Inbreeding and sex-biased gene flow in the ant Formica exsecta.

The objective of this study was to assess breeding and dispersal patterns of both males and females in a monogyne (a single queen per colony) population of ants. Monogyny is commonly associated with extensive nuptial flights, presumably leading to considerable gene flow over large areas. Opposite to these expectations we found evidence of both inbreeding and sex-biased gene flow in a monogyne population of Formica exsecta. We found a significant degree of population subdivision at a local scale (within islands) for queens (females heading established colonies) and workers, but not for colony fathers (the males mated to the colony queens). However, we found little evidence of population subdivision at a larger scale (among islands). More conclusive support for sex-biased gene flow comes from the analysis of isolation by distance on the largest island, and from assignment tests revealing differences in female and male philopatry. The genetic similarity between pairs of queens decreased significantly when geographical distance increased, demonstrating limited dispersal and isolation by distance in queens. By contrast, we found no such pattern for colony fathers. Furthermore, a significantly greater fraction of colony queens were assigned as having originated from the population of residence, as compared to colony fathers. Inbreeding coefficients were significantly positive for workers, but not for mother queens. The queen-male relatedness coefficient of 0.23 (regression relatedness) indicates that mating occurs between fairly close relatives. These results suggest that some monogyne species of ants have complex dispersal and mating systems that can result in genetic isolation by distance over small geographical scales. More generally, this study also highlights the importance of identifying the relevant scale in analyses of population structure and dispersal.

Alternative reproductive strategies in Formica lugubris Zett (Hymenoptera, Formicidae)

A long term study on the reproductive strategies of Formica lugubris (Formica rufa group) has revealed many new important facts. Within a supercolony the sex-ratio is strongly female biased. Some of the sexuals mate on the nest surface, whereas others fly from the nest. Those sexuals participating in flights aggregate in particular meadow sites (mating places). On these places females attract males by releasing a sex pheromone.

Hay competencia en el mercado europeo de transporte aéreo?: el caso español

La liberalización del transporte aéreo que se llevó a término en la Unión Europea a principios de los años noventa ha tenido efectos positivos sobre el bienestar del viajero. No obstante, existe un consenso en la literatura académica que estos efectos dependen de la existencia de una competencia efectiva en el nivel de la ruta. En este sentido, se plantea el problema que puede llegar a suponer las ventajas de escalera de las compañías dominantes en cada mercado interior. Además, se pretende capturar la diferenciación de productos como característica esencial de la industria del transporte aéreo. El análisis de estas cuestiones se realiza de la forma siguiente. En primer lugar, se hace referencia a los principales aspectos económicos que condicionan la competencia en el transporte aéreo. Y en segundo lugar, se implementa un modelo empírico basado en un sistema de tres ecuaciones, que se estima mediante la técnica de las variables instrumentales. La muestra utilizada hace referencia al año 2001 para la mayoría de las rutas del mercado interior español de vuelos regulares en dónde hay competencia. Los resultados de la estimación muestran la existencia de unas condiciones de competencia diferentes según el segmento del mercado al cual se dirigen las compañías aéreas. Efectivamente, la competencia en precios (calidad) parece ser predominante en el segmento de viajeros por motivos personales (negocios). Adicionalmente, el dominio que la compañía dominante tiene sobre la mayoría de las rutas parece descansar en las ventajas competitivas, tanto en términos de costes como en términos de demanda, que le proporciona el control de la red aeroportuaria nacional. De todo esto se puede inferir que el mantenimiento y/o aumento de los beneficios de la liberalización de los servicios de transporte aéreo exige extender la liberalización al uso del aeropuertos así como descentralizar su gestión.

Le vol nuptial chez Formica lugubris Zett. (Hymenoptera, Formicidae). 1. Facteurs influençant l 'apparition et l 'envol des sexués

Nuptial flight in Formica lugubris was studied within a super-colony located in the Swiss Jura. Sexuals (imago) were present in the nests during one month (June). The flight season was ea. 2-3 weeks. The presence of sexuals at nest surface as well as take-off were temperature-dependant, occuring above l0°C and l8°C, respectively. Length of daily flights, number of sexuals leaving the nest as well as number of sexuals produced were estimated. There was no proof of any circadian rhythm and no marked differences between males and females except in mixed nests where females did not fly and copulated at nest surface.

Executive Summary, Feasibility Report on Proposed Amtrak Service Quad Cities-Chicago, January 7, 2008

Since the introduction of expanded levels of intrastate service on October 30, 2006, Amtrak trains in Illinois have produced impressive gains in both ridership and ticket revenue. This success and continuing stakeholder support has given rise to a formal request from the Illinois Department of Transportation (“Ill. DOT”) to Amtrak to develop a feasibility study regarding possible service consisting of a morning and an evening train in each direction between Chicago and the Quad Cities. The area between Chicago and the Quad Cities includes many rapidly growing communities. From Chicago toward the West and South, many towns and cities have experienced double digit growth increases in population since the year 2000. Southern DuPage, Cook and Will counties have seen especially strong growth, pressuring highway infrastructure, utilities, and schools. Community development and highway congestion are readily apparent when traveling the nearly 3 hour, 175 mile route between Chicago and the Quad Cities. As information, there are only three weekday round trip bus frequencies available between Chicago and the Quad Cities. The Quad City International Airport offers a total of 10 daily scheduled round trip flights to Chicago's O'Hare International Airport via two separate carriers flying regional jets. The Quad Cities (Davenport, Moline, Rock Island, and Bettendorf) are located along the Mississippi River. Nearly 60% of its visitors are from the Chicago area. With dozens of miles of scenic riverfront, river boating, casinos, and thousands of acres of expansive public spaces, the Quad Cities area is a major draw from both Iowa and Illinois. The huge Rock Island Arsenal, one of the largest military arsenals in the country and located along the river, is transitioning to become the headquarters of the United States First Army. As will be discussed later in the report, there is only one logical rail route through the Quad Cities themselves. The Iowa Interstate Railroad operates through the Quad Cities along the river and heads west through Iowa. The Quad Cities are considering at least three potential locations for an Amtrak station. A study now underway supported by several local stakeholders will recommend a site which will then be considered, given available local and other financial support. If Amtrak service were to terminate in the Quad Cities, an overnight storage track of sufficient length along with ample parking and certain other requirements covered elsewhere in the report would be required.

Hay competencia en el mercado europeo de transporte aéreo?: el caso español

La liberalización del transporte aéreo que se llevó a término en la Unión Europea a principios de los años noventa ha tenido efectos positivos sobre el bienestar del viajero. No obstante, existe un consenso en la literatura académica que estos efectos dependen de la existencia de una competencia efectiva en el nivel de la ruta. En este sentido, se plantea el problema que puede llegar a suponer las ventajas de escalera de las compañías dominantes en cada mercado interior. Además, se pretende capturar la diferenciación de productos como característica esencial de la industria del transporte aéreo. El análisis de estas cuestiones se realiza de la forma siguiente. En primer lugar, se hace referencia a los principales aspectos económicos que condicionan la competencia en el transporte aéreo. Y en segundo lugar, se implementa un modelo empírico basado en un sistema de tres ecuaciones, que se estima mediante la técnica de las variables instrumentales. La muestra utilizada hace referencia al año 2001 para la mayoría de las rutas del mercado interior español de vuelos regulares en dónde hay competencia. Los resultados de la estimación muestran la existencia de unas condiciones de competencia diferentes según el segmento del mercado al cual se dirigen las compañías aéreas. Efectivamente, la competencia en precios (calidad) parece ser predominante en el segmento de viajeros por motivos personales (negocios). Adicionalmente, el dominio que la compañía dominante tiene sobre la mayoría de las rutas parece descansar en las ventajas competitivas, tanto en términos de costes como en términos de demanda, que le proporciona el control de la red aeroportuaria nacional. De todo esto se puede inferir que el mantenimiento y/o aumento de los beneficios de la liberalización de los servicios de transporte aéreo exige extender la liberalización al uso del aeropuertos así como descentralizar su gestión.

