On semidirectly closed pseudovarieties of aperiodic semigroups

The aim of this work is to study the unknown intervals of the lattice of aperiodic pseudovarieties which are semidirectly closed and answer questions proposed by Almeida in his book “Finite Semigroups and Universal Algebra”. The main results state that the intervals [V^*(B₂),ER∩LR] and [V^*(B₂¹),ER∩A] are not trivial, and that both contain a chain isomorphic to the chain of real numbers. These results are a consequence of the study of the semidirectly closed pseudovariety generated by the aperiodic Brandt semigroup B₂.     

Solid hulls of concrete categories

This paper deals with the problem of the existence of solid hulls for concrete categories. We present sufficient conditions for a concrete category to have a solid hull. For concrete categories over Set with a small finally dense subcategory, we observe that the existence of solid hulls is equivalent to Weak Vopenka's Principle.Research partially supported by TEMPUS JEP 2692 and by Centro de Matemática da Universidade de Coimbra     

Investigations into the mechanism of action of nitrobenzene as a mild dehydrogenating agent under acid-catalysed conditions

Protonated nitrobenzene can be used to dehydrogenate a range of hydrocarbons, which already possess at least one double bond. Kinetic and spectroscopic results, together with known electrode potentials, yield approximate limits within which protonated nitrobenzenes can be expected to effect dehydrogenation of hydroaromatic compounds. A high yielding synthesis of benzo[j]fluoranthene is described.     

Remote optical fibre microsensor for monitoring BTEX in confined industrial atmospheres

A portable optical fibre sensor has been developed for remote monitoring of benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene (BTEX). Firstly, the analyser was tested for calibration and its analytical performance for BTEX monitoring compared with a more classical analytical method, namely gas chromatography coupled to a flame ionization detector (GC-FID). The developed remote sensor shows several analytical advantages such as, high analytical sensitivity and accuracy, good linearity and stability of the analytical signal and short analytical time. Secondly, the optical fibre based sensor was applied to air monitoring for detection and quantification of BTEX in a confined industrial environment. The analytical signal measurement was performed by wireless at 20 m of distance from the local of analysis. Besides, the reported sensor showed a high degree of portability, compact design and high analytical performance for remote BTEX monitoring, in situ and in real-time.     

Vibrational spectra and structure of 1-phenyltetrazole and 5-chloro-1-phenyltetrazole: A combined study by low temperature matrix isolation and solid state FTIR spectroscopy and DFT calculations

Infrared spectra of 1-phenyltetrazole (C₇N₄H₆) and 5-chloro-1-phenyltetrazole (C₇N₄H₅Cl) isolated in argon matrixes (T=8 K) and in the solid state (at room temperature) were studied. DFT(B3LYP)/6-31G* calculations predict the minimum energy conformation of 1-phenyltetrazole as being non-planar, with the two rings (phenyl and tetrazole) twisted by 29°. For 5-chloro-1-phenyltetrazole, the optimized dihedral angle between the two rings is larger (48°). The theoretically calculated IR spectra of both compounds fit well the spectra observed experimentally. This allowed a reliable assignment of observed IR absorption bands.     

Sigmatropic rearrangements in 5-allyloxytetrazoles

Mechanisms of thermal isomerization of allyl tetrazolyl ethers derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol were investigated. In the process of the syntheses of the three 1-aryl-5-allyloxytetrazoles, their rapid isomerization to the corresponding 1-aryl-4-allyltetrazol-5-ones occurred. The experiments showed that the imidates rearrange exclusively through a [3,3']-sigmatropic migration of the allylic system from O to N, with inversion. Mechanistic proposals are based on product analysis and extensive quantum chemical calculations at the DFT(B3LYP) and MP2 levels, on O-allyl and N-allyl isomers and on putative transition state structures for [1,3']- and [3,3']-sigmatropic migrations. The experimental observations could be only explained on the basis of the MP2/6-31G(d,p) calculations that favoured the [3,3']-sigmatropic migrations, yielding lower energies both for the transition states and for the final isomerization products.     

Analysis of the basis set and correlation effects on the computation of molecular polarizabilities using molecular polarization maps

In the present report, we analyze the effect of augmenting the basis set and the level of the theory in the computation of the molecular polarization potential and it is used as a tool to understand their spatial effects in the calculation of molecular polarizabilities. This is analyzed in the present report through the results obtained for three reference molecules: hydrogen cyanide, formaldehyde and urea. Accordingly, different basis sets were used for the calculations, including: 6-31G(D), 6-31G(D,P), 6-31G(2D,2P) and 6-31++G(2D,2P). On the other hand, calculations at different levels of the theory were considered, including: Hartree–Fock, Moller–Plesset second order (MP2) and fourth order (MP4) as well as the functionals BLYP and B3LYP at the density functional theory. The results of the polarization maps reveal similar trends observed with the calculation of the different components of the polarizability tensor. However, the use of the maps permits to understand spatial effects specific for each level of calculation and each basis set.     

Optimal cycle for a signalized intersection using Global Optimization and Complementarity

A queueing system resulting from a signalised intersection regulated by pre-timed control in an urban traffic network is considered in this paper. Subsequently, we analyse the manner in which Global Optimisation and Complementarity may be used to determine the optimal cycle length and green split allocation for an isolated signalised intersection. The model in question has been formulated as a Mathematical Program with Equilibrium (or Complementarity) Constraints (MPEC). A?sequential complementarity algorithm for computing a global minimum for the MPEC is also subject to analysis in this paper. Furthermore, computational experience is included to demonstrate the efficiency of this method as an effective solution for the problem in question.     

Novel efficient synthesis of 3,4-dihydro-6-substituted-3-phenylpyrimidin-2(1H)-ones

A new attractive and convenient strategy for the synthesis of 3,4-dihydro-6-substituted-3-phenylpyrimidin-2(1H)-ones is described. Photolysis (λ = 254 nm) of 4-allyl-tetrazolones in alcoholic solutions produces the corresponding pyrimidinones as the sole product in nearly quantitative yields, with simultaneous extrusion of molecular nitrogen. Work-up procedures consist in the simple evaporation of the solvent under reduced pressure, in mild conditions. Heats of reaction for the photocleavage process of 4-allyltetrazolones were calculated, indicating high stability of the resulting products.