• 천문학회보
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• 제46권1호
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• pp.37.2-37.2
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• 2021

One of the main limitations to the ground- based gravitational-wave (GW) detector sensitivity is quantum noise, which is induced by vacuum fluctuations entering the detector output port. The replacement of this ordinary vacuum field with a squeezed vacuum field has proven to be effective approach to mitigate the quantum noise in the interferometer detector and it is currently used in advanced detectors. However, the current frequency-independent squeezed vacuum cannot reduce quantum radiation pressure noise at low frequencies. A possible solution to reduce quantum noise in the broadband spectrum is the injection of frequency-dependent squeezed (FDS) vacuum. We will report the current status of squeezing experiment at KASI and introduce to the EPR (Einstein-Podolsky-Rosen) entangled state of light, which can realize FDS light without the need for an additional, external cavity.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.97-106
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• 2004

Stability of laminar premixed planar flames inclined in gravitational field which generate vorticity is asymptotically examined. The flame structure is resolved by a large activation energy asymptotics and a long wave approximation. The coupling between hydrodynamics and diffusion processes is included and near-unity Lewis number is assumed. The results show that as the flame is more inclined from the horizontal plane it becomes more unstable due to not only the decrease of stabilizing effect of gravity but also the increase of destabilizing effect of rotational flow. The obtained dispersion relation involves the Prandtl number and shows the destabilizing effect of viscosity. The analysis predicts that the phase velocity of unstable flame wave depends on not only the flame angle but also the Lewis number. For relatively short wave disturbances, still much larger than flame thickness, the most unstable wavelength is nearly independent on the flame angle and the flame can be stabilized by gravity and diffusion mechanism.

• 천문학회보
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• 제40권1호
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• pp.57.5-58
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• 2015

We describe relations between modern cosmology and general relativity in the historical context. We reveal some ironies imbedded in Einstein's final correction of his gravitational field equation in the context of cosmology in 1917 which has apparently opened a new era of modern physical cosmology. The ugly (according to Einstein) correction term was introduced only to build a static cosmology which turns out to be in flat contradiction with observation. Somehow, however, it is the correction term which has saved the modern cosmology from the genuine creativity of nature continuously revealed by astronomical observations. Whether the present precision cosmology is also a correct one is often ignored by the practitioners but still a pressing open question left for future theoretical and observational pursuits.

• 천문학논총
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• 제27권4호
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• pp.305-310
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• 2012

AKARI's all-sky survey resolves the far-infrared emission in many thousands of nearby galaxies, providing essential local benchmarks against which the evolution of high-redshift populations can be measured. This review presents some recent results in the resolved galaxy populations, covering some well-known nearby targets, as well as samples from major legacy surveys such as the Herschel Reference Survey and the JCMT Nearby Galaxies Survey. This review also discusses the prospects for higher redshifts surveys, including strong gravitational lens clusters and the AKARI NEP field.

• 대한기계학회논문집A
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• 제22권4호
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• pp.743-752
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• 1998

Numerical analysis for the flow and heat transfer in solid particle moving beds of heat exchangers is presented. The solid particle flow through the bundle of heat source tubes by the gravitational force. The heat energy is transferred through the direct contact of particles with the heat source tubes. The viscous-plastic fluid model and the convective heat transfer model are employed in the analysis. The flow field dominantly influences the total heat transfer in a heat exchanger. As the velocities of solid particles around the heat source tubes increase, the amount of heat transfer from the tubes increases. Some examples are presented to show the performance of the numerical model. The flow effect on the heat transfer is also studied through the examples.

• 한국자동차공학회논문집
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• 제10권1호
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• pp.9-16
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• 2002

The particles velocity in the instantaneous flow field and velocity change of particles along the jet centerline for various particle diameter in a circular turbulent impingement jet are investigated by using particle image velocimetry(PIV) and an equation of particle motion simplified by terms of inertia forces, drag and gravitational force. The jet Reynolds number was 3300 and 8700, and glass beads of 30,58 and 100$\mu$m in diameter were used. The PIV results show that the direction and size of velocity depends not only on the number density of particle but also on the particle momentum. The results obtained form calculation suggest that the particle velocity near the first impingement region deviated from local air velocity, which accords well with the PIV results. The rebound height of particle increase with the particle diameter. In the second-impingement, particle velocities increased sluggishly with Re=3300 but particle velocities uniformed with Re=8700 in stagnation region.

• 한국연소학회지
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• 제9권4호
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• pp.9-21
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• 2004

Stability of laminar premixed planar flames inclined in the gravitational field is asymptotically examined. The flame structure is resolved by a large activation energy asymptotics and a long wave approximation. The coupling between hydrodynamics and diffusion processes is included and near-unity Lewis number is assumed. The results show that as the flame is more inclined from the horizontal plane it becomes more unstable due to not only the decrease of stabilizing effect of gravity but also the increase of destabilizing effect of rotational flow. The obtained dispersion relation involves the Prandtl number and shows the destabilizing effect of viscosity. The analysis predicts that the phase velocity of unstable flame wave depends on not only the flame angle but also the Lewis number. For relatively short wave disturbances, still much larger than flame thickness, the most unstable wavelength is nearly independent on the flame angle and the flame can be stabilized by gravity and diffusion mechanism.

• 한국소음진동공학회논문집
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• 제24권4호
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• pp.317-323
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• 2014

This study is concerned with the free vibration analysis of an inextensible uniform rope with a spring-mass system at the tip. The rope is hanged vertically in a gravitational field. This problem is related to the free vibration of an elevator rope connected to an elevator cage. The equation of motion and the corresponding boundary conditions are derived by using the Hamilton's principle. The general solution of the governing equation of motion is expressed in terms of Bessel functions. The characteristic equation was derived by applying the boundary conditions. The characteristic values which are in fact non-dimensionalized natural frequencies were obtained numerically. The effects of mass and spring constant were investigated. The numerical results show how the tip mass and spring affect the natural frequencies of the rope.

• Journal of Astronomy and Space Sciences
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• 제20권4호
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• pp.319-326
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• 2003

The motion of each satellite in a tethered satellite system is non-Keplerian in the Earth's gravitational field. In this paper, the tether perturbation force is formulated and compared with the perturbation force due to the Earth's oblateness. Also, the center of mass motion of the tethered satellite system is analyzed. The tether perturbing force on the one of satellites in a tethered satellite system is much bigger than the Earth's oblateness perturbation. The two-body motion approximation of the center of mass is acceptable to describe the motion of the system, when the libration is small.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.229-232
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• 1997

In this paper, the case study of reducing rotational errors is done for a grinding spindle with an active magnetic bearing system. The rotational errors acting on the magnetic bearing spindle are due to mass unbalance of rotor, runout, grinding excitation and unmodeled nonlinear dynamics of electromagnets. For the most case, the electrical runout of sensor target is big even in well-finished surface; this runout can cause a rotation error amplified by feedback control system. The adaptive feedforward method based on LMS algorithm is discussed to compensate this kind of runout effects, and investigated its effectiveness by numerical simulation and experimental analysis. The rotor orbit size in both bearings is reduced about to 5 pin due to lX rejection by feedforward control up to 50,000 rpm.