Pose consensus in networks of heterogeneous robots with variable time delays

This paper proposes a novel pose (position and orientation) consensus controller for networks of heterogeneous robots modeled in the operational space. The proposed controller is a distributed proportional plus damping scheme that, with a slight modification, solves both the leader–follower and leaderless consensus problems. A singularity‐free representation, unit quaternion, is used to describe the robots orientation, and the network is represented by an undirected and connected interconnection graph. Furthermore, it is shown that the controller is robust to interconnection variable time delays. Experiments with a network of two 6‐degrees‐of‐freedom robots are presented to illustrate the performance of the proposed scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

EXAM: a comprehensive environment for the analysis of access control policies

Policy integration and inter-operation is often a crucial requirement when parties with different access control policies need to participate in collaborative applications and coalitions. Such requirement is even more difficult to address for dynamic large-scale collaborations, in which the number of access control policies to analyze and compare can be quite large. An important step in policy integration and inter-operation is to analyze the similarity of policies. Policy similarity can sometimes also be a pre-condition for establishing a collaboration, in that a party may enter a collaboration with another party only if the policies enforced by the other party match or are very close to its own policies. Existing approaches to the problem of analyzing and comparing access control policies are very limited, in that they only deal with some special cases. By recognizing that a suitable approach to the policy analysis and comparison requires combining different approaches, we propose in this paper a comprehensive environment—EXAM. The environment supports various types of analysis query, which we categorize in the paper. A key component of such environment, on which we focus in the paper, is the policy analyzer able to perform several types of analysis. Specifically, our policy analyzer combines the advantages of existing MTBDD-based and SAT-solver-based techniques. Our experimental results, also reported in the paper, demonstrate the efficiency of our analyzer.     

ACAR: Adaptive Connectivity Aware Routing for Vehicular Ad Hoc Networks in City Scenarios

Multi-hop vehicle-to-vehicle communication is useful for supporting many vehicular applications that provide drivers with safety and convenience. Developing multi-hop communication in vehicular ad hoc networks (VANET) is a challenging problem due to the rapidly changing topology and frequent network disconnections, which cause failure or inefficiency in traditional ad hoc routing protocols. We propose an adaptive connectivity aware routing (ACAR) protocol that addresses these problems by adaptively selecting an optimal route with the best network transmission quality based on statistical and real-time density data that are gathered through an on-the-fly density collection process. The protocol consists of two parts: 1) select an optimal route, consisting of road segments, with the best estimated transmission quality, and 2) in each road segment of the chosen route, select the most efficient multi-hop path that will improve the delivery ratio and throughput. The optimal route is selected using our transmission quality model that takes into account vehicle densities and traffic light periods to estimate the probability of network connectivity and data delivery ratio for transmitting packets. Our simulation results show that the proposed ACAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, throughput and data packet delay. Since the proposed model is not constrained by network densities, the ACAR protocol is suitable for both daytime and nighttime city VANET scenarios.     

Wet-etching of precipitation-based thin film microstructures for micro-solid oxide fuel cells

In micro-solid oxide fuel cells (μ-SOFCs) ceramic thin films are integrated as free-standing membranes on micromachinable substrates such as silicon or Foturan^® glass ceramic wafers. The processing of μ-SOFCs involves unavoidable dry- or wet-chemical etching for opening the substrate below the free-standing fuel cell membranes. In the first part of this paper current dry- and wet-chemical etchants for structuring of ceria-based electrolyte materials are reviewed, and compared to the etch-rates of common μ-SOFCs substrates. Wet-chemical etchants such as hydrofluoric acid are of high interest in μ-SOFC processing since they allow for homogeneous etching of ceria-based electrolyte thin films contrary to common dry-etching methods. In addition, HF acid is the only choice for substrate etching of μ-SOFC based on Foturan^® glass ceramic wafers. Etching of Ce_0.8Gd_0.2O_1.9?x spray pyrolysis electrolyte thin films with 10% HF:H₂O is investigated. The etch-resistance and microstructures of these films show a strong dependency on post deposition annealing, i.e. degree of crystallinity, and damage for low acid exposure times. Their ability to act as a potential etch-resistance for μ-SOFC membranes is broadly discussed. Guidance for thermal annealing and etching of Ce_0.8Gd_0.2O_1.9?x thin films for the fabrication of Foturan^®-based μ-SOFCs is given.     

Performance comparison of battery power consumption in wireless multiple access protocols

Energy efficiency is an important issue in mobile wireless networks since the battery life of mobile terminals is limited. Conservation of battery power has been addressed using many techniques such as variable speed CPUs, flash memory, disk spindowns, and so on. We believe that energy conservation should be an important factor in the design of networking protocols for mobile wireless networks. In particular, this paper addresses energy efficiency in medium access control (MAC) protocols for wireless networks. The paper develops a framework to study the energy consumption of a MAC protocol from the transceiver usage perspective. This framework is then applied to compare the performance of a set of protocols that includes IEEE 802.11, ECMAC, PRMA, MDRTDMA, and DQRUMA*. The performance metrics considered are transmitter and receiver usage times for packet transmission and reception. The time estimates are then combined with power ratings for a Proxim RangeLAN2 radio card to obtain an estimate of the energy consumed for MAC related activities. The analysis here shows that protocols that aim to reduce the number of contentions perform better from an energy consumption perspective. The receiver usage time, however, tends to be higher for protocols that require the mobile to sense the medium before attempting transmission. The paper also provides a set of principles that could be applied when designing access protocols for wireless networks.*ECMAC: energyconserving MAC. PRMA: packet reservation multiple access. MDRTDMA: multiservices dynamic reservation TDMA. DQRUMA: distributedqueuing request update multiple access.     

Study on the RF Sputtered hydrogenated amorphous silicon–germanium thin films

In this study mechanical and electrical properties of the RF sputtered hydrogenated amorphous silicon germanium thin films deposited at room temperature have been discussed. Interesting correlation between the resistance and the flow of hydrogen is observed. Further, both band and hopping conduction mechanisms are found to exist simultaneously for the studied amorphous silicon germanium films.     

Fast Intra-Network and Cross-Layer Handover (FINCH) for WiMAX and Mobile Internet

To support fast and efficient handovers in mobile WiMAX, we propose Fast Intra-Network and Cross-layer Handover (FINCH) for intradomain (intra-CSN) mobility management. FINCH is a complementary protocol to Mobile IP (MIP), which deals with interdomain (inter-CSN) mobility management in mobile WiMAX. FINCH can reduce not only the handover latency but also the end-to-end latency for MIP. Paging extension for FINCH is also proposed to enhance the energy efficiency. The proposed FINCH is especially suitable for real-time services in frequent handover environment, which is important for future mobile WiMAX networks. In addition, FINCH is a generic protocol for other IEEE 802-series standards. This is especially beneficial for the integration of heterogeneous networks, for instance, the integration of WiMAX and WiFi networks. Both mathematical analysis and simulation are developed to analyze and compare the performance of FINCH with other protocols. The results show that FINCH can support fast and efficient link layer and intradomain handovers. The numerical results can also be used to select proper network configurations.