▲ Abstract：New particle formation (NPF) in the tropical upper troposphere is 文导闻科a globally important source of atmospheric aerosols. It is known to occur over the Amazon basin, but the nucleation mechanism and chemical precursors have yet to be identified. Here we present comprehensive in situ aircraft measurements showing that extremely low-volatile oxidation products of isoprene, particularly certain organonitrates, drive NPF in the Amazonian upper troposphere. The organonitrates originate from OH-initiated oxidation of isoprene from forest emissions in the presence of nitrogen oxides from lightning. Nucleation bursts start about 2?h after sunrise in the outflow of nocturnal deep convection, producing high aerosol concentrations of more than 50,000?particles?cm?3. We report measurements of characteristic diurnal cycles of precursor gases and particles. Our observations show that the interplay between biogenic isoprene, deep tropical convection with associated lightning, oxidation photochemistry and the low ambient temperature uniquely promotes NPF. The particles grow over time, undergo long-range transport and descend through subsidence to the lower troposphere, in which they can serve as cloud condensation nuclei (CCN) that influence the Earth’s hydrological cycle, radiation budget and climate.
▲ Abstract：Cross-electrophile coupling reactions have evolved into a major strategy for rapidly assembling important organic molecules. Two readily accessible electrophiles are coupled to form new C–C bonds, providing a key advantage over traditional cross-coupling strategies that require the preformation of reactive organometallic species. Yet, the formation of C(sp3)–C(sp3) bonds that form the core of nearly all organic compounds remains highly challenging with current approaches, calling for the design of innovative new strategies. Here we report a distinct, transition-metal-free platform to form such bonds without the need for activating or stabilizing groups on the coupling partners. The reaction is enabled by an unusual single-electron transfer in a frustrated ion pair, and it can couple fragments containing functional groups that would be challenging in related transition-metal-catalysed processes. Moreover, we could further leverage this new mechanistic manifold in the design of other reactions, showing the broad potential of this type of reactivity. We anticipate that our results will provide a framework for further exploration of this reactivity pattern to tackle challenging problems in organic synthesis.
地球科学Earth Science
Isoprene nitrates drive new particle formation in Amazon’s upper troposphere
异戊二烯硝酸盐驱动亚马逊上对流层形成新粒子
▲ 作者：Joachim Curtius, Martin Heinritzi, Lisa J. Beck, Mira L. P?hlker, Nidhi Tripathi, Bianca E. Krumm, et al.
▲ Abstract：Most stars in today’s Universe reside within spheroids, which are bulges of spiral galaxies and elliptical galaxies. Their formation is still an unsolved problem. Infrared/submillimetre-bright galaxies at high redshifts have long been suspected to be related to spheroid formation. Proving this connection has been hampered so far by heavy dust obscuration when focusing on their stellar emission or by methodologies and limited signal-to-noise ratios when looking at submillimetre wavelengths. Here we show that spheroids are directly generated by star formation within the cores of highly luminous starburst galaxies in the distant Universe. This follows from the ALMA submillimetre surface brightness profiles, which deviate substantially from those of exponential disks, and from the skewed-high axis-ratio distribution. Most of these galaxies are fully triaxial rather than flat disks: the ratio of the shortest to the longest of their three axes is half, on average, and increases with spatial compactness. These observations, supported by simulations, reveal a cosmologically relevant pathway for in situ spheroid formation through starbursts that is probably preferentially triggered by interactions (and mergers) acting on galaxies fed by non-coplanar gas accretion streams.
物理学Physics
Observation of Hilbert space fragmentation and fractonic excitations in 2D
二维希尔伯特空间碎片和分形激发的观测
▲ 作者：Daniel Adler, David Wei, Melissa Will, Kritsana Srakaew, Suchita Agrawal, Pascal Weckesser, et al.
