从银电极上氢析出的温度效应得到的反应动力学启示

利用循环伏安法研究了多晶银电极在0.1 mol/L HClO₄溶液中氢析出反应的温度效应. 发现当从析氢起始电位负向扫描至零电荷电位(-0.4 V)时,氢析出反应的表观活化能(E_a,app)和指前因子(A)均随着电势的负移而增大(对应的E_a,app从24 kJ/mol增大至32 kJ/mol).继续负向扫描至零电荷电位以后,E_a,app随电势的负移而减小但A不随电势变化. 推测E_a,app和A在零     

不同pH酸性溶液中铂电极上氢析出和二氧化碳还原的电化学研究

本文利用循环伏安法和电化学原位红外光谱的联用,研究了Pt(111)和Pt膜电极在CO₂饱和的酸性溶液中氢析出和CO₂还原的竞争. 发现：(i)在pH>2的溶液中,主要反应是氢析出,界面pH值随着氢析出突然增加;(ii)通过红外光谱检测,CO_ad是CO₂还原过程中唯一的吸附中间体;(iii)CO_ad生成速率随着欠电位沉积氢(UPD-H)覆盖的增加而增大,并在氢析出的起始电位达到最大值;(iv)在氢析出时,CO_ad的减少与CO₂吸附和还原所必需的的中间产物(H_ad)有限的可用位点和停留时间相关.     

钽在无水乙醇中的腐蚀

采用动电位极化、循环伏安、交流阻抗和扫描电镜等技术研究了钽在四乙基氯化铵(TEA)乙醇溶液中的腐蚀行为．在循环伏安曲线的扫描初期,电极表面因存在一薄层氧化物膜而使得电流密度缓慢增 加．后来钝化膜因受到氯离子的攻击而被击穿,即点蚀．扫描电镜图很好地显示出蚀孔的生长过程．点蚀电位随着TEA浓度的增加而下降,随着水含量的增加而上升．在所研究的温度范围内,电化学反应的活化能为36 kJ/mol．所有电极电位下的交流阻抗图谱都包含两个时间常数,钝化膜电阻和电荷传递电阻均随电极电位的增加而下降．     

Au(111)上过氧化氢在碱性介质中氧化反应的pH效应

本文经过系统地研究Au(111)上过氧化氢在pH值从10到13的不同碱性溶液体系中氧化反应(HPOOR),发现随着溶液pH的增大,HPOOR的活性增大,电流电势i-iE极化曲线的斜率减小. HO₂^-是碱性溶液中HPOOR的主要反应物种,在高pH溶液下有很快的动力学反应主要是由于电极表面的正电荷与体系中的阴离子HO₂^-和OH^-等有静电相互作用的原因. 因此在溶液反应物随pH增大的时候,热力学的驱动力也加快了HO₂^-的氧化过程.     

不同pH酸性溶液中铂电极上氢析出和二氧化碳还原的电化学研究（英文）

本文利用循环伏安法和电化学原位红外光谱的联用,研究了Pt(111)和Pt膜电极在CO_2饱和的酸性溶液中氢析出和CO_2还原的竞争.发现:(i)在pH2的溶液中,主要反应是氢析出,界面pH值随着氢析出突然增加;(ii)通过红外光谱检测,CO_(ad)是CO_2还原过程中唯一的吸附中间体;(iii)CO_(ad)生成速率随着欠电位沉积氢(UPDH)覆盖的增加而增大,并在氢析出的起始电位达到最大值;(iv)在氢析出时,CO_(ad)的减少与CO_2吸附和还原所必需的的中间产物(H_(ad))有限的可用位点和停留时间相关.     

