Nature
6 Oct 2022
Volume 610 | Issue 7930
1.Magnetic fields of 30 to 100kG in the cores of red giant star 
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First Author:
Gang Li①
Corresponding Author:
Sébastien Deheuvels②
Affiliation:
IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France①②
Abstract:
A red giant star is an evolved low- or intermediate-mass star that has exhausted its central hydrogen content, leaving a helium core and a hydrogen-burning shell. Oscillations of stars can be observed as periodic dimmings and brightenings in the optical light curves. In red giant stars, non-radial acoustic waves couple to gravity waves and give rise to mixed modes, which behave as pressure modes in the envelope and gravity modes in the core. These modes have previously been used to measure the internal rotation of red giants, leading to the conclusion that purely hydrodynamical processes of angular momentum transport from the core are too inefficient. Magnetic fields could produce the additional required transport. However, owing to the lack of direct measurements of magnetic fields in stellar interiors, little is currently known about their properties. Asteroseismology can provide direct detection of magnetic fields because, like rotation, the fields induce shifts in the oscillation mode frequencies. Here we report the measurement of magnetic fields in the cores of three red giant stars observed with the Kepler satellite. The fields induce shifts that break the symmetry of dipole mode multiplets. We thus measure field strengths ranging from about 30 kilogauss to about 100 kilogauss in the vicinity of the hydrogen-burning shell and place constraints on the field topology.
2.Discovering faster matrix multiplication algorithms with reinforcement learning 下载原文
First/ Corresponding Author:
Alhussein Fawzi
Affiliation:
DeepMind, London, UK
Abstract:
Improving the efficiency of algorithms for fundamental computations can have a widespread impact, as it can affect the overall speed of a large amount of computations. Matrix multiplication is one such primitive task, occurring in many systems—from neural networks to scientific computing routines. The automatic discovery of algorithms using machine learning offers the prospect of reaching beyond human intuition and outperforming the current best human-designed algorithms. However, automating the algorithm discovery procedure is intricate, as the space of possible algorithms is enormous. Here we report a deep reinforcement learning approach based on Alpha Zero for discovering efficient and provably correct algorithms for the multiplication of arbitrary matrices. Our agent, Alpha Tensor, is trained to play a single-player game where the objective is finding tensor decompositions within a finite factor space. Alpha Tensor discovered algorithms that outperform the state-of-the-art complexity for many matrix sizes. Particularly relevant is the case of 4 × 4 matrices in a finite field, where Alpha Tensor’s algorithm improves on Strassen’s two-level algorithm for the first time, to our knowledge, since its discovery 50 years ago. We further showcase the flexibility of Alpha Tensor through different use-cases: algorithms with state-of-the-art complexity for structured matrix multiplication and improved practical efficiency by optimizing matrix multiplication for runtime on specific hardware. Our results highlight Alpha Tensor’s ability to accelerate the process of algorithmic discovery on a range of problems, and to optimize for different criteria.
3.Extending the spectrum of fully integrated photonics to submicrometre wavelengths 下载原文
First Author:
Minh A. Tran①
Corresponding Author:
Lin Chang②
Affiliations:
Nexus Photonics, Goleta, CA, USA①
Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA, USA②
Abstract:
Integrated photonics has profoundly affected a wide range of technologies underpinning modern society. The ability to fabricate a complete optical system on a chip offers unrivalled scalability, weight, cost and power efficiency. Over the last decade, the progression from pure III–V materials platforms to silicon photonics has significantly broadened the scope of integrated photonics, by combining integrated lasers with the high-volume, advanced fabrication capabilities of the commercial electronics industry. Yet, despite remarkable manufacturing advantages, reliance on silicon-based waveguides currently limits the spectral window available to photonic integrated circuits (PICs). Here, we present a new generation of integrated photonics by directly uniting III–V materials with silicon nitride waveguides on Si wafers. Using this technology, we present a fully integrated PIC at photon energies greater than the bandgap of silicon, demonstrating essential photonic building blocks, including lasers, amplifiers, photodetectors, modulators and passives, all operating at submicrometre wavelengths. Using this platform, we achieve unprecedented coherence and tunability in an integrated laser at short wavelength. Furthermore, by making use of this higher photon energy, we demonstrate superb high-temperature performance and kHz-level fundamental linewidths at elevated temperatures. Given the many potential applications at short wavelengths, the success of this integration strategy unlocks a broad range of new integrated photonics applications.
