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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Influence of Transient Atmospheric Circulation on the Surface Heating of the Pacific Warm Pool

Analyses of data on clouds, winds, and surface heat fluxes show that the transient behavior of basin-wide large-scale circulation has a significant influence on the warm pool sea surface temperature (SST). Trade winds converge to regions of the highest SST in the equatorial western Pacific. These regions have the largest cloud cover and smallest wind speed. Both surface solar heating and evaporative cooling are weak. The reduced evaporative cooling due to weakened winds exceeds the reduced solar heating due to enhanced cloudiness. The result is a maximum surface heating in the strong convective and high SST regions. Data also show that the maximum surface heating in strong convective regions is interrupted by transient atmospheric and oceanic circulation. Due to the seasonal variation of the insolation at the top of the atmosphere, trade winds and clouds also experience seasonal variations. Regions of high SST and low-level convergence follow the Sun, where the surface heating is a maximum. As the Sun moves away from a convective region, the strong trade winds set in, and the evaporative cooling enhances, resulting in a net cooling of the surface. During an El Nino, the maximum SST and convective region shifts eastward from the maritime continent to the equatorial central Pacific. Following the eastward shift of the maximum SST, the region of maximum cloudiness and surface heating also shift eastward. As the atmospheric and oceanic circulation returns to normal situations, the trade winds increase and the surface heating decreases. We conclude that the evaporative cooling associated with the seasonal and interannual variations of trade winds is one of the major factors that modulate the SST distribution of the Pacific warm pool.

Chou, Ming-Dah↗
NASA NTRS2004

Transient Liquid Water as a Mechanism for Induration of Soil Crusts on Mars

The Viking and the Mars Exploration Rover missions observed that the surface of Mars is encrusted by a thinly cemented layer tagged as "duricrust". A hypothesis to explain the formation of duricrust on Mars should address not only the potential mechanisms by which these materials become cemented, but also the textural and compositional components of cemented Martian soils. Elemental analyzes at five sites on Mars show that these soils have sulfur content of up to 4%, and chlorine content of up to 1%. This is consistent with the presence of sulfates and halides as mineral cements. . For comparison, the rock "Adirondack" at the MER site, after the exterior layer was removed, had nearly five times lower sulfur and chlorine content , and the Martian meteorites have ten times lower sulfur and chlorine content, showing that the soil is highly enriched in the saltforming elements compared with rock.Here we propose two alternative models to account for the origin of these crusts, each requiring the action of transient liquid water films to mediate adhesion and cementation of grains. Two alternative versions of the transient water hypothesis are offered, a top down hypothesis that emphasizes the surface deposition of frost, melting and downward migration of liquid water and a bottom up alternative that proposes the presence of interstitial ice/brine, with the upward capillary migration of liquid water.

Landis, G. A.↗
NASA NTRS2003

Transient Simulation of the Integrated Powerhead Demonstrator (IPD) Rocket Engine

The IPD rocket engine is the product of a joint Air Force/NASA program to demonstrate the concept of a full-flow staged combustion power cycle. In this type of rocket engine cycle, both the entire fuel flow and the entire oxidizer flow are combusted in one of two pre-bumers and used to drive two turbopumps, thus utilizing the flow work of the total propellant flow. The basis of the IPD engine program relies on integrating newly developed and pre-existing hardware to demonstrate the component and material technologies to make this concept feasible, while simultaneously saving development time and costs. To provide insight to the project team and contractors during engine development and test phases, the engine system was modeled at MSFC using the Rocket Engine Transient Simulation (ROCETS) software to analyze system performance and determine component integration issues. The ROCETS software is used extensively a MSFC to perform steady-state power-balances and transient simulations of thermodynamic power and general fluid systems. The software is favored for its capability to solve large systems of non-linear equations, its librarie of fluid properties and flow devices, its flexibility to modify existing code to improve the physics-derived approximations of real fluid thermodynamic behavior, and the ability to add unique system constraints. The purpose of this paper is to present the methodology used to model the IPD engine system, detail the pitfalls encountered with the software, and explain the approximations made to more accurately represent engine component and fluid behavior. Engine system performance output from the model will be presented and explained in comparison with real fluid and component behavior.

Guidos, Mike↗
NASA NTRS2004

Transient Region Coverage in the Propulsion IVHM Technology Experiment

Over the last several years researchers at NASA Glenn and Ames Research Centers have developed a real-time fault detection and isolation system for propulsion subsystems of future space vehicles. The Propulsion IVHM Technology Experiment (PITEX), as it is called follows the model-based diagnostic methodology and employs Livingstone, developed at NASA Ames, as its reasoning engine. The system has been tested on,flight-like hardware through a series of nominal and fault scenarios. These scenarios have been developed using a highly detailed simulation of the X-34 flight demonstrator main propulsion system and include realistic failures involving valves, regulators, microswitches, and sensors. This paper focuses on one of the recent research and development efforts under PITEX - to provide more complete transient region coverage. It describes the development of the transient monitors, the corresponding modeling methodology, and the interface software responsible for coordinating the flow of information between the quantitative monitors and the qualitative, discrete representation Livingstone.

Balaban, Edward↗
NASA NTRS2004

Radiation-Induced Transient Effects in Near Infrared Focal Plane Arrays

This viewgraph presentation describes a test simulate the transient effects of cosmic ray impacts on near infrared focal plane arrays. The objectives of the test are to: 1) Characterize proton single events as function of energy and angle of incidence; 2) Measure charge spread (crosstalk) to adjacent pixels; 3) Assess transient recovery time.

Reed, Robert A.↗
NASA NTRS2004

Numerical Simulation of Roughness-Induced Transient Growth in a Laminar Boundary Layer

Numerical simulations are used to examine the roughness-induced transient growth in a laminar boundary-layer flow. Based on the spectral element method, these simulations model the stationary disturbance field associated with a nonsmooth roughness geometry, such as the spanwise periodic array of circular disks used by White and co-workers during a series of wind tunnel experiments at Case Western Reserve University. Besides capturing the major trends from the recent measurements by White and Ergin, the simulations provide additional information concerning the relative accuracy of the experimental findings derived from two separate wall-finding procedures. The paper also explores the dependence of transient growth on geometric characteristics of the roughness distribution, including the height and planform shape of the roughness element and the ratio of roughness due to spacing between an adjacent pair of elements. Results are used for a preliminary assessment of the differences between recently reported theoretical results of Tumin and Reshotko and the measurements by White and Ergin.

Fischer, Paul↗
NASA NTRS2004

Torque Transient of Magnetically Drive Flow for Viscosity Measurement

Viscosity is a good indicator of structural changes for complex liquids, such as semiconductor melts with chain or ring structures. This paper discusses the theoretical and experimental results of the transient torque technique for non-intrusive viscosity measurement. Such a technique is essential for the high temperature viscosity measurement of high pressure and toxic semiconductor melts. In this paper, our previous work on oscillating cup technique was expanded to the transient process of a magnetically driven melt flow in a damped oscillation system. Based on the analytical solution for the fluid flow and cup oscillation, a semi-empirical model was established to extract the fluid viscosity. The analytical and experimental results indicated that such a technique has the advantage of short measurement time and straight forward data analysis procedures

Ban, Heng↗
NASA NTRS1998

Tape-Drop Transient Model for In-Situ Automated Tape Placement of Thermoplastic Composites

Composite parts of nonuniform thickness can be fabricated by in-situ automated tape placement (ATP) if the tape can be started and stopped at interior points of the part instead of always at its edges. This technique is termed start/stop-on-the-part, or, alternatively, tape-add/tape-drop. The resulting thermal transients need to be managed in order to achieve net shape and maintain uniform interlaminar weld strength and crystallinity. Starting-on-the-part has been treated previously. This paper continues the study with a thermal analysis of stopping-on-the-part. The thermal source is switched off when the trailing end of the tape enters the nip region of the laydown/consolidation head. The thermal transient is determined by a Fourier-Laplace transform solution of the two-dimensional, time-dependent thermal transport equation. This solution requires that the Peclet number Pe (the dimensionless ratio of inertial to diffusive heat transport) be independent of time and much greater than 1. Plotted isotherms show that the trailing tape-end cools more rapidly than the downstream portions of tape. This cooling can weaken the bond near the tape end; however the length of the affected region is found to be less than 2 mm. To achieve net shape, the consolidation head must continue to move after cut-off until the temperature on the weld interface decreases to the glass transition temperature. The time and elapsed distance for this condition to occur are computed for the Langley ATP robot applying PEEK/carbon fiber composite tape and for two upgrades in robot performance. The elapsed distance after cut-off ranges from about 1 mm for the present robot to about 1 cm for the second upgrade.

Costen, Robert C.↗
NASA NTRS2003

Tidal volume single-breath washin of SF6 and CH4 in transient microgravity

We performed tidal volume single-breath washins (SBW) by using tracers of different diffusivity and varied the time spent in microgravity (microG) before the start of the tests to look for time-dependent effects. SF(6) and CH(4) phase III slopes decreased by 35 and 26%, respectively, in microG compared with 1 G (P < 0.05), and the slope difference between gases disappeared. There was no effect of time in microG, suggesting that neither the hypergravity period preceding microG nor the time spent in microG affected gas mixing at volumes near functional residual capacity. In previous studies using SF(6) and He (Lauzon A-M, Prisk GK, Elliott AR, Verbanck S, Paiva M, and West JB. J Appl Physiol 82: 859-865, 1997), the vital capacity SBW showed an increase in slope difference between gases in transient microG, the opposite of the decrease in sustained microG. In contrast, tidal volume SBW showed a decrease in slope difference in both microG conditions. Because it is only the behavior of the more diffusive gas that differed between maneuvers and microG conditions, we speculate that, in the previous vital capacity SBW, the hypergravity period preceding the test in transient microG provoked conformational changes at low lung volumes near the acinar entrance.

Parabolic Flight↗
NASA NTRS2004

Interaction of Strong Transient Interplanetary Disturbances with the Dayside Magnetosphere

The objective of the investigation was to gain an understanding of the complex response of the magnetosphere to strong transient interplanetary disturbances. Because the project was only funded for a year, the investigation focused on only one of the three topics proposed in the original three year proposal. We investigated the response of the dayside auroral region to strong transient interplanetary disturbances. The method of the investigation was to use three-dimensional magnetohydrodynamic (MHD) simulations that employ measurements of the solar wind conditions upstream the bow shock to model actual events and then to compare the simulation results with observations from spacecraft located at downstream locations. We modeled an event that occurred on July 14,2000, for which both CLUSTER and IMAGE simultaneous observations were available. The event was marked by high solar wind dynamic pressure and a strong IMF By component. Comparisons showed a very good agreement between intensifications in the auroral emissions measured by IMAGE

Berchem, Jean↗
NASA NTRS2000

Transient cardio-respiratory responses to visually induced tilt illusions

Although the orthostatic cardio-respiratory response is primarily mediated by the baroreflex, studies have shown that vestibular cues also contribute in both humans and animals. We have demonstrated a visually mediated response to illusory tilt in some human subjects. Blood pressure, heart and respiration rate, and lung volume were monitored in 16 supine human subjects during two types of visual stimulation, and compared with responses to real passive whole body tilt from supine to head 80 degrees upright. Visual tilt stimuli consisted of either a static scene from an overhead mirror or constant velocity scene motion along different body axes generated by an ultra-wide dome projection system. Visual vertical cues were initially aligned with the longitudinal body axis. Subjective tilt and self-motion were reported verbally. Although significant changes in cardio-respiratory parameters to illusory tilts could not be demonstrated for the entire group, several subjects showed significant transient decreases in mean blood pressure resembling their initial response to passive head-up tilt. Changes in pulse pressure and a slight elevation in heart rate were noted. These transient responses are consistent with the hypothesis that visual-vestibular input contributes to the initial cardiovascular adjustment to a change in posture in humans. On average the static scene elicited perceived tilt without rotation. Dome scene pitch and yaw elicited perceived tilt and rotation, and dome roll motion elicited perceived rotation without tilt. A significant correlation between the magnitude of physiological and subjective reports could not be demonstrated.

NASA Center JSC↗
NASA NTRS1984

Voltage transients elicited by sudden step-up of auxin

It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 microvolts and possessing risetimes (10-90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ ionophore.

Calcium/metabolism↗
NASA NTRS1999

Steady and transient fluid shear stress stimulate NO release in osteoblasts through distinct biochemical pathways

Fluid flow has been shown to be a potent stimulus in osteoblasts and osteocytes and may therefore play an important role in load-induced bone remodeling. The objective of this study was to investigate the characteristics of flow-activated pathways. Previously we reported that fluid flow stimulates rapid and continuous release of nitric oxide (NO) in primary rat calvarial osteoblasts. Here we demonstrate that flow-induced NO release is mediated by shear stress and that this response is distinctly biphasic. Transients in shear stress associated with the onset of flow stimulated a burst in NO production (8.2 nmol/mg of protein/h), while steady flow stimulated sustained NO production (2.2 nmol/mg of protein/h). Both G-protein inhibition and calcium chelation abolished the burst phase but had no effect on sustained production. Activation of G-proteins stimulated dose-dependent NO release in static cultures of both calvarial osteoblasts and UMR-106 osteoblast-like cells. Pertussis toxin had no effect on NO release. Calcium ionophore stimulated low levels of NO production within 15 minutes but had no effect on sustained production. Taken together, these data suggest that fluid shear stress stimulates NO release by two distinct pathways: a G-protein and calcium-dependent phase sensitive to flow transients, and a G-protein and calcium-independent pathway stimulated by sustained flow.

Non-NASA Center↗
NASA NTRS1999

Transient and sustained increases in inositol 1,4,5-trisphosphate precede the differential growth response in gravistimulated maize pulvini

The internodal maize pulvinus responds to gravistimulation with differential cell elongation on the lower side. As the site of both graviperception and response, the pulvinus is an ideal system to study how organisms sense changes in orientation. We observed a transient 5-fold increase in inositol 1,4,5-trisphosphate (IP3) within 10 s of gravistimulation in the lower half of the pulvinus, indicating that the positional change was sensed immediately. Over the first 30 min, rapid IP3 fluctuations were observed between the upper and lower halves. Maize plants require a presentation time of between 2 and 4 h before the cells on the lower side of the pulvinus are committed to elongation. After 2 h of gravistimulation, the lower half consistently had higher IP3, and IP3 levels on the lower side continued to increase up to approximately 5-fold over basal levels before visible growth. As bending became visible after 8-10 h, IP3 levels returned to basal values. Additionally, phosphatidylinositol 4-phosphate 5-kinase activity in the lower pulvinus half increased transiently within 10 min of gravistimulation, suggesting that the increased IP3 production was accompanied by an up-regulation of phosphatidylinositol 4, 5-bisphosphate biosynthesis. Neither IP3 levels nor phosphatidylinositol 4-phosphate 5-kinase activity changed in pulvini halves from vertical control plants. Our data indicate the involvement of IP3 and inositol phospholipids in both short- and long-term responses to gravistimulation. As a diffusible second messenger, IP3 provides a mechanism to transmit and amplify the signal from the perceiving to the responding cells in the pulvinus, coordinating a synchronized growth response.

NASA Discipline Plant Biology↗
NASA NTRS2004

The Burst and Transient Source Experiment (BATSE) Earth Occultation Catalog of Low-Energy Gamma-Ray Sources

The Burst and Transient Source Experiment (BATSE), aboard the Compton Gamma Ray Observatory (CGRO), provided a record of the low-energy gamma-ray sky (approx. 20-1000 keV) between 1991 April and 2000 May (9.1 yr). BATSE monitored the high-energy sky using the Earth occultation technique (EOT) for point sources whose emission extended for times on the order of the CGRO orbital period (approx. 92 min) or greater. Using the EOT to extract flux information, a catalog of sources using data from the BATSE Large Area Detectors has been prepared. The first part of the catalog consists of results from the all-sky monitoring of 58 sources, mostly Galactic, with intrinsic variability on timescales of hours to years. For these sources, we have included tables of flux and spectral data, and outburst times for transients. Light curves (or flux histories) have been placed on the World Wide Web. We then performed a deep sampling of these 58 objects, plus a selection of 121 more objects, combining data from the entire 9.1 yr BATSE data set. Source types considered were primarily accreting binaries, but a small number of representative active galaxies, X-ray-emitting stars, and supernova remnants were also included. The sample represents a compilation of sources monitored and/or discovered with BATSE and other high-energy instruments between 1991 and 2000, known sources taken from the HEAO 1 A-4 and Macomb & Gehrels catalogs. The deep sample results include definite detections of 83 objects and possible detections of 36 additional objects. The definite detections spanned three classes of sources: accreting black hole and neutron star binaries, active galaxies, and Supernova remnants. The average fluxes measured for the fourth class, the X-ray emitting stars, were below the confidence limit for definite detection.

Harmon, B. A.↗
NASA NTRS1997

Human circadian pacemaker is sensitive to light throughout subjective day without evidence of transients

Fifty-six resetting trials were conducted across the subjective day in 43 young men using a three-cycle bright-light (approximately 10,000 lx). The phase-response curve (PRC) to these trials was assessed for the presence of a "dead zone" of photic insensitivity and was compared with another three-cycle PRC that had used a background of approximately 150 lx. To assess possible transients after the light stimulus, the trials were divided into 43 steady-state trials, which occurred after several baseline days, and 13 consecutive trials, which occurred immediately after a previous resetting trial. We found that 1) bright light induces phase shifts throughout subjective day with no apparent dead zone; 2) there is no evidence of transients in constant routine assessments of the fitted temperature minimum 1-2 days after completion of the resetting stimulus; and 3) the timing of background room light modulates the resetting response to bright light. These data indicate that the human circadian pacemaker is sensitive to light at virtually all circadian phases, implying that the entire 24-h pattern of light exposure contributes to entrainment.

NASA Discipline Regulatory Physiology↗
NASA NTRS2005

Transient Mathematical Modeling for Liquid Rocket Engine Systems: Methods, Capabilities, and Experience

The subject of mathematical modeling of the transient operation of liquid rocket engines is presented in overview form from the perspective of engineers working at the NASA Marshall Space Flight Center. The necessity of creating and utilizing accurate mathematical models as part of liquid rocket engine development process has become well established and is likely to increase in importance in the future. The issues of design considerations for transient operation, development testing, and failure scenario simulation are discussed. An overview of the derivation of the basic governing equations is presented along with a discussion of computational and numerical issues associated with the implementation of these equations in computer codes. Also, work in the field of generating usable fluid property tables is presented along with an overview of efforts to be undertaken in the future to improve the tools use for the mathematical modeling process.

Seymour, David C.↗
NASA NTRS2006

The Galactic Black Hole Transient H1743-322 During Outburst Decay Connections Between Timing Noise, State Transitions, And Radio Emission

Multiwavelength observations of Galactic black hole transients during outburst decay are instrumental for our understanding of the accretion geometry and the formation of outflows around black hole systems. H1743-322, a black hole transient observed intensely in X-rays and also covered in the radio band during its 2003 decay, provides clues about the changes in accretion geometry during state transitions and also the general properties of X-ray emission during the intermediate and low-hard states. In this work, we report on the evolution of spectral and temporal properties in X-rays and the flux in the radio band, with the goal of understanding the nature of state transitions observed in this source. We concentrate on the transition from the thermal dominant state to the intermediate state that occurs on a timescale of 1 day. We show that the state transition is associated with a sudden increase in power-law flux. We determine that the ratio of the power-law flux to the overall flux in the 3-25 keV band must exceed 0.6 for us to observe strong timing noise. Even after the state transition, once this ratio was below 0.6, the system transited back to the thermal dominant state for 1 day. We show that the emission from the compact radio core does not turn on during the transition from the thermal dominant state to the intermediate state but does turn on when the source reaches the low-hard state, as seen in 4U 1543-47 and GX 339-4. We find that the photon index correlates strongly with the QPO frequency and anticorrelates with the rms amplitude of variability. We also show that the variability is more likely to be associated with the power-law emission than the disk emission.

Kalemci, E.↗