Cooperativity, dynamics positive

To analyse the occurrence of an intermolecular cooperativity, the compatible blends of BPA-PC and TMBPA-PC offer quite a useful opportunity [17,26, 28]. The dynamic mechanical results [28] are shown in Fig. 32. At first, two peaks are observed. They are located in the temperature range of each component. However, a more precise examination of the peak positions shows that the blend composition affects the two peaks differently (Fig. 33). Indeed, the TMBPA-PC peak is unchanged, whereas a downward temperature shift is observed for the BPA-PC peak with increasing TMBPA-PC content. Actually, the temperature shift of the maximum does not correspond to a shift of the whole low-temperature peak, but it results from the disappearance of the high-temperature peak when increasing the TMBPA-PC content, as clearly shown in Fig. 34. 

Flavin-dependent le -transfer in enzymes and chemical model systems can he differentiated from 2e -transfer activities, i.e., (de)hydrogenation and oxygen activation, by chemical structure and dynamics. For le -transfer, two types of contacts are discussed, namely outer sphere for interflavin and flavin-heme and inner sphere for flavinr-fenedoxin contacts. Flavin is the indispensable mediator between 2e - and le -transfer in all biological redox chains, and there is a minimal requirement of three cooperating redox-active sites for this activity. The switch between 2e - and le -transfer is caused by apoprotein-dependent prototropy between flavin positions N(l)/0(2a) and N(5) or by N(5)-metal contact. 

Thus, 8 > 1 yields subdiffusion and 8 < 1 superdiffusion. Both cases imply memory. The condition 8 < 1 implies that a strong fluctuation in the positive direction is most probably followed by a fluctuation in the same direction. The condition 8 > 1, on the contrary, implies that after a positive fluctuation, a fluctuation in the opposite direction ensues. Both conditions are a form of memory. In conclusion, the dynamic approach to FBM is a nice way to create memory, with the memory of the variable being the signature of a coordinated and cooperative process, provided that 8 / 1. 

Another proving ground for mathematical modeling in cell signaling has been the dynamics of intracellular calcium. Spurred by the nonlinear nature of the calcium release mechanisms, which exhibit cooperativity and both positive and negative feedbacks, and by the availability of fluorescent dyes for... 

Positive pair-binding energies, and hence the effective attractive interaction between electrons, arc necessarily a core polarization effect. If all of the 60 valence electrons were treated as an inert Fermi sea, the net interaction between two electrons added to a given molecule would necessarily be repulsive there is no bound-state solution to the Cooper problem with purely repttlsive interactions. It is the dynamic interactions with the valence electrons that are crucial in producing overscreening of the purely bare repulsive interaction. Although the first-order term does not involve any virtual excitations, the second-order theory includes important core-polarization effects. 

The exact temperature of the phase transition in the experiments above is subject to some uncertainty, which we attribute to the stoichiometric variations in both the central atom of the counterion (P,As) and the type of the halide. The picture that emerges, however, is compatible with the full scope of experimental results a dynamic Jahn-Teller effect at high temperature, a structural phase transition in the 120-150 K range, and a distortion of the molecular ion in the low-temperature phase, arising from the positive synergy of the cooperative Jahn-Teller effect and the low symmetry of the environment. The static-to-dynamic transition does not coincide with the structural transition and its temperature depends on the detection method whereas ESR spectra are isotropic at room temperature, infrared lines are still split, indicating a distorted state on the time scale of the measurement. This... 

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