Processing of silica foam using steam heating and its characterization

Silica foams with 50–86 vol.% porosity have been developed through steam-heating route using slurries containing ovalbumin as binder, as well as sucrose and colloidal silica as additives. On steam-heating, only 1 h is required for drying of as-cast foams, as the cell-walls being restrained from shrinking by intra-cellular gas pressure, and simultaneously strengthened by ovalbumin protein coagulation, show minimum damage. Scanning electron microscopic studies of sintered foams have shown near-spherical pores with size distribution having mean of ≈250–300 μm. These pores appear interconnected through finer pores of ≈15–25 μm size along their walls. Solid loading, binder and sucrose concentrations of slurries for optimum viscosity have been obtained through rheological studies to tailor desirable pore content and size distributions in the sintered foams. Young's moduli and compressive strengths are found to be in the ranges of 14.4–544 MPa and 0.3–8.6 MPa, respectively for sintered foams having ≈55–90 vol.% porosity content.     

Small‐Molecule Mechanism of Action Studies in Caenorhabditis elegans

A general protocol for exogenous small‐molecule pull‐down experiments with Caenorhabditis elegans is described; it provides a link between small‐molecule screens in worms and existing mutant and RNAi technologies, thereby enabling organismal mechanism of action studies for the natural product clovanemagnolol. Forward chemical genetic screens followed by mechanism of action studies with C. elegans, when coupled with genetic validation of identified targets to reproduce the small molecule's phenotypic effects, provide a unique platform for discovering the biological targets of compounds that affect multicellular processes. First, the use of an immobilized FK506 derivative and soluble competition experiments with optimally prepared soluble C. elegans proteome successfully identified interactions with FK506 binding proteins 1 to 6. This approach was used to determine an unknown mechanism of action for clovanemagnolol, a small molecule that promotes axonal branching in both primary neuronal cultures and in vivo in C. elegans. Following the synthesis of an appropriately functionalized solid‐phase reagent bearing a clovanemagnolol analogue pull‐down experiments employing soluble competition identified kinesin light chain‐1 (KLC‐1), a protein involved in axonal cargo transport, as a putative target. This was corroborated through the use of mutant worms lacking klc‐1 and possessing GFP neuronal labeling, reproducing the axonal branching phenotype induced by the small molecule clovanemagnolol.     

Incorporation of chitosan nanoparticles into silk fibroin-based porous scaffolds: Chondrogenic differentiation of stem cells

A silk fibroin-chondroitin sulfate-sodium alginate (SF-CHS-SA) porous scaffold containing chitosan nanoparticles (NPs) was investigated. The proliferation of adipose-derived stem cells (ASCs) was studied by SEM, fluorescent microscopy, alcian blue staining, dimethylmethylene blue assay, and real-time polymerization chain reaction. The results showed that incorporation of NPs into the scaffold improved compressive modulus (5.6 ± 0.15 MPa). The amount of glycosaminoglycan expression of the ASCs was reached to 8.9 ± 0.3 µg/mL. The gene expressions of aggrecan, collagen II, and SOX9 of the ASCs were significantly improved. This study revealed that the prepared scaffold can be used as a substrate for cartilage tissue engineering.     

Potential production and preservation of dahi by Lactococcus lactis W8, a nisin-producing strain

Lactococcus lactis W8 produced nisin concomitantly while fermenting milk to “dahi”, a traditional Indian fermented milk. The activity of nisin was detected at 3 h of fermentation, which increased in parallel to growth of the organism and reached its maximum at 6 h. The activity remained essentially stable thereafter. At 7 h of fermentation of milk with the strain L. lactis W8 the pH of the medium dropped to 4.2, when the milk became converted to dahi. The produced dahi displayed antibacterial property against spoilage and pathogenic bacteria including Listeria monocytogenes. When L. monocytogenes was mixed with dahi at 5.2 log CFU/ml and stored at 4 °C, the number of L. monocytogenes gradually decreased and became undetectable at 10 h. L. lactis W8 appeared to be a suitable starter culture for production of dahi from milk and preservation of the dahi.     

