SEARCH · Engineering Papers

Results for “Natural Probabilities”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17

All sources NASA NTRS DOE OSTI

NASA NTRS1994

Broad features of surface ozone variations over Indian region

Surface ozone concentration at three Indian stations - New Delhi (28.6 deg N), Pune (18.5 deg N) and Thiruvananthapuram (formerly Trivandrum (8.3 deg N) - has been measured since 1973 with the help of an electrochemical continuous ozone recorder. These stations show diurnal, seasonal and annual cycles in surface ozone. Daily changes show that the minimum value occurs at sunrise and maximum in the afternoon. As regards seasonal variations, Thiruvananthapuram and Pune have a minimum value during monsoon season (June to August) while at New Delhi the minimum value occurs in January. However, New Delhi also records low ozone amount during monsoon season identical to the amounts show at Thiruvananthapuram and Pune. The annual cycles at these stations have been compared with similar measurements in the northern and southern hemispheres. The Indian measurements agree well with the annual cycles at these stations. Further, the analysis of the Indian data indicates that the major contribution in surface ozone comes from the natural sources like stratospheric-tropospheric exchange, turbulence, and mixing in the boundary layer; however, a small contribution from anthropogenic sources cannot be ruled out at Pune and probably at New Delhi, especially in winter and summer seasons.

Shende, R. R.↗

NASA NTRS1995

Whisker/Cone growth on the thermal control surfaces experiment no. S0069

An unusual surface 'growth' was found during scanning electron microscope (SEM) investigations of the Thermal Control Surface Experiment (TCSE) S0069 front thermal cover. This 'growth' is similar to the cone type whisker growth phenomena as studied by G. K. Wehner beginning in the 1960's. Extensive analysis has identified the most probable composition of the whiskers to be a silicate type glass. Sources of the growth material are outgassing products from the experiment and orbital atomic oxygen, which occurs naturally at the orbital altitudes of the LDEF mission in the form of neutral atomic oxygen. The highly ordered symmetry and directionality of the whiskers are attributed to the long term (5.8 year) stable flight orientation of the LDEF.

Zwiener, James M.↗

NASA NTRS1994

Ultrasound as a Noninvasive Method to Assess Changes of Intracranial Volume and Pressure During Simulated Microgravity

Headaches are commonly experienced by astronauts in microgravity and by subjects undergoing head-down tilt (simulated microgravity on Earth). Exposure to microgravity probably elevates blood pressure and flow in the head which may increase intracranial volume (ICV) and pressure (ICP) and in turn cause headache. Due to the slightly compliant nature of the cranial vault and the encasement of brain and its vasculature within this vault, any increase of ICV will increase ICP and slightly distend the cranium. Previous studies document perivascular edema and increased ICP in rhesus monkeys during head-down tilt. Elevated ICP has also been reported in humans during head-down tilt. ICP measurements in healthy humans are rare because of the invasiveness of currently-available measurement techniques. Therefore, we proposed a noninvasive ultrasound technique to assess changes of ICV and JCP. The ultrasound principle is based on compliance of the cranial vault. A 450 kHz ultrasound stimulus is transmitted through the cranium by a transducer every 7.5-10 msec. The ultrasound wave enters the brain tissue, reflects off the opposite side of the cranium and is received by the same transducer. The detected wave is compared for phase quadrature (90 deg.to transmitted wave). Because the electronic circuitry of the device maintains a 90 deg. phase (phi), any alterations in the detected wave caused by an increase of ICV and ICP will be reflected as a change in the wave frequency. Phase shift is directly proportional to path length of the wave, DELTA x, which is expressed as DELTA x = phi lambda/2 pi where lambda is wavelength. Elevated ICV and ICP expand the cranial vault and increase path length of the wave (a measure of intracranial distance). Increased path length equals reduced frequency of the detected wave. Reduced frequency is then related to elevated ICP. This technique has potential uses for ICP studies of astronauts in space and head trauma patients on Earth.

Murthy, G.↗

NASA NTRS2006

The Effects of Ultra-Long-Range Flights on the Alertness and Performance of Aviators

This investigation assessed the impact of ultra-long-range (ULR) simulator flights, departing either in the morning or late evening, on the alertness and performance of 17 commercial aviators. Immediately prior to and throughout each flight, alertness and performance were assessed via a computerized test of sustained attention, subjective questionnaires, and "hand-flying" tasks. There were fatigue-related effects on the majority of assessments, and the nature of these effects was consistent across the vigilance and self-report measures. However, the operational "hand-flying" manuevers proved insensitive to the impact of fatigue probably due to procedural factors. Regardless, the results of the present study suggest that fatigue associated with prolonged wakefulness in ULR flight operations will interact with flight schedules due to circadian and homeostatic influences. In this study, the pilots departing at night were at a greater initial disadvantage (during cruise) than pilots who departed earlier in the day; whereas those who departed earlier tended to be most impaired towards the end of the flight prior to landing. In real-world operations, airlines should consider the ramifications of flight schedules and what is known about human sleep and circadian rhythms to optimize safety.

Caldwell, John A.↗

NASA NTRS1992

Nature and evolution of the early Martian atmosphere: Evidence from highland crater populations

Release of water in a CO2 rich atmosphere by precipitation and channel forming processes has led to speculation on the creation of Martian carbonate deposits. On Mars water probably was not on the surface long enough to allow eroded material to concentrate, raise the pH, and induce the formation of carbonates. This suggests that the Martian primordial atmosphere could be thinner (approximately 5 bars) and still allow highland degradation to occur over a long period of time (.45 to 1.2 billion years).

Craddock, Robert A.↗

NASA NTRS1978

Determination of the Solar Energy Microclimate of the United States Using Satellite Data

The determination of total solar energy reaching the ground over the United States using measurements from meteorological satellites as the basic data set is examined. The methods of satellite data processing are described. Uncertainty analysis and comparison of results with well calibrated surface pyranometers are used to estimate the probable error in the satellite-based determination of ground insolation. It is 10 to 15 percent for daily information, and about 5 percent for monthly values. However, the natural space and time variability of insolation is much greater than the uncertainty in the method. The most important aspect of the satellite-based technique is the ability to determine the solar energy reaching the ground over small areas where no other measurements are available. Thus, it complements the widely spaced solar radiation measurement network of ground stations.

Vonderharr, T. H.↗

NASA NTRS1981

Two major dust storms, one Mars year apart - Comparison from Viking data

The Viking Mars Landers have been on the Mars surface for over two Mars years. During the first year two major, probably global, dust storms occurred. The first was unusually early compared to most previous earth-based observations. A major storm occurred during the second year, almost precisely one year after the first storm of the first year. Meteorological data show roughly similar atmospheric behavior for the two early storms. Of particular note is the increase in amplitude of pressure oscillations (probably of baroclinic origin) and concurrent increases in wind speed during the build-up phase of all three storms. The generation of these waves appears to be a natural consequence of seasonal effects not associated with the dust storms. It is suggested that baroclinic waves, should they exist in the Southern Hemisphere during the time of dust storm generation, could be an important factor in the growth and development of the dust storms.

Ryan, J. A.↗

NASA NTRS1981

Kaman 40 kW wind turbine generator - control system dynamics

The generator design incorporates an induction generator for application where a utility line is present and a synchronous generator for standalone applications. A combination of feed forward and feedback control is used to achieve synchronous speed prior to connecting the generator to the load, and to control the power level once the generator is connected. The dynamics of the drive train affect several aspects of the system operation. These were analyzed to arrive at the required shaft stiffness. The rotor parameters that affect the stability of the feedback control loop vary considerably over the wind speed range encountered. Therefore, the controller gain was made a function of wind speed in order to maintain consistent operation over the whole wind speed range. The velocity requirement for the pitch control mechanism is related to the nature of the wind gusts to be encountered, the dynamics of the system, and the acceptable power fluctuations and generator dropout rate. A model was developed that allows the probable dropout rate to be determined from a statistical model of wind gusts and the various system parameters, including the acceptable power fluctuation.

Perley, R.↗

NASA NTRS1985

Reliability of void detection in structural ceramics using scanning laser acoustic microscopy

The reliability of scanning laser acoustic microscopy (SLAM) for detecting surface voids in structural ceramic test specimens was statistically evaluated. Specimens of sintered silicon nitride and sintered silicon carbide, seeded with surface voids, were examined by SLAM at an ultrasonic frequency of 100 MHz in the as fired condition and after surface polishing. It was observed that polishing substantially increased void detectability. Voids as small as 100 micrometers in diameter were detected in polished specimens with 0.90 probability at a 0.95 confidence level. In addition, inspection times were reduced up to a factor of 10 after polishing. The applicability of the SLAM technique for detection of naturally occurring flaws of similar dimensions to the seeded voids is discussed. A FORTRAN program listing is given for calculating and plotting flaw detection statistics.

Roth, D. J.↗

NASA NTRS1984

Thermoluminescence and the shock and reheating history of meteorites. II - Annealing studies of the Kernouve meteorite

Samples of the unshocked, equilibrated chondrite, Kernouve (H6), have been annealed for 1-100 hours at 500-1200 C, their thermoluminescence sensitivity measured and Na, K, Mn, Ca, and Sc determined by instrumental neutron activation analysis. The TL sensitivity decreased with temperature until by 1000 C it had fallen by 40 percent. The process responsible has an activation energy of 8 kcal/mole and probably involves diffusion. Samples annealed 1000-1200 C had TL sensitivities 0.01 times the unannealed values, most of the decrease occurring at 1100 C. This process has an activation energy of 100 kcal/mole and is probably related to the melting of the TL phosphor, feldspar, with some decomposition and loss of Cs, Na and K. Meteorites whose petrography indicates heating above 1100 C by natural shock heating events (shock facies d-f), have TL sensitivities similar to samples annealed above 1100 C.

Sears, D. W. G.↗

NASA NTRS1986

Reliability of void detection in structural ceramics by use of scanning laser acoustic microscopy

Roth, D. J.↗

NASA NTRS1993

Hypervelocity impact facility for simulating materials exposure to impact by space debris

As a result of man's venturing into space, the local debris contributed by his presence exceeds, at some orbital altitudes, that of the natural component. Man's contribution ranges from fuel residue to large derelect satellites that weigh many kilograms. Current debris models are able to predict the growth of the problem and suggest that spacecraft must employ armor or bumper shields for some orbital altitudes now, and that, the problem will become worse as a function of time. The practical upper limit to the velocity distribution is on the order of 40 km/s and is associated with the natural environment. The maximum velocity of the man-made component is in the 14-16 km/s range. The Long Duration Exposure Facility (LDEF) has verified that the 'high probability of impact' particles are in the microgram to milligram range. These particles can have significant effects on coatings, insulators, and thin metallic layers. The surface of thick materials becomes pitted and the local debris component is enhanced by ejecta from the debris spectrum in a controlled environment. The facility capability is discussed in terms of drive geometry, energetics, velocity distribution, diagnostics, and projectile/debris loading. The facility is currently being used to study impact phenomena on Space Station Freedom's solar array structure, other solar array materials, potential structural materials for use in the station, electrical breakdown in the space environment, and as a means of clarifying or duplicating the impact phenomena on the LDEF surfaces. The results of these experiments are described in terms of the mass/velocity distribution incident on selected samples, crater dynamics, and sample geometry.

Rose, M. F.↗

NASA NTRS1996

The General Necessary Condition for the Validity of Dirac's Transition Perturbation Theory

For the first time, from the natural requirements for the successive approximation the general necessary condition of validity of the Dirac's method is explicitly established. It is proved that the conception of 'the transition probability per unit time' is not valid. The 'super-platinium rules' for calculating the transition probability are derived for the arbitrarily strong time-independent perturbation case.

Quang, Nguyen Vinh↗

NASA NTRS1994

Metabolic activity of microorganisms in evaporites

Crystalline salt is generally considered so hostile to most forms of life that it has been used for centuries as a preservative. Here, we present evidence that prokaryotes inhabiting a natural evaporite crust of halite and gypsum are metabolically active while inside the evaporite for at least 10 months. In situ measurements demonstrated that some of these "endoevaporitic" microorganisms (probably the cyanobacterium Synechococcus Nageli) fixed carbon and nitrogen. Denitrification was not observed. Our results quantified the slow microbial activity that can occur in salt crystals. Implications of this study include the possibility that microorganisms found in ancient evaporite deposits may have been part of an evaporite community.

