Context-Sensitive Visibility

An improvement to the so-called visual verification approach is presented. Visual verification is a method for checking the correctness of the behaviour of a reactive or concurrent system. It shares a great deal of common ground with ordinary formal state space verification, but is more user-friendly. This is because the user does not need to specify in detail the properties that the system must satisfy to be correct. Instead, the user only lists the atomic actions that are relevant for the property. Computer tools are used to obtain a graphical representation which is a summary of all possible alternative behaviours of the system, and the user then analyses the result. The improvement presented in this article allows the user to pick a region of the graphical representation and investigate it in more detail, without being overwhelmed by the details outside the region. The improvement is illustrated by analysing the livelocks in a model of the alternating bit protocol.     

Using linear algebra in decomposition of Farkas interpolants

The use of propositional logic and systems of linear inequalities over reals is a common means to model software for formal verification. Craig interpolants constitute a central building block in this setting for over-approximating reachable states, e.g. as candidates for inductive loop invariants. Interpolants for a linear system can be efficiently computed from a Simplex refutation by applying the Farkas’ lemma. However, these interpolants do not always suit the verification task—in the worst case, they can even prevent the verification algorithm from converging. This work introduces the decomposed interpolants, a fundamental extension of the Farkas interpolants, obtained by identifying and separating independent components from the interpolant structure, using methods from linear algebra. We also present an efficient polynomial algorithm to compute decomposed interpolants and analyse its properties. We experimentally show that the use of decomposed interpolants in model checking results in immediate convergence on instances where state-of-the-art approaches diverge. Moreover, since being based on the efficient Simplex method, the approach is very competitive in general.

     

Breakdown of Zero-Energy Quantum Hall State in Graphene in the Light of Current Fluctuations and Shot Noise

We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate a decrease in correlations with increasing bias.     

C-terminal truncations of a thermostable Bacillus stearothermophilus {alpha}-amylase

A series of truncated proteins from a thermostable Bacillusstearothermophilus -amylase was prepared to study the importanceof the extension in the C-terminus compared with other liquefyingBacillus -amylases. The mutations introducing new translationtermination sites shortened the 515 amino acid residue-longwild type enzyme by 17, 32, 47, 73 or 93 residues. The longerthe truncation, the lower the specific activity of the enzyme.Only the two longest mutant proteins were active: the specificactivity of the 498 residue variant was 97% and protein 483was 36% that of the parental enzyme. The K_m values of starchhydrolysis changed from 1.09 for wild type enzyme to 0.35 and0.21 for mutants 498 and 483, respectively, indicating alteredsubstrate binding. The mutant enzymes had almost identical pHand temperature optima with the wild type amylase, but enhancedthermal stability and altered end product profile. The consequencesof the truncation to the structure and function of the enzymeswere explored with molecular modeling. The liquefying amylasesseem to require {small tilde}480 residues to be active, whereasthe C-terminal end of B.stearothermophilus amylase is requiredfor increased activity.     

Mineralogical and elemental composition of fly ash from pilot scale fluidised bed combustion of lignite, bituminous coal, wood chips and their blends

The chemical and mineralogical composition of fly ash samples collected from different parts of a laboratory and a pilot scale CFB facility has been investigated. The fabric filter and the second cyclone of the two facilities were chosen as sampling points. The fuels used were Greek lignite (from the Florina basin), Polish coal and wood chips. Characterization of the fly ash samples was conducted by means of X-ray fluorescence (XRF), inductive coupled plasma-optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), particle size distribution (PSD) and X-ray diffraction (XRD). According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, SiO₂ is the dominant oxide in fly ash with Al₂O₃ and Fe₂O₃ found in considerable quantities. Results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite. The ICP-OES analysis showed rather low levels of trace elements, especially for As and Cr, in many of the ashes included in this study compared to coal ash from fluidised bed combustion in general.     

Modelling non-stationary noise with spectral factorisation in automatic speech recognition

Speech recognition systems intended for everyday use must be able to cope with a large variety of noise types and levels, including highly non-stationary multi-source mixtures. This study applies spectral factorisation algorithms and long temporal context for separating speech and noise from mixed signals. To adapt the system to varying environments, noise models are acquired from the context, or learnt from the mixture itself without prior information. We also propose methods for reducing the size of the bases used for speech and noise modelling by 20–40 times for better practical applicability. We evaluate the performance of the methods both as a standalone classifier and as a signal-enhancing front-end for external recognisers. For the CHiME noisy speech corpus containing non-stationary multi-source household noises at signal-to-noise ratios ranging from +9 to ?6 dB, we report average keyword recognition rates up to 87.8% using a single-stream sparse classification algorithm.     

Tailored surface properties of semi-fluorinated block copolymers by electrospinning

Diblock copolymers based on polystyrene (PS) macroinitiators and four different fluorinated monomers (perfluorooctyl ethyl methacrylate (FMA), pentafluorostyrene (FS), perfluorooctyl-ethylene oxymethyl styrene (EMS), 2,3,5,6-tetrafluoro-4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecaoxy)styrene (FSF)) were synthesized via atom transfer radical polymerization (ATRP). The lengths of the PS and fluorinated blocks were altered and the surface and self-assembling properties of the polymers were compared with respect to the fluorinated monomer used and the fluorine content. The surface properties, contact angles and surface tension, were enhanced by the existence of the CF₃ groups at the end of the alkyl chains compared with poly(pentafluorostyrene). Hydrophobicity of the surfaces was further enhanced by electrospinning the polymer solutions, which yielded superhydrophobic surfaces with water contact angles >150° for polymers having CF₃ groups.     

Studying the catechol binding cavity in comparative models of human dopamine D2 receptor

Obtaining more structural information of human dopamine D(2) receptor may help in the design of better therapeutic agents against diseases such as Parkinson. In this study attempts have been made to develop a functional model for the catechol binding site of the human dopamine D(2) receptor, with two primary models being postulated based on the presence of a disulfide bridge in the second extracellular loop. The models have been subjected to subsequent molecular dynamics simulation and receptor based virtual screening of catechol structures. During steady state of the simulations, representative models with the reduced disulfide bridge were more capable of discriminating between active and inactive catechol structures. It is postulated that similar conformational changes of the second extracellular loop observed in 5-HT4 and β-adrenergic receptors, might also take place in the human D(2) receptor during its interaction with agonist ligands.