• Row of shear cracks moving in one-dimensional hexagonal quasicrystalline materials

      Tupholme, Geoffrey E. (2015-01)
      Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.
    • RSSI and throughput evaluation of an LTE system using a distributed MIMO antenna with a site specific channel propagation model

      Dama, Yousef A.S.; Anoh, Kelvin O.O.; Asif, Rameez; Abd-Alhameed, Raed A.; Jones, Steven M.R.; Ghazaany, Tahereh S.; Zhu, Shaozhen (Sharon); Excell, Peter S. (2013)
    • A Runtime Safety Analysis Concept for Open Adaptive Systems

      Kabir, Sohag; Sorokos, I.; Aslansefat, K.; Papadopoulos, Y.; Gheraibia, Y.; Reich, J.; Saimler, M.; Wei, R. (Springer, 2019-10-16)
      In the automotive industry, modern cyber-physical systems feature cooperation and autonomy. Such systems share information to enable collaborative functions, allowing dynamic component integration and architecture reconfiguration. Given the safety-critical nature of the applications involved, an approach for addressing safety in the context of reconfiguration impacting functional and non-functional properties at runtime is needed. In this paper, we introduce a concept for runtime safety analysis and decision input for open adaptive systems. We combine static safety analysis and evidence collected during operation to analyse, reason and provide online recommendations to minimize deviation from a system’s safe states. We illustrate our concept via an abstract vehicle platooning system use case.
    • A Runtime Safety Analysis Concept for Open Adaptive Systems

      Kabir, Sohag; Sorokos, I.; Aslansefat, K.; Papadopoulos, Y.; Gheraibia, Y.; Reich, J.; Saimler, M.; Wei, R. (2019)
      In the automotive industry, modern cyber-physical systems feature cooperation and autonomy. Such systems share information to enable collaborative functions, allowing dynamic component integration and architecture reconfiguration. Given the safety-critical nature of the applications involved, an approach for addressing safety in the context of reconfiguration impacting functional and non-functional properties at runtime is needed. In this paper, we introduce a concept for runtime safety analysis and decision input for open adaptive systems. We combine static safety analysis and evidence collected during operation to analyse, reason and provide online recommendations to minimize deviation from a system’s safe states. We illustrate our concept via an abstract vehicle platooning system use case.
    • Safety + AI: A novel approach to update safety models using artificial intelligence

      Gheraibia, Y.; Kabir, Sohag; Aslansefat, K.; Sorokos, I.; Papadopoulos, Y. (2019-09-16)
      Safety-critical systems are becoming larger and more complex to obtain a higher level of functionality. Hence, modeling and evaluation of these systems can be a difficult and error-prone task. Among existing safety models, Fault Tree Analysis (FTA) is one of the well-known methods in terms of easily understandable graphical structure. This study proposes a novel approach by using Machine Learning (ML) and real-time operational data to learn about the normal behavior of the system. Afterwards, if any abnormal situation arises with reference to the normal behavior model, the approach tries to find the explanation of the abnormality on the fault tree and then share the knowledge with the operator. If the fault tree fails to explain the situation, a number of different recommendations, including the potential repair of the fault tree, are provided based on the nature of the situation. A decision tree is utilized for this purpose. The effectiveness of the proposed approach is shown through a hypothetical example of an Aircraft Fuel Distribution System (AFDS).
    • The safety of common steel beam/column connections in fire

