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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Three-dimensional quadratic modeling and quantitative evaluation of the diaphragm on a volumetric CT scan in patients with chronic obstructive pulmonary disease

Purpose: In patients with chronic obstructive pulmonary disease (COPD), diaphragm function may deteriorate due to reduced muscle fiber length. Quantitative analysis of the morphology of the diaphragm is therefore important. In the authors current study, they propose a diaphragm segmentation method for COPD patients that uses volumetric chest computed tomography (CT) data, and they provide a quantitative analysis of the diaphragmatic dimensions. Methods: Volumetric CT data were obtained from 30 COPD patients and 10 normal control patients using a 16-row multidetector CT scanner (Siemens Sensation 16) with 0.75-mm collimation. Diaphragm segmentation using 3D ray projections on the lower surface of the lungs was performed to identify the draft diaphragmatic lung surface, which was modeled using quadratic 3D surface fitting and robust regression in order to minimize the effects of segmentation error and parameterize diaphragm morphology. This result was visually evaluated by an expert thoracic radiologist. To take into consideration the shape features of the diaphragm, several quantification parameters—including the shape index on the apex (SIA) (which was computed using gradient set to 0), principal curvatures on the apex on the fitted diaphragm surface (CA), the height between the apex and the base plane (H), the diaphragm lengths along the x-, y-, and z-axes (XL, YL, ZL), quadratic-fitted diaphragm lengths on the z-axis (FZL), average curvature (C), and surface area (SA)—were measured using in-house software and compared with the pulmonary function test (PFT) results. Results: The overall accuracy of the combined segmentation method was 97.22% ± 4.44% while the visual accuracy of the models for the segmented diaphragms was 95.28% ± 2.52% (mean ± SD). The quantitative parameters, including SIA, CA, H, XL, YL, ZL, FZL, C, and SA were 0.85 ± 0.05 (mm{sup −1}), 0.01 ± 0.00 (mm{sup −1}), 17.93 ± 10.78 (mm), 129.80 ± 11.66 (mm), 163.19 ± 13.45 (mm), 71.27 ± 17.52 (mm), 61.59 ± 16.98 (mm), 0.01 ± 0.00 (mm{sup −1}), and 34 380.75 ± 6680.06 (mm{sup 2}), respectively. Several parameters were correlated with the PFT parameters. Conclusions: The authors propose an automatic method for quantitatively evaluating the morphological parameters of the diaphragm on volumetric chest CT in COPD patients. By measuring not only the conventional length and surface area but also the shape features of the diaphragm using quadratic 3D surface modeling, the proposed method is especially useful for quantifying diaphragm characteristics. Their method may be useful for assessing morphological diaphragmatic changes in COPD patients.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

CONSTRAINTS ON THE PRESENCE OF SiO GAS IN THE DEBRIS DISK OF HD 172555

We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J = 8–7 rotational transition from the vibrational ground state, carried out with the Atacama Pathfinder EXperiment (APEX) submillimeter telescope and heterodyne receiver at 863 μ m and (2) a search at 8.3 μ m for the P(17) ro-vibrational transition of gas phase SiO, carried out with the Very Large Telescope (VLT)/VISIR with a resolution, λ /Δ λ , of 30,000. The APEX measurement resulted in a 3.3 σ detection of an interstellar feature, but only an upper limit to emission at the radial velocity and line width expected from HD 172555. The VLT/VISIR result was also an upper limit. These were used to provide limits for the abundance of gas phase SiO for a range of temperatures. The upper limit from our APEX detection, assuming an 8000 K primary star photospheric excitation, falls more than an order of magnitude below the self-shielding stability threshold derived by Johnson et al. (2012). Our results thus favor a solid-state origin for the 8.3 μ m feature seen in the Spitzer IRS spectrum of the circumstellar excess emission and the production of circumstellar O i and Si i by SiO UV photolysis. The implications of these estimates are explored in the framework of models of the HD 172555 circumstellar disk.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Numerical modeling of quasi-static coronal loops. I - Uniform energy input

