847 research outputs found
Suzaku observation of IGR J16318-4848
We report on the first Suzaku observation of IGR J16318-4848, the most
extreme example of a new group of highly absorbed X-ray binaries that have
recently been discovered by the International Gamma-Ray Astrophysics Laboratory
INTEGRAL. The Suzaku observation was carried out between 2006 August 14 and 17,
with a net exposure time of 97 ks.
The average X-ray spectrum of the source can be well described with a
continuum model typical for neutron stars i.e., a strongly absorbed power law
continuum with a photon index of 0.676(42) and an exponential cutoff at 20.5(6)
keV. The absorbing column is 1.95(3)x10e24 cm-2. Consistent with earlier work,
strong fluorescent emission lines of Fe Kalpha, Fe Kbeta, and Ni Kalpha are
observed. Despite the large absorbing column, no Compton shoulder is seen in
the lines, arguing for a non-spherical and inhomogeneous absorber.
Seen at an average 5-60 keV absorbed flux of 3.4x10e-10 erg cm-2 s-1, the
source exhibits significant variability on timescales of hours.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in A&
High Density Fabrication Process for Single Flux Quantum Circuits
We implemented, optimized and fully tested over multiple runs a
superconducting Josephson junction fabrication process tailored for the
integrated digital circuits that are used for control and readout of
superconducting qubits operating at millikelvin temperatures. This process was
optimized for highly energy efficient single flux quantum (ERSFQ) circuits with
the critical currents reduced by factor of ~10 as compared to those operated at
4.2 K. Specifically, it implemented Josephson junctions with 10 uA unit
critical current fabricated with a 10 uA/um2 critical current density. In order
to circumvent the substantial size increase of the SFQ circuit inductors, we
employed a NbN high kinetic inductance layer (HKIL) with a 8.5 pH/sq sheet
inductance. Similarly, to maintain the small size of junction resistive shunts,
we used a non-superconducting PdAu alloy with a 4.0 ohm/sq sheet resistance.
For integration with quantum circuits in a multi-chip module, 5 and 10 um
height bump processes were also optimized. To keep the fabrication process in
check, we developed and thoroughly tested a comprehensive Process Control
Monitor chip set.Comment: 10 pages, 5 figures, 1 tabl
Electron spectral function and algebraic spin liquid for the normal state of underdoped high superconductors
We propose to describe the spin fluctuations in the normal state of
underdoped high superconductors as a manifestation of an algebraic spin
liquid. We have performed calculations within the slave-boson model to support
our proposal. Under the spin-charge separation picture, the normal state (the
spin-pseudogap phase) is described by massless Dirac fermions, charged bosons,
and a gauge field. We find that the gauge interaction is a marginal
perturbation and drives the mean-field free-spinon fixed point to a more
complicated spin-quantum-fixed-point -- the algebraic spin liquid, where
gapless excitations interact at low energies. The electron spectral function in
the normal state was found to have a Luttinger-liquid-like line shape as
observed in experiments. The spectral function obtained in the superconducting
state shows how a coherent quasiparticle peak appears from the incoherent
background as spin and charge recombine.Comment: 4 pages, 3 figures. published versio
Refining Inductive Types
Dependently typed programming languages allow sophisticated properties of
data to be expressed within the type system. Of particular use in dependently
typed programming are indexed types that refine data by computationally useful
information. For example, the N-indexed type of vectors refines lists by their
lengths. Other data types may be refined in similar ways, but programmers must
produce purpose-specific refinements on an ad hoc basis, developers must
anticipate which refinements to include in libraries, and implementations must
often store redundant information about data and their refinements. In this
paper we show how to generically derive inductive characterisations of
refinements of inductive types, and argue that these characterisations can
alleviate some of the aforementioned difficulties associated with ad hoc
refinements. Our characterisations also ensure that standard techniques for
programming with and reasoning about inductive types are applicable to
refinements, and that refinements can themselves be further refined
Quantum trajectories for Brownian motion
We present the stochastic Schroedinger equation for the dynamics of a quantum
particle coupled to a high temperature environment and apply it the dynamics of
a driven, damped, nonlinear quantum oscillator. Apart from an initial slip on
the environmental memory time scale, in the mean, our result recovers the
solution of the known non-Lindblad quantum Brownian motion master equation. A
remarkable feature of our approach is its localization property: individual
quantum trajectories remain localized wave packets for all times, even for the
classically chaotic system considered here, the localization being stronger the
smaller .Comment: 4 pages, 3 eps figure
Recommended from our members
Perspectives on weak interactions in complex materials at different length scales
Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties
Astrometry and geodesy with radio interferometry: experiments, models, results
Summarizes current status of radio interferometry at radio frequencies
between Earth-based receivers, for astrometric and geodetic applications.
Emphasizes theoretical models of VLBI observables that are required to extract
results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the
achievements of VLBI during the past two decades in reference frames, Earth
orientation, atmospheric effects on microwave propagation, and relativity.Comment: 83 pages, 19 Postscript figures. To be published in Rev. Mod. Phys.,
Vol. 70, Oct. 199
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