10,517 research outputs found

### Testing the Metal of Late-Type Kepler Planet Hosts with Iron-Clad Methods

It has been shown that F, G, and early K dwarf hosts of Neptune-sized planets
are not preferentially metal-rich. However, it is less clear whether the same
holds for late K and M dwarf planet hosts. We report metallicities of Kepler
targets and candidate transiting planet hosts with effective temperatures below
4500 K. We use new metallicity calibrations to determine [Fe/H] from visible
and near-infrared spectra. We find that the metallicity distribution of late K
and M dwarfs monitored by Kepler is consistent with that of the solar
neighborhood. Further, we show that hosts of Earth- to Neptune-sized planets
have metallicities consistent with those lacking detected planets and rule out
a previously claimed 0.2 dex offset between the two distributions at 6sigma
confidence. We also demonstrate that the metallicities of late K and M dwarfs
hosting multiple detected planets are consistent with those lacking detected
planets. Our results indicate that multiple terrestrial and Neptune-sized
planets can form around late K and M dwarfs with metallicities as low as 0.25
of the solar value. The presence of Neptune-sized planets orbiting such
low-metallicity M dwarfs suggests that accreting planets collect most or all of
the solids from the disk and that the potential cores of giant planets can
readily form around M dwarfs. The paucity of giant planets around M dwarfs
compared to solar-type stars must be due to relatively rapid disk evaporation
or a slower rate of core accretion, rather than insufficient solids to form a
core.Comment: 9 pages, 5 figures. Accepted to Ap

### Application of advanced technologies to small, short-haul transport aircraft (STAT)

The benefits of selected advanced technologies for 19 and 30 passenger, short-haul aircraft were identified. Advanced technologies were investigated in four areas: aerodynamics, propulsion, structures, and ride quality. Configuration sensitivity studies were conducted to show design tradeoffs associated with passenger capacity, cabin comfort level, and design field length

### Stabilized hot electron bolometer heterodyne receiver at 2.5 THz

We report on a method to stabilize a hot electron bolometer (HEB) mixer at 2.5 THz. The technique utilizes feedback control of the local oscillator (LO) laser power by means of a swing-arm actuator placed in the optical beam path. We demonstrate that this technique yields a factor of 50 improvement in the spectroscopic Allan variance time which is shown to be over 30â€‰s in a 12â€‰MHz noise fluctuation bandwidth. Furthermore, broadband signal direct detection effects may be minimized by this technique. The technique is versatile and can be applied to practically any local oscillator at any frequency

### Chiral black hole in three-dimensional gravitational Chern-Simons

A chiral black hole can be defined from the three-dimensional pure
gravitational Chern-Simons action as an independent gravitational theory. The
third order derivative of the Cotton tensor gives a dimensional constant which
plays a role of the cosmological constant. The handedness of angular momentum
depends on the signature of the Chern-Simons coefficient. Even in the massless
black hole which corresponds to the static black hole, it has a nonvanishing
angular momentum. We also study statistical entropy and thermodynamic
stability.Comment: 6 pages, a reference added, minor changes to introductio

### Interaction cost of non-local gates

We introduce the interaction cost of a non-local gate as the minimal time of
interaction required to perform the gate when assisting the process with fast
local unitaries. This cost, of interest both in the areas of quantum control
and quantum information, depends on the specific interaction, and allows to
compare in an operationally meaningful manner any two non-local gates. In the
case of a two-qubit system, an analytical expression for the interaction cost
of any unitary operation given any coupling Hamiltonian is obtained. One gate
may be more time-consuming than another for any possible interaction. This
defines a partial order structure in the set of non-local gates, that compares
their degree of non-locality. We analytically characterize this partial order
in a region of the set of two-qubit gates.Comment: revtex, 4 pages, no pictures, typos corrected, small changes in
nomenclatur

