Involving two or more types

Interactions between chemically and structurally complementary macromolecules have usually a cooperative character. Probably, the formation of cooperative systems involving two (or more) types of bonds at the same time (e.g. of ionic and hydrogen bonds)63 is possible. It should be mentioned here that hydrophobic interactions play an important role in the stabilization of synthetic and natural polyelectrolyte complexes and also of complexes with hydrogen bonds. The contribution of either interactions may be different, depending on the chemical structure of the components of the polycomplex and the nature of the medium. 

The more challenging forms of tissue culture involve two or more types or animal cells grown simultaneously. Good progress has been made on skin replacements with products approved by the FDA Administration. Martin and Vermette (2005) discuss the reaction engineering aspects of tissue culture and conclude that the womb with its good mass transfer and essentially zero shear is ideal for growing complicated structures. 

The theoretical basis for electric breakdown in solids is still limited. Several types of breakdown in solids are recognized intrinsic breakdown, breakdown dependent on physical defect, thermal breakdown, discharge-dependent breakdown, failure by electrical treeing, and failure by water (electrochemical) treeing. Conditions and material characteristics determine the type of breakdown which takes place. Actual electrical breakdown may involve two or more types simultaneously or sequentially. 

A domino Diels-Alder reaction (the term was chosen from the well-known game) is a one-pot process involving two or more Diels-Alder reactions carried out under the same reaction conditions without adding additional reagents or catalyst such that the second, third, etc., cycloaddition is the consequence of the functionality generated in the previous reaction. A historical example is illustrated in Equation 1.28 [60]. This type of transformation is sometimes named tandem or cascade, but these terms seem less appropriate for describing a time-resolved transformation. 

Potentially hazardous reactions. Bretherick (1990) used a few general types of potentially hazardous reactions to classify the majority of exothermic reactions involving two or more components. By far the most common type is that involving an oxidant and an oxidizable material. The most common oxidant is air. Some materials will react so rapidly with air that ignition occurs. spontaneously. Finely divided metals or metal hydrides, or fully alkylated... 

The mechanical properties of a material describe how it responds to the application of either a force or a load. When this is compared to an area, it is called stress, another term for pressure. Three types of mechanical stress can affect a material tension (pulling), compression (pushing), and shear (tearing). Figure 15.27 shows the direction of the forces for these stresses. The mechanical tests consider each of these forces individually or in some combination. For example, tensile, compression, and shear tests only measure those individual forces. Flexural, impact, and hardness tests involve two or more forces simultaneously. 

In fact, we know only a few propagations which involve only a single elementary reaction. Usually we must consider two or more types of active centre, each of which can add monomer at a rate characterized by its own kp... 

There are very few known chemical reactions which fit precisely into this scheme of two consecutive first-order reactions, but all of the well-known schemes of radioactive decay which involve two or more consecutive steps are characterized precisely by this type of behavior. 

For reactions with non-simple pathways or networks, the formulas and procedures described so far are not valid. Any step involving two or more molecules of intermediates as reactants destroys the linearity of mathematics, and any intermediate that builds up to higher than trace concentrations makes the Bodenstein approximation inapplicable. Such non-simple reactions are quite common. Among them are some of the kinetically most interesting combustion reactions, detonations, periodic reactions, and reactions with chaotic behavior. However, a discussion of more than only the most primitive types of non-simple reactions is beyond the scope of this book. The reader interested in more than this is referred to another recent volume in this series [1], in which such problems are specifically addressed. 

All silica immobilized phase transfer catalysts previously reported involve two or more steps for the immobilization. Problems with preparations of this type include the difficulty in obtaining maximum functionality on the substrate and residual substrate bond intermediates which may interfere in final applications. The purpose of this work was to prepare well-characterized functionalized phase transfer catalysts that could be immobilized on siliceous substrates in a single step. As will be shown the preparation of functionalized onium catalysts proceeds readily. The route to facile immobilization of crown ether was not so direct. Avenues for high yield chemistry employing accessible or economic intermediates were not available. A new class of crown ethers which are readily functionalized during synthesis was developed. We have designated than "silacrowns". This report concentrates upon the properties and characterization of these new phase transfer catalysts. 

Hyphenated methods Methods involving the combination of two or more types of instrumentation the product is an instrument with greater capabilities than any one instrument alone. Hypothesis testing The process of testing a tentative assertion with various statistical tests. See t-test, F-test, Q-test, onA ANOVA. 

Salt type mixed oxides involving two or more insoluble oxides. 

By dehnition, a supramolecular device comprises more than one component, and this may well involve two or more photophysically active or redox centres. The nature of the interaction between these components will depend strongly on the nature of the bridge between them. In the case of two interacting metal centres of the type discussed above, we can distinguish three classes of behaviour, denoted class I, II and... 

Thennoplastics are heat softening materials which can be repeatedly heated, made mobile and then reset to a solid state by cooling. Under conditions of fabrication these materials can be moulded (shaped in a mould) by temperature and pressure. Examples of thermoplastics are more numerous than thermosets, e.g. polyethylene, polyvinylchloride, polystyrene, polypropylene, nylon, polyester, polyvinylidene chloride, polycarbonate. Thermoplastics may be further divided into homopolymers which involve one type of monomer, e.g. ethylene polymerised to polyethylene, and copolymers, terpolymers, etc., which involve two or more monomers of different chemical substances. Polymerisation producing thermoplastics and thermoset materials usually follows two basic chemical mechanisms, i.e. condensation and addition polymerisation. 

The fourth model of biphasic regulation (type IV) requires two inputs to affect the response rather than one as in the preceding cases. This is seen in combinatorial inhibition when a molecule binds with two or more interacting molecules to form a single functional complex as is the case with scaffold proteins. A second type rV receptor involves two or more interactions between an activator and the activated molecules for full activation. Examples of both biphasic regulation with scaffold protein concentrations and distributive activators are seen in the MAPk cascades. A third category of type IV biphasic regulation acts via immediate enzymatic feedback from the activated molecule onto the activator molecule. 

It is convenient to classify the different possible reaction schemes by using letters to signify the nature of the steps. E represents an electron transfer at the electrode surface, and C represents a homogeneous chemical reaction (10). Thus a reaction mechanism in which the sequence involves a chemical reaction of the product after the electron transfer would be designated an EC reaction. In the equations that follow, substances designated X, Y, and Z are assumed to be not electroactive in the potential range of interest. It is also convenient to subdivide the different types of reactions into (1) those that involve only a single electron-transfer reaction at the electrode and (2) those that involve two or more E-steps. 

Multiburner tests involve two or more burners simultaneously firing in a furnace. These types of tests are common in ethylene applications where one or more wall-fired burners on the furnace floor and several radiant wall burners are firing simultaneously. Thus, the furnace needs to be tall enough to approximate the dimensions of a cracking furnace. It is also common to test the radiant wall burner individually prior to the multiburner test. For this reason, small box type furnaces are available to accommodate the small firing rate of a horizontally installed radiant wall burner. 

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