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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

A new observational and numerical study of tidal interactions in M81-M82-NGC3077 system

A nearby system of interacting galaxies M81-M82-NGC3077 triplet (D = 3.3 Mpc; Freeman & Madore 1988) has been studied using multi-wavelength observations and numerical simulations to obtain a comprehensive understanding on the dynamics and the consequences of tidal interactions in a group environment. The VLA 12-field Mosaic H I observations of 2 x 1.5 deg. region have revealed a vast array of H I filaments which suggests that the severity and extent of tidal disruptions far exceed the previous estimates. A tidal remnant of the former H I disk of M82 extending up to 30 kpc (in projection) is identified for the first time, and the pervasive effects of the tidal disruption are traced into the inner disk by optical and CO observations, including a kinematic trace of a large scale bar potential (Yun, Ho, & Lo 1992). The H I disk of M81 is traced out to 40 kpc in radius, and a large scale (l approx. 20 kpc) velocity anomaly ('High Velocity Trough'), which may be a remnant of a gaseous collision, is found within the disk of M81. The large H I bridge between M81 and NGC 3077 (van der Hulst 1979) is also found to extend approx. greater than 50 kpc further, bending around NGC 3077, toward M82. The total H I detected in this experiment, 5.6 x 10(exp 9) solar mass, represents the majority of the single-dish flux (Appleton, Davies, & Stephenson 1981) and suggests that the bulk of H I found in the region belongs to the three galaxies and the tidal filaments. The impact and details of the tidal interactions have been further examined through the use of numerical techniques. The 'restricted 3-body' approach was used to simulate the observed distribution of tidal H I streamers connecting the three galaxies, and the success of the simulation is further strengthened by the accurate predictions on the gas kinematics.

Yun, M. S.↗
NASA NTRS1989

Progress in computing nozzle/plume flow fields

The long-term goal is to develop the capability to predict chemically-reacting, multi-stream nozzle and plume flow fields. Two basic Navier-Stokes solvers, including the widely used F-3D code, are upgraded to include several upwind difference schemes and portable chemistry packages. Current computational capabilities for solving equilibrium single-stream and multi-stream, frozen gas, and finite rate chemistry problems are described. A variety of complex nozzle and plume flows were computed. Solutions presented include axisymmetric plume flow for ideal and equilibrium air, 3-D NASP nozzle/afterbody flow, and an internal nozzle calculation comparing various finite-rate chemistry packages.

Ruffin, Stephen M.↗
NASA NTRS2013

Einstein@Home All-Sky Search for Periodic Gravitational Waves in LIGO S5 Data

This paper presents results of an all-sky search for periodic gravitational waves in the frequency range [50, 1 190] Hzand and with frequency derivative range of approx. [-20,1.1] x 10(exp-10) H(sub 0)z s(exp-1) for the fifth LIGO science run (S5). The search uses a noncoherent Hough-transform method to combine the information from coherent searches on time scales of about one day. Because these searches are very computationally intensive, they have been carried out with the Einstein@Home volunteer distributed computing project. Postprocessing identifies eight candidate signals; deeper follow-up studies rule them out. Hence, since no gravitational wave signals have been found, we report upper limits on the intrinsic gravitational wave strain amplitude ho. For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h(exp 0) greater than 7.6 x 10(exp-25) at a 90% confidence level. This search is about a factor 3 more sensitive than the previous Einstein@Home search of early S5 LIGO data.

J Aasi↗
NASA NTRS2022

The First Gradual Solar Energetic Particle Event With an Enhanced He-3 Abundance on Solar Orbiter

The origin of 3 He abundance enhancements in gradual solar energetic particle (SEP) events remains largely unexplained. Two mechanisms have been suggested: the reacceleration of remnant flare material by coronal mass ejection (CME)-driven shocks in interplanetary space, and concomitant activity in the corona. We explore the first gradual SEP event with enhanced 3 He abundance that was observed by Solar Orbiter. The event started on 2020 November 24 and was associated with a relatively fast halo CME. During the event, the spacecraft was at 0.9 au from the Sun. The event-averaged 3 He/ 4 He abundance ratio is 24 times higher than the coronal or solar wind value, and the timing of the 3He intensity was similar to that of other species. We inspected available imaging, radio observations, and the spacecraft magnetic connection to the CME source. The most probable cause of the enhanced 3He abundance apparently are residual 3He ions remaining from a preceding long period of 3 He-rich SEPs on 2020 November 17–23.

