《自然》（20200910出版）一周論文導讀

編譯 | 李言

Nature, 10 September 2020, Volume 585 Issue 7824

《自然》2020年9月10日，第585卷，7824期

天文學Astronomy

The Magellanic Corona as the key to the formation of the Magellanic Stream

麥哲倫日冕是麥哲倫星流形成的關鍵

▲ 作者：S. Lucchini, E. D’Onghia, A. J. Fox, C. Bustard, J. Bland-Hawthorn & E. Zweibel

▲ 鏈接：https://www.nature.com/articles/s41586-020-2663-4

▲ 摘要

星系暈中主要的氣體結構是麥哲倫星流。

最近幾項發現——包括與麥哲倫星群相關的矮星系的發現、LMC高質量的測定、LMC中恆星附近高度電離氣體的探測以及宇宙學模擬預測——都支持在LMC（麥哲倫日冕）附近有一圈溫暖的（約500,000 k）電離氣體存在。

在這裡我們報告，通過在水動力學模擬麥哲倫雲落在銀河系的麥哲倫日冕，我們可以重現麥哲倫星流和它的主導臂。我們的模擬解釋了麥哲倫星流的絲狀結構、空間範圍、徑向速度梯度和總電離氣體質量。

我們預測，在LMC附近的背景類星體紫外光譜的高電離吸收線中，麥哲倫日冕將是明確可見的。

▲ Abstract

The dominant gaseous structure in the Galactic halo is the Magellanic Stream. Several recent developments—including the discovery of dwarf galaxies associated with the Magellanic group, determination of the high mass of the LMC, detection of highly ionized gas near stars in the LMC and predictions of cosmological simulations —support the existence of a halo of warm (roughly 500,000 kelvin) ionized gas around the LMC (the ‘Magellanic Corona’). Here we report that, by including this Magellanic Corona in hydrodynamic simulations of the Magellanic Clouds falling onto the Milky Way, we can reproduce the Magellanic Stream and its leading arm. Our simulations explain the filamentary structure, spatial extent, radial-velocity gradient and total ionized-gas mass of the Magellanic Stream. We predict that the Magellanic Corona will be unambiguously observable via high-ionization absorption lines in the ultraviolet spectra of background quasars lying near the LMC.

量子物理Quantum Physics

Experimental deterministic correction of qubit loss

量子位丟失的實驗確定校正

▲ 作者：Roman Stricker, Davide Vodola, Alexander Erhard, Lukas Postler, Michael Meth, Martin Ringbauer, et al.

▲ 鏈接：https://www.nature.com/articles/s41586-020-2667-0

▲ 摘要

量子計算機的成功運行依賴於保護量子位不受退相干和噪聲的影響，如果不進行校正，這些噪聲將導致錯誤的結果。

在此，我們實現了一個全周期的量子丟失檢測和校正的拓撲表面代碼的最小實例在捕獲離子量子處理器。

用於校正的關鍵技術是通過輔助量子位元執行的量子非破壞測量，它充當了一個最小侵入探針，檢測缺失的量子位元，同時將最小的量子力學可能的干擾傳遞給剩餘的量子位元。

一旦檢測到量子位丟失，一個恢復程序就會被實時觸發，該程序將邏輯信息映射到剩餘量子位上的新編碼上。

雖然目前的演示是在一個截留離子量子處理器中進行的，但該協議適用於其他量子計算架構和糾錯碼，包括領先的二維和三維拓撲碼。

▲ Abstract

The successful operation of quantum computers relies on protecting qubits from decoherence and noise, which—if uncorrected—will lead to erroneous results. Here we experimentally implement a full cycle of qubit loss detection and correction on a minimal instance of a topological surface code in a trapped-ion quantum processor. The key technique used for this correction is a quantum non-demolition measurement performed via an ancillary qubit, which acts as a minimally invasive probe that detects absent qubits while imparting the smallest quantum mechanically possible disturbance to the remaining qubits. Upon detecting qubit loss, a recovery procedure is triggered in real time that maps the logical information onto a new encoding on the remaining qubits. Although the current demonstration is performed in a trapped-ion quantum processor, the protocol is applicable to other quantum computing architectures and error correcting codes, including leading two- and three-dimensional topological codes.

