Being one of the most promising candidates for the modeling of localized failure in solids, so far the phase-field method has been applied only to brittle fracture with very few exceptions. In this ...work, a unified phase-field theory for the mechanics of damage and quasi-brittle failure is proposed within the framework of thermodynamics. Specifically, the crack phase-field and its gradient are introduced to regularize the sharp crack topology in a purely geometric context. The energy dissipation functional due to crack evolution and the stored energy functional of the bulk are characterized by a crack geometric function of polynomial type and an energetic degradation function of rational type, respectively. Standard arguments of thermodynamics then yield the macroscopic balance equation coupled with an extra evolution law of gradient type for the crack phase-field, governed by the aforesaid constitutive functions. The classical phase-field models for brittle fracture are recovered as particular examples. More importantly, the constitutive functions optimal for quasi-brittle failure are determined such that the proposed phase-field theory converges to a cohesive zone model for a vanishing length scale. Those general softening laws frequently adopted for quasi-brittle failure, e.g., linear, exponential, hyperbolic and Cornelissen et al. (1986) ones, etc., can be reproduced or fit with high precision. Except for the internal length scale, all the other model parameters can be determined from standard material properties (i.e., Young’s modulus, failure strength, fracture energy and the target softening law). Some representative numerical examples are presented for the validation. It is found that both the internal length scale and the mesh size have little influences on the overall global responses, so long as the former can be well resolved by sufficiently fine mesh. In particular, for the benchmark tests of concrete the numerical results of load versus displacement curve and crack paths both agree well with the experimental data, showing validity of the proposed phase-field theory for the modeling of damage and quasi-brittle failure in solids.
Solid‐state batteries are hindered from practical applications, largely due to the retardant ionic transportation kinetics in solid electrolytes (SEs) and across electrode/electrolyte interfaces. ...Taking advantage of nanostructured UIO/Li‐IL SEs, fast lithium ion transportation is achieved in the bulk and across the electrode/electrolyte interfaces; in UIO/Li‐IL SEs, Li‐containing ionic liquid (Li‐IL) is absorbed in Uio‐66 metal–organic frameworks (MOFs). The ionic conductivity of the UIO/Li‐IL (15/16) SE reaches 3.2 × 10−4 S cm−1 at 25 °C. Owing to the high surface tension of nanostructured UIO/Li‐IL SEs, the contact between electrodes and the SE is excellent; consequently, the interfacial resistances of Li/SE and LiFePO4/SE at 60 °C are about 44 and 206 Ω cm2, respectively. Moreover, a stable solid conductive layer is formed at the Li/SE interface, making the Li plating/stripping stable. Solid‐state batteries from the UIO/Li‐IL SEs show high discharge capacities and excellent retentions (≈130 mA h g−1 with a retention of 100% after 100 cycles at 0.2 C; 119 mA h g−1 with a retention of 94% after 380 cycles at 1 C). This new type of nanostructured UIO/Li‐IL SEs is very promising for solid‐state batteries, and will open up an avenue toward safe and long lifespan energy storage systems.
After absorbing ionic liquid Li‐IL, nanostructured MOFs of Uio‐66 become a new kind of solid electrolyte (UIO/Li‐IL). The UIO/Li‐IL solid electrolyte shows a high ionic conductivity, good stability against metallic Li electrode, and low solid electrolyte/electrode interfacial resistances. The solid‐state lithium batteries using the UIO/Li‐IL solid electrolyte exhibit a high capacity and excellent retention.
Recently several non-standard phase-field models different from the standard one for brittle fracture (Bourdin et al. 2000, 2008; Miehe et al. 2010a) have been proposed for the modeling of damage and ...fracture in solids. On the one hand, linear elastic behavior before the onset of damage and even cohesive cracking induced quasi-brittle failure can be considered by such non-standard phase-field models. On the other hand, they present great challenges to the numerical implementation since the damage boundedness is no longer automatically fulfilled. In this work, the numerical implementation of the unified phase-field damage model (Wu 2017, 2018) is addressed, though it also applies to the standard and other non-standard ones. In particular, an iterative alternate minimization (AM) algorithm enhanced with path-following strategies is presented. The phase-field or damage sub-problem is solved by the bound-constrained optimization solver in which the boundedness and irreversibility conditions of the crack phase-field are exactly enforced. Moreover, material softening induced snap-backs typically for localized failure in solids can also be effectively dealt with. The equilibrium paths in terms of the fracture surface and of the indirect displacement (e.g., the crack mouth opening or sliding displacement) are discussed in the context of the AM algorithm. The AM algorithm with the indirect displacement control is advocated, since both prescribed external forces and displacements can be naturally dealt with, which is more versatile than the one with the fracture surface control applicable only for prescribed displacements. Representative examples of benchmark tests show that the AM algorithm enhanced with the indirect displacement control is extremely robust even for large increment sizes. The insensitivity of the unified phase-field damage model to the incorporated length scale and mesh size is also confirmed.
