Search

Micro-milling is a low-cost, efficient, and high-precision machining method for manufacturing tiny parts, and has significant application value in various fields. In order to meet the high-accuracy requirements, several composite micro-milling methods have been proposed. However, these methods cannot change surface characteristics of materials, and poor permeability of cooling medium on the tool-workpiece interface remains unsolved. Atmospheric pressure plasma jet can efficiently improve surface wettability without obviously changing surface microstructures and may have promising application potential in machining of difficult-to-cut materials. Here, we propose to induce atmospheric pressure plasma jet to the micro-milling area to improve machinability and surface quality of TC4 titanium alloy. The influences of plasma jet on material wettability and mechanical property are firstly investigated by conducting plasma modification and tensile experiments. Then, micro-milling experiments of TC4 titanium alloy are performed under different atmospheres (dry, nitrogen jet, plasma jet, minimum quantity lubrication, and plasma jet + minimum quantity lubrication). The experimental results indicate that plasma jet can promote material fracture of TC4 titanium alloy, as well as reduce cutting force and cutting temperature, thereby obtaining better surface quality.

In high-frequency hydraulic vibration and impact systems, the high-speed reciprocating motion of the impact piston, as controlled by the main valve, transfers energy to the target. Therefore, the main valve must have a fast response speed and strong flow capacity. A novel two-stage large-flowrate on–off valve is developed in this study. The first stage is a small-flowrate servo valve, and the second stage is a large-flowrate hydraulic control valve with a hollow spool. The hollow structure not only reduces the quality of the spool and improves the valve dynamic characteristics but also improves the flow capacity and reduces the pressure drop at the valve port. A structural strength simulation is performed, and the deformation and stress of the spool are calculated. Then, the internal flow channel is extracted and the pressure drop characteristics of valve are obtained by simulation. To obtain the dynamic characteristics of the valve, the control equations of the valve are established, and the simulation model is built in Simcenter Amesim software. Then, the structural parameters of the valve body are optimized in this model. Finally, a prototype is developed for hydraulic vibration and impact systems. The experimental results show that the prototype works well, the opening time of the second-stage valve is within 6 ms, and the port pressure drop at a flow rate of 1000 L/min is only 30% of the conventional opening and closing valve of the same diameter.

In this study, hydrophobic polytetrafluoroethylene (PTFE) and hydrophilic polyetheretherketone (PEEK) membranes were used as heat exchangers in rich‐split CO2 capture process to recover the waste heat from the stripped gas (i.e., mixture of water vapor and CO2). Technical feasibilities of these two membrane exchangers were assessed by heat recovery and energy intensity in the monoethanolamine (MEA)‐based carbon capture process. The heat recovery of these two membrane exchangers with different pore sizes were then systematically compared under various operating parameters. The underlying mass and heat transfer mechanisms of two membranes were also investigated and compared to figure out the suitable candidate for heat recovery. Additionally, the potential risks of using these membrane exchangers were identified and investigated. Results showed that the PTFE membrane displays a better heat recovery performance than the PEEK membrane with the same pore size. The heat recovery of both PTFE and PEEK membranes first increases to a plateau and then drops slightly with the increased CO2‐rich solvent flow rate. The heat recovery of PTFE and PEEK membranes decreases with the increased flow rate and water vapor fraction of the inlet stripped gas, MEA temperature, and MEA concentration. Furthermore, the larger pore size results in higher heat recovery for both PTFE and PEEK membranes. PTFE membranes displayed lower MEA transfer flux than PTFE membranes at any rich MEA flow rate as the enhanced MEA transfer from the cold solution to the other side via PEEK membrane pores filled with liquid water. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Ce-modified Mn–Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction, Raman, N2 adsorption-desorption, infrared spectra, H2 temperature-programmed reduction and thermogravimetric analyses. Their catalytic properties were investigated in ozone (O3) decomposition reaction. Results show that the small amount of rare earth metal Ce added during Mn–Fe (FM) mixed-oxide synthesis greatly improves the catalytic performance in O3 decomposition. Among the prepared catalysts, the C0.04(FM)0.96 mixed-oxide catalyst exhibits the highest catalytic activity and stability. The O3 conversion over C0.04(FM)0.96 is 98% after 24 h reaction at 25 °C under dry condition, and that over FM decreases to 90% after 16 h reaction. At 0 °C, the O3 conversion over C0.04(FM)0.96 is 95% after 7 h reaction under dry condition, and that over FM slows down to 70%. Under humid condition (RH = 65%), the O3 conversion over C0.04(FM)0.96 is 63% after 6.5 h reaction at 25 °C, while that over FM decreases to 55%. When Ce is doped into Mn–Fe mixed oxides, the small amount of Ce enters the crystal lattice of MnO2, and partial Fe is separated to form Fe2O3. This changes cause lattice distortion and increase defects and enable the as-synthesized Ce–Fe–Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area, thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts forO3 decomposition.

