Bulge Area Research Articles

Unusual partners: a rare cause of small bowel bulges and a common cause of anemia.

A 67-year-old female, without prior medical history, presented to the emergency department due to dizziness and asthenia, where iron deficiency anemia, without visible blood loss, was identified. A previous abdominal computed tomography revealed intestinal pneumatosis of the proximal jejunum and right colon. The upper endoscopy showed non-atrophic gastritis associated with H.pylori infection, which was treated, and the colonoscopy revealed right colic pneumatosis, without other alterations. A small bowel capsule endoscopy was performed, revealing bulging areas of the intestinal wall, lymphangiectasias and angioectasias, in the proximal small bowel. A single balloon assisted anterograde enteroscopy reached the proximal jejunum, showing several areas of bulging with endoscopically normal mucosa, compatible with intestinal pneumatosis. In 3 bulging areas, there were multiple lymphangiectasias and friable punctate angioectasias, which were treated with argon-plasma coagulation and through-the-scope clip with haemostatic success. The procedure was uneventful. After 6 months of follow-up, the patient was asymptomatic, without anemia or iron deficiency.

Transcription factor KROX20 marks epithelial stem cells for hair follicle formation.

Epidermal stem cells control homeostasis and regeneration of skin and hair. In the hair follicle (HF) bulge of mammals, populations of slow-cycling stem cells regenerate the HF during cyclical rounds of anagen (growth), telogen (quiescence), and catagen (regression). Multipotent epidermal cells are also present in the HF above the bulge area, contributing to the formation and maintenance of sebaceous gland and upper and middle portions of the HF. Here, we report that the transcription factor Krox20 is enriched in an epidermal stem cell population located in the upper/ middle HF. Expression analyses and lineage tracing using inducible Krox20-CreERT showed that Krox20-lineage cells migrate out of this HF region and contribute to the formation of bulge in the HF, serving as ancestors of bulge stem cells. In vivo depletion of these cells arrests HF morphogenesis. This study identifies a novel marker for an epidermal stem cell population that is indispensable for hair homeostasis.

Image-based simulation of mitral valve dynamic closure including anisotropy

Simulation of the dynamic behavior of mitral valve closure could improve clinical treatment by predicting surgical procedures outcome. We propose here a method to achieve this goal by using the immersed boundary method. In order to go towards patient-based simulation, we tailor our method to be adapted to a valve extracted from medical image data. It includes investigating segmentation process, smoothness of geometry, case setup and the shape of the left ventricle. We also study the influence of leaflet tissue anisotropy on the quality of the valve closure by comparing with an isotropic model. As part of the anisotropy analysis, we study the influence of the principal material direction by comparing methods to obtain them without dissection.Results show that our method can be scaled to various image-based data. We evaluate the mitral valve closure quality based on measuring bulging area, contact map, and flow rate. The results show also that the anisotropic material model more precisely represents the physiological characteristics of the valve tissue. Furthermore, results indicate that the orientation of the principal material direction plays a role in the effectiveness of the valve seal.

Finite element analysis of Cu-water nanofluid flow and heat transfer in a dynamically bulging enclosure

PurposeThe main purpose of this study is to analyze the heat transfer phenomena in a dynamically bulging enclosure filled with Cu-water nanofluid. This study examines the convective heat transfer process induced by a bulging area considered a heat source, with the enclosure's side walls having a low temperature and top and bottom walls being treated as adiabatic. Various factors, such as the Rayleigh number (Ra), nanoparticle volume fraction, Darcy effects, Hartmann number (Ha) and effects of magnetic inclination, are analyzed for their impact on the flow behavior and temperature distribution.Design/methodology/approachThe finite element method (FEM) is employed for simulating variations in flow and temperature after validating the results. Solving the non-linear partial differential equations while incorporating the modified Darcy number (10−3 ≤ Da ≤ 10−1), Ra (103 ≤ Ra ≤ 105) and Ha (0 ≤ Ha ≤ 100) as the dimensionless operational parameters.FindingsThis study demonstrates that in enclosures with dynamically positioned bulges filled with Cu-water nanofluid, heat transfer is significantly influenced by the bulge location and nanoparticle volume fraction, which alter flow and heat patterns. The varying impact of magnetic fields on heat transfer depends on the Rayleigh and Has.Practical implicationsThe geometry configurations employed in this research have broad applications in various engineering disciplines, including heat exchangers, energy storage, biomedical systems and food processing.Originality/valueThis research provides insights into how different shapes of the heated bulging area impact the hydromagnetic convection of Cu-water nanofluid flow in a dynamically bulging-shaped porous system, encompassing curved surfaces and various multi-physical conditions.

