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At least 451 records · Page 25
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NASA NTRS1990

The kinematics and morphology of NGC 520: One, two, or three galaxies

The peculiar galaxy NGC 520 (Arp 157) is often interpreted as an interacting pair of galaxies. The identification of the two bulges and overall morphology of the two galaxies has long been a puzzle which the authors attempt to solve here. New longslit optical spectroscopy and near-infrared images of NGC 520 are presented. These data suggest that the northwest peak is the bulge of one of two galaxies in the system. The other larger bulge is clearly evident in the K band image in the middle of the dust lane. The stellar radial velocity profile in the central 10 seconds of the larger bulge is consistent with counterrotation seen in the molecular gas component. This kinematic subsystem could be the remains of a merged gas-rich irregular.

Stanford, S. A.↗
NASA NTRS1990

A two-dimensional kinematic dynamo model of the ionospheric magnetic field at Venus

The results of a high-resolution, two-dimensional, time dependent, kinematic dynamo model of the ionospheric magnetic field of Venus are presented. Various one-dimensional models are considered and the two-dimensional model is then detailed. In this model, the two-dimensional magnetic induction equation, the magnetic diffusion-convection equation, is numerically solved using specified plasma velocities. Origins of the vertical velocity profile and of the horizontal velocities are discussed. It is argued that the basic features of the vertical magnetic field profile remain unaltered by horizontal flow effects and also that horizontal plasma flow can strongly affect the magnetic field for altitudes above 300 km.

Cravens, T. E.↗
NASA NTRS1990

Studies of the local interstellar medium. VIII - Morphology and kinematics of the diffuse interstellar clouds toward Orion

Interstellar clouds in the direction of the Orion association show only positive velocities for target stars within 190 pc of the sun, and both positive and negative velocities for more distant target stars, confirming an earlier prediction by Cowie, Songaila, and York (1979). The nearby positive velocity cloud, designated here as Orion-Lepus 70 (OL 70), is a standard diffuse interstellar cloud: it is subject to the ambient galactic radiation field, with properties consistent with T about equal to 100 K and n about equal to 3/cu cm. Combined with a column density log N(H) = 19.8-20.0/sq cm, these values imply a cloud thickness of about 7 pc. The kinematics of OL 70 are consistent with either an origin as part of the expanding Loop I superbubble shell, or as part of Lindbald's expanding ring, or a synthesis of the two models. The negative velocity interstellar components seen in stars at d not less than 200 pc are caused by interstellar matter accelerated by the expanding Ori-Eri superbubble. Relatively dense interstellar gas at positive LSR velocities is also found within the Orion association, so that it is difficult to pick out OL 70 components in the spectra of the distant stars.

Frisch, P. C.↗
NASA NTRS1990

Obtaining consistent models of helicopter flight-data measurement errors using kinematic-compatibility and state-reconstruction methods

A new method was developed for application of Kalman Filter/Smoothers to post-flight processing of helicopter flight test dynamic measurements. This processing includes checking for kinematic compatibility among the measurements, identification of a measurement error model, and reconstruction of both measured and unmeasured time histories. Emphasis is placed on identification of a parametric measurement error model which is valid for a set of flight test data. This is facilitated through a new method of concatenating several maneuver time histories. The method also includes a model structure determination step which ensures that a physically realistic parameterization has been achieved. Application of the method to a set of BO-105 flight test data is illustrated. The resulting minimally parameterized error model is shown to characterize the measurement errors of the entire data set with very little variation in the parameter values. Reconstructed time histories are shown to have increased bandwidths and signal to noise ratios.

Fletcher, Jay W.↗
NASA NTRS1990

Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico

A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

Demets, Charles↗
NASA NTRS1991

Kinematics and ionization of extended gas in active galaxies. VI - The Seyfert 2 galaxy NGC 1386

Results are presented of direct imaging with a CCD detector and long-slit medium- and low-dispersion spectroscopy of the spatially extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 1386. The distribution, kinematics, and ionization structure of the excited gas were examined in the regions surrounding the nucleus out to a distance of about 1.0. Results present evidence for a spiral structure in this galaxy and for the presence of H II regions in the disk (supporting the classification of NGC 1386 as a Sa galaxy).

Weaver, K. A.↗
NASA NTRS1991

Structure and kinematics of the broad-line regions in active galaxies from IUE variability data

IUE archival data are used here to investigate the structure nad kinematics of the broad-line regions (BLRs) in nine AGN. It is found that the centroid of the line-continuum cross-correlation functions (CCFs) can be determined with reasonable reliability. The errors in BLR size estimates from CCFs for irregularly sampled light curves are fairly well understood. BLRs are found to have small luminosity-weighted radii, and lines of high ionization tend to be emitted closer to the central source than lines of low ionization, especially for low-luminosity objects. The motion of the gas is gravity-dominated with both pure inflow and pure outflow of high-velocity gas being excluded at a high confidence level for certain geometries.

