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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.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The tip of the red giant branch as a distance indicator for resolved galaxies. 2: Computer simulations

Based on both empirical data for the nearby galaxies, and on computer simulations, we show that measuring the position of the tip of the first-ascent red-giant branch provides a means of obtaining the distances to nearby galaxies with a precision and accuracy comparable to using Cepheids and/or RR Lyrae variables. We present an analysis of synthetic I vs (V-I) color magnitude diagrams of Population 2 systems to investigate the use of the observed discontinuity in the I-band luminosity function as a primary distance indicator. In the simulations we quantify the effects (1) signal to noise, (2) crowding, (3) population size, and (4) non-giant-branch-star contamination, on the method adopted for detecting the discontinuity,, measuring its luminosity, and estimating its uncertainity. We discuss sources of systematic error in the context of observable parameters, such as the signal-to-noise ratio and/or surface brightness. The simulations are then scaled to observed color-magnitude diagrams. It is concluded, that from the ground the tip of the red-giant-branch method can be sucessfully used to determine distances accurate to +/- 10% for galaxies out to 3 Mpc (mu approximately 27.5 mag); and from space a factor of four further in distance (mu approximately 30.6 mag) can be reached using HST. This method can be applied whereever a metal-poor population (-2.0 less than Z less than -0.7) of red-giant stars is detected (whose age is in the range 7-17 Gyr), whether that population resides in the halo of a spiral galaxy, the extended outer disk of a dwarf irregular, or in the outer periphery of an elliptical galaxy.

Madore, Barry F.↗
NASA NTRS1995

The Mode 1 mechanical crack tip stress field in hyperelastic and incompressible materials

The finite deformation field of a plane strain Mode 1 crack in a hyperelastic and incompressible material was examined under the assumptions of small scale nonlinearity. Finite element analyses were performed for two different material laws, a Neo-Hookean material and a third order invariant of a Rivlin material. The numerical results for both materials were compared to the appropriate theoretical asymptotic solution. A local cavitation locus surrounding the crack tip was identified for the Neo-Hookean material. For the third order invariant Rivlin material, maximum values of the dominant stress component were found close to the surface of the crack, above and below the deformed crack tip.

Quigley, Claudia J.↗
NASA NTRS1995

Control effectiveness and tip-fin dihedral effects for the HL-20 lifting-body configuration at Mach numbers from 1.6 to 4.5

Wind tunnel tests were made with a scale model of the HL-20 in the Langley Unitary Plan Wind Tunnel. Pitch control was investigated by deflecting the elevon surfaces on the outboard fins and body flaps on the fuselage. Yaw control tests were made with the all movable center fin deflected 5 deg. Almost full negative body flap deflection (-30 deg) was required to trim the HL-20 (moment reference center at 0.54-percent body length from nose) to positive values of life in the Mach number range from 1.6 to 2.5. Elevons were twice as effective as body flaps as a longitudinal trim device. The elevons were effective as a roll control, but because of tip-fin dihedral angle, produced about as much adverse yawing moment as rolling moment. The body flaps were less effective in producing rolling moment, but produced little adverse yawing moment. The yaw effectiveness of the all movable center fin was essentially constant over the angle-of-attack range at each Mach number. The value of yawing moment, however, was small. Center-fin deflection produced almost no rolling moments. The model was directionally unstable over most of the Mach number range with tip-fin dihedral angles less than the baseline value of 50 deg.

Cruz, Christopher I.↗
NASA NTRS1996

Time Dependence of Tip Morphology during Cellular/Dendritic Arrayed Growth

Succinonitrile-1.9 wt pct acetone has been directionally solidified in 0.7 X 0.7-cm-square cross section pyrex ampoules in order to observe the cell/dendrite tip morphologies, not influenced by the 'wall effects', which are present during growth in the generally used thin (about 200 gm) crucibles. The tips do not maintain a steady-state shape, as is generally assumed. Instead, they fluctuate within a shape envelope. The extent of fluctuation increases with decreasing growth speed, as the micro structure changes from the dendritic to cellular. The influence of natural convection has been examined by comparing these morphologies with those grown, without convection, in the thin ampoules.

Song, H.↗
NASA NTRS1998

Reduced Perceived Noise Low Tip Speed Fans as a Result of Abandoning Cutoff Stator Vane Numbers

As fan tip speeds are reduced, broadband noise is becoming more important in the calculation of perceived noise. Past experience indicates that lower vane number stators with either constant chord or constant solidity may be a way to reduce broadband noise caused by the interaction of the rotor wake turbulence with the stators. A baseline fan and a low blade number fan were investigated to determine if a noise reduction was possible. The low vane number fan showed a 2 PndB and a 1.5 PNLT noise reduction. These reductions show that this is a viable technique for reducing the perceived noise of low tip speed fans.

Dittmar, James↗
NASA NTRS1959

The Effects of Streamwise-Deflected Wing Tips on the Aerodynamic Characteristics of an Aspect Ratio-2 Triangular Wing, Body, and Tail Combination

An investigation has been conducted on a triangular wing and body combination to determine the effects on the aerodynamic characteristics resulting from deflecting portions of the wing near the tips 900 to the wing surface about streamwise hinge lines. Experimental data were obtained for Mach numbers of 0.70, 1.30, 1.70, and 2.22 and for angles of attack ranging from -5 deg to +18 deg at sideslip angles of 0 deg and 5 deg. The results showed that the aerodynamic center shift experienced by the triangular wing and body combination as the Mach number was increased from subsonic to supersonic could be reduced by about 40 percent by deflecting the outboard 4 percent of the total area of each wing panel. Deflection about the same hinge line of additional inboard surfaces consisting of 2 percent of the total area of each wing panel resulted in a further reduction of the aerodynamic center travel of 10 percent. The resulting reductions in the stability were accompanied by increases in the drag due to lift and, for the case of the configuration with all surfaces deflected, in the minimum drag. The combined effects of reduced stability and increased drag of the untrimmed configuration on the trimmed lift-drag ratios were estimated from an analysis of the cases in which the wing-body combination with or without tips deflected was assumed to be controlled by a canard. The configurations with deflected surfaces had higher trimmed lift-drag ratios than the model with undeflected surfaces at Mach numbers up to about 1.70. Deflecting either the outboard surfaces or all of the surfaces caused the directional stability to be increased by increments that were approximately constant with increasing angle of attack at each Mach number. The effective dihedral was decreased at all angles of attack and Mach numbers when the surfaces were deflected.

Peterson, Victor L.↗
NASA NTRS1998

Chemical Silver Coating of Fiber Tips in Near-Field Scanning Optical Microscopy

We report what is believed to be the first experimental demonstration of silver coating by a wet chemical process on tapered fiber tips used in near-field scanning optical microscopy. The process is at room temperature and pressure and takes only a few minutes to complete. Many tips can be simultaneously coated.

Vikram, Chandra S.↗
NASA NTRS1998

Quantum Molecular Dynamics Simulations of Nanotube Tip Assisted Reactions

In this report we detail the development and application of an efficient quantum molecular dynamics computational algorithm and its application to the nanotube-tip assisted reactions on silicon and diamond surfaces. The calculations shed interesting insights into the microscopic picture of tip surface interactions.

Menon, Madhu↗
NASA NTRS2000

BOREAS HYD-9 Tipping Bucket Rain Gauge Data

The BOREAS HYD-9 team collected several data sets containing precipitation and strearnflow measurements over the BOREAS study areas. This data set contains the measurements from the tipping bucket rain gauges at the BOREAS NSA and SSA. These measurements were submitted in 15-minute and 1-hour intervals. Only the 15-minute interval data set was loaded into the data base tables. Data were collected from the tipping bucket gauges from mid-April until mid-October in 1994, 1995, and 1996. The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884) or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Kouwen, Nick↗
NASA NTRS2001

An Airplane Design having a Wing with Fuselage Attached to Each Tip

This paper describes the conceptual design of an airplane having a low aspect ratio wing with fuselages that are attached to each wing tip. The concept is proposed for a high-capacity transport as an alternate to progressively increasing the size of a conventional transport design having a single fuselage with cantilevered wing panels attached to the sides and tail surfaces attached at the rear. Progressively increasing the size of conventional single body designs may lead to problems in some area's such as manufacturing, ground-handling and aerodynamic behavior. A limited review will be presented of some past work related to means of relieving some size constraints through the use of multiple bodies. Recent low-speed wind-tunnel tests have been made of models representative of the inboard-wing concept. These models have a low aspect ratio wing with a fuselage attached to each tip. Results from these tests, which included force measurements, surface pressure measurements, and wake surveys, will be presented herein.

