Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Systemic experimental research was carried out on high- cycle fatigue behavior of FV520B steel based on the theory and calculation model of intrinsic dissipation. The experiment results show that the intrinsic dissipation of FV520B steel increases with the increase of the applied stress amplitude. Generally, the inflection point of intrinsic dissipation corresponds to the transition of the generation mechanism of intrinsic dissipation: from the reversible motion of the microstructure (the swing of dislocation lines between strong pinning points) to the combined effects of the reversible and irreversible motion of the microstructure (the generation of permanent slip, the unpinning from strong points and the multiplication of dislocation). And the stress amplitude corresponding to the inflection point is just the critical stress value inducing fatigue damage accumulation. Moreover, the results also indicate that FV520B steel subjected to constant stress amplitude keeps a relatively steady rate related to the applied stress amplitude and independent of the loading sequences. Additionally, the loading frequency has no effect on the fatigue damage per loading cycle. Fatigue failure will occur once the amount of the intrinsic dissipation, due to the irreversible motion of the microstructure, accumulates to a threshold value. And the energy threshold is found to be independent of the loading history.
Subjects: Geosciences >> Geography submitted time 2019-01-11 Cooperative journals: 《干旱区地理》
Abstract：本研究利用MODIS-NDVI产品生成中亚天山2000-2016年植被覆盖度，利用线性回归法和偏相关法分析了中亚天山植被时空变化特征及驱动因子。结果表明：中亚天山植被生长及变化趋势具有显著的区域分异性，纬度分区上，中天山和北天山西部植被覆盖度较高的草原、农田和森林在2000-2016年呈现退化趋势；南天山和北天山东部植被覆盖度较低的荒漠、草原和灌丛在同期表现出改善趋势，而中国境内的东天山与境外的西天山相比具有较低的植被覆盖度以及总体改善的变化趋势。中亚天山气候在2000-2016年显示出“暖湿化”特征，温度升高幅度（5.9%）远大于降水增加幅度（1.3%），温度、降水与植被覆盖度的显著相关比例为18.0%和42.6%，降水是中亚天山植被变化的主要气候驱动因素。以巴音布鲁克草原为代表的东天山部分草原受到过度放牧的影响而退化严重，建议加强植被退化区的生态修复与保护力度。
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-12-13 Cooperative journals: 《计算机应用研究》
Abstract： Since the traditional clustering method has an impoverished clustering effect on the multidimensional data, this paper used the clustering method based on community detection of complex networks to achieve better results. Firstly, the method extracted the features of original data and formed the feature vectors of each object for a multidimensional data set. Then it measured the similarity between different feature vectors by calculating Pearson correlation coefficients and constructed a similarity network. Finally, it used the Blondel algorithm which detects the community of the network to achieve the clustering effect. Experimental results show that this method can get better clustering results in multidimensional data clustering with an accuracy rate 92.5%, which is better than k-means algorithm with the accuracy rate 75%.
Subjects: Computer Science >> Integration Theory of Computer Science submitted time 2018-04-24 Cooperative journals: 《计算机应用研究》
Abstract： Investigating the dynamics of long-term memory in online rating behaviors is significant for understanding the evolution mechanism of collective behaviors and trust formation for online social networks. Since users are allowed to deliver ratings in many online systems, ratings can well reflect the user’s opinions. This paper empirically investigated the long-term memory, measured by the Detrended Fluctuation Analysis, in collective rating behaviors before and after the trust formation. The results for the Epinions data set show that, comparing with the null model generated by the reshuffle process, the Hurst exponent of trustors decreases 8.06% before and increases 8.43% after trust formation, which stably remains close to 0.5 in null model I and 0.6 in null model II, suggesting that the collective rating behavior plays an important role for the trust formation. Furthermore, the paper divided users into 8 groups according to the user degree and find that the correlation of the user degree and the variation of Hurst exponent, measured by the Pearson Correlation Coefficient, is 0.9358 and 0.9278 before and after trust formation respectively, reflecting a significant correlation between user degrees and collective rating behavior patterns. This work helps deeply understand the intrinsic feedback effects between collective behaviors and trust relationship.
