Surface modification of polypropylene film by grafting with vinyl monomers for the attachment of chitosan

Polypropylene (PP) film activated by corona discharge treatment was grafted with methyl methacrylate (MMA) and acrylic acid (AA). The grafted PP was characterized by spectral, thermal analysis and swelling behavior which confirmed the occurrence of the grafting. The water vapor and oxygen permeability (OTR and WVTR) as well as the mechanical properties have been enhanced by grafting with both AA and MMA. The grafted PP was further immobilized with chitosan (CS) using ceric ammonium nitrate (CAN) as an initiator under ultraviolet radiation. The chitosan immobilized grafted film was characterized by FTIR, mechanical properties, thermal properties and swelling measurements. Scanning electron microscope (SEM) confirmed that the CS is bonded to the grafted PP film. The CS modified PP film has acquired enhanced antibacterial and antifungal properties.     

Space Vector Modulation for Low Switching Frequency Current Source Converters With Reduced Low-Order Noncharacteristic Harmonics

High-power current source converters (CSCs) are usually implemented with gate turn off thyristors (GTOs) or integrated gate commutated thyristors (IGCTs) that present a maximum switching frequency of a few kilohertz. Space vector modulation (SVM) offers a very elegant way of generating CSC gating signals online with increased gain and reduced switching frequency. However, for very low switching frequency, SVM results in low-order (5th and 7th) noncharacteristic harmonics complicating the design of the input filter. The reduction of the magnitude of these harmonics has been sought mostly through new sequences of space vectors (states) that present better performance for different ranges of modulation index and power factor. Moderate improvement can be obtained by calculating the statespsila on times for the reference vector in the middle of an SVM cycle. This paper proposes calculating the statespsila on times as the reference vector rotates. Simulation results show that this approach results in a significant reduction in the harmonic distortion of these two components, which, for a selected sequence of states, can be limited to 0.3% of the fundamental component as the modulation index varies from 0.05 to 1.0. Experimental results obtained with a digital signal processor development kit are also provided to show the superior performance of the proposed techniques.     

Increase of open‐cell content by plasticizing soft regions with secondary blowing agent

This article describes the effects of n‐butane mixed with primary CO₂ as a secondary blowing agent on the cell‐population density, the volume expansion ratio, and the open‐cell content of low‐density polyethylene (LDPE) and LDPE/polystyrene (PS) blends in extrusion. With the plasticizing effect of n‐butane, a high open‐cell content (up to 100%) over a wide range of processing temperatures was successfully achieved. POLYM. ENG. SCI., 45:1445–1451, 2005. © 2005 Society of Plastics Engineers     

Creep Analysis of Axially Loaded Fiber Reinforced Polymer-Confined Concrete Columns

An analytical model is developed to study the time-dependent behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) and fiber-wrapped concrete columns (FWCC) under sustained axial loads. The model utilizes the double power law creep function for concrete in the framework of rate of flow method, and the linear viscoelastic creep model for FRP. It follows geometric compatibility and static equilibrium, and considers the effects of sealed concrete, multiaxial state of stresses, creep Poisson’s ratio, stress redistribution, variable creep stress history, and creep rupture. The model is verified against previous creep tests by the writers on FWCC and CFFT columns. It is then used to study the practical design parameters that may affect creep of FRP-confined concrete under service loads, or lead to creep rupture at high levels of sustained load. Creep of FWCC is shown to be close to that of sealed concrete of the same mix, as the effect of confinement on creep of concrete is not very significant. CFFT columns, on the other hand, creep much less than FWCC, mainly due to axial stress redistribution. As the stiffness of the tube increases relative to the concrete core, larger stress redistributions take place further reducing the creep. However, there is a threshold, beyond which, stiffer tubes would not significantly lower the creep of concrete. Creep rupture life expectancy of CFFT columns is shown to be quite acceptable.     

