Electrochemical determination of urea using a gold nanoparticle-copolymer coated-enzyme modified gold electrode

A new amperometric urea biosensor based on gold nanoparticle embedded poly(propylene-co-imidazole) was developed for the determination of urea. The urease adsorbed on the polymeric film catalyzed the hydrolysis of urea to ammonium and bicarbonate ions and the ammonium was then electrooxidized on the gold electrode with the aid of gold nanoparticles at +0.2?V versus Ag/AgCl using differential pulse voltammetry. The biosensor provided a linear current response to urea concentration from 0.1 to 30?mM, a detection limit of 36?µM, a relative standard deviation of 2.43% (n?=?18), and excellent storage stability, as the current decrease was only 3% after 75 days. The operation of the biosensor was evaluated by the analysis of municipal sewage wastewater collected from the inlet pipe of the treatment plant of Zonguldak City in Turkey. The effects of possible interferants were also characterized.     

Electrochemical degradation of 4-chloroguaiacol for wastewater treatment using PbO2 anodes

Electrochemical oxidation of 4-chloroguaiacol (4-CG) at Nb/PbO(2) anodes was studied under different experimental conditions such as initial concentration of substrate, electrolysis time, temperature and pH. We measured the concentrations of 4-chlorocatechol (4-CC), 2-methoxyhydroquinone (2-MHQ), maleic acid (MA) and carbon dioxide as the main products. Black solid particles consisting mainly of polymers were formed during electrolysis. A mechanism of electrochemical oxidation of 4-CG was investigated. The oxidation of 4-CG can generally be described by simple pseudo first-order kinetics. The degradation of 4-CG was favoured at high temperature and lower initial concentration of 4-CG and low solution pH. However, the increase of temperature has not a significant effect on the mineralization of carboxylic acids. Moreover, these products required long electrolysis time.     

Polymer bilayers with enhanced dielectric permittivity and low dielectric losses by Maxwell–Wagner–Sillars interfacial polarization: Characteristic frequencies and scaling laws

An efficient approach to obtain polymeric materials with high permittivity values and low dielectric losses is presented in the current study. For this purpose, dielectric measurements by means of broadband dielectric spectroscopy, numerical simulations, and analytical calculations have been carried out for bilayer structures consisting in an insulating and a conductive polymer layer. Polyethyleneterephtalate and polytetrafluoroethylene have been used as insulating layers while, as conductive materials, blends of polyvinyl acetate with an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. The dielectric properties of the samples have been investigated in a broad frequency (from 10⁻¹ to 10⁷ Hz) and temperature range in order to determine, through the analysis of the scaling laws governing the interfacial polarization effects, the characteristic frequency ranges and the amplitude of the enhanced permittivity. An excellent agreement is found between the experimental results, the numerical simulations, and the analytical calculations. Finally, we show that bilayer polymeric materials with permittivity values as high as ε′ = 556 and with low dielectric losses (tan(δ) = 0.001) can be readily obtained by the current approach. This could have multiple applications, especially in the field of organic electronics. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47551.     

Linear-time border-tracing algorithms for quadtrees

In applications where the quadtree is used as an underlying object representation, a number of basic operations are implemented as a trace along the border of the object's region. A technique is presented that determines a way to shift any given scene (as well as its quadtree), so that the border of all the objects in the scene can be traversed in time proportional to the length of all the borders in the scene (or the number of blocks when the scene is represented as a quadtree). This determination is shown to be performed in time proportional to the length of all the borders in the scene. This allows the direct translation of a number of chain-code algorithms into quadtree algorithms without loss of asymptotic worst-case efficiency. This results in improved worst-case analyses of algorithms that convert chain codes into quadtrees and that perform connected component labeling of images represented as quadtrees.The support of the National Science Foundation under Grant IRI-88-02457 is gratefully acknowledged.     

Speeding up construction of PMR quadtree-based spatial indexes

Spatial indexes, such as those based on the quadtree, are important in spatial databases for efficient execution of queries involving spatial constraints, especially when the queries involve spatial joins. In this paper we present a number of techniques for speeding up the construction of quadtree-based spatial indexes, specifically the PMR quadtree, which can index arbitrary spatial data. We assume a quadtree implementation using the “linear quadtree”, a disk-resident representation that stores objects contained in the leaf nodes of the quadtree in a linear index (e.g., a B-tree) ordered based on a space-filling curve. We present two complementary techniques: an improved insertion algorithm and a bulk-loading method. The bulk-loading method can be extended to handle bulk-insertions into an existing PMR quadtree. We make some analytical observations about the I/O cost and CPU cost of our PMR quadtree bulk-loading algorithm, and conduct an extensive empirical study of the techniques presented in the paper. Our techniques are found to yield significant speedup compared to traditional quadtree building methods, even when the size of a main memory buffer is very small compared to the size of the resulting quadtrees. Edited by R. Sacks-Davis. Received: July 10, 2001 / Accepted: March 25, 2002 Published online: September 25, 2002     

A geographic information system using quadtrees

We describe the current status of an ongoing research effort to develop a geographic information system based on quadtrees. Quadtree encodings were constructed for area, point and line features for a small area in Northern California. The encoding used was a variant of the linear quadtree. The implementation used a B-tree to organize the list of leaves and allow management of trees too large to fit in core memory. Several database query functions have been implemented, including set operations, region property computations, map editing functions and map subset and windowing functions. A user of the system may access the database via an English-like query language.     

Using a distributed quadtree index in peer-to-peer networks

Peer-to-peer (P2P) networks have become a powerful means for online data exchange. Currently, users are primarily utilizing these networks to perform exact-match queries and retrieve complete files. However, future more data intensive applications, such as P2P auction networks, P2P job-search networks, P2P multiplayer games, will require the capability to respond to more complex queries such as range queries involving numerous data types including those that have a spatial component. In this paper, a distributed quadtree index that adapts the MX-CIF quadtree is described that enables more powerful accesses to data in P2P networks. This index has been implemented for various prototype P2P applications and results of experiments are presented. Our index is easy to use, scalable, and exhibits good load-balancing properties. Similar indices can be constructed for various multidimensional data types with both spatial and non-spatial components.