Lower bounds on the information rate of secret sharing schemes with homogeneous access structure

We present some new lower bounds on the optimal information rate and on the optimal average information rate of secret sharing schemes with homogeneous access structure. These bounds are found by using some covering constructions and a new parameter, the k-degree of a participant, that is introduced in this paper. Our bounds improve the previous ones in almost all cases.     

Influence of DNA repair by ada and ogt alkyltransferases on the mutational specificity of alkylating agents

We investigated the influence of the alkyltransferases (ATases) encoded by the ada and ogt genes of Escherichia coli on the mutational specificity of alkylating agents. A new mutational assay for selection of supF- mutations in shuttle-vector plasmids was used. Treating plasmid-bearing bacteria with N-methyl-N-nitrosourea (MNU), N-ethyl-N-nitrosourea (ENU), and ethyl methanesulfonate (EMS) dramatically increased the mutation frequency (from 33-fold to 789-fold). The vast majority of mutations (89-100%) were G:C-->A:T transitions. This type of mutation increased in ada- (MNU) or ogt- (ENU) bacteria, suggesting that repair of O6-methylguanine by ada ATase and repair of O6-ethylguanine by ogt ATase contribute mainly to the decrease in G:C-->A:T transitions. The analysis of neighboring base sequences revealed an overabundance of G:C-->A:T transitions at 5'-GG sequences. The 5'-PuG bias increased in ATase-defective cells, suggesting that these sequences were not refractory to repair. G:C-->A:T transitions occurred preferentially in the untranscribed strand after in vivo exposure. That this strand specificity was detected even in bacteria devoid of ATase activity (ada- ogt-) and not after in vitro mutagenesis suggests a bias for damage induction rather than for DNA repair. Highly significant differences were found between the in vivo and in vitro incidences of G:C-->A:T substitutions at the two major hotspots, positions 123 (5'-GGG-3'; antisense strand) and 168 (5'-GGA-3'; sense strand). These results are explained by differences in the probability of formation of stem-loop structures in vivo and in vitro.     

On the hardness of solving edge matching puzzles as SAT or CSP problems

Edge matching puzzles have been amongst us for a long time now and traditionally they have been considered, both, a children’s game and an interesting mathematical divertimento. Their main characteristics have already been studied, and their worst-case complexity has been properly classified as a NP-complete problem. It is in recent times, specially after being used as the problem behind a money-prized contest, with a prize of 2US$ million for the first solver, that edge matching puzzles have attracted mainstream attention from wider audiences, including, of course, computer science people working on solving hard problems. We consider these competitions as an interesting opportunity to showcase SAT/CSP solving techniques when confronted to a real world problem to a broad audience, a part of the intrinsic, i.e. monetary, interest of such a contest. This article studies the NP-complete problem known as edge matching puzzle using SAT and CSP approaches for solving it. We will focus on providing, first and foremost, a theoretical framework, including a generalized definition of the problem. We will design and show algorithms for easy and fast problem instances generation, generators with easily tunable hardness. Afterwards we will provide with SAT and CSP models for the problems and we will study problem complexity, both typical case and worst-case complexity. We will also provide some specially crafted heuristics that result in a boost in solving time and study which is the effect of such heuristics.     

DipGame: A challenging negotiation testbed

There is a chronic lack of shared application domains to test advanced research models and agent negotiation architectures in Multiagent Systems. In this paper we introduce a friendly testbed for that purpose. The testbed is based on The Diplomacy Game where negotiation and the relationships between players play an essential role. The testbed profits from the existence of a large community of human players that know the game and can easily provide data for experiments. We explain the infrastructure in the paper and make it freely available to the AI community.     

Agent-Mediated Electronic Commerce

Electronic commerce has been one of the traditional arenas for agent technology. The complexity of these applications has been a challenge for researchers that have developed methodologies, products, and systems, having in mind the specificities of trade, the interaction particularities of commerce, the strict notion of commitment and contract, and the clearly shaped conventions and norms that structure the field. In this paper I survey some key areas for agent technology which, although general, are of special importance in electronic commerce, namely, solid development methodologies, negotiation technologies and trust-building mechanisms. I give examples of systems in which I have directly participated, although I also try to refer to the work of other AgentLink Special Interest Group members over the last few years.     

Electrode surface treatments in sludge electro-osmosis dewatering

The sewage sludge dewatering produced by wastewater treatment plants (WWTP) is a multifaceted process due to the presence of colloid fractions. Electro-osmosis could be a suitable technique to reduce the water content of the final sludge. Electric fields of 10, 15, and 20?V/cm have been studied for electro-osmosis tests under the pressure of a static or rotating piston, obtaining a dry solids content up to 40–45%, with respect to 25–30% obtained by mechanical methods. In order to optimize the process, the corrosion behavior and the wear of the anodic material appear to be the main critical aspects, due to the high circulating current density and the use of a rotating electrode. We compared the efficiency and the corrosion resistance of dimensionally stable anodes (DSA) with respect to bare stainless steel (AISI 304) and stainless steel coated by PVD technique with TiN, AlTiN, and DLC. Characterization of the anode surfaces by SEM and potentiodynamic tests show that DSA is the most suitable material for our application. However, efficiencies of the electro-osmosis processes have been found comparable, in terms of developed current densities and total energy consumptions, for short-test duration.     

Distributed parameter model simulation tool for PEM fuel cells

In this work, a simulation tool for proton exchange membrane fuel cells (PEMFC) has been developed, based on a distributed parameter model. The tool is designed to perform studies of time and space variations in the direction of the gas channels. Results for steady-state and dynamic simulations for a single cell of one channel are presented and analyzed. Considered variables are concentrations of reactants, pressures, temperatures, humidification, membrane water content, current density, among others that have significant effects on the performance and durability of PEMFC.     

Evaluation of Carbon Partitioning in New Generation of Quench and Partitioning (Q&P) Steels

Quenching and partitioning (Q&P) and a novel combined process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble®3S50 thermomechanical simulator. The heat treatments involved intercritical annealing at 800 °C and a two-step Q&P heat treatment with a partitioning time of 100 seconds at 400 °C. The “optimum” quench temperature of 318 °C was selected according to the constrained carbon equilibrium (CCE) criterion. The effects of high-temperature deformation (isothermal and non-isothermal) on the carbon enrichment of austenite, carbide formation, and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT) and scanning transmission electron microscopy (STEM). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples, it was significantly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the deformation-induced austenite-to-ferrite transformation (DIFT) phenomenon. By APT, the carbon accumulation at austenite/martensite interfaces was observed, with higher values for HSQ&P deformed isothermally (≈ 11 at. pct), when compared with non-isothermal HSQ&P (≈ 9.45 at. pct) and Q&P (≈ 7.6 at. pct). Moreover, a local Mn enrichment was observed in a ferrite/austenite interface, indicating ferrite growth under local equilibrium with negligible partitioning (LENP).