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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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NASA NTRS1990

A comparison of two major earth radiation budget data sets

Temporally overlapping data from earth-radiation-budget instruments on the Nimbus-7, ERBS, and NOAA-9 satellites during 1984-1986 are compiled in extensive tables and graphs and analyzed comparatively. It is found that Nimbus-7 top-of-the-atmosphere wide-FOV short-wave measurements are about 2.5 percent higher than those by the ERBS instruments, and that Nimbus-7 total-spectrum measurements are about 1 percent higher than ERBS measurements near noon but 1 percent lower near midnight. The combined NOAA-9/ERBS scanner data products are shown to agree with the Nimbus-7 global averages and the NOAA-9/ERBS wide-FOV products to within 0.16 and 0.17 percent, respectively, in outgoing longwave radiation and to within 0.03 percent and 3.55 percent in albedo.

Kyle, H. Lee↗

NASA NTRS1987

Particle paths and phase plane for time-dependent similarity solutions of the one-dimensional Vlasov-Maxwell equations

The phase trajectories of particles in a plasma described by the one-dimensional Vlasov-Maxwell equations are determined qualitatively, analyzing exact general similarity solutions for the cases of temporally damped and growing (sinusoidal or localized) electric fields. The results of numerical integration in both untransformed and Lie-group point-transformed coordinates are presented in extensive graphs and characterized in detail. The implications of the present analysis for the stability of BGK equilibria are explored, and the existence of nonlinear solutions arbitrarily close to and significantly different from the BGK solutions is demonstrated.

Roberts, Dana Aaron↗

NASA NTRS1990

The inviscid stability of supersonic flow past a sharp cone

The effects of lateral curvature on the development of supersonic laminar inviscid boundary-layer flow on a sharp cone with adiabatic wall conditions are investigated analytically, with a focus on the linear temporal inviscid stability properties. The derivation of the governing equations and of a 'triply generalized' inflexion condition is outlined, and numerical results for freestream Mach number 3.8 are presented in extensive graphs and characterized in detail. A third instability mode related to the viscous mode observed by Duck and Hall (1990) using triple-deck theory is detected and shown to be more unstable and to have larger growth rates than the second mode in some cases. It is found that the 'sonic' neutral mode is affected by the lateral curvature and becomes a supersonic neutral mode.

Duck, Peter W.↗

NASA NTRS2012

HURON (HUman and Robotic Optimization Network) Multi-Agent Temporal Activity Planner/Scheduler

HURON solves the problem of how to optimize a plan and schedule for assigning multiple agents to a temporal sequence of actions (e.g., science tasks). Developed as a generic planning and scheduling tool, HURON has been used to optimize space mission surface operations. The tool has also been used to analyze lunar architectures for a variety of surface operational scenarios in order to maximize return on investment and productivity. These scenarios include numerous science activities performed by a diverse set of agents: humans, teleoperated rovers, and autonomous rovers. Once given a set of agents, activities, resources, resource constraints, temporal constraints, and de pendencies, HURON computes an optimal schedule that meets a specified goal (e.g., maximum productivity or minimum time), subject to the constraints. HURON performs planning and scheduling optimization as a graph search in state-space with forward progression. Each node in the graph contains a state instance. Starting with the initial node, a graph is automatically constructed with new successive nodes of each new state to explore. The optimization uses a set of pre-conditions and post-conditions to create the children states. The Python language was adopted to not only enable more agile development, but to also allow the domain experts to easily define their optimization models. A graphical user interface was also developed to facilitate real-time search information feedback and interaction by the operator in the search optimization process. The HURON package has many potential uses in the fields of Operations Research and Management Science where this technology applies to many commercial domains requiring optimization to reduce costs. For example, optimizing a fleet of transportation truck routes, aircraft flight scheduling, and other route-planning scenarios involving multiple agent task optimization would all benefit by using HURON.

Hua, Hook↗

NASA NTRS1989

Significance of light and social cues in the maintenance of temporal organization in man

The effects of light:darkness (LD) cycles and social interaction on the response to long-term confinement (105 days) were investigated experimentally in three groups of three male subjects aged 20-24 years. Data from measurements of physiological parameters indicating changes in circadian rhythms are presented in graphs and analyzed; it is found that the LD-induced rhythm changes observed in previous studies of subjects isolated singly do not appear when subjects are confined in groups of three, suggesting a positive adaptive effect of social contact. In one subject who was transferred to a different group at day 84, hostile social interactions and poor circadian-rhythm entrainment were observed; the possible reasons for this response are considered.

Winget, C. M.↗

NASA NTRS2008

GRB Studies with Fermi

This slide presentation reviews the studies of Gamma Ray Bursts (GRB) with the Fermi Gamma Ray Space Telescope. Included are pictures of the observatory, with illustrations of the Large Area Telescope (LAT), and the Gamma-ray Burst Monitor (GBM) including information about both their capabilities. Graphs showing the GBM count rate over time after the GBM trigger for three GRBs, preliminary charts showing the multiple detector light curves the spectroscopy of the main LAT peak and the spectral evolution of GRB 080916C Burst Temporally-extended LAT emission.

