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Nd:GdVO4 has the advantages of a small thermal expansion coefficient, a large absorption bandwidth, and a large absorption and emission cross section, making it a good gain material for LED-pumping without active temperature control. In this paper, the LED-pumped Nd:GdVO4 laser was first generated in the quasi-continuous-wave and the passively Q-switched regime. With the incident pump energy of 8.0 mJ, the Nd:GdVO4 laser demonstrated energy of 195 μJ at 1063 nm in the quasi-continuous-wave regime, the slope efficiency was 4.7%, and the optical conversion efficiency was 2.4%. In the passively Q-switched regime, Cr:YAG was used as a saturable absorber and the energy obtained was 6.53 μJ with a pulse duration of 806.8 ns. These experimental results indicated the application prospect of LED-pumped lasers. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide is commonly used as a coagulant for treating reactive dyes wastewater. However, the flocs are relatively small and coagulation process needs longer sedimentation time. Large flocs and short operation time are important for good coagulation performance. Coagulation floc formation and growth processes using magnesium hydroxide and polyacrylamide (PAM) dual-coagulant were investigated with controlled experiments through flocculation index (FI), floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. The final average floc size reached 58.5 and 4.96 μm with and absence of PAM addition during slow mixing periods. PAM feeding time and magnesium hydroxide formation time can affect the floc formation and growth processes. The results showed that floc formed rapidly during magnesium hydroxide generation within 90 s and flocs aggregated together by PAM bridging function. Reactive orange removal efficiency reached 99.3% with rapid mixing 250 rpm at 90 s during 100 mg/L magnesium ion addition, then adding 6 mg/L PAM at the beginning of slow mixing period in dual-coagulant system. [ABSTRACT FROM AUTHOR]

A 300 kW superconducting homopolar generator has been jointly developed and tested by Wuhan Marine Electrical Propulsion Research Institute and Institute of Electrical Engineering, Academia Sinica. It is a drum-type machine with superconducting excitation and solid brush current collection, 1300 rpm rotating speed, 230-330 V output voltage. The armature rotor diameter is 620 mm, effective length is 600 mm, the average radial magnetic field in the armature region is 0.75 T. During test it reached 300 kW nominal output power and worked stably. The design and development of the machine and its main components, together with its test results are presented.

In this paper, the multilevel classification model of high-speed railway signal equipment fault based on text mining technology is proposed for the data of high-speed railway signal fault. An improved feature representation method of TF-IDF is proposed to extract the feature of fault text data of signal equipment. In the multilevel classification model, the single-layer classification model was designed based on stacking integrated learning idea; the recurrent neural network BiGRU and BiLSTM were used as primary learners, and the weight combination calculation method was designed for secondary learners, and k-fold cross verification was used to train the stacking model. The multitask cooperative voting decision tree was designed to correct the membership relationship of classification results of each layer. Ten years of signal switch machine fault data of high-speed railway are used for experimental analysis; the experiment shows that the multilevel classification model can effectively improve the classification of signal equipment fault multilevel classification task evaluation index and can ensure the correctness of the subordinate relations' classification results. [ABSTRACT FROM AUTHOR]

A simple and reliable method of preparing high-quality perovskite layers is essential for the high photovoltaic performance of perovskite solar cells. Here, a new low-boiling-point solvent system composed of methylamine solution in ethanol and tetrahydrofuran is designed for methylammonium lead iodide precursor solutions. Concentrated methylammonium lead iodide precursor solutions with a concentration of 2.1 M are obtained, and smooth and compact methylammonium lead iodide films with an area of up to 600 cm2 are prepared directly by one-step spin-coating or blade-coating the precursor solution at room temperature. The rapid evaporation of the solvent and strong interaction between methylamine and methylammonium lead iodide lead to a high crystal nucleus density and intermediate-free crystallization path, and consequently result in a compact and smooth film. The high-quality methylammonium lead iodide films show excellent photovoltaic performance in conventional mesoporous solar cells with efficiencies of 20.0% (0.1 cm2) and 15.6% (10 cm2). Because of the low cost and ease of operation, the solvent system developed in this work is promising both in the laboratory and for future industrialization. [ABSTRACT FROM AUTHOR]

The power transformer is the major electrical equipment in the power system and should be able to resist the damage that caused by the abnormal conditions, like the influence of the inrush current and the electromagnetic force. However, the residual flux, which is the most common influence factor of the inrush, can result in large current magnitude. This paper is to analyse inrush current and the electromagnetic force that as the result of inrush current for the impact of the safe operation of the large power transformer. The research of the inrush current under various factors has practical significance. In order to study the electromechanical forces influenced by the residual flux, the inrush current was analysed by Jiles-Atherton (J-A) hysteresis model. During transient switching process, electromechanical forces under the different residual fluxes were calculated, using the finite-element method coupled to the external circuit. The studies presented in this paper would be used in the design of the power transformer and power network protection. [ABSTRACT FROM AUTHOR]