A quasi-static numerical model for coronal loops is considered for the case of a uniform energy input per unit volume into the loops. A line dipole model is used to represent the loop magnetic field, and the variations in loop cross section observed in X-ray photographs are parameterized by the ratio between the cross-sectional areas at the loop apex and base. The results of numerical modeling indicate that for an area ratio greater than unity, increases in the area ratio of a loop with a given length and apex area cause a general rise in electron density and a fall in the temperature gradient, leading to large increases in the differential emission factor at high temperatures. The differential function obtained is significantly different from that predicted by analytical models; however, analytical predictions for the temperature-electron density relations are comparable to numerical results. It is also concluded that even a symmetrical loop may have a maximum temperature away from the apex.

Vesecky, J. F.↗
NASA NTRS1987

Fuel-air mixing and combustion in a two-dimensional Wankel engine

A two-equation turbulence model, an algebraic grid generalization method, and an approximate factorization time-linearized numerical technique are used to study the effects of mixture stratification at the intake port and gaseous fuel injection on the flow field and fuel-air mixing in a two-dimensional rotary engine model. The fuel distribution in the combustion chamber is found to be a function of the air-fuel mixture fluctuations at the intake port. It is shown that the fuel is advected by the flow field induced by the rotor and is concentrated near the leading apex during the intake stroke, while during compression, the fuel concentration is highest near the trailing apex and is lowest near the rotor. It is also found that the fuel concentration near the trailing apex and rotor is small except at high injection velocities.

Shih, T. I.-P.↗
NASA NTRS1992

Deriving the velocity distribution of meteoroids from the measured meteoroid impact directionality on the various LDEF surfaces

Because of spacecraft orbital motion about the Earth, a much higher flux of meteoroids is expected to strike spacecraft surfaces that face in the direction of spacecraft motion (apex direction) than would strike apex facing or trailing edge surfaces. Impact velocities are also higher on apex facing surfaces compared to antapex facing surfaces which futher increases the apex/antapex ratio of spatial density of impact craters of a given size. Measurements of the areal densities of impact craters on the different LDEF surfaces should give important clues about the velocity distribution, and therefore the origins, of meteoroids. Preliminary results appear to support the meteoroid velocity distributions derived by Erickson and by Kessler, which would lead to a mean impact velocity on the LDEF spacecraft of about 19 km/s.

Zook, Herbert A.↗
NASA NTRS1992

Asteroidal versus cometary meteoroid impacts on the Long Duration Exposure Facility (LDEF)

Meteoroids that enter the Earth's atmosphere at low velocities will tend to impact the apex side (that surface facing the spacecraft direction of motion) of a spacecraft at a very high rate compared to the rate with which they will impact an antapex-facing surface. This ratio -- apex to antapex impact rates -- will become less as meteoroid entry velocities increase. The measured ratio, apex to antapex, for 500 micron diameter impact craters in 6061-T6 aluminum on LDEF seems to be about 20 from the work of the meteoroid SIG group and from the work of Humes that was presented at the first LDEF symposium. Such a ratio is more consistent with the meteoroid velocity distributions derived by Erickson and by Kessler, than it is with others that have been tested. These meteoroid velocity distributions have mean entry velocities into the Earth's atmosphere of 16.5 to 16.9 km/s. Jackson and Zook (in a paper submitted to Icarus) have numerically simulated the orbital evolution of small dust grains emitted from asteroids and comets. For those asteroidal grains small enough (below about 100 microns diameter) to drift from the asteroid belt to the orbit of the Earth, under P-R and solar wind drag, without suffering collisional destruction, the following results are found: as their ascending or descending nodes cross the Earth's orbit (and when they might collide with the Earth), their orbital eccentricities and inclinations are quite low (e less than 0.3, i less than 20 degrees), and their mean velocity with respect to the Earth is about 5 or 6 km/s. When gravitational acceleration of the Earth is taken into account, the corresponding mean velocities relative to the top of the Earth's atmosphere are 12 to 13 km/s. This means that, at best, these small asteroidal particles can not comprise more than 50 percent of the particles entering the Earth's atmosphere. And when gravitational focusing is considered, they cannot comprise more than a few percent of those in heliocentric orbit at 1 AU. The rest are presumably of cometary origin.

