来源:科学网 发布时间:2019/3/29 14:14:51
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《科学》论文导读:2019年3月8日

 

 
材料学Materials
 
 
 
 
Volumetric additive manufacturing via tomographic reconstruction
 
通过层析重建的容积增材制造
 
▲ 作者:Brett E. Kelly, Indrasen Bhattacharya, Hossein Heidari1, et al
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1075
 
 
 
▲ 摘要:
 
增材制造展示出巨大的几何自由度和组合材料实现复杂功能的潜力。增材过程的速度、几何结构和表面质量限制与它们对材料分层的依赖有关。
 
 
 
我们用动态演化的光模式照亮旋转的光敏材料体,从而演示了一个三维物体内所有点的并行打印。
 
 
 
我们在工程丙烯酸酯聚合物内打印出小至0.3毫米的功能模块,并将拥有异常光滑表面的软结构打印成明胶甲基丙烯酸酯水凝胶。这一工艺使我们构建的组件能封装其他先前存在的实体物体,从而实现多材料制造。
 
 
 
▲ Abstract
 
Additive manufacturing promises enormous geometrical freedom and the potential to combine materials for complex functions. The speed, geometry, and surface quality limitations of additive processes are linked to their reliance on material layering. We demonstrated concurrent printing of all points within a three-dimensional object by illuminating a rotating volume of photo sensitive material with a dynamically evolving light pattern. We printed features as small as 0.3 millimeters in engineering a crylate polymers and printed soft structures with exceptionally smooth surfaces into a gelatin methacrylate hydrogel. Our process enables us to construct components that encase other preexisting solid objects, allowing for multimaterial fabrication.
 
 
 
Tuning superconductivity in twisted bilayer grapheme
 
调控旋转双层石墨烯的超导性
 
▲ 作者:Matthew Yankowitz, Shaowen Chen, Hryhoriy Polshyn, et al
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1059
 
 
 
▲ 摘要:
 
具有扁平电子带的材料由于具有很强的相关性,常常表现出奇异的量子现象。在双层石墨烯中,只要简单地旋转1.1°,就可以诱导出一个孤立的低能扁平带,从而产生栅压调控的超导和相关绝缘相。
 
 
 
在本研究中,我们证明,除了扭转角度,层间耦合可被改变以精确调整这些相位。我们通过改变层间间距与静水压力的关系,在大于1.1°的扭转角下诱导超导。
 
 
 
在这个角度,相关相原本是不存在的。
 
 
 
我们的低无序器件揭示了超导相图的细节及其与附近绝缘体的关系。我们的研究结果表明,旋转双层石墨烯是探索相关状态的一个独特的可调控平台。
 
 
 
▲ Abstract
 
Materials with flat electronic bands often exhibit exotic quantum phenomena owing to strong correlations. An isolated low-energy flat band can be induced in bilayer graphene by simply rotating the layers by 1.1°, resulting in the appearance of gate-tunable superconducting and correlated insulating phases. In this study, we demonstrate that in addition to the twist angle, the interlayer coupling canbe varied to precisely tune these phases. We induce superconductivity at atwist angle larger than 1.1°—in which correlated phases are otherwise absent—by varying the interlayer spacing with hydrostatic pressure. Our low-disorderdevices reveal details about the superconducting phase diagram and its relationship to the nearby insulator. Our results demonstrate twisted bilayer graphene to be a distinctively tunable platform for exploring correlated states.
 
 
 
 
生物学Biology
 
 
 
 
Stoichiometry controls activity of phase-separated clusters of actin signaling proteins
 
化学计量学控制相分离的肌动信号蛋白簇活性
 
▲ 作者:Lindsay B. Case, Xu Zhang, Jonathon A. Ditlev, Michael K. Rosen
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1093
 
 
 
▲ 摘要:
 
生物分子缩合物将大分子浓缩成没有细胞膜的焦点。许多缩合物似乎是通过多价相互作用形成的,这些相互作用驱动液—液相分离(LLPS)。
 
 
 
LLPS通过Arp2/3复合体增加肌动蛋白调控蛋白对肌动蛋白组装的特异性活性。
 
 
 
