Effect of silica nanoparticles on reinforcement of poly(phenylene ether) based thermoplastic elastomer

Reinforcement of a novel poly(phenylene ether) (PPE) based thermoplastic elastomer (TPE), i.e., styrene-ethylene-butylene-styrene (SEBS)/ethylene vinyl acetate (EVA) and PPE-polystyrene (PS), was studied to develop a reinforced thermoplastic elastomer or thermoplastic vulcanizate (TPV). An effort was made to reinforce selectively the elastomeric dispersed phase of EVA by silica nanoparticles and silica sol-gel precursors, like alkoxy orthosilanes, using twin-screw extrusion and injection molding processes. Improvement of tensile strength and percent elongation at break was observed both with silica nanoparticles and tetraethoxy orthosilane (TEOS). Addition of TEOS transformed the dispersed EVA lamellar morphology into semispherical domains as a consequence of possible crosslinking. Soxhlet extraction was done on the silica and TEOS reinforced materials. The insoluble residues collected from both the silica and TEOS reinforced samples were analyzed in detail using both morphological and spectroscopic studies. This extensive study also provided an in-depth conceptual understanding of the PPE based TPE behavior upon reinforcement with silica nanoparticles and silica sol-gel precursors and the effect of reinforcement on recycling behavior.     

Growth and Luminescence of Polytypic InP on Epitaxial Graphene

Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO₂/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer‐sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc‐blende and wurtzite phases, forming a type‐II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano‐cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc‐blende phase and the indirect transitions at ≈ 1.31 eV originating from the alternating zinc‐blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO₂/Si substrate, show optical transition across the gap of the wurtzite phase at ≈ 1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices.     

Reductions between disjoint NP-Pairs

Disjoint NP-pairs are pairs (A, B) of nonempty, disjoint sets in NP. We prove that all of the following assertions are equivalent: There is a many-one complete disjoint NP-pair; there is a strongly many-one complete disjoint NP-pair; there is a Turing complete disjoint NP-pair such that all reductions are smart reductions; there is a complete disjoint NP-pair for one-to-one, invertible reductions; the class of all disjoint NP-pairs is uniformly enumerable. Let A, B, C, and D be nonempty sets belonging to NP. A smart reduction between the disjoint NP-pairs (A, B) and (C, D) is a Turing reduction with the additional property that if the input belongs to A B, then all queries belong to C D. We prove under the reasonable assumption that UP ∩ co-UP has a P-bi-immune set that there exist disjoint NP-pairs (A, B) and (C, D) such that (A, B) is truth-table reducible to (C, D), but there is no smart reduction between them. This paper contains several additional separations of reductions between disjoint NP-pairs. We exhibit an oracle relative to which DistNP has a truth-table-complete disjoint NP-pair, but has no many-one-complete disjoint NP-pair.     

“MeshUp”: Self-organizing mesh-based topologies for next generation radio access networks

The phenomenal growth in wireless technologies has brought about a slew of new services. Incumbent with the new technology is the challenge of providing flexible, reconfigurable, self-organizing architectures which are capable of catering to the dynamics of the network, while providing cost-effective solutions for the service providers. In this paper, we focus on mesh-based multi-hop access network architectures for next generation radio access networks. Using short, high bandwidth optical wireless links to interconnect the various network elements, we propose a non-hierarchical, multi-hop access network framework. We study two generic family of mesh-based topologies: GPeterNet, a graph theoretic framework, and FraNtiC, a fractal geometric architecture, for arbitrary access network deployments. The performance of these topologies is analyzed in terms of different system metrics – topological robustness and reliability, system costs and network exposure due to failure conditions. Our analysis shows that a combination of different mesh-based multi-hop access topologies, coupled with emerging wireless backhaul technologies, can cater carrier-class services for next generation radio access networks, providing significant advantages over existing access technologies.     

Compositional analysis for verification of parameterized systems

Many safety-critical systems that have been considered by the verification community are parameterized by the number of concurrent components in the system, and hence describe an infinite family of systems. Traditional model checking techniques can only be used to verify specific instances of this family. In this paper, we present a technique based on compositional model checking and program analysis for automatic verification of infinite families of systems. The technique views a parameterized system as an expression in a process algebra (CCS) and interprets this expression over a domain of formulas (modal mu-calculus), considering a process as a property transformer. The transformers are constructed using partial model checking techniques. At its core, our technique solves the verification problem by finding the limit of a chain of formulas. We present a widening operation to find such a limit for properties expressible in a subset of modal mu-calculus. We describe the verification of a number of parameterized systems using our technique to demonstrate its utility.     

DPSM modeling for studying interaction between bounded ultrasonic beams and corrugated plates with experimental verification

Periodically corrugated structures play an important role in the field of vibration control and for designing structures with desired acoustic band gaps. Analytical solutions for corrugated plates are available for well-defined, smooth corrugations, such as sinusoidal corrugations that are not very common in the real world. Often corrugated plates are fabricated by cutting grooves at regular intervals in a flat plate. No analytical solution is available to predict the wave propagation behavior in such a periodically corrugated plate in which the equation of the plate surface changes periodically between a planar fiat surface and a nonplanar parabolic groove. This problem is solved here for steady-state case by a newly developed semianalytical technique called distributed point source method (DPSM), and the theoretical predictions are compared with the experimental results generated by reflecting a bounded 2.25 MHz ultrasonic beam by a fabricated corrugated plate. The main difference that is observed in the reflected beam profile from a flat plate and a corrugated plate is that the back-scattering effect is much stronger for the corrugated plate, and the forward reflection is stronger for the flat plate. The energy distribution inside the corrugated plate also shows backward propagation of the ultrasonic energy.     

Anomalous mechanical behavior upon recycling of poly(phenylene‐ether)‐based thermoplastic elastomer

Recycling of thermoplastic elastomers based on poly (phenylene ether) (PPE) was studied in detail. The quaternary blend comprising of styrene–ethylene–butylene–styrene (SEBS)/ethylene vinyl acetate (EVA)/PPE‐PS (polystyrene) showed improvement in mechanical properties upon recycling, which was correlated with the formation of crosslinked network in the system. Presence of crosslinked network was confirmed by the gel content analysis. The blend components involved in the crosslinking were evaluated by gel morphology analysis. Fourier transform infrared spectroscopy revealed the chemical composition of the crosslinked gel. Crosslinking mechanism was established based on the reactivity of allylic EVA radical during recycling. Rheological study supported the notion of crosslinking upon recycling that resulted in higher storage modulus (G′) as a manifestation of restrained flow by network formation. On the basis of the earlier data, a reaction mechanism for crosslinking was proposed. Finally, structure–property correlation was developed through morphological, chemical, and rheological analysis to understand the anomalous enhancement in mechanical properties upon recycling. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers