Performance modeling of DTN routing with heterogeneous and selfish nodes

The performance modeling study of Delay-Tolerant Network routing, in general, assumes the nodes to be homogeneous (in terms of features such as the coverage range) and uncompromised (in terms of forwarding messages). However, in realistic settings this may not be the case. The routing performance modeling of such realistic scenarios that involve multifariously-featured and egotistic nodes would be interesting and insightful. To this end, in this paper, we analytically model the routing behavior of such nodes using Ordinary Differential Equations for two different routing protocols namely, Epidemic Routing and Two-Hop Routing. Furthermore, we also study the degradation in the routing performance caused by an increase in the fraction of selfish nodes present in the heterogeneous node population. The proposed analytical model is validated via extensive simulations.     

Shear buckling characteristics of cold-formed steel channel beams

Cold-formed steel members are increasingly used as primary structural elements in the building industries around the world due to the availability of thin and high strength steels and advanced cold-forming technologies. Cold-formed lipped channel beams (LCB) are commonly used as flexural members such as floor joists and bearers. However, their shear capacities are determined based on conservative design rules. For the shear design of LCB web panels, their elastic shear buckling strength must be determined accurately including the potential post-buckling strength. Currently the elastic shear buckling coefficients of LCB web panels are determined by assuming conservatively that the web panels are simply supported at the junction between their flange and web elements. Hence finite element analyses were conducted to investigate the elastic shear buckling behavior of LCBs. An improved equation for the higher elastic shear buckling coefficient of LCBs was proposed based on finite element analysis results and included in the ultimate shear capacity equations of the North American cold-formed steel codes. Finite element analyses show that relatively short span LCBs without flange restraints are subjected to a new combined shear and flange distortion action due to the unbalanced shear flow. They also show that significant post-buckling strength is available for LCBs subjected to shear. New equations were also proposed in which post-buckling strength of LCBs was included.     

Numerical method for predicting the elastic lateral distortional buckling moment of a mono-symmetric beam with web openings

When used as floor joists, the new mono-symmetric LiteSteel beam (LSB) sections require web openings to provide access for inspections and various services. The LSBs consist of two rectangular hollow flanges connected by a slender web, and are subjected to lateral distortional buckling effects in the intermediate span range. Their member capacity design formulae developed to date are based on their elastic lateral buckling moments, and only limited research has been undertaken to predict the elastic lateral buckling moments of LSBs with web openings. This paper addresses this research gap by reporting the development of web opening modelling techniques based on an equivalent reduced web thickness concept and a numerical method for predicting the elastic buckling moments of LSBs with circular web openings. The proposed numerical method was based on a formulation of the total potential energy of LSBs with circular web openings. The accuracy of the proposed method's use with the aforementioned modelling techniques was verified through comparison of its results with those of finite strip and finite element analyses of various LSBs.     

A strain criterion for pull-through failures in crest-fixed steel claddings

Crest-fixed steel claddings made of thin, high strength steel often suffer from local pull-through failures at their screw connections during high wind events such as storms and hurricanes. Adequate design provisions are not available for these cladding systems except for the expensive testing provisions. Since the local pull-through failures in the less ductile steel claddings are initiated by transverse splitting at the fastener holes, numerical studies have not been able to determine the pull-through failure loads. Numerical studies could be used if a reliable splitting criterion is available. Therefore, a series of two-span cladding and small scale tests was conducted on a range of crest-fixed steel cladding systems under simulated wind uplift loads. The strains in the sheeting around the critical central support screw fastener holes were measured until the pull-through failure occurred. This paper presents the details of the experimental investigation and the results including a strain criterion for the local pull-through failures in crest-fixed steel claddings.     

Diamond-like carbon coating of alternative metal alloys for medical and surgical applications

The effectiveness of a plasma-deposited, diamond-like carbon (DLC) coating on aluminium alloy based surgical instruments is investigated. Surgical instruments must satisfy a number of important criteria including biocompatibility, functional performance, sterility and cleanability, structural integrity, and fatigue resistance. The integrity of the DLC layer and the diffusion barrier properties are of paramount importance due to biocompatibility considerations of the underlying aluminium metal. We investigate the optimisation of the coating with incorporation of silicon and variation in negative self bias, and highlight the design and manufacture of a lightweight laparoscopic assist instrument from aluminium alloy coated with diamond-like carbon, which has been used successfully in the clinical environment to improve operations such as cholecystectomy (gall bladder removal) and exploratory techniques for the diagnosis of cancer.     

