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161.
This experimental study examined the causal effects of transformational and transactional leadership and the mediating role of trust and value congruence on follower performance. A total of 194 student participants worked on a brainstorming task under transformational and transactional leadership conditions. Leadership styles were manipulated using two confederates, and followers' performance was evaluated via three measures—quantity, quality, and satisfaction. Results, based on path analyses using LISREL, indicated that transformational leadership had both direct and indirect effects on performance mediated through followers' trust in the leader and value congruence. However, transactional leadership had only indirect effects on followers' performance mediated through followers' trust and value congruence. Implications of these results for future research on leadership are provided. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
162.
Seungho Jung Dedy Ng Carl D. Laird M. Sam Mannan 《Journal of Loss Prevention in the Process Industries》2010,23(6):824-830
The present work is focused on developing a methodology to find the optimal placement of a hazardous process unit and other facilities using optimization theory while considering a risk map in the plant area. Incidents can have possible consequences resulting from flammable gas releases, which can be evaluated by using consequence modeling programs. The probability of each incident can be derived from initial leak hole size estimation through event tree analysis. In this methodology the plant area was divided into square grids and risk scores were estimated for each grid. The overall cost is a function of the probable cost of property damage due to fires or explosions and the interconnection cost including piping, cable, and management. The proposed approach uses a mixed integer linear optimization programming (MILP) that identifies attractive locations by minimizing the overall cost. A case study is presented for a hexane–heptane separation facility that considers the meteorological data for the given area in order to show the applicability of the proposed methodology. Results from this study will be useful in assisting the selection of locations for facilities and for risk management. 相似文献
163.
Seungho Jung Dedy Ng Jin-Han Lee Richart Vazquez-Roman M. Sam Mannan 《Journal of Loss Prevention in the Process Industries》2010,23(1):139-148
In this work, a new approach to optimize facility layout for toxic release is presented. By integrating a risk analysis in the optimization formulation, we propose a safer assignment for facility layout and siting. Accompanying with the economical concepts used in a plant layout, the new model considers the cost of willing to avoid a fatality, i.e. the potential injury cost due to accidents associated with toxic release near residential areas. The proposed formulation incorporates a real meteorological data to calculate the injury risk through the probit model and Monte Carlo simulation using dense gas dispersion modeling (DEGADIS). The overall problem was initially modeled as a disjunctive program where the coordinates of each facility and cost-related variables are the main unknowns. Then, the convex hull approach was used to reformulate the problem as a Mixed Integer Non-Linear Program (MINLP) that identifies potential layouts by minimizing overall costs. This approach gives the coordinates of each facility, and estimates for the total length of pipes, the land area, and the selection of safety devices. Finally, the 3D-computational fluid dynamics (CFD) was used to compare between the initial layout and the final layout. Moreover, analyses of separation distances fr2om hazard facilities and hindrance effects will be discussed based on the approach used in this work. 相似文献
164.
Chang-Keun Kang Eun Jung Choy Yongsoo Son Jae-Young Lee Jong Kyu Kim Youngdae Kim Kun-Seop Lee 《Marine Biology》2008,153(6):1181-1198
Loss of macroalgae habitats has been widespread on rocky marine coastlines of the eastern Korean peninsula, and efforts for
restoration and creation of macroalgal beds have increasingly been made to mitigate these habitat losses. Deploying artificial
reefs of concrete pyramids with kelps attached has been commonly used and applied in this study. As a part of an effort to
evaluate structural and functional recovery of created and restored habitat, the macroalgal community and food web structure
were studied about a year after the establishment of the artificial macroalgal bed, making comparisons with nearby natural
counterparts and barren ground communities. Dominant species, total abundance, and community structure of macroalgal assemblage
at the restored macroalgal bed recovered to the neighboring natural bed levels during the study period. The main primary producers
(phytoplankton and macroalgae) were isotopically well separated. δ13C and δ15N values of consumers were very similar between restored and natural beds but varied greatly among functional feeding groups.
