Comparison of tunneling currents in graphene nanoribbon tunnel field effect transistors calculated using Dirac-like equation and Schrödinger's equation

The tunneling current in a graphene nanoribbon tunnel field effect transistor (GNR-TFET) has been quantum mechanically modeled. The tunneling current in the GNR-TFET was compared based on calculations of the Dirac-like equation and Schrödinger's equation. To calculate the electron transmittance, a numerical approach-namely the transfer matrix method (TMM)-was employed and the Launder formula was used to compute the tunneling current. The results suggest that the tunneling currents that were calculated using both equations have similar characteristics for the same parameters, even though they have different values. The tunneling currents that were calculated by applying the Dirac-like equation were lower than those calculated using Schrödinger's equation.     

Magnesium-Catalyzed Asymmetric Thia-Michael Addition to α,β-Unsaturated Ketones

We demonstrate the application of chiral magnesium complexes in an asymmetric carbon-sulfur bond-forming reaction. Enantioselective and cost-effective methodology under mild condition for the thia-Michael addition, utilizing an in situ generated chiral dinuclear magnesium-ProPhenol complex, has been developed. The versatility of this protocol is demonstrated with a broad range of thiol nucleophiles and a wide selection of enones. Enantioenriched β-ketosulfides are obtained in good to excellent yields and moderate to excellent enantioselectivity. The presented catalytic system exhibits excellent tolerance for structurally different substrates while maintaining high enantioselectivity. This observation aligns with proposed mechanism, wherein the sulfur atom coordinates to the catalyst in close proximity to the reaction center.     

Feasibility of Kelvin probe force microscopy to measure the surface potential decay of polystyrene film due to relative humidity

The feasibility of measuring the surface potential decay of polystyrene (PS) film is investigated at room temperature by using Kelvin probe force microscopy (KPFM). The PS film was charged by an ion injection method utilizing Bruker's atomic force microscope (AFM) Nanoman module with a pulse duration of 1 ms, SCM-PIT electrically conductive probe, and a voltage pulse of −250 mV. The surface potential decayed linearly on a semi-log scale with time, where the time decay constant was quantified for relative humidity (RH) = 5% by KPFM at room temperature. The surface potential decayed due to the interaction of the PS film with the hydronium ions available in the environment. Furthermore, the effect of the material forms (film vs. microspheres) on the time decay constant at RH = 5% was investigated. The time decay constants measured using different methods exhibited excellent correlation with the AFM-KPFM. This also confirmed that the results are independent of the material form (microspheres vs. film form). As a result, the proposed method can be used to measure the effect of RH for any PS surface (i.e., particles of various sizes and films) exposed to these environmental conditions.     

Additive-additive and additive-surface interactions in lubrication

Combinations of additives are often found to exhibit antagonistic or synergistic effects compared to the performance of the individual additives. This paper reviews the state of knowledge concerning such effects. Direct interactions, where two additives combine at a molecular level, are distinguished from complementary or exclusary effects where the individual contributions of separate additives enhance or reduce overall performance but with no direct interaction. Additive interactions take place in solution and at surfaces, and both are discussed.     

Evaluating thermal and thermooxidation stability for lubricating oils via microscale methods

Differential thermal analysis (DTA) and thermogravimetry (TG) methods have been developed to evaluate the thermal and thermooxidation stability of different lubricating oils. Measurements are carried out either by heating the oil sample at a constant rate (direct programme) or by keeping it at a fixed high temperature (isothermal programme). Oxygen at a constant flow rate is used for thermooxidation measurements. Tested samples included different viscosity grades: neutral base oils, unadditivated lubricating oil blends, and industrial oils. The mechanism of thermal decomposition for ZDDP and the estimation of its optimum concentration was also considered.     

Fracture of ultrafine calcium carbonate/polypropylene composites

The strength and fracture properties of a polypropylene filled with ultrafine calcium carbonate (0.07 μm) have been studied in the composition range of 0 to 40 percent by volume. Untreated and surface treated (with stearic acid and a titanate coupling agent) grades have been considered. The untreated filler caused a decrease of toughness whereas a maximum, at ∼10 percent, was observed for the treated filler. The fracture energy was analyzed in terms of the crack pinning model. Due to the very small size of particles the pinning contribution proved to be negligible.     

Parameters affecting interlaminar stresses in tapered laminates under static loading conditions

Tapered laminates by internal ply drop-offs have been studied. An extensive finite element program has been developed for microcomputers using displacement formulation. A 20 node, three dimensional element was used. Parameters which can influence the strength of the laminate were studied. These parameters include the location of the drop-off in the thickness direction, the degree of resin filling inside the drop-off, the shape of the drop-off, the effect of width of laminate, and the orientation of the lamina where the drop-off was made. Locations of failure based on maximum stress criterion were btained. Crack growth stimulation was also performed by consecutive removal of failed elements. Results show that crack growth is not continuous.     

Preparation and Calcium Complexation of Oxidized Polysaccharides. Part I: Oxidation of Maltodextrins and Starch with Alkaline Sodium Hypochlorite

The oxidation of maltodextrins and starch with aqueous alkaline sodium hypochloride has been studied. At an oxidant level of 3 moles hypochlorite per anhydroglucose unit at pH 8–9, a C2, C3-glycol-cleaved dicarboxy polysaccharide was obtained containing up to 45% ring-opened glucose units. Hydrolysis of the oxidation products yielded (apart from glucose) erythronic and glyoxylic acids, but no glucuronic acid evidencing the absence of C6-oxidation. The average degree of polymerization of the products ranged from 14 to 87 and indicated severe chain degradation during the oxidation. The products were shown to be effective calcium complexing agents and behaved as regular polyelectrolytes with identical complexing sites.