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1.
为探究水牛角的结构性能关系,基于上海同步辐射光源搭建了高分辨原位CT系统,对水牛角角鞘进行初始表征和准静态压缩下的实时表征,并通过Top-Hat方法提取了角鞘内孔洞三维形貌。结果显示,水牛角角鞘孔隙率在1%左右,椭圆柱状孔洞沿牛角生长方向排列成线,首尾相连却并未连通,均匀分布在波浪状片层之间。孔洞特征椭球的轴长分布满足对数正态分布,长轴和短轴的长度均值分别为7μm和3μm。原位CT结果表明,角鞘在屈服之后,初始孔洞首先扩张而形成微裂纹,随后微裂纹沿着片层界面由外向内发生桥接,片层发生局部屈曲和层间开裂,形成宏观裂纹,导致角鞘内裂纹密度急剧上升。片层之间不仅存在大量纤维黏接(提高了层间拉伸/剪切强度),而且孔洞互不连通,这些因素抑制了层间裂纹的快速传播,使得各处裂纹只能独立缓慢发展而无法贯通样品。波浪状片层使裂纹传播路径更加曲折,层间屈曲增加了片层摩擦耗能。这些机制使得牛角表现出加工硬化,也是牛角在纵向方向呈现优良韧性的主要原因。  相似文献   
2.
Polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) composite nanofibrous membranes immobilized with nano-titanium dioxide (TiO2) and graphene oxide (GO) were prepared by electrospinning and ultrasonic-assisted electrospinning. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) confirmed that TiO2 and GO were more evenly dispersed on the surface and inside of the nanofibers after 45 min of ultrasonic treatment. Adding TiO2 and GO reduced the fiber diameter; the minimum fiber diameter was 84.66 ± 40.58 nm when the mass ratio of TiO2-to-GO was 8:2 (PAN/β-CD nanofibrous membranes was 191.10 ± 45.66 nm). Using the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB) as pollutant models, the photocatalytic activity of the nanofibrous membrane under natural sunlight was evaluated. It was found that PAN/β-CD/TiO2/GO composite nanofibrous membrane with an 8:2 mass ratio of TiO2-to-GO exhibited the best degradation efficiency for the dyes. The degradation efficiency for MB and MO were 93.52 ± 1.83% and 90.92 ± 1.52%, respectively. Meanwhile, the PAN/β-CD/TiO2/GO composite nanofibrous membrane also displayed good antibacterial properties and the degradation efficiency for MB and MO remained above 80% after 3 cycles. In general, the PAN/β-CD/TiO2/GO nanofibrous membrane is eco-friendly, reusable, and has great potential for the removal of dyes from industrial wastewaters.  相似文献   
3.
Suspension culture is an essential large-scale cell culture technique for biopharmaceutical development and regenerative medicine. To transition from monolayer culture on the culture surface of a flask to suspension culture in a bioreactor, a pre-specified cell number must first be reached. During this period of preparation for suspension culture, static suspension culture in a flask is generally performed because the medium volume is not large enough to use a paddle to circulate the medium. However, drawbacks to this static method include cell sedimentation, leading to high cell density near the bottom and resulting in oxygen and nutrient deficiencies. Here, we propose a suspension culture method with acoustic streaming induced by ultrasonic waves in a T-flask to create a more homogeneous distribution of oxygen, nutrients, and waste products during the preparation period preceding large-scale suspension culture in a bioreactor. To demonstrate the performance of the ultrasonic method, Chinese hamster ovary cells were cultured for 72 h. Results showed that, on average, the cell proliferation was improved by 40% compared with the static method. Thus, the culture time required to achieve a 1000-fold increase could be reduced by 32 h (a 14% reduction) compared with the static method. Furthermore, the ultrasonic irradiation did not compromise the metabolic activity of the cells cultured using the ultrasonic method. These results demonstrate the effectiveness of the ultrasonic method for accelerating the transition to large-scale suspension culture.  相似文献   
4.
为简化构架避雷针风振时域计算从而有效降低计算耗时,以单跨和三跨构架避雷针结构为例,根据构架体系的结构特性和风振特点,提出一种简化计算方法,即对每个塔架单独建模并考虑结构刚度和质量系统的一致性和横梁荷载的等效加载,从而对每个塔架单独进行动力计算,并对这种简化方法的合理性进行了验证.研究发现,构架避雷针的频率较小,风振效应较为显著,但在各方向均以一阶振型为绝对主力;构架避雷针的塔架在平面外的荷载耦联效应极小,平面内也仅表现有位移均值的耦联效应:这两个结构特性也为风振简化计算提供了便利.对每个塔架的简化模型,通过在塔架与原横梁连接处设置弹簧和附加质量来实现对原结构一阶振型的等效,并通过影响线法将横梁分布风荷载等效为塔架的集中荷载.由此简化方法所得的结构风振静动力响应结果均与原始结构有良好一致性,并且计算效率得以显著提升.  相似文献   
5.
