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《科学》（20230901出版）一周论文导读2023-09-04 09:37·科学网编译 | 冯维维Science, VOLUME 381, ISSUE 6661, 1 SEP 2023《科学》，第381卷，6661期，2023年9月1日物理学PhysicsObservations of a black hole -ray binary indicate formation of a magnetically arrested disk黑洞X射线双星或能形成磁性圆盘▲ 作者：BEI YOU, XINWU CAO, ZHEN YAN, JEAN-MARIE HAMEURY, BOZENA CZERNY, YUE WUTIANYU XIA, MAREK SIKORA, SHUANG-NAN ZHANG, AND PIOTR T. ZYCKI▲ 链接：https://www.science.org/doi/full/10.1126/science.abo4504▲ 摘要：黑洞中物质的吸积会将磁场向内拖曳，从而增强磁场的强度。理论预测，足够强的磁场可以阻止吸积流，产生磁阻盘（MAD）。研究者分析了2018年黑洞X射线双星MAXI J1820+070爆发的多波长观测档案。与X射线通量相比，射电通量和光通量分别延迟了约8天和17天。他们将此解释为MAD形成的证据。在这种情况下，磁场被不断膨胀的日冕放大，在射电峰值前后形成一个磁极。研究者认为光延迟是由于外盘的热粘性不稳定性造成的。▲ Abstract：Accretion of material onto a black hole drags any magnetic fields present inwards, increasing their strength. Theory predicts that sufficiently strong magnetic fields can halt the accretion flow, producing a magnetically arrested disk (MAD). We analyzed archival multiwavelength observations of an outburst from the black hole x-ray binary MAXI J1820+070 in 2018. The radio and optical fluxes were delayed compared with the x-ray flux by about 8 and 17 days, respectively. We interpret this as evidence for the formation of a MAD. In this scenario, the magnetic field is amplified by an expanding corona, forming a MAD around the time of the radio peak. We propose that the optical delay is due to thermal viscous instability in the outer disk.化学ChemistryA machine-learning tool to predict substrate-adaptive conditions for Pd-catalyzed C–N couplings预测钯催化碳氮偶联的底物自适应条件的机器学习工具▲ 作者：N. IAN RINEHART, RAKESH K. SAUNTHWAL, JO?L WELLAUER, ANDREW F. ZAHRT, LUKAS SCHLEMPER, ALEXANDER S. SHVED, RAPHAEL BIGLER, SERENA FANTASIA , AND SCOTT E. DENMARK▲ 链接：https://www.science.org/doi/full/10.1126/science.adg2114▲ 摘要：机器学习方法在加速识别化学转化的反应条件方面具有很大的潜力。研究者提出了一种工具，给出了钯（Pd）催化碳氮（C-N）偶联的底物自适应条件。该工具的设计和构建需要生成一个实验数据集，该数据集可以在一系列反应条件下探索不同的反应物配对网络。通过系统的实验设计过程，研究者利用神经网络模型主动学习大范围的碳氮耦合。模型在实验验证中表现出良好的性能：从一系列与样品外反应物的耦合中分离出10个产物，产率超过85%。重要的是，随着数据量的增长，开发的工作流可不断提高工具的预测能力。▲ Abstract：Machine-learning methods have great potential to accelerate the identification of reaction conditions for chemical transformations. A tool that gives substrate-adaptive conditions for palladium (Pd)–catalyzed carbon-nitrogen (C–N) couplings is presented. The design and construction of this tool required the generation of an experimental dataset that explores a diverse network of reactant pairings across a set of reaction conditions. A large scope of C–N couplings was actively learned by neural network models by using a systematic process to design experiments. The models showed good performance in experimental validation: Ten products were isolated in more than 85% yield from a range of couplings with out-of-sample reactants designed to challenge the models. Importantly, the developed workflow continually improves the prediction capability of the tool as the corpus of data grows.Ring-opening polymerization of cyclic oligosiloxanes without producing cyclic oligomers不产生环低聚物的环低聚硅氧烷开环聚合▲ 作者：LIMIAO SHI, AUR?LIE BOUL?GUE-MONDI?RE, DELPHINE BLANC, ANTOINE BACEIREDO, VICEN? BRANCHADELL, AND TSUYOSHI KATO▲ 链接：https://www.science.org/doi/full/10.1126/science.adi1342▲ 摘要：硅氧链的稳定增长促进了有机硅的大规模生产。然而，这些链中有一小部分在反应后期不可避免地反咬自己，产生循环杂质。作者报道称，苯甲醇可通过氢键与链端络合，抑制咬背过程。他们还描述了一种磷反离子，也被酒精稳定，但在没有酒精的情况下会分解，以抑制链的生长，同样防止副产物的形成。▲ Abstract：Mass production of silicones proceeds by the steady growth of silicon–oxygen chains. However, there is a small fraction of these chains that inevitably bite back on themselves late in the reaction to produce cyclic impurities. Shi et al. report that benzyl alcohol can complex with the chain end through hydrogen bonding and inhibit the back-biting process. Moreover, they describe a phosphonium counterion that is also stabilized by the alcohol but decomposes in its absence to deactivate chain growth, likewise preventing the by-product formation.