Hybrid propulsion for launch vehicle boosters: A program status update

Results obtained in studying the origin and suppression of large-amplitude pressure oscillations in a 24 in. diameter hybrid motor using a liquid oxygen/hydroxylterminated polybutadiene/polycyclopentadiene propellant system are discussed. Tests conducted with liquid oxygen flow rates varying from 10 to 40 lbm/sec were designed to gauge the effectiveness of various vaporization chamber flow fields, injector designs, and levels of heat addition in suppressing high-frequency longitudinal mode oscillations. Longitudinal acoustic modes did not arise in any tests. However, initial testing revealed the presence of high-amplitude, sinusoidal, nonacoustic oscillations persisting throughout the burn durations. Analysis showed this to be analogous to chug mode instability in liquid rocket engines brought about by a coupling of motor combustion processes and the liquid oxygen feed system. Analytical models were developed and verified by test data to predict the amplitude and frequency of feed-system-coupled combustion pressure oscillations. Subsequent testing showed that increasing the feed system impedance eliminated the bulk mode instability. This paper documents the work completed to date in performance of the Hybrid Propulsion Technology for Launch Vehicle Boosters Program (NAS8-39942) sponsored by NASA's George C. Marshall Space Flight Center

CuSCN Nanowires as Electrodes for p-Type Quantum Dot Sensitized Solar Cells: Charge Transfer Dynamics and Alumina Passivation

Quantum dot sensitized solar cells (QDSSCs) are a promising photovoltaic technology due to their low cost and simplicity of fabrication. Most QDSSCs have an n-type configuration with electron injection from QDs into TiO2, which generally leads to unbalanced charge transport (slower hole transfer rate) limiting their efficiency and stability. We have previously demonstrated that p-type (inverted) QD sensitized cells have the potential to solve this problem. Here we show for the first time that electrodeposited CuSCN nanowires can be used as a p-type nanostructured electrode for p-QDSSCs. We demonstrate their efficient sensitization by heavy metal free CuInSxSe2-x quantum dots. Photophysical studies show efficient and fast hole injection from the excited QDs into the CuSCN nanowires. The transfer rate is strongly time dependent but the average rate of 2.5 × 109 s–1 is much faster than in previously studied sensitized systems based on NiO. Moreover, we have developed an original experiment allowing us to calculate independently the rates of charge injection and QD regeneration by the electrolyte and thus to determine which of these processes occurs first. The average QD regeneration rate (1.3 × 109 s–1) is in the same range as the hole injection rate, resulting in an overall balanced charge separation process. To reduce recombination in the sensitized systems and improve their stability, the CuSCN nanowires were coated with thin conformal layers of Al2O3 using atomic layer deposition (ALD) and fully characterized by XPS and EDX. We demonstrate that the alumina layer protects the surface of CuSCN nanowires, reduces charge recombination, and increases the overall charge transfer rate up to 1.5 times depending on the thickness of the deposited Al2O3 layer

Thermal Behavior in the Lens Process

Direct laser metal deposition processing is a promising manufacturing technology which could significantly impact the length oftime between initial concept and finished part. For adoption ofthis technology in the manufacturing environment, further understanding is required to ensure robust components with appropriate properties are routinelyfabricated. This requires a complete understanding ofthe thermal history.during part fabrication and control ofthis behavior. This paper will describe our research to understand the thermal behavior for the Laser Engineered Net Shaping (LENS) process!, where a component is fabricated by focusing a laser beam onto a substrate to create a molten pool in which powder particles are simultaneously injected to build each layer. The substrate is moved beneath the l~ser beam to deposit a thin cross section, thereby creating the desired geometry for each layer. After deposition of each layer, the powder delivery nozzle and focusing lens assembly is incremented in the positive Z-direction, thereby building a three dimensional component layer additively. It is important to control the thermal behavior to reproducibly fabricate parts. The ultimate intent is to monitor the thermal signatures and to incorporate sensors and feedback algorithms to control part fabrication. With appropriate control, the geometric properties (accuracy, surface finish, low warpage) as well as the materials' properties (e.g. strength, ductility) of a component can be dialed into the part through the fabrication parameters. Thermal monitoring techniques will be described, and their particular benefits highlighted. Preliminary details in correlating thermal behavior with processing results will be discussed.Mechanical Engineerin

