Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Differential Experiments”

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.

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

At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

First-Principles Modeling of IAT-Driven Anomalous Resistivity in Hollow Cathode Discharges II: Numerical Simulations and Comparisons with Experiments

We present a model that quantifies the magnitude of the ion-acoustic turbulence (IAT) in the plume of hollow cathodes and its effect on the resistivity and ion heating. The model takes the form of a partial differential equation (PDE) that can be solved concurrently with the equations of motion for a partially ionized plasma already included in our numerical code for the simulation of the plasma discharge in hollow cathodes, OrCa2D. We also determine that self-induced magnetic fields are not negligible in hollow cathodes operating at large discharge currents and implement in our code Ampere’s law and modifications to Ohm’s law that account for this effect. Numerical simulations that employed these models show large improvements in our agreement with experimental measurements with respect to a previous model, which assumed complete saturation of the IAT and did not account for the growth stage of the waves. In particular, the model is able to accurately predict the location and magnitude of the maximum resitivity to the electron current along the cathode centerline.

Lopez Ortega, Alejandro↗
NASA NTRS1978

Experimental petrology of very low Ti /VLT/ basalts

Synthetic analogs of Luna 24 ferrobasalt and an Apollo 15 green glass were subjected to iron capsule experiments to test hypotheses concerning the generation of Luna 24 ferrobasalt. Results of the experiments indicated that the Luna 24 ferrobasalt may be generated by near-surface fractionation of a Luna 24 green glass parent. Evidence for the parent magma which differentiated at or near the Mare Crisium site to yield the Luna 24 ferrobasalt may be found in the Luna 24 green glass and lithic fragments of vitrophyres.

Grove, T. L.↗
NASA NTRS1983

Log N-log S in inconclusive

The log N-log S data acquired by the Pioneer Venus Orbiter Gamma Burst Detector (PVO) are presented and compared to similar data from the Soviet KONUS experiment. Although the PVO data are consistent with and suggestive of a -3/2 power law distribution, the results are not adequate at this state of observations to differentiate between a -3/2 and a -1 power law slope.

Klebesadel, R. W.↗
NASA NTRS1987

The comet rendezvous asteroid flyby mission

The Comet Rendezvous Asteroid Flyby Mission (CRAF) is described. After gravity assists from Venus and Earth, the spacecraft will fly by the asteroid 46 Hestia en route to a rendezvous with P/Tempel 2 in Nov. 1996, when the comet is near aphelion. The scientific experiments for the CRAF mission are: an imaging system; a visual and infrared mapping spectrometer; an infrared radiometer; a penetrator carrying a gamma-ray spectrometer, a scanning differential calorimeter and evolved gas analyzer, accelerometers, and temperature probes; a neutral gas and thermal ion mass spectrometer; a secondary ion mass spectrometer for analyzing dust, gas, and thermal ions; a scanning electron microscope and particle analyzer; an X-ray fluorescence and gas chromatographic analyzer for collected dust and ice samples; a dust counter and velocity analyzer; a retarding potential ion mass spectrometer; a supra-thermal ion mass spectrometer and electron analyzer; a magnetometer; and a coordinated radio, electron, and plasma wave analyzer.

Neugebauer, M.↗
NASA NTRS1991

Damping in coupled bending and torsion - An experiment

Traditional experimental modal testing methods are used to determine the damping properties of a Euler-Bernoulli beam with offset inertial tip mass. Both viscous and strain rate damping models are considered in bending and in torsion. A partial differential equation model of the coupled system is used. Eigenfunctions are derived for the coupled system by using a Green's function approach to derive the approximate uncoupled eigenfunctions. These eigenfunctions are used in a decoupled fashion with experimental modal data to estimate the damping parameters of the coupled system. The experimental modal data were obtained from both free and impulse responses using a combined translational and rotational accelerometer.

