Dispersion analysis and computational efficiency of elastic lattice methods for seismic wave propagation

Discrete particle methods or elastic lattice methods represent a 3D elastic solid by a series of interconnected springs arranged on a regular lattice. Generally, these methods only consider nearest neighbour interactions, i.e. they are first-order in space. These interconnected springs interacted through a force term (Hooke's Law for an elastic body), which when viewed on a macroscopic scale provide a numerical solution for the elastodynamic wave equations. Along with solving the elastodynamic wave equations these schemes are capable of simulating elastic static deformation. However, as these methods rely on nearest neighbour interactions they suffer from more pronounced numerical dispersion than traditional continuum methods. By including a new force term, the numerical dispersion can be reduced while keeping the flexibility of the nearest neighbour interaction rule. We present results of simulations where the additional force term reduces the numerical dispersion and increases the accuracy of the elastic lattice method solution. The computational efficiency and parallel scaling of this method on multiple processors is compared with a finite-difference solution to assess the computational cost of using this approach for simulating seismic wave propagation. We also show the applicability of this method to modelling seismic propagation in a complex Earth model.     

Assessing the Accuracy of Cash Flow Models: The Significance of Payment Conditions

Cash flow forecasting methods have evolved to allow detailed predictions for individual projects. These methods, principally the cost-schedule integration (CSI) technique, make extensive use of project estimate and schedule data. An implicit assumption of these methods has been that accuracy is largely a function of the quality of data available to the model. To the writers’ knowledge, there has been no assessment of the ability of project specific cash-flow models to accurately predict cash flows given accurate input data. This paper makes two contributions. First, two complementary methods are presented—pattern matching logic and factorial analysis—that provide an ability to assess the accuracy of cash flow models. Second, through demonstration of these methods using data from two projects, a critique is made of the ability of existing CSI models to accurately predict cash flows. The paper concludes by recommending extensions of CSI models to include more detailed payment conditions, including differential payment lags, components for materials and labor, and payment frequency. A further conclusion is the call for more research to better understand the balance between managers’ need for information and the ability of predictive models to provide that information.     

A Combined Multi-Technique In Situ Approach Used to Probe the Stability of Iron Molybdate Catalysts During Redox Cycling

A setup combining a number of techniques (WAXS, XANES and UV–Vis) has been used to probe the stability of an iron molybdate catalyst during redox cycling. The catalyst was first reduced under anaerobic methanol/helium conditions, producing formaldehyde and then regenerated using air. Although in this test-case the catalyst and conditions differ from that of a commercial catalyst bed we demonstrate how such a setup can reveal new information on catalyst materials. In particular we observe the formation of two phases during reduction; one which we propose to be an oxygen deficient ‘pseudo-molybdate phase’, the other a molybdenum carbide-like phase, both produced as oxygen is removed from the catalyst. Standard in situ techniques could detect such transient phases, however, the information from multiple techniques, allows us to more accurately identify the nature of these materials and to carry out appropriate complementary ex situ measurements to aid in the analysis. This and similar setups therefore offer a way to more quickly and accurately observe reaction pathways within a catalyst, which may for example, result in the deactivation of the material by different routes to those observed previously. Additionally, the specific combination of these techniques with on-line mass spectrometry, allows us to monitor the activity of the catalyst surface and here observe that different catalytic mechanisms may occur during different stages of the redox process. Therefore this setup should allow for the observation of many novel variations in a catalyst’s reactivity, leading to the improvement of current and development of new materials. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Influence of Compression and Shear on the Strength of Composite Laminates with Z-Pinned Reinforcement

The influence of compression and shear loads on the strength of composite laminates with z-pins is evaluated parametrically using a 2D Finite Element Code (FLASH) based on Cosserat couple stress theory. Meshes were generated for three unique combinations of z-pin diameter and density. A laminated plate theory analysis was performed on several layups to determine the bi-axial stresses in the zero degree plies. These stresses, in turn, were used to determine the magnitude of the relative load steps prescribed in the FLASH analyses. Results indicated that increasing pin density was more detrimental to in-plane compression strength than increasing pin diameter. Compression strengths of lamina without z-pins agreed well with a closed form expression derived by Budiansky and Fleck. FLASH results for lamina with z-pins were consistent with the closed form results, and FLASH results without z-pins, if the initial fiber waviness due to z-pin insertion was added to the fiber waviness in the material to yield a total misalignment. Addition of 10% shear to the compression loading significantly reduced the lamina strength compared to pure compression loading. Addition of 50% shear to the compression indicated shear yielding rather than kink band formation as the likely failure mode. Two different stiffener reinforced skin configurations with z-pins, one quasi-isotropic and one orthotropic, were also analyzed. Six unique loading cases ranging from pure compression to compression plus 50% shear were analyzed assuming material fiber waviness misalignment angles of 0, 1, and 2°. Compression strength decreased with increased shear loading for both configurations, with the quasi-isotropic configuration yielding lower strengths than the orthotropic configuration.     

