Corrosion resistance of nanocrystalline Mg–Cr alloys deposited by magnetron sputtering

Nanocrystalline Mg–Cr alloys were formed by dc magnetron sputtering in a wide range of concentrations. Structure, composition and grain sizes of the deposits were studied by XRD and XPS. EIS and dc-voltammetry showed that small chromium concentrations (2–8 at.%) had detrimental effect, while high corrosion resistance was observed when chromium content reached one third or so. Chromium refinement effect on alloy crystalline structure was found by XRD. The values of grain sizes were determined as follows: Mg–3Al (chromium-free) – over 100 nm, Mg–2Cr – 60.5 nm, Mg–8Cr – 44.6 nm, Mg–20Cr – 31.0 nm, Mg–45Cr, Mg–53Cr – ∼11.0 nm and ∼15 nm for sputtered Cr. Mott–Schottky plots showed that the spontaneous oxide layers formed on the alloys with high Cr content (Mg–36Cr, Mg–53Cr) were highly doped semiconductors of n-type. A conductivity change n–p was observed at E = 0.0 V (Ag/AgCl) in a buffer solution (pH 9.9). The conductivity change was also confirmed by photo-electrochemical measurements. Surface enrichment by chromium during initial stages of corrosion was determined, which promote corrosion resistance and provides an opportunity of surface auto-protection (self-healing) in damaged locations.     

Interaction of electrons with optical phonons localized in a quantum well

The scattering rate of electrons in a quantum well by localized polar optical and interface phonons is considered. The dependence of the force of the electron-phonon interaction on the frequency of optical phonons in materials of the heterostructure forming the electron and phonon quantum wells is determined. It is shown that, by varying the composition of semiconductors forming the quantum well and its barriers, it is possible to vary the scattering rates of electrons by a factor of several times. The scattering rates of electrons by polar optical phonons are calculated depending on the fractions In _x and In _y in the composition of semiconductors forming the In _x Al_{1 ? x} As/In _y Ga_{1 ? y} As quantum wells. Dependences of the mobility and saturated drift velocity of electrons in high electric fields and quantum wells In _y Ga_{1 ? y} As on the composition of the In _x Al_{1 ? x} As barriers introduced into quantum wells are determined experimentally. The electron mobility increases, while the saturated drift velocity decreases as the fraction of In _x in the composition of barriers is increased.     

Photostability of phenothiazinyl-substituted ethylenes

Photostability of phenothiazinyl-substituted ethylenes in both solution and in solid state (thin films) was investigated as a function of UV exposure time. Fluorescence intensity and spectral variation measurements in the presence and absence of ambient air were used to determine the effect of oxygen on the degradation of the compounds. The observed reduction in the fluorescence efficiency of air-saturated solutions and thin films subjected to UV was attributed to permanent photo-oxidative degradation. Photostability was higher in the cases of molecules that contained two bulky phenothiazinyl groups as compared to those containing only one phenothiazinyl group and a smaller phenyl substituent. Fully reversible fluorescence intensity decay in the degassed phenothiazine solutions was attributed to photo-isomerization, whereas the partially reversible changes in fluorescence intensity that were observed for films in the absence of air were ascribed to both photoexcited carrier capture by deep-traps acting as exciton quenching centres and degradation imparted by UV-induced bond scission.     

The effects of different UV‐B radiation intensities on morphological and biochemical characteristics in Ocimum basilicum L.

BACKGROUND: The effects of short‐term ultraviolet B (UV‐B) irradiation on sweet basil (Ocimum basilicum L. cv. Cinnamon) plants at the 3–4 leaf pair and flowering stages were examined in controlled environment growth chambers. Plants were exposed to 0 (reference), 2 and 4 kJ UV‐B m^?2 day^?1 over 7 days. RESULTS: Exposure of basil plants to supplementary UV‐B light resulted in increased assimilating leaf area, fresh biomass and dry biomass. Stimulation of physiological functions in young basil plants under either applied UV‐B dose resulted in increased total chlorophyll content but no marked variation in carotenoid content. At the flowering stage the chlorophyll and carotenoid contents of basil were affected by supplementary UV‐B radiation, decreasing with enhanced UV‐B exposure. Both total antioxidant activity (2,2‐diphenyl‐1‐picrylhydrazyl free radical assay) and total phenolic compound content were increased by UV‐B light supplementation. Young and mature basil plants differed in their ascorbic acid content, which was dependent on UV‐B dose and plant age. UV‐B radiation resulted in decreased nitrate content in young basil plants (3–4 leaf pair stage). CONCLUSION: These results indicate that the application of short‐exposure UV‐B radiation beneficially influenced both growth parameters and biochemical constituents in young and mature basil plants. © 2012 Society of Chemical Industry     

Computational analysis of impact of a bullet against the multilayer fabrics in LS-DYNA

A finite element model of the ballistic test against the multi-layer paraaramid textiles package structure has been developed in LS-DYNA. The bullet has been considered as a deformable body in contact with the fabric package represented by an interwoven yarn structure. The simplification of the model has been achieved by means of the “mezzo-mechanical” approach by avoiding the direct modeling of filaments comprising the yarns. Instead, yarns have been modeled by using thin shell elements the thickness of which represents the real thickness of yarns as it can be measured in the weave. The zones of the fabric remote from the point of impact have been presented as a roughly meshed uniform orthotropic thin shell model. The junction between the two types of zones of the fabric has been performed by means of the tie constraint and by proper adjustment of material parameters ensuring the same speeds of wave propagation in the interwoven yarn structure and in the uniform shell. Physical and numerical experiments have been performed in order to identify the material model parameters and to validate the model.     

