Flow Amplitude Research Articles

Event-Based Visual Flow

This paper introduces a new methodology to compute dense visual flow using the precise timings of spikes from an asynchronous event-based retina. Biological retinas, and their artificial counterparts, are totally asynchronous and data-driven and rely on a paradigm of light acquisition radically different from most of the currently used frame-grabber technologies. This paper introduces a framework to estimate visual flow from the local properties of events' spatiotemporal space. We will show that precise visual flow orientation and amplitude can be estimated using a local differential approach on the surface defined by coactive events. Experimental results are presented; they show the method adequacy with high data sparseness and temporal resolution of event-based acquisition that allows the computation of motion flow with microsecond accuracy and at very low computational cost.

Causality detection and turbulence in fusion plasmas

This work explores the potential of an information-theoretical causality detection method for unravelling the relation between fluctuating variables in complex non-linear systems. The method is tested on some simple though non-linear models, and guidelines for the choice of analysis parameters are established. Then, measurements from magnetically confined fusion plasmas are analysed. The selected data bear relevance to the all-important spontaneous confinement transitions often observed in fusion plasmas, fundamental for the design of an economically attractive fusion reactor. It is shown how the present method is capable of clarifying the interaction between fluctuating quantities such as the turbulence amplitude, turbulent flux and zonal flow amplitude, and uncovers several interactions that were missed by traditional methods.

Mixing and transport near the shallow-crested Rumble III seamount and the implications for plankton distribution

Vessel-based observations of water column structure and flow near a shallow-crested seamount are used to quantify the physical disturbance induced by that seamount. The implications of this disturbance on the ‘feeding hole’ hypothesis are then examined based on data from moored thermistors and acoustic current profilers, as well as vessel-based acoustic sounding-derived biomass estimates, currents, and conductivity-temperature-depth profiles from a 55 km square grid of stations around the crest. Mean currents in the region of 0.2 m s−1 are comparable to observations from surface drifters whereas the semidiurnal tidal flow amplitude was one third of this. Thorpe Scale-based estimates of energy dissipation rate were in the range 10−9 to 2.10−8 W kg−1 and vertical diffusivities Kz were in the range 10−4 to 10−3 m2 s−1. Turbulence levels were higher upstream of the seamount–likely due to the influence of nearby seamounts Rumble IV and V. There was no evidence of a Taylor Cap in the Rumble III velocity field. The sounder data provide some evidence of a feeding hole and analysis based on diffusivities suggests that this might persist downstream of the seamount for as much as 7 days.

Linking the river to the estuary: influence of river discharge on tidal damping

Abstract. The effect of river discharge on tidal damping in estuaries is explored within one consistent theoretical framework where analytical solutions are obtained by solving four implicit equations, i.e. the phase lag, the scaling, the damping and the celerity equation. In this approach the damping equation is obtained by subtracting the envelope curves of high water and low water occurrence, taking into account that the flow velocity consists of a tidal and river discharge component. Different approximations of the friction term are considered in deriving the damping equation, resulting in as many analytical solutions. In this framework it is possible to show that river discharge affects tidal damping primarily through the friction term. It appears that the residual slope, due to nonlinear friction, can have a substantial influence on tidal wave propagation when including the effect of river discharge. An iterative analytical method is proposed to include this effect, which significantly improved model performance in the upper reaches of an estuary. The application to the Modaomen and Yangtze estuaries demonstrates that the proposed analytical model is able to describe the main tidal dynamics with realistic roughness values in the upper part of the estuary where the ratio of river flow to tidal flow amplitude is substantial, while a model with negligible river discharge can be made to fit observations only with unrealistically high roughness values.

