• Journal of Power Electronics
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• v.19 no.6
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• pp.1544-1553
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• 2019

The efficiency of photovoltaic generation systems depends on the maximum power point tracking (MPPT) technique. Among the various schemes presented in the literature, the incremental conductance (INC) method is one of the most frequently used due to its superb tracking ability under changes in insolation and temperature. Generally, conventional INC algorithms implement a simple duty-cycle updating rule that is mainly found on the polarity of the peak-power evaluation function. However, this fails to maximize the performance in both steady-state and transient conditions. In order to overcome this limitation, a novel regulated INC (r-INC) method is proposed in this paper. Like the compensators in automatic control systems, this method applies a digital compensator to evaluate the INC function and improve the capability of power tracking. Precise modeling of a new MPPT system is also presented in the optimized design process. A 120W boost peak power tracker is utilized to obtain comparative test results and to confirm the superiority of the proposed method over existing techniques.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.9
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• pp.1638-1643
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• 2010

HVDC is better economic method than HVAC in case of long distance transmission and it is possible to interconnect transmission lines regardless of difference of power frequency. The electrical environment problems of HVDC overhead transmission line are electric field, charged voltage, ion current and so on. For biopolar HVDC lines, most of the ions are directed toward the opposite polarity conductor, but a significant fraction is also directed toward the ground. These problems are major factor to design configuration of HVDC overhead transmission line. Therefore, It is necessary to test an environmental characteristics of HVDC overhead transmission line. In this paper, to assess the ion characteristic of HVDC transmission line, continuous measurements have been done on the biopolar single circuit line with ACSR 480mm2-6 bundle conductors of Gochang HVDC Test line. And then the ion characteristics were analyzed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1791-1795
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• 2007

Small ions generated at conductor corona sources remain in the atmosphere until they recombine with ions of opposite polarity, attach to aerosols, or make contact with an object. Ion current density is major factor to design conductor configuration of DC overhead transmission line. Several techniques have been used to measure the ion current of HVDC overhead transmission line. In this study, the ion current density was measured by a plate electrode made of a metal flat board at DC corona cage. The sensitivity of the plate electrode is $0.156uA/m^2/V$. To obtain an useful database on corona discharge, it is necessary to do corona test on several kinds of conductor bundles. Therefore, a number of experiments were conducted on several kinds of conductor bundles. To reliably analyze ion effects, corona cage test data were obtained over a long period of time under various weather conditions and expressed as a statistical distribution. Ion current density distribution in foul weather shows a significant increase in levels over the corresponding fair weather. Based on this results, we evaluated the environmental characteristic caused by ion flow of three candidated conductor bundles.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.107-112
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• 2002

Ferritic stainless steels would be the most important alloys under the chloride environment. They are a cheaper alternative to austenitic stainless steels [1]. The present study is related to gas tungsten arc welding (GTAW) characteristics of Type 444 stainless steels. The heat of welding leads to grain coarsening in the HAZ and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferritc phase without any intermediate phase transformation. It is therefore recommended that these alloys be welded with a low heat input and at high welding speeds. Attempts to improve weldability were made by using of direct current straight polarity (DCSP) and pulsed current GTAW processes in this study. Measuring weld bead, grain size and Erichsen test were performed and the effects of heat input, pulse frequency on the weld metal and HAZ were studied. The main results were obtained as followings: decreasing heat input was effective to control the width of weld both in DCSP welding and in pulsed current welding; pulsed current welding was found to refine the grain size effectively and the finest grain size was found at the frequency of 150Hz in pulsed current welding; it was found that decreasing heat input also refine the HAZs effectively and the frequency had no different effect on HAZ at the same heat input; the ductility could be improved effectively in pulsed current welding.

