• Proceedings of the KIEE Conference
• /
• 1988.07a
• /
• pp.305-308
• /
• 1988

Pole assignment controller with variable forgetting factor is generalizaed to allow the output and/or input variance to be reduced. The algorithm can give significant reductions in variance for little extra computational effort and is presented for servo-tracking using leat-squares estimation. Moreover, the use of a variable forgetting factor with correct choice of information bound can avoid 'blowing-up' of the covariance matrix of the estimates and subsequent unstable control.

• Journal of Power Electronics
• /
• v.14 no.2
• /
• pp.226-236
• /
• 2014

A new active LED driver with high power factor (PF) and low total harmonic distortion (THD) compatible with a rapid-start ballast is proposed. An LC input filter is attached to the ballast to increase PF and reduce THD. A boost converter is then installed to regulate the LED current, where an unstable operating region has been newly identified. The unstable region is successfully stabilized by feedback control with two zeroes. The extremely high overall system of the 10th order is completely analyzed by the newly introduced phasor transformed circuits in static and dynamic analyses. Although a small DC capacitor is utilized, the flicker percentage of the LED is drastically mitigated to 1% by the fast controller. The proposed LED driver that employs a simple controller with a start-up circuit is verified by extensive experiments whose results are in good agreement with the design.

• Journal of the Korean Society of Safety
• /
• v.35 no.3
• /
• pp.49-57
• /
• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• Clinics in Shoulder and Elbow
• /
• v.1 no.2
• /
• pp.198-204
• /
• 1998

Unstable fractures of the proximal humerus continue to be difficult problems for orthopaedic surgeons. The optimum treatment of these fractures has remained a matter of controversy. We analyzed the clinical results of open reduction and plate fixation underwent for patients of unstable fractures of proximal humerus after minimum 12 months follow up. The purpose of this study is to evaluate the efficacy of open reduction and rigid plate fixation. Twenty-two patients were managed with open reduction and plate fixation. Mean follow up duration was 20.6 months(range, 12 to 28 mon.). Because the age of patient as a maker of degree of osteoporosis was considered the key factor in the success of anatomic reconstruction, we divided into two groups according to age. Group A was comprised of 12 cases with younger than 50 yrs of age. Ten cases of older than 50 yrs of age were Group B. According to Neer's classification, five cases(22%) were two part fracture, 12 cases(64%) were three part fracture, and three cases(14%) were four part fracture. We used the Neer rating system for evaluating the results. In Group A, overall scores were 79.1. In Group B, overall scores were 76.8. Overall scores in two part fracture were 85, overall scores in three part fracture 78.4 and overall scores in three part fracture 68.3. We achieved excellent or good results in nine cases(75%) of Group A and seven cases(70%) of Group B. Also, we obtained excellent or good results in all cases of two part fracture, ten cases(71%) of three fracture and one case(33%) of four part fracture. The complications were three metal loosening, one avascular necrosis of humeral head, one severe stiff shoulder, one superficial wound infection and one ectopic ossification. The results were excellent or good in 16 cases(73%) out of 22 cases. In conclusion, rigid fixation and supervised early exercise would be a good option for unstable fracture of the proximal humerus.

• Journal of muscle and joint health
• /
• v.9 no.2
• /
• pp.187-202
• /
• 2002

This study was aim to provide rheumatoid arthritis patients the basic data of development of nursing intervention to help psychosocial adaptation of rheumatoid arthritis patients as exploring the relationship among causal perception, coping pattern, psychosocial adaptation of rheumatoid arthritis. As the results of this study the mean score of causal perception of the subjects was 3.37. The score of the internal-unstable was the highest. which was followed by extra-stable, internal factor, internal-stable, external factor and external-unstable in order among the factor of causal perception. The mean score of coping pattern was 2.64. The type of coping patterns the score of the receptive coping was the highest, which was followed by wishful coping active coping and negative coping in order among the type of coping pattern. The mean score of psychosocial adaptation was 3.28. The subconcept of psychosocial adaptation the score for personal relationship was the highest, which was followed by role function and mental state in order among the psychosocial adaptation. The analysis of the relation among causal perception, coping pattern and psychosocial adaptation showed significant negative correlation between causal perception and psychosocial adaptation(r=-0.3219, P=0.002). The analysis of the relation between the type of coping pattern and psychosocial adaptation showed significant negative correlation between psychosocial adaptation and active coping(r=-0.3210, P=0.002), negative coping(r=-0.2296, P=0.032). Only causal perception(-.36) and period of illness(-.26) effected on the psychosocial adaptation were shown to the negative direction significantly. The psychosocial adaptation was explained the 17% by these two variables. Based on this study results the factor of causal perception and the type of coping pattern of rheumatoid arthritis were shown significant relations between psychosocial adaptation. We suggests that nurses in practice apply to assessing the factor of causal perception of individuals illness and the type of coping patterns when nursing interventions in rheumatoid arthritis patients.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.3
• /
• pp.325-331
• /
• 2013

