• Title, Summary, Keyword: host density

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Environmental dependence of AGN activity in the SDSS main galaxy sample

  • Kim, Minbae;Choi, Yun-Young;Kim, Sungsoo S.
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.48.1-48.1
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    • 2015
  • We investigate the role of small-scale and large-scale environments in triggering nuclear activity of the local galaxies using a volume-limited sample with $M_r$ < -19.5 and 0.02 < z < 0.0685 from the Sloan Digital Sky Survey Data Release 7. To fix the mass of the supermassive black hole in its host galaxy, we limit the central velocity dispersion of the sample galaxies. The active galactic nuclei (AGN) host sample is composed of Type II AGNs identified with flux ratios of narrow emission lines with S/N > 6. In this study, we find that the AGN fraction of late-type host galaxies are commonly larger than of early type galaxies. The AGN fraction of host galaxy with late-type nearest neighbor starts to increase as the host galaxy approaches the virial radius of the nearest neighbor (about a few hundred kpc scale). Our result may support the idea that the hydrodynamic interaction with the nearest neighbor plays an important role in triggering the nuclear activity of galaxy. The early-type galaxies in high density regions show decline of AGN activity compared to ones in lower density regions, whereas the direction of the environmental dependence of AGN activity for late-type galaxies is rather opposite. We also find that the environmental dependence of star formation rate is analogous to one of AGN activity except in the high density region.

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Molecular Dynamics Simulation and Density Functional Theory Investigation for Thiacalix[4]biscrown and its Complexes with Alkali-Metal Cations

  • Hong, Joo-Yeon;Lee, Che-Wook;Ham, Si-Hyun
    • Bulletin of the Korean Chemical Society
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    • v.31 no.2
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    • pp.453-456
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    • 2010
  • The structural and energetic preferences of thiacalix[4]biscrown-5 with and without alkali metal ions ($Na^+$, $K^+$, $Rb^+$, and $Cs^+$) have been theoretically investigated for the first time using molecular dynamic (MD) simulations and density functional theory (MPWB1K/6-31G(d)//B3LYP/6-31G(d)) methods. The formation of the metal ion complex by the host is mainly driven by the electrostatic attraction between crown-5 oxygens and a cation together with the minor contribution of the cation-$\pi$ interaction between two facing phenyl rings around the cation. The computed binding energies and the atomic charge distribution analysis for the metal binding complexes indicate the selectivity toward a potassium ion. The theoretical results herein explain the experimentally observed extractability order by this host towards various alkali metal ions. The physical nature and the driving forces for cation recognition by this host are discussed in detail.

Improved Performance of White Phosphorescent Organic Light-Emitting Diodes through a Mixed-Host Structure

  • Lee, Jong-Hee;Lee, Jeong-Ik;Chu, Hye-Yong
    • ETRI Journal
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    • v.31 no.6
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    • pp.642-646
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    • 2009
  • Highly efficient white phosphorescent organic light-emitting diodes with a mixed-host structure are developed and the device characteristics are studied. The introduction of a hole-transport-type host (N, N'-dicarbazolyl-3-3-benzen (mCP)) into an electron-transport-type host (m-bis-(triphenylsilyl)benzene (UGH3)) as a mixed-host emissive layer effectively achieves higher current density and lower driving voltage. The peak external quantum and power efficiency with the mixed-host structure improve up to 18.9% and 40.9 lm/W, respectively. Moreover, this mixed-host structure device shows over 30% enhanced performance compared with a single-host structure device at a luminance of 10,000 $cd/m^2$ without any change in the electroluminescence spectra.