Spheroidization cycles for medium carbon steels

An investigation has been made of spheroidization of medium carbon steels used in the bolt industry. Two process cycles were considered. One was the intercritical cycle, widely used in industry, in which the steel was heated above the lower critical, A1, temperature for approximately 2 hours; then cooled below it; and held for various periods to allow the austenite to transform and carbides to spheroidize. The other process was a subcritical cycle, which involved heating to below the A1 for various times. Wire samples of two steels were studied: AISI 1541, which is high in manganese and considered difficult to spheroidize, and AISI 4037, which is considered easier to spheroidize and is used extensively in industrial applications. Both cycles produced similar drops in hardness. However, 1 hour of the subcritical cycle yielded greater ductility than 32 hours of the intercritical process, as measured by tensile tests. Results of a new flare test designed to evaluate formability also indicated much faster spheroidization in the subcritical cycle. The level of spheroidization was defined in this study to be the percentage of carbide particles with aspect ratios less than 3. In 30 minutes, the subcritical cycle produced the same percentage of particles with an aspect ratio of less than 3 as produced by the intercritical cycle in 32 hours. The fast spheroidization in the subcritical process is attributed to the fine pearlite generated by the current practice of rapid cooling off the hot mill. This advantage is lost in the intercritical process as the original pearlite is dissolved above the A1 temperature.     

Management of Construction Firm Performance Using Benchmarking

In today’s highly competitive construction industry, there is a critical need for managers to continuously improve their firm’s efficiency and effectiveness. More specifically, managers need to know which performance measures are most critical in determining their firm’s overall success. Benchmarking, when done properly, can accurately identify both successful companies and the underlying reasons for their success. However, rigorous benchmarking within the construction industry still remains an embryonic field. This paper analyzes and critiques both the performance measures and metrics used traditionally in the construction industry and the benchmarking models developed to date for the industry. Based on the results of this analysis, benchmarking models using data envelope analysis are proposed that offer significant improvements over current models. The proposed models measure construction firm performance on a company-wide basis, foster trade-off analyses among various performance metrics, and tie the resources expended by construction firms to how well those firms perform overall. The models also provide managers guidance in determining how specific company resources can be reallocated to improve overall company performance.     

Designing systems for new users

This paper discusses the relationship between a system and ‘noncaptive’ users and the qualities which make a good system. Various methods for designing systems are considered and the author's development of meeting design (shared experience events) is presented.     

Towards predicting post-editing productivity

Machine translation (MT) quality is generally measured via automatic metrics, producing scores that have no meaning for translators who are required to post-edit MT output or for project managers who have to plan and budget for translation projects. This paper investigates correlations between two such automatic metrics (general text matcher and translation edit rate) and post-editing productivity. For the purposes of this paper, productivity is measured via processing speed and cognitive measures of effort using eye tracking as a tool. Processing speed, average fixation time and count are found to correlate well with the scores for groups of segments. Segments with high GTM and TER scores require substantially less time and cognitive effort than medium or low-scoring segments. Future research involving score thresholds and confidence estimation is suggested.     

Parent and peer relationships and relational spirituality in adolescents and young adults.

Research showing the protective qualities of Relational Spirituality, the experience of an ongoing dynamic personal relationship with G-d, against psychopathology in adolescents prompted the current investigation of its developmental correlates. Relational Spirituality in adolescence has been shown to have an unfolding heritable contribution and to be intertwined with a process of spiritual individuation, to which the current study adds the contribution of parents and peers to the developmental process. Participants were 615 adolescents and young adults representing a diverse range of ethnicities and religious affiliations. To measure parenting and friend variables, the Parental Bonding Instrument (PBI), Parental Spiritual Support Scale, and Friends Spiritual Support Scale were utilized. Relational Spirituality was measured using items from several subscales of the Brief Multidimensional Measure of Religiousness/Spirituality to obtain a composite score. Findings of multivariate regression analyses indicated that Maternal Spiritual Support, Paternal Care, and Friends Spiritual Support were significantly positively associated with Relational Spirituality, with Maternal Spiritual Support influencing the selection of peers who offer Friends Spiritual Support. These results underscore the importance of parents and peers in facilitating the development of Relational Spirituality, particularly through maternal openness to discussion about spirituality/religiosity and through paternal affection. (PsycINFO Database Record (c) 2011 APA, all rights reserved)