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Existing aeolian transport models often fail in field environments. The discrepancy between models and prediction has been attributed to inadequate field measurements and uncertainty in the general knowledge of the fundamental physical processes (turbulence) driving sand transport. The main challenges of measured and modeled aeolian transport include (1) coarse resolution measurements (relative to fluid-grain scale physics) made with obtrusive instrumentation that disrupt natural fluid and sediment flow, (2) an inadequate understanding of the fundamental physical relationships between turbulence and sediment transport, and (3) the inability of aeolian transport models, derived from wind-tunnel observations, to simulate natural boundary layer processes at the appropriate field scales (mm - cm).Here, we introduce F-PTV, a Field-based Particle Tracking Velocimetry system. The field-based system is capable of providing the first unobtrusive measurements of turbulence and the resulting sand transport by wind in a field environment and consists of 3 integral components: (1) an illuminated volume, (2) neutrally-buoyant seeding material in the form of helium bubbles, and (3) 4 high speed cameras. The 527 nm laser and 4, high-resolution, high-frame rate cameras are mounted on rigid frames to be deployed on the subaerial beach. The laser beam is directed to the surface through a fiber-to-volume optics collimator at a height of 2.23 m and directs a defocused beam vertically down to create an ellipsoidal cone of light over the sampling area. At 1200 frames per second, the cameras capture the scattered light from helium bubbles and sand particles passing through the illuminated volume, enabling us to track individual helium bubbles and sand grains. The F-PTV system has the capability to provide the first unobtrusive observations of turbulence and transport in a field environment.

Ice scallops are a small-scale (5–20 cm) quasi-periodic ripple pattern that occurs at the ice–water interface. Previous work has suggested that scallops form due to a self-reinforcing interaction between an evolving ice-surface geometry, an adjacent turbulent flow field and the resulting differential melt rates that occur along the interface. In this study, we perform a series of laboratory experiments in a refrigerated flume to quantitatively investigate the mechanisms of scallop formation and evolution in high resolution. Using particle image velocimetry, we probe an evolving ice–water boundary layer at sub-millimetre scales and 15 Hz frequency. Our data reveal three distinct regimes of ice–water interface evolution: a transition from flat to scalloped ice; an equilibrium scallop geometry; and an adjusting scallop interface. We find that scalloped-ice geometry produces a clear modification to the ice–water boundary layer, characterized by a time-mean recirculating eddy feature that forms in the scallop trough. Our primary finding is that scallops form due to a self-reinforcing feedback between the ice-interface geometry and shear production of turbulent kinetic energy in the flow interior. The length of this shear production zone is therefore hypothesized to set the scallop wavelength.

Purpose: Human respiratory aerosols may have important implications for transmission of pathogens. The study of aerosol production during vigorous breathing activities such as exercise is limited. Data on aerosol production during cardiopulmonary exercise testing (CPET) are lacking. Methods: We used a high-powered, pulsed Nd:YAG laser to illuminate a region of interest in front of two healthy adult subjects during CPET. Subjects exercised to the point of respiratory compensation. Images were captured with a high-speed, high-resolution camera to determine net exhaled particle (NEP) counts at different phases of CPET, including resting breathing, submaximal exercise, peak exercise, and active recovery. Experiments were performed with the room ventilation activated.Results: NEP counts remained relatively constant until late/peak exercise when they decreased prior to rebounding into recovery. NEP counts at resting breathing were higher than those reported using other methods of measurement. Exhaled particles were in the submicron size range. Conclusion: Our method of aerosol particle quantification enables measurement of significant quantities of ultrafine particles and dynamic assessment of aerosol production during CPET. The unique pattern of aerosol production observed during submaximal and peak exercise suggests that extension of results from resting breathing to CPET may not be appropriate.

