796 research outputs found
Unitarity versus Renormalizability of Higher Derivative Gravity in 3D
It has been suggested that new massive gravity with higher order terms in the
curvature may be renormalizable and thus a candidate for renormalizable quantum
gravity. We show that three-dimensional gravity that contains quadratic scalar
curvature and Ricci tensor is renormalizable, but those theories with special
relation between their coefficients including new massive gravity are not.Comment: 9 pages. v2: title changed, minor modification. v3: minor corrections
to match the published versio
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
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.
Effects of NK-4, a Cyanine Dye with Antioxidant Activities: Attenuation of Neuronal Deficits in Animal Models of Oxidative Stress-Mediated Brain Ischemia and Neurodegenerative Diseases
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