Entrapment Phenomena Research Articles

Air bubble entrapment during drop impact on solid and liquid surfaces

The phase-field modeling (PFM) of water drop impact onto a dielectric hydrophobic parafilm surface is performed to explore air entrapment and its influence on deposition and rebound phenomena. Local and global characteristics of the drop impact are taken into account by using the combined Cahn-Hilliard and Navier-Stokes equations. The modeling results of water drop impact are directly compared with our experimental measurements in terms of maximum spreading distance, and air bubble size. The simulation results reveal that air can be trapped under the liquid drop during the initial impact as well as during the retraction phase at the center of the drop due to the closure of the liquid layer above a cavity. It is found that the drop diameter and the impact velocity play significant roles in the air entrapment phenomena. The probability of air bubble formation is higher at lower impact velocity and for larger drop size. The model is also capable of simulating the case of drop impact onto a water surface, and the results are validated using prior literature data. In addition, the influence of the phase-field variables and the mesh adaptation scheme on the PFM is studied and discussed. Thus, our findings provide new qualitative and quantitative insights into the influence of air entrapment on drop deposition onto hydrophobic and liquid surfaces.

Szemelvények az elmúlt két évtized ELTE-n végzett, medenceléptékű hidrogeológiai kutatásaiból

Az Eötvös Loránd Tudományegyetem (ELTE) Általános és Alkalmazott Földtani Tanszékének hidrogeológiai kutató és oktatócsoportja (Tóth József és Erzsébet Hidrogeológia Professzúra) tevékenységének középpontjában a felszínalatti vízáramlásoknak és kapcsolódó jelenségeknek a hidraulikus folytonosság alaptételére épülő medenceléptékű és rendszer szemléletű megközelítése áll. A jelen tanulmány e megközelítést történeti felvezetéssel és a korábbi, rétegtani (hidrosztratigráfiai) alapú „artézi” paradigmával szembeállítva mutatja be. A folyamatosan fejlesztett medenceléptékű hidrogeológiai kutatási módszertant röviden tárgyaljuk, a technikai részletek helyett kiemelve az alkalmazott módszertani megközelítések magyarázatát. Ezek közül legnagyobb jelentőséggel a kutakban mérhető hidraulikai adatok medenceléptékű, azaz medencehidraulikai elemzése bír, amelynek eredménye a „valós vízáramlási rendszermodell” felállítása. Ennek megfelelően kutatás történetünkből a medenceléptékű és különösen a medencehidraulikai eredményeket szemlézzük a továbbiakban, említve az ezekáltal összefüggésrendszerbe helyezett és egyéb módszerekkel vizsgált jelenségeket is. Az ország területének nagyrészét lefedő kutatásaink domborzattól és kőzettípustól (sziliciklasztos vagy karbonátos) függetlenül kimutatták a kőzetváz hidraulikus folytonosságát és a gravitáció vezérelte regionális felszínalatti vízáramlási rendszerek jelenlétét. Ezek medenceléptékben fedetlen, csapadékvízből utánpótlódó és közel hidrosztatikus nyomásrezsimű tartománya alatt a mélymedencékben abnormális nyomásrezsimek (túlnyomásos vagy alulnyomásos) fedett, és nem vagy csak korlátozottan utánpótlódó tartományai találhatók. E komplex hidraulikai helyzettel és a felszínalatti víz áramlások földtani és környezeti hatótényező szerepével számos felszíni (szikesedés, felszín alatti víztől függő ökoszisztémák, FAVÖKO-k stb.), és felszín alatti (hipogénbarlangképződés, szénhidrogén csapdázódás stb.) jelenség és folyamat nyert magyarázatot.

Anti-pathogenic activity of graphene nanomaterials: A review

Graphene and its derivatives are promising candidates for a variety of biological applications, among which, their anti-pathogenic properties are highly attractive due to the outstanding physicochemical characteristics of these novel nanomaterials. The antibacterial, antiviral and antifungal performances of graphene are increasingly becoming more important due to the pathogen's resistance to existing drugs. Despite this, the factors influencing the antibacterial activity of graphene nanomaterials, and consequently, the mechanisms involved are still controversial. This review aims to systematically summarize the literature, discussing various factors that affect the antibacterial performance of graphene materials, including the shape, size, functional group and the electrical conductivity of graphene flakes, as well as the concentration, contact time and the pH value of the graphene suspensions used in related microbial tests. We discuss the possible surface and edge interactions between bacterial cells and graphene nanomaterials, which cause antibacterial effects such as membrane/oxidative/photothermal stresses, charge transfer, entrapment and self-killing phenomena. This article reviews the anti-pathogenic activity of graphene nanomaterials, comprising their antibacterial, antiviral, antifungal and biofilm-forming performance, with an emphasis on the antibacterial mechanisms involved.

Hydrogen Permeation in X65 Steel under Cyclic Loading.

This experimental work analyzes the hydrogen embrittlement mechanism in quenched and tempered low-alloyed steels. Experimental tests were performed to study hydrogen diffusion under applied cyclic loading. The permeation curves were fitted by considering literature models in order to evaluate the role of trapping—both reversible and irreversible—on the diffusion mechanism. Under loading conditions, a marked shift to the right of the permeation curves was noticed mainly at values exceeding the tensile yield stress. In the presence of a relevant plastic strain, the curve changes due to the presence of irreversible traps, which efficiently subtract diffusible atomic hydrogen. A significant reduction in the apparent diffusion coefficient and a considerable increase in the number of traps were noticed as the maximum load exceeded the yield strength. Cyclic loading at a tensile stress slightly higher than the yield strength of the material increases the hydrogen entrapment phenomena. The tensile stress causes a marked and instant reduction in the concentration of mobile hydrogen within the metal lattice from 55% of the yield strength, and it increases significantly in the plastic field.

Numerical Simulation of Transient Multiphase Flow in a Five-Strand Bloom Tundish during Ladle Change

The steel-slag-air multiphase flow in a bloom tundish with five strands during the transient casting of the ladle change was simulated using the Volume of Fluid (VOF) model, and the formation mechanisms of macro-inclusions and the behavior of the steel-slag-air interface during the filling process were investigated. Water model experiments were conducted to validate the multiphase model. The results showed that the numerical results of slag entrapment behavior and the exposed area of steel are basically consistent with the experimental results. The flow of molten steel in the tundish is weak except for the region around the stopper rods at the end of the emptying process. Strong fluctuations in liquid level were formed during the filling process, showing two wave crests in front of and behind the shroud in the impact zone, which intensified with the increase in filling time and then declined gradually. Entrapment phenomena and exposure of liquid steel could not be observed before the filling stage. While the entrapped slag droplets mostly float up and can be removed within 40 s during the filling process, the remainder enters the casting zone through the baffle. The maximum exposed area of molten steel is 252 cm2 when the filling time is 4.0 s.

Evaluation of Different Modalities of Anterior Cervical Discectomy for Treatment of Single and Double Level Cervical Disc Herniation

Introduction: Cervical disc herniation and degenerative disease of the cervical spine are the most common causes of cervical cord and nerve root dysfunction. The surgical treatment of cervical radiculopathy is still controversial. Instead of two possibilities, nowadays three possible treatments concur with each other: anterior cervical discectomy without implantation of any structure, anterior cervical discectomy with fusion, and finally, cervical discectomy with implantation of disc prosthesis. Patients and methods: Twenty patients with cervical disc herniation with radiculopathy, which had not responded to conservative treatment were treated by anterior decompression and cervical disc replacement. All these patients were evaluated preoperatively clinically and radiologically (plain X-rays of cervical spine; A-P, Lateral and dynamic films: flexion, extension and oblique and MRI cervical spine). Nerve conduction study was done to exclude peripheral compression neuropathy and to confirm radiculopathy in selected cases where double entrapment phenomena suspected and followed up for a period of 1 month to 12 months. The technique followed anterior decompression differed according to the way of reconstruction at each level and the patients were accordingly classified into three groups: group A (1-level fusion); where the anterior decompression was accomplished by single level cervical discectomy, and then insertion of cervical cage at this leve, group B (2-level fusion); where the anterior decompression was accomplished by double level cervical discectomy, and then insertion of cervical cage at both levels, group C (hybrid construct); where the anterior decompression was in the form of one level cervical discectomy, followed by cage implantation at this level and another level cervical discectomy followed by insertion of cervical disc prosthesis at the same time. Functional outcome was assessed according to Odom’s criteria. Postoperative plain X-rays of cervical spine (A-P and Lateral) were done at follow-up visits (immediate postoperative, 3 months, 6 months 12 month postoperatively. MRI or CT of the cervical spine is done for patients routinely and for patients not improving or with persistent preoperative complaint or any new neurologic deficit. Results and Discussion: The ages in our patient population ranged from 30 to 50 years, with a mean of 40 ± 5.9 years (mean ± standard deviation). 11/20 patients (55%) were males, and 9/20 (45%) were females. The commonest level affected is C5-C6 level. The most common complaint of patients is neck pain and radiculopathy. Anterior cervical discectomy followed by single level cervical fusion was done on 13 patients, while 5 patients were subjected to anterior cervical discectomy followed by double level cervical fusion and another 2 patients had anterior cervical discectomy followed by cervical artificial disc replacement at one level and zero profile implant insertion and fusion at another level. Regarding the mean duration of hospital stay it was 2.4 days in the single level group while it was 3.8 days in the double level group and 4 days in the hybrid group. Regarding the functional outcome 9 patients (69.2%) had excellent outcome in the single level group versus 3 patients (60%) In the double level group and 2 patients (100%) in the hybrid group, while there were 3 patients (23.1%) who had good outcome in the single level group and 1 patient (20%) in the double level group, finally only one patient in the single level group and 1 patient in the double level group who had satisfactory outcome. There were 2 complications in this study, one (7.7%) in the single level group and one (20%) in the double level group. In the single level group 1 patient had removal of prosthesis due to device failure and hypermobility. In the double level group, one patient had temporary dysphagia and dysphonia. Conclusion: Ideal treatment for cervical degenerative disc disease must deal with and improve its three components (axial neck pain, radiculopathy, and myelopathy), normalize cervical spine biomechanics so not to act as a nidus accelerating the degenerative process, and improves the functional outcome of the patient without serious complications. CDR and ACDF are both effective treatment strategies for managing degenerative conditions of the cervical spine. There is insufficient evidence to show which technique is the most effective and provides the longest-lasting symptom relief.

