Evolution of social learning when high expected payoffs are associated with high risk of failure

In an environment where the availability of resources sought by a forager varies greatly, individual foraging is likely to be associated with a high risk of failure. Foragers that learn where the best sources of food are located are likely to develop risk aversion, causing them to avoid the patches that are in fact the best; the result is sub-optimal behaviour. Yet, foragers living in a group may not only learn by themselves, but also by observing others. Using evolutionary agent-based computer simulations of a social foraging game, we show that in an environment where the most productive resources occur with the lowest probability, socially acquired information is strongly favoured over individual experience. While social learning is usually regarded as beneficial because it filters out maladaptive behaviours, the advantage of social learning in a risky environment stems from the fact that it allows risk aversion to be circumvented and the best food source to be revisited despite repeated failures. Our results demonstrate that the consequences of individual risk aversion may be better understood within a social context and suggest one possible explanation for the strong preference for social information over individual experience often observed in both humans and animals.     

Enhanced‐image‐quality raster‐scanning chipset using feedback‐control actuation

Abstract— A new raster‐scanning chipset which provides enhanced projection performance is presented. The design is novel in that it combines electrostatic and electromagnetic actuation methods, along with a unique feedback‐control scheme to produce SVGA and WVGA projected images. A micromirror, the actuators, and drive electronics are integrated into a small, power‐efficient system, a scanning chipset, to increase its reliability and manufacturability.     

Evidence for a short-range sex pheromone in female Maladera matrida beetle

Laboratory studies with live and frozen Maladera matrida female and male beetles showed that males were attracted to chemical substances emanating from the females at dusk. Beetles exhibited sexual activity (including mating) at dusk towards frozen females but not towards frozen males. Frozen females that had been extracted with methanol together with either hexane or dichloromethane or with a mixture of all three solvents did not elicit male sexual activity. Activity was fully restored when a concentrate of the extract was applied to the previously extracted frozen females. Males also responded with vigorous sexual activity to frozen males to which female extract had been applied. Deterrent chemicals appear to be absent from the male body. Males exposed to females that had been frozen during the morning displayed weak sexual activity, indicating that females lack active semiochemicals. Differences between dusk and morning extracts were found with respect to more than 20 compounds, some of which were present in much higher concentrations at dusk than in the morning, while others were not detected in the morning extract. The active component(s) of the short-range sex pheromone of female M. matrida is (are) presumably to be found among these compounds.     

Crystallization of crystalline/crystalline blends: Polypropylene/polybutene-1

The crystallization, from molten blends, of polypropylene (PP) and polybutene-1 (PB), two highly crystallizable, polymers, their interaction in the amorphous phase, and the resulting tensile mechanical properties were studied. The crystallization was followed by DSC, showing two separate PP and PB crystallization processes which are affected each by the presence of the other component. The crystallization temperature of PP is significantly affected only in PB rich blends whereas that of PB is affected in the whole composition range. The PP crystalline phase, acting as a nucleating agent, increases the PB crystallization temperature whereas the PP amorphous phase, acting as a high viscosity polymeric diluent, reduces the PB crystallization temperature. The first effect is dominant at low PP content, and the second one becomes increasingly effective with increasing PP content in the blend. The interaction between the two polymers in the amorphous phase was studied by applying dynamic mechanical analysis, in which a single glass transition was observed for the blends and its temperature was found to vary with the blends' composition. Tensile mechanical properties of blends were found to be more sensitive to thermal treatments, such as isothermal crystallization or annealing at elevated temperatures, than single component systems. Such thermal treatments enable better structured blends to be formed, resulting in mechanical properties with no abrupt changes in the whole composition range.     

Deriving an upper bound on the average operation time of a wireless sensor network

One of the main challenges in implementing wireless sensor networks (WSN) is to minimize power consumption in order to maximize network lifetime. To accomplish this, we derive an upper bound on the average network lifetime. The upper bound was derived for a code division multiple access (CDMA) communication system. The communication procedure that consumes most of the energy is transmission. But, it is possible to reduce energy consumption by increasing the antenna gain of the base station which collects information from the sensors. However, a problem that arises is that the spot size of high gain antenna is smaller than low gain antenna and as a result the base station provides only partial coverage to the network, which is obviously an undesirable situation. Therefore we propose to shape the base-station antenna gain in such a way that maximizes network lifetime, by taking advantage of the spatial nonuniformity distribution of the sensors on the ground.     

Influence of barium titanate content and particle size on electromechanical coupling coefficient of lead-free piezoelectric ceramic-Portland cement composites

The 0–3 lead-free piezoelectric ceramic-Portland cement composites were prepared by mixing and pressing the Portland cement (PC) and barium titanate (BT) ceramic powder. The influences of BT particle size and BT content on the electromechanical coupling coefficient (K_t) of the composites were investigated. The results indicate that the particle size of BT used to produce the composite under the conditions of the same BT content (at 50% BT) and fabrication technique has an influence on the K_t values. The electromechanical coupling coefficient was found to increase with the particle size of BT used where the values of K_t are found to be at 10.8% and 14.1% for composites with median particle size of 75 μm and 425 μm, respectively. Furthermore, K_t of composites increase with increasing content of BT (at the same particle size of 425 μm) when the content of BT reaches 70%, K_t is 16.6%. In addition, the acoustic impedance of the composite also increase with an increase of BT content.