Use of GPS for Photogrammetry, HR-342, 1993

Five test flights were conducted to study the use of Global Positioning System (GPS) in Photogrammetry, three in Iowa, one each in California and Texas. These tests show that GPS can be used to establish ground control by the static method and to determine camera location by the kinematic method. In block triangulation, six GPS controls are required and additional elevation control along the centerline is also required in strip triangulation. The camera location determined by aerial triangulation depends on the scale of the photography. The 1:3000 scale photography showed that the absolute accuracy of the camera location by GPS is better than five centimeters. The 1:40000 scale photography showed that the relative accuracy of the camera location by GPS is about one millimeter. In a strip triangulation elevation control is required in addition to the camera location by GPS. However, for block triangulation camera location by GPS is sufficient. Pre-targeting of pass and tie points gives the best results in both block and strip triangulation. In normal mapping for earth work computations the use of 1:6000 scale photography with GPS control instead of 1:3000 scale is recommended. It is recommended that research be done in the use of GPS for navigation in aerial photographic missions. It is highly recommended that research be done in the use of GPS to determine tip and tilt of the aerial camera, that is required in stereoplotting.

Airborne GPS Final Report, HR-359, 1995

The objective of this project was to use a Global Positioning System (GPS) to determine the aerial camera location and orientation that best facilitated mapping done from aerial photographs without any ground control. Four test flights were conducted. The first test flight was performed in June 1993 at St. Louis, with the objective of testing the multiantenna concept using two antenna on the aircraft. The second test in August 1993 was conducted over the Iowa State University (ISU) campus at Ames. This flight evaluated the use of GPS for pinpoint navigation. The third test flight over St. Louis was flown in October 1993, with four antenna on aircraft; its objective was to evaluate the 3DF GPS receiver and the antenna locations. On the basis of the results of these three tests, a final test flight over the Mustang Project area in Ames and the ISU campus was conducted in June 1994. Analysis of these data showed that airborne GPS can be used (1) in pinpoint navigation with an accuracy of 25 m or better, (2) to determine the location of the camera nodal point with an accuracy of 10 cm or better, and (3) to determine the orientation angles of the camera with an accuracy of 0.0001 radians or better. In addition, the exterior orientation elements determined by airborne GPS can be used to rectify aerial photos, to produce orthophotos, and in direct stereo plotting. Further research is recommended in these areas to maximize the use of airborne GPS. The report is organized in the following chapters: (1) Introduction; (2) Photogrammetry and Kinematic GPS; (3) Analysis of First Test; (4) Analysis of Second Test; (5) Analysis of Third Test; (6) Analysis of Final Test; (7) Applications of Airborne GPS; and (8) Conclusion and Recommendation.

The evolution of unicoloniality in ant societies : recognition, dispersal and population genetic structure

