• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.4
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• pp.7-14
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• 2000

A Bi$_{4}$Ti$_{3}$O$_{12}$ (BIT) thin film is prepared by sol-gel method using acetate precursors and evaluated whether it could be applied to NVFRAM (Non-Volatile Ferroelectric RAM). The drying and the annealing temperature are 40$0^{\circ}C$ and $650^{\circ}C$, respectively and they are determined from the DT-TG (Differential Thermal-Thermal Gravimetric) analysis. The BIT thin film deposited on Pt/Ta/SiO$_{2}$/Si substrate shows orthorhombic perovskite phase. The grain size and the surface roughness are about 100 nm and 70.2$\AA$, respectively. The dielectric constant and the loss tangent at 10 KHz are 176 and 0.038, respectively, and the leakage current density at 100 ㎸/cm is 4.71 $mutextrm{A}$/$\textrm{cm}^2$. In the results of hysteresis loops measured at $\pm$250 ㎸/cm, the remanent polarization (Pt) and the coercive field (Ec) are 5.92 $\mu$C/$\textrm{cm}^2$ and 86.3 ㎸/cm, respectively. After applying 10$^{9}$ square pulses of $\pm$5V, the remanent polarization of the BIT thin film decreases as much as about 33% from 5.92 $\mu$C/$\textrm{cm}^2$ of initial state to 3.95 $\mu$C/$\textrm{cm}^2$.

• Journal of the Economic Geographical Society of Korea
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• v.22 no.4
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• pp.405-421
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• 2019

International aid to North Korea remains far below the humanitarian needs of vulnerable people. This paper examines the trajectory of international humanitarian assistance to North Korea over the last two decades with the focus on its decline in the context of the country's nuclear standoff and corresponding stringent sanctions. In so doing, the paper addresses major problems associated with North Korea's reception of foreign aid and operational constraints placed on humanitarian activities in the country. It shows that humanitarian assistance to North Korea has been largely shaped by geopolitical dynamics. A survey of UN reports and statistics also suggests a shifting trend in recent international aid to North Korea. The decline of aid and multiple operational obstacles faced by humanitarian organizations, for instance, have led to a fall in agricultural support and a proportional rise in health and related services. While UN Security Council resolutions include an exemption provision, humanitarian assistance to North Korea has been constrained by stringent sanctions, which have led to adverse consequences for the civilian population. In this regard, the paper suggests some policy directions for international aid to North Korea amidst negotiations over denuclearization, while stressing an urgent need to address the negative impact of sanctions on vulnerable groups in the country.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.15 no.3
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• pp.226-232
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• 1982

The measurements of the jerking force and the tail beat by hooked carp were carried out using a strain gauge at a fish pond from July to August 1981. The maximum jerking force was sustained for a while in the initial state after a carp was hooked, but the jerking force was gradually decreased as a function of the time elapsed until the fish was utterly exhausted, and it converged to the body weight at last. The results are as follows : 1. The maximum jerking force $F_m(g)$ can be expressed with empirical formula : $$F_m=3.23W+105$$ where W (g) is the body weight. 2. Dynamic change of the maximum jerking force $F_n(g)$ by one tail beat with time $t_{n}(-10T/2{\leq}\;t_n{\leq}10T/2)$ can he induced with the equation as follows : $$F_n=(0.27W-6.52)(|t_n|+C)^{-2.10}$$ where the period T (sec) is given by the following equation with the body weight : T=0.000385W+0.193 3. The jerking force at each of the peak points $F_p$ (g) varies with the time elapsed t (sec) as following equation : $$F_{p}=(2.23W+105)e^{-{\beta}t}+W$$. The value of durability index $\beta$ was nearly zero in the initial state and about 1.7 in the exhausted state at last. 4. It was clearly shown that the change of jerking force by hooked carp was closely related to the tail beat from a paired difference T-test.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.4
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• pp.511-518
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• 2015

Purpose: The purpose of this study is to evaluate correlation between convergence insufficiency and concentration by evaluating attentiveness in children who have convergence insufficiency symptoms. Methods: The CISS survey and examination for the near point of convergence were conducted to 74 in children aged 12 to 13 years in order to divide them into a normal binocular vision (NBV) and a convergence insufficiency (CI) group. The attentiveness examination was used to all subjects to figure out their emotional problems, hyperactivity and impulsiveness problems, and managerial or functional problems with a 5-point scale. Correlation between convergence insufficiency-related symptoms included in CISS and attentiveness problems was analyzed. Results: there were 29 children (39.2%) in the CI group, the mean scores of CISS of the NBV and CI group were $5.91{\pm}3.69$ and $18.31{\pm}7.00$ each (p<0.001). On the survey of CISS symptoms, children in the CI group frequently expressed such symptoms as eye fatigue, loss of attentiveness, blurry vision, and forgetting the line they have been reading. In the attentiveness examination, the CI group ($74.83{\pm}9.83$) gained higher scores in problematic concentration than the NBV group ($46.80{\pm}11.30$). Convergence insufficiency had significantly positive correlation with total attentiveness (r=0.798). Conclusions: In elementary school students, it has been found that when perceived symptoms related with convergence insufficiency are more serious, problematic attentiveness gets serious, too.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.336-343
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• 2017

