Spatial distribution of the temperature and the number densities of electrons and atomic and ionic species in an inductively coupled RF argon plasma

A survey of the literature shows that the values found for the excitation parameters (temperature and electron number density) in an inductively coupled radio-frequency argon plasma at atmospheric pressure (ICP) depend on the plasma configuration and the measuring procedure. The present study proposes a novel method for measuring excitation temperatures that does not require a knowledge of transition probabilities. The experimental work concerns measurements of the spatial distributions of the temperature, the number densities of the electrons and various atomic and ionic species in a low-power (～0.5 kW) ICP for analytical purposes operated at either of two extreme carrier gas flow rates. Observations were made at three different heights above the induction coil. At high flow rate (～51/min) the familiar hollow configuration of the plasma is demonstrated by off-axis maxima for the temperature and the number densities of electrons and atomic species at all observation heights. At low flow rate (～1 l./min), the radial atom number density distributions are parabolically shaped and constricted to a smaller channel at all observation heights. The authors conclude from the results that both the plasma configurations are not in a state of complete local thermal equilibrium at observation heights used for analytical work (i.e., above the coil).     

Noise-power spectra of optical and acoustic emission signals from an inductively coupled plasma

Noise power spectra of emission signals from an ICP discharge have been measured. Below 5 Hz the noise power spectra show a marked dependence on the type of nebulizer used. While a strict 1/f character was not observed the spectra were clearly dominated by low frequency components. Above 5 Hz the noise power spectra were, broadly speaking, independent of the nebulizer. Distinct peaks were observed in the noise power spectra in the 200–400 Hz region. The exact position and intensity of these peaks were dependent on R.F. power, coolant gas flow rate and torch design. In addition the intensity of these peaks is dependent on the exact spatial region viewed by the spectrometer. The position of these peaks correspond exactly to similar peaks found in the acoustic noise power spectrum of the ICP. It is believed these peaks are the result of plasma rotation.     

Electrochemical noise of a hydrogen-air polymer electrolyte fuel cell operating at different loads

The electrochemical noise of a polymer membrane hydrogen-air fuel cell operating at different load currents was measured in serial experiments. Spectral power densities of the noise are shown to be divided into three regions. At frequencies greater than 3–10 Hz, the spectrum dependence has a constant slope of ??2 in the bilogarithmic coordinates. At frequencies 0.3–5 Hz, there is a horizontal plateau in which length is determined by the value of a load. At frequencies less than 0.3 Hz, the dependence of spectral power density has a slope of ??2. Medium-frequency plateau and high-frequency slope of spectral power densities of the noise were approximated by model RC circuits. The values of Faradic resistance and double-layer capacitance connected in parallel were obtained from the electrochemical impedance data. At load voltages higher 0.5 V, the height of the plateau was shown to be proportional to the 2.68 power of the load current value.     

ICP-AES中Ca、Al之间相互干扰的研究

本文在不同条件下比较详细地研究了Ca与Al在ICP-AES中的相互干扰,结果表明:这种干扰的垂直空间分布与其它元素的基体效应不同,特别在低观察区域Ca、Al之间呈现较为明显的相互抑制效应,说明Ca和Al之间产生了溶质挥发干扰。对分析条件特别是入射功率、载气流量及观察高度进行最优化可以使这种干扰减至最小。     

The microstructure of and charge transfer in thin films based on metal-polymer nanocomposites

Charge transfer in nanostructured metal-polymer composites was studied. The frequency dependences of film conductance and susceptance were obtained at various metal concentrations. The susceptance of samples above the percolation threshold was negligibly small, which corresponded to the purely metallic conductivity type. For samples below the percolation threshold, susceptance and conductance were comparable in magnitude, which was evidence of an important role played by susceptance mechanisms. At low frequencies, the samples behaved as quasi-linear RC circuits and both the active and reactive impedance components increased linearly as the frequency grew. At high frequencies, the dispersion of susceptance, which was inversely proportional to frequency, was observed. The conclusion was drawn that the hopping conductivity mechanism through polymeric matrix surface states prevailed in films below the percolation threshold. At high frequencies, when the applied voltage period was shorter than the characteristic time of surface state recharging, these states began to be eliminated from charge transfer processes. It was suggested that a decrease in the reactive impedance component with an increase in frequency might be the reason for the dispersion observed experimentally.     

