NodeWiz: Fault-tolerant grid information service

Large scale grid computing systems may provide multitudinous services, from different providers, whose quality of service will vary. Moreover, services are deployed and undeployed in the grid with no central coordination. Thus, to find out the most suitable service to fulfill their needs, or to find the most suitable set of resources on which to deploy their services, grid users must resort to a Grid Information Service (GIS). This service allows users to submit rich queries that are normally composed of multiple attributes and range operations. The ability to efficiently execute complex searches in a scalable and reliable way is a key challenge for current GIS designs. Scalability issues are normally dealt with by using peer-to-peer technologies. However, the more reliable peer-to-peer approaches do not cater for rich queries in a natural way. On the other hand, approaches that can easily support these rich queries are less robust in the presence of failures. In this paper we present the design of NodeWiz, a GIS that allows multi-attribute range queries to be performed efficiently in a distributed manner, while maintaining load balance and resilience to failures.     

Understanding interference and carrier sensing in wireless mesh networks [Accepted from Open Call]

Wireless mesh networks aim to provide high-speed Internet service without costly network infrastructure deployment and maintenance. The main obstacle in achieving high-capacity wireless mesh networks is interference between the mesh links. In this article, we analyze the carrier sensing and interference relations between two wireless links and measure the impact of these relations on link capacity on an indoor 802.11a mesh network testbed. We show that asymmetric carrier sensing and/or interference relations commonly exist in wireless mesh networks, and we study their impact on the link capacity and fair-channel access. In addition, we investigate the effect of traffic rate on link capacity in the presence of interference.     

On-Demand Multicast Routing Protocol in Multihop Wireless Mobile Networks

An ad hoc network is a dynamically reconfigurable wireless network with no fixed infrastructure or central administration. Each host is mobile and must act as a router. Routing and multicasting protocols in ad hoc networks are faced with the challenge of delivering data to destinations through multihop routes in the presence of node movements and topology changes. This paper presents the On-Demand Multicast Routing Protocol (ODMRP) for wireless mobile ad hoc networks. ODMRP is a mesh-based, rather than a conventional tree-based, multicast scheme and uses a forwarding group concept; only a subset of nodes forwards the multicast packets via scoped flooding. It applies on-demand procedures to dynamically build routes and maintain multicast group membership. ODMRP is well suited for ad hoc wireless networks with mobile hosts where bandwidth is limited, topology changes frequently, and power is constrained. We evaluate ODMRP performance with other multicast protocols proposed for ad hoc networks via extensive and detailed simulation.     

Transmission power control in wireless ad hoc networks: challenges, solutions and open issues

Recently, power control in mobile ad hoc networks has been the focus of extensive research. Its main objectives are to reduce the total energy consumed in packet delivery and/or increase network throughput by increasing the channel's spatial reuse. In this article, we give an overview of various power control approaches that have been proposed in the literature. We discuss the factors that influence the selection of the transmission power, including the important interplay between the routing (network) and the medium access control (MAC) layers. Protocols that account for such interplay are presented.     

Inherent sensing and interfacial evaluation of carbon nanofiber and nanotube/epoxy composites using electrical resistance measurement and micromechanical technique

Inherent sensing of load, micro-damage and stress transferring effects were evaluated for carbon nanotube (CNT) and carbon nanofiber (CNF)/epoxy composites (with various added contents) by an electro-micromechanical technique, using the four-point probe method. Carbon black (CB)/epoxy composites, with conventional nanosize material added, were used for the comparison with CNT and CNF composites. Subsequent fracture of the carbon fiber in the dual matrix composites (DMC) was detected by acoustic emission (AE) and by the change in electrical resistance, ΔR due to electrical contacts of neighboring CNMs. Stress/strain sensing of the nanocomposites was detected by an electro-pullout test under uniform cyclic loading/subsequent unloading. CNT/epoxy composites showed the best sensitivity to fiber fracture, matrix deformation and stress/strain sensing, whereas CB/epoxy composite exhibited poorer sensitivity. From the apparent modulus (as a result of matrix modulus and interfacial adhesion), the stress transferring effects reinforced by CNT was highest among three CNMs. The thermodynamic work of adhesion, W_a as found by dynamic contact angle measurements of the CNT/epoxy composite as a function of added CNT content was correlated and found to be consistent with the apparent mechanical modulus. Uniform dispersion and interfacial adhesion appear to be key factors for improving both sensing and mechanical performance of nanocomposite. Thermally treated-CNF composites exhibited a slightly higher apparent modulus, whereas higher testing temperatures appeared to lower the apparent modulus.     

