Thermo-protective properties of polymer composites with nano-titanium dioxide

International Journal of Mechanics and Materials in Design - The present work investigates the ablative and thermal properties of an epoxy resin which was modified with titanium dioxide...     

Effect of beam divergence from the optic axis in an electro-optic experiment to measure an induced Jones birefringence

Certain optical properties can be described in terms of two linear birefringences existing in separate Jones platelets of a medium. One of these, known as Jones birefringence, although occurring naturally in some crystals is too small to be measurable. However, the two birefringences can be induced by an electric field in 4 and 6 crystals for propagation along the optic axis. For an even slightly divergent light beam, natural birefringence may affect accuracy of measurement. Calculations show that in an experiment with a static field the error depends critically on beam divergence, whereas with a modulated field this is not so.     

Influence of the lubricant on temperature distribution in the forging dies

Experimental and theoretical analysis of the influence of the lubricant on the temperature distribution in the tool during forging is presented. Finite element solution of the general diffusion equation is used to calculate the heat transfer contact between the die and the hot workpiece and during the interpass times. The results of calculations are compared with the results of measurements carried out using thermocouples inserted in the die. Two ways of modelling heat transfer through the contact surface are considered. The first treats a lubricant as a separate layer with the relevant thermal properties. The second assumes a temperature discontinuity at the interface and introduces the heat transfer coefficient. Insulating properties of various lubricants are compared. White-water lubricant shows the best insulating properties. The values of the heat transfer coefficient obtained from the inverse analysis vary from 2600 (without lubrication) to 1500 W/m²K (white lubricant).     

Robotic System for Closed-Bore MRI-Guided Prostatic Interventions

This paper reports on the development of a new closed-bore magnetic resonance imaging (MRI) compatible robotic system for image-guided prostatic interventions: ablation, brachytherapy, and biopsy. The first stage of development addresses only laser-based ablation. The robot actuators are ultrasonic motors. The first physical robot prototype was manufactured and tested in the MRI with an ablation tool. The tests covered magnetic resonance (MR) compatibility, tool visualization, and robot control accuracy. Robot tip position error is less than 2 mm at points closer than 0.5 m to the isocenter. A method to control ultrasonic motors for MRI-compatibility is reported.     

Effect of Pd additive on the activity of monolithic LaMnO3-based catalysts for methane combustion

When the perovskites are calcined at 750 °C, the incorporation of Pd into LaMnO₃ enhances the activity of the catalyst in methane combustion at temperatures below 750 °C upon substitution of 0.1 mol La with Pd, and at temperatures below 600 °C when Pd is substituted for 0.1–0.15 mol Mn. Monolith catalysts based on La_1−xPd_xMnO₃ (x = 0.1, 0.15) display a higher activity in methane combustion than do LaMn_1−xPd_xO₃-based catalysts, which is due to the higher Pd/(Pd + Mn + La) ratio. The activities of the two perovskite types increase when calcination temperature is raised from 650 to 800 °C. With the increase in calcination temperature, an increase in the Pd content and a decrease in the La content is observed on the surfaces (X-ray photoelectron spectroscopy (XPS)). The rise in the temperature of perovskite calcination to 850 °C produces sintering which leads to the lowering in both the Pd content on the surfaces and the specific surface areas (SSAs) of the perovskites and, consequently, decreases catalytic activity.     

Effect of washcoat modification with metal oxides on the activity of a monolithic Pd-based catalyst for methane combustion

