Local perturbation responses and checkerboard tests: Characterization tools for nonlinear MRI methods

2021 ◽  
Author(s):  
Chin‐Cheng Chan ◽  
Justin P. Haldar
Keyword(s):  
Local Perturbation

Stabilization of Dominant Structures in an Ionic Reaction-Diffusion System

1998 ◽  
Vol 63 (6) ◽  
pp. 761-769 ◽  
Author(s):  
Roland Krämer ◽  
Arno F. Münster
Keyword(s):  
Reaction Diffusion ◽  
Dominant Mode ◽  
Reaction Diffusion System ◽  
Diffusion System ◽  
Local Perturbation ◽  
Dimensional System ◽  
One Dimensional ◽  
Brusselator Model ◽  
The One ◽  
Dominant Structure

We describe a method of stabilizing the dominant structure in a chaotic reaction-diffusion system, where the underlying nonlinear dynamics needs not to be known. The dominant mode is identified by the Karhunen-Loeve decomposition, also known as orthogonal decomposition. Using a ionic version of the Brusselator model in a spatially one-dimensional system, our control strategy is based on perturbations derived from the amplitude function of the dominant spatial mode. The perturbation is used in two different ways: A global perturbation is realized by forcing an electric current through the one-dimensional system, whereas the local perturbation is performed by modulating concentrations of the autocatalyst at the boundaries. Only the global method enhances the contribution of the dominant mode to the total fluctuation energy. On the other hand, the local method leads to simple bulk oscillation of the entire system.

scholarly journals Effect of a Local Perturbation in a Fermionic Ladder

2011 ◽  
Vol 106 (12) ◽  
Author(s):  
Sam T. Carr ◽  
Boris N. Narozhny ◽  
Alexander A. Nersesyan
Keyword(s):  
Local Perturbation

scholarly journals Study Rheological Behavior of Polymer Solution in Different-Medium-Injection-Tools

Polymers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 319 ◽  
Author(s):  
Bin Huang ◽  
Xiaohui Li ◽  
Cheng Fu ◽  
Ying Wang ◽  
Haoran Cheng
Keyword(s):  
Molecular Weight ◽  
Polymer Solution ◽  
Oil Recovery ◽  
Injection Pressure ◽  
Injection Rate ◽  
Injection Velocity ◽  
Structural Parameter ◽  
Local Perturbation ◽  
Polymer Injection ◽  
Single Pipe

Previous studies showed the difficulty during polymer flooding and the low producing degree for the low permeability layer. To solve the problem, Daqing, the first oil company, puts forward the polymer-separate-layer-injection-technology which separates mass and pressure in a single pipe. This technology mainly increases the control range of injection pressure of fluid by using the annular de-pressure tool, and reasonably distributes the molecular weight of the polymer injected into the thin and poor layers through the shearing of the different-medium-injection-tools. This occurs, in order to take advantage of the shearing thinning property of polymer solution and avoid the energy loss caused by the turbulent flow of polymer solution due to excessive injection rate in different injection tools. Combining rheological property of polymer and local perturbation theory, a rheological model of polymer solution in different-medium-injection-tools is derived and the maximum injection velocity is determined. The ranges of polymer viscosity in different injection tools are mainly determined by the structures of the different injection tools. However, the value of polymer viscosity is mainly determined by the concentration of polymer solution. So, the relation between the molecular weight of polymer and the permeability of layers should be firstly determined, and then the structural parameter combination of the different-medium-injection-tool should be optimized. The results of the study are important for regulating polymer injection parameters in the oilfield which enhances the oil recovery with reduced the cost.

Effect of Time Dependent Excitation Signals on Gating in Nanofluidic Channels

2015 ◽  
Author(s):  
C. Boone ◽  
M. Fuest ◽  
K. Wellmerling ◽  
S. Prakash
Keyword(s):  
Electric Field ◽  
Ionic Transport ◽  
Local Variation ◽  
Time Dependent ◽  
Local Perturbation ◽  
Gate Electrode ◽  
Nanofluidic Channels ◽  
Field Effect Devices ◽  
Dc Excitation ◽  
Dependent Signal

Nanofluidic field effect devices feature a gate electrode embedded in the nanochannel wall. The gate electrode creates local variation in the electric field allowing active, tunable control of ionic transport. Tunable control over ionic transport through nanofluidic networks is essential for applications including artificial ion channels, ion pumps, ion separation, and biosensing. Using DC excitation at the gate, experiments have demonstrated multiple current states in the nanochannel, including the ability to switch off the measured current; however, experimental evaluation of transient signals at the gate electrode has not been explored. Modeling results have shown ion transport at the nanoscale has known time scales for diffusion, electromigration, and convection. This supports the evidence detailed here that use of a time-dependent signal to create local perturbation in the electric field can be used for systematic manipulation of ionic transport in nanochannels. In this report, sinusoidal waveforms of various frequencies were compared against DC excitation on the gate electrode. The ionic transport was quantified by measuring the current through the nanochannels as a function of applied axial and gate potentials. It was found that time varying signals have a higher degree of modulation than a VRMS matched DC signal.

scholarly journals Cardiac Spiral Wave Drifting Due to Spatial Temperature Gradients – a Numerical Study

