• Communications of Mathematical Education
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• v.26 no.4
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• pp.351-362
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• 2012

Until the 1950s, linear algebra was considered only as one of abstract and advanced mathematics subject among in graduate mathematics courses, mainly dealing with module in algebra. Since the 1960s, it has been a main subject in undergraduate mathematics education because matrices has been used all over. In Korea, it was considered as a course only for mathematics major students until 1980s. However, now it is a subject for all undergraduate students including natural science, engineering, social science since 1990s. In this paper, we investigate the early history of linear algebra and its development from a historical perspective and mathematicians who made contributions. Secondly, we explain why linear algebra became so popular in college mathematics education in the late 20th century. Contributions of Chinese and H. Grassmann will be extensively examined with many newly discovered facts.

• Journal of Radiation Protection and Research
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• v.43 no.2
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• pp.75-84
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• 2018

Background: Gamma-ray spectrometry helps in radiation shielding problems and different applications of radioisotopes. Experimental arrangements including broad beam geometries are widely used. The aim is to investigate and evaluate the ${\gamma}-ray$ spectra via attenuation by environmental materials. Materials and Methods: The photo peak to nominated parts in the ${\gamma}-ray$ spectra and the attenuation coefficients ${\mu}_b/{\rho}$ from broad beam geometries are measured for the materials water, soil, sand and cement at the energies 0.662, 1.25, and 1.332 MeV with a $3{^{\prime}^{\prime}}{\times}3{^{\prime}^{\prime}}$ NaI(Tl) detector. Results and Discussion: The ${\gamma}-ray$ spectra vary according to changes in the effective atomic number $Z_{eff}$ of the attenuator, the photon energy and the solid angle. The peak to total ratios are the most sensitive parts to variations in the experimental conditions and overturn in the region 0.663 MeV to 1.332 MeV. This is indicated as inversion trend. The results are discussed in view of $Z_{eff}$ and the experimental conditions. The intensity build-up is larger at the lower energy and larger scattering angles in agreement with Klein-Nishina formula and other results. The build-up factor B is$${\sim_=}$$1 at high ${\gamma}-energies$ and small scattering angles. Conclusion: The sensitivity to material characteristics decrease gradually from peak: to total, to Compton valley, to Compton plateau ratios. Rigorous collimation is necessary at small energies. Cement, of the largest $Z_{eff}$, is characterized by the maximum broad beam mass attenuation coefficients ${\mu}_b/{\rho}$. The obtained results provide information to decide for the suitable experimental set-up based on aim of the work.

• Parasites, Hosts and Diseases
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• v.58 no.1
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• pp.99-102
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• 2020

Two-point mutations (V419L and L925I) on the voltage-sensitive sodium channel of bed bugs (Cimex lectularius) are known to confer pyrethroid resistance. To determine the status of pyrethroid resistance in bed bugs in Korea, resistance allele frequencies of bed bug strains collected from several US military installations in Korea and Mokpo, Jeollanamdo, from 2009-2019 were monitored using a quantitative sequencing. Most bed bugs were determined to have both of the point mutations except a few specimens, collected in 2009, 2012 and 2014, having only a single point mutation (L925I). No susceptible allele was observed in any of the bed bugs examined, suggesting that pyrethroid resistance in bed bug populations in Korea has reached a serious level. Large scale monitoring is required to increase our knowledge on the distribution and prevalence of pyrethroid resistance in bed bug populations in Korea. Based on present study, it is urgent to restrict the use of pyrethroids and to introduce effective alternative insecticides. A nation-wide monitoring program to determine the pyrethroid resistance level in bed bugs and to select alternative insecticides should be implemented.

• Corrosion Science and Technology
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• v.16 no.1
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• pp.1-7
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• 2017

When aiming for an increased and more sustainable use of metals a thorough knowledge of the corrosion phenomenon as function of the local metal microstructure is of crucial importance. In this work, we summarize the information presented in our previous publications[1-3] and present an overview of the different local (electrochemical) techniques that have been proven to be effective in studying the relation between different microstructural variables and their different electrochemical behavior. Atomic force microscopy (AFM)[1], scanning electrochemical microscopy (SECM)[2], and electrochemical scanning tunneling microscopy (EC-STM)[3] were used in combination with electron backscatter diffraction (EBSD). Consequently, correlations could be identified between the grain orientation and grain boundary characteristics, on the one hand, and the electrochemical behavior on the other hand. The grain orientation itself has an influence on the corrosion, and the orientation of the neighboring grains also seems to play a decisive role in the dissolution rate. With respect to intergranular corrosion, only coherent twin boundaries seem to be resistant.

