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Hamam H.,University of Moncton | Hamam H.,Canadian Institute of Technology
Physics Essays | Year: 2017

Time dilation is one of the consequences of special relativity (SR) or the special theory of relativity. For one given object (or person), time flows slower the faster the object travels. The object is traveling inside a system, whether the universe, the given galaxy, the solar system or even a smaller system. We will have two worlds: the world of the fast-moving object and another world, namely, the rest of the system, which is observed by the moving object as stationary. We may consider them as two worlds, since each has its own time running differently. Since one world is included in the other, both worlds interact with each other in many aspects, including energy, flow of material, pressure, and temperature to name few. Since energy (just like temperature and the flow of material) depends on time, the situation gives birth to a number of paradoxes. During the interaction between both worlds, which time should we refer to and, therefore, which energy, flow of material and temperature should we consider? Should we consider the time of World 1 (the fast moving object) or that of World 2 (the relatively stationary environment or system)? The present article illustrates these paradoxes through thought experiments and scenarios. In the end, we should either (1) find an explanation to these paradoxes within the framework of SR, (2) modify some aspects of SR or add more postulates to cover these paradoxes, or (3) abandon SR if neither (1) nor (2) is possible. © 2017 Physics Essays Publication.


Xhafa F.,Polytechnic University of Catalonia | Herrero X.,Polytechnic University of Catalonia | Barolli A.,Canadian Institute of Technology | Takizawa M.,Hosei University
Lecture Notes in Electrical Engineering | Year: 2013

Ground Station Scheduling arises in satellite mission planning and belongs to scheduling family with time windows. It is know for its high computational complexity and hardness to solve to optimality. In fact, in some cases it is even hard to find a feasible solution that satisfies all user requirements and resource constraints. In this paper we present a Hill Climbing (HC) algorithm for the problem, which is a fast local search algorithm. Despite of being a simple search method, HC showed a good performance for small size instance while could not cope with medium and large size instances. The Satellite Toolkit is used for its experimental study and performance evaluation. © 2013 Springer Science+Business Media Dordrecht.


Xhafa F.,Polytechnic University of Catalonia | Herrero X.,Polytechnic University of Catalonia | Barolli A.,Canadian Institute of Technology | Takizawa M.,Hosei University
Proceedings - 16th International Conference on Network-Based Information Systems, NBiS 2013 | Year: 2013

Among different versions of Satellite Scheduling, there is the Ground Station Scheduling, whose aim is mission allocation of ground stations to spacecrafts. This scheduling problem belongs to the family of scheduling with time windows, and besides complexities of classical scheduling problems, it has additional requirements that make it over-constrained and challenging to solve to optimality. In fact, in some cases it is even hard to find a feasible solution that satisfies all user requirements and resource constraints. As with other computationally hard combinatorial optimization problems, heuristic solutions are employed to find high quality solutions in reasonable amount of computation time. In this paper we present a Simulated Annealing (SA) algorithm for the problem, which is a local search based algorithm that simulates the cooling process by gradually lowering the temperature of the system until it converges to a stable state. The Satellite Toolkit is used for the experimental study and performance evaluation of the algorithm through a family of instances of small, medium and large sizes. Keywords: Ground station scheduling, Satellite scheduling, Simulated Annealing Algorithm, Constraint programming, Spacecrafts, Multi-objective Optimization, Satellite Simulation Toolkit. © 2013 IEEE.


Oda T.,Fukuoka Institute of Technology | Sakamoto S.,Fukuoka Institute of Technology | Spaho E.,Fukuoka Institute of Technology | Barolli A.,Canadian Institute of Technology | And 2 more authors.
Proceedings - 2013 8th International Conference on Broadband, Wireless Computing, Communication and Applications, BWCCA 2013 | Year: 2013

In this paper, we deal with connectivity and coverage problems of Wireless Mesh Networks (WMNs). Because these problems are known to be NP-Hard, we propose and implement a system based on GA. We call the proposed system: WMN-GA. We evaluate the performance of WMN-GA considering Giant Component and Covered Mesh Clients metrics. We evaluate and compare the performance of different initial router node placement methods in a wireless mesh network considering different distributions of mesh clients. Our WMN-GA System have a good behavior and can find the best initial router node placement methods for every distribution of mesh clients. © 2013 IEEE.


Barolli A.,Canadian Institute of Technology | Oda T.,Fukuoka Institute of Technology | BaroUi L.,Fukuoka Institute of Technology | Spaho E.,Canadian Institute of Technology | And 2 more authors.
Proceedings - 2013 8th International Conference on Broadband, Wireless Computing, Communication and Applications, BWCCA 2013 | Year: 2013

In this paper, we evaluate the performance of WMN-GA system for node placement problem in WMNs. For evaluation, we consider Weibull Distribution of mesh clients and different selection operators. The population size is considered 64 and the number of generation 200. For evaluation, we consider the giant component and the number of covered users metrics. The simulation results show that for small and medium grid sizes and big density of mesh clients WMN-GA performs better for Linear Ranking. For big grid sizes and low density of mesh clients WMN-GA performs better for Exponential Ranking. © 2013 IEEE.


Barolli A.,University of Tirana | Sakamoto S.,Canadian Institute of Technology | Sakamoto S.,Fukuoka Institute of Technology | Sakamoto S.,University of Barcelona | And 12 more authors.
Human-centric Computing and Information Sciences | Year: 2014

Wireless Mesh Networks (WMNs) distinguish for their low cost nature that makes them very attractive for providing wireless Internet connectivity. Such infrastructures can be used to deploy community networks, metropolitan area networks, municipal and corporative networks, and to support applications for urban areas, medical, transport and surveillance systems. The main issues in WMNs are achievement of network connectivity and stability as well as QoS in terms of user coverage. In this paper, we deal with the effect of changes in population size and number of generations for node placement problem in WMNs for Normal distribution of mesh clients. We consider two population sizes 8 and 512 and for every population size the number of generations are 200 and 20,000. As evaluation metrics we used size of giant component and number of covered users. The simulation results have shown that the increase of the population size results in better performance. Best results are obtained for the number of generation 20,000. However, when the number of generation is increased, the computation time is also increased. © 2014, Barolli et al.; licensee Springer.


Barolli A.,Canadian Institute of Technology | Oda T.,Fukuoka Institute of Technology | Xhafa F.,University of Barcelona | Barolli L.,Canadian Institute of Technology | And 3 more authors.
Lecture Notes in Electrical Engineering | Year: 2013

In this paper, we evaluate the performance of WMN-GA system for node placement problem in WMNs. For evaluation, we consider Weibull Distribution of mesh clients and different selection and mutation operators. The population size is considered 64 and the number of generation 200. For evaluation, we consider the giant component and the number of covered users metrics. The simulation results show that the WMN-GA system performs better for Single Mutation and Linear Ranking. © 2013 Springer Science+Business Media Dordrecht.


Barolli A.,Canadian Institute of Technology | Oda T.,Fukuoka Institute of Technology | Barolli L.,Fukuoka Institute of Technology | Xhafa F.,University of Barcelona | And 2 more authors.
Proceedings - 2013 7th International Conference on Complex, Intelligent, and Software Intensive Systems, CISIS 2013 | Year: 2013

In this paper, we evaluate the performance of WMN-GA system for node placement problem in WMNs. For evaluation, we consider Exponential and Uniform Distribution of mesh clients and different selection and mutation operators. The population size is considered 64 and the number of generation 200. For evaluation, we consider the giant component and the number of covered users metrics. The simulation results shows that the WMN-GA system performs better for Exponential distribution of mesh clients. © 2013 IEEE.


Oda T.,Fukuoka Institute of Technology | Barolli A.,Canadian Institute of Technology | Spaho E.,Fukuoka Institute of Technology | Barolli L.,Fukuoka Institute of Technology | Xhafa F.,University of Barcelona
Proceedings - 2013 7th International Conference on Complex, Intelligent, and Software Intensive Systems, CISIS 2013 | Year: 2013

In this paper, we evaluate the performance of WMN-GA system for node placement problem in WMNs. For evaluation, we consider Normal and Uniform Distribution of mesh clients and different grid shapes. The simulation results shows that grid shape effects in the performance of WMN-GA. With the increasing of grid size, the mesh routers can not cover all mesh clients in the grid size and the performance of the system is decreased. The system performs better for Normal distribution of mesh clients. © 2013 IEEE.


Xhafa F.,University of Barcelona | Herrero X.,University of Barcelona | Barolli A.,Canadian Institute of Technology | Takizawa M.,Hosei University
Proceedings - 2013 7th International Conference on Complex, Intelligent, and Software Intensive Systems, CISIS 2013 | Year: 2013

The satellite scheduling and its version of ground station scheduling are increasingly attracting the attention of researchers from aerospace and optimization domain. While in the recent past satellite mission arise from large aero-spacial agencies, nowadays even smaller companies are interested in satellite missions for basic tasks such as telemetry, imaging, remote sensing, etc. The ground station scheduling problem consists in computing an optimal planning of communications between satellites or spacecraft (SC) and operations teams of Ground Station (GS). The problem is highly complex and multi-objective and in its general formulation has been shown NP-hard. Therefore, its resolution is tackled by heuristic and meta-heuristic methods. Although heuristic and meta-heuristic methods are well understood, their evaluation for specific problems, like ground station scheduling, remain a challenge. The design and development of benchmarks of instances is thus needful to evaluate such methods and also to provide the community with means to reproduce the experimental study for the same benchmark under the same or different parameter setting. In this paper, we present an XML-based benchmark of instances for the ground station scheduling generated with the STK simulation toolkit. Then we show the experimental evaluation of a Basic Genetic Algorithm using the benchmark. © 2013 IEEE.

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