科研
科研
编译|冯维维
Nature, Volume 634 Issue 8035, 24 October 2024
《自然》,第634卷，8035期，2024年10月24日
物理学Physics
Two waves of massive stars running away from the young cluster R136
两波大质量恒星正从年轻的星团R136中逃逸
▲ 作者：Mitchel Stoop, Alex de Koter, Lex Kaper, Sarah Brands, Simon Portegies Zwart, Hugues Sana, Fiorenzo Stoppa, Mark Gieles, Laurent Mahy, Tomer Shenar, Difeng Guo, Gijs Nelemans & Steven Rieder
▲链接：
https://www.nature.com/articles/s41586-024-08013-8
▲摘要：
大质量恒星主要在星团或星协中形成的。它们的辐射场、恒星风和超新星强烈地影响着当地的环境。在星团生命的最初几百万年里，大质量恒星被动态地喷射出来，并以高速逃离星团。然而，动态弹射脱轨的产率约束较差。
研究者报告了从大麦哲伦星云的年轻星团R136中喷射出的55颗大质量逃逸恒星的样本。对盖亚数据的天体测量学分析揭示了两个动态弹出的逃逸通道。第一个通道向各个方向喷射大质量恒星，与R136诞生期间和之后的动力学相互作用一致。第二个通道以首选方向发射恒星，可能与星团相互作用有关。
他们发现，最初诞生于R136的最亮恒星中，有23%~33%是逃逸恒星。模型预测明显低估了大质量恒星的动态逃逸率。因此，它们在塑造和加热星际和星系介质中的作用，以及它们在驱动星系外流中的作用，比以前想象的要重要得多。
▲ Abstract：
Massive stars are predominantly born in stellar associations or clusters. Their radiation fields, stellar winds and supernovae strongly impact their local environment. In the first few million years of a cluster’s life, massive stars are dynamically ejected and run away from the cluster at high speed. However, the production rate of dynamically ejected runaways is poorly constrained. Here we report on a sample of 55 massive runaway stars ejected from the young cluster R136 in the Large Magellanic Cloud. An astrometric analysis of Gaia data reveals two channels of dynamically ejected runaways. The first channel ejects massive stars in all directions and is consistent with dynamical interactions during and after the birth of R136. The second channel launches stars in a preferred direction and may be related to a cluster interaction. We found that 23–33% of the most luminous stars initially born in R136 are runaways. Model predictionshave significantly underestimated the dynamical escape fraction of massive stars. Consequently, their role in shaping and heating the interstellar and galactic media and their role in driving galactic outflows are far more important than previously thought.
Harnessing plasticity in sequential metamaterials for ideal shock absorption
利用序贯超材料的塑性实现理想的减震
▲ 作者：Wenfeng Liu, Shahram Janbaz, David Dykstra, Bernard Ennis & Corentin Coulais
▲链接：
https://www.nature.com/articles/s41586-024-08037-0
▲摘要：
机械超材料表现出低密度下的高刚度、增强的能量吸收、形状变形、顺序变形、互动性和鲁棒波导等有趣的特性。到目前为止，超材料设计主要依赖于几何，材料的非线性，如粘弹性、断裂和塑性，在很大程度上被排除在设计原理之外。事实上，塑性变形传统上被视为一种失效模式，因此被小心地避免。
在这里，研究者拥抱塑性，而不是发现塑性和屈曲不稳定性之间的微妙平衡，并将其称之为“获得屈曲”。他们利用“获得屈曲”来设计在任意大的步骤序列中依次屈曲的超材料，同时保持承载能力，并利用连续屈服屈曲来制造结合了刚度和耗散的超材料。这两种特性通常是不相容的，而且可以多次使用。
这种高超材料表现出优异的减震性能。研究者表示，该发现为超材料工具箱增加了可塑性，使机械超材料成为一项具有大规模生产潜力的新兴技术。
▲ Abstract：
Mechanical metamaterials exhibit interesting properties such as high stiffness at low density, enhanced energy absorption, shape morphing, sequential deformations, auxeticity and robust waveguiding. Until now, metamaterial design has primarily relied on geometry, and materials nonlinearities such as viscoelasticity, fracture and plasticity have been largely left out of the design rationale. In fact, plastic deformations have been traditionally seen as a failure mode and thereby carefully avoided. Here we embrace plasticity instead and discover a delicate balance between plasticity and buckling instability, which we term ‘yield buckling’. We exploit yield buckling to design metamaterials that buckle sequentially in an arbitrary large sequence of steps whilst keeping a load-bearing capacity. We make use of sequential yield buckling to create metamaterials that combine stiffness and dissipation—two properties that are usually incompatible—and that can be used several times. Hence, our metamaterials exhibit superior shock-absorption performance. Our findings add plasticity to the metamaterial toolbox and make mechanical metamaterials a burgeoning technology with serious potential for mass production.
