自然（20230216）一周论文导读

　　编译 | 冯维维
　　Nature , 16 February 2023, Volume 614 Issue 7948
　　《自然》 2023年2月16日，第614卷7948期
　　物理学  Physics
　　Spherical symmetry in the kilonova AT2017gfo/GW170817
　　千新星AT2017gfo/GW170817的球形对称性
　　▲ 作者：Albert Sneppen, Darach Watson, Andreas Bauswein, Oliver Just, Rubina Kotak, Ehud Nakar, Dovi Poznanski & Stuart Sim
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05616-x
　　▲ 摘要：
　　中子星合并会释放出富含重元素的火球，天文学家将这种现象称为千新星。千新星的几何形状是中子星并合的关键判断依据，由超致密物质的性质和坍缩成黑洞的能量学决定。目前的流体动力学合并模型通常表现为非球面喷射。此前，Sr+ 在唯一被充分研究的千新星AT2017gfo的光谱中被发现，与引力波事件GW170817有关。
　　研究者结合强烈的Sr+  P Cygni吸收-发射光谱特征和千新星光谱的黑体性质确定，千新星在早期是高度球形的。线形分析结合已知的源倾角也显示出相同的球形度。作者认为，放射性衰变所注入的能量不足以使喷出物变成球形。来自黑洞盘的磁星风或射流可以注入足够的能量，在整个喷射物中诱导一个更球形的分布；然而，为了使元素分布均匀，似乎还需要一个额外的过程。
　　▲ Abstract：
　　The mergers of neutron stars expel a heavy-element enriched fireball that can be observed as a kilonova. The kilonova’s geometry is a key diagnostic of the merger and is dictated by the properties of ultra-dense matter and the energetics of the collapse to a black hole. Current hydrodynamical merger models typically show aspherical ejecta. Previously, Sr+  was identified in the spectrum of the only well-studied kilonova AT2017gfo, associated with the gravitational wave event GW170817. Here we combine the strong Sr+  P Cygni absorption-emission spectral feature and the blackbody nature of kilonova spectrum to determine that the kilonova is highly spherical at early epochs. Line shape analysis combined with the known inclination angle of the source also show the same sphericity independently. We conclude that energy injection by radioactive decay is insufficient to make the ejecta spherical. A magnetar wind or jet from the black-hole disk could inject enough energy to induce a more spherical distribution in the overall ejecta; however, an additional process seems necessary to make the element distribution uniform.
　　Electronic metadevices for terahertz applications
　　用于太赫兹应用的电子元设备
　　▲ 作者：Mohammad Samizadeh Nikoo & Elison Matioli
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05595-z
　　▲ 摘要：
　　电子技术的发展在很大程度上要依赖于规模的缩小，以满足对更快和高度集成设备的持续需求。随着通道长度的缩短，传统电子设备面临着阻碍充分发挥材料潜力并最终进一步小型化的根本问题。例如，通过隧道结注入的载流子控制了通道电阻，而高寄生电容极大地限制了最大工作频率。此外，由于极高的电场，这些超大尺寸的器件只能容纳几伏电压，这限制了它们的最大传输功率。
　　作者挑战了这种传统的限制，并提出了电子元器件的概念，其中射频场的微观操作导致了非凡的电子特性。该器件在深亚波长尺度的集体电磁相互作用的静电控制基础上运行，作为控制传统器件（如二极管和晶体管）中电子流的替代方案。这使得一类新的电子设备具有远超过10太赫兹的截止频率，记录高电导值，极高的击穿电压和皮秒级的开关速度。这项工作为下一代超快半导体器件奠定了基础，并提出了一种新的范式，有可能弥合电子和光学之间的差距。
　　▲ Abstract：
　　The evolution of electronics has largely relied on downscaling to meet the continuous needs for faster and highly integrated devices. As the channel length is reduced, however, classic electronic devices face fundamental issues that hinder exploiting materials to their full potential and, ultimately, further miniaturization. For example, the carrier injection through tunnelling junctions dominates the channel resistance, whereas the high parasitic capacitances drastically limit the maximum operating frequency. In addition, these ultra-scaled devices can only hold a few volts due to the extremely high electric fields, which limits their maximum delivered power. Here we challenge such traditional limitations and propose the concept of electronic metadevices, in which the microscopic manipulation of radiofrequency fields results in extraordinary electronic properties. The devices operate on the basis of electrostatic control of collective electromagnetic interactions at deep subwavelength scales, as an alternative to controlling the flow of electrons in traditional devices, such as diodes and transistors. This enables a new class of electronic devices with cutoff frequency figure-of-merit well beyond ten terahertz, record high conductance values, extremely high breakdown voltages and picosecond switching speeds. This work sets the stage for the next generation of ultrafast semiconductor devices and presents a new paradigm that potentially bridges the gap between electronics and optics.
