Study on the Material Properties of Microconcrete by Dynamic Model Test

As an important water conveying structure, the seismic safety of the hydraulic aqueduct has attracted considerable interest. Different from the general bridge structure, the seismic analysis of the aqueduct structure needs to consider its fluid–structure interaction. The existing numerical simulation methods cannot truly reflect the fluid–solid coupling mechanism. Therefore, scholars began to use shaking table tests to study the fluid–structure interaction mechanism. However, the research is immature, and it is mostly focused on the seismic response analysis, and there are few studies on the model test similarity ratio and model material properties. Based on this, in this paper, according to the requirements of the test similarity ratio, the orthogonal experiment was used to explore the influence of barite sand content, water–cement ratio, fine sand ratio, and lime ratio on the mechanical properties of microconcrete. The performance indicators of microconcrete under different mix ratios vary widely, with a minimum variation of 19% and a maximum of 102%. Barite sand has the most significant control effect on the density, and the water–cement ratio has the most significant control effect on the compressive strength and elastic modulus. The density variation range is 2.37–2.81 g/cm³, the cube compressive strength variation range is 18.37–36.94 MPa, and the elastic modulus variation range is 2.11 × 10⁴–3.28 × 10⁴ MPa. This study will provide certain evidence for the similarity ratio design and material selection of the scaled model test of the fluid–solid coupling structure.     

早期无创正压通气治疗在重症肺炎中的观察

目的：探讨早期无创正压通气在重症肺炎中的效果。方法：选取2010年1月～2013年10月我科收治的重症肺炎46例,在常规治疗上,治疗组31例给予早期无创通气,记录二组呼吸频率、心率、PH、PaO2、PaCO2、气管插管率等,作统计学分析。结果：治疗48h后,治疗组呼吸窘迫得到明显缓解,氧分压改善,心率下降,气管插管率降低,有显著差异（P＜0.05）, PH、PaCO2的变化无统计学意义（P＞0.05）。结论：重症肺炎患者早期使用无创正压通气治疗,可以纠正缺氧,改善氧合及自觉症状,一定程度上避免有创通气,从而改善预后。     

Mechanical coupling of supracellular stress amplification and tissue fluidization during exit from quiescence

Cellular quiescence is a state of reversible cell cycle arrest that is associated with tissue dormancy. Timely regulated entry into and exit from quiescence is important for processes such as tissue homeostasis, tissue repair, stem cell maintenance, developmental processes, and immunity. However, little is known about processes that control the mechanical adaption to cell behavior changes during the transition from quiescence to proliferation. Here, we show that quiescent human keratinocyte monolayers sustain an actinomyosin-based system that facilitates global cell sheet displacements upon serum-stimulated exit from quiescence. Mechanistically, exposure of quiescent cells to serum-borne mitogens leads to rapid amplification of preexisting contractile sites, leading to a burst in monolayer tension that subsequently drives large-scale displacements of otherwise motility-restricted monolayers. The stress level after quiescence exit correlates with the level of quiescence depth at the time of activation, and a critical stress magnitude must be reached to overcome the cell sheet displacement barrier. The study shows that static quiescent cell monolayers are mechanically poised for motility, and it identifies global stress amplification as a mechanism for overcoming motility restrictions in confined confluent cell monolayers.

