Measurement and Stochastic Computational Modeling of the Elastic Properties of Parallel Strand Lumber

This paper describes a model for the spatial variation of the elastic modulus of parallel strand lumber (PSL) that is based on bending experiments and also describes a validated stochastic computational model that incorporates orthotropic elasticity and uncertainty in strand geometry and material properties. The PSL exhibits significant variability both within members and between members, but this variability is less than that of equivalent sawn-wood members, and decreases with increasing member size. The correlation length of the elastic modulus is found to be several meters and is independent of the cross-sectional size. The variance of PSL elastic modulus is found to scale inversely with the number of strands in the cross section. The validated computational model is flexible enough to allow preliminary exploration of the properties of new mixes of species and strand sizes in PSL material design.     

Electrohydrodynamic atomization (EHDA) of high-conductivity pure solvent

ABSTRACT

In this study, the effects of flow rate, liquid conductivity and neutralizer strength on the operating and output characteristics are examined for an Electrohydrodynamic atomization (EHDA)-based aerosol generator system, designed and built in our laboratory. Ethylene glycol is used for generating the droplets. It is seen that stable cone-jet mode could be obtained for solvent conductivity as high as 240 μS/cm. While the output number concentration was found to increase with both flow rate and conductivity, the mean particle diameters decreased with increasing conductivity and increased with flow rate. The mean droplet size and output number concentration are found to be about three times more sensitive to changes in conductivity as compared to that of flow rate in the range of 26–150 μS/cm. It is also observed that throughput from the system is strongly dependent on the strength of the charge neutralizer. In the present setup, 8 μCi ²⁴¹Am bipolar neutralizer in axisymmetric configuration was found to be sufficient to neutralize the generated droplets.     

Data Replication in Cooperative Mobile Ad-Hoc Networks

The mobile computing environment provides many benefits such as ubiquitous access to computing but includes constraints on resources such as available bandwidth and battery life. Replication is a widely recognized method for balancing the demands of storage space with bandwidth and battery life. We propose a novel scheme that seeks to strategically balance these constrained resources through a cooperative game-theory approach for replication in a mobile environment. Our replication strategy relies on the cooperation of the nodes within the network to make replica caching decisions which are spatiotemporally local-optimal for the network from an energy and bandwidth conservation standpoint. In cooperative altruistic data replication, each node calculates the net global benefit, for caching a replica of the requested data, as the result data is returned from the responding node to the requesting node, where it determines the spatiotemporally local-optimal node for replicating the data item. Performance results from our research indicate that our scheme, CADR, improves the query response time by 25 and 45 %, mean hop count is improved by 26 and 46 %, query error is reduced by 30 and 48 %, while energy utilization is reduced 30 and 57 % when compared with both another game theoretic replication approach and standard cooperative caching respectively.     

Multiple sourcing decisions using integrated AHP and knapsack model: a case on carton sourcing

Purchase allocation is a multi criteria decision making (MCDM) problem. Multitude of qualitative and quantitative factors is involved in the multiple sourcing decisions. Analytic hierarchy process (AHP) has widely been used to find out the relative rankings of suppliers. AHP can be combined with regular supplier quantitative audit process. In classical AHP, decision maker (DM) has to pair wise compare suppliers for each factor, whereas the proposed audit based simplified AHP will remove the complexity of comparison. Quarterly audit-based AHP rankings and supplier performance probability products can be used in place of revenues in the backward recursive resource allocation knapsack model. This combined model will decompose purchase allocation problem into different stages and combine one supplier at each stage and provide the optimum and feasible solution in the end. Solution at each stage is also a feasible option. This model is only applicable when the total order quantity and the capacity of all suppliers are integer multiples of economic or minimum order quantity. This integrated model thus provides number of orders/supplier.     

Field Assessment of the Performance of a Ballasted Rail Track with and without Geosynthetics

Understanding the complex mechanisms of stress transfer and strain accumulation in layers of track substructure under repeated wheel loading is essential to predict the desirable track maintenance cycle as well as the design of the new track. Various finite element and analytical techniques have been developed in the past to understand the behavior of composite track layers subjected to repeated wheel loads. The mechanical behavior of ballast is influenced by several factors, including the track confining pressure, type of aggregates, and the number of loading cycles. A field trial was conducted on an instrumented track at Bulli, New South Wales, Australia, with the specific aims of studying the benefits of a geocomposite installed at the ballast-capping interface, and to evaluate the performance of moderately graded recycled ballast in comparison to traditionally very uniform fresh ballast. It was found that recycled ballast can be effectively reused if reinforced with a geocomposite. It was also found that geocomposite can effectively reduce vertical and lateral strains of the ballast with obvious implications for improved track stability and reduced maintenance costs.     

