• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.88.2-88.2
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• 2013

Exploration of the wave-mode identification and its propagating property in the solar pore is desirable to study the energy transfer in the solar atmosphere. The Fast Imaging Solar Spectrograph (FISS) installed at the New Solar Telescope (NST) is a unique system that can do imaging of H-alpha and Ca II 8542 band simultaneously, which is quite suitable for studying of dynamics of chromosphere. In this study, we inspect a relationship between the cross-sectional area and intensity of the pore at continuum (-0.4 nm) near the Ca II line. We find coherent oscillations of the area and intensity. They shows out-of-phase (~ 180 degree difference) in photosphere, which implies that the oscillation is fast sausage mode. We also investigate a relationship between LOS velocities above the pore obtained from the Ca II and the Ha line cores, and find no significant difference of the phase (~10 degree) between the formation heights of the lines in chromosphere.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.12
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• pp.1763-1773
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• 1998

In the present experimental study, the flow behavior in a semi-closed two-phase natural circulation loop was examined. Water was used as the working fluid. Heat flux, heater-inlet subcooling, and flow restrictions at the heater-inlet and at the expansion-tank-line were taken as the controlling parameters Six circulation modes were identified by changing heat flux and inlet subcooling conditions ; single-phase continuous circulation, periodic circulation (A), two-phase continuous circulation, and periodic circulations (B), (C), and (D). Among these, the single-phase and two-phase continuous-circulation modes exhibit no significant oscillations and are considered to be stable. Periodic circulation (A) is characterized by the large amplitude two-phase f10w oscillations with the temporal single-phase circulation between them, while periodic circulation (B) featured by the flow oscillations with continuous boiling inside the heater section. Periodic circulation (C) appears to be the manometric oscillation with continuous boiling. Periodic circulation (D) has the longer period than periodic circulation (B) and a substantial amount of liquid flow back and forth through the expansion-tank-line periodically ; this mode is considered the pressure drop oscillation. Parametric study shows that the increases of the inlet- and expansion-tank-line- restrictions and the decrease of inlet subcooling broaden the range of the stable two-phase(continuous circulation) mode.

• The KSFM Journal of Fluid Machinery
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• v.11 no.3
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• pp.14-21
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• 2008

A numerical simulation on the flow field of a valveless bidirectional piezoelectric micropump has been performed. In this type of micropump, the oscillation of the piezoelectric diaphragm generates the blowing and suction flow through the oblique channel from the pumping chamber. The angle between the oblique and main channel causes the variation of flow distribution through upstream and downstream channels in suction and blowing modes. In the suction flow mode, the working fluid flows from both the upstream and downstream of the main channel to the pumping chamber through the oblique channel. However, in the blowing flow mode, the fluid pushed out of the pumping chamber flows more toward the downstream of the main channel due to the inertia of the fluid. In the present study, the effects of geometries such as the angle of oblique channel and the shape of main channel on the flow rate of the up/downstream were investigated. The flow rate obtained from the pump and the energy required to the pump were also analyzed for various displacements and frequencies of the oscillation of the diaphragm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.104-109
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• 2000

The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoutic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding. Acoustic radiation is more intense, with multiple frequencies present.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.984-989
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• 2008

An estimation of high-order damping in flexible multibody dynamic simulation is introduced in this paper. The suggested damping model based on the experimental modal analysis leads to more accurate correlation results comparing to the traditional linear damping model because it directly uses the modal parameters of each mode achieved from experiment even high frequency modes. The modal parameters until the 5th mode are extracted from the experimental modal testing of the flexible beam using a high speed camera. And using the measured damping ratio and natural frequency until the 5th mode, the generic damping model is constructed. Then, the ANCF (absolute Nodal Coordinate Formulation) simulation results are compared to experimental results until the 5th mode.

• Journal of Electrical Engineering and information Science
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• v.2 no.3
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• pp.88-94
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• 1997

This paper presents the sliding mode observer-model following (SMO-MF) power system stabilizer(PSS) for unmeasurable state variables. This SMO-MF PSS is obtained by combining the sliding mode-model following (SM-MF) including closed-loop feedback(CLF) with the full-order observer(FOO). The control input of the proposed MO-MF PSS is derived by Lyapunov's second method to determine a control input that keeps the system stable for unmeasurable plant state variables. Simulation results show that the proposed SMO-MF PSS including CLF is able to reduce the low frequency oscillation and to achieve asymptotic tracking error between the reference mode state and the estimated plant state at different initial conditions.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.12
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• pp.51-57
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• 2004

