Nature, 6 July 2023, VOL 619, ISSUE 7968

《天然》2023年7月6日，第619卷，7968期

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天文学Astronomy

X-ray polarization evidence for a 200-year-old flare of Sgr A*

Sgr A* 200年耀斑的X射线偏振证据

▲ 作者：Frédéric Marin, Eugene Churazov, Ildar Khabibullin, Riccardo Ferrazzoli, Laura Di Gesu, Thibault Barnouin, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06064-x

▲ 择要：

星河系中央有一个品质约为太阳400万倍的黑洞（人马座A* ，Sgr A），今朝很是寂静，其亮度比活跃星系核低几个数目级。星系中央区域致密气体对于SgrA* X射线的反射为研究其已往数百年以及数千年的耀斑勾当提供了一种要领。

从Sgr A*四周伟大份子云不雅测到的X射线持续体的外形以及强荧光铁线与反射情景一致。假如这类注释准确，反射的持续辐射应该是极化的。

研究组报导了使用成像X射线偏振探测器于星河系中央份子云标的目的上的偏振X射线发射的不雅测成果。经丈量偏振度为31%±11%，偏振角为- 48°±11°。

所测偏振角与Sgr A*为重要发射源的偏振角相一致，偏振度注解约莫200年前，Sgr A*的X射线光度与塞弗特星系的光度曾经短暂相称。

▲ Abstract：

The centre of the Milky Way Galaxy hosts a black hole with a solar mass of about 4 million (Sagittarius A* (Sgr A)) that is very quiescent at present with a luminosity many orders of magnitude below those of active galactic nuclei. Reflection of X-rays from Sgr A* by dense gas in the Galactic Centre region offers a means to study its past flaring activity on timescales of hundreds and thousands of years. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A* are consistent with the reflection scenario. If this interpretation is correct, the reflected continuum emission should be polarized. Here we report observations of polarized X-ray emission in the direction of the molecular clouds in the Galactic Centre using the Imaging X-ray Polarimetry Explorer. We measure a polarization degree of 31%±11%, and a polarization angle of 48°±11°. The polarization angle is consistent with Sgr?A* being the primary source of the emission, and the polarization degree implies that some 200 years ago, the X-ray luminosity of Sgr?A* was briefly comparable to that of a Seyfert galaxy.

质料科学Materials Science

Liquid metal for high-entropy alloy nanoparticles synthesis

液态金属用在高熵合金纳米颗粒的合成

▲ 作者：Guanghui Cao, Jingjing Liang, Zenglong Guo, Kena Yang, Gang Wang, Huiliu Wang, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06082-9

▲ 择要：

高熵合金纳米颗粒（HEA-NPs）作为功效质料具备广漠的运用远景。然而，到今朝为止，已经实现的高熵合金仅限在相似元素的调色板，这极年夜地拦阻了差别运用的质料设计、机能优化以及机理摸索。

研究组发明，付与其他元素负混淆焓的液态金属可提供不变的热力学前提，并作为抱负的动态混淆储层，从而于暖和反映前提下合成多种金属元素的HEA-NPs。所触及的元素具备广泛的原子半径（1.24-1.97 ?）以及熔点（303-3683 K）。

研究组经由过程混淆焓调谐实现了纳米颗粒的切确打造布局，此外还原位捕捉了及时转换历程（即从液态金属到结晶HEA-NPs），证明了合金化历程中的动态裂变-聚变举动。

▲ Abstract：

High-entropy alloy nanoparticles (HEA-NPs) show great potential as functional materials. However, thus far, the realized high-entropy alloys have been restricted to palettes of similar elements, which greatly hinders the material design, property optimization and mechanistic exploration for different applications. Herein, we discovered that liquid metal endowing negative mixing enthalpy with other elements could provide a stable thermodynamic condition and act as a desirable dynamic mixing reservoir, thus realizing the synthesis of HEA-NPs with a diverse range of metal elements in mild reaction conditions. The involved elements have a wide range of atomic radii (1.24–1.97 ) and melting points (303–3,683 K). We also realized the precisely fabricated structures of nanoparticles via mixing enthalpy tuning. Moreover, the real-time conversion process (that is, from liquid metal to crystalline HEA-NPs) is captured in situ, which confirmed a dynamic fission–fusion behaviour during the alloying process.

