Streaming potential analysis on the hydrodynamic transport of pressure-driven flow through a rotational microchannel

In this study, the streaming potential and electrokinetic energy conversion efficiency are discussed under the low zeta potential approximation through a microparallel channel with consideration of rotational effect. By solving Poisson-Boltzmann equation and modified Navier–Stokes equation, the analytical expressions of the streaming potential and electrokinetic energy conversion efficiency in the electrolyte solution are obtained. Combining with the numerical calculation, the influences of the dimensionless electrokinetic width K and the rotational angular velocity ω on streaming potential and the electrokinetic energy conversion efficiency are discussed. The results show that the streaming potential fields decrease both in mainstream and secondary directions with the electrokinetic width K, it decreases with the non-dimensional rotational angular velocity in the mainstream direction and it shows a first increasing then decreasing trend in the secondary flow direction. In addition, the influences of related non-dimensional parameters, including electrokinetic width, wall electric potential and rotational angular velocity, on the electrokinetic energy conversion efficiency are also discussed in detail. The rotating effect can enhance conversion efficiency comparing to the case of no rotation. The increase of wall electric potential gives rise to an augment in electrokinetic energy conversion efficiency. These theoretical results make sense to the energy harvesting in the rotating microfluidic systems.     

具有聚电解质层圆柱形纳米通道中的电动能量转换效率

柔性纳米通道是在刚性纳米通道壁面处添加一层带某种电荷的聚电解质层或固定电荷层的纳米通道. 本文在低Zeta势近似下, 通过解析求解电势满足的线性化Poisson-Boltzmann方程和速度满足的Cauchy动量方程, 给出了圆柱形柔性纳米通道中电解质溶液的流向势和电动能量转换效率的解析解. 在表面Zeta势取值相同, 且管径相同(聚电解质层厚度远小于管径前提下)的情形下, 将圆柱形柔性纳米通道和刚性纳米通道中电解质溶液的流向势和电动转换效率进行了比较. 结果表明, 柔性纳米通道中的流向势和转换效率明显高于刚性通道中的流向势和转换效率. 在本文选取的参数范围内, 柔性纳米通道中的电动转换效率比刚性纳米通道中的转换效率提高1.5-3倍.     

Intense laser-driven energetic proton beams from solid density targets

The effects of target density on proton acceleration driven by an intense sub-ps laser pulse are investigated using two-dimensional hybrid particle-in-cell simulations. Results show that at higher density the target-normal-sheath acceleration (TNSA) is more effective than shock acceleration for protons from a plastic target. Furthermore a lower-density target is favorable to higher energy of the TNSA protons. Moreover, the longitudinal electric fields at the target surfaces may reveal typical inhomogeneous structures for a long acceleration time. The conversion efficiency of laser energy into particle (electron, proton, and C(+) ion) energy is found to increase with decreasing target density.     

Anomalous light scattering by small particles

Light scattering by a small spherical particle with a low dissipation rate is discussed based upon the Mie theory. It is shown that if close to the plasmon (polariton) resonance frequencies the radiative damping prevails over dissipative losses, sharp giant resonances with very unusual properties may be observed. In particular, the resonance extinction cross section increases with an increase in the order of the resonance (dipole, quadrupole, etc.); the characteristic values of electric and magnetic near fields for the scattered light are singular in the particle size, while energy circulation in the near field is rather complicated, so that the Poynting vector field includes singular points whose number, types, and positions are very sensitive to fine changes in the incident light frequency. The results may provide new opportunities for a giant, controlled, highly frequency-sensitive enhancement and variation of electromagnetic field at nanoscales.     

355 nm Nd:YAG激光在H2中的高效一级斯托克斯转换

对脉冲Nd:YAG激光(355 nm)在H2和H2:He-Ar混合气体中的受激拉曼散射(SRS)进行了研究.在0.5 MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大能量转化效率达44%(对应量子效率为63%).由于高级斯托克斯的竞争,纯氢气中一级斯托克斯的最大能量转换效率不超过43%.通过向3 MPa氢气中掺入2 MPaAr气后,很好地抑制了二级斯托克斯的产生,从而获得了能量转换效率高达71%(对应量子效率为83%)的一级斯托克斯输出.对四波混频和级联受激拉曼散射在氢气多级斯托克斯产生中的作用以及惰性气体对它们的影响进行了讨论.     

