Yb3+-doped large-mode-area photonic crystal fiber laser with 210 W continuous-wave output power

An Yb^3＋-doped double-clad large-mode-area photonic crystal fiber （LMA PCF） laser with up to 210 W of continuous-wave output power centered at 1.05 lira is demonstrated. The length of the fiber used is 2 m and the produced laser power per meter can attain 105 W. The PCF is pumped by two diode lasers with central wavelength of 976 nm. The slope efficiency is 76%, and the beam quality factor M^2 at x and y axes are measured to be 1.06 and 1.08, respectively. No thermo-optical problems and other roll-over even are observed at the highest output power.     

High pulse energy femtosecond large-mode-area photonic crystal fiber laser

A high pulse energy femtosecond fiber laser based on a large-mode-area photonic crystal fiber is demonstrated. A segment of Yb-doped single-polarization large-mode-area photonic crystal fiber with extremely low nonlinearity is explored as gain media of this fiber laser, resulting in intrinsically envi- ronmentally stability. The fiber laser is based on a linear cavity with dispersion compensation free con- figuration, and the stable mode-locking is obtained by a semiconductor saturable absorber mirror （SESAM）. The fiber laser directly generates 2.5 W of average power at a repetition rate of 51.4 MHz, corresponding to a single pulse energy of 50 nJ. The output pulse duration is 4.2 ps, which is dechirped to 410 fs after extracavity dispersion compensation. The nonlinear absorption of SESAM determines the pulse shaping at low output power, while the mode-locking mechanism is under the balance between spectrum broadening from self-phase-modulation and gain filtering at the high output power.     

Emission characteristics of surface second-order metal grating distributed feedback semiconductor lasers

To obtain high-power semiconductor lasers with stable operation in a single longitudinal mode and improve the characteristics of the output beam,an end-emitting surface second-order metal grating distributed feedback(DFB) laser emitting at around 940 nm is fabricated.The characteristics of the uncoated devices with and without gratings are tested under room temperature continuous-wave conditions without any temperature-control device and compared.The devices with gratings achieve high powers of up to 385 mW/facet and a small lateral far-field angle of 2.7° at 1.5 A,have only 4.13 nm/A wavelength-shift,and 0.09 nm spectral linewidth at 600 mA,and operate in a stable longitudinal mode.Devices without gratings operate in multimode,with a larger lateral far-field angle(7.3°) and spectral linewidth(1.3 nm),although with higher output powers.Because of the integration of second-order metal gratings and their very high coupling capability,the output beam quality is improved greatly,the lasing wavelength is stable and varies slowly with changes in injection current,while the spectrum is narrowed dramatically,and the far-field angles are greatly reduced.This opens the way for the realization of watt-scale power broad-stripe(>100 μm) surface second-order metal grating end and surface-emitting DFB lasers and arrays with single frequency,single mode operation and high output beam quality.     

A facile and green preparation of durian shell-derived carbon electrodes for electrochemical double-layer capacitors

A facile and green preparation of high surface area activated carbons with mixed microporosity and mesoporosity from durian shell waste is reported in this work. The pore structure and surface chemistry of the parent carbon were modified by the combination of ultrasonication and microwave irradiation techniques. The effects of temperature and time in the ultrasonication treatment and power output and time in the microwave irradiation were studied. The electrochemical performance of carbon electrodes for supercapacitors was tested by cyclic voltammeter (CV) and galvanostatic charge–discharge. The results show that the capacitive energy storage of electrodes is critically dependent on the microporosity and surface chemistry of activated carbons. The highest electrode capacitance in this work was 103.6 F/g that prepared from activated carbon modified at an ultrasonication temperature of 323.15 K for 10 min and microwave power output of 900 W for 10 min.     

Fabrication and performance evaluation of the thermoelectric generation and performance measuring system

A novel thennoelectric generating and performance measuring system （TGPMS） was designed and fabricated. TGPMS can not only achieve the function of thennoelectric generation, but also measure the thennoelectric performance parameters of the bismuth-telluride-based thennoelectric device accurately. These thennoelectric performance parameters mainly include the dependence of the Seebeck coefficient of the thennoelectric device on the device＇s temperature in the low temperature range （about 40 ~ 190~C ）, and the dependence of the power output and thermoelectric conversion efficiency on the temperature dif- ference or output load. With the optimum load, the optimal value of the power output is 3.39W when the temperature difference reaches 231.2~C, and the optimal value of the conversion efficiency is 3.22% when the temperature difference reaches 208.9~C. TGPMS provides an experimental foundation for the application of the thennoelectric generators in the space field.     

