• ETRI Journal
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• v.21 no.1
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• pp.1-27
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• 1999

We present a new description of envelope-function equation of the superlattice (SL). The SL wave function and corresponding effective-mass equation are formulated in terms of a linear combination of Bloch states of the constituent material with smaller band gap. In this envelope-function formalism, we review the fundamental concept on the motion of a wave packet in the SL structure subjected to steady and uniform electric fields F. The review confirms that the average of SL crystal momentums K = ($k_x,k_y,q$), where ($K_x,k_y$) are bulk inplane wave vectors and q SL wave vector, included in a wave packet satisfies the equation of motion = $_0+Ft/h$; and that the velocity and acceleration theorems provide the same type of group velocity and definition of the effective mass tensor, respectively, as in the Bulk. Finally, Schlosser and Marcus's method for the band theory of metals has been by Altarelli to include the interface-matching condition in the variational calculation for the SL structure in the multi-band envelope-function approximation. We re-examine this procedure more thoroughly and present variational equations in both general and reduced forms for SLs, which agrees in form with the proposed envelope-function formalism. As an illustration of the application of the present work and also for a brief investigation of effects of band-parameter difference on the subband energy structure, we calculate by the proposed variational method energies of non-strained $GaAs/Al_{0.32}Ga_{0.68}As$ and strained $In_{0.63}Ga_{0.37}As/In_{0.73}Ga_{0.27}As_{0.58}P_{0.42}SLs$ with well/barrier widths of $60{\AA}/500{\AA}$ and 30${\AA}/30{\AA}$, respectively.

• Computational Structural Engineering
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• v.10 no.2
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• pp.213-223
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• 1997

Calculation of elastic wave fields has important applications in a variety of engineering fields including NDE (Non-destructive evaluation). Scattering problems have been investigated by numerous authors with different solution schemes. For simple geometries of the scatterers (e.g., cylinders or spheres), the analysis of steady-state elastic wave scattering has been carried out using analytical techniques. For arbitrary geometries and multiple inclusions, numerical methods have been developed. Special finite element methods, e.g., the infinite element method and a hybrid method called the Global-Local finite element method have also been developed for this purpose. Recently, the boundary integral equation method has been used successfully to solve scattering problems. In this paper, a volume integral equation method (VIEM) is proposed as a new numerical solution scheme for the solution of general elasto-dynamic problems in unbounded solids containing multiple inclusions and voids or cracks. A boundary integral equation method (BIEM) is also presented for elastic wave scattering problems. The relative advantage of the volume and boundary integral equation methods for solving scattering problems is discussed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.671-686
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• 2004

The shock-induced combustion ramjet (shcramjet) is a hypersonic airbreathing propulsion concept which over-comes the drawbacks of the long, massive combustors present in the scramjet by using a standing oblique detonation wave (a coupled shock-combustion front) as a means of nearly instantaneous heat addition. A novel shcramjet combustor design that makes use of wedge-shaped flameholders to avoid detonation wave-wall interactions is proposed and analyzed with computational fluid dynamics (CFD) simulations in this study. The laminar, two-dimensional Navier-Stokes equations coupled with a non-equilibrium hydrogen-air combustion model based on chemical kinetics are used to represent the physical system. The equations are solved with the WARP (window-allocatable resolver for propulsion) CFD code (see: Parent, B. and Sislian, J. P., “The Use of Domain Decomposition in Accelerating the Convergence of Quasihyperbolic Systems”, J. of Comp. Physics, Vol. 179, No. 1,2002, pages 140-169). The solver was validated with experimental results found in the literature. A series of steady-state numerical simulations was conducted using WARP and it was deter-mined by means of thrust potential calculations that this combustor design is a viable one for shcramjet propulsion: assuming a shcramjet flight Mach number of twelve at an altitude of 36,000 m, the geometrical dimensions used for the combustor give rise to an operational range for combustor inlet Mach numbers between six and eight. Different shcramjet flight Mach numbers would require different combustor dimensions and hence a variable geometry system in or-der to be viable.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.77.1-77.1
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• 2013

Atomic layer deposition (ALD) is known for its self-limiting reaction, which offers atomic-level controllability of the growth of thin films for a wide range of applications. The self-limiting mechanism leads to very useful properties, such as excellent uniformity over a large area and superior conformality on complex structures. These unique features of ALD provide promising opportunities for future electronics. Although the ALD of Al2O3 film (using trimethyl-aluminum and water as a metal precursor and oxygen source, respectively) can be regarded as a representative example of an ideal ALD based on the completely self-limiting reaction, there are many cases deviating from the ideal ALD reaction in recently developed ALD processes. The nonconventional aspects of the ALD reactions may strongly influence the various properties of the functional materials grown by ALD, and the lack of comprehension of these aspects has made ALD difficult to control. In this respect, several dominant factors that complicate ALD reactions, including the types of metal precursors, non-metal precursors (oxygen sources or reducing agents), and substrates, will be discussed in this presentation. Several functional materials for future electronics, such as higher-k dielectrics (TiO2, SrTiO3) for DRAM application, and resistive switching materials (NiO) for RRAM application, will be addressed in this talk. Unwanted supply of oxygen atoms from the substrate or other component oxide to the incoming precursors during the precursor pulse step, and outward diffusion of substrate atoms to the growing film surface even during the steady-state growth influenced the growth, crystal structure, and properties of the various films.

• Korean Journal of Social Welfare Studies
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• v.48 no.4
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• pp.33-57
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• 2017

As there is a growing concern about the steady increase in the consumer debt and its potential consequences on individuals and families, this study examined the association between personal debt and the risk of domestic violence, which in this study is referred to as violence between man and woman who have a spousal relationship. We used the data from the Korea Welfare Panel Study collected from 2009 to 2016. We applied a generalized estimating equation approach for the analysis of panel data. The results show that the higher the ratio of personal debt to disposable income and the ratio of debt payment to disposal income is, the greater the risk of domestic violence. While the debt to income ratio played a role regarding was related to a heightened risk of domestic violence among the poor group, the debt payment to income ratio was associated with a higher risk of domestic violence among the non-poor group. Implications of the study were discussed.

