Crystallization behavior of polypropylene in polypropylene/nylon 6 blend

This article describes the crystallization behavior of polypropylene (PP) in the presence of a crystallizable polymer, namely, nylon 6, in the binary blend of PP/nylon 6 in the composition range from 0 to 30 wt % of nylon 6 content in the blend. The crystallization behavior was studied through variation of the crystallinity with the blend composition and changes in the crystallization exotherms were recorded by differential scanning calorimetry (DSC) and the spherulite morphology was observed via polarized light microscopy (PLM). Comparison of the crystallization exotherms and melting endotherms revealed some differences which are attributed to the role of a sufficiently high thermal energy of the nylon 6 crystals on the melting of PP. The crystallinity of PP decreased in the presence of nylon 6, whereas the crystallinity of nylon 6 increased considerably in the presence of PP. The rate of nucleation of PP on addition of nylon 6 decreased rapidly in the region 0–10 wt % nylon 6 content, and, thereafter, at a higher nylon 6 content, decrease of the nucleation rate was relatively slow. PLM observation revealed the presence of composite spherulites with PP spherulites grown on the surface of the already‐formed nylon 6 spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1153–1161, 1999     

Guest–host interaction in ferroelectric liquid crystal–nanoparticle composite system

The present paper deals with the characterization of a ferroelectric liquid crystal–nanoparticle (FLC–NP) composite system. The dielectric, electrical and polarization property of the FLC–NP composite system have been studied as a function of temperature and frequency. Ferroelectric Cu-doped ZnO (Cu–ZnO) nanoparticles have been added to the pure ferroelectric liquid crystal (FLC) Felix 17/100. The nanoparticles are bigger in size as compared to FLC molecules; therefore, they distort the existing geometry of FLC matrix and set up an antiparallel correlation with the dipole moments of the host FLC molecules. This antiparallel correlation of guest–host geometry reduces the net ferroelectricity of the composite system and modifies all the physical properties of the pure FLC. The change in properties has been analysed and explained in the light of guest–host interaction.     

A BER Based Selection Combining Protocol for Adaptive Cooperative Cognitive Radios

This paper illustrates the performance of bit error rate based selection combining (BER-SC) protocol for adaptive cooperative cognitive radios. In the proposed framework, the unlicensed (i.e. secondary) system utilizes an adaptive mode of transmission to help the licensed (i.e. primary) system to achieve the desired quality of service in exchange for opportunistic spectrum access. The total transmission is divided in two phases. In Phase I, the primary transmitter (PT) broadcasts the data to the primary receiver (PR), which is overheard by the secondary transmitter (ST) and secondary receiver (SR). In Phase II, ST decodes the primary data and linearly combines its own data with the primary data. Using M-QAM the combined data is adaptively modulated, where M = 4, 16 or 64 depending on the received channel feedback, and relayed to PR and SR. At PR, BER-SC is employed to retrieve the primary data, and at SR interference cancellation is used to retrieve the secondary data. The analytical expressions are derived for the BER and the outage probability. The obtained results demonstrate the higher performance gains for both primary and secondary system by using adaptive mode of transmission at ST and BER-SC at PR.

     

Some Thermodynamic Aspects of the Oxides of Chromium

To understand Cr emissions from slag melts to a vapor phase, an assessment of the stabilities of the chromium oxides at high temperatures has been carried out. The objective of the present study is to present a set of consistent data corresponding to the thermodynamic properties of the oxides of chromium, with special reference to the emission of hexavalent chromium from slags. In the current work, critical analysis of the experimental data available and a third analysis in the case of Cr₂O₃ have been carried out. Commercial databases, Fact Sage and ThermoCalc along with NIST-JANAF Thermochemical Tables, have been used for the analysis and comparisons of the results that are presented. The significant discrepancies in the available data have been pointed out. The data from NIST-JANAF Thermochemical Tables have been found to provide a set of consistent data for the various chromium oxides. An Ellingham diagram and the equations for the ΔG° (standard Gibbs free energy change) of formation of CrO _x have been proposed. The present analysis shows that CrO₃(g) is likely to be emitted from slag melts at high oxygen partial pressures.     

Bailout forward contracts for edge-to-edge internet services

Despite the huge success of the Internet in providing basic communication services, its economic architecture needs to be upgraded so as to provide end-to-end guaranteed or more reliable services to its customers. Currently, a user or an enterprise that needs end-to-end bandwidth guarantees between two arbitrary points in the Internet for a short period of time has no way of expressing its needs. To allow these much needed basic services, we propose a single-domain edge-to-edge (g2g) dynamic capacity contracting mechanism, where a network customer can enter into a bandwidth contract on a g2g path at a future time, at a predetermined price. For practical and economic viability, such forward contracts must involve a bailout option to account for bandwidth becoming unavailable at service delivery time, and must be priced appropriately to enable Internet Service Providers (ISPs) manage risks in their contracting and investments. Our design allows ISPs to advertise point-to-point different prices for each of their g2g paths instead of the current point-to-anywhere prices, allowing discovery of better end-to-end paths, temporal flexibility and efficiency of bandwidth usage. We compute the risk-neutral prices for these g2g bailout forward contracts (BFCs), taking into account correlations between different contracts due to correlated demand patterns and overlapping paths. We apply this multiple g2g BFC framework on network models with Rocketfuel topologies. We evaluate our contracting mechanism in terms of key network performance metrics like fraction of bailouts, revenue earned by the provider, and adaptability to link failures. We also explore the tradeoffs between complexity of pricing and performance benefits of our BFC mechanism.     

Modification of Tribological Properties of Silicon by Boron Ion Implantation

Friction and wear properties of silicon used in the fabrication of microelectromechanical systems (MEMS) are important for their long-term reliability. In the present study, the authors have implanted single-crystal and polycrystalline silicon wafers with boron ions to improve their mechanical and tribological properties. The authors have studied the effects of ion implantation on the crystallinity, microstructure, nanohardness, and friction and wear properties and have found that silicon remains crystalline after ion bombardment at doses up to 2 × 10¹⁷ ions.cm^?2 but with a large amount of defects. The ion bombardment modifies elastic/plastic deformation characteristics and crack nucleation that occurs during indentation. There is a minor increase, ? 10-15 percent, in the nanohardness as a result of boron-ion implantation. Ion bombarded single-crystal silicon exhibits very low friction (0.05) and low wear factor (10^?6 mm³·N^?1m^?1) while slid against a 52100 steel ball. The coefficient of friction of bombarded silicon in dry air and dry nitrogen is even lower.