Deep Pool Research Articles

Onset of periodic oscillations as a precursor of a transition to pore-generating turbulence in laser melting

• Narrowband oscillations of laser absorption precede multimodal oscillations. • Melt pool hydrodynamics drive oscillations when laser is stationary or scanned. • Simulations and X-ray imaging shows pore formation during multimodal oscillations. Laser melting technologies in welding and additive manufacturing, such as laser powder bed fusion, promises to revolutionize manufacturing. However, a challenge remains in preventing pore defects produced by melt pool instabilities, which degrade part quality. Using X-ray imaging synchronized with ultrahigh-speed (40 ns) absorption radiometry and coupled with high-fidelity simulations, we discovered that periodic oscillations in the melt pool's morphology existed prior to a transition to chaotic and pore-generating turbulence. Over-extension by recoil waves followed by surface-tension driven recession created temporary pores that persisted longer in a multimodal regime. This non-linear hydrodynamics exists in both shallow and deep melt pools, but most strongly affects the latter. Early prevention of this transition will help improve the quality of manufactured parts. This work demonstrates that remote sensing of these oscillations is possible by very high time resolution total light scattering measurements, which is more readily achievable in an industrial setting than 2-dimensional melt pool imaging.

Crystal growth control of Ni-based alloys by modulation of the melt pool morphology in DED

In additive manufacturing especially in directed energy deposition, it is hard to control crystal growth pattern due to the high temperature gradient in AM. Essentially, the crystal grows epitaxially from the substrate and columnar crystals with strong texture are exhibited in AM components. Here, small spot diameter was used for DED-L of Ni-based alloys and various crystal growth patterns were obtained by changing power density. Samples processed under low power density were shown to exhibit wide and shallow spindle-like melt pool, along with apparently hierarchical planar-columnar-equiaxed microstructure. While samples prepared under relatively high power density were shown to exhibit narrower and deeper melt pool with two sharp turning points, exhibiting inclined columnar grains and several discontinuous central axial columnar crystals. When highest power density and small spot diameter were applied, crystal growth with weak texture was achieved. Under this deep and narrow melt pool, the crystal growth can be separated into four regions: nearly-equiaxed grains with random grain orientations; horizontally symmetrically grown crystal grains; axial columnar in the center; columnar grains grew approximately vertical to the boundary of melt pool. Correlations were investigated between melt pool shape, solidification parameters and microstructure. The transformation of melt pool morphology was mainly attributed to the change of power density. Solidification parameters were shown to be different under different melt pool morphology. Diverse crystal growth patterns were achieved under different melt pool morphology controlled by power density, showing the feasibility of site-specific of microstructure control in DED-L according to the required mechanical properties.

Phenomena of single water droplet impacting a heptane layer on water pool

The behavior of single water drop impacting an oil layer on the deep water pool was recorded using a high-speed camera. Heptane was used as the target liquid layer on the water pool. A particular phenomenon of double crown can be observed. The formation of double crown is not only related to the impact Weber number of the water droplet, but also the thickness of the oil layer. The critical Weber number for the formation of double crown decreases sharply as the decrease of the oil layer thickness. With the increase of Weber number and the decrease of oil layer thickness, there are four typical phenomena: single crown-jet, single crown-bubble, double crown-bubble and double crown-jet. Moreover, the effects of oil layer thickness and impact Weber number on surface bubble lifetime and the geometry size of crown, crater and jet were quantitatively analyzed.

Confined Evaporation-Mediated Enhanced Residence Time of Levitated Water Drops over Deep Oil Pools.

We observe the impact of bouncing and floating of water drops on a pool of immiscible volatile oil pools at low Weber numbers. The residence time of the impacting drop ranges from a few milliseconds to a few seconds before it sinks into the lighter oil phase. It is hypothesized that the confined evaporation from the volatile oil pool replenishes the thin film draining and results in prolonged floating and delayed sinking of drops into the oil pool. Water drops are released from a low height to impact on volatile hydrocarbon oil deep pools of various volatilities. The floating dynamics and residence times are captured using high-speed imaging. A theoretical model for the residence time has been developed to evaluate the hypothesis. The drop residence time is found to be directly proportional to the volatility of the oil pool in accordance with the hypothesis. The mathematical model incorporating the coupled confined evaporation and film draining dynamics is found to be in well agreement with the experimentally observed residence time. The bouncing-sinking regime map has been developed based on the experimental data.

