anisotropy

各向异性
  • 文章类型: Journal Article
    大自然为我们设计仿生功能曲面提供了丰富的灵感。许多类型的植物叶子具有特殊的润湿性,各向异性,和附着力广泛用于许多工程应用。受润湿性的启发,各向异性,和黏土叶的粘附,使用激光扫描和化学修饰相结合的简便方法成功制备了indocalamus叶片的仿生上下表面(BUS和BLSs)。结果表明,BUSs和BLSs获得了与indocalamus叶的上表面和下表面相似的结构特征,并表现出增强和更可控的润湿性,各向异性,和附着力。更重要的是,我们对润湿性进行了详细的比较分析,各向异性,BUSs和BLSs之间的附着力。最后,还探索了BUS和BLS的相应潜在应用,包括自我清洁,液体操纵,和雾的收集,从而扩大其实际效用。我们相信,这项研究可以促进新型生物模型的研究,并为多功能仿生表面的发展提供重要的见解。
    Nature provides us with a wealth of inspiration for the design of bionic functional surfaces. Numerous types of plant leaves with exceptional wettability, anisotropy, and adhesion are extensively employed in many engineering applications. Inspired by the wettability, anisotropy, and adhesion of indocalamus leaves, bionic upper and lower surfaces (BUSs and BLSs) of the indocalamus leaf were successfully prepared using a facile approach combining laser scanning and chemical modification. The results demonstrated the BUSs and BLSs obtained similar structural features to the upper and lower surfaces of the indocalamus leaf and exhibited enhanced and more-controllable wettability, anisotropy, and adhesion. More importantly, we conducted a detailed comparative analysis of the wettability, anisotropy, and adhesion between BUSs and BLSs. Finally, BUSs and BLSs were also explored for the corresponding potential applications, including self-cleaning, liquid manipulation, and fog collection, thereby broadening their practical utility. We believe that this study can contribute to the enrichment of the research on novel biological models and provide significant insights into the development of multifunctional bionic surfaces.
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  • 文章类型: Journal Article
    利用各向异性Drucker模型研究了5754-H111铝合金在不同应力条件下三种塑性工作的屈服行为。发现当塑性工作为30MPa时,各向异性Drucker模型具有最准确的预测。将Hill48和Yld91模型与Drucker模型进行比较,结果表明,各向异性Drucker和Yld91模型均能准确预测合金的屈服行为。在AFR下进行圆柱拉伸有限元分析,但是无法准确预测耳部外观的位置和高度。各向异性Drucker模型用于预测非AFR下的耳部行为,可以准确预测耳部现象。使用三种不同的屈服函数组合进行了数值模拟:各向异性屈服函数和各向异性塑性势函数(AYAPP),各向异性屈服函数和各向同性塑性势函数(AYIPP),以及各向同性屈服函数和各向异性塑性势函数(IYAPP)。结论是,塑性势函数对预测抽穗行为的影响比屈服函数更重要。
    The yield behavior of aluminum alloy 5754-H111 under different stress conditions for three kinds of plastic work is studied using an anisotropic Drucker model. It is found that when the plastic work is 30 MPa, the anisotropic Drucker model has the most accurate prediction. Comparing the Hill48 and Yld91 models with the Drucker model, the results show that both the anisotropic Drucker and Yld91 models can accurately predict the yield behavior of the alloy. Cylinder drawing finite element analysis is performed under the AFR, but it is not possible to accurately predict the position and height of earing appearance. The anisotropic Drucker model is used to predict the earing behavior under the non-AFR, which can accurately predict the earing phenomenon. Numerical simulation is conducted using three different combinations of yield functions: the anisotropic yield function and the anisotropic plastic potential function (AYAPP), the anisotropic yield function and the isotropic plastic potential function (AYIPP), and the isotropic yield function and the anisotropic plastic potential function (IYAPP). It is concluded that the influence of the plastic potential function on predicting earing behavior is more critical than that of the yield function.
