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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

First interferometric observations of solar microwave millisecond spike bursts

Observations, with one-dimensional spatial resolution, of solar microwave millisecond spikes at 2.8 GHz are reported. The observations were made with the Owens Valley frequency-agile interferometer with 20 ms time resolution. It is found that the spikes occur at a position different from that of the underlying gyrosynchrotron radio burst source. All of the spikes during the rising part of the burst come from the same one-dimensional location to within + or - 1 arcsec, despite the fact that rapid evolution in the sense and degree of circular polarization was observed. The one-dimensional position of the spikes is consistent with a location over a large sunspot, suggesting that the emission occurs in a region of strong, converging magnetic field. The observations support the suggestion that the spikes are due to the electron-cyclotron maser mechanism.

Gary, Dale E.↗
NASA NTRS1994

Effect of B(sub y) on neutral line ridges and dynamical source ordering

In this paper we study the effect of a uniform magnetic field B(sub y) in the cross-tail y direction on the dynamics and distribution of energetic ions in a current sheet model including a neutral line. Martin and Speiser (1988) have previously shown that a 'ridge' in the velocity space distribution function is a remote neutral line signature in a two-dimensional field without B(sub y). Our results show that as B(sub y) is increased, using nominal tail parameters, there is very little change in the ridge signature for small B(sub y) (up to about 4 times B(sub z)). For intermediate values (up to about 10 times times B(sub Y)) the ridge becomes observable further from the neutral line, while close to the X line the ridge is strongly modified. For large B(sub y) (of the order of B(sub x)) the ridge evolves into the new neutral line signatures which depend strongly on whether the observations point is above or below the current sheet. These results are used to estimate B(sub y) less than 2 nT in the Active Magentospheric Particle Traces Explorers/Ion Release Module (AMPTE/IRM) event modeled by Speiser and Martin (1994), which is consistent with onboard magnetometer measurements. We further show that the cause of the new structures appearing at large B(sub Y) is the same source seperation effect that produced the original ridge and that all these signatures are relatively insensitive to a small parallel electric field. Finally, we point our a dynamical ordering which occurs at large B(sub y): Using high-resolution simulations, we find a common boundary separating regions of positive and negative initial x, y, and z position, as well as initial pitch angle. This boundary is purely dynamical in nature and is independent of modeled source distributions.

Martin, R. F., Jr.↗
NASA NTRS1995

High angular resolution 30 microns observations of the Galactic Center

We have mapped the central 2 min (5 pc) of the Galaxy with 4 sec resolution at 30 microns, using the MSFC bolometer array on the NASA Infrared Telescope Facility at Mauna Kea. Complementary maps at 10 and 20 microns covering the same region were obtained contemporaneously with the same instrumentation. The maps encompass both the central cavity at the very center of the Galaxy and the disk of gas and dust which surrounds it. Our data show thermal emissions from dust particles within the cavity and - for the first time at this resolution - within the disk itself. The emission peaks at the position of IRS1 at all three wavelengths, and the 20/30 micron brightness ratio falls uniformly from this peak toward the outer regions of the source. The 30 micron emission correlates well with the HCN emission in the southwest portion of the circumnuclear disk and with the (O I) emission in the north. No feature is apparent at the position of SgrA at any of the three wavelengths. The circumnuclear disk was discovered from the KAO and has been extensively studied in both continuum and line emission in numerous subsequent flights. The poster will attempt to show how these latest ground-based observations intersect and build upon these airborne investigations.

Telesco, Charles M.↗
NASA NTRS2003

Search for X-Ray Emission in the Nearest Known Brown Dwarf

The XMM observation were obtained on 2001 January 07-08 for 51767 s. The Optical Monitor (OM) was used with the V filter for 4 exposures of 5000 s each in imaging mode. We used the data given by the OM to confirm the presence of the source in the field of view. The European Photon Imaging Camera (EPIC) MOS 1 and MOS2 were used 48724 s each in prime full window mode with 2.5 s time resolution. The EPIC PN was used 46618 s in prime full window mode with 73.4 ms time resolution. The X-ray source closest to the expected position of our target is offset by delta R.A=2.5 arcsec and delta Dec=-28.37 arcsec. This offset is high in comparison with the 0.4 arcsec observed with the optical data. So at this point we already knew that the target was not detected. To confirm that conclusion, we performed the identification of all X-ray sources in the field of view by comparing source to source our image with the one obtained by Rutledge et al. with Chandra. This allowed us to identify all the X-ray sources in our field of view in an area of 20 arcsec times 10 arcsec centered on the expected coordinates of LP944-20. We were then able to conclude that the target was not detected during this observation. This result allowed us to determine a new and better 3 sigma upper limit of X-Ray emission for this object. We have also derived duty cycles for X-ray flares as a function of X-ray luminosity by comparing the XMM data with Chandra and ROSAT data. One student has been supported with the grant during four months (Herve Bouy). A Sun workstation was purchased for him.

