編譯｜李言
Nature, 16 March 2023, Volume 615 Issue 7952
《自然》，2023年3月16日，第615卷，7952期
材料科學Material science
Photonically active bowtie nanoassemblies with chirality continuum
具有手性連續體的光子活性領結形納米組件
▲ 作者：Prashant Kumar, Thi Vo, Minjeong Cha et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-023-05733-1
▲ 摘要：
在此，我們展示了具有各向異性領結形狀的納米結構微粒可展示手性連續體，并且可以調整其角度、間距、寬度、厚度和長度。領結形的自限制組裝使其在不同條件下呈現的幾何形狀具有較高的合成再現性、尺寸單分散性和計算可預測性。
領結形納米組件在吸收和散射現象下，顯示出一些強圓二色性峰。與經典的手性分子不同，這些粒子表現出連續的手性測量，與圓二色性峰的光譜位置呈指數相關。
具有可變極化旋轉的領結形粒子可打印具有光譜可調正負極化特征的光子活性超表面，用于激光探測及測距設備。
▲ Abstract：
Here we show that nanostructured microparticles with an anisotropic bowtie shape display chirality continuum and can be made with widely tuneable twist angle, pitch, width, thickness and length. The self-limited assembly of the bowties enables high synthetic reproducibility, size monodispersity and computational predictability of their geometries for different assembly conditions. The bowtie nanoassemblies show several strong circular dichroism peaks originating from absorptive and scattering phenomena. Unlike classical chiral molecules, these particles show a continuum of chirality measures that correlate exponentially with the spectral positions of the circular dichroism peaks. Bowtie particles with variable polarization rotation were used to print photonically active metasurfaces with spectrally tuneable positive or negative polarization signatures for light detection and ranging (LIDAR) devices.
化學Chemistry
Control of stereogenic oxygen in a helically chiral oxonium ion
螺旋手性氧鎓離子中立體異構氧的控制
▲ 作者：Owen Smith, Mihai V. Popescu, Madeleine J. Hindson et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-023-05719-z
▲ 摘要：
在此，我們描述了一個螺旋手性三芳氧鎓離子的設計、合成和表征，通過幾何限制可防止氧孤對的轉化，使其能夠作為構型的行列式發揮作用。
我們使用組合合成和量子計算的方法標明其設計原則，使結構穩定和室溫隔離鹽能夠產生。據我們所知，這構成了手性非外消旋和構型穩定的分子中氧原子是單一立體異構中心的唯一案例。
▲ Abstract：
Here we describe the design, synthesis and characterization of a helically chiral triaryloxonium ion in which inversion of the oxygen lone pair is prevented through geometric restriction to enable it to function as a determinant of configuration. A combined synthesis and quantum calculation approach delineates design principles that enable configurationally stable and room-temperature isolable salts to be generated. We show that the barrier to inversion is greater than 110?kJ?mol?1 and outline processes for resolution. This constitutes, to our knowledge, the only example of a chiral non-racemic and configurationally stable molecule in which the oxygen atom is the sole stereogenic centre.
地理學Geography
The carbon sink of secondary and degraded humid tropical forests
次生和退化的潮濕熱帶森林碳匯
▲ 作者：Viola H. A. Heinrich, Christelle Vancutsem, Ricardo Dalagnol et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05679-w
▲ 摘要：
在此，我們量化了三個主要熱帶濕潤地區（亞馬遜、婆羅洲和中非）中正在恢復的森林地上碳匯。在衛星數據的基礎上，我們的分析涵蓋了退化森林和次生林受關鍵環境和人為驅動因素影響的異質時空生長模式。在森林恢復期的頭20年里，婆羅洲的再生率分別比中非和亞馬遜高出45%和58%。
這是由于溫度、水分虧缺和擾動等變量造成的。我們發現，在1984年至2018年期間，再生退化森林和次生林累積了107百萬噸每年，抵消了潮濕熱帶森林在同期損失的碳排放的26%。
因此，保護原始森林是優先要務。此外，我們估計在主要熱帶地區，保護正在恢復的退化森林和次生林未來的碳匯潛力可能為53百萬噸每年。
▲ Abstract：
Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa. On the basis of satellite data products, our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20?years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107Tg C year?1(90–130 Tg C year?1) between 1984 and 2018, counterbalancing 26% (21–34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year?1(44–62 Tg C year?1) across the main tropical regions studied.
