《自然》揭露“大科学”背后沉重真相：团队规模与颠覆性创新反相关

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《自然》揭露“大科学”背后沉重真相：团队规模与颠覆性创新反相关

《自然》（20210729出版）一周论文导读

《自然》（20210408出版）一周论文导读

《科学》和《自然》杂志是怎么回事？

一、《自然》揭露“大科学”背后沉重真相：团队规模与颠覆性创新反相关

《自然》发文揭开“大科学”背后的沉重真相

作者 | 华春雷

英国《自然》杂志Letter栏目发表了（中国时间2月14日, 英国时间2月13日）一篇重量级的调查统计性的论文Large teams develop and small teams disrupt science and technology（《大型团队成长性发展科学技术 小型团队则破坏性创造科学技术》) 。

论文作者是：Lingfei Wu, Dashun Wang, James A. Evans （中文音译：吴凌峰、王大顺、詹姆斯·艾文, 前两位可能是华人，了不起！)。

论文分析了60年来（1954年~2014年）6500多万篇论文/专利/软件等，提出了一个重大的研究结论：大型科研团队更多地在比较成熟的前沿领域做后续的成长性的工作, 而独立科学家或小型团队往往更专注于还不成熟的前沿领域和真正的巅覆性创新。

他们的统计发现，团队规模与影响力呈正相关性，但与颠覆性创新呈反相关性。

参考链接: https:///articles/s41586-019-0941-9?wpisrc=nl_science&wpmm=1

这篇论文非常重要，研究者以他们富有说服力的统计数据，揭开了隐藏在“大科学背后的沉重的真相”，说明大研究团队更重视和追求在科学技术领域中的那些现实影响力和知名度很大的项目。

这种项目往往在当时那个时代很风光，舆论度高，媒体更关注，往往是热点，往往是焦点，往往是记者追逐的对象，也往往容易受到投资人的关切和政府的支持

这种项目获得资金更容易，获得的金额量巨大。各种奖金奖励等也往往将聚光灯照向他们。

但是令人深思的事实是，那些科学领域中不知名的独立学者或小团队，却在科学和技术的最前沿的天际线上拓荒和耕作。

他们在选择研究课题上，往往更重视真正的难题和最尖端性问题，因此他们才真正承担了科学前沿区的最大的风险性。

正是他们的努力和工作，才维持了科学的后驱力，维持了科学的生命力。

但是，他们却往往得不到舆论的关注，没有记者的注意，无法被聚光灯照射，在资金上也往往更困难。

这就是该论文所揭示的当今科学界原始森林中的沉重的生态真相。

特别需要说明的是，在科技发展的组织方式上，多数舆论对“大科学”的组织模式往往给予过多的虚夸赞美，严重脱离实际，而对“小科学”往往当做是过时的组织模式给予贬低。

但愿这篇重量级的论文给这种“以大为美”的头脑发热，泼上一盆清醒的凉水。

转载本文请联系原作者获取授权，同时请注明本文来自华春雷科学网博客。

链接地址：http://blog.sciencenet.cn/blog-2910327-1162214.html

请按下方二维码3秒识别

一、《自然》（20210729出版）一周论文导读

编译 | 未玖

Nature , 29 July 2021, VOL 595 , ISSUE 7869

《自然》 2021年7月29日，第595卷，7869期

天文学 Astronomy

Light bending and X-ray echoes from behind a supermassive black hole

超大质量黑洞背后的光弯曲和X射线回声

作者： D. R. Wilkins, L. C. Gallo, E. Costantini, W. N. Brandt & R. D. Blandford

链接：

摘要

黑洞周围吸积盘的最内层区域受到X射线的强烈辐射，这些X射线是由黑洞附近一个高度可变的致密冕区发射出来的。吸积盘反射的X射线和时间延迟提供了事件视界外的环境视图。IZwicky1（IZw1）是附近的窄线赛弗特1星系。

