混凝土结构内冲击波应力传感器设计及其行为

为测量混凝土结构内的冲击波应力,研制了PVDF压力传感器;介绍了传感器的原理和设计思想,通过传感器的标定试验,得出传感器与混凝土介质匹配性能稳定,通过修正传感器灵敏度或采用将传感器打入包体标定的方法可减小应力测量误差;最后介绍了传感器在混凝土结构内药包爆炸应力波测试中的应用。     

着靶速度对刚玉块石混凝土抗侵彻性能的影响

着重对不同着靶速度下,弹体在刚玉块石混凝土中的侵彻情况进行了试验。研究结果表明,弹体的侵彻深度不随靶速度的提高而增加。这与弹体在普通混凝土和岩石中的侵彻现象明显不同,主要是由侵彻弹体发生破坏失去了继续侵彻能力造成的。而且,与普通混凝土或岩石相比,着靶速度越高,刚玉块石混凝土的抗侵彻性能越强。     

固体火箭推进剂起爆技术

针对便携式防空导弹的聚醚复合推进剂进行了余药起爆试验。试验表明,在聚能装药起爆器作用下成功地起爆了推进剂药柱。该技术对战斗部 发动机一体化设计有重要应用价值。     

气泡高速摄影和载荷测试技术综述

气泡运动学和动力学一直为流体力学研究热点之一. 近年来,高速摄影技术和气泡载荷测试设备发展迅速,为人们研究气泡行为和载荷分析提供了强有力的支持. 本文综述高速摄影和载荷测试技术在气泡动力学中的应用与发展. 首先,简要回顾气泡现象的成因和分类;其次,详述高速摄影技术在捕获气泡形态中的应用;再次,回顾和讨论了气泡载荷测试设备以及试验手段的发展;最后,在上述基础上提出了一些尚需进一步完善的问题.     

-196 ℃奥氏体不锈钢母材与焊缝的动态断裂韧性

在-196 ℃对S30408奥氏体不锈钢的母材和焊缝进行了夏比摆锤冲击实验,采用改进的柔度变化率法得到了低温下不锈钢母材夏比试样的起裂点。结果表明,采用改进的柔度变化率法得到的结果比采用传统的柔度变化率法得到的结果更准确。根据实验得到的载荷-位移曲线,结合采用Schindler法和关键曲线法各自所得结果的优点,得到了不锈钢母材的动态裂纹扩展阻力曲线（动态J-R曲线）。依据不锈钢焊缝在低温动载下的载荷-位移曲线及其断裂特征,通过线弹性断裂力学计算获得其动态断裂韧性。     

Chemical Composition and Antibacterial Activity of Lippia multiflora Moldenke Essential Oil from Different Regions of Angola

The purpose of the study was to determine the chemical composition and antibacterial activity of Lippia multiflora Moldenke essential oils (EOs) collected in different regions of Angola. Antibacterial activity was evaluated using the agar wells technique and vapour phase test. Analysis of the oils by GC/MS identified thirty-five components representing 67.5 to 100% of the total oils. Monoterpene hydrocarbons were the most prevalent compounds, followed by oxygenated monoterpenes. The content of the compounds varied according to the samples. The main components were Limonene, Piperitenone, Neral, Citral, Elemol, p-cymene, Transtagetone, and Artemisia ketone. Only one of the eleven samples contained Verbenone as the majority compound. In the vapour phase test, a single oil was the most effective against all the pathogens studied. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of components of the selected EOs and inhibition zone diameter values of agar wells technique allowed us to identify a variability between the plants from the two provinces, but also intraspecific variability between sub-groups within a population. Each group of essential oils constituted a chemotype responsible for their bacterial inhibition capacity. The results presented here suggest that Angolan Lippia multiflora Moldenke has antibacterial properties and could be a potential source of antimicrobial agents for the pharmaceutical and food industry.     

Weighted Cumulative Past Extropy and Its Inference

This paper introduces and studies a new generalization of cumulative past extropy called weighted cumulative past extropy (WCPJ) for continuous random variables. We explore the following: if the WCPJs of the last order statistic are equal for two distributions, then these two distributions will be equal. We examine some properties of the WCPJ, and a number of inequalities involving bounds for WCPJ are obtained. Studies related to reliability theory are discussed. Finally, the empirical version of the WCPJ is considered, and a test statistic is proposed. The critical cutoff points of the test statistic are computed numerically. Then, the power of this test is compared to a number of alternative approaches. In some situations, its power is superior to the rest, and in some other settings, it is somewhat weaker than the others. The simulation study shows that the use of this test statistic can be satisfactory with due attention to its simple form and the rich information content behind it.     