Subjects: Medicine, Pharmacy >> Preclinical Medicine submitted time 2017-12-07 Cooperative journals: 《南方医科大学学报》
Abstract： Objective To establish a systematic method for isolation and identification of aerobic and facultative anaerobic bacteria in the oral cavity. Methods Samples of the saliva, dental plaque and periapical granulation tissue were collected from 20 subjects with healthy oral condition and from 8 patients with different oral diseases. The bacteria in the samples were identified by morphological identification, VITEK automatic microorganism identification and 16s rRNA gene sequencing. Results VITEK automatic microorganism identification and 16s rRNA gene sequencing showed an agreement rate of 22.39% in identifying the bacteria in the samples. We identified altogether 63 bacterial genus (175 species), among which Streptococcus, Actinomyces and Staphylococcus were the most common bacterial genus, and Streptococcus anginosus, Actinomyces oris, Streptococcus mutans and Streptococcus mitis were the most common species. Streptococcus anginosus was commonly found in patients with chronic periapical periodontitis. Streptococcus intermedius and Staphylococcus aureus were common in patients with radiation caries, and in patients with rampant caries, Streptococcus mutans was found at considerably higher rate than other species. Conclusion Aerobic and facultative anaerobic bacteria are commonly found in the oral cavity, and most of them are gram-positive. 16s rRNA gene sequencing is more accurate than VITEK automatic microorganism identification in identifying the bacteria.
Subjects: Medicine, Pharmacy >> Preclinical Medicine submitted time 2017-12-07 Cooperative journals: 《南方医科大学学报》
Abstract： Objective To investigate the effects of acute hypervolemic hemodilution (AHH) and intraoperative blood salvage (IOBS) on the morphology and biomechanics of erythrocytes using atomic force microscopy (AFM). Methods Blood samples were collected from 20 patients undergoing orthopedic surgery before operation (T1), immediately after AHH (T2), and after blood salvage (T3). AFM at nanometer resolution was used to examine the morphology and biomechanics of the collected erythrocytes. Results The blood samples collected at T1 showed a significantly lower ratio of heteromorphous erythrocytes than those collected at T2 and T3 [(2.6士1.3)%vs (19.3士1.6)% and (17.6士1.4)%, P<0.05]. AFM revealed significant differences in the morphology and biomechanics of the single erythrocyte in salvaged blood and blood after AHH compared with those of venous blood. Conclusion AHH and IOBS may cause significant changes in the morphology and biomechanics of erythrocytes in the salvaged blood
Subjects: Biology >> Zoology submitted time 2017-10-23 Cooperative journals: 《动物营养学报》
Abstract：本试验旨在研究饲粮铜水平对冬毛期雌性蓝狐生长性能、营养物质消化率、血清生化指标及毛皮品质的影响。试验选取115日龄左右的健康雌性蓝狐50只，随机分成5组，每组10个重复，每个重复1只。以五水硫酸铜（CuSO4·5H2O）为铜源，在基础饲粮中分别添加0、12.22、32.22、72.22、152.22 mg/kg的铜配成5种试验饲粮，5种试验饲粮铜水平分别为7.78（Ⅰ组，作为对照组）、20（Ⅱ组）、40（Ⅲ组）、80（Ⅳ组）、160 mg/kg（Ⅴ组）。预试期为7 d，正试期为60 d。结果表明：1)Ⅲ、Ⅳ和Ⅴ组蓝狐的平均日增重显著高于对照组（P0.05）。2)各组蓝狐的干物质消化率、蛋白质消化率及氮沉积差异不显著（P>0.05）；Ⅲ、Ⅳ组蓝狐的脂肪消化率显著高于对照组（P0.05）；铜排出量随着饲粮铜水平的升高极显著的增加（P0.05），Ⅳ组蓝狐血清铜锌超氧化物歧化酶活性显著高于对照组及Ⅱ和Ⅲ组(P0.05）。5)饲粮铜水平并未显著影响蓝狐的体长和干皮长（P>0.05）；Ⅲ和Ⅴ组蓝狐针毛长和绒毛长显著大于Ⅱ和Ⅳ组（P<0.05）；Ⅴ组蓝狐皮张颜色显著深于对照组（P<0.05）。由此可见，在饲粮中添加32.22 mg/kg铜即铜水平为40.00 mg/kg时，冬毛期雌性蓝狐可获得较好的生长性能、营养物质消化率及毛皮品质，同时铜的排放量较低。
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：基于固有耗散理论和计算模型，对FV520B钢的高周疲劳性能进行了较为系统的实验研究。结果表明：随着施加的交变应力幅的增大，FV520B钢的固有耗散也不断增大。其变化规律的拐点对应于固有耗散产生机制的转变：从单纯地由材料微结构的可逆运动（位错线在强钉扎点之间的摆动）引起，到由材料微结构的可逆运动和不可逆运动（永久滑移的产生、强钉扎点的脱钉以及位错的增殖）共同引起。并且，固有耗散拐点的应力幅值就是导致材料疲劳损伤累积的临界应力幅值，即疲劳极限。另外，实验还表明：FV520B钢在等幅交变应力下具有相对稳定的损伤演化速率，且损伤演化速率由应力幅值决定，与加载次序无关；每一周加载造成的疲劳损伤也不受加载频率的影响。当FV520B钢在疲劳过程中累积的与微结构不可逆演化相关的固有耗散部分达到一个临界值时，材料即发生疲劳断裂，且这个临界值是一个与加载历史无关的材料常数。
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