      Wang, Y.C.; Davison, J.B.; Burgess, I.W.; Plank, R.J.; Yu, H.X.; Dai, Xianghe (2010)
      This paper summarises recent experimental research on structural steel I-section beam/column connections for fire safety, based on a programme of research on robustness of different types of steel beam/column connections, carried out in collaboration between the Universities of Sheffield and Manchester. In this research project, two series of connection tests were conducted, one on isolated connections under different combinations of axial load, shear and moment at different elevated temperatures, and one on steel beam-to-column assemblies in fire, in which the resulting connection forces were varied during the fire exposure. This paper summarises the results and the main findings of these tests, focusing on connection failure modes, tying resistance, the rotation capacity of different types of connection and their potential influences on fire resistance of the connected members. The principal objective of this paper is to discuss the implications of this research project on integrating fire resistance into the design of steel-framed structures, firstly to highlight connection characteristics which contribute most to overall robustness, and to suggest how connection detailing might change to enable connections to possess such desirable characteristics.
    • Safety on stairs: Influence of a tread edge highlighter and its position

      Foster, Richard J.; Hotchkiss, John; Buckley, John G.; Elliott, David B. (2014-07)
      Background: Falls sustained when descending stairs are the leading cause of accidental death in older adults. Highly visible edge highlighters/friction strips (often set back from the tread edge) are sometimes used to improve stair safety, but there is no evidence for the usefulness of either. Objective: To determine whether an edge highlighter and its location relative to the tread edge affect foot placement/clearance and accidental foot contacts when descending stairs. Method: Sixteen older adults (mean ± 1 SD age; 71 ± 7 years) with normal vision (experiment 1) and eight young adults (mean ± 1 SD age; 24 ± 4 years) with visual impairment due to simulated age-related cataract (experiment 2) completed step descent trials during which a high contrast edge highlighter was either not present, placed flush with the tread edge, or set back from the edge by 10 mm or 30 mm. Foot placement/ clearance and the number of accidental foot contacts were compared across conditions. Results: In experiment 1, a highlighter set back by 30 mm led to a reduction in final foot placement (p b 0.001) and foot clearance (p b 0.001) compared to a highlighter placed flush with the tread edge, and the percentage of foot clearances that were less than 5 mm increased from 2% (abutting) to 17% (away30). In experiment 2, a highlighter placed flushwith the tread edge led to a decrease in within-subject variability in final foot placement (p = 0.004) and horizontal foot clearance (p = 0.022), a decrease in descent duration (p = 0.009), and a decrease in the number of low clearances (b5 mm, from 8% to 0%) and the number of accidental foot contacts (15% to 3%) when compared to a tread edge with no highlighter present. Conclusions: Changes to foot clearance parameters as a result of highlighter presence and position suggest that stairswith high-contrast edge highlighters positioned flushwith the tread edgewill improve safety on stairs, particularly for those with age-related visual impairment.
    • Sagging and hogging strengthening of continuous reinforced concrete beams using CFRP sheets.

      El-Refaie, S.A.; Ashour, Ashraf F.; Garrity, S.W. (2003-07)
      This paper reports the testing of 11 reinforced concrete (RC) two-span beams strengthened in flexure with externally bonded carbon fiber-reinforced polymer (CFRP) sheets. The beams were classified into two groups according to the arrangement of the internal steel reinforcement. Each group included one unstrengthened control beam. The main parameters studied were the position, length, and number of CFRP layers. External strengthening using CFRP sheets was found to increase the beam load capacity. All strengthened beams exhibited less ductility compared with the unstrengthened control beams, however, and showed undesirable sudden failure modes. There was an optimum number of CFRP layers beyond which there was no further enhancement in the beam capacity. Extending the CFRP sheet length to cover the entire hogging or sagging zones did not prevent peeling failure of the CFRP sheets, which was the dominant failure mode of beams tested.
    • Saliency-directed prioritization of visual data in wireless surveillance networks

      Mehmood, Irfan; Sajjad, M.; Ejaz, W.; Baik, S.W. (2015-07)
      In wireless visual sensor networks (WVSNs), streaming all imaging data is impractical due to resource constraints. Moreover, the sheer volume of surveillance videos inhibits the ability of analysts to extract actionable intelligence. In this work, an energy-efficient image prioritization framework is presented to cope with the fragility of traditional WVSNs. The proposed framework selects semantically relevant information before it is transmitted to a sink node. This is based on salient motion detection, which works on the principle of human cognitive processes. Each camera node estimates the background by a bootstrapping procedure, thus increasing the efficiency of salient motion detection. Based on the salient motion, each sensor node is classified as being high or low priority. This classification is dynamic, such that camera nodes toggle between high-priority and low-priority status depending on the coverage of the region of interest. High-priority camera nodes are allowed to access reliable radio channels to ensure the timely and reliable transmission of data. We compare the performance of this framework with other state-of-the-art methods for both single and multi-camera monitoring. The results demonstrate the usefulness of the proposed method in terms of salient event coverage and reduced computational and transmission costs, as well as in helping analysts find semantically relevant visual information.
    • Saliency-weighted graphs for efficient visual content description and their applications in real-time image retrieval systems

      Ahmad, J.; Sajjad, M.; Mehmood, Irfan; Rho, S.; Baik, S.W. (2017-09)
      The exponential growth in the volume of digital image databases is making it increasingly difficult to retrieve relevant information from them. Efficient retrieval systems require distinctive features extracted from visually rich contents, represented semantically in a human perception-oriented manner. This paper presents an efficient framework to model image contents as an undirected attributed relational graph, exploiting color, texture, layout, and saliency information. The proposed method encodes salient features into this rich representative model without requiring any segmentation or clustering procedures, reducing the computational complexity. In addition, an efficient graph-matching procedure implemented on specialized hardware makes it more suitable for real-time retrieval applications. The proposed framework has been tested on three publicly available datasets, and the results prove its superiority in terms of both effectiveness and efficiency in comparison with other state-of-the-art schemes.
    • Saltwater-freshwater mixing fluctuation in shallow beach aquifers

      Han, Q.; Chen, D.; Guo, Yakun; Hu, W. (2018-07-31)
      Field measurements and numerical simulations demonstrate the existence of an upper saline plume in tidally dominated beaches. The effect of tides on the saltwater-freshwater mixing occurring at both the upper saline plume and lower salt wedge is well understood. However, it is poorly understood whether the tidal driven force acts equally on the mixing behaviours of above two regions and what factors control the mixing fluctuation features. In this study, variable-density, saturated-unsaturated, transient groundwater flow and solute transport numerical models are proposed and performed for saltwater-freshwater mixing subject to tidal forcing on a sloping beach. A range of tidal amplitude, fresh groundwater flux, hydraulic conductivity, beach slope and dispersivity anisotropy are simulated. Based on time sequential salinity data, the gross mixing features are quantified by computing the spatial moments in three different aspects, namely, the centre point, length and width, and the volume (or area in a two-dimensional case). Simulated salinity distribution varies significantly at saltwater-freshwater interfaces. Mixing characteristics of the upper saline plume greatly differ from those in the salt wedge for both the transient and quasi-steady state. The mixing of the upper saline plume largely inherits the fluctuation characteristics of the sea tide in both the transverse and longitudinal directions when the quasi-steady state is reached. On the other hand, the mixing in the salt wedge is relatively steady and shows little fluctuation. The normalized mixing width and length, mixing volume and the fluctuation amplitude of the mass centre in the upper saline plume are, in general, one-magnitude-order larger than those in the salt wedge region. In the longitudinal direction, tidal amplitude, fresh groundwater flux, hydraulic conductivity and beach slope are significant control factors of fluctuation amplitude. In the transverse direction, tidal amplitude and beach slope are the main control parameters. Very small dispersivity anisotropy (e.g., α_L⁄α_T <5) could greatly suppress mixing fluctuation in the longitudinal direction. This work underlines the close connection between the sea tides and the upper saline plume in the aspect of mixing, thereby enhancing understanding of the interplay between tidal oscillations and mixing mechanisms in tidally dominated sloping beach systems.
    • Sandra fault analysis and simulation

