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Mental health profile of Greece

George Christodoulou, Dimitris Ploumpidis, Nikos Christodoulou, Dimitris Anagnostopoulos
2010 International Psychiatry  
19th century (Christodoulou et al, 2010).  ...  Since the mid-1980s, a profound reform in the organisation of mental health provision has been taking place in Greece (Madianos & Christodoulou, 2007; Christodoulou, 2009).  ...  the 19th century ( Christodoulou et al, 2010) .  ... 
pmid:31508042 pmcid:PMC6734981 fatcat:447n7pmyl5hdljfss7lvrqls2a

Management of the psychosocial effects of economic crises

Nikos G. Christodoulou, George N. Christodoulou
2013 World Psychiatry  
doi:10.1002/wps.20043 pmid:23737430 pmcid:PMC3683273 fatcat:tjxmdohmnbge7g7jywxkjggrs4

Impartial selection with prior information [article]

Ioannis Caragiannis, George Christodoulou, Nicos Protopapas
2021 arXiv   pre-print
We study the problem of impartial selection, a topic that lies at the intersection of computational social choice and mechanism design. The goal is to select the most popular individual among a set of community members. The input can be modeled as a directed graph, where each node represents an individual, and a directed edge indicates nomination or approval of a community member to another. An impartial mechanism is robust to potential selfish behavior of the individuals and provides
more » ... e incentives to voters to report their true preferences by ensuring that the chance of a node to become a winner does not depend on its outgoing edges. The goal is to design impartial mechanisms that select a node with an in-degree that is as close as possible to the highest in-degree. We measure the efficiency of such a mechanism by the difference of these in-degrees, known as its additive approximation. In particular, we study the extent to which prior information on voters' preferences could be useful in the design of efficient deterministic impartial selection mechanisms with good additive approximation guarantees. We consider three models of prior information, which we call the opinion poll, the a prior popularity, and the uniform model. We analyze the performance of a natural selection mechanism that we call approval voting with default (AVD) and show that it achieves a O(√(nlnn)) additive guarantee for opinion poll and a O(ln^2n) for a priori popularity inputs, where n is the number of individuals. We consider this polylogarithmic bound as our main technical contribution. We complement this last result by showing that our analysis is close to tight, showing an Ω(lnn) lower bound. This holds in the uniform model, which is the simplest among the three models.
arXiv:2102.09002v1 fatcat:yb2zg2jn3zalzlydkki4qr5xxu

Financial Crises: Impact on Mental Health and Suggested Responses

Nikos G. Christodoulou, George N. Christodoulou
2013 Psychotherapy and Psychosomatics  
doi:10.1159/000351268 pmid:23942174 fatcat:il7hr55t4raf5eyjq7zzhrqqfi

Psychiatric reform revisited

GEORGE CHRISTODOULOU
2009 World Psychiatry  
The main points of criticism are the following: Psychiatric reform revisited PERSPECTIVE GeorGe Christodoulou Hellenic Centre for Mental Health and Research, Athens, Greece The trend towards the  ... 
doi:10.1002/j.2051-5545.2009.tb00227.x pmid:19516938 pmcid:PMC2694516 fatcat:vn7ro2vwanhb7poz5vsehlqjpu

The Royal College of Psychiatrists goes 'international': the European International Division

Athanasios Douzenis, Nikos Christodoulou, George Christodoulou
2005 International Psychiatry  
The initiative of the Royal College of Psychiatrists to establish international divisions has created considerable enthusiasm. College members have some common characteristics, mainly their training and success in the Royal College examination. Thus College members share a common approach to the practice of psychiatry as well as some common experiences; it can be argued that they share a common language in psychiatry.
pmid:31507822 pmcid:PMC6733139 fatcat:oe2ih23xp5fmnkme7vft3nhzpq

Strategic Contention Resolution in Multiple Channels [article]

George Christodoulou, Themistoklis Melissourgos, Paul G. Spirakis
2018 arXiv   pre-print
The theoretical works that relate the most to the current paper are the seminal paper by Fiat, Mansour and Nadav [11] and two by Christodoulou et al.  ... 
arXiv:1810.04565v1 fatcat:4h72mdgxc5cxppwcyf27rhaiei

A deterministic truthful PTAS for scheduling related machines [article]

George Christodoulou, Annamaria Kovacs
2009 arXiv   pre-print
Scheduling on related machines (Q||C_) is one of the most important problems in the field of Algorithmic Mechanism Design. Each machine is controlled by a selfish agent and her valuation can be expressed via a single parameter, her speed. In contrast to other similar problems, Archer and Tardos AT01 showed that an algorithm that minimizes the makespan can be truthfully implemented, although in exponential time. On the other hand, if we leave out the game-theoretic issues, the complexity of the
more » ... roblem has been completely settled -- the problem is strongly NP-hard, while there exists a PTAS HS88,ES04. This problem is the most well studied in single-parameter algorithmic mechanism design. It gives an excellent ground to explore the boundary between truthfulness and efficient computation. Since the work of Archer and Tardos, quite a lot of deterministic and randomized mechanisms have been suggested. Recently, a breakthrough result DDDR08 showed that a randomized truthful PTAS exists. On the other hand, for the deterministic case, the best known approximation factor is 2.8 Kov05,Kov07. It has been a major open question whether there exists a deterministic truthful PTAS, or whether truthfulness has an essential, negative impact on the computational complexity of the problem. In this paper we give a definitive answer to this important question by providing a truthful deterministic PTAS.
arXiv:0907.3068v1 fatcat:mgyvvuysjvhixir6jcdnnlgjg4

