giant期刊最新论文

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：

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：

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：

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：

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：

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：

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.

编译 | 未玖

Nature , 21 October 2021, VOL 598, ISSUE 7881

《自然》 2021年10月21日，第598卷，7881期

天文学 Astronomy

Carbon monoxide gas produced by a giant impact in the inner region of a young system

年轻星系内部发生巨大碰撞产生一氧化碳气体

作者：Tajana Schneiderman, Luca Matrà, Alan P. Jackson, Grant M. Kennedy, Quentin Kral, Sebastián Marino, et al.

链接：

摘要

类地行星形成的模型预测，行星组合的最后阶段（年轻的原行星盘扩散之后持续的数千万年间）主要发生行星碰撞。正是通过这些巨大的撞击，像年轻的地球这样的行星才能成长到最终质量，并实现长期稳定的轨道结构。

一个关键预测是这些撞击会产生碎片。到目前为止，关于撞击后碎片最令人信服的观测证据来自于附近2300万年前的A型恒星HD172555周围的行星系。该星系显示大量细尘，具有异常陡峭的粒度分布和非典型的尘埃组成，此前将其归因于超高速撞击或巨大的小行星带。

研究组报道了一个与HD172555周围的尘埃碎片共轨的一氧化碳气体环的光谱分辨率探测结果，气体环与HD172555相距大约6到9个天文单位，类似于太阳系的外类地行星区域。

综上所述，尘埃和一氧化碳的检测结果有助于理解大型、易挥发性天体之间的巨大碰撞。这表明行星级的碰撞类似于月球形成的碰撞，可释放大量的气体和碎片，并且这种气体是可观测的，为了解年轻行星的组成提供了一个窗口。

Abstract

Models of terrestrial planet formation predict that the final stages of planetary assembly—lasting tens of millions of years beyond the dispersal of young protoplanetary disks—are dominated by planetary collisions. It is through these giant impacts that planets like the young Earth grow to their final mass and achieve long-term stable orbital configurations. A key prediction is that these impacts produce debris. So far, the most compelling observational evidence for post-impact debris comes from the planetary system around the nearby 23-million-year-old A-type star HD 172555. This system shows large amounts of fine dust with an unusually steep size distribution and atypical dust composition, previously attributed to either a hypervelocity impact or a massive asteroid belt. Here we report the spectrally resolved detection of a carbon monoxide gas ring co-orbiting with dusty debris around HD 172555 between about six and nine astronomical units—a region analogous to the outer terrestrial planet region of our Solar System. Taken together, the dust and carbon monoxide detections favour a giant impact between large, volatile-rich bodies. This suggests that planetary-scale collisions, analogous to the Moon-forming impact, can release large amounts of gas as well as debris, and that this gas is observable, providing a window into the composition of young planets.

材料科学 Materials Science

Half- and quarter-metals in rhombohedral trilayer graphene

菱面体三层石墨烯中的半金属和四分之一金属

作者：Haoxin Zhou, Tian Xie, Areg Ghazaryan, Tobias Holder, James R. Ehrets, Eric M. Spanton, et al.

链接：

摘要

铁磁性在电子占据高度局域化d轨道的过渡金属化合物中最为常见。然而，在低密度二维电子系统中也可能出现铁磁有序。

研究组证明了菱面体三层石墨烯中的门调谐范霍夫奇点，驱动电子系统的自发铁磁极化转变为一种或多种自旋和谷型。

通过电容和输运测量，研究组观察到调谐至相位间载流子浓度和电位移场的一系列跃迁，其中量子振荡具有四重、二重或一重简并度，分别对应自旋和谷简并的“正常金属态”、自旋极化的“半金属态”以及自旋极化和谷极化的“四分之一金属态”。

对于电子掺杂，包含谷各向异性相互作用的唯象斯通纳模型很好地捕捉到了数据的显著特征。对于空穴填充，研究组观察到一个更丰富的相图，其特征是费米面拓扑中对称性破缺和跃迁的微妙相互作用。

最后，研究组通过旋转对齐的六方氮化硼衬底引入莫尔超晶格。值得注意的是，研究组发现同位旋序仅受到弱扰动，当迁移的半金属态或四分之一金属态填充半超晶格带或四分之一超晶格带时，莫尔势会催化拓扑非平凡间隙态的形成。

