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Source‐to‐sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post‐extensional subsidence in the Jurassic‐Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source‐to‐sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source‐to‐sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta‐sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near‐source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post‐rift stage. Key Points: Provenance changed from a point source from skarns during the syn‐rift stage to multiple sources during the post‐rift stageHigher relief in the Tianshan in the Triassic was reduced during the Jurassic‐CretaceousSediment recycling took place in the Early Cretaceous [ABSTRACT FROM AUTHOR]

Inertial impactors are an important part of aerosol science where they are used to obtain particle size distributions in a wide range of practical and scientific applications. A shortcoming of these devices is that the number of bins in the resulting distribution is limited to the number of impactors in an impactor cascade. Recent work has shown that if the ratio of the nozzle-to-impactor distance (S) to the nozzle diameter (W) is very small, S/W ∼ O(0.01), the normally disk shaped particle impaction pattern becomes a ring. Under these conditions the ring diameter is proportional to the particle diameter, presenting an opportunity for developing impactors capable of sub-stage particle diameter sizing. Before such impactors may be developed, however, further information is required regarding how the diameter of the aforementioned rings vary with S/W and particle diameter. Herein, experiments are presented where ring-shaped deposition patterns are obtained for a range of particle diameters and S/W. These results are consolidated to provide a relationship between the relevant dimensionless variables: the Stokes number (dimensionless particle diameter), S/W, and dimensionless ring diameter. Computer simulations of particle trajectories under the experimental conditions are presented and are used to reveal the underlying mechanism of this effect. Finally, a discussion is presented of practical approaches for using these results to obtain high resolution particle size distributions from impactor cascades. Copyright © 2021 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Surface waves are excited by mechanical vibration of a cylindrical container having an air/water interface pinned at the rim, and the dynamics of pattern formation is analysed from both an experimental and theoretical perspective. The wave conforms to the geometry of the container and its spatial structure is described by the mode number pair (n, ) that is identified by long exposure time white light imaging. A laser light system is used to detect the surface wave frequency, which exhibits either a (i) harmonic response for low driving amplitude edge waves or (ii) sub-harmonic response for driving amplitude above the Faraday wave threshold. The first 50 resonant modes are discovered. Control of the meniscus geometry is used to great effect. Specifically, when flat, edge waves are suppressed and only Faraday waves are observed. For a concave meniscus, edge waves are observed and, at higher amplitudes, Faraday waves appear as well, leading to complicated mode mixing. Theoretical predictions for the natural frequency of surface oscillations for an inviscid liquid in a cylindrical container with a pinned contact line are made using the Rayleigh-Ritz procedure and are in excellent agreement with experimental results. [ABSTRACT FROM AUTHOR]

Detrital geochronology provides insight into a broad range of Earth Science questions. However, detrital zircon U‐Pb age distributions are inherently univariate, and thus quantitative comparison methods are limited to one‐dimension (1D) and subject to nonunique results due to overlapping age groups. We developed two‐dimensional (2D) quantitative comparison measures for bivariate kernel density estimates (KDEs) and cumulative distribution functions (CDFs). These methods are extensions of 1D quantitative comparison measures commonly used in detrital geochronology: Similarity, Likeness, and Cross‐correlation of KDEs and Kolmogorov‐Smirnov (K‐S) and Kuiper tests of CDFs. We demonstrate the efficacy of these methods by applying them to a global compilation of detrital and igneous zircon univariate U‐Pb data (n = 767,660) and bivariate U‐Pb and Hf (i.e., εHfT) data (n = 114,311) parsed geographically into eight continental landmasses demarcated by Paleozoic sutures. The 2D quantitative comparison measures behave in a similar fashion to their 1D counterparts in terms of sensitivity and consistency regardless of parameterization (e.g., kernel bandwidth and discretization interval). Results show that the detrital record reliably reflects the igneous record for both univariate U‐Pb and bivariate εHfT distributions between 4,400 and 0 Ma. In contrast, 1D and 2D quantitative comparison results differ over the narrower Ediacaran‐Cambrian time interval due to nonunique univariate zircon U‐Pb age groups; the 2D quantitative results consistently identify continental landmasses involved in the formation of Gondwana. We implemented the 2D methods in a new MATLAB‐based graphical user interface, DZstats2D, which is available as open‐source code and as standalone applications for macOS and Windows. Key Points: Quantitative comparison methods in detrital studies are extended into two dimensions and applied to a zircon U‐Pb and Hf global compilationTwo‐dimensional measures behave in a similar fashion to their one‐dimensional counterparts in terms of sensitivity and consistencyDetrital and igneous zircon records are similar for individual continents and reveal the unique Hf isotopic signature of Gondwana [ABSTRACT FROM AUTHOR]

