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At least 613 records · Page 34

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NASA NTRS2012

Simulated Space Radiation and Weightlessness: Vascular-Bone Coupling Mechanisms to Preserve Skeletal Health

Weightlessness causes a cephalad fluid shift and reduction in mechanical stimulation, adversely affecting both cortical and trabecular bone tissue in astronauts. In rodent models of weightlessness, the onset of bone loss correlates with reduced skeletal perfusion, reduced and rarified vasculature and lessened vasodilation, which resembles blood-bone symbiotic events that can occur with fracture repair and aging. These are especially serious risks for long term, exploration class missions when astronauts will face the challenge of increased exposure to space radiation and abrupt transitions between different gravity environments upon arrival and return. Previously, we found using the mouse hindlimb unloading model and exposure to heavy ion radiation, both disuse and irradiation cause an acute bone loss that was associated with a reduced capacity to produce bone-forming osteoblasts from the bone marrow. Together, these findings led us to hypothesize that exposure to space radiation exacerbates weightlessness-induced bone loss and impairs recovery upon return, and that treatment with anti-oxidants may mitigate these effects. The specific aims of this recently awarded grant are to: AIM 1 Determine the functional and structural consequences of prolonged weightlessness and space radiation (simulated spaceflight) for bone and skeletal vasculature in the context of bone cell function and oxidative stress. AIM 2 Determine the extent to which an anti-oxidant protects against weightlessness and space radiation-induced bone loss and vascular dysfunction. AIM 3 Determine how space radiation influences later skeletal and vasculature recovery from prolonged weightlessness and the potential of anti-oxidants to preserve adaptive remodeling.

Alwood, J. S.↗

NASA NTRS1980

Coherence bandwidth loss in transionospheric radio propagation

In this report a theoretical model is developed that predicts the single-point, two-frequency coherence function for transionospheric radio waves. The theoretical model is compared to measured complex frequency correlation coefficients using data from the seven equispaced, phase-coherent UHF signals transmitted by the Wideband satellite. The theory and data are in excellent agreement. The theory is critically dependent upon the power-law index, and the frequency coherence data clearly favor the comparatively small spectral indices that have been consistently measured from the wideband satellite phase data. A model for estimating the pulse delay jitter induced by the coherence bandwidth loss is also developed and compared with the actual delay jitter observed on synthesized pulses obtained from the Wideband UFH comb. The results are in good agreement with the theory. The results presented in this report, which are based on an asymptotic theory, are compared with the more commonly used quadratic theory. The model developed and validated in this report can be used to predict the effects of coherence bandwidth loss in disturbed nuclear environments. Simple formulas for the resultant pulse delay jitter are derived that can be used in predictive codes.

Rino, C. L.↗

NASA NTRS2014

Understanding the Effects of Long-duration Space Flight on Astronant Functional Task Performance

Space flight is known to cause alterations in multiple physiological systems including changes in sensorimotor, cardiovascular, and neuromuscular systems. These physiological changes cause balance, gait and visual disturbances, cardiovascular deconditioning, and loss of muscle mass and strength. These changes may affect a crewmember's ability to perform critical mission tasks immediately after landing on a planetary surface. To understand how changes in physiological function affect functional performance, an interdisciplinary pre- and postflight testing regimen, Functional Task Test (FTT), was developed to systematically evaluate both astronaut functional performance and related physiological changes. Ultimately this information will be used to assess performance risks and inform the design of countermeasures for exploration class missions. We are currently conducting the FTT study on International Space Station (ISS) crewmembers before and after 6-month expeditions. Additionally, in a corresponding study we are using the FTT protocol on subjects before and after 70 days of 6deg head-down bed-rest as an analog for space flight. Bed-rest provides the opportunity for us to investigate the role of prolonged axial body unloading in isolation from the other physiological effects produced by exposure to the microgravity environment of space flight. Therefore, the bed rest analog allows us to investigate the impact of body unloading on both functional tasks and on the underlying physiological factors that lead to decrement in performance and then compare them with the results obtained in our space flight study. Functional tests included ladder climbing, hatch opening, jump down, manual manipulation of objects and tool use, seat egress and obstacle avoidance, recovery from a fall and object translation tasks. Physiological measures included assessments of postural and gait control, dynamic visual acuity, fine motor control, plasma volume, heart rate, blood pressure, orthostatic intolerance, upper- and lower-body muscle strength, power, endurance, control, and neuromuscular drive. ISS crewmembers were tested three times before flight, and on 1, 6, and 30 days after landing. Bed-rest subjects were tested three times before bed-rest and immediately after getting up from bed-rest as well as 1, 6, and 12 days after reambulation.