•Robust numerical implementation of non-standard phase-field damage models is presented.•The crack irreversibility is exactly enforced by the bounded-constrained optimization solver.•The alternate minimization algorithm enhanced with the indirect displacement control is justified.•Robustness of the presented numerical algorithm is verified by examples of benchmark tests.
Aiming to bridge the gap between damage and fracture mechanics for modeling localized failure in solids, this paper addresses a novel geometrically regularized gradient-damage model with energetic ...equivalence for cracking evolution. With the free energy potential defined as usual in terms of the local strain and damage fields, the constitutive relations are derived consistently from the standard framework of thermodynamics. Upon the sharp crack topology geometrically regularized by the damage localization band with a length scale, the ensuing energetic equivalence naturally yields the damage evolution law of gradient-type and the associated boundary condition of Neumann-type. Compared to other gradient-damage models, no extra assumptions like the nonlocal energy residual and insulation condition are introduced. Moreover, the damage gradient, physically accounting for microscopic nonlocal interactions, is fully dissipative as expected. In line with the unified phase-field theory recently proposed by the author (Wu, 2017) during failure processes the material behavior is uniquely characterized by two constitutive functions, i.e., the degradation function defining the free energy potential of the bulk and the geometric function regularizing the sharp crack topology. In particular, optimal constitutive functions defining an equivalent cohesive zone model of general softening laws are postulated, with the involved parameters calibrated from standard material properties. The proposed model is numerically implemented into the multi-field finite element method and applied to several benchmark tests of concrete under mode-I and mixed-mode failure. It is found that the incorporated length scale can be regarded either a numerical parameter or a material property. For the former considered in this work, the length scale has negligible, if not no, effects on the global responses, so long as the sharp crack topology and the damage field of high gradients within the localization band are well resolved. Furthermore, the localization bandwidth does not exhibit spurious widening, but rather, it approaches to a finite value proportional to the length scale. Comparison between the numerical and experimental results, regarding the curve of load versus displacement and crack path, confirms validity of the proposed gradient-damage model for characterizing localized failure in quasi-brittle solids.
•A geometrically regularized gradient-damage model with energetic equivalence is proposed.•The damage evolution law emerges from the geometric regularization and energetic equivalence.•The crack is implicitly represented, and cumbersome crack tracking strategies are not required.•The length scale can be regarded either as a small numerical parameter or as a material property.•The localization bandwidth approaches to a finite limit value, not exhibiting spurious damage growth.
Knowledge hiding has been a variable of interest that has led to major intangible losses to organizations, especially in this pandemic era when everything has shifted to online platforms and social ...media. Knowledge hiding has taken a new turn into the field of knowledge management. Moreover, the major players in knowledge hiding are the personality characteristics of individuals that have now found a way of expression without coming into the spotlight. This study is a necessary one in this time of online working environments where the role of personality traits and psychological ownership has been explored to understand their impact on the knowledge hiding within the organizations of China, and furthermore, to understand what role social status plays in moderating these relationships. The sampling design used is convenient random sampling with a sample size of 298 managers. This study has used the software Smart-PLS 3.3.3 for analyzing the data. The data relied on and was validated using preliminary tests of reliability and discriminant and convergent validities using the measurement model algorithm. Further, the partial least square technique was used to find the equation modeling for the variables, with the help of a structural model algorithm using 500 iterations for bootstrapping. The findings of the current study show that the personality traits of the "BIG FIVE" model positively predict knowledge hiding, except for openness to experience. At the same time, psychological ownership plays a partial mediating role.
A novel approach based on long short-term memory (LSTM) networks that can incorporate multivariate time series data, including historical tourism volume data, search engine data and weather data, is ...proposed for forecasting the daily tourism volume of tourist attractions. The proposed approach is applied to forecast the daily tourism volume of Jiuzhaigou and Huangshan Mountain Area, two famous tourist attractions in China. Through these two applications, the validity of the proposed approach is verified. In addition, the forecasting power of the approach with historical data, search engine data and weather data is stronger than that without search engine data or without both search engine data and weather data, which provides evidence that search engine data and weather data are of great significance to tourism volume forecasting.
•A forecasting approach with long short-term memory networks is proposed.•Historical data, search engine data and weather data are all used in modelling.•The forecasting approach can automatically learn the time lags of observations.•Daily tourism volume for two tourist attractions is forecasted with the new approach.•Search engine data and weather data are of great significance for forecasting.
Reported herein is an unprecedented synthesis of C3‐fluorinated oxindoles through cross‐dehydrogenative coupling of C(sp3)‐H and C(sp2)‐H bonds from malonate amides. Under the unique and mild ...electrochemical conditions, the requisite oxidant and base are generated in a continuous fashion, allowing the formation of the base‐ and heat‐sensitive 3‐fluorooxindoles in high efficiency with broad substrate scope. The synthetic usefulness of the electrochemical method is further highlighted by its easy scalability and the diverse transformations of the electrolysis product.
