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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Discrete event simulation tool for analysis of qualitative models of continuous processing systems

An artificial intelligence design and qualitative modeling tool is disclosed for creating computer models and simulating continuous activities, functions, and/or behavior using developed discrete event techniques. Conveniently, the tool is organized in four modules: library design module, model construction module, simulation module, and experimentation and analysis. The library design module supports the building of library knowledge including component classes and elements pertinent to a particular domain of continuous activities, functions, and behavior being modeled. The continuous behavior is defined discretely with respect to invocation statements, effect statements, and time delays. The functionality of the components is defined in terms of variable cluster instances, independent processes, and modes, further defined in terms of mode transition processes and mode dependent processes. Model construction utilizes the hierarchy of libraries and connects them with appropriate relations. The simulation executes a specialized initialization routine and executes events in a manner that includes selective inherency of characteristics through a time and event schema until the event queue in the simulator is emptied. The experimentation and analysis module supports analysis through the generation of appropriate log files and graphics developments and includes the ability of log file comparisons.

Malin, Jane T.↗
NASA NTRS1997

Linear and nonlinear ARMA model parameter estimation using an artificial neural network

This paper addresses parametric system identification of linear and nonlinear dynamic systems by analysis of the input and output signals. Specifically, we investigate the relationship between estimation of the system using a feedforward neural network model and estimation of the system by use of linear and nonlinear autoregressive moving-average (ARMA) models. By utilizing a neural network model incorporating a polynomial activation function, we show the equivalence of the artificial neural network to the linear and nonlinear ARMA models. We compare the parameterization of the estimated system using the neural network and ARMA approaches by utilizing data generated by means of computer simulations. Specifically, we show that the parameters of a simulated ARMA system can be obtained from the neural network analysis of the simulated data or by conventional least squares ARMA analysis. The feasibility of applying neural networks with polynomial activation functions to the analysis of experimental data is explored by application to measurements of heart rate (HR) and instantaneous lung volume (ILV) fluctuations.

NASA Discipline Regulatory Physiology↗
NASA NTRS1991

The effect of anisotropic emission from thick accretion disks on the luminosity functions of active galactic nuclei

High-luminosity active galactic nuclei (AGNs) powered by accretion onto a massive black hole (or other compact object) may have bolometric luminosities dominated by thermal emission from a geometrically thick accretion disk. Radiation from these disks is strongly anisotropic, which has important consequences for the observed luminosity distribution, and therefore for systematic biases in flux-limited samples. The effect of anisotropic emission from an ensemble of AGNs with random oriented thick disks radiating at or near the Eddington limit is calculated. Because of their higher luminosities, it is predicted face-on disks should constitute an increasing fraction of observed high-redshift, high-luminosity AGNs. Comparison of the results with observed quasar luminosity functions suggests a narrow mass distribution with an upper limit of about a billion solar masses for high-redshift quasars.

Urry, C. M.↗
NASA NTRS1972

Functions and activities of the Arizona Regional Ecological Test Site

The Arizona Regional Ecological Test Site (ARETS) project and its efforts to coordinate and transfer satellite remote sensing techniques to solving earth resources and environmental problems in the Arizona area are discussed. Project objectives include: (1) establishing a multidiscipline resources and environment team in Arizona capable of applying satellite and supporting aircraft data to expedite remote sensing technology transfer to user agencies; (2) determine future resources and environment information needs for Arizona; (3) conduct coordinated multidiscipline experiments in the use of ERTS data; and (4) provide and recommend facilities, instruments, and training necessary to support the practical uses of remote sensing data.

Lepley, L. K.↗
NASA NTRS2010

Multifunctional and biologically active matrices from multicomponent polymeric solutions

The present invention relates to a biologically active functionalized electrospun matrix to permit immobilization and long-term delivery of biologically active agents. In particular the invention relates to a functionalized polymer matrix comprising a matrix polymer, a compatibilizing polymer and a biomolecule or other small functioning molecule. In certain aspects the electrospun polymer fibers comprise at least one biologically active molecule functionalized with low molecular weight heparin. Examples of active molecules that may be used with the multicomponent polymer of the invention include, for example, a drug, a biopolymer, for example a growth factor, a protein, a peptide, a nucleotide, a polysaccharide, a biological macromolecule or the like. The invention is further directed to the formation of functionalized crosslinked matrices, such as hydrogels, that include at least one functionalized compatibilizing polymer capable of assembly.

Kiick, Kristi L.↗
NASA NTRS1984

A new minimax algorithm

The representation min t s.t. F(I)(x). - t less than or equal to 0 for all i is examined. An active set strategy is designed of functions: active, semi-active, and non-active. This technique will help in preventing zigzagging which often occurs when an active set strategy is used. Some of the inequality constraints are handled with slack variables. Also a trust region strategy is used in which at each iteration there is a sphere around the current point in which the local approximation of the function is trusted. The algorithm is implemented into a successful computer program. Numerical results are provided.