该结果表明，菱面体石墨烯是一个多体理论控制测试的理想平台，并揭示了莫尔材料的磁性本质上是迁移的。

Abstract

Ferromagnetism is most common in transition metal compounds where electrons occupy highly localized d orbitals. However, ferromagnetic order may also arise in low-density two-dimensional electron systems. Here we show that gate-tuned van Hove singularities in rhombohedral trilayer graphene drive spontaneous ferromagnetic polarization of the electron system into one or more spin and valley flavours. Using capacitance and transport measurements, we observe a cascade of transitions tuned to the density and electronic displacement field between phases in which quantum oscillations have fourfold, twofold or onefold degeneracy, associated with a spin- and valley-degenerate normal metal, spin-polarized ‘half-metal’, and spin- and valley-polarized ‘quarter-metal’, respectively. For electron doping, the salient features of the data are well captured by a phenomenological Stoner model that includes valley-anisotropic interactions. For hole filling, we observe a richer phase diagram featuring a delicate interplay of broken symmetries and transitions in the Fermi surface topology. Finally, we introduce a moiré superlattice using a rotationally aligned hexagonal boron nitride substrate. Remarkably, we find that the isospin order is only weakly perturbed, with the moiré potential catalysing the formation of topologically nontrivial gapped states whenever itinerant half- or quarter-metal states occur at half- or quarter-superlattice band filling. Our results show that rhombohedral graphene is an ideal platform for well-controlled tests of many-body theory, and reveal magnetism in moiré materials to be fundamentally itinerant in nature.

Superconductivity in rhombohedral trilayer graphene

菱面体三层石墨烯的超导性

作者：Haoxin Zhou, Tian Xie, Takashi Taniguchi, Kenji Watanabe & Andrea F. Young.

链接：

摘要

在一个干净的二维器件中通过电场效应获得超导性是纳米电子学的一个核心目标。最近，石墨烯莫尔异质结构已实现超导性；然而，其中许多结构在机械上并不稳定，实验显示出强无序特征。

研究组报道了在亚开尔文温度下表现为低电阻率或零电阻率的晶体菱面三层石墨烯（一种结构上亚稳态的碳同素异形体）的超导性。超导性发生在两个不同的门调谐区（SC1和SC2），且深度在由平均自由程和超导态相干长度之比定义的干净极限内。

量子振荡对常态费米面的映射显示，这两种超导体都来自环形费米海，并且接近同位旋对称性破缺转变，其中费米面简并度发生变化。SC1从顺磁正常态出现，而SC2则从自旋极化、谷简并的半金属态中出现，且违反了面内磁场的泡利极限至少一个数量级。

研究组讨论了该结果的各种机制，包括传统的声子介导配对，近同位旋序波动产生的配对，以及环形费米液体的固有不稳定性导致的配对。

研究组为干净且结构简单的二维金属中超导性的观察提供了一个模型系统，用于测试相互竞争的超导理论模型，而不会出现建模混乱的复杂情况，同时使基于相关电子现象和弹道电子输运的新型场效应控制电子器件成为可能。

Abstract

To access superconductivity via the electric field effect in a clean, two-dimensional device is a central goal of nanoelectronics. Recently, superconductivity has been realized in graphene moiré heterostructures; however, many of these structures are not mechanically stable, and experiments show signatures of strong disorder. Here we report the observation of superconductivity—manifesting as low or vanishing resistivity at sub-kelvin temperatures—in crystalline rhombohedral trilayer graphene, a structurally metastable carbon allotrope. Superconductivity occurs in two distinct gate-tuned regions (SC1 and SC2), and is deep in the clean limit defined by the ratio of mean free path and superconducting coherence length. Mapping of the normal state Fermi surfaces by quantum oscillations reveals that both superconductors emerge from an annular Fermi sea, and are proximal to an isospin-symmetry-breaking transition where the Fermi surface degeneracy changes. SC1 emerges from a paramagnetic normal state, whereas SC2 emerges from a spin-polarized, valley-unpolarized half-metal and violates the Pauli limit for in-plane magnetic fields by at least one order of magnitude. We discuss our results in view of several mechanisms, including conventional phonon-mediated pairing, pairing due to fluctuations of the proximal isospin order, and intrinsic instabilities of the annular Fermi liquid. Our observation of superconductivity in a clean and structurally simple two-dimensional metal provides a model system to test competing theoretical models of superconductivity without the complication of modelling disorder, while enabling new classes of field-effect controlled electronic devices based on correlated electron phenomena and ballistic electron transport.