材料科學Material Science

Co-designing electronics with microfluidics for more sustainable cooling

與微流體協同設計電子器件，實現更可持續的冷卻

▲ 作者：Remco van Erp, Reza Soleimanzadeh, Luca Nela, Georgios Kampitsis & Elison Matioli

▲ 鏈接：https://www.nature.com/articles/s41586-020-2666-1

▲ 摘要

將液體冷卻直接嵌入芯片內部是一種很有前途的更有效的熱管理方法。然而，即使在最先進的方法，電子和冷卻分開處理，留下充分的節能潛力的嵌入式冷卻未開發。

在這裡，我們表明，通過在同一半導體襯底內共同設計微流體和電子元件，我們可以生產一個整體集成的流形微通道冷卻結構，其效率超過目前可用的。我們的結果表明，超過1.7千瓦每平方厘米的熱流可以提取僅使用0.57瓦每平方厘米的泵送功率。

我們觀察到，對於每平方厘米超過1千瓦的熱通量的單相水冷卻具有前所未有的性能係數（超過10,000），對應於直線微通道50倍的增長，以及非常高的平均努塞爾數16。

▲ Abstract

Embedding liquid cooling directly inside the chip is a promising approach for more efficient thermal management. However, even in state-of-the-art approaches, the electronics and cooling are treated separately, leaving the full energy-saving potential of embedded cooling untapped. Here we show that by co-designing microfluidics and electronics within the same semiconductor substrate we can produce a monolithically integrated manifold microchannel cooling structure with efficiency beyond what is currently available. Our results show that heat fluxes exceeding 1.7 kilowatts per square centimetre can be extracted using only 0.57 watts per square centimetre of pumping power. We observed an unprecedented coefficient of performance (exceeding 10,000) for single-phase water-cooling of heat fluxes exceeding 1 kilowatt per square centimetre, corresponding to a 50-fold increase compared to straight microchannels, as well as a very high average Nusselt number of 16.

化學Chemstry

Evidence for supercritical behaviour of high-pressure liquid hydrogen

高壓液氫的超臨界行為的證據

▲ 作者：Bingqing Cheng, Guglielmo Mazzola, Chris J. Pickard & Michele Ceriotti

▲ 鏈接：https://www.nature.com/articles/s41586-020-2677-y

▲ 摘要

氫是宇宙中最簡單、最豐富的元素，在壓縮過程中會表現出非常複雜的特性。

在這裡，我們提出了一個理論研究的相圖的緻密氫使用機器學習從參考計算中“學習”勢能表面和原子間的力，然後預測他們在低計算成本、克服長度和時間尺度的限制。我們重現了重入熔點的行為和固相的多態性。

使用基於機器學習的電勢的模擬為液體中連續的分子到原子轉變提供了證據，在熔融線上沒有觀察到一級轉變。這表明，在巨大的氣體行星中，絕緣層和金屬層之間存在着平穩的過渡，同時也調和了實驗中存在的超臨界現象的差異。

▲ Abstract

Hydrogen, the simplest and most abundant element in the Universe, develops a remarkably complex behaviour upon compression. Here we present a theoretical study of the phase diagram of dense hydrogen that uses machine learning to ‘learn’ potential-energy surfaces and interatomic forces from reference calculations and then predict them at low computational cost, overcoming length- and timescale limitations. We reproduce both the re-entrant melting behaviour and the polymorphism of the solid phase. Simulations using our machine-learning-based potentials provide evidence for a continuous molecular-to-atomic transition in the liquid, with no first-order transition observed above the melting line. This suggests a smooth transition between insulating and metallic layers in giant gas planets, and reconciles existing discrepancies between experiments as a manifestation of supercritical behaviour.

Rare-earth–platinum alloy nanoparticles in mesoporous zeolite for catalysis

稀土-鉑合金納米顆粒在介孔沸石中的催化作用

▲ 作者：Ryong Ryoo, Jaeheon Kim, Changbum Jo, Seung Won Han, Jeong-Chul Kim, Hongjun Park, Jongho Han, et al.

