Numerical Studies of Injection Process Control With Spatial Gradients of Electrical Conductivity

2003 ◽  
Author(s):  
Liqing Ren ◽  
Dongqing Li
Keyword(s):  
Transport Phenomena ◽  
Glass Plate ◽  
Concentration Field ◽  
Lab On A Chip ◽  
Theoretical Models ◽  
Spatial Gradient ◽  
Precise Control ◽  
Spatial Gradients ◽  
Injection Process ◽  
Numerical Studies

The systematic design and precise control of the microfluidic dispenser (crossing microchannels etched into a plastic or glass plate) is key to the performance of many lab-on-a-chip devices. The fundamental understanding of the complicated electrokinetic phenomena in microfluidic dispensers therefore is necessary. In the literature, a few theoretical models studying the transport phenomena in similar crossing microchannels didn’t consider the spatial gradients of conductivity due to its complexity. A new theoretical model was developed in this paper to simulate the transport phenomena in a microfluidic dispenser with the consideration of a large range of spatial gradient of electric conductivity. This developed model was used to simulate the potential field, flow field, and concentration field of the injection processes where the conductivity of the sample-carrying buffer differs significantly from that of the driving buffer. The transport phenomena are found to be very sensitive to the conductivity difference between the sample-carrying buffer and the driving buffer. The developed model can be employed to find the optimal voltages for controlling the dispensed sample size and to provide guidance for designing such a microfluidic dispenser in lab-on-a-chip devices.

Numerical Simulation of On-Chip Injection Process With Spatial Gradients of Electrical Conductivity

2003 ◽  
Author(s):  
Liqing Ren ◽  
Dongqing Li
Keyword(s):  
Transport Phenomena ◽  
Glass Plate ◽  
Concentration Field ◽  
Lab On A Chip ◽  
Theoretical Models ◽  
Spatial Gradient ◽  
Precise Control ◽  
Spatial Gradients ◽  
Injection Process ◽  
On Chip

The systematic design and precise control of the microfluidic dispenser (crossing microchannels etched into a plastic of glass plate) is key to the performance of many lab-on-a-chip devices. The fundamental understanding of the complicated electrokinetic phenomena in microfluidic dispensers therefore is necessary. In the literature, a few theoretical models studying the transport phenomena in similar crossing microchannels didn’t consider the spatial gradients of conductivity due to its complexity. A new theoretical model was developed in this paper to simulate the transport phenomena in a microfluidic dispenser with the consideration of a large range of spatial gradient of electric conductivity. This developed model was used to simulate the potential field, flow field, and concentration field of the injection processes where the conductivity of the sample-carrying buffer differs significantly from that of the driving buffer. The transport phenomena are found to be very sensitive to the conductivity difference between the sample-carrying buffer and the driving buffer. The developed model can be employed to find the optimal voltages for controlling the dispensed sample size and to provide guidance for designing such a microfluidic dispenser in lab-on-a-chip devices.

Justification of Non-Dimensional Schemes and Identification of Parameters on Modelling Electrokinetic Transport Phenomena in Microchannels

2010 ◽  
Author(s):  
Zhanjie Shao ◽  
Gerry Schneider ◽  
Carolyn Ren
Keyword(s):  
Initial Conditions ◽  
Transport Phenomena ◽  
Concentration Field ◽  
Electrokinetic Transport ◽  
Dimensional Model ◽  
Applied Potential ◽  
Governing Equations ◽  
Numerical Studies ◽  
Electrokinetic Flows ◽  
On Chip

The electrokinetic transport phenomena are to be numerically studied based on cross-linked microchannel networks, which have been commonly employed for on-chip capillary electrophoresis applications. Applied potential field, flow field and concentration field should be solved to predict the species transport process under electrokinetic flows. Together with the well-designed channel geometry, a detailed physical model was firstly formulated through a series of governing equations and corresponding boundary/initial conditions, which was briefly re-presented from our previous publications. The emphasis of current work was to justify the simplest non-dimensional scheme and identify the most beneficial parameters so that an effective and simplified non-dimensional model was developed for numerical studies.

scholarly journals Epidermal Growth Factor Receptor Distribution during Chemotactic Responses

2000 ◽  
Vol 11 (11) ◽  
pp. 3873-3883 ◽  
Author(s):  
Maryse Bailly ◽  
Jeffrey Wyckoff ◽  
Boumediene Bouzahzah ◽  
Ross Hammerman ◽  
Vonetta Sylvestre ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Egf Receptor ◽  
Fluorescent Protein ◽  
Growth Factor Receptor ◽  
Spatial Gradient ◽  
Spatial Gradients ◽  
Epidermal Growth ◽  
Green Fluorescent

To determine the distribution of the epidermal growth factor (EGF) receptor (EGFR) on the surface of cells responding to EGF as a chemoattractant, an EGFR-green fluorescent protein chimera was expressed in the MTLn3 mammary carcinoma cell line. The chimera was functional and easily visualized on the cell surface. In contrast to other studies indicating that the EGFR might be localized to certain regions of the plasma membrane, we found that the chimera is homogeneously distributed on the plasma membrane and becomes most concentrated in vesicles after endocytosis. In spatial gradients of EGF, endocytosed receptor accumulates on the upgradient side of the cell. Visualization of the binding of fluorescent EGF to cells reveals that the affinity properties of the receptor, together with its expression level on cells, can provide an initial amplification step in spatial gradient sensing.

