PULSEACADEMIC PERSONAL VCARD
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ABOUT

PERSONAL DETAILS
Ashton Building, Ashton Street, Liverpool, L69 3BX
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theofila {at} liverpool.ac.uk
+44 7588332121

BIO

ABOUT ME

I am currently a third-year PhD student in the Computer Science Department at the University of Liverpool, United Kingdom, under the supervision of Prof. Paul G. Spirakis, Dr. Othon Michail, and Prof. Piotr Krysta. My research interests include Distributed Algorithms, Graph Theory, and Machine Learning. I am also working on the development of efficient heuristic and machine learning algorithms for the Crystal Structure Prediction problem; one of the major problems in computational chemistry.
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RESUME

EDUCATION
  • 2017
    2021
    Liverpool, UK

    PhD in Computer Science

    University of Liverpool

    Advanced Algorithms and Formal Methods for the Design of New Materials
  • 2011
    2017
    Patras, Greece

    Computer Engineering and Informatics

    University of Patras

    Grade: 8.40/10
PROFESSIONAL EXPERIENCE
  • 2016
    2017
    Patras, Greece

    Traineeship

    SystServ SA

    Optional and competitive three-month work placement facilitated by the University of Patras. The topic of my internship was the development of an android application which gives the opportunity to people with health problems to easily send an alert to a patient service center. Also, I implemented the website of the service center using AngularJS.
  • 2016
    2017
    Patras, Greece

    Software Engineer

    SystServ SA

    Development of the Android and iOS applications, web platform and the backend for an mHealth system (TreatMeOut).
HONORS AND AWARDS
  • 2018
    2010
    Athens

    Masters & Mates Union Of Greek Merchant Marine (P.E.P.E.N) award for Academic Excellence

    P.E.P.E.N.

  • 2017
    2021
    Liverpool

    Leverhulme Research Centre, Postgraduate Research Scholarship

    University of Liverpool

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PUBLICATIONS

PUBLICATIONS LIST
SORTING BY DATE
27 Mar 2020

Crystal Structure Prediction via Oblivious Local Search

18th Symposium on Experimental Algorithms

Click here to download paper.

Conferences Dmytro Antypov, Argyrios Deligkas, Vladimir Gusev, Matthew J. Rosseinsky, Paul G. Spirakis, Michail Theofilatos

Crystal Structure Prediction via Oblivious Local Search

Dmytro Antypov, Argyrios Deligkas, Vladimir Gusev, Matthew J. Rosseinsky, Paul G. Spirakis, Michail Theofilatos
Conferences
About The Publication
We study Crystal Structure Prediction, one of the major problems in computational chemistry. This is essentially a continuous optimization problem, where many different, simple and sophisticated, methods have been proposed and applied. The simple searching techniques are easy to understand, usually easy to implement, but they can be slow in practice. On the other hand, the more sophisticated approaches perform well in general, however almost all of them have a large number of parameters that require fine tuning and, in the majority of the cases, chemical expertise is needed in order to properly set them up. In addition, due to the chemical expertise involved in the parameter-tuning, these approaches can be biased towards previously-known crystal structures. Our contribution is twofold. Firstly, we formalize the Crystal Structure Prediction problem, alongside several other intermediate problems, from a theoretical computer science perspective. Secondly, we propose an oblivious algorithm for Crystal Structure Prediction that is based on local search. Oblivious means that our algorithm requires minimal knowledge about the composition we are trying to compute a crystal structure for. In addition, our algorithm can be used as an intermediate step by any method. Our experiments show that our algorithms outperform the standard basin hopping, a well studied algorithm for the problem.  
14 Nov 2019

Fault Tolerant Network Constructors

21st International Symposium on Stabilization, Safety, and Security of Distributed Systems (SSS 2019)

Click here to download paper.
Open in Google Scholar.

Conferences Othon Michail, Paul G. Spirakis, Michail Theofilatos

Fault Tolerant Network Constructors

Othon Michail, Paul G. Spirakis, Michail Theofilatos
Conferences
About The Publication
In this work, we consider adversarial crash faults of nodes in the network constructors model [Michail and Spirakis, 2016]. We first show that, without further assumptions, the class of graph languages that can be (stably) constructed under crash faults is nonempty but small. In particular, if an unbounded number of crash faults may occur, we prove that (i) the only constructible graph language is that of spanning cliques and (ii) a strong impossibility result holds even if the size of the graphs that the protocol outputs in populations of size n need only grow with n (the remaining nodes being waste). When there is a finite upper bound f on the number of faults, we show that it is impossible to construct any non-hereditary graph language and leave as an interesting open problem the hereditary case. On the positive side, by relaxing our requirements we prove that: (i) permitting linear waste enables to construct on n/(2f) − f nodes, any graph language that is constructible in the fault-free case, (ii) partial constructibility (i.e., not having to generate all graphs in the language) allows the construction of a large class of graph languages. We then extend the original model with a minimal form of fault notifications. Our main result here is a fault-tolerant universal constructor : We develop a fault-tolerant protocol for spanning line and use it to simulate a linear-space Turing Machine M. This allows a fault-tolerant construction of any graph accepted by M in linear space, with waste min{n/2 + f(n), n}, where f(n) is the number of faults in the execution. We then prove that increasing the permissible waste to min{2n/3+f(n), n} allows the construction of graphs accepted by an O(n^2)-space Turing Machine, which is asymptotically the maximum simulation space that we can hope for in this model. Finally, we show that logarithmic local memories can be exploited for a no-waste faulttolerant simulation of any such protocol.   Cite paper:
@inproceedings{michail2019fault,
  title={Fault tolerant network constructors},
  author={Michail, Othon and Spirakis, Paul G and Theofilatos, Michail},
  booktitle={International Symposium on Stabilizing, Safety, and Security of Distributed Systems},
  pages={243--255},
  year={2019},
  organization={Springer}
}
13 May 2018

Exact size counting in uniform population protocols in nearly logarithmic time

32nd International Symposium on Distributed Computing (DISC 2018)

Click here to download (full) paper.
Open in Google Scholar.

