scholarly journals SELF-EXCITED OSCILLATIONS IN A COLLAPSIBLE CHANNEL WITH APPLICATIONS TO RETINAL VENOUS PULSATION

2019 ◽  
Vol 61 (3) ◽  
pp. 320-348
Author(s):  
PETER S. STEWART ◽  
ALEXANDER J. E. FOSS
Keyword(s):  
Single Channel ◽  
External Pressure ◽  
Flow Profile ◽  
Neutral Stability ◽  
One Dimensional ◽  
Primary Mode ◽  
Excited Oscillation ◽  
In Series ◽  
Walled Channel ◽  
Venous Pulsation

We consider a theoretical model for the flow of Newtonian fluid through a long flexible-walled channel which is formed from four compliant and rigid compartments arranged alternately in series. We drive the flow using a fixed upstream flux and derive a spatially one-dimensional model using a flow profile assumption. The compliant compartments of the channel are assumed subject to a large external pressure, so the system admits a highly collapsed steady state. Using both a global (linear) stability eigensolver and fully nonlinear simulations, we show that these highly collapsed steady states admit a primary global oscillatory instability similar to observations in a single channel. We also show that in some regions of the parameter space the system admits a secondary mode of instability which can interact with the primary mode and lead to significant changes in the structure of the neutral stability curves. Finally, we apply the predictions of this model to the flow of blood through the central retinal vein and examine the conditions required for the onset of self-excited oscillation. We show that the neutral stability curve of the primary mode of instability discussed above agrees well with canine experimental measurements of the onset of retinal venous pulsation, although there is a large discrepancy in the oscillation frequency.

scholarly journals Self-excited oscillations in a collapsible channel with applications to retinal venous pulsation

2019 ◽  
Vol 61 ◽  
pp. 320-348
Author(s):  
Peter S. Stewart ◽  
Alexander J. E. Foss
Keyword(s):  
Single Channel ◽  
External Pressure ◽  
Flow Profile ◽  
Neutral Stability ◽  
One Dimensional ◽  
Primary Mode ◽  
Excited Oscillation ◽  
In Series ◽  
Walled Channel ◽  
Venous Pulsation

We consider a theoretical model for the flow of Newtonian fluid through a long flexible-walled channel which is formed from four compliant and rigid compartments arranged alternately in series. We drive the flow using a fixed upstream flux and derive a spatially one-dimensional model using a flow profile assumption. The compliant compartments of the channel are assumed subject to a large external pressure, so the system admits a highly collapsed steady state. Using both a global (linear) stability eigensolver and fully nonlinear simulations, we show that these highly collapsed steady states admit a primary global oscillatory instability similar to observations in a single channel. We also show that in some regions of the parameter space the system admits a secondary mode of instability which can interact with the primary mode and lead to significant changes in the structure of the neutral stability curves. Finally, we apply the predictions of this model to the flow of blood through the central retinal vein and examine the conditions required for the onset of self-excited oscillation. We show that the neutral stability curve of the primary mode of instability discussed above agrees well with canine experimental measurements of the onset of retinal venous pulsation, although there is a large discrepancy in the oscillation frequency. doi:10.1017/S1446181119000117

Damping of Self-Excited Pressure Pulsations in Petrodiesel Pipeline

2014 ◽  
Vol 630 ◽  
pp. 375-382 ◽  
Author(s):  
Daniel Himr ◽  
Vladimir Haban
Keyword(s):  
Hydraulic System ◽  
Check Valve ◽  
Control Valve ◽  
Sampling Frequency ◽  
Pressure Pulsations ◽  
One Dimensional ◽  
Fuel Storage ◽  
Excited Oscillation ◽  
Subsequent Measurement ◽  
And Control

A pumping station in a fuel storage suffered from pressure pulsations in a petrodiesel pipeline. Check valves protecting the station against back flow made a big noise when disc hit a seat. Due to employees complaints we were asked to solve the problem, which could lead to serious mechanical problems. Pressure measurement in the pipeline showed great pulsations, which were caused by self-excited oscillation of control valves at the downstream end of pipeline. The operating measurement did not catch it because of too low sampling frequency. One dimensional numerical model of the whole hydraulic system was carried out. The model consisted of check valve, pipeline and control valve, which could oscillate, so it was possible to simulate the unsteady flow. When the model was validated, a vessel with nitrogen was added to attenuate pressure pulsations. According to the results of numerical simulation, the vessel was installed on the location. Subsequent measurement proved noticeably lower pulsations and almost no noise.

scholarly journals Slow light bimodal interferometry in one-dimensional photonic crystal waveguides

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Luis Torrijos-Morán ◽  
Amadeu Griol ◽  
Jaime García-Rupérez
Keyword(s):  
Photonic Crystal ◽  
Group Velocity ◽  
Communication Networks ◽  
Slow Light ◽  
Single Channel ◽  
Point Of Care ◽  
Semiconductor Industry ◽  
Optical Modulator ◽  
One Dimensional ◽  
Dimensional Photonic Crystal

AbstractStrongly influenced by the advances in the semiconductor industry, the miniaturization and integration of optical circuits into smaller devices has stimulated considerable research efforts in recent decades. Among other structures, integrated interferometers play a prominent role in the development of photonic devices for on-chip applications ranging from optical communication networks to point-of-care analysis instruments. However, it has been a long-standing challenge to design extremely short interferometer schemes, as long interaction lengths are typically required for a complete modulation transition. Several approaches, including novel materials or sophisticated configurations, have been proposed to overcome some of these size limitations but at the expense of increasing fabrication complexity and cost. Here, we demonstrate for the first time slow light bimodal interferometric behaviour in an integrated single-channel one-dimensional photonic crystal. The proposed structure supports two electromagnetic modes of the same polarization that exhibit a large group velocity difference. Specifically, an over 20-fold reduction in the higher-order-mode group velocity is experimentally shown on a straightforward all-dielectric bimodal structure, leading to a remarkable optical path reduction compared to other conventional interferometers. Moreover, we experimentally demonstrate the significant performance improvement provided by the proposed bimodal photonic crystal interferometer in the creation of an ultra-compact optical modulator and a highly sensitive photonic sensor.

Statistical Thermodynamics and Surface Phase Transitions of Interacting Particles Adsorbed on One-Dimensional Channels Arranged in a Triangular Cross-Sectional Structure

2009 ◽  
Vol 150 ◽  
pp. 73-100 ◽  
Author(s):  
P.M. Pasinetti ◽  
F. Romá ◽  
J.L. Riccardo ◽  
A.J. Ramirez-Pastor
Keyword(s):  
Monte Carlo ◽  
Interaction Energy ◽  
Lattice Gas ◽  
Nearest Neighbor ◽  
Single Channel ◽  
Scaling Analysis ◽  
Surface Phase ◽  
Cross Sectional ◽  
One Dimensional ◽  
Sectional Structure

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer lattice-gas, which mimics a nanoporous environment. In this model, one-dimensional chains of atoms were arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) wL, interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) wT, interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverse interactions (wT > 0), where a rich variety of structural orderings are observed in the adlayer, depending on the value of the parameters kBT/wT (kB being the Boltzmann constant) and wL /wT. For wL /wT = 0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, and the well-known [ ] ordered phase is found at low temperatures and a coverage, , of 1/3 [2/3]. In the more general case (wL /wT  0), the competition between interactions along a single channel and the transverse coupling between sites in neighboring channels leads to a three-dimensional adsorbed layer. Consequently, the and structures “propagate” along the channels and new ordered phases appear in the adlayer. The influence of each ordered phase on adsorption isotherms, differential heat of adsorption and configurational entropy of the adlayer has been analyzed and discussed in the context of the lattice-gas theory. Finally, the Monte Carlo technique was combined with the recently reported free energy minimization criterion approach (FEMCA) [F. Romá et al.: Phys. Rev. B Vol. 68 (2003), art. no. 205407] to predict the critical temperatures of the surface-phase transformations occurring in the adsorbate. The excellent qualitative agreement between simulated data and FEMCA results allows us to interpret the physical meaning of the mechanisms underlying the observed transitions.

Single channel tunable wavelength demultiplexer using nonlinear one dimensional defect mode photonic crystal

Optik ◽  
2014 ◽  
Vol 125 (17) ◽  
pp. 4895-4897 ◽  
Author(s):  
Sanjeev Sharma ◽  
Rajendra Kumar ◽  
Kh. S. Singh ◽  
Vipin Kumar ◽  
Arun Kumar
Keyword(s):  
Photonic Crystal ◽  
Single Channel ◽  
Defect Mode ◽  
One Dimensional ◽  
Wavelength Demultiplexer ◽  
Tunable Wavelength

One Dimensional Thermal-Hydraulic Stability Analysis of Supercritical Fluid Cooled Reactors

2004 ◽  
Author(s):  
Jiyun Zhao ◽  
Pradip Saha ◽  
Mujid S. Kazimi
Keyword(s):  
Flow Rate ◽  
Single Channel ◽  
Flow Instability ◽  
Density Wave ◽  
Reactor Power ◽  
Rate System ◽  
One Dimensional ◽  
Velocity Amplitude ◽  
System Pressure ◽  
Induced Velocity

A one-dimensional single-channel thermal-hydraulics model has been developed to investigate possible occurrence of density-wave instability in two U. S. Gen-IV reactors cooled by supercritical fluids, i. e., the Supercritical Water-cooled Reactor (SCWR) and Gas-cooled Fast Reactor (GFR). Water density in the SCWR core changes from 780 kg/m3, to 90 kg/m3, whereas the density of supercritical carbon-dioxide in the reference GFR changes from 155 kg/m3 to around 110 kg/m3. The standard frequency domain approach with a decay ratio of induced velocity amplitude of 0.5 has been used to determine the onset of flow instability. With suitable inlet orificing, the hot channel of SCWR has been found to be stable. Sensitivity studies show that the hot channel decay ratio reaches the critical value of 0.5 when either the reactor power is raised to 118% of full power or the core flow rate is reduced to 86% of nominal flow rate. System pressure has only a moderate effect. Detailed 3-D studies, preferably with neutronic feedback, should be carried out for the SCWR design because of its sensitivity to various important parameters. The GFR reference design has been found to be very stable since the density change in the GFR core is rather small compared to that in the SCWR design.

