Germany
Germany

Time filter

Source Type

News Article | October 5, 2016
Site: www.nature.com

The ExbB construct with and without a C-terminal 6×His tag was subcloned into pET26b (Novagen). ExbD was subcloned into pACYCDuet-1 vector (Novagen) with an N-terminal Strep-tag and a C-terminal 10×His tag. ExbD was also subcloned into a pCDF-1b vector (Novagen) containing a C-terminal TEV protease site followed by a 10×His tag. An ExbD construct containing a C-terminal TEV protease site (preceded by a Gly-Gly-Gly linker for efficient digestion by TEV protease) followed by a 10×His tag was constructed by deletion of the sequence encoding the periplasmic domain of ExbD (residues 50–141). TonB was cloned into a pACYCDUET-1 vector with an N-terminal 10×His tag followed by a TEV protease site. Mutants of TonB (C18A), ExbD (D25A, N78C and E113C), and ExbB (C25S) were prepared by site-directed mutagenesis (primer sequences for all cloning and mutagenesis experiments are available upon request). The sequences of all plasmid constructs and mutations were verified by sequence analysis (Macrogen USA and Eurofins Genomics GmbH). Expression of ExbB with a C-terminal 6×His tag was performed by transforming E. coli BL21(DE3) cells (NEB) with the pET26b/ExbB vector. Co-expression was performed by co-transforming E. coli BL21(DE3) cells with the respective ExbB, ExbD, and/or TonB plasmids. For all transformations, cells were plated onto LB agar plates supplemented with appropriate antibiotics. Colonies were then used for a starter culture to inoculate 12 flasks containing either 1 l 2×YT medium (Ton subcomplex) or SelenoMet medium supplemented with l-methionine at 40 mg/l (Molecular Dimensions) (Ton complex), with appropriate antibiotics. Cultures were grown at 37 °C with shaking at 220 r.p.m. until they reached an OD of 0.5–1.0, induced with isopropyl β-d-1-thiogalactopyranoside (IPTG) to 0.1 mM final concentration, and then allowed to continue to grow overnight at 28 °C. For selenomethionine-substituted samples for experimental phasing, B834(DE3) cells (NEB) were co-transformed with pET26b/ExbB and pCDF-1b/ExbD plasmids. Single colonies were used to inoculate 12 flasks containing 1 l SelenoMet medium (Molecular Dimensions) supplemented with 40 mg/ml l-selenomethionine and appropriate antibiotics. Cultures were grown at 37 °C with shaking at 220 r.p.m. until they reached an OD of 0.5–1.0, induced with IPTG to 0.1 mM final concentration, and then allowed to continue to grow overnight at 28 °C. Cells were harvested and used immediately or stored at −80 °C. For purification, cells were resuspended in either 1×PBS (Ton subcomplex) or TBS (Ton complex) supplemented with 100 μM 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF), 100 μM DNase, and 50 μg/ml lysozyme, and disrupted with two passages through an EmulsiFlex-C3 (Avestin) operating at ~15,000 p.s.i. Membranes were pelleted by ultracentrifugation in a Type 45 Ti Beckman rotor at 200,000g for 1 h at 4 °C. Membranes were then resuspended in 1×PBS or TBS using a dounce homogenizer and solubilized by the addition of Triton X-100 (Ton subcomplex) or DDM (Anatrace) (Ton complex) to a final concentration of 1% by stirring at medium speed for 1 h to overnight at 4 °C. Insoluble material was pelleted by ultracentrifugation in a Type 45 Ti Beckman rotor at 200,000g for 1 h at 4 °C and the supernatant was used immediately. Immobilized metal affinity chromatography (IMAC) was performed on an AkTA Purifier (GE Healthcare) using a 15-ml Ni-NTA agarose column (Qiagen) equilibrated with 1×PBS or TBS supplemented with 0.1% Triton X-100 or 0.1% DDM. The supernatant was supplemented with 10 mM imidazole and loaded onto the column. The column was washed in three steps with 1×PBS or TBS supplemented with 20, 40 and 60 mM imidazole, respectively, and eluted with 1×PBS or TBS supplemented with 250 mM imidazole in 2-ml fractions. Fractions were analysed by SDS–PAGE and those fractions containing the complex were pooled. To remove the 10×His tag, TEV protease was added to the sample at 0.1 mg/ml final concentration and rocked overnight at 4 °C. For the Ton complex, the sample was then diluted 2–3 times with 25 mM HEPES, pH 7.3, and 0.1% DDM and loaded onto an anion exchange 6-ml ResourceQ column (GE Healthcare). Elution was performed with a 0–1 M NaCl gradient over 5 column volumes. For the Ton subcomplex, the sample was concentrated using an Amicon Ultra-15 Centrifugal Filter Unit with a 50-kDa MW cut-off (Millipore), filtered, and purified by size-exclusion chromatography using a Superdex 200 HL 16/600 column (GE Healthcare) at a flow rate of 0.5–1.0 ml/min. The buffer consisted of 20 mM HEPES-NaOH, pH 7.0, 150 mM NaCl, 0.01% NaN , and 0.08% C E . For the Ton complex, eluted fractions were concentrated using an Amicon Ultra-15 Centrifugal Filter Unit with a 100-kDa MW cut-off (Millipore), and passed over a Superose6HR 10/30 column (GE Healthcare) at a flow rate of 0.5 ml/min using 20 mM HEPES-NaOH, pH 7.0, 150 mM NaCl, and 0.05% DDM. Far-UV circular dichroism (CD) spectra (185–260 nm) were measured in 0.1 M NaP , pH 7.0, and 0.03% DDM using quartz cuvettes with a 0.02–0.2 mm optical path length. The results were analysed using the DichroWeb package of programs42 and different sets of reference proteins, including the SMP180 set of membrane proteins. The analysis of the thermal stability of the complexes reconstituted into liposomes was measured by the temperature dependence of the CD signal amplitude at 222 nm. Thermal melting was performed in a magnetically stirred 1-cm quartz cuvette containing 10 mM HEPES, pH 7.0, and 100 mM NaCl with a rate of temperature increase of 0.5 °C/min. Melting curves were normalized to the measured value of the molar ellipticity change at 10 °C. For crystallization, samples were concentrated to ~10 mg/ml and sparse matrix screening was performed using a TTP Labtech Mosquito crystallization robot using hanging drop vapour diffusion and plates incubated at 15–21 °C. Initially, many lead conditions were observed to produce crystals with hexagonal morphology; however, none diffracted to better than ~7 Å and most suffered from anisotropy. To avoid this packing, we performed reductive methylation of our samples before crystallization using the Reductive Alkylation Kit (Hampton Research), followed by an additional size-exclusion chromatography step. This led to a condition which produced diffraction spots to ~4 Å resolution. Further optimization and screening allowed us to grow crystals in 100 mM Na-acetate, pH 4.5, 100 mM MgCl , and 25% PEG 400 that routinely diffracted to ~3.5 Å resolution or better. For heavy atom soaking, crystals were transferred to a drop containing 1 mM HgCl and incubated overnight at room temperature and then harvested directly from the soaking condition. The best native crystals for the ExbB–ExbD complex, however, were grown from 100 mM HEPES-NaOH, pH 7.0, 100 mM CaCl , and 22% PEG MME 550 and diffracted to 2.6 Å resolution; these crystals were also used for heavy atom soaking experiments. Unfortunately, none of the heavy atom soaked crystals (nor the selenomethionine substituted crystals) were useful for phasing owing to crystal pathologies, which we suspected were twinning related. However, selenomethionine substituted crystals of the ExbB –ExbD complex were obtained using 100 mM MES/imidazole, pH 6.5, 30 mM MgCl , 30 mM CaCl , 50% ethylene glycol, and 8% PEG 8000 and diffracted to 5.2 Å resolution with no twinning-related issues. Both native and selenomethionine-substituted crystals were harvested directly from the crystallization drops. Screening for diffraction quality was performed at the GM/CA-CAT and SER-CAT beamlines at the Advanced Photon Source at Argonne National Laboratory and at beamlines 5.0.1 and 8.2.1 at the Advanced Light Source at Lawrence Berkeley National Laboratory. Final datasets were collected at the SER-CAT beamline and all data were processed using either HKL200043 or Xia244. A summary of the data collection statistics can be found in Supplementary Table 1. The presence of both components of the Ton subcomplex within the crystals was confirmed by SDS–PAGE and mass spectrometry analyses of harvested crystals. For phasing the ExbB–ExbD complex structure, three datasets were collected on selenomethionine substituted crystals of the ExbB –ExbD complex at a wavelength of 0.979 Å. The data were processed with Xia244 and, based on non-isomorphism, one dataset was removed. The final two datasets were processed together in space group P4 2 2 to a final resolution of 5.2 Å. Selenium sites (35 total) were located using HKL2MAP45 after 5,000 tries within SHELXD at a resolution range of 20–6 Å. The sites were then fed into AutoSol (PHENIX)46 which removed one site, producing a phase-extended density-modified electron density map into which we could build an initial poly-alanine model. Five-fold symmetry was clearly observed, with each monomer consisting of very elongated α-helices, and directionality was determined on the basis of the predicted topology of ExbB, which contains a single large cytoplasmic domain. This model was then used as a search model to solve the native and Hg-soaked structures by molecular replacement using PHASER/PHENIX46, 47 and the sequence docked on the basis of anomalous peaks from the SeSAD dataset. The ExbB–ExbD complex was solved in space group P2 to 2.6 Å resolution with R/R values of 0.21/0.26 and the Hg-soaked structure in space group P2 2 2 to 3.5 Å resolution with R/R values of 0.25/0.30. All model building was performed using COOT and subsequent refinement done in PHENIX46. r.m.s.d. analysis was performed within PyMOL (Schrödinger). Electrostatic surface properties (calculated using the Linearized Poisson-Boltzman Equation mode with a solvent radius of 1.4), including generation of the electric field lines, were analysed and visualized using the APBS plugin within PyMOL (Schrödinger). Buried surface area was calculated using the PDBePISA server48. Structure-related figures were made with PyMOL (Schrödinger) and Chimera49 and annotated and finalized with Adobe Photoshop and Illustrator. Coordinates and structure factors for the ExbB/ExbD complexes have been deposited into the Protein Data Bank (PDB accession codes 5SV0 and 5SV1). For 2D crystallization experiments, the Ton subcomplex (ExbB–ExbD) was extracted and purified by IMAC as previously described. The sample was passed over a Superose 12 HR 10/30 column using 20 mM Tris-HCl, pH 7, 150 mM NaCl, 0.01% NaN , and 0.035% Triton X-100. The purified complex was then mixed with a solution stock of E. coli polar lipid (Avanti Polar Lipids, Inc.) at 10 mg/ml in 2% Triton X-100, to reach final concentrations of 0.5–1.0 mg/ml protein and 0.1–0.4 mg/ml lipid. The lipid-protein-detergent samples solutions were placed into Mini Slide-A-Lyser dialysis devices (Pierce) with a 20-kDa MW cutoff, and dialysed in 1 l of 25 mM Tris-HCl, pH 7.0, 150 mM NaCl, and 0.01% NaN at 4 °C. Aliquots of dialysed samples were observed periodically by electron microscopy to monitor the formation of 2D crystals. Sample preparation