Deep Pool Research Articles

Atomization mechanisms of a wall-impinging jet in a shallow pool

Atomization of a liquid jet in an immiscible liquid–liquid system is essential for maintaining safety in the nuclear industry. The Japan Atomic Energy Agency has developed a method to evaluate the behavior of molten fuel entering a shallow coolant pool using numerical and experimental simulations in an immiscible liquid–liquid system, focusing on hydrodynamic interaction between the fuel and pool. However, the atomization behavior associated with the spreading of the wall-impinging liquid jet immediately after entering a shallow pool in the system is quite different from jet-breakup regimes in a deep pool, and there are a few reports. Such atomization behavior can change subsequences in severe accidents in the nuclear industry, and the investigation of the atomization behavior of the wall-impinging liquid jet is significant. Herein, we investigate the atomization behavior of a wall-impinging liquid jet in terms of droplet formation and its flow field using numerical simulation and a dispersed-phase tracking method. The results show that the atomization behavior comprises droplet formation with three patterns. We obtain droplet properties immediately after droplet formation and develop theoretical boundaries enclosing two regions for droplet formation using dimensionless numbers. We characterize the patterns by comparing them with the theoretical regions and elucidate the droplet formation mechanisms of each source. Moreover, we establish the relationship between droplet formation as the local behavior and atomization as the whole behavior of the jet. Thus, this paper clarifies the atomization mechanisms in the liquid film flow of the wall-impinging liquid jet in a shallow pool.

USING MODERN INNOVATIVE METHODS AND TECHNOLOGIES IN TEACHING SWIMMING TO CHILDREN OF PRESCHOOL AGE

In the last decade, many comprehensive programs for physical education of children in preschool institutions have been approved in Ukraine, but they do not take into account the great potential of modern innovative methods and technologies. Therefore, their research opens up new opportunities for practical improvement of the process of teaching preschoolers to swim. The purpose of the article is to outline modern innovative methods and technologies for teaching swimming to preschool children, which can be gradually introduced into the process of physical education in preschool educational institutions of Ukraine. During the study of the problem, the authors used the methods of analysis of scientific sources, specification, comparison, and pedagogical observation. According to the results of the research, taking into account the personnel and material and technical capabilities of preschool educational institutions, it is recommended to introduce swimming lessons using general developmental and dance music-rhythmic exercises from the arsenal of artistic gymnastics, synchronized swimming, aquastep. The authors draw attention to swimming lessons with elements of aquaaerobics, hydroaerobics, hydroplastics, funk aerobics, children's yoga in a playful form, as well as classes in applied swimming. The article points to the experience of studying the possibility of multi-phase swimming training in deep water conditions. Music-rhythmic exercises in water have already partially entered the practice of teaching children, but all their possibilities are not only not used, but even not thoroughly studied. With preschoolers who have already mastered the basic swimming skills, figure-swimming lessons can be held, where complexes of choreographic elements are performed using gymnastic and acrobatic combinations. Applied swimming lessons are designed to form skills in children that allow them to perform various actions in water in non-standard situations of everyday life. Children's yoga in the water helps to form a correct posture, strengthen muscular corset, promotes concentration of attention, coordination of breathing and development of all physical qualities, especially flexibility and strength. Innovative methods and technologies of teaching older preschoolers to swim can be used in lessons held in the conditions of a deep swimming pool. On the lessons, not only standard, but also modular equipment should be used. In the process of introducing innovative technologies into the process of teaching swimming to children of preschool age, it is necessary to adhere to such technological criteria as scientific, systematic, structured, procedural, and efficient.

