一种超宽带光电混合结构A/D转换器

现代宽带数字接收机对高性能模数转换器(ADC)的需求逐渐增大,而电子学ADC因载流子迁移速率限制无法实现超宽带直接数字采样。基于光子技术超宽带、超高速的特性,文章提出了一种光电混合结构的ADC技术。通过采用基于超短光脉冲的光学采样代替基于电子学半导体技术的采样/保持(S/H)电路来大幅提高采样带宽。采用时分复用及多通道电学ADC量化技术实现信号数字编码。最后通过数字域均衡与线性化处理提高系统性能,实现了对频率大于24 GHz的微波信号的直接采样,采样信噪比大于40 dB,为超宽带微波信号高精度直接数字化提供了有效途径。

Corrosion behavior of T2 copper in 3.5% sodium chloride solution treated by rotating electromagnetic field

Copper is susceptible to producing corrosion problems in corrosive environments, which leads to serious safety problems. Thus, investigating the corrosion behavior of copper is of great significance. The effects of rotating electromagnetic field on corrosion behavior of T2 copper in 3.5% sodium chloride solution with electrochemical measurements were investigated. The results showed that rotating electromagnetic field changed properties of 3.5% sodium chloride solution by increasing the values of temperature and pH and decreasing the values of conductivity and dissolved oxygen. The rotating electromagnetic field improved the corrosion resistance of T2 copper. The corrosion products of T2 copper in treated 3.5% sodium chloride solution were composed of Cu20 and CuCl. The low corrosion rate of T2 copper was resulted from the decrease of dissolved oxygen in 3.5% sodium chloride solution treated by rotating electromagnetic field.

Electrochemical behavior of mesh and plate oxide coated anodes during zinc electrowinning

The catalytic performance of two oxides coated anodes （OCSs） meshes and one OCA plate was investigated in a zinc electrowinning electrolyte at 38 ℃. Their electrochemical behaviors were compared with that of a conventional Pb-0.7%Ag alloy anode. Electrochemical measurements such as cyclic voltammetric, galvanostatic, potentiodynamic, open-circuit potential （OCP） and in situ electrochemical noise measurements were considered. After 2 h of OCP test, the linear polarization shows that the corrosion current density of the Ti/（IrO2-Ta2O5） mesh electrode is the lowest （3.37μA/cm^2） among the three OCAs and shows excellent performance. Additionally, after 24 h of galvanostatic polarization at 50 mA/cm^2and 38 ℃, the Ti/MnO2mesh anode has the highest potential （1.799 V）, followed by the Ti/（IrO2-Ta2O5） plate （1.775 V） and Ti/（IrO2-Ta2O5） mesh （1.705 V） anodes. After 24 h of galvanostatic polarization followed by 16 h of decay, the linear polarization method confirms the sequence obtained after 2 h of OCP test, and the Ti/（IrO2-Ta2O5） mesh attains the lowest corrosion current density. The Ti/（IrO2-Ta2O5） mesh anode also shows better performance after 24 h of galvanostatic polarization with the overpotential lower than that of the conventional Pb-Ag anode by about 245 mV.

Electrochemical performances of AB_5-type hydrogen storage alloy modified with Co_3O_4

Anodic electrodes with the mixture of hydrogen storage alloys and different contents of Co3O4（2%,4%,6% and 8%,mass fraction） powders were made.The effects of Co3O4 on the electrochemical performance of the alloy electrodes were studied.The constant charge-discharge tests show that the discharge capacity of alloy electrodes with Co3O4 significantly increases,and the maximum discharge capacities of electrodes with 2%,4%,6% and 8% Co3O4 are higher than the electrode with no Co3O4 by 0.83%,4.86%,7.18% and 9.21%,accordingly.Linear polarization（LP） and electrochemical impedance spectroscopy（EIS） tests suggest that charge-transfer resistance decreases by the addition of Co3O4.Cyclic voltammogram（CV）,scanning electron microscopy（SEM） and energy dispersive spectrum（EDS） tests indicate that Co3O4 can partly dissolve and experience a reversible oxidation-reduction process of Co to Co（OH）2,leading to the improvement in the electrochemical performance of hydrogen storage alloy.

Corrosion behavior of Mg-Al-Pb and Mg-Al-Pb-Zn-Mn alloys in 3.5% NaCl solution

Mg-6%Al-5%Pb and Mg-6%Al-5%Pb-0.55%Zn-0.22%Mn(mass fraction) alloys were prepared by induction melting with the protection of argon.The corrosion behaviors of these alloys were studied by electrochemical measurements and immersion tests.The results show that at the corrosion onset of Mg-Al-Pb anode there is an incubation period that can be shortened with 0.55%Zn and 0.22%Mn additions in the magnesium matrix.The corrosion rate of Mg-Al-Pb anode is mainly determined by the incubation period.Short incubation period always leads to high corrosion rate while long incubation period leads to low corrosion rate.The corrosion rates based on the corrosion current density by the electrochemical measurements do not agree with the measurements evaluated from the evolved hydrogen volume.