Solar particle emission↗
NASA NTRS2016

An Efficient Single Frequency Ho:YLF Laser for IPDA Lidar Applications

A highly efficient, versatile, single frequency 2-micron pulsed laser can be used in a pulsed Differential Absorption Lidar (DIAL) / Integrated Path Differential Absorption (IPDA) instrument to make precise, high-resolution measurements to investigate sources and sinks of CO2. For a direct detection IPDA lidar, the desired 2 m Ho:YLF laser should generate 30-40 mJ pulses at the repetition rate of 100 to 200 Hz, with short pulse length (<100 ns) and better than 2% wall plug efficiency. A Tm fiber laser in-band pumped Ho:YLF laser has been developed to meet this technical challenge. This Ho:YLF laser is designed in a four mirror ring resonator with bow tie configuration, which helps to obtain high beam quality. It is end-pumped by a 40 W linearly polarized Tm fiber laser at 1.94μm. The resonator length is 1.10 meters with output coupler reflectivity at 45%. The laser crystal size is 3 x 3 x 60 mm (w, h, l) with a doping concentration of 0.5% Holmium. The laser beam and pump beam are mode-matched in the active medium. Thus, the pump and laser beams have the same confocal parameters. Mode-matching is also helpful for operating the laser in a single transverse mode. The laser beam waist is slightly less than 0.5 mm at the center of the laser crystal. Based on quasi-four level modeling, pump absorption and saturation depend on laser intensity. Laser amplification and saturation also depend on the pump intensity in the crystal. The laser is injection seeded to obtain the single frequency required by an IPDA lidar measurement. The seed beam is entered into the resonator through an output coupler. The laser is mounted on a water cooled optical bench for stable and reliable operation. The size of the optical bench is 22.16 x 9.20 x 1.25 inches. It is stiffened so that the laser can be operated in any orientation of the optical bench. This packaged Ho:YLF laser is designed for either mobile trailer or airborne platform operation. The engineering prototype Ho:YLF laser has been fully characterized to demonstrate laser performance. Figure 1 shows the laser output power as a function of pump power at different pulse repetition rates from 100 Hz to 333 Hz. The threshold of the laser is less than 14 W. The slope efficiencies are 28%, 40%, 41% and 43% for pulse repetition rates of 100, 200, 250 and 333 Hz, respectively. Maximum power increases with the pulse repetition rate. Output power of 4.2 W, 6 W, 6.7 W, and 7.7 W is achieved for pulse repetition rates of 100, 200, 250 and 333Hz, respectively. This represents the optical conversion efficiency of 16.7%, 22.4%, 23.7%, and 26.5% at these various pulse repletion rates. It is the most efficient and compact Ho:YLF laser demonstrated in the high pulse energy (>20mJ) and moderate pulse repetition rate (100's Hz) operation range. As shown in Figure 1, the maximum pulse energy at 100 Hz is 42 mJ. This is limited due to optical damage. The laser stability is characterized and found to be very stable. A relative pulse energy standard deviation of 2% was measured. The beam quality of the Ho:YLF was measured by a Spiricon infrared laser beam camera. Figure 2 shows the beam profile image of the laser. Both the X-profile of the beam (horizontal direction) and the Y-profile of the beam (vertical direction) are well fitted by a Gaussian profile. The qualitative beam quality measurement shows excellent beam quality in both axis. The M-square value for the laser beam is measured at 1.06 and 1.09 for the x and y axis respectively.-

Yu, J.↗
NASA NTRS1991

Complex-coordinate calculation of D-(1,3) resonances in two-electron systems

Feshbach-type D-(1,3)resonances in two-electron systems, Z = 2-10, have been investigated using the method of complex rotation. These states lie below the n = 2 and 3 thresholds of hydrogenic systems. Wave functions containing up to 1230 Hylleraas functions have been used, giving accurate results for positions and widths. Comparisons between various calculations are given.

