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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Capillary Pressure Balance with Repeated Head-Up Tilt in Humans

We measured blood density (BD). plasma density (PD) and hematocrit (Ht) during repeated 70 deg head-up tilt (HUT) consisting of a pre-drink period with two supine (P and P3) and two HUT (P2 and P4) phases of 45 min each. At the end of P4 test subjects (N=8) drank 10 ml/kg body weight of isotonic (290 mOsm/kg) sodium chloride (ISO) or hypotonic (<10 mOsm/kg) unsweetened us (HYP), or nothing (control: CON). The following periods continued the supine (P5, P7) / upright (P6) sequence. Mass density of plasma and whole blood using a "mechanical oscillation" technique were measured from ear lobe blood. Tilting altered (p<0.001) BD, PD, and Ht in all consecutive Phases. BD and PD were different (p<0.05) between CON. HYP. and ISO Phases 6 and 7. The computed mass density of fluid (FD). which moved between intra. and extravascular compartments. averaged 1008 g/l and was the same in any conditions. In the non-drink treatment (P3, P5, P7), supine PV steadly decreased when compared to P1. Tilt-induced PV shifts ranged from 9.7 to 16.7% when compared to PV du. ring the respective previous Phases. After drinking, PV increased above CON values at the end of Phase 7 by 12.9% with ISO, and by 6.6% with HYP. Progressive hemoconcentration. occurred during non-drink supine; isotonic saline ingestion increased supine PV a control level but did not stop or reverse the decrease of upright hemoconcentration. Upright density values were not slowed with repeated upright tilting; decreased fluid loss occurred in consecutive upright periods. Upright capillary pressure balance was achieved with diminished plasma volume loss during repeated tilting.

Hinghofer-Szalkay, H. G.↗
NASA NTRS2000

High Head Unshrouded Impeller Pump Stage Technology

Objective to develop an unshrouded impeller design, which a meets the performance requirements of a 3-stage fuel pump with a 2-stage pump design, has been accomplished. Performance of the baseline unshrouded impeller has been experimentally verified. Unshrouded impeller trade study and final 6+6 unshrouded impeller configuration has been presented. Structurally viable, 6+6-impeller design concept has been produced. Based on results presented in this study, at a nominal 10% tip-clearance, the 6+6 impeller design would increase payload to orbit by almost 625 lbs. per engine. The RLV vehicle requires 7 engines, therefore, application of high head unshrouded technology would increase payload capability by as much as 4,375 lbs. per vehicle.

Williams, Robert W.↗
NASA NTRS1994

Head-Down Tilt with Balanced Traction as a Model for Simulating Spinal Acclimation to Microgravity

Astronauts experience total body height increases of 4 to 7 cm in microgravity. Thus, stretching of the spinal cord, nerve roots, and muscular and ligamentous tissues may be responsible for the hyperreflexia, back pain, and muscular atrophy associated with exposure to microgravity. Axial compression of the spine makes 6 deg. head-down tilt (HDT) an unsuitable model for spinal acclimation to microgravity. However, this axial compression may be counteracted by balanced traction consisting of 10% body weight (sin 6 deg. = 0.1) applied to the legs. Six healthy male subjects underwent 3 days each of 60 HDT with balanced traction and horizontal bed rest (HBR), with a 2 week recovery period between treatments. Total body and spine length, lumbar disc height, back pain, erector spinae intramuscular pressure, and ankle joint torque were measured before, during and after each treatment. Total body and spine (processes of L5 - C7) lengths increased significantly more during HDT with balanced traction (22 +/- 8 mm and 25 +/- 8 mm, respectively) than during HBR (16 +/- 4 mm and 14 +/- 9 mm, respectively). Back and leg pain were significantly greater during HDT with balanced traction than during HBR. The distance between the lower end plate of L4 and the upper endplate of S1, as measured by sonography, increased significantly in both treatments to the same degree (2.9 +/- 1.9 mm, HDT with balanced traction; 3.3 +/- 1.5 mm, HBR). Intramuscular pressure of the erector spinae muscles and maximal ankle joint torque were unaltered with both models. While neither model increased height to the magnitude observed in microgravity, HDT with balanced traction may be a better model for simulating the body lengthening and back pain experienced in microgravity.