Electrochemical hydrogen storage performance of as-cast and as-spun RE-Mg-Ni-Co-Al-based alloys applied to Ni/MH battery

The La-Mg-Ni-Co-Al-based AB2-type La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1(x=0,0.05,0.1,0.15,0.2)alloys were prepared via melt spinning.The analyses of the X-ray diffraction(XRD)and scanning electron microscopy(SEM)proved that the experimental alloys contain the main phase LaMgNi4 and the second phase LaNi5.Increasing Y content and spinning rate lead to grain refinement and obvious change of the phase abundance without changing phase composition.Y substitution for La and melt spinning make the life-span of the alloys improved remarkably,which is attributed to the improvement of anti-oxidation,anti-pulverization and anti-corrosion abilities.In addition,the discharge capacity visibly decreases with increasing the Y content,while it firstly increases and then decreases with increasing spinning rate.The electrochemical kinetics increases to the optimum performance and then reduces with increasing spinning rate.Moreover,all the alloys achieve to the highest discharge capacities just at the initial cycle without activation.

Effects of trace element and purification on properties of AZ80 magnesium allo

The effects of trace element Fe on the corrosion behavior of AZ80 magnesium alloy were investigated by salt spray test and electrochemical measurements.The results show that the corrosion rate decreases with decreasing the trace element Fe content in an approximately linear relation even though the amount of trace element Fe reduces to 0.000 2%(mass fraction).The electrochemical measurements show that the corrosion potential(φcorr)of the alloy with lower trace element Fe content shifts to less negative value.It is suggested that the control trace element by purification is an effective way to enhance the corrosion resistance of AZ80 magnesium alloy.

Synthesis of Li_2Fe_(0.9)Mn_(0.1)SiO_4/C composites using glucose as carbon source

Li2Fe0.9Mn0.1SiO4/C composites were synthesized by using X-ray diffractometry （XRD）, scanning electron microscopy （SEM） glucose as carbon source. The samples were characterized by and electrochemical measurements. All Li2Fe0.9Mn0.1SiO4/C composites are of the similar crystal structure. With increasing the carbon content in the range of 5%-20% （mass fraction）, the diffraction peaks in XRD patterns broaden and the particle sizes and the tap density of samples decrease. The Li2Fe0.9Mn0.1SiO4/C composites with carbon content of 14.12% show excellent electrochemical performances with an initial discharge capacity of 154.7 mA.h/g at C/16 rate, and the capacity retention remains 92.2% after 30 cycles.

2,3,5-Triphenyl-2H-tetrazolium Chloride and 2,4,6-Tri（2-pyridyl）-s-triazine on the Corrosion of Mild Steel in HCl

Electrochemical measurement, quantum chemical method, and scanning electron microscopy （SEM） were performed to investigate the inhibitive effect of 2,3,5-triphenyl-2H-tetrazolium chloride （TTC） and 2,4,6-tri（2-pyridyl） -s-triazine（TPT） on the corrosion of mild steel in lmol.L^-1 HCl at room temperature. Impedance spectroscopy measurement showed that the polarization resistance increased and that double layer capacitance decreased with the increase in the inhibitive concentration, and the results of potentiodynamic polarization showed that the inhibitors suppressed both cathodic and anodic processes of steel corrosion without change in the mecha-nism. Higher the orbital density distribution strength of the lowest unoccupied molecular orbital, higher is the molecule dipole, and lower energy gap between the energy of the highest occupied molecular orbital and the energy of the lowest unoccupied molecular orbital resulted in higher inhibitory efficiency. The results of SEM analysis showed that the metal-was protected from aggressive corrosion by the addition of TTC and TPT.