4. P-type electrical contacts for 2D transition-metal dichalcogenides 下载原文
First author:
Yan Wang①
Corresponding Author:
Manish Chhowalla②
Affiliation:
Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK①②
Abstract:
Digital logic circuits are based on complementary pairs of n- and p-type field effect transistors (FETs) via complementary metal oxide semiconductor technology. In three-dimensional (3D) or bulk semiconductors, substitutional doping of acceptor or donor impurities is used to achieve p- and n-type FETs. However, the controllable p-type doping of low-dimensional semiconductors such as two-dimensional (2D) transition-metal dichalcogenides (TMDs) has proved to be challenging. Although it is possible to achieve high-quality, low-resistance n-type van der Waals (vdW) contacts on 2D TMDs, obtaining p-type devices by evaporating high-work-function metals onto 2D TMDs has not been realized so far. Here we report high-performance p-type devices on single- and few-layered molybdenum disulfide and tungsten diselenide based on industry-compatible electron beam evaporation of high-work-function metals such as palladium and platinum. Using atomic resolution imaging and spectroscopy, we demonstrate near-ideal vdW interfaces without chemical interactions between the 2D TMDs and 3D metals. Electronic transport measurements reveal that the Fermi level is unpinned and p-type FETs based on vdW contacts exhibit low contact resistance of 3.3 kΩ µm, high mobility values of approximately 190 cm2 V−1 s−1 at room temperature, saturation currents in excess of 10−5 A μm−1 and an on/off ratio of 107. We also demonstrate an ultra-thin photovoltaic cell based on n- and p-type vdW contacts with an open circuit voltage of 0.6 V and a power conversion efficiency of 0.82%.
5. Compositionally complex doping for zero-strain zero-cobalt layered cathodes 下载原文
First Author:
Rui Zhang①
Corresponding Author:
Huolin L. Xin②
Affiliation:
Department of Physics and Astronomy, University of California, Irvine, CA, USA①②
Abstract:
The high volatility of the price of cobalt and the geopolitical limitations of cobalt mining have made the elimination of Co a pressing need for the automotive industry1. Owing to their high energy density and low-cost advantages, high-Ni and low-Co or Co-free (zero-Co) layered cathodes have become the most promising cathodes for next-generation lithium-ion batteries2,3. However, current high-Ni cathode materials, without exception, suffer severely from their intrinsic thermal and chemo-mechanical instabilities and insufficient cycle life. Here, by using a new compositionally complex (high-entropy) doping strategy, we successfully fabricate a high-Ni, zero-Co layered cathode that has extremely high thermal and cycling stability. Combining X-ray diffraction, transmission electron microscopy and nanotomography, we find that the cathode exhibits nearly zero volumetric change over a wide electrochemical window, resulting in greatly reduced lattice defects and local strain-induced cracks. In-situ heating experiments reveal that the thermal stability of the new cathode is significantly improved, reaching the level of the ultra-stable NMC-532. Owing to the considerably increased thermal stability and the zero volumetric change, it exhibits greatly improved capacity retention. This work, by resolving the long-standing safety and stability concerns for high-Ni, zero-Co cathode materials, offers a commercially viable cathode for safe, long-life lithium-ion batteries and a universal strategy for suppressing strain and phase transformation in intercalation electrodes.
