The effects of natural weathering ages on mineralogical, physical, and chemical properties of stacking molybdenum tailings.

This study investigated the influence of natural weathering on the mineralogical, physical, and chemical properties of molybdenum tailings from Shaanxi Province, China, stored at different stacking ages. The results showed that the mineralogical and chemical compositions of the molybdenum tailings remained stable after stacking for different years. The analysis of bulk density, porosity, field moisture capacity, and aggregate characteristics indicated that the physical structure of the molybdenum tailings was similar to a nearby soil with increasing stacking age in spite of a time-consuming process. In addition, 10 years of the natural weathering process resulted in the formation of more aggregates with the surface of microaggregates roughened, and displayed more debris and fine particles than stocking for 1 year. The findings showed that the bulk density of molybdenum tailings reduced from 1.45 to 1.42 g/cm3 after 10 years of storage, while its porosity rose from 46.5 to 49.4%. The fraction of large aggregate (> 0.25 mm) and mean weight diameter increased from 7.91 to 42.07% and from 0.1482 to 0.1864 mm, respectively, which demonstrated that the natural weathering significantly improved the physical properties of the aggregate and enhanced the structural stability. Thus, natural weathering provides an ecological basis for restoring and reconstructing the soil ecosystem in molybdenum tailings. The results confirmed that long-term deposition can improve the soil structure of tailings, which provides a reference for further research on restoring and reconstructing the soil ecosystem in molybdenum tailings.

Abdominal-B regulates structure and development of the Harmonia axyridis cremaster.

The ladybird Harmonia axyridis is an insect that exhibits pupal attachment to plants, which facilitates development and environmental adaptation. The cremaster is highly specialized for this behavior. However, the underlying molecular regulation of the cremaster remains unclear; therefore, we performed experiments to investigate the transcriptional regulation of cremaster development. First, we examined the morphological structure of the cremaster to reveal its function in pupal attachment of H. axyridis. Next, we analyzed the Hox gene Ha-Abd-B using RNA interference (RNAi) to determine its function in regulating cremaster formation; Ha-Abd-B up-regulation promoted effective pupal attachment, whereas successful RNAi caused severe down-regulation of this gene, and pupae were unable to attach. Furthermore, successful RNAi and subsequent Ha-Abd-B down-regulation caused phenotypic changes in cremaster structure, including its complete disappearance from some individuals. Finally, we observed unique development of the cremaster and dynamic expression of Ha-Abd-B during pre-pupal development; consequently, we hypothesized that there was specific pre-pupal development of the cremaster. Overall, based on these results, the specialized cremasteric structure located on the posterior side of H. axyridis was determined to be a key organ for pupal attachment. Cremaster identification in H. axyridis is regulated by Ha-Abd-B and exhibits preferential development. Pupal attachment of H. axyridis reveals an environmental adaptation of this species; thus, this study and future molecular studies will help determine the role of Hox genes in regulation of insect attachment and further our understanding of the multiple functions of Hox genes.

Superficially Similar Adaptation Within One Species Exhibits Similar Morphological Specialization but Different Physiological Regulations and Origins.

Animals have developed numerous strategies to contend with environmental pressures. We observed that the same adaptation strategy may be used repeatedly by one species in response to a certain environmental challenge. The ladybird Harmonia axyridis displays thermal phenotypic plasticity at different developmental stages. It is unknown whether these superficially similar temperature-induced specializations share similar physiological mechanisms. We performed various experiments to clarify the differences and similarities between these processes. We examined changes in the numbers and sizes of melanic spots in pupae and adults, and confirmed similar patterns for both. The dopamine pathway controls pigmentation levels at both developmental stages of H. axyridis. However, the aspartate-ß-alanine pathway controls spot size and number only in the pupae. An upstream regulation analysis revealed the roles of Hox genes and elytral veins in pupal and adult spot formation. Both the pupae and the adults exhibited similar morphological responses to temperatures. However, they occurred in different body parts and were regulated by different pathways. These phenotypic adaptations are indicative of an effective thermoregulatory system in H. axyridis and explains how insects contend with certain environmental pressure based on various control mechanisms.

Iterative Trajectory Optimization for Physical-Layer Secure Buffer-Aided UAV Mobile Relaying.

With the fast development of commercial unmanned aerial vehicle (UAV) technology, there are increasing research interests on UAV communications. In this work, the mobility and deployment flexibility of UAVs are exploited to form a buffer-aided relaying system assisting terrestrial communication that is blocked. Optimal UAV trajectory design of the UAV-enabled mobile relaying system with a randomly located eavesdropper is investigated from the physical-layer security perspective to improve the overall secrecy rate. Based on the mobility of the UAV relay, a wireless channel model that changes with the trajectory and is exploited for improved secrecy is established. The secrecy rate is maximized by optimizing the discretized trajectory anchor points based on the information causality and UAV mobility constraints. However, the problem is non-convex and therefore difficult to solve. To make the problem tractable, we alternatively optimize the increments of the trajectory anchor points iteratively in a two-dimensional space and decompose the problem into progressive convex approximate problems through the iterative procedure. Convergence of the proposed iterative trajectory optimization technique is proved analytically by the squeeze principle. Simulation results show that finding the optimal trajectory by iteratively updating the displacements is effective and fast converging. It is also shown by the simulation results that the distribution of the eavesdropper location influences the security performance of the system. Specifically, an eavesdropper further away from the destination is beneficial to the system's overall secrecy rate. Furthermore, it is observed that eavesdropper being further away from the destination also results in shorter trajectories, which implies it being energy-efficient as well.