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Literatura académica sobre el tema "Velocimetry of blood flows"

Autor: Grafiati

Publicado: 25 de mayo de 2024

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Artículos de revistas sobre el tema "Velocimetry of blood flows"

Bitsch, L., L. H. Olesen, C. H. Westergaard, H. Bruus, H. Klank y J. P. Kutter. "Micro particle-image velocimetry of bead suspensions and blood flows". Experiments in Fluids 39, n.º 3 (29 de junio de 2005): 507–13. http://dx.doi.org/10.1007/s00348-005-0967-7.

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Kiel, J. W., G. L. Riedel, G. R. DiResta y A. P. Shepherd. "Gastric mucosal blood flow measured by laser-Doppler velocimetry". American Journal of Physiology-Gastrointestinal and Liver Physiology 249, n.º 4 (1 de octubre de 1985): G539—G545. http://dx.doi.org/10.1152/ajpgi.1985.249.4.g539.

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To determine the feasibility of measuring gastric mucosal blood flow by laser-Doppler velocimetry (LDV), we utilized two LDV flowmeters to monitor blood flow in mucosa and serosa of chambered canine stomach. In isolated, nonautoregulating gastric segments vasodilated with isoproterenol, LDV mucosal and muscularis blood flows were both linearly related to total electromagnetic blood flow during step increases in perfusion pressure. To assess the depth of the LDV measurement, we recorded reactive hyperemia following arterial occlusion. Reactive hyperemia was frequently registered in the mucosa but rarely in muscularis. Placing a layer of nonperfused mucosa-submucosa between the probe and the perfused mucosa abolished the resting LDV mucosal flow signal and attenuated the recording of peak hyperemia by 85%. Furthermore, intra-arterial infusions of both adenosine and isoproterenol frequently increased LDV mucosal flow and decreased LDV muscularis flow, although total flow was consistently increased. These findings indicate that our LDV instruments yield linear, superficial measurements of gastric blood flow in either mucosa or muscularis. Although calibration in absolute units remains to be achieved, our results demonstrate that LDV is a practical means of studying the gastric mucosal microcirculation.

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Raghav, Vrishank, Chris Clifford, Prem Midha, Ikechukwu Okafor, Brian Thurow y Ajit Yoganathan. "Three-dimensional extent of flow stagnation in transcatheter heart valves". Journal of The Royal Society Interface 16, n.º 154 (mayo de 2019): 20190063. http://dx.doi.org/10.1098/rsif.2019.0063.

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The recent unexpected discovery of thrombosis in transcatheter heart valves (THVs) has led to increased concerns of long-term valve durability. Based on the clinical evidence combined with Virchow's triad, the primary hypothesis is that low-velocity blood flow around the valve could be a primary cause for thrombosis. However, due to limited optical access in such unsteady three-dimensional biomedical flows, measurements are challenging. In this study, for the first time, we employ a novel single camera volumetric velocimetry technique to investigate unsteady three-dimensional cardiovascular flows. Validation of the novel volumetric velocimetry technique with standard planar particle image velocimetry (PIV) technique demonstrated the feasibility of adopting this new technique to investigate biomedical flows. This technique was used to quantify the three-dimensional velocity field in the vicinity of a validated, custom developed, transparent THV in a bench-top pulsatile flow loop. Large volumetric regions of flow stagnation were observed in the neo-sinus throughout the cardiac cycle, with stagnation defined as a velocity magnitude lower than 0.05 m s −1 . The volumetric scalar viscous shear stress quantified via the three-dimensional shear stress tensor was within the range of low shear-inducing thrombosis observed in the literature. Such high-fidelity volumetric quantitative data and novel imaging techniques used to obtain it will enable fundamental investigation of heart valve thrombosis in addition to providing a reliable and robust database for validation of computational tools.

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Lee, Sang Joon, Han Wook Park y Sung Yong Jung. "Usage of CO2microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows". Journal of Synchrotron Radiation 21, n.º 5 (31 de julio de 2014): 1160–66. http://dx.doi.org/10.1107/s1600577514013423.

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X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2gas were mechanically agitated to fabricate CO2microbubbles. The optimal fabricating conditions of CO2microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

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Starodumov, Ilya, Sergey Sokolov, Ksenia Makhaeva, Pavel Mikushin, Olga Dinislamova y Felix Blyakhman. "Obtaining Vortex Formation in Blood Flow by Particle Tracking: Echo-PV Methods and Computer Simulation". Inventions 8, n.º 5 (9 de octubre de 2023): 124. http://dx.doi.org/10.3390/inventions8050124.

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Micrometer-sized particles are widely introduced as fluid flow markers in experimental studies of convective flows. The tracks of such particles demonstrate a high contrast in the optical range and well illustrate the direction of fluid flow at local vortices. This study addresses the theoretical justification on the use of large particles for obtaining vortex phenomena and its characterization in stenotic arteries by the Echo Particle Velocimetry method. Calcite particles with an average diameter of 0.15 mm were chosen as a marker of streamlines using a medical ultrasound device. The Euler–Euler model of particle motion was applied to simulate the mechanical behavior of calcite particles and 20 µm aluminum particles. The accuracy of flow measurement at vortex regions was evaluated by computational fluid dynamics methods. The simulation results of vortex zone formation obtained by Azuma and Fukushima (1976) for aluminum particles with the use of the optical velocimetry method and calcite particles were compared. An error in determining the size of the vortex zone behind of stenosis does not exceed 5%. We concluded that the application of large-size particles for the needs of in vitro studies of local hemodynamics is possible.