A simple fiber length measurement technique has been demonstrated by using a self-seeding laser oscillation of a Fabry-Perot laser diode. We induced a self-seeding laser oscillation through a closed-loop by adjusting the modulation frequency of a Fabry-Peort laser diode when the output optical pulse of the laser reinjected into the laser after passing through the closed-loop. The length of a fiber-under-test was calculated from the difference between my two modulation frequencies at which self-seeding laser oscillation occurs at a specific mode. We have experimentally confirmed the technique for various fiber lengths from 0.1 km to 75 km. The relative error between the measurement result of the proposed technique and that of a commercial instrument was less than 0.24 %. The repeatability of the proposed technique was better than 0.1 %.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.5
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• pp.515-525
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• 2014

In this paper, we present a design and implementation of a Voltage-tuned Planar Composite Resonator Oscillator(Vt-PCRO) with a low phase noise. The designed Vt-PCRO is composed of a resonator, two phase shifters, and an amplifier. The resonator is designed using a dual mode SIW(Substrate Integrated Waveguide) resonator and has a group delay of about 40 nsec. Of the two phase shifters (PS1 and PS2), PS1 with a phase shift of $360^{\circ}$ is used for the open loop gain to satisfy oscillation condition without regard to the electrical lengths of the employed microstrip lines in the loop. PS2 with a phase shift of about $70^{\circ}$ is used to tune oscillation frequency. The amplifier is constructed using two stages to compensate for the loss of the open loop. Through the measurement of the open loop gain, the tune voltage of the PS1 can be set to satisfy the oscillation condition and the loop is then closed to form the oscillator. The oscillator with a oscillation frequency of 5.345 GHz shows a phase noise of -130.5 dBc/Hz at 100 kHz frequency offset. The oscillation power and the electrical frequency tuning range is about 3.5 dBm and about 4.2 MHz for a tuning voltage of 0~10 V, respectively.

• Molecules and Cells
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• v.43 no.3
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• pp.276-285
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• 2020

Circadian rhythm is an endogenous oscillation of about 24-h period in many physiological processes and behaviors. This daily oscillation is maintained by the molecular clock machinery with transcriptional-translational feedback loops mediated by clock genes including Period2 (Per2) and Bmal1. Recently, it was revealed that gut microbiome exerts a significant impact on the circadian physiology and behavior of its host; however, the mechanism through which it regulates the molecular clock has remained elusive. 3-(4-hydroxyphenyl)propionic acid (4-OH-PPA) and 3-phenylpropionic acid (PPA) are major metabolites exclusively produced by Clostridium sporogenes and may function as unique chemical messengers communicating with its host. In the present study, we examined if two C. sporogenes-derived metabolites can modulate the oscillation of mammalian molecular clock. Interestingly, 4-OH-PPA and PPA increased the amplitude of both PER2 and Bmal1 oscillation in a dose-dependent manner following their administration immediately after the nadir or the peak of their rhythm. The phase of PER2 oscillation responded differently depending on the mode of administration of the metabolites. In addition, using an organotypic slice culture ex vivo, treatment with 4-OH-PPA increased the amplitude and lengthened the period of PER2 oscillation in the suprachiasmatic nucleus and other tissues. In summary, two C. sporogenes-derived metabolites are involved in the regulation of circadian oscillation of Per2 and Bmal1 clock genes in the host's peripheral and central clock machineries.

• Journal of The Korean Astronomical Society
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• v.26 no.2
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• pp.115-134
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• 1993

The light curve and radial velocity curve of multiperiodic dwarf cepheid VI719 Cyg (HD200925) with peculiar light curve have been reanalyzed in order to identify the oscillation modes to confirm the helium settling within the envelope. To do these, through the period search for the photometric and radial velocity data from the literature, two different periods were determined and the oscillation modes corresponding to the first and second periods were identified as the fundamental and first radial overtones. Hence the helium settling within the envelope was confirmed from the period ratio. The color excess, metallicity, effective temperature, and surface gravity corresponding to two different modes were determined and it was found that these parameters almost do not depend upon different oscillation mode. By utilizing the surface brightness method, we investigated the variation of angular diameter and radial displacement and it was found that the angular variation is very peculiar. Also by referring to the stellar models, mass and age were determined as $2.7M_{\bigodot}$ and 0.42 Gyr respectively which make this variable star heavier and younger than other multimode dwarf cepheids. Preliminary spectroscopic CCD observations were carried out and it was found that Mg in VI719 Cygni is nearly solar abundent according to the analysis of $5172.68{\AA}MgI$ line which is inconsistent with the photometric result. It was suggested that VI719 Cyg may be classified as a $\rho$ Pup stars according to the photometric characteristics.