Vardi, A.↗
NASA NTRS1974

Payload/orbiter contamination control requirement study

A study was conducted to determine and quantify the expected particulate and molecular on-orbit contaminant environment for selected space shuttle payloads as a result of major shuttle orbiter contamination sources. Individual payload susceptibilities to contamination are reviewed. The risk of payload degradation is identified and preliminary recommendations are provided concerning the limiting factors which may depend on operational activities associated with the payload/orbiter interface or upon independent payload functional activities. A basic computer model of the space shuttle orbiter which includes a representative payload configuration is developed. The major orbiter contamination sources, locations, and flux characteristics based upon available data have been defined and modeled.

Bareiss, L. E.↗
NASA NTRS2006

A Thermodynamically Consistent Damage Model for Advanced Composites

A continuum damage model for the prediction of damage onset and structural collapse of structures manufactured in fiber-reinforced plastic laminates is proposed. The principal damage mechanisms occurring in the longitudinal and transverse directions of a ply are represented by a damage tensor that is fixed in space. Crack closure under load reversal effects are taken into account using damage variables established as a function of the sign of the components of the stress tensor. Damage activation functions based on the LaRC04 failure criteria are used to predict the different damage mechanisms occurring at the ply level. The constitutive damage model is implemented in a finite element code. The objectivity of the numerical model is assured by regularizing the dissipated energy at a material point using Bazant's Crack Band Model. To verify the accuracy of the approach, analyses of coupon specimens were performed, and the numerical predictions were compared with experimental data.

Maimi, Pere↗
NASA NTRS1974

Heliobiology, its development, successes and tasks

Heliobiology studies the influence of changes in solar activity on life. Considered are the influence of periodic solar activity on the development and growth of epidemics, mortality from various diseases, the functional activity of the nervous system, the development of psychic disturbances, the details of the development of microorganisms and many other phenomena in the living world.

Platonova, A. T.↗
NASA NTRS1974

Payload/orbiter contamination control requirement study, volume 1, exhibit A

This study is to identify and quantify the expected molecular and particulate on orbit contaminant environment for selected shuttle payloads as a result of major spacelab and shuttle orbiter contaminant sources. This investigation reviews individual payload susceptibilities to contamination, identifies the combined induced environment, identifies the risk of spacelab/payload critical surface(s) degradation, and provides preliminary contamination recommendations. It also establishes limiting factors which may depend upon operational activities associated with the payloads, spacelab, and the shuttle orbiter interface or upon independent payload functional activities.

Bareiss, L. E.↗
NASA NTRS1992

Membership generation using multilayer neural network

There has been intensive research in neural network applications to pattern recognition problems. Particularly, the back-propagation network has attracted many researchers because of its outstanding performance in pattern recognition applications. In this section, we describe a new method to generate membership functions from training data using a multilayer neural network. The basic idea behind the approach is as follows. The output values of a sigmoid activation function of a neuron bear remarkable resemblance to membership values. Therefore, we can regard the sigmoid activation values as the membership values in fuzzy set theory. Thus, in order to generate class membership values, we first train a suitable multilayer network using a training algorithm such as the back-propagation algorithm. After the training procedure converges, the resulting network can be treated as a membership generation network, where the inputs are feature values and the outputs are membership values in the different classes. This method allows fairly complex membership functions to be generated because the network is highly nonlinear in general. Also, it is to be noted that the membership functions are generated from a classification point of view. For pattern recognition applications, this is highly desirable, although the membership values may not be indicative of the degree of typicality of a feature value in a particular class.

Kim, Jaeseok↗
NASA NTRS2002

Molecular cloning and characterization of a tumor-associated, growth-related, and time-keeping hydroquinone (NADH) oxidase (tNOX) of the HeLa cell surface

NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide interchange and exhibit prion-like properties. The two enzymatic activities alternate to generate a regular period length of about 24 min. Here we report the expression, cloning, and characterization of a tumor-associated NADH oxidase (tNOX). The cDNA sequence of 1830 bp is located on gene Xq25-26 with an open reading frame encoding 610 amino acids. The activities of the bacterially expressed tNOX oscillate with a period length of 22 min as is characteristic of tNOX activities in situ. The activities are inhibited completely by capsaicin, which represents a defining characteristic of tNOX activity. Functional motifs identified by site-directed mutagenesis within the C-terminal portion of the tNOX protein corresponding to the processed plasma membrane-associated form include quinone (capsaicin), copper and adenine nucleotide binding domains, and two cysteines essential for catalytic activity. Four of the six cysteine to alanine replacements retained enzymatic activity, but the period lengths of the oscillations were increased. A single protein with two alternating enzymatic activities indicative of a time-keeping function is unprecedented in the biochemical literature.

