Area Of Intimate Contact Research Articles

The Hemibiotrophic Apple Scab Fungus Venturia inaequalis Induces a Biotrophic Interface but Lacks a Necrotrophic Stage

Microscopic evidence demonstrated a strictly biotrophic lifestyle of the scab fungus Venturia inaequalis on growing apple leaves and characterised its hemibiotrophy as the combination of biotrophy and saprotrophy not described before. The pathogen–host interface was characterised by the formation of knob-like structures of the fungal stroma appressed to epidermal cells as early as 1 day after host penetration, very thin fan-shaped cells covering large parts of the host cell lumen, and enzymatic cuticle penetration from the subcuticular space limited to the protruding conidiophores. The V. inaequalis cell wall had numerous orifices, facilitating intimate contact with the host tissue. Pathogen-induced modifications of host cells included partial degradation of the cell wall, transition of epidermal cells into transfer cells, modification of epidermal pit fields to manipulate the flow of nutrients and other compounds, and formation of globular protuberances of mesophyll cells without contact with the pathogen. The non-haustorial biotrophy was characterised by enlarged areas of intimate contact with host cells, often mediated by a matrix between the pathogen and plant structures. The new microscopic evidence and information on the pathogens’ biochemistry and secretome from the literature gave rise to a model of the lifestyle of V. inaequalis, lacking a necrotrophic stage that covers and explains its holomorphic development.

The achievement of lap weld and gap control for laser impact welding with water as the confinement layer

Laser impact welding (LIW) with water as the confinement layer is investigated for the first time to join aluminum (Al) and titanium (Ti). A series of experiments of spot welding under different energies and lap welding were carried out. Both spot welds and lap welds were achieved, which is a significant progress in LIW, especially for the lap weld which hasn't been accomplished by means of LIW previously. Another advantage with water as the confinement layer is that it can control the central gap and create the intimate contact between the flyer and the target, that may favor the weld area increase with the subsequent post weld heat treatment for the intense interfacial diffusion. The interfacial interaction mechanism between the flyer and the target in the close intimate contact area was revealed with the substrate stretching test and energy dispersive spectroscopy (EDS) test. The characteristics of the welds, like wave length, wave height and weld area are also quantified to provide detailed information. Our findings in this work reveal the feasibility and advantages of using flexible media for confinement, broadening the application range of LIW in dissimilar materials joining.

UTILIZATION OF CITRIC ACID AS BONDING AGENT IN SEMBILANG BAMBOO (Dendrocalamus giganteus Munro) PARTICLEBOARD PRODUCTION

Citric acid was utilized as a bonding agent in the production of Sembilang bamboo particleboard. The limitation in using bamboo for particleboard production is that the silica content in bamboo skin can accelerate particleboard processing machines' bluntness and reduce particle adherence in particleboard manufacturing. This research aimed to investigate the influence of bamboo skin and citric acid content on the characteristics of Sembilang bamboo particleboard. Particleboards were prepared using bamboo particles (type A) and unskinned bamboo particles (type B). The citric acid solution (59%) was sprayed over the surface of bamboo particles to obtain three different levels of citric acid, i.e., 15, 20, and 25 % (based on bamboo particles’ dry weight). The Sembilang bamboo particleboards were manufactured using a hot-pressing machine at 200°C, 5 MPa for 10 min. The particleboard targeted density was 0.8 g/cm3. The type B particleboards’ internal bond (IB), modulus of rupture (MOR), water absorption (WA), and thickness swelling (TS) were superior compared to the type A particleboards. This was influenced by the lower concentration of silica in type B particleboards, which tend to allow an intimate contact area among particles and citric acid then produced better quality particleboards compared to type A particleboards. The type B particleboards met the obligation of JIS A 5908 for type 18 particleboard in terms of modulus of rupture, modulus of elasticity, and internal bond, however, only fulfilled the type 8 particleboard in terms of screw holding power. The physical properties of Sembilang bamboo particleboard were also improved when using type B bamboo particles and adhered with citric acid at a level of 25%.

