Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “time shift”

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 829 records · Page 46

Dynamics of plasma, energetic particles, and fields near synchronous orbit in the nighttime sector during magnetospheric substorms

Two phases of substorm-associated magnetospheric dynamics are discussed in terms of particles and fields at synchronous orbit. The first phase corresponds to the 'decreases' of energetic particle flux. The second phase is the conventional expansion phase that begins with the 'onset', characterized in the study by (1) a sudden decrease in the tail current and a return of the inflated magnetosphere to a dipolelike configuration, (2) a sudden shift of trapped high-energy particles toward the tail again following contours of constant B, and at the same time (3) a surge of tail plasma toward the earth as the induced electric field now increases the total convection field.

Sauvaud, J.-A.↗

A dispersion law for solar oscillations

The simple model of p-mode solar oscillations of Liebacher and Stein (1981), in which the acoustic vibrations are trapped in a resonant cavity taking the form of a spherical shell below the solar surface, is compared with Doppler shift observations of vertical velocities. The model is shown to predict a modified dispersion law in which the sound travel time across the cavity is a function of the ratio of the temporal frequency to the horizontal wavenumber, resulting in a single curve when the temporal frequency is plotted against the wavenumber. Frequencies derived from a two-dimensional power spectrum of velocity observations are found to conform to a modified version of the dispersion relation, and that only when the fundamental mode is excluded. Results thus suggest that all modes with the same frequency/wavenumber ratio are trapped in an identical cavity, or, more plausibly, that the difference in upper boundary conditions for different modes has minimal effect on the resulting frequencies.

Duvall, T. L., Jr.↗

Evaluation of land cover change detection techniques using Landsat MSS data

Four techniques for detecting land cover change with Landsat MSS data were evaluated for a test site in east central Louisiana where forestland is being converted to cropland and pasture. The four techniques were: (1) post-classification differencing, (2) composite classification, (3) radiance value shift, and (4) regression modeling. Three of the techniques gave acceptable accuracies. The main differences were the amount of computer time and the level of complexity.

Burns, G. S.↗

Limits on photospheric Doppler signatures for solar giant cells

Mount Wilson solar-velocity data taken since improvement of the spectrograph in May 1982 are analyzed to search for photospheric traces of persistent velocity patterns that are anticipated in recent model predictions. The method involves time-averaged autocorrelations and cross correlations of the residuals that remain after least-squares fits for differential rotation, limb shift, and meridional circulation are extracted from the daily-magnetogram velocity arrays. It is argued that, owing to the supergranular motions in the photosphere, the sensitivity in applying the present method to the new Mount Wilson data is close to the ultimate sensitivity possible for detection of this phenomenon. The following limits are currently established through this analysis: (1) there is no sharply peaked power spectrum with amplitude above about 1 m/s per wavenumber, and (2) there is no broad-band power spectrum for which the total integrated power is greater than about 10 sq m/sq sec.

Snodgrass, H. B.↗

Pressure induced ageing of polymers

The nonlinearly viscoelastic response of an amorphous homopolymer is considered under aspects of time dependent free volume behavior. In contrast to linearly viscoelastic solids, this model couples shear and volume deformation through a shift function which influences the rate of molecular relaxation or creep. Sample computations produce all those qualitative features one observes normally in uniaxial tension including the rate dependent formation of a yield point as a consequence of the history of an imposed pressure.

Emri, I.↗

Effects of heat release on the large-scale structure in turbulent mixing layers

The effects of chemical heat release on the large-scale structure in a chemically reacting turbulent mixing layer have been studied using three-dimensional time-dependent simulations. Moderate heat release is found to slow the development of the large-scale structures and to shift their wavelengths to larger scales. The results suggest that previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers may be the result of vorticity generation by baroclinic torques.

Mcmurtry, P. A.↗

Data acquisition and processing

Fundamental methods of signal processing used in normal mesosphere stratosphere troposphere (MST) radar observations are described. Complex time series of received signals obtained in each range gate are converted into Doppler spectra, from which the mean Doppler shift, spectral width and signal-to-noise ratio (SNR) are estimated. These spectral parameters are further utilized to study characteristics of scatterers and atmospheric motions.

Tsuda, Toshitaka↗

UBV photometry of the Ap variable UZ Psc = HD 10783

The photometric variability of the Ap star HD 10783 = UZ Psc is discussed. New UBV photometry, obtained between late 1965 and early 1969, is presented and it is combined with existing published photometry to derive an improved ephemeris for times of maximum brightness: 2439758.00 + 4d.1328 n. It is concluded that the results are not very sensitive to the small shifts applied to the blue photometry.

