High char‐yielding poly[acrylonitrile‐co‐(itaconic acid)‐co‐(methyl acrylate)]: synthesis and properties

Polyacrylonitrile terpolymers of various compositions consisting of acrylonitrile (AN), itaconic acid (IA) and methyl acrylate (MA) were synthesized by solution polymerization in dimethylsulfoxide. Increase in concentration of either IA or MA retarded the overall polymerization rate and the polymer molecular weight. The system consisting of AN + MA and varying IA concentration was more prone to retardation in comparison with the system composed of AN + IA with variable MA concentration. The retardation factors were quantified. Minor quantities of MA boost the reactivity of IA in the terpolymer system. The terpolymer was richer in MA vis‐à‐vis the feed. The thermal characteristics of the terpolymer were examined as a function of its composition. In contrast to the copolymer of AN and IA requiring 1–1.5 mol% IA, the terpolymer required an IA content of approximately 2.5 mol% for optimum thermal stability. The polymer with 90 mol% AN, 2.5 mol% IA and 7.5 mol% MA exhibited reasonably good char‐forming characteristics and thermal stability. The overall crystallinity and crystallite size of the polymers were found to decrease on incorporation of the comonomers. The ‘aromatization index’ of the copolymer increased with the temperature of pyrolysis through re‐organization of the tetrahydropyridine ladder structure. Copyright © 2005 Society of Chemical Industry     

Geometric Representation of Graphs in Low Dimension Using Axis Parallel Boxes

An axis-parallel k-dimensional box is a Cartesian product R ₁×R ₂×???×R _k where R _i (for 1≤i≤k) is a closed interval of the form [a _i ,b _i ] on the real line. For a graph G, its boxicity box?(G) is the minimum dimension k, such that G is representable as the intersection graph of (axis-parallel) boxes in k-dimensional space. The concept of boxicity finds applications in various areas such as ecology, operations research etc. A number of NP-hard problems are either polynomial time solvable or have much better approximation ratio on low boxicity graphs. For example, the max-clique problem is polynomial time solvable on bounded boxicity graphs and the maximum independent set problem for boxicity d graphs, given a box representation, has a $\lfloor 1+\frac{1}{c}\log n\rfloor^{d-1}An axis-parallel k-dimensional box is a Cartesian product R ₁×R ₂×⋅⋅⋅×R _k where R _i (for 1≤i≤k) is a closed interval of the form [a _i ,b _i ] on the real line. For a graph G, its boxicity box (G) is the minimum dimension k, such that G is representable as the intersection graph of (axis-parallel) boxes in k-dimensional space. The concept of boxicity finds applications in various areas such as ecology, operations research etc. A number of NP-hard problems are either polynomial time solvable or have much better approximation ratio on low boxicity graphs. For example, the max-clique problem is polynomial time solvable on bounded boxicity graphs and the maximum independent set problem for boxicity d graphs, given a box representation, has a ?1+\frac1clogn?^d-1\lfloor 1+\frac{1}{c}\log n\rfloor^{d-1} approximation ratio for any constant c≥1 when d≥2. In most cases, the first step usually is computing a low dimensional box representation of the given graph. Deciding whether the boxicity of a graph is at most 2 itself is NP-hard.     

In vitro evaluation of bioactive strontium-based ceramic with rabbit adipose-derived stem cells for bone tissue regeneration

