4,477 research outputs found
TarTar: A Timed Automata Repair Tool
We present TarTar, an automatic repair analysis tool that, given a timed
diagnostic trace (TDT) obtained during the model checking of a timed automaton
model, suggests possible syntactic repairs of the analyzed model. The suggested
repairs include modified values for clock bounds in location invariants and
transition guards, adding or removing clock resets, etc. The proposed repairs
are guaranteed to eliminate executability of the given TDT, while preserving
the overall functional behavior of the system. We give insights into the design
and architecture of TarTar, and show that it can successfully repair 69% of the
seeded errors in system models taken from a diverse suite of case studies.Comment: 15 pages, 7 figure
Unveiling the origin of shape coexistence in lead isotopes
The shape coexistence in the nuclei Pb is analyzed within the
Hartree-Fock-Bogoliubov approach with the effective Gogny force. A good
agreement with the experimental energies is found for the coexisting spherical,
oblate and prolate states. Contrary to the established interpretation, it is
found that the low-lying prolate and oblate states observed in this mass
region are predominantly characterized by neutron correlations whereas the
protons behave as spectators rather than playing an active role.Comment: 5 pages, 6 postscript figure
Dipolar particles in a double-trap confinement: Response to tilting the dipolar orientation
We analyze the microscopic few-body properties of dipolar particles confined
in two parallel quasi-one-dimensional harmonic traps. In particular, we show
that an adiabatic rotation of the dipole orientation about the trap axes can
drive an initially non-localized few-fermion state into a localized state with
strong inter-trap pairing. For an instant, non-adiabatic rotation, however,
localization is inhibited and a highly excited state is reached. This state may
be interpreted as the few-body analog of a super-Tonks-Girardeau state, known
from one-dimensional systems with contact interactions
A trick for passing degenerate points in Ashtekar formulation
We examine one of the advantages of Ashtekar's formulation of general
relativity: a tractability of degenerate points from the point of view of
following the dynamics of classical spacetime. Assuming that all dynamical
variables are finite, we conclude that an essential trick for such a continuous
evolution is in complexifying variables. In order to restrict the complex
region locally, we propose some `reality recovering' conditions on spacetime.
Using a degenerate solution derived by pull-back technique, and integrating the
dynamical equations numerically, we show that this idea works in an actual
dynamical problem. We also discuss some features of these applications.Comment: 9 pages by RevTeX or 16 pages by LaTeX, 3 eps figures and epsf-style
file are include
Extreme points of the set of density matrices with positive partial transpose
We present a necessary and sufficient condition for a finite dimensional
density matrix to be an extreme point of the convex set of density matrices
with positive partial transpose with respect to a subsystem. We also give an
algorithm for finding such extreme points and illustrate this by some examples.Comment: 4 pages, 2 figure
Causal structure and degenerate phase boundaries
Timelike and null hypersurfaces in the degenerate space-times in the Ashtekar
theory are defined in the light of the degenerate causal structure proposed by
Matschull. Using the new definition of null hypersufaces, the conjecture that
the "phase boundary" separating the degenerate space-time region from the
non-degenerate one in Ashtekar's gravity is always null is proved under certain
circumstances.Comment: 13 pages, Revte
Coexistence of antiferrodistortive and ferroelectric distortions at the PbTiO (001) surface
The c(22) reconstruction of (001) PbTiO surfaces is studied by
means of first principles calculations for paraelectric (non-polar) and
ferroelectric ([001] polarized) films. Analysis of the atomic displacements in
the near-surface region shows how the surface modifies the antiferrodistortive
(AFD) instability and its interaction with ferroelectric (FE) distortions. The
effect of the surface is found to be termination dependent. The AFD instability
is suppressed at the TiO termination while it is strongly enhanced,
relative to the bulk, at the PbO termination resulting in a c(2x2) surface
reconstruction which is in excellent agreement with experiments. We find that,
in contrast to bulk PbTiO, in-plane ferroelectricity at the PbO termination
does not suppress the AFD instability. The AFD and the in-plane FE distortions
are instead concurrently enhanced at the PbO termination. This leads to a novel
surface phase with coexisting FE and AFD distortions which is not found in
PbTiO bulk
High fidelity readout scheme for rare-earth solid state quantum computing
We propose and analyze a high fidelity readout scheme for a single instance
approach to quantum computing in rare-earth-ion-doped crystals. The scheme is
based on using different species of qubit and readout ions, and it is shown
that by allowing the closest qubit ion to act as a readout buffer, the readout
error can be reduced by more than an order of magnitude. The scheme is shown to
be robust against certain experimental variations, such as varying detection
efficiencies, and we use the scheme to predict the expected quantum fidelity of
a CNOT gate in these solid state systems. In addition, we discuss the potential
scalability of the protocol to larger qubit systems. The results are based on
parameters which we believed are experimentally feasible with current
technology, and which can be simultaneously realized.Comment: 7 pages, 5 figure
Scanning tunneling microscopy and spectroscopy of sodium-chloride overlayers on the stepped Cu(311) surface: Experimental and theoretical study
The physical properties of ultrathin NaCl overlayers on the stepped Cu(311)
surface have been characterized using scanning tunneling microscopy (STM) and
spectroscopy, and density functional calculations. Simulations of STM images
and differential conductance spectrum were based on the Tersoff-Hamann
approximation for tunneling with corrections for the modified tunneling barrier
at larger voltages and calculated Kohn-Sham states. Characteristic features
observed in the STM images can be directly related to calculated electronic and
geometric properties of the overlayers. The measured apparent barrier heights
for the mono-, bi-, and trilayers of NaCl and the corresponding
adsorption-induced changes in the work function, as obtained from the distance
dependence of the tunneling current, are well reproduced by and understood from
the calculated results. The measurements revealed a large reduction of the
tunneling conductance in a wide voltage region, resembling a band gap. However,
the simulated spectrum showed that only the onset at positive sample voltages
may be viewed as a valence band edge, whereas the onset at negative voltages is
caused by the drastic effect of the electric field from the tip on the
tunneling barrier
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