Martin, Eduardo↗
NASA NTRS2003

Visual Cueing Effects Investigation for a Hovering Task

In simulators, as in actual aircraft, pilots conduct their missions according to perceived vehicle performance and spatial orientation from out-the-window (OTW) information. Ground-based flight simulations rely upon computer-generated OTW visual scenes. The realism and fidelity of a specific OTW simulation therefore has a significant impact on mission effectiveness. This study investigates effects of three visual parameters of the computer-generated image system (field-of-view, collimation, and resolution) on a disturbance-rejection hovering task. Pilots' performance and workload were studied under the following conditions: collimated optics vs. noncollimated optics, wide field-of-view (FOV) vs. narrow FOV, and higher resolution vs. lower resolution. Subjects were instructed to maintain a station-keeping position during disturbances while piloting an uncoupled four degrees-of-freedom (DOF) helicopter model, which had a satisfactory rate-command system in pitch and roll axes and ideal heading and altitude hold. Display collimation and FOV were found to have significant effects on pilots performance and subjective their subjective perception of visual cueing quality.

Chung, William W. Y.↗
NASA NTRS2010

Ultra-Wideband Time-Difference-of-Arrival High Resolution 3D Proximity Tracking System

This paper describes a research and development effort for a prototype ultra-wideband (UWB) tracking system that is currently under development at NASA Johnson Space Center (JSC). The system is being studied for use in tracking of lunar./Mars rovers and astronauts during early exploration missions when satellite navigation systems are not available. U IATB impulse radio (UWB-IR) technology is exploited in the design and implementation of the prototype location and tracking system. A three-dimensional (3D) proximity tracking prototype design using commercially available UWB products is proposed to implement the Time-Difference- Of-Arrival (TDOA) tracking methodology in this research effort. The TDOA tracking algorithm is utilized for location estimation in the prototype system, not only to exploit the precise time resolution possible with UWB signals, but also to eliminate the need for synchronization between the transmitter and the receiver. Simulations show that the TDOA algorithm can achieve the fine tracking resolution with low noise TDOA estimates for close-in tracking. Field tests demonstrated that this prototype UWB TDOA High Resolution 3D Proximity Tracking System is feasible for providing positioning-awareness information in a 3D space to a robotic control system. This 3D tracking system is developed for a robotic control system in a facility called "Moonyard" at Honeywell Defense & System in Arizona under a Space Act Agreement.

Ni, Jianjun↗
NASA NTRS2012

GeV/TeV Cooperation: Ongoing Strategies

Although many of their scientific interests overlap, current GeV and reV telescopes have many properties that show strong contrasts. Field of view, duty cycle, speed of analysis, photon counting statistics, background, and data release policies differ markedly. The challenge for cooperative studies has been to make the best use of complementary properties. One example is GeV discovery and monitoring surveys for AGN coupled with rev time variability studies. Another is GeV spectral measurements for Galactic sources joined with reV spatial resolution. In many cases, sharing of information has been a positive factor, and continuing to explore ways to exchange results and ideas will help to maximize the scientific return from all gamma-ray observatories.