Theory for the coalescence of viscous lenses

Drop coalescence occurs through the rapid growth of a liquid bridge that connects the two drops. At early times after contact, the bridge dynamics is typically self-similar, with details depending on the geometry and viscosity of the liquid. In this paper we analyse the coalescence of two-dimensional viscous drops that float on a quiescent deep pool; such drops are called liquid lenses. The analysis is based on the thin-sheet equations, which were recently shown to accurately capture experiments of liquid lens coalescence. It is found that the bridge dynamics follows a self-similar solution at leading order, but, depending on the large-scale boundary conditions on the drop, significant corrections may arise to this solution. This dynamics is studied in detail using numerical simulations and through matched asymptotics. We show that the liquid lens coalescence can involve a global translation of the drops, a feature that is confirmed experimentally.

Fragmentation of a liquid metal droplet falling in a water pool

This paper focuses on the experimental investigation of breakup regimes of a molten fusible metallic droplet in water, at intermediate Weber numbers with emphasis on mass and energy balance. The experiment consists in impacting perpendicularly a molten drop onto the interface of a deep water pool, at a controlled temperature. Using a drop-on-demand device and high-speed shadowgraph, a single drop can be visualized during its evolution. There is a noticeable velocity jump when the droplet crosses the interface that can be modeled using an unsteady Bernoulli equation. As observed for liquid–gas systems, the drop experiences different regimes of fragmentation, depending on its Weber number: oscillations, bag oscillations, prolate drop stretching breakup, and then bowl-shaped bag breakup. However, opposite to the gas–liquid case, a Rayleigh–Taylor instability mechanism seems to be absent and this seems related to the bowl-shaped bag breakup mechanism when compared to the dome-shaped gas–liquid case. Statistics of the daughter droplets are then given, using either image analysis for large droplets size distribution or sieving and weighting of the solidified fragments for measurement of the Sauter mean diameter and surface energy creation. Finally, a simple relation between the Sauter mean diameter and the Weber number is presented based on the energy and mass balances. When comparing with previous higher Weber number results, a viscous transition corresponding to a strong increase in the energy loss is also shown to occur for the higher Weber number.

Simultaneous impact of twin drops on a semi-infinite liquid target

We take the enduring topic of drop impact on a deep pool of similar liquid further by allowing twin drops to impact simultaneously. Impacts are sufficiently proximal that impact crowns and craters interact, distorting and merging craters, and creating previously undocumented supersurface fluid interactions. The unique features of twin impacts occur when crowns collide to create a central veil that bifurcates the two craters and the expulsion of jet-like features atop colliding crowns. The emergence of a plethora of splash features is dependent on the Froude number (Fr=30−200) and drop separation distance. We analyze proximal crater evolution using theory developed for singular drops and develop scaling relations to predict crown and jet height. Crater and jet energies are compared for various impact velocities and drop separation distances. We find that craters close enough to merge produce thicker, but not higher, rebound jets.

Integrating regional and local monitoring data and assessment tools to evaluate habitat conditions and inform river restoration

