Science,  3 NOV 2023, Volume 382, Issue 6670

《科学》，2023年11月3日，第382卷，6670期

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物理学Physics

Supermassive black hole feeding and feedback observed on subparsec scales

超大质量黑洞在亚秒差距尺度上的馈入和反馈

▲ 作者：TAKUMA IZUMI, KEIICHI WADA, MASATOSHI IMANISHI, KOUICHIRO NAKANISHI, KOTARO KOHNO, YUKI KUDOH, TAIKI KAWAMURO, SHUNSUKE BABA, NAOKI MATSUMOTO, AND KONRAD R. W. TRISTRAM

▲ 链接：https://www.science.org/doi/full/10.1126/science.adf0569

▲ 摘要：

大多数星系的中心都有一个超大质量黑洞。当气体落向黑洞时，它会被加热并发出辐射，可以被观察到是一个活跃的星系核。然而，目前尚不清楚气体是如何从更广阔的星系输送到黑洞周围的内部区域的。

研究者结合对附近活动星系核环星系中心几个气体示踪剂的亚毫米观测结果，通过比较分子、原子和电离气体的运动学，在中心秒差距中识别出密集的分子气体流入，为黑洞提供能量。

▲ Abstract：

Most galaxies contain a supermassive black hole at their center. When gas falls toward the black hole, it heats up and emits radiation and can be observed as an active galactic nucleus. However, it is not known how gas is delivered from the wider galaxy to the inner region around the black hole. Izumi et al. combined submillimeter observations of several gas tracers in the center of the Circinus Galaxy, a nearby active galactic nucleus. By comparing the kinematics of molecular, atomic, and ionized gas, they were able to identify an inflow of dense molecular gas in the central parsec, feeding the black hole. 

Electrically gated molecular thermal switch

电门控分子热开关

▲ 作者：MAN LI, HUAN WU, ERIN M. AVERY, ZIHAO QIN, DOMINIC P. GORONZY, HUU DUY NGUYEN, TIANHAN LIU, PAUL S. WEISS, AND YONGJIE HU

▲ 链接：https://www.science.org/doi/full/10.1126/science.abo4297

▲ 摘要：

控制热流是从电子热管理到能源系统、工业加工和热治疗等应用的关键挑战。然而，相关进展通常受到慢响应时间和热导率低可调性的限制。研究者展示了一种使用自组装分子结的电子门控固态热开关，在室温下实现了优异的性能。

在这个三端装置中，热流通过精心控制的化学键和分子界面内的电荷分布被电场连续可逆地调制。该器件具有超过1兆赫兹的超高开关速度，热导率的开/关比大于1300%，并且可以切换超过100万次。研究者预计这些进展将为热管理系统和热电路设计的分子工程带来机会。

▲ Abstract：

Controlling heat flow is a key challenge for applications ranging from thermal management in electronics to energy systems, industrial processing, and thermal therapy. However, progress has generally been limited by slow response times and low tunability in thermal conductance. In this work, we demonstrate an electronically gated solid-state thermal switch using self-assembled molecular junctions to achieve excellent performance at room temperature. In this three-terminal device, heat flow is continuously and reversibly modulated by an electric field through carefully controlled chemical bonding and charge distributions within the molecular interface. The devices have ultrahigh switching speeds above 1 megahertz, have on/off ratios in thermal conductance greater than 1300%, and can be switched more than 1 million times. We anticipate that these advances will generate opportunities in molecular engineering for thermal management systems and thermal circuit design.

Universal chiral Luttinger liquid behavior in a graphene fractional quantum Hall point contact

石墨烯分数量子霍尔点接触中的通用手性卢廷格液体行为

▲ 作者：LIAM A. COHEN, NOAH L. SAMUELSON, TAIGE WANG, TAKASHI TANIGUCHI, KENJI WATANABE, MICHAEL P. ZALETEL, AND ANDREA F. YOUNG

▲ 链接：https://www.science.org/doi/full/10.1126/science.adf9728

▲ 摘要：

一维电子系统以一种不寻常的方式运行，这种方式被卢廷格（Luttinger）液体理论所描述。研究一维系统的一种方法是关注二维分数量子霍尔（FQH）态的边界，这是手性边缘模式的本垒。边缘模式形成手性卢廷格液体，可以通过将电子隧穿到其中来研究。

为此，研究者在石墨烯中填充1/3的FQH态和填充1的整数量子霍尔态之间创建了一种称为量子点接触的收缩。通过量子点接触的电导表现出手性卢廷格液体的标度规律。

▲ Abstract：

One-dimensional systems of electrons behave in an unusual way that is described by the so-called Luttinger liquid theory. One way to study a one-dimensional system is to focus on the boundary of a two-dimensional fractional quantum Hall (FQH) state, which is home to chiral edge modes. The edge modes form chiral Luttinger liquids, which can be studied by tunneling electrons into them. To that end, Cohen et al. created a constriction known as a quantum point contact between an FQH state with 1/3 filling and an integer quantum Hall state with a filling of 1 in graphene. The conductance across the quantum point contact exhibited scaling laws characteristic of a chiral Luttinger liquid.

