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A 1/8 scale jet-effects model was tested in the NASA Ames 11 ft transonic tunnel at static conditions and over a range of Mach numbers from 0.4 to 1.4. The data presented show that significant differences in aeropropulsion performance can be expected by varying the exhaust nozzle type and its geometric parameters on a V/STOL underwing nacelle installation.
The equations describing the change in orbital elements of interplanetary dust due to Lorentz-force accelerations are presented in a simplified form. Such accelerations depend on the charge state of the dust; results of theoretical calculations for five possible dust materials are presented. Under present-day conditions, it is possible that semiconducting material such as graphite might carry a net voltage near zero, compared with a roughly 10-V charge expected for other grains. The scattering of dust by a randomly changing magnetic field can be viewed analogously to the dust diffusing in space; the equations presented thus can be used to interpret observations of the present distribution of dust in terms of its possible sources and sinks. The stronger magnetic fields of the early solar system would have led to more vigorous scattering of the dust; particles as large as 1 mm could have been significantly transported by Lorentz scattering during this time.
Sulfur dioxide has a strong and complex rotational spectrum in the microwave and far infrared regions. The microwave absorption due to SO2 in a CO2 mixture is calculated for conditions applicable to the Venus atmosphere. It is shown that at the concentrations detected by Pioneer-Venus in situ measurements, SO2 may be expected to contribute significantly to the microwave opacity of the Venus atmosphere. In particular, SO2 might provide the major source of opacity in the atmospheric region immediately below the main sulfuric acid cloud deck. The spectrum is largely nonresonant at the pressures where SO2 is expected to occur, however.
Two numerical models of aircraft performance are developed to relate atmospheric wind signals in wind-shear situations to aircraft response. Both models produce time histories of pitch angle, airspeed, height above the ground, and other parameters for simulating aircraft making precision approaches along a 3-deg glide slope to the runway. Simulations conducted using thunderstorm environment wind data indicate that the horizontal wind component is at least as important as the vertical component in determining aircraft response to wind shear. Obtaining quantitative measurements of aircraft approach or departure quality is found to depend on several factors, including the knowledge of winds along the expected flight track, clear-air detection in a quasi-horizontal path, and a near continuous estimate of approach deterioration due to shear conditions.
The intergalactic cloud of neutral hydrogen in the M96 group are examined for signs of emission over a wide range of frequencies, from radio waves to X rays. Past or present stellar activity in the gas might have been expected to produce detectable visual infrared, CO, OH, or radio recombination-line emission. None was detected. The limits are used to study physical conditions in the intergalactic gas. In particular, B and V band limits on starlight and IRAS limits on the presence of dust strongly constrain the presence of stars or stellar by-products. However, given the uncertainties about physical conditions in the intergalactic environment, it is difficult to rule out entirely the presence of stellar-processed materials. Results of neutral hydrogen mapping from a large-scale survey of the intergalactic cloud and surrounding region are also presented. These observations confirm that the gas is confined to a large ringlike structure. The simplest interpretation remains that the intergalactic gas in Leo is primordial.
Extensive correlations of computer code results with experimental data are employed to illustrate the use of a linearized theory, attached flow method for the estimation and optimization of the longitudinal aerodynamic performance of wing-canard and wing-horizontal tail configurations which may employ simple hinged flap systems. Use of an attached flow method is based on the premise that high levels of aerodynamic efficiency require a flow that is as nearly attached as circumstances permit. The results indicate that linearized theory, attached flow, computer code methods (modified to include estimated attainable leading-edge thrust and an approximate representation of vortex forces) provide a rational basis for the estimation and optimization of aerodynamic performance at subsonic speeds below the drag rise Mach number. Generally, good prediction of aerodynamic performance, as measured by the suction parameter, can be expected for near optimum combinations of canard or horizontal tail incidence and leading- and trailing-edge flap deflections at a given lift coefficient (conditions which tend to produce a predominantly attached flow).
Opportunities for transfer of twenty Geminid meteoroids from Phaethon were found by integrating the equations of motion back in time along with Phaethon. Examination of the conditions for transfer show that the meteoroids could have been ejected under circumstances (location, speed and directions of ejection) that are possible or even expected during cometary activity. Phaethon's active period would be no more than 2000 years ago and may have been within the last 600 years. While other means of formation of the Geminid meteoroids cannot be ruled out, they are less likely based on this investigation.
Results are reported from a three-dimensional MHD simulation of magnetotail reconnection, which, in contrast to earlier ones, starts from an equilibrium configuration that contains a region 1 type field-aligned current system at the plasma sheet/lobe boundary. This current system is found from equilibrium theory as the consequence of boundary conditions, which require that field lines at large distances from the earth become aligned-with the tail axis, consistent with observations and the expected consequences of the interaction with the solar wind. As in earlier simulations, the dynamic evolution develops from a slow diffusion to the fast growth of a three-dimensional tearing mode, initiated by the sudden occurrence or increase of resistivity, leading again to the formation and subsequent tailward ejection of a plasmoid, associated with fast plasma flows. In addition there are changes of the electric current system which are consistent with the substorm current wedge picture inferred from observations.