Quasi-periodic X-ray eruptions years after a nearby tidal disruption event
准周期性的x射线喷发，发生在附近的潮汐破坏事件数年后
▲ 作者：M. Nicholl, D. R. Pasham, A. Mummery, M. Guolo, K. Gendreau, G. C. Dewangan, E. C. Ferrara, R. Remillard, C. Bonnerot, J. Chakraborty, A. Hajela, V. S. Dhillon, A. F. Gillan, J. Greenwood, M. E. Huber, A. Janiuk, G. Salvesen, S. van Velzen, A. Aamer, K. D. Alexander, C. R. Angus, Z. Arzoumanian, K. Auchettl, E. Berger, …D. R. Young
▲链接：
https://www.nature.com/articles/s41586-024-08023-6
▲摘要：
准周期爆发（QPEs）是来自星系核心的软X射线的发光爆发，在数小时到数周的时间尺度上重复。这些罕见系统背后的机制尚不确定，但大多数理论都涉及超大质量黑洞（SMBHs）周围的吸积盘经历不稳定或与近轨道上的恒星物体相互作用。
有人提出，当SMBH破坏一颗路过的恒星时，可能会形成这个圆盘，这意味着许多QPE应该在可观测到的潮汐破坏事件（TDEs）之前发生。两个已知的QPE源显示出与TDE一致的静态光度的长期衰减，两个观测到的TDE也显示出与个别喷发一致的X射线耀斑。TDE和QPE也优先出现在类似的星系中。然而，没有确认的重复QPE与光谱确认的TDE或在峰值亮度下观察到的光学TDE有关。
在这里，研究者报告了从AT2019qiz探测到的9个平均复发时间约为48小时的X射线QPE， AT2019qiz是一个附近和广泛研究的光学选择TDE。他们检测并模拟了吸积盘的X射线，紫外线（UV）和光学发射，并表明轨道天体与吸积盘碰撞为QPE提供了合理的解释。
▲ Abstract：
Quasi-periodic eruptions (QPEs) are luminous bursts of soft X-rays from the nuclei of galaxies, repeating on timescales of hours to weeks. The mechanism behind these rare systems is uncertain, but most theories involve accretion disks around supermassive black holes (SMBHs) undergoing instabilities or interacting with a stellar object in a close orbit. It has been suggested that this disk could be created when the SMBH disrupts a passing star, implying that many QPEs should be preceded by observable tidal disruption events (TDEs). Two known QPE sources show long-term decays in quiescent luminosity consistent with TDEs and two observed TDEs have exhibited X-ray flares consistent with individual eruptions. TDEs and QPEs also occur preferentially in similar galaxies15. However, no confirmed repeating QPEs have been associated with a spectroscopically confirmed TDE or an optical TDE observed at peak brightness. Here we report the detection of nine X-ray QPEs with a mean recurrence time of approximately 48 h from AT2019qiz, a nearby and extensively studied optically selected TDE. We detect and model the X-ray, ultraviolet (UV) and optical emission from the accretion disk and show that an orbiting body colliding with this disk provides a plausible explanation for the QPEs.
