編譯｜馮維維
Science,13 NOVEMBER 2020, VOL 370, ISSUE 6518
《科學》2020年11月13日，第370卷，6518期
天體物理Astrophysics
Hydrogen escape from Mars is driven by seasonal and dust storm transport of water
沙塵暴導致火星水流失
▲ 作者：Shane W. Stone, Roger V. Yelle, Mehdi Benna, Daniel Y. Lo, Meredith K. Elrod, Paul R. Mahaffy
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/824
▲ 摘要
火星曾經是一顆潮溼的行星，由於發生反應產生氫，它失去了大部分的水，氫從上層大氣逃逸到太空中。
作者利用來自火星大氣和揮發演化航天器的數據來研究水是如何被輸送到高層大氣並轉化為氫氣的。
他們發現，水可以到達比之前預想的更高的高度，特別是在整個星球或區域沙塵暴期間。光化學模擬顯示，這一過程主導了目前火星水分的流失，並影響了火星氣候的演變。
▲ Abstract
Mars was once a wet planet, but it has lost most of its water through reactions that produce hydrogen, which escapes from the upper atmosphere into space. Stone et al. used data from the Mars Atmosphere and Volatile Evolution spacecraft to study how water is transported to the upper atmosphere and converted to hydrogen. They found that water can reach higher altitudes than previously thought, especially during global or regional dust storms. Photochemical modeling shows that this process dominates the current loss of water from Mars and influenced the evolution of its climate.
Astronomical context of Solar System formation from molybdenum isotopes in meteorite inclusions
通過隕石內含物衡量太陽系形成時間
▲ 作者：Gregory A. Brennecka, Christoph Burkhardt, Gerrit Budde, Thomas S. Kruijer, Francis Nimmo, Thorsten Kleine
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/837
▲ 摘要
隕石中富含鈣鋁的內含物（CAIs）是太陽系中最早形成的固體物質，在絕對時間尺度上定義了它的誕生時期。這為恆星形成的天文觀測和太陽系形成的宇宙化學研究提供了聯繫。
作者發現CAI中獨特的鉬同位素組成幾乎覆蓋了在原行星盤中形成的所有物質的組成範圍。
他們認為CAIs形成於太陽從原恆星到恆星形成前主序階段的過渡時期，將太陽系的形成置於一個天文背景中。研究結果表明，大部分構成太陽和太陽系的物質是在持續不到20萬年的CAIs形成時期累積的。
▲ Abstract
Calcium-aluminum–rich inclusions (CAIs) in meteorites are the first solids to have formed in the Solar System, defining the epoch of its birth on an absolute time scale. This provides a link between astronomical observations of star formation and cosmochemical studies of Solar System formation. We show that the distinct molybdenum isotopic compositions of CAIs cover almost the entire compositional range of material that formed in the protoplanetary disk. We propose that CAIs formed while the Sun was in transition from the protostellar to pre–main sequence (T Tauri) phase of star formation, placing Solar System formation within an astronomical context. Our results imply that the bulk of the material that formed the Sun and Solar System accreted within the CAI-forming epoch, which lasted less than 200,000 years.
納米技術Nano-Tech
Constrained minimal-interface structures in polycrystalline copper with extremely fine grains
鎖定納米級金屬的強度
▲ 作者：X. Y. Li, Z. H. Jin, X. Zhou, K. Lu
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/831
▲ 摘要
具有納米大小晶粒的金屬具有超高強度，但在較高的溫度下，它們通常不能保持自己的結構。這一特性削弱了它們的高強度，使其在應用中具有挑戰性。
作者在銅中發現了一種10納米晶粒的最小界面結構，當與納米晶粒晶體孿晶網絡結合時，該結構在接近熔點的溫度下仍能保持高強度。這一發現為穩定納米顆粒金屬提供了一條不同的道路。
▲ Abstract
Metals with nanometer-sized crystal grains are super strong, but they do not generally retain their structure at higher temperatures. This property undermines their high strength and makes their use in applications challenging. Li et al. found a minimum-interface structure in copper with 10-nanometer-sized grains that, when combined with a nanograin crystallographic twinning network, retains high strength to temperatures just below the melting point. This discovery suggests a different path forward for stabilizing nanograined metals.