机械项目Mechanical Engineering

Harnessing a paper-folding mechanism for reconfigurable DNA origami

哄骗折纸机构举行可重构DNA折纸

▲ 作者：Myoung搜索引擎优化k Kim, Chan搜索引擎优化k Lee, Kyounghwa Jeon, Jae Young Lee, Young-Joo Kim, Jae Gyung Lee, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06181-7

▲ 择要：

折纸机构因其于将可变外形以及刚度编程到布局中的怪异威力以及上风，已经被广泛用在可重构宏不雅体系的构建。然而，只管基在DNA自拆卸的各类动态布局已经被开发出来，但因为缺少适合的设计准则，很少被用在构建份子程度体系。

研究组提出了一种哄骗折纸机构来创立可重构DNA折纸布局的要领。其重要思惟是成立一个参考平面线框布局，边沿遵照折纸中的折痕图案，以便折叠成各类方针外形。

研究组哄骗DNA链位移以高产率实现了几品种似纸张的折叠以及睁开模式，并展示了正交折叠、可反复折叠以及睁开、基在折叠的microRNA检测以及荧光旌旗灯号节制。由pH值或者光源变迁触发的刺激相应性折叠以及睁开也能够实现。

此外，经由过程接纳分层拆卸，研究组以高度可编程的体式格局扩大了折纸机构的设计空间以及繁杂性。因其高可编程性以及可扩大性，研究组希冀所提出的基在折纸的重构要领将鞭策繁杂份子体系的成长。

▲ Abstract：

The paper-folding mechanism has been widely adopted in building of reconfigurable macroscale systems because of its unique capabilities and advantages in progra妹妹ing variable shapes and stiffness into a structure. However, it has barely been exploited in the construction of molecular-level systems owing to the lack of a suitable design principle, even though various dynamic structures based on DNA self-assembly have been developed. Here we propose a method to harness the paper-folding mechanism to create reconfigurable DNA origami structures. The main idea is to build a reference, planar wireframe structure whose edges follow a crease pattern in paper folding so that it can be folded into various target shapes. We realized several paper-like folding and unfolding patterns using DNA strand displacement with high yield. Orthogonal folding, repeatable folding and unfolding, folding-based microRNA detection and fluorescence signal control were demonstrated. Stimuli-responsive folding and unfolding triggered by pH or light-source change were also possible. Moreover, by employing hierarchical assembly we could expand the design space and complexity of the paper-folding mechanism in a highly progra妹妹able manner. Because of its high progra妹妹ability and scalability, we expect that the proposed paper-folding-based reconfiguration method will advance the development of complex molecular systems.

化学Chemistry

General cross-coupling reactions with adaptive dynamic homogeneous catalysis

具备自顺应动态均相催化的通用交织偶联反映

▲ 作者：Indrajit Ghosh, Nikita Shlapakov, Tobias A. Karl, Jonas Düker, Maksim Nikitin, Julia V. Burykina, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06087-4

▲ 择要：

交织偶联反映是现代无机合成中最主要的转化之一。虽然思量到各类方案，今朝已经报导的（杂）芳基卤化物以及亲核试剂偶联配体的规模很是年夜，但差别化合物种别的反映前提差异很年夜，需要从头逐个优化反映前提。

研究组先容了于可见光驱动的氧化还原反映前提下，镍自顺应动态均相催化（AD-HoC）对于通用C（sp2）-（杂）原子偶联反映的催化作用。催化系统的自调治性子实现了交织偶联反映中数十种差别类型亲核试剂的简朴分类。

于可猜测的反映前提下，九种����APP差别成键反映（即C（sp2）–S、Se、N、P、B、O、C（sp三、sp二、sp）、Si、Cl）数以百计的合成实例综合证实了这一点。催化反映中央以及前提因插手的亲核试剂或者（假如需要）贸易重价胺碱而有所差别。

▲ Abstract：

Cross-coupling reactions are among the most important transformations in modern organic synthesis. Although the range of reported (het)aryl halides and nucleophile coupling partners is very large considering various protocols, the reaction conditions vary considerably between compound classes, necessitating renewed case-by-case optimization of the reaction conditions. Here we introduce adaptive dynamic homogeneous catalysis (AD-HoC) with nickel under visible-light-driven redox reaction conditions for general C(sp2)–(hetero)atom coupling reactions. The self-adjustive nature of the catalytic system allowed the simple classification of dozens of various classes of nucleophiles in cross-coupling reactions. This is synthetically demonstrated in nine different bond-forming reactions (in this case, C(sp2)–S, Se, N, P, B, O, C(sp3, sp2, sp), Si, Cl) with hundreds of synthetic examples under predictable reaction conditions. The catalytic reaction centre(s) and conditions differ from one another by the added nucleophile, or if required, a co妹妹ercially available inexpensive amine base.

