Volumetric additive manufacturing via tomographic reconstruction

通過(guò)層析重建的容積增材制造

▲ 作者：Brett E. Kelly, Indrasen Bhattacharya, Hossein Heidari1, et al

▲ 鏈接：

http://science./content/363/6431/1075

▲ 摘要：

增材制造展示出巨大的幾何自由度和組合材料實(shí)現(xiàn)復(fù)雜功能的潛力。增材過(guò)程的速度、幾何結(jié)構(gòu)和表面質(zhì)量限制與它們對(duì)材料分層的依賴有關(guān)。

我們用動(dòng)態(tài)演化的光模式照亮旋轉(zhuǎn)的光敏材料體，從而演示了一個(gè)三維物體內(nèi)所有點(diǎn)的并行打印。

我們?cè)诠こ瘫┧狨ゾ酆衔飪?nèi)打印出小至0.3毫米的功能模塊，并將擁有異常光滑表面的軟結(jié)構(gòu)打印成明膠甲基丙烯酸酯水凝膠。這一工藝使我們構(gòu)建的組件能封裝其他先前存在的實(shí)體物體，從而實(shí)現(xiàn)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

調(diào)控旋轉(zhuǎn)雙層石墨烯的超導(dǎo)性

▲ 作者：Matthew Yankowitz, Shaowen Chen, Hryhoriy Polshyn, et al

▲ 鏈接：

http://science./content/363/6431/1059

▲ 摘要：

具有扁平電子帶的材料由于具有很強(qiáng)的相關(guān)性，常常表現(xiàn)出奇異的量子現(xiàn)象。在雙層石墨烯中，只要簡(jiǎn)單地旋轉(zhuǎn)1.1°，就可以誘導(dǎo)出一個(gè)孤立的低能扁平帶，從而產(chǎn)生柵壓調(diào)控的超導(dǎo)和相關(guān)絕緣相。

在本研究中，我們證明，除了扭轉(zhuǎn)角度，層間耦合可被改變以精確調(diào)整這些相位。我們通過(guò)改變層間間距與靜水壓力的關(guān)系，在大于1.1°的扭轉(zhuǎn)角下誘導(dǎo)超導(dǎo)。

在這個(gè)角度，相關(guān)相原本是不存在的。

我們的低無(wú)序器件揭示了超導(dǎo)相圖的細(xì)節(jié)及其與附近絕緣體的關(guān)系。我們的研究結(jié)果表明，旋轉(zhuǎn)雙層石墨烯是探索相關(guān)狀態(tài)的一個(gè)獨(dú)特的可調(diào)控平臺(tái)。

▲ 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.

Stoichiometry controls activity of phase-separated clusters of actin signaling proteins

化學(xué)計(jì)量學(xué)控制相分離的肌動(dòng)信號(hào)蛋白簇活性

▲ 作者：Lindsay B. Case, Xu Zhang, Jonathon A. Ditlev, Michael K. Rosen

▲ 鏈接：

http://science./content/363/6431/1093

▲ 摘要：

生物分子縮合物將大分子濃縮成沒(méi)有細(xì)胞膜的焦點(diǎn)。許多縮合物似乎是通過(guò)多價(jià)相互作用形成的，這些相互作用驅(qū)動(dòng)液—液相分離（LLPS）。

LLPS通過(guò)Arp2/3復(fù)合體增加肌動(dòng)蛋白調(diào)控蛋白對(duì)肌動(dòng)蛋白組裝的特異性活性。

我們發(fā)現(xiàn)，這種增加是由于脂質(zhì)雙層膜上Nephrin-Nck-N-WASP信號(hào)通路的LLPS增加了N-WASP和Arp2/3復(fù)合體的膜停留時(shí)間，從而增加了肌動(dòng)蛋白的組裝。

停留時(shí)間隨信號(hào)蛋白在相分離簇中的相對(duì)化學(xué)計(jì)量數(shù)的變化而變化，使N-WASP和Arp2/3活性化學(xué)計(jì)量數(shù)存在依賴性。這種控制蛋白質(zhì)活性的機(jī)制是由生物大分子縮合物尚不明確的化學(xué)計(jì)量學(xué)性質(zhì)所決定的。

▲ 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介導(dǎo)的膽固醇外排影響造血干細(xì)胞和祖細(xì)胞命運(yùn)

▲ 作者：Qilin Gu, Xiaojie Yang, Jie Lv, Jiaxiong Zhang, et al

▲ 鏈接：

http://science./content/363/6431/1085

▲ 摘要：

高膽固醇血癥是動(dòng)脈粥樣硬化的驅(qū)動(dòng)力，會(huì)加速造血干細(xì)胞和祖細(xì)胞（HSPCs）的擴(kuò)增。高膽固醇血癥與造血作用的分子決定因素尚不清楚。

