Forming Static Characteristics

OSITs based on pentacene thin films have been fabricated on TTO formed on glass substrafes. It is well known that the work function of TTO is con-frolled by the method used to clean its surface. OSITs were fabricated based on pentacene thin films wifh a high-work function ITO of 5.3 eV and a low-work function of 4.2 eV. The effect of the work function of ITO on the static characteristics of fhe OSITs was investigated using I-V measurements and ultraviolet photoemission spectroscopy (UPS) [34]. These results provided an important clue, in that the characteristics of the OSITs were strongly associated with the work function of ITO used as a source electrode. In general, the hole injection barrier at the organic semiconductor/metal interface is influenced by the work function of fhe metal. 

We can now collect together the various characteristics of a measurement system, except for hysteresis, and express the general model for the system in the form of a block diagram. Such a block diagram representation is shown in Figure 4. The dynamic and static characteristics are shown decoupled in the diagram. The dynamic characteristics will be discussed shortly. 

The information about cushion performance is most often transmitted in the form of characteristic cushion curves that relate the average deceleration to the static loading as a function of drop height, cushion thickness, temperature, and number of impacts (see Fig. 13.2). Computer programs that contain mathematical models of cushion curves for various types of foams, sometimes along with cost information, are also available. Relatively simple calculations then permit selection of an appropriate cushion thickness and load-bearing area that can reasonably be expected to provide adequate protection for a given product. 

All the foregoing pertains to sohds of approximately the same physical characteristics. There is evidence that sohds of widely different characleristics wih classify one from the other at certain gas flow rates [Geldart, Baeyens, Pope, and van de Wijer, Powder Technol., 30(2), 195 (1981)]. Two fluidized beds, one on top of the other, may be formed, or a lower static bed with a fluidized bed above may result. The latter frequently occurs when agglomeration takes place because of either fusion in the bed or poor dispersion of sticl feed solids. 

Rancidity measurements are taken by determining the concentration of either the intermediate compounds, or the more stable end products. Peroxide values (PV), thiobarbituric acid (TBA) test, fatty acid analysis, GC volatile analysis, active oxygen method (AOM), and sensory analysis are just some of the methods currently used for this purpose. Peroxide values and TBA tests are two very common rancidity tests however, the actual point of rancidity is discretionary. Determinations based on intermediate compounds (PV) are limited because the same value can represent two different points on the rancidity curve, thus making interpretations difficult. For example, a low PV can represent a sample just starting to become rancid, as well as a sample that has developed an extreme rancid characteristic. The TBA test has similar limitations, in that TBA values are typically quadratic with increasing oxidation. Due to the stability of some of the end-products, headspace GC is a fast and reliable method for oxidation measurement. Headspace techniques include static, dynamic and solid-phase microextraction (SPME) methods. Hexanal, which is the end-product formed from the oxidation of Q-6 unsaturated fatty acids (linoleate), is often found to be a major compound in the volatile profile of food products, and is often chosen as an indicator of oxidation in meals, especially during the early oxidative changes (Shahidi, 1994). 

Let us consider that the solvent has nonoverlapping domains that have distinct static and dynamic characteristics. The diffusion in such a system can be considered as a random walk in a random environment formed by the independently relaxing domain [95], Hence the diffusions in three dimensions is the weighted average of the diffusion in all these different domains [84], The average diffusion D can then be written as... 

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