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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 NTRS1995

A search for T Tauri stars in high-latitude molecular clouds. 2: The IRAS Faint Source Survey catalog

We present a catalog of infrared point sources from the IRAS Faint Source Survey at Galactic latitudes the absolute magnitude of b is greater than or equal to 30 deg. The aim of this paper is to provide a list of possible star-forming sites at high Galactic latitudes in order to address the question of whether or not the translucent molecular clouds (which are most easily identified at high latitudes) are capable of star formation. The primary list of sources has 12, 25, 60, and 100 micron fluxes within the range typical of pre-main-sequence or T Tauri stars. A secondary list has the same range of 12, 25, and 60 micron fluxes, but only upper limits at 100 microns. A total of 127 candidates from the first category and 65 candidates from the second category are identified and their positions and infrared spectral characteristics tabulated. Although the colors and fluxes of these sources are typical of T Tauri or pre-main-sequence stars and YSOs, extragalactic sources and planetary nebulae sometimes have similar colors. These lists provide a starting point for optical spectroscopy or other techniques to positively identify these objects. We can determine an upper limit to the star forming efficiency of high-latitude molecular clouds assuming all the candidates in our sample are pre-main sequence stars of one solar mass. The upper limit of a few tenths of 1% is less than the star-forming efficiency of local dark cloud complexes such as the Taurus-Auriga or rho Ophiuchus clouds.

Magnani, Loris↗
NASA NTRS1994

Effects of head-down bed rest on complex heart rate variability: Response to LBNP testing

Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 deg head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on a 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal 'complexity' (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ('chaos theory'), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.

Goldberger, Ary L.↗
NASA NTRS1995

Is walking a random walk? Evidence for long-range correlations in stride interval of human gait

Complex fluctuation of unknown origin appear in the normal gait pattern. These fluctuations might be described as being (1) uncorrelated white noise, (2) short-range correlations, or (3) long-range correlations with power-law scaling. To test these possibilities, the stride interval of 10 healthy young men was measured as they walked for 9 min at their usual rate. From these time series we calculated scaling indexes by using a modified random walk analysis and power spectral analysis. Both indexes indicated the presence of long-range self-similar correlations extending over hundreds of steps; the stride interval at any time depended on the stride interval at remote previous times, and this dependence decayed in a scale-free (fractallike) power-law fashion. These scaling indexes were significantly different from those obtained after random shuffling of the original time series, indicating the importance of the sequential ordering of the stride interval. We demonstrate that conventional models of gait generation fail to reproduce the observed scaling behavior and introduce a new type of central pattern generator model that sucessfully accounts for the experimentally observed long-range correlations.

Hausdorff, Jeffrey M.↗
NASA NTRS1995

Head perturbations during walking while viewing a head-fixed target

Inexpensive, head-fixed computer displays are now available that subjects can wear during locomotion. Our hypothesis is that viewing a head-fixed visual display will change the character- istics of rotational head perturbations during natural walking. Using a 3-axis angular rate sensor, we measured head rotations during natural or treadmill walking, in 10 normal subjects and 2 patients with deficient vestibular function, as they attempted to view (1) a stationary target at optical infinity; and (2) a target at a distance of 20 cm rigidly attached to the head. Normal subjects and patients showed no significant change in the predominant frequency of head rotations in any plane (ranging 0.7-5.7 Hz) during the two different viewing tasks. Mean peak head velocities also showed no difference during the two viewing conditions except in the yaw plane, in which values were greater while viewing the near target. Predominant frequencies of head rotations were similar in the pitch plane during natural or treadmill walking; however, peak velocities of pitch head rotations were substantially greater during natural walking. One vestibular patient showed modest increases of head velocity during natural walking compared with normal subjects. Rotational head perturbations that occur during natural walking are largely unaffected when subjects view a head-fixed target. There is need to study how such perturbations, which induce vestibular eye movements, affect vision of head-fixed displays.