Ballard, R. E.↗
NASA NTRS2001

Renal Function of Rats in Response to 37 Days of Head-Down Tilt

Spaceflight induces changes in human renal function, suggesting similar changes may occur in rats. Since rats continue to be the prime mammalian model for study in space, the effects of chronic microgravity on rat renal function should be clarified. Acute studies in rats using the ground-based microgravity simulation model, head-down tilt (HDT), have shown increases in glomerular filtration rate (GFR), electrolyte excretion, and a diuresis. However, long term effects of HDT have not been studied extensively. This study was performed to elucidate rat renal function following long-term simulated microgravity. Chronic exposure to HDT will cause an increase in GFR and electrolyte excretion in rats, similar to acute exposures, and lead to a decrease in the fractional excretion of filtered electrolytes. Experimental animals (HDT, n=10) were tail-suspended for 37 days and renal function compared to ambulatory controls (AMB, n=10). On day 37 of HDT, GFR, osmolal clearance, and electrolyte excretion were decreased, while plasma osmolality and free water clearance were increased. Urine output remained similar between groups. The fractional excretion of the filtered electrolytes was unchanged except for a decrease in the percentage of filtered calcium excreted. Chronic exposure to HDT results in decreased GFR and electrolyte excretion, but the fractional excretion of filtered electrolytes remained primarily unaffected.

Wang, Tommy J.↗
NASA NTRS1995

Hemodynamic and Thermal Responses to Head and Neck Cooling in Men and Women

Personal cooling systems are used to alleviate symptoms of multiple sclerosis and to prevent increased core temperature during daily activities. Configurations of these systems include passive ice vests and circulating liquid cooling garments (LCGs) in the forms of vests, cooling caps and combined head and neck cooling systems. However, little information is available oil the amount or heat that can be extracted from the body with these systems or the physiologic changes produced by routine operation of these systems. The objective of this study was to determine the operating characteristics and the physiologic change, produced by short term use of one commercially available thermal control system.

Ku, Yu-Tsuan E.↗
NASA NTRS1995

Binocular Convergence and Errors in Judged Distance While Using Head-mounted See-through Displays

Previous observations have shown that optical superposition of a physical backdrops at the judged depth of a stereoscopic virtual image moves the judged depth closer to the observer. This effect was more pronounced for slowly moving physical backdrops and was not enhanced when the virtual image was rendered as a flat shaded solid object rather than a open wire-frame. Since this change in rendering making the virtual image more completely occlude the backdrop did not effect its judged depth and since the motion of the backdrop which would have attracted visual attention and binocular convergence did Increase its perceptual displacement, it was concluded that the change In Judged depth was not due to the perceived occlusion. Rather it was concluded to be due to an increase in binocular convergence. An experimental test of this hypothesis using a unobtrusive nonius technique to detect absolute and relative convergence has confirmed the presence of convergence correlated with the magnitude of the change in judged position of this virtual Image. The practical implications of this cause are demonstrated by a second study using monocular, biocular and stereoscopic viewing conditions and the consequences for the design of head-mounted see-through displays for near work are discussed.

