Structure gradient

Voids often look similar to air bubbles. The appearance of voids in filaments or films, however, results for different reasons. Voids can be produced during stretching in the area of necking by a kind of folding mechanism. The formation of voids may also depend on the generation of a radial gradient structure during solidification of the threads. 

Figure 1.82 Cross-section of corn stalk exhibiting functionally graded strnctnre. From Shigeyasu Amada, Hierarchical fnnctionally gradient structures of bamboo, barley, and com, MRS Bulletin, Vol. XX(1), 35 (1995). Reprodnced by permission of MRS Bulletin.

We have now identified the presence of structured flows in a wide variety of ternary systems of polymer/polymer/solvent 52-53>. in all cases associated with structured flow formation there was concomitant rapid transport of the polymer as compared to its behaviour in water. Indeed, even in the presence of dextran concentration gradients structures are formed which move relatively slowly but are nevertheless highly regular. The only conditions where structures have not been observed is at dextran concentrations below C values where, incidentally, polymer transport is not rapid. (See also the low rate of transport of PVP 360 in a dextran T10 medium with a concentration of 40 kg m 3 as measured in the ultracentrifuge Fig. 9.) These studies confirm the striking correlation between this parameter and the onset of rapid polymer transport and structured flow formation. 

Although the functionally graded materials concept has been known since 1972, the production of functionally graded SiAlON ceramics is still a subject to explore. Especially, the formation mechanisms of the functional gradient structure have not yet been fully understood. If diffusion mechanisms are explored, compositional design would be easy and the thickness of the graded... 

To overcome the bias resulting from uneven dispersal of tracer or inhibitor, sediment rate measurements are often made in slurries, which destroy the gradient structure of sediments, which is essential to the in situ fluxes. Slurries may provide useful information on potential rates, but not in situ rates. Potential nitrification rates and rates measured in intact cores were not correlated in estuarine sediments (Caffrey et ah, 2003). The lack of correlation was explained by the inclusion of variable amounts of anoxic sediments in the slurries from which the potential rates were derived. 

Copolymerizations of an equimolar mixture of MMA and MA (R-10) or nBA (R-11) with the nickel catalysts led to simultaneous consumption of the two monomers and gave their random copolymers with controlled molecular weights and relatively narrow MWDs (MwIMn 1.5).135 The copper-catalyzed systems also induced controlled random copolymerizations of MMA and nBA in organic solvents and in emulsion (MJMn 1.2).254-267 However, methacrylate/ acrylate copolymerization may result in gradient structures rather than random structures (section III.F). 

The possibility of tailormaking the substrate simply by variations in powders and/or in sintering technology (recent examples gradiented structures and WC plate reinforcement). 

It is believed that excellent pore-gradient structures can be obtained from well-stabilized and less-concentrated suspensions. Thus, a stabilized suspension with 250 particles and the above-mentioned discrete size distribution have been generated in a square box of 70 fim. X 20.53/im without contacts for the simulations (see Fig. 2(a)). This corresponds to an area density of pA 5%. Hereby periodic boundaries in the horizontal direction and walls in the centrifuging direction have been assumed. 

The Society ofNon-traditional Technology, Development of Energy Conversion Materials through Formation of Gradient Structures, (1994). 

Fig. 2 shows scanning electron micrograph (SEM) of the top layer of a sintered body prepared by stabilized suspension with 5 vol% solid content. Hereby the homogeneous distribution of pores with d 1 gm can be observed. This range of pore size can be used for the UF filtration applications. The SEM pictures at five different positions across the thickness have been shown in Fig. 3. These pictures indicate a clear pore-gradient structure.

In order to quantify this pore-gradient structure, the corresponding mercury-porosimetry data have been shown in Fig. 4(a-c). From (a) to (c) in Fig. 4, a pore-gradient can be observed. This pore-gradient shows the largest pores with d 250 nm in the bottom layer and the smallest pores with d w 40 nm in the top layer. According to Kruyer [10] and Mason [11] (see 2.1), the particles which contribute to this pore size of d 40 nm, have a... 

A gradient structure emitter, in which the molybdenum substrate is covered by a ((XX)1) rhenium layer with a three-dimensional surface and an intermediate tungsten layer was fabricated, and the work function and thermionic power generation characteristics were evaluated. The following results were obtained. 

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