Hellenic Air Force Academy

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Athens, Greece
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Andreatos A.S.,Hellenic Air Force Academy
IEEE Global Engineering Education Conference, EDUCON | Year: 2017

This paper describes a competition-based learning scenario for teaching some basic concepts of network security. The scenario is conducted on an ad-hoc LAN using Linux and Windows operating systems running on real and virtual machines. Students were expected to learn how to: 1) set up a wired or wireless ad-hoc LAN and connect to it; 2) run Linux and Windows Operating systems on VirtualBox and connect the virtual machines to the ad-hoc LAN; 3) set up the required services on an Apache web server and tools for attack and defense, as well as, traffic monitoring; 4) test DoS attack tools running on Linux and Windows platforms; 5) run packet sniffing tools for monitoring the volume of traffic against the server; and 6) explore defense mechanisms. The instructor demonstrated the methods and tools before the experiments. Students were separated in two groups, group A and group B. At first, group A acted as the red team (attackers) and group B played the blue team (defenders). The following week group roles were exchanged. The instructor had a multiple role. During the preparation phase he acted as a teacher building the necessary background, designing, modifying and applying the educational scenario. During the execution phase he acted as coach and motivator offering advice and technical support; he also acted as a researcher, observing student participation, decision-making and initiatives, in order to assess the scenario as well as the students. Scenario performance contributed 10 percent of the oral grade of the course. Students' evaluation of this lab exercise was positive. Lessons learned from this effort will help the instructor to improve the scenario and incorporate additional tools as well as more types of cyber attacks in the future. © 2017 IEEE.


Bolanakis D.E.,Hellenic Air Force Academy
IEEE Global Engineering Education Conference, EDUCON | Year: 2017

This communication identifies the importance of educating engineers in MEMS sensors, and reveals the practical difficulties in arranging experiments peculiar to this technology with a focus on (barometric) pressure sensors. The paper attempts to promote the great potentials present in wireless MEMS-based barometers, in terms of a creative experimentation in several engineering disciplines. Indicative examples are in agreement with the education of Aerospace Engineering, Biomedical Engineering, Electrical & Computer Engineering, and Industrial Engineering. Recommendations on the development of low-cost wireless sensor network systems for the laboratory are also given. © 2017 IEEE.


Bolanakis D.E.,Hellenic Air Force Academy
VCACS 2016 - 2016 IEEE Virtual Conference on Application of Commercial Sensors, Proceedings | Year: 2017

Some of the potential applications of barometric altitude readings (derived from atmospheric pressure measurements) include, but are not limited to, a) floor identification inside large buildings (e.g. museums, shopping malls, etc.), b) fall detection of a human body in the direction of medical monitoring systems and c) determination of an airplane's position angles. Implementation of these pioneer applications is feasible when addressing cutting-edge equipment of high accuracy, which in this respect is the Micro- Electro-Mechanical-Systems (MEMS) sensors technology. Several applications in the literature exploit the MEMS barometric pressure sensors, found in smartphones, in order detect vertical displacement in position location applications. However, the beneficial effects of this approach are limited to the utilization of the default sensors devices found in mobile phones, with the latter being of considerable cost. This paper presents a low-cost wireless sensor network system for realtime monitoring of barometric pressure on a LabVIEW-based computer interface. The system admits up to four individual measurement devices, allowing the simultaneous evaluation of ambient air pressure in vertical displacements. The minimum hardware involvement required by the system, along with an offline analysis of the available measurement data using Matlab script code, render the proposed experimentation model a particularly helpful reference guide to the implementation of position location systems and applications. © 2016 IEEE.


Rakopoulos D.C.,National Technical University of Athens | Rakopoulos C.D.,National Technical University of Athens | Papagiannakis R.G.,Hellenic Air Force Academy | Kyritsis D.C.,University of Illinois at Urbana - Champaign
Fuel | Year: 2011

An experimental study is conducted to evaluate the effects of using blends of diesel fuel with either ethanol in proportions of 5% and 10% or n-butanol in 8% and 16% (by vol.), on the combustion behavior of a fully-instrumented, six-cylinder, turbocharged and after-cooled, heavy duty, direct injection (DI), 'Mercedes-Benz' engine installed at the authors' laboratory. Combustion chamber and fuel injection pressure diagrams are obtained at two speeds and three loads using a developed, high-speed, data acquisition and processing system. A heat release analysis of the experimentally obtained cylinder pressure diagrams is developed and used. Plots of histories in the combustion chamber of the heat release rate and temperatures reveal some interesting features, which shed light into the combustion mechanism when using these promising bio-fuels that can be derived from biomass (bio-ethanol and bio-butanol). The key results are that with the use of these bio-fuels blends, fuel injection pressure diagrams are very slightly displaced (delayed), ignition delay is increased, maximum cylinder pressures are slightly reduced and cylinder temperatures are reduced during the first part of combustion. These results, combined with the differing physical and chemical properties of the ethanol and n-butanol against those for the diesel fuel, which constitutes the baseline fuel, aid the correct interpretation of the observed engine behavior performance- and emissions-wise. © 2010 Elsevier Ltd. All rights reserved.