Some Considerations on the Population Regulation of the Green Rice Leafhopper, Nephotettix cincticeps Uhler (끝동매미충 개체군의 밀도조절에 관여하는 몇가지 요인에 관한 연구)

  • Kim S.S.;Hyun J.S.
    • Korean journal of applied entomology
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    • v.18 no.1
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    • pp.15-21
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    • 1979
  • To determine the population regulation mechanism of the Green rice leafhopper (Nephotettix cincticeps Uhler), the responses of the population increase to initial densities and the effect of host conditions and temperatures during developmental period were investigated. In the out door experiment, the increasing ratio of population density of this pest was reduced as initial density increased and this density-dependent effect was differ in accordance with host condition. Host conditioning through feeding resulted in reduction in numbers of eggs produced and it seemed to be affected by some inhibiting materials secreted by the pest during feeding. though the direct effect of feeding can't be excluded. The population growth was related with population density and host stage. Thus in late planted units, the host stage was favourable to the growth of population at low initial insect density but unfavourable at relatively high initial insect density and in early planted units, vice versa. The temperature during developmental stages definitely affected the determination of sex ratio of adult population and reduced numbers of eggs produced. The most favourable temperature to the population increase was $290^{\circ}C$, and at high temperature, $33^{\circ}C$, severe reduction of fecundity was shown ana it seemed to be caused by the simple reduction in numbers of eggs produced.

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Examining the factors influencing leaf disease intensity of Kalopanax septemlobus (Thunb. ex Murray) Koidzumi (Araliaceae) over multiple spatial scales: from the individual, forest stand, to the regions in the Japanese Archipelago

  • Sakaguchi, Shota;Yamasaki, Michimasa;Tanaka, Chihiro;Isagi, Yuji
    • Journal of Ecology and Environment
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    • v.35 no.4
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    • pp.359-365
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    • 2012
  • We investigated leaf disease intensity of Kalopanax septemlobus (prickly castor oil tree) caused by the parasitic fungus Mycosphaerella acanthopanacis, in thirty natural host populations in the Japanese Archipelago. The disease intensity observed for individual trees were analyzed using a generalized additive model as a function of tree size, tree density, climatic terms and spatial trend surface. Individual tree size and conspecific tree density were shown to have significant negative and positive effects on disease intensity, respectively. The findings suggest that the probability of disease infection is partly determined by dispersal of infection agents (ascospores) from the fallen leaves on the ground, which can be enhanced by aggregation of host trees in a forest stand. Regional-scale spatial bias was also present in disease intensity; the populations in northern Japan and southern Kyushu were more severely infected by the fungus than those in southwestern Honshu and Shikoku. Regional variation of disease intensity was explained by both climatic factors and a trend surface term, with a latitudinal cline detected, which increases towards the north. Further research should be conducted in order to understand all of the factors generating the latitudinal cline detected in this study.

Impact of maternal crowd on the reproductive performance of an ecto-pupal parasitoid Nesolynx thymus (Hymenoptera: Eulophidae)

  • Siddaiah, Aruna Ambadahalli;Danagoudra, Manjunath
    • International Journal of Industrial Entomology
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    • v.29 no.1
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    • pp.128-134
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    • 2014
  • Nesolynx thymus Girault (Hymenoptera: Eulophidae) is one among 20 hymenopteran parasitoids reported to attack the uzi fly, Exorista bombycis, which in turn infests the silkworm, Bombyx mori accounting a cocoon yield loss of 10-20%. A host of factors viz., age and size of host, age and size of parasitoid, availability of host, temperature and quality of host are reported to influence the reproductive efficiency of the parasitoids. In the present study an attempt was made to record the influence of foraging parasitoid density on their reproductive performance. Three day-old uzi pupae were offered to varying numbers (1 - 10) of 2 day old Nesolynx thymus adults for parasitization. The progeny production per pupa (84.44 - 132.77) increased significantly with increase in the number of foraging parasitoid adults (1 - 10) however, progeny production per female decreased. The sex ratio (M : F) (1:25.49 - 1:1.53) decreased significantly with increase in foraging parasitoid adults. The morphometric parameters except female abdomen width of first generation parasitoid showed significant negative correlation with number of foraging adults. However, correlation between the parasitoid size in first generation and their reproductive performance was nonsignificant.