Experimental investigation on debris bed formation from metallic melt coolant interactions

Motivated by risk quantification of severe core meltdown accidents which may occur light water reactors, an extensive DEFOR (DEbris FORmation) test series with various molten oxidic materials was conducted previously at Royal Institute of Technology to investigate the characteristics of debris beds formed from oxidic melt-water interactions, which are important to the coolability of debris beds and thus the retention of core melt. Yet, little attention has been paid to metallic melt which exist in the core melt. The present study is intended to fill in the knowledge gap, i.e., to characterize metallic melt-water interactions when a melt jet falls into a deep water pool. Nine DEFOR-M tests are carried out to clarify the effects of melt jet diameter, free fall height and water pool depth on metallic debris formation characteristics. Molten tin of 20 kg is employed as the simulant of metallic melt. A melt sensor and a mass sensor are installed to detect the discharging period of coherent jet and the mass accumulation of debris bed, respectively. A high-speed camera is applied to record the process of jet breakup, debris fragmentation and solidification, and debris bed formation. The experimental results show that the water pool depth has a significant influence on steam explosion and debris bed formation characteristics. Moreover, the jet breakup length is sensitive to jet diameter and free fall height. Finally, the features of metallic debris beds are compared with those of oxidic ones in respects of debris bed's configuration and porosity, particles' morphology and size distribution.

Developing in drying ponds could leave frogs unprepared for climate change

Dependable wet seasons are essential for the survival of many frogs, which rely on full pools in spring for their aquatic young to develop and mature. But recently, some regions have suffered unusually dry winters, threatening vital watercourses, and spring conditions are predicted to become even drier. ‘Development is a particularly sensitive period for many animals’, says Michel Ohmer, at University of Mississippi, USA, explaining that growing as a tadpole in a dwindling warm pool could affect the animal later in life. But no one knew how. As the conditions that southern leopard frog (Rana sphenocephala) tadpoles grow up in are predicted to change, Ohmer, Jeff Bednark and Trina Wantman (while at University of Pittsburgh, USA) headed down to Fort Polk, Louisiana, USA, to collect eggs freshly laid by the frogs to find out how the animals fared as young adults after a dry or warm start.Recreating 18 tadpole ponds in plastic pools in Louisiana, the team covered each with cloth providing 50% shade for shelter before introducing 40 tadpoles to their new homes and warming some to simulate future climate conditions. Then, the team recreated a drought by lowering the water rapidly in six tanks over 9 weeks until almost dry, while draining the water more slowly from six other tanks and keeping the water level unchanged in the remaining ponds. By doing so, the team created a range of conditions from future droughts to the current climate. But how did the different pond environments affect the developing youngsters?The team measured the tadpoles’ growth and development, and it was clear that the loss of water from their tank homes caused the tadpoles to develop faster, while growing in the warmer pools drove them to develop even faster, emerging as fully formed froglets in about 10 weeks. And when the team compared the tadpoles’ size when they finally lost their tails, the youngsters in the drying tanks were always smaller than the froglets from the deeper pools. But how did the changing and warming environments impact the frogs later in life?After transporting the froglets to Pittsburgh, Ohmer spooked the 1- to 2-month-old amphibians into jumping at different temperatures by gently prodding them, and found that the froglets that had developed in a cool, deep pond outleapt the froglets from the warmer, drier ponds, bounding 12% further at 32°C. The team also checked how well the froglets could withstand the heat, discovering that the fastest developing youngsters were unable to cope with high temperatures, regardless of the water conditions in their pools. And up to the age of 7 months, the froglets that had developed in the warmest and most rapidly drying pools were more timid and less keen to explore than the other frogs, while preferring to hang out in warmer conditions.‘The environment tadpoles develop in can impact frogs both in the short- and long-term, leading to changes not only in how they can handle the heat, but also the temperatures they choose in their habitat’, says Ohmer. So, growing up in drying ponds could be detrimental for adult frogs as the climate continues warming. And Ohmer warns that the impacts of climate change ‘may be amplified beyond what has been predicted’, as more timid frogs that develop in dwindling pools may avoid picking up microbes that offer protection from other pathogens. However, she points out that the frogs’ preference for warmer conditions may also make them less vulnerable to fungal infections that thrive in the cold.