我们发现,这种增加是由于脂质双层膜上Nephrin-Nck-N-WASP信号通路的LLPS增加了N-WASP和Arp2/3复合体的膜停留时间,从而增加了肌动蛋白的组装。
 
 
 
停留时间随信号蛋白在相分离簇中的相对化学计量数的变化而变化,使N-WASP和Arp2/3活性化学计量数存在依赖性。这种控制蛋白质活性的机制是由生物大分子缩合物尚不明确的化学计量学性质所决定的。
 
 
 
▲ Abstract
 
Biomolecular condensates concentrate macromolecules into foci without a surrounding membrane. Many condensates appear to form through multivalent interactions that drive liquid-liquid phase separation (LLPS). LLPS increases the specific activity of actin regulatory proteins toward act in assembly by the Arp2/3 complex. We show that this increase occurs because LLPS of the Nephrin–Nck–N-WASP signaling pathway on lipid bilayers increases membrane dwell time of N-WASP and Arp2/3 complex, consequently increasing actin assembly. Dwell time varies with relative stoichiometry of the signaling proteins in the phase-separated clusters, rendering N-WASP and Arp2/3 activity stoichiometry dependent. This mechanism of controlling protein activity is enabled by the stoichiometrically undefined nature of biomolecular condensates.
 
 
 
AIBP-mediated cholesterol efflux instructs hematopoietic stem and progenitor cell fate
 
AIBP介导的胆固醇外排影响造血干细胞和祖细胞命运
 
▲ 作者:Qilin Gu, Xiaojie Yang, Jie Lv, Jiaxiong Zhang, et al
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1085
 
 
 
▲ 摘要:
 
高胆固醇血症是动脉粥样硬化的驱动力,会加速造血干细胞和祖细胞(HSPCs)的扩增。高胆固醇血症与造血作用的分子决定因素尚不清楚。
 
 
 
我们发现,一个源自体节的支持造血的线索——AIBP协调来自造血内皮细胞的HSPC的出现。这是一种显示造血潜能的特殊内皮细胞。
 
 
 
在机制上,AIBP介导的胆固醇外排激活了内皮细胞Srebp2。这是胆固醇生物合成的主转录因子,进而激活Notch并促进HSPC的出现。
 
 
 
抑制Srebp2会损伤高胆固醇血症诱导的HSPC扩张。Srebp2的激活和Notch上调与高胆固醇血症人类受试者体内HSPC的扩张有关。
 
 
 
▲ Abstract
 
Hypercholesterolemia, the driving force of atherosclerosis, accelerates the expansion and mobilization of hematopoietic stem and progenitor cells (HSPCs). The molecular determinants connecting hypercholesterolemia with hematopoiesis are unclear. Here, we report that a somite-derived prohematopoietic cue, AIBP, orchestrates HSPC emergence from the hemogenic endothelium, a type of specialized endothelium manifesting hematopoietic potential. Mechanistically, AIBP-mediated cholesterol efflux activates end othelial Srebp2, the master transcription factor for cholesterol biosynthesis, which in turn transactivates Notch and promotes HSPC emergence. Srebp2 inhibition impairs hypercholesterolemia-induced HSPC expansion. Srebp2 activation and Notch up-regulation are associated with HSPC expansion in hypercholesterolemic human subjects.
 
 
 
 
物理学Physics
 
 
 
 
Coherentsingle-photon emission from colloidal lead halide perovskite quantum dots
 
胶体卤化铅钙钛矿量子点的相干单光子发射
 
▲ 作者:Hendrik Utzat, Weiwei Sun, Alexander E. K. Kaplan, et al
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1068
 
 
 
▲ 摘要:
 
化学制备的胶体半导体量子点一直被认为是量子光学中可伸缩、颜色可调的单发射体,但它们通常会遭受严重的非相干发射。
 
 
 
我们现在证明,单个胶体卤化铅钙钛矿量子点(PQDs)显示出高效的单光子发射。其光学相干时间可达80皮秒,是其210皮秒辐射寿命的一个可观部分。
 
 
 
这些测量结果表明,PQDs应该作为不可分辨的单光子和纠缠光子对源的构建块进行探索。
 
 
 
我们的研究结果为基于卤化铅钙钛矿的量子发射器的合理设计提供了一个起点。这种量子发射器具有发射速度快、光谱可调性广、可扩展的生产能力,并得益于与纳米光子组件的混合集成。这种集成已被证明用于胶体材料。
 
 
 
▲ Abstract
 
Chemically made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210-picosecond radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photonpairs. Our results present a starting point for the rational design of lead halide perovskite–based quantum emitters that have fast emission, wide spectraltunability, and scalable production and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.
 
