《科學》一周論文導讀

編譯｜馮維維

Science, 11 September 2020,Vol 369 Issue 6509

《科學》2020年9月11日，第369卷，6509期

Physical chemistry物理化學

Scale-free ferroelectricity induced by flat phonon bands in HfO2

氧化鉿薄膜具有持久鐵電性

▲ 作者：Hyun-Jae Lee, Minseong Lee, Kyoungjun Lee, Jinhyeong Jo, Hyemi Yang, Yungyeom Kim, Seung Chul Chae, Umesh Waghmare, Jun Hee Lee

▲ 連結：

https://science.sciencemag.org/content/369/6509/1343

▲ 摘要

鐵電材料之所以具有吸引力，是因為它們提供了一種利用電場改變電阻的方法。作者通過模擬解釋了氧化鉿薄膜中鐵電行為的持久性。

作者的計算表明，在1納米厚度以下的薄膜中應該存在鐵電性質。這使得這種材料對下一代隨機存取存儲器非常有吸引力。

▲ Abstract

Ferroelectric materials are attractive because they provide a way to change electrical resistance by using an electric field. Lee et al. used simulations to explain the persistence of ferroelectric behavior in very thin films of hafnium oxide. The authors' calculations show that ferroelectric properties should be found in films below 1 nanometer thick. This makes the material very attractive for the next generation of random access memory.

Self-limiting directional nanoparticle bonding governed by reaction stoichiometry

反應化學計量控制的自限定向納米顆粒鍵合

▲ 作者：Chenglin Yi, Hong Liu, Shaoyi Zhang, Yiqun Yang, Yan Zhang, Zhongyuan Lu, Eugenia Kumacheva, Zhihong Nie

▲ 連結：

https://science.sciencemag.org/content/369/6509/1369

▲ 摘要

從二聚體一直到三維晶格，當前已經開發了許多途徑將膠體粒子連接到受控的超結構，但它們通常依賴於以特定方式覆蓋到納米粒子表面來控制連接的方式。

與此相對，作者開發了一種配體化學，當兩個粒子連接在一起時，它會改變靜電性質以限制隨後的成鍵。

粒子被塗上互補的聚合物鏈，這些聚合物鏈經過酸鹼中和反應。這種結合是由靈活配體的長度控制的，而結合粒子的排列是由靜電排斥控制的，因此有兩個參數來調整組合的形狀。

▲ Abstract

Although many routes have been developed to link together colloidal particles into controlled superstructures from dimers all the way up to three-dimensional lattices, they generally depend on coating the nanoparticle surfaces in specific ways to control the way they link up. By contrast, Yi et al. developed a ligand chemistry such that, when two particles link together, it changes the electrostatic properties to limit subsequent bonding. Particles are coated with complementary polymer strands that undergo an acid-base neutralization reaction. This bonding is controlled by the length of the flexible ligands, whereas the arrangement of the bonded particles is controlled by electrostatic repulsions, thus giving two parameters to tune the shape of the assemblies that form.

Geophysics地球物理學

Multiphase buffer theory explains contrasts in atmospheric aerosol acidity

多相緩衝理論解釋大氣氣溶膠酸度的差異

▲ 作者：Guangjie Zheng, Hang Su, Siwen Wang, Meinrat O. Andreae, Ulrich Pöschl, Yafang Cheng

▲ 連結：

https://science.sciencemag.org/content/369/6509/1374

▲ 摘要

氣溶膠對大氣化學產生主要影響。它們內部化學成分的主要控制因素之一是酸度，因此了解哪些因素決定了氣溶膠的pH值是確定它們對環境影響的基礎。

作者考慮了多相氣溶膠系統的緩衝能力與整體溶液的不同，發現水含量在氨緩衝區域的pH值測定中起著重要作用。他們的結論強調了氨排放對人類世的重要影響。

▲ Abstract

Aerosols exert a primary influence on atmospheric chemistry. One of the main controls on their internal chemistry is their acidity, so understanding what determines aerosol pH is fundamental for determining their environmental effects. Zheng et al. considered how buffering capacity in a multiphase aerosol system differs from bulk solution and found an important role for water content in determining pH in ammonia-buffered regions. Their conclusions underscore the important influence of ammonia emissions in the Anthropocene.

