Design and Applications of Volume Holographic Optical Elements

Volume gratings were studied both theoretically and experimentally in order to design and analyze practical volume holographic optical elements. The diffraction of finite (Gaussian) beams by transmission gratings is investigated. A closed form solution for the off-Bragg profiles is obtained, and the distortion in the resulting profiles is analyzed. Criteria for when the finiteness of the beam has a minimal effect on the angular selectivity response are given. A model is developed to investigate the cross talk in multiplexed gratings Experimental verification in LiNb03 and PTR glass is demonstrated. The diffraction efficiency and output profiles of finite beams diffracted from reflection gratings on and off-Bragg are investigated. Using these beams decreases the diffraction efficiency, and the diffracted profiles are shown to be distorted, with higher distortion off-Bragg. The fidelity is shown to improve with increasing grating strength. The output profiles of diffraction by overlap gratings is investigated. Lateral shift and beam distortion are observed. When the diffraction efficiency reaches 83% the diffracted beam is shown to split into multiple sections. A method is given to obtain a diffracted beam with any desired profile. It is shown that most of the previously mentioned effects can be corrected, however the splitting of the beam at 83% cannot. Multiplexing in reflection gratings is also investigated. A narrow transmission peak is shown to occur midway between the Bragg wavelengths of the individual gratings. By adding more gratings, additional peaks are obtained. Similar devices are designed using thin film stacks. These devices have many advantages, including simpler scaling and no sidelobes. The number of transmission peaks is found using multi-mirror Fabry-Perot interferometer theory, and expressions are given for their location and width. The effects of including the variation in average index when modeling gratings recorded in the presence of absorption is presented. These effects are seen to increase as the grating type goes from un-slanted transmission to un-slanted reflection. Finally, the characteristics of plane waves incident on over-modulated transmission gratings are investigated. It is shown that they will experience one of three types of off-Bragg behavior

Direction and Integration of Experimental Ground Test Capabilities and Computational Methods

This paper groups and summarizes the salient points and findings from two AIAA conference panels targeted at defining the direction, with associated key issues and recommendations, for the integration of experimental ground testing and computational methods. Each panel session utilized rapporteurs to capture comments from both the panel members and the audience. Additionally, a virtual panel of several experts were consulted between the two sessions and their comments were also captured. The information is organized into three time-based groupings, as well as by subject area. These panel sessions were designed to provide guidance to both researchers/developers and experimental/computational service providers in defining the future of ground testing, which will be inextricably integrated with the advancement of computational tools

Embracing Safe Ground Test Facility Operations and Maintenance

Conducting integrated operations and maintenance in wind tunnel ground test facilities requires a balance of meeting due dates, efficient operation, responsiveness to the test customer, data quality, effective maintenance (relating to readiness and reliability), and personnel and facility safety. Safety is non-negotiable, so the balance must be an "and" with other requirements and needs. Pressure to deliver services faster at increasing levels of quality in under-maintained facilities is typical. A challenge for management is to balance the "need for speed" with safety and quality. It s especially important to communicate this balance across the organization - workers, with a desire to perform, can be tempted to cut corners on defined processes to increase speed. Having a lean staff can extend the time required for pre-test preparations, so providing a safe work environment for facility personnel and providing good stewardship for expensive National capabilities can be put at risk by one well-intending person using at-risk behavior. This paper documents a specific, though typical, operational environment and cites management and worker safety initiatives and tools used to provide a safe work environment. Results are presented and clearly show that the work environment is a relatively safe one, though still not good enough to keep from preventing injury. So, the journey to a zero injury work environment - both in measured reality and in the minds of each employee - continues. The intent of this paper is to provide a benchmark for others with operational environments and stimulate additional sharing and discussion on having and keeping a safe work environment

Structured Transition of Wind Tunnel Operations Skills from Government-to Contractor-Managed

In 2004, NASA awarded the Research, Operations, Maintenance, and Engineering (ROME) contract at NASA Langley Research Center to a team led by Jacobs Technology, Inc. A key component of the contract was the transitioning of the five large wind tunnel facilities from NASA managed and NASA or NASA/contractor workforces to fully contractor operated. The contractor would manage daily operations while NASA would continue to develop long-term strategies, make decisions regarding commitment of funds and commitment of facilities, and provide oversight of the contractor's performance. A major challenge would be the transition of knowledge of facility operations and maintenance from the incumbent civil servant workforce to the contractor workforce. While the contract has since been modified multiple times, resulting in a blended NASA/ROME workforce across the facilities, the processes developed and implemented to capture and document facility knowledge from the incumbent subject matter experts, build training and certification programs, and grow individual skills across subject areas and across facilities, are worthy of documentation. This is the purpose of this paper

Guidance on the Stand Down, Mothball, and Reactivation of Ground Test Facilities

The development of aerospace and aeronautics products typically requires three distinct types of testing resources across research, development, test, and evaluation: experimental ground testing, computational "testing" and development, and flight testing. Over the last twenty plus years, computational methods have replaced some physical experiments and this trend is continuing. The result is decreased utilization of ground test capabilities and, along with market forces, industry consolidation, and other factors, has resulted in the stand down and oftentimes closure of many ground test facilities. Ground test capabilities are (and very likely will continue to be for many years) required to verify computational results and to provide information for regimes where computational methods remain immature. Ground test capabilities are very costly to build and to maintain, so once constructed and operational it may be desirable to retain access to those capabilities even if not currently needed. One means of doing this while reducing ongoing sustainment costs is to stand down the facility into a "mothball" status - keeping it alive to bring it back when needed. Both NASA and the US Department of Defense have policies to accomplish the mothball of a facility, but with little detail. This paper offers a generic process to follow that can be tailored based on the needs of the owner and the applicable facility

