材料科学Materials Science Plasticity in single-crystalline Mg3Bi2 thermoelectric material 单晶Mg3Bi2热电材料的塑性 ▲ 作者：Peng Zhao, Wenhua Xue, Yue Zhang, Shizhen Zhi, Xiaojing Ma, Jiamin Qiu, et al. ▲链接： https://www.nature.com/articles/s41586-024-07621-8 ▲摘要： 年夜大都最早进的热电材料是无机半导体。因为定向共价键，其凡是在室温下表示出有限的塑性，例如，拉伸应变小在5%。 研究组发现单晶Mg3Bi2在沿（0001）平面（即ab平面）施加张力时显示出高达100%的室温拉伸应变。该值比传统热电材料最少超出跨越一个数目级，且优在很多以近似布局结晶的金属。 尝试成果注解，变形的Mg3Bi2中存在滑移带和位错，注解位错滑动是塑性变形的微不雅机制。化学键阐发揭露了多个低滑移势垒能面，注解Mg3Bi2中存在多种滑移系统。另外，滑移进程中持续的动态键合避免了原子面解理，从而连结了较年夜的塑性变形。 主要的是，碲搀杂的单晶Mg3Bi2在室温下沿ab平面显示出约55 W/cm K2平方的功率因数和约0.65的品质系数，优在现有的延展性热电材料。 ▲ Abstract： Most of the state-of-the-art thermoelectric materials are inorganic semiconductors. Owing to the directional covalent bonding, they usually show limited plasticity at room temperature, for example, with a tensile strain of less than five per cent. Here we discover that single-crystalline Mg3Bi2 shows a room-temperature tensile strain of up to 100 per cent when the tension is applied along the (0001) plane (that is, the ab plane). Such a value is at least one order of magnitude higher than that of traditional thermoelectric materials and outperforms many metals that crystallize in a similar structure. Experimentally, slip bands and dislocations are identified in the deformed Mg3Bi2, indicating the gliding of dislocations as the microscopic mechanism of plastic deformation. Analysis of chemical bonding reveals multiple planes with low slipping barrier energy, suggesting the existence of several slip systems in Mg3Bi2. In addition, continuous dynamic bonding during the slipping process prevents the cleavage of the atomic plane, thus sustaining a large plastic deformation. Importantly, the tellurium-doped single-crystalline Mg3Bi2 shows a power factor of about 55 microwatts per centimetre per kelvin squared and a figure of merit of about 0.65 at room temperature along the ab plane, which outperforms the existing ductile thermoelectric materials. 工程学Engineering 3D printable elastomers with exceptional strength and toughness 具有不凡强度和韧性的3D打印弹性体 ▲ 作者：Zizheng Fang, Hongfeng Mu, Zhuo Sun, Kaihang Zhang, Anyang Zhang, Jiada Chen, et al. ▲链接： https://www.nature.com/articles/s41586-024-07588-6 ▲摘要： 三维（3D）打印已成为一种颇具吸引力的制造手艺，因其在实现几何复杂的可定制产物方面具有不凡的自由度。但是，其年夜范围出产的潜力遭到低制造效力（打印速度）和产物质量不足（机械机能）的阻碍。 光聚合物超快速3D打印手艺的最新进展减缓了制造效力的问题，但典型打印聚合物的机械机能仍远远掉队在传统加工手艺。这是由于打印要求限制了份子设计实现高机械机能的潜力。 研究组报导了一种3D光打印树脂化学策略，其发生的弹性体抗拉强度为94.6 MPa，韧性为310.4 MJ m-3，二者均远远跨越任何3D打印弹性体。从机理上讲，这经由过程打印聚合物中的动态共价键来实现，同时还实现了收集拓扑布局重构。 这有助在构成分层氢键（特殊是酰胺氢键）、微相分手和互穿布局，从而协同增进出色的机械机能。该工作为利用3D打印进行年夜范围制造供给了一个更光亮的前景。 ▲ Abstract： Three-dimensional (3D) printing has emerged as an attractive manufacturing technique because of its exceptional freedom in accessing geometrically complex customizable products. Its potential for mass manufacturing, however, is hampered by its low manufacturing efficiency (print speed) and insufficient product quality (mechanical properties). Recent progresses in ultra-fast 3D printing of photo-polymers have alleviated the issue of manufacturing efficiency, but the mechanical performance of typical printed polymers still falls far behind what is achievable with conventional processing techniques. This is because of the printing requirements that restrict the molecular design towards achieving high mechanical performance. Here we report a 3D photo-printable resin chemistry that yields an elastomer with tensile strength of 94.6 MPa and toughness of 310.4 MJ m-3, both of which far exceed that of any 3D printed elastomer. Mechanistically, this is achieved by the dynamic covalent bonds in the printed polymer that allow network topological reconfiguration. This facilitates the formation of hierarchical hydrogen bonds (in particular, amide hydrogen bonds), micro-phase separation and interpenetration architecture, which contribute synergistically to superior mechanical performance. Our work suggests a brighter future for mass manufacturing using 3D printing. 人工智能Artificial Intelligence AI models collapse when trained on recursively generated data AI模子在利用递归生成数据进行练习时会解体 ▲ 作者：Ilia Shumailov, Zakhar Shumaylov, Yiren Zhao, Nicolas Papernot, Ross Anderson Yarin Gal ▲链接： https://www.nature.com/articles/s41586-024-07566-y ▲摘要： 不变分散完全改变了描写性文本的图象建立。GPT-2、GPT-3.5和GPT-4在各类说话使命中表示优良。ChatGPT向公家推行了这类说话模子。此刻很较着，年夜说话模子（LLMs）等生成式人工智能（AI）将持久存在，并将极年夜地改变在线文本和图象的生态系统。 研究组斟酌一旦LLM进献了在线找到的年夜量文本，GPT-{n}可能会产生甚么。他们发现，在练习中滥用模子生成的内容会致使生成的模子呈现不成逆转的缺点，即原始内容散布的尾部会消逝。 研究组将这类效应称为 模子解体 ，并注解其可能产生在LLM和变分自编码器（VAEs）和高斯夹杂模子（GMMs）中。他们在该现象背后构建了理论直觉，并描画了其在所有进修生成模子中的遍及性。 研究组注解，若要保持从收集上抓取的年夜范围数据进行练习的好处，就必需当真看待这个问题。事实上，在从互联网抓取的数据中存在LLM生成内容的环境下，搜集到的关在人类与系统间真实交互数据的价值将愈来愈高。 ▲ Abstract： Stable diffusion revolutionized image creation from descriptive text. GPT-2, GPT-3(.5) and GPT-4 demonstrated high performance across a variety of language tasks. ChatGPT introduced such language models to the public. It is now clear that generative artificial intelligence (AI) such as large language models (LLMs) is here to stay and will substantially change the ecosystem of online text and images. Here we consider what may happen to GPT-{n} once LLMs contribute much of the text found online. We find that indiscriminate use of model-generated content in training causes irreversible defects in the resulting models, in which tails of the original content distribution disappear. We refer to this effect as model collapse and show that it can occur in LLMs as well as in variational autoencoders (VAEs) and Gaussian mixture models (GMMs). We build theoretical intuition behind the phenomenon and portray its ubiquity among all learned generative models. We demonstrate that it must be taken seriously if we are to sustain the benefits of training from large-scale data scraped from the web. Indeed, the value of data collected about genuine human interactions with systems will be increasingly valuable in the presence of LLM-generated content in data crawled from the Internet. 