Umland, Jeffrey W.↗
NASA NTRS2017

Machine Learning Approaches to Increasing Value of Spaceflight Omics Databases

The number of spaceflight bioscience mission opportunities is too small to allow all relevant biological and environmental parameters to be experimentally identified. Simulated spaceflight experiments in ground-based facilities (GBFs), such as clinostats, are each suitable only for particular investigations -- a rotating-wall vessel may be 'simulated microgravity' for cell differentiation (hours), but not DNA repair (seconds) -- and introduce confounding stimuli, such as motor vibration and fluid shear effects. This uncertainty over which biological mechanisms respond to a given form of simulated space radiation or gravity, as well as its side effects, limits our ability to baseline spaceflight data and validate mission science. Machine learning techniques autonomously identify relevant and interdependent factors in a data set given the set of desired metrics to be evaluated: to automatically identify related studies, compare data from related studies, or determine linkages between types of data in the same study. System-of-systems (SoS) machine learning models have the ability to deal with both sparse and heterogeneous data, such as that provided by the small and diverse number of space biosciences flight missions; however, they require appropriate user-defined metrics for any given data set. Although machine learning in bioinformatics is rapidly expanding, the need to combine spaceflight/GBF mission parameters with omics data is unique. This work characterizes the basic requirements for implementing the SoS approach through the System Map (SM) technique, a composite of a dynamic Bayesian network and Gaussian mixture model, in real-world repositories such as the GeneLab Data System and Life Sciences Data Archive. The three primary steps are metadata management for experimental description using open-source ontologies, defining similarity and consistency metrics, and generating testing and validation data sets. Such approaches to spaceflight and GBF omics data may soon enable unique insight into which measured phenomena correlate to biological mechanisms that are truly affected by spaceflight conditions; which are most likely to be confounded by other variables; and which are insufficiently characterized, significantly increasing existing and future science return from ISS and spaceflight missions.

Gentry, Diana↗
NASA NTRSDate not supplied

Total Variation Majorization Minimization (TV-MM) Approach to Radiometer Brightness Temperature Gridding and Reconstruction

This paper presents the implementation of an algorithm to enhance the image resolution of the Earth's surface brightness temperature (T B ) data measured by radiometers such as the one onboard of the Soil Moisture Active Passive (SMAP) mission. A key step in radiometer T B processing is the conversion of the swath-based calibrated antenna temperature (T A ) measurements to the Level 3 Earth-centered grid. The simplest algorithm to transform this data from swath to gridded format is called drop-in-the-bucket which simply averages surrounding noisy T A samples to form a T B value at the gridded location. This method reduces noise, however produces low resolution products. To obtain a higher resolution product, SMAP uses other techniques such the Backus-Gilbert (BG) algorithm, which is the conventional method used in microwave radiometry. Although this method performs the required interpolation, it is not effective in denoising and removing blurring effects due to antenna filtering of the radiometer image data. Our motivation for this development is to further improve the resolution through post-processing of the radiometer T B image, a highly cost-effective method of image enhancement. The approach adapted in this work is based on the minimization of the Total Variation (TV) regularized objective function that is used extensively in solving general ill-posed linear inverse problems in image processing. Since the TV-based objective function is convex but not everywhere differentiable, there exists many numerical algorithms that can estimate the solution and the one selected for this work is called Majorization- Minimization (MM). By applying this algorithm, simulation experiments were performed based on synthetic data from the Geophysical model as well as real SMAP data to demonstrate the effectiveness of the technique. Results were then compared against the BG method.

