An extended core‐based framework for delay‐constrained group communication

Multipoint communications is the simultaneous transmission of data streams from a number of sources to a set of receivers in a group according to predetermined metrics. The core‐based approach in multipoint communication enhances potential solutions in terms of quality‐of‐service (QoS)‐efficiency and feasibility of the results in inter and intra‐domain routing. In this paper, we first analyse the solution space for constrained multipoint communication problems under the core‐based approach. We show that the range of solutions examined by the models proposed to date is restricted to a subset of the entire solution space, which restricts the potential efficiency of the results. We propose SPAN, a core‐based framework processing on our identified extended solution space for constrained multi‐source group applications. SPAN consists of core selection and tree construction as two modular components complimenting one another to achieve more efficient solutions in distributed processing. SPAN is also asymmetric, hence potentially operates in domains in which link weights are not necessarily equal in both directions. We analyse the computational and message complexity of our framework and show its feasibility for distributed deployment. Our performance results show that SPAN consistently outperforms its counterparts in the literature in terms of cost and QoS‐efficiency. Copyright © 2007 John Wiley & Sons, Ltd.     

On lifetime-oriented device provisioning in heterogeneous wireless sensor networks: approaches and challenges

With the promise of being a revolutionary innovation for ubiquitous surveillance and monitoring, wireless sensor networks have attracted increasing interest from both academia and industry. One of the critical challenges facing successful WSN implementation is limited lifetime, which is imposed by the limited power supply of non-replenishable batteries on devices. In this article we concentrate on the impact of device provisioning on the usable system lifetime. We introduce a device provisioning framework based on hierarchical communication architecture. The device provisioning strategies are classified into two groups based on the application scenarios: deterministic and random. We investigate and compare the latest approaches for deterministic and random device provisioning. We also discuss open issues in each category.     

Factors affecting the bidding behaviour of contractors in Egypt

The financing source was determined to be the most important to the category of contractors included in the study. Other qualitative factors such as nationality of expected competitors were determined as influencing the decision. The factors and their influence on the bid/no bid decision differed between the Egyptian and foreign large size contractors operating in the country.     

Experimental analysis of energy recovery for humidity control in split A/C system

This study presents a proposed idea about making use of the thermal energy rejected by the condenser in a water-cooled split-air-conditioning systems to decrease the relative humidity of the cold air supplied by such air conditioners. Most of split air-conditioner systems cool air without controlling its humidity. An amount of heat is rejected from the air conditioner, through the condenser, into the surrounding in order to allow the refrigerant to cool down and condense, thus, part of the lost energy can be exploited to decrease the relative humidity of the sub-cooled air that leaves the evaporator as saturated humid air. Four variables, viz. the coil type (single or double), the amount of flowing water, water, temperature, and the cooled air velocity were studied to find out the optimum conditions required for this purpose. The requisite amount of heat that may adjust the relative humidity of the conditioned air was also determined. The experimental results suggest an optimum design of a heat exchanger for performing the use of the heat rejected from the condenser to achieve the aim. As a result, the proposed heat recovery concept can be worthily adopted to achieve economic results in large-scale systems.     

On the effect of reservation period on performance of IEEE 802.16 R‐MAC protocol

The IEEE 802.16 standard is gaining broad consideration to serve the expanding demand for broadband access networks. In this standard, the best effort traffic uses the reservation multiple access control (MAC) mechanism, which is widely adopted in recent broadband network technologies. The goal of this paper is to study the performance of the MAC protocol of the best effort traffic in the IEEE 802.16 standard with emphasis on the size of the reservation period. We use a two‐stage Markov chain model to capture all possible events on the reservation and service periods. This allows the computation of the inflow and outflow of bandwidth requests (BWRs) and their associated data packets which leads to the delay and throughput formulas. By means of illustrative examples and numerical results, validated through simulation, we investigate the key importance of the size of reservation period. We highlight potential performance improvement, through opportunistic dynamic control of the size of the reservation period to enhance the performance of reservation MAC protocol. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental investigation on concrete-filled stainless steel stiffened tubular stub columns