Minimize Low-Order Harmonics in Low-Switching-Frequency Space-Vector-Modulated Current Source Converters With Minimum Harmonic Tracking Technique

Gate turnoffs (GTOs) are usually used in high-power current source converters (CSCs), i.e., rectifiers and inverters. Space vector modulation (SVM) technique for CSC is established by dividing ac-side line current cycle into six sectors. Each sector is divided into a certain number of SV cycles. SV cycle is divided into three states: two active and one zero state. For low switching frequency as required by GTOs, the SVM technique generates fifth and seventh harmonics (HD_5-7) in the CSC ac-side current. Minimal reduction in HD_5-7 was achieved with certain states sequence inside the SV cycle. Moderate reduction in HD_5-7 was obtained by calculating states on -times at once in the middle of each SV cycle. In this paper, larger reduction in HD_5-7 at CSC ac-side current is achieved by new techniques for calculating states on-times. First, two straightforward techniques are proposed. One calculates states on-times from SVM equations in the middle of each state on-time. The other calculates all states on -times when the state changes from one active state to the other. Both techniques are effective in reducing HD_5-7. Then, minimum harmonics tracking (MHT) technique for calculating states on-times in SVM CSC is proposed. Tracking technique adjusts states on-times once per four ac-side line current cycles to give the least HD_5-7. In CSC with a large overlap period, power factor affects HD_5-7, so two-variables MHT technique for both active states on-times inside SV cycle is proposed to give the least HD_5-7. Also, a variable perturbation tracking technique is proposed to reduce transient time with unperturbed steady-state operation. Finally, experimental investigations and obstacles are introduced.     

Graft copolymerization of itaconic acid onto chitin and its properties

Modification of chitin by grafting with itaconic acid (IA) was carried out using potassium persulfate as redox initiator. In complimentary experiments, grafting was performed using γ‐radiation. Grafting was confirmed by FTIR spectroscopy. The effect of monomer concentration, initiator concentration and copolymerization temperature on the percentage of grafting were studied. The effect of radiation dose was also investigated. Values for percentages of grafting of up to 300 % were reached. It was observed that the percentage of grafting increased with increasing monomer concentration and showed a tendency to level off at IA concentration of 0.1 mol l^?1. The percentage of grafting increased with temperature up to 60 °C and then decreased. The solubility of the grafted chitin was studied in organic and inorganic solvents. The complexation of the grafted chitin with some cations, namely copper, nickel, cobalt, zinc and lead, was also investigated. The metal uptake was measured by UV spectroscopy. Thermogravimetric analysis of the grafted chitin was also studied. Copyright © 2004 Society of Chemical Industry     

Endobronchial intubation causes an immediate increase in peak inflation pressure in pediatric patients

Our purpose was to determine whether endobronchial intubation always causes an immediate increase in peak inflation pressure and, if so, the magnitude of the increase. Fourteen children scheduled for central line placement for prolonged antibiotic administration comprised the study group. After routine premedication and induction of anesthesia (halothane in oxygen), an endotracheal tube was inserted, and its position was verified by auscultation and fluoroscopy. Children were mechanically ventilated using a preset volume pressure-limited ventilator with a 5-L fresh gas flow. All children received a constant tidal volume using a similar circuit, similar tubing, and a similar compression volume. The lowest peak inflation pressure to deliver a tidal volume of 15 mL/kg was used. After adjusting the respiratory rate (end-tidal CO2 30 mm Hg) and anesthetic level (halothane end-tidal 1.2%), the peak inflation pressure at this endotracheal position was recorded. The endotracheal tube was advanced into a bronchus, the position was verified as above, and peak inflation pressure was recorded. The endobronchial tube was then pulled back into the trachea, and placement of the central line proceeded. The peak inflation pressure at the endobronchial position was significantly greater than the peak inflation pressure at the endotracheal position (P < 0.0001). The increase was instantaneous at the endobronchial position. Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation. Implications: Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation.