2,682 research outputs found
Reconstructing the solar integrated radial velocity using MDI/SOHO
Searches for exoplanets with radial velocity techniques are increasingly
sensitive to stellar activity. It is therefore crucial to characterize how this
activity influences radial velocity measurements in their study of the
detectability of planets in these conditions. In a previous work we simulated
the impact of spots and plages on the radial velocity of the Sun. Our objective
is to compare this simulation with the observed radial velocity of the Sun for
the same period. We use Dopplergrams and magnetograms obtained by MDI/SOHO over
one solar cycle to reconstruct the solar integrated radial velocity in the Ni
line 6768 \AA. We also characterize the relation between the velocity and the
local magnetic field to interpret our results. We obtain a stronger redshift in
places where the local magnetic field is larger (and as a consequence for
larger magnetic structures): hence we find a higher attenuation of the
convective blueshift in plages than in the network. Our results are compatible
with an attenuation of this blueshift by about 50% when averaged over plages
and network. We obtain an integrated radial velocity with an amplitude over the
solar cycle of about 8 m/s, with small-scale variations similar to the results
of the simulation, once they are scaled to the Ni line. The observed solar
integrated radial velocity agrees with the result of the simulation made in our
previous work within 30%, which validates this simulation. The observed
amplitude confirms that the impact of the convective blueshift attenuation in
magnetic regions will be critical to detect Earth-mass planets in the habitable
zone around solar-like stars.Comment: 17 pages, 11 figures, accepted in Astronomy and Astrophysic
A synthetic small molecule for rapid induction of multiple pluripotency genes in mouse embryonic fibroblasts.
Cellular reprogramming involves profound alterations in genome-wide gene expression that is precisely controlled by a hypothetical epigenetic code. Small molecules have been shown to artificially induce epigenetic modifications in a sequence independent manner. Recently, we showed that specific DNA binding hairpin pyrrole-imidazole polyamides (PIPs) could be conjugated with chromatin modifying histone deacetylase inhibitors like SAHA to epigenetically activate certain pluripotent genes in mouse fibroblasts. In our steadfast progress to improve the efficiency of SAHA-PIPs, we identified a novel compound termed, δ that could dramatically induce the endogenous expression of Oct-3/4 and Nanog. Genome-wide gene analysis suggests that in just 24 h and at nM concentration, δ induced multiple pluripotency-associated genes including Rex1 and Cdh1 by more than ten-fold. δ treated MEFs also rapidly overcame the rate-limiting step of epithelial transition in cellular reprogramming by switching "[Formula: see text]" the complex transcriptional gene network
Single Crystal Growth and Characterization of the Iron-Based Superconductor KFe2As2 Synthesized by KAs Flux Method
Centimeter sized platelet single crystals of KFe2As2 were grown using a
self-flux method. An encapsulation technique using commercial stainless steel
container allowed the stable crystal growth lasting for more than 2 weeks.
Ternary K-Fe-As systems with various starting compositions were examined to
determine the optimal growth conditions. Employment of KAs flux led to the
growth of large single crystals with the typical size of as large as 15 mm x 10
mm x 0.4 mm. The grown crystals exhibit sharp superconducting transition at 3.4
K with the transition width 0.2 K, as well as the very large residual
resistivity ratio exceeding 450, evidencing the good sample quality.Comment: 4 pages, 6 Postscript figure
Estimation of drag coefficient of trees considering the tree bending or overturning situations
Drag coefficients of a real tree trunk and the sheltering effects of an upstream trunk on a
downstream one in a linear arrangement with different spacings and inclinations were investigated in
detail. In addition, for elucidating the change of drag coefficient for an overturned tree, drag force acting
on a real tree with roots was also measured in this study. For the measurement of drag force with different
inclinations, Terminalia Cattapa and Albizia sp., vegetated in Sri Lanka, were selected in this study. Drag
coefficient of inclined tree trunk has the similar tendency in relation to the Reynolds number with that of
vertical standing tree investigated in Tanaka et al.(2011). For the vertical tree trunk with rough surface,
drag coefficient of rear-side tree trunk was decreased with decreasing L/d (where, L is spacing and d is
the diameter of trunk). In addition, as a result of mutual interference experiment of two inclined tree trunk,
the drag coefficient of rear-side trunk decreased with the increase of the inclination. Under the influence of
the increment of projected area due to existence of roots and shear force acting on tree trunk surface, the
drag coefficient of a tree with roots became similar value (1.0-1.2) comparing with that of a vertical
standing tree
Scattering of massless particles in one-dimensional chiral channel
We present a general formalism describing a propagation of an arbitrary
multiparticle wave packet in a one-dimensional multimode chiral channel coupled
to an ensemble of emitters which are distributed at arbitrary positions. The
formalism is based on a direct and exact resummation of diagrammatic series for
the multiparticle scattering matrix. It is complimentary to the Bethe Ansatz
and to approaches based on equations of motion, and it reveals a simple and
transparent structure of scattering states. In particular, we demonstrate how
this formalism works on various examples, including scattering of one- and
two-photon states off two- and three-level emitters, off an array of emitters
as well as scattering of coherent light. We argue that this formalism can be
constructively used for study of scattering of an arbitrary initial photonic
state off emitters with arbitrary degree of complexity.Comment: 25 pages, 5 figure
Doping-Dependent and Orbital-Dependent Band Renormalization in Ba(Fe_1-xCo_x)_2As_2 Superconductors
Angle resolved photoemission spectroscopy of Ba(Fe1-xCox)2As2 (x = 0.06,
0.14, and 0.24) shows that the width of the Fe 3d yz/zx hole band depends on
the doping level. In contrast, the Fe 3d x^2-y^2 and 3z^2-r^2 bands are rigid
and shifted by the Co doping. The Fe 3d yz/zx hole band is flattened at the
optimal doping level x = 0.06, indicating that the band renormalization of the
Fe 3d yz/zx band correlates with the enhancement of the superconducting
transition temperature. The orbital-dependent and doping-dependent band
renormalization indicates that the fluctuations responsible for the
superconductivity is deeply related to the Fe 3d orbital degeneracy.Comment: 5 pages, 4 figure
Wave Packet Echoes in the Motion of Trapped Atoms
We experimentally demonstrate and systematically study the stimulated revival
(echo) of motional wave packet oscillations. For this purpose, we prepare wave
packets in an optical lattice by non-adiabatically shifting the potential and
stimulate their reoccurence by a second shift after a variable time delay. This
technique, analogous to spin echoes, enables one even in the presence of strong
dephasing to determine the coherence time of the wave packets. We find that for
strongly bound atoms it is comparable to the cooling time and much longer than
the inverse of the photon scattering rate
Linear atomic quantum coupler
In this paper, we develop the notion of the linear atomic quantum coupler.
This device consists of two modes propagating into two waveguides, each of them
includes a localized and/or a trapped atom. These waveguides are placed close
enough to allow exchanging energy between them via evanescent waves. Each mode
interacts with the atom in the same waveguide in the standard way, i.e. as the
Jaynes-Cummings model (JCM), and with the atom-mode in the second waveguide via
evanescent wave. We present the Hamiltonian for the system and deduce the exact
form for the wavefunction. We investigate the atomic inversions and the
second-order correlation function. In contrast to the conventional linear
coupler, the atomic quantum coupler is able to generate nonclassical effects.
The atomic inversions can exhibit long revival-collapse phenomenon as well as
subsidiary revivals based on the competition among the switching mechanisms in
the system. Finally, under certain conditions, the system can yield the results
of the two-mode JCM.Comment: 14 pages, 3 figures; comments are most welcom
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