Radial Flow Pattern Research Articles

Variation in the radial patterns of sap flux density in pubescent oak (Quercus pubescens) and its implications for tree and stand transpiration measurements

Radial variation in sap flux density across the sapwood was assessed by the heat field deformation method in several trees of Quercus pubescens Wild., a ring-porous species. Sapwood depths were delimited by identifying the point of zero flow in radial patterns of sap flow, yielding tree sapwood areas that were 1.5-2 times larger than assumed based on visual examinations of wood cores. The patterns of sap flow varied both among trees and diurnally. Rates of sap flow were higher close to the cambium, although there was a significant contribution from the inner sapwood, which was greater (up to 60% of total flow) during the early morning and late in the day. Accordingly, the normalized difference between outer and inner sapwood flow was stable during the middle of the day, but showed a general decline in the afternoon. The distribution of sap flux density across the sapwood allowed us to derive correction coefficients for single-point heat dissipation sap flow measurements. We used daytime-averaged coefficients that depended on the particular shape of the radial profile and ranged between 0.45 and 1.28. Stand transpiration calculated using the new method of estimating sapwood areas and the radial correction coefficients was similar to (Year 2003), or about 25% higher than (Year 2004), previous uncorrected values, and was 20-30% of reference evapotranspiration. We demonstrated how inaccuracies in determining sapwood depths and mean sap flux density across the sapwood of ring-porous species could affect tree and stand transpiration estimates.

Dynamic models for mantle flow and seismic anisotropy in the North Atlantic region and comparison with observations

Dynamic mantle flow and temperature models for the North Atlantic based on a regionalized P‐wave and a global S‐wave tomography model were derived under the constraint of a maximum fit to the observed gravity field. For the regional flow model Cartesian geometry, temperature‐ and depth‐dependent viscosity and a free slip surface were assumed, while the global model assumed a radially dependent viscosity and kinematic plate velocity boundary conditions. Both models show pronounced upwellings within the upper mantle beneath the Iceland area and the lower mantle beneath, the regional model containing a lateral shift associated with a horizontal flow near 660 km depth. The upper mantle temperature field of the regional model shows two distinct anomalies, one beneath Iceland and the westerly adjacent regions with a connection to a deep mantle root and an excess temperature of 200°C, and a second one below 300 km at the Kolbeinsey Ridge with an excess temperature of 120°C. These anomalies do not appear to be connected. An essentially radial flow pattern is found south of Iceland with ridge parallel flow along Reykjanes and divergent flow at the Kolbeinsey Ridge. The long‐wavelength global model does not show such details but is characterized by a NE‐SW elongated upwelling flow beneath Iceland and a ridge perpendicular flow within the upper mantle. From the modeled flow fields, lattice preferred orientations (LPO) of olivine are calculated. For the regional model, azimuthal seismic anisotropy is predicted with fast directions diverging away from Iceland and the Kolbeinsey ridge. The global model predicts roughly ridge perpendicular fast directions. Comparison of predicted with observed seismic anisotropy models shows regions of good agreement north, east, and SE of Iceland, as well as for Iceland. No agreement is found beneath the Reykjanes Ridge area, leading to the speculation that the fast directions are perpendicular to the flow due to a change in the LPO generating mechanism. Regarding geochemical findings, the regional flow model can explain plume‐related geochemical signatures observed on the Reykjanes Ridge and predicts a deep, hot melt zone beneath the Kolbeinsey Ridge without plume tracers.

Cue integration for the perception and control of self-movement in ageing and Alzheimer's disease

The perception and control of self-movement relies on visual cues derived from the radial patterns of optic flow and from the relative motion of objects within view. Optic flow and object motion processing impairments might limit independent self-movement in a manner like that seen in ageing and in Alzheimer's disease. We used optic flow and object motion stimuli to simulate aspects of the self-movement scene. Stimulus salience was individualized to present comparable stimuli to young [n = 18; mean age = 25.6, standard error of measurement (SEM) = 1.4], middle-aged (n = 17; mean age = 53.9, SEM = 0.9), older adult (n = 30; mean age = 72.4, SEM = 1.4) and Alzheimer's disease (n = 15; mean age 75.2, SEM = 1.6) subjects. All groups were tested in two tasks: pointing towards the simulated direction of self-movement and steering the simulated self-movement towards a straight-ahead direction. We found that young and middle-aged subjects show similar pointing accuracy using either optic flow or object motion, but steer better with object motion than with optic flow. Older adult subjects show better performance with optic flow than object cues for pointing (P < 0.001), but their performance improves when both cues are combined in the pointing (P = 0.012) and steering (P = 0.02) tasks. Alzheimer's disease patients show poorer performance with optic flow and object motion than all other groups and do not benefit from the combined presentation of cues for either pointing or steering. We conclude that ageing and Alzheimer's disease are associated with distinct profiles of visual processing deficits that limit the ability to use optic flow and object motion to perceive and control self-movement.

