Removal of the high-resistivity layer at the n on n/+/ liquid phase epitaxial GaAs layer-substrate interface by controlled in situ etch-back
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Seabaugh, A. C.↗
SEARCH · Engineering Papers
Results for “phase control”
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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Surface scattering properties estimated from modeling airborne multiple emission angle reflectance data
Here, researchers apply the Hapke function to airborne bidirectional reflectance data collected over three terrestrial surfaces. The objectives of the study were to test the range of natural surfaces that the Hapke model fits and to evaluate model parameters in terms of known surface properties. The data used are multispectral and multiple emission angle data collected during the Geologic Remote Sensing Field Experiment (GRSFE) over a mud-cracked playa, an artificially roughened playa, and a basalt cobble strewn playa at Lunar Lake Playa in Nevada. Airborne remote sensing data and associated field measurements were acquired at the same time. The airborne data were acquired by the Advanced Solid State Array Spectroradiometer (ASAS) instrument, a 29-spectral band imaging system. ASAS reflectance data for a cobble-strewn surface and an artificially rough playa surface on Lunar Lake Playa can be explained with the Hanke model. The cobble and rough playa sites are distinguishable by a single scattering albedo, which is controlled by material composition; by the roughness parameter, which appears to be controlled by the surface texture and particle size; and the symmetry factor of the single particle phase function, which is controlled by particle size and shape. A smooth playa surface consisting of compacted, fine-grained particles has reflectance variations that are also distinct from either the cobble site or rough playa site. The smooth playa appears to behave more like a Lambertian surface that cannot be modeled with the Hapke function.
Guinness, Edward A.↗
The influence of air traffic control message length and timing on pilot communication
The present paper outlines an approach to air traffic control (ATC) communication that is based on theories of dialogue organization and describes several steps or phases in routine controller-pilot communication. The introduction also describes several kinds of communication problems that often disrupt these steps, as well as how these problems may be caused by factors related to ATC messages, the communication medium (radio vs. data link) and task workload. Next, a part-task simulation study is described. This study focused on how problems in radio communication are related to message factors. More specifically, we examined if pilots are more likely to misunderstanding longer ATC messages. A more general goal of the study is to show that communication analysis can help trace where problem occur and why.
Morrow, Daniel↗
Phase Transitions in Protein Solutions: Dynamics, Structures and Control Strategies
No abstract available
Vekilov, P. G.↗
Phase Transitions is Protein Solutions: Structures, Dynamics and Control Pathways
No abstract available
Vekilov, Peter G.↗
CFD Jet Mixing Model Validation Against Zero-Boil-Off Tank (ZBOT) Microgravity Experiment
The Zero-Boil-Off Tank (ZBOT) experiments are a series of small scale two-phase fluids physics experiments conducted aboard the International Space Station (ISS) in 2017. A goal of these experiments is to study various fundamental fluid flow, heat and mass transport, and phase change phenomena that control storage tank pressurization and pressure control in microgravity. In this paper, results of a state-of-the-art two-phase CFD (Computational Fluid Dynamics) storage tank model are presented and validated against jet mixing data provided by microgravity ZBOT experiments. Jet-ullage interaction was studied in the experiment for different jet speeds representing different flow regimes, and tank fill levels. Effects of various physical parameters, such as, jet angle, gravitational acceleration and surface tension value were investigated. Computational parameters, such as turbulence and surface tension models and interface capturing scheme, affecting jet-ullage interaction were also studied. Computational results were compared to experimental results for model validation.
Turbulence↗
CFD Jet Mixing Model Validation against Zero-Boil-Off Tank (ZBOT) Microgravity Experiment
The Zero-Boil-Off Tank (ZBOT) experiments are a series of small scale two-phase fluids physics experiments conducted aboard the International Space Station (ISS) in 2017. A goal of these experiments is to study various fundamental fluid flow, heat and mass transport, and phase change phenomena that control storage tank pressurization and pressure control in microgravity. In this paper, results of a state-of-the-art two-phase CFD storage tank model are presented and validated against jet mixing data provided by microgravity ZBOT experiments. Jet-ullage interaction was studied in the experiment for different jet speeds representing different flow regimes, and tank fill levels. Effects of various physical parameters, such as, jet angle, gravitational acceleration and surface tension value were investigated. Computational parameters, such as turbulence and surface tension models and interface capturing scheme, affecting jet-ullage interaction were also studied. Computational results were compared to experimental results for model validation.