Restoring degraded rivers requires initial assessment of the fluvial landscape to identify stressors and riverine features that can be enhanced. We associated local-scale river habitat data collected using standardized national monitoring tools with modeled regional water temperature and flow data on mid-sized northwest U.S. rivers (30–60 m wide). We grouped these rivers according to quartiles of their modeled mean August water temperature and examined their physical habitat structure and flow. We then used principal components analysis to summarize the variation in several dimensions of physical habitat. We also compared local conditions in the Priest River, a river targeted for restoration of native salmonid habitat in northern Idaho, with those in other rivers of the region to infer potential drivers controlling water temperature. The warmest rivers had physical structure and fluvial characteristics typical of thermally degraded rivers, whereas the coldest rivers had higher mean summer flows and greater channel planform complexity. The Priest River sites had approximately twice as many deep residual pools (>50, >75, and >100 cm) and incision that averaged approximately twice that in the coldest rivers. Percentage fines and natural cover in the Priest were also more typical of the higher-temperature river groups. We found generally low instream cover and low levels of large wood both across the region and within the Priest River. Our approach enabled us to consider the local habitat conditions of a river in the context of other similarly sized rivers in the surrounding region. Understanding this context is important for identifying potential influences on river water temperature within the focal basin and for defining attainable goals for management and restoration of thermal and habitat conditions.

The Politics of Tribal Perseverance

There is a short answer to the question that has been posed to the participants in this roundtable. Tribes have a great deal of currency in modern Yemen because they provide an effective means to govern and protect local society. Tribalism is a deep pool of widely accepted customary practices in Yemen that people draw upon to provide security, manage agricultural resources (Yemen's tribespeople are mostly settled agriculturalists), and resolve local disputes.

High-Throughput Griess Assay of Nitrite and Nitrate in Plasma and Red Blood Cells for Human Physiology Studies under Extreme Conditions.

The metabolism of nitric oxide plays an increasingly interesting role in the physiological response of the human body to extreme environmental conditions, such as underwater, in an extremely cold climate, and at low oxygen concentrations. Field studies need the development of analytical methods to measure nitrite and nitrate in plasma and red blood cells with high requirements of accuracy, precision, and sensitivity. An optimized spectrophotometric Griess method for nitrite–nitrate affords sensitivity in the low millimolar range and precision within ±2 μM for both nitrite and nitrate, requiring 100 μL of scarcely available plasma sample or less than 50 μL of red blood cells. A scheduled time-efficient procedure affords measurement of as many as 80 blood samples, with combined nitrite and nitrate measurement in plasma and red blood cells. Performance and usefulness were tested in pilot studies that use blood fractions deriving from subjects who dwelt in an Antarctica scientific station and on breath-holding and scuba divers who performed training at sea and in a land-based deep pool facility. The method demonstrated adequate to measure low basal concentrations of nitrite and high production of nitrate as a consequence of water column pressure-triggered vasodilatation in deep-water divers.

Imagist Poetry and Clinical Medicine: Arts of Observation, Precision, and Expression.

Microcosm Ajay Soni, MD A sympathetic drop in the tiny deep dark pool: the passage widens . . . A soft incandescent glow illuminates the bowl. The calculated curve of a smooth glass lens condenses reflected rays. A floating real image in glistening clarity: the web of blood and neurons onto which all the world projects. Vision Gurwant Kaur, MD Amber urine spin, don’t splash drop on glass. Focus. Here it comes: crystals and casts. Screening Sanam Razeghi, MD It comes into view the monster within this tunnel. Ominous tentacles of tissue climbing these walls while she sleeps. Time stutters. The clock spins faster. Life sputters on. Epinephrine Ann Ouyang, MD Pulsing plume on a gelatinous lake washed with cool water repools, flooding the plain carrying life away. The needle plunges a frost blanches the surface: crimson column wavering, collapsing. Water clears the murky lake restores the landscape. Heart Failure José Stoute, MD A horse gallops water settles and bubbles; the ground swells. Wisdom of Fingers George Simms, MD, PhD Light touch, soft belly; warm sun on the skin. Deep touch, firm mass; clouds move across a darkening sky. Progress Karuna Spiegelman, MD Bloody beefy breasts dripping crimson red, stench of rotting flesh as the tumor spreads. Tactile Navigation Shane Kinard, MD Glacially gliding, sinews submitting, a pop? Crystal elixir! Solitary Kathleen Julian, MD A dark building, lone doctor’s office light still on. Beacon bright. Burning…

Ecosystem vulnerability of floodplain wetlands of the Lower Brahmaputra Valley to climatic and anthropogenic factors

