编译 | 未玖
Nature , 27 May 2021, VOL 593, ISSUE 7860
《自然》 2021年5月27日，第593卷，7860期
天文学 Astronomy
Evidence of hydrogen helium immiscibility at Jupiter-interior conditions
木星内部条件下氢-氦不混溶的证据
作者：S. Brygoo, P. Loubeyre, M. Millot, J. R. Rygg, P. M. Celliers, J. H. Eggert, et al.
链接：
https://www.nature.com/articles/s41586-021-03516-0
摘要
温致密氢 氦（H-He）混合物的相行为影响了人们对木星和土星及其内部结构演化的理解。然而，尽管H-He相具有重要意义，但在相关的行星条件下，它的相行为仍然很难约束，因为通过计算来确定它极具挑战性，且极端温度和压力也难以通过实验达到。
研究组报道了通过激光驱动的冲击压缩已在钻石砧电池中预压缩的H2 He样品，可以达到适当的温度和压力。这使研究组能够探测木星内部条件下H-He混合物的性质，揭示了沿雨贡纽曲线的一个不混溶区域。
样品反射率的明显不连续变化表明，在10200 K时，该区域结束于150吉帕以上；在4700 K时，93吉帕以上的反射率发生了更细微的变化。考虑到木星的压力-温度分布，这些近原太阳混合物的实验不混溶约束表明H-He相分离影响了木星内部的很大一部分，研究组估计该部分大约占木星半径的15%。
这一发现为木星模型提供了微物理支持，该模型利用分层内部来解释朱诺号和伽利略号航天器的观测。
Abstract
The phase behaviour of warm dense hydrogen helium (H He) mixtures affects our understanding of the evolution of Jupiter and Saturn and their interior structures. But despite its importance, H He phase behaviour under relevant planetary conditions remains poorly constrained because it is challenging to determine computationally and because the extremes of temperature and pressure are difficult to reach experimentally. Here we report that appropriate temperatures and pressures can be reached through laser-driven shock compression of H2 He samples that have been pre-compressed in diamond-anvil cells. This allows us to probe the properties of H He mixtures under Jovian interior conditions, revealing a region of immiscibility along the Hugoniot. A clear discontinuous change in sample reflectivity indicates that this region ends above 150 gigapascals at 10,200 kelvin and that a more subtle reflectivity change occurs above 93 gigapascals at 4,700 kelvin. Considering pressure–temperature profiles for Jupiter, these experimental immiscibility constraints for a near-protosolar mixture suggest that H He phase separation affects a large fraction—we estimate about 15 per cent of the radius—of Jupiter’s interior. This finding provides microphysical support for Jupiter models that invoke a layered interior to explain Juno and Galileo spacecraft observations.
材料科学 Materials Science
Long-range nontopological edge currents in charge-neutral graphene
电荷中性石墨烯中的长程非拓扑边缘电流
作者：A. Aharon-Steinberg, A. Marguerite, D. J. Perello, K. Bagani, T. Holder, Y. Myasoedov, et al.
链接：
https://www.nature.com/articles/s41586-021-03501-7
摘要
范德华异质结构显示出许多独特的电子性质。单层、双层和薄层石墨烯、过渡金属二卤化物和莫尔超晶格已被发现显示出明显的非局域效应。
然而，这些效应的起源却引起了激烈的争论。尤其是石墨烯，在电荷中性时表现出巨大的非局域性，这一惊人行为吸引了各种不同的解释。
利用尖端超导量子干涉装置（SQUID-on-tip）进行纳米尺度的热成像和扫描门成像，研究组证明了石墨烯边缘常见的电荷积累会导致巨大的非局域性，产生了支持长程电流的狭窄导电通道。
出乎意料的是，虽然边缘电导对零磁场中的电流流动影响不大，但在中等磁场下，它会导致边缘和体输运之间的场诱导解耦。由此产生的巨大非局域性在电荷中性和远离电荷时产生了对边缘无序敏感的奇异流型，在这种流型中电荷可以对抗全局电场流动。
所观察到的一维边缘输运是通用和非拓扑的，有望支持许多电子系统中的非局域输运，为深入研究众多争论提供了线索，并将它们与系统边缘的远程引导电子态联系起来。
Abstract
Van der Waals heterostructures display numerous unique electronic properties. Monolayer, bilayer and few-layer graphene, transition-metal dichalcogenides and moiré superlattices have been found to display pronounced nonlocal effects. However, the origin of these effects is hotly debated. Graphene, in particular, exhibits giant nonlocality at charge neutrality, a striking behaviour that has attracted competing explanations. Using a superconducting quantum interference device on a tip (SQUID-on-tip) for nanoscale thermal and scanning gate imaging, here we demonstrate that the commonly occurring charge accumulation at graphene edges leads to giant nonlocality, producing narrow conductive channels that support long-range currents. Unexpectedly, although the edge conductance has little effect on the current flow in zero magnetic field, it leads to field-induced decoupling between edge and bulk transport at moderate fields. The resulting giant nonlocality at charge neutrality and away from it produces exotic flow patterns that are sensitive to edge disorder, in which charges can flow against the global electric field. The observed one-dimensional edge transport is generic and nontopological and is expected to support nonlocal transport in many electronic systems, offering insight into the numerous controversies and linking them to long-range guided electronic states at system edges.
