Application of sustained off-resonance irradiation: The beat frequency measurement and radial separation of mass-selected ions

Newer applications of sustained off-resonance irradiation (SORI) in Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry are described. SORI induced circular gyrations of ions with their cyclotron radii varying sinusoidally at the corresponding beat frequency. The beat is observed in the temporal variation of FT-ICR peak height as a function of the duration of the SORI burst, and it allows the direct measurement of the beat frequency. The effective cyclotron frequency is determined from the measured beat frequency and the applied burst frequency. The frequency uncertainty is greatly reduced by nearly 3 orders of magnitude compared with the uncertainty in FT-ICR peak frequency that fluctuates with the rf burst duration. In addition, the oscillating cyclotron radii of the irradiated ions allow the radial separation of mass-selected ions so that the mass-selective photodissociation can be carried out with m-bromotoluene ions.     

Noise power spectra of the inductively coupled plasma

Noise power spectra for the ICP were determined under various conditions, by Fast Fourier Transform (FFT) digital techniques. The major noise types observed were white noise, low frequency noise, and high frequency proportional noise. The high frequency proportional noise increased with concentration of analyte and radio frequency input power. The high frequency proportional noise decreased with increasing nebulizer flow rate and coolant gas flow rate.. The low frequency noise components extended to higher frequencies as the resonance wavelengths of the measured transitions increased. Changing the observation height in the plasma determined which noise types were present in the noise power spectrum. At observation heights near the power coils, all three noise types were present, whereas, low frequency noise predominated at significantly greater heights. Changing the torch design changed the relative amplitudes of the different high frequency proportional noise components, but did not greatly change their respective peak frequencies.     

Unusual hydration behavior of dielectric loss in KA zeolite

Two relaxations measured in dehydrated KA zeolite showed different hydration behaviors; the higher frequency relaxation shifted to higher frequency with increasing hydration whereas the lower frequency relaxation shifted to lower frequency; the latter behavior being contrary to present theory.     

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.     

A phase sensitive modulated thermography of debondings in the insulator of SRMs

Solid rocket motors (SRMs) have been widely applied in missiles, space rockets and shuttles. However, because of some technological and environmental reasons, debonding or poor bonding usually appears in the insulator of SRMs. To evaluate the bonding state between the insulator and the shell during manufacturing, a phase sensitive modulated thermography (MT) is proposed. In order to optimize the operating condition, the influences of the modulation frequency, insulator thickness and debonding lateral size on defect signals are studied through experimentation and 3D numerical simulation. Finite element analysis (FEA) using ANSYS software is applied to simulate the thermal process of the structures precisely. The results show that phase sensitive MT is an effective approach to detect the debondings in the adhesion interfaces. The phase difference at the modulation frequency can be expressed as a quintic polynomial of the modulation frequency in the usual operating frequency range, and the best modulation frequency and detectable frequency band can be determined by the polynomial; when the insulator thickness increases, the best modulation frequency and the maximum phase difference decrease; when the debonding lateral size increases, the maximum phase difference increases while the best modulation frequency remains unchanged. The results provide a guideline for the MT of debondings in SRMs.     

A Novel Method of Spectral Analysis of Oscillatory Belousov–Zhabotinsky Reaction

This paper is a preliminary study of time–frequency behavior of homogenous Belousov–Zhabotinsky reaction in a batch reactor. A series of measurements performed for a variable concentration of the reaction substrates led to the conclusion that there exists time-dependency of an instantaneous frequency of fundamental frequency and harmonics and of electrode potential fluctuations generated during the process discussed. The Short Time Fourier Transformation (STFT) was proposed for analyzing electrode potential registers. On the basis of STFT analysis a decrease in frequency of oscillations of exponential character has been postulated.     

Electromechanical characterization of biomimetic membranes using electrodeformation of vesicles

We describe a facile method to simultaneously measure the bending rigidity and capacitance of biomimetic lipid bilayers. Our approach utilizes the ellipsoidal deformation of quasi-spherical giant unilamellar vesicles induced by a uniform AC electric field. Vesicle shape depends on the electric field frequency and amplitude. Membrane bending rigidity can be obtained from the variation of the vesicle elongation on either field amplitude at fixed frequency or frequency at fixed field amplitude. Membrane capacitance is determined from the frequency at which the vesicle shape changes from prolate to oblate ellipsoid as the frequency is increased at a given field amplitude.     

Study of dielectric properties of styrene-acrylonitrile graphite sheets composites in low and high frequency region

Conducting polymer composites should have a high dielectric constant and a high dissipation factor in the low and high frequency regions if they are to be used in charge storing devices, decoupling capacitors and electromagnetic interference shielding applications. Currently, extensive research is being carried out to enhance the dielectric constants of graphite-polymer, ceramic powder-polymer, metal powder-polymer and nanotube-polymer composites in the low frequency region. In this paper, we present the dielectric properties of styrene-acrylonitrile (SAN)-graphite sheets (GS) composites in the low and high frequency ranges. SAN-GS composites were prepared by the mixing process and by the hot compression mold technique. The composites showed a high dielectric constant and a high dissipation factor in the low and radio frequency region. Furthermore, the EMI shielding properties of these composites are evaluated in the radio frequency range. The conductivity and the dielectric constant of the SAN/GS composites increased with the addition of GS composites, and followed the power law model of percolation theory. The dielectric constant and the dissipation factor of the composites were analyzed according to the low and high frequency region.     

