《自然》（20201008出版）一周論文導讀

編譯 | 未玖

nature,8 October 2020,VOL 586,ISSUE 7828

《自然》2020年10月8日，第586卷，7828期

天文學Astronomy

Four annular structures in a protostellar disk less than 500,000 years old

小於50萬年的原恆星盤中有四個環狀結構

▲ 作者：Dominique M. Segura-Cox, Anika Schmiedeke, Jaime E. Pineda, Ian W. Stephens, Manuel Fernández-López, Leslie W. Looney, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2779-6

▲ 摘要

行星形成可能在第I類階段的更年輕盤狀物中進行，那時原恆星還嵌在更大範圍的緻密氣體和塵埃中。僅在過去十年裡，人們才觀察到最早恆星形成階段的塵埃盤的詳細特性。

研究組報告了1.3毫米塵埃排放的觀測結果，其解析度為5個天文單位，顯示了年輕（小於50萬歲）原恆星IRS 63的塵埃盤中有四個環狀子結構。IRS 63是一個單獨的I類源，位於附近蛇夫座分子雲中，距離為144秒差距，是毫米波長下最亮的I類原恆星之一。與其他年輕盤相比，IRS 63的盤相對較大（大於50個天文單位）。

在幼年階段觀測到的塵埃盤中多個環狀子結構可以作為塵埃顆粒生長的早期立足點，這是行星形成的先決條件。不論IRS 63盤中是否已經存在行星，很明顯，行星形成過程始於原始恆星的初始階段，早於當前的行星形成理論預測。

▲ Abstract

Planet formation may already be underway in even younger disks in the class I phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than 500,000 years old) protostar IRS 63. IRS 63 is a single class I source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs, and is one of the brightest class I protostars at millimetre wavelengths. IRS 63 also has a relatively large disk compared to other young disks (greater than 50 astronomical units). Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS 63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories.

物理學Physics

Emergent electromagnetic induction in a helical-spin magnet

螺旋自旋磁體中出現的電磁感應

▲ 作者：Tomoyuki Yokouchi, Fumitaka Kagawa, Max Hirschberger, Yoshichika Otani, Naoto Nagaosa & Yoshinori Tokura

▲ 連結：

https://www.nature.com/articles/s41586-020-2775-x

▲ 摘要

電感是現代電子設備中最基本的電路元件之一，它產生的電壓與輸入電流的時間導數成正比。傳統的電感器通常由一個螺旋線圈組成，並遵循法拉第電磁感應定律，誘導一個電壓來抵消穿過線圈的時變磁通量。這種常規電感的大小與電感線圈的體積成正比，阻礙了電感的小型化。

研究組展示了一個量子力學起源的電感，由磁體中自旋螺旋的電流驅動動力學引起的層展電場產生。在具有納米級自旋螺旋的微型矩形磁性器件中，研究組觀察到典型電感高達-400納亨，其量級可與商用電感器相媲美，但體積卻小約一百萬倍。

自旋螺旋結構電流驅動的動力學特性使電感因電流非線性而增強，並表現出非單調的頻率依賴性。與傳統的電感器相比，電感的大小隨著器件橫截面的減小而迅速增加。研究組的發現可能為基於與量子力學貝裡相位的新興電磁學的微型、簡單形狀的電感器鋪平道路。

▲ Abstract

An inductor, one of the most fundamental circuit elements in modern electronic devices, generates a voltage proportional to the time derivative of the input current. Conventional inductors typically consist of a helical coil and induce a voltage as a counteraction to time-varying magnetic flux penetrating the coil, following Faraday’s law of electromagnetic induction. The magnitude of this conventional inductance is proportional to the volume of the inductor’s coil, which hinders the miniaturization of inductors. Here, we demonstrate an inductance of quantum-mechanical origin, generated by the emergent electric field induced by current-driven dynamics of spin helices in a magnet. In microscale rectangular magnetic devices with nanoscale spin helices, we observe a typical inductance as large as −400 nanohenry, comparable in magnitude to that of a commercial inductor, but in a volume about a million times smaller. The observed inductance is enhanced by nonlinearity in current and shows non-monotonous frequency dependence, both of which result from the current-driven dynamics of the spin-helix structures. The magnitude of the inductance rapidly increases with decreasing device cross-section, in contrast to conventional inductors. Our findings may pave the way to microscale, simple-shaped inductors based on emergent electromagnetism related to the quantum-mechanical Berry phase.