Mechanisms controlling the long‐ and short‐term variability of the Indian Summer Monsoon (ISM) and high‐elevation environmental change have largely been examined using low‐elevation or marine records with less emphasis on high‐elevation non‐marine records. We address this using a high‐resolution, long‐term record from upper Miocene–lower Pleistocene (~9.0–2.2 Ma) fluvio‐lacustrine strata in the Zhada Basin, southwestern Tibetan Plateau. Long‐term changes include the onset of lacustrine deposition, a decrease in mean grain size, and an increase in δ18Ocarb and δ13Ccarb values at ~6.0 Ma in response to basin closure following regional extension. This was followed by a return to palustrine/fluvial deposition, an increase in mean grain size, and a decrease in δ18Ocarb and δ13Ccarb values at ~3.5 Ma in response to tectonically driven long‐term ISM weakening. Spectral analysis reveals that high‐frequency variations in the δ18Ocarb record are dominated by 100 and ~20 kyr cycles from ~6.0–2.2 Ma. Wavelet and spectral analysis of the most densely sampled interval (4.23–3.55 Ma), tuned to the record of daily insolation (21 June at 35°N) confirms and highlights 100 and 20 kyr cycles. The tuned Pliocene δ18Ocarb record is coherent with the record of Northern Hemisphere insolation at precession periods but not at obliquity or eccentricity periods. Additionally, the tuned δ18Ocarb record is anticorrelated to the insolation record, indicating that stronger Northern Hemisphere insolation correlates with a stronger ISM. These results suggest that variations in daily insolation drove late Miocene–early Pleistocene high‐frequency ISM variability and environmental changes in the high‐elevation southwestern Tibetan Plateau. Plain Language Summary: The Indian Summer Monsoon is a planetary‐scale climate system. It currently affects >1.8 billion people, and changes in the monsoon likely led to major changes in plant and animal populations ~7 million years ago. Whether the Himalayan mountains, Tibetan Plateau, or the Southern Hemisphere are the major players in controlling the strength of the monsoon remains unclear. We address this question using the first long‐term, high‐resolution isotopic and sedimentological record from the Zhada Basin on the Tibetan Plateau. Changes in oxygen isotopes in carbonate rocks track the increase or decrease in precipitation amount. The frequency of the changes in the isotopic record match the frequency of changes in Earth's orbit. Changes in the isotope record also show that when the Tibetan Plateau received more sunlight, which is determined by changes in Earth's orbit, the monsoon was more intense. These observations point to the conclusion that Earth's orbit changes the solar heating received by the plateau surface, which in turn plays a major role in the amount of precipitation on the Tibetan Plateau. Key Points: Isotope, sedimentology, and grain size data record low‐ and high‐frequency Miocene–Pleistocene environmental change on the Tibetan PlateauAll data record low‐frequency tectonic and climate changes, whereas O isotope data document high‐frequency changes at Milankovitch periodsAnticorrelation between the isotope record and Northern Hemisphere insolation suggests insolation exerts a primary control on monsoon strength [ABSTRACT FROM AUTHOR]