• Applied Biological Chemistry
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• v.32 no.3
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• pp.255-264
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• 1989

The minimum concentrations of organic solvents inducing phytotoxicity were investigated after spraying or flooding solvent solutions to annual plants. In the foliar treatment of upland test, solvents with high-boiling point or low-polarity induced severe phytotoxicity. Especially, aromatic solvents induced severe phytotoxicity. The most sensitive plant to phytotoxicity was soybean. In the pre-emergence treatment of upland test, the solvents with high-boiling point only induced phytotoxicity at high concentration. The degree of phytotoxicity induced by foliar spray in the condition of paddy field was similiar to that of upland test, but in the pre-emergence test, the former was more severe than the latter. Among 6 treatments, phytotoxicity induced by solvents was most severe in the pre-emergence test under the condition of flooding paddy field. Generally, alcohols induced severe phytotoxicity, especially, ethanol at 0.001%.

• Journal of Intelligence and Information Systems
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• v.22 no.1
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• pp.63-82
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• 2016

Individuals gather information online to resolve problems in their daily lives and make various decisions about the purchase of products or services. With the revolutionary development of information technology, Web 2.0 has allowed more people to easily generate and use online reviews such that the volume of information is rapidly increasing, and the usefulness and significance of analyzing the unstructured data have also increased. This paper presents an analysis on the lexical features of expert product reviews to determine their influence on consumers' purchasing decisions. The focus was on how unstructured data can be organized and used in diverse contexts through text mining. In addition, diverse lexical features of expert reviews of contents provided by a third-party review site were extracted and defined. Expert reviews are defined as evaluations by people who have expert knowledge about specific products or services in newspapers or magazines; this type of review is also called a critic review. Consumers who purchased products before the widespread use of the Internet were able to access expert reviews through newspapers or magazines; thus, they were not able to access many of them. Recently, however, major media also now provide online services so that people can more easily and affordably access expert reviews compared to the past. The reason why diverse reviews from experts in several fields are important is that there is an information asymmetry where some information is not shared among consumers and sellers. The information asymmetry can be resolved with information provided by third parties with expertise to consumers. Then, consumers can read expert reviews and make purchasing decisions by considering the abundant information on products or services. Therefore, expert reviews play an important role in consumers' purchasing decisions and the performance of companies across diverse industries. If the influence of qualitative data such as reviews or assessment after the purchase of products can be separately identified from the quantitative data resources, such as the actual quality of products or price, it is possible to identify which aspects of product reviews hamper or promote product sales. Previous studies have focused on the characteristics of the experts themselves, such as the expertise and credibility of sources regarding expert reviews; however, these studies did not suggest the influence of the linguistic features of experts' product reviews on consumers' overall evaluation. However, this study focused on experts' recommendations and evaluations to reveal the lexical features of expert reviews and whether such features influence consumers' overall evaluations and purchasing decisions. Real expert product reviews were analyzed based on the suggested methodology, and five lexical features of expert reviews were ultimately determined. Specifically, the "review depth" (i.e., degree of detail of the expert's product analysis), and "lack of assurance" (i.e., degree of confidence that the expert has in the evaluation) have statistically significant effects on consumers' product evaluations. In contrast, the "positive polarity" (i.e., the degree of positivity of an expert's evaluations) has an insignificant effect, while the "negative polarity" (i.e., the degree of negativity of an expert's evaluations) has a significant negative effect on consumers' product evaluations. Finally, the "social orientation" (i.e., the degree of how many social expressions experts include in their reviews) does not have a significant effect on consumers' product evaluations. In summary, the lexical properties of the product reviews were defined according to each relevant factor. Then, the influence of each linguistic factor of expert reviews on the consumers' final evaluations was tested. In addition, a test was performed on whether each linguistic factor influencing consumers' product evaluations differs depending on the lexical features. The results of these analyses should provide guidelines on how individuals process massive volumes of unstructured data depending on lexical features in various contexts and how companies can use this mechanism from their perspective. This paper provides several theoretical and practical contributions, such as the proposal of a new methodology and its application to real data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.74-80
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• 2006

