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At least 397 records · Page 22

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NASA NTRS1979

Review of selected geomagnetic activity indices

Magnetic activity indexes are reviewed. Classifications of magnetograms from single observatories and the global range of potential associated with the equivalent currents which could have produced the variations monitored at a large array of recording sides are addressed. Principal magnetic activity indexes discussed include: the auroral electrojet index and its associated indexes (AU, AL and AO) useful for auroral zone studies; the Kp, ap, aa and am indexes which are measures of midlatitude geomagnetic activity; and the Dst index of magnetic activity recorded at low latitudes. It is concluded that geomagnetic activity indexes are useful in studies of the interaction between solar activity, the interplanetary magnetic field and solar wind, the magnetosphere, ring current, field aligned currents, and ionospheric currents.

Allen, J. H.↗

NASA NTRS1981

A global tectonic activity map with orbital photographic supplement

A three part map showing equatorial and polar regions was compiled showing tectonic and volcanic activity of the past one million years, including the present. Features shown include actively spreading ridges, spreading rates, major active faults, subduction zones, well defined plates, and volcanic areas active within the past one million years. Activity within this period was inferred from seismicity (instrumental and historic), physiography, and published literature. The tectonic activity map was used for planning global geodetic programs of satellite laser ranging and very long base line interferometry and for geologic education.

Lowman, P. D., Jr.↗

NASA NTRS1982

Studies of neutron and proton nuclear activation in low-Earth orbit

The expected induced radioactivity of experimental material in low Earth orbit was studied for characteristics of activating particles such as cosmic rays, high energy Earth albedo neutrons, trapped protons, and secondary protons and neutrons. The activation cross sections for the production of long lived radioisotopes and other existing nuclear data appropriate to the study of these reactions were compiled. Computer codes which are required to calculate the expected activation of orbited materials were developed. The decreased computer code used to predict the activation of trapped protons of materials placed in the expected orbits of LDEF and Spacelab II. Techniques for unfolding the fluxes of activating particles from the measured activation of orbited materials are examined.

Laird, C. E.↗

NASA NTRS1983

Magnetic fields and activity of the sun and stars - An overview

Recent work on the observation and theory of solar and stellar magnetic field activity and its relation to stellar activity is reviewed, emphasizing those aspects relevant to the problem of activity of red dwarf stars. New observational facts relevant to understanding the root cause of stellar surface activity are summarized and theoretical questions concerning the underlying physical basis for the observed correlations between stellar activity, rotation, and magnetic fields are addressed. These include dyanamo theory and the rotation-activity connection as well as flux tube dynamics and plasma heating.

Rosner, R.↗

NASA NTRS1985

Method for measuring surface activity of silicon nitride powder

Amorphous, alpha-, and beta-Si3N4 powders were activated by vibration ball milling in purified MeOH, and the surface activity of ground powders was determined by the temperature programmed desorption (TPD) method using NH3 gas. The concentration of active sites with a potential energy equivalent to the peak temperature in the spectrum increased was markedly by ball milling the amorphous Si3N4. The alpha- and beta-Si3N4 also had active sites produced by ball milling. The concentration of active site increased with increased ball milling time. A method for measuring surface activity of ceramic raw materials by TPD is proposed.

Kanno, Y.↗

NASA NTRS1986

A description of the active and passive sidewall-boundary-layer removal systems of the 0.3-meter transonic cryogenic tunnel

Results are presented for an operational checkout and shakedown of the active sidewall-boundary-layer removal system newly installed in the Langley 0.3-meter Transonic Cryogenic Tunnel (0.3-m TCT). Prior to the installation of this active removal system, the sidewall-boundary layer was removed passively by exhausting directly to the atmosphere (i.e., no reinjection). With the active removal system using the reinjection compressor, the removal capability is greatly expanded to cover the entire operating envelope of the 0.3-m TCT. Details of the active removal system are presented including the compressor reinjection circuit, the compressor pressure ratio/surge control, and the compressor recirculation loop. The control logic and features of the compressor surge control are explained. Initial tests covering critical operating conditions show mass flow removal rates of about 5 percent at lower Mach numbers can be obtained with the active system. Measured performance characteristics of the compressor are presented. As part of the validation of the active system, limited airfoil tests were made using the new system.

