Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Thermal conductivity is one of the key parameters in the figure of merit of thermoelectric materials. Over the past decade, most progress in thermoelectric materials has been made by reducing their thermal conductivity while preserving their electrical properties. The phonon scattering mechanisms involved in these strategies are reviewed here and divided into three groups, including (i) disorder or distortion of unit cells, (ii) resonant scattering by localized rattling atoms and (iii) interface scattering. In addition, we propose construction of a ‘natural superlattice’ in thermoelectric materials by intercalating an MX layer into the van der Waals gap of a layered TX₂ structure which has a general formula of (MX)_1+x(TX₂)_n (M=Pb, Bi, Sn, Sb or a rare earth element; T=Ti, V, Cr, Nb or Ta; X=S or Se and n=1, 2, 3). We demonstrate that one of the intercalation compounds (SnS)_1.2(TiS₂)₂ has better thermoelectric properties compared with pure TiS₂ in the direction parallel to the layers, as the electron mobility is maintained while the phonon transport is significantly suppressed owing to the reduction in the transverse phonon velocities.     

Iron Loss Analysis of Permanent Magnet Motors Fed by PWM Inverter

Carrier harmonic losses that consist of iron loss, eddy current loss, and ac copper loss are produced in a permanent magnet machine driven by a PWM inverter. It is already known that a higher motor inductance can lead to lower carrier harmonic losses. This paper investigates the carrier harmonic loss composition of two motors with identical dimensions but different inductances. The results of finite element analysis (FEA) showed that the eddy current loss in the iron core accounts for most of the carrier harmonic loss. It is also shown that the carrier harmonic loss of the iron core is quantifiable using theoretical calculations.     

Properties of Bi-doped PbTe layers grown by liquid phase epitaxy under controlled Te vapor pressure

Effects of Bi doping in PbTe liquid-phase epitaxial layers grown by the temperature difference method under controlled vapor pressure (TDM-CVP) are investigated. For Bi concentrations in the solution, x_Bi, lower than 0.2 at.%, an excess deep-donor level (activation energy E_d≈0.03–0.04 eV) appears, and Hall mobility is low. In contrast, for x_Bi>0.2 at.%, Hall mobility becomes very high, while carrier concentration is in the range of 10¹⁷ cm⁻³. Inductive coupled plasma (ICP) emission analysis shows that, for x_Bi=1 at.%, Bi concentration in the epitaxial layer is as high as N_Bi=2.3–2.7 × 10¹⁹ cm⁻³. These results indicate that Bi behaves not only as a donor but also as an acceptor, and the nearest neighbor or very near donor-acceptor (D-A) pairs are formed, so that strong self-compensation of Bi takes place. Carrier concentration for highly Bi-doped layers shows a minimum at a Te vapor pressure of 2.2 × 10⁻⁵ torr for growth temperature 470°C, which is coincident with that of the undoped PbTe.     

SH4 RISC multimedia microprocessor

Unique, floating-point length-4 vector instructions prove more effective than conventional SIMD architecture for 3D graphics processing     

Phylogenetic analysis of Rhodococcus erythropolis based on the variation of ribosomal proteins as observed by matrix-assisted laser desorption ionization-mass spectrometry without using genome information

Rhodococcus erythropolis strains characterized as antibiotic producers can be classified into three groups according to their antibiotic spectrum and growth compatibility. Due to their high genotypic similarity, the taxonomic relationship of these strains has not been elucidated. In this study, ribosomal protein profiling using matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) was employed to classify twenty-one strains of R. erythropolis (15 antibiotic producers and 6 non-antibiotic producers). In the first step in this method, a total of 30 intense peaks observed for purified ribosomal subunit proteins of the type strain (R. erythropolis JCM 3201^T) were selected as the reference peaks. The mass spectra observed for the cell lysates of each sample strain were then checked as to whether peaks were observed at the same masses of the reference peaks. The results of peak matching were processed by cluster analysis, generating a dendrogram. Four major clusters of the R. erythropolis strains corresponded to three antibiotic groups and the non-antibiotic group. Furthermore, the topology of the dendrogram was highly comparable with the phylogenetic tree based on DNA gyrase subunit B gene (gyrB) sequencing. These results indicate that our proposed ribosomal protein profiling method using MALDI-MS is a potentially reliable and sufficiently high-throughput technique for the taxonomic analysis of closely related bacterial strains without using DNA sequence information.     

13C NMR spectrum analysis of electrochemically prepared poly(3-methylthienylene) films

The ¹³C NMR spectrum analysis of electrochemically prepared poly(3-methylthienylene) films has been investigated. Both a film doped with ClO₄ ions (P3MT-ClO₄) and an undoped film (P3MT₀) give only two distinct absorption bands through the electrochemical reduction of P3MT-ClO₄. These distinct bands are definitely attributable to the methyl group (upper field) and the thiophene ring (lower field), respectively, and are characteristic of well-defined poly(3-methylthienylene). The correlation between conductivity and ¹³C NMR spectra will be discussed.     

Organosilicon Derivatives of Buckminsterfullerene (C60): First Preparation of A Fullerene Silirane

C₆₀ reacts with photochemically generated bis(2,6-diisopropylphenyl)silylene (1) to give adducts, 2-4, as the isolable products. Spectroscopic analysis and theoretical investigation strongly support the silirane structure 2a, and not the isomeric 1,6-silamethano[10]annulene 2b.     

Ozonization of amides

Ozonization of various amides was carried out as a model reaction for the degradation of polyamides with ozone. N-alkylamides and N,N-dialkylamides were found to be reactive compared with those amides which have no alkyl group on the nitrogen atom, and it was suggested that ozone attacks preferentially N-methylene or N-methyl group of amides in the first step of ozonization.     

13C NMR and Fourier transform infrared study of electrochemically prepared polythienylene film

The ¹³C NMR and Fourier transform infrared (FTIR) spectra of an electrochemically prepared polythienylene film have been obtained. The polythienylene film displays only two sharp absorption bands, at 124.8 and 136.5 ppm downfield from TMS (tetramethylsilane) in the ¹³C NMR, these being attributable to the carbon atoms in the β-position and the α-position, respectively, relative to the sulfur atom of poly(2,5-thienylene). The polythienylene film also shows a sharp absorption band at 789 cm^?1 in the IR, which is definitely ascribable to the C-H out-of-plane vibration of poly(2,5-thienylene). The polythienylene film will be shown to have a highly defined structure with a dominance of poly(2,5-thienylene).