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Benefited from the fast switching speed, Gallium nitride (GaN) high electron mobility transistors (HEMTs) have been widely used in high switching frequency converters. However, due to the significant correlation between the turn-off time and operating conditions (more than 20 times difference of the turn-off time between the high load current and small load current for GaN HEMTs), using a fixed dead time will introduce extra dead-time losses in inverters where the output voltage and current are constantly varying. Therefore, this paper proposes a high-efficiency adaptive method to dynamically adjust the GaN-inverter dead-time with operating conditions. An improved transient model including the parasitic inductance and output voltage with bidirectional solution flow has been proposed for GaN HEMTs to increase the accuracy of dead-time adjustment. Based on this model, the dynamic dead-time adjustment can be realized without extra sensors for GaN-inverters. Using the dynamic dead-time adjustment, the experimental results show a peak efficiency of 98.25% in a 1200W inverter with triangular current mode modulation. Compared with using the fixed dead-time, the dynamic dead-time method can reduce the power loss by 26.7% under full load and 49.14% under light load.

Resonant gate driver (RGD) is a premium solution for driving power transistors in high-frequency and high-power-density applications, with the merits of much less power loss and more design freedoms in adjusting driving time. This article aims at providing a thorough review of RGDs and guidelines for constructing the most suitable RGDs under different design specifications. The classification of RGDs based on resonance characteristics is first proposed. It results in more straightforward, precise RGD categories without complex hierarchy, and cross coincidences. The dynamic energy distributions in the switching transients of each type of RGDs are deeply investigated, and energy utilization rates are concluded and compared. The key parameters affecting driving energy and driving time for each type of RGDs are further explored, as the resonant inductor, gate resistor, and initial inductor current. A top–down design approach is also summarized to guide the optimized RGD designs under different converter requirements.

A gallium nitride (GaN) boundary conduction mode (BCM) dual-boost ac–dc converter for low-voltage electromagnetic energy harvesting (EH) is presented in this article. The μ W-to-mW EH system is very susceptible to any tiny losses from power converters, interconnections, and system parasitic. To have better utilizations of harvested energy, an output power enhanced power conversion design is proposed. First, impedance matching is satisfied between electromagnetic generator and ac–dc converter to achieve maximum delivered power. The ac–dc converter is designed under BCM for constant input impedance. EH's winding inductance is employed as the boost inductor in the ac–dc converter. A codesign principle for converter on -time with electromagnetic generator's winding characteristics is revealed. Second, power transistors in EH low-voltage conversion are optimized to realize high efficiency. Power transistors’ low-voltage switching characteristics are significantly different from high-voltage situation with no or little miller plateau region. Low-voltage power transistors are compared from both device characteristics and calculated power loss to provide device selection guidance. A GaN-based dual-boost ac–dc converter under BCM operation with constant on -time controller is designed in this article to provide 3.3 V output for a 500-Ω load resistor. It achieves peak efficiency of 82.4% for open-loop operation at 0.6 V/100 Hz input and peak efficiency of 72.3% for close-loop operation at 0.75 V/100 Hz.

A novel “time-segmented” transient analysis approach is proposed in this article for resonant gate driver (RGD) with triaspect optimization. RGD is a more advanced solution in high-frequency and high-power-density applications than the conventional gate driver (CGD). RGD will achieve lower gate driver loss, faster driving speed, and better SiC switching characteristics. However, the majority of current works on RGD only focused on gate driver loss and ignored its effect on power transistors’ switching behavior. The characteristics of RGD are not well understood and modeled due to the ignorance of nonlinear components, such as power transistor’s nonlinear input capacitor and nonlinear resonant intervals, and driving resistances. All of those result in false estimation of switching time and energy, which will cause underdesign of gate driver power supply and overdesign of resonant inductor. To fully investigate the potential of RGD, a “time-segmented” analysis approach proposed in this article utilizes the second-order equivalent circuit with actual switching transients. Different equivalent input capacitors are adopted for each segment. The impacts of the resonant inductor and gate resistor are studied. An optimized resonant inductor design is summarized by considering the three aspects mentioned earlier. Based on these, a full-bridge series RGD is designed for SiC power transistors. Compared with CGD, RGD can realize a 25% reduction in power consumption and 75.5% faster driving time. The designed RGD also improves SiC’s di / dt and dv / dt up to 32%.

In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 aluminum alloy was performed via scanning electron microscope, electron backscatter diffraction, and transmission electron microscope technology. The nanomechanical behavior of FSW joint was systematically studied using nanoindentation technique. The relationship between microstructure and nanomechanical behavior was established and the nano-hardness and microhardness were analyzed. The results show that FSW led to grain refinement of aluminum alloy and continuous dynamic recrystallization and geometric dynamic recrystallization were the primary mechanisms of grain refinement. The precipitated phase dissolved and coarsened during FSW, which led to a decrease in the microhardness of the joint. The nano-hardness of each zone of the joint displayed indentation size effect. The creep behavior at room temperature conformed to the Voigt model, and dislocation glide was the primary creep mechanism. The stir zone (SZ) and thermo-mechanically affected zone (TMAZ) had high nano-hardness and elastic modulus, while TMAZ and heat-affected zone (HAZ) had high creep resistance at room temperature. The nanomechanical behavior was mainly affected by precipitation in the grain interior.