Perfect fluidity of the quark–gluon plasma core as seen through its dissipative hadronic corona

The agreement of hydrodynamic predictions of differential elliptic flow and radial flow patterns with Au + Au data at s N N = 200 GeV is one of the main lines of evidence suggesting the nearly perfect fluid properties of the strongly coupled quark–gluon plasma, sQGP, produced at RHIC. We study the sensitivity of this conclusion to different hydrodynamic assumptions on hadro-chemical and thermal freezeout after the sQGP hadronizes. We show that if chemical freezeout occurs at the hadronization time, as required to reproduce the observed hadron yields, then, surprisingly, the differential elliptic flow, v 2 ( p T ) , for pions continues to increase with proper time in the late hadronic phase until thermal freezeout and leads to a discrepancy with the v 2 ( p T ) data. In contrast, if both hadro-chemical and thermal equilibrium are maintained past the hadronization point, then the mean transverse momentum per pion increases in a way that accidentally preserves v 2 ( p T ) from the sQGP phase in agreement with the data, but at the cost of the agreement with the observed hadronic yields. In order that all the data on (1) hadronic ratios, (2) radial flow, as well as (3) differential elliptic flow be reproduced, the sQGP core must expand with a minimal viscosity, η ≈ T c 3 , that is however even greater than the viscosity, η H ≈ T / σ H , of its hadronic corona. However, because of the large entropy density difference of the two phases of QCD matter, the larger viscosity in the sQGP phase leads to nearly perfect fluid flow in that phase while the smaller entropy density of the hadronic corona strongly hinders the applicability of Euler hydrodynamics in that phase. The “perfect fluid” property of the sQGP is thus not due to a sudden reduction of the viscosity at the critical temperature T c , but to a sudden increase of the entropy density of QCD matter and is therefore an important signature of deconfinement.

Free Convective Heat Transfer Structures as a Function of the Width of Isothermal Horizontal Rectangular Plates

Results are presented for the experimental investigations of free convection heat transfer from upward facing isothermal horizontal rectangular plates as a function of the plate width. Two models of the convective fluid flow structures above horizontal rectangular plates were proposed as a result of flow visualization. Solutions of these models are presented in the form of Nusselt-Rayleigh relations with the aspect ratio as a parameter. Analysis of the visualization results provided a basis for preferring the radial flow pattern at small values of the Rayleigh number, especially for square plates or at the ends of rectangular plates, and a basis for preferring the parallel flow model at large values of the Rayleigh number. From the previous experimental results and the present experimental and interferometric studies, it is shown that the transition Rayleigh number at which the flow changes from the concentric to the parallel flow pattern is a function of the width of the plate.

Computational analyses for illusory transformations in the optic flow field and heading perception in the presence of moving objects

When we see a stimulus of a radial flow field (the target flow) overlapped with a lateral flow field or another radial flow field, the focus of expansion (FOE) of the target radial flow appears to be shifted in a direction. Royden and Conti [(2003). A model using MT-like motion-opponent operators explains an illusory transformation in the optic flow field. Vision Research, 43, 2811–2826] argued that local motion subtraction is crucial for explanation of this phenomenon. The flow field which causes the illusory displacement of FOE was computationally analyzed. It was shown that the flow field is approximately a rigid-motion flow; the flow can be generated by simulating a situation where an observer moves toward a stationary scene. The heading direction for the observer corresponds to the perceived position of the FOE of the radial flow pattern. It implies that any algorithms which assume rigidity of the scene and recover veridical heading explain the bias in perceived FOE. There is no need for local motion subtraction in order to explain the phenomena. Furthermore, the flow for an observer’s translation in the presence of objects moving laterally or in depth was computationally analyzed. It was found that algorithms which minimizes standard error functions with less weights to the independently moving objects show similar biases in recovered heading to the bias of human observers. It implies that local motion subtraction is not necessary for explanation of the bias in perceived heading due to an object moving laterally or in depth, contrary to the argument of Royden [(2002). Computing heading in the presence of moving objects: a model that uses motion-opponent operators. Vision Research, 42, 3043–3058].

