Using a custom-FPGA architecture to extend the scale of atomistic magnetic spin simulations

New computational solutions are required to understand how atomic-scale properties affect magnetic behaviour at micrometer dimensions. We describe a field-programmable-gate-array (FPGA) based simulation of a dilute antiferromagnet with a large number of Ising spins using Glauber dynamics. The simple atomic model qualitatively reproduces experimental findings when scaled up to sufficiently large spatial dimensions, and provides insight into the finite size thresholds separating nanoscale from microscale behaviour. A real-time visualisation module was used to study the dynamics of the fractal domain structure and non-exponential relaxation mechanism. A performance comparison with contemporary GPU and CPU implementations suggests that a FPGA route is a competitive alternative.     

Multigraft copolymer superelastomers: Synthesis morphology, and properties

The synthesis of well-defined multigraft copolymers having a polydiene backbone with polystyrene side chains is briefly reviewed, with particular focus on controlling branch point spacing and branch point functionality. Use of living anionic polymerization and chlorosilane linking chemistry has led to the synthesis of series of materials having regularly spaced trifunctional (comb), tetrafunctional (centipede), and hexafunctional (barbwire) branch points. The morphologies of these materials were characterized by transmission electron microscopy and small-angle X-ray scattering, and it was found that the morphologies were controlled by the local architectural asymmetry associated with each branch point. Mechanical properties studies revealed that such multigraft copolymers represent a new class of thermoplastic elastomers (TPEs) with superior elongation at break and low residual strains as compared to conventional TPEs.     

Performance of two-hop infrastructure based multi-antenna regenerative relaying in Rayleigh fading channel

Cooperative relaying is considered as an effective technique to enlarge the coverage area and enhance the system capacity for the future wireless systems. In this paper, an infrastructure based multi-antenna cooperative relay network has been investigated. Closed form expressions of outage probability and average error rate have been derived, when the relay and the destination perform selection combining of the signals. The relay is assumed to operate in the adaptive decode and forward mode. The effect of number of antennas installed on the relay and their placement has also been studied.     

Reputation-based network selection mechanism using game theory

Current and future wireless environments are based on the coexistence of multiple networks supported by various access technologies deployed by different operators. As wireless network deployments increase, their usage is also experiencing a significant growth. In this heterogeneous multi-technology multi-application multi-terminal multi-user environment users will be able to freely connect to any of the available access technologies. Network selection mechanisms will be required in order to keep mobile users “always best connected” anywhere and anytime. In such a heterogeneous environment, game theory techniques can be adopted in order to understand and model competitive or cooperative scenarios between rational decision makers. In this work we propose a theoretical framework for combining reputation-based systems, game theory and network selection mechanism. We define a network reputation factor which reflects the network’s previous behaviour in assuring service guarantees to the user. Using the repeated Prisoner’s Dilemma game, we model the user–network interaction as a cooperative game and we show that by defining incentives for cooperation and disincentives against defecting on service guarantees, repeated interaction sustains cooperation.     

The combination of living radical polymerization and click chemistry for the synthesis of advanced macromolecular architectures

Since its introduction, click chemistry has received a considerable amount of interest. In this contribution, the term click chemistry and the reactions that fall under this term are briefly explained. The main focus of this review is on the application of click chemistry in conjunction with living radical polymerization for the synthesis of advanced macromolecular architectures. Therefore the most powerful living radical polymerization (LRP) techniques are discussed and an overview of click chemistry in the different synthetic schemes is given. A large number of examples are shown that include the synthesis of block copolymers, star-shaped polymers, surface modified particles, and polymer-protein conjugates. The enormous potential of LRP/click chemistry is probably best exemplified by the synthesis of different miktoarm star copolymers, to which a separate section is dedicated.     

