Techniques for measurement

Some of the approaches and techniques for measuring performance and managing the constraints of the subsurface and surface facilities, and the internal and external factors will be discussed in this section. 

Wlodarczyk S., Dybiec Cz., Wlodarczyk W, The application of eddy currents and other techniques for measuring corrosion of metal tanks during exploitation. Materials CCl National Conference about Science and practice in fighting against corrossion , Kule May 1994. 

While field ion microscopy has provided an effective means to visualize surface atoms and adsorbates, field emission is the preferred technique for measurement of the energetic properties of the surface. The effect of an applied field on the rate of electron emission was described by Fowler and Nordheim [65] and is shown schematically in Fig. Vlll 5. In the absence of a field, a barrier corresponding to the thermionic work function, prevents electrons from escaping from the Fermi level. An applied field, reduces this barrier to 4> - F, where the potential V decreases linearly with distance according to V = xF. Quantum-mechanical tunneling is now possible through this finite barrier, and the solufion for an electron in a finite potential box gives... 

Loesch H J and Remscheid A 1990 Brute force in molecular reaction dynamics a novel technique for measuring steric effects J. Chem. Phys. 93 4779-90... 

Lewis J W, Tilton R F, Einterz C M, Milder S J, Kuntz I D and Kliger D S 1985 New technique for measuring circular dichroism changes on a nanosecond time scale. Application to (carbonmonoxy)myoglobin and (carbonmonoxy)hemoglobin J. Rhys. Chem. 89 289-94... 

Molecular chirality is most often observed experimentally through its optical activity, which is the elfect on polarized light. The spectroscopic techniques for measuring optical activity are optical rotary dispersion (ORD), circular di-chroism (CD), and vibrational circular dichroism (VCD). 

The previous discussion demonstrates that measurement of precise isotope ratios requires a substantial amount of operator experience, particularly with samples that have not been examined previously. A choice of filament metal must be made, the preparation of the sample on the filament surface is important (particularly when activators are used), and the rate of evaporation (and therefore temperature control) may be crucial. Despite these challenges, this method of surface ionization is a useful technique for measuring precise isotope ratios for multiple isotopes. Other chapters in this book discuss practical details and applications. 

The deterrnination of impurities in the hehum-group gases is also accompHshed by physical analytical methods and by conventional techniques for measuring the impurity in question (93), eg, galvanic sensors for oxygen, nondispersive infrared analysis for carbon dioxide, and electrolytic hygrometers for water. 

Frequency-Modulation Spectroscopy. Frequency-modulation spectroscopy (tins) is a high sensitivity null-background infrared technique for measuring absorbances down to 10 with fast acquisition speeds. Fms involves frequency-modulating a laser source at COq to produce a carrier frequency having sidebands at cJq where is an integral multiple of the modulation frequency. Dye lasers and many other single-line sources can... 

Textile fibers must be flexible to be useful. The flexural rigidity or stiffness of a fiber is defined as the couple required to bend the fiber to unit curvature (3). The stiffness of an ideal cylindrical rod is proportional to the square of the linear density. Because the linear density is proportional to the square of the diameter, stiffness increases in proportion to the fourth power of the filament diameter. In addition, the shape of the filament cross-section must be considered also. For textile purposes and when flexibiUty is requisite, shear and torsional stresses are relatively minor factors compared to tensile stresses. Techniques for measuring flexural rigidity of fibers have been given in the Hterature (67—73). 

X-ray fluorescence spectrometry is a technique for measuring the elemental composition of samples. The basis of the technique is the relationship between the wavelength or energy of the emitted incoherently scattered x-ray photons and the atomic number of the element. This relationship estabHshed in 1913 is... 

For dilute systems it can be assumed that Gm, Em, and Pl are constant, and it normaUv is assumed that the interfacial area a of the packing is constant and is equal to the value that would exist without reaction. This last assumption needs careful consideration, since different methods for measuring a may give different results. Sharma and Danckwerts [Br Chem. Eng., 15(4), 522 (1970)] have reviewed various techniques for measuring interfacial areas. 

Shock-wave data have seen most applications in the measurement of density at high pressure. Other properties of compressed condensed materials whose measurements are discussed in this chapter include sound speed and temperature. Review articles by Grady (1977), Yakushev (1978), Davison and Graham (1979), Murri et al. (1974), Al tshuler (1965), and Miller and Ahrens (1991) summarize experimental techniques for measuring dynamic yielding. 

