編譯 | 馮維維
Nature, 16 February 2023, Volume 614 Issue 7948
《自然》2023年2月16日，第614卷7948期
物理學 Physics
Spherical symmetry in the kilonova AT2017gfo/GW170817
千新星AT2017gfo/GW170817的球形對稱性
▲ 作者：Albert Sneppen, Darach Watson, Andreas Bauswein, Oliver Just, Rubina Kotak, Ehud Nakar, Dovi Poznanski & Stuart Sim
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05616-x
▲ 摘要：
中子星合併會釋放出富含重元素的火球，天文學家將這種現象稱為千新星。千新星的幾何形狀是中子星併合的關鍵判斷依據，由超緻密物質的性質和坍縮成黑洞的能量學決定。目前的流體動力學合併模型通常表現為非球面噴射。此前，Sr+在唯一被充分研究的千新星AT2017gfo的光譜中被發現，與引力波事件GW170817有關。
研究者結合強烈的Sr+ P Cygni吸收-發射光譜特徵和千新星光譜的黑體性質確定，千新星在早期是高度球形的。線形分析結合已知的源傾角也顯示出相同的球形度。作者認為，放射性衰變所注入的能量不足以使噴出物變成球形。來自黑洞盤的磁星風或射流可以注入足夠的能量，在整個噴射物中誘導一個更球形的分佈；然而，為了使元素分佈均勻，似乎還需要一個額外的過程。
▲ 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
用於太赫茲應用的電子元設備
▲ 作者：Mohammad Samizadeh Nikoo & Elison Matioli
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05595-z
▲ 摘要：
電子技術的發展在很大程度上要依賴於規模的縮小，以滿足對更快和高度集成設備的持續需求。隨着通道長度的縮短，傳統電子設備面臨著阻礙充分發揮材料潛力並最終進一步小型化的根本問題。例如，通過隧道結注入的載流子控制了通道電阻，而高寄生電容極大地限制了最大工作頻率。此外，由於極高的電場，這些超大尺寸的器件只能容納幾伏電壓，這限制了它們的最大傳輸功率。
作者挑戰了這種傳統的限制，並提出了電子元器件的概念，其中射頻場的微觀操作導致了非凡的電子特性。該器件在深亞波長尺度的集體電磁相互作用的靜電控制基礎上運行，作為控制傳統器件（如二極管和晶體管）中電子流的替代方案。這使得一類新的電子設備具有遠超過10太赫茲的截止頻率，記錄高電導值，極高的擊穿電壓和皮秒級的開關速度。這項工作為下一代超快半導體器件奠定了基礎，並提出了一種新的範式，有可能彌合電子和光學之間的差距。
▲ 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.
生物物理學 Biophysics
Autonomous self-burying seed carriers for aerial seeding
用於航空播種的自動自埋式播種機
▲ 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
▲ 鏈接：
hhttps://www.nature.com/articles/s41586-022-05656-3
▲ 摘要：
對於面積大且難以到達的地區來說，飛機播種是一項關鍵的播種技術，能加速火災後的重新造林或是荒地恢復。不過，當種子落在地表時，容易受到天氣破壞或是被野生動物吞食，導致發芽率很低。不同牧草種的種子有自埋能力，這種能力可以給不同類型的種子帶來優勢。
研究者描述了一個受牻牛兒苗種子自鑽孔行為啟發的可生物降解種子載體。這個種子載體的種植成功率比牻牛兒苗種子還要高。這項技術或能提高飛機播種的效果，幫助應對土地退化地區的農業和環境壓力。
他們設計了一種模擬牻牛兒苗種子的木基可生物降解種子載體。牻牛兒苗屬的種子能打開捲曲的尾巴，以類似鑽頭的方式把種子埋到地下。這個種子載體有三個捲曲的尾巴，能在加濕後打開，搬運的最大種子和白皮松樹種子一般大，約有11毫米長，72毫克重。增加能打開的尾巴數量，可以確保鑽頭部分與地表形成一個更適合挖掘的角度。這個種子載體在平地（難度最大的地形）上的播種成功率為80%，降低了被風吹走或被動物吞食的風險。在相同的地形條件下，天然的牻牛兒苗種子的成功率為0%。該載體或許還能用於播撒肥料或是有利於農業和保育應用的其他物質（如傳感器）。
▲ 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.
雨中的種子。圖片來自：卡內基梅隆大學
設計理念圖。圖片來自：卡內基梅隆大學
A universal interface for plug-and-play assembly of stretchable devices
可拉伸設備即插即用組裝的通用接口
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05579-z
▲ 摘要：
可拉伸混合設備已經實現了高保真的植入式和皮膚上的生理信號監測。這些設備通常包含與人類和軟體機械人的機械要求相匹配的軟模塊，包含硅基微電子和保護性封裝模塊的剛性模塊。為了使這種系統在機械上符合要求，模塊之間的連接需要承受應力集中，這可能會限制它們的拉伸，最終導致脫膠失敗。
作者開發了一個通用接口，它可以可靠地將軟模塊、剛性模塊和封裝模塊連接在一起，以即插即用的方式形成健壯的和高度可拉伸的設備。該界面由互穿聚合物和金屬納米結構組成，通過簡單的按壓來連接模塊，而無需使用漿料。它的形成由雙相網絡增長模型描述。通過該接口連接的軟-軟模塊的機械和電氣拉伸性能分別達到600%和180%。軟模塊和硬模塊也可以使用上述接口進行電連接。具有該界面的軟模塊的封裝具有強粘接性，界面韌性為0.24 N mm−1。
作為概念證明，他們使用該接口組裝可拉伸裝置，用於體內神經調節和皮膚肌電圖，具有高信號質量和機械阻力。研究者希望這種即插即用的接口可以簡化和加速皮膚上和可植入的可拉伸設備的開發。
▲ 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.
古生物學和地球物理學
Paleontology & Geophysics
Exceptional fossil preservation and evolution of the ray-finned fish brain
特殊化石保存和鰩鰭魚大腦進化
▲ 作者：Rodrigo T. Figueroa, Danielle Goodvin, Matthew A. Kolmann, Michael I. Coates, Abigail M. Caron, Matt Friedman & Sam Giles
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05666-1
▲ 摘要：
大腦解剖學為鰩鰭魚之間的關係提供了關鍵證據，但有兩個主要的局限性模糊了人們對這一主要脊椎動物類群神經解剖學進化的理解。首先，最深分支的生物譜系與該群體的共同祖先分離了數億年，有跡象表明，它們大腦形態的某些方面——就像其解剖學的其他方面一樣——相對於原始條件是專門的。其次，在最早的鰭魚中，除了顱骨內窺鏡提供的粗略圖像之外，沒有任何直接的限制大腦形態的因素：顱骨內空洞空間的自然或虛擬填充。
研究者報告了一種大約3.19億歲的射線鰭魚（Coccocephalus wildi）的大腦和腦神經軟組織保存。這個保存完好的脊椎動物大腦的例子為鰩鰭魚系統發育的深層神經解剖提供了一扇窗口。其球頭類表明了一種比現存物種更複雜的大腦進化模式，突出了分支的異形現象，並為聯合所有現存鰭魚的特徵的起源提供了時間限制。這一發現以及在其他動物群體中越來越多的研究，都指出了古代軟組織保存在理解骨骼組織狹窄亞群之外主要解剖系統的深層進化組合中的重要性。
▲ 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
思韋茨冰川接地線附近的非均勻融化
▲ 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
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05691-0
▲ 摘要：
思韋茨冰川屬於西南極冰蓋，其損失的冰量或使海平面在下一個世紀里快速上升。思韋茨冰川的完全崩塌預計會使全球海平面升高約65厘米。崩塌可能還會使周圍的冰川變得不穩固，令未來海平面再升高3米。思韋茨冰川所在基岩朝着海岸向下傾斜，使其特別容易不穩定，這種不穩定可能會導致迅速而不可逆的冰損失。已知海洋條件、冰蓋融化、冰流速會影響思韋茨冰川接地線的消退，接地線是指冰川與陸地分離並開始漂浮的地方，不過這些因素的具體作用方式一直不太明確。
為了研究思韋茨冰川崩塌的脆弱性，研究團隊報道了思韋茨冰川和周圍海洋的融冰速率和特性。這些觀測數據來自接地線下游約1.5-2.0千米處在冰下587米鑽取的一個檢查孔。研究者利用一台水下航行器測量了該區域的海洋性質，以及更大區域下的冰型。他們發現，融冰速率在冰層急劇傾斜的海洋界面處很高，在平緩的界面處則受到抑制。這些觀測結果證明了冰層形貌對冰損失的影響。研究結果增進了人們對一個重要西南極冰川當前狀態的理解，並指出了未來氣候建模面臨的主要挑戰。
▲ 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.
