Driven many-body systems exhibit diverse and 学网complex dynamical behaviors. Here, we report the observation of Shapiro steps in periodically driven Josephson junctions between strongly interacting Fermi superfluids of ultracold atoms. The height and the width of the observed quantized plateaus in the current-potential characteristics mirror the external drive frequency and the junction nonlinear response. Direct measurements of the current-phase relationship showcase how Shapiro steps arise from the synchronization between the relative phase of the two reservoirs and the external drive. Such a mechanism is further supported by the detection of periodic phase-slippage processes, in the form of vortex-antivortex pairs. Our results are corroborated by a circuital model and numerical simulations. Our work may open prospects for studying emergent nonequilibrium dynamics in quantum many-body systems under external drives.
Observation of Shapiro steps in an ultracold atomic Josephson junction
超冷原子約瑟夫森結(jié)中夏皮罗阶跃的觀測
▲ 作者：ERIK BERNHART, MARVIN R?HRLE, VIJAY PAL SINGH, LUDWIG MATHEY, LUIGI AMICO AND HERWIG OTT
The current-voltage characteristic of a driven superconducting Josephson junction displays discrete steps. This phenomenon, called the Shapiro steps, forms today’s voltage standard. In this work, we report the observation of Shapiro steps in a driven Josephson junction in a gas of ultracold atoms. We demonstrate that the steps exhibit universal features and provide insight into the microscopic dissipative dynamics that we directly observe in the experiment. We find that the steps are directly connected to phonon emission and nucleation of solitonic excitations, whose dynamics we follow in space and time. The experimental results are underpinned by extensive numerical simulations based on classical-field dynamics and may enable metrological and fundamental advances.
材料科学Materials Science
Mesoporous optically clear heat insulators for sustainable building envelopes
用于可持续建筑外墙的介孔光学透明隔热材料
▲ 作者：AMIT BHARDWAJ, BLAISE FLEURY, BOHDAN SENYUK, ELDHO ABRAHAM, JAN BART TEN HOVE, TAEWOO LEE, ET AL.
Mesoporous materials exhibit highly controlled nanoscale structures, often templated by liquid crystalline assemblies of surfactants, with emergent and often designable physical properties. However, scaling their fabrication to be suitable for uses such as envelopes of buildings is challenging. In this work, we describe fabrication of flexible square-meter-sized films and multicentimeter-thick slabs made of three-dimensional spatial graphs of mesopore tubes that have all structural features under 50 nanometers. A solution-based kinetic fabrication process templates growing networks of cylindrical surfactant micelles with thin tubes of polysiloxane-forming gel networks and, upon replacing surfactants and solvents with air, yields lightweight materials with greater than 99% visible-range optical transparency and approximately 10 milliwatts per kelvin per meter thermal conductivity. Such predesigned metamaterials enable transparent thermal barriers for wall-grade insulated glass units, square-meter window retrofits, and unconcentrated solar thermal energy harnessing.
植物学Botany
Infrared radiation is an ancient pollination signal
红外辐射是一种古老的传粉信号
▲ 作者：WENDY A. VALENCIA-MONTOYA, MARJORIE A. LIéNARD, NEIL ROSSER, MICHAEL CALONJE, SHAYLA SALZMAN, CHENG-CHIA TSAI, ET AL.
Color and scent are well-known pollinator cues. Some plants also produce heat, but its role remains unclear. Here, we report that plant-generated thermal infrared radiation serves as a pollination signal and describe the underlying mechanisms of heat production and infrared detection. Mitochondrial adaptations heat plant reproductive structures in a circadian pattern, radiating infrared that is sufficient to attract beetle pollinators. Beetle antennae contain infrared-activated neurons with thermosensitive ion channels that are structurally tuned to match host plant thermogenesis. Comparative analyses revealed that infrared is among the earliest pollination signals, and indicate a deep-time transition from infrared-based to color-dominated signaling in flowering plants. Our findings uncover an ancient sensory modality shaping the early evolution of pollination, one of the world’s most vital processes linking plants and animals.
地球科学Earth Science
Substantial water retained early in Earth’s deep mantle
地球深地幔早期保留了大量水源
▲ 作者：WENHUA LU, YA-NAN YANG, TAO LONG, HAIYANG XIAN, YUAN LI AND ZHIXUE DU
Earth’s water was likely acquired early, when our planet was extensively molten because of large to giant impacts. How such early water was retained and distributed within a crystallizing mantle remains unclear. In this study, we investigated partitioning of water between bridgmanite, the first and primary mantle mineral to crystallize, and coexisting melt through systematic high-pressure experiments. Our results demonstrate that partitioning of water into bridgmanite is strongly enhanced by increasing temperature. Thus, appreciable amounts of water may have been retained in the lower mantle after its crystallization. Circulation of such early stored water in Earth’s interior could have modulated mantle dynamics and influenced the transition of early Earth to a habitable planet.
Global energy sector methane emissions estimated by using facility-level satellite observations
利用设施级卫星观测估计全球能源部门的甲烷排放量
▲ 作者：IANLUCA PETRIS, SIMONA GRAZIOLI, LINDA VAN BIJSTERVELDT, PIERRE MURAT, KIM C. LIU, JAKOB BIRNBAUM, JULIAN E. SALE, AND JASON W. CHIN
Methane emissions from energy sector facilities (oil, gas, and coal) represent a substantial contribution to greenhouse gas emissions with substantial mitigation potential. We estimated global 2023 methane emissions from energy sector point sources using the high spatial resolution GHGSat satellite constellation. GHGSat detected 8.30 ± 0.24 million tonnes per year of methane emissions from 3114 emission sites. Detected oil and gas– and coal-emitting sites were found to be emitting 16 and 48% of the time, respectively, above GHGSat’s detection limit without obvious continental variation. Compared with the Global Fuel Exploitation Inventory (GFEIv3) estimate, GHGSat’s estimate comprises 12% of GFEIv3′s total emissions, or 24% over GHGsat-observed locations, with good spatial correlation at the country scale but only weak spatial correlation at 0.2°-×-0.2° grid cell scale.
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