Spearman, Leroy M.↗
NASA NTRS2001

Carbon Nanotube Tip Probes: Stability and Lateral Resolution in Scanning Probe Microscopy and Application to Surface Science to Semiconductors

In this paper we present results on the stability and lateral resolution capability of carbon nanotube (CNT) scanning probes as applied to atomic force microscopy (AFM). Surface topography images of ultra-thin films (2-5 nm thickness) obtained with AFM are used to illustrate the lateral resolution capability of single-walled carbon nanotube probes. Images of metal films prepared by ion beam sputtering exhibit grain sizes ranging from greater than 10 nm to as small as approximately 2 nm for gold and iridium respectively. In addition, imaging stability and lifetime of multi-walled carbon nanotube scanning probes are studied on a relatively hard surface of silicon nitride (Si3N4). AFM images Of Si3N4 surface collected after more than 15 hrs of continuous scanning show no detectable degradation in lateral resolution. These results indicate the general feasibility of CNT tips and scanning probe microscopy for examining nanometer-scale surface features of deposited metals as well as non-conductive thin films. AFM coupled with CNT tips offers a simple and nondestructive technique for probing a variety of surfaces, and has immense potential as a surface characterization tool in integrated circuit manufacturing.

Nguyen, Cattien V.↗
NASA NTRS2002

Influence of Crack-Tip Configurations on the Fracture Response of 0.04-Inch Thick 2024-T3 Aluminum Alloy Sheet

A series of fracture tests were conducted on Middle-crack tension M(T) and compact tension C(T) specimens to determine the effects of specimen type, specimen width, notch tip sharpness and buckling on the fracture behavior of cracked thin sheet (0.04 inch thick) 2024-T3 aluminum alloy material. A series of M(T) specimens were tested with three notch tip configurations: (1) a fatigue pre-cracked notch, (2) a 0.010-inch-diameter wire electrical discharge machined (EDM) notch, and (3) a EDM notch sharpened with a razor blade. The test procedures are discussed and the experimental results for failure stress, load vs. crack extension and the material stress-strain response are reported.

Johnston, William M.↗
NASA NTRS2003

Noise Generation by Fans with Supersonic Tip Speeds

Fan noise continues to be a significant issue for commercial aircraft engines and there still exists a requirement for improved understanding of the fundamental issues associated with fan noise source mechanisms. At the present time, most of the prediction methods identify the dominant acoustic sources to be associated with the stator vanes or blade trailing edges which are downstream of the fan face. However recent studies have shown that acoustic waves are significantly attenuated as they propagate upstream through a rotor, and if the appropriate corrections are applied, sound radiation from the engine inlet is significantly underpredicted. The prediction models can only be applied to fans with subsonic tip speeds. In contrast, most aircraft engines have fan tip speeds which are transonic and this implies an even higher attenuation for upstream propagating acoustic waves. Consequently understanding how sound propagates upstream through the fan is an important, and not well understood phenomena. The objective of this study is to provide improved insight into the upstream propagation effects through a rotor which are relevant to full scale engines. The focus of this study is on broadband fan noise generated by boundary layer turbulence interacting with the trailing edges of the fan blades. If this source mechanism is important upstream of the fan, the sound must propagate upstream through a transonic non uniform flow which includes large gradients and non linearities. Developing acoustic propagation models in this type of flow is challenging and currently limited to low frequency applications, where the frequency is of the same order as the blade passing frequency of the fan. For trailing edge noise, much higher frequencies are relevant and so a suitable approach needs to be developed, which is not limited by an unacceptably large computational effort. In this study we are in the process of developing a computational method which applies for the high frequencies of interest, and allows for any type of flow field associated with the fan. In this progress report the approach to be used and the basic equations will be presented. Some initial results will be given, but these are preliminary and need further verification.

Glegg, Stewart↗
NASA NTRS2003

A Reduced Model for Prediction of Thermal and Rotational Effects on Turbine Tip Clearance

This paper describes a dynamic model that was developed to predict changes in turbine tip clearance the radial distance between the end of a turbine blade and the abradable tip seal. The clearance is estimated by using a first principles approach to model the thermal and mechanical effects of engine operating conditions on the turbine sub-components. These effects are summed to determine the resulting clearance. The model is demonstrated via a ground idle to maximum power transient and a lapse-rate takeoff transient. Results show the model demonstrates the expected pinch point behavior. The paper concludes by identifying knowledge gaps and suggesting additional research to improve the model.