A method for obtaining the elasticity, surface tension, and viscosity of ultrasonically levitated gel drops is presented. The drops examined were made of agarose, a hydrogel. In contrast to previous studies where fluid properties are obtained using ultrasonic levitation of a liquid drop, herein the material studied was a gel which has a significant elasticity. The work presented herein is significant in that gels are of growing importance in biomedical applications and exhibit behaviors partially determined by their elasticities and surface tensions. Obtaining surface tension for these substances is important but challenging since measuring this quantity using the standard Wilhelmy plate or DuNuoy ring methods is not possible due to breakage of the gel. The experiments were conducted on agarose gels having elasticities ranging from 12.2 to 200.3 Pa. A method is described for obtaining elasticity, surface tension, and viscosity, and the method is experimentally demonstrated for surface tension and viscosity. For the range of elasticities explored, the measured surface tension ranged from 0.1 to 0.3 N/m, and the viscosity ranged from 0.0084 to 0.0204 Pa s. The measurements of surface tension are, to the authors' knowledge, the first obtained of a gel using ultrasonic levitation. [ABSTRACT FROM AUTHOR]

Investigates the Raman effect in aluminum (Al)-gallium (Ga)-arsenic (As) waveguides. Measurement of the spontaneous Raman scattering cross sections; Energy interaction between pump and probe pulses by modyfying the coupled propagation equations for AlGaAs waveguides; Overview of coupled equations for AlGaAs waveguides.

Experiments were carried out in an impactor, where the distance between the impactor nozzle and the impactor plate was small, much less than one nozzle diameter in separation. The aerosol deposition patterns in this impactor were investigated for aerosols in the 3–15m diameter range. Ring-shaped deposition patterns were observed where the internal diameter and thickness of the rings were a function of the particle diameter. Specifically, the inner diameter and ring thickness were correlated to the Stokes number,Stk; the ring diameter decreased withStk, and the ring thickness increased withStk. Atthe ring closed up, leaving a mostly uniform disk deposition pattern. These ring patterns do not appear to correspond to patterns previously described in the literature, and an order of magnitude analysis shows that this is an inertially dominated process. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Removing drops from an air flow can be challenging, particularly, for small drops. Herein a method for demisting is presented that employs ultrasonics to force small drops to combine. Specifically, a cylindrical ultrasonic standing wave field is established in a tube, forming pressure nodes that take the form of cylinders located within the tube and having the same axis as the tube. Droplets are driven toward these pressure nodes by the acoustic radiation force, forcing smaller drops to combine to form larger drops, which eventually fall due to gravity, thereby demisting the flow. Experiments presented herein show that, for the setup employed, this method can remove a fraction of drops that approaches 0.8 and that the improvement due to ultrasonics, compared to the case without ultrasonics, is as large as 2.8. The effect of air flow rate and power is investigated. [ABSTRACT FROM AUTHOR]

Satellite measurements of water surface temperature can benefit several environmental applications such as predictions of lake evaporation, meteorological forecasts, and predictions of lake overturning events, among others. Limitations on the temporal resolution of satellite measurements can restrict these improvements. A model of the diurnal variation in lake surface temperature could potentially increase the effective temporal resolution of satellite measurements of surface temperature, thereby enhancing the utility of these measurements in the above applications. As a step in this direction, herein a one-dimensional thermal model of a lake is used in combination with surface temperature measurements from the moderate resolution imaging spectroradiometer instrument aboard the Aqua and Terra satellites, along with ambient atmospheric conditions from local weather stations, to calculate the diurnal surface temperature variation for Lake Hartwell in South Carolina. The calculated solutions are used to obtain a functional form for the diurnal surface temperature variation of this lake, a result which has not been obtained heretofore. This functional form was obtained by averaging over several years worth of data and, therefore, represents the diurnal variation of surface temperature of the average day. Accordingly, attempts to use this averaged function to predict surface temperature in between satellite overpasses on any given day did not perform well due to day-to-day variations in cloud cover, wind speed, and other factors. It is possible that use of this averaged function combined with daily meteorological data may enable better performance. [ABSTRACT FROM PUBLISHER]

