編譯 | 未玖
Nature, 29 February 2024, VOL 626, ISSUE 8001
《自然》2024年2月29日，第626卷，8001期
天文學(xué)Astronomy
Most of the photons that reionized the Universe came from dwarf galaxies
使宇宙再電離的大多數(shù)光子來自矮星系
▲ 作者：Hakim Atek, Ivo Labbé, Lukas J. Furtak, Iryna Chemerynska, Seiji Fujimoto, David J. Setton, et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07043-6
▲ 摘要：
宇宙再電離是宇宙大爆炸后約600~800 Myr從中性氫到電離等離子體的主要相變，但人們對(duì)確定驅(qū)動(dòng)宇宙再電離的來源一直存在爭(zhēng)議。一些模型表明，類星體的高電離發(fā)射率和逃逸分?jǐn)?shù)（fesc）支持其在推動(dòng)宇宙再電離中發(fā)揮作用。
另一些人提出，明亮星系的高fesc值會(huì)產(chǎn)生足夠的電離輻射來驅(qū)動(dòng)這一過程。最后，一些研究表明，當(dāng)與電離效率和fesc的恒星質(zhì)量依賴模型結(jié)合時(shí)，微弱星系的數(shù)量密度可以有效控制宇宙再電離。然而迄今為止，由于低質(zhì)量星系極其微弱，尚未對(duì)其進(jìn)行全面的光譜研究。
研究組報(bào)道了在再電離時(shí)期對(duì)8個(gè)超微弱星系（在一個(gè)非常小的場(chǎng)中）的分析，絕對(duì)星等在MUV≈?17等和?15等之間（低至0.005L?）。結(jié)果發(fā)現(xiàn)，在宇宙的前10億年間，微弱星系產(chǎn)生了log[ξion?(Hz?erg?1)]= 25.80±0.14的電離光子，比通常假設(shè)的值高出4倍。
如果這個(gè)場(chǎng)代表了微弱星系的大規(guī)模分布，那么電離光子的速率就超過了再電離所需的速率，即使fesc為5%數(shù)量級(jí)時(shí)亦是如此。
▲ Abstract：
The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600–800?Myr after the Big Bang, has been a matter of debate. Some models suggest that high ionizing emissivity and escape fractions (fesc) from quasars support their role in driving cosmic reionization. Others propose that the high fesc values from bright galaxies generate sufficient ionizing radiation to drive this process. Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and fesc, can effectively dominate cosmic reionization. However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between MUV?≈??17?mag and ?15?mag (down to 0.005L?). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[ξion?(Hz?erg?1)]= 25.80±0.14, a factor of 4 higher than commonly assumed values. If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%.
材料科學(xué)Materials Science
High fatigue resistance in a titanium alloy via near-void-free 3D printing
通過幾乎無氣孔的3D打印工藝實(shí)現(xiàn)鈦合金的高抗疲勞性
▲ 作者：Zhan Qu, Zhenjun Zhang, Rui Liu, Ling Xu, Yining Zhang, Xiaotao Li, et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07048-1
▲ 摘要：
3D打印（即結(jié)構(gòu)材料的增材制造，AM）的優(yōu)勢(shì)因其差強(qiáng)人意的疲勞性能而受到嚴(yán)重?fù)p害。通常，較差的疲勞性能似乎因當(dāng)前印刷工藝過程中產(chǎn)生氣孔所造成。因此，研究組提出疑問，消除這些氣孔是否可為顯著提高無孔AM（Net-AM）合金的抗疲勞性提供可行的解決方案？
通過了解相變和晶粒生長(zhǎng)的異步性，研究組進(jìn)一步開發(fā)Net-AM工藝技術(shù)，成功地在Ti-6Al-4V鈦合金中重建了幾乎無氣孔的AM微結(jié)構(gòu)。他們確定了這種AM微結(jié)構(gòu)的抗疲勞性，并表明其約1 GPa的高疲勞極限超越了所有AM和鍛造鈦合金以及其他金屬材料的抗疲勞性能。
研究結(jié)果證實(shí)了Net-AM微結(jié)構(gòu)具有高抗疲勞性能，以及AM工藝在生產(chǎn)具有最大疲勞強(qiáng)度結(jié)構(gòu)部件方面的潛在優(yōu)勢(shì)，這有利于AM技術(shù)在工程領(lǐng)域的進(jìn)一步應(yīng)用。
▲ Abstract：
The advantage of 3D printing—that is, additive manufacturing (AM) of structural materials—has been severely compromised by their disappointing fatigue properties. Commonly, poor fatigue properties appear to result from the presence of microvoids induced by current printing process procedures. Accordingly, the question that we pose is whether the elimination of such microvoids can provide a feasible solution for marked enhancement of the fatigue resistance of void-free AM (Net-AM) alloys. Here we successfully rebuild an approximate void-free AM microstructure in Ti-6Al-4V titanium alloy by development of a Net-AM processing technique through an understanding of the asynchronism of phase transformation and grain growth. We identify the fatigue resistance of such AM microstructures and show that they lead to a high fatigue limit of around 1?GPa, exceeding the fatigue resistance of all AM and forged titanium alloys as well as that of other metallic materials. We confirm the high fatigue resistance of Net-AM microstructures and the potential advantages of AM processing in the production of structural components with maximum fatigue strength, which is beneficial for further application of AM technologies in engineering fields.
