Stochastic finite element analysis of the free vibration of laminated composite plates

Using the Stochastic Finite Element Method (SFEM) to perform reliability analysis of the free vibration of composite plates with material and fabrication uncertainties has received much attention lately. In this work the stochastic analysis is performed using the First-Order Reliability Method (FORM-method 2) and the Second-Order Reliability Method (SORM). The basic random variables include laminae stiffness properties and material density, as well as the randomness in ply orientation angles. Modeling of the composite behavior utilizes a nine-noded isoparametric Lagrangian element based on the third-order shear deformation theory. Calculating the eigenvectors at the mean values of the variables proves to be a reasonable simplification which significantly increases solution speed. The stochastic finite element code is validated using comparisons with results of Monte Carlo simulation technique with importance sampling. Results show that SORM is an excellent rapid tool in the stochastic analysis of free vibration of composite plates, when compared to the slower Monte Carlo simulation techniques.     

Survey and Analysis of VoIP Frame Aggregation Methods over A-MSDU IEEE 802.11n Wireless Networks

The IEEE 802.11n standard has provided prominent features that greatly contribute to ubiquitous wireless networks. Over the last ten years, voice over IP (VoIP) has become widespread around the globe owing to its low-cost or even free call rate. The combination of these technologies (VoIP and wireless) has become desirable and inevitable for organizations. However, VoIP faces a bandwidth utilization issue when working with 802.11 wireless networks. The bandwidth utilization is inefficient on the grounds that (i) 80 bytes of 802.11/RTP/UDP/IP header is appended to 10–730 bytes of VoIP payload and (ii) 765 µs waiting intervals follow each 802.11 VoIP frame. Without considering the quality requirements of a VoIP call, be including frame aggregation in the IEEE 802.11n standard has been suggested as a solution for the bandwidth utilization issue. Consequently, several aggregation methods have been proposed to handle the quality requirements of VoIP calls when carried over an IEEE 802.11n wireless network. In this survey, we analyze the existing aggregation methods of VoIP over the A-MSDU IEEE 802.11n wireless standard. The survey provides researchers with a detailed analysis of the bandwidth utilization issue concerning the A-MSDU 802.11n standard, discussion of the main approaches of frame aggregation methods and existing aggregation methods, elaboration of the impact of frame aggregation methods on network performance and VoIP call quality, and suggestion of new areas to be investigated in conjunction with frame aggregation. The survey contributes by offering guidelines to design an appropriate, reliable, and robust aggregation method of VoIP over 802.11n standard.     

Stochastic Finite element analysis of the free vibration of functionally graded material plates

The superior properties of functionally graded materials (FGM) are usually accompanied by randomness in their properties due to difficulties in tailoring the gradients during manufacturing processes. Using the stochastic finite element method (SFEM) proved to be a powerful tool in studying the sensitivity of the static response of FGM plates to uncertainties in their material properties. This tool is yet to be used in studying free vibration of FGM plates. The aim of this work is to use both a First Order Reliability Method (FORM) and the Second Order Reliability Method (SORM), combined with a nine-noded isoparametric Lagrangian element based on the third order shear deformation theory to investigate sensitivity of the fundamental frequency of FGM plates to material uncertainties. These include the effect of uncertainties on both the metal and ceramic constituents. The basic random variables include ceramic and metal Young’s modulus and Poisson’s ratio, their densities and ceramic volume fraction. The developed code utilizes MATLAB capabilities to derive the derivatives of the stiffness and mass matrices symbolically with a considerable reduction in calculation time. Calculating the eigenvectors at the mean values of the variables proves to be a reasonable simplification which significantly increases solution speed. The stochastic finite element code is validated using available data in the literature, in addition to comparisons with results of the well-established Monte Carlo simulation technique with importance sampling. Results show that SORM is an excellent rapid tool in the stochastic analysis of free vibration of FGM plates, when compared to the slower Monte Carlo simulation techniques.     

