Junction Growth Research Articles

Analysis of Displacement-Controlled Fretting Between a Hemisphere and a Flat Block in Elasto-Plastic Contacts

This work employs a three-dimensional (3D) finite element analysis (FEA) to investigate the fretting metallic contact between a deformable hemisphere and a deformable flat block. Fretting is governed by displacement-controlled action where the materials of the two contacting bodies are set to have identical properties; studied first is steel-on-steel and then copper-on-copper. At contact onset, a normal interference (indentation) is applied, which is then followed by transverse cyclic oscillations. A large range of coefficients of friction (COFs) is imposed at the interface. The results show that the maximum von Mises stress is confined under the contacting surface for small COFs; however, that maximum reaches the contacting surface when the COFs are sufficiently large. It is also shown that fretting under sufficiently large COFs forms large plastic strains in “ring” like patterns at the contacting surfaces. Junction growth is found where the contacting region is being stretched in the direction of the fretting motion. At large COFs, pileups show up at the edges of the contact. The fretting loops of the initial cycles are found along with the total work invested into the system. At certain interference, there exists a certain COF, which results in the largest work consumption. The magnitude of the COF is found to produce either partial slip (prone for fretting fatigue) or gross slip (prone for fretting wear). A scheme of normalization is proposed, and it is shown to be effective for the two said materials that have vastly different material properties. Hence, the normalized results may well characterize a range of contact scales (from micro to macro) of various ductile material pairs that behave in an elastic–plastic manner with strain hardening.

Junction growth in ultrasonic spot welding and ultrasonic additive manufacturing

The processes of ultrasonic spot welding and ultrasonic additive manufacturing are modelled by approximating the weld interface as rough metallic surfaces in sliding contact. It is assumed that bonding is due to athermal plastic deformation of surface asperities and the associated growth of metallic junctions along the weld interface. To link the process variables and the extent of junction growth, an expression for the real contact area at the weld interface is combined with process-specific frictional heating models developed here. The resulting framework is validated by comparing its predictions of the weld strength with data from the ultrasonic welding literature. The close agreement between the framework's predictions and the experimental data demonstrates that the surface asperities soften due to frictional heating, while acoustic softening effects are insignificant. The junction growth model is used to identify parameter sets for ultrasonic spot welding and ultrasonic additive manufacturing that maximize the weld strength while simultaneously minimizing the thermal excursion at the weld interface. It is found that in ultrasonic spot welding, certain processing conditions can cause interfacial melting, although melting is not required to form strong bonds. It is also shown that in ultrasonic additive manufacturing, the deposition rate is highest when the positions of the peak temperature and complete interfacial bonding coincide underneath the sonotrode. If the position of complete interfacial bonding leads the position of the peak temperature, there is excessive heating of the build, and the sonotrode velocity can be increased without degrading bond quality.

A fretting finite element investigation of a plane-strain cylindrical contact of Inconel 617/Incoloy 800H at room and high temperatures

This work presents a finite element study of a 2D plane strain fretting model of a half-cylinder in contact with a flat block under oscillatory tangential loading. The two bodies are deformable and are set to Inconel 617 and Incoloy 800H at room temperature (20 ℃) and 800 ℃. However, because the results are normalized, they can characterize a range of contact scales (micro to macro). Different coefficients of friction are used at the interface. This work finds that the edges of the contacting areas experience large von Mises stresses along with significant residual plastic strains, while pileup could also appear when the coefficients of friction are sufficiently large. In addition, junction growth is investigated, showing that the direction of the growth is in the same direction of the tangential force that the weaker material (Incoloy alloy 800H) experiences. The fretting loop (caused by the tangential force during the fretting motion) for the initial few cycles of loading is generated, and it compares well with the reported experimental results. The different extents of damage at room temperature and 800 ℃ are also compared.