Site-specific reactivity of stepped Pt surfaces driven by stress release
應(yīng)力釋放驅(qū)動(dòng)臺(tái)階型Pt表面的位點(diǎn)特異性反應(yīng)性
▲ 作者：Guangdong Liu, Arthur J. Shih, Huiqiu Deng, Kasinath Ojha, Xiaoting Chen, Mingchuan Luo, et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07090-z
▲ 摘要：
多相催化劑被廣泛用于促進(jìn)化學(xué)反應(yīng)。雖然已知化學(xué)反應(yīng)通常發(fā)生在催化劑表面，但只有特定的表面位點(diǎn)具有高催化活性。因此，確定活性位點(diǎn)并使其最大限度地發(fā)揮作用是催化研究的核心，其中經(jīng)典模型是根據(jù)不同的表面構(gòu)型（如平臺(tái)面和臺(tái)階）對(duì)活性位點(diǎn)進(jìn)行分類。
然而，這種簡(jiǎn)單的分類往往會(huì)導(dǎo)致催化劑活性預(yù)測(cè)的數(shù)量級(jí)誤差和活性位點(diǎn)的定性不確定，從而限制了催化劑設(shè)計(jì)的機(jī)會(huì)。
以臺(tái)階型Pt（111）表面和電化學(xué)氧還原反應(yīng)（ORR）為例，研究組證明了較大誤差和不確定性的根本原因是簡(jiǎn)化了分類，忽略了由表面應(yīng)力釋放驅(qū)動(dòng)的原子位點(diǎn)特異性反應(yīng)性。具體而言，各臺(tái)階的表面應(yīng)力釋放引入了不均勻的應(yīng)變場(chǎng)，壓縮率高達(dá)5.5%，導(dǎo)致具有相同局部配位的平臺(tái)面原子具有不同的電子結(jié)構(gòu)和反應(yīng)性，并導(dǎo)致原子位點(diǎn)特異性的ORR活性增強(qiáng)。
對(duì)于臺(tái)階邊緣兩側(cè)的平臺(tái)面原子，其活性增強(qiáng)程度比平臺(tái)面中間的原子高出50倍，這實(shí)現(xiàn)了通過改變平臺(tái)面寬度或控制外部應(yīng)力來控制ORR反應(yīng)性。因此，上述協(xié)同作用的發(fā)現(xiàn)為催化活性原子位點(diǎn)的基本認(rèn)識(shí)和多相催化劑的設(shè)計(jì)原理提供了新視角。
▲ Abstract：
Heterogeneous catalysts are widely used to promote chemical reactions. Although it is known that chemical reactions usually happen on catalyst surfaces, only specific surface sites have high catalytic activity. Thus, identifying active sites and maximizing their presence lies at the heart of catalysis research, in which the classic model is to categorize active sites in terms of distinct surface motifs, such as terraces and steps. However, such a simple categorization often leads to orders of magnitude errors in catalyst activity predictions and qualitative uncertainties of active sites, thus limiting opportunities for catalyst design. Here, using stepped Pt(111) surfaces and the electrochemical oxygen reduction reaction (ORR) as examples, we demonstrate that the root cause of larger errors and uncertainties is a simplified categorization that overlooks atomic site-specific reactivity driven by surface stress release. Specifically, surface stress release at steps introduces inhomogeneous strain fields, with up to 5.5% compression, leading to distinct electronic structures and reactivity for terrace atoms with identical local coordination, and resulting in atomic site-specific enhancement of ORR activity. For the terrace atoms flanking both sides of the step edge, the enhancement is up to 50 times higher than that of the atoms in the middle of the terrace, which permits control of ORR reactivity by either varying terrace widths or controlling external stress. Thus, the discovery of the above synergy provides a new perspective for both fundamental understanding of catalytically active atomic sites and design principles of heterogeneous catalysts.