Wing Lee↗
NASA NTRS2017

Exploring the Utilization of Low-Pressure, Piston-Cylinder Experiments to Determine the Bulk Compositions of Finite, Precious Materials

Determining the bulk composition of precious materials with a finite mass (e.g., meteorite samples) is extremely important in the fields of Earth and Planetary Science. From meteorite studies we are able to place constraints on large scale planetary processes like global differentiation and subsequent volcanism, as well as smaller scale processes like crystallization in a magma chamber or sedimentary compaction at the surface. However, with meteorite samples in particular, far too often we are limited by how precious the sample is as well as its limited mass. In this study, we have utilized aliquots of samples previously studied for toxicological hazards, including both the fresh samples (lunar mare basalt NWA 4734, lunar regolith breccia NWA 7611, martian basalt Tissint, martian regolith breccia NWA 7034, a vestian basalt Berthoud, a vestian regolith breccia NWA 2060, and a terrestrial mid-ocean ridge basalt (MORB)), and those that underwent iron leaching (Tissint, NWA 7034, NWA 4734, MORB). With these small masses of material, we performed low pressure (approx. 0.75 GPa), high temperature (greater than 1600 degrees Celsius) melting experiments. Each sample was analyzed using a JEOL 8530F electron microprobe to determine the bulk composition of the materials that were previously examined. When available, the results of our microprobe data were compared with bulk rock compositions in the literature. The results of this study show that with this technique, only approx. 50 mg of sample is required to accurately determine the bulk composition of the materials of interest.

Vander Kaaden, K. E.↗
NASA NTRS1986

Feasibility experiments on time-resolved fluorosensing applied to oil slicks

The introduction of time resolved observations can provide a very penetrating tool in the practice of laser fluorosensing. The investigations have demonstrated a relevance of multispectral, time resolved analysis for oil fingerprinting. By comparative studies on a variety of crude oils and their most significant fractions, it was found that the process of time decay in a composite oil is characterized by a few steps, which are associated with specific components in the medium light range. The average decay times of these pure fractions are markedly differentiated as to absolute values and spectral spread; as a consequence, the corresponding parameters in the resultant crude are quite sensitive to the particular mixture of these components. Measurements of the time response give then a finer discrimination between oil classes, depending on the relative content of certain fractions. Experiments were pursued with an improved fluorosensor facility, in order to test the application of time resolved fluorosensing to remote samples on water.

Camagni, P.↗
NASA NTRS1993

The combustion program at CTR

Understanding and modeling of turbulent combustion are key problems in the computation of numerous practical systems. Because of the lack of analytical theories in this field and of the difficulty of performing precise experiments, direct numerical simulation (DNS) appears to be one of the most attractive tools to use in addressing this problem. The general objective of DNS of reacting flows is to improve our knowledge of turbulent combustion but also to use this information for turbulent combustion models. For the foreseeable future, numerical simulation of the full three-dimensional governing partial differential equations with variable density and transport properties as well as complex chemistry will remain intractable; thus, various levels of simplification will remain necessary. On one hand, the requirement to simplify is not necessarily a handicap: numerical simulations allow the researcher a degree of control in isolating specific physical phenomena that is inaccessible in experiments. CTR has pursued an intensive research program in the field of DNS for turbulent reacting flows since 1987. DNS of reacting flows is quite different from DNS of non-reacting flows: without reaction, the equations to solve are clearly the five conservation equations of the Navier Stokes system for compressible situations (four for incompressible cases), and the limitation of the approach is the Reynolds number (or in other words the number of points in the computation). For reacting flows, the choice of the equations, the species (each species will require one additional conservation equation), the chemical scheme, and the configuration itself is more complex.

Poinsot, Thierry J.↗
NASA NTRS1992

Turbulence modeling and experiments

The best way of verifying turbulence is to do a direct comparison between the various terms and their models. The success of this approach depends upon the availability of the data for the exact correlations (both experimental and DNS). The other approach involves numerically solving the differential equations and then comparing the results with the data. The results of such a computation will depend upon the accuracy of all the modeled terms and constants. Because of this it is sometimes difficult to find the cause of a poor performance by a model. However, such a calculation is still meaningful in other ways as it shows how a complete Reynolds stress model performs. Thirteen homogeneous flows are numerically computed using the second order closure models. We concentrate only on those models which use a linear (or quasi-linear) model for the rapid term. This, therefore, includes the Launder, Reece and Rodi (LRR) model; the isotropization of production (IP) model; and the Speziale, Sarkar, and Gatski (SSG) model. Which of the three models performs better is examined along with what are their weaknesses, if any. The other work reported deal with the experimental balances of the second moment equations for a buoyant plume. Despite the tremendous amount of activity toward the second order closure modeling of turbulence, very little experimental information is available about the budgets of the second moment equations. Part of the problem stems from our inability to measure the pressure correlations. However, if everything else appearing in these equations is known from the experiment, pressure correlations can be obtained as the closing terms. This is the closest we can come to in obtaining these terms from experiment, and despite the measurement errors which might be present in such balances, the resulting information will be extremely useful for the turbulence modelers. The purpose of this part of the work was to provide such balances of the Reynolds stress and heat flux equations for the buoyant plume.

