scholarly journals Dual-Wavelength Continuous Wave Photoacoustic Doppler Flow Measurement

2021 ◽  
Author(s):  
Hongcai Zhao ◽  
Yanbin Liu ◽  
Tayyab Farooq ◽  
Hui Fang
Keyword(s):  
Flow Measurement ◽  
Continuous Wave ◽  
Flow Direction ◽  
Power Spectra ◽  
Experimental System ◽  
Flow Speed ◽  
Doppler Flow ◽  
Multiple Wavelengths ◽  
Doppler Power ◽  
Near Future

AbstractPhotoacoustic Doppler flow measurement based on continuous wave laser excitation owns the merit of clearly presenting the Doppler power spectra. Extending this technique to dual wavelengths can gain the spectral information of the flow sample extra to the flow speed information. An experimental system with two laser diodes respectively operated at 405 nm and 660 nm wavelengths is built and the flow measurement with black and red dyed polystyrene beads is performed. The measured Doppler power spectra can vividly reflect the flow speed, the flow direction, as well as the bead color. Since it is straightforward to further apply the same principle to multiple wavelengths, we can expect this type of spectroscopic photoacoustic Doppler flow measurement will be developed in the near future which will be very useful for studying the metabolism of the slowly moving red blood cell inside microvessels.

scholarly journals Flow angle dependent photoacoustic Doppler power spectra under intensity-modulated continuous wave laser excitation

AIP Advances ◽  
2016 ◽  
Vol 6 (2) ◽  
pp. 025109 ◽  
Author(s):  
Yu Tong ◽  
Hongcai Zhao ◽  
Hui Fang ◽  
Youquan Zhao ◽  
Xiaocong Yuan
Keyword(s):  
Continuous Wave ◽  
Laser Excitation ◽  
Power Spectra ◽  
Continuous Wave Laser ◽  
Flow Angle ◽  
Intensity Modulated ◽  
Wave Laser ◽  
Doppler Power

scholarly journals Microstructure and Crystallographic Texture of Laser Additive Manufactured Nickel-Based Superalloys with Different Scanning Strategies

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 591
Author(s):  
Xingbo Liu ◽  
Hui Xiao ◽  
Wenjia Xiao ◽  
Lijun Song
Keyword(s):  
Additive Manufacturing ◽  
Epitaxial Growth ◽  
Crystallographic Texture ◽  
Continuous Wave ◽  
Flow Direction ◽  
Fiber Texture ◽  
Laves Phase ◽  
Solidification Structure ◽  
Columnar Grains ◽  
Scanning Strategies

Control of solidification structure and crystallographic texture during metal additive manufacturing is a challenging work which attracts the increasing interest of researchers. In the present work, two kinds of scanning strategies (i.e., single-directional scanning (SDS) and cross-directional scanning (CDS) were used to control the solidification structure and crystallographic texture during quasi-continuous-wave laser additive manufacturing (QCW-LAM) of Inconel 718. The results show that the solidification structure and texture are strongly dependent on scanning strategies. The SDS develops a typical fiber texture with unidirectional columnar grains, whereas the CDS develops a more random texture with a mixture of unidirectional and multidirectional grains. In addition, the SDS promotes the continuously epitaxial growth of columnar dendrites and results in the linearly distributed Laves phase particles, while the CDS leads to the alternately distributed Laves phase particles with chain-like morphology and discrete morphology. The changed stacking features of molten-pool boundary and the switched heat flow direction caused by different scanning strategies plays a crucial role on the epitaxial growth of dendrites and the final solidification structure of the fabricated parts.

Stability of slender inverted flags and rods in uniform steady flow

2016 ◽  
Vol 809 ◽  
pp. 873-894 ◽  
Author(s):  
John E. Sader ◽  
Cecilia Huertas-Cerdeira ◽  
Morteza Gharib
Keyword(s):  
Multiple Equilibria ◽  
Complex Dynamics ◽  
Flow Direction ◽  
Flow Speed ◽  
Uniform Flow ◽  
Biological Phenomena ◽  
Cantilever Length ◽  
The Stability ◽  
Elastic Sheets ◽  
Clamped Edge

Cantilevered elastic sheets and rods immersed in a steady uniform flow are known to undergo instabilities that give rise to complex dynamics, including limit cycle behaviour and chaotic motion. Recent work has examined their stability in an inverted configuration where the flow impinges on the free end of the cantilever with its clamped edge downstream: this is commonly referred to as an ‘inverted flag’. Theory has thus far accurately captured the stability of wide inverted flags only, i.e. where the dimension of the clamped edge exceeds the cantilever length; the latter is aligned in the flow direction. Here, we theoretically examine the stability of slender inverted flags and rods under steady uniform flow. In contrast to wide inverted flags, we show that slender inverted flags are never globally unstable. Instead, they exhibit bifurcation from a state that is globally stable to multiple equilibria of varying stability, as flow speed increases. This theory is compared with new and existing measurements on slender inverted flags and rods, where excellent agreement is observed. The findings of this study have significant implications to investigations of biological phenomena such as the motion of leaves and hairs, which can naturally exhibit a slender geometry with an inverted configuration.