Friction stir lap welding (FSLW) was employed to weld dissimilar joints of zirconium and stainless steel for the first time. The microstructure, evolution mechanism of intermetallic compounds (IMCs) and mechanical properties of joint were investigated. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred in zirconium, while DDRX occurred in stainless steel during FSLW. The formation sequence of IMCs at the interface was FeZr3, FeZr2, Fe2Zr, and Fe23Zr6. The crack nucleated at the hook zone on the advancing side (HookAS), and IMCs in the Zr/SS mixed zone accelerated crack propagation. The fracture surface exhibited ductile-brittle mixed fracture characteristic.

Lack of directional bonding between two-dimensional crystals like graphene or monolayer transition metal dichalcogenides provides unusual freedom in the selection of components for vertical van der Waals heterostructures. However, even for identical layers, their stacking, in particular the relative angle between their crystallographic directions, modifies properties of the structure. We demonstrate that the interatomic coupling between two two-dimensional crystals can be determined from angle-resolved photoemission spectra of a trilayer structure with one aligned and one twisted interface. Each of the interfaces provides complementary information and together they enable self-consistent determination of the coupling. We parametrise interatomic coupling for carbon atoms by studying twisted trilayer graphene and show that the result can be applied to structures with different twists and number of layers. Our approach demonstrates how to extract fundamental information about interlayer coupling in a stack of two-dimensional crystals and can be applied to many other van der Waals interfaces., Here, the authors show that the interatomic coupling between two layers of a 2D crystal can be determined by studying the angle-resolved photoemission spectra of a trilayer structure with one aligned and one twisted interface, and obtain the inter-atomic coupling for carbon atoms in twisted trilayer graphene.

High-voltage (HV) generators with a wide load range are widely adopted for X-ray beam excitation and density adjustment. A SiC-based LCC HV inverter at high switching frequency will benefit fast transient because of the more efficient utilization of an X-ray beam and its smaller size. A precise prediction of SiC switching characteristics provides important prerequisites for efficiency, thermal and power density, and reliability co-optimized design. Understanding the SiC switching loss at different switching conditions will help the resonant network design to achieve required gain and efficiency over wide operation ranges. SiC switching characteristics are strongly dependent on its parasitic capacitors. A Miller capacitor, existing across the gate–source loop and the drain–source loop, presents strong nonlinear characteristics. This article proposes an accuracy-enhanced Miller capacitor-modeling approach. An internal cascaded configuration of a fixed capacitor and a voltage-dependent capacitor with segmentations based on different doping concentrations is employed. The maximum mismatch between the proposed approach and the datasheet’s $C$ – $V$ data is within 28%. Prediction accuracy improves two times compared with the device SPICE model. An enhanced double-pulse-test (DPT) circuit is used for comprehensive switching behavior verification. The proposed model has highest accuracy in switching loss prediction with up to $15\times $ less mismatch compared with the state of the arts. The hard turn-on and turn-off losses are 157.7 and $48.1~\mu \text{J}$ at 500 V/40 A. The ZVS turn on loss is $1.67~\mu \text{J}$ at 40 A. The soft turn-off loss is reduced to $4.43~\mu \text{J}$ with a 3.2-nF snubber capacitor. A SiC transistor with ZVS-ON and soft turn-off has the lowest overall switching loss of $6.1~\mu \text{J}$ . Such a switching condition corresponds to the region of a switching frequency higher than the resonant frequency in an LCC inverter. Therefore, both high efficiency and high power density will be achieved under this optimal region.

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) has the advantages of high switching speed and low ON-resistance, which make it widely used in high-frequency applications to realize high power density. Triangular current mode (TCM) modulation has been used in GaN-based converters to simultaneously achieve high power density and high efficiency through full-range zero voltage switching (ZVS). However, as switching frequency increases, the effect of dead time becomes more significant. Meanwhile, because of the junction capacitors of GaN HEMTs, the optimum dead time changes greatly with the turn-off current. Inappropriate dead time will induce extra loss that goes against the further improvement of power density. In order to minimize the dead-time loss in GaN HEMT-based TCM converter, this article proposes a strategy of adaptive dead-time control. An accurate turn-off transient model is proposed to calculate optimal dead time with consideration of the nonlinear capacitors. Based on this model, a loss model is established to evaluate the effect of dead time involving the short circuit in dead time. A new method of drive signal generation in TCM is proposed to increase the accuracy of dead-time control and reduce the current ripple. By reusing the detection signal in TCM, the adaptive dead-time control is realized without extra sensors. The proposed model is verified by a dual-pulse test, which shows the maximum error between the calculated and the experimental turn-off time is below 3 ns. The proposed adaptive dead-time control is implemented in a GaN HEMT-based boost converter. The experimental results show that the adaptive dead-time control can improve the efficiency over all operation conditions compared with using the fixed dead time, and the total loss is reduced by 26.7% at 800-W load and 70.8% at 50-W load.