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Park, Cheol Woo, Se Hyun Shin, Gyu Man Kim, Jin Hong Jang y Yoon Hee Gu. "A Hemodynamic Study on a Marginal Cell Depletion Layer of Blood Flow Inside a Microchannel". Key Engineering Materials 326-328 (diciembre de 2006): 863–66. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.863.

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Biological flows, especially blood flow, have attracted a great deal of attention from fluid engineering and hemodynamic investigation fields with advances in bio-technology. The flow of blood carries dissolved gases, nutrients, hormones, and metabolic waste through the circulatory system in the human body. In the present study, the characteristics of blood flow inside a microchannel are investigated by using a micro-particle image velocimetry (micro-PIV) and an optical image processing technique. The motion of red blood cells (RBCs) was visualized with a high-speed CCD camera. The microchannel is made of polydimethylsiloxane (PDMS) material and a slide-glass is attached to the top. The thickness of the margin cell depletion layer is calculated from an acquired raw image through the image processing method, with variations in microchannel width.

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Weng, Yiming. "The influence of vortices on hemodynamics in blood vessels". Theoretical and Natural Science 6, n.º 1 (3 de agosto de 2023): 172–80. http://dx.doi.org/10.54254/2753-8818/6/20230216.

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Blood flow in vessels is affected by several factors like vessel shape, blood thickness, and heart function. Swirling patterns of flow, called vortices, are often seen in blood vessels and can affect how blood flows. This study aims to understand how vortices affect blood flow and the reasons behind these changes. Different instruments, like particle image velocimetry (PIV), computational fluid dynamics (CFD), and magnetic resonance imaging (MRI), were used to measure and analyze blood flow. CFD simulations were done using realistic blood vessel models to study how vortices form and how they affect blood velocity and pressure. The results show that vortices can cause significant changes in blood velocity and pressure, which can lead to changes in blood flow. The increased wall shear stress may contribute to the development of heart disease. This research highlights the importance of considering the impact of vortices on blood flow dynamics when designing and assessing cardiovascular devices and treatments.

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Kvietys, P. R., A. P. Shepherd y D. N. Granger. "Laser-Doppler, H2 clearance, and microsphere estimates of mucosal blood flow". American Journal of Physiology-Gastrointestinal and Liver Physiology 249, n.º 2 (1 de agosto de 1985): G221—G227. http://dx.doi.org/10.1152/ajpgi.1985.249.2.g221.

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In autoperfused preparations of feline jejunum, blood flow was measured from the mucosal surface with laser-Doppler velocimetry (LDV) and hydrogen gas (H2) clearance techniques while blood flow was altered by intra-arterial infusions of isoproterenol. LDV and H2 clearance estimates of blood flow were compared with total-wall and mucosal-submucosal blood flows measured with the radiolabeled microsphere technique. Over the range (26.3–73.6 ml X min-1 X 100 g-1) of blood flows attained, a series of direct linear relationships were obtained among LDV, H2 clearance, and microsphere estimates of jejunal blood flow. The slopes of these relationships indicated that the H2 clearance technique over-estimates total intestinal blood flow but reflects mucosal-submucosal flow as measured with microspheres. LDV measurements of blood flow from the mucosal surface were equally well correlated with total and mucosal-submucosal blood flow measured by microspheres, thereby not allowing for a definitive conclusion on the measurement depth of the LDV method. However, the ability of the LDV method to detect changes in blood flow in the perfused gut, even through 3 mm of unperfused tissue, casts a doubt on the assumption that the LDV method has a spatial resolution of less than 0.5–1.0 mm. The results of this study indicate that the H2 clearance technique can be used to measure mucosal blood flow in the small intestine. By contrast, the precise measurement depth of the LDV method is still uncertain and requires further evaluation.

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Coutinho, G., M. Rossi, A. Moita y A. L. N. Moreira. "3D Particle Tracking Velocimetry Applied To Platelet-Size Particles In Red Blood Cells Suspensions Flows Through Squared Microchannels". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 20 (11 de julio de 2022): 1–12. http://dx.doi.org/10.55037/lxlaser.20th.44.

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General defocusing particle tracking (GDPT) method is used to characterize the motion of platelet-size particles within red blood cell (RBC) suspension flows through straight-square microchannels. The method is able to characterize the three-dimensional (3D) nature of particle-RBC interactions, however the measurement depth is limited by the height of the microchannel and hematocrit level (Hct). The RBC mask the particle images and detection becomes impossible above a limit depth. The pressure-driven flow is characterized by velocity distributions and 3D trajectories of platelet-size particles within the RBC suspensions. At large hematocrit levels (Hct=30 %), the velocity distribution exhibits a blunter profile typical of blood flow in capillary-size microchannels. In addition, the interplay between blood viscosity and pressure-driven flow causes the velocity magnitude to decrease, in the center region, with increasing hematocrit. The platelet-size particles exhibit larger velocity fluctuations along the spanwise and vertical directions as Hct is increased, both inside the RBC-rich region and cell-free layer (CFL). On one hand, inside the RBC-rich zone the increasing number of flowing RBC leads to more frequent particle-RBC collisions. On the other hand, even though the particle movement inside the CFL is confined between the boundary of the RBC and the wall of the microchannel, as the thickness of the CFL decreases (i.e. increasing Hct) the collisions with RBC become more frequent. To the authors knowledge, these results represent the first experimental characterization of 3D platelet-size particle behaviour and near-wall dynamics within RBC-suspensions, and it paves the way for more detailed particle-cell flows characterization.

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Jung, Sung Yong, Han Wook Park, Bo Heum Kim y Sang Joon Lee. "Time-resolved X-ray PIV technique for diagnosing opaque biofluid flow with insufficient X-ray fluxes". Journal of Synchrotron Radiation 20, n.º 3 (1 de marzo de 2013): 498–503. http://dx.doi.org/10.1107/s0909049513001933.

