編譯 |渭九
nature, 29 february 2024, vol 626, issue 8001
《自然》，2024年2月29日，第626卷，第8001期
天文學
most of the photons that reionized the universe came from dwarf galaxies
大多數使宇宙再電離的光子來自矮星系
作者： Hakim Atek， Ivo Labbé， Lukas J furtak, iryna chemerynska, seiji fujimoto, d**id j. setton, et al.
鏈結：
總結：
宇宙再電離是宇宙大後約600 800 MYR從中性氫到電離等離子體的主要相變，但對於確定驅動宇宙再電離的因素一直存在爭議。 一些模型表明，類星體的高電離發射率和逃逸分數（FeSC）支援其在驅動宇宙再電離中的作用。
其他人則提出，明亮星系中的高FESC值會產生足夠的電離輻射來驅動這一過程。 最後，一些研究表明，當結合FESC的電離效率和恆星質量依賴模型時，暗星系的數量密度可以有效地控制宇宙再電離。 然而，迄今為止，由於低質量星系的極弱性質，尚未對其進行充分的光譜研究。
該研究小組報告了在再電離期間對8個超暗星系（在乙個非常小的場中）的分析，絕對星等在MUV 17和15之間（低至0）。005l⋆）。人們發現，在宇宙的前十億年中，微弱的星系產生了log[離子（hz erg 1）] = 2580±0.14個電離光子，比通常假設的值高4倍。
如果這個場代表了微弱星系的大尺度分布，那麼光子的電離速率就超過了再電離所需的速率，即使在FeSC約為5%的情況下也是如此。
▲ 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%.
材料科學
high fatigue resistance in a titanium alloy via near-void-free 3d printing
鈦合金的高抗疲勞性是通過幾乎多孔的 3D 列印工藝實現的
作者： Zhan Qu， Zhenjun Zhang， Rui Liu， Ling Xu， Yining Zhang， Xiaotao Li， et al
鏈結：
總結：
3D列印的優勢，即結構材料的增材製造，因其較差的疲勞效能而受到嚴重損害。 一般來說，疲勞效能差似乎是由當前印刷過程中的孔隙引起的。 因此，研究小組質疑消除這些孔隙是否可以提供一種可行的解決方案，以顯著提高無孔AM（NET-AM）合金的抗疲勞性。
通過了解相變和晶粒擴充套件的非同步性，課題組進一步開發了NET-AM工藝技術，並成功重建了Ti-6Al-4V鈦合金中幾乎無孔隙的AM微觀結構。 他們確定了這種增材製造微觀結構的抗疲勞性，並表明其約1 GPA的高疲勞極限超過了所有增材製造和鍛造鈦合金以及其他金屬材料的抗疲勞性。
結果證實了NET-AM微觀結構的高抗疲勞性以及增材製造工藝在生產具有最大疲勞強度的結構構件中的潛在優勢，有利於增材製造技術在工程領域的進一步應用。
▲ 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
由應力消除驅動的階梯式PT表面的特定位點反應性
作者： Guangdong Liu， Arthur J shih, huiqiu deng, kasinath ojha, xiaoting chen, mingchuan luo, et al.
鏈結：
總結：
非均相催化劑被廣泛用於促進化學反應。 雖然已知化學反應通常發生在催化劑表面，但只有特定的表面位點具有高催化活性。 因此，識別活性位點並最大限度地提高其有效性是催化研究的核心，其中經典模型是根據不同的表面結構（例如平台和台階）對活性位點進行分類。
然而，這種簡單的分類往往會導致催化劑活性的數量級誤差和活性位點的定性不確定性，從而限制了催化劑設計的機會。
以階梯式PT（111）表面和電化學氧還原（ORR）反應為例，研究組證明，誤差和不確定性較大的根本原因是分類的簡化和忽視了表面應力釋放驅動的原子位點特異性反應性。 具體來說，各個步驟的表面應力消除引入了乙個不均勻的應變場，壓縮比高達 55%，導致具有相同區域性配位的高原原子的不同電子結構和反應性，並導致原子位點特異性ORR活性增強。
對於階梯邊緣兩側的高原原子，活性增強比高原中部原子高50倍，從而可以通過改變平台寬度或控制外部應力來控制ORR反應性。 因此，上述協同效應的發現為對催化活性原子位點的基本認識和多相催化劑的設計原理提供了新的視角。
▲ 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 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
超分子聚合物通過液-液相分離形成結晶團簇
作者： Hailin Fu， Jingyi Huang， Joost J b. van der tol, lu su, yuyang wang, swayandipta dey, et al.
