编译 |渭九
nature, 29 february 2024, vol 626, issue 8001
《自然》，2024年2月29日，第626卷，第8001期
天文学
most of the photons that reionized the universe came from dwarf galaxies
大多数使宇宙再电离的光子来自矮星系
作者： Hakim Atek， Ivo Labbé， Lukas J furtak, iryna chemerynska, seiji fujimoto, d**id j. setton, et al.
链接：
总结：
宇宙再电离是宇宙大后约600 800 MYR从中性氢到电离等离子体的主要相变，但对于确定驱动宇宙再电离的因素一直存在争议。 一些模型表明，类星体的高电离发射率和逃逸分数（FeSC）支持其在驱动宇宙再电离中的作用。
其他人则提出，明亮星系中的高FESC值会产生足够的电离辐射来驱动这一过程。 最后，一些研究表明，当结合FESC的电离效率和恒星质量依赖模型时，暗星系的数量密度可以有效地控制宇宙再电离。 然而，迄今为止，由于低质量星系的极弱性质，尚未对其进行充分的光谱研究。
该研究小组报告了在再电离期间对8个超暗星系（在一个非常小的场中）的分析，绝对星等在MUV 17和15之间（低至0）。005l⋆）。人们发现，在宇宙的前十亿年中，微弱的星系产生了log[离子（hz erg 1）] = 2580±0.14个电离光子，比通常假设的值高4倍。
如果这个场代表了微弱星系的大尺度分布，那么光子的电离速率就超过了再电离所需的速率，即使在FeSC约为5%的情况下也是如此。
▲ 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 h**e 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%.
材料科学
high fatigue resistance in a titanium alloy via near-void-free 3d printing
钛合金的高抗疲劳性是通过几乎多孔的 3D 打印工艺实现的
作者： Zhan Qu， Zhenjun Zhang， Rui Liu， Ling Xu， Yining Zhang， Xiaotao Li， et al
链接：
总结：
3D打印的优势，即结构材料的增材制造，因其较差的疲劳性能而受到严重损害。 一般来说，疲劳性能差似乎是由当前印刷过程中的孔隙引起的。 因此，研究小组质疑消除这些孔隙是否可以提供一种可行的解决方案，以显着提高无孔AM（NET-AM）合金的抗疲劳性。
通过了解相变和晶粒扩展的异步性，课题组进一步开发了NET-AM工艺技术，并成功重建了Ti-6Al-4V钛合金中几乎无孔隙的AM微观结构。 他们确定了这种增材制造微观结构的抗疲劳性，并表明其约1 GPA的高疲劳极限超过了所有增材制造和锻造钛合金以及其他金属材料的抗疲劳性。
结果证实了NET-AM微观结构的高抗疲劳性以及增材制造工艺在生产具有最大疲劳强度的结构构件中的潜在优势，有利于增材制造技术在工程领域的进一步应用。
▲ 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
由应力消除驱动的阶梯式PT表面的特定位点反应性
作者： Guangdong Liu， Arthur J shih, huiqiu deng, kasinath ojha, xiaoting chen, mingchuan luo, et al.
链接：
总结：
非均相催化剂被广泛用于促进化学反应。 虽然已知化学反应通常发生在催化剂表面，但只有特定的表面位点具有高催化活性。 因此，识别活性位点并最大限度地提高其有效性是催化研究的核心，其中经典模型是根据不同的表面结构（例如平台和台阶）对活性位点进行分类。
然而，这种简单的分类往往会导致催化剂活性的数量级误差和活性位点的定性不确定性，从而限制了催化剂设计的机会。
以阶梯式PT（111）表面和电化学氧还原（ORR）反应为例，研究组证明，误差和不确定性较大的根本原因是分类的简化和忽视了表面应力释放驱动的原子位点特异性反应性。 具体来说，各个步骤的表面应力消除引入了一个不均匀的应变场，压缩比高达 55%，导致具有相同局部配位的高原原子的不同电子结构和反应性，并导致原子位点特异性ORR活性增强。
对于阶梯边缘两侧的高原原子，活性增强比高原中部原子高50倍，从而可以通过改变平台宽度或控制外部应力来控制ORR反应性。 因此，上述协同效应的发现为对催化活性原子位点的基本认识和多相催化剂的设计原理提供了新的视角。
▲ 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 h**e 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 **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
超分子聚合物通过液-液相分离形成结晶团簇
作者： Hailin Fu， Jingyi Huang， Joost J b. van der tol, lu su, yuyang wang, swayandipta dey, et al.
