编译|冯维维
Nature, Volume 634 Issue 8032, 3 October 2024
《自然》，第634卷，8032期，2024年10月3日
物理学Physics
Mars’s induced magnetosphere can degenerate
火星感应磁层会退化
▲ 作者：Qi Zhang, Stas Barabash, Mats Holmstrom, Xiao-dong Wang, Yoshifumi Futaana, Christopher M. Fowler, Robin Ramstad & Hans Nilsson
▲链接：
https://www.nature.com/articles/s41586-024-07959-z
▲摘要：
行星和恒星风之间的相互作用会导致大气的损失，因此对行星大气的演变很重要。太阳系中的行星通常与太阳风相互作用，太阳风的速度与嵌入的恒星磁场成很大的角度。
对于没有固有磁场的行星，这种相互作用会在行星前方产生感应磁层和弓形激波。然而，当太阳风速度与太阳风磁场的夹角（锥角）较小时，相互作用就大不相同。
研究表明，当锥角在火星上很小时，感应磁层退化。在白天没有冲击，只有微弱的侧面冲击。横流羽流出现，双极场驱动行星离子逆流而上。4°锥角的混合模拟结果与火星大气与挥发性演化任务和火星快车的观测结果一致。简并的感应磁球是复杂的，尚未被探索过的物体。至于离子逸出对大气损失等过程的二次影响，还有待研究。
▲ Abstract：
The interaction between planets and stellar winds can lead to atmospheric loss and is, thus, important for the evolution of planetary atmospheres1. The planets in our Solar System typically interact with the solar wind, whose velocity is at a large angle to the embedded stellar magnetic field. For planets without an intrinsic magnetic field, this interaction creates an induced magnetosphere and a bow shock in front of the planet. However, when the angle between the solar wind velocity and the solar wind magnetic field (cone angle) is small, the interaction is very different. Here we show that when the cone angle is small at Mars, the induced magnetosphere degenerates. There is no shock on the dayside, only weak flank shocks. A cross-flow plume appears and the ambipolar field drives planetary ions upstream. Hybrid simulations with a 4° cone angle show agreement with observations by the Mars Atmosphere and Volatile Evolution mission and Mars Express. Degenerate, induced magnetospheres are complex and not yet explored objects. It remains to be studied what the secondary effects are on processes like atmospheric loss through ion escape.
Space radiation measurements during the Artemis I lunar mission
阿尔忒弥斯1号月球任务期间的空间辐射测量
▲ 作者：Stuart P. George, Ramona Gaza, Daniel Matthi, Diego Laramore, Jussi Lehti, Thomas Campbell-Ricketts, Martin Kroupa, Nicholas Stoffle, Karel Marsalek, Bartos Przybyla, Mena Abdelmelek, Joachim Aeckerlein, Amir A. Bahadori, Janet Barzilla, Matthias Dieckmann, Michael Ecord, Ricky Egeland, Timo Eronen, Dan Fry, Bailey H. Jones, Christine E. Hellweg, Jordan Houri, Robert Hirsh, Mika Hirvonen, Thomas Berger
▲链接：
https://www.nature.com/articles/s41586-024-07927-7
▲摘要：
空间辐射是长时间载人航天飞行的显著危害。相关风险包括癌症、白内障、退行性疾病和大量急性暴露引起的组织反应。空间辐射的来源多种多样，包括银河宇宙射线、捕获粒子(范艾伦)带和太阳粒子事件。
以前的辐射数据来自近地轨道上的国际空间站和航天飞机。它们受到重屏蔽和地球磁场的保护，以及火星科学实验室和月球侦察轨道器等轻度屏蔽的行星际机器人探测器。来自阿波罗任务和地面测量的有限数据也有大量的警告。
研究报告了在无人驾驶的阿尔忒弥斯1号月球任务中，由重屏蔽的猎户座飞船进行的辐射测量。在飞行器内部不同的屏蔽位置，在质子带通过期间观察到的剂量率相差4倍，这与大型参考太阳粒子事件相似。猎户座的行星际宇宙射线剂量当量比以前的观测结果低了60%。
此外，在质子带过境期间，航天器方向的改变导致辐射剂量率减少了约50%。这些测量结果验证了猎户座未来的载人探索，并为未来的载人航天任务设计提供了信息。
▲ Abstract：
