Tokyo University of Science

About: Tokyo University of Science is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Catalysis & Thin film. The organization has 15800 authors who have published 24147 publications receiving 438081 citations. The organization is also known as: Tōkyō Rika Daigaku & Science University of Tokyo.

Matter perturbations in Galileon cosmology

Abstract: We study the evolution of matter density perturbations in Galileon cosmology where the late-time cosmic acceleration can be realized by a field kinetic energy. We obtain full perturbation equations at linear order in the presence of five covariant Lagrangians L{sub i} (i=1,{center_dot}{center_dot}{center_dot},5) satisfying the Galileon symmetry {partial_derivative}{sub {mu}}{phi}{yields}{partial_derivative}{sub {mu}}{phi}{sup +}b{sub {mu}} in the flat space-time. The equations for a matter perturbation as well as an effective gravitational potential are derived under a quasistatic approximation on subhorizon scales. This approximation can reproduce full numerical solutions with high accuracy for the wavelengths relevant to large-scale structures. For the model parameters constrained by the background expansion history of the Universe, the growth rate of matter perturbations is larger than that in the {Lambda}-cold dark matter model, with the growth index {gamma} today typically smaller than 0.4. We also find that, even on very large scales associated with the integrated-Sachs-Wolfe effect in cosmic microwave background temperature anisotropies, the effective gravitational potential exhibits a temporal growth during the transition from the matter era to the epoch of cosmic acceleration. These properties are useful to distinguish the Galileon model from the {Lambda}-cold dark matter model in future high-precision observations.

In-crystal and surface charge transport of electric-field-induced carriers in organic single-crystal semiconductors

Abstract: Gate-voltage dependence of carrier mobility is measured in high-performance field-effect transistors of rubrene single crystals by simultaneous detection of the longitudinal conductivity ${\ensuremath{\sigma}}_{\ensuremath{\square}}$ and Hall coefficient ${R}_{H}$. The Hall mobility ${\ensuremath{\mu}}_{H}$ ($\ensuremath{\equiv}{\ensuremath{\sigma}}_{\ensuremath{\square}}{R}_{H}$) reaches nearly $10\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{s}$ when relatively low-density carriers ($l{10}^{11}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$) distribute into the crystal. ${\ensuremath{\mu}}_{H}$ rapidly decreases with higher-density carriers as they are essentially confined to the surface and are subjected to randomness of the amorphous gate insulators. The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.

Development of the Face Robot SAYA for Rich Facial Expressions

Abstract: The purpose of this study is to develop an interactive communication system that communicates with human beings emotionally. Since the face and its expressions are the most important role for natural communication, we have been developing a face robot that can express facial expressions similar to human beings. In this study, we show a new type face robot SAYA. All McKibben pneumatic actuators are distributed to the surface of the face like a human muscle in order to improve the structure of the face robot and facial muscle movement (Action unit) for natural facial expressions. Since the bending manner of coil spring might be similar to human cervical vertebra, we developed the new head motion mechanism by using coil spring for realizing human like head motion. In this paper, we describe the structure of face robot SAYA and the way of constructing new neck mechanism. We have confirmed that SAYA has ability to express fine facial expressions.

Electrochemical and In Situ XAFS-XRD Investigation of Nb2O5 for Rechargeable Lithium Batteries

Abstract: Nb 2 O 5 exhibits various crystal systems, such as orthorhombic (o), tetragonal (t), and monoclinic (m), among which Nb 2 O 5 synthesized at 900-1000°C is commercially used as a cathode material of the 2-V lithium ion battery. The battery performances depended on the structure of Nb 2 O 5 , and the t-Nb 2 O 5 synthesized at 1000°C exhibited an excellent cycling performance with a large discharge capacity of 190 mAh (g oxide) -1 . The structural variations of Nb 2 O 5 during electrochemical reaction were examined. The in situ synchrotron radiation-X-ray diffraction (XRD) measurement indicated that o- and t-Nb 2 O 5 maintain their original crystal lattices, accompanying a small change in the cell volume even after the Li intercalation. The in situ X-ray absorption fine structure (XAFS) analysis of o- and t-Nb 2 O 5 revealed that the continuous variation from Nb 5+ to Nb 4+ took place during the intercalation process. A significant rearrangement of the Nb-O octahedra accompanied by the change of Nb-O and Nb-Nb interactions occurred in both structures with Li intercalation. XRD and XAFS data suggests that the two-dimensional layer structure of t-Nb 2 O 5 seems to be more flexible regarding the Li intercalation compared with the three-dimensional structure of o-Nb 2 O 5 . This may account for the better cyclic performance of the former material as the electrode material.

Electrochemical Insertion of Li and Na Ions into Nanocrystalline Fe3O4 and α‐Fe2O3 for Rechargeable Batteries

Abstract: Fe 3 O 4 powders with different particle sizes on average (400, 100, and 10 nm) were prepared and characterized by X-ray diffraction, transmission electron microscopy, Mossbauer spectroscopy, and electrochemical methods. To examine the electrochemical activity of Fe 3 O 4 in relation to the particle size effect, galvanostatic cycling tests in aprotic electrolytes containing lithium or sodium ions were conducted. The electrochemical activity was significantly enhanced as the mean particle size decreased. The nanocrystallized Fe 3 O 4 (10 nm) prepared by precipitation method delivered 190 mA h g ―1 of the rechargeable capacity in the voltage range of 2-3 V in a lithium-ion containing electrolyte, whereas the 400 and 100 nm Fe 3 O 4 powders showed 10 and 80 mA h g ―1 of the rechargeable capacity, respectively. An ex situ X-ray diffraction study for the electrochemically cycled samples suggested the partly reversible Fe ion migration from the tetrahedral sites to the octahedral sites with a retained spinel framework structure. The nanocrystallized Fe 3 O 4 as well as α-Fe 2 O 3 were highly electrochemically active in the sodium salt electrolyte. The rechargeable capacity of 160 or 170 mA h g ―1 with excellent capacity retention was obtained for nanocrystalline Fe 3 O 4 or α-Fe 2 O 3 , respectively.