▲ Abstract：The relaxation behaviour of isolated quantum systems taken out of equilibrium is among the most intriguing questions in many-body physics. Quantum systems out of equilibrium typically relax to thermal equilibrium states by scrambling local information and building up entanglement entropy. However, kinetic constraints in the Hamiltonian can lead to a breakdown of this fundamental paradigm owing to a fragmentation of the underlying Hilbert space into dynamically decoupled subsectors in which thermalization can be strongly suppressed. Here we experimentally observe Hilbert space fragmentation in a two-dimensional tilted Bose–Hubbard model. Using quantum gas microscopy, we engineer a wide variety of initial states and find a rich set of manifestations of Hilbert space fragmentation involving bulk states, interfaces and defects, that is, two-, one- and zero-dimensional objects. Specifically, uniform initial states with equal particle number and energy differ strikingly in their relaxation dynamics. Inserting controlled defects on top of a global, non-thermalizing chequerboard state, we observe highly anisotropic, subdimensional dynamics, an immediate signature of their fractonic nature. An interface between localized and thermalizing states in turn shows dynamics depending on its orientation. Our results mark the observation of Hilbert space fragmentation beyond one dimension, as well as the concomitant direct observation of fractons, and pave the way for in-depth studies of microscopic transport phenomena in constrained systems.
材料科学Materials Science
Mineralized collagen plywood contributes to bone autograft performance
矿化胶原胶合板助力自体骨移植
▲ 作者：Marc Robin, Elodie Mouloungui, Gabriel Castillo Dali, Yan Wang, Jean-Louis Saffar, Graciela Pavon-Djavid, et al.
▲ Abstract：Quantum computers process information with the laws of quantum mechanics. Current quantum hardware is noisy, can only store information for a short time and is limited to a few quantum bits, that is, qubits, typically arranged in a planar connectivity. However, many applications of quantum computing require more connectivity than the planar lattice offered by the hardware on more qubits than is available on a single quantum processing unit (QPU). The community hopes to tackle these limitations by connecting QPUs using classical communication, which has not yet been proven experimentally. Here we experimentally realize error-mitigated dynamic circuits and circuit cutting to create quantum states requiring periodic connectivity using up to 142 qubits spanning two QPUs with 127 qubits each connected in real time with a classical link. In a dynamic circuit, quantum gates can be classically controlled by the outcomes of mid-circuit measurements within run-time, that is, within a fraction of the coherence time of the qubits. Our real-time classical link enables us to apply a quantum gate on one QPU conditioned on the outcome of a measurement on another QPU. Furthermore, the error-mitigated control flow enhances qubit connectivity and the instruction set of the hardware thus increasing the versatility of our quantum computers. Our work demonstrates that we can use several quantum processors as one with error-mitigated dynamic circuits enabled by a real-time classical link.
化学Chemistry
Coupling of unactivated alkyl electrophiles using frustrated ion pairs
用受阻离子对偶联非活化烷基亲电试剂
▲ 作者：Sven Roediger, Emilien Le Saux, Philip Boehm & Bill Morandi
▲ Abstract：Autologous bone (AB) is the gold standard for bone-replacement surgeries, despite its limited availability and the need for an extra surgical site. Traditionally, competitive biomaterials for bone repair have focused on mimicking the mineral aspect of bone, as evidenced by the widespread clinical use of bioactive ceramics. However, AB also exhibits hierarchical organic structures that might substantially affect bone regeneration. Here, using a range of cell-free biomimetic-collagen-based materials in murine and ovine bone-defect models, we demonstrate that a hierarchical hybrid microstructure—specifically, the twisted plywood pattern of collagen and its association with poorly crystallized bioapatite—favourably influences bone regeneration. Our study shows that the most structurally biomimetic material has the potential to stimulate bone growth, highlighting the pivotal role of physicochemical properties in supporting bone formation and offering promising prospects as a competitive bone-graft material.
信息科学Information Science
Combining quantum processors with real-time classical communication
将量子处理器与实时经典通信相结合
▲ 作者：Almudena Carrera Vazquez, Caroline Tornow, Diego Ristè, Stefan Woerner, Maika Takita & Daniel J. Egger
