RESUMO
The use of particle accelerators as photon sources has enabled advances in science and technology1. Currently the workhorses of such sources are storage-ring-based synchrotron radiation facilities2-4 and linear-accelerator-based free-electron lasers5-14. Synchrotron radiation facilities deliver photons with high repetition rates but relatively low power, owing to their temporally incoherent nature. Free-electron lasers produce radiation with high peak brightness, but their repetition rate is limited by the driving sources. The steady-state microbunching15-22 (SSMB) mechanism has been proposed to generate high-repetition, high-power radiation at wavelengths ranging from the terahertz scale to the extreme ultraviolet. This is accomplished by using microbunching-enabled multiparticle coherent enhancement of the radiation in an electron storage ring on a steady-state turn-by-turn basis. A crucial step in unveiling the potential of SSMB as a future photon source is the demonstration of its mechanism in a real machine. Here we report an experimental demonstration of the SSMB mechanism. We show that electron bunches stored in a quasi-isochronous ring can yield sub-micrometre microbunching and coherent radiation, one complete revolution after energy modulation induced by a 1,064-nanometre-wavelength laser. Our results verify that the optical phases of electrons can be correlated turn by turn at a precision of sub-laser wavelengths. On the basis of this phase correlation, we expect that SSMB will be realized by applying a phase-locked laser that interacts with the electrons turn by turn. This demonstration represents a milestone towards the implementation of an SSMB-based high-repetition, high-power photon source.
RESUMO
In coherent radiation of an ensemble of electrons, the radiation field from electrons resonantly drives the other electrons inside to produce stimulated emission. The radiation reaction force on the electrons accounting for this stimulated radiation loss is classically described by the Liénard-Wiechert potential. Despite its being the foundation of beam physics for decades, we show that using the "acceleration field" in Liénard-Wiechert potential to describe radiative interactions leads to divergences due to its implicit dependence on instantaneous interactions. Here, we propose an alternative theory for electromagnetic radiation by decomposing the interactions into an instantaneous part and retarded part. It is shown that only the retarded part contributes to the irreversible radiation loss and the instantaneous part describes the space charge related effects. We further apply this theory to study the coherent synchrotron radiation energy loss, which hopefully will reshape our understanding of coherent radiation and collective interactions.
RESUMO
Despite the health benefits of Vitis vinifera L. leaves, its anti-obesity potential has not been fully explored. In this work, we showed that Vitis vinifera L. leaf extract (VLE) inhibits the pancreatic lipase activity. Intragastric administration of VLE to mice led to a significant decrease in the body weight, tissue fat accumulation, levels of cholesterol, low-density lipoprotein and triglyceride compared to mice fed with high fat diet. We also found a lower level of neuropeptide-Y (NPY) in the serum and hypothalamus and a higher level of fibroblast growth factor 15 in mice supplemented with VLE. These results suggested that VLE regulates both the NPY-mediated pathway and the bile acid-FGF15 pathway to control energy metabolism and body weight gain. The composition of VLE was further investigated by a targeted metabolomics approach, which identified 21 compounds including phenolic acids, flavones, flavanols, flavanones, coumarins, and stilbenes. Taken together, we demonstrated the capacity of grape leaves in reducing obesity, which could be mediated by NPY and bile acids. Identification of putative active compounds in VLE also open the path for further studies to determine their effectiveness individually to treat obesity.