Characterization of size-quantized PbTe thin films synthesized by an electrochemical co-deposition method

Size-quantized thin films of PbTe were electrodeposited on Au (1 1 1) substrates using a practical electrochemical method, based on the simultaneous underpotential deposition of Pb and Te from the same solution containing ethylenediamine tetraacetic acid, Pb²⁺, and TeO₃²⁻ at a constant potential. These thin films were characterized by X-ray diffraction (XRD), scanning tunneling microscopy (STM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and reflection absorption-FTIR (RA-FTIR). AFM, STM, and XRD results indicate that the growth of PbTe thin films follows the nucleation and two dimensional growth mechanism, resulting in high crystalline films of PbTe (2 0 0) in cubic structure, which was grown at a kinetically preferred orientation on Au (1 1 1). The EDS analyses of the films reveal that Pb and Te are present in an atomic ratio of approximately 1:1. The quantum-confined effect of the PbTe thin films are confirmed by the RA-FTIR measurements.     

Optimum design of cellular beams using harmony search and particle swarm optimizers

Cellular beams became increasingly popular as an efficient structural form since their introduction. Their sophisticated design and profiling process provide greater flexibility in beam proportioning for strength, depth, size and location of circular holes. The main goal of manufacturing these beams is to increase the moment of inertia and section modulus, which results in greater strength and rigidity. Cellular beams are used as primary or secondary floor beams in order to achieve long spans and service integration. In this study, the design problem of cellular beams is formulated as optimum design problem. The minimum weight is taken as the design objective while the design constraints are implemented from The Steel Construction Institute Publication Number 100. The design methods adopted in this publication are consistent with BS5950 parts 1 and 3. The formulation of the design problem considering the limitations of the above mentioned turns out to be a discrete programming problem. Harmony search and particle swarm optimization methods are used for obtaining the solution of the design problem. The design algorithms based on these two techniques select the optimum UB section to be used in the production of a cellular beam subjected to a general loading, the optimum hole diameter and the optimum number of holes in the cellular beam. Furthermore, this selection is also carried out such that the design limitations are satisfied and the weight of the cellular beam is the minimum. A number of design examples are considered to demonstrate the efficiency of the algorithm presented.     

Mechanical and thermal properties of wood‐plastic composites reinforced with hexagonal boron nitride

Mechanical, thermal, and morphological properties of injection molded wood‐plastic composites (WPCs) prepared from poplar wood flour (50 wt%), thermoplastics (high density polyethlyne or polypropylene) with coupling agent (3 wt%), and hexagonal boron nitride (h‐BN) (2, 4, or 6 wt%) nanopowder were investigated. The flexural and tensile properties of WPCs significantly improved with increasing content of the h‐BN. Unlike the tensile and flexural properties, the notched izod impact strength of WPCs decreased with increasing content of h‐BN but it was higher than that of WPCs without the h‐BN. The WPCs containing h‐BN were stiffer than those without h‐BN. The tensile elongation at break values of WPCs increased with the addition of h‐BN. The differential scanning calorimetry (DSC) analysis showed that the crystallinity, melting enthalpy, and crystallization enthalpy of the WPCs increased with increasing content of the h‐BN. The increase in the crystallization peak temperature of WPCs indicated that h‐BN was the efficient nucleating agent for the thermoplastic composites to increase the crystallization rate. POLYM. COMPOS., 35:194–200, 2014. © 2013 Society of Plastics Engineers     

Taxonomic significance of foliar epidermal morphology in Lamiaceae from Pakistan

Foliar micromorphological features are useful to elucidate the taxonomy and systematics of the Lamiaceae species. Leaf epidermal morphology using scanning electron microscopy and light microscopy of 22 Lamiaceae species from 15 genera have been investigated with an aim to solve its taxonomic problem in the correct identification. Various foliar micromorphological features were observed to explain their importance in resolving the correct identification of Lamiaceae taxa. Two main types of trichomes were observed; glandular trichomes (GTs) and nonglandular trichomes (NGTs). GTs were further divided into seven subtypes including the capitate, subsessile capitate, sessile capitate, sunken, barrel, peltate, and clavate. Similarly, NGTs were also divided into simple unicellular and multicellular including conical, falcate, cylindrical, dendrite, papillose, and short hook shape. Quantitative measurement includes the length and width of the trichomes, stomatal complex, epidermal cells, stomata, and trichomes index. Based on the foliar micromorphological characters, a taxonomic key was developed to delimit and correctly identify studied taxa. Further molecular, other anatomical and phylogenetic studies are recommended to strengthen the systematics of Lamiaceae.     

Real-time monitoring of railroad track tension using a fiber Bragg grating-based strain sensor

Railway and train security are very important in preventing service disruption and ensuring quality and safe journeys. Conventional gauges are used in laboratory environments for the strain measurement of rails used in railways. However, the use of these electrical sensors is not practical in long-distance railways. Instead, access to long distances is possible with fiber optic sensors. In this study, the strain of 49E1 type rail with R260 hardness and quality was calculated theoretically. These results were compared with an experimentally established fiber Bragg grating system. Moreover, a user-friendly interface was prepared for real-time monitoring of the system. Upon examining the results, the maximum deviation at a rate of 2.5% occurred in the strain measurement in the rail in response to force changes between 0 and 200 kN. A value of approximately 1.38?pm/µε was calculated between the wavelength/strain changes.     

Microstructural Characterization of Reactively Sintered Mullites

Mullite ceramics have been produced by reaction sintering of powders prepared using pseudoboehmite–colloidal silica and aluminum sulfate–colloidal silica mixtures. The microstructural development of these mullites was studied by a number of transmission electron microscopy based techniques including diffuse dark field, Fresnel fringe defocus imaging, and high-resolution transmission electron microscopy. This characterization procedure showed that mullite ceramics free from glassy phases at triple junctions and grain boundaries could be produced from both mixtures using suitable sintering temperatures and alumina/silica ratios. The wetting of grain boundaries by glass, occurring in the mullite ceramics from either incomplete reaction between alumina and silica components or release of silica from the mullite structure with increasing temperature, was found to depend on the prior thermal history of the ceramics.     

Electrochemical impedance study of polyaniline electrocoated porous carbon foam

Electropolymerization of aniline on mesophase pitch based carbon foam has been studied in order to evaluate the influence of conductive polymer coating on the properties of carbon foam. The surface morphology of the coating was determined by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of resulting modified carbon foam samples. Polyaniline (PANI) electrocoated-mesophase pitch based carbon foam showed good capacitor behavior in 0.5 M H₂SO₄. Better capacitive behavior is obtained for 100 and 150 mV/s compared to other scan rates, under these faster scan rates thinner films of PANI coatings were combined with more porous structure of carbon foam. Conductivity of the carbon foam was increased from 9.23 to 13.73 S/cm by electrocoating of PANI.     

Lipid Emulsions Containing Medium Chain Triacylglycerols Blunt Bradykinin-Induced Endothelium-Dependent Relaxation in Porcine Coronary Artery Rings

Lipid emulsions for parenteral nutrition are used to provide calories and essential fatty acids for patients. They have been associated with hypertriglyceridemia, hypercholesterolemia, and metabolic stress, which may promote the development of endothelial dysfunction in patients. The aim of the present study was to determine whether five different industrial lipid emulsions may affect the endothelial function of coronary arteries. Porcine coronary artery rings were incubated with lipid emulsions 0.5, 1, or 2% (v/v) for 30 min before the determination of vascular reactivity in organ chambers and the level of oxidative stress using electron paramagnetic resonance. Incubation of coronary artery rings with either Lipidem^®, Medialipid^® containing long- and medium-chain triacylglycerols (LCT/MCT), or SMOFlipid^® containing LCT, MCT, omega-9, and -3, significantly reduced the bradykinin-induced endothelium-dependent relaxation, affecting both the nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) components, whereas, Intralipid^® containing LCT (soybean oil) and ClinOleic^® containing LCT (soybean and olive oil) did not have such an effect. The endothelial dysfunction induced by Lipidem^® was significantly improved by indomethacin, a cyclooxygenase (COX) inhibitor, inhibitors of oxidative stress (N-acetylcysteine, superoxide dismutase, catalase) and transition metal chelating agents (neocuproine, tetrathiomolybdate, deferoxamine and l-histidine). Lipidem^® significantly increased the arterial level of oxidative stress. The present findings indicate that lipid emulsions containing LCT/MCT induce endothelial dysfunction in coronary artery rings by blunting both NO- and EDH-mediated relaxations. The Lipidem^®-induced endothelial dysfunction is associated with increased vascular oxidative stress and the formation of COX-derived vasoconstrictor prostanoids.     

Pressure effects on the phonon modes in beryllium chalcogenides

We report first-principles calculations of the structural, lattice-dynamical and dielectric properties for zinc-blend beryllium chalcogenides: BeS, BeSe, and BeTe. The ground state properties, such as the lattice structure and bulk modulus, are calculated using a plane wave pseudopotential method within the density functional theory. A linear response approach is employed in order to derive the high-frequency dielectric constants, Born effective charges and phonon frequencies. Furthermore, the pressure dependence of phonon modes is also detailed.