C−H functionalization: A ferrocene‐catalyzed electrochemical cross‐coupling reaction of C(sp3)‐H and C(sp2)‐H centers has been developed to give access to C3‐fluorinated oxindoles using fluorinated malonate amides. The electrosynthetic method is characterized by mild reaction conditions, broad substrate scope, high functional group tolerance, and easy scalability.
Circular RNAs (circRNAs) are a novel type of endogenous noncoding RNA gaining research interest in recent years. Despite this increase in interest, the mechanism of circRNAs in the pathogenesis of ...multiple cardiovascular diseases, particularly myocardial fibrosis, is rarely reported. In the following study, the expression profiles and potential mechanisms of circRNAs in mice myocardial fibrosis models in vitro are investigated. Previous research examining circRNA expression profiles of diabetic db/db mice myocardium using circRNA microarray found 43 circRNAs were abnormally expressed, including 24 up-regulated circRNAs and 19 down-regulated circRNAs. Furthermore, circRNA_010567 was markedly up-regulated in diabetic mice myocardium and cardiac fibroblasts (CFs) treated with Ang II. Bioinformatics analysis predicted circRNA_010567, sponge miR-141 and miR-141 directly target TGF-β1, which was validated by dual-luciferase assay. Subsequently, functional experiments revealed circRNA_010567 silencing could up-regulate miR-141 and down-regulate TGF-β1 expression, and suppress fibrosis-associated protein resection in CFs, including Col I, Col III and α-SMA. Results demonstrate the circRNA_010567/miR-141/TGF-β1 axis plays an important regulatory role in the diabetic mice myocardial fibrosis model. The present study characterizes a new function of circRNA in the pathogenesis of myocardial fibrosis in a diabetic mouse model, providing novel insight for circRNA-miRNA-mRNA in cardiovascular disease.
•A novel identified circular RNA, circRNA_010567, is up-regulated in diabetic mice myocardium.•CircRNA_010567 knockdown suppresses fibrosis-associated protein secretion in cardiac fibroblasts.•CircRNA_010567 acts as an endogenous sponge of miR-141.•miR-141 targets TGF-β1.•CircRNA_010567/miR-141/TGF-β1 axis plays an important regulation in mice myocardial fibrosis.
•Microbial fermentation is the key factor controlling the quality of dark tea.•Serial reactions modify the chemical constituents of tea leaves during fermentation.•Multi-omics approaches are used to ...reveal microbial impact on dark tea quality.
Dark tea is a unique fermented tea produced by solid-state fermentation of tea leaves (Camellia sinensis). It includes ripe Pu-erh tea, Fu brick tea, Liupao tea, and other teas. Microbial fermentation is considered to be the key factor controlling the quality of dark tea. It involves a series of reactions that modify the chemical constituents of tea leaves. These chemical conversions during microbial fermentation of dark tea are associated with a variety of functional core microorganisms. Further, Multi-omics approaches have been used to reveal the microbial impact on the conversion of the chemical components in dark tea. In the present review, we provide an overview of the most recent advances in the knowledge of the microbial bioconversion of the chemical components in dark tea, including the chemical composition of dark tea, microbial community composition and dynamics during the fermentation process, and the role of microorganisms in biotransformation of chemical constituents.
•A phase-field regularized cohesive zone model for brittle fracture is proposed.•The relations to other phase-field models and Barenblatt’s CZM are clarified.•Neither explicit crack ...representation/tracking nor penalty stiffness is needed.•The numerical result is insensitive to the incorporated length scale parameter.
Being able to model complex nucleation, propagation, branching and merging of cracks in solids within a unified framework, the classical phase-field models for brittle fracture fail in predicting length scale independent global responses for a solid lacking elastic singularities (e.g., corners, notches, etc.). Motivated from Barenblatt’s approximation of Griffith’s brittle fracture with a vanishing Irwin’s internal length, this paper extends our recent work in quasi-brittle failure (Wu, 2017, 2018a) and presents for the first time a length scale insensitive phase-field damage model for brittle fracture. More specifically, with a set of optimal characteristic functions, a phase-field regularized cohesive zone model (CZM) with linear softening law is addressed and applied to brittle fracture. Both the failure strength and the traction – separation law are independent of the incorporated length scale parameter. Compared to other phase-field models and CZM based discontinuous approaches for brittle fracture, the proposed phase-field regularized CZM is of several merits. On the one hand, being theoretically equivalent to Barenblatt’s CZM (at least in the 1-D case), it needs neither the explicit crack representation/tracking nor the elastic penalty stiffness which both are necessary but cumbersome for discontinuous approaches. On the other hand, it gives length scale independent global responses for problems with or without elastic singularities while preserving the expected Γ-convergence property of phase-field models. Representative numerical examples of several well-known benchmark tests support the above conclusions, validating its capability of modeling both mode-I and mixed-mode brittle fracture.
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