Doppler ultrasonographic evaluation of the radial and ulnar arteries in hemiparetic patients after stroke

To evaluate blood flow of hand arteries (using Doppler ultrasonography) and sympathetic skin response (SSR) in patients with hemiparesis. Fifty-six stroke patients (30 M, 26 F) with unilateral hemiparesis (age 53.5 ± 10.8 years, mean disease duration 12.0 ± 19.1 months) were included. The patients' arm and hand motor functions were assessed according to Brunnstrom's stages. SSR was evaluated bilaterally from median nerves at the wrist level. Radial and ulnar artery blood flow was measured at the wrist in the neutral position. Both radial and ulnar artery volume flow and end diastolic velocity, and radial artery diameter were smaller on the paretic side (all p < 0.0125). Radial artery resistance and pulsatility index were greater on the paretic side (both p < 0.0125). SSR amplitude was lower on the paretic side of patients with right-sided hemiparesis patients (p = 0.009). Hand Brunnstrom's stage was negatively correlated with nonparetic-paretic difference in radial artery volume flow and SSR amplitudes (all p < 0.025). Hand blood flow was lower on the paretic side and was accompanied by a similar decrease in SSR amplitudes in patients with right-sided hemiparesis.

Method for a detailed evaluation of respiratory cardiac contributions to blood flow in Fontan circulation

Background A recent MRI pilot study [1] indicated that hemodynamics in the Fontan circulation are mainly dependent on respiration according to flow amplitudes and suggested using a respiratory-triggered 4D PC MRI instead of a ECG-triggered 4D PC MRI. The detailed validation of this conclusion with double-triggered PC on acquisition level requires an extensive development of the pulse sequence. In this study, we outline techniques to justify and derive the recent findings in detail on the stage of post-processing using Realtime PC measurements. The regular respiratory-triggered cine measurement is not decoupled but involves the average cardiac effect as offset. The proposed method allows a complete separation of flow into its components stemming from respiration and ventricular function and it allows to study correlation effects. Methods Three children with hypoplastic left heart syndrome were evaluated after surgical completion of the Fontan circulation (TCPC with lateral intraatrial tunnel). In each patient, a 2D Realtime PC measurement with an acquisition time of 38 ms per image was acquired in the inferior vena cava (IVC). Using the physiology data on ECG and respiration, each image of the realtime MRI is assigned to its phase in the cardiac cycle and in the respiratory cycle and allows to determine a twofold triggered flow-matrix with 40 respiratory phases and 10 ECG phases. Conventional cine distributions are then derived for a single trigger by averaging over the other component. The flow reached the end of the resting expiratory position is attributed to the cardiac function offset and allows for a complete separation of the two effects. Results The proposed method was applied successfully to the IVC in the three children with completed TCPC. In none of the studied cases, a significant correlation between the flow due to respiration cardiac function was found. A single triggering to each of these physiological parameters is therefore justified. A separation of flow into respiratory and cardiac components was performed. The observed flow amplitudes in the respiratory distributions were found to be larger than those in the ECG distributions in agreement to previous findings. Conclusions

D113 音波を用いた熱輸送デバイスに関する基礎的研究(OS8 外熱機関・廃熱利用技術(1))

The "dream pipe" is the name of a heat transport device that was first proposed by Kruzweg and Zhao. Their dream pipe has hot and cold liquid-reservoirs connected by a capillary bundle. If the liquid columns in the bundle reciprocate with a tidal-displacement amplitude smaller than the bundle length, the heat flow rate from the hot to cold reservoir increases remarkably depending on the amplitude and frequency of the oscillatory liquid flow. In previous studies of dream pipes, liquid working fluids were used, but their operating temperature ranges were limited in the liquid state, and one cannot apply a higher operating frequency until around 10 Hz. We propose overcoming this disadvantage using a gas working fluid. In this paper, we choose air as a working fluid, and study experimentally whether the same high heat transport process is present as for liquids.

Planckintermediate results

Using Planck data combined with the Meta Catalogue of X-ray detected Clusters of galaxies (MCXC), we address the study of peculiar motions by searching for evidence of the kinetic Sunyaev-Zeldovich effect (kSZ). By implementing various filters designed to extract the kSZ generated at the positions of the clusters, we obtain consistent constraints on the radial peculiar velocity average, root mean square (rms), and local bulk flow amplitude at different depths. For the whole cluster sample of average redshift 0.18, the measured average radial peculiar velocity with respect to the cosmic microwave background (CMB) radiation at that redshift, i.e., the kSZ monopole, amounts to 72 ± 60 km s-1. This constitutes less than 1% of the relative Hubble velocity of the cluster sample with respect to our local CMB frame. While the linear ΛCDM prediction for the typical cluster radial velocity rms at z = 0.15 is close to 230 km s-1, the upper limit imposed by Planck data on the cluster subsample corresponds to 800 km s-1 at 95% confidence level, i.e., about three times higher. Planck data also set strong constraints on the local bulk flow in volumes centred on the Local Group. There is no detection of bulk flow as measured in any comoving sphere extending to the maximum redshift covered by the cluster sample. A blind search for bulk flows in this sample has an upper limit of 254 km s-1 (95% confidence level) dominated by CMB confusion and instrumental noise, indicating that the Universe is largely homogeneous on Gpc scales. In this context, in conjunction with supernova observations, Planck is able to rule out a large class of inhomogeneous void models as alternatives to dark energy or modified gravity. The Planck constraints on peculiar velocities and bulk flows are thus consistent with the ΛCDM scenario.

Peripheral blood flow in patients with graves’ disease depending on level of thyroid status compensation

Aim. To study the features of peripheral blood flow using laser Doppler flowmetry in patients with Graves’ disease depending on level of thyroid status compensation. Methods. 45 patients with Graves’ disease were divided into three groups 15 patients each depending on level of thyroid status compensation. The first group included patients with compensated hyperthyroidism, the second - with subcompensated hyperthyroidism, the third - with decompensated hyperthyroidism. All patients received combined thyrotropic (thiamazole 15-30 mg, average dose 22.4±1.7 mg) and cardio- and vasotropic therapy (metoprolol 50-100 mg, average dose 72.1±3.3 mg, and fozinopril 10-20 mg, average dose 17.8±2.4 mg), doses were individually adjusted. Results were compared with the control group (15 healthy patients). The peripheral blood flow was evaluated using LAKK-01 («LAZMA», Russia) device. Results. The comparison of control group and patients with Graves’ disease depending on level of thyroid status compensation demonstrated substantial differences. Doppler flowmetry registered increased blood flow, square deviation, variation coefficient in patients with diffuse thyrotoxic goitre, reflecting increase of tissue blood perfusion and reduced vascular tone. The analysis of the frequency histogram showed that the increase of average blood flow amplitude in case of hyperthyroidism was initiated by increase in amplitudes of all flaxmotions characterizing metabolic processes in capillaries. The relevant correlation between registered variables of blood flow and level of thyroid status compensation was registered. The most marked changes were revealed in patients with subcompensated and decompensated hyperthyroidism. In patients with compensated hyperthyroidism, the blood flow was altered the least compared to control group. Increased impact of active blood flow modulation mechanisms due to neurogenic activity and vascular tone was revealed. At the same time, endothelial activity was decreased. Predominance of sympathetic stimuli and compensatory mechanisms intensifying were discovered. Conclusion. The changes of peripheral blood flow in patients with Graves’ disease were typical for congestive-hyperemic type of microcirculation. Intensity of blood flow alterations is defined by thyroid status compensation. However, even the complete clinical and laboratory compensation doesn’t result in total recovery of capillary blood flow compared to healthy people.

Feedbacks between deforestation, climate, and hydrology in the Southwestern Amazon: implications for the provision of ecosystem services

Forests, through the regulation of regional water balances, provide a number of ecosystem services, including water for agriculture, hydroelectric power generation, navigation, industry, fisheries, and human consumption. Large-scale deforestation triggers complex non-linear interactions between the atmosphere and biosphere, which may impair such important ecosystem services. This is the case for the Southwestern Amazon, where three important river basins (Juruá, Purus, and Madeira) are undergoing significant land-use changes. Here, we investigate the potential impacts of deforestation throughout the Amazon on the seasonal and annual water balances of these river basins using coupled climatic and hydrologic models under several deforestation scenarios. Simulations without climate response to deforestation show an increase in river discharge proportional to the area deforested in each basin, whereas those with climate response produce progressive reductions in mean annual precipitation over all three basins. In this case, deforestation decreases the mean annual discharge of the Juruá and Purus rivers, but increases that of the Madeira, because the deforestation-induced reduction in evapotranspiration is large enough to increase runoff and thus offset the reduction in precipitation. The effects of Amazon deforestation on river discharge are scale-dependent and vary across and within river basins. Reduction in precipitation due to deforestation is most severe at the end of the dry season. As a result, deforestation increases the dry-season length and the seasonal amplitude of water flow. These effects may aggravate the economic losses from large droughts and floods, such as those experienced in recent years (2005, 2010 and 2009, 2012, respectively).

Triple-flame propagation against a Poiseuille flow in a channel with porous walls

We present an essentially numerical study of triple-flame propagation in a non-strained two-dimensional mixing layer against a Poiseuille flow, within a thermo-diffusive model. The aim of the study is twofold. First, to examine the recent analytical findings derived in the asymptotic limit of infinite Zeldovich number β for flame fronts thin compared with their typical radius of curvature and to extend these to finite-values of β. Second, to gain insight into the influence of the flow on the flame in situations where the flame in not necessarily thin, as assumed analytically. The study has focused on the effect of two main non-dimensional parameters on flame propagation, namely the flow amplitude A and the flame-front thickness ε. For moderate values of A, the flow is found to have a negligible effect on the structure of the flame, while modifying its speed by an amount proportional to A, in agreement with the asymptotic findings. Two new qualitative behaviours are found however. The first is obtained for sufficiently large values of A where the flow is shown to modify the flame structure significantly for small values of ε; more precisely, the concavity of the triple-flame front is found to turn towards the unburnt gas for A larger than a critical value. This inversion of the front curvature, which cannot be captured by the infinitely-large β asymptotic study, is found to be intimately linked to the finite values of β, which are necessarily found in any realistic model or computational study. The second new behaviour, which is also obtained for small ε, is the existence of termination-points on the flame front, or flame-tips. These termination-points are shown to exist for ε ≪ 1 only if A takes on positive values of order unity or larger; in particular they are absent for thin triple-flames without the presence of a non-uniform flow field. Furthermore, several additional novel contributions are made in the present context of triple-flame interaction with a non-uniform parallel flow. These include a fairly complete description of the flame propagation regimes for a wide range of variations in A and ε. In particular, it is found that larger values of A promote combustion by increasing the ε-range of existence of ignition fronts, while a decrease in the value of A towards zero or negative values increases the ε-range of existence of extinction fronts.

Global streamflow and thermal habitats of freshwater fishes under climate change

Climate change will affect future flow and thermal regimes of rivers. This will directly affect freshwater habitats and ecosystem health. In particular fish species, which are strongly adapted to a certain level of flow variability will be sensitive to future changes in flow regime. In addition, all freshwater fish species are exotherms, and increasing water temperatures will therefore directly affect fishes’ biochemical reaction rates and physiology. To assess climate change impacts on large-scale freshwater fish habitats we used a physically-based hydrological and water temperature modelling framework forced with an ensemble of climate model output. Future projections on global river flow and water temperature were used in combination with current spatial distributions of several fish species and their maximum thermal tolerances to explore impacts on fish habitats in different regions around the world. Results indicate that climate change will affect seasonal flow amplitudes, magnitude and timing of high and low flow events for large fractions of the global land surface area. Also, significant increases in both the frequency and magnitude of exceeding maximum temperature tolerances for selected fish species are found. Although the adaptive capacity of fish species to changing hydrologic regimes and rising water temperatures could be variable, our global results show that fish habitats are likely to change in the near future, and this is expected to affect species distributions.

Independent constraints on local non-Gaussianity from the peculiar velocity and density fields

Primordial, non-Gaussian perturbations can generate scale-dependent bias in the galaxy distribution. This in turn will modify correlations between galaxy positions and peculiar velocities at late times, since peculiar velocities reflect the underlying matter distribution, whereas galaxies are a biased tracer of the same. We study this effect, and show that non-Gaussianity can be constrained by comparing the observed peculiar velocity field to a model velocity field reconstructed from the galaxy density field assuming linear bias. The amplitude of the spatial correlations in the residual map obtained after subtracting one velocity field from the other is directly proportional to the strength of the primordial non-Gaussianity. We construct the corresponding likelihood function use it to constrain the amplitude of the linear flow $\beta$ and the amplitude of local non-Gaussianity $f^{\rm NL}_{\rm local}$. Applying our method to two observational data sets, the Type-Ia supernovae (A1SN) and Spiral Field \textit{I}-band (SFI++) catalogues, we obtain constraints on the linear flow parameter consistent with the values derived previously assuming Gaussianity. The marginalised 1-D distribution of $|f^{\rm NL}_{\rm local}|$ does not show strong evidence for non-zero $f^{\rm NL}_{\rm local}$, and we set 95% upper limits $|f^{\rm NL}_{\rm local}|<51.4$ from A1SN and $|f^{\rm NL}_{\rm local}|<92.6$ from SFI++. These limits on $f^{\rm NL}_{\rm local}$ are as tight as any set by previous large-scale structure measurements. Our method can be applied to any survey with radial velocities and density field data, and provides an independent check of recent CMB constraints on $f^{\rm NL}_{\rm local}$, extending these to smaller spatial scales.