化学Chemistry Unlocking carbene reactivity by metallaphotoredox -elimination 金属光氧化还原 -消弭解锁卡宾反映性 ▲ 作者：Benjamin T. Boyle, Nathan W. Dow, Christopher B. Kelly, Marian C. Bryan David W. C. MacMillan ▲链接： https://www.nature.com/articles/s41586-024-07628-1 ▲摘要： 把握高能中心体的能力对合成化学很是主要，它使复杂份子的构建成为可能，并鞭策合成范畴的前进。沿着这些线路，卡宾和类卡宾中心体颇具吸引力，但常常是未知的高能中心体。获得金属卡宾中心体的经典方式是操纵双电子化学构成碳-金属键。但是，因为试剂平安问题，这些方式凡是被制止，限制了其在合成中的普遍利用。 从机理上讲，可避免这些缺点的卡宾中心体的替换方式触及两个单电子步调：自由基加到金属中构成最初的碳-金属键，然后氧化还原增进 -消弭，发生所需的金属卡宾中心体。 研究组经由过程金属光氧化还原平台实现了这一策略，操纵铁卡宾的反映性，利用易在取得的化学原料作为自由基来历，并从六种先前未开辟的离去基团中进行 -消弭。这些发现可实现丰硕且不变的羧酸、氨基酸和醇类进行环丙烷化，并将 键插入到N-H、S-H和P-H键中，从而为卡宾介导的化学多样化挑战供给了一个通用解决方案。 ▲ Abstract： The ability to tame high-energy intermediates is important for synthetic chemistry, enabling the construction of complex molecules and propelling advances in the field of synthesis. Along these lines, carbenes and carbenoid intermediates are particularly attractive, but often unknown, high-energy intermediates. Classical methods to access metal carbene intermediates exploit two-electron chemistry to开云体育app form the carbon metal bond. However, these methods are usually prohibitive because of reagent safety concerns, limiting their broad implementation in synthesis. Mechanistically, an alternative approach to carbene intermediates that could circumvent these pitfalls would involve two single-electron steps: radical addition to metal to forge the initial carbon metal bond followed by redox-promoted -elimination to yield the desired metal carbene intermediate. Here we realize this strategy through a metallaphotoredox platform that exploits iron carbene reactivity using readily available chemical feedstocks as radical sources and -elimination from six classes of previously underexploited leaving groups. These discoveries permit cyclopropanation and -bond insertion into N H, S H and P H bonds from abundant and bench-stable carboxylic acids, amino acids and alcohols, thereby providing a general solution to the challenge of carbene-mediated chemical diversification. 地球科学Earth Science Global atmospheric methane uptake by upland tree woody surfaces 高地树木木质概况对全球年夜气甲烷的接收 ▲ 作者：Vincent Gauci, Sunitha Rao Pangala, Alexander Shenkin, Josep Barba, David Bastviken, Viviane Figueiredo, et al. ▲链接： https://www.nature.com/articles/s41586-024-07592-w ▲摘要： 甲烷是一种主要的温室气体，但树木在甲烷预算中的感化仍不肯定。固然已有研究注解湿地和一些高地树木可在茎干部释放泥土来历的甲烷，但也有人认为高地树木可作为年夜气甲烷的净汇。 课题组研究了热带、温带高地和北方丛林树木的原位木质概况甲烷互换。成果发现，木质概况的甲烷接收，特殊是在丛林地面以上约2米处，可以主导树木的净生态系统进献，致使树木的甲烷净汇。木质概况室空气中甲烷的不变碳同位素丈量和提取木芯的进程程度研究成果与甲烷营养一致，注解微生物介导的甲烷在木质概况和组织中削减。 经由过程利用陆地激光扫描衍生的异速丈量来量化全球丛林树木木质概况积，初步估量树木可能进献24.6~49.9 Tg的全球年夜气甲烷接收。该研究成果注解，热带和温带丛林庇护和再造林的天气效益可能比此前假定的要年夜。 ▲ Abstract： Methane is an important greenhouse gas, but the role of trees in the methane budget remains uncertain. Although it has been shown that wetland and some upland trees can emit soil-derived methane at the stem base, it has also been suggested that upland trees can serve as a net sink for atmospheric methane. Here we examine in situ woody surface methane exchange of upland tropical, temperate and boreal forest trees. We find that methane uptake on