Various aspects of ultrasound assisted emulsion polymerization process

In this paper, the effects of ultrasonic (US) power, pulse ratio, probe area and recipe composition were investigated on two process responses namely, monomer (methyl methacrylate, MMA) conversion and electrical energy consumption per mass of product polymer (PMMA). Pulsed mode US is more suitable than continuous mode US for emulsion polymerization. The probe (tip) area has little effect on the yield of polymerization when comparing 19 and 13 mm probes, 13 mm probe performing slightly better for high conversion levels. Meanwhile, large probe area is beneficial for high conversion efficiency of electric energy to US energy as well as for high radical generation yield per energy consumed. The conversion increased slightly and electrical energy consumption decreased substantially by using a recipe with high SDS and monomer concentrations. Conclusions presented in this paper may be useful for scale-up of US assisted emulsion polymerization.     

pH effect on the physicochemical characteristics and efficiency of electroflotation extraction of low-soluble iron subgroup metal compounds from aqueous solutions

This paper reports on our study of the pH effect of solutions on the average hydrodynamic diameter (d_av) of the particles of the disperse phase and the electrokinetic potential (ζ) of the particles of low-soluble iron subgroup metals compounds using Fe(II, III), Ni(II), and Co(II) compounds as an example. The pH effect of solutions on the efficiency of the electroflotation extraction of metal ions from aqueous solutions containing these ions in individual form or in mixture was studied. The efficiency of the electroflotation extraction of the low-soluble compounds of iron subgroup metals is directly related to the particle size and electrokinetic potential of the particles, which depend on рН. The maximum degree of particle extraction α reached 97–99% at рН values characterized by the maximum hydrodynamic diameter of particles (over 20 μm for Fe(II) and Co(II) compounds and over 50 μm for Fe(III) and Ni(II) compounds) at ζ potentials of up to–10 mV for systems approximated to real wastewater. In the case of the extraction of the disperse phase of the Fe(III)–Ni(II)–Co(II) multicomponent system, the synergic effect was observed: the coextraction of metals was more complete and effective, which may be due to suppressed negative charge. In the range of рН 10–11, the degree of extraction of the Fe(III) disperse phase did not exceed 74%; in the ternary system, it reached 94%.     

Parameter-dependent photon echo induced in CdSe/ZnS quantum dot quantum well

The two pulse photon echo (2PPE) phenomena induced by the 1s-1s electronic transition in CdSe/ZnS quantum dot quantum well (QDQW) has been studied by employing semiconductor Bloch equations. The energy eigenvalues and eigenfunctions of electrons and holes have been obtained by solving the stationary Schrödinger equation under effective-mass approximation. The Coulomb interaction, which changes with the size variation of QDQW, has been calculated and analyzed as a perturbation. The variations of the electric transition dipole moment and the energy interval with the changing of the size and structure of the QDQW have also been obtained. It has been shown from the numerical calculation results that the efficiency of 2PPE can be controlled by the variation of the size and structure of the QDQW and the mechanism has been explained in terms of the quantum size confined effect (QSCE) theory.     

Macro-performance of multilayered thermoelectric medium

The effective properties of thermoelectric composites are well known to depend on boundary conditions, which causes the macro performance of thermoelectric composite to be difficult to assess. The overall macro-performance of multilayered thermoelectric medium is discussed in this paper. The analytical solutions are obtained, including the heat flux, temperature,electric potential, and the overall energy conversion efficiency. The results show that there are unique relationships between the temperature/electric potential and the electric current/energy flux in the material, and whether the material is independent of or embedded in thermoelectric composites. Besides, the Peltier effect at the interface can significantly improve the overall energy conversion efficiency of thermoelectric composites. These results provide a powerful tool to analyze the effective behaviors of thermoelectric composites.     