Preparation and properties of pitch carbon based supercapacitor

Using the mesophase pitch as precursor, KOH and CO2 as activated agents, the activated carbon electrode material was fabricated by physical-chemical combined activated technique for supercapacitor. The influence of activated process on the pore structure of activated carbon was analyzed and 14 F supercapacitor with working voltage of 2.5 V was prepared. The charge and discharge behaviors, the properties of cyclic voltammetry, specific capacitance, equivalent serials resistance （ESR）, cycle properties, and temperature properties of prepared supercapacitor were examined. The cyclic voltammetry curve results indicate that the carbon based supercapacitor using the self-made activated carbon as electrode materials shows the desired capacitance properties. In 1 mol/L Et4NBF4/AN electrolyte, the capacitance and ESR of the supercapacitor are 14.7 F and 60 mΩ respectively, The specific capacitance of activated carbon electrode materials is 99.6 F/g; its energy density can reach 2,96 W.h/kg under the large current discharge condition, There is no obvious capacitance decay that can be observed after 5000 cycles, The leakage current is below 0,2 mA after keeping the voltage at 2.5 V for l h, Meanwhile, the supercapacitor shows desired temperature property; it can be operated normally in the temperature ranging from -40 ℃to 70 ℃,

Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole(Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)-1-oxoethan-2-yl-N,N-diethyldithiocarbamate(Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-Oethyl xanthate(Pr06) on the aqueous oxidation of chalcopyrite(CuFeS2) in air-equilibrated solution at a temperature of 25 ℃ and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electrochemical impedance spectroscopy(EIS), scanning electron microscopy coupled with energy dispersive X-ray(SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared(FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH > Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

Inhibiting Effect of Ciprofloxacin,Norfloxacin and Ofloxacin on Corrosion of Mild Steel in Hydrochloric Acid

The inhibiting effect of ciprofloxacin,norfloxacin and ofloxacin on the corrosion of mild steel in 1 mol·L-1 HCl and the mechanism were studied at different temperatures using mass loss measurement,electrochemical method,and X-ray photoelectron spectroscopy(XPS) .Effective inhibition was shown by mass loss,potentiodynamic polarization and impedance spectroscopy measurement.The corrosion rate of the metal in the mass loss measurement,and the corrosion reaction on cathode and anode in the electrochemical measurement were accelerated when temperature was increased.XPS results showed that the inhibitors adsorbed effectively on the metal surface.

On-line Measurement for Ohmic Resistance in Direct Methanol Fuel Cell by Current Interruption Method

Electrochemical impedance spectroscopy (EIS) is widely used in fuel cell impedance analysis. However, for ohmic resistance (R Ω), EIS has some disadvantages such as long test period and complex data analysis with equivalent circuits. Therefore, the current interruption method is explored to measure the value of RΩ in direct methanol fuel cells (DMFC) at different temperatures and current densities. It is found that RΩ decreases as temperature increase, and decreases initially and then increases as current density increases. These results are consistent with those measured by the EIS technique. In most cases, the ohmic resistances with current interruption (R iR ) are larger than those with EIS (R EIS ), but the difference is small, in the range from –0.848% to 5.337%. The errors of R iR at high current densities are less than those of R EIS . Our results show that the R iR data are reliable and easy to obtain in the measurement of ohmic resistance in DMFC.

Dielectric properties and point defect behavior of antimony oxide doped Ti deficient barium strontium titanate ceramics

The microstructures and dielectric properties of Sb2O3-doped Ti deficient barium strontium titanate ceramics prepared by solid state method were investigated with non-stoichiometric level and Sb2O3content by SEM,XRD and LCR measure system.It is found that with the increase ofδ,(Ba0.75Sr0.25)Ti1-δO3-2δceramics transform from single phase solid solutions with typical cubic perovskite structure to multiphase compounds while(Ba0.75Sr0.25)Ti0.998O2.996ceramics remain to be single-phase with the increasing Sb2O3content.The distortion of the ABO3perovskite lattice caused by VTi″″and VO..induces the drop of Curie temperature and the rise of relative dielectric constant in(Ba0.75Sr0.25)Ti1-δO3-2δceramics with increasingδvalue.The orientation of VO??elastic dipoles results in the domain-wall pinning and thus the reduction of the dielectric loss.With increasing Sb2O3content,the relative dielectric constant,dielectric constant maximum and Curie temperature of(Ba0.75Sr0.25)Ti0.998O2.996ceramics decrease dramatically while the dielectric loss increases.

Synthesis and thermoelectric properties of Mg_2Si_(1-x)Sn_x solid solutions by microwave irradiation

In order to reduce the oxidizing and volatilizing caused by Mg element in the traditional methods for synthesizing Mg2Sil-xSnx （x=0.2, 0.4, 0.6, 0.8） solid solutions, microwave irradiation techniques were used in preparing them as thermoelectric materials. Structure and phase composition of the obtained materials were investigated by X-ray diffraction （XRD）. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured as a function of temperature from 300 to 750 K. It is found that Mg2Si1-xSnx solid solutions are well formed with excessive content of 5% （molar fraction） Mg from the stoichiometric MgESil.xSnx under microwave irradiation. A maximum dimensionless figure of merit, ZT, of about 0.26 is obtained for Mg2Si1-xSnx solid solutions at about 500 K for x=0.6.

