編譯 | 未玖
Nature,13 February 2025, Volume 638, Issue 8050《自然》2025年2月13日，第638卷，8050期
天文學Astronomy
Directly imaging the cooling flow in the Phoenix cluster
直接成像鳳凰星團中的冷卻流
▲ 作者：Michael Reefe, Michael McDonald, Marios Chatzikos, Jerome Seebeck, Richard Mushotzky, Sylvain Veilleux, et al.
▲ 鏈接：https://www.nature.com/articles/s41586-024-08369-x
▲ 摘要：在許多星系團的中心，熾熱（大約107開爾文）星系團內介質可變得足夠致密，以至于其本應在短時間內冷卻。然而，在大質量中心星系中測量到的恒星形成率很低，且冷卻氣體中沒有軟X射線，這表明大多數氣體從未冷卻過。這就是所謂的冷卻流問題。
最新觀測表明，黑洞噴流使絕大多數氣體保持在高溫狀態。任何星系團中的所有氣相中，冷卻流尚未實現全繪制。
研究組展示了使用詹姆斯韋伯太空望遠鏡對鳳凰星團的觀測，繪制了[Ne vi] λ 7.652-μm發射線，使人們能夠在大尺度上探測105.5? K的氣體。這些數據顯示了擴展的[Ne vi]發射，與星系團內介質的冷卻峰、最冷的氣相和活躍恒星形成的位置同空間存在。
綜上所述，這意味著最近發生了一次快速冷卻，導致了冷卻速度短暫飆升，研究組估計為每年5000~23000個太陽質量。這些數據提供了星系團核心溫度在105 K到106 K之間的大規模氣體分布圖景，并強調了黑洞反饋在調節冷卻和促進冷卻方面的關鍵作用。
▲ Abstract：In the centres of many galaxy clusters, the hot (approximately 107 kelvin) intracluster medium can become dense enough that it should cool on short timescales. However, the low measured star formation rates in massive central galaxies and the absence of soft X-ray lines from the cooling gas suggest that most of this gas never cools. This is known as the cooling flow problem. The latest observations suggest that black hole jets are maintaining the vast majority of gas at high temperatures. A cooling flow has yet to be fully mapped through all the gas phases in any galaxy cluster. Here we present observations of the Phoenix cluster using the James Webb Space Telescope to map the [Ne vi] λ 7.652-μm emission line, enabling us to probe the gas at 105.5?kelvin on large scales. These data show extended [Ne vi] emission that is cospatial with the cooling peak in the intracluster medium, the coolest gas phases and the sites of active star formation. Taken together, these imply a recent episode of rapid cooling, causing a short-lived spike in the cooling rate, which we estimate to be 5,000–23,000 solar masses per year. These data provide a large-scale map of gas at temperatures between 105?kelvin and 106?kelvin in a cluster core, and highlight the critical role that black hole feedback has in not only regulating cooling but also promoting it.
The bulk motion of gas in the core of the Centaurus galaxy cluster
半人馬座星系團核心氣體的整體流動
▲ 作者：XRISM collaboration
▲ 鏈接：https://www.nature.com/articles/s41586-024-08561-z
▲ 摘要：星系團包含大量被稱為星系團內介質（ICM）的熱電離氣體。在疏散星系團核心中，ICM的輻射冷卻時間短于星系團年齡。
然而，與冷卻相關的線發射缺失表明加熱機制抵消了冷卻，來自活動星系核（AGNs）的反饋是最有可能的來源。湍流和整體流動，如星系團勢阱中核心氣體的振蕩（沖擊）運動，也被認為是核心外部熱量分布的機制。
研究組用X射線成像和光譜任務衛星對半人馬座星系團進行X射線光譜觀測。結果發現，熱氣體沿著相對于中心星系的視線流動，在距離中心約30 kpc的范圍內，速度從130 km s?1到310 km s?1。這表明整體流動與核心氣體晃動一致。
雖然整體流動可防止中心冷卻氣體的過度積聚，但亦可分散AGN注入的熱量，并從周圍的ICM中引入熱能。核心氣體的速度色散僅為≤120 km s?1，甚至在AGN的10 kpc范圍內亦是如此。這表明AGN對周圍ICM流動的影響在星系團中是有限的。
▲ Abstract：Galaxy clusters contain vast amounts of hot ionized gas known as the intracluster medium (ICM). In relaxed cluster cores, the radiative cooling time of the ICM is shorter than the age of the cluster. However, the absence of line emission associated with cooling suggests heating mechanisms that offset the cooling, with feedback from active galactic nuclei (AGNs) being the most likely source. Turbulence and bulk motions, such as the oscillating (‘sloshing’) motion of the core gas in the cluster potential well, have also been proposed as mechanisms for heat distribution from the outside of the core. Here we present X-ray spectroscopic observations of the Centaurus galaxy cluster with the X-Ray Imaging and Spectroscopy Mission satellite. We find that the hot gas flows along the line of sight relative to the central galaxy, with velocities from 130?km?s?1 to 310?km?s?1 within about 30?kpc of the centre. This indicates bulk flow consistent with core gas sloshing. Although the bulk flow may prevent excessive accumulation of cooled gas at the centre, it could distribute the heat injected by the AGN and bring in thermal energy from the surrounding ICM. The velocity dispersion of the gas is found to be only ?120?km?s?1 in the core, even within about 10?kpc of the AGN. This suggests that the influence of the AGN on the surrounding ICM motion is limited in the cluster.