Active interface bulging in Bacillus subtilis swarms promotes self-assembly and biofilm formation

Microbial communities such as biofilms are commonly found at interfaces. However, it is unclear how the physical environment of interfaces may contribute to the development and behavior of surface-associated microbial communities. Combining multimode imaging, single-cell tracking, and numerical simulations, here, we found that activity-induced interface bulging promotes colony biofilm formation in Bacillus subtilis swarms presumably via segregation and enrichment of sessile cells in the bulging area. Specifically, the diffusivity of passive particles is ~50% lower inside the bulging area than elsewhere, which enables a diffusion-trapping mechanism for self-assembly and may account for the enrichment of sessile cells. We also uncovered a quasilinear relation between cell speed and surface-packing density that underlies the process of active interface bulging. Guided by the speed-density relation, we demonstrated reversible formation of liquid bulges by manipulating the speed and local density of cells with light. Over the course of development, the active bulges turned into striped biofilm structures, which eventually give rise to a large-scale ridge pattern. Our findings reveal a unique physical mechanism of biofilm formation at air-solid interface, which is pertinent to engineering living materials and directed self-assembly in active fluids.

The value of immunohistochemical expression of SOX9 and CD34 in alopecia areata

ABSTRACT Background Alopecia areata (AA), an immune-mediated disorder, is marked by temporary, nonscarring hair loss. The bulge area is protected from immune attacks by immune privilege; however, recent studies demonstrated immune cells infiltrating the bulge area. Objective This study aims to investigate the immunohistochemical expression of the sex-determining region Y-box 9 (SOX9) and cluster of differentiation 34 (CD34) in AA patients as markers of hair follicle stem cells (HFSCs) and progenitor cells, respectively. Methods Immunohistochemical staining of SOX9 and CD34 was applied on skin samples of 20 AA patients and 20 healthy controls. Results SOX9 and CD34 were significantly lower in lesional samples of cases compared to perilesional and control skin biopsies. Furthermore, SOX9 level was negatively correlated with the severity of alopecia tool score (SALT score) among the studied AA patients. Moreover, lowered SOX9 expression was present in patients with recurrent attacks. Conclusions The significant reduction of stem cell markers (SOX9 and CD34) in our studied AA cases signifies the pathological affection of HFSCs and their progeny in AA. This is thought to cause a loss of competence in generating new hair in some AA cases, which needs to be validated in further research. Limitations of the study This study has a small sample size.

Hydrocarbon-generating potential of the Middle Permian Lucaogou source rock in the eastern Junggar Basin, China