Zook, Herbert A.↗
NASA NTRS1992

The effect of the low Earth orbit environment on space solar cells: Results of the advanced photovoltaic experiment (S0014)

The Advanced Photovoltaic Experiment (APEX), containing over 150 solar cells and sensors, was designed to generate laboratory reference standards as well as to explore the durability of a wide variety of space solar cells. Located on the leading edge of the Long Duration Exposure Facility (LDEF), APEX received the maximum possible dosage of atomic oxygen and ultraviolet radiation, as well as enormous numbers of impacts from micrometeoroids and debris. The effect of the low earth orbital (LEO) environment on the solar cells and materials of APEX will be discussed in this paper. The on-orbit performance of the solar cells, as well as a comparison of pre- and postflight laboratory performance measurements, will be presented.

Brinker, David J.↗
NASA NTRS1992

Autonomous power system: Integrated scheduling

The Autonomous Power System (APS) project at NASA Lewis Research Center is designed to demonstrate the abilities of integrated intelligent diagnosis, control and scheduling techniques to space power distribution hardware. The project consists of three elements: the Autonomous Power Expert System (APEX) for fault diagnosis, isolation, and recovery (FDIR), the Autonomous Intelligent Power Scheduler (AIPS) to determine system configuration, and power hardware (Brassboard) to simulate a space-based power system. Faults can be introduced into the Brassboard and in turn, be diagnosed and corrected by APEX and AIPS. The Autonomous Intelligent Power Scheduler controls the execution of loads attached to the Brassboard. Each load must be executed in a manner that efficiently utilizes available power and satisfies all load, resource, and temporal constraints. In the case of a fault situation on the Brassboard, AIPS dynamically modifies the existing schedule in order to resume efficient operation conditions. A database is kept of the power demand, temporal modifiers, priority of each load, and the power level of each source. AIPS uses a set of heuristic rules to assign start times and resources to each load based on load and resource constraints. A simple improvement engine based upon these heuristics is also available to improve the schedule efficiency. This paper describes the operation of the Autonomous Intelligent Power Scheduler as a single entity, as well as its integration with APEX and the Brassboard. Future plans are discussed for the growth of the Autonomous Intelligent Power Scheduler.

Ringer, Mark J.↗
NASA NTRS1993

Asteroidal versus cometary meteoroid impacts on the Long Duration Exposure Facility (LDEF)

Meteoroids that enter the Earth's atmosphere at low velocities will tend to impact the apex side (that surface facing the spacecraft direction of motion) of a spacecraft at a very high rate compared to the rate with which they will impact an antapex-facing surface. This ratio--apex to antapex impact rates--will become less as meteoroid entry velocities increase. The measured ration, apex to antapex, for 500 micron diameter impact craters in 6061-T6 aluminum on LDEF seems to be about 20 from the work of the meteoroid SIG group and others, that was presented at the first LDEF symposium. Such a ratio is more consistent with the meteoroid velocity distributions derived by Erickson and by Kessler, than it is with others that have been tested. These meteoroid velocity distributions have mean entry velocities into the Earth's atmosphere of 16.5 to 16.9 km/s. Others have numerically simulated the orbital evolution of small dust grains emitted from asteroids and comets. For those asteroidal grains small enough (below about 100 microns diameter) to drift from the asteroid belt to the orbit of the Earth, under P-R and solar wind drag, without suffering collisional destruction, the following results are found: as the ascending or descending nodes cross the Earth's orbit, their orbital eccentricities and inclinations are quite low (e less than 0.3, i less than 20 deg), and their mean velocity with respect to the Earth is about 5 or 6 km/s. When gravitational acceleration of the Earth is taken into account, the corresponding mean velocities relative to the top of the Earth's atmosphere are 12 to 13 km/s. This means that, at best, these small asteroidal particles cannot comprise more than 50 percent of the particles entering the Earth's atmosphere. When gravitational focusing is considered, they cannot comprise more than a few percent of those in heliocentric orbit at 1 AU. The rest are presumably of cometary origin.