Long range interactions between object-motion and self-motion in the perception of movement in depth

Self-motion through a three-dimensional array of objects creates a radial flow pattern on the retina. We superimposed a simulated object moving in depth on such a flow pattern to investigate the effect of the flow pattern on judgments of both the time to collision (TTC) with an approaching object and the trajectory of that object. Our procedure allowed us to decouple the direction and speed of simulated self motion-in-depth (MID) from the direction and speed of simulated object MID. In Experiment 1 we found that objects with the same closing speed were perceived to have a higher closing speed when self-motion and object-motion were in the same direction and a lower closing speed when they were in the opposite direction. This effect saturated rapidly as the ratio between the speeds of self-motion and object-motion was increased. In Experiment 2 we found that the perceived direction of object-MID was shifted towards the focus of expansion of the flow pattern. In Experiments 3 and 4 we found that the erroneous biases in perceived speed and direction produced by simulated self-motion were significantly reduced when binocular information about MID was added. These findings suggest that the large body of research that has studied motion perception using stationary observers has limited applicability to situations in which both the observer and the object are moving.

Radial patterns of sap flow in woody stems of dominant and understory species: scaling errors associated with positioning of sensors.

We studied sap flow in dominant coniferous (Pinus sylvestris L.) and broadleaf (Populus canescens L.) species and in understory species (Prunus serotina Ehrh. and Rhododendron ponticum L.) by the heat field deformation (HFD) method. We attempted to identify possible errors arising during flow integration and scaling from single-point measurements to whole trees. Large systematic errors of -90 to 300% were found when it was assumed that sap flow was uniform over the sapwood depth. Therefore, we recommend that the radial sap flow pattern should be determined first using sensors with multiple measuring points along a stem radius followed by single-point measurements with sensors placed at a predetermined depth. Other significant errors occurred in the scaling procedure even when the sap flow radial pattern was known. These included errors associated with uncertainties in the positioning of sensors beneath the cambium (up to 15% per 1 mm error in estimated xylem depth), and differences in environmental conditions when the radial profile applied for integration was determined over the short term (up to 47% error). High temporal variation in the point-to-area correction factor along the xylem radius used for flow integration is also problematic. Compared with midday measurements, measurements of radial variation of sap flow in the morning and evening of sunny days minimized the influence of temporal variations on the point-to-area correction factor, which was especially pronounced in trees with a highly asymmetric sap flow radial pattern because of differences in functioning of the sapwood xylem layers. Positioning a single-point sensor at a depth with maximum sap flow is advantageous because of the high sensitivity of maximum sap flow to water stress conditions and changes in micro-climate, and because of the lower random errors associated with the positioning of a single-point sensor along the xylem radius.

Flow Generated by an Aerated Rushton Impeller: Two‐phase PIV Experiments and Numerical Simulations

AbstractA two‐camera PIV technique was used to obtain angle resolved velocity and turbulence data of the flow in a lab‐scale stirred tank, equipped with a Rushton turbine. Two cases were investigated: a single‐phase flow and a gas‐liquid flow. In the former case, the classical radial jet flow pattern accompanied by two trailing vortices was observed. In the latter case, the velocity of the radial jet was reduced, and the vortices were diminished by the presence of the gas. Gas cavities clinging to the back of the impeller blades were observed. Both cases were also investigated with the use of three‐dimensional transient CFD simulations. For the single‐phase flow the simulations in the impeller region correspond very well with the experimental data. For the gas‐liquid flow both the mean and fluctuating liquid velocities in the impeller region are well predicted. This is also the case for the mean radial gas velocities.