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  • 文章类型: Journal Article
    增材制造(AM)是一种逐层构建零件的技术。在过去的十年里,金属增材制造(AM)技术发展迅速,形成了完整的产业链。AM金属零件在众多行业中使用,包括生物医学,航空航天,汽车,海洋,和离岸。与现有制造工艺相比,可以在更大程度上改进部件的设计,这可以显著提高性能。已经报道了增材制造金属材料各向异性的研究,他们描述了使用增材制造工艺制备不同金属材料的优点和缺点;然而,在同一篇文章中,很少有深入而全面的研究总结不同类型增材制造金属材料的微观结构和力学性能。本文首先概述了增材制造过程之间的复杂关系,微观结构,和金属属性。然后解释了粉末床融合(PBF)和定向能量沉积(DED)的基本原理。接着描述了增材制造过程中的熔池和热影响区,并分析了它们对成形零件微观结构的影响。随后,增材制造钛合金的机械性能和典型的微观结构,不锈钢,镁铝合金,和高温合金,随着它们的各向异性,进行了总结和介绍。总结表明,导致金属AM零件机械性能各向异性的因素是其独特的微观结构特征或制造缺陷。该各向异性可以通过后热处理来改善。最后,介绍了金属AM各向异性的最新研究。
    Additive manufacturing (AM) is a technology that builds parts layer by layer. Over the past decade, metal additive manufacturing (AM) technology has developed rapidly to form a complete industry chain. AM metal parts are employed in a multitude of industries, including biomedical, aerospace, automotive, marine, and offshore. The design of components can be improved to a greater extent than is possible with existing manufacturing processes, which can result in a significant enhancement of performance. Studies on the anisotropy of additively manufactured metallic materials have been reported, and they describe the advantages and disadvantages of preparing different metallic materials using additive manufacturing processes; however, there are few in-depth and comprehensive studies that summarize the microstructural and mechanical properties of different types of additively manufactured metallic materials in the same article. This paper begins by outlining the intricate relationship between the additive manufacturing process, microstructure, and metal properties. It then explains the fundamental principles of powder bed fusion (PBF) and directed energy deposition (DED). It goes on to describe the molten pool and heat-affected zone in the additive manufacturing process and analyzes their effects on the microstructure of the formed parts. Subsequently, the mechanical properties and typical microstructures of additively manufactured titanium alloys, stainless steel, magnesium-aluminum alloys, and high-temperature alloys, along with their anisotropy, are summarized and presented. The summary indicates that the factors leading to the anisotropy of the mechanical properties of metallic AM parts are either their unique microstructural features or manufacturing defects. This anisotropy can be improved by post-heat treatment. Finally, the most recent research on the subject of metal AM anisotropy is presented.
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  • 文章类型: Journal Article
    长老会,或年龄相关的听力损失,影响老年人和狗,显著损害他们的社交互动和认知。在人类中,老年性耳聋涉及周围和中枢听觉系统的变化,中央变化可能独立发生。虽然狗的外周性老年性耳聋是有据可查的,关于中央变化的研究仍然有限。扩散张量成像(DTI)是检测和量化脑白质异常的有用工具。本研究使用DTI探索老年犬的中枢听觉通路,旨在提高我们对犬类老年性耳聋的认识。招募超过预期寿命75%的狗,并通过脑干听觉诱发反应测试进行筛查,以选择没有严重周围听力损失的狗。使用3T磁共振扫描仪扫描16只符合标准的狗。基于轨迹的空间统计用于分析中枢听觉通路。在声辐射中发现分数寿命与分数各向异性之间存在显着负相关。提示中枢听觉系统中与年龄相关的白质变化。这些变化,在没有严重周围听力损失的狗中观察到,可能有助于中央长老会的发展。
    Presbycusis, or age-related hearing loss, affects both elderly humans and dogs, significantly impairing their social interactions and cognition. In humans, presbycusis involves changes in peripheral and central auditory systems, with central changes potentially occurring independently. While peripheral presbycusis in dogs is well-documented, research on central changes remains limited. Diffusion tensor imaging (DTI) is a useful tool for detecting and quantifying cerebral white matter abnormalities. This study used DTI to explore the central auditory pathway of senior dogs, aiming to enhance our understanding of canine presbycusis. Dogs beyond 75% of their expected lifespan were recruited and screened with brainstem auditory evoked response testing to select dogs without severe peripheral hearing loss. Sixteen dogs meeting the criteria were scanned using a 3 T magnetic resonance scanner. Tract-based spatial statistics was used to analyze the central auditory pathways. A significant negative correlation between fractional lifespan and fractional anisotropy was found in the acoustic radiation, suggesting age-related white matter changes in the central auditory system. These changes, observed in dogs without severe peripheral hearing loss, may contribute to central presbycusis development.
