Resonance-frequency shift

The parent skeleton of the alkaloids containing the indolo[2,3-n] quinolizinium ring system 321 was examined spectroscopically (Scheme 99). On conversion to the deprotonated form 322 in CD3OD, all resonance frequencies shift to higher field and this tendency is particularly... 

In a nonattaching gas electron, thermalization occurs via vibrational, rotational, and elastic collisions. In attaching media, competitive scavenging occurs, sometimes accompanied by attachment-detachment equilibrium. In the gas phase, thermalization time is more significant than thermalization distance because of relatively large travel distances, thermalized electrons can be assumed to be homogeneously distributed. The experiments we review can be classified into four categories (1) microwave methods, (2) use of probes, (3) transient conductivity, and (4) recombination luminescence. Further microwave methods can be subdivided into four types (1) cross modulation, (2) resonance frequency shift, (3) absorption, and (4) cavity technique for collision frequency. 

In a microwave cavity containing an ionized gas, the resonant frequency shifts in proportion to the electron density n (Slater, 1946). This effect has been used by Warman and Sauer (1970, 1975) to measure n as a function of time... 

J.H. Lee, K.S. Hwang, J. Park, K.H. Yoon, D.S. Yoon, and T.S. Kim, Immunoassay of prostate-specific antigen (PSA) using resonant frequency shift of piezoelectric nanomechanical microcantilever. Biosens. Bioelectron. 20, 2157-2162 (2005). 

So far, in label-free chemical sensing applications, the interaction of a WGM s evanescent component with an analyte in the ambient or adsorbed on the microresonator s surface has led to the development of two sensing methods. These are monitoring of the WGM resonance frequency shift due to the analyte s change of... 

The shear-mode acoustic wave sensor, when operated in liquids, measures mass accumulation in the form of a resonant frequency shift, and it measures viscous perturbations as shifts in both frequency and dissipation. The limits of device operation are purely rigid (elastic) or purely viscous interfaces. The addition of a purely rigid layer at the solid-liquid interface will result a frequency shift with no dissipation. The addition of a purely viscous layer will result in frequency and dissipation shifts, in opposite directions, where both of these shifts will be proportional to the square root of the liquid density-viscosity product v Pifti-... 

The lateral motion of the tip leads to a shear-force generated between the tip and the sample. The oscillation amplitude of the tip is decreased under a constant excitation due to the damping as the tip approaches to the surface. This can be detected at a distance as far as 30 nm away from a sample surface, depending on the oscillation amplitude of the tip [69]. Detailed characteristics of a TF shear-force sensor were also reported and it was shown that the quality factor is decreased as well as that the resonance frequency shifts to higher frequencies as the tip-sample distance is decreased [52]. Due to the jump-in-contact behavior caused by... 

In a sensor experiment (e.g., in a typical biochemical experiment) the sensor has been functionalized with a sensitive film, which is in contact with an analyte containing buffer solution. The new resonance frequencies / can be calculated when replacing Ls and Rs by =Ls + Lc + Liiq and R = Rs + Knq, respectively (neglecting Qiq and Guq). Usually frequency shifts are determined and of interest only. Some example data are added to Table 2. Series and parallel resonance frequency shifts vary by a few percent. All the parallel resonance frequencies are very much affected by external capacitance (values in brackets). The same holds for all frequency shifts in a Hquid except /s. Oscillators based on parallel resonance should not be used because stray capacitance is hardly to avoid and hardly to keep constant in an experimental setup. Deviations of/r and/m from s are also ampHfied by external capacitance. 

In order to analyze the influence of the different loading mechanisms on the QCM response one has to model a dependence of the mechanical impedance Zl or the complex resonance frequency shift on the chemical and physical properties of the contacting mediiun. Various models for the mechanical contact between the oscillating quartz crystal and the outer medium are discussed below. The QCM is now so widely and extensively used that, in the framework of this chapter, it is not possible to review all the available literature. Hence we limited ourselves here to a review of the experimental data and theoretical ideas concerning the studies of structure and interaction at solid-hquid interface. Furthermore, we did not present here studies on... 

Within the QCM measurements the slip boundary condition (Eq. 18) results in the following equations for the resonant frequency shift and the... 

It seems to be essential to measure the admittance spectrum and determine both the resonant frequency shift and the width of the resonance simultaneously. This yields additional information not available from measurement of the resonant frequency alone, and can hence provides more detailed interpretation of processes occurring at the solid-liquid interface. 

For deflagration experiments the cantilevers were first exposed to controlled amounts of TNT vapour from the vapour generator. The amount of TNT adsorbed on the cantilever was calculated from the resonance frequency shift using Equation (1). The variation in the resonance frequency of the cantilever due to TNT adsorption is shown in Figure 5. The initial mass of the cantilever was calculated to be approximately 130 ng. 

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