先前对来自吸积盘的X射线混响的研究表明，冕区由两部分组成：一个扩展的、缓慢变化的组成部分，延伸到内部吸积盘的表面；以及一个准直的核心，其光度波动从底部向上传播，主导着更快速的变化。

研究组报告了在IZw1中超大质量黑洞周围发射的X射线耀斑的观测结果。他们通过X射线发射谱中相对展宽的铁K线和康普顿峰，探测到来自吸积盘的X射线反射。对X射线耀斑的分析揭示了光子的短暂闪烁，与黑洞后面重新出现的辐射相一致。

这些光子的能级移动确定了它们来自吸积盘的不同部分。这些光子在吸积盘的远端反射，在黑洞周围弯曲并被强大的引力场放大。观察黑洞周围弯曲的光子证实了广义相对论的一个关键预测。

Abstract

The innermost regions of accretion disks around black holes are strongly irradiated by X-rays that are emitted from a highly variable, compact corona, in the immediate vicinity of the black hole. The X-rays that are seen reflected from the disk, and the time delays, provide a view of the environment just outside the event horizon. I Zwicky 1 (I Zw 1) is a nearby narrow-line Seyfert 1 galaxy. Previous studies of the reverberation of X-rays from its accretion disk revealed that the corona is composed of two components: an extended, slowly varying component extending over the surface of the inner accretion disk, and a collimated core, with luminosity fluctuations propagating upwards from its base, which dominates the more rapid variability. Here we report observations of X-ray flares emitted from around the supermassive black hole in I Zw 1. X-ray reflection from the accretion disk is detected through a relativistically broadened iron K line and Compton hump in the X-ray emission spectrum. Analysis of the X-ray flares reveals short flashes of photons consistent with the re-emergence of emission from behind the black hole. The energy shifts of these photons identify their origins from different parts of the disk. These are photons that reverberate off the far side of the disk, and are bent around the black hole and magnified by the strong gravitational field. Observing photons bent around the black hole confirms a key prediction of general relativity.

材料科学 Materials Science

Spectroscopic evidence for a gold-coloured metallic water solution

金色金属水溶液的光谱证据

作者：Philip E. Mason, H. Christian Schewe, Tillmann Buttersack, Vojtech Kostal, Marco Vitek, Ryan S. McMullen, et al.

链接：

摘要

绝缘材料原则上可以通过施加压力制成金属。如果是纯水，估计需要48兆巴的压力，这超出了目前的实验能力，可能只存在于大型行星或恒星的内部。事实上，最近的估计和实验表明，在实验室可达到的压力下，水充其量是只具有高质子导电性的超离子水，而不是具有导电电子的金属水。

研究组表明，在水与碱金属反应时，通过大量掺杂电子可制备金属水溶液。尽管具有高浓度溶剂化电子的液氨类似金属溶液早已为人所知并被表征，但碱金属与水之间的爆炸性相互作用迄今为止仅允许制备具有较低的亚金属电子浓度的水溶液。

研究组发现，水-碱金属反应的爆炸行为可以通过在1 0-4 毫巴的低压下将水蒸气吸附到真空室喷射的钠-钾合金液滴上来抑制。这种设计导致在金属合金液滴表面形成短暂的金色金属水液层。利用光学反射和同步辐射X射线光电子能谱证实了该液层的金属特性，每立方厘米掺杂约5 1 021 个电子。

