50 research outputs found
Incremental QBF Solving
We consider the problem of incrementally solving a sequence of quantified
Boolean formulae (QBF). Incremental solving aims at using information learned
from one formula in the process of solving the next formulae in the sequence.
Based on a general overview of the problem and related challenges, we present
an approach to incremental QBF solving which is application-independent and
hence applicable to QBF encodings of arbitrary problems. We implemented this
approach in our incremental search-based QBF solver DepQBF and report on
implementation details. Experimental results illustrate the potential benefits
of incremental solving in QBF-based workflows.Comment: revision (camera-ready, to appear in the proceedings of CP 2014,
LNCS, Springer
Evaluating QBF Solvers: Quantifier Alternations Matter
We present an experimental study of the effects of quantifier alternations on
the evaluation of quantified Boolean formula (QBF) solvers. The number of
quantifier alternations in a QBF in prenex conjunctive normal form (PCNF) is
directly related to the theoretical hardness of the respective QBF
satisfiability problem in the polynomial hierarchy. We show empirically that
the performance of solvers based on different solving paradigms substantially
varies depending on the numbers of alternations in PCNFs. In related
theoretical work, quantifier alternations have become the focus of
understanding the strengths and weaknesses of various QBF proof systems
implemented in solvers. Our results motivate the development of methods to
evaluate orthogonal solving paradigms by taking quantifier alternations into
account. This is necessary to showcase the broad range of existing QBF solving
paradigms for practical QBF applications. Moreover, we highlight the potential
of combining different approaches and QBF proof systems in solvers.Comment: preprint of a paper to be published at CP 2018, LNCS, Springer,
including appendi
DepQBF 6.0: A Search-Based QBF Solver Beyond Traditional QCDCL
We present the latest major release version 6.0 of the quantified Boolean
formula (QBF) solver DepQBF, which is based on QCDCL. QCDCL is an extension of
the conflict-driven clause learning (CDCL) paradigm implemented in state of the
art propositional satisfiability (SAT) solvers. The Q-resolution calculus
(QRES) is a QBF proof system which underlies QCDCL. QCDCL solvers can produce
QRES proofs of QBFs in prenex conjunctive normal form (PCNF) as a byproduct of
the solving process. In contrast to traditional QCDCL based on QRES, DepQBF 6.0
implements a variant of QCDCL which is based on a generalization of QRES. This
generalization is due to a set of additional axioms and leaves the original
Q-resolution rules unchanged. The generalization of QRES enables QCDCL to
potentially produce exponentially shorter proofs than the traditional variant.
We present an overview of the features implemented in DepQBF and report on
experimental results which demonstrate the effectiveness of generalized QRES in
QCDCL.Comment: 12 pages + appendix; to appear in the proceedings of CADE-26, LNCS,
Springer, 201
Understanding and Extending Incremental Determinization for 2QBF
Incremental determinization is a recently proposed algorithm for solving
quantified Boolean formulas with one quantifier alternation. In this paper, we
formalize incremental determinization as a set of inference rules to help
understand the design space of similar algorithms. We then present additional
inference rules that extend incremental determinization in two ways. The first
extension integrates the popular CEGAR principle and the second extension
allows us to analyze different cases in isolation. The experimental evaluation
demonstrates that the extensions significantly improve the performance
N-glycans of Human Protein C Inhibitor: Tissue-Specific Expression and Function
Protein C inhibitor (PCI) is a serpin type of serine protease inhibitor that is found in many tissues and fluids in human, including blood plasma, seminal plasma and urine. This inhibitor displays an unusually broad protease specificity compared with other serpins. Previous studies have shown that the N-glycan(s) and the NH2-terminus affect some blood-related functions of PCI. In this study, we have for the first time determined the N-glycan profile of seminal plasma PCI, by mass spectrometry. The N-glycan structures differed markedly compared with those of both blood-derived and urinary PCI, providing evidence that the N-glycans of PCI are expressed in a tissue-specific manner. The most abundant structure (m/z 2592.9) had a composition of Fuc3Hex5HexNAc4, consistent with a core fucosylated bi-antennary glycan with terminal Lewisx. A major serine protease in semen, prostate