Effect of shear stress on adhesive contact with a generalized Maugis-Dugdale cohesive zone model

The interplay between interfacial shear stress and adhesion has been an active but controversial subject of adhesive contact mechanics, which is currently plagued by diverse, sometimes contradicting, predictions. Recently, McMeeking et al. showed that a reversible interface slip parameter plays an essential role in determining how interfacial shear stress affects adhesion for a Johnson-Kendall-Roberts (JKR) contact interface. In this paper, adhesive contact between a rigid spherical indenter and an elastic half-space is studied with a generalized Maugis-Dugdale (M-D) model, where a constant frictional shear stress presents in the intimate contact area while a constant adhesive stress exists in a cohesive zone near the contact edge. The model solution predicts that the contact behavior is governed by a non-dimensional reversible shear index ατ¯2 as well as the Maugis parameter λ. More specifically, it is found that the impact of interfacial shear stress on adhesion is most significant when the model approaches the JKR limit, and it gets less pronounced in the transitional regime and eventually becomes negligible in the Derjaguin-Mulller-Toporov (DMT) limit. Such behavior is in distinct contrast to Johnson's phenomenological solution. Finally, the proposed model is experimentally validated by adhesion tests on contact interfaces with varying Maugis parameters, where the reversible slip factor is experimentally extracted for the first time.

Orchestration of Immunological Synapse Assembly by Vesicular Trafficking.

Ligation of the T-cell antigen receptor (TCR) by cognate peptide bound to the Major Histocompatibility Complex on the surface of an antigen-presenting cell (APC) leads to the spatial reorganization of the TCR and accessory receptors to form a specialized area of intimate contact between T cell and APC, known as the immunological synapse (IS), where signals are deciphered, coordinated, and integrated to promote T cell activation. With the discovery that an endosomal TCR pool contributes to IS assembly and function by undergoing polarized recycling to the IS, recent years have witnessed a shift from a plasma membrane-centric view of the IS to the vesicular trafficking events that occur at this location following the TCR-dependent translocation of the centrosome toward the synaptic membrane. Here we will summarize our current understanding of the trafficking pathways that are responsible for the steady delivery of endosomal TCRs, kinases, and adapters to the IS to sustain signaling, as well as of the endocytic pathways responsible for signal termination. We will also discuss recent evidence highlighting a role for endosomes in sustaining TCR signaling after its internalization at the IS and identifying the IS as a site of formation and release of extracellular vesicles that allow for transcellular communication with the APC.

Statistical contact model of rough surfaces: The role of surface tension

The sizes of most asperities on actual rough surfaces range from nanometers to microns. Recent investigations reveal that surface tension plays an important role in micro-/nano-sized contact. Therefore, in this paper, we address the influence of surface tension on the elastic contact of rough surfaces. Nayak's model is employed to describe rough surface with stochastic distribution of both heights and curvatures. As a fundament, we present the general relations of contact area and load as the function of indent depth for a single micro-/nano-sized asperity by accounting for surface tension. Based on the refined relations, we derive the general relations concerned in the contact of rough surfaces. Compared with the conventional multi-asperity contact models based on the Hertzian contact theory, the existence of surface tension decreases the real contact area and requires higher load to generate a given indent depth. It is found that the area of intimate contact is still approximately proportional to the external load, but the proportionality depends on the surface tension.

A Macrophage Response to Mycobacterium leprae Phenolic Glycolipid Initiates Nerve Damage in Leprosy

SummaryMycobacterium leprae causes leprosy and is unique among mycobacterial diseases in producing peripheral neuropathy. This debilitating morbidity is attributed to axon demyelination resulting from direct interaction of the M. leprae-specific phenolic glycolipid 1 (PGL-1) with myelinating glia and their subsequent infection. Here, we use transparent zebrafish larvae to visualize the earliest events of M. leprae-induced nerve damage. We find that demyelination and axonal damage are not directly initiated by M. leprae but by infected macrophages that patrol axons; demyelination occurs in areas of intimate contact. PGL-1 confers this neurotoxic response on macrophages: macrophages infected with M. marinum-expressing PGL-1 also damage axons. PGL-1 induces nitric oxide synthase in infected macrophages, and the resultant increase in reactive nitrogen species damages axons by injuring their mitochondria and inducing demyelination. Our findings implicate the response of innate macrophages to M. leprae PGL-1 in initiating nerve damage in leprosy.

