Distributed information-based guidance of multiple mobile sensors for urban target search

We present a framework for distributed mobile sensor guidance to locate and track a target inside an urban environment. Our approach leverages the communications between robots when a link is available, but it also allows them to act independently. Each robot actively seeks the target using information maximization. The robots are assumed to be capable of communicating with their peers within some distance radius, and the sensor payload of each robot is a camera modeled to have target detection errors of types I and II. Our contributions include an optimal information fusion algorithm for discrete distributions which allows each agent to combine its local information with that of its neighbors, and a path planner that uses the fused estimate and a recent coverage result for information maximization to guide the agents. We include simulations and laboratory experiments involving multiple robots searching for a moving target within model cities of different sizes.     

A fuzzy inference approach to template-based visual tracking

The tracking of visual features using appearance models is a well studied but still open area of computer vision. In the absence of knowledge about the structural constraints of the tracked object, the validity of the model can be compromised if only appearance information is used. We propose a fuzzy inference scheme that can be used to selectively update a given template-based model in tracking tasks. This allows us to track moving objects under translation, rotation, and scale changes with minimal feature drift. Moreover, no rigidity constraint needs to be enforced on the moving target. Some experiments have been performed using several targets, and the results are very close to the ground truth paths. The computational cost of our approach is low enough to allow its application in real-time tracking using modest hardware requirements.     

Microalgae growth-promoting bacteria as "helpers" for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater

A combination of microalgae (Chlorella vulgaris or C. sorokiniana) and a microalgae growth-promoting bacterium (MGPB, Azospirillum brasilense strain Cd), co-immobilized in small alginate beads, was developed to remove nutrients (P and N) from municipal wastewater. This paper describes the most recent technical details necessary for successful co-immobilization of the two microorganisms, and the usefulness of the approach in cleaning the municipal wastewater of the city of La Paz, Mexico. A. brasilense Cd significantly enhanced the growth of both Chlorella species when the co-immobilized microorganisms were grown in wastewater. A. brasilense is incapable of significant removal of nutrients from the wastewater, whereas both microalgae can. Co-immobilization of the two microorganisms was superior to removal by the microalgae alone, reaching removal of up to 100% ammonium, 15% nitrate, and 36% phosphorus within 6 days (varied with the source of the wastewater), compared to 75% ammonium, 6% nitrate, and 19% phosphorus by the microalgae alone. This study shows the potential of co-immobilization of microorganisms in small beads to serve as a treatment for wastewater in tropical areas.     

Arsenic accumulation and distribution in relation to young seedling growth in Atriplex atacamensis Phil.

Even at trace levels, arsenic is of environmental and health concern due to its high toxicity. The xerohalophyte plant species Atriplex atacamensis grows on an arsenic-contaminated mining area in North Chile. Young seedlings that were grown from seeds collected from these plants were grown in a nutrient solution under controlled environmental conditions and were exposed for 14 and 28 days to 0, 100 or 1000 μM arsenate. More than 75% of the plants that were exposed to the highest As dose survived until the end of the treatment. The seedling growth was reduced (100 μM As) or inhibited (1000 μM As) in the stress conditions, but the plants were able to efficiently close their stomata and perform osmotic adjustments to avoid secondary water stress. Arsenic accumulated up to 400 μg g^?1 DW in the shoots and 3500 μg g^?1 DW in the roots. Arsenate drastically impaired the P content and increased glycinebetaine content, although no arsenobetaine was found in the tissues. With the exception of arsenite and arsenate, no As-containing organic compound was detected. Arsenic was not excreted by the trichomes that were present at the leaf surface. Although an increase in the total level of non-protein thiols suggested that arsenite fixation on the sulfhydryl groups could occur in the stressed tissues, the majority of the soluble arsenic remained in its oxidized state As(V). Arsenate induced an increase in the free soluble polyamine concentrations in all of the organs, and it increased the proportion of spermidine and spermine and decreased the proportion of putrescine in the polyamine pool. Therefore, it is likely that these polycationic molecules may assist in arsenate sequestration in the stressed tissues, and A. atacamensis may represent a promising plant species that can be tested in field trials for its phytomanagement of As-contaminated sites in desert areas.     

Removal of ammonium and phosphorus ions from synthetic wastewater by the microalgae Chlorella vulgaris coimmobilized in alginate beads with the microalgae growth-promoting bacterium Azospirillum brasilense

Coimmobilization of the freshwater microalga Chlorella vulgaris in alginate beads with the microalgae growth-promoting bacterium Azospirillum brasilense under semi-continuous synthetic wastewater culture conditions significantly increased the removal of ammonium and soluble phosphorus ions compared to immobilization of the microalgae alone. In continuous or batch cultures removal of these ions followed a similar trend but was less efficient than in semi-continuous culture. It is proposed that coimmobilization of a microalgae with microalgae growth-promoting bacteria can serve as a tool in devising novel wastewater treatments.     

A switched-system approach to formation control and heading consensus for multi-robot systems

This paper proposes a novel, hybrid and decentralized, switched-system approach for formation and heading consensus control of mobile robots under switching communication topology, including collision avoidance capability. The set of robots consists of nonholonomic wheeled mobile robots and can include a teleoperated UAV. The key feature of this approach is a virtual graph, which is derived by adding a set of relative translation vectors to the real graph of the multiple robots. Our approach results in the robots in the real graph moving to the desired formation and achieving heading consensus while the virtual robots on the virtual graph reach pose consensus. If any robot detects a nearby obstacle or other robot, the robot will temporarily move along an avoidance vector, which is perpendicular and positively projected onto the attractive vector, such that collision is avoided while minimally deviating from its formation control path. Experimental results are provided by two different research groups to demonstrate the effectiveness of our approach. These experiments extend the theoretical development by introducing a teleoperated quadrotor as a leader robot of the multi-robot systems. The same control law works for the extended system, with no modifications.     

Effect of the medium characteristics and the heating and cooling rates on the nonisothermal heat resistance of Bacillus sporothermodurans IC4 spores

In recent years, highly thermo-resistant mesophilic spore-forming bacteria belonging to the species Bacillus sporothermodurans have caused non-sterility problems in industrial sterilization processes. The aim of this research was to evaluate the effect of the heating medium characteristics (pH and buffer/food) on the thermal inactivation of B. sporothermodurans spores when exposed to isothermal and non-isothermal heating and cooling treatments and the suitability of non-linear Weibull and Geeraaerd models to predict the survivors of these thermal treatments. Thermal treatments were carried out in pH 3, 5 and 7 McIlvaine buffer and in a courgette soup. Isothermal survival curves showed shoulders that were accurately characterized by means of both models. A clear effect of the pH of the heating medium was observed, decreasing the D₁₂₀ value from pH 7 to pH 3 buffer down to one third. Differences in heat resistance were similar, regardless of the model used and were kept at all temperatures tested. The heat resistance in courgette soup was similar to that shown in pH 7 buffer. When the heat resistance values obtained under isothermal conditions were used to predict the survival in the non-isothermical experiments, the predictions estimated the experimental data quite accurately, both with Weibull and Geeraerd models.