EEG classification based on probabilistic neural network with supervised learning in brain computer interface

Aiming at the topic of electroencephalogram （EEG） pattern recognition in brain computer interface （BCI）, a classification method based on probabilistic neural network （PNN） with supervised learning is presented in this paper. It applies the recognition rate of training samples to the learning progress of network parameters. The learning vector quantization is employed to group training samples and the Genetic algorithm （GA） is used for training the network＇ s smoothing parameters and hidden central vector for detemlining hidden neurons. Utilizing the standard dataset I （a） of BCI Competition 2003 and comparing with other classification methods, the experiment results show that the best performance of pattern recognition Js got in this way, and the classification accuracy can reach to 93.8%, which improves over 5% compared with the best result （88.7 % ） of the competition. This technology provides an effective way to EEG classification in practical system of BCI.

Experimental study on micro-electrolysis technology for pharmaceutical wastewater treatment

Experiments were conducted to study the role of micro-electrolysis in removing chromaticity and COD and improving the biodegradability of pharmaceutical wastewater. The results showed that the use of micro-electrolysis technology could remove more than 90% of chromaticity and more than 50% of COD and greatly improved the biodegradability of pharmaceutical wastewater. Lower initial pH could be advantageous to the removal of chromaticity. A retention time of 30 minutes was recommended for the process design of micro-electrolysis.

Hydrogen storage behavior of nanocrystalline and amorphous La-Mg-Ni-based LaMg_(12)-type alloys synthesized by mechanical milling

Nanocrystalline and amorphous LaMg11Ni+x%Ni(x=100,200,mass fraction)alloys were synthesized by mechanicalmilling.The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system.The gaseous hydrogen absorption and desorption properties were investigated by Sievert’s apparatus and differential scanningcalorimeter(DSC)connected with a H2detector.The results indicated that increasing Ni content significantly improves the gaseousand electrochemical hydrogen storage performances of the as-milled alloys.The gaseous hydrogen absorption capacities andabsorption rates of the as-milled alloys have the maximum values with the variation of the milling time.But the hydrogen desorptionkinetics of the alloys always increases with the extending of milling time.In addition,the electrochemical discharge capacity andhigh rate discharge(HRD)ability of the as-milled alloys both increase first and then decrease with milling time prolonging.

Preparation and Electrochemical Performances of Nickel Metal Hydride Batteries with High Specific Volume Capacity

Cylindrical nickel metal hydride （Ni-MH） battery with high specific volume capacity was prepared by using the oxyhydroxide Ni（OH）2 and AB5 type hydrogen storage alloy and adjusting the designing parameters of positive and negative electrodes. The oxyhydroxide Ni（OH）2 was synthesized by oxidizing spherical β-Ni（OH）2 with chemical method. The X-ray diffraction （XRD） patterns and the Fourier transform infrared （PT-IR） spectra indicated that 7-NiOOH was formed on the oxyhydroxide Ni（OH）2 powders, and some H2O molecules were inserted into their crystal lattice spacing. The battery capacity could not be improved when the oxyhydroxide Ni（OH）2 sample was directly used as the positive active materials. However, based on the conductance and residual capacity of the oxyhydroxide Ni（OH）2 powders, AA size Ni-MH battery with 2560 mA.h capacity and 407 W·h·L^-1 specific volume energy at 0.2C was obtained by using the commercial spherical β-Ni（OH）2 and AB5-type hydrogen-storage alloy powders as the active materials when 10% mass amount of the oxyhydroxide Ni（OH）2 with 2.50 valence was added to the positive active materials and subsequently the battery designing parameters were adjusted as well. The as-prepared battery showed 70% initial capacity after 80 cycles at 0.5C. The possibility for adjusting the capacity ratio of positive and negative electrodes from 1 ： 1.35 to 1 ： 1.22 was demonstrated preliminarily. It is considered the as-prepared battery can meet the requirement of some special portable electrical instruments.

Preparation of calcium phosphate coatings on Mg-1.0Ca alloy

The calcium phosphate coatings were prepared by virtue of electrochemical deposition in order to improve the corrosion resistance of Mg-1.0Ca alloys in simulated body fluids.The chemical compositions,structures and morphologies of the coatings were investigated by energy dispersive spectroscopy(EDS),X-ray diffractometry(XRD)and scanning electron microscopy(SEM), respectively.The potentiodynamic electrochemical technique was employed to investigate the bio-degradation behavior of Mg-1.0Ca alloys with Ca-P coatings in Hank's solutions.The experimental results show that the deposited coatings predominately consist of flake-shape brushite(DCPD,CaHPO4·2H2O)crystallites.The corrosion resistance of the substrates with coatings is improved in Hank's solutions significantly.