A comparative study on thermo-economic performance between subcritical and transcritical Organic Rankine Cycles under different heat source temperatures

In this paper, the net power output, exergy efficiency and levelized energy cost of system were selected as performance indicators for assessing Organic Rankine Cycle （ORC）. Firstly, the turbine inlet temperature and pressure meeting the requirement of pinch point temperature difference of evaporator in transcritical ORC （trans-ORC） were determined based on performance opti- mization. Subsequently, the thermo-economic performance of a subcritical ORC （sub-ORC） using R601 as working fluid and a trans-ORC using R134a as working fluid were compared under different heat source temperatures and a fixed outlet temperature of flue gas. Results show that for trans-ORC, when the pinch point temperature difference of evaporator lies between the inlet and outlet of evaporator, a lower inlet pressure of turbine is favorable; when the pinch point temperature difference of evaporator is located at the outlet of evaporator, there exists an optimal inlet pressure of turbine. Either for sub-ORC or trans-ORC, the net power output increases and levelized energy cost decreases with the increase in heat source temperature. For sub-ORC, exergy efficiency of system increases monotonously with heat source temperature, while for trans-ORC, exergy efficiency of system grows up firstly and then reduces （or keeps constant） with the increasing of heat source tem- perature. Moreover, for net power output and exergy efficiency of system, there exist a range of heat source temperatures making trans-ORC better than sub-ORC, and the heat source temperature region extends with the increase in pinch point temperature difference of evapo- rator. For levelized energy cost of system, the sub-ORC is always superior to trans-ORC.     

Reactive ion etching of poly(vinylidene fluoride-trifluoroethylene) copolymer for flexible piezoelectric devices

A microfabrication process for poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)) based flexible piezoelectric devices is proposed using heat controlled spin coating and reactive ion etching(RIE) techniques.Dry etching of P(VDF-TrFE) in CF 4 +O2 plasma is found to be more effective than that using SF 6 +O2 or Ar+O2 feed gas with the same radiofrequency power and pressure conditions.A maximum etching rate of 400 nm/min is obtained using the CF 4 +O2 plasma with an oxygen concentration of 60% at an antenna power of 200 W and a platen power of 20 W.The oxygen atoms and fluorine atoms are found to be responsible for the chemical etching process.Microstructuring of P(VDF-TrFE) with a feature size of 10 m is achieved and the patterned films show a high remanent polarization of 63.6mC/m 2.     

Photocatalytic property of TiO2 sensitized by different crystal phase CdS

TiO2 samples sensitized by different crystal phase CdS(CT) are synthesized by hydrothermal process at different reaction temperature. The samples are characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), and UV-Vis diffuse reflectance(UV-Vis). The XRD result reveals that the crystal phase of CdS is transformed from cubic phase to hexagonal phase with the increase of hydrothermal reaction temperature(120-160 ℃). The absorption edge of CT is extended from 498 nm to 546 nm. The photocatalytic degradation of rhodamin B(RhB) in aqueous solution is used to evaluate the photocatalytic activity of CT. With the increase of the preparation temperature, the photocatalytic activity of CT becomes stronger. The degradation rate of RhB by CdS/TiO2 at 160 ℃(CT-160 ℃)reaches 78%.     

Sub-10 fs laser pulses with repetition rate of 1.1 GHz by a Ti: sapphire oscillator

We demonstrate a compact Ti： sapphire oscillator with ring cavity configuration. By optimizing the intra-cavity dispersion with chirped mirrors, pulses with repetition rate of 1.1 GHz are coupled out by the uncoated wedges in the cavity. Under 7W CW pump laser centered at 532 nm, the average power of the output pulses is about 30 mW, the duration is less than lOfs and the spectrum spans from 670 nm to 920 nm.     