• Journal of Convergence for Information Technology
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• v.8 no.4
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• pp.153-161
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• 2018

Given that reviewing domestic articles on dating violence since 2009 has not been produced in Korea compared to the seriousness of dating violence, this study aimed to suggest research directions for future studies by exploring trends of recent domestic academic literature on dating violence. For this, the study searched for domestic articles in academic data base using key words related to dating violence. Using content analysis, 70 articles selected were analyzed according to year of publication, research subjects, themes, and methods. The results showed that steady academic effort has been made on this topic and university students were studied the most. The theme of analyzing factors affecting dating violence behavior appeared the most and empirical research was more frequent than non-empirical ones. The results suggested a need to extend the scope of research themes, subjects and methods in this field.

• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.19-24
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• 2021

The low normal zone propagation velocity (NZPV) of high-temperature superconducting (HTS) tape leads to a quench protection problem in HTS magnet applications. To overcome this limitation, various studies were conducted on HTS coils without turn-to-turn insulation (NI coils) that can achieve self-protection. On the other hand, NI coils have some disadvantages such as slow charging and discharging time. Previously, the HTS coils with turn-to-turn insulation (INS coils) were operated in power supply (PS) driven mode, which requires physical contact with the external PS at room-temperature, not in persistent current mode. When a quench occurs in INS coils, the low NZPV delays quench detection and protection, thereby damaging the coils. However, the rotary HTS flux pump supplies the DC voltage to the superconducting circuit with INS coils in a non-contact manner, which causes the INS coils to operate in a persistent current mode, while enabling quench protection. In this paper, a new protection characteristic of HTS coils is investigated with INS coils charging through the rotary HTS flux pump. To experimentally verify the quench protection characteristic of the INS coil, we investigated the current magnitude of the superconducting circuit through a quench, which was intentionally generated by thermal disturbances in the INS coil under charging or steady state. Our results confirmed the protection characteristic of INS coils using a rotary HTS flux pump.

• Ecology and Resilient Infrastructure
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• v.8 no.4
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• pp.245-252
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• 2021

A turbidity current in a river and a lake occurs due to diverse nutrient loading including suspended sediment in sediment runoff, which affects water withdrawal and river environments. We developed one dimensional time-variant numerical model based on Python for the Nagdonggang mainstream. We examined the numerical stability and the applicability of the model by performing the simulation of quasi-steady flow in non-flooding for three cases, which are different according to the point and the amount of turbidity inflows in the Nagdonggang upstream and a tributary. The result was reasonable in the respect of the conservation of matter. The model will facilitate to simulate a large river if we can secure the data of turbidity variations in a target river reach or measured points in a field.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1138-1147
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• 2018

Delayed hydride cracking (DHC) is an important failure mechanism for Zircaloy tubes in the demanding environment of nuclear reactors. The threshold stress intensity factor, $K_{IH}$, and critical hydride length, $l_C$, are important parameters to evaluate DHC. Theoretical models of them are developed for Zircaloy tubes undergoing non-homogenous temperature loading, with new stress distributions ahead of the crack tip and thermal stresses involved. A new stress distribution in the plastic zone ahead of the crack tip is proposed according to the fracture mechanics theory of second-order estimate of plastic zone size. The developed models with fewer fitting parameters are validated with the experimental results for $K_{IH}$ and $l_C$. The research results for radial cracking cases indicate that a better agreement for $K_{IH}$ can be achieved; the negative axial thermal stresses can lessen $K_{IH}$ and enlarge the critical hydride length, so its effect should be considered in the safety evaluation and constraint design for fuel rods; the critical hydride length $l_C$ changes slightly in a certain range of stress intensity factors, which interprets the phenomenon that the DHC velocity varies slowly in the steady crack growth stage. Besides, the sensitivity analysis of model parameters demonstrates that an increase in yield strength of zircaloy will result in a decrease in the critical hydride length $l_C$, and $K_{IH}$ will firstly decrease and then have a trend to increase with the yield strength of Zircaloy; higher fracture strength of hydrided zircaloy will lead to very high values of threshold stress intensity factor and critical hydride length at higher temperatures, which might be the main mechanism of crack arrest for some Zircaloy materials.

• Journal of Power Electronics
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• v.19 no.3
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• pp.784-793
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• 2019

Two objectives can be pursued simultaneously with the ${\delta}$ control of a single-phase electric spring (ES). These objectives are the stabilization of the voltage across the critical load (CL) of a power system, and the achievement of a specific functionality similar to the pure compensation of reactive power or the correction of the power factor. However, existing control systems implementing the ${\delta}$ control do not cope with non-ideal operating conditions, such as line voltage distortions, and exhibit a somewhat sluggish regulation of the CL voltage. In an effort to improve both the steady-state and transient performances of an ES power system, this paper proposes implementing the ${\delta}$ control by means of a control system built up on the repetitive control and assisted by state feedback with pole assignment. This paper starts by analyzing the dynamics of an ES power system in terms of its poles and zeros. After that, a reduced second-order model of the dynamics is formulated to avoid a notch filter in the pole assignment. A repetitive control for an ES power system is then designed to meet the two above mentioned objectives. Experimental tests carried out on a laboratory setup demonstrate the effectiveness of the proposed control system in significantly improving the ES power system performance, while reaching the two objectives. In particular, the tests outline the large mitigation of harmonics in the CL voltage under line voltage distortions and its fast stabilization action.