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In situ Mo K-edge X-ray absorption spectroscopy reveals different carburization pathways for unsupported and supported MoO3 yielding Mo2C and Mo2C/SiO2. Mo2C/SiO2 features higher resistance to oxidation under dry reforming of methane than Mo2C.

Platinum nanoparticles (NPs) supported by titania exhibit a strong metal-support interaction (SMSI)[1] that can induce overlayer formation and encapsulation of the NP's with a thin layer of support material. This encapsulation modifies the catalyst's properties, such as increasing its chemoselectivity[2] and stabilizing it against sintering.[3] Encapsulation is typically induced during high-temperature reductive activation and can be reversed through oxidative treatments.[1] However, recent findings indicate that the overlayer can be stable in oxygen.[4, 5] Using in situ transmission electron microscopy, we investigated how the overlayer changes with varying conditions. We found that exposure to oxygen below 400 °C caused disorder and removal of the overlayer upon subsequent hydrogen treatment. In contrast, elevating the temperature to 900 °C while maintaining the oxygen atmosphere preserved the overlayer, preventing platinum evaporation when exposed to oxygen. Our findings demonstrate how different treatments can influence the stability of nanoparticles with or without titania overlayers. expanding the concept of SMSI and enabling noble metal catalysts to operate in harsh environments without evaporation associated losses during burn-off cycling., Angewandte Chemie. International Edition, 62 (27), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

International audience; Dilemmas related to the use of environmental resources concern diverse populations at local or global scales. Frequently, individuals are unable to visualize the consequences of their actions, where they belong in the decision-making line, and have no information about past choices or the time horizon. We design a new one-shot extraction game to capture these dynamic decisions. We present results from a nationwide common pool resource experiment, conducted simultaneously in eleven French cities, involving a total of 2813 participants. We examine, for the first time, the simultaneous impact of several variables on the amount of resource extracted: the local vs. the national scale of the resource, the size of the group (small vs. big), the low vs. high recovery rate of the resource, and the available information. We show that individuals significantly reduce extraction levels in local as compared to national level dilemmas and that providing recommendations on sustainable extraction amounts significantly improves the sustainability of the resource. Overall, women extract significantly less, but care more about preserving the local resource; older participants extract significantly more resources but extract less from the national resource. Our experiment also fulfills a science popularization pedagogical aim, which we discuss..

Les attendus d’une approche d’économie comportementale pour les décisions individuelles face à la pandémie de COVID-19 : succès et déceptions.Dans le cadre du premier appel à projet « Flash-COVID-19 » de l’Agence nationale de la recherche, nous avons mobilisé des méthodes récentes de l’économie comportementale afin de mieux comprendre les décisions des individus face à la crise sanitaire due à la pandémie de COVID-19 (coronavirus disease 2019) et d’identifier les paramètres pouvant influencer le respect des mesures sanitaires. Cet article introduit brièvement l’économie comportementale, présente un compte rendu des attendus du projet CONFINOBS (Observance et observation des mesures barrières et du confinement : une approche d’économie comportementale) et de ses méthodes, puis il propose une synthèse des résultats obtenus.

Heterogeneous catalysts in the form of atomically dispersed metals on a support provide the most efficient utilization of the active component, which is especially important for scarce and expensive late transition metals. These catalysts also enable unique opportunities to understand reaction pathways through detailed spectroscopic and computational studies. Here, we demonstrate that atomically dispersed iridium sites on indium tin oxide prepared via surface organometallic chemistry display exemplary catalytic activity in one of the most challenging electrochemical processes, the oxygen evolution reaction (OER). In situ X-ray absorption studies revealed the formation of Ir-V=O intermediate under OER conditions with an Ir-O distance of 1.83 angstrom. Modeling of the reaction mechanism indicates that Ir-V=O is likely a catalyst resting state, which is subsequently oxidized to Ir-VI enabling fast water nucleophilic attack and oxygen evolution. We anticipate that the applied strategy can be instrumental in preparing and studying a broad range of atomically dispersed transition metal catalysts on conductive oxides for (photo) electrochemical applications., ACS Central Science, 6 (7), ISSN:2374-7951

