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NASA NTRS1983

Space motion sickness and vestibular adaptation to weightlessness

Theories of space motion sickness are discussed together with near future vestibular experiments for three Spacelab missions. The sensory conflict theory is covered, as well as theories involving unequal otolith masses, semicircular canals, cardiovascular adaptation and fluid shift toward the head, and extra-labyrinthine effects. Experiments will test the hypothesis that the sensitivity of the otolith organ response is shifted during weightlessness and that this shift carries over to the post-flight experience. Visual-vestibular-tactile interaction, vestibulo-ocular reflexes, ocular counterrolling, awareness of body position, otolith-spinal reflexes, and motion sickness susceptibility are among the parameters to be studied. Preflight and postflight tests will emphasize evaluation of any residual effects of the seven day weightless exposure on vestibulo-spinal and vestibulo-ocular pathways.

Young, L. R.↗

DOE OSTI2020

Disentangling Sources of Gene Tree Discordance in Phylogenomic Data Sets: Testing Ancient Hybridizations in Amaranthaceae s.l

Gene tree discordance in large genomic data sets can be caused by evolutionary processes such as incomplete lineage sorting and hybridization, as well as model violation, and errors in data processing, orthology inference, and gene tree estimation. Species tree methods that identify and accommodate all sources of conflict are not available, but a combination of multiple approaches can help tease apart alternative sources of conflict. Here, using a phylotranscriptomic analysis in combination with reference genomes, we test a hypothesis of ancient hybridization events within the plant family Amaranthaceae s.l. that was previously supported by morphological, ecological, and Sanger-based molecular data. The data set included seven genomes and 88 transcriptomes, 17 generated for this study. We examined gene-tree discordance using coalescent-based species trees and network inference, gene tree discordance analyses, site pattern tests of introgression, topology tests, synteny analyses, and simulations. We found that a combination of processes might have generated the high levels of gene tree discordance in the backbone of Amaranthaceae s.l. Furthermore, we found evidence that three consecutive short internal branches produce anomalous trees contributing to the discordance. Overall, our results suggest that Amaranthaceae s.l. might be a product of an ancient and rapid lineage diversification, and remains, and probably will remain, unresolved. This work highlights the potential problems of identifiability associated with the sources of gene tree discordance including, in particular, phylogenetic network methods. Our results also demonstrate the importance of thoroughly testing for multiple sources of conflict in phylogenomic analyses, especially in the context of ancient, rapid radiations. We provide several recommendations for exploring conflicting signals in such situations.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS2001

Evidence for central venous pressure resetting during initial exposure to microgravity

We measured central venous pressure (CVP); plasma volume (PV); urine volume rate (UVR); renal excretion of sodium (UNa); and renal clearances of creatinine, sodium, and osmolality before and after acute volume infusion to test the hypothesis that exposure to microgravity causes resetting of the CVP operating point. Six rhesus monkeys underwent two experimental conditions in a crossover counterbalance design: 1) continuous exposure to 10 degrees head-down tilt (HDT) and 2) a control, defined as 16 h/day of 80 degrees head-up tilt and 8 h prone. After 48 h of exposure to either test condition, a 120-min course of continuous infusion of isotonic saline (0.4 ml. kg(-1). min(-1) iv) was administered. Baseline CVP was lower (P = 0.011) in HDT (2.3 +/- 0.3 mmHg) compared with the control (4.5 +/- 1.4 mmHg) condition. After 2 h of saline infusion, CVP was elevated (P = 0.002) to a similar magnitude (P = 0.485) in HDT (DeltaCVP = 2.7 +/- 0.8 mmHg) and control (DeltaCVP = 2.3 +/- 0.8 mmHg) conditions and returned to preinfusion levels 18 h postinfusion in both treatments. PV followed the same pattern as CVP. The response relationships between CVP and UVR and between CVP and UNa shifted to the left with HDT. The restoration of CVP and PV to lower preinfusion levels after volume loading in HDT compared with control supports the notion that lower CVP during HDT may reflect a new operating point about which vascular volume is regulated. These results may explain the ineffective fluid intake procedures currently employed to treat patients and astronauts.