      Ali, Muhammad; Cheng, Yongqiang; Li, Jian-Ping; Hu, Yim Fun; Pillai, Prashant; Pillai, Anju; Xu, Kai J. (2013)
      Fault management is one of the important management functions of a telecommunication network and mainly deals with fault monitoring and diagnosis. This paper applies reliability theories and methodologies for the fault management of an aeronautical communication system developed within the EU FP7 SANDRA project. The failure of the SANDRA terminal demonstrator is an undesirable event and the corresponding fault tree was built upon a reliability function analysis and was used to quickly monitor failures in the system. By using Monte Carlo simulations, the SANDRA demonstrator's reliability can be predicted and important components, which have major contributions to system failures, can be identified. The results can be used to improve the system reliability by adding parallel components in weak and important places.
    • SAR and Radiation Performance of Balanced and Unbalanced Mobile Antennas using a Hybrid Computational Electromagnetics Formulation.

      Abd-Alhameed, Raed A.; Excell, Peter S.; Khalil, Khaled; Alias, R.; Mustafa, J. (2004)
      A procedure to reduce the effect of the mobile antenna on the handset by using balanced antennas has been investigated. Use of this type of antenna may degrade the antenna performance, such as bandwidth and gain, although it can cause less effect on the body to which they are adjacent. If the antennas are well designed, the maximum specific absorption rate (SAR) values are likely to be reduced when placed next to the head, since the coupling of such antennas to the body of the handset is very weak. A study on balanced and unbalanced antennas for mobile handsets next to the human head is presented, using a hybrid electromagnetics method for the analysis. The method uses the hybridisation technique between the frequency-domain method of moments (MoM) and the finite-difference time-domain method (FDTD). The antenna was modelled using MoM whereas the head tissues were modelled using FDTD. Two antennas were designed and investigated with respect to the SAR and radiation performance for two different antenna positions on the top edge of a mobile handset. Radiation patterns are presented and compared, with and without the head, and the maximum SAR values and field distributions inside the head are discussed. The balanced antenna shows good improvements with respect to the unbalanced antenna in terms of the SAR values and variations of the input impedances.
    • Satellite Communications [Editorial]

      Sheriff, Ray E.; Donner, A.; Vanelli-Coralli, A. (Hindawi Publishing Corporation., 09/12/2007)
      We are delighted to bring to you this special issue on satellite communications, which we have prepared as part of the spreading of excellence remit of the satellite communications network of excellence (SatNEx). The SatNEx project, which began in 2004, is funded for five years under the European Union¿s Sixth Framework Programme (FP6) Information Society Technologies (IST) Thematic Area. Led by the German Aerospace Center, SatNEx brings together a network of 24 partners, distributed throughout Europe, with membership drawn from ten countries. The philosophy underlying the SatNEx approach revolves around the selection of focused actions under Joint Programmes of Activities, which are carried out collectively by the partners and include research, integration, and dissemination activities. Training represents an important part of the SatNEx remit and is supported through a number of initiatives including the hosting of internship projects and an annual summer school. The call for papers resulted in a high number of submissions, from which we have been able to select 12 excellent papers dealing with the different aspects of satellite communications and navigation.
    • Satellite mobile multicast for aeronautical communication

      Jaff, Esua K.; Ali, Muhammad; Pillai, Prashant; Hu, Yim Fun (2014)
      Satellite communication with its world-wide coverage has now become an indispensable part of the Aeronautical communication. Support for high-speed Internet access by the new generation satellite systems has made the provision of IP-based multimedia applications on-board the aircraft possible at all times. Considering the expensive nature of satellite resources, IP multicast can provide a cost-effective and bandwidth saving means of delivering real-time group communication and streaming media to air passengers and crew during a flight. In IP multicast communication, traffic from the source travels along the established multicast tree to reach all group members. For mobile receivers like the aircraft which may move from one satellite beam to another, then special techniques are required to ensure that a branch of the multicast tree follows the mobile receiver into the target beam. This paper proposes a novel technique based on the Proxy Mobile IPv6 (PMIPv6) protocol to support IP multicast receiver mobility over satellite networks for an aircraft as it moves and changes its point of attachment from one satellite gateway (GW) to another. Performance evaluation shows that the proposed scheme is better than the Mobile IPv6-based approach in terms of GW handover (GWH) latency and number of packets lost during GWH.
    • SatNEx: A Network of Excellence Providing Training in Satellite Communications