In this study, we analyze the relationship between long-term care workers' emotional labor, professional quality of life, and service quality. The subjects of this study were 211 long-term care workers working in long-term care facilities. Self-administered questionnaires were used. In the research model, emotional labor(surface behavior, internal behavior) was verified using independent variables, with professional quality of life (compassion satisfaction, compassion fatigue) as the parameters and service quality as the dependent variables. The results of this study are as follows. First, the fit of the model was good. Second, the direct effects of emotional labor on service quality were not significant. However, there was a positive correlation between internal behavior and service quality, and a negative correlation between surface behavior and service quality. Third, professional quality of life(empathy satisfaction) was the most influential variable in terms of service quality. The results of this study demonstrate the necessity to payclinical and academic attention to long-term care workers' emotional labor and quality of life.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.164-172
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• 2020

The fuel oil/heat exchanger installed in military aircraft is a device that cools the lubricant oil supplied to other devices, such as an AMAD, and a hydraulic pump using the low temperature of the fuel is cracked at the AMAD lubricant inlet port. If a crack in the heat exchanger occurs, the lubricant oil supplied to other equipment is not cooled. Therefore, the flight can no longer be performed. In this study, non-destructive inspection and microscopic examination of the fracture surface of the oil port were performed to analyze the crack tendency. The oil pipe connected to the oil port is a titanium pipe, which is fastened with over torque and has been identified as the leading cause of heat exchanger oil port cracks. In addition, it was verified as the main reason for cracking by finite element analysis. The material and diameter of the pipe were changed to improve this defect, and the applied torque was adjusted. In addition, the bending value of the pipe was adjusted to minimize the fatigue accumulation due to pulsating pressure. As a result, no cracks occurred on the heat exchanger via the ground test after the installation of an improved pipe under the same conditions.

• Clinical and Experimental Pediatrics
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• v.53 no.4
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• pp.571-578
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• 2010

Purpose : To evaluate the efficacy and safety of levetiracetam adjunctive therapy for reducing the rate of seizure frequency in children with intractable pediatric epilepsy. Methods : We reviewed the medical records of 86 patients with intractable pediatric epilepsy who visited our hospital between March 1989 and February 2009. Levetiracetam was included in the previous anticonvulsant regimen for at least 6 months and the reduction in the rate of seizure frequency was determined in follow-up examinations. We analyzed demographic data, seizure types, antiepileptic drug history, levetiracetam dose, adverse effects of levetiracetam therapy, treatment outcome, electroencephalogram findings, etc. Results : More than 50% reduction in the seizure frequency was observed in 62 of the 86 (72.1%) patients; 44 patients (51.1%) became seizure free, while the seizure frequency increased in 5.8% patients. The associations between seizure reduction rate and age, associated diseases, seizure types, and seizure frequency before treatment were not significant. However, the duration of disease, dose of levetiracetam, duration and frequency of anticonvulsant administration before levetiracetam therapy were significantly correlated. Electroencephalogram findings and the cause of epilepsy showed partial correlation. Forty (46%) patients showed adverse symptoms; the symptoms in the order of their frequency were somnolence, hyperactivity, irritability, aggressiveness, tiredness, etc. Conclusion : The findings of our study provide the evidence that levetiracetam adjunctive therapy is efficacious and well tolerated in various refractory childhood epilepsy cases.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.6
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• pp.678-682
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• 2007

Effects of medicinal herbs on the improvement of muscular strength along with the related fatigue factors were evaluated in SD rats. Nine types of treatment groups were fed diets supplemented with 1% herb hot-water extracts (Liriope spicata (LS), Schizandra chinensis (SC), Acanthopanax sessiliflorus (AS), Saliconia herbacea (SH), Eucommia ulmoides (EU), Lycium chinensis (LC), Panax ginseng (red ginseng) (PG), Polygonum multifloum (PM), Glycyrrhizae uralensis (GU)) for 4 weeks. The muscular strength of all groups were measured weekly for 4 weeks. After 4 weeks serum was collected and liver dissected out for the analysis of glycogen and fatigue factors. The liver glycogen contents of all treatment groups ($21.0{\sim}25.9mg/g$) were higher than that of control group (18.1 mg/g). A significantly increase of muscular strength in the fourth week were found in the AS (282.5 gf), SH (277.4 gf), PG (287.2 gf) groups (p<0.05). LS (7.88 mg/dL), SC (7.85 mg/dL), AS (7.64 mg/dL), EU (7.54 mg/dL), LC (7.81 mg/dL) and PG (7.75 mg/dL) groups were significantly reduced in serum inorganic phosphorus concentration measured after 4 weeks (p<0.05). Serum lactate levels of treatment groups ($8.61{\sim}12.18{\mu}g/dL$) were significantly lower than that of control group ($17.45{\mu}g/dL$). These results suggest that medicinal herbs enhanced muscular strength of rats by delaying accumulation of muscular fatigue factor.

• Journal of Korean Society of Steel Construction
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• v.23 no.6
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• pp.747-761
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• 2011

This paper presents an investigation on the change in the statical behavior and the ultimate capacity of steel cable-stayed bridges after cable failure. Cable failure can occur due to fire, direct vehicle clash accidents, cable or anchorage fatigue, and so on. Moreover, the cable may be temporarily disconnected during cable replacement work. When cable failure occurs, the load, that was supported by the broken cable is first transferred to another cable. Then the structural state changes due to the interaction between the girder, mast, and cables. Moreover, it can be predicted that the ultimate capacity will decrease after cable failure, because of the loss of the support system. In this study, the analysis method is suggested to find the new equilibrium state after cable failure based on the theory of nonlinear finite element analysis. Moreover, the ultimate analysis method is also suggested to analyze the ultimate behavior of live loads after cable failure. For a more rational analysis, a three-step analysis procedure is suggested and used, which consisted of initial shape analysis, cable failure analysis, and live load analysis. Using this analysis method, an analytical study was performed to investigate the changes in the structural state and ultimate behavior of steel cable-stayed bridges.