1,721,053 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
An evaluation of produced water treatment and the associated costs
No full textProduced waters are characterized with respect to the amounts and chemical constituents generated in oil and gas production. Removal of portions of total suspended solids, total dissolved solids, volatile organic chemicals, and adsorbable organic chemicals were simulated and costs associated with each treatment scenario have been estimated. Treatment facility size is a key parameter in determining unit cost. Desalination was the most costly process evaluated. Produced water treatment costs range from \sp34.00 \\sp335.00/m due to desalting costs
Deposition of Nano-scale Particles in Aqueous Environments --Influence of Particle Size, Surface Coating, and Aggregation State
No full textThis work considers the transport and attachment of nanoscale particles to surfaces and the associated phenomena that dictate particle-surface interactions. A consideration of the deposition of nano-scale particles on surfaces is a natural outgrowth of more than a century of research in the area of colloid science, and has taken on new pertinence in the context of understanding the fate and transport of engineered nanoparticles in aqueous environments. More specifically, the goal of this work is to better understand the effects of particle size, surface polymer coatings, and aggregation state on the kinetics of nanoparticle deposition. Theoretical tools such as those developed by Derjaguin-Landau-Verwey-Overbeek (DLVO) and Flory-Krigbaum , as well as the soft particle theory and surface element integration scaling methods are employed to address certain problems that were not considered with the existing theoretical frameworks for the conventional colloidal problems. Consequences of theoretical predictions are evaluated experimentally using column experiments or the quartz crystal microbalance techniques to monitor deposition kinetics. One of the key findings of this work is the observation that polymer coatings may stabilize nanoparticles against deposition or increase deposition, depending on whether the polymer coatings exist on both of the interacting surfaces and the interaction between the polymer and the collector surface. Both steric and bridging mechanisms are possible depending on whether contact between the polymer and collector surface can result in successful attachment. In addition, limitations in the use of conventional, equilibrium-based DLVO theory to describe the deposition of nano-scale particles at very low ionic strength are also identified and discussed. Moreover, it is demonstrated that the interaction between the aggregated nano-scale particles and environmental surfaces is controlled by the characteristic size of the primary particles rather than that of the aggregates. Thus despite an increase in hydrodynamic diameter, aggregation is predicted to reduce deposition only from the hydrodynamic aspects, but not from the colloidal interaction aspect. The affinity between aggregated nanoparticles and a surface may be increased at the initial stage of deposition while being unaffected by aggregation state during later stages of deposition. The results of this study lead to better understandings, at least on a qualitative level, of the factors that controlling the kinetics of deposition and, in a broader sense, the fate and transport of nanoscale particles in the aqueous environment.</p
Settling characteristics of fractal aggregates
No full textThe settling velocity of aggregates found in engineered water and wastewater treatment facilities are usually assumed to follow Stokes' law. These particles, however, are typically porous and may be fractal in nature. As a result, they have very different sedimentation characteristics. This study focuses on the comparison of several techniques used to characterize the settling properties of fractal aggregates. Aggregates made of latex particles destabilized using calcium nitrate were formed in the laboratory. Settling velocity and size were then determined for each floc using latex particles ranging 0.03 mum, 0.05 mum, and 2.65 mum in diameter. Light scattering techniques were used to calculate the fractal dimension of the aggregates. Fractal dimension ranged from 1.6 to 2.3 in the experiments. A settling column was constructed to analyze actual settling velocities of flocs. Observed settling velocities of these flocs were consistently higher than those predicted using Stokes' law (which assumes an impermeable sphere)
Characterization of particles, metals and water quality in urban runoff
No full textThis study was designed to characterize the quality of Houston area stormwater and its potential impact on receiving waters, including Galveston Bay. Stormwater samples were analyzed with regard to standard water quality parameters, as well as for metals.
