167,601 research outputs found
Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells
We propose a ferromagnetic/ferroelectric hybrid double quantum well
structure, and present an investigation of the Curie temperature (Tc)
modulation in this quantum structure. The combined effects of applied electric
fields and spontaneous electric polarization are considered for a system that
consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well.
We calculate the change in the envelope functions of carriers at the lowest
energy sub-band, resulting from applied electric fields and switching the
dipole polarization. By reversing the depolarizing field, we can achieve two
different ferromagnetic transition temperatures of the ferromagnetic quantum
well in a fixed applied electric field. The Curie temperature strongly depends
on the position of the Mn \delta-doped layer and the polarization strength of
the ferroelectric well.Comment: 9 pages, 5 figures, to be published in Phys. Rev. B (2006) minor
revision: One of the line types is changed in Fig.
Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)
We investigated the electronic structures of the two-dimensional layered
perovskite Sr\textit{M}O (\textit{M}=4\textit{d} Ru, 4\textit{d}
Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O
1\textit{s} x-ray absorption spectroscopy. While the ground states of the
series of compounds are rather different, their optical conductivity spectra
exhibit similar interband transitions, indicative of the
common electronic structures of the 4\textit{d} and 5\textit{d} layered oxides.
The energy splittings between the two orbitals, ,
and , are about 2 eV, which is much larger
than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The
electronic properties of the Sr\textit{M}O compounds are discussed
in terms of the crystal structure and the extended character of the 4\textit{d}
and 5\textit{d} orbitals
Calculation of a circular jet in crossflow with a multiple-time-scale turbulence model
Numerical calculation of a three dimensional turbulent flow of a jet in a crossflow using a multiple time scale turbulence model is presented. The turbulence in the forward region of the jet is in a stronger inequilibrium state than that in the wake region of the jet, while the turbulence level in the wake region is higher than that in the front region. The calculated flow and the concentration fields are in very good agreement with the measured data, and it indicated that the turbulent transport of mass, concentration, and momentum is strongly governed by the inequilibrium turbulence. The capability of the multiple time scale turbulence model to resolve the inequilibrium turbulence field is also discussed
Rapidly increasing collimation and magnetic field changes of a H2O maser outflow
W75N(B) is a massive star-forming region that contains three radio continuum
sources (VLA 1, VLA 2, and VLA 3), which are thought to be three massive young
stellar objects at three different evolutionary stages. VLA 1 is the most
evolved and VLA 2 the least evolved source. The 22 GHz H2O masers associated
with VLA 1 and VLA 2 have been mapped at several epochs over eight years. While
the H2O masers in VLA 1 show a persistent linear distribution along a radio
jet, those in VLA 2 are distributed around an expanding shell. Furthermore, H2O
maser polarimetric measurements revealed magnetic fields aligned with the two
structures. Using new polarimetric observations of H2O masers, we aim to
confirm the elliptical expansion of the shell-like structure around VLA 2 and,
at the same time, to determine if the magnetic fields around the two sources
have changed. The NRAO Very Long Baseline Array was used to measure the linear
polarization and the Zeeman-splitting of the 22 GHz H2O masers towards the
massive star-forming region W75N(B). The H2O maser distribution around VLA 1 is
unchanged from that previously observed. We made an elliptical fit of the H2O
masers around VLA 2. We find that the shell-like structure is still expanding
along the direction parallel to the thermal radio jet of VLA 1. While the
magnetic field around VLA 1 has not changed in the past 7 years, the magnetic
field around VLA 2 has changed its orientation according to the new direction
of the major-axis of the shell-like structure and it is now aligned with the
magnetic field in VLA 1.Comment: 10 pages (5 + online material), 3 figures, 4 tables, accepted by
Astronomy & Astrophysics Lette
Is the CMB asymmetry due to the kinematic dipole?
Parity violation found in the Cosmic Microwave Background (CMB) radiation is
a crucial clue for the non-standard cosmological model or the possible
contamination of various foreground residuals and/or calibration of the CMB
data sets. In this paper, we study the directional properties of the CMB parity
asymmetry by excluding the modes in the definition of parity parameters.
We find that the preferred directions of the parity parameters coincide with
the CMB kinematic dipole, which implies that the CMB parity asymmetry may be
connected with the possible contamination of the residual dipole component. We
also find that such tendency is not only localized at , but in the
extended multipole ranges up to .Comment: 17 pages, 5 figures, 2 tables, improved version, ApJ accepte
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