Droplets Of Various Sizes Research Articles

Sensing area-variable electrode for wide-range droplet size detection

Microfluidic droplets of various sizes are applied in a broad spectrum of biological and chemical processes and require high uniformity for reliable outcomes. Although various droplet detection methods have been employed to achieve monodisperse droplets, the capacitive method stands out for its ease of use and rapid response, enabling real-time feedback control. However, this method has limitations in terms of significantly altering the droplet size, resulting in increased continuous phase consumption and the need for microchannel and sensing component replacements. In response, we present the Sensing Area-Variable Electrode (SAVE), which is designed to produce monodisperse droplets across a broad size range without excessive continuous phase consumption and without requiring the frequent replacement of sensing components. The experimental results demonstrate that using the SAVE electrode enables the generation of monodisperse 0.2, 0.4, and 1.0 nL droplets by simply replacing the disposable microchannel while reusing the sensing components. Moreover, the adaptable number of droplets achieved by microchannel replacement allows the SAVE electrode to be effectively utilized in droplet digital polymerase chain reaction (ddPCR) assays, providing a balance between sensitivity and throughput. Consequently, the SAVE electrode addresses the limitations of the capacitive detection method and offers a versatile solution for various droplet-based biological and chemical processes, including ddPCR assays.

Investigation of Automotive LiDAR Vision in Rain from Material and Optical Perspectives.

With the emergence of autonomous functions in road vehicles, there has been increased use of Advanced Driver Assistance Systems comprising various sensors to perform automated tasks. Light Detection and Ranging (LiDAR) is one of the most important types of optical sensor, detecting the positions of obstacles by representing them as clusters of points in three-dimensional space. LiDAR performance degrades significantly when a vehicle is driving in the rain as raindrops adhere to the outer surface of the sensor assembly. Performance degradation behaviors include missing points and reduced reflectivity of the points. It was found that the extent of degradation is highly dependent on the interface material properties. This subsequently affects the shapes of the adherent droplets, causing different perturbations to the optical rays. A fundamental investigation is performed on the protective polycarbonate cover of a LiDAR assembly coated with four classes of material-hydrophilic, almost-hydrophobic, hydrophobic, and superhydrophobic. Water droplets are controllably dispensed onto the cover to quantify the signal alteration due to the different droplets of various sizes and shapes. To further understand the effects of droplet motion on LiDAR signals, sliding droplet conditions are simulated using numerical analysis. The results are validated with physical optical tests, using a 905 nm laser source and receiver to mimic the LiDAR detection mechanism. Comprehensive explanations of LiDAR performance degradation in rain are presented from both material and optical perspectives. These can aid component selection and the development of signal-enhancing strategies for the integration of LiDARs into vehicle designs to minimize the impact of rain.

Real-Time Droplet Detection for Agricultural Spraying Systems: A Deep Learning Approach

Nozzles are ubiquitous in agriculture: they are used to spray and apply nutrients and pesticides to crops. The properties of droplets sprayed from nozzles are vital factors that determine the effectiveness of the spray. Droplet size and other characteristics affect spray retention and drift, which indicates how much of the spray adheres to the crop and how much becomes chemical runoff that pollutes the environment. There is a critical need to measure these droplet properties to improve the performance of crop spraying systems. This paper establishes a deep learning methodology to detect droplets moving across a camera frame to measure their size. This framework is compatible with embedded systems that have limited onboard resources and can operate in real time. The method leverages a combination of techniques including resizing, normalization, pruning, detection head, unified feature map extraction via a feature pyramid network, non-maximum suppression, and optimization-based training. The approach is designed with the capability of detecting droplets of various sizes, shapes, and orientations. The experimental results demonstrate that the model designed in this study, coupled with the right combination of dataset and augmentation, achieved a 97% precision and 96.8% recall in droplet detection. The proposed methodology outperformed previous models, marking a significant advancement in droplet detection for precision agriculture applications.

