Densification and Properties of α-Silicon Carbide

Densification of a-Sic powders with no premixed sintering aids (type 1) and with premixed B and C (type 2) was investigated by sintering them at 2150° to 2200°C for 30 min. Flexure strengths, Weibull moduli, and fracture flaws were characterized for type 2 α-SiC only. The results were compared with those for a state-of-the-art sintered a-Sic material.     

A novel technique to prepare LiNbO3 at low temperature

Fresh niobium hydroxide was first precipitated from NbF₅ solution using an aqueous ammonium hydroxide under basic conditions. Then a simple procedure of mixing lithium and niobium hydroxides together and heating at a low temperature (400 °C) produced pure ultrafine single phase LiNbO₃ (LN). In the literature, this is the lowest temperature so far reported on the formation of LN. The phase content and lattice parameters are determined by X-ray diffraction (XRD). The average particle size and morphology were studied by transmission electron microscopy (TEM).     

Structural and magnetic properties of Co1+ySnyFe2-2y-xCrxO4 ferrite system

The samples of the series Co_1+ySn_yFe_{2- 2y- x}Cr_xO₄ ferrites with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and y = 0.05, were prepared by the usual double sintering ceramic technique. The single- phase spinel structure of the samples was confirmed by using X- ray diffractometry technique. The lattice parameter ’a’ with an accuracy of ± 0.002 Å were determined using Bragg peaks of XRD pattern. The lattice parameter ’a’ decreases with concentration, x, which is due to the difference in the ionic radii of Cr³⁺ and Fe³⁺ ions. The X- ray intensity calculations were carried out in order to determine the possible cation distribution amongst tetrahedral (A) and octahedral [B] sites. The X- ray intensity calculations show Cr³⁺ ions occupying B site. The saturation magnetization, σ_s, and magneton number, n_B (the saturation magnetization per formula unit), measured at 300 K determined from high field hysteresis loop technique decrease with increase in concentration, x, suggesting a decrease in ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility measurements from room temperature to about 800 K exhibits almost normal ferrimagnetic behaviour and the Curie temperature, T_C determined from a.c. susceptibility data decreases with increase in x.

     

A comparative study of short nylon fiber—Natural rubber composites prepared from dry rubber and latex masterbatch

A novel method for the preparation of short nylon fiber–natural rubber composites was developed in which short fibers chopped to approximately 6 mm were incorporated in the latex stage and processed into sheet form. By this method, mixing cycle time was reduced without compromising the fiber dispersion. Fiber breakage during mixing was reduced. The new composites when compounded with a dry bonding system based on hexamethylenetetramine, resorcinol and hydrated silica (HRH) showed improved modulus, tensile strength and abrasion resistance compared to conventional composites. Tear strength, resilience, and compression set were similar to the conventional composites. SEM analysis indicated better interaction between matrix and fibers in the case of latex master batch. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The synthesis of symmetrical and unsymmetrical P1/P1' cyclic ureas as HIV protease inhibitors

Cyclic urea SD146, a potent HIV protease inhibitor bearing a flat resistance profile, possessed poor solubility and bioavailability, which precluded further development of the compound. In an effort to improve upon the pharmacokinetic profile of the compound, several analogs modified at the P1/P1' residues were prepared and evaluated. Several of those compounds displayed significant improvement of physical properties.     

Polyamide-6,6/in situ silica hybrid nanocomposites by sol-gel technique: synthesis, characterization and properties

