1,019 research outputs found
Factors affecting trust and communication in global virtual teams
No full textAuthor Georgios GousiasMasterarbeit Universität Linz 2022Arbeit auf den öffentlichen PCs in den Bibliotheken der JKU+Medizin abrufba
Factors affecting trust and communication in global virtual teams
No full textAuthor Georgios GousiasMasterarbeit Universität Linz 2022Arbeit auf den öffentlichen PCs in den Bibliotheken der JKU+Medizin abrufba
Distributionally robust stability of payoff allocations in stochastic coalitional games
No full textWe consider multi-agent coalitional games with uncertainty in the coalitional values. We provide a novel methodology to study the stability of the grand coalition in the case where each coalition constructs ambiguity sets for the (possibly) unknown probability distribution of the uncertainty. As a less conservative solution concept compared to worst-case approaches for coalitional stability, we consider a stochastic version of the so-called core set, i.e., the expected value core. Unfortunately, without exact knowledge of the probability distribution, the evaluation of the expected value core is an extremely challenging task. Hence, we propose the concept of distributionaly robust (DR) core. Leveraging tools from DR optimization under the Wasserstein distance, we provide finite-sample guarantees that any allocation which lies in the DR core is also stable with respect to the true probability distribution and show the asymptotic consistency of the DR core. We dedicate the last section to the computational tractability of finding an allocation in the DR core
Der griechische Gelehrte Georgios Zachariadis und sein Beitrag zum slawischen Schrifttum im 19. Jahrhundert
No full textAmong the Greek scholars who lived during the 19th century in the north-eastern Balkans, and also in Central Europe, and by their work contributed to the spiritual development of the Balkan Slavs, pride of place must be given to Georgios Zachariadis. Unfortunately, however, no detailed monograph on Zachariadis exists. On this account the problems that arise concerning the life and activities of this Greek scholar are still many and varied. In his study the author tries to fill one part of this lacuna. At the beginning of the work the following are examined, on the basis of new historical evidence: the date and place of Georgios Zachariadis’ birth, his studies and tenure as teacher in the Greek school at Zemun, the Serbian school at Šabac, and the Greek school in Vienna. The author continues his study by analyzing the various works of Zachariadis, which are written on Old Church^Slavonic, and the translations this Greek scholar made from Greek into Old Church Slavonic. Finally, the extent of Georgios Zachariadis’ contribution to Slavonic letters is made clear
The political program of Hellenism in Turkey
No full textTitle: Tό πoλιτικόν πρόγραμμα τοῦ Έλληνισμοῦ έν Tουρκία (The political program of Hellenism in Turkey) Originally published: as a leaflet in Istanbul, 1912 Language: GreekThe excerpts used are from the original which can be found at the ‘Ion Dragoumis archive’ in the Gennadion Library in Athens, pp. 7–9, 11–13, 24–25. About the author Georgios Boussios [1876, Grevena (Ottoman Macedonia) – 1929, Athens]: activist, politician and journalist. He was born into a well-off family of merchants. He c..
Correction: Do chemistry and rheology follow the same laboratory ageing trends in bitumen?
No full text Correction to: Materials and Structures (2022) 55:146 https://doi.org/10.1617/s11527-022-01986-w The article “Do chemistry and rheology follow the same laboratory ageing trends in bitumen?”, written by Georgios Pipintakos, Caitlin Lommaert, Aikaterini Varveri and Wim Van den bergh, was originally published in volume 55, issue 5, ID 146 without open access. With the society's decision to grant Open Choice the copyright of the article changed in February 2023 to © The Author(s) 2022 and the article is forthwith distributed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0. Open access funding enabled and organized by RILEM.Pavement Engineerin
Data-driven algorithms for multi-agent optimization and games
No full textMulti-agent optimization and game theory constitute fundamental frameworks for
modelling a plethora of engineering problems. In some systems, agents cooperate to
optimize a collective cost, thus giving rise to multi-agent optimization programs. In
other cases, agents act as selfish entities wishing to minimize their own individual
cost subject to local or global constraints. To model such behaviour, non-cooperative
game theory is required. Finally, agents though selfish can opt towards the formation
of coalitions such that they receive a higher payoff. Such systems are studied under
the lenses of cooperative game theory.
One of the most crucial challenges in such problems is finding solutions that are
robust against the effects of uncertainty. Uncertainty represents our lack of knowledge
about how the underlying system behaves and usually originates from unmodelled
dynamics or external factors. Its significance is apparent in modern applications such
as the electric vehicle charging problem, the optimal power flow problem with power
generation from renewable energy sources, transportation and social networks.