Bloomberg, Jacob J.↗

NASA NTRS1987

On the saturation of the refractive index structure function. II - Influence of the correlation length on astronomical 'seeing'

A physical length scale in the wavefront corresponding to the parameter (r sub 0) characterizing the loss in detail in a long exposure image is identified, and the influence of the correlation scale of turbulence as r sub 0 approaches this scale is shown. Allowing for the effect of 2-point correlations in the fluctuations of the refractive index, Venkatakrishnan and Chatterjee (1987) proposed a modified law for the phase structure function. It is suggested that the departure of the phase structure function from the 5/3 power law for length scales in the wavefront approaching the correlation scale of turbulence may lead to better 'seeing' at longer wavelengths.

Venkatakrishnan, P.↗

NASA NTRS1977

Total Born approximation cross sections for single electron loss by atoms and ions colliding with atoms

The first born approximation (FBA) is applied to the calculation of single electron loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions were used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors were used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge was explored in the case of hydrogen-like ions. Scaling of the cross section with respect to the target nuclear charge for electron loss by Fe (+25) in collision with neutral atoms ranging from H to Fe is also examined. These results were compared to those of the binary encounter approximation and to the FBA for the case of ionization by completely stripped target ions.

Rule, D. W.↗

NASA NTRS2017

The Functional Task Test: Results from the One-Year Mission

Exposure to the microgravity conditions of spaceflight causes astronauts to experience alterations in multiple physiological systems including sensorimotor disturbances, cardiovascular deconditioning, and loss of muscle mass and strength. Some or all of these changes might affect the ability of crewmembers to perform critical mission tasks immediately after landing on a planetary surface. The goal of our recently completed Functional Task Test (FTT) study was to determine the effects of spaceflight on functional tests that are representative of high priority exploration mission tasks and to identify the key underlying physiological factors that contribute to decrements in performance. The FTT is comprised of seven functional tests and a corresponding set of interdisciplinary physiological measures specifically targeting the sensorimotor, cardiovascular and muscular changes associated with exposure to spaceflight. Both Shuttle and International Space Station (ISS) astronauts were tested before and after spaceflight. Additionally, we conducted a supporting study in which subjects performed the FTT protocol before and after 70 days of 6 deg head-down bed rest, an analog for spaceflight. Two groups of bed rest subjects were studied: one group who performed aerobic and resistive exercise during bed rest using protocols similar to astronauts and one group who served as non-exercise controls. The bed rest analog allowed us to isolate the impact of body unloading without other spaceflight environmental factors on both functional tasks and on the underlying physiological factors that lead to decrements in performance, and then to compare those results with the results obtained in our spaceflight study. As an extension to the FTT study we collected data from one ISS crewmember who experienced 340 days in space using the same FTT protocol used previously to test spaceflight and bed rest subjects. Data were collected three times preflight and 1.7, 7.5 and 36.5 days after landing. The FTT one-year results will be presented at the meeting, and a comparison will be made with data previously obtained using the same protocol on astronauts tested before and after 6 months in space. Future work will focus on collecting data from additional subjects from one-year flights to gain a better assessment of extreme long-duration exposure to spaceflight on both functional measure of performance and physiological metrics.

Bloomberg, J. J↗

NASA NTRS2017

Renin-Angiotensin System (RAS) in Hematopoietic Stem/Progenitor Cells (HS/PC) Predicts Vaso-Reparative Dysfunction and Progression of Diabetic Retinopathy (DR)

Purpose: We tested the hypothesis that loss of angiotensin converting enzyme 2 (ACE2) within diabetic HS/PCs (Hematopoietic Stem/Progenitor Cells) would be detrimental to HS/PC reparative function, and alter their ability to contribute to vascular remodeling in human subjects and rodent models of DR (Diabetic Retinopathy). Methods: Subjects (n52) were recruited as controls (n13) or diabetics (n39) with either no DR, mild non-proliferative DR (NPDR), moderate NPDR, severe NPDR or proliferative DR (PDR). Fluorescein angiograms were analyzed using Vessel Generation Analysis (VESGEN) software in a cohort of subjects. CD34+ HS/PCs were isolated from peripheral blood. RAS (Renin-Angiotensin System) gene expression and migration was measured. Diabetic ACE2 knockout (KO)C57BL6-Ins2 (Akita) mice at 3, 6 and 9 months of diabetes were compared to age-matched controls. Bone marrow HS/PC populations were analyzed by flow cytometry and migration and proliferation studies performed. Results: ACE2 gene expression in human CD34+ cells from diabetics without DR was increased compared to controls (p0.0437). Mas receptor mRNA was also increased in diabetics without DR, but reduced with the onset of NPDR (p0.0002), suggesting a loss of compensation. DR was associated with CD34+ cell migratory dysfunction. By VESGEN analysis, vessel density measured by several confirming parameters in early NPDR (n3) was greater than in normal retina (n6) in both arteries and veins, which suggests active retinal remodeling. ACE2KO-Akita and Akita cohorts showed reduced retinal thickness by OCT (Optical Coherence Tomography) at 9 months of diabetes. Absence of ACE2 in 9-month Akita mice led to an accelerated increase in acellular capillaries compared to diabetic alone. Electroretinogram (ERG) in ACE2KO-Akita mice resulted in persistent deterioration of the neural retina. Reparative function studies showed that ACE2KO exacerbated diabetes-induced impairment of LK (Low Potassium) cell migration and proliferative functions as early as 3-month of diabetes (p0.0019). Conclusions: Retinopathy and adverse vascular remodeling in subjects with diabetes was associated with a loss of the protective arm of RAS in HS/PCs. Loss of ACE2 exacerbated vascular dysfunction in diabetic mice.

retina↗

NASA NTRS1977

Total Born-approximation cross sections for single-electron loss by atoms and ions colliding with atoms

The first Born approximation (FBA) is applied to the calculation of single-electron-loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions are used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors are used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge is explored in the case of hydrogenlike ions. Also examined is the scaling of the cross section with respect to the target nuclear charge for electron loss by Fe(25+) in collision with neutral atoms ranging from H to Fe. These results are compared with those of the binary-encounter approximation (BEA) and with the FBA for the case of ionization by completely stripped target ions. Electron-loss cross sections are also calculated for the ions O(i+) (i = 3-7) and N(i+) (i = 0-6) in collision with He targets in the energy range of approximately 0.1 to 100 MeV/nucleon. These results are found to be in excellent agreement with the available data near the peak of the ionization cross section.