• Journal of Species Research
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• v.9 no.4
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• pp.492-531
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• 2020

This study is based on crane fly specimens collected from 1936-2019 and are in collections maintained at the United States National Museum, Smithsonian Institution, Washington DC, USA; the Snow Entomological Museum, University of Kansas, Lawrence, KS, USA; the Hungarian Natural History Museum in Budapest, Hungary, and the National Institute of Biological Resources, Incheon, South Korea. The genus Dicranophragma Osten Sacken, 1860 with two species D. (Brachylimnophila) transitorium (Alexander, 1941) and D. (Dicranophragma) melaleucum melaleucum (Alexander, 1933), is a new record for the Korean Peninsula. New findings of Dicranomyia (Erostrata) submelas Kato et al., 2018, Dicranoptycha venosa Alexander, 1924a, Austrolimnophila (Archilimnophila) subunicoides(Alexander, 1950b), A. (A.) unica (Osten Sacken, 1869), A. (Austrolimnophila) asiatica (Alexander, 1925), Conosia irrorata (Wiedemann, 1828), Eloeophila persalsa (Alexander, 1940), E. serenensis (Alexander, 1940), E. subaprilina (Alexander, 1919), E. ussuriana ussuriana (Alexander, 1933), E. yezoensis (Alexander, 1924b), Paradelphomyia chosenica Alexander, 1950b, and P. macracantha Alexander, 1957 are discussed. General information on genera and subgenera morphological characters, redescriptions of species based on Korean specimens, illustrations of both sexes, elevation range, period of activity, habitat information, general distribution, and a distribution map for the Korean Peninsula (including North Korea) are presented for each species.

• Koreanishche Zeitschrift fur Deutsche Sprachwissenschaft
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• v.5
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• pp.289-310
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• 2002

Die Arbeit versucht, den Textbegriff aus prototypentheoretischer Sicht neu zu orientieren. Damit wird unter Text immer eine monologisch geschriebene sprachliche $\"{A}u{\ss}erung$ aus mehreren $S\"{a}tzen$ verstanden. Die in de Beaugrande/Dressler(l98l) als wichtig bezeichnete Textmerkmale wird dann in Bezug auf Vater(1992), $L\"{o}tscher(1987)$ und Klein/von Stutterheim (1991) kritisch $gekl\"{a}rt$. Daraus ergibt sich eine merkmalsorientierte Textbestimmung: Ein Text ist eine abgeschlossene themenorientierte kommunikative Einheit in einem konkreten Kontext; er hat eine bestimmte kommunikative Funktion und $erf\"{u}llt\;koh\"{a}rente$ Bedingungen. Meine These ist: Typische Texte sind auf Mustern, $n\"{a}mlich$ auf Prototypen bezogen. Textmuster sind als Prototypen bezeichnet, die in unterschiedlichem $Ma\ss\;Spielraum\;f\"{u}r\;Variationen\;und\;Kreativit\"{a}t$ lassen. Textmuster sind zu beschreiben $\"{u}ber$ das Zusammenspiel von nichtsprachlichem Handlungstyp und sprachlicher Textsorte. Dieses Zusammenspiel yon Handlungsaspekten wird in prototypischer Weise mit bestimmten Textmerkmalen verbalisiert. Mit Textmusterbeschreibungen werden jeweils prototypische Exemplare beschrieben: die beste Exemplare, die klar als solehe erkennbar sind. Die Formulierung 'Es war einmal....'. ist $f\"{u}r\M\"{a}rchen$ zwar prototypische Anfangsform, aber sie wird nur in etwa einem drittel der $F\"{a}lle$ verwendet. Prototypische Textmustermerkmale sind also nicht obligatorisch. Das $hei{\ss}t$, dass die Realiseirungen je nach individueller bzw. kultureller Situation und damit verfolgtem Zweck variabel sind Damit habe ich mich am Beispiel der Textsorte $besch\"{a}ftigt$.

• Journal of Periodontal and Implant Science
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• v.48 no.1
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• pp.12-21
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• 2018

Purpose: The goal of this study was to develop and validate a standardized in vitro pathogenic biofilm attached onto saliva-coated surfaces. Methods: Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis) strains were grown under anaerobic conditions as single species and in dual-species cultures. Initially, the bacterial biomass was evaluated at 24 and 48 hours to determine the optimal timing for the adhesion phase onto saliva-coated polystyrene surfaces. Thereafter, biofilm development was assessed over time by crystal violet staining and scanning electron microscopy. Results: The data showed no significant difference in the overall biomass after 48 hours for P. gingivalis in single- and dual-species conditions. After adhesion, P. gingivalis in single- and dual-species biofilms accumulated a substantially higher biomass after 7 days of incubation than after 3 days, but no significant difference was found between 5 and 7 days. Although the biomass of the F. nucleatum biofilm was higher at 3 days, no difference was found at 3, 5, or 7 days of incubation. Conclusions: Polystyrene substrates from well plates work as a standard surface and provide reproducible results for in vitro biofilm models. Our biofilm model could serve as a reference point for studies investigating biofilms on different surfaces.