NASA Discipline Cell Biology↗
NASA NTRS1992

Adaptability of the oxidative capacity of motoneurons

Previous studies have demonstrated that a chronic change in neuronal activation can produce a change in soma oxidative capacity, suggesting that: (i) these 2 variables are directly related in neurons and (ii) ion pumping is an important energy requiring activity of a neuron. Most of these studies, however, have focused on reduced activation levels of sensory systems. In the present study the effect of a chronic increase or decrease in motoneuronal activity on motoneuron oxidative capacity and soma size was studied. In addition, the effect of chronic axotomy was studied as an indicator of whether cytoplasmic volume may also be related to the oxidative capacity of motoneurons. A quantitative histochemical assay for succinate dehydrogenase activity was used as a measure of motoneuron oxidative capacity in experimental models in which chronic electromyography has been used to verify neuronal activity levels. Spinal transection reduced, and spinal isolation virtually eliminated lumbar motoneuron electrical activity. Functional overload of the plantaris by removal of its major synergists was used to chronically increase neural activity of the plantaris motor pool. No change in oxidative capacity or soma size resulted from either a chronic increase or decrease in neuronal activity level. These data indicate that the chronic modulation of ionic transport and neurotransmitter turnover associated with action potentials do not induce compensatory metabolic responses in the metabolic capacity of the soma of lumbar motoneurons. Soma oxidative capacity was reduced in the axotomized motoneurons, suggesting that a combination of axoplasmic transport, intracellular biosynthesis and perhaps neurotransmitter turnover represent the major energy demands on a motoneuron. While soma oxidative capacity may be closely related to neural activity in some neural systems, e.g. visual and auditory, lumbar motoneurons appear to be much less sensitive to modulations in chronic activity levels.

NASA Discipline Musculoskeletal↗
NASA NTRS2009

Initial Investigation of Operational Concept Elements for NASA's NextGen-Airportal Project Research

The NextGen-Airportal Project is organized into three research focus areas: Safe and Efficient Surface Operations, Coordinated Arrival/Departure Operations Management, and Airportal Transition and Integration Management. The content in this document was derived from an examination of constraints and problems at airports for accommodating future increases in air traffic, and from an examination of capabilities envisioned for NextGen. The concepts are organized around categories of constraints and problems and therefore do not precisely match, but generally reflect, the research focus areas. The concepts provide a framework for defining and coordinating research activities that are, and will be, conducted by the NextGen-Airportal Project. The concepts will help the research activities function as an integrated set focused on future needs for airport operations and will aid aligning the research activities with NextGen key capabilities. The concepts are presented as concept elements with more detailed sub-elements under each concept element. For each concept element, the following topics are discussed: constraints and problems being addressed, benefit descriptions, required technology and infrastructure, and an initial list of potential research topics. Concept content will be updated and more detail added as the research progresses. The concepts are focused on enhancing airportal capacity and efficiency in a timeframe 20 to 25 years in the future, which is similar to NextGen's timeframe.

Lohr, Gary↗
NASA NTRS1972

The geography and human cultural resources working group of the EROS program

The functions, activities, and objectives of the Geography and Human-Cultural Resources Working Group of the EROS program are outlined. The Group's primary function is to coordinate remote sensing experiments of physical scientists and the needs of socioeconomic and culturally orientated planners, policy makers, administrators, and other user groups. Other functions of the Group include land use analysis, resource mapping, and development of an operational automatic information system receptive to land use and environmental data.

Gerlach, A. C.↗
NASA NTRS1995

Review of spaceflight and hindlimb suspension unloading induced sarcomere damage and repair

Hindlimb suspension unloading (HSU) and spaceflight microgravity induce atrophy of the slow adductor longus muscle fibers which, following reloading, exhibit eccentric contraction (EC)-like lesions (abnormal widening of sarcomeres with A band disruption and excessively wavy, extracted Z lines). These lesions are similar morphologically to those produced in normal muscles after strenuous eccentric exercise. It appears that atrophic muscles exhibit increased susceptibility to eccentric damage because lesions are produced during nonstressful voluntary movements upon return to weightbearing. The EC-like lesions are absent in the unweighted conditions, but appear in HSU rats 15-60 minutes after reloading and in space-flown rates about 4 hrs after landing. By 12 hours, many EC-like lesioned sarcomeres are fully covered by longitudinal patches of Z line-like material which increases in density by 48 hours, producing the so-called "Z line streaming" morphology. In this case, Z line streaming is indicative of rapid repair of damaged sarcomeres rather than the onset of sarcomere breakdown. Immunoelectron microscopy is necessary to determine the composition of this dense material. By 9 days of reloading at 1 gravity, sarcomeres have regained normal structure, except for very rare persistence of faint Z patches. The morphological data indicate that Z patches serve at least two functions: 1) to permit contractile force to be transmitted across the damaged sarcomeres and 2) to provide a scaffold upon which sarcomeres are reconstructed in an active functional muscle.

NASA Discipline Number 00-00↗