This paper presents an experimental investigation on concrete-filled normal-strength stainless steel stiffened tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). The stiffened stainless steel tubes were fabricated by welding four lipped angles or two lipped channels at the lips. Therefore, the stiffeners were formed at the mid-depth of the sections. In total, five hollow columns and ten concrete-filled columns were tested. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to behave as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. A series of tests was performed to investigate the effects of cross-section shape and concrete strength on the behavior and strength of concrete-filled stainless steel stiffened tubular stub columns. The measured average overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. Different lengths of columns were selected to fix the length-to-depth ratio to a constant value of 3. The concrete-filled stiffened stainless steel tubular columns were subjected to uniform axial compression over the concrete core and the stainless steel tube to force the entire section to undergo the same deformations by blocking action. The column strengths, load–axial strain relationships and failure modes of the columns are presented. Several comparisons were made to evaluate the test results. The results of the experimental study showed that the design rules, as specified in the European specifications and the ASCE, are highly conservative for square and rectangular cold-formed concrete-filled normal-strength stainless steel stiffened stub columns.     

Testing for stability: Motor gasoline demand and distillate fuel oil demand

The structural stability of energy demand relationships is an important question in light of the events of the 1970s. This paper looks at this issue for two energy types, motor gasoline and distillate fuel oil (home heating oil). From the results of a statistical test developed by Brown, Durbin and Evans, it appears that the demand for motor gasoline destabilized following the 1979 Iranian revolution while the demand for distillate fuel oil destabilized following the very severe winter of 1976–1977. Once destabilized, neither of the demand relationships returned to their prior form.     

Quantile Estimates in Complete and Censored Samples From Extreme-Value and Weibull Distributions

This paper deals with the problem of estimating the quantiles (?) = 0.01, 0.05(0.05)0.95, 0.99 of the largest extreme-value distribution by using order statistics in small samples. Linear unbiased estimators, with minimum variance, based on ordered observations are constructed for sample sizes 5(5)20 for both complete and right-censored samples.     

Prediction of material erosion and lifetime during major plasma instabilities in tokamak devices

Surface and structural damage to plasma-facing components due to the frequent loss of plasma confinement remains a serious problem for the tokamak reactor concept. The deposited plasma energy during major disruptions, edge-localized modes (ELMs), and vertical displacement events (VDEs) causes significant surface erosion, possible structural failure, and frequent plasma contamination. Surface damage consists of vaporization, spallation, and liquid splatter of metallic materials. Structural damage includes large temperature increases and high thermal stresses in structural materials and at the interfaces between surface coatings and structural members. To evaluate the lifetimes of plasma-facing materials and nearby components and to predict the various forms of damage that they experience, comprehensive models (contained in the computer simulation package) are developed, integrated self-consistently, and enhanced. Splashing mechanisms such as bubble boiling and various liquid magnetohydrodynamic (MHD) instabilities and brittle destruction mechanisms of nonmelting materials can be serious erosion mechanisms and are being studied in detail. The ejected macroscopic particles (MPs) will interact with incoming plasma particles and with the vapor cloud above the surface. Therefore, the dynamic behavior of MPs in the vapor cloud and their influence on total erosion rate is important. Results of self-consistent MHD calculations are presented in which the dynamics of both the vapor cloud and MP interaction are coupled with incoming plasma ions and electrons from the scrape-off layer during a disruption. The design requirements and implications of plasma facing and nearby components are discussed, along with recommendations to mitigate and reduce the effects of plasma instabilities on reactor components.     

The impact of distractions on the usability and intention to use mobile devices for wireless data services

Mobile technology has quickly become ingrained in society due to the flexibility of anywhere/anytime usage. However, factors associated with and that impact mobility, mobile users, and mobile use of products and services are still poorly understood. For example, even though distractions are ever present during everyday use of mobile devices, the nature and extent to which user perceptions and performance are affected by their presence is unknown. An empirical study was undertaken to investigate the impact of distractions and confirmation of pre-trial expectations on usability and its subsequent effect on consumers’ behavioral intention toward using a mobile device for wireless data services. Distractions were simulated in this study in the form of either user motion or environmental noise (i.e. background auditory and visual stimuli). A Structural Equation Modelling (SEM) analysis confirmed the impacts of distractions on efficiency and effectiveness, and in turn the users’ satisfaction and behavioral intention to use a mobile device for wireless data services. Support was also obtained for a mediating effect of post-trial confirmation of expectations between perceived performance and satisfaction. Implications of these findings for theory, practice, and future research are outlined.