Das, Vallabh E.↗
NASA NTRS1995

Observations of the CO bulge on Venus and implications for mesospheric winds

Observations of CO at 2.6 mm (115.27 GHz) were made with the Owens Valley Radio Observatory (OVRO) millimeter interferometer in 1986 and 1988, yielding high-quality disk-resolved spectra which were inverted to determine the CO mixing ratio profile from distinct regions on the disk, allowing us to map the distribution of CO in the upper mesosphere of Venus both horizontally and vertically. The 1986 observations were of the morning terminator and were particularly useful in searching for a suspected CO maximum ('bulge') on the nightside. The resulting CO mixing ratio profiles were mapped for various altitudes as functions of latitude and local time, and we report that we have resolved the previously inferred CO bulge. The bulge increases in magnitude from a small day-night variation at 90 km to an extensive nightside peak at 100 km, the upper limit of our observations. The peak bulge-to-dayside ratio approached 20-30 at 100 km in 1986 and may have been as large as 50-100, assuming late-afternoon CO abundances found in 1988 were similar to those in 1986. Three-dimensional mapping shows that in the upper mesosphere the bulge was displaced from local midnight toward the morning equator, centered at 3:30 AM local time. Using the qualitative model of mesospheric circulation on Venus proposed by Clancy and Muhleman (1985, 1991), we explain this shift in terms of strong retrograde zonal winds throughout the mesosphere, matching the directly detected mesospheric circulation (Shah, K., D. O. Muhleman, and G. L. Berge 1991) observed with the same dataset in 1988.

Gurwell, Mark A.↗
NASA NTRS1996

The Development of Novel, High-Flux, Heat Transfer Cells for Thermal Control in Microgravity

In order to meet the future needs of thermal management and control in space applications such as the Space Lab, new heat-transfer technology capable of much larger heat fluxes must be developed. To this end, we describe complementary numerical and experimental investigations into the fundamental fluid mechanics and heat-transfer processes involved in a radically new, self contained, heat transfer cell for microgravity applications. In contrast to conventional heat pipes, the heat transfer in this cell is based on a forced droplet evaporation process using a fine spray. The spray is produced by a novel fluidic technology recently developed at Georgia Tech. This technology is based on a vibration induced droplet atomization process. In this technique, a liquid droplet is placed on a flexible membrane and is vibrated normal to itself. When the proper drop size is attained, the droplet resonates with the surface motion of the membrane and almost immediately bursts into a shower of very fine secondary droplets. The small droplets travel to the opposite end of the cell where they impact a heated surface and are evaporated. The vapor returns to the cold end of the cell and condenses to form the large droplets that are fragmented to form the spray. Preliminary estimates show that a heat transfer cell based on this technology would have a heat-flux capacity that is an order of magnitude higher than those of current heat pipes designs used in microgravity applications.

Smith, Marc K.↗
NASA NTRS1998

Time-Critical Volume Rendering

For the past twelve months, we have conducted and completed a joint research entitled "Time- Critical Volume Rendering" with NASA Ames. As expected, High performance volume rendering algorithms have been developed by exploring some new faster rendering techniques, including object presence acceleration, parallel processing, and hierarchical level-of-detail representation. Using our new techniques, initial experiments have achieved real-time rendering rates of more than 10 frames per second of various 3D data sets with highest resolution. A couple of joint papers and technique reports as well as an interactive real-time demo have been compiled as the result of this project.

Kaufman, Arie↗
NASA NTRS1997

Advanced Algorithms and High-Performance Testbed for Large-Scale Site Characterization and Subsurface Target Detecting Using Airborne Ground Penetrating SAR

A team of US Army Corps of Engineers, Omaha District and Engineering and Support Center, Huntsville, let Propulsion Laboratory (JPL), Stanford Research Institute (SRI), and Montgomery Watson is currently in the process of planning and conducting the largest ever survey at the Former Buckley Field (60,000 acres), in Colorado, by using SRI airborne, ground penetrating, Synthetic Aperture Radar (SAR). The purpose of this survey is the detection of surface and subsurface Unexploded Ordnance (UXO) and in a broader sense the site characterization for identification of contaminated as well as clear areas. In preparation for such a large-scale survey, JPL has been developing advanced algorithms and a high-performance restbed for processing of massive amount of expected SAR data from this site. Two key requirements of this project are the accuracy (in terms of UXO detection) and speed of SAR data processing. The first key feature of this testbed is a large degree of automation and a minimum degree of the need for human perception in the processing to achieve an acceptable processing rate of several hundred acres per day. For accurate UXO detection, novel algorithms have been developed and implemented. These algorithms analyze dual polarized (HH and VV) SAR data. They are based on the correlation of HH and VV SAR data and involve a rather large set of parameters for accurate detection of UXO. For each specific site, this set of parameters can be optimized by using ground truth data (i.e., known surface and subsurface UXOs). In this paper, we discuss these algorithms and their successful application for detection of surface and subsurface anti-tank mines by using a data set from Yuma proving Ground, A7, acquired by SRI SAR.

