Critical power of keyhole formation in CW Nd:YAG laser deep penetration welding

The energy model was founded to calculate the critical power of keyhole formation by using the limit principle in CW （ continuous wave ） Nd： YAG laser deep penetration welding process. The model was validated by experiments. The results show that ＇.there are two errors between the calculated critical power of keyhole formation and that of experiments ： one is that the calculated results is less than those of experiments, which is caused by not considering the energy loss by heat conduction in the model of keyhole formation. The other is that there is 0. 9 mm error between the axis of the calculated curve of critical power with location of laser focus and that of experimental curve, which is induced by the excursion of laser focus in laser deep penetration welding. At last, the two errors were revised according to the analyses of the errors.

Polarization effect on critical power and luminescence in an air filament

We demonstrate that the filamentation process is strongly influenced by the polarization state of the driver laser. When the laser polarization changes from linear to circular, the critical power for the self-focusing of a Ti：Sapphire laser （800 nm, 40 fs） in air increases from about 9.6 ± 1.0 to 14.9± 1.5 GW, while the second nonlinear refractive index n2 of air decreases from 9.9 × 10-2o to 6.4 ×10-20 cm2/W. We also demonstrate that the luminescence from the neutral nitrogen molecules at 337 nm is dependent on both the laser intensity and plasma density inside the filament.

The state-of-the-art of steel technology used for chinese power plants and its future

The development and construction of Ultra Super Critical(USC) fossil fired power plants and advanced nuclear power plants are the most important and effective issue to improve national electricity structure in China and to fulfill the national emission aim which had been proposed and promised.Further, steel technology is one of the most imperative fundamentals to ensure the development and construction of USC fossil fired power plants and advanced nuclear power plants.This paper briefly introduced the state-of-the -art and achievement of steel technology used for USC fossil fired power plants and advanced nuclear power plants in China so far.Meanwhile,the authors also analyzed and discussed the potential research and development plans of the important steel technology in China in the near future.

Quantitative evaluation of LAL productivity of colloidal nanomaterials:Which laser pulse width is more productive,ergonomic,and economic?

Near-IR(wavelength≈1μm)laser ablation of bulk,chemically-inert gold in water was compared for different laser pulse width in broad the range of 300 fs–100 ns,comparing a number of key ablation characteristics:mass loss,singleshot crater volume and extinction coefficient of the generated colloidal solutions taken in the spectral ranges of interband transitions and localized plasmon resonance.Comparing to related air-based ablation results,at the given fluences laser ablation in the liquid resulted in the maximum ablation yield per unit energy and maximum NP yield per pulse and per unit energy for the picosecond lasers,occurring at subcritical peak pulse powers for laser self-focusing.The self-focusing effect was demonstrated to yield in incomplete,effectively weaker focusing in the water filaments of ultrashort laser pulses with supercritical peak powers,comparing to linear(geometrical)focusing at sub-critical peak powers.At the other,nanosecondpulse extreme the high ablation yield per pulse,but low ablation yield per unit energy and low NP yield per pulse and per unit energy were related to strong ablation plasma screening,providing mass removal according to the well-established scaling relationships for plasma.Illustrative comparison of the ablation and nanoparticle generation efficiency versus the broad fs–ns laser pulse width range was enabled in terms of productivity,economicity,and ergonomicity,using the proposed universal quantitative criteria.

Simulation of Secondary Electron and Backscattered Electron Emission in A6 Relativistic Magnetron Driven by Different Cathode

Prticle-in-cell（PIC） simulations demonstrated that,when the relativistic magnetron with diffraction output（MDO） is applied with a 410 kV voltage pulse,or when the relativistic magnetron with radial output is applied with a 350 kV voltage pulse,electrons emitted from the cathode with high energy will strike the anode block wall.The emitted secondary electrons and backscattered electrons affect the interaction between electrons and RF fields induced by the operating modes,which decreases the output power in the radial output relativistic magnetron by about 15%（10%for the axial output relativistic magnetron）,decreases the anode current by about 5%（5%for the axial output relativistic magnetron）,and leads to a decrease of electronic efficiency by 8%（6%for the axial output relativistic magnetron）.The peak value of the current formed by secondary and backscattered current equals nearly half of the amplitude of the anode current,which may help the growth of parasitic modes when the applied magnetic field is near the critical magnetic field separating neighboring modes.Thus,mode competition becomes more serious.

Repeatability and Variability of the 3-Min All-Out Test at the Subject Level

Purpose The constant work-rate to exhaustion tests must be repeated several times at each work-rate to estimate subject-level trial-to-trial variance(intra-individual variability,IIV)of critical power(CP)and work capacity(W').Alternatively,these parameters and their variance can be estimated by repeating the 3-min all-out test(3MT)fewer times.The purpose of this study was to propose a method to determine subject-level repeatability of the 3MT and demonstrate the need to repeat the test multiple times to estimate IIV.Methods Seven cyclists performed a ramp test and four 3MTs on a CompuTrainer.The parameters CP,W',peak power(Pp),and total work(TW)were compared across trials using repeated measures ANOVA,Bland-Altman analysis,Intraclass Cor-relation Coefficients(ICC),Typical Error(TE)of measurement,and Coefficient of Variation(CV).Results For the group,average CP and W'were 284±58 W and 10.214±3.143 kJ.The reliability statistics,CP(ICC=0.97,TE=8 W,CV=2.94%)and W'(ICC=0.88,TE=1.11 kJ,CV=10.87%),indicated strong agreement.Subject-level repeatability was determined by comparing time-to-peak power(TPp),absolute difference in Pp(δPp),and TW(δTW)for pairs of 3MTs.The average IIVs estimated by the 95%confidence intervals were±15 W for CP and±1.68 kJ for W'.Conclusions Thresholds are proposed for TPp(7 s),δPp(10%),andδTW(3%)to determine subject-level repeatability of the 3MT before computing the IIV of CP and W'.It is suggested that the 3MT is repeated at least three times to estimate the IIV,which aids in personalized measurement of training improvements and performance optimization。

Effect of Ag substitution on structural,magnetic and magnetocaloric properties of Pr_(0.6)Sr_(0.4–x)Ag_xMnO_3 manganites

A systematic investigation on the structural, magnetic and magnetocaloric properties of Pr_（0.6）Sr_（0.4-x）Ag_xMnO_3（x=0.05 and 0.1） manganites was reported. Rietveld refinements of the X-ray diffraction patterns confirmed that all samples were single phase and crystallized in the orthorhombic structure with Pnma space group. Magnetic measurements in a magnetic applied field of 0.01T revealed that the ferromagnetic-paramagnetic transition temperature T_C decreased from about 293 to 290 K with increasing silver content from x=0.05 to 0.1. The reported magnetocaloric entropy change and relative cooling power for both samples were considerably remarkable with a △S_（max） value of 1.9 J/（kg·K）and maximum RCP values of 100 J/kg, under a magnetic field change（？μ0H） equal to 1.8T. The analysis of the universal curves gave an evidence of a second order magnetic transition for the studied samples. The magnetic field influence on both the magnetic entropy change and the relative cooling power was also studied and discussed.