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The aim of this study was to quantify the effects of different mulch planting patterns on soil enzyme activity and organic carbon mineralization in a tea plantation. The cover crop diversity experiment was conducted in the Tanjiawan tea garden, Yunyang District, Shiyan City, Hubei Province. Four cover crop planting modes were set up, namely no crop cover(A0), two cover crops(A1), four cover crops (A2), and eight cover crops(A3). The enzyme activity, organic carbon mineralization rate, and cumulative mineralization of the 0~20 cm and 20~40 cm soil layers in the tea plantation were measured, and the data was fitted to the first order kinetic equation to obtain the mineralization potential(Cp)and mineralization constant(k)of organic carbon. The results showed that, the soil enzyme activity in the mulch plot was generally higher than that in the control plot, and the enzyme activity in the 0~20 cm soil layer was higher than that in the 20~40 cm layer. Different mulch types had significant effects on soil catalase and urease activity(PPCp/k value was as follows:A1 > A2 > A3 > A0. In the 20~40 cm soil layer, the Cp/k value was as follows:A1 > A2 > A0 > A3. This suggests that the organic carbon mineralization of A1 was the strongest in both soil layers. Moreover, the microbial biomass carbon and soluble organic carbon of A1 were higher than those of the other treatments, thereby providing sufficient nutrients for crop growth and development. A1 had the highest pH value, which was conducive to soil acidification.

This study was performed in a tea garden in Xupingsi Village, Tanjiawan Town, Yunyang District, Shiyan City, Hubei Province, to evaluate the effects of different mulching crop patterns on soil microbial community functions in 0~15 and 15~30 cm soil layers of the tea garden. Four treatments were selected:Natural grasses(CK), ryegrass+white clover(EZ), ryegrass+white clover+bluegrass+red clover(SZ), and ryegrass+white clover+bluegrass+red clover+purple fescue+hairy raccoon+cosmos+zinnia(BZ). The results showed that the activities of urease, invertase, catalase, and phosphatase in the 0~15 cm soil layer treated with SZ were higher than those in the other treatments; The activities of urease, catalase, and phosphatase in the 15~30 cm soil layer treated with SZ were higher than those in the other treatments, whereas the activity of invertase was lower than that in the other mulching treatments. The mulching crops increased the average well color development(AWCD)of microbial communities in the 0~15 cm soil layer; AWCD was the highest in the SZ treatment, indicating the highest utilization efficiency of the carbon source. The mulching crops improved the soil microbial richness index, evenness index, and dominance index in the 0~15 cm soil layer, but had few effects on these parameters in the 15~30 cm soil layer. The results indicate that the mulching crops can improve soil enzyme activity and microbial community functional diversity, and SZ treatment had the best effect on the 0~15 cm soil layer. The findings of this study would be able to provide a theoretical basis for analyzing the effects of different mulching crop patterns on soil functional diversity of microbial communities in tea plantations in the future.

The effect of different arrangements of grasses, flowering plants(Asteraceae), and legume crops on the number and diversity dynamics of arthropod communities was determined in a tea orchard in Xupingsi Village, Tanjiawan Town, Yunyang District, Shiyan City, Hubei Province. For this, 4 treatments were established:Natural grasses(CK), ryegrass+white clover(EZ), ryegrass+white clover+bluegrass+ red clover(SZ), and ryegrass+white clover+bluegrass+red clover+purple fescue+hairy raccoon+cosmos+zinnia(BZ). The community composition and dynamics of richness index, divesity index, and evenness index of arthropods were determined. The results showed that the arthropod community composition in the tea orchard with different cover crops was similar to that in the tea orchard with CK, with the largest number of Diptera and the least number of Araneae insects. Compared with that in the CK, the number of Lepidoptera increased significantly under the different cover crop treatments(PP>0.05). Homoptera insects increased significantly by 92.47%(PP>0.05). The dynamics of diversity, evenness, and richness indices of arthropod communities in the tea orchard with different cover crops were basically the same; The richness index was the highest on August 26 and was higher in the tea orchard with different cover crops than in that with natural grasses on September 30. The arthropod community diversity index for EZ treatment, the diversity, richness, and evenness indices for SZ treatment, and the diversity and evenness indices for BZ treatment were significantly higher than those of the CK in the tea orchard.