• Journal of The Korean Astronomical Society
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• v.47 no.2
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• pp.49-67
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• 2014

A novel method to characterize the topology of the early-universe intergalactic medium during the epoch of cosmic reionization is presented. The 21-cm radiation background from high redshift is analyzed through calculation of the 2-dimensional (2D) genus. The radiative transfer of hydrogen- ionizing photons and ionization-rate equations are calculated in a suite of numerical simulations under various input parameters. The 2D genus is calculated from the mock 21-cm images of high-redshift universe. We construct the 2D genus curve by varying the threshold differential brightness temperature, and compare this to the 2D genus curve of the underlying density field. We find that (1) the 2D genus curve reflects the evolutionary track of cosmic reionization and (2) the 2D genus curve can discriminate between certain reionization scenarios and thus indirectly probe the properties of radiation-sources. Choosing the right beam shape of a radio antenna is found crucial for this analysis. Square Kilometre Array (SKA) is found to be a suitable apparatus for this analysis in terms of sensitivity, even though some deterioration of the data for this purpose is unavoidable under the planned size of the antenna core.

• Parasites, Hosts and Diseases
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• v.49 no.3
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• pp.313-316
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• 2011

Vivax malaria is a significant military and civilian health threat in the north of the Republic of Korea (ROK). The island of Baengnyeong-do is the westernmost point of the ROK and is located close to the southwestern coast of the Democratic People's Republic of Korea (DPRK). Mosquitoes were collected using a black light trap on Baengnyeong-do, and Anopheles spp. were assayed by PCR, to identify the species, and screened for sporozoites of Plasmodium vivax. Of a subsample of 257 mosquitoes, Anopheles lesteri was the most frequently collected (49.8%), followed by Anopheles sinensis (22.6%), Anopheles pullus (18.7%), Anopheles kleini (7.8%), and Anopheles belenrae (1.2%). The overall sporozoite rate was 3.1%, with the highest rates observed in An. kleini (15.0%), An. sinensis (5.2%), and An. lesteri (1.6%). No sporozoite positive An. pullus or An. belenrae were observed. The results extend our knowledge of the distribution and potential role in malaria transmission of An. kleini, An. lesteri, and An. sinensis, for an area previously considered to be at a low risk for contracting vivax malaria.

• Economic and Environmental Geology
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• v.11 no.1
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• pp.21-37
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• 1978

The depositional environment of the Manhang and the Geumcheon Formation of the Pennsylvanian Gomog Croup is revealed to the shallow neritic marine milieu in this paper also as the results of Park (1963), Cheong(1975) and Kim (1976), through the analyses of stratigraphy, paleocurrent, properties of cross-beddings and sedimentational features. The formations contains some possible terrestrial sediments suggesting the paralic environment, which are however not recognized definitely within them. The paleocurrent analysis is made to the Manhang Formation only. The paleocurrent of the formation is known to belong to the shallow neritic longshore current. The paleocurrent analysis is based chiefly on the cross-bedding analysis, and subordinately on the texture of elastic coarse sediments. The paleocurrent mean is determined to $269^{\circ}$, that is, from east to west, of which direction is interpreted to the right angle to the slope of the basinal depository plane and also the parallel with die depositional strike, according to Klein (1960) and Selley's (1968) criteria. The variance value of paleocurrent directions of the Manhang Formation in the whole area studied is 6,374, and the values range from 3,394 to 6,957 according to the dirstricts. The paleocurreut pattern of the whole area shows polymodel, and the patterns in each district range from trimodel to quadrimodel. Those models approach to the shallow marine or paralic model of Tohill and Picard (1966), Picard and High (1968 a), Pisnak (1957) and Pettijohn (1962). The mean value of maximum inclinations of cross-beddings of the whole area is $19.9^{\circ}$ with the standard deviation of 8.4, and ranges from $15.6^{\circ}$ to $21.7^{\circ}$ in the districts. Comparing the histogram showing the frequency distribution of the maximum inclinations of cross-beddings of the Manhang Formation with the Pettijohn's (1962) histogram, it is found that the model approaches to his marine model. The Pennsylvanian Gomog Group of the coalfield is considered to have had been deposited in the pseudogeosynclinal zone on the plateau by the transgression of the Tethyan sea caused by the epirogenic movements during the Pennsylvanian Period.