Computational Aspects of Nearly Single-Peaked Electorates

Manipulation, bribery, and control are well-studied ways of changing the outcome of an election. Many voting rules are, in the general case, computationally resistant to some of these manipulative actions. However when restricted to single-peaked electorates, these rules suddenly become easy to manipulate. Recently, Faliszewski, Hemaspaandra, and Hemaspaandra studied the computational complexity of strategic behavior in nearly single-peaked electorates. These are electorates that are not single-peaked but close to it according to some distance measure. In this paper we introduce several new distance measures regarding single-peakedness. We prove that determining whether a given profile is nearly single-peaked is NP-complete in many cases. For one case we present a polynomial-time algorithm. In case the single-peaked axis is given, we show that determining the distance is always possible in polynomial time. Furthermore, we explore the relations between the new notions introduced in this paper and existing notions from the literature.Comment: Published in the Journal of Artificial Intelligence Research (JAIR). A short version of this paper appeared in the proceedings of the Twenty-Seventh AAAI Conference on Artificial Intelligence (AAAI 2013). An even earlier version appeared in the proceedings of the Fourth International Workshop on Computational Social Choice 2012 (COMSOC 2012

Conformant Planning as a Case Study of Incremental QBF Solving

We consider planning with uncertainty in the initial state as a case study of incremental quantified Boolean formula (QBF) solving. We report on experiments with a workflow to incrementally encode a planning instance into a sequence of QBFs. To solve this sequence of incrementally constructed QBFs, we use our general-purpose incremental QBF solver DepQBF. Since the generated QBFs have many clauses and variables in common, our approach avoids redundancy both in the encoding phase and in the solving phase. Experimental results show that incremental QBF solving outperforms non-incremental QBF solving. Our results are the first empirical study of incremental QBF solving in the context of planning and motivate its use in other application domains.Comment: added reference to extended journal article; revision (camera-ready, to appear in the proceedings of AISC 2014, volume 8884 of LNAI, Springer

Backdoors to planning

Backdoors measure the distance to tractable fragments and have become an important tool to find fixed-parameter tractable (fpt) algorithms for hard problems in AI and beyond. Despite their success, backdoors have not been used for planning, a central problem in AI that has a high computational complexity. In this work, we introduce two notions of backdoors building upon the causal graph. We analyze the complexity of finding a small backdoor (detection) and using the backdoor to solve the problem (evaluation) in the light of planning with (un)bounded plan length/domain of the variables. For each setting we present either an fpt-result or rule out the existence thereof by showing parameterized intractability. For several interesting cases we achieve the most desirable outcome: detection and evaluation are fpt. In addition, we explore the power of polynomial preprocessing for all fpt-results, i.e., we investigate whether polynomial kernels exist. We show that for the detection problems, polynomial kernels exist whereas we rule out the existence of polynomial kernels for the evaluation problems

Development of a mixed-reality-based simulation environment for surgical team training

