Cross-over designs defined

Catalytic reactors can roughly be classified as random and structured reactors. In random reactors, catalyst particles are located in a chaotic way in the reaction zone, no matter how carefully they are packed. It is not surprising that this results in a nonuniform fiow over the cross-section of the reaction zone, leading to a nonuniform access of reactants to the outer catalyst surface and, as a consequence, undesired concentration and temperature profiles. Not surprisingly, this leads, in general, to lower yield and selectivity. In structured reactors, the catalyst is of a well-defined spatial structure, which can be designed in more detail. The hydrodynamics can be simplified to essentially laminar, well-behaved uniform fiow, enabling full access of reactants to the catalytic surface at a low pressure drop. 

Dimensionless equations - some empirical and some with theoretical bases - are often used in chemical engineering calculations. Most dimensionless numbers are usually called by the names of person(s) who first proposed or used such numbers. They are also often expressed by the first two letters of a name, beginning with a capital letter for example, the well-known Reynolds number, the values of which determine conditions of flow (laminar or turbulent) is usually designated as Re, or sometimes as The Reynolds number for flow inside a round straight tube is defined as dvp p, in which d is the inside tube diameter (L), V is the fluid velocity averaged over the tube cross section (LT ), p is the fluid density (ML" ), and p is the fluid viscosity (ML T" ) (this is defined... 

A field shielded pixel structure is used. The cross-section of the active-matrix stack is shown in Fig. 14.6. The first four layers, defining the TFT, are identical with the stack presented in Section 14.2. The rows of the display are processed on the first metal level whereas the columns are processed on the second metal level. In the field-shielded pixel design, the pixel electrode is defined in a third metal level of gold, resulting in a six-mask process. The pixel pad overlaps the storage capacitor, TFT, and column lines with a 6 pm thick polyvinylphenol layer acting as inter-layer dielectric. The optical aperture thereby increases to over 95%. The TFT channel length (L) and width (W) are 5 pm and 140 pm, respectively. 

Metal deposition in a catalyst pellet yields a characteristic deposition profile that is determined by the pellet and pore size of the catalyst particle, since the mass transport of metal bearing species is controlled by diffiision [7], For convenience, many research groups have defined a simple parameter to characterize the deposition profile. In the present publication, this parameter is designated Qv and has been defined in the experimental section. High Qv means uniform deposition over the whole cross section of the catalyst pellet, whereas low Qv means that the deposition of metals mainly takes place in the outer layer of the catalyst particle. 

Here dS is a surface element of the lump, n its inner normal, is the unit vector in the direction of the solid angle element dQ, The integration is over the solid angle to the inside of the body and over its total siuface. So is the total macroscopic cross section in the lump formerly designated by 2, and f is the mean chord length in the absorber. Finally, To is defined as... 

Olefin metathesis is a reaction that is over fifty years old and has been developed over this time period from a process nm at high temperatures with ill-defined catalysts by unknown mechanisms to a process that can be conducted imder nuld conditions with designed catalysts by mechanisms that occur by established steps. Olefin metathesis, and the related alk3me metathesis, fully cleaves carbon-carbon double and triple bonds and reforms these bonds to generate new alkenes and alkynes. The reaction is often under equilibrium control, but certain classes of reactions can be conducted in a selective fashion that is controlled by relative rates or thermod)mamic preferences. This reaction can open strained rings to form polymers or small dienes. It can close small rings and macrocycles by a reaction that is driven by the expulsion of ethylene that makes the reaction favored entropically or by running in an open system under non-equilibrium conditions. It can also be run as a "cross metathesis" to form imsymmetrical alkenes when the steric or electronic properties of the two alkenes properly match. 

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