Influence of Aging Parameters on the Tensile Properties and Quality Index of Al-9?Pct Si-1.8?Pct Cu-0.5?Pct Mg 354-Type Casting Alloys

The current study was carried out with a view to investigating the influence of age-hardening parameters, aging temperature and time, on the tensile properties and quality indices of a high-strength Al-9 pct Si casting alloy, namely, 354-Al-9 pct Si-1.8 pct Cu-0.5 pct Mg. Quality charts were used as an evaluation tool for selecting the optimum conditions to be applied, in practice, in order to develop high strength and optimum quality in 354 casting alloy. Aging at a low temperature of 428 K (155 °C) was observed to produce the greatest strength and optimum quality in the 354-type castings compared to aging at higher temperatures. The peak strength observed for 354 alloy may be attained after shorter aging times on the condition that the aging temperature is increased. The aging times required for reaching peak strength in 354 alloys are 72 hours, 40 hours, 8 hours, 1 hour, and 15 minutes at aging temperatures of 428 K, 443 K, 468 K, 493 K, and 518 K (155 °C, 170 °C, 195 °C, 220 °C, and 245 °C), respectively. Aging treatment at higher temperatures is accompanied by a reduction in the tensile properties and quality index values of the castings; however, it also introduces the possibility of a significant economical strategy for minimizing the time and the cost of this same treatment. Aging treatment at a lower temperature of 428 K (155 °C) produces fine and dense precipitates displaying smaller interparticle spacing, while at higher aging temperatures, such as 518 K (245 °C), the precipitates are coarser in size, less dense, and more widely dispersed. The quality charts developed in the course of the current research facilitate the interpretation and evaluation of the tensile properties of the 354 alloy. Such charts provide a logical evaluation tool, from the metallurgical point of view, for an accurate prediction of the influence of aging parameters studied on the properties of the alloys. Depending on the required level of tensile properties and based on the quality charts developed, it is possible to make a rigorous selection as to the most suitable aging parameters to be applied to the 354 alloy so as to obtain the best possible cost-effective compromise between alloy strength and quality.     

A scenario-based reliability analysis approach for component-based software

This paper introduces a reliability model, and a reliability analysis technique for component-based software. The technique is named Scenario-Based Reliability Analysis (SBRA). Using scenarios of component interactions, we construct a probabilistic model named Component-Dependency Graph (CDG). Based on CDG, a reliability analysis algorithm is developed to analyze the reliability of the system as a function of reliabilities of its architectural constituents. An extension of the proposed model and algorithm is also developed for distributed software systems. The proposed approach has the following benefits: 1) It is used to analyze the impact of variations and uncertainties in the reliability of individual components, subsystems, and links between components on the overall reliability estimate of the software system. This is particularly useful when the system is built partially or fully from existing off-the-shelf components; 2) It is suitable for analyzing the reliability of distributed software systems because it incorporates link and delivery channel reliabilities; 3) The technique is used to identify critical components, interfaces, and subsystems; and to investigate the sensitivity of the application reliability to these elements; 4) The approach is applicable early in the development lifecycle, at the architecture level. Early detection of critical architecture elements, those that affect the overall reliability of the system the most, is useful in delegating resources in later development phases.     

Blind Channel Identifiability for Generic Linear Space-Time Block Codes

Linear space-time block codes (STBCs) have proven their effectiveness in performance improvement of wireless multiple-input multiple-output communication systems. Their successful decoding, however, requires reliable channel knowledge at the receiver. In this paper, we present a semiblind channel estimation method for linear STBC without the usual code orthogonality condition. We provide a set of identification conditions that are mostly verifiable a priori in terms of code parameters and antenna array configuration. We also present a simple channel estimation algorithm. Finally, we provide simulation results that illustrate the performance of the proposed scheme     

A low-dispersion 3-D second-order in time fourth-order in space FDTD scheme (M3d/sub 24/)

A second-order in time fourth-order in space modified finite-difference time-domain (FDTD) scheme for three dimensional electromagnetic problems "M3d/sub 24/" is presented. The algorithm enables the numerical phase error to be minimized, so that it leads to high accuracy with low resolution grids. The advantage of this method is demonstrated by considering the long distance propagation of the wave radiated from a time harmonic elementary dipole using a low resolution grid, and comparing the results with other FDTD schemes.     

