Low Suction Research Articles

Measurement and Uniform Formulation of Soil-Water Characteristic Curve for Compacted Loess Soil with Different Dry Densities

To investigate the effect of dry density on the soil-water characteristics of compacted soil, loess used as filling in the land-making project of the Yan’an new district was collected and compacted to five initial dry densities of 1.40, 1.50, 1.60, 1.70, and 1.80 g/cm3, respectively. The soil-water characteristic curves (SWCCs) of all specimens in the range of 0–105 kPa were measured using the filter paper method. The measured data were fitted using the Fredlund and Xing equation for each initial dry density. The SWCCs have obvious differences in a suction range below 100 kPa and overlap when the suction range is higher. This suggests that the SWCC of compacted soil is independent of the initial dry density in the high suction range, but the correlation with the initial dry density exists in the low suction range. Therefore, the correlation functions of the parameters in the Fredlund and Xing equation with respect to the initial dry density were regressed, respectively. By substituting these functions into the Fredlund and Xing equation, the state surface function of θ w − ψ − ρ d was obtained and can reflect the SWCCs of all densities of the filled soil to support the further investigation of the unsaturated behavior of compacted soil.

Influence of soil density on gas permeability and water retention in soils amended with in-house produced biochar

Biochar has been used as an environment-friendly enhancer to improve the hydraulic properties (e.g. suction and water retention) of soil. However, variations in densities alter the properties of the soil–biochar mix. Such density variations are observed in agriculture (loosely compacted) and engineering (densely compacted) applications. The influence of biochar amendment on gas permeability of soil has been barely investigated, especially for soil with different densities. The major objective of this study is to investigate the water retention capacity, and gas permeability of biochar-amended soil (BAS) with different biochar contents under varying degree of compaction (DOC) conditions. In-house produced novel biochar was mixed with the soil at different amendment rates (i.e. biochar contents of 0%, 5% and 10%). All BAS samples were compacted at three DOCs (65%, 80% and 95%) in polyvinyl chloride (PVC) tubes. Each soil column was subjected to drying–wetting cycles, during which soil suction, water content, and gas permeability were measured. A simplified theoretical framework for estimating the void ratio of BAS was proposed. The experimental results reveal that the addition of biochar significantly decreased gas permeability k g as compared with that of bare soil (BS). However, the addition of 5% biochar is found to be optimum in decreasing k g with an increase of DOC (i.e. k g,65% > k g,80% > k g,95% ) at a relatively low suction range (< 200 kPa) because both biochar and compaction treatment reduce the connected pores.

Swelling pressure of compacted expansive soil over a wide suction range

A series of wetting experiments was performed on a compacted expansive clay to evaluate the swelling pressure generated over a wide suction range. Both osmotic and vapor equilibrium techniques were introduced and implemented to apply the suction required in the swelling pressure measurements. It is shown that, associated with the evolution of the microstructure of soil during wetting, the development of swelling pressure with decreasing suction is nonmonotonic. The soil water retention characteristics were independent of dry density at high suction in the adsorption regime, and a threshold suction was identified to distinguish adsorbed and capillary waters. The development of swelling pressure was closely related to the water retention characteristics. At high suction, the swelling pressure stems mainly from interlayer hydration; at low suction, however, the swelling pressure was controlled by the development of double layers, accompanied by the collapse of some macropores. The nuclear magnetic resonance (NMR) technique was introduced to determine the specific amount of adsorbed and capillary water contents, shedding new insights into the swelling behavior of compacted expansive soil during the wetting process under confined conditions.

Fast Stereolithography Printing of Large-Scale Biocompatible Hydrogel Models.

Large size cell-laden hydrogel models hold great promise for tissue repair and organ transplantation, but their fabrication using 3D bioprinting is limited by the slow printing speed that can affect the part quality and the biological activity of the encapsulated cells. Here a fast hydrogel stereolithography printing (FLOAT) method is presented that allows the creation of a centimeter-sized, multiscale solid hydrogel model within minutes. Through precisely controlling the photopolymerization condition, low suction force-driven, high-velocity flow of the hydrogel prepolymer is established that supports the continuous replenishment of the prepolymer solution below the curing part and the nonstop part growth. The rapid printing of centimeter-sized hydrogel models using FLOAT is shown to significantly reduce the part deformation and cellular injury caused by the prolonged exposure to the environmental stresses in conventional 3D printing methods. Embedded vessel networks fabricated through multiscale printing allows media perfusion needed to maintain the high cellular viability and metabolic functions in the deep core of the large-sized models. The endothelialization of this vessel network allows the establishment of barrier functions. Together, these studies demonstrate a rapid 3D hydrogel printing method and represent a first step toward the fabrication of large-sized engineered tissue models.

