Synthesis of nitrogen-containing carbon nanofibers by catalytic decomposition of ethylene/ammonia mixture

The formation of carbon nanofibers (CNFs) doped with nitrogen was investigated during decomposition of C₂H₄/NH₃ mixtures at 450-675 °C over metal catalysts: 90Ni-Al₂O₃, 82Ni-8Cu-Al₂O₃, 65Ni-25Cu-Al₂O₃, 45Ni-45Cu-Al₂O₃, 90Fe-Al₂O₃, 85Fe-5Co-Al₂O₃, 62Fe-8Co-Al₂O₃, 62Fe-8Ni-Al₂O₃. It was found that the yield of CNFs, their structural and textural properties, as well as nitrogen content in CNFs are strongly dependent on the synthesis conditions such as: catalyst used, feed composition, temperature and duration. The 65Ni-25Cu-Al₂O₃ was proved to be the most efficient catalyst for the production of nitrogen-containing carbon nanofibers (N-CNFs) with nitrogen content up to 7 wt.%. Ammonia concentration in the feed equal 75 vol.%, temperature 550 °C and duration 1 h were found to be the optimum reaction parameters to reach the maximum nitrogen content in N-CNFs. TEM studies revealed that the nanofibers have a helical morphology and a “herringbone” structure composed of graphite sheets. According to the XPS data, the nitrogen incorporation in the N-CNF structure leads to the formation of two types of nitrogen coordination: pyridinic and quaternary, and their abundance depends on the reaction conditions.     

Efficient removal of microcystin-LR by UV-C/H₂O₂ in synthetic and natural water samples

The destruction of the commonly found cyanobacterial toxin, microcystin-LR (MC-LR), in surface waters by UV-C/H₂O₂ advanced oxidation process (AOP) was studied. Experiments were carried out in a bench scale photochemical apparatus with low pressure mercury vapor germicidal lamps emitting at 253.7 nm. The degradation of MC-LR was a function of UV fluence. A 93.9% removal with an initial MC-LR concentration of 1 μM was achieved with a UV fluence of 80 mJ/cm² and an initial H₂O₂ concentration of 882 μM. When increasing the concentration of MC-LR only, the UV fluence-based pseudo-first order reaction rate constant generally decreased, which was probably due to the competition between by-products and MC-LR for hydroxyl radicals. An increase in H₂O₂ concentration led to higher removal efficiency; however, the effect of HO scavenging by H₂O₂ became significant for high H₂O₂ concentrations. The impact of water quality parameters, such as pH, alkalinity and the presence of natural organic matter (NOM), was also studied. Field water samples from Lake Erie, Michigan and St. Johns River, Florida were employed to evaluate the potential application of this process for the degradation of MC-LR. Results showed that the presence of both alkalinity (as 89.6-117.8 mg CaCO₃/L) and NOM (as ∼2 to ∼9.5 mg/L TOC) contributed to a significant decrease in the destruction rate of MC-LR. However, a final concentration of MC-LR bellow the guideline value of 1 μg/L was still achievable under current experimental conditions when an initial MC-LR concentration of 2.5 μg/L was spiked into those real water samples.     

Preservation of the negative image of tooth enamel with dental impression material enhances morphometric measurements of gingival overgrowth

Gingival overgrowth is a common health problem caused by genetic and environmental risk factors. Animal models for quantitative histological studies are needed to uncover genetic predisposition and dose-response data that might put individuals at increased risk for gingival disease. Gingival height, thickness, inflammation, and the degree of encroachment of gingiva over the tooth, are clinical measures of overgrowth; most of these parameters can be measured histologically, but in order to quantify gingival coverage of the tooth, the image of the crown must be present. Tooth and bone typically require decalcification for histology; thus, the tooth crown, a critical landmark, is lost. We describe a method for imaging the crown histologically, using impression materials applied to dissected mouse mandibles. Four dental alginates, three polyvinyl siloxanes, and one polyether and gelatin were used. The impression-material/mandibular tissue blocks were processed routinely. Polyvinyl siloxanes were incompatible with embedding resin; alginates, polyether and gelatin could be fixed, decalcified, embedded, and sectioned. Alginates and gelatin could be stained. Success in imaging the tooth crown varied with the preparation, but the alginates, polyether, and gelatin permitted a useful degree of measurement of exposed crown and enamel thickness, along with other morphometric parameters such as thickness of the dentin, lateral mandibular ramus, rete pegs, height of the gingiva, and volume density of vessels and inflammatory cells in the lamina propria. In conclusion, this new application for impression materials allows gingival coverage of tooth crown, as well as numerous other parameters to be measured for comparison with clinical data.     

