Shock Waves in Nanomechanical Resonators

The dream of every surfer is an extremely steep wave propagating at the highest speed possible. The best waves for this would be shock waves, but are very hard to surf. In the nanoscopic world the same is true: the surfers in this case are electrons riding through nanomechanical devices on acoustic waves [1]. Naturally, this has a broad range of applications in sensor technology and for communication electronics for which the combination of an electronic and a mechanical degree of freedom is essential. But this is also of interest for fundamental aspects of nano-electromechanical systems (NEMS), when it comes to quantum limited displacement detection [2] and the control of phonon number states [3]. Here, we study the formation of shock waves in a NEMS resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves we are able to determine the anomalous acoustocurrent. This current is only found in the regime of shock wave formation. We ontain very good agreement with model calculations.Comment: 14 Pages including 4 figure

Linguistic Preprocessing and Tagging for Problem Report Trend Analysis

Mr. Robert Beil, Systems Engineer at Kennedy Space Center (KSC), requested the NASA Engineering and Safety Center (NESC) develop a prototype tool suite that combines complementary software technology used at Johnson Space Center (JSC) and KSC for problem report preprocessing and semantic tag extraction, to improve input to data mining and trend analysis. This document contains the outcome of the assessment and the Findings, Observations and NESC Recommendations

International Space Station (ISS) Anomalies Trending Study

The NASA Engineering and Safety Center (NESC) set out to utilize data mining and trending techniques to review the anomaly history of the International Space Station (ISS) and provide tools for discipline experts not involved with the ISS Program to search anomaly data to aid in identification of areas that may warrant further investigation. Additionally, the assessment team aimed to develop an approach and skillset for integrating data sets, with the intent of providing an enriched data set for discipline experts to investigate that is easier to navigate, particularly in light of ISS aging and the plan to extend its life into the late 2020s. This document contains the Appendices to the Volume I report

Shuttle Ground Support Equipment (GSE) T-0 Umbilical to Space Shuttle Program (SSP) Flight Elements Consultation

The NASA Engineering and Safety Center (NESC) was tasked with assessing the validity of an alternate opinion that surfaced during the investigation of recurrent failures at the Space Shuttle T-0 umbilical interface. The most visible problem occurred during the Space Transportation System (STS)-112 launch when pyrotechnics used to separate Solid Rocket Booster (SRB) Hold-Down Post (HDP) frangible nuts failed to fire. Subsequent investigations recommended several improvements to the Ground Support Equipment (GSE) and processing changes were implemented, including replacement of ground-half cables and connectors between flights, along with wiring modifications to make critical circuits quad-redundant across the interface. The alternate opinions maintained that insufficient data existed to exonerate the design, that additional data needed to be gathered under launch conditions, and that the interface should be further modified to ensure additional margin existed to preclude failure. The results of the assessment are contained in this report

AN-Type Fittings in the International Space System (ISS) Node 2 Ammonia System Technical Assessment Report

Based on an anonymous request, an NESC Assessment Team was formed to investigate potential leakage problems from the ISS Program's Node 2 Anhydrous Ammonia System AN fittings. The Team's charter was to provide the ISS Program with a path to follow, which could include testing, to ensure the ISS Program felt confident that the AN fittings' leakage would not exceed specified limits in orbit. The findings from that assessment are contained in this document

Review of the Constellation Level II Safety, Reliability, and Quality Assurance (SR&QA) Requirements Documents during Participation in the Constellation Level II SR&QA Forum

At the request of the Exploration Systems Mission Directorate (ESMD) and the Constellation Program (CxP) Safety, Reliability; and Quality Assurance (SR&QA) Requirements Director, the NASA Engineering and Safety Center (NESC) participated in the Cx SR&QA Requirements forum. The Requirements Forum was held June 24-26; 2008, at GRC's Plum Brook Facility. The forums purpose was to gather all stakeholders into a focused meeting to help complete the process of refining the CxP to refine its Level II SR&QA requirements or defining project-specific requirements tailoring. Element prime contractors had raised specific questions about the wording and intent of many requirements in areas they felt were driving costs without adding commensurate value. NESC was asked to provide an independent and thorough review of requirements that contractors believed were driving Program costs, by active participation in the forum. This document contains information from the forum

The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx)

1. Climate change is a world‐wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high‐quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re‐use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. 2. To overcome these challenges, we collected best‐practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re‐use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re‐use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second‐order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world

Magnetotransport in freely suspended two-dimensional electron systems for integrated nanomechanical resonators

We present magnetotransport measurements on freely suspended two-dimensional electron gases. Samples are prepared from GaAs/AlGaAs-heterostructures containing an additional sacrificial layer. The electronic properties of the system are characterized in standard magnetotransport measurements whereas the mechanical degrees of freedom are investigated in radio frequency resonance experiments. The interplay of both can be exploited for ultrasensitive displacement detection