Meegan, Charles A.↗

NASA NTRS1988

Temporal and spatial adaptive algorithm for reacting flows

A numerical integration scheme for quasi-one-dimensional unsteady flows with finite-rate chemistry is developed and demonstrated. The governing Euler and species-conservation equations are derived; the integration method and the spatial and temporal grid embedding techniques are explained; and results for sample problems involving stream-tube flow with one dissociating gas, shock-tube flow with one dissociating gas, and diverging-channel flow with multiple reactions are presented in extensive graphs and briefly characterized. Accuracy comparable to that of globally fine grid solutions is obtained with significant savings in CPU time.

Pervaiz, Mehtab M.↗

NASA NTRS1990

Model checking for linear temporal logic: An efficient implementation

This report provides evidence to support the claim that model checking for linear temporal logic (LTL) is practically efficient. Two implementations of a linear temporal logic model checker is described. One is based on transforming the model checking problem into a satisfiability problem; the other checks an LTL formula for a finite model by computing the cross-product of the finite state transition graph of the program with a structure containing all possible models for the property. An experiment was done with a set of mutual exclusion algorithms and tested safety and liveness under fairness for these algorithms.

Sherman, Rivi↗

NASA NTRSDate not supplied

Aerial Vehicle Routing and Scheduling for UAS Traffic Management: A Monte Carlo Tree Search Approach

Numerous unmanned aircraft systems operating at low altitudes to deliver goods and services may one day become ubiquitous in our cities. In the Unmanned Aircraft Systems (UAS) Traffic Management (UTM) framework, such a concept is envisioned, where aerial vehicles operate beyond visual line of sight (BVLOS) within specifically reserved and time stamped “corridors” in the airspace. For example, these corridors or operational intent volumes can connect an aerial vehicle’s origin site to its destination site for package delivery operations. There may also be more than one corridor available for an aerial vehicle to choose from and often different corridors may intersect with one another. Thus, it is imperative to ensure flight trajectories belonging to different aerial vehicles are not in conflict. Per the UTM CONOPs, we assume that a vehicle almost always stays inside its corridor or operational volume. This work provides a framework for strategic deconfliction of UTM or package delivery drones, where we schedule the departure time of all vehicles subject to various temporal constraints (including the corridor deconfliction at the intersections). We present the “multi-route weighted package delivery problem” which serves as an exemplifying model for strategic deconfliction in UTM. In the multi-route weighted package delivery problem, a graph network is given which consists of a set of depots (source) and drop-off (destination) nodes, with multiple routes (defined as a sequence of waypoints) connecting the depots to drop-off nodes. In addition, routes are weighted by the associated ground risk and total travel distance for package delivery. The goal is for a known set of aerial vehicles to depart from the depots, choose a route and take off time, while avoiding conflicts with other aerial vehicles, and minimizing both risk and distance traveled. We provide a mixed integer linear programming (MILP) formulation of the problem, as well as a heuristic solution based on Monte Carlo Tree Search (MCTS) – a method used in game theory and artificial intelligence – to overcome limitations inherent to optimal solvers. Computational results show the advantages of using MCTS over the MILP formulation; the former can provide a sub-optimal solution quickly, and may sometimes even reach an optimal solution, whereas the latter may not even produce a solution in reasonable time. Furthermore, results from both the MILP formulation and MCTS methods were validated using a preliminary agent-based simulator implementing the UTM concept of operations. Thus, the MCTS method can be seen as a scalable solution to the complex multi-route weighted package delivery problem and may possibly be extended to similar complex optimization problems.

Kenny Chour↗

NASA NTRS1975

Magnetospheric plasma regions and boundaries

The boundaries of the various regions of the magnetospheric plasma are considered, taking into account the bow shock, the magnetopause, the outer boundary of the plasma sheet, the inner boundary of the plasma sheet, and the trapping boundary for energetic particles. Attention is given to the steady state, or quasi-steady state, to substorm effects in which temporal changes are important, and to primary auroral processes. A description is presented of the high latitude lobes of the magnetotail. The characteristics of magnetic field topology associated with interconnected interplanetary and geomagnetic field lines are illustrated with the aid of a graph.

Heikkila, W. J.↗

NASA NTRS1991

Flexible Envelope Request Notation (FERN)

The following topics are presented in view graph form and include the following: scheduling application; the motivation for the Flexible Envelope Request Notation (FERN); characteristics of FERN; types of information needed in requests; where information is stored in requests; FERN structures; generic requests; resource availability for pooled resources; expressive notation; temporal constraints; time formats; changes to FERN; sample FERN requests; the temporal relationship between two steps; maximum activity length to limit step delays; alternative requests; the temporal relationship between two activities; and idle resource usage between steps.