Large increases in the concentration of particles, suspended solids, organic carbon, iron, mercury and zinc were observed in storm runoff. Concentrations of barium and strontium, which occur naturally in area soils, decreased as result of a storm. Data suggested a link between increasing concentrations of smaller solids (0.45-20m) and that of iron and mercury. Organic carbon showed evidence of being similarly related to zinc and larger solids (20m). Higher concentrations of these materials, in conjunction with increased runoff flows, resulted in storm loadings equivalent to months or even years of background flow. Particle size distributions measured in situ and laboratory simulations indicated significant aggregation in the runoff stream
Development of nanostructured membranes for environmental applications
No full textTwo new methods for the fabrication of porous membranes were studied. Ceramic membranes were obtained from alumoxane and ferroxane nanoparticles casted onto porous support materials. The synthesis of ferroxane nanoparticles was further investigated, in particular the kinetics of the reaction and the structure of the materials obtained by particle size measurements and EXAFS. The ceramics were characterized by nitrogen absorption isotherms, scanning electron microscope, and atomic force microscope. The permeability and molecular weight cut off (MWCO) of the ferroxane derived membranes were measured. These membranes have an average pore size of 24 run and a MWCO of 180,000 Daltons, which corresponds to the ultrafiltration range. The ferroxane nanoparticles were reacted with compounds containing other metallic atoms and mixed metal oxide nanoparticles were obtained. The nanoparticles can be applied to the fabrication of mixed metal oxide ceramics used in catalysis, fuel cells and other applications. The conductivity and surface acidity were determined in order to evaluate these materials as possible proton exchange membranes for fuel cells.
The second fabrication method considered in this study is the template-derived process. Deposits of silica nanoparticles of variable morphology were prepared to be used as templates for porous membranes. The variables that control the morphology of the deposits were investigated, in particular those related to the solvent chemistry of the nanoparticle suspensions. The templates were obtained by self-assembly and Langmuir-Blodgett layer-by-layer deposition. By controlling the template deposition process, the self-assembly method was used to create dendritic templates with an asymmetric structure. The Langmuir-Blodgett technique was used to create bilayers of different pore size. Polystyrene membranes were fabricated as replicas of these template structures. The pore structure of the polymeric membranes was studied by scanning electron microscopy
Lights, Camera, Reaction! The Influence of Interfacial Chemistry on Nanoparticle Photoreactivity
No full textThe ability of photocatalytic nanoparticles (NPs) to produce reactive oxygen species (ROS) has inspired research into several new applications and technologies, including water purification, contaminant remediation, and self-cleaning surface coatings. As a result, NPs continue to be incorporated into a wide variety of increasingly complex products. With the increased use of NPs and nano-enabled products and their subsequent disposal, NPs will make their way into the environment. Currently, many unanswered questions remain concerning how changes to the NP surface chemistry that occur in natural waters will impact reactivity. This work seeks to investigate potential influences on photoreactivity – specifically the impact of functionalization, the influence of anions, and interactions with biological objects - so that ROS generation in natural aquatic environments may be better understood.To this aim, titanium dioxide nanoparticles (TiO2) and fullerene nanoparticles (FNPs) were studied in terms of their reactive endpoints: ROS generation measured through the use of fluorescent or spectroscopic probe compounds, virus and bacterial inactivation, and contaminant degradation. Physical characterization of NPs included light scattering, electron microscopy and electrophoretic mobility. These systematic investigations into the effect of functionalization, sorption, and aggregation on NP aggregate structure, size, and reactivity improve our understanding of trends that impact nanoparticle reactivity.Engineered functionalization of FNPs was shown to impact NP aggregation, ROS generation, and viral affinity. Fullerene cage derivatization can lead to a greater affinity for the aqueous phase, smaller mean aggregate size, and a more open aggregate structure, favoring greater rates of ROS production. At the same time however, fullerene derivatization also decreases the 1O2 quantum yield and may either increase or decrease the affinity for a biological surface. These results suggest that the biological impact of fullerenes will be influenced by changes in the type of surface functionalization and extent of cage derivatization, potentially increasing the ROS generation rate and facilitating closer association with biological targets.Investigations into anion sorption onto the surface of TiO2 indicate that reactivity will be strongly influenced