National audience; This article provides a formal model of the value creation-appropriation dilemma in coopetition for innovation, that is, alliances among competing firms. The model determines the levels of cooperation that maximize the profit of each firm in an innovative coopetition agree¬ment regardless of the number of firms and their respective budget endowments dedicated to the coopetitive project. We answer the following questions: within an innovative coopetition agreement, will the partners cooperate more or less when their budget endowments change? What is the impact on profit? When is it profitable to accept a new partner into the agreement? What happens to the remaining firms when a partner withdraws from the agreement? We show that when the coopetitive budget of the focal firm increases, the focal firm allocates a larger part of this budget to value creation activities and increases its profit. In contrast, when a partnering firm increases its coopetitive budget, the focal firm reduces its budget for value creation activities to maintain a sufficient budget for value appropriation activities. We also show that the addition of a competitor with a large coopetitive budget to the innovative coopetition agreement decreases the cooperation of the focal firm but increases the profit of the initial partnering firms. In contrast, the exit of a partnering firm with a large coopetitive budget from the agreement intensifies the cooperation among the remaining firms but reduces their profit. competing firms. The model determines the levels of cooperation that maximize the profit of each firm in an innovative coopetition agreementregardless of the number of firms and their respective budget endowments dedicated to the coopetitive project. We answer thefollowing questions: within an innovative coopetition agreement, will the partners cooperate more or less when their budget endowmentschange? What is the impact on profit? When is it profitable to accept a new partner into the agreement? What happens to the remainingfirms when a partner withdraws from the agreement? We show that when the coopetitive budget of the focal firm increases, the focal firmallocates a larger part of this budget to value creation activities and increases its profit. In contrast, when a partnering firm increases itscoopetitive budget, the focal firm reduces its budget for value creation activities to maintain a sufficient budget for value appropriationactivities. We also show that the addition of a competitor with a large coopetitive budget to the innovative coopetition agreementdecreases the cooperation of the focal firm but increases the profit of the initial partnering firms. In contrast, the exit of a partnering firmwith a large coopetitive budget from the agreement intensifies the cooperation among the remaining firms but reduces their profit.

This paper investigates the relationship between mindfulness and well-being within the context of compliance with prophylactic measures in the time of COVID-19. We conducted a large-scale survey among a representative sample of the French population. We measured mindfulness, using the Mindful Attention Awareness Scale, and the extent to which respondents were impacted by COVID-19 in terms of their mood and quality of sleep, as well as how they complied with prophylactic measures. Our results suggest that more mindful individuals were less negatively impacted by COVID-19 with regard to their sleep and mood. Concerning the prophylactic measures, we obtained mixed results: more mindful participants were more likely to respect lockdowns, physical distancing and to cough in their sleeves, but did not wash their hands, wear masks or avoid touching their face more often than less mindful individuals.

The properties of two-dimensional (2D) van der Waals (vdW) materials can be tuned through nanostructuring or controlled layer stacking, where interlayer hybridization induces exotic electronic states and transport phenomena. Here, we describe an assisted self-assembly of twisted layer graphene. The process, which can be implemented in standard chemical vapour deposition (CVD) growth, is best described using the analogy to Origami and Kirigami of paper and involves wrinkle formation, folding, tearing, and re-growth. Inherent to the process is the formation of intertwined graphene spirals and conversion of the chiral angle of one-dimensional (1D) wrinkles into a 2D twist angle of a three-dimensional (3D) superlattice. The approach can be extended to other foldable 2D materials and facilitates the production of miniaturized electronic components, including capacitors, resistors, inductors, and super-conductors.

Graphene nanoribbons (GNRs) are considered one of the most promising materials for next generation electronics, however a reliable and controllable synthesis method is still lacking. Here, we report the CVD growth of GNRs on a copper surface and the corresponding mechanisms of growth. One-dimensional GNR growth is enabled by a vapor-liquid-solid (VLS) graphene growth guided by on-surface propagation of a liquid catalyst particle. Controlling the suppression of vapor-solid-solid (VSS) graphene growth along the width direction of the GNR by tuning the flow of H2 during growth gives rise to a spear head-shaped graphene that we term graphene nanospears (GNSs). The real-time visual and spatially resolved observations confirm the VSS growth of graphene can be fully suppressed and lead to GNR formation on Cu surface. These findings reveal key insight into the growth mechanism of graphene and open a door for achieving a facile and scalable method of synthesizing free standing GNRs.

