《自然》（20230119出版）一周论文导读

编译 | 未玖

Nature, 19 January 2023, VOL 613, ISSUE 7944

《自然》2023年1月19日，第613卷，7944期

天文学Astronomy

Stellar initial mass function varies with metallicity and time

恒星初始质量函数随金属丰度和时间而变化

▲ 作者：Jiadong Li, Chao Liu, Zhi-Yu Zhang, Hao Tian, Xiaoting Fu, Jiao Li, et al.

▲ 链接：

https://www.nature.com/articles/s41586-022-05488-1

▲ 摘要：

星系的大多数结构和演化特性强烈依赖于恒星初始质量函数（IMF），即在恒星形成各个阶段的恒星质量分布。IMF确定了所有恒星系统中的恒星数量，因此已成为现代天文学最基本的概念之一。

尽管人们进行了大量的理论和观测工作，但不同环境下的恒定和可变IMF均已被证实。然而，银河系恒星群中IMF的测量受到光度观测恒星数量相对较少的限制，导致了很高的不确定性。

研究组报道了一个基于大约93000颗（比此前研究高出一个数量级）光谱观测到的M型矮星的恒星计数结果，位于太阳附近100~300秒差距处。他们发现了一个多变IMF的明确证据，它取决于金属丰度和恒星年龄。

具体来说，与标准IMF相比，早期形成的恒星群包含更少的低质量恒星，与恒星金属丰度无关。然而，在最近的时间里，低质量恒星的比例随着恒星金属丰度的增加而增加。银河系中低质量恒星的可变丰度为恒星形成模型建立了一个强大的基准，并可能严重影响银河系化学富集建模、星系质量估计和行星形成效率的结果。

▲ Abstract：

Most structural and evolutionary properties of galaxies strongly rely on the stellar initial mass function (IMF), namely the distribution of the stellar mass formed in each episode of star formation. The IMF shapes the stellar population in all stellar systems, and so has become one of the most fundamental concepts of modern astronomy. Both constant and variable IMFs across different environments have been claimed despite a large number of theoretical and observational efforts. However, the measurement of the IMF in Galactic stellar populations has been limited by the relatively small number of photometrically observed stars, leading to high uncertainties. Here we report a star-counting result based on approximately 93,000 spectroscopically observed M-dwarf stars, an order of magnitude more than previous studies, in the 100–300 parsec solar neighbourhood. We find unambiguous evidence of a variable IMF that depends on both metallicity and stellar age. Specifically, the stellar population formed at early times contains fewer low-mass stars compared with the canonical IMF, independent of stellar metallicities. In more recent times, however, the proportion of low-mass stars increases with stellar metallicity. The variable abundance of low-mass stars in our Milky Way establishes a powerful benchmark for models of star formation and can heavily affect results in Galactic chemical-enrichment modelling, mass estimation of galaxies and planet-formation efficiency.

物理学Physics

Observation of intrinsic chiral bound states in the continuum

连续域中内禀手性束缚态的观测

▲ 作者：Yang Chen, Huachun Deng, Xinbo Sha, Weijin Chen, Ruize Wang, Yu-Hang Chen, et al.

▲ 链接：

https://www.nature.com/articles/s41586-022-05467-6

▲ 摘要：

自旋角动量的光子具有内禀手性，这是非线性光学、量子光学、拓扑光子学和手性光子学等许多现象的基础。自然材料中的内禀手性很弱，最近的理论建议旨在通过支持连续域中束缚态的共振超表面来扩大圆二色性，从而增强手性光-物质相互作用。

这些颇有见地的研究诉诸于三维复杂的几何结构，这对于光学频率来说极具挑战性。因此，大多数显示强圆二色性的实验尝试都依赖于使用斜入射或结构各向异性的伪/非内禀的手性。

研究组报道了利用共振超表面实现真实/内禀手性响应的实验，其中设计的倾斜几何结构破坏了面内和面外对称性。该研究结果标志着在连续域中首次观测到内禀手性束缚态，其近单位圆二色性为0.93，可见频率的高质量因子超过2663。

该手性超表面有望在手性光源和探测器、手性传感、能谷电子学和不对称光催化等领域得到广泛应用。

▲ Abstract：

Photons with spin angular momentum possess intrinsic chirality, which underpins many phenomena including nonlinear optics, quantum optics, topological photonics and chiroptics. Intrinsic chirality is weak in natural materials, and recent theoretical proposals aimed to enlarge circular dichroism by resonant metasurfaces supporting bound states in the continuum that enhance substantially chiral light–matter interactions. Those insightful works resort to three-dimensional sophisticated geometries, which are too challenging to be realized for optical frequencies. Therefore, most of the experimental attempts showing strong circular dichroism rely on false/extrinsic chirality by using either oblique incidence or structural anisotropy. Here we report on the experimental realization of true/intrinsic chiral response with resonant metasurfaces in which the engineered slant geometry breaks both in-plane and out-of-plane symmetries. Our result marks, to our knowledge, the first observation of intrinsic chiral bound states in the continuum with near-unity circular dichroism of 0.93 and a high quality factor exceeding 2,663 for visible frequencies. Our chiral metasurfaces may lead to a plethora of applications in chiral light sources and detectors, chiral sensing, valleytronics and asymmetric photocatalysis.

材料科学Materials Science

Vertical organic electrochemical transistors for complementary circuits

用于互补电路的垂直有机电化学晶体管

▲ 作者：Wei Huang, Jianhua Chen, Yao Yao, Ding Zheng, Xudong Ji, Liang-Wen Feng, et al.

▲ 链接：

https://www.nature.com/articles/s41586-022-05592-2

▲ 摘要：

有机电化学晶体管（OECTs）和基于OECT的电路因其极低的驱动电压（<1 V）、低功耗（<1 µW）、高跨导（>10 mS）和生物相容性等优势，在生物电子、可穿戴电子器件和人工神经态电子器件方面具有巨大潜力。

然而，关键互补逻辑OECT的成功实现目前受到时间和/或操作不稳定性、较慢的氧化还原过程和/或切换、与高密度单片集成不兼容以及较差的n型OECT性能的限制。

研究组通过将氧化还原活性半导体聚合物与氧化还原非活性光固化和/或光图案化聚合物混合，形成离子渗透半导体通道，并在一个致密、不渗透顶部接触的简单、可扩展垂直结构中实现，从而展示了具有平衡和超高性能的p型和n型垂直OECT。

该研究首次在垂直堆叠互补垂直OECT逻辑电路中实现了低于±0.7 V时超过1 kA cm−2的足迹电流密度、0.2~0.4 S的跨导、快于1 ms的短瞬态时间和超过50000次循环的超稳定切换。这种架构为纳米级受限空间中有机半导体氧化还原化学和物理学的基础研究以及可穿戴和可植入设备的应用提供了诸多可能性，而无需宏观电解质接触。

▲ Abstract：

Organic electrochemical transistors (OECTs) and OECT-based circuitry offer great potential in bioelectronics, wearable electronics and artificial neuromorphic electronics because of their exceptionally low driving voltages (<1 V), low power consumption (<1 µW), high transconductances (>10 mS) and biocompatibility. However, the successful realization of critical complementary logic OECTs is currently limited by temporal and/or operational instability, slow redox processes and/or switching, incompatibility with high-density monolithic integration and inferior n-type OECT performance. Here we demonstrate p- and n-type vertical OECTs with balanced and ultra-high performance by blending redox-active semiconducting polymers with a redox-inactive photocurable and/or photopatternable polymer to form an ion-permeable semiconducting channel, implemented in a simple, scalable vertical architecture that has a dense, impermeable top contact. Footprint current densities exceeding 1 kA cm−2 at less than ±0.7 V, transconductances of 0.2–0.4 S, short transient times of less than 1 ms and ultra-stable switching (>50,000 cycles) are achieved in, to our knowledge, the first vertically stacked complementary vertical OECT logic circuits. This architecture opens many possibilities for fundamental studies of organic semiconductor redox chemistry and physics in nanoscopically confined spaces, without macroscopic electrolyte contact, as well as wearable and implantable device applications.

地球科学Earth Science

Modern temperatures in central–north Greenland warmest in past millennium

格陵兰岛中北部的现代气温近千年来最高

▲ 作者：M. Hörhold, T. Münch, S. Weißbach, S. Kipfstuhl, J. Freitag, I. Sasgen, et al.

▲ 链接：

https://www.nature.com/articles/s41586-022-05517-z

▲ 摘要：

格陵兰冰盖因其规模、辐射效应和淡水储量在全球气候系统中发挥着核心作用，同时也是一个潜在临界点。气象站显示，沿海地区正在变暖，但由于缺少长期观测，全球变暖在冰盖中部的影响尚不清楚。目前基于冰芯的温度重建很难从自然变异中准确分离出全球变暖信号，因为其信号噪音太大，且不包括最近几十年的数据。

通过系统地重新钻取冰芯，研究组对公元1000年至2011年格陵兰岛中北部进行了高质量温度重建。他们表明，最近重建的十年变暖实质上超出了过去千年工业化前的温度变化范围（P < 0.001），平均比20世纪高出1.5±0.4℃（1个标准差）。

该研究结果表明，这些异常温度源于自然变异与长期变暖趋势的叠加，自公元1800年以来该趋势愈发明显。不成比例的变暖伴随着格陵兰岛融水径流的增加，这意味着格陵兰岛中北部也受到了人为影响，可能进一步加速格陵兰岛的整体质量损失。

▲ Abstract：

The Greenland Ice Sheet has a central role in the global climate system owing to its size, radiative effects and freshwater storage, and as a potential tipping point. Weather stations show that the coastal regions are warming, but the imprint of global warming in the central part of the ice sheet is unclear, owing to missing long-term observations. Current ice-core-based temperature reconstructions are ambiguous with respect to isolating global warming signatures from natural variability, because they are too noisy and do not include the most recent decades. By systematically redrilling ice cores, we created a high-quality reconstruction of central and north Greenland temperatures from AD 1000 until 2011. Here we show that the warming in the recent reconstructed decade exceeds the range of the pre-industrial temperature variability in the past millennium with virtual certainty (P < 0.001) and is on average 1.5 ± 0.4 degrees Celsius (1 standard error) warmer than the twentieth century. Our findings suggest that these exceptional temperatures arise from the superposition of natural variability with a long-term warming trend, apparent since AD 1800. The disproportionate warming is accompanied by enhanced Greenland meltwater run-off, implying that anthropogenic influence has also arrived in central and north Greenland, which might further accelerate the overall Greenland mass loss.