Fluid Control with Hydrophobic Pillars in Paper-Based Microfluidics

2021 ◽  
Author(s):  
Jingji Liu ◽  
Boyang Zhang ◽  
Yajun Zhang ◽  
Yiqiang Fan
Keyword(s):  
Propagation Velocity ◽  
Control Method ◽  
Flow Direction ◽  
Flow Speed ◽  
Hydrophobic Barrier ◽  
Pillar Arrays ◽  
Paper Based Microfluidics ◽  
Fluid Control ◽  
Medical Analysis ◽  
Fluid Manipulation

Abstract Paper-based microfluidics has been widely used in chemical and medical analysis applications. In the conventional paper-based microfluidic approach, fluid is propagating inside the porous structure, and the flow direction of the fluid propagation is usually controlled with the pre-defined hydrophobic barrier (e.g. wax). However, the fluid propagation velocity inside the paper-based microfluidic devices largely depends on the material properties of paper and fluid, the relative control method is rarely reported. In this study, a fluid propagation velocity control method is proposed for paper-based microfluidics: hydrophobic pillar arrays with different configurations were deposited in the microchannels in paper-based microfluidics for flow speed control, result indicates the deposited hydrophobic pillar arrays can effectively slow down the fluid propagation at different levels and can be used to passively control the fluid propagation inside microchannels for paper-based microfluidics. For the demonstration of the proposed fluid control methods, a paper-based microfluidic device for nitrite test in water was also fabricated. The proposed fluid control method for paper-based microfluidics may have significant importance for applications that involve sequenced reactions and more actuate fluid manipulation.

ANALYSIS OF CAROTID ARTERIAL DOPPLER SIGNALS USING STFT AND WIGNER–VILLE DISTRIBUTION (WVD)

2009 ◽  
Vol 09 (01) ◽  
pp. 49-62
Author(s):  
MELLE SEDDIK AMINA ◽  
M. BEREKSI REGUIG FETHI
Keyword(s):  
Power Spectra ◽  
Doppler Imaging ◽  
Time Frequency ◽  
Ultrasound Frequency ◽  
Doppler Signals ◽  
Cross Terms ◽  
Noticeable Reduction ◽  
Doppler Power ◽  
Short Time

The study presented in this paper is concerned with the analysis of the ultrasound Doppler signal of the carotid arteries in the time-frequency domain using the short time Fourier transform (STFT) and the Wigner–Ville distribution (WVD). This study is carried out in order to investigate the behavior of the spectral broadening index (SBI) derived from spectra obtained using these methods. The variations in the shape of the Doppler power spectra as a function of time are presented in the form of sonograms in order to determine the degree of primitive carotid artery stenosis. The obtained results show a qualitative improvement in the appearance of the sonograms generated using the WVD over the STFT. However, despite this qualitative improvement the WVD suffers from some drawbacks: the presence of the cross terms which are primarily due to its quadratic nature. The application of the Choi–Williams distribution (CWD) in this analysis shows a noticeable reduction of these cross terms, improving therefore the quality of the sonograms. From these generated sonograms, the ultrasound frequency envelopes are extracted. The maximum and the mean frequencies in these envelopes are used to determine the SBI. The magnitude of the CWD-SBI is significantly greater than that of the STFT-SBI. In addition, there is a correlation between the SBIs obtained using the STFT and the CWD and the degree of severity of stenosis measured by 2D Doppler imaging.

Intracoronary doppler flow measurement and TC-99m MIBI uptake in the assessment of intermediate coronary artery stenosts

1995 ◽  
Vol 2 (2) ◽  
pp. S14-S14
Author(s):  
M UNLU ◽  
O CAYMAZ ◽  
B TURGUT ◽  
M ALKAN ◽  
R YALCIN ◽  
...  
Keyword(s):  
Coronary Artery ◽  
Flow Measurement ◽  
Doppler Flow ◽  
Intracoronary Doppler

Doppler flow measurement using surface integration of velocity vectors (Sivv): in vitro validation

2000 ◽  
Vol 26 (2) ◽  
pp. 255-262 ◽  
Author(s):  
Michelle S Chew ◽  
Joakim Brandberg ◽  
Peter Canard ◽  
Erik Sloth ◽  
Per Ask ◽  
...  
Keyword(s):  
Flow Measurement ◽  
Doppler Flow ◽  
Surface Integration

scholarly journals Large amplitude, short wave peristalsis and its implications for transport

2015 ◽  
Author(s):  
Lindsay D Waldrop ◽  
Laura A. Miller
Keyword(s):  
Fluid Flow ◽  
Large Amplitude ◽  
Compression Wave ◽  
Wave Speed ◽  
Flow Direction ◽  
Short Wave ◽  
Flow Speed ◽  
Biological Pumps ◽  
Flow Speeds ◽  
Flow Compression

Valveless, tubular pumps are widespread in the animal kingdom, but the mechanism by which these pumps generate fluid flow are often in dispute. Where the pumping mechanism of many organs was once described as peristalsis, other mechanisms, such as dynamic suction pumping, have been suggested as possible alternative mechanisms. Peristalsis is often evaluated using criteria established in a technical definition for mechanical pumps, but this definition is based on a small-amplitude, long-wave approximation which biological pumps often violate. In this study, we use a direct numerical simulation of large-amplitude, short-wave peristalsis to investigate the relationships between fluid flow, compression frequency, compression wave speed, and tube occlusion. We also explore how the flows produced differ from the criteria outlined in the technical definition of peristalsis. We find that many of the technical criteria are violated by our model: fluid flow speeds produced by peristalsis are greater than the speeds of the compression wave; fluid flow is pulsatile; and flow speed have a non-linear relationship with compression frequency when compression wave speed is held constant. We suggest that the technical definition is inappropriate for evaluating peristalsis as a pumping mechanism for biological pumps because they too frequently violate the assumptions inherent in these criteria. Instead, we recommend that a simpler, more inclusive definition be used for assessing peristalsis as a pumping mechanism based on the presence of non-stationary compression sites that propagate uni-directionally along a tube without the need for a structurally fixed flow direction.

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