Parallelism Mechanics

Wingert, A., Litcher, M.D., and Dubowsky, S., On the kinematics of parallel mechanisms with bi-stable polymer actuators, demonstrated on the website http //scripts.mit.edu/ robots/robots/publications/ papers /2002 06 Win LicDub. pdf... 

An alternative, possibly parallel, mechanism for cis-trans isomerization122 has been resurrected by single crystal experiments.123 During studies of double... 

There is now known to be a second mechanism allowing competition between association and reaction, which can be termed the parallel mechanism. In this... 

Surface nucleation and the surface spiral mechanism are parallel mechanisms. Consequently the growth rate will be equal to the sum of the rates of these two mechanisms, and in extreme cases approximately equal to the rate of the faster one among them. 

A formal synthesis of ( )-Eseroline (69) via a 3-aza-4-oxa-Cope rearrangement was reported. An iV-aryl A-hydroxycarbamate was reacted with 2-phenylsulfanylpropanoic acid to yield the O-acylhydroxamic acid derivative 65, R = H that rearranged in the presence of potassium bis(trimethylsilyl)amide. The [3,3] and [3,5] rearrangement products, respectively 66 and 67, were formed (equation 22). If the para-substituted hydroxamic acid 65, R = OCOBu-t is used, no [3,5] rearrangement product is observed and the [3,3] rearrangement product 68 is the only product formed (equation 23). The authors proposed two parallel mechanisms, a concerted pathway and an ionic mechanism by an ion-pair recombination. 

A parallel mechanism has been indentified in the case of polymerisation of p-methoxystyrene by C7H7 SbCl where the corresponding methanolysis product... 

In diglyme or 2-hydroxyethanol, perfluoropropyl vinyl ether [355 R = F(CF2)30] reacts with sodium carbonate to give (356 same R) which on heating at 113-132 °C gives rise to (357 same R) and (358 same R) via parallel mechanisms.319... 

The uncatalysed Belousov-Zhabotinsky (B-Z) reaction between malonic acid and acid bromate proceeds by two parallel mechanisms. In one reaction channel the first molecular products are glyoxalic acid and carbon dioxide, whereas in the other channel mesoxalic acid is the first molecular intermediate. The initial reaction for both pathways, for which mechanisms have been suggested, showed first-order dependence on malonic acid and bromate ion.166 The dependence of the maximal rate of the oxidation of hemin with acid bromate has the form v = [hemin]0-8 [Br03 ] [H+]12. Bromate radical, Br02, rather than elemental bromine, is said to play the crucial role. A mechanism has been suggested taking into account the bromate chemistry in B-Z reactions and appropriate steps for hemin. Based on the proposed mechanism, model calculations have been carried out. The results of computation agree with the main experimental features of the reaction.167... 

It is noted, however, that both of the above CaF2 and Ti02 nanoceramics had some amount of porosity. This may account for an apparent soft behavior related to the superplastic deformation at low temperature, which does not yet reveal the plastic deformation characteristics in nanoceramics. Localized superplastic deformation under cyclic tensile fatigue tests was observed by Yan et al. on 3Y-TZP nanoceramics at room temperature [25], The micromechanism behind this phenomenon is argued to be essentially governed by grain-boundary diffusion. The contribution of dislocation slip might be in operation as a parallel mechanism to develop slip band-like microfeatures. 

There is evidence of a parallel mechanism which forms polymers with vinyl end-groups without hydride as an intermediate via /3-hydrogen abstraction. 

Since the classic papers by Ingold and his co-workers,110, 111 nitration has for a long time been considered as the standard electrophilic substitution. Many orientation and relative rate data on the nitration of both carbocyclic and heterocyclic substrates have been accumulated and the results have been generalized as valid for all electrophilic substitutions. As a matter of fact, this popularity is partially undeserved nitration is a complicated reaction, which can occur by a multiplicity of parallel mechanisms.112 In particular, in the case of the very reactive substrates that five-membered heterocycles are, two complications may make meaningless both kinetic measurements and competitive experiments.113 (i) Due to the great reactivity of both partners the encounter limiting rate may be achieved in this case, of course, all the substrates react at the same rate and the effect of structure on the reactivity cannot be studied. (ii) Nitrous acid, always present in traces, may exert an anticatalytic effect in some cases and a markedly catalytic effect in others with a very reactive substrate, nitration may proceed essentially via nitrosa-tion, followed by oxidation. For these reasons, the nitration data must be handled with much caution. 