River ecosystem metabolism and carbon biogeochemistry in a changing world

全球变化中的河流生态系统代谢与碳生物地球化学

▲ 作者：Tom J. Battin, Ronny Lauerwald, Emily S. Bernhardt, Enrico Bertuzzo, Lluís Gómez Gener, Robert O. Hall Jr, et al.

▲ 链接：

https://www.nature.com/articles/s41586-022-05500-8

▲ 摘要：

河网代表着大陆、海洋和大气之间最大的生物地球化学联结。目前人们对河流在全球碳循环中作用的认识仍然有限，因此很难预测全球变化将如何改变河流碳封存和温室气体排放的时间和空间分布。

研究组回顾了河流生态系统代谢研究的现状，并综合了目前河流生态系统代谢的最佳可用估计。他们量化了从陆地到全球河流的有机和无机碳通量，并表明其净生态系统生产和二氧化碳排放在从陆地到沿海海洋的过程中将有机碳平衡转变为无机碳平衡。

此外，研究组还讨论了全球变化对河流生态系统代谢和相关碳通量的影响，并确定了有助于更好预测全球变化影响河流生态系统过程的研究方向。他们认为，在全球碳预算的背景下，全球河流观测系统将在理解河网及其未来演变方面发挥关键作用。

▲ Abstract：

River networks represent the largest biogeochemical nexus between the continents, ocean and atmosphere. Our current understanding of the role of rivers in the global carbon cycle remains limited, which makes it difficult to predict how global change may alter the timing and spatial distribution of riverine carbon sequestration and greenhouse gas emissions. Here we review the state of river ecosystem metabolism research and synthesize the current best available estimates of river ecosystem metabolism. We quantify the organic and inorganic carbon flux from land to global rivers and show that their net ecosystem production and carbon dioxide emissions shift the organic to inorganic carbon balance en route from land to the coastal ocean. Furthermore, we discuss how global change may affect river ecosystem metabolism and related carbon fluxes and identify research directions that can help to develop better predictions of the effects of global change on riverine ecosystem processes. We argue that a global river observing system will play a key role in understanding river networks and their future evolution in the context of the global carbon budget.

经济学Economics

Financial incentives for vaccination do not have negative unintended consequences

疫苗接种的经济激励措施不会产生意想不到的负面后果

▲ 作者：Florian H. Schneider, Pol Campos-Mercade, Stephan Meier, Devin Pope, Erik Wengström & Armando N. Meier

▲ 链接：

https://www.nature.com/articles/s41586-022-05512-4

▲ 摘要：

鼓励健康和亲社会行为的经济激励通常会引发初始行为改变，但大量学术文献警告不要使用这种方法。批评人士警告说，经济激励可能会排挤亲社会动机，降低安全感和信任感，从而在不支付报酬的情况下减少健康行为，并在更大程度上侵蚀道德。

研究组报道了瑞典一项大规模、预登记研究的结果，该研究从因果关系上衡量了为接种第一剂新冠疫苗提供经济激励的意外后果。他们采用了一种独特的组合方法，即随机暴露于经济激励、全民行政接种记录和丰富的调查数据。

研究组未发现经济激励的负面后果；且可以不考虑提供经济激励对未来疫苗接种、道德、信任和安全感的微小负面影响。在一项补充研究中，他们还发现，告知美国居民国家激励计划的存在也没有负面影响。

该发现不仅为关于行为改变经济激励的学术辩论提供了信息，也为考虑使用经济激励来改变行为的决策者提供了参考。

▲ Abstract：

Financial incentives to encourage healthy and prosocial behaviours often trigger initial behavioural change, but a large academic literature warns against using them. Critics warn that financial incentives can crowd out prosocial motivations and reduce perceived safety and trust, thereby reducing healthy behaviours when no payments are offered and eroding morals more generally. Here we report findings from a large-scale, pre-registered study in Sweden that causally measures the unintended consequences of offering financial incentives for taking the first dose of a COVID-19 vaccine. We use a unique combination of random exposure to financial incentives, population-wide administrative vaccination records and rich survey data. We find no negative consequences of financial incentives; we can reject even small negative impacts of offering financial incentives on future vaccination uptake, morals, trust and perceived safety. In a complementary study, we find that informing US residents about the existence of state incentive programmes also has no negative consequences. Our findings inform not only the academic debate on financial incentives for behaviour change but also policy-makers who consider using financial incentives to change behaviour.