Model Checking Abilities of Agents: A Closer Look

Alternating-time temporal logic (atl) is a logic for reasoning about open computational systems and multi-agent systems. It is well known that atl model checking is linear in the size of the model. We point out, however, that the size of an atl model is usually exponential in the number of agents. When the size of models is defined in terms of states and agents rather than transitions, it turns out that the problem is (1) Δ ₃ ^P -complete for concurrent game structures, and (2) Δ ₂ ^P -complete for alternating transition systems. Moreover, for “Positive atl” that allows for negation only on the level of propositions, model checking is (1) Σ ₂ ^P -complete for concurrent game structures, and (2) NP-complete for alternating transition systems. We show a nondeterministic polynomial reduction from checking arbitrary alternating transition systems to checking turn-based transition systems, We also discuss the determinism assumption in alternating transition systems, and show that it can be easily removed. In the second part of the paper, we study the model checking complexity for formulae of atl with imperfect information (atl _ir ). We show that the problem is Δ ₂ ^P -complete in the number of transitions and the length of the formula (thereby closing a gap in previous work of Schobbens in Electron. Notes Theor. Comput. Sci. 85(2), 2004). Then, we take a closer look and use the same fine structure complexity measure as we did for atl with perfect information. We get the surprising result that checking formulae of atl _ir is also Δ ₃ ^P -complete in the general case, and Σ ₂ ^P -complete for “Positive atl _ir ”. Thus, model checking agents’ abilities for both perfect and imperfect information systems belongs to the same complexity class when a finer-grained analysis is used.     

On Reduction Systems Equivalent to the Non-associative Lambek Calculus with the Empty String

The article concludes a series of results on cut-rule axiomatizabilityof the Lambek calculus. It is proved that the non-associativeproduct-free Lambek calculus with the empty string (NL₀) isnot finitely axiomatizable if the only rule of inference admittedis Lambek's cut rule. The proof makes use of the (infinitely)cut-rule axiomatized calculus NC designed by the author exactlyfor that purpose.     

Segmentation of microscope images of living cells

This paper describes a segmentation method combining a texture based technique with a contour based method. The technique is designed to enable the study of cell behaviour over time by segmenting brightfield microscope image sequences. The technique was tested on artificial images, based on images of living cells and on real sequences acquired from microscope observations of neutrophils and lymphocytes as well as on a sequence of MRI images. The results of the segmentation are compared with the results of the watershed and snake segmentation methods. The results show that the method is both effective and practical.

The structure of subword graphs and suffix trees of Fibonacci words

We use automata-theoretic approach to analyze properties of Fibonacci words. The directed acyclic subword graph (dawg) is a useful deterministic automaton accepting all suffixes of the word. We show that dawg's of Fibonacci words have particularly simple structure. Our main result is a unifying framework for a large collection of relatively simple properties of Fibonacci words. The simple structure of dawgs of Fibonacci words gives in many cases simplified alternative proofs and new interpretation of several well-known properties of Fibonacci words. In particular, the structure of lengths of paths corresponds to a number-theoretic characterization of occurrences of any subword. Using the structural properties of dawg's it can be easily shown that for a string w$w$ we can check if w$w$ is a subword of a Fibonacci word in time O(|w|)$\mathrm{O}(|w|)$ and O(1)$\mathrm{O}(1)$ space. Compact dawg's of Fibonacci words show a very regular structure of their suffix trees and show how the suffix tree for the Fibonacci word grows (extending the leaves in a very simple way) into the suffix tree for the next Fibonacci word.     

Structural and spectroscopic characteristics of synthetic hydrohaematite

In order to investigate the identity of water-containing haematite, a method of preparation has been elaborated which leads to samples of hydrohaematite which are structurally pure and free of amorphous iron hydroxide. Differential thermal analysis by a lack of endothermic effect at 423 to 473 K on the DTA-curves and by a steady fall of the TG curves up to 1150 K revealed that water in the preparations must be tightly held in the lattice of haematite. Measurements of intensities of X-ray reflections of the (1 0 4) and (0 2 4) planes in relation to the (1 1 3) plane confirmed Fe³⁺-deficiency in the haematite cationic sublattice brought about by the presence of OH^– ions in the anionic sublattice. The infrared spectrum of hydrohaematite, in addition to six bands from Fe-O variations, exhibits three bands from hydroxyl groups. The effect of silicates on the pattern of the infrared spectra of natural and synthetic hydrohaematites and the discrepancies in the infrared spectra of haematites published to date are discussed.     