Aggregating Bandwidth for Multihomed Mobile Collaborative Communities

Multihomed, mobile wireless computing and communication devices can spontaneously form communities to logically combine and share the bandwidth of each other's wide-area communication links using inverse multiplexing. But, membership in such a community can be highly dynamic, as devices and their associated WWAN links randomly join and leave the community. We identify the issues and trade-offs faced in designing a decentralized inverse multiplexing system in this challenging setting and determine precisely how heterogeneous WWAN links should be characterized and when they should be added to, or deleted from, the shared pool. We then propose methods of choosing the appropriate channels on which to assign newly arriving application flows. Using video traffic as a motivating example, we demonstrate how significant performance gains can be realized by adapting allocation of the shared WWAN channels to specific application requirements. Our simulation and experimentation results show that collaborative bandwidth aggregation systems are, indeed, a practical and compelling means of achieving high-speed Internet access for groups of wireless computing devices beyond the reach of public or private access points     

Development of peristaltic antithrombogenic micropumps for in vitro and ex vivo blood transportation tests

This study involves the design, fabrication and characterization of a biocompatible silicon micropump. Three experiments were conducted to study the performance of this pump in clinical environments. They were a blood compatibility test, and in vitro and ex vivo studies. Whole blood is an intrinsically complex material and difficult to manipulate using a microsystem device. In the blood compatibility experiments, two materials N-(triethosilylpropyl)-O-polyethylene oxide urethane (PEOU) and polyethylene glycol (PEG) were employed to form a self-assembled monolayer (SAM) on a chip surface. According to the platelet remaining test and a 30-min blood transportation test, PEOU protected the micropump from thrombus. In the second experiment, the micropump handled several liquids, including DI water and whole blood. When the pump was operated at a voltage of 140 V_pp, the flow rates of the DI water and whole blood were 121.6 μl/min at 500 Hz and 50.2 μl/min at 450 Hz, respectively. The maximum back pressure of the water and the blood in the micropump were 3.2 and 1.8 kPa, respectively. Finally, the micropump injected phosphated buffered saline (PBS) and whole blood into the veins of rats. The pump was characterized ex vivo and discussed. The third experiment reveals that the micropump fulfilled the dosing condition for clinical medicine and did not affect the physiological function of the rats. This pump is highly promising for biomedical applications, such as in drug delivery for patients, or in clinical care. Moreover, the pump has potentials to control precisely medication to improve conventional clinical treatments.     

Mobility prediction and routing in ad hoc wireless networks

By exploiting non-random behaviors for the mobility patterns that mobile users exhibit, we can predict the future state of network topology and perform route reconstruction proactively in a timely manner. Moreover, by using the predicted information on the network topology, we can eliminate transmissions of control packets otherwise needed to reconstruct the route and thus reduce overhead. In this paper, we propose various schemes to improve routing protocol performances by using mobility prediction. We then evaluate the effectiveness of using mobility prediction via simulation. Copyright © 2001 John Wiley & Sons, Ltd.     

The design, implementation, and performance evaluation of theon-demand multicast routing protocol in multihop wireless networks

Multicasting has emerged as one of the most focused areas in the field of networking. As the technology and popularity of the Internet grow, applications such as video conferencing that require the multicast feature are becoming more widespread. Another interesting development has been the emergence of dynamically reconfigurable wireless ad hoc networks to interconnect mobile users for applications ranging from disaster recovery to distributed collaborative computing. In this article we describe the on-demand multicast routing protocol for mobile ad hoc networks. ODMRP is a mesh-based, rather than conventional tree-based, multicast scheme and uses a forwarding group concept (only a subset of nodes forwards the multicast packets packets via scoped flooding). It applies on-demand procedures to dynamically build routes and maintain multicast group membership. We also describe our implementation of the protocol in a real laptop testbed     

Interfacial evaluation and self-sensing on residual stress and microfailure of toughened carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composites

Interfacial evaluation and self-sensing of tensile loading/subsequent unloading and microfailure detection of the carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composites were investigated using micromechanical test and electrical resistance measurement with an aid of acoustic emission (AE). As AT-PEI content increased, both fracture toughness of epoxy-AT-PEI matrix and interfacial shear strength (IFSS) increased due to the optimized matrix modulus for energy absorption. With increasing curing temperature and time, the IFSS increased and then decreased. During curing process, the change in electrical resistance, ΔR increased gradually with adding AT-PEI contents because of different thermal and curing shrinkage of epoxy matrices. Moisture adsorption under durability test could cause to the change in matrix modulus and thus resulted in the change in electrical resistivity correspondently. Under changeable cyclic loading/subsequent unloading, apparent modulus and electrical resistivity during curing process were consistent well with the fracture toughness of epoxy modified with AT-PEI. In compressive test, the electrical resistivity decreased gradually initially and then increased rapidly during subsequent progress of microfailure including fiber fracture showing the buckling pattern.