AC frequency characteristics of coplanar impedance sensors as design parameters

Glass-based microchannel chips were fabricated using photolithographic technology, and Pt thin-film microelectrodes, as coplanar impedance sensors, were integrated on them. Longitudinal design parameters, such as interelectrode spacing and electrode width, of coplanar impedance sensors were changed to determine AC frequency characteristics as design parameters. Through developing total impedance equations and modeling equivalent circuits, the dominant components in each frequency region were illustrated for coplanar impedance sensors and the measured results were compared with fitted values. As the ionic concentration increased, the value of the frequency-independent region decreased and cut-off frequencies increased. As the interelectrode spacing increased, cut-off frequencies decreased and total impedance increased. However, the width of each frequency-independent region was similar. As the electrode area increased, f(low) decreased but f(high) was fixed. We think that the decrease in R(Sol) dominated over the influence of other components, which resulted in heightening f(low) and f(high). The interelectrode spacing is a more significant parameter than the electrode area in the frequency characteristics of coplanar sensors. The deviation of experimentally obtained results from theoretically predicted values may result from the fringing effect of coplanar electrode structure and parasitic capacitance due to dielectric substrates. We suggest the guidelines of dominant components for sensing as design parameters.     

Dynamic mechanical properties of suspensions of micellar casein particles

Small micellar casein particles, so-called submicelles, were obtained by removing colloidal calcium phosphate from native casein by adding sodium polyphosphate. Aqueous submicelle suspensions were characterized using light scattering and rheology as a function of concentration and temperature. The casein submicelles behave like soft spheres that jam at a critical concentration (C(c)) of about 100 g L(-1). The viscosity does not diverge at C(c), but increases sharply, similarly to that of multiarm star polymers. C(c) increases weakly with increasing temperature, which leads to a strong decrease of the viscosity close to and above C(c). Concentrated submicelle suspensions show strong shear-thinning above a critical shear rate and the shear stress becomes independent of the shear rate. The critical shear rates at different temperatures and concentrations are inversely proportional to the zero-shear viscosity. At much higher shear rates, the shear stress fluctuates strongly in time indicating inhomogeneous flow. The frequency dependence of casein submicelle suspensions is characterized by elastic behavior at high frequencies (concentrations) and viscous behavior at low frequencies (concentrations).     

溴碘化银T-颗粒乳剂晶体的表面形貌研究

用原子力显微镜研究了T-颗粒卤化银晶体、掺杂有浅电子陷阱掺杂剂K₄[Ru(CN)₆]的掺杂乳剂晶体、经硫加金化学增感后的掺杂乳剂晶体的表面形貌以及曝光后表面形貌的变化.观察结果表明,T-颗粒晶体表面存在很多突起,经曝光后这些突起高度增加,更集中.掺入浅电子陷阱掺杂剂K₄[Ru(CN)₆]后,T-颗粒晶体对光更敏感,曝光后表面突起高度的增加幅度大于未掺杂乳剂光照后表面高度的变化.同时硫增感剂对表面突起的分布也有很大的影响.     

Resonant Excitation of Boundary Layer Instability of DC Arc Plasma Jet by Current Modulation

Instabilities of thermal plasma jets were studied on the basis of analysis of plasma radiation fluctuations recorded by an array of high frequency photodiodes. Characteristic frequencies of jet oscillations were found and spatial distribution of amplitude of plasma fluctuations was determined. The influence of arc current ripple on plasma instabilities was investigated for two types of power supply—classical thyristor controlled unit with the frequency of the current ripple 300 Hz and the rectifier with the high frequency converter and frequency of the current modulation 30 kHz. Generation of boundary layer instability with the current modulation frequency and its harmonics was proved using fast Fourier transform, contour plots and phase portraits. It was found that the character of fluctuations of plasma jet was substantially influenced by current ripple with the frequency or its harmonics close to the frequency of oscillations generated by boundary layer instability.     

