编译｜冯维维
Science, 19 March 2021 Vol 371, Issue 6535
《科学》2021年3月19日，第371卷6535期
物理学Physics
Generating arbitrary topological windings of a non-Hermitian band
开放的拓扑
▲ 作者：Kai Wang, Avik Dutt, Ki Youl Yang, Casey C. Wojcik, Jelena Vučković, Shanhui Fan
▲ 链接：
https://science.sciencemag.org/content/371/6535/1240
▲ 摘要
控制系统的拓扑结构提供了一条路线来开发抗缺陷的鲁棒的设备。虽然早期的拓扑带理论发展集中在厄米特（封闭）系统上，但最近的努力已转向非厄米特（开放）系统。
作者报告了非厄密能带的拓扑非平凡绕组的测量和控制。通过在已调制的环形谐振器中实现由光学频率模构成的频率合成维上的非厄米特晶格哈密顿量，他们直接可视化了非平凡拓扑带绕组，并证明了该绕组是可以控制的。
这种控制为开放物理系统中拓扑非平凡相的实验合成、表征和控制提供了一条途径。
▲ Abstract
Controlling the topology of a system provides a route to develop devices that are robust against defects. Whereas earlier developments of topological band theory focused on Hermitian (closed) systems, recent efforts have been toward non-Hermitian (open) systems. K. Wang et al. report on the measurement and control of topologically nontrivial windings of a non-Hermitian energy band. By implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed by optical frequency modes in a modulated ring-resonator, they directly visualized the nontrivial topological band winding and showed that the winding can be controlled. Such control provides a route for the experimental synthesis, characterization, and control of topologically nontrivial phases in open physical systems.
Tuning electron correlation in magic-angle twisted bilayer graphene using Coulomb screening
调节扭曲双层石墨烯中电子相关性
▲ 作者：Xiaoxue Liu, Zhi Wang, K. Watanabe, T. Taniguchi, Oskar Vafek, J. I. A. Li
▲ 链接：
https://science.sciencemag.org/content/371/6535/1261
▲ 摘要
要在扭曲双分子层石墨烯（MATBG）中解释超导状态的性质被证明很棘手。为了研究电子-电子关联在这种状态下的作用，作者在MATBG样品附近放置了另一层石墨烯双分子层，这一层采用了传统的石墨烯薄片排列方式。
通过改变传统双层膜中的载流子密度，研究人员控制了MATBG中的相互作用强度。减弱相互作用会增强超导性，这与电子-声子耦合与库仑相互作用竞争以稳定超导相的情况一致。
▲ Abstract
Elucidating the nature of the superconducting state in magic-angle twisted bilayer graphene (MATBG) has proven tricky. To study the role of electron-electron correlations in this state, Liu et al. placed another graphene bilayer, this one having a conventional arrangement of the graphene sheets, in the immediate vicinity of a sample of MATBG. By varying the carrier density in the conventional bilayer, the researchers controlled the strength of interactions in MATBG. Weakening the interactions strengthened superconductivity, consistent with scenarios in which the electron-phonon coupling competes against Coulomb interactions to stabilize the superconducting phase.
化学Chemistry
Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering
星际多环芳烃的识别
▲ 作者：Brett A. McGuire, Ryan A. Loomis, Anthony J. Remijan, Michael C. McCarthy. Etc.
▲ 链接：
https://science.sciencemag.org/content/371/6535/1265
▲ 摘要
中红外光谱分析表明，多环芳烃（PAHs）大量存在于许多天体中，但该技术无法确定具体存在的多环芳烃分子。如果分子足够丰富且偶极矩很大，射电天文学可以提供单独的鉴定，但多环芳烃预计会产生大量非常弱的线。
作者对位于金牛座星际分子云内的TMC-1进行了叠加和匹配过滤分析，在射电观测中寻找多环芳烃。他们鉴定了小的多环芳烃氰基萘的两个同分异构体，两个连接着CN基团的苯环。
▲ Abstract
Midinfrared spectroscopy has shown that polycyclic aromatic hydrocarbons (PAHs) are abundant in many astronomical objects, but this technique cannot determine which specific PAH molecules are present. Radio astronomy could provide individual identifications if the molecule is sufficiently abundant and has a large dipole moment, but PAHs are expected to produce large numbers of very weak lines. McGuire et al. performed a stacking and matched filter analysis to search for PAHs in radio observations of TMC-1, located within the interstellar Taurus Molecular Cloud. They identified emission from two isomers of the small PAH cyanonapthalene, two fused benzene rings with a CN group attached.
