Slip-twinning interdependent activation across phase boundaries: An in-situ investigation of a Ti-Al-V-Fe (α+β) alloy

© 2020 Microstructural plastic strain distribution evolution is highly heterogeneous even in single-phase alloys. One of the important factors that govern this heterogeneity is slip/twinning transfer across grain/phase boundaries. In this regard, the fundamentals of transfer across grain boundaries have drawn significant attention in the literature, while the understanding of phase boundaries remains comparatively limited. (α+β) titanium alloys provide a profound platform to explore these phenomena, since: (i) both of the present phases can exhibit plastic deformation at similar microscopic strain levels; and (ii) both dislocation slip and mechanical twinning can be triggered to accommodate plastic strain. In the present work, we evidenced a deformation transfer unit involving dislocation slip in the β-phase and {101¯2}-mechanical twin in the α-phase. We revealed by crystallographic calculations that the combination of Schmid factor and the Luster-Morris compatibility factor enables a rational quantification for the inception propensity of the slip-twinning transfer event. Our in-situ strain mapping approach verified that this sort of transfer activity can plausibly alleviate strain incompatibility/localization, demonstrating the potential to facilitate deformation homogeneity

Rheological manifestation of the second self-similar structure in gelation process of PAN/DMSO/H2O system

The gelation process in Polyacrylonitrile (PAN)/Dimethyl Sulfoxide (DMSO)/Water (H2O) systems was studied by rheology. Chambon-Winter criterion was used to detect the critical gelation temperature variation. Interestingly, we found that the loss tangent coincided at two different temperatures in different frequency periods with the temperature decreased. By using the physical and mathematical analysis, we were able to tell that the first one was the critical sol-gel transition temperature, which appeared at higher temperatures under lower frequencies; and the second point was an indication of another self-similar structure, which appeared at lower temperatures under higher frequencies. We analyzed the coarsening mechanism in the gelation process of ternary blends, and considered that the volume growth of the physical linkage can interpret this unusual phenomenon. A 'Joint Point to Joint Section' model, similar to nucleation process, was proposed to interpret the mechanism of the growth of the physical linkages. Based on the above data, phase boundaries of critical gel and the second self-similar structure can be drawn. As the PAN or water content increased, both transition temperatures increased, which indicated the non-solvent water favored the aggregation of PAN molecules and promoted the forming of the second self-similar structure. (C) 2015 Elsevier Ltd. All rights reserved

Hybridization and introgression in sympatric and allopatric populations of four oak species

Background Hybridization and introgression are vital sources of novel genetic variation driving diversification during reticulated evolution. Quercus is an important model clade, having extraordinary diverse and abundant members in the Northern hemisphere, that are used to studying the introgression of species boundaries and adaptive processes. China is the second-largest distribution center of Quercus, but there are limited studies on introgressive hybridization. Results Here, we screened 17 co-dominant nuclear microsatellite markers to investigate the hybridization and introgression of four oaks (Quercus acutissima, Quercus variabilis, Quercus fabri, and Quercus serrata) in 10 populations. We identified 361 alleles in the four-oak species across 17 loci, and all loci were characterized by high genetic variability (HE = 0.844–0.944) and moderate differentiation (FST = 0.037–0.156) levels. A population differentiation analysis revealed the following: allopatric homologous (FST = 0.064) < sympatric heterogeneous (FST = 0.071) < allopatric heterogeneous (FST = 0.084). A Bayesian admixture analysis determined four types of hybrids (Q. acutissima × Q. variabilis, Q. fabri × Q. serrata, Q. acutissima × Q. fabri, and Q. acutissima × Q. variabilis × Q. fabri) and their asymmetric introgression. Our results revealed that interspecific hybridization is commonly observed within the section Quercus, with members having tendency to hybridize. Conclusions Our study determined the basic hybridization and introgression states among the studied four oak species and extended our understanding of the evolutionary role of hybridization. The results provide useful theoretical data for formulating conservation strategies.Forestry, Faculty ofNon UBCForest and Conservation Sciences, Department ofReviewedFacult

