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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Competing atomic processes in Ba and Sr injection critical velocity experiments

The critical ionization velocity effect requires a superthermal electron population to ionize through collisional impact. Such superthermal electrons can however lose energy to competing atomic processes, as well as to ionization, thus limiting the efficiency of the effect. Considering Ba and Sr magnetospheric injection experiments designed to test the CIV theory, it is found that in both cases roughly 60 percent of the superthermal electron energy is lost on exciting line radiation. Moreover, energy loss to background neutral oxygen places a strict limit on the injected cloud densities for which critical velocity effects are possible; a finding which explains the consistently negative results in radial injection experiments.

Newell, P. T.↗
NASA NTRS1986

Reliability bounds for fault-tolerant systems with competing responses to component failures

Bounds are established on the probability of system failure for fault-tolerant systems of the type used, for example, in aviation control. Event series leading to system failure are assumed to follow a semi-Markov model in which the potential sojourn times associated with component failures have exponential distributions and those associated with system responses have distributions with unspecified form. A product form of the bounds is derived by using a model that provides for multiple competing system responses to component failures.

Lee, L. D.↗
NASA NTRS1986

Evaluation of competing software reliability predictions

Different software reliability models can produce very different answers when called upon to predict future reliability in a reliability growth context. Users need to know which, if any, of the competing predictions are trustworthy. Some techniques are presented which form the basis of a partial solution to this problem. Rather than attempting to decide which model is generally best, the approach adopted here allows a user to decide upon the most appropriate model for each application.

Abdel-Ghaly, A. A.↗
NASA NTRS1996

From Competence to Efficiency: A Tale of GA Progress

Genetic algorithms (GAs) - search procedures based on the mechanics of natural selection and genetics - have grown in popularity for the solution of difficult optimization problems. Concomitant with this growth has been a rising cacaphony of complaint asserting that too much time must be spent by the GA practitioner diddling with codes, operators, and GA parameters; and even then these GA cassandras continue, and the user is still unsure that the effort will meet with success. At the same time, there has been a rising interest in GA theory by a growing community - a theorocracy - of mathematicians and theoretical computer scientists, and these individuals have turned their efforts increasingly toward elegant abstract theorems and proofs that seem to the practitioner to offer little in the way of answers for GA design or practice. What both groups seem to have missed is the largely unheralded 1993 assembly of integrated, applicable theory and its experimental confirmation. This theory has done two key things. First, it has predicted that simple GAs are severely limited in the difficulty of problems they can solve, and these limitations have been confirmed experimentally. Second, it has shown the path to circumventing these limitations in nontraditional GA designs such as the fast messy GA. This talk surveys the history, methodology, and accomplishment of the 1993 applicable theory revolution. After arguing that these accomplishments open the door to universal GA competence, the paper shifts the discussion to the possibility of universal GA efficiency in the utilization of time and real estate through effective parallelization, temporal decomposition, hybridization, and relaxed function evaluation. The presentation concludes by suggesting that these research directions are quickly taking us to a golden age of adaptation.

Goldberg, David E.↗
NASA NTRS2002

Competing Classical and Quantum Effects in Shape Relaxation of a Metallic Island

Pb islands grown on a silicon substrate transform at room temperature from the initially flattop facet geometry into an unusual ring, shape with a volume-preserving mass transport process catalysed by the tip electrical field of a scanning tunnelling microscope. The formation of such ring shape morphology results from the competing classical and quantum effects in the shape relaxation. The latter also leads to a sequential regrowth on alternating, strips of the same facet defined by the underlying substrate steps, showing for the first time the dynamical impact of the quantum size effect on the stability of a nanostructure.

