On the inexact scaled gradient projection method

Computational Optimization and Applications - The purpose of this paper is to present an inexact version of the scaled gradient projection method on a convex set, which is inexact in two sense....     

Tunable L-band erbium-doped fibre ring laser by means of induced cavity loss using a fibre taper

In this paper, we present a continuous-wave tunable fibre ring laser operating in the L-band. A bi-directional pumped L-band erbium-doped fibre amplifier provides gain to the loop. Tunability is achieved by bending a single-mode fibre taper using a micrometer drive, controlling in this way the spectral cavity losses. Laser emission is achieved between 1587 and 1606 nm, and low variation of the output laser power is observed over all the tuning range. PACS 42.55.Wd; 42.60.Da     

Optimization model for a production,inventory, distribution and routing problem in small furniture companies

Production and distribution are two key decisions in supply chain planning. In order to achieve an effective operational performance, it is important for these two decisions to be integrated, especially in supply chains with low inventory levels. In this paper, we propose a mixed integer programming model to integrate production, inventory, distribution and routing decisions in a single framework. The model was inspired by small Brazilian furniture companies and focuses on production and distribution decisions at an operational level. In particular, we consider a scenario in which only one production line and one vehicle, which makes multiple trips over the planning horizon, are available to produce items and deliver final products, respectively. We also take into account some features rarely considered in the literature, but commonly found in real-world applications, such as producing and stocking multiple items, distribution routes extending over one or more periods, multiple time windows and customers’ due dates. Computational tests on a set of randomly generated instances were carried out using a well-known optimization software and six relax-and-fix heuristics, which explore different criteria for partitioning and fixing variables. We also implemented two hybrid heuristics in which an initial solution is first constructed and then fed into the optimization software to improve it. The results showed that one relax-and-fix and the two hybrid heuristics performed better than the solver on the largest instances.     

A genetic algorithm with neural network fitness function evaluation for IMRT beam angle optimization

Intensity Modulated Radiotherapy Treatment (IMRT) is a technique used in the treatment of cancer, where the radiation beams are modulated by a multileaf collimator allowing the irradiation of the patient using non-uniform radiation fields from selected angles. Beam angle optimization consists in trying to find the best set of angles that should be used in IMRT planning. The choice of this set of angles is patient and pathology dependent and, in clinical practice, most of the times it is made using a trial and error procedure or simply using equidistantly distributed angles. In this paper we propose a genetic algorithm that aims at calculating good sets of angles in an automated way, given a predetermined number of angles. We consider the discretization of all possible angles in the interval [0 \(^{\circ }\) , 360 \(^{\circ }\) ], and each individual is represented by a chromosome with 360 binary genes. As the calculation of a given individual’s fitness is very expensive in terms of computational time, the genetic algorithm uses a neural network as a surrogate model to calculate the fitness of most of the individuals in the population. To explicitly consider the estimation error that can result from the use of this surrogate model, the fitness of each individual is represented by an interval of values and not by a single crisp value. The genetic algorithm is capable of finding improved solutions, when compared to the usual equidistant solution applied in clinical practice. The genetic algorithm will be described and computational results will be shown.     

Solutions in Bessel‐potential spaces for wave equations with nonlinear damping

We consider a semilinear wave equation with nonlinear damping in the whole space . Local‐in‐time existence and uniqueness results are obtained in the class of Bessel‐potential spaces . Copyright © 2017 John Wiley & Sons, Ltd.     

Fundamental solution of the time‐fractional telegraph Dirac operator

In this work, we obtain the fundamental solution (FS) of the multidimensional time‐fractional telegraph Dirac operator where the 2 time‐fractional derivatives of orders α∈]0,1] and β∈]1,2] are in the Caputo sense. Explicit integral and series representation of the FS are obtained for any dimension. We present and discuss some plots of the FS for some particular values of the dimension and of the fractional parameters α and β. Finally, using the FS, we study some Poisson and Cauchy problems.     