Abstract This study assessed the vulnerability of 16 floodplain wetlands (beels) of the Lower Brahmaputra Valley, Assam, India, in relation to a range of natural and anthropogenic factors including climate change. The total water-spread area of the selected beels varied widely (8–50 ha), with 68.75% of the beels showing a reduction in water-spread area over the past 30 years. High levels of siltation and encroachment and detachment of marginal areas through the construction of roads were the major factors responsible for the reduction in the water-spread area of the beels. The reduction was observed to be in the range of over 33% in three beels (Raghunath Sora, Chulkani, and Dudua beel) to 83% in Bhoishpuri beel. In addition, one beel (Chulkani) experienced reduction in its deep pool area, which is an important wetland area that provides shelter to brood fishes during the dry season. Only 12.5% of the beels studied practiced enclosure (pen) culture for rearing fish. None practiced cage culture. Our study showed that only two beels (Bhoishpuri and Tariachora) were free from exotic fishes; the remaining surveyed beels reported exotic species such as, Cyprinus carpio (Common Carp), Ctenopharyngodon idella (Grass Carp), Hypophthalmichthys molitrix (Silver Carp), H. nobilis (Bighead Carp) and Piaractus brachypomus (Pacu). The prevalence of exotic fishes in the majority of the beels (due both to escape from nearby aquaculture ponds during floods and intentional stocking in certain beels) would have adversely affected the diversity of indigenous fishes in those wetlands. From discussion with the fishers, 50% of the beels surveyed experienced a reduction in the number of fish species from that recorded 10–20 years ago. In addition to climate change-related factors (e.g. abnormal rains, floods, or drought-like situations), other factors – both natural (e.g. hyper-nutrification) and anthropogenic (e.g. construction of roads, houses, and other structures) – also adversely affected the studied wetlands. To help cope with these factors and increase the adaptive capacity of fishers, four measures aimed at mitigation are suggested. These are: the practice of enclosure aquaculture in beels; the construction of floating macrophyte refuges (katal); deep pool refuges; and stock enhancement programmes with climate-resilient indigenous fishes.

Deep Pools: Ecological Sanctuaries for Steindachneridion melanodermatum, a Large Endemic and Endangered Pimelodid of the Iguaçu River

Steindachneridion melanodermatum, an endemic and endangered species, is the largest catfish in the Lower Iguaçu River basin. Currently, the wild population of this species no longer exists in most of this basin, probably due to the loss of habitat by successive hydroelectric dams. This study evaluated the spatial distribution and abundance of S. melanodermatum in the last free-flowing river stretch of approximately 190 km downstream from the Salto Caxias Dam, upstream of the Iguaçu Falls, as well as some tributaries. Hydroacoustic and fishing campaigns were performed between September 2010 to December 2016 to characterize the preferred habitat. A total of 180 specimens was sampled with higher abundances in a protected area near Iguaçu Falls in the Iguaçu National Park. Twenty-four deep pools were identified with maximum depths ranging from 5 to 25 m: 21 pools were along the main channel of the Iguaçu River, and three pools were in tributaries. Deep pools are preferential habitats for this species, especially the deep pool called Poço Preto (P23) and its surroundings. Conservation strategies are required to protect these habitats and prevent S. melanodermatum from becoming extinct, such as establishing deep pools as ecological sanctuaries, intensifying the inspection of illegal fishing, and maintaining dam-free tributaries.

Local scale interventions dominate over catchment scale controls to accelerate the recovery of a degraded stream.

