Wall Rearrangement Research Articles

Diverging cell wall strategies for drought adaptation in two maize inbreds with contrasting lodging resistance.

The plant cell wall is a plastic structure of variable composition that constitutes the first line of defence against environmental challenges. Lodging and drought are two stressful conditions that severely impact maize yield. In a previous work, we characterised the cell walls of two maize inbreds, EA2024 (susceptible) and B73 (resistant) to stalk lodging. Here, we show that drought induces distinct phenotypical, physiological, cell wall, and transcriptional changes in the two inbreds, with B73 exhibiting lower tolerance to this stress than EA2024. In control conditions, EA2024 stalks had higher levels of cellulose, uronic acids and p-coumarate than B73. However, upon drought EA2024 displayed increased levels of arabinose-enriched polymers, such as pectin-arabinans and arabinogalactan proteins, and a decreased lignin content. By contrast, B73 displayed a deeper rearrangement of cell walls upon drought, including modifications in lignin composition (increased S subunits and S/G ratio; decreased H subunits) and an increase of uronic acids. Drought induced more substantial changes in gene expression in B73 compared to EA2024, particularly in cell wall-related genes, that were modulated in an inbred-specific manner. Transcription factor enrichment assays unveiled inbred-specific regulatory networks coordinating cell wall genes expression. Altogether, these findings reveal that B73 and EA2024 inbreds, with opposite stalk-lodging phenotypes, undertake different cell wall modification strategies in response to drought. We propose that the specific cell wall composition conferring lodging resistance to B73, compromises its cell wall plasticity, and renders this inbred more susceptible to drought.

Molecular Signaling and Metabolic Responses during the Interaction between Human Keratinocytes (HaCaT) and the Dermatophyte Trichophyton rubrum.

Trichophyton rubrum is the leading causative agent of dermatophytosis worldwide. Keratinocytes are the first line of defense that drives an immune response against fungal invasion. Host-specific pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns (PAMPs) to trigger immunological pathways. Fungal cell wall components are the primary sources of fungal PAMPs, and some pathogens increase cell wall rearrangement to evade the immune system. Glycolysis and enhanced lactate levels are critical for improving host immune responses to fungal infections. Using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), we evaluated the transcriptional responses of human genes involved in fungal recognition and glycolytic metabolism and fungal cell-wall-related genes in a co-culture model of human keratinocytes with T. rubrum. We observed the upregulation of several Toll-like receptors (TLRs), NOD-like receptors (NLRs), and glycolytic genes. Complementarily, we measured intra- and extracellular glucose levels and the increase in lactate production in the co-culture supernatant. We noted a distinct transcriptional regulation pattern of fungal cell-wall-related genes from fungal growth on keratin as the primary carbon source compared to co-culture with human keratinocytes. Our results showed new insights into the transcriptional adaptation of keratinocytes, particularly in regulating genes involved in sensing and metabolic processes, during the interaction with T. rubrum.

Economical production of Pichia pastoris single cell protein from methanol at industrial pilot scale

BackgroundMethanol, synthesized from CO2, is a potentially sustainable one-carbon (C1) resource for biomanufacturing. The use of methanol as a feedstock to produce single cell protein (SCP) has been investigated for decades as an alternative to alleviate the high global demand for animal-derived proteins. The methylotrophic yeast Pichia pastoris is an ideal host for methanol-based SCP synthesis due to its natural methanol assimilation ability. However, improving methanol utilization, tolerance to higher temperature, and the protein content of P. pastoris are also current challenges, which are of great significance to the economical industrial application using methanol as a feedstock for SCP production.ResultsIn the present work, adaptive laboratory evolution (ALE) has been employed to overcome the low methanol utilization efficiency and intolerance to a higher temperature of 33 °C in P. pastoris, associated with reduced carbon loss due to the lessened detoxification of intracellular formaldehyde through the dissimilation pathway and cell wall rearrangement to temperature stress resistance following long-term evolution as revealed by transcriptomic and phenotypic analysis. By strengthening nitrogen metabolism and impairing cell wall synthesis, metabolic engineering further increased protein content. Finally, the engineered strain via multi-strategy produced high levels of SCP from methanol in a pilot-scale fed-batch culture at 33 °C with a biomass of 63.37 g DCW/L, methanol conversion rate of 0.43 g DCW/g, and protein content of 0.506 g/g DCW. SCP obtained from P. pastoris contains a higher percentage of protein compared to conventional foods like soy, fish, meat, whole milk, and is a source of essential amino acids, including methionine, lysine, and branched-chain amino acids (BCAAs: valine, isoleucine, leucine).ConclusionsThis study clarified the unique mechanism of P. pastoris for efficient methanol utilization, higher temperature resistance, and high protein synthesis, providing a P. pastoris cell factory for SCP production with environmental, economic, and nutritional benefits.