Generation of Liposomes to Study the Effect of Mycobacterium Tuberculosis Lipids on HIV-1 cis- and trans-Infections

Tuberculosis (TB) is the leading cause of death among HIV-1-infected individuals and Mycobacterium tuberculosis (Mtb) co-infection is an early precipitate to AIDS. We aimed to determine whether Mtb strains differentially modulate cellular susceptibility to HIV-1 infection (cis- and trans-infection), via surface receptor interaction by their cell envelope lipids. Total lipids from pathogenic (lineage 4 Mtb H37Rv, CDC1551 and lineage 2 Mtb HN878, EU127) and non-pathogenic (Mycobacterium bovis BCG and Mycobacterium smegmatis) Mycobacterium strains were integrated into liposomes mimicking the lipid distribution and antigen accessibility of the mycobacterial cell wall. The resulting liposomes were tested for modulating in vitro HIV-1 cis- and trans-infection of TZM-bl cells using single-cycle infectious virus particles. Mtb glycolipids did not affect HIV-1 direct infection however, trans-infection of both R5 and X4 tropic HIV-1 strains were impaired in the presence of glycolipids from M. bovis, Mtb H37Rv and Mtb EU127 strains when using Raji-DC-SIGN cells or immature and mature dendritic cells (DCs) to capture virus. SL1, PDIM and TDM lipids were identified to be involved in DC-SIGN recognition and impairment of HIV-1 trans-infection. These findings indicate that variant strains of Mtb have differential effect on HIV-1 trans-infection with the potential to influence HIV-1 disease course in co-infected individuals.     

Dry Coating of Soft Gelatin Capsules with HPMCAS

Dry coating is an innovative powder-layering technique that enables the formation of coatings on solid dosage forms with no need for using water or organic solvents. This technique envisages the distribution of polymer powder blends onto substrate cores and the concurrent or alternate nebulization of liquid plasticizers. In this work, a dry coating process based on hydroxypropyl methylcellulose acetate succinate (HPMCAS) was set up in a rotary fluid bed equipment to prepare enteric-coated soft gelatin capsules. Promising results were obtained in terms of process feasibility and product characteristics, thus suggesting the possibility of advantageous applications for the investigated technique when dealing with gelatin capsule substrates.     

The effects of residual stresses and degradation on the response of viscoplastic functionally graded materials

Functionally graded materials (FGMs), having ceramic and metallic constituents, are commonly used for extreme temperature applications. Under extreme temperature changes, the mismatches in the thermo-mechanical properties of the ceramics and metallic constituents could cause pronounced thermal stresses and could lead to degradation in the properties of the constituents. High stresses in the metallic constituent lead to plastic deformations and high tensile stresses in the ceramic constituent induce cracking. An elastic–viscoplastic micromechanical model is formulated for analyzing residual stresses and strains and degradation in ceramic–metal FGMs undergoing temperature changes due to conduction of heat. A degradation parameter that depends on the temperature and strain is introduced in order to determine the level of material degradation in the ceramics and metallic constituents. The Perzyna viscoplastic model is considered for the metallic constituent while the ceramic constituent is assumed linear elastic. The material parameters in these constituents change with the degradation. The problem leads to time-dependent coupled thermal, deformation, and degradation behaviors. The micromechanical model is implemented in a displacement based finite element (FE), which is used to determine the performance of the viscoplastic functionally graded structures subject to external thermo-mechanical stimuli.     

A two-scale homogenization framework for nonlinear effective thermal conductivity of laminated composites

In this study, we formulate the effective temperature-dependent thermal conductivity of laminated composites. The studied laminated composites consist of laminas (plies) made of unidirectional fiber-reinforced matrix with various fiber orientations. The effective thermal conductivity is obtained through a two-scale homogenization scheme. A simplified micromechanical model of a unidirectional fiber-reinforced lamina is formulated at the lower scale. Thermal conductivities of fiber and matrix constituents are allowed to change with temperature. The upper scale uses a sublaminate model to homogenize temperature-dependent thermal conductivities of only a representative lamina stacking sequence in laminated composites. The effective thermal conductivity of each lamina, in the sublaminate model, is obtained using the simplified micromechanical model. The thermal conductivities from the micromechanical and sublaminate models represent average nonlinear properties of fictitiously homogeneous composite media. Interface conditions between fiber and matrix constituents and within laminas are assumed to be perfect. Experimental data available in the literature are used to verify the proposed multi-scale framework. We then analyze transient heat conduction in the homogenized composites. Temperature profiles, during transient heat conduction, in the homogenized composites are compared to the ones in heterogeneous composites. The heterogeneous composites, having different fiber arrangements and sizes, are modeled using finite element (FE) method.     

Analysis of the gas phase of cigarette smoke by gas chromatography coupled with UV-diode array detection

A gas chromatography method, coupled with diode array photometric spectral detection in the ultraviolet region (167-330 nm), was developed for the analysis of the gas phase of cigarette smoke. The method enabled us to identify more than 20 volatiles present in the vapor phase of cigarette smoke. In that way, all major volatile organic compounds (including aldehydes, conjugated dienes, ketones, sulfides, furans, and single-ring aromatics), as well as nitric oxide (NO) and hydrogen sulfide (H(2)S), can be analyzed in a straightforward manner through a single chromatographic run of <50-min duration. The method can easily be applied by the introduction of a small volume of the gas-phase stream into the GC injection loop directly through the smoking apparatus exhaust circuit, thus providing an excellent alternative to available methods, which usually require extraction or concentration steps prior to any chromatographic analysis. Furthermore, all problems concerning aging of the gas phase are eliminated. Twelve compounds (including NO) were chosen for quantification through the use of appropriate calibration standards. Comparison of the vapor phase yields of these compounds for the reference cigarette Kentucky 1R4F with already reported data indicates that this method is very reliable as far as accuracy and reproducibility of the results are concerned. Finally, the proposed methodology was used to compare the concentration of these cigarette smoke gas-phase constituents among individual puffs.