Thompson, David J.↗
NASA NTRS2012

SURF IA Conflict Detection and Resolution Algorithm Evaluation

The Enhanced Traffic Situational Awareness on the Airport Surface with Indications and Alerts (SURF IA) algorithm was evaluated in a fast-time batch simulation study at the National Aeronautics and Space Administration (NASA) Langley Research Center. SURF IA is designed to increase flight crew situation awareness of the runway environment and facilitate an appropriate and timely response to potential conflict situations. The purpose of the study was to evaluate the performance of the SURF IA algorithm under various runway scenarios, multiple levels of conflict detection and resolution (CD&R) system equipage, and various levels of horizontal position accuracy. This paper gives an overview of the SURF IA concept, simulation study, and results. Runway incursions are a serious aviation safety hazard. As such, the FAA is committed to reducing the severity, number, and rate of runway incursions by implementing a combination of guidance, education, outreach, training, technology, infrastructure, and risk identification and mitigation initiatives [1]. Progress has been made in reducing the number of serious incursions - from a high of 67 in Fiscal Year (FY) 2000 to 6 in FY2010. However, the rate of all incursions has risen steadily over recent years - from a rate of 12.3 incursions per million operations in FY2005 to a rate of 18.9 incursions per million operations in FY2010 [1, 2]. The National Transportation Safety Board (NTSB) also considers runway incursions to be a serious aviation safety hazard, listing runway incursion prevention as one of their most wanted transportation safety improvements [3]. The NTSB recommends that immediate warning of probable collisions/incursions be given directly to flight crews in the cockpit [4].

Jones, Denise R.↗
NASA NTRS2021

Determining Planetary Boundary Layer Height by Micro-pulse Lidar with Validation by UAV Measurements

Planetary boundary layer height (PBLH) is often used to characterize the structure of the lower atmosphere. Aerosol lidar, a ground-based remote sensing method, provides the vertical distribution of aerosol at a high temporal resolution observation data, from which, the PBL structure and the position of the PBL top can be comprehensively studied. PBLH determination with lidar data depends primarily on the characteristic turbulent motions in the atmosphere and the geophysical location. However, lidar determination of PBLH over densely populated subtropical locations has rarely been discussed; thus, developing retrieval techniques suitable to these areas is necessary. In this study, four PBLH determination methods (Gradient, δ–threshold, Haar wavelet transform, and hybrid image processing) are applied to estimate the PBLH from lidar observations over an urban area in East Asia, and one—the Gradient method—relied on potential temperature measurements from an unmanned aerial vehicle (UAV) flights to validate our results. Our results indicate that a combination of the gradient method and δ-threshold method can provide better results, in terms of diurnal pattern, than using either method individually. Furthermore, the Haar wavelet and the Hybrid image processing can detect the PBL development comparably well, but both methods are dependent on their initial conditions and optimized algorithm settings. In addition, the accompanying UAV observations are conclusively shown to have a high degree of efficacy for validating the lidar data. This research highlights that a combination of PBLH determination methods can better describe the PBLH evolution throughout a day in some cases, while in others less common determination methods are proving useful, and a suite of retrieval methods should still be explored for precisely mapping the PBL in densely populated subtropical areas.

Yueh-Chen Wang↗
NASA NTRS1989

A high resolution electro-optical displacement measurement system

An improved electrooptical system has been developed to sense wind tunnel model position. The original system using 25.6 mm, 1024-element linear photodiode arrays (PDAs) is being successfully used at a NASA wind tunnel but has a limited range. A new two-channel system using 61.44 mm, 4096-element PDAs has been developed to double the range of vertical and pitch measurement and increase the resolution by 60 percent. The PDAs are illuminated by expanding the beam of a single low power helium neon laser into a collimated sheet of light. An object placed in front of the two parallel PDAs produces a shadow on the array apertures which determines the object's position or size. The system has an overall precision of 12.7 microns and + or - 0.015 degrees in linear and angular measurements.

Schott, Timothy D.↗
NASA NTRS1998

Line Intensity and Position Measurements and Derived Band Parameters of the 31103-00001 C-12 O-16(2) Band and its Two Nearby Hot Bands

A set of CO2 spectra from 4500 to 4780/cm has been obtained an Ames with 1500 m path length using a Bomem DA8 FTS. This spectral region contains a number of weak bands and minor isotopic bands that have been studied at high resolution in the reflection spectrum of Venus by Mandin. Improved laboratory intensity and position measurements should assist modeling the Venus reflection spectra and improve understanding of Venus' upper atmosphere. Also, the laboratory measurements will assist DND intensity computations of weaker bands that cannot be measured, but which are nevertheless significant absorbers in Venus' hot, deep CO2, atmosphere. For example, some of the weaker bands that are members of the same polyads as the bands in this presentation lie in the nearby 2.3 microns emission window in Venus' night-side spectrum.

