共查询到19条相似文献,搜索用时 484 毫秒
1.
2.
3.
4.
声波飞渡时间的准确测量是声学法测温中影响温度场测温准确性的主要因素。采用互相关分析法计算单一频率声波信号及宽带频率声波信号的声波飞渡时间,仿真结果表明宽带频率信号由于具有较强的抗噪能力在计算声波飞渡时间时不受声波信号周期、信号延时时间等因素的限制,可用于工程实践。同时采用频率为40kHz的正弦波超声波探测器在均匀温场条件下对超声波信号的衰减程度进行试验研究,试验结果表明40kHz的正弦波超声信号在不经过放大处理条件下,其可测温场的距离仅为160mm。 相似文献
5.
6.
7.
主要研究了一种新的电磁超声激发方法.脉冲电磁超声的激发,旨在提高电磁超声换能器的磁声转换效率,解决其灵敏度低以及热效应的不良影响等问题。设计制作了脉冲电磁超声的激发装置。通过实验验证,该方式超声信号强度较强,激发装置发热量小。最后分析了超声波信号的激发强度与初始电压、电容容值等因素的关系,认为线圈中铁芯的加入在一定程度上可以提高磁声转换的效率。但目前产生的超声波信号频率仍在低频范围内,在今后的研究中还将进一步考虑采用信号压缩等方法来提高频率。 相似文献
8.
9.
为减少MGH956合金熔焊焊缝内的气孔量,利用高频调制TIG电弧激发超声电弧作用于MGH956合金的焊接,通过对比不同激励频率对焊缝气孔及性能的影响,分析了电弧超声激励频率对焊缝气孔及性能的作用机制及影响规律.运用理论计算的方法对焊缝中气孔的运动进行数学分析,理论计算结果与试验结果相一致.控制激励电流在15 A的条件下,激励频率为30 kHz时,焊缝的气孔量最少,且焊接接头强度达到最高,为521 MPa,达到母材的72%.实现了焊接接头断裂方式由脆性断裂转化为韧-脆混合断裂方式. 相似文献
10.
《纳米技术与精密工程》2017,(1)
针对研究功能性电刺激治疗贲门失弛缓症的需求,设计了一种基于多通道电刺激的食管起搏系统.系统以低功耗单片机MSP430为核心处理器,通过对前端脉冲发生信号的处理,控制低功率压控精密恒流电路,采用软件精确延时等技术实现了刺激脉冲的生成、多通道顺序输出、脉冲参数可调等功能.组织5名受试者参加了吞咽信号采集与处理实验.结果显示,系统可以100%检测到受试者吞咽引起的电压变化.将经采集处理后的电压变化值作为比较电路的阈值参数,进一步生成有效的脉冲发生信号.并且利用高精度示波器和万用表对系统生成的刺激脉冲的强度、频率、脉宽3种性能指标进行测试,对所有数据进行误差计算和分析.数据表明,实际测量值与理论值相对误差均小于2.5%,验证了设计原理的正确性和系统的可行性. 相似文献
11.
12.
以斑马鱼和稀有(鱼句)鲫的基因组DNA进行RAPD分析,获得特异的RAPD标记,经克隆、测序,合成特异性引物并优化SCAR-PCR反应条件,将四个特异的RAPD标记转化成稳定的SCAR标记.SCAR1、SCAR3和SCAR2、SCAR4分别在斑马鱼与稀有(鱼句)鲫基因组DNA扩增中产生单一的条带,可作为区分斑马鱼和稀有(鱼句)鲫的分子标记.此外,SCAR3和SCAR4还可以分别将斑马鱼和稀有(鱼句)鲫从鲫鱼、白鲢、鲤鱼、鳊鱼等其它鱼类中鉴别出来,从而成为良好的种质鉴定分子标记.在此基础上,选用SCAR标记进行了斑马鱼与稀有(鱼句)鲫配合的鱼类异种克隆胚胎鉴定研究,结果发现,克隆胚由供体核支持发育而来.SCAR标记的获得,为鱼类异种间克隆胚胎和克隆鱼的检验,以及细胞核再程序化机制等重大理论问题的探索提供了重要的技术支持. 相似文献
13.
Vladislav Kopman Jeffrey Laut Giovanni Polverino Maurizio Porfiri 《Journal of the Royal Society Interface》2013,10(78)
In this paper, we study the response of zebrafish to a robotic-fish whose morphology and colour pattern are inspired by zebrafish. Experiments are conducted in a three-chambered instrumented water tank where a robotic-fish is juxtaposed with an empty compartment, and the preference of live subjects is scored as the mean time spent in the vicinity of the tank''s two lateral sides. The tail-beating of the robotic-fish is controlled in real-time based on feedback from fish motion to explore a spectrum of closed-loop systems, including proportional and integral controllers. Closed-loop control systems are complemented by open-loop strategies, wherein the tail-beat of the robotic-fish is independent of the fish motion. The preference space and the locomotory patterns of fish for each experimental condition are analysed and compared to understand the influence of real-time closed-loop control on zebrafish response. The results of this study show that zebrafish respond differently to the pattern of tail-beating motion executed by the robotic-fish. Specifically, the preference and behaviour of zebrafish depend on whether the robotic-fish tail-beating frequency is controlled as a function of fish motion and how such closed-loop control is implemented. 相似文献
14.