　　生物物理学  Biophysics
　　Autonomous self-burying seed carriers for aerial seeding
　　用于航空播种的自动自埋式播种机
　　▲ 作者：Danli Luo, Aditi Maheshwari, Andreea Danielescu, Jiaji Li, Yue Yang, Ye Tao, Lingyun Sun, Dinesh K. Patel, Guanyun Wang, Shu Yang, Teng Zhang & Lining Yao
　　▲ 链接：
　　hhttps://www.nature.com/articles/s41586-022-05656-3
　　▲ 摘要：
　　对于面积大且难以到达的地区来说，飞机播种是一项关键的播种技术，能加速火灾后的重新造林或是荒地恢复。不过，当种子落在地表时，容易受到天气破坏或是被野生动物吞食，导致发芽率很低。不同牧草种的种子有自埋能力，这种能力可以给不同类型的种子带来优势。
　　研究者描述了一个受牻牛儿苗种子自钻孔行为启发的可生物降解种子载体。这个种子载体的种植成功率比牻牛儿苗种子还要高。这项技术或能提高飞机播种的效果，帮助应对土地退化地区的农业和环境压力。
　　他们设计了一种模拟牻牛儿苗种子的木基可生物降解种子载体。牻牛儿苗属的种子能打开卷曲的尾巴，以类似钻头的方式把种子埋到地下。这个种子载体有三个卷曲的尾巴，能在加湿后打开，搬运的最大种子和白皮松树种子一般大，约有11毫米长，72毫克重。增加能打开的尾巴数量，可以确保钻头部分与地表形成一个更适合挖掘的角度。这个种子载体在平地（难度最大的地形）上的播种成功率为80%，降低了被风吹走或被动物吞食的风险。在相同的地形条件下，天然的牻牛儿苗种子的成功率为0%。该载体或许还能用于播撒肥料或是有利于农业和保育应用的其他物质（如传感器）。
　　▲ Abstract：
　　Aerial seeding can quickly cover large and physically inaccessible areas to improve soil quality and scavenge residual nitrogen in agriculture, and for postfire reforestation and wildland restoration. However, it suffers from low germination rates, due to the direct exposure of unburied seeds to harsh sunlight, wind and granivorous birds, as well as undesirable air humidity and temperature. Here, inspired by Erodium seeds, we design and fabricate self-drilling seed carriers, turning wood veneer into highly stiff (about 4.9 GPa when dry, and about 1.3 GPa when wet) and hygromorphic bending or coiling actuators with an extremely large bending curvature (1,854 m−1 ), 45 times larger than the values in the literature. Our three-tailed carrier has an 80% drilling success rate on flat land after two triggering cycles, due to the beneficial resting angle (25°–30°) of its tail anchoring, whereas the natural Erodium seed’s success rate is 0%. Our carriers can carry payloads of various sizes and contents including biofertilizers and plant seeds as large as those of whitebark pine, which are about 11 mm in length and about 72 mg. We compare data from experiments and numerical simulation to elucidate the curvature transformation and actuation mechanisms to guide the design and optimization of the seed carriers. Our system will improve the effectiveness of aerial seeding to relieve agricultural and environmental stresses, and has potential applications in energy harvesting, soft robotics and sustainable buildings.