Velocity field and cavity dynamics in drop impact experiments.

Drop impact experiments allow to model a wide variety of natural processes, from raindrop impacts to planetary impact craters. In particular, interpreting the consequences of the planetary impacts requires an accurate description of the flow associated with the cratering process. In our experiments, we release a liquid drop above a deep liquid pool to investigate simultaneously the dynamics of the cavity and the velocity field produced around the air-liquid interface. Using particle image velocimetry, we analyse quantitatively the velocity field using a shifted Legendre polynomials decomposition. We show that the velocity field is more complex than considered in previous models, in relation to the non-hemispherical shape of the crater. In particular, the velocity field is dominated by the degrees 0 and 1, with contributions from the degree 2, and is independent of the Froude and the Weber number when these numbers are large enough. We then derive a semi-analytical model based on the Legendre polynomials expansion of an unsteady Bernoulli equation coupled with a kinematic boundary condition at the crater boundary. This model explains the experimental observations and can predict the time evolution of both the velocity field and the shape of the crater, including the initiation of the central jet.

Development of a surrogate model for quenching estimation of ex-vessel debris beds and its coupling with MELCOR

In the severe accident management (SAM) strategy for Nordic boiling water reactors (BWRs), a flooded reactor cavity is conceived to receive corium in case of vessel failure, with the hope that the discharged corium will fragment and form a coolable particulate debris bed in the deep water pool. The so-formed debris bed on the cavity basement is supposed to be very hot at the beginning and therefore its quenching is a prerequisite for long-term coolability. In previous study the coupled MELCOR/COCOMO simulation was employed to simulate quench process of ex-vessel debris beds in severe accident scenarios. Although it successfully extended the MELCOR capability, the calculation was dramatically slowed down by explosive computational cost of COCOMO. To overcome the limitation, the present study is to develop a surrogate model (SM) which can replace the mechanical code COCOMO and realize quick estimations of the quench process of ex-vessel debris beds. It was then coupled with MELCOR code for integral severe accident analyses of a Nordic BWR with cooling of ex-vessel debris beds. The SM was developed based on a database generated from COCOMO calculations of various one-dimension (1D) debris beds quenched in the reactor cavity, using artificial neural networks (ANNs). Finally, the coupled MELCOR/SM simulation was applied to safety analyses of postulated severe accident scenarios due to station blackout (SBO) in the BWR, where MELCOR performs integral analysis of accident progression while SM predicts the consequences (e.g. energy transfer) of debris bed quench. The simulation results show that the coupled MELCOR/SM simulation can predict the trends of containment pressure and pool temperature similar to those of the coupled MELCOR/COCOMO simulation. Compared with MELCOR standalone simulation, the coupled MELCOR/SM simulation predicted earlier pool saturation and containment venting.

Metagenomic profiling of antibiotic resistance genes in Red Sea brine pools.

Antibiotic resistance (AR) is an alarming global health concern, causing an annual death rate of more than 35,000 deaths in the US. AR is a natural phenomenon, reported in several pristine environments. In this study, we report AR in pristine Red Sea deep brine pools. Antimicrobial resistance genes (ARGs) were detected for several drug classes with tetracycline and macrolide resistance being the most abundant. As expected, ARGs abundance increased in accordance with the level of human impact with pristine Red Sea samples having the lowest mean ARG level followed by estuary samples, while activated sludge samples showed a significantly higher ARG level. ARG hierarchical clustering grouped drug classes for which resistance was detected in Atlantis II Deep brine pool independent of the rest of the samples. ARG abundance was significantly lower in the Discovery Deep brine pool. A correlation between integrons and ARGs abundance in brine pristine samples could be detected, while insertion sequences and plasmids showed a correlation with ARGs abundance in human-impacted samples not seen in brine pristine samples. This suggests different roles of distinct mobile genetic elements (MGEs) in ARG distribution in pristine versus human-impacted sites. Additionally, we showed the presence of mobile antibiotic resistance genes in the Atlantis II brine pool as evidenced by the co-existence of integrases and plasmid replication proteins on the same contigs harboring predicted multidrug-resistant efflux pumps. This study addresses the role of non-pathogenic environmental bacteria as a silent reservoir for ARGs, and the possible horizontal gene transfer mechanism mediating ARG acquisition.

