Preparation mullite/Si3N4 composites by reaction spark plasma sintering and their characterization

In the present study, in-situ mullite/Si₃N₄ composites were prepared successfully by reaction spark plasma sintering. For this purpose, 5, 10 and 15?wt% of Si₃N₄ were added to stoichiometric mullite made of mechanically milled mixture of alumina and kaolin clay to investigate the effect of reinforcement content on the final properties of the prepared composites. The sintering processes were performed at 1400?°C under the initial and final applied pressures of 10 and 30?MPa and the vacuum condition of 17?Pa. The XRD patterns revealed the mullite and Si₃N₄ peaks as the dominant crystalline phases. Microstructural investigations demonstrated a uniform distribution of Si₃N₄ inside mullite matrix for the composites containing 5 and 10?wt% of the reinforcement particles. Meanwhile, some agglomerates of Si₃N₄ were observed in the microstructure of the mullite-15?wt%Si₃N₄ composite. Moreover, no evidence of reaction between the starting materials was detected through XRD and FESEM analyses. The highest values of hardness, bending strength, and fracture toughness obtained for the composite containing 15?wt% of Si₃N₄ were 19.14?GPa, 481?MPa and 3.85?MPa?m^?1/2, respectively. The fracture toughness mechanisms were detected as crack branching, breaking and deflection, as well as particles pulling-out, all of which were observed in the mullite-15?wt%Si₃N₄ composite.     

Superabsorbent,Breathable Graphene Oxide-Based Nanocomposite Hydrogel as a Dense Membrane for Use in Protective Clothing

This study examines the synthesis, fabrication and characterization of poly acrylamido methyl propane sulfonic acid (PAMPS)/graphene oxide (GO) nanocomposites. PAMPS-GO nanocomposite hydrogel was synthesized by radical initiated polymerization and its swelling properties, water vapor permeability (WVP), and stress-strain behavior were evaluated. The swelling behavior of hydrogel nanocomposites were improved at the presence of 0.2 wt% GO, as confirmed by water uptake experiments. It should be noted that as GO loading increased, so did the WVP of the hydrogel. The stress-strain test also revealed that the incorporation of just 0.1% of GO raised the tensile strength and young modulus of the hydrogels by 42% and 37% respectively. These fabricated dense membranes can have applications in protective clothing and wound dressing.     

Type I Interferon α/β Receptor-Mediated Signaling Negatively Regulates Antiviral Cytokine Responses in Murine Bone-Marrow-Derived Mast Cells and Protects the Cells from Virus-Induced Cell Death

Mast cells (MCs) are critical for initiating inflammatory responses to pathogens including viruses. Type I interferons (IFNs) that exert their antiviral functions by interacting with the type I IFN receptor (IFNAR) play a central role in host cellular responses to viruses. Given that virus-induced excessive toxic inflammatory responses are associated with aberrant IFNAR signaling and considering MCs are an early source of inflammatory cytokines during viral infections, we sought to determine whether IFNAR signaling plays a role in antiviral cytokine responses of MCs. IFNAR-intact, IFNAR-blocked, and IFNAR-knockout (IFNAR^−/−) bone-marrow-derived MCs (BMMCs) were treated in vitro with a recombinant vesicular stomatitis virus (rVSVΔm51) to assess cytokine production by these cells. All groups of MCs produced the cytokines interleukin-6 and tumor necrosis factor-α in response to rVSVΔm51. However, production of the cytokines was lowest in IFNAR-intact cells as compared with IFNAR^−/− or IFNAR-blocked cells at 20 h post-stimulation. Surprisingly, rVSVΔm51 was capable of infecting BMMCs, but functional IFNAR signaling was able to protect these cells from virus-induced death. This study showed that BMMCs produced pro-inflammatory cytokines in response to rVSVΔm51 and that IFNAR signaling was required to down-modulate these responses and protect the cells from dying from viral infection.     

Rheology,injectability, and bioactivity of bioactive glass containing chitosan/gelatin,nano pastes

Bioactive pastes containing bioactive sol–gel derived glass (BG) and various amounts of chitosan (Cn) and gelatin (Gel) were prepared in this study. To be exact, three pastes were prepared by mixing 25 parts by weight of glass powder with (a) 100 parts by weight of a 3 wt% acetic acid-based chitosan solution, (b) 100 parts by weight of a 3 wt% water-based gelatin solution, and (c) 100 parts by weight of a solution containing equal amounts of the above-mentioned solutions. The bioactivity of the composite samples was evaluated by the immersion of the prepared pastes into the simulated body fluid (SBF) solution. The samples were also analyzed by X-ray diffractometry (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), Fourier transform infrared (FTIR), and atomic absorption spectroscopy (AAS). The results indicated better apatite formation capacity on the glass-/chitosan-/gelatin-injected paste after 14 days. Furthermore, unlike the chitosan containing paste, the gelatin-containing sample was injectable and displayed viscoelastic behavior as determined by conducting the rheology test in oscillation mode. In addition, while chitosan made the paste more viscous, it improved the washout resistance when compared to the gelatin-containing sample. The experimental results also indicate the formation of spherical calcites in the pastes prior to immersion into the SBF solution.     