for electron microscopy was carried out by applying a 5-μl drop of protein-lipid material on a glow discharged carbon-coated electron microscopy grid. Staining was performed by addition of 1% (w/v) uranyl acetate and incubation for 1 min. Grids were then imaged on a Tecnai G2 200 LaB6 electron microscope operating at 200 kV at the Institut de Microbiologie de la Méditerranée. Images were recorded with a 2K Eagle CCD camera. The best 2D crystals were selected through observation of the power spectrum of the images using ImageJ software41. Selected images were processed using the IPLT Correlation Averaging suite program50. A filtered image was generated by optical filtering of the low resolution spots, and padded to contain only 4–6 unit cells. The padded image was cross-correlated with the original large image. The positions of the cross-correlation peaks were determined and used to extract sub-images that were summed to generate an average image of the 2D unit cell. Site-directed spin labelling was used to covalently attach the spin label (1-oxyl-2,2,5,5-tetramethyl-∆3-pyrroline-3-methyl) methanethiosulfonate (MTSL) (Toronto Research Chemicals) to Cys25 on ExbB and to cysteines engineered at positions 78 and 113 on ExbD (N78C, E113C; ExbD constructs were in the pACYC vector containing an N-terminal strep-tag and a C-terminal 10×His tag for the Ton subcomplex, and in the pCDF-1b vector for the Ton complex). For labelling with MTSL, samples were first incubated with 2–10 mM dithiothreitol (DTT) for 1–2 h and the DTT then removed by passage over a HiTrap desalting column (GE Healthcare) or during anion exchange (Ton complex). Samples were then incubated with a 10× molar excess of MTSL overnight at 4 °C and then passed over a Superose 6HR 10/30 gel filtration column (GE Healthcare) using 20 mM HEPES-NaOH, pH 7.5, 200 mM NaCl, 0.08% C E or 0.03% DDM (Ton subcomplex); or 20 mM HEPES-NaOH, pH 7.0, 150 mM NaCl, and 0.05% DDM (Ton complex). For DEER measurements, the samples were diluted with D O to a final concentration of 30% and cryoprotected with 10% v/v D8-glycerol before being flash frozen in liquid nitrogen. Continuous wave (CW) electron paramagnetic resonance (EPR) experiments were carried out at room temperature on a bench-top X-band MiniScope MS 400 (Magnettech by Freiberg Instrument) at 9.5 GHz (X-band) with 2.5 mW microwave power, 15 mT sweep width and 0.15 mT modulation amplitude. Spin labelling efficiency was calculated from the second integral of the derivative spectra compared to a standard spin concentration of 100 μM (Tempol in water). The ExbB native cysteine C25 was labelled with a 50% efficiency, while the ExbD mutants were labelled with efficiencies >80%. DEER measurements were initially performed at ETH Zurich on a commercial Bruker ELEXSYS-II E580 Q-band spectrometer (34–35 GHz) and later on a Bruker ELEXSYS E580Q-AWG dedicated pulse Q-band spectrometer operating at 34–35 GHz. Both spectrometers were equipped with a TWT amplifier (150 W) and a home-made rectangular resonator (from ETH Zurich) enabling the insertion of 30–40 μl sample volume in quartz tubes with 3 mm outer diameter51. Dipolar time evolution data were acquired using the four-pulse DEER experiment at 50 K. All pulses were set to be rectangular with 12 ns length, with the pump frequency at the maximum of the echo-detected field swept spectrum, 100 MHz higher than the observer frequency. Deuterium nuclear modulations were averaged by increasing the first interpulse delay by 16 ns for 8 steps as previously described51. The background of the normalized DEER primary data (V(t)/V(0)) was fitted with optimized dimensions from 2.5 to 3.2 and the resulting normalized secondary data (F(t)/F(0)) were converted by model-free Tikhonov regularization to distance distributions with the software DeerAnalysis201552, 53. The simulation of the possible spin label rotamers populated at selected positions in the protein was performed using the Matlab program package MMM2015.1 using the MTSL ambient temperature library54. The ExbB –ExbD complex (ExbD was in the pACYC vector containing an N-terminal strep-tag and a C-terminal 6×HIS tag) was expressed and purified as described earlier. To prepare the sample for crosslinking, the sample was incubated at 4 °C with 5 mM DTT for at least 1 h. The DTT was then removed using a desalting column in 20 mM HEPES, pH 7.0, 150 mM NaCl, and 0.1% DDM. The crosslinker 1,8-bismaleimidodiethylenglycol (BM(PEG) ) (Pierce) was added at a final concentration of 0.2 mM and the reaction was incubated at 4 °C overnight. The sample was concentrated and passed over a Superose 6HR 10/30 gel filtration column using 20 mM HEPES-NaOH, pH 7.0, 150 mM NaCl, and 0.035% DDM on an AkTA Purifier system (GE Healthcare). The results were visualized by SDS–PAGE analysis. Protein complexes were reconstituted into liposomes by dialysis of the protein–lipid–detergent mixture. Lipids (DOPG, DOPC and DOPE) dissolved in chloroform were mixed in a molar ratio of 2:3:5. Chloroform was removed by vortexing in a stream of nitrogen gas in a glass tube followed by drying in vacuum for 2–3 h. The lipid film was hydrated in 1 ml TN buffer (10 mM Tris-HCl, pH 7.5, 50 mM NaCl), followed by five cycles of freeze–thaw and sonication using a water bath sonicator until the suspension of lipids became clear (10–15 min). For proteoliposome preparation, small unilamellar vesicles (SUVs) were mixed with octylglucoside (final concentration, 2%) and then proteins added to achieve a molar ratio of total lipid to protein ∼500–2,000 mol/mol. After 1 h incubation in ice, the lipid–protein–detergent mixture was dialysed into 10 mM Tris-HCl, pH 7.5, 0.3 M sucrose, and 50 mM KCl for 30–40 h using a dialysis membrane with a MW cut-off pore size of 10 kDa. Mueller-Rudin type planar bilayer membranes were formed on a 0.2-mm diameter aperture in a partition that separates two 1-ml compartments, using a mixture of lipids, DOPG, DOPC and DOPE, at a molar ratio of 2:3:5 (10 mg/ml) in n-decane, applied by a brush technique55. The aqueous solution in both compartments consisted of 2 mM KP , pH 7.0, and 0.1 M and 0.4 M KCl in the cis- and trans-compartments, respectively. To study the pH dependence of channel activity, bathing solutions were buffered with 2 mM Na-acetate (pK 4.8), Na-cacodylate (pK 6.2), and Tris (pK 8.3). The pH of the bathing solution was changed by adding 10–20 μl 0.1 M HCl or KOH. The cis-side of the planar bilayer is defined as that to which the electrical potential is applied. Proteoliposomes, 0.1–2 μl, were added to the trans-compartment, and the solutions were stirred until the transmembrane current appeared. A large concentration of an osmolyte inside of the liposomes and the transmembrane KCl concentration gradient caused proteoliposome fusion with the pre-formed planar lipid membrane bilayer. The transmembrane current was measured in voltage-clamp mode with Ag/AgCl electrodes and agar bridges, using a BC-525C amplifier (Warner Instruments). The single-channel conductance of the ExbB–ExbD complexes was measured in symmetrical salt conditions: 0.1 M KCl solution, pH 7.5, at a holding potential of +50 or −50 mV. For ion selectivity experiments, zero-current potential (V ) was determined from volt-ampere characteristics measured in asymmetric salt conditions. Relative cation/anion permeability was calculated using the Goldman-Hodgkin-Katz equation56.


