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In this paper, a magnetorheological (MR) fluid damper based on a multi-stage radial flow mode is put forward, compared with traditional ones with annular damping channel which are of low magnetic field utilization and high energy consumption. The equivalent magnetic circuit model is derived, along with the relation between the magnetic induction at the working gap and the exciting current in the field coils. The finite-element software ANYSY is used to analyze the distribution of the magnetic field in the MR valve. The flow differential equation for a MR fluid in radial flow is theoretically set up, and the numerical solution is validated by means of the Herschel–Bulkley constitutive model. A MR damper was designed and fabricated in Chongqing University in accordance with the technical requirements of a railway vehicle anti-yaw damper, and the force–displacement characteristic of the damper was tested with J95-I type shock absorber test-bed. The results show that the experimental damping forces are in good agreement with the analytical ones, and the methodology is believed to help predict the damping force of a MR damper.

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Atmospheric aerosol plays critical roles in suppressing planetary boundary layer (PBL) and deteriorating air quality. However, comprehensive understanding on how aerosol optical properties (absorption and scattering) affect PBL remains lacking. Utilizing a large‐eddy simulation model incorporated with in situ observations, we demonstrate distinct impacts of absorption aerosol on PBL development when it is present below (stove effect and promotion) or above morning residual layer (dome effect and strong inhibition) and similar inhibition umbrella effects of scattering aerosol on PBL regardless of its vertical locations. There exists a transition height, above which absorption aerosol is more effective in suppressing PBL and below which scattering aerosol dominates the suppression. This height is highly related to the height of morning residual layer. Aerosol stove, dome, and umbrella effects enrich our knowledge on aerosol‐PBL interactions and the latter two can be interpreted as “double inhibitions” in promoting haze episodes in the North China Plain.

The existing registration algorithms suffer from low precision and slow speed when registering a large amount of point cloud data. In this paper, we propose a point cloud registration algorithm based on feature extraction and matching; the algorithm helps alleviate problems of precision and speed. In the rough registration stage, the algorithm extracts feature points based on the judgment of retention points and bumps, which improves the speed of feature point extraction. In the registration process, FPFH features and Hausdorff distance are used to search for corresponding point pairs, and the RANSAC algorithm is used to eliminate incorrect point pairs, thereby improving the accuracy of the corresponding relationship. In the precise registration phase, the algorithm uses an improved normal distribution transformation (INDT) algorithm. Experimental results show that given a large amount of point cloud data, this algorithm has advantages in both time and precision.

The vegetation of alpine tundra is undergoing significant changes and topography has played a significant role in mediating such changes. The roles of topography varied at different scales. In this study, we intended to identify topographic controls on tundra vegetation changes within the Changbai Mountains of Northeast China and reveal the scale effects. We delineated the vegetation changes of the last three decades using the normalized difference vegetation index (NDVI) time series. We conducted a trend analysis for each pixel to reveal the spatial change and used binary logistic regression models to analyze the relationship between topographic controls at different scales and vegetation changes. Results showed that about 30% of tundra vegetation experienced a significant (p < 0.05) change in the NDVI, with 21.3% attributable to the encroachment of low-altitude plants resulting in a decrease in the NDVI, and 8.7% attributable to the expansion of tundra endemic plants resulting in an increase in the NDVI. Plant encroachment occurred more severely in low altitude than in high altitude, whereas plant expansion mostly occurred near volcanic ash fields at high altitude. We found that plant encroachment tended to occur in complex terrains and the broad-scale mountain aspect had a greater effect on plant encroachment than the fine-scale local aspect. Our results suggest that it is important to include the mountain aspect in mountain vegetation change studies, as most such studies only use the local aspect.

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