Introduction Simulators are becoming increasingly important in medical education, and the adaptation of virtual reality (VR)-based technology into surgical simulation environments offers many advantages. However, the implementation of VR simulators in the field of spinal interventions has been low so far. In addition, the majority of available simulators are aimed at training individual users and their technical skills instead of at teams and their non-technical skills. The goal of our research project and this doctoral thesis was to develop a simulation environment for the training and assessment of spine surgery that can train both individual users and surgical teams in both technical and non-technical skills. Methods A variety of methods were used for this multi-step developmental process. As a first step, a systematic review was performed in order to give an accurate overview and synthesis of the current state of VR simulation in the field of spinal procedures (publication 1). This was followed by observations, interviews, and expert panels to gather information and requirements for the simulation environment of a vertebroplasty procedure (publication 2). As a next step, a simulation study was conducted to test the validity of the simulated procedure (publication 3). For this purpose, think-aloud protocols, user questionnaires, and expert ratings were applied. Results In the systematic review, the current state of VR-based simulation in the area of spinal interventions was shown and the current evidence base was systematically synthesized. In publication 2, the individual steps of a vertebroplasty for the three participating surgical professions were systematically elicited and a novel method for the specification of simulation requirements was introduced. In publication 3, we presented a newly developed classification system that systematically categorized the surgeon’s comments expressed during the operation of the surgical simulator. Conclusions Development projects like the one presented here are necessary to create new medical learning environments. Our work provides developers with tools for similar projects. In addition, we have developed a fully functional simulation environment designed for vertebroplasty training and assessment of surgical teams to train surgeons, anesthetists, and nurses.Einleitung Simulatoren gewinnen immer mehr an Bedeutung in der medizinischen Ausbildung. Besonders die Ergänzung von Virtual Reality (VR) in die Simulationsumgebungen bringt viele Vorteile mit sich. Allerdings ist die Verbreitung von VR Simulatoren im Bereich der Wirbelsäulenchirurgie bisher gering. Außerdem zielt das Gros der verfügbaren Simulatoren auf das Training von Einzelanwendern und deren technische Fähigkeiten, nicht jedoch auf Teams und deren nicht-technische Fähigkeiten. Das Ziel unseres Forschungsvorhabens und dieser Doktorarbeit war es, eine Simulationsumgebung für das Training und Assessment eines Wirbelsäuleneingriffes zu entwickeln, in der sowohl technische als auch nicht-technische Fähigkeiten von Einzelanwendern und chirurgischen Teams trainiert werden können. Methoden Für den Entwicklungsprozess kam eine Vielzahl an Methoden zur Anwendung. Als erster Schritt wurde eine systematische Aufarbeitung der bisherigen Veröffentlichungen zu VR-Simulatoren für Wirbelsäuleneingriffe durchgeführt (Publikation 1). Für Publikation 2 kamen Beobachtungen, Interviews und ein Expertenpanel zum Einsatz, um Informationen und Voraussetzungen für eine Simulationsumgebung zu definieren. Daraufhin wurde in Publikation 3 eine Nutzerstudie auf der Basis von Think-aloud-Protokollen, Nutzerfragebögen und Bewertungen durch Experten durchgeführt, um die Validität der simulierten Prozedur zu testen. Ergebnisse In der systematischen Literaturübersicht (Publikation 1) wurde der aktuelle Stand der Simulation im Bereich Wirbelsäuleneingriffe abgebildet. In der Publikation 2, wurden die einzelnen Schritte einer Vertebroplastie für die drei beteiligten chirurgischen Professionen systematisch erhoben und ein neues Verfahren zur Durchführung von Anforderungsanalysen von medizinischen Simulatoren vorgestellt. Ein weiteres Ergebnis, welches in Publikation 3 präsentiert wird, war die Entwicklung eines neuen Klassifikationssytems, um Kommentare von Chirurgen während der Simulatornutzung zu kategorisieren. Schlussfolgerungen Entwicklungsprojekte, wie dieses hier, sind notwendig, um neue medizinische Lernumgebungen zu erstellen. Unsere Arbeit hat dabei geholfen, Entwicklern Werkzeuge für ähnliche Projekte zur Verfügung zu stellen. Außerdem haben wir eine voll funktionstüchtige Simulationsumgebung entwickelt, die für das Training und Assessment von chirurgischen Teams anhand der Vertebroplastie bestimmt ist und Chirurgen, Anästhesisten und Pflegekräfte gemeinsam schulen wird

Development of a mixed-reality-based simulation environment for surgical team training