PdGpaA controls the growth and virulence of Penicillium digitatum by regulating cell wall reorganization, energy metabolism, and CDWEs production

Penicillium digitatum could infect citrus and cause devastating green mold disease. One of the essential parts of the G protein is the Gα subunit, which is essential to signal transduction in filamentous fungi but has not been reported in P. digitatum. In this study, PdGpaA was identified as a homolog of Gα in P. digitatum, and deletion of the PdGpaA gene significantly accelerated early-stage spore germination and inhibited late-stage hyphal growth and conidiophore formation. The ΔPdGpaA strain showed faster growth in sodium dodecyl sulfate (SDS) and calcofluor white (CFW) but more sensitivity to Congo red (CR). We predicted that cell wall integrity had been compromised due to cell wall rearrangement. Moreover, the increased quantity of septa and the reorganization of cell walls were confirmed by CFW staining and quantitative real-time PCR analysis. Deletion of the PdGpaA gene increased intracellular reactive oxygen species (ROS)and mitochondrial deterioration, which obstruct the TCA cycle and hinder energy metabolism. A pathogenicity test revealed that the lesion diameter was decreased by 90.62 % in the ΔPdGpaA strain, probably as the result of a decline in the activity of pectinase and cellulase. In addition, the ΔPdGpaA strain was more sensitive to prochloraz, KCl and H2O2. In conclusion, this study provides multiple functions for the PdGpaA gene, which might have broad application space and prospects in the control of citrus green mold.

Isolation and Characteristics of Extracellular Vesicles Produced by Probiotics: Yeast Saccharomyces boulardii CNCM I-745 and Bacterium Streptococcus salivarius K12

Numerous probiotic microorganisms have repeatedly been shown to produce nanometer-sized structures named extracellular vesicles (EVs). Recently, it has been suggested that similarly to whole microbial cells, EVs produced by probiotics may also demonstrate health benefits to the host, while their application does not involve the risk of infection caused by live microorganisms. In this work, we isolated EVs from two probiotic species originating from different taxonomic domains — yeast Saccharomyces boulardii CNCM I-745 and bacterium Streptococcus salivarius K12. The diameters of S. boulardii EVs were about 142 nm and for S. salivarius EVs about 123 nm. For S. boulardii EVs, 1641 proteins and for S. salivarius EVs, 466 proteins were identified with a liquid chromatography-coupled tandem mass spectrometry and then functionally classified. In both microbial species, metabolic proteins significantly contributed to the cargo of EVs comprising 25% and 26% of all identified vesicular proteins for fungi and bacteria, respectively. Moreover, enzymes associated with cell wall rearrangement, including enzymatically active glucanases, were also identified in EVs. Furthermore, probiotic EVs were shown to influence host cells and stimulate the production of IL-1β and IL-8 by the human monocytic cell line THP-1, and, at the same time, did not cause any remarkable reduction in the survival rate of Galleria mellonella larvae in this invertebrate model commonly used to evaluate microbial EV toxicity. These observations suggest that the EVs produced by the investigated probiotic microorganisms may be promising structures for future use in pro-health applications.

