DC tolerance analysis of electronic circuits by polyhedral circuits

Real equilibrium solutions of electronic circuits are affected by deviation of real characteristics of devices from their nominal values, producing the displacement of solution points from their nominal position. In this paper, a method to determine all the equilibrium regions in which real equilibrium points may fall is presented. The analysis is based on the introduction of the so‐called strip characteristics that represent the characteristics of devices affected by tolerances. They are modeled by polyhedral characteristics. Different situations may occur as tolerances grow. A nominal solution point may disappear, or on the other end, some solution point not present with nominal characteristics may appear. These possible events call for a classification of the equilibrium regions in either certain or uncertain, depending on the existence or not of an equilibrium point for any choice of real characteristics. The algorithm adopts linear programming techniques and a clustering algorithm. Copyright © 2015 John Wiley & Sons, Ltd.     

Photocatalytic Activity of Epoxy/CNT Nanocomposite Films

The efficiency of epoxy/CNT nanocomposites as photocatalyst on adsorbed, aqueous and gas phases is investigated. Epoxy films containing SWNTs in the range between 0.1 and 0.3 wt% are prepared by means of UV‐induced polymerization and the achieved materials are used as photocatalysts on adsorbed, aqueous, and gas phases. The activity of this new photocatalytic materials is evaluated in the adsorbed state by using the methylene blue target molecule, in the aqueous phase by following the photodegradation of phenol and 3,5‐dichlorophenol, and in the gas phase using nitrogen monoxide as probe molecule. It is demonstrated that the catalyst is suitable for both oxidative and reductive degradation reactions.

     

Solvent‐Free Non‐Covalent Organocatalysis: Enantioselective Addition of Nitroalkanes to Alkylideneindolenines as a Flexible Gateway to Optically Active Tryptamine Derivatives

A catalytic asymmetric addition of nitroalkanes to alkylideneindolenines, generated in situ from arylsulfonylindoles, is presented. Despite the weakness of the non‐covalent H‐bond interactions between catalyst and substrates, the performance of the bifunctional organocatalyst used was found to be essentially unaffected by the polarity of the reaction medium. Nitroalkanes, mostly used in nearly stoichiometric amounts, could thus function both as solvents and reagents, resulting in a truly solvent‐free reaction. The broad substrate scope shown by the present transformation allowed the preparation of some optically active tryptamine precursors that are not accessible through the previous catalytic asymmetric methods.     

Galloflavin (CAS 568-80-9): a novel inhibitor of lactate dehydrogenase

One of the most prominent alterations in cancer cells is their strict dependence on the glycolytic pathway for ATP generation. This observation led to the evaluation of glycolysis inhibitors as potential anticancer agents. The inhibition of lactate dehydrogenase (LDH) is a promising way to inhibit tumor cell glucose metabolism without affecting the energetic balance of normal tissues. However, the success of this approach depends chiefly on the availability of inhibitors that display good selectivity. We identified a compound (galloflavin, CAS 568‐80‐9) which, in contrast to other inhibitors of human LDH, hinders both the A and B isoforms of the enzyme. To determine the mechanism of action, we collected LDH‐A and ‐B inhibition data in competition reactions with pyruvate or NADH and evaluated the results using software for enzyme kinetics analysis. We found that galloflavin inhibits both human LDH isoforms by preferentially binding the free enzyme, without competing with the substrate or cofactor. The calculated K_i values for pyruvate were 5.46 μM (LDH‐A) and 15.06 μM (LDH‐B). In cultured tumor cells, galloflavin blocked aerobic glycolysis at micromolar concentrations, did not interfere with cell respiration, and induced cell death by triggering apoptosis. To our knowledge, the inhibition of LDH is, to date, the only biochemical effect described for galloflavin. Because galloflavin is not commercially available, we also describe herein a procedure for its synthesis and report its first full chemical characterization.     

Effect of vacuum application on the physical,rheological and sensory characteristics of an artisanal ice cream

Four milk-based ice cream samples were produced by heating (65°C) the ingredients at different pressures (0.5, 1.0 bar) and times (5, 30 min). Overrun, melting behaviour, particle size, viscosity and sensory analysis were conducted for each time/temperature combination. The 5-min vacuum application resulted in a reduction of overrun and air bubbles size, whereas ice cream viscosity increased. Opposite outcomes were found for the sample treated with vacuum for 30 min, which also showed a significant fat globule size reduction (<3.0 μm). Sensory analysis revealed that the use of vacuum improved sweetness, milky and creamy sensations regardless the treatment times.     

