Frequency-modulation effect

Chapter 3 is devoted to pressure transformation of the unresolved isotropic Raman scattering spectrum which consists of a single Q-branch much narrower than other branches (shaded in Fig. 0.2(a)). Therefore rotational collapse of the Q-branch is accomplished much earlier than that of the IR spectrum as a whole (e.g. in the gas phase). Attention is concentrated on the isotropic Q-branch of N2, which is significantly narrowed before the broadening produced by weak vibrational dephasing becomes dominant. It is remarkable that isotropic Q-branch collapse is indifferent to orientational relaxation. It is affected solely by rotational energy relaxation. This is an exceptional case of pure frequency modulation similar to the Dicke effect in atomic spectroscopy [13]. The only difference is that the frequency in the Q-branch is quadratic in J whereas in the Doppler contour it is linear in translational velocity v. Consequently the rotational frequency modulation is not Gaussian but is still Markovian and therefore subject to the impact theory. The Keilson-... 

Selective experiments can also be performed by the tailored excitation method of Tomlinson and Hill. The selective pulse is frequency-modulated with a function designed to yield zero effective field at the resonance offset of the neighboring nuclei. Although this technique is especially promising for studies of more-complex spin systems, its use is as yet very limited, in part because the instrumentation needed is not yet commercially available. 

Analysis of Zje and Z- as a function of the frequency of potential modulation (Randles plots) provides the phenomenological ET rate constant [63,74]. It should be noted that the extrapolation of Z at high frequency gives effectively the sum 7 ct + where 7 ct is the charge transfer resistance. 

Porter VA, Bonev AD, Knot HJ et al 1998 Frequency modulation of Ca2+ sparks is involved in regulation of arterial diameter by cyclic nucleotides. Am J Physiol 274 C1346—C1355 Pucovsky V, Gordienko D V, Bolton TB 2002 Effect of nitric oxide donors and noradrenaline on Ca2+ release sites and global intracellular Ca2+ in myocytes from guinea-pig small mesenteric arteries. J Physiol 539 25—39... 

ESE envelope modulation. In the context of the present paper the nuclear modulation effect in ESE is of particular interest110, mi. Rowan et al.1 1) have shown that the amplitude of the two- and three-pulse echoes1081 does not always decay smoothly as a function of the pulse time interval r. Instead, an oscillation in the envelope of the echo associated with the hf frequencies of nuclei near the unpaired electron is observed. In systems with a large number of interacting nuclei the analysis of this modulated envelope by computer simulation has proved to be difficult in the time domain. However, it has been shown by Mims1121 that the Fourier transform of the modulation data of a three-pulse echo into the frequency domain yields a spectrum similar to that of an ENDOR spectrum. Merks and de Beer1131 have demonstrated that the display in the frequency domain has many advantages over the parameter estimation procedure in the time domain. 

Actually, however, at least for an isolated XH Y system, the change in length of the H-bonds occurs rhythmically with the frequency of the v(XH Y) vibration. In effect the vKK vibration is frequency modulated by the v(XB. Y) vibration. From a consideration of this more precise classical picture Batuev [29, 30] has shown that the broad band should actually consist of a series of sub-bands of frequencies rXH (XH Y). This is the frequency modulation theory of the origin of the broad vXH bands. This explanation also implies that the band should become narrow at low temperatures when the amplitude of the H-bond stretching vibration is small. 

As a method to control wavepackets, alternative to the use of ultra-short pulses, I would like to propose use of frequency-modulated light. Since it is very difficult to obtain a well-controlled pulse shape without any chirp, it is even easier to control the frequency by the electro-optic effect and also by appropriate superposition of several continuous-wave tunable laser light beams. 

In addition to natural quartz. Rochelle salts, and tourmaline, synthetic crystals, such as ethylenediamine tartrate (EDT), dipotassium tartrate (DKT), and ammonium dihydrogen phosphate (ADPj have varying suitability as piezoelectric elements. While Rochelle salt has a greater piezoelectric effect than any other crystal, it has the disadvantage uf a greater sensitivity to temperature change than quartz. EDT has an advantage over quartz when used in frequency-modulated oscillators because of... 

The graphical representation of this protocol is shown schematically in Fig. 10.15. Signals from two amperometric electrodes, representing channel 1 (blue) and channel 2 (red) detect to electroactive species, which is delivered to them with frequency modulation of, for example, 1 Hz. The experiment is performed in the benchtop fluid setup shown in Fig. 10.16. The first interesting observation is the presence of higher harmonics in the coherence spectrum. They arise as the effect of nonsinusoidal modulation. A pure sine wave would transform to the frequency domain as a single line. Any other waveform of the same frequency will contain higher harmonics in the spectrum. 

The most widespread opinion is that the phase need not be modified because of the properties of the human auditory system [Lim and Oppenheim, 1979]. Strictly speaking however, the assertion that the ear is insensitive to the phase was highlighted by psychoacoustic findings only in the case of stationary sounds and for the phase of the Fourier transform [Moore, 1997]. Moreover, it is well known that in the case of STFT, phase variations between successive short-time frames can give rise to audible effects (such as frequency modulation) [Vary, 1985]. 

Blackman, C. S. Elder, J. A. Weil, C. M. Eichinger, D.C. and House, D. E. Induction of calcium-ion efflux from brain tissue by radio frequency radiation effects of modulation frequency and field strength. In "International Union of Radio Science, Symposium on Bioeffects of Electromagnetic Waves, Washington,... 

G. Eichinger, D. C. House, D. E. Induction of calcium-ion efflux from brain tissue by radio-frequency radiation Effects of modulation frequency and field strength. 

Figure 12.2c shows the temporal variation of the instantaneous frequencies for the two modes. It is interesting to observe how the frequency of the fast mode is modulated in a fairly regular manner. With about 17 modulation cycles for fjast during the 500 s of observation time, we conclude that the frequency of the fast mode is modulated by the presence of the slow mode, indicating that the two modes interact with one another. If one compares the phase of the tubular pressure variations in Fig. 12.2a with the phase of the frequency modulation in Fig. 12.2c it appears that the maximum of ffast occurs about 60° after the maximum of Pt. It is important to note, however, that the various steps of our wavelet analysis may have introduced a certain phase lag. We are presently trying to correct for such effects in order to obtain a better understanding of the instantaneous relation between the two variables. 

The center portion of Fig. 9.2 shows the modulation effect on the spin echo of spin coupling between nuclei / and S. How would this vector picture differ for an IS2 spin system What would be the modulation frequency ... 

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