High variability

Note that in liquid phase chromatography there are no detectors that are both sensitive and universal, that is, which respond linearly to solute concentration regardless of its chemical nature. In fact, the refractometer detects all solutes but it is not very sensitive its response depends evidently on the difference in refractive indices between solvent and solute whereas absorption and UV fluorescence methods respond only to aromatics, an advantage in numerous applications. Unfortunately, their coefficient of response (in ultraviolet, absorptivity is the term used) is highly variable among individual components. 

The effectiveness of the approach is demonstrated on two rqjresentative NDT techniques intapretation of data acquired with an ultrasonic rail inspection system and interpretation of eddy-current data from heat exchangers in (petro-)chemical industry. The results show that it is possible to provide a high level of automation in combination with efficient operator support for highly variable NDT measurements where up to now use of automated interpretation was only limited. 

In addition to the many applications of SERS, Raman spectroscopy is, in general, a usefiil analytical tool having many applications in surface science. One interesting example is that of carbon surfaces which do not support SERS. Raman spectroscopy of carbon surfaces provides insight into two important aspects. First, Raman spectral features correlate with the electrochemical reactivity of carbon surfaces this allows one to study surface oxidation [155]. Second, Raman spectroscopy can probe species at carbon surfaces which may account for the highly variable behaviour of carbon materials [155]. Another application to surfaces is the use... 

Vitamins A, D, and E are required by mminants and, therefore, their supplementation is sometimes necessary. Vitamin A [68-26-8] is important in maintaining proper vision, maintenance and growth of squamous epitheHal ceUs, and bone growth (23). Vitamin D [1406-16-2] is most important for maintaining proper calcium absorption from the small intestine. It also aids in mobilizing calcium from bones and in optimizing absorption of phosphoms from the small intestine (23). Supplementation of vitamins A and D at their minimum daily requirement is recommended because feedstuffs are highly variable in their content of these vitamins. 

In general, the geometric properties of the natural fibers are highly variable from fiber to fiber, both within a given lot and among lots of the same fiber type. In the synthetic fibers, the geometric properties are extremely uniform in view of the production control possible in a chemical plant but not in an agricultural product. 

Direct conversion of natural gas to Hquids has been actively researched. Process economics are highly variable and it is unclear whether direct natural gas conversion technologies are competitive with the estabUshed indirect processes. Some emerging technologies in this area are presented herein. 

The composition of natural gas at the wellhead depends on the characteristics of the reservoir and is highly variable with respect to both the constituents present and the concentrations of these constituents. Compositions of various natural gases are given in Table 4. 

Catalytic Incinerators. Catalytic incinerators, often used to remove hydrocarbons from exhaust gas streams, are more compact than direct-flame incinerators, operate at lower temperatures, often require Htfle fuel, and produce Httle or no NO from atmospheric fixation. However, the catalytic bed must be preheated and carefliUy temperature controlled. Thus these are generally unsuited to intermittent and highly variable gas flows. 

Apatite and other phosphorites constitute a substantial resource of rare earths. The REO content is highly variable and ranges from trace amounts to over 1%. Apatite- [1306-05-4] rich tailings of the iron ore at Mineville, New York, have been considered a potential source of yttrium and lanthanides. Rare-earth-rich apatites are found at the Kola Peninsula, Russia, and the Phalaborwa complex in South Africa. In spite of low REO content apatites could become an important source of rare earths because these are processed in large quantities for the manufacturing of fertilisers (qv). 

Economic Aspects. Prices for pyromeUitic acid were about 14/kg in 1994. The dianhydride sold for about 19—25/kg depending on purity, and prices of the dianhydride ground to a fine 3-p.m size were 2/kg higher (153). Production amounts are not released and are dictated by market needs. The use of some multipurpose units to make this product means that the amounts produced are highly variable. 

Historically, the use of xanthines has been hampered by poor aqueous solubiUty, rapid but highly variable metaboHsm, and the existance of a low therapeutic index. SolubiUty problems were partially solved by the preparation of various salt forms, eg, aminophylline. However, it was since recognized that the added base in aminophylline only increases solubiUty by increasing pH and thus does not affect the rate of absorption from the gut (65). Thus, in more recent medical practice, theophylline is commonly dispensed in anhydrous form and aminophylline is only recommended for iv adrninistration. 

