4,421 research outputs found
Experimental realization of a broadband illusion optics device
We experimentally demonstrate the first metamaterial "illusion optics" device
- an "invisible gateway" by using a transmission-line medium. The device
contains an open channel that can block electromagnetic waves at a particular
frequency range. We also demonstrate that such a device can work in a broad
frequency range.Comment: 9 pages, 5 figure
A resonant feature near the Perseus arm revealed by red clump stars
We investigate the extinction together with the radial velocity dispersion
and distribution of red clump stars in the anti-center direction using spectra
obtained with Hectospec on the MMT. We find that extinction peaks at
Galactocentric radii of about 9.5 and 12.5 kpc, right in front of the locations
of the Perseus and Outer arms and in line with the relative position of dust
and stars in external spiral galaxies. The radial velocity dispersion peaks
around 10kpc, which coincides with the location of the Perseus arm, yields an
estimated arm-interarm density contrast of 1.3-1.5 and is in agreement with
previous studies. Finally, we discover that the radial velocity distribution
bifurcates around 10-11 kpc into two peaks at +27 km/s and -4 km/s. This seems
to be naturally explained by the presence of the outer Lindblad resonance of
the Galactic bar, but further observations will be needed to understand if the
corotation resonance of the spirals arms also plays a role.Comment: 8 pages, 2 figures, accepted for publication in ApJ
Quantum Anomalous Hall Effect in HgMnTe Quantum Wells
The quantum Hall effect is usually observed when the two-dimensional electron
gas is subjected to an external magnetic field, so that their quantum states
form Landau levels. In this work we predict that a new phenomenon, the quantum
anomalous Hall effect, can be realized in HgMnTe quantum wells,
without the external magnetic field and the associated Landau levels. This
effect arises purely from the spin polarization of the atoms, and the
quantized Hall conductance is predicted for a range of quantum well thickness
and the concentration of the atoms. This effect enables dissipationless
charge current in spintronics devices.Comment: 5 pages, 3 figures. For high resolution figures see final published
version when availabl
Azimuthal distributions of radial momentum and velocity in relativistic heavy ion collisions
Azimuthal distributions of radial (transverse) momentum, mean radial
momentum, and mean radial velocity of final state particles are suggested for
relativistic heavy ion collisions. Using transport model AMPT with string
melting, these distributions for Au + Au collisions at 200 GeV are presented
and studied. It is demonstrated that the distribution of total radial momentum
is more sensitive to the anisotropic expansion, as the anisotropies of final
state particles and their associated transverse momentums are both counted in
the measure. The mean radial velocity distribution is compared with the radial
{\deg}ow velocity. The thermal motion contributes an isotropic constant to mean
radial velocity
Gravitational waves from intermediate-mass-ratio inspirals for ground-based detectors
We explore the prospects for Advanced LIGO to detect gravitational waves from
neutron stars and stellar mass black holes spiraling into intermediate-mass
( to ) black holes. We estimate an event rate
for such \emph{intermediate-mass-ratio inspirals} (IMRIs) of up to --. Our numerical simulations show that if the central
body is not a black hole but its metric is stationary, axisymmetric, reflection
symmetric and asymptotically flat then the waves will likely be tri-periodic,
as for a black hole. We report generalizations of a theorem due to Ryan (1995)
which suggest that the evolutions of the waves' three fundamental frequencies
and of the complex amplitudes of their spectral components encode (in
principle) a full map of the central body's metric, full details of the energy
and angular momentum exchange between the central body and the orbit, and the
time-evolving orbital elements. We estimate that Advanced LIGO can measure or
constrain deviations of the central body from a Kerr black hole with modest but
interesting accuracy.Comment: Accepted for publication in Physical Review Letter
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
Metallic helix array as a broadband wave plate
This study proposes that a metallic helix array can operate as a
highly-transparent broadband wave plate in propagation directions perpendicular
to the axis of helices. The functionality arises from a special property of the
helix array, namely that the eigenstates of elliptically right-handed and
left-handed polarization are dominated by Bragg scattering and local resonance
respectively, and can be modulated separately with nearly fixed difference
between their wavevectors in a wide frequency range. The wave plate
functionality is theoretically and experimentally demonstrated by the
transformation of polarized states in a wide frequency range
Trees over Infinite Structures and Path Logics with Synchronization
We provide decidability and undecidability results on the model-checking
problem for infinite tree structures. These tree structures are built from
sequences of elements of infinite relational structures. More precisely, we
deal with the tree iteration of a relational structure M in the sense of
Shelah-Stupp. In contrast to classical results where model-checking is shown
decidable for MSO-logic, we show decidability of the tree model-checking
problem for logics that allow only path quantifiers and chain quantifiers
(where chains are subsets of paths), as they appear in branching time logics;
however, at the same time the tree is enriched by the equal-level relation
(which holds between vertices u, v if they are on the same tree level). We
separate cleanly the tree logic from the logic used for expressing properties
of the underlying structure M. We illustrate the scope of the decidability
results by showing that two slight extensions of the framework lead to
undecidability. In particular, this applies to the (stronger) tree iteration in
the sense of Muchnik-Walukiewicz.Comment: In Proceedings INFINITY 2011, arXiv:1111.267
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