Ellis, Stephen R.↗
NASA NTRS1996

Effect of Spaceflight on Vestibulo-Ocular Reflexes (VORS) During Angular Head Motion

Vestibulo-ocular reflexes (VORs) stabilize the eyes during head motion. During Earth-horizontal (E-H) pitch or roll rotations, canal and otolith stimuli occur together. In Earth-vertical (E-V) pitch or roll rotations, only canal signals occur. In cats and squirrel monkeys, pitch/roll VOR gains during E-H motion have been shown to be larger than during E-V motion, implying that otolith modulation plays a role in producing angular VORs (aVORs). The present experiments replicated this experiment in rhesus monkeys, and examined how spaceflight affected AVOR gain. During yaw, pitch and roll (0.5 - 1.0 Hz, 40-50 deg/s pk) motion, 3-d eye movements were recorded in four Rhesus monkeys using scleral search coils. Mean E-H and E-V pitch VOR gains were 0.85 and 0.71. Torsional VOR gains during E-H and E-V were 0.47 and 0.39. Gains are more compensatory during E-H pitch or roll. Two of the four monkeys flew for 11 days on the COSMOS 2229 Biosatellite. E-H pitch VOR gains were attenuated immediately (72 hrs) post-flight, with similar values to pre-flight E-V pitch gains. Horizontal yaw VOR gains were similar pre- and post-flight.

Tomko, David L.↗
NASA NTRS2003

Developing A Contoured Deposition Head for In-Situ Tape Laying and Fiber Placement

A conformable compaction system employing three individual compactors has been designed for integration into fiber placement and tape laying deposition heads for out-of-autoclave fabrication of thermoplastic contoured parts. The compactors are intended to perform against two geometry specifications: (1) a general minimum radius of curvature limit of 180cm (71-in), and (2) a pad-up specification with a maximum height of 2.5mm (0.1-in) and a minimum ramp of 2.5mm (1-in). The mirrored specification is applicable to a pan-down. The three designs include a hot line compactor capable of a 1000N (400-lb) force at 450C over a 114mm (4.5-in) width, a hot area compactor capable of a 400N (100-lb) force at 450C over a 114mm width by 76mm length (4.5-in by 3-in), and a cold compactor that combines the features of a line and an area compactor. The cold compactor s line segments act with a 2800N (700-lb) force across a 127mm (5-in) width, while the cold compactor's area segments act with a 1000N (250-lb) force over a 127mm by 102mm (5-in by 4-in) area. Two of the designs, the hot line and hot area compactors, have been constructed, developed, and proven out in hot mode to compact actual thermoplastic composite plies over undulating geometry. IM-7PEEK [0/90/0/90]s pan-down and IM-7PEEK [0/-45/90/45]2s pad-up laminates have been fabricated and photomicrographs show good microstructure.

Lamontia, Mark A.↗
NASA NTRS2003

Terrain Portrayal for Head-Down Displays Flight Test

The Synthetic Vision Systems General Aviation (SVS-GA) element of NASA's Aviation Safety Program is developing technology to eliminate low visibility induced General Aviation (GA) accidents through the application of synthetic vision techniques. SVS displays present computer generated 3-dimensional imagery of the surrounding terrain to greatly enhance pilot's situation awareness (SA), reducing or eliminating Controlled Flight into Terrain (CFIT), as well as Low-Visibility Loss of Control (LVLOC) accidents. In addition to substantial safety benefits, SVS displays have many potential operational benefits that can lead to flight in instrument meteorological conditions (IMC) resembling those conducted in visual meteorological conditions (VMC). Potential benefits could include lower landing minimums, more approach options, reduced training time, etc. SVS conducted research will develop display concepts providing the pilot with an unobstructed view of the outside terrain, regardless of weather conditions and time of day. A critical component of SVS displays is the appropriate presentation of terrain to the pilot. The relationship between the realism of the terrain presentation and resulting enhancements of pilot SA and pilot performance has been largely undefined. Comprised of coordinated simulation and flight test efforts, the terrain portrayal for head-down displays (TP-HDD) test series examined the effects of two primary elements of terrain portrayal: variations of digital elevation model (DEM) resolution and terrain texturing. Variations in DEM resolution ranged from sparsely spaced (30 arc-sec/2,953ft) to very closely spaced data (1 arc-sec/98 ft). Variations in texture involved three primary methods: constant color, elevation-based generic, and photo-realistic, along with a secondary depth cue enhancer in the form of a fishnet grid overlay. The TP-HDD test series was designed to provide comprehensive data to enable design trades to optimize all SVS applications, as well as develop requirements and recommendations to facilitate the implementation and certification of SVS displays. The TP-HDD flight experiment utilized the NASA LaRC Cessna 206 Stationaire and evaluated eight terrain portrayal concepts in an effort to confirm and extend results from the previously conducted TP-HDD simulation experiment. A total of 15 evaluation pilots, of various qualifications, accumulated over 75 hours of dedicated research flight time at Newport News (PHF) and Roanoke (ROA), VA, airports from August through October, 2002. This report will present results from the portion of testing conducted at Roanoke, VA.