AWRO mobile robot: Aid for water rescue operations

AWRO Mobile Robot: Aid for Water Rescue Operations, is a mobile robot that takes the appearance of a watercraft, which helps a lifeguard rescue a drowning person in deep swimming pools. AWRO is short for “Aid for Water Rescue Operations”. The mobile robot detects the drowning person by determining the splashing patterns of the person, which can be seen in the output image taken from an onboard camera. The system makes use of a PIC18F242 microcontroller to control the vehicle’s functions and movements. Also, communication between the PC and mobile robot is done through the use of serial communication. The control program of the mobile robot is implemented using several modules: the PIC microcontroller code, the main PC software running on top of the .NET framework, and the RoboRealm image processing software. With this, more lives can be saved, since it will be able to reach people who are drowning in areas where humans cannot normally reach. Test results show that the proposed robot can efficiently act as a rescue robot and can be further enhanced using some more advanced additive features.

Aquatic biomass is a major source to particulate organic matter export in large Arctic rivers

Arctic rivers provide an integrated signature of the changing landscape and transmit signals of change to the ocean. Here, we use a decade of particulate organic matter (POM) compositional data to deconvolute multiple allochthonous and autochthonous pan-Arctic and watershed-specific sources. Constraints from carbon-to-nitrogen ratios (C:N), δ13C, and Δ14C signatures reveal a large, hitherto overlooked contribution from aquatic biomass. Separation in Δ14C age is enhanced by splitting soil sources into shallow and deep pools (mean ± SD: -228 ± 211 vs. -492 ± 173‰) rather than traditional active layer and permafrost pools (-300 ± 236 vs. -441 ± 215‰) that do not represent permafrost-free Arctic regions. We estimate that 39 to 60% (5 to 95% credible interval) of the annual pan-Arctic POM flux (averaging 4,391 Gg/y particulate organic carbon from 2012 to 2019) comes from aquatic biomass. The remainder is sourced from yedoma, deep soils, shallow soils, petrogenic inputs, and fresh terrestrial production. Climate change-induced warming and increasing CO2 concentrations may enhance both soil destabilization and Arctic river aquatic biomass production, increasing fluxes of POM to the ocean. Younger, autochthonous, and older soil-derived POM likely have different destinies (preferential microbial uptake and processing vs. significant sediment burial, respectively). A small (~7%) increase in aquatic biomass POM flux with warming would be equivalent to a ~30% increase in deep soil POM flux. There is a clear need to better quantify how the balance of endmember fluxes may shift with different ramifications for different endmembers and how this will impact the Arctic system.

Hanging droplets from liquid interfaces

The impact of a heavier droplet falling into a deep pool of lighter liquid is investigated using three-dimensional numerical simulations. We demonstrate that the heavier droplets can hang from the surface of a lighter liquid using surface tension. The impact phenomenon and the evolution of the heavier droplet as a function of its size and release height are explored. A theoretical model is also formulated to understand the role of different forms of energy associated with the hanging droplet. We further solve the force balance equations for the hanging droplets analytically, and demonstrate that the results obtained from our simulations match very well the analytical solution. This research offers opportunities in many areas, including drug and gene delivery, encapsulation of biomolecules, microfluidics, soft robots, and remediation of oil spills.

Experimental Study on the Airborne Noise of Rain

Rainfall noise is investigated experimentally in this paper. The modern high-speed camera and microphone are employed to study both drop dynamics and sound signals. Sound signals produced by single-drop impacts on deep pools, thin liquid films, steel plates, and sandy surfaces were analyzed through a combination of videos and audio. Classical Fourier transforms are performed for converting the original signal to a power spectrum. Results show that in the deep-water cases, the noise is proved to be the entrapment of a tiny breathing bubble that sheds from the dimple. The dominant frequencies of droplets impacting water film, rigid walls, and sandy surfaces are much compared with deep pool cases.

