▲ Abstract:
Here we analyse the energy budget of a sample of 54 well-observed stripped-envelope supernovae of all sub-types and present statistically significant,largely model-independent,observational evidence for a non-radioactive power source in most of them(and possibly in all).We consider various energy sources,or alternatively,plausible systematic errors,that could drive this result,and conclude that the most likely option is the existence of a long-lived central engine,operating over ≈103–106?s after the explosion.We infer,from the observations,constraints on the engine properties.If,for example,the central engine is a magnetized neutron star,then the initial magnetic field is ≈1015?G and the initial rotation period is 1–100?ms,suggesting that stripped-envelope supernovae may constitute the formation events of the objects known as magnetars。
物理学Physics
One-dimensional proximity superconductivity in the quantum Hall regime
量子霍尔体系中的一维超导体
▲ Abstract:
Here we show that domain walls in minimally twisted bilayer graphene support exceptionally robust proximity superconductivity in the quantum Hall regime,allowing Josephson junctions to operate in fields close to the upper critical field of superconducting electrodes.The critical current is found to be non-oscillatory and practically unchanging over the entire range of quantizing fields,with its value being limited by the quantum conductance of ballistic,strictly one-dimensional,electronic channels residing within the domain walls.The system described is unique in its ability to support Andreev bound states at quantizing fields and offers many interesting directions for further exploration。
Optical clocks at sea
海上光学钟
▲ Abstract:
Here we report the development of optical clocks with the requisite combination of size,performance and environmental insensitivity for operation on mobile platforms.The 35?l clock combines a molecular iodine spectrometer,fibre frequency comb and control electronics.Three of these clocks operated continuously aboard a naval ship in the Pacific Ocean for 20 days while accruing timing errors below 300?ps per day.The clocks have comparable performance to active hydrogen masers in one-tenth the volume.Operating high-performance clocks at sea has been historically challenging and continues to be critical for navigation.This demonstration marks a significant technological advancement that heralds the arrival of future optical timekeeping networks。
材料科学Material Science
Graphene nanoribbons grown in hBN stacks for high-performance electronics
用于高性能电子器件的hBN堆叠中生长的石墨烯纳米带
▲ Abstract:
Here we report the transfer-free direct growth of high-quality graphene nanoribbons(GNRs)in hBN stacks.The as-grown embedded GNRs exhibit highly desirable features being ultralong(up to 0.25?mm),ultranarrow(<5?nm)and homochiral with zigzag edges.Our atomistic simulations show that the mechanism underlying the embedded growth involves ultralow GNR friction when sliding between AA′-stacked hBN layers.Using the grown structures,we demonstrate the transfer-free fabrication of embedded GNR field-effect devices that exhibit excellent performance at room temperature with mobilities of up to 4,600?cm2?V–1?s–1 and on–off ratios of up to 106。
Digital colloid-enhanced Raman spectroscopy by single-molecule counting
单分子计数数字胶体增强拉曼光谱
▲ 作者:Xinyuan Bi,Daniel M.Czajkowsky,Zhifeng Shao & Jian Ye
▲ Abstract:
Here,as a proof of concept,we show that,using digital(nano)colloid-enhanced Raman spectroscopy,reproducible quantification of a broad range of target molecules at very low concentrations can be routinely achieved with single-molecule counting,limited only by the Poisson noise of the measurement process.As metallic colloidal nanoparticles that enhance these vibrational signatures,including hydroxylamine–reduced-silver colloids,can be fabricated at large scale under routine conditions,we anticipate that digital(nano)colloid-enhanced Raman spectroscopy will become the technology of choice for the reliable and ultrasensitive detection of various analytes,including those of great importance for human health。
生物学Biology
Hybrid speciation driven by multilocus introgression of ecological traits
由生态性状多点引入驱动的杂交物种形成
▲ Abstract:
Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies.We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years.This is despite pervasive and oNGOing gene flow with one parent,Heliconius pardalinus,which homogenizes 99% of their genomes.The remaining 1% introgressed from the other parent,Heliconius melpomene,and is scattered widely across the H.elevatus genome in islands of divergence from H.pardalinus.These islands contain multiple traits that are under disruptive selection,including colour pattern,wing shape,host plant preference,sex pheromones and mate choice.Collectively,these traits place H.elevatus on its own adaptive peak and permit coexistence with both parents.Our results show that speciation was driven by introgression of ecological traits,and that speciation with gene flow is possible with a multilocus genetic architecture。