Following a data-driven approach, this thesis builds a theoretical framework for the
provision of robustness certificates for solutions to multi-agent optimization problems
and non-cooperative games with an arbitrary cost function and uncertainty in the
constraints. The theoretical tools developed allow the provision of collective certificates
for sets (and subsets) of solutions that do not necessarily need to be optimal. Focusing
on the class of aggregative games, agents’ deviations from an equilibrium solution and
uncertain constraints are considered. A data-driven equilibrium seeking algorithm is
then proposed such that tunable collective guarantees can be provided for all possible
feasible deviations from the equilibrium.
Shifting our attention towards a particular class of optimization programs with
uncertain cost, prevalent in practical applications, we provide probabilistic guarantees
for the randomized optimizer that do not depend on the number of agents but only on
the size of the decision vector of each agent. As such, the probabilistic guarantees
provided are scalable as the number of agents increases.
Finally, a data-driven theoretical framework is established for multi-agent cooperative
games with uncertain value functions. Collective stability guarantees for the
entire core set, a fundamental concept in cooperative game theory, are provided based
on data from the value functions in a probably approximately correct learning fashion.
The case where the core can be empty is considered and a methodology to accompany
allocations in a relaxed core with stability certificates is proposed
Stereotactic interstitial radiosurgery with the Photon Radiosurgery System (PRS) for malignant glioma and cerebral metastases
No full textZiel dieser Studie war die Durchführbarkeit und Sicherheit der stereotaktischen Radiochirurgie mit dem Photon Radiosurgery System zu ermitteln und die Effizienz der Therapie anhand von klinisch-radiologischen und biologischen Endpunkten zu berechnen.
Die PRS-Radiochirurgie an 35 Patienten mit singulären Hirnmetastasen kleiner als 3,5 cm war sicher und komplikationsarm. Die Toxizität und Morbidität (34,3% und 37%), überwiegend infolge einer Verstärkung eines bestehenden perifokalen Hirnödems, war in den meisten Fällen reversibel. Betroffen waren häufig Patienten mit Tumoren im Bereich der Zentralregion oder mit größerem Tumorvolumen. Irreversible Nebenwirkungen wurden bei zusätzlicher Radiotherapie (2 Fälle von Leukenzephalopathie, eine späte Radionekrose) oder bei zystischer Umwandlung des bestrahlten Tumors beobachtet. Die meisten Patienten sind infolge des systemischen Tumorleidens verstorben. Das mediane Überl
leben (7,37 Monate) entspricht den Daten von Studien zur externen Radiochirurgie. Das mediane funktionell unabhängige Überleben bei einem Karnofsky-Index >70% betrug 3 Monate und die mediane Zeit zur neurologischen Progression war 5,2 Monate. Während der ersten 3 Monate zeigten 30 Patienten (85,7%) eine Besserung oder Stabilität der neurologischen Symptome und 28 Patienten (82,3%) eine lokale Tumorkontrolle. Die niedrige endgültige Ansprech- und Tumorkontrollrate (35,3% und 50%) ist teilweise bedingt durch die Auswahl von strengen Kriterien zur Beurteilung einer Remission sowie durch die engen Verlaufskontrollen. Ein erhöhtes Risiko für ein frühes Lokalrezidiv hatten Patienten mit PRS als Rezidivtherapie und mit unregelmäßig konfiguriertem Tumor. Das mediane progressionsfreie Überleben betrug 3,55 Monate. Ungünstig wirkten sich ein großer PRS-Radius und eine niedrige Dosisrate aus. Im Verlauf entwickelten 28 Patienten (82,3%) ein Rezidiv (17 Lokal-, 18 Fernrezidiv). Die 16 Patienten mit Rezidivbehandlung (Radiotherapie, Radiochirurgie, Operation, Chemotherapie) hatten eine längere mediane Überlebenszeit als die 12 Patienten ohne Therapie.
