2,845 research outputs found
Effective interaction for pf-shell nuclei
An effective interaction is derived for use in the full pf basis. Starting
from a realistic G-matrix interaction, 195 two-body matrix elements and 4
single-particle energies are determined by fitting to 699 energy data in the
mass range 47 to 66. The derived interaction successfully describes various
structures of pf-shell nuclei. As examples, systematics of the energies of the
first 2+ states in the Ca, Ti, Cr, Fe, and Ni isotope chains and energy levels
of 56,57,58Ni are presented. The appearance of a new magic number 34 is seen.Comment: 5 pages, 4 figures, to be published in Phys. Rev.
Criterion for Generation of Winds from Magnetized Accretion Disks
An analytic model is proposed for non-radiating accretion flows accompanied
by up or down winds in a global magnetic field. Physical quantities in this
model solution are written in variable-separated forms, and their radial parts
are simple power law functions including one parameter for wind strength.
Several, mathematically equivalent but physically different expressions of the
criterion for wind generation are obtained. It is suggested also that the
generation of wind is a consequence of the intervention of some mechanism that
redistributes the locally available gravitational energy, and that the
Bernoulli sum can be a good indicator of the existence of such mechanisms.Comment: 24 pages, 0 figures, ApJ accepte
Optical and CO Radio Observations of Poor Cluster Zwicky 1615.8+3505
The cluster Zwicky 1615.8+3505 is considered to be a dynamically young poor
cluster. To investigate the morphology and star-formation activity of galaxies
under the environment of a dynamically young poor cluster, we have performed V,
R, and I surface photometry, optical low-resolution spectroscopy, and 12CO
(J=1-0) line observations for member galaxies. Our data show that more than 90%
of the observed galaxies show regular morphologies and no star-formation
activities, indicating that the environment does not affect these galaxy
properties. Among sixteen galaxies observed, only NGC 6104 shows a significant
star-formation activity, and shows a distorted morphology, indicating a tidal
interaction. This galaxy contains double knots, and only one knot possesses
Seyfert activity, though the sizes and luminosities are similar to each other;
we also discuss this feature.Comment: LaTeX manuscript (text.tex, use PASJ style files), four PS figures
(fig[a-d].ps), and three PASJ style files. text.tex, figb.ps, and figd.ps are
up-dated. To be appeared in The Publications of the Astronomical Society of
Japan, Vol. 51, No. 3 (1999 June issue
Nuclear Shell Model by the Quantum Monte Carlo Diagonalization Method
The feasibility of shell-model calculations is radically extended by the
Quantum Monte Carlo Diagonalization method with various essential improvements.
The major improvements are made in the sampling for the generation of
shell-model basis vectors, and in the restoration of symmetries such as angular
momentum and isospin. Consequently the level structure of low-lying states can
be studied with realistic interactions. After testing this method on Mg,
we present first results for energy levels and properties of Ge,
indicating its large and -soft deformation.Comment: 12 pages, RevTex, 2 figures, to be published in Physical Review
Letter
Sialic acid transporter NanT participates in Tannerella forsythia biofilm formation and survival on epithelial cells
Tannerella forsythia is a periodontal pathogen implicated in periodontitis. This gram-negative pathogen depends on exogenous peptidoglycan amino sugar N-acetylmuramic acid (NAM) for growth. In the biofilm state the bacterium can utilize sialic acid (Neu5Ac) instead of NAM to sustain its growth. Thus, the sialic acid utilization system of the bacterium plays a critical role in the growth and survival of the organism in the absence of NAM. We sought the function of a T. forsythia gene annotated as nanT coding for an inner-membrane sugar transporter located on a sialic acid utilization genetic cluster. To determine the function of this putative sialic acid transporter, an isogenic nanT-deletion mutant generated by allelic replacement strategy was evaluated for biofilm formation on NAM or Neu5Ac, and survival on KB epithelial cells. Moreover, since T. forsythia forms synergistic biofilms with Fusobacterium nucleatum, co-biofilm formation activity in mixed culture and sialic acid uptake in culture were also assessed. The data showed that the nanT-inactivated mutant of T. forsythia was attenuated in its ability to uptake sialic acid. The mutant formed weaker biofilms compared to the wild-type strain in the presence of sialic acid and as co-biofilms with F. nucleatum. Moreover, compared to the wild-type T. forsythia nanT-inactivated mutant showed reduced survival when incubated on KB epithelial cells. Taken together, the data presented here demonstrate that NanT-mediated sialic transportation is essential for sialic acid utilization during biofilm growth and survival of the organism on epithelial cells and implies sialic acid might be key for its survival both in subgingival biofilms and during infection of human epithelial cells in vivo
Rotating and infalling motion around the high-mass young stellar object Cepheus A-HW2 observed with the methanol maser at 6.7 GHz
We have measured the internal proper motions of the 6.7 GHz methanol masers
associated with Cepheus A (Cep A) HW2 using Very Long Baseline Interferometery
(VLBI) observations. We conducted three epochs of VLBI monitoring observations
of the 6.7 GHz methanol masers in Cep A-HW2 with the Japanese VLBI Network
(JVN) over the period between 2006-2008. In 2006, we were able to use
phase-referencing to measure the absolute coordinates of the maser emission
with an accuracy of a few milliarcseconds. We compared the maser distribution
with other molecular line observations that trace the rotating disk. We
measured the internal proper motions for 29 methanol maser spots, of which 19
were identified at all three epochs and the remaining ten at only two epochs.