75 mW robust single frequency Yb-doped DFB fiber Bragg grating laser

Incorporating the shielded method and post-processing method, a 75 mW single frequency Yb-doped DFB fiber laser was obtained with a 250 mW laser diode pump source at 978 nm. The threshold of the laser is 2 mW. The laser is single-polarization operation and the output power fluctuation is less than 0.2 mW in one hour when the pump power is 250 mW.     

Y-shaped beam splitter by graded structure design in a photonic crystal

We propose a method to bend a self-collimated beam in a photonic crystal. The beam bending relies on the gradual variation of the constitutive parameters of the photonic crystal. A new Y-shaped beam splitter is designed with a composite structure constructed using two graded photonic crystals. We demonstrate that the incident beam is divided into two output beams by the designed splitter. The power ratio of the two beams can be adjusted easily by changing the location of the input beam.     

Hamilton-Jacobi-Bellman equations and dynamic programming for power-optimization of a multistage heat engine system with generalized convective heat transfer law

A multistage endoreversible Carnot heat engine system operating between a finite thermal capacity high-temperature fluid reservoir and an infinite thermal capacity low-temperature environment with generalized convective heat transfer law [q∝(ΔT) m ] is investigated in this paper.Optimal control theory is applied to derive the continuous Hamilton-Jacobi-Bellman (HJB) equations,which determine the optimal fluid temperature configurations for maximum power output under the conditions of fixed initial time and fixed initial temperature of the driving fluid.Based on the universal optimization results,the analytical solution for the Newtonian heat transfer law (m=1) is also obtained.Since there are no analytical solutions for the other heat transfer laws (m≠1),the continuous HJB equations are discretized and dynamic programming algorithm is performed to obtain the complete numerical solutions of the optimization problem.The relationships among the maximum power output of the system,the process period and the fluid temperature are discussed in detail.The results obtained provide some theoretical guidelines for the optimal design and operation of practical energy conversion systems.     

Preparation of High Shrinkage Polypropylene

The common PP chips have been used to prepare high shrinkage PP fibers with shrinkage in boiling water higher than 50%. Meanwhile, the process conditions on fiber structure and properties have been discussed in detail. With the increase of drawing temperature, the shrinkage in boiling water of the fiber increases at first, and then decreases in the temperature range from 70℃to lOO℃. The better drawing temperature is from 75℃ to 85℃ according to the melt index of the PP material. The shrinkage in boiling water of PP fiber increases with the increase of pump delivery. The orientation factor and crystallinity increase with the increase of drawing temperature. With an increase in drawing temperature, unit-cell numbers and monomer unit numbers in every crystal nucleus tend to increase, but unit volume crystal nucleus tend to reduce.     

A novel portable transmitter with 8dBm output power for wireless communication equipments

In this paper,a portable 2.42 GHz transmitter for wireless communication systems,with 8dBm output power and small size is proposed.Several novel features exist in this transmitter.First,power consumption and output are balanced by introducing a differential oscillator with input signal controlled biasing,which acts as both a carrier generator and an OOK modulator.Then,power consumption of the transmitter is reduced by the OOK modulated signal via switching the oscillator and the power amplifier at the same time.Furthermore,the area size is also reduced by a class-AB power amplifier,which uses the PCB antenna as the resonance inductance.With these features,the total chip area is reduced to 670μm×740μm(In a 0.18μm CMOS process).     

Platinium Nanoparticles Deposited on Oxygen-Containing Functional Groups at Carbon Vulcane XC-72 as a Cathode Catalyst for Direct Methanol Fuel Cell

1 Results Surface oxidized carbon vulcane XC-72 as catalyst support, prepared by chemically anchoring Pt onto the surface modified carbon vulcane XC-72. The nanoparticles of Pt are synthesized by reduction of H2PtCl6 with sodium borohydride in a 5.5 buffer solution of sodium citrate, the complexation of citrate with metal ions is beneficial to the formation of nanoparticles. For comparison, an electrode is prepared by E-Tek Pt/C 20 Wt% with a typical Pt loading of 50 μg·cm-2, that shows higher specific surface area of Pt than an E-TEK electrode with Pt loading of 50 μg·cm-2. TEM images show that the Pt particle size is in the range of 1-2.5 nm with a peak at 1.8 nm. The electro-oxidation of liquid methanol of this catalyst as a thin layer on glassy carbon electrode is investigated at room temperature by cyclic voltammetry. The results show that surface oxidized carbon vulcane support allows to obtain higher power density (four time higher) in comparision to carbon vulcane XC-72 based electrode.     