Shabbir, Aamir↗
NASA NTRS1999

Cell Culture in Microgravity: Opening the Door to Space Cell Biology

Adaptational response of human cell populations to microgravity is investigated using simulation, short-term Shuttle experiments, and long-term microgravity. Simulation consists of a clinostatically-rotated cell culture system. The system is a horizontally-rotated cylinder completely filled with culture medium. Low speed rotation results in continuous-fall of the cells through the fluid medium. In this setting, cells: 1) aggregate, 2) propagate in three dimensions, 3) synthesize matrix, 4) differentiate, and 5) form sinusoids that facilitate mass transfer. Space cell culture is conducted in flight bioreactors and in static incubators. Cells grown in microgravity are: bovine cartilage, promyelocytic leukemia, kidney proximal tubule cells, adrenal medulla, breast and colon cancer, and endothelium. Cells were cultured in space to test specific hypotheses. Cartilage cells were used to determine structural differences in cartilage grown in space compared to ground-based bioreactors. Results from a 130-day experiment on Mir revealed that cartilage grown in space was substantially more compressible due to insufficient glycosaminoglycan in the matrix. Interestingly, earth-grown cartilage conformed better to the dimensions of the scaffolding material, while the Mir specimens were spherical. The other cell populations are currently being analyzed for cell surface properties, gene expression, and differentiation. Results suggest that some cells spontaneously differentiate in microgravity. Additionally, vast changes in gene expression may occur in response to microgravity. In conclusion, the transition to microgravity may constitute a physical perturbation in cells resulting in unique gene expressions, the consequences of which may be useful in tissue engineering, disease modeling, and space cell biology.

Pellis, Neal R.↗
NASA NTRS1990

Preosteoblast production 55 hours after a 12.5-day spaceflight on Cosmos 1887

The influence of 12.5 days of spaceflight and a 55 h stressful recovery period (at 1 g) on fibroblastlike osteoblast precursor cells was assessed in the periodontal ligament (PDL) of rats that were 91 days old at launch. Nuclear morphometry was used as a marker for precursor cell differentiation in 3 microns sections cut in the midsagittal plane from the maxillary first molar. According to nuclear volume, cells were classified as preosteoblasts (C + D cells, greater than or equal to 120 microns 3) and less differentiated progenitor cells (A + A' cells, 40-79 microns 3). Compared with synchronous controls (simulated flight conditions), the 55 h postflight recovery period at 1 g resulted in a 40% decrease in the A + A' cell population, a 42% increase in the C + D cells, and a 39% increase in the number of PDL fibroblastlike cells near the bone surface. These results are consistent with a postflight osteogenic response in PDL. This recovery response occurred despite physiological stress in the flight animals that resulted in a highly significant (P less than or equal to 0.001) increase in adrenal weight. The data suggest that after spaceflight there is a strong and rapid recovery mechanism for osteoblast differentiation that is not suppressed by physiological stress.

Cosmos 1887 Project↗
NASA NTRS1979

'Coronae' of rotating interstellar clouds

This letter considers differential rotation of cool interstellar clouds in the presence of internal magnetic fields, and shows that because of the relative ineffectiveness of field dissipation within the clouds, magnetized gas experiences buoyant forces. The resulting field loops emerge from the cloud and dissipate their energy by field reconnection. The consequent heating is sufficient to produce relatively hot (T approximately 10,000 K) 'coronae' about the clouds.

