Local lowest-rank dynamic mode decomposition for transient feature extraction of rolling bearings.

The fault diagnosis mainly relies on the detection of periodic pulse components caused by the local damage. However, the impulsive component in bearing vibration signals is usually disturbed by noise and some harmonics due to the harsh working environment, which makes great challenge to fault diagnosis. To enhance the performance in fault diagnosis of rolling bearing, a local lowest-rank dynamic mode decomposition (LLRDMD) is proposed in this paper. Firstly, an improved projection operator is proposed to reduce the noise of augmented snapshot matrix and thus eliminating the bias of high-dimension dynamic system matrix. Secondly, by solving a local lowest-rank optimization problem, the impulsive component and interference components in the high-dimension dynamic system matrix are separated. Compared with DMD, the proposed method achieves better performance in the extraction of transient pulse component while avoiding the problems of parameter selection and mode selection. Lastly, the proposed method is applied to three sets of real datasets. Compared with existing methods, LLRDMD achieves a higher accuracy in fault diagnosis.

Application and exploration of Smile Lite MDP portable photography system in aesthetic photography of anterior teeth / 北京大学学报(医学版)

OBJECTIVE@#To explore the possibility of the Smile Lite MDP (Smile Lite Mobile Dental Photograph) portable dental photography system applying in anterior teeth aesthetic photography, and to provide the chance to simplify aesthetic photography process and facilitate communication among patients, dentists and dental technitians.@*METHODS@#The Smile Lite MDP photography system combined with the smartphone were used to photograph the front occlusal phase photos of anterior teeth. The photographic conditions including the color temperature parameter, the Smile Lite MDP light position and the intensity settings were explored. The best photographic conditions were chosen by blind evaluation within experienced dentists and technicians through the method of the visual analogue scale/score (VAS) evaluation, which went through statistical analysis to figure out the optimum photograghic conditions. Smile Lite MDP photography system was used to photograph the front occlusal phase photos of anterior teeth under the optimum parameter by different magnifications. The width/height ratio of the central incisor and the front width ratio of the upper anterior teeth in those photos were measured and calculated respectively. The accuracy of the anterior teeth photos taken by Smile Lite MDP photography system was analyzed based on the photographs taken by digital single lens reflex (DSLR) camera.@*RESULTS@#The optimum color temperature parameter of Smile Lite MDP portable camera system was 5 000 K, the optimum magnification was 4 times, the best light position was the side lights of Smile Lite MDP, the optimum intensity of lights was 2 grades. Photos taken by the optimum parameters won the highest score during the VAS evaluation and the result of statistical analysis had significant difference compared with other groups (P<0.05). When comparing the photos of the upper anterior teeth taken by the Smile Lite MDP portable photography system using 4 times magnification or by DSLR using the standard parameters, there was no significant difference neither in the width/hieght ratio of the central incisor nor in the front width ratio of the upper anterior teeth (P>0.05).@*CONCLUSION@#The Smile Lite MDP portable dental photography system applying in anterior teeth aesthetic analysis photography was capable to show the color and shape of anterior teeth in an accurate way by using the right photography parameters. Therefore, Smile Lite MDP portable dental photography system was considered to be a simple and easy photographic tool in clinical work.

Improved Dynamic Mode Decomposition and Its Application to Fault Diagnosis of Rolling Bearing.

To solve the intractable problems of optimal rank truncation threshold and dominant modes selection strategy of the standard dynamic mode decomposition (DMD), an improved DMD algorithm is introduced in this paper. Distinct from the conventional methods, a convex optimization framework is introduced by applying a parameterized non-convex penalty function to obtain the optimal rank truncation number. This method is inspirited by the performance that it is more perfectible than other rank truncation methods in inhibiting noise disturbance. A hierarchical and multiresolution application similar to the process of wavelet packet decomposition in modes selection is presented so as to improve the algorithm's performance. With the modes selection strategy, the frequency spectrum of the reconstruction signal is more readable and interference-free. The improved DMD algorithm successfully extracts the fault characteristics of rolling bearing fault signals when it is utilized for mechanical signal feature extraction. Results demonstrated that the proposed method has good application prospects in denoising and fault feature extraction for mechanical signals.