An assessment of the Beerkan method for determining the hydraulic properties of a sandy loam soil

Establishing the ability of the Beerkan Estimation of Soil Transfer parameters (BEST) procedure to reproduce soil properties is necessary for specific soil types. In this investigation, the BEST predictions for a sandy loam soil were compared with water retention data obtained by a standard laboratory method and with the saturated soil hydraulic conductivity, Ks, obtained by both the Wu et al. (1999) method, applied to the BEST infiltration data, and the Simplified Falling Head (SFH) technique. When the original BEST-slope algorithm with the infiltration constants fixed at β=1.9 and γ=0.79 was applied, the agreement between the predicted and the measured retention data was satisfactory in terms of similarity of the means and correlation and coincidence between the regression and identity lines. The prediction of Ks at a sampling point differed by not more than a factor of two from the Ks value obtained by the Wu et al. (1999) method. The SFH technique yielded Ks values approximately five times higher than those of BEST, probably because soil disturbance during water application, swelling and air entrapment phenomena had a lower impact on the measured infiltration data with the former technique. In conclusion, BEST is a promising approach for easily characterizing a soil, but its method of application should be adapted to the particular situation under consideration. Additional investigations carried out on different soils would allow development of more general procedures for applying BEST.

Quasi-cellular systems: stochastic simulation analysis at nanoscale range.

BackgroundThe wet-lab synthesis of the simplest forms of life (minimal cells) is a challenging aspect in modern synthetic biology. Quasi-cellular systems able to produce proteins directly from DNA can be obtained by encapsulating the cell-free transcription/translation system PURESYSTEM™(PS) in liposomes. It is possible to detect the intra-vesicle protein production using DNA encoding for GFP and monitoring the fluorescence emission over time. The entrapment of solutes in small-volume liposomes is a fundamental open problem. Stochastic simulation is a valuable tool in the study of biochemical reaction at nanoscale range. QDC (Quick Direct-Method Controlled), a stochastic simulation software based on the well-known Gillespie's SSA algorithm, was used. A suitable model formally describing the PS reactions network was developed, to predict, from inner species concentrations (very difficult to measure in small-volumes), the resulting fluorescence signal (experimentally observable).ResultsThanks to suitable features specific of QDC, we successfully formalized the dynamical coupling between the transcription and translation processes that occurs in the real PS, thus bypassing the concurrent-only environment of Gillespie's algorithm. Simulations were firstly performed for large liposomes (2.67µm of diameter) entrapping the PS to synthetize GFP. By varying the initial concentrations of the three main classes of molecules involved in the PS (DNA, enzymes, consumables), we were able to stochastically simulate the time-course of GFP-production. The sigmoid fit of the GFP-production curves allowed us to extract three quantitative parameters which are significantly dependent on the various initial states. Then we extended this study for small-volume liposomes (575 nm of diameter), where it is more complex to infer the intra-vesicle composition, due to the expected anomalous entrapment phenomena. We identified almost two extreme states that are forecasted to give rise to significantly different experimental observables.ConclusionsThe present work is the first one describing in the detail the stochastic behavior of the PS. Thanks to our results, an experimental approach is now possible, aimed at recording the GFP production kinetics in very small micro-emulsion droplets or liposomes, and inferring, by using the simulation as a reverse-engineering procedure, the internal solutes distribution, and shed light on the still unknown forces driving the entrapment phenomenon.