Spectroscopic and theoretical study of vibrational spectra of hydrogen‐bonded tropolone

Theoretical simulation of the bandshape and fine structure of the ν_s stretching band is presented for tropolone‐H and tropolone‐D taking into account an adiabatic coupling between the high‐frequency O–H(D) stretching and the low‐frequency intra‐ and intermolecular OO stretching modes, and linear and quadratic distortions of the potential energies for the low‐frequency vibrations in the excited state of the O–H(D) stretching vibration. In order to determine the low‐frequency vibrations, the experimental spectra of the polycrystalline tropolone in the far‐infrared and the low‐frequency Raman range have been recorded for the first time. The experimental frequencies in the low‐frequency region are compared with the results of the HF/6‐31G** and Becke3LYP/6‐31G** calculations carried out for the tropolone dimer. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 275–282, 1999     

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.     

Evaluation of the Effect of Plasma Treatment Frequency on the Activation of Polymer Particles

This study investigates the influence of treatment frequency (1–150 kHz) on the atmospheric plasma activation of both silicone and polyethylene terephthalate (PET) particles. These polymer particles with diameters in the range 3–5 mm, were treated using either helium or helium/oxygen gas mixtures, in a barrel atmospheric plasma system. The level of polymer particles activation was monitored using water contact angle measurements. The effect of plasma treatment frequency on barrel heating was monitored using an infrared thermographic camera, the maximum barrel temperature after 15 min treatment was found to be 98 °C at a frequency of 130 kHz. Optical emission spectroscopy was used as a diagnostic tool to monitor changes in atomic and molecular species spectral intensity with experimental conditions, as well as a change in electron energy distribution function. Electrical characterisation studies demonstrated an increase in plasma power with increasing frequency, in the range investigated. X-ray photoelectron spectroscopy analysis indicate an increase of oxygen content on polymer surfaces after plasma treatment. For silicone particles, the minimum polymer water contact angle was obtained by using a frequency of 130 kHz. After 15 min treatment time, the water contact angle decreased from 141° to 11°. While for PET particles the optimum treatment frequency was found to be 70 kHz, resulting in a water contact angle decreased from 94° to 32°. This lower frequency was used due to the partial melting of the PET (Tg of 80 °C), when treated at the higher frequency.     

Reduction of axial kinetic energy induced perturbations on observed cyclotron frequency

With Fourier transform ion cyclotron resonance (FTICR) mass spectrometry one determines the mass-to-charge ratio of an ion by measuring its cyclotron frequency. However, the need to confine ions to the trapping region of the ion cyclotron resonance (ICR) cell with electric fields induces deviations from the unperturbed cyclotron frequency. Additional perturbations to the observed cyclotron frequency are often attributed to changes in space charge conditions. This study presents a detailed investigation of the observed ion cyclotron frequency as a function of ion z-axis kinetic energy. In a perfect three-dimensional quadrupolar field, cyclotron frequency is independent of position within the trap. However, in most ICR cell designs, this ideality is approximated only near the trap center and deviations arise from this ideal quadrupolar field as the ion moves both radially and axially from the center of the trap. To allow differentiation between deviations in observed cyclotron frequency caused from changes in space charge conditions or differences in oscillation amplitude, ions with identical molecular weights but different axial kinetic energy, and thus amplitude of z-axis motion, were simultaneously trapped within the ICR cell. This allows one to attribute deviations in observed cyclotron frequency to differences in the average force from the radial electric field experienced by ions of different axial amplitude. Experimentally derived magnetron frequency is compared with the magnetron frequency calculated using SIMION 7.0 for ions of different axial amplitude. Electron promoted ion coherence, or EPIC, is used to reduce the differences in radial electric fields at different axial positions. Thus with the application of EPIC, the differences in observed cyclotron frequencies are minimized for ions of different axial oscillation amplitudes.     

Cell spreading on quartz crystal microbalance elicits positive frequency shifts indicative of viscosity changes

Cell attachment and spreading on solid surfaces was investigated with a home-made quartz crystal microbalance (QCM), which measures the frequency, the transient decay time constant and the maximal oscillation amplitude. Initial interactions of the adsorbing cells with the QCM mainly induced a decrease of the frequency, coincident with mass adsorption. After about 80 min, the frequency increased continuously and after several hours exceeded the initial frequency measured before cell adsorption. Phase contrast and fluorescence microscopy indicated that the cells were firmly attached to the quartz surface during the frequency increase. The measurements of the maximal oscillation amplitude and the transient decay time constant revealed changes of viscoelastic properties at the QCM surface. An important fraction of these changes was likely due to alterations of cytosolic viscosity, as suggested by treatments of the attached cells with agents affecting the actin and microtubule cytoskeleton. Our results show that viscosity variations of cells can affect the resonance frequency of QCM in the absence of apparent cell desorption. The simultaneous measurements of the maximal oscillation amplitude, the transient decay time constant and the resonance frequency allow an analysis of cell adsorption to solid substratum in real time and complement cell biological methods.     

