• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.35D no.11
• /
• pp.62-69
• /
• 1998

The general degradation model has been applied to analyze the hot carrier induced degradation of the DC and RF characteristics of RF-nMOSFET. The degradation of cut-off frequency has been severer than the degradation of bulk MOSFET drain current. The value of the degradation rate n and the degradation parameter m for RF-nMOSFET has been equal to those for bulk MOSFET. The decrease of device degradation with the increase of fingers could be explained by the large source/drain parasitic resistance and drain saturation voltage. It has been also found that the RF performance degradation could be explained by the decrease of $g_{m}$ and $C_{gd}$ and the increase of $g_{ds}$ after stress. The degradation of the DC and RF characteristics of RF-nMOSFET could be predicted by the measurement of the substrate current.t.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1998.10a
• /
• pp.93-99
• /
• 1998

Mathematical model can be obtained by physical law or engineering theory. However it is always incomplete expression of the real system. In active controls to suppress vibration due to earthquake or wind load, modeling errors can often cause the problems of instability and performance degradation. In this paper, robust optimal controller design method using H$\infty$ control theory is developed for the systems which have uncertain natural frequency and design constraints. Numerical results show that the proposed H$\infty$ controller can avoid the performance degradation due to several errors and has better performance than conventional LQR method.

• IE interfaces
• /
• v.12 no.3
• /
• pp.448-457
• /
• 1999

Accelerated degradation is concerned with models and data analyses for degradation of product performance over time at overstress and design conditions. Although there have been numerous studies with accelerated degradation theory in reliability, very few actually apply to parametric statistical analyses. This paper shows how to analyze degradation data, provides tests for how well the assumptions hold. Reel sensors, a sort of photointerrupters in home VCR, hive been tested, and least-square analyses are used to illustrate our approach. Tests for linearity of the performance-time relationship, dependence of the lognormal distribution, and the standard deviation on time are performed. The mean life of tested sensors is assessed at about 414,000 hours, and the Arrhenius activation energy of this reaction is concluded to be 0.39 eV as results.

• Korean Journal of Remote Sensing
• /
• v.39 no.4
• /
• pp.395-407
• /
• 2023

Super-resolution (SR) has great significance in image processing because it enables downstream vision tasks with high spatial resolution. Recently, SR studies have adopted deep learning networks and achieved remarkable SR performance compared to conventional example-based methods. Deep-learning-based SR models generally require low-resolution (LR) images and the corresponding high-resolution (HR) images as training dataset. Due to the difficulties in obtaining real-world LR-HR datasets, most SR models have used only HR images and generated LR images with predefined degradation such as bicubic downsampling. However, SR models trained on simple image degradation do not reflect the properties of the images and often result in deteriorated SR qualities when applied to real-world images. In this study, we propose an image degradation model for HR satellite images based on the modulation transfer function (MTF) of an imaging sensor. Because the proposed method determines the image degradation based on the sensor properties, it is more suitable for training SR models on remote sensing images. Experimental results on HR satellite image datasets demonstrated the effectiveness of applying MTF-based filters to construct a more realistic LR-HR training dataset.

• Journal of Environmental Science International
• /
• v.30 no.5
• /
• pp.399-406
• /
• 2021

The dissolution of ionized gas in dielectric barrier plasma, similar to the principle of ozone generation, is a major performance-affecting factor. In this study, the plasma gas dissolving performance of a gas mixing-circulation plasma process was evaluated using an experimental design methodology. The plasma reaction is a function of four parameters [electric current (X₁), gas flow rate (X₂), liquid flow rate (X₃) and reaction time (X₄)] modeled by the Box-Behnken design. RNO (N, N-Dimethyl-4-nitrosoaniline), an indictor of OH radical formation, was evaluated using a quadratic response surface model. The model prediction equation derived for RNO degradation was shown as a second-order polynomial. By pooling the terms with poor explanatory power as error terms and performing ANOVA, results showed high significance, with an adjusted R² value of 0.9386; this indicate that the model adequately satisfies the polynomial fit. For the RNO degradation, the measured value and the predicted values by the model equation agreed relatively well. The optimum current, gas flow rate, liquid flow rate and reaction time were obtained for the highest desirability for RNO degradation at 0.21 A, 2.65 L/min, 0.75 L/min and 6.5 min, respectively.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.1
• /
• pp.39-47
• /
• 1994

The drain current reduction effect due to the side-gating phenomena resulted from interaction between the neighbor gates is lead to degradation of circuit performance. In this paper, these effect were modelized for circuit simulation with the shift of threshold voltage resulting from negative charge formation and the analysis of substrate leakage current resulting trapping effect. To remove dificiencies of the conventional three terminal structure, these model were implemented in SPICE with the four terminal structure, and then the constructed environment enables the simulation of circuit performance degradation resulted from side-gating effect. The validity of implemented model is proved by comparisoin with experiment data.