Dexterous magnetic manipulation of conductive non-magnetic objects

导电非磁性物体的灵巧磁操控

作者：Lan N. Pham, Griffin F. Tabor, Ashkan Pourkand, Jacob L. B. Aman, Tucker Hermans & Jake J. Abbott.

链接：

摘要

对铁磁物体的灵巧磁操控已很好建立，根据物体的几何结构，可能有三到六个自由度。有些物体需要非接触式灵巧操作，它们不含有大量的铁磁性材料，但含有导电材料。

时变磁场在导电材料中产生涡流，涡流与磁场相互作用产生力和力矩。这种现象曾被用于诱导阻力，以减少物体通过静态场时的运动，或使用动态场在单个方向上对物体施加力，但尚未被用于对导电物体进行如铁磁物体那样的灵活操控。

研究组表明，通过使用多个旋转磁偶极子场可在六个自由度下操控导电物体。利用量纲分析，结合多物理场数值模拟和实验验证，研究组描述了在旋转磁偶极子场中导电球体上产生的力和力矩。利用该模型，研究组在仿真和物理实验中实现了灵活操控。

Abstract

Dexterous magnetic manipulation of ferromagnetic objects is well established, with three to six degrees of freedom possible depending on object geometry. There are objects for which non-contact dexterous manipulation is desirable that do not contain an appreciable amount of ferromagnetic material but do contain electrically conductive material. Time-varying magnetic fields generate eddy currents in conductive materials, with resulting forces and torques due to the interaction of the eddy currents with the magnetic field. This phenomenon has previously been used to induce drag to reduce the motion of objects as they pass through a static field, or to apply force on an object in a single direction using a dynamic field, but has not been used to perform the type of dexterous manipulation of conductive objects that has been demonstrated with ferromagnetic objects. Here we show that manipulation, with six degrees of freedom, of conductive objects is possible by using multiple rotating magnetic dipole fields. Using dimensional analysis, combined with multiphysics numerical simulations and experimental verification, we characterize the forces and torques generated on a conductive sphere in a rotating magnetic dipole field. With the resulting model, we perform dexterous manipulation in simulations and physical experiments.

地球科学 Earth Science

Pliocene decoupling of equatorial Pacific temperature and pH gradients

上新世赤道太平洋温度和pH梯度的解耦

作者：Madison G. Shankle, Natalie J. Burls, Alexey V. Fedorov, Matthew D. Thomas, Wei Liu, Donald E. Penman, et al.

链接：

摘要

赤道太平洋的海洋动力学驱动热带气候模式，影响全球海洋和陆地生态系统。该地区如何应对全球变暖对全球气候、经济稳定和生态系统 健康 具有深远影响。因此，许多研究调查了上新世（530-260万年前）和中新世晚期（约600万年前）期间的赤道太平洋动力学，作为该地区在全球变暖下未来行为的模拟。

这一时期的古海洋学记录提出了一个明显的悖论，即沿着赤道太平洋东西向的海面温度梯度降低表明风驱动的上升流减少，这与东太平洋生物生产力增强的证据相冲突，后者通常由更强的上升流引起。

研究组通过提供新的证据，证明上新世早期/中新世晚期与现代环流体制完全不同，导致更古老、更酸性和更富营养的水到达赤道太平洋，从而调和了这些观察结果。这些结果为上新世早期/中新世晚期东太平洋生产力的提高提供了一种新机制，即使在风力驱动上升流较弱的情况下也是如此。

该发现为赤道太平洋动力学提供了新的线索，并有助于限制它们在不久的将来可能发生的变化，因为预计下个世纪地球将达到上新世那样的变暖水平。

Abstract

Ocean dynamics in the equatorial Pacific drive tropical climate patterns that affect marine and terrestrial ecosystems worldwide. How this region will respond to global warming has profound implications for global climate, economic stability and ecosystem health. As a result, numerous studies have investigated equatorial Pacific dynamics during the Pliocene (– million years ago) and late Miocene (around 6 million years ago) as an analogue for the future behaviour of the region under global warming. Palaeoceanographic records from this time present an apparent paradox with proxy evidence of a reduced east–west sea surface temperature gradient along the equatorial Pacific—indicative of reduced wind-driven upwelling—conflicting with evidence of enhanced biological productivity in the east Pacific that typically results from stronger upwelling. Here we reconcile these observations by providing new evidence for a radically different-from-modern circulation regime in the early Pliocene/late Miocene that results in older, more acidic and more nutrient-rich water reaching the equatorial Pacific. These results provide a mechanism for enhanced productivity in the early Pliocene/late Miocene east Pacific even in the presence of weaker wind-driven upwelling. Our findings shed new light on equatorial Pacific dynamics and help to constrain the potential changes they will undergo in the near future, given that the Earth is expected to reach Pliocene-like levels of warming in the next century.

