1,287 research outputs found
Modeling the Gas Flow in the Bar of NGC 1365
We present new observations of the strongly-barred galaxy NGC 1365, including
new photometric images and Fabry-Perot spectroscopy, as well as a detailed
re-analysis of the neutral hydrogen observations from the VLA archive. We find
the galaxy to be at once remarkably bi-symmetric in its I-band light
distribution and strongly asymmetric in the distribution of dust and in the
kinematics of the gas in the bar region. The velocity field mapped in the
H-alpha line reveals bright HII regions with velocities that differ by 60 to 80
km/s from that of the surrounding gas, which may be due to remnants of
infalling material. We have attempted hydrodynamic simulations of the bar flow
to estimate the separate disk and halo masses, using two different dark matter
halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar
pattern speeds (Omega_p). None of our models provides a compelling fit to the
data, but they seem most nearly consistent with a fast bar, corotation at sim
1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully
maximal, disk. The fitted dark halos are unusually concentrated, a requirement
driven by the declining outer rotation curve.Comment: 43 pages, 15 figures, accepted to appear in Ap
Star Formation Thresholds in Galactic Disks
We report the first results of a detailed study of the star formation law in
a sample of 32 nearby spiral galaxies with well-measured rotation curves, HI
and H (as traced by CO) surface density profiles, and new \Ha CCD
photometry. Our results strongly support the view that the formation of
gravitationally bound interstellar clouds regulates the onset of widespread
star formation -- at least in the outer regions of galactic disks.Comment: Will appear in July 1 ApJ. Abbreviated abstract. Postscript version
available at http://www.astro.caltech.edu/~clm
New Observations of Extra-Disk Molecular Gas in Interacting Galaxy Systems, Including a Two-Component System in Stephan's Quintet
We present new CO (1 - 0) observations of eleven extragalactic tails and
bridges in nine interacting galaxy systems, almost doubling the number of such
features with sensitive CO measurements. Eight of these eleven features were
undetected in CO to very low CO/HI limits, with the most extreme case being the
NGC 7714/5 bridge. This bridge contains luminous H II regions and has a very
high HI column density (1.6 X 10^21 cm^-2 in the 55" CO beam), yet was
undetected in CO to rms T(R)* = 2.4 mK. The HI column density is higher than
standard H2 and CO self-shielding limits for solar-metallicity gas, suggesting
that the gas in this bridge is metal-poor and has an enhanced N(H2)/I(CO) ratio
compared to the Galactic value. Only one of the eleven features in our sample
was unambiguously detected in CO, a luminous HI-rich star formation region near
an optical tail in the compact group Stephan's Quintet. We detect CO at two
widely separated velocities in this feature, at ~6000 km/s and ~6700 km/s. Both
of these components have HI and H-alpha counterparts. These velocities
correspond to those of galaxies in the group, suggesting that this gas is
material that has been removed from two galaxies in the group. The
CO/HI/H-alpha ratios for both components are similar to global values for
spiral galaxies.Comment: 39 pages, Latex, 15 figures, Astronomical Journal, in pres
Superconductivity and magnetism in RbxFe2-ySe2: Impact of thermal treatment on mesoscopic phase separation
An extended study of the superconducting and normal-state properties of
various as-grown and post-annealed RbxFe2-ySe2 single crystals is presented.
Magnetization experiments evidence that annealing of RbxFe2-ySe2 at 413 K, well
below the onset of phase separation Tp=489 K, neither changes the magnetic nor
the superconducting properties of the crystals. In addition, annealing at 563
K, well above Tp, suppresses the superconducting transition temperature Tc and
leads to an increase of the antiferromagnetic susceptibility accompanied by the
creation of ferromagnetic impurity phases, which are developing with annealing
time. However, annealing at T=488K=Tp increases Tc up to 33.3 K, sharpens the
superconducting transition, increases the lower critical field, and strengthens
the screening efficiency of the applied magnetic field. Resistivity
measurements of the as-grown and optimally annealed samples reveal an increase
of the upper critical field along both crystallographic directions as well as
its anisotropy. Muon spin rotation and scanning transmission electron
microscopy experiments suggest the coexistence of two phases below Tp: a
magnetic majority phase of Rb2Fe4Se5 and a non-magnetic minority phase of
Rb0.5Fe2Se2. Both microscopic techniques indicate that annealing the specimens
just at Tp does not affect the volume fraction of the two phases, although the
magnetic field distribution in the samples changes substantially. This suggests
that the microstructure of the sample, caused by mesoscopic phase separation,
is modified by annealing just at Tp, leading to an improvement of the
superconducting properties of RbxFe2-ySe2 and an enhancement of Tc.Comment: 13 pages, 12 figure
Derived equivalence classification of the cluster-tilted algebras of Dynkin type E
We obtain a complete derived equivalence classification of the cluster-tilted
algebras of Dynkin type E. There are 67, 416, 1574 algebras in types E6, E7 and
E8 which turn out to fall into 6, 14, 15 derived equivalence classes,
respectively. This classification can be achieved computationally and we
outline an algorithm which has been implemented to carry out this task. We also
make the classification explicit by giving standard forms for each derived
equivalence class as well as complete lists of the algebras contained in each
class; as these lists are quite long they are provided as supplementary
material to this paper. From a structural point of view the remarkable outcome
of our classification is that two cluster-tilted algebras of Dynkin type E are
derived equivalent if and only if their Cartan matrices represent equivalent
bilinear forms over the integers which in turn happens if and only if the two
algebras are connected by a sequence of "good" mutations. This is reminiscent
of the derived equivalence classification of cluster-tilted algebras of Dynkin
type A, but quite different from the situation in Dynkin type D where a
far-reaching classification has been obtained using similar methods as in the
present paper but some very subtle questions are still open.Comment: 19 pages. v4: completely rewritten version, to appear in Algebr.
