Explore the vast range of titles available.

Porosity is a common process-induced defect in laser powder bed fusion (LPBF) metal additive manufacturing, which will have detrimental effects on the mechanical performance of the fabricated products. In this study, an analytical modeling method with closed-form solutions is developed for the prediction of keyhole-induced porosity in LPBF. A two-dimensional model which considers the keyhole pores formation and trapping is employed to calculate the keyhole porosity, with the molten pool geometries, average pore size, velocity of melt flow, and frequency of pore formation as inputs. An analytical temperature prediction model is used to compute the temperature distribution in LPBF. The molten pool shapes and dimensions are determined by comparing the predicted temperature profiles with melting temperature. The relationship between average pore size and laser power energy density is obtained by regression analysis. The velocity of melt flow and frequency of keyhole pore formation are adapted from the literature. To validate the model, the predictions of keyhole porosity under various process conditions are compared with experimental measurements of Ti6Al4V in LPBF. The predicted results are in good agreement with experimental data, which demonstrates the acceptable predictive accuracy of the proposed model. Also, the analytical modeling method does not include any iteration-based numerical calculations, which makes it computationally efficient. Thus, the proposed model can be an acceptable tool for the fast prediction of keyhole porosity and can also help the researchers understand the physics behind the formation of part porosity.

Proteins and peptides with hydrophobic and amphiphilic segments are responsible for many biological functions. The sensing and generation of membrane curvature are the functions of several protein domains or motifs. While some specific membrane proteins play an essential role in controlling the curvature of distinct intracellular membranes, others participate in various cellular processes such as clathrin-mediated endocytosis, where several proteins sort themselves at the neck of the membrane bud. A few membrane-inserting proteins form nanopores that permeate selective ions and water to cross the membrane. In addition, many natural and synthetic small peptides and protein toxins disrupt the membrane by inducing nonspecific pores in the membrane. The pore formation causes cell death through the uncontrolled exchange between interior and exterior cellular contents. In this article, we discuss the insertion depth and orientation of protein/peptide helices, and their role as a sensor and inducer of membrane curvature as well as a pore former in the membrane. We anticipate that this extensive review will assist biophysicists to gain insight into curvature sensing, generation, and pore formation by membrane insertion.

α-Latrotoxin (α-LTX) was found to form two-dimensional (2D) monolayer arrays in solution at relatively low concentrations (0.1 mg/mL), with the toxin tetramer constituting a unit cell. The crystals were imaged using cryogenic electron microscopy (cryoEM), and image analysis yielded a ~12 Å projection map. At this resolution, no major conformational changes between the crystalline and solution states of α-LTX tetramers were observed. Electrophysiological studies showed that, under the conditions of crystallization, α-LTX simultaneously formed multiple channels in biological membranes that displayed coordinated gating. Two types of channels with conductance levels of 120 and 208 pS were identified. Furthermore, we observed two distinct tetramer conformations of tetramers both when observed as monodisperse single particles and within the 2D crystals, with pore diameters of 11 and 13.5 Å, suggestive of a flickering pore in the middle of the tetramer, which may correspond to the two states of toxin channels with different conductance levels. We discuss the structural changes that occur in α-LTX tetramers in solution and propose a mechanism of α-LTX insertion into the membrane. The propensity of α-LTX tetramers to form 2D crystals may explain many features of α-LTX toxicology and suggest that other pore-forming toxins may also form arrays of channels to exert maximal toxic effect.

The fluid action mechanism and diagenetic evolution of tuff reservoirs in the Cretaceous Huoshiling Formation of the Dehui fault depression are discussed herein. The fluid properties of the diagenetic flow are defined, and the pore formation mechanism of the reservoir space is explained by means of thin sections, X-ray diffraction, electron probes, scanning electron microscopy (SEM), cathodoluminescence, and stable carbon and oxygen isotopic composition and fluid inclusion tests. The results reveal that the tuff reservoir of the Huoshiling Formation is moderately acidic, and the physical properties of the reservoir are characterized by middle to high porosity and ultralow permeability. The pore types are complex, comprising both primary porosity and secondary porosity, with dissolution pores and devitrification pores being the most dominant. Mechanical compaction and cementation are identified as key factors reducing reservoir porosity and permeability, while dissolution and devitrification processes improve pore structure and enhance pore connectivity. Diagenetic fluids encompass alkaline fluids, acidic fluids, deep-seated CO+-rich hydrothermal fluids, and hydrocarbon-associated fluids. These fluids exhibit dual roles in reservoir evolution: acidic fluids enhance the dissolution of feldspar, tuffaceous materials, and carbonate minerals to generate secondary pores and improve reservoir quality, whereas alkaline fluids induce carbonate cementation, and clay mineral growth (e.g., illite) coupled with late-stage mineral precipitation obstructs pore throats, reducing permeability. The interplay among multiple fluid types and their varying dominance at different burial depths collectively governs reservoir evolution. This study underscores the critical role of fluid–rock interactions in controlling porosity–permeability evolution within tuff reservoirs.

