Migration definition

Lastly, the positive charge is neutralized via loss of a proton, giving the alkene lanosterol. There is no obvious energy advantage in such tertiary-to-tertiary cation changes, but it must be appreciated that this is an enzyme-catalysed reaction, and the enzyme plays a crucial role in the reactions that occur. These hydride and methyl migrations definitely do occur, as demonstrated by isotopic labelling studies. 

As seen from Fig. 5, upon absoption of photons with the energy hv > Eg, an electron and hole centres are formed. They migrate to different sites on the PC surface, thus becoming spatially separated. Note, that what solid state physisists call surface electron and hole centers, in fact are some definite chemical species with strong reducing and oxidizing... 

By definition the partial current density ij is the number of charges that in unit time cross the unit cross-sectional area due to the migration of ions j that is,... 

Salts such as silver chloride or lead sulfate which are ordinarily called insoluble do have a definite value of solubility in water. This value can be determined from conductance measurements of their saturated solutions. Since a very small amount of solute is present it must be completely dissociated into ions even in a saturated solution so that the equivalent conductivity, KV, is equal to the equivalent conductivity at infinite dilution which according to Kohlrausch s law is the sum of ionic conductances or ionic mobilities (ionic conductances are often referred to as ionic mobilities on account of the dependence of ionic conductances on the velocities at which ions migrate under the influence of an applied emf) ... 

Assume that both the initial substances and the products of the electrode reaction are soluble either in the solution or in the electrode. The system will be restricted to two substances whose electrode reaction is described by Eq. (5.2.1). The solution will contain a sufficient concentration of indifferent electrolyte so that migration can be neglected. The surface of the electrode is identified with the reference plane, defined in Section 2.5.1. In this plane a definite amount of the oxidized component, corresponding to the material flux J0x and equivalent to the current density j, is formed or... 

Molecular diffusion (or self-diffusion) is the process by which molecules show a net migration, most commonly from areas of high to low concentration, as a result of their thermal vibration, or Brownian motion. The majority of reactive transport models are designed to simulate the distribution of reactions in groundwater flows and, as such, the accounting for molecular diffusion is lumped with hydrodynamic dispersion, in the definition of the dispersivity. 

There is no precise definition for the frequently used term application fastness of a pigment. It usually refers to the behavior exhibited by a finished product used in accordance with the specifications. The term may thus refer to a print, a coated object, or a plastic product, and the list of features ranges from properties such as lightfastness and weatherfastness to migration fastness and fastness to solvents. In this context, there is a certain amount of emphasis on features which play a role in connection with packaging materials and packed articles. 

The definition of a food additive in Section 201(s) of the Federal Food, Drug, and Cosmetic Act, as amended ( the Act ) refers to substances whose intended use results directly or indirectly in the substance becoming a component of food. The FDA refers to direct food additives as those added to a food to accomplish an intended effect. Indirect additives are those that unintentionally, though predictably, become components of food. Components of plastic packaging materials that can migrate to food are indirect additives. 

Internal resistance relates to the diffusion of the molecules from the external surface of the catalyst into the pore volume where the major part of the catalyst s surface is found. To determine the diffusion coefficients inside a porous space is not an easy task since they depend not only on the molecules diffusivity but also on the pore shape. In addition, surface diffusion should be taken into account. Data on protein migration obtained by confocal microscopy [8] definitely demonstrate that surface migration of the molecules is possible, even though the mechanism is not yet well understood. All the above-mentioned effects are combined in a definition of the so-called effective diffusivity [7]. 

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