Carbon-silica materials with hierarchical pores consisting of micropores and mesopores were prepared by introducing nanocarbon microspheres derived from biomass sugar into silica gel channels in a hydrothermal environment. The physicochemical properties of the materials were characterized by nitrogen physical adsorption (BET), scanning electron microscopy (SEM), and thermogravimetric (TG), and the adsorption properties of various organic waste gases were investigated. The results showed that microporous carbon materials were introduced successfully into the silica gel channels, thus showing the high adsorption capacity of activated carbon in high humidity organic waste gas, and the high stability and mechanical strength of the silica gel. The dynamic adsorption behavior confirmed that the carbon-silica material had excellent adsorption capacity for different volatile organic compounds (VOCs). Furthermore, the carbon-silica material exhibited excellent desorption characteristics: adsorbed toluene was completely desorbed at 150°C, thereby showing superior regeneration characteristics. Both features were attributed to the formation of hierarchical pores.

Nickel-based superalloy Inconel 718 is one of the hardest materials owing to its high hardness and additional physical properties. It is the most commonly used superalloy in gas turbine, aerospace, and automobile sectors. Micro-milling is generally employed for precision manufacturing of tiny structures, but it is difficult to obtain good surface quality with micro-milling Inconel 718 because of its excellent mechanical properties like high strength and hardness. Atmospheric pressure cold plasma jet can effectively improve surface wettability without changing surface micromorphology, which is expected to have positive lubricating effects in micro-machining of difficult-to-cut materials. In addition, minimum quantity lubrication can induce coolants into the machining area more efficiently, and is especially appropriate for micro-machining. In this paper, we propose a composite micro-milling method combining plasma jet and minimum quantity lubrication to machine Inconel 718. The effect of plasma jet on machinability is investigated by performing micro-milling experiments under different atmospheres (dry, nitrogen jet, plasma jet, minimum quantity lubrication, and plasma + minimum quantity lubrication). Surface roughness, cutting forces, and residual stress are the measures using corresponding techniques. The results indicate that the atmospheric pressure cold plasma jet can efficiently improve surface quality and reduce cutting forces of Inconel 718.

In this paper, a temperature thermostat used for the hydrogen maser is designed and fabricated based on the analysis of heat dissipation of the hydrogen maser. The high power and precise temperature control is realized by using the PID temperature control and semiconductor refrigeration techniques in the design and fabrication of thermostat. Under the condition of 300 W heat dissipation, the temperature fluctuation is within ±0.05 ℃, better than the existing similar products in the worldwide. The thermostat could provide excellent temperature environment for a high performance hydrogen maser.

In this paper, the multi-channel low additional stability phase comparator is designed and fabricated based on the technique of digital double mixing cascaded analog double mixing while noise suppression is used in the frequency doubling link. Compared to the single analog double mixing technique, the method presented in this paper is more advanced in the low additional stability. When the input frequency is 10 MHz, the additional stability reaches 1.7E−14@1s 2.7E−15@10s, 4.6E−16@100s, 1.37E−16@1000s, 4.4E−17@10000s. The multi-channel comparator designed in this paper will satisfy the requirement of high performance atomic clocks in the time keeping lab and novel frequency clocks and microwave sources.