Zoch, David R.↗

NASA NTRS1995

Model checking

Automatic formal verification methods for finite-state systems, also known as model-checking, successfully reduce labor costs since they are mostly automatic. Model checkers explicitly or implicitly enumerate the reachable state space of a system, whose behavior is described implicitly, perhaps by a program or a collection of finite automata. Simple properties, such as mutual exclusion or absence of deadlock, can be checked by inspecting individual states. More complex properties, such as lack of starvation, require search for cycles in the state graph with particular properties. Specifications to be checked may consist of built-in properties, such as deadlock or 'unspecified receptions' of messages, another program or implicit description, to be compared with a simulation, bisimulation, or language inclusion relation, or an assertion in one of several temporal logics. Finite-state verification tools are beginning to have a significant impact in commercial designs. There are many success stories of verification tools finding bugs in protocols or hardware controllers. In some cases, these tools have been incorporated into design methodology. Research in finite-state verification has been advancing rapidly, and is showing no signs of slowing down. Recent results include probabilistic algorithms for verification, exploitation of symmetry and independent events, and the use symbolic representations for Boolean functions and systems of linear inequalities. One of the most exciting areas for further research is the combination of model-checking with theorem-proving methods.

Dill, David L.↗

NASA NTRS1987

Intrinsically variable stars

The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

Bohm-Vitense, Erika↗

NASA NTRS1979

Temporal studies of compact galactic X-ray sources

Advances in X-ray astronomy due to temporal studies are discussed. Attention is given to X-ray temporal variability categorized into periodic, quasi-periodic, and chaotic. Approximately 95% of all known X-ray sources exhibit chaotic variability, in which there is no apparent pattern or periodicities. The orbits of seven binary X-ray sources are presented, along with empirical findings of neutron star masses. In addition, the interior structure of a supergiant star, HD 77581, is investigated by attempting to measure its apsidal motion. Graphs are provided for the power density spectrum of 4U 1626-67, GX301-2 Doppler delay data, and empirically determined error contours for the mass and radius of four companions stars in X-ray binary systems.

Rappaport, S.↗

NASA NTRS2015

Groundwater Variability Across Temporal and Spatial Scales in the Central and Northeastern U.S.

Depth-to-water measurements from 181 monitoring wells in unconfined or semi-confined aquifers in nine regions of the central and northeastern U.S. were analyzed. Groundwater storage exhibited strong seasonal variations in all regions, with peaks in spring and lows in autumn, and its interannual variability was nearly unbounded, such that the impacts of droughts, floods, and excessive pumping could persist for many years. We found that the spatial variability of groundwater storage anomalies (deviations from the long term mean) increases as a power function of extent scale (square root of area). That relationship, which is linear on a log-log graph, is common to other hydrological variables but had never before been shown with groundwater data. We describe how the derived power function can be used to determine the number of wells needed to estimate regional mean groundwater storage anomalies with a desired level of accuracy, or to assess uncertainty in regional mean estimates from a set number of observations. We found that the spatial variability of groundwater storage anomalies within a region often increases with the absolute value of the regional mean anomaly, the opposite of the relationship between soil moisture spatial variability and mean. Recharge (drainage from the lowest model soil layer) simulated by the Variable Infiltration Capacity (VIC) model was compatible with observed monthly groundwater storage anomalies and month-to-month changes in groundwater storage.

Groundwater↗

NASA NTRS2015

Groundwater Variability Across Temporal and Spatial Scales in the Central and Northeastern U.S.

water cycle↗

NASA NTRS2016

The Mathematics of Dispatchability, Revisited

Dispatchability is an important property for the efficient execution of temporal plans where the temporal constraints are represented as a Simple Temporal Network (STN). It has been shown that every STN may be reformulated as a dispatchable STN, and dispatchability ensures that the temporal constraints need only be satisfied locally during execution. Recently, it has also been shown that Simple Temporal Networks with Uncertainty, augmented with wait edges, are Dynamically Controllable provided every projection is dispatchable. Thus, dispatchability has considerable theoretical as well as practical significance. One thing that hampers further work in this area is the underdeveloped theory. Moreover, the existing foundation is inadequate in certain respects. In this paper, we develop a new mathematical theory of dispatchability and its relationship to execution. We also provide several characterizations of dispatchability, including characterizations in terms of the structural properties of the STN graph. This facilitates the potential application of the theory to other areas.

mathematical models↗

NASA NTRS2001

Studying Earth's Environment From Space: Classroom and Laboratory Activities with Instructor Resources

Standard, text-book based learning for earth, ocean, and atmospheric sciences has been limited by the unavailability of quantitative teaching materials. While a descriptive presentation, in a lecture format, of discrete satellite images is often adequate for high school classrooms, this is seldom the case at the undergraduate level. In order to address these concerns, a series of numerical exercises for the Macintosh was developed for use with satellite-derived Sea Surface Temperature, pigment and sea ice concentration data. Using a modified version of NIH Image, to analyze actual satellite data, students are able to better understand ocean processes, such as circulation, upwelling, primary production, and ocean/atmosphere coupling. Graphical plots, image math, and numerical comparisons are utilized to substantiate temporal and spatial trends in sea surface temperature and ocean color. Particularly for institutions that do not offer a program in remote sensing, the subject matter is presented as modular units, each of which can be readily incorporated into existing curricula. These materials have been produced in both CD-ROM and WWW format, making them useful for classroom or lab setting. Depending upon the level of available computer support, graphics can be displayed directly from the CD-ROM, or as a series of color view graphs for standard overhead projection.

Smith, Elizabeth A.↗