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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Afferent projections to the mammillary complex of the rat, with special reference to those from surrounding hypothalamic regions

To better understand the functional organization of the mammillary nuclei, we investigated the afferents to this nuclear complex in the rat with iontophoretically injected wheat germ agglutinin conjugated to horseradish peroxidase. Particular attention was paid to tracing local hypothalamic afferents to these nuclei. Injections into the medial mammillary nucleus (MMN) revealed strong projections from the subicular region, and weaker projections from the prefrontal cortex, medial septum, and the nucleus of the diagonal band of Broca. Other descending subcortical projections to the MMN arise from the anterior and the lateral hypothalamic area, the medial preoptic area, and the bed nucleus of the stria terminalis. Ascending afferents to the MMN were found to originate in the raphe and various tegmental nuclei. Following all injections into the MMN, labelled neurons were found in nuclei surrounding the mammillary body. The lateral and posterior subdivisions of the tuberomammillary nucleus projected mainly to the pars medianus and pars medialis of the MMN. The dorsal and ventral premammillary nuclei projected to the pars lateralis of the MMN. The supramammillary nucleus at rostral level had a small projection to the pars medialis and lateralis of the MMN. However, the most obvious projection from this nucleus was to the pars posterior of the MMN, chiefly from the lateral part of the caudal supramammillary nucleus. Injections into the lateral mammillary nucleus revealed inputs from the presubiculum, parasubiculum, septal region, dorsal tegmental nucleus, dorsal raphe nucleus, and periaqueductal gray. In addition, the lateral mammillary nucleus was found to receive a moderate projection from the medial part of the supramammillary nucleus and stronger projections from the lateral part of the caudal supramammillary nucleus. A very light projection was also seen from the lateral and posterior subdivisions of the tuberomammillary nucleus. These findings add to our knowledge of the extensive and complex connectivity of the mammillary nuclei. In particular, the local connections we have demonstrated with the supramammillary and tuberomammillary nuclei indicate the existence of significant local circuits as well as circuits involving more distant brain regions such as the septal nuclei, subiculum, prefrontal cortex, and brain stem tegmentum.

Non-NASA Center↗
NASA NTRS2005

Efficient Construction of Discrete Adjoint Operators on Unstructured Grids Using Complex Variables

A methodology is developed and implemented to mitigate the lengthy software development cycle typically associated with constructing a discrete adjoint solver for aerodynamic simulations. The approach is based on a complex-variable formulation that enables straightforward differentiation of complicated real-valued functions. An automated scripting process is used to create the complex-variable form of the set of discrete equations. An efficient method for assembling the residual and cost function linearizations is developed. The accuracy of the implementation is verified through comparisons with a discrete direct method as well as a previously developed handcoded discrete adjoint approach. Comparisons are also shown for a large-scale configuration to establish the computational efficiency of the present scheme. To ultimately demonstrate the power of the approach, the implementation is extended to high temperature gas flows in chemical nonequilibrium. Finally, several fruitful research and development avenues enabled by the current work are suggested.

Nielsen, Eric J.↗
NASA NTRS2005

A Comparison of Geographic Information Systems, Complex Networks, and Other Models for Analyzing Transportation Network Topologies

This report reviews six classes of models that are used for studying transportation network topologies. The report is motivated by two main questions. First, what can the "new science" of complex networks (scale-free, small-world networks) contribute to our understanding of transport network structure, compared to more traditional methods? Second, how can geographic information systems (GIS) contribute to studying transport networks? The report defines terms that can be used to classify different kinds of models by their function, composition, mechanism, spatial and temporal dimensions, certainty, linearity, and resolution. Six broad classes of models for analyzing transport network topologies are then explored: GIS; static graph theory; complex networks; mathematical programming; simulation; and agent-based modeling. Each class of models is defined and classified according to the attributes introduced earlier. The paper identifies some typical types of research questions about network structure that have been addressed by each class of model in the literature.