On the pressure dependence of the muon spin polarization in mixtures of noble gases

In muon spin rotation (μSR) experiments, where spin-polarized positive muons are stopped in condensed matter, three magnetically distinguishable chemical environments can be observed. That is, the Larmor frequencies associated with diamagnetic environments and two types of paramagnetic environments (muonium and radicals) can be resolved. The chemical identities of the latter two are distinct since their Larmor frequencies are distinct, whereas the chemical identities of the possible diamagnetic species are not determined by the Larmor frequency since chemical shifts can not be resolved in μSR experiments. However, two different diamagnetic species have been observed in experiments performed on mixtures of noble gases. Their distinction arises through different thermal rate constants that lead to “fast” and “slow” relaxing components of the diamagnetic signal. The pressure dependencies of the amplitudes associated with these components are related to the stopping dynamics of muons in noble gas targets. A set of coupled rate equations for muon spin dynamics, based upon quantal Boltzmann equations, have been developed to describe this process in single component gases. This theory is now extended to mixtures. In particular, the dynamics of the muon spin is generated by the muonium hyperfine interaction and by time dependent rate constants for the various chemical species that are assumed to be present, namely, muonium and three diamagnetic species. Radicals have not yet been observed in low pressure gases. The coupled quantal rate equations are solved for two models of the stopping dynamics wherein the rates are taken as square box functions of time.     

Novel frequency dependence of dielectric biaxiality of surface stabilized ferroelectric liquid crystals

The frequency dependence of the dielectric biaxiality of surface stabilized ferroelectric liquid crystals (SSFLCs) was studied. The principal values of the dielectric tensor ε₁, ε₂ and ε₃ were measured by the MOM (molecular orientational model) method. Three dielectric permittivities were measured for each of two samples. These were the permittivity of the homeotropic cell and the permittivity of the planar homogeneous cell with and without the DC bias. Then the dielectric tensor components were calculated based on the molecular orientational models. We present the theory and experimental procedure of the MOM method. Measurements have been performed on Merck FLC compound SCE-8. The following novel dielectric behaviour was observed, as the DC bias voltage was increased the dielectric permittivity of the planar homogeneous cell decreased at the low frequencies (∼ 1 kHz) while increased at the high frequencies (10kHz ∼). The sign of the dielectric biaxiality ∂εε (= ε₂ - ε₁) inverted around 1 kHz, being negative at low frequencies and positive at high frequencies. The roles of the biaxiality on the dielectric behaviour of SSFLC cells are discussed.     

A novel bottom-viewed inductively coupled plasma-atomic emission spectrometry

A novel optical configuration for inductively coupled plasma (ICP)-atomic emission spectrometry is presented. Plasma emission is measured axially via the bottom end of the ICP torch. Analytical performance, such as increase in signal-to-background ratio (SBR) over radially viewed ICP and linear dynamic range, is comparable to that of end-on axially viewed ICP reported in the literatures. Under typical ICP operating conditions (forward power=1.0–1.6 kW, central channel gas flow rate=0.8–1.4 l/min), SBR is generally five times or more that of radial-viewing mode (observation heights=3–20 mm) for atomic lines of elements of low to medium ionization potential (Na, K, Sr and Ba). The enhancement factor in SBR is two to four times for ionic lines (e.g. MgII) and atomic lines of elements of high ionization potential (Zn). The influence of ICP forward power and carrier gas flow rate on analyte emission intensity and SBR were also studied. Similar to radially viewed ICP, as forward power increases, the net emission intensity increases and SBR decreases. Using a constant flux of analyte aerosols, the net intensity decreases as the central channel gas flow rate increases. No trend of SBR vs. central channel gas flow rate, however, is found. The linear dynamic range starts and ends at analyte concentration 0.5–1 order of magnitude lower than the corresponding radial-viewing mode. As a result, the span of linear dynamic range is similar for all viewing modes. Matrix effects of K and Ca on atomic lines are different from those reported for end-on axially viewed ICPs, probably due to the difference in the plasma regions that were probed. The matrix effects on ionic lines, however, are similar in magnitude.     