Koratkar, Anuradha P.↗
NASA NTRS1991

A kinematic study of the Fornax dwarf spheroidal galaxy

Precise radial velocities of 44 stars and four globular clusters located in two fields of the Fornax dwarf spheroidal galaxy are obtained on the basis of photon-counting echelle spectroscopy with a resolution of approximately 14 km/s. BV CCD photometry of the giant branch of Fornax in both fields are presented as well. A variety of kinematic and photometric criteria are used to identify 10-12 probable nonmembers in the present sample of spectroscopically observed stars. Based on the most probable members, the mean heliocentric systemic velocity of Fornax is 53.0 + or - 1.8 km/s, with no evidence of any significant rotation about the minor axis. The intrinsic velocity dispersion of the stars in Fornax's central field is 9.9 + or - 1.7 km/s, while for the outer field the velocity dispersion is 1.20 + or - 2.8 km/s. The true central velocity dispersion is not more than 1.6 km/s larger than the observed central dispersions for a number of reasonable models.

Mateo, Mario↗
NASA NTRS1992

Analyzing Robotic Kinematics Via Computed Simulations

Computing system assists in evaluation of kinematics of conceptual robot. Displays positions and motions of robotic manipulator within work cell. Also displays interactions between robotic manipulator and other objects. Results of simulation displayed on graphical computer workstation. System includes both off-the-shelf software originally developed for automotive industry and specially developed software. Simulation system also used to design human-equivalent hand, to model optical train in infrared system, and to develop graphical interface for teleoperator simulation system.

Carnahan, Timothy M.↗
NASA NTRS1992

The double universal joint wrist on a manipulator: Solution of inverse position kinematics and singularity analysis

This paper presents three methods to solve the inverse position kinematics position problem of the double universal joint attached to a manipulator: (1) an analytical solution for two specific cases; (2) an approximate closed form solution based on ignoring the wrist offset; and (3) an iterative method which repeats closed form position and orientation calculations until the solution is achieved. Several manipulators are used to demonstrate the solution methods: cartesian, cylindrical, spherical, and an anthropomorphic articulated arm, based on the Flight Telerobotic Servicer (FTS) arm. A singularity analysis is presented for the double universal joint wrist attached to the above manipulator arms. While the double universal joint wrist standing alone is singularity-free in orientation, the singularity analysis indicates the presence of coupled position/orientation singularities of the spherical and articulated manipulators with the wrist. The cartesian and cylindrical manipulators with the double universal joint wrist were found to be singularity-free. The methods of this paper can be implemented in a real-time controller for manipulators with the double universal joint wrist. Such mechanically dextrous systems could be used in telerobotic and industrial applications, but further work is required to avoid the singularities.

Williams, Robert L., III↗
NASA NTRS1991

Flow downstream of the heliospheric terminal shock - Magnetic field kinematics

A kinematic model of the interplanetary magnetic field in the heliosheath beyond the solar wind terminal shock is presented in order to evaluate the possible importance of MHD effects in that region of space. The need for this evaluation arises because the interplanetary magnetic field is compressed across the terminal shock and further amplified by the decreasing flow speed beyond the shock. Streamlines which approach the stagnation point before turning in the downstream direction lead to the strongest effects due to the extreme slowing of the solar wind and consequent compression of the embedded magnetic field. The magnetic volume force therefore cannot be neglected on streamlines that approach the heliopause in the upstream direction, where the volume containing them is a large fraction of the overall of the heliosheath in the upstream direction. The increase in the magnetic pressure may act to bring the upstream terminal shock significantly closer to the sun, potentially reconciling a conflict between models and observations.

Nerney, S.↗
NASA NTRS1992

Motion at the ionization front in the Orion nebula - A kinematic study of the forbidden O I line

The kinematics of the ionization front in H II regions is investigated via a study of the collisionally excited forbidden O I emission at 630 nm. Slit spectra of 5/km s resolution are used to examine the velocities of forbidden O I across the inner few arcminutes of M42. The mean velocity is significantly more positive than for other ions, which confirms the argument that the ionization front is formed against the parent molecular cloud OMC 1. It is inferred that there is acceleration of material in the ionization front at the parent molecular cloud. A new model for M42 based largely on optical emission-line and radio absorption-line studies is presented. A detailed statistical analysis indicates agreement between the structure function and the Kolmogorov theory for turbulence.