Rearrangement of cell wall polymers in flax infected with a pathogenic strain of Fusarium culmorum

A pathogenic strain of Fusarium culmorum caused flax disease whose first visible symptom was pigmentation and possible necrosis of the root tip. To better understand the process of infection we tried to determine the role of cell wall polymers in flax treated with F. culmorum. F. culmorum infection caused cell wall rearrangement which was associated with changes in the cell wall structure without changes in the amount of polymers. Moreover, pathogenic fungi strongly induced chitinase, β-1,3-glucanase, cellulase2, α-galactosidase and lignin-related genes, while mRNA levels of the majority of genes involved in metabolism of cell wall polysaccharide polymers decreased in time.

Aging peach palm (Bactris gasipaes Kunth) cultures lose embryogenic potential and metabolic cellular function due to continuous culture in hypoxic environments

Formerly-embryogenic 8-year-old and 2-year-old embryogenic peach palm (Bactris gasipaes Kunth.) cultures were treated with 0, 4, 16, or 64 µM 5-azacytidine, an inhibitor of cytosine methylation, to evaluate its ability to restore embryogenic potential to old cultures and observe its effects on younger embryogenic tissue. Either 16 or 64 µM 5-azacytidine restored the ability of a small proportion of older cultures to produce somatic embryos, but the same concentration also caused somatic embryos from the 2-year-old embryogenic culture line to lose regulation, resulting in non-embryogenic cultures and fast-growing yellow callus. Two-year-old embryogenic tissue had slightly lower global methylation, but only 4 µM 5-azacytidine caused a drop in global methylation. Two-year-old and 5-azacytidine-treated 8-year-old embryogenic cultures both showed an up-accumulation of proteins involved in a number of cellular functions: cellular redox control, anaerobic fermentation, protein degradation, NO-related synthesis and storage, and several forms of epigenetic regulation, including the highly-conserved Argonaute 4 protein; and untreated 8-year-old cultures showed increased amounts of proteins involved in cell wall formation and rearrangement, defense-related peroxidases associated with the cell wall, and phospholipidase D. All three tissues showed proteins involved in hypoxia response. HPLC analysis of 8-year-old cultures with embryogenic and non-embryogenic 2-year-old cultures revealed that 8-year-old cultures lacked any detectable carbohydrates, whereas the younger ones contained measurable amounts of arabinose, ribose, and sucrose. Aging of in vitro cultures is, therefore, likely related to loss of metabolic ability due to constant hypoxia, leading to low vigor, inability to adapt to stress, and loss of embryogenic potential. Embryogenesis loss in ageing peach palm cultures is associated with hypoxia, leading to loss in detectable carbohydrates and down-accumulation of proteins associated with metabolism, nitric oxide storage, and epigenetic regulation

Enzymes and vitamin C as factors influencing the presence of arabinogalactan proteins (AGPs) in Solanum lycopersicum fruit

Arabinogalactan proteins (AGPs) are ubiquitous components of the amorphous plant extracellular matrix. They are characterized by a high proportion of sugar moieties, heterogeneity of their protein backbone and carbohydrate chains. It is known that AGPs form a complex network with other basic constituents in cell wall thus it may also play a role in softening process of fruit. The use of enzymatic degradation and cell wall polysaccharide directed probes are valid analytical tools for the study of developmental modification of the fruit structure. However, it is unknown whether pectolytic enzymes affect AGPs. Thus, the aim of the current work is to detect AGP epitopes in situ to understand the impact of selected degradation enzymes on various carbohydrate moieties of AGPs. Secondly, there are no data with clarification of the impact of vitamin C on fruit ripening processes at the cellular level; hence, we also focused on the effect of vitamin C on the arrangement of AGPs as important constituents of the polysaccharide-proteoglycan network in the fruit cell wall. The results indicate that the distribution of the examined AGP carbohydrate moieties differs, which are related to changes in tissue architecture. The absence of glycan chains causes disruption in establishment of correlations between cell wall constituents and rearrangement in the cell wall structure. The induced modifications of cell walls are not comparable to alterations occurring in naturally ripening fruit, which allows a conclusion that the synergistic action of a wide variety of factors influences ripening.