An experimental study is presented of the ability of fine meshes to remove fog drops from an airflow. Specifically, the collection efficiency (CE) was measured for fog drops passing through mesh fabrics. Meshes composed of cotton, nylon, and Teflon were investigated, and the effect of the material as well as mesh porosity was determined. Collection efficiencies ranging from 5% to 50% were obtained. The ultimate goal of this work is to employ such meshes in a parachute configuration above power plant cooling towers, so that condensed fog may be collected and returned to the cooling loop. It is shown that the drop diameters and velocities investigated here are similar to those observed above cooling towers. [ABSTRACT FROM AUTHOR]

When viscous corrections to the inviscid acoustic radiation force theory are implemented and applied to a standing wave field, the direction of the acoustic radiation force on particles varies from theory to theory. Specifically, some theories predict that the direction of the force depends on the particle diameter, while others reveal that the direction of the force is independent of particle diameter. The present study is an experimental investigation of the direction of the acoustic radiation force which suggests that particle diameter does affect the direction. Experiments were conducted in air using an ultrasonic standing wave field with a nominal frequency of 30 kHz. Smoke particles and fine water droplets having a range of diameters were flowed into the region of a standing wave field. The direction of the acoustic radiation force was determined by observing whether the particles accumulated in the nodes or the anti-nodes of the standing wave. Results show a change in the direction of the acoustic radiation force at a particle diameter of 0.3±0.1 µm, which corresponds to a particle diameter to acoustic-boundary-layer thickness ratio of 0.023±0.008 . [ABSTRACT FROM AUTHOR]

An experiment in a rectangular basin of water is used to demonstrate that a large-scale circulation will result from a zero-mean thermal forcing. The thermal force is a spatially periodic pattern of heating and cooling at the top surface, achieved with an interdigitated array of hot and cold tubes. The experimental results show a very robust, steady flow with ascending flows at each end of the tank and a single descending jet near the left wall. These results suggest that small-scale forcing in surface-driven flows may result in significant large-scale subsurface motion [ABSTRACT FROM AUTHOR]

Presented here is an experimental investigation of the effects of several surfactant monolayers on evaporation driven by natural convection in the air above a water surface. Experiments were performed in a controlled laboratory setting with tanks of heated water for the following cases: (1) a clean water surface, and for surfaces covered with monolayers of (2) oleyl alcohol, (3) stearic acid, and (4) stearyl alcohol. Evaporation rates were measured using a laser-based method, and the Sherwood and Rayleigh numbers, Sh and Ra, were computed from the data. Power law scalings of the form Sh = B·Ra m were developed for each case which yielded, essentially, m = 1/3 for all four surface conditions. The oleyl alcohol and stearic acid conditions give essentially the same value for B as for the clean surface case. For stearyl alcohol, B is smaller than for all other surface conditions; this result is attributed to the ability of the stearyl alcohol monolayer to inhibit evaporation by blocking the passage of water molecules through the monolayer: the barrier effect. The surface temperature is measured in this work enabling a separation of the effect of surfactants on evaporation due to a reduction in surface temperature from their effect on evaporation due to a true barrier effect. This has not been accomplished heretofore. © 2012 American Institute of Chemical Engineers AIChE J, 59: 303-315, 2013 [ABSTRACT FROM AUTHOR]

Mesler entrainment is the formation of large numbers of small bubbles which occurs when a drop strikes a liquid reservoir at a relatively low velocity. Existing studies of Mesler entrainment have focused almost exclusively on water as the working fluid in a nominally clean state, where even very small levels of contamination can cause significant changes in surface tension that affect the repeatability of the results. Herein water combined with the soluble surfactant Triton X-100 is used as the working fluid in an attempt to stabilize the state of the water surface. Despite this approach, nominally identical drops did not always result in the same bubble formation event. Accordingly, Mesler entrainment was quantified by its frequency of occurrence for drops having the same nominal diameter and impact velocity. This frequency of occurrence was found to be well correlated to both the Weber number and the shape of the drop on impact. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

