We study small perturbations around an arbitrary static kink solution of a two-dimensional (2D) gravity-scalar system, where the gravity part is described by a subclass of 2D dilaton gravity theory, ...and the scalar matter field has generalized dynamics. We expand the action around an arbitrary static solution and keep terms up to the second order of the perturbations. After variation the linear-order action leads to background field equations, as expected. The quadratic action of the normal modes are obtained after fixing the gauge and using the constraint equation. The linear perturbation equations obtained from the quadratic action are consistent with those obtained by linearizing the field equations under the dilaton gauge. All the calculations are assisted by a Mathematica code, which is also provided as a supplementary material.
A
bstract
In the study of three-dimensional flat holography, the BMS field theory manifests the infinite-dimensional BMS
3
symmetry, a powerful tool in elucidating numerous universal phenomena. This ...paper explores a certain low-temperature limit of the BMS field theory. The primary focus lies in the calculation of the thermal correction to the Rényi entropy of the single interval on the cylinder from the replica trick and the uniformizing map. As a double check, an alternative method calculating the entanglement entropy is introduced, with the entanglement first law and the modular Hamiltonian.
Spider silk is one of the most robust natural materials, which has extremely high strength in combination with great toughness and good elasticity. Inspired by spider silk but beyond it, a healable ...and recyclable supramolecular elastomer, possessing superhigh true stress at break (1.21 GPa) and ultrahigh toughness (390.2 MJ m−3), which are, respectively, comparable to and ≈2.4 times higher than those of typical spider silk, is developed. The elastomer has the highest tensile strength (ultimate engineering stress, 75.6 MPa) ever recorded for polymeric elastomers, rendering it the strongest and toughest healable elastomer thus far. The hyper‐robust elastomer exhibits superb crack tolerance with unprecedentedly high fracture energy (215.2 kJ m−2) that even exceeds that of metals and alloys, and superhigh elastic restorability allowing dimensional recovery from elongation over 12 times. These extraordinary mechanical performances mainly originate from the meticulously engineered hydrogen‐bonding segments, consisting of multiple acylsemicarbazide and urethane moieties linked with flexible alicyclic hexatomic spacers. Such hydrogen‐bonding segments, incorporated between extensible polymer chains, aggregate to form geometrically confined hydrogen‐bond arrays resembling those in spider silk. The hydrogen‐bond arrays act as firm but reversible crosslinks and sacrificial bonds for enormous energy dissipation, conferring exceptional mechanical robustness, healability, and recyclability on the elastomer.
Healable and recyclable elastomers with superhigh strength (tensile strength ≈ 75.6 MPa, true stress at break ≈ 1.21 GPa) and ultrahigh toughness (≈390.2 MJ m−3) are reported. The elastomer has unprecedented crack tolerance with fracture energy of 215.2 kJ m−2 that even exceeds that of metals and alloys. The elastomer exhibits superhigh elastic restorability allowing dimensional recovery from elongation over 12 times.
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bstract
We report a two-dimensional (2D) gravitating kink model, for which both the background field equations and the linear perturbation equation are exactly solvable. The background solution ...describes a sine-Gordon kink that interpolating between two asymptotic AdS
2
spaces, and can be regarded as a 2D thick brane world solution. The linear perturbation equation can be recasted into a Schrödinger-like equation with singular Pöschl-Teller II potentials. There is no tachyonic state in the spectrum, so the solution is stable against the linear perturbations. Besides, there can be
n
= 0
,
1
,
2
,
⋯ bounded vibrational modes around the kink. The number of these vibrational modes varies with model parameters.
Over the past decade, transition metal phosphate materials have attracted enormous interest for various functional devices. In addition to being low‐cost, earth‐abundant and environmentally benign, ...transition metal phosphates have several unique advantages including high stability, unique chemical/physical characteristics and tunable multifunctionality, making them ideally suited for advanced highly‐efficiency energy conversion and storage applications. In this Review, the synthetic strategies for transition metal phosphates are summarized, and the most recent advances in the development of transition metal phosphates are described for efficient electrocatalysis such as oxygen evolution, hydrogen evolution and oxygen reduction reactions, highlighting the impact of their morphologies and structures on the electrochemical performance and practical applications in overall water splitting and rechargeable metal‐air batteries. Finally, the challenges facing the development of transition metal phosphates in the field of energy conversion and storage are outlined, together with directions of further research and perspectives.
Earth‐abundant electrocatalysts: The synthetic strategies and the most recent advances of transition metal phosphates for efficient electrocatalysis are reviewed, highlighting the impact of their morphologies and structures on electrochemical performance. The challenges facing their development in the hydrogen‐ and oxygen‐involving electrocatalytic reactions are outlined, together with directions of further research and perspectives.
Solar‐driven water electrolysis has been considered to be a promising route to produce green hydrogen, because the conventional water electrolysis system is not completely renewable as it requires ...power from nonrenewable fossil fuel sources. This review emphasizes the strategies for solar‐driven water electrolysis, including the construction of photovoltaic (PV)‐water electrolyzer systems, PV‐rechargeable energy storage device‐water electrolyzer systems with solar energy as the sole input energy, and photoelectrochemical water splitting systems. The basic discussions of the above strategies for solar‐driven water electrolysis are first presented. Meanwhile, replacing the oxygen evolution reaction with the electrooxidation of organic compounds can effectively improve the efficiency of water splitting. Also, solar‐driven seawater electrolysis greatly broadens the practical applications due to the abundant reserves of seawater. Recent years have witnessed great development in the field of solar‐driven water electrolysis. The recent research development in the area is subsequently reviewed. Finally, perspectives on the existing challenges along with some opportunities for the further development of solar‐driven water electrolysis are provided.