Hughes, Monica F.↗
NASA NTRS2004

Pathway Design Effects on Synthetic Vision Head-Up Displays

NASA s Synthetic Vision Systems (SVS) project is developing technologies with practical applications that will eliminate low visibility conditions as a causal factor to civil aircraft accidents while replicating the operational benefits of clear day flight operations, regardless of the actual outside visibility condition. A major thrust of the SVS project involves the development/demonstration of affordable, certifiable display configurations that provide intuitive out-the-window terrain and obstacle information with advanced pathway guidance for transport aircraft. This experiment evaluated the influence of different tunnel and guidance concepts upon pilot situation awareness (SA), mental workload, and flight path tracking performance for Synthetic Vision display concepts using a Head-Up Display (HUD). Two tunnel formats (dynamic, minimal) were evaluated against a baseline condition (no tunnel) during simulated IMC approaches to Reno-Tahoe International airport. Two guidance cues (tadpole, follow-me aircraft) were also evaluated to assess their influence on the tunnel formats. Results indicated that the presence of a tunnel on an SVS HUD had no effect on flight path performance but that it did have significant effects on pilot SA and mental workload. The dynamic tunnel concept with the follow-me aircraft guidance symbol produced the lowest workload and provided the highest SA among the tunnel concepts evaluated.

Kramer, Lynda J.↗
NASA NTRS2002

Acute and chronic head-down tail suspension diminishes cerebral perfusion in rats

The purpose of this study was to test the hypothesis that regional brain blood flow and vascular resistance are altered by acute and chronic head-down tail suspension (HDT). Regional cerebral blood flow, arterial pressure, heart rate, and vascular resistance were measured in a group of control rats during normal standing and following 10 min of HDT and in two other groups of rats after 7 and 28 days of HDT. Heart rate was not different among conditions, whereas mean arterial pressure was elevated at 10 min of HDT relative to the other conditions. Total brain blood flow was reduced from that during standing by 48, 24, and 27% following 10 min and 7 and 28 days of HDT, respectively. Regional blood flows to all cerebral tissues and the eyes were reduced with 10 min of HDT and remained lower in the eye, olfactory bulbs, left and right cerebrum, thalamic region, and the midbrain with 7 and 28 days of HDT. Total brain vascular resistance was 116, 44, and 38% greater following 10 min and 7 and 28 days of HDT, respectively, relative to that during control standing. Vascular resistance was elevated in all cerebral regions with 10 min of HDT and remained higher than control levels in most brain regions. These results demonstrate that HDT results in chronic elevations in total and regional cerebral vascular resistance, and this may be the underlying stimulus for the HDT-induced smooth muscle hypertrophy of cerebral resistance arteries.

