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101.
It has been developed an automatic stop-flow procedure for sequential photometric determination of anionic and cationic surfactants in a same sample of water. The flow system was based on multicommutation process that was designed employing two solenoid micro-pumps and six solenoid pinch valves, which under microcomputer control carry out fluid propelling and reagent solutions handling. A homemade photometer using a photodiode as detector and two light emitting diodes (LEDs) with emission at 470 nm (blue) and 650 nm (red) as radiation sources, which was tailored to allow the determination of anionic and cationic surfactants in waters. The procedure for anionic surfactant determination was based on the substitution reaction of methyl orange (MO) by the anionic surfactant sodium dodecylbenzene sulfonate (DBS) to form an ion-pair with the cetyl pyridine chloride (CPC). Features such as a linear response ranging from 0.35 to 10.5 mg L−1 DBS (R = 0.999), a detection limit of 0.06 mg L−1 DBS and a relative standard deviation of 0.6% (n = 11) were achieved. For cationic surfactant determination, the procedure was based on the ternary complex formation between cationic surfactant, Fe(III) and chromazurol S (CAS) using CPC as reference standard solution. A linear response range between 0.34 and 10.2 mg L−1 CPC (R = 0.999), a detection limit of 0.05 mg L−1 CPC and a relative standard deviation of 0.5% (n = 11) were obtained. In both cases, the sampling throughput was 60 determinations per hour. Reagents consumption of 7.8 μg MO, 8.2 μg CPC, 37.2 μg CAS and 21.6 μg Fe(III) per determination were achieved. Analyzing river water samples and applying t-test between the results found and those obtained using reference procedures for both surfactant types provide no significant differences at 95% confidence level. 相似文献
102.
The permanent deformation of a rigid perfectly plastic beam subjected to a time-dependent line load is calculated. The beam has finite length, and the load is applied transversely in the middle of the span. At the initial time, the load is zero. Thereafter, the load has a triangular time dependence. For sufficiently large values of the peak load, static and moving plastic hinges appear, and the beam is subjected to plastic bending. Previous studies of this problem have provided a numerical solution of a system of approximate equations. In this article, a numerical solution of the system of exact equations is provided. The numerical results represent a significant improvement over those that were previously available. 相似文献
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Lorenzo A. Picos‐Corrales Angel Licea‐Claveríe Karl‐Friedrich Arndt 《Journal of polymer science. Part A, Polymer chemistry》2012,50(20):4277-4287
A synthetic methodology is described for the preparation of core–shell nanogels by reversible addition‐fragmentation chain transfer. Well‐defined macro chain transfer agents (macro‐CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro‐CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core‐crosslinked star to a core–shell nanogel. Controlling the molecular weight of the macro‐CTA and the type of comonomer in the core forming step, core–shell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012. 相似文献
106.
Luis Angel García-Escudero Alfonso Gordaliza Carlos Matrán Agustín Mayo-Iscar 《Advances in Data Analysis and Classification》2010,4(2-3):89-109
Deviations from theoretical assumptions together with the presence of certain amount of outlying observations are common in many practical statistical applications. This is also the case when applying Cluster Analysis methods, where those troubles could lead to unsatisfactory clustering results. Robust Clustering methods are aimed at avoiding these unsatisfactory results. Moreover, there exist certain connections between robust procedures and Cluster Analysis that make Robust Clustering an appealing unifying framework. A review of different robust clustering approaches in the literature is presented. Special attention is paid to methods based on trimming which try to discard most outlying data when carrying out the clustering process. 相似文献
107.
Morais S Casino P Marín ML Puchades R Maquieira A 《Analytical and bioanalytical chemistry》2002,374(2):262-268
A highly sensitive and specific indirect enzyme-linked immunosorbent assay is described for Silvex, 2-(2,4,5 trichlorophenoxy)propionic acid, (2,4,5-TP). One specific feature of the immunoassay is the use of simple chemical activation of chlorophenoxy acids to prepare both the immunizing and coating conjugates. The assay is based on the use of polyclonal antibodies raised against 2,4,5-TP, and a peroxidase-labeled secondary antibody for colorimetric detection. The effect of different chemical conditions (pH, and salt and detergent concentration) on immunoassay performance has been studied. Under the best conditions the least detectable dose and the sensitivity (IC(50)) for 2,4,5-TP were 0.05 micro g L(-1) and 0.80 micro g L(-1), respectively. The optimized immunoassay was also highly specific, showing little (6.9% for 2,4,5-T) or no cross-reactivity with other similar herbicides. The assay was used to determine 2,4,5-TP in water and soils. The excellent recoveries obtained (mean values ranging between 89% and 104%) make this immunoassay a suitable screening method for either environmental monitoring or laboratory quantification of 2,4,5-TP. 相似文献
108.
We describe the characteristics of a double-exposure specklegram obtained through a double-aperture system, by introduction of a wedge in front of one aperture in one exposure. It is assumed that a uniform displacement of the diffuser is produced between exposures. The average intensity distribution and visibility of the interferometric fringes in the Fourier plane are analyzed. An alternative interferometric technique for phase-object detection is proposed. 相似文献
109.
Pérez-Jiménez AJ 《The journal of physical chemistry. B》2005,109(20):10052-10060
Here, the fascinating connection between the chemical and the transport properties of recently fabricated 4,4'-bipyridine/gold nanobridges is addressed. By means of first-principles ab initio calculations, the remarkable reproducibility of the 4,4'-bipyridine conductance properties is explained as the combined result of (i) the bonding of the molecule to the metallic leads through hybridization between the 4,4'-bipyridine highest occupied molecular orbitals and lowest unoccupied molecular orbitals (LUMOs) with s and d orbitals at low-coordination gold atoms, (ii) the limited number of molecule-lead arrangements due to gold-hydrogen steric repulsions, and (iii) the electron transmission through a LUMO-derived resonance, whose positioning with respect to the Fermi level determines which of the above arrangements yields nonnegligible conductance. Structural and electronic interpretations to the stepped dependence reported for the electronic transport of 4,4'-bipyridine as a function of the distance between the gold tips are also given. 相似文献
110.
A new strategy for carotenoid butenolides has been developed that is based in part in halogen-selective Stille cross-coupling of dihalogenated ylidenebutenolide segment 2 and highly functionalized alkenylstannanes. [reaction: see text] 相似文献