A Polynomial Interval Shortest-Route Algorithm for Acyclic Network
Hossain M. Akter
Key Words:
Interval; interval shortest-route problem; interval algorithm; uncertainty.
Abstract:
A method and algorithm is presented for solving the shortest-route problem. New algorithm is applicable to the case when the generalized length (distance, cost, time, etc.) associated with each arc is nonnegative, interval or real. An interval algorithm is developed on the base of midpoint and half-width representation of intervals and the new algorithm is more efficient than the interval algorithm that could be proposed by using traditional interval description. The complexity of the new algorithm is evaluated.

Simulation Model of Risk for Participants in the Movement through Level Crossing
Ts. Simeonova, E. Ivanov
Key Words:
Individual risk; hazard; exploitation; ensure systems.
Abstract:
A block diagram has been developed based on a simulation model for the assessment of individual risk, taking into account the influence of the insuring systems of the level crossing. A detailed description of the model's segments is made: rail, road vehicles and pedestrians, automatic crossing devices of level crossing, dangers, realized hazards (incidents), consequences of incidents. In order to describe it we take into consideration the existing connections before level crossing area traffic lights with a barrier and adopted the level crossing hazards, which allow the possibility for improper passing (circumvent of the half-barrier) the level crossing by the road vehicles and pedestrians. The simulation model has allowed to study the dependencies of the influencing parameters on individual risk.

Social Networks as a Virtual Teaching and Learning Environment in Higher Education
B. Cubukcuoglu, A. Elci
Key Words:
Social networks; Technology Enhanced Learning; preservice teacher education; higher education; student engagement.
Abstract:
Over the last two decades, technology infused into education in various creative ways. One of them is using virtual learning environments. This research investigates pre-service teachers' use of social networks to support their learning in the classroom. It is anticipated that this research may provide an opportunity for educators and researchers to discover a pedagogical use of social networks for teacher education in developing countries by analysing the weaknesses and shortcomings of the matter. Social networks, when used efficiently, could be beneficial for students and teachers. A mix method research was used in discovering students' use of social networks. The data was collected through pre- and post-surveys and followed by semi-structured interviews. It is stipulated that social networks can be used as a supportive virtual learning environment where the role of teacher and student can be reversed time to time. Students benefitted from using social networks and were engaged in learning through networking with peers and teachers. Although sustainability of the network was not achieved, its effects on connection, collaboration, and communication among all are appreciated.

Classifications' Constructing by Means of a Task-Oriented Environment
I. Zheliazkova, A. Borodzhieva
Key Words:
Classification; constructing; task; UML project; implementation; teacher's tool; preliminary study.
Abstract:
Classifications are frequently used declarative knowledge units that facilitate understanding different subject concepts by professionals and researchers. Almost each lecture course includes different classifications so their effective teaching and learning by means of special purpose applications is of research interest. The current paper deals with a Task-Oriented Environment for Constructing Classifications to support both teacher and learner. An ontology model of a task for this purpose and mining its pedagogical parameters from teacher's and learner's side are proposed. The results of a preliminary study for verification of the proposed metrics are also discussed.

A Method for Balanced Truncation of Singular Systems
K. Perev
Key Words:
Singular or descriptor variable system; model order reduction; approximation by residualization; approximation by balanced truncation.
Abstract:
This paper considers the problem of balanced model reduction for singular systems. The proposed method uses the second canonical form description of the singular or descriptor variable system represented as a combination of dynamic and static equations. The static equations are considered as constraints over the system variables. The method is performed in two steps. First, singular perturbation approximation is used in order to solve for the fast variables in the singular system. These variables are substituted into the dynamical equations representing a regular state space model. Second, balanced truncation on the state space model is performed to reduce the system order. Three special cases are considered depending on the singularity of one of the system block matrices. Different experiments are performed for all three cases showing good approximation properties of the method.