Boosting the Brassica napus L. tolerance to salinity by the halotolerant strain Pseudomonas stutzeri ISE12

Soil salinisation is one of the major pervasive environmental hazards and abiotic stress factors limiting plant productivity worldwide. Since most of the known crops are susceptible to high salinity, there is great interest in improving technologies in agriculture and making major crop species more robust and productive under saline conditions. In our work, we hypothesized that halotolerant plant growth promoting endophytic bacteria may have a beneficial effect on the growth and development of Brassica napus L. cultivated under salt stress conditions. The main aim of our study was to evaluate the role of the Pseudomonas stutzeri ISE12 strain, isolated from the halophyte Salicornia europaea, in mitigating salt stress in Brassica napus L. Verification of the influence of P. stutzeri on B. napus was based on the wide range of plant parameters responsible for abiotic and biotic stress factors: growth and biochemical parameters, the level of RSH gene expression, and changes in the chemical composition and physical properties of cell walls.In accordance with our assumption, salinity decreased plant growth and increased levels of proline, total glutathione and lipid peroxidation in plants. Inoculation of plants with the halotolerant P. stutzeri ISE12 increased the plant growth in both types of substrate (non-saline and saline) and decreased the accumulation of non-enzymatic antioxidants. The RSH1 and RSH3 gene expression in B. napus organs depended on the level of salinity and bacterial inoculation, while we have not observed effect of these biotic and abiotic factors in the case of CRSH and RSH2 genes. Moreover, increased levels and changes in the distribution of homogalacturonans (HGs) with varying de-esterification patterns were observed in cell walls in response to saline stress.In conclusion, inoculation of B. napus with the halotolerant strain P. stutzeri ISE12 alleviates the salt stress experienced by host plants by activating their antioxidant defence system and triggering the rearrangement of cell walls, which, consequently, promotes plant growth.

Genome-wide identification and expression analyses of the pectate lyase (PEL) gene family in cotton (Gossypium hirsutum L.)

BackgroundPectin is a major component and structural polysaccharide of the primary cell walls and middle lamella of higher plants. Pectate lyase (PEL, EC 4.2.2.2), a cell wall modification enzyme, degrades de-esterified pectin for cell wall loosening, remodeling and rearrangement. Nevertheless, there have been few studies on PEL genes and no comprehensive analysis of the PEL gene family in cotton.ResultsWe identified 53, 42 and 83 putative PEL genes in Gossypium raimondii (D5), Gossypium arboreum (A2), and Gossypium hirsutum (AD1), respectively. These PEL genes were classified into five subfamilies (I-V). Members from the same subfamilies showed relatively conserved gene structures, motifs and protein domains. An analysis of gene chromosomal locations and gene duplication revealed that segmental duplication likely contributed to the expansion of the GhPELs. The 2000 bp upstream sequences of all the GhPELs contained auxin response elements. A transcriptomic data analysis showed that 62 GhPELs were expressed in various tissues. Notably, most (29/32) GhPELs of subfamily IV were preferentially expressed in the stamen, and five GhPELs of subfamily V were prominently expressed at the fiber elongation stage. In addition, qRT-PCR analysis revealed the expression characteristics of 24 GhPELs in four pollen developmental stages and significantly different expression of some GhPELs between long- and short-fiber cultivars. Moreover, some members were responsive to IAA treatment. The results indicate that GhPELs play significant and functionally diverse roles in the development of different tissues.ConclusionsIn this study, we comprehensively analyzed PELs in G. hirsutum, providing a foundation to better understand the functions of GhPELs in different tissues and pathways, especially in pollen, fiber and the auxin signaling pathway.

Evaluation of the protective role of exogenous growth regulators against Ni toxicity in woody shrub Daphne jasminea

