A Unifying Splitting Framework

International audienceAVATAR is an elegant and effective way to split clauses in a saturation prover using a SAT solver. But is it refutationally complete? And how does it relate to other splitting architectures? To answer these questions, we present a unifying framework that extends a saturation calculus (e.g., superposition) with splitting and embeds the result in a prover guided by a SAT solver. The framework also allows us to study locking, a subsumption-like mechanism based on the current propositional model. Various architectures are instances of the framework, including AVATAR, labeled splitting, and SMT with quantifiers

Teaching Tip: developing an intercollegiate Twitter forum to aid student exam study and the development of digital professionalism

#VetFinals has been developed as a novel online Twitter teaching event designed to support intercollegiate veterinary teaching using social media. Previous studies in other fields have suggested that Twitter use within universities may have benefits for undergraduate education. This “teaching tip” paper describes a project using Twitter to host online exam study sessions. The project has been a highly successful collaborative effort between the Royal Veterinary College and Nottingham Veterinary School in the UK. Over 4 years, the #VetFinals project has developed into a long-term, self-sustaining enterprise. This initiative provides a semi-structured means for student exam preparation with direct real-time input from a faculty member. It also creates a network of peers both horizontally across institutions and vertically throughout year groups. Based on similar initiatives in other disciplines, an anticipated outcome of this project was to contribute to student online professionalism. This could help address the veterinary community's recently highlighted problems with professional conduct and appropriate use of social media. Analysis of the success of this endeavor will be available in a future publication

The Effect of Large Amplitude Fluctuations in the Ginzburg-Landau Phase Transition

The lattice Ginzburg-Landau model in d=3 and d=2 is simulated, for different values of the coherence length $\xi$ in units of the lattice spacing $a$, using a Monte Carlo method. The energy, specific heat, vortex density $v$, helicity modulus $\Gamma_\mu$ and mean square amplitude are measured to map the phase diagram on the plane $T-\xi$. When amplitude fluctuations, controlled by the parameter $\xi$, become large ($\xi \sim 1$) a proliferation of vortex excitations occurs changing the phase transition from continuous to first order.Comment: 4 pages, 5 postscript (eps) figure

Precursors of Cytochrome Oxidase in Cytochrome-Oxidase-Deficient Cells of Neurospora crassa

Three different cell types of Neurospora crassa deficient in cytochrome oxidase were studied: the nuclear mutant cni-1, the cytoplasmic mutant mi-1 and copper-depleted wild-type cells. * 1. The enzyme-deficient cells have retained a functioning mitochondrial protein synthesis. It accounted for 12–16% of the total protein synthesis of the cell. However, the analysis of mitochondrial translation products by gel electrophoresis revealed that different amounts of individual membrane proteins were synthesized. Especially mutant cni-1 produced large amounts of a small molecular weight translation product, which is barely detectable in wild-type. * 2. Mitochondrial preparations of cytochrome-oxidase-deficient cells were examined for precursors of cytochrome oxidase. The presence of polypeptide components of cytochrome oxidase in the mitochondria was established with specific antibodies. On the other hand, no significant amounts of heme a could be extracted. * 3. Radioactively labelled components of cytochrome oxidase were isolated by immunoprecipitation and analysed by gel electrophoresis. All three cell types contained the enzyme components 4–7, which are translated on cytoplasmic ribosomes. The mitochondrially synthesized components 1–3 were present in mi-1 mutant and in copper-depleted wild-type cells. In contrast, components 2 and 3 were not detectable in the nuclear mutant cni-1. Both relative and absolute amounts of these polypeptides in the enzyme-deficient cells were quite different from those in wild-type cells. * 4. The components of cytochrome oxidase found in the enzyme-deficient cells were tightly associated with the mitochondrial membranes. * 5. Processes, which affect and may control the production of enzyme precursors or their assembly to a functional cytochrome oxidase are discussed

Solid--on--Solid Model for Adsorption on Self--Affine Substrate: A Transfer Matrix Approach

We study a $d=2$ discrete solid--on--solid model of complete wetting of a rough substrate with random self--affine boundary, having roughness exponent $\zeta_s$. A suitable transfer matrix approach allows to discuss adsorption isotherms, as well as geometrical and thermal fluctuations of the interface. For $\zeta_s\leq 1/2$ the same wetting exponent $\psi=1/3$ as for flat substrate is obtained for the dependence of the coverage, $\theta$, on the chemical potential, $h$ ($\theta\sim h^{-\psi}$ for $h\to 0$). The expected existence of a zero temperature fixed point, leading to $\psi=\zeta_s /(2-\zeta_s)$ for $\zeta_s>1/2$, is verified numerically in spite of an unexpected, very slow convergence to asymptotics.Comment: Standard TeX, 13 pages. 5 PostScript figures available on request. Preprint UDPHIR 94/04/G

Phase-field modelling of ternary eutetic solidification in hot dip galvanization

Continuous hot dip galvanizing is one of the commercially most important process techniques used for protecting steel sheets against corrosion. Preheated steel sheets are con-tinuously drawn through a pot with a molten zinc alloy. After passing a gas jet that controls the layer thickness multiple cooling units act to cool down the sheet. During passing these aggregates nucleation, dendritic primary solidification and the formation of a binary and ter-nary eutectic occurs. In the present paper, the coupled modelling of macroscopic heat flow, multiphase thermodynamics and crystal growth during solidification of a Zn-2.5 wt.% Al-1.5 wt.% Mg alloy is presented. The heat flow problem requires a numerical domain in the order of meters, growth of primary Zn-dendrites in the order of several hundred micrometers, and the interdendritic eutectic in the order of several nanometers. For technical alloys like the ternary system considered here, a thermodynamic database has been online linked to a phase-field model to describe phase transformations including all occurring solid/liquid or sol-id/solid interfaces. Process simulations have been used for getting appropriate thermal bound-ary conditions for 3D phase field simulations which were performed at three different length-scales. For modelling primary dendritic Zn-a seed density model was used for predicting the grain structure within the Zn layer. At a smaller length-scale, a small part of a Zn-dendrite surface was taken as starting point for simulating the transition between primary binary eutec-tic and ternary eutectic coupled growth of Zn-rich, Al-rich, and MgZn2-phases. Finally, the morphology of the ternary eutectic has been evaluated at the smallest length scale. The com-parison with real solidification microstructure reveals encouraging agreements

On the theory of diamagnetism in granular superconductors

We study a highly disordered network of superconducting granules linked by weak Josephson junctions in magnetic field and develop a mean field theory for this problem. The diamagnetic response to a slow {\it variations} of magnetic field is found to be analogous to the response of a type-II superconductor with extremely strong pinning. We calculate an effective penetration depth $\lambda_g$ and critical current $j_c$ and find that both $\lambda_g^{-1}$ and $j_c$ are non-zero but are strongly suppressed by frustration.Comment: REVTEX, 12 pages, two Postscript figure