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Science, 26 JAN 2024, VOL 383, ISSUE 6681
Science, January 26, 2024, Vol. 383, No. 6681
Astronomy
Acceleration and transport of relativistic electrons in the jets of the microquasar SS 433
Acceleration and transport of relativistic electrons in the jet stream of the microquasar SS 433
▲ 作者：H.E.S.S. Collaboration
▲ Links:
https://www.science.org/doi/10.1126/science.adi2048
▲ Abstract:
SS 433 is a microquasar and a binary star system that emits collimated, relativistic jets.
The research team observed the gamma rays of SS 433 using a high-energy stereostereo system (H.E.S.S.) and found that the apparent position of gamma ray emission in the second-scale jet was shifted in energy dependence. These observations tracked the number of high-energy electrons and showed that inverse Compton scattering is the emitting mechanism of gamma rays.
The team's modeling of energy-dependent gamma-ray morphology limits where the particles can accelerate, and requires abrupt deceleration of the jet. They deduced that there was a shock wave between the distance of 25 and 30 parsecs on either side of the binary system, and that the self-collimation of the precession jet formed a shock wave, which then effectively accelerated the electrons.
▲ Abstract：
SS 433 is a microquasar, a stellar binary system that launches collimated relativistic jets. We observed SS 433 in gamma rays using the High Energy Stereoscopic System (H.E.S.S.) and found an energy-dependent shift in the apparent position of the gamma-ray emission from the parsec-scale jets. These observations trace the energetic electron population and indicate that inverse Compton scattering is the emission mechanism of the gamma rays. Our modeling of the energy-dependent gamma-ray morphology constrains the location of particle acceleration and requires an abrupt deceleration of the jet flow. We infer the presence of shocks on either side of the binary system, at distances of 25 to 30 parsecs, and that self-collimation of the precessing jets forms the shocks, which then efficiently accelerate electrons.
材料科学Materials Science
Super-tetragonal Sr4Al2O7 as a sacrificial layer for high-integrity freestanding oxide membranes
The ultratetragonal phase Sr4Al2O7 is used as a sacrificial layer for high-integrity independent oxide films
▲作者:Jinfeng Zhang, Ting Lin, Ao Wang, Xiaochao Wang, Qingyu He, Huan Ye, et al.
▲ Links:
https://www.science.org/doi/10.1126/science.adi6620
▲ Abstract:
Identifying the right water-soluble sacrificial layer is critical to creating large-scale, independent oxide films that provide attractive functionality and are combined with advanced semiconductor technologies.
The research group introduced a water-soluble sacrificial layer, the "supertetragonal" Sr4Al2O7 (SAOT). The low-symmetry crystal structure gives it the superior ability to maintain epitaxial strains, enabling wide tunability of lattice constants. The co-lattice structure and defect-free interface in the perovskite ABO3/SAOT heterostructure effectively inhibit the formation of cracks during the release of independent oxide films.
For a wide range of non-ferroelectric oxide films, the crack-free area can range up to one millimeter. This compelling feature, combined with its inherently high water solubility, makes SAOT a versatile and viable sacrificial layer that can be used to produce high-quality, independent oxide films, thereby increasing its potential for innovative device applications.
▲ Abstract：
Identifying a suitable water-soluble sacrificial layer is crucial to fabricating large-scale freestanding oxide membranes, which offer attractive functionalities and integrations with advanced semiconductor technologies. Here, we introduce a water-soluble sacrificial layer, “super-tetragonal” Sr4Al2O7 (SAOT). The low-symmetric crystal structure enables a superior capability to sustain epitaxial strain, allowing for broad tunability in lattice constants. The resultant structural coherency and defect-free interface in perovskite ABO3/SAOT heterostructures effectively restrain crack formation during the water release of freestanding oxide membranes. For a variety of nonferroelectric oxide membranes, the crack-free areas can span up to a millimeter in scale. This compelling feature, combined with the inherent high water solubility, makes SAOT a versatile and feasible sacrificial layer for producing high-quality freestanding oxide membranes, thereby boosting their potential for innovative device applications.