Main conclusionThe results provide a significant verification of the activity of exogenously applied phytohormones: gibberellic acid, jasmonic acid, and brassinolide in the modulation of the plant’s response to nickel treatment.The study investigated nickel accumulation and its toxicity to Daphne jasminea shoots cultured in vitro with or without exogenous supplementation with phytohormones: gibberellic acid (GA3), jasmonic acid (JA), and brassinolide (BL). The aim was to verify the modulatory effect of exogenous plant growth regulators (PGRs) on plant reaction to Ni excess. The combined action of Ni and PGRs was evaluated at the anatomical, ultrastructural, and biochemical levels. Nickel toxicity was manifested in decreased biomass accretion and growth tolerance index (83–53.6%), attributed to enhanced synthesis of growth inhibitors, mainly abscisic acid. As a defence reaction, endogenous gibberellins accumulated. Exogenous GA3 ameliorated the plant reaction to Ni stress, inducing proliferation and growth rate. Ni tolerance in the presence of GA3 was attributed to peroxisomal reactions that stimulated the synthesis of endogenous JA. In contrast, the application of BL caused enhanced Ni accumulation. Plants suffered from pronounced stress due to massive oxidation. The defence strategy of plants subjected to Ni and BL involved cell wall rearrangements. Exogenous JA stimulated the synthesis of active auxins and salicylic acid, contributing to enhanced mitotic activity within explants. However, JA disturbed the integrity of chloroplasts and lamellar compartments. Our study revealed that an action of exogenous PGRs may either enhance tolerance to Ni or increase metal toxicity in D. jasminea. Particularly in in vitro culture, where explants are subjected to external phytohormonal stimuli, the combined effects of supplemental PGRs may enhance stress and substantially affect plant development. Our results provide a significant verification of exogenous PGRs activity in the modulation of plant response to nickel.

Stink bug nezara viridula sustains late MAPKs phosphorylation status and induces expression of genes related with cell wall rearrangement in developing soybean seeds

The southern green stink bug (Nezara viridula) is a serious invasive pest in United States and South America that decreases the quantity and quality of soybean seeds. Plants respond to insect attack recognizing cell injury and oral secretions, triggering mitogen-activated protein kinases (MAPK) pathway and inducing defenses against herbivores. Our field studies were conducted to evaluate late MAPKs involvement in defense modulation and the transcriptional response of soybean genes implicated in cell wall modification after stink bugs fed on developing seeds. We observed an induction in MPK3 and MPK6 transcription at 24 and 72 h after insects attacked soybean pods, while MPK6 was the only gene up-regulated after mechanically damaging the seeds. Exposure to JA and SA stimuli increased MPK3 and MPK6 levels. While SA triggered MPK4 activation, MPK3 and MPK6 were phosphorylated after both JA and SA treatments. Stink bugs feeding and SA treatment specifically increased the expression of expansine (EXP), xyloglucan endo-transferase (EXT), pectate lyase (PL), and polygalacturonase (PG) genes, all involved in the relaxation and restructuration of the cell wall. Moreover, examination of safranin-stained seed sections revealed that stink bug damage resulted in thickening of cell walls even on distal undamaged areas of cotyledons. Our study shows that stink bug damage elicits activation of MAPK signal in soybean seeds and induced SA that may induce genes related with cell wall restructuration, and could increase resistance to new insect attack by hardening cell walls.

Neofusicoccum parvum Colonization of the Grapevine Woody Stem Triggers Asynchronous Host Responses at the Site of Infection and in the Leaves.

Grapevine trunk diseases cause important economic losses in vineyards worldwide. Neofusicoccum parvum, one of the most aggressive causal agents of the trunk disease Botryosphaeria dieback, colonizes cells and tissues of the grapevine wood, leading to the formation of an internal canker. Symptoms then extend to distal shoots, with wilting of leaves and bud mortality. Our aim was to characterize the transcriptional dynamics of grapevine genes in the woody stem and in the leaves during Neofusicoccum parvum colonization. Genome-wide transcriptional profiling at seven distinct time points (0, 3, and 24 hours; 2, 6, 8, and 12 weeks) showed that both stems and leaves undergo extensive transcriptomic reprogramming in response to infection of the stem. While most intense transcriptional responses were detected in the stems at 24 hours, strong responses were not detected in the leaves until the next sampling point at 2 weeks post-inoculation. Network co-expression analysis identified modules of co-expressed genes common to both organs and showed most of these genes were asynchronously modulated. The temporal shift between stem vs. leaf responses affected transcriptional modulation of genes involved in both signal perception and transduction, as well as downstream biological processes, including oxidative stress, cell wall rearrangement and cell death. Promoter analysis of the genes asynchronously modulated in stem and leaves during N. parvum colonization suggests that the temporal shift of transcriptional reprogramming between the two organs might be due to asynchronous co-regulation by common transcriptional regulators. Topology analysis of stem and leaf co-expression networks pointed to specific transcription factor-encoding genes, including WRKY and MYB, which may be associated with the observed transcriptional responses in the two organs.