Investigation of Laminar Pulsating Nanofluid Flow and Heat Transfer in a Rectangular Channel

In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The effects of several parameters, such as volume fraction of different nanoparticles, Reynolds number, and the amplitude and frequency of pulsation flow, on the rate of heat transfer and pressure drop are examined. The results show that the heat transfer enhancement on the target surface obtained by the flow pulsation highly depends on pulsating velocity. It can also be seen that total Nusselt number increases significantly due to increase in amplitude of pulsation and volume fraction of nanoparticles. Analysis also reveals that pressure drop for the alumina nanoparticles is much greater than that of the base fluid.

Subglottal Impedance-Based Inverse Filtering of Voiced Sounds Using Neck Surface Acceleration.

A model-based inverse filtering scheme is proposed for an accurate, non-invasive estimation of the aerodynamic source of voiced sounds at the glottis. The approach, referred to as subglottal impedance-based inverse filtering (IBIF), takes as input the signal from a lightweight accelerometer placed on the skin over the extrathoracic trachea and yields estimates of glottal airflow and its time derivative, offering important advantages over traditional methods that deal with the supraglottal vocal tract. The proposed scheme is based on mechano-acoustic impedance representations from a physiologically-based transmission line model and a lumped skin surface representation. A subject-specific calibration protocol is used to account for individual adjustments of subglottal impedance parameters and mechanical properties of the skin. Preliminary results for sustained vowels with various voice qualities show that the subglottal IBIF scheme yields comparable estimates with respect to current aerodynamics-based methods of clinical vocal assessment. A mean absolute error of less than 10% was observed for two glottal airflow measures -maximum flow declination rate and amplitude of the modulation component- that have been associated with the pathophysiology of some common voice disorders caused by faulty and/or abusive patterns of vocal behavior (i.e., vocal hyperfunction). The proposed method further advances the ambulatory assessment of vocal function based on the neck acceleration signal, that previously have been limited to the estimation of phonation duration, loudness, and pitch. Subglottal IBIF is also suitable for other ambulatory applications in speech communication, in which further evaluation is underway.

A reduced model for ion temperature gradient turbulent transport in helical plasmas

A novel reduced model for ion temperature gradient (ITG) turbulent transport in helical plasmas is presented. The model enables one to predict nonlinear gyrokinetic simulation results from linear gyrokinetic analyses. It is shown from nonlinear gyrokinetic simulations of the ITG turbulence in helical plasmas that the transport coefficient can be expressed as a function of the turbulent fluctuation level and the averaged zonal flow amplitude. Then, the reduced model for the turbulent ion heat diffusivity is derived by representing the nonlinear turbulent fluctuations and zonal flow amplitude in terms of the linear growth rate of the ITG instability and the linear response of the zonal flow potentials. It is confirmed that the reduced transport model is in a good agreement with nonlinear gyrokinetic simulation results for high ion temperature plasmas in the large helical device.

Stability of model flocks in turbulent-like flow

We report numerical simulations of a simple model of flocking particles in the presence of an uncertain background environment. We consider two types of environmental perturbations: random noise applied separately to each particle, and spatiotemporally correlated ‘noise’ provided by a turbulent-like flow field. The effects of these two types of noise are very different; surprisingly, the applied flow field tends to destroy the global order of the flocking model even for vanishingly small flow amplitudes. Local order, however, is preserved in smaller sub-flocks, although their composition changes dynamically. Our results suggest that realistic perturbations must be considered in assessing the stability of models of collective animal behavior, and that random noise is not a sufficient proxy.

