Biocompatibility studies of polyacrylonitrile membranes modified with carboxylated polyetherimide

Poly (ether-imide) (PEI) was carboxylated and used as the hydrophilic modification agent for the preparation of polyacrylonitrile (PAN) membranes. Membranes were prepared with different blend compositions of PAN and CPEI by diffusion induced precipitation. The modified membranes were characterized by thermo gravimetric analysis (TGA), mechanical analysis, scanning electron microscopy (SEM) and contact angle measurement to understand the influence of CPEI on the properties of the membranes. The biocompatibility studies exhibited reduced plasma protein adsorption, platelet adhesion and thrombus formation on the modified membrane surface. The complete blood count (CBC) results of CPEI incorporated membranes showed stable CBC values and significant decrease in the complement activation were also observed. In addition to good cytocompatibility, monocytes cultured on these modified membranes exhibited improved functional profiles in 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Thus it could be concluded that PAN/CPEI membranes with excellent biocompatibility can be useful for hemodialysis.     

Workability studies on powder metallurgy pure iron preforms during hot forging under triaxial stress state condition

An experimental research work was performed for the understanding of the workability behavior of pure iron preforms produced through powder metallurgy route during hot forging under triaxial stress state condition. Relationship was established between the formability stress index and the axial strain. A relationship between the relative density and the axial strain was also established. Various stress ratio parameter under triaxial stress state condition which indicates the workability behavior of the material namely, , and were studied. An attempt has also been made to relate the stress ratio parameters with the relative density (R).     

Evaluation of Mechanical and Tribological Behavior of Al–4 %Cu–x %SiC Composites Prepared Through Powder Metallurgy Technique

This article presents characterization of 99.85 % pure aluminum with 4 % copper, reinforced with varying proportions of silicon carbide. Al–Cu–SiC metal matrix composite (MMC’s) are prepared by powder metallurgy route for 0, 2.5, 5, 7.5, 10, 12.5 and 15 % of SiC addition. To investigate the effects of adding SiC particles, microstructural analysis and mechanical properties by micro-hardness, compression, wear and thermal conductivity are studied. Scanning electron microscope image shows uniform distribution of particulates. Results show that upon increasing addition of SiC particles, micro-hardness and compression strength increases, whereas thermal conductivity decreases. Wear rate increases till 7.5 % SiC addition, with further addition of SiC, wear rate increases due to the un-bonding of SiC particles from the MMC, aiding in the increase of wear rate. Addition of SiC up to 7.5 % play an important role in improving wear resistance, thermal and mechanical properties of Al–Cu–SiC MMC.     

Correlation of atomic force–distance microscopy and spectrophotometric techniques in the analysis of optical multilayer spectral aging process

Aging-related multilayer spectral instabilities can pose severe performance limiting constraints to optical multilayer devices. In this study such instabilities of some periodic Gd₂O₃/SiO₂ optical multilayer systems have been explored using scanning probe force–distance microscopy and spectrophotometric techniques. In the present case, a strong correlation between the spectral instabilities and the viscoelastic properties of the associated thin film layers has been distinctly noticed. From the experimental analysis it was quite evident that the spectral instability, which starts during the nucleation and growth stage in thin films, continues to persist at a much longer time scale following aging processes. In this study it is shown that the elastic properties of the constituent thin films, the layer design and the bilayer thickness have established a strong interrelation which ultimately contributes to the multilayer instabilities. These spectral instabilities also have strong interconnections with the morphological and viscoelastic changes in such multilayers. Other multilayer parameters like the total number of layers, the layer structure, the microroughness evolutions, related stiffness factors and the adhesion properties of the periodic layer systems contribute substantially to this instability process.     

Enhancement to IEEE 802.11 Distributed Coordination Function to Reduce Packet Retransmissions Under Imperfect Channel Conditions

In this paper, we provide an extended model for analytical analysis of IEEE 802.11 wireless local area networks under noisy wireless channel. A reservation stage is introduced in the Markov chain model to reduce unnecessary retransmissions in the case of transmission failure due to channel error. A lot of work has been carried out to enhance the performance of 802.11 distributed coordination function in the error free channel. Throughput enhancement of 802.11 medium access control protocol under error prone channel was still missing in the available literature. Through the analysis result it is shown that the proposed method significantly improves the performance of the backoff algorithm when the reservation stage is employed in the Markov chain model. The analysis result is validated by using the network simulator tool ns-2. The proposed modifications can be employed in the Markov chain model of any backoff algorithm.