編譯 | 唐一塵
Science, 01 MAY 2020, VOL 368, ISSUE 6490
《科學》2020年5月1日，第368卷，6490期
物理學Physics
The Sun is less active than other solar-like stars
太陽不如其他類太陽恆星活躍
▲ 作者：Timo Reinhold、Alexander I. Shapiro、Sami K. Solanki，et al.
▲ 鏈接：https://science.sciencemag.org/content/368/6490/518
▲ 摘要
太陽擁有強大的磁場，會產生昏暗的太陽黑子、明亮的太陽耀斑和其他可見的特徵。這些磁性印記會隨時間而變化，並會一時性地影響該恆星光輸出的可變性，導致太陽經歷週期為11年的活動增高或降低。
瞭解太陽的磁場對預測該恆星的未來至關重要，但科學家對太陽的活動是否會減弱或磁性可能變得更活躍存在爭議。
本文將太陽的亮度變化與所觀察到的有著相似質量、溫度、組成和旋轉特性的369顆恆星進行了比較，這些數據選自開普勒太空望遠鏡為期4年的觀測，並與來自蓋亞航天器的數據相結合。
通過量化這些恆星的亮度變化，研究人員發現，大多數的恆星比太陽更為活躍；在過去的140年中，它們的可變性常常比太陽高5倍。
▲ Abstract
The magnetic activity of the Sun and other stars causes their brightness to vary. We investigated how typical the Sun’s variability is compared with other solar-like stars, i.e., those with near-solar effective temperatures and rotation periods. By combining 4 years of photometric observations from the Kepler space telescope with astrometric data from the Gaia spacecraft, we were able to measure photometric variabilities of 369 solar-like stars. Most of those with well-determined rotation periods showed higher variability than the Sun and are therefore considerably more active. These stars appear nearly identical to the Sun except for their higher variability. Therefore, we speculate that the Sun could potentially also go through epochs of such high variability.
Ferromagnetic order beyond the superconducting dome in a cuprate superconductor
銅酸鹽超導體中超出超導圓頂的鐵磁序
▲ 作者：Tarapada Sarkar、D. S. Wei、J. Zhang，et al.
▲ 鏈接：https://science.sciencemag.org/content/368/6490/532
▲ 摘要
根據傳統觀點，銅高溫超導體的非凡性能是由於摻雜了一種強烈相關的反鐵磁絕緣體而產生的。高摻雜的銅被認為是傳統的費米液體金屬。
研究人員報告了在摻雜電子的La2–xCexCuO4 (LCCO)薄膜中，超導圓頂外的摻雜出現了低於4開爾文的流動鐵磁序。負的、各向異性的、滯後磁阻、滯後磁化和極克爾效應證明了鐵磁序的存在，這些都是金屬中流動鐵磁性的標準標誌。
這一令人驚訝的結果表明，過量的銅酸鹽受到電子關聯的強烈影響。
▲ Abstract
According to conventional wisdom, the extraordinary properties of the cuprate high-temperature superconductors arise from doping a strongly correlated antiferromagnetic insulator. The highly overdoped cuprates—whose doping lies beyond the dome of superconductivity—are considered to be conventional Fermi liquid metals. We report the emergence of itinerant ferromagnetic order below 4 kelvin for doping beyond the superconducting dome in thin films of electron-doped La2–xCexCuO4 (LCCO). The existence of this ferromagnetic order is evidenced by negative, anisotropic, and hysteretic magnetoresistance, hysteretic magnetization, and the polar Kerr effect, all of which are standard signatures of itinerant ferromagnetism in metals. This surprising result suggests that the overdoped cuprates are strongly influenced by electron correlations.
生物學Biology
A noncanonical inhibitory circuit dampens behavioral sensitivity to light
非典型抑制迴路抑制了對光行為敏感性
▲ 作者：Takuma Sonoda、Jennifer Y. Li、Nikolas W. Hayes，et al.
▲ 鏈接：https://science.sciencemag.org/content/368/6490/527
▲ 摘要
以前，研究人員認為眼睛只發出興奮信號。本文發現視網膜神經元的一個子集能向大腦發送抑制信號。通常，興奮性信號使神經元更加興奮，抑制性信號使神經元活動減弱。
研究人員在小鼠模型中阻斷了負責抑制信號傳導的視網膜神經元。結果顯示，當這種信號被阻斷時，昏暗的光線能更有效地改變小鼠的晝夜節律。
研究人員表示，這部分視網膜神經元與潛意識行為有關，比如晝夜節律與亮/暗週期的同步，以及瞳孔對強光的收縮。通過更好地理解這些神經元如何運作，研究人員可以探索光影響人們行為的新途徑。
▲ Abstract
Retinal ganglion cells (RGCs) drive diverse, light-evoked behaviors that range from conscious visual perception to subconscious, non–image-forming behaviors. It is thought that RGCs primarily drive these functions through the release of the excitatory neurotransmitter glutamate. We identified a subset of melanopsin-expressing intrinsically photosensitive RGCs (ipRGCs) in mice that release the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at non–image-forming brain targets. GABA release from ipRGCs dampened the sensitivity of both the pupillary light reflex and circadian photoentrainment, thereby shifting the dynamic range of these behaviors to higher light levels. Our results identify an inhibitory RGC population in the retina and provide a circuit-level mechanism that contributes to the relative insensitivity of non–image-forming behaviors at low light levels.
Interleukin-13 drives metabolic conditioning of muscle to endurance exercise
白介素-13驅動肌肉代謝調節以進行耐力運動
▲ 作者：Nelson H. Knudsen、Kristopher J. Stanya、Alexander L. Hyde，et al.
