Ambiguity aversion as a reason to choose tournaments

We test the implications of ambiguity aversion in a principal-agent problem with multiple agents. When output distributions are uncertain, models of ambiguity aversion suggest that tournaments may become more attractive than independent wage contracts, in contrast to the case where output distributions are known. We do so by presenting agents with a choice between tournaments and independent contracts, which are designed in a way that under uncertainty about output distribution (that is, under ambiguity), ambiguity averse agents should typically prefer tournaments, while ambiguity neutral agents prefer independent contracts, independent of their degree of risk aversion. This is the case, because the tournament removes all ambiguity about the equilibrium wages. We compare the share of participants who choose the tournament under ambiguity with the share of participants choosing the tournament in a control treatment, where output distributions are know. As the theory predicts, we find indeed that under ambiguity the share of agents who choose the tournaments is higher than in the case of known output distributions.Ambiguity aversion, tournaments, Ellsberg urn, contract design

A Semidefinite Hierarchy for Containment of Spectrahedra

A spectrahedron is the positivity region of a linear matrix pencil and thus the feasible set of a semidefinite program. We propose and study a hierarchy of sufficient semidefinite conditions to certify the containment of a spectrahedron in another one. This approach comes from applying a moment relaxation to a suitable polynomial optimization formulation. The hierarchical criterion is stronger than a solitary semidefinite criterion discussed earlier by Helton, Klep, and McCullough as well as by the authors. Moreover, several exactness results for the solitary criterion can be brought forward to the hierarchical approach. The hierarchy also applies to the (equivalent) question of checking whether a map between matrix (sub-)spaces is positive. In this context, the solitary criterion checks whether the map is completely positive, and thus our results provide a hierarchy between positivity and complete positivity.Comment: 24 pages, 2 figures; minor corrections; to appear in SIAM J. Opti

The principal-agent problem with smooth ambiguity

We study a principal-agent model in which the (effort-dependent) realisation of output levels is ambiguous, and the agent is ambiguity averse (while the principal is ambiguity neutral). We show that introducing ambiguity aversion will lower profits if the action that the principal wants to implement is the most ambiguous one, while they may increase otherwise. Regarding the design of the optimal contract, we show that under ambiguity aversion the optimal incentive scheme may not be monotone even if a natural generalization of the monotone likelihood ratio property is satisfied, and illustrate how this fact could affect the design of contracts in an applied economic context. We also find that the individual rationality constraint need not bind in the presence of ambiguity aversion unless preferences satisfy constant absolute ambiguity aversion

Modes of ambiguous communication

We study cheap talk communication in a simple two actions-two states model featuring ambiguous priors. First, we find that in equilibrium, S often mixes between messages triggering different beliefs and behavior by R while R also occasionally randomizes. We interpret randomization by respectively S and R as embodying two different modes of ambiguous communication. Second, we find that for sufficiently high ambiguity, more than two messages are often necessary to implement the optimal decision rule of S. If only two messages are available and S faces his preference twin, S may be unable to implement his optimal decision rule and influential communication may be altogether impossible. We stress the non replicability of these results within an expected utility environment. Third, we show that the addition of a little ambiguity may generate influential communication that is unambiguously advantageous to S

Implementierung und Bewertung von L-MIFA im Netzwerksimulator NS-2

. . .All-IP networks become increasingly visible. The various communication networksare aimed to be connected with each other through a common IP core, so that the userwill stay always online, anytime and anywhere. We believe that these networks will bethe popular network in the future. However a lot of challenges remain unsolved untiltoday. One of the major challenges is how to achieve a seamless and fast handoff whilemoving from one point of attachment to another. Low Latency Mobile IP Fast AuthenticationProtocol (L-MIFA) is proposed to avoid the problems of Mobile IP (MIP)and to match the real-time requirements without introducing intermediate nodes andwithout making any restriction on the network topology. In this work we evaluate theperformance of L-MIFA compared to MIP, Handoff-Aware Wireless Access InternetInfrastructure (HAWAII) and Mobile IP Fast Authentication (MIFA) . The evaluationis performed by means of network simulator 2 (ns-2). The four protocols are evaluateddeploying the same topology.Our simulation results have shown that L-MIFA and MIFA outperforms HAWAII andMIP with respect to handoff latency and the number of dropped packets for uplink anddownlink traffic. This is because L-MIFA and MIFA needs only to register with the newForeign Agent (FA) to be able to resume sending of packets, while MIP needs to registerwith the Home Agent (HA) and HAWAII requires updating the new location at the oldFA. For downlink traffic HAWAII and MIFA perform comparable to each other. Thehandoff latency and packet dropping of L-MIFA is near zero and better than MIFA inup- and downlink. . . .. . . All-IP Netze finden zunehmend wachsende Verbreitung. Diese vielfältigen Kommunikationsnetze sind durch ein gemeinsames IP Core verbunden. Dies ermöglicht dem Nutzer unabhängig vom Aufenthaltsort online zu bleiben. Diese Netzwerke erfreuen sich wachsender Beliebtheit. Jedoch sind eine Vielzahl von Problemen bis heute ungelöst. Eine der Hauptaufgaben ist ein schneller und nahtloser Übergang zwischen den Zugangspunkten des Netzwerkes. Low Latency Mobile IP Fast Authentication Protocol(L-MIFA) vermeidet Probleme von Mobile IP (MIP). L-MIFA erfüllt Echtzeitanforderungen ohne Verwendung spezialisierter Router oder anderer Einschränkungen der Netzwerktopologie. In dieser Arbeit wird die Performanz von L-MIFA bewertet und mit MIP, Handoff-Aware Wireless Access Internet Infrastructure (HAWAII) und Mobile IP Fast Authentication (MIFA) verglichen. Die Bewertung erfolgt im Netzwerksimulator2 (ns-2). Alle vier Protokolle werden in derselben Topologie betrachtet. Die Simulationsergebnisse haben gezeigt, dass bei L-MIFA und MIFA die Handoff Latenzzeiten und Paketverlustraten in Up- und Downlink deutlich geringer sind als bei HAWAII und MIP. Die wird dadurch erreicht, dass L-MIFA und MIFA sich nur mit dem neuen Foreign Agent (FA) zu registrieren brauchen, um wieder Pakete sendenzu können. MIP hingegen muss sich bei dem Home Agent (HA) registrieren. HAWAII muss die neue Postion dem alten FA mitteilen. Für Downlink-Quellen erzielen HAWAII und MIFA vergleichbare Werte. Die Handoff Latenzzeiten und Paketverlustraten von L-MIFA sind nahe 0 und somit besser als MIFA in Up- und Downlink. . . .Ilmenau, Techn. Univ., Diplomarbeit, 200

Inflammatory bowel disease-specific autoantibodies in HLA-B27-associated spondyloarthropathies: Increased prevalence of ASCA and pANCA

Aims: An association between inflammatory bowel disease (IBD) and spondyloarthropathies (SpA) has repeatedly been reported. The aim of the present study was to investigate whether serologic markers of IBD, e. g. antibodies against Saccharomyces cerevisiae (ASCA), antibodies against exocrine pancreas (PAB) and perinuclear antineutrophil cytoplasmic antibodies (pANCA) are present in HLA-B27-associated SpA. Methods: 87 patients with HLA-B27-positive SpA and 145 controls were tested for ASCA, PAB and pANCA employing ELISA or indirect immunofluorescence, respectively. Antibody-positive patients were interviewed regarding IBD-related symptoms using a standardized questionnaire. Results/Conclusion: When compared to the controls, ASCA IgA but not ASCA IgG levels were significantly increased in patients with SpA, in particular in ankylosing spondylitis (AS) and undifferentiated SpA (uSpA). pANCA were found in increased frequency in patients with SpA whereas PAB were not detected. The existence of autoantibodies was not associated with gastrointestinal symptoms but sustains the presence of a pathophysiological link between bowel inflammation and SpA. Copyright (C) 2004 S. Karger AG, Basel

Secure and authenticated data communication in wireless sensor networks

© 2015 by the authors; licensee MDPI, Basel, Switzerland. Securing communications in wireless sensor networks is increasingly important as the diversity of applications increases. However, even today, it is equally important for the measures employed to be energy efficient. For this reason, this publication analyzes the suitability of various cryptographic primitives for use in WSNs according to various criteria and, finally, describes a modular, PKI-based framework for confidential, authenticated, secure communications in which most suitable primitives can be employed. Due to the limited capabilities of common WSN motes, criteria for the selection of primitives are security, power efficiency and memory requirements. The implementation of the framework and the singular components have been tested and benchmarked in our tested of IRISmotes

Evidence for topological band inversion of the phase change material Ge2Sb2Te5

We present an angle-resolved photoemission study of a ternary phase change material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar being 0.3 eV below the Fermi level E_F and a circular Fermi contour around Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in agreement with density functional theory calculations of the Petrov stacking sequence in the cubic phase which exhibits a topological surface state. The topologically trivial cubic KH stacking shows a valence band maximum at Gamma in line with all previous calculations of the hexagonal stable phase exhibiting the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0 and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy exhibits a band gap of 0.4 eV around E_F