Charalampos Stergiopoulos

Using New Technologies for Teaching Power Electronics and Assessing Students

In the Technological Educational Institution (T.E.I.) of Athens, new technologies are used for teaching electronic engineering modules for some time. This work presents the teaching of the module of power electronics by introducing a number of new methods. The educational portal, software simulations and electronic examinations support the teaching process and finally evaluate knowledge assimilation. Features and advantages of their implementation are presented and discussed

Unified Platform for M2M Virtual Object Interoperability

Sensor networks contribute to the interconnection of a large variety of devices (i.e. transducers, sensors, actuators) thus, enable monitoring and control processes. While new wireless technologies are emerging, a major issue of interoperability has to be addressed in terms of data communications, controlling and interfacing in order to confront the heterogeneity of networks and connected devices and enable end-to-end communication, as well as efficient resource management. A proposed solution to this problem is the provision of a unified service access architecture, which will support common interfaces for data communications, as well as device management and control that will be based on open standards. The concept of object virtualization and IP based networking is introduced for resolving interoperability issues. In this context, the architecture can serve applications that are in line with Machine-to-Machine (M2M) and Internet-of-Things (IoT) concepts.

The Use of PSC Technique to Estimate the Damage Extension During Three Point Bending Test

It is already known that when a mechanical loading is applied to cement-based specimens weak electrical currents are generated. Their existence is attributed to the creation of cracks and the eventual evolution of the cracks’ network in the bulk of the specimen. This work introduces the simultaneous recording of electrical signal emissions at both the tension and the compression region of cement mortar beams of rectangular cross-section that were subjected to mechanical loading using the Three-Point-Bending technique. During the experiments the behavior of the electrical signal was studied during four sequential load stages: (1) Abrupt load increase up to the vicinity of 3 PB strength, (2) maintaining the high load level for relatively long time, (3) abrupt load decrease to a low load level (i.e. 50 % of the 3 PB strength approximately), (4) maintaining the low load level for relatively long time. The electrical signal analysis was conducted using non extensive statistical physics (NESP) and specifically the Tsallis entropy model studying the values of its q-parameter. The aim of this work was to study the electrical signal relaxation process that follows the change of the mechanical load and the law that describes this relaxation with respect to the mechanical status of the specimen using statistical physics analysis.

Comparing Multiple-Choice and Constructed Response Questions Applied to Engineering Courses

A study was performed on the comparison of multiple-choice questions (MCQs) and constructed-response questions (CRQs) in terms of objective grading. A CRQ exam is graded by a tutor though an MCQ is automatically graded. An MCQs drawback is the infiltration of the “guessing” factor during selection thus producing unreliable results that do not reflect students’ knowledge. To eliminate this problem MCQs pairs were composed that addressed the same topic. A student who did not possess adequate knowledge could not tell this similarity. A group of undergraduate students enrolled to the “project management” module were examined. A software for electronic examinations was used during the process. A statistical evaluation was performed in order to check whether there was statistically significant difference between the scores provided using CRQs and MCQs. By applying a suitable scoring rule to the MCQs, very similar results are obtained when compared to those of the CRQs examination.

A WiMAX Network Architecture Based on Multi-Hop Relays

It has become apparent in the recent years that in order for the next generation of wireless technology (whether this is WiMAX, LTE or any other 4G implementation) to be able to deliver ubiquitous broadband content, the network is required to provide excellent coverage, both outdoor and indoor, and significantly higher bandwidth per subscriber [Voudouris et al., 2009]. In order to achieve that at frequencies above 2 and 3 GHz, which are targeted for future wireless technologies, network architecture must reduce significantly the cell size or the distance between the network and subscribers’ antennas. While micro, pico and femto Base Transceiver Station (BTS) technologies reduce the cost of base-station equipment, they still rely on a dedicated backhaul. One solution introduced with the WiMAX 802.16j standard is the wireless Multi-hop Relay Station (MRS), intended to overcome these challenges. On one hand, it should be small, cost-effective and easy to install for enabling mass deployment in indoor and outdoor environments and creating relatively small areas with excellent coverage and high capacity availability. On the other hand, it does not require any dedicated backhaul equipment as it receives its capacity from centralized base-stations via the same resources used for the access service. In a setting where a MRS exists, enabling MIMO transmission, the link referred to needs to be specified. This means that, when a 2x2 setting is mentioned, there can be either two transmit antennas on the base station and two receive antennas on the relay station, or two transmit antennas on the relay station and two receive antennas on the subscriber’s device [Chochliouros et al., 2009].Wireless Multi-hop Relay Stations (MRSs), when deployed in various sights, result in increased throughput or coverage. A general case, where a relay station can be used, is in situations with coverage constraints such as areas where there is presence of physical obstacles (e.g. buildings, forests), or in indoor coverage cases. Some examples are large office buildings, University campuses, and villages in unreachable areas on rockier uplands etc. Another scenario, where MRSs can be used, is for high mobility users with increased bandwidth requirements, such as trains with a great number of wireless users. Such a mobile subscriber will more likely have data rate degradations due to non-fixed position. In this case, a relay station can be considered as the most feasible solution in terms of cost and

An adaptive soft-sensor for non-destructive cement-based material testing, through the use of RBF networks

This paper presents the development of a soft-sensor receiving as inputs Pressure Stimulated Current (PSC) characteristics in order to predict a critical mechanical property of cement-based materials, in a non-destructive manner. The soft-sensor is based on a Radial Basis Function (RBF) network that starts with an empty hidden layer and evolves its structure and synaptic weights as new data become available. Results have shown that the proposed approach can be used successfully to evolve a predictive tool based on input-output data, whereas it is superior compared to other adaptive modeling techniques.