编译 | 李言 Nature, 21 July 2022, Volume 607 Issue 7919 《自然》2022年7月21日，第607卷，7919期
天文学Astronomy
Extended far-ultraviolet emission in distant dwarf galaxies 遥远矮星系中延伸的远紫外辐射 ▲ 作者：Anshuman Borgohain, Kanak Saha, Bruce Elmegreen et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04905-9 ▲ 摘要： 在此，我们报告在南天区域11个蓝致密矮星（BCDs）的外部区域观测到的过量远紫外线（FUV)发射情况，其红移在0.1到0.24之间，对应于标准宇宙学中13 - 28亿年的回溯时间。这些观测是由天文卫星AstroSat上的紫外线成像望远镜进行的。 对于10个蓝致密矮星，经仪器点扩散函数校正后的本征FUV辐射的径向分布比用哈勃太空望远镜观测到的光学对应物有更大的尺度长度。 这种简单的FUV剖面表明，在宇宙吸积盘中形成了扩展的恒星。FUV中的团块结构也表明其外盘在引力上是不稳定的。团块上的动力摩擦推动它们向内移动，其速度平均超过106个太阳质量/ 10亿年。 ▲ Abstract： Here we report the observation of excess far-ultraviolet (FUV) emission in the outer regions of 11 BCDs in the GOODS South field at redshifts between 0.1 and 0.24, corresponding to look-back times of 1.3–2.8 billion years in standard cosmology. These observations were made by the Ultra-Violet Imaging Telescope on AstroSat. For ten BCDs, the radial profiles of the intrinsic FUV emission, corrected for the instrument point spread function, have larger scale lengths than their optical counterparts observed with the Hubble Space Telescope. Such shallow FUV profiles suggest extended star formation in cosmically accreting disks. Clumpy structure in the FUV also suggests that the outer FUV disks are gravitationally unstable. Dynamical friction on the clumps drives them inwards at an average rate exceeding 106 solar masses per billion years.
物理学Physics
Digital quantum simulation of Floquet symmetry-protected topological phases Floquet对称保护拓扑相的数字量子模拟 ▲ 作者：Xu Zhang, Wenjie Jiang, Jinfeng Deng, Ke Wang et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04854-3 ▲ 摘要： 在此，我们报告对一种独特的物质非平衡状态的观察，即通过可编程超导量子比特阵列的数字量子模拟实现的Floquet对称保护拓扑相。 在长达40个驱动周期中，使用深度超过240且作用于26个量子比特的电路，我们观察到边缘自旋的鲁棒长寿命时间相关性和亚谐波时间响应。 我们证明了亚谐波响应与初始状态无关，并通过实验绘制出了Floquet对称保护拓扑和热相之间的相边界。我们的结果建立了一个通用的数字模拟方法，以探索奇异的非平衡相的物质与当前嘈杂的中等规模量子处理器。 ▲ Abstract： Here we report the observation of a distinct type of non-equilibrium state of matter, Floquet symmetry-protected topological phases, which are implemented through digital quantum simulation with an array of programmable superconducting qubits. We observe robust long-lived temporal correlations and subharmonic temporal response for the edge spins over up to 40 driving cycles using a circuit of depth exceeding 240 and acting on 26 qubits. We demonstrate that the subharmonic response is independent of the initial state, and experimentally map out a phase boundary between the Floquet symmetry-protected topological and thermal phases. Our results establish a versatile digital simulation approach to exploring exotic non-equilibrium phases of matter with current noisy intermediate-scale quantum processors.
Perpendicular full switching of chiral antiferromagnetic order by current 垂直全开关电流的手性反铁磁顺序 ▲ 作者：Tomoya Higo, Kouta Kondou, Takuya Nomoto et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04864-1 ▲ 摘要： 在此，我们报告在实验中实现了反铁磁二元态垂直转矩和全自旋轨道转矩转换。我们使用手性反铁磁Mn3Sn。由于在其手性反铁磁态下的团簇八极磁极具有铁性秩序，它表现出无磁化反常霍尔效应。 我们利用分子束外延制备了重金属/Mn3Sn的异质结构，并利用外延面内拉伸应变引入八极垂直磁各向异性。通过使用反常霍尔效应作为读数，我们在一个30纳米厚的Mn3Sn薄膜中展示了百分之百的八极垂直极化开关，其临界电流密度小于每平方厘米15兆安。 ▲ Abstract： Here we report the experimental realization of perpendicular and full spin–orbit torque switching of an antiferromagnetic binary state. We use the chiral antiferromagnet Mn3Sn (ref.), which exhibits the magnetization-free anomalous Hall effect owing to a ferroic order of a cluster magnetic octupole hosted in its chiral antiferromagnetic state. We fabricate heavy-metal/Mn3Sn heterostructures by molecular beam epitaxy and introduce perpendicular magnetic anisotropy of the octupole using an epitaxial in-plane tensile strain. By using the anomalous Hall effect as the readout, we demonstrate 100 per cent switching of the perpendicular octupole polarization in a 30-nanometre-thick Mn3Sn film with a small critical current density of less than 15 megaamperes per square centimetre.