Optical Interface for Bose-Einstein Condensates Using Permanent Magnetic Traps and Cavity QED

We propose a new type of a hybrid architecture based on the interaction of magnetically trapped ultracold quantum gases in a cavity QED structure. Permanent magnetic traps are integrated with silica based cavity QEDs and waveguides to facilitate the interaction between the atomic Bose-Einstein condensates with optical fields on an atomchip. One of the advantages of the permanent magnetic traps is negligible technical noise, and thus minimal decoherence is achieved in comparison to other conventional methods using current-carrying-wires. The proposed design allows an efficient delivery of optical fields (control/probe) to the magnetically trapped atoms through the fabricated silica waveguides coupled to the micro-cavities. In addition to the control of the ultracold atoms, the optical interface allows for the possibility of connecting several nodes together on the same atom chip, and could be used as part of future quantum information processing devices.     

Contractor Performance Evaluation for the Best Value of Superpave Projects

The best-value (BV) procurement process uses other key factors as well as bid price in the evaluation and selection of the best-performing contractor for the job. Contract time, lane rental, warranty, and quality of delivered product are examples of the key factors that indicate the contractor-expected performance. Literature on best value shows a need for analyzing the past performance of the contractor in similar jobs as an indicator of his/her qualification trend. This paper addresses this issue and proposes a methodology to incorporate quality of delivered product in the BV procurement system of asphalt construction. The paper uses past quality control (QC) testing results and utilizes Monte Carlo simulation to estimate the probability that the contractor gets full payment as an indication of qualification trend. The QC data were obtained from the Nebraska Department of Roads for a number of Superpave pavement projects. The results show the possibility of assigning a quality score for the contractor based on the past performance. This paper contributes to the current practice of best value with a new approach of employing QC as part of the selection process.     

Exploiting wavefront parallelism on large-scale shared-memorymultiprocessors

Wavefront parallelism, in which parallelism is limited to hyperplanes in an iteration space, can arise when compilers apply tiling to loop nests to enhance locality. Previous approaches for scheduling wavefront parallelism focused on maximizing parallelism; balancing workloads, and reducing synchronization. In this paper, we show that on large-scale shared-memory multiprocessors, locality is a crucial factor. We make the distinction between intratile and intertile locality and show that as the number of processors grows, intertile locality becomes more important. We consider and experimentally evaluate existing strategies for scheduling wavefront parallelism. We show that dynamic self-scheduling can be efficiently used on a small number of processors, but performs poorly at large scale because it does not enhance intertile locality. By contrast, static scheduling strategies enhance intertile locality for small tiles, maintaining parallelism and resulting in better performance at large scale. Results from a Convex SPP1000 multiprocessor demonstrate the importance of taking intertile locality into account. Static scheduling outperforms dynamic self-scheduling by a factor of up to 2.3 on 30 processors     

Functional Characterization of the MYO6 Variant p.E60Q in Non-Syndromic Hearing Loss Patients

Hereditary hearing loss (HHL) is a common genetic disorder accounting for at least 60% of pre-lingual deafness in children, of which 70% is inherited in an autosomal recessive pattern. The long tradition of consanguinity among the Qatari population has increased the prevalence of HHL, which negatively impacts the quality of life. Here, we functionally validated the pathogenicity of the c.178G>C, p.E60Q mutation in the MYO6 gene, which was detected previously in a Qatari HHL family, using cellular and animal models. In vitro analysis was conducted in HeLa cells transiently transfected with plasmids carrying MYO6^WT or MYO6^p.E60Q, and a zebrafish model was generated to characterize the in vivo phenotype. Cells transfected with MYO6^WT showed higher expression of MYO6 in the plasma membrane and increased ATPase activity. Modeling the human MYO6 variants in zebrafish resulted in severe otic defects. At 72 h post-injection, MYO6^p.E60Q embryos demonstrated alterations in the sizes of the saccule and utricle. Additionally, zebrafish with MYO6^p.E60Q displayed super-coiled and bent hair bundles in otic hair cells when compared to control and MYO6^WT embryos. In conclusion, our cellular and animal models add support to the in silico prediction that the p.E60Q missense variant is pathogenic and damaging to the protein. Since the c.178G>C MYO6 variant has a 0.5% allele frequency in the Qatari population, about 400 times higher than in other populations, it could contribute to explaining the high prevalence of hearing impairment in Qatar.