Zook, Herbert A.↗
NASA NTRS1993

Measurements of circulation and vorticity in the leading-edge vortex of a delta wing

The present cross-wire measurements of the flowfield above a 75-deg flat-plate delta wing have yielded distributions of velocity, axial vorticity, and circulation which exhibit strongly conical behavior upstream of the breakdown region and away from the apex and trailing edge regions. The conical character of these properties is most pronounced over the central portion of the planform, away from the apex and trailing-edge regions. This behavior is further documented by the roughly linear increase in vortex strength with distance from the apex over the forward area of the wing.

Visser, K. D.↗
NASA NTRS1951

Formulas for the Supersonic Loading, Lift, and Drag of Flat Swept-Back Wings with Leading Edges Behind the Mach Line

The method of superposition of linearized conical flows has been applied to the calculation of the aerodynamic properties, in supersonic flight, of thin flat, swept-back wings at an angle of attack. The wings are assumed to have rectilinear plan forms, with tips parallel to the stream, and to taper in the conventional sense. The investigation covers the moderately supersonic speed range where the Mach lines from the leading-edge apex lie ahead of the wing. The trailing edge may lie ahead of or behind the Mach lines from its apex. The case in which the Mach cone from one tip intersects the other tip is not treated. Formulas are obtained for the load distribution, the total lift, and the drag due to lift. For the cases in which the trailing edge is outside the Mach cone from its apex the formulas are complete. For wings with both leading and trailing edges behind their respective Mach lines, a degree of approximation is necessary. Charts of some of the functions derived are included to facilitate computing, and several examples are worked out in outline.

Cohen, Doris↗
NASA NTRS1993

Results of thermal vacuum tests for the PASP+ flight modules

The PASP PLUS (Photovoltaic Array Space Power Plus Diagnostics) program is a photovoltaic experiment which will be flown on the Air Force satellite APEX (Advanced Photovoltaic And Electronic Experiment). APEX will be launched with a Pegasus during the summer of 1993. There are two other small experiments on APEX but PASP+ is the largest, uses the most power, and accounts for over 90 percent of the data requirements. The orbit is elliptical with apogee and perigee of 1050 and 190 nautical miles respectively. The inclination is 70 deg. The two main objectives of PASP+ are to determine the interactions between high voltage arrays and the space plasma environment and to determine the radiation damage characteristics of several newer types of solar cells. In order to determine the interactions with the space plasma, several of the individual cell strings will be biased to voltages up to plus or minus 500 V, and leakage currents and arcing rates will be measured. The radiation degradation characteristics will be determined by the continuous monitoring of I-V data for all of the cell strings. As part of an overall testing program, the PASP+ panels and controller were put through a thermal vacuum test in order to check the thermal analysis, obtain temperature coefficients for the individual modules, and have an end-to-end test of the entire PASP+ experiment. This thermal vacuum test is described briefly and the results obtained during that testing are discussed.

Curtis, Henry↗
NASA NTRS1994

Design of a walking robot

Carnegie Mellon University's Autonomous Planetary Exploration Program (APEX) is currently building the Daedalus robot; a system capable of performing extended autonomous planetary exploration missions. Extended autonomy is an important capability because the continued exploration of the Moon, Mars and other solid bodies within the solar system will probably be carried out by autonomous robotic systems. There are a number of reasons for this - the most important of which are the high cost of placing a man in space, the high risk associated with human exploration and communication delays that make teleoperation infeasible. The Daedalus robot represents an evolutionary approach to robot mechanism design and software system architecture. Daedalus incorporates key features from a number of predecessor systems. Using previously proven technologies, the Apex project endeavors to encompass all of the capabilities necessary for robust planetary exploration. The Ambler, a six-legged walking machine was developed by CMU for demonstration of technologies required for planetary exploration. In its five years of life, the Ambler project brought major breakthroughs in various areas of robotic technology. Significant progress was made in: mechanism and control, by introducing a novel gait pattern (circulating gait) and use of orthogonal legs; perception, by developing sophisticated algorithms for map building; and planning, by developing and implementing the Task Control Architecture to coordinate tasks and control complex system functions. The APEX project is the successor of the Ambler project.