This result is in sharp contrast to what is predicted by a parallel mechanism. The parallel mechanism predicts that similar kinetics should be observed for both and 0° emissions both should rise with the decay of the F state, and decay with the 7.8 ns emission lifetime. 

The most remarkable and central observation of these experiments is the direct characterization of the emission kinetic curves for the T[, 0 and 0° transitions and the observation of the 10b transition following excitation at T7 of the aniline(N2)1 cluster (see Figure 5-7). The pumped state, an intermediate state populated by IVR, and two bare molecule product states populated by the IVR/VP process are observed. These data are consistent with, and therefore provide strong evidence in support of, the serial IVR/VP mechanism applied to clusters containing a polyatomic chromophore. A parallel mechanism simply cannot explain the observed results. 

This approach has been taken for the reaction of chlorinated ethenes with Zn° [125,165] and Fe° [88,166], resulting in separate rate constants for all the reactions shown in Fig. 3. Care must be taken in using these parameters in predictive modeling, however, as it is not yet known how sensitive the relative values of these rate constants are to pH, thickness and composition of the oxide film, etc. The same caution applies where the approach represented by Eq. (25) is used to describe parallel mechanisms of transformation. For example, it has recently been reported that several experimental factors influence the relative contributions of dissociative electron transfer, hydrogen atom transfer, and reductive elimination to the dechlorination of carbon tetrachloride and TCE by Fe° [177],... 

The results showed that the parallel mechanism had a better correlation coefficient than the consecutive mechanism. The coke compound would be more likely formed from the cumene by parallel mechanism at low conversions of cumene cracking because the partial pressure of cumene would be much greater than that of the products. 

Correlation plots of the parallel mechanism and the combined mechanism are shown in Figure 2. The parallel mechanism can be considered as a reasonable deactivation mechanism. This k K.L parameter can be expressed as c c... 

Parallel mechanisms exist to produce CO2 on reduced catalyst... 

The curves plotted on Fig la illustrate the variation of the rate of site blockage inside the pore, calculated on the assumption that coke precursors arise by a simple parallel mechanism, through surface transformations of intermediates [AZ].. The plots below on Fig. lb show the corresponding fractions of blocked sites. The curves plotted on all the figures represented, refer to values of the parameters D- 0.001 [cm /s], P (gas) = 0.72, — 0.4. The curve labels 1, 2 and 3 are relevant to time intervals characterized by the dimensionless parameters tl=0.14 t2 = 0.5, t3 = 1.0. 

Figure L Profiles relevant to simple parallel mechanism of coke formation a - rate of blocking the active sites versus normalized distance from the pellet centre b - fraction of blocked sites versus normalized distance from the pellet centre ...

In view of the uncertainty in determining whether single or dual site mechanisms controlled the dehydrogenation reaction, simple single site La ngmuir-Hinshel wood expressions for parallel and series coking were used to fit the experimental cokinjg data. For a parallel mechanism. 

E will be different from 1 only if R4 is small relative to / 2, resulting in a bulk concentration of c — 0 and in a real parallel mechanism of the enhancement. The advantage of the concept of the enhancement factor as defined by eq 33 is the separation of the influence of hydrodynamic effects on gas-liquid mass transfer (incorporated in Al) and of the effects induced by the presence of a solid surface (incorporated in E ), indeed in a similar way as is common in mass transfer with homogeneous reactions. The above analysis shows that an adequate description of mass transfer with chemical reaction in slurry reactors needs reliable data on ... 

The third assumption above is that methanol chemisorbs at lower potentials essentially solely to give the chemisorbed intermediate(s), with only a negligible quantity of charge being associated with either any parallel oxidation pathway or with further conversion of the intermediate to C02. This problem was first tackled by Breiter [27-30], who suggested a parallel mechanism rather than a serial one at lower potentials, with the formation of a second active intermediate in a scheme of the form... 

Also, for the Fe(n)-induced degradation of the antimalarial sulfonyl dioxocin 227 (an analogue of yingzhaosu A), a parallel mechanism was proposed with the difference that the carbon-centered radical 235, an analogue of 223, instead of undergoing polymerization, gives well-defined monomeric products. Thus, the cleavage of the peroxide... 

The DSA technique allows for the calculation of the storage and loss components of the resin modulus from the composite response using a simple parallel mechanical model ... 

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