Tandem In2O3-Pt/Al2O3 catalyst for coupling of propane dehydrogenation to selective H2 combustion
克服丙烯氧化
▲ 作者：Huan Yan, Kun He, Izabela A. Samek, Dian Jing, Macy G. Nanda, Peter C. Stair, Justin M. Notestein
▲ 链接：
https://science.sciencemag.org/content/371/6535/1257
▲ 摘要
丙烷氧化脱氢制丙烯和水的催化剂的选择性随着转化率的增加而降低，因为丙烯本身比丙烷更容易被氧化。
作者通过在丙烷脱氢催化剂上生长一种选择性氢燃烧催化剂氧化铟（一种约2纳米的外壳），并将铂纳米颗粒支撑在氧化铝球上，从而创造了纳米级串联催化剂。这种涂层使铂纳米颗粒暴露，以便丙烷脱氢。
在氧化铟-铂界面处，表面氢原子被氧化。这种方法使丙烯的产量提高到30%。
▲ Abstract
Catalysts for the oxidative dehydrogenation of propane to propylene and water become less selective with increasing conversion because propylene itself is more readily oxidized than propane. Yan et al. created nanoscale tandem catalysts by growing an ∼2-nanometer shell of indium oxide, a selective hydrogen combustion catalyst, over a propane dehydrogenation catalyst, platinum nanoparticles supported on alumina spheres. This overcoat exposed the platinum nanoparticles for propane dehydrogenation. Surface hydrogen atoms were oxidized at the indium oxide–platinum interface. This approach boosted yields of propylene to up to 30%.
地球科学Earth sciences
Record-breaking aerosol levels explained by smoke injection into the stratosphere
平流层烟雾可解释破纪录气溶胶含量
▲ 作者：Eitan Hirsch, Ilan Koren
▲ 链接：
https://science.sciencemag.org/content/371/6535/1269
▲ 摘要
2020年，澳大利亚大规模的森林大火向平流层排放了大量烟雾。赫希和科伦发现，这种烟雾在南半球造成了破纪录的悬浮颗粒水平，其程度堪比一次中度火山爆发。
造成这种严重程度的原因是火灾的强度及其所处纬度的对流层顶较浅和中纬度气旋带。这种气溶胶的增加导致了海洋无云地区的大量降温。
▲ Abstract
Intense, widespread bushfires in Australia injected huge amounts of smoke into the stratosphere in 2020. Hirsch and Koren found that this smoke caused record-breaking levels of aerosols over the Southern Hemisphere, as much as that from a moderate volcanic eruption. The severity was caused by a combination of the vigor of the fires and their location at a latitude with a shallow tropopause and within the midlatitude cyclones belt. This aerosol increase caused considerable cooling over oceanic cloud-free areas.
Manta-like planktivorous sharks in Late Cretaceous oceans
恐龙时代的浮游食性鲨鱼
▲ 作者：Romain Vullo, Eberhard Frey, Christina Ifrim, Margarito A. González González, Eva S. Stinnesbeck, Wolfgang Stinnesbeck
▲ 链接：
https://science.sciencemag.org/content/371/6535/1253
▲ 摘要
现代鲨鱼占据了世界各地的海洋生态系统，但形态多样性很少，它们大多是流线型的掠食者。作者描述了一种来自晚白垩纪的鲨鱼新物种，这表明当前缺乏变异并非由于过去有限的形态学“探索”。
具体来说，这种鲨鱼（Aquilolamna milarcae）显示出许多与现代蝠鲼相似的特征，特别是细长的鳍和似乎适合滤食的嘴，这表明它是以浮游生物为食。
这一发现表明，板鳃亚目动物在进化过程中尝试了其他形式的动物，同时也表明，以浮游生物为食的“翱翔者”在这一类群中出现的时间比先前所认识的至少早了3000万年。
▲ Abstract
Modern sharks occupy marine ecosystems across the world but display little morphological diversity, being mostly streamlined predators. Vullo et al. describe a new species of shark from the late Cretaceous that shows that the lack of current variation is not due to limited morphological “exploration” in the past. Specifically, Aquilolamna milarcae displays many features similar to modern manta rays, notably long, slender fins and a mouth seemingly adapted to filter feeding, suggesting that it was planktivorous. This finding indicates both that elasmobranchs evolutionarily experimented with other forms and that the planktivorous “soarers” emerged in this group at least 30 million years earlier than previously recognized.