Giver, Lawrence P.↗
DOE OSTI2024

Fast timing with µRWELL-PICOSEC detector technology

The µWELL-PICOSEC detector, which is based on Resistive Micro-Well (µRWELL) technology, is a novel concept for fast timing gaseous detectors that can provide timing resolution in the tens of picosecond range, making it ideal candidate for time-of-flight (TOF) technology for particle identification (PID) in particle physics experiments as well as for future medical instrumentation. The µRWELL-PICOSEC concept is based on a Cerenkov radiator that produces Cerenkov photons from high energetic charged particles, a photocathode layer that converts the Cerenkov photons into primary electrons, a µRWELL amplification layer that multiply the electrons through amplification in a CF4-based gas mixture and a pad-segmentation anode readout coupled with fast timing electronics to provide fast signal. Beam tests were carried out at the CERN SPS H4 beamline in summer 2023 and 2024. Preliminary results show timing performance of the order of 23 ps achievable with µRWELL-PICOSEC prototype. and position scan of the 100-pads of a multi-channel prototype was also performed to study time response uniformity of large area detector. In this talk, after a brief overview of the PICOSEC technology, we will present recent results with different single channel µRWELL-PICOSEC prototype designs and also the position scan results of the 100-pads large prototype to study timing response uniformity for large area µRWELL-PICOSEC detector. Finally, we will discuss the ongoing R&D effort to further improve the timing resolution and allow good position capabilities through charge sharing for large area.

Gnanvo, Kondo↗
DOE OSTI2025

Improved Simulation of East Asian Summer Monsoon in the High-resolution CESM1 and Its Causes

Based on the high- and low-resolution Community Earth System Model, version 1 (CESM1), and corresponding simulations from phase 6 of the Coupled Model Intercomparison Project (CMIP6), we compare the interannual variability of the East Asian summer monsoon (EASM). The EASM interannual variability is characterized by the anomalous western North Pacific anticyclone (WNPAC) circulation and the dipole rainfall pattern with a negative southern lobe over the western North Pacific and a positive northern lobe along the Meiyu–Baiu region, which is better reproduced by the high-resolution models. Here, the reason for the improvement in the high-resolution models has been attributed to the better simulation of the warm temperature advection from the wind anomalies on the climatological temperature gradient. Positive sea surface temperature (SST) anomalies over the tropical Indian Ocean are the key to the improved wind anomalies featuring a WNPAC in the high-resolution models. The warm SST anomalies over the tropical Indian Ocean strengthen the WNPAC by triggering a Kelvin-wave response to the enhanced heat release induced by the increased precipitation. Based on the mixed-layer heat budget analysis, the warm SST anomalies over the western Indian Ocean in the high-resolution CESM1 are tied to the anomalous easterly wind along the equator, which reduces surface evaporation and upwelling. Therefore, the better simulations of air-sea feedback and the oceanic mesoscale eddy over the western Indian Ocean are the key for the improved simulation of the EASM interannual variations in the high-resolution CESM1.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2009

