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发布日期：2024-09-28 作者：开博
Nature, Volume 632 Issue 8026, 22 August 2024《天然》，第632卷，8026期，2024年8月22日
物理学Physics Attosecond delays in X-ray molecular ionization X射线份子电离的阿秒延迟 ▲ 作者：Taran Driver, Miles Mountney, Jun Wang, Lisa Ortmann, Andre Al-Haddad, Nora Berrah, Christoph Bostedt, Elio G. Champenois, Louis F. DiMauro, Joseph Duris, Douglas Garratt, James M. Glownia, Zhaoheng Guo, Daniel Haxton, Erik Isele, Igor Ivanov, Jiabao Ji, Andrei Kamalov, Siqi Li, Ming-Fu Lin, Jon P. Marangos, Razib Obaid, Jordan T. O Neal, Philipp Rosenberger, James P. Cryan Show authors ▲ 链接：https://www.nature.com/articles/s41586-024-07771-9 ▲ 摘要：光电效应并不是真正瞬时的，而是表示出阿秒的延迟，可以揭露复杂的份子动力学。亚飞秒延续时候的光脉冲为解决光电离动力学供给了需要的东西。曩昔十年，人们对单光子接收极紫外光子后的光电离延迟进行了年夜量的研究。但是，丈量时候分辩核能级的光离依然遥不成和。所需的X射线光子能量所需的焦点级光电离是不成用阿秒桌面源。 研究者陈述了对焦点能级电子的X射线光发射延迟的丈量，其延迟出乎料想地年夜，在氧K壳层阈值四周的NO中高达700阿秒（1阿秒=10-18秒）。这些丈量操纵来自自由电子激光器的阿秒软X射线脉冲扫描K壳层阈值四周的全部区域。 研究者还发现延迟谱是丰硕调制的，这注解有几个进献，包罗因为外形共振引发的光电子的瞬态捕捉，在份子的快速非辐射弛豫中发射的与奥格-迈特纳电子的碰撞和多电子散射效应。成果注解，在综公道论模子的撑持下，X射线阿秒尝试可以揭露核能级光电离复杂的相干动力学。 ▲ Abstract：The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700?as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization. A hot-emitter transistor based on stimulated emission of heated carriers 基在受热载流子受激起射的热发射极晶体管 ▲ 作者：Chi Liu, Xin-Zhe Wang, Cong Shen, Lai-Peng Ma, Xu-Qi Yang, Yue Kong, Wei Ma, Yan Liang, Shun Feng, Xiao-Yue Wang, Yu-Ning Wei, Xi Zhu, Bo Li, Chang-Ze Li, Shi-Chao Dong, Li-Ning Zhang, Wen-Cai Ren, Dong-Ming Sun Hui-Ming Cheng▲ 链接：https://www.nature.com/articles/s41586-024-07785-3 ▲摘要：热载流子晶体管是一类操纵载流子的过剩动能的器件。与依靠稳态载流子传输的常规晶体管分歧，热载流子晶体管将载流子调制到高能状况，从而提高了器件的速度和功能。这些特征对需要快速切换和高频操作的利用相当主要，例如进步前辈的电信和尖真个计较手艺。 但是，传统的热载流子发生机制要末是载流子注入，要末是加快，这在功耗和负差分电阻方面限制了器件机能。夹杂维器件连系了年夜块材料和低维材料，可以经由过程操纵由能带组合构成的各类势垒，为热载流子发生供给分歧的机制。 研究者陈述了一种基在双夹杂维石墨烯/锗肖特基结的热发射极晶体管，该晶体管操纵受热载流子的受激起射，实现了跨越玻尔兹曼极限的每十年低在1毫伏的亚阈值摆幅，和在室温下峰谷电流比年夜在100的负差分电阻。进一步演示了具有高逆变增益和可重构逻辑状况的多值逻辑。 这项工作陈述了一种多功能热发射极晶体管，具有低功耗和负差分电阻利用的庞大潜力，标记着后摩尔时期的一个有但愿的前进。 ▲ Abstract：Hot-carrier transistors are a class of devices that leverage the excess kinetic energy of carriers. Unlike regular transistors, which rely on steady-state carrier transport, hot-carrier transistors modulate carriers to high-energy states, resulting in enhanced device speed and functionality. These characteristics are essential for applications that demand rapid switching and high-frequency operations, such as advanced telecommunications and cutting-edge computing technologies. However, the traditional mechanisms of hot-carrier generation are either carrier injection or acceleration, which limit device performance in terms of power consumption and negative differential resistance. Mixed-dimensional devices, which combine bulk and low-dimensional materials, can offer different mechanisms for hot-carrier generation by leveraging the diverse potential barriers formed by energy-band combinations. Here we report a hot-emitter transistor based on double mixed-dimensional graphene/germanium Schottky junctions that uses stimulated emission of heated carriers to achieve a subthreshold swing lower than 1?millivolt per开博体育 decade beyond the Boltzmann limit and a negative differential resistance with a peak-to-valley current ratio greater than 100 at room temperature. Multi-valued logic with a high inverter gain and reconfigurable logic states are further demonstrated. This work reports a multifunctional hot-emitter transistor with significant potential for low-power and negative-differential-resistance applications, marking a promising advancement for the post-Moore era. 生态学Ecology Unforeseen plant phenotypic diversity in a dry and grazed world 干旱和放牧世界中不成预感的植物表型多样性 ▲ 作者：Nicolas Gross, Fernando T. Maestre, Pierre Liancourt, Miguel Berdugo, Rapha?l Martin, Beatriz Gozalo, Victoria Ochoa, Manuel Delgado-Baquerizo, Vincent Maire, Hugo Saiz, Santiago Soliveres, Enrique Valencia, David J. Eldridge, Emilio Guirado, Franck Jabot, Sergio Asensio, Juan J. Gait n, Miguel Garc a-G mez, Paloma Mart nez, Jaime Mart nez-Valderrama, Betty J. Mendoza, Eduardo Moreno-Jim nez, David S. Pescador, C sar Plaza,Yoann Le Bagousse-Pinguet▲ 链接：https://www.nature.com/articles/s41586-024-07731-3 ▲摘要：地球具有不凡的植物表型多样性，但正遭到延续的全球转变的要挟。但是，今朝尚不清晰日趋增添的干旱和畜生放牧压力 这两个全球转变的首要驱动身分 若何塑造植物表型多样性根本上的性状共变。研究者评估了全球干旱地域20种化学和形态特点的共变对干旱和放牧压力的响应。 他们的阐发触及6年夜洲326个样地查询拜访的301种多年生植物的133769个性状丈量值，1347个不雅测值。跨越约0.7的干旱阈值(接近半干旱区和干旱区之间的过渡)致使性状多样性不测增添88%。这个阈值呈现在放牧动物存在的环境下，并跟着放牧压力的增添向较低的干旱程度移动。 另外，57%不雅察到的性状多样性仅产生在最干旱和放牧的旱地，凸起了这些极端情况的表型怪异性。研究注解，旱地是全球植物表型多样性的贮存库，挑战了卑劣情况前提下降植物性状多样性的遍及不雅点。他们还强调，很多替换策略可能使植物可以或许应对天气转变和地盘操纵集约化引发的情况压力增添。 ▲ Abstract：Earth harbours an extraordinary plant phenotypic diversity1 that is at risk from ongoing global changes. However, it remains unknown how increasing aridity and livestock grazing pressure two major drivers of global change shape the trait covariation that underlies plant phenotypic diversity. Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity. They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification. Low-latitude mesopelagic nutrient recycling controls productivity and export 低纬度中上层的营养轮回节制着出产力和出口 ▲ 作者：Keith B. Rodgers, Olivier Aumont, Katsuya Toyama, Laure Resplandy, Masao Ishii, Toshiya Nakano, Daisuke Sasano, Daniele Bianchi Ryohei Yamaguchi ▲ 链接：https://www.nature.com/articles/s41586-024-07779-1 ▲ 摘要：低纬度海洋（LL）占全球净低级出产和出口的一半。研究认为，南年夜洋主导着海洋低级出产和出口，这对全球低级出产和出口对天气转变的响应具有启迪意义。新研究对单个模子进行了不雅察阐发和敏感性研究，成果注解，72%的LL低级出产和55%的出口受本地中上层宏量营养素轮回的节制。 整体而言，34%的LL输出是由南年夜洋供给的预构成的年夜量营养物资保持的，这些营养物资经由过程较深的翻覆单位供给，而浅层预构成的向北供给，穿过南纬30度，经由过程亚极和温跃层水团，仅保持7%的LL输出。 对1850-2300年高排放低减缓[同享社会经济路径（SSP5-8.5）]和低排放高减缓（SSP1-2.6）天气情形下运行的5个耦合模式比对项目第6阶段（CMIP6）模式的阐发注解，它们对LL低级出产的预估不但在幅度上，并且在标记上都存在显著差别。 在更强的SSP5-8.5逼迫下，跟着上层海洋变暖加倍较着，斟酌温度依靠的再矿化感化的CMIP6模式增进了增温前提下LL中上层营养物资潴留的加强，这对不变或增添（而不是削减）高排放低减缓前提下LL产量供给了一级进献。这强调了对中远洋再矿化和其对海洋变暖敏感性的机制理解对猜测将来生态系统转变的主要性。 ▲ Abstract：Low-latitude (LL) oceans account for up to half of global net primary production and export. It has been argued that the Southern Ocean dominates LL primary production and export, with implications for the response of global primary production and export to climate change. Here we applied observational analyses and sensitivity studies to an individual model to show, instead, that 72% of LL primary production and 55% of export is controlled by local mesopelagic macronutrient cycling. A total of 34% of the LL export is sustained by preformed macronutrients supplied from the Southern Ocean via a deeper overturning cell, with a shallow preformed northward supply, crossing 30 ?S through subpolar and thermocline water masses, sustaining only 7% of the LL export. Analyses of five Coupled Model Intercomparison Project Phase 6 (CMIP6) models, run under both high-emissions low-mitigation (shared socioeconomic pathway (SSP5-8.5)) and low-emissions high-mitigation (SSP1-2.6) climate scenarios for 1850 2300, revealed significant across-model disparities in their projections of not only the amplitude, but also the sign, of LL primary production. Under the stronger SSP5-8.5 forcing, with more substantial upper-ocean warming, the CMIP6 models that account for temperature-dependent remineralization promoted enhanced LL mesopelagic nutrient retention under warming, with this providing a first-order contribution to stabilizing or increasing, rather than decreasing, LL production under high emissions and low mitigation. This underscores the importance of a mechanistic understanding of mesopelagic remineralization and its sensitivity to ocean warming for predicting future ecosystem changes. 化学Chemistry The catalytic asymmetric polyene cyclization of homofarnesol to ambrox 同型芳尼醇催化不合错误称多烯环化制氨溴 ▲ 作者：Na Luo, Mathias Turberg, Markus Leutzsch, Benjamin Mitschke, Sebastian Brunen, Vijay N. Wakchaure, Nils N?thling, Mathias Schelwies, Ralf Pelzer Benjamin List ▲ 链接：https://www.nature.com/articles/s41586-024-07757-7 ▲摘要：多烯环化是生物学中最复杂和最具挑战性的转化之一。在一个反映步调中，多个碳碳键、环系统和立体中间由简单的无环前体构成。同时实现这类对产物散布和立体化学的切确节制对化学家来讲是一项艰难的使命。 特殊是，(3E,7E)-同型芳醇的多烯环化成自然存在的有价值的龙柏喷鼻气息剂(?)-降龙涏喷鼻醚被认为是化学合成中持久存在的挑战。 研究者陈述了在氟化醇存鄙人，利用高布朗斯特酸性和限制性咪胺二磷酰化催化剂，经由过程催化不合错误称多烯环化合成(?)-降龙涏喷鼻醚和倍半萜内酯自然产品(+)-喷鼻紫苏内酯的非对映选择性和对映选择性。 包罗氘标识表记标帜研究在内的几个尝试注解，该反映首要经由过程与Stork-Eschenmoser假说一致的路子进行。机理研究注解，咪胺二磷酰化催化剂的酶样微情况对取得异常高的选择性具有主要意义，而之前认为只有在酶催化的多烯环化中才能实现。 ▲ Abstract：Polyene cyclizations are among the most complex and challenging transformations in biology. In a single reaction step, multiple carbon carbon bonds, ring systems and stereogenic centres are constituted from simple, acyclic precursors. Simultaneously achieving this kind of precise control over product distribution and stereochemistry poses a formidable task for chemists. In particular, the polyene cyclization of (3E,7E)-homofarnesol to the valuable naturally occurring ambergris odorant (?)