Role of lattice distortion and A site cation in the phase transitions of methylammonium lead halide perovskites

The rapid increase in power conversion efficiencies of photovoltaic devices incorporating lead halide perovskites has resulted in intense interest in the cause of their excellent properties. In the present paper, resonant ultrasound spectroscopy has been used to determine the elastic and anelastic properties of CH3NH3PbX3(where X=Cl, Br, or I) and CD3ND3PbI3 perovskites in the 5–380 K temperature range. This is coupled with differential scanning calorimetry, variable temperature neutron powder diffraction, and variable temperature photoluminescence studies to provide insights into the underlying processes and structural instabilities in the crystal structure. By comparing measurements on CH3NH3PbI3 with the deuterated equivalent, it has been possible to distinguish processes which are related to the hydrogen bonding between the methylammonium cation and the perovskite framework. We observe that replacing hydrogen with deuterium has a significant impact on both the elastic and photophysical properties, which shows that hydrogen bonding plays a crucial role in the material performance. Temperature-dependent photoluminescence studies show that the light emission is unaffected by the tetragonal-orthorhombic phase transition, but a blueshift in the emission and a steep increase in photoluminescence quantum yield are seen at temperatures below 150 K. Finally, observations of peaks in acoustic loss occurring in CH3NH3PbCl3 have revealed freezing processes in the vicinity of ∼150−170K, with activation energies in the range of 300 to 650 meV. These processes are attributed to freezing of the motion of methylammonium cations, and could explain the changes in photoluminescence seen in CH3NH3PbI3 at the same temperature. © 2018 American Physical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1103/PhysRevMaterials.2.06540

Probing the energy levels of perovskite solar cells via Kelvin probe and UV ambient pressure photoemission spectroscopy

This work was supported by the Engineering and Physical Sciences Research Council (grant codes EP/M506631/1, EP/ K015540/01, EP/K022237/1 and EP/M025330/1). IDWS and JTSI acknowledge Royal Society Wolfson research merit awards.The field of organo-lead halide perovskite solar cells has been rapidly growing since their discovery in 2009. State of the art devices are now achieving efficiencies comparable to much older technologies like silicon, while utilising simple manufacturing processes and starting materials. A key parameter to consider when optimising solar cell devices or when designing new materials is the position and effects of the energy levels in the materials. We present here a comprehensive study of the energy levels present in a common structure of perovskite solar cell using an advanced macroscopic Kelvin probe and UV air photoemission setup. By constructing a detailed map of the energy levels in the system we are able to predict the importance of each layer to the open circuit voltage of the solar cell, which we then back up through measurements of the surface photovoltage of the cell under white illumination. Our results demonstrate the effectiveness of air photoemission and Kelvin probe contact potential difference measurements as a method of identifying the factors contributing to the open circuit voltage in a solar cell, as well as being an excellent way of probing the physics of new materials.Publisher PDFPeer reviewe

Role of lattice distortion and A site cation in the phase transitions of methylammonium lead halide perovskites

