Global versus local interaction in coordination games: an experimental investigation.

We study experimentally the outcome of a 50 periods repetition of a two-player coordination game, which admits two-pure strategy Nash equilibria that are Pareto-ranked: a payoff-dominant equilibrium and a risk-dominant equilibrium. The experiment consists of a 2x3 factorial design, with two different matching rules –global an local interaction–, and three sizes for the basin of attraction of the risk-dominant equilibrium. Under global interaction, each player can be matched in each period with any player in the population. Under local interaction, each player can be matched only with one of his two neighbours. Our results confirm earlier experimental results obtained under global interaction (for a survey see Ochs (1995)). On the contrary, the results contrast sharply with Keser, Ehrhart & Berninghaus (1998), who found that subjects interacting ‘locally’ with their neighbours around a circle, coordinate mostly on the risk-dominant equilibrium. Moreover, we found no evidence for a faster convergence to an equilibrium under local interaction than under global interaction. Keywords: Coordination games, Experimental economics, Evolutionary game theory, Local interactions

Road Traffic Congestion and Public Information: An Experimental Investigation

This paper reports two laboratory studies designed to study the impact of public information about past departure rates on congestion levels and travel costs. Our experimental design is based on a discrete version of Arnott, de Palma, and Lindsey’s (1990) bottleneck model where subjects have to choose their departure time in order to reach a common destination. Experimental treatments in our first study differ in terms of the level of public information on past departure rates and the relative cost of delay. In all treatments, congestion occurs and the observed travel costs are quite similar to the predicted ones. In other words, subjects’ capacity to coordinate does not seem to be affected by the availability of public information on past departure rates or by the relative cost of delay. This seemingly absence of treatment effects is confirmed by our finding that a parameter-free reinforcement learning model best characterizes individual behavior. The number of experimental subjects taking the role of drivers is four times larger in our second study than in our first study. We observe that coordination failures in our congestion situation do not become more severe when the number of drivers increases.Travel behavior; Congestion; Information in intelligent transportation systems; Laboratory experiments.

Vietnamese American women’s beliefs and perceptions on cervical cancer, cervical cancer screening, and cancer prevention vaccines: A community-based participatory study

Cervical cancer remains commonly diagnosed in Vietnamese American women. Despite efforts to increase cervical cancer screening among Vietnamese American women, participation rates are persistently lower than the national goal. The objective of this study is to explore beliefs of Vietnamese American women about cervical cancer, cervical cancer screening, and cancer prevention vaccines. A qualitative descriptive investigation captured group perceptions about meaning and beliefs of cervical cancer, screening, and cancer prevention vaccines, and participants’ stories using a community-based participatory research approach. Forty Vietnamese American women were recruited from the Portland, Oregon metropolitan area into four focus groups. Using a process of directed content analysis, focus group transcripts were coded for themes. We found that cervical cancer continues to be a difficult topic to discuss, and Vietnamese American women may not bring the topic up themselves to their health care providers. Some women experienced intense emotions of fear or shame of having their cervix examined. Women delayed seeking cervical cancer screening and needed to have early warning signs, which guided them as to when to seek health care. Women focused on cleanliness through vaginal and/or perineal washing as primary prevention for cervical cancer. There were limited awareness and knowledge about cancer prevention vaccines, specifically the human papillomavirus. Some women relied heavily on their informal social networks of family, friends, or community for health knowledge. Fear and misunderstanding dominated the beliefs of Vietnamese American women about cervical cancer screening and prevention. These findings underscored the importance of having culturally-specific findings, which will inform a multicomponent intervention to promote cervical cancer screening and cancer prevention vaccine uptake within this population

Anti-Reflection Coating for Nitrogen-Vacancy Optical Measurements in Diamond

We realize anti-reflection (AR) coatings for optical excitation and fluorescence measurements of nitrogen-vacancy (NV) color centers in bulk diamond by depositing quarter-wavelength thick silica layers on the diamondsurface. These AR coatings improve NV-diamond optical measurements by reducing optical reflection at the diamond-air interface from ≈17% to ≈2%, which allows more effective NV optical excitation and more efficient detection of NV fluorescence. We also show that diamondAR coatings eliminate standing-wave interference patterns of excitation laser intensity within bulk diamond, and thereby greatly reduce spatial variations in NV fluorescence, which can degrade spatially resolved magnetic field sensing using NV centers.Engineering and Applied SciencesPhysic

Structure d’interactions et problème de coordination : une approche expérimentale