-ambrox is recognized as a longstanding challenge in chemical synthesis. Here we report a diastereoselective and enantioselective synthesis of (?)-ambrox and the sesquiterpene lactone natural product (+)-sclareolide by a catalytic asymmetric polyene cyclization by using a highly Br?nsted-acidic and confined imidodiphosphorimidate catalyst in the presence of fluorinated alcohols. Several experiments, including deuterium-labelling studies, suggest that the reaction predominantly proceeds through a concerted pathway in line with the Stork Eschenmoser hypothesis. Mechanistic studies show the importance of the enzyme-like microenvironment of the imidodiphosphorimidate catalyst for attaining exceptionally high selectivities, previously thought to be achievable only in enzyme-catalysed polyene cyclizations. 人工智能Artificial Intelligence Loss of plasticity in deep continual learning 在深度延续进修中损失可塑性 ▲ 作者：Shibhansh Dohare, J. Fernando Hernandez-Garcia, Qingfeng Lan, Parash Rahman, A. Rupam Mahmood Richard S. Sutton ▲ 链接：https://www.nature.com/articles/s41586-024-07711-7 ▲摘要：人工神经收集、深度进修方式和反向传布算法组成了现代机械进修和人工智能的根本。这些方式几近老是在两个阶段利用，一个阶段是更新收集的权重，另外一个阶段是在利用或评估收集时连结权重不变。这与天然进修和很多需要延续进修的利用构成对照。 今朝还不清晰深度进修方式在延续进修情况中是不是有用。研究者证实了它们并不是如斯 尺度的深度进修方式在延续进修情况中逐步掉去可塑性，直到它们的进修结果不如浅收集。 研究者利用经典的ImageNet数据集和跨收集和进修算法的普遍转变的强化进修问题来显示这类可塑性的损失。只有经由过程不竭向收集中注入多样性的算法，才能无穷期地连结可塑性，例如延续反向传布算法，这是反向传布的一种变体，此中一小部门较少利用的单位不竭地随机从头初始化。 研究成果注解，基在梯度降落的方式是不敷的 延续的深度进修需要一个随机的、非梯度的成份来连结可变性和可塑性。 ▲ Abstract：Artificial neural networks, deep-learning methods and the backpropagation algorithm1 form the foundation of modern machine learning and artificial intelligence. These methods are almost always used in two phases, one in which the weights of the network are updated and one in which the weights are held constant while the network is used or evaluated. This contrasts with natural learning and many applications, which require continual learning. It has been unclear whether or not deep learning methods work in continual learning settings. Here we show that they do not that standard deep-learning methods gradually lose plasticity in continual-learning settings until they learn no better than a shallow network. We show such loss of plasticity using the classic ImageNet dataset and reinforcement-learning problems across a wide range of variations in the network and the learning algorithm. Plasticity is maintained indefinitely only by algorithms that continually inject diversity into the network, such as our continual backpropagation algorithm, a variation of backpropagation in which a small fraction of less-used units are continually and randomly reinitialized. Our results indicate that methods based on gradient descent are not enough that sustained deep learning requires a random, non-gradient component to maintain variability and plasticity.特殊声明：本文转载仅仅是出在传布信息的需要，其实不意味着代表本网站不雅点或证实其内容的真实性；如其他媒体、网站或小我从本网站转载利用，须保存本网站注明的“来历”，并自大版权等法令责任；作者假如不但愿被转载或联系转载稿费等事宜，请与我们联系。