2NE1 2012首支強勢回歸最新單曲《I love you》數位單曲發行就是今天

《科學》（20200522出版）一周論文導讀

編譯 | 未玖 Science, 22 May 2020, VOL 368 ISSUE 6493 《科學》2020年5月22日，第368卷，6493期 [attachimg]9752657[/attachimg] 地球化學Geochemistry Global threat of arsenic in groundwater 地下水砷的全球威脅 ▲ 作者：Joel Podgorski, Michael Berg ▲ 連結：https://science.sciencemag.org/content/368/6493/845 ▲ 摘要地下水中天然存在的砷影響著全球數百萬人。研究組使用隨機森林機器學習模型，基於11個地理空間環境參數，以及50000多個測量的地下水砷濃度匯總數據點，創建了地下水砷含量超過10 mg/L的全球預測圖。該預測圖包括已知的砷污染區和此前未記錄的相關區域。通過將全球砷預測模型與家庭地下水使用統計數據相結合，研究組估計有9400萬至2.2億人可能暴露在高砷濃度地下水中，其中絕大多數（94%）在亞洲。為緩解因氣候變化引起的水資源短缺，越來越多的人使用地下水來支持不斷增長的人口，該研究工作對於提高認識、確定安全井的區域以及幫助優先檢測至關重要。 ▲ Abstract Naturally occurring arsenic in groundwater affects millions of people worldwide. We created a global prediction map of groundwater arsenic exceeding 10 micrograms per liter using a random forest machine-learning model based on 11 geospatial environmental parameters and more than 50,000 aggregated data points of measured groundwater arsenic concentration. Our global prediction map includes known arsenic-affected areas and previously undocumented areas of concern. By combining the global arsenic prediction model with household groundwater-usage statistics, we estimate that 94 million to 220 million people are potentially exposed to high arsenic concentrations in groundwater, the vast majority (94%) being in Asia. Because groundwater is increasingly used to support growing populations and buffer against water scarcity due to changing climate, this work is important to raise awareness, identify areas for safe wells, and help prioritize testing. 材料學Materials Science Precise pitch-scaling of carbon nanotube arrays within three-dimensional DNA nanotrenches 三維DNA納米溝槽內碳納米管陣列的精準間距縮放 ▲ 作者：Wei Sun, Jie Shen, Zhao Zhao, Noel Arellano, Charles Rettner, Jianshi Tang ▲ 連結：https://science.sciencemag.org/content/368/6493/874 ▲ 摘要對於超規模技術節點，需將半導體碳納米管（CNT）精確製成密集排列的均勻間隔的陣列。研究組報告了使用超分子組裝方法（稱為空間受限的納米管電子集成）來精確縮放CNT間距。具體而言，研究組使用基於DNA磚晶體的納米溝槽，通過DNA雜交排列DNA包裹的CNT，構建了平行CNT陣列，其均勻間距小至10.4納米，角度偏差<2°，組裝產率> 95%。 ▲ Abstract Precise fabrication of semiconducting carbon nanotubes (CNTs) into densely aligned evenly spaced arrays is required for ultrascaled technology nodes. We report the precise scaling of inter-CNT pitch using a supramolecular assembly method called spatially hindered integration of nanotube electronics. Specifically, by using DNA brick crystal-based nanotrenches to align DNA-wrapped CNTs through DNA hybridization, we constructed parallel CNT arrays with a uniform pitch as small as 10.4 nanometers, at an angular deviation <2° and an assembly yield >95%. 物理學Physics Coherent optical clock down-conversion for microwave frequencies with 10-18 instability 光學原子鐘有望應用於電子領域 ▲ 作者：Takuma Nakamura, Josue Davila-Rodriguez, Holly Leopardi, Jeff A. Sherman, Tara M. Fortier, Xiaojun Xie, et al. ▲ 連結：https://science.sciencemag.org/content/368/6493/889 ▲ 摘要光學原子鐘由於其穩定性和準確度比目前的微波原子鐘標準高出100多倍，有望重新定義國際單位秒。然而，最好的光學鍾尚未將其性能應用到電子領域，在該領域中，雷達、導航、通信和基礎研究都依賴於不太穩定的微波鍾。通過比較兩個獨立的光電信號發生器，研究組演示了一個10千兆赫茲的微波信號，其相位精確跟蹤從其導出的光學鐘相位，從而在電子領域產生1×10-18的絕對分數頻率不穩定性。光學鐘相位的精準再現擴展了光學鍾在技術和科學層面上應用於時間傳播、導航和長基線干涉成像方面的機會。 ▲ Abstract Optical atomic clocks are poised to redefine the Système International (SI) second, thanks to stability and accuracy more than 100 times better than the current microwave atomic clock standard. However, the best optical clocks have not seen their performance transferred to the electronic domain, where radar, navigation, communications, and fundamental research rely on less stable microwave sources. By comparing two independent optical-to-electronic signal generators, we demonstrate a 10-gigahertz microwave signal with phase that exactly tracks that of the optical clock phase from which it is derived, yielding an absolute fractional frequency instability of 1 × 10-18 in the electronic domain. Such faithful reproduction of the optical clock phase expands the opportunities for optical clocks both technologically and scientifically for time dissemination, navigation, and long-baseline interferometric imaging. Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction 通過超快電子衍射同時觀察核和電子動力學 ▲ 作者：Jie Yang, Xiaolei Zhu, J. Pedro F. Nunes, Jimmy K. Yu, Robert M. Parrish, Thomas J. A. Wolf, et al. ▲ 連結：https://science.sciencemag.org/content/368/6493/885 ▲ 摘要同時觀察原子核和電子的運動對於完全理解激發電子態中的分子動力學至關重要。單次實驗同時獨立跟蹤電子動力學和核動力學是一項挑戰。研究組證實超快電子衍射可以同時記錄分離的吡啶分子中的電子動力學和核動力學，可將這兩部分自然分離開。電子狀態變化（S1→S0內轉換）由小角度非彈性散射中的強瞬態信號反映，核結構變化（環皺褶）由大角度彈性衍射監測。在從頭計算的非絕熱分子動力學和衍射模擬的支持下，研究組的實驗清楚地揭示了光激發吡啶分子的電子動力學和核動力學之間的相互作用。 ▲ Abstract Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule. 地理學Geography Long-term thermal sensitivity of Earth’s tropical forests 地球熱帶森林的長期熱敏感性 ▲ 作者：Martin J. P. Sullivan, Simon L. Lewis, Kofi Affum-Baffoe, Carolina Castilho, Flávia Costa, Aida Cuni Sanchez, et al. ▲ 連結：https://science.sciencemag.org/content/368/6493/869 ▲ 摘要熱帶森林碳對氣候的敏感性是預測全球氣候變化的關鍵不確定因素。雖然已知短期乾燥和變暖會影響森林，但尚不清楚這種影響是否會轉化為長期反應。在此，研究組分析了590個橫跨熱帶的永久性樣地，以獲得森林碳的平衡氣候控制。最高溫度是地上生物量（每公頃每℃-9.1兆克碳）最重要的預測因子，其主要通過降低木本生產力，在最熱的森林（32.2℃以上）中，每℃的影響更大。儘管如此，與短期變化顯示的觀測結果相比，研究組的結果顯示出更大的熱彈性。要實現熱帶森林的長期氣候適應潛力，既需要保護它們，又需要穩定地球的氣候。 ▲ Abstract The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater impact per °C in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth’s climate. 動物學Zoology Bumble bees damage plant leaves and accelerate flower production when pollen is scarce 大黃蜂在花粉稀少時破壞植物葉片，加速開花 ▲ 作者：Foteini G. Pashalidou, Harriet Lambert, Thomas Peybernes, Mark C. Mescher, Consuelo M. De Moraes ▲ 連結：https://science.sciencemag.org/content/368/6493/881 ▲ 摘要對於授粉媒介而言，保持與花朵的物候同步是一個關鍵的生態挑戰，而環境的不斷變化可能會加劇這一挑戰。研究組發現，當花粉不足時，大黃蜂工蜂會破壞無花植物的葉片，從而加速開花。實驗室研究表明，葉片損傷行為受授粉有效性的影響很大，而大黃蜂損傷的植株開花時間明顯早於未受損或機械損傷的對照植株。之後的戶外實驗表明，植株被大黃蜂傷害的程度隨當地花卉供應而變化；此外，還觀察到來自另外兩種大黃蜂野生群落的工蜂破壞了植物葉片。該結果闡明了大黃蜂工蜂的行為特徵，該行為會影響當地花卉資源的可用性。 ▲ Abstract Maintaining phenological synchrony with flowers is a key ecological challenge for pollinators that may be exacerbated by ongoing environmental change. Here, we show that bumble bee workers facing pollen scarcity damage leaves of flowerless plants and thereby accelerate flower production. Laboratory studies revealed that leaf-damaging behavior is strongly influenced by pollen availability and that bee-damaged plants flower significantly earlier than undamaged or mechanically damaged controls. Subsequent outdoor experiments showed that the intensity of damage inflicted varies with local flower availability; furthermore, workers from wild colonies of two additional bumble bee species were also observed to damage plant leaves. These findings elucidate a feature of bumble bee worker behavior that can influence the local availability of floral resources. 0 人閱讀過

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2NE1 2012首支強勢回歸最新單曲《I love you》數位單曲發行就是今天