Systemic considerations head, applications

To illustrate the use of the simplified analysis in design, we compare the actuation sequence analyzed above to a six-step three-chamber sequence also reported in the literature [6], and shown in Fig. 5. The analysis is similar to the three-step sequence, except for steps 1 and 6, where an actuator closes with no closed actuators between it and either the inlet or the outlet. By rule 5, the expelled fluid is divided evenly between the inlet and the outlet. Two considerations make application of the simplified model more problematic in this case. The first is the all-actuators-open configuration in step 1. If there is significant head across the puirp, this may produce an unmodeled backflow. The second is the assumption mentioned above, that the flow splits evenly in step 1 and 6. If the external system flow resistances as seen from the input and output are different, or if there is significant head, the split wiU not be even. These issues aside, we find that a volume 2V is pumped in each six-step cycle. 

A review is given of the application of Molecular Dynamics (MD) computer simulation to complex molecular systems. Three topics are treated in particular the computation of free energy from simulations, applied to the prediction of the binding constant of an inhibitor to the enzyme dihydrofolate reductase the use of MD simulations in structural refinements based on two-dimensional high-resolution nuclear magnetic resonance data, applied to the lac repressor headpiece the simulation of a hydrated lipid bilayer in atomic detail. The latter shows a rather diffuse structure of the hydrophilic head group layer with considerable local compensation of charge density. 

The [2 + 2] photodimerization of a, j8-unsaturated sulfones is correctly viewed as a photoreaction of alkenes, rather than the sulfone group, and this aspect has been reviewed recently by Reid, as part of a wider survey of the photoreaction of O- and S-heterocycles. The topic continues to attract considerable interest and a few recent examples, as well as some synthetic applications, will be discussed here. Much of the photodimerization work has been carried out on the benzo[fc]thiophene (thianaphthene) 1,1-dioxide system. For example. Porter and coworkers have shown that both 3-carboxybenzo[i]thiophene 1,1-dioxide (65) and its methyl ester give only the head-to-head (hth), anti dimer (66) on irradiation in ethanol. In a rather unusual finding for such systems, the same dimer was obtained on thermal dimerization of 65. Similar findings for a much wider variety of 3-substituted benzo[fi]thiophene 1,1-dioxides have been reported more recently by Geneste and coworkers . In the 2-substituted analogs, the hth dimer is accompanied by some of the head-to-tail (htt), anti dimer. The formation of the major dimer appears to proceed by way of an excited triplet and the regiochemistry observed is in accord with frontier MO theory. 

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