When bubbler systems are used for collection, the gaseous species generally undergoes hydration or reaction with water to form anions or cations. For example, when SOj and NH3 are absorbed in bubblers they form HSO3 and NH4, and the analytical techniques for measurement actually detect these ions. Table 13-1 gives examples of gases which may be sampled with bubbler systems. 

Other techniques for measuring flow through the compressor include ... 

The technique for measurement which is most easily interpreted is the inversion-recovery method, in which the distribution of the nuclear spins among the energy levels is inverted by means of a suitable 180° radiofrequency pulse A negative signal is observed at first, which becomes increasingly positive with time (and hence also with increasing spin-lattice relaxation) and which... 

There are several techniques for measuring P and A, and a common one is discussed below. 

NRA is an effective technique for measuring depth profiles of light elements in solids. Its sensitivity and isotope-selective character make it ideal for isotopic tracer experiments. NRA is also capable of profiling hydrogen, which can be characterized by only a few other analytical techniques. Future prospects include further application of the technique in a wider range of fields, three-dimensional mapping with microbeams, and development of an easily accessible and comprehensive compilation of reaction cross sections. 

In this last chapter we cover techniques for measuring surfece areas, surfece roughness, and surface and thin-fdm magnetism. In addition, the effects that sputter-induced surface roughness has on depth profiling methods are discussed. 

Today dynamic SIMS is a standard technique for measurement of trace elements in semiconductors, high performance materials, coatings, and minerals. The main advantages of the method are excellent sensitivity (detection limit below 1 pmol mol ) for all elements, the isotopic sensitivity, the inherent possibility of measuring depth profiles, and the capability of fast direct imaging and 3D species distribution. 

Recent development of techniques for measuring the rates of very fast reactions has permitted absolute rates to be measured for some fundamental types of free-radical reactions. Some examples of absolute rates and values are given in Table 12.2. 

Another useful technique for measuring the rates of certain reactions involves measuring the quantum yield as a function of quencher concentration. A plot of the inverse of the quantum yield versus quencher concentration is then made Stern-Volmer plot). Because the quantum yield indicates the fraction of excited molecules that go on to product, it is a function of the rates of the processes that result in other fates for the excited molecule. These processes are described by the rate constants (quenching) and k (other nonproductive decay to ground state). 

It is seen that the value of (H) is completely dependent on the diffusivity of the solute in the mobile phase, the column radius and the linear velocity of the mobile phase. The simple uncoated open tube can clearly be used to determine the diffusivity of any solute in any given solvent (the mobile phase). This technique for measuring diffusivities will be discussed in a later chapter. 

Freitas dos Santos, L.M., Livingston, A.G., Membrane attached biofilms novel technique for measurement of biofilm thickness, density and diffusivity, Proc. lAWQ Conf. Workshop on Biofilm Structure, Growth and Dynamics - Need for New Concept , Noordwijkerjout, The Netherlands, August 1995. 

A technique for measuring an organization s products, services, and operations against those of its competitors, resulting in a search for best practice that will lead to superior performance. 

The competitive method employed for determining relative rates of substitution in homolytic phenylation cannot be applied for methylation because of the high reactivity of the primary reaction products toward free methyl radicals. Szwarc and his co-workers, however, developed a technique for measuring the relative rates of addition of methyl radicals to aromatic and heteroaromatic systems. - In the decomposition of acetyl peroxide in isooctane the most important reaction is the formation of methane by the abstraction of hydrogen atoms from the solvent by methyl radicals. When an aromatic compound is added to this system it competes with the solvent for methyl radicals, Eqs, (28) and (29). Reaction (28) results in a decrease in the amount... 

The solubility of various gases in ionic liquids is extremely important in evaluating ILs as solvents for reactions, separations, and materials processing. There are a number of viable techniques for measuring gas solubilities in ILs, including the... 

The classic chemical technique for measuring the degree of unsaturation in diene polymers is iodometry (iodine value) [102]. Kubo et al. [103] extensively measured the iodine value to determine the amount of residual double bonds present in the HNBR. However, this method exhibited significantly poorer precision as compared with IR and NMR spectroscopies [99-101]. Acid... 

At its simplest, mass spectrometry (MS) is a technique for measuring the mass, and therefore the molecular weight (MW), of a molecule. In addition, it s often possible to gain structural information about a molecule by measuring the masses of the fragments produced when molecules are broken apart. 

Integration (Section 13.10) A technique for measuring the area under an NMR peak to determine the relative number of each kind of proton in a molecule. Integrated peak areas are superimposed over the spectrum as a "stair-step" line, with the height of each step proportional to the area underneath the peak. 

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