Self-assembled polyaniline 12-tungstophosphate micro/nanostructures

Polyaniline (PANI) micro/nanostructures were synthesized by the external-template-free oxidative polymerization of aniline in aqueous solution of 12-tungstophosphoric acid (WPA), using ammonium peroxydisulfate (APS) as an oxidant and starting the oxidation of aniline from slightly acidic media (pH 5.4–5.9). The effect of the initial weight ratio of WPA to aniline on molecular structure, morphology, and physicochemical properties of polyaniline 12-tungstophosphate (PANI-WPA) was investigated by FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and conductivity measurements. The morphological change of polymerization products during a single polymerization process, from non-conducting submicro-/microspherical oligoaniline intermediates to semiconducting PANI-WPA consisted of self-assembled nanotubes and/or nanorods co-existing with submicro-/microspheres, has been revealed by SEM and TEM. The average diameter of nanorods in PANI-WPA samples decreased with increasing the initial WPA/aniline weight ratio. The incorporation of 12-tungstophosphate counter-ions into PANI matrix has been proved by FTIR, Raman and ICP-OES spectroscopies, TGA and DTA analysis. Electrical conductivity of PANI-WPA increased in the range (2.5–5.3) × 10^?3 S cm^?1 with the increase of the initial WPA/aniline weight ratio. The presence of branched structures and phenazine units besides the ordinary paramagnetic and diamagnetic emeraldine salt structural features in PANI-WPA was proved by FTIR and Raman spectroscopies.     

Calculated and experimental analysis of cause of the appearance of cracks in the running bogie frame of diesel multiple units of Serbian railways

In this paper an analysis of possible causes of crack occurrence on reconstructed diesel multiple units (DMU) exploited on sideline in Serbia was performed. Analyzed DMU were designed in the sixties of the last century in accordance with standards and UIC regulations of that time. During exploitation cracks appeared on the frame of the running bogie and they were locally repaired. With the purpose of eliminating this negative occurrence that has been reducing the availability of DMU, reconstruction of primary suspension and reconstruction of the DMU running bogie frame was performed. The new construction solution of primary suspension is with rubber springs. In the designing of the new running bogie frame fatigue loads were taken into account. After approximately two and a half years of exploitation, cracks appeared again on frames of the running bogie of DMU and they are the subject of this work. This work gives an analysis of the cause of crack occurrence and investigates links between specific exploitation conditions on tracks of Serbian railways and calculations/investigations performed using currently valid UIC regulations. The analysis also includes other influential factors such as welding quality, track quality, DMU and track maintenance quality.     

Nitric oxide-releasing porous silicon nanoparticles

In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment.     

Electronic structure of memory traps in silicon nitride

From experiments on photoluminescence in Si₃N₄ the polaron energy of 1.4 eV was determined. This value is in agreement with the energy of thermal ionization determined from electron and hole transport. Quantum-chemical simulation showed that Si–Si bond is able to capture holes and electrons in Si₃N₄.     

The effect of processing conditions on the morphology, thermomechanical, dielectric, and piezoelectric properties of P(VDF-TrFE)/BaTiO3 composites

In this study (0–3) P(VDF-TrFE)/BaTiO₃ composites containing up to 60 vol% of ceramic phase were prepared by solvent casting or compression molding. Their thermomechanical, dielectric, and piezoelectric properties were investigated, and discussed in the light of the properties of the basic components, the processing route and the resulting morphology. The crystalline structure of the P(VDF-TrFE) matrix was found to be highly dependent on the processing route, while the structure of BaTiO₃ was not affected by any of the processing steps. The mechanical properties of the solvent cast materials showed a maximum at 30 vol% BaTiO₃, while they increased monotonically with BaTiO₃ content for compression molded materials. This difference was attributed to a higher amount of porosity and inhomogeneities in the solvent cast composites. Permittivity as high as 120 and piezoelectric coefficient d ₃₃ up to 32 pC/N were obtained for compression molded composites, and the observed decrease in d ₃₃ with aging time was attributed to the effect of mechanical stress release in the polymer matrix.     

Phase transformations in the ternary Ag–Ga–Sb system

Phase diagram of the Ag–Ga–Sb ternary system was extrapolated using calculation of phase diagrams (CALPHAD) method. Phase transition temperatures of the alloys with compositions along three vertical sections with constant molar ratios Ga/Sb = 1, Ag/Ga = 1 and Ag/Sb = 1 were measured using differential scanning calorimetry (DSC). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) was used for identification of phases in equilibrated samples. Experimental results were compared with thermodynamic prediction.     

Prospects of wind energy sector development in Serbia with relevant regulatory framework overview

The growth of the renewable energy sector in the world in the first decade of the twenty-first century was rapid. Wind energy sector was one of the fastest growing renewable energy technologies. In this paper, authors have tried to review the current state of wind power utilization in Serbia as one of the most penetrating RES technologies in the world. The brief overview of electric power sector in Serbia was given in order to describe the environment for emerging wind energy sector development. Sufficient wind energy resources were identified in several regions of the country. Current energy policy in Serbia was reviewed in terms of the regulations that have to be followed in order to meet the requirements for RES power plants, i.e. wind power plant construction. In subsequent section short reviews of wind energy projects which are in their initial phases are provided. The wind energy sector in Serbia is emerging despite the difficulties faced by the investors, regulatory bodies and other shareholders, in the course of the past several years. There is an urgent need of a broader transfer of specific knowledge and technologies related to wind farms and wind turbines in order to speed up the current wind energy sector development.     

Perspective on the Development of Lead-free Piezoceramics

A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.     

Multimodal spectral imaging of cells using a transmission diffraction grating on a light microscope

A multimodal methodology for spectral imaging of cells is presented. The spectral imaging setup uses a transmission diffraction grating on a light microscope to concurrently record spectral images of cells and cellular organelles by fluorescence, darkfield, brightfield, and differential interference contrast (DIC) spectral microscopy. Initially, the setup was applied for fluorescence spectral imaging of yeast and mammalian cells labeled with multiple fluorophores. Fluorescence signals originating from fluorescently labeled biomolecules in cells were collected through triple or single filter cubes, separated by the grating, and imaged using a charge-coupled device (CCD) camera. Cellular components such as nuclei, cytoskeleton, and mitochondria were spatially separated by the fluorescence spectra of the fluorophores present in them, providing detailed multi-colored spectral images of cells. Additionally, the grating-based spectral microscope enabled measurement of scattering and absorption spectra of unlabeled cells and stained tissue sections using darkfield and brightfield or DIC spectral microscopy, respectively. The presented spectral imaging methodology provides a readily affordable approach for multimodal spectral characterization of biological cells and other specimens.     

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).