Facile Synthesis of Cu@CeO2 and Its Catalytic Behavior for the Hydrogenation of Methyl Acetate to Ethanol

AbstractThe hydrogenation of methyl acetate (MA) is one of the key steps in the synthesis of ethanol from syngas. Given previous studies in this area, synergy of the Cu0 and Cu+ species is the crux to improving catalytic performance. However, neither Cu0 nor Cu+ is easy to maintain under reaction conditions comprising abundant H2 and high temperature. Here, a Cu@CeO2 core–shell catalyst was fabricated by using a facile sol–gel method, and this catalyst exhibited excellent activity and stability in the hydrogenation of MA. It was revealed that the Cu@CeO2 core–shell structure prevented the metallic copper particles from migrating and aggregating and also significantly increased the amount of Cu+ species by enlarging the intimate contact area of copper and ceria. Furthermore, the Cu0 and Cu+ species were found to be well distributed on the interface between the Cu core and the CeO2 shell. The close relative position of the two active sites is probably the main reason for the enhanced synergetic effect in the hydrogenation of MA. New insight into the core–shell structure–function relationship introduces new possibilities for the rational design of catalysts.

Optimal force magnitude loaded to orthodontic microimplants: A finite element analysis.

To find an optimal force that can be loaded onto an orthodontic microimplant to fulfill the biomechanical demands of orthodontic treatment without diminishing the stability of the microimplant. Using the finite element analysis method, 3-D computer-aided design models of a microimplant and four cylindrical bone pieces (incorporating cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm) into which the microimplant was inserted were used. Various force magnitudes of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 N were then horizontally and separately applied to the microimplant head as inserted into the different bone assemblies. For each bone/force assembly tested, peak stresses developed at areas of intimate contact with the microimplant along the force direction were then calculated using regression analysis and compared with a threshold value at which pathologic bone resorption might develop. The resulting peak stresses showed that bone pieces with thicker cortical bone tolerated higher force magnitudes better than did thinner ones. For cortical bone thicknesses of 0.5, 1.2, 2.0, and 3.0 mm, the maximum force magnitudes that could be applied safely were 3.75, 4.1, 4.3, and 4.45 N, respectively. For the purpose of diminishing orthodontic microimplant failure, an optimal force that can be safely loaded onto a microimplant should not exceed a value of around 3.75-4.5 N.

Atomic layer deposition derived amorphous TiO2 thin film decorating graphene nanosheets with superior rate capability

Composites consisting of graphene nanosheets (GNSs) decorated with amorphous TiO2 thin films were synthesized by an atomic layer deposition (ALD) technique. It was revealed that the TiO2 thin films were uniformly deposited onto the worm-like GNSs. When used as anode materials in lithium ion batteries (LIBs), the TiO2–GNS composites deliver a stable capacity of ~ 140 mAh g− 1 after 100 cycles at a specific current of 100 mA g− 1 as well as superior rate capability, accounting for a sustainable 95 mAh g− 1 capacity at a specific current of 1200 mA g− 1. It is believed that the remarkable electrochemical performance lied in the unique features of the composites, i.e., the amorphous nature of the TiO2 films and the large surface area of GNSs. The former rendered short Li+ diffusion pathways in TiO2 thin film, while the latter offered excellent electronic conductivity as well as a large intimate contact area between the electrolyte and TiO2. This work laid a venue for designing new electrodes for high-performance LIBs.

Yersinia enterocolitica exploits different pathways to accomplish adhesion and toxin injection into host cells.