The shapes of falling raindrops are often significantly altered by drop oscillations, complicating dual-polarization radar methods that rely on a predictable, monotonic variation of drop axis ratio α with equivolume drop diameter d. This oscillation behavior varies with d so that time-averaged shapes, which are determined by oscillation mode, sometimes deviate from the d-dependent quiescent shape. The literature identifies a predominance of particular oscillation modes at discrete d, as well as the onset of oscillations at d ≈ 1 mm; however, the specific mechanisms of this phenomenon are unknown. In the present work, measurements of drop axis ratio α were obtained from observations of drops levitated in a vertical wind tunnel. Discordance of the present data with the literature suggests a correlation between oscillation mode and fall trajectory, as well as a steady-state mechanism for the excitation of specific modes for d = 1.3–3-mm drops. [ABSTRACT FROM AUTHOR]

Presented here is an effective low-cost method for the temperature calibration of infrared cameras, for applications in the 0–100 °C range. The calibration of image gray level intensity to temperature is achieved by imaging an upwelling flow of water, the temperature of which is measured with a thermistor probe. The upwelling flow is created by a diffuser located below the water surface of a constant temperature water bath. The thermistor probe is kept immediately below the surface, and the distance from the diffuser outlet to the surface is adjusted so that the deformation of the water surface on account of the flow is small, yet the difference between the surface temperature seen by the camera and the bulk temperature measured by the thermistor is also small. The benefit of this method compared to typical calibration procedures is that, without sacrificing the quality of the calibration, relatively expensive commercial blackbodies are replaced by water as the radiative source ([variant_greek_epsilon]≈0.98 for the wavelengths considered here). A heat transfer analysis is provided, which improves the accuracy of the calibration method and also provides the user with guidance to further increases in accuracy of the method. [ABSTRACT FROM AUTHOR]

Recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre- and post-mid-Miocene uplift of the southern Tibetan Plateau. We examined this issue by analysis of well-preserved fossil mollusks and plant remains from the Thada Basin in southwestern Tibet, which ranges in age from ~ 9.2 to <1 Ma. Based on δ18Occ values from shell aragonite, we estimate that oxygen isotope ratios of Miocene - ccPleistocene paleo-surface water (δ18Opsw) in Thada Basin ranged from -24.5 to -2.2%̥ (VSMOW). The lowest of these calculated values are lower than δ18Osw values [-17.9 to -11.9%̥ (VSMOW)] of modern water in the basin. The extremely low values from fluvial mollusks and evaporatively elevated values from lacustrine mollusks, show that the peaks surrounding the Thada Basin were at elevations at least as high as, and possibly up to 1.5 km higher than today, and that conditions have been arid since at least 9 Ma. A decrease in elevation since the Miocene is not specifically predicted by any existing mechanical models for the development of the Tibetan Plateau. Paleoenvironmental modeling and physical evidence shows that the climate in Zhada Basin was cold and arid, indistinguishable from modern. The δ13Cpm values of well-preserved vascular plant material increase from -23.4 to -26.8 permil at the base of the Zhada Formation to as high as -8.4 pennil above 250 to 300 m. This shift denotes the expansion of C4 biomass in this high, arid watershed at ~ 7 Ma, and thus corresponds to the C3 - C4 transition observed in Neogene deposits of the northern Indian sub-continent. [ABSTRACT FROM AUTHOR]

The study of heat, mass, and momentum transport across an air/water interface is an aspect of fluid mechanics where the presence of surfactant monolayers can play a significant role. Experimental studies of air/water transport typically require a method for cleaning the air/water interface so that it is free from any contaminating surfactant monolayer. This may be for the sake of running an experiment under clean surface conditions, or to clean the surface prior to deposition of a known surfactant. Herein a method is described for maintaining a clean air/water interface during conditions of finite air flow over the water surface. The unique aspect of this method is its ability to maintain clean surfaces while experiments are conducted. [ABSTRACT FROM AUTHOR]