Introduction Simulators are becoming increasingly important in medical education, and the adaptation of virtual reality (VR)-based technology into surgical simulation environments offers many advantages. However, the implementation of VR simulators in the field of spinal interventions has been low so far. In addition, the majority of available simulators are aimed at training individual users and their technical skills instead of at teams and their non-technical skills. The goal of our research project and this doctoral thesis was to develop a simulation environment for the training and assessment of spine surgery that can train both individual users and surgical teams in both technical and non-technical skills. Methods A variety of methods were used for this multi-step developmental process. As a first step, a systematic review was performed in order to give an accurate overview and synthesis of the current state of VR simulation in the field of spinal procedures (publication 1). This was followed by observations, interviews, and expert panels to gather information and requirements for the simulation environment of a vertebroplasty procedure (publication 2). As a next step, a simulation study was conducted to test the validity of the simulated procedure (publication 3). For this purpose, think-aloud protocols, user questionnaires, and expert ratings were applied. Results In the systematic review, the current state of VR-based simulation in the area of spinal interventions was shown and the current evidence base was systematically synthesized. In publication 2, the individual steps of a vertebroplasty for the three participating surgical professions were systematically elicited and a novel method for the specification of simulation requirements was introduced. In publication 3, we presented a newly developed classification system that systematically categorized the surgeon’s comments expressed during the operation of the surgical simulator. Conclusions Development projects like the one presented here are necessary to create new medical learning environments. Our work provides developers with tools for similar projects. In addition, we have developed a fully functional simulation environment designed for vertebroplasty training and assessment of surgical teams to train surgeons, anesthetists, and nurses.Einleitung Simulatoren gewinnen immer mehr an Bedeutung in der medizinischen Ausbildung. Besonders die Ergänzung von Virtual Reality (VR) in die Simulationsumgebungen bringt viele Vorteile mit sich. Allerdings ist die Verbreitung von VR Simulatoren im Bereich der Wirbelsäulenchirurgie bisher gering. Außerdem zielt das Gros der verfügbaren Simulatoren auf das Training von Einzelanwendern und deren technische Fähigkeiten, nicht jedoch auf Teams und deren nicht-technische Fähigkeiten. Das Ziel unseres Forschungsvorhabens und dieser Doktorarbeit war es, eine Simulationsumgebung für das Training und Assessment eines Wirbelsäuleneingriffes zu entwickeln, in der sowohl technische als auch nicht-technische Fähigkeiten von Einzelanwendern und chirurgischen Teams trainiert werden können. Methoden Für den Entwicklungsprozess kam eine Vielzahl an Methoden zur Anwendung. Als erster Schritt wurde eine systematische Aufarbeitung der bisherigen Veröffentlichungen zu VR-Simulatoren für Wirbelsäuleneingriffe durchgeführt (Publikation 1). Für Publikation 2 kamen Beobachtungen, Interviews und ein Expertenpanel zum Einsatz, um Informationen und Voraussetzungen für eine Simulationsumgebung zu definieren. Daraufhin wurde in Publikation 3 eine Nutzerstudie auf der Basis von Think-aloud-Protokollen, Nutzerfragebögen und Bewertungen durch Experten durchgeführt, um die Validität der simulierten Prozedur zu testen. Ergebnisse In der systematischen Literaturübersicht (Publikation 1) wurde der aktuelle Stand der Simulation im Bereich Wirbelsäuleneingriffe abgebildet. In der Publikation 2, wurden die einzelnen Schritte einer Vertebroplastie für die drei beteiligten chirurgischen Professionen systematisch erhoben und ein neues Verfahren zur Durchführung von Anforderungsanalysen von medizinischen Simulatoren vorgestellt. Ein weiteres Ergebnis, welches in Publikation 3 präsentiert wird, war die Entwicklung eines neuen Klassifikationssytems, um Kommentare von Chirurgen während der Simulatornutzung zu kategorisieren. Schlussfolgerungen Entwicklungsprojekte, wie dieses hier, sind notwendig, um neue medizinische Lernumgebungen zu erstellen. Unsere Arbeit hat dabei geholfen, Entwicklern Werkzeuge für ähnliche Projekte zur Verfügung zu stellen. Außerdem haben wir eine voll funktionstüchtige Simulationsumgebung entwickelt, die für das Training und Assessment von chirurgischen Teams anhand der Vertebroplastie bestimmt ist und Chirurgen, Anästhesisten und Pflegekräfte gemeinsam schulen wird

