Choice of Size and Shape

Catalyst pieces are sold in the form of daisy rings, simple rings and cylindrical pellets, Fig. 8.1. 

Daisy rings have the largest surface area and lowest resistance to gas flow. Pellets have the smallest surface area and highest resistance to flow. Simple rings are intermediate. 

Industrial data (Table 7.2) suggest that daisy rings and rings are equally favored. Pellets are only used to ensure well distributed gas flow through catalyst beds in low gas velocity converters (Topsoe, 2004). 

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Coercivity of Thin-Film Media. The coercivity ia a magnetic material is an important parameter for appHcations but it is difficult to understand its physical background. It can be varied from nearly zero to more than 2000 kA/m ia a variety of materials. For thin-film recording media, values of more than 250 kA / m have been reported. First of all the coercivity is an extrinsic parameter and is strongly iafluenced by the microstmctural properties of the layer such as crystal size and shape, composition, and texture. These properties are directly related to the preparation conditions. Material choice and chemical inborn ogeneties are responsible for the Af of a material and this is also an influencing parameter of the final In crystalline material, the crystalline anisotropy field plays an important role. It is difficult to discriminate between all these parameters and to understand the coercivity origin ia the different thin-film materials ia detail. 

The choice of size, shape, and type of electrode is based on economic considerations and is usually determined by the characteristics of the gas and suspended matter and by mechanical considerations such as flue arrangement, the available space, and previous experience with the electrodes on similar problems. The spacing between collecting electrodes in plate-type precipitators and the pipe diameter... 

Three principal layup processes for laminated fiber-reinforced composite materials are winding, laying, and molding. The choice of a layup process (as well as a curing process) depends on many factors part size and shape, cost, schedule, familiarity with particular techniques, etc. 

One of the basic criteria for the process choice is the optimum size and shape of the dispersed phase leading to better overall properties. As a brief guideline. Table 7 can be used to choose the correct manufacturing process. 

In practice there is often not an extensive range of suitable anode sizes from which to select. Economics may dictate an off-the-shelf choice from a manufacturer or the anode shape may have to conform with the geometric limitations of the structure. Consequently, the choice of anode size and shape is often limited. 

This analysis gives satisfactory results concerning the average crystallite sizes even in unfavorable experimental conditions such as overlapped or very weak and noisy peaks, and it allows an easy treatment of non-perfect monochromaticity of the radiation. But, it is important to emphasize that it is almost impossible to obtain the promised detailed description of the crystallite size and strain distributions. This is a fundamental problem related to the adopted procedure that is based on the a priori choice of the peak shape that inevitably imposes the general shape of such distributions [40]. For these reasons, the average dimension and strains remain the only reliable information. 

The choice of the carrier depends on several factors. The texture (size and shape of the pores, the way the pores are connected, etc.) of the support determines, to a large extent,... 

MW is often taken as the size descriptor of choice, while it is easy to calculate and is in the chemist s mind. However, other size and shape properties are equally simple to calculate, and may offer a better guide to estimate potential for permeability. Thus far no systematic work has been reported investigating this in detail. Cross-sectional area Ad obtained from surface activity measurements have been reported as a useful size descriptor to discriminate compounds which can access the brain (Ad<80A ) of those that are too large to cross the blood-brain barrier (BBB) [55]. Similar studies have been performed to define a cut-off for oral absorption [56]. 

For the automated solid-phase synthesis of oligonucleotides, however, silica was found to be the support of choice [192-197]. Silica with large pore size (25-300 nm), so-called controlled pore glass (CPG), is generally used for this purpose. The main advantages of CPG, as compared with silica gel, are its more regular particle size and shape, and greater mechanical stability. 

Filter sticks of a range of dimensions and porosities are available from J. Bibby Science Products Ltd. The choice of size of flasks and filter sticks will be governed by the scale of the recrystallisation. Broadly speaking pear-shaped flasks are more suitable for the range 100 mg to 5 g, but may be replaced by round-bottomed flasks for operations on a larger scale. 

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