In contrast, Howarth [12] derived J,(w) for the 3t model corresponding to p = 3, where three independent motions are assumed to be superposed for the overall motion of the C—H vector as shown in Fig. 3.6. Namely, the C—H vector undergoes diffusional rotation about the Z axis in the Oi frame, whereas the zi axis librates within a cone whose axis is parallel to the Z2 axis in the O2 frame. Moreover, the Z2 axis undergoes the isotropic random reorientation in the laboratory frame. Although an empirical approximation was made in the previous calculation, we obtained the following equations by the exact mathematical derivation [8-10] ... [Pg.61]

Fig. 3.6. A schematic representation of the 3t model describing the motion of the C—H internuclear vector. |

motional mode of the internuclear vector (C-H vector) to describe the magnetic relaxation of macromolecules have been proposed. Examples are the ellipsoidal or spherical rotational models where an ellipsoidal or spherical molecule undergoes independent diffusional rotations around the long and short axes and the C-H vectors are embedded in the ellipsoidal or spherical molecule.Here consider one model including three independent motions as a pertinent model for long-chain molecules (referred to as the 3t model). In this model, schematically depicted in Fig. 6, the... [Pg.199]

Although we have started with a particular 3t model, the result becomes equivalent to the general case that three independent random motions with sufficiently different correlation times are involved, in spite of the model adopted. [Pg.201]

As mentioned above, the relaxation phenomena of macromolecules seldom follow the single correlation time theory dictated by eqn (36). In such cases, a wide distribution is usually introduced in the correlation time. However, as discussed elsewhere, the distribution of correlation time not only fails to explain the temperature dependencies of Ti, T2 and the NOE of the non-crystalline components observed by scalar decoupled NMR on linear polyesters and polyethylene, but also overlooks the intrinsic motion of long-chain molecules. On the contrary, the 3r theory dictated by eqn (41) was found to be very effective to describe such temperature dependencies of the relaxation parameters. Irrespectively of whether the motional mode assumed in the 3t model for the C-H vector is really true, the concept that the C-H vector in macromolecules involves plural independent diffusional motions with discretely different correlation times is very useful to explain the magnetic relaxation phenomena of macromolecules, as will be shown later. [Pg.201]

Transient Heat Conduction. Our next simulation might be used to model the transient temperature history in a slab of material placed suddenly in a heated press, as is frequently done in lamination processing. This is a classical problem with a well known closed solution it is governed by the much-studied differential equation (3T/3x) - q(3 T/3x ), where here a - (k/pc) is the thermal diffuslvity. This analysis is also identical to transient species diffusion or flow near a suddenly accelerated flat plate, if q is suitably interpreted (6). [Pg.274]

A first principle mathematical model of the extruder barrel and temperature control system was developed using time dependent partial differential equations in cylindrical coordinates in two spatial dimensions (r and z). There was no angular dependence in the temperature function (3T/30=O). The equation for this model is (from standard texts, i.e. 1-2) ... [Pg.493]

Both characteristic X-ray line and continuous spectra were used to evaluate the performances of the resists. To determine exposure parameters (i.e. sensitivity and contrast) irradiations were carried gut in this study using the aluminum Kot- 2 emission line at 8.3t A generated by means of a modified Vacuum Generators Limited model EG-2 electron beam evaporation gun. The resist samples were exposed through a mask (A) consisting of a range of aluminum foils of different thicknesses supported on an absorbing nickel frame in order to vary the X-ray flux. [Pg.279]

Fig. 3.13 Step function model for the gas-phase reaction that starts at x = X and ends 3t X =... |

The choice of cluster model size is critical. It is essential that the cluster model be neutral and not subjected to optimization constraints. Both these restrictions have been shown to lead to artifactual behavior. Small clusters cannot be used to investigate concentration dependence, and if this dependence is to be considered, a larger model must be used. Similarly, a cluster should not be so small that it artificially constrains the spatial extent of the adsorbate complex or transition state. The acidity of the cluster—quantified by the deprotonation energy—is found to change as a function of cluster size. The deprotonation energy of a 3T atom cluster terminated with hydro-... [Pg.86]

The ratio A Cp D)/A Cp(N D) should be a measure of the relative burial of hydrophobic surface areas in the transition and folded states, if the hydrophobic model is correct. The ratio is 0.51 for CI2, compared with a value of /3T of 0.6,27 which is a measure of the overall change in surface area (equation 18.9). [Pg.612]

Within the frame of the simplified energy transfer model ( S 3T Ln ), eq. (11)... [Pg.238]

With this change to the Jacobian generator and a user supplied routine to evaluate the extents of reaction and at the user s option the partial derivatives 3r/3x, 3r/3l, and 3R/3T along with the ECES generated subroutines, this form of process can be successfully modeled. This type of model has been successfully used to simulate proprietary processes developed by our clients. [Pg.317]

Let us now consider how the limitations imposed by the size of these clusters may influence the results for the chemical reaction step. In spite of the fact that only one type of acid site can be modeled by the 3T and 5T clusters, it must be remembered that the difference in acidic strength of the different sites is much smaller than the activation energy of most reactions. Thus, in the absence of other effects, the fact that the clusters used cannot distinguish different... [Pg.57]

M. R. McHenry and B. Laub, Ablative Radome Materials Thermal-Ablation and Erosion Modelling( 3t]i Intersociety Conf. on Environmental Systems,... [Pg.7]

The percolation probability (q) for the lattice models is defined as the probability that a given site (or bond) belongs to an infinite open cluster (47). It is fundamental to percolation theory that there exists a critical value qc of q such that 9(q) = 0 3t q < qc, and (q) > 0 if > qc. The value qc is called the critical probability or the percolation threshold. Mathematical methods of calculating this threshold are so far restricted to two dimensions, consistent with the experience in the field of phase transitions that three-dimensional problems in general cannot be solved exactly (12,13). Almost all quantitative information available on the percolation properties of specific lattices has come from Monte Carlo calculations on finite specimens (8,11,12). In particular. Table I summarizes exactly and approximately known percolation thresholds for the most important two- and three-dimensional lattices. For the bond problem, the data presented in Table I support the following well-known empirical invariant (8)... [Pg.11]

© 2019 chempedia.info