Ho, Y. K.↗
NASA NTRS2023

Solar Activities Associated with 3 He-rich Solar Energetic Particle Events Observed by Solar Orbiter

A series of 3 He-rich solar energetic particle (SEP) events was observed by Solar Orbiter in May 2021 at a radial distance of 0.95 AU. An isolated active region AR 12824 was likely the ultimate source of these SEP events. The period of the enhanced flux of 3He was also a period of frequent type III bursts in the decametric-hectometric range, confirming their close relationship. As in past studies, we try to find the solar activities possibly responsible for 3 He-rich SEP events, using the type III bursts close to the particle injection times estimated from the velocity dispersion. But this exercise is not as straightforward as in many of the past studies since the region produced many more type III bursts and jet-like eruptions than the SEP injections. We may generalize the solar activities for the 3 He-rich SEP events in question as coronal jets, but their appearances do not necessarily conform to classic jets that consist of a footpoint and a spire. Conversely, such jets often did not accompany type III bursts. The areas that produced jet-like eruptions changed within the active region from the first to the second set of 3 He-rich SEP events, which may be related to the extended coronal mass ejection that launched stealthily.

Sun↗
NASA NTRS1983

Oscillator strengths and collision strengths for S II

Calculations are presented of the collision strengths for electron impact excitation of S II from the ground 3s(2)3p(3)(4)S0 state to excited states 3s3p(4)(4)p, 3s(2(3p(2)4s(4)P, and 3s(2)3p(2)3d(4)P. The collision strengths are calculated in a close-coupling approximate ion for the energy range up to 10 to the 6th K. In addition, oscillator strengths are given for these transitions, as well as for some UV lines which have lower states 3s(2)3p(3)(2)D(O) and 3s(2)3p(3)(2)P(0). The calculation of the collision strengths involves the use of configuration interaction target wave functions which give oscillator strengths accurate to 30 percent in most cases.

Ho, Y. K.↗
NASA NTRS1997

HO(x) Measurements in SONEX with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS)

SONEX, which was delayed by aircraft inspection problems, began the second week of October and concluded in mid-November with 16 flights. These flights covered the Pacific Ocean off the western United States, transits across the United States, the western coast of Europe, and the North and Central Atlantic Ocean. Particular attention was paid to the North Atlantic Flight Corridor. ATHOS collected high-quality HO(x) data on 15 flights. Observations taken at 5 Hz were typically averaged into 20-second measurements. Each 20-second measurement has precision 1(sigma) of less than 0.01 pptv. OH measurements were generally made from the surface to flight altitudes. HO2 measurements, which require reagent NO flow, were made from flight altitudes to near the top of the planetary boundary layer. Measured OH and HO2 during SONEX was generally lower than the measured OH and HO2 during SUCCESS (April-May, 1996, central United States). Whereas during SUCCESS midday OH was 0.1-0.5 pptv and HO2 was 3-15 pptv, during SONEX midday OH was 0.02-0.2 pptv and HO2 was 0.5-8 pptv. Part of this difference results from the midday solar zenith angles, which were larger during SONEX than during SUCCESS due to both the season and the generally higher latitudes sampled during SONEX. However, some of the difference may be due to differences in HOx sources, since less air influenced by convection was sampled during SONEX. These possibilities await post-flight calibrations of ATHOS and analysis of observations of HO(x) and simultaneously measured meteorology and trace species.

Brune, William M.↗
NASA NTRS1988

Global gravity survey by an orbiting gravity gradiometer

The scientific aims, design, and mission profile of the Superconducting Gravity Gradiometer Mission (SGGM), a NASA spacecraft mission proposed for the late 1990s, are discussed and illustrated with drawings and diagrams. SGGM would complement the two other planned gravimetry missions, GRM and Aristoteles, and would provide gravitational-field measurements with accuracy 2-3 mGal in 55 x 55-km blocks. The principal instruments are a (1) three-axis superconducting gravity gradiometer with intrinsic sensitivity 100 microeotvos/sq rt Hz, (2) a six-axis superconducting accelerometer with sensitivity 100 fg(E)/sq rt Hz linear and 10 prad/sec squared sq rt Hz angular, and (3) a six-axis shaker for active control of the platform. Consideration is given to the error budget and platform requirements, the orbit selection criteria, and the spacecraft design.

Paik, Ho Jung↗
NASA NTRS2000

A High Energy 2-microns Laser for Multiple Lidar Applications

Solid-state 2-microns laser has been receiving considerable interest because of its eye-safe property and efficient diode pump operation, It has potential for multiple lidar applications to detect water vapor. carbon dioxide and winds. In this paper, we describe a 2-microns double pulsed Ho:Tm:YLF laser and end-pumped amplifier system. A comprehensive theoretical model has been developed to aid the design and optimization of the laser performance. In a single Q-switched pulse operation the residual energy stored in the Tm atoms will be wasted. However, in a double pulses operation mode, the residual energy stored in the Tm atoms will repopulate the Ho atoms that were depleted by the extraction of the first Q-switched pulse. Thus. the Tin sensitized Ho:YLF laser provides a unique advantage in applications that require double pulse operation, such as Differential Absorption Lidar (DIAL). A total output energy of 146 mJ per pulse pair under Q-switch operation is achieved with as high as 4.8% optical to optical efficiency. Compared to a single pulse laser, 70% higher laser efficiency is realized. To obtain high energy while maintaining the high beam quality, a master-oscillator-power-amplifier 2-microns system is designed. We developed an end-pumped Ho:Tm:YLF disk amplifier. This amplifier uses two diode arrays as pump source. A non-imaging lens duct is used to couple the radiation from the laser diode arrays to the laser disk. Preliminary result shows that the efficiency of this laser can be as high as 3%, a factor of three increases over side-pump configuration. This high energy, highly efficient and high beam quality laser is a promising candidate for use in an efficient, multiple lidar applications.

Yu, Jirong↗
NASA NTRS1994

Validation of Multitemperature Nozzle Flow Code

A computer code nozzle in n-temperatures (NOZNT), which calculates one-dimensional flows of partially dissociated and ionized air in an expanding nozzle, is tested against three existing sets of experimental data taken in arcjet wind tunnels. The code accounts for the differences among various temperatures, i.e., translational-rotational temperature, vibrational temperatures of individual molecular species, and electron-electronic temperature, and the effects of impurities. The experimental data considered are (1) the spectroscopic emission data; (2) electron beam data on vibrational temperature; and (3) mass-spectrometric species concentration data. It is shown that the impurities are inconsequential for the arcjet flows, and the NOZNT code is validated by numerically reproducing the experimental data.

Park, Chul↗
NASA NTRS1999

Tropospheric Diagnostic Modeling Studies of PEM-Tropics Field Data: Investigation of the HO(x)/NO(x)/O3 Photochemical System and Its Coupling to Sulfur and Halogen Chemistry

Over the time period of this NASA grant the PI has helped plan and execute in the PEM-Tropics A field program. He has also helped organize and co-chair three data workshops which have focused on the detailed analysis of PEM-Tropics A data. His direct participation in these analyses has led to his major involvement in 10 manuscripts, 5 of which are in print, 3 in press, and 2 submitted. A complete list of papers is included in the report.