Abstract

Insulating materials can in principle be made metallic by applying pressure. In the case of pure water, this is estimated to require a pressure of 48 megabar, which is beyond current experimental capabilities and may only exist in the interior of large planets or stars. Indeed, recent estimates and experiments indicate that water at pressures accessible in the laboratory will at best be superionic with high protonic conductivity, but not metallic with conductive electrons. Here we show that a metallic water solution can be prepared by massive doping with electrons upon reacting water with alkali metals. Although analogous metallic solutions of liquid ammonia with high concentrations of solvated electrons have long been known and characterized, the explosive interaction between alkali metals and water has so far only permitted the preparation of aqueous solutions with low, submetallic electron concentrations. We found that the explosive behaviour of the water–alkali metal reaction can be suppressed by adsorbing water vapour at a low pressure of about 1 0-4 millibar onto liquid sodium–potassium alloy drops ejected into a vacuum chamber. This set-up leads to the formation of a transient gold-coloured layer of a metallic water solution covering the metal alloy drops. The metallic character of this layer, doped with around 5 1 021 electrons per cubic centimetre, is confirmed using optical reflection and synchrotron X-ray photoelectron spectroscopies.

Linear-in temperature resistivity from an isotropic Planckian scattering rate

各向同性普朗克散射率的线性温度电阻率

作者：Gaël Grissonnanche, Yawen Fang, Anaëlle Legros, Simon Verret, Francis Laliberté, Clément Collignon, et al.

链接：

摘要

传统金属的电阻率随温度呈二次方下降，而各种“奇异金属”的电阻率当温度降至零时却随温度呈线性下降。这种线性温度电阻率归因于电荷载流子以 ħ/τ = αkBT 给出的速率散射，α为统一阶常数，ħ为普朗克常数， kB 为玻尔兹曼常数。

散射率和温度之间的这种简单关系在各种各样的材料中都可以观察到，这表明散射的基本上限是“普朗克极限”，但对这个极限的根本起源，人们知之甚少。

研究组报告了对 La1.6 xNd0.4SrxCuO4 （一种空穴掺杂铜酸盐）的角相关磁阻测量，在最低测量温度下呈现出线性温度电阻率。角相关磁阻显示了一个明确定义的费米面，该面与角分辨光电子能谱测量结果定量一致，并显示了在普朗克极限下饱和的线性温度散射率，即α=1.2 0.4。

值得注意的是，研究组发现这个普朗克散射率是各向同性的，也就是说，它与方向无关，这与“热点”模型的预期相反。该研究表明，奇异金属的线性温度电阻率源于达到普朗克极限的与动量无关的非弹性散射率。

Abstract

A variety of ‘strange metals’ exhibit resistivity that decreases linearly with temperature as the temperature decreases to zero, in contrast to conventional metals where resistivity decreases quadratically with temperature. This linear-in-temperature resistivity has been attributed to charge carriers scattering at a rate given by ħ/τ = αkBT , where α is a constant of order unity, ħ is the Planck constant and kB is the Boltzmann constant. This simple relationship between the scattering rate and temperature is observed across a wide variety of materials, suggesting a fundamental upper limit on scattering—the ‘Planckian limit’—but little is known about the underlying origins of this limit. Here we report a measurement of the angle-dependent magnetoresistance of La1.6 xNd0.4SrxCuO4 —a hole-doped cuprate that shows linear-in-temperature resistivity down to the lowest measured temperatures. The angle-dependent magnetoresistance shows a well defined Fermi surface that agrees quantitatively with angle-resolved photoemission spectroscopy measurements and reveals a linear-in-temperature scattering rate that saturates at the Planckian limit, namely α = 1.2 0.4. Remarkably, we find that this Planckian scattering rate is isotropic, that is, it is independent of direction, in contrast to expectations from ‘hotspot’ models. Our findings suggest that linear-in-temperature resistivity in strange metals emerges from a momentum-independent inelastic scattering rate that reaches the Planckian limit.

Incoherent transport across the strange-metal regime of overdoped cuprates

过掺杂铜酸盐奇异金属区的非相干输运

作者：J. Ayres, M. Berben, M. Čulo, Y.-T. Hsu, E. van Heumen, Y. Huang, et al.

链接：

摘要

奇异金属具有非常规的电学性质，如线性温度电阻率、随温度平方变化的逆霍尔角和线性场磁电阻。即使是在具有简单能带结构的空穴掺杂铜酸盐材料中，确定这些集体异常的起源也颇有难度。普遍共识是，铜酸盐中奇异金属丰度与超导圆顶内掺杂p*处的量子临界点有关。

课题组研究了两个掺杂水平超过p*的超导铜酸盐家族的高场面内磁阻。在所有掺杂中，磁阻呈现正交标度，在高场温比下变为线性，这表明奇异金属区域远远超出p*。

此外，磁阻的大小比传统理论预测的要大得多，并且对杂质散射和磁场方向都不敏感。这些观察结果，再加上对零场和霍尔电阻的分析，均表明尽管铜酸盐奇异金属区域只有一个带，但它有两个电荷区，一个包含相干准粒子，另一个包含标度不变的“普朗克”耗散体。

Abstract

Strange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity, an inverse Hall angle that varies as temperature squared and a linear-in-field magnetoresistance. Identifying the origin of these collective anomalies has proved fundamentally challenging, even in materials such as the hole-doped cuprates that possess a simple bandstructure. The prevailing consensus is that strange metallicity in the cuprates is tied to a quantum critical point at a doping p* inside the superconducting dome. Here we study the high-field in-plane magnetoresistance of two superconducting cuprate families at doping levels beyond p*. At all dopings, the magnetoresistance exhibits quadrature scaling and becomes linear at high values of the ratio of the field and the temperature, indicating that the strange-metal regime extends well beyond p*. Moreover, the magnitude of the magnetoresistance is found to be much larger than predicted by conventional theory and is insensitive to both impurity scattering and magnetic field orientation. These observations, coupled with analysis of the zero-field and Hall resistivities, suggest that despite having a single band, the cuprate strange-metal region hosts two charge sectors, one containing coherent quasiparticles, the other scale-invariant ‘Planckian’ dissipators.

化学 Chemistry

A radical approach for the selective C–H borylation of azines

氮杂芳环选择性C-H硼化反应的自由基途径

作者：Ji Hye Kim, Timothée Constantin, Marco Simonetti, Josep Llaveria, Nadeem S. Sheikh & Daniele Leonori

链接：

摘要

硼官能团通常被引入取代芳香碳氢键，以通过分子片段的偶联加速小分子多样化。目前基于过渡金属催化碳氢键活化的方法对许多（杂）芳香族衍生物的硼化是有效的，但对氮杂芳环（含氮芳香族杂环）的适用性有限，而氮杂芳环是许多医药和农药产品的关键成分。

研究组报告了一种使用稳定且廉价的胺硼烷试剂的氮杂芳环硼化策略。光催化作用将这些低分子量材料转化为高活性的硼自由基，并将其有效地添加到氮杂芳环构建块中。

这种反应活性为s p2 碳-硼键组装提供了一种机械上的替代策略，其中过渡金属介导的碳-氢键活化和氮杂芳环有机金属中间体的还原消除的基本步骤被直接的、Minisci式的自由基加成所取代。

胺-硼基自由基的强亲核特性通过靶向氮杂芳环最活跃的位置，包括与碱性氮原子相邻的具有挑战性的位置，使碳-硼键的形成具有可预测性和位置选择性。这种方法使目前基于碳氢键活化策略无法靠近的芳香族位置得以靠近，并成功制备出硼化材料，否则将很难制备。

