1,664 research outputs found

    Development of Vibration During the Electromagnetic Ring Expansion Test

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    Magnetic pulse forming (MPF) techniques work on the principle of Lorentz force induced by eddy current which can cause plastic deformation in a metal workpiece. Lorentz force depends on parameters such as frequency and amplitude of input current, electromagnetic properties of materials and distance between the work piece and coil. The development of vibration as a consequence of elastic strain recovery in a ring expansion process using a MPF technique has been identified and presented in this paper. Coupled mechanicalelectromagnetic 3D simulations were carried out to investigate the effect of various magnetic pulse currents in the development of reversal of motion during the MPF process using LS-DYNA package. Ring expansion using a multi-turn helix coil with an applied pulse current, with the rings made of aluminum alloy AA6061 –T6 is investigated for the effect of vibration during the process. The numerical results show good agreement with the experimental work for various currents. The underlying principle of vibration and formability has respectively been studied using force analysis and stress analysis. The results also show that the 5.6kJ energy already increased the formability by ~66 percent in comparison with the quasi-static formability value from the literature

    The Effects of Fiscal Policy on Human Capital Accumulation: Evidence from OECD Countries

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    By using dynamic panel data estimation techniques for twenty-one OECD countries, this paper investigates the effects of government expenditures and four different types of tax policy innovations on the human capital accumulation process. Our results show that only income taxes have a significant negative effect on investment in human capital, measured by the tertiary enrolment rate

    Coupling Experiment and Simulation in Electromagnetic Forming Using Photon Doppler Velocimetry

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    Modeling electromagnetic forming processes is in many ways simpler than modeling traditional metal forming processes. In electromagnetic forming the problem is often dominated by inertial acceleration by a magnetic field. This is a much better posed problem than the more traditional ones that are often dominated by complex three dimensional constitutive behavior and frictional effects. However, important aspects of the problem are dominated by the constitutive properties of the material, and often electromagnetic forming is performed in a regime where there is little reliable material strength data. Strain rates are often high (102 to 104 s-1 is the typical range for electromagnetic forming). Also, heat is generated both by ohmic heating as well as by plastic deformation, and peak temperatures can be quite high. Also, while hightemperature, high-strain-rate data is scarce, there is little or no data in cases where temperature rises significantly over very short times (tens of micro-seconds) as happens in electromagnetic metal forming. This rapid temperature rise is very important to the material response because the short time scales largely preclude the material from recovery and recrystallization processes and precipitates cannot dissolve as they normally would in an age-hardening alloy in these time scales. This presentation will show how advanced instrumentation, particularly the Photon Doppler Velocimeter (PDV) can be coupled with electromagnetic forming and provide both avenues to characterize material as well as to provide very critical tests of numerical models of the process

    Comparing Mean & Peak Barbell Velocity During Traditional and Accentuated Eccentric Loaded Back Squats

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    MV: There were statistically significant main effects present for both condition (p = 0.002; g = 0.10-0.23) and load (p \u3c 0.001; g = 0.95-3.93). However, the condition x time interaction effect was not statistically significant (p = 0.259). • PV: There were statistically significant main effects present for both condition (p = 0.016; g = 0.11-0.23) and load (p \u3c 0.001; g = 0.42-1.6), but there was no statistically significant condition x time interaction effect (p = 0.101). • Post hoc analysis indicated that there was a significant difference between MV (p = 0.006) and PV (p = 0.032) between the traditional and 100% AEL conditions. • Moderate effect sizes were found with MV between the traditional and 100% AEL conditions at both 70% CON (g = 0.55) and 80% CON (g = 0.70). • No practically significant differences were found for PV

    English secondary students’ thinking about the status of scientific theories: consistent, comprehensive, coherent and extensively evidenced explanations of aspects of the natural world – or just ‘an idea someone has’

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    Teaching about the nature of science (NOS) is seen as a priority for science education in many national contexts. The present paper focuses on one central issue in learning about NOS: understanding the nature and status of scientific theories. A key challenge in teaching about NOS is to persuade students that scientific knowledge is generally robust and reliable, yet also in principle always open to challenge and modification. Theories play a central role, as they are a form of conjectural knowledge that over time may be abandoned, replaced, modified, yet sometimes become well established as current best scientific understanding. The present paper reports on findings from interviews with 13–14 year olds in England where target knowledge presents theories as ‘consistent, comprehensive, coherent and extensively evidenced explanations of aspects of the natural world’. Student thinking reflected a two-tier typology of scientific knowledge in which largely unsupported imaginative ideas (‘theories’) became transformed into fairly definitive knowledge (such as laws) through relatively straightforward testing. These results are considered in relation to research into intellectual development which indicates that effective teaching in this area requires careful scaffolding of student learning, but has potential to contribute to supporting intellectual development across the curriculum.This is the author accepted manuscript. The final version is available from Taylor & Francis via http://dx.doi.org/10.1080/09585176.2015.104392

    A Cognitive Model of an Epistemic Community: Mapping the Dynamics of Shallow Lake Ecosystems

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    We used fuzzy cognitive mapping (FCM) to develop a generic shallow lake ecosystem model by augmenting the individual cognitive maps drawn by 8 scientists working in the area of shallow lake ecology. We calculated graph theoretical indices of the individual cognitive maps and the collective cognitive map produced by augmentation. The graph theoretical indices revealed internal cycles showing non-linear dynamics in the shallow lake ecosystem. The ecological processes were organized democratically without a top-down hierarchical structure. The steady state condition of the generic model was a characteristic turbid shallow lake ecosystem since there were no dynamic environmental changes that could cause shifts between a turbid and a clearwater state, and the generic model indicated that only a dynamic disturbance regime could maintain the clearwater state. The model developed herein captured the empirical behavior of shallow lakes, and contained the basic model of the Alternative Stable States Theory. In addition, our model expanded the basic model by quantifying the relative effects of connections and by extending it. In our expanded model we ran 4 simulations: harvesting submerged plants, nutrient reduction, fish removal without nutrient reduction, and biomanipulation. Only biomanipulation, which included fish removal and nutrient reduction, had the potential to shift the turbid state into clearwater state. The structure and relationships in the generic model as well as the outcomes of the management simulations were supported by actual field studies in shallow lake ecosystems. Thus, fuzzy cognitive mapping methodology enabled us to understand the complex structure of shallow lake ecosystems as a whole and obtain a valid generic model based on tacit knowledge of experts in the field.Comment: 24 pages, 5 Figure
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