Effect of Inorganic Nutrient Enrichment and Water Temperature Increment on the Zooxanthellae Density in the Scleractinian Coral Tissues (무기영양염 농도와 수온 상승이 산호 갈색공생조류의 밀도에 미치는 영향)

  • Kim, Taihun;Park, Heung-Sik
    • Ocean and Polar Research
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    • v.35 no.2
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    • pp.85-92
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    • 2013
  • The coral symbiotic algae zooxanthellae is often expelled from the host as the host coral is under physiological stress, causing the coral to turn completely white. Such coral bleaching events are occurring more frequently with the increase in the global warming, ocean acidification and increased level of anthropogenic impacts such as eutrophication. In the present study, we investigated the effects of inorganic nutrients including ammonium, nitrate, phosphate and elevated water temperature on the symbiotic zooxanthellae density in the fragment of branching coral Acropora nobilis. Zooxanthellae density in the host coral decreased 8 hrs after the experiment at a given elevated water temperature ($32^{\circ}C$, p < 0.05). In contrast, no clear coral bleaching or decrease in the symbiotic algae density was observed from the branching coral exposed to a normal water temperature of $30^{\circ}C$ and high levels of nutrients such as 20 ${\mu}M$ of $NH_4Cl$, 20 ${\mu}M$ of $NaNO_3$ and, 10 ${\mu}M$ $KH_2PO_4$. Accordingly, the data indicated high water temperature is one of the stressful factors to cause bleaching in A. nobilis, whereas the high levels of nutrients is not a factor. It is believed that the results obtained in the present study are useful as baseline information in the management of the coral reefs.

Occurrence and Host Plant of Metcalfa Pruinosa (Say) (Hemiptera: Flatidae) in Korea (국내 미국선녀벌레의 분포 및 기주식물)

  • Kim, Dong-Eon;Kil, Jihyon
    • Journal of Environmental Science International
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    • v.23 no.8
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    • pp.1385-1394
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    • 2014
  • Metcalfa pruinosa was considered to be a very harmful invasive species, due to its high species density in nature and wide range of its host plants. M. pruinosa was distributed in 28 sites among 143 sites. M. pruinosa has wide range and diverse host plants of 52 families 110 species including crop, fruits and forest trees. At present, the identified host plant of M. pruinosa are composed of 62 families and 145 species in total since their first appearance was reported. M. pruinosa was found in roadside 46.7%, followed by forests 33.3% and orchard 20%. Nymphs and adults cause damage to crop and orchard by sucking juice, outbreak of fungi through secretion of wax, and reduction of plant assimilation due to the nectar of nymphs. Also, it reduces the merchantable quality of fruits and thus causes economic damage. It is judged that M. pruinosa has been moved along major road via the traffic vehicles.

Parasitism of Liriomyza trifolii (Diptera: Agromyzidae) by Hemiptarsenus zilahisebessi(Hymenoptera: Eulophidae) on Tomato (토마토에서 Hemiptarsenus zilahisebessi에 의한 아메리카잎굴파리 기생율)

  • 문형철;최정식;황창연
    • Korean journal of applied entomology
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    • v.41 no.1
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    • pp.61-65
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    • 2002
  • This study was conducted to investigate percentage of parasitism and control effect of Liriomyza trifolii by Hemiptarsenus zilahisebessi on tomato. Percentages of parasitism on L. trifolii larva by ectopatasitoids war e 26∼45% Among them the parasitism by H. zilahisebessi was highest as 47∼75% in tomato. The parasitoids preferred 1 st to 3rd instar of host larvae. In laboratory test, the parasitoids showed high parasitism on 3rd instar larvae of host by 89.8∼93.1% when the female parasitoids were introduced by the ratios of 1 : 10, 1 : 20, and 1 : 30. In field test, 3 or 5 female parasitoids were introduced per plant. In the case, the parasitism increased to 80% 4 weeks after introduction of the parasitoids. This increased parasitism was resulted from density reduction of the host larvae There were no significant differences in parasitism, density of alive host, and percentage of damaged leaf between inoculation density.