Introduction Societies of ants, bees, wasps and termites dominate many terrestrial ecosystems (Wilson 1971). Their evolutionary and ecological success is based upon the regulation of internal conflicts (e.g. Ratnieks et al. 2006), control of diseases (e.g. Schmid-Hempel 1998) and individual skills and collective intelligence in resource acquisition, nest building and defence (e.g. Camazine 2001). Individuals in social species can pass on their genes not only directly trough their own offspring, but also indirectly by favouring the reproduction of relatives. The inclusive fitness theory of Hamilton (1963; 1964) provides a powerful explanation for the evolution of reproductive altruism and cooperation in groups with related individuals. The same theory also led to the realization that insect societies are subject to internal conflicts over reproduction. Relatedness of less-than-one is not sufficient to eliminate all incentive for individual selfishness. This would indeed require a relatedness of one, as found among cells of an organism (Hardin 1968; Keller 1999). The challenge for evolutionary biology is to understand how groups can prevent or reduce the selfish exploitation of resources by group members, and how societies with low relatedness are maintained. In social insects the evolutionary shift from single- to multiple queens colonies modified the relatedness structure, the dispersal, and the mode of colony founding (e.g. (Crozier & Pamilo 1996). In ants, the most common, and presumably ancestral mode of reproduction is the emission of winged males and females, which found a new colony independently after mating and dispersal flights (Hölldobler & Wilson 1990). The alternative reproductive tactic for ant queens in multiple-queen colonies (polygyne) is to seek to be re-accepted in their natal colonies, where they may remain as additional reproductives or subsequently disperse on foot with part of the colony (budding) (Bourke & Franks 1995; Crozier & Pamilo 1996; Hölldobler & Wilson 1990). Such ant colonies can contain up to several hundred reproductive queens with an even more numerous workforce (Cherix 1980; Cherix 1983). As a consequence in polygynous ants the relatedness among nestmates is very low, and workers raise brood of queens to which they are only distantly related (Crozier & Pamilo 1996; Queller & Strassmann 1998). Therefore workers could increase their inclusive fitness by preferentially caring for their closest relatives and discriminate against less related or foreign individuals (Keller 1997; Queller & Strassmann 2002; Tarpy et al. 2004). However, the bulk of the evidence suggests that social insects do not behave nepotistically, probably because of the costs entailed by decreased colony efficiency or discrimination errors (Keller 1997). Recently, the consensus that nepotistic behaviour does not occur in insect colonies was challenged by a study in the ant Formica fusca (Hannonen & Sundström 2003b) showing that the reproductive share of queens more closely related to workers increases during brood development. However, this pattern can be explained either by nepotism with workers preferentially rearing the brood of more closely related queens or intrinsic differences in the viability of eggs laid by queens. In the first chapter, we designed an experiment to disentangle nepotism and differences in brood viability. We tested if workers prefer to rear their kin when given the choice between highly related and unrelated brood in the ant F. exsecta. We also looked for differences in egg viability among queens and simulated if such differences in egg viability may mistakenly lead to the conclusion that workers behave nepotistically. The acceptance of queens in polygnous ants raises the question whether the varying degree of relatedness affects their share in reproduction. In such colonies workers should favour nestmate queens over foreign queens. Numerous studies have investigated reproductive skew and partitioning of reproduction among queens (Bourke et al. 1997; Fournier et al. 2004; Fournier & Keller 2001; Hammond et al. 2006; Hannonen & Sundström 2003a; Heinze et al. 2001; Kümmerli & Keller 2007; Langer et al. 2004; Pamilo & Seppä 1994; Ross 1988; Ross 1993; Rüppell et al. 2002), yet almost no information is available on whether differences among queens in their relatedness to other colony members affects their share in reproduction. Such data are necessary to compare the relative reproductive success of dispersing and non-dispersing individuals. Moreover, information on whether there is a difference in reproductive success between resident and dispersing queens is also important for our understanding of the genetic structure of ant colonies and the dynamics of within group conflicts. In chapter two, we created single-queen colonies and then introduced a foreign queens originating from another colony kept under similar conditions in order to estimate the rate of queen acceptance into foreign established colonies, and to quantify the reproductive share of resident and introduced queens. An increasing number of studies have investigated the discrimination ability between ant workers (e.g. Holzer et al. 2006; Pedersen et al. 2006), but few have addressed the recognition and discrimination behaviour of workers towards reproductive individuals entering colonies (Bennett 1988; Brown et al. 2003; Evans 1996; Fortelius et al. 1993; Kikuchi et al. 2007; Rosengren & Pamilo 1986; Stuart et al. 1993; Sundström 1997; Vásquez & Silverman in press). These studies are important, because accepting new queens will generally have a large impact on colony kin structure and inclusive fitness of workers (Heinze & Keller 2000). In chapter three, we examined whether resident workers reject young foreign queens that enter into their nest. We introduced mated queens into their natal nest, a foreign-female producing nest, or a foreign male-producing nest and measured their survival. In addition, we also introduced young virgin and mated queens into their natal nest to examine whether the mating status of the queens influences their survival and acceptance by workers. On top of polgyny, some ant species have evolved an extraordinary social organization called 'unicoloniality' (Hölldobler & Wilson 1977; Pedersen et al. 2006). In unicolonial ants, intercolony borders are absent and workers and queens mix among the physically separated nests, such that nests form one large supercolony. Super-colonies can become very large, so that direct cooperative interactions are impossible between individuals of distant nests. Unicoloniality is an evolutionary paradox and a potential problem for kin selection theory because the mixing of queens and workers between nests leads to extremely low relatedness among nestmates (Bourke & Franks 1995; Crozier & Pamilo 1996; Keller 1995). A better understanding of the evolution and maintenance of unicoloniality requests detailed information on the discrimination behavior, dispersal, population structure, and the scale of competition. Cryptic genetic population structure may provide important information on the relevant scale to be considered when measuring relatedness and the role of kin selection. Theoretical studies have shown that relatedness should be measured at the level of the `economic neighborhood', which is the scale at which intraspecific competition generally takes place (Griffin & West 2002; Kelly 1994; Queller 1994; Taylor 1992). In chapter four, we conducted alarge-scale study to determine whether the unicolonial ant Formica paralugubris forms populations that are organised in discrete supercolonies or whether there is a continuous gradation in the level of aggression that may correlate with genetic isolation by distance and/or spatial distance between nests. In chapter five, we investigated the fine-scale population structure in three populations of F. paralugubris. We have developed mitochondria) markers, which together with the nuclear markers allowed us to detect cryptic genetic clusters of nests, to obtain more precise information on the genetic differentiation within populations, and to separate male and female gene flow. These new data provide important information on the scale to be considered when measuring relatedness in native unicolonial populations.

