编译 | 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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天文学Astronomy

Precessing jet nozzle connecting to a spinning black hole in M87

进动喷流连接M87旋转黑洞

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

▲ 链接：

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

▲ 摘要：

邻近射电星系M87为探索中央超大质量黑洞和相对论喷流之间的相关性提供了一个独特机会。先前对M87内部区域的研究显示，起源于黑洞附近的喷流有一个大开口角。

事件视界望远镜对中央射电源进行了解析，发现了一个与广义相对论预测相符的不对称环状结构。根据17年的观测基线，喷流横向位置发生了变化，这可能由8到10年的准周期性引发。然而，这种横向转变的起源仍不清楚。

研究组报道了对22年来射电观测的分析，表明喷流位置角度的变化周期约为11年，因而推断观测到的是一个旋转的黑洞，它引起了一个错位吸积盘的兰斯-蒂林进动。类似的喷流进动通常也发生在其他活动星系核中，但由于其变化幅度小且周期长，因此很难探测到。

▲ 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.

物理学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.

▲ 链接：

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

▲ 摘要：

热机将热能转化为经典和量子状态下的机械功。然而，量子理论提供了真正的非经典形式的能量，不同于迄今为止尚未在循环发动机中得到利用的热能。

研究组通过实验实现了一个由费米子和玻色子超冷粒子系综之间的能量差驱动的量子多体引擎，且遵循泡利不相容原理。

使用一种由近磁性费什巴赫共振6Li原子组成的谐波捕获超流体气体，通过磁场调节玻色子分子的玻色-爱因斯坦凝聚体和酉费米气体（以及返回）之间的气体，有效改变了从玻色-爱因斯坦到费米-狄拉克的量子统计。

通过将泡利引擎与经典热机和纯相互作用驱动的设备进行对比，泡利引擎的量子性质得以揭示。研究组获得了每周期几个106振动量子的功输出，效率高达25%。该发现将量子统计学确立为可做功的有用热力学资源。

▲ 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.

材料科学Materials Science

Electrically driven organic laser using integrated OLED pumping

采用集成OLED泵浦的电驱动有机激光器

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

▲ 链接：

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

▲ 摘要：

有机半导体是一种碳基材料，它结合了光电性能与简单制造，通过改变化学结构来调整范围。有机半导体已成功用于制造有机发光二极管（OLEDs，现广泛应用于手机显示屏和电视）、太阳能电池、晶体管和传感器。

然而，制造电驱动的有机半导体激光器颇具挑战性。这很困难，因为有机半导体通常只支持低电流密度，受到注入电荷和三重态的大量吸收，并且由于接触而有额外损耗。简而言之，将电荷注入增益介质会导致无法容忍的损耗。

研究组采取了另一种方法，其中电荷注入和激光在空间上分离，从而大大减少了损耗。通过开发一种集成器件结构实现了这一目标，将具有极高内部光生成的OLED与聚合物分布式反馈激光器有效耦合在一起。在集成结构的电驱动下，研究组观察到光输出相对于驱动电流的阈值，其发射光谱窄，在阈值以上形成光束。这些观测证实了激光发射。

该研究结果提供了一种前所未有的有机电子器件，并表明OLED的间接电泵浦是实现电驱动有机半导体激光器的一种非常有效的方法。这为可见激光提供了一种策略，有望应用于光谱学、计量学和传感。

▲ 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.

化学Chemistry

Light-enabled deracemization of cyclopropanes by Al-salen photocatalysis

Al-salen光催化助力环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.