Численное исследование полидисперсных двухфазных течений в осесимметричном сопле Лаваля с учетом силы Магнуса, действующей на вращающиеся капли

The available papers on two-phase flows in de Laval nozzles are focused on the effect of various initial conditions, models of coagulation, fragmentation, and rotation of droplets on their local and integral characteristics. Some papers note that due to the difference in the velocities of the gas and droplets along the nozzle axis, the Magnus force acts on the rotating droplets perpendicular to the specified difference and deflects the trajectories of the droplets toward the nozzle wall. In an earlier paper, the authors proposed a mathematical model of a two-phase flow in an axisymmetric de Laval nozzle that accounts for the Magnus force on the basis of the kinetic equation. The present article is devoted to a numerical study of a polydisperse two-phase flow in a de Laval nozzle with account for the coagulation, fragmentation, and rotation of droplets and the Magnus force. This study is based on the “monodisperse” model of fragments developed by I.M. Vasenin and A.A. Shreiber, the method of labeled drops (the Lagrange method), and the finite-difference schemes of second order accuracy. The calculations are carried out for a test nozzle configuration with condensate formation on the nozzle wall both with and without the Magnus force accounted. The calculated results show that the Magnus force has different impacts on the trajectories of droplets of various sizes. It should be noted that the limiting trajectories of the droplets approach the nozzle wall due to the Magnus force, resulting in the earlier dropout on the wall. Therefore, when designing the divergent section of the nozzle, it is necessary to consider the revealed approach of the location of the dropout, which is associated with the Magnus force, to the nozzle throat.

FORMS OF OIL PRODUCTS IN THE AQUATIC ENVIRONMENT

In the aquatic environment petroleum products (PP) are in different migration forms: in the homogeneous phase in the form of droplets of various sizes and films with thickness from 1 to 200 microns; in the emulsified form; in the form of molecular soluti

Using Fume Hood to Reduce Nurses' Exposure to Particulate Matters Dispersed Into the Air During Pill Crushing.

Pill crushing is a common practice in patient care settings. Crushing pills can disperse particulate matter (PM) into indoor air. The PM is a widespread air pollutant composed of microscopic particles and droplets of various sizes and may carry active and/or inactive ingredients nurses can inhale. This study aimed to quantify PM sizes and concentration in indoor air when pills are crushed and examine the role of a fume hood in reducing particulate pollution. Two scenarios (with and without a fume hood) representing nurses' pill-crushing behaviors were set up in a positive-pressure cleanroom. Two acetaminophen tablets (325 mg/tablet) were crushed into powder and mixed with unsweetened applesauce. The PM sizes and concentrations were measured before and during crushing. Different sizes of PM, including inhalable, respirable, and thoracic particles, were emitted during medication crushing. The total count of all particle sizes and mass concentrations of particles were significantly lower during crushing when a fume hood was used (p = .00). Pill crushing increases PM and should be considered a workplace safety health hazard for nurses. Healthcare professionals should work under a fume hood when crushing pills and wear proper protective equipment. The findings of significant particulate pollution related to pill crushing suggest that further research is warranted.

Microstructure evolution and mechanical performance of tetrahedral amorphous carbon coatings with dense droplets during annealing

Tetrahedral amorphous carbon (ta-C) coatings with approximately 50% sp3C were deposited onto cemented carbide alloy YG6 and Si wafers via direct vacuum cathode arc (DVCA) evaporation at different substrates temperatures. Coated specimens were annealed in a 5 Pa argon atmosphere. The micromorphology and chemical bonding structure of these coatings with different treatments were characterized using field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The mechanical performance was tested using a nanoindenter and film stress instrument. The obtained ta-C coatings contained dense droplets of various sizes (“abnormal particles” (An-Ps)). The densities of the An-Ps were controlled by the graphite cathode target arc rather than the substrate temperature, and their ID/IG ratios were close to their counterpart coating matrix. Increasing the substrate temperature was beneficial for increasing the sp2C fraction and the number of aromatic ring sp2C sites. Growth, coalescence, and leveling-diffusion of aggregates in the coating matrix and An-Ps occurred during annealing, which was related to the existing state of the sp2C sites, including the olefinic chain and aromatic ring. The residual stress variation with annealing temperature also depended on the sp2C state. The residual stress in the coating increased during annealing when the number of aromatic ring sp2C sites exceeded a certain critical value.