NASA Discipline Cardiopulmonary↗

NASA NTRS1992

Determining stress states using dike swarms: The Lauma Dorsa example

Initial examination of the Magellan coverage of Venus has revealed between 150 and 300 large, radially lineated landforms distributed across the planet's surface. Where the lineaments have been examined in detail, the majority fail to exhibit signatures indicative of relief at or above the resolution of the radar; however, when the sense of topographic relief may be ascertained, the lineaments commonly appear as fissures or flat-floored trenches interpreted as graben. Individual lineaments can display graben, fissure, and zero relief behavior along their length, suggesting either that these differences are a function of the resolution of the radar, or that the morphological distinctions are real but somehow genetically linked. In many instances, radial lineaments exhibiting these characteristics are directly associated with surface volcanism, including flanking and terminal flows, superimposed shield domes and pit chains, and central, calderalike topographic lows. These observable characteristics, as well as theoretical studies and comparison with similar terrestrial features, have led to the working hypothesis that many of the radial fracture systems on Venus are the surface manifestation of subsurface dikes propagating laterally from a central magma source. If this interpretation is correct, studies of terrestrial dikes suggest that the lineament directions, with localized exceptions and barring subsequent deformation, should be perpendicular to the orientation of the least compressive stress at the time of their formation. To test this hypothesis, we briefly examine a radial fracture system (63.7 degrees N, 195 degrees E) located between two deformation belts in Vinmara Planitia, and verify that the lineaments to the east behave in the expected manner. We have also chosen this feature, however, because of its proximity to Lauma Dorsa to the west. On the basis of Venera 15/16 data, both compressional and extensional origins for this deformation belt have been proposed. By examining the stratigraphy and applying our interpretation that the fracture system is linked to the presence of subsurface dikes, we present an independent evaluation of the stress state associated with Lauma Dorsa, and thus contribute to the assessment of its origin.

Grosfils, Eric B.↗

NASA NTRS1998

Head-down-tilt bed rest alters forearm vasodilator and vasoconstrictor responses

To test the hypothesis that head-down-tilt bed rest (HDBR) for 14 days alters vascular reactivity to vasodilatory and vasoconstrictor stimuli, the reactive hyperemic forearm blood flow (RHBF, measured by venous occlusion plethysmography) and mean arterial pressure (MAP, measured by Finapres) responses after 10 min of circulatory arrest were measured in a control trial (n = 20) and when sympathetic discharge was increased by a cold pressor test (RHBF + cold pressor test; n = 10). Vascular conductance (VC) was calculated (VC = RHBF/MAP). In the control trial, peak RHBF at 5 s after circulatory arrest (34.1 +/- 2.5 vs. 48.9 +/- 4.3 ml . 100 ml-1 . min-1) and VC (0.34 +/- 0.02 vs. 0.53 +/- 0.05 ml . 100 ml-1 . min-1 . mmHg-1) were reduced in the post- compared with the pre-HDBR tests (P < 0. 05). Total excess RHBF over 3 min was diminished in the post- compared with the pre-HDBR trial (84.8 vs. 117 ml/100 ml, P < 0.002). The ability of the cold pressor test to lower forearm blood flow was less in the post- than in the pre-HDBR test (P < 0.05), despite similar increases in MAP. These data suggest that regulation of vascular dilation and the interaction between dilatory and constrictor influences were altered with bed rest.

NASA Discipline Musculoskeletal↗

NASA NTRS2001

Midodrine prevents orthostatic intolerance associated with simulated spaceflight

Many astronauts after being weightless in space become hypotensive and presyncopal when they assume an upright position. This phenomenon, known as orthostatic intolerance, may interfere with astronaut function during reentry and after spaceflight and may limit the ability of an astronaut to exit a landed spacecraft unaided during an emergency. Orthostatic intolerance is more pronounced after long-term spaceflight and is a major concern with respect to the extended flights expected aboard the International Space Station and for interplanetary exploration class missions, such as a human mission to Mars. Fully effective countermeasures to this problem have not yet been developed. To test the hypothesis that alpha-adrenergic stimulation might provide an effective countermeasure, we conducted a 16-day head-down-tilt bed-rest study (an analog of weightlessness) using normal human volunteers and administered the alpha(1)-agonist drug midodrine at the end of the bed-rest period. Midodrine was found to significantly ameliorate excessive decreases in blood pressure and presyncope during a provocative tilt test. We conclude that midodrine may be an effective countermeasure for the prevention of orthostatic intolerance following spaceflight.

