60,358 research outputs found
Six Degrees of Freedom Control with Each Hand?
For some time man has made six degree of freedom inputs to a pair of dextrous manipulators using both hands simultaneously by the use of the master/slave concept. The advent of the microprocessor has the potential to make the master/slave concept redundant by replacing the master with a mathematical model. All spacecraft to date, including the space shuttle, that were flown in six degrees of freedom were controlled by using both hands, the left hand controlling translation and the right rotation. Almost inevitably the same principle was applied to the CANADARM. At the instigation of NASA the development of a device whereby both translation and rotation could be combined allowing full control with one hand was developed. The development and testing of the device, and the extension of its application into spaceflight control are described. Also the concept of an adaptable workstation for multi-maniipulator and spacecraft flight control is discussed
Multi-axis manual controllers: A state-of-the-art report
A literature search was carried out to examine the feasibility of a six degree of freedom hand controller. Factors addressed included related areas, approaches to manual control, applications of manual controllers, and selected studies of the human neuromuscular system. Results are presented
Design and development of a six degree of freedom hand controller
The design objectives of a six degree of freedom manual controller are discussed with emphasis on a space environment. Details covered include problems associated with a zero-g environment, the need to accommodate both 'shirt sleeve' and space suited astronauts, the combination of both manipulator operation and spacecraft flight control in a single device, and to accommodate restraints in space. A variable configuration device designed as a development tool in which rotational axes can be moved relative to one another, is described and its limitations discussed. Two additional devices were developed for concept testing. Each device combines the need for good quality with its ability achieve a wide range of adjustments
The exact power envelope of tests for a unit root
We show how to obtain the exact power envelope of tests for a unit root against trend-stationary alternatives, under normality. This is in contrast to the asymptotic power envelope derived by Elliott, Rothenberg and Stock (1996), and is used to indicate the lack of power of unit root tests in fixed sample sizes. <br><br> Keywords; power envelope, unit root tests <br><br> JEL classification: C12, C22
Six degree of freedom manual controls study report
The feasibility of using degree of freedom manual controls in space in an on orbit environment was determined. Several six degree of freedom controls were tested in a laboratory environment, and replica controls were used to control robot arms. The selection of six degrees of freedom as a design goal was based on the fact that six degrees are sufficient to define the location and orientation of a rigid body in space
A Firm Upper Limit to the Radius of the Neutron Star in SAX J1808.4-3658
We show that observations of X-ray pulsing from SAX J1808.4-3658 place a firm
upper limit of 13.8 m^{1/3} km on the radius of the neutron star, where m is
its mass in solar units. The limit is independent of distance or assumptions
about the magnetospheric geometry, and could be significantly tightened by
observations of the pulsations in the near future. We discuss the implications
for the equation of state and the possible neutron star mass.Comment: (7 pages, 1 figure, accepted for publication in ApJ Letters
The AGN-starburst connection, Galactic superwinds, and M_BH - sigma
Recent observations of young galaxies at redshifts z ~ 3 have revealed
simultaneous AGN and starburst activity, as well as galaxy-wide superwinds. I
show that there is probably a close connection between these phenomena by
extending an earlier treatment of the M_BH - sigma relation (King, 2003). As
the black hole grows, an outflow drives a shell into the surrounding gas. This
stalls after a dynamical time at a size determined by the hole's current mass
and thereafter grows on the Salpeter timescale. The gas trapped inside this
bubble cools and forms stars and is recycled as accretion and outflow. The
consequent high metallicity agrees with that commonly observed in AGN
accretion. Once the hole reaches a critical mass this region attains a size
such that the gas can no longer cool efficiently. The resulting energy-driven
flow expels the remaining gas as a superwind, fixing both the M_BH - sigma
relation and the total stellar bulge mass at values in good agreement with
observation. Black hole growth thus produces starbursts and ultimately a
superwind.Comment: ApJ, in press, 4 page
Li I and K I Scatter in Cool Pleiades Dwarfs
We utilize high-resolution (R~60,000), high S/N (~100) spectroscopy of 17
cool Pleiades dwarfs to examine the confounding star-to-star scatter in the
6707 Li I line strengths in this young cluster. Our Pleiads, selected for their
small projected rotational velocity and modest chromospheric emission, evince
substantial scatter in the linestrengths of 6707 Li I feature that is absent in
the 7699 K I resonance line. The Li I scatter is not correlated with that in
the high-excitation 7774 O I feature, and the magnitude of the former is
greater than the latter despite the larger temperature sensitivity of the O I
feature. These results suggest that systematic errors in linestrength
measurements due to blending, color (or color-based T_eff) errors, or line
formation effects related to an overlying chromosphere are not the principal
source of Li I scatter in our stars. There do exist analytic spot models that
can produce the observed Li scatter without introducing scatter in the K I line
strengths or the color-magnitude diagram. However, these models predict factor
of >3 differences in abundances derived from the subordinate 6104 and resonance
6707 Li I features; we find no difference in the abundances determined from
these two features. These analytic spot models also predict CN line strengths
significantly larger than we observe in our spectra. The simplest explanation
of the Li, K, CN, and photometric data is that there must be a real abundance
component to the Pleiades Li dispersion. We suggest that this real abundance
component is the manifestation of relic differences in erstwhile
pre-main-sequence Li burning caused by effects of surface activity on stellar
structure. We discuss observational predictions of these effects.Comment: 35 pages, 7 figures; accepted by Ap
- …