Rule, D. W.↗

NASA NTRS1999

Novel Receptor-Based Countermeasures to Microgravity-Induced Bone Loss

The biological actions mediated by the estrogen receptor (ER), vitamin D receptor (VDR) and Ca(sup 2+) (sub o) -sensing receptor (CaR) play key roles in the normal control of bone growth and skeletal turnover that is necessary for skeletal health. These receptors act by controlling the differentiation and/or function of osteoblasts and osteoclasts, and other cell types within the bone and bone marrow microenvironment. The appropriate use of selective ER modulators (SERMS) which target bone, vitamin D analogs that favor bone formation relative to resorption, and CaR agonists may both stimulate osteoblastogenesis and inhibit osteoclastogenesis and the function of mature osteoclasts, should make it possible to prevent the reduction in bone formation and increase in bone resorption that normally contribute to the bone loss induced by weightlessness. Indeed, there may be synergistic interactions among these receptors that enhance the actions of any one used alone. Therefore, we proposed to: 1) assess the in vitro ability of novel ER, VDR and CaR agonists, alone or in combination, to modulate osteoblastogenesis and mature osteoblast function under conditions of 1g and simulated microgravity; 2) assess the in vitro ability of novel ER, VDR and CaR agonists, alone or in combination, to modulate osteoclastogenesis and bone resorption under conditions of lg and simulated microgravity; and 3) carry out baseline studies on the skeletal localization of the CaR in normal rat bone as well as the in vivo actions of our novel ER- and VDR-based therapeutics in the rat in preparation for their use, alone or in combination, in well-established ground-based models of microgravity and eventually in space flight.

OMalley, Bert W.↗

NASA NTRS2015

The Integrated Medical Model: A Probabilistic Simulation Model Predicting In-Flight Medical Risks

The Integrated Medical Model (IMM) is a probabilistic model that uses simulation to predict mission medical risk. Given a specific mission and crew scenario, medical events are simulated using Monte Carlo methodology to provide estimates of resource utilization, probability of evacuation, probability of loss of crew, and the amount of mission time lost due to illness. Mission and crew scenarios are defined by mission length, extravehicular activity (EVA) schedule, and crew characteristics including: sex, coronary artery calcium score, contacts, dental crowns, history of abdominal surgery, and EVA eligibility. The Integrated Medical Evidence Database (iMED) houses the model inputs for one hundred medical conditions using in-flight, analog, and terrestrial medical data. Inputs include incidence, event durations, resource utilization, and crew functional impairment. Severity of conditions is addressed by defining statistical distributions on the dichotomized best and worst-case scenarios for each condition. The outcome distributions for conditions are bounded by the treatment extremes of the fully treated scenario in which all required resources are available and the untreated scenario in which no required resources are available. Upon occurrence of a simulated medical event, treatment availability is assessed, and outcomes are generated depending on the status of the affected crewmember at the time of onset, including any pre-existing functional impairments or ongoing treatment of concurrent conditions. The main IMM outcomes, including probability of evacuation and loss of crew life, time lost due to medical events, and resource utilization, are useful in informing mission planning decisions. To date, the IMM has been used to assess mission-specific risks with and without certain crewmember characteristics, to determine the impact of eliminating certain resources from the mission medical kit, and to design medical kits that maximally benefit crew health while meeting mass and volume constraints.

Risk Analysis↗

NASA NTRS2015

The Integrated Medical Model: A Probabilistic Simulation Model for Predicting In-Flight Medical Risks

Risk Analysis↗

NASA NTRS1975

A design study of a photorefractive page composer

A laboratory demonstration and preliminary system analysis of a page composer designed to have the dual advantages of low optical loss and small size, were reported. The current page composer is optically addressed and functions by virtue of optically induced refractive index changes in the active material. Laboratory demonstrations of the device were successfully performed using 10 x 10 bit and 128 x 128 bit data arrays. It was established that the only significant obstacle to the construction of a brass-board model working at megabit data rates is the lack of sensitivity of the photorefractive materials which were considered during the course of this study. Possible materials for future consideration are the photoplastics. While they have more than the required sensitivity, their stability and suitability for double exposure holography was not investigated. If a sufficiently sensitive material is found, then the photorefractive page composer could be built to perform in a highly efficient fashion which would result in a overall reduction of the size of the memory system and an easing of the requirements upon the sensitivity of the holographic recording material.

Source record↗

NASA NTRS1978

Eddy diffusivities within Jupiter

The Flasar and Gierasch (1977) model for small-scale thermally driven turbulent convection in rapidly rotating systems is used to estimate eddy diffusivities within Jupiter's atmosphere and interior. It is assumed that heat transport is governed by a mixing-length law, that Jupiter's interior heat flow derives from thermal cooling, and that the entropy loss per nucleon is uniform throughout. A characteristic scalar diffusivity is obtained as a function of pressure level and latitude. The results show that the latitude variation in the diffusivity might be as large as a factor of 100 at 4600 bars. The consequences of such variations are considered.