This review discusses the strategies for solar‐driven water electrolysis including the construction of photovoltaic (PV)‐water electrolyzer systems, PV‐rechargeable energy storage device‐water electrolyzer systems with solar energy as the sole input energy, and photoelectrochemical (PEC) water splitting systems. The advances in organic compound‐assisted water splitting systems and solar‐driven seawater electrolysis systems are also given.
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bstract
Self-gravitating kink solutions of a two-dimensional dilaton gravity are revisited in this work. Analytical kink solutions are derived from a concise superpotential formalism of the ...dynamical equations. A general analysis on the linear stability is conducted for an arbitrary static solution of the model. After gauge fixing, a Schrödinger-like equation with factorizable Hamiltonian operator is obtained, which ensures the linear stability of the solution.
Hydrogen peroxide (H2O2) is a highly value‐added and environmentally friendly chemical with various applications. The production of H2O2 by electrocatalytic 2e− oxygen reduction reaction (ORR) has ...drawn considerable research attention, with a view to replacing the currently established anthraquinone process. Electrocatalysts with low cost, high activity, high selectivity, and superior stability are in high demand to realize precise control over electrochemical H2O2 synthesis by 2e− ORR and the feasible commercialization of this system. This Review introduces a comprehensive overview of non‐noble metal‐based catalysts for electrochemical oxygen reduction to afford H2O2, providing an insight into catalyst design and corresponding reaction mechanisms. It starts with an in‐depth discussion on the origins of 2e−/4e− selectivity towards ORR for catalysts. Recent advances in design strategies for non‐noble metal‐based catalysts, including carbon nanomaterials and transition metal‐based materials, for electrochemical oxygen reduction to H2O2 are then discussed, with an emphasis on the effects of electronic structure, nanostructure, and surface properties on catalytic performance. Finally, future challenges and opportunities are proposed for the further development of H2O2 electrogeneration through 2e− ORR, from the standpoints of mechanistic studies and practical application.
Nobility not required: Hydrogen peroxide is a highly value‐added and environmentally friendly chemical with various applications. This Review summarizes various strategies for the engineering of non‐noble metal‐based catalysts to generate hydrogen peroxide by electrochemical oxygen reduction. Some insights into future directions are also proposed and discussed.
The key challenge to developing renewable energy conversion and storage devices lies in the exploration and rational engineering of cost‐effective and highly efficient electrocatalysts for various ...energy‐related electrochemical reactions. Transition‐metal phosphates and phosphonates have shown remarkable performances for these reactions based on their unique physicochemical properties. Compared with transition‐metal oxides, phosphate groups in transition‐metal phosphates and phosphonates show flexible coordination with diverse orientations, making them an ideal platform for designing active electrocatalysts. Although numerous efforts have been spent on the development of transition‐metal phosphate and phosphonate electrocatalysts, some urgent issues, such as low intrinsic catalytic efficiency and low electronic conductivity, have to be resolved in accordance with their applications. In this Review, we focus on the design strategies of highly efficient transition‐metal phosphate and phosphonate electrocatalysts, with special emphasis on the tuning of transition‐metal‐center coordination environment, optimization of electronic structures, increase of catalytically active site densities, and construction of heterostructures. Guided by these strategies, recently developed transition‐metal phosphate and phosphonate materials have exhibited excellent activity, selectivity, and stability for various energy‐related electrocatalytic reactions, showing great potential for replacing noble‐metal‐based catalysts in next‐generation advanced energy techniques. The existing challenges and prospects regarding these materials are also presented.
Phosphorus the true hero: In this Review, the recent progresses of engineering strategies for high‐efficiency transition‐metal phosphate and phosphonate electrocatalysts towards sustainable energy devices are summarized, including regulation of transition‐metal center coordination environment, optimization of electronic structure, increase of catalytically active site density, and construction of heterostructure. Some insights into future directions are also proposed and discussed.
As hydrogen has been increasingly considered as promising sustainable energy supply, electrochemical overall water splitting driven by highly efficient non‐noble metal electrocatalysts has aroused ...extensive attention. Transition metal phosphides (TMPs) have demonstrated remarkable electrocatalytic performance, including high activity and robust durability towards hydrogen evolution reaction (HER) in acidic and alkaline as well as neutral electrolytes. In this Review, up‐to‐date progress of TMP‐based HER electrocatalysts is summarized. Various synthesis strategies of TMPs based on selected phosphorus sources are presented, and the reaction mechanisms of HER as well as the contribution of phosphorus in the TMPs to HER activity are briefly discussed. The multiscale approaches for promoting the activity and stability of TMP‐based catalysts are discussed with respect to intrinsic electronic structure, hybrids, microstructure, and working electrode interface. Some crucial issues and future perspectives of TMPs are pointed out. These modulated approaches and challenges are also instructive for constructing other high‐activity energy‐related electrocatalysts.
Transitioning to hydrogen: In this Review, up‐to‐date progress of transition metal phosphide (TMP)‐based hydrogen evolution reaction (HER) electrocatalysts is summarized. Various synthesis strategies and the HER reaction mechanisms of TMP‐based catalysts are briefly discussed. In addition, multiscale approaches with respect to electronic structure, hybrids, microstructure, and working electrode interface are discussed for promoting HER performances.
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