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X-ray imaging is used to visualize the biofluid flow phenomena in a nondestructive manner. A technique currently used for quantitative visualization is X-ray particle image velocimetry (PIV). Although this technique provides a high spatial resolution (less than 10 µm), significant hemodynamic parameters are difficult to obtain under actual physiological conditions because of the limited temporal resolution of the technique, which in turn is due to the relatively long exposure time (∼10 ms) involved in X-ray imaging. This study combines an image intensifier with a high-speed camera to reduce exposure time, thereby improving temporal resolution. The image intensifier amplifies light flux by emitting secondary electrons in the micro-channel plate. The increased incident light flux greatly reduces the exposure time (below 200 µs). The proposed X-ray PIV system was applied to high-speed blood flows in a tube, and the velocity field information was successfully obtained. The time-resolved X-ray PIV system can be employed to investigate blood flows at beamlines with insufficient X-ray fluxes under specific physiological conditions. This method facilitates understanding of the basic hemodynamic characteristics and pathological mechanism of cardiovascular diseases.

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Tesis sobre el tema "Velocimetry of blood flows"

Pitts, Katie Lynn. "Rheological and Velocity Profile Measurements of Blood in Microflow Using Micro-particle Image Velocimetry". Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24038.

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Microhemodynamics is the study of blood flow in small vessels, usually on the order of 50 to 100 µm. The in vitro study of blood flow in small channels is analogous to the in vivo study of the microcirculation. At this scale the Reynolds and Womersly numbers are significantly less than 1 and the viscous stress and pressure gradient are the main determinant of flow. Blood is a non-homogeneous, non-Newtonian fluid and this complex composition and behavior has a greater impact at the microscale. A key parameter is the shear stress at the wall, which is involved in many processes such as platelet activation, gas exchange, embryogenesis and angiogenesis. In order to measure the shear rate in these blood flows the velocity profile must be measured. The measured profile can be characterized by the maximum velocity, the flow rate, the shear rate at the wall, or a shape parameter reflecting the bluntness of the velocity profile. The technique of micro-particle image velocimetry (µPIV) was investigated to measure the velocity profiles of blood microflows. The material of the channel, the type of tracer particles, the camera used, and the choice in data processing were all validated to improve the overall accuracy of µPIV as a blood microflow measurement method. The knowledge gained through these experiments is of immediate interest to applications such as the design of lab-on-a-chip components for blood analysis, analysis of blood flow behavior, understanding the shear stress on blood in the microcirculation and blood substitute analysis. Polymer channels were fabricated from polydimethylsiloxane (PDMS) by soft lithography in a clean room. PDMS was chosen for ease of fabrication and biocompatibility. The contacting properties of saline, water, and blood with various polymer channel materials was measured. As PDMS is naturally hydrophilic, surface treatment options were explored. Oxygenated plasma treatment was found to be less beneficial for blood than for water. The choice of camera and tracer particles were validated. Generally, for in vivo studies, red blood cells (RBCs) are used as tracer particles for the µPIV method, while for in vitro studies, artificial fluorescent micro particles are added to the blood. It is demonstrated here that the use of RBCs as tracer particles creates a large depth of correlation (DOC), which can approach the size of vessel itself and decreases the accuracy of the method. Next, the accuracy of each method is compared directly. Pulsed images used in conjunction with fluorescing tracer particles are shown to give results closest to theoretical approximations. The effect of the various post-processing methods currently available were compared for accuracy and computation time. It was shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. Using the greatest amount of correlation window overlap with elongated windows aligned with the flow was shown to give the best results when coupled with a image pre-processing method previously published for microflows of water. Finally the developed method was applied to a relevant biomedical engineering problem: the evaluation of blood substitutes and blood viscosity modifiers. Alginate is a frequently used viscosity modifier which has many uses in industry, including biomedical applications. Here the effect of alginate on the blood rheology, i.e., the shape of the velocity profile and the maximum velocity of blood flow in microchannels, was investigated. Alginate was found to blunt the shape of the velocity profile while also decreasing the shear rate at the wall. Overall, the accuracy of µPIV measurements of blood flows has been improved by this thesis. The work presented here has extended the known methods and accuracy issues of blood flow measurements in µPIV, improved the understanding of the blood velocity profile behavior, and applied that knowledge and methods to interesting, relevant problems in biomedical and biofluids engineering.

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Karolyi, Daniel Roberts. "Hemodynamic wall shear stress in models of atherosclerotic plaques using phase contrast magnetic resonance velocimetry and computational fluid dynamics". Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/20132.

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Buchmann, Nicolas. "Development of Particle Image Velocimetry for In-Vitro Studies of Arterial Haemodynamics". Thesis, University of Canterbury. Mechanical Engineering, 2010. http://hdl.handle.net/10092/4928.

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Atherosclerosis and related cardiovascular diseases (CVDs) are amongst the largest causes of morbidity and mortality in the developed world, causing considerable monetary pressure on public health systems worldwide. Atherosclerosis is characterised by the build up of vascular plaque in medium and large arteries and is a direct precursor to acute vascular syndromes such a myocardial infarction, stroke or peripheral arterial diseases. The causative factors leading to CVD still remain relatively poorly understood, but are becoming increasingly identifiable as a dysfunction of the endothelial cells that line the arterial wall. It is well known that the endothelium responds to the prevailing fluid mechanic (i.e. haemodynamic) environment, which plays a crucial role in the localised occurrence of atherosclerosis near vessel bends and bifurcations. In these areas, disturbed haemodynamics lead to flow separation and very low wall shear stress (WSS), which directly affects the functionality of the endothelium and impedes the transport of important blood borne agonists and antagonists. Detailed full field measurements assessing complex haemodynamics are sparse and consequently this thesis aims to address some of the important questions related to arterial haemodynamics and CVD by performing in-vitro flow measurements in physiologically relevant conditions. In particular, this research develops and uses state-of-the-art Particle Image Velocimetry (PIV) techniques to measure three-dimensional velocity and WSS fields in scaled models of the human carotid artery. For this purpose, the necessary theoretical and experimental concepts are developed and in-depth analyses of the underlying factors affecting the local haemodynamics and their relation to CVD are carried out. In the first part, a methodology for the construct of transparent hydraulic flow phantoms from medical imaging data is developed. The arterial geometries are reproduced in optically clear silicone and the flowing blood is modelled with a refractive index matched blood analogue. Subsequently, planar and Stereo-PIV techniques are developed and verified. A novel interfacial PIV (iPIV) technique is introduced to directly measure WSS by inferring the velocity gradient from the recorded particle images. The new technique offers a maximal achievable resolution of 1 pixel and therefore removes the resolution limit near the wall usually associated with PIV. Furthermore, the iPIV performance is assessed on a number of numerical and experimental test cases and iPIV offers a significantly improved measurement accuracy compared to more traditional techniques. Subsequently, the developed methodologies are applied in three studies to characterise the velocity and WSS fields in the human carotid artery under a number of physiological and experimental conditions. The first study focuses on idealised vessel geometries with and without disease and establishes a general understanding of the haemodynamic environment. Secondly, a physiological accurate vessel geometry under pulsatile flow conditions is investigated to provide a more realistic representation of the true in-vivo flow conditions. The prevailing flow structure in both cases is characterised by flow separation, strong secondary flows and large spatial and temporal variations in WSS. Large spatial and temporal differences exist between the different geometries and flow conditions; spatial variations appear to be more significant than transient events. Thirdly, the three-dimensional flow structure in the physiological carotid artery model is investigated by means of stereoscopic and tomographic PIV, permitting for the first time the measurement of the full 3D-3C velocity field and shear stress tensor in such geometries. The flow field within the model is complex and three-dimensional and inherently determined by the vessel geometry and the build up of an adverse pressure gradient. The main features include strong heliocoidal flow motions and large spatial variations in WSS. Lastly, the physiological implications of the current results are discussed in detail and reference to previous work is given. In summary, the present research develops a novel and versatile PIV methodology for haemodynamic in vitro studies and the functionality and accuracy is demonstrated through a number of physiological relevant flow measurements.

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Jun, Brian H. "In vitro micro particle image velocimetry measurements in the hinge region of a bileaflet mechanical heart valve". Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53380.

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A number of clinical, in vitro and computational studies have shown the potential for thromboembolic complications in bileaflet mechanical heart valves (BMHV), primarily due to the complex and unsteady flows in the valve hinges. These studies have focused on quantitative and qualitative parameters such as velocity magnitude, turbulent shear stresses, vortex formation and platelet activation to identify potential for blood damage. However, experimental characterization of the whole flow fields within the valve hinges has not yet been conducted. This information can be utilized to investigate instantaneous damage to blood elements and also to validate numerical studies focusing on the hinge’s complex fluid dynamics. The objective of this study was therefore to develop a high-resolution imaging system to characterize the flow fields and global velocity maps in a BMHV hinge. Subsequently, the present study investigated the effect of hinge gap width on flow fields in a St. Jude Medical BMHV. The results from this study suggest that the BMHV hinge design is a delicate balance between reduction of fluid shear stresses and areas of flow stasis during leakage flow, and needs to be optimized to ensure minimal thromboembolic complications. Overall, the current study demonstrates the ability of high-resolution Micro Particle Image Velocimetry to assess the fluid flow fields within the hinges of bileaflet mechanical heart valves, which can be extended to investigate micro-scale flow domains in critical regions of other cardiovascular devices to assess their blood damage potential.

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Gliah, Omemah Rajab. "In Vitro Investigation of Cell-Free Layer Formation in Microchannels: Dependency on the Red Blood Cell Aggregation and Field of Shear". Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37211.

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Red blood cells (RBCs) form approximately 40 to 45% of the human blood volume, and their behaviour and characteristics are the main determinant of blood properties, such as viscosity. RBCs are deformable species and stack together under low shear rate to form aggregates or rouleaux. Flowing RBCs migrate away from the wall leaving a cell-depleted layer known as the cell-free layer (CFL). This layer contributes to the blood viscosity and exchange between the RBCs and the target cells: a thinner CFL enhances the exchange process by reducing the diffusion distance. The formation of this CFL, however, is not yet completely understood. The goal of this study is to improve the understanding of the formation of the CFL in the micro-flow. This was accomplished by studying the effects of changing both the flow rate and the microchannel geometry on blood flow in microchannels. In this work, 10% hematocrit human blood suspensions were prepared in native plasma and flowed through poly-dimethylsiloxane (PDMS) microchannels of 100 μm x 34 μm cross-section. Investigation of the flowing cells was performed by using micro particle image velocimetry (μPIV) coupled with a high-speed camera. First, the high-speed camera images were processed with customized Matlab programs to detect and measure the CFL thickness and the RBC aggregates sizes. Second, the blood flow velocity profiles were measured using μPIV in order to determine the actual flow rate, the RBCs’ centerline velocity, and the shear rate. The results showed that the increase in both flow rate and shear rate significantly reduced the CFL thickness and RBC aggregates size. Comparison of the upstream and downstream measurements in the bifurcating microchannel showed that the change in microchannel geometry did not significantly influence CFL thickness and RBC aggregate size, while within the daughter branches, RBCs tended to flow close to the inner wall resulting in an undetectable CFL at the inner wall and in a larger CFL at the outer wall of the branch. These in vitro results quantitatively relate CFL thickness and RBC aggregate size at different shear rates. The findings are of immediate interest regarding the understanding of microcirculation and improved designs of microchips.