Agri‐mats are solid organic mulch mats derived from various organic waste materials such as straw, grass, weed biomass, algae residues, etc. These agri‐mats are created by hot‐ or cold‐pressing biomass into solid, bio degradable mats. Although agri‐mats provide remarkable benefits to agricultural soils, including improved soil fertility and crop productivity, their effect on topsoil structure has not been adequately explored. The aim of this study was to determine the aggregate stability and physical architecture of two contrasting soils using the fast‐wetting method and X‐ray microfocus computed tomography (CT), respectively. The following five treatments were established in two sites (Durban with loam soil and Pretoria with sandy loam soil): (i) full agri‐mat cover (100% AG), (ii) half agri‐mat cover (50% AG), (iii) bare or no cover (control), (iv). 6 tons.ha−1 of grass mulch (6 t.GM) and (v) 3 tons.ha−1 grass mulch (3 t.GM). The two sites were planted with maize in summer and spinach in winter for two consecutive seasons (2017/18 and 2018/19). The aggregate stability test results indicated that 100% agri‐mat (100% AG) mulch had greater aggregate stabilizing ability than all other mulching treatments in both soil types. In the loam soil, the 100% AG treatment increased the stability of the aggregates by 58% and by 65% in the sandy loam soil after two years. The X‐ray CT analysis results showed that under the loam soil, 50% AG mulch treatment produced more (89%) macro‐aggregates (> 250 μm) compared to 100% AG (77%). However, the 100% AG treatment produced more (71%) macro‐aggregates compared with the 50% AG (65%) under the sandy loam soil. Based on the overall morphological characteristics of the soil aggregates, the 100% AG treatment was superior to the other organic mulching treatments in terms of soil pore structure formation and aggregate stability regardless of the soil type after two years.

The adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) is a key virulence factor of the whooping cough agent Bordetella pertussis. CyaA targets myeloid phagocytes expressing the complement receptor 3 (CR3, known as αMβ2 integrin CD11b/CD18 or Mac-1) and translocates by a poorly understood mechanism directly across the cytoplasmic membrane into cell cytosol of phagocytes an adenylyl cyclase(AC) enzyme. This binds intracellular calmodulin and catalyzes unregulated conversion of cytosolic ATP into cAMP. Among other effects, this yields activation of the tyrosine phosphatase SHP-1, BimEL accumulation and phagocyte apoptosis induction. In parallel, CyaA acts as a cytolysin that forms cation-selective pores in target membranes. Direct penetration of CyaA into the cytosol of professional antigen-presenting cells allows the use of an enzymatically inactive CyaA toxoid as a tool for delivery of passenger antigens into the cytosolic pathway of processing and MHC class I-restricted presentation, which can be exploited for induction of antigen-specific CD8+ cytotoxic T-lymphocyte immune responses. This review covers recent advances in our understanding of mechanism of membrane penetration of Bordetella pertusis adenylate cyclase toxin.

Cryptococcus neoformans is a multidrug-resistant pathogen responsible for infections in immunocompromised patients. Here, itraconazole (ITR), a commercial antifungal drug with low effectiveness against C. neoformans, was combined with different synthetic antimicrobial peptides (SAMPs), Mo-CBP3-PepII, RcAlb-PepII, RcAlb-PepIII, PepGAT, and PepKAA. The Mo-CBP3-PepII was designed based on the sequence of MoCBP3, purified from Moringa oleifera seeds. RcAlb-PepII and RcAlb-PepIII were designed using Rc-2S-Alb, purified from Ricinus communis seed cakes. The putative sequence of a chitinase from Arabidopsis thaliana was used to design PepGAT and PepKAA. All SAMPs have a positive liquid charge and a hydrophobic potential ranging from 41–65%. The mechanisms of action responsible for the combined effect were evaluated for the best combinations using fluorescence microscopy (FM). The synthetic peptides enhanced the activity of ITR by 10-fold against C. neoformans. Our results demonstrated that the combinations could induce pore formation in the membrane and the overaccumulation of ROS on C. neoformans cells. Our findings indicate that our peptides successfully potentialize the activity of ITR against C. neoformans. Therefore, synthetic peptides are potential molecules to assist antifungal agents in treating Cryptococcal infections.

