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Low temperature and overcast rain are harmful to directly seeding early rice, it can hinder rice growth and lower rice biomass during the seedling stage, which in turn lowers rice yield. Farmers usually use N to help rice recuperate after stress and minimize losses. However, the effect of N application on the growth recovery for rice seedlings after such low temperature stress and its associated physiological changes remain unclearly. Two temperature settings and four post-stress N application levels were used in a bucket experiment to compare B116 (strong growth recovery after stress) with B144 (weak growth recovery). The results showed that the stress (average daily temperature at 12°C for 4 days) inhibited the growth of rice seedlings. Compared to the zero N group, the N application group's seedling height, fresh weight and dry weight significantly increased after 12 days. In particular, the increases in all three growth indicators were relatively higher than that of N application at normal temperature, indicating the importance of N application to rice seedlings after low temperature stress. The antioxidant enzyme activity of rice seedlings increased significantly after N application, which reduced the damaging effect of ROS (reactive oxygen species) to rice seedlings. At the same time, the soluble protein content of seedlings showed a slow decrease, while the H2O2 and MDA (malondialdehyde) content decreased significantly. Nitrogen could also promote nitrogen uptake and utilization by increasing the expression of genes related to NH4+ and NO3- uptake and transport, as well as improving the activity of NR (nitrate reductase) and GS (glutamine synthetase) in rice. N could affect GA3 (gibberellin A3) and ABA (abscisic acid) levels by regulating the anabolism of GA3 and ABA. The N application group maintained high ABA levels as well as low GA3 levels from day 0 to day 6, and high GA3 levels as well as low ABA levels from day 6 to day 12. The two rice varieties showed obvious characteristics of accelerated growth recovery and positive physiological changes by nitrogen application after stress, while B116 generally showed more obvious growth recovery and stronger growth-related physiological reaction than that of B144. The N application of 40 kg hm-2 was more conducive to the rapid recovery of rice growth after stress. The above results indicated that appropriate N application promoted rice seedling growth recovery after low temperature stress mainly by increasing the activities of antioxidant enzymes and nitrogen metabolizing enzymes as well as regulating the levels of GA3 and ABA. The results of this study will provide a reference for the regulation of N on the recovery of rice seedling growth after low temperature and weak light stress. [ABSTRACT FROM AUTHOR]

We report a Yb-doped all-fiber laser system generating burst-mode pulses with high energy and high peak power at a GHz intra-burst repetition rate. To acquire the uniform burst envelope, a double-pre-compensation structure with an arbitrary waveform laser diode driver and an acoustic optical modulator is utilized for the first time. The synchronous pumping is utilized for the system to reduce the burst repetition rate to 100 Hz and suppress the amplified spontaneous emission effect. By adjusting the gain of every stage, uniform envelopes with different output energies can be easily obtained. The intra-burst repetition rate can be tuned from 0.5 to 10 GHz actively modulated by an electro-optic modulator. Optimized by timing control of eight channels of analog signal and amplified by seven stages of Yb-doped fiber amplifier, the pulse energy achieves 13.3 mJ at 0.5 ns intra-burst pulse duration, and the maximum peak power reaches approximately 3.6 MW at 48 ps intra-burst pulse duration. To the best of our knowledge, for reported burst-mode all-fiber lasers, this is a record for output energy and peak power with nanosecond-level burst duration, and the widest tuning range of the intra-burst repetition rate. In particular, this flexibly tunable burst-mode laser system can be directly applied to generate high-power frequency-tunable microwaves. [ABSTRACT FROM AUTHOR]

We propose a 2.1 µm high-energy dissipative soliton resonant (DSR) fiber laser system based on a mode-locked seed laser and dual-stage amplifiers. In the seed laser, the nonlinear amplifying loop mirror technique is employed to realize mode-locking. The utilization of an in-band pump scheme and long gain fiber enables effectively exciting 2.1 µm pulses. A section of ultra-high numerical aperture fiber (UHNAF) with normal dispersion and high nonlinearity and an output coupler with a large coupling ratio are used to achieve a high-energy DSR system. By optimizing the UHNAF length to 55 m, a 2103.7 nm, 88.1 nJ DSR laser with a 3-dB spectral bandwidth of 0.48 nm and a pulse width of 17.1 ns is obtained under a proper intracavity polarization state and pump power. The output power and conversion efficiency are 0.233 W and 4.57%, respectively, both an order of magnitude higher than those of previously reported holmium-doped DSR seed lasers. Thanks to the high output power and nanosecond pulse width of the seed laser, the average power of the DSR laser is linearly scaled up to 50.4 W via a dual-stage master oscillator power amplifier system. The 3-dB spectral bandwidth broadens slightly to 0.52 nm, and no distortion occurs in the amplified pulse waveform. The corresponding pulse energy reaches 19.1 µJ, which is the highest pulse energy in a holmium-doped mode-locked fiber laser system to the best of our knowledge. Such a 2.1 µm, high-energy DSR laser with relatively wide pulse width has prospective applications in mid-infrared nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