研究组已将此工艺应用于将胺-硼烷官能团引入复杂和工业相关产品中。主流交叉偶联技术使硼化氮杂芳环产品多样化，从而使芳香族氨基硼烷成为化学合成的重要组成部分。

Abstract

Boron functional groups are often introduced in place of aromatic carbon–hydrogen bonds to expedite small-molecule persification through coupling of molecular fragments. Current approaches based on transition-metal-catalysed activation of carbon–hydrogen bonds are effective for the borylation of many (hetero)aromatic derivatives but show narrow applicability to azines (nitrogen-containing aromatic heterocycles), which are key components of many pharmaceutical and agrochemical products. Here we report an azine borylation strategy using stable and inexpensive amine-borane reagents. Photocatalysis converts these low-molecular-weight materials into highly reactive boryl radicals that undergo efficient addition to azine building blocks. This reactivity provides a mechanistically alternative tactic for s p2 carbon–boron bond assembly, where the elementary steps of transition-metal-mediated carbon–hydrogen bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci-style, radical addition. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective carbon–boron bond formation by targeting the azine’s most activated position, including the challenging sites adjacent to the basic nitrogen atom. This approach enables access to aromatic sites that elude current strategies based on carbon–hydrogen bond activation, and has led to borylated materials that would otherwise be difficult to prepare. We have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The persification of the borylated azine products by mainstream cross-coupling technologies establishes aromatic amino-boranes as a powerful class of building blocks for chemical synthesis.

地球科学 Earth Science

A process-based approach to understanding and managing triggered seismicity

用基于过程的方法来理解和管理人为触发的地震活动

作者：Bradford H. Hager, James Dieterich, Cliff Frohlich, Ruben Juanes, Stefano Mantica, John H. Shaw, et al.

链接：

摘要

人们越来越担心由人类活动引发的地震活动，即应力的微小增加会导致构造承载的断层破裂。这些人类活动包括采矿、蓄水、开发地热田、提取碳氢化合物和水，以及向地下储层注入水、C O2 和C H4 等。

在缺乏足够信息来理解和控制人为触发地震过程的情况下，政府建立了基于经验监管的框架，并取得了不同程度的成功。20世纪70年代初在美国科罗拉多州Rangely油田进行的现场试验表明，地震活动可能通过循环地下流体压力高于或低于某阈值来开启或关闭。

研究组报告了一种多学科方法的开发、测试和实施，用于管理人为触发的地震活动，使用全面和详细的地下信息来校准地质力学和震源物理学模型。然后，他们通过将这些模型的预测结果与校准后的后续观测结果进行比较，来进行验证。

研究组在意大利南部地震活跃的Val d'Agri油田使用了该模型，证明了基于过程的方法可成功管理人为触发的地震活动，并将其应用于油气田开发。在其他地方应用该方法亦有助于管理和减轻人为触发的地震活动。

Abstract

There is growing concern about seismicity triggered by human activities, whereby small increases in stress bring tectonically loaded faults to failure. Examples of such activities include mining, impoundment of water, stimulation of geothermal fields, extraction of hydrocarbons and water, and the injection of water, C O2 and methane into subsurface reservoirs. In the absence of sufficient information to understand and control the processes that trigger earthquakes, authorities have set up empirical regulatory monitoring-based frameworks with varying degrees of success. Field experiments in the early 1970s at the Rangely, Colorado (USA) oil field suggested that seismicity might be turned on or off by cycling subsurface fluid pressure above or below a threshold. Here we report the development, testing and implementation of a multidisciplinary methodology for managing triggered seismicity using comprehensive and detailed information about the subsurface to calibrate geomechanical and earthquake source physics models. We then validate these models by comparing their predictions to subsequent observations made after calibration. We use our approach in the Val d’Agri oil field in seismically active southern Italy, demonstrating the successful management of triggered seismicity using a process-based method applied to a producing hydrocarbon field. Applying our approach elsewhere could help to manage and mitigate triggered seismicity.

二、《自然》（20210408出版）一周论文导读

编译 | 李言

Nature , 8 April 2021, Volume 592 Issue 7853

《自然》 2021年4月8日，第592卷，7853期

天文学 Astronomy

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

在炎热巨型行星大气层中的五种含碳和氮的物质

作者：Paolo Giacobbe, Matteo Brogi, Siddharth Gandhi, Patricio E. Cubillos, et al.