Self-cleaning and anti-fogging hierarchical structure arrays inspired by termite wing

Wings of the Formosan subterranean termite (Coptotermes formosanus Shiraki) covered with micrometer-scale hairs and nanometer-scale wax patches, allow them to greatly reduce adhesions to water droplets of various sizes. Inspired by the anti-wetting structures, we develop a colloidal lithography-based strategy integrated with a scalable self-assembly approach to engineer hierarchical conical structure arrays. The resulting structure arrays provided a water contact angle as high as 175.3° and a low contact angle hysteresis of 2.7° after surface modification. Importantly, the resulting superhydrophobic structures even feature distinguished self-cleaning and anti-fogging capabilities. The dependence of structure configuration on the anti-wetting functionalities is also investigated in this research.

Simplified Interfacial Area Modeling in Polydisperse Two-Phase Flows under Explosion Situations

The aim of the present work is to account for polydisperse effects in a two-phase flow with a simple and fast method. Polydisperse two-phase flows arise in numerous applications. Fire sprinkler systems are relevant examples as they release clouds of polydisperse droplets. Another relevant example is the polydisperse two-phase flow created by the detonation of an explosive charge surrounded by a liquid layer. In such a situation, material interfaces are initially present and the created two-phase flow consists of a carrier gas phase and a liquid phase involving many droplets of various sizes. Spherical particles or droplets are usually assumed in two-phase flow computations. When dealing with explosion situations involving both dense and dilute flow regimes, multiple particle diameters can be addressed but at the price of introducing as many additional equations that describe mass, momentum and energy balance of the various particle classes. Consequently, the computation time needed to address numerical resolution increases tremendously. Under explosion situations involving many particle diameters, the method becomes intractable and is usually reduced to a single diameter, which is often insufficient. A simplified approach is developed in the present work to account for a substantial number of particles of different sizes with few extra computational cost. The approach is said to be simplified as a single velocity and a single temperature are considered for all the spherical particles, regardless of their diameters. This type of modeling seems apt for the target explosion situations. The focus is placed on the interfacial area, which is the main parameter involved in the coupling of the two phases. In the present work, Gamma-like continuous probability distributions are considered to address the various sizes of particles. The effects of the size distribution are only summarized in the specific interfacial area, yielding consequently few code modifications while taking into account the polydisperse aspect of the two-phase flow.

VISUALIZATION RESEARCH OF DROPLET FREEZING ON AN INCLINED TITANIUM SURFACE

Freezing of droplets on inclined cold surfaces was investigated through their visualization. A DSA100 Droplet Surface Analyzer was employed to study the effects of surface tilt angle and temperature on the phase transition time of droplets of various sizes. The post-freezing contact diameter and contact angle between the droplets and the titanium surface were measured and analyzed. From these experimental studies and the related analysis it appears that the freezing time of droplets on cold surfaces at different tilt angles (15°, 30°, 45°, 60°, 75°, and 90°) is the longest when the bottom plate is tilted at 45°. As the tilted surface temperature is reduced, the droplet shape as it froze hardly changes with increasing tilt angle, and at the same time the freezing time of the droplets at each inclination angle is further reduced with decreasing bottom plate temperature. The experiments show that the deformation of a freezing 20-μL droplet on an inclined cold surface is more pronounced than that of a 1-μL droplet. The phase transition time of a large-volume droplet also decreases as the cold plate inclination increases. Thermodynamic equations are also employed to explain the longest droplet phase transition time which occurs at an inclination of 45°.