Quasi-cellular systems: stochastic simulation analysis at nanoscale range

Motivations. The artificial creation of the simplest forms of life (minimal cells) is a challenging aspect in modern synthetic biology. Quasi/cellular systems able to produce proteins directly from DNA can be created by encapsulating a cell-free transcription/translation system (PURESYSTEM) in microemulsion droplets and liposomes (10^(-5) - 10^(-7) m of diameter). It is possible to detect the overall protein production inside these compartments using DNA encoding for GFP and monitoring the fluorescence emission over time. The entrapment of solutes in microemulsion droplets and liposomes is a complex process that creates a population of compartments with different internal compositions of molecular species, which affects the final protein production. A complete understanding of the distribution of solutes inside the different compartments and on its effect on the course of internal reactions are two relevant and still open issues in the field. Stochastic simulation is a valuable tool in the study of biochemical reaction at nanoscale range; QDC (Quick Direct-Method Controlled), a stochastic simulation software which uses the well-known Gillespie's SSA algorithm, was used; a suitable model reproducing the PURESYSTEM reactions network was hence created, with the aim to describe how the different composition of species affects the overall translation process, thus trying to infer the internal composition of each microcompartment from its observable fluorescent signal emission. Methods. In order to understand how the protein production is affected by the reactants concentration, we first generate experimental data by combining different amounts of DNA, enzymes, translation factors and consumable. Consequently, a set of fluorescence vs. time curves were generated. Next, the pre-existing translation model was improved to describe in detail a coupled transcription/translation system with simultaneous elongation events on the same molecule. The dynamical coupling between the transcription and translation systems was assessed using logical formulations allowed in QDC's syntax, thus creating sequentially dependent processes in the concurrent-only environment of Gillespie's algorithm. Stochastic simulations were performed in order to globally fit, by sigmoid curves (R^2 > 0.98), the entire experimental dataset for protein production. The comparison of the parameters estimates for the different inputs showed how protein production is strongly affected by enzymes concentration. Results. Different kinetic parameters were considered, such as the final plateau of production and the initial time required to release the first complete proteins from elongating ribosomes. Further analysis demonstrates how the transcription process plays a fundamental role, determining the rate of GTP depletion from the system, hence preventing ulterior elongation of peptide chains.To the best of our knowledge, the present work is the first one describing in detail the stochastic behavior of the PURESYSTEM™. The developed model allows us to scale the system down to compartment diameters where anomalous entrapment phenomena are presumed. Thanks to our results, an experimental approach is now possible, aimed at recording the GFP production kinetics in very small microemulsion droplets or liposomes, and inferring, by using the simulation as a hypotheses test benchmark, the internal solutes distribution, and shed light on the still unknown forces driving the entrapment phenomenon.

Analysis of fluid lubrication mechanisms in metal forming at mesoscopic scale

The lubricant entrapment and escape phenomena in metal forming are studied experimentally as well as numerically. Experiments are carried out in strip reduction of aluminium sheet applying a transparent die to study the fluid flow between mesoscopic cavities. The numerical analysis involves two computation steps. The first one is a fully coupled fluid-structure Finite Element computation, where pockets in the surface are plastically deformed leading to the pressurization of the entrapped fluid. The second step computes the fluid exchange between cavities through the plateaus of asperity contacts with the plane tool, one cavity at a time.

Literature Survey on Porosity and Microporosity in Cast Irons Related to Expansion and Gas Entrapment Phenomena

Macro and microporosity in castings are a problem that persists at many foundries, despite the use of advance simulation software’s. This fact indicates that other parameters rather then the casting shape/design or the “standard” metallurgical characteristics are not properly controlled, considered or modelled in the solidification simulation. In this paper we present the Phase I of a research project, which consists on a bibliographic review of the previous attempts to evaluate the relationship between solidification sequence and the measurement of expansion of molten metal during eutectic solidification and is relation to porosity and shrinkage defects.