We replicate Bocquého et al. (2014), who used multiple price lists to investigate the risk preferences of 107 French farmers. We collected new data from 1430 participants in 11 European farming systems. In agreement with the original study, farmers' risk preferences are best described by Cumulative Prospect Theory. Structural model estimates show that farmers in the new samples are, on average, less loss averse and more susceptible to probability distortion than in the original study. Explorative analyses indicate differences between estimation approaches, as well as heterogeneity between and within samples. We discuss challenges in replications of economic experiments with farmers across farming contexts.

International audience; The public acceptability of a policy is an important issue in democracies, in particular for anti-COVID-19 policies, which require the adherence of the population to be applicable and efficient. Discrete choice experiment (DCE) can help elicit preference ranking among various policies for the whole population and subgroups. Using a representative sample of the French population, we apply DCE methods to assess the acceptability of various anti-COVID-19 measures, separately and as a package. Owing to the methods, we determine the extent to which acceptability depends on personal characteristics: political orientation, health vulnerability, or age. The young population differs in terms of policy preferences and their claim for monetary compensation, suggesting a tailored policy for them. The paper provides key methodological tools based on microeconomic evaluation of individuals’ preferences for improving the design of public health policies.

International audience; We study experimentally the reaction of asset markets to fundamental value (FV) shocks. The pre-shock and post-shock FV are both constant, but after the shock the FV is either higher or lower than before. We compare treatments with expected shocks (the date and the magnitude are known in advance, but not the direction) to treatments with unexpected shocks (subjects only know that a shock may occur but are unaware of the date and the magnitude). We observe mispricing in markets without shocks and in markets with shocks. Shocks tend to reduce the post-shock price deviation and to increase the difference of opinions (DO), whatever the type of the shock (expected or unexpected) and its direction (upwards or downwards). In contrast to standard predictions, the larger DO after a shock is not accompanied by an increase in transaction volumes, but by sharp depression of share turnover.

Metal catalysts play an important role in industrial redox reactions. Although extensively studied, the state of these catalysts under operating conditions is largely unknown, and assignments of active sites remain speculative. Herein, an operando transmission electron microscopy study is presented, which interrelates the structural dynamics of redox metal catalysts to their activity. Using hydrogen oxidation on copper as an elementary redox reaction, it is revealed how the interaction between metal and the surrounding gas phase induces complex structural transformations and drives the system from a thermodynamic equilibrium toward a state controlled by the chemical dynamics. Direct imaging combined with the simultaneous detection of catalytic activity provides unparalleled structure–activity insights that identify distinct mechanisms for water formation and reveal the means by which the system self-adjusts to changes of the gas-phase chemical potential. Density functional theory calculations show that surface phase transitions are driven by chemical dynamics even when the system is far from a thermodynamic phase boundary. In a bottom-up approach, the dynamic behavior observed here for an elementary reaction is finally extended to more relevant redox reactions and other metal catalysts, which underlines the importance of chemical dynamics for the formation and constant re-generation of transient active sites during catalysis. ISSN:0935-9648 ISSN:1521-4095

We propose a five-player common-pool resource (CPR) game with endogenous coalition formation. We show that the level of extraction from the CPR depends on the size of each coalition that is formed and on the final coalition structure. These predictions are tested in a laboratory experiment. We consider two treatments: dictator vs. veto. In the dictator treatment, at each stage of the coalition formation game, a randomly chosen player imposes the coalition size and selected members cannot refuse to become a member. In the veto treatment, players have the right to refuse joining the current coalition if they want to and make counter-proposals. We observe that the formation of the grand coalition is more frequent in the dictator treatment. However, with the repetition of the coalition formation game, the grand coalition becomes more frequent under both treatment, and past experience of a grand coalition increases the likelihood that the current coalition structure is the grand coalition. Finally, the possibility to form coalitions is beneficial at reducing CPR extractions, compared to the singleton structure, in both treatments.