Non-NASA Center↗
NASA NTRS1997

Coupling of fingertip somatosensory information to head and body sway

Light touch contact of a fingertip with a stationary surface can provide orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip provide sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, we asked to which extent somatosensory cues are part of the postural control system, that is, which sensory signal supports this coupling? We investigated postural control not only when the contact surface was stationary, but also when it was moving rhythmically (from 0.1 to 0.5 Hz). In doing so, we brought somatosensory cues from the hand into conflict with other parts of the postural control system. Our focus was the temporal relationship between body sway and the contact surface. Postural sway was highly coherent with contact surface motion. Head and body sway assumed the frequency of the moving contact surface at all test frequencies. To account for these results, a simple model was formulated by approximating the postural control system as a second-order linear dynamical system. The influence of the touch stimulus was captured as the difference between the velocity of the contact surface and the velocity of body sway, multiplied by a coupling constant. Comparison of empirical results (relative phase, coherence, and gain) with model predictions supports the hypothesis of coupling between body sway and touch cues through the velocity of the somatosensory stimulus at the fingertip. One subject, who perceived movement of the touch surface, demonstrated weaker coupling than other subjects, suggesting that cognitive mechanisms introduce flexibility into the postural control scheme.

NASA Discipline Neuroscience↗
NASA NTRS1993

Metabolic responses to head-down suspension in hypophysectomized rats

Rats exposed to head-down suspension (HDS) exhibit reductions in maximal O2 consumption (VO2max) and atrophy of select hindlimb muscles. This study tested the hypothesis that an endocrine-deficient rat exposed to HDS would not exhibit reductions in VO2max or hindlimb muscle mass. Hypophysectomized (HYPX) and sham-operated (SHAM) rats were tested for VO2max before and after 28 days of HDS or cage control (CC) conditions. No significant reductions in VO2max were observed in HYPX rats. In contrast, SHAM-HDS rats exhibited a significant reduction in absolute (-16%) and relative (-29%) measures of aerobic capacity. Time course experiments revealed a reduction in VO2max in SHAM-HDS rats within 7 days, suggesting that cardiovascular adjustments to HDS occurred in the 1st wk. HDS was associated with atrophy of the soleus (-42%) in SHAM rats, whereas HYPX rats exhibited atrophy of the soleus (-36%) and plantaris (-13%). SHAM-HDS rats had significantly lower (-38%) soleus citrate synthase activities per gram muscle mass than SHAM-CC, but no significant differences existed between HYPX-HDS and -CC rats. HDS rats had an impaired ability to thermoregulate, as indicated by significantly greater temperature increases per unit run time, compared with their CC counterparts. Pretreatment plasma epinephrine levels were significantly lower in HYPX than in SHAM rats. Norepinephrine concentration was similar for all groups except HYPX-HDS, in which it was significantly higher. HDS had no significant effect on thyroxine or triiodothyronine. SHAM-HDS rats had significantly lower concentrations of testosterone and growth hormone.(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Discipline Number 14-10↗
NASA NTRS1993

Gender differences in endocrine responses to posture and 7 days of -6 degrees head-down bed rest

Endocrine regulation of fluids and electrolytes during 7 days of -6 degrees head-down bed rest (HDBR) was compared in male (n = 8) and, for the first time, female (n = 8) volunteers. The subjects' responses to quiet standing for 2 h before and after HDBR were also tested. In both sexes, diuresis and natriuresis were evident during the first 2-3 days of HDBR, resulting in a marked increase in the urinary Na(+)-to-K+ ratio and significant Na+ retention on re-ambulation. After the 1st day of HDBR, plasma renin activity (PRA) was increased relative to aldosterone (Aldo), plasma volume was decreased, and the renal response to Aldo appeared to be appropriate. Circulating levels of arginine vasopressin, cortisol, and ACTH were unchanged during HDBR. Plasma testosterone decreased slightly on day 2 of HDBR in males. The ratio of early morning ACTH to cortisol was lower in females than in males because ACTH was lower in females. Urinary cortisol increased and remained elevated throughout the HDBR in males only. There were no gender differences in the responses to 7 days of HDBR, except those in the pituitary-adrenal system; those differences appeared unrelated to the postural change. The provocative cardiovascular test of quiet standing before and after HDBR revealed both sex differences and effects of HDBR. There were significant sex differences in cardiovascular responses to standing before and after HDBR. Females had greater PRA and Aldo responses to standing before HDBR and larger Aldo responses to standing after HDBR than males.(ABSTRACT TRUNCATED AT 250 WORDS).

