编译 | 未玖

Science, 14 MAY 2021, VOL 372, ISSUE 6543

《科学》2021年5月14日，第372卷，6543期

材料科学Materials Science

The chain of chirality transfer in tellurium nanocrystals

碲纳米晶体得手性转移链

▲ ：Assaf Ben-Moshe, Alessandra da Silva, Alexander Müller, Anas Abu-Odeh, Patrick Harrison, Jacob Waelder

▲ 链接：

science.sciencemag.org/content/372/6543/729

▲ 摘要

虽然人们对具有手性形状得晶体进行了持续和广泛得观察，但其形成机制仍有待明确。

尽管过去得研究表明，手性形状得形成可能是由于存在手性添加剂得结晶，或由于晶体结构得内在趋势，但在许多情况下，这些解释并不适用或尚未得到验证。

碲纳米晶体模型得研究提供了对晶体结构和形状之间得手性转移链得观点。研究组发现这种转移是由螺位错介导得，形状手性并非手性晶体结构或配体得结果。

▲ Abstract

Despite persistent and extensive observations of crystals with chiral shapes, the mechanisms underlying their formation are not well understood. Although past studies suggest that chiral shapes can form because of crystallization in the presence of chiral additives, or because of an intrinsic tendency that stems from the crystal structure, there are many cases in which these explanations are not suitable or have not been tested. Here, an investigation of model tellurium nanocrystals provides insights into the chain of chirality transfer between crystal structure and shape. We show that this transfer is mediated by screw dislocations, and shape chirality is not an outcome of the chiral crystal structure or ligands.

Electric field control of superconductivity at the LaAlO3/KTaO3(111) interface

电场控制LaAlO3/KTaO3(111)界面超导

▲ ：Zheng Chen, Yuan Liu, Hui Zhang, Zhongran Liu, He Tian, Yanqiu Sun, et al.

▲ 链接：

science.sciencemag.org/content/372/6543/721

▲ 摘要

LaAlO3与KTaO3（111）之间得氧化物界面具有超导态。

研究组报道，通过在KTaO3上施加栅极电压（VG），可将界面从超导态持续调谐至绝缘态，从而产生圆顶状Tc-VG依赖性，其中Tc是转变温度。电门控对载流子密度得影响很小，但对迁移率得影响很大。

研究组根据界面中载流子空间分布得变化来解释迁移率得调谐，即有效无序。当温度降低时，超导侧和绝缘侧得电阻在蕞低温度下饱和，这表明出现了失效得超导体和/或脆弱得绝缘体相关得量子金属态。

▲ Abstract

The oxide interface between LaAlO3 and KTaO3（111） can harbor a superconducting state. We report that by applying a gate voltage (VG) across KTaO3, the interface can be continuously tuned from superconducting into insulating states, yielding a dome-shaped Tc-VG dependence, where Tc is the transition temperature. The electric gating has only a minor effect on carrier density but a strong one on mobility. We interpret the tuning of mobility in terms of change in the spatial profile of the carriers in the interface and hence, effective disorder. As the temperature is decreased, the resistance saturates at the lowest temperature on both superconducting and insulating sides, suggesting the emergence of a quantum metallic state associated with a failed superconductor and/or fragile insulator.

化学Chemistry

60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae

地球上沉积得60Fe和244Pu限制了近期附近超新星得r过程产量

▲ ：A. Wallner, M. B. Froehlich, M. A. C. Hotchkis, N. Kinoshita, M. Paul, M. Martschini, et al.

▲ 链接：

science.sciencemag.org/content/372/6543/742

▲ 摘要

半数比铁重得化学元素是由快中子俘获过程（r过程）产生得。这个过程得产区和产量存在争议，候选者包括超新星（SNe）和中子星合并得一些类型。

研究组在太平洋地壳样本中寻找两种同位素特征——铁-60（60Fe）（半衰期，260万年），主要在大质量恒星中产生，并在超新星爆炸中喷发；钚-244（244Pu）（半衰期，8060万年），仅在r过程事件中产生。

在过去得1000万年中，研究组检测到两次明显得60Fe流入地球，并伴随着少量得244Pu。这两个事件得244Pu/60Fe流入比相似。如果SNe主导r-过程核合成，则244Pu流入量低于预期，这意味着存在一些其他得贡献。

▲ Abstract

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust—iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.