Constmction and dem olition (C D) debris is a potentiahy large source of recyclables. However, as of 1995, generation rates and ferrous scrap content were not weh estabUshed and estimates were highly variable. Eerrous materials in C D debris are typicahy reinforcing bars, wire mesh, and stmctural steel. Some of the scrap is sold for recycling once concrete is effectively removed and the scrap is sized to specification (17). 

Economic Aspects. Most hydrogen sulfide is made and used captively or sold by pipeline at prices which are highly variable, depending on locahty. Production ia the United States exceeds 1.1 X 10 t/yr-It has been estimated that 2.4 x 10 t/yr of sulfur are recovered from H2S-containing refinery streams and 1.8 x 10 t/yr of sulfur are recovered from H S-containing natural gas (120). 

Because of its low neutron absorption, zirconium is an attractive stmctural material and fuel cladding for nuclear power reactors, but it has low strength and highly variable corrosion behavior. However, ZircaHoy-2, with a nominal composition of 1.5 wt % tin, 0.12 wt % iron, 0.05 wt % nickel, 0.10 wt % chromium, and the remainder zirconium, can be used ia all nuclear power reactors that employ pressurized water as coolant and moderator (see... 

If the wastewater flow and strength are highly variable, as in a batch process chemical plant, a variable-volume basin with a variable inflow and a constant outflow is employed to equalize both flow and strength. 

The identification of PCB residues in fish, wildlife, and human tissues has been reported since the 1970s (9—13,20—26). The results of these analytical studies led to the ultimate ban on further use and production of these compounds. The precise composition of PCB extracts from biota samples is highly variable and depends, in part, on the specific analyte and the commercial PCB preparations associated with a contaminated area (14). PCBs found in a composite human milk sample from Michigan (26) were highly complex, and the congener composition and their relative concentrations did not resemble any of the commercial PCB preparations. This fact raises obvious problems with regard to the ha2ard assessment of PCB mixtures (27). 

The composition of dairy substitutes is highly variable and generally represents the least-cost formulation consistent with consumer acceptance of the product. These imitations invariably have lower fat and protein levels than the dairy products that they are made to resemble. The gross compositions of filled milk, meUorine, synthetic milk, sour cream, coffee whiteners, whipped toppings, and cheese are Hsted in Table 10. A comparison of the composition of certain dairy products and their substitutes is presented in Table 11. 

Land cost, a part of the direct plant cost, is placed in a separate capital category because it is not depreciable. Land cost is site-specific and highly variable. 

Solid-Fluid Equilibria The phase diagrams of binai y mixtures in which the heavier component (tne solute) is normally a solid at the critical temperature of the light component (the solvent) include solid-liquid-vapor (SLV) cui ves which may or may not intersect the LV critical cui ve. The solubility of the solid is vei y sensitive to pressure and temperature in compressible regions where the solvent s density and solubility parameter are highly variable. In contrast, plots of the log of the solubility versus density at constant temperature exhibit fairly simple linear behavior. 

Detonation arresters are typically used in conjunction with other measures to decrease the risk of flame propagation. For example, in vapor control systems, the vapor is often enriched, diluted, or inerted, with appropriate instrumentation and control (see Effluent Disposal Systems, 1993). In cases where ignition sources are present or pre-dic table (such as most vapor destruct systems), the detonation arrester is used as a last-resort method anticipating possible failure of vapor composition control. Where vent collec tion systems have several vapor/oxidant sources, stream compositions can be highly variable and... 

Sulfides are intermixed with iron oxides and hydroxides on carbon steels and cast irons. The oxides are also produced in the corrosion process (Reaction 6.6). Although theoretical stoichiometry of 1 to 3 is often suggested between sulfide and ferrous hydroxide, empirically the ratio of iron sulfide to ferrous hydroxide is highly variable. Sulfide decomposes spontaneously upon exposure to moist air. Additionally, corrosion-product stratification is marked, with sulfide concentration being highest near metal surfaces. 

Make a list, based on your own observations, of selected examples of components and structures made from cement and concrete. Discuss how the way in which the materials are used in each example is influenced by the low (and highly variable) tensile strength of cement and concrete. 

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