A hardness equation for sharp indentation of elastic-power-law strain-hardening materials

Abstract This investigation is predicated upon work by Mata et al. on the contact deformation regimes for strain-hardening materials. The results allow us to derive a general hardness equation for sharp indentation of elastic-power-law plastic materials. The formula H/σr = 1.440 + 0.264 ln(E/σr) is found to provide estimates of hardness H for a wide range of elastoplastic responses as long as the contact deformation regime lies within the elastic-plastic transition. This formulation is a modification to previous formulae derived for solids that do not exhibit strain hardening; where E is Young's modulus and the yield strength σys has been replaced by σr, the stress level in the uniaxial stress-strain curve at a characteristic strain ϵr of 0.1. The development of radial flow patterns is regarded as a necessary condition to the validity of the above equation. As the deformation underneath the indenter evolves to an uncontained mode, the radial flow patterns that are characteristic of the elastic-plastic tra...

A hardness equation for sharp indentation of elastic-power-law strain-hardening materials

Abstract This investigation is predicated upon work by Mata et al. on the contact deformation regimes for strain-hardening materials. The results allow us to derive a general hardness equation for sharp indentation of elastic-power-law plastic materials. The formula H/σr = 1.440 + 0.264 ln(E/σr) is found to provide estimates of hardness H for a wide range of elastoplastic responses as long as the contact deformation regime lies within the elastic-plastic transition. This formulation is a modification to previous formulae derived for solids that do not exhibit strain hardening; where E is Young's modulus and the yield strength σys has been replaced by σr, the stress level in the uniaxial stress-strain curve at a characteristic strain ϵr of 0.1. The development of radial flow patterns is regarded as a necessary condition to the validity of the above equation. As the deformation underneath the indenter evolves to an uncontained mode, the radial flow patterns that are characteristic of the elastic-plastic transition are increasingly disrupted to a point where non-radial flow leads to piling-up of material at the contact boundary.

Dynamics of obsidian flows inferred from microstructures: insights from microlite preferred orientations

The flow of obsidian lava leads to crystal alignments that reflect both the accumulated strain and the type of flow across the surface. Microlite preferred orientations are used to investigate the emplacement dynamics, strain history, and structural evolution of Obsidian Dome, eastern California. Measurements of three-dimensional microlite trend and plunge in samples from the near-vent region, distal flow, and flow front show: (1) the flow directions along the dome margins, (2) the deformation style (e.g., pure versus simple shear) at the dome margins, and (3) the variation in strain as a function of position within the flow. Microlites form well-developed lineations in the plane of flow banding in all samples. Stereographic projections indicate that lineations trend normal to the western flow front and plunge shallowly away from the margin. The radial flow pattern indicated by measurements made along the western margin suggests that extrusion was from a roughly elliptical vent. These results highlight a strong correlation between microlite trend and the bulk flow direction inferred from the geometry of the flow. Along most of the eastern periphery, lineations trend parallel to the margin and likely reflect the local flow direction as influenced by compression against the thickening flow crust, marginal talus piles, and topography. Orientation distributions imply that radial spreading accompanied by flattening was the dominant mechanism for flow emplacement. Comparisons of measured orientation distributions with theoretical predictions suggest that microlite fabrics in flow front and near-vent samples developed in a pure shear flow. Microstructures in a sample from near the distal flow base records a component of simple shear. Variance in microlite trend provides a measure of the amount of strain acquired during flow. Standard deviation in trend decreases from the near-vent region to the flow margins, reflecting progressive alignment of microlites during transport. Pure shear strain inferred from orientation distributions increases from approximately 0.3 near the vent to about 1.1 at the flow front. The difference between these strains (0.8) is an estimate of the strain associated with flow emplacement. Such strain is similar in size to that estimated from mesoscopic structures (∼1) and for horizontal spreading of a fluid whose volume is equal to that of Obsidian Dome (∼1.6). This suggests that flow on the surface was sufficient to produce observed microlite preferred orientations in the flow front. These techniques can be applied to interpret older dissected lavas where erosion has erased much of the original flow front or where larger-scale structures indicative of flow directions are poorly preserved.

Evaluation of heat balance and heat dissipation methods for sapflow measurements in pine and spruce

The tissue heat-balance method (Cy and the heat-dissipation method (Granier) were compared in three Scots pines and two Norway spruces in a forest in central Sweden. The Granier system measured up to 50% lower sapflow than the Cy system at high flow rates. New coefficients for the Granier system were estimated, based on sapflow density from the Cy measurements. Wi- thout compensation, natural temperature gradients may cause large errors in measurements made by the Granier system. By using a hori- zontal reference sensor, no compensation was necessary. It was also shown that radial flow patterns must be considered when calculating total tree sapflow. Transpiration of two adjacent stands, one measured by the Granier method and the other by the Cy method, sho- wed good agreement internally and with total evaporation measured by the eddy-correlation method.