Alexandrov, Natalia↗
NASA NTRS2005

The Influence of Model Complexity on the Impact Response of a Shuttle Leading-Edge Panel Finite Element Simulation

LS-DYNA simulations were conducted to study the influence of model complexity on the response of a typical Reinforced Carbon-Carbon (RCC) panel to a foam impact at a location approximately midway between the ribs. A structural model comprised of Panels 10, 11, and TSeal 11 was chosen as the baseline model for the study. A simulation was conducted with foam striking Panel 10 at Location 4 at an alpha angle of 10 degrees, with an impact velocity of 1000 ft/sec. A second simulation was conducted after removing Panel 11 from the model, and a third simulation was conducted after removing both Panel 11 and T-Seal 11. All three simulations showed approximately the same response for Panel 10, and the simplified simulation model containing only Panel 10 was shown to be significantly less expensive to execute than the other two more complex models.

Jones, Lisa E.↗
NASA NTRS2005

Monitoring a Complex Physical System using a Hybrid Dynamic Bayes Net

The Reverse Water Gas Shift system (RWGS) is a complex physical system designed to produce oxygen from the carbon dioxide atmosphere on Mars. If sent to Mars, it would operate without human supervision, thus requiring a reliable automated system for monitoring and control. The RWGS presents many challenges typical of real-world systems, including: noisy and biased sensors, nonlinear behavior, effects that are manifested over different time granularities, and unobservability of many important quantities. In this paper we model the RWGS using a hybrid (discrete/continuous) Dynamic Bayesian Network (DBN), where the state at each time slice contains 33 discrete and 184 continuous variables. We show how the system state can be tracked using probabilistic inference over the model. We discuss how to deal with the various challenges presented by the RWGS, providing a suite of techniques that are likely to be useful in a wide range of applications. In particular, we describe a general framework for dealing with nonlinear behavior using numerical integration techniques, extending the successful Unscented Filter. We also show how to use a fixed-point computation to deal with effects that develop at different time scales, specifically rapid changes occuring during slowly changing processes. We test our model using real data collected from the RWGS, demonstrating the feasibility of hybrid DBNs for monitoring complex real-world physical systems.

Lerner, Uri↗
NASA NTRS2005

Drive Motor Improved for 8- by 6-Foot Supersonic Wind Tunnel/9- by 15-Foot Low-Speed Wind Tunnel Complex

An operational change made recently in the drive motor system for the 8- by 6-Foot Supersonic Wind Tunnel (8x6 SWT)/9- by 15-Foot Low-Speed Wind Tunnel (9x15 LSWT) complex resulted in dramatic power savings and expanded operating range. The 8x6 SWT/9x15 LSWT complex offers a unique combination of wind tunnel conditions for both high- and low-speed testing. Prior to the work discussed in this article, the 8- by 6-ft test section offered airflows ranging from Mach 0.36 to 2.0. Subsonic testing was done in the 9-ft high, 15-ft wide test area in the return leg of the facility. The air speed in this test section can range from 0 to 175 mph (Mach 0.23). In the past, we varied the air speed by using a combination of the compressor speed and the position of the tunnel flow-control doors. When very slow speeds were required in the 9x15 LSWT, these large tunnel flow control doors might be very nearly full open, bleeding off large quantities of air, even with the drive system operating at its previous minimum speed of about 510 rpm. Power drawn during this mode of operation varied between 15 and 18 MW/hr, but clearly much of this power was not being used to provide air that would be used for testing in the test section. The air exiting these large doors represented wasted power. Early this year, the facility's tunnel drive system was run on one motor instead of three to see if lower drive speeds could be achieved that would, in turn, result in large power savings because unnecessary air would not be blown out of the flow-control doors unnecessarily. In addition, if the drive could be run slower, then slower speeds would also be possible in the 8x6 SWT test section as an added benefit. Results of the first tests performed early last year showed that in fact the drive, when operating on only one motor, actually reached a steady-state speed of only 337 rpm and drew an amazingly small 6 MW/hr of electrical power. During daytime operation of the drive, this meant that it would be possible to save as much as 10 MW/hr, or nearly $600 per hour of operation, for many of the 9x15 LSWT's testing regimes. An added benefit of this power-saving venture was that since the 8x6 SWT and 9x15 LSWT are indeed on a common loop, if the compressor is slowed down to benefit the 9x15 LSWT, then the air moving through the 8x6 SWT is also moving slower than ever before. In fact, testing has proven that the 8x6 SWT can now achieve Mach 0.25, whereas its previous lower limit was Mach 0.36. This added benefit has attracted additional customers

