1,944 research outputs found
Anthropogenic CO2 flux constraints in the Tokyo Bay Area from Lagrangian diffusive backward trajectories and high resolution in situ measurements
A Dynamical Model for the Orbit of the Andromeda Galaxy M31 and the Origin of the Local Group of Galaxies
We propose a new model for the origin and evolution of the Local Group of
Galaxies (LGG) which naturally explains the formation of the Magellanic Clouds
and their large orbital angular momenta around the Galaxy. The basic idea is
that an off-center hydrodynamical collision occurred some 10 Gyr ago between
the primordial gas-rich Andromeda galaxy and the similar Galaxy, and compressed
the halo gas to form the LGG dwarf galaxies including the Magellanic Clouds. In
this model, new-born dwarf galaxies can be expected to locate near the orbital
plane of these two massive galaxies. In order to see the reality of this model,
we reexamine the two-dimensional sky distribution of the LGG members and the
Magellanic Stream, we confirm an earlier and widely-discussed idea that they
align along two similar great circles, each with an angular width of , and the planes of these circles are approximately normal to the
line joining the present position of the sun and the Galactic center. Further
we make a three-dimensional distribution map of these objects, and observe it
from various directions. A well-defined plane of finite thickness is found,
within which most of the member galaxies are confined, supporting the existence
of the above circles on the sky. Thus we could determine the orbital elements
of M31 relative to the Galaxy through reproducing the well-studied dynamics of
the LMC and the SMC around the Galaxy. The expected proper motion of M31 is
. Probable orbital motions of the
other dwarfs are also determined, and the corresponding proper motion for each
object is given to compare with observations in near future.Comment: Submitted and revised to PASJ, 21 pages, 14 figures and 2 table
Exact and Approximate Distributions of the Maximum Likelihood Estimator of a Slope Coefficient: The LIML Estimator for a Known Covariance Matrix
When the errors are normally independently distributed with equal variance, the maximum likelihood estimator of the slope of a linear functional relationship is the slope of the line minimizing the sum of squared deviations orthogonal to the line. The exact density and distribution of this estimator are obtained. Approximate distributions are obtained, and their accuracies are discussed
Multivalued memory effects in electronic phase-change manganites controlled by Joule heating
Non-volatile multivalued memory effects caused by magnetic fields, currents,
and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and
(Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic
region between ferromagnetic metallic and charge-ordered insulating states. The
current/voltage effects observed in this study are explained by the
self-heating effect, which enable us to control the colossal electroresistance
effects. This thermal-cycle induced switching between electronic solid and
liquid states can be regarded as electronic version of atomic crystal/amorphous
transitions in phase-change chalcogenides.Comment: 5 pages, 4 figures. to appear in Phys. Rev.
Hysteretic current-voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO/SrTiNbO
Transport properties have been studied for a perovskite heterojunction
consisting of SrRuO (SRO) film epitaxially grown on
SrTiNbO (Nb:STO) substrate. The SRO/Nb:STO interface
exhibits rectifying current-voltage (-) characteristics agreeing with
those of a Schottky junction composed of a deep work-function metal (SRO) and
an -type semiconductor (Nb:STO). A hysteresis appears in the -
characteristics, where high resistance and low resistance states are induced by
reverse and forward bias stresses, respectively. The resistance switching is
also triggered by applying short voltage pulses of 1 s - 10 ms duration.Comment: 3 pages, 3 figures, Appl. Phys. Lett., in pres
Theory of Josephson effect in chiral p-wave superconductor / diffusive normal metal / chiral p-wave superconductor junctions
We study the Josephson effect between chiral p-wave superconductor /
diffusive normal metal (DN) / chiral p-wave superconductor (CP/DN/CP) junctions
using quasiclassical Green's function formalism with proper boundary
conditions. The px+ipy-wave symmetry of superconducting order parameter is
chosen which is believed to be a pairing state in Sr2RuO4. It is shown that the