Farmland management measures can have a significant impact on the carbon cycle of farmland ecosystems, which can affect soil fertility, agricultural production, and food security, and more broadly, climate change and environmental health. In this paper, the effects of different farmland management measures(fertilization methods, planting systems, and farming models)on soil organic carbon, greenhouse gas emissions, and soil microorganisms were reviewed. The increase in soil organic carbon was fastest when organic and inorganic fertilizer were applied. Moreover, there was a threshold effect between the amount of fertilizer applied and the soil carbon inventory. The application of organic fertilizer increased the CO2 emissions flux in the soil, and the application of phosphorus and potassium fertilizers reduced the globe warming potential of farmland soil more than nitrogen fertilizer. Increasing the application ratio of organic fertilizer to phosphate fertilizer was beneficial, leading to an increase in microbial richness in the soil and accumulation of microbial biomass carbon. Planting structure and planting density both affected the carbon storage of farmland soil, and planting structure had a significant impact on greenhouse gas emissions in farmland ecosystems. Compared with traditional monoculture planting, crop rotation and intercropping could effectively reduce the greenhouse gas emissions of farmland. At the same time, crop rotation was more conducive to increasing soil microbial diversity than continuous cropping. Conservation tillage improved the efficiency of farmland soil carbon, reduced greenhouse gas emissions, and had a positive impact on microbial activity, diversity, community structure, and carbon source utilization. Finally, we summarized the application of international mainstream carbon models to farmland ecosystems, and present future development prospects.

The 1319 nm lasers have important applications in the fields of optical fiber communication, laser medical treatment and laser color display. The Nd:YAG laser pumped by 808 nm laser diode is an efficient alternative to achieving 1319 nm laser output. In recent years, direct pump technology using 885 nm laser diodes has become more promising due to the dramatically reduced thermal effect and improved optical conversion efficiency. Quasi-continuous sodium beacon laser with microsecond pulse duration generated by the sum-frequency of 1319 nm and 1064 nm lasers can provide a gatable pulse format to eliminate the interference of atmospheric Rayleigh scattering and mitigate the spot elongation of sodium guide star to improve imaging accuracy. However, relaxation oscillation in the microsecond pulse could cause the damage to the nonlinear crystal and reduce the efficiency of sum-frequency generation. It is effective to suppress the relaxation by taking advantage of second harmonic generation, in which a nonlinear crystal is utilized to reduce the pulse peaks with higher intensity. In this paper, we demonstrate a high-power relaxation-oscillation-free quasi-continuous microsecond pulse 1319 nm laser by using the dual-end 885 nmdiode-pumped three-mirror ring-cavity. Intra-cavity etalon and customized mirror coating are employed to prevent the 1064 nmand 1338 nmline of Nd:YAG laser crystal from oscillating. A power tuning device, including a thin-film polarizer and a halfwave plate is implemented as the output mirror of ring cavity, which enables continuous adjustment of the out coupling ratio. The output power of the 1319 nm polarized laser is 22.5 W pumped by 150 W 885 nm laser diode. The repetition rate is 800 Hz and pulse width is 150 s. The corresponding optical conversion efficiency is 15%. The beam quality factor M2 is measured to be Mx2= 1.35 and My2=1.24. By precisely adjusting the temperature of etalon viz. adjusting refractive index as well as thickness of the etalon material, laser wavelength is tuned from 1318.888 nm to 1319.358 nm, corresponding to a tunable range of 470 pm and tuning accuracy of 0.7 pm. A 1319 nm frequency doubling crystal KTiOPO4 (5 mm5 mm15 mm, = 59:8 and ϕ = 0) is inserted into the cavity to suppress the relaxation oscillation. The pulse waveform quickly reaches a smooth regime, followed by a pulse spike at the initial stage and the loss of laser output power is only 1%. It is proved that it can be efficiently suppressed by inserting a frequency doubling crystal with negligible power loss. In conclusion, this paper provides a practical and effective technical means for achieving the high-power relaxation-oscillation-free quasi-continuous 1319 nm laser with microsecond pulse duration.

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO4 crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 m by an achromatic lens. The sum-frequency generation takes place in a 1 mm2 mm20 mm phase-matched type-I periodically poled KTiOPO4 crystal with a matching temperature of 55℃ and polarization period of 12.35 m The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M2=1.14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO4 temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.

