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.
Accidental degeneracy in a photonic crystal consisting of a square array of elliptical dielectric cylinders leads to both a semi-Dirac point at the center of the Brillouin zone and an electromagnetic ...topological transition (ETT). A perturbation method is deduced to affirm the peculiar linear-parabolic dispersion near the semi-Dirac point. An effective medium theory is developed to explain the simultaneous semi-Dirac point and ETT and to show that the photonic crystal is either a zero-refractive-index material or an epsilon-near-zero material at the semi-Dirac point. Drastic changes in the wave manipulation properties at the semi-Dirac point, resulting from ETT, are described.
The gut microbiota has been implicated in cancer and shown to modulate anticancer drug efficacy. Altered gut microbiota is associated with resistance to chemo drugs or immune checkpoint inhibitors ...(ICIs), whereas supplementation of distinct bacterial species restores responses to the anticancer drugs. Accumulating evidence has revealed the potential of modulating the gut microbiota to enhance the efficacy of anticancer drugs. Regardless of the valuable findings by preclinical models and clinical data of patients with cancer, a more thorough understanding of the interactions of the microbiota with cancer therapy helps researchers identify novel strategy for cancer prevention, stratify patients for more effective treatment and reduce treatment complication. In this review, we discuss the scientific evidence on the role of gut microbiota in cancer treatment, and highlight the latest knowledge and technologies leveraged to target specific bacteria that contribute to tumourigenesis. First, we provide an overview of the role of the gut microbiota in cancer, establishing the links between bacteria, inflammation and cancer treatment. Second, we highlight the mechanisms used by distinct bacterial species to modulate cancer growth, immune responses, as well as the efficacy of chemotherapeutic drugs and ICIs. Third, we demonstrate various approaches to modulate the gut microbiota and their potential in translational research. Finally, we discuss the limitations of current microbiome research in the context of cancer treatment, ongoing efforts to overcome these challenges and future perspectives.
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.
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•Design of artificial metalloenzymes has achieved significant progress in the last decade.•Artificial metalloenzymes were designed from single to multiple active sites in native or de ...novo proteins.•Artificial metalloenzymes exhibit diverse functions, even beyond those of natural metalloenzymes.•The progress elucidates the structure-function relationship of natural metalloenzymes.•The progress provides clues for design of advanced artificial metalloenzymes with potential applications.
Artificial metalloenzymes combine the advantages of both natural enzymes and chemically synthesized models, which have achieved significant progress in the last decade. This review summarizes the recent achievements in rational design of metalloenzymes from single to multiple active sites in natural or de novo protein scaffolds, with a diverse range of functionalities, even beyond those of natural metalloenzymes. These achievements include construction of mononuclear active site by metal substitution or incorporation, design of homo- or hetero-dinuclear site, introduction of Fe-sulfur or other metal clusters, reconstitution of metallo-porphyrins or other metal complexes, and design of dual or multiple active sites in single, dimeric proteins, de novo proteins, protein-protein interfaces, as well as protein oligomers and polymers. Other new trends in recent designs are also discussed. The progress not only elucidates the structural and functional relationship of natural metalloenzymes, but also provides practical clues for design of advanced artificial metalloenzymes with potential applications.
•A thermal and electric model of PV–TE system adopting nanofluid is established.•Performance comparisons between glazed and unglazed systems are presented.•Not all larger figure of merits are ...favorable to PV–TE system.•Coupling effect of wind velocity and nanofluid flow rate is analyzed.
This paper establishes a theoretical model for assessing the performance of glazed/unglazed photovoltaic–thermoelectric (PV–TE) hybrid system. To enhance the heat removal, nanofluid is served as heat sink. Firstly, a performance comparison between glazed and unglazed system is given. It is suggested that, under the condition of higher figure of merit Z and concentration ratio C, as well as enhanced transmissivity of glass cover, glazed system may be competitive or even superior to the unglazed one. Environmental effect such as wind velocity, is also a significant factor which may be ignored in the existing researches. Therefore, considering the coupling effect of wind velocity and nanofluid flow rate, the impacts of some key parameters on the system overall efficiency are examined in the following part. It is found for certain TE modules, a higher figure of merit Z may still cause a decrease in the system overall efficiency resulting from the different parameter values, that is, Seebeck coefficient s, electrical resistivity ρ and thermal conductivity λ. When thermoelectric efficiency ηTE reaches maximum, the obtained optimal load resistance Rl is larger than that corresponding to maximum overall efficiency η. With varying wind velocity, the maximum overall efficiency could achieve at maximum or minimum wind velocity, corresponding to Z=0.0021K−1 and Z=0.0085K−1 conditions, respectively. In addition, nanofluid shows better performance than water.
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•Biodegradation of environmental pollutants has been favored for decades.•Significant progress has been made in the biodegradation of aromatic pollutants by metalloenzymes.•Both ...native and artificial metalloenzymes have been applied for biodegradation.•The progress sheds light on the structure-function relationship of metalloenzymes.•The progress provides clues for applications of metalloenzymes in environmental protection.