Superhydrophobic surfaces with hydrophilic patterns have great application potential in various fields, such as microfluidic systems and water harvesting. However, many reported preparation methods involve complicated devices and/or masks, making fabrication of these patterned surfaces time-consuming and inefficient. Here, we propose a highly efficient, simple, and maskless microplasma jet (MPJ) treatment method to prepare hydrophilic patterns such as dots, lines, and curves on superhydrophobic aluminum substrates. Contact angles, sliding angles, adhesive forces, and droplet impact behavior of the created patterns are investigated and analyzed. The prepared "dot" patterns exhibit great water adhesion, whereas the "line" patterns show anisotropic adhesion. Additionally, the MPJ treatment does not obviously change the surface structures, which makes it possible to achieve repeatable patterning on one substrate. The adhesion behavior of these patterns could be adjusted using MPJs with different diameters. MPJs with larger diameters are efficient for the creation of patterns with high water adhesion, which can be potentially used for open-channel lab-on-chip systems (e.g., continuous water transportation), whereas MPJs with smaller diameters are preferable in preparing patterns with low water adhesion for diverse applications in biomedical fields (e.g., lossless liquid droplet mixing and cell screening).

Water wettability patterns on superhydrophobic surfaces have been widely designed to meet requirements of many fields, such as lab-on-a-chip devices and bioengineering. However, these systems are easily invalidated by oily liquids. Therefore, oil wettability patterns, which have rarely been focused on, are urgently needed. In this work, the authors successfully control oil wettability of superoleophobic surface by an atmospheric pressure dielectric barrier discharge (DBD) plasma jet. The results indicate that oil wettability is strongly influenced by treatment time, applied voltage and distance between plasma jet outlet and samples. They find that superoleophobic surfaces can be modified to be superoleophilic within 15 s, and that small holes can be etched on the surfaces under high applied voltages. Then, superoleophobic-superoleophilic patterns are prepared via selective plasma jet irradiation on superoleophobic surfaces, and both directional and antigravity transport of water and oily liquids are thus realised without external electrical or magnetic field. Additionally, ageing experiments show that the plasma-treated areas can maintain the induced wettability for >30 days storing under normal ambients, demonstrating superior time stability. The results presented here show the potential of atmospheric pressure DBD plasma jet for rapid oil wettability control and fabrication of long-time-effective oil wettability patterns.

Tubes are indispensable in our daily life, mechanical engineering and biomedical fields. However, the practical applications of tubes are sometimes limited by their poor wettability. Reported herein is hydrophilization of the tube inner wall by transferred atmospheric pressure plasma (TAPP). An Ar atmospheric pressure plasma jet (APPJ) is used to induce He TAPP inside polytetrafluoroethylene (PTFE) tube to perform inner wall surface modification. Optical emission spectrum (OES) is used to investigate the distribution of active species, which are known as enablers for surface modification, along the TAPP. Tubes’ surface properties demonstrate that after TAPP treatment, the wettability of the tube inner wall is well improved due to the decrease of surface roughness, the removal of surface fluorine and introduction of oxygen. Notably, a deep surface modification can significantly retard the aging of the obtained hydrophilicity. The results presented here clearly demonstrate the great potential of TAPP for surface modification of the inner wall of tube or other hollow bodies, and thus a uniform, effective and long-lasting surface modification of tube with any length can be easily realized by moving the tube along its axis.

Fabrication of porous carbon supported plasmonic photocatalysts with the low-cost carbon waste is a promising strategy for resource utilization. Herein, a sewage sludge was chosen for the synthesis of the sewage sludge activated carbon (SSC) supported Bi3+-doped TiO2 and Bi0 (SSCTB) photocatalysts. Through the pyrolytic carbonization, the sewage sludge was simultaneously displayed as the carbon precursor and reduction agent for the formation of SSC and Bi0, respectively. The results showed that the monodispersed Bi3+-doped TiO2 nanoparticles embedded with Bi0 were in-situ formed on the porous SSC. The synergistic effect of the localized surface plasmon resonance (LSPR) of Bi0, Bi3+ doping in TiO2, and the carbon of SSC greatly improved the light response ability and charge separation efficiency of the SSCTB samples. Under UV–Vis-NIR light irradiation for 60 min, the SSCTB sample with 5% of Bi (SSCTB5) possessed higher degradation rate of 47% for methyl orange compared with those of other samples. The photocatalytic mechanism was proposed based on the LSPR effect and the charge transfer process, where SSCTB5 was able to yield the highest numbers of OH and O2 − radicals. The fabrication of the SSC supported plasmonic photocatalysts provides a cost-efficient strategy for the resource utilization of sewage sludge.