Ultraviolet laser operating at 355 nm has been found to have wide applications in scientific and industrial fields of laser radar, biological fluorescence medicine, micro processing, laser marking and laser ablation, owing to its superior properties of short wavelength, high single-photon energy, and high resolution. In addition, 355 nm laser plays a vital role in promoting the development of RGB full color display because it can be used as an excitation source for investigating the blue light emitting materials. LiB3O5 (LBO) crystal possesses relatively high nonlinear coefficient and high optical damage threshold. Therefore, it is generally employed to generate 355 nm light through the third harmonic generation (THG) of the Nd:YAG laser (1064 nm). However, the CsB3O5(CBO) crystal, which also belongs to B3O7 group has attracted more attention for its larger nonlinear coefficient. The temperature sensitivity is another important characteristic of the nonlinear crystal. Temperature fluctuation can cause the variation of refractive index of nonlinear optical crystal, which leads to phase mismatch and thus affects the nonlinear conversion efficiency. The principal refractive index of CBO crystal was accurately measured using the auto-collimation method in a temperature range from 40 to 190 ℃ for the first time by Zhang et al. in 2013 [Zhang G C, et al. 2013 Opt. Lett. 38 1594], while the temperature bandwidth of CBO for 355 nm THG has not been reported. In the present paper, a high-power 355 nm laser is produced by efficient THG of an acousto-optic Q-switched quasicontinuous wave 1064 nm laser in CBO crystal. The master-oscillation power-amplification (MOPA) system with Nd:YAG crystal which is side pumped by high-power pulsed laser diode (LD) array delivers 210 W of a quasi-continuous Q-switched 1064 nm laser power. The laser operates at a 1 kHz repetition rate, and each pulse train contains five Q-switched pulses each with a duration of 40 ns. The 98 W of 532 nm green light is produced by second-harmonic generated in type-I LBO crystal. The 28.3 W ultraviolet laser is achieved by a 30-mm type-II CBO crystal through the sum frequency of 1064 nm and 532 nm light. The conversion efficiency from the fundamental light to the third harmonic reaches 13.5%, which is 28.6% higher than that obtained with a type-II LBO crystal under the same experimental conditions. The temperature sensitivity of CBO crystal in the 355 nm THG process is studied. Its temperature bandwidth is 25, which is much broader than that of LBO crystal. The experimental results show that the CBO crystal is superior to LBO crystal in the sense of conversion efficiency and temperature sensitivity for THG of 355 nm.

In this paper, combined with the latest development in relevant diagnostic and modeling techniques, the intense-pulsed ion beam (IPIB) energy deposition model in solid targets is established. The power density distribution induced by IPIB is simulated by Monte Carlo method on the basis of energy balance. By taking the power density as the source term, the thermal field distribution and evolution on a 100 μm stainless steel target irradiated by IPIB are simulated using the finite element method (FEM) in a time scale of several ms. Results reveal that in a time scale of several μups after IPIB irradiation, the main feature in the induced thermal field is a thermal shock within the depth of several times of the ion range. In the time scale of ms, thermal equilibrium can be established between the front and rear surfaces of the target, and the cross-sectional temperature field profile has a similar profile to the cross-sectional energy density distribution of the ion beam. This proves that by the infrared imaging diagnostic method, high resolution cross-sectional energy density diagnostics of IPIB can be achieved with a shooting time delay in ms scale.

Based on the review of previous experimental and theoretical studies on the surface processing by a pulsed intense electron beam, the induced temperature field in aluminum and 304 stainless steel is simulated by the finite element method (FEM) to estimate the existing time and depth of molten metal flow field on the irradiated surface. The generation of craters is attributed to the thermal resistance formed by the grain boundaries, and the influence of material properties on the mechanism of crater evolution is also discussed. Two-phase flow field simulation on molten metal is carried out with a combination of level-set method and FEM to estimate the mass transfer behavior at the craters and surface protuberance. It is revealed that the mass transfer effect driven by surface tension is an important factor for the formation and evolution of round-shaped craters on the surface of metals with high melting point, viscosity and surface tension coefficient. However, for metals with low melting point, due to the strong disturbance by ablating gas plume and low surface tension effect, the craters are more likely to have irregular splashing edges.

In this paper, diamond crystals are coated with titanium films in order to improve the chemical properties of diamond. The impact strength, oxidisation characteristics and the effects of sintering temperature on vitrified bond and diamond are investigated. It is found that when a titanium film is coated on the surface of diamond the contact angle between vitrified bond and diamond decreased from 39.5% to 34.5% at 993 K and that the degree of oxidisation on the surface of diamond will significantly decrease.