Perovskite-type superlattices from lead halide perovskite nanocubes
卤化铅钙钛矿纳米立方体的钙钛矿型超晶格
作者：Ihor Cherniukh, Gabriele Rainò, Thilo Stöferle, Max Burian, Alex Travesset, Denys Naumenko, et al.
链接：
https://www.nature.com/articles/s41586-021-03492-5
摘要
铯-铅卤化物钙钛矿型纳米晶体是长程有序超晶格很有前途的构建基块，因其明亮三重态激子的高振荡强度、缓慢失相（高达80皮秒的相干时间）和最小发射线不均匀展宽。到目前为止，人们从这些纳米晶体中仅设计出来单组分超晶格与简单立方堆积。
研究组提出了钙钛矿型（ABO3）二元和三元纳米晶超晶格，通过立体稳定、高发光的立方CsPbBr3纳米晶（占据B和/或O晶格位）、球形Fe3O4或NaGdF4纳米晶（A位）和截角立方PbS纳米晶（B位）的形状定向共组装而成。
这些ABO3超晶格，以及研究组展示的二元NaCl和AlB2超晶格结构，均表明了CsPbBr3纳米立方体的高度取向有序性。它们还表现出超荧光——一种集体发射，导致超快辐射衰减（22皮秒）的光子爆发，可用于定制超亮（量子）光源。
研究组的工作为进一步 探索 复杂有序、功能有用的钙钛矿介观结构奠定了基础。
Abstract
Caesium lead halide perovskite nanocrystals are promising building blocks for long-range-ordered superlattices, owing to the high oscillator strength of bright triplet excitons, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines. So far, only single-component superlattices with simple cubic packing have been devised from these nanocrystals. Here we present perovskite-type (ABO3) binary and ternary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr3 nanocrystals (which occupy the B and/or O lattice sites), spherical Fe3O4 or NaGdF4 nanocrystals (A sites) and truncated-cuboid PbS nanocrystals (B sites). These ABO3 superlattices, as well as the binary NaCl and AlB2 superlattice structures that we demonstrate, exhibit a high degree of orientational ordering of the CsPbBr3 nanocubes. They also exhibit superfluorescence—a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.
地球科学 Earth Science
A 10 per cent increase in global land evapotranspiration from 2003 to 2019
2003-2019年，全球陆地蒸散量增加10%
作者：Madeleine Pascolini-Campbell, John T. Reager, Hrishikesh A. Chandanpurkar & Matthew Rodell
链接：
https://www.nature.com/articles/s41586-021-03503-5
摘要
准确量化全球陆地蒸散量对于理解全球水循环的变异性是必要的，在气候变化下，这种变异性预计将加剧。目前的全球蒸散量产品来源很多，包括模型、遥感和现场观测。
然而，现有的方法包含广泛不确定性；例如，与模型结构相关，或将观测值提升到全球水平。因此，全球蒸散量的变异性和趋势仍不清楚。
研究组表明，2003至2019年，全球陆地蒸散量增加了10 2%，陆地降水越来越多地被划分为蒸散量，而非径流。
该结果基于全球陆地蒸散量的独立水平衡集合时间序列和相应的不确定性分布，使用的数据来自重力恢复及气候实验（GRACE）和GRACE后续（GRACE-FO）卫星。
全球陆地蒸散量的变异性与厄尔尼诺-南方涛动正相关。然而，这种趋势的主要驱动力是不断升高的地表温度。
研究组的发现为全球陆地蒸散量提供了一个观测约束，且与全球蒸散量在气候变暖下增加的假设相一致。
Abstract
Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify under climate change. Current global evapotranspiration products are derived from a variety of sources, including models, remote sensing and in situ observations. However, existing approaches contain extensive uncertainties; for example, relating to model structure or the upscaling of observations to a global level. As a result, variability and trends in global evapotranspiration remain unclear. Here we show that global land evapotranspiration increased by 10 2 per cent between 2003 and 2019, and that land precipitation is increasingly partitioned into evapotranspiration rather than runoff. Our results are based on an independent water-balance ensemble time series of global land evapotranspiration and the corresponding uncertainty distribution, using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) satellites. Variability in global land evapotranspiration is positively correlated with El Niño–Southern Oscillation. The main driver of the trend, however, is increasing land temperature. Our findings provide an observational constraint on global land evapotranspiration, and are consistent with the hypothesis that global evapotranspiration should increase in a warming climate.
Overriding water table control on managed peatland greenhouse gas emissions
地下水位控制泥炭地温室气体排放
作者：C. D. Evans, M. Peacock, A. J. Baird, R. R. E. Artz, A. Burden, N. Callaghan, et al.