Nous étudions expérimentalement les résultats d’un jeu de coordination à deux joueurs et deux actions par joueur répété sur 50 périodes. Ce jeu de coordination de type « chasse au cerf » possède deux équilibres de Nash en stratégie pure qui sont Pareto ordonnés : un équilibre Pareto dominant et un équilibre risque dominant. Un protocole expérimental factoriel composé de 2 x 3 traitements est utilisé afin d’étudier l’effet de la règle d’appariement (interaction globale versus interaction locale) et de la taille du bassin d’attraction de l’équilibre risque dominant (trois tailles) sur la dynamique de jeu. En interaction globale, un joueur peut interagir à chaque période avec tout autre joueur de la population alors qu’en interaction locale, il ne peut interagir qu’avec ses deux plus proches voisins. En interaction globale, nos résultats confirment ceux obtenus précédemment à savoir que i) les situations hors équilibre sont rares, ii) le choix modal en première période est la stratégie Pareto dominante, et iii) les choix de première période déterminent fortement les choix de dernière période, la distribution des choix finals se trouvant généralement dans le même bassin d’attraction que celle des choix initiaux. Les deux premiers faits stylisés s’observent également en interaction locale mais, contrairement aux dynamiques observées en interaction globale, la convention vers laquelle les choix convergent dépend fortement de la taille du bassin d’attraction de l’équilibre risque dominant. Ainsi, nous constatons une convergence vers la convention Pareto dominante lorsque les bassins d’attraction des deux équilibres sont de taille identique et une convergence vers la convention risque dominante pour le plus large des trois bassins d’attraction de l’équilibre risque dominant. Enfin, nous n’observons pas de différence significative quant à la vitesse de convergence vers un équilibre pour les deux règles d’appariement.We report the results of an experiment that examines play in a 50 periods repetition of a two-player coordination game (Stag Hunt game), which admits two pure strategy Nash equilibria that are Pareto-ranked : a payoff-dominant equilibrium and a risk-dominant equilibrium. We consider a 2x3 factorial design, with two different matching rules -global and local interaction- and three sizes for the basin of attraction of the risk-dominant equilibrium. Under global interaction, each player can be matched in each period with any player in the population. Under local interaction, each player can be matched only with his two closest neighbours. Our results confirm earlier experimental results obtained under global interaction : i) non-equilibrium outcomes are rarely observed, ii) the first period modal choice is the payoff-dominant strategy, and iii) the first period play determines strongly the steady-state which will be reached, as it generally lies in the same basin of attraction as the initial state. The two first stylised facts are also observed under local interaction but unlike the dynamics observed under global interaction, the convention towards which choices converge is strongly dependent on the size of the basin of attraction of the risk-dominant equilibrium. We observe convergence towards the payoff dominant convention when the two basins of attraction are of the same size and towards the risk dominant convention for the largest of the three basins of attraction of the risk dominant equilibrium. We found no evidence for a faster convergence under local interaction than under global interaction

Efficient photon detection from color centers in a diamond optical waveguide

A common limitation of experiments using color centers in diamond is the poor photon collection efficiency of microscope objectives due to refraction at the diamond interface. We present a simple and effective technique to detect a large fraction of photons emitted by color centers within a planar diamond sample by detecting light that is guided to the edges of the diamond via total internal reflection. We describe a prototype device using this “side-collection” technique, which provides a photon collection efficiency ≈47% and a photon detection efficiency ≈39%. We apply the enhanced signal-to-noise ratio gained from side collection to ac magnetometry using ensembles of nitrogen-vacancy (NV) color centers, and demonstrate an ac magnetic field sensitivity ≈100pT/Hz‾‾‾√, limited by added noise in the prototype side-collection device. Technical optimization should allow significant further improvements in photon collection and detection efficiency as well as subpicotesla NV-diamond magnetic field sensitivity using the side-collection technique.Physic

Dressed-State Resonant Coupling between Bright and Dark Spins in Diamond

Under ambient conditions, spin impurities in solid-state systems are found in thermally mixed states and are optically “dark”; i.e., the spin states cannot be optically controlled. Nitrogen-vacancy (NV) centers in diamond are an exception in that the electronic spin states are “bright”; i.e., they can be polarized by optical pumping, coherently manipulated with spin-resonance techniques, and read out optically, all at room temperature. Here we demonstrate a scheme to resonantly couple bright NV electronic spins to dark substitutional-nitrogen (P1) electronic spins by dressing their spin states with oscillating magnetic fields. This resonant coupling mechanism can be used to transfer spin polarization from NV spins to nearby dark spins and could be used to cool a mesoscopic bath of dark spins to near-zero temperature, thus providing a resource for quantum information and sensing, and aiding studies of quantum effects in many-body spin systems.Engineering and Applied SciencesPhysic

Enhanced metrology using preferential orientation of nitrogen-vacancy centers in diamond

We demonstrate preferential orientation of nitrogen-vacancy (NV) color centers along two of four possible crystallographic axes in diamonds grown by chemical vapor deposition on the {100} face. We identify the relevant growth regime and present a possible explanation of this effect. We show that preferential orientation provides increased optical readout contrast for NV multispin measurements, including enhanced ac magnetic-field sensitivity, thus providing an important step towards high-fidelity multispin-qubit quantum information processing, sensing, and metrology.Physic