A Man of the Theater: Survival as an Artist in Iran by Nasser Rahmaninejad

Reviewed by: A Man of the Theater: Survival as an Artist in Iran by Nasser Rahmaninejad Suzi Elnaggar A MAN OF THE THEATER: SURVIVAL AS AN ARTIST IN IRAN. By Nasser Rahmaninejad. New York: New York University Press, 2020. 266 pp. Paperback, $21.95. Nasser Rahmaninejad is an Iranian artist who began working in theatre in 1959. During the Shah’s regime, he formed an independent theatre group called Mehr, which later became known as the Iran Theatre Association. His work in Iran spanned a period of cultural and political shifts, as well as strict censorship. After surviving both revolution and imprisonment, Rahmaninejad left Iran. He continues his work in theatre, now outside Iran, by writing and translating essays and articles, speaking and lecturing at academic institution and artistic spaces, and continuing to write plays, including My Heart, My Homeland (1995), One Page of Exile (1996), and Between the Grave and the Moon (2016). He now lives in the Bay Area in California. Rahmaninejad’s memoir, A Man of the Theater: Survival as an Artist in Iran, is the story of a man, a country, and the love for theatre that keeps bringing them into conflict. In his opening chapter, Water (Aab), he relates the relationship of water to Iranians of his generation, opening with, “We did not have tap water” (p. 1). This opening perfectly encapsulates the flowing fluidity of the narrative that Rahmaninejad weaves through his memoir. Some tales, like the childhood of traditional Iranian theatre with neighborhood friends, are gentle eddies while others, like his early childhood memory of the death of his sister, Manijeh, are deep pools of memory in which we can barely see past the surface. Theatre flows throughout, first a small trickle, then a rushing river that significantly alters the course of his life as a young artist in pre-Revolution Iran. Chapter One introduces the quality of the memoir, meditative and free flowing, focused on small details of life while building a narrative. In the next three chapters, Rahmaninejad recounts his childhood and years as a young man, before he became a well-known theatre practitioner in Iran. In Chapter Two, he recounts his very first [End Page 220] performance at two years old. However, the darker shades of memory creep in, as he reflects on the opium dens and the downtrodden women (saghi) that worked there. It was a family connection that started his love for theatre; his father’s second cousin, an actor and singer named Abdolvahab Shahidi provided free admission for his family to many plays, and this became a place of refuge for Rahmaninejad. In Chapters Three and Four, he recounts his efforts to establish himself as a professional theatre maker after high school but being unable to do so with any real stability—or without working for the Shah’s government. Here, Rahmaninejad begins to weave in his burgeoning political consciousness, and the events in both the country and his life that shaped his artistic journey. In Chapter Five, Interlude, Rahmaninejad recounts a harrowing and some comical tale of his first serious encounter with SAVAK, the Iranian Secret Police. After intending to cross the border into Pakistan with several friends, he was apprehended. Their juvenile attempts to get themselves out of a situation way beyond their depth end with Rahmaninejad attempting to get back to Tehran, ragged and hungry, without money for the fare home. This interlude is one of the longer complete narratives in the book, and perfectly encompasses the feeling that Rahmaninejad would do anything to practice theatre—even things that he recounts later as unwise or risky decisions. In Chapters Six through Eight, Rahmaninejad reminisces on the events that led him and other artistic friends to establish the Mehr Theatre Group and the Iranian Theatre Association. They began with adapting Miller’s Incident at Vichy, an endeavor for which they garnered American backing and support. As the group and Rahmaninejad grew more confident and established, they began to perform both original works and adaptations. As the theatre he put on grew bolder, SAVAK took an increased interest in Rahmaninejad and his compatriots. This interest eventually led to his arrest in 1971 and his detention...