A premise of stream restoration theory and practice is that it is often futile to attempt to restore a stream at the reach scale (101–103 metres) until catchment scale problems have been addressed. This study considers reach scale restoration actions undertaken in Bryan Creek, a sand bed river in south east Australia impacted by a sediment pulse, after catchment sediment sources have been addressed. Local scale interventions, which were in-stream sand extraction, fencing to exclude stock and riparian revegetation, were evaluated by quantifying cross-section and thalweg variability, mapping in-stream and riparian vegetation and by classifying the morphology that emerged following each intervention. Following intervention channel reaches moved to one of three distinct states: simple clay bed, eroding reaches dominated by Juncus acutus, and reaches with deep pools and Phragmites australis. Boundaries between the intervention reaches were sharp, suggesting local scale interventions dominate over catchment scale processes. The magnitude and spread of variability metrics were similar between all reaches and differences in variability bore no relation to intervention type, despite the stark difference in post-intervention morphology. These findings suggest that cross-section and thalweg variability metrics are an inadequate proxy for the effectiveness of local scale interventions in accelerating the recovery of sand bed reaches from a bedload pulse. The most important implications for river managers is that local scale interventions can lead to substantial and rapid improvements in condition, and the change in condition of these reaches is almost independent of other reaches. In this case, the key to the pattern of reach scale geomorphic recovery is excluding stock from waterways so that a specific macrophyte can establish, trap sediment and develop pools.

Prediction on Changes of Seabed due to Sluice Built on entrance of Haiyou Branch in Sanmen Bay

Haiyou branch is the main branch of Sanmen Bay, it is an optional plan to construct sluice at the entrance of Haiyou branch to store fresh water for the utilization of freshwater resources in the Sanmen Bay basin. Basing on the verification of historical tidal currents and seabed erosion and deposition, numerical and physical models are established. Numerical calculations and physical model test show that the impact on hydrodynamic and seabed environment after the construction of sluice will be limited to the local sea area outside the sluice, where the downstream area of sluice, Shepan waterway and Maotou waterway are located, and the siltation strength decreases from the sluice towards Maotou waterway. After the construction of the sluice, the tidal inflow volume of Shepan section will decrease by 11.3% to 17.1%, the tidal volume of Maotou section decrease by 1.7% to 4.3%, and the tidal volume of Qinshan section and Qimen section remain basically unchanged. Within one year, the downstream area of sluice will be deposited with 0.5m∼0.7m, Maotou waterway with about 0.15m, and there is also little siltation at Qimen waterway and other waterway. Due to the impact of the sluice construction of Haiyou branch, after a long time, the deposition of deep pool in Maotou waterway is 2.0m∼2.5m. A once-in-50-year flood from the upper reaches will not cause significant seabed changes in the deep pool of Maotou waterway.

Enhanced polarotaxis can explain water-entry behaviour of mantids infected with nematomorph parasites

A wide range of parasites manipulate the behaviours of their hosts in order to complete their life cycle1. Alteration of phototaxis is thought to be involved in host manipulation in many cases2,3. However, very little is known about what features of the light (intensity, spectrum, polarization) alter behaviour. Here we report that arboreal mantids (Hierodula patellifera) infected by nematomorph parasites (Chordodes sp.) are attracted to horizontally polarized light, which could induce the mantids to enter water, where the parasites can then emerge and reproduce. In a two-choice test, infected mantids were attracted to horizontally but not vertically polarized light. Uninfected mantids were not attracted to either. In a field experiment, 14 infected mantids entered a deep pool, where the water surface strongly reflected horizontally polarized light. By contrast, only two mantids entered a shallow pool, where the surface reflection had higher light intensity but weaker polarization. To our knowledge, this is the first study demonstrating that a manipulative parasite can take advantage of its hosts' ability to perceive polarized light stimuli to alter host behaviour. VIDEO ABSTRACT.

Effects of the Deep Pool on Groundwater Flow and Salinization in Coastal Reservoir and Adjacent Aquifer

Effects of the Deep Pool on Groundwater Flow and Salinization in Coastal Reservoir and Adjacent Aquifer

Emergency Medicine Cases in Underwater and Hyperbaric Environments: The Use of in situ Simulation as a Learning Technique.