This paper presents the characteristics of electromagnetic field uniformity in a reverberation chamber that can be used alternatively for the analysis, test and evaluation of electromagnetic interference and immunity. The dual-band diffuser, which can be used at two different frequency bands in a reverberation chamber, is applied, and it is made of two different single-band Schroeder's Quadratic Residue Diffusers. The FDTD method is used to analyze the field characteristics. Compared with single-band diffuser, the dual-band diffuser shows the improvement in not only expansion of test frequency band but also in characteristics of the field uniformity, polarity, power efficiency, and tolerance. Therefore, the reverberation chamber with the dual-band diffuser is a better facility, for the analysis and measurement of electromagnetic interference and immunity, than the reverberation chamber with a single-band diffuser.

• Economic and Environmental Geology
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• v.26 no.4
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• pp.519-539
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• 1993

A total of 264 independently oriented core samples were collected from 26 sites in the southwestern part (the Naktong Trough) of the Cretaceous $Ky{\check{o}}ngsang$ Basin in south Korea. The sampled formations comprise the sedimentary Shindong and the Hayang Groups of the Lower Cretaceous age. Alternating field and thermal demagnetizations were conducted. Characteristic remanent magnetization (ChRM) was relatively easily isolated in each formation except in the Chinju formation, from which only remagnetization circles were observed. Even though an extensive use of the fold test was not possible due to the nearly homoclinal nature of the strata in the area, we believe that the ChRM of each formation is of primary origin based on the following grounds: The in-situ ChRM direction of each formation is different from the present geomagnetic field direction. Fisherian precision parameter becomes enhanced through the tilt correction in all formations, closely to the values required for a positive fold test. Three out of the five studied formations pass the reversal test. The mean palaeomagnetic pole position from the studied area is found to be statistically different from the contemporary pole from the Chinese block exclusive of the Shandong area. The difference in magnetic declination suggests a $14.5^{\circ}$ (${\pm}10.5^{\circ}$) clockwise rotation of the studied area relative to the Chinese block comprising the west of the Tan-Lu fault. On the other hand, any significant difference in magnetic inclination and concurrent palaeolatitude is not observed between the studied area and China as well as the other area (Taegu-Andong area) in the $Ky{\check{o}}ngsang$ Basin. The dual nature of the magnetic polarity confirmed in all formations suggests an older than 124 Ma (Neocomian or older) age of the studied sedimentary strata.

• Language and Information
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• v.19 no.2
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• pp.127-153
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• 2015

Negative expressions have their semantic function of classical negation as a pure reverser of truth-values. They also have various kin and foes of their pragmatic functions such as association of bad feelings (Russell 1948), emphasis/attenuation by negative polarity items, sarcasm, and metalinguistic negation (MN). This paper explores how MN and descriptive negation (DN) differ and whether the difference creates pragmatic ambiguity (Horn 1987) or reflects merely contextual variations of one logical negation (Carston 1996). To test the debate, this paper treats certain degree modifiers licensed exclusively by MN as in Mia-ka POTHONG/Yekan yeppu-n key an-i-a [external neg] (vs. modifier NPIs like cenhye 'at all', licensed only by DN) and contrasts them with bad utterances of the MN modifiers in [short form neg] sentences (not for MN) such as Mia-ka POTHONG an yeppu-e. The ERP results of the well-formed vs. ill-formed conditions evoked the N400 at Cz in written stimuli and the N400 near the center on both hemispheres in spoken stimuli. The results suggest that the anomalies are meaning-related and tend to support the pragmatic ambiguity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1700-1704
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• 2004

In this paper a novel power converter for some notches generation in the point of common coupling is described. The magnitude, width, polarity, and position of the notches generated by the proposed scheme can be varied arbitrary with simple control. The scheme has good features of simple structure, high reliability, low cost, high efficiency, and the capability of arbitrary several notches generation. The converter can be used for the test of custom power devices such as UPS, DVR, active power filter, etc. The circuit operation is described and the usefulness of the scheme is verified through simulations.