On the Efficiency of All-Pay Mechanisms [article]

George Christodoulou, Alkmini Sgouritsa, Bo Tang
2015 arXiv   pre-print
Christodoulou , Kovács and Schapira [7] initiated the study of the (Bayesian) price of anarchy of simultaneous auctions with item-bidding.  ...  Christodoulou et al. [8] constructed tight lower bounds for first-price auctions and showed a tight price of anarchy bound of 2 for all-pay auctions with subadditive valuations.  ... 
arXiv:1508.01130v1 fatcat:zczivforszb3bfvb24n3waltxu

Contention Resolution under Selfishness

George Christodoulou, Katrina Ligett, Evangelia Pyrga
2013 Algorithmica  
In many communications settings, such as wired and wireless local-area networks, when multiple users attempt to access a communication channel at the same time, a conflict results and none of the communications are successful. Contention resolution is the study of distributed transmission and retransmission protocols designed to maximize notions of utility such as channel utilization in the face of blocking communications. An additional issue to be considered in the design of such protocols is
more » ... hat selfish users may have incentive to deviate from the prescribed behavior, if another transmission strategy increases their utility. The work of Fiat et al. [8] addresses this issue by constructing an asymptotically optimal incentive-compatible protocol. However, their protocol assumes the cost of any single transmission is zero, and the protocol completely collapses under non-zero transmission costs. In this paper, we treat the case of non-zero transmission cost c. We present asymptotically optimal contention resolution protocols that are robust to selfish users, in two different channel feedback models. Our main result is in the Collision Multiplicity Feedback model, where after each time slot, the number of attempted transmissions is returned as feedback to the users. In this setting, we give a protocol that has expected cost 2n + c log n and is in o(1)-equilibrium, where n is the number of users.
doi:10.1007/s00453-013-9773-4 fatcat:7axnizr2hfbn3aznzimooonam4

Coordination Mechanisms [chapter]

George Christodoulou, Elias Koutsoupias, Akash Nanavati
2004 Lecture Notes in Computer Science  
We introduce the notion of coordination mechanisms to improve the performance in systems with independent selfish and noncolluding agents. The quality of a coordination mechanism is measured by its price of anarchy-the worst-case performance of a Nash equilibrium over the (centrally controlled) social optimum. We give upper and lower bounds for the price of anarchy for selfish task allocation and congestion games.
doi:10.1007/978-3-540-27836-8_31 fatcat:h4ovmqoo5nf5bj5fielifq72ai

Coordination mechanisms

George Christodoulou, Elias Koutsoupias, Akash Nanavati
2009 Theoretical Computer Science  
We introduce the notion of coordination mechanisms to improve the performance in systems with independent selfish and noncolluding agents. The quality of a coordination mechanism is measured by its price of anarchy-the worst-case performance of a Nash equilibrium over the (centrally controlled) social optimum. We give upper and lower bounds for the price of anarchy for selfish task allocation and congestion games.
doi:10.1016/j.tcs.2009.01.005 fatcat:trpp2kb3jzex3pikstvhna7qr4

The Role of Twitter in YouTube Videos Diffusion [chapter]

George Christodoulou, Chryssis Georgiou, George Pallis
2012 Lecture Notes in Computer Science  
This work is supported in part by the Startup Grant [George Pallis, 2011], funded by the University of Cyprus.  ... 
doi:10.1007/978-3-642-35063-4_31 fatcat:jovnlzihbzckzafncxjpmhu2gy

Truthful Aggregation of Budget Proposals with Proportionality Guarantees [article]

Ioannis Caragiannis, George Christodoulou, Nicos Protopapas
2022 arXiv   pre-print
We study a participatory budgeting problem, where a set of strategic agents wish to split a divisible budget among different projects, by aggregating their proposals on a single division. Unfortunately, the straight-forward rule that divides the budget proportionally is susceptible to manipulation. In a recent work, Freeman et al. [arXiv:1905.00457] proposed a class of truthful mechanisms, called moving phantom mechanisms. Among others, they propose a proportional mechanism, in the sense that
more » ... the extreme case where all agents prefer a single project to receive the whole amount, the budget is assigned proportionally. While proportionality is a naturally desired property, it is defined over a limited type of preference profiles. To address this, we expand the notion of proportionality, by proposing a quantitative framework which evaluates a budget aggregation mechanism according to its worst-case distance from the proportional allocation. Crucially, this is defined for every preference profile. We study this measure on the class of moving phantom mechanisms, and we provide approximation guarantees. For two projects, we show that the Uniform Phantom mechanism is the optimal among all truthful mechanisms. For three projects, we propose a new, proportional mechanism which is virtually optimal among all moving phantom mechanisms. Finally, we provide impossibility results regarding the approximability of moving phantom mechanisms.
arXiv:2203.09971v1 fatcat:slnkpzny65bfznezzoyyq7fnoe
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