Masking Effects

The masking of the normal reaetions of simple ligands, such as the nitro, cyano, and ammonia groups, by coordination to a metal is a phenomenon encountered early by a chemist. One of the first examples of masking in a chelate complex was reported, signifieantly, in biological journals. It involves the protection by copper ion of the a-amino group in ornithine and lysine  

Partial protection of the — NHj group by copper ion results in a fiftyfold decrease in the rate of the ring-closure reaction  

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Flavor-Masking Deodorant. In addition to its use as a constituent of perfume compositions, vanillin is also useful as a deodorant to mask the unpleasant odor of many manufactured goods. As a masking agent for numerous types of ill-smelling mass-produced industrial products, particularly those of synthetic mbber, plastics, fiber glass, inks, etc, vanillin finds extensive use. It is often the most inexpensive material for the amount of masking effect it provides. Only traces are required for this purpose as the odor of vanillin is perceptible in dilutions of 2 x 10 mg/m of air. Cmde vanillin is acceptable for such purposes. 

In the case of polymer deposition, it has been pointed out [293] that the masking effect at the scale edges may be less important than mutual adhesion of fibres in the yarn, since the thickness of the polymer film (0.1 pm) is much less than the average height of scale edges (1 pm). This effect is more analogous to spot-welding. 

To illustrate the masking effects that arise from intraparticle and external mass transfer effects, consider a surface reaction whose intrinsic kinetics are second-order in species A. For this rate expression, equation 12.4.20 can be written as... 

A. Legin, A. Rudnitskaya, D. Clapham, B. Seleznev, K. Lord, and Y. Vlasov, Electronic tongue for pharmaceutical analytics quantification of tastes and masking effects. Anal. Bioanal. Chem. 380, 36-45 (2004). 

K. Kulpa, Z. Czekala, Short Distance Clutter Masking Effects in Noise Radars , Proceedings of the International Conference on the Noise Radar Technology. Kharkiv, Ukraine, 21-23 October 2003. 

Urine volume increased steadily during the first three months before levelling off (Table IV). Neither urine volume nor urine pH were significantly affected by the level or type of dietary protein or by their interaction (Tables IV and V). For pH, this could be a masking effect resulting from combining different proteins which individually may appreciably affect urine pH. 

Still-gauging methods are adequate for only the largest leaks. The accuracy of most tank-installed liquid level gauges is usually /s in. at best. A product loss reflected by a 0.062-in. level drop for a 100-ft-diameter tank translates to a 306 gal/day leak. If this Vi6-in. drop in product level is not discernible from the masking effects of fluid expansion, losses in excess of 2650 barrels annually will go undetected. At, for example, 20 per barrel, this loss amounts to over 53,000 for a single tank. Most importantly, the associated liability risks of groundwater contamination could involve much greater potential costs. 

The exact mechanism by which HIER works is unknown. It is thought to reverse the masking effects of formaldehyde fixation and routine tissue processing. Hydrolytic-proteolytic cleavage of formaldehyde-related crosslinks, unfolding of inner epitopes, as well as the extraction of calcium ions from coordination complexes with proteins are among the hypothesized mechanisms (13-15). 

Let us now consider featnres of trap employment in cases, which are free from masking effects. 

Alternatively (or initially) the mixture is treated as a whole and tested in its crude state. The advantage of this strategy includes the relevancy of the tested sample to its environmental counterpart, decreased potential for artefact formation, and inclusion of combined effects of chemicals in the mixture. Moreover if the mixture is representative of others in its class (e.g., diesel emissions from different sources would share certain characteristics), it may be possible to extrapolate results across samples. This method also circumvents the labor-intensive process of individual testing of multiple chemicals. But sometimes a complex mixture is too cytotoxic to be tested directly in a bioassay. Furthermore, it may be incompatible with the test system because of the physical matrix. Other disadvantages include the inability to specify the constituent of the mixture responsible for the toxicity, as well as potential masking effects (e.g., the masking of mutagenicity by cytotoxicity). 

In view of the fact that irradiation odor was exhibited by mixtures which varied widely in the relative proportions of methional, 1-nonanal, and phenylacetaldehyde, it was somewhat puzzling to determine that irradiation odor production in enzyme-inactivated nonirradiated slurries depended on adding these compounds in 20 2 1 amounts, respectively. Although no attempt was made to determine whether these proportions could be varied within limits, the general impression was that variations probably would not result in irradiation odor. It is therefore suspected that factors such as masking effects by other components must be operative in the concurrently processed isolates to allow them to exhibit irradiation odor. 

Let us now consider some features of the use of traps in cases that are free of masking effects. 

Figure 2.1 (according to [Zwicker, 1982]) shows a masked threshold derived from the threshold in quiet and the masking effect of a narrow band noise (1 kHz, 60 dB sound pressure level masker not indicated in the figure). All signals with a level below... 

More advanced models try to estimate a time-dependent Signal-to-Mask-Ratio (SMR) for each band used in the coder. Because the knowledge about masking effects is limited at this time and because different theories about additivity of masking or the effects of tonality exist, there is no such thing as the correct psychoacoustic model . 

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