The current paradigm suggests that Yersinia enterocolitica (Ye) adheres to host cells via the outer membrane proteins Yersinia adhesin A (YadA) or invasin (Inv) to facilitate injection of Yops by the type III secretion system. In this process Inv binds directly to β1 integrins of host cells while YadA may bind indirectly via extracellular matrix proteins to β1 integrins. Here we challenged this paradigm and investigated the requirements for Yop injection. We demonstrate that Inv- but not YadA-mediated adhesion depends on β1 integrin binding and activation, and that tight adhesion is a prerequisite for Yop injection. By means of novel transgenic cell lines, shRNA approaches and RGD peptides, we found that YadA, in contrast to Inv, may use a broad host cell receptor repertoire for host cell adhesion. In the absence of β1 integrins, YadA mediates Yop injection by interaction with αV integrins in cooperation with yet unknown cofactors expressed by epithelial cells, but not fibroblasts. Electron microscopic and flow chamber studies revealed that a defined intimate contact area between Ye and host cells resulting in adhesion forces resisting shear stress is required for Yop injection. Thus, the indirect binding of YadA to a broad extracellular matrix (ECM) binding host cell receptor repertoire of different cell types makes YadA a versatile tool to ensure Yop injection. In conclusion, given the differential expression of the outer membrane proteins Inv and YadA in the course of Ye infection and differential expression of integrins by various host cell populations, the data demonstrate that Ye is flexibly armed to accomplish Yop injection in different host cell types, a central event in its immune evasion strategy.

Low temperature reactivity in agglomerates containing iron oxide

In this study, we have attempted to explain the complex reactions that occur during the dehydration of Ca(OH)2, in the presence of solid carbon and Fe2O3, in order to clarify their role as eventual precursors to the reduction and high temperature strength characteristics in feedstock agglomerates of iron and steelmaking by-products. A series of simultaneous thermo-gravimetric (TG), differential thermal analytic (DTA), and mass spectrometric (MS) tests were performed on agglomerated sample mixes of Ca(OH)2, C, and Fe2O3 to test the influence of heating rate and particle size on the transformations occurring below 1,073 K in inert atmosphere. The overall transformation begins with calcium hydroxide dehydration. Nucleation and growth of CaO grains during dehydration, as well as subsequent gasification of solid carbon, are highly dependent on the governing interstitial particle porosity and mildly dependent on the heating rate in and around agglomerates. The reduction of hematite in current agglomerates is, by association to preceding reactions, partly dependent on porosity and heating rate, but the mechanism of reduction was also found to be highly dependent on the particle size of iron oxides. Furthermore, in areas of intimate contact between CaO and iron oxide, a calcium ferrite phase appears in the form of angular and calcium-rich particles.

Adhesion Performance of Polymer Nanofibres Under Shear Loading

Geckos have extraordinary wall-climbing ability because of the millions of hairs with micro/nano fibrillar structures on their feet. Mimicking gecko's feet is of scientific and engineering importance for development of physical adhesion materials and devices. The design of gecko-inspired physical adhesives seems to be geometry dominated. In this study, Finite Element Method (FEM) has been used to analyse the vertical peel-off force of polyporpylene (PP) nanofibres having different fibre dimensions, inclining angels and contact areas on a flat glass substrate. It has been found that the main parameters affecting the frictional adhesion are fibre diameter and fibre aspect ratio, the inclining angle between the fibre and the substrate surface, and the intimate contact areas. Our analysis has shown that PP nanofibres with a diameter of less than 200nm can generate less peel-off force than fibres of larger diameters, indicating more stable adhesion with the glass substrate for thinner fibres. A bent fibre with more intimate contact area can bear more shear force than a straight fibre with less contact area. Also, under the same shear loading, fibres with an inclining angle of less than 30° provide a low peel off force.

Protein kinase a dependent phosphorylation of apical membrane antigen 1 plays an important role in erythrocyte invasion by the malaria parasite.

Apicomplexan parasites are obligate intracellular parasites that infect a variety of hosts, causing significant diseases in livestock and humans. The invasive forms of the parasites invade their host cells by gliding motility, an active process driven by parasite adhesion proteins and molecular motors. A crucial point during host cell invasion is the formation of a ring-shaped area of intimate contact between the parasite and the host known as a tight junction. As the invasive zoite propels itself into the host-cell, the junction moves down the length of the parasite. This process must be tightly regulated and signalling is likely to play a role in this event. One crucial protein for tight-junction formation is the apical membrane antigen 1 (AMA1). Here we have investigated the phosphorylation status of this key player in the invasion process in the human malaria parasite Plasmodium falciparum. We show that the cytoplasmic tail of P. falciparum AMA1 is phosphorylated at serine 610. We provide evidence that the enzyme responsible for serine 610 phosphorylation is the cAMP regulated protein kinase A (PfPKA). Importantly, mutation of AMA1 serine 610 to alanine abrogates phosphorylation of AMA1 in vivo and dramatically impedes invasion. In addition to shedding unexpected new light on AMA1 function, this work represents the first time PKA has been implicated in merozoite invasion.

Reducing Contact Resistance Using Compliant Nickel Nanowire Arrays

Electrical contact resistance can be reduced using an array of compliant and conductive nanowires which make a large area of intimate contact with an opposing surface. In this paper, analyses of electrical contact resistance, fabrication methods, and experimental results of contact resistance for compliant nickel nanowires are presented. To analyze, predict, and measure the contact resistance, models of surface contact between an array of conductive nanowires and a spherical tip probe are presented. Then, an estimate of real area of contact from the measured contact resistance is discussed. The fabrication methods elaborate on electroforming nickel fibers using commercially available nano-porous filters. Finally, experimental results of contact resistance between a spherical tip probe and arrays of nickel nanowires as well as the contact resistance between a flat tip probe and arrays of nickel nanowires are presented. From these experimental results, we show resistance reduction by a factor of more than 20 at a load of 10 mN or less, compared to contact with a flat sheet, and a reduction by a factor of 3 using a spherical probe.

Dislocation-induced nonuniform interfacial reactions of Ti∕Al∕Mo∕Au ohmic contacts on AlGaN∕GaN heterostructure

Transmission electron microscopy (TEM) is utilized to elucidate the postannealing interfacial microstructure of Ti∕Al∕Mo∕Au metallization with AlGaN∕GaN heterostructures to gain insight into the formation mechanism of low-resistance ohmic contacts. The reaction between the metal and the AlGaN layer does not proceed uniformly. Localized penetration through the AlGaN layer beyond the two-dimensional electron gas (2DEG) is observed while partial consumption of the AlGaN layer is noted in other areas. Analytical TEM analyses confirm that the main reaction product is TiN. A correlation between the appearance of TiN islands and threading dislocations is observed. Threading dislocations serve as short-circuit diffusion channels, and are responsible for the nonuniform reaction. TiN islands have a large total area of intimate contact with the 2DEG, and since no tunneling of electron through the AlGaN is required, a low-resistance ohmic contact is obtained.

Mechanism of eutectic formation upon compaction and its effects on tablet properties

The unique property of a eutectic mixture is a lower melting temperature than that of any of its pure components. What differentiates a eutectic mixture from a simple physical mixture is less well understood. This impedes the ability to anticipate and/or detect unintentional eutectic formation during pharmaceutical tablet manufacturing and any potential negative impact. In this study, a thermodynamic/heat transfer approach was used to explain the mechanism of eutectic formation upon exposure to a physical stress, i.e. compaction, and a differential scanning calorimetric (DSC) method was developed to detect and quantify the amount of eutectic formed in the compacts. Furthermore, the mechanism of eutectic formation upon compaction was tested experimentally by correlating the amount of eutectic formed in tablets with the particle size, compaction force, the estimated intimate contact area between the eutectic-forming materials, calculated tablet tensile strength, and tablet porosity. The effect of the presence of eutectics on tablet properties was also investigated. The results show that intimate contact and mutual solubility between eutectic-forming materials are the necessary and sufficient criteria for eutectic formation upon compaction. The systems of acetaminophen (APAP)/caffeine and APAP/propylphenazone were both shown to exhibit eutectic behavior upon compaction and the extent of formation was dependent upon the amount of intimate contact between eutectic-forming materials. Finally, it was found that eutectic had no negative effect on tablet hardness.

