Cl and NH2NHBoc. The CF2H radical, generated through ferrocene-mediated electrochemical oxidation, participates in an unexplored alkyne addition reaction followed by a challenging 7-membered ring-forming homolytic aromatic substitution step to afford fluorinated dibenzazepines.
Quantifying the triboelectric series Zou, Haiyang; Zhang, Ying; Guo, Litong ...
Nature communications,
03/2019, Volume:
10, Issue:
1
Journal Article
Peer reviewed
Open access
Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its ...quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing.
A metal- and reagent-free, electrochemical intramolecular oxidative amination reaction of tri- and tetrasubstituted alkenes has been developed. The electrosynthetic method proceeds through radical ...cyclization to form the key C–N bond, allowing a variety of hindered tri- and tetrasubstituted olefins to participate in the amination reaction. The result is the efficient synthesis of a host of alkene-bearing cyclic carbamates and ureas and lactams.
Electrochemical 1,2‐hydroxydifluoromethylation and C−H difluoromethylation of acrylamides were developed by using CF2HSO2NHNHBoc as the source of the CF2H group. These electricity‐powered oxidative ...alkene functionalization reactions do not need transition‐metal catalysts or chemical oxidants. The reaction outcome, 1,2‐difuntionalization or C−H functionalization, is determined by the substituents on the amide nitrogen atom of the acrylamides instead of by the reaction conditions.
Turn up the power: Electrochemical 1,2‐hydroxydifluoromethylation and C−H difluoromethylation of acrylamides is developed by using CF2HSO2NHNHBoc as the source of the CF2H group. These electricity‐powered oxidative alkene functionalization reactions do not need transition‐metal catalysts or chemical oxidants.
A long debate on the charge identity and the associated mechanisms occurring in contact‐electrification (CE) (or triboelectrification) has persisted for many decades, while a conclusive model has not ...yet been reached for explaining this phenomenon known for more than 2600 years! Here, a new method is reported to quantitatively investigate real‐time charge transfer in CE via triboelectric nanogenerator as a function of temperature, which reveals that electron transfer is the dominant process for CE between two inorganic solids. A study on the surface charge density evolution with time at various high temperatures is consistent with the electron thermionic emission theory for triboelectric pairs composed of Ti–SiO2 and Ti–Al2O3. Moreover, it is found that a potential barrier exists at the surface that prevents the charges generated by CE from flowing back to the solid where they are escaping from the surface after the contacting. This pinpoints the main reason why the charges generated in CE are readily retained by the material as electrostatic charges for hours at room temperature. Furthermore, an electron‐cloud–potential‐well model is proposed based on the electron‐emission‐dominatedcharge‐transfer mechanism, which can be generally applied to explain all types of CE in conventional materials.
Real‐time charge transfer in contact electrification (CE) is investigated quantitatively as a function of temperature via a triboelectric nanogenerator, revealing that electron transfer is the dominant process for CE between two inorganic solids. An electron‐cloud–potential‐well model is proposed for understanding all types of CE in conventional materials.
Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an ...established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering.
PdCo nanotube arrays (NTAs) supported on carbon fiber cloth (CFC) (PdCo NTAs/CFC) are presented as high‐performance flexible electrocatalysts for ethanol oxidation. The fabricated flexible PdCo ...NTAs/CFC exhibits significantly improved electrocatalytic activity and durability compared with Pd NTAs/CFC and commercial Pd/C catalysts. Most importantly, the PdCo NTAs/CFC shows excellent flexibility and the high electrocatalytic performance remains almost constant under the different distorted states, such as normal, bending, and twisting states. This work shows the first example of Pd‐based alloy NTAs supported on CFC as high‐performance flexible electrocatalysts for ethanol oxidation.
PdCo nanotube arrays supported on carbon fiber cloth for use as high‐performance electrocatalysts were synthesized for ethanol electrooxidation. The system of nanotube arrays on carbon fiber cloth is highly flexible, and its high electrocatalytic performance is almost constant regardless of the distorted state, such as normal, bent, and twisted.
Rotated Sphere Packing Designs He, Xu
Journal of the American Statistical Association,
12/2017, Volume:
112, Issue:
520
Journal Article
Peer reviewed
Open access
We propose a new class of space-filling designs called rotated sphere packing designs for computer experiments. The approach starts from the asymptotically optimal positioning of identical balls that ...covers the unit cube. Properly scaled, rotated, translated, and extracted, such designs are excellent in maximin distance criterion, low in discrepancy, good in projective uniformity and thus useful in both prediction and numerical integration purposes. We provide a fast algorithm to construct such designs for any numbers of dimensions and points with R codes available online. Theoretical and numerical results are also provided. Supplementary materials for this article are available online.
Spin‐controlled vortex generation and spin‐Hall effect, two distinct effects discovered in optics, have been extensively studied recently. However, while physical origins of two effects are both due ...to spin‐orbit interactions, their inherent connections remain obscure which also hinders further explorations on the manipulations of them. Here, in studying the scattering of a spin‐polarized light beam at sharp interfaces, an intriguing phase transition between vortex generation and spin‐Hall shift trigged by varying the incidence angle is revealed. After reflection/refraction, the beam contains two components: normal and abnormal modes acquiring spin‐redirection‐Berry phases and Pancharatnam–Berry phases, respectively. Inside the abnormal beam, two classes of wave components gain Pancharatnam–Berry phases with distinct topological natures, generating intrinsic and extrinsic orbital angular momenta (OAM), respectively. Enlarging incidence angle changes the relative portions of these two contributions, making the abnormal beam undergo a phase transition from vortex generation to spin‐Hall shift. Such intriguing effect is experimentally observed at a purposely designed metamaterial slab, exhibiting efficiency enhanced by several‐thousand times compared to that at a conventional slab. These findings unify two previously discovered effects in a single framework, reinterpret previous results with clearer pictures, and shed light on understanding other physical effects involving the competition between intrinsic and extrinsic OAM.
Two previously discovered effects are unified in optics, spin‐controlled vortex generation and photonic spin‐Hall effect, in a single framework, and it is revealed that an intriguing topology‐induced phase transition between two effects can be trigged under certain conditions. The physical origin is that the two classes of wave components inside the beam can gain Pancharatnam–Berry phases with distinct topological natures.
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