452 research outputs found
Quantum Arthur-Merlin Games
This paper studies quantum Arthur-Merlin games, which are Arthur-Merlin games
in which Arthur and Merlin can perform quantum computations and Merlin can send
Arthur quantum information. As in the classical case, messages from Arthur to
Merlin are restricted to be strings of uniformly generated random bits. It is
proved that for one-message quantum Arthur-Merlin games, which correspond to
the complexity class QMA, completeness and soundness errors can be reduced
exponentially without increasing the length of Merlin's message. Previous
constructions for reducing error required a polynomial increase in the length
of Merlin's message. Applications of this fact include a proof that logarithmic
length quantum certificates yield no increase in power over BQP and a simple
proof that QMA is contained in PP. Other facts that are proved include the
equivalence of three (or more) message quantum Arthur-Merlin games with
ordinary quantum interactive proof systems and some basic properties concerning
two-message quantum Arthur-Merlin games.Comment: 22 page
Predicting fatigue crack growth rate in a welded butt joint: The role of effective R ratio in accounting for residual stress effect
A simple and efficient method is presented in this paper for predicting fatigue
crack growth rate in welded butt joints. Three well-known empirical crack growth
laws are employed using the material constants that were obtained from the base
material coupon tests. Based on the superposition rule of the linear elastic
fracture mechanics, welding residual stress effect is accounted for by replacing
the nominal stress ratio (R) in the empirical laws by the effective stress
intensity factor ratio (Reff). The key part of the analysis process is to
calculate the stress intensity factor due to the initial residual stress field
and also the stress relaxation and redistribution due to crack growth. The
finite element method in conjunction with the modified virtual crack closure
technique was used for this analysis. Fatigue crack growth rates were then
calculated by the empirical laws and comparisons were made among these
predictions as well as against published experimental tests, which were
conducted under either constant amplitude load or constant stress intensity
factor range. Test samples were M(T) geometry made of aluminium alloy 2024-T351
with a longitudinal weld by the variable polarity plasma arc welding process.
Good agreement was achieved
Quantum Optimization Problems
Krentel [J. Comput. System. Sci., 36, pp.490--509] presented a framework for
an NP optimization problem that searches an optimal value among
exponentially-many outcomes of polynomial-time computations. This paper expands
his framework to a quantum optimization problem using polynomial-time quantum
computations and introduces the notion of an ``universal'' quantum optimization
problem similar to a classical ``complete'' optimization problem. We exhibit a
canonical quantum optimization problem that is universal for the class of
polynomial-time quantum optimization problems. We show in a certain relativized
world that all quantum optimization problems cannot be approximated closely by
quantum polynomial-time computations. We also study the complexity of quantum
optimization problems in connection to well-known complexity classes.Comment: date change
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