Linear Actuator Has Long Stroke and High Resolution

The term precision linear actuator, direct drive ( PLADD ) refers to a robust linear actuator designed to be capable of repeatedly performing, over a lifetime of the order of 5 to 10 years, positioning maneuvers that include, variously, submicron increments or slews of the order of a centimeter. The PLADD is capable of both long stroke (120 mm) and high resolution (repeatable increments of 20 nm). Unlike precise linear actuators of prior design, the PLADD contains no gears, levers, or hydraulic converters. The PLADD, now at the prototype stage of development, is intended for original use as a coarse-positioning actuator in a spaceborne interferometer. The PLADD could also be adapted to terrestrial applications in which there are requirements for long stroke and high resolution: potential applications include medical imaging and fabrication of semiconductor devices. The PLADD (see figure) includes a commercially available ball-screw actuator driven directly by a commercially available three-phase brushless DC motor. The ball-screw actuator comprises a spring-preloaded ball nut on a ball screw that is restrained against rotation as described below. The motor is coupled directly (that is, without an intervening gear train) to a drive link that, in turn, is coupled to the ball nut. By eliminating the gear train, the direct-drive design eliminates the complexity, backlash, and potential for misalignment associated with a gear train. To prevent inadvertent movement, there is a brake that includes flexured levers compressed against the drive link by preload springs. This is a power-off brake: There are also piezoelectric stacks that can be activated to oppose the springs and push the levers away from the drive link. Hence, power must be applied to the piezoelectric stacks to release the drive link from braking. To help ensure long operational life, all of the mechanical drive components are immersed in an oil bath within hermetically sealed bellows. The outer end of the bellows holds the outer end of the ball screw, thereby preventing rotation of the ball screw. Positioning is controlled by an electronic control system that includes digital and analog subsystems that interact with the motor and brake and with two sensor/encoder units: a Hall-effect-sensor rotation encoder and a linear glass-scale encoder. This system implements a proportional + integral + derivative control algorithm that results in variation of voltage commands to each of the three pairs of windings of the brushless DC motor. In one of two alternative control modes, the voltages are applied to the windings in a trapezoidal commutation scheme on the basis of timing signals obtained from the Hall-effect sensors; this scheme yields relatively coarse positioning - 24 steps per motor revolution. The second control mode involves a sinusoidal commutation scheme in which the output of the linear glass-scale encoder is transposed to rotational increments to yield much finer position feedback - more than 400,000 steps per revolution.

Cook, Brant T.↗
NASA NTRS1994

Dust extinction and molecular gas in the dark cloud IC 5146

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

Lada, Charles J.↗
NASA NTRS1981

VLA observations of positions 42 6 centimeter burst peaks associated with hard X-ray burst spikes

Using the Very Large Array with a spatial resolution of 3 arcsec, two-dimensional, 10-second synthesis maps are produced of four 6-cm lambda bursts associated with multiply spiked hard X-ray bursts (20-300 keV). The positional, structural, and polarization characteristics are investigated. It is noted that three of the four burst sources are rather compact (less than approximately 10 arcsec). It is found that the positions of the individual peaks or spikes within a single burst are the same within plus or minus 2 arcsec. Interpreting these different peaks as separate electron acceleration events, the results suggest repeated acceleration of electrons within the same magnetic trap. The trap situation is found to be consistent with the bipolar nature of the burst sources except in one case.

Kundu, M. R.↗
NASA NTRS1984

A position-sensitive germanium detector for gamma-ray astronomy

The critical problem in high-resolution cosmic gamma-ray spectroscopy in the energy range from 0.02 to 10 MeV is the limited spectral sensitivity of the detectors used. This results from the small effective area of the detectors and the high background noise due to induced radioactivity and scattering in the detectors' high-energy particle environment. The effective area can be increased by increasing the number of detectors, but this becomes prohibitive because of the size and expense of the resulting instrument. We have taken a new approach: a segmented large-volume germanium gamma-ray detector which can effectively discriminate against internal background yet maintain the high spectral resolution and efficiency of conventional coaxial Ge detectors. To verify this concept, a planar detector divided into two segments has been fabricated and laboratory measurements agree well with Monte Carlo calculations. A large coaxial detector which will be divided into five segments is being built using the techniques developed for the planar detector. Monte Carlo calculations show that the sensitivity (minimum detectable flux) of the segmented coaxial detector is a factor of 2-3 better than conventional detectors because of the reduction in the internal background.

Varnell, L. S.↗
NASA NTRS2017

Trajectory Specification for Terminal Air Traffic: Pairwise Conflict Detection and Resolution

Trajectory specification is the explicit bounding and control of aircraft trajectories such that the position at each point in time is constrained to a precisely defined volume of space. The bounding space is defined by cross-track, along-track, and vertical tolerances relative to a reference trajectory that specifies position as a function of time. The tolerances are dynamic and will be based on the aircraft navigation capabilities and the current traffic situation. A standard language will be developed to represent these specifications and to communicate them by datalink. Assuming conformance, trajectory specification can guarantee safe separation for an arbitrary period of time even in the event of an air traffic control (ATC) system or datalink failure, hence it can help to achieve the high level of safety and reliability needed for ATC automation. As a more proactive form of ATC, it can also maximize airspace capacity and reduce the reliance on tactical backup systems during normal operation. It applies to both enroute airspace and the terminal area around airports, but this paper focuses on the terminal area and presents algorithms and software for spacing arrivals and deconflicting both arrivals and departures.

air traffic control↗