Simulations are presented of particle deposition beneath shallow, standing capillary waves. The standing waves occur on the surface of a thin liquid film. The film is sufficiently thin such that the wave motion affects the trajectories of the settling particles. The simulations reveal that particles of all size tend to accumulate at specific nodal regions beneath the waves, and that there is an optimal particle diameter for which this accumulation is maximized. The diameter at which this maximal accumulation occurs is a function of the wave field, the fluid thickness, the particle density, and the fluid properties. The accumulation is quantified by the standard deviation of the final location of the settling particles and plots are presented of this standard deviation as a function of particle diameter. Previous experimental work has shown that this method can be implemented by generating standing Faraday waves on the surface of thin films of a liquid/particulate mixture. The present work shows how these films can be tailored via the particle diameter, liquid thickness, and wavelength. Some aspects relevant to the practical implementation of the method are also discussed. [ABSTRACT FROM AUTHOR]

Flow visualizations are presented of the wakes behind water droplets traveling at terminal velocity in a vertically directed airflow. These images, obtained by levitating water drops in a vertical wind tunnel, reveal vortices in the wake behind the drop. It has long been postulated that such wakes trigger transverse oscillations in raindrops. Although such transverse oscillations were not observed here, the images do show a canting of the oblate drop which appears to be connected to the vortex shedding process. These are the first images of simulated raindrops that visualize both the shape of the drop and the vortices in the wake immediately behind the drop. [ABSTRACT FROM AUTHOR]

Metabolic syndrome, defined as a cluster of obesity, hypertension, dyslipidemia, and insulin resistance/glucose intolerance, has been identified as a major risk factor for coronary heart disease in women. Nurses should increase their awareness of metabolic syndrome to help identify and treat the current estimated 47 million US residents who have metabolic syndrome. [ABSTRACT FROM AUTHOR]

Faraday waves were used to create a patterned particulate film on the surface of a glass substrate. The process involves deposition of a thin liquid film on the substrate, where the liquid is comprised of water and a concentrated suspension of particles. Faraday waves were created on the surface of the liquid film by subjecting the substrate and film to a vertical oscillation. Because the films are thin, the standing waves create velocity fluctuations that are not negligible near the substrate surface. As the particles in the liquid settled to the bottom, the flow field caused by the waves caused preferential particle deposition organized in a pattern determined by the Faraday wave field. Subsequent evaporation of the liquid film left a particulate film on the solid substrate that retained the pattern of the original wave field. We refer to these particulate films as Faraday films. The length scale of the patterns in these films was on the order of millimeters in the experiments described here. Use of higher frequency oscillations could permit the formation of Faraday films having smaller spatial scales. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The measurement of water drops using direct optical imaging involves a tradeoff between the camera depth of field and the accuracy of the measured droplet size. A large depth of field increases the length of that portion of the optical axis that is in focus. However, since drops closer to the camera appear larger than those farther away, increasing the depth of field also increases errors in the measured drop size unless a priori knowledge exists concerning the location of the drop along the optical axis. Herein a method is presented for ascertaining drop location using a single camera. The method uses a characteristic of the droplet image which is observed when droplets are illuminated from behind. Once the location of the droplet is obtained, the appropriate magnification ratio is applied, permitting an accurate droplet size measurement. This method has been tested on glass spheres of various size. The relevance of this work to precipitation science is discussed. [ABSTRACT FROM AUTHOR]