 
 
Magneto-Seebeck tunneling on the atomic scale
 
原子尺度的磁—塞贝克隧穿
 
▲ 作者:Cody Friesen, Hermann Osterhage, Johannes Friedlein, et al
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1065
 
 
 
▲ 摘要:
 
自旋极化电子在温度梯度驱动下通过磁性隧道结的隧穿,是电子自旋输运热控制的基本过程。
 
 
 
我们实验研究了这种磁—塞贝克隧穿的原子尺度细节,方法是在低温下将一个磁性探针尖端靠近磁性样品,并以真空作为隧穿屏障。
 
 
 
当扫描样品的自旋结构时,加热针尖并测量结的热电势,可以得到自旋分辨的塞贝克系数。该系数可在原子尺度的横向分辨率下进行映射。
 
 
 
我们提出了一种自旋电子应用的自旋探测器,它完全由余热驱动,利用磁—塞贝克隧穿将自旋信息转换成电压,可用于进一步的数据处理。
 
 
 
▲ Abstract
 
The tunneling of spin-polarized electrons across a magnetic tunnel junction driven by a temperature gradient is a fundamental process for the thermal control of electron spin transport. We experimentally investigated the atomic-scale details of this magneto-Seebeck tunneling by placing a magnetic probe tip inclose proximity to a magnetic sample at cryogenic temperature, with a vacuum as the tunneling barrier. Heating the tip and measuring the thermopower of the junction while scanning across the spin texture of the sample lead to spin-resolved Seebeck coefficients that can be mapped at atomic-scale lateral resolution. We propose a spin detector for spintronics applications that is driven solely by waste heat, using magneto-Seebeck tunneling to convert spin information into a voltage that can be used for further data processing.
 
 
 
 
古气候学Paleoclimatology
 
 
 
 
The residence time of Southern Ocean surface waters and the 100,000-year ice age cycle
 
南大洋地表水的停留时间和10万年冰期周期
 
▲ 作者:Adam P. Hasenfratz, Samuel L. Jaccard, Alfredo Martínez-García, etal
 
▲ 链接:
 
http://science.sciencemag.org/content/363/6431/1080
 
 
 
▲ 摘要:
 
从125万年前到70万年前,地球冰川期的强度增加,周期长度也从4.1万年延长到10万年。这一转变至今仍无法解释。
 
 
 
利用来自南大洋南极区的海洋表面和底栖有孔虫重建过去150万年冰川期从深层到表面的水供应,我们发现,深层供水减少和相伴随的海洋表面水淡化,同高振幅的10万年冰川循环相一致。
 
 
 
我们认为,这种从深层到表面的循环(即南极表层海水停留时间的延长)变慢,通过使南极盐跃层得到增强而延长了冰期。这增加了南极上层水柱的停留,并成为二氧化碳释放速度过快的驱动因素。
 
 
 
▲ Abstract
 
From 1.25 million to 700,000 years ago, the ice age cycle deepened and lengthened from41,000- to 100,000-year periodicity, a transition that remains unexplained. Using surface- and bottom-dwelling foraminifera from the Antarctic Zone of the Southern Ocean to reconstruct the deep-to-surface supply of water during the ice ages of the past 1.5 million years, we found that a reduction in deep water supply and a concomitant freshening of the surface ocean coincided with the emergence of the high-amplitude 100,000-year glacial cycle. We propose that this slowing of deep-to-surface circulation (i.e., a longer residence time for Antarctic surface waters) prolonged ice ages by allowing the Antarctic halocline to strengthen, which increased the resistance of the Antarctic upper water column to orbitally paced drivers of carbon dioxide release.
 
(宗华)
 
 
 

 

 
 
 
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