Probiotics are expected to be an ideal alternative for antibiotics in the poultry industry. This study aimed to investigate the effect of Lactobacillus plantarum on growth traits, slaughter performance, serum markers and intestinal bacterial community of Daheng broilers. A total of 2400 healthy one-day-old Daheng broilers were randomly divided into 5 groups with 6 replicates per group and 40 individuals per replicate. Birds in control group were fed a basal diet, and others were fed basal diets supplemented with 105 , 106 , 107 and 108 CFU/kg Lactobacillus plantarum, respectively. It turned out that adding Lactobacillus plantarum to diet could significantly improve the serum immune performance of broilers (p 0.05), but had no significant effect on growth traits and slaughter performance. Moreover, Lactobacillus plantarum could improve the diversity of intestinal bacterial community, but with the increase of addition concentration, the diversity would gradually decrease. In conclusion, Lactobacillus plantarum can be used as feed additive in broiler production, but whether it is more effective than antibiotics needs further investigation.

In the middle or late stage of oilfield exploitation in China, the storage speed of oil well does not match pumping speed, resulting in pumping unit in the state of “non-full pumping” or “empty pumping”, which wastes lots of electricity. This paper used overdetermined equation and neural networks to predict liquid production after eliminating dimensional influence among oil well feature data with normalization method. Comparing the results with the regression equation, the effect of neural network is better than the other two methods in the case of large amounts of data. Even under the same training set, the results of the two neural networks are quite different. According to the prediction results of regular data, the effect of neural networks are significantly affected by the characteristics and quantity of the sample data. Therefore, appropriate prediction method in the prediction of liquid production can provide reference for oilfield management.

A new master-and-slave resonant tank switch approach is proposed to realize narrow switching frequency range and whole range zero voltage switching (ZVS) for series-parallel resonant converter (LCC) with wide operation range. A systematic switch strategy employing paralleled series capacitor (C s ) tanks is fully explored. A master resonant tank is firstly derived based on converter actual operation range. A series of slave resonant tanks are derived using geometric progressions, as 1/2i. The voltage gain is divided into different pieces and different resonant tanks are employed. The switching frequency range maintained similar for each segments. A 5kW SiC LCC converter is built to demonstrate the proposed concept. Three resonant tanks with C s of 5nF, 10nF and 20nF are adopted respectively. With single resonant tank of C s equaling to 20nF, switching frequency need to be adjusted from 280 kHz to 470 kHz for gain range from 0.3-1.05. With the proposed master-and-slave tank switch technique, switching range is shrink to the 390 kHz to 470 kHz for the same gain range by adopting two slave tanks. A 58% reduction of frequency range is achieved.

A potent cathode catalyst of octahedral cobalt oxide (Co3O4) was synthesized onto graphene (GR) nanosheets via a two-step preparation method. The precursor cobalt solution reacted with GR during the initial hydrolysis step to form intermediates. A subsequent hydrothermal reaction promoted Co3O4 crystallinity with a crystalline size of 73 nm, resulting in octahedral particles of 100&ndash, 300 nm in size. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analysis confirmed the successful formation of the Co3O4/GR composite. This catalyst composite was sprayed onto a carbon cloth to form a cathode for the hybrid electrolyte lithium-air battery (HELAB). This catalyst demonstrated improved oxygen reduction and oxygen evolution capabilities. The HELAB containing this catalyst showed a higher discharge voltage and stable charge voltage, resulting in a 34% reduction in overall over-potential compared to that without the Co3O4/GR composite. The use of saturated LiOH in 11.6 M LiCl aqueous electrolyte at the cathode further reduced the over-potential by 0.5 V. It is proposed that the suppressed dissociation of LiOH expedites the charging reaction from un-dissociated LiOH. This Co3O4/GR composite is a promising bi-functional catalyst, suitable as a cathode material for a HELAB operating in high relative humidity and highly alkaline environment.

Resonant gate drive (RGD) is the more efficient solution to drive SiC MOSFETs at high switching frequencies with effective gate driver energy saving. It adjusts driving characteristics from RC step response to RLC resonant response at the risk of reduced power transistors’ switching speed and increased switching loss. Resonant inductor becomes the most important component in RGD design and is mutually restraint for gate driver loss reduction and power transistor switching characteristics improvement. Current studies on RGD vaguely uses MOSFET input capacitor (Ciss) from datasheet or total gate charge (Qg) to analyze driver characteristics. The non-linear feature brought by MOSFET miller capacitor is completely ignored, which leads to un-optimized resonant inductor selection and poor understanding in RGD influence on MOSFET switching behaviors. To overcome these issues, a novel time segmented methodology is proposed to provide comprehensive analysis of RGD and understand its impacts on different aspects. The driving loss and SiC switching speed co-optimized series resonant gate driver is demonstrated with 25.5% saving on gate driver loss and 44.4% improvement in driving speed at 200 kHz switching frequency.

Pulse generator in an ultrasound system produces electrical pulsing signals to drive piezoelectric transducer, which causes mechanical vibration of the crystals and generates sound waves. Different from conventional imaging short pulses, high-power ultrasonic system for therapeutic applications requires MHz pulses bursts of up to tens of milliseconds. The capability of switching high voltage (±90 V) at multi-MHz, delivering effective power efficiently, is crucial for practical systems. The advantages of low device loss at high switching frequency, and high power density make gallium nitride (GaN) high electron mobility transistors better devices than traditional silicon (Si) MOSFETs in such system. The GaN-based high-frequency transformer push–pull inverter presented in this paper is capable to produce high energy pulsating output with burst pulse length up to 50 ms and bipolar pulse amplitude of 180 Vpp. The maximum pulse frequency can be up to 10 MHz. The peak output power is 90 W with power density of 50.85 W/in2. The peak power for all the 128 pulser channels reaches up to 11.5 KW with average power of 192 W. This is the highest output power for pulse drivers that have been reported. A novel power transistor based RF switch circuit is also proposed in this design as the interface between image signal, high power signal, and return signal.

