In order to obtain creditable data an applicable method to optimize parameters of the Langmuir probes and circuits in a stationary laboratory device is investigated and an experimental criterion of the probe dimension...In order to obtain creditable data an applicable method to optimize parameters of the Langmuir probes and circuits in a stationary laboratory device is investigated and an experimental criterion of the probe dimension is developed. To obtain the electron temperature and density the Electron Energy Distribution Function （EEDF） approach with less computing time and more accurate results is applied, instead of the conventional slope approach. Moreover the influence of the vessel wall materials on the plasma density is discussed briefly, indicating that the dielectric wall is helpful to enhancing the electron density.展开更多
In many physical situations where a laser or electron beam passes through a dense plasma,hot low-density electron populations can be generated,resulting in a particle distribution function consisting of a dense cold p...In many physical situations where a laser or electron beam passes through a dense plasma,hot low-density electron populations can be generated,resulting in a particle distribution function consisting of a dense cold population and a small hot population.Presence of such low-density electron distributions can alter the wave damping rate.A kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions.Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma.Strong damping is found for highly nonMaxwellian distributions as well as plasmas with a higher density and hot electron population.Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian.These results may be applied in both experimental and space physics regimes.展开更多
科研人员近年来提出了石墨烯热电子能量转换器件(graphene thermionic energy converter,GTEC)的模型,对其物理机理与参数优化展开了研究,为高品位热能开发提供了新途径.然而,空间电荷积累和近场热辐射效应对GTEC能量转换性能的影响却...科研人员近年来提出了石墨烯热电子能量转换器件(graphene thermionic energy converter,GTEC)的模型,对其物理机理与参数优化展开了研究,为高品位热能开发提供了新途径.然而,空间电荷积累和近场热辐射效应对GTEC能量转换性能的影响却鲜有报道.本文结合热电子发射、朗缪尔空间电荷、非平衡态热力学和涨落电动力学等理论,考虑热电子输运、近场热辐射输运、牛顿换热的相互作用对GETC的影响,进而构建完善的物理模型.首先,分析极板温度恒定时的电流密度、阴极板附加势垒、功率密度、转换效率、热流对电压和真空间隙的依赖特性,结果表明真空间隙对功率密度的影响显著,而对效率的影响较小,可在不同的电压处获得最高功率密度和效率.其次,分析了极板温度受能量平衡约束条件下,功率密度与效率随电压的变化情况,研究发现:相比于恒温模型,牛顿换热对功率密度的影响显著,而对效率的影响较小;在最优功率密度时的阳极板温度高于环境温度,而最优效率时的阳极板温度趋于环境温度;折衷考虑功率密度和效率,确定了电压、真空间隙和阳极板温度的优化区间.本文所获结果可为实际器件的研制提供理论支撑.展开更多
This study was based on the evaluation of the potential effectiveness of Moringa oleifera seeds biomass as a biosorbent in the removal of copper (Cu) in water which was justified by the level of toxicity, environmenta...This study was based on the evaluation of the potential effectiveness of Moringa oleifera seeds biomass as a biosorbent in the removal of copper (Cu) in water which was justified by the level of toxicity, environmental unfriendliness and costly nature of chemical coagulants presently used. Fourier transform infrared (FTIR) analysis was used to identify the Moringa oleifera seeds biomass functional groups present in the adsorption of metal ions and found to be the carboxylic acid and amine functional groups (-COOH and -NH). The effects of contact time, adsorbent dosage, metal ion concentration and pH were studied. The maximum adsorption capacity at pH 5, room temperature and 0.8 g dosage was 70% for Cu(II). The adsorption data fitted better to the Langmuir than the Freundlich models as the sorption capacity (q<sub>m</sub>) of Moringa oleifera seeds biomass for Cu(II) was 3.64 mg/g. The separation factor (R<sub>L</sub>) was within the range of 0 and 1 which showed that the Cu(II) biosorption processes were favourable for Moringa oleifera biosorbent. The results showed that Moringa oleifera seed biomass is an effective adsorbent in the removal of the studied heavy metals in water. The effective pH for the Cu(II) removal was 5.0 as equilibrium was achieved practically in 35 min. The quantitative analysis of defatted Moringa oleifera should be studied in order to have a fair mixing ratio between Moringa oleifera seeds biomass and the adsorbate. There is also the ardent need to work on environmentally friendly disposal of adsorbent after saturation of adsorbent by analyte to avoid secondary pollution.展开更多
Space plasmas often possess non-Maxwellian distribution functions which have a significant effect on the plasma waves. When a laser or electron beam passes through a dense plasma, hot low density electron populations ...Space plasmas often possess non-Maxwellian distribution functions which have a significant effect on the plasma waves. When a laser or electron beam passes through a dense plasma, hot low density electron populations can be generated to alter the wave damping/growth rate. In this paper, we present theoretical analysis of the nonlinear Landau damping for Langmuir waves in a plasma where two electron populations are found. The results show a marked difference between the Maxwellian and non-Maxwellian instantaneous damping rates when we employ a non-Maxwellian distribution function called the generalized （r, q） distribution function, which is the generalized form of the kappa and Maxwellian distribution functions. In the limiting case of r = 0 and q→∞, it reduces to the classical Maxwellian distribution function, and when r = 0 and q→k ＋1, it reduces to the kappa distribution function.展开更多
文摘In order to obtain creditable data an applicable method to optimize parameters of the Langmuir probes and circuits in a stationary laboratory device is investigated and an experimental criterion of the probe dimension is developed. To obtain the electron temperature and density the Electron Energy Distribution Function （EEDF） approach with less computing time and more accurate results is applied, instead of the conventional slope approach. Moreover the influence of the vessel wall materials on the plasma density is discussed briefly, indicating that the dielectric wall is helpful to enhancing the electron density.