Fijany, Amir↗
NASA NTRS1999

Next Generation Remote Agent Planner

In May 1999, as part of a unique technology validation experiment onboard the Deep Space One spacecraft, the Remote Agent became the first complete autonomous spacecraft control architecture to run as flight software onboard an active spacecraft. As one of the three components of the architecture, the Remote Agent Planner had the task of laying out the course of action to be taken, which included activities such as turning, thrusting, data gathering, and communicating. Building on the successful approach developed for the Remote Agent Planner, the Next Generation Remote Agent Planner is a completely redesigned and reimplemented version of the planner. The new system provides all the key capabilities of the original planner, while adding functionality, improving performance and providing a modular and extendible implementation. The goal of this ongoing project is to develop a system that provides both a basis for future applications and a framework for further research in the area of autonomous planning for spacecraft. In this article, we present an introductory overview of the Next Generation Remote Agent Planner. We present a new and simplified definition of the planning problem, describe the basics of the planning process, lay out the new system design and examine the functionality of the core reasoning module.

Jonsson, Ari K.↗
NASA NTRS1999

A Framework for Dynamic Constraint Reasoning Using Procedural Constraints

Many complex real-world decision and control problems contain an underlying constraint reasoning problem. This is particularly evident in a recently developed approach to planning, where almost all planning decisions are represented by constrained variables. This translates a significant part of the planning problem into a constraint network whose consistency determines the validity of the plan candidate. Since higher-level choices about control actions can add or remove variables and constraints, the underlying constraint network is invariably highly dynamic. Arbitrary domain-dependent constraints may be added to the constraint network and the constraint reasoning mechanism must be able to handle such constraints effectively. Additionally, real problems often require handling constraints over continuous variables. These requirements present a number of significant challenges for a constraint reasoning mechanism. In this paper, we introduce a general framework for handling dynamic constraint networks with real-valued variables, by using procedures to represent and effectively reason about general constraints. The framework is based on a sound theoretical foundation, and can be proven to be sound and complete under well-defined conditions. Furthermore, the framework provides hybrid reasoning capabilities, as alternative solution methods like mathematical programming can be incorporated into the framework, in the form of procedures.

Jonsson, Ari K.↗
NASA NTRS1999

Marked Exacerbation of Orthostatic Intolerance After Long vs. Short-Duration Spaceflight in Veteran Astronauts

The incidence of postflight orthostatic intolerance following short-duration spaceflight is about 20%. However, the incidence following long-duration spaceflight is unknown. We performed tilt tests on six astronauts before and after their long-duration (129 - 190 days) spaceflights and compared these data to those obtained during stand tests before and after their previous short-duration missions and also to tilt test data from 20 different short-duration (8 - 16 days) flight astronauts. Five of these six became presyncopal during tilt testing after long-duration flights: only one had become presyncopal during stand testing after short-duration flights. Five of the twenty astronauts who flew on other short-duration flights, became presyncopal during upright tilt on landing day. Long-duration presyncopal subjects had lower stroke volumes, lower cardiac outputs and higher peripheral vascular resistance than short-duration presyncopal subjects, but their heart rate responses were not different. One subject had subnormal norepinephrine release with upright posture after a long but not short flight. Plasma volume losses were not greater after long flights. Long-duration spaceflight markedly increases orthostatic intolerance, probably related to altered autonomic function.

Fritsch-Yelle, Janice M.↗
NASA NTRS2000

Bridging the Gap Between Planning and Scheduling

Planning research in Artificial Intelligence (AI) has often focused on problems where there are cascading levels of action choice and complex interactions between actions. In contrast. Scheduling research has focused on much larger problems where there is little action choice, but the resulting ordering problem is hard. In this paper, we give an overview of M planning and scheduling techniques, focusing on their similarities, differences, and limitations. We also argue that many difficult practical problems lie somewhere between planning and scheduling, and that neither area has the right set of tools for solving these vexing problems.

Smith, David E.↗
NASA NTRS2000

Generalizing Backtrack-Free Search: A Framework for Search-Free Constraint Satisfaction

Tractable classes of constraint satisfaction problems are of great importance in artificial intelligence. Identifying and taking advantage of such classes can significantly speed up constraint problem solving. In addition, tractable classes are utilized in applications where strict worst-case performance guarantees are required, such as constraint-based plan execution. In this work, we present a formal framework for search-free (backtrack-free) constraint satisfaction. The framework is based on general procedures, rather than specific propagation techniques, and thus generalizes existing techniques in this area. We also relate search-free problem solving to the notion of decision sets and use the result to provide a constructive criterion that is sufficient to guarantee search-free problem solving.