链接：
总结：
生物聚合物的液-液相分离（LLPS）最近被证明在形成具有多种生物学功能的无膜细胞器中起着核心作用。 LLPS与大分子凝固之间的相互作用是正在进行的研究的一部分。 合成的超分子聚合物是大分子的非共价群，但LLPS的发生很少被报道。
研究小组表明，通过合成组分的超分子聚合获得的不断生长的原纤维负责通过熵驱动途径相分离成高度各向异性的水滴（变质团簇）。 受右旋苷浓度调控的拥挤环境不仅影响超分子聚合动力学，还影响LLPS的性质，包括相分离动力学、形貌、内部有序性、流动性和最终晶状团簇的力学性能。
此外，基底-液体和液-液体界面已被证明可以加速超分子聚合物的LLPS，从而产生无数的三维有序结构，包括具有高度有序表面的微米长团簇阵列。 几种超分子聚合物证明了超分子聚合在控制新兴形式方面的普遍性和许多可能性，开辟了一个新的物质领域，从稳定LLP的高度结构化水溶液到纳米级软物质。
▲ 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.
化学
identifying general reaction conditions by bandit optimization
采用匪徒优化法确定一般反应条件
作者： Jason Y王杰森 M stevens, st**ros k. kariofillis, mai-jan tom, dung l. golden, jun li, et al.
链接：
总结：
迫切需要能够普遍应用于各种基材的反应条件，特别是在制药和化学工业中。 虽然有许多方法可用于评估所开发条件的一般适用性，但在优化过程中有效识别这些条件的通用方法很少。
课题组报告了强化学习匪徒优化模型的设计、实现和应用，通过有效的条件抽样和实验反馈评估，确定了普遍适用的条件。 现有数据集的性能基准统计表明，该模型在识别常见条件方面的准确率很高，比模拟最先进优化方法的基线高出31%。
课题组对钯催化的咪唑-h芳基化、苯胺偶联和苯酚烷基化进行了实验研究，以评估强盗优化模型在实践中的应用和功能。 在研究了专家设计的反应空间中不到15%后，该研究确定了在上述三种情况下最普遍适用但尚未得到充分研究的反应条件。
▲ 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 **ailable 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.
社会学
online images amplify gender bias
网络图片放大性别偏见
作者： Douglas Guilbeault， Solène Delecourt， Tasker Hull， Bharg** Srinivasa Desikan， Mark Chu & Ethan Nadler
链接：
总结：
每年，人们花在阅读上的时间越来越少，而花在网络上图像扩散上的时间却越来越多。 每天有数百万人通过谷歌和维基百科等平台进行互动，还有数百万人通过Instagram和TikTok等社交网络进行互动，主要是为了换取视觉内容。 与此同时，新闻机构和数字广告商越来越多地在线参与处理图像，这些图像处理速度更快、更微妙、更容易记住。
研究团队表明，网络图像的兴起大大加剧了性别偏见，无论是在统计普遍性还是心理影响方面。 他们研究了来自谷歌、维基百科和互联网电影数据库（IMDB）的100多万个**以及来自这些平台的数十亿个单词的3,495个社会类别（如“**”或“银行家”）中的性别关联。
结果发现，在两性的社会类别中，性别偏见在图像中始终比在文本中更为普遍。 与此同时，记录在案的女性网络代表性不足，这一缺陷在图像中比在文本、公共**和美国人口普查数据中更为严重。 最后，一项具有全国代表性的预注册实验表明，在谷歌上搜索职业**而不是文字描述会放大参与者信念中的性别偏见。
解决这种向视觉传播的大规模转变所产生的社会影响，对于发展公平和包容的互联网未来至关重要。
▲ 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.