Synthesizing high-quality two-dimensional nanomaterials of non-layered metal oxide is a grand challenge because it requires long range single-crystallinity and clean high-energy surfaces. Here, we report the synthesis of single-crystalline MgO(111) nanosheets via a two-step process involving the formation of ultrathin Mg(OH)2 nanosheets as precursor and their selective topotactic conversion upon heating under dynamic vacuum. The defect-rich surface displays terminal -OH groups, 3-coordinated O2- sites, low-coordinated Mg2+ sites as well as single electrons trapped at oxygen vacancies, that render MgO nanosheets highly reactive as evidenced by the activation of CO molecules at low temperatures and pressures, with formation of strongly adsorbed red-shifted CO and coupling of CO molecules into C2 species.

Heterogeneous catalysts in the form of atomically dispersed metals on a support provide the most efficient utilization of the active component, which is especially important for scarce and expensive late transition metals. These catalysts also enable unique opportunities to understand reaction pathways through detailed spectroscopic and computational studies. Here we demonstrate that atomically dispersed iridium sites on indium tin oxide prepared via surface organometallic chemistry display exemplary catalytic activity in one of the most challenging electrochemical processes, oxygen evolution reaction (OER). In situ X-ray absorption studies revealed the formation of IrV=O intermediate under OER conditions with an Ir–O distance of 1.83 Å. Modelling of the reaction mechanism indicates that Ir(V)=O is likely a catalyst resting state, which is subsequently oxidized to Ir(VI) enabling fast water nucleophilic attack and oxygen evolution. We anticipate that the applied strategy can be instrumental in preparing and studying a broad range of atomically dispersed transition metal catalysts on conductive oxides for (photo)electrochemical applications.

International audience; We study embezzlement when donations have to pass through intermediaries to reach recipients, by means of a sequential game tested in a laboratory experiment conducted in Tanzania. We investigate the impact on the amount embezzled of both the number of intermediaries in transfer chains and transparency about the donation. We show that donors are less generous in the presence of intermediaries. When transfer chains are shorter, aggregate embezzlement decreases, at least when donations are transparent. At the individual level, intermediaries embezzle less, the longer the transfer chain; this is due to less embezzlement at the beginning of the chain. We fail finding significant positive effects of transparency on the honesty of individual transfers through social judgment. JEL Codes: C91, D73, O19

Fluorine-containing bismuth vanadate (F:BiVO4) powder was synthesized using a new, clean, and simple solid-vapor reaction. Incorporation of fluorine mainly leads to the formation of cation vacancies. Electrodes were fabricated from the pre-synthesized powder samples by electrophoretic deposition onto fluorine-doped tin oxide coated glass slides and subsequent calcination. The photoelectrochemical performance concerning the water oxidation reaction was investigated and compared to pristine BiVO4 revealing strongly enhanced photoelectrochemical behavior for the F-containing BiVO4.

ZnO has prominent electron transport and optical properties, beneficial for photovoltaic application, but its surface is prone to the formation of defects. To overcome this problem, we deposited nanostructured TiO2 thin film on ZnO nanorods to form a stable shell. ZnO nanorods synthesized by wet-chemistry are single crystals. Three different procedures for deposition of TiO2 were applied. The influence of preparation methods and parameters on the structure, morphology, electrical and optical properties were studied. Nanostructured TiO2 shells show different morphologies dependent on deposition methods: (1) separated nanoparticles (by pulsed laser deposition (PLD) in Ar), (2) a layer with nonhomogeneous thickness (by PLD in vacuum or DC reactive magnetron sputtering), and (3) a homogenous thin layer along the nanorods (by chemical deposition). Based on the structural study, we chose the preparation parameters to obtain an anatase structure of the TiO2 shell. Impedance spectroscopy shows pure electron conductivity that was considerably better in all the ZnO@TiO2 than in bare ZnO nanorods or TiO2 layers. The best conductivity among the studied samples and the lowest activation energy was observed for the sample with a chemically deposited TiO2 shell. Higher transparency in the visible part of spectrum was achieved for the sample with a homogenous TiO2 layer along the nanorods, then in the samples with a layer of varying thickness.

Novel forms of black TiO2 nanotubes-based photocatalysts for water purification were prepared. Two features were combined: decoration of TiO2 nanotube arrays with Ag nanoparticles (sample TiO2-NT's@Ag) and further hydrogenation of this material (TiO2-NT's@Ag-HA). Obtained photocatalysts show high efficiency for degradation of salicylic acid, a typical water-borne pollutant. The photocatalysts considerably exceed the photocatalytic properties of TiO2 nanotubes and commercial TiO2 P25 taken as a reference for modeling of the photocatalytic process. The comparison of photocatalytic activities between novel photocatalyst was based on a numerical approach supported by the complex kinetic model. This model allowed a separate study of different contributions on overall degradation rate. The contributions include: salicylic acid photolysis, photocatalysis in UVB, UVA and in the visible part of applied simulated solar irradiation. The superior photocatalytic performance of the photocatalyst TiO2-NT's@Ag-HA, particularly under visible irradiation, was explained by the combined effect of a local surface plasmon resonance (LSPR) due to Ag nanoparticles and creation of additional energy levels in band-gap of TiO2 due to Ti3+ states at nanotube surfaces. The presence of Ag also positively influence charge separation of created electron-holes pairs. The synergy of several effects was quantified by a complex kinetic model through the factor of synergy, fSyn. Stability testing indicated that the catalysts were stable for at least 20 h. The novel design of catalysts, attached on Ti foils, presents a solid base for the development of more efficient photocatalytic reactors for large-scale with a long-term activity.

Platinum and iridium polycrystalline foils were oxidized electrochemically through anodization to create thin platinum and iridium hydrous oxide layers, which were analyzed through laboratory photoelectron spectroscopy during heating and time series (temperature-programmed spectroscopy). The films contain oxygen in the form of bound oxides, water, and hydroxides and were investigated by depth profiling with high-energy photoelectron spectroscopy. The Pt films are unstable and begin to degrade immediately after removal from the electrolyte to form core–shell structures with a metallic inner core and a hydrous oxide outer shell almost devoid of Pt. However, evidence was found for metastable intermediate states of degradation; therefore, it may be possible to manufacture PtOx phases with increased stability. Heating the film to even 100 °C causes accelerated degradation, which shows that stoichiometric oxides such as PtO2 or PtO are not the active species in the electrolyte. The Ir films exhibit increased stability and higher surface Ir content, and gentle heating at low temperatures leads to a decrease in defect density. Although both layers are based on noble metals, their surface structures are markedly different. The complexity of such hydrous oxide systems is discussed in detail with the goal of identifying the film composition more precisely.

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.

Conventional finance models indicate that the magnitude of stock prices should not influence portfolio choices or future returns. This view is contradicted, however, by empirical evidence. In this paper, we report the results of an experiment showing that trading prices, in experimental markets, are processed differently by participants, depending on their magnitude. Our experiment has two consecutive treatments. One where the fundamental value is a small number (the small price market) and a second one where the fundamental value is a large number (the large price market). Small price markets exhibit greater mispricing than large price markets. We obtain this result both between-participants and within-participants. Our findings show that price magnitude influences the way people perceive the distribution of future returns. This result is at odds with standard finance theory but is consistent with: (1) a number of observations in the empirical finance and accounting literature; and (2) evidence in neuropsychology on the use of different mental scales for small and large numbers.

Recent experimental studies have shown that observed outcomes deviate significantly morefrom the Nash equilibrium when actions are strategic complements than when they are strategic substitutes. This "strategic environment effect" offers promising insights into the aggregate consequences of interactions among heterogeneous boundedly rational agents, but its macroeconomic implications have been questioned because the underlying experiments involve a small number of agents. We studied beauty contest games with a unique interior Nash equilibrium to determine the critical group size for triggering the strategic environment effect, and we use both theory and experiments to shed light on its effectiveness. Based on cognitive hierarchy and level-K models, we show theoretically that the effect is operative for interactions among three or more agents. Our experimental results show a statistically significant strategic environment effect for groups of five or more agents, establishing its robustness against the increase in the population size. Our results bolster other experimental ndings on the strategic environment effects that are relevant for macroeconomic issues such as price fluctuations and nominal rigidity.