链接：

摘要

先前对热木星的观测表明，它们在其主星前面经过时大气层中经常存在水蒸气和一氧化碳；这已经通过在通常的化学平衡假设下根据太阳的比例组成进行了研究。

氰化氢和这两种分子都在HD 209458b的大气中被发现。HD 209458b是一个被充分研究过的热木星（平衡温度在1500 k左右），曾经检测出氨，但随后被否认。

在此，我们报告HD 209458b的观察结果，显示存在水、一氧化碳、氰化氢、甲烷、氨和乙炔，每个分子5.3到9.9个标准偏差。辐射和化学平衡的大气模型表明，探测到的物质具有富碳化学成分，碳氧比接近或大于1，高于太阳的值（0.55）。

根据现有的关于大气化学与行星形成和迁移情景的模型，这可能表明HD 209458b在远离目前位置的地方形成，随后向内迁移。

Abstract

Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour and carbon monoxide in their atmospheres; this has been studied in terms of scaled solar composition under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there and subsequently refuted. Here we report observations of HD 209458b that indicate the presence of water ( H2 O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (C H4 ), ammonia (N H3 ) and acetylene ( C2H2 ), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards.

考古学 Archaeology

Innovative Homo sapiens behaviours 105,000 years ago in a wetter Kalahari

发生在105000年前卡拉哈里盆地中的人类创新行为

作者：Jayne Wilkins, Benjamin J. Schoville, Robyn Pickering, Luke Gliganic, et al.

链接：

摘要

非洲的考古记录为智人复杂的符号和技术行为的出现提供了最早的证据。然而，保存完好、年代学较强的晚更新世地层遗址在南非内陆非常罕见，因此海岸假说仍未得到验证。

在此，我们展示了与大约10.5万年前南部非洲沿海地区的人类发明相似的早期人类发明，他们大约在同一时期生活在600多公里外的内陆地区。我们报告了有意收集非实用物体（方解石晶体）和鸵鸟蛋壳的证据。

这些证据来自对于卡拉哈里盆地南部的一个层状岩石矿床的挖掘现场，我们通过光释光测年技术确定其距今约10.5万年。残存凝灰岩矿床的铀钍定年法表明，这里偶尔会有大量淡水流动；这些岩层中最古老的可以追溯到11至10万年之间，与考古发现相一致。

我们的结果表明，南部非洲内陆人类的创新行为并不落后于靠近海岸的人群，而且这些创新行为可能是在潮湿的大草原环境中发展起来的。

Abstract

The archaeological record of Africa provides the earliest evidence for the emergence of the complex symbolic and technological behaviours that characterize Homo sapiens. However, stratified Late Pleistocene sites with good preservation and robust chronologies are rare in the interior of southern Africa, and the coastal hypothesis therefore remains untested. Here we show that early human innovations that are similar to those dated to around 105 thousand years ago (ka) in coastal southern Africa existed at around the same time among humans who lived over 600 km inland. We report evidence for the intentional collection of non-utilitarian objects (calcite crystals) and ostrich eggshell from excavations of a stratified rockshelter deposit in the southern Kalahari Basin, which we date by optically stimulated luminescence to around 105 ka. Uranium–thorium dating of relict tufa deposits indicates sporadic periods of substantial volumes of fresh, flowing water; the oldest of these episodes is dated to between 110 and 100 ka and is coeval with the archaeological deposit. Our results suggest that behavioural innovations among humans in the interior of southern Africa did not lag behind those of populations near the coast, and that these innovations may have developed within a wet savannah environment.

材料科学 Material Science

Entropic evidence for a Pomeranchuk effect in magic-angle graphene

魔角石墨烯中波梅兰丘克效应的熵证据

作者：Asaf Rozen, Jeong Min Park, Uri Zondiner, Yuan Cao, Daniel Rodan-Legrain, et al.

