The impact of natural and artificial weathering on the visual,colour and structural changes of seven tropical woods

This study investigates the effects of wood weathering on changes in its macroscopic and colour characteristics in connection with changes in its molecular and anatomical structure. Seven hardwoods suitable for outdoor architecture—bangkirai, cumaru, cumaru rosa, ipé, jatobá, kusia, and massaranduba—were exposed to the exterior out of ground contact for 1–36 months according to EN 927-3, and for 1–12 weeks in Xenotest with water spraying according to partly modified EN 927-6. With prolonged weathering, the following changes occurred in the top surfaces of all tropical woods: (1) visual—creation of longitudinal macro-cracks, (2) spectrophotometry and CIE-L ^? a ^? b ^? —darkening in exterior exposure mainly due to pollutants, except for ipé, and vice versa lightening in Xenotest, as well as greening and blueing in both modes of exposure, (3) FTIR—faster decrease of guaiacyl than syringyl lignin, absolute decrease of conjugated and unconjugated carbonyl groups in the newly formed lignin-polysaccharide-extractive substrate in the photo-oxidized and washed-out cell walls, and decrease of cellulose crystallinity, (4) SEM—damaging of cell-walls by micro-cracks, and their degradation by thinning. Connections between changes of the individual characteristics of weathered woods, for example, between the colour (ΔE*, etc.) and the molecular structure (carbonyls, etc.), were also determined.     

Solvothermal synthesis of Ag/ZnO micro/nanostructures with different precursors for advanced photocatalytic applications

Micro/nanostructured systems based on metallic oxide (ZnO) with noble metal (Ag) on the surface (Ag/ZnO) are synthesized by solvothermal method from zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), zinc acetylacetonate hydrate (Zn(C₅H₇O₂)₂·xH₂O) and silver nitrate (Ag(NO₃)) as precursors. In these systems, polyvinylpyrrolidone (PVP) is used as surfactant for controlling particle morphology, size and dispersion. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (DRS), N₂ gas adsorption–desorption (BET) and Raman spectroscopy (RS). By XRD results, all major peaks are indexed to the hexagonal wurtzite-type structure of the ZnO and samples with noble metal, extra diffraction peaks are detected which correspond to the face-centered-cubic (fcc) structure of the metallic Ag. Depending on used precursor, different morphologies have been obtained. Mainly, ZnO prims-like rods – NRs (with 0.8 ? aspect ratio ? 3.4) – have been observed. Quasi-spherical particles of metallic Ag (with diameters between 558 ± 111 μm and 22 ± 1 nm) have been detected on the ZnO surface. Photocatalytic results (all samples studied >30% MB degradation) verify the important effect of surfactant and the viability of synthesized Ag/ZnO micro/nanocomposites for environmental applications.     

Thermal oxidative cutting of multi-walled carbon nanotubes

Commercially available, multi-walled carbon nanotubes grown by CVD are usually inherently entangled, but can be separated by cutting. However, most cutting methods both cause damage to the nanotubes and involve a lengthy work-up procedure. The use of abrupt, repeated exposure to oxidising conditions in air proved to be an efficient (68% yield) means of producing material with open ends, moderate functionalisation, and enhanced solvent dispersibility; the average lengths were reduced from over 5 μm to approximately 650 nm. Additionally, the character of the surface oxides can be tuned to have either an acidic or basic character by using a simple thermal treatment. These approaches could be deliberately integrated into conventional CVD processes, but also have implications for the products of standard nanotube syntheses. Raman spectroscopy and electron microscopy were used to study the impact of cutting on the intrinsic graphitic structure and the length distribution. X-ray photoelectron spectroscopy was used to determine the extent of functionalisation. The cut carbon nanotubes were dispersed in dimethylformamide (DMF), a Lewis basic solvent, and chloroform, a Lewis acidic solvent, using mild sonication. Through the use of an experimentally determined extinction coefficient (ε = 35.10 ml mg⁻¹ cm⁻¹), the relative dispersibility of the cut and functionalised carbon nanotubes in DMF and chloroform was determined.     

