Steady state orientation factor

The steady-state orientation factor increases sigmoidally with the electric field on Fig. 8 for =100, and the inset shows that at low field, i.e., far from saturation, in agreement with experiments.44... 

One exception to that is apparently the steady-state orientation factor measured by LD. Our BRM predicts that this orientation factor should be slightly molecular-size dependent in the vicinity of the band-inversion phenomenon, but otherwise size-independent. Experiments showed a fairly strong size dependence up to large molecular sizes, even if these large molecules had a size-independent mobility. This is possibly due to an intra-tube effect which can induce local fluctuations in the average tube orientation but, since the tube stays oriented, retain the molecular-size independence of the mobility. 

IV.6.1 Steady-State Orientation Using Eq. (I6c) for , the steady-state tube orientation factor is found to be S 0 /15. This simple result predicts that the degree of orientation of the molecule increases as the second power of E, but is molecular-size independent. Experimentally,44 ld showed that but the orientation factor was also observed to be molecular-size dependent45 for E=10 V/cm, A=1.0% and iC= 40-200 kbp, it was reported that SaL . 

The dashed line on Fig. 10 shows a typical experimental 5,46 curve (only schematic here). The orientation factor S goes first through an overshoot at time with S x )>S x ) j where x is the time needed to reach the steady-state orientation, and then through an undershoot at time un> before it reaches the steady-state orientation discussed in the previous subsection for Since the over- and under-shoots occur only for 0transient effects are not likely to change the mobility of DNA fragments in continuous field experiments. However, it has been reported that the overshoot time x may be related to the critical pulse duration used in certain pulse-field techniques. 5 This effect may thus be very important in this case. 

The FT model improves the predictions of the steady-state fiber orientation but has little effect on the strain at which the steady-state orientation occurs. In an attempt to control the rate of fiber reorientation, Sepehr et al., (2004) included a term to reduce the rate of fiber orientation termed the strain reduction factor or the slip coefficient. The slip coefficient, a, can be added to the FT model as follows,... 

The most common states of a pure substance are solid, liquid, or gas (vapor), state property See state function. state symbol A symbol (abbreviation) denoting the state of a species. Examples s (solid) I (liquid) g (gas) aq (aqueous solution), statistical entropy The entropy calculated from statistical thermodynamics S = k In W. statistical thermodynamics The interpretation of the laws of thermodynamics in terms of the behavior of large numbers of atoms and molecules, steady-state approximation The assumption that the net rate of formation of reaction intermediates is 0. Stefan-Boltzmann law The total intensity of radiation emitted by a heated black body is proportional to the fourth power of the absolute temperature, stereoisomers Isomers in which atoms have the same partners arranged differently in space, stereoregular polymer A polymer in which each unit or pair of repeating units has the same relative orientation, steric factor (P) An empirical factor that takes into account the steric requirement of a reaction, steric requirement A constraint on an elementary reaction in which the successful collision of two molecules depends on their relative orientation. 

This section deals with a single donor-acceptor distance. Let us consider first the case where the donor and acceptor can freely rotate at a rate higher than the energy transfer rate, so that the orientation factor k2 can be taken as 2/3 (isotropic dynamic average). The donor-acceptor distance can then be determined by steady-state measurements via the value of the transfer efficiency (Eq. 9.3) ... 

Wu P. and Brand L. (1992) Orientation Factor in Steady-State and Time-Resolved Resonance Energy Transfer Measurements, Biochemistry 31, 7939-7947. 

Example 9.3 Effectiveness factor for first-order irreversible reaction-diffusion system Consider a first-order reaction occurring on the pore walls of a catalyst with equimolar counter diffusion. Assume that isothermal conditions are maintained, and a catalyst with simple slab geometry is used (Figure 9.1). If the -coordinate is oriented from the centerline to the surface, the steady-state reaction diffusion equation for reaction A — B between reactant A and product B is... 

Wu P, Brand L. Orientation factor in steady-state and time-resolved resonance energy transfer measurements. Biochemistry 1992 31 7939-7947. 

The value of df represents the depolarization factor due to segmental motion of the donor (di ) or acc or (di ), but not the dqrolaiization due to overall rotational diffusion of the protein. Overall rotational diffusion is not important because it does not change the D-A orientation. The values of n and n are often taken as the steady-state and fundamental anisotropies, respectively, of the donor or acceptor. If the donor and acceptor do n ot rotate relative to each other during the excited-state lifetime, then di =di = 1.0, and = 0 and 1 1= 4. If both D and A ate independently and rapidly rotating over all space, = Km =. ... 

Suppose we consider any bimolecular reaction in solution, whatever its rate, and apply Pick s laws to the general case where activation energy and orientational factors are important as well as diffusion. Carrying through the calculation (see below. Chapter 3, Section 3.3.2), one finds that in the steady state the observed second-order rate constant k will be given by (in place of Equation (2.1)) the following equation ... 

In general, TC is low for plastics and the plastic s structure does not alter its value significandy. TC of plastics depends on several variables and cannot be reported as a single factor. But it is possible to ascertain the two principal dependencies of temperature and molecular orientation (MO). In fact, MO may vary within a product producing a variation in TC. It is important for the product designer and processor to recognize such a situation. Certain products require personal skill to estimate a part s performance under steady-state heat flow. 

Fig.9 Result of a computer simulation of the BRM Steady-state tube orientation factor as a function of the molecular size N (in segments) for three different field intensities 0=0.5, 1.0,...

Steady-state tube orientation factor as a function of the... 

Fig. 10. Mechanisms of steady-slqte kinetics of sugar phosphorylation catalyzed by E-IIs in a non-compartmentalized system. (A) The R. sphaeroides 11 model. The model is based on the kinetic data discussed in the text. Only one kinetic route leads to phosphorylation of fructose. (B) The E. coli ll " model. The model in Fig. 8 was translated into a kinetic scheme that would describe mannitol phosphorylation catalyzed by Il solubilized in detergent. Two kinetic routes lead to phosphorylation of mannitol. Mannitol can bind either to state EPcy, or EPpe,. E represents the complex of SF (soluble factor) and 11 and II in A and B, respectively. EP represents the phosphorylated states of the E-IIs. Subscripts cyt and per denote the orientation of the sugar binding site to the cytoplasm and periplasm, respectively. PEP, phosphoenolpyruvate.

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