2018 ◽  
Author(s):  
Guy Malki ◽  
Sharon Zlochiver
Keyword(s):  
Numerical Simulations ◽  
Single Cell ◽  
Numerical Study ◽  
Spiral Wave ◽  
Spiral Waves ◽  
Temperature Gradients ◽  
Effect Of Temperature ◽  
Local Perturbation ◽  
Marginal Effect ◽  
Spatial Temperature

ABSTRACTCardiac rotors are believed to be a major driver source of persistent atrial fibrillation (AF), and their spatiotemporal characterization is essential for successful ablation procedures. However, electrograms guided ablation have not been proven to have benefit over empirical ablation thus far, and there is a strong need of improving the localization of cardiac arrhythmogenic targets for ablation. A new approach for characterize rotors is proposed that is based on induced spatial temperature gradients (STGs), and investigated by theoretical study using numerical simulations. We hypothesize that such gradients will cause rotor drifting due to induced spatial heterogeneity in excitability, so that rotors could be driven towards the ablating probe. Numerical simulations were conducted in single cell and 2D atrial models using AF remodeled kinetics. STGs were applied either linearly on the entire tissue or as a small local perturbation, and the major ion channel rate constants were adjusted following Arrhenius equation. In the AF-remodeled single cell, recovery time increased exponentially with decreasing temperatures, despite the marginal effect of temperature on the action potential duration. In 2D models, spiral waves drifted with drifting velocity components affected by both temperature gradient direction and the spiral wave rotation direction. Overall, spiral waves drifted towards the colder tissue region associated with global minimum of excitability. A local perturbation with a temperature of T=28°C was found optimal for spiral wave attraction for the studied conditions. This work provides a preliminary proof-of-concept for a potential prospective technique for rotor attraction. We envision that the insights from this study will be utilize in the future in the design of a new methodology for AF characterization and termination during ablation procedures.

Local Perturbation Analysis of Linear Programming with Functional Relation Among Parameters

2013 ◽  
pp. 1-24
Author(s):  
Payam Hanafizadeh ◽  
Abolfazl Ghaemi ◽  
Madjid Tavana
Keyword(s):  
Sensitivity Analysis ◽  
Linear Programming ◽  
Objective Function ◽  
Perturbation Analysis ◽  
Functional Relation ◽  
Local Perturbation ◽  
Nonlinear Functional ◽  
Functional Relations ◽  
Software Packages ◽  
The Right

In this paper, the authors study the sensitivity analysis for a class of linear programming (LP) problems with a functional relation among the objective function parameters or those of the right-hand side (RHS). The classical methods and standard sensitivity analysis software packages fail to function when a functional relation among the LP parameters prevail. In order to overcome this deficiency, the authors derive a series of sensitivity analysis formulae and devise corresponding algorithms for different groups of homogenous LP parameters. The validity of the derived formulae and devised algorithms is corroborated by open literature examples having linear as well as nonlinear functional relations between their vector b or vector c components.

Ancient Bug Bites on Ancient Plants Record Forest Ecosystem Response to Environmental Perturbations

2013 ◽  
Vol 19 ◽  
pp. 157-174 ◽  
Author(s):  
Ellen D. Currano
Keyword(s):  
Trophic Interactions ◽  
Insect Herbivory ◽  
Fossil Flora ◽  
Local Perturbation ◽  
Insect Damage ◽  
Ecosystem Response ◽  
Insect Feeding ◽  
First Case ◽  
The Impact

Leaf-compression fossils with insect feeding traces are unique in providing rich, direct evidence of two levels in a fossil food web. Plant-insect associations dominate terrestrial trophic interactions, emphasizing the need to understand their ecological and evolutionary history. This paper first discusses methods of recognizing insect herbivore damage on fossil leaves and quantifying fossil insect herbivory. By conducting an unbiased insect damage census, damage frequency (percent of leaves with insect feeding damage), percent of leaf surface area removed by insects, and damage diversity (the number of discrete damage morphotypes, or DTs, found on a fossil flora or individual host plant) can all be measured. Three examples of responses of past plant-insect trophic interactions to environmental stresses are examined. In the first case study, late Oligocene fossil floras from Ethiopia document forest response to local perturbation and key characteristics to recognize disturbance in the plant fossil record. The second case study considers the terrestrial ecosystem response to the catastrophic global perturbation at the Cretaceous–Paleogene boundary. In the third case study, the impact of past global warming events—including the Paleocene–Eocene Thermal Maximum—on insect herbivory is discussed. Productive avenues for further research include: insect damage studies conducted outside the North American Cretaceous and Paleogene, actualistic and taphonomic studies of insect herbivory, and tighter collaboration across paleobotany, paleoentomology, botany, and entomology.

scholarly journals Directed nanoscale metal deposition by the local perturbation of charge screening at the solid–liquid interface

Nanoscale ◽  
2019 ◽  
Vol 11 (40) ◽  
pp. 18619-18627
Author(s):  
Mark Aarts ◽  
Esther Alarcon-Llado
Keyword(s):  
Atomic Force Microscope ◽  
Electrochemical Deposition ◽  
Metal Deposition ◽  
Liquid Interface ◽  
Electrochemical Reactions ◽  
Local Perturbation ◽  
Atomic Force ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Micrometer Scale

Understanding and directing electrochemical reactions below the micrometer scale is a long-standing challenge in electrochemistry. Here, we demonstrate the directed electrochemical deposition of copper nanostructures by using an oscillating nanoelectrode operated with an atomic force microscope.

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