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Human influence on ecological niches can drive rapid changes in the diet, behaviour and evolutionary trajectories of small mammals. Archaeological evidence from the Late Neolithic Loess Plateau of northern China suggests that the expansion of millet cultivation created new selective pressures, attracting small mammals to fields and settlements. Here, the authors present direct evidence for commensal behaviour in desert hares (Lepus capensis), dating to c. 4900 years ago. Stable isotope ratio analysis of hare bones from the Neolithic site at Yangjiesha shows a diachronic increase in a C4 (millet-based) diet, revealing, for the first time, the expansion of ancient human-hare interactions beyond the predator-prey relationship.
The X-ray emissions in the interaction of 3–6 MeV Xe23+ ions into thick solid In target are measured. The projectile-to-target and target Lα/Lβ X-ray production intensity ratios are observed to strongly depend on the projectile energy. The dependence deviates from Coulomb ionization predictions, which implies the important roles of coupling between subshells and the activation of 4fσ rotational couplings for projectile energy larger than 5 MeV.
An all-fiberized and narrow-bandwidth master oscillator power amplification (MOPA) system with record output power of 4 kW level and slope efficiency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced into the narrow-bandwidth MOPA system for thermally induced mode instability (TMI) suppression. The stimulated Brillouin scattering (SBS) effect is balanced by simply using one-stage phase modulation technique. With different phase modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths accounting for 90% power of
0.025, 0.17 and
0.89 nm. Compared with our previous 976 nm pumping system, TMI threshold is overall boosted to be
5 times in which tandem pumping increases the TMI threshold of
3 times. The beam quality (
factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the influence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow-bandwidth fiber amplifiers.
We demonstrate an all-fiber high-power Yb-doped 1018 nm fiber laser with a Gaussian-shaped output beam profile based on a mismatched structure, which consists of a pair of single-mode fiber Bragg gratings and a section of few-mode double-cladding gain fiber. The output power is up to 107.5 W with an optical-to-optical efficiency of 63%, and the 3 dB band is 0.26 nm at this power level. Such a structure of single-mode–few-mode–single-mode fiber oscillator can be used to generate high-power narrow-linewidth lasing with excellent beam quality in other spectral ranges.
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