6. Continuous air purification by aqueous interface filtration and absorption 下载原文
First Author:
Yunmao Zhang①
Corresponding Author:
Xu Hou②
Affiliations:
State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China①②
Collaborative Innovation Center of Chemistry for Energy Materials, Xiamen University, Xiamen, China②
Department of Physics, Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Laboratory for Soft Functional Materials Research, Jiujiang Research Institute, College of Physical Science and Technology, Xiamen University, Xiamen, China②
Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen, China②
Abstract:
The adverse impact of particulate air pollution on human health has prompted the development of purification systems that filter particulates out of air. To maintain performance, the filter units must inevitably be replaced at some point, which requires maintenance, involves costs and generates solid waste. Here we show that an ion-doped conjugated polymer-coated matrix infiltrated with a selected functional liquid enables efficient, continuous and maintenance-free air purification. As the air to be purified moves through the system in the form of bubbles, the functional fluid provides interfaces for filtration and for removal of particulate matter and pollutant molecules from air. Theoretical modelling and experimental results demonstrate that the system exhibits high efficiency and robustness: its one-time air purification efficiency can reach 99.6%, and its dust-holding capacity can reach 950 g m−2. The system is durable and resistant to fouling and corrosion, and the liquid acting as filter can be reused and adjusted to also enable removal of bacteria or odours. We anticipate that our purification approach will be useful for the development of specialist air purifiers that might prove useful in a settings such as hospitals, factories and mines.
7.Photoexcited nitroarenes for the oxidative cleavage of alkenes 下载原文
First Authors:
Alessandro Ruffoni①, Charlotte Hampton②
Corresponding Authors:
Marco Simonetti③, Daniele Leonori④
Affiliations:
Institute of Organic Chemistry, RWTH Aachen University, Aachen, Germany①④
Department of Chemistry, University of Manchester, Manchester, UK②③
Abstract:
The oxidative cleavage of alkenes is an integral process that converts feedstock materials into high-value synthetic intermediates. The most viable method to achieve this in one chemical step is with ozone; however, this poses technical and safety challenges owing to the explosive nature of ozonolysis products. Here we report an alternative approach to achieve oxidative cleavage of alkenes using nitroarenes and purple-light irradiation. We demonstrate that photoexcited nitroarenes are effective ozone surrogates that undergo facile radical [3+2] cycloaddition with alkenes. The resulting ‘N-doped’ ozonides are safe to handle and lead to the corresponding carbonyl products under mild hydrolytic conditions. These features enable the controlled cleavage of all types of alkenes in the presence of a broad array of commonly used organic functionalities. Furthermore, by harnessing electronic, steric and mediated polar effects, the structural and functional diversity of nitroarenes has provided a modular platform to obtain site selectivity in substrates containing more than one alkene.
8. Molecular editing of aza-arene C–H bonds by distance, geometry and chirality 下载原文
First Author:
Zhoulong Fan①, Xiangyang Che
Corresponding Author:
K. N. Houk③, Jin-Quan Yu ④
Affiliations:
Department of Chemistry, The Scripps Research Institute, La Jolla, CA, USA①④
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, USA②③
Abstract:
Direct molecular editing of heteroarene carbon–hydrogen (C–H) bonds through consecutive selective C–H functionalization has the potential to grant rapid access into diverse chemical spaces, which is a valuable but often challenging venture to achieve in medicinal chemistry. In contrast to electronically biased heterocyclic C–H bonds, remote benzocyclic C–H bonds on bicyclic aza-arenes are especially difficult to differentiate because of the lack of intrinsic steric/electronic biases. Here we report two conceptually distinct directing templates that enable the modular differentiation and functionalization of adjacent remote (C6 versus C7) and positionally similar (C3 versus C7) positions on bicyclic aza-arenes through careful modulation of distance, geometry and previously unconsidered chirality in template design. This strategy enables direct C–H olefination, alkynylation and allylation at adjacent C6 and C7 positions of quinolines in the presence of a competing C3 position that is spatially similar to C7. Notably, such site-selective, iterative and late-stage C–H editing of quinoline-containing pharmacophores can be performed in a modular fashion in different orders to suit bespoke synthetic applications. This Article, in combination with previously reported complementary methods, now fully establishes a unified late-stage ‘molecular editing’ strategy to directly modify bicyclic aza-arenes at any given site in different orders.
