Size‐Dependent Electrocatalytic Activity of Free Gold Nanoparticles for the Glucose Oxidation Reaction

Understanding the fundamental relationship between the size and the structure of electrode materials is essential to design catalysts and enhance their activity. Therefore, spherical gold nanoparticles (GNSs) with a mean diameter from 4 to 15 nm were synthesized. UV/Vis spectroscopy, transmission electron microscopy, and under‐potential deposition of lead (UPD_Pb) were used to determine the morphology, size, and surface crystallographic structure of the GNSs. The UPD_Pb revealed that their crystallographic facets are affected by their size and the growth process. The catalytic properties of these GNSs toward glucose electrooxidation were studied by cyclic voltammetry, taking into account the scan rate and temperature effects. The results clearly show the size‐dependent electrocatalytic activity for glucose oxidation reactions that are controlled by diffusion. Small GNSs with an average size of 4.2 nm exhibited high catalytic activity. This drastic increase in activity results from the high specific area and reactivity of the surface electrons induced by their small size. The reaction mechanism was investigated by in situ Fourier transform infrared reflectance spectroscopy. Gluconolactone and gluconate were identified as the intermediate and the final reaction product, respectively, of the glucose electrooxidation.     

Modeling dendritic solidification of Al–3%Cu using cellular automaton and phase-field methods

We compared a cellular automaton (CA)–finite element (FE) model and a phase-field (PF)–FE model to simulate equiaxed dendritic growth during the solidification of cubic crystals. The equations of mass and heat transports were solved in the CA–FE model to calculate the temperature field, solute concentration, and the dendritic growth morphology. In the PF–FE model, a PF variable was used to identify solid and liquid phases and another PF variable was considered to determine the evolution of solute concentration. Application to Al–3.0 wt.% Cu alloy illustrates the capability of both CA–FE and PF–FE models in modeling multiple arbitrarily-oriented dendrites in growth of cubic crystals. Simulation results from both models showed quantitatively good agreement with the analytical model developed by Lipton–Glicksman–Kurz (LGK) in the tip growth velocity and the tip equilibrium liquid concentration at a given melt undercooling. The dendrite morphology and computational time obtained from the CA–FE model are compared to those of the PF–FE model and the distinct advantages of both methods are discussed.     

阳离子型聚乙烯吡咯烷酮的制备及其负载RNA性能

将二甲基二烯丙基氯化铵（DADMAC）与乙烯吡咯烷酮（VP）共聚得到阳离子型的聚乙烯吡咯烷酮（CPVP）,并分别合成了聚二甲基二烯丙基氯化铵（PDADMAC）和聚乙烯吡咯烷酮（PVP）均聚物,用粘度法测定了三者的粘均相对分子质量,用红外光谱表征了其结构。 将合成的CPVP与核糖核酸（RNA）以不同比例混合,研究CPVP负载RNA的能力,并与PDADMAC及PVP的负载性能做比较。 结果发现,与PDADMAC及PVP相比,当CPVP与RNA按质量比2∶1混合时,形成的复合体纳米粒的平均粒径约为300 nm,分散度指数为0.0966,粒径分布较窄。     

The Axially Modulated, Cusp-Injected, Slowly Varied Section Opened Cavity, Magnicon Amplifier

I introduce a novel hybrid microwave amplifier that utilizes the axial bunching mechanism of klystrons in conjunction with the energy extraction mechanism of cyclotron resonance masers on TM mode. A simpler analytic model is used to show the viability of the device configuration and to explore limitations of the scheme. An example of an 11.5 GHz, fourth harmonic amplifier is presented. Adopting a multi-particle in azimuth range of (0, /2) whose divide thickness of beam into three share approach, numerical simulation are used to demonstrate bunching in physical space and to estimate system efficiency et al. It shall be shown that this configuration enables the design of eficient, high harmonic devices over a wide range of parameters. Magnicon [1]-[11] is a kind of microwave amplifier tabe, it operates on the mode of rotating E_n10 in cylindrical cavity and there is solid focus fine electrons beam. In it from theory, the paper researches the new type magnicon, it is changed into using annular electron beam and using slowly variable section opened cavity. Compared with magnicon, its pervence beams will may be increased, its frequency may be increased up to millimeter wave band, its bandwidth also will may be increased same times. Than model of new type magnicon is put forward. Starting from large signal's theory, interacting of the annular electron beam into driver cavity in between the mode of rotating E_n10, numerical value to simulate. It done on the small current density and small density of electron in space that electrons dynamic are simulated, which may uses Runge-Kutta method to do it.     

