Application of Smart Solid State Sensor Technology in Aerospace Applications

Aerospace applications require a range of chemical sensing technologies to monitor conditions in both space vehicles and aircraft operations. One example is the monitoring of oxygen. For example, monitoring of ambient oxygen (O2) levels is critical to ensuring the health, safety, and performance of humans living and working in space. Oxygen sensors can also be incorporated in detection systems to determine if hazardous leaks are occurring in space propulsion systems and storage facilities. In aeronautic applications, O2 detection has been investigated for fuel tank monitoring. However, as noted elsewhere, O2 is not the only species of interest in aerospace applications with a wide range of species of interest being relevant to understand an environmental or vehicle condition. These include combustion products such as CO, HF, HCN, and HCl, which are related to both the presence of a fire and monitoring of post-fire clean-up operations. This paper discusses the development of an electrochemical cell platform based on a polymer electrolyte, NAFION, and a three-electrode configuration. The approach has been to mature this basic platform for a range of applications and to test this system, combined with "Lick and Stick" electronics, for its viability to monitor an environment related to astronaut crew health and safety applications with an understanding that a broad range of applications can be addressed with a core technology

Silicon Carbide Gas Sensors for Propulsion Emissions and Safety Applications

Silicon carbide (SiC) based gas sensors have the ability to meet the needs of a range of aerospace propulsion applications including emissions monitoring, leak detection, and hydrazine monitoring. These applications often require sensitive gas detection in a range of environments. An effective sensing approach to meet the needs of these applications is a Schottky diode based on a SiC semiconductor. The primary advantage of using SiC as a semiconductor is its inherent stability and capability to operate at a wide range of temperatures. The complete SiC Schottky diode gas sensing structure includes both the SiC semiconductor and gas sensitive thin film metal layers; reliable operation of the SiC-based gas sensing structure requires good control of the interface between these gas sensitive layers and the SiC. This paper reports on the development of SiC gas sensors. The focus is on two efforts to better control the SiC gas sensitive Schottky diode interface. First, the use of palladium oxide (PdOx) as a barrier layer between the metal and SiC is discussed. Second, the use of atomically flat SiC to provide an improved SiC semiconductor surface for gas sensor element deposition is explored. The use of SiC gas sensors in a multi-parameter detection system is briefly discussed. It is concluded that SiC gas sensors have potential in a range of propulsion system applications, but tailoring of the sensor for each application is necessary

Comparison Testings between Two High-temperature Strain Measurement Systems

An experimental evaluation was conducted at NASA Lewis Research Center to compare and contrast the performance of a newly developed resistance strain gage, the PdCr temperature-compensated wire strain gage, to that of a conventional high-temperature extensometry. The evaluation of the two strain measurement systems was conducted through the application of various thermal and mechanical loading spectra using a high-temperature thermomechanical uniaxial testing system equipped with quartz lamp heating. The purpose of the testing was not only to compare and contrast the two strain sensors but also to investigate the applicability of the PdCr strain gage to the testing environment typically employed when characterizing the high-temperature mechanical behavior of structural materials. Strain measurement capabilities to 8OO C were investigated with a nickel base superalloy IN100 substrate material, and application to titanium matrix composite (TMC) materials was examined with the SCS-6/Ti-15-3 08 system. PdCr strain gages installed by three attachment techniques, namely, flame spraying, spot welding and rapid infrared joining were investigated

Effect of Nanotopography on the Attachment and Proliferation of Osteoblasts on Ti-6Al-4V Surface in the Absence of Exogeneous Adhesion Proteins

Attachment and proliferation of UMR 106-01 osteosarcoma cells on nano-pitted and nano-textured surfaces of Ti-6Al-4V have been examined in the presence of bovine serum albumin (BSA) in order to mimic the very early stages of in vivo implantation, and to understand the role of nano-topography. The nano-pittted topography produced by anodization of titanium contains a uniform distribution of about 50 nm diameter pits of approximately similar depth on otherwise a smooth titanium oxide surface. The nano-textured topography produced by NaOH etching contains spiky features and micro/nano-pits, and closely resembles the cytoskeletal morphology of osteoblasts. Osteoblast cells attach to the albumin coated NaOH etched titanium surface with a significantly better efficiency than on the polished or the anodized surfaces. However, both, the NaOH etched and the anodized surfaces are less conducive to the cell proliferation as compared to the polished surface

Effect of Nanotopography on the Attachment and Proliferation of Osteoblasts on Ti-6Al-4V Surface in the Absence of Exogeneous Adhesion Proteins

Attachment and proliferation of UMR 106-01 osteosarcoma cells on nano-pitted and nano-textured surfaces of Ti-6Al-4V have been examined in the presence of bovine serum albumin (BSA) in order to mimic the very early stages of in vivo implantation, and to understand the role of nano-topography. The nano-pittted topography produced by anodization of titanium contains a uniform distribution of about 50 nm diameter pits of approximately similar depth on otherwise a smooth titanium oxide surface. The nano-textured topography produced by NaOH etching contains spiky features and micro/nano-pits, and closely resembles the cytoskeletal morphology of osteoblasts. Osteoblast cells attach to the albumin coated NaOH etched titanium surface with a significantly better efficiency than on the polished or the anodized surfaces. However, both, the NaOH etched and the anodized surfaces are less conducive to the cell proliferation as compared to the polished surface

SiC-Based Gas Sensor Development

Silicon carbide based Schottky diode gas sensors are being developed for applications such as emission measurements and leak detection. The effects of the geometry of the tin oxide film in a Pd/SnO2/SiC structure will be discussed as well as improvements in packaging SiC-based sensors. It is concluded that there is considerable versatility in the formation of SiC-based Schottky diode gas sensing structures which will potentially allow the fabrication of a SiC-based gas sensor array for a variety of gases and temperatures

Preclinical modeling of surgery and steroid therapy for glioblastoma reveals changes in immunophenotype that are associated with tumor growth and outcome

PURPOSE: Glioblastoma (GBM) immunotherapy clinical trials are generally initiated after standard-of-care treatment, including surgical resection, perioperative high-dose steroid therapy, chemotherapy, and radiation treatment, has either begun or failed. However, the impact of these interventions on the anti-tumoral immune response is not well studied. While discoveries regarding the impact of chemotherapy and radiation on immune response have been made and translated into clinical trial design, the impact of surgical resection and steroids on the anti-tumor immune response has yet to be determined. EXPERIMENTAL DESIGN: We developed a murine model integrating tumor resection and steroid treatment and used flow cytometry to analyze systemic and local immune changes. These mouse model findings were validated in a cohort of 95 primary GBM patients. RESULTS: Using our murine resection model, we observed a systemic reduction in lymphocytes corresponding to increased tumor volume and decreased circulating lymphocytes that was masked by dexamethasone treatment. The reduction in circulating T cells was due to reduced CCR7 expression, resulting in T-cell sequestration in lymphoid organs and the bone marrow. We confirmed these findings in a cohort of primary GBM patients and found that prior to steroid treatment, circulating lymphocytes inversely correlated with tumor volume. Lastly, we demonstrated that peripheral lymphocyte content varies with progression-free and overall survival, independent of tumor volume, steroid use, or molecular profiles. CONCLUSIONS: These data reveal that prior to intervention, increased tumor volume corresponds with reduced systemic immune function and that peripheral lymphocyte counts are prognostic when steroid treatment is taken into account