Issues in multi-media information networks

In an integrated service environment, where users exchange various types of aural and visual information, networks should appear friendly to its users providing tools for management of multi-media information. Networks should also efficiently satisfy diverse performance requirements of different information being exchanged.In this paper we present new architecture for integrated service networks being investigated and developed by the Distributed Computation and Communication Group at the Department of Computer Science in the Columbia University. Research efforts are devoted to developing both (1) document management software to allow users to manipulate and relate text/graphics/voice information in a dynamic way, and (2) a tree network architecture for reliable and efficient exchange of multi-media information

Dynamics of vitrimers: defects as a highway to stress relaxation

We propose a coarse-grained model to investigate stress relaxation in star-polymer networks induced by dynamic bond exchange processes. We show how the swapping mechanism, once activated, allows the network to reconfigure, exploring distinct topological configurations, all of them characterised by complete extent of reaction. Our results reveal the important role played by topological defects in mediating the exchange reaction and speeding up stress relaxation. The model provides a representation of the dynamics in vitrimers, a new class of polymers characterized by bond swap mechanisms which preserve the total number of bonds, as well as in other bond-exchange materials.Comment: 5 pages, 5 figures, with 6 pages SI appende

Distributed and Load-Adaptive Self Configuration in Sensor Networks

Proactive self-configuration is crucial for MANETs such as sensor networks, as these are often deployed in hostile environments and are ad hoc in nature. The dynamic architecture of the network is monitored by exchanging so-called Network State Beacons (NSBs) between key network nodes. The Beacon Exchange rate and the network state define both the time and nature of a proactive action to combat network performance degradation at a time of crisis. It is thus essential to optimize these parameters for the dynamic load profile of the network. This paper presents a novel distributed adaptive optimization Beacon Exchange selection model which considers distributed network load for energy efficient monitoring and proactive reconfiguration of the network. The results show an improvement of 70% in throughput, while maintaining a guaranteed quality-of- service for a small control-traffic overhead

Synthesis and Characterization of Covalent Adaptable Networks Comprised of Dynamic Imine and Aminal Covalent Bonds

The dissertation is about the design, synthesis and characterization of materials comprised of covalent adaptable networks (CANs). There are three chapters within this dissertation. Chapter 1 contains a short overview of conventional thermosets and thermoplastics. A new strategy of combining advantages from thermosets and thermoplastics is utilizing dynamic covalent chemistry (DCC) for material design. Dynamic covalent bonds are able to undergo dynamic exchange which allow the material to adapt to a new state when under stimuli such as stress or strain. Material comprised of such reversible networks is called covalent adaptable networks (CANs). These types of reversible covalent bonds followed two types of exchange mechanisms: dissociation and association. A review of dissociative-pathway-based materials includes retro-Diels-Alder, [2+2] and [4+4] cycloaddition, boronate ester, and alkoxyamines. CANs followed associative mechanism including radical addition fragmentation chain transfer reaction, anionic disulfide exchange, and transesterification are also reviewed. Lastly, a general consideration in designing CANs includes the importance of each experiment, the information obtained from the experiments, and general experimental procedures. Chapter 2 is about the design, synthesis and characterization of solvent-swelled polyimine networks. The presence of reversible imine bond exchange was found to influence the dynamical properties of the polymer networks. Investigation of the imine bond exchange kinetics and characterization of the creep and stress relaxation properties of the polyimine networks have been conducted. A correlation was found between the relative imine bond exchange rate in different solvents and the relative stress relaxation rate of the solvent-swelled networks. The polyimine networks can also be re-mended and recycled by hydrolysis. Chapter 3 is focused on CANs based on aminal linkage. The thermodynamics and kinetics of the aminal dissociation as well as transaminalation reaction have been investigated using model compounds. Temperature-dependent stress relaxation behavior of the polyamine networks have also been characterized by dynamic mechanical analysis (DMA) method, allowing for an assessment of the activation energy of the transaminalation in the network. Aminal exchange was found to occur by a dissociative mechanism that requires the presence of catalytic protic sources to facilitate the formation of iminium intermediates. The polyaminal networks can be reprocessed as a viscoelastic solid (above the gel point) rather than a viscoelastic liquid. These materials were shown to be elastomers and can be thermally reprocessed and re-mended