• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.10a
• /
• pp.136-136
• /
• 1998

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.6 s.249
• /
• pp.523-530
• /
• 2006

One of the fascinating prospects is the possibility of new hydrodynamics technology on micro-scale system since oscillations of micro-droplets are of practical and scientific importance. It has been widely conceived that the lowest oscillation mode of a pendant droplet is the longitudinal vibration, i.e. periodic elongation and contraction along the longitudinal direction. Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. The rotation of the droplet about the longitudinal axis is the oscillation mode of the lowest resonance frequency. This rotational mode can be invoked by periodic acoustic forcing and is analogous to the pendulum rotation. It is also found that the natural frequency of a pendant droplet is independent of the drop density and surface tension but inversely proportional to the square root of the droplet size.

• Journal of Industrial Technology
• /
• v.15
• /
• pp.123-135
• /
• 1995

In this paper, we performed the modeling of a tunable three section DFB-LD with continuous phase using the coupled-wave equation. It was also proposed new modeling method for ${\lambda}/4$ phase shifted one. We got the characteristics of oscillation wavelength, gain, and photon density profiles according to parameters such as coupling coefficient K and current into the third sections for two case of continuous phase and ${\lambda}/4$ shifted phase one. The simulations for ${\lambda}/4$ phase shifted tunable three section DFB-LD prove that the continuous tuning range is about 4.2nm for $K=120cm^{-1}$, $L=180{\mu}m$, and the oscillation mode be within the stop-bands. Also when changed a current of both end sections, it is shown that a photon density reaches the maximum at the center.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.11a
• /
• pp.341-344
• /
• 2008

Numerical simulations have been carried out for a supersonic two-dimensional flow over open, rectangular cavities (length-to-depth ratios are L/D = 1.0) in order to investigate the effect of non-equilibrium condensation of moist air on supersonic flows around the cavity for the flow Mach number 1.83 at the cavity entrance. In the present computational investigation, a condensing flow was produced by an expansion of moist air in a Laval nozzle. The results obtained showed that in the case with non-equilibrium condensation for L/D = 1.0, amplitudes of oscillation in the cavity became smaller than those without the non-equilibrium condensation. Furthermore, the occurrence of the non-equilibrium condensation reduced the peaks of power spectrum density and the frequency of the flow field oscillation increased in comparison with the case of $S_0$ = 0.

• Journal of The Korean Astronomical Society
• /
• v.41 no.6
• /
• pp.173-180
• /
• 2008

Using the MHD coronal seismology technique, we estimated the magnetic field for three spicules observed in 2008 June. For this study, we used the high resolution Ca II H line ($3968.5\;{\AA}$) images observed by the Hinode SOT and considered a vertical thin flux tube as a spicule model. To our knowledge, this is the first attempt to estimate the spicule magnetic field using the Hinode observation. From the observed oscillation properties, we determined the periods, amplitudes, minimum wavelengths, and wave speeds. We interpreted the observed oscillations as MHD kink waves propagating through a vertical thin flux tube embedded in a uniform field environment. Then we estimated spicule magnetic field assuming spicule densities. Major results from this study are as follows : (1) we observed three oscillating spicules having durations of 5-7 minutes, oscillating periods of 2-3 minutes, and transverse displacements of 700-1000 km. (2) The estimated magnetic field in spicules is about 10-18 G for lower density limit and about 43-76 G for upper density limit. (3) In this analysis, we can estimate the minimum wavelength of the oscillations, such as 60000 km, 56000 km, and 45000 km. This may be due to the much longer wavelength comparing with the height of spicules. (4) In the first event occurred on 2008 June 03, the oscillation existed during limited time (about 250 s). This means that the oscillation may be triggered by an impulsive mechanism (like low atmospheric reconnection), not continuous. Being compared with the ground-based observations of spicule oscillations, our observation indicates quite different one, i.e., more than one order longer in wavelength, a factor of 3-4 larger in wave speed, and 2-3 times longer in period.

