581 research outputs found
Progress in the Fabrication and Testing of Telescope Mirrors for the James Webb Space Telescope
Get PDFThe telescope of the James Webb Space Telescope (JWST) is an f/20, three mirror anastigmat design, passively cooled (40K) in an L2 orbit. The design provides diffraction limited performance (Strehl > or = 0.8) at .=2 m. To fit within the launch vehicle envelope (Arianne V), the 6.6 meter primary mirror and the secondary mirror support structure are folded for launch, then deployed and aligned in space. The primary mirror is composed of 18 individual, 1.3 meter (flat flat) hexagonal segments, each adjustable in seven degrees of freedom (six rigid body + radius of curvature) provided by a set of high precision actuators. The actuated secondary mirror (approx.0.74m) is similarly positioned in six degrees of rigid body motion. The approx..70x.51m, fixed tertiary and approx. 0.17m, flat fine steering mirror complete the telescope mirror complement. The telescope is supported by a composite structure optimized for performance at cryogenic temperatures. All telescope mirrors are made of Be with substantial light-weighting (21 kg for each 1.3M primary segment). Additional Be mounting and supporting structure for the high precision (approx.10nm steps) actuators are attached to the primary segments and secondary mirror. All mirrors undergo a process of thermal stabilization to reduce stress. An extensive series of interferometric measurements guide each step of the polishing process. Final polishing must account for any deformation between the ambient temperature of polishing and the cryogenic, operational temperature. This is accomplished by producing highly precise, cryo deformation target maps of each surface which are incorporated into the final polishing cycle. All flight mirrors have now completed polishing, coating with protected Au and final cryo testing, and the telescope is on track to meet all system requirements. We here review the measured performance of the component mirrors and the predicted performance of the flight telescope
Hawala, Money Laundering, and Terrorism Finance: Mirco-Lending as an End to Illicit Remittance
Get PDFThe role of production agronomists and crop advisors in the Food Safety Modernization Act
Get PDFWhile the unexpectedly favorable weather after Labor Day removed most of the potential for crop quality issues, the newly released Food Safety Modernization Act Human Food and Animal Food Preventive Control Rules will have ongoing impact on the grain supply chain from farm to user. Requests by grain users (feed mills, ethanol plants, corn wet mills, and others) for verification of hazard control are likely to become common. Farms and elevators will become a source of risk in users’ required hazard analysis. Most hazards in bulk grain originate in production (mycotoxins, diseases) which will make advance forecasting and monitoring by trained professionals an important element of risk control documentation. Mycotoxin management is an example of the supply chain preventive control that will be needed
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