Oxidation behavior of hot pressed ZrB2–SiC and HfB2–SiC composites

Non-isothermal, isothermal and cyclic oxidation behavior of hot pressed ZrB₂–20 (vol.%) SiC (ZS) and HfB₂–20 SiC (HS) composites have been compared. Studies involving heating in thermogravimetric analyzer have shown sharp mass increases at 740 and 1180 °C for ZS, and mass gain till 1100 °C followed by loss for HS. Isothermal oxidation tests for 1, 24 and 100 h durations at 1200 or 1300 °C have shown formation of partially and completely stable oxide scales after ～24 h exposure for ZS and HS, respectively. X-ray diffraction, scanning electron microscopy and energy or wavelength dispersive spectroscopy has confirmed presence of ZrO₂ or HfO₂ in oxide scales of ZS or HS, respectively, besides B₂O₃–SiO₂. Degradation appears more severe in isothermally oxidized ZS due to phase transformations in ZrO₂; and is worse in HS on cyclic oxidation at 1300 °C with air cooling, because of higher thermal residual stresses in its oxide scale.     

Comparative study on the corrosion and wear behavior of plasma-sprayed vs. high velocity oxygen fuel-sprayed Al8Si20BN ceramic coatings

Corrosion and wear are common problems encountered in the oil and gas industry. These entail the gradual destruction of materials by mechanical action on the opposite surface, and the chemical and/or electrochemical reaction with their environment. In this research, Al8Si20BN ceramic powder with specific properties against corrosion and wear was selected, and it was sprayed with high velocity oxygen fuel (HVOF) and plasma spray methods onto carbon steel substrates. The coatings were characterized with respect to phase composition, microstructure, microhardness and adhesion strength. Their wear behavior was inspected by applying 5, 10, 15 and 20?N loads by pin-on-disc machine, after which the results of both methods were compared. According to the results, the HVOF-coated models were more durable than the plasma-coated models under different loads in the same condition. In addition, the corrosion deterioration of the coated specimens in both brine (3.5% NaCl) and fossil oil were tested for one month (30 days). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) assessment in 3.5% NaCl solution indicated that the HVOF-sprayed specimens had better corrosion protection than the plasma-sprayed specimens. Generally, the HVOF technique facilitated more durable coats with greater corrosion and tribological resistance compared to the plasma coating technique.     

NUMERICAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER AND PRESSURE DROP IN WAVY DUCTS

Flow field and heat transfer in corrugated ducts have been investigated from the numerical solutions of the Navier-Stokes equations in the laminar to transitional range of Reynolds numbers (600 - 2000). First, the geometric parameters for the best ratio of heat transfer to pressure drop have been determined for two-dimensional channels. Then for these parameters, flow structure and heat transfer have been investigated for three-dimensional (3-D) channels consisting of corrugated plates. The angles 45^o and 90^o between the corrugations and the main stream direction have been considered. A performance evaluation criterion identifies the 3-D corrugated plate at 45^o with the best ratio between heat transfer and pressure drop.     

An Insight Into The Modeling of Short-Pulse Laser Transport Through A Participating Medium

Thermal radiation is a time-dependent process in the analysis of a short-pulse laser irradiation. The numerical modeling of the radiative phenomenon considers a finite number of intensity directions over a spherical space. Thus, in time-dependent radiative transfer problems, radiative intensities take different times to reach a particular location in the medium, and accordingly, collectively they remain available for durations different than the laser pulse width. The present work proposes that the above aspect be taken into account in the analysis of transient radiative transfer problems. To validate this concept, transport of a short square-pulse laser in a plane-parallel participating medium is studied. It is found that the magnitude of the transmittance signals differ for higher values of the extinction coefficient and also that the signals remain available for a longer duration. Reflectance signals are found to be less affected.