Grid-Controlled Lightpaths for High Performance Grid Applications

Grid applications call for high performance networking support. One attractive solution is to deploy Grids over optical networks. However, resource management in optical domains is traditionally very rigid and cannot successfully meet the requirements of Grid applications, such as flexible provisioning and configuration. In this paper, we present a customizable resource management solution for optical networks where users can create lightpaths on demand and manage their own network resources. Thanks to a Grid-centric system architecture, lightpath resources can be shared among users and easily integrated with data and computation Grids.     

Using Convex Sets for Exploratory Data Analysis and Visualization

In this paper a new, abstract method for analysis and visualization of multidimensional data sets in pattern recognition problems is introduced. It can be used to determine the properties of an unknown, complex data set and to assist in finding the most appropriate recognition algorithm. Additionally, it can be employed to design layers of a feedforward artificial neural network or to visualize the higher-dimensional problems in 2-D and 3-D without losing relevant data set information. The method is derived from the convex set theory and works by considering convex subsets within the data and analyzing their respective positions in the original dimension. Its ability to describe certain set features that cannot be explicitly projected into lower dimensions sets it apart from many other visualization techniques. Two classical multidimensional problems are analyzed and the results show the usefulness of the presented method and underline its strengths and weaknesses.     

On the Consistency of the Normalized Eight-Point Algorithm

A recently proposed argument to explain the improved performance of the eight-point algorithm that results from using normalized data (Chojnacki, W., et al. in IEEE Trans. Pattern Anal. Mach. Intell. 25(9):1172–1177, 2003) relies upon adoption of a certain model for statistical data distribution. Under this model, the cost function that underlies the algorithm operating on the normalized data is statistically more advantageous than the cost function that underpins the algorithm using unnormalized data. Here we extend this explanation by introducing a more refined, structured model for data distribution. Under the extended model, the normalized eight-point algorithm turns out to be approximately consistent in a statistical sense. The proposed extension provides a link between the existing statistical rationalization of the normalized eight-point algorithm and the approach of Mühlich and Mester for enhancing total least squares estimation methods via equilibration. The paper forms part of a wider effort to rationalize and interrelate foundational methods in vision parameter estimation.     

A Partial Order Approach to Branching Time Logic Model Checking

Partial order techniques enable reducing the size of the state space used for model checking, thus alleviating the “state space explosion” problem. These reductions are based on selecting a subset of the enabled operations from each program state. So far, these methods have been studied, implemented, and demonstrated for assertional languages that model the executions of a program as computation sequences, in particular the linear temporal logic. The present paper shows, for the first time, how this approach can be applied to languages that model the behavior of a program as a tree. We study here partial order reductions for branching temporal logics, e.g., the logics CTL and CTL* (with the next time operator removed) and process algebra logics such as Hennesy–Milner logic (withτactions). Conditions on the selection of subset of successors from each state during the state-space construction, which guarantee reduction that preserves CTL* properties, are given. The experimental results provided show that the reduction is substantial.     

Melatonin and the Brain–Heart Crosstalk in Neurocritically Ill Patients—From Molecular Action to Clinical Practice

Brain injury, especially traumatic brain injury (TBI), may induce severe dysfunction of extracerebral organs. Cardiac dysfunction associated with TBI is common and well known as the brain–heart crosstalk, which broadly refers to different cardiac disorders such as cardiac arrhythmias, ischemia, hemodynamic insufficiency, and sudden cardiac death, which corresponds to acute disorders of brain function. TBI-related cardiac dysfunction can both worsen the brain damage and increase the risk of death. TBI-related cardiac disorders have been mainly treated symptomatically. However, the analysis of pathomechanisms of TBI-related cardiac dysfunction has highlighted an important role of melatonin in the prevention and treatment of such disorders. Melatonin is a neurohormone released by the pineal gland. It plays a crucial role in the coordination of the circadian rhythm. Additionally, melatonin possesses strong anti-inflammatory, antioxidative, and antiapoptotic properties and can modulate sympathetic and parasympathetic activities. Melatonin has a protective effect not only on the brain, by attenuating its injury, but on extracranial organs, including the heart. The aim of this study was to analyze the molecular activity of melatonin in terms of TBI-related cardiac disorders. Our article describes the benefits resulting from using melatonin as an adjuvant in protection and treatment of brain injury-induced cardiac dysfunction.