资源环境科技发展态势分析平台

Monitoring cells of the mouse presomitic mesoderm using the Achilles reporter fused to HES7 sheds light on the mechanisms that underpin synchronous oscillations in the expression of clock genes between neighbouring cells.

When a magnetic impurity exists in a metal, conduction electrons form a spin cloud that screens the impurity spin. This basic phenomenon is called the Kondo effect(1,2). Unlike electric-charge screening, the spin-screening cloud(3-6) occurs quantum coherently, forming spin-singlet entanglement with the impurity. Although the spins interact locally around the impurity, the Kondo cloud can theoretically spread out over several micrometres. The cloud has not so far been detected, and so its physical existence-a fundamental aspect of the Kondo effect-remains controversial(7,8). Here we present experimental evidence of a Kondo cloud extending over a length of micrometres, comparable to the theoretical length xi(K). In our device, a Kondo impurity is formed in a quantum dot(2,9-11), coupling on one side to a quasi-one-dimensional channel(12) that houses a Fabry-Perot interferometer of various gate-defined lengths L exceeding one micrometre. When we sweep a voltage on the interferometer end gate-separated by L from the quantum dot-to induce Fabry-Perot oscillations in conductance we observe oscillations in the measured Kondo temperature T-K, which is a signature of the Kondo cloud at distance L. When L is less than xi(K) the T-K oscillation amplitude becomes larger as L becomes smaller, obeying a scaling function of a single parameter L/xi(K), whereas when L is greater than xi(K) the oscillation is much weaker. Our results reveal that xi(K) is the only length parameter associated with the Kondo effect, and that the cloud lies mostly within a length of xi(K). Our experimental method offers a way of detecting the spatial distribution of exotic non-Fermi liquids formed by multiple magnetic impurities or multiple screening channels(13-16) and of studying spin-correlated systems.

Predator-prey cycles rank among the most fundamental concepts in ecology, are predicted by the simplest ecological models and enable, theoretically, the indefinite persistence of predator and prey(1-4). However, it remains an open question for how long cyclic dynamics can be self-sustained in real communities. Field observations have been restricted to a few cycle periods(5-8) and experimental studies indicate that oscillations may be short-lived without external stabilizing factors(9-19). Here we performed microcosm experiments with a planktonic predator-prey system and repeatedly observed oscillatory time series of unprecedented length that persisted for up to around 50 cycles or approximately 300 predator generations. The dominant type of dynamics was characterized by regular, coherent oscillations with a nearly constant predator-prey phase difference. Despite constant experimental conditions, we also observed shorter episodes of irregular, non-coherent oscillations without any significant phase relationship. However, the predator-prey system showed a strong tendency to return to the dominant dynamical regime with a defined phase relationship. A mathematical model suggests that stochasticity is probably responsible for the reversible shift from coherent to non-coherent oscillations, a notion that was supported by experiments with external forcing by pulsed nutrient supply. Our findings empirically demonstrate the potential for infinite persistence of predator and prey populations in a cyclic dynamic regime that shows resilience in the presence of stochastic events.