Two-dimensional electron systems have attracted attention as thermoelectric materials, which can directly convert waste heat into electricity. It has been theoretically predicted that thermoelectric power factor can be largely enhanced when the two-dimensional electron layer is far narrower than the de Broglie wavelength. Although many studies have been made, the effectiveness has not been experimentally clarified thus far. Here we experimentally clarify that an enhanced two-dimensionality is efficient to enhance thermoelectric power factor. We fabricated superlattices of [N unit cell SrTi1−xNbxO3|11 unit cell SrTiO3]10—there are two different de Broglie wavelength in the SrTi1−xNbxO3 system. The maximum power factor of the superlattice composed of the longer de Broglie wavelength SrTi1−xNbxO3 exceeded ∼5 mW m−1 K−2, which doubles the value of optimized bulk SrTi1−xNbxO3. The present approach—use of longer de Broglie wavelength—is epoch-making and is fruitful to design good thermoelectric materials showing high power factor.

Thermoelectric energy conversion -the exploitation of the Seebeck effect to convert waste heat into electricity -has attracted an increasing amount of research attention for energy harvesting technology. Niobium-doped strontium titanate (SrTi 1−x Nb x O 3 ) is one of the most promising thermoelectric material candidates, particularly as it poses a much lesser environmental risk in comparison to materials based on heavy metal elements. Two-dimensional electron confinement, e.g. through the formation of superlattices or two-dimensional electron gases, is recognized as an effective strategy to improve the thermoelectric performance of SrTi 1−x Nb x O 3 . Although electron confinement is closely related to the electronic structure, the fundamental electronic phase behavior of the SrTi 1−x Nb x O 3 solid solution system has yet to be comprehensively investigated. Here, we present a thermoelectric phase diagram for the SrTi 1−x Nb x O 3 (0.05 ≤ x ≤ 1) solid solution system, which we derived from the characterization of epitaxial films. We observed two thermoelectric phase boundaries in the system, which originate from the step-like decrease in carrier effective mass at x ~ 0.3, and from a local minimum in carrier relaxation time at x ~ 0.5. The origins of these phase boundaries are considered to be related to isovalent/heterovalent B-site substitution: parabolic Ti 3d orbitals dominate electron conduction for compositions with x < 0.3, whereas the Nb 4d orbital dominates when x > 0.3. At x ~ 0.5, a tetragonal distortion of the lattice, in which the B-site is composed of Ti 4+ and Nb 4+ ions, leads to the formation of tail-like impurity bands, which maximizes the electron scattering. These results provide a foundation for further research into improving the thermoelectric performance of SrTi 1−x Nb x O 3 .

Among many thermoelectric materials, oxide-based materials draw significant interest due to their environmental compatibility. In particular, layered cobaltite, Na0.75CoO2, shows a large thermoelectric power factor parallel to the layers. However,...

Various CuS nanostructures, including nanoflowers, doughnut-shaped nanospheres, dense nanospheres, and mixtures of nanoneedles, nanoparticles, and nanoplates, were synthesized from different copper and sulfur sources by a solvothermal method. The formation mechanisms along with photocatalytic properties for the degradation of rhodamine B (RhB) under visible-light irradiation were investigated in this study. The experimental results indicate that when the sulfur source is fixed at CS(NH 2 ) 2 in the solvothermal reaction, spherical nanoflowers, doughnut-shaped nanospheres, and dense nanospheres could be synthesized by using CuCl 2 , Cu-(NO 3 ) 2 , and CuSO 4 as the copper source, respectively. Furthermore, atypical nanoflowers and a mixture of [a]

Artificial crystals synthesized by atomic-scale epitaxy provides the ability to control the dimensions of the quantum phases and associated phase transitions via precise thickness modulation.In particular, reduction in dimensionality via quantized control of atomic layers is a powerful approach to revealing hidden electronic and magnetic phases. Here, we demonstrate a dimensionalitycontrolled and induced metal-insulator transition (MIT) in atomically designed superlattices by synthesizing a genuine two dimensional (2D) SrRuO3 crystal with highly suppressed charge transfer.The tendency to ferromagnetically align the spins in SrRuO3 layer diminishes in 2D as the interlayer exchange interaction vanishes, accompanying the 2D localization of electrons. Furthermore, electronic and magnetic instabilities in the two SrRuO3 unit cell layers induce a thermally-driven MIT along with a metamagnetic transition.

Cyclodipeptide synthases (CDPSs) catalyse the formation of cyclodipeptides using aminoacylated-tRNAs as substrates and have great potentials in the production of diverse 2,5-diketopiperazines (2,5-DKPs). Genome mining of Streptomyces leeuwenhoekii NRRL B-24963 revealed a two-gene locus saz encoding a CDPS SazA and a unique fused enzyme SazB harboring two domains: phytoene-synthase-like prenyltransferase (PT) and methyltransferase (MT). Heterologous expression of the saz gene(s) in Streptomyces albus J1074 led to the production of four prenylated indole alkaloids, among which streptoazines A-C (3–5) are new compounds. Expression of different gene combinations showed that the SazA catalyzes the formation of cyclo (L-Trp-L-Trp) (cWW, 1), followed by consecutive prenylation and methylation by SazB. Biochemical assays demonstrated that SazB is a bifunctional enzyme, catalyzing sequential C3/C3’-prenylation(s) by SazB-PT and N1/N1’-methylation(s) by SazB-MT. Of note substrate selectivity of SazB-PT and SazB-MT was probed, revealing the stringent specificity of SazB-PT but relative flexibility of SazB-MT. IMPORTANCE Natural products with 2,5-DKP skeleton have long sparked the interest in drug discovery and development. Recent advances in microbial genome sequencing have revealed that the potentials of CDPS-dependent pathways encoding new 2,5-DKPs are underexplored. In this study, we report the genome mining of a new CDPS-containing two-gene operon and activation of this cryptic gene cluster through heterologous expression, leading to the discovery of four indole 2,5-DKP alkaloids. The cWW-synthesizing CDPS SazA and the unusual PT-MT fused enzyme SazB were characterized. Our results expand the repertoire of CDPSs and associated tailoring enzymes, setting the stage for accessing diverse prenylated alkaloids using synthetic biology strategies.

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The ratio of triglyceride (TG) to high-density lipoprotein cholesterol (HDL-C) is an objective approach to predicting poor outcomes in acute ischemic stroke (AIS). The impact of TG/HDL-C on hemorrhagic transformation (HT) after AIS remains unknown. The aim of this study was to explore the accurate effect of TG/HDL-C on HT after AIS. We enrolled a total of 1423 patients with AIS in the training cohort from a prospective, consecutive hospital-based stroke registry. Of the 1423 patients, HT occurred in 155 (10.89%) patients. The incidence of HT after AIS was significantly increased when there were low levels of TG (P=0.016) and TG/HDL-C (P=0.006) in patients with AIS attributable to large artery atherosclerosis (LAA), but not in those who suffered from cardioembolic stroke. After adjustment for covariates, a lower TG/HDL-C (OR=0.53, 95%CI=0.20-0.93) that was more than TG alone (OR=0.61, 95%CI=0.27-0.98) independently increased the risk of HT in LAA. Furthermore, our established nomogram indicated that lower TG/HDL-C was an indicator of HT. These findings were further validated in the test cohort of 558 patients with AIS attributable to LAA. In summary, a low level of TG/HDL-C is correlated with greater risk of HT after AIS attributable to LAA.