Sequential versus Simultaneous Contributions to Public Goods: Experimental Evidence

We report an experiment comparing sequential and simultaneous contributions to a public good in a quasi-linear two-person setting (Varian, Journal of Public Economics, 1994). Our findings support the theoretical argument that sequential contributions result in lower overall provision than simultaneous contributions. However, the distribution of contributions is not as predicted: late contributors are sometimes willing to punish early low contributors by contributing less than their best response. This induces early contributors to contribute more than they otherwise would. A consequence of this is that we fail to observe a predicted first mover advantage.public goods, voluntary contributions, sequential moves, experiment

Who Makes a Good Leader? Social Preferences and Leading-by-Example

We examine the effects of social preferences and beliefs about the social preferences of others in a simple leader-follower voluntary contributions game. We find that groups perform best when led by those who are reciprocally oriented. Part of the effect can be explained by a false consensus effect: selfish players tend to think it more likely that they are matched with another selfish player and reciprocators tend to think it more likely that they are matched with another reciprocator. Thus, reciprocators contribute more as leaders partly because they are more optimistic than selfish players about the reciprocal responses of followers. However, even after controlling for beliefs we find that reciprocally-oriented leaders contribute more than selfish leaders. Thus, we conclude that differing leader contributions by differing types of leader must in large part reflect social motivations.reciprocity, contribution preferences, leadership, leading-by-example, false consensus effect

The minimal communication cost for simulating entangled qubits

We analyze the amount of classical communication required to reproduce the statistics of local projective measurements on a general pair of entangled qubits, $|\Psi_{AB}>=\sqrt{p}\ |00>+\sqrt{1-p}\ |11>$ (with $1/2\leq p \leq 1$). We construct a classical protocol that perfectly simulates local projective measurements on all entangled qubit pairs by communicating one classical trit. Additionally, when $\frac{2p(1-p)}{2p-1} \log{\left(\frac{p}{1-p}\right)}+2(1-p)\leq1$, approximately $0.835 \leq p \leq 1$, we present a classical protocol that requires only a single bit of communication. The latter model even allows a perfect classical simulation with an average communication cost that approaches zero in the limit where the degree of entanglement approaches zero ($p \to 1$). This proves that the communication cost for simulating weakly entangled qubit pairs is strictly smaller than for the maximally entangled one.Comment: 6 pages main text, 8 pages appendices, 3 figure

Correspondence between entangled states and entangled bases under local transformations

We investigate whether pure entangled states can be associated to a measurement basis in which all vectors are local unitary transformations of the original state. We prove that for bipartite states with a local dimension that is either $2, 4$ or $8$, every state corresponds to a basis. Via numerics we strongly evidence the same conclusion also for two qutrits and three qubits. However, for some states of four qubits we are unable to find a basis, leading us to conjecture that not all quantum states admit a corresponding measurement. Furthermore, we investigate whether there can exist a set of local unitaries that transform \textit{any} state into a basis. While we show that such a state-independent construction cannot exist for general quantum states, we prove that it does exist for real-valued $n$-qubit states if and only if $n=2,3$, and that such constructions are impossible for any multipartite system of an odd local dimension. Our results suggest a rich relationship between entangled states and iso-entangled measurements with a strong dependence on both particle numbers and dimension

EU Security Policy regarding China. Its Nature and the Reasons for its continuous Stability, 1995-2014

The scholarly literature on EU security policy regarding China reveals a remarkable shortcoming: The concept of security is taken for granted and the discussions of the last decades in the field of International Security Studies are practically ignored. This lack of conceptual clarity leads to contradictory verdicts on the nature of EU security policy regarding China as well as to a lack of consensus whether or not this policy has changed during the years between 2005 and 2008. Therefore, this thesis sets out to address two research questions. First: What is EU security policy regarding China and how can we analytically and conceptually capture it? And second, based on previous empirical research which suggested a continuity of the policy: Why has the EU’s security policy regarding China remained continuously stable over the last 20 years? The thesis will address these questions in the framework of a poststructuralist discourse-analytical approach. First, four ideal-types of security are developed which serve as ‘analytical lenses’ for the reconstruction of the EU’s security discourse regarding China. It will be shown that the EU’s security policy regarding China can be labeled as liberal-relational security policy, which is marked by efforts to reconcile contradictory interests and to manage relationships. In a second step, the continuous stability of this liberal-relational security policy is explained by constellations of discursive constructions of security between the EU-level and the so-called ‘big three’ member states United Kingdom, France and Germany. The relational security discourses in the three member states reinforce the liberal-relational security discourse on EU-level instead of challenging it. Hence, this thesis argues that there has been no change but, instead, continuity in the EU’s security policy regarding China over the last two decades

Classical Cost of Transmitting a Qubit

We consider general prepare-and-measure scenarios in which Alice can transmit qubit states to Bob, who can perform general measurements in the form of positive operator-valued measures (POVMs). We show that the statistics obtained in any such quantum protocol can be simulated by the purely classical means of shared randomness and two bits of communication. Furthermore, we prove that two bits of communication is the minimal cost of a perfect classical simulation. In addition, we apply our methods to Bell scenarios, which extends the well-known Toner and Bacon protocol. In particular, two bits of communication are enough to simulate all quantum correlations associated to arbitrary local POVMs applied to any entangled two-qubit state.Comment: 4 pages main text, 10 pages appendix, matches published versio

PLA/WOOD BIOCOMPOSITES: IMPROVING COMPOSITE STRENGTH BY CHEMICAL TREATMENT OF THE FIBERS

A resol type phenolic resin was prepared for the impregnation of wood particles used for the reinforcement of PLA. A preliminary study showed that the resin penetrates wood with rates depending on the concentration of the solution and on temperature. Treatment with a solution of 1 wt% resin resulted in a considerable increase of composite strength and decrease of water absorption. Composite strength improved as a result of increased inherent strength of the wood, but interfacial adhesion might be modified as well. When wood was treated with resin solutions of larger concentrations, the strength of the composites decreased, first slightly, then drastically to a very small value. A larger amount of resin results in a thick coating on wood with inferior mechanical properties. At large resin contents the mechanism of deformation changes; the thick coating breaks very easily leading to the catastrophic failure of the composites at very small loads

Pairing in disordered s-wave superconductors and the effect of their coupling

Inhomogeneity is introduced through random local interactions (Ui) in an attractive Hubbard model on a square lattice and studied using mean-field Bogoliubov-de Gennes formalism. Superconductivity is found to get suppressed by the random Ui contrary to the results of a bimodal distribution of Ui. The proximity effect of superconductivity is found to be strong, all sites develop non-zero pairing amplitude. The gap in the density of states is always non-zero and does not vanish even for strong disorder. When two such superconductors are coupled via a channel, the effect of one on the other is negligible. The length and width of the connector, do not seem to have any noticeable effect on the superconductivity in either systems. The superconducting blocks behave as independent entity and the introduction of the channel have no effect on them.Comment: 9 pages, 14 figure