Hardie, Robert H.↗

Open-Loop Acquisition Of Suppressed Carrier Signals

Three digital techniques for open-loop acquisition of suppressed carrier signals in presence of binary-phase-shift-keyed (BPSK) modulation representing non-return-to-zero (NRZ) data symbols. Based on assumption that offset, tau, between timing of symbols and clock in receiver unknown, but fixed fraction of symbol period, T. In all three, fast Fourier transforms (FFT's) performed on outputs of integrate-and-dump filters that are parts of Costas-type loops used to demodulate BPSK signals. Timing of integrate-and-dump filters constant. Outputs mixed to obtain an error signal.

Shah, Biren N.↗

Positioning Fixtures For X-Ray Inspection

Flanged fixtures designed to position x-ray source at fixed locations within welded parts inspected radiographically. Eliminates need for tedious measurements to find proper locations and alignments of x-ray source. Reduces setup time and eliminates waste of film occurring when x-radiographs taken at incorrect positions. Variability among parts, inspectors, and shifts eliminated. Each fixture essentially flanged plastic cylinder holding x-ray tube on its axis. Fixture designed to fit specific part to hold x-ray source at internal position from which x rays are required to emanate to illuminate region of interest.

Lee, Jerry W.↗

Observations of the CO bulge on Venus and implications for mesospheric winds

Observations of CO at 2.6 mm (115.27 GHz) were made with the Owens Valley Radio Observatory (OVRO) millimeter interferometer in 1986 and 1988, yielding high-quality disk-resolved spectra which were inverted to determine the CO mixing ratio profile from distinct regions on the disk, allowing us to map the distribution of CO in the upper mesosphere of Venus both horizontally and vertically. The 1986 observations were of the morning terminator and were particularly useful in searching for a suspected CO maximum ('bulge') on the nightside. The resulting CO mixing ratio profiles were mapped for various altitudes as functions of latitude and local time, and we report that we have resolved the previously inferred CO bulge. The bulge increases in magnitude from a small day-night variation at 90 km to an extensive nightside peak at 100 km, the upper limit of our observations. The peak bulge-to-dayside ratio approached 20-30 at 100 km in 1986 and may have been as large as 50-100, assuming late-afternoon CO abundances found in 1988 were similar to those in 1986. Three-dimensional mapping shows that in the upper mesosphere the bulge was displaced from local midnight toward the morning equator, centered at 3:30 AM local time. Using the qualitative model of mesospheric circulation on Venus proposed by Clancy and Muhleman (1985, 1991), we explain this shift in terms of strong retrograde zonal winds throughout the mesosphere, matching the directly detected mesospheric circulation (Shah, K., D. O. Muhleman, and G. L. Berge 1991) observed with the same dataset in 1988.

Gurwell, Mark A.↗

Rocket Science for the Internet

Rainfinity, a company resulting from the commercialization of Reliable Array of Independent Nodes (RAIN), produces the product, Rainwall. Rainwall runs a cluster of computer workstations, creating a distributed Internet gateway. When Rainwall detects a failure in software or hardware, traffic is shifted to a healthy gateway without interruptions to Internet service. It more evenly distributes workload across servers, providing less down time.

Source record↗

New Insights on the Accretion Disk-Winds Connection in Radio-Loud AGNs from Suzaku

From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ,,approx.0.1 c in three of them, namely 3C III, 3C 120 and 3C 390.3. They are consistent with being accretion disk winds/outflows. We also performed a follow-up on 3C III to monitor its outflow on approx.7 days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disc-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.

Tombesi, F.↗

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk Around PDS 70: Observations of the Disk

We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is approx.70 AU. Our data show that the geometric center of the disk shifts by approx.6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of SED fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit mass of companions at approx.30 to approx.50MJ within the gap. Taking account of the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap. Subject headings: planetary systems - protoplanetary disks - stars: individual (PDS 70) - stars: pre-main sequence - polarization

Hashimoto, J.↗

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk Around PDS 70: Observations of the Disk

We present high-resolution H-band polarized intensity (FWHM=0".1:14AU) and L'-band imaging data(FWHM= 0".11:15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0".2) up to 210 AU (1".5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is approx.70 AU. Our data show that the geometric center of the disk shifts by approx.6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of spectral energy distribution fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit of approx.30 to approx.50 M(sub J) on the mass of companions within the gap. Taking into account the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap. Key words: planetary systems - polarization - protoplanetary disks - stars: individual (PDS 70) - stars: pre-main sequence.

