The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Luowei Zhou - One of the best experts on this subject based on the ideXlab platform.
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A hybrid modulation method for lifetime extension of power semiconductors in wind power converters
2015 IEEE Applied Power Electronics Conference and Exposition (APEC), 2015Co-Authors: Xiong Du, Gaoxian Li, Luowei ZhouAbstract:Pulse width modulation (PWM) techniques can be classified into continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) types. The switching loss of power devices in DPWM converters is lower than that in CPWM converters. Lower loss could reduce the junction temperature fluctuation in converters of wind turbine generator system (WTGS) and may result in longer power devices lifetime. However, employing DPWM scheme under all WTGS operation conditions will lead to power Quality Concern. To solve this problem, a new hybrid modulation scheme which combines the CPWM and DPWM methods for WTGS converters is presented in this paper. In the presented hybrid modulation method, two modulation schemes are switched back and forth according to the wind speed in the wind farm site. The performance of the presented modulation scheme is verified and compared with that of other PWM schemes through a case study of 1.2 MW WTGS in long-term mission profiles. The results show that the lifetime of power devices with the presented hybrid approach is longer than that with the CPWM, and is shorter than that with the DPWMs. Moreover, the power Quality of the power converters with the hybrid modulation scheme can be guaranteed in all operation conditions, which may not be achieved with DPWMs.
Zachary M Easton - One of the best experts on this subject based on the ideXlab platform.
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impact of climate change and climate anomalies on hydrologic and biogeochemical processes in an agricultural catchment of the chesapeake bay watershed usa
Science of The Total Environment, 2018Co-Authors: Moges B Wagena, Amy S Collick, Andrew C Ross, Raymond G Najjar, Andrew R Sommerlot, Daniel R Fuka, Peter J A Kleinman, Zachary M EastonAbstract:Abstract Nutrient export from agricultural landscapes is a water Quality Concern and the cause of mitigation activities worldwide. Climate change impacts hydrology and nutrient cycling by changing soil moisture, stoichiometric nutrient ratios, and soil temperature, potentially complicating mitigation measures. This research quantifies the impact of climate change and climate anomalies on hydrology, nutrient cycling, and greenhouse gas emissions in an agricultural catchment of the Chesapeake Bay watershed. We force a calibrated model with seven downscaled and bias-corrected regional climate models and derived climate anomalies to assess their impact on hydrology and the export of nitrate (NO3-), phosphorus (P), and sediment, and emissions of nitrous oxide (N2O) and di-nitrogen (N2). Model-average (±standard deviation) results indicate that climate change, through an increase in precipitation and temperature, will result in substantial increases in winter/spring flow (10.6 ± 12.3%), NO3- (17.3 ± 6.4%), dissolved P (32.3 ± 18.4%), total P (24.8 ± 16.9%), and sediment (25.2 ± 16.6%) export, and a slight increases in N2O (0.3 ± 4.8%) and N2 (0.2 ± 11.8%) emissions. Conversely, decreases in summer flow (−29.1 ± 24.6%) and the export of dissolved P (−15.5 ± 26.4%), total P (−16.3 ± 20.7%), sediment (−20.7 ± 18.3%), and NO3- (−29.1 ± 27.8%) are driven by greater evapotranspiration from increasing summer temperatures. Decreases in N2O (−26.9 ± 15.7%) and N2 (−36.6 ± 22.9%) are predicted in the summer and driven by drier soils. While the changes in flow are related directly to changes in precipitation and temperature, the changes in nutrient and sediment export are, to some extent, driven by changes in agricultural management that climate change induces, such as earlier spring tillage and altered nutrient application timing and by alterations to nutrient cycling in the soil.
G. M. Hill - One of the best experts on this subject based on the ideXlab platform.
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Water Quality and the grazing animal.
Journal of animal science., 2004Co-Authors: R K Hubbard, G L Newton, G. M. HillAbstract:Grazing animals and pasture production can affect water Quality both positively and negatively. Good management practices for forage production protect the soil surface from erosion compared with conventionally produced crops. Grazing animals and pasture production can negatively affect water Quality through erosion and sediment transport into surface waters, through nutrients from urine and feces dropped by the animals and fertility practices associated with production of high-Quality pasture, and through pathogens from the wastes. Erosion and sediment transport is primarily associated with high-density stocking and/or poor forage stands. The two nutrients of primary Concern relating to animal production are N and P. Nitrogen is of Concern because high concentrations in drinking water in the NO(3) form cause methemoglobinemia (blue baby disease), whereas other forms of N (primarily nitrite, NO(2)) are considered to be potentially carcinogenic. Phosphorus in the PO(4) form is of Concern because it causes eutrophication of surface water bodies. The effect of grazing animals on soil and water Quality must be evaluated at both the field and watershed scales. Such evaluation must account for both direct input of animal wastes from the grazing animal and also applications of inorganic fertilizers to produce Quality pastures. Watershed-scale studies have primarily used the approach of nutrient loadings per land area and nutrient removals as livestock harvests. A number of studies have measured nutrient loads in surface runoff from grazed land and compared loads with other land uses, including row crop agriculture and forestry. Concentrations in discharge have been regressed against standard grazing animal units per land area. Watersheds with concentrated livestock populations have been shown to discharge as much as 5 to 10 times more nutrients than watersheds in cropland or forestry. The other major water Quality Concern with grazing animals is pathogens, which may move from the wastes into surface water bodies or ground water. Major surface water Quality problems associated with pathogens have been associated with grazing animals, particularly when they are not fenced out from streams and farm ponds. This paper presents an overview of water Quality issues relating to grazing animals.
