scholarly journals Seeing the future: predictive control in neural models of ocular accommodation

2021 ◽  
Author(s):  
Jenny C. A. Read ◽  
Christos Kaspiris-Rousellis ◽  
Toby Wood ◽  
Bing Wu ◽  
Björn N. S. Vlaskamp ◽  
...  
Keyword(s):  
Nonlinear Resonance ◽  
Crystalline Lens ◽  
Smith Predictor ◽  
Integral Control ◽  
Ocular Accommodation ◽  
Steady Fixation ◽  
Wide Range ◽  
Sinusoidal Oscillations ◽  
Motor Actions ◽  
Low Amplitude

Ocular accommodation is the process of adjusting the eye's crystalline lens so as to bring the retinal image into sharp focus. The major stimulus to accommodation is therefore retinal defocus, and in essence, the job of accommodative control is to send a signal to the ciliary muscle which will minimise the magnitude of defocus. In this paper, we first provide a tutorial introduction to control theory to aid vision scientists without this background. We then present a unified model of accommodative control that explains properties of the accommodative response for a wide range of accommodative stimuli. Following previous work, we conclude that most aspects of accommodation are well explained by dual integral control, with a "fast" or "phasic" integrator enabling response to rapid changes in demand, which hands over control to a "slow" or "tonic" integrator which maintains the response to steady demand. Control is complicated by the sensorimotor latencies within the system, which delay both information about defocus and the accommodation changes made in response, and by the sluggish response of the motor plant. These can be overcome by incorporating a Smith predictor, whereby the system predicts the delayed sensory consequences of its own motor actions. For the first time, we show that critically-damped dual integral control with a Smith predictor accounts for adaptation effects as well as for the gain and phase for sinusoidal oscillations in demand. In addition, we propose a novel proportional-control signal to account for the power spectrum of accommodative microfluctuations during steady fixation, which may be important in hunting for optimal focus, and for the nonlinear resonance observed for low-amplitude, high-frequency input. Complete Matlab/Simulink code implementing the model is provided at https://doi.org/10.25405/data.ncl.14945550

A variety of surface waves in ocean-bottom DAS records

2021 ◽  
Author(s):  
Zack Spica ◽  
Loïc Viens ◽  
Jorge Castillo Castellanos ◽  
Takeshi Akuhara ◽  
Kiwamu Nishida ◽  
...  
Keyword(s):  
Surface Wave ◽  
Acoustic Waves ◽  
Fiber Optic ◽  
Acoustic Noise ◽  
Seismic Exploration ◽  
Ocean Bottom ◽  
Wide Range ◽  
Ocean Layer ◽  
Noise Cross Correlation ◽  
Low Amplitude

<p>Distributed acoustic sensing (DAS) can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recordings over tens of kilometers. Recently, DAS has demonstrated its utility for many seismological applications onshore. However, the use of offshore cables for seismic exploration and monitoring is still in its infancy.<br>In this work, we introduce some new results and observations obtained from a fiber-optic cable offshore the coast of Sanriku, Japan. In particular, we focus on surface wave retrieved from various signals and show that ocean-bottom DAS can be used to extract dispersion curves (DC) over a wide range of frequencies. We show that multi-mode DC can be easily extracted from ambient seismo-acoustic noise cross-correlation functions or F-K analysis. Moderate magnitude earthquakes also contain multiple surface-wave packets that are buried within their coda. Fully-coupled 3-D numerical simulations suggest that these low-amplitude signals originate from the continuous reverberations of the acoustic waves in the ocean layer. </p>

scholarly journals A New Method of Low Amplitude Signal Detection and Its Application in Acoustic Emission

2019 ◽  
Vol 10 (1) ◽  
pp. 73 ◽  
Author(s):  
Einar Agletdinov ◽  
Dmitry Merson ◽  
Alexei Vinogradov
Keyword(s):  
Time Series ◽  
Acoustic Emission ◽  
Logarithmic Derivative ◽  
Random Noise ◽  
Synthetic Data ◽  
Spectral Density Function ◽  
Integrity Assessment ◽  
Wide Range ◽  
Time Average ◽  
Low Amplitude

A novel methodology is proposed to enhance the reliability of detection of low amplitude transients in a noisy time series. Such time series often arise in a wide range of practical situations where different sensors are used for condition monitoring of mechanical systems, integrity assessment of industrial facilities and/or microseismicity studies. In all these cases, the early and reliable detection of possible damage is of paramount importance and is practically limited by detectability of transient signals on the background of random noise. The proposed triggering algorithm is based on a logarithmic derivative of the power spectral density function. It was tested on the synthetic data, which mimics the actual ultrasonic acoustic emission signal recorded continuously with different signal-to-noise ratios (SNR). Considerable advantages of the proposed method over established fixed amplitude threshold and STA/LTA (Short Time Average / Long Time Average) techniques are demonstrated in comparative tests.