We report on a within-subject experiment, with substantial monetary incentives, designed to test whether or not people are risk vulnerable. In the experiment, subjects face the standard portfolio choice problem in which the investor has to allocate part of his wealth between one safe asset and one risky asset. We elicit risk vulnerability by observing each subject's portfolio choice in two different contexts that differ only by the presence or absence of an actuarially neutral background risk. Our main result is that most of the subjects are risk vulnerable: 81% chose a less risky portfolio when exposed to background risk. More precisely, 47% invested a strictly smaller amount in the risky asset, whereas 34% were indifferent. Furthermore, contrasting the predictions provided by competing decision-theoretic models, we conclude that expected utility theory best fits our experimental data. This paper was accepted by Uri Gneezy, behavioral economics.

International audience; We present the implementation of an economic experiment conducted simultaneously in 11 French cities, with over 2700 participants, during four uninterrupted hours, during a popular-science event held in September 2015. Our goal is both to provide a roadmap for a possible replication and to discuss how the discipline can invest in new fields (science popularization, popular education, public communication).; Nous présentons la mise en place d'une expérience lors d'un évènement grand public national, de manière simultanée dans 11 villes françaises, en septembre 2015. L’expérience a impliqué plus de 2700 participants et a duré quatre heures ininterrompues. L’objectif de cet article est à la fois de fournir une feuille de route pour une éventuelle réplication et de penser à la manière dont la discipline peut investir des terrains nouveaux (vulgarisation, pédagogie populaire, communication grand public).

Nanoscale NiO/Ni heterostructures on oxygen-functionalized carbon nanotubes with low Ni loading (3–4 wt%) are fabricated by delicate thermal-annealing treatments, which are designed according to the temperature-programmed thermal analysis. Activity and stability tests demonstrate that NiO/Ni heterostructures with a stable Ni core inside an oxyhydroxide shell (in solution) exhibit enhanced stability and catalytic activity for methanol oxidation.

Humans have colonized and adapted to extremely diverse environments, and the genetic basis of some such adaptations, for example to high altitude, is understood. In some cases, local or regional variation in selection pressure could also cause behavioural adaptations. Numerous genes influence behaviour, such as alleles at the dopamine receptor locus D4 (DRD4), which are associated with attitude toward risk in experimental settings. We demonstrate genetic differentiation for this gene, but not for five unlinked microsatellite loci, between high- and low risk environments around Mount Merapi, an active volcano in Java, Indonesia. Using a behavioural experiment, we further show that people inhabiting the high risk environment are significantly more risk averse. We provide evidence of a genetic basis for this difference, showing that heterozygotes at the DRD4 locus are more risk averse than either homozygotes. In the high risk environment, allele frequencies are equilibrated, generating a high frequency of heterozygotes. Thus it appears that overdominance (i.e. selective advantage of heterozygotes) generates negative frequency dependent selection, favouring the rarer allele at this locus. Our results therefore provide evidence for adaptation to a marginal habitat through the selection of a neurocognitive trait with a genetic basis.

International audience; Based on data from a field-experiment in rural Uganda, we show that impatient farmers are more risk-averse than patient farmers. We relied on a simplified version of the Convex Time Budget (CTB) method to elicit farmers’ time preferences and on an independent method for eliciting their risk-preferences. We report two important findings. First, we show that our simplified CTB method applied to farmers from Uganda replicates the key findings of Andreoni and Sprenger’s lab experiments that involved student subjects. Second, we establish the existence of a negative correlation between risk tolerance and impatience, based on two independent measures.