材料科學Materials Science
Metal-halide porous framework superlattices
金屬鹵化物多孔骨架超晶格
▲ 作者：Wenqiang Zhang, Hong Jiang, Yikuan Liu, Yue Hu, Athulya Surendran Palakkal, Yujie Zhou, et al.
▲ 鏈接：https://www.nature.com/articles/s41586-024-08447-0
▲ 摘要：通過構建具有化學成分空間調制的超晶格結構，可創建具有可定制周期性電勢景觀和可調諧電子和光學特性的人造材料。具有一維可設計電位調制的傳統半導體超晶格實現了高電子遷移率晶體管和量子級聯激光器。
最近，通過多尺度構建單元的自組裝或引導組裝，人們構建了一組多樣化的超晶格，包括零維納米簇和納米顆粒、一維納米棒和納米線、二維納米層和納米片，以及混合二維分子組裝體。這些自組裝超晶格具有二維或三維的周期性結構調制，但由于組成單元之間界面處不可避免的結構無序，通常缺乏原子精度。
研究組報告了由零維、一維和二維構建單元的周期性排列組成的多維單晶超晶格的一鍋合成法。利用鋯（IV）金屬有機骨架作為主模板，通過配位輔助組裝策略實現金屬鹵化物亞晶格的定向成核和精確生長，他們合成了一系列單晶多孔超晶格。
單晶X射線晶體學和高分辨率透射電子顯微鏡清晰地分辨出具有確定性原子坐標的高階超晶格結構。用選定的胺分子進一步處理可產生具有高度可調光致發光和手性光學性質的鈣鈦礦樣超晶格。
該研究創建了一個高階單晶多孔超晶格平臺，為定制傳統晶體固體無法實現的電子、光學和量子特性提供了機遇。
▲ Abstract：The construction of superlattices with a spatial modulation of chemical compositions allows for the creation of artificial materials with tailorable periodic potential landscapes and tunable electronic and optical properties. Conventional semiconductor superlattices with designable potential modulation in one dimension has enabled high-electron-mobility transistors and quantum-cascade lasers. More recently, a diverse set of superlattices has been constructed through self-assembly or guided assembly of multiscale building units, including zero-dimensional nanoclusters and nanoparticles, one-dimensional nanorods and nanowires, two-dimensional nanolayers and nanosheets, and hybrid two-dimensional molecular assemblies. These self-assembled superlattices feature periodic structural modulation in two or three dimensions, but often lack atomic precision owing to the inevitable structural disorder at the interfaces between the constituent units. Here we report a one-pot synthesis of multi-dimensional single-crystalline superlattices consisting of periodic arrangement of zero-, one- and two-dimensional building units. By exploiting zirconium (IV) metal–organic frameworks as host templates for directed nucleation and precise growth of metal-halide sublattices through a coordination-assisted assembly strategy, we synthesize a family of single-crystalline porous superlattices. Single-crystal X-ray crystallography and high-resolution transmission electron microscopy clearly resolve the high-order superlattice structure with deterministic atomic coordinates. Further treatment with selected amine molecules produces perovskite-like superlattices with highly tunable photoluminescence and chiroptical properties. Our study creates a platform of high-order single-crystalline porous superlattices, opening opportunities to tailor the electronic, optical and quantum properties beyond the reach of conventional crystalline solids.
化學Chemistry
Two-dimensional polyaniline crystal with metallic out-of-plane conductivity
具有面外金屬性電導率的二維聚苯胺晶體
▲ 作者：Tao Zhang, Shu Chen, Petko St. Petkov, Peng Zhang, Haoyuan Qi, Nguyen Ngan Nguyen, et al.