Degradation of alpha-synuclein by dendritic cell factor 1 delays neurodegeneration and extends lifespan in Drosophila

Parkinson's disease (PD) is a common neurodegenerative disease associated with the progressive loss of dopaminergic neurons in the substantia nigra. Proteinaceous depositions of alpha-synuclein (α-syn) and its mutations, A30P and A53T, are one important characteristic of PD. However, little is known about their aggregation and degradation mechanisms. Dendritic cell factor 1 (DCF1) is a membrane protein that plays important roles in nerve development in mouse. In this study, we aimed to show that DCF1 overexpression in a PD Drosophila model significantly ameliorates impaired locomotor behavior in third instar larvae and normalizes neuromuscular junction growth. Furthermore, climbing ability also significantly increased in adult PD Drosophila. More importantly, the lifespan dramatically extended by an average of approximately 23%, and surprisingly, DCF1 could prevent α-syn-induced dopaminergic neuron loss by aggregating α-syn in the dorsomedial region of Drosophila. Mechanistically, we confirmed that DCF1 could degrade α-syn both invivo and invitro. Our findings revealed an important role of DCF1 in PD process and may provide new potential strategies for developing drugs to treat neurodegenerative diseases.

An Elastoplastic Finite Element Study of Displacement-Controlled Fretting in a Plane-Strain Cylindrical Contact

This work presents a finite element study of a two-dimensional (2D) plane strain fretting model of a half cylinder in contact with a flat block under oscillatory tangential loading. The two bodies are deformable and are set to the same material properties (specifically steel), however, because the results are normalized, they can characterize a range of contact scales (micro to macro), and are applicable for ductile material pairs that behave in an elastic-perfectly plastic manner. Different coefficients of friction (COFs) are used in the interface. This work finds that the edges of the contacting areas experience large von Mises stresses along with significant residual plastic strains, while pileup could also appear there when the COFs are sufficiently large. In addition, junction growth is investigated, showing a magnitude that increases with the COF, while the rate of growth stabilization decreases with the COF. The fretting loop (caused by the tangential force during the fretting motion) for the initial few cycles of loading is generated, and it compares well with reported experimental results. The effects of boundary conditions are also discussed where a prestressed compressed block is found to improve (i.e., reduce) the magnitude of the plastic strain compared to an unstressed block.

Prediction of static friction coefficient in rough contacts based on the junction growth theory

The classic approach to the slip-stick contact is based on the framework advanced by Mindlin, in which localized slip occurs on the contact area when the local shear traction exceeds the product between the local pressure and the static friction coefficient. This assumption may be too conservative in the case of high tractions arising at the asperities tips in the contact of rough surfaces, because the shear traction may be allowed to exceed the shear strength of the softer material. Consequently, the classic frictional contact model is modified in this paper so that gross sliding occurs when the junctions formed between all contacting asperities are independently sheared. In this framework, when the contact tractions, normal and shear, exceed the hardness of the softer material on the entire contact area, the material of the asperities yields and the junction growth process ends in all contact regions, leading to gross sliding inception. This friction mechanism is implemented in a previously proposed numerical model for the Cattaneo-Mindlin slip-stick contact problem, which is modified to accommodate the junction growth theory. The frictionless normal contact problem is solved first, then the tangential force is gradually increased, until gross sliding inception. The contact problems in the normal and in the tangential direction are successively solved, until one is stabilized in relation to the other. The maximum tangential force leading to a non-vanishing stick area is the static friction force that can be sustained by the rough contact. The static friction coefficient is eventually derived as the ratio between the latter friction force and the normal force.

Effects of Doping Elements on the Friction and Wear of SUJ2 Steel Sliding against Aluminum Alloys

Damage to mechanical components caused by wear is considered to be an important issue for mechanical engineers. For the purpose of wear resistance, it is necessary to improve the material properties of the mechanical elements. Furthermore, low friction plays an important role in saving energy. Hence, it is important to establish a key technology for wear resistance and low friction through appropriate materials science for related industries. In general, the tribological properties of aluminum alloys are very different from those of steels. Hence, aluminum alloys should be specially considered and clarified for their tribological properties before being applied industrially. This paper therefore aims to further investigate the effects of the content of doping elements on the friction and wear of the selected aluminum alloys. From the experimental results, it can be concluded that the higher the Si content, the smaller the friction coefficient, and the milder the variation. The higher the content of iron and copper, the more materials are removed, showing better machinability. Moreover, three frictional models and wear mechanisms that describe the effects of the content of doping elements on the friction and wear are proposed. The wear mechanisms change as the silicon content increases, from the junction growth to the wedge and the ploughing particles. As a result, better choices of aluminum alloys with regards to friction and wear can then be made. These results have great practical importance.

Elastic–Plastic Sinusoidal Waviness Contact Under Combined Normal and Tangential Loading

The behavior of an elastic plastic contact between a deformable three-dimensional sinusoidal asperity and a rigid flat under combined normal and tangential loading is investigated using the finite element method. The sliding inception is determined by the maximum shear stress criterion. The resulting junction growth and static friction coefficient are investigated. It is found that for a general case, at the low dimensionless contact pressures, the static friction coefficient decreases sharply with increasing contact pressure. However, at the medium contact pressures, the static friction coefficient nearly approaches a constant value (around 0.23). Nevertheless, as the contact pressure further increases, the static friction coefficient keeps on reducing at a linear rate. The effects of material properties, geometric properties and critical shear strength on the static friction coefficient are also studied. An empirical expression for the static friction coefficient is provided.

New insights into the regulatory function of CYFIP1 in the context of WAVE- and FMRP-containing complexes.

ABSTRACTCytoplasmic FMRP interacting protein 1 (CYFIP1) is a candidate gene for intellectual disability (ID), autism, schizophrenia and epilepsy. It is a member of a family of proteins that is highly conserved during evolution, sharing high homology with its Drosophila homolog, dCYFIP. CYFIP1 interacts with the Fragile X mental retardation protein (FMRP, encoded by the FMR1 gene), whose absence causes Fragile X syndrome, and with the translation initiation factor eIF4E. It is a member of the WAVE regulatory complex (WRC), thus representing a link between translational regulation and the actin cytoskeleton. Here, we present data showing a correlation between mRNA levels of CYFIP1 and other members of the WRC. This suggests a tight regulation of the levels of the WRC members, not only by post-translational mechanisms, as previously hypothesized. Moreover, we studied the impact of loss of function of both CYFIP1 and FMRP on neuronal growth and differentiation in two animal models – fly and mouse. We show that these two proteins antagonize each other's function not only during neuromuscular junction growth in the fly but also during new neuronal differentiation in the olfactory bulb of adult mice. Mechanistically, FMRP and CYFIP1 modulate mTor signaling in an antagonistic manner, likely via independent pathways, supporting the results obtained in mouse as well as in fly at the morphological level. Collectively, our results illustrate a new model to explain the cellular roles of FMRP and CYFIP1 and the molecular significance of their interaction.

Increased acetylation of microtubules rescues human tau-induced microtubule defects and neuromuscular junction abnormalities in Drosophila.

ABSTRACTTau normally associates with and stabilizes microtubules (MTs), but is hyperphosphorylated and aggregated into neurofibrillary tangles in Alzheimer's disease and related neurodegenerative diseases, which are collectively known as tauopathies. MTs are regulated by different forms of post-translational modification, including acetylation; acetylated MTs represent a more stable microtubule population. In our previous study, we showed that inhibition of histone deacetylase 6 (HDAC6), which deacetylates tubulin at lysine 40, rescues defects in MTs and in neuromuscular junction growth caused by tau overexpression. However, HDAC6 also acts on other proteins that are involved in distinct biological processes unrelated to tubulins. In order to examine directly the role of increased tubulin acetylation against tau toxicity, we generated a site-directed α-tubulinK40Q mutation by CRISPR/Cas9 technology to mimic the acetylated MTs and found that acetylation-mimicking α-tubulin rescued tau-induced MT defects and neuromuscular junction developmental abnormalities. We also showed that late administration of ACY-1215 and tubastatin A, two potent and selective inhibitors of HDAC6, rescued the tau-induced MT defects after the abnormalities had already become apparent. Overall, our results indicate that increasing MT acetylation by either genetic manipulations or drugs might be used as potential strategies for intervention in tauopathies.

Time-dependent hysteresis friction behaviors of linear rolling bearings

Hysteresis friction behaviors of linear rolling bearings (LRBs) are important for precision positioning applications, which are related to the displacement and the traversed trajectory history within pre-rolling friction region. Although these behaviors have been pointed out in literature, the time dependence of transient hysteresis friction behaviors has not been reported before. In this work, the effects of initial conditions induced by the applied forces prior to commencement of the hysteresis motion are considered, which are denoted by the differences between the magnitudes of positive endpoints and the magnitudes of negative endpoints of virgin curves for the obtained asymmetrical hysteresis loops. The evolution of the time dependence is denoted by the decaying of the differences with the increasing dwell time. The effects of the damping and the junction growth during the dwell time are used to explain the time-dependent hysteresis friction behaviors of the LRB. The experiments of higher preload and lubrication-free conditions have been implemented as well, and the results indicate that the conditions are positive to diminish the time-dependent hysteresis friction behaviors.

Standard human chorionic gonadotropin versus double trigger for final oocyte maturation results in different granulosa cells gene expressions: a pilot study

To investigate the messenger RNA (mRNA) expression of reproduction-related genes in granulosa cells (GCs) of patients triggered with hCG compared with patients triggered with GnRH agonist and hCG (double trigger) for final oocyte maturation. Granulosa cells were obtained at the time of oocyte retrieval, and gene expression was analyzed using quantitative real-time polymerase chain reaction. Referral center. Fifteen women undergoing controlled ovarian hyperstimulation for IVF who received hCG for final follicular maturation and in a subsequent IVF cycle received double trigger. Granulosa cells collection. The expression of genes related to ovarian hyperstimulation syndrome, gap junction, and epidermal-like growth factor in GCs. The mRNA expressions of amphiregulin (2.1 vs. 1, arbitrary unit) and epiregulin (2.5 vs. 1, arbitrary unit) were significantly higher in the double trigger group compared with the hCG group. We found no difference in luteinizing hormone receptor and follicle stimulating hormone receptor mRNA expressions between the two groups. Moreover, although the mRNA expression of pigment epithelium-derived factor (1.5 vs. 1, arbitrary unit) was significantly higher in the double trigger group, no between-group differences were observed in the expression of vascular endothelial growth factor and GnRH receptor. The mRNA expression of conexin43 in cumulus cells (0.7 vs. 1, arbitrary unit) was significantly lower in the double trigger group compared with the hCG group. Our findings suggest that the decreased expression of conexin43 and the increased expression of epiregulin and amphiregulin in the GCs from patients receiving the double trigger may explain the suggested improved oocyte and embryo quality related to the double triggering group.

Modeling of the Friction Behavior in Metal Forming Process Considering Material Hardening and Junction Growth

In various plastic forming processes of metals, friction has been revealed to play an important role in the determination of the material flow, fracture, and surface quality. The precise description of friction behavior is thus a critical issue for the accurate prediction and analysis of these formability indicators. Generally, the friction behavior is inevitably affected by material hardening and junction growth. However, few of the previous models have taken both of them into consideration, especially for the nonlinear hardening materials. In this study, the classical contact model was modified to include the power-law hardening material, and the general friction law combined with Tabor's equation was employed to estimate the friction stress with the junction growth of asperities. An asperity-based friction model for rough surfaces in metal forming process was then obtained by summarizing the normal and tangential stresses of all the asperities on the surface using Greenwood and Williamson (GW) method. The model was validated by comparing to the finite element (FE) results and the experimental results. And its comparison with Kogut and Etsion (KE) model and Cohen's model revealed a wider range of application for the present model. It was also found to be able to predict the friction coefficient and the real contact area of nonlinear hardening materials under various contact conditions. This work is helpful to understand the friction behavior and further guide the simulation and optimization of forming processes.