An astronomically dated record of Earth’s climate and its predictability over the last 66 million years

追溯6600萬年前的地球氣候

▲ 作者：Thomas Westerhold, Norbert Marwan, Anna Joy Drury, Jun Tian, Roy H. Wilkens, Paul A. Wilson, etc.

▲ 連結：

https://science.sciencemag.org/content/369/6509/1383

▲ 摘要

深海底棲有孔蟲通過氧和碳的同位素組成保存了地球過去氣候的重要記錄。

但這些記錄在某些地方缺乏足夠的時間解析度和/或年齡控制，以確定哪種氣候強迫和反饋機制是最重要的。作者對過去6600萬年的底棲生物的碳和氧同位素進行了深入解析和年代推演。

其結果表明，地球的氣候可以被歸為離散的狀態，這些狀態被與溫室氣體水平變化和極地冰原增長相關的轉變所分離。每一種氣候狀態都受軌道周期的影響，但又以與狀態相關的方式對輻射力的變化作出反應。

▲ Abstract

Deep-sea benthic foraminifera preserve an essential record of Earth's past climate in their oxygen- and carbon-isotope compositions. However, this record lacks sufficient temporal resolution and/or age control in some places to determine which climate forcing and feedback mechanisms were most important. Westerhold et al. present a highly resolved and well-dated record of benthic carbon and oxygen isotopes for the past 66 million years. Their reconstruction and analysis show that Earth's climate can be grouped into discrete states separated by transitions related to changing greenhouse gas levels and the growth of polar ice sheets. Each climate state is paced by orbital cycles but responds to variations in radiative forcing in a state-dependent manner.

Ecology生態學

Long-term forest degradation surpasses deforestation in the Brazilian Amazon

亞馬遜長期森林退化超森林砍伐

▲ 作者：Eraldo Aparecido Trondoli Matricardi, David Lewis Skole, Olívia Bueno Costa, Marcos Antonio Pedlowski, Jay Howard Samek, Eder Pereira Miguel

▲ 連結：

https://science.sciencemag.org/content/369/6509/1378

▲ 摘要

森林退化是人類對森林景觀普遍存在的一種幹擾形式。選擇性砍伐和開採等活動沒有達到全部森林砍伐的程度，但會導致生物量的損失和（或）碎片化。

作者以30米空間解析度的遙感數據為基礎，分析了巴西整個亞馬遜流域22年（截至2014年）來森林退化程度。

他們發現森林退化的程度和速度等於或大於森林砍伐，這對碳、生物多樣性和能源平衡有著重要的影響。

▲ Abstract

Forest degradation is a ubiquitous form of human disturbance of the forest landscape. Activities such as selective logging and extraction fall short of total deforestation but lead to loss of biomass and/or fragmentation. On the basis of remote sensing data at 30-meter spatial resolution, Matricardi et al. analyzed the extent of forest degradation across the entire Brazilian Amazon over a ∼22-year period up to 2014. They found that the extent and rate of forest degradation was equal to or greater than deforestation, which has important implications for carbon, biodiversity, and energy balance.

Keystone predators govern the pathway and pace of climate impacts in a subarctic marine ecosystem

關鍵食肉動物控制氣候影響的路徑和速度

▲ 作者：Douglas B. Rasher, Robert S. Steneck, Jochen Halfar, Isaac T. Westfield, James A. Estes, etc.