Regime shift in Arctic Ocean sea ice thickness
北冰洋海冰厚度的變化
▲ 作者：Hiroshi Sumata, Laura de Steur, Dmitry V. Divine, Mats A. Granskog & Sebastian Gerland
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05686-x
▲ 摘要：
在此，我們展示了北極海冰冰蓋在2007年從更厚和形態不規則到更薄和形態更一致的變化。過去三十年來，在弗拉姆海峽持續進行的海冰監測揭示了這種變化。
變化之后，厚冰和不規則冰的比例下降了一半，至今仍未恢復。在這一轉變之前，北極盆地海冰留存時間曾有兩次縮短，第一次始于2005年，第二次是2007年。
我們證明了一個描述動態海冰增厚隨機過程的簡單模型解釋了由于留存時間減少而觀測到的冰蓋厚度變化。我們的研究強調了，在冰蓋留存時間減少的情況下，氣候變化對北極海冰的長期影響，以及它與相鄰邊緣海和大陸架中海洋-海冰耦合過程的聯系。
▲ Abstract：
Here we show that the Arctic sea ice regime shifted in 2007 from thicker and deformed to thinner and more uniform ice cover. Continuous sea ice monitoring in the Fram Strait over the last three decades revealed the shift. After the shift, the fraction of thick and deformed ice dropped by half and has not recovered to date. The timing of the shift was preceded by a two-step reduction in residence time of sea ice in the Arctic Basin, initiated first in 2005 and followed by 2007. We demonstrate that a simple model describing the stochastic process of dynamic sea ice thickening explains the observed ice thickness changes as a result of the reduced residence time. Our study highlights the long-lasting impact of climate change on the Arctic sea ice through reduced residence time and its connection to the coupled ocean–sea ice processes in the adjacent marginal seas and shelves of the Arctic Ocean.
地質學Geology
Deep, ultra-hot-melting residues as cradles of mantle diamond
深層超熱熔殘體是地幔金剛石的搖籃
▲ 作者：Carl Walsh, Balz S. Kamber & Emma L. Tomlinson
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05690-1
▲ 摘要：
在此，我們展示了在足夠高的溫度下熔化產生克拉通根的鎂質橄欖石的熱力學和地球化學模擬的結果。通過極深（約200公里）和極高溫熱熔（≥1800°C）消除了淺層熔化和堆積的需要，新的封閉系統和開放系統模型再現了觀測到的克拉通地幔礦物組成。
就像在克拉通化石表面的綠巖帶中觀察到的那樣，模擬中的富鎂液體（科馬提巖）發展成富鋁和缺少鈦的形式。缺鈦的科馬提巖意味著先進封閉系統等化學熔化（1825°C）遠不如深層液體和現有難熔地幔之間的開放系統相互作用常見。
▲ Abstract：
Here we present results from thermodynamic and geochemical modelling of melting at sufficiently high temperatures to produce the very magnesian olivine of cratonic roots. The new closed-system and open-system modelling reproduces the observed cratonic mantle mineral compositions by deep (about 200?km) and very hot melting (≥1,800°C), obviating the need for shallow melting and stacking. The modelled highly magnesian liquids (komatiites) evolve to Al-enriched and Ti-depleted forms, as observed in the greenstone belts at the fossil surface of cratons. The paucity of Ti-depleted komatiite implies that advanced closed-system isochemical melting (>1,825°C) was much less common than open-system interaction between deeper liquids and melting of existing refractory mantle.
Weak upper-mantle base revealed by postseismic deformation of a deep earthquake
深源地震后形變所揭示的上地幔基底薄弱
▲ 作者：Sunyoung Park, Jean-Philippe Avouac, Zhongwen Zhan & Adriano Gualandi
▲ 鏈接：
https://www.nature.com/articles/s41586-022-05689-8
▲ 摘要：
在此，我們利用位于上地幔底部附近的深源地震（約560 km）導致的震后變形來研究地幔粘度結構。我們成功地探測和了解了2018年斐濟8.2級地震引起的震后變形情況。為了尋找可以解釋檢測到的信號的粘度結構，我們使用一系列粘度結構進行正向粘彈性松弛建模。
我們發現，我們的觀測需要在地幔過渡帶底部有一個相對較薄（約100 km）、低粘性（1017到1018Pa s）的層。這樣的弱帶可以解釋在許多俯沖帶中觀察到的平板扁平化和孤立現象，這些很難放到整個地幔對流體系中去研究。低粘性層可能是尖晶石后轉變、弱硅酸鈣礦、高含水量或脫水熔融誘導的超塑性形成的結果。
▲ Abstract：
Here, we study the mantle viscosity structure by using the postseismic deformation following a deep (approximately 560 km) earthquake located near the bottom of the upper mantle. We apply independent component analysis to geodetic time series to successfully detect and extract the postseismic deformation induced by the moment magnitude 8.2, 2018 Fiji earthquake. To search for the viscosity structure that can explain the detected signal, we perform forward viscoelastic relaxation modelling with a range of viscosity structures. We find that our observation requires a relatively thin (approximately 100 km), low-viscosity (1017to 1018Pa s) layer at the bottom of the mantle transition zone. Such a weak zone could explain the slab flattening and orphaning observed in numerous subduction zones, which are otherwise challenging to explain in the whole mantle convection regime. The low-viscosity layer may result from superplasticity induced by the postspinel transition, weak CaSiO3 perovskite, high water content or dehydration melting.
