다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.

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2D metal carbides and nitrides (MXenes) for energy storage

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

Weyl and Dirac semimetals in three-dimensional solids

Co3Sn2S2 is a recently identified magnetic Weyl semimetal in Shandite compounds. Upon cooling, Co3Sn2S2 undergoes a ferromagnetic transition with c-axis polarized moments (∼0.3 µB/Co) around TC = 175 K, followed by another magnetic anomaly around TA ≈ 140 K. A large intrinsic anomalous Hall effect is observed in the magnetic state below TC with a maximum of anomalous Hall angle near TA. Here, we report an elastic neutron scattering on the crystalline lattice of Co3Sn2S2 in a magnetic field up to 10 T. A strongly anisotropic magnetoelastic response is observed-while only a slight enhancement of the Bragg peaks is observed when B//c. The in-plane magnetic field (B//ab) dramatically suppresses the Bragg peak intensity probably by tilting the moments and lattice toward the external field direction. The in-plane magnetoelastic response commences from TC, and as it is further strengthened below TA, it becomes nonmonotonic against the field between TA and TC because of the competition from another in-plane magnetic order. These results suggest that a magnetic field can be employed to tune the Co3Sn2S2 lattice and its related topological states.

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co 3 Sn 2 S 2

Topological materials is one of the hottest topics in condensed matter physics because of its exotic properties such as robust metallic boundary states, Fermi arcs, and the spin‐momentum‐locking helicity. The topologically protected conducting boundary states spanning the whole bandgap are expected to serve as robust and wide‐range‐energy transition states facilitating catalytic reactions. Recently, some topological materials have been found to be high‐performance catalysts, which might open an emerging research field. Herein, an overview of topological materials is given and then recent progress in topological material catalysts (TMCs) is presented. As it is a new field, more detailed and accurate mechanisms behind the high performance of TMCs are urgently needed. Combining theoretical and experimental studies is a promising way to resolve these puzzles. Heterostructures, dopants, and defects have the chance to tune the catalytic activity of TMCs while retaining topological surface states (TSSs). Also, more TMCs are needed to be discovered, and more catalytic reactions are to be investigated for TMCs in the future.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/smsc.202100106

Progress, Advantages, and Challenges of Topological Material Catalysts

Based on the first-principles calculations and experimental measurements, we report that the hexagonal phase of ternary transition metal pnictides TT'X (T=Zr, Hf; T'=Ru; X=P, As), which are well-known noncentrosymmetric superconductors with relatively high transition temperatures, host nontrivial bulk topology. Before the superconducting phase transition, we find that HfRuP belongs to a Weyl semimetal phase with 12 pairs of type-II Weyl points, while ZrRuAs, ZrRuP and HfRuAs belong to a topological crystalline insulating phase with trivial Fu-Kane $\mathbb Z_2$ indices but $nontrivial$ mirror Chern numbers. High-quality single crystal samples of the noncentrosymmetric superconductors with these two different topological states have been obtained and the superconductivity is verified experimentally. The wide-range band structures of ZrRuAs have been identified by ARPES and reproduced by theoretical calculations. Combined with intrinsic superconductivity, the nontrivial topology of the normal state may generate unconventional superconductivity in both bulk and surfaces. Our findings could largely inspire the experimental searching for possible topological superconductivity in these compounds.

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Topological Electronic States in HfRuP Family Superconductors

The zigzag edge graphene nanoribbon, which is an antiferromagnetic insulator, is found from the density-function theory calculation to display a robust Dirac point after N and B doping at the zigzag edge. More interestingly, we found that the robust Dirac point is a common feature of the honeycomb structure nanoribbon with appropriate edge sites. The zigzag edge honeycomb nanoribbon is therefore expected to provide a very useful platform for material design and development.

Robust Dirac point in honeycomb-structure nanoribbons with zigzag edges

Predicting new Dirac semimetals, as well as other topological materials, is challenging since the relationship between crystal structure, atoms and band topology is complex and elusive. Here, we demonstrate an approach to design Dirac semimetals via exploring chemical degree of freedom. Based on understanding of the well-known Dirac semimetal, Na3Bi, three compounds in one family, namely Na2MgSn, Na2MgPb, and Na2CdSn, are located. Furthermore, hybrid-functional calculations with improved accuracy for estimation of band inversion show that Na2MgPb and Na2CdSn have the band topology of Dirac semimetals. The nontrivial surface states with Fermi arcs on the (100) and (010) surfaces are shown to connect the projection of bulk Dirac nodes. Most importantly, the candidate compounds are dynamically stable and have been experimentally synthesized. The ideas in this work could stimulate further predictions of topological materials based on understanding of existing ones. First-principle calculations leveraging the chemical degree of freedom are used to establish an approach for finding new Dirac semimetals, which are exciting topological materials, but challenging to identify theoretically. Hao Zhang, Hongming Weng and colleagues from different Chinese institutions propose a chemically intuitive approach to the search for new Dirac semimetals. Starting from a known material, Na3Bi, they computationally vary the chemical composition while maintaining the crystal and electronic structure as close as possible to that of the original compound and single out three promising compounds. They also identify chemical rules that help predict whether a material will display band inversion, a key ingredient for obtaining topological properties, finding that two of the material candidates should display it. Their design strategy could be applied also to other classes of topological materials.

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Hongming Weng

Papers

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co 3 Sn 2 S 2

Progress, Advantages, and Challenges of Topological Material Catalysts

Topological Electronic States in HfRuP Family Superconductors

Robust Dirac point in honeycomb-structure nanoribbons with zigzag edges

Predicting Dirac semimetals based on sodium ternary compounds