2,349,528 research outputs found
An index to characterize the spatial distribution of land use within watersheds and implications for river network nutrient removal and export
The spatial distribution of land use and associated nutrient inputs may influence the efficacy of in-stream nutrient removal; however, the effect of source location on N removal and watershed N export has not been quantified. We present the skewness index, a metric to quantify the spatial distribution of land use within watersheds. Using this index and a river network nitrogen removal model, we quantified the effect of varying the location of developed land use within two watersheds on nutrient removal and export. The quantity and location of developed land use as well as runoff affected nitrogen removal and export. Because river network nitrogen removal is bypassed when sources are skewed toward the watershed mouth, varying the location of land use alone can double aquatic nitrogen removal. Nutrient sources skewed toward the distant headwaters maximized in-stream removal which in turn can reduce watershed export
Using Box–Behnken experimental design to optimize the degradation of Basic Blue 41 dye by Fenton reaction
Degradation of a Basic Blue 41 dye using Fenton reagent was examined at laboratory scale in batch experiments using Box-Behnken statistical experiment design. Dyestuff, hydrogen peroxide (H2O2) and ferrous ion (Fe2+) concentrations were selected as independent factors. On the other hand, color and chemical oxygen demand (COD) removal were considered as the response functions. The value of coefficient of determination (R-2) for both color and chemical oxygen demand removal with values 0.98 and 0.99 shows the best agreement between predicted value and experimental values. Perturbation plots indicated that iron dosage has the most effect on both color and COD removal. Normalized plot of residuals also indicated that the models were adequate to predict for both responses. Color and COD removal increased with increasing H2O2 and Fe2+ concentrations up to a certain level. High concentrations of H2O2 and Fe2+ did not result in better removal of color and COD due to hydroxyl radical being gradually consumed by both oxidant and catalyst. Percent color removal was higher than COD removal indicating the production of colorless compounds. The second-order polynomial model revealed optimal process factor ratio. The ratio of H2O2/Fe2+/dyestuff which gives a complete color removal and 95% COD removal was found to be 1195 mg/L/90 mg/L/255 mg/L
Graph removal lemmas
The graph removal lemma states that any graph on n vertices with o(n^{v(H)})
copies of a fixed graph H may be made H-free by removing o(n^2) edges. Despite
its innocent appearance, this lemma and its extensions have several important
consequences in number theory, discrete geometry, graph theory and computer
science. In this survey we discuss these lemmas, focusing in particular on
recent improvements to their quantitative aspects.Comment: 35 page
Random triangle removal
Starting from a complete graph on vertices, repeatedly delete the edges
of a uniformly chosen triangle. This stochastic process terminates once it
arrives at a triangle-free graph, and the fundamental question is to estimate
the final number of edges (equivalently, the time it takes the process to
finish, or how many edge-disjoint triangles are packed via the random greedy
algorithm). Bollob\'as and Erd\H{o}s (1990) conjectured that the expected final
number of edges has order , motivated by the study of the Ramsey
number . An upper bound of was shown by Spencer (1995) and
independently by R\"odl and Thoma (1996). Several bounds were given for
variants and generalizations (e.g., Alon, Kim and Spencer (1997) and Wormald
(1999)), while the best known upper bound for the original question of
Bollob\'as and Erd\H{o}s was due to Grable (1997). No nontrivial
lower bound was available.
Here we prove that with high probability the final number of edges in random
triangle removal is equal to , thus confirming the 3/2 exponent
conjectured by Bollob\'as and Erd\H{o}s and matching the predictions of Spencer
et al. For the upper bound, for any fixed we construct a family of
graphs by gluing triangles sequentially
in a prescribed manner, and dynamically track all homomorphisms from them,
rooted at any two vertices, up to the point where edges
remain. A system of martingales establishes concentration for these random
variables around their analogous means in a random graph with corresponding
edge density, and a key role is played by the self-correcting nature of the
process. The lower bound builds on the estimates at that very point to show
that the process will typically terminate with at least edges
left.Comment: 42 pages, 4 figures. Supercedes arXiv:1108.178
General removal lemma
We formulate and prove a general result in spirit of hypergraph removal lemma
for measurable functions of several variables.Comment: 5 page
Air removal device
The disclosure concerns a device suitable for removing air from water under both zero and one 'g' gravity conditions. The device is comprised of a pair of spaced membranes on being hydrophobic and the other being hydrophilic. The air-water mixture is introduced into the space therebetween, and the selective action of the membranes yields removal of the air from the water
Synthesis and Characterization of Graphene oxide Polydopamine Aerogels for Contaminant Removal in Water
Graphene, a two dimensional nanomaterial with remarkable properties, often requires assembly into three dimensional (3D) macroscopic monoliths while retaining its intrinsic nanoscale properties for different functional applications including contaminant removal from water. Recently, Graphene based aerogel monolithic structures have been pursued for contaminant removal application due to porous structure and mechanical strength. However, conventional synthesis methods are unable to control shape and architecture aerogel assembly, limiting potential application in water treatment devices. In this study, we synthesized a freeze casting method with optimized graphene-oxide polydopamine (GO-PDA) to fabricate GO-PDA aerogels of controllable architecture. This approach involved fabricating molds of desired geometric structure (1 mL cube) through fused deposition model printing. A GO-PDA ink was freeze casted into molds and further freeze dried to obtain GO-PDA aerogels identical to the mold\u27s architecture. Polydopamine contributed to aerogel structure integrity through functionalization of graphene surface due to spontaneous polymerization and providing active contaminant adsorption sites. The mold assisted GO-PDA aerogel exhibited high removal capacity for methylene blue (57.29 [46.49% removal efficiency after 12 hrs], 55.49, and 52.28 mg/g respectively), Evans blue (40.96 mg/g [36.93% removal efficiency after 36 hrs]), lead (51.67 mg/g [48.36% removal efficiency after 6 hrs]), and hexavalent chromium (33.13 mg/g [28.13% removal efficiency after 24 hrs]) from aqueous solution. It also exhibited high removal capacity through recycling and regeneration (3 cycles) for methylene blue (\u3e87% removal). Characterization of GO-PDA aerogels was conducted through Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction Spectroscopy, and Raman Spectroscopy to prove functionality of polydopamine
Film breakers prevent migration of aqueous potassium hydroxide in fuel cells
Electrolyte film breakers made from polytetrafluoroethylene are installed in the reactant and water vapor removal outlets of each cell and sealed by elastomers. Use of these devices in the water vapor removal cavity outlets prevents loss of KOH solution through film migration during water removal
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