Supporting constant-bit-rate-encoded MPEG-2 transport over local ATM networks

As one of the fast-developing switch-based high-speed networks, asynchronous transfer mode (ATM) is a promising network standard which may satisfy various requirements of multimedia computing. The Moving Picture Experts Group (MPEG) standard was designed to support full motion video stored on digital storage media at compression ratios up to 200:1. MPEG-2 is the second development phase of the MPEG standard and is designed for higher resolutions (including but not restricted to interlaced video) and higher bit rates (up to 20 Mbits/s). In this paper, the ATM adaptation layer type 5 (AAL-5) protocol was used to encapsulate constant-bit-rate-encoded MPEG-2 transport packets because of AAL-5's general availability. However, there is a mismatch of size between MPEG-2's transport packets (188 bytes) and ATM AAL-5's protocol data units (up to 65 535 bytes). In this paper, we examine and analyze four different packing schemes, 1TP, 2TP, nTP-Tight, and nTP-Loose (the scheme we propose), which encapsulated a certain number of MPEG-2 transport packets into one AAL-5 PDU. nTP-Loose scheme is proposed to have (1) better end-to-end performance than schemes 1TP and 2TP, (2) better error-recovery capability than scheme nTP-Tight, and (3) the same buffer requirement as scheme 2TP. A Power Macintosh ATM platform was used to identify the range of possible ways of packing MPEG-2 transport packets into one ATM AAL-5 PDU, when schemes with more than two MPEG-2 transport packets are chosen. Based on the test results, 10 or 12 MPEG-2 transport packets, which can yield throughputs of 70.36 and 78.98 Mbits/s, respectively, are recommended. Fast forward and backward playing of MPEG-2 movies (several times the video display speed) can be easily achieved via ATM networks.     

Synthesis,characterization, and reactivity ratios of copolymers derived from 4‐nitrophenyl acrylate and n‐butyl methacrylate

Free‐radical copolymerization of 4‐nitrophenyl acrylate (NPA) with n‐butyl methacrylate (BMA) was carried out using benzoyl peroxide as an initiator. Seven different mole ratios of NPA and BMA were chosen for this study. The copolymers were characterized by IR, ¹H‐NMR, and ¹³C‐NMR spectral studies. The molecular weights of the copolymers were determined by gel permeation chromatography and the weight‐average (M _w) and the number‐average (M _n) molecular weights of these systems lie in the range of 4.3–5.3 × 10⁴ and 2.6–3.0 × 10⁴, respectively. The reactivity ratios of the monomers in the copolymer were evaluated by Fineman–Ross, Kelen–Tudos, and extended Kelen–Tudos methods. The product of r₁, r₂ lies in the range of 0.734–0.800, which suggests a random arrangement of monomers in the copolymer chain. Thermal decomposition of the polymers occurred in two stages in the temperature range of 165–505°C and the glass transition temperature (T_g) of one of the systems was 97.2°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1817–1824, 2003     

Prediction of mean drop size in batch agitated vessels

A correlation is proposed for prediction of mean drop size in agitated vessels in the two major hydrodynamic regimes of importance as observed in this study covering a wide range of holdup from 0.01 to 0.5 and impeller Weber numbers from 35–200,000.     

Synthesis and characterization of 1,1-bis(3-methyl-4-hydroxy phenyl)cyclohexane polybenzoxazine–organoclay hybrid nanocomposites

Typical high-performance polybenzoxazines were prepared from benzoxazines based on 1,1-bis(3-methyl-4-hydroxy phenyl) cyclohexane, paraformaldehyde and three distinctive aromatic diamines, namely 4,4’-diaminodiphenylmethane, 4,4’-diaminodiphenylether and 4,4’-diaminodiphenylsulfone, through ring-opening self-polymerization upon heating. The formation of benzoxazines was confirmed by Fourier transform infrared, ¹H and ¹³C nuclear magnetic resonance spectra. Polybenzoxazine–clay hybrid nanocomposites were prepared by a solvent method using polybenzoxazine precursors and organoclay (OMMT) (up to 5 wt.%). The hybrid mixture was subjected to ultrasonication for effective blending. The thermal properties of the resulting polybenzoxazine–clay nanocomposites were studied using differential scanning calorimetry and thermogravimetric analysis. The dispersion of OMMT in the polybenzoxazine and nanostructure of the composites was confirmed by X-ray diffraction analysis. The d spacing of the organoclay interlayers was found to be increased from 1.69 to 2.10 nm. Thermal decomposition temperatures of the nanocomposites were in the range 294–637 °C. These nanocomposites exhibited a high char yield relative to unfilled polybenzoxazines depicting interfacial interactions between the organic and inorganic phases. The homogeneous morphological behavior was studied by scanning electron microscopy.     

Thermo mechanical behaviour of unsaturated polyester toughened epoxy–clay hybrid nanocomposites

The intercrosslinked networks of unsaturated polyester (UP) toughened epoxy–clay hybrid nanocomposites have been developed. Epoxy resin (DGEBA) was toughened with 5, 10 and 15% (by wt) of unsaturated polyester using benzoyl peroxide as radical initiator and 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of unsaturated polyester with the epoxy resin was carried out thermally in presence of benzoyl peroxide-radical initiator and the resulting product was analyzed by FT-IR spectra. Epoxy and unsaturated polyester toughened epoxy systems were further modified with 1, 3 and 5% (by wt) of organophilic montmorillonite (MMT) clay. Clay filled hybrid UP-epoxy matrices, developed in the form of castings were characterized for their thermal and mechanical properties. Thermal behaviour of the matrices was characterized by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Mechanical properties were studied as per ASTM standards. Data resulted from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improved the thermal stability and impact strength to an appreciable extent. The impact strength of 3% clay filled epoxy system was increased by 19.2% compared to that of unmodified epoxy resin system. However, the introduction of both UP and organophilic MMT clay into epoxy resin enhanced the values of mechanical properties and thermal stability according to their percentage content. The impact strength of 3% clay filled 10% UP toughened epoxy system was increased by 26.3% compared to that of unmodified epoxy system. The intercalated nanocomposites exhibited higher dynamic modulus (from 3,072 to 3,820 MPa) than unmodified epoxy resin. From the X-ray diffraction (XRD) analysis, it was observed that the presence of d ₀₀₁ reflections of the organophilic MMT clay in the cured product indicated the development of intercalated clay structure which in turn confirmed the formation of intercalated nanocomposites. The homogeneous morphologies of the UP toughened epoxy and UP toughened epoxy–clay hybrid systems were ascertained from scanning electron microscope (SEM).     

Synthesis and characterization of Pt supported on multiwalled carbon nanotubes for improved catalytic performance in fuel cell applications

Journal of Porous Materials - Commercially available multiwalled carbon nanotubes (MWCNTs) were functionalized using a mixture of HNO3 and H2SO4 in refluxing condition under three different...     

Preparation and Characterization of Footwear Soling Materials Based on Biodegradable Polyurethane

The aim of this research work is to prepare biodegradable polyurethane composites and study their physical, mechanical, thermal, and biodegradation properties. Rigid biodegradable polyester-based polyurethane was synthesized by reacting excess of isocyanate with poly(ε-caprolactone)diol to obtain prepolymer which was then reacted with chain extender. The polyurethane composites are prepared with nanoclay and titanium(IV)oxide nanopowder in different concentrations, and polyurethane containing 2% w/w of nanopowder had shown better properties. Biodegradation studies showed that the developed polyurethane materials when used as shoe soles will retain their strength while storage and use, but will decompose only after disposal into the environment.