Local and tissue-scale forces drive oriented junction growth during tissue extension.

Convergence-extension is a widespread morphogenetic process driven by polarized cell intercalation. In the Drosophila germ band, epithelial intercalation comprises loss of junctions between anterior-posterior neighbours followed by growth of new junctions between dorsal-ventral neighbours. Much is known about how active stresses drive polarized junction shrinkage. However, it is unclear how tissue convergence-extension emerges from local junction remodelling and what the specific role, if any, of junction growth is. Here we report that tissue convergence and extension correlate mostly with new junction growth. Simulations and in vivo mechanical perturbations reveal that junction growth is due to local polarized stresses driven by medial actomyosin contractions. Moreover, we find that tissue-scale pulling forces at the boundary with the invaginating posterior midgut actively participate in tissue extension by orienting junction growth. Thus, tissue extension is akin to a polarized fluid flow that requires parallel and concerted local and tissue-scale forces to drive junction growth and cell-cell displacement.

Leiomyomas in the gastric cardia: CT findings and differentiation from gastrointestinal stromal tumors

ObjectiveTo describe CT findings of leiomyomas and gastrointestinal stromal tumors (GISTs) in the gastric cardia and to identify their differentiating features. Materials and methodsCT images of pathologically proven leiomyomas (n=26) and GISTs (n=19) in the gastric cardia were retrospectively reviewed for esophagogastric junction (EGJ) involvement, contour, surface, growth pattern, enhancement pattern and degree of the tumor, and the presences of intralesional low attenuation, calcification and surface dimples or ulcers. The long (LD) and short diameters (SD), LD/SD ratio, and attenuation value of each lesion were measured. ResultsEGJ involvement, homogeneous enhancement, intermediate or low enhancement, absences of intralesional low attenuation and surface dimples or ulcers, LD/SD ratio >1.2, and attenuation value ≤71.2HU were significant findings for differentiating leiomyomas from GISTs (P<0.05 for each finding). An LD/SD ratio of >1.2 and attenuation value of ≤71.2HU yielded sensitivities of 84.6% and 61.5%, and specificities of 52.6% and 84.2%, respectively, on the receiver operating characteristic curve analysis. When at least five of these seven criteria were used in combination, the sensitivity and specificity for diagnosing leiomyomas were 100% (26 of 26) and 89.5% (17 of 19), respectively. When any six of these criteria were used, a specificity of 100% was achieved. ConclusionsCT features including EGJ involvement, enhancement pattern and degree, presences of intralesional low attenuation and surface dimples or ulcers, LD/SD ratio, and attenuation value could help differentiating leiomyomas from GISTs in the gastric cardia, particularly in the manner of combination.

Middle Miocene swift migration of the TTT triple junction and rapid crustal growth in SW Japan

Middle Miocene swift migration of the TTT triple junction and rapid crustal growth in SW Japan

A mathematical model for rolling/sliding line contacts in boundary and near boundary lubrication

This paper presents a mathematical model for rolling/sliding line contacts operating in boundary and near boundary lubrication. The model is developed with first-principle formulations and incorporates key mechanical, thermal and tribo-chemical aspects of the problem including mode of deformation of the contact, friction, flash temperature, boundary film characterization and fluid–solid load sharing. For given load, speeds, bulk temperature and proportion of solid load-sharing, the model outputs a number of variables that are useful for the assessment of the state and severity of the problem. They include contact pressure, temperature, degree of plastic deformation, friction coefficient, friction power intensity, degree of friction-induced junction growth and integrity of the boundary film. The model may be implemented into a gear contact model to study gear systems under loss of lubrication. It may also be integrated with the light mixed-lubrication model of the authors to develop a more complete mixed-lubrication model covering the entire regime of the mixed lubrication. The model is evaluated with a limited scope and more extensive evaluations are needed in time of its validity and applicability through various means and in various settings.