9.PD-1-cis IL-2R agonism yields better effectors from stem-like CD8+T cells 下载原文
First Author:
Laura Codarri Deak①
Corresponding Author:
Pablo Umaña②
Affiliation:
Roche Innovation Center Zurich, Schlieren, Switzerland①②
Abstract:
Expansion and differentiation of antigen-experienced PD-1+TCF-1+stem-like CD8+T cells into effector cells is critical for the success of immunotherapies based on PD-1 blockade. Hashimoto et al. have shown that, in chronic infections, administration of the cytokine interleukin (IL)-2 triggers an alternative differentiation path of stem-like T cells towards a distinct population of ‘better effector’ CD8+T cells similar to those generated in an acute infection. IL-2 binding to the IL-2 receptor α-chain (CD25) was essential in triggering this alternative differentiation path and expanding better effectors with distinct transcriptional and epigenetic profiles. However, constitutive expression of CD25 on regulatory T cells and some endothelial cells also contributes to unwanted systemic effects from IL-2 therapy. Therefore, engineered IL-2 receptor β- and γ-chain (IL-2Rβγ)-biased agonists are currently being developed. Here we show that IL-2Rβγ-biased agonists are unable to preferentially expand better effector T cells in cancer models and describe PD1-IL2v, a new immunocytokine that overcomes the need for CD25 binding by docking in cis to PD-1. Cis binding of PD1-IL2v to PD-1 and IL-2Rβγ on the same cell recovers he ability to differentiate stem-like CD8+T cells into better effectors in the absence of CD25 binding in both chronic infection and cancer models and provides superior efficacy. By contrast, PD-1- or PD-L1-blocking antibodies alone, or their combination with clinically relevant doses of non-PD-1-targeted IL2v, cannot expand this unique subset of better effector T cells and instead lead to the accumulation of terminally differentiated, exhausted T cells. These findings provide the basis for the development of a new generation of PD-1cis-targeted IL-2R agonists with enhanced therapeutic potential for the treatment of cancer and chronic infections.
10. PD-1 combination therapy with IL-2 modifies CD8+T cell exhaustion program 下载原文
First Author:
Masao Hashimoto①
Corresponding Author:
Rafi Ahmed②
Affiliations:
Emory Vaccine Center, Emory University School of Medicine, Atlanta, GA, USA①②
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA, USA①②
Winship Cancer Institute, Emory University, Atlanta, GA, USA②
Abstract:
Combination therapy with PD-1 blockade and IL-2 is highly effective during chronic lymphocytic choriomeningitis virus infection. Here we examine the underlying basis for this synergy. We show that PD-1+IL-2 combination therapy, in contrast to PD-1 monotherapy, substantially changes the differentiation program of the PD-1+TCF1+stem-like CD8+T cells and results in the generation of transcriptionally and epigenetically distinct effector CD8+T cells that resemble highly functional effector CD8+T cells seen after an acute viral infection. The generation of these qualitatively superior CD8+T cells that mediate viral control underlies the synergy between PD-1 and IL-2. Our results show that the PD-1+TCF1+stem-like CD8+T cells, also referred to as precursors of exhausted CD8+T cells, are not fate-locked into the exhaustion program and their differentiation trajectory can be changed by IL-2 signals. These virus-specific effector CD8+T cells emerging from the stem-like CD8+T cells after combination therapy expressed increased levels of the high-affinity IL-2 trimeric (CD25–CD122–CD132) receptor. This was not seen after PD-1 blockade alone. Finally, we show that CD25 engagement with IL-2 has an important role in the observed synergy between IL-2 cytokine and PD-1 blockade. Either blocking CD25 with an antibody or using a mutated version of IL-2 that does not bind to CD25 but still binds to CD122 and CD132 almost completely abrogated the synergistic effects observed after PD-1+IL-2 combination therapy. There is considerable interest in PD-1+IL-2 combination therapy for patients with cancer, and our fundamental studies defining the underlying mechanisms of how IL-2 synergizes with PD-1 blockade should inform these human translational studies.