Interhospital aeromedical transfers: need for a specific training

Introduction: The interhospital aeromedical transfers concern mainly unstable patients presenting with multiple organ failure and among whom the intensity, as well as the difficulty of care are often underestimated. Material and method: Retrospective analysis of 2094 interhospital transfers made by the Rega helicopter of Lausanne between 2003 and 2008, with description of the pathologies, the demographic characteristics, as well as the medical and technical difficulties. Results: Male patient are overrepresented (65 vs 35%), their age being 40-80 years old. On the other hand, we note an important number (10%) of patients less than 10 years. The average time of flight is 13 minutes, with a high rate of night transfers (34%). In 73% of the cases, the transfers concern medical, especially cardiovascular and neurological situations. Trauma and surgical situations account for less than 20%. The transferred patients often require mechanical ventilation (27%), as well as invasive measure of blood pressure (11%), particularly in cases of neurological, pulmonary or cardiac diseases. In 6% of the cases, we note a haemodynamic instability, requiring the use of catecholamines. In 1% a cardiopulmonary resuscitation was initiated during the flight. The overall mortality at 48 hours is about 5%. Conclusions: In spite of relatively brief flights, the complexity and the variety of the pathologies require a specific training for the medical teams involved in the transfers, concerning the aspects of resuscitation, mechanical ventilation, and the knowledge of advanced life support in paediatrics, traumatology and cardiopulmonary intensive care.

