GRE tests, TOEFL, Greek national foundation examinations (1990-1991) Participation in exams for TOEFL, GRE general test, GRE subject test and Greek national foundation. I got the first prize and scholarship in the exams for theoretical physics for graduates of all Greek universities.
Στις γραπτές πανελλήνιες εξετάσεις του ΙΚΥ (Μαθηματικά, Φυσική και Αστροφυσική) ήρθα πρώτος και
Tufts University of USA offered me a scholarship for postgraduate studies in Physics-mathematics.
M.Sc. in Astronomy, University of Sussex
Department of Physics, (1991 - 1992)
(Ph.D.) from University of Newcastle upon Tyne, England, United Kingdom.
Department of Physics,
Mathematical Physics Group, (now shifted to Department of Mathematics (1992- 1996)
(Supervisor Prof. Ian Moss, External Prof. Tom Kibble )
Title of Ph.D. thesis, "Aspects of Early Universe Phase Transitions".
We present the mathematical analysis of the phase transition for the two-Higgs electroweak model. We have found that for a wide range of parameters the universe first tunnels to a new intermediate phase. This feature not only is very important by itself, but also provides the essential requirements for producing baryon asymmetry with only small explicit CP-violating terms in the two Higgs tree Lagrangian.
2.Ian.Moss and Vasilios Zarikas
"One loop corrected nucleation rates for the electroweak phase transition", preprint NCL95-TP5 Abstract
Bubble nucleation rates for the electroweak phase transition are calculated from the Higgs field effective action, up to first order in quantum corrections. A new parameterized form of the effective potential is presented and terms up to second order in derivatives are included in the effective action. These derivative terms enhance the nucleation rate, but they change the action by only a small amount as required by consistency, contrary to the previous estimations.
3. Vasilios Zarikas
"Derivative expansion for a general ‘t Hooft gauge fixing"
A derivative expansion technique is developed to compute functional determinants of quadratic operators, non diagonal in spacetime indices. This kind of operators arise in general 't Hooft gauge fixed Lagrangians. The derived formulae can be applied easily to any soliton or instanton background in order to find quantum corrections.
4.A. B. Lahanas, V.C. Spanos and Vasilios Zarikas
“Charge asymmetry in two-Higgs doublet models”
hep-ph 9812535, Phys.Lett.B472:119,2000 .
We discuss the features of a two-Higgs doublet model exhibiting a two stage phase transition. At finite temperatures electric charge violating stationary points are developed. In conjunction with CP violation in the Higgs or the Yukawa sector, the phase transition to the charge conserving vacuum, generates a net charge asymmetry Q, in the presence of heavy leptons, which may be well above the astrophysical bounds put on Q unless the heavy leptons are sufficiently massive. This type of transition may be of relevance for supersymmetric extensions of the Standard Model, since it shares the same features, namely two Higgs doublets and similar CP violating sources.
T. Christodoulakis, G. Kofinas and Vasilios Zarikas
“The general untilted diffuse matter Bianchi V Universe”
The Bianchi Type V Universe composed by diffuse matter is studied. We examine its anisotropic behaviour as well as the distortion it would cause to CMBR. Next the parameter region allowed by the present cosmological constraints is given. The gauge dependency of the temperature pattern, induced by the geometric anisotropies, is exhibited.
6.E. Kiritsis, G. Kofinas, N. Tetradis, T.N. Tomaras and Vasilios Zarikas
“Cosmological evolution with brane-bulk energy exchange”
Journal of High Energy Physics, JHEP 0302 (2003) 035 Abstract
The consequences for the brane cosmological evolution of energy exchange between the brane and the bulk are analysed in detail, in the context of a non-factorizable background geometry with vanishing effective cosmological constant on the brane. A rich variety of brane cosmologies is obtained, depending on the precise mechanism of energy transfer, the equation of state of brane-matter and the spatial topology. An accelerating era is generically a feature of our solutions. In the case of low-density flat universe more dark matter than in the conventional FRW picture is predicted. Spatially compact solutions are found to delay their recollapse.
“A brane based solution to the small cosmological constant problem”
Ready to be submitted
8. Vasilios Zarikas
“A 4-dim solution to the cosmological constant problem”
Ready to be submitted Β. Applied mathematics in Technology
( 33 known citations) (In the following publications the order of the authors indicates their amount of contribution to the paper)
This paper discusses the employment of decision-theoretic approaches in adaptive user interfaces, towards the goal of Universal Access. Specifically, the paper examines ways in which the requirements posed by Universal Access on human-computer interaction can be addressed through automatic user interface adaptation, using decision-theoretic frameworks. Furthermore, the paper discusses some of the implications of employing such adaptation frameworks in user interfaces intended for use by diverse user groups, in differing contexts of use.