Space radiation is a notable hazard for long-duration human spaceflight. Associated risks include cancer, cataracts, degenerative diseases and tissue reactions from large, acute exposures. Space radiation originates from diverse sources, including galactic cosmic rays, trapped-particle (Van Allen) belts and solar-particle events. Previous radiation data are from the International Space Station and the Space Shuttle in low-Earth orbit protected by heavy shielding and Earth’s magnetic field and lightly shielded interplanetary robotic probes such as Mars Science Laboratory and Lunar Reconnaissance Orbiter. Limited data from the Apollo missions and ground measurements with substantial caveats are also available. Here we report radiation measurements from the heavily shielded Orion spacecraft on the uncrewed Artemis I lunar mission. At differing shielding locations inside the vehicle, a fourfold difference in dose rates was observed during proton-belt passes that are similar to large, reference solar-particle events. Interplanetary cosmic-ray dose equivalent rates in Orion were as much as 60% lower than previous observations9. Furthermore, a change in orientation of the spacecraft during the proton-belt transit resulted in a reduction of radiation dose rates of around 50%. These measurements validate the Orion for future crewed exploration and inform future human spaceflight mission design.
Highly dynamic gamma-ray emissions are common in tropical thunderclouds
高动态伽马射线辐射在热带雷雨云中很常见
▲ 作者：M. Marisaldi, N.?stgaard, A. Mezentsev, T. Lang, J. E. Grove, D. Shy, G. M. Heymsfield, P. Krehbiel, R. J. Thomas, M. Stanley, D. Sarria, C. Schultz, R. Blakeslee, M. G. Quick, H. Christian, I. Adams, R. Kroodsma, N. Lehtinen, K. Ullaland, S. Yang, B. Hasan Qureshi, J. S?ndergaard, B. Husa, D. Walker, A. Santos
▲链接：
https://www.nature.com/articles/s41586-024-07936-6
▲摘要：
雷暴发出的伽马射线通量被称为伽马射线发光，偶尔被飞机、气球和地面观测到。观测报告说，伽马射线的发射增加了百分之十，达到背景上方两个数量级，有时因闪电放电而突然终止。发光是由雷雨云内高电场区域的高能电子加速产生的，并有助于电荷耗散。发光一直被认为是准静止现象，持续时间可达几十秒，空间尺度可达10~20公里。
然而，到目前为止，还没有对伽玛射线辉光区域在空间和时间上的全面扩展及其发生频率的测量报告。
研究者展示了海洋和沿海地区的热带雷雨云通常在几千平方公里的区域内连续数小时发射伽马射线。发射与深部对流核有关；它不是均匀和连续的，但具有1~10秒甚至亚秒的个别发光的特征时间尺度。
伽马发光雷云的动力学与准静止的发光图像强烈矛盾，相反，在模式和行为上都类似于一个巨大的伽马发光“沸腾锅”。
▲ Abstract：
Thunderstorms emit fluxes of gamma rays known as gamma-ray glows, sporadically observed by aircraft, balloons and from the ground. Observations report increased gamma-ray emissions by tens of percent up to two orders of magnitude above the background, sometimes abruptly terminated by lightning discharges. Glows are produced by the acceleration of energetic electrons in high-electric-field regions within thunderclouds8 and contribute to charge dissipation. Glows had been considered as quasi-stationary phenomena, with durations up to a few tens of seconds and spatial scales up to 10–20?km. However, no measurements of the full extension in space and time of a gamma-ray-glow region and their occurring frequency have been reported so far. Here we show that tropical thunderclouds over ocean and coastal regions commonly emit gamma rays for hours over areas up to a few thousand square kilometres. Emission is associated with deep convective cores; it is not uniform and continuous but shows characteristic timescales of 1–10?s and even subsecond for individual glows. The dynamics of gamma-glowing thunderclouds strongly contradicts the quasi-stationary picture of glows and instead resembles that of a huge gamma-glowing ‘boiling pot’ in both pattern and behaviour.