A more accurate miller capacitor model is proposed in this paper to achieve precise SiC switching characteristic prediction for high frequency and high power density designs. The SPICE models of power transistors are either not provided or fail to represent parasitic capacitor accurately, which will lead to poor estimation of device switching loss. For SiC transistor used in this paper, LTSPICE simulation shows up to 53.7% mismatch in miller capacitor compared with measurement data provided in datasheet. Accurate switching loss prediction will help to use SiC more effectively and thermally optimized in high frequency, high power density systems. The physical mechanism of miller capacitor reflects an internal cascaded configuration of a fixed capacitor with a voltage depended capacitor. The voltage depended capacitance is further influenced by different doping concentrations in vertical power MOSFET and can be splitted into four stages. Based upon these, the Segmented-and-Cascaded miller capacitor approximation method is proposed. It shows descent agreement with datasheet C-V curve of less than 15% mismatch, which is three times less than SiC SPICE model. Experimental results using double pulse test circuit are provided to verify the proposed miller capacitor model. The maximum mismatches under hard switching at 500V are 9.5% for dv/dt and 8.4% for di/dt.

LCC high voltage generator is widely adopted for X-ray beam excitation and control. It has the requirement of wide load range, fast transients, high efficiency and reduced system size. Therefore, SiC based high voltage generator switching at 2X-3X of current frequency will be a better option. Accurate prediction of SiC switching characteristics as well as comprehensive switching behavior evaluation are important prerequisites for thermally optimized and efficient SiC system design. This paper proposed on a novel miller capacitor modeling approach: Segmented-and-Cascaded approach. The mismatch between modeled capacitor curve and measurements data from datasheet is within 15%, which is three times as less as the SPICE model. A comprehensive switching characterization is also revealed. The hard turn on loss is $157.7\boldsymbol{\mu} \mathbf{J}$ at 500V/40A and will be significantly reduced under ZVS-ON. The turn off energy loss under hard switching is $48.1\boldsymbol{\mu} \mathbf{J}$ at 500V/40A. It is reduced to $4.43\boldsymbol{\mu} \mathbf{J}$ with 3.2nF snubber capacitor at soft turn off. Good consistency is observed of predicted data vs. measurements with maximum deviation of 17.2%. SiC power transistor with ZVS turn on and soft turn off has the lowest switching loss of $9.12\boldsymbol{\mu} \mathbf{J}$ . Therefore, designing the LCC inverter at switching frequency higher than resonant frequency will achieve both high efficiency and high power density.

In this paper, investigation is made on the coupled variable-coefficient fourth-order nonlinear Schrodinger equations, which describe the simultaneous propagation of optical pulses in an inhomogeneous optical fiber. Via the generalized Darboux transformation, the first- and second-order rogue wave solutions are constructed. Based on such solutions, effects of the group velocity dispersion coefficient and the fourth-order dispersion coefficient on the rogue waves are graphically analyzed. The first-order rogue waves with the eye-shaped distribution, the interactions between the first-order rogue waves with solitons, and the second-order rogue waves with one highest peak and with the triangular structure are displayed. When the value of the group velocity dispersion coefficient or the fourth-order dispersion increases, range of the first-order rogue wave increases. Composite rogue waves are obtained, where the temporal separation between two adjacent rogue waves can be changed if we adjust the group velocity dispersion coefficient and fourth-order dispersion coefficient. Periodic rogue waves are presented. Periods of such rogue waves decrease with the periods of the group-velocity dispersion and fourth-order dispersion coefficient decreasing.

Under investigation in this paper is a discrete (2+1)-dimensional Ablowitz-Ladik equation, which is used to model the nonlinear waves in the nonlinear optics and Bose-Einstein condensation. Employing the Kadomtsev-Petviashvili hierarchy reduction, we obtain the rogue wave solutions in terms of the Gramian. We graphically study the first-, second- and third-order rogue waves with the influence of the focusing coefficient and coupling strength. When the value of the focusing coefficient increases, both the peak of the rogue wave and background decrease. When the value of the coupling strength increases, the rogue wave raises and decays in a shorter time. High-order rogue waves are exhibited as one single highest peak and some lower humps, and such lower humps are shown as the triangular and circular patterns.

In this paper, under investigation is a coupled variable-coefficient higher-order nonlinear Schrodinger system, which describes the simultaneous propagation of optical pulses in an inhomogeneous optical fiber. Based on the Lax pair and binary Darboux transformation, we present the nondegenerate N -dark-dark soliton solutions. With the graphical simulation, soliton propagation and interaction are discussed with the group velocity dispersion and fourth-order dispersion effects, which affect the velocity but have no effect on the amplitude. Linear, parabolic and periodic one dark-dark solitons are displayed. Interactions between the two solitons are presented as well, which are all elastic.

Nowadays, with respect to the nonlinear birefringent optical fibers, efforts have been put into investigating the coupled nonlinear Schrodinger (NLS) systems. In this paper, symbolic computation on...