Synthesis of new hole-transporting molecular glass with pendant carbazolyl moieties

The synthesis and properties of amorphous hole-transporting 4,4′-bis[11-carbazol-9-yl)-6,8,10-tri(carbazol-9-methyl)-3-hydroxy-5,7,9-trioxa-1-thia]thiobisbenzene with two end and six pendant carbazolyl moieties, separated from the main chain by CH₂ spacers, is reported. It was prepared by a multistep synthesis route from 1,6-di(carbazol-9-yl)-5-(carbazol-9-methyl)-4-oxa-2-hexanol glycidyl ether. Glass transition temperatures of intermediate and final products established by differential scanning calorimetry are reported. The hole drift mobility, measured by the time of flight technique, in this well defined molecular glass depends little on the strength of the electric field and exceeds 10⁻⁵ cm² V⁻¹ s⁻¹. The ionization potentials measured by electron photoemission method, light absorption and fluorescence spectra are closed to those reported for the other organic photoconductors containing electronically isolated carbazole moieties.     

Influence of temperature on the properties of Mn coatings electrodeposited from the electrolyte containing Te(VI) additive

The influence of the bath temperature on composition, current efficiency, structure, morphology, internal stresses and microhardness of Mn coatings obtained from manganese-ammonium sulphate electrolyte with 2.20 mM of Te(VI) additive at the current density of 15 A dm^?2 was investigated. It has been found that with rising of the bath temperature from 20 to 80 °C the current efficiency increases from 37 to 71 %, the total concentration tellurium in the deposits increases from 0.9 to 1.6 wt% and the average size of crystallites of the coatings declines approx. from 24 to 15 nm. The structure of Mn coatings changes from the mixture of α-Mn and β-Mn phases at the lower temperatures to α-Mn phase at higher temperatures. Large tensile stresses (from 76 to 106 MPa) were determined for the Mn coatings with the thickness of 1.5–2.0 μm obtained at the initial stage of the deposition process.     

The influence of distribution and deposit of conductive coating on shielding effectiveness of textiles

This study presents the investigation of electrically conductive fabrics with low resistivity, coated with formulation containing the conjugated polymer system – poly(3,4-ethylenedioxythiophene)-polystyrene sulphonate (PEDOT-PSS). The samples of fabrics were coated with PEDOT-PSS, using a screen printing method, by different patterns or coating their surface fully with different coating deposit. Methods for measurement of electrostatic properties, reflection and transmission as well as the assessment of electromagnetic radiation (EMR) shielding effectiveness were used for the characterization of electrical properties of developed samples. EMR shielding properties were investigated within 2–12 GHz frequency bands. The highest attenuation of the electromagnetic energy among tested fabrics was obtained on the fabrics fully coated with paste and it depended on deposit considerably. The influence of distribution and deposit of conductive coating on shielding effectiveness of textiles were determined. Correlation between shielding effectiveness and electrostatic properties of developed coated fabrics was also discussed. Electrical properties of samples coated with formulation containing PEDOT-PSS were compared with these of fabrics with metalized yarns, developed by us earlier. The results of EMR shielding measurements showed that fabrics coated with the paste containing conductive polymer system compared to fabrics with in-weaved conductive metalized yarns have certain advantages as EMR shields.     

Drift velocity of electrons in quantum wells of selectively doped In0.5Ga0.5As/AlxIn1 ? xAs and In0.2Ga0.8As/AlxGa1 ? xAs heterostructures in high electric fields

The field dependence of drift velocity of electrons in quantum wells of selectively doped In_0.5Ga_0.5As/Al _x In_{1 − x} As and In_0.2Ga_0.8As/Al _x Ga_{1 − x} As heterostructures is calculated by the Monte Carlo method. The influence of varying the molar fraction of Al in the composition of the Al _x Ga_{1 − x} As and Al _x In_{1 − x} As barriers of the quantum well on the mobility and drift velocity of electrons in high electric fields is studied. It is shown that the electron mobility rises as the fraction x of Al in the barrier composition is decreased. The maximum mobility in the In_0.5Ga_0.5As/In_0.8Al_0.2As quantum wells exceeds the mobility in a bulk material by a factor of 3. An increase in fraction x of Al in the barrier leads to an increase in the threshold field E _th of intervalley transfer (the Gunn effect). The threshold field is E _th = 16 kV/cm in the In_0.5Ga_0.5As/Al_0.5In_0.5As heterostructures and E _th = 10 kV/cm in the In_0.2Ga_0.8As/Al_0.3Ga_0.7As heterostructures. In the heterostructures with the lowest electron mobility, E _th = 2–3 kV/cm, which is lower than E _th = 4 kV/cm in bulk InGaAs.