Hiroyuki Takeda

Constitutive activation of Src family kinases in mouse embryos that lack Csk

Csk is a novel cytoplasmic protein-tyrosine kinase that has been shown to inactivate members of the Src family of protein-tyrosine kinases in vitro. To examine the function of Csk in vivo, Csk-deficient mouse embryos were generated by gene targeting in embryonic stem cells. These embryos were developmentally arrested at the 10 to 12 somite stage and exhibited growth retardation and necrosis in the neural tissues. The kinase activity of p60c-src, p59fyn, and p53/56lyn in these embryos was greatly enhanced as an apparent consequence of enhanced specific activity. The increase in kinase activity was associated with an increase in tyrosine phosphorylation of several proteins, especially those around 85 and 120 kd. Thus, these results suggest that Csk indeed acts as an indispensable negative regulator of Src family kinases in vivo.

Tunable photonic band schemes of opals and inverse opals infiltrated with liquid crystals

When an optically birefringent nematic liquid crystal is infiltrated into the void regions of opals and inverse opals, degeneracies seen in photonic band schemes are found theoretically to disappear, resulting in the appearance of several new weak peaks in the reflection spectra. Tunabilities of the reflection peaks upon applied electric fields are discussed as a function of refractive indices and anisotropies of liquid crystals. Much larger tunabilities are demonstrated in inverse opals infiltrated with liquid crystals.

Tunable light propagation in Y-shaped waveguides in two-dimensional photonic crystals composed of semiconductors depending on temperature

We theoretically demonstrate the tunability of light propagation in Y-shaped waveguides in two-dimensional photonic crystals composed of semiconductors that depend on temperature. Refractive indices of semiconductors for light near the plasma frequency can be changed under the influence of temperature. Thus, we can control the direction of light propagation in Y-shaped waveguides in two-dimensional photonic crystals, which may provide novel application of waveguides.

Energy resolution of gas ionization chamber for high-energy heavy ions

The energy resolution is reported for high-energy heavy ions with energies of nearly 340 MeV/nucleon and was measured using a gas ionization chamber filled with a 90%Ar/10%CH4 gas mixture. We observed that the energy resolution is proportional to the inverse of the atomic number of incident ions and to the inverse-square-root of the gas thickness. These results are consistent with the Bethe–Bloch formula for the energy loss of charged particles and the Bohr expression for heavy ion energy straggling. In addition, the influence of high-energy δ-rays generated in the detector on the energy deposition is discussed.

Flat photonic bands in two-dimensional photonic crystals with kagome lattices

We theoretically demonstrate flat photonic bands in two-dimensional photonic crystals with kagome lattices. In such photonic crystals composed of circular rods, electromagnetic waves localizing at the rods form flat photonic bands. The flat photonic bands are important for the omnidirectional lasing and the enhancement of the omnidirectional electromagnetic interaction of materials. Dependences of flat photonic bands on the dielectric constant and radii of rods are discussed.

Photonic band schemes of opals composed of periodic arrays of cored spheres depending on thickness of outer shells

Photonic band schemes of opals as pseudophotonic crystals composed of three-dimensional arrays of cored spheres are calculated theoretically. Pseudophotonic band gaps are confirmed to be dependent on the thickness of outer shells and also refractive indices of the inner core and outer shells. Tunabilities of photonic band schemes of these types of opals are also discussed.

Systematic investigation of surface and bulk electronic structure of undoped In-polar InN epilayers by hard X-ray photoelectron spectroscopy

The surface and bulk electronic structure of undoped In-polar InN (u-InN) epilayers with surface electron accumulation (SEA) layer was investigated by soft and hard X-ray photoelectron spectroscopies (SX-PES and HX-PES, respectively). The potential-energy profile was obtained by fitting the N 1s core-level spectra accounting for the probing depth of both SX-PES and HX-PES and the surface downward band bending. In this study, we found that a significant potential-energy bending as large as 1.2 ± 0.05 eV occurred from surface to the depth of ∼20 nm. Taking into account such a large downward bending, the valence band maximum (VBM) with respect to Fermi energy (EF) level in the bulk was determined to be 0.75 ± 0.05 eV. A weak signal with a peak position at 0.3 ± 0.05 eV was reproducibly observed from the VBM to EF level in the HX-PES spectrum. The peak position was in agreement with the calculated energy of the E1 sub-band in the surface quantum well. HX-PES is powerful tool for revealing the intrinsic bulk e...

Photonic band structures for three-dimensionally periodic arrays of coated spheres

Photonic band structures of three-dimensional periodic structures of opals composed of nanoscale spheres coated with various materials have been studied theoretically. Opals composed of silica spheres coated with different materials can have smaller and larger band gaps at the L and X points, respectively, in the Brillouin zone of the face-centered cubic structure, although the magnitude of the gap at the X point is generally much smaller than that at the L point in conventional opals. Moreover, such a behavior can be explained by applying the same method as the free electron approximation in solid-state physics to photonic crystals. These phenomena may be suitable for practical application of photonic crystals even when the refractive indices of the materials are low.

Impact of Mg concentration on energy-band-depth profile of Mg-doped InN epilayers analyzed by hard X-ray photoelectron spectroscopy

The electronic structures of Mg-doped InN (Mg-InN) epilayers with the Mg concentration, [Mg], ranging from 1 × 1019 to 5 × 1019 cm−3 were systematically investigated by soft and hard X-ray photoelectron spectroscopies. The angle-resolved results on the core-level and valence band photoelectron spectra as a function of [Mg] revealed that the energy band of Mg-InN showed downward bending due to the n+ surface electron accumulation and p type layers formed in the bulk. With an increase in [Mg], the energy-band changed from monotonic to two-step n+p homojunction structures. The oxygen concentration rapidly increased at the middle-bulk region (∼4.5 to ∼7.5 nm) from the surface, which was one of the reasons of the transformation of two-step energy band.

Tunable Photonic Band Schemes in Two- and Three-Dimensional Photonic Crystals with Double Periodicity and Their Applications

Photonic band schemes of two- and three-dimensional photonic crystals with double periodicity have been studied theoretically with consideration of the special arrangements of rods or spherical bodies with two kinds of dielectric indices. In photonic crystals with double periodicity, band gaps appear at about half the frequencies of conventional photonic crystals. The origin of these characteristics and the tunability of the photonic band schemes in photonic crystals of organic materials under the influence of temperature are discussed. Moreover, novel applications such as the tunabilities of second harmonic generation, lasing and large hops of peak frequencies due to the change to double periodicity are also discussed.