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Kaissas I.,Greek Atomic Energy Commission | Papadimitropoulos C.,Technological Educational Institute of Sterea Ellada | Karafasoulis K.,Hellenic Army Academy | Potiriadis C.,Greek Atomic Energy Commission | Lambropoulos C.P.,Technological Educational Institute of Sterea Ellada
Journal of Physics: Conference Series | Year: 2015

Several small gamma cameras for radioguided surgery using CdTe or CdZnTe have parallel or pinhole collimators. Coded aperture imaging is a well-known method for gamma ray source directional identification, applied in astrophysics mainly. The increase in efficiency due to the substitution of the collimators by the coded masks renders the method attractive for gamma probes used in radioguided surgery. We have constructed and operationally verified a setup consisting of two CdTe gamma cameras with Modified Uniform Redundant Array (MURA) coded aperture masks of rank 7 and 19 and a video camera. The 3-D position of point-like radioactive sources is estimated via triangulation using decoded images acquired by the gamma cameras. We have also developed code for both fast and detailed simulations and we have verified the agreement between experimental results and simulations. In this paper we present a simulation study for the spatial localization of two point sources using coded aperture masks with rank 7 and 19.


Alamaniotis M.,Purdue University | Bargiotas D.,Technological Educational Institute of Sterea Ellada | Bourbakis N.G.,Wright State University | Tsoukalas L.H.,Purdue University
IEEE Transactions on Smart Grid | Year: 2015

Price-directed demand in smart grids operating within deregulated electricity markets calls for real-time forecasting of the price of electricity for the purpose of scheduling demand at the nodal level (e.g., appliances, machines, and devices) in a way that minimizes energy cost to the consumer. In this paper, a novel hybrid methodology for electricity price forecasting is introduced and applied on a set of real-world historical data taken from the New England area. The proposed approach is implemented in two steps. In the first step, a set of relevance vector machines (RVMs) is adopted, where each RVM is used for individual ahead-of-time price prediction. In the second step, individual predictions are aggregated to formulate a linear regression ensemble, whose coefficients are obtained as the solution of a single objective optimization problem. Thus, an optimal solution to the problem is found by employing the micro-genetic algorithm and the optimized ensemble is employed for computing the final price forecast. The performance of the proposed methodology is compared with performance of autoregressive-moving-average and naïve forecasting methods, as well as to that taken from each individual RVM. Results clearly demonstrate the superiority of the hybrid methodology over the other tested methods with regard to mean absolute error for electricity signal pricing forecasting. © 2015 IEEE.


Vourdas N.,Technological Educational Institute of Sterea Ellada | Dalamagkidis K.,Technological Educational Institute of Sterea Ellada | Stathopoulos V.N.,Technological Educational Institute of Sterea Ellada
MATEC Web of Conferences | Year: 2016

Active control of droplet mobility through low cost tools is highly desirable in applications entailing microfluidics, Lab-on-Chip devices and pertinent technologies. Here, we present the design concepts of a versatile, low cost tool for dynamic droplet mobility manipulation, employing a scheme with backpressure application. Initially sticky open- or closed- channel fluidics with hydrophobic, porous walls are rendered slippery with the application of backpressure through the porous walls. Deliberate control of backpressure directs the wetting phenomena to the desired state. Operation parameters, and control system considerations are presented. Ultra-low backpressure values, are needed for channels with small cross-sections, which in turn are compatible with ultra-low energy demands. © Owned by the authors, published by EDP Sciences, 2016.


Sarafis P.,Technological Educational Institute of Sterea Ellada
Global journal of health science | Year: 2014

While medical ethics place a high value on providing truthful information to patients, disclosure practices are far from being the norm in many countries. Transmitting bad news still remains a big problem that health care professionals face in their every day clinical practice. Through the review of relevant literature, an attempt to examine the trends in this issue worldwide will be made. Various electronic databases were searched by the authors and through systematic selection 51 scientific articles were identified that this literature review is based on. There are many parameters that lead to the concealment of truth. Factors related to doctors, patients and their close environment, still maintain a strong resistance against disclosure of diagnosis and prognosis in terminally ill patients, while cultural influences lead to different approaches in various countries. Withholding the truth is mainly based in the fear of causing despair to patients. However, fostering a spurious hope, hides the danger of its' total loss, while it can disturb patient-doctor relationship.


Vourdas N.,Technological Educational Institute of Sterea Ellada | Tserepi A.,Institute of Microelectronics, Greece | Stathopoulos V.N.,Technological Educational Institute of Sterea Ellada
Applied Physics Letters | Year: 2013

We present a generic method to reversibly switch the mobility of a droplet after impingement onto a hydrophobic porous surface, from a sticky to a slippery state and back. By means of a pneumatic system, the backpressure of the porous medium is adjusted to favor the pressure balance towards the desired state. By applying overpressure above a certain threshold, the antiwetting pressures increase over the wetting pressures, which eventually results to a slippery state, while vacuum enhances the wetting pressures, thus, rendering the droplet sticky. This pressure-induced switching method is very flexible and can be applied even after decay of the hydrophobic character of the porous medium, does not entail the use of a superhydrophobic or hierarchical surface, and can be applied for actuation and valving in microfluidics. © 2013 AIP Publishing LLC.