What is the optimal level of suction on digital chest drainage devices following pulmonary lobectomy?

A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was: what is the optimal level of suction on digital chest drainage devices following pulmonary lobectomy? Altogether 367 papers were found using the reported search, of which 4 randomized controlled trials using digital chest drainage devices represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. The new digital drainage systems enhance early mobilization as recommended in the enhanced recovery after surgery programme. There is, however, no consensus on the optimal level of suction to apply after pulmonary lobectomy. This is especially the case for digital drainage devices. Surgeon preference will likely continue to guide practice, until the evidence gives clear-cut recommendations. According to the current data, a low suction reduces total fluid drainage and perhaps air leak duration compared to higher suction levels in both video-assisted thoracoscopic surgery and open pulmonary lobectomies using digital drainage devices, although the evidence is not overwhelming.

Mechanisms on the Injection Conformance Reversion during Polymer Flooding of Offshore Heterogeneous Heavy-Oil Reservoirs

Injection conformance reversion commonly observed during polymer flooding in offshore heterogeneous heavy-oil reservoirs weakens the volumetric sweep of polymer solution and compromises its EOR results. To investigate its mechanisms and impact factors, one mathematical model to predicate injection conformance behavior is constructed for heterogeneous reservoirs based on the Buckley-Leverett function. The different suction capability of each layer to polymer solution results in distinct change law of the flow resistance force, which in turn reacts upon the suction capability and creates dynamic redistribution of injection between layers. Conformance reversion takes place when the variation ratio of flow resistance force of different layers tends to be the same. The peak value and scope of conformance reversion decrease and reversion timing is advanced as oil viscosity or permeability contrast increases, or polymer concentration or relative thickness of low permeable layer decreases, which compromises the ability of polymer flooding to improve the volumetric sweep and lower suction of the low permeable layer. The features of offshore polymer flooding tend to make the injection conformance V-type and create low-efficiency circulation of polymer in a high permeable layer more easily. These results can provide guidance to improve the production performance of polymer flooding in offshore heterogeneous heavy-oil reservoirs.

Evaluating contaminated dental aerosol and splatter in an open plan clinic environment: Implications for the COVID-19 pandemic

ObjectivesIdentify splatter/aerosol distribution from dental procedures in an open plan clinic and explore aerosol settling time after dental procedures. MethodsIn two experimental designs using simulated dental procedures on a mannequin, fluorescein dye was introduced: (1) into the irrigation system of an air-turbine handpiece; (2) into the mannequin's mouth. Filter papers were placed in an open plan clinic to collect fluorescein. An 8-metre diameter rig was used to investigate aerosol settling time. Analysis was by fluorescence photography and spectrofluorometry. ResultsContamination distribution varied across the clinic depending on conditions. Unmitigated procedures have the potential to deposit contamination at large distances. Medium volume dental suction (159 L/min air) reduced contamination in the procedural bay by 53%, and in other areas by 81-83%. Low volume suction (40 L/min air) was similar. Cross-ventilation reduced contamination in adjacent and distant areas by 80-89%. In the most realistic model (fluorescein in mouth, medium volume suction), samples in distant bays (≥5 m head-to-head chair distance) gave very low or zero readings (< 0.0016% of the fluorescein used during the procedure). Almost all (99.99%) of the splatter detected was retained within the procedural bay/walkway. After 10 min, very little additional aerosol settled. ConclusionsCross-infection risk from dental procedures in an open plan clinic appears small when bays are ≥ 5 m apart. Dilution effects from instrument water spray were observed, and dental suction is of benefit. Most settled aerosol is detected within 10 min indicating environmental cleaning may be appropriate after this. Clinical Significance: Aerosols produced by dental procedures have the potential to contaminate distant sites and the majority of settled aerosol is detectable after 10 min. Dental suction and ventilation have a substantial beneficial effect. Contamination is likely to be minimal in open plan clinics at distances of 5 m or more.

