8,476 research outputs found
The JKind Model Checker
JKind is an open-source industrial model checker developed by Rockwell
Collins and the University of Minnesota. JKind uses multiple parallel engines
to prove or falsify safety properties of infinite state models. It is portable,
easy to install, performance competitive with other state-of-the-art model
checkers, and has features designed to improve the results presented to users:
inductive validity cores for proofs and counterexample smoothing for test-case
generation. It serves as the back-end for various industrial applications.Comment: CAV 201
Macroscopic coherence effects in a mesoscopic system: Weak localization of thin silver films in an undergraduate lab
We present an undergraduate lab that investigates weak localization in thin
silver films. The films prepared in our lab have thickness, , between 60-200
\AA, a mesoscopic length scale. At low temperatures, the inelastic dephasing
length for electrons, , exceeds the thickness of the film (), and the films are then quasi-2D in nature. In this situation, theory
predicts specific corrections to the Drude conductivity due to coherent
interference between conducting electrons' wavefunctions, a macroscopically
observable effect known as weak localization. This correction can be destroyed
with the application of a magnetic field, and the resulting magnetoresistance
curve provides information about electron transport in the film. This lab is
suitable for Junior or Senior level students in an advanced undergraduate lab
course.Comment: 16 pages, 9 figures. Replaces earlier version of paper rejected by
Am. J. Phys. because of too much content on vacuum systems. New version deals
with the undergraduate experiment on weak localization onl
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
Investigating the Physical Origin of Unconventional Low-Energy Excitations and Pseudogap Phenomena in Cuprate Superconductors
We investigate the physical origin of unconventional low-energy excitations
in cuprate superconductors by considering the effect of coexisting competing
orders (CO) and superconductivity (SC) and of quantum fluctuations and other
bosonic modes on the low-energy charge excitation spectra. By incorporating
both SC and CO in the bare Green's function and quantum phase fluctuations in
the self-energy, we can consistently account for various empirical findings in
both the hole- and electron-type cuprates, including the excess subgap
quasiparticle density of states, ``dichotomy'' in the fluctuation-renormalized
quasiparticle spectral density in momentum space, and the occurrence and
magnitude of a low-energy pseudogap being dependent on the relative gap
strength of CO and SC. Comparing these calculated results with experiments of
ours and others, we suggest that there are two energy scales associated with
the pseudogap phenomena, with the high-energy pseudogap probably of magnetic
origin and the low-energy pseudogap associated with competing orders.Comment: 10 pages, 5 figures. Invited paper for the 2006 Taiwan International
Conference on Superconductivity. Correspondence author: Nai-Chang Yeh
(e-mail: [email protected]
Correlation between the reliability of HEMT devices and that of a combined oscillator-amplifier
We evaluate an oscillator-amplifier MMIC submitted to high-temperature operating life time tests. To relate adequately these results with individual components’ results, it is important to realise that failure mechanisms in non-linear MMICs are governed by the maximally instantaneous voltages/currents and hence that comparisons should be conducted at equal instantaneous conditions
Dynamics of photoinduced Charge Density Wave-metal phase transition in K0.3MoO3
We present first systematic studies of the photoinduced phase transition from
the ground charge density wave (CDW) state to the normal metallic (M) state in
the prototype quasi-1D CDW system K0.3MoO3. Ultrafast non-thermal CDW melting
is achieved at the absorbed energy density that corresponds to the electronic
energy difference between the metallic and CDW states. The results imply that
on the sub-picosecond timescale when melting and subsequent initial recovery of
the electronic order takes place the lattice remains unperturbed.Comment: Phys. Rev. Lett., accepted for publicatio
Black-body radiation induced photodissociation and population redistribution of weakly bound states in H
Molecular hydrogen ions in weakly bound states close to the first
dissociation threshold are attractive quantum sensors for measuring the
proton-to-electron mass ratio and hyperfine-induced ortho-para mixing. The
experimental accuracy of previous spectroscopic studies relying on fast ion
beams could be improved by using state-of-the-art ion trap setups. With the
electric dipole moment vanishing in H and preventing fast spontaneous
emission, radiative lifetimes of the order of weeks are found. We include the
effect of black-body radiation that can lead to photodissociation and
rovibronic state redistribution to obtain effective lifetimes for trapped ion
experiments. Rate coefficients for bound-bound and bound-continuum processes
were calculated using adiabatic nuclear wave functions and nonadiabatic
energies, including relativistic and radiative corrections. Effective lifetimes
for the weakly bound states were obtained by solving a rate equation model and
lifetimes in the range of 4 to 523~ms and 215~ms were found at room
temperature and liquid nitrogen temperature, respectively. Black-body induced
photodissociation was identified as the lifetime-limiting effect, which
guarantees the purity of state-selectively generated molecular ion ensembles.
The role of hyperfine-induced -mixing, which allows pure rovibrational
transitions, was found to be negligible.Comment: 13 pages, 5 figure
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