Vourna P.,National Technical University of Athens | Ktena A.,Technological Educational Institute of Sterea Ellada | Tsakiridis P.E.,National Technical University of Athens | Hristoforou E.,National Technical University of Athens
Measurement: Journal of the International Measurement Confederation | Year: 2015

In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten Inert Gas, Plasma and Electron Beam were used as the welding methods. Residual stress was directly determined through deformation measurements and appropriate math calculations. Two methods were used: The magnetic, non-destructive method of Barkhausen noise and the semi-destructive method of X-ray diffraction. In order to evaluate accuracy and reliability of the magnetic method applied, the steel samples were subjected in both compressive and tensile stresses and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. The results were then verified by the XRD method. Then, these were further evaluated by examining the microstructure and mechanical properties of as received and welded samples by scanning electron microscopy and macrohardness measurements, respectively. It was found that the deviation between the two methods was within acceptable limits, thus implying potential applicability of the MBN method in non-destructive testing of materials. © 2015 Elsevier Ltd. All rights reserved.


Hatziefremidis A.,Technological Educational Institute of Sterea Ellada
International Conference on Transparent Optical Networks | Year: 2014

Nowadays Free Space Optical (FSO) systems are a promising approach for a variety of applications such as interconnection of network nodes and as rapidly deployable communication systems in disaster recovery situations. In particular deploying FSO technology for mobile links between Unmanned Aerial Vehicles (UAVs) and fixed Ground Stations (GS) introduces several interesting challenges. In this paper, we investigate the ability of a mobile FSO system to operate in different atmospheric conditions. Specifically, we report a detailed optical amplification model able to support a constant Quality of Service for different distances from 1 km up to 35 km at 10 Gbps with 1550 nm wavelength. A high power optical amplifier and a low noise optical amplifier with adaptive power controlled are proposed that are able to support different environment attenuation factors. An extensive analysis among different distances for the FSO configurations links considering the Bit Error Rate (BER), the Q factor, the received signal and noise is provided. © 2014 IEEE.


Vourdas N.,Technological Educational Institute of Sterea Ellada | Stathopoulos V.N.,Technological Educational Institute of Sterea Ellada
Technical Proceedings of the 2014 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2014 | Year: 2014

We present our work on the droplet actuation and mobility manipulation on hydrophobic porous medium. We use a porous medium under which the pressure is controlled (backpressure), thus ensuring a constant gas flow under the droplet. Different modes of droplet actuation are identified, depending on the droplet volume. For large droplets, movement is recorded upon bubble rupturing, while for smaller droplets a gas cushion is formed after a critical pressure value. The sliding angle of droplets with various volumes was measured for a range of backpressure values. The sliding angle, e.g. for a 50 μl droplet decreases from 22° to 0° when the backpressure increases to 0.800 bar. Application is demonstrated on a fluidic, thus providing an alternative means for valving.


Vourna P.,National Technical University of Athens | Ktena A.,Technological Educational Institute of Sterea Ellada | Tsakiridis P.E.,National Technical University of Athens | Hristoforou E.,National Technical University of Athens
NDT and E International | Year: 2015

In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten inert gas was used for the welding method. Residual stress was directly determined through deformation measurements and appropriate math calculations. Two methods were used: the magnetic, non-destructive method of Barkhausen noise and the semi-destructive method of X-ray diffraction. In order to evaluate the accuracy and reliability of the magnetic method applied, the steel samples were subjected to both compressive and tensile stresses and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. The results were then verified by the XRD method and were further evaluated by examining the microstructure and the mechanical properties of the as received and welded samples through scanning electron microscopy and hardness measurements, respectively. It was found that the deviation between the two methods was within acceptable limits, thus implying potential applicability of the MBN method in non-destructive testing of materials. © 2015 Elsevier Ltd.


Stathopoulos V.N.,Ceramics and Refractories Technological Development Company | Stathopoulos V.N.,Technological Educational Institute of Sterea Ellada | Papandreou A.,Ceramics and Refractories Technological Development Company | Kanellopoulou D.,Ceramics and Refractories Technological Development Company | Stournaras C.J.,Ceramics and Refractories Technological Development Company
Journal of Hazardous Materials | Year: 2013

In the present work the stabilization of electric arc furnace dust EAFD waste in structural clay ceramics was investigated. EAFD was collected over eleven production days. The collected waste was characterized for its chemical composition by Flame Atomic Absorption Spectroscopy. By powder XRD the crystal structure was studied while the fineness of the material was determined by a laser particle size analyzer. The environmental characterization was carried out by testing the dust according to EN12457 standard. Zn, Pb and Cd were leaching from the sample in significant amounts.The objective of this study is to investigate the stabilization properties of EAFD/clay ceramic structures and the potential of EAFD utilization into structural ceramics production (blocks). Mixtures of clay with 2.5% and 5% EAFD content were studied by TG/DTA, XRD, SEM, EN12457 standard leaching and mechanical properties as a function of firing temperature at 850, 900 and 950. °C. All laboratory facilities maintained 20. ±. 1. °C. Consequently, a pilot-scale experiment was conducted with an addition of 2.5% and 5% EAFD to the extrusion mixture for the production of blocks. During blocks manufacturing, the firing step reached 950. °C in a tunnel kiln. Laboratory heating/cooling gradients were similar to pilot scale production firing.The as produced blocks were then subjected to quality control tests, i.e. dimensions according to EN772-17, water absorbance according to EN772-6, and compressive strength according to EN772-1 standard, in laboratory facilities certified under EN17025. The data obtained showed that the incorporation of EAFD resulted in an increase of mechanical strength. Moreover, leaching tests performed according to the Europeans standards on the EAFD-block samples showed that the quantities of heavy metals leached from crushed blocks were within the regulatory limits. Thus the EAFD-blocks can be regarded as material of no environmental concern. © 2013 Elsevier B.V.

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