Selection of a pull production control policy under different demand situations for a manufacturing system by AHP-algorithm

A multistage serial production system is considered in the present paper. A generalized model has been developed with the use of probabilistic demand situations for the end product. The demand situations considered are binomial, exponential, lognormal and Poisson. These demand patterns are used as input parameter for various production control policies. The output values for performance parameters are obtained by simulation. The production policies analyzed are Kanban, CONWIP and Hybrid as alternatives for controlling the engineering manufacture. In the presence of several performance measures, it often becomes difficult for the management to select the most appropriate policy. Analytic hierarchy process (AHP) has been implemented for the purpose of selection. Computational results have been reported along with the sensitivity analysis after designing and conducting various experiments.     

Design and manufacturing advisor for turbine disks

The design and manufacturing advisor (DMA) is a generic architecture for an expert system which assists in the process of product design. It integrates various parts of the production environment which affect the final product—such as fabrication, assembly, inspection and inventory. The design process can be partitioned into four stages: problem specification, feature specification, testing and generation. DMA facilitates the development of tractable designs, defined by the intersection of three spaces relating to specifications, features and productibility. The system consists of a domain-independent module and a domain-dependent module, each of which contains subcomponents; this modular structure facilitats system modification, expansion, and portability. The DMA has been validated by specializing the architecture to the design of gas-turbine disks for jet engines.     

Scanning electron microscopy studies of abraded rubber surfaces

The surfaces of polybutadiene rubber (BR) and styrene-butadiene rubber (SBR) subjected to different degrees of abrasion have been studied by scanning electron microscopy (SEM). In the case of SBR it has been shown that abrasion begins with marks in the direction of rotation which are followed by fine ribbing and then by the formation of coarse, angular and prominent ridges. Prolonged abrasion produces folding and cavities on the surface. This change in abrasion mechanism has been explained as a result of heat build-up and high crack growth rate in SBR which occur beyond a certain stage. These help in softening the matrix and removing the surface. On the other hand, fractured surfaces of BR show that ridges begin to form at about 250 revolutions and there is no characteristic difference between the abraded surfaces at lower or higher degrees of abrasion.     

A transaction model and multiversion concurrency control for mobile database systems

Transaction management on Mobile Database Systems (MDS) has to cope with a number of constraints such as limited bandwidth, low processing power, unreliable communication, and mobility etc. As a result of these constraints, traditional concurrency control mechanisms are unable to manage transactional activities to maintain availability. Innovative transaction execution schemes and concurrency control mechanisms are therefore required to exploit the full potential of MDS. In this paper, we report our investigation on a multi-versions transaction processing approach and a deadlock-free concurrency control mechanism based on multiversion two-phase locking scheme integrated with a timestamp approach. We study the behavior of the proposed model with a simulation study in a MDS environment. We have compared our schemes using a reference model to argue that such a performance comparison helps to show the superiority of our model over others. Experimental results demonstrate that our model provide significantly higher throughput by improving degree of concurrency, by reducing transaction wait time, and by minimizing restarts and aborts.     

Adaptive searching and replication of images in mobile hierarchical peer-to-peer networks

Due to the limitation of resources in mobile handheld devices and bandwidth constraints in wireless networks, it is important to efficiently manage image content and traffic to improve network throughput and response time. The efficient distribution of images in wireless networks is based on many parameters like the quality of service requirement, available bandwidth, restricted memory and diverse user profiles. We consider digital images as data objects accessed in a hierarchical mobile ad-hoc peer-to-peer network, referred as M-P2P. Our objective is to optimize the number of replicas of images in such a network architecture based on the resource limitations of the requesting peers equipped with miniature mobile devices as well as of wireless constraints in mobile ad-hoc networks (MANET). While replicating images, fragments of different resolution and their residues are used to optimize the traffic in the network and to decrease the search turnaround time. We call this replication algorithm as Ada-Rep. Performance evaluation is done by simulating Ada-Rep, base replication and uniform replication methods to evaluate parameters such as response time, failure rate, memory usage, traffic etc. Our results prove the efficiency and better performance of Ada-Rep.