Yb3 + : KY (WO4)2 (Yb:KYW) possesses various excellent properties, such as its highly polarized emission cross section, that makes it an excellent option for developing highly efficient diode-pumped solid-state lasers. A high-energy, high-beam-quality passively Q-switched Yb:KYW laser was demonstrated. The small-signal gain characteristics of the Yb:KYW crystal under quasi-continuous-wave laser diode (LD) pumping were obtained by theoretical analysis. Under LD end-pumping at a repetition rate of 500 Hz and a pumping width of 200 μs, the Q-switched Yb : KYW / Cr4 + : YAG laser operated at a wavelength of 1025 nm, and a single-pulse energy of 0.5 mJ was obtained with a pulse width of 5.8 ns. Near-diffraction-limited beam quality with an M2 value of ∼1.02 was achieved. The compact setup provided efficient second-harmonic generation at 512.5 nm via type-I phase matching using a LiB3O5 (LBO) crystal, and the output single-pulse energy was 0.13 mJ. We believe that these results further demonstrate the utility of Yb:KYW as a passively Q-switched laser crystal for solid-state lasers, particularly for applications that require nonlinear frequency conversion. [ABSTRACT FROM AUTHOR]

Purpose: To track variations in the deformation of the arterial wall noninvasively by estimating the accumulated displacement and strain over a cardiac cycle may provide useful indicators of vascular health. Methods: In this paper, we propose an approach to track a region of interest (ROI) locally and estimate arterial stiffness variation in a familial hypercholesterolemic swine model of spontaneous atherosclerosis that allows for systematic and reproducible study of progression of the disease mechanism. Results: Strain and displacement indices may be derived from the variations of the accumulated displacement and accumulated strain (obtained from the gradient of the accumulated displacement) over a cardiac cycle to predict not only the likelihood of developing vascular diseases, but also the sites where they may occur. Currently, an ROI thickness value of less than one mm within the arterial wall is necessary for the axial accumulated displacement and strain to obtain reproducible estimates. Conclusions: Accumulated axial displacement and strain estimation on the artery wall shown in this paper indicate the repeatability of these measurements over several cardiac cycles and over five familial hypercholesterolemic swine. Our results also demonstrate the need for a small region of interest within the arterial walls for accurate and robust estimates of arterial function. [ABSTRACT FROM AUTHOR]

We report high power continuous-wave (CW) and passively mode-locked lasers with Yb,Na:CaF2 crystal as gain material. A maximum CW output power of 14.5 W was achieved at the absorbed pump power of 22.8 W, corresponding to the slope efficiency of 63.6%. Furthermore, by using a semiconductor saturable absorber mirror, the CW mode-locking operation was achieved. A shortest duration of 175 fs with the average power of 352 mW, and a highest average power of 510 mW with duration of 190 fs were obtained. The dynamics of soliton mode-locking in the laser concerned with the absorbed pump power and the intra-cavity negative group delay dispersion were experimentally investigated. [ABSTRACT FROM AUTHOR]

When the electromagnetic transients occur in a power transformer, an inrush current is generated in its winding. The inrush current not only affects the performance of the transformer windings, but also affects the lifetime of the transformer. Many factors affect the inrush current, the most influential ones among which are the closing phase angle and the residual flux. In this paper, a dry-type transformer simulation model is built to analyze the influence of the inrush current on the performance of transformer windings during no-load reclosing conditions. Firstly, the inrush current was generated in the transformer windings during the no-load reclosing operation under different residual fluxes. Secondly, the field-circuit coupling 3d finite element method is used to analyze the electromagnetic force at different locations of the transformer windings under the influence of different inrush currents. The results of winding structural parameter variations are obtained through electromagnetic-structural coupling simulation, and the electromagnetic forces are used as the input parameter for the structural analysis. Finally, the residual flux is generated by controlling the opening and closing angle of the transformer through the phase-controlled switch, and the winding electromechanical characteristics are tested under different residual fluxes. Finally, comparisons of the test and simulation results are drawn to verify the impact of the closing angle and residual flux on inrush current and the winding deformation during the no-load reclosing conditions. [ABSTRACT FROM AUTHOR]

