New materials for micro-scale sensors and actuators: An engineering review

This paper provides a detailed overview of developments in transducer materials technology relating to their current and future applications in micro-scale devices. Recent advances in piezoelectric, magnetostrictive and shape-memory alloy systems are discussed and emerging transducer materials such as magnetic nanoparticles, expandable micro-spheres and conductive polymers are introduced. Materials properties, transducer mechanisms and end applications are described and the potential for integration of the materials with ancillary systems components is viewed as an essential consideration. The review concludes with a short discussion of structural polymers that are extending the range of micro-fabrication techniques available to designers and production engineers beyond the limitations of silicon fabrication technology.     

Dynamic broadcasting in parallel computing

We consider the problem where broadcast requests are dynamically generated at random time instants at each node of a multiprocessor network. In particular, in our model packets arrive at each node of a network according to a Poisson process, and each packet has to be broadcast to all the other nodes. We propose an on-line, distributed routing scheme to execute the broadcasts in this dynamic environment. Our scheme consists of repeated execution of a partial multinode broadcast task, which is a static communication task where any M⩽N arbitrary nodes of an N-processor network broadcast a packet to all the other nodes. The dynamic broadcasting scheme that we propose can be used in any topology, regular or not, for which partial multinode broadcast algorithms with certain properties can be found. We derive such an algorithm and we analyze the corresponding dynamic broadcasting scheme for the hypercube network. We show that its stability region tends to the maximum possible as the number of nodes of the hypercube tends to infinity. Furthermore, for any fixed load in the stability region, the average delay is of the order of the diameter of the hypercube. Our analysis does not use any approximating assumptions     

Macro-star networks: efficient low-degree alternatives to stargraphs

We propose a new class of interconnection networks, called macro-star networks, which belong to the class of Cayley graphs and use the star graph as a basic building module. A macro-star network can have node degree that is considerably smaller than that of a star graph of the same size, and diameter that is sublogarithmic and asymptotically within a factor of 1.25 from a universal lower bound (given its node degree). We show that algorithms developed for star graphs can be emulated on suitably constructed macro-stars with asymptotically optimal slowdown. This enables us to obtain through emulation a variety of efficient algorithms for the macro-star network, thus proving its versatility. Basic communication tasks, such as the multimode broadcast and the total exchange, can be executed in macro-star networks in asymptotically optimal time under both the single-port and the all-port communication models. Moreover, no interconnection network with similar node degree can perform these communication tasks in time that is better by more than a constant factor than that required in a macro-star network. We show that macro-star networks can embed trees, meshes, hypercubes, as well as star, bubble-sort, and complete transposition graphs with constant dilation. We introduce several variants of the macro-star network that provide more flexibility in scaling up the number of nodes. We also discuss implementation issues and compare the new topology with the star graph and other popular topologies     

Hop distance–based bandwidth allocation technique for elastic optical networks

Elastic optical networks (EON) have emerged as a solution to the growing needs of the future internet, by allowing for greater flexibility, spectrum efficiency, and scalability, when compared to WDM solutions. EONs achieve those improvements through finer spectrum allocation granularity. However, due to the continuity and contiguity constrains, distant connections that are routed through multiple hops suffer from increased bandwidth blocking probability (BBP), while more direct connections are easier to form. This paper proposes HopWindows, a novel method that strategically allocates bandwidth to connections based on their hop distance. This new algorithm applies masks that control the range of frequency slots (FSs) allocated to each n‐hop connection. Furthermore, a new network metric is introduced, the normalized bandwidth blocking probability (normalized BBP). Utilization of this metric ensures increased fairness to distant connections. Extended simulation results are presented which indicate that the proposed HopWindows method achieves a superior performance over the well‐known FirstFit algorithm. The proposed algorithm may achieve a decrease in bandwidth blocking probability of up to 50%.     

A Grid-enabled CPU Scavenging Architecture and a Case Study of its Use in the Greek School Network

In this paper we present a CPU scavenging architecture suitable for desktop resources, and we study its appropriateness in exploiting the PC Laboratory resources of the Greek School Network and their integration to the existing HellasGrid national infrastructure. School laboratories form an extensive network equipped with computational systems and fast Internet connections. As this infrastructure is utilized at most 8 h per day and 5 days per week, it could be made available during its remaining idle time for computational purposes through the use of Grid technology. The structure and organization of the school laboratories and backbone network enables the CPU scavenging service, as an independent and additional service, which will not violate the operational rules and policies of the school network, while it will add additional resources to the current HellasGrid infrastructure with low adaptation cost.     

Performance of Uplink NOMA with User Mobility Under Short Packet Transmission

Wireless Personal Communications - The scenario of an uplink two-user non-orthogonal multiple access (NOMA) communication system is analytically studied when it operates in the short packet...     

Structure–properties relationships in clay nanocomposites based on PVDF/(ethylene–vinyl acetate) copolymer blends

The relationships between the microscopic structure and the macroscopic properties in two sets of clay nanocomposites based on polymer blends comprised of poly(vinylidene fluoride) (PVDF) and ethylene–vinyl acetate copolymer (EVAc) were examined. In nanocomposites based on a polymer blend matrix with high content of polar groups (VAc) the dispersion of polar nanoclay leads to significant enhancement in toughness and a substantial increase in viscosity. However, in nanocomposite blends based on a less polar matrix (i.e. with fewer VAc groups) it is the hydrophobic organoclay that leads to higher modulus and stronger viscoelasticity. The dispersion of nanoparticles and the mechanical response are discussed in terms of emulsifying efficiency of the clay particles in the immiscible polymer blend, an effect that largely depends on the localized interactions between the polymer groups and the clay surface modifier. The potential of nanoclays to serve as matrix sensitive structure-directing agents in tailor-made materials is demonstrated.     

Improving hydrogen storage capacity of MOF by functionalization of the organic linker with lithium atoms

A combination of quantum and classical calculations have been performed in order to investigate hydrogen storage in metal-organic frameworks (MOFs) modified by lithium alkoxide groups. Ab initio calculations showed that the interaction energies between the hydrogen molecules and this functional group are up to three times larger compared with unmodified MOF. This trend was verified by grand canonical Monte Carlo (GCMC) simulations in various thermodynamic conditions. The gravimetric capacity of the Li-modified MOFs reached the value of 10 wt % at 77 K and 100 bar, while our results are very promising at room temperature, too, with 4.5 wt %.     

Joint multi-cost routing and power control in wireless ad hoc networks

In this work we study the combination of multi-cost routing and adjustable transmission power in wireless ad hoc networks, so as to obtain dynamic energy- and interference-efficient routes to optimize network performance. In multi-cost routing, a vector of cost parameters is assigned to each network link, from which the cost vectors of candidate paths are calculated. Only at the end these parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. The multi-cost routing problem is a generalization of the multi-constrained problem, where no constraints exist, and is also significantly more powerful than single-cost routing. Since energy is an important limitation of wireless communications, the cost parameters considered are the number of hops, the interference caused, the residual energy and the transmission power of the nodes on the path; other parameters could also be included, as desired. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multi-cost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.