563 research outputs found
Dual-Frequency VSOP Observations of AO 0235+164
AO 0235+164 is a very compact, flat spectrum radio source identified as a BL
Lac object at a redshift of z=0.94. It is one of the most violently variable
extragalactic objects at both optical and radio wavelengths. The radio
structure of the source revealed by various ground-based VLBI observations is
dominated by a nearly unresolved compact component at almost all available
frequencies.
Dual-frequency space VLBI observations of AO 0235+164 were made with the VSOP
mission in January-February 1999. The array of the Japanese HALCA satellite and
co-observing ground radio telescopes in Australia, Japan, China and South
Africa allowed us to study AO 0235+164 with an unprecedented angular resolution
at frequencies of 1.6 and 5 GHz. We report on the sub-milliarcsecond structural
properties of the source. The 5-GHz observations led to an estimate of T_B >
5.8 x 10^{13} K for the rest-frame brightness temperature of the core, which is
the highest value measured with VSOP to date.Comment: 8 pages, 8 figures, to appear in Publ. Astron. Soc. Japa
Divergent LIN28-mRNA associations result in translational suppression upon the initiation of differentiation
LIN28 function is fundamental to the activity and behavior of human embryonic stem cells (hESCs) and induced pluripotent stem cells. Its main roles in these cell types are the regulation of translational efficiency and let-7 miRNA maturation. However, LIN28-associated mRNA cargo shifting and resultant regulation of translational efficiency upon the initiation of differentiation remain unknown. An RNA-immunoprecipitation and microarray analysis protocol, eRIP, that has high specificity and sensitivity was developed to test endogenous LIN28-associated mRNA cargo shifting. A combined eRIP and polysome analysis of early stage differentiation of hESCs with two distinct differentiation cues revealed close similarities between the dynamics of LIN28 association and translational modulation of genes involved in the Wnt signaling, cell cycle, RNA metabolism and proteasomal pathways. Our data demonstrate that change in translational efficiency is a major contributor to early stages of differentiation of hESCs, in which LIN28 plays a central role. This implies that eRIP analysis of LIN28-associated RNA cargoes may be used for rapid functional quality control of pluripotent stem cells under manufacture for therapeutic applications
Influence of major mergers on the radio emission of elliptical galaxies
We investigate the influence of major mergers on the radio emission of
elliptical galaxies. We use a complete sample of close pairs, which contains
475 merging and 1828 non-merging paired elliptical galaxies of M_r<-21.5
selected from the Sloan Digital Sky Survey. In addition, a control sample of
2000 isolated field galaxies is used for comparison. We cross-identify the
optical galaxies with the radio surveys of FIRST and NVSS. We find that the
radio fraction of merging paired galaxies is about 6%, which is slightly higher
than the 5% obtained for non-merging paired galaxies, although these values are
consistent with each other owing to the large uncertainty caused by the limited
sample. The radio fraction is twice as that of isolated galaxies, which is less
than 3%. Radio emission of elliptical galaxies is only slightly affected by
major mergers, but predominantly depends on their optical luminosities.
Therefore, merging is not important in triggering the radio emission of
elliptical galaxies.Comment: 5 pages, 5 figures, 1 table, accepted for publication in A&A, minor
change
Vortices on Higher Genus Surfaces
We consider the topological interactions of vortices on general surfaces. If
the genus of the surface is greater than zero, the handles can carry magnetic
flux. The classical state of the vortices and the handles can be described by a
mapping from the fundamental group to the unbroken gauge group. The allowed
configurations must satisfy a relation induced by the fundamental group. Upon
quantization, the handles can carry ``Cheshire charge.'' The motion of the
vortices can be described by the braid group of the surface. How the motion of
the vortices affects the state is analyzed in detail.Comment: 28 pages with 10 figures; uses phyzzx and psfig; Caltech preprint
CALT-68-187
Symmetry of Traveling Wave Solutions to the Allen-Cahn Equation in \Er^2
In this paper, we prove even symmetry of monotone traveling wave solutions to
the balanced Allen-Cahn equation in the entire plane. Related results for the
unbalanced Allen-Cahn equation are also discussed
Random Matrix Model for Superconductors in a Magnetic Field
We introduce a random matrix ensemble for bulk type-II superconductors in the
mixed state and determine the single-particle excitation spectrum using random
matrix theory. The results are compared with planar tunnel junction experiments
in PbBi thin films. More low energy states appear than in the
Abrikosov-Gor'kov-Maki or Ginzburg-Landau descriptions, consistent with
observations.Comment: 4 pages, 1 postscript figure, to appear in Phys. Rev. Let
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. II. Numeric Code and Tests
Based on a second-order approximation of nonlinear force-free magnetic field
solutions in terms of uniformly twisted field lines derived in Paper I, we
develop here a numeric code that is capable to forward-fit such analytical
solutions to arbitrary magnetogram (or vector magnetograph) data combined with
(stereoscopically triangulated) coronal loop 3D coordinates. We test the code
here by forward-fitting to six potential field and six nonpotential field cases
simulated with our analytical model, as well as by forward-fitting to an
exactly force-free solution of the Low and Lou (1990) model. The
forward-fitting tests demonstrate: (i) a satisfactory convergence behavior
(with typical misalignment angles of ), (ii)
relatively fast computation times (from seconds to a few minutes), and (iii)
the high fidelity of retrieved force-free -parameters ( for simulations and for the Low and Lou model). The
salient feature of this numeric code is the relatively fast computation of a
quasi-forcefree magnetic field, which closely matches the geometry of coronal
loops in active regions, and complements the existing {\sl nonlinear force-free
field (NLFFF)} codes based on photospheric magnetograms without coronal
constraints.Comment: Solar PHysics, (in press), 25 pages, 11 figure
Gamma-loud quasars: a view with BeppoSAX
We present SAX observations of the -ray emitting quasars
0836+710, 1510-089 and 2230+114. All the objects have been detected in the PDS
up to 100 keV and have extremely flat power-law spectra above 2 keV (=0.3--0.5). 0836+710 shows absorption higher than the galactic value and
marginal evidence for the presence of the redshifted 6.4 keV Iron line.
1510-089 shows a spectral break around 1 keV, with the low energy spectrum
steeper (=1.6) than the high energy power-law (=0.3). The
data are discussed in the light of current Inverse Compton models for the high
energy emission.Comment: 4 pages, 2 figures, to appear in the proceedings of the conference
"X-Ray Astronomy '99", Bologna, Italy, September 199
Weak localization and electron-electron interactions in Indium-doped ZnO nanowires
Single crystal ZnO nanowires doped with indium are synthesized via the
laser-assisted chemical vapor deposition method. The conductivity of the
nanowires is measured at low temperatures in magnetic fields both perpendicular
and parallel to the wire axes. A quantitative fit of our data is obtained,
consistent with the theory of a quasi-one-dimensional metallic system with
quantum corrections due to weak localization and electron-electron
interactions. The anisotropy of the magneto-conductivity agrees with theory.
The two quantum corrections are of approximately equal magnitude with
respective temperature dependences of T^-1/3 and T^-1/2. The alternative model
of quasi-two-dimensional surface conductivity is excluded by the absence of
oscillations in the magneto-conductivity in parallel magnetic fields.Comment: 13 pages, Corrected forma
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