(2+1)-dimensional non-linear optical waves through the coherently excited resonant medium doped with the erbium atoms can be described by a (2+1)-dimensional non-linear Schrodinger equation coupled with the self-induced transparency equations. For such a system, via the Hirota method and symbolic computation, linear forms, one-, two- and N-soliton solutions are obtained. Asymptotic analysis is conducted and suggests that the interaction between the two solitons is elastic. Bright solitons are obtained for the fields E and P, while the dark ones for the field N, with E as the electric field, P as the polarization in the resonant medium induced by the electric field, and N as the population inversion profile of the dopant atoms. Head-on interaction between the bidirectional two solitons and overtaking interaction between the unidirectional two solitons are seen. Influence of the averaged natural frequency ω on the solitons are studied: (1) ω can affect the velocities of all the solitons; (2) Amplitu...

The optical fiber communication system is one of the supporting systems of the modern internet age. In this paper, we study the three-component coupled Hirota equations, which govern the simultaneous propagation of three fields in the normal dispersion regime of an optical fiber. We derive a Lax pair and construct the corresponding Darboux transformation. Via the Darboux transformation, rogue wave solutions with the corresponding characteristic polynomial admiting a quadruple root and two/one double roots are obtained. Via such solutions, we depict the first-order vector rational rogue wave with the two components containing the four-petaled rogue wave, and the other component containing one eye-shaped rogue wave; increasing the value of the real parameter which denotes the integrable perturbation, we observe that the range of the first-order vector rational rogue wave along an axis increases; we display the first-order vector rational rogue waves with each component containing two/three merged and separated rogue waves. The second-order rogue waves are graphically displayed, with each component containing five, seven or nine rogue waves, which form the pentagon, triangle, clawlike, hexagon, arrow, line or trapezoid structures. The first- and second-order vector rational/semi-rational rogue waves are graphically exhibited. Two types of the vector semi-rational rogue waves are presented: the one with each component containing the rogue waves and line breathers, and the other with each component containing the rogue waves and Y-shaped breathers.

In this paper, we investigate the three coupled variable-coefficient nonlinear Schrodinger equations, which describe the amplification or attenuation of the picosecond pulse propagation in the inhomogeneous multicomponent optical fibre with different frequencies or polarisations. Based on the Darboux dressing transformation, semirational rogue wave solutions are derived. Semirational rogue waves, Peregrine combs and Peregrine walls are obtained and demonstrated. Splitting behaviour of the semirational Peregrine combs and attenuating phenomenon of the semirational Peregrine wall are exhibited. Effects of the group velocity dispersion, nonlinearity and fibre gain / loss are discussed according to the different fibres. We find that the maximum amplitude of the hump of the semirational rogue wave is less than nine times the background height due to the interaction between the soliton part and rogue wave part. Further, there is a bent in the soliton part of the semirational rogue.

This paper proposed a new hybrid converter with SiC power transistor for 400V-to-48V power conversion. The hybrid converter is based upon mixed and series concept from traditional forward and flyback topology, where the flyback output is inserted at the input side and in series with the primary winding. High DC conversion gain, full usage of the transformer energy, DCX operation and simple output regulation are the main merits of the proposed topology. The resonant network at the secondary stage brings zero current switching and therefore, high switching frequency can be adopted to obtain smaller passive devices. A compact three winding transformer with well-designed leakage inductance as resonant inductor is employed to further improve power density. A 400V-to-48V DC/DC converter with 10A output current is implemented to demonstrate the concept.

A new series hybrid DC-DC converter targeting for communication power supply with wide input range is designed in this paper implemented with Silicon Carbic (SiC) power transistor. The proposed hybrid converter is a combination of forward and flyback converter with full usage of transformer energy and optimized efficiency. Forward converter is the main energy delivery part and resonant network is utilized for full energy transferring and soft switching. Forward converter resets the magnetizing energy and delivers it to the output. The forward and flyback part are connected in such a novel way where flyback output is in series with the primary side. A highly compact architecture is realized with shared power switch and single core, multi-winding transformer. Due to its low gate charge and parasitic capacitance, SiC devices are premium power transistors for high frequency and high power applications. With a proper transformer design, an efficient series hybrid SiC converter is demonstrated for lOOV-to-400V input at 480W output power.

Traditional conductive/anti-static polymer fibers are easily invalid because the conductive networks formed by fillers such as carbon black, carbon nanotubes or titanium dioxides are easy to be destroyed during drawing process. In order to overcome the insurmountable weakness of current conductive/anti-static polymer fibers, a new type of conductive/anti-static fiber has been developed by using low melting point alloy (LMPA) as the conductive filler. The metal filament filled conductive/anti-static fibers perform much better than normal fibers because drawing could make their conductive networks denser instead of destroying them. Another notable finding of our research is that blending of nonconductive montmorillonite could improve the dispersity and stability of metal filaments, and further the conductivity of the polymer fibers. Based on this method, a composite polypropylene fiber with 2 vol% LMPA and 2 vol% carbon nanotubes is fabricated, of which the resistivity can be as low as 8.3×104 Ω m.