Six years of fluvial response to a large dam removal on the Carmel River, California, USA

AbstractMeasuring river response to dam removal affords a rare, important opportunity to study fluvial response to sediment pulses on a large field scale. We present a before–after/control–impact study of the Carmel River, California, measuring fluvial geomorphic and grain‐size evolution over 8 years, six of which postdated removal of a 32 m‐high dam (one of the largest dams removed worldwide) and included 11 flow events exceeding the 2‐year flood magnitude. We find that the reservoir‐sediment pulse following dam removal was relatively small (97 000 ± 24 000 t over 4 years), owing to deliberate reservoir‐sediment stabilization. Scaled to the size of the Carmel River watershed and compared against long‐term bedrock denudation rates, the post‐dam‐removal sediment release was slightly less than the annualized long‐term sediment export from this basin. New sediment transited >30 km to the river mouth in less than 2 years, assisted by floods 2 and 4 years after dam removal. The sediment pulse fined the downstream riverbed while causing mostly low‐magnitude bed‐elevation changes: commonly 0.5 to 1 m or smaller, occurring as discontinuous sediment patches or interstitial deposits, aside from the filling and subsequent partial scour of deep pools. There was no major geomorphic reset downstream from the dam site. Geomorphic changes were driven almost entirely by flow rather than by the modest increase in sediment supply, in contrast to recent examples from other large dam removals. The relatively minor disturbance caused by dam removal on the Carmel River is likely analogous to many future dam removals: a relatively small sediment pulse after deliberate limitation of reservoir‐sediment erosion, and with an upstream dam remaining in place. Thus, a large dam removal need not lead to major downstream impacts.

A Biomolecular Toolbox for Precision Nanomotors.

The application of nanomotors for cancer diagnosis and therapy is a new and exciting area of research, which when combined with precision nanomedicine, promises to solve many of the issues encountered by previous development of passive nanoparticles. The goal of this article is to introduce nanomotor and nanomedicine researchers to the deep pool of knowledge available regarding cancer cell biology and biochemistry, as well as provide a greater appreciation of the complexity of cell membrane compositions, extracellular surfaces, and their functional consequences. A short description of the nanomotor state-of-art for cancer therapy and diagnosis is first provided, as well as recommendations for future directions of the field. Then, a biomolecular targeting toolbox has been collated for researchers looking to apply their nanomaterial of choice to a biological setting, as well as providing a glimpse into currently available clinical therapies and technologies. This toolbox contains an overview of different classes of targeting molecules available for high affinity and specific targeting and cell surface targets to aid researchers in the selection of a clinical disease model and targeting methodology. It is hoped that this review will provide biological context, inspiration, and direction to future nanomotor and nanomedicine research.

Experimental investigation on ex-vessel debris bed formation using low melting-point melt of binary metals

During severe accidents in a light water reactor, the core melt (corium) may relocate to the lower head and fail the reactor pressure vessel (RPV). The corium will be ejected to the reactor cavity upon the RPV failure and undergo melt coolant interactions (FCI) if the cavity is flooded with water. The FCI process does not only determines the characteristics of the resulting debris bed which are important to coolability, but also induces a steam explosion risk which may threaten containment integrity. The present study is concerned with characterization of debris bed formed from FCI of metal-rich corium failing into a deep water pool in the reactor cavity. Low melting-point metals Tin and Tin–Bismuth (20 kg) were employed as the simulant materials of metal-rich corium melt. Ten tests were carried out on the DEFOR-M test facility at KTH to investigate the effects of various parameters on debris bed formation, such as melt superheat, coolant subcooling, material. The melt jet fragmentation and fragments movement in the water pool as well as debris deposition on the pool floor were recorded by high-speed cameras. Melt sensors and weight sensors were installed to detect the period of melt jet discharge and the mass of forming debris bed. The porosity of debris bed was obtained through the debris bed volume measured by a three-dimensional laser scanner and the pore volume measured by water absorption. The final configuration of debris bed was also reconstructed through the laser scanner data, and the debris particles were sieved for their size distribution. The experimental results revealed the FCI phenomena and debris bed characteristics including configuration and porosity of debris bed as well as morphology and size distribution of debris particles under different melt superheats, coolant subcooling, materials.

