Aziridines. 69. Reactions of N-Acylaziridines with Sodium Metal and Sodium Naphthalenide. Elimination of olefines

Reactions of N-acylaziridines 1a – g (N-benzoyl except 1d ) with sodium or naphthalenide N ^.− in THF provide a variety of products that usually arise via the aziridino ketyls 2 . Homolytic ring opening of 2 generates the amidatoalkyl radicals 3 . Only with a very short reaction time were small amounts of benzil or benzoylnaphthalenes obtained indicating a reversible trapping of 2 by dimerization or coupling with N^.−. Homolysis of 2 produced always the more stable 3 apart from reactions of monomethylaziridines 1c , d where the primary radical i-3c , d is kinetically favoured. The amides R¹CONHCHR⁴CHR²R³ ( 9 , isopropylamides i - 9c , d from 1c , d ) were usually the main products. 9 arise from 3 either by H atom abstraction from THF (probably in sodium metal runs) or by reduction of 3 to carbanions 5 that abstract a proton from THF ( N^.− runs). Addition of 5a (R²⁻⁴ = H) to 1a gives finally the ketone 8a . Self reaction of primary radical 3a is dimerization. Self reaction of tertiary or secondary radicals is disproportionation when an allylamide arises. This isomerizes to an enamide unless it is conjugated. R²R³CCHR⁴ and R¹CONH₂ arise (probably) always. The mechanism, possibly a cyclic process of anion 6 , is not clear.     

Multiscale modelling of bi-crystal grain boundaries in bcc iron

Atomistic simulations have provided much insight into grain boundary (GB) structures and mechanisms which are important in understanding the properties of materials. In this paper, the ∑3{1 1 2}, ∑3{1 1 1} and ∑5{0 1 3} (coincidence site lattice) GBs of bcc iron are investigated using molecular statics (MS) simulations, ab initio DFT calculations and the simulated HRTEM method. For the MS calculations, four empirical potentials, the Ackland potential (1997), Mendelev potentials 2 and 4 and the Dudarev-Derlet potential have been used. The MS results for all three symmetrical grain boundaries show the results to be independent of the empirical potential implemented. After relaxation, the symmetrical structures of the GBs remain, in agreement with ab initio calculation results.     

Selection of Process Conditions for High Pressure Pasteurization of Sea Buckthorn Juice Retaining High Antioxidant Activity

Sea buckthorn berries juice is a nutritious beverage, rich in vitamin C and carotenoids with high antioxidant activity. The main requirements for a freshly squeezed sea buckthorn juice production are the cloud stability and antioxidant activity retention after processing. Appropriate process technologies and conditions have to be applied in order to inactivate pectin methyl esterase (PME), responsible for cloud loss, while maintaining the nutritional characteristics and antioxidant activity of the juice. The objectives of the present work were to study and model the effect of thermal treatment and high pressure (HP) processing on the inactivation kinetics of endogenous PME and on total antioxidant activity alteration. Thermal treatment significantly affected PME inactivation and residual antioxidant activity. Processing even at mild process conditions (60 °C for 1 min) resulted in 2.5-fold antioxidant activity reduction and 50 % PME inactivation compared to untreated sample. Pressure and temperature acted synergistically for PME inactivation that followed first-order kinetics with a residual PME activity at all pressure–temperature combinations used (200–600 MPa and 25–35 °C). The effect of temperature and pressure on the inactivation rate constants was expressed through the activation energy and activation volume, respectively. Values of 163 kJ/mol and ?17 mL/mol at reference pressure of 600 MPa and reference temperature of 35 °C were estimated, respectively. Antioxidant activity of the samples was expressed through the determination of the effective concentration (EC₅₀). A slight increase in sea buckthorn antioxidant activity when applying pressures (200–600 MPa) at ambient temperature (25 °C) was observed compared to the corresponding value of untreated juice. Processing at higher temperatures did not significantly alter the total antioxidant activity of sea buckthorn juice. For sample treated at 600 MPa–35 °C for 5 min, a 5 % reduction of total antioxidant activity was observed. These conditions are proposed as effective process conditions for sea buckthorn juice cold pasteurization, based on the higher antioxidant activity retention and simultaneous PME inactivation.     

