MicroRNAs (miRNAs) are endogenous small non-coding RNAs regulating gene expression in animals and plants. To find some differentially expressed miRNAs that may be associated with age-dependent behavioural changes in honey bees (Apis mellifera), we applied next-generation high-throughput sequencing technology to detect small RNAs in nurses and foragers. Our results showed that both nurses and foragers had a complicated small RNA population, and the length of small RNAs varied, 22 nucleotides being the predominant length. Combining deep sequencing and bioinformatic analysis, we discovered that nine known miRNAs were significantly different between nurses and foragers (P < 0.01; absolute value of fold-change ≥ 1). Some of their target genes were related to neural function. Moreover, 67 novel miRNAs were identified in nurses and foragers. Ame-miR-31a and ame-miR-13b were further validated using quantitative reverse-transcription PCR assays. The present study provides new information on the miRNA abundance of honey bees, and enhances our understanding of miRNA function in the regulation of honey bee development.

In the present study we demonstrate that autonomous repair of high-temperature creep damage can be achieved in iron by alloying with a small amount of gold. Adopting a heat treatment that provides mobile gold within the iron matrix is found to significantly extend the creep lifetime at a temperature of 550°C. Combined electron-microscopy techniques demonstrate that the improved creep properties originate from selective precipitation of gold atoms within early-stage creep cavities, before they can merge into micro-cracks along the grain boundaries. The selective precipitation of gold atoms at the free surface of a creep cavity results in pore filling, and as a result autonomous repair of the creep damage. Grain boundaries and dislocations act as fast routes for solute gold transport from the matrix to the creep damage. Pore filling preferentially takes place at the highest loaded grain boundaries oriented perpendicular to the applied load. The efficiency to heal creep damage is found to depend strongly on the applied stress. For lower stress levels filling fractions of up to 80% of the open-volume creep damage have been observed.Steels are among the most widely used construction materials since their mechanical properties can be tuned over a wide range in strength and formability by a proper selection of composition and heat treatment. However, when exposed for long times to high temperatures even the most optimized steels exhibit premature and low-ductility creep fracture, which arises from the formation and growth of grain-boundary cavities, which coalesce into cracks that ultimately cause failure. [1,2] Traditionally, extensive efforts are spent to prevent, or at least postpone, crack initiation. Alternatively, self healing of earlystage damage is a promising new approach that has recently been put forward to enhance the component lifetime for a wide range of materials including polymers, coatings, ceramics, concrete, and asphalt. [3][4][5][6][7][8] In the present study we demonstrate that self healing of creep damage can be achieved in pure iron by alloying with a small amount of gold. The type of healing described for this system is autonomous and does not require a change in temperature or stress state. This new finding is expected to revolutionarize the design strategies of creepresistant steels for demanding high-temperature applications such as next generation power stations.As schematically shown in Figure 1, the healing is accomplished by homogeneously incorporating gold as a solute healing agent within the iron matrix. At constant load and high temperature, cavities nucleate and subsequently grow along grain boundaries. In response to the formation of open-volume creep cavities, the mobile healing agents are triggered to move toward the cavity surface and segregate there by the combined action of volume and grain-boundary diffusion. The damage is subsequently healed by continuous precipitation within the cavity. Once the cavity is completely filled further growth is immobilized.The first attempts to he...

We have investigated the autonomous repair of creep damage by site-selective precipitation in a binary Fe-Mo alloy (6.2 wt pct Mo) during constant-stress creep tests at temperatures of 813 K, 823 K, and 838 K (540°C, 550°C, and 565°C). Scanning electron microscopy studies on the morphology of the creep-failed samples reveal irregularly formed deposits that show a close spatial correlation with the creep cavities, indicating the filling of creep cavities at grain boundaries by precipitation of the Fe 2 Mo Laves phase. Complementary transmission electron microscopy and atom probe tomography have been used to characterize the precipitation mechanism and the segregation at grain boundaries in detail.

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