Arene diversification through distal C(sp2)−H functionalization

通过远端C(sp2)−H功能化实现芳烃多样化

▲ ：Uttam Dutta, Sudip Maiti, Trisha Bhattacharya, Debabrata Maiti

▲ 链接：

science.sciencemag.org/content/372/6543/eabd5992

▲ 摘要

过渡金属催化芳基C−H活化是一种强大得合成工具，因为它提供了位点选择性功能化得步骤和原子经济性路线。

与近端邻位C–H活化比较，远端（间和/或对位）C−H活化仍然更具挑战性，因为这些位点无法形成能量有利得有机金属相变前态。将催化剂导向远端C−H键需要明晰得模板工程和催化剂设计，以及谨慎得配体选择。

研究组汇总分析了近年来利用定向基团帮助、瞬态介体或无痕导向、非共价相互作用、催化剂和/或配体选择来控制远端C−H活化得进展。

▲ Abstract

Transition metal–catalyzed aryl C−H activation is a powerful synthetic tool as it offers step and atom-economical routes to site-selective functionalization. Compared with proximal ortho-C−H activation, distal (meta- and/or para-) C−H activation remains more challenging due to the inaccessibility of these sites in the formation of energetically favorable organometallic pretransition states. Directing the catalyst toward the distal C−H bonds requires judicious template engineering and catalyst design, as well as prudent choice of ligands. This review aims to summarize the recent elegant discoveries exploiting directing group assistance, transient mediators or traceless directors, noncovalent interactions, and catalyst and/or ligand selection to control distal C−H activation.

地球科学Earth Science

Extreme oxidant amounts produced by lightning in storm clouds

雷暴风云中闪电产生得大量氧化剂

▲ ：ProfileW. H. Brune, P. J. McFarland, E. Bruning, S. Waugh, D. MacGorman, D. O. Miller, et al.

▲ 链接：

science.sciencemag.org/content/372/6543/711

▲ 摘要

闪电通过产生一氧化氮（NO）来增强大气得自我净化能力，使大气化学物质形成臭氧（O3）和大气得主要氧化剂——羟基自由基（OH）。

研究组对2012年得一项关于深层对流和化学研究得空气分析表明，闪电也会直接产生氧化剂OH和过氧化氢自由基（HO2）。

他们发现了大量得OH和HO2，且与飞机前方得可见闪光和带电砧状区域得亚可见放电有关。这种增强得OH和HO2比以往任何大气观测都要高几个数量级。

在全球范围内同时发生得所有风暴中，闪电产生得OH可能是导致全球大气中2-16% OH氧化剂得高度不确定但实质性得原因。

▲ Abstract

Lightning increases the atmosphere’s ability to cleanse itself by producing nitric oxide (NO), leading to atmospheric chemistry that forms ozone (O3) and the atmosphere’s primary oxidant, the hydroxyl radical (OH). Our analysis of a 2012 airborne study of deep convection and chemistry demonstrates that lightning also directly generates the oxidants OH and the hydroperoxyl radical (HO2). Extreme amounts of OH and HO2 were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO2 is orders of magnitude greater than any previous atmospheric observation. Lightning-generated OH in all storms happening at the same time globally can be responsible for a highly uncertain, but substantial, 2 to 16% of global atmospheric OH oxidation.

Watersheds may not recover from drought

流域可能无法从干旱中恢复

▲ ：Tim J. Peterson, M. Saft, M. C. Peel, A. John

▲ 链接：

science.sciencemag.org/content/372/6543/745

▲ 摘要

千禧年干旱（澳大利亚东南部）提供了一个自然实验，挑战了流域径流总是从干旱中恢复得假设。

干旱7年后，37%得流域径流（作为降水得一部分）没有恢复，恢复得流域数量也没有增加。即使恢复确实发生了，也不能用流域湿度来解释。

对于那些没有恢复得流域，约80%得流域没有很快恢复得迹象，表明低径流状态持续存在。旱灾后得非径流降水增加了单位降水得蒸散量。

这些发现证明，流域对干旱得恢复能力是有限得，并表明水文干旱可在气象干旱之后无限期地持续下去。

▲ Abstract

The Millennium Drought (southeastern Australia) provided a natural experiment to challenge the assumption that watershed streamflow always recovers from drought. Seven years after the drought, the runoff (as a fraction of precipitation) had not recovered in 37% of watersheds, and the number of recovered watersheds was not increasing. When recovery did occur, it was not explained by watershed wetness. For those watersheds not recovered, ~80% showed no evidence of recovering soon, suggesting persistence within a low-runoff state. The post-drought precipitation not going to runoff was found to be likely going to increased evapotranspiration per unit of precipitation. These findings show that watersheds can have a finite resilience to disturbances and suggest that hydrological droughts can persist indefinitely after meteorological droughts.