EMA-PRBDS: efficient multi-attribute packet rank based data scheduling in wireless sensor networks for real-time monitoring systems

ABSTRACT

In recent years, Wireless Sensor Networks (WSNs) are widely placed in real-time monitoring systems like environmental, structural, patient monitoring, etc. The major criterion for WSN includes energy efficiency and network lifetime. Scheduling is used as a large number of data packets focus on the same queue at the same time. Only limited data scheduling schemes have been implemented in WSN to enhance the performance. The existing First Come First Serve (FCFS) and Dynamic Multilevel Priority (DMP) have some technical challenges like delay, packet drop and high energy consumption due to starvation and deadlock. In this paper, we proposed a new algorithm to optimise and rank the incoming data packets based on multi-attributes decision-making methodology named as Packet Rank Based Data Scheduling (PRBDS), the algorithm selects packet priority, deadline, and size as the metrics to rank the incoming data packets. A simulation result shows when compared with existing scheduling, PRBDS not only provides less energy consumption, also significantly reduces the packet drop and increases the lifetime. Thus, the proposed algorithm is most suitable for real-time monitoring system since it combines data ranking method with scheduling algorithm to create accurate and reliable results to evaluate the incoming data packets.     

Investigation of antimicrobial properties and in-vitro bioactivity of Ce3+-Sr2+dual-substituted nano hydroxyapatites

Dual doped calcium apatite has been widely focused as it enhances the osteoconductive property for the possible applications in orthopedic and dental implants. In this work, we investigate the antimicrobial and bioactive properties of cerium/strontium (Ce³⁺/Sr²⁺) co-substituted hydroxyapatite (HA) nanoparticles synthesized by sol-gel assisted precipitation method. The structure, morphology, functional groups, photoluminescence, and thermal stability of the developed systems are examined. The comparative studies performed among the pure HA, Sr²⁺, and Ce³⁺-substituted HA nanoparticles illustrate higher antibacterial activity with lowered apatite-forming ability and biocompatibility for the Ce³⁺-substituted HA. However, the Ce³⁺/Sr²⁺co-substituted HA exhibits better biocompatibility, apatite-forming ability, and good antimicrobial properties. Sr²⁺ ion inclusion leads to better biological properties and compromise the cytotoxic nature of the Ce³⁺-HA. In addition, the Ce³⁺/Sr²⁺-HA nanoparticles prevent thermal decomposition up to 700°C, pointing also toward the possibility of this co-substituted HA in bone implant applications.     

Comparative life cycle costs for new steel portal frame building systems

Life cycle costs of a new steel portal frame building system incorporating energy efficient sandwich panels are compared with those of a conventional steel portal frame building system for use in industrial and commercial buildings. The economic benefits of the new building system have been demonstrated through cost assessment of energy in use. The results from life cycle cost analysis of both the new and conventional portal frame building systems indicate that, despite slightly higher initial costs, the new building system costs significantly less than the conventional system over its complete life cycle of 50 years. The new system provides improved economic performance along with a more energy-efficient model for commercial/industrial building design in the Australian climate. Le coût du cycle de vie d'un nouveau système de bâtiment à portique en acier comportant des panneaux en sandwich efficaces au plan énergétique est comparé à un système classique pour un emploi dans des bâtiments industriels et commerciaux. Les avantages économiques du nouveau système ont été démontrés par une évaluation des dépenses énergétiques. Il ressort de l'analyse comparative du coût du cycle de vie du nouveau et de l'ancien système qu'en dépit d'une légère augmentation du coût de départ, le nouveau système est nettement moins onéreux que l'ancien sur un cycle de vie complet de 50 ans. Les performances économiques du nouveau système sont supérieures à celles du système classique, avec de meilleures performances énergétiques pour la conception de bâtiments commerciaux et industriels sous le climat australien.     

Developing diffusion bonding windows for joining AZ31B magnesium and copper alloys

In this investigation, Mg–Cu dissimilar materials are joined by diffusion bonding process. The principal difficulty when joining Mg–Cu lies in the existence of hard-to-remove oxide films on the magnesium surfaces and the formation of brittle metallic interlayers and oxide inclusions in the bond region. In this investigation, an attempt was made to develop diffusion bonding windows for effective joining of AZ31B Magnesium and commercial grade copper alloys. Joints were fabricated using different combination of process parameters such as bonding temperature, bonding pressure and holding time. The bonding quality was checked by microstructure analysis and lap shear tensile test. Based on the results, diffusion bonding windows were constructed, and they are presented in this paper. These windows will act as reference maps for selecting appropriate diffusion bonding process parameters to get good quality bonds for Mg–Cu alloys.