Johnson, C. B.↗

NASA NTRS1987

Control of abdominal and expiratory intercostal muscle activity during vomiting - Role of ventral respiratory group expiratory neurons

The role of ventral respiratory group (VRG) expiratory (E) neurons in the control of abdominal and internal intercostal muscle activity during vomiting was investigated in cats. Two series of experiments were performed: in one, the activity of VRG E neurons was recorded during fictive vomiting in cats that were decerebrated, paralyzed, and artificially ventilated; in the second, the abdominal muscle activity during vomiting was compared before and after sectioning the axons of descending VRG E neurons in decerebrate spontaneously breathing cats. The results show that about two-thirds of VRG E neurons that project at least as far caudally as the lower thoracic cord contribute to internal intercostal muscle activity during vomiting. The remaining VRG E neurons contribute to abdominal muscle activation. As shown by severing the axons of the VRG E neurons, other, as yet unidenified, inputs (either descending from the brain stem or arising from spinal reflexes) can also produce abdominal muscle activation.

Miller, Alan D.↗

NASA NTRS1989

Ionospheric effects of the extreme solar activity of February 1986

During February 1986, near the minimum of the 11 year Solar sunspot cycle, after a long period of totally quiet solar activity (R sub z = 0 on most days in January) a period of a suddenly enhanced solar activity occurred in the minimum between solar cycles 21 and 22. Two proton flares were observed during this period. A few other flares, various phenomena accompanying proton flares, an extremely severe geomagnetic storm and strong disturbances in the Earth's ionosphere were observed in this period of enhanced solar activity. Two active regions appeared on the solar disc. The flares in both active regions were associated with enhancement of solar high energy proton flux which started on 4 February of 0900 UT. Associated with the flares, the magnetic storm with sudden commencement had its onset on 6 February 1312 UT and attained its maximum on 8 February (Kp = 9). The sudden enhancement in solar activity in February 1986 was accompanied by strong disturbances in the Earth's ionosphere, SIDs and ionospheric storm. These events and their effects on the ionosphere are discussed.

Boska, J.↗

NASA NTRS1990

Effect of voluntary vs. artificial activation on the relationship of muscle torque to speed

The suggestion by Phillips and Petrofsky (1980) and Wickiewicz et al. (1984) that artificial activation of the knee extensor muscles should result in greater relative changes in torque than those evident with maximal voluntary activation is examined by investigating the speed-torque relationship of the right knee extensor muscle group in eight human subjects in whom activation was achieved by 'maximal' voluntary effort or by electrical stimulation. Torque was measured at a specific knee angle during isokinetic concentric or eccentric actions at velocities between 0.17 and 3.66 rad/s and during isometric actions. It is shown that, with artificial activation, the relative changes in both eccentric and concentric torque were greater as the speed increased; the speed-torque relationship was independed of the extent of activation and was similar to that of an isolated muscle. On the other hand, activation by the central nervous system during maximal effort depended on the speed and the type of muscle action performed.

Dudley, Gary A.↗

NASA NTRS1992

Induced activation study of LDEF

Analysis of the induced radioactivity of LDEF is continuing with extraction of specific activities for various spacecraft materials. Data and results of activation measurements from eight national facilities are being collected for interpretation. The major activation mechanisms in LDEF components is the proton flux in the South Atlantic Anomaly (SAA) inner radiation belt. This flux is highly anisotropic, and exposes the west side of the spacecraft to higher radiation doses. The directionally dependent activation due to these protons has clearly been observed in the data from Al experiment tray clamps, steel trunnions, and is also indicated by the presence of a variety of radioisotopes in other materials. A secondary production mechanism, thermal neutron capture, was observed in two materials having large capture cross sections, Co and Ta. The neutrons could be thermalized in nearby low Z material, although this has yet to be verified. Specific activities are presented for a number of materials which show SAA effects and thermal neutron capture. Trends are examined in the measured results that show the effect of shielding and non-SAA related activation.

