资源环境科技发展态势分析平台

Data analysis workflows in many scientific domains have become increasingly complex and flexible. Here we assess the effect of this flexibility on the results of functional magnetic resonance imaging by asking 70 independent teams to analyse the same dataset, testing the same 9 ex-ante hypotheses(1). The flexibility of analytical approaches is exemplified by the fact that no two teams chose identical workflows to analyse the data. This flexibility resulted in sizeable variation in the results of hypothesis tests, even for teams whose statistical maps were highly correlated at intermediate stages of the analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Notably, a meta-analytical approach that aggregated information across teams yielded a significant consensus in activated regions. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset(2-5). Our findings show that analytical flexibility can have substantial effects on scientific conclusions, and identify factors that may be related to variability in the analysis of functional magnetic resonance imaging. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for performing and reporting multiple analyses of the same data. Potential approaches that could be used to mitigate issues related to analytical variability are discussed.

The results obtained by seventy different teams analysing the same functional magnetic resonance imaging dataset show substantial variation, highlighting the influence of analytical choices and the importance of sharing workflows publicly and performing multiple analyses.

Charged pions(1) are the lightest and longest-lived mesons. Mesonic atoms are formed when an orbital electron in an atom is replaced by a negatively charged meson. Laser spectroscopy of these atoms should permit the mass and other properties of the meson to be determined with high precision and could place upper limits on exotic forces involving mesons (as has been done in other experiments on antiprotons(2-9)). Determining the mass of the pi(-) meson in particular could help to place direct experimental constraints on the mass of the muon antineutrino(10-13). However, laser excitations of mesonic atoms have not been previously achieved because of the small number of atoms that can be synthesized and their typically short (less than one picosecond) lifetimes against absorption of the mesons into the nuclei(1). Metastable pionic helium (pi He-4(+)) is a hypothetical(14-16) three-body atom composed of a helium-4 nucleus, an electron and a pi(-) occupying a Rydberg state of large principal (n approximate to 16) and orbital angular momentum (l approximate to n - 1) quantum numbers. The pi He-4(+) atom is predicted to have an anomalously long nanosecond-scale lifetime, which could allow laser spectroscopy to be carried out(17). Its atomic structure is unique owing to the absence of hyperfine interactions(18,19) between the spin-0 pi(-) and the He-4 nucleus. Here we synthesize pi He-4(+) in a superfluid-helium target and excite the transition (n, l) = (17, 16) -> (17, 15) of the pi(-)-occupied pi He-4(+) orbital at a near-infrared resonance frequency of 183,760 gigahertz. The laser initiates electromagnetic cascade processes that end with the nucleus absorbing the pi(-) and undergoing fission(20,21). The detection of emerging neutron, proton and deuteron fragments signals the laser-induced resonance in the atom, thereby confirming the presence of pi He-4(+). This work enables the use of the experimental techniques of quantum optics to study a meson.

Long-lived pionic helium atoms (composed of a helium-4 nucleus, an electron and a negatively charged pion) are synthesized in a superfluid-helium target, as confirmed by laser spectroscopy involving the pion-occupied orbitals.

The neurotransmitter dopamine is required for the reinforcement of actions by rewarding stimuli(1). Neuroscientists have tried to define the functions of dopamine in concise conceptual terms(2), but the practical implications of dopamine release depend on its diverse brain-wide consequences. Although molecular and cellular effects of dopaminergic signalling have been extensively studied(3), the effects of dopamine on larger-scale neural activity profiles are less well-understood. Here we combine dynamic dopamine-sensitive molecular imaging(4) and functional magnetic resonance imaging to determine how striatal dopamine release shapes local and global responses to rewarding stimulation in rat brains. We find that dopamine consistently alters the duration, but not the magnitude, of stimulus responses across much of the striatum, via quantifiable postsynaptic effects that vary across subregions. Striatal dopamine release also potentiates a network of distal responses, which we delineate using neurochemically dependent functional connectivity analyses. Hot spots of dopaminergic drive notably include cortical regions that are associated with both limbic and motor function. Our results reveal distinct neuromodulatory actions of striatal dopamine that extend well beyond its sites of peak release, and that result in enhanced activation of remote neural populations necessary for the performance of motivated actions. Our findings also suggest brain-wide biomarkers of dopaminergic function and could provide a basis for the improved interpretation of neuroimaging results that are relevant to learning and addiction.

Molecular and functional magnetic resonance imaging in the rat reveals distinct neuromodulatory effects of striatal dopamine that extend beyond peak release sites and activate remote neural populations necessary for performing motivated actions.

Pure spin currents are simultaneously generated and detected electrically through sub-terahertz magnons in the antiferromagnetic insulator Cr2O3, demonstrating the potential of magnon excitations in antiferromagnets for high-frequency spintronic devices.

Spin dynamics in antiferromagnets has much shorter timescales than in ferromagnets, offering attractive properties for potential applications in ultrafast devices(1-3). However, spin-current generation via antiferromagnetic resonance and simultaneous electrical detection by the inverse spin Hall effect in heavy metals have not yet been explicitly demonstrated(4-6). Here we report sub-terahertz spin pumping in heterostructures of a uniaxial antiferromagnetic Cr2O3 crystal and a heavy metal (Pt or Ta in its beta phase). At 0.240 terahertz, the antiferromagnetic resonance in Cr2O3 occurs at about 2.7 tesla, which excites only right-handed magnons. In the spin-canting state, another resonance occurs at 10.5 tesla from the precession of induced magnetic moments. Both resonances generate pure spin currents in the heterostructures, which are detected by the heavy metal as peaks or dips in the open-circuit voltage. The pure-spin-current nature of the electrically detected signals is unambiguously confirmed by the reversal of the voltage polarity observed under two conditions: when switching the detector metal from Pt to Ta, reversing the sign of the spin Hall angle(7-9), and when flipping the magnetic-field direction, reversing the magnon chirality(4,5). The temperature dependence of the electrical signals at both resonances suggests that the spin current contains both coherent and incoherent magnon contributions, which is further confirmed by measurements of the spin Seebeck effect and is well described by a phenomenological theory. These findings reveal the unique characteristics of magnon excitations in antiferromagnets and their distinctive roles in spin-charge conversion in the high-frequency regime.