• IEMEK Journal of Embedded Systems and Applications
• /
• v.11 no.2
• /
• pp.79-86
• /
• 2016

In wireless sensor networks, increasing the sensing rate of each node to improve the data accuracy usually incurs a decrease of network lifetime. In this study, an energy-adaptive data compression scheme is proposed to efficiently control the sensing rate in an energy-harvesting wireless sensor network (WSN). In the proposed scheme, by utilizing the surplus energy effectively for the data compression, each node can increase the sensing rate without any rise of blackout time. Simulation result verifies that the proposed scheme gathers more amount of sensory data per unit time with lower number of blackout nodes than the other compression schemes for WSN.

• Proceedings of the KIEE Conference
• /
• 1996.11a
• /
• pp.84-87
• /
• 1996

This paper presents a energy function to reflect the control effect of speed governor which has a cut-off property which means position and rate limit The proposed energy function satisfies the semi-negativeness of its time derivative and well reflects the parameters of speed governor to the energy function. The transient stability analysis by the direct method for the single machine infinite bus system has been conducted with the use of the proposed energy function, which shows that the results by the direct method well agree with that by the conventional time simulation method. This thesis shows a possibility of more accurate stability analysis by taking into account the cut-off property of speed governor's output.

• Bulletin of the Korean Chemical Society
• /
• v.19 no.3
• /
• pp.308-313
• /
• 1998

A thermally irreversible photochromic system, 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (MTMA), has been studied by semi-empirical molecular orbital methods. There are one pair of stable conformations for the closed-ring form and three pairs for the open-ring form, each pair consisting of two mirror-image conformations. Interconversion between the parallel and anti-parallel conformations of the open-ring form is restricted due to high energy barriers. Only the anti-parallel conformation appears to be responsible for photochromic cyclization. Thermostability of the compound is attributed to an avoided crossing at high energy in the ground states of the isomers, whereas the photoreactivity can be explained by the mutually connected excited singlet (S1) states of the isomers, forming a double well potential with a low energy barrier. The large solvent effects can be partly explained with the low dipole moment of the anti-parallel conformation of MTMA in the S1 state. The large variation of quantum efficiency suggests that excess vibronic energy can be utilized to provide the activation energy for the photochromic reaction.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.3
• /
• pp.168-177
• /
• 1992

Some features of tidal energy horizontal flux in the ocean are considered. using the concept of “energy flux ellipses” which is a hodograph of momentary fluxes over a tidal semi-period. A number of characteristics of this ellipse are considered as well as some peculiarities of energy flux field in different types of tidal waves and their combinations (plane, Kelvin, Sverdrup, Poincare, amphidromic system). For forced tidal waves in equatorial channels some results are obtained explaining the dependence of energy flux direction on the channel dimensions.

• Journal of the Korea Society of Computer and Information
• /
• v.22 no.3
• /
• pp.115-122
• /
• 2017

In this paper, we propose an adaptive data aggregation and compression scheme for wireless sensor networks with energy-harvesting nodes, which increases the amount of data arrived at the sink node by efficient use of the harvested energy. In energy-harvesting wireless sensor networks, sensor nodes can have more than necessary energy because they harvest energy from environments continuously. In the proposed scheme, when a node judges that there is surplus energy by estimating its residual energy, the node compresses and transmits the aggregated data so far. Conversely, if the residual energy is estimated to be depleted, the node turns off its transceiver and collects only its own sensory data to reduce its energy consumption. As a result, this scheme increases the amount of data collected at the sink node by preventing the blackout of relay nodes and facilitating data transmission. Through simulation, we show that the proposed scheme suppresses the occurrence of blackout nodes and collect the largest amount of data at the sink node compared to previous schemes.

• Journal of the Korean Solar Energy Society
• /
• v.37 no.2
• /
• pp.35-45
• /
• 2017

The types of installation of the photovoltaic system applied to domestic residential buildings are classified as follows: Mounted modules with air circulation, semi-integrated modules with air duct behind, integrated modules with fully insulated back. In order to study generation characteristics of PV system, we verified the validity of interpretation program based on long-term measurement data of demonstration house installed in BAPV form and also analyzed the generation characteristics and performance of each installation type. The results are as follows. First, the RMSE of amount of generation and simulation according to annual daily insolation of demonstration system located in Daejeon was 0.98kWh and the range of relative error of monthly power generation was -5.8 to 3.1. Second, the average annual PR of mounted modules was 82%, semi-integrated modules 76.1% and integrated modules 71.9%. This differences were attributed to temperature loss. Third, the range of operating temperature of annual hourly photovoltaic modules was -6.5 to $61.0^{\circ}C$ for mounted modules, $-6.0{\sim}73.9^{\circ}C$ for semi-integrated modules and -5.5 to $88.9^{\circ}C$ for integrated modules. The temperature loss of each installation type was -14.0 to 16.1%, -13.8 to 21.9%, and -13.6 to 28.5%, respectively.

• Smart Structures and Systems
• /
• v.19 no.4
• /
• pp.341-350
• /
• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• KEPCO Journal on Electric Power and Energy
• /
• v.6 no.2
• /
• pp.157-161
• /
• 2020

Regarding greenhouse gas reduction, BIPV (Building Integrated Photovoltaics) is an important technology that can generate its own power in urban buildings based on clean energy resources. In particular, the perovskite material is attracting attention as a BIPV solar cell because it can have various colors and transparency. However, it is not easy to increase both transparency and efficiency factors because solar cell transparency and efficiency are inversely related to each other. Therefore, in this paper, we propose a semi-transparent perovskite solar cell structure that can improve both transparency and efficiency, and evaluate the stability according to international standard.

• Korean Journal of Community Nutrition
• /
• v.7 no.2
• /
• pp.277-285
• /
• 2002

The purpose of this study was to develop a semi-quantitative food frequency questionnaire (SQ-FFQ) for subjects aged 50yr and over and to evaluate the validity of this SQ-FFQ. Dietary intake was assessed using SQ-FFQ that included 98 commonly consumed flood items selected from the results of the Korean Health and Nutritional Survey, 1998. Subjects (n = 2,660) aged 50yr and over were recruited from 7 metropolitan cities and 8 small cities. Each subject was interviewed using this SQ-FFQ developed in our laboratory and 24hr-recall method. Excluding incomplete data, Data from 1,149 subjects were used in this validity study. The nutrient intakes assessed by this SQ-FFQ were validated by comparing with the results from 1 day 24-hour recalls. Pearson's correlation coefficients between two methods were 0.71, 0.64, 0.53, and 0.43 for energy, carbohydrate, protein, and fat, respectively for all subjects. Spearman's correlation coefficients were higher than those of Pearson's correlation coefficients. Kappa values for energy, carbohydrate, protein, and fat were 0.79, 0.72, 0.70, and 0.64, respectively. The percentage for misclassification of the lowest quartile into the highest quartile or vice versa was 1.25-1.39% for all nutrients. Therefore, this SQ-FFQ seems to be useful in assessing the nutritional status of the middle-aged and elderly subjects in Korea.

• The KIPS Transactions:PartB
• /
• v.12B no.4 s.100
• /
• pp.421-428
• /
• 2005

A new method of Semi-fragile image watermarking which ensures the integrity of the contents of digital image is presented. Proposed watermarking scheme embeds watermark in the form of quantization noise on the wavelet transform coefficients in a specific mid frequency subbands selected from a wavelet packet decomposition based on energy distribution of wavelet transform coefficients. By controlling the strength of embedded watermark using HVS (Human Visual System) characteristic, it is imperceptible by a human viewer while robust against non-malicious attack such as compression for storage and/or transmission. When an attack is applied on the original image, it is highly probable that wavelet transform coefficients not only at the exact attack positions but also the neighboring ones are modified. Therefore, proposed authentication method utilizes whether both current coefficient and its neighbors are damaged. together. So it can efficiently detect and accurately localize attacks inflicted on the content of original image. Decision threshold for authentication can be user controlled for different application areas as needed.