O'Dell, C. R.↗
NASA NTRS1990

Electrical and kinematic structure of an Oklahoma mesoscale convective system

The case study examines the dynamics and kinematics of a mesoscale convective system (MCS) by comparing its meteorological parameters with in situ electrical measurements. Conventional MCS characteristics are reported including a rear inflow jet, wake low, and a bipolar cloud-to-ground pattern, but some nonclassical conditions are also reported. Horizontally long cloud-to-ground electrical strikes are noted which demonstrate that cloud-to-ground electrical data alone cannot entirely characterize stratiform electrification in MCSs.

Hunter, Steven M.↗
NASA NTRS1992

The kinematics of the molecular gas in Centaurus A

The CO (2-1) emission along the inner dust lane of Centaurus A, observed with the Caltech Submillimeter Observatory on Mauna Kea, shows the molecular gas to be in a thin disk, with a velocity dispersion of only about 10 km/s. The observed line profiles are broadened considerably due to beam smearing of the gas velocity field. The profile shapes are inconsistent with planar circular and noncircular motion. However, a warped disk in a prolate potential provides a good fit to the profile shapes. The morphology and kinematics of the molecular gas is similar to that of the ionized material, seen in H-alpha. The best-fitting warped disk model not only matches the optical appearance of the dust lane but also agrees with the large-scale map of the CO emission and is consistent with H I measurements at larger radii.

Quillen, A. C.↗
NASA NTRS1991

Kinematic analysis of generalized adaptive trusses

Adaptive trusses offer the greatest stiffness and strength for a given weight of any articulated structure or mechanism. Because of this, there are many potential extraterrestrial applications of these variable-geometry trusses, including serpentine manipulators, payload isolation, tracking, pointing and docking mechanisms, and gimbals. All of these applications will require the ability to precisely control the kinematic parameters of the mechanism, including position, velocity, and acceleration. This paper explores the fundamental nature of adaptive trusses by examining the basic truss elements or unit cells. A general method for analyzing forward and inverse motion of all the basic truss units is presented, followed by a more efficient formulation for the octahedral unit cell. Finally, general closed-form techniques are presented for finding velocity, acceleration, and all higher derivatives of truss motion.

Tidwell, Paul H.↗
NASA NTRS1990

A computationally efficient error-based adaptive control scheme for kinematically redundant manipulators

A Cartesian-space control scheme is developed to control the motion of kinematically redundant manipulators with 7 degrees of freedom (DOF). The control scheme consists mainly of proportional-derivative (PD) controllers whose gains are adjusted by an adaptation law driven by the errors between the desired and actual trajectories. The adaptation law is derived using the concept of model reference adaptive control (MRAC) and Liapunov direct method under the assumption that the manipulator performs noncompliant and slowly-varying motions. The developed control scheme is computationally efficient because its implementation does not require the computation of the manipulator dynamics. Computer simulation performed to evaluate the control scheme performance is presented and discussed.

Nguyen, Charles C.↗
NASA NTRS1993

Kinematics of the New Zealand plate boundary: Relative motion by GPS across networks of 1000 km and 50 km spacing

The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the field investigations are given in the appendix. An overview of the 1992 GPS field program is also given in the appendix.

Meertens, Charles M.↗
NASA NTRS1993

Kinematics of compact groups and morphologies of the member galaxies

We present the results of a kinematical and morphological study of galaxies in the Hickson compact groups. The redshift survey of 457 galaxies has been completed. The great majority of the galaxies have velocities within about 1000 km/s(exp -1) of the median velocity of the group. The velocities of the groups range from 1380 to 41731 km/s(exp -1) with a median of 8889 km/s(exp -1), corresponding to a median distance of 89 h(exp -1)Mpc. With the addition of the radial velocity selection criterion, a relatively large sample of physically dense compact groups was defined. The nature of the velocity dispersion-morphology relation (Hickson, Kindl and Huchra 1989, hereafter HKH) is investigated. This is the tendency of groups with high velocity dispersions to contain fewer late type galaxies. We find that this strong correlation is not due to any sample selection effects. The morphology concordance in compact groups (HKH), which is the trend for galaxies in a group to have similar morphological types, can be fully explained by the velocity dispersion-morphology correlation. A significant correlation is found between crossing time and the fraction of gas-rich galaxies in the groups. Groups with short crossing times typically contain fewer late-type galaxies. This may be evidence that significant dynamical evolution has occurred in these groups.

Mendesdeoliveira, Claudia↗