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The influence of atmospheric turbulence on the coherence of a dual-frequency laser beam is studied experimentally. An atmospheric turbulence simulator is inserted in one arm of a Mach-Zehnder interferometer. A single frequency laser beam and a dual-frequency laser beam with a frequency difference of 100 MHz travel through the interferometer, respectively. The visibilities of the interference fringes of the single and dual-frequency laser beams under different turbulent forces are compared. When the turbulence becomes stronger, the visibilities of the interference pattern of the single frequency interferometer decrease more rapidly. This shows that the atmospheric turbulence has less influence on the coherence of the dual-frequency laser beam. The linewidths broadened by the turbulence are calculated with the Wiener-Khintchine theory.
Along with the introduction of the concept of dual-channel communication, we utilized the finite-difference time-domain (FDTD) method to simulate and measure the radiation pattern under certain plasma densities and plasma collision frequencies. Results show that under certain settings, the radiation pattern of a plasma antenna resembles that of a metallic antenna. In contrast to a metallic antenna, a plasma antenna possesses other functionalities, such as dynamic reconfiguration and digital controllability. The data from simulation are similar to the measurement results, indicating that column plasma antenna can realize dual-channel communication. This work confirms the viability of realizing dual-channel communication by column plasma antenna, which adds a new but promising method for modern intelligent communication.
Background: Plants have adapted to fine-scale environmental heterogeneity through ecologically important traits, leading to new lineages. This suggests that differentiation of important traits has been beneficial to habitat partitioning among closely related species. However, the pattern of ecological divergences and differentiation of functional traits in combination with phylogenetic relationships have not been widely examined. Material and methods: To illustrate the pattern of ecological divergences of nine Picea species, spatial evolutionary and ecological vicariance analysis (seeva) was used to quantify and test the divergence between sister lineages. Five functional traits were measured in a common garden experiment. For all traits the quantitative convergence index (QVI) was determined. Furthermore, their relationships with divergent environmental variables were analyzed in the context of phylogenetic relationships. Results: Temperature variables (maximum temperature of warmest month and temperature annual range) split at basal nodes and precipitation variables (annual precipitation and precipitation of driest quarter) split at terminal nodes. Conservative traits were leaf mass per area (LMA) and net photosynthetic rate (Pn), which reflected selective retention when ancestors suffered cold environmental separation. Meanwhile, linear stomatal density (LSD), carbon-13 isotope ratio (δ 13 C) and water potential at 50% loss of hydraulic conductivity (P 50) were convergent between species, but only P 50 exhibited adaption to different precipitation conditions. The nine Picea species exhibit a distinct environmental divergence pattern. LMA and Pn were selectively retained when their ancestors were subjected to cold environmental separation. P 50 was an important trait with respect to adaptation to precipitation differences. This research provided a new way of expounding the correlation between environment, functional traits and phylogeny, deepening our understanding of environmental divergence, trait differentiation and speciation.
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