Effect of the resin/hardener ratio on curing,structure and glass transition temperature of nanofilled epoxies

The curing reaction, structure, and glass transition behavior of epoxy‐clay nanocomposites prepared using several different resin/hardener ratios were investigated. Nonisothermal DSC experiments evidenced that the incorporation of the organoclay did not induce appreciable changes in the curing enthalpy, but determined a slight acceleration of the curing reaction, without modifying the activation energy. TEM and SEM analyses of the nanocomposite resins showed the presence of micrometric aggregates for all the resin/hardener ratios investigated, even though these materials showed good optical clarity and their WAXD analyses did not evidence any organoclay peak. In addition, the higher the hardener content, the lower the tendency toward exfoliation and the broader the distribution of the interlamellar distances. The degree of cross‐linking of cured resins was evaluated both from measurements of the elastic modulus in the rubbery plateau and from solvent sorption experiments. A maximum in cross‐link density was observed near the stoichiometric composition. Both modulus and sorption experiments suggested that filler‐matrix adhesion increased with increasing the resin/hardener ratio, a trend that was confirmed also by glass transition temperature data. An analysis of ethyl acetate sorption curves evidenced that a gradual transition from Fickian to Case II diffusion occurred as the resin/hardener ratio was raised and that the organoclay promoted deviation from the Fickian behavior. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effect of the resin/hardener ratio on yield,post‐yield,and fracture behavior of nanofilled epoxies

In this work, the effect of the resin/hardener ratio on the small deformation, yield, post‐yield, and fracture behavior of a series of DGEBA‐Jeffamine epoxy‐clay nanocomposites with a fixed organo‐clay content (6 phr), and of the corresponding unfilled resins, was investigated. The mechanical behavior at small deformation was studied by means of uniaxial tensile tests, whereas compression tests were employed to investigate the large (yield and post‐yield) deformation levels. The fracture behavior was studied by the application of fracture mechanics testing methods. The results pointed out that small variations in the resin/hardener ratio used for the preparation of the resin can give rise to remarkable differences in the mechanical behavior at large deformation levels and at fracture. These effects were related to the parameters characteristic of the macromolecular architecture of the resins (chain segments flexibility and crosslink density). The results obtained on nanofilled systems showed that the effect of the resin/hardener ratio on the mechanical behavior of the resins is reduced in presence of organoclay particles. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

A mathematical model for the prediction of the injected mass diagram of a S.I. engine gas injector

A mathematical model of gaseous fuel solenoid injector for spark ignition engine has been realized and validated through experimental data. The gas injector was studied with particular reference to the complex needle motion during the opening and closing phases, which strongly affects the amount of fuel injected. As is known, in fact, when the injector nozzle is widely open, the mass flow depends only on the fluid pressure and temperature upstream the injector: this allows one to control the injected fuel mass acting on the “injection time” (the period during which the injector solenoid is energized). This makes the correlation between the injected fuel mass and the injection time linear, except for the lower injection times, where we experimentally observed strong nonlinearities. These nonlinearities arise by the injector outflow area variation caused by the needle bounces due to impacts during the opening and closing transients [1] and may seriously compromise the mixture quality control, thus increasing both fuel consumption and pollutant emissions, above all because the S.I. catalytic conversion system has a very low efficiency for non-stoichiometric mixtures. Moreover, in recent works [2, 3] we tested the simultaneous combustion of a gaseous fuel (compressed natural gas, CNG, or liquefied petroleum gas, LPG) and gasoline in a spark ignition engine obtaining great improvement both in engine efficiency and pollutant emissions with respect to pure gasoline operation mode; this third operating mode of bi-fuel engines, called “double fuel” combustion, requires small amounts of gaseous fuel, hence forcing the injectors to work in the non-monotonic zone of the injected mass diagram, where the control on air-fuel ratio is poor. Starting from these considerations we investigated the fuel injector dynamics with the aim to improve its performance in the low injection times range. The first part of this paper deals with the realization of a mathematical model for the prediction of both the needle motion and the injected mass for choked flow condition, while the second part presents the model calibration and validation, performed by means of experimental data obtained on the engine test bed of the internal combustion engine laboratory of the University of Palermo.     

Correlating mechanical and electrical properties of filler‐loaded polyurethane fluoroelastomers: The influence of carbon black

The dynamic mechanical properties and electrical conductivity of a class of polyurethane fluoroelastomers filled with different carbon black types and loadings were investigated. In particular, finely structured and coarsely structured carbon blacks were considered. Dynamic mechanical analysis (DMA) on the unfilled fluoroelastomer confirmed the phase‐segregated nature of this copolymer. The dynamic mechanical behavior of elastomeric compounds reinforced with finely structured carbon black was found to be strongly influenced by the filler content above a threshold value. This behavior may be attributed to the formation of carbon black aggregates and three‐dimensional anisotropic structures at increasing filler loading. Such an effect was not observed in compounds filled with coarsely structured carbon black particles, which do not seem to form higher level structures. These observations were supported by calculations on the hydrodynamic effect of the filler on the storage modulus G′ of carbon black–loaded compounds. Electrochemical impedance spectroscopy measurements on filled fluoroelastomers revealed the presence of an electrical percolation threshold for finely structured carbon black–filled compounds that supports the hypothesis of the presence of a three‐dimensional anisotropic network forming at high filler loading. No percolation threshold was found in coarsely structured carbon black–filled compounds in accordance with DMA. These results can provide useful guidelines for the design of high‐performance carbon black–filled polyurethane fluoroelastomers. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers