120 research outputs found
Abstract Data Types in Event-B - An Application of Generic Instantiation
Integrating formal methods into industrial practice is a challenging task.
Often, different kinds of expertise are required within the same development.
On the one hand, there are domain engineers who have specific knowledge of the
system under development. On the other hand, there are formal methods experts
who have experience in rigorously specifying and reasoning about formal
systems. Coordination between these groups is important for taking advantage of
their expertise. In this paper, we describe our approach of using generic
instantiation to facilitate this coordination. In particular, generic
instantiation enables a separation of concerns between the different parties
involved in developing formal systems.Comment: In Proceedings of DS-Event-B 2012: Workshop on the experience of and
advances in developing dependable systems in Event-B, in conjunction with
ICFEM 2012 - Kyoto, Japan, November 13, 201
Renormalization of hopping integrals in coexistence phase of stripe and d-wave superconductivity in two-dimensional Hubbard model
AbstractWe have performed a variational Monte Carlo simulation on a two-dimensional Hubbard model with first- and second-neighbor hopping terms in order to study the coexistence state of a static stripe state and a modulated d-wave superconductivity in the underdoped cuprates. In addition to a Gutzwiller, a Jastrow and a doublon-holon correlation effects, the band-renormalization effect was considered in the trial wave function. The condensation energies of an 8-period stripe state was computed as a function of a Coulomb energy under the hole-density x=1/8. Our results reveal that the renormalization of higher hopping parameters due to the strong correlation effect enhances the one-dimensional hole motion on a quarter-filled band in the stripe state, and brings quasi-Fermi surface close to the magnetic zone boundary in the coexistence state
Verifying a signature architecture: a comparative case study
We report on a case study in applying different formal methods to model and verify an architecture for administrating digital signatures. The architecture comprises several concurrently executing systems that authenticate users and generate and store digital signatures by passing security relevant data through a tightly controlled interface. The architecture is interesting from a formal-methods perspective as it involves complex operations on data as well as process coordination and hence is a candidate for both data-oriented and process-oriented formal methods. We have built and verified two models of the signature architecture using two representative formal methods. In the first, we specify a data model of the architecture in Z that we extend to a trace model and interactively verify by theorem proving. In the second, we model the architecture as a system of communicating processes that we verify by finite-state model checking. We provide a detailed comparison of these two different approaches to formalization (infinite state with rich data types versus finite state) and verification (theorem proving versus model checking). Contrary to common belief, our case study suggests that Z is well suited for temporal reasoning about process models with complex operations on data. Moreover, our comparison highlights the advantages of proving theorems about such models and provides evidence that, in the hands of an experienced user, theorem proving may be neither substantially more time-consuming nor more complex than model checkin
Stripe formation in high-Tc superconductors
The non-uniform ground state of the two-dimensional three-band Hubbard model
for the oxide high-Tc superconductors is investigated using a variational Monte
Carlo method. We examine the effect produced by holes doped into the
antiferromagnetic (AF) background in the underdoped region. It is shown that
the AF state with spin modulations and stripes is stabilized du to holes
travelling in the CuO plane. The structures of the modulated AF spins are
dependent upon the parameters used in the model. The effect of the boundary
conditions is reduced for larger systems. We show that there is a region where
incommensurability is proportional to the hole density. Our results give a
consistent description of stripes observed by the neutron- scattering
experiments based on the three-band model for CuO plane.Comment: 8 pages, 9 figure
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