Opto-twistronic Hall effect in a three-dimensional spiral lattice
三维螺旋晶格中的光-旋回霍尔效应
▲ 作者：Zhurun Ji, Yuzhou Zhao, Yicong Chen, Ziyan Zhu, Yuhui Wang, Wenjing Liu, Gaurav Modi, Eugene J. Mele, Song Jin & Ritesh Agarwal
▲链接：
https://www.nature.com/articles/s41586-024-07949-1
▲摘要：
对摩尔系的研究解释了超晶格调制对其性质的影响，展示了新的相关相。然而，大多数实验研究都集中在二维系统的几个层上。将扭转电子学扩展到三维，其中扭转延伸到第三维度，由于与手动堆叠层相关的挑战，仍然未被充分探索。研究者利用多层WS2的自组装螺旋超晶格研究了三维涡旋电子学。
该研究结果显示了一种由结构手性和相干长度驱动的光旋电子霍尔效应，由螺旋超晶格的莫尔势调制。这是系统非交换几何的实验证明。
研究者观察到增强的光-物质相互作用和霍尔系数对光子动量的依赖改变。模型表明，高阶量子几何量对这一观察的贡献，为设计具有大非线性的基于量子材料的光电晶格提供了机会。
▲ Abstract：
Studies of moiré systems have explained the effect of superlattice modulations on their properties, demonstrating new correlated phases. However, most experimental studies have focused on a few layers in two-dimensional systems. Extending twistronics to three dimensions, in which the twist extends into the third dimension, remains underexplored because of the challenges associated with the manual stacking of layers. Here we study three-dimensional twistronics using a self-assembled twisted spiral superlattice of multilayered WS2. Our findings show an opto-twistronic Hall effect driven by structural chirality and coherence length, modulated by the moiré potential of the spiral superlattice. This is an experimental manifestation of the noncommutative geometry of the system. We observe enhanced light–matter interactions and an altered dependence of the Hall coefficient on photon momentum. Our model suggests contributions from higher-order quantum geometric quantities to this observation, providing opportunities for designing quantum-materials-based optoelectronic lattices with large nonlinearities.
化学Chemistry
Nitrogen-doped amorphous monolayer carbon
氮掺杂非晶单层碳
▲ 作者：Xiuhui Bai, Pengfei Hu, Ang Li, Youwei Zhang, Aowen Li, Guangjie Zhang, Yufeng Xue, Tianxing Jiang, Zezhou Wang, Hanke Cui, Jianxin Kang, Hewei Zhao, Lin Gu, Wu Zhou, Li-Min Liu, Xiaohui Qiu & Lin Guo
▲链接：
https://www.nature.com/articles/s41586-024-07958-0
▲摘要：
单原子层状碳材料，如石墨烯和非晶单层碳，由于其前所未有的物理特性和广泛的应用前景，激发了激烈的基础和应用研究。到目前为止，这类材料主要是通过化学气相沉积生产。与液相合成相比，化学气相沉积通常需要严格的反应条件。
在此，我们展示了通过在可移动层状双氢氧化物模板的封闭层间腔内聚合吡咯，制备具有混合五、六、七元(5-6-7元)环的独立氮掺杂非晶态单层碳的溶液。结构表征和第一性原理计算表明，氮掺杂的非晶态单层碳是在反应空间的限制下由吡咯在α、β和N位自由基聚合形成的，从而通过Stone-Wales转变实现键重排。
空间约束抑制了聚合过程中C-C键的旋转和链纠缠，形成了具有平面内π共轭电子结构的原子厚连续非晶层。使用固体模板和离子交换策略的空间限制自由基聚合显示出作为获得二维共价网络的通用合成方法的潜力，如成功合成单层聚噻吩和聚咔唑的例子。
▲ Abstract：
Monoatomic-layered carbon materials, such as graphene1 and amorphous monolayer carbon, have stimulated intense fundamental and applied research owing to their unprecedented physical properties and a wide range of promising applications. So far, such materials have mainly been produced by chemical vapour deposition, which typically requires stringent reaction conditions compared to solution-phase synthesis. Herein, we demonstrate the solution preparation of free-standing nitrogen-doped amorphous monolayer carbon with mixed five-, six- and seven-membered (5-6-7-membered) rings