With improvements in light-emitting diode (LED) performance and a sharp decline in price, a light source with the irradiance of a laser and the cost of an LED is worthy of further study. We demonstrated a LED-pumped Nd:YVO4 laser in quasi-continuous-wave (QCW) and passively Q-switched (PQS) regime. With an incident pump energy of 6.28 mJ (150 μs pulses at 1 Hz), the Nd:YVO4 laser has an energy of 206 μJ at 1064 nm in the QCW regime. The optical conversion efficiency of the system is 4.1%, and the slope efficiency is 9.0%. A pulsed energy of 2.5 μJ was obtained with a duration of 897 ns (FWHM) in the PQS regime, which means the peak power is 2.79 W. The output energy stability is 97.54%. [ABSTRACT FROM AUTHOR]

Abstract We demonstrate a passively Q-switched laser based on Polygonal Active Mirror (PAM). Cr:YAG with different initial transmittance were used as saturable absorber (SA). To improve the output timing jitter, an intracavity aperture was used. Without the intracavity aperture, the maximum average output power of 726 mW was obtained with SA initial transmittance of 98%, and the corresponding optical-to-optical efficiency was 23.3%. With 92% initial transmittance SA, the maximum slope efficiency of 49.9% was obtained, and the maximum single pulse energy was 132.8 uJ. By applying the intracavity aperture, the output beam quality and timing jitter were improved. With 98% initial transmittance Cr:YAG SA, the beam quality (M2) was improved from 1.40 × 1.22 to 1.33 × 1.19 after applying the aperture, while timing jitter was improved from 18. 4 μ s (31.68%) to 4. 8 μ s (8.61%). [ABSTRACT FROM AUTHOR]

A visible supercontinuum (SC) with high energy is of vital importance to applications in remote sensing and hyperspectral light detection and ranging. A fiber laser with a wavelength of 1030 nm is frequency doubled through a LBO (LiB 3 O 5 ) crystal, and a high-energy 515 nm laser is obtained after wavelength conversion. Two kinds of seven-core photonic crystal fibers (PCFs) are used in this Letter. One is a uniform seven-core PCF (USC-PCF), and the other is a tapered seven-core PCF (TSC-PCF). Pumped by a 515 nm laser with a pulse width in nanosecond level, an SC covering 400 to 900 nm is efficiently generated in both PCFs. A maximum energy of 4.24 μJ is obtained in a USC-PCF. To prevent fiber damage of the coupling fiber end, the TSC-PCF which contains a transition fiber and a meters-long small core fiber is fabricated. One end of the transition fiber possesses a larger core diameter, and the pump laser can be coupled into the TSC-PCF without fiber damage. The meters-long small core fiber has the same core size with a USC-PCF and is utilized as the nonlinear medium to generate an SC. The dispersive wave in the short wavelength band is excited when more energy is shed into a fiber anomalous dispersion region. Up to 15th-order Raman peaks are observed during the SC evolution process.

An active Q-switching light-emitting diode (LED)-pumped laser is demonstrated by Nd:YLF crystal with acousto-optic modulation for the first time. The spectrum-band pump characteristic is grasped to describe the essential difference between an LED pump and single-absorption-peak matching of laser-diode pump or no matching of lamp pump. An effective absorption spectrum concept is proposed to characterize the absorption features of the gain material with LED-band pumping. According to this new theory, a flat-top beam profile is designed for pumping Nd:YLF crystal with only a 14  W/cm 2 peak power, resulting in 165 μJ output energy at 1047 nm. More importantly, by using the acousto-optic Q-switching technique, this LED-pumped Nd:YLF laser has successfully realized a TEM 00 mode output with a pulse energy of 10.6 μJ and a pulse width of 452 ns.

In laser systems, it is well known that beam pointing is shifted due to many un-modeled factors, such as vibrations from the hardware platform and air disturbance. In addition, beam-pointing shift also varies with laser sources as well as time, rendering the modeling of shifting errors difficult. While a few works have addressed the problem of predicting shift dynamics, several challenges still remain. Specifically, a generic approach that can be easily applied to different laser systems is highly desired. In contrast to physical modeling approaches, we aim to predict beam-pointing drift using a well-established probabilistic learning approach, i.e., the Gaussian mixture model. By exploiting sampled datapoints (collected from the laser system) comprising time and corresponding shifting errors, the joint distribution of time and shifting error can be estimated. Subsequently, Gaussian mixture regression is employed to predict the shifting error at any query time. The proposed learning scheme is verified in a pulsed laser system (1064 nm, Nd:YAG, 100 Hz), showing that the drift prediction approach achieves remarkable performances.