The Middle Permian Lucaogou Formation is the most significant source rock in the eastern Junggar Basin. Previous studies have confirmed its excellent hydrocarbon-generating potential in the Jimsar Sag. However, its potential in other areas of the eastern Junggar Basin remains uncertain. Based on total organic carbon and pyrolysis, organic petrology, hydrocarbon simulation experiments, basin simulation, and combined well-seismic coupling interpretation, this study systematically compares the hydrocarbon-generating potential of the Lucaogou source rock in the Jimsar Sag with other areas of the eastern Junggar Basin. It discusses the sedimentary environment of high-quality source rocks and depicts the distribution of practical source kitchens. The Lucaogou source rocks in the eastern Junggar Basin are oil-prone, dominated by type I–II kerogen, and generally classified as good to excellent source rocks. Nowadays, the area of the Lucaogou source rocks that have entered the main oil-generating window is approximately 11 × 103 km2. Except for the bulge area, the Lucaogou source rocks in the eastern Junggar Basin successively entered the hydrocarbon-generating threshold during the Jurassic and the main oil-generating window in the Cretaceous. The Lucaogou source rocks in the Jimsar Sag and other parts of the eastern Junggar Basin share similar biomarker fingerprints, characterized by relatively low ratios of Pr/Ph, Pr/n-C17, Tm/C30 hopane, C19/C20 tricyclic terpene, and C24 tetracyclic terpene/C26 tricyclic terpene, and high β-carotene content, gammacerane index, and Ts/Tm ratios. These characteristics reflect deposition in a strongly reducing brackish lacustrine environment with parental sources dominated by lower organisms such as algae and bacteria. Generally, the Lucaogou source rocks in the eastern Junggar Basin have an oil-generating intensity of more than 3 × 106 t/km2. Several oil-generating centers with an intensity of more than 5 × 106 t/km2 have developed in the front of the Bogda Mountain, Jimsar Sag, Dongdaohaizi Sag, Wucaiwan Sag, and Shazhang Fault Zone, covering a total area of approximately 12,500 km2. These characteristics of the Lucaogou source rocks promise favorable potential for forming large and medium oil fields. The results further consolidated the oil and gas resources in the eastern Junggar Basin and provided valuable references for exploring future oil and gas fields.

Local ozone injection compared to local glucocorticoid injection in carpal tunnel syndrome: A randomized controlled trial.

This study aimed to compare the effectiveness of local ozone (O3) injection versus corticosteroid injection in the treatment of mild to moderate carpal tunnel syndrome (CTS). This double-blind randomized controlled trial was performed on 42 patients (9 males, 33 females; mean age: 46.7±2.1 years; range, 18 to 70 years) with mild to moderate CTS between May 2021 and June 2021. The corticosteroid group (n=21) was injected with 40 mg triamcinolone, and in the O3 group B (n=21), 4 mL of a 10 mcg/mL oxygen (O2)-O3 mixture was injected. Symptom severity and functional impairments were assessed using a Visual Analog Scale and Boston Carpal Tunnel Questionnaire. Electrodiagnostic and ultrasonographic parameters were obtained at baseline and eight weeks after the procedure. The O2-O3 solution improved pain and Boston Carpal Tunnel Questionnaire score after eight weeks (p<0.001); however, the change was nonsignificant compared to the corticosteroid group (p>0.05). Sensory nerve and compound muscle action potential latencies were not significantly changed eight weeks after O2-O3 injection (p>0.05), while both were significantly decreased in the steroid injection group (p<0.001). Volar bulging and median nerve cross-section surface area were not improved after O2-O3 injection, while the improvement was significant in the corticosteroid arm (p=0.02). Symptoms in patients with mild to moderate CTS may be alleviated by local O2-O3 injection; however, electrodiagnostic and ultrasonographic indices may be unchanged. Corticosteroid local injection may alleviate patient symptoms along with electrodiagnostic and ultrasonographic parameters.

