Resonance frequency

Resonant Sound Absorbers. Two other types of sound-absorbing treatments, resonant panel absorbers and resonant cavity absorbers (Helmholtz resonators), are used in special appHcations, usually to absorb low frequency sounds in a narrow range of frequencies. Resonant panel absorbers consist of thin plywood or other membrane-like materials installed over a sealed airspace. These absorbers are tuned to specific frequencies, which are a function of the mass of the membrane and the depth of the airspace behind it. Resonant cavity absorbers consist of a volume of air with a restricted aperture to the sound field. They are tuned to specific frequencies, which are a function of the volume of the cavity and the size and geometry of the aperture. 

Both of the current models for the central mode scattering contain the implicit assumption of cubic symmetry above Tm. Possibly because of the dramatic nature of the soft-mode behaviour and a ready understanding of the structural transformation in terms of it, there was a strong incentive to establish a link between it and the central mode scattering. A consistent difficulty with this approach is the failure to establish an intrinsic line-width for the central mode peak and the unspecified nature of the mechanism responsibly for a low-frequency resonance in the energy of the soft mode. ... 

High Frequency Resonance Raman Bands of Ni(OEP) in Piperidine... 

The signals for transition metal hydrides, MH(L) , M = Ru, Rh, Ir, Pt etc., afford very low frequency resonance positions, usually in the range S ca. -5 to -30. Several values for palladium hydrides, 50, (often postulated in catalysis, but rarely observed) are shown below [39]. 

Conjugation of the carbonyl group tends to shift the stretch to a lower frequency. Resonance may occur when a double bond or nitrogen atom is adjacent to the carbonyl group. 

Another technique that often utilises the UV spectral range is Fluorescence Spectroscopy, ft also relies on a UV excitation, and subsequent emission perpendicular to the incident beam (see Figure 7.9). The emission can either take place with the same frequency (resonance fluorescence) or at a lower frequency (stimulated fluorescence). The latter phenomenon is rooted in the ability of the UV excited state to interact with the local enviromnent, typically through the excitation of vibrational states of the surrounding part of the protein molecule or of the solvent molecules. 

Fig. 2. (a) Coherent Response of the NH mode at 90K after impulsive excitation and the Fourier transform spectra (b), for probe frequencies resonant with the absorption peaks in the linear spectrum at 3295 Cm1 (grey lines) and 3195 cm 1 (black lines). Part of the NH band of crystalline ACN (c) and NMA-D6 (d). The free excitons are marked by dotted lines and the self-trapped states by black bars. Response of the sample upon selective excitation of the free exciton peak (e, f) and the self-trapped states (g, h) for delay times 400 fs (black line) and 4 ps (grey line). The arrows indicate the position of the narrow band pump pulse. 

The carbide atom in 1 is located in the center of the square face such that it is partially exposed whereas the carbide atom in 2 is completely encapsulated by the six ruthenium atoms. From a spectroscopic viewpoint, carbide atoms are very distinctive and the earlier reviews have dealt with these aspects in detail.7 8 The IR spectrum of 1 contains peaks at 701 (s) and 670(m) cm 1, and 2 contains peaks at 717(sh), 703(s), 680(m), and 669(m) cm-1.22 I3C-NMR spectra of 1 and 2 do not appear to have been reported. This is probably due to the low yields in which these compounds were initially obtained at a time when, 3C-NMR was still not in widespread use in cluster chemistry. In general, the 13C-NMR resonance of carbide atoms ranges from 8 250 to 500. The high frequency resonances exhibited in 13C-NMR spectra reflect the different diamagnetic and paramagnetic effects experienced by a nucleus in such an unusual chemical environment.23... 

In closing this section, we note that although the Koopmans picture is a simplification of the ionization dynamics, it provides a very useful zeroth order picture from which to consider the TRPES results. Any potential failure of this independent electron picture can always be experimentally tested directly through variation of the photoionization laser frequency resonance structures should lead to variations in the form of the spectra with electron kinetic energy, although the effect of resonances is more likely to be prominent in PAD measurements, and indeed an observation of a shape resonance in p-difluorobenzene has been reported [153, 154]. 

One of the oldest and best known ultrasonic testing systems for NDT is the Fokker Bond Tester. This method uses a sweep frequency resonance method of ultrasonic inspection. Some degree of quantitative analysis is claimed with the Fokker Bond Tester in the aircraft industry. 

NiFe2 Alx04 is another spinel exhibiting a compensation point that has been studied. McGuire (423) has measured g n as a function of x at T = — 196°C and 10 kMc/sec. The anomalous increase in <7 ff for compositions with TCOmp — 196°C is shown in Figure 27. McGuire has also observed the high-frequency resonance mode in this system. 

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