Purpose Human respiratory aerosols may have important implications for transmission of pathogens. The study of aerosol production during vigorous breathing activities such as exercise is limited. In particular, data on aerosol production during cardiopulmonary exercise testing (CPET) are lacking. Methods In this pilot project, we used a high-powered, pulsed Nd:YAG laser to illuminate a region of interest in front of two healthy adult subjects during CPET. Subjects exercised to the point of respiratory compensation. Images were captured with a high-speed, high-resolution camera to determine net exhaled particle (NEP) counts at different phases of CPET, including resting breathing, submaximal exercise, peak exercise, and active recovery. Experiments were performed with the room ventilation activated. Results Net exhaled particle counts remained relatively constant until late/peak exercise when they decreased prior to rebounding into recovery. NEP counts at resting breathing were higher than those reported using other methods of measurement. Exhaled particles were in the submicron size range. Conclusion Our method of aerosol particle quantification enables measurement of significant quantities of ultrafine particles and dynamic assessment of aerosol production during CPET. The unique pattern of aerosol production observed during submaximal and peak exercise suggests that extension of results from resting breathing to CPET may not be appropriate.

Tomographic background oriented schlieren (Tomo-BOS) imaging measures density or temperature fields in 3D using multiple camera BOS projections, and is particularly useful for instantaneous flow visualizations of complex fluid dynamics problems. We propose a new method based on physics-informed neural networks (PINNs) to infer the full continuous 3D velocity and pressure fields from snapshots of 3D temperature fields obtained by Tomo-BOS imaging. PINNs seamlessly integrate the underlying physics of the observed fluid flow and the visualization data, hence enabling the inference of latent quantities using limited experimental data. In this hidden fluid mechanics paradigm, we train the neural network by minimizing a loss function composed of a data mismatch term and residual terms associated with the coupled Navier-Stokes and heat transfer equations. We first quantify the accuracy of the proposed method based on a 2D synthetic data set for buoyancy-driven flow, and subsequently apply it to the Tomo-BOS data set, where we are able to infer the instantaneous velocity and pressure fields of the flow over an espresso cup based only on the temperature field provided by the Tomo-BOS imaging. Moreover, we conduct an independent PIV experiment to validate the PINN inference for the unsteady velocity field at a center plane. To explain the observed flow physics, we also perform systematic PINN simulations at different Reynolds and Richardson numbers and quantify the variations in velocity and pressure fields. The results in this paper indicate that the proposed deep learning technique can become a promising direction in experimental fluid mechanics., Comment: 17 pages, supplementary materials attached

Summary We report the case of a 65-year-old female who presented with symptomatic hypercalcaemia (corrected calcium of 4.57 mmol/L) with confusion, myalgias and abdominal discomfort. She had a concomitant metabolic alkalosis (pH 7.46, HCO3- 40 mmol/L, pCO2 54.6 mmHg). A history of significant Quick-Eze use (a calcium carbonate based antacid) for abdominal discomfort, for 2 weeks prior to presentation, suggested a diagnosis of milk-alkali syndrome (MAS). Further investigations did not demonstrate malignancy or primary hyperparathyroidism. Following management with i.v. fluid rehydration and a single dose of i.v. bisphosphonate, she developed symptomatic hypocalcaemia requiring oral and parenteral calcium replacement. She was discharged from the hospital with stable biochemistry on follow-up. This case demonstrates the importance of a detailed history in the diagnosis of severe hypercalcaemia, with MAS representing the third most common cause of hypercalcaemia. We discuss its pathophysiology and clinical importance, which can often present with severe hypercalcaemia that can respond precipitously to calcium-lowering therapy. Learning points: Milk-alkali syndrome is an often unrecognised cause for hypercalcaemia, but is the third most common cause of admission for hypercalcaemia. Calcium ingestion leading to MAS can occur at intakes as low as 1.0–1.5 g per day in those with risk factors. Early recognition of this syndrome can avoid the use of calcium-lowering therapy such as bisphosphonates which can precipitate hypocalcaemia.

The structure factor for electric field correlations in the two dimensional Coulomb fluid is simulated and compared to theories of the dielectric function. Singular changes in the structure factor occur at the BKT insulator to conductor transition, as well as at a higher temperature correlation transition between a poor electrolyte and perturbed Debye-H\"uckel fluid. Structure factors are found to differ in the canonical and grand canonical ensembles, with the poor electrolyte showing full ensemble inequivalence. We identify mechanisms of `underscreening' and `pinch point' scattering that are relevant to experiments on ionic liquids and artificial spin ice respectively., Comment: 18 pages, 9 figures

Planar (2 dimensional) particle image velocimetry (PIV) was compared against the established clearance rate method of estimating bulk flow through suspension-feeding organisms to evaluate PIV as a technique to estimate feeding activity. The study of ciliary pumps has relied on advances in technology, as it is difficult to access the pump without excessively disturbing the animal. We used PIV to examine feeding velocities in five species of suspension-feeding, benthic invertebrates including one ascidian (Styela clava) and four bivalves (Mytilus edulis, Crassostrea virginica, Argopecten irradians and Mercenaria mercenaria). In calibration experiments using pipes of varying diameters, we were able to resolve flow with498.5% accuracy. We extended the pipe model to study water processing in the mussel M. edulis. Both velocity and bulk flow through the mussel changed in predictable ways in relation to clearance rate (P50.05). Application of PIV to the study of suspension feeding will further our understanding of the behavior and physiology of economically- and ecologically-important organisms.