Mixing↗
Satellite power system (SPS) magnetron tube assessment study
Taks performed to extend the data base and to define a technology development program for the magnetron directional amplifier for the SPS are reviewed. These include: (1) demonstrating the tracking of phase and amplitude of the microwave output to phase and amplitude references; (2) expanding the range of power over which the directional amplifier will operate; (3)recognizing the importance of amplitude control in overall system design and in simplifying power conditioning; (4) developing a preliminary design for the overall architecture of the power module; (5) demonstrating magnetron starting using the amplitude control system; (6) mathematically modelling and performing a computerized study of the pyrolytic graphite radiating fin; (7) defining the mass of the magnetic circuit for the SPS tube; (8) noise measurement; (9) achieving harmonic suppression by notch reflection filters; (10) estimating the mass of the transmitting antenna; (11) developing a magnetron package with power generation, phase control, and power condition functions; and (12) projecting magnetron package characteristics.
Source record↗
Mariner Mars 1971 attitude control subsystem flight performance
The flight performance of the Mariner 71 attitude control subsystem is discussed. Each phase of the mission is delineated and the attitude control subsystem is evaluated within the observed operational environment. Performance anomalies are introduced and discussed within the context of general performance. Problems such as the sun sensor interface incompatibility, gas valve leaks, and scan platform dynamic coupling effects are given analytical considerations.
Schumacher, L.↗
Application of active controls to civil transport aircraft
The impact of active controls on civil transport aircraft and some of the complex problems involved are described. The approach taken by NASA as part of the Active Control Technology Program is discussed to integrate active controls in the conceptual design phase. It is shown that when handled correctly, active controls improve aircraft performance.
Taylor, L. W., Jr.↗
Synthesis and evaluation of phase detectors for active bit synchronizers
Self-synchronizing digital data communication systems usually use active or phase-locked loop (PLL) bit synchronizers. The three main elements of PLL synchronizers are the phase detector, loop filter, and the voltage controlled oscillator. Of these three elements, phase detector synthesis is the main source of difficulty, particularly when the received signals are demodulated square-wave signals. A phase detector synthesis technique is reviewed that provides a physically realizable design for bit synchronizer phase detectors. The development is based upon nonlinear recursive estimation methods. The phase detector portion of the algorithm is isolated and analyzed.
Mcbride, A. L.↗
The control of manual entry accuracy in management/engineering information systems, phase 1
It was shown that clerical personnel can be tested for proofreading performance under simulated industrial conditions. A statistical study showed that errors in proofreading follow an extreme value probability theory. The study showed that innovative man/machine interfaces can be developed to improve and control accuracy during data entry.
Hays, Daniel↗
Olympus receiver evaluation and phase noise measurements
A set of measurements performed by the Michigan Tech Sensing and Signal Processing Group on the analog receiver built by the Virginia Polytechnic Institute (VPI) and the Jet Propulsion Laboratory (JPL) for propagation measurements using the Olympus Satellite is described. Measurements of local oscillator (LO) phase noise were performed for all of the LOs supplied by JPL. In order to obtain the most useful set of measurements, LO phase noise measurements were made using the complete VPI receiver front end. This set of measurements demonstrates the performance of the receiver from the Radio Frequency (RF) input through the high Intermediate Frequency (IF) output. Three different measurements were made: LO phase noise with DC on the voltage controlled crystal oscillator (VCXO) port; LO phase noise with the 11.381 GHz LO locked to the reference signal generator; and a reference measurement with the JPL LOs out of the system.
Campbell, Richard L.↗
Entry Guidance for the Reusable Launch Vehicle
The X-33 Advanced Technology Demonstrator is a half-scale prototype developed to test the key technologies needed for a full-scale single-stage reusable launch vehicle (RLV). The X-33 is a suborbital vehicle that will be launched vertically, and land horizontally. The goals of this research were to develop an alternate entry guidance scheme for the X-33 in parallel to the actual X-33 entry guidance algorithms, provide comparative and complementary study, and identify potential new ways to improve entry guidance performance. Toward these goals, the nominal entry trajectory is defined by a piecewise linear drag-acceleration-versus-energy profile, which is in turn obtained by the solution of a semi-analytical parameter optimization problem. The closed-loop guidance is accomplished by tracking the nominal drag profile with primarily bank-angle modulation on-board. The bank-angle is commanded by a single full-envelope nonlinear trajectory control law. Near the end of the entry flight, the guidance logic is switched to heading control in order to meet strict conditions at the terminal area energy management interface. Two methods, one on ground-track control and the other on heading control, were proposed and examined for this phase of entry guidance where lateral control is emphasized. Trajectory dispersion studies were performed to evaluate the effectiveness of the entry guidance algorithms against a number of uncertainties including those in propulsion system, atmospheric properties, winds, aerodynamics, and propellant loading. Finally, a new trajectory-regulation method is introduced at the end as a promising precision entry guidance method. The guidance principle is very different and preliminary application in X-33 entry guidance simulation showed high precision that is difficult to achieve by existing methods.