Experiments conducted in a modified Langmuir trough are described. Measurements of surface tension were obtained using a Wilhelmy plate, while infrared (IR) images of the water surface adjacent to the Wilhelmy plate were simultaneously recorded. A contaminating surfactant film was allowed to form on the surface while the experiments were being conducted. The data reveal a substantial change in the IR imagery due to the film in all cases. The difference between the appearance of the clean and surfactant-covered regions of the surface is clear and distinct. For some of these experiments the change in the IR imagery is accompanied by no observable change in surface tension. This, along with several other aspects of this work, suggest that IR imagery may be a superior tool, compared to traditional surface tension measurements, for ascertaining the cleanliness of a liquid substrate. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Turbulence measurements are reported for the flow beneath an air/water interface undergoing evaporative convection. Measurements were obtained using a two component laser Doppler velocimeter system. Two hydrodynamic boundary conditions were considered for the free surface: a shear free surface, which is the case when surfactants are absent, and a constant elasticity surface, created by depositing a monolayer of oleyl alcohol. The shear free boundary condition case results in significantly higher levels of near surface turbulence than the constant elasticity case. This difference between the two cases decreases with distance from the free surface. Profiles of the turbulent fluctuations were obtained for the horizontal and vertical velocity components and are compared with the somewhat analogous case of a heated solid wall. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Measurements of the surface temperature field are presented for a water surface undergoing evaporation. These temperature fields were measured using an infrared camera for a range of heat fluxes q[sup ″]=30-500 W/m[sup 2]. Experiments were conducted for water surfaces with and without a surfactant monolayer. A statistical analysis of the data is presented which shows the effect of heat flux and surfactants on the root mean square and skewness of the field. The data reveals a linear increase in the rms with increasing heat flux, which is similar for clean and surfactant conditions. In contrast, the skewness is markedly different for the clean and surfactant-covered cases. For clean surface conditions, the skewness attains large, negative values, becoming increasingly negative as q[sup ″] increases. When the surface is covered with a surfactant monolayer, however, the skewness exhibits small, negative values which approach zero as the heat flux increases. This behavior is reflected in the pdf which is clearly asymmetric in the clean case and virtually symmetric in the surfactant case. A physical mechanism is presented to explain these results. Temporal power spectra are presented which reveal the role of heat flux and surfactants on the temporal evolution of the surface temperature field. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The expected value Eχ≡E(χ,θ=θ0) of the dissipation rate χ of a passive scalar θ conditioned on the scalar value θ=θ0 has been measured in three varieties of turbulent shear flows: heated wakes, dyed liquid jets, and the atmospheric surface layer. The quantity Eχ depends fairly strongly on θ0 and on the flow. For the wake, Eχ exhibits two peaks—one on the low-temperature end and the other on the high-temperature end—and the peaks are separated by an approximately flat region. The relative strength of the two peaks varies with the spatial position. Measured in the turbulent part alone, Eχ tends to have only one peak on the hot side, but is still nonuniform. The related quantity, Eθ‘≡(∇2θ,θ=θ0), which is the expected value of the Laplacian of the scalar conditioned on the scalar concentration, has also been measured on the wake centerline and shows a simpler dependence on θ0 than Eχ. For jets, Eχ has a single peak on the high-concentration side. This feature appears to be essentially independent of the use of Taylor’s hypothesis and on whether or not the dissipation rate χ is approximated by only one of its components. It is, however, sensitive to the resolution of measurement. For the temperature fluctuation in the atmospheric boundary layer, the peak in Eχ on the cold side is far weaker than that on the hot side. From this combination of experiments, it is argued that the different shapes of Eχ in different flows are related to differences in the nature of the scalar pdf itself and, for the high-Schmidt-number dyes in water flows, on whether or not the finest scales of the scalar are resolved. [ABSTRACT FROM AUTHOR]

Respirable coal mine dust represents a serious health hazard for miners. Monitoring methods are needed that enable fractionation of dust into its primary components, and that do so in real time. Near the production face, a simple capability to monitor the coal versus mineral dust fractions would be highly valuable for tracking changes in dust sources—and supporting timely responses in terms of dust controls or other interventions to reduce exposures. In this work, the premise of dust monitoring with polarized light microscopy was explored. Using images of coal and representative mineral particles (kaolinite, crystalline silica, and limestone rock dust), a model was built to exploit birefringence of the mineral particles and effectively separate them from the coal. The model showed >95% accuracy on a test dataset with known particles. For composite samples containing both coal and minerals, the model also showed a very good agreement with results from the scanning electron microscopy classification, which was used as a reference method. Results could further the concept of a "cell phone microscope" type monitor for semi-continuous measurements in coal mines. [ABSTRACT FROM AUTHOR]