▲ 連結：

https://science.sciencemag.org/content/369/6509/1351

▲ 摘要

研究已經證明，捕食者對於構建和維持生物群落必不可少。這種重要性的首批證據之一，便是海獺對維持海藻林的重要性的研究。作者研究表明，氣候變暖會進一步加劇捕食者的消失所造成的影響。

在北太平洋的海藻「森林」中，水獺的消失導致了緩慢生長的鈣質海藻的減少，而氣溫的升高又加劇了這種模式。因此，關鍵的捕食者不僅對其營養結構至關重要，而且對減輕氣候變化的影響也至關重要。

▲ Abstract

It is well established that predators are essential for the structuring and maintenance of biotic communities. One of the first demonstrations of this importance came from studies of the importance of sea otters to the maintenance of kelp forests. Rasher et al. now show that the effects caused by the absence of this predator can be further exacerbated by climate warming. In North Pacific kelp forests, otter absence led to a decline of slow-growing calcareous algae through sea urchin herbivory, and this pattern was amplified by warming temperatures. Keystone predators are thus essential not only for trophic structure but also for mitigating the impacts of climate change.

Physics物理學

An excess of small-scale gravitational lenses observed in galaxy clusters

星系團中的引力透鏡

▲ 作者：Massimo Meneghetti, Guido Davoli, Pietro Bergamini, Piero Rosati, Priyamvada Natarajan, Carlo Giocoli

▲ 連結：

https://science.sciencemag.org/content/369/6509/1347

▲ 摘要

大質量的星系團會使來自背景物體的光偏轉，這種現象被稱為引力透鏡。由整個星系團引起的大尺度引力透鏡可以被星系團內較小尺度的質量濃度（如單個星系）修正。

作者在對11個星系團的觀察中檢查了這些小型引力透鏡。他們發現了比宇宙模擬中預期的要小一個數量級的小透鏡。作者的結論是，在流行的模擬方法或標準宇宙學中存在一個未被確認的問題。

▲ Abstract

The large mass of a galaxy cluster deflects light from background objects, a phenomenon known as gravitational lensing. The large-scale gravitational lens caused by the whole cluster can be modified by smaller-scale mass concentrations within the cluster, such as individual galaxies. Meneghetti et al. examined these small-scale gravitational lenses in observations of 11 galaxy clusters. They found small lenses that were an order of magnitude smaller than would be expected from cosmological simulations. The authors conclude that there is an unidentified problem with either prevailing simulation methods or standard cosmology.

微生物學Microbiology

Structural basis of transcription-translation coupling and collision in bacteria

細菌中轉錄-翻譯耦合與碰撞的結構基礎

▲ 作者：Michael William Webster, Maria Takacs, Chengjin Zhu, Vita Vidmar, Ayesha Eduljee, Mo’men Abdelkareem, Albert Weixlbaume

▲ 連結：

https://science.sciencemag.org/content/369/6509/1355

▲ 摘要

原核信使RNAs （mRNAs）在被轉錄時被翻譯。鉛核糖體可能與RNA聚合酶（RNAP）接觸，形成一種稱為表達體的超分子複合物。

表達組裝的基礎及其對轉錄和翻譯的影響尚不清楚。作者提出了一系列代表由低溫電子顯微鏡確定的非耦合、耦合和碰撞表達狀態的結構。

轉錄因子NusG可以在核糖體和RNAP之間形成一座橋，它穩定了一個其他可變的相互作用界面。其間mRNA的縮短導致實質性的重排，使核糖體進入通道與RNAP退出通道對齊。

在這個碰撞的複合體中，NusG連接不再可能。這些結構揭示了轉錄和翻譯之間的協調機制，並為今後的研究提供了一個框架。

▲ Abstract

Prokaryotic messenger RNAs (mRNAs) are translated as they are transcribed. The lead ribosome potentially contacts RNA polymerase (RNAP) and forms a supramolecular complex known as the expressome. The basis of expressome assembly and its consequences for transcription and translation are poorly understood. Here, we present a series of structures representing uncoupled, coupled, and collided expressome states determined by cryo–electron microscopy. A bridge between the ribosome and RNAP can be formed by the transcription factor NusG, which stabilizes an otherwise-variable interaction interface. Shortening of the intervening mRNA causes a substantial rearrangement that aligns the ribosome entrance channel to the RNAP exit channel. In this collided complex, NusG linkage is no longer possible. These structures reveal mechanisms of coordination between transcription and translation and provide a framework for future study.

編輯｜宗華

排版｜華園

不想錯過科學網的推送？

方法如下

喜歡本文？點讚 + 在看 支持一下！