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51.
Rio?Saitou Shin’ichi?NojiriEmail author 《The European Physical Journal C - Particles and Fields》2011,71(8):1712
By using the formulation of the reconstruction, we explicitly construct models of k-essence, which unify the inflation in the early universe and the late accelerating expansion of the present universe by a
single scalar field. Due to the higher derivative terms, the solution describing the unification can be stable in the space
of solutions, which makes the restriction for the initial condition relaxed. The higher derivative terms also eliminate tachyon.
Therefore we can construct a model describing the time development, which cannot be realized by a usual inflaton or quintessence
models of the canonical scalar field due to the instability or the existence of tachyon. We also propose a mechanism of the
reheating by the quantum effects coming from the variation of the energy density of the scalar field. 相似文献
52.
Kihong Son Haijo Jung Sang Hun Shin Hyun-Ho Lee Mi-Sook Kim Young Hoon Ji Kum Bae Kim 《Radiation measurements》2011,46(10):1117-1122
We aimed to evaluate the suitability of a glass dosimeter (GD) for high-energy photon and electron beams in experimental and clinical use, especially for radiation therapy. We examined the expanded dosimetric characteristics of GDs including dose linearity up to 500 Gy, uniformity among GD lots and for individual GDs, the angular dependence, and energy dependence of 4 therapeutic x-ray qualities. In addition, we measured the dosimetric features (dose linearity, uniformity, angular dependence, and energy dependence) of the GD for electron beams of 10 different electron energy qualities. All measurements with the exception of dose linearity for photon beam were performed in a water phantom. For high-energy photon beams, dose linearity has a linear relationship for a dose ranging from 1 to 500 Gy with the coefficient of determination; R2 of 0.998. The uniformity of each GD of dose measurements was within ±0.5% for four GD lots and within ±1.2% for 80 GDs. In terms of the effects of photon beam angle, lower absorbed doses of within 1.0% were observed between 60° and 105° than at 90°. The GD energy dependence of 4 photon beam energy qualities was within ±2.0%. On the other hand, the result of the dose linearity for high-energy electron beams showed well fitted regression line with the coefficient of determination; R2 of 0.999 between 6 and 20 MeV. The uniformity of GDs exposed to the nominal electron energies 6, 9, 12, 16, and 20 MeV was ±1.2%. In terms of the angular dependence to electron beams, absorbed doses were within 2.0% between 60° and 105° than at 90°. In evaluation of the energy dependence of the GD at nominal electron energies between 5 and 20 MeV, we obtained responses between 1.1% and 3.5% lower than that for a cobalt-60 beam. Our results show that GDs can be used as a detector for determining doses when a high-energy photon beam is used, and that it also has considerable potential for dose measurement of high-energy electron beam. 相似文献
53.
Lee KI Joo SJ Lee JH Rhie K Kim TS Lee WY Shin KH Lee BC LeClair P Lee JS Park JH 《Physical review letters》2007,98(10):107202
Tunneling magnetoresistance was found to be suppressed with decreasing temperature for magnetic tunnel junctions (MTJs) oxidized under high plasma power. A strong temperature dependence of the junction resistance was observed, along with zero-bias anomalies of dynamic resistance at low temperatures. Resistance shows a logarithmic dependence on temperature, and resistance versus temperature exhibits a scaling behavior. Our experimental data can be explained in a consistent way by the Kondo effect in the MTJs with the Kondo temperature TK=20-30 K. 相似文献
54.
55.
We investigate the relationship between the eye-penalty and the clock amplitude of the transmission signal. The simulation results for return-to-zero (RZ) signals show a good correspondence between the clock amplitude and the eye-penalty. For a non-return-to-zero (NRZ) signal, however, the correspondence between them is satisfied within the reasonable range of the transmission distance. Thus, we can monitor the eye-penalty by measuring the clock amplitude of the transmission signal. The proposed scheme may provide a cost-effective monitoring of the chromatic dispersion-induced signal distortion in optical transmission systems and networks. 相似文献
56.
In this paper, we report on the generation and the stabilization of ultrafast optical pulse trains exceeding 100 GHz from monolithic mode-locked laser diodes (MLLDs) combined with some new techniques such as subharmonic synchronous mode-locking (SSML) and repetition-frequency multiplication (RFM) method. Key subjects to increase the pulse repetition frequencies of the MLLDs such as fast absorption recovery and harmonic mode-locking operation are discussed. 500 GHz optical pulse generation from a short-cavity, graded-index separated confinement heterostructure MLLD and THz-rate pulse generation by harmonic mode-locking are reported. We also demonstrate the stabilization of a 160 GHz MLLD by the SSML with subharmonic-frequency optical pulse injection and reveal that the SSML is very promising as a stabilization technique of the ultrafast MLLD beyond the limitations by the electronic device speed. A method to accurately measure the timing jitter of such ultrafast optical pulse train, all-optical down converting using a nonlinear optical device, is also presented. We also mention another choice for ultrafast optical pulse generation using the MLLD combined with a dispersive medium such as an optical fiber. We demonstrate here the generations of stable 84–256 GHz optical pulse trains by the RFM method of the MLLD stabilized by the SSML. 相似文献
57.
T. J. Kim S. W. Lee B. K. Kang D. S. Kim A. S. Kim K. H. Shin M. K. Park Y. K. Sin 《Optical and Quantum Electronics》1995,27(5):465-471
High-quality and uniform bulk layers of (Al
x
Ga1–x
)0.5In0.5P (x=0–0.7) and AlGalnP/GainP quantum wells (QWs) are grown on 2°-off (100) GaAs substrates by low-pressure metal organic vapour phase epitaxy at a low growth rate of 0.3 nm s-1. The amount of lattice mismatch and the variation of PL peak energy of (Al0.5Ga0.5)0.5In0.5P on the 50-mm substrate are less than 6×10-4 and 2 meV, respectively. (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P SQWs show narrow PL spectra even from a 0.6 nm well measured at 20 K. The variation of PL peak energy from (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P MQWs is less than 10 meV. Also, as-cleaved AlGalnP/GalnP lasers fabricated by a three-step MOVPE show a pulsed threshold current of 82 mA at room temperature, output power of 12 mW, and the lasing wavelength at 668.2 nm. 相似文献
58.
We propose a color vision model that can be used to predict color appearance in mesopic vision as well as photopic and scotopic vision. It is based on a two-stage model which consists of the cone and opponent stages and it assumes rod intrusion at the opponent stage. The model has the following features to describe the color appearance in mesopic vision. First, it includes a gradual and nonlinear shift in spectral luminous efficiency from V (LD) to V (LD) to cope with the spectral sensitivity difference between photopic and scotopic vision and the nonlinearity of rod influence on the luminance channel. Second, the model assumes decrease of the chromatic component with decreasing illuminance to explain the reduction of saturation at low illuminance levels. Third, it assumes that red/green and yellow/blue components change with illuminance levels independently, thus explaining hue shifts with decreasing illuminance. We applied the model for color appearance simulation of natural scenes in a mesopic visual environment. 相似文献
59.
Jongho Shin Kyungsik Jang Ki-Soo Lim Ik-Bu Sohn Young-Chul Noh Jongmin Lee 《Applied Physics A: Materials Science & Processing》2008,93(4):1015-927
We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold
ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation
and annealing treatment produced different absorption and emission characteristics in Au3+ doped and Au3+, Ag+ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated
by TEM and absorption band analysis. 相似文献
60.
In this paper, we propose a method that controls the depth of the three-dimensional (3D) object existing over the depth-of-focus in integral imaging. The depth control method is performed only in a computer by synthesizing the intermediate sub-images between original sub-images obtained by transforming the captured elemental images. In the reconstruction process, we can obtain reconstructed 3D images with the better image quality within depth-of-focus than that reconstructed over the depth-of-focus. To demonstrate the feasibility of our method, optical and computational experiments are carried out and its results are presented. 相似文献