Numerical investigation of air cushioning in the impact of micro-droplet under electrostatic fields

Air cushioning widely occurs when a droplet impacts onto a solid or fluid surface at low velocity, which is mediated by the lubrication pressure of a thin air layer. Such air cushioning phenomena for micro-sized droplets bear important implications for precision coating and inkjet printing. In this study, we investigate numerically the air cushioning in the micro-sized droplets of various sizes impacting on a solid surface based on the volume of fluid method as implemented in the OpenFOAM framework. We find that the critical impact speed for bouncing on the air cushion increases as the droplet radius decreases, while the Weber number remains in a narrow range from 1 to 4. The scaling law of the critical impact speed for bouncing is derived by balancing the lubrication pressure of the air cushion with the capillary pressure and droplet inertia. The impact mode transforms from bouncing to wetting with an electric field. A group of phase diagrams of the electric Bond number vs the Weber number is presented for various droplet sizes. The diagrams are consistent with the scaling law of the critical electric field for the wetting-without-bubble mode. The findings provide insights for applications based on micro-droplet deposition, such as inkjet/electrohydrodynamic printing and spray coating, to avoid the adverse effect of air cushioning or air entrapment.

Entirely soft valve leveraging snap-through instability for passive flow control

The softness and flexibility of soft robots would be greatly enhanced with more soft parts in their makeup. This paper presents an entirely soft valve that leverages the snap-through instability of an elastomeric dome for flow control. The geometric instability enables the dome to snap upward or downward, depending on the pneumatic pressure on the surface. The dome can be configured to be bistable, pseudo-biostable, or monostable in its response to the actuation pressure. As the valve changes states, the dome alternately closes and opens a top and bottom hemispherical microchannel sitting above and below the dome, exhibiting the function of a switch for flow via the channels. When used in a microfluidic droplet system, the valve acts as a pneumatic switch to control droplet formation. Droplets of various sizes are continually created by adjusting the opening time and control pressure of the valve. The soft valve can also be applied as a low-pass filter to control the actuation of a soft pneumatic actuator. When the supply pressure exceeds the critical snap-upward pressure of the valve, the air built up in the bottom chamber to induce the snapping is vented out, relieving system pressure and keeping it within safe limits. The proposed soft valve is a viable alternative to hard commercial valves that could be useful in developing totally soft robotics or soft automation systems.

Airborne spread of SARS-CoV-2 – a commentary by the Division of Internal Medicine, University Medical Centre Ljubljana

Slovenia is one of the countries that have been most affected by the autumn/winter 2020/21 wave of the COVID-19 pandemic regarding the incidence and excess mortality among the general population as well as regarding the incidence among health care workers and nursing personnel. The World Health Organization has underestimated the importance of the airborne spread of SARS-CoV-2 and the recommended safety measures have not been entirely sufficient. When people breathe, talk, sing, cough, or sneeze, they emit respiratory droplets of various sizes, most of which are always smaller than 1 μm. Respiratory droplets smaller than 5 μm stay airborne in indoor spaces for a long time and travel over distances much longer than 2 m. Thus, an infected person in an indoor environment creates an infectious aerosol that may infect other people without close interpersonal contact. This short review presents the mathematical model and internet application by authors from the Massachusetts Institute of Technology for calculating the safe time before probable airborne infection occurs in indoor spaces. The importance of ventilation, air filtration, air humidity, and air disinfection by ultraviolet light is briefly discussed. The principles of preventing the airborne spread of SARS-CoV-2 are summarized.

Droplet Degeneration of Hippocampal and Cortical Neurons Signifies the Beginning of Neuritic Plaque Formation.

