Applying GRASP to solve the multi-item three-echelon uncapacitated facility location problem

This paper considers a production–distribution problem that consists of defining the flow of produced products from manufacturing plants to clients (markets) via a set of warehouses. The problem also consists of defining the location of such warehouses that have unlimited storage capacity. This problem is known in the literature as the three-echelon uncapacitated facility location problem (TUFLP), and is known to be NP-hard when the objective function is to minimize the total cost of warehouse location and production and distribution of products. This paper proposes a Greedy Randomized Adaptive Search Procedure (GRASP) to solve the multi-item version of the TUFLP. Computational experiments are conducted using known instances from the literature. Solutions obtained using GRASP are compared against both optimal solutions and lower bounds obtained using mathematical programming. Results show that proposed algorithm performs well, obtaining good solutions (and even the optimal values) in less computational time than the mixed-integer linear programming model.     

LDA approximation based analysis of the adsorption of O<Subscript>3</Subscript> by boron nitride sheet

Based on the density functional theory whitin the local density aproximation, we investigated the adsorption of the ozone molecule by the boron nitride sheet. To model the sheet we used a planar C _n H _m cluster; four high symmetry sites in the mesh were considered. A total energy calculation indicates that the boron nitride sheet remains planar and the ozone is adsorbed with an energy of 0.41 eV; the ozone reacts with the sheet forming an epoxy group and an oxygen molecule in an unstable configuration.     

Reducing Antioxidant Capacity Evaluated by Means of Controlled Potential Electrolysis

An analytical method suitable for an antioxidant sensor is presented following the response of these substances to an extensive oxidation imposed by electrochemical means. The electrochemical assay simulates the action of a reactive oxygen species (ROS) by means of electrolyses carried out at a potential which is settled at the formal potential of the ROS. The antioxidant activities of trolox and ascorbic, gallic and caffeic acids and of mixtures of these antioxidants were estimated from the charge required for the complete oxidation of the antioxidants from assays where the oxidative attack by O₂ and by O₂^.? were simulated.     

Robust output synchronization of second-order systems

A technique to synchronize a network of dynamical systems described by second-order ordinary differential equations is presented. Each system can be driven by a coupling control signal, which is synthesized such that, at steady-state, the outputs of two given systems, say y _i and y _j , i ≠ j, satisfy a specified ratio, that is, y _i /y _j = α _i /α _j , α _i ≠ 0 ≠ α _j . Among others, this includes the cases where the outputs are synchronized in-phase or anti-phase. The proposed synchronization technique is robust; this means that a small synchronization error is preserved at steady-state, even if the systems were perturbed by external disturbances. Some level of parameter uncertainty can also be tolerated. The coupling control signals are synthesized based on a classical controller and a robust observer that estimates the generalized velocities and provides an estimation of the perturbation terms. Some experimental results, showing the performance of the proposed synchronization technique, are included.     

Pyrolysis kinetics of elephant grass pretreated biomasses

The Elephant Grass (Pennisetum purpureum Schum) was pretreated by two independent processes, through washing with hot water (W-EG) and acid solution (AW-EG) to improve its energy properties to apply it in a thermochemical process conversion into fuel. The biomasses were analyzed by proximate and ultimate analysis; and the pyrolysis kinetics, before and after pretreatments, were evaluated by the apparent activation energy (E _a) for decomposition in the temperature range of greater volatile matter through the Model-free kinetics using thermogravimetric analysis data. The kinetics of the microcrystalline cellulose Avicel PH-101 was performed to evaluate the E _a result of pure cellulose. The pretreatments were efficient in increasing the volatile matter and heating value, decreasing moisture and ash content, and improving its energetic power to the application in fast pyrolysis process for bio-oil production. The TG results have shown that the reduction in ash content facilitates the pyrolysis process, increasing the volatile matter and decreasing the apparent activation energy required to biomasses degradation, due to less diffusional resistances to heat and mass transfer of W-EG and AW-EG. The Avicel PH-101 showed the highest value of apparent activated energy (E _a = 276.2 kJ mol^?1) which could be explained by its crystallinity, suggesting that crystalline cellulose regions are less accessible to heat diffusion than amorphous regions, requiring more energy to its degradation.     

Tris-(1,2-N,N-dimethylaminomethylferrocenyl)stibine and its heterotrimetallic complex

New tertiary chloro-bis(1,2-N,N-dimethylaminomethylferrocenyl)stibine (1) and tris-(1,2-N,N-dimethylaminomethylferrocenyl)stibine ligand (2) containing CH₂NMe₂ pendenant arm at the ortho-position have been synthesized. Stibine (2) reacts with PtCl₄^2? and hetero trimetallic cis-PtCl₂L (3) complex is obtained, where stibine (2) acts as a bidentate ligand. All these compounds were characterized by various physicochemical methods and their molecular structures were determined by X-ray diffraction analyses. It is to be noted that tris(1,2-aminomethylferrocenyl)stibine represents the first example of a structurally characterized ferrocenyl pnictogen where three 1,2-disubstituted ferrocenyl groups are attached to the central antimony atom and phosphorus analogue of the stibine is missing in the literature. Stibine (1) shows a hypervalent Sb–N interaction while stibine (2) does not show this interaction in solid state.     

New stibines containing acetal and formyl group: Platinum complex and unexpected oxastibol derivative

A new tertiary stibine ligand (1) containing acetal group at the ortho-position has been synthesized. This new stibine was then complexed with to obtain trans-PtCl₂L₂ (2) where stibine acts as a monodentate ligand. The acetal was hydrolyzed in a slightly acidic medium and forms a very new stibine (3) containing formyl group at the ortho-position. When (3) was reduced with NaBH₄ an unusual oxastibol (4) derivative was obtained under the experimental conditions used.All the compounds were characterized by IR, mass, ¹H, ¹³C, COSY and HETCOR NMR spectroscopy. The molecular structures of (2), (3) and (4) were determined. Compound (3) crystallizes in two different polymorphs (3a) and (3b) and both the polymorphs show hypervalent antimony with three Sb?O interactions and the molecule exists in O-cis-exo configuration. Compound (4) shows intramolecular Sb?O interactions. To the best of our knowledge this is the first report on organoantimony compounds containing carbonyl groups though their phosphorus and bismuth analogues are well known. Compound (2) shows helicoidal chirality, which is a very new concept in antimony chemistry     

The further unified theory for modifications of <Emphasis Type="Italic">λ</Emphasis>-closed sets and gΛ-sets using minimal structures

We introduce and study two new notions of sets called (Λ, mn)-closed sets and gΛ _mn -sets, which are defined on a nonempty set with two minimal structures. These sets enables us to unify modifications of λ-closed sets [1] and generalized Λ-sets [15], respectively. Moreover, we give a new characterization of the class of mn-T _1/2 [17] by using gΛ _mn -sets.     

Rotational isomers of methyl trans-cinnamate: A Raman study

The Raman and infrared spectra of methyl trans-cinnamate were measured as a function of temperature in the liquid and solid phases. The temperature dependence of the band intensities established the presence of two conformers in the liquid phase (the s-cis and s-trans forms, with CC CO dihedral angles equal to 0° and 180°, respectively; ΔH_{(s-trans)-(s-cis)} = 3.43 ± 0.84 kJ mol⁻¹) and led to the conclusion that the thermodynamically most stable s-cis form is the only form present in the solid.