Analog systems

While there had been concern about the reliability of computer systems, they are currently receiving wide acceptance and are fast replacing analog systems. 

The argument that an analog system dedicated to each measurement parameter provides better protection than a scanning system simply is not true. An analog system has inherent time delays that result in finite... 

The relative importance of the potential catalytic mechanisms depends on pH, which also determines the concentration of the other participating species such as water, hydronium ion, and hydroxide ion. At low pH, the general acid catalysis mechanism dominates, and comparison with analogous systems in which the intramolecular proton transfer is not available suggests that the intramolecular catalysis results in a 25- to 100-fold rate enhancement At neutral pH, the intramolecular general base catalysis mechanism begins to operate. It is estimated that the catalytic effect for this mechanism is a factor of about 10. Although the nucleophilic catalysis mechanism was not observed in the parent compound, it occurred in certain substituted derivatives. 

In a more general approach toward pentacyclic heteroaromatics from tricyclic ketones, treatment of the N-methylated derivative of 112 with p-tolylhydrazine, followed by Fischer indolization of the resulting phenylhydrazone in a mixture of trifluoroacetic acid and acetic acid, produced only a low yield of 114, although this method proved to be considerably mrae efficient for synthesis of analogous systems containing other heteroatoms than nitrogen (98SC1239). 

J. C. Giddings, Plate height of nonuniform cliromatographic columns. Gas compression effects, coupled columns and analogous systems . Anal. Chem. 35 353-356 (1963). 

In Chapter 14, one of the least-used applications of TLC and PLC is described, namely inorganics and organometallics. These separations in the analytical mode often require quite unusual stationary phases (e.g., inorganic ion exchangers and impregnated and mixed layers) combined with a variety of diverse mobile phases. This means that the use of the analogous systems in the preparative mode represents an unusually difficult challenge. 

A wide range of catalytic materials have been investigated for the selective catalytic reduction of NOx. For stationary emissions, NH3-SCR using vanadium-tungsten oxides supported on titania is the most used method however, when there is a simultaneous emission of NO and NOz (in tail gas from nitric acid plants), copper-based zeolites or analogous systems have been proven to be preferable [31b], In fact, there are two main reactions for NH3-SCR ... 

The problems are of both industrial and purely scientific importance, and they can also be approached qualitatively and quantitatively. The reaction prediction question, for example, might be directed not so much at what the products might be, but rather how likely the reaction might be in comparison with an analogous system. The scope of the problems is indeed vast, and Figs. 2 and 3 give some indication of the width of the spectrum of organic synthesis and reactivity. 

In such cases, the binding energy on the low-spin surface may of course be significant. There may also be analogous systems in which the spin-state splitting is much smaller or indeed the ground state of the metal fragment is low-spin, and for those... 

The samples had dry matter over 85% and were ground to pass through a 1 mm screen and then packed in a quartz-windowed cup. The unit was demonstrated at the 1971 Illinois State Fair. After the success of this instrument, Neotec (later Pacific Scientific, then NIR Systems, then Perstorp, then FOSS) built a rotating (tilting) filter instrument. Both instruments were dedicated, analog systems, neither of which was considered user-friendly. ... 

An analogous system to the cation sensors is the use of optically nonactive anion ionophores together with a pH-sensitive chromophore for the anion sensing. In this system, simultaneous extraction of H+ and anion X- from the aqueous solution into an organic phase results in protonation of the chromophore anion C, e.g. 

Table 2. Activation energies for the reaction of protonated benzyl methyl ketoximes and their sulfur analogous systems calculated by MP2/6-31G. ... 

This approximate value was taken as an average from analogous systems. 

Fig. 5.15. Block diagram of the differential analog system architecture for high operation temperatures...

Fig. 5.20. Discrepancy between ambient temperature and bulk-chip temperatm-e as a function of the microhotpiate temperatm-e for the differential analog system chip (DIL package)...

Kang et al. first studied the wetting properties of 4 -methyl- (MMB) and 4 -hy-droxy-4-mecaptobiphenyls (HMB) as an analog system for the ahphatic HUT/DDT mixed monolayer [97]. In Fig. 9.10 the results of analog wetting experiments for the two systems are compared. 

Metal-catalyzed allylic substitution reactions have been a mainstay of synthetic chemistry because of their ability to proceed irreversibly and with high selectivity [42]. It is also feasible, however, to produce analogous systems that are completely reversible and nonselective, or ideally situated for use in DCC. These are essentially metal-catalyzed transesterification reactions, with the added feature of potentially providing stereochemical scrambling (and selection) as well as constitutional variation. An early example of this was provided in 2000 by Kaiser and Sanders [43]. In the absence of a template, reaction of diallyl diacetate 22 with a dicarboxylic acid in the presence of catalytic Pd(0) produced a negligible amount of the cycfized compound 23 (Fig. 1.9). However, when templated with 1,3-bis(4-pyridyl) benzene, yield of the cyclic structure increased to roughly 10%, independent of the dicarboxylic acid used. 

Though the formation of the unsaturated lactones (102) and (103) would be readily explained by base-catalyzed elimination of nitrite from the nitrolactone precursors — a reaction observed in several analogous systems 42,54,55) attempted conversions of (99)—(101) with bases to the corresponding unsaturated compounds, (102) and (103) respectively, were not successful. A rationalization of these results is not possible at present. 

The ring-chain tautomerism of tetrahydro-l,3-oxazines is very sensitive to the stability differences, the substituents and the ring-fusion effect (Section IV,A). It also reveals a considerable stability difference in favor of the cis isomers. In the reactions of the cis- and trans-2-amino-l-cyclohexanols, as compared with the hydrindane analog systems, where the heteroatoms form an oxazolidine ring cis- or tra 5-fused with cyclohexane, the corresponding stability differences were again found to be in favor of the cis isomer (93JOC1967). 

Estimated by comparison of limited data with an analogous system in the correlation. 

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