A Theory of the Self-Consistent and Space-Charge Effect in Hybrid-Magnicon Amplifier

A novel axially modulated, annular electron beam cusp-injected, slowly varied section opened cavity, hybrid-magnicon amplifier had been proposed I once. The hybrid-magnicon has wavelength up to millimeter wave bend. The while its non-self-consistent non-space-charge nonlinear numerical calculation method was discussed. But due to bunch effect is changing uniform distribution state of the annular electron beam in the driver cavity, and then dynamic force balances of the beam is changing. Therefore, besides the interaction force between electron beam and the rotating TM_n10 mode electromagnetic field also must consider the electromagnetic force of current density and the action force between the space-charges and the action force of the charge density grade, et al. effect. For some problems of theory, this report try discuss from Maxwell Equations.     

Analysis for the new type long-pulsed and high efficient microwave amplifier—magnicon

This paper begins with the cylindrical cavity field expression of the rotating TM_n10 mode in magnicon, and obtains its dissipated power, cold quality formula and so on, which are different from those in the static state TM_n10. Furthermore starting from the dynamics equations, the passive deflect cavity electron velocity and position solution, as well as the interact instantaneous power solution between electron and wave have been solved. The cylindrical coordinate electron energy dynamics equation in the output cavity, and the modification of terminal parameter formula for relativity have also been discussed. This work is supported by the Sic. & Tech. Funds of CAEP.     

Linear Theory of Electron Dynamic for the Slowly Varied Section Waveguide Resonator with the TM Mode in a Hybrid-Magnicon

Based on fundamental principles of magnicon, we posed hybrid-magnicon amplifier. It are adopted that beforehand axially modulating annular electron beam, a vertical cylindrical wave-guide opened driver cavity, a slowly varied section waveguide opened output cavity, whoever with TM-mode. Pass basic concept analysis of this new type tube that after consider who suitably make small power or MW pulsed tube with suitable wide-band. For example, if operate at the third harmonic then can reach 8% bandwidth. This paper expounded the linear theory for hybrid-magnicon. Use simply new method, which solve for Dispersion Equation. Give Dispersion Equation with the self-consistent effect and the space charge effect of the slowly varied section waveguide rotating TM-mode opened resonator cavity. Give the interact power between wave and electrons, et al.     

Electrocatalytic activity of carbon-supported metallophthalocyanine catalysts toward oxygen reduction reaction in alkaline solution

Carbon-supported metallophthalocyanine catalysts, composed of a transition central metal M (M = Co, Mn, Ni, Fe) in the phthalocyanine ring, were synthesized in this work. As cathodic reaction in a fuel cell, the oxygen reduction reaction (ORR) was investigated in alkaline medium with linear scanning voltammetry at the surface of these electrocatalysts deposited onto a rotating disk electrode (RDE). It was found that the number of electrons transferred depended on the nature of the metallic cation in the catalyst. Evidences provided with Koutecky-Levich approach showed that iron phthalocyanine (FePc) exhibited the better electrocatalytic ability toward the ORR with four electrons exchanged and low activation overpotential. Among these different as-prepared materials, MnPc and FePc led to a four-electron pathway, while CoPc and NiPc proceeded by a two-electron route. The latter reaction process was also determined with a rotating ring-disk electrode (RRDE), which allowed the determination of hydrogen peroxide formed as O₂ reduction intermediate in a small amount, i.e., less than 1.2 %.     

Electrochemistry as an Attractive and Effective Tool for the Synthesis and Immobilization of Porphyrins on an Electrode Surface

Magnesium(II) 10‐phenyl‐5,15‐p‐ditolylporphyrin is easily and cleanly transformed by electrolysis. A nitro group is first introduced at the free meso position by anodic substitution. Hydrogenation into the amine is then carried out electrocatalytically under ambient conditions with water as a hydrogen supplier. The synthesized porphyrin under the nickel(II) form can be covalently grafted onto a platinum electrode by electrochemical reduction of the diazonium cation, generated in situ by a reaction of the nickel(II) aminoporphyrin with sodium nitrite and trifluoroacetic acid. The electrosynthesized thin film gives an electrochemical response typical of a porphyrin material. Films grown under our conditions have a maximum surface coverage of approximately 5×10^?10 mol cm^?2. The modified electrode exhibits a reproducible electrochemical behavior and a good level of stability over potential cycling and exposition to air.     

磁旋管谐振腔旋转TMn10模的冷品质因数

 从场的表达式出发, 根据Bessel函数的积分公式,推导了旋转TMn₁₀模的腔内储能,时均损耗功率,和冷品质因数等公式。求得了与静态TMn₁₀模不同的相应公式, 它更接近于实验值。为了比较,又推导了该静态模的相应参数公式,得出与现有静态模固有冷品质因素不同的公式。