1,821 research outputs found
Dynamic transverse debondong of a single s-2 fiber
Fiber reinforced composites are becoming increasingly common due to their high strength to weight ratios as compared to more conventional materials. Along with this increased used comes the need to have a higher level of understanding of the material characteristics. Specifically, the interface between the fiber and matrix is of particular interest. Loss of adhesion at this interface, known as debonding, can greatly decrease material strength. There has been significant research into debdonding phenomena at low strain rates. However, there is still a need for further insight at higher strain rates. In addition, given the opacity of many epoxy resins, conventional imaging is often unable to record debonding events or is restricted to only transparent matrices. By integrating a Kolsky tension bar along with X-Ray Phase Contrast Imaging and a high speed camera, high strain rate debonding events of an opaque fiber reinforced composite are recorded and analyzed. Specifically, imaging of transverse debonding initiation and progression along with debonding loads are obtained in this researc
Stars in the USNO-B1 Catalog with Proper Motions Between 1.0 and 5.0 arcseconds per year
This paper examines a subset of objects from the USNO-B1 catalogue with
listed proper motions between 1.0 and 5.0 arcseconds per year. We look at the
degree of contamination within this range of proper motions, and point out the
major sources of spurious high proper motion objects. Roughly 0.1% of the
objects in the USNO-B1 catalogue with listed motions between 1.0 and 5.0
arcseconds per year are real. Comparison with the revised version of Luyten's
Half Second catalogue indicates that USNO-B1 is only about 47% complete for
stars in this range. Preliminary studies indicate that there may be a dip in
completeness in USNO-B1 for objects with motions near 0.1 arcseconds per year.
We also present two new stars with motions between 1.0 and 5.0 arcseconds per
year, 36 new stars with confirmed motions between 0.1 and 1.0 arcseconds per
year, several new common proper motion pairs, and the recovery of LHS237a
(VBs3).Comment: 42 pages, 16 figures, uses AASTeX v5.2, accepted by A
The Nucleus of Comet 10P/Tempel 2 in 2013 and Consequences Regarding Its Rotational State: Early Science from the Discovery Channel Telescope
We present new lightcurve measurements of Comet 10P/Tempel 2 carried out with
Lowell Observatory's Discovery Channel Telescope in early 2013 when the comet
was at aphelion. These data represent some of the first science obtained with
this new 4.3-m facility. With Tempel 2 having been observed to exhibit a small
but ongoing spin-down in its rotation period for over two decades, our primary
goals at this time were two-fold. First, to determine its current rotation
period and compare it to that measured shortly after its most recent perihelion
passage in 2010, and second, to disentangle the spin-down from synodic effects
due to the solar day and the Earth's orbital motion and to determine the sense
of rotation, i.e. prograde or retrograde. At our midpoint of 2013 Feb 24, the
observed synodic period is 8.948+/-0.001 hr, exactly matching the predicted
prograde rotation solution based on 2010 results, and yields a sidereal period
of the identical value due to the solar and Earth synodic components just
canceling out during the interval of the 2013 observations. The retrograde
solution is ruled out because the associated sidereal periods in 2010 and 2013
are quite different even though we know that extremely little outgassing,
needed to produce torques, occurred in this interval. With a definitive sense
of rotation, the specific amounts of spin-down to the sidereal period could be
assessed. The nominal values imply that the rate of spin-down has decreased
over time, consistent with the secular drop in water production since 1988. Our
data also exhibited an unexpectedly small lightcurve amplitude which appears to
be associated with viewing from a large, negative sub-Earth latitude, and a
lightcurve shape deviating from a simple sinusoid implying a highly irregularly
shaped nucleus.Comment: Accepted by AJ; 12 pages of text (pre-print style), 3 tables, 2
figure
The Stellar and Gas Kinematics of Several Irregular Galaxies
We present long-slit spectra of three irregular galaxies from which we
determinethe stellar kinematics in two of the galaxies (NGC 1156 and NGC 4449)
and ionized-gas kinematics in all three (including NGC 2366). We compare this
to the optical morphology and to the HI kinematics of the galaxies. In the
ionized gas, we see a linear velocity gradient in all three galaxies. In NGC
1156 we also detect a weak linear velocity gradient in the stars of (5+/-1/sin
i) km/s/kpc to a radius of 1.6 kpc. The stars and gas are rotating about the
same axis, but this is different from the major axis of the stellar bar which
dominates the optical light of the galaxy. In NGC 4449 we do not detect
organized rotation of the stars and place an upper limit of (3/sin i) km/s/kpc
to a radius of 1.2 kpc. For NGC 4449, which has signs of a past interaction
with another galaxy, we develop a model to fit the observed kinematics of the
stars and gas. In this model the stellar component is in a rotating disk seen
nearly face-on while the gas is in a tilted disk with orbits whose planes
precess in the gravitational potential. This model reproduces the apparent
counter-rotation of the inner gas of the galaxy. The peculiar orbits of the gas
are presumed due to acquisition of gas in the past interaction.Comment: To be published in ApJ, November 20, 200
A model for lopsided galactic disks
Many disk galaxies are lopsided: their brightest inner parts are displaced
from the center of the outer isophotes, or the outer contours of the HI disk.
