Diffusion interstitial-like

This patient has the subjective symptoms of weight loss, decreased appetite, shortness of breath, and cough. Abnormal laboratory values include elevated temperature, decreased hemoglobin and hematocrit, and decreased CD4 count. Chest x-ray shows diffuse interstitial infiltrates bilaterally. Physical exam reveals thrush. The assessment is possible AIDS with CD4 count of 150 cells/mm3, thrush, a respiratory illness (possibly Pneumocystis jiroveci pneumonia), and anemia of chronic disease. He also has a history of hepatitis B, hypertension, and GERD (on famotidine), poor adherence to his anti hypertensive medications, and likely has an irregular daily regimen due to his occupation as a truck driver. 

In the case of interstitial diffusion in which we have only a few diffusing interstitial atoms and many available empty interstitial sites, random-walk equations would be accurate, and a correlation factor of 1.0 would be expected. This will be so whether the interstitial is a native atom or a tracer atom. When tracer diffusion by a colinear intersticialcy mechanism is considered, this will not be true and the situation is analogous to that of vacancy diffusion. Consider a tracer atom in an interstitial position (Fig. 5.18a). An initial jump can be in any random direction in the structure. Suppose that the jump shown in Figure 5.18b occurs, leading to the situation in Figure 5.18c. The most likely next jump of the tracer, which must be back to an interstitial site, will be a return jump (Fig. 5.18c/). Once again the diffusion of the interstitial is different from that of a completely random walk, and once again a correlation factor, / is needed to compare the two situations. 

The success of this method depends on the rapid diffusion of the impurities in the rare earth metal in a strong electric field. Most of the non-metallic elements (carbon, nitrogen and oxygen) and the small interstitial-like transition metals (iron, cobalt, nickel and copper) migrate from the cathode towards the anode, purifying the cathode portion of the rod. After 100 to 1000 hours a steady-state condition is built-up after which the forward diffusion from the cathode to the anode due to the electric field is equal to the backward diffusion due to the chemical concentration difference, and no further purification is realized. 

As mentioned above, high values of X are characteristic of the new interstitial-like diffusion of metallic solutes. Table 12.3 shows that these values of Ka vary in a quasi continuous manner from X <1 to X = 2xl0. Such an extended, continuous range for X has also been observed in other metals such... 

The defects generated in ion—soHd interactions influence the kinetic processes that occur both inside and outside the cascade volume. At times long after the cascade lifetime (t > 10 s), the remaining vacancy—interstitial pairs can contribute to atomic diffusion processes. This process, commonly called radiation enhanced diffusion (RED), can be described by rate equations and an analytical approach (27). Within the cascade itself, under conditions of high defect densities, local energy depositions exceed 1 eV/atom and local kinetic processes can be described on the basis of ahquid-like diffusion formalism (28,29). 

At present the iron-based alloys diffusion saturation by nitrogen is widely used in industry for the increase of strength, hardness, corrosion resistance of metal production. Inexhaustible and unrealized potentialities of nitriding are opened when applying it in combination with cold working [1-3], It is connected with one of important factors, which affects diffusion processes and phase formation and determines surface layer structure, mechanical and corrosion properties, like crystal defects and stresses [4, 5], The topical question in this direction is clarification of mechanisms of interstitial atoms diffusion and phase formation in cold worked iron and iron-based alloys under nitriding. 

Molecular reorientations at Bjerrum fault sites are responsible for the dielectric properties of ice. A second type of fault (proton jumps from one molecule to a neighbor) accounts for the electrical conductivity of ice, but cannot account for the high dielectric constant of ice. Further discussion of such ice faults is provided by Franks (1973), Franks and Reid (1973), Onsager and Runnels (1969), and Geil et al. (2005), who note that interstitial migration is a likely self-diffusion mechanism. 

The physical factors include mechanical stresses and temperature. As discussed above, IFP is uniformly elevated in solid tumors. It is likely that solid stresses are also increased due to rapid proliferation of tumor cells (Griffon-Etienne et al., 1999 Helmlinger et al., 1997 Yuan, 1997). The increase in IFP reduces convective transport, which is critical for delivery of macromolecules. The temperature effects on the interstitial transport of therapeutic agents are mediated by the viscosity of interstitial fluid, which directly affects the diffusion coefficient of solutes and the hydraulic conductivity of tumor tissues. The temperature in tumor tissues is stable and close to the body temperature under normal conditions, but it can be manipulated through either hypo- or hyper-thermia treatments, which are routine procedures in the clinic for cancer treatment. 

---