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Ziegenhein, Thomas y Dirk Lucas. "On sampling bias in multiphase flows: Particle image velocimetry in bubbly flows". Helmholtz-Zentrum Dresden - Rossendorf, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-197551.

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Measuring the liquid velocity and turbulence parameters in multiphase flows is a challenging task. In general, measurements based on optical methods are hindered by the presence of the gas phase. In the present work, it is shown that this leads to a sampling bias. Here, particle image velocimetry (PIV) is used to measure the liquid velocity and turbulence in a bubble column for different gas volume flow rates. As a result, passing bubbles lead to a significant sampling bias, which is evaluated by the mean liquid velocity and Reynolds stress tensor components. To overcome the sampling bias a window averaging procedure that waits a time depending on the locally distributed velocity information (hold processor) is derived. The procedure is demonstrated for an analytical test function. The PIV results obtained with the hold processor are reasonable for all values. By using the new procedure, reliable liquid velocity measurements in bubbly flows, which are vitally needed for CFD validation and modeling, are possible. In addition, the findings are general and can be applied to other flow situations and measuring techniques.

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Faure, M. A. "Particle image velocimetry measurement of in-cylinder flows". Thesis, University of Brighton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387818.

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Jessen, Wilhelm. "Particle image velocimetry measurements of film cooling flows /". Aachen : Mainz, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017075640&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.

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Brady, Michael Richard. "Subpixel Resolution Schemes for Multiphase Flows". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36104.

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This effort explores novel sub-resolution particle center estimation algorithms for Digital Particle Tracking Velocimetry (DPIV). The errors of these new methods were classified through Monte-Carlo simulations. These schemes provide direct measurements of the apparent particle image diameter and the subpixel position. The new methods significantly reduce the bias error due to pixel discretization, thus reducing the total error in the position and sizing measurement compared to the classic three point and least squares Gaussian estimators. In addition, the accuracy of the least-squares fits were essentially independent of the true particle diameter and significantly reduced the particle position error compared with current estimation schemes. The results of the Monte Carlo simulations were validated in a high pressure spray atomization experiment.
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Fratantonio, Dominique. "Molecular tagging velocimetry in rarefied and confined gas flows". Thesis, Toulouse, INSA, 2019. http://www.theses.fr/2019ISAT0027.

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Le marquage moléculaire est une technique expérimentale permettant d’effectuer de manière peu intrusive de la vélocimétrie au sein des écoulements. La mesure est basée sur le suivi de molécules capable d’émettre de la lumière suite à une excitation par une source laser. La mesure locale de vitesse est alors déduite de la visualisation du déplacement des molécules traceuses. Bien que la vélocimétrie par marquage moléculaire (MTV) ait déjà été utilisée avec succès pour des écoulements liquides ou gazeux, son application à des écoulements gazeux raréfiés internes reste encore un défi en raison de la diffusion moléculaire élevée et de la faiblesse de l’émission lumineuse à basse pression. Néanmoins, pouvoir appliquer la MTV en condition de gaz raréfié est intéressant du fait du manque de données expérimentales locales nécessaires à une meilleure compréhension des mécanismes d’interaction moléculaire entre le gaz et une surface solide. Dans ce travail, une étude expérimentale a été menée sur l’intensité et le temps de vie de la photoluminescence des traceurs moléculaires utilisés, à savoir l’acétone et le diacétyle vapeurs. Cette analyse a permis d’estimer les conditions expérimentales optimales pour l’application de la MTV aux gaz raréfiés. Ainsi, la MTV a été appliquée à des écoulements de mélanges gaz-traceur à basses pressions dans un canal millimétrique de section rectangulaire, fournissant ainsi les premiers résultats de vélocimétrie en régime d’écoulement légèrement raréfié
Molecular tagging velocimetry (MTV) is an optic experimental technique widely employed for measuring the velocity field in fluid flows. The measuring principle is based on the tracking of molecules able to emit light in response to a laser excitation. By seeding the flow with this tracer, local velocity measurements can be carried out by following the displacement of the emitting molecules. While this technique has already been successfully applied in liquid and gas flows, the application to rarefied and confined gas flows is still a challenge due to the high molecular diffusion and the low emitted light from the tracer at low pressures. The interest in applying MTV in rarefied conditions derives from the absence of local experimental data that can allow a better understanding on the mechanisms of interaction between the gas molecules and the wall surface. In this work, an experimental analysis of the intensity and lifetime of the photoluminescence of the molecular tracers employed, i.e., acetone and diacetyl, is presented. This analysis allowed to estimate the best working conditions in order to be able to apply MTV to rarefied gas flows. Thus, MTV has been applied to gas-tracer mixtures at low pressures in a millimetric rectangular channel producing the first preliminary results in the slip flow regime

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Libros sobre el tema "Velocimetry of blood flows"

Lepicovsky, J. Seeding for laser velocimetry in confined supersonic flows with shocks. [Washington, DC]: National Aeronautics and Space Administration, 1996.

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Lepicovsky, J. Seeding for laser velocimetry in confined supersonic flows with shocks. [Washington, DC]: National Aeronautics and Space Administration, 1996.

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Pierre, Péronneau, ed. Vélocimétrie Doppler: Applications en pharmacologie cardiovasculaire animale et clinique. Paris: Editions INSERM, 1991.

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Krothapalli, Anjaneyulu. The development of laser speckle velocimetry for the study of vortical flows. Moffett Field, Calif: National Aeronautics and Space Administration, Ames Research Center, 1991.

