319 research outputs found
The Ds(2317) and Ds(2463) Mesons as Scalar and Axial-Vector Chiralons in the Covariant Level-Classification Scheme
The new narrow mesons observed recently in the final states Ds+ pi0 and Ds*+
pi0 are pointed out to be naturally assigned as the ground-state scalar and
axial-vector chiralons in the c sbar system, which would newly appear in the
covariant hadron-classification scheme proposed a few years ago.Comment: 8 pages, 1 figure, uses ptptex.st
Sensor Reduction for Backing-Up Control of a Vehicle With Triple Trailers
This paper presents a cost-effective design based on sensor reduction for backing-up control of a vehicle with triple trailers. To realize a cost-effective design, we newly derive two linear-matrix-inequality (LMI) conditions for a discrete Takagi-Sugeno fuzzy system. One is an optimal dynamic output feedback design that guarantees desired control performance. The other is an avoidance of jackknife phenomenon for the use of the optimal dynamic output feedback controller. Our results demonstrate that the proposed LMI-based design effectively achieves the backing-up control of the vehicle with triple trailers while avoiding the jackknife phenomenon. More importantly, we demonstrate that the designed optimal control can achieve the backing-up control without, at least, two potentiometers that were employed to measure the relative angles (of a vehicle with triple trailers) in our previous experiments. Since the relative angles directly relate to the jackknife phenomenon, the successful control results without two potentiometers are very interesting and important from the cost-effective design point of view
Discovery of X rays from Class 0 protostar candidates in OMC-3
We have observed the Orion Molecular Clouds 2 and 3 (OMC-2 and OMC-3) with
the Chandra X-ray Observatory (CXO). The northern part of OMC-3 is found to be
particularly rich in new X-ray features; four hard X-ray sources are located in
and along the filament of cloud cores. Two sources coincide positionally with
the sub- dust condensations of MMS 2 and 3 or an outflow radio source
VLA 1, which are in a very early phase of star formation. The X-ray spectra of
these sources show an absorption column of (1-3) x 10^23 H cm-2. Assuming a
moderate temperature plasma, the X-ray luminosity in the 0.5-10 keV band is
estimated to be ~10^30 erg s^-1 at a distance of 450 pc. From the large
absorption, positional coincidence and moderate luminosity, we infer that the
hard X-rays are coming from very young stellar objects embedded in the
molecular cloud cores. We found another hard X-ray source near the edge of the
dust filament. The extremely high absorption of 3 x 10^23 H cm^-2 indicates
that the source must be surrounded by dense gas, suggesting that it is either a
YSO in an early accretion phase or a Type II AGN (e.g. a Seyfert 2), although
no counterpart is found at any other wavelength. In contrast to the hard X-ray
sources, soft X-ray sources are found spread around the dust filaments, most of
which are identified with IR sources in the T Tauri phase.Comment: 9 pages, To be appeared in ApJ v554 n2 Jun 20, 2001 issue, related
press release is available at http://science.psu.edu/alert/Tsuboi11-2000.htm,
Figure 1 and figure 2 with the best resolution is available at
ftp.astro.psu.edu/pub/tsuboi/OMC/010205
Origin of optically passive spiral galaxies with dusty star-forming regions: Outside-in truncation of star formation?
Recent observations have revealed that red, optically--passive spiral
galaxies with little or no optical emission lines, harbour significant amounts
of dust-obscured star formation. We propose that these observational results
can be explained if the spatial distributions of the cold gas and star-forming
regions in these spiral galaxies are significantly more compact than those in
blue star-forming spirals. Our numerical simulations show that if the sizes of
star-forming regions in spiral galaxies with disk sizes of R_d are ~ 0.3R_d,
such galaxies appear to have lower star formation rates as well as higher
degrees of dust extinction. This is mainly because star formation in these
spirals occurs only in the inner regions where both the gas densities and
metallicities are higher, and hence the dust extinction is also significantly
higher. We discuss whether star formation occurring preferentially in the inner
regions of spirals is closely associated with the stripping of halo and disk
gas via some sort of environmental effect. We suggest that the "outside-in
truncation of star formation" is the key to a better understanding of
apparently optically--passive spirals with dusty star-forming regions.Comment: 5 pages, 4 figures, accepted in MNRAS Letter
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