Sampling-based methods are popular in the motion planning of robots, especially in high-dimensional spaces. Among the many such methods, the Rapidly-exploring Random Tree (RRT) algorithm has been widely used in multi-degree-of-freedom manipulators and has yielded good results. However, existing RRT planners have low exploration efficiency and slow convergence speed and have been unable to meet the requirements of the intelligence level in the Industry 4.0 mode. To solve these problems, a general autonomous path planning algorithm of Node Control (NC-RRT) is proposed in this paper based on the architecture of the RRT algorithm. Firstly, a method of gradually changing the sampling area is proposed to guide exploration, thereby effectively improving the search speed. In addition, the node control mechanism is introduced to constrain the extended nodes of the tree and thus reduce the extension of invalid nodes and extract boundary nodes (or near-boundary nodes). By changing the value of the node control factor, the random tree is prevented from falling into a so-called “local trap” phenomenon, and boundary nodes are selected as extended nodes. The proposed algorithm is simulated in different environments. Results reveal that the algorithm greatly reduces the invalid exploration in the configuration space and significantly improves planning efficiency. In addition, because this method can efficiently use boundary nodes, it has a stronger applicability to narrow environments compared with existing RRT algorithms and can effectively improve the success rate of exploration.
This paper presents a scalable 1024-element transmit dual-circularly-polarized phased array for Ka-band satellite communication (SATCOM) terminal applications. The transmit array based on the CMOS beamformer and a multilayer printed circuit board (PCB) can steer up to large scan angles (±60°) with a scan loss less than 4.5 dB. With the 8-channel transmit beamformer, the array can realize dual circular polarization and the axial ratio (AR) of the array is less than 3 dB in the scanning range of ±30° in both lefthand circular polarization (LHCP) and right-hand circular polarization (RHCP) mode. The effective isotropic radiated power (EIRP) of the array achieves 74 dBm from 29.5 GHz to 30 GHz. The design and measurement of the 1024-element transmit array have presented a feasible way for mass production of a low cost active phased array.
Most of the COVID-19 cases in Singapore have primarily come from foreign worker dormitories. This people group is especially vulnerable partly because of behavioural habits, but the built environment they live in also plays a significant role. These dormitories are typically densely populated, so the living conditions are cramped. The short lease given to most dormitories also means the design does not typically focus on environmental performance, like good natural ventilation. This paper seeks to understand how these dormitories' design affects natural ventilation and, subsequently, the spread of the COVID-19 particles by looking at two existing worker dorms in Singapore. Findings show that some rooms are poorly orientated against the prevailing wind directions, so there is dominant stagnant air in these rooms, leading to respiratory droplets' long residence times. These particles can hover in the air for 10 min and more. Interventions like increased bed distance and removing upper deck beds only showed limited ventilation improvements in some rooms. Comparatively, internal wind scoops' strategic placement was more effective at directing wind towards more stagnant zones. Large canyon aspect ratios were also effective at removing particles from higher elevations.
The application of diffuse light can potentially improve the homogeneity of light distribution and other microclimatic factors such as temperature inside greenhouses. In this study, diffuse light plastic films with different degrees of light diffuseness (20% and 29%) were used as the south roof cover of Chinese solar greenhouses to investigate the spatial distribution of microclimatic factors and their impacts on the growth and yield of tomato. The horizontal and vertical photosynthetic photon flux density (PPFD) distributions, air temperature distribution, and leaf temperature distribution inside the canopy, tomato leaf net photosynthesis (Pn), and fruit production during the growth period were determined. The results showed that diffuse light plastic film continuously improved the light distribution in the vertical and horizontal spaces of the crop canopy in terms of light interception and uniformity. A more diffuse light fraction also decreased the air and leaf temperatures of the middle canopy and upper canopy during the summer, thereby promoting the photosynthesis of the tomato plants. Pn of the middle and lower canopies with higher haze film were significantly greater than those with lower haze film (19.0% and 27.2%, respectively). The yields of higher stem density and lower stem density planted tomatoes in the 29% haze compartment were increased by 5.5% and 12.9% compared with 20% in the haze group, respectively. Diffuse light plastic films can improve the homogeneity of the canopy light distribution and increase crop production in Chinese solar greenhouses.
For rational disposal of solid wastes, low-cost cemented paste backfills (CPB) were prepared with iron tailings, ground granulated blast-furnace slag (GGBS), and calcium carbide slag (CS). To ensure that CPB can be effectively utilized in mine backfill projects, the effects of solid contents, GGBS content, CS/GGBS ratio, and mixing water on the workability and mechanical properties of CPB were investigated. The results indicated that when the solid content was 70%, the GGBS content was 14%, the CS/GGBS ratio was 0.4, the mixing water was tap water, the fluidity of fresh CPB slurry was 167 mm, and 28d unconfined compressive strength (UCS) of CPB reached 2.89 MPa, at which time the effect of the activation of the GGBS with CS was optimal. The analysis of X-ray diffraction (XRD), scanning electron microscopic imaging (SEM), thermogravimetric analysis (TG-DTG), and Fourier transform infrared spectroscopy (FTIR) demonstrated that the hydration products are mainly C-S-H gels, C-A-S-H, hemicarbonate, and hydrotalcite in CS-GGBS cementitious material. The C-S-H gel content gradually increased with increasing curing time and CS content (15%–35%). When the CS content was increased to 25%, the C-S-H gel content significantly increased, which improved the overall structural compactness and increased the UCS of CPB.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.