It is a common, puzzling, and often disheartening experience for teachers at all levels to realize that they may have little credibility in the eyes of their students, especially regarding the applicability of the les...
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It is a common, puzzling, and often disheartening experience for teachers at all levels to realize that they may have little credibility in the eyes of their students, especially regarding the applicability of the lessons taught in the classroom to 'real world' situations. This paper analyzes the results of using a reflective writing/research paper in a freshman engineering design course to assist students in making real world connections to classroom topics. In addition to writing a standard research paper on topics related to engineering design, students were required to write a personal reflection on the assignment before and after its completion. Comparisons of these pre-assignment and post-assignment reflections show a substantial shift in the students' attitudes toward the credibility of their instructor and the choice of curriculum and topics for the course. The results also show that students spent time in metacognitive reflection on their own beliefs about the applicability of course work to the world of the working engineer. While not every student experienced these attitude shifts, review of these papers did show a substantial enough positive shift occurred through this writing process to promote further research in this area.
This paper discusses the changes in attitudes about engineering before and after an introductory course in engineering design offered to in-service secondary math and science teachers. The course is part of a series o...
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This paper discusses the changes in attitudes about engineering before and after an introductory course in engineering design offered to in-service secondary math and science teachers. The course is part of a series of courses offered through the NSF-sponsored MSP (Math and science Partnership): Project Pathways designed to help integrate mathematic and science and can be taken as partial fulfillment of a Master's degree in science/Math Education. An attitude survey based on the well-documented PFEAS (Pittsburgh Freshmen engineering Attitude Survey) was administered to the teachers taking the course. The survey was given at the beginning and end of the Fall 2006 semester. The greatest difference in the teachers' attitudes was in the area of engineering being perceived as an exact science. On a 5-point Likert scale, the teachers' mean responses to the group of questions regarding engineering being perceived as an exact science had a statistically significant mean difference of -.68, p<.01. The teachers showed significant differences on three other scales as well (engineering compatibility, confidence in basic engineering knowledge and skills, and overall computer skills). Additional open-ended questions showed a gain in the teachers' general knowledge about engineering as a profession and their ability to recognize students in their courses that might be successful as engineering students following their graduation from high school.
This paper describes the fabrication of near infra-red (NIR) antireflective micro structures on a phosphorus doped Si-wafer by direct write EB- lithography followed by RIE-etching. The Fourier transform infra-red (FTI...
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This paper describes the fabrication of near infra-red (NIR) antireflective micro structures on a phosphorus doped Si-wafer by direct write EB- lithography followed by RIE-etching. The Fourier transform infra-red (FTIR) measurement done from the structured surface clearly shows a reflection dip at 1.42 μm and 2.5 μm respectively. It is also found that a change in pattern size, shape and its periodicity results a shift in reflection dip accordingly. This dip in reflection spectra is caused by the surface plasmon excitation due to interaction between the incoming photon and surface plasmon resonance. Its application in the frequency selective surfaces (FSS) such as antireflection surface for effective solar radiation absorption can be realized.
Reactive materials are being intensively studied for projectile applications in military operations in urban terrain (MOUT). The requirements are a high density and exothermic reaction initiation upon impact and fract...
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ISBN:
(纸本)1604232226
Reactive materials are being intensively studied for projectile applications in military operations in urban terrain (MOUT). The requirements are a high density and exothermic reaction initiation upon impact and fracture. This paper is concerned with PTFE/Al/W granular materials that underwent high-strain, high-strain-rate deformation in drop-weight tests. The primary function of W is to increase the density of the mixture, although it may also participate in the exothermic reactions with Al. The purpose of this research is to investigate mechanical response, including fracture mechanism, of a PTFE/Al/W mixture under high-strain and high-strain-rate flow. Therefore, the drop-weight technique was adopted, since the weight has sufficient energy to subject the specimens to large strains at controlled conditions. The PTFE/Al/W composite was fabricated by cold uniaxial pressing at a pressure of 100 MPa. The initial powders had the following average sizes: AI: 2 and 95 μm (ValimeH-2 and H-95);W: 44 μm (Teledyne, -325mesh);PTFE: 100 nm (DuPont, PTFE 9002-84-0, type MP 1500J). The unconfined and confined specimens were tested. The use of confinement rings of an aluminum alloy 7075-T6 enabled arrest of the deformation at different strains. Aluminum rings with the same height as the specimens and thicknesses of 0.5, 1, 1.5, and 2 mm were used. The impact velocities were 3.5 and 5 m/s. Due to the presence of the confinement ring, the velocity of the drop weight decreases faster with increase of the thickness of aluminum rings. As the confinement ring thickness increased the total deformation undergone by specimens decreased. The 0.5 mm ring underwent total buckling and folding, whereas the 1mm ring underwent barreling and lateral cracking. On the other hand, the 1.5 and 2 mm rings retained their cylindrical shape. The aluminum ring (2 mm thick) was tested separately both quasistatically and dynamically. The results indicate that the dynamic strength of the aluminum alloy used
The shock wave structure in a one-dimensional lattice (e.g., granular chain of elastic particles) with a power law dependence of force on displacement between particles (F∝δn) with viscous dissipation is considered ...