### Back Reaction of Hawking Radiation on Black Hole Geometry

We propose a model for the geometry of a dynamical spherical shell in which
the metric is asymptotically Schwarzschild, but deviates from Ricci-flatness in
a finite neighbourhood of the shell. Hence, the geometry corresponds to a
`hairy' black hole, with the hair originating on the shell. The metric is
regular for an infalling shell, but it bifurcates, leading to two disconnected
Schwarzschild-like spacetime geometries. The shell is interpreted as either
collapsing matter or as Hawking radiation, depending on whether or not the
shell is infalling or outgoing. In this model, the Hawking radiation results
from tunnelling between the two geometries. Using this model, the back reaction
correction from Hawking radiation is calculated.Comment: Latex file, 15 pages, 4 figures enclosed, uses eps

### Photon position measure

The positive operator valued measure (POVM) for a photon counting array
detector is derived and found to equal photon flux density integrated over
pixel area and measurement time. Since photon flux density equals number
density multiplied by the speed of light, this justifies theoretically the
observation that a photon counting array provides a coarse grained measurement
of photon position. The POVM obtained here can be written as a set of
projectors onto a basis of localized states, consistent with the description of
photon position in a recent quantum imaging proposal [M. Tsang, Phys. Rev.
Lett. \textbf{102}, 253601 (2009)]. The wave function that describes a photon
counting experiment is the projection of the photon state vector onto this
localized basis. Collapse is to the electromagnetic vacuum and not to a
localized state, thus violating the text book rules of quantum mechanics but
compatible with the theory of generalized observables and the nonlocalizability
of an incoming photon

### Optimum Quantum Error Recovery using Semidefinite Programming

Quantum error correction (QEC) is an essential element of physical quantum
information processing systems. Most QEC efforts focus on extending classical
error correction schemes to the quantum regime. The input to a noisy system is
embedded in a coded subspace, and error recovery is performed via an operation
designed to perfectly correct for a set of errors, presumably a large subset of
the physical noise process. In this paper, we examine the choice of recovery
operation. Rather than seeking perfect correction on a subset of errors, we
seek a recovery operation to maximize the entanglement fidelity for a given
input state and noise model. In this way, the recovery operation is optimum for
the given encoding and noise process. This optimization is shown to be
calculable via a semidefinite program (SDP), a well-established form of convex
optimization with efficient algorithms for its solution. The error recovery
operation may also be interpreted as a combining operation following a quantum
spreading channel, thus providing a quantum analogy to the classical diversity
combining operation.Comment: 7 pages, 3 figure

### Softly broken supersymmetric Yang-Mills theories: Renormalization and non-renormalization theorems

We present a minimal version for the renormalization of softly broken
Super-Yang-Mills theories using the extended model with a local gauge coupling.
It is shown that the non-renormalization theorems of the case with unbroken
supersymmetry are valid without modifications and that the renormalization of
soft-breaking parameters is completely governed by the renormalization of the
supersymmetric parameters. The symmetry identities in the present context are
peculiar, since the extended model contains two anomalies: the Adler-Bardeen
anomaly of the axial current and an anomaly of supersymmetry in the presence of
the local gauge coupling. From the anomalous symmetries we derive the exact
all-order expressions for the beta functions of the gauge coupling and of the
soft-breaking parameters. They generalize earlier results to arbitrary
normalization conditions and imply the NSVZ expressions for a specific
normalization condition on the coupling.Comment: 24 pages, LaTeX, v2: one reference adde

### Giant vesicles at the prolate-oblate transition: A macroscopic bistable system

Giant phospholipid vesicles are shown to exhibit thermally activated
transitions between a prolate and an oblate shape on a time scale of several
seconds. From the fluctuating contour of such a vesicle we extract ellipticity
as an effective reaction coordinate whose temporal probability distribution is
bimodal. We then reconstruct the effective potential from which we derive an
activation energy of the order of $k_BT$ in agreement with theoretical
calculations. The dynamics of this transition is well described within a
Kramers model of overdamped diffusion in a bistable potential. Thus, this
system can serve as a model for macroscopic bistability.Comment: 10 pages, LaTeX, epsfig, 4 eps figures included, to appear in
Europhys. Let

- â€¦