Human activities have altered fire-climate relations in arid Central Asia since~1000 a BP:evidence from a 4200-year-old sedimentary archive

Fire has crucial effects on ecosystem succession,the carbon cycle,and atmospheric chemical composition[1-3].Previous studies have shown that fire dynamics are closely related to regional vegetation and climate.Arid Central Asia(ACA)is sensitive to climate change,and grassland fires in ACA account for over 80%of the total burned area[4].In the face of intense global climate change,it is vital to understand how grassland burning responds long-term to climate and vegetation.Developing such an understanding would help predict fire activity and thus assist in the development of future fire management policies.

Insights into the nucleation,grain growth and phase transformation behaviours of sputtered metastableβ-W films

Metastable phase in tungsten film is of great interests in recent years due to its giant spin Hall effects,however,little information has been known on its nucleation,growth and phase transformation.In this paper,a 900 nm-thick tungsten film with double-layer structure(α-W underlayer andβ-W above it)was produced on SiO_(2)/Si substrate by high vacuum magnetron sputtering at room temperature.The structural properties ofβ-W were systemically investigated by X-ray diffraction,transmission electron microscopy,thermodynamic calculation,first-principle and phase-field simulations.It is found that theβ-W nucleation is energetically favoured on the SiO_(2)surface compared to theα-W one.As the film thickening proceeds,β-W[211]turns to be preferred direction of growth owing to the elastic strain energy minimization,which is verified by phase-field simulations.Moreover,theβ→αphase transformation takes place near the film-substrate interface while the rest of the film keeps theβ-W phase,leading to a doublelayer structure.This localized phase transition is induced by lower Gibbs free energy ofα-W phase at larger grain sizes,which can be confirmed by thermodynamic calculation.Further in-situ heating TEM analysis of the as-deposited film reveals that theβ→αphase transformation is fulfilled byα/βinterface propagation rather than local atomic rearrangements.Our findings offer valuable insights into the intrinsic properties of metastable phase in tungsten.

Optoelectronic hybrid oscillating fiber-optic sensor with attosecond precision and reconfigurable sensitivity

The fiber-optic sensor is a great candidate in the field of metrology,developed to rely on the optical phase to convey valuable information.Some phase amplification methods have attracted wide attention due to their ability to improve measurement sensitivity;nevertheless,the precision is generally restricted in phase measurement.Here,we report a novel optoelectronic hybrid oscillating fiber-optic sensor by mapping the measurand loaded on the sensing fiber to the frequency shift of the microwave signal,which is generated by an all-electric oscillating cavity with a frequency conversion pair.Two branch signals assisted in twice frequency conversion are obtained by heterodyne interference,with the sensing information scaled up by two optical comb line frequencies contained,and then,the phase difference is cumulatively enhanced in the closed feedback loop.Thanks to the introduction of the oscillating cavity,a detection limit improvement of 42 dB at a 10 Hz frequency offset can be achieved in theory with a cavity delay of 1μs.The sensing precision depends on the cavity noise limit and is independent of the instrument and cavity delay.A proof-of-concept experiment is carried out to demonstrate sensors with a sensitivity of 8.3 kHz/ps and 22.3 kHz/ps for a range of 50 ps,and 62 kHz/ps and 162 kHz/ps for a range of 6.7 ps.The minimum Allan deviation reaches 2.7 attoseconds at an averaging time of 0.2 s with a frequency interval of 150 GHz,indicating that the proposal may pave a new path for sensing interrogation systems,especially for high-precision measurement.