This study assembles lithium-air batteries with aqueous/aprotic hybrid electrolytes designed for ambient air-breathing in a high relative humidity environment. Cobalt oxide/graphene (Co3O4/GR) nanocomposites are synthesized for improved oxygen reduction and oxygen evolution reaction functionalities. The Co3O4/GR composites with Co3O4 loads of 33.7 wt%, 48.2 wt%, and 62.5 wt% are prepared using hydrothermal synthesis. The Co3O4/GR composites’ catalytic activities on oxygen reduction reaction and oxygen evolution reaction is shown to reduce the polarization of pristine carbon cloth electrode by 40% and serve as a good cathode catalyst. Lithium/air batteries are assembled with a lithium metal/organic electrolyte/ceramic lithium-ion conductive membrane/aqueous electrolyte/air cathode configuration. These batteries with the developed catalysts demonstrate good long-term stability over 120 h when fed with high (70–100%) relative humidity ambient air. More importantly, the results indicate the Co3O4/GR composite in 48.2:51.8 (w/w) is the optimal load for the hybrid electrolyte lithium-air battery due to its balanced amount of catalytic Co3O4 and charge-transfer mediated graphene, and good dispersibility of the nanocatalyst on the planar graphene surface.

Effect of the rotation rate on the low-cycle fatigue (LCF) of friction-stir welding joint of AZ31 magnesium (Mg) alloys was studied. The rotation rate had a significant impact on the grain size but only slightly affected the texture in the nugget zone (NZ) and thermo-mechanically affected zone (TMAZ). Grain coarsening and texture softening resulted in the fracture at the boundary between the NZ and TMAZ at the advancing side. Decreasing rotation rate enhanced the fatigue life. The LCF behavior was well expressed by the Coffin-Manson and Basquin relations. The basal slip was the main deformation mechanism associated with coordinated twinning.

Optical-fiber communication is an indispensable part of the modern communication. In this letter, we study a higher-order coupled nonlinear Schrodinger system, which describes the simultaneous propagation of two electric fields in an optical fiber. We construct the N th-order dark–bright semi-rational soliton solutions for the mixed interactions, and the N th-order breather solutions for the focusing interactions, where N is a positive integer. For the mixed interactions, we show the first- and second-order dark–bright semi-rational solitons. For the focusing interactions, we present the first- and second-order Y-shaped breathers, and the line-shaped breather with one component possessing an anti-eye-shaped breather and the other component containing an eye-shaped breather, as well as the second-order breather with each component consisting of two curved breathers.

Optical fiber communication is widely applied in the information transmission and capacity handling of information. In this paper, coupled fourth-order nonlinear Schrodinger system, which describes the propagation of ultrashort optical pulses in a birefringent optical fiber, is studied. The Nth-order Darboux transformation and corresponding vector breather solutions are constructed, where N is a positive integer. Based on such solutions, we graphically show four different types of breathers: (1) the one with the one component containing the anti-eye-shaped breather and the other component containing the eye-shaped breather; (2) the one with each component containing the four-petaled breather; (3) the one with each component containing the eye-shaped breather; (4) the one with each component containing the Y-shaped breather. Moreover, we find that the range of the breather along the time axis decreases, and the angle between the breather and the time axis increases as the value of |γ| decreases, where γ represents the strength of higher-order linear and nonlinear effects.

For deep imaging depth and least invasiveness, people commonly use 1100-1300 nm femtosecond laser sources to perform label-free in vivo microscopy. The modalities include reflectance confocal, two & three photon fluorescence, and second & third harmonic generation microscopy. However, most of the laser sources are typically based on bulky oscillators, which are sensitive to environment conditions and less stable for routine clinical use. In contrast, fiber-based lasers have simpler cavity design and potentially compact size for movable use. In this presentation, we demonstrate a fiber-based 1150 nm femtosecond laser source, with 6.5 nJ pulse energy, 86 fs pulse-width, and 11.25 MHz pulse repetition rate. It was achieved by a Bismuth Borate (BIBO) or Magnesium-doped periodically poled Lithium Niobate (MgO:PPLN) mediated frequency doubling of the 2300 nm solitons, generated from an excitation of 1550 nm Er:fiber femtosecond laser pulses on a large mode area photonic crystal fiber. Combined with a laser scanned microscope and a home-build data acquisition card, we achieve a pulse-per-pixel harmonic generation microscopy in vivo at a 30 Hz frame rate. In the future, this solution is potential to be used for label-free clinical virtual optical biopsy.

Ambient contrast ratio (A-CR) is a critically important characteristic for mobile displays. For transmissive and emissive displays (such as liquid crystal display, light-emitting diode, and organic light-emitting diode), A-CR decreases dramatically as the ambient light increases, which degrades the image quality, especially for outdoor applications. Moth-eye-like structure greatly reduces the surface reflection and improves A-CR. For a touch panel display, the surface should be robust enough to resist possible mechanical scratches and to self-clean possible contaminations from fingerprints and dusts. In this paper, we demonstrate the moth-eye-like structure fabricated on a hard-coating layer with additional surface treatment for self-cleaning property upon the flexible film. By laminating the film unto a display device, the luminous reflectance is reduced to ~0.23%, which improves the A-CR by ~4X under the sun. Note that although the surface reflection is reduced, the haze remains negligible, implying that the image quality is not blurred. The nanostructure was fabricated on the hard-coating layer which is typically used as the protective film of the mobile display and hence it is anti-scratched. Typically, nanostructure exhibits hydrophobic and olephobic properties. With suitable surface treatment by amphiphilic molecules, such characteristics are further improved with excellent self-cleaning properties. Besides, our nanostructured hard-coating film can be fabricated on different flexible films, such as TAC and PET, which means this broadband antireflection film can be used for flexible displays.

