Exponential stability in thermoviscoelastic mixtures of solids

In this paper we investigate the asymptotic behavior of solutions to the initial boundary value problem for a one-dimensional mixture of thermoviscoelastic solids. Our main result is to establish the exponential stability of the corresponding semigroup and the lack of exponential stability of the corresponding semigroup.     

Multiresolution schemes for strongly degenerate parabolic equations in one space dimension

An adaptive finite volume method for one‐dimensional strongly degenerate parabolic equations is presented. Using an explicit conservative numerical scheme with a third‐order Runge‐Kutta method for the time discretization, a third‐order ENO interpolation for the convective term, and adding a conservative discretization for the diffusive term, we apply the multiresolution method combining two fundamental concepts: the switch between central interpolation or exact computing of numerical flux and a thresholded wavelet transform applied to cell averages of the solution to control the switch. Applications to mathematical models of sedimentation‐consolidation processes and traffic flow with driver reaction, which involve different types of boundary conditions, illustrate the computational efficiency of the new method. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2007     

Synthesis and Chemical Reactivity of 5-Methoxy-2-vinyl-4-azaindoles

2-Vinyl-4-azaindoles are less reactive with dienophiles than 2-vinylindoles. 5-Methoxy-2-vinyl-4-azaindole 2a and its 1-methyl derivative 2a reacts with N-phenylmaleimide to yield cycloadducts only under vigorous conditions. 2b produces a cycloadduct with dimethyl acetylenedicarboxylate, while 2a yields a Michael-type adduct. Reactions with more reactive dienophiles gave only polymeric products.     

A Facile Route to 9-Phosphorylated Neuraminic Acid Derivatives

The phosphitylation of 2-α-O-Benzyl-N-acetylneuraminic acid (2) and of the methyl 2-α-O-methyl-N-acetylneuraminate (3) with 2-chloro-4H-1,2,3-benzodioxaphosphorin-4-one (4) is described. The reaction affords a ready access to 9-phosphorylated derivatives of N-acetylneuraminic acid (1).     

An architecture for solving sequencing and resource allocation problems using approximation methods

In the search for better optimisation techniques, new methods that mix artificial intelligence and operations research have emerged. Search heuristics are integrated with optimisation algorithms. Approximation methods, like Hill Climbing, Simulated Annealing, and Tabu Search, that have been used with success in combinatorial optimisation problems, are one of such research lines. This paper presents the key elements of approximation methods and combines them in a tool appropriate for solving sequencing and resource allocation problems. The system permits a clear division between problem specification and problem solving, allowing a declarative representation and therefore minimising developing costs. The key issues discussed in this work are a model for representing this class of problems in a standard form, a set of strategies for applying the approximation methodology, and an expert system that dynamically manipulates the strategies' parameters.     

Determination of pentachlorophenol and tribromophenol in sawdust by ultrasound-assisted extraction and MEKC

An ultrasonic bar-assisted extraction and CE separation procedure for the determination of pentachlorophenol (PCP) and 2,4,6-tribromophenol (TBP) residues in sawdust was developed and applied. For this purpose, micellar electrokinetic capillary chromatography (MEKC) was used and compared with a GC/MS methodology. This methodology allowed the quantification of PCP and TBP in a concentration range of 2.5-12.0 mg/kg for TBP and 2.8-12.0 mg/kg for PCP. Different sample treatment processes were evaluated in order to extract these compounds from sawdust. Better results were obtained when the residues were extracted with ultrasound-assisted hexane, filtered, evaporated, dissolved in Na(2)CO(3), and injected into the CE equipment. The optimal option for GC/MS was extraction with Na(2)CO(3 )followed by a derivation using acetic anhydride and liquid-liquid extraction with hexane. This method allowed the quantification of TBP and PCP in sawdust in a concentration range of 0.19-12.00 mg/kg and 0.14-12.00 mg/kg, respectively. The CE method was compared with the GC/MS as reference method. The results were shown to be statistically similar by both methods for PCP as well as for TBP.     

Isolation and characterization of cellulose nanoplatelets from the parenchyma cells of <Emphasis Type="Italic">Agave salmiana</Emphasis>

We present a novel nanostructure in the form of cellulose nanoplatelets (CNPs) with an inner array of entangled nanofibrils. The planar structure was isolated from the parenchyma cells of Agave salmiana first using basic pretreatment, then by dissolving lignin and hemicellulose using acid hydrolysis, and finally by modifying the cellulose with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). The crystallinity index was calculated following the purification process, and it was found that nanocellulose was 30% more crystalline than the raw material. Using transmission electron microscopy, it was found that the nanoplatelets comprise ~2–3 nm long cellulose entangled nanofibrils. In addition, via atomic force microscopy, the morphology of the nanoplatelets was confirmed; they were 90 nm thick for the acid hydrolyzed sample and 70 nm thick for the TEMPO-modified sample; their lateral size varied from a few to hundreds of micrometers, presenting large aspect ratios. Finally, CNPs were isolated and processed into thin paper with a thickness of 100 µm and transmittance of 86%, demonstrating great potential as a transparent film.     

Use of dimethyldioxirane in the epoxidation of the main constituents of the essential oils obtained from Tagetes lucida, Cymbopogon citratus, Lippia alba and Eucalyptus citriodora

Dimethyldioxirane (DMDO), a widely used oxidant in organic synthesis is considered an environmentally friendly oxygen transfer reagent because acetone is the only byproduct formed in its oxidation reactions. This work describes the isolation of the main constituents (terpenes) in the essential oils obtained from Tagetes lucida, Cymbopogon citratus, Lippia alba and Eucalyptus citriodora, their epoxidation with DMDO in acetone solution and the characterization of the resulting epoxides by GC-MS (EI) and NMR. This is one of the first reports involving the application of dioxirane chemistry to essential oils in order to generate modified compounds with potential uses in several areas of medicine and industry.     

Analyticity and Smoothing Effect for the Coupled System of Equations of Korteweg-de Vries Type with a Single Point Singularity

Using Bourgain spaces and the generator of dilation P=3t ? _t +x ? _x , which almost commutes with the linear Korteweg-de Vries operator, we show that a solution of the initial value problem associated for the coupled system of equations of Korteweg-de Vries type which appears as a model to describe the strong interaction of weakly nonlinear long waves, has an analyticity in time and a smoothing effect up to real analyticity if the initial data only have a single point singularity at x=0.