Supramolecular polymers form tactoids through liquid–liquid phase separation
超分子聚合物通過液-液相分離形成類晶簇
▲ 作者：Hailin Fu, Jingyi Huang, Joost J. B. van der Tol, Lu Su, Yuyang Wang, Swayandipta Dey, et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07034-7
▲ 摘要：
生物聚合物的液—液相分離（LLPS）最近被證明在具有多種生物功能的無膜細(xì)胞器形成中起著核心作用。LLPS和大分子凝聚之間的相互作用是持續(xù)研究的一部分。合成的超分子聚合物是大分子的非共價(jià)擁擠物，但鮮有報(bào)道其發(fā)生LLPS。
研究組表明，通過合成組分的超分子聚合獲得的連續(xù)生長(zhǎng)的原纖維，通過熵驅(qū)動(dòng)的途徑負(fù)責(zé)相分離成高度各向異性的水性液滴（類晶簇）。受右旋糖苷濃度調(diào)節(jié)的擁擠環(huán)境不僅影響超分子聚合動(dòng)力學(xué)，還影響LLPS的性質(zhì)，包括相分離動(dòng)力學(xué)、形態(tài)、內(nèi)部有序、流動(dòng)性和最終類晶簇的力學(xué)性能。
此外，基底—液和液—液界面被證明能夠加速超分子聚合物的LLPS，可產(chǎn)生無數(shù)的三維有序結(jié)構(gòu)，包括表面高度有序的微米長(zhǎng)的類晶簇陣列。幾種超分子聚合物證明了超分子聚合控制新興形態(tài)的普遍性和諸多可能性，開辟了一個(gè)從穩(wěn)定LLPS的高度結(jié)構(gòu)化水溶液到納米級(jí)軟物質(zhì)的新物質(zhì)領(lǐng)域。
▲ Abstract：
Liquid–liquid phase separation (LLPS) of biopolymers has recently been shown to play a central role in the formation of membraneless organelles with a multitude of biological functions. The interplay between LLPS and macromolecular condensation is part of continuing studies. Synthetic supramolecular polymers are the non-covalent equivalent of macromolecules but they are not reported to undergo LLPS yet. Here we show that continuously growing fibrils, obtained from supramolecular polymerizations of synthetic components, are responsible for phase separation into highly anisotropic aqueous liquid droplets (tactoids) by means of an entropy-driven pathway. The crowding environment, regulated by dextran concentration, affects not only the kinetics of supramolecular polymerizations but also the properties of LLPS, including phase-separation kinetics, morphology, internal order, fluidity and mechanical properties of the final tactoids. In addition, substrate–liquid and liquid–liquid interfaces proved capable of accelerating LLPS of supramolecular polymers, allowing the generation of a myriad of three-dimensional-ordered structures, including highly ordered arrays of micrometre-long tactoids at surfaces. The generality and many possibilities of supramolecular polymerizations to control emerging morphologies are demonstrated with several supramolecular polymers, opening up a new field of matter ranging from highly structured aqueous solutions by means of stabilized LLPS to nanoscopic soft matter.
化學(xué)Chemistry
Identifying general reaction conditions by bandit optimization
用bandit優(yōu)化法確定通用反應(yīng)條件
▲ 作者：Jason Y. Wang (王億珩), Jason M. Stevens, Stavros K. Kariofillis, Mai-Jan Tom, Dung L. Golden, Jun Li, et al.
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07021-y
▲ 摘要：
目前亟需普遍適用于各種底物的反應(yīng)條件，特別是在制藥和化學(xué)工業(yè)中。盡管有許多方法可用于評(píng)估所開發(fā)條件的普遍適用性，但在優(yōu)化過程中有效發(fā)現(xiàn)這些條件的通用方法卻很少。
研究組報(bào)道了強(qiáng)化學(xué)習(xí)bandit優(yōu)化模型的設(shè)計(jì)、實(shí)現(xiàn)和應(yīng)用，通過有效的條件采樣和實(shí)驗(yàn)反饋的評(píng)估來識(shí)別普遍適用的條件?，F(xiàn)有數(shù)據(jù)集的性能基準(zhǔn)統(tǒng)計(jì)顯示，該模型識(shí)別通用條件的準(zhǔn)確性很高，與模仿最先進(jìn)優(yōu)化法的基線相比提高了31%。
研究組對(duì)鈀催化的咪唑C-H芳基化反應(yīng)、苯胺酰胺偶聯(lián)反應(yīng)和苯酚烷基化反應(yīng)進(jìn)行了實(shí)驗(yàn)研究，以評(píng)估bandit優(yōu)化模型在實(shí)踐中的應(yīng)用情況和功能。在調(diào)查了不到15%的專家設(shè)計(jì)的反應(yīng)空間后，研究確定了上述三種情況下最普遍適用但尚未進(jìn)行充分研究的反應(yīng)條件。
▲ Abstract：
Reaction conditions that are generally applicable to a wide variety of substrates are highly desired, especially in the pharmaceutical and chemical industries. Although many approaches are available to evaluate the general applicability of developed conditions, a universal approach to efficiently discover these conditions during optimizations is rare. Here we report the design, implementation and application of reinforcement learning bandit optimization models to identify generally applicable conditions by efficient condition sampling and evaluation of experimental feedback. Performance benchmarking on existing datasets statistically showed high accuracies for identifying general conditions, with up to 31% improvement over baselines that mimic state-of-the-art optimization approaches. A palladium-catalysed imidazole C–H arylation reaction, an aniline amide coupling reaction and a phenol alkylation reaction were investigated experimentally to evaluate use cases and functionalities of the bandit optimization model in practice. In all three cases, the reaction conditions that were most generally applicable yet not well studied for the respective reaction were identified after surveying less than 15% of the expert-designed reaction space.
社會(huì)學(xué)Sociology
Online images amplify gender bias
網(wǎng)絡(luò)圖像放大了性別偏見
▲ 作者：Douglas Guilbeault, Solène Delecourt, Tasker Hull, Bhargav Srinivasa Desikan, Mark Chu & Ethan Nadler
▲ 鏈接：
https://www.nature.com/articles/s41586-024-07068-x
▲ 摘要：
每年，人們花在閱讀上的時(shí)間越來越少，而花在觀看網(wǎng)絡(luò)激增圖像上的時(shí)間越來越多。每天有數(shù)百萬人下載來自谷歌和維基百科等平臺(tái)的圖片，還有數(shù)百萬人通過Instagram和TikTok等社交媒體進(jìn)行互動(dòng)，主要為交換視覺內(nèi)容。與此同時(shí)，新聞機(jī)構(gòu)和數(shù)字廣告商越來越多地通過使用圖像在網(wǎng)上吸引人們的注意力，人們對(duì)圖像的處理相比文本速度更快、更含蓄、更容易記住。
研究組表明，網(wǎng)絡(luò)圖像的興起大大加劇了性別偏見，在統(tǒng)計(jì)普遍性和心理影響上均是如此。他們從谷歌、維基百科和互聯(lián)網(wǎng)電影數(shù)據(jù)庫（IMDb）的100多萬張圖片以及這些平臺(tái)的數(shù)十億個(gè)單詞中，研究了3495個(gè)社會(huì)類別（如“護(hù)士”或“銀行家”）的性別關(guān)聯(lián)。
結(jié)果發(fā)現(xiàn)，在兩性的社會(huì)類別中，性別偏見在圖像中始終比在文本中更普遍。同時(shí)，有記錄的女性網(wǎng)絡(luò)代表性不足，這種不足在圖像中比在文本、公眾輿論和美國(guó)人口普查數(shù)據(jù)中要嚴(yán)重得多。最后，一項(xiàng)具有全國(guó)代表性的預(yù)注冊(cè)實(shí)驗(yàn)表明，在谷歌上搜索職業(yè)圖片而非文字描述會(huì)放大參與者信念中的性別偏見。
解決這種大規(guī)模轉(zhuǎn)向視覺傳播的社會(huì)影響，對(duì)于發(fā)展一個(gè)公平包容的互聯(lián)網(wǎng)未來至關(guān)重要。
▲ Abstract：
Each year, people spend less time reading and more time viewing images, which are proliferating online. Images from platforms such as Google and Wikipedia are downloaded by millions every day, and millions more are interacting through social media, such as Instagram and TikTok, that primarily consist of exchanging visual content. In parallel, news agencies and digital advertisers are increasingly capturing attention online through the use of images, which people process more quickly, implicitly and memorably than text. Here we show that the rise of images online significantly exacerbates gender bias, both in its statistical prevalence and its psychological impact. We examine the gender associations of 3,495 social categories (such as ‘nurse’ or ‘banker’) in more than one million images from Google, Wikipedia and Internet Movie Database (IMDb), and in billions of words from these platforms. We find that gender bias is consistently more prevalent in images than text for both female- and male-typed categories. We also show that the documented underrepresentation of women online is substantially worse in images than in text, public opinion and US census data. Finally, we conducted a nationally representative, preregistered experiment that shows that googling for images rather than textual descriptions of occupations amplifies gender bias in participants’ beliefs. Addressing the societal effect of this large-scale shift towards visual communication will be essential for developing a fair and inclusive future for the internet.
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