• Journal of applied mathematics & informatics
• /
• 제29권3_4호
• /
• pp.901-908
• /
• 2011

In this paper, we establish a sharp condition of global existence for the solution of the Gross-Pitaevskii equation with an angular momentum rotational term. This condition is related to the ground state solution of some steady-state nonlinear Schrodinger equation.

• Applied Microscopy
• /
• 제45권3호
• /
• pp.115-118
• /
• 2015

In this review paper, I'd like to introduce the basics of angle-resolved photoemission spectroscopy (ARPES) and some of my results taken at the Pohang Accelerator Laboratory (PAL), the only synchrotron radiation in South Korea. The results show that ARPES is very useful, in particular, for studying two-dimensional materials. It looks like a microscope in momentum space similar to transmission electron microscope imaging atoms in real space.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2013년도 제46회 KOSCO SYMPOSIUM 초록집
• /
• pp.47-49
• /
• 2013

Entrainment length and recirculation ratio that are important factors of flameless combustion systems were analyzed by injection conditions using three dimensional numerical simulation. As a result, the entrainment length increased with an increase of momentum ratio and distance of between nozzle. Also, in case of increasing in momentum of oxidation, recirculation ratio was increased and the average temperature was decreased.

• Current Optics and Photonics
• /
• 제3권4호
• /
• pp.292-297
• /
• 2019

We propose a ring resonator-based orbital angular momentum carrying vortex beam generator design with high vertical directional emission efficiency. By adopting a vertically asymmetric grating structure in the ring resonator, optimized for enhanced vertical emission, an emission efficiency in one direction reaches as high as 78%, exceeding the 50% theoretical limit of previously designed vertically symmetric grating-assisted ring resonator-based structures.

• Current Optics and Photonics
• /
• 제3권4호
• /
• pp.298-303
• /
• 2019

We propose a photonic quasi-crystal fiber (PQF) for supporting up to 14 orbital angular momentum (OAM) modes with low and ultra-flat dispersion characteristics over the C+L bands. The designed PQF which consists of a large hollow center and quasi structural small air holes in the clad region exhibits low confinement losses and a large effective index separation (>$10^{-4}$) between the vector modes. This proposed fiber could potentially be exploited for mode division multiplexing and other OAM mode applications in fibers.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.1747-1753
• /
• 2004

CMG(Control Momentum Gyro) is a control device being used for spacecraft attitude control constructing relatively large amount of torque compared to conventional body-fixed reaction wheels. The CMG produces gyroscopic control torque by continuously varying the angular momentum vector direction with respect to the spacecraft body. The VSCMG(Variable Speed Control Momentum Gyro) has favorable advantages with variable speed to lead to better control authority as well as singularity avoidance capability. Attitude dynamics with a VSCMG mounted on a two-axis gimbal system are derived in this study. The dynamic equation may be considered as an extension of the single-axis counterpart. Also, a feedback control law design is addressed in conjunction with the dynamic equations of motion.

• 한국분무공학회지
• /
• 제25권3호
• /
• pp.126-131
• /
• 2020

Throttleable rocket engines are in high demand due to the diversification of space missions. Pintle injector is known to be suitable for throttleable rocket engines, because of its high efficiency in overall thrust zone. In this study, the relationship between spray angle of a throttleable pintle injector and total momentum ratio based on hot fire test conditions was investigated. As a result, the spray angle in 100% and 60% throttling level is higher than the spray angle obtained by the case which considers only propellant mass flow rate, owing to higher total momentum ratio (TMR). The results of this study may be useful for predicting spray angle in hot fire test.

• 한국연소학회지
• /
• 제10권3호
• /
• pp.34-41
• /
• 2005

Hydrogen safety is one of the key technical issue with growing attention on utilization of hydrogen energy. This study is aimed to predict behavior of momentum-controlling buoyant jet and flame caused by hydrogen leakage from a high pressured tank. Approximate solutions were derived for the case of turbulent buoyant jet and diffusion flame in still air. In case of hydrogen jet with low Froude number (100-4000), computed jet trajectories were compared with experimental data and showed good agreement with them. Jet and flame trajectories and flame length of hydrogen are predicted and compared with the buoyant flame of propane. The results well show that buoyancy is dominant in the range of low Froude number, while initial momentum is dominant in the range of high Froude number. That effect is more distinct for hydrogen flame than the case of propane.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2004년도 한국우주과학회보 제13권1호
• /
• pp.70-70
• /
• 2004

Lower thermospheric winds are forced primarily by non-uniform solar heating, atmospheric tides and other waves coming from below, and energy and momentum forcing associated with high-latitude magnetosphere-ionosphere coupling, particularly ion drag and Joule heating. To understand the physical processes that control the thermospheric dynamics, we quantify the momentum forces that are mainly responsible for maintaining the high-latitude lower thermospheric wind system and examine the resulting momentum balance with the aid of the Thermosphere-Ionosphere Electrodynamics General Circulation Model (NCAR-TIEGCM) developed by the National Center for Atmospheric Research. (omitted)

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
• /
• pp.207-214
• /
• 2005

Hydrogen safety is one of the key technical issue with growing attention on utilization of hydrogen energy. This study is aimed to predict behavior of momentum-controlling buoyant jet and flame caused by hydrogen leakage from a high pressured tank. Approximate solutions were derived for the case of turbulent buoyant jet and diffusion flame in still air. In case of hydrogen jet with low Froude number (100-4000), computed jet trajectories were compared with experimental data and showed good agreement with them. Jet and flame trajectories and flame length of hydrogen are predicted and compared with the buoyant flame of propane. The results well show that buoyancy is dominant in the range of low Froude number, while initial momentum is dominant in the range of high Froude number. That effect is more distinct for hydrogen flame than the case of propane.