dispersion grating;frequency modulation-to-amplitude modulation conversion;high-power laser facility;inertial confinement fusion;phase modulation

Frequency modulation(FM)-to-amplitude modulation(AM) conversion is an important factor that affects the time±power curve of inertial confinement fusion(ICF) high-power laser facilities. This conversion can impact uniform compression and increase the risk of damage to optics. However, the dispersive grating used in the smoothing by spectral dispersion technology will introduce a temporal delay and can spatially smooth the target. The combined effect of the dispersive grating and the focusing lens is equivalent to a Gaussian low-pass filter, which is equivalent to 8 GHz bandwidth and can reduce the intensity modulation on the target to below 5% with 0.3 nm @ 3 GHz + 20 GHz spectrum phase modulation. The results play an important role in the testing and evaluating of the FM-to-AM on the final optics and the target, which is beneficial for comprehensively evaluating the load capacity of the facility and isentropic compression experiment for ICF.

Climate factors affect forest biomass allocation by altering soil nutrient availability and leaf traits

Biomass in forests sequesters substantial amounts of carbon;although the contribution of aboveground biomass has been extensively studied, the contribution of belowground biomass remains understudied. Investigating the forest biomass allocation is crucial for understanding the impacts of global change on carbon allocation and cycling.Moreover, the question of how climate factors affect biomass allocation in natural and planted forests remains unresolved. Here, we addressed this question by collecting data from 384 planted forests and 541 natural forests in China. We evaluated the direct and indirect effects of climate factors on the belowground biomass proportion(BGBP). The average BGBP was 31.09% in natural forests and was significantly higher(38.75%) in planted forests. Furthermore, we observed a significant decrease in BGBP with increasing temperature and precipitation. Climate factors, particularly those affecting soil factors, such as p H,strongly affected the BGBP in natural and planted forests. Based on our results, we propose that future studies should consider the effects of forest type(natural or planted) and soil factors on BGBP.

Digitally programmable organic light‐emitting tetrodes

Limited to the structure of traditional light‐emitting devices,electronic devices that can directly convert machine language into human visual information without introducing any back‐end circuit are still not easy to achieve.Based on a specially designed three‐phase co‐planar electrode structure,a new type of three‐phase alternating current driven organic light‐emitting device with the integration of emission and control functions,full‐color tunability and simple device structure is demonstrated in this study.We integrate the light‐emitting function of color‐tunable light‐emitting devices and the switching of three triodes in a single three phase organic light‐emitting device.The state control of luminous color and luminance intensity merely requires the introduction of a kind of machine language,that is an easy‐to‐program 6‐bit binary number coded digital signals.The color adjustable area covers 66%of the color triangle of the National Television System Committee.Such simple and easy‐to‐integrate light‐emitting system has great potential applications in the next‐generation man‐machine interface.

Status and development of high-power laser facilities at the NLHPLP

In this paper, we review the status of the multifunctional experimental platform at the National Laboratory of High Power Laser and Physics(NLHPLP). The platform, including the SG-II laser facility, SG-II 9th beam, SG-II upgrade(SG-II UP) facility, and SG-II 5 PW facility, is operational and available for interested scientists studying inertial confinement fusion(ICF) and a broad range of high-energy-density physics. These facilities can provide important experimental capabilities by combining different pulse widths of nanosecond, picosecond, and femtosecond scales. In addition, the SG-II UP facility, consisting of a single petawatt system and an eight-beam nanosecond system, is introduced including several laser technologies that have been developed to ensure the performance of the facility. Recent developments of the SG-II 5 PW facility are also presented.

Progress of the injection laser system of SG-Ⅱ

A high power laser system was used to drive the ignition of inertial confinement fusion(ICF), of which the high energy,the uniform focal spot, the accurate laser waveform, and the synchronization between the laser beams are key parameters.To accomplish this, global laser characteristics control should be assured, which was the main purpose of the injection laser system. In this paper, the key technological progress involved in the improvement of the performance of the injection laser of SG-II is reported, including frequency domain control, time domain control, near-field spatial shaping, preamplifier technology, and the optical parametric chirped pulse amplification pump source.