化學Chemistry

Near-perfect photon utilization in an air-bridge thermophotovoltaic cell

氣橋熱光伏電池中近乎完美的光子利用率

▲ 作者：Dejiu Fan, Tobias Burger, Sean McSherry, Byungjun Lee, Andrej Lenert & Stephen R. Forrest

▲ 連結：https://www.nature.com/articles/s41586-020-2717-7

▲ 摘要

為了達到高效率，熱光伏電池必須利用輻射熱源的全波段。但是，當前的光子恢復方法受到帶寬不足或寄生吸收的限制，導致相對於理論極限存在巨大效率損失。

研究組通過在In0.53Ga0.47As薄膜電池中嵌入一層空氣（氣橋）來實現低能量光子的近乎完美反射。相對於現有的熱光伏電池，該結果表明寄生吸收減少了四倍。用大約1455-K的碳化矽發射器測量，由此產生的絕對效率增益超過6%，導致了超過30%的高功率轉換效率。

隨著帶外反射率趨於一致，熱光電效率變得幾乎不受電池帶隙增加或發射極溫度降低的影響。進入這種狀態可解鎖一系列此前無法進行熱光伏能量轉換的可能材料和熱源。

▲ Abstract

To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. Here we demonstrate near-perfect reflection of low-energy photons by embedding a layer of air (an air bridge) within a thin-film In0.53Ga0.47As cell. This result represents a fourfold reduction in parasitic absorption relative to existing thermophotovoltaic cells. The resulting gain in absolute efficiency exceeds 6 per cent, leading to a very high power conversion efficiency of more than 30 per cent, as measured with an approximately 1,455-kelvin silicon carbide emitter. As the out-of-band reflectance approaches unity, the thermophotovoltaic efficiency becomes nearly insensitive to increasing cell bandgap or decreasing emitter temperature. Accessing this regime may unlock a range of possible materials and heat sources that were previously inaccessible to thermophotovoltaic energy conversion.

Intercepting fleeting cyclic allenes with asymmetric nickel catalysis

環狀聯烯參與的不對稱鎳催化

▲ 作者：Michael M. Yamano, Andrew V. Kelleghan, Qianzhen Shao, Maude Giroud, Bryan J. Simmons, Bo Li, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2701-2

▲ 摘要

一個多世紀以來，張力環狀有機分子，例如芳烴、環狀炔烴和環狀烯，以其非同尋常的結構和高化學反應性吸引著化學家們。

研究組報導了在催化不對稱反應中獲得外消旋環狀聯烯中間體的情況，並提供了在這種轉化中控制絕對立體化學的兩種不同機制的證據：聯烯對映體的動力學拆分和中間體π-烯丙基鎳配合物的去對稱化。

計算研究暗示了一種催化機制，包括通過插入立體選擇性的烯烴對環狀聯烯對映體進行初始動力學拆分，去掉所產生的立體化學信息，以及隨後通過中間體π-烯丙基鎳配合物的去對稱化引入絕對立體化學。

這些結果揭示了環狀聯烯可利用的反應活性超越了先前報導的傳統環加成和親核加成，從而擴大了此類中間體可獲得的產物類型。此外，研究組的計算研究提出了兩種潛在的策略，用於控制環狀聯烯反應中的立體控制。總之，該結果為包括張力中間體的催化不對稱反應奠定了基礎。

▲ Abstract

Strained cyclic organic molecules, such as arynes, cyclic alkynes and cyclic allenes, have intrigued chemists for more than a century with their unusual structures and high chemical reactivity. Here we report the interception of racemic cyclic allene intermediates in a catalytic asymmetric reaction and provide evidence for two distinct mechanisms that control absolute stereochemistry in such transformations: kinetic differentiation of allene enantiomers and desymmetrization of intermediate π-allylnickel complexes. Computational studies implicate a catalytic mechanism involving initial kinetic differentiation of the cyclic allene enantiomers through stereoselective olefin insertion, loss of the resultant stereochemical information, and subsequent introduction of absolute stereochemistry through desymmetrization of an intermediate π-allylnickel complex. These results reveal reactivity that is available to cyclic allenes beyond the traditional cycloadditions and nucleophilic trappings previously reported, thus expanding the types of product accessible from this class of intermediates. Additionally, our computational studies suggest two potential strategies for stereocontrol in reactions of cyclic allenes. Combined, these results lay the foundation for the development of catalytic asymmetric reactions involving these classically avoided strained intermediates.

氣候學Climatology

A comprehensive quantification of global nitrous oxide sources and sinks

全面量化全球一氧化二氮的源和匯

▲ 作者：Hanqin Tian, Rongting Xu, Josep G. Canadell, Rona L. Thompson, Wilfried Winiwarter, Parvadha Suntharalingam, et al.