Super-nucleation in nanocomposites and confinement effects on the crystallizable components within block copolymers, miktoarm star copolymers and nanocomposites

In this paper we reexamine recent results obtained by our group on the crystallization of nanocomposites and linear and miktoarm star copolymers in order to obtain some general features of their crystallization properties. Different nanocomposites have been prepared where a close interaction between the polymer matrix and the nano-filler has been achieved: in situ polymerized high density polyethylene (HDPE) on carbon nanotubes (CNT); and polycaprolactone (PCL) and poly(ethylene oxide) (PEO) covalently bonded to carbon nanotubes. In all these nanocomposites a “super-nucleation” effect was detected where the CNTs perform a more efficient nucleating action than the self-nuclei of the polymer matrix. It is believed that such a super-nucleation effect stems from the fact that the polymer chains are tethered to the surface of the CNT and can easily form nuclei. For polystyrene (PS) and PCL block copolymers, miktoarm star copolymers (with two arms of PS and two arms of PCL) were found to display more compact morphologies for equivalent compositions than linear PS-b-PCL diblock copolymers. As a consequence, the crystallization of the PCL component always experienced much higher confinement in the miktoarm stars case than in the linear diblock copolymer case. The consequences of the topological confinement of the chains in block copolymers and nanocomposites on the crystallization were the same even though the origin of the effect is different in each case. For nanocomposites a competition between super-nucleation and confinement was detected and the behavior was dominated by one or the other depending on the nano-filler content. At low contents the super-nucleation effect dominates. In both cases, the confinement increases as the nano-filler content increases or the second block content increases (in this case a non-crystallizable block such as PS). The consequences of confinement are: a reduction of both crystallization and melting temperatures, a strong reduction of the crystallinity degree, an increase in the supercooling needed for isothermal crystallization, a depression of the overall crystallization rate and a decrease in the Avrami index until values of one or lower are achieved indicating a nucleation control on the overall crystallization kinetics.     

Amphiphilic block copolymers by a combination of anionic polymerization and selective post-polymerization functionalization

Anionic polymerization is the oldest known living/controlled polymerization methodology that leads to well defined macromolecules. It has been also used, with considerable success, for the synthesis of amphiphilic block copolymers (AmBC), a class of functional copolymers having interesting self-assembling properties and high potential for applications in various technological fields. The use of mild and effective post-polymerization functionalization/chemical modification reactions on block copolymers has substantially increased the synthetic capabilities of anionic polymerization methodologies, toward the creation of a variety of AmBC. In this feature article we review work done on these directions in the last ten years. Some perspectives and future work on this particular field of polymer science are also discussed.     

Synthesis of glycopolymers via click reactions

This mini-review describes recent work in the field of glycopolymer synthesis, with a focus on methods that have employed “click chemistry” and controlled polymerization methodology. A variety of carbohydrates with clickable groups such as azide, alkyne, and thiol moieties provide new routes to glycopolymers. Several studies use copper catalyzed azide-alkyne cycloaddition (CuAAC) reactions to synthesize glycomonomers or to incorporate carbohydrates into a clickable polymeric backbone. Alternatively, there are many thiol based click reactions which provide metal-free synthesis, which are discussed in details.     

Electro-responsive transdermal drug delivery behavior of PVA/PAA/MWCNT nanofibers

The electro-responsive transdermal drug delivery system was prepared by electrospinning of poly(vinyl alcohol)/poly(acrylic acid)/multi-walled carbon nanotubes (MWCNTs) nanocomposites. The surface modification of MWCNTs was carried out by oxyfluorination to introduce the functional groups on the hydrophobic MWCNTs. The dispersion of MWCNTs and the compatibility with polymer matrices were improved by oxyfluorination. The MWCNT content and oxyfluorination condition played important roles in the swelling and drug release characteristics of nanofibers. The conductivity of nanofibers increased by increasing the content of MWCNTs and performing oxyfluorination with higher oxygen content. Uniform distribution of the oxyfluorinated MWCNTs in the nanofibers was crucial to the electro-responsive swelling and drug releasing behaviors of nanofibers.