Predicting Charpy impact energy of Al6061/SiCp laminated nanocomposites in crack divider and crack arrester forms

Charpy impact energy of the produced Al6061–SiC_p laminated nanocomposites by mechanical alloying was modeled by adaptive neuro-fuzzy interfacial systems (ANFIS) in both crack divider and crack arrester configurations. The model was constructed by training, validating and testing of 171 gathered input–target data. The thickness of layers, the number of layers, the adhesive type, the crack tip configuration and the content of SiC nanoparticles were five independent input parameters utilized for modeling. The output parameter was Charpy impact energy of the nanocomposites. The performance of the proposed models was evaluated by absolute fraction of variance, the absolute percentage error and the root mean square error and the best values of 0.9945, 3.521 and 8.224, respectively acquired for them. The results introduced ANFIS as an influential tool for predicting the Charpy impact energy of the considered Al6061–SiC_p laminate nanocomposites.     

Urea impregnated multiwalled carbon nanotubes; a formaldehyde scavenger for urea formaldehyde adhesives and medium density fiberboards bonded with them

Multiwalled carbon nanotubes (MWCNTs) were subjected to modification by urea to use as formaldehyde scavenger in urea formaldehyde (UF) adhesive and reducing the free formaldehyde emission of the medium density fiberboards (MDFs). Morphological differences besides elemental analysis was investigated using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy. The effect of urea impregnated MWCNTs filler on the physical, morphological and thermal properties of the UF resin has investigated. Furthermore, characterization of the mechanical properties, free formaldehyde emission and thickness swelling were carried out for the MDF panels. From the results, the free formaldehyde of the UF resins was significantly decreased. The lowest free formaldehyde was belonged to the sample with 3 wt% of scavenger which was about 71% lower than the value for neat UF resin. Accordingly, the formaldehyde emission of the fiberboards was also showed a descending trend by incorporation of MWCNTs-U to the composite structure. It was decreased from 9.67 to 3.89 mg/100 g dried board. These results indicated that the prepared nano modifier was successfully performed as a formaldehyde scavenger for the UF resin and could prevent the hazards of the free formaldehyde emission from MDF panels.     

Experimental and Numerical Simulation of Dry Pressure Drop in High‐Capacity Structured Packings

Experimental and numerical studies were conducted on the performance and capacity of structured packings for mixture separation with very low separation factor. Different formations and conditions of the innovative structured packing PACK‐2100 with high surface area were studied to evaluate the main characteristics such as dry pressure drop. In addition, numerical simulation was performed to describe the details of the flow structure in these modified structured packings. Three‐dimensional computational fluid dynamics modeling of PACK‐2100 allowed for comparing the pressure drop in both laminar and turbulent flow regime. The obtained experimental and numerical data demonstrate the potential contribution of the packing to high‐efficiency systems with low separation factor.     

Excess volume of polymer/solvent mixtures and proposed model for prediction of activity of solvents based on excess volume data

Density measurements were used to evaluate the excess volume of binary mixtures of poly(ethylene glycol) in water and ethanol solvents, poly(propylene glycol) in water and ethanol solvents, and poly(vinyl alcohol) in water solvent at different temperatures for various molecular weights of polymers. The excess volumes were correlated and expressed by a polynomial in terms of the weight fraction of the polymer. The activity of the solvent was expressed in terms of three parts: excess internal energy, excess entropy, and excess volume. The excess volume was derived from the expression obtained in this work, the excess entropy was derived from Flory's lattice model, and the excess internal energy was used as a weight average of the excess volume and entropy parts. The results indicated good agreement between the activity of the solvent calculated by the proposed model and the experimental data. The proposed model has the advantage that using only simple density measurements the activity values that are necessary in the calculation of thermodynamic properties can be evaluated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1219–1227, 2005     

Response of coplanar transmission lines to an incident EM field

In the present article, a new concept is being proposed to find the voltages and currents induced by external EM fields on an arbitrary transmission line like coplanar lines. In this new method, a 3D problem of the “transmission line excited by external EM field” is subdivided into two problems. The first problem called “forced terms problem” is a 2D problem of the “cross section of the transmission line excited by external EM field.” The second problem is a one‐dimensional problem of the “transmission line excited by external EM field” called “TL problem.” The first problem can be solved using a two‐dimensional analysis. The second problem can be described by a pair of simple nonhomogeneous differential equations of the transmission lines with forced terms. The forced terms of the differential equations are obtained solving the first problem. The method is fast and validated with conventional 3D full wave analysis software like HFSS. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.