Source record↗
NASA NTRS2005

You Can't Get There From Here! Problems and Potential Solutions in Developing New Classes of Complex Systems

The explosion of capabilities and new products within the sphere of Information Technology (IT) has fostered widespread, overly optimistic opinions regarding the industry, based on common but unjustified assumptions of quality and correctness of software. These assumptions are encouraged by software producers and vendors, who at this late date have not succeeded in finding a way to overcome the lack of an automated, mathematically sound way to develop correct systems from requirements. NASA faces this dilemma as it envisages advanced mission concepts that involve large swarms of small spacecraft that will engage cooperatively to acheve science goals. Such missions entail levels of complexity that beg for new methods for system development far beyond today's methods, which are inadequate for ensuring correct behavior of large numbers of interacting intelligent mission elements. New system development techniques recently devised through NASA-led research will offer some innovative approaches to achieving correctness in complex system development, including autonomous swarm missions that exhibit emergent behavior, as well as general software products created by the computing industry.

Hinchey, Michael G.↗
NASA NTRS2005

Investigation of the Dynamics of Coherent Structure, BBF, and Intermittent Turbulence in Earth's Magnetotail: A Study of Complexity in Nonlinear Space Plasmas

We have achieved all the goals stated in our grant proposal. Specifically, these include: 1. The understanding of the complexity induced nonlinear spatiotemporal coherent structures and the coexisting propagating modes. 2. The understanding of the intermittent turbulence and energization process of the observed Bursty Bulk Flows (BBF's) in the Earth s magnetotail. 3. The development of "anisotropic three-dimensional complexity" in the plasma sheet due to localized merging and interactions of the magnetic coherent structures. 4. The study of fluctuation-induced nonlinear instabilities and their role in the reconfiguration of magnetic topologies in the magnetotail based on the concepts of the dynamic renormalization group. 5. The acceleration of ions due to the intermittent turbulence of propagating and nonpropagating fluctuations. In the following, we include lists of our published papers, invited talks, and professional activities. A detailed description of our accomplished research results is given..

Chang, Tom↗
NASA NTRS2005

Building Blocks for Reliable Complex Nonlinear Numerical Simulations

This chapter describes some of the building blocks to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations.

Yee, H. C.↗
NASA NTRS2004

Role of shielding in modulating the effects of solar particle events: Monte Carlo calculation of absorbed dose and DNA complex lesions in different organs

Distributions of absorbed dose and DNA clustered damage yields in various organs and tissues following the October 1989 solar particle event (SPE) were calculated by coupling the FLUKA Monte Carlo transport code with two anthropomorphic phantoms (a mathematical model and a voxel model), with the main aim of quantifying the role of the shielding features in modulating organ doses. The phantoms, which were assumed to be in deep space, were inserted into a shielding box of variable thickness and material and were irradiated with the proton spectra of the October 1989 event. Average numbers of DNA lesions per cell in different organs were calculated by adopting a technique already tested in previous works, consisting of integrating into "condensed-history" Monte Carlo transport codes--such as FLUKA--yields of radiobiological damage, either calculated with "event-by-event" track structure simulations, or taken from experimental works available in the literature. More specifically, the yields of "Complex Lesions" (or "CL", defined and calculated as a clustered DNA damage in a previous work) per unit dose and DNA mass (CL Gy-1 Da-1) due to the various beam components, including those derived from nuclear interactions with the shielding and the human body, were integrated in FLUKA. This provided spatial distributions of CL/cell yields in different organs, as well as distributions of absorbed doses. The contributions of primary protons and secondary hadrons were calculated separately, and the simulations were repeated for values of Al shielding thickness ranging between 1 and 20 g/cm2. Slight differences were found between the two phantom types. Skin and eye lenses were found to receive larger doses with respect to internal organs; however, shielding was more effective for skin and lenses. Secondary particles arising from nuclear interactions were found to have a minor role, although their relative contribution was found to be larger for the Complex Lesions than for the absorbed dose, due to their higher LET and thus higher biological effectiveness. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Non-NASA Center↗
NASA NTRS2005