Rosner, R.↗
NASA NTRS1984

Telecommunications and data acquisition support for the Pioneer Venus Project: Pioneers 12 and 13, prelaunch through March 1984

The support provided by the Telecommunications and Data Acquisition organization of the Jet Propulsion Laboratory (JPL) to the Pioneer Venus missions is described. The missions were the responsibility of the Ames Research Center (ARC). The Pioneer 13 mission and its spacecraft design presented one of the greatest challenges to the Deep Space Network (DSN) in the implementation and operation of new capabilities. The four probes that were to enter the atmosphere of Venus were turned on shortly before arrival at Venus, and the DSN had to acquire each of these probes in order to recover the telemetry being transmitted. Furthermore, a science experiment involving these probes descending through the atmosphere required a completed new data type to be generated at the ground stations. This new data type is known as the differential very long baseline interferometry. Discussions between ARC and JPL of the implementation requirements involved trade-offs in spacecraft design and led to a very successful return of science data. Specific implementation and operational techniques are discussed, not only for the prime mission, but also for the extended support to the Pioneer 12 spacecraft (in orbit around Venus) with its science instruments including that for radar observations of the planet.

Miller, R. B.↗
NASA NTRS1991

Correlating DSC and X-Ray Measurements Of Crystallinity

Experiment demonstrated approximate linear correlation between degree of crystallinity of multiphase polymer (as calculated from x-ray diffraction measurements) and heat of fusion of polymer (as calculated from differential scanning calorimetry (DSC) measurements). Correlation basis of simple new technique for estimating degree of crystallinity of specimens of polymer from DSC measurements alone.

Yen, Shiao-Ping S.↗
NASA NTRS1995

Search for life on Mars: Evaluation of techniques

An important question for exobiology is, did life evolve on Mars? To answer this question, experiments must be conducted on the martian surface. Given current mission constraints on mass, power, and volume, these experiments can only be performed using proposed analytical techniques such as: electron microscopy, X-ray fluorescence, X-ray diffraction, a-proton backscatter, g-ray spectrometry, differential thermal analysis, differential scanning calorimetry, pyrolysis gas chromatography, mass spectrometry, and specific element detectors. Using prepared test samples consisting of 1% organic matter (bovine serum albumin) in palagonite and a mixture of palagonite, clays, iron oxides, and evaporites, it was determined that a combination of X-ray diffraction and differential thermal analysis coupled with gas chromatography provides the best insight into the chemistry, mineralogy, and geological history of the samples.

Schwartz, D. E.↗
NASA NTRS1995

A review of solar wind ion and electron plasma distribution functions: Present understanding and Ulysses results

Our present understanding of the distribution functions of the solar wind ion and electron thermal/suprathermal populations will be reviewed covering selected theoretical and observational topics. Roughly half the review will be devoted to recent discoveries (since Solar Wind 7). Among recent results are those of the Ulysses mission. The SWICS experiment observed pick-up protons and alpha particles, and acceleration of these particles at interplanetary shocks. Positive ion phenomena observed by SWOOPS include enhanced proton-alpha particle differential streaming both: (1) at high latitudes; and (2) in the ecliptic beyond 1 AU in the vicinity of shocks. The SWOOPS positive ion observations also demonstrate relative constancy of the entropy per proton at high latitudes beyond about 2.5 AU. Double beaming in both protons and alphas is observed by SWOOPS on either side of the current sheet, but not within; a possible explanation is reconnection at the edge of the current sheet. SWOOPS observed bi-directional streaming of electrons beyond 2 AU not only within Coronal Mass Ejections, but also upstream of corotating interplanetary shocks. Latitudinal and radial gradients of Ulysses electron core and halo temperatures will be discussed, as will work in progress on the three dimensional (in velocity space) properties of ion distributions.

Goldstein, B. E.↗