Bikos A.N.,University of Patras |
Sklavos N.,Technological Educational Institute of Patra
IEEE Security and Privacy | Year: 2013
The authors give an overview on the state of the art of potential security issues that occur in the deployment of the LTE/SAE (Long-Term Evolution/System Architecture Evolution) protocol in emerging 4G wireless technologies. Although security concerns and challenges in wireless networks will remain a hot topic in the future, the LTE/SAE standard could adapt to these rising challenges, becoming more robust and secure. By looking at the authentication and ciphering algorithms, such as EAP-AKA (Extensible Authentication Protocol for Authentication and Key Agreement), currently operating within the LTE protocol, the authors analyze several vulnerabilities in LTE/SAE security architecture-specifically, insecure AKA key derivation procedures and the lack of fast reauthentications during handovers. © 2003-2012 IEEE.
Karageorgopoulos D.,Technological Educational Institute of Patra |
Karageorgopoulos D.,University of Patras |
Stathatos E.,Technological Educational Institute of Patra |
Vitoratos E.,University of Patras
Journal of Power Sources | Year: 2012
Thin transparent ZnO nanocrystalline films are prepared through a novel facile method based on an amino double edged polypropylene oligomer and zinc precursor. While amines were reacted with acetate groups of zinc acetate starting material, the polypropylene oligomers acted as template for the oxide formation. Different structural properties of the ZnO films were achieved varying the quantity of the oligomer in the starting solution. Spherical aggregated or monodispersed particles were formed with average sizes ranging from 10 to 30 nm. The films were employed in the construction of quantum dot sensitized solar cells using both CdS and CdSe. For first time a quasi solid state electrolyte was applied succeeding a maximum overall efficiency of 4.5% in the case of aggregated particles which could probably act as scattering centers. The quasi solid state electrolyte was a hybrid organic-inorganic material with SiO 2 edged groups while no water was used in any step of preparation of the host electrolyte for a polysulfide redox couple. © 2012 Elsevier B.V. All rights reserved.
Lampropoulou S.,Technological Educational Institute of Patra |
Nowicky A.V.,Brunel University
European Journal of Applied Physiology | Year: 2012
The aim of the study was to examine the reliability and validity of the numerical rating scale (0-10 NRS) for rating perception of effort during isometric elbow flexion in healthy people. 33 individuals (32 ± 8 years) participated in the study. Three re-test measurements within one session and three weekly sessions were undertaken to determine the reliability of the scale. The sensitivity of the scale following 10 min isometric fatiguing exercise of the elbow flexors as well as the correlation of the effort with the electromyographic (EMG) activity of the flexor muscles were tested. Perception of effort was tested during isometric elbow flexion at 10, 30, 50, 70, 90, and 100% MVC. The 0-10 NRS demonstrated an excellent test-retest reliability [intra class correlation (ICC) = 0.99 between measurements taken within a session and 0.96 between 3 consecutive weekly sessions]. Exploratory curve fitting for the relationship between effort ratings and voluntary force, and underlying EMG showed that both are best described by power functions (y = ax b). There were also strong correlations (range 0.89-0.95) between effort ratings and EMG recordings of all flexor muscles supporting the concurrent criterion validity of the measure. The 0-10 NRS was sensitive enough to detect changes in the perceived effort following fatigue and significantly increased at the level of voluntary contraction used in its assessment (p < 0.001). These findings suggest the 0-10 NRS is a valid and reliable scale for rating perception of effort in healthy individuals. Future research should seek to establish the validity of the 0-10 NRS in clinical settings. © Springer-Verlag 2011.
Giannopoulos G.I.,Technological Educational Institute of Patra |
Liosatos I.A.,Technological Educational Institute of Patra |
Moukanidis A.K.,Technological Educational Institute of Patra
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011
The elastic mechanical behavior of different sized zigzag and armchair graphene nanoribbons is numerically investigated and predicted using a new structural mechanic approach. According to the proposed method three dimensional, two nodded spring elements of three degrees of freedom per node, which remain straight when deformed, are combined in order to simulate realistically the interatomic interactions appearing within the graphene nanostructure. The computed variations of mechanical elastic properties are fitted by appropriate size dependent non-linear functions of two independent variables i.e. length and width, in order to express the analytical rules governing the elastic behavior of graphene nanoribbons within specific dimension limits. The numerical results, which are compared with corresponding data given in the open literature, demonstrate thoroughly the important influence of size and chirality of a narrow graphene monolayer on its elastic behavior. © 2011 Elsevier B.V. All rights reserved.
Bisdounis L.,Technological Educational Institute of Patra
2010 IEEE International Conference on Electronics, Circuits, and Systems, ICECS 2010 - Proceedings | Year: 2010
A considerable part of the energy dissipation in CMOS buffers is due to short-circuit currents. In this paper, an accurate, analytical and compact model for this part of energy, i.e. the short-circuit energy dissipation, is presented. The model is based on closed-form expressions of the CMOS inverter output waveform, which include the influences of both transistor currents and the gate-drain coupling capacitance. An accurate version of the alpha-power law MOSFET model is used to relate the terminal voltages to the drain current in sub-100nm devices, with an extension for varying transistor widths. The resulting energy model accounts for the influences of input voltage transition time, transistors' sizes, device carrier velocity saturation and narrow-width effects, gate-drain and short-circuiting transistor's gate-source capacitances, and output load. The model has been validated for a 90-nm CMOS technology, for different input transition times, capacitive loads & inverter sizes. The results show very good agreement with BSIM4 HSPICE simulations. ©2010 IEEE.