Quiescence refers to a state of cell cycle arrest in which cells are retained in a standby mode, ready to re-enter the cell cycle upon activation by a given physiological stimuli. The pool of quiescent cells in the human body is typically represented by tissue-specific stem and progenitor cells, naive immune cells, fibroblasts, and epithelial cells (1, 2). In addition, certain cancer cells have the ability to evade cancer therapy by entering a dormant quiescence-like state (1, 2). Accordingly, careful regulation of entry into and exit out of quiescence is important for several physiological processes such as tissue homeostasis and repair, stem cell maintenance, immunity, reproduction, and development (1, 2).During homeostasis, the balance between quiescent and proliferating cells is controlled by constituents of the microenvironment such as soluble factors, extracellular matrix components, blood vessels, and neighboring cells. On the other hand, during episodes that require extensive tissue renewal and remodeling, for example after injury, coordinated stimulation of quiescent cells into proliferation is facilitated by increased exposure to blood-borne and cell-secreted mitogens through local inflammatory responses such as increased blood flow, increased vascular permeability (vasodilation), and immune cell recruitment (3, 4). Accordingly, a commonly used methodology for studies of quiescence in cultured mammalian cells involves consecutive treatments with serum-free and serum-containing growth medium (1).Quiescent cells are required to maintain a high level of preparedness in order to facilitate rapid activation of specialized cell functions once cell division is stimulated. In agreement with this, quiescent stem cells and naive immune cells have been shown to possess multiple epigenetic and posttranslation mechanisms that facilitate the rapid expression of linage-specific genes following stimulation of quiescence exit (2, 5–14). However, little is known about mechanical forces that facilitate adaptation to cell cycle–activated behaviors.Quiescence exit is frequently associated with activation of cell motility. For example, quiescent stem and naive immune cells migrate out of their niches in response to cell cycle activation in order to support tissue homeostasis, repopulate injured tissue, or to perform immune surveillance at distal locations (15–18). In addition, reawakening of dormant quiescent cancer cells can cause tumor relapse and formation of metastases years after remission (19). In multilayered epithelial tissue, like the skin, exit from quiescence during homeostasis is associated with lateral migration to suprabasal regions, while skin injury evokes massive reawakening of basally localized keratinocytes concomitant with activation of cell sheet displacement by collective migration to restore damaged epidermal surfaces (20–23). The strong correlation between quiescence exit and cell migration in multiple physiological settings suggests the existence of mechanisms that link quiescence exit to activation of cell motility.The dynamics of epithelial collectives is largely regulated by mechanical forces generated through cell–cell interactions as well as interactions between cells and the extracellular environment (24). Key components involved in controlling these forces are cytoskeletal components such as actinomyosin and adhesion complexes such as adherent junctions and focal adhesion complexes (25). Additional factors that have been reported to influence the dynamic behavior of epithelial monolayers include the presence of epithelial edges (24, 26), mechanical stretching or compression (27, 28), expression of the endosomal Rab5 protein (29), exposure of cells to growth factors (30–32), local changes in cell shape (33), and the ability of cells to undergo neighbor exchange (34, 35). In addition, recent studies have also identified a functional link between cell cycle progression and force fluctuation leading to dynamic behavior of cultured epithelial monolayers (36, 37).In this study, we have investigated a mechanical link between quiescence exit and activation of large-scale cell sheet displacements. Using traction force microscopy (TFM), we found that confluent cell monolayers install an actinomyosin-based system during quiescence that produces a coordinated burst of contractile forces and intercellular tension across the epithelial monolayer immediately following exposure to serum-borne mitogens. By combining experiments and theoretical modeling, we show that the amplified forces are essential for driving coordinated cell sheet displacements within otherwise motility-restricted cell monolayers. Furthermore, the magnitude of mechanical forces created during quiescence exit and the extent of cell sheet displacement correlate with quiescence depth. Our study provides evidence that quiescent keratinocyte monolayers possess mechanical preparedness for motility and establish monolayer stress amplification as a strategy for overcoming the motility barrier in confined cell sheets.     