In this study, a complex eigenvalue analysis is implemented to verify the unstable mode of a brake system using ABAQUS software. The component participation factors and component modal participation factors are used to analyze the total contributions from each component and each component mode to a particular unstable system mode. This study shows that the 1.4-kHz unstable system mode comes from mode coupling between the 2nd nodal diametric mode and 3rd lateral axial mode (LAM) in the baseline model. A sensitivity analysis with a linking index is performed to prevent the mode coupling of the component modes. This linking index analysis shows the optimum mass loading position to move away the natural frequency of the 3rd LAM, which contributes to the unstable mode. Finally, a complex eigenvalue analysis is implemented with mass loading in the tie bar position, and no unstable system mode is generated in the low-frequency range (below 2 kHz).

• Journal of Korean Association for Spatial Structures
• /
• v.2 no.4 s.6
• /
• pp.61-76
• /
• 2002

The structure system that is discreterized by continuous shells is usually used to make a large space structures and these structures show the collapse mechanisms that are captured at over the limit load, and snap-through and bifurcation are most well known of it. For the collapse mechanism, rise-span ratio, element stiffness and load mode are main factor, which it give an effect to unstable behavior. Moreover, resist force of structure can be reduced by initial condition and initial imperfection significantly. In order to investigate the instability of shell structures, the finite deformation theory can be applied and it becomes a nonlinear mathematics in which use equation of tangential stiffness incrementally. With an initial imperfection, using simple example and Flow Truss Dome, the buckling characteristics of space truss is main purpose of this paper, and unstable behavior is studied by proposed the numerical method. Also, by using MIDAS, this research work analyzes displacements and inner forces as the design load of model, and the ratio of buckling load of design load is investigated.

• International Journal of Aeronautical and Space Sciences
• /
• v.7 no.2
• /
• pp.26-32
• /
• 2006

This paper targets a direct and quantitative prediction of characteristics of unstable waves in a combustion chamber, which employs the governing equations derived in terms of amplification factors of flow variables. A freshly formulated nonlinear acoustic equation is obtained and the analysis of unsteady waves in a rocket engine is attempted. In the present formalism, perturbation method decomposes the variables into time-averaged part that can be obtained easily and accurately and time-varying part which is assumed to be harmonic. Excluding the use of conventional spatially sinusoidal eigenfunctions, a direct numerical solution of wave equation replaces the initial spatial distribution of standing waves and forms the nonlinear space-averaged terms. Amplification factor is also calculated independently by the time rate of changes of fluctuating variables, and is no longer an explicit function for compulsory representation. Employing only the numerical computation, major assumptions inevitably inherent, and in erroneous manner, in up to date analytical methods could be avoided. With two definitions of amplification factor, 1-D stable wave and 3-D unstable wave are examined, and clearly demonstrated the potentiality of a suggested theoretical-numerical method of combustion instability.

• Journal of the Korean Regional Science Association
• /
• v.13 no.2
• /
• pp.45-54
• /
• 1997

A regional economy is characterized as a spatial economy. However the literature shows that it has been treated as a point economy since space is little recognized in regional modeling due to mathematical complication. This leads to the fact that regional model does not sufficiently represent regional characteristic. This paper attempts to construct a regional growth model in a partial equilibrium framework specifically taking into consideration land as a primary factor. The model is formulated largely neoclassical. Labor is assumed to move in response to differences in the wage rate, while capital is perfectly mobile across regions. The paper shows that two growth equilibrium points exist, one stable equilibrium point and the other unstable equilibrium point. The unstable growth equilibrium indicates the existence of minimum threshold that a region must overcome the minimum threshold to grow constantly. Consequently, directions of regional growth are characterized by two growth paths depending on the initial condition of a region. That is to say, a region below the minimum threshold is converging toward the lower stable equilibrium point over time. When a regional economy initially lies above the minimum threshold, it will grow forever. A regional economy is not thus necessarily converging a stationary is not thus necessarily converging a stationary equilibrium point through factor movement. Finally, the impacts of the presence of agglomeration economies and diseconomies are analyzed through the phase diagram. The paper also shows that agglomeration economies result in lowering the minimum threshold and in escalating the level of stable equilibrium However, when agglomeration diseconomies prevail, the results are opposite, i.e., rising the minimum threshold of growth and lowering the growth level of stable equilibrium.

• 제어로봇시스템학회:학술대회논문집
• /
• 1995.10a
• /
• pp.340-343
• /
• 1995

In this paper, we get a reduced order controller in $H^{\infty}$ mixed sensitivity problem with weighting functions. For this purpose, we define frequency weighted coprime factor of plant in $H^{\infty}$ mixed sensitivity problem and reduce the coprime factor using the frequency weighted balanced truncation technique. The we design the controller for plant with reduced order coprime factor using J-lossless coprime factorization technique. Using this approach, we can derive the robust stability condition and achieve good performance preservation in the closed loop system with reduced order controller. And it behaves well in both stable plant and unstable plant.t.