Search Results - (Author, Cooperation:Y. Nomura)

2015-09-30

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-03-31

American Physical Society (APS)

0031-9007

1079-7114

Physics

Atomic, Molecular, and Optical Physics

2018-01-25

BMJ Publishing Group

0022-2593

1468-6244

Medicine

Genetics

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The Fourier-expansion density matrix method is developed to describe the multiphoton processes of molecules interacting with the heat bath under the strong laser light. This method is applied to deriving expressions for the absorption spectra in the case in which a single-mode laser interacts with the molecular system of a three-level taking into account the dynamic Stark effect. Model calculations are performed to demonstrate the dynamic Stark effects on the absorption ability in the three-level system, and compared with the results of the weak laser light case. The calculated band shapes of the two-photon absorption are analyzed in terms of the simultaneous and sequential mechanisms. The sequential mechanism is characterized by bath-induced intramolecular transitions. As the laser intensity is increased the simultaneous mechanism makes a dominant contribution with increased dynamic Stark effects.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Effects of the coherence transfer induced by the molecule–heat bath interactions on the ultrashort time-resolved coherent anti-Stokes Raman scattering (CARS) from molecules in liquids are theoretically studied. Based on the perturbative density matrix formalism an expression for the CARS intensity is derived taking into account the coherence transfer between the Raman active vibrational transitions of two molecules in liquids. The coherence transfer constants and dephasing constants are properly incorporated with the aid of Liouville space Feynman diagrams. The structure of the coherence transfer matrix element which expresses the time evolution of the coherence between the relevant transitions is clarified by solving the Master equation with the coherence transfer and dephasing constants in the Markoff approximation. Frequency shifts of the quantum beats appear in the time-resolved CARS as a result of the coherence transfer. A multispherical layer model is adopted in evaluating the coherence transfer effects in liquids in femtosecond time domains. Model calculations of time-resolved CARS spectra have been carried out to demonstrate the coherence transfer effects in both short and long range coherence transfer cases. It is predicted that the quantum beats are amplified in the time-resolved CARS spectra of molecules in liquids in a long range coherence transfer case when there exist differences in the coherence transfer constants between each spherical layer.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Low-temperature (∼4 K) photoluminescence has been studied on as-grown and thermally annealed Si-doped GaAs grown by molecular beam epitaxy. The peak intensities of the defect-related emissions, due to the defect-induced bound exciton (d, X) and the defect complex (d) are decreased by thermal annealing. On the other hand, Hall measurements show that free carrier concentrations are decreased only slightly by thermal annealing.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We demonstrate laser emission by photopumping at room temperature from a distributed feedback structure for a surface-emitting laser constructed by alternating growths of a GaAs/AlGaAs multiquantum well and an Al0.7Ga0.3As layer using molecular-beam epitaxy. A threshold photoexcitation intensity lower than 3.1×105 W/cm2, a 34-nm longitudinal mode spacing, and a 2.3-nm peak width of the laser emission were observed for the 6-μm-thick multilayer.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Using ionized Mg beams accelerated to energies from 130 to 500 eV, Mg doping was studied in molecular-beam epitaxy of GaAs. The incorporation coefficient of Mg increases by a factor of about 100 when compared with the use of neutral Mg beams. Hole concentrations as high as about 1×1019 cm−3 have been achieved. Photoluminescence measurements suggest that the damage due to Mg-ion bombardment is negligible when the ion accelerating voltage (Va) (approximately-less-than)130 V. For higher Va , the damage can be removed by postgrowth annealing.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

GaAs/Al0.22Ga0.78As single quantum wells with localized Si doping were grown by molecular beam epitaxy. Low-temperature (1.8, 4.2 K) photoluminescence due to excitons bound to Si donors, which were located at the center of wells, was observed. The binding energies of the exciton are 1.8–1.3 meV for well widths ranging from 7.4–15.4 nm, and substantially agree with the theoretical results obtained by Kleinman [Phys. Rev. B 28, 871 (1983)].

