Adaptive Pre-Aim Control of Driverless Vehicle Path Tracking Based on a SSA-BP Neural Network

Aiming at the problem that the tracking accuracy of unmanned vehicle path tracking preview control is greatly affected by the preview time, a BP neural network adaptive preview control method is proposed. Considering that the prediction effect of the BP neural network is limited to the initial value setting, a preview time adjuster based on the SSA-BP neural network was established; by establishing the relationship between the front wheel steering angle and the preview time, a new direction control driver model was formed. The driver model and the preview time adjuster together constitute an adaptive steering controller. In order to solve the influence of the longitudinal speed change on the vehicle stability, a PID variable-speed controller was designed to realize the horizontal and vertical coordinated control of the path tracking of the unmanned vehicle. Compared with the fixed preview time and the BP preview time control method, the results show that the proposed method has strong tracking ability when driving at various speeds on three consecutive curves and Alt 3 test roads, and can be used when driving at a variable speed

Functional characterization of phenylalanine ammonia-lyase- and cinnamate 4-hydroxylase-encoding genes from Lycoris radiata, a galanthamine-producing plant

Galanthamine (GAL), the well-known Amaryllidaceae alkaloid, is a clinically used drug for the treatment of Alzheimer's disease. L-Phenylalanine (Phe) and trans-cinnamic acid (CA) were enzymatically transformed into the catechol portion of GAL Herein, a Phe ammonia-lyase-encoding gene LrPAL3 and a cinnamate 4hydroxylase-encoding gene LrC4H were cloned from Lycoris radiata, a GAL-producing plant. LrPAL3 was overexpressed in Escherichia coli and purified to homogeneity. LrPAL3 catalyzes the forward deamination conversion of L-Phe into trans-CA. The 3-chloro- and 4-fluoro-L-Phe were deaminated to generate the corresponding 3-chloro- and 4-fluoro-trans-CA by LrPAL3. LrPAL3-catalyzed reverse hydroamination was confirmed by the conversion of trans-CA into L-Phe with exceptional regio- and stereo-selectivity. LrC4H was overexpressed in E. coli with tCamCPR, a cytochrome P450 reductase-encoding gene. LrC4H catalyzes the regioselective parahydroxylation on trans-CA to form p-coumaric acid. The transcriptional levels of both LrPAL3 and LrC4H were positively associated with the GAL contents within the leaves and flowers of L radiata, which suggested that their expression and function are co-regulated and involved in the biosynthesis of GAL The present investigations on the biosynthetic genes of GAL will promote the development of synthetic biology platforms for this kind of important drug via metabolic engineering. (C) 2018 Elsevier B.V. All rights reserved

Lanostane-type C-31 triterpenoid derivatives from the fruiting bodies of cultivated Fomitopsis palustris

Fifteen undescribed and five known lanostane-type C-31 triterpenoid derivatives were isolated from the aqueous EtOH extract of the fruiting bodies of cultivated Fomitopsis palustris. Their structures were identified from the spectroscopic data and chemical degradation studies. The structures of palustrisoic acids A and H were confirmed by X-ray crystallography. Polyporenic acid B showed strong cytotoxicity against the HCT116, A549, and HepG2 cell lines with IC50 values of 8.4, 12.1, and 12.2 mu M, respectively. Palustrisolides A, C, and G displayed weak cytotoxicity. (C) 2018 Elsevier Ltd. All rights reserved

Effect of Cold Expansion on Fatigue Life of Hole Structure of TC17 Titanium Alloy

In order to improve the fatigue performance of TC17 central hole specimen, the hole wall surface integrity was characterized by scanning electron microscopy (SEM), roughness meter, X-ray diffraction, and the influence of hole cold expansion(HCE) parameter on the fatigue performance of the hole specimens was investigated. The results show that the minimum fatigue life (14718 cycle) of the HCE specimens with an expansion value of 0.18 mm is higher than the original specimen (13965 cycle). Compared to the specimens with the expansion values of 0.28 mm and 0.38 mm, the fatigue life dispersion is less, no obvious stress concentration phenomenon is found, and it has the best fatigue performance than the other two. The surface roughness value of hole wall is the lowest after the HCE with 0.18 mm, the inner hole wall forms a certain depth of strengthened layer, the residual compressive stress produced in the hole side effectively suppresses the produce of fatigue cracks in the inner hole wall, so the fatigue performance of hole structure is improved

Effect of Double Cold Expansion of Hole on Fatigue Property of TB6 Titanium Alloy

To improve the fatigue resistance of the bolt connecting hole, the effect of double cold expansion (DCE) of the hole on the fatigue life of TB6 titanium alloy was investigated. The fatigue fracture, surface roughness, residual stress, hardness and microstructure of the hole wall were characterized by scanning electron microscopy (SEM), roughmeter, X-ray diffraction (XRD), microhardness tester and optical microscopy. The mechanism of DCE on the fatigue life of the hole was also investigated. The results show that the mean value of the fatigue life of DCE specimen is much higher than that of the interference fit specimen. The surface integrity of the hole wall is improved after DCE. The roughness decreases remarkably. The deep surface-strengthen-layer with high hardness and deep residual compressive stress field are formed around the hole through severe plastic deformation of the microstructure of the hole wall. It is considered that the improvement of surface integrity plays an important role on the enhancement of fretting fatigue life