气候和古人类学Climate and PaleoanthropologyFluctuating Atlantic inflows modulate Arctic atlantification波动大西洋流入调节北极“大西洋化”▲ 作者：IGOR V. POLYAKOV, RANDI B. INGVALDSEN, ANDREY V. PNYUSHKOV, UMA S. BHATT, JENNIFER A. FRANCIS, MARKUS JANOUT, RONALD KWOK, AND ?YSTEIN SKAGSETH▲ 链接：https://www.science.org/doi/10.1126/science.adh5158▲ 摘要：过去几十年，北极海冰一直在消失，原因之一是来自大西洋的温水正越来越多地平流到高纬度的海洋中，这一过程被称为“大西洋化”。是什么推动了这个过程呢？作者研究表明，被称为北极偶极子的大尺度天气模式导致大气风模式，这种模式调节穿过弗拉姆海峡和巴伦支海的北大西洋流入，导致北冰洋环流、流入亚美亚盆地的淡水通量、海洋分层和热通量的变化。▲ Abstract：One of the reasons that Arctic sea ice has been disappearing over the past decades is that warm water from the Atlantic is being advected into the high-latitude ocean in increasing amounts, a process called “atlantification.” But what drives this process? Polyakov et al. show that the large-scale weather pattern called the Arctic Dipole causes atmospheric wind patterns that modulate North Atlantic inflows across the Fram Strait and within the Barents Sea, resulting in variations in Arctic Ocean circulation, freshwater fluxes into the Amerasian Basin, ocean stratification, and heat fluxes.Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition早更新世到中更新世过渡时期严重人类瓶颈的基因组推断▲ 作者：WANGJIE HU, ZIQIAN HAO, PENGYUAN DU, FABIO DI VINCENZO, GIORGIO MANZI, JIALONG CUI, YUN-XIN FU, YI-HSUAN PAN , AND HAIPENG LI▲ 链接：https://www.science.org/doi/full/10.1126/science.abq7487▲ 摘要：今天，地球上有80多亿人，主宰着地球。但在80万到90万年前，情况大不相同。研究者使用一种新开发的凝聚模型，从3000多个现代人类基因组中预测过去人类的人口规模。该模型发现，人类祖先的规模曾从大约10万人减少到大约1000人，这种情况持续了大约10万年。这种下降似乎与主要的气候变化和随后的物种形成事件同时发生。▲ Abstract：Today, there are more than 8 billion human beings on the planet. We dominate Earth’s landscapes, and our activities are driving large numbers of other species to extinction. Had a researcher looked at the world sometime between 800,000 and 900,000 years ago, however, the picture would have been quite different. Hu et al. used a newly developed coalescent model to predict past human population sizes from more than 3000 present-day human genomes. The model detected a reduction in the population size of our ancestors from about 100,000 to about 1000 individuals, which persisted for about 100,000 years. The decline appears to have coincided with both major climate change and subsequent speciation events.计量学MetrologyEstablishing a new standard of care for calculus using trials with randomized student allocation利用随机分配学生试验建立微积分学习新标准▲ 作者：LAIRD KRAMER, EDGAR FULLER, CHARITY WATSON, ADAM CASTILLO, PABLO DURAN OLIVA▲ 链接：https://www.science.org/doi/full/10.1126/science.ade9803▲ 摘要：在美国高校，微积分是获得STEM学位的入门课程。在所有最初攻读STEM学位的学生中，超过一半的人毕业时没有获得学位，通常是在努力完成课程之后。教师默认采用传统的以讲座为基础的教学方式，加剧了不合格率的差异；这对女性、西班牙裔和黑人学生的影响尤为严重，剥夺了劳动力中来自不同群体的人才和见解。作者进行了一项大型试验，将学生随机分配到微积分教室，教师积极地与学生合作（治疗），或者依赖传统的授课方式，将他们视为被动的学习者（对照）。在不同的人口统计群体中，这种治疗更有效，因为参与培养了对微积分的更深理解，提高了成绩，并促进了代表性不足的学生的融入。这表明微积分教学的新标准和完成STEM学位的机会增加。▲ Abstract：Across US universities, calculus is a gateway course for STEM degrees. Of all students who initially pursue STEM degrees, more than half graduate without one, often after struggling through coursework. Instructors defaulting to traditional lecture-based instruction exacerbates disparities in failure rates; this disproportionately affects women, Hispanic, and Black students, depriving the workforce of talent and insights from diverse groups. Kramer et al. conducted a large trial that randomized students into calculus classrooms where instructors actively engaged students collaboratively (treatment) or relied on traditional lecture styles that treated them as passive learners (control). Across demographic groups, the treatment was more effective, as engagement fostered a deeper understanding of calculus, improved grades, and promoted the inclusion of underrepresented students.
2024年12月19日，招聘岗位：自动啤机长；招聘人数：4人
包含"欧美"、"性爱"、"S8"的内容视频社区在线,包含...起价207.68万成话题车型 奥迪S8购买手册_易车
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在先锋领航看来，预期2023年欧元区经济全年增长约为0.5%，但或在今年稍晚时间陷入温和衰退。“所有的优越感，都不是来自容貌、身材、知识、家族、财富、地位、成就和权力，它只来自缺见识和缺悲悯。”