Acoustic tomography for urban tree inspection typically uses stress wave data to reconstruct tomographic images for the trunk cross section using interpolation algorithm. This traditional technique does not take into account the stress wave velocity patterns along tree height. In this study, we proposed an analytical model for the wave velocity in the longitudinal-radial (LR) plane of a live tree. Both field and laboratory stress wave testing were conducted to determine the stress wave velocity patterns in healthy and defective trees. The results showed that the ratio of the wave velocity at a propagation path angle θ(with respect to the radial direction) to the radial velocity in healthy trees approximated a second-order parabolic curve with respect to the symmetric axis (θ = 0). Our analysis of the velocity patterns indicated that the measured velocities in healthy trees were in a good agreement with the theoretical models. The results of

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The main objective of MAC protocol design is introduced, and the typical S-MAC protocol in wireless sensor networks is analyzed Then, this paper proposes a MAC protocol called the Traffic-Aware Medium Access Control (TA-MAC), a contention-based Medium Access Control protocol for wireless sensor networks, aimed to the defects of the use of fixed window when S-MAC carrier sense. In order to create a trade-off between the energy consumption and latency in some time-critical applications, TA-MAC adaptively adjusts the contention window size, based on some relevant network statistics. NS2 is used to simulate TA-MAC, which has proved that new TA-MAC achieves the best tradeoffs between latency and energy-efficiency according to this dynamic adaptation of contention window-sizes. Especially, TA-MAC's performance improved significantly, compared with fixed contention window size of S-MAC protocol in the wireless sensors network having a larger load change.

Experiments were conducted to investigate the heat transfer and flow characteristics of the vertical upward smooth and rifled tubes from subcritical to supercritical pressure. The distributions of wall temperature and heat transfer coefficient (HTC) were obtained, and the HTC correlations and friction resistance coefficient correlations were fitted with experimental data. In addition, the influences of heat flux and type of tube on heat transfer performance were analyzed. The research shows that heat flux has different influences on the heat transfer characteristics under different pressures. The increase in heat flux improves the heat transfer characteristics in the nucleate boiling region, yet it leads to the advance in heat transfer deterioration. However, for supercritical water, the increase in heat flux reduces the heat transfer ability. In addition, using the rifled tube not only improves the heat transfer performance, but also inhibits the occurrence of heat transfer deterioration. The fitted correlations have great predictive ability for the heat transfer coefficient and friction resistance coefficient, and the average relative fitting errors are limited to 20%.

In this paper, the compound heat transfer of convection and radiation in an internal circulating fluidized bed for low temperature oxidation of pulverized coal was numerically simulated. The numerical prediction about the compound heat transfer characteristics and its relationship of convection and radiation was compared with the experimental measurements of low temperature radiation. The discrete ordinate model (DOM) was employed to investigate the radiation heat transfer in the low temperature oxidation internally fluidized bed, and user-defined function (UDF) was compiled by considering the effect of the particle flow emissivity on radiation heat transfer. The convection heat transfer coefficient increases with the increase of gas inlet volume flow rate and initial bed material height, however, thermal radiation coefficient was opposite. An increase of the thermal flux results in an increase of the surface temperature of the fluid and the heater surface, and the thermal transfer coefficient between bed material and heater surface is also increased. The results have the application reference to complex thermal transfer design of circulating fluidized bed systems wherein thermal radiation transfer must be considered as a significant mode.