链接：

摘要

20世纪50年代，波梅兰丘克预测，液态氦-3加热后可能会凝固，这与我们的直觉相反。这种效应是由于固相中原子在空间局部的高过量核自旋熵引起的。在此，我们发现在魔角扭曲双层石墨烯中也发生了类似的效应。

使用局部和全局电子熵测量，我们发现，在每摩尔单胞填充近一个电子时，电子熵显著增加到约每单胞1 k B。这个巨大的过量熵被指向其磁源的平面内磁场淬灭。可压缩性随电子密度的变化而急剧下降，伴随着费米能级的重置回到狄拉克点附近，标志着两相之间的清晰边界。

我们将这种跃变映射为电子密度，温度和磁场的函数。这揭示了一个相图，与波梅兰丘克一样，温度和磁场驱动了从低熵电子液体到具有几乎自由磁矩的高熵相关态转变。

相关态的特征是表面上相互矛盾性质的不寻常组合，一些与流动的电子有关——例如缺乏热力学间隙、金属性和狄拉克式的可压缩性——另一些与局部矩有关，例如大的熵及其在磁场下的消失。

Abstract

In the 1950s, Pomeranchuk predicted that, counterintuitively, liquid 3He may solidify on heating. This effect arises owing to high excess nuclear spin entropy in the solid phase, where the atoms are spatially localized. Here we find that an analogous effect occurs in magic-angle twisted bilayer graphene. Using both local and global electronic entropy measurements, we show that near a filling of one electron per moiré unit cell, there is a marked increase in the electronic entropy to about 1 k B per unit cell ( k B is the Boltzmann constant). This large excess entropy is quenched by an in-plane magnetic field, pointing to its magnetic origin. A sharp drop in the compressibility as a function of the electron density, associated with a reset of the Fermi level back to the vicinity of the Dirac point, marks a clear boundary between two phases. We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram that is consistent with a Pomeranchuk-like temperature- and field-driven transition from a low-entropy electronic liquid to a high-entropy correlated state with nearly free magnetic moments. The correlated state features an unusual combination of seemingly contradictory properties, some associated with itinerant electrons—such as the absence of a thermodynamic gap, metallicity and a Dirac-like compressibility—and others associated with localized moments, such as a large entropy and its disappearance under a magnetic field.

Isospin Pomeranchuk effect in twisted bilayer graphene

扭曲双层石墨烯的同位旋波梅兰丘克效应

作者：Yu Saito, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Takashi Taniguchi, Kenji Watanabe, et al.

链接：

摘要

在此，我们展示了一种机制来描述魔角扭曲双层石墨烯中自旋和波谷同位旋的有限温度动力学。

值得注意的是，在超晶格填充因子 1附近，高温时电阻率出现峰值，而在低温极限时则没有出现相应的相。倾斜磁场的磁输运和面内磁矩的热力学测量表明，电阻率峰值与系统发展为有限同位旋极化的有限场磁相变有关。这些数据提示了一种波梅兰丘克型机制。

在这种机制中，相对于同位旋未极化的费米液相，铁磁相中的无序同位旋矩的熵在更高的温度下使相稳定。

Abstract

Here we show that a similar mechanism describes the finite-temperature dynamics of spin and valley isospins in magic-angle twisted bilayer graphene. Notably, a resistivity peak appears at high temperatures near a superlattice filling factor of 1, despite no signs of a commensurate correlated phase appearing in the low-temperature limit. Tilted-field magnetotransport and thermodynamic measurements of the in-plane magnetic moment show that the resistivity peak is connected to a finite-field magnetic phase transition at which the system develops finite isospin polarization. These data are suggestive of a Pomeranchuk-type mechanism, in which the entropy of disordered isospin moments in the ferromagnetic phase stabilizes the phase relative to an isospin-unpolarized Fermi liquid phase at higher temperatures.

Diversity-oriented synthesis of polymer membranes with ion solvation cages

基于离子溶剂化聚合物膜的多样性取向合成

作者：Miranda J. Baran, Mark E. Carrington, Swagat Sahu, Artem Baskin, Junhua Song, et al.