Represent. Theory. v3: Main theorem strengthened by including "good"
mutations (cf. also arXiv:1001.4765). Minor editorial changes. v2: Third
author added. Major revision. All questions left open in the earlier version
by the first two authors are now settled in v2 and the derived equivalence
classification is completed. arXiv admin note: some text overlap with
arXiv:1012.466
Local governance and business performance in Vietnam:the transaction costs’ perspective
Local governance and business performance in Vietnam: the transaction costs’ perspective. Regional Studies. This paper adopts a transaction costs’ perspective to explain why the growth of small and medium-sized enterprises (SMEs) may vary across regions of an emerging economy. Furthermore, it is argued that young and small firms gain more from the improvement of local governance than do old and large firms. In addition, depending on the institutional history, SMEs will respond differently to the incentives provided by local governance. Analysing more than 300,000 SMEs in Vietnam during 2006–12, it is shown that higher-quality local governance positively influences local SME revenue growth; this effect is stronger for young and small firms, and matters more where institutional history suggests there is less support for entrepreneurship
Speaker-independent emotion recognition exploiting a psychologically-inspired binary cascade classification schema
In this paper, a psychologically-inspired binary cascade classification schema is proposed for speech emotion recognition. Performance is enhanced because commonly confused pairs of emotions are distinguishable from one another. Extracted features are related to statistics of pitch, formants, and energy contours, as well as spectrum, cepstrum, perceptual and temporal features, autocorrelation, MPEG-7 descriptors, Fujisakis model parameters, voice quality, jitter, and shimmer. Selected features are fed as input to K nearest neighborhood classifier and to support vector machines. Two kernels are tested for the latter: Linear and Gaussian radial basis function. The recently proposed speaker-independent experimental protocol is tested on the Berlin emotional speech database for each gender separately. The best emotion recognition accuracy, achieved by support vector machines with linear kernel, equals 87.7%, outperforming state-of-the-art approaches. Statistical analysis is first carried out with respect to the classifiers error rates and then to evaluate the information expressed by the classifiers confusion matrices. © Springer Science+Business Media, LLC 2011
Non-circular Gas Kinematics and Star Formation in the Ringed Galaxy NGC 4736
We analyze the gas kinematics and star formation properties of the nearby
RSab galaxy NGC 4736 using interferometric and single-dish CO(1-0) data and
previously published Halpha and HI data. The CO morphology is dominated by a
central molecular bar and tightly wound spiral arms associated with a bright
ring of star formation. Strong HI emission is also found in the ring, but HI is
absent from the central regions. Comparison of the HI and Halpha distributions
suggests that HI in the ring is primarily dissociated H. Modeling of the CO
kinematics reveals gas motion in elliptical orbits around the central bar, and
we argue that the ring represents both the OLR of the bar and the ILR of a
larger oval distortion. The HI kinematics show evidence for axisymmetric inflow
towards the ring and are inconsistent with streaming in aligned elliptical
orbits, but the highly supersonic (~40 km/s) inflow velocities required,
corresponding to mass inflow rates of ~2 Msol/yr, suggest that more
sophisticated models (e.g., gas orbiting in precessed elliptical orbits) should
be considered. The radial CO and Halpha profiles are poorly correlated in the
vicinity of the nuclear bar, but show a better correlation (in rough agreement
with the Schmidt law) at the ring. Even along the ring, however, the azimuthal
correspondence between CO and Halpha is poor, suggesting that massive stars
form more efficiently at some (perhaps resonant) locations than at others.
These results indicate that the star formation rate per unit gas mass exhibits
strong spatial variations and is not solely a function of the available gas
supply. The localization of star formation to the ring is broadly consistent
with gravitational instability theory, although the instability parameter on average in the ring, only falling below 1 in localized regions.Comment: Revised version accepted by ApJ, with new section on p-v diagrams. 24
pages with 24 figures (emulateapj5). Full resolution and color versions are
available at http://astro.berkeley.edu/~twong/preprint
Open Questions in Classical Gravity
We discuss some outstanding open questions regarding the validity and
uniqueness of the standard second order Newton-Einstein classical gravitational
theory. On the observational side we discuss the degree to which the realm of
validity of Newton's Law of Gravity can actually be extended to distances much
larger than the solar system distance scales on which the law was originally
established. On the theoretical side we identify some commonly accepted but
actually still open to question assumptions which go into the formulating of
the standard second order Einstein theory in the first place. In particular, we
show that while the familiar second order Poisson gravitational equation (and
accordingly its second order covariant Einstein generalization) may be
sufficient to yield Newton's Law of Gravity they are not in fact necessary. The
standard theory thus still awaits the identification of some principle which
would then make it necessary too. We show that current observational
information does not exclusively mandate the standard theory, and that the
conformal invariant fourth order theory of gravity considered recently by
Mannheim and Kazanas is also able to meet the constraints of data, and in fact
to do so without the need for any so far unobserved non-luminous or dark
matter.Comment: UCONN-93-1, plain TeX format, 22 pages (plus 7 figures - send
requests to [email protected]). To appear in a special issue of
Foundations of Physics honoring Professor Fritz Rohrlich on the occasion of
his retirement, L. P. Horwitz and A. van der Merwe Editors, Plenum Publishing
Company, N.Y., Fall 199
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