共查询到19条相似文献,搜索用时 140 毫秒
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超声外场对复合材料注射成型流动行为影响的可视化实验 总被引:1,自引:0,他引:1
利用自主研制开发的基于可视化技术的超声激励注射成型装置,对超声频率为19.5kHz时,不同超声功率、不同注射速度以及不同玻纤含量条件下,短玻纤增强聚丙烯(GF/PP)复合材料熔体前沿充填型腔的状况进行直接观测记录,并对超声外场对复合熔体充型流动行为的影响进行研究。结果表明,超声外场在一定程度上改善了10%GF/PP的熔体充型流动行为,而且最佳超声功率值随着注射速度不同而有所改变,超声外场对于20%GF/PP的熔体充型流动行为改善效果并不明显。为后续研究超声外场对复合材料注塑成型特性的影响可以提供可靠依据。 相似文献
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采用超声技术对车前草中总黄酮提取进行强化,选择料液比、超声提取时间、提取温度、超声功率四因素进行正交实验,得出影响总黄酮提取率大小的次序先后为:提取温度〉超声功率〉超声提取时间〉料液比。在实验参数的基础上,为了获得较高的提取率和节省溶剂用量,各因素的优化工艺参数为:料液比1:20,超声提取时间30min,超声提取温度为50℃,超声功率为200W,在这个最佳条件下试验,总黄酮的提取率为0.645%。相对常规回流提取法而言,采用超声法提取具有快速、节省溶剂、节省时间、提取的有效成分含量较高等优点。 相似文献
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提出超声背散射Tsallis信息熵成像评价脂肪肝的新方法。利用滑动窗口法,估算窗口内局部背散射包络信号的Tsallis信息熵参数值,对信息熵参数值矩阵进行扫描变换、颜色映射及感兴趣区域设置,叠加到超声B模式图像,实现Tsallis信息熵成像。分析72名肝脏捐献者和204名患者的超声背散射信号,参考标准分别为磁共振波谱测得的肝脏脂肪分数(Hepatic Fat Fraction, HFF)和肝活检组织学检查测得的脂肪肝程度。对于72名肝脏捐献者,Tsallis信息熵与lg(HFF)的相关系数r=0.67(P<0.000 1)。对于204名患者,受试者工作特征曲线下面积分别为0.82、0.88、0.89(≥轻度、≥中度、≥重度),而超声背散射零差K成像分别为0.76、0.82、0.82。超声背散射Tsallis信息熵成像可以直观定征并定量评价脂肪肝的严重程度,其诊断性能优于超声背散射零差K成像,可作为一种超声评价脂肪肝的新方法。 相似文献
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目的:观察超声引导下恒河猴肝穿刺活体组织检查技术在动物实验中的应用情况,探讨超声引导下经皮恒河猴肝脏穿刺活检的价值和意义。方法:采用PHILIPS i U22超声仪、9~3 MHz探头、Bard 16G活检枪及活检针对22只恒河猴肝纤维化疾病进行穿刺,对穿刺组织进行病理检查。结果:22只恒河猴均穿刺成功,病理学染色良好,能够进行肝脏疾病的病理分析和诊断。结论:在动物实验中,超声引导下肝脏穿刺活检术是一项微创、安全、方便的取材方法,能确定肝脏损害的病理性质,对实验动物疾病模型诊断和治疗有重要的临床价值。 相似文献
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为了提高医学超声内镜系统中的探测深度、分辨率及成像质量,在超声内镜成像系统中采用编码激励技术,首次将普遍用于开关电源电路设计中的"半桥"电路引入超声内镜编码激励电路.在只有正电压电源供电的情况下产生正负高压激励脉冲,利用电机转动的编码信号,设计了基于CPLD的同步编码激励电路,在保证与超声内镜主机FPGA同步的基础上,简化了超声内镜系统内信号的传递.实验中,同步编码激励电路发射的编码激励信号与理论码型一致,通过人体体模实验,获得的回波波形幅度达1.0Vpp,噪声20×10-3VPP~30×10-3Vpp,信噪比高达34 dB,波形与仿真结果一致. 相似文献
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针对SYS510e型空气弹簧底板的金属橡胶粘接结构橡胶脱粘缺陷超声检测难以辨识问题,提出采用改进的线性调频脉冲代替传统窄脉冲作为超声波激励信号,增大超声检测的信号能量和频谱宽度。在宽频带超声检测的基础上,采用小波包-奇异值分解方法解析超声回波在不同粘接状态、不同频率范围的时频能量分布,提取更稳定、一致性更好的橡胶脱粘辨识特征值。根据特征训练BP神经网络对空气弹簧的橡胶脱粘缺陷进行超声C扫描检测。结果显示,基于改进的线性调频脉冲激励的超声检测方法能够准确有效地辨识橡胶脱粘缺陷的位置和轮廓,满足对SYS510e型空气弹簧的超声脱粘检测需求。 相似文献
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当超声波在煤岩固体材料中传播时,受其机械效应,煤岩基质固体颗粒间相互作用。从超声波的机械效应角度结合断裂力学,对围压影响的超声激励破岩机制进行探讨,利用 RFPA2D 岩石破裂过程分析系统对超声激励不同围压下煤岩致裂过程进行了数值试验验证。研究表明:围压降低了煤岩内部裂纹的断裂强度因子,改变裂纹尖端应力场;围压对煤岩破裂具有抑制作用,在相同功率超声作用下,围压越大,超声激励碎岩程度越低;数值实验表明,随着围压增加,超声致裂煤岩影响区域逐渐减小,煤岩破坏形式由低围压下的张拉和剪切破坏共同作用逐渐向高围压下单一剪切破坏过渡。相同有效声压作用下,煤岩破裂过程中主应力随煤岩围压升高而增大。 相似文献
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Motion of contrast envelopes: peace and noise 总被引:1,自引:0,他引:1
Cropper SJ Johnston A 《Journal of the Optical Society of America. A, Optics, image science, and vision》2001,18(9):2237-2254
We examined the effect of changing the composition of the carrier on the perception of motion in a drifting contrast envelope. Human observers were required to discriminate the direction of motion of contrast modulations of an underlying carrier as a function of temporal frequency and scaled (carrier) contrast. The carriers were modulations of both color and luminance, defined within a cardinal color space. Random-noise carriers had either binary luminance profiles or flat (gray-scale-white) or 1/f (pink) spectral power functions. Independent variables investigated were the envelope spatial frequency and temporal-drift frequency and the fundamental spatial frequency, color, and temporal-update frequency of the carrier. The results show that observers were able to discriminate