NASA Center JSC↗

DOE OSTI2024

The Radiation-Induced Fate of Fission Product Iodine in Molten Salts

Understand and Predict Radiation-Induced Iodine Speciation, Chemistry, and Transport in High-Temperature Molten Salts Award Number: DE-AC07-05ID1451 Gregory P. Holmbeck (Gregory.Holmbeck@inl.gov), Center for Radiation Chemistry Research, Idaho National Laboratory, 1955 N. Fremont Avenue Idaho Falls, ID, 83415, USA. Project Scope The goal of this Chemical and Materials Sciences to Advance Clean Energy Technologies and Low-Carbon Manufacturing project is to understand and predict the radiation-induced speciation, chemistry, and transport of fission product iodine in the triumvirate extremes of high-temperature, ionizing radiation, and corrosive molten salts. This missing fundamental information is critical for the accelerated development and deployment of safe, clean nuclear energy based on molten salt reactor (MSR) and pyrochemical reprocessing technologies. The central hypothesis driving this research is, the radiation-induced conversion of iodide will yield an extensive suite of transient and steady-state iodine radiolysis products that will alter the bulk chemical and physical properties of the irradiated molten salt system—the speciation, distribution, and chemical transport of which will be dictated by the composition and the availability of multivalent metal cations and metal alloy interfaces. To test this hypothesis, this project initiated three synergistic Research Objectives: (1) determine how the inclusion of iodine/iodide influences the chemical and physical properties of complex molten salt mixtures; (2) elucidate the speciation and fundamental chemical behavior of transient and steady-state iodine/iodide species formed by the irradiation of molten and solid salt mixtures; and (3) understand the influence of interfacial processes on determining the final disposition of iodine in high temperature molten salts, notably the structure and chemical speciation of iodine at metal-salt interfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1994

An evaluation of criteria that may be used to identify species surviving a mass extinction

One of the most difficult obstacles to establishing a causal connection between mass extinctions and large body impacts is the existence of what appear to be many more KT survivor species than previously suspected. Though interpretations of 'Cretaceous' faunal elements in lowermost Danian sediments differ, this enigmatic fauna has not been recovered from every biozone-complete boundary section, including the El Kef stratotype. In terms of their potential for providing constraints on scenarios seeking to account for the KT extinction event, the significance of such observations cannot be overstated. Owing to the consistency with which these observations have been made over the last several years, the possibility of widespread trans-KT biotic survivorship can no longer be dismissed. Rather, the survivorship hypothesis must be tested alongside its alternative (the reworking hypothesis) to determine which explains the available data in the most complete yet parsimonious manner. Moreover, valid tests for survivorship cannot be based on negative evidence or on the assumption that only a small cohort of species could have survived the KT boundary event. Several authors have recently proposed various criteria that might be used to test alternative interpretations for this aspect lowermost Danian biotic record.

Macleod, N.↗

NASA NTRS1997

Hypovolemia in syncope and orthostatic intolerance role of the renin-angiotensin system

PURPOSE: Orthostatic intolerance is the cause of significant disability in otherwise normal patients. Orthostatic tachycardia is usually the dominant hemodynamic abnormality, but symptoms may include dizziness, visual changes, discomfort in the head or neck, poor concentration, fatigue, palpitations, tremulousness, anxiety and, in some cases, syncope. It is the most common disorder of blood pressure regulation after essential hypertension. There is a predilection for younger rather than older adults and for women more than men. Its cause is unknown; partial sympathetic denervation or hypovolemia has been proposed. METHODS AND MATERIALS: We tested the hypothesis that reduced plasma renin activity, perhaps from defects in sympathetic innervation of the kidney, could underlie a hypovolemia, giving rise to these clinical symptoms. Sixteen patients (14 female, 2 male) ranging in age from 16 to 44 years were studied. Patients were enrolled in the study if they had orthostatic intolerance, together with a raised upright plasma norepinephrine (> or = 600 pg/mL). Patients underwent a battery of autonomic tests and biochemical determinations. RESULTS: There was a strong positive correlation between the blood volume and plasma renin activity (r = 0.84, P = 0.001). The tachycardic response to upright posture correlated with the severity of the hypovolemia. There was also a correlation between the plasma renin activity measured in these patients and their concomitant plasma aldosterone level. CONCLUSIONS: Hypovolemia occurs commonly in orthostatic intolerance. It is accompanied by an inappropriately low level of plasma renin activity. The degree of abnormality of blood volume correlates closely with the degree of abnormality in plasma renin activity. Taken together, these observations suggest that reduced plasma renin activity may be an important pathophysiologic component of the syndrome of orthostatic intolerance.

Non-NASA Center↗

NASA NTRS1994

Evidence against a hypothesis of vestibular efferent function

Efferent stimulation and nicotinic agonists can either decrease or increase the frequency of occurrence of EPSPs recorded from VIIIth nerve afferents in the frog. It has been hypothesized that the distribution of hair cell resting membrane potentials overlaps the equilibrium potential dictated by the nicotinic-gated channels on the hair cells. Nicotinic mediated increases in EPSP frequency would then be due to depolarization of hair cells that were more hyperpolarized at rest, while decreases in EPSP frequency would be due to hyperpolarization of hair cells more depolarized at rest. In order to test this hypothesis, while recording from afferents which showed an increase in EPSP frequency due to bath application of the nicotinic agonist DMPP (1,1-dimethyl-4-phenylpiperizinium iodide), hair cells were depolarized with 10 mM K+ in the bath, and then the effects of DMPP on EPSP frequency were assessed. In this situation, DMPP still increased EPSP frequency, suggesting that the equilibrium potential for the nicotinic-gated channel was much more positive than the resting potentials of the hair cells. An alternative hypothesis then seems likely, that the nicotinic receptors on hair cells are able to activate different iontophores that result in either hair cell depolarization or hyperpolarization, dependent upon which iontophore predominates in the hair cells innervating a particular afferent.

NASA Discipline Neuroscience↗

DOE OSTI2023

Organic preservation of vase‐shaped microfossils from the late Tonian Chuar Group, Grand Canyon, Arizona, USA

Abstract Vase‐shaped microfossils (VSMs) are found globally in middle Neoproterozoic (800–730 Ma) marine strata and represent the earliest evidence for testate (shell‐forming) amoebozoans. VSM tests are hypothesized to have been originally organic in life but are most commonly preserved as secondary mineralized casts and molds. A few reports, however, suggest possible organic preservation. Here, we test the hypothesis that VSMs from shales of the lower Walcott Member of the Chuar Group, Grand Canyon, Arizona, contain original organic material, as reported by B. Bloeser in her pioneering studies of Chuar VSMs. We identified VSMs from two thin section samples of Walcott Member black shales in transmitted light microscopy and used scanning electron microscopy to image VSMs. Carbonaceous material is found within the internal cavity of all VSM tests from both samples and is interpreted as bitumen mobilized from Walcott shales likely during the Cretaceous. Energy dispersive X‐ray spectroscopy (EDS) and wavelength dispersive X‐ray spectroscopy (WDS) reveal that VSM test walls contain mostly carbon, iron, and sulfur, while silica is present only in the surrounding matrix. Raman spectroscopy was used to compare the thermal maturity of carbonaceous material within the samples and indicated the presence of pyrite and jarosite within fossil material. X‐ray absorption spectroscopy revealed the presence of reduced organic sulfur species within the carbonaceous test walls, the carbonaceous material found within test cavities, and in the sedimentary matrix, suggesting that organic matter sulfurization occurred within the Walcott shales. Our suite of spectroscopic analyses reveals that Walcott VSM test walls are organic and sometimes secondarily pyritized (with the pyrite variably oxidized to jarosite). Both preservation modes can occur at a millimeter spatial scale within sample material, and at times even within a single specimen. We propose that sulfurization within the Walcott Shales promoted organic preservation, and furthermore, the ratio of iron to labile VSM organic material controlled the extent of pyrite replacement. Based on our evidence, we conclude that the VSMs are preserved with original organic test material, and speculate that organic VSMs may often go unrecognized, given their light‐colored, translucent appearance in transmitted light.

58 GEOSCIENCES↗

NASA NTRS2003

Scheduling Earth Observing Satellites with Evolutionary Algorithms

We hypothesize that evolutionary algorithms can effectively schedule coordinated fleets of Earth observing satellites. The constraints are complex and the bottlenecks are not well understood, a condition where evolutionary algorithms are often effective. This is, in part, because evolutionary algorithms require only that one can represent solutions, modify solutions, and evaluate solution fitness. To test the hypothesis we have developed a representative set of problems, produced optimization software (in Java) to solve them, and run experiments comparing techniques. This paper presents initial results of a comparison of several evolutionary and other optimization techniques; namely the genetic algorithm, simulated annealing, squeaky wheel optimization, and stochastic hill climbing. We also compare separate satellite vs. integrated scheduling of a two satellite constellation. While the results are not definitive, tests to date suggest that simulated annealing is the best search technique and integrated scheduling is superior.

Globus, Al↗

NASA NTRS2003

Common 5S rRNA variants are likely to be accepted in many sequence contexts

Over evolutionary time RNA sequences which are successfully fixed in a population are selected from among those that satisfy the structural and chemical requirements imposed by the function of the RNA. These sequences together comprise the structure space of the RNA. In principle, a comprehensive understanding of RNA structure and function would make it possible to enumerate which specific RNA sequences belong to a particular structure space and which do not. We are using bacterial 5S rRNA as a model system to attempt to identify principles that can be used to predict which sequences do or do not belong to the 5S rRNA structure space. One promising idea is the very intuitive notion that frequently seen sequence changes in an aligned data set of naturally occurring 5S rRNAs would be widely accepted in many other 5S rRNA sequence contexts. To test this hypothesis, we first developed well-defined operational definitions for a Vibrio region of the 5S rRNA structure space and what is meant by a highly variable position. Fourteen sequence variants (10 point changes and 4 base-pair changes) were identified in this way, which, by the hypothesis, would be expected to incorporate successfully in any of the known sequences in the Vibrio region. All 14 of these changes were constructed and separately introduced into the Vibrio proteolyticus 5S rRNA sequence where they are not normally found. Each variant was evaluated for its ability to function as a valid 5S rRNA in an E. coli cellular context. It was found that 93% (13/14) of the variants tested are likely valid 5S rRNAs in this context. In addition, seven variants were constructed that, although present in the Vibrio region, did not meet the stringent criteria for a highly variable position. In this case, 86% (6/7) are likely valid. As a control we also examined seven variants that are seldom or never seen in the Vibrio region of 5S rRNA sequence space. In this case only two of seven were found to be potentially valid. The results demonstrate that changes that occur multiple times in a local region of RNA sequence space in fact usually will be accepted in any sequence context in that same local region.

NASA Discipline Exobiology↗

NASA NTRS2002

Water drinking as a treatment for orthostatic syndromes

PURPOSE: Water drinking increases blood pressure in a substantial proportion of patients who have severe orthostatic hypotension due to autonomic failure. We tested the hypothesis that water drinking can be used as a practical treatment for patients with orthostatic and postprandial hypotension, as well as those with orthostatic tachycardia. SUBJECTS AND METHODS: We studied the effect of drinking water on seated and standing blood pressure and heart rate in 11 patients who had severe orthostatic hypotension due to autonomic failure and in 9 patients who had orthostatic tachycardia due to idiopathic orthostatic intolerance. We also tested the effect of water drinking on postprandial hypotension in 7 patients who had autonomic failure. Patients drank 480 mL of tap water at room temperature in less than 5 minutes. RESULTS: In patients with autonomic failure, mean (+/- SD) blood pressure after 1 minute of standing was 83 +/- 6/53 +/- 3.4 mm Hg at baseline, which increased to 114 +/- 30/66 +/- 18 mm Hg (P <0.01) 35 minutes after drinking. After a meal, blood pressure decreased by 43 +/- 36/20 +/- 13 mm Hg without water drinking, compared with 22 +/- 10/12 +/- 5 mm Hg with drinking (P <0.001). In patients with idiopathic orthostatic intolerance, water drinking attenuated orthostatic tachycardia (123 +/- 23 beats per minute) at baseline to 108 +/- 21 beats per minute after water drinking ( P <0.001). CONCLUSION: Water drinking elicits a rapid pressor response in patients with autonomic failure and can be used to treat orthostatic and postprandial hypotension. Water drinking moderately reduces orthostatic tachycardia in patients with idiopathic orthostatic intolerance. Thus, water drinking may serve as an adjunctive treatment in patients with impaired orthostatic tolerance.

