3,867 research outputs found
Image analysis of the AXAF VETA-I x ray mirror
Initial core scan data of the VETA-I x-ray mirror proved disappointing, showing considerable unpredicted image structure and poor measured FWHM. 2-D core scans were performed, providing important insight into the nature of the distortion. Image deconvolutions using a ray traced model PSF was performed successfully to reinforce our conclusion regarding the origin of the astigmatism. A mechanical correction was made to the optical structure, and the mirror was tested successfully (FWHM 0.22 arcsec) as a result
Cell patterning on photolithographically defined parylene-C:SiO2 substrates
Cell patterning platforms support broad research goals, such as construction of predefined in vitro neuronal networks and the exploration of certain central aspects of cellular physiology. To easily combine cell patterning with Multi-Electrode Arrays (MEAs) and silicon-based ‘lab on a chip’ technologies, a microfabrication-compatible protocol is required. We describe a method that utilizes deposition of the polymer parylene-C on SiO(2 )wafers. Photolithography enables accurate and reliable patterning of parylene-C at micron-level resolution. Subsequent activation by immersion in fetal bovine serum (or another specific activation solution) results in a substrate in which cultured cells adhere to, or are repulsed by, parylene or SiO(2) regions respectively. This technique has allowed patterning of a broad range of cell types (including primary murine hippocampal cells, HEK 293 cell line, human neuron-like teratocarcinoma cell line, primary murine cerebellar granule cells, and primary human glioma-derived stem-like cells). Interestingly, however, the platform is not universal; reflecting the importance of cell-specific adhesion molecules. This cell patterning process is cost effective, reliable, and importantly can be incorporated into standard microfabrication (chip manufacturing) protocols, paving the way for integration of microelectronic technology
The Borders of Solidarity: How Countries Determine the Public/Private Mix in Spending and the Impact on Health Care
Comparing introductory and beyond-introductory students' reasoning about uncertainty
Uncertainty is an important concept in physics laboratory instruction.
However, little work has examined how students reason about uncertainty beyond
the introductory (intro) level. In this work we aimed to compare intro and
beyond-intro students' ideas about uncertainty. We administered a survey to
students at 10 different universities with questions probing procedural
reasoning about measurement, student-identified sources of uncertainty, and
predictive reasoning about data distributions. We found that intro and
beyond-intro students answered similarly on questions where intro students
already exhibited expert-level reasoning, such as in comparing two data sets
with the same mean but different spreads, identifying limitations in an
experimental setup, and predicting how a data distribution would change if more
data were collected. For other questions, beyond-intro students generally
exhibited more expert-like reasoning than intro students, such as when
determining whether two sets of data agree, identifying principles of
measurement that contribute to spread, and predicting how a data distribution
would change if better data were collected. Neither differences in student
populations, lab courses taken, nor research experience were able to fully
explain the variability between intro and beyond-intro student responses. These
results call for further research to better understand how students' ideas
about uncertainty develop beyond the intro level.Comment: 19 pages, 12 figure
AXAF VETA-I mirror encircled energy measurements and data reduction
The AXAF VETA-I mirror encircled energy was measured with a series of apertures and two flow gas proportional counters at five X-ray energies ranging from 0.28 to 2.3 keV. The proportional counter has a thin plastic window with an opaque wire mesh supporting grid. Depending on the counter position, this mesh can cause the X-ray transmission to vary as much as +/-9 percent, which directly translates into an error in the encircled energy. In order to correct this wire mesh effect, window scan measurements were made, in which the counter was scanned in both horizontal (Y) and vertical (Z) directions with the aperture fixed. Post VETA measurement of the VXDS setup were made to determine the exact geometry and position of the mesh grid. Computer models of the window mesh were developed to simulate the X-ray transmission based on this measurement. The window scan data were fitted to such mesh models and corrections were made. After this study, the mesh effect was well understood and the final results of the encircled energy were obtained with an uncertainty of less than 0.8 percent
Acoustic Test Characterization of Melamine Foam for Usage in NASA's Payload Fairing Acoustic Attenuation Systems
The external acoustic liftoff levels predicted for NASA's future heavy lift launch vehicles are expected to be significantly higher than the environment created by today's commercial launch vehicles. This creates a need to develop an improved acoustic attenuation system for future NASA payload fairings. NASA Glenn Research Center initiated an acoustic test series to characterize the acoustic performance of melamine foam, with and without various acoustic enhancements. This testing was denoted as NEMFAT, which stands for NESC Enhanced Melamine Foam Acoustic Test, and is the subject of this paper. Both absorption and transmission loss testing of numerous foam configurations were performed at the Riverbank Acoustical Laboratory in July 2013. The NEMFAT test data provides an initial acoustic characterization and database of melamine foam for NASA. Because of its acoustic performance and lighter mass relative to fiberglass blankets, melamine foam is being strongly considered for use in the acoustic attenuation systems of NASA's future launch vehicles
NASA Engineering and Safety Center (NESC) Enhanced Melamine (ML) Foam Acoustic Test (NEMFAT)
The NASA Engineering and Safety Center (NESC) funded a proposal to achieve initial basic acoustic characterization of ML (melamine) foam, which could serve as a starting point for a future, more comprehensive acoustic test program for ML foam. A project plan was developed and implemented to obtain acoustic test data for both normal and enhanced ML foam. This project became known as the NESC Enhanced Melamine Foam Acoustic Test (NEMFAT). This document contains the outcome of the NEMFAT project
Report drawn up on behalf of the Committee on Agriculture on the proposals from the Commission of the European Communities to the Council (doc. 479/77) on the fixing of prices for certain agricultural products and on certain related measures for the 1978-1979 marketing year. EP Working Documents, document 579/77, 13 March 1978
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