A method of improving the efficiency of thermoelectric energy conversion by utilizing potential barriers is considered. Since potential barriers act as carrier energy filters, elimination of lower energy carriers results in an improvement of the efficiency of thermoelectric energy conversion (energy filtering method). The optimal height of potential barriers and the distance between the barriers is estimated within a semiclassical framework, i.e. using Boltzmann equation. Our calculated results show that this method works effectively for materials, in which acoustic phonon scattering is dominant compared with other scattering processes.

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We present a theoretical framework for estimating the effects of a superlattice (SL) on the thermoelectric (TE) transport in semiconductors. We consider both transverse and parallel conduction through the SL, and in the latter case, the possibility of modulation doping. Our calculations of electron and phonon transport are based on a two-band single-valley model for heavily doped n-type Si80Ge20, with modifications to account for the effects of parallel and transverse transport through a SL. For parallel transport, we find modest improvement in the TE figure-of-merit, only for the narrowest SL (5.4 Å). For transverse conduction, we find that if the SL can be designed to inhibit the conduction of low-energy carriers, then large improvements in the TE figure-of-merit are possible, as large as +100% over the bulk.

Epilepsy after aneurysmal subarachnoid hemorrhage (post-SAH epilepsy) is a critical complication that influences clinical and social prognoses. However, the underlying mechanisms remain unclear. We investigated the relationship between hemosiderosis and the incidence of post-SAH epilepsy. About 50 patients with aneurysmal SAH who were admitted to Sapporo Medical University and Oji General Hospital between April 2010 and June 2016 were enrolled in this retrospective study. Hemosiderosis detected by T2*-weighted magnetic resonance imaging(MRI) and the incidence of post-SAH epilepsy were retrospectively analyzed. Post-SAH epilepsy was defined as an unprovoked seizures occurring more than 1 week after the onset of SAH. Six patients (12%) developed post-SAH epilepsy. In all patients, hemosiderosis in the cortex or cerebral parenchyma was detected by T2*-weighted MRI. Statistical analyses revealed that hemosiderosis and the co-existence of intracerebral hemorrhage (ICH) related with post-SAH epilepsy (Fisher’s exact test, univariate exact logistic regression analysis: P < 0.05). Post-SAH epilepsy was predicted by hemosiderosis and the co-existence of ICH. The present results suggest that hemosiderin is the principal cause of post-SAH epilepsy and may be a predictor of this critical complication.

For the design of functionally gradient materials (FGMs), necessary material properties, such as thermal-expansion-coefficient and Young's modulus in the specific region, are optimized by controlling the distribution profiles of composition and microstructures, as well as micropores in the materials. For this purpose, our research team employs the inverse design procedure in which both the basic material combination and the optimum profile of the composition and microstructures are determined with respect to the objective structural shape and the thermomechanical boundary conditions. Figure 1 shows the inverse design procedure for FGM, in which the final structure to be developed, as well as the boundary conditions, are specified first. After the fabrication method and an allowable material combination are selected from the FGM database, the estimation rules for the material properties of the intermediate compositions are determined based upon the micro-structure. Then, the temperature distribution and the thermal-stress distribution are calculated with the assumed profiles of the distribution functions for the constituents. Other possible combinations and different profiles are also investigated until the optimum is obtained.