A WELL KNOWN CARDIOMYOPATHY BEHIND A FAMILY DRAMA: A CASE REPORT

Abstract We report a case of a 55–year–old woman who came to our regional reference center for cardiomyopathies. Her cardiovascular risk factors were systemic arterial hypertension, dyslipidemia, family history of sudden cardiac death. Her first son –20 years old– had died of sudden cardiac death during a football match, at the peak of the exertion, one year before. The autopsy had showed biventricular, diffuse fibro–fatty replacement areas diagnostic for arrhythmogenic cardiomyopathy. DNA extraction in tissue was evaluated for genetic testing. According to 2022 ESC Guidelines, familial evaluation of descendents of patients died of sudden cardiac death should include: genetic testing, gathering of medical history and performing physical examination, standard and high precordial leads ECG, echocardiography and exercise testing, CMR and ambulatory cardiac rhythm monitoring. All of these were normal, except for cardio RM which revealed: aneurysmatic bulging of the right ventricular wall, most prominent at the apex and free wall with normal contractility. Absence of both left and right ventricular dilatation. Left ventricular and right ventricular ejection fraction measured 58% and 55% respectively. According to Padua’s criteria the woman had borderline arrhythmogenic cardiomyopathy. Instead, her 18 years old little son used to practice sports and used anabolics. His cardio–RMN demonstrated: reduced function of the right ventricle with mild dilation and biventricular bulging areas. The patient met the criteria for definite Arrhythmogenic Cardiomyopathy since he had two major criteria. In the meantime of the results of genetic testing, suspension of the smoking habit and reduction of strenuous physical activity were advised. Conclusions Arrhythmogenic displasia of right ventricle is characterized histopathologically by the extensive replacement of right ventricular myocardium with fibro–fatty tissue (dysplasia triangle). Involvement of the left ventricle has been documented on a lesser frequency and has a higher mortality. Different from other conditions, in arrhythmogenic cardiomyopathy, sports practice not only conveys arrhythmic risk to that specific moment (as it happens to the little patient) but also accelerates disease progression.

The occurrence of myopathies and meat abnormalities in modern broiler farming

Over the past few decades, there has been a significant increase in the production and consumption of poultry meat due to its high-quality nutritional profile, relatively low production costs, and ease of meat processing. This growing demand has led to progressive improvements in genetic selection for fast-growing broilers, triggering several spontaneous idiopathic muscle abnormalities along with an increased susceptibility to stress-induced myopathy. These muscle abnormalities have a negative impact on the quality of both fresh and processed chicken meat, primarily affecting the large breast muscle (m. pectoralis major) of broilers, which is also the most valuable part of the carcass. Frequent meat abnormalities include the occurrence of pale, soft, and exudative meat, primarily characterized by reduced water-holding capacity, while Deep Pectoral Myopathy results in a change in colour and a significant reduction in the attractive appearance of the small breast muscle (m. pectoralis minor). Myopathies labelled as "White Striping" are characterized by superficial white stripes, "Wooden Breast" is marked by pale and bulging areas of significant hardness, while "Spaghetti Meat" is described by the separation of muscle fibres resembling spaghetti pasta. These mentioned abnormalities and myopathies negatively impact the economic aspect of the poultry industry during the removal of affected parts and, furthermore, reduce the qualitative and nutritional value of the meat, posing challenges during technological processes. This paper describes recent findings on the occurrence, characteristics, and prevalence of the most common myopathies affecting modern broiler farming.

Forming Characteristics Investigation of Natural Bulging Area of Thin-Walled Metallic Tubes in Liquid Impact Forming Method

Forming Characteristics Investigation of Natural Bulging Area of Thin-Walled Metallic Tubes in Liquid Impact Forming Method

Rat hair-follicle-associated pluripotent (HAP) stem cells can differentiate into atrial or ventricular cardiomyocytes in culture controlled by specific supplementation.

There has been only limited success to differentiate adult stem cells into cardiomyocyte subtypes. In the present study, we have successfully induced beating atrial and ventricular cardiomyocytes from rat hair-follicle-associated pluripotent (HAP) stem cells, which are adult stem cells located in the bulge area. HAP stem cells differentiated into atrial cardiomyocytes in culture with the combination of isoproterenol, activin A, bone morphogenetic protein 4 (BMP4), basic fibroblast growth factor (bFGF), and cyclosporine A (CSA). HAP stem cells differentiated into ventricular cardiomyocytes in culture with the combination of activin A, BMP4, bFGF, inhibitor of Wnt production-4 (IWP4), and vascular endothelial growth factor (VEGF). Differentiated atrial cardiomyocytes were specifically stained for anti-myosin light chain 2a (MLC2a) antibody. Ventricular cardiomyocytes were specially stained for anti-myosin light chain 2v (MLC2v) antibody. Quantitative Polymerase Chain Reaction (qPCR) showed significant expression of MLC2a in atrial cardiomyocytes and MLC2v in ventricular cardiomyocytes. Both differentiated atrial and ventricular cardiomyocytes showed characteristic waveforms in Ca2+ imaging. Differentiated atrial and ventricular cardiomyocytes formed long myocardial fibers and beat as a functional syncytium, having a structure similar to adult cardiomyocytes. The present results demonstrated that it is possible to induce cardiomyocyte subtypes, atrial and ventricular cardiomyocytes, from HAP stem cells.