Although the closed pore structure plays a key role in contributing low-voltage plateau capacity of hard carbon anode for sodium-ion batteries, the formation mechanism of closed pores is still under debate. Here, we employ waste wood-derived hard carbon as a template to systematically establish the formation mechanisms of closed pores and their effect on sodium storage performance. We find that the high crystallinity cellulose in nature wood decomposes to long-range carbon layers as the wall of closed pore, and the amorphous component can hinder the graphitization of carbon layer and induce the crispation of long-range carbon layers. The optimized sample demonstrates a high reversible capacity of 430 mAh g −1 at 20 mA g −1 (plateau capacity of 293 mAh g −1 for the second cycle), as well as good rate and stable cycling performances (85.4% after 400 cycles at 500 mA g −1 ). Deep insights into the closed pore formation will greatly forward the rational design of hard carbon anode with high capacity. It is essential to investigate the formation mechanism of closed pore, which contributes to low-voltage plateau capacity of hard carbon anode in sodium ion batteries. Herein, the authors explore the impact of wood precursor components and carbonization temperature on closed pore formation in hard carbon for enhanced battery performance.

Porous Ti3SiC2 was fabricated with high purity, 99.4 vol %, through reactive sintering of titanium hydride (TiH2), silicon (Si) and graphite (C) elemental powders. The reaction procedures and the pore structure evolution during the sintering process were systematically studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). Our results show that the formation of Ti3SiC2 from TiH2/Si/C powders experienced the following steps: firstly, TiH2 decomposed into Ti; secondly, TiC and Ti5Si3 intermediate phases were generated; finally, Ti3SiC2 was produced through the reaction of TiC, Ti5Si3 and Si. The pores formed in the synthesis procedure of porous Ti3SiC2 ceramics are derived from the following aspects: interstitial pores left during the pressing procedure; pores formed because of the TiH2 decomposition; pores formed through the reactions between Ti and Si and Ti and C powders; and the pores produced accompanying the final phase synthesized during the high temperature sintering process.

Key Points Pore-forming toxins (PFTs), which are expressed as virulence factors by many pathogenic bacteria, and pore-forming proteins (PFPs) have been found in all kingdoms of life PFTs and PFPs undergo a structural and functional metamorphosis from soluble, inactive monomers to active, complex multimeric transmembrane pores that insert into the membranes of target cells Based on their structure and mechanism of pore formation, six families of PFTs and PFPs have been described, each of which has a distinct structure and mechanism of pore formation. These families can be grouped into two larger classes, α-PFTs and β-PFTs (or PFPs), based on the secondary structures of their transmembrane pore domains Owing to substantial recent advances in the structural biology of PFTs, we are beginning to understand the pore architecture and the mechanism of pore formation for all six families The specificity of PFTs and PFPs is determined by their interactions with lipids, sugars and/or protein receptors present in, or on, the target cell membrane Structural modularity enables toxins with the same pore-forming mechanism to target different host cell types by binding to different receptors For PFTs that contribute to infection, examining their structures, dynamics and interactions with host cells at molecular resolution provides cues for the development of therapeutics that could be highly effective in fighting disease Pore-forming toxins (PFTs) are produced as virulence factors by many pathogenic bacteria. In this Review, Dal Peraro and van der Goot describe new mechanistic insights into the assembly of these toxins and their target specificity, and discuss recent therapeutic developments. Pore-forming toxins (PFTs) are virulence factors produced by many pathogenic bacteria and have long fascinated structural biologists, microbiologists and immunologists. Interestingly, pore-forming proteins with remarkably similar structures to PFTs are found in vertebrates and constitute part of their immune system. Recently, structural studies of several PFTs have provided important mechanistic insights into the metamorphosis of PFTs from soluble inactive monomers to cytolytic transmembrane assemblies. In this Review, we discuss the diverse pore architectures and membrane insertion mechanisms that have been revealed by these studies, and we consider how these features contribute to binding specificity for different membrane targets. Finally, we explore the potential of these structural insights to enable the development of novel therapeutic strategies that would prevent both the establishment of bacterial resistance and an excessive immune response.