We investigate experimentally the relevance of Warr's neutrality theorem (1983). In our test treatments we implement an unexpected income redistribution among group members. We compare treatments with equalizing (unequalizing) redistribution to benchmark treatments without redistribution, starting either with an equal or unequal income distribution. Our data are consistent with the neutrality theorem: redistribution (either equalizing or unequalizing) does not affect the amount of voluntarily provided public good. However at the individual level we observe that subjects tend to under-adjust with respect to the predicted Nash-adjustment. We also observe an insignificant adjustment asymmetry between the poor and the rich: after redistribution subjects who become poorer lower their contribution by a larger amount than subjects who become richer increase their contribution. Finally we also observe a general tendency for poor subjects to over-contribute significantly more than rich subjects.

Under the assumption of weakly morally motivated agents, average voluntary contributions decline with repetition of the game, provided that the aggregate moral motivation cannot increase. Our model is compatible with the conditional cooperation hypothesis.

Mass production of high-quality semiconductor nanowire arrays (SNAs) with precisely controlled orientation and structure is essential for their application in nanoelectronics and optoelectronics. Here, we present a single-step approach for large-scale fabrication of [0001]-oriented SNAs via direct heating of their bulk components in a H2/Ar atmosphere. Real-time imaging during in-situ SEM experiments clearly demonstrates that the SNAs form through a selective vaporization process with respect to the crystallography of wurtzite crystals. We propose that the selective vaporization relies on the low symmetry of the wurtzite structure with large differences between surface energies of low-index planes. Further, we demonstrate that the approach can be extended to zinc-blende type structures through a cation exchange process. Finally, the high-quality of the SNAs is demonstrated by fabrication of photodetectors that present outstanding optoelectronic performances. We believe that our method represents a transformative new fabrication platform for large-scale fabrication of orientated SNAs with novel functionalities. Keywords: semiconductor nanowire arrays; wurtzite structure; selective vaporization

International audience; Why humans cooperate in large groups and with non-kin remains a puzzle for researchers across the natural and social sciences. Investigating whether cooperation is sexually selected could contribute to an understanding of the evolution of human cooperation. Competition for access to mates could indeed select for cooperation. Using controlled laboratory experiments, we analyse whether and how the sex composition of a social environment, testosterone level, and relationship status affect contributions to a public good. The results show that variation in sex composition alters the amount of money that single men (but not men in a couple or women) contribute to a public good. Notably, in line with the competitive helping hypothesis, awareness of the presence of a woman leads to larger contributions by single men, most likely by triggering their competitiveness to be the most cooperative man in the group. However, we find no link between basal testosterone level and cooperativeness. We argue that men, notably single men, adopt cooperative behaviours as a signalling strategy in the context of mate choice and hence that cooperation is partly sexually selected. Our findings highlight the need to consider sexual selection as an additional mechanism for cooperation. The evolution of cooperation between unrelated individuals remains a challenging issue for evolutionary biologists 1. The puzzle is that cooperative behaviour is beneficial to recipients but is costly to the actor. Theory suggests that cooperative acts can only be selected if the costs of cooperation are compensated by fitness benefits 2. Some theoretical 3–5 and experimental studies 6,7 have shown that sexual benefits could maintain cooperation in a group. Investigations into whether cooperation is sexually selected could thus contribute to our understanding of the evolution of cooperation. Based on controlled and incentivized laboratory experiments, we show that variation in the sex composition of a group of four individuals alters the amount of money that single men (but not men in a couple or women) contribute to a public good, when the sex composition is common knowledge. Notably, in line with the competitive helping hypothesis, awareness of the presence of a woman in the group likely increases single men's competitiveness in their willingness to appear as the most cooperative individual, leading to larger contributions by those men. We also investigate the potential influence of basal testosterone as a proximate mechanism of this behaviour. However, no association between male testosterone level and contribution to a public good is detected. Despite the absence of testosterone influence on cooperation, we argue that men, especially single men, adopt cooperative behaviours as a signalling strategy in the context of mate choice, and hence that cooperation is – at least partly-sexually selected in humans. Observations in non-human animal species suggest that sexual selection could be implicated in the evolution of cooperation. Male Lance-tailed Manakins (Chiroxiphia lanceolata) perform cooperative efforts, such as singing duets and dancing with other males, which increases their chances of mating with females 8. In chimpanzees (Pan troglodytes), males exchange political support from the dominant male for mating opportunities 9 : dominant males, in turn, tolerate males who support them most frequently in conflicts, with the result that supporters copulate more often than other males. In humans, there is also evidence that cooperative behaviour toward non-kin could be sexually selected. For example, several studies suggest that cooperative traits are implicated in mate choice 10–12 and that women are more sensitive to those traits in sexual partners than men are 10 .