Chromium complexes based on thiophene–imine ligands for ethylene oligomerization

A new set of Cr(III) complexes, {L}CrCl₃(THF), based on thiophene–imine ( 2a , L = PhOC₆H₄(N═CH)‐2‐SC₄H₃; 2b , L = PhOC₂H₄(N═CH)‐2‐SC₄H₃; 2c , L = Ph(NH)C₂H₄(N═CH)‐2‐SC₄H₃; 2d , L = PhOC₆H₄(N═CH)‐2‐SC₄H₂‐5‐Ph; 2e , L = Ph(NH)C₂H₄(N═CH)‐2‐SC₄H₂‐5‐Ph) have been prepared and characterized using elemental analysis and infrared spectroscopy. Upon activation with methylaluminoxane, all the chromium complexes generated active systems affording a nonselective distribution of α‐olefins with turnover frequencies in the range 9500–93 500 (mol ethylene) (mol Cr)^?1 h^?1, and producing mostly oligomers (95.0–99.3 wt% of total products). Small amounts of polymer were produced in these oligomerization reactions (0.8–8.2 wt%). The catalytic activities were quite sensitive to the ligand environment. Moreover, the effects of oligomerization parameters (temperature, [Al]/[Cr] molar ratio, time) on the activity and on the product distribution were examined.     

Derivative spectrophotometric determination of nickel using Br-PADAP

A major problem with spectrophotometric methods for nickel is cobalt interference, because many of the reagents for nickel also react with cobalt. In this work, the interference of cobalt in the determination of nickel using 2-(5-bromo-2-pyridylaxo)-5-diethylaminophenol (Br-PADAP) was eliminated by the use of derivative spectrophotometry, using the zero-crossing method for evaluation of the derivative signal. Br-PADAP reacts with nickel(II) in the presence of Triton X-100 to form a red complex with absorption maxima at 530 and 562 nm. The reactions parameters and the conditions for the measurements of the first-derivative signal were studied and the results demonstrated that using the derivative technique, Br-PADAP can be used for nickel determination with a selectivity higher than that of ordinary spectrophotometry and with a limit of detection of 0.2 ng ml(-1). The pH should be in the range 5.0-6.0 using an acetate buffer. The determination of nickel in the presence of cobalt was performed with conventional and derivative procedures, and the results demonstrated that only the derivative method should be used and, of the methods used for evaluation of the derivative signal, the zero-crossing method is the best. The proposed procedure was used for nickel determination in steels standards. The results demonstrated that the procedure has satisfactory accuracy and precision. Cobalt interference can be also eliminated by using dual-wave-length spectroscopy.     

Multifunctional natural fibers: the potential of core shell MgO–SiO2 nanoparticles

Cellulose - Core–shell nanoparticles (NPs) based on metal oxides, namely magnesium oxide (MgO) and silica (SiO2), are a fantastic alternative for natural fibers’ functionalization. In...     

Electrochemical properties of Meldola's Blue immobilized on silica-titania phosphate prepared by the sol-gel method

The mixed oxide phosphate (≡SiO)₂Ti(O₃POH)₂ having a specific surface area of S_BET= 595 m² g⁻¹ and an average pore volume of 0.43 mL g⁻¹ was prepared by the sol-gel processing method. The material showed the following characteristics: Ti=11.6 wt% and P=10.5 wt%; ion exchange capacity of 0.60 mmol g⁻¹. Meldola's Blue (MLB) dye was adsorbed, by an ion exchange reaction, from an aqueous solution in a quantity of 0.62 mmol g⁻¹. The dye was strongly retained and was not easily leached from the matrix even in presence of 0.5 M electrolyte solution. Changing the solution pH between 2.5 and 7.0, the midpoint potential of the dye-adsorbed (≡SiO)₂ Ti(O₃POMLB)₂ matrix carbon paste electrode remained practically constant, i.e. about 20 mV vs. SCE. This is not the usual behaviour of MLB since its midpoint potential changes considerably in solution phase as the pH is changed. The modified electrode has proved to be stable and electrocatalytically active for hydrazine oxidation at pH 6. Received: 22 June 1999 / Accepted: 7 September 1999