Evidence from gabbro of the Troodos ophiolite for lateral magma transport along a slow-spreading mid-ocean ridge.

The lateral flow of magma and ductile deformation of the lower crust along oceanic spreading axes has been thought to play a significant role in suppressing both mid-ocean ridge segmentation and variations in crustal thickness. Direct investigation of such flow patterns is hampered by the kilometres of water that cover the oceanic crust, but such studies can be made on ophiolites (fragments of oceanic crust accreted to a continent). In the Oman ophiolite, small-scale radial patterns of flow have been mapped along what is thought to be the relict of a fast-spreading mid-ocean ridge. Here we present evidence for broad-scale along-axis flow that has been frozen into the gabbro of the Troodos ophiolite in Cyprus (thought to be representative of a slow-spreading ridge axis). The gabbro suite of Troodos spans nearly 20 km of a segment of a fossil spreading axis, near a ridge-transform intersection. We mapped the pattern of magma flow by analysing the rocks' magnetic fabric at 20 sites widely distributed in the gabbro suite, and by examining the petrographic fabric at 9 sites. We infer an along-axis magma flow for much of the gabbro suite, which indicates that redistribution of melt occurred towards the segment edge in a large depth range of the oceanic crust. Our results support the magma plumbing structure that has been inferred indirectly from a seismic tomography experiment on the slow-spreading Mid-Atlantic Ridge.

Radial variation in sap flow in five laurel forest tree species in Tenerife, Canary Islands.

Variations in radial patterns of xylem water content and sap flow rate were measured in five laurel forest tree species (Laurus azorica (Seub.) Franco, Persea indica (L.) Spreng., Myrica faya Ait., Erica arborea L. and Ilex perado Ait. ssp. platyphylla (Webb & Berth.) Tutin) growing in an experimental plot at Agua García, Tenerife, Canary Islands. Measurements were performed around midday during warm and sunny days by the heat field deformation method. In all species, water content was almost constant (around 35% by volume) over the whole xylem cross-sectional area. There were no differences in wood color over the whole cross-sectional area of the stem in most species with the exception of E. arborea, whose wood became darker in the inner layers. Radial patterns of sap flow were highly variable and did not show clear relationships with tree diameter or species. Sap flow occurred over the whole xylem cross-sectional area in some species, whereas it was limited to the outer xylem layers in others. Sap flow rate was either similar along the xylem radius or exhibited a peak in the outer part of the xylem area. Low sap flow rates with little variation in radial pattern were typical for shaded suppressed trees, whereas dominant trees exhibited high sap flow rates with a peak in the radial pattern. Stem damage resulted in a significant decrease in sap flow rate in the outer xylem layers. The outer xylem is more important for whole tree water supply than the inner xylem because of its larger size. We conclude that measurement of radial flow pattern provides a reliable method of integrating sap flow from individual measuring points to the whole tree.

Global-perspective jitter improves vection in central vision.

Previous vection research has tended to minimise visual-vestibular conflict by using optic-flow patterns which simulate self-motions of constant velocity. Here, experiments are reported on the effect of adding 'global-perspective jitter' to these displays--simulating forward motion of the observer on a platform oscillating in horizontal and/or vertical dimensions. Unlike non-jittering displays, jittering displays produced a situation of sustained visual-vestibular conflict. Contrary to the prevailing notion that visual-vestibular conflict impairs vection, jittering optic flow was found to produce shorter vection onsets and longer vection durations than non-jittering optic flow for all of jitter magnitudes and temporal frequencies examined. On the basis of these findings, it would appear that purely radial patterns of optic flow are not the optimal inducing stimuli for vection. Rather, flow patterns which contain both regular and random-oscillating components appear to produce the most compelling subjective experiences of self-motion.

Short-latency visual stabilization mechanisms that help to compensate for translational disturbances of gaze.