The hydroxide precipitation with CaO or Ca(OH)2 is frequently applied in the ferrite formation process of electroplating wastewater, but the excess Ca2+ ions present often weaken the quality of the resultant mixed-ferrite (M−Fe3O4) precipitates. In this work, for resource utilization of the M−Fe3O4 and the Ca2+ sources introduced from Ca(OH)2 in the hydroxide precipitate process, the upconversion assisted magnetite near-infrared (NIR) photocatalysts of M−Fe3O4/Tm3+/Yb3+-doped CaF2/TiO2 (FCT) are synthesized. The M−Fe3O4 phases possess the advantages of magnetic separation, broadband spectrum absorption, and the heterostructure with TiO2, and absorb the strong upconversion luminescence emitted from Tm3+/Yb3+-CaF2 for photocatalysis. The TiO2 phase contributes to the large improvement of upconversion luminescence and photocatalytic activity. Because of the stronger UV–Vis-NIR absorption, upconversion luminescence, and electron-hole pair separation for the FCT sample with Ti: Ca molar ratio of 3: 1 (FCT3), higher yields of OH and O2 − radicals are generated, which enable FCT3 to possess much enhanced degradation rate (87.3%) of ciprofloxacin compared with those of other FCT samples under UV–Vis-NIR light irradiation. The fabrication of the upconversion magnetite NIR photocatalysts from electroplating wastewater is a promising strategy for its resource utilization and the environmental remediation.

In this paper, a random method to simulate atomic behavior in magnetic state selector of atomic hydrogen maser (H-maser) is reported. Using this method, the trajectory of each atom and atomic distribution in the entrance plane to the storage bulb is provided. The effect of the geometry and properties of magnetic state selector on the results are also discussed. We take H0 and L3 as examples and discuss the number of effective hydrogen atoms which are focused into storage bulb. When H0 = 0.9T, the number of effective atoms is at most and the optimum value of L3 is between 60 mm and 100 mm in the simulation condition. This approach can be possessed to improve the performance of H-maser.

In order to reduce the reboiler duty, the conventional CO2 chemical absorption process had been retrofitted by splitting some cold CO2-rich solvent prior to the lean-rich heat exchanger to recover the latent heat of hot stripped gas vented from CO2 desorber, which was called the rich-split carbon capture process. In this study, we promoted this rich-split carbon capture process by introducing 4 nm pore size tubular ceramic membranes, in which the coupled heat and water transfers from the stripped gas into the split CO2-rich monoethanolamine (MEA) aqueous solution across the membrane were permitted. Five types of ceramic membrane arrangements (Mode A to Mode E) were experimentally investigated and compared at different operating conditions in terms of the heat flux per volume of ceramic membrane (QCM). Results showed that among all the five ceramic membrane arrangements, the best heat recovery performance in terms of QCM value can be achieved using Mode-A where the stripped gas and rich MEA solvent flows were serially arranged in two serial ceramic membranes. Additionally, Mode-A has the best operating flexibility to the changes of water vapor content and stripped gas flow rate. Our study demonstrated that Mode-A may be an excellent candidate for recovering more waste heat at a high stripped gas flow rate. Furthermore, Mode-E can obtain a comparable heat recovery performance to Mode-A. In Mode-E, four parallel ceramic membrane tubes were bundled to form a heat exchanger with the same membrane volume to Mode-A. So if the layout of membrane tubes and shell size in Mode-E can be optimized elaborately, Mode-E will show a competitiveness in making the heat exchanger more compact on the premise of high heat recovery performance.

Plasma induced hydrophilization of superhydrophobic surfaces is highly-efficient, reversible and less destructive, and has therefore been applied into fields like fabrication of wettability patterns; however, plasma treated surfaces tend to recover back to their original wettability during storage, and different time stabilities are required for diverse applications. This paper focuses on regulating the time stability of plasma treated superhydrophobic surfaces by different surface modification methods or microstructures, and the recovery time could be adjusted as either 10 hours or more than 100 days under normal ambient conditions. These differences in recovery could also be observed in wettability patterns prepared by dissimilar methods. The adjustment methods developed should facilitate applications of plasma induced hydrophilization, especially for those that require rapid recovery or long-time stability.

We report a facile and general strategy for the preparation of metallic monolithic catalysts. Our strategy involved subjecting the surfaces of FeCrAl fibers to thermal treatment and the spraying of Pt nanoparticles suspension liquid. The catalyst exhibited high catalytic activity and good stability in the combustion of volatile organic compounds to CO2 and H2O at mild temperature. The exceptional activity of the catalyst can be attributed to the well-adhered alumina coating that formed on the surfaces of the FeCrAl fibers after thermal treatment and the highly dispersed Pt nanoparticles on the surface of the alumina coating.