用数值计算方法研究具有特殊结构的侧壁式压水室离心泵,分析小流量工况时模型泵的非稳态旋转失速特性,用快速傅里叶变换(FFT)获得压力脉动信号的频谱特征。结果表明,小流量工况时模型泵的扬程曲线呈驼峰状,压水室不同位置处压力分布不均;受叶轮旋转产生的非稳态作用影响,叶轮不同叶片流道内流动结构差异较大。不同流量下,叶轮内部分离涡结构诱发的激励频率各异,0.4ФN工况时模型泵压力脉动频谱图出现0.5fR及高次谐波频率,压力脉动最大幅值出现于4fR频率处;0.2ФN流量时非定常流动结构会诱发0.18fR及高次谐波频率;0.05ФN流量时压力脉动频谱图同时出现0.1fR、0.28fR两种激励频率。旋转失速现象出现时,频谱图中叶频处压力脉动幅值不再起主导作用。 相似文献
15.
Toxicity of silver nanoparticles in zebrafish models 总被引:1,自引:0,他引:1
This study was initiated to enhance our insight on the health and environmental impact of silver nanoparticles (Ag-np). Using starch and bovine serum albumin (BSA) as capping agents, silver nanoparticles were synthesized to study their deleterious effects and distribution pattern in zebrafish embryos (Danio rerio). Toxicological endpoints like mortality, hatching, pericardial edema and heart rate were recorded. A concentration-dependent increase in mortality and hatching delay was observed in Ag-np treated embryos. Additionally, nanoparticle treatments resulted in concentration-dependent toxicity, typified by phenotypes that had abnormal body axes, twisted notochord, slow blood flow, pericardial edema and cardiac arrhythmia. Ag(+) ions and stabilizing agents showed no significant defects in developing embryos. Transmission electron microscopy (TEM) of the embryos demonstrated that nanoparticles were distributed in the brain, heart, yolk and blood of embryos as evident from the electron-dispersive x-ray analysis (EDS). Furthermore, the acridine orange staining showed an increased apoptosis in Ag-np treated embryos. These results suggest that silver nanoparticles induce a dose-dependent toxicity in embryos, which hinders normal development. 相似文献
16.
为研究铂-全氟磺酸(Pt-PFSA)复合材料的传感特性,首先,测试了在阶跃激励和正弦激励下,Pt-PFSA复合材料的响应输出电压;然后,采用化学镀方法,将铂原子沉积在由Nafion溶液制备的0.4mm厚的Nafion阳离子交换膜的两个表面上;最后,考察了含水量对Pt-PFSA复合材料输出电压的影响,预测了正弦激励下PtPFSA复合材料的传感性能,进行了不同频率的正弦激励实验。结果表明:采取保湿措施后,含水量变化导致的输出电压降低幅度低于5%;在阶跃激励信号下,当Pt-PFSA复合材料的应变为0.1%时,输出电压具有时延;给出了Pt-PFSA复合材料的灵敏系数表达式,当正弦激励信号频率为5.9Hz时,复合材料的灵敏系数为3.555 8mV/0.2%,得到的实验结果与预测吻合较好。研究为Pt-PFSA复合材料传感性能模型的建立奠定了基础。 相似文献
17.
针对传统压电式人工中耳输出增益较小、工作频带窄的问题,提出利用压电叠堆型压电振子激振砧骨体来补偿听力。为验证该方案的可行性,搭建由送声器、测声探管、压电振子及激光测振仪等构成的颞骨实验台,对振子动态特性、听骨链在声激励下及压电振子激振下的动态特性进行了测量。通过对比分析镫骨在两种激励下的运动情况,研究压电振子的听力补偿情况。结果显示,该砧骨激励式压电振子在低功耗、低电压下,便能对听力损伤进行有效补偿。此外,该压电振子听力补偿时还具有高频性能优异的特点,一方面在同等驱动电压下,高频补偿能力更强,能激起高达130 dB鼓膜声激励对应的运动幅度;另一方面,对高频段听力补偿时,具有较高的清晰度。 相似文献
18.
19.
Bai W Tian W Zhang Z He X Ma Y Liu N Chai Z 《Journal of nanoscience and nanotechnology》2010,10(12):8670-8676
The environmental behavior and the potential toxicity of copper nanoparticles (nano-Cu) in water are major concerns for assessing their environmental safety. The present study was undertaken to characterize the properties of nano-Cu in E3 medium, such as size changes, solubility, zeta-potential and pH, and to test the toxicity of nano-Cu suspension to zebrafish embryos. Dynamic light scattering and solubility experiments showed that three components coexisted in the nano-Cu exposure system, including small nano-Cu aggregates still suspended in E3 medium, large nano-Cu aggregates deposited on the container bottom and dissolved copper species (Cu(dis)). Both the zeta-potential of nano-Cu particles in E3 medium and the pH of the nano-Cu suspension showed no change during a 24 hour period. It is found that nano-Cu retarded the hatching of zebrafish embryos and caused morphological malformation of the larvae, and high concentrations (>0.1 mg/L) of nano-Cu even killed the gastrula-stage zebrafish embryos. Cu2+ ions were used to study the toxicity caused by nano-Cu dissolution. The embryo toxicity of nano-Cu at 0.01 and 0.05 mg/L showed no significant difference from Cu2+ at the corresponding concentrations (0.006 and 0.03 mg/L), but 0.1 mg/L nano-Cu had a greater toxicity than 0.06 mg/L Cu2+. 相似文献