Hall factor

Finally, the reliability of the various activation energy measurements should be judged. The TDH measurement is unambiguous as long as the Hall factor [Eq. (A17)] is either close to unity or else is not very temperature dependent (or both), and if mixed conductivity effects are either small or can be taken into account. Usually, neither of these problems is very important as far as a major change in the slope of the Arrhenius plot is concerned. The emission experiments, on the other hand, lead to an apparent activation energy of Ei0 + Eai, where Eai is given by the relationship [Pg.122]

This is the well-known Hall factor or r factor, which, in the low magnetic field limit, makes the Hall mobility different from the conductivity mobility. To see this relationship, consider the limit (or B- 0). Then... 

It is apparent from our discussion so far that the Hall factor is sometimes difficult to calculate and even more difficult to measure. However, it rarely varies by more than 20% from a value of 1.2 (Stillman et al., 1970 Debney and Jay, 1980). Such a situation is entirely tolerable, especially when one realizes the range of semiconductor carrier concentrations (103-1020 cm-3 in our laboratory) that can be measured by this simple technique. 

Equations 1-4 can easily be set up on a PC and used to simulate or fit temperature-dependent mobility data. In an n-type sample, the only undetermined parameter is the acceptor concentration Na, so usually Na is varied to give the best fit to the data. (For this fit, the approximate carrier concentration, nn = 1/Re, can be used when n is required in the various scattering formulas.) Then, the Hall factor r = can be calculated at... 

It was supposed, that each of the phases is characterized by two parameters the ohmic conductivity <7o(r) and the Hall factor p(r). However each of properties CTo(r) and p(r) from the conductivity tensor (285) admit of only two values Co = cii and p [5, in the first phase, cto = ct2 and p = p2 in the second phase. The essence of ideas described in [118,119] consists in linear transformations from the old fields (j,E) to new fields (j,E ) such that the macroscopic properties of the new system are equivalent to those of the original system. These transformations can be applied only to a two-dimensional system, since they do not then change the laws governing a direct current ... 

The transformations (286) allow one [118,119] to calculate the effective galvanomagnetic properties of a 2D inhomogeneous medium when conductivity fluctuates only, and the Hall factors of the components are equal that is, cti / c>2, Pi = p2. If we apply complementarity—that is, in the first phase (cr. p ) we have cr = cr2. p = — p2, and in the second phase (a2, p2) we have a a. p = — pj—then we shall obtain the following results for the effective Hall properties ... 

Figure 40. The dependence of the Hall coefficient (a) and the relative effective conductivity (b) on the concentration and on the magnetic field when the Hall factors of components differs essentially, and their conductivities are equal (x = 1, y = 10-10)).

Now the effective conductivity ia the direction of the electric field is <7/(1 + /5 ), ie, the scalar conductivity reduced by a factor of (1 + /5 ) by the magnetic field. Also, the electric current no longer flows in the direction of the electric field a component j exists which is perpendicular to both the electric and magnetic fields. This is the Hall current. The conductivity in the direction of the Hall current is greater by a factor of P than the conductivity in the direction of the electric field. The calculation of the scalar conductivity starts from its definition ... 

The resulting overall energy balance for the plant at nominal load conditions is shown in Table 3. The primary combustor operates at 760 kPa (7.5 atm) pressure the equivalence ratio is 0.9 the heat loss is about 3.5%. The channel operates in the subsonic mode, in a peak magnetic field of 6 T. AH critical electrical and gas dynamic operating parameters of the channel are within prescribed constraints the magnetic field and electrical loading are tailored to limit the maximum axial electrical field to 2 kV/m, the transverse current density to 0.9 A/cm , and the Hall parameter to 4. The diffuser pressure recovery factor is 0.6. 

Table 9-51 fflves typical values of such factors for carbon steel installations taken from the data of D. R. Woods Financial Decision Making in the Process Industiy, Prentice Hall, Englewood Cliffs, NJ, 1975, p. 184). Auxiliaries and site preparation are given as factors of the delivered-equipment cost in Table 9-51, whereas C. A. Miller [Chem. 

Decompositions may be exothermic or endothermic. Solids that decompose without melting upon heating are mostly such that can give rise to gaseous products. When a gas is made, the rate can be affected by the diffusional resistance of the product zone. Particle size is a factor. Aging of a solid can result in crystallization of the surface that has been found to affect the rate of reaction. Annealing reduces strains and slows any decomposition rates. The decompositions of some fine powders follow a first-order law. In other cases, the decomposed fraction x is in accordance with the Avrami-Erofeyev equation (cited by Galwey, Chemistry of Solids, Chapman Hall, 1967)... 

T he target level for particles in the air of a paper printing machine hall is 0..5 mg/m, but in some cases the level can be as low as one-tenth of this number. Tissue paper mills are very complicated in this respect. Depending on the process and other factors, the particle level can be as high as 10 mg/m but levels as low as 1 mg/m- can be found. The targets ate selected between those figures depending on the type of paper mill. 

Obviously, the sensors have to be installed in a correct and representative place in the process. Determining an optimal installation of sensors for measuring environmental conditions in large halls is not a simple task. Many different factors have to be taken into account. The main place where a certain climate is to be maintained is given priority. Secondly, the influence of infiltration and radiation from surrounding surfaces must be considered. 

In many industrial halls, conduction inro the ground is a major factor for heat loss. Therefore, an adequate modeling of the floor slab and the underlying, thermally active, soil is very crucial for reliable simulation resuirs. In this case, the soil model in the TRNSYS model was established using results from an additionally performed finite-element program analysis. 

Hall, D.G., 1972. Thermodynamic treatment of some factors affecting the interaction between colloidal particles. Journal of the Chemical Society Faraday Transactions, 68(2), 2169-2182. 

Ridley, A.J., Hall, A. (1992). The small GTP-binding protein rho regulates the assembly of focal adhesions and actin stress fibers in response to growth factors. Cell 70,389-399. 

Brew BJ, Halman M, Catalan J, Sacktor N, Price RW, Brown S, Atkinson H, Clifford DB, Simpson D, Torres G, Hall C, Power C, Marder K, Me Arthur JC, Symonds W, Romero C (2007) Factors in AIDS dementia complex trial design results and lessons from the abacavir trial. PLoS Clin Trials 2(3) el3... 

At the present time it is difficult to single out any one factor that could be held ultimately responsible for cell death after cerebral ischaemia. Recent studies, however, have provided us with sufficient evidence to conclude that free radical damage is at least one component in a chain of events that leads to cell death in ischaemia/reperfiision injury. As noted earlier in this review, much of the evidence for free radicals in the brain and the sources of free radicals come from studies in animals subjected to cerebral ischaemia. Perhaps the best evidence for a role for free radicals or reactive oxygen species in cerebral ischaemia is derived from studies that demonstrate protective effects of antioxidants. Antioxidants and inhibitors of lipid peroxidation have been shown to have profound protective effects in models of cerebral ischaemia. Details of some of these studies will be mentioned later. Several reviews have been written on the role of oxygen radicals in cerebral ischaemia (Braughler and HaU, 1989 Hall and Btaughler, 1989 Kontos, 1989 Floyd, 1990 Nelson ef /., 1992 Panetta and Clemens, 1993). 

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