10. Vasilios Zarikas, G. Papatzanis, and C. Stephanidis
“An architecture for a self-adapting information system for tourists”.
Proceedings of the conference: “Human Computer Interaction with Mobile Devices, 10 Sept 2001, at IHM-HCI 2001, Lille, France”. Abstract
The paper briefly describes the design of the architecture of the PALIO system (Personalised Access to Local Information and services for tourists), focusing on the support for extensive adaptation. The framework provides a location-aware information system for tourists, capable of delivering fully adaptive information to a wide range of devices, including mobile ones. Its open and expandable architecture can integrate a variety of pre-existing or forthcoming services and retrieve information from a collection of different databases. It supports adaptability and dynamic adaptivity, according to user and context characteristics, both in the content and the presentation of information.
C. Stephanidis, A. Paramythis, Vasilios Zarikas, A Savidis
“User-, platform-, and location- adapted information services over the Web - The PALIO Framework for Adaptive Information Services.”
Chapter in the book “Multi-Device User Interfaces: Engineering and Application Frameworks”. published by Wiley, 2004.
with editors Ahmed Seffah and Homa Javahery, Computer Science Department, Faculty of Engineering and Computer Science, Concordia University, Quebec, Canada
Abstract: In this chapter we describe the architecture of an information system that provides personalised provision of information to users through a variety of devices and networks and in a variety of different contexts of use. The design of the architecture is rooted on the concept of universal design, as it has evolved over the past decade. Universal design refers to the conscious effort to consider and take into account the widest possible range of end-user requirements throughout the development life-cycle of a product or service.
The main motivation is the development of an open system for accessing and retrieving information without constraints and limitations (imposed by space, time, access technology, etc). Therefore, the system should be modular and capable of interoperating with other existing information systems. In this respect, mobile communication systems play an essential role, because they enable access to services from anywhere and at anytime. An example is the support of a wide range of communication technologies (mobile or wired) to access services. In particular, it will be possible for a user, who is equipped either with a common cellular phone or an advanced WAP phone, to access services from any place.
“Modeling decisions under uncertainty in adaptive interfaces’’.
Universal Access in the Information Society 6(1): 87-101 (2007)
International Journal, ISSN: 1615-5289 (print version) Abstract:
The present work proposes a mathematical approach for modeling adaptation decisions and for solving the problem of integrating existing as well as acquired knowledge in the decision module of an adaptive interface. So far, most applications do not exploit in full the value of data originating from user models or knowledge acquisition engines that monitor the user and/or the context. The proposed decision mathematical method is represented by influence diagrams structured in a specific way. Our proposal allows the designer/developer to encode user and context information as well as other crucial decision factors, consequently used in the decision making process regarding interface adaptation actions. The decision making process is driven by the definition of relevant utilities referring to the design of a user interface. The proposed model allows designers/developers of an adaptive/intelligent interface to integrate, without conflicts and incoherence, design strategies, design goals (e.g., performance, accuracy, ease of use), user goals, alternative constituents (e.g., text vs. graphics vs. audio), user profile, context and application domain knowledge. Our method’s outcome provides a simple, yet computable, structure for decision process modeling and generalizes previous published works. Methodology is further analyzed with an example coming from the context-aware mobile computing domain. Various useful tips have also been given.
Vasilios Zarikas, and C. Stephanidis
“An Influence Diagram-Based Approach to Location Aware Mobile Computing”
Proceedings of the “HCI International 2003”, 10th International Conference on Human - Computer Interaction, June 22-27, 2003. Abstract:
The present paper discusses issues related to the demands of forthcoming location aware mobile computing. A design for building adaptive interfaces following the principles of Universal access is proposed as a proper and potential solution for the new technological challenges. Next, the paper recommends the use of influence diagrams (Bayesian decision networks) for nesting uncertainty, inherit in these novel user machine interactions.