基于电化学噪声研究模拟海洋大气环境下304不锈钢的点蚀行为

基于电化学噪声技术建立了不锈钢海洋大气点蚀监测系统,利用该系统对处于干湿循环环境下不锈钢的点蚀行为进行监测. 使用时域谱图、时域统计、频域谱图和散粒噪声理论等分析方法对采集到的电化学噪声数据进行处理分析,并结合动电位极化法,形貌分析法共同研究不锈钢的点蚀行为. 研究结果表明,304不锈钢在模拟海洋大气环境下的点蚀行为分为钝化、亚稳态点蚀和稳态点蚀三个阶段. 在钝化阶段,电位电流噪声信号出现少量的同步异向波动,腐蚀事件发生频率高,平均电量低;在亚稳态点蚀阶段,电位电流噪声信号出现大量的同步同向波动,腐蚀事件发生频率降低,平均电量上升,通过扫描电镜观察蚀点;在稳态点蚀阶段,电位电流噪声信号不仅存在大量的同步同向波动,还出现了同步异向波动,腐蚀事件发生频率较低,平均电量大幅度上升,通过扫描电镜观察到电极表面出现小而浅的蚀点. 而动电位极化法可以证实304不锈钢点蚀的发生. 两种分析方法所得结果具有较好的一致性,证明该监测系统很好地实现了对模拟海洋大气环境下304不锈钢点蚀行为的连续监测,并能判断点蚀的发生.     

Effect of driving frequency on the operation of a radiofrequency glow discharge emission source

Several characteristics of the r.f. glow discharge were examined to determine their dependence on driving frequency. The cathode potential exhibited a strong dependence on frequency, as would be expected, because of the capacitive nature of the discharge. As the frequency was dropped from 13 to 6 MHz there was a dramatic rise in the r.f. voltage of the discharge (with a conductive sample), attributed to a change in the mode of power coupling. The sputtering rates of a conductive sample were dramatically greater at the lower frequencies, in part due to higher energy of the sputtering ions. The emission characteristics of the source also changed as the frequency was varied from 6 to 13 MHz. At the higher operating frequencies, atomic emission peaked at a particular r.f. power level, whereas at lower frequencies the neutral-atom signal generally increased monotonically with power. The highest signal levels were found at 20 MHz, the highest frequency studied. Detection limits were determined for both conductors and insulators; in both cases they are detector-noise-limited because of the low throughput of the spectrometer. Detection limits for a conducting sample ranged from 0.1 μ g⁻¹ at 20 MHz to 20 μ g⁻¹ at 3 MHz. The emission from an insulating sample showed the same trends as those from a conducting sample but required higher r.f. power; the greatest signals were found at 6 and 13 MHz because not enough power was available from the r.f. amplifier to reach the optimum power for the 20 MHz discharge. Detection limits for elements in a Macor^® ceramic sample ranged from 30 to 110 μg g⁻¹.     

Electrochemical Noise Measurement of Polymer Membrane Fuel Cell under Load

Electrochemical noise of a polymer membrane hydrogen–air fuel cell under different currents is measured. Frequency and amplitude dependences of the current-noise power spectral density are calculated. In the frequency interval from 10 to 200 Hz a linear segment of the frequency characteristic has a slope of ?2. The current-noise power spectral density is found to be proportional to the 4th power of the fuel cell loading DC current. Thus found frequency dependence of the fuel cell electrochemical noise was shown to differ markedly from that of the electrochemical impedance real component.     