▲ 鏈接：https://www.nature.com/articles/s41586-024-08387-9
▲ 摘要：線性導電聚合物表現出由沿聚合物鏈移動的移動載流子施加的彈道傳輸，但由于缺乏分子間有序和電子耦合，在擴展維度（即聚合物鏈或層之間）上的電導率仍然很弱。
研究組報道了一種多層堆疊的二維聚苯胺（2DPANI）晶體，其具有高導電性的面外金屬性電荷輸運。該材料包括層間距為3.59 ?的柱狀π陣列和由聚苯胺鏈交織形成的周期性菱面體晶格。電子自旋共振譜揭示了2DPANI晶格中顯著的電子離域。第一性原理計算表明，Cl -橋接層堆疊促進了2DPANI的面內二維共軛和層間強電子耦合。
為了評估局部光學電導率，研究組使用太赫茲和紅外納米光譜技術來揭示德魯德型電導率，其紅外等離子體頻率及外推的局部直流電導率約為200 S cm?1 。導電掃描探針顯微鏡顯示，其面外電導率異常高，約為15 S cm?1 。通過垂直和橫向微器件進行的電荷傳輸測量顯示，面外電導率（約7 S cm?1 ）和面內電導率（約16 S cm?1 ）相當高。
垂直微器件的電導率隨溫度的降低而增強，表現出獨特的面外金屬性輸運行為。通過使用這種多層堆疊的二維導電聚合物設計，研究組預測在面內相互作用之外實現強電子耦合，有望實現三維金屬性電導率。
▲ Abstract：Linear conducting polymers show ballistic transport, imposed by mobile carriers moving along the polymer chains, whereas conductance in the extended dimension, that is, between polymer strands or layers, remains weak due to the lack of intermolecular ordering and electronic coupling. Here we report a multilayer-stacked two-dimensional polyaniline (2DPANI) crystal, which shows metallic out-of-plane charge transport with high electrical conductivity. The material comprises columnar π arrays with an interlayer distance of 3.59?? and periodic rhombohedral lattices formed by interwoven polyaniline chains. Electron spin resonance spectroscopy reveals significant electron delocalization in the 2DPANI lattices. First-principles calculations indicate the in-plane 2D conjugation and strong interlayer electronic coupling in 2DPANI facilitated by the Cl-bridged layer stacking. To assess the local optical conductivity, we used terahertz and infrared nanospectroscopy to unravel a Drude-type conductivity with an infrared plasma frequency and an extrapolated local d.c. conductivity of around 200?S?cm?1. Conductive scanning probe microscopy showed an unusually high out-of-plane conductivity of roughly 15?S?cm?1. Transport measurements through vertical and lateral micro-devices revealed comparable high out-of-plane (roughly 7?S?cm?1) and in-plane conductivity (roughly 16?S?cm?1). The vertical micro-devices further showed increasing conductivity with decreasing temperature, demonstrating unique out-of-plane metallic transport behaviour. By using this multilayer-stacked 2D conducting polymer design, we predict the achievement of strong electronic coupling beyond in-plane interactions, potentially reaching three-dimensional metallic conductivity.
H-bonded organic frameworks as ultrasound-programmable delivery platform
氫鍵有機框架助力超聲可編程傳輸平臺
▲ 作者：Wenliang Wang, Yanshu Shi, Wenrui Chai, Kai Wing Kevin Tang, Ilya Pyatnitskiy, Yi Xie, et al.
