High focal depth with fractional-power wave fronts

We explore the use of phase profiles with fractional power for tailoring modulation transfer functions with high focal depth at high pupil apertures. We present numerical simulations of the images that can be obtained with certain fractional-power profiles.     

Calculating Steady States for a Fokker–Planck Equation

We characterize vector fields for which the Fokker–Planck equation with -diffusion has a stationary solution in exponential form. These ideas are extended to every vector field associating to it a sequence of functions in order to generalize such exponential form.     

Determination of the optimal wavelength for temperature independent detection of commercial gasoline with a polymer cladding optical fiber

An influence of temperature variations on transmission of a polymer cladding silica core (PCS) optical fiber was investigated in a wide spectral range covering the first (1710 nm) and the second (1170 nm) vibrational overtone bands of gasoline absorption. Thermo-induced changes of the fiber background transmittance have strong dependence on wavelength. A narrow wavelength band around 1214 nm was found to be almost free from the thermal effects while maintaining sufficient sensitivity for gasoline detection.     

Synthesis of cobalt ferrite core/metallic shell nanoparticles for the development of a specific PNA/DNA biosensor

Controlled synthesis of cobalt ferrite superparamagnetic nanoparticles covered with a gold shell has been achieved by an affinity and trap strategy. Magnetic nanoparticles are functionalized with a mixture of amino and thiol groups that facilitate the electrostatic attraction and further chemisorption of gold nanoparticles, respectively. Using these nanoparticles as seeds, a complete coating shell is achieved by gold salt-iterative reduction leading to monodisperse water-soluble gold-covered magnetic nanoparticles, with an average diameter ranging from 21 to 29 nm. These constitute a versatile platform for immobilization of biomolecules via thiol chemistry, which is exemplified by the immobilization of peptide nucleic acid (PNA) oligomers that specifically hybridize with complementary DNA molecules in solution. Hybridation with DNA probes has been measured using Rhodamine 6G fluorescence marker and the detection of a single nucleotide mutation has been achieved. These results suggest the PNA-nanoparticles application as a biosensor for DNA genotyping avoiding commonly time-consuming procedures employed.     

Using biased randomization for solving the two-dimensional loading vehicle routing problem with heterogeneous fleet

This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L-CVRP) with heterogeneous fleet (2L-HFVRP). The 2L-CVRP can be found in many real-life situations related to the transportation of voluminous items where two-dimensional packing restrictions have to be considered, e.g.: transportation of heavy machinery, forklifts, professional cleaning equipment, etc. Here, we also consider a heterogeneous fleet of vehicles, comprising units of different capacities, sizes and fixed/variable costs. Despite the fact that heterogeneous fleets are quite ubiquitous in real-life scenarios, there is a lack of publications in the literature discussing the 2L-HFVRP. In particular, to the best of our knowledge no previous work discusses the non-oriented 2L-HFVRP, in which items are allowed to be rotated during the truck-loading process. After describing and motivating the problem, a literature review on related work is performed. Then, a multi-start algorithm based on biased randomization of routing and packing heuristics is proposed. A set of computational experiments contribute to illustrate the scope of our approach, as well as to show its efficiency.     

Quantitative determination of alpha(s2)- and alpha(s1)-casein in goat's milk with different genotypes by capillary electrophoresis

A capillary electrophoresis (CE) method has been applied for the quantitative determination of alpha(s1)- and alpha(s2)-CN in goat's milk. Several analytical parameters were evaluated showing the reliability of this CE method. Coefficients of determination (R2) greater than 99% were obtained and determination limits of 1.23 and 0.98 mg/ml were achieved for alpha(s1)- and alpha(s2)-CN, respectively. The analytical parameters studied in terms of accuracy, precision and recovery were within acceptable limits. Among 18 samples of 4 different genotypes (BB, EE, BF and FF) for alpha(s1)-CN were analysed, different amounts were obtained from the genotypes.     

Three-state 2',7'-difluorofluorescein excited-state proton transfer reactions in moderately acidic and very acidic media

2',7'-Difluorofluorescein (Oregon Green 488, OG488) is a novel fluorescein dye derivative which presents important advantages for improving the fluorimetric applications in the biomedical and biochemical sciences. In aqueous solution it displays four prototropic forms, namely cation (C), neutral (N), monoanion (M), and dianion (D). In previous works, we found (J. Phys. Chem. A 2005, 109, 734-747, 2840-2846) that OG488 undergoes excited-state proton transfer reactions, which may affect the results from applications using this dye. We established that the excited-state proton transfer (ESPT) reactions between neutral, monoanionic, and dianionic forms of OG488 are promoted by acetate buffer, and we characterized the ground and excited species involved. We also solved the kinetics of the prototropic reactions using global compartmental analysis. In the present paper, we extend our study on the ESPT reactions of OG488 to acidic media, in which only the three prototropic species cation, neutral, and monoanion coexist. We have solved the kinetics of the three-state ESPT reaction by means of global three-compartmental analysis of a fluorescence decay surface in moderately acidic media (pH between 1.1 and 3.0), recovering the kinetic and spectral parameters of this three-state system. This system is one of the most complex solved to date, due to the strong overlap of the absorption and emission spectra of the neutral and monoanionic forms of OG488. We also found that the cation behaves as "super" photoacid, showing a very high deprotonation rate constant (1.04 x 10(11) s(-1)) and an enhanced acidity. Therefore, we also carried out experiments at very high perchloric acid concentrations, dealing with some other effects which become noteworthy at these [H(+)]. The presence of xanthylium cation quenching due to "free" water molecules, and the reduction in the amount of water clusters acting as proton acceptors, are processes which alter notably the time course of the excited-species in this high [H(+)] range.     

Determination of propazine by differential pulse polarography in micellar and emulsified media

An electroanalytical study of the herbicide propazine's reduction process in micellar solutions and oil-in-water emulsions is reported. The anionic surfactant sodium pentanesulphonate was chosen as the most suitable. The differential pulse polarograms of micellar solutions had two reduction peaks below pH 2.0, whereas only one peak was obtained above pH 2.O. Ethyl acetate was chosen as the organic solvent to form propazine emulsions. Unlike in micellar solutions, the DPP polarograms of propazine emulsions showed only one peak even at pH < 2.0, suggesting that propazine hydrolysis was hindered in the emulsified medium. The limiting current is diffusion-controlled and the electrode process is irreversible. Propazine can be determined by differential pulse polarography over the 1.0 × 10^–1 – 1.0 × 10^–1moll^–1 and 1.0 × 10^–15 – 4.0 × 10^–1 moll^–1 concentration ranges and the limit of detection was 2.8 × 10^–1 moll^–1. Of the potential interferents simazine, methoprotryne and terbutryn (alls-triazines), thiram (a dithiocarbamate), dinoseb (nitrophenolic), and heptachlor (chlorinated cyclo-diene herbicide), only the first two were significant (10% error for equimolar concentrations). The method was applied to the determination of propazine in spiked drinking water. At a concentration level of 2.0 × 10^–1 moll^–1 a recovery of 94 ± 6% was obtained, after tenfold concentration on Sep-Pak.