693 research outputs found
Exact Ground States of Large Two-Dimensional Planar Ising Spin Glasses
Studying spin-glass physics through analyzing their ground-state properties
has a long history. Although there exist polynomial-time algorithms for the
two-dimensional planar case, where the problem of finding ground states is
transformed to a minimum-weight perfect matching problem, the reachable system
sizes have been limited both by the needed CPU time and by memory requirements.
In this work, we present an algorithm for the calculation of exact ground
states for two-dimensional Ising spin glasses with free boundary conditions in
at least one direction. The algorithmic foundations of the method date back to
the work of Kasteleyn from the 1960s for computing the complete partition
function of the Ising model. Using Kasteleyn cities, we calculate exact ground
states for huge two-dimensional planar Ising spin-glass lattices (up to
3000x3000 spins) within reasonable time. According to our knowledge, these are
the largest sizes currently available. Kasteleyn cities were recently also used
by Thomas and Middleton in the context of extended ground states on the torus.
Moreover, they show that the method can also be used for computing ground
states of planar graphs. Furthermore, we point out that the correctness of
heuristically computed ground states can easily be verified. Finally, we
evaluate the solution quality of heuristic variants of the Bieche et al.
approach.Comment: 11 pages, 5 figures; shortened introduction, extended results; to
appear in Physical Review E 7
Gauge and Poincare' Invariant Regularization and Hopf Symmetries
We consider the regularization of a gauge quantum field theory following a
modification of the Polchinski proof based on the introduction of a cutoff
function. We work with a Poincare' invariant deformation of the ordinary
point-wise product of fields introduced by Ardalan, Arfaei, Ghasemkhani and
Sadooghi, and show that it yields, through a limiting procedure of the cutoff
functions, to a regularized theory, preserving all symmetries at every stage.
The new gauge symmetry yields a new Hopf algebra with deformed co-structures,
which is inequivalent to the standard one.Comment: Revised version. 14 pages. Incorrect statements eliminate
Subextensive singularity in the 2D Ising spin glass
The statistics of low energy states of the 2D Ising spin glass with +1 and -1
bonds are studied for square lattices with , and =
0.5, where is the fraction of negative bonds, using periodic and/or
antiperiodic boundary conditions. The behavior of the density of states near
the ground state energy is analyzed as a function of , in order to obtain
the low temperature behavior of the model. For large finite there is a
range of in which the heat capacity is proportional to .
The range of in which this behavior occurs scales slowly to as
increases. Similar results are found for = 0.25. Our results indicate that
this model probably obeys the ordinary hyperscaling relation , even though . The existence of the subextensive behavior is
attributed to long-range correlations between zero-energy domain walls, and
evidence of such correlations is presented.Comment: 13 pages, 7 figures; final version, to appear in J. Stat. Phy
Closed-Loop Manufacturing for Aerospace Industry: An Integrated PLM-MOM Solution to Support the Wing Box Assembly Process
The aim of this research is to provide an example of the importance that integrated Product Lifecycle Management (PLM) and Manufacturing Operation Management (MOM) systems have in realizing the Digital Manufacturing. The research first examines what the Digital Manufacturing involves and then identifies Digital Twin and the related Digital Thread as key elements. PLM and MOM solutions support the Digital Twin and the Digital Thread allowing the exchange of product-related information between the digital manufacturing model and the physical manufacturing execution. A Digital Twin of a wing box and its assembly process is created in PLM by building the bill of material and bill of process. Then it is shown how in MOM system the production phase is facilitated by managing production operations, advanced scheduling and supporting the execution of the processes and how the analysis of the manufacturing performance is possible. The result integrating these systems is to have the right information at the right place at the right time along with the related benefits in terms of costs, time and quality. The activity has been developed in Siemens Industry Software under the European Project AirGreen 2, an integrated research action of the REG IADP (Regional Innovative Aircraft Demonstration Platform) part of the Joint Technical Programme, the steering and coordination of LEONARDO Aircraft. The AirGreen 2 project is an Innovation Action funded by the Clean Sky 2 Joint Undertaking under the European Union\u2019s Horizon 2020 research and innovation programme, under Grant Agreement N\ub0807089 REG IADP)
Error threshold in the evolution of diploid organisms
The effects of error propagation in the reproduction of diploid organisms are
studied within the populational genetics framework of the quasispecies model.
The dependence of the error threshold on the dominance parameter is fully
investigated. In particular, it is shown that dominance can protect the
wild-type alleles from the error catastrophe. The analysis is restricted to a
diploid analogue of the single-peaked landscape.Comment: 9 pages, 4 Postscript figures. Submitted to J. Phy. A: Mat. and Ge
Experimental results of crystal-assisted slow extraction at the SPS
The possibility of extracting highly energetic particles from the Super
Proton Synchrotron (SPS) by means of silicon bent crystals has been explored
since the 1990's. The channelling effect of a bent crystal can be used to
strongly deflect primary protons and eject them from the synchrotron. Many
studies and experiments have been carried out to investigate crystal
channelling effects. The extraction of 120 and 270 GeV proton beams has already
been demonstrated in the SPS with dedicated experiments located in the ring.
Presently in the SPS, the UA9 experiment is performing studies to evaluate the
possibility to use bent silicon crystals to steer particle beams in high energy
accelerators. Recent studies on the feasibility of extraction from the SPS have
been made using the UA9 infrastructure with a longer-term view of using
crystals to help mitigate slow extraction induced activation of the SPS. In
this paper, the possibility to eject particles into the extraction channel in
LSS2 using the bent crystals already installed in the SPS is presented. Details
of the concept, simulations and measurements carried out with beam are
presented, before the outlook for the future is discussed.Comment: 4 pages, 7 figures, submitted to to International Particle
Accelerator Conference (IPAC) 2017 in Copenhagen, Denmar
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