Heterogenous, definition

Several small clinical trials have suggested that total intravenous anesthesia with propofol reduces the incidence of postoperative nausea and vomiting and results in shorter emergence times. However, a systematic review (52) and a meta-analysis (53) have shown that most studies were small, did not have follow-up for more than 6 hours postoperatively, and were sponsored by industry. The results were difficult to combine, owing to heterogeneous definitions of postoperative nausea and vomiting. 

An important difference between nonlinear lattice vibration models and molecular systems is that the latter have heterogeneity in their models, while the former do not. It would be difficult to specify the term heterogeneity definitely, but one can say that the FPU model is a homogeneous extreme and contains any seeds of heterogeneity in the model, because it is composed of identical particles that interact with each other via a common potential function. On the contrary, molecular systems of our interest sometimes have internal degrees of freedom, or are composed of several species of molecules or potentials. The purpose of this section is to show that introducing heterogeneity into the system leads to an alternative view that possibly solves several controversial points addressed in the previous section. 

Definition of the association (or avidity) constant for such multivalent antibody—antigen reactions must consider not only the heterogeneity of the antibodies and the antigen determinant site(s), but also an apparent additive effect of binding two antigen molecules to a single antibody. Such effects lead... 

When a process is continuous, nucleation frequently occurs in the presence of a seeded solution by the combined effec ts of mechanical stimulus and nucleation caused by supersaturation (heterogeneous nucleation). If such a system is completely and uniformly mixed (i.e., the product stream represents the typical magma circulated within the system) and if the system is operating at steady state, the particle-size distribution has definite hmits which can be predic ted mathematically with a high degree of accuracy, as will be shown later in this section. 

Micromechanics — The study of composite material behavior wherein the interaction of the constituent materials is examined in detail as part of the definition of the behavior of the heterogeneous composite material. 

Thus far, Ft has never found a definite position in Ea vs. correlations, more for the uncertainty in the reliability of its pzc than for its work function. On the other hand, Pt is a highly heterogeneous metal and the fact that only polycrystalline surfaces have been used in double-layer studies has not helped remove suspicions. According to Frumkin s data,10,14 the pzc ofpc-Pt is around 0.2 V(SHE) (in acidic solution). If this value is introduced into Fig. 14 (the 0 of pc-Pt is around 5.5 eV),22,65 343,856 865,866 the point of Pt would fall far distant from the line of mercurylike metals and near the line of d-metals. 

The yield of a gas-solid heterogeneous reaction depends not on the total time that molecules spend in the reactor but on the time that they spend on the catalyst surface. The contact time distribution provides a standardized measure of times spent in the absorbed state. A functional definition is provided by the following equation applicable to a first-order, heterogeneous reaction in an isothermal reactor ... 

Another problem that required solving was the moderate yield obtained in the cyclopropanation reaction when only one equivalent of styrene was used. By increasing the amount of styrene up to its use as the reaction solvent, a noticeable effect on the selectivities was observed when laponite was used as the support [58]. The active role of the clay support was definitely estabhshed when the results in homogeneous and heterogeneous phases were compared (Table 9). These effects involved the reversal of the trans preference in solution to the cis preference with the laponite-supported catalyst in styrene, and also a reversal in the absolute configuration of the major cis enantiomer ob-... 

Adt M, Marone G Human heart mast cells a definitive case of mast cell heterogeneity. Int Arch Allergy 29 Immunol 1995 106 386. 

By definition all catalysts must be heterogeneous or homogeneous within and across these two categories there are other classifications that are important to green chemistry. Most important among these are ... 

Attempts to determine how the activity of the catalyst (or the selectivity which is, in a rough approximation, the ratio of reaction rates) depends upon the metal particle size have been undertaken for many decades. In 1962, one of the most important figures in catalysis research, M. Boudart, proposed a definition for structure sensitivity [4,5]. A heterogeneously catalyzed reaction is considered to be structure sensitive if its rate, referred to the number of active sites and, thus, expressed as turnover-frequency (TOF), depends on the particle size of the active component or a specific crystallographic orientation of the exposed catalyst surface. Boudart later expanded this model proposing that structure sensitivity is related to the number of (metal surface) atoms to which a crucial reaction intermediate is bound [6]. 

Let us start with a definition. Semiconductor chemical sensor is an electronic device designed to monitor the content of particles of a certain gas in surrounding medium. The operational principle of this device is based on transformation of the value of adsorption directly into electrical signal. This signal corresponds to amount of particles adsorbed from surrounding medium or deposited on the surface of operational element of the sensor due to heterogeneous diemical reaction. 

A disperse system is defined as a heterogenous, two-phase system in which the internal (dispersed, discontinuous) phase is distributed or dispersed within the continuous (external) phase or vehicle. Various pharmaceutical systems are included in this definition, the internal and external phases being gases, liquids, or solids. Disperse systems are also important in other fields of application, e.g., processing and manufacturing of household and industrial products such as cosmetics, foods, and paints. 

The technical terms homogeneity and inhomogeneity defined in analytical chemistry must be distinguished from the physicochemical concept of homogeneity and heterogeneity (Danzer and Ehrlich [1984]). Whereas the thermodynamical definition refers to morphology and takes one-phase-or multi-phase states of matter as the criterion, the analytical-chemical definition is based on the concentration function... 

In many cases, however, the interfacial area is not known, particularly when one is dealing with a heterogeneous catalytic reaction involving a liquid phase and a solid catalyst. Consequently, the following definitions of the reaction rate are sometimes useful. 

In the treatment of rate expressions for heterogeneous catalytic reactions the definition of local reaction rates in terms of interfacial areas (3.0.10) is appropriate. 

Vocabulary of Terms Used in Reactor Design. There are several terms that will be used extensively throughout the remainder of this text that deserve definition or comment. The concepts involved include steady-state and transient operation, heterogeneous and homogeneous reaction systems, adiabatic and isothermal operation, mean residence time, contacting and holding time, and space time and space velocity. Each of these concepts will be discussed in turn. 

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