Strong Robustness of Randomized Rumor Spreading Protocols

Randomized rumor spreading is a classical protocol to disseminate information across a network. At SODA 2008, a quasirandom version of this protocol was proposed and competitive bounds for its run-time were proven. This prompts the question: to what extent does the quasirandom protocol inherit the second principal advantage of randomized rumor spreading, namely robustness against transmission failures? In this paper, we present a result precise up to $(1 \pm o(1))$ factors. We limit ourselves to the network in which every two vertices are connected by a direct link. Run-times accurate to their leading constants are unknown for all other non-trivial networks. We show that if each transmission reaches its destination with a probability of $p \in (0,1]$, after (1+\e)(\frac{1}{\log_2(1+p)}\log_2n+\frac{1}{p}\ln n) rounds the quasirandom protocol has informed all $n$ nodes in the network with probability at least 1-n^{-p\e/40}. Note that this is faster than the intuitively natural $1/p$ factor increase over the run-time of approximately $\log_2 n + \ln n$ for the non-corrupted case. We also provide a corresponding lower bound for the classical model. This demonstrates that the quasirandom model is at least as robust as the fully random model despite the greatly reduced degree of independent randomness.Comment: Accepted for publication in "Discrete Applied Mathematics". A short version appeared in the proceedings of the 20th International Symposium on Algorithms and Computation (ISAAC 2009). Minor typos fixed in the second version. Proofs of Lemma 11 and Theorem 12 fixed in the third version. Proof of Lemma 8 fixed in the fourth versio

Back to Work – mit Peer Support : der Einbezug von Peers in die Reintegration von Menschen nach erworbener Hirnschädigung in den ersten Arbeitsmarkt

Einleitung: Für viele Menschen ist nach erworbener Hirnschädigung die Rückkehr zur Arbeit ein priorisiertes Ziel und stellt gleichzeitig eine enorme Herausforderung dar. In der Vergangenheit ist bereits belegt worden, dass Betroffene von Peer Support in unterschiedlichen Settings profitieren. Ziel: Es wird aufgezeigt, welche Herausforderungen Menschen nach erworbener Hirnschädigung in der Arbeitsreintegration erleben und daraus abgeleitet, wie bisherige Erfahrungen mit Peer Support in der Arbeitswiedereingliederung unterstützend eingesetzt werden könnten. Methode: Anhand einer Literaturrecherche sind neun Studien und ein Review ausgesucht und kritisch beurteilt worden. Die Ergebnisse sind mittels einer Template-Analyse auf das Model of Human Occupation übertragen, kategorisiert und interpretiert worden. Ergebnisse: Menschen nach erworbener Hirnschädigung erleben vielfältige Herausforderungen in der Arbeitsreintegration. Die Erfahrungen aus anderen Settings zeigen, dass Peers den Betroffenen zu mehr Akzeptanz und einem besseren Selbstbild verhelfen können, indem sie eine Vorbildfunktion übernehmen und spezifische Bewältigungsstrategien vermitteln. Peer Support-Programme bringen jedoch logistische Herausforderungen mit sich und bedürfen einer ausreichenden Supervision. Schlussfolgerung: Die Ergebnisse deuten darauf hin, dass sich Peer Support auf die Arbeitsreintegration von Menschen nach erworbener Hirnschädigung positiv auswirkt. Es kann allerdings kein deckender Übertrag gemacht werden, sondern es braucht weiterführende Forschung für das neurologische Setting

Reaping the Benefits of Migration in an Ageing Europe. Policy Brief No. 7

Unless labour force participation in Europe increases enormously in the coming decades, the current demographic dynamics will pose gigantic challenges to the sustainability of public finance. Migration (and thus migration policy) can thus be seen as a central topic which will remain on top of the policy agenda. The aim of this policy brief is to summarize the knowledge gained by the research efforts on this issue in the framework of WWWforEurope and to provide policymakers with new methods and research results which will allow them to better quantify the effects of policy changes.Series: WWWforEurop