The deposition of Ni, Co, Ce or Fe oxides onto the washcoat surface in the 0.5%Pd/Al₂O₃ catalyst enhances conversion of CH₄. Catalytic activity of the Pd-catalysts containing cobalt oxide depends on the incorporated amount of cobalt oxide and the method of incorporation. The highest activities were those of the 0.5%Pd/0.3%Co/Al₂O₃ and 1%Pd/0.3%Co/Al₂O₃ catalysts (cobalt oxide deposited onto the surface of Al₂O₃) and the 0.5%Pd/5%Co₃O₄–Al₂O₃ catalyst (mixed washcoat). Total SSA, Pd dispersion and Pd crystallite size in the x%Pd/y%Co/Al₂O₃ catalysts depend on the incorporated amount of PdO and cobalt oxide. Pd dispersion in the 1%Pd/Al₂O₃ catalyst increases from 4% to 20% upon deposition of 14 wt.% Co₃O₄ (by mass Al₂O₃) onto the Al₂O₃ surface (1%Pd/0.3%Co/Al₂O₃). This increase in Pd dispersion influence the increase in the activity of the 1%Pd/Al₂O₃ catalyst. On the surface of the 0.5%Pd/5%Co₃O₄–Al₂O₃ catalyst Pd occurs mainly in the form of PdO and displays considerable mobility under conditions of temperature variations—cyclically undergoing reduction and oxidation. At 500 °C, in vacuo, the reduction was irreversible and parallelled by the agglomeration of metallic Pd crystallites. At room temperature, cobalt occurred on the catalyst surface in the form of Co⁺² ions (CoAl₂O₄) and was reduced to Co⁰ at 500 °C (in vacuo). Up to 500 °C, the reduction of Co was reversible.     

High-speed MR imaging of ischemic brain injury following stenosis of the middle cerebral artery

Magnetic susceptibility contrast-enhanced and diffusion-weighted echo planar magnetic resonance (MR) imaging was performed using a cat model of acute regional cerebral ischemia induced by partial stenosis of the right middle cerebral artery (MCA). The imaging data were correlated with triphenyltetrazolium chloride (TTC)-stained histopathologic coronal brain sections to determine the prognostic efficacy of high-speed MR imaging techniques in differentiating mild, moderate, and severe cerebral hypoperfusion. Brains of animals without cortical injury on TTC staining were found to have a reduction in peak contrast enhancement of 32 +/- 6% (mean +/- SD) below control values with no significant change in the apparent diffusion coefficient (ADC), determined from the diffusion-weighted MR images. In cases where moderate ischemic injury was observed in the TTC-stained sections, a 10-20% drop in the ADC was found over the 6-h study period, accompanied by a much wider variation in peak contrast enhancement. Finally, where TTC staining showed severe ischemic brain damage, a 40-50% drop in ADC and a reduction in peak contrast enhancement effect of > 95% were observed as early as 1 h following MCA stenosis. The significant correlation between imaging observations and histologically confirmed cerebral ischemia indicates that magnetic susceptibility contrast-enhanced echo planar MR imaging is sensitive to slight reductions in cerebral perfusion that fall below the threshold for reliably detectable ischemia-induced alterations in ADC. First-pass perfusion-sensitive imaging may thus be diagnostically useful in differentiating severely hypoperfused permanently injured tissue from the mildly hypoperfused ischemic penumbra.     

Reprint of: Surface electronic structure of Ti-covered W(1 1 1) by photofield emission

Photofield emission (PFE) measurements are employed to examine modifications of the surface electronic structure of the tungsten (1 1 1) facet upon deposition of thin films (1-3 monolayers) of titanium. With the help of DFT simulations, the observed PFE features are interpreted as adsorbate-induced resonance states with energies just below the Fermi level, localized predominantly at the exposed surface atoms. Comparison between the computed surface DOS distributions and the measured PFE spectra is also used to verify various possible arrangements of the Ti adatoms, supporting the DFT-favored model of Ti growth in registry with the W(1 1 1) substrate until a full physical overlayer of the adsorbate is completed.     

Plastic waste minimization: Compatibilization of polypropylene/polyamide 6 blends by polyalkenyl‐poly‐maleic‐anhydride‐based agents

The present article discloses the properties improvement in PP/PA 6 blends by new type experimental coupling additives. By the experimental agents especially the tensile properties could be improved. For example, the tensile strength and the elongation were 16.5 MPa and 4.4% without additive, which increased to 25.5, 20.1, 46.8 MPa and 8.1, 6.4, 8.6% in specimens containing polyalkenyl‐poly‐maleic‐anhydride‐amide, polyalkenyl‐poly‐maleic‐anhydride‐ester, and MA‐grafted‐low‐polymer additives, respectively. DSC curves shows that compatibilizers influenced thermal properties of the polymer blends and reveal affecting of crystalline phase formation process in the blends due to the compatibilization step. Additives A and B rather leads to influencing of PA crystallinities. According to the SEM and FTIR analysis well separated polypropylene and polyamide phases was observed in case of specimens absence of additives but only one well distributed phase by the applying of the synthetized coupling agents. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013