The range of consumer δ13C was as wide as that of primary producers, indicating the trophic importance of both producers. There was a stepwise trophic
enrichment in δ15N with increasing trophic level. A comparison of isotope signatures between primary producers and consumers showed that, while
suspension feeders are highly dependent on pelagic sources, invertebrates of other feeding guilds and fishes mainly use macroalgae-derived
organic matter as their ultimate nutritional sources in both macroalgal beds, emphasizing the high equivalency of trophic
structure between both beds. Isotopic signatures of a few mollusks and sea urchins showed that they use different dietary
items in macroalgal-barren grounds compared with macroalgal beds, probably reflecting their feeding plasticity according to
the low macroalgal biomass. However, isotopic signatures of most of the consumers at the barren ground were consistent with
those at the macroalgal beds, supporting the important trophic role of drifting algae. Our results revealed the recoveries
of the macroalgal community and trophic structure at the restored habitat. Further studies on colonization of early settlers
and the following succession progress are needed to better understand the process and recovery rate in the developing benthic
community. 相似文献
165.
Survey of coastal inland pollution sources and their influence on seawater quality in Doam bay,Korea
Jinsoo Suh Seyeon Shin Hyung-Yeel Kahng Samyoung Ahn Young-Sun Lee Jae-Sung Jung 《Environmental monitoring and assessment》2018,190(10):605
Inland pollution sources of Doam bay were investigated from August to October in 2013. A total of 210 sources including rivers, streams, domestic, agricultural and industrial discharge points were identified along the coast, including 32 sources that had outflow. Agricultural sources were the largest inland pollution sources (139, 66.2%). Fecal coliform concentrations were measured. These data were combined with water discharge data to determine daily loads of pollutants discharged from each source into the bay. Fecal coliform concentrations were the highest in domestic discharges. However, they only had slight influence because their discharge volume was small. The most significant pollution source was Tamjin River (St.85) due to large amount of discharge volume. The influence of St.85 reached almost half of Doam bay. Fecal coliform levels of streams increased after rainfall, but decreased overtime. Domestic pollution sources were not affected upon rain event. 相似文献
166.
Previous studies have proposed that Pardosa astrigera L. Koch (Lycosidae) can be used as a biological indicator of heavy metal contamination in soil. In this study, we estimated
the bioaccumulation levels and the bioconcentration factors (BCF) of four heavy metals (Cd, Cu, Pb, and Zn) in adult female
P. astrigera collected from various field sites according to heavy metal content gradient and broods. The relationship between heavy metal
content in the soil and that in spiders was different depending on the heavy metals and the broods. However, heavy metal content
in P. astrigera increased with increasing heavy metal content in the soil. While the heavy metal content in the soil was in the order of
Zn > Pb > Cu > Cd, its content in P. astrigera was in the order Zn > Cu > Cd > Pb. The BCF for Cd in both of the broods was distinctly higher than those of the other heavy
metals evaluated. These results indicate that P. astrigera may be useful as a biological indicator of Cd soil contamination. 相似文献
167.
An enhanced dual coil 2,4-dinitrophenylhydrazine (DNPH) derivatization method (dual coil/DNPH) allowed the quantitative determination
of formaldehyde (HCHO) in ambient air. In this method, traceable HCHO was collected using a coil sampler connected in series
and lacking a long sampling tube. It was then analyzed using liquid chromatography followed by UV detection of the DNPH derivatives.
The method is based on the reaction of formaldehyde with DNPH to produce 2,4-dinitrophenylhydrazone. The detection limits
(3σ) were 0.10–0.40 ppbv with a precision ranging from 0.84 to 4.09% RSD. The results of dual coil/DNPH and conventional DNPH
cartridge methods were generally well correlated: HCHO (dual coil/DNPH) = 0.97 (±0.13) vs. HCHO (DNPH Cartridge) + 0.33 (±0.33),
r = 0.82. The dual coil/DNPH method was used to measure gaseous HCHO in the atmosphere of Metropolitan Seoul during the summer
2000 and 2001, and in Gwangju during the fall of 2001 and 2002. The daytime mean concentration of HCHO was 4.52 (±5.69) and
3.21 (±1.27) ppbv in Metropolitan Seoul for 10–12 August 2000 and 29–31 May 2001, respectively, and 1.73 (±0.98), 3.04 (±2.25),
2.70 (±1.70), and 2.01 (±2.28) ppbv in Gwangju City during 22–27 September 2001, 17–24 October 2001, 9–13 October 2002, and
28 October to 2 November 2002, respectively. The HCHO in Seoul from 10–12 August 2000 was mainly the result of photochemical
processes, while direct emissions from vehicles and long-range transport of air from China contributed during 29–31 May 2001.
