《科學》（20190222出版）一周論文導讀

知識 02-25

翻譯 | 宗華

Science, 22 FEBRUARY 2019, Vol. 363, No. 6429

《科學》2019年2月22日，第6429期363卷

《科學》（20190222出版）一周論文導讀

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物理學Physics

Keyhole threshold and morphology in lasermelting revealed by ultrahigh-speed x-ray imaging

超高速X射線成像揭示激光熔融中的鎖孔閾值和形態學

作者：Ross Cunningham, Cang Zhao, Niranjan Parab, et al

鏈接：

http://science.sciencemag.org/content/363/6429/849

摘要：

我們利用超高速同步加速器X射線成像，對增材製造中激光熔化金屬期間的蒸汽抑制現象（又被稱為「鎖孔」）進行了量化。

利用高能X射線對鎖孔形態和動力學進行的直接可視化表明：（1）鎖孔出現在用於激光粉末床熔融的整個功率和掃描速度範圍內；（2）基於激光功率密度的從傳導模式到鎖孔存在明確的閾值；（3）這一過渡遵循汽化、液態表面抑制、不穩定性，然後是深度鎖孔形成的序列。

這些為激光粉末床機器的三維列印提供了物理學基礎。

Abstract

We used ultrahigh-speed synchrotron x-ray imaging to quantify the phenomenon of vapor depressions (also known as keyholes) during laser melting of metals as practiced in additive manufacturing. The direct visualization of the keyhole morphology and dynamics with high-energy x-rays shows that (i) keyholes are present across the range of power and scanning velocity used in laser powder bed fusion; (ii) there is a well-defined threshold from conduction mode to keyhole based on laser power density; and (iii) the transition follows the sequence of vaporization, depression of the liquid surface, instability, and then deep keyhole formation. These and other aspects provide a physical basis for three-dimensional printing in laser powder bed machines.

A degenerate Fermi gas of polar molecules

簡併費米氣體極性分子

作者：Luigi De Marco, Giacomo Valtolina, Kyle Matsuda, et al

鏈接：

http://science.sciencemag.org/content/363/6429/853

摘要：

在實驗上實現量子簡併分子氣體將為研究分子和量子科學中的一系列現象提供途徑。

不過，讓這些超冷分子如此迷人的極度複雜性，使實現簡併成為過去10年間面臨的一項重要的實驗挑戰。

如今，我們報告了鉀—銣超冷極性簡併費米氣體分子的產生。通過銣玻色—愛因斯坦凝聚態和鉀費米氣體的深度簡併混合物中的持續絕熱關聯，我們在低於0.3倍費米溫度的溫度下產生了這些分子。

Abstract

Experimental realization of a quantum degenerate gas of molecules would provide access to a wide range of phenomenain molecular and quantum sciences. However, the very complexity that makes ultra cold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of adegenerate Fermi gas of ultracold polar molecules of potassium-rubidium. Through coherent adiabatic association in a deeply degenerate mixture of arubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature.

古地質學Paleogeology

U-Pb constraints on pulsed eruption of theDeccan Traps across the end-Cretaceous mass extinction

鈾—鉛對白堊紀末期大規模滅絕期間德乾地盾脈衝式火山噴發的限制

作者：Blair Schoene, Michael P. Eddy, Kyle M. Samperton, et al

鏈接：

http://science.sciencemag.org/content/363/6429/862

摘要：

一些大陸洪流玄武岩噴發和大規模滅絕之間的時間相關性被認為表現出因果關係，噴出的揮發物釋放驅動環境退化和物種滅絕。我們利用印度德乾地盾洪流玄武岩省測試了這一模型。

洪流玄武岩噴發和希克蘇魯伯彗星撞擊與大約6600萬年前發生的白堊紀古新世（K-Pg）滅絕有關。

我們利用鈾—鉛鋯石年代學估測了德乾地盾噴發速率，並且確定了4個高通量噴發階段。根據這一模型，最大噴發速率發生在K-Pg滅絕前後，其中一次這樣的脈衝式噴發在火流星撞擊和滅絕之前的上萬年便已開始。

Abstract

Temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality, with eruptive volatile release driving environmental degradation and extinction. We tested this model for the Deccan Traps flood basalt province, which, along with the Chicxulub bolide impact, is implicatedin the Cretaceous-Paleogene (K-Pg) extinction approximately 66 million yearsago. We estimated Deccan eruption rates with uranium-lead (U-Pb) zircon geochronology and resolved four high-volume eruptive periods. According to this model, maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction.

