Laser speckle measurements of transient Bénard convection

1978 ◽  
Vol 89 (4) ◽  
pp. 665-671 ◽  
Author(s):  
P. G. Simpkins ◽  
T. D. Dudderar
Keyword(s):  
Harmonic Component ◽  
Laser Speckle ◽  
Horizontal Distance ◽  
Short Side ◽  
Full Field ◽  
Third Harmonic ◽  
Velocity Information ◽  
Field Velocity ◽  
Oriented Parallel ◽  
Moving Liquid

Quantitative velocity measurements of unsteady convection in a Bénard cell suddenly cooled from above to a supercritical Rayleigh number are reported. The results are obtained by a novel application of laser speckle photography adapted for the study of fluid dynamics. This technique allows two-dimensional full-field velocity information to be obtained solely from a selected plane within the volume of moving liquid at any given instant in time. The convective rolls are found to be regular and oriented parallel to the short side of the cell. The number of rolls within the cell is approximately twice as great as the number reported for steady conditions. The maximum vertical velocity distribution is observed to be a sinusoidal function of the horizontal distance with a detectable third-harmonic component.

Heterodyne speckle interferometer for full-field velocity profile measurements of a vibrating membrane by electronic scanning

2007 ◽  
Vol 45 (6) ◽  
pp. 677-683 ◽  
Author(s):  
Mauro V. Aguanno ◽  
Fereydoun Lakestani ◽  
Maurice P. Whelan ◽  
Michael J. Connelly
Keyword(s):  
Velocity Profile ◽  
Full Field ◽  
Speckle Interferometer ◽  
Field Velocity ◽  
Vibrating Membrane

Imaging Cracks in Bones Using Acoustic Nonlinearity: A Simulation Study

2011 ◽  
Vol 97 (5) ◽  
pp. 728-733
Author(s):  
Yang Liu ◽  
Xiasheng Guo ◽  
Zhao Da ◽  
Dong Zhang ◽  
Xiufen Gong
Keyword(s):  
Time Reversal ◽  
Three Dimensional ◽  
Harmonic Component ◽  
Ultrasonic Signal ◽  
Long Bone ◽  
Third Harmonic ◽  
Acoustic Nonlinearity ◽  
The Third ◽  
Nonlinear Approach ◽  
Radial Depth

This article proposes an acoustic nonlinear approach combined with the time reversal technique to image cracks in long bones. In this method, the scattered ultrasound generated from the crack is recorded, and the third harmonic nonlinear component of the ultrasonic signal is used to reconstruct an image of the crack by the time reversal process. Numerical simulations are performed to examine the validity of this approach. The fatigue long bone is modeled as a hollow cylinder with a crack of 1, 0.1, and 0.225 mm in axial, radial and circumferential directions respectively. A broadband 500 kHz ultrasonic signal is used as the exciting signal, and the extended three-dimensional Preisach-Mayergoyz model is used to describe the nonclassical nonlinear dynamics of the crack. Time reversal is carried out by using the filtered third harmonic component. The localization capability depends on the radial depth of the crack.

scholarly journals Separation of cortical arteries and veins in optical neurovascular imaging

2014 ◽  
Vol 07 (03) ◽  
pp. 1350069 ◽  
Author(s):  
Linna Zhao ◽  
Yao Li ◽  
Hongyang Lu ◽  
Lu Yuan ◽  
Shanbao Tong
Keyword(s):  
Cerebral Cortex ◽  
Optical Imaging ◽  
Signal To Noise Ratio ◽  
Vascular Diseases ◽  
Region Growing ◽  
Field Method ◽  
Laser Speckle ◽  
Cerebral Vessel ◽  
Full Field ◽  
Arteries And Veins

Separation of arteries and veins in the cerebral cortex is of significant importance in the studies of cortical hemodynamics, such as the changes of cerebral blood flow, perfusion or oxygen concentration in arteries and veins under different pathological and physiological conditions. Yet the cerebral vessel segmentation and vessel-type separation are challenging due to the complexity of cortical vessel characteristics and low spatial signal-to-noise ratio. In this work, we presented an effective full-field method to differentiate arteries and veins in cerebral cortex using dual-modal optical imaging technology including laser speckle imaging (LSI) and optical intrinsic signals (OIS) imaging. The raw contrast images were acquired by LSI and processed with enhanced laser speckle contrast analysis (eLASCA) algorithm. The vascular pattern was extracted and segmented using region growing algorithm from the eLASCA-based LSI. Meanwhile, OIS images were acquired alternatively with 630 and 870 nm to obtain an oxyhemoglobin concentration map over cerebral cortex. Then the separation of arteries and veins was accomplished by Otsu threshold segmentation algorithm based on the OIS information and segmentation of LSI. Finally, the segmentation and separation performances were assessed using area overlap measure (AOM). The segmentation and separation of cerebral vessels in cortical optical imaging have great potential applications in full-field cerebral hemodynamics monitoring and pathological study of cerebral vascular diseases, as well as in clinical intraoperative monitoring.