• International Journal of Aeronautical and Space Sciences
• /
• v.13 no.1
• /
• pp.64-73
• /
• 2012

Pointing stability of high precision observation satellites must satisfy the stringent requirements to perform at a designed level. As even a small vibrational disturbance can result in severe degradation of the optical performance, the effects of inorbit vibrational environment on the performance of optical payload must be predicted and analyzed in the design phase in order to ensure that the requirements imposed on the payload are fully met. In this paper, an integrated framework for the evaluation of the performance of optical payloads is developed. The developed simulation tool comprises of the reaction wheel induced disturbance model, state space model of a structure in modal form and Cassegrain reflector model. The performance degradation of the optical system due to jitter is expressed by using modulation transfer function (MTF) and image simulation. Moreover, vibration isolator model is also added to show the effectiveness of using a vibration isolator for the elimination of the effects of jitter in the acquisition of an image.

• Journal of Positioning, Navigation, and Timing
• /
• v.12 no.4
• /
• pp.379-389
• /
• 2023

According to the Korea Urban Air Mobility (K-UAM) Concept of Operation (ConOps), the Global Navigation Satellite System (GNSS) is recommended as the primary navigation system and the performance specification will be implemented considering the standard of Performance Based Navigation (PBN). However, by taking into account the characteristics of an urban environment and the concurrent operations of multiple UAM aircraft, the current PBN standards for civil aviation seem difficult to be directly applied to an UAM aircraft. Therefore, by referring to technical documents published in the literature, this paper examines the feasibility of applying the proposed performance requirements to K-UAM, which follows the recommendation of navigation performance requirements for K-UAM. In accordance with the UAM ConOps, the UAM aircraft is anticipated to maintain low altitude during approach and landing phases. Subsequently, the navigation performance degradation could occur in the urban environment, and the primary degradation factor is identified as multipath error. For this reason, to ensure the safety and reliability of the K-UAM aircraft, it is necessary to analyze the degree of performance degradation related to the urban environment and then propose an alternative aid to enhance the navigation performance. To this end, the aim of this paper is to model the multipath effects of the GNSS in an urban environment and to carry out the simulation studies using the real GNSS datasets. Finally, the initial navigation performance requirement is proposed based on the results of the numerical simulation for the K-UAM.

• Journal of Applied Reliability
• /
• v.3 no.2
• /
• pp.103-116
• /
• 2003

We carry out reliability tests and investigate the failure mechanisms. of the wafer level vacuum packaged MEMS gyroscope sensor using an accelerated degradation test. The accelerated degradation test (ADT) is used to evaluate reliability (and/or life) of the MEMS vacuum package and to select the accelerated test conditions, which reduce the reliability testing time. Using the failure distribution model and stress-life model, we are able to estimate the average life time of the vacuum package, which is well agreed with the measured data. After improving several package reliability issues such as prevention of gas diffusion through package, we carry out another set of accelerated tests at the chosen acceleration level. The results show that reliability of the vacuum packaged gyroscope has been greatly improved and can survive without degradation of performance, which is the Q-factor in gyroscope sensor, during environmental stress reliability tests.

• 유체기계공업학회:학술대회논문집
• /
• 2000.12a
• /
• pp.176-183
• /
• 2000

The performance of gas turbines decreases as their operating hours increase. Compressor fouling is the main reason for this time-dependent performance degradation. Airborne particles adhere to the blade surface and results in the change in the blade shape. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth is very small compared with blade dimensions. In this study, an analytic method to predict the motion of particles and their deposition inside axial flow compressors is proposed. The analytic model takes into account the blade shape and the flow within the blade passage. Comparison of simulation result with field data shows the feasibility of the model. Influence of the particle distribution on the compressor fouling is also examined.