Davis, Douglas D.↗
NASA NTRS1981

Aircraft NO/x/ emissions and stratospheric ozone reductions - Another look

New estimates for stratospheric ozone perturbations attributable to supersonic transport (SST) emissions are presented. First, a review is given of recent data pointing to lower OH concentrations below 30 km, as compared to the values predicted by photochemical models. The evidence for lower OH comes from a wide range of laboratory and atmospheric studies. The sensitivity of theoretical estimates of ozone change to OH abundances, and the coupling mechanisms between the O(x)-NO(x)-HO(x)-Cl(x) families which are responsible for the sensitivity, are discussed. Updated calculations for SST-induced ozone alterations are compared with older predictions. For example, assuming continuous aircraft injection of NO2 at 20 km at a rate of 1 x 10 to the 9th kg per year (globally), a 4% ozone decrease, is now calculated where earlier a 3% ozone increase was found. This large variance from previous forecasts suggests that new assessments of certain other polluting agents, particularly nitrogen fertilizers, are needed.

Turco, R. P.↗
NASA NTRS2011

Howardite Noble Gases as Indicators of Asteroid Surface Processing

The HED (Howardite, Eucrite and Diogenite) group meteorites likely or iginate from the Asteroid 4 Vesta - one of two asteroid targets of NA SA's Dawn mission. Whilst Howardites are polymict breccias of eucriti c and diogenitic material that often contain "regolithic" petrologica l features, neither their exact regolithic nature nor their formation processes are well defined. As the Solar Wind (SW) noble gas compon ent is implanted onto surfaces of solar system bodies, noble gas anal yses of Howardites provides a key indicator of regolithic origin. In addition to SW, previous work by suggested that restricted Ni (300-12 00 micro g/g) and Al2O3 (8-9 wt%) contents may indicate an ancient we ll-mixed regolith. Our research combines petrological, compositional and noble gas analyses to help improve understanding of asteroid reg olith formation processes, which will play an intergral part in the i nterpretation of Dawn mission data. Following compositional and petrological analyses, we developed a regolith grading scheme for our sampl e set of 30 Howardites and polymict Eucrites. In order to test the r egolith indicators suggested by, our 8 selected samples exhibited a r ange of Ni, Al2O3 contents and regolithic grades. Noble gas analyses were performed using furnace stepheating on our MAP 215-50 noble gas mass spectrometer. Of our 8 howardites, only 3 showed evidence of SW noble gases (e.g approaching Ne-20/Ne-22 approximately equals 13.75, Ne-21/Ne-22 approximately equals 0.033). As these samples display low regolithic grades and a range of Ni and Al2O3 contents, so far we are unable to find any correlation between these indicators and "regolit hic" origin. These results have a number of implications for both Ho wardite and Vesta formation, and may suggest complex surface stratigr aphies and surface-gardening processes.

Cartwright, J. A.↗
NASA NTRS1990

Dynamic fracture responses of alumina and two ceramic composites

A hybrid experimental-numerical procedure was used to characterize the dynamic fracture response of Al2O3 and TiB2-particulate/SiC-matrix and SiC-whisker/Al2O3-matrix composites. Unlike metals and polymers, dynamic arrest stress intensity factors (SIFs) did not exist in the monolithic ceramics and the two ceramic composites considered. Thus a running crack in these materials cannot be arrested by lowering the driving force, i.e., the dynamic SIF. Fractography study of the alumina specimens showed that the area of transgranular failure varied from about 3 percent to about 16 percent for rapid crack extensions in statically and impact loaded specimens, respectively. The influence of kinematic constraints which enforces transgranular flat crack extension, despite the higher fracture energy of transgranular fracture, is discussed.

Yang, Kwan-Ho↗
NASA NTRS1990

Complex-coordinate calculation of 1D(e) resonances using Hylleraas functions

The lowest 1D(e) resonances below the n = 2 and n = 3 thresholds are calculated using a method of complex-coordinate rotation. The results, obtained with the use of Hylleraas functions, are believed to be of high accuracy. This work should serve as a useful reference for other investigations.

Bhatia, A. K.↗