圆锥角膜发病的力学因素及其机制

圆锥角膜是一种以角膜进行性变薄前突为特征的角膜扩张性疾病。其发病机制尚不清楚。体外实验表明力学刺激可能通过升高氧化应激水平和炎症因子浓度而损伤角膜基质细胞,造成角膜细胞外基质降解等一系列变化。大量临床研究证实揉眼、由睡姿引起的眼球压迫等力学因素可能在圆锥角膜发生发展的过程中起重要作用。它们可能通过增加泪液炎症因子水平、造成眼压变化、改变角膜生物力学性能以及机械摩擦直接损伤角膜组织、升高角膜上皮温度等机制对角膜造成影响。本文就力学因素对角膜基质细胞、角膜组织的影响及其在圆锥角膜发病机制中可能的作用进行阐述,以期为预防和管理圆锥角膜提供参考。     

Estimating Low- and High-Cyclic Fatigue of Polyimide-CF-PTFE Composite through Variation of Mechanical Hysteresis Loops

The fatigue properties of neat polyimide and the “polyimide + 10 wt.% milled carbon fibers + 10 wt.% polytetrafluoroethylene” composite were investigated under various cyclic loading conditions. In contrast to most of the reported studies, constructing of hysteresis loops was performed through the strain assessment using the non-contact 2D Digital Image Correlation method. The accumulation of cyclic damage was analyzed by calculating parameters of mechanical hysteresis loops. They were: (i) the energy losses (hysteresis loop area), (ii) the dynamic modulus (proportional to the compliance/stiffness of the material) and (iii) the damping capacity (calculated through the dissipated and total mechanical energies). On average, the reduction in energy losses reached 10–18% at the onset of fracture, whereas the modulus variation did not exceed 2.5% of the nominal value. The energy losses decreased from 20 down to 18 J/m³ (10%) for the composite, whereas they reduced from 30 down to 25 J/m³ (17%) for neat PI in the low-cycle fatigue mode. For high-cycle fatigue, energy losses decreased from 10 to 9 J/m³ (10%) and from 17 to 14 J/m³ (18%) for neat PI and composite, respectively. For this reason, the changes of the energy losses due to hysteresis are of prospects for the characterization of both neat PI and the reinforced PI-based composites.     

Effects of Forging and Heat Treatment on Martensite Lath,Recrystallization and Mechanical Properties Evolution of 18Ni(250) Maraging Steel

The manufacturing process of maraging steel parts include forging, heat treatment and other technological links, and the strengthening mechanism at different stages is different, which has an important impact on the process design of forgings. To investigate the strengthening behavior of maraging steel, forging experiments with different deformation amounts and heat treatment conditions were carried out, and the microstructural and mechanical properties evolution of 18Ni(250) steel was analyzed. The experimental results show that the size of the martensite lath is affected by multiple factors such as the influence of grain size, recrystallization and martensite substructure fraction. The strengthening mechanism of maraging steel during forging and heat treatment is different. Forging combined with heat treatment can refine grains, and the internal defects of the original material can be better eliminated. The thermal deformation can better play the role of grain refinement compared with cyclic phase transformation, which can improve the plasticity of 18Ni(250) maraging steel.     

Network Structure and Properties of Lithium Aluminosilicate Glass

Based on lithium aluminosilicate glass, the composition of glass was optimized by replacing SiO₂ with B₂O₃, and the influence of glass composition on structure and performance was studied. With the increase in B₂O₃ concentrations from 0 to 6.5 mol%, Al₂O₃ always existed in the form of four-coordinated [AlO₄] in the network structure, and B₂O₃ mainly entered the network in the form of four-coordinated [BO₄]. The content of Si-O-Si linkages (Q₄^(0Al)) was always dominant. The incorporation of boron oxide improved the overall degree of polymerization and connectivity of the lithium aluminosilicate glass network structure. An increase in the degree of network polymerization led to a decrease in the thermal expansion coefficient of the glass and an increase in Vickers hardness and density. The durability of the glass in hydrofluoric acid and NaOH and KOH solutions was enhanced overall.     