Vasilios Zarikas, and K. Vlachos
«A self-consistent model for a SOA-based fiber ring laser including the mode-locked pulse properties»,
In this paper, we present a self-consistent mathematical model of an optically mode-locked semiconductor fiber ring laser. The fiber laser uses a semiconductor optical amplifier -SOA- as the gain medium, while mode-locking is achieved by its gain modulation, via an external optical pulsed signal. The model was solved analytically and revealed the locus of the laser parameters to achieve mode-locking. In particular, it was found that SOA gain and energy of the externally introduced signal are two critical parameters that must simultaneously set properly for exact mode-locking. Furthermore, in our analysis we have assumed double saturation of the SOA by both the mode-locked and the externally introduced pulsed signal. Gaussian pulse profiles were assumed with an initial chirp.
Objective: VEMPs recording is a new method for testing the otolith receptors and vestibulospinal pathways. The aim of this study is to compare four different techniques of VEMP eliciting and identify a reliable and easy applicable method.
Material and methods. Twenty healthy persons, ten males and ten females with ages ranged from 20 to 57 years (mean value 41) were enrolled in this study. Eliciting of VEMPs by using monaural or binaural acoustic stimulation and unilateral or bilateral SCM contraction was evaluated. 105 dB NHL acoustic stimulation consisted of 145 dB rarefaction clicks was applied. Latencies of p13, n23, n34, p44 peaks, amplitudes p13n23 and n34p44 and the interaural amplitude differences (IAD) were assessed.
Results. All the four methods were evaluated as reliable for the latencies and especially the amplitudes; however the higher scores of reliability were for the monaural/ipsilateral recording. Results reveal no statistically significant difference between right and left side apart from the n34p44 factor in the binaural ipsilateral type of recording. The value of the numerator of the IAD variable is not statistically different from zero in almost all cases. No correlation was found between IAD13-23 and IAD34-44 for all the four methods. Statistical significant differences were found only for p13, n23 and p34 factors among the four methods.
Conclusion. All the four methods elicit constant and evident waveforms. IAD13-23, p13n23L and p13n23R give independent information (regarding normal ear behavior). No statistical significant differences were found between left and right sides for all the four types of recording. The norm for healthy subjects of both IAD variables is zero. Therefore results do not favour the use of IAD or the use of relative amplitudes against the use of amplitudes for describing healthy subjects.
The intraclass correlation coefficients of type C following a two way random model for measuring reliability was calculated. Left Rigth differences for all the factors were compared with the Wilcoxon signed ranks test. Wilcoxon signed ranks test was used because most of our variables are not normally distributed. In addition, t paired test for related groups was carried out, for the variables that follow more closely normality. Comparisons among the four methods were performed following again non parametric methods i.e Friedman and Kendall’s tests. Further we checked for possible correlations calculating the Spearman's rank correlation coefficient.
In all cases a significant difference indicates P<0.05.
“Test - retest Reliability. VEMP eliciting in normal subjects. Normative data of Vestibular Evoked Myogenic Potential Stimulation (VEMPS) in a large healthy population”
J Otolaryngol Head Neck Surg. 2009 Aug;38(4):462-7. Abstract:
Objective: The aim of this study is to evaluate the characteristics of VEMPs recording in a large number of healthy subjects
Material and methods. VEMP recording was applied on 75 healthy volunteers. 39 of them were males and 36 were females. Their age varied between 25 and 63 years (mean value 43). The procedure was performed by monaural stimulation and ipsilateral contraction Latencies of p13, n23, n34, p44 peaks, amplitudes p13n23 and n34p44 and the interaural amplitude differences (IAD) were assessed.
Results. The stability of latencies, amplitudes and relative amplitudes of the first and second waveforms was verified. The second wave form was present in 76%. No factor indicates statistically significant side difference for both runs. IAD variable was not statistically different from zero in all cases. Results show very good reliability for amplitudes, good for some latencies, poor for some other lattencies and IAD34-44 and very poor for IAD13-23. No strong and significant correlations were also found between IAD34-44 and IAD13-23 and between p13n23 and n34p44.
Conclusion. We do not confirm that amplitude measures are more likely to show side difference than latency measures in VEMPS. It is the first time that the reliability of IAD for both waveforms is studied in a large sample of subjects and it is shown that IAD has the disadvantage of low reliability.
We tested reliability using the intraclass correlation coefficients of type C following a two way random model for measuring reliability. The between measure variance is excluded from the denominator variance. Side differences for all the factors were compared with the Wilcoxon signed ranks test since most of variables are not normally distributed. Further we checked for possible correlations calculating the Spearman's rank correlation coefficient. In all cases a significant difference indicates P<0.05.