Using sulfur as a tracer of outdoor fine particulate matter

Six homes in the metropolitan Boston area were sampled between 6 and 12 consecutive days for indoor and outdoor particle volume and mass concentrations, particle elemental concentrations, and air exchange rates (AERs). Indoor/outdoor (I/O) ratios of nighttime (i.e., particle nonindoor source periods) sulfur, PM2.5 and the specific particle size intervals were used to provide estimates of the effective penetration efficiency. Mixed models and graphical displays were used to assess the ability of the I/O ratios for sulfur to estimate corresponding I/O ratios for PM2.5 and the various particle sizes. Results from this analysis showed that particulate sulfur compounds were primarily of outdoor origin and behaved in a manner that was representative of total PM2.5 in Boston, MA. These findings support the conclusion that sulfur can be used as a suitable tracer of outdoor PM2.5 for the homes sampled in this study. Sulfur was more representative of particles of similar size (0.06-0.5 microm), providing evidence that the size composition of total PM2.5 is an important characteristic affecting the robustness of sulfur-based estimation methods.     

Dispersive liquid–liquid microextraction for the determination of organochlorine pesticides residues in honey by gas chromatography-electron capture and ion trap mass spectrometric detection

A simple dispersive liquid–liquid microextraction (DLLME) protocol for the determination of 15 organochlorine pesticides residues in honey is proposed. The selected pesticides were separated using gas chromatography and detected by electron capture (ECD) or ion trap mass spectrometry (GC-IT/MS). Several parameters affecting the extraction efficiency namely type and volume of organic extraction solvent, type and volume of disperser solvent, sample pH, ionic strength, extraction time and centrifugation speed were systematically investigated. The final DLLME protocol involved the addition of 750 μL acetonitrile (disperser) and 50 μL chloroform (extraction solvent) into a 5 mL aqueous honey solution followed by centrifugation. The sedimented organic phase (chloroform) were analysed directly by GC-IT/MS or evaporated and reconstituted in acetonitrile prior to the GC-ECD analysis. The analytical performance of the GC-ECD and GC-IT/MS methods was compared and discussed. Under the selected experimental conditions, the enrichment factors varied between of 36 and 114. The limits of detection (LOD) were in the range of 0.02–0.15 μg L⁻¹ (0.4–3 ng g⁻¹) for GC-ECD and 0.01–0.2 μg L⁻¹ (0.2–4 ng g⁻¹) for GC-IT/MS which is adequate to verify compliance of products to legal tolerances. The proposed method was applied to the analysis of the selected organochlorine pesticides residues in various honey samples obtained from Greek region. Mean recoveries were ranged from 75% to 119% while the precision was better than 20% in both methodologies.     

Depinning transition of a dislocation line in ferritic oxide strengthened steels

The dynamics of an edge dislocation in a medium with random oxide dispersoid particles acting as pinning centres is analysed. The dislocation line undergoes a depinning transition, where the order parameter is the dislocation line velocity v, which increases from zero for driving external resolved shear stresses τ beyond to a threshold value τ_c, known as the critical resolved shear stress. The critical stress is obtained by means of statistical analysis of the motion of a single dislocation in its glide plane, using overdamped, discrete dislocation dynamics simulations.     

Transforming communicating X-machines into P systems

Tissue P systems (tPS) represent a class of P systems in which cells are arranged in a graph rather than a hierarchical structure. On the other hand, communicating X-machines (XMs) are state-based machines, extended with a memory structure and transition functions instead of simple inputs, which communicate via message passing. One could use communicating XMs to create models built out of components in a rather intuitive way. There are investigations showing how various classes of P systems can be modelled as communicating XMs. In this paper, we define a set of principles to transform communicating XMs into tPS. We describe the rules that govern such transformations, present an example to demonstrate the feasibility of this approach and discuss ways to extend it to more general models, such as population P systems, which involve dynamic structures.     

An exterior simplex type algorithm for the Minimum Cost Network Flow Problem

In this paper a new Network Exterior Point Simplex Algorithm (NEPSA) for the Minimum Cost Network Flow Problem (MCNFP) is analytically presented. NEPSA belongs to a special simplex type category and is a modification of the classical network simplex algorithm. The main idea of the algorithm is to compute two flows. One flow is basic but not always feasible and the other is feasible but not always basic. A complete proof of correctness for the proposed algorithm is also presented. Moreover, the computational behavior of NEPSA is shown by an empirical study carried out for randomly generated sparse instances created by the well-known GRIDGEN network problem generator.     

Performance evaluation of S-ALOHA over non-stationary wirelessinfrared channels

The authors present the throughput analysis of a slotted ALOHA protocol over non-stationary wireless infrared channels. The protocol operation is modelled as a four-dimensional Markov chain and equilibrium point analysis is employed to carry out the performance evaluation. Theoretical predictions are in good agreement with simulation results