A Novel Force Control Strategy for Improved Surface Integrity in Low Plasticity Burnishing

Ball burnishing is a cold work process where a hard ceramic or diamond ball rolls on a metal surface and flattens the roughness peaks under high local pressure. The small deformation created on the surface imposes compressive residual stresses and raises hardness in a shallow sub-surface layer, leading to improved fatigue, corrosion, and foreign object damage performances. Trial-and-error type experimental work to determine the optimum process parameters for a cold-forming process like ball burnishing for acceptable performance is costly. Therefore, the article aims to investigate the effects of various force control strategies in the double-sided low plasticity burnishing (LPB) process to find the effects on deformation and residual stresses on thin Ti6Al4V flat sheets. A 3D static-implicit finite element model was developed with an elastic-rigid plastic flow curve. Simulations were conducted to predict residual stresses and deformationі on the surface. As a result, it was proven that ball burnishing can produce a deterministically controlled surface. An increased vertical force produced higher deformation normal to the surface and, therefore, a deeper pool. As the ball proceeded further, a plowing effect developed such that when a 3.5–4.8 mm deep pool was formed (at a vertical force of 150 N), a peak of 2.8 mm was produced at the front end. Overall, the deformation on the surface and the residual stresses were directly interrelated. Parallel to the deformation on the surface, residual stresses on and beneath the surface also showed some variation. Nevertheless, the predicted residual stress variations were not big. They did not switch to the tensile mode in the burnished zone. Therefore, the whole sheet surface should be burnished to obtain all the compressive residual stresses.

Interaction and motion of two neighboring Leidenfrost droplets on oil surface

Evaporation of droplets on a hot oil surface is a natural phenomenon. However, most of existing studies focus on the evaporation of a single droplet, and the evaporation of multiple droplets is insufficiently understood. Here, we explore the Leidenfrost evaporation of two identical FC-72 droplets on the surface of a hot oil bath. The oil temperature ranges from 73.6 to 126.6 ℃, and the evaporation of droplets each with an initial diameter of 1.5 mm is recorded by an infrared thermographer and a high-speed camera. The shallow oil depth keeps the oil temperature uniform relatively in the slot compared with that in the deep liquid pool due to the larger ratio of the surface area for copper-oil contact to the slot volume. We find that the neighboring droplets evaporate in three stages: non-coalescing, bouncing, and separating. The radius of neighboring Leidenfrost droplets follows the power law <i>R</i>(<i>t</i>)~(1−<i>t</i>/<i>τ</i>)<sup><i>n</i></sup>, where <i>τ</i> is the characteristic droplet lifetime and <i>n</i> is an exponent factor. Moreover, the diffusion-mediated interaction between the neighboring droplets slows down the evaporation process compared with the action of isolated Leidenfrost droplet and leads to an asymmetric temperature field on the droplet surface, thereby breaking the balance of the forces acting on the droplets. A simple dual-droplet evaporation model is developed which considers four forces acting horizontally on the droplet, namely, the Marangoni force resulting from the non-uniform droplet temperature, the gravity component, the lubrication-propulsion force, and the viscous drag force. Scale analysis shows that the Marangoni force and gravity component dominate dual-droplet evaporation dynamics. In the non-coalescence stage, the gravity component induces the droplets to attract each other, while the vapor film trapped between droplets prevents them from directly contacting. When the droplets turn smaller, the gravity component is insufficient to overcome the Marangoni force. Hence, the droplets separate in the final evaporation stage. Finally, we conclude that the competition between Marangoni force and gravitational force is the origin of the bounce evaporation by comparing the theoretical and experimental transition times at distinct stages. This study contributes to explaining the complex Leidenfrost droplet dynamics and evaporation mechanism.