• Ocean Systems Engineering
• /
• v.13 no.2
• /
• pp.123-146
• /
• 2023

In this paper, Moore-Gibson-Thompson theory of thermoelasticity is considered to investigate the fundamental solution and vibration of plane wave in an isotropic photothermoelastic solid. The governing equations are made dimensionless for further investigation. The dimensionless equations are expressed in terms of elementary functions by assuming time harmonic variation of the field variables (displacement, temperature distribution and carrier density distribution). Fundamental solutions are constructed for the system of equations for steady oscillation. Also some preliminary properties of the solution are explored. In the second part, the vibration of plane waves are examined by expressing the governing equation for two dimensional case. It is found that for the non-trivial solution of the equation yield that there exist three longitudinal waves which advance with the distinct speed, and one transverse wave which is free from thermal and carrier density response. The impact of various models (i)Moore-Gibson-Thomson thermoelastic (MGTE)(2019), (ii) Lord and Shulman's (LS)(1967) , (iii) Green and Naghdi type-II(GN-II)(1993) and (iv) Green and Naghdi type-III(GN-III)(1992) on the attributes of waves i.e., phase velocity, attenuation coefficient, specific loss and penetration depth are elaborated by plotting various figures of physical quantities. Various particular cases of interest are also deduced from the present investigations. The results obtained can be used to delineate various semiconductor elements during the coupled thermal, plasma and elastic wave and also find the application in the material and engineering sciences.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.2
• /
• pp.187-196
• /
• 2013

A numerical model was developed to predict the density wave oscillation (DWO) in the furnace wall tubes of a fossil-fired once-through boiler. The transient flow fields in the tubes were obtained using a 1D finite volume method in the time domain. A header model was also implemented to simulate the parallel tube connection of the wall tubes. The inlet and outlet mass flow variation in one of the parallel tubes was examined after a heat perturbation to find the DWO. After successful verification with experimental results reported in literature, the developed model was applied to the wall tubes of a 700-MW boiler furnace. In contrast to the simulation of Takitani's experiment, in which the unstable power thresholds tended to rise in the reduced bypass channel flow, no remarkable changes were observed in the power thresholds in the parallel channel modeling of the wall tubes of the boiler furnace.

• Journal of the Korean Magnetics Society
• /
• v.15 no.1
• /
• pp.7-11
• /
• 2005

A single slab in which one Ni(001) atom layer embedded between two of four Rh layers is considered to examine the oscillation of magnetic moment in each layer. The all electron total-energy full-potential linearized augmented plane wave(FLAPW) method was used to calculate the spin densities, magnetic moments, density of states(DOS), and the number of electrons within each muffin-tin(MT) sphere. The magnetic moment of the center layer Ni(C) in the system of 4Rh/Ni/4Rh is calculated to be 0.34${\mu}_B$, which is 40% have magnetic moment at the interface layers by strong band hybridization with Ni(C) when Ni(001) monolayers is inserted, and the magnetic moment shows a damped oscillation as we go from center Ni(C) layer to the surface Rh(S). From the calculated density of states, it is found that the Fermi level shifts inside the energy band of the Ni(C) in affection of Rh(001).

• Journal of IKEEE
• /
• v.16 no.2
• /
• pp.116-120
• /
• 2012

We reported on a high performance InGaAs/InAlAs metamorphic HEMT with 50 nm gate length on a GaAs substrate. The fabricated $50nm{\times}60{\mu}m$ MHEMT showed good DC and RF characteristics. Typical drain current density of 740 mA/mm and extrinsic transconductance(gm) of 1.02 S/mm were obtained with our devices. The current gain cut-off frequency(fT) and maximum oscillation frequency(fmax) obtained for the fabricated MHEMT device were 430 GHz and 406 GHz, respectively.

• Progress in Superconductivity
• /
• v.14 no.1
• /
• pp.24-29
• /
• 2012

$(TMTSF)_2BF_4$ containing non-centrosymmetric anions is well known to exhibit a metal insulator transition around 37 K by ordering of the anions with a $q_2$=(1/2, 1/2, 1/2) wave vector. We established pressure-temperature phase diagram of the $(TMTSF)_2BF_4$ compound and showed that it can belong to the general phase diagram of the $(TMTSF)_2X$ family. Application of hydrostatic pressure decreases the anion ordering transition temperature and the superconducting state is finally stabilized below 3.77 K under 7.7 kbar. Magnetoresistance measurement on the $(TMTSF)_2BF_4$ under 7.8 kbar is performed but neither the field-induced spin-density-wave state nor the rapid oscillation is observed up to 9 T.