Resonance measurement methods

Another technique often used to examine the stmcture of double-heUcal oligonucleotides is two-dimensional nmr spectroscopy (see AfAGNETiC SPIN resonance). This method rehes on measurement of the nuclear Overhauser effects (NOEs) through space to determine the distances between protons (6). The stmcture of an oligonucleotide may be determined theoretically from a set of iaterproton distances. As a result of the complexities of the experiment and data analysis, the quality of the stmctural information obtained is debated. However, nmr spectroscopy does provide information pertaining to the stmcture of DNA ia solution and can serve as a complement to the stmctural information provided by crystallographic analysis. 

Resonance ionization methods (RIMS) have also been explored for improving Th ionization efficiency for mass spectrometric measurement (Johnson and Fearey 1993). As shown in Figure 3, two lasers are required, a continuous resonant dye laser for resonance of thorium atoms, and a continuous UV argon laser for transition from resonance to ionization. Consequently, sophisticated laser instrumentation is required for these methods. 

The objectives of this review are to discuss the fundamental and more recently discovered properties of water alone and to critically examine the system properties and measurement methods used to measure the mobility of water and solids in foods—specifically water activity, nuclear magnetic resonance (NMR), and the glass transition. 

Three different methods have been used to make microwave resonance measurements of intervals between alkaline earth Rydberg states. In all of these measurements state selective laser excitation of alkaline earth atoms in a beam was combined with one of three forms of state selective ionization of the final states. 

Hyperfine structure measurements using on-line atomic-beam techniques are of great importance in the systematic study of spins and moments of nuclei far from beta-stability. We will discuss the atomic-beam magnetic resonance (ABMR) method, and laser spectroscopy methods based on crossed-beam geometry with a collimated thermal atomic-beam and collinear geometry with a fast atomic-beam. Selected results from the extensive measurements at the ISOLDE facility at CERN will be presented. 

In most cases, resonance measurements are made at low excitation levels, so that small signal numbers are derived. Methods of extending resonance methods to higher powers are discussed in [11]. 

Frequently, values of P for wavelengths where experimental data do not exist are estimated by extrapolation using a two-level model description of the resonance enhancement of P (see Appendix). Levine and co-workers [170] have also shown how to estimate the wavelength (frequency) dispersion of two-photon contributions to p. Because of the potential of significant errors associated with each measurement method, it is important to compare results from different measurement techniques. Perhaps the ultimate test of the characterization of the product of pP is the slope of electro-optic coefficient versus chromophore number density at low chromophore loading. It is, after all, optimization of the electro-optic coefficient of the macroscopic material that is our ultimate objective. 

The diffusion coefficient may be measured via several experimental techniques. The most prominent ones at present are the direct observation of a diffusion boundary in either a field electron microscope [159, 160] or a photoelectron emission microscope [158] or via laser desorption experiments [161, 162], In the latter case a short laser pulse is used to heat the surface to momentarily desorb the adsorbate from a well defined region of the crystal. Subsequent laser pulses with well defined time delays with respect to the first one, and measurement of the number of particles leaving the surface, allow one to determine the rate of diffusion into the depicted zone. Other methods to determine surface diffusion are spectroscopic measurements which cover the proper time window, for example magnetic resonance-based methods [163, 164]. In favorable cases these methods may even be applied to single crystal surfaces [165],... 

The experiments discussed in this book are diverse, but they break down into two broad categories (1) resonant infrared methods in which ultrafast IR pulses are tuned to the wavelength of the vibrational transition and (2) Raman methods (in some instances referred to as impulsive stimulated scattering), in which two visible wavelengths have a difference in frequency equal to the vibrational frequency. In some experiments, infrared and Raman techniques are combined in a single measurement. 

To avoid these pitfalls two different techniques have recently been used to measure the intracellular pH in intact A. nigra blood cells97. One technique combines a measurement of the ratio of intracellular to extracellular concentration of amine with measurement of the extracellular pH to yield the intracellular pH. Another technique involves intracellular 31P-NMR (nuclear magnetic resonance) measurements. These methods led to a determination of pH7.39 0.10 for unfractionated cells, and 7.2 for the vanadocyte fraction. 

Because of the high sensitivity required, this generally involves the measurement of intense electronic transitions. In principle, infrared or Raman detection could be more widely applicable, but, except for resonance Raman methods, which again depend on the presence of UV-visible bands, these methods are too insensitive to be of much use at present. 

The measurement of complexation has been accomplished by a variety of techniques. For alkali metal cations with simple crowns, calorimetric and ion selective electrodes have been, by far, the most common. Nuclear magnetic resonance (NMR) methods have also been used commonly and increasingly as the receptors and their substrates become more complex. 

The measurement method described in this article is an embodiment of the non-resonance, direct-force-excitation approach that subjects a double-lap shear sample of damping polymer to force from a vibration shaker. In concept this approach can be applied irrespective of whether the material is in a rubbery, glassy, or intermediate state. Each material specimen is small in size and behaves as a damped spring over the entire frequency range. The small specimen size is in contrast with some alternate approaches in which the specimens have sufficiently large dimensions to be wave-bearing. 

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