Relaxed state

The lower bound 0 in the integration refers to the time at which the first contact is made after attaining the fully relaxed state. The upper bound / is the actual time spent in the loading experiment when the load P(i) is recorded. 

Figure 9. A schematic representation of crossbridge orientation assumed from electron micrographs of insect flight muscle in relaxed and rigor states by Reedy et al. (1965). The crossbridge is thought to have an orientation of 90° to the thick filament axis in the relaxed state and an orientation of 45° to the thick filament axis in rigor.

One source of calcium ions, which cause contraction of smooth muscle in arterial walls, is inflow through ion-specific channels. So, the calcium blockers block the channels, limiting inflow of calcium and keeping muscle cells in relaxed states for a longer time. 

Figure 8.31 shows central sections of two original SAXS patterns of PEE 1000/4394 in strained and relaxed state. In the strained state (Fig. 8.31a) a 6-point-diagram is detected. During relaxation (Fig. 8.31b) a well-separated 4-point-diagram is observed. Interpretation of the patterns is restricted to description and speculation. 

In observing the time dependent changes in birefringence and stress-optical coefficient, for elongated samples at 25 C, it was found that the rate of crystallization of high trans SBR s was very much faster, some 10 times more rapid, than that for NR (8). This is consistent with the reported rates of isothermal crystallization for NR (2.5 hours at -26°C) and for 807. trans-1,4 polybutadiene (0.3 hours at -3°C) in the relaxed state (12). 

Here, u2,r is the polymer volume fraction in the relaxed state, which is defined as the state of the polymer immediately after crosslinking but before swelling. 

The model most often invoked to rationalize cooperative behavior is the MWC (Monod-Wyman-Changeaux), or concerted, model. This model is 1.5 times more complicated than the Michaelis-Menten model and took three people to develop instead of two. Most texts describe it in detail. In the absence of substrate, the enzyme has a low affinity for substrate. The MWC folks say that the enzyme is in a T (for tense or taut) state in the absence of substrate. Coexisting with this low-affinity T state is another conformation of the enzyme, the R (for relaxed) state, that has a higher affinity for substrate. The T and R states coexist in the absence of substrate, but there s much more of the T state than the R. This has always seemed backward, since one would expect the enzyme to be more tense in the presence of substrates when some work is actually required. In keeping with the tradition of biochemistry, the MWC folks obviously wanted this to be backward too (Fig. 8-8). 

An interesting idea is that in small arteries such as the rat basilar STOCs elicited by sparks can exert a negative feedback on the membrane potential of the smooth muscle syncytium (cells are linked by low resistance pathways) the hyperpolarization so produced will reduce Ca2+ entry through voltage-dependent Ca2+ channels. Thus, in pressurized arteries where the membrane potential is lower than in the relaxed state and there is significant Ca2+ influx into... 

If solvent (or environment) relaxation is complete, equations for the dipole-dipole interaction solvatochromic shifts can be derived within the simple model of spherical-centered dipoles in isotropically polarizable spheres and within the assumption of equal dipole moments in Franck-Condon and relaxed states. The solvatochromic shifts (expressed in wavenumbers) are then given by Eqs (7.3) and (7.4) for absorption and emission, respectively ... 

Equations (7.6) and (7.7) provide a means of determining excited dipole moments together with dipole vector angles, but they are valid only if (i) the dipole moments in the FC and relaxed states are identical, (ii) the cavity radius remains unchanged upon excitation, (iii) the solvent shifts are measured in solvents of the same refractive index but of different dielectric constants. 

One may consider the relaxation process to proceed in a similar manner to other reactions in electronic excited states (proton transfer, formation of exciplexes), and it may be described as a reaction between two discrete species initial and relaxed.1-7 90 1 In this case two processes proceeding simultaneously should be considered fluorescence emission with the rate constant kF= l/xF, and transition into the relaxed state with the rate constant kR=l/xR (Figure 2.5). The spectrum of the unrelaxed form can be recorded from solid solutions using steady-state methods, but it may be also observed in the presence of the relaxed form if time-resolved spectra are recorded at very short times. The spectrum of the relaxed form can be recorded using steady-state methods in liquid media (where the relaxation is complete) or using time-resolved methods at very long observation times, even as the relaxation proceeds. 

According to the two-state model, the spectrum of the relaxed state has a mean frequency vR and is shifted relative to the spectrum of the initial state, which has a mean frequency vF. If relaxation does not occur during the process of emission (xR xF), the mean frequency of the fluorescence... 

Figure 2.5. Energy level diagram (top) and spectra (bottom) illustrating the two-state model of relaxation. The energy of the absorbed quantum is Av , and the energies of the emitted quanta are hvfl (unrelaxed) and hvF (relaxed). The fluorescence spectrum of the unrelaxed state (solid curve) is shifted relative to the absorption spectrum (dotted curve) due to the Stokes shift. The emission intensity from the unrelaxed state decreases and that from the relaxed state (dashed curve) increases as a result of relaxation.

J. R. Lakowicz and A. Baiter, Resolution of initially excited and relaxed states of tryptophan fluorescence by differential-wavelength deconvolution of time-resolved fluorescence decays, Biophys. Chem. 15, 353-360 (1982). 

The iFi terms are the fluorescence lifetimes of fractional contributions a, and the xRJ indicate decay constants due to solvent relaxation (or other excited-state processes) of fractional contribution Pj. The negative sign is indicative of a relaxation process (red shift). Usually, the relaxation process is approximated to a single relaxation time x R by assuming an initial excited state and a final fully relaxed state (see, e.g., Ref. 128). A steady-state fluo-... 

Photolysis of diazoaJkanes in liquid phase yields carbenes in a vibrationally relaxed state, since deactivation in solution immediately removes all excess vibrational energy. The addition of carbenes to the olefins, which results in nonstereospecific formation of cyclopropanes, must therefore result from the different multiplicity of carbenes — singlet or triplet. Since most of these multiplicity... 

Diagrammatic interpretation showing individual filaments in relaxed state... 

The decrease in the cytosolic Ca ion concentration reverses these changes, so that the actin-binding sites are concealed and the relaxed state of the muscle is restored. 

AP through the entire cell. If the AP fails, the muscle fiber remains in a relaxed state. 

FIGURE 2.18 Elongation of an elastomer as a function of applied force, stress, where A is the original relaxed state, B represents movement to full extension, C is the point at which the elastomer breaks, and D represents the force necessary to pull two separate pieces of elastomer apart. 

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