Randomized rounding and rumor spreading with stochastic dependencies

Randomness is an important ingredient of modern computer science. The present thesis is concerned with two uses of randomness, viz. randomized roundings and randomized rumor spreading algorithms. The theorem of Beck and Fiala (1981) asserts that for every hypergraph and every set of vertex weights there is a rounding of the vertex weights such that the additive rounding error for all hyperedges is bounded by the maximum degree. In Chapter 2 this theorem will be extended to randomized roundings, that is, to roundings that are efficiently generated at random in such a way that each value is rounded up with probability equal to its fractional part. The larger part of this thesis deals with randomized rumor spreading algorithms. These are protocols for disseminating information on graphs. The classical randomized rumor spreading was introduced and first investigated by Frieze and Grimmett on the complete graph (1985). In Chapter 3 a generalization of their results both in terms of the model used and in terms of the underlying graph will be shown. In Chapter 4 a quasirandom rumor spreading protocol introduced by Doerr, Friedrich, and Sauerwald (2008) will be considered. We present a detailed analysis of its evolution and show that its performance and robustness match performance and robustness of the randomized rumor spreading protocol. The unifying idea is to use dependencies so as to obtain results that are superior or equal to those obtained via independent randomness.Die Verwendung von Zufallselementen ist ein wichtiger Bestandteil der modernen Informatik. Die vorliegende Arbeit untersucht zwei Bereiche, in denen randomisierte Methoden Verwendung finden, nämlich randomisierte Rundungen und randomisierte Algorithmen zur Gerüchteverbreitung. Der Satz von Beck und Fiala (1981) sagt aus, dass es für jeden Hypergraphen und für jeden Satz von Knotengewichten eine Rundung gibt derart, dass der Rundungsfehler pro Kante vom Maximalgrad beschränkt wird. Im ersten Teil der Arbeit wird dieser Satz auf den Fall randomisierter Rundungen verallgemeinert, das heißt auf zufällige Rundungen, bei denen jede Zahl mit der Wahrscheinlichkeit entsprechend ihren Nachkommastellen aufgerundet wird. Der zweite, größere Teil der Arbeit handelt von randomisierten Algorithmen zur Gerüchteverbreitung. Das klassische "Randomized Rumor Spreading" wurde von Frieze und Grimmett (1985) eingeführt. Ihre Ergebnisse werden in Kapitel 3 sowohl hinsichtlich des Modells als auch hinsichtlich des zugrundegelegten Graphen verallgemeinert. In Kapitel 4 wird ein quasizufälliges Modell zur Gerüchteverbreitung betrachtet und gezeigt, dass es bezüglich Laufzeit und Robustheit dem klassischen Modell gleichwertig ist. Gemeinsam liegt beiden Teilen der Arbeit die Idee zugrunde, stochastische Abhängigkeiten zu nutzen um Ergebnisse zu erzielen, die den unter Verwendung stochastischer Unabhängigkeit erzielten gleichwertig oder überlegen sind

Combining experimental evidence with machine learning to assess anti-corruption educational campaigns among Russian university students

This paper examines how anti-corruption educational campaigns affect the attitudes of Russian university students towards corruption and academic integrity. About 2,000 survey participants were randomly assigned to one of four different information materials (brochures or videos) about the negative consequences of corruption or to a control group. Using machine learning to detect effect heterogeneity, we find that various groups of students react to the same information differently. Those who commonly plagiarize, who receive excellent grades, and whose fathers are highly educated develop stronger negative attitudes towards corruption in the aftermath of our intervention. However, some information materials lead to more tolerant views on corruption among those who rarely plagiarize, who receive average or above average grades, and whose fathers are less educated. Therefore, policy makers aiming to implement anti-corruption education at a larger scale should scrutinize the possibility of (undesired) heterogeneous effects across student groups

Evaluating an information campaign about rural development policies in (FYR) Macedonia

This paper investigates the effects of an information campaign about a governmental rural development program (RDP) in the Former Yugoslav Republic of Macedonia on the farmers’ intention to participate in the RDP. In the course of a survey among farmers, the treatment group received an information brochure with relevant details on selected RDP measures, while the control group received no information. Even though the intervention had been planned as experiment, randomization was not properly conducted, requiring sample adjustments and controlling for observed covariates in the estimation process. The results suggest that while the intervention succeeded in informing farmers, it had a negative, albeit marginally statically significant, effect on farmers’ reported possibility and intention to use RDP support in the near future. Evidence from further outcome variables suggests that this may be due to the information about administrative burden associated with RDP participation provided in the brochure. We also find that the negative effect is driven by the subsample of unprofitable farmers

The effect of brumation on memory retention

Long-term torpor is an adaptive strategy that allows animals to survive harsh winter conditions. However, the impact that prolonged torpor has on cognitive function is poorly understood. Hibernation causes reduced synaptic activity and experiments with mammals reveal that this can have adverse effects on memories formed prior to hibernation. The impact of brumation, the winter dormancy that is observed in ectotherms, on memory remains unknown. The aim of this study was to examine whether an amphibian, the fire salamander (Salamandra salamandra), was able to retain learned spatial information after a period of brumation. Twelve fire salamanders were trained to make a simple spatial discrimination using a T-maze. All subjects learned the initial task. Upon reaching criterion, half of the subjects were placed into brumation for 100 days while the other half served as controls and were maintained under normal conditions. A post-brumation memory retention test revealed that animals from both conditions retained the learned response. Control tests showed that they solved the task using learned information and not olfactory cues. This finding contrasts with much of the mammalian research and suggests that the processes involved in prolonged torpor may have a fundamentally different impact on memory in mammals and amphibians

Geometric inequalities from phase space translations

We establish a quantum version of the classical isoperimetric inequality relating the Fisher information and the entropy power of a quantum state. The key tool is a Fisher information inequality for a state which results from a certain convolution operation: the latter maps a classical probability distribution on phase space and a quantum state to a quantum state. We show that this inequality also gives rise to several related inequalities whose counterparts are well-known in the classical setting: in particular, it implies an entropy power inequality for the mentioned convolution operation as well as the isoperimetric inequality, and establishes concavity of the entropy power along trajectories of the quantum heat diffusion semigroup. As an application, we derive a Log-Sobolev inequality for the quantum Ornstein-Uhlenbeck semigroup, and argue that it implies fast convergence towards the fixed point for a large class of initial states.Comment: 37 pages; updated to match published versio