The development of bone replacement materials is an important objective in the field of orthopaedic surgery. Due to the drawbacks of treating bone defects with autografts, synthetic bone graft materials have become optional. So in this work, a bone tissue engineering approach with radiopaque bioactive strontium incorporated calcium phosphate was proposed for the preliminary cytocompatibility studies for bone substitutes. Accumulating evidence indicates that strontium containing biomaterials promote enhanced bone repair and radiopacity for easy imaging. Hence, strontium calcium phosphate (SrCaPO₄) and hydroxyapatite scaffolds have been investigated for its ability to support and sustain the growth of rabbit adipose-derived mesenchymal stem cells (RADMSCs) in vitro. They were characterized via Micro-CT for pore size distribution. Cells used were isolated from New Zealand White rabbit adipose tissue, characterized by FACS and via differentiation into the osteogenic lineage by alkaline phosphatase, Masson’s trichome, Alizarin Red and von Kossa staining on day 28. Material-cell interaction was observed by SEM imaging of cell morphology on contact with material. Live–Dead analysis was done by confocal laser scanning microscopy and cell cluster analysis via μCT. The in vitro biodegradation, elution and nucleation of apatite formation of the material was evaluated using simulated body fluid and phosphate buffered saline in static regime up to 28 days at 37 °C. These results demonstrated that SrCaPO₄ is a good candidate for bone tissue engineering applications and with osteogenically-induced RADMSCs, they may serve as potential implants for the repair of critical-sized bone defects.     

Changes in free volume and gas permeation properties of poly(vinyl alcohol) nanocomposite membranes modified using cage-structured polyhedral oligomeric silsesquioxane

The present work reports the effect of various organically functionalized polyhedral oligomeric silsesquioxane (POSS) particles on the gas transport properties (N₂, O₂, and CO₂ molecules) in poly(vinyl alcohol) (PVA) membranes. The incorporation of polyethylene glycol-POSS (PEG-POSS), octa-tetramethylammonium-POSS (Octa-TMA-POSS) and m-POSS (Octa-TMA-POSS molecule was modified using cetyltrimethyl ammonium bromide) led to the enhancement in CO₂ separation performance of PVA, among which, PEG-POSS exhibited highest CO₂ separation due to the dipole-quadrupolar interaction of CO₂ with ethylene oxide group in POSS. Octa-TMA-POSS and m-POSS reduced the O₂ and N₂ permeability of the PVA membrane due to the reduction in the number of permeating pathways as compared to pure PVA. Free volume of the membranes was evaluated by positron annihilation lifetime spectroscopic (PALS) and coincidence Doppler broadening measurements. PALS confirms the increase in polymer free volume in PVA/POSS system due to the presence of rigid and spherical POSS molecule, which could enter in the polymer chain and provide viable pathway for molecular transport. Maxwel–Wagner–Sillar and Higuchi models were applied for the theoretical prediction of permeability of the fabricated membranes.     

Structure-property correlation on AA 2219 aluminium alloy weldments

AA 2219 aluminium alloy is the material proposed for the construction of tanks for liquid cryogenic fuels like liquid oxygen and liquid hydrogen, in Indian launch vehicle programmes. To meet the material requirement, ISRO has developed the alloy AA 2219 indigenously on an industrial scale. Process development and structure-property correlation of auto TIG weldments of AA 2219 Al alloy reported in this paper establishes that postweld reaging of AA 2219 weldments in T62 condition enhances both strength and ductility.     

Comparing the impact of different rescheduling strategies on the entropic-related complexity of manufacturing systems

The primary objective of this paper is to compare five rescheduling strategies according to their effectiveness in reducing entropic-related complexity arising from machine breakdowns in manufacturing systems. Entropic-related complexity is the expected amount of information required to describe the state of the system. Previous case studies carried out by the authors have guided computer simulations, which were carried out in Arena 5.0 in combination with MS Excel. Simulation performance is measured by: (1) entropic-related complexity measures, which quantify: (a) the complexity associated with the information content of schedules, and (b) the complexity associated with the variations between schedules; and (2) mean flow time. The results highlight two main points: (a) the importance of reducing unbalanced machine workloads by using the least utilised machine to process the jobs affected by machine breakdowns, and (b) low disruption strategies are effective at reducing entropic-related complexity; this means that applying rescheduling strategies in order to manage complexity can be beneficial up to a point, which, in low disruption strategies, is included in their threshold conditions. The contribution of this paper is two-fold. First, it extends the application of entropic-related complexity to every schedule generated through rescheduling, whereas previous work only applied it to the original schedule. Second, recommendations are proposed to schedulers for improving their rescheduling practice in the face of machine breakdowns. Those recommendations vary according to the manufacturing organisations’ product type and scheduling objectives. Further work includes: (a) preparing a detailed workbook to measure entropic-related complexity at shop-floor level; and (b) extending the analysis to other types of disturbances, such as customer changes.     

