347 research outputs found
Lift-off dynamics in a simple jumping robot
We study vertical jumping in a simple robot comprising an actuated
mass-spring arrangement. The actuator frequency and phase are systematically
varied to find optimal performance. Optimal jumps occur above and below (but
not at) the robot's resonant frequency . Two distinct jumping modes
emerge: a simple jump which is optimal above is achievable with a squat
maneuver, and a peculiar stutter jump which is optimal below is generated
with a counter-movement. A simple dynamical model reveals how optimal lift-off
results from non-resonant transient dynamics.Comment: 4 pages, 4 figures, Physical Review Letters, in press (2012
The Sloan Bright Arcs Survey: Four Strongly Lensed Galaxies with Redshift >2
We report the discovery of four very bright, strongly-lensed galaxies found
via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and
6. These were followed-up with spectroscopy and imaging data from the
Astrophysical Research Consortium 3.5m telescope at Apache Point Observatory
and found to have redshift . With isophotal magnitudes
and 3\arcsec-diameter magnitudes , these systems are some of
the brightest and highest surface brightness lensed galaxies known in this
redshift range. In addition to the magnitudes and redshifts, we present
estimates of the Einstein radii, which range from 5.0 \arcsec to 12.7
\arcsec, and use those to derive the enclosed masses of the lensing galaxies
The Sloan Bright Arcs Survey : Six Strongly Lensed Galaxies at z=0.4-1.4
We present new results of our program to systematically search for strongly
lensed galaxies in the Sloan Digital Sky Survey (SDSS) imaging data. In this
study six strong lens systems are presented which we have confirmed with
follow-up spectroscopy and imaging using the 3.5m telescope at the Apache Point
Observatory. Preliminary mass models indicate that the lenses are group-scale
systems with velocity dispersions ranging from 466-878 km s^{-1} at z=0.17-0.45
which are strongly lensing source galaxies at z=0.4-1.4. Galaxy groups are a
relatively new mass scale just beginning to be probed with strong lensing. Our
sample of lenses roughly doubles the confirmed number of group-scale lenses in
the SDSS and complements ongoing strong lens searches in other imaging surveys
such as the CFHTLS (Cabanac et al 2007). As our arcs were discovered in the
SDSS imaging data they are all bright (), making them ideally
suited for detailed follow-up studies.Comment: 13 pages, 3 figures, submitted to ApJL, the Sloan Bright Arcs page is
located here: http://home.fnal.gov/~kubo/brightarcs.htm
Discovery of A Very Bright, Strongly-Lensed z=2 Galaxy in the SDSS DR5
We report on the discovery of a very bright z = 2.00 star-forming galaxy that
is strongly lensed by a foreground z=0.422 luminous red galaxy (LRG). This
system was found in a systematic search for bright arcs lensed by LRGs and
brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5
sample. Follow-up observations on the Subaru 8.2m telescope on Mauna Kea and
the Astrophysical Research Consortium 3.5m telescope at Apache Point
Observatory confirmed the lensing nature of this system. A simple lens model
for the system, assuming a singular isothermal ellipsoid mass distribution,
yields an Einstein radius of 3.82 +/- 0.03 arcsec or 14.8 +/- 0.1 kpc/h at the
lens redshift. The total projected mass enclosed within the Einstein radius is
2.10 +/- 0.03 x 10^12 M_sun/h, and the magnification factor for the source
galaxy is 27 +/- 1. Combining the lens model with our gVriz photometry, we find
an (unlensed) star formation rate for the source galaxy of 32 M_sun/h / yr,
adopting a fiducial constant star formation rate model with an age of 100 Myr
and E(B-V) = 0.25. With an apparent magnitude of r = 19.9, this system is among
the very brightest lensed z >= 2 galaxies, and provides an excellent
opportunity to pursue detailed studies of the physical properties of an
individual high-redshift star-forming galaxy.Comment: 31 pages, 12 figures, 4 tables, submitted to Ap
The sensory feedback mechanisms enabling couples to walk synchronously: An initial investigation
The inattentive eye often will not notice it, but synchronization among human walking partners is quite common. In this first investigation of this phenomenon, we studied its frequency and the mechanisms that contribute to this form of "entrainment." Specifically, by modifying the available communication links between two walking partners, we isolated the feedback mechanisms that enable couples to synchronize their stepping pattern when they walk side-by-side. Although subjects were unaware of the research aims and were not specifically asked to walk in synchrony, we observed synchronized walking in almost 50% of the walking trials, among couples who do not usually walk together. The strongest in-phase synchrony occurred in the presence of tactile feedback (i.e., handholding), perhaps because of lower and upper extremity coupling driven in part by arm swing. Interestingly, however, even in the absence of visual or auditory communication, couples also frequently walked in synchrony while 180 degrees out-of-phase, likely using different feedback mechanisms. These findings may partially explain how patients with certain gait disorders and disturbed rhythm enhance their gait when they walk with a partner and suggest alternative interventions that might improve the stepping pattern. Further, this preliminary investigation highlights the relatively ubiquitous nature of an interesting phenomenon that has not previously been studied and suggests that further work is needed to better understand the mechanisms that entrain the gait of two walking partners and allows couples to walk in synchrony with minimal or no conscious effort
- …