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Thiriet, Marc. Biology and Mechanics of Blood Flows. New York, NY: Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-74847-4.

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Thiriet, Marc. Biology and Mechanics of Blood Flows. New York, NY: Springer New York, 2008. http://dx.doi.org/10.1007/978-0-387-74849-8.

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Biology and mechanics of blood flows. New York: Springer, 2008.

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Lee, Wing Kai. The application of 2D and 3D particle image velocimetry (PIV) for measurement in high speed flows. [s.l.]: typescript, 1999.

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Hild, Jack. Blood flows on the desert wind: Point Blank. Toronto ; New York: Gold Eagle Books, 1988.

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Alfio, Quarteroni, Rozza Gianluigi y SpringerLink (Online service), eds. Modeling of Physiological Flows. Milano: Springer Milan, 2012.

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Capítulos de libros sobre el tema "Velocimetry of blood flows"

Kajiya, Fumihiko, Osamu Hiramatsu, Yasuo Ogasawara, Keiichiro Mito y Katsuhiko Tsujioka. "A Study of Coronary Circulation by Laser Doppler Velocimetry". En Regulation of Coronary Blood Flow, 11–23. Tokyo: Springer Japan, 1991. http://dx.doi.org/10.1007/978-4-431-68367-4_2.

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Braaf, Boy, Maximilian G. O. Gräfe, Néstor Uribe-Patarroyo, Brett E. Bouma, Benjamin J. Vakoc, Johannes F. de Boer, Sabine Donner y Julian Weichsel. "OCT-Based Velocimetry for Blood Flow Quantification". En High Resolution Imaging in Microscopy and Ophthalmology, 161–79. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-16638-0_7.

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Schulman, Harold. "Doppler Velocimetry of Fetal and Placental Blood Flow". En The High-Risk Fetus, 336–51. New York, NY: Springer New York, 1993. http://dx.doi.org/10.1007/978-1-4613-9240-8_18.

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Riva, Charles E. y Benno L. Petrig. "Retinal Blood Flow: Laser Doppler Velocimetry and Blue Field Simulation Technique". En Noninvasive Diagnostic Techniques in Ophthalmology, 390–409. New York, NY: Springer New York, 1990. http://dx.doi.org/10.1007/978-1-4613-8896-8_20.

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Buchmann, N. A., M. C. Jermy y T. David. "Experimental Investigation of Blood Flow in the Brain by Means of Particle Image Velocimetry — A Preliminary Study". En New Trends in Fluid Mechanics Research, 622–25. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-75995-9_208.

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Raffel, Markus, Christian E. Willert, Fulvio Scarano, Christian J. Kähler, Steven T. Wereley y Jürgen Kompenhans. "Applications: Transonic Flows". En Particle Image Velocimetry, 439–76. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-68852-7_12.

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Carlsohn, Matthias F., André Kemmling, Arne Petersen y Lennart Wietzke. "Light Field Particle Image Velocimetry by Plenoptic Image Capturing for 3D-Display of Simulated Blood Flow in Cerebral Aneurysms". En Informatik aktuell, 230–35. Berlin, Heidelberg: Springer Berlin Heidelberg, 2016. http://dx.doi.org/10.1007/978-3-662-49465-3_41.

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Raffel, Markus, Christian E. Willert, Fulvio Scarano, Christian J. Kähler, Steven T. Wereley y Jürgen Kompenhans. "Applications: Flows at Different Temperatures". En Particle Image Velocimetry, 523–46. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-68852-7_15.

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Seeger, A., U. Kertzscher, K. Affeld, L. Goubergrits y E. Wellnhofer. "X-ray Based Particle Tracking Velocimetry for Bubble Columns with High Void Fraction". En Bubbly Flows, 129–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-642-18540-3_11.

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Pitz, Robert W. y Paul M. Danehy. "Molecular Tagging Velocimetry in Gases". En Optical Diagnostics for Reacting and Non-Reacting Flows: Theory and Practice, 539–88. Reston, VA: American Institute of Aeronautics and Astronautics, Inc., 2023. http://dx.doi.org/10.2514/5.9781624106330.0539.0588.

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Actas de conferencias sobre el tema "Velocimetry of blood flows"

Wereley, Steven T., Carl D. Meinhart, Juan G. Santiago y Ron J. Adrian. "Velocimetry for MEMS Applications". En ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1284.

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Abstract Particle image velocimetry (PIV), a technique commonly used at macroscopic length scales to measure velocity fields of particle-seeded flows, is adapted to measure velocity fields in microfluidic MEMS devices, where micron-scale spatial resolution is critical. Adapting PIV to the microscopic level presents a number of challenges, including visualizing tracer particles that are smaller than the wavelength of light and minimizing errors due to the Brownian motion of the tracer particles. High numerical aperture video microscopy is used to record the faint signals from fluorescent 300 nm particles. Innovative ensemble averaging and adaptive spatial shifting algorithms are used to extract maximal information from the recorded images. The PIV technique is used to measure a low Reynolds number Hele-Shaw flow around an 8 μm human red blood cell. The velocity vector field presented has a maximal spatial resolution of 3.2 × 3.2 × 1.5 μm.

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Fountain, Thomas W. R. y Steven W. Day. "Design and Particle Image Velocimetry Investigation of a Turbulent Mini-Jet Hemolysis Testing Apparatus". En ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62320.