Cyclization reaction in poly(acrylonitrile/itaconic acid) copolymer: An isothermal differential scanning calorimetry kinetic study

The kinetics of the cyclization reaction in the poly(acrylonitrile/itaconic acid) (PAN) copolymer in the temperature range 175–200°C was studied by isothermal differential scanning calorimetry (DSC). The reaction conforms to an n^th‐order autocatalytic model, with an overall order of 2. The kinetic parameters were derived by multiple regression analysis. The activation energy is 110.3 kJ/mol for the acid‐catalyzed reaction and 153.2 kJ/mol for the autocatalytic part. The autocatalysis indicates the catalysis of the nitrile group cyclization by the initially formed pyrimidine groups. The kinetic parameters were used to predict the reaction profile at a given temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 915–920, 2003     

Transparent Hydroxyapatite Ceramics through Gelcasting and Low-Temperature Sintering

Transparent hydroxyapatite (HAP) was prepared by sintering gel-cast powder compacts at 1000°C for 2 h; the resultant HAP material was studied using X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, and microhardness measurement. Nanoscale HAP crystallites were prepared using a precipitation method that involved calcium nitrate and ammonium dihydrogen orthophosphate solutions; the preparation was conducted at a temperature of 0°C. The precipitate was gel-cast and sintered at 1000°C in the form of a transparent ceramic that had a uniform grain size of 250 μm. The maximum Vickers microhardness obtained for a sample sintered at 1000°C was 6.57 GPa. The sintering behavior of gel-cast samples prepared from high-temperature-precipitated HAP was compared with that of material prepared at 0°C.     

A novel magnetic suspension cum linear actuator system forsatellite cryo coolers

Stirling cycle cryogenic coolers have been widely used for device cooling in satellites. Various types of magnetic bearings and linear actuators find application in such systems. The most widely used configurations have two-axis-radially-active suspension stations placed at either end of a reciprocating shaft in the compression and expansion sections. Separate or integral linear motors are provided in each section for axial shaft movement. It may be noted that such configurations are rather complicated and less reliable because of the presence of numerous electro-mechanical components, sensors and electronic servo channels. In this paper, a simple and reliable scheme is suggested which axially stabilizes and linearly perturbs the piston so that the need of a separate motor for axial actuation can be totally dispensed with. The piston is radially supported by passive repulsive bearings. In the axial direction, a servo actuator `balances' the piston and also actuates it bi-directionally. Implementation of this `bearing cum motor theme', reduces the number of electromechanical and electronic components required to operate the system and hence minimizes the chances of system failure. Apart from this, the system's power consumption is reduced and efficiency is improved as electrical heating losses caused by quiescent-operating currents are removed and electromagnetic losses on the moving parts are minimized. The necessary system parameters have been derived using finite element analysis techniques. Finally, the proposed design is validated by computer-aided system simulation     

Efficient cage structured polyhedral oligomeric silsesquioxane embedded poly(vinyl alcohol) membranes: Thermal degradation and mechanical stability in hydrated condition

In this work, the thermal degradation of functionalized cage structured polyhedral oligomeric silsesquioxane (POSS) incorporated poly(vinyl alcohol) (PVA) and poly(vinyl alcohol)-poly (ethylene oxide) (PEO) blend membranes were discussed. PVA-PEO/POSS and cross-linked PVA/POSS systems exhibited excellent improvement in thermal stability at lower loading of POSS as compared to pure PVA and uncross-linked PVA/POSS system. Uncross-linked PVA and PVA/POSS systems exhibited mainly two degradation steps. However, cross-linked PVA/POSS systems showed more degradation steps due to the formation of 3-dimentional network structure in the polymer. The mechanical stability of PVA/POSS and PVA-PEO/POSS systems at hydrated state were analyzed and observed a remarkable stability even in the wet condition.