Nano-acoustic resonator with ultralong phonon lifetime
具有超長聲子壽命的納米聲學諧振器
▲ 作者：Gregory S. MacCabe, Hengjiang Ren, Jie Luo, Justin D. Cohen,Hengyun Zhou, Alp Sipahigil, Mohammad Mirhosseini, Oskar Painter
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/840
▲ 摘要
量子計算和量子傳感應用的理想平臺可能是一個混合系統，它結合了不同組件的最佳特性。超導電路相對先進，找到能夠控制和操縱微波的元件將是至關重要的。
作者探索了高質量微諧振器的使用，其中的聲學環境可以被改造，使聲子壽命可以延長到1秒以上。在5千兆赫的微波頻率下工作，這些量子聲動力裝置可以與超導電路耦合。
▲ Abstract
The ideal platform for quantum-computing and quantum-sensing applications is likely to be a hybrid system that combines the best features of different components. Superconducting circuits are relatively advanced, and finding components that can control and manipulate the microwaves will be essential. MacCabe et al. explored the use of high-quality microresonators in which the acoustic environment could be engineered such that the phonon lifetime could be extended to more than 1 second. Operating at microwave frequencies of 5 gigahertz, these quantum acoustic-dynamic devices could be coupled with superconducting circuits.
物理學Physics
Stretchable distributed fiber-optic sensors
可伸縮分佈式光纖傳感器
▲ 作者：Hedan Bai, Shuo Li, Jose Barreiros, Yaqi Tu, Clifford R. Pollock, Robert F. Shepherd
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/848
▲ 摘要
分佈式光纖傳感器已用於監測剛性基礎設施（如橋樑、道路和建築物）的機械變形，但它們要麼僅限於測量一個變量，要麼需要複雜的光學來測量多個屬性。
作者演示了雙核彈性光纖，其中一種包含有圖案的染料區域。該波導由商業上可獲得的彈性體模壓而成，集成了一個清晰的核心和一個相鄰的核心，其中摻雜了多達三個宏觀尺度的染料區域。
兩個核中光路的變化檢測變形並將其映射到一個顏色空間。通過監測兩種彈性體纖維顏色和強度的變化，研究人員可以區分彎曲、拉伸和局部按壓，其空間分辨率可高達1釐米。
▲ Abstract
Distributed fiber-optic sensors have been used for monitoring mechanical deformations in stiff infrastructures such as bridges, roads, and buildings, but they either are limited to measuring one variable or require complex optics to measure multiple properties. Bai et al. now demonstrate dual-core elastomeric optical fibers, one of which contains patterned dye regions. The waveguides are fabricated by molding out of commercially available elastomers and integrate a clear core and an adjacent core doped with up to three macroscale dye regions. Changes in optical paths in the two cores detect deformation and map it onto a color space. By monitoring changes in the color and intensity in both elastomer-based fibers, the researchers could distinguish bending, stretching, and localized pressing with a spatial resolution down to ∼1 centimeter.
生命科學Life Science
A thalamocortical top-down circuit for associative memory
聯想記憶的丘腦皮層自上而下回路
▲ 作者：M. Belén Pardi, Johanna Vogenstahl, Tamas Dalmay, Teresa Spanò, De-Lin Pu, Laura B. Naumann, Friedrich Kretschmer, Henning Sprekeler, Johannes J. Letzkus
▲ 鏈接：
https://science.sciencemag.org/content/370/6518/844
▲ 摘要
感官信息只有與大腦內部產生的自上而下的信號相結合並進行比較，才能在大腦中有意義地發揮作用。但人們對傳達這種自上而下信號的腦寬傳入神經、它們的信息內容以及與學習相關的可塑性知之甚少。
作者發現，高階丘腦是鼠類聽覺皮層自上而下輸入的主要來源，並研究了皮層1中促進可塑性變化和靈活反應的迴路。
這些結果表明，自上而下的反饋信息是如何通過非皮層結構到達皮層區域的，而非皮層結構雖然與皮層有廣泛的聯繫，卻很少受到關注。
▲ Abstract
Sensory information can only be used meaningfully in the brain when integrated with and compared with internally generated top-down signals. However, we know little about the brainwide afferents that convey such top-down signals, their information content, and learning-related plasticity. Pardi et al. identified the higher-order thalamus as a major source of top-down input to mouse auditory cortex and investigated a circuit in cortical layer 1 that facilitates plastic changes and flexible responses. These results demonstrate how top-down feedback information can reach cortical areas through a noncortical structure that has received little attention despite its widespread connections with the cortex.