An Experimental and Numerical Study of Flow Patterns and Air Entrapment Phenomena During the Filling of a Vertical Die Cavity

One of the most important problems encountered in die-casting processes is porosity due to air entrapment in the molten metal during the injection process. The aim of this work is to study experimentally and numerically the different air entrapment phenomena that may take place in the early stages of the filling of a vertical die cavity with a rectangular shape for operating conditions typically used in low and medium-pressure die-casting processes. Special attention is given to determining the influence of the gravitational forces on the flow pattern. Numerical simulation of the flow in the die cavity is carried out for the liquid phase using a commercial computational fluid dynamics (CFD) code (FLOW-3D) based on the solution algorithm-volume of fluid (SOLA-VOF) approach to solve the coupling between the momentum and mass conservation equations and to treat the free-surface, while the amount of air evacuated through vents is calculated by using an unsteady one-dimensional adiabatic model that retains friction effects. The main characteristics of the flow at the early instants of the die cavity filling are analyzed for different operating conditions, and the different flow patterns are summarized in a map as a function of the Reynolds and Froude numbers. Also, filling visualization experiments are carried out on a test bench using water as working fluid in a transparent die model and a high-speed camera. The numerical and experimental results obtained for the free-surface profile evolution are compared for different inlet velocities of the fluid and the viability of the numerical tools used to predict the final amount of trapped air in the die cavity is discussed.

Air entrapment under an impacting drop

When a drop impacts on a liquid surface it entraps a small amount of air under its centre as the two liquid surfaces meet. The contact occurs along a ring enclosing a thin disk of air. We use the next-generation ultra-high-speed video camera, capable of 1 million f.p.s. (Etoh et al. 2002), to study the dynamics of this air sheet as it contracts due to surface tension, to form a bubble or, more frequently, splits into two bubbles. During the contraction of the air disk an azimuthal undulation, resembling a pearl necklace, develops along its edge. The contraction speed of the sheet is accurately described by a balance between inertia and surface tension. The average initial thickness of the air sheet decreases with higher impact Reynolds numbers, becoming less than one micron. The total volume of air entrapped depends strongly on the bottom curvature of the drop at impact. A sheet of micro-bubbles is often observed along the original interface. Oguz–Prosperetti bubble rings are also observed. For low Weber numbers (We<20) a variety of other entrapment phenomena appear.

Determination of the Isothermal Moisture Transport Properties of Porous Building Materials

A multiscale network approach is proposed as a practical method for estimating the isothermal permeability of porous building materials covering hygroscopic and overhygroscopic ranges. The multiscale approach is based on the concept of examining the porous space at different levels of magnification, and it allows modeling of combined liquid water and water vapor transfer over a wide saturation range. The proposed method simply requires the knowledge of common moisture properties, such as the capillary pressure curve, the capillary absorption coefficient and water vapor permeability, which can be determined from standard experiments. Hysteresis between drainage and wetting due to air entrapment can be adequately modeled by considering only those pores that become filled by water. The calculated network permeability is validated comparing experimental and simulation results of isothermal capillary absorption and drying processes in ceramic brick and calcium silicate. It is shown that transient moisture processes of capillary absorption from a dry sample and the isothermal drying from an initially capillary saturated sample can be accurately modeled by a single nonlinear permeability and capillary pressure curve. The capillary pressure curve to be used is the main wetting curve, which describes the moisture content relationship from the dry state to the capillary moisture content, correctly taking into account air entrapment phenomena. The description of the absorption or drying moisture processes by a single or a double exponential diffusivity relation was found to be less accurate.

A SIMPLIFIED MODEL FOR MERCURY POROSIMETRY HYSTERESIS

A modified Random Corrugated Pore Structure Model (CPSM) simulating Mercury Porosimetry (MP) hysteresis and entrapment phenomena is proposed. The model have been applied in parametric sensitivity studies and data regression tests by using a single parameter Bell Shape Distribution (BSD) function as the intrinsic pore size distribution (psd). The new CPSM version proved to be superior compared to its original counterpart since it achieves a sensible evaluation of the trapped mercury distribution, enables the construction of a “closed” (zero entrapment) hysteresis loop and makes realistic predictions of the intrinsic pore volume and surface area distributions. CPSM predicted intrinsic psd's for reservoir sand stones compare satisfactorily with those measured independently by a photomicrography method. The model also provides the basis for the development of a least square computer code suitable for further improved psd calculations.