　　雨中的种子。图片来自：卡内基梅隆大学
　　设计理念图。图片来自：卡内基梅隆大学
　　A universal interface for plug-and-play assembly of stretchable devices
　　可拉伸设备即插即用组装的通用接口
　　▲ 作者：Ying Jiang, Shaobo Ji, Jing Sun, Jianping Huang, Yuanheng Li, Guijin Zou, Teddy Salim, Changxian Wang, Wenlong Li, Haoran Jin, Jie Xu, Sihong Wang, Ting Lei, Xuzhou Yan, Wendy Yen Xian Peh, Shih-Cheng Yen, Zhihua Liu, Mei Yu, Hang Zhao, Zechao Lu, Guanglin Li, Huajian Gao, Zhiyuan Liu, Zhenan Bao & Xiaodong Chen
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05579-z
　　▲ 摘要：
　　可拉伸混合设备已经实现了高保真的植入式和皮肤上的生理信号监测。这些设备通常包含与人类和软体机器人的机械要求相匹配的软模块，包含硅基微电子和保护性封装模块的刚性模块。为了使这种系统在机械上符合要求，模块之间的连接需要承受应力集中，这可能会限制它们的拉伸，最终导致脱胶失败。
　　作者开发了一个通用接口，它可以可靠地将软模块、刚性模块和封装模块连接在一起，以即插即用的方式形成健壮的和高度可拉伸的设备。该界面由互穿聚合物和金属纳米结构组成，通过简单的按压来连接模块，而无需使用浆料。它的形成由双相网络增长模型描述。通过该接口连接的软-软模块的机械和电气拉伸性能分别达到600%和180%。软模块和硬模块也可以使用上述接口进行电连接。具有该界面的软模块的封装具有强粘接性，界面韧性为0.24 N mm−1 。
　　作为概念证明，他们使用该接口组装可拉伸装置，用于体内神经调节和皮肤肌电图，具有高信号质量和机械阻力。研究者希望这种即插即用的接口可以简化和加速皮肤上和可植入的可拉伸设备的开发。
　　▲ Abstract：
　　Stretchable hybrid devices have enabled high-fidelity implantable and on-skin monitoring of physiological signals. These devices typically contain soft modules that match the mechanical requirements in humans and soft robots, rigid modules containing Si-based microelectronics and protective encapsulation modules. To make such a system mechanically compliant, the interconnects between the modules need to tolerate stress concentration that may limit their stretching and ultimately cause debonding failure. Here, we report a universal interface that can reliably connect soft, rigid and encapsulation modules together to form robust and highly stretchable devices in a plug-and-play manner. The interface, consisting of interpenetrating polymer and metal nanostructures, connects modules by simply pressing without using pastes. Its formation is depicted by a biphasic network growth model. Soft–soft modules joined by this interface achieved 600% and 180% mechanical and electrical stretchability, respectively. Soft and rigid modules can also be electrically connected using the above interface. Encapsulation on soft modules with this interface is strongly adhesive with an interfacial toughness of 0.24 N mm−1 . As a proof of concept, we use this interface to assemble stretchable devices for in vivo neuromodulation and on-skin electromyography, with high signal quality and mechanical resistance. We expect such a plug-and-play interface to simplify and accelerate the development of on-skin and implantable stretchable devices.