Hair-follicle associated pluripotent (HAP)-cell-sheet implantation enhanced wound healing in diabetic db/db mice.

Diabetes often results in chronic ulcers that fail to heal. Effective treatment for diabetic wounds has not been achieved, although stem-cell-treatment has shown promise. Hair-follicle-associated-pluripotent (HAP)-stem-cells from bulge area of mouse hair follicle have been shown to differentiate into keratinocytes, vascular endothelial cells, smooth muscle cells, and some other types of cells. In the present study, we developed HAP-cell-sheets to determine their effects on wound healing in type-2 diabetes mellitus (db/db) C57BL/6 mouse model. Flow cytometry analysis showed cytokeratin 15 expression in 64% of cells and macrophage expression in 3.6% of cells in HAP-cell-sheets. A scratch cell migration assay in vitro showed the ability of fibroblasts to migrate and proliferate was enhanced when co-cultured with HAP-cell-sheets. To investigate in vivo effects of the HAP-cell-sheets, they were implanted into 10 mm circular full-thickness resection wounds made on the back of db/db mice. Wound closure was facilitated in the implanted group until day 16. The thickness of epithelium and granulation tissue volume at day 7 were significantly increased by the implantation. CD68 positive area and TGF-β1 positive area were significantly increased; meanwhile, iNOS positive area was reduced at day 7 in the HAP-cell-sheets implanted group. After 21 days, CD68 positive areas in the implanted group were reduced to under the control group level, and TGF-β1 positive area had no difference between the two groups. These observations strongly suggest that the HAP-cell-sheets implantation is efficient to facilitate early macrophage activity and to suppress inflammation level. Using immuno-double-staining against CD34 and α-SMA, we found more vigorous angiogenesis in the implanted wound tissue. The present results suggest autologous HAP-cell-sheets can be used to heal refractory diabetic ulcers and have clinical promise.

Reversibly immortalization establishes a hair follicle stem cell line with hair follicle reconstruction ability.

Hair follicle stem cells (HFSCs) play critical roles in the periodic regeneration of hair follicles. HFSCs are also a good model for stem cell biology research. However, no stable mouse HFSC cell line has been reported, which restricts the research and application of HFSCs. We isolated HFSCs from mouse hair follicles and immortalized them by inducing a reversible SV40 large T antigen. Through monoclonal screening, we identified a reversibly immortalized cell line, immortalized HFSC (iHFSC2). RNA sequencing, fluorescence-activated cell sorting, western blotting and immunofluorescence experiments revealed that the expression patterns of iHFSC2 and HFSC were similar at the protein and mRNA levels. After that, iHFSC2s were passaged and morphologically monitored for up to 40 times to detect their long-term culture potential. The long-term cultured iHFSC2 could regenerate hair follicles with complete hair follicle structure and HFSCs in the bulge area. This work successfully established an HFSC cell line with the ability of hair follicle reconstruction.

Self-potential variations associated with the slip of Huangnibazi Landslide

The electrical self-potential (SP) responds to the relative fluid flow in porous materials caused by the electrokinetic mechanism, also known as the streaming potential. This characteristic can be used to study landslides induced by rainfall, particularly when subsurface flows cannot be directly observed from the ground surface or landslide scars. The study focuses on the Huangnibazi Landslide, which occurred in 2017 and continued to slide slowly until early 2018 at an average rate of 60 mm/d. SP monitoring was implemented on the slope during the post-failure period to study the characteristics of streaming current. In addition to the diurnal variations of the geoelectric field, localized electric field variations were observed on the morning of Jan. 9, 2018. To examine the spatial distribution and the temporal variation of the streaming current, we processed the measured SP data using a weighted upward continuing method, namely the multi-scale wavelet tomography (MWT). Based on the processing results obtained with the MWT method, we observed variations in the estimated SP sources concentrated in a bulge area. To further investigate these variations, we conducted a numerical modeling test by deforming the geometrical structure of the estimated source. The results suggested that extrusion within the sliding process could be responsible for the variations in SP sources.