Enhancement of surface roughness in electrochemical machining of Ti6Al4V by pulsating electrolyte

Electrochemical machining (ECM) is widely used in machining a variety of components used in aerospace, defence, automotive and medical applications. The surface roughness of the ECM process has become important because of increased quality demands. Considerable attention has been paid to achieving low surface roughness in ECM. Surface roughness is closely related to the distribution of gases and Joule heat produced during the ECM process, which affect the electrolyte electric conductivity and directly determine the surface roughness. In this report, a pulsating electrolyte, which is one of the unsteady flows that are characterized by periodic fluctuations of the mass flow rate and pressure, is first introduced to the ECM process. The ECM process is affected by the pulsating electrolyte because it can modify the heat transfer. The goal of this report is to present experimental results of the surface roughness obtained on Ti6Al4V samples using a developed pulsating electrolyte supply system in ECM. It is observed that a lower surface roughness and higher material removal rate could be obtained by using a pulsating electrolyte with proper pulsating frequency and amplitude. In direct current ECM, the surface roughness Ra is 5.7 μm, the material removal rate is 0.85 g/min at a constant electrolyte, the lowest surface roughness is 3.69 μm and the largest material removal rate is 0.92 g/min, which are obtained at a pulsating frequency of 10 Hz and amplitude of 0.2 MPa. In pulsed current ECM, the surface roughness Ra and material removal rate are 0.67 μm and 0.38 g/min at a constant electrolyte, respectively, and both the minimum surface roughness Ra of 0.53 μm and maximum material removal rate of 0.39 g/min are observed when the proper pulsating electrolyte flow frequency and amplitude are used.

Conjugate heat transfer during oscillatory laminar flow in porous media

Hydrodynamics and conjugate heat transfer in porous media subject to unidirectional-steady state as well as steady-periodic flow conditions were numerically studied. Two-dimensional flows in porous media composed of periodically configured arrays of square cylinders were simulated using a computational fluid dynamics tool, with sinusoidal time variation of inlet and exit boundaries and conjugate heat transfer between the solid and fluid domains. The simulated domain contained seven unit cells, with each unit cell representing a square cylinder. Simulations showed that the end effects did not persist more than two unit cells. Simulations were conducted for flow oscillation frequencies of 0–60Hz, and low and high velocity amplitudes (representing tidal fluid penetration amplitudes of 8 and 2 times the hydraulic diameter, respectively, at inlet) for a 75% porous domain. Using the simulation results, pore-scale volume-average Darcy permeability, Forchheimer coefficient, and Nusselt number associated with the standard volume-average porous media momentum and thermal energy equations were calculated. These parameters were calculated in instantaneous as well as cycle-averaged forms. The Forchheimer coefficient and Nusselt number were significantly different in unidirectional-steady and oscillatory flow conditions. These parameters strongly depend on the flow oscillation frequency and amplitude. Furthermore, significant phase lag occurs among velocity, pressure, temperature and heat transfer processes. The results confirm that unidirectional-steady flow models and correlations are not suitable for applications involving flow oscillations.

Dynamics of the solar tachocline – III. Numerical solutions of the Gough and McIntyre model

We present the first numerical simulations of the solar interior to exhibit a tachocline consistent with the Gough and McIntyre (1998) model. We find nonlinear, axisymmetric, steady-state numerical solutions in which: (1) a large-scale primordial field is confined within the radiation zone by downwelling meridional flows that are gyroscopically pumped in the convection zone (2) the radiation zone is in almost-uniform rotation, with a rotation rate consistent with observations (3) the bulk of the tachocline is magnetic free, in thermal-wind balance and in thermal equilibrium and (4) the interaction between the field and the flows takes place within a very thin magnetic boundary layer, the tachopause, located at the bottom of the tachocline. We show that the thickness of the tachocline scales with the amplitude of the meridional flows exactly as predicted by Gough and McIntyre. We also determine the parameter conditions under which such solutions can be obtained, and provide a simple explanation for the failure of previous numerical attempts at reproducing the Gough and McIntyre model. Finally, we discuss the implications of our findings for future numerical models of the solar interior, and for future observations of the Sun and other stars.