N,N′-alkylated Imidazolium-Derivatives Act as Quorum-Sensing Inhibitors Targeting the Pectobacterium atrosepticum-Induced Symptoms on Potato Tubers

Bacteria belonging to the Pectobacterium genus are the causative agents of the blackleg and soft-rot diseases that affect potato plants and tubers worldwide. In Pectobacterium, the expression of the virulence genes is controlled by quorum-sensing (QS) and N-acylhomoserine lactones (AHLs). In this work, we screened a chemical library of QS-inhibitors (QSIs) and AHL-analogs to find novel QSIs targeting the virulence of Pectobacterium. Four N,N′-bisalkylated imidazolium salts were identified as QSIs; they were active at the μM range. In potato tuber assays, two of them were able to decrease the severity of the symptoms provoked by P. atrosepticum. This work extends the range of the QSIs acting on the Pectobacterium-induced soft-rot disease.     

Perceptions of Antarctic tourism: A question of tolerance

Perceptions of tourism held by a sample of New Zealand's Antarctic community are explored, and the small, mixed group of scientists and support workers that populate Scott Base (New Zealand's research base in the Ross Dependency, Antarctica) are treated as proxy for a ‘host’ community. This exploration is part of a wider study that set out to investigate the nature and meanings of Antarctic heritage. Although the research did not explicitly set out to survey perceptions of tourism, approximately one-half of those interviewed in the wider study gave an insight into this topic. The qualitative data reported were gathered during two visits to Scott Base in 1999. From the responses a three-fold classification was derived, indicating degrees of tolerance toward tourism: cautious, complex and comfortable tolerance.     

Natural silica fiber as reinforcing filler of nylon 6

Short silica fiber (SF) content on the mechanical and morphological properties of composites based on nylon 6 and rubber-toughened nylon 6 matrices was examined. Binary nylon 6/SF and ternary [nylon 6/EPDM-g-MA (ethylene–propylene–diene grafted with maleic anhydride)/SF] composites containing 0–20 wt% SF were formulated. The flexural modulus increased with the SF content at all fiber compositions investigated; however, the value of this property gradually diminished when 20 wt% rubber was added to the polymer. Notched Izod impact strength of 80/20 nylon 6/EPDM-g-MA blend was reduced up to 50% with the addition of 5 wt% SF. However, these composites still retained good stiffness and toughness and presented a good interfacial adhesion between the phases. The results suggest that silica fibers can be employed as an alternative reinforcement of nylon 6 matrices, resulting in materials with useful properties.     

Thinking about Antarctic Heritage: Kaleidoscopes and filters

The preliminary results of a project that is currently investigating the nature and range of meanings of Antarctic heritage are explored. The project involves two visits to Scott Base, and the subjects of the qualitative research are the members of the New Zealand Antarctic community. Work so far suggests that different meanings do exist, and a four-fold typology of meanings is suggested which needs to be considered in decisions affecting the future of Antarctica.     

Thermo-reversible sol–gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol–gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 °C of titanium tetraisopropoxide (Ti(OⁱPr)₄) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 °C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of ≈2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the thermo-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between –SO₃ groups of p-toluene sulfonic acid.     

Investigating Strategies of an Irrigation Conflict

The understanding and modeling of human behavior in conflict situations is a challenge that researches investigate by developing, modifying and applying computational models. This paper aims to analyze how changes in the strategies of the various groups involved in a water use conflict can influence the decision process. The case study is an irrigation system supplied by a main canal in Rio de Janeiro State, Southeastern Brazil. Conflicts arise due to hydraulic constraints of the canal, resulting in water unavailability for some irrigators or damage to potentially irrigable lands caused by adjacent floods. The investigation strategy has been developed, considering three groups of irrigators. They can be geographically identified over the main canal’s hydrographical limits. Six different scenarios are considered to analyze the conflict. These scenarios are built taking into account six different policies of water conveyance. Additionally, the decision of the state government related to water charging has been considered. The final decision is taken by the management institution of the canal which also has two different tendencies: to opt for the scenarios providing highest net profits or to be impartial in the final decision. The Graph Model for Conflict Resolution, which solves non-cooperative games based on graph theory, was adopted to evaluate all these strategies. The results show that, according to the level of exigency of irrigator groups, state government and management institution, the conflict can in fact, be resolved.     

Model and heuristic for a generalized access network design problem

The generalized access network design problem consists of finding a topology, capacity assignment and routing that minimize the sum of costs to connect every pair of remote unit and its central node specified by the telecommunication company. We consider an integer programming formulation with a partial multicommodity structure. We analyze some aspects and extensions of the proposed model and we introduce a heuristic based on Lagrangian relaxation and the subgradient method. We report computational results for a set of randomly generated test problems. They include networks with up to 300 nodes and show that even problem instances defined in small networks can be extremely difficult problems. The heuristic generates effective and acceptable designs from the practical point of view. We compare our heuristic with a commercial code. This revised version was published online in June 2006 with corrections to the Cover Date.     

Energy Evaluation for Ramberg–Osgood Hysteretic Model

Response of structures to static and dynamic loads may be assessed in terms of energy. The energy evaluation depends on hysteretic models used to describe inelastic behavior of structures and their elements. One of the hysteretic models often employed in structural analysis is the Ramberg–Osgood model. In the paper a physically motivated model, which leads to the Ramberg–Osgood force–displacement relationship under monotonic loading and exhibits Masing type of behavior for unloading/reloading, is described. Based on the model formulas to calculate recoverable elastic strain energy and irrecoverable hysteretic energy for systems/elements under monotonic loading are derived. It is also shown how recoverable elastic strain energy and irrecoverable hysteretic energy can be evaluated at any point of unloading/reloading curves for a system/element of Masing type. The application of the derived formulas is illustrated by evaluating the energy of a single-degree-of-freedom system subjected to impulse and seismic loading.     

Optical Spectra of Arsenic Chalcogenide Glasses over a Wide Energy Range of Fundamental Absorption

The complete sets of the spectra of optical fundamental functions for vitreous arsenic chalcogenides in the energy range 0–40 eV are compared for the first time. The general features of the spectra and their dependence on the nature of the chalcogen anion are revealed.