Direct radiative effects of airborne microplastics

空气中微塑料的直接辐射效应

作者：Laura E. Revell, Peter Kuma, Eric C. Le Ru, Walter R. C. Somerville & Sally Gaw

链接：

摘要

微塑料现在被认为是大气中广泛存在的污染物，由于其体积小、密度低，可以随风绕地球传播。大气气溶胶，如矿物粉尘和其他类型的空气悬浮颗粒物，通过吸收和散射辐射（直接辐射效应）影响地球气候，其影响通常用有效辐射强迫（ERF）度量进行量化。然而，空气中微塑料的辐射效应及其对全球气候的影响尚不清楚。

研究组计算了空气中微塑料的光学性质和直接辐射效应（不包括气溶胶-云相互作用）。假设平均表面浓度为1个微塑料颗粒/ m3 ，且垂直分布在10公里高空，则计算出当今大气中空气微塑料的ERF为 mW/ m2 。

然而，微塑料的地理和垂直分布存在很大的不确定性。假设它们局限于边界层，短波效应占主导地位，微塑料ERF约为 mW/ m2 。与气溶胶-辐射相互作用引起的总ERF相比（ 至 W/ m2 ），微塑料ERF很小。

然而，塑料产量在过去70年中迅速增长；如果不认真改革塑料生产和废物管理实践，空气中微塑料的丰度和ERF将继续增加。

Abstract

Microplastics are now recognized as widespread contaminants in the atmosphere, where, due to their small size and low density, they can be transported with winds around the Earth. Atmospheric aerosols, such as mineral dust and other types of airborne particulate matter, influence Earth’s climate by absorbing and scattering radiation (direct radiative effects) and their impacts are commonly quantified with the effective radiative forcing (ERF) metric. However, the radiative effects of airborne microplastics and associated implications for global climate are unknown. Here we present calculations of the optical properties and direct radiative effects of airborne microplastics (excluding aerosol–cloud interactions). The ERF of airborne microplastics is computed to be milliwatts per square metre in the present-day atmosphere assuming a uniform surface concentration of 1 microplastic particle per cubic metre and a vertical distribution up to 10 kilometres altitude. However, there are large uncertainties in the geographical and vertical distribution of microplastics. Assuming that they are confined to the boundary layer, shortwave effects dominate and the microplastic ERF is approximately milliwatts per square metre. Compared with the total ERF due to aerosol–radiation interactions ( to watts per square metre), the microplastic ERF is small. However, plastic production has increased rapidly over the past 70 years; without serious attempts to overhaul plastic production and waste-management practices, the abundance and ERF of airborne microplastics will continue to increase.

在北欧的神话中，深海里存在着一种体长150米的 巨型怪物 ，它们居住在挪威和格陵兰岛海岸附近，所以又被称之为挪威海怪（名字叫做克拉肯，Kraken）。

一般认为挪威海怪是一种体型巨大的章鱼或者乌贼，很多小说或者影视剧中都出现过(比如《加勒比海盗》)。对于航船来说，挪威海怪代表的就是死亡。据说当它浮在水面的时候，有些水手会误把它的身体当作一座“小岛”，甚至会登上这座小岛，在上面安营扎寨，结果在它沉下去的时候葬身海底。最恐怖的还是挪威海怪的巨型触角，随便一拍就可以打碎一艘航船。

19世纪以来，随着现代生物学的发展，人们对海洋有了更多的了解，大多数人已经相信挪威海怪其实就是巨型乌贼! 海里发现五六米，甚至十多米长的巨型乌贼并非没有可能，有时巨型乌贼也确实会袭击过往船只，因此，过于荒诞的海怪传说逐渐消失。

巨型乌贼 （giant squid，拉丁学名Architeuthis dux），也叫 大王乌贼 ，这种神秘的巨型头足类动物，分布在除南北极以外的其他深海区。它们拥有 无脊椎动物中最大的大脑，行为复杂而敏捷，还拥有出色的伪装和模仿等不可思议的技能，这使得科学研究进行的十分困难 。

迄今为止， 几乎没有一只巨型乌贼被活捉 ，所以它们的许多生物特性仍然是个谜。仅有的一些被研究过的标本，都是被冲上岸或被渔民意外拖上来的尸体。

但是，令人惊喜的是，2020年1月16日，哥本哈根大学领导的一个研究小组在华大基因大数据期刊 GigaScience 发表了题为：A draft genome sequence of the elusive giant squid, Architeuthis dux 的研究论文。

该研究 首次公布了神秘巨型乌贼的全基因组序列，揭示了其解剖和进化的重要线索，让我们对这种神秘生物的认知又进了一大步 。

巨型乌贼全基因组数据的发布为未来研究这个令人敬畏的生物奠定了基础，也进一步增加了我们对地球上生命多样性的理解。

研究人员发现 巨型乌贼的基因组很大 ， 据估计有27亿个DNA碱基对，大约是人类基因组的90%。

参与测序研究的科学家 Caroline Albertin 介绍说：就基因而言，我们发现巨型乌贼和其他动物很像。这意味着我们可以通过研究这种奇怪的动物来更多地了解人类自己。她在2015年还曾领导一个团队，对头足类动物(包括乌贼、章鱼、墨鱼和鹦鹉螺)进行了首次基因组测序。

Albertin分析了巨型乌贼中几个古老、知名的基因家族，并与已测序的其他四种头足类物种以及人类基因组进行了比较。

她发现几乎所有动物中重要的发育基因（Hox和Wnt）在巨型乌贼基因组中仅呈单拷贝存在。这意味着 这种巨大的无脊椎动物并不是通过全基因组复制才变得如此庞大的，而是进化很久以前就采取了这种策略来增加体积 。

所以，了解这个物种是如何变得如此巨大的，还需要进一步 探索 它的基因组。

Albertin说：“基因组是回答这些神秘动物的许多生物学问题的第一步。例如，它们如何获得无脊椎动物中最大的大脑、复杂的行为和敏捷性以及令人难以置信的瞬时伪装技能等。虽然头足类动物有许多复杂而精细的特征，但它们被认为是独立于脊椎动物进化而来的。通过比较它们的基因组，我们可以回答头足类动物和脊椎动物的构造是否相同或不同。”

Albertin还在巨型乌贼基因组中发现了100多个原钙粘蛋白（procadadherin）家族的基因，而这些基因在无脊椎动物中并不常见。

她说:“人们认为原钙粘蛋白在正确连接复杂的大脑方面很重要。而且，原钙粘蛋白被认为是脊椎动物的创新，所以当我们在巨型乌贼基因组中发现超过100个原钙粘蛋白基因的时候，我们感到非常惊讶。”

最后，她分析了一个迄今为止头足类动物独有的基因家族，叫做 反光蛋白 （reflectin）。反光蛋白非常独特，在数据库中几乎找不到其他任何相似的同源蛋白。此外，反光蛋白的氨基酸组成也非常不同寻常，在普通蛋白质中常见的几种氨基酸（比如丙氨酸、亮氨酸、异亮氨酸和赖氨酸）几乎不存在于这一蛋白质中，而相对稀少的氨基酸（如酪氨酸、色氨酸、甲硫氨酸和精氨酸）在反光蛋白中的含量却达到了一半以上。

这种蛋白质 具有非常高的折光率，可以几乎反射所有可见光 ，高于其他所有目前所知天然存在的蛋白质。反光蛋白编码一种与彩虹色有关的蛋白质。颜色是伪装的重要组成部分，所以我们试图了解这个基因家族的作用及作用方式。

拥有这个巨型乌贼的基因组是帮助我们理解什么促使了头足类动物进化的一个重要节点。它还可以帮助我们了解新的基因是如何在进化和发育中出现的。

近年来，海洋变暖和酸化、污染、缺氧和捕鱼已经影响了头足类动物的数量。在巨型乌贼标本组织中发现了高浓度的汞，在深海头足类动物组织中也发现了大量的阻燃化学物质。因此，迫切需要对这些重要但很少见的动物有更深入的生物学了解，以帮助对它们进行正确的保护。

论文链接：