Attenuation resonant

Sensing techniques that are applicable to the measurement of solids concentration can be classified into four groups electrical, attenuation, resonance, and tomographic. The electrical methods utilize the dielectric and electrostatic properties of solids. Typical electrical sensors are capacitive and electrodynamic sensors the capacitive sensors measure the dielectric property of the solids, whereas the electrodynamic sensors detect the static charges that develop because of collisions between particles, impacts between particles and pipe wall, and friction between particles and gas stream. Attenuation methods are used with optical, acoustic, and radiometric sensors. Both optical and acoustic sensors are applicable to relatively low concentrations of solids. Radiometric sensors, in which y-rays or X-rays are used, are expensive and may raise safety concerns. They can, however, offer accurate and absolute measurement of particle velocity and thus can be used as calibration tools for other low-cost sensors such as the capacitive sensor. Resonance and tomographic methods, which are still in developmental stages, will be briefly introduced in Section 6.5. 

Cortical astrocytes, cerebellar neurons and 0-2A progenitor cells have been investigated with MASS H NMR. All cells contained creatine and significant amounts of lipid resonances even when a T2-edited CPMG pulse sequence was used to selectively attenuated resonances from macromolecules. Principle component analysis readily differentiated the spectra, however the lipid content of the cells contributed most to the separation of cell types. The nature of the NMR-visible mobile lipid signal that is observed under certain conditions in... 

Waveguides are coimnonly used to transmit microwaves from the source to the resonator and subsequently to the receiver. For not-too-high-frequency radiation (<10 GHz) low-loss MW transmission can also be achieved usmg strip-lines and coaxial cables. At the output of a klystron an isolator is often used to prevent back-reflected microwaves to perturb the on-resonant klystron mode. An isolator is a microwave-ferrite device that pemiits the transmission of microwaves in one direction and strongly attenuates their propagation in the other direction. The prmciple of this device involves the Faraday effect, that is, the rotation of the polarization... 

The amount of MW power reaching the sample in the resonator is controlled by a variable attenuator. Like the isolator, the circulator is a non-reciprocal device that serves to direct the MW power to the resonator (port 1 port 2) and simultaneously allows the signal reflected at resonance to go from the resonator directly to the receiver (port 2 port 3). 

The underlying principle of the PEOE method is that the electronic polarization within the tr-bond skeleton as measured by the inductive effect is attenuated with each intervening o -bond. The electronic polarization within /r-bond systems as measured by the resonance or mesomeric effect, on the other hand, extends across an entire nr-system without any attenuation. The simple model of an electron in a box expresses this fact. Thus, in calculating the charge distribution in conjugated i -systems an approach different from the PEOE method has to be taken. 

The degree of attenuation at the critical frequency can be very large, but this type of silencer has a very narrow bandwidth. This device may be suitable when the machine being dealt with emits sound predominantly of a single wavelength. Lining the chamber with absorbers can expand the absorber bandwidth of a Helmholtz resonator, but this has the effect of reducing the efficiency. The perforated absorber, which forms the basis of many acoustic enclosures and silencers, is a development of the resonator principle. 

A number of techniques have been employed that are capable of giving information about amorphous phases. These include infrared spectroscopy, especially the use of the attenuated total reflection (ATR) or Fourier transform (FT) techniques. They also include electron probe microanalysis, scanning electron microscopy, and nuclear magnetic resonance (NMR) spectroscopy. Nor are wet chemical methods to be neglected for they, too, form part of the armoury of methods that have been used to elucidate the chemistry and microstructure of these materials. 

We are interested in the transmission of y-quanta through the absorber as a function of the Doppler velocity. The radiation is attenuated by resonant absorption, in as much as emission and absorption lines are overlapping, but also by mass absorption due to photo effect and Compton scattering. Therefore, the number Tt E2)AE of recoilless y-quanta with energies EXo E + AE traversing the absorber is given by... 

So far we have considered only the recoil-free fraction of photons emitted by the source. The other fraction (1 —/s), emitted with energy loss due to recoil, cannot be resonantly absorbed and contributes only as a nonresonant background to the transmitted radiation, which is attenuated by mass absorption in the absorber... 

Conclusions. A Mossbauer sample with a low content of the resonance nuclide has ideal thickness when it attenuates the incident radiation by ca. 63-85% (/ie t = 1-2, C /Co e - e ). However, the optimization should be subordinated to the requirement of a thin absorber having an effective thickness / < 1 to avoid excessive line broadening. 

B. Balinov, B. Jonsson, P. Linse, O. So-derman 1993, (The NMR self-diffusion method applied to restricted diffusion -simulation of echo attenuation from molecules in spheres and between planes),/. Mag. Reson. A 104, 17. 

Pulsed field gradient NMR has become a standard method for measurement of diffusion rates. Stilbs [272] and others have exploited in particular the FT version for the study of mixtures. An added advantage of PFG-NMR is that it can be employed to simplify complex NMR spectra. This simplification is achieved by attenuation of resonances based on the differential diffusion properties of components present in the mixture. 

Quantitative information may also be gained from the data. If the amino acid composition is accurately known, it may prove possible to integrate portions of the 13C-n.m.r. spectra in order to gain quantitative information about the oligosaccharide structure. This also assumes that no differential nuclear Overhauser effects (n.O.e. s) exist between the various resonances and that none of the resonances in question are attenuated by the use of short recycle-times. 

Wilson PS, Roy RA, Carey WM (2005) Phase speed and attenuation in bubbly liquids inferred from impedance measurements near the individual bubble resonance frequency. J Acoust Soc Am 117 1895-1910... 

On their way from the source to the resonator the intensity of the microwaves must be attenuable for two reasons (1) full power may be too much for the sample leading to saturation (treated in Chapter 4) or (2) it may be impossible to critically couple the cavity at full incident power (e.g., because the sample contains too much water). Therefore, the main waveguide contains an attenuator, usually of the dissipative, rotary-vane type. Dissipative means that the eliminated power is converted to heat and is not reflected as radiation to the source. Rotary vane means that it contains a section of circular waveguide, in which a flat piece of material is located that can be rotated over an angle 0, where 0 = 0 means no attenuation and 0 = 90° causes full attenuation. The amount of attenuation is expressed in decibels, a non-SI,... 

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