During 22–27 September 2001, 17–24 October 2001, and 9–13 October 2002 in Gwangju, the HCHO came primarily from photochemical
processes, although some air affected by biomass burning admixed in the late afternoon. The increase in the HCHO concentration
on 20 October 2001 and from 28 October to 2 November 2002 was attributed mainly to direct emissions from biomass burning in
farmland near the measurement site. 相似文献
168.
Ha-il Jung Jinwook Lee Mi-Jin Chae Myung-Suk Kong Chang-Hoon Lee Seong-Soo Kang Yoo-Hak Kim 《Environmental monitoring and assessment》2017,189(12):638
Arsenic (As) accumulation in rice owing to uptake from the soil is a critical human health issue. Here, we studied the chemical properties of As-treated soils, growth inhibition patterns of As-stressed rice plants, changes in the As content of soil and soil solutions, and the relationship between As accumulation and As transfer factor from the soil to the rice organs. Rice plants were cultivated in a greenhouse under four concentrations of As: 0 (control), 25, 50, and 75 mg kg?1. A significant positive correlation was found between available P2O5 and exchangeable K and between As concentration and available P2O5 or exchangeable K. The As concentration for 50% shoot growth inhibition was 50 mg kg?1. As levels in roots and shoots were positively correlated with the growth stages of rice. The transfer factor (TF)root/soil increased with As concentration at the tillering stage but decreased at the heading stage. TFroot/soil and TFshoot/soil were higher at the heading stage than at the tillering stage. As accumulation in the 25 mg kg?1 treatment was higher during the heading stage, whereas no difference was found at the tillering stage. As accumulation was related to plant biomass and soil As concentration. We found that As accumulation was greater at As concentrations that allowed for plant growth and development. Thus, species-specific threshold concentrations must be determined based on As phytotoxicity for the phytoremediation of As-contaminated soils. Hence, developing practical approaches for managing safe crop production in farmlands with an As contamination of 25 mg kg?1 or less is necessary. 相似文献
169.
Spatially variable refuse gas permeability and landfill gas (LFG) generation rate, cracking of the soil cover, and reduced refuse gas permeability because of liquid addition can all affect CH4 collection efficiency when intermediate landfill covers are installed. A new gas collection system that includes a near-surface high permeability layer beneath the landfill cover was evaluated for enhancing capture of LFG and mitigating CH4 emissions. Simulations of gas transport in two-dimensional domains demonstrated that the permeable layer reduces CH4 emissions up to a factor of 2 for particular spatially variable gas permeability fields. When individual macrocracks formed in the cover soil and the permeable layer was absent, CH4 emissions increased to as much as 24% of the total CH4 generated, double the emissions when the permeable layer was installed. CH4 oxidation in the cover soil was also much more uniform when the permeable layer was present: local percentages of CH4 oxidized varied between 94% and 100% across the soil cover with the permeable layer, but ranged from 10% to 100% without this layer for some test cases. However, the permeable layer had a minor effect on CH4 emissions and CH4 oxidation in the cover soil when the ratio of the gas permeability of the cover soil to the mean refuse gas permeability ?0.05. The modeling approach employed in this study may be used to assess the utility of other LFG collection systems and management practices. 相似文献
170.
Distribution of perfluorochemicals between sera and milk from the same mothers and implications for prenatal and postnatal exposures 总被引:1,自引:0,他引:1
Kim SK Lee KT Kang CS Tao L Kannan K Kim KR Kim CK Lee JS Park PS Yoo YW Ha JY Shin YS Lee JH 《Environmental pollution (Barking, Essex : 1987)》2011,159(1):169-174
The levels of six perfluorocarboxylates (PFCAs), four perfloroalkylsulfonates (PFASs), and one sulfonamide were measured in paired samples of maternal serum, umbilical cord serum, and breast milk. The maternal and cord sera were strongly correlated with each other for all measured compounds (r > 0.5 and p < 0.01). Nevertheless, there was a significant difference in compound composition profile between the two sera matrices, with a more depletion of the longer chain compounds in cord serum. The transfer efficiency values from maternal to cord serum (TFCS/MS) decreased by 70% with each increasing unit of -CF2 chain within a PFCA group, and for perfluorooctanesulfonate (PFOS), by a half compared to perfluorooctanoate (PFOA). In contrast to the strong correlation in concentrations between the two sera matrices, the pattern of compounds in breast milk differed considerably with those in sera. Accordingly, compound- and matrix-specific transfer must be considered when assessing prenatal and postnatal exposure. 相似文献