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The shock wave structure in a one-dimensional lattice (e.g., granular chain of elastic particles) with a power law dependence of force on displacement between particles (F∝δn) with viscous dissipation is considered and compared to the corresponding long wave approximation. A dissipative term depending on the relative velocity between neighboring particles is included to investigate its influence on the shape of a steady shock. The critical viscosity coefficient pc, defining the transition from an oscillatory to a monotonic shock profile in strongly nonlinear systems, is obtained from the long-wave approximation for arbitrary values of the exponent n. The expression for the critical viscosity is comparable to the value obtained in the numerical analysis of a discrete system with a Hertzian contact interaction (n=3∕2). The expression for pc in the weakly nonlinear case converges to the known equation for the critical viscosity. An initial disturbance in a discrete system approaches a stationary shock profile after traveling a short distance that is comparable to the width of the leading pulse of a stationary shock front. The shock front width is minimized when the viscosity is equal to its critical value.
Mechano-active scaffolds were fabricated from very elastic poly(L-lactide-co-Ε-carprolactone). The scaffolds with 80% porosity and 300-500 um pore size were prepared by a gel-pressing method. As a control group for e...
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Mechano-active scaffolds were fabricated from very elastic poly(L-lactide-co-Ε-carprolactone). The scaffolds with 80% porosity and 300-500 um pore size were prepared by a gel-pressing method. As a control group for elastic properties of polymer scaffolds, rigid poly L-lactide scaffolds were fabricated. The scaffolds were seeded with chondrocytes and cultured to evaluate the effect of elastic properties of polymer scaffolds for the differentiation and the ECM secretion of chondrocytes. Also, the chondrocytes-seeded constructs were implanted in nude mice subcutaneously to investigate their biocompatibility and cartilage formation. From the biochemical analyses, chondrogenic differentiation was sustained and enhanced significantly and chondral extracellular matrix was increased through mechanical stimulation of dynamic environment in the dynamic body systems. Histological analysis showed that implants of PLCL constructs formed mature and well-developed cartilaginous tissue, as evidenced by chondrocytes within lacunae. Consequently, the elastic PLCL scaffolds could be used to engineer cartilage in mechanically dynamic environments.
The observation of helices and coils in nano-tube/-fiber (NT/NF) syntheses is explained on the basis of the interactions between specific catalyst particles and the growing nanostructure. In addition to rationalizing ...
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Strongly nonlinear behavior of granular phononic crystals composed of stainless steel cylinders and PTFE spheres is considered experimentally and numerically. The tenability of phononic band gap in this two‐mass pres...
Strongly nonlinear behavior of granular phononic crystals composed of stainless steel cylinders and PTFE spheres is considered experimentally and numerically. The tenability of phononic band gap in this two‐mass prestressed chain was investigated. The results show that the phononic band gap exists within audible frequency regime (20–20,000 Hz) and can be tuned by changing the value of prestress. Influence of the weak and strong nonlinearity on the propagation of signals with frequencies inside band gap was investigated. The mechanical properties of reactive materials (e.g., high density mixtures of polytetraflouroethylene (PTFE), aluminum (Al) and tungsten (W) powders) where unconsolidated granular packing of metal particles plays significant role in the dynamic behavior was investigated. It was found that dynamic strength can be tailored by changing the morphology of the particles and porosity. Cold isostatically pressed PTFE‐Al‐W powder composites with fine metallic particles and a higher porosity exhibited higher ultimate compressive strength than less porous composites having equivalent mass ratios with coarse W particles. Based on the numerical analysis it was concluded that a mesoscale force chains between the fine metallic particles are responsible for this unusual phenomenon. This work was supported by the NSF DCMS03013220 and by MURI ONR N00014‐07‐1‐0740.
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