This asymmetry is particularly common in small, low-luminosity galaxies. We
argue here that long-lived lopsidedness is a consequence of the disk lying
off-center in the potential of the galaxy's extended dark halo, and spinning in
a sense retrograde to its orbit about the halo center. The stellar velocity
field predicted by our gravitational N-body simulations is clearly asymmetric.Comment: 10 pages and 2 figures, AASTEX (aaspp4), to appear in ApJ
The Shape of LITTLE THINGS Dwarf Galaxies DDO 46 and DDO 168: Understanding the stellar and gas kinematics
We present the stellar and gas kinematics of DDO 46 and DDO 168 from the
LITTLE THINGS survey and determine their respective Vmax/sigma_z,0 values. We
used the KPNO's 4-meter telescope with the Echelle spectrograph as a long-slit
spectrograph. We acquired spectra of DDO 168 along four position angles by
placing the slit over the morphological major and minor axes and two
intermediate position angles. However, due to poor weather conditions during
our observing run for DDO 46, we were able to extract only one useful data
point from the morphological major axis. We determined a central stellar
velocity dispersion perpendicular to the disk, sigma_z,0, of 13.5+/-8 km/s for
DDO 46 and of 10.7+/-2.9 km/s for DDO 168. We then derived the
maximum rotation speed in both galaxies using the LITTLE THINGS HI data. We
separated bulk motions from non-circular motions using a double Gaussian
decomposition technique and applied a tilted-ring model to the bulk velocity
field. We corrected the observed HI rotation speeds for asymmetric drift and
found a maximum velocity, Vmax, of 77.4 +/- 3.7 and 67.4 +/- 4.0 km/s for DDO
46 and DDO 168, respectively. Thus, we derived a kinematic measure,
Vmax/sigma_z,0, of 5.7 +/- 0.6 for DDO 46 and 6.3 +/- 0.3 for DDO 168.
Comparing these values to ones determined for spiral galaxies, we find that DDO
46 and DDO 168 have Vmax/sigma_z,0 values indicative of thin disks, which is in
contrast to minor-to-major axis ratio studies
The stellar velocity dispersion in the inner 1.3 disk scale-lengths of the irregular galaxy NGC 4449
We present measurements of the stellar velocity dispersion in the inner 1
arcmin radius (1.3 disk scale-lengths) of the irregular galaxy NGC 4449
determined from long-slit absorption-line spectra. The average observed
dispersion is 29 +/-2 km/s, the same as predicted from NGC 4449's luminosity.
No significant rotation in the stars is detected. If we assume a maximum
rotation speed of the stars from the model determined from the gas kinematics
of Hunter et al. (2002), the ratio V_max/sigma_z measured globally is 3. This
ratio is comparable to values measured in spiral galaxies, and implies that the
stellar disk in NGC 4449 is kinematically relatively cold. The intrinsic
minor-to-major axis ratio (b/a)_0 is predicted to be in the range 0.3-0.6,
similar to values derived from the distribution of observed b/a of Im galaxies.
However, V/sigma_z measured locally is 0.5-1.1, and so the circular velocity of
NGC 4449 is comparable or less than the velocity of the stars within the
central 1.3 disk scale-lengths of the galaxy.Comment: To be published in ApJ, Nov 200
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