Relationship between Muscle Flexibility and Characteristics of Muscle Contraction in Healthy Women during Different Menstrual Phases

Objective: Skeletal muscle function is vital for preventing injury during exercise. It has been reported that skeletal muscle function fluctuates with the menstrual cycle and is considered one of the causes of injury. This study aimed to clarify the relationship between muscle flexibility and muscle contraction characteristics and their changes with the menstrual cycle. Methods: The subjects were healthy women who voluntarily participated in the study through recruitment posters. Muscle flexibility was measured with the passive knee extension (PKE) test, isokinetic knee flexor strength, and the maximum muscle strength exertion angle under two conditions of 60°/s and 120°/s in dominant hamstrings. Additionally, their correlations were analyzed and compared between the menstrual and ovulatory phases. Results: Sixteen subjects (mean age: 20.56 ± 0.73 years; body mass index: 20.21 ± 1.60) participated in the study. Correlation analysis showed a significant negative correlation between PKE and the maximum muscle strength exertion angle under the condition of 60°/s during the menstrual phase (r = –0.54; p = 0.03). No significant difference was observed in the two-group comparison of the variables measured during the menstrual and ovulatory phases. Conclusion: This study confirmed that the more flexible muscles generate the maximum strength at a more contracted position during the menstrual phase in women. In the future, it is necessary to examine the relationship between the results of this study and exercise performance and injury occurrence.     

Milk-Compositional Study of Metabolites and Pathogens in the Milk of Bovine Animals Affected with Subclinical Mastitis

Bovine milk is an important food component in the human diet due to its nutrient-rich metabolites. However, bovine subclinical mastitis alters the composition and quality of milk. In present study, California mastitis testing, somatic cell count, pH, and electrical conductivity were used as confirmatory tests to detect subclinical mastitis. The primary goal was to study metabolome and identify major pathogens in cows with subclinical mastitis. In this study, 29 metabolites were detected in milk using gas chromatography–mass spectrometry. Volatile acidic compounds, such as hexanoic acid, hexadecanoic acid, lauric acid, octanoic acid, n-decanoic acid, tricosanoic acid, tetradecanoic acid, and hypogeic acid were found in milk samples, and these impart good flavor to the milk. Metaboanalyst tool was used for metabolic pathway analysis and principal component estimation. In this study, EC and pH values in milk were significantly increased (p < 0.0001), whereas fat (p < 0.04) and protein (p < 0.0002) significantly decreased in animals with subclinical mastitis in comparison to healthy animals. Staphylococcus aureus was the predominant pathogen found (n = 54), followed by Escherichia coli (n = 30). Furthermore, antibiotic sensitivity revealed that Staphylococcus aureus was more sensitive to gentamicin (79.6%), whereas Escherichia coli showed more sensitivity to doxycycline hydrochloride (80%).     

An Experimental Study on the Preparation of Soft Rock Similar Materials Using Redispersible Latex Powder as a Modifier

The engineering geological problems of soft rock are common in large slope engineering and underground engineering surrounding rock. In order to study the change in mechanical properties of soft rock under the action of loading, excavation and rainfall, this paper carried out experimental research on similar materials of soft rock. The similar material of soft rock is prepared by using iron fine powder, barite powder and quartz sand as aggregate, gypsum as binder and redispersible latex powder as regulator. A single-factor influence test was designed with the content of redispersible latex powder as variation parameter. Analysis the influence of redispersible latex powder from the perspectives of physical and mechanical indexes, failure forms, stress–strain states and changes after water seepage. In addition, evaluate the feasibility of this similar material in geomechanical model test. Experimental results show that the density, compressive strength and Poisson’s ratio of similar materials can be improved to a certain extent by the redispersible latex powder with low dosage. However, the above indexes show a significant downward trend with the increase in dosage when the dosage exceeds 2%. The deformation modulus always shows a downward trend, and this trend becomes more significant especially when the dosage exceeds 2%. With the increase in the redispersible latex powder, the stress–strain curves of similar materials show obvious elastic and plastic stages. The failure mode gradually changes to X-shaped conjugate failure, which is common in soft rock, and the material changes from brittle failure to plastic failure. In addition, this type of similar material with gypsum as cementing agent will cause serious damage and loss of bearing capacity after seepage. These methods produce similar materials with low strength, low deformation modulus and plastic failure form, which can be used to simulate the stability of soft rock engineering caused by loading or excavation. At the same time, it also sheds lights on preparing similar materials of hard rock.