Surge protection of centrifugal compressors using advanced anti-surge control system

Centrifugal Compressors (CCs) are widely used equipment to transport the natural gas over long-distance pipelines from the gas processing facility to end consumers. Surge protection is of vital importance for such compressors to avoid costly damage to machine and production loss due to process interruption. In this paper, the dynamic behaviour of CCs has been studied during four critical scenarios: high header pressure, low suction pressure, startup of the new unit, and emergency shutdown of the unit. The dynamic simulation has been carried out using HYSYS software and validated with an industrial scale CC plant. The advanced Anti-Surge Control (ASC) consists of a split PID control in contrast to conventional PID control. The simulation results demonstrate the superior performance of advanced ASC over a conventional one for the severe surge in the event of high header pressure and low suction pressure. The occurrence of surge during start-up and the emergency shutdown was handled with the full open operation of the Anti-Surge Valve (ASV). The proposed algorithm has proved successful in protecting the compressor during fast transients of the operating point towards the surge limit line. The study is significant for the oil and gas plants and other process industry professionals for designing effective ASC systems.

Investigation to Quantify Suction Characteristics of Marine Soil during Drying and Wetting Cycles

Abstract The water retention characteristics of soil play a significant role in controlling its behavior (viz., strength, volume change, and cracking characteristics) during drying and wetting. In the case of marine soils, the water retention characteristics during drying and wetting cycles depend on both matric suction and osmotic suction. Studies by earlier researchers have mainly focused on soils with low osmotic suction and are applicable to higher degrees of saturation. Furthermore, there is a lack of studies that quantify the hysteresis associated with drying and wetting cycles for marine soils. In this context, the present work attempts the estimation of osmotic suction for marine soil by the experimental measurement of total and matric suction at different stages of drying and wetting by employing Dewpoint PotentiaMeter (WP4C). The study also evaluates hysteresis associated with matric, osmotic, and total suction. It has been observed from the study that osmotic suction has a significant influence on water retention characteristics of marine soils and attains a threshold value for a relatively dry state of the specimen. Furthermore, the hysteresis associated with matric suction is observed to be quite reproducible for different specimens, whereas for osmotic suction, some deviation is observed. The study presents the methodology for experimental quantification of osmotic suction, which would be quite useful in understanding the water retention behavior of marine soils in a more scientific way. It is opined that the findings of the study would be useful for understanding the influence of osmotic suction on marine soil behavior with respect to desiccation cracking during drying and time rate of settlement.

Prediction on the operation performance of axial piston pump at low suction pressure

The operation performance of the axial piston pump is affected by external environment pressure, and its conditions at low suction pressure are less studied. The oil model and fluid dynamic model of the axial piston pump are developed and a novel approach for predicting the operation performance of such machines at low suction pressure based on this model is presented. It was found that the inlet pressure of the suction chamber changes linearly with the environment pressure. Compared to the present data from the product manual, this approach is proved to be valid and is used to predict the maximum operating speed and suction pressure at other environment pressure, therefore the low-pressure operating performance map is enriched for the referring of more users of the pump. In future, this study provides a new method for the prediction and the design guide of pump operation at low suction pressures.

Hydraulic transport in small livestock farms

The article highlights the advantages and benefits of pipeline transport of liquid feed mixtures on small pig farms, the device and the principle of operation and technical characteristics of the improved rotor pump developed by the authors of the article. Methods of experimental research to determine the concentration of feed mixtures, the influence of the shape of the separator on the performance characteristics, the required power and the flow of an improved pump are presented. The results of the experiments showed that one of the bottlenecks limiting the operation of rotary pumps on feed mixtures of increased concentration is the low suction capacity of the pump, that is, the design of the suction pipe of the pump, where an increase in resistance with an increase in the concentration of feed mixtures causes a breakdown of the operating mode and cavitation. To resolve this issue, we used a screw feeder installed in front of the pump suction nozzles. It was found that if the screw feeder provides excess pressure within (about, 0.25 ... 0.3) 105 Pa per suction cavity, the pump operates stably and reliably.