A Proposed Approach for Prioritizing Maintenance at NASA Centers

The National Aeronautics and Space Administration (NASA) manages a vast array of infrastructure assets across ten National Centers with a worth of at least 30 billion dollars. Eighty percent of this infrastructure is greater than 40 years old and is in degraded condition. Maintenance budgets are typically less than one percent of current replacement value (CRV), much less than the 2-4% recommended by the National Research Council. The maintenance backlog was 2.55 billion dollars in FY10 and growing. NASA s annual budgets have flattened and are at risk of being reduced, so the problem is becoming even more difficult. NASA Centers utilize various means to prioritize and accomplish maintenance within available budgets, though data is suspect and processes are variable. This paper offers a structured means to prioritize maintenance based on mission criticality and facility performance (ability of the facility to deliver on its purpose). Mission alignment is assessed using the current timeframe Mission Dependence Index and a measure of facility alignment with the 2011 NASA Strategic Plan for the long-term perspective. Facility performance is assessed by combining specific findings from a structured facility condition assessment and an assessment of actual functional output. These are then combined in a matrix to identify the facilities most critical to mission and able to deliver services. The purpose of this approach is to provide the best benefits for the available funding. Additionally, this rationale can also be applied to the prioritization of investment (recapitalization) projects so that the ultimate customers of this paper, the senior infrastructure managers at each NASA Center, are better able to strategically manage their capabilities

GTTC Future of Ground Testing Meta-Analysis of 20 Documents

National research, development, test, and evaluation ground testing capabilities in the United States are at risk. There is a lack of vision and consensus on what is and will be needed, contributing to a significant threat that ground test capabilities may not be able to meet the national security and industrial needs of the future. To support future decisions, the AIAA Ground Testing Technical Committees (GTTC) Future of Ground Test (FoGT) Working Group selected and reviewed 20 seminal documents related to the application and direction of ground testing. Each document was reviewed, with the content main points collected and organized into sections in the form of a gap analysis current state, future state, major challenges/gaps, and recommendations. This paper includes key findings and selected commentary by an editing team

Esophageal sphincter device for gastroesophageal reflux disease

BACKGROUND Patients with gastroesophageal reflux disease who have a partial response to proton-pump inhibitors often seek alternative therapy. We evaluated the safety and effectiveness of a new magnetic device to augment the lower esophageal sphincter. METHODS We prospectively assessed 100 patients with gastroesophageal reflux disease before and after sphincter augmentation. The study did not include a concurrent control group. The primary outcome measure was normalization of esophageal acid exposure or a 50% or greater reduction in exposure at 1 year. Secondary outcomes were 50% or greater improvement in quality of life related to gastroesophageal reflux disease and a 50% or greater reduction in the use of proton-pump inhibitors at 1 year. For each outcome, the prespecified definition of successful treatment was achievement of the outcome in at least 60% of the patients. The 3-year results of a 5-year study are reported. RESULTS The primary outcome was achieved in 64% of patients (95% confidence interval [CI], 54 to 73). For the secondary outcomes, a reduction of 50% or more in the use of proton-pump inhibitors occurred in 93% of patients, and there was improvement of 50% or more in quality-of-life scores in 92%, as compared with scores for patients assessed at baseline while they were not taking proton-pump inhibitors. The most frequent adverse event was dysphagia (in 68% of patients postoperatively, in 11% at 1 year, and in 4% at 3 years). Serious adverse events occurred in six patients, and in six patients the device was removed. CONCLUSIONS In this single-group evaluation of 100 patients before and after sphincter augmentation with a magnetic device, exposure to esophageal acid decreased, reflux symptoms improved, and use of proton-pump inhibitors decreased. Follow-up studies are needed to assess long-term safety. (Funded by Torax Medical; ClinicalTrials.gov number, NCT00776997.

Seasonal Controls on the Exchange of Carbon and Water in an Amazonian Rain Forest

The long-term resilience of Amazonian forests to climate changes and the fate of their large stores of organic carbon depend on the ecosystem response to climate and weather. This study presents 4 years of eddy covariance data for CO2 and water fluxes in an evergreen, old-growth tropical rain forest examining the forest's response to seasonal variations and to short-term weather anomalies. Photosynthetic efficiency declined late in the wet season, before appreciable leaf litter fall, and increased after new leaf production midway through the dry season. Rates of evapotranspiration were inelastic and did not depend on dry season precipitation. However, ecosystem respiration was inhibited by moisture limitations on heterotrophic respiration during the dry season. The annual carbon balance for this ecosystem was very close to neutral, with mean net loss of 890 ± 220 kg C ha−1 yr−1, and a range of −221 ± 453 (C uptake) to +2677 ± 488 (C loss) kg C ha−1 yr−1 over 4 years. The trend from large net carbon release in 2002 towards net carbon uptake in 2005 implies recovery from prior disturbance. The annual carbon balance was sensitive to weather anomalies, particularly the timing of the dry-to-wet season transition, reflecting modulation of light inputs and respiration processes. Canopy carbon uptake rates were largely controlled by phenology and light with virtually no indication of seasonal water limitation during the 5-month dry season, indicating ample supplies of plant-available-water and ecosystem adaptation for maximum light utilization.Earth and Planetary SciencesEngineering and Applied SciencesOrganismic and Evolutionary Biolog

New Antitrust Concern in Labor Markets

The final panel will center on how antitrust regulators should deal with concerns in labor markets. Several antitrust authorities have dealt with it. For instance, the DOJ issued Guidance for HR professionals in 2016, discussing potential antitrust violations in HR activities. In addition, the panelists will discuss recent developments in the U.S. and abroad regarding how antitrust should tackle labor law concerns