      Sheriff, Ray E.; Hu, Yim Fun; Chan, Pauline M.L.; Bousquet, M.; Corazza, G.E.; Donner, A.; Vanelli-Coralli, A.; Werner, M. (IEEE, 30/05/2005)
      Satellite communications represents a specialised area of telecommunications. While the development of satellite technology is relatively slow in comparison to wireless networks evolution, due to the need for high reliability, the services that satellites are able to offer are evolving at much the same pace as their terrestrial counterparts. It is within this context that the satellite communications network of excellence (SatNEx) has evolved its initiative, the aim being to serve the engineering community with the latest technological trends, while also providing a solid grounding in the fundamentals for those new to the subject area.
    • Scheduling Infrastructure Renewal for Railway Networks

      Dao, Cuong D.; Hartmann, A.; Lamper, A.; Herbert, P. (2019-12)
      The pressing necessity to renew infrastructure assets in developed railway systems leads to an increased number of activities to be scheduled annually. Scheduling of renewal activities for a railway network is a critical task because these activities often require a significant amount of time and create a capacity conflict in operation scheduling. This paper discusses economic and technological aspects, opportunities, and constraints in the renewals of multiple rail infrastructure components at several locations in a railway network. We addressed and modeled a challenging situation in which there were interrelationships between different track lines, and thus, possession of a track line could affect the other track lines and prevent renewal works on them. A mathematical formulation for the railway infrastructure renewal scheduling problem in the network context was presented to minimize the total renewal and unavailability costs. A method based on a triple-prioritization rule and an optimal sharing of renewal times allocated for different types of rail infrastructure components in a possession is proposed to solve the problem. The method was applied to a real case of a regional railway network in Northern Netherlands and it was shown that up to 13% of total costs can be saved compared with the current scheduling practice.
    • Scheduling of tasks in multiprocessor system using hybrid genetic algorithms

      Varghese, B.; Hossain, M. Alamgir; Dahal, Keshav P. (Springer Verlag, 2007)
      This paper presents an investigation into the optimal scheduling of realtime tasks of a multiprocessor system using hybrid genetic algorithms (GAs). A comparative study of heuristic approaches such as `Earliest Deadline First (EDF)¿ and `Shortest Computation Time First (SCTF)¿ and genetic algorithm is explored and demonstrated. The results of the simulation study using MATLAB is presented and discussed. Finally, conclusions are drawn from the results obtained that genetic algorithm can be used for scheduling of real-time tasks to meet deadlines, in turn to obtain high processor utilization.
    • Scope and limitations of the irreversible thermodynamics and the solution diffusion models for the separation of binary and multi-component systems in reverse osmosis process

      Al-Obaidi, M.A.; Kara-Zaitri, Chakib; Mujtaba, Iqbal M. (2017-05)
      Reverse osmosis process is used in many industrial applications ranging from solute-solvent to solvent-solvent and gaseous separation. A number of theoretical models have been developed to describe the separation and fluxes of solvent and solute in such processes. This paper looks into the scope and limitations of two main models (the irreversible thermodynamics and the solution diffusion models) used in the past by several researchers for solute-solvent feed separation. Despite the investigation of other complex models, the simple concepts of these models accelerate the feasibility of the implementation of reverse osmosis for different types of systems and variety of industries. Briefly, an extensive review of these mathematical models is conducted by collecting more than 70 examples from literature in this study. In addition, this review has covered the improvement of such models to make them compatible with multi-component systems with consideration of concentration polarization and solvent-solute-membrane interaction.