Prediction on the operation performance of axial piston pump at low suction pressure

Prediction on the operation performance of axial piston pump at low suction pressure

Improvement of three common methods for determining hydraulic conductivity curve of unsaturated soil upon wetting

Boltzmann transform method, wetting front advancing method and instantaneous profile method are widely used in measuring hydraulic conductivity of unsaturated soils. However, all the three methods are based on relatively strong assumptions. In this study, a new Boltzmann variable was proposed based on the experimental observation that the wetting front advancing distance is not always proportional to the square of time. The improved Boltzmann transform method incorporating the new Boltzmann variable can significantly improve the accuracy of hydraulic conductivity determination. For the wetting front advancing method, a new formula for calculating the hydraulic gradient using central difference was proposed to reduce the fluctuation of determined hydraulic conductivity curve while using data recorded with small time intervals. A series of numerical tests including the horizontal absorption test, vertical ponding test and vertical capillary rise test were performed to verify the accuracy of hydraulic gradient and water flow rate calculated by wetting front advancing method. Results show that the calculated hydraulic gradients in low suction range are far from the real values except for the vertical ponding test and only the vertical ponding test can give reasonable hydraulic conductivity in both low and high suction ranges. For the instantaneous profile method applied in infiltration test with one end of soil column maintained at saturation, using the connected linear line with consideration of the location of wetting front to represent profiles of water content and suction can improve the accuracy significantly.

Hydro-mechanical behavior from small strain to failure of tuffs amended with dune sand – Application to pavements design in Saharan areas

In the context of valorizing local materials at Saharan region for road constructions, a mixture composed of 65% tuff and 35% dune sand (named 65T35DS) was previously studied. The 65T35DS was shown to have the optimum geotechnical and mechanical properties. As an extension, this study consists in investigating the behavior of the 65T35DS mixture under coupled hydro-mechanical loadings. Suction-controlled drying-wetting tests were performed on the 65T35DS statically compacted at the modified Proctor optimum (MPO) state. A series of small-strain cyclic triaxial tests under constant water content condition was then followed. Key findings of this paper include i) the 65T35DS prepared at MPO state is able to resist severe drought condition without inducing significant shrinkage. However, it swells during wetting and the swelling indices are quantified by correlations; ii) the elastic modulus under small-strains is governed by suction and the applied confining stress. The effect of confining stress becomes dominant at lower suction level and negligible when suction increases; iii) at failure, the apparent cohesion drops quickly on the dry side of the MPO, on wet side, it decreases a little. The apparent friction angle decreases for the specimens with water content larger than 5.5%, i.e. wMPO – 5. The studied mixture satisfies the design standards of Saharan pavements and seems to be a good compromise for the valorization of local materials.

S2335 Nasopleural Drainage of Empyema via Esophago-Pleural Fistula: A Novel Endoscopic Rescue Technique

INTRODUCTION: Esophago-pleural fistulas (EPF) are rare entities. These can occur spontaneously or following surgical manipulation and can result in empyema formation. Treatment of empyema in this patient population is difficult, and a variety of techniques have been described. Here, we present a novel rescue technique for empyema management via endoscopy, when percutaneous and surgical techniques were not feasible. CASE DESCRIPTION/METHODS: A 90-year-old female presented with acute gastric volvulus requiring emergent partial gastrectomy and gastrostomy tube placement. Her clinical course was complicated by necrosis of the gastric cardia resulting in perforation and contamination of the mediastinum, requiring distal esophageal stump creation and multiple washouts. She was started on long term antimicrobial agents, with plans of maintaining esophageal discontinuity for six months prior to considering re-anastomosis. She was admitted five months later with high-grade fevers and leukocytosis of 21 k/uL. CT scan showed left-sided thick, loculated pleural effusion containing air, with a suggestion of EPF. She was unstable for surgical drainage. Due to complicated anatomy and dense fibrosis, a percutaneous chest tube could not be placed. An urgent transnasal endoscopy was performed using an ultra-slim scope. A small fistulous connection was noted between the distal esophageal stump and the left pleural cavity. The left pleural space was explored, and immediately upon entry, a large amount of purulent material was suctioned. After extensive lavage and cleaning with normal saline, a 16Fr nasopleural drain was placed over a soft tip 0.035 wire (450 cm) under fluoroscopic guidance. The drain was left on low intermittent suction. She had a remarkable clinical improvement within 24 hours. A week after conservative management, a percutaneous drain placement was successfully performed. Subsequently, the nasopleural drain was removed, and she was discharged on enteral nutrition via gastric tube. DISCUSSION: Empyema management ranges from conservative chest tube placement to aggressive surgical management. Endoscopic drainage is another option when percutaneous and surgical options are not possible. Our case demonstrates a novel rescue technique for the management of empyema in patients who already have an EPF and are not good candidates for conventional treatment. This technique can only be used short-term, as a bridge to definitive treatment.Figure 1.: A large amount of purulent material was found in the lower third of the esophagus. This was in continuity to the left pleural cavity.Figure 2.: This image demonstrates the irritation of the underlying mucosa, following extensive suctioning and lavage of purulent material.Figure 3.: A fluoroscopic view of the drain placement.