Environmental security is closely related to public health. Aromatic pollutants constitute a class of hazardous environmental chemicals, such as halophenols and polycyclic aromatic hydrocarbons. Biodegradation of environmental pollutants has been favored for decades. As reviewed herein, significant progress has been made in biodegradation of aromatic pollutants by native metalloenzymes, including heme enzymes (peroxidases and cytochrome P450s), non-heme iron-containing enzymes (Rieske dioxygenases), and copper-containing enzymes (catechol oxidase, tyrosinase, and laccase), and artificial metalloenzymes, including engineered myoglobins, designed manganese peroxidase and de novo designed metalloenzymes, such as those in helical bundles and peptide assemblies, as well as synthetic structural and functional models of natural enzymes. These advances shed light on the structure–function relationship of metalloenzymes, providing clues for potential applications in environmental protection. Future directions for making full use of native and artificial metalloenzymes in environmental science are also prospected.
In this work, several commonly used conductive substrates as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions were studied, ...including nickel foam (Ni foam), copper foam (Cu foam), nickel mesh (Ni mesh) and stainless steel mesh (SS mesh). Ni foam and SS mesh are demonstrated as high-performance and stable electrocatalysts for HER and OER, respectively. For HER, Ni foam exhibited an overpotential of 0.217 V at a current density of 10 mA cm
−2
with a Tafel slope of 130 mV dec
−1
, which were larger than that of the commercial Pt/C catalyst, but smaller than that of the other conductive substrates. Meanwhile, the SS mesh showed the best electrocatalytic performance for OER with an overpotential of 0.277 V at a current density of 10 mA cm
−2
and a Tafel slope of 51 mV dec
−1
. Its electrocatalytic performance not only exceeded those of the other conductive substrates but also the commercial RuO
2
catalyst. Moreover, both Ni foam and SS mesh exhibited high stability during HER and OER, respectively. Furthermore, in the two-electrode system with Ni foam used as the cathode and SS mesh used as the anode, they enable a current density of 10 mA cm
−2
at a small cell voltage of 1.74 V. This value is comparable to or exceeding the values of previously reported electrocatalysts for overall water splitting. In addition, NiO on the surface of Ni foam may be the real active species for HER, NiO and FeO
x
on the surface of SS mesh may be the active species for OER. The abundant and commercial availability, long-term stability and low-cost property of nickel foam and stainless steel mesh enable their large-scale practical application in water splitting.
Efficient electrocatalytic overall water splitting is achieved with commercially-available and low-cost nickel foam and stainless steel mesh as cathode and anode electrodes.
Kiwifruit (Actinidia spp.) is a climacteric fruit with high sensitivity to ethylene, influenced by multiple ethylene-responsive structural genes and transcription factors. However, the roles of other ...post-transcriptional regulators (e.g. miRNAs) necessary for ripening remain elusive.
High-throughput sequencing sRNAome, degradome and transcriptome methods were used to identify further contributors to ripening control in the kiwifruit (A. deliciosa cv ‘Hayward’).
Two NAM/ATAF/CUC domain transcription factors (AdNAC6 and AdNAC7), both predicted targets for miR164, showed significant upregulation by exogenous ethylene. Gene expression analysis and luciferase reporter assays indicated that Ade-miR164 and one of its precursor miRNAs (Ade-MIR164b) were repressed by ethylene treatment and negatively correlated with AdNAC6/7 expression. Subsequent analysis indicated that both AdNAC6 and AdNAC7 proteins are transcriptional activators and physically bind the promoters of AdACS1 (1-aminocyclopropane-1-carboxylate synthase), AdACO1 (1-aminocyclopropane-1-carboxylic acid oxidase), AdMAN1 (endo-β-mannanase) and AaTPS1 (terpene synthase). Moreover, subcellular analysis indicated that the location of the AdNAC6/7 proteins was influenced by Ade-miR164.
Multiple omics-based approaches revealed a novel regulatory link for fruit ripening that involved ethylene-miR164-NAC. The regulatory pathway for miR164-NAC is present in various fruit (e.g. Rosaceae fruit, citrus, grape), with implications for fruit ripening regulation.
The nuclear ribosomal DNA internal transcribed spacer (ITS) has been widely used to assess the fungal composition in different environments by deep sequencing. To evaluate the ITS in the analysis of ...fungal diversity, comparisons of the clustering and taxonomy generated by sequencing with different portions of the whole fragment were conducted in this study. For a total of 83,120 full-length ITS sequences obtained from the UNITE database, it was found that, on average, ITS1 varied more than ITS2 within the kingdom Fungi; this variation included length and GC content variations and polymorphisms, with some polymorphisms specific to particular fungal groups. The taxonomic accuracy for ITS was higher than that for ITS1 or ITS2. The commonly used operational taxonomic unit (OTU) for evaluating fungal diversity and richness assigned several species to a single OTU even with clustering at 99.00% sequence similarity. The clustering and taxonomic capacities did not differ between ITS1 and ITS2. However, the OTU commonality between ITS1 and ITS2 was very low. To test this observation further, 219,741 pyrosequencing reads, including 39,840 full-length ITS sequences, were obtained from 10 soil samples and were clustered into OTUs. The pyrosequencing results agreed with the results of the in silico analysis. ITS1 might overestimate the fungal diversity and richness. Analyses using ITS, ITS1 and ITS2 yielded several different taxa, and the taxonomic preferences for ITS and ITS2 were similar. The results demonstrated that ITS2 alone might be a more suitable marker for revealing the operational taxonomic richness and taxonomy specifics of fungal communities when the full-length ITS is not available.
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