Development of Chrysomya megacephala at constant temperatures within its colony range in Yangtze River Delta region of China

Chrysomya megacephala (Fabricius,1794) is the most abundant and predominant species which arrives and colonizes a cadaver first in most parts of China.Therefore,its growth and development patterns have great implications in the estimation of the minimum postmortem interval (PMImin).In this study,C megacephala was collected from the Yangtze River Delta region and reared at seven constant temperatures ranging from 16 ℃ to 34 ℃.The developmental duration and accumulated degree hours,larval body length and morphological changes of C.megacephala were examined.Furthermore,we constructed three developmental models,isomorphen diagram,isomegalen diagram and thermal summation model,which can be used for estimating PMImin.The developmental durations of C.megacephala at 16 ℃,19 ℃,22 ℃,25 ℃,28 ℃,31 ℃ and 34 ℃ are (794.8 ± 14.7),(533.2 ± 10.1),(377.8 ± 16.8),(280.8 ± 15.1),(218.9 ± 8.5),(190.8 ± 10.1) and (171.8 ± 6.8) h,respectively.The developmental threshold temperature D0 is (11.41 ± 0.32) ℃,and the thermal summation constant K is (3 418.7 ± 137.0) degree hours.Regression analysis was conducted to obtain equations of the variation in larval body length with time after hatching,and variation in time after hatching with body length.Moreover,our study divides the intra-puparial morphological changes of C.megacephala into 11 sub-stages,and provides the time range experienced by each sub-stage.The results of this study provide fundamental development data for the use of C.megacephala in PMImin estimations.

A hybrid lattice Boltzmann flux solver for integrated hypersonic fluid-thermal-structural analysis

In this paper,a hybrid Lattice Boltzmann Flux Solver(LBFS)with an improved switch function is proposed for simulation of integrated hypersonic fluid-thermal-structural problems.In the solver,the macroscopic Navier–Stokes equations and structural heat transfer equation are discretized by the finite volume method,and the numerical fluxes at the cell interface are reconstructed by the local solution of the Boltzmann equation.To compute the numerical fluxes,two equilibrium distribution functions are introduced.One is the D1Q4 discrete velocity model for calculating the inviscid flux across the cell interface of Navier–Stokes equations,and the other is the D2Q4 model for evaluating the flux of structural energy equation.In this work,a new dual thermal resistance model is proposed to calculate the thermal properties at the fluid–solid interface.The accuracy and stability of the present hybrid solver are validated by simulating several numerical examples,including the fluid-thermal-structural problem of cylindrical leading edge.Numerical results show that the present solver can accurately predict the thermal properties of hypersonic fluid-thermalstructural problems and has the great potential for solving fluid-thermal-structural problems of long-endurance high-speed vehicles.

High-power, Joule-class, temporally shaped multi-pass ring laser amplifier with two Nd:glass laser heads

A high-power, Joule-class, nanosecond temporally shaped multi-pass ring laser amplifier system with two neodymiumdoped phosphate glass(Nd:glass) laser heads is demonstrated. The laser amplifier system consists of three parts: an all-fiber structure seeder, a diode-pumped Nd:glass regenerative amplifier and a multi-pass ring amplifier, where the thermally induced depolarization of two laser heads is studied experimentally and theoretically. Following the injection of a square pulse with the pulse energy of 0.9 m J and pulse width of 6 ns, a 0.969-J high-energy laser pulse at 1 Hz was generated, which had the ability to change the waveform arbitrarily, based on the all-fiber structure front end. The experimental results show that the proposed laser system is promising to be adopted in the preamplifier of high-power laser facilities.

Improvements in long-term output energy performance of Nd:glass regenerative amplifiers

Optical damages, which severely degrade the output energy performance of Nd:glass regenerative amplifiers, are discussed in detail in this paper. By a series of experiments, it has been confirmed that these damages result from laser-induced contamination. Based on this work, several improvements are made to boost output energy performance of the regenerative amplifier. The output energy of the regenerative amplifier after improvements declines 4% after 1000 h of operation, much less than it used to, 60% after 560 h of operation.

A high energy nanosecond cryogenic cooled Yb:YAG active-mirror amplifier system

A diode-pumped master oscillator power amplifier system based on a cryogenic Yb:YAG active-mirror laser has been developed.The performances of the laser amplifier at low temperature and room temperature have been investigated theoretically and experimentally.A maximum output energy of 3.05 J with an optical-to-optical efficiency of 14.7% has been achieved by using the master amplifier system.

Impact of connected and autonomous vehicles on traffic safety of mixed traffic flow:from the perspective of connectivity and spatial distribution

Equipped with high driving automation and advanced communication technologies, connected and autonomous vehicles (CAV) areexpected to possess a shorter reaction time and a wider vision,which are promising to improve traffic safety and efficiency. However,little attention has been paid to the effect of connectivity and spatial distribution on the safety performance of mixed traffic flow. Inthis paper, we attempt to investigate the impact of CAV on traffic safety considering these factors. To this end, a car-following modelfor CAV is proposed first. Then, the cooperative driving strategy for CAVs is designed. Precisely, the feedback gains of the informationare adjusted in real-time and are designed based on the derived stability criterion of the mixed traffic flow. Microscopic simulations ofmixed traffic flow in traffic oscillation are designed and conducted to explore how the distribution and connectivity of CAV affect thesafety performance ofmixed traffic flow. Simulation results show that increasing the penetration rate of CAV is promising to shift thesafety performance ofmixed traffic flow. In addition, the safety performance of mixed traffic flow is related to the spatial distributionand communication range of CAV. Besides, increasing communication range does not inevitably improve the safety performance ofmixed traffic flow when the penetration rate of CAV is low. Moreover, it is also found from the spatial–temporal trajectory of themixedtraffic flow that introducing CAV can mitigate the propagation of the stop-and-go wave and increase the throughput.

