Deep Space 1 Autonomous Navigation
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Navigation Autonomous DS1 New Millenium↗
Engineering topics
Wang, M.
Publications and source records attributed to Wang, M..
Angiotensin-(1-7) antagonist [D-Ala7-Ang-(1-7);A-779] attenuates post-suspension hypotension in Sprague-Dawley rats
Cardiovascular deconditioning manifested by reduction in mean arterial pressure (MAP) and cardioaccleration are usually observed in astronauts during standing postflight. The head-down tilt (HDT) rat model with "unloaded" hindlimbs has been extensively studied because some of the observed responses mimic observations made during exposure to microgravity. Angiotensin-(1-7) is a biologically active component of the renin-angiotensin system that acts to oppose the pressor and proliferative actions of Angiotensin II. It produces a hypotensive response by either stimulating production of vasodilator prostaglandins (i.e., prostacyclin), increasing nitric oxide or both. In the present study, we have evaluated the role of a specific inhibitor of Ang-(1-7), D-Ala7-Ang-(1-7)[A-779], as a countermeasure against post-suspension hypotension.
Hindlimb Suspension↗
Intrinsic Stability of Concentration Field in Diffusion Limited Growth and its Effects on Crystallization
No abstract available
Wang, M.↗
Hydroacoustic forcing function modeling using DNS database
A wall pressure frequency spectrum model (Blake 1971 ) has been evaluated using databases from Direct Numerical Simulations (DNS) of a turbulent boundary layer (Na & Moin 1996). Good agreement is found for moderate to strong adverse pressure gradient flows in the absence of separation. In the separated flow region, the model underpredicts the directly calculated spectra by an order of magnitude. The discrepancy is attributed to the violation of the model assumptions in that part of the flow domain. DNS computed coherence length scales and the normalized wall pressure cross-spectra are compared with experimental data. The DNS results are consistent with experimental observations.
Zawadzki, I.↗
An optimized index of human cardiovascular adaptation to simulated weightlessness
Prolonged exposure to weightlessness is known to produce a variety of cardiovascular changes, some of which may influence the astronaut's performance during a mission. In order to find a reliable indicator of cardiovascular adaptation to weightlessness, we analyzed data from nine male subjects after a 24-hour period of normal activity and after a period of simulated weightlessness produced by two hours in a launch position followed by 20 hours of 6 degrees head-down tilt plus pharmacologically induced diuresis (furosemide). Heart rate, arterial pressure, thoracic fluid index, and radial flow were analyzed. Autoregressive spectral estimation and decomposition were used to obtain the spectral components of each variable from the subjects in the supine position during pre- and post-simulated weightlessness. We found a significant decrease in heart rate power and an increase in thoracic fluid index power in the high frequency region (0.2-0.45 Hz) and significant increases in radial flow and arterial pressure powers in the low frequency region (<0.2 Hz) in response to simulated weightlessness. However, due to the variability among subjects, any single variable appeared limited as a dependable index of cardiovascular adaptation to weightlessness. The backward elimination algorithm was then used to select the best discriminatory features from these spectral components. Fisher's linear discriminant and Bayes' quadratic discriminant were used to combine the selected features to obtain an optimal index of adaptation to simulated weightlessness. Results showed that both techniques provided improved discriminant performance over any single variable and thus have the potential for use as an index to track adaptation and prescribe countermeasures to the effects of weightlessness.
NASA Discipline Number 14-10↗
Cardiovascular regulation in humans in response to oscillatory lower body negative pressure
The frequency response characteristics of human cardiovascular regulation during hypotensive stress have not been determined. We therefore exposed 10 male volunteers to seven frequencies (0.004-0.1 Hz) of oscillatory lower body negative pressure (OLBNP; 0-50 mmHg). Fourier spectra of arterial pressure (AP), central venous pressure (CVP), stroke volume (SV), cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) were determined and first harmonic mean, amplitude, and phase angles with respect to OLBNP are presented. AP was relatively well regulated as demonstrated by small oscillations in half amplitude (3.5 mmHg) that were independent of OLBNP frequency and similar to unstressed control spectra. Due to the biomechanics of the system, the magnitudes of oscillations in calf circumference (CC) and CVP decreased with increasing frequency; therefore, we normalized responses by these indexes of the fluid volume shifted. The ratios of oscillations in AP to oscillations in CC increased by an order of magnitude, whereas oscillations in CVP to oscillations in CC and oscillations in AP to oscillations in CVP both tripled between 0.004 and 0.1 Hz. Therefore, even though the amount of fluid shifted by OLBNP decreased with increasing frequency, the magnitude of both CVP and AP oscillations per volume of fluid shifted increased (peaking at 0.08 Hz). The phase relationships between variables, particularly the increasing lags in SV and TPR, but not CVP, indicated that efferent responses with lags of 5-6 s could account for the observed responses. We conclude that, at frequencies below 0.02 Hz, the neural system of humans functioned optimally in regulating AP; OLBNP-induced decreases in SV (by as much as 50%) were counteracted by appropriate oscillations in HR and TPR responses. As OLBNP frequency increased, SV, TPR, and HR oscillations increasingly lagged the input and became less optimally timed for AP regulation.
NASA Discipline Cardiopulmonary↗
Dynamic testbed laboratory and micro-optics
Objectives of this research are as follows: to understand the three classes of superresolution and their behavior in optical data storage systems; to investigate new and improved components and techniques in the optical system for data detection and servo control; to apply micro-optic components to the optical system to reduce size and weight; to investigate techniques, such as near-field optical probes, for recording data densities beyond that possible with superresolution; and to understand and find solutions for problems associated with dynamic testing, especially those that arise when evaluating blue-sensitive media.
Milster, T.↗
Spectral analysis of resting cardiovascular variables and responses to oscillatory LBNP before and after 6 degree head dowm bedrest
A major focus of our research program is to develop noninvasive procedures for determining changes in cardiovascular function associated with the null gravity environment. We define changes in cardiovascular function to be (1) the result of the regulatory system operating at values different from 'normal' but with an overall control system basically unchanged by the null gravity exposure, or (2) the result of operating with a control system that has significantly different regulatory characteristics after an exposure. To this end, we have used a model of weightlessness that consisted of exposing humans to 2 hrs. in the launch position, followed by 20 hrs. of 6 deg head down bedrest. Our principal objective was to use this model to measure cardiovascular responses to the 6 deg head down bedrest protocol and to develop the most sensitive 'systems identification' procedure for indicating change. A second objective, related to future experiments, is to use the procedure in combination with experiments designed to determine the degree to which a regulatory pathway has been altered and to determine the mechanisms responsible for the changes.
Knapp, Charles F.↗
Far-infrared laser power measurements.
Peak and average output power of cyanide laser in far IR measured, indicating usefulness of available oversize waveguide instrumentation at HF
FAR INFRARED↗