Conventional silicon-metal schottky barrier diodes, known for zero reverse recovery and ultra-low forward voltage, have intrinsic limitations of low reverse voltage rating and high leakage current. Majority of Si schottky diodes are well below 200V. High voltage schottky diodes are implemented with SiC at limited voltage ratings above 600V. SiC schottky diodes have comparative high forward voltage with high voltage Si P-N diodes. Although fast recovery PIN diodes are developed, they still tend to suffer high reverse recovery loss at high voltages. Both high voltage SiC schottky and Si fast recovery diodes are also quite expensive. A novel technology to enhance voltage rating and performance for diode module is proposed in this paper as a cost-effective solution to achieve schottky characteristics at 200V and above. A cascode configuration formed by schottky diode and self-driven MOSFET is developed. This configuration is capable to achieve extended reverse voltage and much lower forward voltage at fast/zero reverse recovery compared with HV Si or SiC diodes.

A novel single switch, hybrid DC-DC converter is proposed in this paper, where an unregulated resonant forward converter is cascoded with a PWM regulated flyback converter. The converter output is formed by resonant forward circuit utilizing transformer leakage inductance and a resonant capacitor. It transfers the energy fully to the output and is only dependent with transformer turns ratio. Zero current turn off is realized at secondary forward diode without reverse recovery loss. Both forward part and flyback part share the same primary transformer winding. The output of the flyback part, instead of delivering magnetizing flux energy to the load directly, is moved to the primary side and connected in series with input source. With fixed transformer turns ratio, a PWM regulated flyback part is employed to regulate the output voltage. The proposed topology maximizes the capability of energy delivering and is able to ensure both high efficiency and simple control methodology with a wide operating range and high output current. To verify the concept, a high frequency 400V to 20V/65W DC-DC converter for adapter power supply at 200 KHz switching frequency is designed and tested with the proposed architecture.

Investigated in this paper is the modified Hirota equation with variable coefficients, which can describe the amplification or absorption of pulses propagating in an inhomogeneous optical fiber. We construct a couple of the Darboux transformations, and obtain the one-soliton, two-soliton, breather and rogue-wave solutions. Effects of the group velocity dispersion, third-order dispersion, nonlinear focus length and velocity of propagation are graphically analyzed. Bell-, parabolic-, cubic- and periodic-type solitons are obtained. Bound state and head-on interactions for the two solitons are presented, with those interactions shown to be elastic. We can see two types of the breathers there, including the Akhmediev breathers and Kuznetsov–Ma solitons, and the rogue-wave pair consisting of two rogue waves is obtained.

A novel method for producing optical burst pulses is demonstrated. Optical pulses having a several tens of picosecond duration, and a 100-200-ps period are generated from a gain-switched laser-diode under CW laser light injection.

Gallium Nitride has shown its potential over traditional Silicon devices with low switching and conduction losses. However, fast switching transition poses great challenges in dynamic device characterization due to sensitivity to parasitics and high requirement in testing equipment. An accurate switching behavior characterization method is proposed in this paper with loop inductance minimization and flat current shunt resistors. Switching losses for GaN transistor under three different current freewheeling patterns are explored and compared: through upper diode, through upper GaN transistor synchronous operation and through upper GaN reverse conduction, which include all the possible operation conditions in practical industry applications. The overall inductance in main power loop is well designed as low as 1.52nH. It is the first cleanest and most accurate GaN switching waveform ever reported. It is also the first time that GaN switching behavior with current reverse conduction through channel is investigated. The fastest switching speeds are dv/dt on = 9.1V/ns, dv/dt off = 8.6V/ns, and di/dt on =7.0A/ns, di/dt off = 5V/ns. The measured turn-on energy loss is 1.4μJ at 30V, 20A and 1.59μJ at 30V, 30A respectively.

Studied in this paper is a ( $$3\,+ 1$$ )-dimensional nonlinear Schrodinger equation with the group velocity dispersion, fiber gain-or-loss and nonlinearity coefficient functions, which describes the evolution of a slowly varying wave packet envelope in the inhomogeneous optical fiber. With the Hirota method and symbolic computation, the bilinear form and dark multi-soliton solutions under certain variable-coefficient constraint are derived. Interactions between the different-type dark two solitons have been asymptotically analyzed and presented. Both velocities and amplitudes of the two linear-type dark solitons do not change before and after the interaction. The two parabolic-type dark solitons propagating with the opposite directions both change their directions after the interaction. Interaction between the two periodic-type dark solitons is also presented. Interactions between the linear-, parabolic- and periodic-type dark two solitons are elastic.

Ceramic Yb:LuAG gain medium were fabricated and lased in the thin disk architecture. An output power of 1.91 kW was achieved with an optical-to-optical efficiency of 72.2% using a smaller disk while a larger disk achieved an output power of 6.66 kW with an optical-to-optical efficiency of 62.7%.

