Roughness external surface

An experimental check of these conclusions showed that the apparent absolute rate of decomposition of powders (Jp ), related to the external surface area of a powder pellet, is always higher than that of crystals (Jc). It was also found that the difference between the decomposition rates is independent of temperature, residual air pressure in the reactor, sample mass and powder particle size. The mean value of Jp /Jc was 2.8 0.4. This value somewhat exceeds the theoretical estimate, which may be due to the rough external surface of the powder. Evidently, the area of a pimpled surface formed by spherical particles should be at least twice that of the flat surface. 

Thus, the rough external surface of the catalyst sphere has two effects firstly the interior of the sphere is made better accessible, and secondly the stagnant layer around the sphere is extended. Schliinder attributed the extension of the stagnant layer to an imperfect flow through the bed of catalyst particles at low gas velocities [15]. However, the thickness of the stagnant layer is dependent on the hydrothermal treatment. This can only be explained by the surface roughness, as the size and shape for all samples and, hence, their stacking in a catalyst bed is the same. 

Close examination revealed that the cracks originate on the external surface. Exposure of the fracture surface revealed a rough contour covered with dark copper oxide. Close examination of the internal surface revealed fewer, tighter fissures corresponding to the locations of cracks on the external surface. 

Thermal characteristics of material layers for each type of wall must be specified, including thickness, conductivity, density, and specific heat. Moreover, the features of internal and external surfaces of each wall must be specified, including solar absorptance and roughness, which affect surface heat transfer coefficients. 

Intracellular antigens could be modified internal proteins, which are continuously removed by the cell, the structure altered and attached to MHC I. This takes place in the rough endoplasmic reticulum. The protein/pep tide-hapten fragments are then presented to the external surface of the cell membrane as a complex with the MHC I. Then cytotoxic T cells (CD8+) accept the protein/peptide and destroy the cell. This mechanism gives rise to a type IV response. 

Figure 18-8 Stereoscopic ribbon diagrams of the chicken bc1 complex (A) The native dimer. The molecular twofold axis runs vertically between the two monomers. Quinones, phospholipids, and detergent molecules are not shown for clarity. The presumed membrane bilayer is represented by a gray band. (B) Isolated close-up view of the two conformations of the Rieske protein (top and long helix at right) in contact with cytochrome b (below), with associated heme groups and bound inhibitors, stigmatellin, and antimycin. The isolated heme of cytochrome c, (left, above) is also shown. (C) Structure of the intermembrane (external surface) domains of the chicken bcx complex. This is viewed from within the membrane, with the transmembrane helices truncated at roughly the membrane surface. Ball-and-stick models represent the heme group of cytochrome cy the Rieske iron-sulfur cluster, and the disulfide cysteines of subunit 8. SU, subunit cyt, cytochrome. From Zhang et al.105...

Many catalysts are porous solids of high surface area and with such materials it is often useful to distinquish between the external and internal surface. The external surface is usually regarded as the envelope surrounding discrete particles or agglomerates, but is difficult to define precisely because solid surfaces are rarely smooth on an atomic scale. It can be taken to include all the prominences plus the surface of those cracks, pores and cavities which are wider than they are deep. The internal surface comprises the walls of the rest of the pores, cavities and cracks. In practice, the demarcation is likely to depend on the methods of assessment and the nature of the pore size distribution. The total surface area (As) equals the sum of the external and internal surface areas. The roughness of a solid surface may be characterized by a roughness factor, i.e. the ration of the external surface to the chosen geometric surface. 

Surface area of unit mass of powder, as determined under stated conditions Area of external surface of particles, as talong account of roughness (l e all cavities which are wider than they are deep), but not porosity Ratio of external surface area to area of smoothed envelope around particles Solid made up of more or less independent particles which may be in the form of a powder, aggregate or agglomerate... 

Interfacial processes take place on the surface of solid (rock or soil), so the specific surface area (area per mass) is one of the most important parameters. The specific surface area depends on the particle size or the particle size distribution, and the roughness of the surface. These factors determine the external specific surface area. In addition, rocks and soils contain a network of pores with different sizes and shapes. Some of them are in a direct connection with the external surface (open pores). Therefore, depending on the relative sizes of the pores and the particles of the substance, the different substances of the surroundings can enter the pores. Two especially important types of pores are... 

FIGURE 7. Structure of the inter-membrane (external surface) domains of the bc complex viewed from within the membrane, with the transmembrane helices truncated at roughly the membrane surface. Cytochrome Cl and Rieske protein are drawn as cylinders, subunit 7,8,10, and 11 as ribbons. The Ci haem, Rieske Fe2 S 2 cluster and the two disulfide cysteines of subunit 8 are drawn as ball-and-stick models. Cytochrome c 1 is painted in dark gray, the Rieske protein in light gray. 

According to Briscall the external surface area of a foam Section equals the product of the geometrical area of the section and a roughness factor Rb, i.e.S , = S,., Rb where ... 

Rates of ion exchange processes are affected by diffusional resistances of ions into and out of the solid particles as well as resistance to external surface diffusion. The particles are not really solid since their volume expands by 50% or more. For monovalent exchanges in strongly ionized resins, half times with intraparticle diffusion controlling are measured in seconds or minutes. For film diffusion, half times range from a few minutes with 0. N solutions up to several hours with 0.0017V solutions. Film diffusion rates also vary inversely with particle diameter. A rough rule is that film... 

Persson and co-workers [265 267] consider a rough, rigid surface with a height prohle h x ). where x is a two-dimensional vector in the x-y plane. In reaction to /z(x) and its externally imposed motion, the rubber will experience a (time-dependent) normal deformation 8z(x, f). If one assumes the rubber to be an elastic medium, then it is possible to relate 52(q, ), which is the Fourier transform (F.T.) of 8z(x, f), to the F.T. of the stress a(q, ). Within linear-response theory, one can express this in the rubber-hxed frame (indicated by a prime) via... 

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