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为探讨脉冲方波电压频率对局部放电特性的影响,基于超高频(UHF)检测方法和IEEE 488.2传输协议,构建了宽频、高速数据采集局部放电测试系统.利用该系统,研究了变频电机耐电晕漆包线的局部放电脉冲幅值、相位和时频特性.研究结果表明:频率200 Hz以上的高频脉冲电压使空间电荷扩散效应减小,增大了局部放电初始电子产生的概率,使得局部放电瞬时电压降低,出现幅值小于200 mV的局部放电脉冲.在高频脉冲电压下,当局部放电发生在电压上升时段时,快速变化的电压幅值将改变局部放电特性,使得局部放电脉冲在1~2 GHz高频能量的比重增大.因此,根据相关标准检测变频电机局部放电时,为易于激发绝缘薄弱点处局部放电,宜采用频率低于200 Hz的低频脉冲方波电压,且局部放电超高频传感器在1.2 GHz及以上频率处应具有较好的增益特性,并采用500 MHz的高通滤波器,以提高测试系统的信噪比. 相似文献
904.
为了研究壁板在亚音速气流和外激扰联合作用下的非线性运动特性,基于Hamilton原理,建立了外激励作用下亚音速粘弹性壁板的非线性运动方程,并采用Galerkin方法将其离散为常微分方程组,研究了系统的平衡点及其稳定性.利用Melnikov方法得到了壁板出现混沌运动时系统参数所满足的临界条件,分析了外激励幅值、频率及气流来流速度之间的临界关系,并与系统混沌运动的数值模拟结果进行了对比.结果表明:当无量纲动压值超过64.42时,壁板系统平衡点的个数及其稳定性均会发生改变;使用Melnikov方法确定的混沌运动临界参数与数值模拟结果相符,该方法可用于判定混沌运动是否发生. 相似文献
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Hydroxyapatite (HA) based materials have been widely used in the field of ligament tissue engineering in the past decades. It has been previously reported that HA can increase the penetration of marrow-derived mesenchymal stem cells (MSCs) and MSCs cells into scaffolds due to increased cell differentiation in biological media. Additionally, it was found that there are much difference between MSCs and anterior cruciate ligament (ACL) cells. For that reason, we mainly evaluate the biocompatibility of polyethylene terephthalate (PET) silk scaffold with fibroblasts cells in vitro. We cultured mouse fibroblasts cells on the substrate of PET fiber and PET-HA scaffold, respectively, and then observed the morphology by using scanning electron microscopy. Our data indicate that PET-HA scaffold has good biocompatibility with fibroblasts cells and can potentially be useful in enhancing the fibroblasts cell differentiation and proliferation. 相似文献
909.
<正>A high-strength Mg-15.3Gd-l.8Ag-0.3Zr(GQ152K,mass fraction) alloy was prepared by conventional ingot metallurgy process.The solution and aging(denoted as T6) treated alloy exhibits remarkable mechanical properties with ultimate tensile strength of 421 MPa and tensile yield strength of 309MPa.It has higher igniting temperature of 1208 K.Moreover,it can stand against flame at 1203 K for over 6 min in vertical burning tests, and its flammabiUty behavior is very similar to that of 6101A1 alloy.Vertical burning tests appear to be able to directly study the flammability behavior of Mg alloys and it appears to be a good approach to study the flammability behavior of Mg alloys in an aircraft fire accident. 相似文献
910.
This paper summed up the characteristics of native arteriovenous fistulas (AVFs) in maintenance hemodialysis patients with type 2 diabetic nephropathy (DN) in Chinese hemodialysis centers. A survey was conducted on AVF in maintenance hemodialysis patients with type 2 DN. A total of 224 cases of maintenance hemodialysis patients were included in this study, among which, 65 cases in DN group, 33 cases in diabetes mellitus (DM) group and 126 cases in non-diabetic control (C) group. Hemoglobin, albumin, blood urea nitrogen, parathyroid hormone and calcium-phosphate product of the three groups of patients were not significantly different. Glycated hemoglobin A1c of DN group and DM group was not significant different. AVF life of (28.7 ± 10.0) months in DN group was significantly shorter than that of (36.5 ± 19.4) months in C group (statistic probability P <0.01), and AVF life of (32.5 ± 10.1) months in DM group (P <0.05) was also shorter than that in C group, while there was no significant difference in AVF life between DN group and DM group. Proportion of upper arm fistula in DN patients (11/65) was significantly higher than that in C group (6/123, P < 0.01). Life of AVF in patients with DN was relatively short, with more times of angioplasty and greater possibility of selecting upper arm internal fistula. 相似文献