Electronic rotons and Wigner crystallites in a two-dimensional dipole liquid
二维偶极子液体中的电子质子和维格纳晶体
▲ 作者：Soobin Park, Minjae Huh, Chris Jozwiak, Eli Rotenberg, Aaron Bostwick & Keun Su Kim
▲链接：
https://www.nature.com/articles/s41586-024-08045-0
▲摘要：
朗道提出的解释超流体液氦的一个关键概念是质子的量子粒子的基本激发。液体中原子的不规则排列导致了质子的非周期色散，这对理解分数量子霍尔液体（磁质子）和玻色-爱因斯坦凝聚体的超固体性起着关键作用。即使对于二维电子或偶极子液体，在没有磁场的情况下，排斥性相互作用也被预测会形成一个旋转最小值，这可以用来追踪向维格纳晶体和超导的转变，尽管这还没有被观察到。
在这里，研究者报告了在碱金属离子的二维偶极子液体中观察到的这种电子质子向黑磷的表层提供电子。他们的数据揭示了惊人的非周期色散，其特征是有限动量下的局部能量最小。随着偶极子密度的降低，相互作用超过了动能，质子间隙减小到0，就像在晶体中一样，这是维格纳结晶的信号。该模型显示了由偶极子之间的斥力引起的短程有序的重要性，这可以看作是漂浮在费米液体海洋中的维格纳晶体（气泡或条纹）的形成。研究结果表明，电子质子（和赝隙）的主要起源是强相关的。
▲ Abstract：
A key concept proposed by Landau to explain superfluid liquid helium is the elementary excitation of quantum particles called rotons. The irregular arrangement of atoms in a liquid leads to the aperiodic dispersion of rotons, which played a pivotal role in understanding fractional quantum Hall liquids (magneto-rotons) and the supersolidity of Bose–Einstein condensates. Even for a two-dimensional electron or dipole liquid, in the absence of a magnetic field, the repulsive interactions have been predicted to form a roton minimum, which can be used to trace the transition to Wigner crystals and superconductivity although this has not yet been observed. Here, we report the observation of such electronic rotons in a two-dimensional dipole liquid of alkali-metal ions donating electrons to surface layers of black phosphorus. Our data reveal the striking aperiodic dispersion of rotons, which is characterized by a local minimum of energy at finite momentum. As the density of dipoles decreases so that interactions dominate over the kinetic energy, the roton gap reduces to 0, as in a crystal, signalling Wigner crystallization. Our model shows the importance of short-range order arising from repulsion between dipoles, which can be viewed as the formation of Wigner crystallites (bubbles or stripes) floating in the sea of a Fermi liquid. Our results reveal that the primary origin of electronic rotons (and the pseudogap) is strong correlations.
生态学Ecology
Islands are key for protecting the world’s plant endemism
岛屿对保护世界特有植物很关键
▲ 作者：Julian Schrader, Patrick Weigelt, Lirong Cai, Mark Westoby, José María Fernández-Palacios, Francisco J. Cabezas, Gregory M. Plunkett, Tom A. Ranker, Kostas A. Triantis, Panayiotis Trigas, Yasuhiro Kubota & Holger Kreft
▲链接：
https://www.nature.com/articles/s41586-024-08036-1
▲摘要：
岛屿是著名的天然进化实验室，支持着许多在其他地方找不到的物种。岛屿的保护也值得高度关注，许多岛屿特有物种目前受到威胁或已灭绝。在这里，研究者提出了一份标准化的清单，列出了所有已知的维管植物，并记录了它们的地理和系统发育分布以及保护风险。
研究者对304103种植物的分析表明，94052种（31%）原生于岛屿，占全球陆地面积的5.3%。其中，63280种是岛屿特有物种，占全球植物多样性的21%。其中四分之三仅限于大型或孤立的岛屿。与世界植物区系相比，岛屿特有植物在生命树中是非随机分布的，共有1.005亿年独特的系统发育历史，其中17个科、1702个属完全是岛屿特有的。
在国际自然保护联盟指定的所有维管植物保护类别中，22%是岛屿特有植物。在这些特有物种中，51%受到威胁，55%有记录的全球灭绝发生在岛屿上。研究者发现，在所有单岛特有物种中，只有6%出现在符合联合国30×30保护目标的岛屿上。需要采取紧急措施，包括恢复生境、清除入侵物种和移地方案，以保护世界岛屿植物群。研究者表示，该清单量化了岛屿生物的独特性，为未来的岛屿植物区系研究提供了基础，并强调了采取保护行动的迫切需要。
▲ Abstract：
Islands are renowned as evolutionary laboratories and support many species that are not found elsewhere. Islands are also of great conservation concern, with many of their endemic species currently threatened or extinct. Here we present a standardized checklist of all known vascular plants that occur on islands and document their geographical and phylogenetic distribution and conservation risk. Our analyses of 304,103 plant species reveal that 94,052 species (31%) are native to islands, which constitute 5.3% of the global landmass4. Of these, 63,280 are island endemic species, which represent 21% of global plant diversity. Three-quarters of these are restricted to large or isolated islands. Compared with the world flora, island endemics are non-randomly distributed within the tree of life, with a total of 1,005 billion years of unique phylogenetic history with 17 families and 1,702 genera being entirely endemic to islands. Of all vascular plants assigned International Union for Conservation of Nature conservation categories, 22% are island endemics. Among these endemic species, 51% are threatened, and 55% of all documented global extinctions have occurred on islands. We find that of all single-island endemic species, only 6% occur on islands meeting the United Nations 30×30 conservation target. Urgent measures including habitat restoration, invasive species removal and ex situ programmes are needed to protect the world’s island flora. Our checklist quantifies the uniqueness of island life, provides a basis for future studies of island floras, and highlights the urgent need to take actions for conserving them.