Based on the Lagrange equation, the dynamic equation of the ideal 6 – SPS parallel mechanism and the variation curve of the torque of the mechanism are obtained. Then, the dynamic characteristics of 6 – SPS parallel mechanism with 6 S pairs' clearances are concerned with the continuous contact model. The S pair's clearance of the moving platform is simplified to a non-mass linkage, and its length is represented by random function; the lubricating oil film is simplified as a spring, and the oil film thickness is simplified as the length of the linkage and the stiffness of the spring is taken as the stiffness of the linkage's massless. Therefore, the dynamic equations of mechanism with clearances are obtained. When the dynamic equations of the mechanism had been analysed, it was obtained that the torque variation curves of the branched chain with clearance mechanism was. It was shown that the stiffness of the linkage had little effect on the moment of the mechanism by the simulation results. It was found that the torque of the mechanism was increased with the increase of the clearance after the torque curves of the ideal mechanism and the mechanism with clearance was analysed, so did the fluctuations. Thereby it was indicated that the clearance of S pair had significant effects on the state of the mechanism's force. In addition, the change of the angular velocity of the moving platform has no significant effect on the fluctuation of the moment curve. However, the change of the angular displacement curve frequency of the moving platform has more influence on the torque than the angular displacement amplitude. [ABSTRACT FROM AUTHOR]

We have experimentally obtained dispersion-managed solitons with sidebands in a passively modelocked thulium-doped fiber laser. The stable single soliton with sidebands can be converted into two soliton pulses at the pump power of 867 mW with appropriate settings of the polarization controllers (PCs). By increasing the pump power and cautiously adjusting the PCs, the three, four, and five soliton pulses with nonuniform intensity operate with stability in the cavity due to the global soliton interaction caused by unstable continuous waves. Furthermore, the soliton bunch can be observed at the pump power of 1 W. The position of solitons in the soliton bunch is random with a fixed separation that is controllable by changing the linear phase delay. Our work gives insight into the dynamics of multipulse dispersion-managed solitons in a 2-μm mode-locked fiber laser. [ABSTRACT FROM AUTHOR]

A 2-D thermal-electric coupling model has been developed, which enables us to evaluate the current distribution ofmonolithically integrated light-emitting diode (MI-LED). Based on the experimental IR images, the current distributions have been evaluated for the MI-LEDs on two types' heat sinks. For the MI-LED on poor thermal conductive chip-on-board heat sink, although there is a large junction temperature variation of 40 °C all over the chip, the current only varies from -16% to 11% due to the high parasitic series resistance and the topological design of MI-LED. The experiments show that the impact of the heatcrowding- induced uneven current distribution on the wallplug efficiency is negligible at a power density of 1 W/mm². The averagejunctiontemperature is still thedominant issue. With a high thermal conductive copper heat sink, the average junction temperature could be suppressed below 50 °C, and there is no obvious heat crowding and uneven current distribution observed. [ABSTRACT FROM AUTHOR]

In this letter, a double-gate AlGaN/GaN high electron mobility transistor operated in a synchronized switching mode is demonstrated, and improved dynamic performances are obtained. The additional gate sits on top of the conventional gate and stretches 2/4 μm to the source/drain electrodes, respectively. A positive voltage pulse is applied to the top gate and is synchronized with the ON-OFF switching pulse applied to the conventional gate. Such a double-gate driving method significantly improves the dynamic performances of the device. Moreover, it allows us to investigate the dynamic on-resistance in the drift region in detail. [ABSTRACT FROM AUTHOR]

A high-power phosphor-converted white LED with 3058 lm is reported. The high-power white LED was manufactured by utilising a single-blue LED chip with a cerium-doped yttrium aluminium garnet phosphor crystal film, and the LED chip consists of 16 LED cells that are connected in series, the chip dimensions are of 4.5 × 4.5 mm2. The electrical and optical characteristics of the LED were measured up to a 500 mA injection current under direct operation conditions. Results show that the luminous flux and luminous efficacy at 500 mA reach to 3058 lm and 128 lm/W, respectively. [ABSTRACT FROM AUTHOR]

Based on the optimised high-voltage network design and the resistance matching technique, a wafer-level light emitting diode (WL-LED) with a light output power of 157 W has been successfully demonstrated for the first time. The external quantum efficiency of the fabricated WL-LED was measured to be 24% at a driving current of 4 A. [ABSTRACT FROM AUTHOR]

Normally-off AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) on Si substrate were fabricated with the fluorine-based treatment technique. By employing a 20nmthick Al2O3 gate dielectric deposited by atomic layer deposition, the fabricated MOS-HEMT exhibits a large positive threshold voltage of + 3.5V, a maximum gate input voltage of 15V, a maximum saturate drain current of 5.3A and an off-state breakdown voltage of 402V. The high threshold voltage and the large input voltage swing is expected to improve the electromagnetic interference immunity and safety of AlGaN/GaN MOS-HEMT power switches. [ABSTRACT FROM AUTHOR]

The article offers information on the study by Desheng Zhao and colleagues on the influence of prenatal antibiotic use on the risk of childhood wheeze/asthma.