Okamoto, Rowland H.↗
NASA NTRS2002

Hypersonic Airbreathing Propulsion: An Aerodynamics, Aerothermodynamics, and Acoustics Competency White Paper

This White Paper examines the current state of Hypersonic Airbreathing Propulsion at the NASA Langley Research Center and the factors influencing this area of work and its personnel. Using this knowledge, the paper explores beyond the present day and suggests future directions and strategies for the field. Broad views are first taken regarding potential missions and applications of hypersonic propulsion. Then, candidate propulsion systems that may be applicable to these missions are suggested and discussed. Design tools and experimental techniques for developing these propulsion systems are then described, and approaches for applying them in the design process are considered. In each case, current strategies are reviewed and future approaches that may improve the techniques are considered. Finally, the paper concentrates on the needs to be addressed in each of these areas to take advantage of the opportunities that lay ahead for both the NASA Langley Research Center and the Aerodynamic Aerothermodynamic, and Aeroacoustics Competency. Recommendations are then provided so that the goals set forth in the paper may be achieved.

Drummond, J. Philip↗
NASA NTRS2003

Competing Classical and Quantum Effects in Shape Relaxation of a Metallic Nanostructure

We demonstrate for the first time that the quantum size effect (QSE) plays a competing role along side the classical thermodynamic effect in the shape relaxation of a small metallic island. Together, these effects transforms a lead(Pb) island grown on Si(111) substrate from its initially flattop faceted morphology to a peculiar ring-shape island, a process catalysed by the tip electric field of a scanning tunnelling microscope (STM). We shall show for the first time how QSE affects the relaxation process dynamically. In particular, it leads to a novel strip-flow growth and double-step growth on selective strips of a plateau inside the ring, defined by the substrate steps more than 60?0?3 below. It appears that atoms diffusing on the plateau can clearly (sub i)(deg)sense(sub i)+/- the quantized energy states inside the island and have preferentially attached to regions that further reduces the surface energy as a result of the QSE, limiting its own growth and stabilizing the ring shape. The mechanism proposed here offers a sound explanation for ring shape metal and semiconductor islands observed in other systems as well.

Chen, Dongmin↗
NASA NTRS2004

Leakage and Power Loss Test Results for Competing Turbine Engine Seals

Advanced brush and finger seal technologies offer reduced leakage rates over conventional labyrinth seals used in gas turbine engines. To address engine manufacturers concerns about the heat generation and power loss from these contacting seals, brush, finger, and labyrinth seals were tested in the NASA High Speed, High Temperature Turbine Seal Test Rig. Leakage and power loss test results are compared for these competing seals for operating conditions up to 922 K (1200 F) inlet air temperature, 517 KPa (75 psid) across the seal, and surface velocities up to 366 m/s (1200 ft/s).

Proctor, Margaret P.↗
NASA NTRS2012

Developing Culture-Adaptive Competency Through Experiences with Expressive Avatars

Modern Warfighters often find themselves in a variety of non-combat roles such as negotiator, peacekeeper, reconstruction, and disaster relief. They are expected to perform these roles within a culture alien to their own. Each individual they encounter brings their own set of values to the interaction that must be understood and reconciled. To navigate the human terrain of these complex interactions, the Warfighter must not only consider the specifics of the target culture, but also identify the stakeholders, recognize the influencing cultural dimensions, and adapt to the situation to achieve the best possible outcome. Vcom3D is using game-based scenarios to develop culturally adaptive competency. The avatars that represent the stakeholders must be able to portray culturally accurate behavior, display complex emotion, and communicate through verbal and non-verbal cues. This paper will discuss the use of emerging game technologies to better simulate human behavior in cross-cultural dilemmas. Nomenclature: culture, adaptive, values, cultural values dimensions, dilemmas, virtual humans, non-verbal communications

Silverglate, Daniel S.↗
NASA NTRS2016

The Climate is A-Changin': Teaching Civic Competence for a Sustainable Climate

A central aim of social studies curriculum is to prepare young people for making "informed and reasoned decisions for the public good" concerning consequential problems like global climate change. By developing students' "vision of a good society" and exploring what actions and policies move our society in this direction, social studies teachers have an important role in preparing students for a world undergoing enormous environmental change. This article discusses elementary curriculum connections between building students' knowledge and understanding about "their community, nation and world" and global climate change. It also suggests ideas for building civic competency and climate literacy while creating opportunities for students to practice high-value skills like "data collection and analysis, collaboration, decision-making and problem-solving."