Chemistry
Automated self-optimization, intensification, and scale-up of photocatalysis in flow
Automatic self-optimization, intensification, and amplification of flow photocatalysis
▲ 作者：Aidan Slattery, Zhenghui Wen, Pauline Tenblad, Jesús Sanjosé-Orduna, Diego Pintossi, Tim den Hartog, et al.
▲ Links:
https://www.science.org/doi/10.1126/science.adj1817
▲ Abstract:
In a manufacturing environment that is primarily geared towards thermochemistry, the optimization, intensification, and scale-up of photochemical processes pose a particular challenge.
The study group proposed a versatile, flow-based robotics platform that solves these challenges by integrating existing hardware and custom software. The open-source platform combines liquid handlers, syringe pumps, tunable continuous streamer reactors, inexpensive IoT devices, and online benchtop NMR spectrometers to enable automated, data-rich optimization through a closed-loop Bayesian optimization strategy.
The user-friendly graphical interface enables chemists with no programming or machine learning expertise to easily detect, analyze, and improve photocatalytic reactions on continuous and discrete variables. By increasing the total reaction yield and improving the spatiotemporal yield, the effectiveness of the system is significantly better than that of previously reported processes.
▲ Abstract：
The optimization, intensification, and scale-up of photochemical processes constitute a particular challenge in a manufacturing environment geared primarily toward thermal chemistry. In this work, we present a versatile flow-based robotic platform to address these challenges through the integration of readily available hardware and custom software. Our open-source platform combines a liquid handler, syringe pumps, a tunable continuous-flow photoreactor, inexpensive Internet of Things devices, and an in-line benchtop nuclear magnetic resonance spectrometer to enable automated, data-rich optimization with a closed-loop Bayesian optimization strategy. A user-friendly graphical interface allows chemists without programming or machine learning expertise to easily monitor, analyze, and improve photocatalytic reactions with respect to both continuous and discrete variables. The system's effectiveness was demonstrated by increasing overall reaction yields and improving space-time yields compared with those of previously reported processes.
Catalytic enantioselective reductive Eschenmoser-Claisen rearrangements
催化对映选择性还原Eschenmoser-Claisen重排
▲ 作者：Guoting Zhang, Matthew D. Wodrich & Nicolai Cramer
▲ Links:
https://www.science.org/doi/10.1126/science.adl3369
▲ Abstract:
An important challenge in enantioselective catalysis is how to accurately synthesize adjacent dense full-carbon quaternary carbon stereocenters. [3,3]-σ The well-defined transition state of the migration rearrangement and its potential stereospecificity make it a powerful tool for synthesizing such arrays. However, this type of pericyclic reaction is still extremely difficult to catalyze, especially in an enantioselective manner.
The study group reported chiral 1,3,2-diazacyclophosphoene hydride-catalyzed enantioselective reduction of Eschenmoser-Claisen rearrangements. This developmental transformation enables complete control of two newly formed acyclic stereocenters, resulting in the formation of amides with adjacent quaternary-tertiary or quaternary-quaternary carbon atoms.
▲ Abstract：
An important challenge in enantioselective catalysis is developing strategies for the precise synthesis of neighboring congested all-carbon quaternary stereocenters. The well-defined transition states of [3,3]-sigmatropic rearrangements and their underlying stereospecificity render them powerful tools for the synthesis of such arrays. However, this type of pericyclic reaction remains notoriously difficult to catalyze, especially in an enantioselective fashion. Herein, we describe an enantioselective reductive Eschenmoser-Claisen rearrangement catalyzed by chiral 1,3,2-diazaphospholene-hydrides. This developed transformation enables full control of the two newly formed acyclic stereogenic centers, leading to amides with vicinal all-carbon quaternary-tertiary or quaternary-quaternary carbon atoms.