Continental-scale nutrient and contaminant delivery by Pacific salmon
太平洋鲑鱼可在大陆层面输送养分和污染物
▲ 作者：Jessica E. Brandt, Jeff S. Wesner, Gregory T. Ruggerone, Timothy D. Jardine, Collin A. Eagles-Smith, Gabrielle E. Ruso, Craig A. Stricker, Kristofor A. Voss & David M. Walters
▲链接：
https://www.nature.com/articles/s41586-024-07980-2
▲摘要：
迁徙动物携带的大量营养物质对食物网具有生态效益，但可能被共同运输的污染物所抵消。鲑鱼产卵洄游是这一过程的典型，将海洋来源的物质带到内陆生态系统。在那里它们刺激了当地的生产力，但也增加了污染物的暴露。现在太平洋鲑鱼的丰度和生物量都比上个世纪高，这反映了群落结构的重大变化，这种变化可能改变了营养物和污染物的输送。
研究者将营养物质和污染物浓度与40年的太平洋鲑鱼年回报结合起来，量化群落结构的变化如何影响北美西部的海洋到淡水输入。鲑鱼每年向淡水输送数吨的营养物质和数公斤的污染物。鲑鱼收益的增加（1976-2015年）使鲑鱼来源的营养物和污染物投入分别增加了30%和20%。这些增加的主要是粉红鲑鱼，它们寿命短，在海洋食物网中的摄取量比其他鲑鱼低，而且营养与污染物的比例最高。
因此，研究者表示，营养物质的输送比污染物的输送速度更快，随着时间的推移，鲑鱼的投入对生态更有益。即便如此，污染物的负荷可能代表了一些鲑鱼捕食者的暴露问题。太平洋鲑鱼的例子展示了长期的环境变化如何与大空间尺度上的营养物质和污染物运动相互作用，并为探索其他迁徙物种的类似模式提供了一个模型。
▲ Abstract：
The movement of large amounts of nutrients by migrating animals has ecological benefits for recipient food webs that may be offset by co-transported contaminants. Salmon spawning migrations are archetypal of this process, carrying marine-derived materials to inland ecosystems where they stimulate local productivity but also enhance contaminant exposure. Pacific salmon abundance and biomass are higher now than in the last century, reflecting substantial shifts in community structure8 that probably altered nutrient versus contaminant delivery. Here we combined nutrient and contaminant concentrations with 40 years of annual Pacific salmon returns to quantify how changes in community structure influenced marine to freshwater inputs to western North America. Salmon transported tonnes of nutrients and kilograms of contaminants to freshwaters annually. Higher salmon returns (1976–2015) increased salmon-derived nutrient and contaminant inputs by 30% and 20%, respectively. These increases were dominated by pink salmon, which are short-lived, feed lower in marine food webs than other salmon species, and had the highest nutrient-to-contaminant ratios. As a result, the delivery of nutrients increased at a greater rate than the delivery of contaminants, and salmon inputs became more ecologically beneficial over time. Even still, contaminant loadings may represent exposure concerns for some salmon predators. The Pacific salmon example demonstrates how long-term environmental changes interact with nutrient and contaminant movement across large spatial scales and provides a model for exploring similar patterns with other migratory species.
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