Vijay P Singh - One of the best experts on this subject based on the ideXlab platform.
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bedload as an indicator of heavy metal contamination in a brazilian anthropized watershed
Catena, 2017Co-Authors: Yuri Jacques Agra Bezerra Da Silva, Vijay P Singh, Jose Ramon Barros Cantalice, Clistenes Williams Araujo Do Nascimento, Ygor Jacques Agra Bezerra Da Silva, Cinthia Maria Cordeiro Atanazio Cruz Silva, Michelangelo De Oliveira Silva, Sergio M S GuerraAbstract:Abstract Heavy metal contamination has long been a water Quality Concern worldwide. Most studies have focused on heavy metal concentration in water through suspended sediment and bottom sediment; however, the concentration transported by river-bottom sediment, known as bedload, has not been taken into account. In order to fill this gap, this study aimed to determine the concentration of Hg, Pb, Cd, Ni, Cu, Cr, Zn, As, Fe and Mn in bedload of Ipojuca River which is an environmentally impacted river in Brazil. The use of bedload in heavy metal contamination studies raises the following question: Is the bedload an adequate indicator of heavy metal contamination? To answer this question, sediment contamination assessment was performed using sediment contamination indices, principal component analysis, and comparison with background values and sediment Quality guidelines (SQGs). Comparing with sediment Quality guidelines, the Probable Effect Level (PEL) and Threshold Effect Level (TEL) seem to underestimate the harmful effect on sediment-dwelling organisms, being essential either to calibrate the SQGs for site specific conditions or develop site specific guidelines. The pollution load index (PLI) indicated that the upstream and downstream sites were not polluted and polluted, respectively. Principal component analysis explained roughly 91% and 81% of the total variance in heavy metal contamination upstream and downstream, respectively, and distinguished natural and anthropogenic contributions in Ipojuca River. Multiple lines of evidence suggested that heavy metal concentrations in bedload were an adequate and feasible indicator of anthropogenic impacts.
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Contamination of water resources by pathogenic bacteria
AMB Express, 2014Co-Authors: Pramod K. Pandey, Sagor Biswas, Michelle L. Soupir, Philip H Kass, Vijay P SinghAbstract:Water-borne pathogen contamination in water resources and related diseases are a major water Quality Concern throughout the world. Increasing interest in controlling water-borne pathogens in water resources evidenced by a large number of recent publications clearly attests to the need for studies that synthesize knowledge from multiple fields covering comparative aspects of pathogen contamination, and unify them in a single place in order to present and address the problem as a whole. Providing a broader perceptive of pathogen contamination in freshwater (rivers, lakes, reservoirs, groundwater) and saline water (estuaries and coastal waters) resources, this review paper attempts to develop the first comprehensive single source of existing information on pathogen contamination in multiple types of water resources. In addition, a comprehensive discussion describes the challenges associated with using indicator organisms. Potential impacts of water resources development on pathogen contamination as well as challenges that lie ahead for addressing pathogen contamination are also discussed.
Pramod K. Pandey - One of the best experts on this subject based on the ideXlab platform.
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Contamination of water resources by pathogenic bacteria
AMB Express, 2014Co-Authors: Pramod K. Pandey, Sagor Biswas, Michelle L. Soupir, Philip H Kass, Vijay P SinghAbstract:Water-borne pathogen contamination in water resources and related diseases are a major water Quality Concern throughout the world. Increasing interest in controlling water-borne pathogens in water resources evidenced by a large number of recent publications clearly attests to the need for studies that synthesize knowledge from multiple fields covering comparative aspects of pathogen contamination, and unify them in a single place in order to present and address the problem as a whole. Providing a broader perceptive of pathogen contamination in freshwater (rivers, lakes, reservoirs, groundwater) and saline water (estuaries and coastal waters) resources, this review paper attempts to develop the first comprehensive single source of existing information on pathogen contamination in multiple types of water resources. In addition, a comprehensive discussion describes the challenges associated with using indicator organisms. Potential impacts of water resources development on pathogen contamination as well as challenges that lie ahead for addressing pathogen contamination are also discussed.
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assessing the impacts of watershed indexes and precipitation on spatial in stream e coli concentrations
Ecological Indicators, 2012Co-Authors: Pramod K. Pandey, Michelle L. Soupir, Monica A Haddad, J J RothwellAbstract:Abstract Pathogen contamination of waterbodies, which is often identified by the presence of pathogen indicators such as Escherichia coli, is a major water Quality Concern in the United States. Reducing in-stream pathogen contamination requires an understanding of the combined impacts of land cover, climatic conditions, and anthropogenic activities at the watershed scale. In this study these factors are considered by assessing linear relationships between in-stream E. coli water Quality data, watershed indexes, and rainfall for the Squaw Creek Watershed, IA, USA. The watershed indexes consider the undisturbed land cover which encompasses the natural land cover area, wetlands, and vegetated stream corridors, and the disturbed land cover extent which includes areas receiving manure from confined animal feeding operations (CAFOs), tile-drained areas, and areas in cropped and urban land. In addition to disturbed and undisturbed land, we also calculated indexes for barren land and slope. Bivariate analysis was used to assess the linkage between E. coli concentrations, watershed indexes and the cumulative rainfall 15, 30, 45, and 60 days prior to water sample collection. To predict in-stream E. coli concentrations, we developed multivariate regression models, and predictions were compared with observed E. coli concentrations at 46 sampling locations over four sampling periods in two years. Results show that areas receiving manure, wetlands, drained land, and cropped land all influence in-stream E. coli concentrations significantly (p