Flight energetics in relation to sexual differences in the mating behaviour of a mayfly, Siphlonurus aestivalis

Mayflies (Ephemeroptera) are known to have short adult life-spans. Adults are unable to feed, and they utilize reserves stored during their aquatic larval stage. Energy reserves (fat, glycogen, and free sugars) of mature larvae, subimagoes and imagoes of both sexes of Siphlonurus aestivalis Eaton were compared. All the stages of both sexes had low glycogen and free sugar contents, and the only significant change occurred during the transformation of the mature larva to subimago when almost all the reserves of free sugars were used up. Glycogen and free sugars may serve as energy sources permitting individuals to swim and fly out of the water during emergence. Fat made up most of the energy reserves of mature larvae and was the main source of energy used during the final development of both sexes. Young adult males had high fat reserves which they used as a source of energy for their swarming flights. In contrast, females did not seem to use a significant amount of fat for flight. This difference is probably related to the different mating strategies of the sexes in this species. Males perform long flights waiting for females, whereas females perform only brief flights to mate and reproduce.

Loss of mating flight and shift in the pattern of carbohydrate storage in sexuals of ants (Hymenoptera; Formicidae)

In ants, energy for flying is derived from carbohydrates (glycogen and free sugars). The amount of these substrates was compared in sexuals participating or not participating in mating flights. Results show that in participating females (Lasius niger, L. flavus, Myrmica scabrinodis, Formica rufa, F. polyctena, F. lugubris), the amount of carbohydrates, especially glycogen, was higher than in non-participating females (Cataglyphis cursor, Iridomyrmex humilis). Similarly, male C. cursor and I. humilis which fly, exhibit a much higher carbohydrate content than do the non-flying females of these species. Furthermore, the quantity of carbohydrates stored was generally higher in males than in females for each species. These results are discussed with regard to the loss of the nuptial flight by some species of ants.

Comparison of lures loaded with codlemone and pear ester for capturing codling moths, Cydia pomonella, in apple and pear orchards using mating disruption

Studies were conducted in apple, Malus domestica Borkhausen and pear, Pyrus communis L. (Rosales: Rosaceae), orchards to evaluate the attractiveness of grey halobutyl septa loaded with 1 (L2) and 10 (Mega) mg of codlemone, 8E,10E-dodecadien-1-ol, 3 mg of pear ester, ethyl (E,Z)- 2,4-decadienoate (DA2313), and 3 mg of pear ester plus 3 mg of codlemone (Combo) to adult codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae). All studies were conducted in orchards treated with pheromone mating disruption. All four lures were tested on diamond-shaped sticky traps placed in 60 plots of apple and 40 plots of pears in 2003/04, and in 62 plots of apples and 30 of pears in 2004-05. Combo lures attracted significantly more moths (males + females) than all the others in both years. Comparisons among flights showed significant differences mainly for flight 1 and 2, but not always for flight 3. Mega lures provided no significant improvement compared with L2 lures during both seasons regarding the total number of moths. Combo and DA2313 lures attracted fewer females than males during the whole season. For most sample dates, more virgin than mated females were attracted to Combo lures, except during the third flight, and the overall ratio was 60:40, although the difference was not statistically significant. We conclude that the Combo lures are better indicators of codling moth activity in pheromone treated orchards, regardless of pest population level, when compared with similar lures containing codlemone or pear ester alone.