Neuritic plaques contain neural and microglial elements, and amyloid-β protein (Aβ), but their pathogenesis remains unknown. Elucidate neuritic plaque pathogenesis. Histochemical visualization of hyperphosphorylated-tau positive (p-tau+) structures, microglia, Aβ, and iron. Disintegration of large projection neurons in human hippocampus and neocortex presents as droplet degeneration: pretangle neurons break up into spheres of numerous p-tau+ droplets of various sizes, which marks the beginning of neuritic plaques. These droplet spheres develop in the absence of colocalized Aβ deposits but once formed become encased in diffuse Aβ with great specificity. In contrast, neurofibrillary tangles often do not colocalize with Aβ. Double-labelling for p-tau and microglia showed a lack of microglial activation or phagocytosis of p-tau+ degeneration droplets but revealed massive upregulation of ferritin in microglia suggesting presence of high levels of free iron. Perl's Prussian blue produced positive staining of microglia, droplet spheres, and Aβ plaque cores supporting the suggestion that droplet degeneration of pretangle neurons in the hippocampus and cortex represents ferroptosis, which is accompanied by the release of neuronal iron extracellularly. Age-related iron accumulation and ferroptosis in the CNS likely trigger at least two endogenous mechanisms of neuroprotective iron sequestration and chelation, microglial ferritin expression and Aβ deposition, respectively, both contributing to the formation of neuritic plaques. Since neurofibrillary tangles and Aβ deposits colocalize infrequently, tangle formation likely does not involve release of neuronal iron extracellularly. In human brain, targeted deposition of Aβ occurs specifically in response to ongoing ferroptotic droplet degeneration thereby producing neuritic plaques.

New measurement method for in-field measurements of liquid phase drift from cooling towers

This contribution introduces a newly proposed thermal based method for measurements of drift for in-field applications on real cooling towers up to an eliminator efficiency of approximately 0.0001% of circulating water flow. This method should thus become the main alternative to the methods used nowadays. The main advantage of this newly proposed measurement procedure should be its easy preparation and implementation and quick analysis of measurement results. The article summarizes the development of an innovative probe, and why this new probe and the entire method is needed for the industry. The design of this new probe consists of two main directions of development pathways: the electronic part and the aerodynamic part. The first one lies in the development of a sensor (and the accompanying electronics) and sums up the theoretical principle of the method (the calculation of droplet sizes scatter based on statistics, and the calculation of power needed for the sensor). The aerodynamics part derives from the desired efficiency and accuracy of the measurement and is based on precedent modelling and calculations of flow, containing droplets of various sizes through various uniquely shaped channels. The contribution also demonstrates an experiment made thus far, showing quantity measured and the drift evaluation process.

Detection of Air Bubbles and Liquid Droplet in a Dielectric Tube by Thermo-Elastic Optical Indicator Microscopy

A new method based on microwave near-field imaging for the detection of water droplets and air bubbles in a dielectric tube is presented. The present method is based on the optical visualization of the microwave near-field distribution excited around a dielectric tube containing water droplets and air bubbles. In this study, the microwave near-field distribution of a dielectric tube containing air bubbles and water droplets of various sizes was visualized analyzed through the thermo-elastic optical indicator microscope. From the experimental results, it was shown that the present method can measure size and distribution of millimeter-scale bubbles and water droplets in an optically opaque dielectric tube (diameter: 1.0 mm) in a non-contact, non-invasive, and non-destructive manner.

Development of FBG Humidity Sensor via Controlled Annealing Temperature of Additive Enhanced ZnO Nanostructure Coating

Hygroscopic materials are often explored and utilized as a sensing element in various devices for many different industries. Optical based sensors operate in conjunction with materials that are reactive to the parametric changes in the environment. Modified synthesis process allows formation of unique and novel nanostructures that can potentially be adapted as a sensor. This study focuses on characterizing hygroscopic behavior and exploring the sensing integration of additive enhanced zinc oxide coating for application in FBG as humidity sensor. ZnO-HMT was observed under a microscope within varied relative humidity levels. All samples of ZnO-HMT annealed at different temperatures showed water adsorption with water droplets of various sizes (∼50 µm). Hygroscopic characterization via technique adopted from ASTM- reveals that sample annealed with 140 °C showed best water adsorption and release. The sample annealed at 140 °C was then coated on to a uniform FBG and tested within sealed chamber with varying humidity range between 40 and 80 RH%. The optical spectrum was combined, and wavelength shifts has been analyzed. The sensitivity of the FBG sensor achieved up to 0.0008 nm/% within range of 40 – 80 % humidity with > 87 % linearity. The development of the low temperature modified ZnO nanostructure coated on the FBG as a humidity sensor was successful. The nanostructure can have potential impact in pharmaceutical and power storage industries due to its simplicity in synthesis which brings about lower manufacturing costs of materials for optical sensors.