climate change↗
NASA NTRS2020

Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes

Quantifying changes in Earth’s ice sheets and identifying the climate drivers are central to improving sea level projections. We provide unified estimates of grounded and floating ice mass change from 2003 to 2019 using NASA’s Ice, Cloud and land Elevation Satellite (ICESat) and ICESat-2 satellite laser altimetry. Our data reveal patterns likely linked to competing climate processes: Ice loss from coastal Greenland (increased surface melt), Antarctic ice shelves (increased ocean melting), and Greenland and Antarctic outlet glaciers (dynamic response to ocean melting) was partially compensated by mass gains over ice sheet interiors (increased snow accumulation). Losses outpaced gains, with grounded-ice loss from Greenland (200 billion tonnes per year) and Antarctica (118 billion tonnes per year) contributing 14 millimeters to sea level. Mass lost from West Antarctica’s ice shelves accounted for more than 30% of that region’s total.

Ben Smith↗
NASA NTRS2021

Developing Compelling and Science-Focused Mission Concepts for NASA Competed Mission Proposals

Since the mid 1990s, NASA has used a competitive selection process to initiate new mission concepts. These competed missions are motivated by high-value science with low implementation and cost risks. Selectable mission concepts require highly focused science approaches—delivering high quality science “on a budget.” Prospective Principal Investigators (PIs) need to convince NASA that the science they are proposing is both compelling and has high programmatic value. Unfortunately, many of these PIs are not trained in the communication skills needed for “selling” a mission concept to stakeholders. This requires a proposal that presents an investigation in an accessible, relatable, authentic, and believable way. It is the onus of the proposing PI to convince NASA of the value of their particular science concept in a competitive environment, addressing any pre-conceived notions reviewers might have about the concept’s value, complexities, urgency, and other impediments to understanding.The importance of this can be seen in the NASA-sponsored PI Launchpad (Nov 2019 & Jun 2021)1 which was designed to help early career scientists understand the skills, methods, processes, and resources needed to develop compelling science mission concepts; as well as in JPL’s update to their concept maturity model (Jan 2020) which included the addition of Story and Strategy dimensions. This paper provides guidance to assist prospective PIs in developing compelling, science-focused mission concepts. It will provide direction for communicating concepts more clearly to make science objectives more relatable to both reviewers and a broader audience, improving the probability of selection.

Ziemer, John↗
NASA NTRS1979

Maximum likelihood estimation for life distributions with competing failure modes

Systems which are placed on test at time zero, function for a period and die at some random time were studied. Failure may be due to one of several causes or modes. The parameters of the life distribution may depend upon the levels of various stress variables the item is subject to. Maximum likelihood estimation methods are discussed. Specific methods are reported for the smallest extreme-value distributions of life. Monte-Carlo results indicate the methods to be promising. Under appropriate conditions, the location parameters are nearly unbiased, the scale parameter is slight biased, and the asymptotic covariances are rapidly approached.

Sidik, S. M.↗
NASA NTRS1979

Cost comparison of competing local distribution systems for communication satellite traffic

The boundaries of market areas which favor various means for distributing communications satellite traffic are considered. The distribution methods considered are: control Earth station with cable access, rooftop Earth stations, Earth station with radio access, and various combinations of these methods. The least cost system for a hypothetical region described by number of users and the average cable access mileage is discussed. The region is characterized by a function which expresses the distribution of users. The results indicate that the least cost distribution is central Earth station with cable access for medium to high density areas of a region combined with rooftop Earth stations or (for higher volumes) radio access for remote users.

Dopfel, F. E.↗