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  • 文章类型: Journal Article
    膨胀收缩特性土壤在干燥过程中表现出很高的开裂敏感性,这对各种地质灾害构成了重大风险。其中,干燥收缩的发生是开裂现象的先决条件。因此,了解与干燥收缩机理相关的具体特征至关重要。为了研究膨胀收缩特征土壤的干燥收缩行为,对红黏土和膨胀土的长条样进行了一系列干缩试验。利用三维数字图像相关(DIC)技术,表面位移,应变,并获得了土壤样品在干燥过程中的各向异性收缩率,分析了尺寸效应对胀缩特征土干燥收缩的影响。研究结果如下:土样在X和Y方向上的位移发展可分为两个阶段:线性生长阶段和稳定位移阶段。在Z方向,土面变形可分为三个阶段:土面拱,垂直收缩,和收缩稳定。胀缩特征土的干缩表现出各向异性,垂直收缩率最大,其次是纵向,然后是横向。此外,土壤样品收缩表现出尺寸效应,其中在所有方向上的收缩率随着样品宽度和厚度的增加而增加。在干燥收缩过程中,土壤表面的应力状态从初始拉伸应变演变为随后的压缩应变。土样内不同位置和时间的应变不均匀,导致样品收缩的不均匀性和各向异性。该研究为研究胀缩特性土的开裂机理提供了重要的见解,并为相关实验室实验提供了有价值的参考。这将有助于更好地预测和控制由胀缩特征土壤干燥收缩引起的地质灾害。
    Swell-shrink characteristic soils exhibit a high susceptibility to cracking during the drying process, which poses a significant risk of various geological disasters. Among these, the occurrence of drying shrinkage acts as a prerequisite for the cracking phenomenon. Therefore, it is of utmost importance to comprehend the specific characteristics associated with the drying shrinkage mechanism. To investigate the drying shrinkage behavior of swell-shrink characteristic soils, a series of drying shrinkage experiments were conducted on long strip samples of red clay and expansive soil. Utilizing three-dimensional digital image correlation (DIC) technology, the surface displacement, strain, and anisotropic shrinkage rates of the soil samples during the drying process were obtained, and the size effect on the drying shrinkage of swell-shrink characteristic soil were analyzed. The research findings are as follows: The displacement development of the soil samples in the X and Y directions can be divided into two stages: a linear growth stage and a stable displacement stage. In the Z direction, the soil surface deformation can be divided into three stages: soil surface arching, vertical shrinkage, and shrinkage stabilization. The drying shrinkage of swell-shrink characteristic soil exhibits anisotropy, with the vertical shrinkage rate being the largest, followed by the longitudinal and then the transverse directions. Additionally, the soil sample shrinkage exhibits a size effect, whereby the shrinkage rates in all directions increase with increasing sample width and thickness. During the drying shrinkage process, the stress state on the soil surface evolves from initial tensile strain to subsequent compressive strain. The strain at different positions and times within the soil sample is not uniform, resulting in the non-uniformity and anisotropy of the sample shrinkage. This study provides important insights into the cracking mechanism of swell-shrink characteristic soils and serves as a valuable reference for related laboratory experiments, which will contribute to better prediction and control the geological hazards caused by the drying shrinkage of swell-shrink characteristic soils.