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1471-4159

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The spatial variation of the growth rate on mesa-etched GaAs (1¯1¯1¯)B substrates during molecular beam epitaxy of GaAs is measured from the period of the reflection high-energy electron diffraction (RHEED) intensity oscillation using in situ scanning microprobe RHEED. The surface diffusion length of Ga adatoms on the (1¯1¯1¯)B surface is determined from the spatial variation of the growth rate. The surface diffusion length on the (1¯1¯1¯)B surface increases as the substrate temperature is raised or the arsenic pressure is decreased. The typical value of the diffusion length is about 10 μm at a substrate temperature of 580 °C and an arsenic pressure of 5.7×10−4 Pa, which is an order of magnitude larger than that on the (100) surface along the [011] direction. The activation energy of the surface diffusion length changes with the surface reconstruction. Anisotropic diffusion, as reported for the (100) surface, is not observed on the (1¯1¯1¯)B surface.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

In situ Auger electron spectroscopy is employed to study the dynamics of the desorption process of carbon and its related species from clean molecular beam epitaxially grown GaAs surfaces exposed to trimethylgallium under the conditions where atomic layer epitaxy takes place by metalorganic molecular beam epitaxy. The direct real time spectroscopic observation of the surfaces by Auger electron spectroscopy shows that, after exposure to trimethylgallium, the initial carbon signal intensity exponentially decreases with an activation energy of 1.3 eV and reaches a steady state level.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Systematic measurements were carried out on the surface-diffusion length of Ga adatoms during the molecular-beam epitaxy of GaAs in the presence of hydrogen atoms (H⋅) or hydrogen molecules (H2). The spatial variation of the growth rate on the (100) surface adjacent to the (111)A surface was measured from the period of the reflection high-energy electron diffraction (RHEED) intensity oscillations using in situ scanning microprobe RHEED. The surface-diffusion length of Ga adatoms, which was derived from the spatial variation of the growth rate, becomes larger along with an increase in the H⋅ or H2 pressure. It also increases as the substrate temperature is raised under H⋅ or H2 pressure. The diffusion length in the case of H⋅ introduction is larger than that in the case of H2 introduction. © 1995 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

An expression for the probability of time-resolved three-photon ionization via coherently excited resonant states of a molecular system is derived in the perturbative density matrix formalism with the aid of the Liouville space Feynman diagram. It is shown how the time evolution of the molecular coherence in the first resonant state can be detected as a function of the delay time between the pumping and probing lasers through the probing two-photon ionization process. The three-photon ionization process consists of the simultaneous and sequential processes which are classified by the Liouville space Feynman diagrams. The possibility of appearance of quantum beats in the pump–probe three-photon ionization is discussed by performing model calculations of the probability of ionization. The role of the direct and redistributed processes is discussed. The redistributed process is induced by intramolecular processes in the resonant state. The theoretical treatment is applied to the (1+2) three-photon ionization of pyrazine observed by Knee et al. It is demonstrated that the fast decay component (110 ps) of the pyrazine spectra originates from the intramolecular dephasing of the vibronic coherence created by the pumping pulse laser, and this component appears only when the redistributed process (the ionization process through triplet levels) is absent.

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Effects of vibration–rotation (Coriolis) couplings on the coherent polarization anisotropy are theoretically studied in a time-resolved two-photon ionization of a symmetric top molecule. This polarization anisotropy originates from a coherent excitation of the resonant rovibronic molecular eigenstates (rovibronic coherence) whose zeroth order states are mixed through the Coriolis coupling. Expressions for the time-dependent degree of polarization after the coherent excitation of the rovibronic states produced by the Coriolis coupling are derived as a function of the delay time in the pump–probe two-photon ionization. Model calculations of the time-dependent degree of polarization as well as the probabilities of the two-photon ionization are performed to demonstrate the Coriolis coupling effects in the low excess energy regions of the resonant intermediate state. It is shown that oscillatory behaviors in the time-dependent degree of polarization should be observed as a result of the creation of the rovibronic coherence. It is demonstrated that oscillations of the degree of polarization involve both contribution of the purely rotational J-coherence and that of the rovibronic coherence in the resonant manifold when the rotational branches are coherently excited and the characteristic rotation–vibration interaction energy is larger than a typical free rotational energy under jet-cooled condition.