Non-NASA Center↗

NASA NTRS1993

Exposure ages of carbonaceous chondrites, 1

The recent exposure histories of carbonaceous chondrites have been investigated using cosmogenic radionuclides. Our results may indicate a clustering of exposure ages of C1 and C2 chondrites into two peaks, 0.2 My and 0.6 My, perhaps implying two collisional events of Earth-crossing parent bodies. Among carbonaceous chondrites are some having short exposure ages which Mazor et al. hypothesized cluster into a small number of families. This hypothesis is based on spallogenic Ne-21 exposure ages, which in some instances are difficult to determine owing to the large amounts of trapped noble gases in carbonaceous chondrites. Also, since Ne-21 is stable, it integrates a sample's entire exposure history, so meteorites with complex exposure histories are difficult to understand using exclusively Ne-21. Cosmogenic radionuclides provide an alternative means of determining the recent cosmic ray exposure duration. To test the hypothesis of Mazor et al. we have begun a systematic investigation of exposure histories of Antarctic and non-Antarctic carbonaceous chondrites especially C2s.

Nishiizumi, K.↗

NASA NTRS2002

Development of a New Membrane Casting Apparatus for Studying Macrovoid Defects in Low-G

A new membrane-casting apparatus is developed for studying macrovoid defects in polymeric membranes made by the wet- and dry-casting process in low-gravity. Macrovoids are large (10-50 micron), open cavities interspersed among the smaller pores in the substructure under the gelled skin surface layer of the cast membrane. Although their occurrence is considered endemic to the wet- and dry-casting process since they can lead to compaction or skin rupture in the membrane process, recent studies suggest several useful applications such as transdermal and osmotic drug delivery systems, miniature bioreactors, etc. However, lack of knowledge about the macrovoid formation mechanism is an obstacle to further development of applications using them. An on-going debate is the role of the surface-tension-driven solutocapillary convection during macrovoid formation. The rapid growth of macrovoids within 1-5 seconds and the high polymer concentration in and near macrovoids make it difficult to explain the mechanism of macrovoid growth by diffusion alone, which is the widely accepted hypothesis proposed by Reuvers et al. The hypothesis advanced by our research group can explain this rapid growth via a mechanism that involves diffusion from the casting solution in the meta-stable region to the macrovoid enhanced by solutocapillary convection induced by the steep nonsolvent concentration gradient in the vicinity of the macrovoid. Since macrovoid growth is hypothesized to be the interplay of a solutocapillary-induced driving force counteracted by viscous drag and buoyancy, eliminate the latter provides a means for testing this hypothesis. Moreover, free convection mass transfer in the nonsolvent immersion bath used to cause phase-separation in membrane casting complicates developing a model for both the wet-casting process and macrovoid growth. The low-g environment minimizes gravitationally induced free convection thereby permitting a tractable solution to the ternary diffusion equations that characterize membrane formation. NASA's Parabolic Flight Research Aircraft provides a small window of low-g (approximately 25 s) that can be used to study macrovoid development in both wet- and dry-cast membranes if an appropriate casting apparatus is used. This casting apparatus should be able to cast the membrane in both low- and high-g in a manner so that essential one-dimensional mass transfer conditions are achieved to insure lateral uniformity in the membrane. The apparatus used in previous research on membrane casting in low-gravity was operated with the plunger driven mechanism. The spring-loaded plunger pushes the bottom block containing the polymer casting solution well directly under the absorbent chamber located in the upper stationary block. However, membranes made via this casting apparatus often displayed lateral nonuniformities that precluded obtaining quantitative information on the macrovoid growth process. Thus, it was necessary to determine the reason for these structural irregularities observed in the low-g casting apparatus. Both experimental as well as computer simulation studies of the low-g casting apparatus established that the impulsive action of the plunger caused the undesired structural nonuniformities. The simulation results showed that the width-to-depth aspect ratio of the shallow well that contains the casting solution in this apparatus was not an important factor in minimizing this problem. Even for a 40:1 (width : depth) aspect ratio, any convection induced by the horizontal motion of the interface of the casting solution will be damped out within 6.25x10(exp 4) seconds. However, the experimental studies revealed that the impulsive motion of the plunger caused a 'sloshing' of the casting solution that had to be eliminated. Therefore, the plungerdriven mechanism was changed to a cam-driven mechanism that did not cause any impulsive motion of the casting solution. Other refinements to this new membrane-casting apparatus include provision for removing the membranes from the casting wells in a less destructive manner. This was accomplished by using a slit geometry for the casting well that permitted disassembly for removal of the cast membrane. The materials used in the construction of this casting apparatus were chosen to insure wetting at the side walls and to maintain precise control of the thickness of the polymer solution in the casting well. An additional provision in this new casting apparatus is the ability to carry out both wet- as well as dry-casting. As such, this apparatus permitted the first studies of the wet-casting of polymeric membranes in low-g. Both wet- and dry-casting experiments on NASA's KC-135 research aircraft employing this new membrane-casting apparatus are scheduled in July 2002. The morphology of the resulting membranes will be characterized using an environmental scanning electron microscope (ESEM). The results of these low-g studies will be reported later.