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Hemolysis is the break up of red blood cells, and is a condition that is of concern during the design process of blood contacting prostheses. In turbulent flows, hemolysis has been most often correlated to Reynolds shear stress. Mini-scale turbulent jets have been used for hemolysis experiments because they allow for explicit control of shear. Quantitative predictions of hemolysis from shear stress are unreliable, with experimentally determined threshold Reynolds stresses for turbulent shear flow range from 400Pa to 5000Pa, with recent experiments at 800Pa. Reynolds stresses are a statistic of large scale turbulence, and act at spatial scales much larger than that of a red blood cell. It has been suggested in literature that hemolysis may be related to stresses induced by turbulent energy dissipation, which acts as a spatial scale closer to that of a red blood cell. The dissipation of turbulence kinetic energy occurs at the Kolmogorov scales, which is generally similar in scale to that of a red blood cell.

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Navitsky, Michael A., Jason C. Nanna, Joseph J. Pearson, Matthew P. Scanlon, Frank C. Lynch, Suzanne M. Shontz y Keefe B. Manning. "Particle Image Velocimetry Flow Measurements About a Vena Cava Filter". En ASME 2010 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2010. http://dx.doi.org/10.1115/sbc2010-19544.

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Deep vein thrombosis (DVT) is a medical condition in which blood clots form in the lower extremities, often times the right leg, or pelvis region. These blood clots are formed through a variety of circumstances including: injury to the vessel wall, decreased blood supply, or increased clotting factors. Complications from DVT often arise when the blood clot breaks free forming a pulmonary embolism (PE). The incidence of such an occurrence is over 600,000 cases per year in the United States. If the PE is allowed to travel through the vascular system, occlusion of the pulmonary arteries and death may result. There are over 200,000 deaths attributed to this cause every year in the United States.

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Petrig, Benno L. y Charles E. Riva. "Towards Computer-Assisted Clinical Retinal Laser Doppler Velocimetry". En Noninvasive Assessment of the Visual System. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/navs.1987.wc5.

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The retina is among the few tissues in the human body where blood circulation can be observed directly and noninvasively. This has facilitated a detailed description of the morphological changes of the retinal vasculature caused by many ocular and systemic diseases. Despite the accessibility of the retinal vasculature and the obvious importance of blood flow, quantitative data on the retinal hemodynamics in the normal and diseased retina is not available to the clinician. Assessments of "normal" or "low" flow based on fluorescein angiography remain qualitative and the fluorescein dye dilution technique has had limited success in providing a quantitative measure of retinal blood flow.

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Lei, Jian, Xun Lang, Bingbing He, Songhua Liu, Hao Tan y Yufeng Zhang. "Ultrasonic Carotid Blood Flow Velocimetry Based on Deep Complex Neural Network". En 2022 IEEE 35th International Symposium on Computer-Based Medical Systems (CBMS). IEEE, 2022. http://dx.doi.org/10.1109/cbms55023.2022.00032.

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Mehri, R., C. Mavriplis y M. Fenech. "Micro Particle Image Velocimetry and Numerical Investigation of Micro Couette Blood Flow". En ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icnmm2012-73177.

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The purpose of the work presented this paper is to design a model to study experimentally and numerically a micro-Couette blood flow to obtain a constant and controlled shear rate that is a suitable environment for analysis of Red Blood Cell (RBC) aggregation. Due to the simplicity of the flow conditions, aggregate size can be related to the constant shear rate applied. This Couette flow is created by the motion of a second fluid that entrains the blood. The experimental work is coupled with 3D numerical simulations performed using a research computational fluid dynamics solver, Nek5000, based on the spectral element method, while the experiments are conducted using a micro-particle image velocimetry system. Two models of microchannels, with different dimensions, 150 × 33μm and 170 × 64μm, are fabricated in the laboratory using standard photolithography methods. The design of the channel is based on several parameters determined by the simulations. A Newtonian model is tested numerically and experimentally. Blood is then tested experimentally to be compared to the simulation results. We find that using a velocity ratio of 4 between the two Newtonian fluids, we create a flow where one third of the channel thickness is filled with the fluid destined to be blood. In the blood experiments, the velocity profile in this layer is approximately linear, resulting in the desired controlled conditions for the study of RBC aggregation.

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Kucukal, E., Y. Man, U. A. Gurkan y B. E. Schmidt. "Blood Flow Velocimetry in a Microchannel During Coagulation Using PIV and wOFV". En ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-24173.

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Abstract This article describes novel measurements of the velocity of whole blood flow in a microchannel during coagulation. The blood is imaged volumetrically using a simple optical setup involving a white light source and a microscope camera. The images are processed using PIV and wavelet-based optical flow velocimetry (wOFV), both of which use images of individual blood cells as flow tracers. Measurements of several clinically relevant parameters such as the clotting time, decay rate, and blockage ratio are computed. The high-resolution wOFV results yield highly detailed information regarding thrombus formation and corresponding flow evolution that is the first of its kind.

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Meissner, Robert, Wade W. Sugden, Arndt F. Siekmann y Cornelia Denz. "Multimodal in vivo blood flow sensing combining particle image velocimetry and optical tweezers-based blood steering". En Diagnostic and Therapeutic Applications of Light in Cardiology 2018, editado por Guillermo J. Tearney, Kenton W. Gregory y Laura Marcu. SPIE, 2018. http://dx.doi.org/10.1117/12.2290974.

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Pitts, Katie L. y Marianne Fenech. "Blood Velocity Profile Measurements in Microchannels Using Micro-Particle Image Velocimetry". En ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icnmm2012-73056.

