107,933 research outputs found
The Maximum Optical Depth Towards Bulge Stars From Axisymmetric Models of the Milky Way
It has been known that recent microlensing results towards the bulge imply
mass densities that are surprisingly high given dynamical constraints on the
Milky Way mass distribution. We derive the maximum optical depth towards the
bulge that may be generated by axisymmetric structures in the Milky Way, and
show that observations are close to surpassing these limits. This result argues
in favor of a bar as a source of significantly enhanced microlensing. Several
of the bar models in the literature are discussed.Comment: Latex, 6 pages, 4 figures, uses aas2pp4 and epsf style files.
Accepted for publication in ApJ Letter
Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering
We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer
Anomalous Hall effect in non-collinear antiferromagnetic antiperovskite MnNiCuN
We report the anomalous Hall effect (AHE) in antiperovskite MnNiN with
substantial doping of Cu on the Ni site (i.e. MnNiCuN),
which stabilizes a noncollinear antiferromagnetic (AFM) order compatible with
the AHE. Observed on both sintered polycrystalline pieces and single
crystalline films, the AHE does not scale with the net magnetization, contrary
to the conventional ferromagnetic case. The existence of the AHE is explained
through symmetry analysis based on the AFM order in Cu doped
MnNiN. DFT calculations of the intrinsic contribution to the AHE reveal
the non-vanishing Berry curvature in momentum space due to the noncollinear
magnetic order. Combined with other attractive properties, antiperovskite
MnAN system offers great potential in AFM spintronics.Comment: Supplemental Materials not include
Tunnelling Effect and Hawking Radiation from a Vaidya Black Hole
In this paper, we extend Parikh' work to the non-stationary black hole. As an
example of the non-stationary black hole, we study the tunnelling effect and
Hawking radiation from a Vaidya black hole whose Bondi mass is identical to its
mass parameter. We view Hawking radiation as a tunnelling process across the
event horizon and calculate the tunnelling probability. We find that the result
is different from Parikh's work because is the function of
Bondi mass m(v)
Coexistence of full which-path information and interference in Wheelers delayed choice experiment with photons
We present a computer simulation model that is a one-to-one copy of an
experimental realization of Wheeler's delayed choice experiment that employs a
single photon source and a Mach-Zehnder interferometer composed of a 50/50
input beam splitter and a variable output beam splitter with adjustable
reflection coefficient (V. Jacques {\sl et al.}, Phys. Rev. Lett. 100,
220402 (2008)). For , experimentally measured values of the
interference visibility and the path distinguishability , a parameter
quantifying the which-path information WPI, are found to fulfill the
complementary relation , thereby allowing to obtain partial WPI
while keeping interference with limited visibility. The simulation model that
is solely based on experimental facts, that satisfies Einstein's criterion of
local causality and that does not rely on any concept of quantum theory or of
probability theory, reproduces quantitatively the averages calculated from
quantum theory. Our results prove that it is possible to give a particle-only
description of the experiment, that one can have full WPI even if D=0, V=1 and
therefore that the relation cannot be regarded as quantifying
the notion of complementarity.Comment: Physica E, in press; see also http://www.compphys.ne
Tracers of chromospheric structure. I. CaII HK emission distribution of 13000 F, G and K stars in SDSS DR7 spectroscopic sample
We present chromospheric activity index measurements for over
13,000 F, G and K disk stars with high signal-to-noise ratio ( 60) spectra
in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic
sample. A parameter S is defined as the difference between
and a `zero' emission line fitted by several of the most inactive stars. The
indices of subgiant stars tend to be much lower than dwarfs, which
provide a way to distinguish dwarfs and giants with relatively low resolution
spectra. Cooler stars are generally more active and display a larger scatter
than hotter stars. Stars associated with the thick disk are in general less
active than those of the thin disk. The fraction of K dwarfs that are active
drops with vertical distance from the Galactic plane. Metallicity affects
measurements differently among F, G and K dwarfs in this sample.
Using the open clusters NGC 2420, M67 and NGC6791 as calibrations, ages of most
field stars in this SDSS sample range from 3-8 Gyr.Comment: 9 pages, 11 figures, AJ, 2013, 145, 14
On several families of elliptic curves with arbitrary large Selmer groups
In this paper, we calculate the Selmer groups
S^{(\phi)} (E / \Q) and S^{(\hat{\varphi})} (E^{\prime} / \Q) of elliptic
curves via descent theory
(see [S, Chapter X]), in particular, we obtain that the Selmer groups of
several families of such elliptic curves can be arbitrary large.Comment: 22 page
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