The effects of uniaxial tensile strain on the ultimate performance of a dual-gated graphene nanoribbon field-effect transistor (GNR-FET) are studied using a fully analytical model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor (3NN) interaction. To calculate the performance metrics of GNR-FETs, analytical expressions are used for the charge density, quantum capacitance, and drain current as functions of both gate and drain voltages. It is found that the current under a fixed bias can change several times with applied uniaxial strain and these changes are strongly related to strain-induced changes in both band gap and effective mass of the GNR. Intrinsic switching delay time, cutoff frequency, and Ion/Ioff ratio are also calculated for various uniaxial strain values. The results indicate that the variation in both cutoff frequency and Ion/Ioff ratio versus applied tensile strain inversely corresponds to that of the band gap and effective mass. Although a significant high frequency and switching performance can be achieved by uniaxial strain engineering, tradeoff issues should be carefully considered. © 2014 Kliros; licensee Springer.


Kliros G.S.,Hellenic Air Force Academy
Proceedings of the International Semiconductor Conference, CAS | Year: 2010

We present a simple phenomenological model for the quantum capacitance of bilayer graphene. Quantum capacitance is calculated from the broadened density of states taking into account electron-hole puddles and possible finite lifetime of electronic states through a Gaussian broadening distribution. The obtained results are in agreement with many features recently observed in quantum capacitance measurements on gated bilayer graphene. The temperature dependence of quantum capacitance is also investigated. © 2010 IEEE.


Kliros G.S.,Hellenic Air Force Academy
Proceedings of the International Conference on Microelectronics, ICM | Year: 2010

Gate voltage control of carrier density and quantum capacitance is an important step for understanding the device physics and assessing the performance of nanoscale transistors. In this paper, we present a simple phenomenological model for the carrier density and quantum capacitance of graphene nanoribbon field-effect transistors as functions of gate voltage, Fermi level position and temperature. Quantum capacitance is calculated from the broadened density of states incorporating the presence of electron-hole puddles and possible finite lifetime of electronic states through a Gaussian broadening distribution. Thin gate-insulators of high-κ dielectric constant are used in our calculations in order to approach the quantum capacitance limit. © 2009 IEEE.


Kliros G.S.,Hellenic Air Force Academy
Microelectronic Engineering | Year: 2013

The width-dependent performance of armchair GNRs-FETs is investigated by developing a fully analytical gate capacitance model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor interaction as well as thermal broadening. To calculate the performance metrics of GNR-FETs, analytical expressions are used for the charge density, quantum capacitance as well as drain current as functions of both gate and drain voltages. Intrinsic gate delay time, cutoff frequency and Ion/Ioff ratio are also calculated for different GNR widths. Numerical results for a double-gate AGNR-FET operating close to quantum capacitance limit show that nanoribbon widths of about 3-4 nm at most are required in order to obtain optimum on/off performance. © 2013 Elsevier B.V. All rights reserved.


Kliros G.S.,Hellenic Air Force Academy
Proceedings of the International Semiconductor Conference, CAS | Year: 2013

We present a simulation study on the current-voltage characteristics of a dual-gated Graphene Nanoribbon Field Effect Transistor (GNR-FET) when its channel is under uniaxial tensile strain. Our study uses a fully analytical model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor (3NN) interaction. It is found that the current under a fixed bias can change several times with applied uniaxial strain and these changes are strongly related to strain induced changes in both band gap and effective mass of the GNR. Furthermore, other characteristics as transconductance, gate capacitance and cutoff frequency are also calculated for various strain values. © 2013 IEEE.


Kliros G.S.,Hellenic Air Force Academy
Superlattices and Microstructures | Year: 2012

A semi-analytical model for the capacitance-voltage characteristics of graphene nanoribbon field-effect transistors (GNR-FETs), in the quantum capacitance limit, is presented. The model incorporates the presence of electron-hole puddles induced by local potential fluctuations assuming a Gaussian distribution associated with these puddles. Our numerical results show that the multi-peaks in the non-monotonic quantum capacitance-voltage characteristics are broadened as the potential fluctuation strength increases and the broadening effect is much more pronounced in wide GNRs. The influence of both gate-insulator thickness and dielectric constant scaling on the total gate-capacitance characteristics is also explored. Gate capacitance has non-monotonic behavior with ripples for thin gate-insulators. However, as we go beyond the quantum capacitance limit by increasing insulator thickness or decreasing dielectric constant, the ripples are suppressed and smooth monotonic characteristics are obtained. © 2012 Elsevier Ltd. All rights reserved.

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