锐钛矿相纳米TiO2晶体生长动力学及生长过程控制

研究了采用溶胶-凝胶法经由前驱物钛酸四异丙酯水解制备纳米TiO2结构相变及锐钛矿晶体生长动力学过程. 研究结果表明,在酸性条件下水解,由于高压热处理温度的变化导致锐钛矿向金红石相的结构相变,锐钛矿相纳米TiO2生长活化能在250℃以下和以上分别为(15.8±4.5) kJ/mol和(80.2±1.0) kJ/mol;而在碱性条件下水解的活化能值为(3.5±0.4 kJ/mol. 在不发生结构相变的条件下,酸性水解条件下锐钛矿相纳米TiO2生长速率相比没有碱性条件下快,即表明在酸性条件下提高锐钛矿生长速率主要依靠提高温度来实现,而在碱性条件下,可以通过延长高压热处理时间使得晶体生长速率加快,该研究成果对实现锐钛矿相纳米TiO2晶体尺寸控制和将来批量化制备提供了理论和实验指导.     

硫酸(氢)根吸附层对Pd(111)电极上甲酸氧化反应的影响研究

本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na₂SO₄的0.1 mol/LH₂SO₄+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为,并与同样条件下0.1 mol/LHClO₄中的动力学行为进行比较. 加入0.05 mol/L或者0.1 mol/LNa₂O₄后,在相同的电位下负向扫描的FAO电流比正向扫描的显著减小. 本文推测在(SO₄^*_ad)_m+[(H₂O)_n-H₃O⁺]或(SO₄^*_ad)_m+[Na⁺(H₂O)_n-H₃O⁺]吸附层相转变电势以正的电位, 这个吸附层的结构可能随着电位的增加或Na₂SO₄的加入变得更加致密和稳定. 因此,破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难,使得FAO 动力学在较高电位和随后的负扫电位受到明显的抑制.     

电流对苯甲醚电催化重整过程的影响

用电催化重整方法和NiCuZn-Al₂O₃催化剂进行生物油模型化合物苯甲醚的水蒸气重整制氢研究,结果表明,在700 oC和4 A条件下,获得的最高碳转化率和氢产率分别为98.3%和88.7%,电催化重整过程中发现的电流促进效应主要归结于重整反应床中温度分布的改变和电阻丝发射的热电子影响. 利用X射线衍射方法分析了反应前后的NiCuZn-Al₂O₃催化剂结构变化. 实验导出的苯甲醚重整反应表观活化能为99.54 kJ/mol,明显高于乙醇、乙酸和生物油轻质组分的重整反应表观活化能.     

利用交流阻抗谱揭示Ir(111)电极在酸性溶液中的氢吸附动力学

本文利用阻抗谱研究Ir(111)电极在HClO₄和H₂SO₄中溶液中的氢吸附行为. 在HClO₄溶液中,随着施加电位从0.2 V降到0.1 V(vs RHE),Ir(111)电极上氢吸附速率从1.74×10^-8 mol·cm^-2·s^-1增大到 3.47×10^-7 mol·cm^-2·s^-1 . 与相同条件下Pt(111)电极上的氢吸附速率相比,Ir(111)上的氢吸附速率要小1∽2个数量级,这是由于Ir(111)电极与H₂O结合能力更强,因此位于水合氢键网络中的氢离子需要克服更高的能垒才能重新定向进而发生欠电位沉积. 在H₂SO₄溶液中,氢吸附电位负移了200 mV,吸附速率也下降了一个数量级,这是由于Ir(111)电极表面强吸附的硫酸根/硫酸氢根物种的阻碍作用. 结果表明,在电化学环境下,位于电极表面附近的水分子的取代和重新定向在很大程度上影响了氢吸附过程.     

硫酸(氢)根吸附层对Pd(111)电极上甲酸氧化反应的影响研究（英文）

本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na_2SO_4的0.1 mol/LH_2SO_4+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为,并与同样条件下0.1 mol/LHClO_4中的动力学行为进行比较.加入0.05 mol/L或者0.1 mol/LNa_2SO_4后,在相同的电位下负向扫描的FAO电流比正向扫描的显著减小.本文推测在(SO_4~*_(ad))m+[(H_2O)_n-H_3O~+]或(SO_4~*_(ad))_m+[Na~+(H_2O)_n-H_3O~+]吸附层相转变电势以正的电位,这个吸附层的结构可能随着电位的增加或Na_2SO_4的加入变得更加致密和稳定.因此,破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难,使得FAO动力学在较高电位和随后的负扫电位受到明显的抑制.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.