　　古生物学和地球物理学
　　Paleontology & Geophysics
　　Exceptional fossil preservation and evolution of the ray-finned fish brain
　　特殊化石保存和鳐鳍鱼大脑进化
　　▲ 作者：Rodrigo T. Figueroa, Danielle Goodvin, Matthew A. Kolmann, Michael I. Coates, Abigail M. Caron, Matt Friedman & Sam Giles
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05666-1
　　▲ 摘要：
　　大脑解剖学为鳐鳍鱼之间的关系提供了关键证据，但有两个主要的局限性模糊了人们对这一主要脊椎动物类群神经解剖学进化的理解。首先，最深分支的生物谱系与该群体的共同祖先分离了数亿年，有迹象表明，它们大脑形态的某些方面——就像其解剖学的其他方面一样——相对于原始条件是专门的。其次，在最早的鳍鱼中，除了颅骨内窥镜提供的粗略图像之外，没有任何直接的限制大脑形态的因素：颅骨内空洞空间的自然或虚拟填充。
　　研究者报告了一种大约3.19亿岁的射线鳍鱼（Coccocephalus wildi）的大脑和脑神经软组织保存。这个保存完好的脊椎动物大脑的例子为鳐鳍鱼系统发育的深层神经解剖提供了一扇窗口。其球头类表明了一种比现存物种更复杂的大脑进化模式，突出了分支的异形现象，并为联合所有现存鳍鱼的特征的起源提供了时间限制。这一发现以及在其他动物群体中越来越多的研究，都指出了古代软组织保存在理解骨骼组织狭窄亚群之外主要解剖系统的深层进化组合中的重要性。
　　▲ Abstract：
　　Brain anatomy provides key evidence for the relationships between ray-finned fishes, but two major limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group’s common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology—like other aspects of their anatomy—are specialized relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalus wildi, an approximately 319-million-year-old ray-finned fish. This example of a well-preserved vertebrate brain provides a window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalus indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies1 and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes. Our findings, along with a growing set of studies in other animal groups, point to the importance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues.
　　Heterogeneous melting near the Thwaites Glacier grounding line
　　思韦茨冰川接地线附近的非均匀融化
　　▲ 作者：B. E. Schmidt, P. Washam, P. E. D. Davis, K. W. Nicholls, D. M. Holland, J. D. Lawrence, K. L. Riverman, J. A. Smith, A. Spears, D. J. G. Dichek, A. D. Mullen, E. Clyne, B. Yeager, P. Anker, M. R. Meister, B. C. Hurwitz, E. S. Quartini, F. E. Bryson, A. Basinski-Ferris, C. Thomas, J. Wake, D. G. Vaughan, S. Anandakrishnan, E. Rignot, …K. Makinson Show authors
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05691-0
　　▲ 摘要：
　　思韦茨冰川属于西南极冰盖，其损失的冰量或使海平面在下一个世纪里快速上升。思韦茨冰川的完全崩塌预计会使全球海平面升高约65厘米。崩塌可能还会使周围的冰川变得不稳固，令未来海平面再升高3米。思韦茨冰川所在基岩朝着海岸向下倾斜，使其特别容易不稳定，这种不稳定可能会导致迅速而不可逆的冰损失。已知海洋条件、冰盖融化、冰流速会影响思韦茨冰川接地线的消退，接地线是指冰川与陆地分离并开始漂浮的地方，不过这些因素的具体作用方式一直不太明确。
　　为了研究思韦茨冰川崩塌的脆弱性，研究团队报道了思韦茨冰川和周围海洋的融冰速率和特性。这些观测数据来自接地线下游约1.5-2.0千米处在冰下587米钻取的一个检查孔。研究者利用一台水下航行器测量了该区域的海洋性质，以及更大区域下的冰型。他们发现，融冰速率在冰层急剧倾斜的海洋界面处很高，在平缓的界面处则受到抑制。这些观测结果证明了冰层形貌对冰损失的影响。研究结果增进了人们对一个重要西南极冰川当前状态的理解，并指出了未来气候建模面临的主要挑战。
　　▲ Abstract：
　　Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment. Because it is grounded below sea level, Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean. Recent ice-flow acceleration and retreat of the ice front and GL indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice–ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.