链接：

摘要

在此，我们描述了一种面向多样性的微孔聚合物膜合成策略，以识别具有FVEs的候选材料，作为锂离子的溶剂笼。

这一策略包括通过曼尼希反应使双联邻苯二酚单体多样化，从而在FVEs中引入锂离子协调功能，加强拓扑聚合使FVEs进入不同的孔结构，以及多种多样的孔几何和介电性能的聚合物反应。

具有离子溶剂化笼的候选膜比控制膜具有更高的离子电导率和更高的阳离子转移数，其中FVEs具有特异性，表明可以克服常规的膜渗透性边界和离子转移的选择性。

Abstract

Here we describe a persity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li+). This strategy includes persification of bis(catechol) monomers by Mannich reactions to introduce Li+-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for persifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome.

地球科学 Geoscience

A 200-million-year delay in permanent atmospheric oxygenation

延迟了2亿年的永久大气氧化

作者：Simon W. Poulton, Andrey Bekker, Vivien M. Cumming, Aubrey L. Zerkle, Donald E. Canfield & David T. Johnston

链接：

摘要

早期大气氧化发生在以多次全球冰期为标志的长期极端气候不稳定时期，氧浓度最初上升到目前大气水平的 10- 5 以上的时间则推定为24.3亿年前。然而，随后大气氧含量的波动一直持续到大约23.2亿年前，这代表了大气中不可逆氧化的估计时间。

在此，我们通过南非德兰士瓦尔超群的海洋沉积物，对古代早期最后两次冰期的大气和局部海洋氧化还原条件进行了高分辨率重建。利用多重硫同位素和铁-硫-碳系统，我们证明了大约23.2亿年前之后大气氧水平的持续振荡，这与海洋氧化还原化学和气候的主要扰动有关。

因此，在大约2亿年的时间里，氧气水平在目前大气水平的 10- 5 的阈值上下波动。永久的大氧化事件比目前估计的晚了大约1亿年。

Abstract

Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations, with the initial rise of oxygen concentration to above 10- 5 of the present atmospheric level constrained to about 2.43 billion years ago. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago, which represents the estimated timing of irreversible oxygenation of the atmosphere. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10- 5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

三、《科学》和《自然》杂志是怎么回事？

《科学》是美国科学促进会出版的一份学术期刊，为全世界最权威的学术期刊之一。《科学》是发表最好的原始研究论文、以及综述和分析当前研究和科学政策的同行评议的期刊之一。该杂志于1880年由爱迪生投资1万美元创办，于1894年成为美国最大的科学团体“美国科学促进会”（American Association for the Advancement of Science ，AAAS)的官方刊物。全年共51期，为周刊，全球发行量超过150万份。

《自然》：《Nature》杂志1869年创刊于英国，是世界上最早的国际性科技期刊，涵盖生命科学、自然科学、临床医学、物理化学等领域。自成立以来，始终如一地报道和评论全球科技领域里最重要的突破，影响因子40.137（17年数据）。其办刊宗旨是“将科学发现的重要结果介绍给公众，让公众尽早知道全世界自然知识的每一分支中取得的所有进展”。

《Nature》网站涵盖的内容相当丰富，不仅提供1997年6月到最新出版的《Nature》杂志的全部内容，其姊妹刊物《Nature》出版集团(The Nature Publishing Group)出版的8种研究月刊，6种评论杂志，2种工具书。

扩展资料：

《科学》资金来源

多数科技期刊都要向读者收取审稿、评论、发表的相关费用。但《科学》杂志发表来稿是免费的。其杂志的资金来源共有三部分：AAAS的会员费、印刷版和在线版的订阅费、广告费。

《科学》竞争对手

在全球，《科学》杂志的主要对手为英国伦敦的《自然》杂志，该杂志创办于1869年，曾发表了大量的达尔文、赫胥黎等大师的文章。21世纪的 前4年中，二者为率先发表人类基因排列的图谱而激烈竞争。