The effect of step height on the performance of three-dimensional ac electro-osmotic microfluidic pumps

Recent numerical and experimental studies have investigated the increase in efficiency of microfluidic ac electro-osmotic pumps by introducing nonplanar geometries with raised steps on the electrodes. In this study, we analyze the effect of the step height on ac electro-osmotic pump performance. AC electro-osmotic pumps with three-dimensional electroplated steps are fabricated on glass substrates and pumping velocities of low ionic strength electrolyte solutions are measured systematically using a custom microfluidic device. Numerical simulations predict an improvement in pump performance with increasing step height, at a given frequency and voltage, up to an optimal step height, which qualitatively matches the trend observed in experiment. For a broad range of step heights near the optimum, the observed flow is much faster than with existing planar pumps (at the same voltage and minimum feature size) and in the theoretically predicted direction of the "fluid conveyor belt" mechanism. For small step heights, the experiments also exhibit significant flow reversal at the optimal frequency, which cannot be explained by the theory, although the simulations predict weak flow reversal at higher frequencies due to incomplete charging. These results provide insight to an important parameter for the design of nonplanar electro-osmotic pumps and clues to improve the fundamental theory of ACEO.     

N80油套管钢应力状态下的CO2腐蚀行为研究

利用交流阻抗技术研究了拉伸、压缩和弯曲三种应力状态下N80油套管钢在饱和CO₂地层水中的腐蚀过程. 结果表明, 三种状态下的阳极电化学阻抗谱均出现了高频容抗弧、中低频感抗弧和低频容抗弧三个时间常数, 其中高频容抗弧与双电层电容和传递电阻有关, 感抗弧对应膜的活性溶解, 低频容抗弧与试样表面膜的生成有关. 随着三种状态下应变的增加, 感抗弧逐渐扩大, 而低频容抗弧则逐渐缩小, 表明应力状态下N80钢的CO₂腐蚀会加剧. 三种状态下的阴极阻抗谱高频均由容抗弧组成, 中低频由Warburg阻抗和容抗弧共同组成, 三种状态下随着应变程度的增加, Warburg阻抗增加, 反应电阻减小, 双电层电容减小, 说明应力会加速阴极反应过程的进行, 从而增加N80钢的CO₂腐蚀速率.     

脉冲电喷雾现象的初步研究

生物质谱方法的发展得益于生物质谱技术的发展,众所周知,电喷雾与基体辅助激光解吸技术的发展,极大地改善了生物质谱的分析性能,对于复杂生命体系的研究,现有的生物质谱面临着新的挑战,复杂体系要求以很少量的样品（nL-μL级）得到功能蛋白质组的许多信息,如各蛋白质的分子量、肽谱、氨基酸序列以及各类转译后修饰结构等,而现有的生物质谱大多要求足够大的样品量（1－10μL）,因此对低流量样品的高通量信息需求是生物质谱分析领域中的难题。     

FOURIER ANALYSIS OF ANGULAR DISTRIBUTIONS FOR MOTILE MICROORGANISMS

The method of Fourier transformation is used to analyze histograms of the angular distribution of organisms moving with respect to a stimulus, in this case the light direction. In the Fourier spectra, the components with the highest amplitudes indicate the modality of orientation, i.e. the number of preferred directions, and the corresponding phase values indicate the deviation from the light direction. In the frequency domain, those components with high amplitude and/or those with low frequencies (low-pass filtering) can be selected and used to reconstruct a smoothed histogram by means of an inverse Fourier transform. This method reduces the noise level and reveals the prominent features of histograms. Examples of unimodal, bimodal and multimodal distributions are shown in their original and smoothed form for the flagellate Euglena gracilis , and for amoebae and pseudoplasmodia or the slime mold Dictyostelium discoideum.     

Optimal frequencies for magnetic acceleration of cytochrome oxidase and Na,K-ATPase reactions

Low frequency magnetic fields increase the activity of the membrane enzymes, Na,K-ATPase and cytochrome oxidase, and the increased activity varies with frequency. Optimal frequencies for increases in the reaction rate constant of cytochrome oxidase and in the rate of splitting of ATP by Na,K-ATPase differ by an order of magnitude, and are in the ranges of the turnover numbers of the respective enzyme reactions. The two frequency dependence curves are similar in that the slope of the low frequency portion is about 10 times greater than the slope of the high frequency portion. The greater slope indicates greater ability to adjust quickly in the low frequency range, which may be significant for optimal biological control of activity.