Hashimoto, J.↗

ISS Payload Operations Training During the COVID-19 Pandemic: Impacts and Solutions

The onset of the COVID-19 pandemic brought a dramatic and rapid transformation to almost every aspect of humanity in 2020. The world’s space agencies and their missions were not immune to the wide-sweeping changes. One discipline principally affected was mission operations and the various groups supporting that function. Mission support teams, especially for complex and crewed missions like the International Space Station were forced to rapidly rethink how and where control center staff performed their vital work. Operations training – an essential element to mission ops, had unique hurdles to overcome. Operations training is responsible for preparing astronaut crews for their missions, providing training to flight controllers, as well as ensuring that new team members are ready to join their colleagues. Every element of training was impacted by COVID restrictions. From orientation and introductory classes for new controllers, simulations and advanced lessons, On the Job Training and final evaluations; all aspects faced new challenges. Trainers at NASA’s Marshall Space Flight Center in Huntsville, Alabama, were forced to become more efficient with trainees and resources to continue supporting payload operations. The pandemic started in the USA in March 2020. Immediately, NASA mandated that the support for ISS real-time operations was critical. As a result, physical access to key facilities was restricted. Trainers and trainees had to quickly shift to 100 percent remote learning. In the short term, this was not a problem. However, instructors discovered lessons that they were accustomed to delivering in a classroom environment did not translate to remote teaching. Another hurdle to operations training was the mandate that all simulations could only be held remotely. The logistics of even small simulations proved to be challenging due to IT restrictions and public internet limitations. With simulations essentially stopped, as well as the restrictions on most OJT, trainees were essentially stopped in their advancement towards certification. Once limitations were identified, trainers prioritized new options. Transitioning to all electronic learning materials was a relatively easy fix. Teaching to large groups took additional shifts in the training paradigm. Methods for preparing astronauts for their missions were revised. Simulation supervisors found more efficient techniques to provide realistic training experience. Communication and approvals from management was essential. In every case, the payload operations instructors found novel solutions to all functions listed. This paper will discuss the factors and solutions payloads operations trainers found to keep scientific research on the ISS flying forward to mission success.

ISS↗

ISS Payload Operations Training Throughout the COVID-19 Pandemic: Impacts, Opportunities and Solutions

The onset of the COVID-19 pandemic brought a dramatic and rapid transformation to almost every aspect of humanity. The world’s space agencies and their missions were not immune to the wide-sweeping changes. One discipline principally affected was mission operations and the various groups supporting that function. Mission support teams, especially for complex and crewed missions like the International Space Station (ISS) were forced to rethink how and where control center staff performed their vital work. Operations training – an essential element to mission ops, had unique hurdles to overcome. Operations training is responsible for preparing astronaut crews for their missions, training and certifying flight controllers, as well as ensuring that new team members are ready to join their colleagues. Every element of training was impacted during the pandemic. From orientation and introductory classes for new controllers, simulations, and advanced lessons, On the Job Training (OJT) and final evaluations; all aspects faced challenges. Trainers at NASA’s Marshall Space Flight Center in Huntsville, Alabama were forced to become more efficient with trainees and resources to continue supporting ISS payload operations. The pandemic arrived in the USA in March 2020. Immediately, NASA mandated that the support for ISS real-time operations was critical. As a result, physical access to key facilities was restricted. Trainers and trainees had to quickly shift to 100% remote learning. In the short term, this was not a problem. However, instructors discovered lessons they were accustomed to delivering in a classroom environment often did not translate to remote teaching. Another hurdle to operations training was the mandate that all simulations could only be held remotely. The logistics of even small simulations proved to be challenging due to Information Technology (IT) restrictions and public internet limitations. With simulations essentially halted, as well as the restrictions on most OJT, trainees were essentially stopped in their advancement towards certification. Once limitations were identified, trainers prioritized new options. Transitioning to all electronic learning materials was a relatively easy fix. Teaching to large groups took additional shifts in the training paradigm. Methods for preparing astronauts for their missions were revised. Simulation supervisors found efficient techniques to provide realistic training experiences. Communication and coordination with management was essential. In every case, the payload operations instructors found novel solutions to all functions listed. This paper discusses the factors and solutions payloads operations trainers found to keep scientific research on the ISS flying forward to mission success.

ISS↗

Extreme Problem Solving II: How Can 4 Astronauts do the Jobs of 80 Experts?

On past and present space missions, resilience is largely dependent on the problem-solving expertise of flight controllers at Mission Control on the ground. Missions to Mars will instead experience long communication delays and blackouts that require a small crew to detect, diagnose, and respond to critical events with only intermittent and limited real-time ground support. Our 2021 SpaceCHI paper “Extreme Problem Solving: The New Challenges of Deep Space Exploration” introduced the paradigm shift of increasingly Earth-independent mission operations and identified the capabilities that are not currently available on-board but will be needed to enable safe exploration beyond low-Earth orbit [1]. This paper investigates how the ground team achieves resilience today to inform what will be needed to achieve human-systems resilience on future long duration exploration missions – how can a crew of four generalists achieve the same outcomes as a team of 80+ experts? An actual ISS anomaly is analyzed and then reimagined under Mars transit conditions, to reveal critical decision-points and the onboard capabilities that will be needed for successful resolution. This paper also presents criteria for what makes urgent, unanticipated events so challenging to resolve.

human-systems integration architecture↗