Lu, Ping↗
Dual physiological rate measurement instrument
The object of the invention is to provide an instrument for converting a physiological pulse rate into a corresponding linear output voltage. The instrument which accurately measures the rate of an unknown rectangular pulse wave over an extended range of values comprises a phase-locked loop including a phase comparator, a filtering network, and a voltage-controlled oscillator, arranged in cascade. The phase comparator has a first input responsive to the pulse wave and a second input responsive to the output signal of the voltage-controlled oscillator. The comparator provides a signal dependent on the difference in phase and frequency between the signals appearing on the first and second inputs. A high-input impedance amplifier accepts an output from the filtering network and provides an amplified output DC signal to a utilization device for providing a measurement of the rate of the pulse wave.
Cooper, Tommy G.↗
Analysis of dual control vibration testing
Analysis of dual control vibration testing is conducted using a two-degree-of-freedom system to represent the interaction between a vibration mode of a test item and a mode of a mounting structure. The results indicate that exact dual control based on specification of the source free acceleration and blocked force is strictly valid only if phase is taken into account. However, extremal dual control without phase alleviates overtesting without risk of undertesting, when the limit acceleration and force specifications are chosen to envelope the coupled system results. Several approaches to deriving appropriate force specifications are explored. Random vibration parametric results from the literature are used to estimate the limit force between coupled oscillators with different source and load masses.
Scharton, Terry D.↗
High-speed electromechanical shutter for imaging spectrographs
The present invention presents a high-speed electromechanical shutter which has at least two rotary beam choppers that are synchronized using a phase-locked loop electronic control to reduce the duty cycle. These choppers have blade means that can comprise discs or drums, each having about 60 (+/-15) slots which are from about 0.3 to about 0.8 mm wide and about 5 to about 20 mm long (radially) which are evenly distributed through out 360?, and a third rotary chopper which is optically aligned has a small number of slots, such as for example, 1 to 10 slots which are about 1 to about 2 mm wide and about 5 to about 20 mm long (radially). Further the blade means include phase slots that allow the blade means to be phase locked using a closed loop control circuit. In addition, in a preferred embodiment, the system also has a leaf shutter. Thus the invention preferably achieves a gate width of less than about 100 microseconds, using motors that operate at 3000 to 10,000 rpm, and with a phase jitter of less than about 1.5 microseconds, and further using an aperture with more than about 75% optical transmission with a clear aperture of about 0.8 mm?10 mm. The system can be synchronized to external sources at 0 6 kHz lasers, data acquisition systems, and cameras.
Nguyen, Quang-Viet↗
High-speed electromechanical chutter for imaging spectrographs
The present invention presents a high-speed electromechanical shutter which has at least two rotary beam choppers that are synchronized using a phase-locked loop electronic control to reduce the duty cycle. These choppers have blade means that can comprise discs or drums, each having about 60 (+/- 15) slots which are from about 0.3 to about 0.8 mm wide and about 5 to about 20 nun long (radially) which are evenly distributed through out 360 deg, and a third rotary chopper which is optically aligned has a small number of slots, such as for example, 1 to 10 slots which are about 1 to about 2 mm wide and about 5 to about 20 mm long (radially). Further the blade means include phase slots that allow the blade means to be phase locked using a closed loop control circuit. In addition, in a preferred embodiment, the system also has a leaf shutter. Thus the invention preferably achieves a gate width of less than about 100 microseconds, using motors that operate at 3000 to 10,OOO rpm, and with a phase jitter of less than about 1.5 microseconds, and further using an aperture with more than about 75% optical transmission with a clear aperture of about 0.8 -10 nun. The system can be synchronized to external sources at 0 6 kHz lasers, data acquisition systems, and cameras.
Quang-Viet Nguyen↗