Hot deformation map and its application of GH4706 alloy

The hot deformation behaviors of GH4706 alloy were investigated using compression tests in a deformation temperature range from 900℃ to 1200℃ with a strain rate range of 0.001–1 s?1. Hot processing maps were developed on the basis of the dynamic material model and compression data. A three-dimensional distribution of power dissipation parameter (η) with strain rate and temperature reveals that η decreases in sensitivity with an increase in strain rate and a decrease in temperature. Microstructure studies show that the grain size of GH4706 alloy increases when η is larger than 0.32, and the microstructure exhibits local deformation when η is smaller than 0.23. The hot processing map at the strain of 0.7 exposes a domain peak at η=0.32 for the temperature between 940℃ and 970℃ with the strain rate from 0.015 s?1 to 0.003 s?1, and these are the optimum parameters for hot working.     

Performance of High-Speed Grease Lubricated Hybrid Ceramic Ball Bearing

To simplify the lubricating system for high-speed bearings and improve its reliability, grease lubricated high-speed hybrid ceramic bearings were theoretically and experimentally researched. Bearings with an outer race of 62 mm and eleven 9.525-mm balls were investigated. Traction coefficient and flash temperature between the bearing races and the balls were calculated and the results show that the traction coefficient of Si3N4 hybrid ceramic bearings is 74% that of the steel AISI 440B ones at 30000r/min and 1750N, and the flash temperature of the hybrid bearings is 49% that of steel ones. Simulating the highspeed bearing rotational conditions, the grease lubricated hybrid ceramic ball bearings were tested and the results show that the power consumption of hybrid ceramic bearing lubricated by grease D at 24000r/min and axial load 1750N is 80% that of steel ones.     

A Steady-State Errors Correction Method for Eliminating Measurement Errors

This paper proposes a steady-state errors correction （SSEC） method for eliminating measurement errors.This method is based on the detections of error signal E（s） and output C（s） which generate an expected output R （s）.In comparison with the conventional solutions which are based on detecting the expected output R （s） and output C （s） to obtain error signal E （s）,the measurement errors are eliminated even the error might be at a significant level.Moreover,it is possible that the individual debugging by regulating the coefficient K for every member of the multiple objectives achieves the optimization of the open loop gain.Therefore,this simple method can be applied to the weak coupling and multiple objectives system,which is usually controlled by complex controller.The principle of eliminating measurement errors is derived analytically,and the advantages comparing with the conventional solutions are depicted.Based on the SSEC method analysis,an application of this method for an active power filter （APF） is investigated and the effectiveness and viability of the scheme are demonstrated through the simulation and experimental verifications.     

A composite thermal insulator based on xonotlite and perlite

A low cost thermal insulating material can be produced by compounding an active xonotlite slurry, fired-perlite, HOMO PAN fibers and glass fibers. The maximum service temperature of the product is 800℃; linear shrinkage after 800℃×16 h firing is 0.9%; the cold crushing strength is 1.56 MPa; the flexural strength at ambient temperature is 0.81 MPa; the thermal conductivity at ambient temperature (25℃) is 0.056 and 0.128 W/(m·K) at 800℃. The production cost of such a composite is only 1/3 of that of the normal xonotlite thermal insulators. It can substitute the normal xonotlite thermal insulators on most occasions with a similar cost to that of normal perlite products.     

Strain rate sensitivity of tensile properties in high Nb containing TiAl alloys

The effect of strain rate on the yield strength of high Nb containing TiAl alloy was studied. The results show that the strain rate sensitivity varies with the test temperature, and the yield strength is not sensitive to the strain rate at room temperature but significantly sensitive to the strain rate at high temperature. An increase of the strain rate or a decrease of the temperature results in an obvious change of fracture mode. It is found that the strain rate sensitivity of this alloy varying with temperature is due to the dislocation climb generated at high temperature.