酪氨酸的分频荧光光谱研究

酪氨酸在300nm处产生一个荧光峰,在600nm处产生一个1／2分频荧光峰,在900nm处产生一个1／3分频荧光峰,此三峰具有相似的荧光特性。根据非线性光学分频荧光原理探讨了酪氨酸分频荧光峰产生的原因。     

混合量子-经典动力学方法研究反胶团水池中I2分子的振动频率位移

结合Monte Carlo模拟技术, 提出了一种反胶团溶液的快速数学建模新方法. 利用量子-经典动力学模拟方法, 考察了I2分子受限于两个不同尺寸的反胶团水池中振动频率的诱导位移及谱分布. 结果表明, 相比于体相水, 受限于反胶团水池中I2分子的诱导位移表现为蓝移, 且蓝移大小随水池尺寸变化不大. 通过对I2分子与周围环境相互作用的分解分析, 得到了水池水、表面活性剂以及有机溶剂分子对I2分子振动频率诱导位移的瞬态贡献, 揭示了I2分子振动弛豫的微观作用机制. 此外, 对于受限水池中水分子的诱导贡献及空间分布的研究表明, I2分子振动频率位移的诱导贡献主要来自于第一溶剂层, 它是由4个水分子蓝移贡献和2个水分子红移贡献组成.     

Application of the thermal frequency response method and of pulsed field gradient NMR to study water diffusion in zeolite NaX

The thermal frequency response and pulsed field gradient NMR methods are applied in a comparative study of water diffusion in zeolite NaX under non-equilibrium and equilibrium conditions. The obtained results are found to be in satisfactory agreement with each other, indicating that by applying the thermal frequency response method, complications due to uncontrolled water adsorption at the chamber walls inherent in conventional frequency response measurements may be circumvented.     

界面张力弛豫法研究不同结构破乳剂油水界面扩张粘弹性

采用界面张力弛豫法研究了支链破乳剂AE121和直链破乳剂SP169在正癸烷-水界面上的扩张粘弹性质，并与小幅周期振荡法获得的结果进行了比较.阐述了两种破乳剂的扩张模量随扩张频率和破乳剂浓度的变化规律.研究发现，在低频率处，两种破乳剂的扩张模量均接近于零；在中间频率范围内，扩张模量随扩张频率的增加而增大；在高频率处，扩张模量的幅度接近于极限扩张弹性.在中间频率范围内，扩张模量随破乳剂浓度增大，在接近临界胶束浓度处出现一个极大值；同时还发现，界面上和界面附近的微观弛豫过程的数目随破乳剂浓度增加而增大，其贡献也呈规律性变化.     

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.     

机械振动理论方法与直链烷烃性质研究

将直链烷烃分子看成是一个多自由度振动系统,用机械振动理论中的传递矩阵法计算了C2～C32直链烷烃的固有频率,分析了固有频率随化合物结构单元的变化规律.发现各阶固有频率中的基频与直链烷烃的结构型性质呈现出优良的相关性,用各阶固有频率之和表示的总频与直链烷烃的加和型性质也呈现出优艮的相关性,将两者组合后还能够反映直链烷烃的凝聚型性质的变化规律.在此基础上建立了直链烷烃的物化性能与基频和总频之间的定量相关模型.用该模型对直链烷烃的电离能、沸点、临界温度、临界压力、密度、粘度、标准生成焓、离子标准生成焓、常压热容、折光指数等10种不同类型性质的实验数据进行回归分析,相关系数均大于0.999.     

An impedance analyzer method to simulate the oscillating characteristic of a series piezoelectric sensor in oscillators with zero or non-zero phases

An impedance analyzer method is employed to simulate the oscillation frequency of a series piezoelectric quartz crystal (SPQC) in electrolyte or non-electrolyte solutions. The influence of the oscillator phase on the oscillation frequency and response sensitivity are theoretically derived and experimentally verified. In non-electrolyte liquids, the oscillator phase has little effect on both the oscillation frequency and the response to the permittivity. But in electrolyte solutions, the oscillator phase has a significant influence on the oscillation frequency and the response sensitivity to the conductivity. Depending on the oscillator phase, the oscillation frequency of the SPQC may increase, be maintained or decrease with increasing conductivity in low or high conductive solutions. The dependence of the oscillation frequency of the SPQC on the supply voltage is explained. As an example of the applications, the SPQC is applied to the determination of the critical micelle concentration of ionic surfactants in aqueous solutions.