A New Model Supporting Stability Quality of Materials and Industrial Products

Stabilizing the quality of industrial product materials remains a challenge. This applies mainly to new or significantly modified materials. It also refers to special processes. The tests of product quality can stabilize the quality of industrial product materials. The popular method for this is using the non-destructive testing (NDT). The NDT identifies incompatibility but does not determine the cause of its occurrence. Hence, it was necessary to support the process of identifying causes of incompatibilities in products. The purpose of the article was to develop a model based on a new approach to determine the ranking of actions that are possible as part of the process of stabilizing the quality of industrial products. The model was developed to improve quality through sequential and systematic methods of identification (and reduce) and incompatibility. The quality management techniques and decision method were applied and combined in this model, i.e., SMART(-ER) the method, method of selecting a team of experts, brainstorming (BM), Ishikawa diagram with the 5M rule, Likert scale validation technique, arithmetic average, and Grey Relational Analysis (GRA). The test of this model was carried out to find cracks in the outer hull of 418 alloy four-point bearing (CPW-S 5616), which was identified by NDT (magnetic-powder method). As a result, a ranking of activities was obtained to stabilize the quality of the product and the main cause of incompatibility was indicated, i.e., the cause which can influence to the most degree influence on occurrence the incompatibility. The originality of the proposed model is an application in the right order of specially selected and combined qualitative methods and supporting decision methods. The finding of causes of incompatibility of products is the basis of product improvement in the area of stabilizing the quality of materials, mainly by the occurrence of special processes. The universality of the model refers to the possibility of its application for any material, processes of its formation, and processes of products, and any incompatibilities where the model can be integrated with quality control.     

A Study on the Design Depth of Permeable Road Pavement through Dynamic Load Experiment

This study investigated vertical strain and stress through a dynamic load experiment at the testing area of Ke-Da Road, Pingtung, Taiwan. A thirty-five-ton truck was moved at constant speeds of 40, 60, and 80 km/h to simulate heavy load conditions to study the mechanical variations. From the results, it was found that the strain and stress curves of the permeable road pavement showed asymmetry due to the viscoelastic property of the open-grade friction course. The results showed that vertical strains and vertical stresses of permeable road pavement were greatly affected by the axle configuration and the change in traffic speed. Furthermore, to propose the design thickness of a permeable road pavement, the pavement strain and stress were modelled with respect to depth using regression based on these collected data. According to the stress regression models and considering the construction uncertainty, the recommend design depth of a permeable pavement is 30 cm. The findings of this study would be helpful in determining the permeable road pavement depth when subjected to heavy traffic load, and the material combination of open-graded friction concrete, porous asphalt concrete, and permeable cement concrete was proposed in this study during the design period.     

Effects of Processing Parameters on the Microstructure and Mechanical Properties of Nanoscaled WC-10Co Cemented Carbide

This work was mainly focused on the processing-parameter-related microstructure and properties of ultrafine WC-10Co-0.4VC-0.5Cr₃C₂ cemented carbide. The samples were prepared via a spark plasma sintering (SPS) technique using nano WC and Co powders and the corresponding inhibitor VC and Cr₃C₂ powders. The influence of the processing process on the microstructure and mechanical properties of ultrafine-grained cemented carbide was investigated under different ball-milling times and sintering temperatures. The results showed that the grain size of WC decreased with increasing ball-milling time and decreasing sintering temperature and that the specific gravity of ε-Co increased with increasing ball-milling time. The hardness of cemented carbide increased with increasing ball-milling time and decreased with increasing sintering temperature due to the corresponding variation in grain size and the relative density of samples. The transverse fracture strength (TRS) was mainly affected by ball-milling time. The increase in ball-milling time led to decreased TRS values, mainly ascribed to the formation of WC particle agglomeration and the decreased WC-Co eutectic temperature. In addition, temperature changes were found to have little effect on TRS. The samples sintered at 1250 °C with a ball-milling time of 60 h had comprehensive mechanical properties. Their average grain size, relative density, hardness, and TRS were 355.5 nm, 95.79%, 2035.5 kg/mm², and 2155.99 MPa, respectively.