Conferences David Doty, Mahsa Eftekhari, Othon Michail, Paul G Spirakis, Michail Theofilatos

Exact size counting in uniform population protocols in nearly logarithmic time

David Doty, Mahsa Eftekhari, Othon Michail, Paul G Spirakis, Michail Theofilatos
Conferences
About The Publication
We study population protocols: networks of anonymous agents whose pairwise interactions are chosen uniformly at random. The size counting problem is that of calculating the exact number n of agents in the population, assuming no leader (each agent starts in the same state). We give the first protocol that solves this problem in sublinear time. The protocol converges in O(log n log log n) time and uses O(n^60) states (O(1)+60 log n bits of memory per agent) with probability 1−O((log log n)/n). The time to converge is also O(log n log log n) in expectation. Crucially, unlike most published protocols with ω(1) states, our protocol is uniform: it uses the same transition algorithm for any population size, so does not need an estimate of the population size to be embedded into the algorithm. A sub protocol is the first uniform sublinear-time leader election population protocol, taking O(log n log log n) time and O(n^18) states. The state complexity of both the counting and leader election protocols can be reduced to O(n^30) and O(n^9) respectively, while increasing the time to O(log^2 n).   Cite paper:
@article{doty2018brief,
  title={Brief announcement: Exact size counting in uniform population protocols in nearly logarithmic time},
  author={Doty, David and Eftekhari, Mahsa and Michail, Othon and Spirakis, Paul G and Theofilatos, Michail},
  journal={Leibniz International Proceedings in Informatics, LIPIcs},
  volume={121},
  year={2018}
}
04 Nov 2018

Simple and Fast Approximate Counting and Leader Election in Populations

International Symposium on Stabilizing, Safety, and Security of Distributed Systems (SSS 2018)

Click here to download paper.
Open in Google Scholar.

Conferences Othon Michail, Paul G Spirakis, Michail Theofilatos

Simple and Fast Approximate Counting and Leader Election in Populations

Othon Michail, Paul G Spirakis, Michail Theofilatos
Conferences
About The Publication
We study the problems of leader election and population size counting for population protocols: networks of finite-state anonymous agents that interact randomly under a uniform random scheduler. We provide simple protocols for approximate counting of the size of the population and for leader election. We show a protocol for leader election that terminates in O(log^2(n)/log(m)) parallel time, where 1 ≤ m ≤ n is a parameter, using O(max{m, log n}) states. By adjusting the parameter m between a constant and n, we obtain a single leader election protocol whose time and space can be smoothly traded off between O(log^2(n)) to O(log n) time and O(log n) to O(n) states. We also give a protocol which provides an upper bound n’ of the size n of the population, where n’ is at most n a for some constant a > 1. This protocol assumes the existence of a unique leader in the population and stabilizes in Θ(log n) parallel time, using constant number of states in every node, except from the unique leader which is required to use Θ(log^2(n)) states.   Cite paper:
@inproceedings{michail2018simple,
  title={Simple and fast approximate counting and leader election in populations},
  author={Michail, Othon and Spirakis, Paul G and Theofilatos, Michail},
  booktitle={International Symposium on Stabilizing, Safety, and Security of Distributed Systems},
  pages={154--169},
  year={2018},
  organization={Springer}
}
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TEACHING

TEACHING HISTORY
  • 2013
    2014
    Patras, Greece

    Teaching Assistant

    Department of Computer Engineering and Informatics, University of Patras, Greece

    Course title: Logic Design Laboratory
    First year course of the department of Computer Engineering and Informatics, University of Patras, Greece.
  • 2013
    2014
    Patras, Greece

    Teaching Assistant

    Department of Computer Engineering and Informatics, University of Patras, Greece

    Course title: Computer Architecture Laboratory
    Second year course of the department of Computer Engineering and Informatics, University of Patras, Greece.
  • 2017
    2019
    Liverpool, UK

    Demonstrator

    Department of Computer Science, University of Liverpool, UK

    Object-Oriented Programming
    First year module of the department of Computer Science, University of Liverpool.
  • 2019
    Liverpool, UK

    Demonstrator

    Department of Computer Science, University of Liverpool, UK

    Data Structures and Algorithms
    First year module of the department of Computer Science, University of Liverpool.
  • 2019
    Liverpool, UK

    Demonstrator

    Department of Computer Science, University of Liverpool, UK

    Advanced Algorithmic Techniques
    Masters module of the department of Computer Science, University of Liverpool.
  • 2019
    Liverpool, UK

    Demonstrator

    Department of Computer Science, University of Liverpool, UK

    Distributed Systems
    Second year module of the department of Computer Science, University of Liverpool.