Waving Effect Characterization for Water-to-Air Optical Wireless Communication

In this paper, we establish and experimentally verify a water-to-air (W2A) visible light communication (VLC) system through dynamic air-water interface. Considering the complexity of waves in real environments, we divide waves into largescale wave and small-scale wave. Monte Carlo simulation and experimental results show that small-scale wave mainly affects the energy distribution of the light spot on the receiving plane and the variation frequency of link gain, while largescale wave mainly affects the coverage of the light spot. In the W2A-VLC system based on light-emitting diode (LED), the statistical characteristics of variation time and link gain are mainly related to the small-scale wave, and the effect of large-scale wave can be treated as slow fading. In order to design a reliable communication system, a large-divergence-angle LED array and avalanche photodiode (APD) array are used under dynamic water surface. We investigate three cases, namely single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO). In the SIMO or MISO systems, the correlation coefficient of channel gain decreases with the inter-receiver or inter-transmitter distance. A significant transmission performance enhancement can be achieved by deploying more transmitters or receivers and increasing the distance between the transmitters or receivers. A MIMO structure can effectively increase the achievable rate. We further establish a W2A-VLC link in a deep wave pool to verify our research in the real environment. The results show that more intensive small-scale wave yields higher bit error rate (BER), and the diversity scheme can improve the transmission stability and decrease BER.

Evaluation of Habitat Suitability Index Model of Indian Gharial in National Chambal Sanctuary, M.P. India

Almost all animals use their habitats in a non-random manner. But the cost and benefits of using specific habitat types remain unknown for many types of organisms. Habitat suitability models aim to assess the relationship between species and their habitat and accurately predict the species response to habitat changes. We developed a riverine habitat model for Gharial (Gavialis gangeticus), a critically endangered species, in the National Chambal Sanctuary in India after reviewing and synthesizing existing information. Based on the model, an index of habitat suitability is produced, ranging from 0 (unsuitable habitat) to 1 (optimal habitat). The results of the present study indicate that the Gharial prefer deep pools in water bodies. The deep waters serve as feeding and breeding grounds for Gharial. They prefer water with a velocity ranging from 20–70 cm.sec-1 . Sandy banks are preferred as basking sites, mainly because they provide moisture during the warm months and because it seems that they find it easier to crawl on sandy surfaces than on rocky or clay surfaces. Insects, tadpoles, tiny fish, and frogs are preferred by young Gharial. A habitat suitability model for Gharial can be used as a decision support system in order to improve conservation efforts at different landscape scales.

Numerical Simulation of Temperature Field and Melt Pool Characteristics of CP-Ti Manufactured by Laser Powder Bed Fusion

A coupled heat source model that combined a Gauss surface heat source with a Gauss cylindrical volumetric heat source was introduced to simulate temperature field distribution and melt pool characteristics using a finite element simulation (FEM) method for the deep and narrow melt pools formed in laser powder bed fusion (L-PBF) aiming at commercial pure titanium (CP-Ti). For comparison, the same simulations using the Gauss surface heat source model and the double ellipsoid heat source model were also performed. The simulated melt pool geometries using the coupled heat source model match well with the measurements, with an average error of 1% for the melt pool depth and 7% for the width. Based on the single-track experimental results, it was found by comparing the simulated results from the three heat source models that the coupled heat source model had better accuracy than the other two. Then, the temperature field and the melt pool geometries of CP-Ti fabricated at different laser power levels from 300 W to 500 W and scanning speeds from 600 mm/s to 4000 mm/s were simulated. According to the simulated maximum temperature and geometries of the melt pool, a suitable process parameters map for CP-Ti was obtained. The reported experimental results agree well with the simulated map. The coupled heat source model is more accurate and applicable for the deep and narrow melt pools formed during L-PBF.