材料科学Material Science
Coherent interfaces govern direct transformation from graphite to diamond 共格界面控制石墨到金刚石的直接转变 ▲ 作者：Kun Luo, Bing Liu, Wentao Hu, Xiao Dong et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04863-2 ▲ 摘要： 在此，我们报告了在静态压缩恢复的部分转化石墨样品中，使用高角度环形暗场扫描透射电子显微镜识别出四个基本结构基序组成的石墨-金刚石界面。这些观察为可能的转化途径提供了见解。理论计算证实，与之前提出的其他路径相比，通过这些相干界面的转换更有利。 石墨到金刚石的转变是由纳米级的共格界面（金刚石成核）控制的，在静态压缩下，该界面提前消耗剩余的石墨（金刚石生长）。这些结果也可以揭示其他碳材料和氮化硼在不同合成条件下的转化机理。 ▲ Abstract： Here we report the identification of coherent graphite−diamond interfaces, which consist of four basic structural motifs, in partially transformed graphite samples recovered from static compression, using high-angle annular dark-field scanning transmission electron microscopy. These observations provide insight into possible pathways of the transformation. Theoretical calculations confirm that transformation through these coherent interfaces is energetically favoured compared with those through other paths previously proposed. The graphite-to-diamond transformation is governed by the formation of nanoscale coherent interfaces (diamond nucleation), which, under static compression, advance to consume the remaining graphite (diamond growth). These results may also shed light on transformation mechanisms of other carbon materials and boron nitride under different synthetic conditions.
古生物学Paleontology
Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots 灭绝后的显生宙海洋和生物多样性热点的恢复 ▲ 作者：Pedro Cermeño, Carmen García-Comas, Alexandre Pohl et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04932-6 ▲ 摘要： 在此，我们提出一个区域多样化模型，重现了大规模灭绝后全球海洋无脊椎动物多样性的主要显生宙趋势。我们发现，全球多样性的动态最好由一个多样化模型描述，模型可以广泛地运行在对数函数的指数增长系统中。 对生物多样性与承载能力之比的空间解析分析表明，在整个显生宙，只有不到2%的全球被淹大陆地区表现出接近生态饱和的生物多样性水平。 我们认为，中生代晚期和新生代全球物种多样性的总体增加是地球系统长期稳定和大陆最大破碎化条件下多样性热点的发展所致。我们称之为“多样性热点假说”，我们将此作为中生代海洋革命引领这一宏观进化趋势假说的一个非相互排斥的替代方案。 ▲ Abstract： Here we present a regional diversification model that reproduces the main Phanerozoic eon trends in the global diversity of marine invertebrates after imposing mass extinctions. We find that the dynamics of global diversity are best described by a diversification model that operates widely within the exponential growth regime of a logistic function. A spatially resolved analysis of the ratio of diversity to carrying capacity reveals that less than 2% of the global flooded continental area throughout the Phanerozoic exhibits diversity levels approaching ecological saturation. We attribute the overall increase in global diversity during the Late Mesozoic and Cenozoic eras to the development of diversity hotspots under prolonged conditions of Earth system stability and maximum continental fragmentation. We call this the ‘diversity hotspots hypothesis’, which we propose as a non-mutually exclusive alternative to the hypothesis that the Mesozoic marine revolution led this macroevolutionary trend.
地球科学Earth science
Climate change increases cross-species viral transmission risk 气候变化增加了病毒跨物种传播的风险 ▲ 作者：Colin J. Carlson, Gregory F. Albery, Cory Merow et al. ▲ 链接： https://www.nature.com/articles/s41586-022-04788-w ▲ 摘要： 在这里，我们利用哺乳动物-病毒网络的系统地理模型模拟了未来病毒共享的潜在热点，并预测了到2070年时气候变化和土地使用情景下3139种哺乳动物的地理范围变化。 我们预测，在亚洲和非洲的高海拔地区、生物多样性热点地区以及人口密度高的地区，物种将以新的组合聚集，导致相关病毒的跨物种传播估计达4000次。由于其独特的传播能力，蝙蝠将参与大部分新病毒共享，并且很可能在进化过程中共享病毒，这将促进未来在人类中出现的风险。 值得注意的是，我们发现这种生态转型可能已经开始，在21世纪将升温控制在2°C以内不会减少未来的病毒共享。我们的研究结果强调，迫切需要将病毒监测和发现工作与生物多样性调查结合起来，跟踪物种的范围变化，特别是在人畜共患病最多且正经历快速变暖的热带地区。 ▲ Abstract： Here we simulate potential hotspots of future viral sharing, using a phylogeographical model of the mammal–virus network, and projections of geographical range shifts for 3,139 mammal species under climate-change and land-use scenarios for the year 2070. We predict that species will aggregate in new combinations at high elevations, in biodiversity hotspots, and in areas of high human population density in Asia and Africa, causing the cross-species transmission of their associated viruses an estimated 4,000 times. Owing to their unique dispersal ability, bats account for the majority of novel viral sharing and are likely to share viruses along evolutionary pathways that will facilitate future emergence in humans. Notably, we find that this ecological transition may already be underway, and holding warming under 2 °C within the twenty-first century will not reduce future viral sharing. Our findings highlight an urgent need to pair viral surveillance and discovery efforts with biodiversity surveys tracking the range shifts of species, especially in tropical regions that contain the most zoonoses and are experiencing rapid warming.