specific antigen (PSA), was used to evaluate the effects of N-glycans and the NH2-terminus on a PCI function related to the reproductive tract. Second-order rate constants for PSA inhibition by PCI were 4.3±0.2 and 4.1±0.5 M−1s−1 for the natural full-length PCI and a form lacking six amino acids at the NH2-terminus, respectively, whereas these constants were 4.8±0.1 and 29±7 M−1s−1 for the corresponding PNGase F-treated forms. The 7–8-fold higher rate constants obtained when both the N-glycans and the NH2-terminus had been removed suggest that these structures jointly affect the rate of PSA inhibition, presumably by together hindering conformational changes of PCI required to bind to the catalytic pocket of PSA
Tree yield and fruit mineral concentrations influence 'Hass' avocado fruit quality
To investigate the variation in quality of ‘Hass’ avocado fruit within an orchard, fruit were harvested at commercial maturity from 15 ‘Hass’ trees of similar appearance, growing in three adjacent rows on the same soil type, and receiving similar management. Fruit were harvested at commercial maturity, and either ripened at 22 °C or stored at 2 or 7 °C for 3 or 5 weeks and then ripened. Significant positive correlations (based on the mean for each datum tree) were noted between fruit flesh calcium (Ca) and magnesium (Mg) concentrations and the (Ca+Mg)/potassium ratio, and the number of days for the fruit to reach the eating ripe stage (DTR). Negative correlations were also observed between these minerals and anthracnose and mesocarp discolouration (MD) severity. Negative correlations were observed between fruit potassium (K) and phosphorus (P) concentrations and DTR. Fruit from trees with high fruit yield were generally smaller, with lower anthracnose and MD severity, ripened more slowly, and had higher flesh Ca concentrations. It is likely that cultural practices that maintain moderate to high fruit yield and reduce variation in yield will improve avocado fruit quality and reduce variability in quality. Since the main differences between adjacent trees in this trial were the seedling rootstocks of unknown origin, it is suggested that rootstocks can have a significant impact on avocado yield and fruit quality
Digital Rights Management for Distributed Multimedia E- Learning Content
Nowadays a steadily increasing amount of multimedia content is generated and requires storage in digital libraries. Current research focuses on identifying user needs to make relevant information available through semantically enhanced retrieval techniques. In this context the already complex task of retrieving multimedia content on a semantic level is further complicated by right management and security issues which are evolving into fundamental topics in the area of digital libraries. Previous research conducted by our group concentrated on topics like extraction of metadata from multimedia content, indexing of metadata and application of indexed metadata for storage, search and retrieval tasks. Our research activities resulted in a semantic technology framework for metadata based multimedia retrieval. Based on these results we have selected promising and emerging technologies to extend our framework according to the application domain E-Learning with special focus on digital rights management in context of distributed multimedia learning content management systems.
Structural origins for selectivity and specificity in an engineered bacterial repressor inducer pair
The bacterial tetracycline transcription regulation system mediated by the tetracycline repressor TetR is widely used to study gene expression in prokaryotes and eukaryotes. To study multiple genes in parallel, a triple mutant TetR K64L135I138 has been engineered that is selectively induced by the synthetic tetracycline derivative 4 de dimethylamino anhydrotetracycline 4 ddma atc and no longer by tetracycline, the inducer of wild type TetR. In the present study, we report the crystal structure of TetR K64L135I138 in the absence and in complex with 4 ddma atc at resolutions of 2.1 amp; 8195; . Analysis of the structures in light of the available binding data and previously reported TetR complexes allows for a dissection of the origins of selectivity and specificity. In all crystal structures solved to date, the ligand binding position, as well as the positioning of the residues lining the binding site, is extremely well conserved, irrespective of the chemical nature of the ligand. Selective recognition of 4 ddma atc is achieved through fine tuned hydrogen bonding constraints introduced by the His64 amp; 8594;Lys substitution, as well as a combination of hydrophobic effect and the removal of unfavorable electrostatic interactions through the introduction of Leu135 and Ile13