Flasar, F. M.↗

NASA NTRS1978

Thorium concentrations in the lunar surface. II - Deconvolution modeling and its application to the regions of Aristarchus and Mare Smythii

The broad angular response which characterized the Apollo gamma ray spectrometer resulted in a loss of spatial resolution and some of the contrast in determining surface concentrations within lunar regions small compared to the field of view. A deconvolution technique has been developed which removes much of this instrumental effect, thereby improving both spatial resolution and accuracy at the cost of a loss in precision. Geometric models of regional thorium distribution are convoluted through the response function of the instrument to yield a predicted distribution which is compared with the observed data field for quality of fit. Application to areas which include Aristarchus and Mare Smythii confirm some geological relationships and fail to support others.

Haines, E. L.↗

NASA NTRS1980

The sensitivity of a very long baseline interferometer

The theoretical sensitivity of various methods of acquiring and processing interferometer data are compared. It is shown that for a fixed digital recording capacity one bit quantization of single sideband data filtered with a rectangular bandpass and sampled at the Nyquist rate yields the optimum signal to noise ratio. The losses which result from imperfect bandpass, poor image rejection, approximate methods of fringe rotation, fractional bit correction, and loss of quadrature are discussed. Also discussed is the use of the complex delay function as a maximum likelihood fringe estimator.

Rogers, A. E. E.↗

NASA NTRS1980

The energy balance of the solar transition region

It is shown how the observed distribution of the emission measure with temperature can be used to limit the range of energy deposition functions suitable for heating the solar transition region and inner corona. The minimum energy loss solution is considered in view of the work by Hearn (1975) in order to establish further scaling laws between the transition region pressure, the maximum coronal temperature and the parameter giving the absolute value of the emission measure. Also discussed is the absence of a static energy balance at the base of the transition region in terms of measurable atmospheric parameters, and the condition for a static energy balance is given. In addition, the possible role of the emission from He II in stabilizing the atmosphere by providing enhanced radiation loss is considered.

Jordan, C.↗

NASA NTRS1981

Stability of individual loudness functions obtained by magnitude estimation and production

A correlational analysis of individual magnitude estimation and production exponents at the same frequency is performed, as is an analysis of individual exponents produced in different sessions by the same procedure across frequency (250, 1000, and 3000 Hz). Taken as a whole, the results show that individual exponent differences do not decrease by counterbalancing magnitude estimation with magnitude production and that individual exponent differences remain stable over time despite changes in stimulus frequency. Further results show that although individual magnitude estimation and production exponents do not necessarily obey the .6 power law, it is possible to predict the slope of an equal-sensation function averaged for a group of listeners from individual magnitude estimation and production data. On the assumption that individual listeners with sensorineural hearing also produce stable and reliable magnitude functions, it is also shown that the slope of the loudness-recruitment function measured by magnitude estimation and production can be predicted for individuals with bilateral losses of long duration. Results obtained in normal and pathological ears thus suggest that individual listeners can produce loudness judgements that reveal, although indirectly, the input-output characteristic of the auditory system.

Hellman, R. P.↗

NASA NTRS1982

Deep space communication - A one billion mile noisy channel

Deep space exploration is concerned with the study of natural phenomena in the solar system with the aid of measurements made at spacecraft on deep space missions. Deep space communication refers to communication between earth and spacecraft in deep space. The Deep Space Network is an earth-based facility employed for deep space communication. It includes a network of large tracking antennas located at various positions around the earth. The goals and achievements of deep space exploration over the past 20 years are discussed along with the broad functional requirements of deep space missions. Attention is given to the differences in space loss between communication satellites and deep space vehicles, effects of the long round-trip light time on spacecraft autonomy, requirements for the use of massive nuclear power plants on spacecraft at large distances from the sun, and the kinds of scientific return provided by a deep space mission. Problems concerning a deep space link of one billion miles are also explored.

Smith, J. G.↗