Dynamical model of a new type of self-balancing tractor-trailer-bicycle

In this paper, we focused on a Self-Balancing Tractor-Trailer-Bicycle(TTB) and developed an under-actuated dynamical model for the system. The bicycle is characterized with two parts, that is a tractor and a trailer, and considering the nonholonomic constrains from no-slipping contacts of its three wheels and the flat ground, we presented a dynamical model for the bicycle by using Chaplygin equation. The model suggest that the TTB should be an under-actuated system with three DOF (degree of freedom) and there are two driving-torque inputs. An inverse dynamics and a virtual prototype simulations are given to demonstrate the correctness of the proposed dynamical model

Dynamical model of a new type of self-balancing tractor-trailer-bicycle

In this paper, we focused on a Self-Balancing Tractor-Trailer-Bicycle(TTB) and developed an under-actuated dynamical model for the system. The bicycle is characterized with two parts, that is a tractor and a trailer, and considering the nonholonomic constrains from no-slipping contacts of its three wheels and the flat ground, we presented a dynamical model for the bicycle by using Chaplygin equation. The model suggest that the TTB should be an under-actuated system with three DOF (degree of freedom) and there are two driving-torque inputs. An inverse dynamics and a virtual prototype simulations are given to demonstrate the correctness of the proposed dynamical model

An Improved Vibe Algorithm Based on Adaptive Thresholding and the Deep Learning-Driven Frame Difference Method

Foreground detection is the main way to identify regions of interest. The detection effectiveness determines the accuracy of subsequent behavior analysis. In order to enhance the detection effect and optimize the problems of low accuracy, this paper proposes an improved Vibe algorithm combining the frame difference method and adaptive thresholding. First, we adopt a shallow convolutional layer of VGG16 to extract the lower-level features of the image. Features images with high correlation are fused into a new image. Second, adaptive factors based on the spatio-temporal domain are introduced to divide the foreground and background. Finally, we construct an inter-frame average speed value to measure the moving speed of the foreground, which solves the mismatch problem between background change rate and model update rate. Experimental results show that our algorithm can effectively solve the drawback of the traditional method and prevent the background model from being contaminated. It suppresses the generation of ghosting, significantly improves detection accuracy, and reduces the false detection rate

Damage Effects and Fractal Characteristics of Coal Pore Structure during Liquid CO2 Injection into a Coal Bed for E-CBM

Pore structure has a significant influence on coal-bed methane (CBM) enhancement. Injecting liquid CO2 into coal seams is an effective way to increase CBM recovery. However, there has been insufficient research regarding the damage effects and fractal characteristics of pore structure at low temperature induced by injecting liquid CO2 into coal samples. Therefore, the methods of low-pressure nitrogen adsorption-desorption (LP-N2-Ad) and mercury intrusion porosimetry (MIP) were used to investigate the damage effects and fractal characteristics of pore structure with full aperture as the specimens were frozen by liquid CO2. The adsorption isotherms revealed that the tested coal samples belonged to type B, indicating that they contained many bottle and narrow-slit shaped pores. The average pore diameter (APD; average growth rate of 18.20%), specific surface area (SSA; average growth rate of 7.38%), and total pore volume (TPV; average growth rate of 18.26%) increased after the specimens were infiltrated by liquid CO2, which indicated the generation of new pores and the transformation of original pores. Fractal dimensions D1 (average of 2.58) and D2 (average of 2.90) of treated coal samples were both larger the raw coal (D1, average of 2.55 and D2, average of 2.87), which indicated that the treated specimens had more rough pore surfaces and complex internal pore structures than the raw coal samples. The seepage capacity was increased because D4 (average of 2.91) of the treated specimens was also higher than the raw specimens (D4, average of 2.86). The grey relational coefficient between the fractal dimension and pore structure parameters demonstrated that the SSA, APD, and porosity positively influenced the fractal features of the coal samples, whereas the TPV and permeability exerted negative influences