Suppressing wrinkles in thin-walled dome parts: A novel deep drawing method with active stress control

The occurrence of wrinkling defects in deep drawing thin-walled dome parts is primarily attributed to circumferential compressive stress. With a decrease in the thickness-to-diameter ratio, preventing wrinkling becomes increasingly challenging during the forming process. This study proposes a novel deep drawing method that effectively suppresses wrinkles in thin-walled dome parts through the utilization of a local reverse bulging tool for active stress control. An analytical model is developed to describe this novel deep drawing method, enabling analysis of the radius variations in the reverse bulging area and the corresponding reverse bulging force. Numerical simulations are carried out to investigate the effect of the reverse bulging loading path on the stress-strain distribution. Furthermore, experimental trials are performed under various loading conditions to explore the impact of loading paths on forming defects and thickness distributions of the formed parts. The findings indicate that the radius of rigid tools and the reverse bulging force play pivotal roles in achieving the desired reverse bulging effect. As the punch stroke increases, the radius of the reverse bulging area decreases, while the reverse bulging force exhibits a pattern of initial increase followed by a subsequent decrease. By employing an appropriate reverse bulging loading path, the circumferential stress at the reverse bulging area transitions from compressive stress to tensile, effectively suppressing the occurrence of wrinkles. This research provides valuable experimental guidance for implementing the novel deep drawing process for dome parts.

Volume Redistribution of the Buccal Fat Pad After Reduction Malarplasty.

During reduction malarplasty, cheek bulging could be found immediately after zygomatic complex is moved inwards, backwards and upwards. As patient is in the supine position during surgery, the effect of gravity is eliminated, so the only reason for the bulge is the redistribution of the soft tissue in the deep facial spaces. The buccal fat pad, with its main body behind the zygomatic arch and buccal extension in the cheek area, is most likely to be responsible for the bulge. 3D buccal extension models were reconstructed from preoperative and long-term follow-up CT images and the volume measured. By comparing the pre- and postoperative 3D models, the shape deviation of the buccal extension and facial soft tissue can be identified. Eleven patients (22 buccal extensions) met the inclusion criteria. Compared with the preoperative buccal extension volume, the postoperative volume increased significantly. By comparing the reconstructed models, the buccal extension volume increase with anteroinferior protrusion can be visually detected, and cheek bulging was clearly identified on the lower face. The bulging area coincided with the projection of the buccal extension on the skin surface. Reduction malarplasty may cause volume redistribution of the buccal fat pad. Therefore, preoperative assessment of the size of the buccal fat pad based on CT images is recommended. The buccal extension volume increase with anteroinferior protrusion is an important cause of postoperative cheek bulging and should be considered during treatment. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Permanent Deformation Monitoring and Remaining Life Prediction of Asphalt Pavement Combining Full-Scale Accelerated Pavement Testing and FEM

Permanent deformation (rutting) is one of the typical failure modes of asphalt pavement with a semirigid base in high-temperature areas. To address issues of pavement structure deformation and remaining life prediction, a method of combining accelerated pavement testing and finite element (FE) simulation was proposed. A modified Burgers model considering creep parameter damage was obtained using strain monitoring data and laboratory test values, which was performed in the FE model to analyze rutting development. The results showed that high temperature and heavy axle loads greatly influenced rutting development: the tested road was loaded 360,000 times at high temperature, contributing 50% to accumulated rutting; rutting increased by 90.7% under the condition of 50% overload under high-temperature seasons from the simulated results. Then, the ratio of the bulge area to the depression area (KR) was proposed to define the rutting deformation mechanism. The KR analysis results illustrated that rutting development was a transition process from compaction rutting to flow rutting. Finally, the relationship between the action times of axle load in the tested and in-service roads was established based on the rutting equivalence principle. When the action times of axle load reach approximately 25 million times (insufficient remaining life) for the investigated Hu-Ning highway, necessary maintenance measures should be taken to treat rutting deformation.