Dynamical Defects in Rotating Magnetic Skyrmion Lattices.

The chiral magnet Cu_{2}OSeO_{3} hosts a Skyrmion lattice that may be equivalently described as a superposition of plane waves or a lattice of particlelike topological objects. A thermal gradient may break up the Skyrmion lattice and induce rotating domains, raising the question of which of these scenarios better describes the violent dynamics at the domain boundaries. Here, we show that in an inhomogeneous temperature gradient caused by illumination in a Lorentz transmission electron microscope different parts of the Skyrmion lattice can be set into motion with different angular velocities. Tracking the time dependence, we show that the constant rearrangement of domain walls is governed by dynamic 5-7 defects arranging into lines. An analysis of the associated defect density is described by Frank's equation and agrees well with classical 2D MonteCarlo simulations. Fluctuations of boundaries show a surgelike rearrangement of Skyrmion clusters driven by defect rearrangement consistent with simulations treating Skyrmions as point particles. Our findings underline the particle character of the Skyrmion.

Proteomic insight into the mitigation of wheat root drought stress by arbuscular mycorrhizae

Arbuscular mycorrhizal fungi (AMF) are plant growth promoters that ameliorate plant-water relations and the nutrient uptake of wheat. In this work, two cultivars of Triticum spp., a bread and a durum wheat, grown under drought stress and inoculated or not by AMF, are evaluated through a shotgun proteomic approach. The AMF association had beneficial effects as compared to non-mycorrhizal roots, in both bread and durum wheat. The beneficial symbiosis was confirmed by measuring morphological and physiological traits. In our work, we identified 50 statistically differential proteins in the bread wheat cultivar and 66 differential proteins in the durum wheat cultivar. The findings highlighted a modulation of proteins related to sugar metabolism, cell wall rearrangement, cytoskeletal organization and sulphur-containing proteins, as well as proteins related to plant stress responses. Among differentially expressed proteins both cultivars evidenced a decrease in sucrose:fructan 6-fructosyltransferas. In durum wheat oxylipin signalling pathway was involved with two proteins: increased 12-oxo-phytodienoic acid reductase and decreased jasmonate-induced protein, both related to the biosynthesis of jasmonic acid. Interactome analysis highlighted the possible involvement of ubiquitin although not evidenced among differentially expressed proteins. The AMF association helps wheat roots reducing the osmotic stress and maintaining cellular integrity. Biological significanceDrought is one of the major constraints that plants must face in some areas of the world, associated to climate change, negatively affecting the worldwide plant productivity. The adoption of innovative agronomic protocols may represent a winning strategy in facing this challenge. The arbuscular mycorrhizal fungi (AMF) inoculation may represent a natural and sustainable way to mitigate the negative effects due to drought in several crop, ameliorating plant growth and development. Studies on the proteomic responses specific to AMF in drought-stressed plants will help clarify how mycorrhization elicits plant growth, nutrient uptake, and stress-tolerance responses. Such studies also offer the potential to find biological markers and genetic targets to be used during breeding for new drought-resistant varieties.

Ultrafast Metamorphosis of a Complex Charge-Density Wave.

Modulated phases, commensurate or incommensurate with the host crystal lattice, are ubiquitous in solids. The transition between such phases involves formation and rearrangement of domain walls and is generally slow. Using ultrafast electron diffraction, we directly record the photoinduced transformation between a nearly commensurate and an incommensurate charge-density-wave phase in 1T-TaS(2). The transformation takes place on the picosecond time scale, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The transition speed and mechanism can be linked to the peculiar nanoscale structure of the photoexcited nearly commensurate phase.

