Efficient paraconsistent reasoning with rules and ontologies for the semantic web

Ontologies formalized by means of Description Logics (DLs) and rules in the form of Logic Programs (LPs) are two prominent formalisms in the field of Knowledge Representation and Reasoning. While DLs adhere to the OpenWorld Assumption and are suited for taxonomic reasoning, LPs implement reasoning under the Closed World Assumption, so that default knowledge can be expressed. However, for many applications it is useful to have a means that allows reasoning over an open domain and expressing rules with exceptions at the same time. Hybrid MKNF knowledge bases make such a means available by formalizing DLs and LPs in a common logic, the Logic of Minimal Knowledge and Negation as Failure (MKNF). Since rules and ontologies are used in open environments such as the Semantic Web, inconsistencies cannot always be avoided. This poses a problem due to the Principle of Explosion, which holds in classical logics. Paraconsistent Logics offer a solution to this issue by assigning meaningful models even to contradictory sets of formulas. Consequently, paraconsistent semantics for DLs and LPs have been investigated intensively. Our goal is to apply the paraconsistent approach to the combination of DLs and LPs in hybrid MKNF knowledge bases. In this thesis, a new six-valued semantics for hybrid MKNF knowledge bases is introduced, extending the three-valued approach by Knorr et al., which is based on the wellfounded semantics for logic programs. Additionally, a procedural way of computing paraconsistent well-founded models for hybrid MKNF knowledge bases by means of an alternating fixpoint construction is presented and it is proven that the algorithm is sound and complete w.r.t. the model-theoretic characterization of the semantics. Moreover, it is shown that the new semantics is faithful w.r.t. well-studied paraconsistent semantics for DLs and LPs, respectively, and maintains the efficiency of the approach it extends

Real-time analysis of intracellular glucose and calcium in pancreatic beta cells by fluorescence microscopy

AbstractGlucose is the physiological stimulus for insulin secretion in pancreatic beta cells. The uptake and phosphorylation of glucose initiate and control downstream pathways, resulting in insulin secretion. However, the temporal coordination of these events in beta cells is not fully understood. The recent development of the FLII12Pglu-700μ-δ6 glucose nanosensor facilitates real-time analysis of intracellular glucose within a broad concentration range. Using this fluorescence-based technique, we show the shift in intracellular glucose concentration upon external supply and removal in primary mouse beta cells with high resolution. Glucose influx, efflux, and metabolism rates were calculated from the time-dependent plots. Comparison of insulin-producing cells with different expression levels of glucose transporters and phosphorylating enzymes showed that a high glucose influx rate correlated with GLUT2 expression, but was largely also sustainable by high GLUT1 expression. In contrast, in cells not expressing the glucose sensor enzyme glucokinase glucose metabolism was slow. We found no evidence of oscillations of the intracellular glucose concentration in beta cells. Concomitant real-time analysis of glucose and calcium dynamics using FLII12Pglu-700μ-δ6 and fura-2-acetoxymethyl-ester determined a glucose threshold of 4mM for the [Ca2+]i increase in beta cells. Indeed, a glucose concentration of 7mM had to be reached to evoke large amplitude [Ca2+]i oscillations. The KATP channel closing agent glibenclamide was not able to induce large amplitude [Ca2+]i oscillations in the absence of glucose. Our findings suggest that glucose has to reach a threshold to evoke the [Ca2+]i increase and subsequently initiate [Ca2+]i oscillations in a KATP channel independent manner

Fluoreszenzmikroskopische Untersuchungen zur intrazellulären Glucosehomöostase in Beta-Zellen und in der Leber

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Generating Functions for Probabilistic Programs

This paper investigates the usage of generating functions (GFs) encoding measures over the program variables for reasoning about discrete probabilistic programs. To that end, we define a denotational GF-transformer semantics for probabilistic while-programs, and show that it instantiates Kozen's seminal distribution transformer semantics. We then study the effective usage of GFs for program analysis. We show that finitely expressible GFs enable checking super-invariants by means of computer algebra tools, and that they can be used to determine termination probabilities. The paper concludes by characterizing a class of -- possibly infinite-state -- programs whose semantics is a rational GF encoding a discrete phase-type distribution

Charge Transport Through Open, Driven Two-Level Systems with Dissipation

We derive a Floquet-like formalism to calculate the stationary average current through an AC driven double quantum dot in presence of dissipation. The method allows us to take into account arbitrary coupling strengths both of a time-dependent field and a bosonic environment. We numerical evaluate a truncation scheme and compare with analytical, perturbative results such as the Tien-Gordon formula.Comment: 14 pages, 6 figures. To appear in Phys. Rev.