Laser-scattering techniques are utilized for the first time to visualize the aerosol droplets in an inductively coupled plasma (ICP) torch from the nebulizer tip to the site of analytical measurements. The resulting images provide key information about the spatial distribution of the aerosol introduced by direct injection and conventional sample introduction devices: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a MicroFlow PFA nebulizer with a PFA Scott-type spray chamber. Moreover, particle image velocimetry is used to study the in situ behavior of the aerosol before interaction with the plasma, while the individual surviving droplets are explored by particle tracking velocimetry. Directly introduced aerosols are highly scattered across the plasma torch as a result of their radial motion, indicating less than optimum sample consumption efficiency for the current direct injection devices. Further, the velocity distribution of the surviving droplets demonstrates the importance of the initial droplet velocities in complete desolvation of the aerosol for optimum analytical performance in ICP spectrometries. These new observations are critical in the design of the next-generation direct injection devices for lower sample consumption, higher sensitivity, lower noise levels, suppressed matrix effects, and developing smart spectrometers.

Two novel laser-based imaging techniques centered on particle image velocimetry and optical patternation are used to map and contrast the size and velocity distributions for indirect and direct pneumatic nebulizations in plasma spectrometry. The flow field of droplets is illuminated by two pulses from a thin laser sheet with a known time difference. The scattering of the laser light from droplets is captured by a charge-coupled device (CCD), providing two instantaneous images of the particles. Pointwise cross-correlation of the corresponding images yields a two-dimensional velocity map of the aerosol velocity field. For droplet size distribution studies, the solution is doped with a fluorescent dye and both laser-induced florescence (LIF) and Mie scattering images are captured simultaneously by two CCDs with the same field of view. The ratio of the LIF/Mie images provides relative droplet size information, which is then scaled by a point calibration method via a phase Doppler particle analyzer. Two major findings are realized for three nebulization systems: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a PFA microflow nebulizer with a PFA Scott-type spray chamber. First, the central region of the aerosol cone from the direct injection nebulizers and the nebulizer-spray chamber arrangement consists of fast (13 and8 m/s, respectively) and fine (10 and5 microm, respectively) droplets as compared to slow (4 m/s) and large (25 microm) droplets in the fringes. Second, the spray chamber acts as a momentum separator, rather than a droplet size selector, as it removes droplets having larger sizes or velocities. The concepts and results presented in this research may be used to develop smart-tunable nebulizers, for example, by using the measured momentum as a feedback control for adjusting the nebulizer, i.e., its operating conditions, its critical dimensions, or both.

One of the major technological difficulties in implementing digital particle image velocimetry (PIV) is associated with acquiring, processing and storing large volumes of image data form high resolution CCD camera(s). Current CCD camera technology provides both very high resolutions and high frame rates typically producing tens of megabytes of data per second. With the need for simultaneous data form two or more image sources the problems of data transmission, processing and storage become extreme. Significant increases in transfer, processing and storage can be achieved by compressing images by removing components of the image that are redundant or of low significance. This paper presents an approach to PIV image compression and methods of processing encoded data. The effect of varying levels of compression on data transfer and processing rates as well as measurements precision is considered and illustrated with results from both real and synthetic image data.

Holography is a method by which information of a 3D object space can be recorded. Used to record the position of neutrally buoyant tracers in a flow at two or more briefly separated instants it provides the means to record complex 3D velocity distributions. The magnitude of data contained in a holographic recording and the complexity of extracting flow displacement values from within a random distribution of holographically recorded seed particles makes automated analysis desirable. The analysis system described here is based on 3D correlation processing and provides an accurate and reliable means of detecting and measuring the local 3D displacements from a background of randomly positioned particles.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.