The magnitude of proper motions ranged from 0.2 to 7.4 km/s, with an average of
3.1 km/s. Although there are large uncertainties in the observed internal
proper motions of the methanol maser spots in Cep A, they are well fitted by a
disk that includes both rotation and infall velocity components. The derived
rotation and infall velocities at the disk radius of 680 au are 0.5 +- 0.7 and
1.8 +- 0.7 km/s, respectively. Assuming that the modeled disk motion accurately
represents the accretion disk around the Cep A-HW2 high-mass YSO, we estimated
the mass infall rate to be 3 x 10^{-4} n_8 Msun/yr (n_8 is the gas volume
density in units of 10^{8} cm^{-3}). The combination of the estimated mass
infall rate and the magnitude of the fitted infall velocity suggests that Cep
A-HW2 is at an evolutionary phase of active gas accretion from the disk onto
the central high-mass YSO. The infall momentum rate is estimated to be 5 x
10^{-4} n_8 Msun/yr km/s, which is larger than the estimated stellar radiation
pressure of the HW2 object, supporting the hypothesis that this object is in an
active gas accretion phase.Comment: 16 pages, 6 figures, 5 tables, accepted for publication in Astronomy
& Astrophysic
Dp-branes, NS5-branes and U-duality from nonabelian (2,0) theory with Lie 3-algebra
We derive the super Yang-Mills action of Dp-branes on a torus T^{p-4} from
the nonabelian (2,0) theory with Lie 3-algebra. Our realization is based on Lie
3-algebra with pairs of Lorentzian metric generators. The resultant theory then
has negative norm modes, but it results in a unitary theory by setting VEV's of
these modes. This procedure corresponds to the torus compactification,
therefore by taking a transformation which is equivalent to T-duality, the
Dp-brane action is obtained. We also study type IIA/IIB NS5-brane and
Kaluza-Klein monopole systems by taking other VEV assignments. Such various
compactifications can be realized in the nonabelian (2,0) theory, since both
longitudinal and transverse directions can be compactified, which is different
from the BLG theory. We finally discuss U-duality among these branes, and show
that most of the moduli parameters in U-duality group are recovered. Especially
in D5-brane case, the whole U-duality relation is properly reproduced.Comment: 1+26 page
A Trigonometric Parallax of Sgr B2
We have measured the positions of water masers in Sgr B2, a massive star
forming region in the Galactic center, relative to an extragalactic radio
source with the Very Long Baseline Array. The positions measured at 12 epochs
over a time span of one year yield the trigonometric parallax of Sgr B2 and
hence a distance to the Galactic center of Ro=7.9 (+0.8/-0.7) kpc. The proper
motion of Sgr B2 relative to Sgr A* suggests that Sgr B2 is about 0.13 kpc
nearer than the Galactic center, assuming a low-eccentricity Galactic orbit.Comment: Submitted to ApJ; 4 tables; 3 figures. Version 2 corrects Fig. 2
which was missing some dat
Intermittent maser flare around the high mass young stellar object G353.273+0.641 I: data & overview
We have performed VLBI and single-dish monitoring of 22 GHz HO maser
emission from the high mass young stellar object G353.273+0.641 with VERA (VLBI
Exploration of Radio Astrometry) and Tomakamai 11-m radio telescope. Two maser
flares have been detected, separated almost two years. Frequent VLBI monitoring
has revealed that these flare activities have been accompanied by structural
change of the prominent shock front traced by H2O maser alignments. We have
detected only blue-shifted emissions and all maser features have been
distributed within very small area of 200 200 au in spite of
wide velocity range (> 100 km s). The light curve shows notably
intermittent variation and suggests that the HO masers in G353.273+0.641
are excited by episodic radio jet. The time-scale of \sim2 yr and
characteristic velocity of \sim500 km s also support this
interpretation. Two isolated velocity components of C50 (-53 \pm 7 km s)
and C70 (-73 \pm 7 km s) have shown synchronised linear acceleration of
the flux weighted V_{\rmn{LSR}} values (\sim-5 km s yr) during
the flare phase. This can be converted to the lower-limit momentum rate of 1.1
\times 10 M_{\sun} km s yr. Maser properties are quite
similar to that of IRAS 20126+4104 especially. This corroborates the previous
suggestion that G353.273+0.641 is a candidate of high mass protostellar object.
The possible pole-on geometry of disc-jet system can be suitable for direct
imaging of the accretion disc in this case.Comment: 13 pages, 5 figures accepted for publication in MNRA
Star Formation Efficiency in the Central 1 kpc Region of Early-Type Spiral Galaxies
It has been reported recently that there are some early-type spiral (Sa--Sab)
galaxies having evident star-forming regions which concentrate in their own
central 1-kpc. In such central region, is the mechanism of the star formation
distinct from that in disks of spiral galaxies? To reveal this, we estimate the
star formation efficiency (SFE) in this central 1-kpc star-forming region of
some early-type spiral galaxies, taking account of the condition for this 1-kpc
region to be self-gravitating. Using two indicators of present star formation
rate (H and infrared luminosity), we estimate the SFE to be a few
percents. This is equivalent to the observational SFE in the disks of late-type
spiral (Sb--) galaxies. This coincidence may support the universality of the
mean SFE of spiral galaxies reported in the recent studies. That is, we find no
evidence of distinct mechanism of the star formation in the central 1-kpc
region of early-type galaxies. Also, we examine the structure of the central
star-forming region, and discuss a method for estimating the mass of
star-forming regions.Comment: accepted by A
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