The possible erosion of a carbon/carbon thermal shield by solar wind-charged particle radiation is reviewed. The present knowledge of erosion data for carbon and/or graphite is surveyed, and an explanation of erosion mechanisms under different charged particle environments is discussed. The highest erosion is expected at four solar radii. Erosion rates are analytically estimated under several conservative assumptions for a normal quiet and worst case solar wind storm conditions. Mass loss analyses and comparison studies surprisingly indicate that the predicted erosion rate by solar wind could be greater than by nominal free sublimation during solar wind storm conditions at four solar radii. The predicted overall mass loss of a carbon/carbon shield material during the critical four solar radii flyby can still meet the mass loss mission requirement of less than 0.0025 g/sec.
Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-microns pores of the porous tube. Water potential in the system was controlled at -0.4, -0.8, and -3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from -0.4 to -3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the mid-day leaf water potential from - 1.3 to - 1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water Potentials, while intercellular C02 concentration remained constant. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts , it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.
Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-micron pores of the porous tube. Water potential in the system was controlled at -0.4, -0.8, and -3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from -0.4 to -3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the midday leaf water potential from -1.3 to -1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water potentials, while intercellular CO2 concentration remained constant. This was associated with a decrease in stomatal conductance to water vapor from 1.90 to 0.98 mol/(sq m sec) and a decrease in total apparent hydraulic conductance from 47 to 12 (micro)mol/(sec MPa). Although the applied water potentials were in the -0.4 to -3.0 kPa range, the actual water potential perceived by the plant roots appeared to be in the range of -0.26 to -0.38 MPa as estimated by the leaf water potential of bagged plants. The amount of K, Ca, Mg, Zn, Cu, and B accumulated with each unit of transpired water increased as the applied water potential became less negative. The increase in accumulation ranged from 1.4-fold for K to 2.2-fold for B. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts, it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.
The solid/liquid (s/1) interfacial Seebeck technique was used to measure interfacial undercooling in a Pb-1 wt.% Sn alloy. For plane front solidification an undercooling in the range of 0.54-0.57C was recorded. However, for growth velocities between 6 to 15 micron/s the undercooling, increased with increase in velocity. 'Tbis is in contradiction to the theoretical predictions based on growth at the extremum condition. A modified analytical expression was developed based on the maro,,inal stability criterion to predict undercooling for growth velocities immediately over the limit of morphological stability. Between 6 to 15 microns/s the trend predicted by this modified expression is in qualitative agreement with the experimental results. This model is more consistent with the analysis of Venugopal and Kirkaldy which states that the extremum condition criterion is not applicable in the marginal stability regime. At higher growth velocities between 20 and 50 microns/s where stable cellular growth is expected the undercooling, decreased with increase in velocity. The predictions of Burden and Hunt based on extremum criterion agree reasonably well with the experimental results in this velocity range. Finally, the importance of non-equilibrium phase diagram parameters such as partition coefficient and liquidus slope were also evaluated using the experimental undercooling results obtained in this investigation.
A computational investigation of the aerodynamic effects on fluidic thrust vectoring has been conducted. Three-dimensional simulations of a two-dimensional, convergent-divergent (2DCD) nozzle with fluidic injection for pitch vector control were run with the computational fluid dynamics code PAB using turbulence closure and linear Reynolds stress modeling. Simulations were computed with static freestream conditions (M=0.05) and at Mach numbers from M=0.3 to 1.2, with scheduled nozzle pressure ratios (from 3.6 to 7.2) and secondary to primary total pressure ratios of p(sub t,s)/p(sub t,p)=0.6 and 1.0. Results indicate that the freestream flow decreases vectoring performance and thrust efficiency compared with static (wind-off) conditions. The aerodynamic penalty to thrust vector angle ranged from 1.5 degrees at a nozzle pressure ratio of 6 with M=0.9 freestream conditions to 2.9 degrees at a nozzle pressure ratio of 5.2 with M=0.7 freestream conditions, compared to the same nozzle pressure ratios with static freestream conditions. The aerodynamic penalty to thrust ratio decreased from 4 percent to 0.8 percent as nozzle pressure ratio increased from 3.6 to 7.2. As expected, the freestream flow had little influence on discharge coefficient.