woody surfaces, in particular at and above about 2m above the forest floor, can dominate the net ecosystem contribution of trees, resulting in a net tree methane sink. Stable carbon isotope measurement of methane in woody surface chamber air and process-level investigations on extracted wood cores are consistent with methanotrophy, suggesting a microbially mediated drawdown of methane on and in tree woody surfaces and tissues. By applying terrestrial laser scanning-derived allometry to quantify global forest tree woody surface area, a preliminary first estimate suggests that trees may contribute 24.6 49.9 Tg of atmospheric methane uptake globally. Our findings indicate that the climate benefits of tropical and temperate forest protection and reforestation may be greater than previously assumed. Deep, hot, ancient melting recorded by ultralow oxygen fugacity in peridotites 橄榄岩超低氧逸度记实的深、热、古熔融事务 ▲ 作者：Suzanne K. Birner, Elizabeth Cottrell, Fred A. Davis Jessica M. Warren ▲链接： https://www.nature.com/articles/s41586-024-07603-w ▲摘要： 脊橄榄岩记实的对流上地幔氧逸度（fO2）转变幅度跨越4个数目级。虽然人们较多存眷驱动组织布景间地幔fO2转变的机制和现代岩石与古地幔衍生岩石之间的fO2比力，但对现代洋中脊布景下橄榄岩记实的fO2高变异性来历知之甚少。 研究组报导了盖克尔海脊和东承平洋海隆（EPR）橄榄岩的岩石学和地球化学，包罗16次新的fO2高精度测定。盖克尔海脊的难熔橄榄岩记实的fO2比地幔平均值低4个数目级以上。经由过程热力学和矿物分派模子，研究组发现，在高位温（Tp）下，从石榴石区最先，延续到尖晶石区，可发生向超低fO2的偏移，这些前提合适古科马提岩而非现代玄武岩的构成进程。 这其实不意味着泰初代情况对流上地幔的铁/亚铁比率低在今天，也不料味着热门石榴石区的现代熔融构成的岩浆削减。相反，这注解古老、难熔、超还原的地幔 筏 继续在现代地幔中轮回，而对现代脊火山勾当进献甚微。 ▲ Abstract： The oxygen fugacity (fO2) of convecting upper mantle recorded by ridge peridotites varies by more than four orders of magnitude. Although much attention has been given to mechanisms that drive variations in mantle fO2 between tectonic settings and to comparisons of fO2 between modern rocks and ancient-mantle-derived rocks, comparatively little has been done to understand the origins of the high variability in fO2 recorded by peridotites from modern mid-ocean ridge settings. Here we report the petrography and geochemistry of peridotites from the Gakkel Ridge and East Pacific Rise (EPR), including 16 new high-precision determinations of fO2. Refractory peridotites from the Gakkel Ridge record fO2 more than four orders of magnitude below the mantle average. With thermodynamic and mineral partitioning modelling, we show that excursions to ultralow fO2 can be produced by large degrees of melting at high potential temperature (Tp), beginning in the garnet field and continuing into the spinel field conditions met during the generation of ancient komatiites but not modern basalts. This does not mean that ambient convecting upper mantle had a lower ferric to ferrous ratio in Archaean times than today nor that modern melting in the garnet field at hotspots produce reduced magmas. Instead, it implies that rafts of ancient, refractory, ultrareduced mantle continue to circulate in the modern mantle while contributing little to modern ridge volcanism.特殊声明：本文转载仅仅是出在传布信息的需要，其实不意味着代表本网站不雅点或证实其内容的真实性；如其他媒体、网站或小我从本网站转载利用，须保存本网站注明的“来历”，并自大版权等法令责任；作者假如不但愿被转载或联系转载稿费等事宜，请与我们联系。
