3,470 research outputs found
Trigonometric Parallaxes of Massive Star Forming Regions: III. G59.7+0.1 and W 51 IRS2
We report trigonometric parallaxes for G59.7+0.1 and W 51 IRS2, corresponding
to distances of 2.16^{+0.10}_{-0.09} kpc and 5.1^{+2.9}_{-1.4} kpc,
respectively. The distance to G59.7+0.1 is smaller than its near kinematic
distance and places it between the Carina-Sagittarius and Perseus spiral arms,
probably in the Local (Orion) spur. The distance to W 51 IRS2, while subject to
significant uncertainty, is close to its kinematic distance and places it near
the tangent point of the Carina-Sagittarius arm. It also agrees well with a
recent estimate based on O-type star spectro/photometry. Combining the
distances and proper motions with observed radial velocities gives the full
space motions of the star forming regions. We find modest deviations of 5 to 10
km/s from circular Galactic orbits for these sources, both counter to Galactic
rotation and toward the Galactic center.Comment: 16 pages, 6 figures; to appear in the Astrophysical Journa
Hall effect of FeTe and Fe(Se_1-x_Te_x_) thin films
The Hall effect is investigated in thin-film samples of iron-chalcogenide
superconductors in detail. The Hall coefficient (RH) of FeTe and Fe(Se1-xTex)
exhibits a similar positive value around 300 K, indicating that the
high-temperature normal state is dominated by hole-channel transport. FeTe
exhibits a sign reversal from positive to negative across the transition to the
low-temperature antiferromagnetic state, indicating the occurrence of drastic
reconstruction in the band structure. The mobility analysis using the carrier
density theoretically calculated reveals that the mobility of holes is strongly
suppressed to zero, and hence the electric transport looks to be dominated by
electrons. The Se substitution to Te suppresses the antiferromagnetic
long-range order and induces superconductivity instead. The similar mobility
analysis for Fe(Se0.4Te0.6) and Fe(Se0.5Te0.5) thin films shows that the
mobility of electrons increases with decreasing temperature even in the
paramagnetic state, and keeps sufficiently high values down to the
superconducting transition temperature. From the comparison between FeTe and
Fe(Se1-xTex), it is suggested that the coexistence of 'itinerant' carriers both
in electron and hole channels is indispensable for the occurrence of
superconductivity.Comment: 16 page, 6 figures, Proceedings of ISS-2010, to be published in
Physica
Disorder Induced Phase Transition in a Random Quantum Antiferromagnet
A two-dimensional Heisenberg model with random antiferromagnetic
nearest-neighbor exchange is studied using quantum Monte Carlo techniques. As
the strength of the randomness is increased, the system undergoes a transition
from an antiferromagnetically ordered ground state to a gapless disordered
state. The finite-size scaling of the staggered structure factor and
susceptibility is consistent with a dynamic exponent .Comment: Revtex 3.0, 10 pages + 5 postscript figures available upon request,
UCSBTH-94-1
Trigonometric Parallax of W51 Main/South
We report measurement of the trigonometric parallax of W51 Main/South using
the Very Long Baseline Array (VLBA). We measure a value of 0.185 +/- 0.010 mas,
corresponding to a distance of 5.41 (+0.31/-0.28) kpc. W51 Main/South is a
well-known massive star-forming region near the tangent point of the
Sagittarius spiral arm of the Milky Way. Our distance to W51 yields an estimate
of the distance to the Galactic center of Ro = 8.3 +/- 0.46 (statistical) +/-
1.0 (systematic) kpc by simple geometry. Combining the parallax and proper
motion measurements for W51, we obtained the full-space motion of this massive
star forming region. We find W51 is in a nearly circular orbit about the
Galactic center. The H2O masers used for our parallax measurements trace four
powerful bipolar outflows within a 0.4 pc size region, some of which are
associated with dusty molecular hot cores and/or hyper- or ultra-compact HII
regions.Comment: Accepted to ApJ; 32 pages; 6 tables; 5 figure
Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards
We present a simple method to stabilize the optical path length of an optical
fiber to an accuracy of about 1/100 of the laser wavelength. We study the
dynamic response of the path length to modulation of an electrically conductive
heater layer of the fiber. The path length is measured against the laser
wavelength by use of the Pound-Drever-Hall method; negative feedback is applied
via the heater. We apply the method in the context of a cryogenic resonator
frequency standard.Comment: Expanded introduction and outlook. 9 pages, 5 figure