Recent studies in primates have revealed short-latency visual tracking mechanisms that help to stabilize the eyes during translational disturbances of the observer, and so operate as backups to otolith-mediated vestibulo-ocular reflexes. One such mechanism generates version eye movements to help stabilize gaze when the moving observer looks off to one side, utilizing binocular disparity to help single out the images in the plane of fixation (ocular following). Two others generate vergence eye movements to help maintain binocular alignment on objects that lie ahead: one responds to the radial patterns of optic flow (radial-flow vergence) and the other to the changes in binocular parallax (disparity vergence). Accumulating evidence suggests that, despite their short latency, all are mediated by the medial superior temporal area of cortex.

Ocular responses to radial optic flow and single accelerated targets in humans

Self-movement in a structured environment induces retinal image motion called optic flow. Optic flow on one hand provides information about the direction of self-motion. On the other hand optic flow presents large field visual motion which will elicit eye movements for the purpose of image stabilization. We investigated oculomotor behavior in humans during the presentation of radial optic flow fields which simulated forward or backward self-motion. Different conditions and oculomotor tasks were compared. In one condition, subjects had to actively pursue single dots in a radial flow pattern. In a second condition, subjects had to pursue single dots over a dark background. These dots accelerated or decelerated similar to single dots in radial optic flow. In a third condition, subjects were asked to passively view the entire optic flow stimulus. Smooth pursuit eye movements with high gain were observed when dots were actively pursued. This was true for single dots moving over a homogeneous background and for single dots in the optic flow. Passive viewing of optic flow stimuli evoked eye movements that resembled an optokinetic nystagmus. Slow phase eye movements tracked the motion of elements in the optic flow. Gain was low for simulated forward self-motion (expanding optic flow) and high for simulated backward movement self-motion (contracting optic flow). Thus, voluntary pursuit and passive optokinetic responses yielded different gain for the tracking of elements of an expanding optic flow pattern. During passive viewing of the optic flow stimulus, gaze was usually at or near the focus of radial flow. Our results give insights into the oculomotor performances and needs for image stabilization during self-motion and in the role of gaze strategy for the detection of the direction of heading.

Visual loss and getting lost in Alzheimer's disease.

AD causes patients to get lost in familiar surroundings, in part because of visuospatial disorientation from parieto-occipital involvement. Parieto-occipital cortex analyzes the radial patterns of visual motion that create optic flow and guide movements through the environment by showing one's direction of self-movement. To determine whether AD patients are impaired in perceiving the visual patterns of optic flow, suggesting a perceptual mechanism of visuospatial disorientation. We studied the ability of young normal subjects, elderly normal subjects, and AD patients to see and interpret visual patterns, including the radial motion of optic flow. Each person sat in front of a panoramic computer display and gave push-button responses to indicate their perception of the projected visual stimuli. Spatial navigation was tested by asking questions about a recently traversed path. Half of the AD subjects showed impaired optic flow perception that was associated with poor performance on the spatial navigation test, even though their perception of simple moving patterns was relatively preserved. Some AD subjects also showed a separate impairment in interpreting optic flow, so that they could not use those stimuli to judge their direction of self-movement. AD greatly impairs the ability to see the radial patterns of optic flow. This may interfere with the use of visual information to guide self-movement and maintain spatial orientation.

The role of central and peripheral vision in postural control during walking.

Three hypotheses have been proposed for the roles of central and peripheral vision in the perception and control of self-motion: (1) peripheral dominance, (2) retinal invariance, and (3) differential sensitivity to radial flow. We investigated postural responses to optic flow patterns presented at different retinal eccentricities during walking in two experiments. Oscillating displays of radial flow (0 degree driver direction), lamellar flow (90 degrees), and intermediate flow (30 degrees, 45 degrees) patterns were presented at retinal eccentricities of 0 degree, 30 degrees, 45 degrees, 60 degrees, or 90 degrees to participants walking on a treadmill, while compensatory body sway was measured. In general, postural responses were directionally specific, of comparable amplitude, and strongly coupled to the display for all flow patterns at all retinal eccentricities. One intermediate flow pattern (45 degrees) yielded a bias in sway direction that was consistent with triangulation errors in locating the focus of expansion from visible flow vectors. The results demonstrate functionally specific postural responses of both central and peripheral vision, contrary to the peripheral dominance and differential sensitivity hypotheses, but consistent with retinal invariance. This finding emphasizes the importance of optic flow structure for postural control regardless of the retinal locus of stimulation.