In this paper, the optical gain characteristics and optical high frequency characteristics of an InP-based uni-traveling-carrier double heterojunction phototransistor (UTC-DHPT) are illustrated. The detailed analysis of UTC effects on those perfomaces show that UTC transport mechanism successfully weaks the space charge effect in the collector junction and breaks the limitation of low mobility of the holes. Compared with traditional single heterojunction phototransistor (SHPT), UTC-DHPT improves its processing ability of high power optical signal and provides high saturation current, high responsivity and high response speed simultaneously.

A novel kind of As 2 Se 3 chalcogenide glass multi-ring photonic crystal fiber is proposed. The characteristics of multi-ring photonic crystal fiber have been studied by the finite element method. Compared with another two kinds of single-core photonic crystal fibers, the multi-ring PCF can make the perfect combination of the effective mode area, the nonlinearity coefficient and multi-zero dispersion. It can achieve high power supercontinuum generation in middle infrared band; It also can be used in high-power pulsed laser fiber amplifier and high-power ultra-short pulse laser transmission in far infrared band.

A novel kind of polarization splitter based on tellurite glass dual-core photonic crystal fiber is proposed. The characteristics of the polarization splitter have been studied by the finite element method. By adjusting the ellipticity of the dual-core PCF, a very high value of birefringence can be reached. The high birefringence can increase the D-value of coupling length in the two orthogonal polarization directions, then the polarization-independent splitter can be achieved. Comparing with the SF57 glass dual-core PCF, the tellurite glass dual-core PCF has higher extinction ratio, the extinction ratio can reach −31 dB at the wavelength λ = 1.55 μ m . The 0.36-mm-long splitter is proposed to achieve extinction ratio better than −10 dB and a bandwidth of 20 nm.

Optical fiber devices and applications in the 2-μm band have been investigated extensively due to its unique advantages, such as eye safety. A fiber sensor based on tilted fiber Bragg grating with a grating plane angle of 2 deg is fabricated and experimentally tested. To the best of the authors’ knowledge, this is the first tilted fiber Bragg grating sensor to realize simultaneous measurements of temperature, axial strain, and a certain range of surrounding refractive index (SRI) at the 2-μm band. This paper uses the wavelength detection method and selects three independent resonant wavelengths as the investigated parameters. Results show that perturbations of temperature, axial strain, and SRI can shift the wavelengths of the core mode resonance and cladding mode resonance to some degree. The temperature sensitivities of the core mode and cladding mode are nearly the same, but their axial-strain sensitivities are different. Furthermore, the core mode is insensitive to the change in SRI. The sensitivities of SRI, temperature, and strain can thus be obtained by experimentally determining the wavelength shifts of the three independent resonance peaks. A 3 × 3 matrix containing the relationship coefficients between the disturbances of temperature, axial strain, and SRI and wavelength shifts is constructed. By reversely solving the matrix equation, variations in temperature, strain, and SRI can be obtained using the experimental determination of wavelength drifts.

International audience; Se with good glass formation ability was gradually doped into the Ge-As-Te glasses, and then the gradual change processes of some key physical and optical properties were observed. A series of Ge10As40Te50-xSex(x=0, 10, 20, 30, 40, 50) chalcogenide glass samples were prepared by the traditional melt-quenching method. The internal microstructure, physical and chemical properties of the glass samples were analyzed by using X-ray diffraction, Raman spectroscopy and thermal dilatometer instruments. Vis-NIR absorption spectra and infrared optical transmission spectra of these glasses were recorded with Spectrophotometer and Fourier transform infrared spectroscopy instrument. Then, the Tauc equation was adopted to calculate the direct and indirect optical band gaps of the glass samples. The results show that with the increasing of the Se, the thermal stability can be effectively improved, the maximum Tg can reach up to 233℃. A obvious blue shift of short infrared absorption spectrum cut-off edge appearance is observed in these glasses, i.e. The optical band gap increases gradually, which shows a wider range of transmission and better transparency spectrum, the maximum transmission rate can reach up to 56%. Infrared cut-off edge remains at 20μm, while Se content is less than 2 mol, its thermal stability is improved obviously and the optical spectral changes little. At last, using metal Mg as an oxide redactor for the purification of these glasses, the results show that the transmission spectra is much smooth and without any obvious impurity absorption peaks after the appropriate purification process. © 2016, Science Press. All right reserved.