Harmon, B. A.↗

NASA NTRS1992

A status of the activities of the NASA/MSFC pump stage technology team

The Consortium for Computational Fluid Dynamics (CFD) Application in Propulsion Technology was established to aid the transfer of CFD related advancements among academia, government agencies, and industry. The specific goals of the Consortium are to develop CFD methodologies necessary to solve propulsion problems, to validate these methodologies, and to apply these methodologies in the design process. To accomplish these goals, a team of experts in various related fields was formed, a schedule of activities necessary to meet the goals was generated, and funding for the activities was obtained from NASA. During the past year (Mar. 1991 - Mar. 1992) the team's activities have focused on preliminary code validation and on the design of an advanced impeller. Six codes were used to calculate the flow in a Rocketdyne 0.3 flow coefficient inducer, and the results were compared to L2F data available for the inducer. This activity identified shortcomings in the experimental data sets and in the analytical solutions which must be surmounted in any future team activity. The design of the advanced impeller relied heavily on CFD results to obtain an optimized geometry. The optimized geometry was analyzed using four different codes, at design and off-design conditions. Activities for the next year include the optimization of a tandem blade impeller design, benchmark of CFD codes for diffuser and volute flows, the collection of L2F data for 'state-of-the-art' impeller and inducer, and the verification of the advanced pump team impeller design in a water rig.

Garcia, R.↗

NASA NTRS1992

Active member vibration control for a 4 meter primary reflector support structure

The design and testing of a new low voltage piezoelectric active member with integrated load cell and displacement sensor is described. This active member is intended for micron level vibration and structural shape control of the Precision Segmented Reflector test-bed. The test-bed is an erectable 4 meter diameter backup support truss for a 2.4 meter focal length parabolic reflector. Active damping of the test-bed is then demonstrated using the newly developed active members. The control technique used is referred to as bridge feedback. With this technique the internal sensors are used in a local feedback loop to match the active member's input impedance to the structure's load impedance, which then maximizes vibrational energy dissipation. The active damping effectiveness is then evaluated from closed loop frequency responses.

Umland, J. W.↗

NASA NTRS1992

The real world and lunar base activation scenarios

A lunar base or a network of lunar bases may have highly desirable support functions in a national or international program to explore and settle Mars. In addition, He-3 exported from the Moon could be the basis for providing much of the energy needs of humankind in the twenty-first century. Both technical and managerial issues must be addressed when considering the establishment of a lunar base that can serve the needs of human civilization in space. Many of the technical issues become evident in the consideration of hypothetical scenarios for the activation of a network of lunar bases. Specific and realistic assumptions must be made about the conduct of various types of activities in addition to the general assumptions given above. These activities include landings, crew consumables, power production, crew selection, risk management, habitation, science station placement, base planning, science, agriculture, resource evaluation, readaptation, plant activation and test, storage module landings, resource transport module landings, integrated operations, maintenance, Base 2 activation, and management. The development of scenarios for the activation of a lunar base or network of bases will require close attention to the 'real world' of space operations. That world is defined by the natural environment, available technology, realistic objectives, and common sense.

Schmitt, Harrison H.↗

NASA NTRS1992

A new activity index for comets

An activity index, AI, is derived from observational data to measure the increase of activity in magnitudes for comets when brightest near perihelion as compared to their inactive reflective brightness at great solar distances. Because the observational data are still instrumentally limited in the latter case and because many comets carry particulate clouds about them at great solar distances, the application of the activity index is still limited. A tentative application is made for the comets observed by Max Beyer over a period of nearly 40 years, providing a uniform magnitude system for the near-perihelion observations. In all, 32 determinations are made for long-period (L-P) comets and 15 for short-period (S-P). Although the correlations are scarcely definitive, the data suggest that the faintest comets are just as active as the brightest and that the S-P comets are almost as active as those with periods (P) exceeding 10(exp 4) years or those with orbital inclinations of i less than 120 deg. Comets in the range 10(exp 2) less than P less than 10(exp 4) yr. or with i greater than 120 deg appear to be somewhat more active than the others. There is no evidence to suggest aging among the L-P comets or to suggest other than a common nature for comets generally.

