24 research outputs found
Qualitative Analysis of POMDPs with Temporal Logic Specifications for Robotics Applications
We consider partially observable Markov decision processes (POMDPs), that are
a standard framework for robotics applications to model uncertainties present
in the real world, with temporal logic specifications. All temporal logic
specifications in linear-time temporal logic (LTL) can be expressed as parity
objectives. We study the qualitative analysis problem for POMDPs with parity
objectives that asks whether there is a controller (policy) to ensure that the
objective holds with probability 1 (almost-surely). While the qualitative
analysis of POMDPs with parity objectives is undecidable, recent results show
that when restricted to finite-memory policies the problem is EXPTIME-complete.
While the problem is intractable in theory, we present a practical approach to
solve the qualitative analysis problem. We designed several heuristics to deal
with the exponential complexity, and have used our implementation on a number
of well-known POMDP examples for robotics applications. Our results provide the
first practical approach to solve the qualitative analysis of robot motion
planning with LTL properties in the presence of uncertainty
Interface Simulation Distances
The classical (boolean) notion of refinement for behavioral interfaces of
system components is the alternating refinement preorder. In this paper, we
define a distance for interfaces, called interface simulation distance. It
makes the alternating refinement preorder quantitative by, intuitively,
tolerating errors (while counting them) in the alternating simulation game. We
show that the interface simulation distance satisfies the triangle inequality,
that the distance between two interfaces does not increase under parallel
composition with a third interface, and that the distance between two
interfaces can be bounded from above and below by distances between
abstractions of the two interfaces. We illustrate the framework, and the
properties of the distances under composition of interfaces, with two case
studies.Comment: In Proceedings GandALF 2012, arXiv:1210.202
Stochastic Shortest Path with Energy Constraints in POMDPs
We consider partially observable Markov decision processes (POMDPs) with a
set of target states and positive integer costs associated with every
transition. The traditional optimization objective (stochastic shortest path)
asks to minimize the expected total cost until the target set is reached. We
extend the traditional framework of POMDPs to model energy consumption, which
represents a hard constraint. The energy levels may increase and decrease with
transitions, and the hard constraint requires that the energy level must remain
positive in all steps till the target is reached. First, we present a novel
algorithm for solving POMDPs with energy levels, developing on existing POMDP
solvers and using RTDP as its main method. Our second contribution is related
to policy representation. For larger POMDP instances the policies computed by
existing solvers are too large to be understandable. We present an automated
procedure based on machine learning techniques that automatically extracts
important decisions of the policy allowing us to compute succinct human
readable policies. Finally, we show experimentally that our algorithm performs
well and computes succinct policies on a number of POMDP instances from the
literature that were naturally enhanced with energy levels.Comment: Technical report accompanying a paper published in proceedings of
AAMAS 201
Optimal Cost Almost-sure Reachability in POMDPs
We consider partially observable Markov decision processes (POMDPs) with a
set of target states and every transition is associated with an integer cost.
The optimization objective we study asks to minimize the expected total cost
till the target set is reached, while ensuring that the target set is reached
almost-surely (with probability 1). We show that for integer costs
approximating the optimal cost is undecidable. For positive costs, our results
are as follows: (i) we establish matching lower and upper bounds for the
optimal cost and the bound is double exponential; (ii) we show that the problem
of approximating the optimal cost is decidable and present approximation
algorithms developing on the existing algorithms for POMDPs with finite-horizon
objectives. While the worst-case running time of our algorithm is double
exponential, we also present efficient stopping criteria for the algorithm and
show experimentally that it performs well in many examples of interest.Comment: Full Version of Optimal Cost Almost-sure Reachability in POMDPs, AAAI
2015. arXiv admin note: text overlap with arXiv:1207.4166 by other author
High-Resolution Quantitative Phase Imaging of Plasmonic Metasurfaces with Sensitivity down to a Single Nanoantenna
Optical metasurfaces have emerged as a new generation of building blocks for multifunctional optics. Design and realization of metasurface elements place everincreasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (nonscanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge. Here, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved by taking full advantage of the polarization selective control of light through the geometric (PancharatnamBerry) phase. The measurement is carried out in an inherently stable common-path setup composed of a standard optical microscope and an add-on imaging module. Phase information is acquired from the mutual coherence function attainable in records created in broadband spatially incoherent light by the self-interference of scattered and leakage light coming from the metasurface. In calibration measurements, the phase was mapped with the precision and spatial background noise better than 0.01 and 0.05 rad, respectively. The imaging excels at the high spatial resolution that was demonstrated experimentally by the precise amplitude and phase restoration of vortex metalenses and a metasurface grating with 833 lines/mm. Thanks to superior light sensitivity of the method, we demonstrated for the first time to our knowledge the widefield measurement of the phase altered by a single nanoantenna while maintaining the precision well below 0.15 rad
Odvodňování uhelných lomů SHR horizontálními a vertikálními vrty z uhelných a skrývkových řezů
PrezenčníNeuvedenoNeuveden
Analýza frekvenčně řízeného pohonu s asynchronní motorem z hlediska dovoleného a maximálního momentu
Import 26/06/2007Prezenční453 - Katedra elektrických strojů a přístroj
Non-alloyed Ni3Al based alloys – preparation and evaluation of mechanical properties
The paper reports on the fabrication and mechanical properties of Ni3Al based alloy, which represents the most
frequently used basic composition of nickel based intermetallic alloys for high temperature applications. The structure
of the alloy was controlled through directional solidifi cation. The samples had a multi-phase microstructure.
The directionally solidifi ed specimens were subjected to tensile tests with concurrent measurement of acoustic
emission (AE). The specimens exhibited considerable room temperature ductility before fracture. During tensile
testing an intensive AE was observed.Web of Science52331230