Cooper pairs induced in DN have an odd-frequency spin-triplet s-wave symmetry,
where pair amplitude is an odd function of Matsubara frequency. Despite the
peculiar symmetry properties of the Cooper pairs, the behavior of the Josephson
current is rather conventional. We have found that the current phase relation
is almost sinusoidal and the Josephson current is proportional to exp(-L/xi),
where xi is the coherence length of the Cooper pair in DN and L is the length
of DN. The Josephson current between CP / diffusive ferromagnet metal (DF) / CP
junctions is also calculated. It is shown that the 0-pi transition can be
realized by varying temperature or junction length L similar to the case of
conventional s-wave junctions. These results may serve as a guide to study
superconducting state of Sr2RuO4.Comment: 9 pages, 9 figure
Angular dependence of Josephson currents in unconventional superconducting junctions
Josephson effect in junctions between unconventional superconductors is
studied theoretically within the model describing the effects of interface
roughness. The particularly important issue of applicability of the frequently
used Sigrist-Rice formula for Josephson current in d-wave superconductor /
insulator / d-wave superconductor junctions is addressed. We show that although
the SR formula is not applicable in the ballistic case, it works well for rough
interfaces when the diffusive normal metal regions exist between the d-wave
superconductor and the insulator. It is shown that the SR approach only takes
into account the component of the d-wave pair potential symmetric with respect
to an inversion around the plane perpendicular to the interface. Similar
formula can be derived for general unconventional superconductors with
arbitrary angular momentum l.Comment: 4 pages, 4 figure
Theory of Josephson effect in Sr2RuO4/diffusive normal metal/Sr2RuO4 junctions
We derive a generalized Nazarov’s boundary condition for diffusive normal metal (DN)/chiral p-wave superconductor (CP) interface including the macroscopic phase of the superconductor. The Josephson effect is studied in CP/DN/CP junctions solving the Usadel equations under the above boundary condition. We find that, enhancement of a critical current at low temperature is small compared with that in px-wave /DN/px-wave junctions. As a result, temperature dependence of the critical current in these junctions is similar to that in conventional junctions. The result is consistent with the experiment in Sr2RuO4–Sr3RuO7 eutectic junctions. Similar feature is also found in current–phase relation
Kinematics and Metallicity of M31 Red Giants: The Giant Southern Stream and Discovery of a Second Cold Component at R = 20 kpc
We present spectroscopic observations of red giant branch (RGB) stars in the
Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck
II 10-m telescope. The three fields targeted in this study are in the M31
spheroid, outer disk, and giant southern stream. In this paper, we focus on the
kinematics and chemical composition of RGB stars in the stream field located at
a projected distance of R = 20 kpc from M31's center. A mix of stellar
populations is found in this field. M31 RGB stars are isolated from Milky Way
dwarf star contaminants using a variety of spectral and photometric
diagnostics. The radial velocity distribution of RGB stars displays a clear
bimodality -- a primary peak centered at v = -513 km/s and a secondary one at v
= -417 km/s -- along with an underlying broad component that is presumably
representative of the smooth spheroid of M31. Both peaks are found to be
dynamically cold with intrinsic velocity dispersions of sigma(v) = 16 km/s. The
mean metallicity and metallicity dispersion of stars in the two peaks is also
found to be similar: [Fe/H] = -0.45 and sigma([Fe/H]) = 0.2. The observed
velocity of the primary peak is consistent with that predicted by dynamical
models for the stream, but there is no obvious explanation for the secondary
peak. The nature of the secondary cold population is unclear: it may represent:
(1) tidal debris from a satellite merger event that is superimposed on, but
unrelated to, the giant southern stream; (2) a wrapped around component of the
giant southern stream; (3) a warp or overdensity in M31's disk at R > 50 kpc
(this component is well above the outward extrapolation of the smooth
exponential disk brightness profile).Comment: 32 pages, 13 figures, 1 table. Accepted for publication in Ap
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