鏈結：
總結：
生物聚合物的液-液相分離（LLPS）最近被證明在形成具有多種生物學功能的無膜細胞器中起著核心作用。 LLPS與大分子凝固之間的相互作用是正在進行的研究的一部分。 合成的超分子聚合物是大分子的非共價群，但LLPS的發生很少被報道。
研究小組表明，通過合成組分的超分子聚合獲得的不斷生長的原纖維負責通過熵驅動途徑相分離成高度各向異性的水滴（變質團簇）。 受右旋苷濃度調控的擁擠環境不僅影響超分子聚合動力學，還影響LLPS的性質，包括相分離動力學、形貌、內部有序性、流動性和最終晶狀團簇的力學效能。
此外，基底-液體和液-液體介面已被證明可以加速超分子聚合物的LLPS，從而產生無數的三維有序結構，包括具有高度有序表面的微公尺長團簇陣列。 幾種超分子聚合物證明了超分子聚合在控制新興形式方面的普遍性和許多可能性，開闢了乙個新的物質領域，從穩定LLP的高度結構化水溶液到奈米級軟物質。
▲ 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
identifying general reaction conditions by bandit optimization
採用匪徒優化法確定一般反應條件
作者： Jason Y王傑森 M stevens, st**ros k. kariofillis, mai-jan tom, dung l. golden, jun li, et al.
鏈結：
總結：
迫切需要能夠普遍應用於各種基材的反應條件，特別是在製藥和化學工業中。 雖然有許多方法可用於評估所開發條件的一般適用性，但在優化過程中有效識別這些條件的通用方法很少。
課題組報告了強化學習匪徒優化模型的設計、實現和應用，通過有效的條件抽樣和實驗反饋評估，確定了普遍適用的條件。 現有資料集的效能基準統計表明，該模型在識別常見條件方面的準確率很高，比模擬最先進優化方法的基線高出31%。
課題組對鈀催化的咪唑-h芳基化、苯胺偶聯和苯酚烷基化進行了實驗研究，以評估強盜優化模型在實踐中的應用和功能。 在研究了專家設計的反應空間中不到15%後，該研究確定了在上述三種情況下最普遍適用但尚未得到充分研究的反應條件。
▲ 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 **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.
社會學
online images amplify gender bias
網路圖片放大性別偏見
作者： Douglas Guilbeault， Solène Delecourt， Tasker Hull， Bharg** Srinivasa Desikan， Mark Chu & Ethan Nadler
鏈結：
總結：
每年，人們花在閱讀上的時間越來越少，而花在網路上影象擴散上的時間卻越來越多。 每天有數百萬人通過谷歌和維基百科等平台進行互動，還有數百萬人通過Instagram和TikTok等社交網路進行互動，主要是為了換取視覺內容。 與此同時，新聞機構和數字廣告商越來越多地線上參與處理影象，這些影象處理速度更快、更微妙、更容易記住。
研究團隊表明，網路影象的興起大大加劇了性別偏見，無論是在統計普遍性還是心理影響方面。 他們研究了來自谷歌、維基百科和網際網絡電影資料庫（IMDB）的100多萬個**以及來自這些平台的數十億個單詞的3,495個社會類別（如“**”或“銀行家”）中的性別關聯。
結果發現，在兩性的社會類別中，性別偏見在影象中始終比在文字中更為普遍。 與此同時，記錄在案的女性網路代表性不足，這一缺陷在影象中比在文字、公共**和美國人口普查資料中更為嚴重。 最後，一項具有全國代表性的預註冊實驗表明，在谷歌上搜尋職業**而不是文字描述會放大參與者信念中的性別偏見。
解決這種向視覺傳播的大規模轉變所產生的社會影響，對於發展公平和包容的網際網絡未來至關重要。
▲ 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.