Sonosynthesis of Microcellulose from Kenaf Fiber: Optimization of Process Parameters

Green composites using cellulose fibers as a reinforcement material provide a sustainable and renewable alternative to petroleum-based polymers. However, controlling the usage of chemicals and processing parameters to extract the cellulose could be sometimes difficult. Therefore, this study aims to optimize the conditions for extracting the microcellulose from kenaf fibers using central composite design (CCD), a statistical tool in design of experiments. Three factors and three levels were chosen for carrying out the analysis. The design was based on sodium hydroxide (NaOH) dosage, Sodium Chlorite (NaClO₂) dosage and sonication time as independent variables, while dependent variables were the fiber size and degradation point. Later, size responses were fitted using quadratic polynomial model and degradation responses using 2-factor interaction model (2FI). The R² values of 0.89 and 0.83 were obtained for the quadratic and the 2FI model, respectively. Further, surface morphology, thermal analysis, Fourier transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD) were also used for design validation. Optimal parameters for microcellulose extraction were found to be 0.15 g of NaOH at first stage, 4.6 mL of NaClO₂ at second stage, and 10 min of sonication during third stage.     

Evidence of irradiation‐induced crosslinking in miscible blends of poly(vinyl chloride)/epoxidized natural rubber in presence of trimethylolpropane triacrylate

Electron‐beam initiated crosslinking of a poly(vinyl chloride)/epoxidized natural rubber blend (PVC/ENR), which contained trimethylolpropane triacrylate (TMPTA), was carried out over a range of irradiation doses (20–200 kGy) and concentrations of TMPTA (1–5 phr). The gelation dose was determined by a method proposed by Charlesby. It was evident from the gelation dose, resilience, hysteresis, glass‐transition temperature (T_g), IR spectroscopy, and scanning electron microscopy studies that the miscible PVC/ENR blend underwent crosslinking by electron‐beam irradiation. The acceleration of crosslinking by the TMPTA was further confirmed in this study. Agreement of the results with a theory relating the T_g with the distance between crosslinks provided further evidence of irradiation‐induced crosslinking. The possible mechanism of crosslinking induced by the irradiation between PVC and ENR is also proposed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1914–1925, 2001     

Differentiated survivability with improved fairness in IP/MPLS-over-WDM optical networks

This paper addresses the priority-fairness problem inherent in provisioning differentiated survivability services for sub-lambda connections associated with different protection-classes in IP/MPLS-over-WDM networks. The priority-fairness problem arises because, high-priority connections requiring high quality of protection such as lambda level pre-configured lightpath protection are more likely to be rejected when compared to low-priority connections which may not need such a high quality of protection. A challenging task in addressing this problem is that, while improving the acceptance rate of high-priority connections, low-priority connections should not be over-penalized. We propose two solution-approaches to address this problem. In the first approach, a new inter-class backup resource sharing (ICBS) technique and a differentiated routing scheme (DiffRoute) are adopted. The ICBS is investigated in two methods: partial- and full-ICBS (p-ICBS and f-ICBS) methods. The DiffRoute scheme uses different routing criteria for the traffic classes. In the second approach, two rerouting schemes are developed. The rerouting schemes are applied with the DiffRoute and ICBS. The rerouting schemes employ inter-layer backup resource sharing and inter-layer primary-backup multiplexing for the benefit of high-priority connections, thus improving fairness. Our findings are as follows. (1) The application of p-ICBS and DiffRoute yields improved performance for high-priority connections. However, it shows penalized performance for low-priority connections. On the other hand, the collective application of f-ICBS and DiffRoute yields significantly improved performance for high-priority connections with no penalized performance as the performance of low-priority connections is also improved. (2) The rerouting schemes, when applied with the DiffRoute and ICBS methods, further improve the performance of high-priority traffic without significantly affecting the performance of other traffic.     

Hydrogel coating of RVNRL film by electron‐beam irradiation

The tackiness properties of radiation‐vulcanized natural rubber latex (RVNRL) film surfaces coated by various monomers were investigated in order to define the suitable hydrogels which reduce the tackiness of the film. In this context, different types of monomers, namely, N‐vinyl‐2‐pyrrolidone (NVP), N,N‐dimethylaminoethylamide (DMAEA), acrylic acid (AAc), n‐butyl acrylate (n‐BA), and 2‐hydroxyethyl methacrylate (HEMA) as well as the monomer mixtures were tried with varying degrees of success. Coating the RVNRL film with 80% HEMA/20% n‐BA by irradiation at 80 kGy using a low‐energy electron beam gave a remarkable reduction in the surface tackiness of the RVNRL film. Several other attempts were made such as priming the RVNRL film with acid and aluminum sulfate prior to coating, mixing the aluminum sulfate into the monomer mixtures, and dipping the partially wet RVNRL film into the monomer to enhance the wettability of the monomers with the film. The photomicrographs taken illustrate that the decrease in tackiness with the coating is due to the increase of the surface roughness at an 80‐kGy irradiation dose. The studies also revealed that the reduction in the contact angle and the increase in water absorption of the RVNRL film after irradiation are due to the formation of the hydrogel layer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1421–1428, 1999     