Results of recent research investigating the use of automated systems have indicated the presence of automation bias, a term describing errors made when decision makers rely on automated cues as a heuristic replacement for vigilant information seeking and processing. Automation commission errors, i.e., errors made when decision makers take inappropriate action because they over-attend to automated information or directives, and automation omission errors, i.e., errors made when decision makers do not take appropriate action because they are not informed of an imminent problem or situation by automated aids, can result from this tendency. In a series of studies, participants who perceived themselves as "accountable" for their strategies of interaction with automation were significantly more likely to verify its correct functioning, and committed significantly fewer automation-related errors than those who did not report this perception. In this study, we focus on two manipulations to encourage verification behaviors within cockpit crews. The first, an information/training manipulation, will focus on explicit information on automation bias, and training for verification of automated functioning. The second manipulation will consist of display prompts to verify automated functioning. Participants (glass-cockpit crews) will fly a series of approaches on the Mini-ACFS, a two-person pan-task flight simulator. Approach scenarios include several automation "events," that is, glitches, malfunctions, or inappropriate recommendations, that can be caught if cross-checked with other cockpit indicators. We anticipate that these manipulations will ameliorate automation bias. Final data analysis will be completed prior to the OSU symposium, and is expected to support the hypotheses that: a) reduced errors are associated with verification behaviors; b) crews will be more likely to verify under training/display conditions than when in the control condition; and c) effects will persist when subjects return for a follow-up exercise 6-9 weeks after their first session. Implications for training and automation design will be discussed.
Orientation selective and local sign mechanisms have been proposed as the basis for vernier acuity judgments. Linear image features contributing to discrimination can be determined for a two choice task by adding external noise to the images and then averaging the noises separately for the four types of stimulus/response trials. This method is applied to a vernier acuity task with different spatial separations to compare the predictions of the two theories. Three well-practiced observers were presented around 5000 trials of a vernier stimulus consisting of two dark horizontal lines (5 min by 0.3 min) within additive low-contrast white noise. Two spatial separations were tested, abutting and a 10 min horizontal separation. The task was to determine whether the target lines were aligned or vertically offset. The noises were averaged separately for the four stimulus/response trial types (e.g., stimulus = offset, response = aligned). The sum of the two 'not aligned' images was then subtracted from the sum of the 'aligned' images to obtain an overall image. Spatially smoothed images were quantized according to expected variability in the smoothed images to allow estimation of the statistical significance of image features. The response images from the 10 min separation condition are consistent with the local sign theory, having the appearance of two linear operators measuring vertical position with opposite sign. The images from the abutting stimulus have the same appearance with the two operators closer together. The image predicted by an oriented filter model is similar, but has its greatest weight in the abutting region, while the response images fall to nonsignificance there. The response correlation image method, previously demonstrated for letter discrimination, clarifies the features used in vernier acuity.
Some studies suggest that the proper initialization of soil moisture in a forecasting model may contribute significantly to the accurate prediction of seasonal precipitation, especially over mid-latitude continents. In order for the initialization to have any impact at all, however, two conditions must be satisfied: (1) the initial soil moisture anomaly must be "remembered" into the forecasted season, and (2) the atmosphere must respond in a predictable way to the soil moisture anomaly. In our previous studies, we identified the key land surface and atmospheric properties needed to satisfy each condition. Here, we tie these studies together with an analysis of an ensemble of seasonal forecasts. Initial soil moisture conditions for the forecasts are established by forcing the land surface model with realistic precipitation prior to the start of the forecast period. As expected, the impacts on forecasted precipitation (relative to an ensemble of runs that do not utilize soil moisture information) tend to be localized over the small fraction of the earth with all of the required land and atmosphere properties.
The organic compounds synthesized in prebiotic experiments are racemic mixtures. A number of proposals have been offered to explain how asymmetric organic compounds formed on the Earth before life arose, with the influence of chiral weak nuclear interactions being the most frequent proposal. This and other proposed asymmetric syntheses give only sight enantiomeric excess and any slight excess will be degraded by racemization. This applies particularly to amino acids where half-lives of 10(5)-10(6) years are to be expected at temperatures characteristic of the Earth's surface. Since the generation of chiral molecules could not have been a significant process under geological conditions, the origins of this asymmetry must have occurred at the time of the origin of life or shortly thereafter. It is possible that the compounds in the first living organisms were prochiral rather than chiral; this is unlikely for amino acids, but it is possible for the monomers of RNA-like molecules.
Actively cooled ceramic matrix composite (CMC) components are enabling or enhancing for a broad range of hypersonic and reusable launch vehicle propulsion systems. Teaming with other NASA centers, the Air Force, and industry, the Glenn Ceramics Branch has successfully tested multiple cooled CMC panel concepts in high-heat-flux, high-pressure, flowing rocket engine combustion gas environments. Sub-element components survived multiple cycles and the severe thermal gradients imposed by combustion gas temperatures in excess of 5500 F and cryogenic hydrogen or ambient temperature water internal coolants. These demonstrations are critical for the continued development of this class of materials, and the research is expected to continue with additional concepts and increasingly larger and more complex geometries being fabricated and tested in a broad range of engine operating conditions.