Optimized Dynamic Mode Decomposition via Non-Convex Regularization and Multiscale Permutation Entropy.

Dynamic mode decomposition (DMD) is essentially a hybrid algorithm based on mode decomposition and singular value decomposition, and it inevitably inherits the drawbacks of these two algorithms, including the selection strategy of truncated rank order and wanted mode components. A novel denoising and feature extraction algorithm for multi-component coupled noisy mechanical signals is proposed based on the standard DMD algorithm, which provides a new method solving the two intractable problems above. Firstly, a sparse optimization method of non-convex penalty function is adopted to determine the optimal dimensionality reduction space in the process of DMD, obtaining a series of optimal DMD modes. Then, multiscale permutation entropy calculation is performed to calculate the complexity of each DMD mode. Modes corresponding to the noise components are discarded by threshold technology, and we reconstruct the modes whose entropies are smaller than a threshold to recover the signal. By applying the algorithm to rolling bearing simulation signals and comparing with the result of wavelet transform, the effectiveness of the proposed method can be verified. Finally, the proposed method is applied to the experimental rolling bearing signals. Results demonstrated that the proposed approach has a good application prospect in noise reduction and fault feature extraction.

Genetic Polymorphisms of 30 InDel Loci in Ewenki Ethnic Group from Inner Mongolia / 法医学杂志

OBJECTIVES@#To study the genetic polymorphisms of 30 insertion/deletion （InDel） loci and evaluate their forensic application in Ewenki ethnic group from Inner Mongolia.@*METHODS@#Peripheral blood samples were collected from 87 unrelated healthy individuals in Ewenki ethnic group. Genomic DNA were extracted, and 30 InDel loci of the samples were multiplex amplified and genotyped. Hardy-Weinberg balance tests were preformed for all loci and genetic parameters were calculated by modified PowerStats v1.2 software. The linkage disequilibrium between loci were tested by SNPAnalyzer v2.0 software. Based on the allele frequencies of 30 InDel loci, the genetic relationships between Ewenki ethnic group and other populations were evaluated by analysis of molecular variance, principal component analysis and phylogenetic reconstruction.@*RESULTS@#After correction, 30 InDel loci conformed to Hardy-Weinberg equilibrium. It was found that the pairwise InDel loci were in linkage equilibrium after Bonferroni correction. The results of population genetics indicated that Ewenki ethnic group had close genetic relationships with Henan Han and Beijing Han populations; whereas it was significantly different from several populations in Europe and Mexico.@*CONCLUSIONS@#There are relatively high genetic polymorphisms on 30 InDel loci of Ewenki ethnic group from Inner Mongolia, which can be used as a helpful supplement application for STR detection system.

[Quantitative histomorphometric observation of distraction osteogenesis during mandibular lengthening].

PURPOSE: To evaluate the regenerating bone during mandibular distraction osteogenesis by bone histomorphometry combining tetracycline bone labeling fluorescence microscopy. METHODS: Osteotomy was performed on bilateral mandibles in ten goats. A custom-made distractor was applied to lengthen the mandible at a rate of 1 mm/d (0.5 mm/12 hrs) for ten days. Every two animals were sacrificed at 10 d, 15 d, 25 d, 35 d and 45 d postoperatively. Two additional goats were used as normal control. The bony specimens were collected and prepared for bone histomorphometry and tetracycline bone labeling fluorescence microscopy with analysis of variance. RESULTS: From 10 days subgroup to 45 days subgroup, bone volume fraction,trabecular thickness,trabecular number and volume density were gradually increased (P<0.05), while trabecular separation distance and surface density were gradually decreased (P<0.05). Between 15 days subgroup and 45 days subgroup,the index of osteoblast was significantly higher than normal control (P<0.05) and index of osteoclast was increased gradually (P<0.05). Compared with normal control, bone formation rate was accelerated by thousand times between 15 days subgroup and 45 days subgroup (P<0.05). CONCLUSIONS: During the process of mandibular distraction osteogenesis, the bone formation is active, the newly formed bone trabecula gradually become mature, and the remodeling activities of regenerated bone are enhanced gradually. The rate of bone formation within distraction period is faster than consolidation period.