Jonsson, Ari K.↗
NASA NTRS2000

On Reformulating Planning as Dynamic Constraint Satisfaction

In recent years, researchers have reformulated STRIPS planning problems as SAT problems or CSPs. In this paper, we discuss the Constraint-Based Interval Planning (CBIP) paradigm, which can represent planning problems incorporating interval time and resources. We describe how to reformulate mutual exclusion constraints for a CBIP-based system, the Extendible Uniform Remote Operations Planner Architecture (EUROPA). We show that reformulations involving dynamic variable domains restrict the algorithms which can be used to solve the resulting DCSP. We present an alternative formulation which does not employ dynamic domains, and describe the relative merits of the different reformulations.

Frank, Jeremy↗
NASA NTRS2001

Planning and Scheduling for Fleets of Earth Observing Satellites

We address the problem of scheduling observations for a collection of earth observing satellites. This scheduling task is a difficult optimization problem, potentially involving many satellites, hundreds of requests, constraints on when and how to service each request, and resources such as instruments, recording devices, transmitters, and ground stations. High-fidelity models are required to ensure the validity of schedules; at the same time, the size and complexity of the problem makes it unlikely that systematic optimization search methods will be able to solve them in a reasonable time. This paper presents a constraint-based approach to solving the Earth Observing Satellites (EOS) scheduling problem, and proposes a stochastic heuristic search method for solving it.

Frank, Jeremy↗
NASA NTRS2001

The Logic of Reachability

In recent years, Graphplan style reachability analysis and mutual exclusion reasoning have been used in many high performance planning systems. While numerous refinements and extensions have been developed, the basic plan graph structure and reasoning mechanisms used in these systems are tied to the very simple STRIPS model of action. In 1999, Smith and Weld generalized the Graphplan methods for reachability and mutex reasoning to allow actions to have differing durations. However, the representation of actions still has some severe limitations that prevent the use of these techniques for many real-world planning systems. In this paper, we 1) separate the logic of reachability from the particular representation and inference methods used in Graphplan, and 2) extend the notions of reachability and mutual exclusion to more general notions of time and action. As it turns out, the general rules for mutual exclusion reasoning take on a remarkably clean and simple form. However, practical instantiations of them turn out to be messy, and require that we make representation and reasoning choices.

Smith, David E.↗
NASA NTRS2001

A Constraint-based Attribute and Interval Planning

In this paper we introduce Constraint-based Attribute and Interval Planning (CAIP), a new paradigm for representing and reasoning about plans. The paradigm enables the description of planning domains with time, resources, concurrent activities, mutual exclusions among sets of activities, disjunctive preconditions and conditional effects. We provide a theoretical foundation for the paradigm using a mapping to first order logic. We also show that CAIP plans are naturally expressed by networks of constraints, and that planning maps directly to dynamic constraint reasoning. In addition, we show how constraint templates are used to provide a compact mechanism for describing planning domains.

Frank, Jeremy↗
NASA NTRS2002

Demonstration of a Spoken Dialogue Interface for Planning Activities of a Semi-autonomous Robot

Planning and scheduling in the face of uncertainty and change pushes the capabilities of both planning and dialogue technologies by requiring complex negotiation to arrive at a workable plan. Planning for use of semi-autonomous robots involves negotiation among multiple participants with competing scientific and engineering goals to co-construct a complex plan. In NASA applications this plan construction is done under severe time pressure so having a dialogue interface to the plan construction tools can aid rapid completion of the process. But, this will put significant demands on spoken dialogue technology, particularly in the areas of dialogue management and generation. The dialogue interface will need to be able to handle the complex dialogue strategies that occur in negotiation dialogues, including hypotheticals and revisions, and the generation component will require an ability to summarize complex plans. This demonstration will describe a work in progress towards building a spoken dialogue interface to the EUROPA planner for the purposes of planning and scheduling the activities of a semi-autonomous robot. A prototype interface has been built for planning the schedule of the Personal Satellite Assistant (PSA), a mobile robot designed for micro-gravity environments that is intended for use on the Space Shuttle and International Space Station. The spoken dialogue interface gives the user the capability to ask for a description of the plan, ask specific questions about the plan, and update or modify the plan. We anticipate that a spoken dialogue interface to the planner will provide a natural augmentation or alternative to the visualization interface, in situations in which the user needs very targeted information about the plan, in situations where natural language can express complex ideas more concisely than GUI actions, or in situations in which a graphical user interface is not appropriate.

Dowding, John↗