Whittaker, William↗
NASA NTRS1995

GPS as an orbit determination subsystems

This paper evaluates the use of Global Positioning System (GPS) receivers as a primary source of tracking data for low-Earth orbit satellites. GPS data is an alternative to using range, azimuth, elevation, and range-rate (RAER) data from the Air Force Satellite Control Network antennas, the Space Ground Link System (SGLS). This evaluation is applicable to missions such as Skipper, a joint U.S. and Russian atmosphere research mission, that will rely on a GPS receiver as a primary tracking data source. The Detachment 2, Space and Missile Systems Center's Test Support Complex (TSC) conducted the evaluation based on receiver data from the Space Test Experiment Platform Mission O (STEP-O) and Advanced Photovoltaic and Electronics Experiments (APEX) satellites. The TSC performed orbit reconstruction and prediction on the STEP-0 and APEX vehicles using GPS receiver navigation solution data, SGLS RAER data, and SGLS anglesonly (azimuth and elevation) data. For the STEP-O case, the navigation solution based orbits proved to be more accurate than SGLS RAER based orbits. For the APEX case, navigation solution based orbits proved to be less accurate than SGLS RAER based orbits for orbit prediction, and results for orbit reconstruction were inconclusive due to the lack of a precise truth orbit. After evaluating several different GPS data processing methods, the TSC concluded that using GPS navigation solution data is a viable alternative to using SGLS RAER data.

Fennessey, Richard↗
NASA NTRS1999

A Numerical Study of Low-Reynolds-Number Separation Bubbles

The present study uses two dimensional numerical simulations to study unsteady low-Reynolds-number separation bubbles. The numerical study is in two parts: (1) a two dimensional time-accurate Navier-Stokes solver is used to simulate flows over the APEX airfoil, and (2) a numerical procedure is developed for localized simulations of transitional separation bubbles. The 2-D computations of flow over the APEX airfoil show that the flow is unsteady with periodic vortex shedding. A linear stability analysis of the separated flow shows that the vortex shedding is caused due to the instability of the separated flow. For transonic flows over the APEX airfoil the vortex shedding is additionally influenced by the presence of shocks. The flowfield has two characteristic time scales, one corresponding to the vortex shedding and another corresponding to the movement of the shocks. The two dimensional (2-D) airfoil simulations also showed the presence of nonlinear effects in the separated region. To better understand the characteristics of separation bubbles a numerical procedure has been developed for localized separation bubble calculations. This procedure is used to perform computations for a flat plate separation bubble test case. The separation bubble is induced by specifying a velocity gradient in the freestream. The growth of disturbances in the separation bubble is analyzed by introducing disturbances upstream of the separation bubble.