▲ 鏈接：https://www.nature.com/articles/s41586-020-2671-4

▲ 摘要

在石油化工過程中，鉑是一種常用的催化劑，通常與其他金屬混合以提高催化活性、選擇性和使用壽命。

這裡我們使用了一種具有孔壁表面框架缺陷的介孔沸石（稱為“硅醇巢”）作為支撐，表明沸石使鉑和稀土元素之間形成合金。我們發現硅醇巢使稀土元素以比大塊氧化物高得多的化學勢以單原子形式存在，使它們有可能擴散到鉑上。

高分辨率的透射電子顯微鏡和氫化學吸附測量表明，負載在介孔沸石上的雙金屬納米顆粒是金屬間化合物，我們發現它是丙烷脫氫反應的穩定、高活性和選擇性催化劑。

當與=過渡金屬一起使用時，同樣的製備策略可以產生含有大量第二金屬的鉑合金催化劑，對於鉑碳合金，在H2中優先氧化一氧化碳時表現出高的催化活性和選擇性。

▲ Abstract

Platinum is a much used catalyst that, in petrochemical processes, is often alloyed with other metals to improve catalytic activity, selectivity and longevity. Here we use as support a mesoporous zeolite that has pore walls with surface framework defects (called ‘silanol nests’) and show that the zeolite enables alloy formation between Pt and rare-earth elements. We find that the silanol nests enable the rare-earth elements to exist as single atomic species with a substantially higher chemical potential compared with that of the bulk oxide, making it possible for them to diffuse onto Pt. High-resolution transmission electron microscopy and hydrogen chemisorption measurements indicate that the resultant bimetallic nanoparticles supported on the mesoporous zeolite are intermetallic compounds, which we find to be stable, highly active and selective catalysts for the propane dehydrogenation reaction. When used with late transition metals, the same preparation strategy produces Pt alloy catalysts that incorporate an unusually large amount of the second metal and, in the case of the PtCo alloy, show high catalytic activity and selectivity in the preferential oxidation of carbon monoxide in H2.

地球科學Geoscience

Satellite isoprene retrievals constrain emissions and atmospheric oxidation

衛星異戊二烯回收裝置限制了排放和大氣氧化

▲ 作者：Kelley C. Wells, Dylan B. Millet, Vivienne H. Payne, M. Julian Deventer, Kelvin H. Bates, Joost A. de Gouw, et al.

▲ 鏈接：https://www.nature.com/articles/s41586-020-2664-3

▲ 摘要

異戊二烯是排放到大氣中的主要非甲烷有機化合物。它驅動臭氧和氣溶膠的產生，調節大氣氧化，並與全球氮循環相互作用。

這裡我們展示了全球異戊二烯的測量從空間使用交叉跟蹤紅外探測器。連同對甲醛（一種異戊二烯氧化產物）的觀察，這些測量提供了對異戊二烯排放和大氣氧化的限制。

我們發現，從空間測量的異戊二烯-甲醛關係與目前對異戊二烯- OH化學的理解大致一致，沒有跡象表明在低氮氧化物濃度下缺失OH循環。我們分析了全球四個異戊二烯熱點數據集與模型預測的關係，並根據衛星對異戊二烯本身的測量結果，給出了對異戊二烯排放量的量化分析。

亞馬遜地區出現了一個重大差異，在那裡，目前對自然氮氧化物排放的低估偏向模擬了OH和異戊二烯。在非洲南部，我們發現一個顯著的異戊二烯熱點在自下而上的預測中消失了。

▲ Abstract

Isoprene is the dominant non-methane organic compound emitted to the atmosphere. It drives ozone and aerosol production, modulates atmospheric oxidation and interacts with the global nitrogen cycle. Here we present global isoprene measurements taken from space using the Cross-track Infrared Sounder. Together with observations of formaldehyde, an isoprene oxidation product, these measurements provide constraints on isoprene emissions and atmospheric oxidation. We find that the isoprene–formaldehyde relationships measured from space are broadly consistent with the current understanding of isoprene–OH chemistry, with no indication of missing OH recycling at low nitrogen oxide concentrations. We analyse these datasets over four global isoprene hotspots in relation to model predictions, and present a quantification of isoprene emissions based directly on satellite measurements of isoprene itself. A major discrepancy emerges over Amazonia, where current underestimates of natural nitrogen oxide emissions bias modelled OH and hence isoprene. Over southern Africa, we find that a prominent isoprene hotspot is missing from bottom-up predictions.