Under investigation in this paper is the Sasa-Satsuma equation, which describes the propagation of ultrashort pulses in a monomode fiber with the third-order dispersion, self-steepening, and stimulated Raman scattering effects. Based on the known bilinear forms, through the modified expanded formulas and symbolic computation, we construct the bright two-soliton solutions. Through classifying the interactions under different parameter conditions, we reveal six cases of interactions between the two solitons via an asymptotic analysis. With the help of the analytic and graphic analysis, we find that such interactions are different from those of the nonlinear Schr\"odinger equation and Hirota equation. When those solitons interact with each other, the singular-I soliton is shape-preserving, while the singular-II and nonsingular solitons may be shape preserving or shape changing. Such elastic and inelastic interaction phenomena in a scalar equation might enrich the knowledge of soliton behavior, which could be expected to be experimentally observed.

A gradient Li 2 O–MgO–Al 2 O 3 –SiO 2 (LMAS) glass ceramics interlayer was designed and prepared by vacuum hot-pressing to join SiC coated carbon/carbon (C/C) composites and Li 2 O–Al 2 O 3 –SiO 2 (LAS) glass ceramics. The SiC transition layer could effectively infiltrate into the C/C substrates and firmly adhere to the LMAS interlayer. Both the Mg content and microhardness decreased gradually from the SiC side to the LAS glass ceramics side in the gradient LMAS interlayer. The thermal expansion coefficient (CTE) of LMAS glass ceramics increased with the increase of Mg content. The obtained shear strength of the welded sample with a gradient interlayer design was about 30.7% higher than that of the sample without the gradient design. The gradient LMAS interlayer could effectively improve the distribution of process-induced thermal stress in the joint, relieve the mismatch of CTE between SiC transition layer and LAS glass ceramics and increase the bonding strength of the joint.

Nowadays, as the development of economy and technology, more and more electric devices need a DC voltage power source to supply a constant current. The Magnetic controllable transformer is also use a DC control module to provide a stable and reliable DC current. By a TMS320F2812 DSP chip as controller, this paper presents a design of DC constant current power supply based on the BUCK topology. A power prototype was set up in the laboratory, test results proved that the design is well applied to a magnetic controllable transformer.

We describe a novel optical pulse source that can generate yellow-orange optical pulses based on the synchronization of two gain-switched laser diodes under continuous-wave laser light injection. Sum frequency generation of amplified 1309 nm and 1064 nm optical pulses produced 587 nm pulses with 1 ns duration and 2 nJ pulse energy at a repetition rate of 5 MHz. The presented optical pulse source can also produce bursts of picosecond optical pulses inside nanosecond pulse envelopes. These optical pulses are applicable to stimulated emission depletion microscopy for super-resolution imaging of biomedical specimens with green- or yellow- fluorescent proteins labels.

In this paper, we study a Kundu–Eckhaus equation with variable coefficients, which describes the ultra-short optical pulses in an inhomogeneous optical fiber. We construct the Lax pair under certain variable-coefficient constraints. With the gauge transformation, one/N-fold binary Darboux transformations and limit forms of the one-fold binary Darboux transformation are obtained. Based on such transformations, one/N-dark (N = 2,3, [Formula: see text]) soliton solutions under those constraints are derived. Linear, periodic and parabolic dark solitons are presented, and numerical simulations are used to investigate the influence of the group velocity dispersion on the structures of the one-dark solitons. Based on the two-dark soliton solutions under certain variable-coefficient constraints, we also discuss the influence of the group velocity dispersion on the structures of the two-dark solitons. Head-on and overtaking collisions between the two linear, parabolic and cubic-type dark solitons are presented.

In this paper, we propose a regulated pulse current laser driver with the frequency double approach to synthesize green laser. Experiment results show that green laser synthesis conducted with the regulated pulse current driving (RPCD) technique has an electrical to optical conversion efficiency improvement of up to 78%, as compared to the DC driving technique with mean driving current of 250 mA at room temperature. This driver was fabricated with a 0.5 μm CMOS process and has a modulation frequency range of 300 kHz-700 kHz, a wide range of peak pulse current between 120 mA-900 mA with the average current range between 0 mA-280 mA. This paper not only demonstrated the synthesize procedure of green laser but also proposed driver with the RPCD technique enhances the electrical to optical conversion efficiency of green laser and its implementation in integrated circuit, making it a good match with green laser microchip to create a low cost, compact-sized device ideal for mobile projector applications.

Carbon/carbon (C/C) composites were joined to lithium aluminum silicate (LAS) glass-ceramic using a joining layer consisting of a SiC transition layer and a multilayer of magnesium aluminum silicate (MAS) and LAS glass-ceramic by a two-step technique of pack cementation and hot-pressing sintering. The microstructures of the as-prepared joint were characterized by scanning electron microscopy and energy dispersive spectrometry. The design of the multilayer structure could provide more possibilities for crack propagation to release the stress in the joint. Results of the thermal shock test showed that the average shear strength of the joined samples increased from 17.9 MPa to 32.6 MPa after 50 thermal cycles between 800 °C and room temperature, which was primarily attributed to the toughening effects of microcracks. However, after 30 thermal cycles between 1000 °C and room temperature, the average shear strength of the joined samples dropped to 14.2 MPa since the crack size was beyond the tolerance of the joint.