Comparative Study of Natural Terpenoid Precursors in Reactive Plasmas for Thin Film Deposition

If plasma polymer thin films are to be synthesised from sustainable and natural precursors of chemically heterogeneous composition, it is important to understand the extent to which this composition influences the mechanism of polymerisation. To this end, a well-studied monoterpene alcohol, terpinen-4-ol, has been targeted for a comparative study with the naturally occurring mix of terpenes (viz. Melaleuca alternifolia oil) from which it is commonly distilled. Positive ion mode mass spectra of both terpinen-4-ol and M. alternifolia oil showed a decrease in disparities between the type and abundance of cationic species formed in their respective plasma environments as applied plasma power was increased. Supplementary biological assay revealed the antibacterial action of both terpinen-4-ol and M. alternifolia derived coatings with respect to S. aureus bacteria, whilst cytocompatibility was demonstrated by comparable eukaryotic cell adhesion to both coatings. Elucidating the processes occurring within the reactive plasmas can enhance the economics of plasma polymer deposition by permitting use of the minimum power, time and precursor pre-processing required to control the extent of monomer fragmentation and fabricate a film of the desired thickness and functionality.     

Polyacrylonitrile molecular weight effect on the structural and magnetic properties of metal–carbon nanomaterial

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Comparison of the Features of Electron Transport and Subterahertz Generation in Diodes Based on 6-, 18-, 70-, and 120-Period GaAs/AlAs Superlattices

Semiconductors - A comparison of the features of electron transport in diodes based on 6-, 18-, 30-, 70-, and 120-period GaAs/AlAs superlattices with a similar design is performed. However, the...     

Optimization of the superlattice parameters for THz diodes

Previously, GaAs/AlAs superlattices with a small active area (~1 μm²) were used by us to design mixer diodes. It was established that these superlattices can efficiently be used in the terahertz (THz) range. It was theoretically and experimentally shown that short-period (i.e., containing few periods) superlattices in the composition of harmonic mixers have significant advantages in comparison with multi-period (with 50–100 or more periods) superlattices at frequencies of up to 5.3 THz. In this study, the superlattice design is optimized and the operation efficiency of short-period superlattices is shown to be determined to a large extent by the transition regions located at the superlattice edges.     

Structure-fluorescence contrast relationship in cyanine DNA intercalators: toward rational dye design

The fluorescence enhancement mechanisms of a series of DNA stains of the oxazole yellow (YO) family have been investigated in detail using steady-state and ultrafast time-resolved fluorescence spectroscopy. The strong increase in the fluorescence quantum yield of these dyes upon DNA binding is shown to originate from the inhibition of two distinct processes: 1) isomerisation through large-amplitude motion that non-radiatively deactivates the excited state within a few picoseconds and 2) formation of weakly emitting H-dimers. As the H-dimers are not totally non-fluorescent, their formation is less efficient than isomerisation as a fluorescent contrast mechanism. The propensity of the dyes to form H-dimers and thus to reduce their fluorescence contrast upon DNA binding is shown to depend on several of their structural parameters, such as their monomeric (YO) or homodimeric (YOYO) nature, their substitution and their electric charge. Moreover, these parameters also have a substantial influence on the affinity of the dyes for DNA and on the ensuing sensitivity for DNA detection. The results give new insight into the development and optimisation of fluorescent DNA probes with the highest contrast.     

The first synthesis of furazano[3,4‐b][1,6]naphthyridines

Reaction of 6‐acetyl‐7‐aminofurazano[3,4‐b]pyridines with DMFDMA afforded N,N‐dimethylformamidines that were cyclized to the novel furazan‐fused [1,6]naphthyridine system by treatment with sodium methylate in good yield. The tricyclic system is characterized by X‐ray crystallography.     

VideoAFM--a new tool for high speed surface analysis

The VideoAFM provides a 1000 fold increase in image rate compared to conventional atomic force microscopes, giving nanometre resolution images of surfaces at a rate of 15 frames s(-1), which is approximately 1 million pixels s(-1). Images of high stiffness surfaces such as calibration grids are provided for the first time, and allow for a more rigorous examination of the meaning of the data obtained with the VideoAFM. Instrumental changes that could provide true topographic images are discussed. The advantages of a high speed scanning technique that is integrated within a conventional AFM are outlined. Particular emphasis is given to the capability to 'tile' images, and hence rapidly map large areas with nanometre resolution. It is found that the inherent increase in stability that comes from a high frame rate leads to the possibility of manually manipulating the sample while maintaining a sharp image, allowing real-time user interaction with the AFM. The possible application of the VideoAFM approach for the very rapid analysis of surface properties and, ultimately, surface chemistry is discussed and some possible routes are given.     

N-unit parallel redundant system with multiple correlated failures

This paper deals with mathematical models of an N-unit parallel redundant system with one repair facility and multiple correlated failures. These models are generalized on the basis of the results obtained previously and related to a system subject to a process of single failures and double and N-unit correlated failures. The method of the supplementary variable in two models differing by the repair policy is used. We obtain the following results: for both models the stationary availability, and for the second model the Laplace transform (L.T.) of the system reliability, L.T. of the pointwise a vailability, and the mean time to system failure (MTSF).     

Fluorescence intensities of chromophores in front of a thin metal film

The fluorescence intensity from a planar multilayered system with a chromophore separated from a gold film by a dielectric spacer is measured quantitatively. The direction of excitation and the spacer thickness are varied and the angular distribution of the emission is recorded as well as its polarization. The experimental data are compared to the predictions obtained from classical electromagnetic theory, taking into account the refractive indices of the layer system as well as the nonradiative decay rate and the relative orientation of absorption and emission dipole moments of the dye. Excellent agreement is found for a spacer thickness above 15 nm if proper values for these parameters are used. Samples with thinner spacer layers show significant deviations from classical theory.