Evolutionary Games in Networked Populations: Models and Experiments

Cooperation and coordination are desirable behaviors that are fundamental for the harmonious development of society. People need to rely on cooperation with other individuals in many aspects of everyday life, such as teamwork and economic exchange in anonymous markets. However, cooperation may easily fall prey to exploitation by selfish individuals who only care about short- term gain. For cooperation to evolve, specific conditions and mechanisms are required, such as kinship, direct and indirect reciprocity through repeated interactions, or external interventions such as punishment. In this dissertation we investigate the effect of the network structure of the population on the evolution of cooperation and coordination. We consider several kinds of static and dynamical network topologies, such as Baraba´si-Albert, social network models and spatial networks. We perform numerical simulations and laboratory experiments using the Prisoner's Dilemma and co- ordination games in order to contrast human behavior with theoretical results. We show by numerical simulations that even a moderate amount of random noise on the Baraba´si-Albert scale-free network links causes a significant loss of cooperation, to the point that cooperation almost vanishes altogether in the Prisoner's Dilemma when the noise rate is high enough. Moreover, when we consider fixed social-like networks we find that current models of social networks may allow cooperation to emerge and to be robust at least as much as in scale-free networks. In the framework of spatial networks, we investigate whether cooperation can evolve and be stable when agents move randomly or performing Le´vy flights in a continuous space. We also consider discrete space adopting purposeful mobility and binary birth-death process to dis- cover emergent cooperative patterns. The fundamental result is that cooperation may be enhanced when this migration is opportunistic or even when agents follow very simple heuristics. In the experimental laboratory, we investigate the issue of social coordination between indi- viduals located on networks of contacts. In contrast to simulations, we find that human players dynamics do not converge to the efficient outcome more often in a social-like network than in a random network. In another experiment, we study the behavior of people who play a pure co- ordination game in a spatial environment in which they can move around and when changing convention is costly. We find that each convention forms homogeneous clusters and is adopted by approximately half of the individuals. When we provide them with global information, i.e., the number of subjects currently adopting one of the conventions, global consensus is reached in most, but not all, cases. Our results allow us to extract the heuristics used by the participants and to build a numerical simulation model that agrees very well with the experiments. Our findings have important implications for policymakers intending to promote specific, desired behaviors in a mobile population. Furthermore, we carry out an experiment with human subjects playing the Prisoner's Dilemma game in a diluted grid where people are able to move around. In contrast to previous results on purposeful rewiring in relational networks, we find no noticeable effect of mobility in space on the level of cooperation. Clusters of cooperators form momentarily but in a few rounds they dissolve as cooperators at the boundaries stop tolerating being cheated upon. Our results highlight the difficulties that mobile agents have to establish a cooperative environment in a spatial setting without a device such as reputation or the possibility of retaliation. i.e. punishment. Finally, we test experimentally the evolution of cooperation in social networks taking into ac- count a setting where we allow people to make or break links at their will. In this work we give particular attention to whether information on an individual's actions is freely available to poten- tial partners or not. Studying the role of information is relevant as information on other people's actions is often not available for free: a recruiting firm may need to call a job candidate's refer- ences, a bank may need to find out about the credit history of a new client, etc. We find that people cooperate almost fully when information on their actions is freely available to their potential part- ners. Cooperation is less likely, however, if people have to pay about half of what they gain from cooperating with a cooperator. Cooperation declines even further if people have to pay a cost that is almost equivalent to the gain from cooperating with a cooperator. Thus, costly information on potential neighbors' actions can undermine the incentive to cooperate in dynamical networks.

Bancs de proves per motors de modelisme

Són habituals entre els aeromodelistes les discussions que giren al voltant de la potència dels motors d’explosió i quina hèlix va millor. La manca d’informació tècnica dels motors i de les hèlix fa que aquestes discussions de vegades tinguin una validesa molt limitada, doncs es fonamenten simplement en les sensacions i percepcions subjectives de cadascun dels pilots, sobretot quan es parla de potència. En aquest projecte s’utilitzarà un dinamòmetre inercial, consistent en un volant d’inèrcia el qual s’accelerarà fins assolir les revolucions per minut màximes. La acceleració d’aquest volant mesurat en intervals de temps regulars i conegut el moment d’inèrcia del volant ens permetrà calcular el parell motor i la potència a diferents règims de revolucions per minut. Per altra banda es pretén comparar diferents hèlix muntades en un mateix motor per poder-ne comparar la tracció a diferents revolucions per minut. La tracció es mesurarà utilitzant una cèl·lula de càrrega. Les dades d’ambdós bancs de proves seran recollits i emmagatzemats per un PC amb un software fet a mida per aquest projecte. Una vegada finalitzat cada test es mostraran les dades obtingudes, tant els numèricament com gràficament, permetent a més comparar el resultat de diferents tests, de diferents motors i de diferents hèlix.