Anti-pheromone as a tool for better exploration of search space

Many animals use chemical substances known as pheromones to induce behavioural changes in other members of the same species. The use of pheromones by ants in particular has lead to the development of a number of computational analogues of ant colony behaviour including Ant Colony Optimisation. Although many animals use a range of pheromones in their communication, ant algorithms have typically focused on the use of just one, a substance that encourages succeeding generations of (artificial) ants to follow the same path as previous generations. Ant algorithms for multi-objective optimisation and those employing multiple colonies have made use of more than one pheromone, but the interactions between these different pheromones are largely simple extensions of single criterion, single colony ant algorithms. This paper investigates an alternative form of interaction between normal pheromone and anti-pheromone. Three variations of Ant Colony System that apply the anti-pheromone concept in different ways are described and tested against benchmark travelling salesman problems. The results indicate that the use of anti-pheromone can lead to improved performance. However, if anti-pheromone is allowed too great an influence on ants' decisions, poorer performance may result

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Ant colony optimisation and local search for bin-packing and cutting stock problems

The Bin Packing Problem and the Cutting Stock Problem are two related classes of NP-hard combinatorial optimization problems. Exact solution methods can only be used for very small instances, so for real-world problems, we have to rely on heuristic methods. In recent years, researchers have started to apply evolutionary approaches to these problems, including Genetic Algorithms and Evolutionary Programming. In the work presented here, we used an ant colony optimization (ACO) approach to solve both Bin Packing and Cutting Stock Problems. We present a pure ACO approach, as well as an ACO approach augmented with a simple but very effective local search algorithm. It is shown that the pure ACO approach can compete with existing evolutionary methods, whereas the hybrid approach can outperform the best-known hybrid evolutionary solution methods for certain problem classes. The hybrid ACO approach is also shown to require different parameter values from the pure ACO approach and to give a more robust performance across different problems with a single set of parameter values. The local search algorithm is also run with random restarts and shown to perform significantly worse than when combined with ACO

Growth performance, cleanliness and lameness of finishing Charolais bulls housed in littered pens of different design

The fattening of beef cattle in Italy is mainly carried out under intensive rearing conditions. The main features of the Italian beef farms are the high stocking rate and the loose housing of the animals in multiple pens indoors. The pen with fully slatted floor is the most frequent housing solution because it does not require any bedding material and it has a lower labour cost to remove slurry

Sensor networks security based on sensitive robots agents. A conceptual model

Multi-agent systems are currently applied to solve complex problems. The security of networks is an eloquent example of a complex and difficult problem. A new model-concept Hybrid Sensitive Robot Metaheuristic for Intrusion Detection is introduced in the current paper. The proposed technique could be used with machine learning based intrusion detection techniques. The new model uses the reaction of virtual sensitive robots to different stigmergic variables in order to keep the tracks of the intruders when securing a sensor network.Comment: 5 page

Parallel formation of differently sized groups in a robotic swarm

Swarm robotics is a branch of collective robotics focused on the study of relatively large groups of robots with limited sensing and communication capabilities. One of the main benefits of such systems is their potential for parallelism. To achieve parallelism in real-world scenarios, it is important to be able to split the swarm into appropriately sized groups for different concurrent tasks

A 20-year experience with surgical management of true and false internal carotid artery aneurysms

Aim of the study: The aim of this study was to retrospectively analyse early and late results of surgical management of internal carotid artery (ICA) true and false aneurysms in a single-centre experience. Materials and methods: From January 1988 to December 2011, 50 consecutive interventions for ICA aneurismal disease were performed; interventions were performed for true ICA aneurysm in 19 cases (group 1) and for ICA post-carotid endarterectomy (CEA) pseudo-aneurysm in the remaining 31 (group 2). Early results (<30 days) were evaluated in terms of mortality, stroke and cranial nerves' injury and compared between the two groups with χ2 test. Follow-up results (stroke free-survival, freedom from ICA thrombosis and reintervention) were analysed with Kaplan-Meier curves and compared with log-rank test. Results: All the patients in group 1 had open repair of their ICA aneurysm; in group 2 open repair was performed in 30 cases, while three patients with post-CEA aneurysm without signs of infection had a covered stent placed. There were no perioperative deaths. Two major strokes occurred in group 1 and one major stroke occurred in group 2 (p = 0.1). The rates of postoperative cranial nerve injuries were 10.5% in group 1 and 13% in group 2 (p = 0.8). Median duration of follow-up was 60 months (range 1-276). Estimated 10-year stroke-free survival rates were 64% in group 1 and 37% in group 2 (p = 0.4, log rank 0.5); thrombosis-free survival at 10 years was 66% in group 1 and 34% in group 2 (p = 0.2, log rank 1.2), while the corresponding figures in terms of reintervention-free survival were 68% and 33%, respectively (p = 0.2, log rank 1.8). Conclusions: Surgical treatment of ICA aneurismal disease provided in our experience satisfactory early and long-term results, without significant differences between true and false aneurysms. In carefully selected patients with non-infected false aneurysm, the endovascular option seems to be feasible.© 2012 European Society for Vascular Surgery

Comparison between Aorto-bifemoral Bypass and Aorto-iliac Kissing Stent in Patients with Complex Aorto-iliac Obstructive Disease

Introduction: To retrospectively compare early and late results of aorto-bifemoral bypass and endovascular recanalization with the kissing stent technique in the management of TASC II C and D lesions in the aorto-iliac district in a multicentre study. Methods: From January 2006 to December 2013, 293 open and endovascular interventions for TASC-II class C and D aorto-iliac obstructive lesions were performed at three Italian teaching hospitals. In 210 patients the intervention was performed for aortic and bilateral iliac involvement: an aorto-bifemoral bypass was performed in 82 patients (Group 1) while in the remaining 128 an endovascular recanalization with the kissing stent technique (Group 2). Early results in the two groups were compared with \u3c72 test. Follow up results were analyzed with Kaplan-Meyer curves and compared with log rank test. Results: There were no differences between the two groups in terms of demographic data, comorbidities, or risk factors for atherosclerosis, except for a higher percentage of females and of diabetic patients in group 2. Critical limb ischemia was present in 29 patients in group 1 (35.5%) and in 31 patients in group 2 (24%, p = 0.07). Technical success in group 2 was 98.5%; two patients required immediate conversion to open surgery for iliac rupture. There was one peri-operative death in group 1 (mortality rate 1.2%, p = 0.2 in comparison with group 2). Four peri-operative thromboses occurred; two in group 1 and two in group 2 (in one case requiring conversion to open surgical intervention) and no amputations at 30 days were recorded. Post-operative local and systemic complications occurred in 20 patients in group 1 (24%) and in 13 patients in group 2 (10% p = 0.006). Mean duration of follow up was 39 months (range 1 \u2013108 months). Survival rates at 6 years were 65% (SE 0.07) in group 1 and 82% (SE 0.05) in group 2 (p = 0.07). At the same time interval, primary, assisted primary and secondary patency rates were similar; re-intervention rates were 6% in group 1 (SE 0.05) and 11% in group 2 (SE 0.04; p = 0.2). Conclusion: Endovascular repair of complex aorto-iliac lesions with the kissing stent technique, in the multicentre experience, provided similar satisfactory early and late results to those obtained with open surgery, however with a lower rate of peri-operative complications and a trend towards better long-term survival