The eruptive tempo of Deccan volcanism inrelation to the Cretaceous-Paleogene boundary

德干火山作用噴發節奏同白堊紀—早第三紀過渡期的關聯性

作者：Courtney J. Sprain, Paul R. Renne, Lo?c Vanderkluysen, et al

鏈接：

http://science.sciencemag.org/content/363/6429/866

摘要：

晚白堊紀環境變化記錄顯示，德乾地盾（DT）火山作用促成了白堊紀—早第三紀過渡期（KPB）生態系統危機。

不過，測試這一假設需要對DT中的KPB進行辨別。我們利用高精度氬-40/氬-30數據，將KPB的位置約束到與岩漿管道系統的變化相一致。

我們還發現，DT並未在3個離散大型脈衝中噴發，並且超過90%的DT量在不到100萬年的時間裡噴發，其中約75%在後KPB時代噴發。

晚白堊紀氣候變化記錄同最小DT相的噴發暫時一致，表明改變氣候的氣體釋放同火山噴發量並未存在直接關聯，同時DT火山作用並不是晚白堊紀氣候變化的源頭。

Abstract

Late Cretaceous records of environmental change suggest that Deccan Traps (DT) volcanism contributed to the Cretaceous-Paleogene boundary (KPB) ecosystem crisis. However, testing this hypothesis requires identification of the KPB in the DT. We constrain the location of the KPB with high-precision argon-40/argon-39 data to be coincident with changes in the magmatic plumbing system. We also found that the DT did noterupt in three discrete large pulses and that >90% of DT volume erupted in<1 million years, with ~75% emplaced post-KPB. Late Cretaceous records of climate change coincide temporally with the eruption of the smallest DT phases, suggesting that either the release of climate-modifying gases is not directly related to eruptive volume or DT volcanism was not the source of Late Cretaceous climate change.

生物學Biology

The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans

醒睡周期調控小鼠大腦組織液tau蛋白和人類腦脊液tau蛋白

作者：Jerrah K. Holth, Sarah K. Fritschi, Chanung Wang, et al

鏈接：

http://science.sciencemag.org/content/363/6429/880

摘要：

醒睡周期調控在阿爾茨海默氏症（AD）中累積的β-澱粉樣蛋白（Aβ）組織液（ISF）和腦脊液（CSF）水平。更重要的是，長期睡眠不足（SD）增加了Aβ斑塊。

不過，tau蛋白而非Aβ的累積似乎驅動了AD神經退化。我們測試了ISF/CSF tau蛋白及其「種植」和擴散是否受到醒睡周期和SD的影響。

小鼠ISF tau蛋白在正常的清醒和睡眠期間增加了約90%，在SD期間增加了約100%。人類的CSF tau蛋白也在SD期間增加了50%多。在tau蛋白「種植」和擴散模型中，慢性SD增加了tau蛋白的病理學擴散。化學基因法驅動的小鼠清醒還顯著增加了ISF Aβ和tau蛋白。

因此，醒睡周期調控了ISF tau蛋白，同時SD增加了ISF和CSF tau蛋白以及tau蛋白的病理學擴散。

Abstract

The sleep-wake cycle regulates interstitial fluid (ISF) and cerebro spinal fluid (CSF) levels of β-amyloid (Aβ) that accumulates in Alzheimer』s disease (AD). Furthermore, chronic sleep deprivation(SD) increases Aβ plaques. However, tau, not Aβ, accumulation appears to drive AD neurodegeneration. We tested whether ISF/CSF tau and tau seeding and spreading were influenced by the sleep-wake cycle and SD. Mouse ISF tau was increased~90% during normal wakefulness versus sleep and ~100% during SD. Human CSF taualso increased more than 50% during SD. In a tau seeding-and-spreading model, chronic SD increased tau pathology spreading. Chemogenetically driven wakefulness in mice also significantly increased both ISF Aβ and tau. Thus, the sleep-wake cycle regulates ISF tau, and SD increases ISF and CSF tau as well astau pathology spreading.