▲ 連結：

https://www.nature.com/articles/s41586-020-2780-0

▲ 摘要

一氧化二氮（N2O）與二氧化碳一樣，是一種長期存在的溫室氣體，會累積在大氣中。在過去的150年中，大氣中N2O濃度的增加導致平流層臭氧消耗和氣候變化，目前的增長率估計為每十年2%。

研究組介紹了一個包含自然和人為來源的全球N2O清單，並解釋了氮添加物與控制N2O排放的生化過程之間的相互作用。研究組使用自下而上（庫存、通量測量值的統計推斷、基於過程的陸地和海洋建模）和自上而下（大氣反演）的方法，對1980-2016年間21個自然和人類部門產生的全球N2O源和匯進行全面量化。

在2007-2016年之間，全球N2O排放量為每年17.0百萬噸氮（自下而上）和每年16.9百萬噸氮（自上而下）。在過去的四十年中，全球人為排放的氮（主要是農田中的氮）增加了30%，達到每年7.3百萬噸，這是造成大氣負擔增加的主要原因。

研究組的發現表明，新興經濟體（尤其是巴西、中國和印度）的N2O排放量正在增加。對基於過程的模型估計分析顯示，氮增加與氣候變化之間的相互作用導致了N2O-氣候反饋的出現。最近N2O排放量的增長超過了某些預計的最高排放情景，這凸顯了減少N2O排放量的緊迫性。

▲ Abstract

Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion and climate change, with the current rate of increase estimated at 2 per cent per decade. Here we present a global N2O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N2O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N2O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N2O emissions were 17.0 teragrams of nitrogen per year (bottom-up) and 16.9 teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O- climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios, underscoring the urgency to mitigate N2O emissions.

社會學Sociology

Local exposure to inequality raises support of people of low wealth for taxing the wealthy

目睹不平等增加了低收入人群對富人徵稅的支持

▲ 作者：Melissa L. Sands & Daniel de Kadt

▲ 連結：

https://www.nature.com/articles/s41586-020-2763-1

▲ 摘要

心理學研究表明，個人與同伴或他人的社會比較會影響態度的形成。隨著全球不平等加劇，這種比較的機會增加了；通過社會階層的信息，日常經歷可使貧富差距更加突出。研究組表明，在社會經濟地位較低的個人中，這種局部不平等會促使人們支持財富的重新分配。

研究組在南非社區中設計了一項安慰劑對照的現場實驗，社會經濟地位低下的人通過隨機出現的豪車目睹了現實世界中的不平等現象。行人被要求籤署一份請願書，增加對富人的稅收，以幫助財富重新分配。

考慮到實驗安慰劑的作用，研究組發現在目睹不平等的情況下簽署請願書的可能性增加了11個百分點。安慰劑效應抑制了個人在請願書上簽名的可能性，這與向上的社會比較降低政治效力的證據一致。經濟不平等的衡量標準建立在社區層面，並與對社會經濟地位低下的個人調查有關。

研究組發現，當地人目睹不平等與支持向富人徵稅以解決貧富差距之間存在正相關關係。目睹不平等似乎會影響當地人對財富再分配的偏好。但研究組的結果表明，不平等也可能抑制參與；因此，該調查結果在國家或地區範圍內的政治影響仍然不確定。

▲ Abstract

Psychological research shows that social comparison of individuals with peers or others shapes attitude formation. Opportunities for such comparisons have increased with global inequality; everyday experiences can make economic disparities more salient through signals of social class. Here we show that, among individuals with a lower socioeconomic status, such local exposure to inequality drives support for the redistribution of wealth. We designed a placebo-controlled field experiment conducted in South African neighbourhoods in which individuals with a low socioeconomic status encountered real-world reminders of inequality through the randomized presence of a high-status car. Pedestrians were asked to sign a petition to increase taxes on wealthy individuals to help with the redistribution of wealth. We found an increase of eleven percentage points in the probability of signing the petition in the presence of inequality, when taking into account the experimental placebo effect. The placebo effect suppresses the probability that an individual signs the petition in general, which is consistent with evidence that upward social comparison reduces political efficacy. Measures of economic inequality were constructed at the neighbourhood level and connected to a survey of individuals with a low socioeconomic status. We found that local exposure to inequality was positively associated with support for a tax on wealthy individuals to address economic disparities. Inequality seems to affect preferences for the redistribution of wealth through local exposure. However, our results indicate that inequality may also suppress participation; the political implications of our findings at regional or country-wide scales therefore remain uncertain.