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Science,31 July 2020,Vol 369, Issue 6503

《科學》2020年7月31日，第369卷，6503期

物理學Physics

A physics-based method that can predict imminent large solar flares

基於物理方法預測大規模太陽耀斑

▲ 作者：Kanya Kusano, Tomoya Iju, Yumi Bamba

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/587

▲ 摘要

太陽磁場的突然釋放會引發強烈的太陽耀斑，這是很難預測的。作者爲大型太陽耀斑的爆發推導了基於物理的閾值，並展示瞭如何通過常規太陽觀測預測它們。作者利用2008年到2019年對太陽的觀測測試了他們的方法。

在大多數情況下，該方法正確地識別出哪些區域將在未來20小時內產生大的耀斑，儘管存在一些誤報和誤報。該方法還提供了每次耀斑開始的確切位置以及其強度的限制。對太陽耀斑的準確預測可以改善對地球周圍空間天氣狀況的預測。

▲ Abstract

The sudden release of magnetic energy on the Sun drives powerful solar flares, which are difficult to predict. Kusano et al. derived physics-based thresholds for the onset of large solar flares and show how they can be predicted from routine solar observations. They tested their method using observations of the Sun from 2008 to 2019. In most cases, the method correctly identifies which regions will produce large flares within the next 20 hours, although there are some false positives and false negatives. The method also provides the exact location where each flare will begin and limits on how powerful it will be. Accurate predictions of solar flares could improve forecasts of space weather conditions around Earth.

Cooling and entangling ultracold atoms in optical lattices

在光晶格中冷卻和糾纏超低溫原子

▲ 作者：Bing Yang, Hui Sun, Chun-Jiong Huang, Han-Yi Wang, Youjin Deng, Han-Ning Dai, Zhen-Sheng Yuan, Jian-Wei Pan

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/550

▲ 摘要

載於光晶格中的原子可以模擬固體中的電子的行爲。然而，要達到極低溫度，即最有趣的量子相可能發生的溫度卻很棘手。作者引入了一種巧妙的實驗技術來減少樣本的熵。

他們創造了一個由交替排列的原子樣本和存儲庫組成的陣列。熵從樣本原子轉移到鄰近的儲層，然後被移除。由此產生的低熵系統可作爲量子模擬和信息的基礎。

▲ Abstract

Atoms loaded in an optical lattice can convincingly mimic the behavior of electrons in solids. However, reaching very low temperatures, where the most interesting quantum phases are expected to occur, is tricky. Yang et al. introduced a clever experimental technique to reduce the entropy of their sample. They created an array consisting of alternating rows of sample atoms and reservoirs. The entropy was transferred from the sample atoms to the adjacent reservoirs, which were then removed. The resulting low-entropy system can be used as a basis for quantum simulation and information.

化學Chemistry

Rational synthesis of atomically precise graphene nanoribbons directly on metal oxide surfaces

在金屬氧化物表面合成石墨烯納米帶

▲ 作者：Marek Kolmer, Ann-Kristin Steiner, Irena Izydorczyk, Wonhee Ko, Mads Engelund, Marek Szymonski, An-Ping Li, Konstantin Amsharov

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/571

▲ 摘要

科學家已經在催化前體環氫化的金屬表面上已經合成了原子級精確的納米石墨烯和納米帶。然而，爲了在設備中使用，這些結構通常必須轉移到絕緣或半導體表面。

作者在金紅石二氧化鈦（TiO2）表面合成了精確的石墨烯納米帶，通過一系列熱觸發轉換，輔助了專門設計的前體分子的環氫氟化。掃描隧道顯微鏡和光譜學證實了納米帶的鋸齒狀末端的形成，以及它們與襯底的弱相互作用。

▲ Abstract

Atomically precise nanographenes and nanoribbons have been synthesized on metal surfaces that catalyze cyclode-hydrogenation of precursors. However, for use in devices, these structures usually must be transferred to insulating or semiconducting surfaces. Kolmer et al. synthesized precise graphene nanoribbons on the surface of rutile titanium dioxide (TiO2) that assisted the cyclode-hydrofluorination of specifically designed precursor molecules through a series of thermally triggered transformations. Scanning tunneling microscopy and spectroscopy confirmed the formation of well-defined zigzag ends of the nanoribbons as well as their weak interaction with the substrate.

Boosted molecular mobility during common chemical reactions

在普通化學反應中提高分子遷移率

▲ 作者：Huan Wang, Myeonggon Park, Ruoyu Dong, Junyoung Kim, Yoon-Kyoung Cho, Tsvi Tlusty, Steve Granick

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/537

▲ 摘要

在化學反應中，溶劑分子的重組不直接與反應物和產物接觸，通常被視爲一個簡單的擴散反應。

作者利用脈衝場梯度核磁共振研究了六種常見反應中的分子擴散，包括銅催化的咔咔反應和Diels-Alder反應。

他們觀察到相對於布朗擴散，遷移率的增加對所研究的催化反應更強。用微流控梯度法驗證了點擊反應的可移動性。他們認爲，能量釋放產生反應中心的瞬時平移運動，從而機械地擾亂溶劑分子。

▲ Abstract

During a chemical reaction, the reorganization of solvent molecules not directly in contact with reactants and products is normally viewed as a simple diffusion response. Wang et al. studied molecular diffusion in six common reactions—including the copper-catalyzed click reaction and the Diels-Alder reaction—with pulsed-field gradient nuclear magnetic resonance. They observed a boost in mobility relative to Brownian diffusion that was stronger for the catalyzed reactions that were studied. The mobilities for the click reaction were verified with a microfluidic gradient method. They argue that energy release produces transient translational motion of reacting centers that mechanically perturbs solvent molecules.

生態學Ecology

Ancient orogenic and monsoon-driven assembly of the world’s richest temperate alpine flora

古造山和季風驅動的世界上最豐富的溫帶高山植物羣

▲ 作者：Wen-Na Ding, Richard H. Ree, Robert A. Spicer, ao-Wu Xing

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/578

▲ 摘要

高山植物區系的演化受到構造和氣候歷史的強烈影響。作者記錄了世界上物種最豐富的高山植物區系——喜馬拉雅—橫斷山區的組合時間、節奏和模式。

該地區的高山組合比以前認爲的更古老，其譜系可追溯至漸新世早期的高山系，比任何其他現代高山系都要古老。

在造山運動和亞洲季風增強時期，高山物種多樣性增長較快，而橫斷山脈作爲該地區物種最豐富的地區，作爲漸新世高山物種多樣化最早爆發的位置，發揮了重要的生物地理作用。

▲ Abstract

The evolution of high mountain floras is strongly influenced by tectonic and climatic history. Ding et al. document the timing, tempo, and mode by which the world's most species-rich alpine flora, that of the Tibet-Himalaya-Hengduan region, was assembled. Alpine assemblages in the region are older than previously thought, with lineages tracing their alpine ancestry to the early Oligocene—older than any other modern alpine system. Alpine species diversified faster during periods of orogeny and intensification of the Asian monsoon, and the Hengduan Mountains—the most species-rich area in this region—played a key biogeographic role as the location of the earliest pulse of alpine diversification in the Oligocene.

環境學

Environmentology

Disparities in PM2.5 air pollution in the United States

美國PM2.5空氣污染的差異

▲ 作者：Jonathan Colmer, Ian Hardman, Jay Shimshack, John Voorheis

▲ 鏈接：

https://science.sciencemag.org/content/369/6503/575

▲ 摘要

近幾十年來，美國周邊地區空氣微粒污染顯著降低，作者分析了36年來的數據，發現細顆粒物濃度的空間分佈在該區間內基本保持不變。

雖然細顆粒物污染水平總體有所下降，但1981年污染最嚴重和最不嚴重的地區今天依然如故。

作者表示，美國或在污染控制方面取得了進展，但在解決不同社區之間暴露程度的差異方面卻沒有那麼成功。

▲ Abstract

Particulate air pollution in the contiguous United States has decreased considerably over recent decades, but where exactly has that progress been made? Colmer et al. analyzed 36 years of data and found that the spatial distribution of fine particulate matter concentrations has remained largely unchanged over that interval. Although, fine particulate pollution levels have dropped overall, those areas that were most and least polluted in 1981 remain so today. We may have made important strides in pollution control, but we have been less successful in addressing disparities of exposure between communities.

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