Numerical Simulations of Hydrodynamics and Heat Transfer in Wavy Falling Liquid Films on Vertical and Inclined Walls

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Hongyi Yu ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Solitary Waves ◽  
Flow Instability ◽  
Liquid Films ◽  
Capillary Waves ◽  
Wave Dynamics ◽  
Disturbance Frequency ◽  
Wide Range ◽  
Falling Liquid Films ◽  
Low Amplitude

The flow of thin falling liquid films is unstable to long-wave disturbances. The flow instability leads to development of waves at the liquid–gas interface. The effect of the waves on heat and mass transfer in falling liquid films is a subject of ongoing scientific discussion. In this work, numerical investigation of the wave dynamics has been performed using a modified volume-of-fluid (VOF) method for tracking the free surface. The surface tension is described using the continuum surface force (CSF) model. With low disturbance frequency, solitary waves of large amplitude are developed, which are preceded by low-amplitude capillary waves. With high disturbance frequency, low amplitude sinusoidal waves are developed. The waveforms dependent on the Reynolds number and disturbance frequency are summarized in a form of a regime map. A correlation describing the separation curve between the sinusoidal waves regime and solitary waves regime is proposed. The wave parameters (peak height, length, and propagation speed) are computed from the simulation results and compared with available experimental correlations in a wide range of parameters. The effects of the disturbance frequency and the plane inclination angle on the wave dynamics have been studied. The interaction of waves initiated by simultaneous disturbances of two different frequencies has been investigated. The heat transfer in the wavy film has been simulated for the constant wall temperature boundary condition. The effects of Prandtl number and disturbance frequency on local and global heat transfer parameters have been investigated. It has been shown that the influence of waves on heat transfer is significant for large Prandtl numbers in a specific range of disturbance frequencies.

Numerical Simulations of Hydrodynamics and Heat Transfer in Wavy Falling Liquid Films on Vertical and Inclined Walls

2012 ◽  
Author(s):  
Hongyi Yu ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Inclination Angle ◽  
Flow Instability ◽  
Liquid Films ◽  
Capillary Waves ◽  
Wave Dynamics ◽  
Disturbance Frequency ◽  
Wide Range ◽  
Falling Liquid Films ◽  
Low Amplitude

The flow of thin falling liquid films is unstable to long-wave disturbances. The flow instability leads to development of waves at the liquid-gas interface. The wave patterns depend on the properties of the liquid, the Reynolds number, the plate inclination angle, and the distance from the film inlet. The effect of the waves on heat and mass transfer in falling liquid films is a subject of ongoing scientific discussion. In this work numerical investigation of the wave dynamics has been performed using a modified Volume of Fluid (VOF) method for tracking the free surface. The surface tension is described using the Continuum Surface Force (CSF) model. At low disturbance frequency solitary waves of large amplitude are developed, which are preceded by low-amplitude capillary waves. At high disturbance frequency low amplitude sinusoidal waves are developed. The wave parameters (peak height, length, propagation speed) are computed from the simulation results and compared with available experimental correlations in a wide range of parameters. The effects of the disturbance frequency and the plane inclination angle on the wave dynamics have been studied. The interaction of waves initiated by simultaneous disturbances of two different frequencies has been investigated. The heat transfer in the wavy film has been simulated for constant wall temperature boundary condition. The effect of the Prandtl number and the disturbance frequency on the local and global heat transfer parameters has been investigated. It has been shown that the influence of waves on heat transfer is significant for large Prandtl numbers in a specific range of disturbance frequencies.

scholarly journals Higher-Order Conditioning in the Spatial Domain

2021 ◽  
Vol 15 ◽  
Author(s):  
Youcef Bouchekioua ◽  
Yutaka Kosaki ◽  
Shigeru Watanabe ◽  
Aaron P. Blaisdell
Keyword(s):  
Learning And Memory ◽  
Higher Order ◽  
Cognitive Map ◽  
Place Learning ◽  
Spatial Learning And Memory ◽  
Trial And Error ◽  
Order Conditioning ◽  
Wide Range ◽  
Living Organisms ◽  
Motor Actions

Spatial learning and memory, the processes through which a wide range of living organisms encode, compute, and retrieve information from their environment to perform goal-directed navigation, has been systematically investigated since the early twentieth century to unravel behavioral and neural mechanisms of learning and memory. Early theories about learning to navigate space considered that animals learn through trial and error and develop responses to stimuli that guide them to a goal place. According to a trial-and error learning view, organisms can learn a sequence of motor actions that lead to a goal place, a strategy referred to as response learning, which contrasts with place learning where animals learn locations with respect to an allocentric framework. Place learning has been proposed to produce a mental representation of the environment and the cartesian relations between stimuli within it—which Tolman coined the cognitive map. We propose to revisit some of the best empirical evidence of spatial inference in animals, and then discuss recent attempts to account for spatial inferences within an associative framework as opposed to the traditional cognitive map framework. We will first show how higher-order conditioning can successfully account for inferential goal-directed navigation in a variety of situations and then how vectors derived from path integration can be integrated via higher-order conditioning, resulting in the generation of higher-order vectors that explain novel route taking. Finally, implications to cognitive map theories will be discussed.

scholarly journals A new stiffness-sensing test to measure damage evolution in solids