Cascade-heterogated biphasic gel iontronics for electronic-to-multi-ionic signal transmission

用于电子到多离子信号传输的级联异质双相凝胶离子电子学

▲ 作者：WEIPENG CHEN, LINXIN ZHAI, SULI ZHANG, ZIGUANG ZHAO, YUHAO HU, YUN XIANG, HUIRONG LIU, ZHIPING XU, LEI JIANG, AND LIPING WEN

▲ 链接：https://www.science.org/doi/full/10.1126/science.adg0059

▲ 摘要：

识别和控制各种生物离子信号，从而调节水相生物介质中的生理过程，是离子电子学领域的主要挑战之一。最先进的电子学仍然局限于电子或单个离子作为信号载体。研究者报道了一种异质双相凝胶离子电子装置，该装置能够进行生物相容的电子离子信号处理和传输，并通过调节牛蛙心脏的心电活动证明了这一点。

这种方法是非生物-生物系统中生物相容信号处理和传输的有希望的一步，并且有可能激发电子学、离子学、化学、生物学和医学交叉领域的跨学科研究。

▲ Abstract：

Recognition and control of diverse bioionic signals, which would allow for the regulation of physiological processes in aqueous-phase biological media, remains one of the main challenges in the field of iontronics. State-of-the-art electronics and iontronics are still limited to electrons or single ions as signal carriers. Chen et al. report a heterogated biphasic gel iontronic device capable of biocompatible electronic-ionic signal processing and transmission, as demonstrated by regulating the cardiac electrical activity of bullfrog hearts. This approach is a promising step toward biocompatible signal processing and transmission in abiotic-biotic systems and has the potential to inspire interdisciplinary research at the intersection of electronics, ionics, chemistry, biology, and medicine. 

化学Chemistry

Reactive high-spin iron(IV)-oxo sites through dioxygen activation in a metal–organic framework

在金属有机骨架中通过双氧活化反应高自旋铁—氧位点

▲ 作者：KAIPENG HOU, JONAS BÖRGEL, HENRY Z. H. JIANG, DANIEL J. SANTALUCIA, HYUNCHUL KWON, HAO ZHUANG, KHETPAKORN CHAKARAWET, RACHEL C. ROHDE, JORDAN W. TAYLOR, AND JEFFREY R. LONG

▲ 链接：https://www.science.org/doi/full/10.1126/science.add7417

▲ 摘要：

氧化还原活性金属蛋白通常擅长与氧结合并控制氧的反应性。作者研究表明，金属—有机框架可类似地激活双氧并对脂肪族底物进行羟基化。他们使用了一系列光谱技术来证明这种机制是通过高自旋铁（IV）氧进行的，类似于在一些双加氧酶中所看到的。

该体系可用于环己烷的氧化催化，对未来双氧活化和碳氢化合物氧化催化剂的开发具有重要意义。

▲ Abstract：

Redox-active metalloproteins are often adept at binding to and controlling the reactivity of oxygen. Hou et al. showed that a metal-organic framework can similarly activate dioxygen and perform hydroxylation of aliphatic substrates. The authors used a range of spectroscopic techniques to demonstrate that the mechanism proceeds through a high-spin iron(IV) oxo species, similar to what is seen in some dioxygenase enzymes. This system can perform catalytic oxygenation of cyclohexane and should inspire future catalyst development for dioxygen activation and hydrocarbon oxidation. 

生态学Ecology

Southern Hemisphere dominates recent decline in global water availability

南半球主导近20年全球可用水量下降趋势

▲ 作者：YONGQIANG ZHANG, CONGCONG LI, FRANCIS H. S. CHIEW, DAVID A. POST, XUANZE ZHANG, NING MA, JING TIAN, DONGDONG KONG, L. RUBY LEUNG, AND CHANGMING LIU

▲ 链接：https://www.science.org/doi/full/10.1126/science.adh0716

▲ 摘要：

全球陆地水是生计、社会经济发展和生态系统的基础。目前尚不清楚近几十年来水资源供应的变化情况。利用一组观测数据，研究者量化了过去20年的全球陆地水资源可用性。研究表明，从2001年到2020年，南半球主导了全球可用水量的下降趋势。显著的减少主要发生在南美洲、非洲西南部和澳大利亚西北部。

在北半球，复杂的区域增减趋势相互抵消，导致半球趋势可以忽略不计。南半球可用水量的变率和趋势在很大程度上是由与气候模式有关的降水驱动的，特别是厄尔尼诺—南方涛动。这项研究强调了它们在控制全球水资源供应方面的主导作用。

▲ Abstract：

Global land water underpins livelihoods, socioeconomic development, and ecosystems. It remains unclear how water availability has changed in recent decades. Using an ensemble of observations, we quantified global land water availability over the past two decades. We show that the Southern Hemisphere has dominated the declining trend in global water availability from 2001 to 2020. The significant decrease occurs mainly in South America, southwestern Africa, and northwestern Australia. In the Northern Hemisphere, the complex regional increasing and decreasing trends cancel each other, resulting in a negligible hemispheric trend. The variability and trend in water availability in the Southern Hemisphere are largely driven by precipitation associated with climate modes, particularly the El Niño-Southern Oscillation. This study highlights their dominant role in controlling global water availability.