Computational Fluid Dynamics Optimization of an Extraoral Vacuum Aerosol Cup for Airborne Disease Control in Dental Offices

Droplet and aerosol transmission of COVID-19 are the most important concerns in dental clinics, due to the generation of large amounts of infected aerosol and droplets mixed with patient’s saliva during the procedures. The current approach to prevent airborne disease transmission is an extraoral aerosol suction unit: a stand-alone vacuum module with a segmented arm and cup. Despite the need for disease control in dental offices, these units are rarely seen due to the loud noise produced by vacuum, bulky size, and high cost. This paper describes the aerodynamic design optimization of an affordable, 3D printable, Extraoral Vacuum Aerosol Cup (EVAC) that can be directly connected to existing standard 7/16″ central vacuum high-volume evacuator (HVE) valves used for intraoral saliva absorption in a dental office. These HVEs are typically unsuitable for extraoral suction due to their low vacuum force. However, they can be used for extraoral suction, if the cup attachment is aerodynamically optimized for maximum suction efficiency. Fifteen different designs of EVAC are proposed and their suction processes were simulated with computational fluid dynamics. Droplets of various sizes are released to mimic the droplets produced during dental operation. The suction performances of EVACs with different sizes and shapes were compared to find out the designs with optimal performance. Prototypes of the optimized EVAC are 3D printed and tested at a dental office. Development and manufacturing of such a device will largely reduce the COVID-19 infection risk, thus improving the safety protection for both patients and doctors at dental offices.Graphic abstract

Physiology to Disease Transmission of Respiratory Tract Infection: A Narrative Review.

In the current scenario of the COVID 19 pandemic, the protective reflexes, namely sneeze and cough, have received great importance. However, it is not in terms of protection but in terms of the spread of infection. The present review tries to bring out the correlation between the physiology of sneeze and cough, taking into consideration the various receptors that initiate the two reflexes, then correlating it with the formation of expelled droplets and the significance of various aspects of droplets that lead to the spread of infection. For the compilation of the present review, we searched the terms "Physiology of cough", "Physiology of sneeze", "droplets", "aerosols" and "Aerosols in COVID 19". The above-mentioned terms were extensively searched on PubMed, Google Scholar, and google search engine. After reviewing the various available material, the most significant research has been considered for this review. Through this review, we conclude that there are various factors responsible for the initiation of sneeze and cough, but in the case of infection, it is mainly the inflammatory reaction that directly stimulates the receptors to produce the reflex outburst air. As the flow of air during expiration is turbulent, it causes damage to the Epithelial Lining Fluid present in the respiratory conduit. In addition, it gets admixed with the saliva in the oropharynx and oral cavity and mucus in the nose to form droplets of various sizes. Large droplets settle close and are responsible for droplet and fomite transmission, but the smaller droplets remain suspended in the air and travel farther distances to cause airborne transmission. The spread of droplet cloud in sneezing may range to 6m or more as compared to cough; hence the concept of 1m to 2m of social distancing does not hold reliable if the patient is sneezing.

Wearable RF Near-Field Cough Monitoring by Frequency-Time Deep Learning.

Coughing is a common symptom for many respiratory disorders, and can spread droplets of various sizes containing bacterial and viral pathogens. Mild coughs are usually overlooked in the early stage, not only because they are barely noticeable by the person and the people around, but also because the present recording method is not comfortable, private, or reliable for long-term monitoring. In this paper, a wearable radio-frequency (RF) sensor is presented to recognize the mild cough signal directly from the local trachea vibration characteristics, and can isolate interferences from nearby people. The sensor operates at the ultra-high-frequency band, and can couple the RF energy to the upper respiratory track by the near field of the sensing antenna. The retrieved tissue vibration caused by the cough airflow burst can then be analyzed by a convolutional neural network trained on the frequency-time spectra. The sensing antenna design is analyzed for performance improvement. During the human study of 5 participants over 100 minutes of prescribed routines, the overall recognition ratio is above 90% and the false positive ratio during other routines is below 2.09%.