11. Biosynthesis of selenium-containing small molecules in diverse microorganisms 下载原文
First Author:
Chase M. Kayrouz①
Corresponding Author:
Mohammad R. Seyedsayamdost②
Affiliations:
Department of Chemistry, Princeton University, Princeton, NJ, USA①②
Department of Molecular Biology, Princeton University, Princeton, NJ, USA②
Abstract:
Selenium is an essential micronutrient in diverse organisms. Two routes are known for its insertion into proteins and nucleic acids, via selenocysteine and 2-selenouridine, respectively. However, despite its importance, pathways for specific incorporation of selenium into small molecules have remained elusive. Here we use a genome-mining strategy in various microorganisms to uncover a widespread three-gene cluster that encodes a dedicated pathway for producing selenoneine, the selenium analogue of the multifunctional molecule ergothioneine. We elucidate the reactions of all three proteins and uncover two novel selenium–carbon bond-forming enzymes and the biosynthetic pathway for production of a selenosugar, which is an unexpected intermediate en route to the final product. Our findings expand the scope of biological selenium utilization, suggest that the selenometabolome is more diverse than previously thought, and set the stage for the discovery of other selenium-containing natural products.
12.Visualizing translation dynamics at atomic detail inside a bacterial cell 下载原文
First Author:
Liang Xue①
Corresponding Author:
Julia Mahamid②
Affiliations:
Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany①②
Collaboration for joint PhD degree between EMBL and Heidelberg University, Faculty of Biosciences, Heidelberg, Germany①
Abstract:
Translation is the fundamental process of protein synthesis and is catalysed by the ribosome in all living cells. Here we use advances in cryo-electron tomography and sub-tomogram analysis to visualize the structural dynamics of translation inside the bacterium Mycoplasma pneumoniae. To interpret the functional states in detail, we first obtain a high-resolution in-cell average map of all translating ribosomes and build an atomic model for the M.pneumoniae ribosome that reveals distinct extensions of ribosomal proteins. Classification then resolves 13 ribosome states that differ in their conformation and composition. These recapitulate major states that were previously resolved in vitro, and reflect intermediates during active translation. On the basis of these states, we animate translation elongation inside native cells and show how antibiotics reshape the cellular translation landscapes. During translation elongation, ribosomes often assemble in defined three-dimensional arrangements to form polysomes. By mapping the intracellular organization of translating ribosomes, we show that their association into polysomes involves a local coordination mechanism that is mediated by the ribosomal protein L9. We propose that an extended conformation of L9 within polysomes mitigates collisions to facilitate translation fidelity. Our work thus demonstrates the feasibility of visualizing molecular processes at atomic detail inside cells.
13. Structure of dynein–dynactin on microtubules shows tandem adaptor binding 下载原文
First Author:
Sami Chaaban①
Corresponding Author:
Andrew P. Carter②
Affiliations:
Division of Structural Studies, Medical Research Council Laboratory of Molecular Biology, Cambridge, UK①②
Abstract:
Cytoplasmic dynein is a microtubule motor that is activated by its cofactor dynactin and a coiled-coil cargo adaptor. Up to two dynein dimers can be recruited per dynactin, and interactions between them affect their combined motile behaviour. Different coiled-coil adaptors are linked to different cargos, and some share motifs known to contact sites on dynein and dynactin. There is limited structural information on how the resulting complex interacts with microtubules and how adaptors are recruited. Here we develop a cryo-electron microscopy processing pipeline to solve the high-resolution structure of dynein–dynactin and the adaptor BICDR1 bound to microtubules. This reveals the asymmetric interactions between neighbouring dynein motor domains and how they relate to motile behaviour. We found that two adaptors occupy the complex. Both adaptors make similar interactions with the dyneins but diverge in their contacts with each other and dynactin. Our structure has implications for the stability and stoichiometry of motor recruitment by cargos.