Ubiquitin-dependent chloroplast-associated protein degradation in plants

植物中依賴於泛素化的同葉綠體相關的蛋白質降解

作者：Qihua Ling, William Broad, Raphael Tr?sch, et al

鏈接：

http://science.sciencemag.org/content/363/6429/eaav4467

摘要：

葉綠體含有上千個編碼細胞核的蛋白質。後者由葉綠體被膜中的移位酶從胞液中輸入。對移位酶的解蛋白調控至關重要，但關於其潛在機制知之甚少。

我們將正向遺傳學和蛋白質組學應用於擬南芥，以辨別葉綠體外被膜（OEM）蛋白質降解所需的因素。我們辨別出OEM的Omp85型β桶通道——SP2和胞液型AAA+（同各種細胞活動相關的腺苷三磷酸酶）分子伴侶。

兩種蛋白質和調控OEM移位酶組分的泛素E3連接酶SP1一樣，在相同的通路中發揮作用。SP2和CDC48合作，促成來自OEM的泛素化基質的反易位，從而使胞液中26S蛋白酶體導致的基質降解成為可能。

這種和葉綠體相關的蛋白質降解（CHLORAD）對於細胞器蛋白功能和植物發育至關重要。

Abstract

Chloroplasts contain thousands of nucleus-encoded proteins that are imported from the cytosol by translocases inthe chloroplast envelope membranes. Proteolytic regulation of the translocasesis critically important, but little is known about the underlying mechanisms. We applied forward genetics and proteomics in Arabidopsis to identify factors required for chloroplast outer envelope membrane (OEM) protein degradation. We identified SP2, an Omp85-type β-barrel channel of the OEM, and CDC48, acytosolic AAA+ (ATPase associated with diverse cellular activities) chaperone. Both proteins acted in the same pathway as the ubiquitin E3 ligase SP1, which regulates OEM translocase components. SP2 and CDC48 cooperated to bring about retrotranslocation of ubiquitinated substrates from the OEM (fulfilling conductance and motor functions, respectively), enabling degradation of the substrates by the 26S proteasome in the cytosol. Such chloroplast-associated protein degradation (CHLORAD) is vital for organellar functions and plantdevelopment.

化學Chemistry

Scalable and safe synthetic organic electroreduction inspired by Li-ion battery chemistry

受鋰離子電池化學啟發的規模化和安全的合成有機物電解還原

作者：Byron K. Peters, Kevin X. Rodriguez, Solomon H. Reisberg, et al

鏈接：

http://science.sciencemag.org/content/363/6429/838

摘要：

還原電合成在大規模應用於複雜有機基質上長期面臨著挑戰。

這裡，我們展示了幾十年來關於鋰離子電池材料、電解質和添加劑的研究，如何為實現針對伯奇還原反應的實際應用中規模化的還原電合成條件提供靈感。

尤其是，我們證實，利用犧牲陽極材料（鎂或者鋁）結合廉價、無毒和可溶於水的質子源（二甲基脲）以及受電池技術啟發的過度充電保護劑，能實現同藥學相關的構建模塊的克數量級規模合成。

Abstract

Reductive electrosynthesis has facedlong-standing challenges in applications to complex organic substrates atscale. Here, we show how decades of research in lithium-ion battery materials, electrolytes, and additives can serve as an inspiration for achieving practically scalable reductive electro synthetic conditions for the Birch reduction. Specifically, we demonstrate that using a sacrificial anode material (magnesium or aluminum), combined with a cheap, nontoxic, and water-soluble proton source (dimethylurea), and an overcharge protectant inspired by battery technology can allow for multigram-scale synthesis of pharmaceutically relevant building blocks.

《科學》（20190222出版）一周論文導讀