地球科学Earth Science
Machine learning predicts which rivers, streams, and wetlands the Clean Water Act regulates
Machine learning predicts rivers, streams, and wetlands regulated by the Clean Water Act
▲ 作者：Simon Greenhill, Hannah Druckenmiller, Sherrie Wang, David A. Keiser, Manuela Girotto, Jason K. Moore, et al.
▲ Links:
https://www.science.org/doi/10.1126/science.adi3794
▲ Abstract:
The study team assessed which waters are protected by the Clean Water Act and how the rules of the Supreme Court and the White House change this provision. A deep learning model was trained using aerial imagery and geophysical data to predict 150,000 jurisdictional decisions from the U.S. Army Corps of Engineers, each corresponding to a water regulation.
According to a 2006 Supreme Court ruling, the Clean Water Act protects two-thirds of the U.S. rivers and more than half of its wetlands. Under a 2020 White House rule, the Clean Water Act protects less than half of the rivers and a quarter of the wetlands, meaning deregulation of waters around 690,000 miles of rivers, 35 million acres of wetlands and 30% of drinking water sources.
The research framework supports licensing, policy design, and the use of machine learning in regulatory implementation issues.
▲ Abstract：
We assess which waters the Clean Water Act protects and how Supreme Court and White House rules change this regulation. We train a deep learning model using aerial imagery and geophysical data to predict 150,000 jurisdictional determinations from the Army Corps of Engineers, each deciding regulation for one water resource. Under a 2006 Supreme Court ruling, the Clean Water Act protects two-thirds of US streams and more than half of wetlands; under a 2020 White House rule, it protects less than half of streams and a fourth of wetlands, implying deregulation of 690,000 stream miles, 35 million wetland acres, and 30% of waters around drinking-water sources. Our framework can support permitting, policy design, and use of machine learning in regulatory implementation problems.
Total organic carbon measurements reveal major gaps in petrochemical emissions reporting
Total organic carbon measurements reveal significant gaps in petrochemical emissions reporting
▲ 作者：Megan He, Jenna C. Ditto, Lexie Gardner, Jo Machesky, Tori N. Hass-Mitchell, Christina Chen, et al.
▲ Links:
https://www.science.org/doi/10.1126/science.adj6233
▲ Abstract:
Anthropogenic organic carbon emissions reporting is largely limited to a chemically specified subset of volatile organic compounds. However, new aircraft-based measurements show that total gas-phase organic carbon emissions are between 1,900 and more than 6,300 percent higher than reported by the oil sands industry, with most of this attributed to unaccounted intermediate and semi-volatile organic compounds.
Measured emissions within the facility area account for about 1% of the oil extracted, resulting in a total organic carbon footprint equivalent to all other Canadian sources combined. These real-world observations suggest that total organic carbon measurements are a means of detecting unknown or lower than reported carbon emissions, regardless of chemical signatures.
As reporting gaps can include hazardous, reactive, or secondary air pollutants, comprehensively limiting the effects of anthropogenic emissions requires routine, comprehensive total organic carbon monitoring as a fixed check for mass closures.
▲ Abstract：
Anthropogenic organic carbon emissions reporting has been largely limited to subsets of chemically speciated volatile organic compounds. However, new aircraft-based measurements revealed total gas-phase organic carbon emissions that exceed oil sands industry–reported values by 1900% to over 6300%, the bulk of which was due to unaccounted-for intermediate-volatility and semivolatile organic compounds. Measured facility-wide emissions represented approximately 1% of extracted petroleum, resulting in total organic carbon emissions equivalent to that from all other sources across Canada combined. These real-world observations demonstrate total organic carbon measurements as a means of detecting unknown or underreported carbon emissions regardless of chemical features. Because reporting gaps may include hazardous, reactive, or secondary air pollutants, fully constraining the impact of anthropogenic emissions necessitates routine, comprehensive total organic carbon monitoring as an inherent check on mass closure.