[en] Acoustic waves generated in nanosecond pulsed-laser ablation of a solid target in both air and water-confined environments were measured experimentally. It was found that the amplitude of the acoustic wave tended to decrease with an increase in water thickness. The waves were analyzed by means of fast Fourier transform. It was shown that there are several frequency components in the acoustic waves with the dominant frequency shifting from high frequency to low frequency as the thickness of the water layer increases. Furthermore, strong acoustic pressure led to enhancement of the coupling of the laser energy to the target in laser plasma propulsion. (plasma technology)

[en] The angular distribution and pressure force of droplets ejected from liquid water and glycerol ablated by nanosecond laser pulses are investigated under different viscosities in laser plasma propulsion. It is shown that with increasing viscosity, the distribution angles present a decrease tendency for two liquids, and the angular distribution of glycerol is smaller than that of water. A smaller distribution leads to a higher pressure force generation. The results indicate that ablation can be controlled by varying the viscosity of liquid propellant in laser plasma propulsion

[en] The Bi_2.93Ce_0.07TiNb_1-xW_xO₉ (BCTNW-100x, x = 0–0.06) high-temperature piezoelectric ceramics were fabricated via a conventional solid-state reaction processing. The influence of tungsten substitution for niobium in the crystal structure of Bi₃TiNbO₉-based ceramics was studied in detail. The crystal structure analysis revealed that the introduction of W⁶⁺ enhanced the octahedral tilt angle along the a axis, which resulted in an optimal piezoelectric property (d₃₃ = 19.2 pC/N) at x = 0.02. While the structural distortion of BCTNW-100x ceramics became weak with W content further increasing, which made the thermal stability of BCTNW-100x ceramics better. When annealing temperature elevated to 700 °C, the d₃₃ value of BCTNW-6 ceramic still remained 92% of its initial value, indicating good thermal stability. Furthermore, the dc conduction mechanism of the ceramics was studied. The oxygen vacancies played an important role in dc conduction mechanism at low temperature and the main conduction mechanism at high temperature was intrinsic conduction.

[en] A new method to measure the target velocity in laser plasma propulsion is proposed. By this method, the target velocity can be directly measured. The target thickness and the probe beam have no effects on measurement results. Compared with theoretical result, the error of experimental result is less than 2%. Furthermore, using this method, target momentum generation in laser-ablation water under different ambient temperatures is measured. Results show that the target momentum increases as the temperature decreases. (authors)

[en] Highlights: • 940 °C sintering PZT have high piezoelectricity: d₃₃ = 640 pC/N, T_c = 303 °C. • The larger the CTP, the lower the E_a. • The larger the CTP, the higher the piezoelectric response. • The lower the E_a, the smaller the domain size. • The smaller the domain size, the higher the piezoelectric response. -- Abstract: Multilayer piezoelectric devices need to co-sinter the piezoelectric ceramic layers and the Ag-rich Ag–Pd internal electrode layers at a low temperature (less than the Ag melting point of 961.78 °C), and need to use Sn–Zn-based lead-free solder to weld the components at 260 °C. This requires low-temperature sintering of high-performance piezoelectric ceramics with a Curie temperature (T_c) higher than 260 °C. Thereby low-temperature (940 °C) sintering 0.09 Pb(Ni_1/3Nb_2/3)O₃‒ 0.03 Pb(Mg_1/2W_1/2)O₃‒0.88 Pb(Zr_0.5Ti_0.5)O₃ ceramics are prepared via the solid-state reaction method. Samples added with different Ta₂O₅ contents are fabricated and compared in terms of phase structure, microstructure, piezo-/ferro-electric properties, and dielectric relaxation. High piezoelectric properties (d₃₃ = 640 pC/N, d₃₃∗ = 676 p.m./V, T_c = 303 °C) are achieved in the 0.70 wt% Ta₂O₅ added ceramic with a minimum activation energy of domain wall movement (E_a) of 0.025 eV. Rietveld refinement and Raman spectroscopy show that all the ceramics exhibit rhombohedral-tetragonal (R-T) coexistence and the distortion degree of crystal structures increases with the increase of Ta₂O₅ content. Our results show that the larger the content of the tetragonal phase (CTP), the lower the E_a, the smaller the domain, and the higher the piezoelectric response. Low E_a favors orientation and extension of polar regions and facilitates the formation of the nanometer-size domain structure (polar nanoregions) which is observed by using piezoresponse force microscopy, thus resulting in high piezoelectric properties. This mechanism associated with the CTP, the E_a and the domain structure reveals the origin of the high piezoelectricity in the low-temperature sintering PZT-based relaxor ferroelectric ceramics.