基金Project supported by the National Natural Science Foundation of China (Grant No. 40931054)the National Basic Research Program of China (Grant No. 2011CB811404)the Higher Education Commission of China (Grant No. 20-1886/R&D/10)
文摘In many physical situations where a laser or electron beam passes through a dense plasma,hot low-density electron populations can be generated,resulting in a particle distribution function consisting of a dense cold population and a small hot population.Presence of such low-density electron distributions can alter the wave damping rate.A kinetic model is employed to study the Landau damping of Langmuir waves when a small hot electron population is present in the dense cold electron population with non-Maxwellian distribution functions.Departure of plasma from Maxwellian distributions significantly alters the damping rates as compared to the Maxwellian plasma.Strong damping is found for highly nonMaxwellian distributions as well as plasmas with a higher density and hot electron population.Existence of weak damping is also established when the distribution contains broadened flat tops at the low energies or tends to be Maxwellian.These results may be applied in both experimental and space physics regimes.
文摘科研人员近年来提出了石墨烯热电子能量转换器件(graphene thermionic energy converter,GTEC)的模型,对其物理机理与参数优化展开了研究,为高品位热能开发提供了新途径.然而,空间电荷积累和近场热辐射效应对GTEC能量转换性能的影响却鲜有报道.本文结合热电子发射、朗缪尔空间电荷、非平衡态热力学和涨落电动力学等理论,考虑热电子输运、近场热辐射输运、牛顿换热的相互作用对GETC的影响,进而构建完善的物理模型.首先,分析极板温度恒定时的电流密度、阴极板附加势垒、功率密度、转换效率、热流对电压和真空间隙的依赖特性,结果表明真空间隙对功率密度的影响显著,而对效率的影响较小,可在不同的电压处获得最高功率密度和效率.其次,分析了极板温度受能量平衡约束条件下,功率密度与效率随电压的变化情况,研究发现:相比于恒温模型,牛顿换热对功率密度的影响显著,而对效率的影响较小;在最优功率密度时的阳极板温度高于环境温度,而最优效率时的阳极板温度趋于环境温度;折衷考虑功率密度和效率,确定了电压、真空间隙和阳极板温度的优化区间.本文所获结果可为实际器件的研制提供理论支撑.
文摘This study was based on the evaluation of the potential effectiveness of Moringa oleifera seeds biomass as a biosorbent in the removal of copper (Cu) in water which was justified by the level of toxicity, environmental unfriendliness and costly nature of chemical coagulants presently used. Fourier transform infrared (FTIR) analysis was used to identify the Moringa oleifera seeds biomass functional groups present in the adsorption of metal ions and found to be the carboxylic acid and amine functional groups (-COOH and -NH). The effects of contact time, adsorbent dosage, metal ion concentration and pH were studied. The maximum adsorption capacity at pH 5, room temperature and 0.8 g dosage was 70% for Cu(II). The adsorption data fitted better to the Langmuir than the Freundlich models as the sorption capacity (q<sub>m</sub>) of Moringa oleifera seeds biomass for Cu(II) was 3.64 mg/g. The separation factor (R<sub>L</sub>) was within the range of 0 and 1 which showed that the Cu(II) biosorption processes were favourable for Moringa oleifera biosorbent. The results showed that Moringa oleifera seed biomass is an effective adsorbent in the removal of the studied heavy metals in water. The effective pH for the Cu(II) removal was 5.0 as equilibrium was achieved practically in 35 min. The quantitative analysis of defatted Moringa oleifera should be studied in order to have a fair mixing ratio between Moringa oleifera seeds biomass and the adsorbate. There is also the ardent need to work on environmentally friendly disposal of adsorbent after saturation of adsorbent by analyte to avoid secondary pollution.
基金Project supported by the Pakistan Science Foundation Project No.PSF/Res/P-GCU/Phys.(143)the National Natural Science Foundation of China(Grant Nos.41074114 and 41274146)the Specialized Research Fund for State Key Laboratories of China
文摘Space plasmas often possess non-Maxwellian distribution functions which have a significant effect on the plasma waves. When a laser or electron beam passes through a dense plasma, hot low density electron populations can be generated to alter the wave damping/growth rate. In this paper, we present theoretical analysis of the nonlinear Landau damping for Langmuir waves in a plasma where two electron populations are found. The results show a marked difference between the Maxwellian and non-Maxwellian instantaneous damping rates when we employ a non-Maxwellian distribution function called the generalized （r, q） distribution function, which is the generalized form of the kappa and Maxwellian distribution functions. In the limiting case of r = 0 and q→∞, it reduces to the classical Maxwellian distribution function, and when r = 0 and q→k ＋1, it reduces to the kappa distribution function.