Lee, Hanyong↗

NASA NTRS2001

Gender affects sympathetic and hemodynamic response to postural stress

We tested the hypothesis that differences in sympathetic reflex responses to head-up tilt (HUT) between males (n = 9) and females (n = 8) were associated with decrements in postural vasomotor responses in women. Muscle sympathetic nerve activity (MSNA; microneurography), heart rate, stroke volume (SV; Doppler), and blood pressure (Finapres) were measured during a progressive HUT protocol (5 min at each of supine, 20 degrees, 40 degrees, and 60 degrees ). MSNA and hemodynamic responses were also measured during the cold pressor test (CPT) to examine nonbaroreflex neurovascular control. SV was normalized to body surface area (SV(i)) to calculate the index of cardiac output (Q(i)), and total peripheral resistance (TPR). During HUT, heart rate increased more in females versus males (P < 0.001) and SV(i) and Q(i) decreased similarly in both groups. Mean arterial pressure (MAP) increased to a lesser extent in females versus males in the HUT (P < 0.01) but increases in TPR during HUT were similar. MSNA burst frequency was lower in females versus males in supine (P < 0.03) but increased similarly during HUT. Average amplitude/burst increased in 60 degrees HUT for males but not females. Both males and females demonstrated an increase in MAP as well as MSNA burst frequency, mean burst amplitude, and total MSNA during the CPT. However, compared with females, males demonstrated a greater neural response (DeltaTotal MSNA) due to a larger increase in mean burst amplitude (P < 0.05). Therefore, these data point to gender-specific autonomic responses to cardiovascular stress. The different MSNA response to postural stress between genders may contribute importantly to decrements in blood pressure control during HUT in females.

Non-NASA Center↗

DOE OSTI2021

Validating Intra-Plate Power Distributions in the Advanced Test Reactor

We report that the neutronics software, HELIOS, was validated in 2015 for performing core reload design and safety analysis of the Advanced Test Reactor. However, when HELIOS was benchmarked against historic fission-wire measurements (i.e., zero-power full-core measurements) a statistically resolved calculation-to-measurement bias was discovered. The azimuthal power along each fuel plate computed by HELIOS has consistently shown to under-predict measurements made by fission-wires in historic zero-power tests near the fuel element side-plates. It was hypothesized during the HELIOS software validation work, that this bias is attributable to local moderation in coolant vents in the side-plates axially just above and below the fission-wires on the fuel-plate edges. This work used detailed MCNP and MC21 models of the side-plate vents to test this hypothesis. By comparing the average azimuthal biases between HELIOS, and 2D and 3D MCNP models, and a 3D MC21 model, it was found that the HELIOS azimuthal bias is not due to the measurement.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