基于准周期光学超晶格的高效电光调制差频转换

为获得尽可能大的差频转换效率,基于准周期极化铌酸锂(QPPLN)光学超晶格,提出了级联电光和差频理论,用于高效的差频转换。其方法是沿QPPLN光学超晶格的y方向施加一个外加电场,用来控制能量在抽运光、信号光、o偏振的差频光和e偏振的差频光四个光波之间的转移。计算结果表明,在一个100℃,40mm长的QPPLN光学超晶格中,当1550nm信号光与1064nm抽运光光强比值r<0.324时,对光强超过特定值的任意抽运光都可以通过施加一个适当的外加电场将抽运光完全转化为1550nm信号光和3393.4nm差频光;当r≥0.324,只当抽运光光强落在一定范围内时,才可以通过施加外加电场使抽运光完全转化为信号光和差频光;超过该范围,外加电场不能增加差频光转换效率。计算结果还表明,电光调制差频转换效率对温度和畴构造误差都不敏感。     

上转换发光的有效增强机制--上转换敏化

频率上转换研究在近十年有了突飞猛进的发展,它有着非常好的应用前景。也仍然面临着进一步提高上转换效率的任务。由于Yb^3 能级结构的特殊性,它的引入既可以通过能量转换传递使共掺稀土离子上转换发光有较大增强,又可能不引起较明显的荧光猝灭。因而研究Yb^3 作为敏化中心的上转换敏化是有重要意义的,而把提高上转换效率与提高材料的物化性能结合起来更是上转换研究的应用的当务之急。本文综述了上转换敏化的提出和发展,介绍了在该领域取得的成果,特别是间接上转换敏化的成果。     

Development and experimental investigation of small-sized thermo-electric generator with diffusion combustion

Laboratory samples of small-sized energy converters based on thermo-electric method of heat conversion which source is diffusion microflame are presented in the work. Processes of combustion, energy conversion, and cooling in the proposed systems have been experimentally studied. Relatively high efficiency of the studied systems (energy-conversion 0.8 % at generated electric power of 130 mW) complying with the current world level for such devices is shown. The advantages of the proposed power generators are absence of forced-cooling system and catalysts, assemblage simplicity and usage of available materials and components. On the basis of investigation results, possible ways of further improvement of test samples have been determined with the view of energy conversion efficiency increase.     

Electric power generation using vibration of a polyurea piezoelectric thin film

An energy harvesting system is proposed, in which mechanical energy is converted to electrical energy through the piezoelectric effect of a polymer polyurea film on the device. Electrical energy harvesting methods that use piezoelectric elements have been reported by several groups, and lead zirconate titanate (PZT) is predominantly employed as the piezoelectric material. An energy harvesting device with a polyurea thin film formed through vapor deposition polymerization with 4,4′-diphenylmethane diisocyanete (MDI) and 4,4′-diamino diphenyl ether (ODA). The conversion efficiency from mechanical to electrical energy was calculated using finite elemental analysis (FEA) of the cantilever configuration. Higher conversion efficiency was obtained using a thinner and shorter cantilever configuration with increased resonance frequency of the device. Experiments were conducted using an electric power generation device with a 3 μm thick polyurea thin film attached to a 0.1-mm-thick, 18-mm-long beryllium copper cantilever. Vibration in the vertical direction, which induces the bending vibration on the cantilever, was applied to the device and the output voltage was measured by connecting load resistances. The output power was measured with a change in the load resistance from 10 kΩ to 10 MΩ, and an optimum output was obtained at 1 MΩ, which corresponds to the value calculated using FEA. The conversion efficiency was improved by changing the cantilever length and an efficiency of 0.233% was obtained with a 4-mm-long cantilever.     

Experimental study on energy characteristics and ignition performance of recessed multichannel plasma igniter

In the extreme conditions of high altitude, low temperature, low pressure, and high speed, the aircraft engine is prone to flameout and difficult to start secondary ignition, which makes reliable ignition of combustion chamber at high altitude become a worldwide problem. To solve this problem, a kind of multichannel plasma igniter with round cavity is proposed in this paper, the three-channel and five-channel igniters are compared with the traditional ones. The discharge energy of the three igniters was compared based on the electric energy test and the thermal energy test, and ignition experiments was conducted in the simulated high-altitude environment of the component combustion chamber. The results show that the recessed multichannel plasma igniter has higher discharge energy than the conventional spark igniter, which can increase the conversion efficiency of electric energy from 26% to 43%, and the conversion efficiency of thermal energy from 25% to73%. The recessed multichannel plasma igniter can achieve greater spark penetration depth and excitation area, which both increase with the increase of height. At the same height, the inlet flow helps to increase the penetration depth of the spark.The recessed multichannel plasma igniter can widen the lean ignition boundary, and the maximum enrichment percentage of lean ignition boundary can reach 31%.     