Goller S.,University of Bremen | Meier A.,Leibniz University of Hanover | Mundhenk M.,Friedrich - Schiller University of Jena | Schneider T.,University of Bremen | And 2 more authors.
Advances in Modal Logic | Year: 2014

Hybrid logic with binders is an expressive specification language. Its satisfiability problem is undecidable in general. If frames are restricted to N or general linear orders, then satisfiability is known to be decidable, but of non-elementary complexity. In this paper, we consider monotone hybrid logics (i.e., the Boolean connectives are conjunction and disjunction only) over N and general linear orders. We show that the satisfiability problem remains non-elementary over linear orders, but its complexity drops to PSPACE-completeness over N. We categorize the strict fragments arising from different combinations of modal and hybrid operators into NP-complete and tractable (i.e. complete for NC1or LOGSPACE). Interestingly, NP-completeness depends only on the fragment and not on the frame. For the cases above NP, satisfiability over linear orders is harder than over N, while below NP it is at most as hard. In addition we examine model-theoretic properties of the fragments in question.


Creignou N.,Aix - Marseille University | Schmidt J.,Aix - Marseille University | Thomas M.,TWT GmbH | Woltran S.,Vienna University of Technology
Argument and Computation | Year: 2011

Many proposals for logic-based formalisations of argumentation consider an argument as a pair (Φ,α), where the support Φ is understood as a minimal consistent subset of a given knowledge base which has to entail the claim α. In case the arguments are given in the full language of classical propositional logic reasoning in such frameworks becomes a computationally costly task. For instance, the problem of deciding whether there exists a support for a given claim has been shown to be Σ 2 p-complete. In order to better understand the sources of complexity (and to identify tractable fragments), we focus on arguments given over formul in which the allowed connectives are taken from certain sets of Boolean functions. We provide a complexity classification for four different decision problems (existence of a support, checking the validity of an argument, relevance and dispensability) with respect to all possible sets of Boolean functions. Moreover, we make use of a general schema to enumerate all arguments to show that certain restricted fragments permit polynomial delay. Finally, we give a classification also in terms of counting complexity. © 2011 Copyright Taylor and Francis Group, LLC.


News Article | November 29, 2016
Site: www.newsmaker.com.au

A majority of people have seen and are familiar with warships, fighter aircrafts, battle tanks, and submarines in action, either directly or via television or films. But fight involving the use of radar emissions and radio waves is also going on in the atmosphere. This silent battle of beams which uses focused energy such as laser light, radio waves to confuse or disable enemy’s electronics is commonly called electronic warfare (EW). Electronic warfare uses entire range of electromagnetic spectrum. Hence it is sometime also known as electromagnetic warfare. Electronic warfare equipment began to be developed back during World War - II, since then electronic warfare system has become more specialized and sophisticated. Electronic Warfare is a military action which involves the use of electromagnetic energy to control, exploit, decrease, or avoid the hostile use of electromagnetic spectrum and it also involves sensing the radar of an incoming missile and listening i.e. collecting an enemy’s radio signals. Development in the electromagnetic spectrum drives the use of electronic equipment and associated weapon systems which are required to sense and counter these weapons that is included among the factor driving the electronic warfare market growth. Increasing adoption of visual and infrared techniques such as laser and other technologies are expected encourage the growth of electronic warfare market. Electronic warfare has become an essential requirement of strategic landscape for all war fighters. Situations such as political conflicts, territorial disputes, and cold-wars are expected to positively impact the electronic warfare market. Increasing popularity of small electronic systems that can be integrated within platforms such as unmanned systems is also expected to drive electronic warfare market growth. Other factors that has a positive impact on the electronic warfare market include increased system reliability, efficiency and effectiveness due to the introduction of travelling-wave tube- (TWT) technology used for electronic warfare application, and emergence of cognitive electronic warfare technology. Lack of technical knowhow, adaptability to the new technology and the laws formed to limit the investment dedicated to the R&D in this sector in some regions are included among a few restraints that negatively impact the growth of global electronic warfare market. Global electronic warfare market can be segmented into category types, product, platform, and region. On the basis of category types, global electronic warfare market can be segmented into electronic protection, electronic warfare support, and electronic attack system. Based on product, global electronic warfare market can be segmented into jammer systems, radar warning receivers, directed energy weapons, and others. By platform, electronic warfare market can be segmented into naval, airborne, ground, and unmanned. On the basis of region, global electronic warfare market can be segmented into North America, Latin America, Western Europe, Eastern Europe, Asia Pacific, Japan, and Middle East and Africa. As of 2015, North America is dominating the electronic warfare market. Asia Pacific is expected to have the highest growth rate. Electronic warfare market is mainly driven by the population base in the region, growing economy, increasing investments in the development of electronic warfare products, and a large number of R&D activities in the APAC region Key vendors of global electronic warfare market include BAE systems Plc., Harris Corporation, General Dynamics, Elbit Systems, Lockheed Martin, Raytheon, Northrop Grumman, Boeing, Cobham Plc., and Tata Power SED. Global electronic warfare market is highly fragmented with several players focusing on joint ventures, mergers and acquisitions  as a part of their growth strategy.


Creignou N.,Aix - Marseille University | Schmidt J.,Aix - Marseille University | Thomas M.,TWT GmbH | Thomas M.,Leibniz University of Hanover
Journal of Logic and Computation | Year: 2012

In this article, we investigate the complexity of abduction, a fundamental and important form of non-monotonic reasoning. Given a knowledge base explaining the world's behaviour, it aims at finding an explanation for some observed manifestation. In this article, we consider propositional abduction, where the knowledge base and the manifestation are represented by propositional formulæ. The problem of deciding whether there exists an explanation has been shown to be Σ2p-complete in general. We focus on formulæ in which the allowed connectives are taken from certain sets of Boolean functions. We consider different variants of the abduction problem in restricting both the manifestations and the hypotheses. For all these variants, we obtain a complexity classification for all possible sets of Boolean functions. In this way, we identify easier cases, namely NP-complete, coNP-complete and polynomial cases. Thus, we get a detailed picture of the complexity of the propositional abduction problem, hence highlighting the sources of intractability. Further, we address the problem of counting the full explanations and prove a trichotomous classification theorem. © 2011 The Author. Published by Oxford University Press. All rights reserved.


Creignou N.,Aix - Marseille University | Meier A.,Leibniz University of Hanover | Vollmer H.,Leibniz University of Hanover | Thomas M.,TWT GmbH
ACM Transactions on Computational Logic | Year: 2012

Autoepistemic logic extends propositional logic by the modal operator L. A formula φ that is preceded by an L is said to be "believed." The logic was introduced by Moore in 1985 for modeling an ideally rational agent's behavior and reasoning about his own beliefs. In this article we analyze all Boolean fragments of autoepistemic logic with respect to the computational complexity of the three most common decision problems expansion existence, brave reasoning and cautious reasoning. As a second contribution we classify the computational complexity of checking that a given set of formulae characterizes a stable expansion and that of counting the number of stable expansions of a given knowledge base. We improve the best known Δ 2 p-upper bound on the former problem to completeness for the second level of the Boolean hierarchy. To the best of our knowledge, this is the first paper analyzing counting problem for autoepistemic logic. © 2012 ACM 1529-3785/2012/04-ART17 $10.00.


Vartziotis D.,National Technical University of Athens | Vartziotis D.,NIKI Ltd. | Vartziotis D.,TWT GmbH | Wipper J.,TWT GmbH
Computer Methods in Applied Mechanics and Engineering | Year: 2012

The geometric element transformation method (GETMe) is an efficient geometry driven approach to mesh smoothing. It is based on regularizing element transformations which, if applied iteratively to a single element, improve its regularity and with this its quality. The smoothing method has already successfully been applied in the case of mixed surface meshes as well as all-tetrahedral and all-hexahedral meshes. In this paper, a GETMe-based approach for smoothing mixed volume meshes is presented. For this purpose, dual element-based regularizing transformations for tetrahedral, hexahedral, pyramidal, and prismatic elements are introduced and analyzed. Furthermore, it is shown that the general concept of GETMe smoothing also applies to mixed volume meshes requiring only minor modifications. Numerical results demonstrate that high quality meshes comparable to those obtained by a state of the art global optimization-based approach can be achieved within significantly shorter runtimes. © 2011 Elsevier B.V.


Thomas M.,TWT GmbH
Information Processing Letters | Year: 2012

For decision problems Π(B) defined over Boolean circuits using gates from a restricted set B only, we have Π(B)≤m AC0Π( B′) for all finite sets B and B′ of gates such that all gates from B can be computed by circuits over gates from B′. In this note, we show that a weaker version of this statement holds for decision problems defined over Boolean formulae, namely that Π(B)≤m NC2Π( B′∪{∧,∨}) and Π(B)≤m NC2Π( B′∪{0,1}) for all finite sets B and B′ of Boolean functions such that all f∈B can be defined in B′. © 2012 Elsevier B.V. © 2012 Elsevier B.V. All rights reserved.


Ostermann J.,Fraunhofer Institute for Industrial Engineering | Renner T.,Fraunhofer Institute for Industrial Engineering | Koetter F.,University of Stuttgart | Hudert S.,TWT GmbH
Annual SRII Global Conference, SRII | Year: 2014

In recent times technical developments in electric mobility have been rapid. With raising economic and ecological concerns about conventional vehicles, individuals and companies need to consider switching to electric vehicles. But due to limited range and charge times such vehicles are currently not sufficient. New mobility concepts are needed as well. In this work we present the Shared E-Fleet architecture used to enable sharing of car fleets between companies. Especially tailored to the needs of SMEs, the architecture is implemented as a cloud service chain, enabling configurability and interchangeability of services. © 2014 IEEE.


News Article | December 26, 2016
Site: marketersmedia.com

The Global Electronic Warfare Market is expected to grow at a CAGR of around 4.5% during 2016-2021. The key factors driving the growth are transnational disputes & wars, emergence of cognitive EW technology, growth in system reliability & efficiency due to the introduction of TWT (travelling-wave tube)-based solutions, advancements due to integrated EW systems, EW in unmanned aerial vehicles, and demand for counter radio-controlled improvised explosive device electronic warfare (CREW) systems. As per the MRFR analysis, defense budget cut, challenges in adoption of new technology, and Issues with emitter classification are the factors restraining the market growth. OpenRFM architectures and next generation electronic warfare are the ongoing trends which will have positive impact on the market during the forecast period. Some of the key players in the Global Electronic Warfare Market are Americas to Dominate the Global Electronic Warfare Market during the Forecast Period As per the MRFR analysis, the Americas region will continue its dominance in the forecast period. Whereas APAC and EMEA will grow at a CAGR of around 7% and 4% during the forecast period. Taste the market data and market information presented through more than 60 market data tables and figures spread over 103 numbers of pages of the project report. Avail the in-depth table of content TOC & market synopsis on “Global Electronic Warfare Market Research Report – Forecast 2016-2021” Brief Table for Contents for Electronic Warfare Market Make an Enquiry for this Report @ https://www.marketresearchfuture.com/enquiry/global-electronic-warfare-market-research-report-forecast-2016-2021 At Market Research Future (MRFR), we enable our customers to unravel the complexity of various industries through our Cooked Research Report (CRR), Half-Cooked Research Reports (HCRR), Raw Research Reports (3R), Continuous-Feed Research (CFR), and Market Research & Consulting Services. MRFR team have supreme objective to provide the optimum quality market research and intelligence services to our clients. Our market research studies by products, services, technologies, applications, end users, and market players for global, regional, and country level market segments, enable our clients to see more, know more, and do more, which help to answer all their most important questions. In order to stay updated with technology and work process of the industry, MRFR often plans & conducts meet with the industry experts and industrial visits for its research analyst members. For more information, please visit https://www.marketresearchfuture.com/reports/global-electronic-warfare-market-research-report-forecast-2016-2021

Loading TWT GmbH collaborators
Loading TWT GmbH collaborators