35,035 research outputs found
Weighted Modal Transition Systems
Specification theories as a tool in model-driven development processes of
component-based software systems have recently attracted a considerable
attention. Current specification theories are however qualitative in nature,
and therefore fragile in the sense that the inevitable approximation of systems
by models, combined with the fundamental unpredictability of hardware
platforms, makes it difficult to transfer conclusions about the behavior, based
on models, to the actual system. Hence this approach is arguably unsuited for
modern software systems. We propose here the first specification theory which
allows to capture quantitative aspects during the refinement and implementation
process, thus leveraging the problems of the qualitative setting.
Our proposed quantitative specification framework uses weighted modal
transition systems as a formal model of specifications. These are labeled
transition systems with the additional feature that they can model optional
behavior which may or may not be implemented by the system. Satisfaction and
refinement is lifted from the well-known qualitative to our quantitative
setting, by introducing a notion of distances between weighted modal transition
systems. We show that quantitative versions of parallel composition as well as
quotient (the dual to parallel composition) inherit the properties from the
Boolean setting.Comment: Submitted to Formal Methods in System Desig
Probabilistic Opacity in Refinement-Based Modeling
Given a probabilistic transition system (PTS) partially observed by
an attacker, and an -regular predicate over the traces of
, measuring the disclosure of the secret in means
computing the probability that an attacker who observes a run of can
ascertain that its trace belongs to . In the context of refinement, we
consider specifications given as Interval-valued Discrete Time Markov Chains
(IDTMCs), which are underspecified Markov chains where probabilities on edges
are only required to belong to intervals. Scheduling an IDTMC produces
a concrete implementation as a PTS and we define the worst case disclosure of
secret in as the maximal disclosure of over all
PTSs thus produced. We compute this value for a subclass of IDTMCs and we prove
that refinement can only improve the opacity of implementations
Compositionality for Quantitative Specifications
We provide a framework for compositional and iterative design and
verification of systems with quantitative information, such as rewards, time or
energy. It is based on disjunctive modal transition systems where we allow
actions to bear various types of quantitative information. Throughout the
design process the actions can be further refined and the information made more
precise. We show how to compute the results of standard operations on the
systems, including the quotient (residual), which has not been previously
considered for quantitative non-deterministic systems. Our quantitative
framework has close connections to the modal nu-calculus and is compositional
with respect to general notions of distances between systems and the standard
operations
Arriving on time: estimating travel time distributions on large-scale road networks
Most optimal routing problems focus on minimizing travel time or distance
traveled. Oftentimes, a more useful objective is to maximize the probability of
on-time arrival, which requires statistical distributions of travel times,
rather than just mean values. We propose a method to estimate travel time
distributions on large-scale road networks, using probe vehicle data collected
from GPS. We present a framework that works with large input of data, and
scales linearly with the size of the network. Leveraging the planar topology of
the graph, the method computes efficiently the time correlations between
neighboring streets. First, raw probe vehicle traces are compressed into pairs
of travel times and number of stops for each traversed road segment using a
`stop-and-go' algorithm developed for this work. The compressed data is then
used as input for training a path travel time model, which couples a Markov
model along with a Gaussian Markov random field. Finally, scalable inference
algorithms are developed for obtaining path travel time distributions from the
composite MM-GMRF model. We illustrate the accuracy and scalability of our
model on a 505,000 road link network spanning the San Francisco Bay Area
L and T Dwarf Models and the L to T Transition
Using a model for refractory clouds, a novel algorithm for handling them, and
the latest gas-phase molecular opacities, we have produced a new series of L
and T dwarf spectral and atmosphere models as a function of gravity and
metallicity, spanning the \teff range from 2200 K to 700 K. The correspondence
with observed spectra and infrared colors for early- and mid-L dwarfs and for
mid- to late-T dwarfs is good. We find that the width in infrared
color-magnitude diagrams of both the T and L dwarf branches is naturally
explained by reasonable variations in gravity and, therefore, that gravity is
the "second parameter" of the L/T dwarf sequence. We investigate the dependence
of theoretical dwarf spectra and color-magnitude diagrams upon various cloud
properties, such as particle size and cloud spatial distribution. In the region
of the LT transition, we find that no one cloud-particle-size and gravity
combination can be made to fit all the observed data. Furthermore, we note that
the new, lower solar oxygen abundances of Allende-Prieto, Lambert, & Asplund
(2002) produce better fits to brown dwarf data than do the older values.
Finally, we discuss various issues in cloud physics and modeling and speculate
on how a better correspondence between theory and observation in the
problematic LT transition region might be achieved.Comment: accepted to the Astrophysical Journal, 21 figures (20 in color);
spectral models in electronic form available at
http://zenith.as.arizona.edu/~burrow
Worm Algorithm for Problems of Quantum and Classical Statistics
This is a chapter of the multi-author book "Understanding Quantum Phase
Transitions," edited by Lincoln Carr and published by Taylor and Francis. In
this chapter, we give a general introduction to the worm algorithm and present
important results highlighting the power of the approachComment: 27 pages, 15 figures, chapter in a boo
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