NASA Discipline Number 14-10↗
NASA NTRS1948

An Investigation of the Aerodynamic Characteristics of a 3/4-Scale Model of the EX-3 Pine-Cone-Head Pellet in the Langley High-Speed 7-by 10-Foot Wind Tunnel

An investigation of the Ex-3 pine-cone-head pellet was made in the Langley high-speed 7-by 10-foot wind tunnel to determine the static force and moment characteristics at high Mach numbers with the reference center of gravity located at 37.5 percent of the over-all length aft of the nose. For this center-of-gravity location there were no secondary trim positions, and the center-of-pressure position was not appreciably affected by Mach number.

Campbell, George S.↗
NASA NTRS2005

Advanced Pathway Guidance Evaluations on a Synthetic Vision Head-Up Display

NASA's Synthetic Vision Systems (SVS) project is developing technologies with practical applications to potentially eliminate low visibility conditions as a causal factor to civil aircraft accidents while replicating the operational benefits of clear day flight operations, regardless of the actual outside visibility condition. A major thrust of the SVS project involves the development/demonstration of affordable, certifiable display configurations that provide intuitive out-the-window terrain and obstacle information with advanced guidance for commercial and business aircraft. This experiment evaluated the influence of different pathway and guidance display concepts upon pilot situation awareness (SA), mental workload, and flight path tracking performance for Synthetic Vision display concepts using a Head-Up Display (HUD). Two pathway formats (dynamic and minimal tunnel presentations) were evaluated against a baseline condition (no tunnel) during simulated instrument meteorological conditions approaches to Reno-Tahoe International airport. Two guidance cues (tadpole, follow-me aircraft) were also evaluated to assess their influence. Results indicated that the presence of a tunnel on an SVS HUD had no effect on flight path performance but that it did have significant effects on pilot SA and mental workload. The dynamic tunnel concept with the follow-me aircraft guidance symbol produced the lowest workload and provided the highest SA among the tunnel concepts evaluated.

Kramer, Lynda J.↗
NASA NTRS2004

Benchmark Tests for Stirling Convertor Heater Head Life Assessment Conducted

A new in-house test capability has been developed at the NASA Glenn Research Center, where a critical component of the Stirling Radioisotope Generator (SRG) is undergoing extensive testing to aid the development of analytical life prediction methodology and to experimentally aid in verification of the flight-design component's life. The new facility includes two test rigs that are performing creep testing of the SRG heater head pressure vessel test articles at design temperature and with wall stresses ranging from operating level to seven times that (see the following photograph).

Krause, David L.↗
NASA NTRS2006

Experimental and Computational Analysis of Unidirectional Flow Through Stirling Engine Heater Head

A high efficiency Stirling Radioisotope Generator (SRG) is being developed for possible use in long-duration space science missions. NASA s advanced technology goals for next generation Stirling convertors include increasing the Carnot efficiency and percent of Carnot efficiency. To help achieve these goals, a multi-dimensional Computational Fluid Dynamics (CFD) code is being developed to numerically model unsteady fluid flow and heat transfer phenomena of the oscillating working gas inside Stirling convertors. In the absence of transient pressure drop data for the zero mean oscillating multi-dimensional flows present in the Technology Demonstration Convertors on test at NASA Glenn Research Center, unidirectional flow pressure drop test data is used to compare against 2D and 3D computational solutions. This study focuses on tracking pressure drop and mass flow rate data for unidirectional flow though a Stirling heater head using a commercial CFD code (CFD-ACE). The commercial CFD code uses a porous-media model which is dependent on permeability and the inertial coefficient present in the linear and nonlinear terms of the Darcy-Forchheimer equation. Permeability and inertial coefficient were calculated from unidirectional flow test data. CFD simulations of the unidirectional flow test were validated using the porous-media model input parameters which increased simulation accuracy by 14 percent on average.

Wilson, Scott D.↗