by the waters they are introduced into. The type and concentration of anion impacted both aggregate state and reactivity to varying degrees. Specific interactions due to inner sphere ligand exchange with phosphate and carbonate have been shown to stabilize NPs. As a result, waters containing chloride or nitrate may have little impact on inherent reactivity but will reduce NP transport via aggregation, while waters containing even low levels of phosphate and carbonate may decrease “acute” reactivity but stabilize NPs such that their lifetime in the water column is increased.Finally, ROS delivery in a multicomponent system was studied under the paradigm of pesticide degradation. The presence of bacteria or chlorpyrifos in solution significantly decreased bulk ROS measurements, with almost no OH detected when both were present. However, the presence of bacteria had no observable impact on the rate of chlorpyrifos degradation, nor chlorpyrifos on bacterial inactivation. These results imply that investigating reactivity in simplified systems may significantly over or underestimate photocatalytic efficiency in realistic environments, depending on the surface affinity of a given target.This dissertation demonstrates that the reactivity of a system is largely determined by NP surface chemistry. Altering the NP surface, either intentionally or incidentally, produces significant changes in reactivity and aggregate characteristics. Additionally, the photocatalytic impact of the ROS generated by a NP depends on the characteristics of potential targets as well as on the characteristics of the NP itself. These are complicating factors, and the myriad potential exposure conditions, endpoints, and environmental systems to be considered for even a single NP highlight the need for functional assays that employ environmentally relevant conditions if risk assessments for engineered NPs are to be made in a timely fashion so as not to be outpaced by, or impede, technological advances.</p
Characteristics of ceramic membranes derived from metal-oxide nanoparticles
No full textCarboxylate alumoxanes were cast onto alpha-alumina supports by slip-coating to develop asymmetric ceramic membranes. Carboxylate ferroxanes were also analyzed as possible precursor for ceramic membranes. Different support materials were studied. Membrane layers as thin as 1 or 2 mum were achieved. The effect of sintering conditions was investigated. The molecular weight cut off was evaluated for these membranes and compared to pore size data obtained by nitrogen adsorption in an effort to correlate pore size and actual performance of the membrane. Membranes were sintered at temperatures between 600°C and 1100°C. The pore sizes increased with higher sintering temperature, from 7 nm at 600°C to 10 nm at 1000°C, followed by a sharp increase due to the transformation to alpha alumina at higher firing temperatures. The molecular weight cut off showed no considerable variation up to 1000°C. These results are in good agreement with equations reported by several authors that correlate molecular weight with size
Investigation of membrane filtration in a rotating disk geometry: Use of computational fluid dynamics and laboratory evaluation
No full textThe feasibility, fluid dynamics and particle transport mechanics of rotary membrane filtration were investigated. The hypothesis tested was that, by rotating a disk membrane filter, a significant back-transport of suspended particles from the membrane could be accomplished due to centrifugal force and high shear rates. This hypothesis was tested by investigating in computational simulations and laboratory experiments the fluid dynamics of rotary membrane filtration, developing a better understanding of particle transport and fouling and evaluating the feasibility of treating feed streams with high solids loading. A commercial prototype rotary membrane disk filtration pilot and a laboratory pilot, which was designed and constructed as part of this research, were evaluated with respect to permeate flux performance as a function of feed solids concentration. The laboratory pilot was further evaluated to investigate particle transport and fouling behavior as a function of the operating parameters of rotation rate and transmembrane pressure drop. A high-fidelity computational fluids dynamics model of the laboratory pilot was developed. Results from simulations carried out with this model were used in concert with results from laboratory experiments to analyze particle transport and to draw general conclusions. Permeate flux in rotary membrane disk filtration was found to be very insensitive to particle loading in the feed stream. The correlation between rotation rate and permeate flux was very strong. Permeate flux performance was linked to high centrifugal force and radial drag near the membrane surface. A performance trade-off existed between the generation of high shear rates and centrifugal accelerations via high rotation rates and the radial distribution of the transmembrane pressure drop across the membrane. Permeate interior to the disk was under the influence of centrifugal force and therefore imparted a back pressure opposing filtration which increased with rotation rate
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