through the polymerization of pyrrole within the confined interlayer cavity of a removable layered-double-hydroxide template. Structural characterizations and first-principles calculations suggest that the nitrogen-doped amorphous monolayer carbon was formed by radical polymerization of pyrrole at the α, β and N sites subjected to confinement of the reaction space, which enables bond rearrangements through the Stone–Wales transformation. The spatial confinement inhibits the C–C bond rotation and chain entanglement during polymerization, resulting in an atom-thick continuous amorphous layer with an in-plane π-conjugation electronic structure. The spatially confined radical polymerization using solid templates and ion exchange strategy demonstrates potential as a universal synthesis approach for obtaining two-dimensional covalent networks, as exemplified by the successful synthesis of monolayers of polythiophene and polycarbazole.
地质Geology
Rules of river avulsion change downstream
河流崩裂的规律在下游发生变化
▲ 作者：James H. Gearon, Harrison K. Martin, Clarke DeLisle, Eric A. Barefoot, David Mohrig, Chris Paola & Douglas A. Edmonds
▲链接：
https://www.nature.com/articles/s41586-024-07964-2
▲摘要：
湍急的河流在洪泛区创造了新的通道，与此相关的洪水会对社会产生深远的影响。人们认为，当水柱在洪泛区上方停留时，或者当河道两侧的斜坡比现有河道的坡度更陡时，就会发生河流冲刷。
研究者通过量化河流周围的地形来验证这些经典观点，并表明这些机制在历史上是分开调用的，但它们是一起发生作用的。
在海岸附近，当远离河道的坡度更陡时，河流会发生颠簸，而不是因为它们处于高位。靠近山麓的情况正好相反；在扇形上，可供选择的路径与下游路径一样陡峭，因此当河流位于周围景观之上时，它们就会消失。
研究者们对这些发现进行了调和，并提出了一个新的理论框架，该框架确定了哪些河流容易受到崩裂的影响，并预测了崩裂河流的路径。
这些一阶崩裂规律表明，在许多沿海环境中，崩裂风险被低估了，崩裂寻路的概率预测可以用最少的信息有效地绘制出危险地图。将这些原则应用于风险评估可能特别有利于受撕脱影响的全球南方国家。
▲ Abstract：
Avulsing rivers create new pathways on the floodplain and the associated flooding can profoundly affect society. River avulsions are thought to occur when the water column becomes perched above the floodplain or when the slope down the flanks of the channel provides a steeper descent than the existing river channe. We test these classical ideas by quantifying the topography around avulsing rivers and show that these mechanisms, historically invoked separately, work together. Near coasts, rivers avulse when the slope away from the channel is steeper, not because they are perched. The opposite is true near mountain fronts; on fans, the alternative paths are similarly steep to the downstream path, so rivers avulse when they are perched above the surrounding landscape. We reconcile these findings and present a new theoretical framework that identifies which rivers are vulnerable to avulsion and predicts the path of an avulsing river. These first-order rules of avulsion suggest that avulsion risks are underestimated in many coastal environments8 and that probabilistic predictions of avulsion pathfinding can efficiently map hazards with minimal information. Applying these principles for risk assessment could particularly benefit the Global South, which is disproportionately affected by avulsions.
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