Activation distance

Equations of this type are most often used by experimentalists to fit their data to theory,52"54 as indications of an exponential 7(E) dependence are numerous. Vervey55 has used a similar approach to consider the volume-limited processes of ionic migration and obtained the same equation. In order to explain deviations of experimental behavior from that predicted by Eq. (40), Vermilyea56 has also taken into consideration the effect of electrostriction modifying the activation distance for migrating ions and obtained the following equation for the ionic current flow ... 

A related effect has been described for IR spectroscopy - Surface Enhanced Infrared Absorption spectroscopy (SEIRA). However, as the enhancement factors are significantly lower than for SERS and both the required metal particle size and the activation distance between the target molecule and the particle are more than one order of magnitude smaller, no practically applicable SEIRA sensors have been demonstrated up to now. 

General activity Distance traveled Locomotor activity Rat Horner et al.192... 

Figure 11. The average sensitizer-activator distances vs. the concentration of the activator /-[SV[So] for Cu(I)Y exposed to oxygen. and [S]/[S ]...

The atoms and molecules in thin adsorption layers are so strongly bound that they are not freely movable and, in regard to adhesion physics, have become a part of the solid. Such layers smooth-out the surface roughnesses of solid particles resulting in a smaller active distance at the coordination points, thus increasing the adhesion force without the need to contact or penetrate each other. 

F Fresnel number min minimum sensitizer-activator distance... 

When the field contribution is written qaE, there is some question as to whether the effective field should not be some form of cavity field. Also, in the kinetic theory one might imagine that the activation distance would be larger than the distance from minimum to maximum potential energy, since the ion presumably starts its run from the other side of the potential-energy minimum. Finally, the effective charge on an ion may not correspond to that associated with the valency in the compound concerned. ... 

The chief one is that any model with independent metal and oxygen ion currents would be expected to display a rapid change with field in the ratio of the two currents unless one had a fortuitously close similarity between values of activation energies and activation distances, which is very unlikely to occur with more than one metal. 

Advani, Gottling, and Osman, " and also Hacskaylo " have observed a region of field where log(///o) = pE. This law would correspond to thermal promotion over a barrier whose activation distance (to borrow a useful term from the ionic-conduction terminology) is not dependent on field. Hacskaylo claims that the... 

W is the activation energy for the ionic transport, q - the ionic charge, a - the activation distance and jo - the constant, depending the nature of metal. The rest of the symbols have the usual meaning. 

The detector setup consists of four 256 x 256 pixel amorphous silicon technology sensor flat panels with 0.75 x 0.75 mm pixel size, having an active area of 192 x 192 mm [5j. These sensors are radiation sensitive up to 25 MeV and therefor well suited for detecting the LINAC radiation. The four devices are mounted onto a steel Irame each having the distance of one active area size from the other. With two vertical and two horizontal movements of the frame it is possible to scan a total area of about 0.8 x 0.8 m with 1024 x 1024 pixel during four independent measurements. 

High-current EC-50 betatron with maximal energy of accelerated electrons equaled to 50 MeV and radiation dose power 220 Gr/min on the distance of Im from the target [3] was made for experimental physical researches and activated analysis. 

A piezo-composite consists of a piezoelectric active phase and a passive plastic phase [2]. In the 1-3-configuration adopted in our case, piezoelectric rods parallely aligned in thickness direction are imbedded in a three-dimensional plastic matrix (Fig. 1). The distance between the rods has to be chosen inferior to the half wave length of the shear wave in the matrix material ensuring that the whole compound is vibrating as a quasi-homogeneous material. 

When an atom or molecule approaches a surface, it feels an attractive force. The interaction potential between the atom or molecule and the surface, which depends on the distance between the molecule and the surface and on the lateral position above the surface, detemiines the strength of this force. The incoming molecule feels this potential, and upon adsorption becomes trapped near the minimum m the well. Often the molecule has to overcome an activation barrier, before adsorption can occur. 

Figure A3.8.3 Quantum activation free energy curves calculated for the model A-H-A proton transfer reaction described 45. The frill line is for the classical limit of the proton transfer solute in isolation, while the other curves are for different fully quantized cases. The rigid curves were calculated by keeping the A-A distance fixed. An important feature here is the direct effect of the solvent activation process on both the solvated rigid and flexible solute curves. Another feature is the effect of a fluctuating A-A distance which both lowers the activation free energy and reduces the influence of the solvent. The latter feature enliances the rate by a factor of 20 over the rigid case.

The pathway model makes a number of key predictions, including (a) a substantial role for hydrogen bond mediation of tunnelling, (b) a difference in mediation characteristics as a function of secondary and tertiary stmcture, (c) an intrinsically nonexponential decay of rate witlr distance, and (d) patlrway specific Trot and cold spots for electron transfer. These predictions have been tested extensively. The most systematic and critical tests are provided witlr mtlrenium-modified proteins, where a syntlretic ET active group cair be attached to the protein aird tire rate of ET via a specific medium stmcture cair be probed (figure C3.2.5). 

The full ab-initio molecular dynamics simulation revealed the insertion of ethylene into the Zr-C bond, leading to propyl formation. The dynamics simulations showed that this first step in ethylene polymerisation is extremely fast. Figure 2 shows the distance between the carbon atoms in ethylene and between an ethylene carbon and the methyl carbon, from which it follows that the insertion time is only about 170 fs. This observation suggests the absence of any significant barrier of activation at this stage of the polymerisation process, and for this catalyst. The absence or very small value of a barrier for insertion of ethylene into a bis-cyclopentadienyl titanocene or zirconocene has also been confirmed by static quantum simulations reported independently... 

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