Investigation of the effect of stainless-steel grain size on the continuity of graphene frictional behavior using molecular dynamics (MD) simulation

Nanograin refinement can improve the strength of stainless steel, but the substrate grain boundaries will cause graphene bulging, so it will affect the lubrication effect of graphene. In this study, the effect of stainless-steel grain size on the frictional strengthening behavior of graphene is investigated, and the mechanism of grain boundary distribution and grain boundary crossing on graphene friction strengthening behavior was revealed. A normal load constraint of 0.8 nN is set for the nano-friction process. Stainless steel grain size greater than or equal to 10 nm, the maximum friction force of graphene does not vary with grain size is about 6 nN. However, the friction strengthening behavior is discontinuous, and the friction force fluctuates significantly, which is not conducive to micromechanical structure lubrication. When the grain size of stainless steel is less than 10 nm, the frictional strengthening behavior is continuous and the friction force after strengthening will maintain small fluctuations. Since the small fluctuations of this stick–slip behavior are material properties of graphene and cannot be avoided, this state is already the ideal result for graphene lubrication. However, as the stainless-steel grain size continues to become smaller, the maximum friction of graphene will increase, which is not good for graphene lubrication. This means that after the grain size is less than 10 nm, the continuation of the grain refinement process for stainless steel will improve the strength of stainless steel, but will weaken the graphene lubrication efficiency. Moreover, the difficulty of the nanograin refinement process will be significantly increased. Therefore, the stainless-steel grain size of 7 nm by grain refinement is the best solution to balance the stainless-steel strength and graphene lubrication efficiency. With a grain size of 7 nm, the stainless-steel grain boundaries are densely distributed, and the graphene bulge area will occupy 65% of the total area, allowing for continuous frictional strengthening behavior. The maximum height of graphene bumps is 2.8 Å and the maximum friction force is about 7 nN. Meanwhile, the relationship between the grain size of stainless steel and the continuity of graphene frictional strengthening behavior was explored, and the mechanism of action of grain boundary crossing by modulating the height of graphene bulge and thus affecting the frictional maximum was revealed. The nano-friction simulation of stainless steel/graphene can clearly capture the details of the nano-friction process and the variation of friction values, providing a basis for nano-friction studies of graphene on polycrystalline material surfaces. The simulation can determine the range of stainless-steel grains that exhibit the best friction state with graphene. The simulation results also provide guidance for the refinement of stainless steel nanograins and insights for the application of nanocrystalline stainless steel/graphene in MEMS.

Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy

Sliver is a common but easily neglected defect in single crystal Ni-based superalloy castings. To date, there is still no unified viewpoint on its formation mechanism and generation causes. In this work, the orientation discontinuity and motion behavior of sliver defects were studied through experiments and numerical simulations. The ultrathin wedge-shaped specimen containing the grain boundary of the sliver and the matrix was prepared at the initial position of the sliver defect for the observation of equal thickness fringes. The discontinuity of equal thickness fringes on both sides of the grain boundary was observed through a transmission electron microscope, which directly confirms the abrupt change in the orientation between the sliver and matrix from the nanoscale. The crystal lattices at the smooth area and the bulging area of the grain boundary were found to have unusually different arrangements. The irregular lattice arrangement at the bulging area shows that the grain boundary has experienced high-stress deformation. Statistical results of sliver orientation deviation with a further composition analysis show the micro protuberance of the mold shell has a noticeable inductive effect on the sliver generation. Furthermore, a self-developed three-dimensional phase-field simulation model coupled with the spatial topology algorithm is established to simulate the orientation deflection behavior and orientation deviation threshold of fractured dendrites. The simulation results indicated that there is an upper limit of the cross-section solid fraction at the fracture position for the motion of the fractured dendrites. When the cross-section solid fraction at the fracture position is higher than this upper limit, it will be difficult to produce large deviation slivers due to the structural limitation of surrounding dendrites. This upper limit does not change with the solidification temperature gradient.