Thermal characterization of high performance PBI and 6F polymers and their alloys

The effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo-oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000? and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be derived.     

Ethylene/styrene copolymerisation by homogeneous metallocene catalysts: experimental and molecular simulations using rac-ethylenebis(tetrahydroindenyl)MCl2 [M=Ti,Zr] systems

Styrene was copolymerised with ethylene using the catalyst systems [rac-Et(H₄Ind)₂TiCl₂]/MAO and [rac-Et(H₄Ind)₂ZrCl₂]/MAO. Keeping other experimental variables under control, we tested different styrene/ethylene ratios in the reactor feed. It was found that the titanium-based catalyst showed very low activity even for ethylene homopolymerisation. In contrast, the zirconium system achieved monomer polymerisation, incorporating small amounts of styrene. When the styrene/ethylene ratio was increased, both catalyst activity and the molecular weight of the resulting copolymers decreased. However, styrene incorporation into the copolymer increased as the styrene/ethylene ratio rose. To gain insight into the copolymerisation mechanisms at play, we undertook a computational study using a high-level hybrid DFT method (B3LYP). Agreement between the experimental and theoretical results was generally good, indicating the usefulness of combined experimental/theoretical studies for clarifying mechanisms of -olefin copolymerisation using organometallic systems.     

Secure sensors data acquisition and communication protection in eHealthcare: Review on the state of the art

Recent advances in hardware technology have led to the development of low cost, power efficient and more feature rich devices that are amongst the most critical parts of communication networks. These devices or sensors can now sense data with more accuracy, process it by themselves and send it to the neighboring node or the sink node. However, robust and reliable security mechanisms are not yet properly implemented on these sensors due to their limited energy and computation power. Sensors also play a very important role in eHealthcare systems where ubiquitous patient monitoring is performed. As data is generated from the sensor nodes, reliable, secure and attack-resistant data acquisition and transmission is important for an efficient eHealthcare systems. This survey focuses on security issues of sensors data acquisition and transmission protocols, describing their main security features and comparing them in the context of a secure eHealthcare system. A taxonomy of open issues and future challenges is also discussed with respect to specific security metrics described in the paper.     

Aerodynamic performance optimization for the rotor design of a hovering agricultural unmanned helicopter

The importance of using Agriculture unmanned helicopters (AUHs), especially for spraying pesticides and fertilizers on any terrain type to ensure crop yields, has been recently acknowledged. Apart from flying these helicopters at a super-low altitude and low speed, using an efficient and optimum rotor blade ensures a uniform and deep penetration of pesticide and fertilizers over a specified area. Accordingly, this work attempts to optimize the rotor blade of an AUH by using coupling statistics and several numerical techniques, including design of experiments, response surface method, and computational fluid dynamics. The experiments are designed using the central composite design method and by selecting the geometric variables that affect the aerodynamic performance of the rotor blade, including the root chord, tip chord, and angle of attack. The angle at the root and tip is optimized in order for the resulting twist to produce a uniform blade loading, achieve maximum lift, and minimize the required hover power. The required aerodynamic forces and limited availability of engine power are identified as constraints. The blade is optimized only when the helicopter is hovering at a persistent rotational speed, and the hover efficiency of the rotor blade with an optimal twist distribution is significantly higher than the baseline.     

Effect of various surface preparation techniques on the delamination properties of vacuum infused Carbon fiber reinforced aluminum laminates (CARALL): Experimentation and numerical simulation

Carbon fiber reinforced aluminum laminates (CARALL) are one of the aluminum based Fiber metal laminates (FMLs) which, due to their high strength to weight ratio and good impact resistance are greatly replacing aluminum alloys in aircraft structures. In this research work, interlaminate shear strength of Vacuum assisted resin transfer molding (VARTM) manufactured CARALL has been investigated. Numerical simulation model incorporated with real time material data has been developed to predict the delamination behavior of CARALL laminates. Standard CARALL specimens with different surface morphologies were prepared by electric discharge machining, mechanical, chemical and electrochemical surface treatments. T-peel tests were carried out according to standard ASTM D1876-08 to find out inter laminate shear strength. FMLs made out of mechanically, chemically and electrochemically cleaned metal sheets depicted high interlaminate shear strength. SEM micrographs of failed surfaces verify the high adhesive strength of epoxy. Developed numerical simulation model accurately predicts the delamination behavior of CARALL as observed during experimentation.     

Comparison of Performance of Packet Scheduling Algorithms in LTE-A HetNets

The concept of usage of heterogeneous networks (HetNets) is about improving the LTE system performance by increasing the capacity and coverage of the Macro cell. In this paper, a performance comparison of various packet scheduling algorithms such as Proportional Fair, Maximum Largest Weighted Delay First and Exponential/Proportional Fair is studied in detail in the HetNets environment. The key performance indicators such as throughput, packet loss ratio, delay and fairness are considered to judge the performance of the scheduling algorithms. Various strategies such as increasing the number of Pico cells in the cell edge were used in the simulation for the performance evaluation study. The results achieved through various simulations show that adding Pico cells to the existing Macros enhances the overall system performance in addition to the various scheduling algorithms implemented in Macros. For reader’s convenience, various types of graphs have been used to represent the simulation results to better understand the performance metrics of various scheduling algorithms. Simulation results shows that overall system gain has increased because of adding Picos and thereby providing better coverage in the cell edge areas and thereby increasing the capacity of the network to provide better quality of service.     

Self-doping Effects on the Superconducting Properties of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = Bi, Hg, Nb, Pd, Li, Na, K)

The effect of self-doping and substitution of elements of higher and lower electronegativity, such as Bi, Hg, Nb, Pd, Li, Na, K, on the superconducting properties of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ with x=0.25 is investigated. These experiments demonstrated that the elements of lower electronegativity such as Li, Na, and K can easily liberate their outer most s-electron that could be supplied to the conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ superconductor, and as a result, we get enhanced superconducting properties. However, highly electro-negative elements hinder the transfer of carriers from charge reservoir layer to the conducting CuO₂ planes and promote inferior superconducting properties. In the present studies, we have investigated the effect of post-annealing in nitrogen and oxygen atmospheres for optimizing the carriers in conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ (M=Bi,Hg,Nb,Pd,Li,Na,K) superconductor. These studies are important since the density of carriers in the conducting CuO₂ planes determines the Fermi-vector k _F and Fermi velocity v _F of the carriers, which ultimately brings about the final superconducting state of the system.      

Generation of electrical energy using lead zirconate titanate (PZT-5A) piezoelectric material: Analytical,numerical and experimental verifications

Energy harvesting is the process of attaining energy from the external sources and transforming it into usable electrical energy. An analytical model of piezoelectric energy harvester has been developed to determine the output voltage across an electrical circuit when it is forced to undergo a base excitation. This model gives an easy approach to design and investigate the behavior of piezoelectric material. Numerical simulations have been carried out to determine the effect of frequency and loading on a Lead zirconate titanate (PZT-5A) piezoelectric material. It has been observed that the output voltage from the harvester increases when loading increases whereas its resonance frequency decreases. The analytical results were found to be in good agreement with the experimental and numerical simulation results.