《自然》（20230928出版）一周論文導讀

原文地址：http://news.sciencenet.cn/htmlnews/2023/9/509580.shtm

編譯 | 未玖

Nature, 28 September 2023, VOL 621, ISSUE 7980

《自然》2023年9月28日，第621卷，7980期

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天文學Astronomy

Precessing jet nozzle connecting to a spinning black hole in M87

進動噴流連接M87旋轉黑洞

▲ 作者：Yuzhu Cui, Kazuhiro Hada, Tomohisa Kawashima, Motoki Kino, Weikang Lin, Yosuke Mizuno, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-023-06479-6

▲ 摘要：

鄰近射電星系M87為探索中央超大質量黑洞和相對論噴流之間的相關性提供了一個獨特機會。先前對M87內部區域的研究顯示，起源于黑洞附近的噴流有一個大開口角。

事件視界望遠鏡對中央射電源進行了解析，發現了一個與廣義相對論預測相符的不對稱環狀結構。根據17年的觀測基線，噴流橫向位置發生了變化，這可能由8到10年的準周期性引發。然而，這種橫向轉變的起源仍不清楚。

研究組報道了對22年來射電觀測的分析，表明噴流位置角度的變化周期約為11年，因而推斷觀測到的是一個旋轉的黑洞，它引起了一個錯位吸積盤的蘭斯-蒂林進動。類似的噴流進動通常也發生在其他活動星系核中，但由于其變化幅度小且周期長，因此很難探測到。

▲ Abstract：

The nearby radio galaxy M87 offers a unique opportunity to explore the connections between the central supermassive black hole and relativistic jets. Previous studies of the inner region of M87 revealed a wide opening angle for the jet originating near the black hole. The Event Horizon Telescope resolved the central radio source and found an asymmetric ring structure consistent with expectations from general relativity. With a baseline of 17 years of observations, there was a shift in the jet’s transverse position, possibly arising from an 8- to 10-year quasi-periodicity. However, the origin of this sideways shift remains unclear. Here we report an analysis of radio observations over 22 years that suggests a period of about 11 years for the variation in the position angle of the jet. We infer that we are seeing a spinning black hole that induces the Lense–Thirring precession of a misaligned accretion disk. Similar jet precession may commonly occur in other active galactic nuclei but has been challenging to detect owing to the small magnitude and long period of the variation.

物理學Physics

A quantum engine in the BEC–BCS crossover

BEC-BCS交叉中的量子引擎

▲ 作者：Jennifer Koch, Keerthy Menon, Eloisa Cuestas, Sian Barbosa, Eric Lutz, Thomás Fogarty, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-023-06469-8

▲ 摘要：

熱機將熱能轉化為經典和量子狀態下的機械功。然而，量子理論提供了真正的非經典形式的能量，不同于迄今為止尚未在循環發動機中得到利用的熱能。

研究組通過實驗實現了一個由費米子和玻色子超冷粒子系綜之間的能量差驅動的量子多體引擎，且遵循泡利不相容原理。

使用一種由近磁性費什巴赫共振6Li原子組成的諧波捕獲超流體氣體，通過磁場調節玻色子分子的玻色-愛因斯坦凝聚體和酉費米氣體（以及返回）之間的氣體，有效改變了從玻色-愛因斯坦到費米-狄拉克的量子統計。

通過將泡利引擎與經典熱機和純相互作用驅動的設備進行對比，泡利引擎的量子性質得以揭示。研究組獲得了每周期幾個106振動量子的功輸出，效率高達25%。該發現將量子統計學確立為可做功的有用熱力學資源。

▲ Abstract：

Heat engines convert thermal energy into mechanical work both in the classical and quantum regimes. However, quantum theory offers genuine non-classical forms of energy, different from heat, which so far have not been exploited in cyclic engines. Here we experimentally realize a quantum many-body engine fuelled by the energy difference between fermionic and bosonic ensembles of ultracold particles that follows from the Pauli exclusion principle. We employ a harmonically trapped superfluid gas of 6Li atoms close to a magnetic Feshbach resonance that allows us to effectively change the quantum statistics from Bose–Einstein to Fermi–Dirac, by tuning the gas between a Bose–Einstein condensate of bosonic molecules and a unitary Fermi gas (and back) through a magnetic field. The quantum nature of such a Pauli engine is revealed by contrasting it with an engine in the classical thermal regime and with a purely interaction-driven device. We obtain a work output of several 106 vibrational quanta per cycle with an efficiency of up to 25%. Our findings establish quantum statistics as a useful thermodynamic resource for work production.

材料科學Materials Science

Electrically driven organic laser using integrated OLED pumping

采用集成OLED泵浦的電驅動有機激光器

▲ 作者：Kou Yoshida, Junyi Gong, Alexander L. Kanibolotsky, Peter J. Skabara, Graham A. Turnbull & Ifor D. W. Samuel

▲ 鏈接：

https://www.nature.com/articles/s41586-023-06488-5

▲ 摘要：

有機半導體是一種碳基材料，它結合了光電性能與簡單制造，通過改變化學結構來調整范圍。有機半導體已成功用于制造有機發光二極管（OLEDs，現廣泛應用于手機顯示屏和電視）、太陽能電池、晶體管和傳感器。

然而，制造電驅動的有機半導體激光器頗具挑戰性。這很困難，因為有機半導體通常只支持低電流密度，受到注入電荷和三重態的大量吸收，并且由于接觸而有額外損耗。簡而言之，將電荷注入增益介質會導致無法容忍的損耗。

研究組采取了另一種方法，其中電荷注入和激光在空間上分離，從而大大減少了損耗。通過開發一種集成器件結構實現了這一目標，將具有極高內部光生成的OLED與聚合物分布式反饋激光器有效耦合在一起。在集成結構的電驅動下，研究組觀察到光輸出相對于驅動電流的閾值，其發射光譜窄，在閾值以上形成光束。這些觀測證實了激光發射。

該研究結果提供了一種前所未有的有機電子器件，并表明OLED的間接電泵浦是實現電驅動有機半導體激光器的一種非常有效的方法。這為可見激光提供了一種策略，有望應用于光譜學、計量學和傳感。

▲ Abstract：

Organic semiconductors are carbon-based materials that combine optoelectronic properties with simple fabrication and the scope for tuning by changing their chemical structure. They have been successfully used to make organic light-emitting diodes (OLEDs, now widely found in mobile phone displays and televisions), solar cells, transistors and sensors. However, making electrically driven organic semiconductor lasers is very challenging. It is difficult because organic semiconductors typically support only low current densities, suffer substantial absorption from injected charges and triplets, and have additional losses due to contacts. In short, injecting charges into the gain medium leads to intolerable losses. Here we take an alternative approach in which charge injection and lasing are spatially separated, thereby greatly reducing losses. We achieve this by developing an integrated device structure that efficiently couples an OLED, with exceptionally high internal-light generation, with a polymer distributed feedback laser. Under the electrical driving of the integrated structure, we observe a threshold in light output versus drive current, with a narrow emission spectrum and the formation of a beam above the threshold. These observations confirm lasing. Our results provide an organic electronic device that has not been previously demonstrated, and show that indirect electrical pumping by an OLED is a very effective way of realizing an electrically driven organic semiconductor laser. This provides an approach to visible lasers that could see applications in spectroscopy, metrology and sensing.

化學Chemistry

Light-enabled deracemization of cyclopropanes by Al-salen photocatalysis

Al-salen光催化助力環丙烷的光致去消旋化

▲ 作者：Carina Onneken, Tobias Morack, Julia Soika, Olga Sokolova, Niklas Niemeyer, Christian Mück-Lichtenfeld, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-023-06407-8

▲ 摘要：

“優越”手性催化劑（具有共同結構特征并在一系列反應中具有對映選擇性的催化劑）持續改變著化學研究的前景。近年來，新反應模式已通過激發態催化（光活化過程）實現，但尚不清楚基態優越催化劑的選擇性是否可匹配。

雖然基態循環對光生中間體的阻斷已部分解決了這一挑戰，但同時調節反應性和選擇性的單一手性光催化劑明顯稀缺。到目前為止，精確的供體-受體識別基序在對映選擇性光催化劑設計中仍至關重要。

研究組表明，手性Al-salen配合物具有明確的光物理性質，可用于環丙基酮的有效光化學去消旋化（對映體比率（e.r.）高達98:2）。λ= 400 nm（紫外光）的輻射增強了商業催化劑的反應性，使反應性和對映選擇性能夠同時調節，而無需定制催化劑-底物識別基序。

據預測，這項研究將促進對激發態過程中許多古老（基態）手性催化劑的重新評估，從而確定在兩種反應性模型中的潛在“優越”候選物。

▲ Abstract：

Privileged chiral catalysts—those that share common structural features and are enantioselective across a range of reactions—continue to transform the chemical-research landscape. In recent years, new reactivity modes have been achieved through excited-state catalysis, processes activated by light, but it is unclear if the selectivity of ground-state privileged catalysts can be matched. Although the interception of photogenerated intermediates by ground-state cycles has partially addressed this challenge, single, chiral photocatalysts that simultaneously regulate reactivity and selectivity are conspicuously scarce. So far, precision donor–acceptor recognition motifs remain crucial in enantioselective photocatalyst design. Here we show that chiral Al-salen complexes, which have well-defined photophysical properties, can be used for the efficient photochemical deracemization of cyclopropyl ketones (up to 98:2 enantiomeric ratio (e.r.)). Irradiation at λ?=?400?nm (violet light) augments the reactivity of the commercial catalyst to enable reactivity and enantioselectivity to be regulated simultaneously. This circumvents the need for tailored catalyst–substrate recognition motifs. It is predicted that this study will stimulate a re-evaluation of many venerable (ground-state) chiral catalysts in excited-state processes, ultimately leading to the identification of candidates that may be considered ‘privileged’ in both reactivity models.

地球科學Earth Science

Climate warming increases extreme daily wildfire growth risk in California

氣候變暖增加了加州每日極端野火增長的風險

▲ 作者：Patrick T. Brown, Holt Hanley, Ankur Mahesh, Colorado Reed, Scott J. Strenfel, Steven J. Davis, et al.

▲ 鏈接：

https://www.nature.com/articles/s41586-023-06444-3

▲ 摘要：

近年來，加州經歷了越來越多的極端野火事件，導致大量的生命和財產損失。野火發生的部分變化可歸因于人為氣候變暖，但由于眾多混雜因素以及野火范圍低于全球氣候模式的網格尺度，很難對該影響進行正式量化。

研究組使用機器學習來量化溫度（以及溫度對干旱的影響）與加利福尼亞州極端每日野火增長（>10000英畝）風險之間的經驗關系，并發現溫度對風險的影響主要是通過其對燃料濕度的影響來調節的。通過將2003—2020年的歷史火災置于不同的背景氣候溫度和干旱條件下，利用未發現的關系來估計人為變暖下極端每日野火增長風險的變化。

研究組發現，人為變暖對極端每日野火增長風險的影響在一場接一場火災和日復一日的基礎上存在明顯差異，這取決于氣候變暖是否推動條件超過某些干旱閾值，例如1.5 kPa的蒸汽壓差和10%的乏燃料水分。

到目前為止，相對于工業化前的條件，人為變暖使極端每日野火增長的總預期頻率平均提高了25%（5-95%的范圍為14-36%）。但對于某些火災卻幾乎沒有變化，而對于其他類型的火災，增強幅度高達461%。

當歷史火災在一系列預測的世紀末條件下時，與工業化前條件相比，在低SSP1-2.6排放情景下，極端每日野火增長事件的總預期頻率增加了59%（47-71%），而在非常高的SSP5-8.5排放情景下，則增加了172%（156-188%）。

▲ Abstract：