我們發(fā)現(xiàn)，一個(gè)源自體節(jié)的支持造血的線索——AIBP協(xié)調(diào)來(lái)自造血內(nèi)皮細(xì)胞的HSPC的出現(xiàn)。這是一種顯示造血潛能的特殊內(nèi)皮細(xì)胞。

在機(jī)制上，AIBP介導(dǎo)的膽固醇外排激活了內(nèi)皮細(xì)胞Srebp2。這是膽固醇生物合成的主轉(zhuǎn)錄因子，進(jìn)而激活Notch并促進(jìn)HSPC的出現(xiàn)。

抑制Srebp2會(huì)損傷高膽固醇血癥誘導(dǎo)的HSPC擴(kuò)張。Srebp2的激活和Notch上調(diào)與高膽固醇血癥人類受試者體內(nèi)HSPC的擴(kuò)張有關(guān)。

▲ 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.

Coherentsingle-photon emission from colloidal lead halide perovskite quantum dots

膠體鹵化鉛鈣鈦礦量子點(diǎn)的相干單光子發(fā)射

▲ 作者：Hendrik Utzat, Weiwei Sun, Alexander E. K. Kaplan, et al

▲ 鏈接：

http://science./content/363/6431/1068

▲ 摘要：

化學(xué)制備的膠體半導(dǎo)體量子點(diǎn)一直被認(rèn)為是量子光學(xué)中可伸縮、顏色可調(diào)的單發(fā)射體，但它們通常會(huì)遭受嚴(yán)重的非相干發(fā)射。

我們現(xiàn)在證明，單個(gè)膠體鹵化鉛鈣鈦礦量子點(diǎn)（PQDs）顯示出高效的單光子發(fā)射。其光學(xué)相干時(shí)間可達(dá)80皮秒，是其210皮秒輻射壽命的一個(gè)可觀部分。

這些測(cè)量結(jié)果表明，PQDs應(yīng)該作為不可分辨的單光子和糾纏光子對(duì)源的構(gòu)建塊進(jìn)行探索。

我們的研究結(jié)果為基于鹵化鉛鈣鈦礦的量子發(fā)射器的合理設(shè)計(jì)提供了一個(gè)起點(diǎn)。這種量子發(fā)射器具有發(fā)射速度快、光譜可調(diào)性廣、可擴(kuò)展的生產(chǎn)能力，并得益于與納米光子組件的混合集成。這種集成已被證明用于膠體材料。

▲ 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—塞貝克隧穿

▲ 作者：Cody Friesen, Hermann Osterhage, Johannes Friedlein, et al

▲ 鏈接：

http://science./content/363/6431/1065

▲ 摘要：

自旋極化電子在溫度梯度驅(qū)動(dòng)下通過(guò)磁性隧道結(jié)的隧穿，是電子自旋輸運(yùn)熱控制的基本過(guò)程。

我們實(shí)驗(yàn)研究了這種磁—塞貝克隧穿的原子尺度細(xì)節(jié)，方法是在低溫下將一個(gè)磁性探針尖端靠近磁性樣品，并以真空作為隧穿屏障。

當(dāng)掃描樣品的自旋結(jié)構(gòu)時(shí)，加熱針尖并測(cè)量結(jié)的熱電勢(shì)，可以得到自旋分辨的塞貝克系數(shù)。該系數(shù)可在原子尺度的橫向分辨率下進(jìn)行映射。

我們提出了一種自旋電子應(yīng)用的自旋探測(cè)器，它完全由余熱驅(qū)動(dòng)，利用磁—塞貝克隧穿將自旋信息轉(zhuǎn)換成電壓，可用于進(jìn)一步的數(shù)據(jù)處理。

▲ 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.

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時(shí)間和10萬(wàn)年冰期周期

▲ 作者：Adam P. Hasenfratz, Samuel L. Jaccard, Alfredo Martínez-García, etal

▲ 鏈接：

http://science./content/363/6431/1080

▲ 摘要：

從125萬(wàn)年前到70萬(wàn)年前，地球冰川期的強(qiáng)度增加，周期長(zhǎng)度也從4.1萬(wàn)年延長(zhǎng)到10萬(wàn)年。這一轉(zhuǎn)變至今仍無(wú)法解釋。

利用來(lái)自南大洋南極區(qū)的海洋表面和底棲有孔蟲(chóng)重建過(guò)去150萬(wàn)年冰川期從深層到表面的水供應(yīng)，我們發(fā)現(xiàn)，深層供水減少和相伴隨的海洋表面水淡化，同高振幅的10萬(wàn)年冰川循環(huán)相一致。

我們認(rèn)為，這種從深層到表面的循環(huán)（即南極表層海水停留時(shí)間的延長(zhǎng)）變慢，通過(guò)使南極鹽躍層得到增強(qiáng)而延長(zhǎng)了冰期。這增加了南極上層水柱的停留，并成為二氧化碳釋放速度過(guò)快的驅(qū)動(dòng)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.