▲ 鏈接：https://science.sciencemag.org/content/368/6490/eaat3987
▲ 摘要
重複運動使肌肉線粒體能適應增加的能量需求，這是一種與改善代謝健康相關的適應性反應。
這裡，研究人員發現，2型細胞因子白介素-13 (IL-13)在運動肌肉中被誘導。在肌肉運動中，它協調代謝重編程，以保留有利於脂肪酸氧化和線粒體呼吸的糖原。
在Il13–/– 小鼠模型中，運動訓練介導的線粒體生物發生、跑步耐力和有益的血糖生成作用均消失。相比之下，增強肌肉IL-13信號足以增加跑步距離、葡萄糖耐量和與運動訓練效果相似的線粒體活動。研究人員表示，協調的免疫和生理反應介導了運動引起的代謝適應，最大限度地提高了肌肉的燃料經濟性。
▲ Abstract
Repeated bouts of exercise condition muscle mitochondria to meet increased energy demand—an adaptive response associated with improved metabolic fitness. We found that the type 2 cytokine interleukin-13 (IL-13) is induced in exercising muscle, where it orchestrates metabolic reprogramming that preserves glycogen in favor of fatty acid oxidation and mitochondrial respiration. Exercise training–mediated mitochondrial biogenesis, running endurance, and beneficial glycemic effects were lost in Il13–/– mice. By contrast, enhanced muscle IL-13 signaling was sufficient to increase running distance, glucose tolerance, and mitochondrial activity similar to the effects of exercise training. In muscle, IL-13 acts through both its receptor IL-13Rα1 and the transcription factor Stat3. The genetic ablation of either of these downstream effectors reduced running capacity in mice. Thus, coordinated immunological and physiological responses mediate exercise-elicited metabolic adaptations that maximize muscle fuel economy.
材料學/化學
Materials Science/ chemistry
A general method to synthesize and sinter bulk ceramics in seconds
短時間合成和燒結大塊陶瓷的一般方法
▲ 作者：Chengwei Wang、Weiwei Ping、Qiang Bai，et al.
▲ 鏈接：https://science.sciencemag.org/content/368/6490/521
▲ 摘要
陶瓷是一類應用廣泛的重要材料，具有良好的熱穩定性、機械穩定性和化學穩定性。計算預測可能成為加速材料發現和改進陶瓷的重要工具，但用實驗證實這些預測的材料特性是必要的。
然而，傳統的陶瓷燒結工藝由於加工時間長，以及揮發性元素損失導致對成分的控制較差，使材料的篩選率受到限制。為了克服這些限制，研究人員開發了一種超快高溫燒結（UHS）工藝——在惰性氣體環境下通過輻射加熱製備陶瓷材料。
研究人員提供了幾個UHS過程案例，展示了其潛在的功效和應用，包括在固態電解質、多組分結構和高通量材料篩選方面的進展。
▲ Abstract
Ceramics are an important class of materials with widespread applications because of their high thermal, mechanical, and chemical stability. Computational predictions based on first principles methods can be a valuable tool in accelerating materials discovery to develop improved ceramics. It is essential to experimentally confirm the material properties of such predictions. However, materials screening rates are limited by the long processing times and the poor compositional control from volatile element loss in conventional ceramic sintering techniques. To overcome these limitations, we developed an ultrafast high-temperature sintering (UHS) process for the fabrication of ceramic materials by radiative heating under an inert atmosphere. We provide several examples of the UHS process to demonstrate its potential utility and applications, including advancements in solid-state electrolytes, multicomponent structures, and high-throughput materials screening.
Antimicrobial peptides: Application informed by evolution
抗菌肽：應用的演變
▲ 作者：Brian P. Lazzaro、Michael Zasloff、Jens Rolff
▲ 鏈接：https://science.sciencemag.org/content/368/6490/eaau5480
▲ 摘要
抗菌肽（AMP）是多細胞生物免疫防禦的重要組成部分，目前正作為抗感染藥物開發。傳統上認為AMP具有廣譜活性和簡單的動力學，但最近的證據表明其具有意想不到的特異性和很高的協同能力。科學家對AMP的深入研究，揭示了其多態性的自適應維持，以及活性的自適應喪失的更多證據。
研究人員表示，AMP還表現出藥效學特性，可減少目標微生物耐藥性的演變，而且其可以與其他抗生素和常規抗生素協同作用。
然而，如果AMP要用於臨床，瞭解它們的自然生物學是至關重要的，以便減少副作用風險，並避免目前傳統抗生素的耐藥性危機。
▲ Abstract
Antimicrobial peptides (AMPs) are essential components of immune defenses of multicellular organisms and are currently in development as anti-infective drugs. AMPs have been classically assumed to have broad-spectrum activity and simple kinetics, but recent evidence suggests an unexpected degree of specificity and a high capacity for synergies. Deeper evaluation of the molecular evolution and population genetics of AMP genes reveals more evidence for adaptive maintenance of polymorphism in AMP genes than has previously been appreciated, as well as adaptive loss of AMP activity. AMPs exhibit pharmacodynamic properties that reduce the evolution of resistance in target microbes, and AMPs may synergize with one another and with conventional antibiotics. Both of these properties make AMPs attractive for translational applications. However, if AMPs are to be used clinically, it is crucial to understand their natural biology in order to lessen the risk of collateral harm and avoid the crisis of resistance now facing conventional antibiotics.
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