1,690 research outputs found
Exploring Disk Galaxy Dynamics Using IFU Data
In order to test the basic equations believed to dictate the dynamics of disk
galaxies, we present and analyze deep two-dimensional spectral data obtained
using the PPAK integral field unit for the early-type spiral systems NGC 2273,
NGC 2985, NGC 3898 and NGC 5533. We describe the care needed to obtain and
process such data to a point where reliable kinematic measurements can be
obtained from these observations, and a new more optimal method for deriving
the rotational motion and velocity dispersions in such disk systems. The data
from NGC 2273 and NGC 2985 show systematic variations in velocity dispersion
with azimuth, as one would expect if the shapes of their velocity ellipsoids
are significantly anisotropic, while the hotter disks in NGC 3898 and NGC 5533
appear to have fairly isotropic velocity dispersions. Correcting the rotational
motion for asymmetric drift using the derived velocity dispersions reproduces
the rotation curves inferred from emission lines reasonably well, implying that
this correction is quite robust, and that the use of the asymmetric drift
equation is valid. NGC 2985 is sufficiently close to face on for the data,
combined with the asymmetric drift equation, to determine all three components
of the velocity ellipsoid. The principal axes of this velocity ellipsoid are
found to be in the ratio sigma_z:sigma_phi:sigma_R ~ 0.7:0.7:1, which shows
unequivocally that this disk distribution function respects a third integral of
motion. The ratio is also consistent with the predictions of epicyclic theory,
giving some confidence in the application of this approximation to even fairly
early-type disk galaxies.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Tire Tread Reinforcement with Short Aramid Fibers
Tensile testing on short fiber reinforced composites is helping to identify the advantages and disadvantages of different rubber compound
Factors Influencing Reinforcement of NR and EPDM Rubbers with Short Aramid Fibers
Among short fiber reinforced composites, those with rubbery matrices have gained great importance due to the advantages they have in processing and low cost, coupled with high strength. These composites combine the elastic behavior of rubbers with strength and stiffness of fibers. Reinforcement with short fibers offers additional features such as design flexibility, high modulus, tear strength, etc. The degree of reinforcement depends on parameters such as: the nature of the rubber matrix, the type of fibers, the concentration and orientation of fibers, fiber to rubber adhesion (generation of a strong interface), fiber length and aspect ratio of the fibers. In this research aramid fibers have been chosen because of their significantly higher modulus and strength, compared to other commercial fibers. Compounds based on NR and EPDM are prepared. Short aramid fibers with different kinds of surface treatments, standard finish and RFL-coating result in different rubber-fiber interfaces. The reinforcing effect of these short aramid fibers is characterized by mechanical and viscoelastic experiments, and by studying the fracture surfaces with microscopic techniques
Confrontation of MOND with the rotation curves of early-type disc galaxies
We extend the MOND analysis to a sample of 17 high surface brightness,
early-type disc galaxies with rotation curves derived from a combination of
21cm HI line observations and optical spectroscopic data. A number of these
galaxies have asymptotic rotation velocities between 250 and 350 km/s making
them among the most massive systems (in terms of baryonic mass) considered in
the context of MOND. We find that the general MOND prediction for such galaxies
-- a rotation curve which gradually declines to the asymptotic value -- is
confirmed, and in most cases the MOND rotation curve, determined from the mean
radial light and gas distribution, agrees in detail with the observed rotation
curve. In the few cases where MOND appears not to work well, the discrepancies
can generally be understood in terms of various observational errors -- such as
incorrect orientation angles and/or distances -- or of unmodelled physical
effects -- such as non-circular motions. The implied mass-to-light ratios for
the stellar disc and bulge constrain the MOND interpolating function; the form
recently suggested by Zhao & Famaey (2005) yields more sensible values than the
one traditionally used in MOND determinations of galaxy rotation curves.Comment: 9 pages, 2 figures, submitted MNRA
The high mass end of the Tully-Fisher relation
We study the location of massive disk galaxies on the Tully-Fisher relation.
Using a combination of K-band photometry and high-quality rotation curves, we
show that in traditional formulations of the TF relation (using the width of
the global HI profile or the maximum rotation velocity), galaxies with rotation
velocities larger than 200 km/s lie systematically to the right of the relation
defined by less massive systems, causing a characteristic `kink' in the
relations. Massive, early-type disk galaxies in particular have a large offset,
up to 1.5 magnitudes, from the main relation defined by less massive and
later-type spirals.
The presence of a change in slope at the high-mass end of the Tully-Fisher
relation has important consequences for the use of the Tully-Fisher relation as
a tool for estimating distances to galaxies or for probing galaxy evolution. In
particular, the luminosity evolution of massive galaxies since z = 1 may have
been significantly larger than estimated in several recent studies.
We also show that many of the galaxies with the largest offsets have
declining rotation curves and that the change in slope largely disappears when
we use the asymptotic rotation velocity as kinematic parameter. The remaining
deviations from linearity can be removed when we simultaneously use the total
baryonic mass (stars + gas) instead of the optical or near-infrared luminosity.
Our results strengthen the view that the Tully-Fisher relation fundamentally
links the mass of dark matter haloes with the total baryonic mass embedded in
them.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Reinforcement of natural rubber by precipitated silica: the influence of processing temperature
The thermal history and in particular the mixing dump temperature is a parameter of paramount importance in mixing rubber and silica with a silane coupling agent in order to achieve proper silanization of silica and to avoid premature scorch reactions. In this work, the influence of mixing dump temperature on the performance of silica reinforced Natural Rubber (NR) is investigated. The investigation also includes the effect of non-rubber constituents, primarily proteins in NR, by using deproteinized Natural Rubber (DPNR) and synthetic polyisoprene (IR). The vulcanization properties and rubber-to-filler interactions of silica reinforced NR in presence and absence of a silane coupling agent are highlighted. With increasing mixing dump temperature, the silanization reaction between silica and silane coupling agent proceeds further. At sufficiently high dump temperature, filler-filler interactions in the NR-silica compounds are reduced and silica-rubber interaction improved as evidenced by a drop in the Payne effect and increment in chemically bound rubber. It is demonstrated that NR and IR compounds mixed till above the optimum dump temperature exhibit cure reversion and reduction in tensile properties. On the other hand, DPNR-silica vulcanizates show slightly more constant physical properties
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