Residual Stresses in Layered Manufacturing

Layered Manufacturing processes accumulate residual stresses during materialbuildup. These stresses may cause part warping and layer delamination. This paper presents work done on investigating residual stress accumulation andp(i,rt distortion of Layered Manufactured artifacts. A simple analyticaLmodel was developed and used to determine how the number of layers and the layer thickness influences part warping. Resllits show that thin layers produce lower part deflection as compared with depositing fewer and thicker layers. In addition to the analytical work, a finite element model wasdeveloped and used to illvestigate the deposition pattern's influence on. the part deflection. Finite element model and corresponding experimental analysis showed that the geometry of the deposition pattern significantly affects the resulting part distortion. This finite element model was also used to investigate an inter-layer surface defect,. known as the Christmas Thee Step, that is associated with Shape Deposition Manufacturing. Results indicate that the features of this defect are influenced only by the material deposited close. to the part·surface and the particular material deposited. The step is not affected by the deposition pattern.Mechanical Engineerin

Evolution of a fluorinated green fluorescent protein

The fluorescence of bacterial cells expressing a variant (GFPm) of the green fluorescent protein (GFP) was reduced to background levels by global replacement of the leucine residues of GFPm by 5,5,5-trifluoroleucine. Eleven rounds of random mutagenesis and screening via fluorescence-activated cell sorting yielded a GFP mutant containing 20 amino acid substitutions. The mutant protein in fluorinated form showed improved folding efficiency both in vivo and in vitro, and the median fluorescence of cells expressing the fluorinated protein was improved {approx}650-fold in comparison to that of cells expressing fluorinated GFPm. The success of this approach demonstrates the feasibility of engineering functional proteins containing many copies of abiological amino acid constituents

Does School Autonomy Make Sense Everywhere? Panel Estimates from PISA

Decentralization of decision-making is among the most intriguing recent school reforms, in part because countries went in opposite directions over the past decade and because prior evidence is inconclusive. We suggest that autonomy may be conducive to student achievement in well-developed systems but detrimental in low-performing systems. We construct a panel dataset from the four waves of international PISA tests spanning 2000-2009, comprising over one million students in 42 countries. Relying on panel estimation with country fixed effects, we identify the effect of school autonomy from within-country changes in the average share of schools with autonomy over key elements of school operations. Our results show that autonomy affects student achievement negatively in developing and low-performing countries, but positively in developed and high-performing countries. These results are unaffected by a wide variety of robustness and specification tests, providing confidence in the need for nuanced application of reform ideas.

Does School Autonomy Make Sense Everywhere? Panel Estimates from PISA

Decentralization of decision-making is among the most intriguing recent school reforms, in part because countries went in opposite directions over the past decade and because prior evidence is inconclusive. We suggest that autonomy may be conducive to student achievement in well-developed systems but detrimental in low-performing systems. We construct a panel dataset from the four waves of international PISA tests spanning 2000-2009, comprising over one million students in 42 countries. Relying on panel estimation with country fixed effects, we identify the effect of school autonomy from within-country changes in the average share of schools with autonomy over key elements of school operations. Our results show that autonomy affects student achievement negatively in developing and low-performing countries, but positively in developed and high-performing countries. These results are unaffected by a wide variety of robustness and specification tests, providing confidence in the need for nuanced application of reform ideas.school autonomy, decentralization, developing countries, educational production, international student achievement tests, panel estimation