Frequency excitation

This behavior is consistent with experimental data. For high-frequency excitation, no fluorescence rise-time and a biexponential decay is seen. The lack of rise-time corresponds to a very fast internal conversion, which is seen in the trajectory calculation. The biexponential decay indicates two mechanisms, a fast component due to direct crossing (not seen in the trajectory calculation but would be the result for other starting conditions) and a slow component that samples the excited-state minima (as seen in the tiajectory). Long wavelength excitation, in contrast, leads to an observable rise time and monoexponential decay. This corresponds to the dominance of the slow component, and more time spent on the upper surface. 

Ground acceleration This is the time history of ground acceleration as a result of an earthquake, where multiple frequency excitation predominates (Figure 14.12(b). A ground response spectrum (GRS) can be derived from this history. 

Floor acceleration This is the time history of acceleration of a partictilar floor nr structure caused by a given ground acceleration (Figure 14.16). It may have an amplified narrow band spectrum due to structural filtration, where single frequency excitation and resonance may predominate, depending upon the dynamic characteristics of the structure. A floor response spectrum (FR.S). as shown in Figure 14.18, can be derived from this history. Consideration of GRS or FRS will depend upon the location of the object under test. 

Since Raman scattered light intensity is very weak, of the order of 10-7 of the excitation line intensity, more powerful laser sources than the He-Ne laser are often needed. The Ar+ laser emits various lines in the region from 457.9 nm to 514.5 nm, of which the most powerful lines (typically — 700 mW) at 488.0 nm (blue) and 514.5 nm (green) are preferred. Furthermore, two other factors which favor the use of the high frequency excitation lines are the peak sensitivity of the photomultipliers in this blue-green region (Fig. 8) and the fourth power Raman intensity law... 

Under low-frequency excitation, the flame front is wrinkled by velocity modulations (Fig. 5.2.5). The number of undulations is directly linked to frequency. This is true as far as the frequency remains low (in this experiment, between 30 and 400 Hz). The flame deformation is created by hydrodynamic perturbations initiated at the base of the flame and convected along the front. When the velocity modulation amplitude is low, the undulations are sinusoidal and weakly damped as they proceed to the top of the flame. When the modulation amplitude is augmented, a toroidal vortex is generated at the burner outlet and the flame front rolls over the vortex near the burner base. Consumption is fast enough to suppress further winding by the structure as it is convected away from the outlet. This yields a cusp formed toward burnt gases. This process requires some duration and it is obtained when the flame extends over a sufficient axial distance. If the acoustic modulation level remain low (typically v /v < 20%),... 

Figure 1.16 Time domain representation and frequency excitation function of a soft pulse. The soft pulse selectively excites a narrow region of a spectral range and leads to a strong offset-dependent amplitude of the excitation function.

Alternative methods of verifying the rotor s dynamic characteristics, for example, variable frequency excitation with the pump at rurming speed to determine the rotor s natural frequeneies, are available. The use of alternative methods and the interpretation of the results shall be mutually agreed between the purchaser and manufacturer. 

The fifth consequence of the theory is that the adsorptivity and catalytic activity of a semiconductor are affected by illumination. When a crystal absorbs light waves of photoelectrically active frequencies (i.e., frequencies exciting the internal photoeffect), this leads, generally speaking, to a change... 

Thus, since ground-state Co+ does not react with dioxygen or N20, in order to produce appreciable amounts of CoO+, N20 can be allowed to react with translationally (produced through radio-frequency excitation) or electronically (produced via laser desorption) excited Co+, leading to a conversion of Co+ to CoO+ of about 20% (222). The... 

On the other hand, additional spectroscopic information can be obtained by making use of this technique The Fourier transform of the frequency-filtered transient (inset in Fig. 8) shows that the time-dependent modulations occur with the vibrational frequencies of the A E and the 2 IIg state. In the averaged Na2+ transient there was only a vanishingly small contribution from the 2 IIg state, because in the absence of interference at the inner turning point ionization out of the 2 IIg state is independent of intemuclear distance, and this wavepacket motion was more difficult to detect. In addition, by filtering the Na2+ signal obtained for a slowly varying pump-probe delay with different multiples of the laser frequency, excitation processes of different order may be resolved. This application is, however, outside the scope of this contribution and will be published elsewhere. 

On the other hand, for very high frequencies, the electrolyte resistance Rs dominates. That is, by the way, the principal reason for using high-frequency excitation in conductometric sensors (Chapter 8) when we want to avoid polarization of the electrodes. 

Fixed Frequency Excitation Selective excitation of a single... 

In summary, piezoelectric coefficients are complex numbers that depend on the measurement frequency, excitation field, temperature, and time (e. g. time after poling in samples that show finite aging rates). Consequently, in reporting piezoelectric data, it is important to specify how the property was measured. 

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