Demystifying the mist: Sources of microbial bioload in dental aerosols.

The risk of transmitting airborne pathogens is an important consideration in dentistry and has acquired special significance in the context of recent respiratory disease epidemics. The purpose of this review, therefore, is to examine (1) what is currently known regarding the physics of aerosol creation, (2) the types of environmental contaminants generated by dental procedures, (3) the nature, quantity, and sources of microbiota in these contaminants and (4) the risk of disease transmission from patients to dental healthcare workers. Most dental procedures that use ultrasonics, handpieces, air‐water syringes, and lasers generate sprays, a fraction of which are aerosolized. The vast heterogeneity in the types of airborne samples collected (spatter, settled aerosol, or harvested air), the presence and type of at‐source aerosol reduction methods (high‐volume evacuators, low volume suction, or none), the methods of microbial sampling (petri dishes with solid media, filter paper discs, air harvesters, and liquid transport media) and assessment of microbial bioload (growth conditions, time of growth, specificity of microbial characterization) are barriers to drawing robust conclusions. For example, although several studies have reported the presence of microorganisms in aerosols generated by ultrasonic scalers and high‐speed turbines, the specific types of organisms or their source is not as well studied. This paucity of data does not allow for definitive conclusions to be drawn regarding saliva as a major source of airborne microorganisms during aerosol generating dental procedures. Well‐controlled, large‐scale, multi center studies using atraumatic air harvesters, open‐ended methods for microbial characterization and integrated data modeling are urgently needed to characterize the microbial constituents of aerosols created during dental procedures and to estimate time and extent of spread of these infectious agents.

A generalized water retention model with soil fabric evolution

This paper introduces a novel soil–water retention curve model that considers two different mechanisms of water retention – namely capillarity and adsorption – and their evolution with soil fabric along a generalized stress path. The model is formulated based on a new developed framework, which is justified against experimental evidence and incorporates the following developments: (i) the characteristics of the capillary and adsorption water retention curves are identified, and an ad-hoc water retention model is developed for each mechanism; (ii) the capillary and adsorption water retention curves are related to the experimentally determinable water retention curve thanks to a newly defined parameter named “contribution factor”, which changes with the evolution of the fabric. The proposed model is an elastoplastic water retention model and it allows to describe satisfactorily the water retention capacity of different soils. All simulation results support the statement that the adsorptive mechanism plays a crucial rule in the high suction range while capillarity is important in the low suction range. Moreover, it is shown that the developed capillary water retention curve allows to easily compute, at any state of the soil, a suitable capillary degree of saturation; the latter, adopted within the generalized effective stress concept, makes it possible to interpret shear strength data under different saturation conditions properly.

A case of refractory massive morel lavallee lesion of the thigh: Pitfalls in diagnosis, management and the role of vac therapy

Morel-Lavallee lesion has been described as a post-traumatic soft tissue degloving injury. It is commonly seen in association with road traffic accidents or sports injuries where there is separation of the hypodermis layer from the deeper fascia caused by a shearing force. These injuries occur around the mid-torso, specifically at the flank, lumbar spine, scapula, buttocks and the knee but are most commonly seen over the greater trochanter. There is a complex serosanguinous fluid collection containing blood, lymph and necrotic material within the separated tissue planes. Various treatment modalities like compression bandaging, sclerodesis, percutaneous aspiration, open debridement, quilting sutures and VAC (vacuum assisted closure) therapy have all been described in literature, however a clear consensus on the management protocol does not exist. Herein we reported a 45 year old gentleman who presented with a persistent fluctuant swelling over his left thigh following a motor vehicle accident. He had a history of multiple aspirations of the collection. Upon presenting to our Institute he underwent incision and drainage with sclerotherapy followed by open drainage and debridement with low suction drains. However on follow up visits there was recurrent swelling over the inferior most dependent aspect of the lesion which was finally managed by VAC therapy. The patient eventually returned to normal activity after 4 months from the initial injury with no residual loss of function. The clinical significance of this case is to emphasize that a high degree of suspicion and early use of imaging modalities like MRI in suspected patients are essential to provide timely and appropriate treatment. We also aim to discuss the efficacy of various forms of treatment as per the available literature which shows that a low threshold for operative management is associated with lower recurrence and complication rates.

Evolution of the leading-edge vortex over a flapping wing mechanism

Leading-edge vortex governs the aerodynamic force production of flapping wing flyers. The primary factor for lift enhancement is the leading-edge vortex (LEV) that allows for stall delay that is associated with unsteady fluid flow and thus generating extra lift during flapping flight. To access the effects of LEV to the aerodynamic performance of flapping wing, the three-dimensional numerical analysis of flow solver (FLUENT) are fully applied to simulate the flow pattern. The time-averaged aerodynamic performance (i.e., lift and drag) based on the effect of the advance ratio to the unsteadiness of the flapping wing will result in the flow regime of the flapping wing to be divided into two-state, unsteady state (J&lt;1) and quasi-steady-state(J&gt;1). To access the benefits of aerodynamic to the flapping wing, both set of parameters of velocities 2m/s to 8m/s at a high flapping frequency of 3 to 9 Hz corresponding to three angles of attacks of α = 0o to α = 30o. The result shows that as the advance ratio increases the generated lift and generated decreases until advance ratio, J =3 then the generated lift and drag does not change with increasing advance ratio. It is also found that the change of lift and drag with changing angle of attack changes with increasing advance ratio. At low advance ratio, the lift increase by 61% and the drag increase by 98% between α =100 and α =200. The lift increase by 28% and drag increase by 68% between α = 200 and α = 300. However, at high advance ratio, the lift increase by 59% and the drag increase by 80% between α =100 and α = 200, while between α =200 and α =300 the lift increase by 20% and drag increase by 64%. This suggest that the lift and drag slope decreases with increasing advance ratio. In this research, the results had shown that in the unsteady state flow, the LEV formation can be indicated during both strokes. The LEV is the main factor to the lift enhancement where it generated the lower suction of negative pressure. For unsteady state, the LEV was formed on the upper surface that increases the lift enhancement during downstroke while LEV was formed on the lower surface of the wing that generated the negative lift enhancement. The LEV seem to breakdown at the as the wing flap toward the ends on both strokes.

Transporte de íons de vinhaça em solos estruturados

Transporte de íons de vinhaça utilizada na fertirrigação tem sido simulado por modelos que levam em consideração a distribuição unimodal do tamanho dos poros. No entanto, solos lateríticos ou estruturados podem apresentar distribuições de tamanho de poros com propriedades geométricas, físicas e hidráulicas diferenciadas. Neste contexto, o presente trabalho apresenta a modelagem numérica do transporte de íons de vinhaça genéricos, a partir da superfície ou fonte de contaminação até ser incorporado à água subterrânea, levando em consideração distribuições uni e bimodal de tamanho de poros. Os resultados da simulação mostram que os íons de vinhaça podem atingir as águas subterrâneas três vezes mais rápido quando considerados os modelos bimodais e que o uso de modelos unimodais em solos lateríticos pode tanto subestimar quanto superestimar as concentrações finais, especialmente em solos em que a descontinuidade da distribuição do tamanho dos poros ocorre para baixos valores de sucção.