編譯｜馮維維
Science, 19 March 2021 Vol 371, Issue 6535
《科學》2021年3月19日，第371卷6535期
物理學Physics
Generating arbitrary topological windings of a non-Hermitian band
開放的拓撲
▲ 作者：Kai Wang, Avik Dutt, Ki Youl Yang, Casey C. Wojcik, Jelena Vučković, Shanhui Fan
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1240
▲ 摘要
控制系統的拓撲結構提供了一條路線來開發抗缺陷的魯棒的設備。雖然早期的拓撲帶理論發展集中在厄米特（封閉）系統上，但最近的努力已轉向非厄米特（開放）系統。
作者報告了非厄密能帶的拓撲非平凡繞組的測量和控制。通過在已調製的環形諧振器中實現由光學頻率模構成的頻率合成維上的非厄米特晶格哈密頓量，他們直接可視化了非平凡拓撲帶繞組，並證明了該繞組是可以控制的。
這種控制為開放物理系統中拓撲非平凡相的實驗合成、表徵和控制提供了一條途徑。
▲ 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
調節扭曲雙層石墨烯中電子相關性
▲ 作者：Xiaoxue Liu, Zhi Wang, K. Watanabe, T. Taniguchi, Oskar Vafek, J. I. A. Li
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1261
▲ 摘要
要在扭曲雙分子層石墨烯（MATBG）中解釋超導狀態的性質被證明很棘手。為了研究電子-電子關聯在這種狀態下的作用，作者在MATBG樣品附近放置了另一層石墨烯雙分子層，這一層採用了傳統的石墨烯薄片排列方式。
通過改變傳統雙層膜中的載流子密度，研究人員控制了MATBG中的相互作用強度。減弱相互作用會增強超導性，這與電子-聲子耦合與庫侖相互作用競爭以穩定超導相的情況一致。
▲ 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.
化學Chemistry
Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering
星際多環芳烴的識別
▲ 作者：Brett A. McGuire, Ryan A. Loomis, Anthony J. Remijan, Michael C. McCarthy. Etc.
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1265
▲ 摘要
中紅外光譜分析表明，多環芳烴（PAHs）大量存在於許多天體中，但該技術無法確定具體存在的多環芳烴分子。如果分子足夠豐富且偶極矩很大，射電天文學可以提供單獨的鑒定，但多環芳烴預計會產生大量非常弱的線。
作者對位於金牛座星際分子雲內的TMC-1進行了疊加和匹配過濾分析，在射電觀測中尋找多環芳烴。他們鑒定了小的多環芳烴氰基萘的兩個同分異構體，兩個連接着CN基團的苯環。
▲ 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
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1257
▲ 摘要
丙烷氧化脫氫制丙烯和水的催化劑的選擇性隨着轉化率的增加而降低，因為丙烯本身比丙烷更容易被氧化。
作者通過在丙烷脫氫催化劑上生長一種選擇性氫燃燒催化劑氧化銦（一種約2納米的外殼），並將鉑納米顆粒支撐在氧化鋁球上，從而創造了納米級串聯催化劑。這種塗層使鉑納米顆粒暴露，以便丙烷脫氫。
在氧化銦-鉑界面處，表面氫原子被氧化。這種方法使丙烯的產量提高到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%.
地球科學Earth sciences
Record-breaking aerosol levels explained by smoke injection into the stratosphere
平流層煙霧可解釋破紀錄氣溶膠含量
▲ 作者：Eitan Hirsch, Ilan Koren
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1269
▲ 摘要
2020年，澳大利亞大規模的森林大火向平流層排放了大量煙霧。赫希和科倫發現，這種煙霧在南半球造成了破紀錄的懸浮顆粒水平，其程度堪比一次中度火山爆發。
造成這種嚴重程度的原因是火災的強度及其所處緯度的對流層頂較淺和中緯度氣旋帶。這種氣溶膠的增加導致了海洋無雲地區的大量降溫。
▲ 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
恐龍時代的浮游食性鯊魚
▲ 作者：Romain Vullo, Eberhard Frey, Christina Ifrim, Margarito A. González González, Eva S. Stinnesbeck, Wolfgang Stinnesbeck
▲ 鏈接：
https://science.sciencemag.org/content/371/6535/1253
▲ 摘要
現代鯊魚佔據了世界各地的海洋生態系統，但形態多樣性很少，它們大多是流線型的掠食者。作者描述了一種來自晚白堊紀的鯊魚新物種，這表明當前缺乏變異並非由於過去有限的形態學“探索”。
具體來說，這種鯊魚（Aquilolamna milarcae）顯示出許多與現代蝠鱝相似的特徵，特別是細長的鰭和似乎適合濾食的嘴，這表明它是以浮游生物為食。
這一發現表明，板鰓亞目動物在進化過程中嘗試了其他形式的動物，同時也表明，以浮游生物為食的“翱翔者”在這一類群中出現的時間比先前所認識的至少早了3000萬年。
▲ 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.