Modeling and simulation of intersection quasi-moving block speed guidance based on connected vehicles

Purpose–This study aims to propose a speed guidance model of the CV environment to alleviate traffic congestion at intersections and improve traffic efficiency.By introducing the theory of moving block section for high-speed train control,a speed guidance model based on the quasi-moving block speed guidance(QMBSG)is proposed to direct platoon including human-driven vehicles and connected vehicles(CV)through the intersection coordinately.Design/methodology/approach–In this model,the green time of the intersection is divided into multiple block intervals according to the minimal safety headway.Connected vehicles can pass through the intersection by following the block interval using the QMBSG model.The block interval is assigned dynamically according to the traveling relation of HV and CV,when entering the communication range of the intersection.To validate the comprehensive guidance effect of the proposed model,a general evaluation function(GEF)is established.Compared to CVs without speed guidance,the simulation results show that the GEF of QMBSG model has an obvious improvement.Findings–Compared to CVs without speed guidance,the simulation results show that the GEF of QMBSG model has an obvious improvement.Also,compared to the single intersection speed guidance model,the GEF value of the QMBSG model improves over 17.1%.To further explore the guidance effect,the impact of sensitivity factors of the CVs’environment,such as intersection environment,communication range and penetration rate(PR)is analyzed.When the PR reaches 75.0%,the GEF value will change suddenly and the model guidance effect will be significantly improved.This paper also analyzes the impact of the length of block interval under different PR and traffic demands.It is found that the proposed model has a better guidance effect when the length of the block section is 2 s,which facilitates traffic congestion alleviation of the intersection in practice.Originality/value–Based on the aforementioned discussion,the contributions of this paper are three-fold.Based on the traveling information of HV/CV and the signal phase and timing plans,the QMBSG model is proposed to direct platoon consisting of HV and CV through the intersection coordinately,by following the block interval assigned dynamically.Considering comprehensively the indexes of mobility,safety and environment,a GEF is provided to evaluate the guidance effect of vehicles through the intersection.Sensitivity analysis is carried out on the QMBSG model.The key communication and traffic parameters of the CV environment are analyzed,such as path attenuation,PR,etc.Finally,the effect of the length of block interval is explored.

Evaluating damage in optical elements using an amplified spontaneous emission beam

A method to evaluate damage in optical elements with the near field of an amplified spontaneous emission(ASE) beam has been developed. Local peak intensities are generally distributed randomly in the near field of a laser beam. The partial coherence of the ASE source results in a very smooth beam profile. The coherence time of ASE is much less than the pulse width. Small-scale intensity modulations can be smoothed out rapidly within the time of a pulse width.In the experiments, ASE is generated from a multifunctional high-performance Nd:glass system, with a pulse duration of 3 ns, a spectral width(full width at half maximum, FWHM) of 1 nm and an adjustable energy range from 1 to 10 J.The damage thresholds of samples induced by ASE are two to three times higher than those induced by a laser with the same size of test spot. Furthermore, the ASE beam has great potential for the detection of defects over a large area and the conditioning of optical elements.

Weighted local polynomial estimations of a non-parametric function with censoring indicators missing at random and their applications

In this paper,we consider the weighted local polynomial calibration estimation and imputation estimation of a non-parametric function when the data are right censored and the censoring indicators are missing at random,and establish the asymptotic normality of these estimators.As their applications,we derive the weighted local linear calibration estimators and imputation estimations of the conditional distribution function,the conditional density function and the conditional quantile function,and investigate the asymptotic normality of these estimators.Finally,the simulation studies are conducted to illustrate the finite sample performance of the estimators.

High-extraction-efficiency, nanosecond bidirectional ring amplifier with twin pulses

The output performances of a bidirectional ring amplifier with twin pulses are demonstrated.Compared to the extraction efficiency of 32% for single-pulse injection,the extraction efficiency of stored energy for twin-pulse injection with bidirectional propagation is increased to 60%.The maximum output energies of the twin pulses are 347 mJ and 351 mJ,and the output energy of a single pulse is only 373 mJ under the same amplifier operating conditions.The experimental results show that the bidirectional ring amplifier with twin pulses can achieve a higher extraction efficiency of stored energy at a lower operating fluence,and has potential applications in high-power and high-energy laser facilities.