NAND/AND/NOT logic gates response in series of mesoscopic quantum rings

2019 ◽  
Vol 33 (34) ◽  
pp. 1950431 ◽  
Author(s):  
E. Dehghan ◽  
D. Sanavi Khoshnoud ◽  
A. S. Naeimi
Keyword(s):  
Current Density ◽  
Spin Current ◽  
Logic Gates ◽  
Nand Gate ◽  
Double Quantum ◽  
Device Performance ◽  
Quantum Rings ◽  
One Dimensional ◽  
Rashba Spin ◽  
In Series

There is a special class of logic gates, called universal gates, any one of which is sufficient to express any desired computation. The NAND gate is truly global, given that it is already known, each Boolean function can be represented in a circuit that contains only NOT and AND gates, it is sufficient to show that these gates can be defined from the NAND gate. The effect of Rashba spin-orbit interaction (SOI) on the gate response and spin current density in a series of non-interacting one-dimensional rings connected to some leads is studied theoretically within the waveguide theory. The gates response and spin current density are computed in geometry of the system containing two terminal double quantum rings. Also, the presence and absence of Rashba SOI are treated as the two inputs of the AND/NAND/NOT gates. Furthermore, simulation of the device performance demonstrates that vital improvement toward spintronic applications can be achieved by optimizing device parameters such as magnetic flux and Rashba coefficient.

Calculation of linear detonation instability: one-dimensional instability of plane detonation

1990 ◽  
Vol 216 ◽  
pp. 103-132 ◽  
Author(s):  
H. I. Lee ◽  
D. S. Stewart
Keyword(s):  
Acoustic Radiation ◽  
Radiation Condition ◽  
Linear Instability ◽  
Arbitrary Parameter ◽  
Neutral Stability ◽  
One Dimensional ◽  
Method Of Solution ◽  
The Laplace Transform ◽  
Detonation Instability ◽  
The One

The detonation stability problem is studied by a normal mode approach which greatly simplifies the calculation of linear instability of detonation in contrast to the Laplace transform procedure used by Erpenbeck. The method of solution, for an arbitrary parameter set, is a shooting method which can be automated to generate easily the required information about instability. The condition on the perturbations applied at the end of the reaction zone is shown to be interpreted as either a boundedness condition or an acoustic radiation condition. Continuous and numerically exact neutral stability curves and boundaries are given as well as growth rates and eigenfunctions which are calculated for the first time. Our calculations include the Chapman–Jouguet (CJ) case which presents no special difficulty. We give representative results for our detonation model and summarize the one-dimensional stability behaviour in parameter space. Comparison with previous results for the neutral stability boundaries and approximations to the unstable discrete spectrum are given. Parametric studies of the unstable, discrete spectrum's dependence on the activation energy and the overdrive factor are given with the implications for interpreting the physical mechanism of instability observed in experiments. This first paper is restricted to the case of one-dimensional linear instability. Extensions to transverse disturbances will be treated in a sequel.

A comparison of one-dimensional methods for estimating discharge capacity of straight compound channels

2004 ◽  
Vol 31 (4) ◽  
pp. 619-631 ◽  
Author(s):  
Galip Seckin
Keyword(s):  
Discharge Capacity ◽  
Single Channel ◽  
Scale Effects ◽  
Compound Channels ◽  
One Dimensional ◽  
Mobile Bed ◽  
Series Of Experiments ◽  
And Performance ◽  
Discharge Estimation ◽  
Fixed Boundaries

A series of experiments was carried out in a two-stage flume having a smooth main channel and smooth or rough floodplains to investigate the reliability and performance of four different one-dimensional methods for computing the discharge capacity of compound channels, namely, the single-channel method (SCM), the divided-channel method (DCM), the exchange discharge method (EDM), and the Ackers method (AM). Additional data from fixed- and mobile-bed compound laboratory channels with smooth and roughened floodplains and of a prototype compound river channel were also used in the computations. The boundary roughness and scale effects associated with the performance of the four methods are also examined. The results show that the EDM and the AM are able to simulate the measured discharge values more accurately than those of the traditional methods, namely, the DCM and the SCM. Although the error in discharge estimation produced by both the AM and the EDM was generally lower than 10% for both smooth and fixed boundaries, it increased up to 20% for mobile boundaries. Overall, the average relative error in discharge estimations using the AM and the EDM was about 5.4% and 7.1%, respectively, with a standard deviation of 6.7% and 6.8%, respectively. Key words: compound channel flow, stage-discharge relationship, one-dimensional methods.

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