Comprehensive Two-Dimensional Gas Chromatography as a Powerful Strategy for the Exploration of Broas Volatile Composition

Broa is a Portuguese maize bread with characteristic sensory attributes that can only be achieved using traditional maize varieties. This study intends to disclose the volatile compounds that are mainly associated with the baking process of broas, which can be important contributors to their aroma. Twelve broas were prepared from twelve maize flours (eleven traditional maize varieties and one commercial hybrid). Their volatile compounds were analyzed by GC×GC–ToFMS (two-dimensional gas chromatography coupled with time-of-flight mass spectrometry) for an untargeted screening of the chemical compounds mainly formed during baking. It was possible to identify 128 volatiles that belonged to the main chemical families formed during this stage. Among these, only 16 had been previously detected in broas. The most abundant were furans, furanones, and pyranones, but the most relevant for the aroma of broas were ascribed to sulfur-containing compounds, in particular dimethyl trisulfide and methanethiol. Pyrazines might contribute negatively to the aroma of broas since they were present in higher amounts in the commercial broa. This work constitutes the most detailed study of the characterization of broas volatile compounds, particularly those formed during the Maillard reaction. These findings may contribute to the characterization of other maize-based foodstuffs, ultimately improving the production of foods with better sensory features.     

Automatic assignment of 1H‐NMR spectra of small molecules

A novel data‐evaluation procedure for the automatic atom to peak or multiplet assignment of ¹H‐NMR spectra of small molecules has been developed using a fast and robust expert system. The applicability and reliability of the method are demonstrated by comparison of a manually assigned database of ¹H‐NMR spectra with the assignments produced by the automatic procedure. The results of this analysis show an excellent success ratio, indicating that this new algorithm can have a major impact as a time saving tool for the organic chemist. A new graphical feature used to illustrate both the stability and quality of the elementary assignments is also introduced. Copyright © 2013 John Wiley & Sons, Ltd.     

General spherically symmetric elastic stars in relativity

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling of star interiors possessing elastic properties such as the ones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the way, a few general results for spacetimes admitting isometries are reviewed, and their consequences are fully exploited in the case of spherical symmetry relating them next to the the case in which the material content of the spacetime is some elastic material. Specific examples are provided satisfying the dominant energy condition and admitting a constitutive equation, including a static two-layer star ‘toy model’ consisting of an elastic core surrounded by a perfect fluid corresponding to the interior Schwarzschild solution matched to the vacuum Schwarzschild solution. This paper extends and generalizes the pioneering work by Magli and Kijowski (Gen Relat Gravit 24:139, 1992), Magli (Gen Relat Gravit 25:1277, 1993; 25:441, 1993), and complements, in a sense, that by Karlovini and Samuelsson in their interesting series of papers (Karlovini and Samuelsson in Class Quantum Grav 20:363, 2003; 21:1559, 21:4531, 2004).     

Exploiting ion-pair formation for the enhancement of electroanalytical determination of pyridoxine (B6) onto polyurethane-graphite electrodes

The present study reports some aspects of ion-pair formation between pyridoxine and dodecyl sulphate under suitable conditions of pH, and its application with analytical purposes. Electrochemical behavior of the analite onto a graphite-polyurethane electrode was assessed by both cyclic and square-wave voltammetries under different conditions (pH from 1.2 to 13.0, with and without surfactant), aiming to study its mechanisms and to define best parameters for such determination exploiting the association of electroanalytical variables and ion-pair formation; besides these, electrochemical impedance spectroscopy was also applied to evaluate ion-pair formation and its influence on interfacial fenomena. Best conditions were reach by square-wave voltammetry in pH 4.2 acetate buffer sweeping from + 0.7 to + 1.2 V (vs. Ag|AgCl_sat) in pulses of 50 mV amplitude and 10 mV step, in a frequency of 10 Hz. The concentration of sodium dodecyl sulphate was optimized being the optimal value a constant submicelar concentration of 3 mmol L^-1. Under such conditions a linear dynamic range from 2 to 18 μmol L^-1 was observed, providing faster, more selective and sensitive system. Interference studies were also carried out showing no relevant influence of thiamine, riboflavine and nicotinamide over the analysis of pyridoxine. The system was successfully applied to commercial parenteral samples containing thiamine and pyridoxine as purchased, without further treatment.     

Pseudo-steady-state solutions for solidification in a wedge

Polubarinova-Kochina's analytical differential equation methodis used to determine the pseudo-steady-state solution to problemsinvolving the freezing (solidification) of wedges of liquidwhich are initially at their fusion temperature. In particular,we consider four distinct problems for wedges which are: freezingwith the same constant boundary temperature, freezing with thesame constant boundary heat fluxes, freezing with distinct constantboundary temperatures and freezing with distinct constant fluxesat the boundaries. For the last two problems, a Heun's differentialequation with an unknown singularity is derived, which in bothcases admits a particularly elegant simple solution for thespecial case when the wedge angle is . The moving boundariesobtained are shown pictorially.     

A particle swarm pattern search method for bound constrained global optimization

In this paper we develop, analyze, and test a new algorithm for the global minimization of a function subject to simple bounds without the use of derivatives. The underlying algorithm is a pattern search method, more specifically a coordinate search method, which guarantees convergence to stationary points from arbitrary starting points. In the optional search phase of pattern search we apply a particle swarm scheme to globally explore the possible nonconvexity of the objective function. Our extensive numerical experiments showed that the resulting algorithm is highly competitive with other global optimization methods also based on function values. Support for Luís N. Vicente was provided by Centro de Matemática da Universidade de Coimbra and by FCT under grant POCI/MAT/59442/2004.     

Non-isothermal polymer melt flow in sudden expansions

This paper presents numerical results for laminar, incompressible and non-isothermal polymer melt flow in sudden expansions. The mathematical model includes the mass, momentum and energy conservation laws within the framework of a generalized Newtonian formulation. Two constitutive relations are adopted to describe the non-Newtonian behavior of the flow, namely Cross and Modified Arrhenius Power-Law models. The governing equations are discretized using the finite difference method based on central, second-order accurate formulas for both convective and diffusive terms. The pressure–velocity coupling is treated by solving a Poisson equation for pressure. The results are presented for two commercial polymers and demonstrate that important flow parameters, such as pressure drop and viscosity distribution, are strongly affected by heat transfer features.     

Reduction of cationic free-base <Emphasis Type="Italic">meso</Emphasis>-tris-<Emphasis Type="Italic">N</Emphasis>-methylpyridinium-4-yl porphyrins in positive mode electrospray ionization mass spectrometry

Reductions involving more than one electron with formation of the M⁺ and [M+2H]⁺ ions were observed for electrosprayed meso-tris(N-methylpyridinium-4-yl)porphyrin iodides, MI₃. These reductions were studied by using different solvents and flow rates. Formation of the [M+2H]⁺ ions occurred only for protic solvents and to a larger extent at lower flow rates. The type of the fourth substituent does not seem to affect the reduction processes. Formation of the two reduced species, M⁺ and [M+2H]⁺ ions, may occur through the participation of counter ion/solvent clusters. Reduction of multiply charged, non-metallated species with formation of [M+nH]⁺ ions (n>1) was not observed before in positive mode electrospray mass spectrometry.