The lithospheric-to-lower-mantle carbon cycle recorded in superdeep diamonds

超深金剛石記錄的岩石圈到下地幔的碳循環

▲ 作者：M. E. Regier, D. G. Pearson, T. Stachel, R. W. Luth, R. A. Stern & J. W. Harris

▲ 鏈接：https://www.nature.com/articles/s41586-020-2676-z

▲ 摘要

碳進入地幔是地球碳循環的重要途徑，影響着氣候和地表和地幔的氧化還原條件。在此，我們展示了對來自幾內亞的金剛石中的礦物包裹體的氧同位素測量，這些包裹體來自於從岩石圈延伸至下地幔的深度（超過660公里）。

結合金剛石的碳和氮同位素含量，這些數據表明，在俯衝到岩石圈深處和過渡帶深處（小於660公里）的板塊中，碳酸化的火成岩海洋殼，而不是沉積物，是主要的含碳儲層。

在這個深度範圍內，亞岩石圈包裹體相對於從地殼原岩中衍生出來的發育岩石圈包裹體的氧同位素明顯富集。這些亞岩石圈包裹體氧同位素含量的增加是由於富含碳酸鹽的俯衝洋殼熔融結晶所致。

相比之下，下地幔礦物包裹體及其宿主金剛石（深度超過660公里）的同位素值範圍很窄，這是很少或沒有發生地殼相互作用的地幔的典型特徵。

由於碳賦存在金屬中，而不是金剛石中，在還原的、揮發性差的下地幔中，碳必須被動員和集中以形成下地幔金剛石。

我們的數據支持了一個模型，在這個模型中，俯衝的海洋岩石圈使上下層地幔的水合作用使含碳金屬不穩定，從而形成金剛石，而不干擾中地幔穩定同位素特徵。這種從過渡帶碳酸鹽岩板融化到下地幔板脫水的轉變為碳俯衝提供了下地幔屏障。

▲ Abstract

The transport of carbon into Earth’s mantle is a critical pathway in Earth’s carbon cycle, affecting both the climate and the redox conditions of the surface and mantle. Here we present oxygen isotope measurements of mineral inclusions within diamonds from Kankan, Guinea that are derived from depths extending from the lithosphere to the lower mantle (greater than 660 kilometres). These data, combined with the carbon and nitrogen isotope contents of the diamonds, indicate that carbonated igneous oceanic crust, not sediment, is the primary carbon-bearing reservoir in slabs subducted to deep-lithospheric and transition-zone depths (less than 660 kilometres). Within this depth regime, sublithospheric inclusions are distinctly enriched in 18O relative to eclogitic lithospheric inclusions derived from crustal protoliths. The increased 18O content of these sublithospheric inclusions results from their crystallization from melts of carbonate-rich subducted oceanic crust. In contrast, lower-mantle mineral inclusions and their host diamonds (deeper than 660 kilometres) have a narrow range of isotopic values that are typical of mantle that has experienced little or no crustal interaction. Because carbon is hosted in metals, rather than in diamond, in the reduced, volatile-poor lower mantle, carbon must be mobilized and concentrated to form lower-mantle diamonds. Our data support a model in which the hydration of the uppermost lower mantle by subducted oceanic lithosphere destabilizes carbon-bearing metals to form diamond, without disturbing the ambient-mantle stable-isotope signatures. This transition from carbonate slab melting in the transition zone to slab dehydration in the lower mantle supports a lower-mantle barrier for carbon subduction.