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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Simulating Activities: Relating Motives, Deliberation and Attentive Coordination

Activities are located behaviors, taking time, conceived as socially meaningful, and usually involving interaction with tools and the environment. In modeling human cognition as a form of problem solving (goal-directed search and operator sequencing), cognitive science researchers have not adequately studied "off-task" activities (e.g., waiting), non-intellectual motives (e.g., hunger), sustaining a goal state (e.g., playful interaction), and coupled perceptual-motor dynamics (e.g., following someone). These aspects of human behavior have been considered in bits and pieces in past research, identified as scripts, human factors, behavior settings, ensemble, flow experience, and situated action. More broadly, activity theory provides a comprehensive framework relating motives, goals, and operations. This paper ties these ideas together, using examples from work life in a Canadian High Arctic research station. The emphasis is on simulating human behavior as it naturally occurs, such that "working" is understood as an aspect of living. The result is a synthesis of previously unrelated analytic perspectives and a broader appreciation of the nature of human cognition. Simulating activities in this comprehensive way is useful for understanding work practice, promoting learning, and designing better tools, including human-robot systems.

Clancey, William J.↗
NASA NTRS2002

Further Examination of the Vibratory Loads Reduction Results from the NASA/ARMY/MIT Active Twist Rotor Test

The vibration reduction capabilities of a model rotor system utilizing controlled, strain-induced blade twisting are examined. The model rotor blades, which utilize piezoelectric active fiber composite actuators, were tested in the NASA Langley Transonic Dynamics Tunnel using open-loop control to determine the effect of active-twist on rotor vibratory loads. The results of this testing have been encouraging, and have demonstrated that active-twist rotor designs offer the potential for significant load reductions in future helicopter rotor systems. Active twist control was found to use less than 1% of the power necessary to operate the rotor system and had a pronounced effect on both rotating- and fixed-system loads, offering reductions in individual harmonic loads of up to 100%. A review of the vibration reduction results obtained is presented, which includes a limited set of comparisons with results generated using the second-generation version of the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD II) rotorcraft comprehensive analysis.

Wilbur, Matthew L.↗
NASA NTRS2003

Observed Helicity of Active Regions in Solar Cycle 21

We report the results of a study of helicity in solar active regions during the peak of activity in solar cycle 21 from observations with the Marshall Space Flight Center's solar vector magnetograph. Using the force-free parameter alpha as the proxy for helicity, we calculated an average value of alpha for each of 60 active regions from a total of 449 vector magnetograms that were obtained during the period 1980 March to November. The signs of these average values of alpha were correlated with the latitude of the active regions to test the hemispheric rule of helicity that has been proposed for solar magnetic fields: negative helicity predominant in northern latitudes, positive in the southern ones. We have found that of the 60 regions that were observed, 30 obey the hemispheric rule and 30 do not.

Hagyard, M. J.↗
NASA NTRS2003

Test Rig for Evaluating Active Turbine Blade Tip Clearance Control Concepts

Improved blade tip sealing in the high pressure compressor and high pressure turbine can provide dramatic improvements in specific fuel consumption, time-on-wing, compressor stall margin and engine efficiency as well as increased payload and mission range capabilities of both military and commercial gas turbine engines. The preliminary design of a mechanically actuated active clearance control (ACC) system for turbine blade tip clearance management is presented along with the design of a bench top test rig in which the system is to be evaluated. The ACC system utilizes mechanically actuated seal carrier segments and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. The purpose of this active clearance control system is to improve upon current case cooling methods. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, re-burst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). The active turbine blade tip clearance control system design presented herein will be evaluated to ensure that proper response and positional accuracy is achievable under simulated high-pressure turbine conditions. The test rig will simulate proper seal carrier pressure and temperature loading as well as the magnitudes and rates of blade tip clearance changes of an actual gas turbine engine. The results of these evaluations will be presented in future works.

Lattime, Scott B.↗
NASA NTRS2003

To Support Research Activities Under the NASA Experimental Program to Stimulate Competitive Research

The Alabama NASA EPSCoR Program is a collaborative venture of The Alabama Space Grant Consortium, The Alabama EPSCoR, and faculty and staff at 10 Alabama colleges and universities as well as the Alabama School of Math and Science in Mobile. There are two Research Clusters which include infrastructure-building and outreach elements embedded in their research activities. Each of the two Research Clusters is in an area of clear and demonstrable relevance to NASA's mission, to components of other Alabama EPSCoR projects, and to the State of Alabama's economic development. This Final Report summarizes and reports upon those additional activities occurring after the first report was submitted in March 2000 (included here as Appendix C). Since the nature of the activities and the manner in which they relate to one another differ by cluster, these clusters function independently and are summarized in parallel in this report. They do share a common administration by the Alabama Space Grant Consortium (ASGC) and by this means, good ideas from each group were communicated to the other, as appropriate. During the past year these research teams, involving 15 scientists, 16 graduate students, 16 undergraduates, and 7 high school students involving 10 Alabama universities had 14 peer reviewed scientific journal articles published, 21 others reviewed for publication or published in proceedings, gave 7 formal presentations and numerous informal presentations to well over 3000 people, received 3 patents and were awarded 14 research proposals for more than $213K dollars in additional research related to these investigations. Each cluster's activities are described and an Appendix summarizes these achievements.

Gregory, John C.↗
NASA NTRS2003

Application of Satellite SAR Imagery in Mapping the Active Layer of Arctic Permafrost

A method of mapping the active layer of Arctic permafrost using a combination of conventional synthetic aperture radar (SAR) backscatter and more sophisticated interferometric SAR (INSAR) techniques is proposed. The proposed research is based on the sensitivity of radar backscatter to the freeze and thaw status of the surface soil, and the sensitivity of INSAR techniques to centimeter- to sub-centimeter-level surface differential deformation. The former capability of SAR is investigated for deriving the timing and duration of the thaw period for surface soil of the active layer over permafrost. The latter is investigated for the feasibility of quantitative measurement of frost heaving and thaw settlement of the active layer during the freezing and thawing processes. The resulting knowledge contributes to remote sensing mapping of the active layer dynamics and Arctic land surface hydrology.

Li, Shu-Sun↗
NASA NTRS2003

A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

Berry, Scott A.↗
NASA NTRS2004

Supergranule Diffusion and Active Region Decay

Models of the Sun's magnetic dynamo include turbulent diffusion to parameterize the effects of convective motions on the evolution of the Sun's magnetic field. Supergranules are known to dominate the evolution of the surface magnetic field structure as evidenced by the structure of both the active and quiet magnetic network. However, estimates for the dif hivity attributed to su perymules differ by an order of magnitude from about 100 km sup2/s to more than 1000 km sup2/s. We examine this question of the e i v i t y using three merent approaches. 1) We study the decay of more than 30,000 active regions by determining the rate of change in the sunspot area of each active region from day-to-day. 2) We study the decay of a single isolated active region near the time of solar minimum by examining the magnetic field evolution over five solar rotations fiom SOHOMDI magnetograms obtained at 96-minute intervals. 3) We study the characteristics of supergranules that influence the estimates of their diffusive properties - flow speeds and lifetimes as functions of size - fiom SOHO/MDI Dopplergrams.

Hathaway, David H.↗
NASA NTRS2004

Rotor Flapping Response to Active Control

Rotor active control using higher harmonic blade pitch has been proposed as a means to reduce both rotor radiated noise and airframe vibration and to enhance rotor performance. The higher harmonic input, however, can affect rotor thrust and cyclic flapping - the basic trim characteristics of the rotor. Some of the trim changes can negate the active control benefits. For example, wind tunnel test results of a full scale BO-105 rotor with individual-blade control indicate some rotor performance improvements, accompanied with changes in rotor trim, using two-per-rev blade pitch input. The observed performance benefits could therefore be a simple manifestation of the trim change rather than an efficient redistribution of the rotor airloads. More recently, the flight test of the BO-105 helicopter equip,ped with individual-blade-control actuators also reported trim changes whenever the two-per-rev blade pitch for noise reduction was activated. The pilot had to adjust the trim control to maintain the aircraft under a constant flight path. These two cases highlight the, importance of trim considerations in the application of active control to rotorcraft.

Nguyen, Khanh↗
NASA NTRS2003

TNF-alpha increases ubiquitin-conjugating activity in skeletal muscle by up-regulating UbcH2/E220k

In some inflammatory diseases, TNF-alpha is thought to stimulate muscle catabolism via an NF-kappaB-dependent process that increases ubiquitin conjugation to muscle proteins. The transcriptional mechanism of this response has not been determined. Here we studied the potential role of UbcH2, a ubiquitin carrier protein and homologue of murine E220k. We find that UbcH2 is constitutively expressed by human skeletal and cardiac muscles, murine limb muscle, and cultured myotubes. TNF-alpha stimulates UbcH2 expression in mouse limb muscles in vivo and in cultured myotubes. The UbcH2 promoter region contains a functional NF-kappaB binding site; NF-kappaB binding to this sequence is increased by TNF-alpha stimulation. A dominant negative inhibitor of NF-kappaB activation blocks both UbcH2 up-regulation and the increase in ubiquitin-conjugating activity stimulated by TNF-alpha. In extracts from TNF-alpha-treated myotubes, ubiquitin-conjugating activity is limited by UbcH2 availability; activity is inhibited by an antiserum to UbcH2 or a dominant negative mutant of UbcH2 and is enhanced by wild-type UbcH2. Thus, UbcH2 up-regulation is a novel response to TNF-alpha/NF-kappaB signaling in skeletal muscle that appears to be essential for the increased ubiquitin conjugation induced by this cytokine.

Non-NASA Center↗
NASA NTRS1970

Integration of experiments for the detection of biological activity in extraterrestrial exploration

Although many experiments have been suggested and described for the detection of biological activity in planetary exploration, each experiment has required its own sample for the detection of a specific phenomenon. An experimental design which could detect growth, catabolic and anabolic activity on a single sample is described. Growth is monitored in a liquid medium which is in contact with, and chemically influenced by, a relatively large sample. Catabolic activity is indicated by changes in the gas composition of the atmosphere above the sample. Anabolic activity is indicated by the appearance of reduced carbon compounds, from oxidized precursors, in the liquid medium.

Space Flight/instrumentation↗
NASA NTRS2003

Patterns of global gene expression in rat skeletal muscle during unloading and low-intensity ambulatory activity

Physical inactivity and unloading lead to diverse skeletal muscle alterations. Our goal was to identify the genes in skeletal muscle whose expression is most sensitive to periods of unloading/reduced physical activity and that may be involved in triggering initial responses before phenotypic changes are evident. The ability of short periods of physical activity/loading as an effective countermeasure against changes in gene expression mediated by inactivity was also tested. Affymetrix microarrays were used to compare mRNA levels in the soleus muscle under three experimental treatments (n = 20-29 rats each): 12-h hindlimb unloading (HU), 12-h HU followed by 4 h of intermittent low-intensity ambulatory and postural activity (4-h reloading), and control (with ambulatory and postural activity). Using a combination of criteria, we identified a small set of genes (approximately 1% of 8,738 genes on the array or 4% of significant expressed genes) with the most reproducible and largest responses to altered activity. Analysis revealed a coordinated regulation of transcription for a large number of key signaling proteins and transcription factors involved in protein synthesis/degradation and energy metabolism. Most (21 of 25) of the gene expression changes that were downregulated during HU returned at least to control levels during the reloading. In surprising contrast, 27 of 38 of the genes upregulated during HU remained significantly above control, but most showed trends toward reversal. This introduces a new concept that, in general, genes that are upregulated during unloading/inactivity will be more resistant to periodic reloading than those genes that are downregulated. This study reveals genes that are the most sensitive to loading/activity in rat skeletal muscle and indicates new targets that may initiate muscle alterations during inactivity.

