Effect of Al_(2)O_(3) Nanoparticle on Cavitation Strengthening of Magnesium Alloys

In order to study the effect of Al_(2)O_(3) nanoparticles in the cavitation-based strengthening process of magnesium alloys,the impact of a micro-jet generated by bubble collapse has been considered.The strengthening mechanism is based on the transfer of the energy of cavitation due to bubble collapse to Al_(2)O_(3) particles,which then undergo collision with the surface of the sample.The hardness,surface morphology,element content and chemical state of the strengthened samples have been analyzed by microhardness tests,SEM(scanning electron microscopy)and XPS(X-ray photoelectron spectroscopy)techniques.The results show that:after 5 min of strengthening,nanoparticles can be found on the surface of the sample through SEM.Combined with XPS tests,the content of Al_(2)O_(3) in the sample can be significantly increased,indicating that Al_(2)O_(3) particles penetrate into the surface and increase its hardness by 29.1 HV.

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.

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.

Detection and analysis of DNA recapture through a solid-state nanopore

Motion control of a single molecule through a solid-state nanopore offers a new perspective on detecting and analyzing single biomolecules.Repeat recapture of a single DNA molecule reveals the dynamics in DNA translocation through a nanopore and may significantly increase the signal-to-noise ratio for DNA base distinguishing.However,the transient current at the moment of voltage reversal prevents the observation of instantly recaptured molecules and invalidates the continuous DNA ping-pong control.We performed and analyzed the DNA translocation and recapture experiment in a silicon nitride solid-state nanopore.Numerical calculation of molecular motion clearly shows the recapture dynamics with different delay times.The prohibited time when the data acquisition system is saturated by the transient current is derived by equivalent circuit analysis and finite element simulation.The COMSOL simulation reveals that the membrane capacitance plays an important role in determining the electric field distribution during the charging process.As a result of the transient charging process,a non-constant driving force pulls the DNA back to nanopores faster than theoretically predicted.The observed long time constant in the transient current trace is explained by the dielectric absorption of the membrane capacitor.

Smooth pulse recovery based on hybrid wavelet threshold denoising and first derivative adaptive smoothing filter

Based on the pulse-shaping unit in the front end of high-power laser facilities,we propose a new hybrid scheme in a closed-loop control system including wavelet threshold denoising for pretreatment and a first derivative adaptive smoothing filter for smooth pulse recovery,so as to effectively restrain the influence of electrical noise and FM-to-AM modulation in the time–power curve,and enhance the calibration accuracy of the pulse shape in the feedback control system.The related simulation and experiment results show that the proposed scheme can obtain a better shaping effect on the high-contrast temporal shape in comparison with the cumulative average algorithm and orthogonal matching pursuit algorithm combined with a traditional smoothing filter.The implementation of the hybrid scheme mechanism increased the signal-to-noise ratio of the laser pulse from about 11 dB to 30 dB,and the filtered pulse is smooth without modulation,with smoothness of about 98.8%.

LD-pumped gas-cooled multislab Nd:glass laser amplification to joule level

We demonstrate a laser diode end-pumped helium gas-cooled multislab Nd:glass laser amplifier. The design and thermal management of the proposed laser amplifier are discussed. The thermally induced wavefront aberration of the slabs was also measured and compared with simulation results. A small-signal single-pass longitudinal gain of 1.8 was measured with a pump energy of 7.3 J. With an injected seed energy of 0.6 m J, the output energy from the amplifier reached 0.5 J at 0.2 Hz and 0.43 J at 0.5 Hz in a multipass extraction geometry, thus demonstrating the feasibility of diode-pumped,high-energy lasers with direct gas cooling.

Rapid fatty acids detection of vegetable oils by Raman spectroscopy based on competitive adaptive reweighted sampling coupled with support vector regression

Objectives:The composition and content of fatty acids are critical indicators of vegetable oil quality.To overcome the drawbacks of traditional detection methods,Raman spectroscopy was investigated for the fast determination of the fatty acids composition of oil.Materials and Methods:Rapeseed and soybean oil at different depths of the oil tank at different storage times were collected and an eighth-degree polynomial function was used to fit the Raman spectrum.Then,the multivariate scattering correction,standard normal variable transformation(SNV),and Savitzky–Golay convolution smoothing methods were compared.Results:Polynomial fitting combined with SNV was found to be the optimal pretreatment method.Characteristic wavelengths were selected by competitive adaptive reweighted sampling.For monounsaturated fatty acids(MUFAs),polyunsaturated fatty acids(PUFAs),and saturated fatty acids(SFAs),44,75,and 92 characteristic wavelengths of rapeseed oil,and 60,114,and 60 characteristic wavelengths of soybean oil were extracted.Support vector regression was used to establish the prediction model.The R^(2)values of the prediction results of MUFAs,PUFAs,and SFAs for rapeseed oil were 0.9670,0.9568,and 0.9553,and the root mean square error(RMSE)values were 0.0273,0.0326,and 0.0340,respectively.The R^(2)values of the prediction results of fatty acids for soybean oil were respectively 0.9414,0.9562,and 0.9422,and RMSE values were 0.0460,0.0378,and 0.0548,respectively.A good correlation coefficient and small RMSE value were obtained,indicating the results to be highly accurate and reliable.Conclusions:Raman spectroscopy,based on competitive adaptive reweighted sampling coupled with support vector regression,can rapidly and accurately analyze the fatty acid composition of vegetable oil.