Electrophoretic deposition of carbon nanotubes

Electrophoretic deposition (EPD) has been gaining increasing interest as an economical and versatile processing technique for the production of novel coatings or films of carbon nanotubes (CNTs) on conductive substrates. The purpose of the paper is to present an up-to-date comprehensive overview of current research progress in the field of EPD of CNTs. The paper specifically reviews the preparation and characterisation of stable CNT suspensions, and the mechanism of the EPD process; it includes discussion of pure CNT coatings and CNT/nanoparticle composite films. A complete discussion of the EPD parameters is presented, including electrode materials, deposition time, electrode separation, deposition voltage and resultant electric field. The paper highlights potential applications of the resulting CNT and CNT/composite structures, in areas such as field emission devices, fuel cells, and supercapacitors.     

The properties of free-standing epoxy polymer multi-mode optical waveguides

The paper reports on the fabrication and characterisation of free-standing multimode optical epoxy polymer waveguides consisting of a core made of EpoCore and EpoClad polymer cladding and cover protection layers. The 50 × 50 μm² rectangular waveguides are intended for short-reach optical interconnection and optimised for an operating wavelength of 850 nm. The waveguides of the proposed shapes were fabricated by a standard photolithography process on a silicon substrate provided with a Poly(vinyl alcohol) thin layer. The free-standing structure was then achieved by peeling the deposited EpoClad/EpoCore/EpoClad structures of that substrate. The optical scattering losses of the created planar waveguides, measured by the fibre probe technique at 632.8 and 964 nm, were 0.30 dB cm⁻¹ at 632.8 nm and 0.17 dB cm⁻¹ at 964 nm. Propagation optical loss measurements for rectangular waveguides were performed by the cut-back method and the best samples had optical losses below 0.55 dB cm⁻¹ at 850 and 1310 nm.

     

Epoxidized perfluoropolyethers: A route to hydrophobic,negative‐tone photoresists

The synthesis, formulation, and wafer level processing conditions of a heavily fluorinated hydrophobic photoresist was demonstrated. The synthesis is based on terminal epoxy modification of commercially available perfluoropolyethers. Structural characterization shows that terminal epoxide can open during the synthetic process, but in a simple formulation has a negligible effect on photoresolution of the photoresist. Formulation into a traditional photoresist requires careful selection of appropriate cosolvents to ensure solubility of the hydrophobic epoxy and hydrophilic photoacid generator while attaining adequate coating quality. Formulation processing conditions are presented and the chemical resistance of the resist through aggressive processing steps is demonstrated. Wafer level patterning using traditional photolithographic tools illustrates the applicability of the formulation and process conditions for traditional resist or microfluidic applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Stressed Skin Design Versus Braced Frame Design Through Efficient Numerical Modelling

International Journal of Steel Structures - Steel frame structures are traditionally designed with bracings that stabilize the main bearing structure. Another approach is to apply the...     

Symbolic target detection in SAR imagery via rotationally invariant-weighted feature extraction

This article introduces the application of a physics-based symbolic image partitioning method to detect targets in synthetic aperture radar (SAR) imagery. ‘Targets’ in this case refer to vehicular objects which produce a distinct radar return pattern, and have spatial characteristics that are known a priori. The proposed Rotationally Invariant Symbolic Histogram (RISH) detection method co-analyses both target and speckle statistics, and significantly reduces computational requirements by partitioning the data into a discrete number of state representations. RISH requires only one pass for robust detection, unlike other SAR detection methods which rely on difference metrics calculated using multiple passes. To improve performance in high-resolution data, RISH uses a weighted feature extraction algorithm to avoid the common requirement of processing each pixel of the image equally. The weighted structure extracts geometrically undefined and rotationally invariant target features. This article details the analysis of 24 experimentally obtained very high-frequency (VHF)-band SAR magnitude images using this novel approach to SAR target detection. In localizing small (~8.4 m²) foliage-concealed targets, without the aid of pre-processing, this method results in high performance characteristics (90% true positive) with a low Type-II error rate of 6.4 false alarms per 1 × 10⁶ m². With the addition of change detection, RISH lowers the error rate by 85%.