Bisdounis L.,Technological Educational Institute of Patra
Journal of Circuits, Systems and Computers | Year: 2011
Modeling of CMOS inverters and consequently, CMOS gates, is a critical task for improving accuracy and speed of simulation in modern sub-100 nm digital circuits. One of the key factors that determine the operation of a CMOS structure is the influence of the input-to-output coupling capacitance, also called overshooting effect. In this paper, an analytical model for this effect is presented, that computes the time period which is necessary to eliminate the extra output charge transferred through the input-to-output capacitance at the beginning of the switching process in a CMOS inverter. In addition, the maximum or minimum output voltage (depending on the considered edge) is analytically computed. The derived model is based on analytical expressions of the CMOS inverter output voltage waveform, which include the influences of both transistor currents and the input-to-output (gate-to-drain) coupling and load capacitances. An accurate version of the alpha-power law MOSFET model is used to relate the terminal voltages to the drain current in sub-100 nm devices, with an extension for varying transistor widths. The resulting model also accounts for the influences of input voltage transition time, transistors' sizes, as well as device carrier velocity saturation and narrow-width effects. The results produced by the presented model for three sub-100 nm CMOS technologies, several input voltage transition times, capacitive loads and device sizes, show very good agreement with BSIM4 HSPICE simulations. © 2011 World Scientific Publishing Company.
Cotfas D.T.,Transilvania University of Brasov |
Cotfas P.A.,Transilvania University of Brasov |
Kaplanis S.,Technological Educational Institute of Patra
Renewable and Sustainable Energy Reviews | Year: 2013
This review article critically outlines and discusses the main issues of 34 methods which have been developed and validated over the past 35 years in order to determine with an acceptable accuracy and reliability fundamental parameters of solar cells. This review covers methodologies which deal with current-voltage characteristic (I-V) analysis either theoretically through elaborated models and/or treated graphically. Methodologies based on the theoretical analysis of the I-V characteristics using the one or two diode model are discussed. The investigation on the I-V characteristics is processed via statistical functions, non-linear regression and stochastic models. A second family of methods to determine the solar cell electric parameters comprises the ones which deal with the graphical treatment and analysis of the I-V characteristics which are measured at different environmental conditions. To the third family belong the methods which use a mix approach of theoretical analysis of the I-V characteristics through modeling on one hand and the graphical analysis of their experimental configuration, on the other. The paper comments on each of the 34 methods and provides pros and cons for the determination of the fundamental electric parameters of solar cells. © 2013 Elsevier Ltd.
Kaplanis S.,Technological Educational Institute of Patra |
Kaplani E.,Technological Educational Institute of Patra
Simulation Modelling Practice and Theory | Year: 2011
The energy performance and degradation of 3 BP PV modules, type BP 1233, operating for a period of just more than 20 years are studied and compared to the nominal power output data. The 3 PV modules power the outdoor lighting of the Solar Campus and perform smoothly for all this period, without any special treatment or maintenance, although they were physically weathered on a continuous basis. Life cycle power degradation was estimated from a series of i, V experiments carried out under field conditions. The experimental analysis led to the determination of the present peak power, at STC, the series and shunt resistances, Rs and Rsh, respectively, and the fill factor, FF. Causes of degradation and especially of its extent were attributed to discolouring, junctions' damage, humidity ingress in the box, encapsulant delamination, hot spots, etc., as realized by in situ inspections. © 2010 Elsevier B.V. All rights reserved.
Okur S.,Izmir Institute of Technology |
Yakuphanoglu F.,Firat University |
Stathatos E.,Technological Educational Institute of Patra
Microelectronic Engineering | Year: 2010
We have fabricated a pentacene based phototransistor by employing a modified nanostructured SiO2 gate dielectric. The photosensing properties of the pentacene thin film transistor fabricated on n-Si substrate with nanostructured SiO2 as gate dielectric have been investigated. The photocurrent of the transistor increases with an increase in illumination intensity. This suggests that the pentacene thin film transistor behaves as a phototransistor with p-channel characteristics. The photosensitivity and responsivity values of the transistor are 630.4 and 0.10 A/W, respectively at the off state under AM 1.5 light illumination. The field effect mobility of the pentacene phototransistor was also found to be 2.96 cm2/Vs. The nanostructured surface of the gate possibly is the cause of the high-mobility value of the phototransistor due to light scattering from the increased surface area. Crown Copyright © 2009.
Giannopoulos G.I.,Technological Educational Institute of Patra
Computational Materials Science | Year: 2012
The elastic buckling behavior of multi sized graphene nanoribbons under compressive loadings is being investigated via a spring based structural mechanics approach. The proposed method utilizes three different types of translational, two-noded spring elements of three degrees of freedom per node to represent separately bond stretching, bond angle bending and bond angle torsion interatomic interactions within graphene nanostructure. The idea is to represent bending and torsional interatomic interactions in such a way that the coupling of deformations between bonds may be achieved in a realistic way. Critical buckling loads of graphene nanoribbons are revealed with respect to their length, width as well as chirality for two different edge boundary conditions. Despite the discrete atomistic structure of nanoribbons, their buckled shapes are found to be sine waved and thus Euler's buckling formulas are adopted to estimate their flexural rigidity. The numerical results, which are compared with corresponding evidence given in the literature where possible, demonstrate thoroughly the influence of size and chirality of graphene monolayer on its buckling behavior and flexural rigidity. © 2011 Elsevier B.V. All rights reserved.