POMDPs under Probabilistic Semantics

We consider partially observable Markov decision processes (POMDPs) with limit-average payoff, where a reward value in the interval [0,1] is associated to every transition, and the payoff of an infinite path is the long-run average of the rewards. We consider two types of path constraints: (i) quantitative constraint defines the set of paths where the payoff is at least a given threshold lambda_1 in (0,1]; and (ii) qualitative constraint which is a special case of quantitative constraint with lambda_1=1. We consider the computation of the almost-sure winning set, where the controller needs to ensure that the path constraint is satisfied with probability 1. Our main results for qualitative path constraint are as follows: (i) the problem of deciding the existence of a finite-memory controller is EXPTIME-complete; and (ii) the problem of deciding the existence of an infinite-memory controller is undecidable. For quantitative path constraint we show that the problem of deciding the existence of a finite-memory controller is undecidable.Comment: Appears in Proceedings of the Twenty-Ninth Conference on Uncertainty in Artificial Intelligence (UAI2013

Sensor Synthesis for POMDPs with Reachability Objectives

Partially observable Markov decision processes (POMDPs) are widely used in probabilistic planning problems in which an agent interacts with an environment using noisy and imprecise sensors. We study a setting in which the sensors are only partially defined and the goal is to synthesize "weakest" additional sensors, such that in the resulting POMDP, there is a small-memory policy for the agent that almost-surely (with probability~1) satisfies a reachability objective. We show that the problem is NP-complete, and present a symbolic algorithm by encoding the problem into SAT instances. We illustrate trade-offs between the amount of memory of the policy and the number of additional sensors on a simple example. We have implemented our approach and consider three classical POMDP examples from the literature, and show that in all the examples the number of sensors can be significantly decreased (as compared to the existing solutions in the literature) without increasing the complexity of the policies.Comment: arXiv admin note: text overlap with arXiv:1511.0845

On the critical character of plasticity in metallic single crystals

Previous acoustic emission (AE) experiments on ice single crystals, as well as numerical simulations, called for the possible occurrence of self-organized criticality (SOC) in collective dislocation dynamics during plastic deformation. Here, we report AE experiments on hcp metallic single crystals. Dislocation avalanches in relation with slip and twinning are identified with the only sources of AE. Both types of processes exhibit a strong intermittent character. The AE waveforms of slip and twinning events seem to be different, but from the point of view of the AE event energy distributions, no distinction is possible. The distributions always follow a power law, even when multi-slip and forest hardening occur. The power law exponent is in perfect agreement with those previously found in ice single crystals. Along with observed time clustering and interactions between avalanches, these results are new and strong arguments in favour of a general, SOC-type, framework for crystalline plasticity.Comment: 12 pages, 10 figure

Coil combination of multichannel MRSI data at 7 T: MUSICAL

The goal of this study was to evaluate a new method of combining multi-channel 1H MRSI data by direct use of a matching imaging scan as a reference, rather than computing sensitivity maps. Seven healthy volunteers were measured on a 7-T MR scanner using a head coil with a 32-channel array coil for receive-only and a volume coil for receive/transmit. The accuracy of prediction of the phase of the 1H MRSI data with a fast imaging pre-scan was investigated with the volume coil. The array coil 1H MRSI data were combined using matching imaging data as coil combination weights. The signal-to-noise ratio (SNR), spectral quality, metabolic map quality and Cramér–Rao lower bounds were then compared with the data obtained by two standard methods, i.e. using sensitivity maps and the first free induction decay (FID) data point. Additional noise decorrelation was performed to further optimize the SNR gain. The new combination method improved significantly the SNR (+29%), overall spectral quality and visual appearance of metabolic maps, and lowered the Cramér–Rao lower bounds (−34%), compared with the combination method based on the first FID data point. The results were similar to those obtained by the combination method using sensitivity maps, but the new method increased the SNR slightly (+1.7%), decreased the algorithm complexity, required no reference coil and pre-phased all spectra correctly prior to spectral processing. Noise decorrelation further increased the SNR by 13%. The proposed method is a fast, robust and simple way to improve the coil combination in 1H MRSI of the human brain at 7 T, and could be extended to other 1H MRSI techniques. © 2013 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd

PREGLED DOSTIGNUĆA PRIMJENE BIM KONCEPTA U HRVATSKOJ, ČEŠKOJ, NJEMAČKOJ I SLOVENIJI

Building information modelling (BIM) may currently be considered the fastest developing concept in the field of construction management, aiming to become a global standard. Although the roots of the concept date back to the mid-1970s, some original expectations are still missing from its implementation. There has been a time gap between its theoretical and practical implementations. While the simultaneous development of information technologies is one reason for the implementation delay, other reasons remain unclear. This paper analyzes the gaps between theoretical and practical BIM application, as well as the legislation regarding BIM implementation in four countries (in alphabetical order: Croatia, the Czech Republic, Germany, and Slovenia). The paper additionally presents a survey of current practical BIM applications as well as general and theoretical feedback from construction projects that implemented BIM.Jedan od najbrže razvijajućih koncepata u domeni metoda i alata za upravljanje građevinskim projektima, uz konačni cilj da postane globalni standard, je informacijsko modeliranje građevina, tj. BIM. Iako se koncept razvija od sredine 1970-ih, neka od originalnih očekivanja u njegovoj primjeni i danas nedostaju. Očito je da postoji vremensko odstojanje između njegove teorijske i praktične primjene. Istovremeno, razvijanje nužnih alata informacijske tehnologije je jedan od razloga zašto praktična primjena zaostaje, no ostali razlozi su još nejasni. U ovome radu autori analiziraju razlike između teoretske i praktične primjene BIM-a u zemljama odakle dolaze (Hrvatske, Češke, Njemačke i Slovenije). Rad predstavlja pregled trenutačnih dostignuća primjene BIM-a te povratnih informacija s projekata na kojima je BIM primijenjen

Pleistocene geology of northern Kidder county, North Dakota

The topography of northern Kidder County is due almost entirely to glacial deposition. This are is covered with glacial drift up to a thickness of at least 269 feet which was deposited during Wisconsin ice advances. Seventy-five percent of the area has stagnation moraine which typically exhibits knob-and-kettle topography, has high local relief with no linear trends, and which was deposited after the ice became stagnant. Many kames and eskers were formed contemporaneously with stagnation moraine. The names, Lake Williams and Woodhouse Lake loops, and proposed for and moraines deposited by Cary and Mankato ice advances, respectively. The Lake Williams loop consists partially of gravelly till while the Woodhouse Lake loop is essentially of clay till. Deposition of outwash accompanied the formation of these end moraines. Mechanical analysis were made of outwash and ice-contact drift, and results are included in the report. A small amount of ground moraine was deposited by Mankato ice in the northeastern part of the region. Calcium carbonate has not been leached from exposed tills, but an oxidized till occurs in a test well. Drift covered elongate bedrock hills preciously considered by others as end moraines are shown to by bedrock highs. Cretaceous and Tertiary bedrock beneath the drift has been considerably deformed, some of which is due to ice-shove

Exploring guest dynamics in nanoporous host materials

Diffusion is an omnipresent phenomenon in nature. In the world of molecules, it describes their irregular thermal motion. The interplay of diffusion and interaction of molecules with pore walls of nanoporous materials constitutes the benefit of using such materials in applications of separation and catalysis. The need for understanding the rate-limiting mechanisms, further optimization and development of new processes makes this topic subject of continued fundamental research [1]