Monitoring the Intrinsic Absorption Complex Toward RXJ123.8+0115

The main focus of this study was changed after it became clear that the object to be observed by the Far Ultraviolet Spectroscopic Explorer (FUSE) could not be observed because of spacecraft attitude control system limitations. Therefore, we replaced the prime object for the program (RXJ1230.8+0115) with a secondary object (H1821+643) and began an analysis of a similar quasar spectrum for comparison with the extant RXJ1230.8+0115 spectrum obtained previously by FUSE. Using high-resolution spectra of the radio-quiet, X-ray bright quasar HE0226-4110 obtained with the Hubble Space Telescope (HST) and FUSE, we have examined the remarkable associated absorption line system. The redshift of the quasar is roughly 0.5 so the FUSE+HST spectra cover the rest-frame wavelength in the extreme ultraviolet range 610-1 160A. In this range, we detect transitions from a wide range of ionization species, including the H I Lyman series, Ne VIII, and, for the first time at this resolution, four adjacent stages of oxygen O III-VI. The high quality of these spectra allow us to disentangle the structure of the gas using the complex kinematics to guide the assessments of the multi-component and multi-phase nature of the system. The kinematics of the absorber indicate that all the H I, C 111, and 0 III reside in a single component, while higher ionization species largely arise in a separate, more kinematically complex structure. An analysis of a ground-based spectrum of the quasar covering the H-beta and [0 III] 5007 emission lines reveal excellent agreement in redshift between the 0 III absorption and emission. Thus, for the first time, we are able to use absorption line diagnostics to place interesting constraints on the location and structure of the narrow emission line region around a quasar. In addition, we detect a narrow absorption line that is only seen O VI and lies roughly 50 km/s redward of the narrow emission line component. Absorption from 0 V, and Ne VIII is also detected at this velocity, but as part of broader, more redshifted, component. The line width of this narrow component imply a maximum temperature that is too small to produce O VI through collisional process, suggesting instead that photoionization from the quasar is the dominant ionization mechanism. The photoionization constraints imply that O VII should be the dominant ionization stage in the component.

Sembach, Kenneth↗
NASA NTRS2005

Determination of Complex Microcalorimeter Parameters with Impedance Measurements

The proper understanding and modeling of a microcalorimeter s response requires the accurate knowledge of a handful of parameters, such as C, G, alpha, . . . . While a few of these, such 8s the normal state resistance and the total thermal conductance to the heat bath (G) are directly determined from the DC IV characteristics, some others, notoriously the heat capacity (C) and alpha, appear in degenerate combinations in most measurable quantities. The case of a complex microcalorimeter, i.e. one in which the absorber s heat capacity is connected by a finite thermal impedance to the sensor, and subsequently by another thermal impedance to the heat bath, results in an added ambiguity in the determination of the individual C's and G's. In general, the dependence of the microcalorimeter s complex impedance on these parameters varies with frequency. This variation allows us to determine the individual parameters by fitting the prediction of the microcalorimeter model to the impedance data. We describe in this paper our efforts at characterizing the Goddard X-ray microcalorimeters. Using the parameters determined with this method we them compare the pulse shape and noise spectra predicted by the microcalorimeter model to data taken with the same devices.

Saab, T.↗
NASA NTRS2005

Enabling Requirements-Based Programming for Highly-Dependable Complex Parallel and Distributed Systems

The manual application of formal methods in system specification has produced successes, but in the end, despite any claims and assertions by practitioners, there is no provable relationship between a manually derived system specification or formal model and the customer's original requirements. Complex parallel and distributed system present the worst case implications for today s dearth of viable approaches for achieving system dependability. No avenue other than formal methods constitutes a serious contender for resolving the problem, and so recognition of requirements-based programming has come at a critical juncture. We describe a new, NASA-developed automated requirement-based programming method that can be applied to certain classes of systems, including complex parallel and distributed systems, to achieve a high degree of dependability.

Hinchey, Michael G.↗
NASA NTRS2005

Low-Complexity Lossless Compression of Hyperspectral Imagery via Adaptive Filtering

A low-complexity, adaptive predictive technique for lossless compression of hyperspectral data is presented. The technique relies on the sign algorithm from the repertoire of adaptive filtering. The compression effectiveness obtained with the technique is competitive with that of the best of previously described techniques with similar complexity.

