60,445 research outputs found
Strong disorder renormalization group on fractal lattices: Heisenberg models and magnetoresistive effects in tight binding models
Full text linkWe use a numerical implementation of the strong disorder renormalization
group (RG) method to study the low-energy fixed points of random Heisenberg and
tight-binding models on different types of fractal lattices. For the Heisenberg
model new types of infinite disorder and strong disorder fixed points are
found. For the tight-binding model we add an orbital magnetic field and use
both diagonal and off-diagonal disorder. For this model besides the gap spectra
we study also the fraction of frozen sites, the correlation function, the
persistent current and the two-terminal current. The lattices with an even
number of sites around each elementary plaquette show a dominant
periodicity. The lattices with an odd number of sites around each elementary
plaquette show a dominant periodicity at vanishing diagonal
disorder, with a positive weak localization-like magnetoconductance at infinite
disorder fixed points. The magnetoconductance with both diagonal and
off-diagonal disorder depends on the symmetry of the distribution of on-site
energies.Comment: 19 pages, 20 figure
W-graph ideals
Get PDFWe introduce a concept of a W-graph ideal in a Coxeter group. The main goal
of this paper is to describe how to construct a W-graph from a given W-graph
ideal. The principal application of this idea is in type A, where it provides
an algorithm for the construction of W-graphs for Specht modules.Comment: 25 page
Interfering directed paths and the sign phase transition
Full text linkWe revisit the question of the "sign phase transition" for interfering
directed paths with real amplitudes in a random medium. The sign of the total
amplitude of the paths to a given point may be viewed as an Ising order
parameter, so we suggest that a coarse-grained theory for system is a dynamic
Ising model coupled to a Kardar-Parisi-Zhang (KPZ) model. It appears that when
the KPZ model is in its strong-coupling ("pinned") phase, the Ising model does
not have a stable ferromagnetic phase, so there is no sign phase transition. We
investigate this numerically for the case of {\ss}1+1 dimensions, demonstrating
the instability of the Ising ordered phase there.Comment: 4 pages, 4 figure
Interacting partially directed self avoiding walk. From phase transition to the geometry of the collapsed phase
Full text linkIn this paper, we investigate a model for a dimensional
self-interacting and partially directed self-avoiding walk, usually referred to
by the acronym IPDSAW. The interaction intensity and the free energy of the
system are denoted by and , respectively. The IPDSAW is known to
undergo a collapse transition at . We provide the precise asymptotic
of the free energy close to criticality, that is we show that
where is computed
explicitly and interpreted in terms of an associated continuous model. We also
establish some path properties of the random walk inside the collapsed phase
. We prove that the geometric conformation adopted by the
polymer is made of a succession of long vertical stretches that attract each
other to form a unique macroscopic bead, we identify the horizontal extension
of the random walk inside the collapsed phase and we establish the convergence
of the rescaled envelope of the macroscopic bead towards a deterministic Wulff
shape.Comment: Accepted for publication in the Annals of Probabilit
Automated Real-Time Testing (ARTT) for Embedded Control Systems (ECS)
Get PDFDeveloping real-time automated test systems for embedded control systems has
been a real problem. Some engineers and scientists have used customized
software and hardware as a solution, which can be very expensive and time
consuming to develop. We have discovered how to integrate a suite of
commercially available off-the-shelf software tools and hardware to develop a
scalable test platform that is capable of performing complete black-box testing
for a dual-channel real-time Embedded-PLC-based control system
(www.aps.anl.gov). We will discuss how the Vali/Test Pro testing methodology
was implemented to structure testing for a personnel safety system with large
quantities of requirements and test cases.
This work was supported by the U.S. Department of Energy, Basic Energy
Sciences, under Contract No. W-31-109-Eng-38.Comment: 6 pages, 8 figures, ICALEPCS 2001, Poster Sessio
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