Continuous-wave method

With the development of Fourier transform (FT) techniques in NMR spectroscopy (early 1970s), the first major advance in the NMR technology was made. A significant increase in the sensitivity, as compared to the conventional continuous wave method, resulted in the NMR spectroscopy of rare nuclei, particularly 13C NMR, which is essential for polymer studies. The 13C NMR analysis of swollen lightly crosslinked polymers was made possible. The relaxation measurements, based on the different pulse sequences, provided additional information on the network dynamics. 

Continuous wave methods are the most accurate means of making ultrasonic measurements. Even so, they are used less frequently than pulse methods because measurements are more time consuming and laborious to carry out, are more difficult to automate, and the measurement cell requires a high degree of precision engineering. These techniques therefore tend to be used in specialized research laboratories where accurate measurements are important. Continuous wave ultrasound is utilized in a variety of different techniques, but the most commonly used is the interferometer [10,11]. 

I assume that you are conversant with basic principles of XH or proton NMR spectroscopy as applied to small molecules. In particular, I assume that you understand the concepts of chemical shift (8) and spin-spin coupling, classical continuous-wave methods of obtaining NMR spectra, and decoupling experiments to determine pairs of coupled nuclei. If these ideas are unfamiliar to you, you may wish to review NMR spectroscopy in an introductory organic chemistry textbook before reading further. 

Continuous wave methods, 5 Correlation function, 66 Correlation time, 66 COSY... 

A major consequence of the introduction of pulse (FT) NMR spectroscopy has been ready access to C data - limited prior to 1970 by factors which render this magnetic nucleus relatively insensitive to continuous wave methods of recording NMR spectra (1 % natural abundance, and low value of the nuclear magnetic moment compared with that of a proton). C-NMR spectra are generally much simpler than corresponding H spectra. When run under conditions where all couplings to protons are removed (by simultaneous wide-band irradiation of proton resonances), a C-NMR spectrum consists of a series of sharp lines, each of which corresponds to the resonance of a nucleus (or nuclei) of specific magnetic environment. Further, since the chemical shift spread of C nuclei (0-200 ppm) is about 20-times that of protons. 

Slow-passage ODMR signals frequently are observed by the continuous wave method in which the optical effect is monitored using broadband detection. On the other hand, if the triplet state decay constants are sufficiently large, the microwave power may be amplitude modulated at an audio frequency which results in modulated phosphorescence when the microwave frequency is at resonance. The phosphorescence is then monitored with narrow-band phase-sensitive detection, for a great improvement in the signal/noise ratio. The latter detection method is frequently used to produce a magnetic resonance-induced phosphorescence spectrum by a technique referred to as phosphorescence-microwave double resonance (PMDR). The microwave frequency is fixed at resonance,... 

The advantage of using Fourier transform spectroscopy is that data are acquired very much faster than via conventional, continuous wave, methods. This means a better signal-to-noise ratio can be achieved for an identical amount of compound in the same period of time. The increase in speed is 50-fold. 

When it is desired to measure the composition of a single component in a mixture, it is necessary to relate the component resonance to that of another compound, an internal standard, which is of known chemical composition and has been added in known weight to a known weight of unknown. Brame and Yeager [46] used dichlorobenzotrifluoride as an internal standard in the continuous wave method for determining the composition of both repeat units in hexafluoropropylene-vinylidene fluoride copolymers. This work demonstrated the utility of the Fourier transform NMR method for the quantitative analysis of the copolymer in relation to results obtained by continuous wave NMR and H NMR. 

The dielectric relaxation techniques can be sub-divided into two groups step response or continuous wave methods,... 

For example, the effect of substitution at the 1-H position of the 2-nitro-5-methylimidazole [2] ring can be analysed (Table 6), Hitherto, different imidazole derivatives have been studied by N NQR, by the continuous wave method, by NMR and Cl NQR (pulse methods). However, the problem of the effect of a substituent at the 1-H position on the... 

The applications discussed above were performed using conventional CW (continuous wave) methods, predominantly at X-band ( 9 GHz) frequency. However, in recent years EPR spectroscopy has experienced an extraordinarily rapid development in two noted areas, namely pulsed techniques and high-frequency EPR. Already both developments have proved to be invaluable tools in important areas of physics, chemistry and biology, and no article on the applications of EPR spectroscopy is complete without an explanation of the powerful attributes of these techniques. 

Fundamentals Pulsed Methods Continuous Wave Methods Musical Instruments Transducer Arrays Medical Ultrasonics Nondestructive Evaluation Geophysical Exploration Marine Sonar and Sonar In Animals Processing Technology Sonochemistry... 

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