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  • 文章类型: Journal Article
    聚酰亚胺(PI)气凝胶在航空航天中具有多种应用,国防,军工,和轨道交通设备。本文报道了一系列超轻量级,高弹性,高强度,低热导率,冰模板法制备的高阻燃rGO/PI纳米复合气凝胶。冻结过程(单向冻结和随机冻结)的影响,化学成分,和环境温度(-196-200°C)对形态,机械,系统研究了气凝胶的热性能。结果表明,单向气凝胶具有各向异性的力学性能和热性能。水平方向的压缩显示出高弹性,高抗疲劳性,和优越的隔热。同时,在垂直方向,它表现出高强度(PI-G-9达到14MPa)。在水平方向上进行10,000次压缩循环后(在50%应变下),单向PI-G-5气凝胶仍保留90.32%的高度保留率,和78.5%的应力保留,并表现出较低的稳定能量损失系数(22.11%)。它还具有低热导率(32.8mWm-1K-1),并通过在200°C下保持30分钟而表现出良好的隔热性能。有趣的是,气凝胶的弹性随着温度的降低而增强,在液氮中压缩时,高度回收率高达100%。更重要的是,rGO/PI气凝胶可以在很宽的温度范围(-196-200°C)内使用,并且具有43.3%至48.1%的高极限氧指数(LOI)。因此,这项工作可以提供一个可行的方法来设计隔热和阻燃保护材料具有优良的机械性能,适用于恶劣的环境。
    Polyimide (PI) aerogels have various applications in aerospace, national defense, military industry, and rail transit equipment. This paper reports a series of ultra-lightweight, high elasticity, high strength, low thermal conductivity, and high flame retardant rGO/PI nanocomposite aerogels prepared by the ice templating method. The effects of freezing processes (unidirectional freezing and random freezing), chemical composition, and environmental temperature (-196-200 °C) on the morphology, mechanical, and thermal properties of the aerogels were systematically studied. The results indicated that unidirectional aerogels exhibit anisotropic mechanical properties and thermal performance. Compression in the horizontal direction showed high elasticity, high fatigue resistance, and superior thermal insulation. Meanwhile, in the vertical direction, it demonstrated high strength (PI-G-9 reaching 14 MPa). After 10,000 cycles of compression in the horizontal direction (at 50 % strain), the unidirectional PI-G-5 aerogel still retains 90.32 % height retention, and 78.5 % stress retention, and exhibited a low stable energy loss coefficient (22.11 %). It also possessed a low thermal conductivity (32.8 mW m-1 K-1) and demonstrated good thermal insulation performance by sustaining at 200 °C for 30 min. Interestingly, the elasticity of the aerogels was enhanced with decreasing temperatures, achieving a height recovery rate of up to 100 % when compressed in liquid nitrogen. More importantly, the rGO/PI aerogels could be utilized over a wide temperature range (-196-200 °C) and had a high limiting oxygen index (LOI) ranging from 43.3 to 48.1 %. Therefore, this work may provide a viable approach for designing thermal insulation and flame-retardant protective materials with excellent mechanical properties that are suitable for harsh environments.