Recycled Coarse Aggregate and Fly Ash Effect on Compressive Strength of Self-Compacting Concrete

The paper presents experimental results of the tests conducted on Self-Compacting Concrete (SCC) with recycled coarse aggregate, and fly ash as filler component. A fine fraction of aggregate originated from a riverbed, while coarse aggregate was obtained either from a riverbed or by crushing laboratory concrete cubes as recycled concrete aggregate. The larger coarse aggregate grains than typical for SCC were used, to highlight the possibility of application in structure elements with sparse reinforcement bars. Four mixtures of concrete were made, in order to compressive strength as the dominant property of any concrete. All of the fresh concrete mixtures displayed proper behavior for this kind of concrete, whereas recycled concrete aggregate induced several challenges. Hardened concrete mixtures showed that beyond the use of natural coarse aggregate, there is the possibility to obtain proper mechanical behavior needed for structural concrete, with moderate amounts of cement. Such an approach paves a way for a cleaner and more sustainable civil engineering practice

Recycled Coarse Aggregate and Fly Ash Effect on Compressive Strength of Self-Compacting Concrete

The paper presents experimental results of the tests conducted on Self-Compacting Concrete (SCC) with recycled coarse aggregate, and fly ash as filler component. A fine fraction of aggregate originated from a riverbed, while coarse aggregate was obtained either from a riverbed or by crushing laboratory concrete cubes as recycled concrete aggregate. The larger coarse aggregate grains than typical for SCC were used, to highlight the possibility of application in structure elements with sparse reinforcement bars. Four mixtures of concrete were made, in order to compressive strength as the dominant property of any concrete. All of the fresh concrete mixtures displayed proper behavior for this kind of concrete, whereas recycled concrete aggregate induced several challenges. Hardened concrete mixtures showed that beyond the use of natural coarse aggregate, there is the possibility to obtain proper mechanical behavior needed for structural concrete, with moderate amounts of cement. Such an approach paves a way for a cleaner and more sustainable civil engineering practice.52nd International October Conference on Mining and Metallurgy : November 29-30, 2021, Bor

The Reaction of Glycerol Carbonate with Primary Aromatic Amines in the Presence of Y- and X-Faujasites: the Synthesis of N-(2,3-dihydroxy)propyl anilines and the Reaction Mechanism

At 140 ◦C, in the presence of alkali metal exchanged faujasites, preferably NaY, as catalysts, glycerine carbonate (GlyC) is an efficient and green alkylating agent of primary aromatic amines (p-XC6H4NH2, X = H, OMe, OH, Cl): the reaction takes place with a high conversion (~90%) and a good selectivity (80–90%) for the formation of N-(2,3-dihydroxy)propyl anilines (p-XC6H4NHCH2CH(OH)CH2OH). The alkylation process does not proceed through an exclusive nucleophilic substitution of anilines at the C5 position of GlyC. Evidence proves that a dehydrative condensation of anilines with GlyC produces intermediate species, and both transesterification and hydrolysis reactions are involved to obtain the final N-alkyl derivatives. A mechanism is proposed accordingly. Experiments show that faujasites are recyclable catalysts on condition that they are exposed to a mild thermal activation (70 ◦C, 18 mbar) prior to their re-use. Otherwise, if zeolites are calcined (400 ◦C, air), both the catalyst activity and the reaction selectivity drop. Isolated yields (60–65%) of N-(2,3-dihydroxy)propyl anilines are somewhat limited by the difficult separation of the unreacted GlyC and of the by-product glycerine. Nonetheless, the overall efficiency of the method is comparable to that of alternative routes based on highly toxic reagents (glycidol and aryl halides)