Highly efficient Raman conversion in O2 pumped by a seeded narrow band second-harmonic Nd:YAG laser

The first-Stokes conversion efficiency for a stimulated Raman scattering (SRS) is usually very low in gaseous oxygen media. In 3.0 Mpa O₂, a single longitudinal mode second harmonic Nd:YAG laser pump source gives a typical vibrational first-Stokes conversion efficiency of only 2.5%, In comparison, the accompanying stimulated Brillouin scattering (SBS) attains a reflectivity of 67%. However, by seeding an OPO beam into the Raman cavity, the first-Stokes photon conversion efficiency now attains a peak value of 54%, while the SBS reflectivity reduces to 5% in a 6.1 Mpa 41:59 O₂/ He mixture. This 54% efficiency was obtained for a seeder laser pulse-width less than one half that of pump laser (6.8 ns). A first-Stokes peak power conversion efficiency as high as 88% has been obtained when the pump and seeder pulse peaks coincide. So, we may expect a higher first-Stokes photon conversion efficiency if the seeder pulse-width can be made equal to or larger than that of the pump pulse. On the other hand, the beam quality of the first-Stokes in an O₂/ He mixture excels that of the pump laser for a seeder energy of 5 mJ and pump energy of 50 mJ. However, at pump energies higher than 105 mJ and a pump laser repetition rate of 10 Hz, the thermal defocusing effect worsens the first-Stokes beam quality. This thermal defocusing effect is a result of the Raman heat release and could be eliminated by fast circulating and cooling the Raman gas medium.     

离子能量分析器测量特性的仿真研究

针对空间等离子体及其模拟环境、空间原子氧及其模拟环境对离子能谱测量的需要,利用仿真软件COMSOL,对离子能量分析器的低能离子测量特性进行了仿真研究。介绍了离子能量分析器的工作原理,对离子能谱测量过程进行了公式推导。通过对三种待选仪器设计方案进行离子透过率仿真分析,确定了一种较优的仪器设计方案。多种离子温度下的误差分析结果也表明,该设计方案能够较为准确地测量离子能量分布。分析了电场畸变、等离子鞘层、栅网对齐方式和离子温度对测量结果的影响,根据仿真结果对一些仿真实验现象做出了合理的解释。     

Overlimiting current in a microchannel

We revisit the classical problem of diffusion-limited ion transport to a membrane (or electrode) by considering the effects of charged sidewalls. Using simple mathematical models and numerical simulations, we identify three basic mechanisms for overlimiting current in a microchannel: (i)?surface conduction carried by excess counterions, which dominates for very thin channels, (ii)?convection by electro-osmotic flow on the sidewalls, which dominates for thicker channels, and (iii) transitions to electro-osmotic instability on the membrane end in very thick channels. These intriguing electrokinetic phenomena may find applications in biological separations, water desalination, and electrochemical energy storage.     

Influence of the stick-slip transition on the electrokinetic behavior of nanoporous material

Electrokinetic phenomena exhibiting discontinuities are described in terms of a stick-slip transition. The flux-force equations are partially linear and in the linear regimes the coefficients satisfy Onsager's reciprocal relations. From an interpretation of existing data on ion exchange membranes we find a linear dependence of the slip length with the surface potential. We conclude that slippage offers an alternative explanation for the so-called anomalous surface conduction, as often found in electrokinetic phenomena. This would imply an enhancement of electrokinetic effects in nanopores.     

Improved conversion efficiency of XeCl radiation to the first stokes at high pump energy

An XeCl laser beam has been used to investigate stimulated Raman scattering in H₂ and in various H₂-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H₂, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H₂ at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated.