SOFTWARE TECHNOUW Rule handling in the day-to-day resource management problem: an object-oriented... more SOFTWARE TECHNOUW Rule handling in the day-to-day resource management problem: an object-oriented approach
Resource scheduling is a difficult and time consuming problem, especially when human resources ar... more Resource scheduling is a difficult and time consuming problem, especially when human resources are involved. The major reason of this difficulty emerges from the complexity and the dynamically changing nature of the regulations that restrict the solutions of problem. Constraint Logic Programming (CLP) is currently considered as the most powerful computational paradigm for stating and solving such problems. However, the statement of complex regulations is still extremely hard and results in a large semantic gap between the implied formalization and the problem regulations, as perceived by the end-user. Ideally, the end-user should be able to represent and modify directly the regulations, but since a high level formalism is not available, the interference of an expert programmer is always required. In this paper, we suggest an Object-Oriented meta-representation for the abstract, natural specification of regulations. With the target of obtaining an efficient scheduling system, we desc...
ABSTRACT A computer program can be represented by a Directed Acyclic Graph (DAG) in order to capt... more ABSTRACT A computer program can be represented by a Directed Acyclic Graph (DAG) in order to capture the dependencies between the individual tasks that should be executed each time the program runs. This paper proposes a mathematical model of Integer Programming that can be applied in order to schedule the tasks in the presence of multiple processors serving as the execution environment. The target is to minimize the overall execution time of the DAG known as schedule length or makespan. An approach called MATH using the full model is applied to small sized problems and then a more elaborate approach called MATHL is presented where the DAG is partitioned to levels. Levels are formed according to the hops needed for each node to be reached starting from the source node. Hence sub-problems have manageable size and can be solved in a timely manner. Consecutive optimal solutions for each level result in a high quality schedule for the overall problem even for cases consisting of several hundreds of nodes. Results show that this method constantly gives very good results and it is compared favorably with other approaches to the problem that can be found in the bibliography.
Abstract In electrical power systems, asset management procedures have developed into a central e... more Abstract In electrical power systems, asset management procedures have developed into a central element of network operations and planning. Hidden Markov models (HMM) can be used to transform various data collected from substation equipment into failure probabilities. Based on these failure probabilities a mathematical decision tool can be created, which could be used in system-level simulation and experimentation. In particular, collected data utilizing the dissolved gas analysis-in-oil (DGA) field methodology for transformers are ...
Abstract This paper describes a system that generates intelligent alarms using sensor data locate... more Abstract This paper describes a system that generates intelligent alarms using sensor data located at various geographical locations. Users are informed, using a rule enabled engine whenever certain conditions demanding attention occur, through an SMS messaging system. The user can easily define, through a graphical user interface, new rules or update existing ones. An agricultural case study of the system is presented.
Abstract In this paper, SchedSP, a middleware framework for providing scheduling solutions as ser... more Abstract In this paper, SchedSP, a middleware framework for providing scheduling solutions as services over the Internet, is presented. Emphasis is given on creating a reusable framework that facilitates the development of specialized clients for the input, output and control interfaces of the various scheduling applications. SchedSP manages the task of preparing and running the required processes and allows the application interface developer to focus on the functionality and efficiency of the interface. The Internet-based ...
International E-Conference of Computer Science 2006~ autofilled~
Abstract: Wireless Sensor Networks (WSN) are a module that can be added to any existing informati... more Abstract: Wireless Sensor Networks (WSN) are a module that can be added to any existing information system in order to extend it's capabilities by capturing and transmitting a dense amount of raw data from the application field back to a central computing system. Depending on the nature of the application, a known and measured level of security must be accomplished. Taking into account the fact that today's security approaches aggravate existing power limitations that are implied by WSN design, the need to establish an ...
Nurse rostering is an NP-hard combinatorial problem which makes it extremely difficult to efficie... more Nurse rostering is an NP-hard combinatorial problem which makes it extremely difficult to efficiently solve real life problems due to their size and complexity. Usually real problem instances have complicated work rules related to safety and quality of service issues in addition to rules about quality of life of the personnel. For the aforementioned reasons computer supported scheduling and rescheduling for the particular problem is indispensable. The specifications of the problem addressed were defined by the First International Nurse Rostering Competition (INRC2010) sponsored by the leading conference in the Automated Timetabling domain, PATAT-2010. Since the competition imposed quality and time constraint requirements, the problem instances were partitioned into sub-problems of manageable computational size and were then solved sequentially using Integer Mathematical Programming. A two phase strategy was implemented where in the first phase the workload for each nurse and for each day of the week was decided while in the second phase the specific daily shifts were assigned. In addition, local optimization techniques for searching across combinations of nurses’ partial schedules were also applied. This sequence is repeated several times depending on the available computational time. The results of our approach and the submitted software produced excellent solutions for both the known and the hidden problem instances, which in respect gave our team the first position in all tracks of the INRC-2010 competition.► Novel partitioning of the nurse rostering problem to sub-problems. ► Optimally solve sub-problems using mathematical programming. ► Combine mathematical programming and local search procedures. ► Excellent results for known data instances.
21st Mediterranean Conference on Control and Automation, 2013
ABSTRACT In this paper, we present a method for global motion planning of underwater vehicle mani... more ABSTRACT In this paper, we present a method for global motion planning of underwater vehicle manipulator systems (UVMS). The algorithm can derive a feasible path for UVMS equipped with an n-degree of freedom manipulator for performing autonomous underwater operations. The environment of the system is represented by a 4D Bump-surface that is used for obstacle avoidance. To improve the performance of the proposed method, the parallel calculation of the obstacle avoidance algorithm is considered, leading to a 46-230 times faster implementation using a Graphics Processing Unit. A path following task in an environment cluttered with obstacles is considered for the validation of the method, while a UVMS with a mounted 6-dof manipulator performs the task. Both parallel and serial approaches are evaluated and discussed.
ABSTRACT Results are presented for the conformational, thermodynamic, structural and solid-state ... more ABSTRACT Results are presented for the conformational, thermodynamic, structural and solid-state chain organization properties of the semifluorinated alkane F(CF2)12(CH2)12H (termed perfluorododecyldodecane and abbreviated as F12H12) from detailed, atomistic-level Molecular Dynamics and Monte Carlo simulations in the isothermal-isobaric ensemble using large simulation cells containing up to 144,000 atomistic units. To cope with the large requirements in CPU time accompanying the use of super-cells in our simulations, we identified the Monte Carlo subroutines with the largest demand in computational resources and took advantage of parallelization by multithreading on NVIDIA graphics processing units (GPUs) to improve code performance by almost one order of magnitude. Consistent simulation results for the most important properties of the system have been obtained from the two methods, especially at the higher temperatures where their predictions for the density, average square chain-end-to-end distance and dihedral angle distributions are indistinguishable (practically identical). Driven by experimental data that provide evidence for two first-order phase transitions in F12H12, we have further investigated its bulk-phase assembly by carrying out gradual cooling runs from an initial configuration of randomly distributed chains. For both methods, the study of the average-squared end-to-end molecular distance indicates that F12H12 molecules prefer to be aligned in ordered zones (lamellae), whereas the dihedral distributions exhibit a favorable trans state with decreasing temperature and/or increasing pressure, verifying the tendency of perfluorododecyldodecane to undergo a structural transition at these conditions. Both the Monte Carlo and the Molecular Dynamics simulation findings support a spontaneous transition of F12H12 from an isotropic phase to a smectic-like phase at a low enough temperature (close to T=315 K based on cooling experiments), at a pressure P=100 atm. Intermolecular pair distribution functions and atomistic configurational snapshots show that the simulated smectic phase consists of bilayer lamellae with a variety of directions, involving tilted and non-interdigitated chains. Experimentally, two solid phases are proposed for F12H12: a high-temperature one consisting of monolayer lamellae and a low temperature one consisting of bilayer lamellae with interdigitated hydrocarbon and fluorocarbon blocks. Despite that our simulations cannot unambiguously predict this second (lower-temperature) monolayer-to-bilayer solid-solid phase transition, they provide convincing evidence for the co-existence of many ordered lamellae in F12H12 below its melting point Tm both in monolayer and bilayer arrangements, with the relative population of bilayer ones increasing with decreasing temperature.
SOFTWARE TECHNOUW Rule handling in the day-to-day resource management problem: an object-oriented... more SOFTWARE TECHNOUW Rule handling in the day-to-day resource management problem: an object-oriented approach
Resource scheduling is a difficult and time consuming problem, especially when human resources ar... more Resource scheduling is a difficult and time consuming problem, especially when human resources are involved. The major reason of this difficulty emerges from the complexity and the dynamically changing nature of the regulations that restrict the solutions of problem. Constraint Logic Programming (CLP) is currently considered as the most powerful computational paradigm for stating and solving such problems. However, the statement of complex regulations is still extremely hard and results in a large semantic gap between the implied formalization and the problem regulations, as perceived by the end-user. Ideally, the end-user should be able to represent and modify directly the regulations, but since a high level formalism is not available, the interference of an expert programmer is always required. In this paper, we suggest an Object-Oriented meta-representation for the abstract, natural specification of regulations. With the target of obtaining an efficient scheduling system, we desc...
ABSTRACT A computer program can be represented by a Directed Acyclic Graph (DAG) in order to capt... more ABSTRACT A computer program can be represented by a Directed Acyclic Graph (DAG) in order to capture the dependencies between the individual tasks that should be executed each time the program runs. This paper proposes a mathematical model of Integer Programming that can be applied in order to schedule the tasks in the presence of multiple processors serving as the execution environment. The target is to minimize the overall execution time of the DAG known as schedule length or makespan. An approach called MATH using the full model is applied to small sized problems and then a more elaborate approach called MATHL is presented where the DAG is partitioned to levels. Levels are formed according to the hops needed for each node to be reached starting from the source node. Hence sub-problems have manageable size and can be solved in a timely manner. Consecutive optimal solutions for each level result in a high quality schedule for the overall problem even for cases consisting of several hundreds of nodes. Results show that this method constantly gives very good results and it is compared favorably with other approaches to the problem that can be found in the bibliography.
Abstract In electrical power systems, asset management procedures have developed into a central e... more Abstract In electrical power systems, asset management procedures have developed into a central element of network operations and planning. Hidden Markov models (HMM) can be used to transform various data collected from substation equipment into failure probabilities. Based on these failure probabilities a mathematical decision tool can be created, which could be used in system-level simulation and experimentation. In particular, collected data utilizing the dissolved gas analysis-in-oil (DGA) field methodology for transformers are ...
Abstract This paper describes a system that generates intelligent alarms using sensor data locate... more Abstract This paper describes a system that generates intelligent alarms using sensor data located at various geographical locations. Users are informed, using a rule enabled engine whenever certain conditions demanding attention occur, through an SMS messaging system. The user can easily define, through a graphical user interface, new rules or update existing ones. An agricultural case study of the system is presented.
Abstract In this paper, SchedSP, a middleware framework for providing scheduling solutions as ser... more Abstract In this paper, SchedSP, a middleware framework for providing scheduling solutions as services over the Internet, is presented. Emphasis is given on creating a reusable framework that facilitates the development of specialized clients for the input, output and control interfaces of the various scheduling applications. SchedSP manages the task of preparing and running the required processes and allows the application interface developer to focus on the functionality and efficiency of the interface. The Internet-based ...
International E-Conference of Computer Science 2006~ autofilled~
Abstract: Wireless Sensor Networks (WSN) are a module that can be added to any existing informati... more Abstract: Wireless Sensor Networks (WSN) are a module that can be added to any existing information system in order to extend it's capabilities by capturing and transmitting a dense amount of raw data from the application field back to a central computing system. Depending on the nature of the application, a known and measured level of security must be accomplished. Taking into account the fact that today's security approaches aggravate existing power limitations that are implied by WSN design, the need to establish an ...
Nurse rostering is an NP-hard combinatorial problem which makes it extremely difficult to efficie... more Nurse rostering is an NP-hard combinatorial problem which makes it extremely difficult to efficiently solve real life problems due to their size and complexity. Usually real problem instances have complicated work rules related to safety and quality of service issues in addition to rules about quality of life of the personnel. For the aforementioned reasons computer supported scheduling and rescheduling for the particular problem is indispensable. The specifications of the problem addressed were defined by the First International Nurse Rostering Competition (INRC2010) sponsored by the leading conference in the Automated Timetabling domain, PATAT-2010. Since the competition imposed quality and time constraint requirements, the problem instances were partitioned into sub-problems of manageable computational size and were then solved sequentially using Integer Mathematical Programming. A two phase strategy was implemented where in the first phase the workload for each nurse and for each day of the week was decided while in the second phase the specific daily shifts were assigned. In addition, local optimization techniques for searching across combinations of nurses’ partial schedules were also applied. This sequence is repeated several times depending on the available computational time. The results of our approach and the submitted software produced excellent solutions for both the known and the hidden problem instances, which in respect gave our team the first position in all tracks of the INRC-2010 competition.► Novel partitioning of the nurse rostering problem to sub-problems. ► Optimally solve sub-problems using mathematical programming. ► Combine mathematical programming and local search procedures. ► Excellent results for known data instances.
21st Mediterranean Conference on Control and Automation, 2013
ABSTRACT In this paper, we present a method for global motion planning of underwater vehicle mani... more ABSTRACT In this paper, we present a method for global motion planning of underwater vehicle manipulator systems (UVMS). The algorithm can derive a feasible path for UVMS equipped with an n-degree of freedom manipulator for performing autonomous underwater operations. The environment of the system is represented by a 4D Bump-surface that is used for obstacle avoidance. To improve the performance of the proposed method, the parallel calculation of the obstacle avoidance algorithm is considered, leading to a 46-230 times faster implementation using a Graphics Processing Unit. A path following task in an environment cluttered with obstacles is considered for the validation of the method, while a UVMS with a mounted 6-dof manipulator performs the task. Both parallel and serial approaches are evaluated and discussed.
ABSTRACT Results are presented for the conformational, thermodynamic, structural and solid-state ... more ABSTRACT Results are presented for the conformational, thermodynamic, structural and solid-state chain organization properties of the semifluorinated alkane F(CF2)12(CH2)12H (termed perfluorododecyldodecane and abbreviated as F12H12) from detailed, atomistic-level Molecular Dynamics and Monte Carlo simulations in the isothermal-isobaric ensemble using large simulation cells containing up to 144,000 atomistic units. To cope with the large requirements in CPU time accompanying the use of super-cells in our simulations, we identified the Monte Carlo subroutines with the largest demand in computational resources and took advantage of parallelization by multithreading on NVIDIA graphics processing units (GPUs) to improve code performance by almost one order of magnitude. Consistent simulation results for the most important properties of the system have been obtained from the two methods, especially at the higher temperatures where their predictions for the density, average square chain-end-to-end distance and dihedral angle distributions are indistinguishable (practically identical). Driven by experimental data that provide evidence for two first-order phase transitions in F12H12, we have further investigated its bulk-phase assembly by carrying out gradual cooling runs from an initial configuration of randomly distributed chains. For both methods, the study of the average-squared end-to-end molecular distance indicates that F12H12 molecules prefer to be aligned in ordered zones (lamellae), whereas the dihedral distributions exhibit a favorable trans state with decreasing temperature and/or increasing pressure, verifying the tendency of perfluorododecyldodecane to undergo a structural transition at these conditions. Both the Monte Carlo and the Molecular Dynamics simulation findings support a spontaneous transition of F12H12 from an isotropic phase to a smectic-like phase at a low enough temperature (close to T=315 K based on cooling experiments), at a pressure P=100 atm. Intermolecular pair distribution functions and atomistic configurational snapshots show that the simulated smectic phase consists of bilayer lamellae with a variety of directions, involving tilted and non-interdigitated chains. Experimentally, two solid phases are proposed for F12H12: a high-temperature one consisting of monolayer lamellae and a low temperature one consisting of bilayer lamellae with interdigitated hydrocarbon and fluorocarbon blocks. Despite that our simulations cannot unambiguously predict this second (lower-temperature) monolayer-to-bilayer solid-solid phase transition, they provide convincing evidence for the co-existence of many ordered lamellae in F12H12 below its melting point Tm both in monolayer and bilayer arrangements, with the relative population of bilayer ones increasing with decreasing temperature.
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Papers by E. Housos