Based on forced vibration tests for high-performance concrete (HPC), the influence of bridge vibration induced by traveling vehicle on compressive strength and durability of HPC has been studied. It is concluded that 1 d and 2 d compressive strength of HPC decreased significantly, and the maximum reduction rate is 9.1%, while 28 d compressive strength of HPC had a slight lower with a 3% maximal drop under the action of two simple harmonic vibrations with 2 Hz, 3 mm amplitude, and 4 Hz, 3 mm amplitude. Moreover, the vibration had a slight effect on the compressive strength of HPC when the simple harmonic vibration had 4 Hz and 1 mm amplitude; it is indicated that the amplitude exerts a more prominent influence on the earlier compressive strength with the comparison of the frequency. In addition, the impact of simple harmonic vibration on durability of HPC can be ignored; this shows the self-healing function of concrete resulting from later hydration reaction. Thus, the research achievements mentioned above can contribute to learning the laws by which bridge vibration affects the properties of concrete and provide technical support for the design and construction of the bridge deck pavement maintenance.

I is a great challenge to fabricate the biological films with patterned structures or ultra-thin thickness for nanolithography in the field of bioelectronics. Many techniques such as optical lithography, electron beam lithography, dip-pen and nanoimprint lithography have been developed and applied to prepare the bio-films. However, most organic molecules are so fragile that the fabrication process of their films requires physiologic and gentle conditions. Here, in our lab we introduce new bio-film possessing methods and the prepared films are of well-patterned structures with ultra-thin thickness. (I) Two-dimension (2D) Xanthan scaffold layers with nanofibril structures were build up through annealing the xanthan solution. In this experiment, temperature plays a critical role to affect the scaffold formation during the annealing process. (II) Porous stearic acid (SA) monolayer films were prepared by means of etching the SA Langmuir-Blodgett (LB) film in salt solution. The pores size and coverage area can be easily adjusted by controlling the salt concentration and immersion duration time. Moreover, the cationic valence in solution and the surface pressure of SA LB film will affect the etching result as well. (III) Uniform ultra-thin chitosan films were fabricated using mechanical manipulating by atomic force microscopy (AFM). The quality of the film is determined by the diameter of chitosan nanoparticles spin-coated on the substrate, the viscoelastic property of the chitosan particles, humidity and temperature of the surrounding enviroment. Adopting these three novel and simple methods to fabricate the bio-films will path a promising way to the nanolithography, biosensors, bioelectronics etc.

The transmission spectrum characteristic of two-segment polarization maintaining fibers Sagnac interferometer was investigated and simulated in detail and the optimal parameters for eliminating the crosstalk between the two polarization maintaining fibers was obtained. A temperature-insensitive pressure sensing technology was proposed. An experimental Sagnac interferometer was built and the solid core polarization maintaining photonic crystal fibers were taken as the sensing probe. The side pressure sensitive coefficients and the temperature crosstalk drift were measured and compared. The experimental results show that the side pressure sensitive coefficient was about 0.287 7 nm/N and the temperature drift was less than 0.1 pm/℃.

The rate of photo-electro-chemical (PEC) etching on N-polar n-GaN using vertical light emitting diodes (V-LEDs) has been investigated in detail, by varying the etching parameters (etchant concentration, etching duration and light intensity). V-LED with optimal hexagonal pyramid structure (the side-wall angle is 31°) has been fabricated, and then the influence of the PEC etching on the electrical and optical properties of V-LED has been analyzed. After PEC etching, the sample has good ohmic contact with the electrode and has lower contact resistance than a reference sample. The electrical characteristics have a better improvement. And the light output power has improved obviously after PEC etching, which shows 86.1% enhancement at 20 mA. Effect of side-wall angle of the pyramids on light extraction efficiency (LEE) in V-LEDs is theoretically calculated by finite difference time domain (FDTD) method. Simulation results show that the LEE is significantly increased for the sidewall angle between 20° and 40°, and the maximum enhancement is realized at a side-wall angle of 23.6° (the total reflection angle at the GaN/air interface).