Die PRS-Radiochirurgie an 17 Patienten mit malignen Gliomen war ebenfalls sicher und komplikations-arm. Eine Zunahme des perifokalen Hirnödems war die Hauptursache für die beobachtete Morbidität (47%) und Toxizität (23,5%). Betroffen waren überwiegend Patienten mit ausgeprägtem Hirnödem vor der PRS und mit einer Tumorlokalisation in der Zentralregion. Fast alle Patienten zeigten im Verlauf Einbußen in der Lebensqualität, vor allem infolge eines Hirnödems und den Auswirkungen einer Steroidabhängigkeit. Steroide nahmen 16 Patienten (94,1%) länger als 3 Monate ein und 11 davon (64,7%) zeigten eine Steroidabhängigkeit. Die mediane Überlebenszeit bei den 8 Glioblastom-Patienten (7,34 Monate) und bei den 7 Patienten mit anaplastischen Gliomen (13,13 Monate) ist vergleichbar mit derjenigen aus verschiedenen Radiochirurgie und Brachytherapie Studien. Das mediane funktionell unabhängige Überleben betrug 4,5 Monate, die mediane Zeit zur neurologischen Progression 3 Monate und die mediane progressionsfreie Überlebenszeit 7 Wochen. Im Verlauf entwickelten 6 Patienten ein Lokal- und ein Fernrezidiv, 10 Patienten nur ein Lokalrezidiv und ein Patient nur ein Fernrezidiv. Eine Rezidivtherapie (Chemo-, Radiotherapie, Operation) erhielten 15 Patienten. Die wenigen Patienten mit länger dauernder radiologischer Stabilität zeigten aufgrund eines perifokalen Hirnödems, einer zystischen Umwandlung des bestrahlten Tumors oder eines Fernrezidivs keine klinische Besserung. Alle evaluierbaren Patienten sind an einer neurologischen Todesursache verstorben.
Die Hauptvorteile der PRS-Radiochirurgie liegen in der interstitiellen Applikation von ionisierenden Strahlen direkt im Tumor im Anschluss an eine stereotaktische Biopsie und in einer kurzen Behandlungszeit. Die Risiken einer weiteren Intervention entfallen, der stationäre Aufenthalt wird kürzer, die Kosten sind niedriger und die Handhabung radioaktiver Isotope wird entbehrlich. Der steile Dosisabfall bei der PRS-Radiochirurgie führt zu einem besseren Schutz des umliegenden Hirnparenchyms, setzt aber ein genaues Positionieren der PRS-Sondenspitze im Zentrum des Tumors voraus. Aufgrund der sphärischen Verteilung der Strahlung ist die Behandlung auf Tumoren mit runder Konfiguration beschränkt. Bei entsprechend günstiger Konstellation von Tumorvolumen und Lokalisation ist die Behandlung von Hirnmetastasen mit PRS eine wichtige therapeutische Option.Objective: The goal of this study was to evaluate the efficacy and the treatment outcome of patients with cerebral metastases or malignant glioma, being treated stereotactically with a miniature x-ray generator (Photon Radiosurgery System).
Methods: Patients older than 18, with a Karnofsky Performance Scale rating of at least 60, with a single brain tumor up to 3.5 cm in greatest diameter and no localization in the brainstem were enrolled in the study. Clinical and neuroimaging evaluation were asessed at 2-, 6- and 12-week intervalls postoperatively and every 3 months thereafter. Survival, local control, distant and overall brain freedom from progression were obtained using the Kaplan-Meier method.
Results: 35 patients with cerebral metastases and 17 patients with malignant glioma were treated with a single fraction of stereotactic interstitial irradiation (median 18 Gy), after being histologically verified by biopsy, between October 1996 and July 2002.
Median survival was 7.37 months for patients with metastastic tumors and the actuarial survival rates at 6 and 12 months were 60 and 34.3% respectively. Acute complications on 6 patients were associated with shorter survival. Local tumor control at the initial and at the last follow-up was 82 and 50% (1 patient with CR, 7 PR, 4 MR, 5 SD, 17 PD). Eighteen patients (53%) developed distant brain metastases. At 1 year the local control rate, the distant and overall brain FFP were 33, 43.3 and 14.7%, respectively. A shorter local tumor control was observed by PRS treatment of a recurrent tumor and by irregular tumor configuration.
The median survival was 7.34 months for the 8 patients with glioblastoma and 13.13 months for the 9 patients with anaplastic glioma. Sixteen tumors (94%) recurred locally and seven patients (41%) experienced recurrences at distant sites. The median time to local progression was 7 weeks, the medial time to neurological progression was 3 months and the median survival with a KPS score ≥70 was 4.5 months. At 1 year the survival rate, the local control, the distant and overall brain FFP were 47, 0, 55.7 and 0%, respectively.
Conclusions: Radiosurgery with the Photon Radiosurgery System is a safe and effective treatment option for selected patients with brain metastases. Patients with malignant glioma did not gain from the PRS treatment in terms of (with regard to) local control or life quality
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