Channel Estimation in OFDM Systems Using a Controlled Superimposition of Training Sequences

This work pertains to the use of superimposed training (ST) for channel estimation in orthogonal frequency division multiplexing (OFDM) based systems. A time domain coherent averaging based channel estimator is derived from the least squares criterion. By exploiting the periodicity of the training sequences in the time domain and inserting zeros instead of data at some of the training sequence subcarrier locations depending on the desired estimation accuracy, a controlled superimposition technique is proposed. This method includes the flexibility to trade off between bandwidth efficiency and performance. The mean squared estimation error (MSEE) performance of such a system is mathematically analyzed and a training sequence selection criterion optimizing the same is proposed. The simulation performance of the scheme is presented in terms of the MSEE and the bit error rate (BER) of the OFDM system. Such a scheme is attractive in high data rate scenarios in closed loop OFDM systems.     

Novel high-voltage silicon-on-insulator MOSFETs

Novel lateral RESURF high voltage SOI MOSFETs capable of withstanding up to 400V are presented in this paper. The design optimization, fabrication and experimental results obtained on these devices are also presented. The devices are implementable using a CMOS-SOI compatible process.     

Bandwidth Partitioning and SINR Threshold Analysis of Fractional Frequency Reuse in OFDMA Cellular Networks for Real Time and Best Effort Traffic

To achieve high capacity in cellular networks, frequency reuse factor of unity is used. However, it suffers from heavy co-channel interference at cell edge regions. This leads to poor Signal to Interference plus Noise Ratio (SINR) and hence poor performance. fractional frequency reuse (FFR) is one of the methods being considered to improve cell edge performance. In this work we present the impact of SINR threshold and bandwidth partitioning on the successful deployment of FFR scheme. We have considered both real time (RT) and best effort (BE) traffic. In FFR, the total frequency resource is divided logically into cell center and cell edge user bands. However, while frequency resource is partitioned into two segments, the amount of bandwidth required by cell center and cell edge users is quite different and influences the system performance. We developed the semi analytical approach to evaluate the average bandwidth required by cell center and edge band users. From the analysis and simulation results it is seen that while grade of service (GoS) fair based method of choosing bandwidth partitioning ratio is best for RT traffic, while the only feasible method for BE traffic is dividing the bandwidth based on probability of a user to be in a given band which we termed as ‘Probability’ method.     

Effects of processing conditions on the mechanical and water absorption properties of resin transfer moulded kenaf fibre reinforced polyester composite laminates

This paper focuses on the mechanical and water absorption properties of kenaf fibre reinforced polyester laminates manufactured by resin transfer moulding. Varying processing conditions were considered as alternatives to fibre treatments, thereby potentially avoiding additional cost and complexity in the manufacturing process. Laminates were produced by altering fibre moisture content, mould temperature and mould pressure following injection. Tensile, flexural, impact and water absorption tests were conducted. Processing conditions were found to have little effect on properties except for pressurisation which increased tensile and flexural strength and decreased water absorption at low fibre volume fractions. Examinations using a scanning electron microscope showed that all the laminates failed by fibre pull-out.     

The mechanical properties of oxyfluorinated hybrids of glass fibre and polypropylene fibre

The mechanical properties of a low-cost system comprising orthophthalic polyester resin reinforced with hybrids of glass and polypropylene fibres were investigated. The fibres were oxyfluorinated to overcome the poor surface adhesion properties of polypropylene. Interlaminar shear tests, Izod-type impact tests and tensile tests were considered. It would be expected that increasing polypropylene fibre content corresponds with a decrease in mechanical properties due to the poor properties of polypropylene. Oxyfluorinated laminates containing approximately 25% and 50% polypropylene in the warp direction were, however, found to exhibit significant improvements in interlaminar shear strength, in peak shear stress under impact loading as well as in impact resistance over untreated glass fibre laminates. Scanning electron microscope images show that the reason for this improvement is that the interfacial bond between the polypropylene fibres and the resin is strengthened to such an extent that failure occurs within the polypropylene fibres rather than at the interface.     

Extension of the layer removal technique for the measurement of residual stresses in layered anisotropic cylinders

An extension of the layer removal technique is presented that allows the residual stresses within multilayered anisotropic pipes of any wall thickness to be determined. The method inherently satisfies the self-equilibrium requirement and limits the effects of measurement errors to the region local to the error. The thickness of each layer that is removed need not be uniform and is entirely independent of the thickness of each ply of material. Four example problems are considered. The first three allow results to be compared between the present method and previous work. The fourth problem demonstrates the method on a thick walled anisotropic pipe built up of +45°/-45° plies for which no solution was previously available.