Ultrastructural Localisation of Sialoadhesin (Siglec- 1) on Macrophages in Rodent Lymphoid Tissues

In previous studies it has been demonstrated that sialoadhesin is a macrophage-restricted adhesion receptor for lymphocytes and myeloid cellsIt is under normal circumstances expressed by subpopulations of macrophages in lymphoid and haemopoietic tissuesIn this study different immunoelectronmicroscopical techniques are used to investigate the ultrastructural localisation of sialoadhesin within the lymph node and spleen of rodentsThe results show that sialoadhesin is selectively expressed by a subset of macrophages in peripheral lymphoid tissuesSialoadhesin was localised predominantly on the plasma membrane and in particular in areas of intimate contact with lymphocytes, thereby visualizing putative local interaction between these cellsInterestingly, sialoadhesin was also detected in intracellular vesicles that were apparently taken up by macrophagesThese findings are consistent with the putative role of sialoadhesin in local cell-cell interactions in lymphoid tissuesSurprisingly, sialoadhesin was also found at contact points of macrophages with other macrophages, sinus-lining cells and reticulum cells, suggesting that sialoadhesin also mediates interactions with these cell types.

Transcellular biosynthesis of lipoxin A4 during adhesion of platelets and neutrophils in experimental immune complex glomerulonephritis

Polymorphonuclear neutrophils are important effectors of injury in host defense and inflammation. Many inflammatory diseases are self-limiting, raising the possibility that compounds are generated in vivo during the course of inflammation that inhibit neutrophil recruitment and tissue destruction. Lipoxins, a more recent addition to the families of bioactive eicosanoids, are potential candidates in this regard. Lipoxins are generated via pathways that initially involve the dual lipoxygenation of arachidonic acid and are potent inhibitors of several neutrophil trafficking events in vitro. Here, we present evidence that lipoxin A4 is generated in rat kidneys during experimental immune complex-mediated glomerulonephritis in vivo. Renal lipoxin A4 levels were markedly reduced by prior depletion of animals of either neutrophils or platelets, suggesting that most lipoxin A4 generated in vivo was derived from transcellular biosynthetic pathways during platelet-neutrophil interactions. Electron microscopic examination of glomerulonephritic kidneys revealed areas of intimate contact between neutrophils and platelets within the lumen of glomerular capillaries. P-selectin on platelets is an important mediator of platelet-neutrophil adhesion in vitro and in vivo. Prior treatment of animals with a blocking monoclonal antibody (mAb) against P-selectin (mAb CY1747), but not an isotype-matched non-blocking control mAb (mAb PNB1.6), caused striking inhibition of lipoxin A4 generation without attenuating neutrophil recruitment. Anti-P-selectin mAb also blunted transcellular lipoxin A4 generation during coincubations of activated neutrophils and platelets in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Interdiffusion in microlayered polymer composites of polycarbonate and a copolyester

AbstractThe interdiffusion of two miscible polymers, polycarbonate (PC) and a copolyester (KODAR), was studied at temperatures from 200 to 230°C. The two polymers were coextruded as microlayer composites with up to 3713 alternating layers. The microlayer structure provided a large area of intimate contact between the two polymers with minimal mixing. Initially, two glass transition temperatures were observed by DSC that were intermediate between the glass transition temperatures of the pure components. Upon annealing, the glass transition temperatures shifted closer together, reflecting the extent to which inter‐diffusion had occurred. After no more than 2 h of annealing, a single glass transition temperature was observed. A model was formulated based on Fick's law of diffusion that related the mutual diffusion coefficient, D, to the change in the glass transition temperatures. The model also incorporated an “equivalent” residence time to account for diffusion that occurred during the coextrusion process. It was not necessary to consider the concentration dependence of D to satisfactorily describe the data with this model. For the temperature range from 200 to 230°C, the value of D varied from 4.0 × 10−16 to 1.6 × 10−15 m2/s. The activation energy of interdiffusion was determined to be 95 kJ/mol. © 1994 John Wiley & Sons, Inc.