The effects of air sparging (0–16 L min−1) and mechanical mixing (0–400 rpm) on enhancing the sonochemical degradation of rhodamine B (RhB) was investigated using a 28 kHz sonoreactor. The degradation of RhB followed pseudo first-order kinetics, where sparging or mixing induced a large sonochemical enhancement. The kinetic constant varied in three stages (gradually increased → increased exponentially → decreased slightly) as the rate of sparging or mixing increased, where the stages were similar for both processes. The highest sonochemical activity was obtained with sparging at 8 L min−1 or mixing at 200 rpm, where the standing wave field was significantly deformed by sparging and mixing, respectively. The cavitational oxidation activity was concentrated at the bottom of the sonicator when higher sparging or mixing rates were employed. Therefore, the large enhancement in the sonochemical oxidation was attributed mainly to the direct disturbance of the ultrasound transmission and the resulting change in the cavitation-active zone in this study. The effect of the position of air sparging and mixing was investigated. The indirect inhibition of the ultrasound transmission resulted in less enhancement of the sonochemical activity. Moreover, the effect of various sparging gases including air, N2, O2, Ar, CO2, and an Ar/O2 (8:2) mixture was compared, where all gases except CO2 induced an enhancement in the sonochemical activity, irrespective of the concentration of dissolved oxygen. The highest activity was obtained with the Ar/O2 (8:2) mixture. Therefore, it was revealed that the sonochemical oxidation activity could be further enhanced by applying gas sparging using the optimal gas.  相似文献   
6.
The aim of this work is to perform design and optimization of a cavitating device based on CFD simulation. A set of operational and geometrical parameters such as convergence angle, divergence angle, length of throat, and inlet pressure that can affect the hydrodynamic cavitation phenomenon generating in a Venturi are evaluated through CFD simulation and experimental approaches. Response surface methodology (RSM) was employed to achieve the optimum geometrical configuration. The CFD results show that the maximum cavitation zone in the Venturi can be obtained when half angle of the convergence section, throat length and half angle of the divergence section are 22.7°, 4 mm, and 6.5°, respectively. A maximum decolorization of 38.8% has been obtained using the designed Venturi at cavitation number (Cv) of 0.12. Additionally, the results were compared to that of various orifice plates. A decolorization of 26.2% using 33 holes orifice plate and 11.55% in one hole orifice plate approved the superiority of the designed Venturi.  相似文献   
7.
In this study, scallop mantle protein was treated by ultrasound at different powers, and then analyzed by ANS fluorescent probes, circular dichroism spectroscopy, endogenous fluorescence spectrum, DNTB colorimetry and in-vitro digestion model to elucidate the structure–function relationship. The results indicated that ultrasound can significantly affect the secondary structure of scallop mantle protein like enhancing hydrophobicity, lowering the particle size, increasing the relative contents of α-helix and decreasing contents of β-pleated sheet, β-turn and random coil, as well as altering intrinsic fluorescence intensity with blue shift of maximum fluorescence peak. But ultrasound had no effect on its primary structure. Moreover, the functions of scallop mantle protein were regulated by modifying its structures by ultrasound. Specifically, the protein had the highest performance in foaming property and in-vitro digestibility under ultrasonic power of 100 W, oil binding capacity under 100 W, water binding capacity under 300 W, solubility and emulsification capacity under 400 W, and emulsion stability under 600 W. These results prove ultrasonic treatment has the potential to effectively improve functional properties and quality of scallop mantle protein, benefiting in comprehensive utilization of scallop mantles.  相似文献   
8.
刘治平 《运筹学学报》2021,25(3):173-182
随着高通量技术的发展,越来越多的生物医学组学数据亟需处理与分析,基于运筹优化的生物信息学方法是有效解析高维生物医学数据的重要途径之一。综述了近年来在基因调控网络推断方面的研究进展。针对不同类型的转录组学数据和研究目的,分别建立了相应的基因调控网络推断方法,主要包括先验基因调控网络数据库的建立、基于条件互信息的因果网络推断、基于微分方程的动态基因调控网络推断、转录调控和转录后调控协同作用的网络推断以及基因调控网络活性评价等,并展望了基因调控网络推断的重要研究方向。  相似文献   
9.
科学评价大学生科研创新能力对我国科研水平的提高具有重要意义.采用机器学习模型来预测大学生科研能力可以起到良好的效果,提出一种GAXGBoost模型来实现对大学生的科研能力预测.此模型是以Xgboost算法为基础,然后充分利用遗传算法的全局搜索能力自动搜索Xgboost最优超参数,避免了人为经验调参不准确的缺陷,最后采用精英选择策略以此确保每一轮都是最佳的进化结果.通过分析表明,所采用的GAXGBoost模型在大学生科研能力预测的结果中具有很高的精度,将此模型与Logistic Regression、Random Forest、SVM等模型进行对比,GAXGBoost模型的预测精度最高.  相似文献   
10.
In this paper we consider minimizers of the functionalmin{λ1(Ω)++λk(Ω)+Λ|Ω|,:ΩD open} where DRd is a bounded open set and where 0<λ1(Ω)λk(Ω) are the first k eigenvalues on Ω of an operator in divergence form with Dirichlet boundary condition and with Hölder continuous coefficients. We prove that the optimal sets Ω have finite perimeter and that their free boundary ΩD is composed of a regular part, which is locally the graph of a C1,α-regular function, and a singular part, which is empty if d<d, discrete if d=d and of Hausdorff dimension at most dd if d>d, for some d{5,6,7}.  相似文献   
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