The rapid increase in power conversion efficiencies of photovoltaic devices incorporating lead halide perovskites has resulted in intense interest in the cause of their excellent properties. In the present paper, resonant ultrasound spectroscopy has been used to determine the elastic and anelastic properties of CH3NH3PbX3 (where X=Cl, Br, or I) and CD3ND3PbI3 perovskites in the 5–380 K temperature range. This is coupled with differential scanning calorimetry, variable temperature neutron powder diffraction, and variable temperature photoluminescence studies to provide insights into the underlying processes and structural instabilities in the crystal structure. By comparing measurements on CH3NH3PbI3 with the deuterated equivalent, it has been possible to distinguish processes which are related to the hydrogen bonding between the methylammonium cation and the perovskite framework. We observe that replacing hydrogen with deuterium has a significant impact on both the elastic and photophysical properties, which shows that hydrogen bonding plays a crucial role in the material performance. Temperature-dependent photoluminescence studies show that the light emission is unaffected by the tetragonal-orthorhombic phase transition, but a blueshift in the emission and a steep increase in photoluminescence quantum yield are seen at temperatures below 150 K. Finally, observations of peaks in acoustic loss occurring in CH3NH3PbCl3 have revealed freezing processes in the vicinity of ∼150−170K, with activation energies in the range of 300 to 650 meV. These processes are attributed to freezing of the motion of methylammonium cations, and could explain the changes in photoluminescence seen in CH3NH3PbI3 at the same temperature

Use of Science in Gulf of Mexico Decision Making Involving Climate Change

This material is based upon research supported by the U.S. Environmental Protection Agency's National Center for Environmental Assessment/Global Change Research Program under Cooperative Agreement No. R-83023601-0. It is a joint project of Texas A&M University's Institute for Science, Technology and Public Policy in The Bush School of Government and Public Service, the Center for Hazards Assessment, Response and Technology at the University of New Orleans, the Center for Socioeconomic Research at the University of Louisiana at Lafayette, and the Environmental Sciences Institute at Florida A&M University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the U.S. Environmental Protection Agency.project final reportsurveyU.S. Environmental Protection Agency (Cooperative Agreement No. R-83023601-0

The Conservation Status of Marine Biodiversity of the Pacific Islands of Oceania

The Pacific Islands of Oceania are small islands and atolls occurring over a vast expanse of ocean that are characterized by immense biodiversity and endemism. This project represents a major expansion of the coverage of the Pacific Islands’ marine biodiversity on the IUCN Red List of Threatened Species. The threats to Pacific Island marine biodiversity are many. Results from IUCN Red List initiatives such as this can guide decision-making and conservation prioritization of Pacific Island governments, non-governmental organizations (NGOs) and the private sector. By shaping regional and national policies with these data in mind, priority sites for maintaining marine biodiversity can be identified and conserved

Informing patients of familial diabetes mellitus risk: How do they respond? A cross-sectional survey

<p>Abstract</p> <p>Background</p> <p>A strong family history of type 2 diabetes mellitus (DM) confers increased DM risk. This survey analysis determined whether patients who were informed by their doctors of familial DM risk acknowledged that risk and took steps to reduce it.</p> <p>Methods</p> <p>We conducted an analysis of the National <it>Health Styles 2004 </it>mail survey. All non-diabetic participants who responded to the question of whether their doctor had or had not informed them of their familial DM risk (<it>n </it>= 3,323) were compared for their risk-reducing behaviour and attitude to DM risk.</p> <p>Results</p> <p>Forty-one percent (<it>n </it>= 616) of the question responders that had DM family histories were informed by their doctors of their familial risk; the chance of being informed increased with the number of relatives that had the disease. Members of the informed group were more likely than those in the non-informed group to report lifestyle changes to prevent DM (odds ratio [OR] 4.3, 95% confidence interval [CI] 3.5–5.2) and being tested for DM (OR 2.9, 95% CI 2.4–3.6), although no significant improvement occurred in their U.S.-recommended exercise activity (OR 0.9, 95% CI 0.7–1.1). Overall, informed responders recognised both their familial and personal DM risk; most discussed diabetes with their family (69%), though less so with friends (42%); however, 44% of them still did not consider themselves to be at risk.</p> <p>Conclusion</p> <p>Responders who were informed by their doctors of being at familial DM risk reported greater incidences of lifestyle changes, DM screening, and awareness of risk than non-informed responders. Doctors were more likely to inform patients with stronger DM family histories. Identifying this higher risk group, either in isolation or in combination with other recognised risk factors, offers doctors the opportunity to target limited health promotion resources efficiently for primary DM prevention.</p