Whipple, Fred L.↗

NASA NTRS1992

Mechanical stimulation of skeletal muscle increases prostaglandin F2(alpha) synthesis and cyclooxygenase activity by a pertussis toxin sensitive mechanism

Repetitive mechanical stimulation of differentiated skeletal muscle in tissue culture increases the production of prostaglandin F(sub 2(alpha)), an anabolic stimulator of myofiber growth. Within 4 h of initiating mechanical activity, the activity of cyclooxygenase, a regulatory enzyme in prostaglandin synthesis, was increased 82% (P is less than .005), and this increase was maintained for at least 24 h. Kinetic analysis of the stretch-activated cyclooxygenase indicated a two to three-fold decrease in the enzyme's K(sub m) with no change in V(sub max). The stretch-induced increase in enzymatic activity was not inhibited by cycloheximide, was independent of cellular electrical activity (tetrodotoxin-insensitive), but was prevented by the G protein inhibitor pertussis toxin. Pertussis toxin also inhibited the stretch-induced increases in PGF(sub 2(alpha)) production, and cell growth. It is concluded that stretch of skeletal muscle increases the synthesis of the anabolic modulator PGF(sub 2(alpha)) by a G protein-dependent process which involves activation of cyclooxygenase by a posttranslational mechanism.

Vandenburgh, Herman H.↗

NASA NTRS1993

Simultaneous observation of the poleward expansion of substorm electrojet activity and the tailward expansion of current sheet disruption in the near-earth magnetotail

A substorm that occurred on 7 June 1985 at 2209 UT for which simultaneous measurements from ground stations and CCE are available is considered. The event occurred during a close conjunction between CCE, the EISCAT magnetometer cross, and the STARE radar, allowing a detailed comparison of satellite and ground-based data. Two discrete activations took place during the first few minutes of this substorm: the expansion phase onset at 2209 UT and an intensification at 2212 UT, corresponding to a poleward expansion of activity. The energetic particle data indicate that the active region of the magnetotail during the 2212 UT intensification was located tailward of the active region at 2209 UT. This is direct evidence for a correspondence between tailward expansion of localized activity in the near-earth magnetotail (current disruption and particle energization) and poleward expansion of activity (electrojet formation) in the ionosphere.

Lopez, R. E.↗

NASA NTRS1993

Human-in-the-loop evaluation of RMS Active Damping Augmentation

Active Damping Augmentation is the insertion of Controls-Structures Integration Technology to benefit the on-orbit performance of the Space Shuttle Remote Manipulator System. The goal is to reduce the vibration decay time of the Remote Manipulator System following normal payload maneuvers and operations. Simulation of Active Damping Augmentation was conducted in the realtime human-in-the-loop Systems Engineering Simulator at the NASA Johnson Space Center. The objective of this study was to obtain a qualitative measure of operational performance improvement from astronaut operators and to obtain supporting quantitative performance data. Sensing of vibratory motions was simulated using a three-axis accelerometer mounted at the end of the lower boom of the Remote Manipulator System. The sensed motions were used in a feedback control law to generate commands to the joint servo mechanisms which reduced the unwanted oscillations. Active damping of the Remote Manipulator System with an attached 3990 lb. payload was successfully demonstrated. Six astronaut operators examined the performance of an Active Damping Augmentation control law following single-joint and coordinated six-joint translational and rotational maneuvers. Active Damping Augmentation disturbance rejection of Orbiter thruster firings was also evaluated. Significant reductions in the dynamic response of the 3990 lb. payload were observed. Astronaut operators recommended investigation of Active Damping Augmentation benefits to heavier payloads where oscillations are a bigger problem (e.g. Space Station Freedom assembly operators).

Demeo, Martha E.↗

NASA NTRS1994

Real-time RMS active damping augmentation: Heavy and very light payload evaluations

Controls-Structures Integration Technology has been applied to the Space Shuttle Remote Manipulator System (RMS) to improve on-orbit performance. The objective was to actively damp undesired oscillatory motions of the RMS following routine payload maneuvering and Shuttle attitude control thruster firings. Simulation of active damping was conducted in the real-time, man-in-the-loop Systems Engineering Simulator at NASA's Johnson Space Center. The simulator was used to obtain qualitative and quantitative data on active damping performance from astronaut operators. Using a simulated three-axis accelerometer mounted on the RMS, 'sensed' vibration motions were used to generate joint motor commands that reduced the unwanted oscillations. Active damping of the RMS with heavy and light attached payloads was demonstrated in this study. Five astronaut operators examined the performance of active damping following operator commanded RMS maneuvers and Shuttle thruster firings. Noticeable improvements in the damping response of the RMS with the heavy, Hubble Space Telescope payload and the very light, astronaut in Manipulator Foot Restraint payload were observed. The potential of active damping to aid in precisely maneuvering payloads was deemed significant.

Demeo, Martha E.↗