correctly the direction of envelope motion for binary-noise carriers at both high (16 Hz) and low (2 Hz) temporal-drift frequencies. Changing the carrier format from binary noise to a flat (gray-scale) or 1/f amplitude profile reduced discrimination performance slightly but only in the high-temporal-frequency condition. Manipulation of the fundamental frequency of the carrier elicited no change in performance at the low temporal frequencies but produced ambiguous or reversed motion at the higher temporal frequencies as soon as the fundamental frequency was higher than the envelope modulation frequency. We found that envelope motion detection was sensitive to the structure of the carrier. 相似文献
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I. Yonenaga 《Journal of Materials Science: Materials in Electronics》2003,14(5-7):279-281
A Vickers indentation method was used to determine the hardness of AlN and GaN, grown by the hydride vapor phase epitaxy technique, in the temperature range 20–1400 °C. At room temperature, the hardnesses of GaN and AlN are 10.2 and 17.7 GPa, respectively. The hardness of GaN and AlN shows a gradual decrease from RT and then a steep decrease from around 1000 °C. AlN is harder than GaN but softer than SiC. The steep decrease of the hardness means the beginning of macroscopic dislocation motion and plastic deformation. The mechanical strength of bulk single-crystal GaN is investigated at elevated temperatures directly by means of compressive deformation. The yield stress of GaN in the temperature range 900–1000 °C is around 100–200 MPa, i.e., similar to that of 6H-SiC and much higher than those of Si, Ge, GaAs. 相似文献
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Chen E.J. Jenkins W.K. O'Brien W.D. Jr. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(3):293-301
The accuracy of displacement and velocity data in ultrasonic motion detection systems depends on a combination of ultrasonic imaging parameters. These include magnitude and direction of target motion, target region dimensions, scattering media, ultrasonic frequency of interrogation, digital sampling frequency, and signal type (envelope detected or RF). Because the impact of scattering media in particular has heretofore received little or no attention, we provide experimental results and computer analysis to evaluate the influence of different scattering media on the accuracy of ultrasonic displacement and velocity estimates using porcine liver, porcine muscle, and woolen sea sponge samples. Our experimental results show that for identical target dimensions and displacements, the accuracy of ultrasonic displacement and velocity estimates in porcine muscle samples are substantially higher than in porcine liver samples. Analysis of experimentally derived autocovariance curves for each tissue type indicates that the improvement in accuracy for muscle samples is not, in fact, due to differences in the speckle characteristics for each tissue type. The improvement is attributed to the presence of well-defined and resolvable image structures from muscle and the lack of such resolvable structures in porcine liver tissue. We provide a summary of the factors impacting ultrasonic displacement and velocity measurements, and discuss why and how a combination of one or more imaging parameters affects these measurements 相似文献
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Marcus A. Gagliardi Bulent H. Sencer A. W. Hunt Stuart A. Maloy George T. GrayIII 《Journal of Nondestructive Evaluation》2011,30(4):221-224
