Porous structure oriented

The main orientations of the porous structure are determined by calculating both the polar coordinates, colatitude (ff) and longitude (coordinate system with axes k, k2, and /c3 ... 

The reason to extend the experiments to tooth material was the idea that the matrix would have a less porous structure compared to human haversian bone and be less exposed to diagenetic alteration. While the porosity in human bone is mainly determined by a complicated network between the Haversian system and the Volk-mann canals that are perpendicular to it, especially enamel is a far denser material than human bone and its organic content is significantly less (2% of organic material only). But in contrast to the enamel, dentine has a similar composition of the organic and the inorganic matrix compared to bone, and it has a high microporosity due to nerve canals that start from the pulpa and stop close to the enamel-dentine junction (edj). However, these nerve canals have a smaller diameter than a haversian pore (70 pm) and the canals are orientated parallel and are not connected with each other. So a fluorine ion cannot percolate from one pore to another, as it is the case in a human bone, but it has to overcome the distance from one canal to the next one by diffusion. So the permeability is low and this results in a smaller diffusion rate D. 

Whereas the formation of a macro PS layer on n-Si nnder front illumination follows the same mechanism as the macro PS formed in the dark, the formation of micro PS is believe to be mainly dne to the effect of the photogenerated carriers. Essentially, the dissolntion reaction nnder illnmination proceeds with a supply of photo holes which are generated near the snrface and distributed uniformly in the porous structure. This results in a dissolntion process different from that in the dark or back illumination and the formation of PS of extremely fine and randomly oriented structures. According to Arita, the anodic current under front illumination consists of three parts ... 

Nickel deposits obtained at a cathodic potential of—1,300 mV/SCE without and with a parallel orientation of magnetic field of 500 Oe, are shown in Fig. 11a, b, respectively. Figure 11a shows that the nickel deposit obtained without an imposed magnetic field consisted of bunch of nickel grains, while it can be seen from Fig. 1 lb that the nickel deposit obtained under a magnetic field with a parallel orientation to the electrode surface was a porous structure and without bunch of nickel grains. 

Pore etching allows to rich the porosity up to 60 % and the pore entrances up to 20-30 nm (Fig. lc). In this case the LC alignment has vertical orientation as shown in Fig. Id. The top left part in Fig. Id is planar non anodized area of the initial aluminum film with the horizontal LC alignment. It should be noted that LC penetration in the alumina porous structure with 60 % porosity was almost complete. 

More general models for the porous structure have also been developed by Johnson and Stewart [60] and by Feng and Stewart [43], called the parallel cross-linked pore model. Here, Eqs. 3.5.b-4 to 6 or Eq. 3.5.b-7 are considered to apply to a single pore of radius r in the solid, and the diffusivities interpreted as fte actual values rather than effective diffusivities corrected for porosity and tortuosity. A pore size and orientation distribution function /(r, Q), similar to Eq. 3.4-2, is defined. Then /(r, Q)dri is the fraction open area of pores with radius r and a direction that forms an angle Q with the pdlet axis. The total porosity is then... 

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