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The effect of intermolecular interaction on the distribution of the harmonic vibrational frequencies of water molecules was investigated through ab initio molecular dynamics simulations based on the Born-Oppenheimer approach. For single water, the effect of the dynamics of the oxygen atom in single water and the simulation time step on the frequency distribution were examined. The distributions of the OH stretching and HOH bending vibrational frequencies of liquid water were compared to those of single water. The probability distributions of the change in OH bond length and the lifetime of the dangling OH bond were also obtained. The distribution of the frequencies was strongly affected by the long lifetime of the dangling OH bond, resulting in the formation of hydrogen bonds between water molecules.
High speed rotating arc process, forming a flat bead surface with shallow penetration depth, can be applied to the automatic seam tracking, because the amplitude of current waveform increases at high rotation speed. Two high speed arc rotation mechanisms have been developed in Japan and Germany b rotating the electrode nozzle using an external motor, which are used prevalently for narrow gap and conventional seam welding. In this study, a new rotation mechanism was developed by using a hallow shaft motor designed to be installed in the electrode nozzle. By rotating the welding arc, the amplitude of current waveform increases remarkably since the self-regulation of arc is not fully performed. Experiments show that the arc sensor with high-speed rotation arc has improved its responsiveness and sensitivity.
In order to investigate the effects of local and synoptic meteorological conditions on urban scale particulate air pollutants observed over the Busan coastal area, power spectrum analysis was applied to observed particulate matter with an aerodynamic diameter ‹10 μm (PM_10) for the period from 1 October, 1993to 31 December, 2004. Fast Fourier Transform (FFT)analysis was used to obtain the hourly mean observed PM10 concentrations to identify different periodicity scales of PM10 concentrations. The results showed that, aside from the typical and well-known periodicities such as diurnal and annual variations caused by anthropogenic influences, three other significant power spectral density peaks were identified: 7-day,21-day and 2.25-year periodicities. Cospectrum analysis indicated that the seven-day variations were closely related to the synoptic meteorological conditions such as weak wind speed, which are relevant to the stagnant high pressure system slowly passing through the Korean Peninsula. The intra-seasonal 21-day variation was negatively correlated with wind speed but was consistently positively correlated with relative humidity, which is related to aerosol formation that can be achieved as a result of the hygroscopic characteristics of aerosols. However, the quasibiennial 2.25-year variation was correlated with the frequency of Asian dust occurrence, the periodicities of which have been recorded inter-annually over the Korean Peninsula.
This study was performed to compare effect of immune activities of Rhodiola sachalinensis by various extraction process with different temperature and extraction solvents. Experiments were performed for investigate the immune activities on human B and T cell growth and secretion of their cytokines. Also, antibodies in serum were investigated in female ICR mouse by feeding the extracts of R. sachalinensis at doses of 40, 120 and 360 mg/kg orally for 15 days. The immune cell growth and secretion of cytokines (IL-6, TNF-α) on human B and T cells were increased by adding R. sachalinensis extracts compare to the control. Also, total serum IgG levels increased by feeding R. sachalinensis extracts. It can be conclude that optimum condition for efficient extraction of R. sachalinensis as functional material is slovent extraction process using water with ultrasonification at below 100℃ than typical process.