NASA Discipline Musculoskeletal↗
NASA NTRS2002

Preferential inhibition of the plasma membrane NADH oxidase (NOX) activity by diphenyleneiodonium chloride with NADPH as donor

The cell-surface NADH oxidase (NOX) protein of plant and animal cells will utilize both NADH and NADPH as reduced electron donors for activity. The two activities are distinguished by a differential inhibition by the redox inhibitor diphenyleneiodonium chloride (DPI). Using both plasma membranes and cells, activity with NADPH as donor was markedly inhibited by DPI at submicromolar concentrations, whereas with NADH as donor, DPI was much less effective or had no effect on the activity. The possibility of the inhibition being the result of two different enzymes was eliminated by the use of a recombinant NOX protein. The findings support the concept that NOX proteins serve as terminal oxidases for plasma membrane electron transport involving cytosolic reduced pyridine nucleotides as the natural electron donors and with molecular oxygen as the electron acceptor.

Non-NASA Center↗
NASA NTRS1996

Changes in autonomic activity preceding onset of nonsustained ventricular tachycardia

Background: The triggering role of the autonomic nervous system in the initiation of ventricular tachycardia has not been established. To investigate the relationship between changes in autonomic activity and the occurrence of nonsustained ventricular tachycardia (NSVT) we examined heart rate variability (HRV) during the 2-hour period preceding spontaneous episodes of NSVT. Twenty-four subjects were identified retrospectively as having had one episode of NSVT during 24-hour Holter ECC recording. Methods: We measured the mean interval between normal heats (meanRR), the standard deviation of the intervals between beats (SD), the percentage of counts of sequential intervals between normal beats with a change of >50 ms (%RR50), the logarithms of low- and high-frequency spectral components (lnLF, lnHF) of HRV for sequential 10-minute segments preceding NSVT. The correlation dimension (CDim) of HRV was calculated similarly for sequential 20-minute segments. We assessed the significance of the time-course change of each marker over the 120-minute period prior to NSVT onset. Results: MeanRR (P < 0.05), lnLF (P < 0.0001), lnHF (P < 0.0001), the natural logarithm of the ratio of LF to HF (ln[LF/HF]; P < 0.05), and CDim (P < 0.05) showed significant time-course changes during that period, while SD and %RR50 did not. MeanRR, lnLF, lnHF, and CDim all decreased prior to the onset of NSVT, whereas ln(LF/HF) increased. We divided the subjects into two groups: one consisting of 12 patients with coronary artery disease; and the second group of 12 patients without known coronary artery disease. Both groups showed significant changes (P < 0.05) of CDim, lnLF, and lnHF preceding the episodes of NSVT. Conclusions: Changes in the pattern of HRV prior to the onset of episodes of NSVT suggest that changes in autonomic activity may commonly play a role in the triggering of spontaneous episodes of NSVT in susceptible patients. The measured changes suggest a reduction in parasympathetic activity, perhaps in conjunction with an increase in sympathetic activity, may trigger NSVT.

Non-NASA Center↗
NASA NTRS1990

Activity and adaptation of nitrilotriacetate (NTA)-degrading bacteria: field and laboratory studies

Adaptation of bacterial activity for the degradation of nitrilotriacetate (NTA) was studied using natural sediment samples and an NTA-degrading bacterium (strain ATCC 29600). Sediment samples from a river with persistent levels of NTA had much higher NTA-degradative activity than comparable samples from a less contaminated control site. When sediment from the control site was exposed to high levels of NTA a 5 day lag preceded an abrupt increase in NTA degradation while strain 29600 colonized on sand and grown in the absence of NTA became induced within eight hours. The induction of strain 29600 was compared between bacteria in suspension and cells attached to sand. The sand-associated bacteria became induced 4 to 5 h before the planktonic suspension and displayed over threefold greater specific activity. Suspensions of strain 29600 became adapted within 8 h when placed in membrane diffusion chambers that were immersed within a municipal wastewater reactor containing NTA. These findings support the concept that induction is a part of the process of bacterial adaptation to degrade NTA and sand-associated bacteria can adapt more quickly to and have a greater degradative activity for NTA than planktonic cells.

NASA Discipline Number 04-10↗
NASA NTRS1990

Somatic proembryo production from excised, wounded zygotic carrot embryos on hormone-free medium: evaluation of the effects of pH, ethylene and activated charcoal

Wounded zygotic embryos of cultivated carrot produce somatic proembryos on hormone-free nutrient medium containing 1 mM NH4+ as the sole nitrogen source. Continued maintenance of proembryos on this medium leads to a "pure" culture of preglobular stage proembryos (PGSPs). Ethylene had no effect on this process. Also, somatic embryo production was not affected by growing cultures on activated charcoal-impregnated filter papers. However, somatic proembyros initiated on activated charcoal papers were not maintainable as PGSPs and developed into later embryo stages. Normally, medium pH dropped from 5.7 to 4 during each subculture period, but when using activated charcoal papers the pH endpoint was around 6 - 7 due to a leachable substance(s) within the filter papers. When powdered, activated charcoal was used in the medium as an adsorbent of products potentially released after wounding, pH dropped at the normal rate and to the expected levels; proembryos did not mature into later embryo stages and were maintainable exclusively as PGSPs. Low pH (approximately 4) is detrimental to proembyro production, but is essential to maintaining PGSPs on hormone-free nutrient medium, whereas a sustained pH > or = 5.7 allows continued development of PGSPs into later embryo stages.

NASA Program Space Biology↗
NASA NTRS2001

Effects of exercise pressor reflex activation on carotid baroreflex function during exercise in humans

1. This investigation was designed to determine the contribution of the exercise pressor reflex to the resetting of the carotid baroreflex during exercise. 2. Ten subjects performed 3.5 min of static one-legged exercise (20 % maximal voluntary contraction) and 7 min dynamic cycling (20 % maximal oxygen uptake) under two conditions: control (no intervention) and with the application of medical anti-shock (MAS) trousers inflated to 100 mmHg (to activate the exercise pressor reflex). Carotid baroreflex function was determined at rest and during exercise using a rapid neck pressure/neck suction technique. 3. During exercise, the application of MAS trousers (MAS condition) increased mean arterial pressure (MAP), plasma noradrenaline concentration (dynamic exercise only) and perceived exertion (dynamic exercise only) when compared to control (P < 0.05). No effect of the MAS condition was evident at rest. The MAS condition had no effect on heart rate (HR), plasma lactate and adrenaline concentrations or oxygen uptake at rest and during exercise. The carotid baroreflex stimulus-response curve was reset upward on the response arm and rightward to a higher operating pressure by control exercise without alterations in gain. Activation of the exercise pressor reflex by MAS trousers further reset carotid baroreflex control of MAP, as indicated by the upward and rightward relocation of the curve. However, carotid baroreflex control of HR was only shifted rightward to higher operating pressures by MAS trousers. The sensitivity of the carotid baroreflex was unaltered by exercise pressor reflex activation. 4. These findings suggest that during dynamic and static exercise the exercise pressor reflex is capable of actively resetting carotid baroreflex control of mean arterial pressure; however, it would appear only to modulate carotid baroreflex control of heart rate.

Non-NASA Center↗
NASA NTRS2000

Patterning of sympathetic nerve activity in response to vestibular stimulation

Growing evidence suggests a role for the vestibular system in regulation of autonomic outflow during postural adjustments. In the present paper we review evidence for the patterning of sympathetic nerve activity elicited by vestibular stimulation. In response to electrical activation of vestibular afferents, firing of sympathetic nerves located throughout the body is altered. However, activity of the renal nerve is most sensitive to vestibular inputs. In contrast, high-intensity simultaneous activation of cutaneous and muscle inputs elicits equivalent changes in firing of the renal, superior mesenteric and lumbar colonic nerves. Responses of muscle vasoconstrictor (MVC) efferents to vestibular stimulation are either inhibitory (Type I) or are comprised of a combination of excitation and inhibition (Type II). Interestingly, single MVC units located in the hindlimb exhibited predominantly Type I responses while those located in the forelimb and face exhibited Type II responses. Furthermore, brachial and femoral arterial blood flows were dissociated in response to vestibular stimulation, such that brachial vascular resistance increased while femoral resistance decreased. These studies demonstrate that vestibulosympathetic reflexes are patterned according to both the anatomical location and innervation target of a particular sympathetic nerve, and can lead to distinct changes in local blood flow.

NASA Discipline Neuroscience↗