▲ 链接：

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

▲ 摘要：

“优越”手性催化剂（具有共同结构特征并在一系列反应中具有对映选择性的催化剂）持续改变着化学研究的前景。近年来，新反应模式已通过激发态催化（光活化过程）实现，但尚不清楚基态优越催化剂的选择性是否可匹配。

虽然基态循环对光生中间体的阻断已部分解决了这一挑战，但同时调节反应性和选择性的单一手性光催化剂明显稀缺。到目前为止，精确的供体-受体识别基序在对映选择性光催化剂设计中仍至关重要。

研究组表明，手性Al-salen配合物具有明确的光物理性质，可用于环丙基酮的有效光化学去消旋化（对映体比率（e.r.）高达98:2）。λ= 400 nm（紫外光）的辐射增强了商业催化剂的反应性，使反应性和对映选择性能够同时调节，而无需定制催化剂-底物识别基序。

据预测，这项研究将促进对激发态过程中许多古老（基态）手性催化剂的重新评估，从而确定在两种反应性模型中的潜在“优越”候选物。

▲ 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.

地球科学Earth Science

Climate warming increases extreme daily wildfire growth risk in California

气候变暖增加了加州每日极端野火增长的风险

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

▲ 链接：

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

▲ 摘要：

近年来，加州经历了越来越多的极端野火事件，导致大量的生命和财产损失。野火发生的部分变化可归因于人为气候变暖，但由于众多混杂因素以及野火范围低于全球气候模式的网格尺度，很难对该影响进行正式量化。

研究组使用机器学习来量化温度（以及温度对干旱的影响）与加利福尼亚州极端每日野火增长（>10000英亩）风险之间的经验关系，并发现温度对风险的影响主要是通过其对燃料湿度的影响来调节的。通过将2003—2020年的历史火灾置于不同的背景气候温度和干旱条件下，利用未发现的关系来估计人为变暖下极端每日野火增长风险的变化。

研究组发现，人为变暖对极端每日野火增长风险的影响在一场接一场火灾和日复一日的基础上存在明显差异，这取决于气候变暖是否推动条件超过某些干旱阈值，例如1.5 kPa的蒸汽压差和10%的乏燃料水分。

到目前为止，相对于工业化前的条件，人为变暖使极端每日野火增长的总预期频率平均提高了25%（5-95%的范围为14-36%）。但对于某些火灾却几乎没有变化，而对于其他类型的火灾，增强幅度高达461%。

当历史火灾在一系列预测的世纪末条件下时，与工业化前条件相比，在低SSP1-2.6排放情景下，极端每日野火增长事件的总预期频率增加了59%（47-71%），而在非常高的SSP5-8.5排放情景下，则增加了172%（156-188%）。

▲ Abstract：

California has experienced enhanced extreme wildfire behaviour in recent years, leading to substantial loss of life and property. Some portion of the change in wildfire behaviour is attributable to anthropogenic climate warming, but formally quantifying this contribution is difficult because of numerous confounding factors and because wildfires are below the grid scale of global climate models. Here we use machine learning to quantify empirical relationships between temperature (as well as the influence of temperature on aridity) and the risk of extreme daily wildfire growth (>10,000 acres) in California and find that the influence of temperature on the risk is primarily mediated through its influence on fuel moisture. We use the uncovered relationships to estimate the changes in extreme daily wildfire growth risk under anthropogenic warming by subjecting historical fires from 2003 to 2020 to differing background climatological temperatures and aridity conditions. We find that the influence of anthropogenic warming on the risk of extreme daily wildfire growth varies appreciably on a fire-by-fire and day-by-day basis, depending on whether or not climate warming pushes conditions over certain thresholds of aridity, such as 1.5 kPa of vapour-pressure deficit and 10% dead fuel moisture. So far, anthropogenic warming has enhanced the aggregate expected frequency of extreme daily wildfire growth by 25% (5–95 range of 14–36%), on average, relative to preindustrial conditions. But for some fires, there was approximately no change, and for other fires, the enhancement has been as much as 461%. When historical fires are subjected to a range of projected end-of-century conditions, the aggregate expected frequency of extreme daily wildfire growth events increases by 59% (5–95 range of 47–71%) under a low SSP1–2.6 emissions scenario compared with an increase of 172% (5–95 range of 156–188%) under a very high SSP5–8.5 emissions scenario, relative to preindustrial conditions.