地球科学Earth Science

Medieval demise of a Himalayan giant su妹妹it induced by mega-landslide

巨型滑坡致使了中世纪时喜马拉雅巨型山岳的消亡

▲ 作者：Jér?me Lavé, Cyrielle Guérin, Pierre G. Valla, Valery Guillou, Thomas Rigaudier, Lucilla Benedetti, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06040-5

▲ 择要：

只管人们对于喜马拉雅山脉的侵蚀举行了年夜量研究，但尚不清晰喜马拉雅山脉的岑岭是怎样被侵蚀的。

虽然谷底被冰川有用侵蚀，但侵蚀从冰斗延长到冰峰线前壁的冰缘历程强度好像跟着海拔升高而急剧降落。这类对于比注解，喜马拉雅最岑岭侵蚀水平较低，且远低在区域岩石抬升率，这激发了人们对于其持久演化的质疑。

研究组报导了公元1190年摆布安纳普尔纳地块（尼泊尔中部）发生的一次伟大岩石滑坡的地质证据，触及岩石整体积约为23 km3。这一事务使一座古山顶坍塌，其岑岭可能于海拔8000米以上。

研究数据注解，高海拔侵蚀的一种模式多是巨型岩石滑坡，致使山脊高程忽然降低数百米，并终极制止喜马拉雅山岳不可比例的增加。这类与陡坡以及高升沉有关的侵蚀模式源自峰值基底更年夜的机械强度，或者因高海拔永世冻土层的存于。

巨型岩石滑坡也对于景不雅蜕变以及天然灾难有影响：年夜量的细碎沉积物可以填满下流150多公里的山谷，于一个世纪或者更长的时间里跨越了喜马拉雅河道的沉积物负荷。

▲ Abstract：

Despite numerous studies on Himalayan erosion, it is not known how the very high Himalayan peaks erode. Although valley floors are efficiently eroded by glaciers, the intensity of periglacial processes, which erode the headwalls extending from glacial cirques to crest lines, seems to decrease sharply with altitude. This contrast suggests that erosion is muted and much lower than regional rock uplift rates for the highest Himalayan peaks, raising questions about their long-term evolution. Here we report geological evidence for a giant rockslide that occurred around 1190 AD in the Annapurna massif (central Nepal), involving a total rock volume of about 23 km3. This event collapsed a palaeo-su妹妹it, probably culminating above 8,000?m in altitude. Our data suggest that a mode of high-altitude erosion could be mega-rockslides, leading to the sudden reduction of ridge-crest elevation by several hundred metres and ultimately preventing the disproportionate growth of the Himalayan peaks. This erosion mode, associated with steep slopes and high relief, arises from a greater mechanical strength of the peak substratum, probably because of the presence of permafrost at high altitude. Giant rockslides also have implications for landscape evolution and natural hazards: the massive supply of finely crushed sediments can fill valleys more than 150 km farther downstream and overwhelm the sediment load in Himalayan rivers for a century or more.

Safe and just Earth system boundaries

保险公道的地球体系界限

▲ 作者：Johan Rockstr?m, Joyeeta Gupta, Dahe Qin, Steven J. Lade, Jesse F. Abrams, Lauren S. Andersen, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06083-8

▲ 择要：

地球体系的不变性以及回复复兴力与人类福祉不成支解地接洽于一路，但人们遍及熟悉不到二者间的彼此依存性；是以，其每每被自力看待。

研究组使用建模以及文献评估来量化全世界以及亚全世界标准上天气、生物圈、水以及养分轮回和气溶胶的保险以及公道的地球体系界限（ESBs）。他们提出ESBs以维持地球体系的回复复兴力以及不变性（保险ESBs），并最年夜限度地削减地球体系变迁对于人类酿成的庞大危险（对于在公理而言须要但非充实的前提）。更严酷的保险或者公道界限设置了综合保险以及公道ESB。

该研究成果注解，对于在天气以及年夜气气溶胶负荷，公道思量比保险思量更能约束综合ESBs。8个全世界量化的保险以及公道ESB中有7个已经越界，于全世界跨越一半的陆地面积内至少有两个区域保险以及公道ESB也已经越界。

研究组以为，该评估为此后针对于所有人掩护全世界公域提供了一个定量根蒂根基。

▲ Abstract：

The stability and resilience of the Earth system and human well-being are inseparably linked, yet their interdependencies are generally under-recognized; consequently, they are often treated independently. Here, we use modelling and literature assessment to quantify safe and just Earth system boundaries (ESBs) for climate, the biosphere, water and nutrient cycles, and aerosols at global and subglobal scales. We propose ESBs for maintaining the resilience and stability of the Earth system (safe ESBs) and minimizing exposure to significant harm to humans from Earth system change (a necessary but not sufficient condition for justice). The stricter of the safe or just boundaries sets the integrated safe and just ESB. Our findings show that justice considerations constrain the integrated ESBs more than safety considerations for climate and atmospheric aerosol loading. Seven of eight globally quantified safe and just ESBs and at least two regional safe and just ESBs in over half of global land area are already exceeded. We propose that our assessment provides a quantitative foundation for safeguarding the global co妹妹ons for all people now and into the future.

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