A Data-Driven Exploratory Approach for Level Curve Estimation With Autonomous Underwater Agents

2017 ◽  
Author(s):  
Hsien-Chung Lin ◽  
Eugen Solowjow ◽  
Masayoshi Tomizuka ◽  
Edwin Kreuzer
Keyword(s):  
Concentration Field ◽  
Real Data ◽  
Support Vector ◽  
Level Curve ◽  
Data Set ◽  
Curve Estimation ◽  
Numerical Studies ◽  
Exploratory Approach ◽  
Vector Machines ◽  
Myopic Strategy

This contribution presents a method to estimate environmental boundaries with mobile agents. The agents sample a concentration field of interest at their respective positions and infer a level curve of the unknown field. The presented method is based on support vector machines (SVMs), whereby the concentration level of interest serves as the decision boundary. The field itself does not have to be estimated in order to obtain the level curve which makes the method computationally very appealing. A myopic strategy is developed to pick locations that yield most informative concentration measurements. Cooperative operations of multiple agents are demonstrated by dividing the domain in Voronoi tessellations. Numerical studies demonstrate the feasibility of the method on a real data set of the California coastal area. The exploration strategy is benchmarked against random walk which it clearly outperforms.

scholarly journals Laser ultrasonic imaging of wavefield spatial gradients for damage detection

2020 ◽  
pp. 147592172095133
Author(s):  
Zihan Wu ◽  
See Yenn Chong ◽  
Michael D Todd
Keyword(s):  
Laser Scanning ◽  
Ultrasonic Imaging ◽  
Image Processing Technique ◽  
Spatial Gradient ◽  
Spatial Covariance ◽  
Laser Ultrasonic ◽  
Spatial Gradients ◽  
Orientation Map ◽  
Scanning Area ◽  
Damage Visualization

This article describes a new damage visualization method to investigate and analyze propagating guided Lamb waves using analyses of wavefield spatial gradients. A laser ultrasonic interrogation system was used to create full-field ultrasonic data measurements for ultrasonic wavefield imaging. The laser scanning process was performed based on both a raster scan and a circle scan. From the high-resolution wavefield data, a spatial gradient–based image processing technique was developed using gradient vectors to extract features sensitive to defects. Local impedance changes at the damaged area would result in a local distortion of the waveform which was captured and quantified by the variation of the gradient vectors in the scanning area as time evolves. Such variation was accumulated over time with a statistical threshold filter to generate a gradient-orientation map for damage visualization. The proposed algorithm was capable of producing distinctive damage patterns when tested experimentally on a 3-mm aluminum plate with multiple simultaneous simulated defects. Compared to conventional techniques like local wavenumber estimation, the generation of the accumulated orientation map involves no filtering process in the frequency or wavenumber domain, at the expense of more accurate shaping of the defect. A spatial covariance analysis was adopted to locate damage from the results as well as to evaluate the correlation between different kinds of defects. Combining the proposed approach with conventional laser ultrasonic imaging techniques enables a fast and robust damage identification and characterization process which requires lower computational burden and practical operation.

Differential Gene Expression of Endothelial Cells Under High Wall Shear Stress and Spatial Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Song Liu ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Flow Acceleration ◽  
Spatial Gradients ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature. Due to the focal nature of aneurysm development it has long been speculated that hemodynamics are an important factor in aneurysm susceptibility. The local hemodynamics of bifurcations are complex, being characterized by flow impingement causing a high frictional force on the vessel wall known as wall shear stress (WSS) and significant flow acceleration or deceleration, manifested as the positive or negative spatial gradient of WSS (WSSG). In vivo studies have recently identified that aneurysm initiation occurs at areas of the vessel wall that experience a combination of both high WSS and positive WSSG [1,2]

scholarly journals Population dynamics of Pseudomonas sp. along a spatial gradient of phosphate: an experimental approach for spatial ecology

2000 ◽  
Vol 60 (4) ◽  
pp. 637-644
Author(s):  
C. T. CODEÇO ◽  
J. P. GROVER
Keyword(s):  
Population Dynamics ◽  
Culture System ◽  
Spatial Ecology ◽  
Experimental Approach ◽  
Theoretical Models ◽  
Spatial Gradient ◽  
Pseudomonas Sp ◽  
Directional Flow ◽  
Experimental Tool ◽  
Theoretical Predictions

Many theoretical models have been proposed to study the effect of space on population dynamics and interactions, but most of them are difficult to translate into experimental setups due to their abstract nature. Here we defend the gradostat as a valuable experimental tool for testing such theories. The gradostat is a culture system with bi-directional flow that forms nutrient gradients at steady state. In this study, we use a 3-vessel gradostat with a phosphate gradient to study the effect of spatial heterogeneity on the spatial distribution of Pseudomonas sp., an heterotrophic aquatic bacterium. The observed distributions partially agree with theoretical predictions, obtained from a mathematical model.