Kypuros, Javier A.↗
NASA NTRS2003

Toward a Fast-Response Active Turbine Tip Clearance Control

This paper describes active tip clearance control research being conducted by NASA to improve turbine engine systems. The target application for this effort is commercial aircraft engines. However, technologies developed for clearance control can benefit a broad spectrum of current and future turbomachinery. The first portion of the paper addresses the research from a programmatic viewpoint. Recent studies that provide motivation for the work, identification of key technologies, and NASA's plan for addressing deficiencies in the technologies are discussed. The later portion of the paper drills down into one of the key technologies by presenting equations and results for a preliminary dynamic model of the tip clearance phenomena.

Melcher, Kevin J.↗
NASA NTRS1990

Comparison of the ultrastructure of conventionally fixed and high pressure frozen/freeze substituted root tips of Nicotiana and Arabidopsis

To circumvent the limitations of chemical fixation (CF) and to gain more reliable structural information about higher plant tissues, we have cryofixed root tips of Nicotiana and Arabidopsis by high pressure freezing (HPF). Whereas other freezing techniques preserve tissue to a relatively shallow depth, HPF in conjunction with freeze substitution (FS) resulted in excellent preservation of entire root tips. Compared to CF, in tissue prepared by HPF/FS: (1) the plasmalemma and all internal membranes were much smoother and often coated on the cytoplasmic side by a thin layer of stained material, (2) the plasmalemma was appressed to the cell wall, (3) organelle profiles were rounder, (4) the cytoplasmic, mitochondrial, and amyloplast matrices were denser, (5) vacuoles contained electron dense material, (6) microtubules appeared to be more numerous and straighter, with crossbridges observed between them, (7) cisternae of endoplasmic reticulum (ER) were wider and filled with material, (8) Golgi intercisternal elements were more clearly resolved and were observed between both Golgi vesicles and cisternae, and (9) larger vesicles were associated with Golgi stacks. This study demonstrates that HPF/FS can be used to successfully preserve the ultrastructure of relatively large plant tissues without the use of intracellular cryoprotectants.

NASA Program Space Biology↗
NASA NTRS1990

Macromolecular differentiation of Golgi stacks in root tips of Arabidopsis and Nicotiana seedlings as visualized in high pressure frozen and freeze-substituted samples

The plant root tip represents a fascinating model system for studying changes in Golgi stack architecture associated with the developmental progression of meristematic cells to gravity sensing columella cells, and finally to "young" and "old", polysaccharide-slime secreting peripheral cells. To this end we have used high pressure freezing in conjunction with freeze-substitution techniques to follow developmental changes in the macromolecular organization of Golgi stacks in root tips of Arabidopsis and Nicotiana. Due to the much improved structural preservation of all cells under investigation, our electron micrographs reveal both several novel structural features common to all Golgi stacks, as well as characteristic differences in morphology between Golgi stacks of different cell types. Common to all Golgi stacks are clear and discrete differences in staining patterns and width of cis, medial and trans cisternae. Cis cisternae have the widest lumina (approximately 30 nm) and are the least stained. Medial cisternae are narrower (approximately 20 nm) and filled with more darkly staining products. Most trans cisternae possess a completely collapsed lumen in their central domain, giving rise to a 4-6 nm wide dark line in cross-sectional views. Numerous vesicles associated with the cisternal margins carry a non-clathrin type of coat. A trans Golgi network with clathrin coated vesicles is associated with all Golgi stacks except those of old peripheral cells. It is easily distinguished from trans cisternae by its blebbing morphology and staining pattern. The zone of ribosome exclusion includes both the Golgi stack and the trans Golgi network. Intercisternal elements are located exclusively between trans cisternae of columella and peripheral cells, but not meristematic cells. In older peripheral cells only trans cisternae exhibit slime-related staining. Golgi stacks possessing intercisternal elements also contain parallel rows of freeze-fracture particles in their trans cisternal membranes. We propose that intercisternal elements serve as anchors of enzyme complexes involved in the synthesis of polysaccharide slime molecules to prevent the complexes from being dragged into the forming secretory vesicles by the very large slime molecules. In addition, we draw attention to the similarities in composition and apparent site of synthesis of xyloglucans and slime molecules.

NASA Program Space Biology↗