Thermopower analysis of the electronic structure around metal-insulator transition in V1-xWxO2

Electronic structure across the metal-insulator (MI) transition of electron-doped V1-xWxO2 epitaxial films (x = 0-0.06) grown on alfa-Al2O3 substrates was studied by means of thermopower (S) measurements. Significant increase of |S|-values accompanied by MI transition was observed, and the transition temperatures of S (TS) decreased with x in good linear relation with MI transition temperatures. |S| values of V1-xWxO2 films at T > TS were constant at low values of 23 microV K-1 independently of x, which reflects a metallic electronic structure, whereas, those at T < TS almost linearly decreased with logarithmic W-concentrations. The gradient of -213 microV K-1 agrees well with -kB/e*ln10 (-198 microV K-1), suggesting that V1-xWxO2 films have insulating electronic structures with a parabolic density of state around the conduction band bottom.Comment: Accepted for publication as a Rapid Commun. in Phys. Rev.

Thermopower analysis of metal-insulator transition temperature modulations in vanadium dioxide thin films with lattice distortion

Insulator-to-metal (MI) phase transition in vanadium dioxide (VO2) thin films with controlled lattice distortion was investigated by thermopower measurements. VO2 epitaxial films with different crystallographic orientations, grown on (0001) alpha-Al2O3, (11-20) alpha-Al2O3, and (001) TiO2 substrates, showed significant decrease of absolute value of Seebeck coefficient (S) from ~200 to 23 microV K-1, along with a sharp drop in electrical resistivity (rho), due to the transition from an insulator to a metal. The MI transition temperatures observed both in rho (Trho) and S (TS) for the VO2 films systematically decrease with lattice shrinkage in the pseudo-rutile structure along c-axis, accompanying a broadening of the MI transition temperature width. Moreover, the onset TS, where the insulating phase starts to become metallic, is much lower than onset Trho. This difference is attributed to the sensitivity of S for the detection of hidden metallic domains in the majority insulating phase, which cannot be detected in rho-measurements. Consequently, S-measurements provide a straightforward and excellent approach for a deeper understanding of the MI transition process in VO2.Comment: To be published in Physical Review

Contributions of heterotrophic and autotrophic prey to the diet of euphausiid, Euphausia pacifica in the coastal waters off northeastern Japan

The contributions of heterotrophic and autotrophic prey to the diet of Euphausia pacifica were examined in coastal waters off northeastern Japan in May and October 1999. The autotrophic contribution was estimated from gut pigment contents, and the heterotrophic contribution from the volume of each taxonomic group in the stomach. Our observations suggest that heterotrophic prey, especially copepods, were more important than autotrophic prey in both seasons. The contributions of heterotrophic prey items in adult E. pacifica ranged from 57-79% in May and from 27-93% of the total ingested carbon in October. The contribution of copepods was largest, ranging from 54-77% in May and from 27-93% in October. We discuss the contribution of athecate ciliates, another possible heterotrophic prey of importance, to the diet of E. pacifica

Infrared-transmittance tunable metal-insulator conversion device with thin-film-transistor-type structure on a glass substrate

Infrared (IR) transmittance tunable metal-insulator conversion was demonstrated on glass substrate by using thermochromic vanadium dioxide (VO2) as the active layer in three-terminal thin-film-transistor-type device with water-infiltrated glass as the gate insulator. Alternative positive/negative gate-voltage applications induce the reversible protonation/deprotonation of VO2 channel, and two-orders of magnitude modulation of sheet-resistance and 49% modulation of IR-transmittance were simultaneously demonstrated at room temperature by the metal-insulator phase conversion of VO2 in a non-volatile manner. The present device is operable by the room-temperature protonation in all-solid-state structure, and thus it will provide a new gateway to future energy-saving technology as advanced smart window.Comment: To appear in APL Mater. (2017

Capability of Tissue Stem Cells to Organize into Salivary Rudiments

Branching morphogenesis (BrM), an essential step for salivary gland development, requires epithelial-mesenchymal interactions. BrM is impaired when the surrounding mesenchyme is detached from the salivary epithelium during the pseudoglandular stage. It is believed that the salivary mesenchyme is indispensable for BrM, however, an extracellular matrix gel with exogenous EGF can be used as a substitute for the mesenchyme during BrM in the developing salivary epithelium. Stem/progenitor cells isolated from salivary glands in humans and rodents can be classified as mesenchymal stem cell-like, bone-marrow-derived, duct cell-like, and embryonic epithelium-like cells. Salivary-gland-derived progenitor (SGP) cells isolated from duct-ligated rats, mice, and swine submandibular glands share similar characteristics, including intracellular laminin and α6β1-integrin expression, similar to the embryonic salivary epithelia during the pseudoglandular stage. Progenitor cells also isolated from human salivary glands (human SGP cells) having the same characteristics differentiate into hepatocyte-like cells when transplanted into the liver. Similar to the dissociated embryonic salivary epithelium, human SGP cells aggregate to self-organize into branching organ-like structures on Matrigel plus exogenous EGF. These results suggest the possibility that tissue stem cells organize rudiment-like structures, and the embryonic cells that organize into whole tissues during development are preserved even in adult tissues