Transport Phenomena Analysis in Proton Exchange Membrane Fuel Cells

2005 ◽  
Vol 127 (12) ◽  
pp. 1363-1379 ◽  
Author(s):  
Hongtan Liu ◽  
Tianhong Zhou ◽  
Ping Cheng
Keyword(s):  
Experimental Investigation ◽  
Fuel Cells ◽  
Fuel Cell ◽  
Proton Exchange Membrane ◽  
Transport Phenomena ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Transport Processes ◽  
Proton Exchange ◽  
Exchange Membrane

The objective of this review is to provide a summary of modeling and experimental research efforts on transport phenomena in proton exchange membrane fuel cells (PEMFCs). Several representative PEMFC models and experimental studies in macro and micro PEMFCs are selected for discussion. No attempt is made to examine all the models or experimental studies, but rather the focus is to elucidate the macro-homogeneous modeling methodologies and representative experimental results. Since the transport phenomena are different in different regions of a fuel cell, fundamental phenomena in each region are first reviewed. This is followed by the presentation of various theoretical models on these transport processes in PEMFCs. Finally, experimental investigation on the cell performance of macro and micro PEMFC and DMFC is briefly presented.

scholarly journals The Internal Phosphodiesterase RegA Is Essential for the Suppression of Lateral Pseudopods duringDictyosteliumChemotaxis

2000 ◽  
Vol 11 (8) ◽  
pp. 2803-2820 ◽  
Author(s):  
Deborah J. Wessels ◽  
Hui Zhang ◽  
Joshua Reynolds ◽  
Karla Daniels ◽  
Paul Heid ◽  
...  
Keyword(s):  
Mutant Cell ◽  
Computer Assisted ◽  
Spatial Gradient ◽  
Wild Type ◽  
Gene Encoding ◽  
Camp Phosphodiesterase ◽  
Temporal Gradient ◽  
Spatial Gradients ◽  
Normal Manner ◽  
Analysis System

Dictyostelium strains in which the gene encoding the cytoplasmic cAMP phosphodiesterase RegA is inactivated form small aggregates. This defect was corrected by introducing copies of the wild-type regA gene, indicating that the defect was solely the consequence of the loss of the phosphodiesterase. Using a computer-assisted motion analysis system,regA−mutant cells were found to show little sense of direction during aggregation. When labeled wild-type cells were followed in a field of aggregatingregA−cells, they also failed to move in an orderly direction, indicating that signaling was impaired in mutant cell cultures. However, when labeled regA−cells were followed in a field of aggregating wild-type cells, they again failed to move in an orderly manner, primarily in the deduced fronts of waves, indicating that the chemotactic response was also impaired. Since wild-type cells must assess both the increasing spatial gradient and the increasing temporal gradient of cAMP in the front of a natural wave, the behavior of regA−cells was motion analyzed first in simulated temporal waves in the absence of spatial gradients and then was analyzed in spatial gradients in the absence of temporal waves. Our results demonstrate that RegA is involved neither in assessing the direction of a spatial gradient of cAMP nor in distinguishing between increasing and decreasing temporal gradients of cAMP. However, RegA is essential for specifically suppressing lateral pseudopod formation during the response to an increasing temporal gradient of cAMP, a necessary component of natural chemotaxis. We discuss the possibility that RegA functions in a network that regulates myosin phosphorylation by controlling internal cAMP levels, and, in support of that hypothesis, we demonstrate that myosin II does not localize in a normal manner to the cortex ofregA−cells in an increasing temporal gradient of cAMP.

scholarly journals Locations of ectopic beats coincide with spatial gradients of NADH in a regional model of low-flow reperfusion

2008 ◽  
Vol 294 (5) ◽  
pp. H2400-H2405 ◽  
Author(s):  
Matthew Kay ◽  
Luther Swift ◽  
Brian Martell ◽  
Ara Arutunyan ◽  
Narine Sarvazyan
Keyword(s):  
High Performance ◽  
Low Flow ◽  
Vessel Occlusion ◽  
Precise Control ◽  
Spatial Gradients ◽  
Rat Hearts ◽  
Nadh Fluorescence ◽  
Tissue Changes ◽  
Ectopic Beats ◽  
Acute Regional Ischemia

We studied the origins of ectopic beats during low-flow reperfusion after acute regional ischemia in excised rat hearts. The left anterior descending coronary artery was cannulated. Perfusate was delivered to the cannula using an high-performance liquid chromatography pump. This provided not only precise control of flow rate but also avoided mechanical artifacts associated with vessel occlusion and deocclusion. Optical mapping of epicardial transmembrane potential served to identify activation wavefronts. Imaging of NADH fluorescence was used to quantify local ischemia. Our experiments suggest that low-flow reperfusion of ischemic myocardium leads to a highly heterogeneous ischemic substrate and that the degree of ischemia between adjacent patches of tissue changes in time. In contrast to transient ectopic activity observed during full-flow reperfusion, persistent ectopic arrhythmias were observed during low-flow reperfusion. The origins of ectopic beats were traceable to areas of high spatial gradients of changes in NADH fluorescence caused by low-flow reperfusion.

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