Electronic Resource

1600-0765

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The effects of various prostaglandins (PGs) on the functions of human gingival fibroblasts (Gin-1 cells; ATCC CRL 1292) were examined by phase-contrast microscopy, cell-counting and radioautographic experiments. Tested PGs were PGA1, PGA2, PGB1, PGB2, PGD2, PGE1, PGE2, PGF1α, PGF2α, PGI2, 6-keto-PGF1α, 9α-11α-methanoepoxy-PGF2α, and thromboxane (TX) B2. PGA1, and PGD2 at 30 μM caused morphological deformation of Gin-1 cells. All the PGs tested at 30 μM suppressed the proliferation of Gin-1 cells in the logarithmic growth phase. Furthermore, all the PGs tested at 10 μM suppressed DNA synthesis, collagen synthesis, and noncollagenous protein synthesis in confluent Gin-1 cells, while exerting no effect on GAG synthesis. The concentrations of PGs used are beyond those found in healthy gingiva. However, in periodontitis the local concentrations of some PGs within the gingiva are expected to be extremely elevated beyond the physiological level. These results suggest that PGs may play an important role as a negative regulator in metabolism and some pathologic gingival conditions by suppressing the functions of gingival fibroblasts.

Electronic Resource

1440-1681

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

1. To determine the possible role of voltage-dependent Ca2+ channels (VDCC) and Ca2+-activated K+ (KCa) channels in the regulation of resting tone of arteries from young spontaneously hypertensive rats (SHR), mechanical responses to the agents which interact with these channels were examined in endothelium-denuded strips of femoral arteries from 4 week old SHR and age-matched normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressures at this age were not significantly different between SHR and WKY.2. The strips from SHR, but not from WKY, maintained a myogenic tone; that is, the resting tone decreased when nifedipine was added.3. Studies using 1 or 5 min pulse labelling of the strips with 45Ca showed that the basal Ca2+ influx was increased in SHR when compared with WKY, and this increase in SHR was abolished by nifedipine. Similar results were obtained when the cytoplasmic Ca2+ concentration ([Ca2+]i) in the resting state of the strips was measured by fura-PE3.4. The addition of charybdotoxin (ChTX, a blocker of large conductance Kca channels) to the resting state caused a concentration-dependent contraction, which was much greater in SHR than in WKY. The ChTX-induced contraction in SHR was abolished by nifedipine.5. In strips preloaded with 86Rb, the basal 86Rb efflux rate constant was significantly greater in SHR than in WKY. The increase in 86Rb efflux in SHR was abolished by nifedipine.6. The results suggest that the Ca2+ influx via L-type VDCC was increased in the resting state of the femoral artery from 4 week old SHR, and therefore the myogenic tone was maintained and ChTX-sensitive K+ channels were highly activated.

Electronic Resource

1365-2842

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

One important mechanical property of dental ceramics is fracture toughness, KIC, which represents the serviceability in the oral cavity, such as the resistance to marginal fracture. KIC values of several dental ceramics, natural tooth enamel and industrial ceramics were examined by use of the indentation microfracture (IM) method. This technique was based on the series of radial cracks emanating from the corners of the Vickers indentation. It was observed that appropriate load levels should be selected on each specimen to induce radial/median cracks. For feldspatic dental porcelains, larger loads of 10, 20 and 30 kg were needed to determine their KIC values in the range 1.5–2.1 MN-rn−3/2. For natural tooth enamel and a new apatite-based castable glass-ceramic, a smaller force of 1 kg was sufficient to decide the respective KIC values of about 0.9 and 1.8 MN-m−3/2. The KIC values of most dental ceramics examined were slightly higher than that of soda lime glass, but less than one-third that of zirconia. It was confirmed that the IM method is simple and cost-effective for evaluation of KIC of dental ceramics.

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