The organic-inorganic hybrid nanocomposites comprising of poly(iminohexamethyleneiminoadipoyl), better known as Polyamide-6,6 (abbreviated henceforth as PA66), and silica (SiO₂) were synthesized through sol-gel technique at ambient temperature. The inorganic phase was generated in situ by hydrolysis-condensation of tetraethoxysilane (TEOS) in different concentrations, under acid catalysis, in presence of the organic phase, PA66, dissolved in formic acid. Infrared (IR) spectroscopy was used to monitor the microstructural evolution of the silica phase in the PA66 matrix. Wide angle X-ray scattering (WAXS) studies showed that the crystallinity in PA66 phase decreased with increasing silica content. Atomic force microscopy (AFM) of the nanocomposite films revealed the dispersion of SiO₂ particle with dimensions of <100 nm in the form of network as well as linear structure. X-ray silicon mapping further confirmed the homogeneous dispersion of the silica phase in the bulk of the organic phase. The melting peak temperatures slightly decreased compared to neat PA66, while an improvement in thermal stability by about 20 °C was achieved with hybrid nanocomposite films, as indicated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) exhibited significant improvement in storage modulus (E′) for the hybrid nanocomposites over the control specimen. An increase in Young's modulus and tensile strength of the hybrid films was also observed with an increase in silica content, indicating significant reinforcement of the matrix in the presence of nanoparticles. Some properties of the in situ prepared PA66-silica nanocomposites were compared with those of conventional composites prepared using precipitated silica as the filler by solution casting from formic acid.     

Moisture absorption by cyanate ester modified epoxy resin matrices. Part I. Effect of spiking parameters

The moisture absorption of cyanate ester modified epoxy resin matrices has been studied under thermal spiking conditions. Enhanced moisture absorption has been observed at spike-temperatures above 120 °C. The results of the desorption studies on both control specimens and the spiked specimens showed that some of the water molecules remained entrained in the polymer. It is postulated that this water could be associated with that which is hydrogen bonded or from the hydrolysis of isolated residual cyanate ester groups because the concentration of entrained water remains constant at spike-temperatures below 180 °C. Above 180 °C a thermally activated process, leading to chain scission as indicated by a reduced recoverability of the glass transition temperature (T_g) on drying.On isothermal resorption, the moisture concentration was found to be similar to that achieved through thermal spiking, showing that the entrained water at the lower spike-temperatures can also be achieved under mild conditions. The T_g is reversibly recovered to within 5 °C, which indicates a degree of relaxation rather than degradation. The moisture diffusion coefficient estimated from the resorption curves is lower than those estimated from the absorption and desorption curves. The isothermal resorption diffusion coefficient also decreased with increasing spike temperature. It is proposed that thermal spiking induced a relaxation of the network but as the spike-temperature approaches the transition region of the wet polymer, further hydrolytically induced relaxation events become feasible.     

Low intensity visual data improvement using DWT and LWT based regularizer

Image Completion plays a vital role in compressed sensing, machine learning, and computer vision applications. The Rank Minimization algorithms are used to perform the image completion. The major problem with rank minimization algorithms is the loss of information in the recovered image at high corruption ratios. To overcome this problem Lifting wavelet transform based Rank Minimization (LwRM), and Discrete wavelet transform based Rank Minimization (DwRM) methods are proposed, which can recover the image, if the corrupted observations are more than 80%. The evaluation of the proposed methods are accomplished by Full Reference Image Quality Assessment (FRIQA) and No Reference Image Quality Assessment (NR-IQA) metrics. The simulation results of proposed methods are superior to state-of-the-art methods.

     

Fabrication and characterization of electrospun psyllium husk-based nanofibers for tissue regeneration

The present study reports for first time the blending of psyllium husk (PH) powder/gelatin (G) in the polymer-rich composition of polyvinyl alcohol (PVA) to make an electrospinnable solution. The composite was prepared in 3 different ratios viz., 100% (wt/wt) (PVA + PH), 75% + 25% (PVA + 75PH + 25G) (wt/wt) and 50% + 50% (PVA + 50PH + 50G) (wt/wt) in 6% PVA solution. Optimum electrospinning parameters were evaluated for all the prepared blends. The fabricated nanofibers were characterized by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared, differential scanning calorimetry, porosity percentage, and fiber orientation using ImageJ software. A qualitative in vitro degradation study at room temperature is supported by SEM images. The cellular interactions were characterized by MTT assay of NIH-3T3 fibroblast cells for 2 and 4 days with an optimum cell growth of >50% by fourth day of culture and long-term cultivation of L929-RFP cells was observed for 10 days. The nanofibers were formed in the range of 49–600 nm. PVA + 75PH + 25G when cultured with L929-RFP cells exhibited highest fluorescence intensity and thus supported cellular proliferation significantly. Based on the results obtained from various analyses, we anticipate that fabricated psyllium-based nanofiber can be used as a promising candidate for wound healing and other biomedical applications.