Residual stress conditions in GaN-based LEDs will have a significant influence on device performance and reliability. In this paper, GaN-based vertical LEDs under different stress conditions are fabricated by bonding with three types of submounts (Al2O3 submount, CuW submount and Si submount), changing the soak temperature (290 ℃, 320 ℃, 350 ℃ and 380 ℃) and using different laser energy densities (875, 945 and 1015 mJ·cm-2). The warpage and Raman scattering spectra of those GaN-based LEDs are measured. The experimental results show that the residual stress conditions in GaN-based vertical LEDs are a consequence of the bonded submounts and bonded metal, and the soak temperature is the primary factor that determines the degree of residual stress in LED chips. In the laser lift-off process, changing laser energy density in an appropriate range has little influence on residual strain of LED chips, and the micro-cracks in GaN layer caused by LLO process will play a role in releasing the residual stress. The warpage of epitaxial sapphire substrate becomes large after boding with Si submount, the residual stress in GaN-based vertical LEDs is tensile stress and becomes larger with the soak temperature rising. When GaN epi wafer bonds with Al2O3 submount and CuW submount, the warpages becomes small and large respectively and the residual stress in chips is compressive stress. Because of the mismatch of coefficient of thermal expansion, the compressive stress in GaN-based LED chips increases for Al2O3 submount and drops for CuW submount with the soak temperature rising.

In this paper, the method of measuring AC magnetization characteristics of magnetic steel sheets with a single sheet tester (SST) is studied. With the help of a computer, the AC magnetization characteristics can be measured automatically under the condition of ensuring the waveform of flux density B to be sinusoidal.

A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed. The dual-core photonic crystal fiber (PCF) consists of two asymmetric cores. The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory. Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm, 261 μm and 271.44 μm for x-polarized mode and y-polarized mode, respectively. It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than −10 dB and a bandwidth of 180 nm.

A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation. The dispersion property and model birefringence are studied by employing the finite element method. The simulation result reveals the changing patten of dispersion parameter versus the geometry. The influence of the large frequency band of terahertz on birefringence is also discussed. The design of low loss, high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.

A real-coded genetic algorithm (GA) combined with a fully vectorial effective index method (FVEIM) is employed to design structures of photonic crystal fibers (PCFs) with user defined dispersion properties theoretically. The structures of PCFs whose solid cores are doped GeO2 with zero-dispersions at 0.7–3.9μm are optimized and the flat dispersion ranges through the R+L+C band and the negative dispersion is −1576.26 pskm−1nm−1 at 1.55 μm. Analyses show that the zero-dispersion wavelength (ZDW) could be one of many ZDWs for the same fiber structure; PCFs could alter the dispersion to be Battened through the R+L+C band with a single air-hole diameter; and negative dispersion requires high air filling rate at 1.55 μm. The method is proved to be elegant for solving this inverse problem.

A kind of midinfrared As2S3 chalcogenide glass photonic crystal fiber is proposed in this paper. The characteristics of this fiber are studied by multipole method, including high birefringence, chromatic dispersion, and high nonlinearity. Through numerical simulation, it is found that at midinfrared wavelength λ = 3.625 μm, the birefringence of this fiber reaches up to 0.098 and nonlinear parameters are 1.69 m-1 ·W-1 and 0.78 m-1 ·W-1 for x-polarized mode and y-polarized mode, respectively. In addition, the fiber keeps normal dispersion in a wavelength range from 3 to 7 μm . In conclusion, the band of transmitted wavelength extends into a midinfrared wavelength range of 3—10 μm, and high birefringence and high nonlinearity in this photonic crystal fiber are perfectly combined. The results are significant for the further development of new photonic devices.

A kind of chalcogenide glass midinfrared dual-core photonic crystal fiber has been proposed in this paper. The coupling characteristic of this fiber has been studied by multipole method using the basic theory of coupling. It is found that the birefringence of dual-core PCF with pitch 5.4 μm, air-hole radius 1.35 μm and air-filling fraction 0.5 is 0.551×10-2 at normalized frequency λ/Λ = 2.04 μm. At normalized frequency λ/Λ = 0.93 μm, coupling lengths are 145.32 μm and 154.68 μm for x-polarized mode and y-polarized mode, respectively. The band extended to midinfrared. This dual-core photonic crystal fiber with coupling length and high polarization is useful for manufacturing midinfrared band optical fiber coupler.