Material inhomogeneities

From a pharmacological point of view the first two strategies raise several distinct disadvantages. First, the exact structures of these fullerene-based systems in solution are usually unknown and, especially for polymeric materials inhomogeneous samples are frequently obtained. Furthermore, in many cases the amount of incorporated fullerene is not clearly determined. In addition, the presence of other molecules like the hosts or polymeric residues can cause unpredictable side effects and in no case the mode of action or activity can doubtlessly be associated with the fullerenes. However, for systematic investigations on structure-function relationships or extensive testings of toxicological or human availability properties, the use of structurally well-defined and characterized materials is mandatory. 

Since it is difficult to control processes for making plastic films in order to limit variability in their physical properties to one percent or less we find that material inhomogeneity is an obstacle to the development of better SRM s. It is also difficult to use such materials as transfer standards because their characteristics often drift with time and test specimens often do not tolerate abuse suffered during the measuring process. 

Fig.l. Optimal functions of thermoelectric material inhomogeneity n-type Bi2Te2jSeo.i + (0,09... O.OSjCdCh p-type Bio.sSbi.sTe + 4% Te... 

Examples of the optimal inhomogeneity functions obtained by computer-aided design method are shown below. Fig. 4 shows an example of the optimal concentration functions for Bi-Te alloys. Fig. 5 - for Pb-Te alloys. Fig. 6 - for Si-Ge alloys. One of the dependencies can be obtained within 10-15 minutes of work of even not very high speed computer of the type IBM-486, which proves the efficiency of the developed program. Naturally, each specific case of FGM use requires individual function of material inhomogeneity, otherwise the use of FGM will be inefficient. 

In conclusion one must note that the search for further qualitative improvement of thermoelectric material is not restricted to creation of FGM structures formed by the monotonous macroscopic material inhomogeneities. Of exceptional interest is creation of the microscopic inhomogeneities with quantum well formation, as well as the inhomogeneous structures allowing to combine on the microscopic level both thermoelectric and emission ways of thermoelectricity generation in a solid body. These possibilities were discussed in detail at the VII International School on Thermoelectricity and published in the Journal of Thermoelectricity [5,6]. 

Case 1 in Fig. 5 shows effects caused by material inhomogeneities resulting from fluctuations in concentration, local differences in particle size distribution and the presence of entrapped air. The fluctuations of the measured pressure-time curves do not produce an unequivocal apparent flow curve. Only a more or less broad flow range can be determined. 

Figure 4. Surface plot representation of2-D diffraction data from a PEG/AbOj (46 nm nom. diameter) composite particle in a 14 1 relative weight ratio. The x and y cooordinates are pixel numbers corresponding to azimuthal and polar scattering angles respectively. The host particle diameter is 7.5 gm. The intensity oscillations along each diffraction fringe signal material inhomogeneity.

Maugin, G.A. Material Inhomogeneities in Elasticity. Chapman and Hall, London (1993) deGroot, S.R. Thermodynamics of Irreversible Processes. North-Holland, Amsterdam (1951) Prigogine, I. Etude Thermodynamique des Phenomenes Irreversibles. Dunod-Desoer, Paris (1947)... 

Maugin, G.A. Material Inhomogeneities in Elasticity. Chapman tmd HtiU, London (1993)... 

In reality, the angle value might diverge shghtly from 45° for reasons concerning material inhomogenity or material-electrode interface quality. 

The results of the reported tests prove the feasibility of 2-D acoustie emission soiu-ce loealization in wooden board-like structurally sized specimens, despite the pronoimced anisotropy of wave velocities in the plane parallel and perpendicular to the fiber direction and despite some material inhomogenities. 

Since AFM is widely used for imaging, the technology is well-developed. Due to its high lateral resolution of 1 nm small samples can be used and material inhomogeneities can be mapped and imaged. The small contact areas ( 10 nm ) reduce the probability of experimental artifacts due to surface contamination and roughness [68]. The high spatial resolution capability makes AFM a complementary approach to the SFA which has been used to measure interfacial forces between proximal surfaces over areas on the order of 1 pm. Moreover, the force resolution of AFM is better than that of the SFA. 

---