Humans have colonized and adapted to extremely diverse environments, and the genetic basis of some such adaptations, for example to high altitude, is understood. In some cases, local or regional variation in selection pressure could also cause behavioural adaptations. Numerous genes influence behaviour, such as alleles at the dopamine receptor locus D4 (DRD4), which are associated with attitude toward risk in experimental settings. We demonstrate genetic differentiation for this gene, but not for five unlinked microsatellite loci, between high- and low risk environments around Mount Merapi, an active volcano in Java, Indonesia. Using a behavioural experiment, we further show that people inhabiting the high risk environment are significantly more risk averse. We provide evidence of a genetic basis for this difference, showing that heterozygotes at the DRD4 locus are more risk averse than either homozygotes. In the high risk environment, allele frequencies are equilibrated, generating a high frequency of heterozygotes. Thus it appears that overdominance (i.e. selective advantage of heterozygotes) generates negative frequency dependent selection, favouring the rarer allele at this locus. Our results therefore provide evidence for adaptation to a marginal habitat through the selection of a neurocognitive trait with a genetic basis.

Embezzlement is a major concern. By means of a sequential dictator game, we investigate theoretically and experimentally whether making information more transparent and reducing the number of intermediaries in transfer chains can reduce embezzlement. Consistent with reference-dependent preferences in terms of moral ideal, we show that the impact of transparency is conditional on the length of the transfer chain and on the position of the intermediary in the chain. Its direct effect on image encourages honesty. Its indirect effect via expectations plays in the opposite direction, motivating intermediaries to embezzle more when expecting that the following intermediary will embezzle less.

We report the results of an experiment investigating the provision of a step-level collective good. This experiment compares the behavior of subjects in a public good game with the behavior of subjects in a club good game. In the club good game, players who do not contribute the membership fee are excluded from the consumption of the collective good. The introduction of a small membership fee has surprisingly strong effects: it increases the provision of the collective good, delays provision failures and increases the number of contributors. The experiment also reveals the limits of the introduction of a small fee. At a high threshold level, the membership fee no longer ensures successful provision.

Our article presents an experimental assessment of a tax-evasion prevention mechanism proposed by Greenberg (1984). Greenberg argued that tax evasion cannot totally be eliminated in a population. On the basis of this observation, he developed a mechanism in which the audit probability is determined by agents’ earlier fraud behavior. We observe that the distribution of subjects differs from the model’s prediction. The discrepancy is due to the existence of an increasing relationship between the decision to commit fraud and income – a relationship that the model does not take into account. Our results suggest that Greenberg’s mechanism is based on an over-restrictive hypothesis., Nous présentons dans cet article une évaluation expérimentale d’un mécanisme de prévention de la fraude fiscale proposé par Greenberg (1984 ). L’auteur soutient l’idée de la tolérance d’une partie de fraudeurs dans une population. Pour cela, il conçoit un mécanisme fondé sur une probabilité d’audit conditionnelle du comportement de fraude antérieur des agents. On observe que la répartition des sujets est différente de celle prédite par le modèle. L’écart est dû à l'existence d’une relation croissante entre la décision de fraude et le revenu. Cette relation n’est pas prise en compte par le modèle. Nos résultats suggèrent que le mécanisme de Greenberg est basé sur une hypothèse trop restrictive., Willinger Marc, Daures Nicolas, Ali Bchir Mohamed. Tolérance de la fraude et évasion fiscale : une analyse expérimentale du modèle de Greenberg. In: Économie & prévision, n°182, 2008-1. pp. 33-46.