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  • 文章类型: Journal Article
    研究表明,肌萎缩侧索硬化症(ALS)损害了白质纤维束的完整性,主要影响电机纤维。然而,尚不确定这些纤维的完整性是否会影响ALS的风险。我们进行了双向双样本孟德尔随机化(MR)和多变量MR分析,以评估纤维束(包括皮质脊髓束(CST)和call体(CC))的完整性与ALS风险之间的关联关系。从已发表的全基因组关联研究(GWAS)获得了特定纤维束的遗传工具变量,包括来自五个扩散磁共振成像(dMRI)数据集的33,292名欧洲个体。ALS的汇总水平GWAS数据来自27,205名ALS患者和110,881名对照。MR结果表明,CC(GCC)类型中分数各向异性(FA)的第一主成分(PC1)的增加与ALS的风险增加相关(PFDR=0.001,比值比=1.363,95%置信区间1.178-1.577)。尽管其他神经影像学表型[CST中的平均扩散率,CST中的径向扩散率(RD),海湾合作委员会中的FA,CC(BCC)正文中的PC1,CST中的PC1,和RD在GCC]没有通过修正,他们也被认为与ALS的风险有暗示性关联.没有证据表明ALS引起纤维束完整性的变化。总之,这项研究的结果为特定纤维束的完整性与ALS风险之间的潜在关联提供了遗传支持.GCC和BCC中更高的纤维完整性可能是ALS的风险因素,而CST中更大的纤维完整性可能对ALS具有保护作用。这项研究提供了对ALS发展的见解。
    Studies suggest that amyotrophic lateral sclerosis (ALS) compromises the integrity of white matter fiber tracts, primarily affecting motor fibers. However, it remains uncertain whether the integrity of these fibers influences the risk of ALS. We performed bidirectional two-sample Mendelian randomization (MR) and multivariable MR analyses to evaluate the associative relationships between the integrity of fiber tracts [including the corticospinal tract (CST) and corpus callosum (CC)] and the risk of ALS. Genetic instrumental variables for specific fiber tracts were obtained from published genome-wide association studies (GWASs), including 33,292 European individuals from five diffusion magnetic resonance imaging (dMRI) datasets. Summary-level GWAS data for ALS were derived from 27,205 ALS patients and 110,881 controls. The MR results suggested that an increase in the first principal component (PC1) of fractional anisotropy (FA) in the genu of the CC (GCC) was correlated with an increased risk of ALS (PFDR = 0.001, odds ratio = 1.363, 95% confidence interval 1.178-1.577). Although other neuroimaging phenotypes [mean diffusivity in the CST, radial diffusivity (RD) in the CST, FA in the GCC, PC1 in the body of the CC (BCC), PC1 in the CST, and RD in the GCC] did not pass correction, they were also considered to have suggestive associations with the risk of ALS. No evidence revealed that ALS caused changes in the integrity of fiber tracts. In summary, the results of this study provide genetic support for the potential association between the integrity of specific fiber tracts and the risk of ALS. Greater fiber integrity in the GCC and BCC may be a risk factor for ALS, while greater fiber integrity in the CST may have a protective effect on ALS. This study provides insights into ALS development.
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  • 文章类型: Journal Article
    该研究调查了用废轮胎制成的橡胶颗粒代替沙子的效果-按体积计高达40%-并包含聚丙烯(PP)纤维。与钢纤维不同,这可能会导致印刷过程中的操作挑战和表面不规则,PP纤维的柔韧性在混凝土基体中很好地结合在一起。这种集成确保了平滑的挤出和高质量的表面光洁度,提高混凝土的可印刷性。研究结果表明,包括橡胶颗粒和PP纤维会影响混凝土的性能,随着橡胶含量的增加,抗压强度和抗弯强度普遍下降。然而,PP纤维增强混合物保持足够的结构强度,证明各向异性抗压强度高于30MPa,弯曲强度为4MPa。这些结果强调了在可持续建筑实践中使用带有PP纤维的橡胶3D打印混凝土的可行性。与标准(ACI318:2018)保持一致,并为环保和创新的施工方法做出贡献。
    The research investigates the effects of substituting sand with rubber particles derived from waste tyres-up to 40% by volume-and the inclusion of polypropylene (PP) fibres. Unlike steel fibres, which can cause operational challenges and surface irregularities in the printing process, PP fibres\' flexibility integrates well within the concrete matrix. This integration ensures smooth extrusion and a high-quality surface finish, enhancing the printability of the concrete. The study\'s findings reveal that including rubber particles and PP fibres impacts the concrete\'s properties, showing a general decline in compressive and flexural strengths as the rubber content increases. Nevertheless, the PP fibre-enhanced mixtures maintain sufficient structural strength, demonstrating an anisotropic compressive strength above 30 MPa and a flexural strength of 4 MPa. These results underscore the feasibility of using rubberised 3D-printed concrete with PP fibres in sustainable construction practices, aligning with standards (ACI 318:2018) and contributing to eco-friendly and innovative construction methodologies.