Tatineni, Mahidhar↗
NASA NTRS2002

Differential Cratering of Synchronously Rotating Satellites by Ecliptic Comets

We use Monte Carlo methods to simulate impacts of ecliptic comets on the synchronously rotating satellites of giant planets. We reconfirm the long-standing prediction that the cratering rate should be much higher on the leading hemispheres than on the trailing hemisphere; indeed we find that previously published analytical formulations modestly underestimate the degree of apex-antapex asymmetry to be expected. We then compare our results to new mapping of impact craters on Ganymede, Callisto, and Triton. Ganymede reveals a pronounced apex-antapex asymmetry that is nonetheless much less than predicted. All of Triton's confirmed impact craters are clustered toward the apex of motion, far exceeding the predicted asymmetry. No asymmetry is observed on Callisto. In each case at least one of our basic assumptions must be wrong. Likely candidates include the following: (i) the surfaces of all but the most sparsely cratered satellites are saturated or nearly saturated with impact craters; (ii) these satellites have rotated nonsynchronously over geological time; (iii) most of the craters are made not by heliocentric (Sun-orbiting) comets and asteroids but rather by planetocentric (planet-orbiting) debris of indeterminate origin; or (iv) pathological endogenic resurfacing has created illusions of structure. Callisto's surface is readily classified as nearly saturated. Ganymede's bright terrains, although less heavily cratered than those of Callisto, can also be explained by crater densities approaching saturation on a world where endogenic processes were active. The leading alternative is nonsynchronous rotation, an explanation supported by the distribution of catenae (crater chains produced by impact of tidally disrupted comets). Triton's craters can be explained by planetocentric debris or by capricious resurfacing, but both hypotheses are inherently improbable.

Zahnle, Kevin↗
NASA NTRS1990

Defective secretion of mucilage is the cellular basis for agravitropism in primary roots of Zea mays cv. Ageotropic

Root caps of primary, secondary, and seminal roots of Z. mays cv. Kys secrete large amounts of mucilage and are in close contact with the root all along the root apex. These roots are strongly graviresponsive. Secondary and seminal roots of Z. mays cv. Ageotropic are also strongly graviresponsive. Similarly, their caps secrete mucilage and closely appress the root all along the root apex. However, primary roots of Z. mays cv. Ageotropic are non-responsive to gravity. Their caps secrete negligible amounts of mucilage and contact the root only at the extreme apex of the root along the calyptrogen. These roots become graviresponsive when their tips are coated with mucilage or mucilage-like materials. Peripheral cells of root caps of roots of Z. mays cv. Kys contain many dictyosomes associated with vesicles that migrate to and fuse with the plasmalemma. Root-cap cells of secondary and seminal (i.e. graviresponsive) roots of Z. mays cv. Ageotropic are similar to those of primary roots of Z. mays cv. Kys. However, root-cap cells of primary (i.e. non-graviresponsive) roots of Z. mays cv. Ageotropic have distended dictyosomal cisternae filled with an electron-dense, granular material. Large vesicles full of this material populate the cells and apparently do not fuse with the plasmalemma. Taken together, these results suggest that non-graviresponsiveness of primary roots of Z. mays cv. Ageotropic results from the lack of apoplastic continuity between the root and the periphery of the root cap. This is a result of negligible secretion of mucilage by cells along the edge of the root cap which, in turn, appears to be due to the malfunctioning of dictyosomes in these cells.

NASA Discipline Number 29-20↗
NASA NTRS2005

The Apollo Capsule Optimization for Improved Stability and Computational/Experimental Data Comparisons

Numerical optimization was employed on the Apollo Command Module to modify its external shape. The Apollo Command Module (CM) that was used on all NASA human space flights during the Apollo Space Program is stable and trimmed in an apex forward (alpha of approximately 40 to 80 degrees) position. This poses a safety risk if the CM separates from the launch tower during abort. Optimization was employed on the Apollo CM to remedy the undesirable stability characteristics of the configuration. Geometric shape changes were limited to axisymmetric modifications that altered the radius of the apex (R(sub A)), base radius (R(sub O)), corner radius (R(sub C)), and the cone half angle (theta), while the maximum diameter of the CM was held constant. The results of multipoint optimization on the CM indicated that the cross-range performance can be improved while maintaining robust apex-aft stability with a single trim point. Navier-Stokes computations were performed on the baseline and optimized configurations and confirmed the Euler-based optimization results. Euler Analysis of ten alternative CM vehicles with different values of the above four parameters are compared with the published experimental results of numerous wind tunnel tests during the late 1960's. These comparisons cover a wide Mach number range and a full 180-degree pitch range and show that the Euler methods are capable of fairly accurate force and moment computations and can separate the vehicle characteristics of these ten alternative configurations.

Cliff, Susan E.↗