Contract signing, optimism, and advantage

A contract signing protocol lets two parties exchange digital signatures on a pre-agreed text. Optimistic contract signing protocols enable the signers to do so without invoking a trusted third party. However, an adjudicating third party remains available should one or both signers seek timely resolution. We analyze optimistic contract signing protocols using a game-theoretic approach and prove a fundamental impossibility result: in any fair, optimistic, timely protocol, an optimistic player yields an advantage to the opponent. The proof relies on a careful characterization of optimistic play that postpones communication to the third party.     

Microstructure and strength of AlN–SiC interface studied by synchrotron X-rays

Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (≤1.5 mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. The AlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between \(\sim \)0.02\(^{\circ }\) misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested.     

Separating models of learning with faulty teachers

We study the power of two models of faulty teachers in Valiant’s PAC learning model and Angluin’s exact learning model. The first model we consider is learning from an incomplete membership oracle introduced by Angluin and Slonim [D. Angluin, D.K. Slonim, Randomly fallible teachers: Learning monotone DNF with an incomplete membership oracle, Machine Learning 14 (1) (1994) 7–26]. In this model, the answers to a random subset of the learner’s membership queries may be missing. The second model we consider is random persistent classification noise in membership queries introduced by Goldman, Kearns and Schapire [S. Goldman, M. Kearns, R. Schapire, Exact identification of read-once formulas using fixed points of amplification functions, SIAM Journal on Computing 22 (4) (1993) 705–726]. In this model, the answers to a random subset of the learner’s membership queries are flipped.     

Model of embedded spaces: Peculiarities of dynamical embedding and geometry

The paper is devoted to construction of a geometry of 4D space-time arising from geometrization of classical electrodynamics and associated with the Model of Embedding Spaces (MES). The basic premise of the model is the assumption that each element of matter has an eigenspace, and the spacetime of the Universe is a result of mutual dynamic embedding of these spaces, such that the magnitude of partial embedding is determined by the relative Lagrangian density of the element interactions. It is shown that the required geometry of the MES is qualified as an inhomogeneous Finsler geometry (the metric is an arbitrary function of $\dot x$ ); the basic variant of the geometry (the unique law of parallel shift of metric and non-metric tensor quantities) is obtained as a differential generalization of the Riemannian geometry by the formal replacement ${\partial \mathord{\left/ {\vphantom {\partial {\partial x^i \mapsto }}} \right. \kern-0em} {\partial x^i \mapsto }}{\partial \mathord{\left/ {\vphantom {\partial {\partial x^i }}} \right. \kern-0em} {\partial x^i }} + {{2u^k \partial ^2 } \mathord{\left/ {\vphantom {{2u^k \partial ^2 } {\partial x^{\left[ i \right.} \partial u^{\left. k \right]} }}} \right. \kern-0em} {\partial x^{\left[ i \right.} \partial u^{\left. k \right]} }}$ , u = dx/ds; and the dynamic embedding provides linearity of this generalization. Additionally, some features ofMES cosmology, which can be caused by the natural electromagnetism of the Universe, are discussed.     

Cleaning secondary effluents with organoclays and activated carbon

BACKGROUND: Flocculation, adsorption and ultrafiltration, alone and in combination, were tested for tertiary treatment of Beer Sheva (southern Israel) municipal wastewater. The focus was on the adsorption of soluble organics with powdered activated carbon (PAC) and with organoclays. RESULTS: Adsorption on 0.6 g L^?1 octadecyltrimethylammonium bromide (ODTMA) ‐ bentonite and flocculation with 130 mg L^?1 FeCl₃ reduced the dissolved organic carbon (DOC) level by 46%, and that was the highest DOC retention obtained with the organoclays. Retention achieved with 0.6 g L^?1 PAC and 130 mg L^?1 FeCl₃ was 65%. Filtration through a more hydrophobic PVDF‐30 membrane for 30 min resulted in 35–40% flux drop. A reasonable 6–7% flux reduction was obtained with filtration through a more hydrophilic PS‐50 membrane. CONCLUSION: Oganoclays at low doses are a good target adsorbent for single low molecular weight molecules. On average, higher TOC retention was achieved with PAC. Introduction of adsorption as a pre‐treatment step can lead to minimization of flux losses, reduced demand for flocculation and improved economics of the entire treatment. Copyright © 2011 Society of Chemical Industry     

Numerical Simulations of Convection Induced by Korteweg Stresses in a Miscible Polymer–Monomer System: Effects of Variable Transport Coefficients, Polymerization Rate and Volume Changes

We modeled a miscible polymer-monomer system with a sharp transition zone separating the two fluids to determine if convection analogous to Marangoni convection in immiscible fluids could occur because of thermal and concentration gradients. We considered three cases: with a temperature gradient along the transition zone, with a variable transition zone width, and one with a gradient in the conversion of polymerization. Using the Navier–Stokes equations with an additional term, the Korteweg stress term arising from non-local interactions in the fluid, we demonstrated with realistic parameters that measurable fluid flow would result in the absence of buoyancy-driven convection for all three cases. We show that even if the Korteweg stress is not a function of temperature, the increase in the diffusion coefficient with temperature can result in convection because a gradient in the transition zone width develops. We also examine the effects of a polymer viscosity that is not only a function of concentration but also temperature. We demonstrate that a constant flux of heat, as would be realistic for a heating element in contact with the side of the reactor, would produce a greater flow than a linear thermal gradient parallel to the transition zone. We demonstrate that qualitatively different flow patterns can be realized by using unusual initial conditions that could be realized with different masks for the photopolymerization. We also demonstrate that the volume change during polymerization and caused by side heating could not cause significant fluid flow that would confound the observation of Korteweg-stress induced flows. To avoid buoyancy-driven convection, the experiment would have to be performed in microgravity.