▲ 鏈接：https://www.nature.com/articles/s41586-024-08401-0
▲ 摘要：使用非侵入性超聲精確控制深層組織內的機械化學激活，對于促進人們對基礎生物醫學科學的理解和徹底改變疾病治療策略具有深遠意義。然而，一種具有明確定義超聲激活的理論指導機械響應材料系統尚待探索。
研究組提出了利用多孔氫鍵有機框架（HOFs）作為聚焦超聲（FUS）可編程觸發藥物激活工具包的概念，通過按需裂解超分子相互作用來控制腦深部的特定細胞事件。他們建立了機械化學斷裂和超聲力學的可視化理論模型，為合理設計機械響應材料以實現可編程控制提供了有價值的指導。
為了證明這種方法的實用性，研究組將設計藥物氯氮平N-氧化物（CNO）封裝到用于FUS門控釋放的最佳HOF納米晶體中，以激活小鼠和大鼠腹側被蓋區（VTA）的工程G蛋白偶聯受體，即使在9毫米深度的組織內也能實現靶神經回路調節，潛伏期僅為數秒。
這項工作證明了超聲精確控制分子相互作用的能力，并開發了超聲波可編程的HOF，以非侵入性和時空性地控制細胞事件，有望實現精確分子治療。
▲ Abstract：The precise control of mechanochemical activation within deep tissues using non-invasive ultrasound holds profound implications for advancing our understanding of fundamental biomedical sciences and revolutionizing disease treatments. However, a theory-guided mechanoresponsive materials system with well-defined ultrasound activation has yet to be explored. Here we present the concept of using porous hydrogen-bonded organic frameworks (HOFs) as toolkits for focused ultrasound (FUS) programmably triggered drug activation to control specific cellular events in the deep brain, through on-demand scission of the supramolecular interactions. A theoretical model is developed to potentially visualize the mechanochemical scission and ultrasound mechanics, providing valuable guidelines for the rational design of mechanoresponsive materials to achieve programmable control. To demonstrate the practicality of this approach, we encapsulate the designer drug clozapine N-oxide (CNO) into the optimal HOF nanocrystals for FUS-gated release to activate engineered G-protein-coupled receptors in the ventral tegmental area (VTA) of mice and rats and hence achieve targeted neural circuit modulation even at depth 9?mm with a latency of seconds. This work demonstrates the capability of ultrasound to precisely control molecular interactions and develops ultrasound-programmable HOFs to non-invasively and spatiotemporally control cellular events, thereby facilitating the establishment of precise molecular therapeutic possibilities.
社會學Sociology
Regional and institutional trends in assessment for academic promotion
學術晉升評估的區域和機構趨勢
▲ 作者：B. H. Lim, C. D’Ippoliti, M. Dominik, A. C. Hernández-Mondragón, K. Vermeir, K. K. Chong, et al.
▲ 鏈接：https://www.nature.com/articles/s41586-024-08422-9
▲ 摘要：研究績效評估被廣泛認為是維持最高質量標準的重要工具，人們認為選擇和競爭會推動進步。學術機構在面臨外部研究評估壓力的同時，亟需在招聘和晉升方面做出關鍵決策。
研究組基于190個學術機構的314項政策和58個政府機構的218項政策（涵蓋北半球32個國家和南半球89個國家），對學術職業發展的研究評估進行了展望，特別關注晉升為正教授的政策。他們調查了各種晉升標準被提及的頻率，并進行了統計分析，以推斷各種政策的共性和差異。盡管定量評估方法仍很流行，但與更受地理限制的研究結果一致，其并非適用所有情況。
研究組發現北半球和南半球之間存在差異，機構和國家政策之間亦存在差異，但學科之間的差異較小。中高收入國家對文獻計量指標的偏好更為明顯。
盡管研究組發現了一些差異，但許多晉升政策都基于對已成為規范的特定職業道路進行假設，而非擁抱多樣性。反過來，這限制了研究人員的機會。這些結果挑戰了當前實踐，并對研究人員、研究管理人員和國家政府具有戰略意義。
▲ Abstract：The assessment of research performance is widely seen as a vital tool in upholding the highest standards of quality, with selection and competition believed to drive progress. Academic institutions need to take critical decisions on hiring and promotion, while facing external pressure by also being subject to research assessment. Here we present an outlook on research assessment for career progression with specific focus on promotion to full professorship, based on 314 policies from 190 academic institutions and 218 policies from 58 government agencies, covering 32 countries in the Global North and 89 countries in the Global South. We investigated how frequently various promotion criteria are mentioned and carried out a statistical analysis to infer commonalities and differences across policies. Although quantitative methods of assessment remain popular, in agreement with what is found in more geographically restricted studies, they are not omnipresent. We find differences between the Global North and the Global South as well as between institutional and national policies, but less so between disciplines. A preference for bibliometric indicators is more marked in upper-middle-income countries. Although we see some variation, many promotion policies are based on the assumption of specific career paths that become normative rather than embracing diversity. In turn, this restricts opportunities for researchers. These results challenge current practice and have strategic implications for researchers, research managers and national governments.
本文鏈接：《自然》（20250213出版）一周論文導讀http://www.lensthegame.com/show-11-17393-0.html
聲明：本網站為非營利性網站，本網頁內容由互聯網博主自發貢獻，不代表本站觀點，本站不承擔任何法律責任。天上不會到餡餅，請大家謹防詐騙！若有侵權等問題請及時與本網聯系，我們將在第一時間刪除處理。
上一篇： 美航天局：一顆小行星有2%的概率在2032年撞擊地球
下一篇： 抬頭向西南看！今天金星亮度迎來極值