Drosophila S6 Kinase like inhibits neuromuscular junction growth by downregulating the BMP receptor thickveins.

Synaptic connections must be precisely controlled to ensure proper neural circuit formation. In Drosophila melanogaster, bone morphogenetic protein (BMP) promotes growth of the neuromuscular junction (NMJ) by binding and activating the BMP ligand receptors wishful thinking (Wit) and thickveins (Tkv) expressed in motor neurons. We report here that an evolutionally conserved, previously uncharacterized member of the S6 kinase (S6K) family S6K like (S6KL) acts as a negative regulator of BMP signaling. S6KL null mutants were viable and fertile but exhibited more satellite boutons, fewer and larger synaptic vesicles, larger spontaneous miniature excitatory junctional potential (mEJP) amplitudes, and reduced synaptic endocytosis at the NMJ terminals. Reducing the gene dose by half of tkv in S6KL mutant background reversed the NMJ overgrowth phenotype. The NMJ phenotypes of S6KL mutants were accompanied by an elevated level of Tkv protein and phosphorylated Mad, an effector of the BMP signaling pathway, in the nervous system. In addition, Tkv physically interacted with S6KL in cultured S2 cells. Furthermore, knockdown of S6KL enhanced Tkv expression, while S6KL overexpression downregulated Tkv in cultured S2 cells. This latter effect was blocked by the proteasome inhibitor MG132. Our results together demonstrate for the first time that S6KL regulates synaptic development and function by facilitating proteasomal degradation of the BMP receptor Tkv.

A systems-level approach to parental genomic imprinting: the imprinted gene network includes extracellular matrix genes and regulates cell cycle exit and differentiation.

Genomic imprinting is an epigenetic mechanism that restrains the expression of ∼100 eutherian genes in a parent-of-origin-specific manner. The reason for this selective targeting of genes with seemingly disparate molecular functions is unclear. In the present work, we show that imprinted genes are coexpressed in a network that is regulated at the transition from proliferation to quiescence and differentiation during fibroblast cell cycle withdrawal, adipogenesis in vitro, and muscle regeneration in vivo. Imprinted gene regulation is not linked to alteration of DNA methylation or to perturbation of monoallelic, parent-of-origin-dependent expression. Overexpression and knockdown of imprinted gene expression alters the sensitivity of preadipocytes to contact inhibition and adipogenic differentiation. In silico and in cellulo experiments showed that the imprinted gene network includes biallelically expressed, nonimprinted genes. These control the extracellular matrix composition, cell adhesion, cell junction, and extracellular matrix-activated and growth factor–activated signaling. These observations show that imprinted genes share a common biological process that may account for their seemingly diverse roles in embryonic development, obesity, diabetes, muscle physiology, and neoplasm.

Phospho-regulated Drosophila adducin is a determinant of synaptic plasticity in a complex with Dlg and PIP2 at the larval neuromuscular junction.

ABSTRACTAdducin is a ubiquitously expressed actin- and spectrin-binding protein involved in cytoskeleton organization, and is regulated through phosphorylation of the myristoylated alanine-rich C-terminal kinase (MARCKS)-homology domain by protein kinase C (PKC). We have previously shown that the Drosophila adducin, Hu-li tai shao (Hts), plays a role in larval neuromuscular junction (NMJ) growth. Here, we find that the predominant isoforms of Hts at the NMJ contain the MARCKS-homology domain, which is important for interactions with Discs large (Dlg) and phosphatidylinositol 4,5-bisphosphate (PIP2). Through the use of Proximity Ligation Assay (PLA), we show that the adducin-like Hts isoforms are in complexes with Dlg and PIP2 at the NMJ. We provide evidence that Hts promotes the phosphorylation and delocalization of Dlg at the NMJ through regulation of the transcript distribution of the PAR-1 and CaMKII kinases in the muscle. We also show that Hts interactions with Dlg and PIP2 are impeded through phosphorylation of the MARCKS-homology domain. These results are further evidence that Hts is a signaling-responsive regulator of synaptic plasticity in Drosophila.