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Experimental studies of blood microflows in rectangular biocompatible polymer microchannels measured using micro-particle image velocimetry are reported. The data processing methods, data collection methods, and choice of channel material are demonstrated to impact the velocity profile measurements obtained. Results show that the use of red blood cells as tracer particles creates a large depth of correlation which can approach the size of the vessel itself and decrease the accuracy of the method. It is shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. The velocity profile is studied as a function of the flow rate of the blood, the hematocrit, or percentage of red blood cells, the shape of the channel, and the channel material. The results highlighted here show that the best processing options include pre-processing, the use of fluorescent tracer particles instead of the red blood cells themselves as tracers give a more accurate prediction of the profile, and the use of silicone as the channel material more closely mimics the behavior of physiology. Acrylic biocompatible polymer channels are shown to give a more parabolic profile at lower levels of hematocrit, while silicone biocompatible polymer channels give a velocity profile that looks more like in vivo flow studies.

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Rahgozar, Saeed, Giuseppe A. Rosi, Lucie Kaucky, Andrew Walker y David E. Rival. "EXPLORING THE INTERACTION OF RED BLOOD CELL ANALOGS WITH TURBULENCE USING PARTICLE TRACKING VELOCIMETRY". En Ninth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2015. http://dx.doi.org/10.1615/tsfp9.1230.

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Informes sobre el tema "Velocimetry of blood flows"

Zhang, Yibin, Daniel Richardson, Garrett Marshall, Steven Beresh y Katya Casper. Spatially and Temporally Resolved Velocimetry for Hypersonic Flows. Office of Scientific and Technical Information (OSTI), septiembre de 2021. http://dx.doi.org/10.2172/1820563.

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Kuhlman, John M. Accuracy and Application of Doppler Global Velocimetry to Complex Aerodynamic Flows. Fort Belvoir, VA: Defense Technical Information Center, junio de 2001. http://dx.doi.org/10.21236/ada388073.

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O`Hern, T. J., J. R. Torczynski, R. N. Shagam, T. K. Blanchat, T. Y. Chu, A. L. Tassin-Leger y J. A. Henderson. Optical diagnostics for turbulent and multiphase flows: Particle image velocimetry and photorefractive optics. Office of Scientific and Technical Information (OSTI), enero de 1997. http://dx.doi.org/10.2172/446382.

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Hassan, T. A. Multiparticle imaging technique for two-phase fluid flows using pulsed laser speckle velocimetry. Office of Scientific and Technical Information (OSTI), diciembre de 1992. http://dx.doi.org/10.2172/6893012.

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Yassin Hassan. Full-Volume, Three-Dimensional, Transient Measurements of Bubbly Flows Using Particle Tracking Velocimetry and Shadow Image Velocimetry Coupled with Pattern Recognition Techniques. Office of Scientific and Technical Information (OSTI), noviembre de 2001. http://dx.doi.org/10.2172/791466.

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Restrepo, Juan M. Particle and Blood Cell Dynamics in Oscillatory Flows Final Report. Office of Scientific and Technical Information (OSTI), septiembre de 2008. http://dx.doi.org/10.2172/953697.

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Hassan, T. A. Multiparticle imaging technique for two-phase fluid flows using pulsed laser speckle velocimetry. Final report, September 1988--November 1992. Office of Scientific and Technical Information (OSTI), diciembre de 1992. http://dx.doi.org/10.2172/10140495.

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Varga, Gabriella A., Amichai Arieli, Lawrence D. Muller, Haim Tagari, Israel Bruckental y Yair Aharoni. Effect of Rumen Available Protein, Amimo Acids and Carbohydrates on Microbial Protein Synthesis, Amino Acid Flow and Performance of High Yielding Cows. United States Department of Agriculture, agosto de 1993. http://dx.doi.org/10.32747/1993.7568103.bard.

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The effect of rumen available protein amino acids and carbohydrates on microbial protein synthesis, amino acid flow and performance of high yielding dairy cows was studied. A significant relationship between the effective degradabilities of OM in feedstuffs and the in vivo ruminal OM degradation of diets of dairy cows was found. The in situ method enabled the prediction of ruminal nutrients degradability response to processing of energy and nitragenous supplements. The AA profile of the rumen undegradable protein was modified by the processing method. In a continuous culture study total N and postruminal AA flows, and bacterial efficiency, is maximal at rumen degradable levels of 65% of the CP. Responses to rumen degradable non carbohydrate (NSC) were linear up to at least 27% of DM. Higher CP flow in the abomasum was found for cows fed high ruminally degradable OM and low ruminally degradable CP diet. It appeared that in dairy cows diets, the ratio of rumen degradable OM to rumenally degradable CP should be at least 5:1 in order to maximize postruminal CP flow. The efficiency of microbial CP synthesis was higher for diets supplemented with 33% of rumen undegradable protein, with greater amounts of bacterial AA reaching the abomasum. Increase in ruminal carbohydrate availability by using high moisture corn increased proportions of propionate, postruminal nutrients flow, postruminal starch digestibility, ruminal availability of NSC, uptake of energy substrates by the mammory gland. These modifications resulted with improvement in the utilization of nonessential AA for milk protein synthesis, in higher milk protein yield. Higher postruminal NSC digestibility and higher efficiency of milk protein production were recorded in cows fed extruded corn. Increasing feeding frequency increased flow of N from the rumen to the blood, reduced diurnal variation in ruminal and ammonia, and of plasma urea and improved postruminal NSC and CIP digestibility and total tract digestibilities. Milk and constituent yield increased with more frequent feeding. In a study performed in a commercial dairy herd, changes in energy and nitrogenous substrates level suggested that increasing feeding frequency may improve dietary nitrogen utilization and may shift metabolism toward more glucogenesis. It was concluded that efficiency of milk protein yield in high producing cows might be improved by an optimization of ruminal and post-ruminal supplies of energy and nitrogenous substrates. Such an optimization can be achieved by processing of energy and nitrogenous feedstuffs, and by increasing feeding frequency. In situ data may provide means for elucidation of the optimal processing conditions.

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