Klimesh, M.↗
NASA NTRS2006

Functional brain imaging of a complex navigation task following one night of total sleep deprivation

Study Objectives: To assess the cerebral effects associated with sleep deprivation in a simulation of a complex, real-world, high-risk task. Design and Interventions: A two-week, repeated measures, cross-over experimental protocol, with counterbalanced orders of normal sleep (NS) and total sleep deprivation (TSD). Setting: Each subject underwent functional magnetic resonance imaging (fMRI) while performing a dual-joystick, 3D sensorimotor navigation task (simulated orbital docking). Scanning was performed twice per subject, once following a night of normal sleep (NS), and once following a single night of total sleep deprivation (TSD). Five runs (eight 24s docking trials each) were performed during each scanning session. Participants: Six healthy, young, right-handed volunteers (2 women; mean age 20) participated. Measurements and Results: Behavioral performance on multiple measures was comparable in the two sleep conditions. Neuroimaging results within sleep conditions revealed similar locations of peak activity for NS and TSD, including left sensorimotor cortex, left precuneus (BA 7), and right visual areas (BA 18/19). However, cerebral activation following TSD was substantially larger and exhibited higher amplitude modulations from baseline. When directly comparing NS and TSD, most regions exhibited TSD>NS activity, including multiple prefrontal cortical areas (BA 8/9,44/45,47), lateral parieto-occipital areas (BA 19/39, 40), superior temporal cortex (BA 22), and bilateral thalamus and amygdala. Only left parietal cortex (BA 7) demonstrated NS>TSD activity. Conclusions: The large network of cerebral differences between the two conditions, even with comparable behavioral performance, suggests the possibility of detecting TSD-induced stress via functional brain imaging techniques on complex tasks before stress-induced failures.

Strangman, Gary↗
NASA NTRS2006

Building Complex Systems

The explosion of capabilities and new products within ICT (Information and Communication Technology) has fostered widespread, overly optimistic opinions regarding the industry, based on common but unjustified assumptions of quality and correctness of software. These assumptions are encouraged by software producers and vendors, who have not succeeded in finding a way to overcome the lack of an automated, mathematically sound way to develop correct systems from requirements. NASA faces this dilemma as it envisages advanced mission concepts in future exploration missions, which may well be the most ambitious computer-based systems ever developed. Such missions entail levels of complexity that beg for new methods for system development. NASA-led research in such areas as sensor networks, formal methods, autonomic computing, and requirements-based programming (to name but a few) will offer some innovative approaches to achieving correctness in complex system development.

Hinchey, Mike↗
NASA NTRS1995

Software Transition Project Retrospectives and the Application of SEL Effort Estimation Model and Boehm's COCOMO to Complex Software Transition Projects

The Multimission Image Processing Subsystem (MIPS) at the Jet Propulsion Laboratory (JPL) has managed transitions of application software sets from one operating system and hardware platform to multiple operating systems and hardware platforms. As a part of these transitions, cost estimates were generated from the personal experience of in-house developers and managers to calculate the total effort required for such projects. Productivity measures have been collected for two such transitions, one very large and the other relatively small in terms of source lines of code. These estimates used a cost estimation model similar to the Software Engineering Laboratory (SEL) Effort Estimation Model. Experience in transitioning software within JPL MIPS have uncovered a high incidence of interface complexity. Interfaces, both internal and external to individual software applications, have contributed to software transition project complexity, and thus to scheduling difficulties and larger than anticipated design work on software to be ported.

SEL Boehm COCOMO↗
NASA NTRS2003

Satellite remote sensing of landscape freeze/thaw state dynamics for complex Topography and Fire Disturbance Areas Using multi-sensor radar and SRTM digital elevation models

We characterize differences in radar-derived freeze/thaw state, examining transitions over complex terrain and landscape disturbance regimes. In areas of complex terrain, we explore freezekhaw dynamics related to elevation, slope aspect and varying landcover. In the burned regions, we explore the timing of seasonal freeze/thaw transition as related to the recovering landscape, relative to that of a nearby control site. We apply in situ biophysical measurements, including flux tower measurements to validate and interpret the remotely sensed parameters. A multi-scale analysis is performed relating high-resolution SAR backscatter and moderate resolution scatterometer measurements to assess trade-offs in spatial and temporal resolution in the remotely sensed fields.

synthetic aperture radars (SARs)↗