Analysis of error motions of axial locking-prevention hydrostatic spindle

2018 ◽  
Vol 233 (1) ◽  
pp. 3-17
Author(s):  
Penghai Zhang ◽  
Yaolong Chen
Keyword(s):  
Significant Influence ◽  
Harmonic Component ◽  
Necessary Condition ◽  
Third Harmonic ◽  
The Third ◽  
Fourth Harmonic ◽  
Radial Error ◽  
Tilt Error ◽  
Error Motion ◽  
Error Averaging

Hydrostatic spindles are widely used in precision optical grinder and lathe. Their high precision comes from the error averaging effect of oil film. The purpose of this paper is to give the quantitative analysis of the error averaging effect for a newly developed axial locking-prevention hydrostatic spindle. An approximate error motion model of the hydrostatic spindle is established to analyze the internal relationship between the geometric errors of the shaft and the error motions of the spindle including radial, tilt and axial error motions. The theoretical analysis shows that, the roundness errors of the two journals have a major impact on error motions while the coaxiality errors of two journals, the perpendicularity errors of front thrust plate and the coaxiality errors of the land of back thrust bearing, have no significant influences on error motions. The elliptical component of roundness errors of the two journals has significant influence on the axial error motion but no influence on the pure radial and tilt error motions, resulting into the fourth harmonic component of axial error motion. The trilobal component of roundness errors of the two journals has significant influence on the pure radial and tilt error motions but no influence on the axial error motion, resulting in the third harmonic component of pure radial and tilt error motions. The changes of recess pressures are not necessary condition for the error motions. Additionally, the experiment analysis shows that, the third harmonic component is the main part of the measured radial error motion and the third, fourth harmonic components are the main parts of the measured face error motion, which can be reasonably explained by the theory. The model proposed in this paper can be used to guide the precision design and optimization of hydrostatic spindle.

scholarly journals Simulation and Experimental Investigation on Carbonized Tracking Failure of EPDM/BN-Based Electrical Insulation

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 582 ◽  
Author(s):  
Muhammad Tariq Nazir ◽  
Faizan Tahir Butt ◽  
Bao Toan Phung ◽  
Guan Heng Yeoh ◽  
Ghulam Yasin ◽  
...  
Keyword(s):  
Leakage Current ◽  
Failure Time ◽  
Harmonic Component ◽  
Experimental Results ◽  
Shielding Effect ◽  
Surface Discharge ◽  
Melt Mixing ◽  
Electrical Field ◽  
Third Harmonic ◽  
Thermal Depolymerization

Ethylene propylene diene monomer (EPDM) is broadly employed as an insulating material for high voltage applications. Surface discharge-induced thermal depolymerization and carbon tracking adversely affect its performance. This work reports the electrical field modeling, carbon tracking lifetime, infrared thermal distribution, and leakage current development on EPDM-based insulation with the addition of nano-BN (boron nitride) contents. Melt mixing and compression molding techniques were used for the fabrication of nanocomposites. An electrical tracking resistance test was carried out as per IEC-60587. Simulation results show that contamination significantly distorted the electrical field distribution and induced dry band arcing. Experimental results indicate that electric field stress was noticed significantly higher at the intersection of insulation and edges of the area of contamination. Moreover, the field substantially intensified with the increasing voltage levels. Experimental results show improved carbonized tracking lifetime with the addition of nano-BN contents. Furthermore, surface temperature was reduced in the critical contamination flow path. The third harmonic component in the leakage current declined with the increase of the nano-BN contents. It is concluded that addition of nano-BN imparts a better tracking failure time, and this is attributed to better thermal conductivity and thermal stability, as well as an improved shielding effect to electrical discharges on the surface of nanocomposite insulators.

scholarly journals Full-field velocity imaging of red blood cells in capillaries with spatiotemporal demodulation autocorrelation

2016 ◽  
Vol 21 (03) ◽  
pp. 1
Author(s):  
Mingyi Wang ◽  
Yaguang Zeng ◽  
Nannan Dong ◽  
Riwei Liao ◽  
Guojian Yang
Keyword(s):  
Red Blood Cells ◽  
Blood Cells ◽  
Full Field ◽  
Velocity Imaging ◽  
Field Velocity
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