Dynamic Host-Group/Multi-Destination Routing for Multicast Sessions

Multicast routing research efforts have mostly focused on supporting the host-group model in which multicast packets are addressed to a host (or multicast) group. Another multicast routing approach uses multi-destination addressing, where a multicast packet carries a list of the unique (unicast) addresses of all the group members. This form of routing can be accomplished using limited or no additional state beyond the existing unicast routing tables. It, therefore, scales well with the number of multicast sessions but does not scale well with the size of the multicast group and, in fact, requires the size of the multicast group to be below a certain threshold. In this paper, we envision a future scenario in which both host-group and multi-destination addressing routing approaches coexist within the Internet. We develop a dynamic routing context for this future scenario wherein a multicast session can adapt among different routing configurations depending on the number of multicast group members and how this number changes over time. We consider three routing options: (1) A single multi-destination addressed flow – suitable for small-group sessions, (2) multiple multi-destination addressed flows – suitable for medium-group sessions and (3) a single host-group addressed flow – suitable for large-group sessions. For multicast sessions that vary in group membership over time, different routing protocols may be best at different points in time. Our work is concerned with the development and evaluation of protocols that allow a multicast session to dynamically switch among these three routing options as the size of the session changes.     

An efficient reduced simulation of residual stresses in composite forming processes

An efficient simulation of thermal and mechanical models involved in thermosetting composites forming needs to overcome some numerical difficulties related to: (i) the multi-scale behaviour; (ii) the complex geometries involved needing too many degrees of freedom; (iii) the large time intervals where the solution has to be computed; (iv) the non-linearity of the involved evolution equations; (v) the numerous couplings… In this work, an efficient strategy based on a separated representation is proposed. This method enables to avoid the use of an incremental strategy and can lead to impressive computing time savings especially when the model involves fine meshes and very small time steps. The local non-linear chemical kinetics and its coupling with the global heat balance equation are naturally introduced in the separated representation algorithm. Moreover, the dependence of the thermal conductivity and the specific heat on the temperature and on the reaction advancement degree are also taken into account. Knowing the history of the temperature field, the separated representation is again used to solve the thermo-mechanical problem in order to determine the residual stresses.     

Evaluation of a cocktail of three bacteriophages for the biocontrol of Salmonella of wastewater

Salmonella serovars are increasing in importance as significant pathogens of both human and animals. Although water and wastewater are treated to eliminate pathogenic microorganisms, they still play an important role in the transmission of Salmonella spp. In this study, bacteriophages infecting Salmonella spp. were isolated from wastewater and evaluated; for their potential to lyse environmental Salmonella strains in vitro at different MOIs and temperatures; and to control the wastewater bacterial community. Three distinct phages designated sww65, sww275, and sww297; as defined by plaque morphology, electron microscopy and host range; were obtained from wastewater. Challenge tests were performed at 37, and 30 °C with the infection of the Salmonella cultures with individual phage, a mixture of two phages, and cocktail of three phages at MOIs of 10⁰, 10², and 10⁴ PFU/CFU. At 30, and 37 °C, a cocktail of three phages reduced all of the Salmonella cultures tested. These results required a high multiplicity of infection. However, when infected with only one phage or a mixture of two phages at MOIs of 10⁰ or 10 ² PFU/CFU, an emergence of bacterial resistance was observed. The dynamic monitoring of wastewater enterobacterial community was conducted using Enterobacterial Repetitive Intergenic Consensus-PCR (ERIC-PCR). The number of bands decreased gradually with the use of individual phage or phage cocktails. Moreover, the dynamic monitoring of Salmonella community during wastewater treatment was performed using PCR detection of virulence gene invA. The results correlated with the ERIC-PCR fingerprints, and suggested that Salmonella community was affected by the phage treatment. Indeed, in wastewater, bacteriophages are reducing Salmonella and other members of the Enterobacteriaceae. These results indicated that dynamic changes are closely related with the process of treatment. The introduction of wide host range bacteriophages in wastewater can have a potential impact on the dynamics of the microbial communities, manifested by the reduction or the elimination of microbial species.     

Thermal Conductivity of Silicate and Borate Glasses

Thermal conductivities of silicate and borate glasses were determined at 30°C by steady-state methods. From the experimental data, factors representing the contribution of individual oxides (on a weight-percent basis) were calculated by the least-squares method. The experimental thermal conductivities and those calculated from the factors obtained agree fairly well.