Magnetic Properties of Ab initio Model for Iron-Based Superconductors LaFeAsO
By using variational Monte Carlo method, we examine an effective low-energy
model for LaFeAsO derived from an ab initio downfolding scheme. We show that
quantum and many-body fluctuations near a quantum critical point largely reduce
the antiferromagnetic (AF) ordered moment and the model not only quantitatively
reproduces the small ordered moment in LaFeAsO, but also explains the diverse
dependence on LaFePO, BaFe2As2 and FeTe. We also find that LaFeAsO is under
large orbital fluctuations, sandwiched by the AF Mott insulator and weakly
correlated metals. The orbital fluctuations and Dirac-cone dispersion hold keys
for the diverse magnetic properties.Comment: 4 pages, 4 figure
Genetic characterization of a rare H12N3 avian influenza virus isolated from a green-winged teal in Japan
This study reports on the genetic characterization of an avian influenza virus, subtype H12N3, isolated from an Eurasian green-winged teal (Anas crecca) in Japan in 2009. The entire genome sequence of the isolate was analyzed, and phylogenetic analyses were conducted to characterize the evolutionary history of the isolate. Phylogenetic analysis of the hemagglutinin and neuraminidase genes indicated that the virus belonged to the Eurasian-like avian lineage. Molecular dating indicated that this H12 virus is likely a multiple reassortant influenza A virus. This is the first reported characterization of influenza A virus subtype H12N3 isolated in Japan and these data contribute to the accumulation of knowledge on the genetic diversity and generation of novel influenza A viruses.National Institute of Allergy and Infectious Diseases (U.S.) (Contracts HHSN266200700009C and HHSN266200700007)Japan Society for the Promotion of Science. Grant-in-Aid for the Bilateral Joint ProjectsHeiwa Nakajima Foundatio
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
Interactions in vivo between the Vif protein of HIV-1 and the precursor (Pr55GAG) of the virion nucleocapsid proteins
The abnormality of viral core structure seen in vif-defective HIV-1 grown in PBMCs has suggested a role for Vif in viral morphogenesis. Using an in vivo mammalian two-hybrid assay, the interaction between Vif and the precursor (Pr55GAG) of the virion nucleocapsid proteins has been analysed. This revealed the amino-terminal (aa 1–22) and central (aa 70–100) regions of Vif to be essential for its interaction with Pr55GAG, but deletion of the carboxy-terminal (aa 158–192) region of the protein had only a minor effect on its interaction. Initial deletion studies carried out on Pr55GAG showed that a 35-amino-acid region of the protein bridging the MA(p17)–CA(p24) junction was essential for its ability to interact with Vif. Site-directed mutagenesis of a conserved tryptophan (Trp21) near the amino terminus of Vif showed it to be important for the interaction with Pr55GAG. By contrast, mutagenesis of the highly conserved YLAL residues forming part of the BC-box motif, shown to be important in Vif promoting degradation of APOBEC3G/3F, had little or no effect on the Vif–Pr55GAG interaction
Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity
The electronic specific heat of as-grown and annealed single-crystals of
FeSe1-xTex (0.6<=x<=1) has been investigated. It has been found that annealed
single-crystals with x=0.6-0.9 exhibit bulk superconductivity with a clear
specific-heat jump at the superconducting (SC) transition temperature, Tc. Both
2Delta_0/kBTc [Delta_0: the SC gap at 0 K estimated using the single-band BCS
s-wave model] and Delta C/(gamma_n-gamma_0)Tc [Delta C$: the specific-heat jump
at Tc, gamma_n: the electronic specific-heat coefficient in the normal state,
gamma_0: the residual electronic specific-heat coefficient at 0 K in the SC
state] are largest in the well-annealed single-crystal with x=0.7, i.e., 4.29
and 2.76, respectively, indicating that the superconductivity is of the strong
coupling. The thermodynamic critical field has also been estimated. gamma_n has
been found to be one order of magnitude larger than those estimated from the
band calculations and increases with increasing x at x=0.6-0.9, which is
surmised to be due to the increase in the electronic effective mass, namely,
the enhancement of the electron correlation. It has been found that there
remains a finite value of gamma_0 in the SC state even in the well-annealed
single-crystals with x=0.8-0.9, suggesting an inhomogeneous electronic state in
real space and/or momentum space.Comment: 22 pages, 1 table, 6 figures, Version 2 has been accepted for
publication in J. Phys. Soc. Jp
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