[en] The burnup equation of nuclides is one of the most equations in nuclear reactor physics, which is generally coupled with transport calculations. The burnup equation describes the variation of the nuclides with time. Because of its very stiffness and the need for large time step, this equation is solved by special methods, for example transmutation trajectory analysis (TTA) or the matrix exponential methods where the matrix exponential is approximated by CRAM. However, TTA or CRAM functions well when the flux is constant. In this work, a new method is proposed when the flux changes. It's an improved method compared to TTA or CRAM. Furtherly, this new method is based on TTA or CRAM, and it is more accurate than them. The accuracy and efficiency of this method are investigated. Several cases are used and the results show the accuracy and efficiency of this method are great

[en] Objective: To study the influence of different heart rates, acquisition time windows and artifacts in CT imaging diagnosis. Methods: 120 patients who underwent coronary CTA scan in our hospital from August 2017 to September 2019 were selected for this study. Coronary CTA scan was performed for each patient, and the optimal imaging period for patients with different heart rates was determined by the phase. The difference between the optimal imaging phase and acquisition time window of patients with different heart rates, the difference between subjective and objective evaluation of image quality, and the radiation of different acquisition time windows were analyzed. Results: The optimal imaging phase and acquisition time window of low heart rate group were higher than those of other two groups (P < 0.05); the subjective scores of image quality of right coronary artery, left anterior descending branch and circumflex branch in low heart rate group were significantly higher than those of other two groups (P < 0.05); the CT value and contrast noise ratio (CNR) of the right coronary artery, left anterior descending branch and circumflex branch in low heart rate group were significantly higher than those of other two groups (P < 0.05), and the fat noise was significantly lower than those of the other two groups (P < 0.05). There was no significant difference between the effective dose index of the best acquisition time window and the effective dose index of the whole cardiac cycle among the three groups (P > 0.05). At the same time, the effective dose index of the best acquisition time window had no statistical significance. It was significantly lower than the total effective dose index (P < 0.05). Conclusion: In the diagnosis of patients with low heart rate, the time of image acquisition should be in the middle and end diastole, while in the diagnosis of patients with high heart rate, the time of image acquisition should be in systole. (authors)

[en] The first path-independent insertion-loss (PILOSS) strictly non-blocking 4×4 silicon electro–optic switch matrix is reported. The footprint of this switch matrix is only 4.6 mm×1.0 mm. Using single-arm modulation, the crosstalk measured in this test is –13 dB∼ –27 dB. And a maximum crosstalk deterioration of 6dB caused by two-path interference is also found. (paper)

[en] The Ca_0.85(LiCe)_0.075Bi₄Ti_4−xZn_xO₁₅ ceramics are prepared via solid‐state reaction method with lower sintering temperature. The influence of lower sintering temperatures (T_s) on structural and electrical properties is investigated. The repressed volatilization of Bi³⁺ reduces the impurity phase proportion and oxygen vacancies content in ceramics, which might lead to increased T_C value (~ 800 °C), piezoelectric constant d₃₃ value (20 pC/N), high resistivity (6.32 × 10⁵ Ω·cm at 600 °C), and good thermal stability up to 600 °C. Therefore, the Zn-modified ceramics are perceived to be one of promising candidates for high-temperature piezoelectric devices.

[en] The effect of viscosity on the coupling coefficient and specific impulse is investigated with water and glycerol as propellants in laser plasma propulsion. It is found that the propulsion is much more correlated with the liquid viscosity. For water in particular, the coupling coefficient and specific impulse presents nearly a linear relationship with the viscosity. The weak dependence of the coupling coefficient on the laser energy at a high viscosity is observed. These results indicate that a liquid propellant with suitable viscosity can be used in laser plasma thruster