IntroductionHyperbaric chambers and underwater environments are challenging and at risk of serious accidents. Personnel aiming to assist patients and subjects should be appropriately trained, and several courses have been established all over the world. In healthcare, simulation is an effective learning technique. However, there have been few peer-reviewed articles published in the medical literature describing its use in diving and hyperbaric medicine.MethodsWe implemented the curriculum of the Master’s degree in hyperbaric and diving medicine held at the University of Padova with emergency medicine seminars created by the faculty and validated by external experts. These seminars integrated traditional lectures and eight in situ simulation scenarios.ResultsFor the hyperbaric medicine seminar, simulations were carried out inside a real hyperbaric chamber at the ATIP Hyperbaric Treatment Centre, only using air and reproducing compression noise without pressurization to avoid damages to the manikins. The four scenarios consisted of hyperoxic seizures, pneumothorax, hypoglycemia, and sudden cardiac arrest. Furthermore, we added a hands-on session to instruct participants to prepare an intubated patient undergoing hyperbaric oxygen treatment with a checklist and simulating the patient transfer inside and outside the hyperbaric chamber. The diving medicine seminar was held at the Y-40 The Deep Joy pool in Montegrotto Terme (Italy), also involving SCUBA/breath-hold diving (BHD) instructors to rescue subjects from the water. These diving medicine scenarios consisted of neurologic syndrome (“taravana/samba”) in BHD, drowning of a breath-hold diver, pulmonary barotrauma in BHD, and decompression illness in a SCUBA diver.ConclusionWith this experience, we report the integration of simulation in the curriculum of a teaching course in diving and hyperbaric medicine. Future studies should be performed to investigate learning advantages, concept retention, and satisfaction of participants.

Microhabitat distribution of aquatic oligochaete communities in the Western Balkans peat bog

AbstractPeat bog pools are rare and fragmented in the Western Balkans. Thus, aquatic macroinvertebrate diversity and the implications for microhabitat loss in these ecosystems are poorly known. Aquatic oligochaetes, widely used as indicators, were sampled using a benthos net in the largest and oldest Croatian bog, in four main water body types: a pond, a deep pool, a shallow pool and a ditch. As these microhabitats lack spatial replication both in the studied bog and in the region, we applied a nested study design with replicates sampled over time. We found a species‐rich aquatic oligochaete fauna, with 11 taxa recorded. Oligochaete communities were strongly affected by vegetation complexity and the morphology of bog water bodies, namely, their size and depth. As revealed by generalised linear mixed models (GLMMs), taxon richness and abundance were significantly higher in the ditch than in other water body types. This could be attributed to the vegetation complexity, supporting many different niches and providing allochthonous food supplies for oligochaetes. The various bog pools contribute to regional biodiversity and promote distinct patterns in the spatial distribution of oligochaetes. However, the predominance of ubiquitous oligochaetes, with high taxon richness, might indicate the degradation of the studied peat bog. This was further confirmed by the spread of vascular plants to the bog area and higher pH water values. All these warning signals suggest that hydro‐ecological conditions should be urgently improved in order to preserve communities in the bog studied.

Impact of pool design on spider and dytiscid recolonization patterns in a restored fen

Peatland pools present unique fauna and flora and contribute significantly to peatland biodiversity. The ecological functionality of artificial pools in restored peatlands is poorly documented. In this study, we investigated arthropod assemblages of 21 artificial pools in a restored fen in southeastern Canada and 16 pools from four pristine fens as reference ecosystems. Three years following restoration, predacious diving beetles (Coleoptera: Dytiscidae) and spiders (Araneae) were sampled within and around pools using minnow traps and pitfall traps, respectively. We used Bayesian community occupancy models to document arthropod recolonization. Twenty‐one dytiscid species were captured in pools. Dytiscid species richness was higher in artificial pools than in reference pools. Three dytiscid species were more likely to occur in deeper pools. Dytiscid species composition in artificial pools differed from reference pools. Seventy‐seven spider species were captured around pools. Spider species richness was higher around artificial pools than around reference pools. Seventeen spider species responded to vegetation cover, either positively or negatively. In contrast, spider species composition was similar between artificial and reference pools. We conclude that artificial pools should be along a gradient of pool depth, but also that fast‐growing vegetation should be introduced on pool margins to foster a quicker return of arthropod assemblages similar to reference ecosystems.