The evolution of microbands and their interaction with NbC precipitates during hot deformation of a Fe–30Ni–Nb model austenitic steel

The present work has investigated the evolution of microbands (MBs) and their interaction with strain-induced NbC precipitates during uniaxial compression of a model austenitic Fe–30Ni–Nb steel at 925°C. The 〈110〉 fibre grains, both without and with copious amounts of precipitates, contained up to large strains crystallographic MBs aligned close to the highly stressed {111} slip planes having large Schmid factors. The MBs thus maintained their crystallographic character during straining, through continuously rearranging themselves, and did not follow the macroscopically imposed rigid body rotation. During double-pass deformation, fine NbC particles formed at short inter-pass holding remained strongly pinned at small reloading strains and appeared to be dragged by rearranging MB walls. With increasing reloading strain, the fine precipitates became progressively released from the above walls. During reloading after increased holding time, the coarsened particles tended with their increased size to become increasingly detached from the MB walls already at a small strain. The precipitate-free MB wall segments rearranged during straining to maintain their crystallographic alignment, while the detached precipitates followed the sample shape change and rotated towards the compression plane. The MB wall rearrangement generally occurred through cooperative migration of the corresponding dislocation networks.

Effect of Core Geometry on Shear Moduli in Cellular Core Sandwich Structures

Cellular structures are lightweight structures with appropriate stiffness properties. Usually these cells are in the form of a honeycomb but various cell geometries can be considered as well, for special applications. Because of the repetitive nature of the cellular array the core can be considered as a homogeneous but anisotropic medium. In present study by changing in the number and positions of nodes, the number of cell walls and changing in size of RVE (Representative Volume Element), and also using homogenization method, the shear components of the elasticity tensor are obtained for heterogeneous geometries by assuming unconstraint core. The results show that the effect of these changes in geometry, increase the quality of shear stiffness and weight reduction for some core geometries of sandwich panels that have not been evaluated yet. Soar effect of rearrangement of walls and their located for transverse shear applications is the main characteristic of present study that results obtained have confirmed these claims. Advantage of the present study is providing new pattern applied for sandwich panels core those shear properties that have higher priority..

Effect of pressing routes on the microstructure and strength in equal channel angular pressing of Cu-3.75Ag

The combined effects of thermo-mechanical treatment and equal channel angular pressing (ECAP) on the strength and microstructure of Cu-3.75Ag were studied. The strength of Cu-3.75Ag at 1% strain after eight passes of ECAP with two intermediate heat treatments reached 758 MPa and 849 MPa in route A and route Bc respectively. The hardness increased upon heat-treatment in route Bc, in contrast to the drop of the hardness in route A, suggesting that the hardening caused by re-precipitation is more active due to more effective dissolution of second-phase particles in route Bc. The flow stress increased more rapidly with intermediate heat treatments and reached 842 MPa after 8 passes, greater than that (791 MPa) without intermeadiate heat treatment in route Bc. The more rapid increase of strength/hardness and the attainment of higher hardness/strength after intermediate heat treatment are likely to be attributed to the formation of more stable wall structure and rearrangement of solute atoms/precipitates. The spacing between precipitates in Cu-3.75Ag ECAPed for 4 pass in route Bc was measured to be approximately 12.5 nm, which is close to the calculated activated length (12.8 nm). The most probable rate controlling mechanism of Cu-3.75 Ag is suggested to be the interaction between dislocations and precipitates.

Magnetoimpedance and Field Sensitivity of CoFeSiB Amorphous Ribbons under Applied Tensile Stress

Magnetoimpedance (MI) and field sensitivity of CoFeSiB amorphous ribbons were investigated at frequencies ranging from 0.2 to 12 MHz after tensile stress applied. Experimental results indicate that the MI of amorphous ribbons can be significantly improved by applying a suitable longitudinal tensile stress. Applying tensile stress induces a rearrangement of domain walls which influences the circumferential anisotropy and magnetic permeability result in improving the MI response. The maximum MI response of 145 % and maximum field sensitivity of 6.32 %/Oe at frequency of 4 MHz were obtained, when tension was equivalent to 120 MPa. So the tensile stress as new method can be effective, cheap, and fast in sensor applications, and result of this investigation can be applied for the design of the stress sensors based on the giant magnetoimpedance effect.