Magnesium hydroxide was used as a coagulant for treating reactive orange wastewater in a real continuous process. Effects of kaolin on coagulation performance and floc properties were investigated with controlled experiments through floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. Kaolin had significant influence on magnesium hydroxide-reactive orange floc formation and growth. The results showed that average floc size reached 16.31, 12.88 and 20.50 μm, respectively, in the rapid mixer, flocculation basin and sedimentation tank when kaolin concentration was 10 mg/L and reactive orange initial concentration was 0.25 g/L. The floc size tended to increase with the increase of kaolin suspension to 10 mg/L. All of the flocs under investigation showed that floc breakage led to decreased average floc size and remained stable in the flocculation basin. Reactive orange and kaolin could be removed effectively in the continuous coagulation process. Reactive orange was adsorbed in the surface of magnesium hydroxide through charge neutralization and adsorption.

We present a high-repetition-rate, high-pulse-energy, high-beam-quality, and high-average-power laser system using an ultraclean closed-type stimulated-Brillouin-scattering phase-conjugate mirror (SBS-PCM). By controlling microparticles of SBS-PCM down to 40 nm, thermal load capacity of such closed-type SBS-PCM was greatly improved, which presented the best reported cleanliness. The closed-type SBS-PCM, lacking scanning wedge plates, achieved reflectivity as high as 92% and showed no optical breakdown phenomena or obvious thermal effects at a 500 Hz pulse-repetition frequency (PRF). Operation at 550 W output power, approximately 1.1 J pulse energy, and beam quality M 2 of approximately 2 represents, to our knowledge, the best reported performance. Thermal phase distortion was compensated, and the maximum-output-power pulse-width compression improved from 30 ns to approximately 10 ns.

We have developed a unique approach for enhancing the sensitivity of pyrenyl probes based on polyelectrolyte-induced nanoassemblies and explored its sensing application toward 2,4,6-trinitrophenol (TNP). The key issue of the method is the formation of the nanoassemblies which possess high-density charges, specific surface area, and inner hydrophobic regions. These properties would help increase the loading of analytes and promote probe-analyte interactions, thereby leading to the prominent enhancement of the sensitivity. In the course of TNP detection, pyrene nanoassemblies can bind TNP efficiently through cooperative noncovalent interactions including electrostatic, π-π stacking, and charge-transfer interactions, resulting in the distinct fluorescent responses of pyrene moieties. This system has excellent selectivity and sensitivity for TNP detection. The detection limit is as low as 5 nM. It may be used for monitoring the TNP concentrations in real-world samples.

The objective was to study the relationship between laser fluence and ablation efficiency of a femtosecond laser with a Gaussian-shaped pulse used to ablate dentin and enamel for prosthodontic tooth preparation. A diode-pumped thin-disk femtosecond laser with wavelength of 1025 nm and pulse width of 400 fs was used for the ablation of dentin and enamel. The laser spot was guided in a line on the dentin and enamel surfaces to form a groove-shaped ablation zone under a series of laser pulse energies. The width and volume of the ablated line were measured under a three-dimensional confocal microscope to calculate the ablation efficiency. Ablation efficiency for dentin reached a maximum value of 0.020 mm3∕J when the laser fluence was set at 6.51 J∕cm2. For enamel, the maximum ablation efficiency was 0.009 mm3∕J at a fluence of 7.59 J∕cm2.Ablation efficiency of the femtosecond laser on dentin and enamel is closely related to the laser fluence and may reach a maximum when the laser fluence is set to an appropriate value., (© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE))

Introduction: The aim of this study was to evaluate the morphological changes and quantitatively assess the roughness of dentin after the ablation with a Ytterbium-Doped Potassium Yttrium Tungstate (YB: KYW) thin-disk femtosecond pulsed laser of different fluences, scanning speeds and scanning distances., Method: Twelve extracted human premolars were sectioned into crowns and roots along the cementum-enamel junction, and then the crowns were cut longitudinally into sheets about 1.5 mm thick with a cutting machine. The dentin samples were fixed on a stage at focus plane. The laser beam was irradiated onto the samples through a galvanometric scanning system, so rectangular movement could be achieved. After ablation, the samples were examined with a scanning electron microscope and laser three-dimensional profile measurement microscope for morphology and roughness study.With increasing laser fluence, dentin samples exhibited more melting and resolidification of dentin as well as debris-like structure and occluded parts of dentinal tubules., Results: When at the scanning speed of 2400mm/s and scanning distance of 24μm, the surface roughness of dentin ablated with femtosecond pulsed laser decreased significantly and varied between values of dentin surface roughness grinded with two kinds of diamond burs with different grits. When at the scanning speed of 1200mm/s and scanning distance of 12μm, the surface roughness decreased slightly, and the surface roughness of dentin ablated with femtosecond pulsed laser was almost equal to that grinded with a low grit diamond bur., Conclusion: This study showed that increased laser influence may lead to more collateral damage and lower dentin surface roughness, while scanning speed and scanning distance were also negatively correlated with surface roughness. Adequate parameters should be chosen to achieve therapeutic benefits, and different parameters can result in diverse ablation results.