链接：
https://www.nature.com/articles/s41586-021-03523-1
摘要
全球泥炭地储存的碳比大气中自然存在的还要多。然而，许多泥炭地受到基于排水的农业、种植开发和火灾的压力，仅相当于排水泥炭地排放的所有人为温室气体的3%左右。通过保护未排水的泥炭地和使排水系统再湿润，人们正加强努力来遏制此类排放。
研究组报道了来自16个地点的 CO2 涡流协方差数据和来自英国和爱尔兰41个地点的 CH4 静态室测量数据，并将这些数据与所有主要泥炭地生物群落公布的数据相结合。
结果表明，年平均有效地下水位（ WTDe ；即通气泥炭层的平均深度）超过了所有其他与温室气体排放相关的生态系统和管理控制。
研究组估计， WTDe 每减少10 cm， CO2 和 CH4 排放（100年全球变暖潜势）的净变暖效应每年每公顷至少减少3吨 CO2 ，直到 WTDe 小于30 cm。进一步提高水位将继续产生净冷却效应，直到 WTDe 位于地表10 cm以内。
研究结果表明，农业泥炭地的温室气体排放可以大大减少，而不必停止其生产性使用。例如，将所有排干的农业泥炭地中的 WTDe 减半，可减少的排放量相当于全球人为排放的1%以上。
Abstract
Global peatlands store more carbon than is naturally present in the atmosphere. However, many peatlands are under pressure from drainage-based agriculture, plantation development and fire, with the equivalent of around 3 per cent of all anthropogenic greenhouse gases emitted from drained peatland. Efforts to curb such emissions are intensifying through the conservation of undrained peatlands and re-wetting of drained systems. Here we report eddy covariance data for carbon dioxide from 16 locations and static chamber measurements for methane from 41 locations in the UK and Ireland. We combine these with published data from sites across all major peatland biomes. We find that the mean annual effective water table depth ( WTDe ; that is, the average depth of the aerated peat layer) overrides all other ecosystem- and management-related controls on greenhouse gas fluxes. We estimate that every 10 centimetres of reduction in WTDe could reduce the net warming impact of CO2 and CH4 emissions (100-year global warming potentials) by the equivalent of at least 3 tonnes of CO2 per hectare per year, until WTDe is less than 30 centimetres. Raising water levels further would continue to have a net cooling effect until WTDe is within 10 centimetres of the surface. Our results suggest that greenhouse gas emissions from peatlands drained for agriculture could be greatly reduced without necessarily halting their productive use. Halving WTDe in all drained agricultural peatlands, for example, could reduce emissions by the equivalent of over 1 per cent of global anthropogenic emissions.
社会 学 Sociology
The universal visitation law of human mobility
人群流动的普遍访问规律
作者：Markus Schläpfer, Lei Dong, Kevin O’Keeffe, Paolo Santi, Michael Szell, Hadrien Salat, et al.
链接：
https://www.nature.com/articles/s41586-021-03480-9
摘要
人的流动性影响着城市的许多方面，从城市的空间结构到城市对流行病的反应。它最终也是 社会 互动、创新和生产力的关键。
研究组揭示了一个简单而稳健的标度律，它基于全球不同城市的人口大规模流动数据，来捕捉人口流动的时空谱。根据这一规律，任何地点的游客人数都会随着其访问频率和旅行距离乘积的平方反比而减少。
研究组进一步证明流向不同地点的时空流产生了显著的空间集群，其区域分布遵循齐夫定律。最后，研究组建立了一个基于 探索 和优先返回的个体流动模型，为所发现的标度律和新兴的空间结构提供了一个机制解释。
该研究结果证实了人文地理学中长期存在的猜想，并允许对人群重复流动进行预测，这为在城市规划、交通工程和减少流行病方面的应用提供了基础。
Abstract
Human mobility impacts many aspects of a city, from its spatial structure to its response to an epidemic. It is also ultimately key to social interactions, innovation and productivity. However, our quantitative understanding of the aggregate movements of inpiduals remains incomplete. Existing models—such as the gravity law or the radiation model—concentrate on the purely spatial dependence of mobility flows and do not capture the varying frequencies of recurrent visits to the same locations. Here we reveal a simple and robust scaling law that captures the temporal and spatial spectrum of population movement on the basis of large-scale mobility data from perse cities around the globe. According to this law, the number of visitors to any location decreases as the inverse square of the product of their visiting frequency and travel distance. We further show that the spatio-temporal flows to different locations give rise to prominent spatial clusters with an area distribution that follows Zipf’s law. Finally, we build an inpidual mobility model based on exploration and preferential return to provide a mechanistic explanation for the discovered scaling law and the emerging spatial structure. Our findings corroborate long-standing conjectures in human geography and allow for predictions of recurrent flows, providing a basis for applications in urban planning, traffic engineering and the mitigation of epidemic diseases.