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  • 文章类型: Journal Article
    背景:基于弥散谱成像(DSI)研究特发性正常压力脑积水(iNPH)中白质变化与心室扩张之间的关系。
    方法:我们纳入了32例使用3TMRI扫描仪进行DSI的iNPH患者。侧脑室被手动分割,并测量心室容积。在研究中使用了两种方法:手动感兴趣区域(ROI)描绘和气道扩散轮廓分析。提取不同白质区域的一般各向异性分数(GFA)和各向异性分数(FA),包括双侧内囊(前肢和后肢)和call体(身体,genu,和splenium)与手动ROI描述。提取每位患者大脑中的18个主要束;计算每个纤维上100个等距节点的扩散指标,用Spearman相关系数确定iNPH患者弥散测量值与心室容积的相关性。
    结果:所有ROI的GFA和FA与侧脑室容积无显著相关性。然而,在道扩散剖面分析中,侧脑室容积与部分扣带束呈正相关,左皮质脊髓束,和双侧丘脑后方辐射,而与双侧海马旁扣带呈负相关(均p<0.05)。
    结论:iNPH中的心室扩大对心室周围一些白质纤维束的影响是有限的,并且是极化的,大多数白质纤维束完整性变化与心室扩大无关;这反映了多种病理机制可能已结合导致iNPH中的白质改变。
    BACKGROUND: To investigate the association between white matter changes and ventricular expansion in idiopathic normal pressure hydrocephalus (iNPH) based on diffusion spectrum imaging (DSI).
    METHODS: We included 32 patients with iNPH who underwent DSI using a 3T MRI scanner. The lateral ventricles were manually segmented, and ventricular volumes were measured. Two methods were utilised in the study: manual region-of-interest (ROI) delineation and tract diffusion profile analysis. General fractional anisotropy (GFA) and fractional anisotropy (FA) were extracted in different white matter regions, including the bilateral internal capsule (anterior and posterior limbs) and corpus callosum (body, genu, and splenium) with manual ROI delineation. The 18 main tracts in the brain of each patient were extracted; the diffusion metrics of 100 equidistant nodes on each fibre were calculated, and Spearman\'s correlation coefficient was used to determine the correlation between diffusion measures and ventricular volume of iNPH patients.
    RESULTS: The GFA and FA of all ROI showed no significant correlation with lateral ventricular volume. However, in the tract diffusion profile analysis, lateral ventricular volume was positively correlated with part of the cingulum bundle, left corticospinal tract, and bilateral thalamic radiation posterior, whereas it was negatively correlated with the bilateral cingulum parahippocampal (all p < 0.05).
    CONCLUSIONS: The effect of ventricular enlargement in iNPH on some white matter fibre tracts around the ventricles was limited and polarizing, and most white matter fibre tract integrity changes were not associated with ventricular enlargement; this reflects that multiple pathological mechanisms may have been combined to cause white matter alterations in iNPH.
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  • 文章类型: Journal Article
    陶瓷晶粒的取向和形状总是被忽视,导致烧结过程中大量的信息没有被挖掘出来。在这项研究中,为了表达晶界能的各向异性,建立了改进的相场模型。详细研究了晶界能各向异性对晶粒取向和形状演化的影响。采用流延法制备铁电陶瓷厚膜。实验和模拟结果的对比表明,晶界能的各向异性导致晶粒取向不均匀和双峰晶粒尺寸分布。晶粒微观结构的定量分析有助于建立与晶界能各向异性程度的关系。我们的发现提供了一种通过计算陶瓷材料SEM图像中的相关参数来判断各向异性程度的新途径。
    The orientation and shape of ceramics grains was always neglected, resulting in a lot of information during sintering has not been excavated. In this study, a modified phase-field model in order to express the anisotropy of grain boundary energy is developed. The effects of the anisotropy of grain boundary energy on the grain orientation and shape evolution are investigated in detail. The ferroelectric ceramic thick films are prepared by tape casting. The comparison of experiment and simulation results shows that the anisotropy of grain boundary energy results in uneven grain orientation and bimodal grain size distribution. The quantitative analysis of grain microstructures helps to establish a relationship with the degree of anisotropy of grain boundary energy. Our findings provide a new way to judge the degree of anisotropy by calculating the relevant parameters in the SEM images of ceramics materials.
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