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Yichi Song ◽  
Doneill J. Magmanlac ◽  
Vito L. Tagarielli
Keyword(s):  
Damage Evolution ◽  
Constitutive Models ◽  
Strain Curve ◽  
Mechanical Tests ◽  
Applied Strain ◽  
Test Method ◽  
Elastic Response ◽  
Cfrp Laminates ◽  
Wide Range ◽  
Low Amplitude

AbstractWe propose and assess a procedure to measure the damage evolution in solids as a function of the applied strain, by conducting stiffness-sensing mechanical tests. These tests consist in superimposing to a monotonically increasing applied strain numerous, low-amplitude unloading/reloading cycles, and extracting the current stiffness of the specimens from the slope of the stress–strain curve in each of the unloading/reloading cycles. The technique is applied to a set of polymeric and metallic solids with a wide range of stiffness, including CFRP laminates loaded through the thickness, epoxy resins, injection-moulded and 3D printed PLA and sintered Ti powders. The tests reveal that, for all the materials tested, damage starts developing at the very early stages of deformation, during what is commonly considered an elastic response. We show that the test method is effective and allows enriching the data extracted from conventional mechanical tests, for potential use in data-driven constitutive models. We also show that the measurements are consistent with the results of acoustic and resistive measurements, and that the method can be used to quantify the viscous response of the materials tested.

Heat exchange in relation to blood flow between thorax and abdomen in bumblebees

1976 ◽  
Vol 64 (3) ◽  
pp. 561-585
Author(s):  
B. Heinrich
Keyword(s):  
Blood Flow ◽  
Heat Exchanger ◽  
Heart Beat ◽  
Thoracic Temperature ◽  
Wide Range ◽  
Narrow Passage ◽  
Switch Mechanism ◽  
Low Amplitude ◽  
Counter Current ◽  
Current Heat

1. The narrow passage within the petiole between thorax and abdomen is anatomically constructed so that counter-current exchange should retain heat in the thorax despite blood flow to and from the cool abdomen. 2. However, the counter-current heat exchanger can be physiologically circumvented. Exogenously heated bumblebees prevented overheating of the thorax by shunting heat into the abdomen. They also regurgitated fluid, which helped to reduce head temperature but had little effect on thoracic temperature. 3. Temperature increases in the ventrum of the abdomen occurred in steps exactly coinciding with the beats of the ventral diaphragm, and with the abdominal ‘ventilatory’ pumping movements when these were present. The ability to prevent overheating of the thorax by transport of heat to the abdomen was abolished when the heart was made inoprative. 4. At low thoracic temperatures the ventral diaphragm beat at a wide range or rates and with varying interbeat intervals, while the heart beat at a high frequency relative to the ventral diaphragm, but at a very low amplitude. However, when thoracic temperature exceeded 43 degrees C the amplitudes of both were high, and the interbeat intervals as well as the beating frequencies of the two pulsatile organs became identical in any one bee. Furthermore, heated bees engaged in vigorous abdominal pumping at the same frequency as that of their heart and ventral diaphragm pulsations. 5. The results indicate that the anatomical counter-current heat exchanger is reduced or eliminated during heat stress by ‘chopping’ the blood flow into pulses, and the blood pulses are shunted through the petiole alternately by way of a switch mechanism.

scholarly journals Shape Deviation of Surface Structures Produced by WaveShape (Structuring by Laser Remelting) on Ti6Al4V and a Method for Deviation Reduction

Micromachines ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 367
Author(s):  
Oleg Oreshkin ◽  
Daniil Panov ◽  
Laura Kreinest ◽  
André Temmler ◽  
Alexander Platonov
Keyword(s):  
Solidification Front ◽  
Solidification Process ◽  
Signal Amplitude ◽  
Surface Structures ◽  
Material Loss ◽  
Shape Deviation ◽  
Wide Range ◽  
Sinusoidal Oscillations ◽  
Titanium Alloy Ti6al4v ◽  
Compensation Signal

Laser structuring by remelting (WaveShape) is a manufacturing process for metal surfaces in which structures are generated without material removal. The structuring principle is based on the controlled motion of the three-phase line in the area of the solidification front. The contour of the solidification front is imprinted into the remelting track during the continuous solidification process. Typically, harmonic surface structures in the form of sinusoidal oscillations are generated by means of WaveShape with virtually no material loss. However, a significant shape deviation is often observed over a wide range of process parameters. In this study, it was found that much of the shape deviation is concentrated at a spatial wavelength equal to half the spatial wavelength used for structuring. Therefore, an approach to reduce the shape deviations was specifically investigated by superimposing a compensation signal on the harmonic structuring signal. In this approach, a compensation signal with half the spatial wavelength was varied in phase and amplitude and superimposed on the structuring signal. Amplitude and phase shift of the compensation signal were further investigated for selected laser beam diameters and spatial wavelengths. This demonstrated that a shape deviation of harmonic surface structures on titanium alloy Ti6Al4V could be reduced by up to 91% by means of an adapted compensation signal.

Sign in / Sign up

Export Citation Format

Share Document