The surface of an annealed 316L stainless steel coupon was laser shock peened and Vickers hardness measurements were subsequently
taken of its surface. This Vickers hardness data was compared with measurements taken using the technique of positron annihilation
Doppler broadening spectroscopy. When compared, a correlation was found between the Vickers hardness data measurements and
those made using Doppler broadening spectroscopy. Although materials with a high defect density can cause the S-parameter
measurements to saturate, variations in the S-parameter measurements suggest that through further research the Doppler broadening
technique could be used as a viable alternative to measuring a material’s hardness. In turn, this technique, could be useful
in industrial settings where surface hardness and surface defects are used to predict lifetime of components. 相似文献
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The behaviour of microhardness under varying load was investigated with an apparatus which measured both load and diamond pyramid motion simultaneously. There have been several experiments with this type of apparatus, which are designed to measure the hardness under load of a material. This type of measurement eliminates the effect of elastic recovery after the diamond is removed from the sample. Two types of load-independent hardness have been proposed on the basis of studies performed on this type of apparatus. The first follows the theory of Tate stating that elastic recovery is responsible for the load dependence of hardness. The second, proposed by Froelichet al. states that the load dependence of hardness is due to surface forces. This investigation used an apparatus similar to that of Froehlichet al. The results indicated that the load-independent hardness of Froehlichet al. was an experimental artifice caused by late detection of the surface, leading to underestimation of the penetration and overestimation of the hardness. Hardness measured under load using the apparatus in the present project was found to be load dependent. 相似文献
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The Rebinder Effect, an environment-caused change in the hardness of rock, ceramic, or glass, was investigated in silicon
nitride using conventional microhardness and electrochemical techniques. As in previous studies of the effect, hardness and
zeta potential varied significantly with the pH of the environment. Unlike previous studies, the pH values at which hardness
was maximum and zeta potential was zero (zero point of charge, or zpc) did not correspond. This lack of correspondence was
deemed the result of the partial oxidation of the surface film of the sample. The presence of the oxide containing film had
a significant effect on zeta potential but little effect on hardness as the hardness indenter penetrated well beyond the film.
Through the use of a simple linear model and published data it was possible to demonstrate that for oxide-free silicon nitride
the pH values at which hardness was maximum and zeta potential was zero do correspond. The Rebinder Effect in this material
is clearly time-dependent; long dwell times resulted in reduced hardness values. This was more noticeable at pH values removed
from the zpc. These observations are consistent with a mechanism for the Rebinder Effect in which environmental pH controls
surface charge, which in turn controls zeta potential and affects dislocation motion and, thereby, hardness. 相似文献