NASA Discipline Exobiology↗

NASA NTRS2004

Proceedings from the 2nd International Symposium on Formation Flying Missions and Technologies

Topics discussed include: The Stellar Imager (SI) "Vision Mission"; First Formation Flying Demonstration Mission Including on Flight Nulling; Formation Flying X-ray Telescope in L2 Orbit; SPECS: The Kilometer-baseline Far-IR Interferometer in NASA's Space Science Roadmap Presentation; A Tight Formation for Along-track SAR Interferometry; Realization of the Solar Power Satellite using the Formation Flying Solar Reflector; SIMBOL-X : Formation Flying for High-Energy Astrophysics; High Precision Optical Metrology for DARWIN; Close Formation Flight of Micro-Satellites for SAR Interferometry; Station-Keeping Requirements for Astronomical Imaging with Constellations of Free-Flying Collectors; Closed-Loop Control of Formation Flying Satellites; Formation Control for the MAXIM Mission; Precision Formation Keeping at L2 Using the Autonomous Formation Flying Sensor; Robust Control of Multiple Spacecraft Formation Flying; Virtual Rigid Body (VRB) Satellite Formation Control: Stable Mode-Switching and Cross-Coupling; Electromagnetic Formation Flight (EMFF) System Design, Mission Capabilities, and Testbed Development; Navigation Algorithms for Formation Flying Missions; Use of Formation Flying Small Satellites Incorporating OISL's in a Tandem Cluster Mission; Semimajor Axis Estimation Strategies; Relative Attitude Determination of Earth Orbiting Formations Using GPS Receivers; Analysis of Formation Flying in Eccentric Orbits Using Linearized Equations of Relative Motion; Conservative Analytical Collision Probabilities for Orbital Formation Flying; Equations of Motion and Stability of Two Spacecraft in Formation at the Earth/Moon Triangular Libration Points; Formations Near the Libration Points: Design Strategies Using Natural and Non-Natural Ares; An Overview of the Formation and Attitude Control System for the Terrestrial Planet Finder Formation Flying Interferometer; GVE-Based Dynamics and Control for Formation Flying Spacecraft; GNC System Design for a New Concept of X-Ray Distributed Telescope; GNC System for the Deployment and Fine Control of the DARWIN Free-Flying Interferometer; Formation Algorithm and Simulation Testbed; and PLATFORM: A Formation Flying, RvD and Robotic Validation Test-bench.

Source record↗

NASA NTRS2010

SERVIR-Africa: Developing an Integrated Platform for Floods Disaster Management in Africa

SERVIR-Africa is an ambitious regional visualization and monitoring system that integrates remotely sensed data with predictive models and field-based data to monitor ecological processes and respond to natural disasters. It aims addressing societal benefits including floods and turning data into actionable information for decision-makers. Floods are exogenous disasters that affect many parts of Africa, probably second only to drought in terms of social-economic losses. This paper looks at SERVIR-Africa's approach to floods disaster management through establishment of an integrated platform, floods prediction models, post-event flood mapping and monitoring as well as flood maps dissemination in support of flood disaster management.

Macharia, Daniel↗

NASA NTRS2012

Uncertainty Quantification for Polynomial Systems via Bernstein Expansions

This paper presents a unifying framework to uncertainty quantification for systems having polynomial response metrics that depend on both aleatory and epistemic uncertainties. The approach proposed, which is based on the Bernstein expansions of polynomials, enables bounding the range of moments and failure probabilities of response metrics as well as finding supersets of the extreme epistemic realizations where the limits of such ranges occur. These bounds and supersets, whose analytical structure renders them free of approximation error, can be made arbitrarily tight with additional computational effort. Furthermore, this framework enables determining the importance of particular uncertain parameters according to the extent to which they affect the first two moments of response metrics and failure probabilities. This analysis enables determining the parameters that should be considered uncertain as well as those that can be assumed to be constants without incurring significant error. The analytical nature of the approach eliminates the numerical error that characterizes the sampling-based techniques commonly used to propagate aleatory uncertainties as well as the possibility of under predicting the range of the statistic of interest that may result from searching for the best- and worstcase epistemic values via nonlinear optimization or sampling.

Crespo, Luis G.↗

NASA NTRS1979

Viking magnetic properties experiment - Extended mission results

The backhoe magnets on Viking Lander (VL) 2 were successfully cleaned, followed by a test involving successive insertions of the cleaned backhoe into the surface. Rapid saturation of the magnets confirmed evidence from primary mission results that the magnetic mineral in the Martian surface is widely distributed, most probably in the form of composite particles of magnetic and nonmagnetic minerals. An image of the VL 2 backhoe taken via the X4 magnifying mirror demonstrates the fine-grained nature of the attracted magnetic material. The presence of maghemite and its occurrence as a pigment in, or a thin coating on, all mineral particles or as discrete, finely divided and widely distributed crystallites, are consistent with data from the inorganic analysis experiments and with laboratory simulations of results of the biology experiments on Mars.

Hargraves, R. B.↗